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Design and Construction of a Reflow Solder Oven

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1. 21 Mainas ment E 21 1 TABLE OF CONTENTS CONTINUED Page Chapter o Ot 012 NEN 22 TRO AUC GO 10 22222225 mE 22 Dystet C OS CH ON etc d ARD Rede O OS BAS BO Mute tutu tb MI o NEM 22 2 19 24252252 rin Serr o datu TE DU 23 and Stability 24 CONE ReC HON ere 28 Al 41018 O 28 ANAS SUAVE 26 POTN E 29 DU See M d d 29 42 NE O 46 BE Automatic Control sys 1118 222526 2122200231422 552235 bote ticas edt ups e d LN 46 Depattinent or Blectrical 46 TNT ROTE 47 47 Reith 47 Wilian fosh Russell Mr m 47 Cerne Nk i Gi 47 Table 1 1 Table 1 2 Table 1 3 Table 1 4 Table 2 1 Table 2 2 Table 2 3 Table 3
2. Eu EL I ELEM CEU M IDE 9 Lo SAC 5 0 PPK OP c EN 10 10 CONTO Deso OR CN 11 Produc 11 COn sua Culto fic 11 11005 d Ut 12 Perii mance Pred O 13 2210 2 011 8 2 O EC 13 te P 028 En ESO 14 Hardware and Software Architecture RE Ek 14 2222 KOS amas etre reer ab 16 Revised Project Dalai dios 17 nac CBS 17 IVI AAC CME IT d d made 17 Chapters Detailed ea ect was teta 18 ECON O O O O M 18 Electrical Fatdwareand DS 02525225 19 DOLE WATS LOOD 25555255 pi dide stet ate iu 19 NGC uie ianuis oit 20 Safety Review Protection System Design 21 Tochited 1 comers oom ION
3. UIWAIT makes EasySolder wait for user response see UIRESUME uiwait handles figurel Outputs from this function are returned to the command line function varargout EasySolder OutputFcn hObject eventdata handles varargout cell array for returning output args see VARARGOUT hObject handle to figure eventdata reserved to be defined in a future version of MATLAB handles Structure with handles and user data see GUIDATA Get default command line output from handles structure varargout 1l handles output Executes on button press in startbuttorn function startButton_Callback hObject eventdata handles hObject handle to startButton see GCBO eventdata reserved to be defined in a future version of MATLAB handles structure with handles and user data see GUIDATA set handles stopButton UserData false lookup 0 3 1 12 2 22 5 32 4 41 5 51 6 61 7 70 8 80 9 90 10 100 11 109 12 119 13 129 14 139 15 148 16 158 17 168 18 178 19 188 20 198 21 208 22 218 23 228 24 238 25 248 2 6 258 27 268 26 278 29 288 30 298 31 309 32 319 33 329 30 34 35 36 37 38 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 5 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 13 74 15 76 77 78 79 80 81 82 83 84 85 86 Bui 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 339 35
4. 120 Fahrenheit Figure 5 7 Temperature Profile with Board and Tray in Lowest Position and Fan Last among the various tests was that of system robustness To test the ability to recover from an unexpected external event a massive disturbance was added to the oven The disturbance consisted in fully opening the oven door and introducing a large volume of outside air into the oven cavity by means of rapid exhalation from a pair of human lungs Figure 5 8 records this event at roughly 190 seconds into the process at a time of closed loop control The system recovered fully from the disturbance though it 15 still suggested not to perform this test while soldering a board EasySolder 200 300 400 600 900 Temperature Soak Time Dwell Time Soak Temp Solder Temp Max Temp 120 sec 120 150 183 220 C 105 Celsius Status 221 Fahrenheit Figure 5 8 Temperature Profile with Optimal Settings and Major Door Open Disturbance The two boards in Figure 5 9 show the results of successful reflow soldering runs Figure 5 9 Boards which have Successfully Endured the Process of Reflow Soldering 26 EE 449 REFLOW SOLDER OVEN CHAPTER 5 For the customer demo Nils Napp working for Professor Klavins in the Self Organizing Systems Lab volunteered to allow the build team to solder one of his boards Figure 5 10 shows the soldered board and components The solder joints ar
5. targetTemp soakTemp controll to soakTemp uold 100 while temperature 1 soakTemp amp stop false less then soakTemp time 2 time 1 Sdouble buffer time time 1 toc delta time 1 time 2 temperature 2 temperature 1 double buffer input voltage round 1000 getsample ai voltage in look up temperature i 1 while voltage gt lookup i 2 i itl end rounded lookup i 2 lookup i 1 2 2 if voltage lookup i 2 lt rounded temperature 1 lookup i 1 else temperature 1 lookup i 1 1 end set handles tempC String num2str temperature 1 Display temp C farenheit round 9 5 temperature 1 4 32 Convert C to F set handles tempF String num2str farenheit Display temp error targetTemp temperature 1 compute error Z gt Ki error ctrlOut u PWMsamples delta Sintegrate error ctrlOut Kp error z compute output if ctrlOut gt 1 if duty factor too large PWMsamples make duty factor 1005 elseif ctrlOut 0 Sif duty too small u 0 smake duty 0 else Sotherwise u round ctrlOut PWMsamples duty stays same end for count 1 u SLOr first part of PWM putvalue dio 1 soutput high getsample ai burn input data end for count 1 PWMsamples u for second part of PWM 37 putvalue dio 0 Soutput low getsample ai burn input data end plot time 2 time 1 temperature 2 tempera
6. z Kd d eset output h figure if ctrlOut gt 1 Sif duty factor too hold on start time large u PWMsamples make duty factor 100 while round 1000 getsample ai 1062 less then elseif ctrlOut lt 0 100 degrees u 0 putvalue dio 1 else u round ctrlOut PWMsamples time 2 time 1 Sdouble buffer time end time 1 toc for count l u stor first part of PWM delta time 1 time 2 putvalue dio 1 output high temperature 2 temperature 1 double buffer Vin getsample ai burn input data input end voltage round 1000 getsample ai for count 1 PWMsamples u for second part of 1 putvalue dio 0 output low while voltage gt lookup i 2 Vin getsample ai burn input data i 1 1 end end plot time 2 time 1 temperature 2 temperature 1 rounded lookup i 2 lookup i 1 2 2 drawnow Splot data as it arrives if voltage lookup i 2 rounded end Figure 4 2 Simplifed MATLAB Code for Control of Reflow Oven 19 EE 449 REFLOW SOLDER OVEN CHAPTER 4 The finalized MATLAB code can be found in the Appendix It contains GUI code in addition to the controller code In the full version there are actually fives sets of while loops The first loop sets heating elements to 100 on while the temperature remains more than 50 C from the soak temperature Then while the temperature 18 less than the soak temperature the oven tracks a ramp Once time 1s less th
7. 0 30 pl 305301 2 soakTemp 30 30 soakTemp p2 1 soakTime solderMeltTemp p4 p3 1 2 maxTemp solderMeltTemp maxTemp p5 p3 1 dwellTime 30 maxTemp p6 p5 1 maxTemp 2 30 traj p0 pi p2 ps p5 plotitrag ls taj dc hold on tic set handles status String Running run to soakTemp 50 while temperature 1 50 amp stop false more then 50 degrees from soakTemp putvalue dio 1 Salways on time 2 time 1 Sdouble buffer time time 1 toc temperature 2 temperature 1 double buffer input voltage round 1000 getsample ai voltage in look up temperature 36 1 while voltage gt lookup i 2 i itl end rounded lookup i 2 lookup i 1 2 2 if voltage lookup i 2 lt rounded temperature 1 lookup i 1 else temperature 1 lookup i 4 1 1 end set handles tempC String num2str temperature 1 Display temp C farenheit round 9 5 temperature 1 32 Convert C to F set handles tempF String num2str farenheit SDisplay temp Splot data as it arrives plot time 2 time 1 temperature 2 temperature 1 plot time 1 100 784712 plot 0 0 Tk legend Projected Profile Actual Profile Open Loop PWM 5 Closed Loop PWM 5 drawnow stop get handles stopButton Userdata end putvalue dio 0
8. aichan addchannel ai 0 add three channels to input targetTemp 150 set aichan 1 InputRange 0 51 Snear sensor z 0 Sintegrator while round 1000 getsample ai lt 1660 Sless then 150 w 0 Santi wind up amount output is degrees larger then 1 time 2 time 1 Sdouble buffer time u 0 Soutput non saturation time 1 toc 0 Sdifferential term delta time 1 time 2 delta 0 Schange in time temperature 2 temperature 1 Sdouble buffer ctrlOut 0 output of controller input temperature 0 0 used for double buffer to plot voltage round 1000 getsample ai time 0 0 used for double buffer to plot 1 Vin getsample ai Sthree column vector while voltage lookup i 2 error 0 0 Sused for derivative i 1 set the first error so d doesn t screw up end voltage round 1000 getsample ai rounded lookup i 2 lookup i 1 2 2 1 if voltage lookup i 2 lt rounded while voltage gt lookup i 2 temperature 1 lookup i 1 itl else end temperature 1 lookup i 1 1 rounded lookup i 2 lookup i 1 2 2 end if voltage lookup i 2 lt rounded error 2 error 1 error 1 targetTemp lookup i 1 error 1 targetTemp temperature 1 else z z Ki error 1 ctrlOut u PWMsamples delta error 1 targetTemp lookup i 1 1 Sintegrate error end d error 1 error 2 delta new figure to plot ctrlOut Kp error 1
9. 1 LIST OF TABLES Page Materials Tor Reflow Solder Oven 2 Reflow Solder Oven Work Breakdowt sais ente kien bee eiat dice I o UE ve 3 Rated Skills of Reflow Solder Oven eee Rei eie 4 Redutrtements Tor Development i Asks n ub tu HUE eot este tento eun 5 Relationship Between Duty Factor Power and Temperature eese 50001200 02228556 a 9 Temperature at Thermocouple Based on Conditioner Output 10 Revised Reflow Solder Oven Work Breakdown 17 1V Figure 1 1 Figute 2 1 Figure 2 2 Figure 2 3 Figure 2 4 Figure 2 5 Figure 3 1 Figure 3 2 Figure 3 3 Figure 3 4 Figure 3 5 Figure 3 6 Figure 3 7 Figure 3 8 Figure 4 1 Figure 4 2 Figure 4 3 Figure 5 1 Figure 5 2 Figure 5 3 Figure 5 4 Figure 5 5 Figure 5 6 Figure 5 7 Figure 5 8 Figure 5 9 Figure 5 10 Figure 5 11 LIST OF FIGURES Page Temperature Profile tot Convecion 2 Retlow solder Oven High Level System Model 6 Value Detereittidtl fisaansdi eet 7 PID Controller Schematic from EE 448 Temperature Control 9 Step Response of Toaster Oven Using SISOTOOT 9 Tempere dnd dod MAGO Ud 9 Re
10. Carlson Senior of Electrical Engineering Ms Sandy Chan Senior of Electrical Engineering Ms Sharon Cheung Senior of Electrical Engineering DEPARTMENT OF ELECTRICAL ENGINEERING Dr Eric Klavins Professor of Electrical Engineering Dr Tim Chinowsky Professor of Electrical Engineering Dr Babak Parviz Professor of Electrical Engineering Mr Nils Napp Graduate Student of Electrical Engineering Mr Chris Morris Graduate Fellow of Electrical Engineering AUTHORS SOLOMON GEBRE Solomon Gebre is a Senior in Electrical Engineering in the University of Washington College of Engineering He 1s specializing in power and control systems When Solomon 18 not studying taking tests or working on lab he serves as husband and father He likes Subway sandwiches Keith Johnson is a Senior in Electrical Engineering in the University of Washington College of Engineering In addition to attending school full time he works as a full time intern at Boeing testing the 787 Upon graduating Keith will work for Boeing as an Engineer His specialty 15 in controls During the length of the design and construction of the reflow oven he managed to survive off no more than four hours of sleep a day WILLIAM JOSH RUSSELL Josh Russell is a Senior in Electrical Engineering in the University of Washington College of Engineering He will be attending the University of California at Santa Barbara in pursuit of a Doctorate in Electrical Engineering Josh en
11. OVEN WHEN IT IS ON IT IS HOT The glass door is also vety hot so use the provided handle to open the oven After the oven 18 on it will remain hot for a while It is best to always assume the oven 1s hot The reflow oven components all run 120V AC DO NOT PUT YOUR FINGERS INSIDE THE ATTACHED CONTROL BOX THIS COULD KILL YOU The small box attached to the tight side of the reflow oven is the control box This box holds the thermocouple conditioner and relay The relay is connected to 120V AC so it can shock you or worse Refrain from putting anything in the control box Setting up the reflow oven requires a few steps There are some hardware and software requirements to get the oven wotking for the first time Once setup 1s complete the oven just requires the GUI to be up for operation 42 Hardware Setup To operate the oven it must be hooked up properly First connect the wires coming out of the control box to the USB 1208FS I O card if it is not already connected Table 1 shows what each wire connection Table 1 Wires from Control Box and Corresponding I O card Port USB 1208FS Card Port Nudus White Black Stripe In addition to above connections ports DGnd AGnd and A1 on the USB 1208FS I O card need to be connected together The I O card is then connected to the PC using a USB cable See the card manual if you have problems setting up Plug the reflow oven into a wall outlet to pr
12. future version of MATLAB handles structure with handles and user data see GUIDATA set hObject Userdata true set handles status String Stopped pause 5 set handles status String Ready 5 Update handles structure guidata hObject handles function soakTime_Callback hObject eventdata handles hObject handle to soakTime see GCBO eventdata reserved to be defined in a future version of MATLAB handles structure with handles and user data see GUIDATA Hints get hObject String returns contents of soakTime as text str2double get hObject String returns contents of soakTime as a double Executes during object creation after setting all properties function soakTime CreateFcn hObject eventdata handles hObject handle to soakTime see GCBO eventdata reserved to be defined in a future version of MATLAB handles empty handles not created until after all CreateFcns called oO Hint edit controls usually have a white background on Windows pee ISPC and COMPUTER if ispc amp amp isequal get hObject BackgroundColor get O defaultUicontrolBackgroundColor set hObject BackgroundColor white end olo function dwellTime Callback hObject eventdata handles hObject handle to dwellTime see GCBO eventdata reserved to be defined in a future version of MATLAB handles Structure with handles and user data see GUIDATA Hints
13. maxTemp as text str2double get hObject String returns contents of maxTemp as a double Executes during object creation after setting all properties function maxTemp CreateFcn hObject eventdata handles hObject handle to maxTemo see GCBO eventdata reserved to be defined in a future version of MATLAB handles empty handles not created until after all CreateFcns called Hint edit controls usually have a white background on Windows eee ISPC and COMPUTER if ispc amp amp isequal get hObject BackgroundColor get O defaultUicontrolBackgroundColor set hObject BackgroundColor white end oe 41 USER MANUAL Introduction Welcome to the world of automated reflow soldering With this easy to use Reflow Solder Oven you will be able to solder surface mount parts and other circuit components with the click of a button The following procedures should be used to setup and operate the reflow solder oven Following these procedures will help prevent damage to circuit components and possible dangers to the operator Precautions First of all safety 1s a priority when using the reflow solder oven There are a few hazards the operator needs to be aware of to prevent any unwanted injury and possible death WARNING HOT DANGER 120V AC Setup Procedure The reflow solder oven 18 an oven By nature ovens produce heat and tend to get hot even on the outside DO NOT TOUCH THE
14. on time 21 CHAPTER 5 PROJECT IMPLEMENTATION INTRODUCTION This chapter will cover how our hardware was constructed and also the results of testing From the detailed discussion of the reflow oven it is possible to accurately reproduce additional units The test results also show the limitations of the oven and optimal operating conditions in which to perform reflow soldering SYSTEM CONSTRUCTION The finished reflow oven converted from a toaster oven appears below in Figure 5 1 Figure 5 1 Photograph of Reflow Oven Temperature Sensor and I O Card The Black and Decker toaster oven was disassembled and the various dials and bells removed Two things were left intact the convection fan switch and the safe mechanism that shuts off power to the heating elements when the door is opened completely The wiring for the heating elements is a simple circuit consisting of four resistors two resistors in series parallel with another set of two resistors in series Alternating current passes into one end of the resistors and exits to ground from EE 449 REFLOW SOLDER OVEN CHAPTER 5 the other These two leads were taken and attached to the high voltage side of the solid state power relay The power relay was also screwed down to a large heat sink for the obvious purpose of heat dissipation Figure 5 1 shows several wires exiting the right side of the oven into a black box bolted to the outer case The power r
15. output high getsample ai burn data end for count 1 PWMsamples u for second part of PWM putvalue dio 0 Soutput low getsample ai burn input data end plot time 2 time 1 temperature 2 temperature 1 plot time 2 time l uold u l0 k drawnow plot data as it arrives stop get handles stopButton uold u 10 end Supto 15 degrees from max while temperature 1 lt maxTemp 10 amp openDoor 0 amp stop false putvalue dio 1 Sall on 38 end if startDwell 0 amp temperature 1 solderMeltTemp Sif above melt temp startDwell toc time at melt temp elseif startDwell 0 amp time 1 gt startDwell dwellTime if past dwell time openDoor 1 door set handles status Struing Open Door end time 2 time 1 Sdouble buffer time time 1 toc delta time 1 time 2 temperature 2 temperature 1 double buffer input voltage round 1000 getsample 1 look up temperature i 1 while voltage gt lookup 2 i itl end rounded lookup i 2 lookup i 1 2 2 if voltage lookup i 2 lt rounded temperature 1 lookup i 1 else temperature 1 lookup i 1 1 end set handles tempC String num2str temperature 1 Display temp farenheit round 9 5 temperature 1 32 Convert C to F set handles tempF String num2str farenheit Display temp p
16. oven case does not reach very high temperatures except on top where all the heat rises For aesthetic purposes the front of the oven was stray painted black to cover up the white dial markings for temperature and whatnot The empty dial receptacles serve as ventilation for the interior of the case where all the wires enter and leave LED displays for temperature and other indicators were considered in filling these openings but it was feared that the temperature might damage or destroy the circuitry INITIAL TESTING Initial testing was done with range of results At first the oven was instructed to track stem inputs and this resulted in a very poor temperature profile often resulting in oscillations and long settling times Figure 5 2 is an example of one such test Step Response of Reflow Solder Oven 200 Temperature C o T o o o 0 0 100 200 300 400 500 600 700 800 900 Time s Figure 5 2 Response of Reflow Solder Oven to a 150 C Step 23 EE 449 REFLOW SOLDER OVEN CHAPTER 5 Since the purpose of the oven is to follow a temperature profile resembling a series of ramps it was through better to conduct tests using ramp inputs Simulation showed a favorable response to a ramp and the actual response to ramps was not bad The problem with a ramp input was that the temperature did not rise fast enough to minimize the time necessary for the reflow solder process However a ramp inp
17. use it for their own purposes The oven will be placed in Bill Lynes lab for department general use TECHNICAL OBSTACLES There were no technical obstacles encountered during the progress of the reflow toaster oven in the final two weeks prior to the fifth milestone report due on June 2 2006 MANAGEMENT REPORT Work was conducted diligently and with full participation of all group members 28 APPENDIX MATLAB CODE The following is the full MATLAB code for the GUI and control of the reflow soldering oven The MATLAB figure for the GUI appears in Chapter 4 in Figure 4 3 function varargout EasySolder varargin EASYSOLDER M file for EasySolder fig EASYSOLDER by itself creates a new EASYSOLDER or raises the existing singleton oe oO H EASYSOLDER returns the handle to a new EASYSOTLDER or the handle to the existing singleton oe EASYSOLDER CALLBACK hObject eventData handles calls the local function named CALLBACK in EASYSOLDER M with the given input arguments o oO EASYSOLDER Property Value creates a new EASYSOLDER or raises the existing singleton Starting from the left property value pairs are applied to the GUI before EasySolder OpeningFunction gets called An unrecognized property name or invalid value makes property application stop All inputs are passed to EasySolder OpeningFcn via varargin oO oo See GUI Options on
18. 0 C hence 5 Originally we assumed the value of to be 20 seconds and to be 5 seconds In determining the actual value of K the steady state temperature of the oven must be compared to the duty factor of the PWM signal that 1s input into the system To determine z the delay between the time when the PWM is input and when the sensors begin to detect a change in temperature is measured Finally in determining the intersection of the steady state temperature and the line created by drawing a straight line up along the maximum slope of the temperature output 2 must be found Figure 2 2 shows the resultant K value found through the method described earlier From the slope K 2 29 C Duty Factor which can be translated to 0 1702 C W Temperature vs Duty Factor 360 4 340 320 300 y 2 2971x 109 38 Temperature C 280 2 R 0 9911 260 240 220 200 50 60 70 80 90 100 Duty Factor Figure 2 2 K Value Determination Since the duty factor is an actual percentage of the maximum voltage it is possible to extract the relationships between temperature duty factor and wattage Table 2 1 shows these relationships EE 449 REFLOW SOLDER OVEN CHAPTER 2 Table 2 1 Relationship Between Duty Factor Power and Temperature Temperature C 219 250 242 297 318 334 Duty Factor 70 50 60 70 90 90 100 Power W 675 610 945 1
19. 0 360 370 380 391 401 411 422 433 443 454 464 475 485 496 506 528 538 549 559 570 581 591 602 613 624 635 646 656 667 678 689 700 711 733 744 IIZ 766 JT 788 799 810 821 833 844 235 866 878 889 900 912 923 934 946 957 969 980 1003 1014 1026 1037 1049 1061 1072 1084 1095 1107 1118 31 106 107 O WO P O1 1 I 1 3 O1 32 Lis 1 79 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 1 99 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 DAS 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 Z395 236 237 238 239 240 241 242 243 244 245 246 247 248 249 2013 2026 2040 2052 2065 2078 2091 2104 2111 2130 2143 2156 2169 2182 2195 2208 2221 2234 2247 2260 2214 2287 2299 2312 2326 2339 2332 2365 2378 2392 2405 2418 2431 2444 2458 2471 2484 2498 2511 2525 2536 2 354 2569 2583 2596 2609 2623 2637 2650 2664 2677 2691 2704 2718 2732 2745 2759 2772 2786 2800 2814 2828 2837 2851 2864 2878 2892 2905 2919 2933 2947 2960 250 251 252 253 254 239 256 Z 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 213 216 24 278 219 280 281 282 283 2
20. 0 399 5145 400 5160 seditable variables soakTemp str2double get handles soakTemp String sdegree C soakTime str2double get handles soakTime String 5100 seconds maxTemp str2double get handles maxTemp String degree C dwellTime str2double get handles dwellTime String Sin seconds solderMeltTemp str2double get handles solderTemp String degree C system variables targetTemp 0 Sinput to controller startSoak 0 time soakTemp is reached startDwell 0 time solderMeltTemp is reached openDoor 0 to open door for cool stop false controller parameters Kp 01 vProportional gain KL 0001 Sintegration gain PWMsamples 1000 number of sapmles in PWM frame 21 60 card initiation dio digitalio mcc 0 initiate digital output dline addline dio 0 Out channel to output ai analoginput mcc 0 initiate analog input aichan addchannel ai 01 add channel to input set aichan 1 InputRange 10 51 7 set voltage range for input system variable initialization z 0 Sintegrator w 0 Santi wind up amount output is larger then 1 u 0 svoutput non saturation delta 0 change in time ctrlOut 0 output of controller temperature 0 0 used for double buffer to plot time 0 0 Sused for double buffer to plot error 0 Sused for derivative Snew figure to plot hold off start time Splot trajectory po
21. 080 1245 1350 Similarly the two time constants were found The data used to find them and the values themselves are shown in Table 2 2 Table 2 2 Determination of and Duty Factor 7o 2 s 7 S 7 At s 7 5 50 31 694 663 31 60 95 631 596 35 70 35 280 245 35 80 40 572 532 40 90 40 566 526 40 100 29 496 457 29 Average 553 17 36 67 Standard Deviation 69 86 3 61 CONTROLLER MODEL The development group believed that a PID controller similar to the temperature control lab in EE 448 Actuators and Sensors would suffice As with all controllers which utilize an integrator an anti windup system 18 necessary to reduce accumulated integration error All that need be done 18 redesign of the gains The general schematic for the PID controller is as shown in Figure 2 3 0 25 Constant e GTCL Output Anti Windup Sub System Figure 2 3 PID Controller Schematic from EE 448 Temperature Control Plant EE 449 REFLOW SOLDER OVEN CHAPTER 2 Unfortunately upon testing the controller with the actual hardware it was determined through much trial and error that a PID controller was overkill That is the differential term was not necessary This is discussed in more detail in the next chapter However the MATLAB used to perform the control calculations retains the parameter in case the customer wishes to make changes to the controller For the current sys
22. 3 for this system we do not have overshoot and have fast rise and settling time Step Response System Closed Loop r to y 1 02 VO rtoy Peak amplitude 1 Overshoot 96 0 055 At time sec 15 e m System Closed Loop r to y VO r to System Closed Loop r to y in 0 98 lO r to y Settling Time sec 8 64 Rise Time sec 5 19 4 2 r4 096 o 4 0 94 0 92 0 9 0 5 10 15 Time sec Figure 3 3 Step Response of the System Using SISOTOOL STABILITY MARGINS To find the stability margin of our system we need to find the gain and phase margin using the Bode diagram According to Dorf and Bishop s Modern Control Systems the gain margin is a measure of how much the system gain would have to be increased for the GH jw locus to pass through the 1 0 point thus resulting in an unstable system The phase margin is a measure of the additional phase lag required before the system becomes unstable So as we can see from Figure 3 4 the system 18 stable for any gain and the phase margin is 96 5 deg at 3 97 radians second Bode Diagram Gm Inf Pm 96 5 deg at 3 97 rad sec Magnitude dB G1 20 1 1 1 E E oae 01 1 1 1 1 Lo 10110111 90 Phase deg Frequency rad sec Figure 3 4 The Bode Diagram Used to Determine System Gain and Phase Margin 13 EE 449
23. 7 3142 268 3226 58 3156 26913240 59 3254 601613 10111072 14211562 183 2078 22412623 26513184 27113268 TECHNICAL OBSTACLES The issue at this juncture in time concerned the deployment of cooling fans The development group planned on using computer case fans mounted outside the oven Louvers open if the fans are operational and close otherwise The main problem with using computer case fans 1s that they are susceptible to damage from high heat Considering the temperatures at which reflow soldering is to occur such fans may be irreparably damaged and thus rendered useless during the critical cooling process It was a high priority to resolve this issue and with all haste MANAGEMENT REPORT Since the components did not yet arrive little Work was done until later when the oven was putchased 10 CHAPTER 3 CONTROL DESIGN INTRODUCTION Control design involves choosing a compensator or controller suitable for the system and which will help it achieve its performance specifications For the reflow soldering oven a PID active controller was decided most appropriate for the task at hand The proportional P integral T and derivative D gains of the controller are difficult to find mathematically Only simulation has proven to consistently produce good gains Actual testing with physical hardware in temperature control can prove to be extremely time consuming so simulation is a good way to reduce the time necessary by reducing the numbe
24. 84 285 286 287 288 289 290 291 292 29 3 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 247 318 o9 320 321 2974 2988 3002 3016 3029 3043 3057 3071 3085 3099 3114 3128 3142 3156 3170 3184 3197 3212 3226 3240 3254 3268 3282 3296 3310 3324 3336 3392 3367 3381 3398 3412 3426 3440 3455 3469 3483 3497 3512 3526 3540 3535 3569 3983 3598 3612 3626 3640 3655 3670 3679 3694 3708 3722 3737 S 51 3765 3780 324 3809 3823 3838 3852 3867 3881 3896 3910 SIZO 3939 3953 3972 3986 34 322 323 324 325 326 327 328 329 330 331 3 32 333 334 335 336 SEN 33 8 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 356 357 358 359 360 361 362 363 364 365 266 367 368 369 370 274 372 218 374 375 376 Sch 378 379 360 381 302 363 384 385 386 387 388 389 390 391 392 393 4001 4016 4030 4045 4060 4074 4089 4104 4119 4133 4148 4163 4177 4192 4207 4222 4237 4251 4264 4279 4294 4309 4323 4338 4353 4368 4383 4398 4413 4428 4442 4457 4472 4487 4502 4517 4532 4547 4560 4575 4590 4605 4620 4635 4650 4665 4680 4695 4710 4725 4740 4756 4771 4786 4801 4816 4831 4846 4857 4872 4887 4902 4917 4932 4947 4963 4978 4993 5008 2023 5038 5054 394 5069 395 5084 396 5099 397 398 513
25. Design and Construction of a Reflow Soldering Oven Solomon Gebre Keith E Johnson William Joshua Russell and Clement Sung Jay Sun gebres xenonl wjar sunc Q u washington edu Dept of EE University of Washington Seattle WA 98195 2500 UWEE Technical Report Number UWEETR 2006 0010 June 16 2006 Electrical Department of Electrical Engineering University of Washington Box 352500 ng ng Seattle Washington 98195 2500 PHN 206 543 2150 FAX 206 543 3842 URL http www ee washington edu EE 449 UNIVERSITY OF WASHINGTON DESIGN AND CONSTRUCTION OF A REFLOW SOLDERING OVEN PREPARED BY THE SUPER HIGH INTELLIGENCE TEAM SOLOMON C GEBRE KEITH ERIC JOHNSON WILLIAM JOSH RUSSELL CLEMENT SUNG JAY SUN JUNE 2 2006 DEDICATED ALL THOSE GREAT SOULS THAT HAVE TOUCHED OUR LIVES AND IN DOING SO MADE THEM BETTER EXECUTIVE SUMMARY Within this summary the goals methods and results of the design and construction of a reflow soldering oven will be discussed The goal of this project was simply to produce a reflow soldering oven for the Professor Blake Hannatord s Biorobotics Lab at the University of Washington It had to track a temperature profile to produce supetiotly soldered joints on surface mounted components The development team decided to convert a conventional toaster oven to this purpose While initially only for one particular lab the customer decided to transfer the oven to the entir
26. Endured the Process of Reflow Soldering 26 Finished PGD BO RTT RET Tm T cm 27 Finalized GUI Showine Performance Of 28 CHAPTER 1 PROBLEM CHARACTERIZATION INTRODUCTION Reflow solder is used to attach surface mounted components to a circuit board The desired effect is adherence of these components to the board by melting the solder particles in the applied paste allowing their surfaces to wet and join together and finally solidifying as soon as the heat is removed Resulting from this process is a strong metallurgical bond between the components and the board The process is also faster and less expensive than soldering individually components by hand with an iron It is therefore economically practical to obtain such reflow soldering ovens if their capabilities are used with relatively high frequency CUSTOMER The organizational customer for the reflow oven was the Biorobotics Lab of the Electrical Engineering Department at the University of Washington The points of contact were Professor Blake Hannaford Phil Roan and Jesse Dosher The purpose of this project was to develop a reflow soldering oven for printed circuit boards suitable for use in small batch prototyping in Professor Hannaford s Biorobotics Lab at the University of Washington The device may be used by other laboratories as well It allows for an adjustable temperature profile via a graphical user interface on a conne
27. GUIDE s Tools menu Choose GUI allows only one instance to run singleton o see also GUIDE GUIDATA GUIHANDLES Edit the above text to modify the response to help EasySolder 5 Last Modified by GUIDE v2 5 21 2006 17 37 03 Begin initialization code DO NOT EDIT gui Singleton 1 gui State struct gui Name mfilename gui Singleton gui Singleton gui_OpeningFcn 0 14 OpeningFon gui OutputFcn EasySolder_OutputFcn ui Lavoutlon Callback 11 if nargin amp amp ischar varargin 1 gui State gui Callback str2func varargin 1 end if nargout varargout l nargout gui mainten gul State 111121 else quai Maanien UL State vararginiil end End initialization code DO NOT EDIT Executes just before EasySolder is made visible function EasySolder OpeningFcn hObject eventdata handles varargin This function has no output args see OutputFcn hObject handle to figure eventdata reserved to be defined in a future version of MATLAB handles structure with handles and user data see GUIDATA varargin command line arguments to EasySolder see VARARGIN 2 Choose default command line output for EasySolder handles output hObject set handles startButton Userdata false set handles stopButton Userdata false 9 Update handles structure guidata hObject handles
28. Materials for Reflow Solder Oven Item Description Cost USD Toaster Oven Black and Decker Convection Toaster Oven Black 40 Power Relay Solid State Power Relay with Large Heat Sink Used 30 Thermocouple Digikey Thermocouple 39 Conditioner K Type AD595 Digikey Conditioner 20 Protoboard Used 15 Op Amp Chip Contains Four Op Amps Borrowed 0 I O Card USB 1208FS I O Catd Borrowed 120 Total Cost Excluding Barrowed Items USD 144 Altera Corporation Reflow Soldering Guidelines for Surface Mount Devices June 2002 Version 4 2 EE 449 SYSTEM INPUTS AND INTERFACES REFLOW SOLDER OVEN CHAPTER 1 Inputs to the system will be the desired temperature and error signal upon taking a difference with respect to the temperature sensors The output is a pulse width modulated PWM wave to the heating elements and possibly a step output to the fans The width of the PWM signal varies depending on the desired temperature The software system interface consists of a start button profile adjust dial and temperature display It was implemented in MATLAB but will be made into an executable for convenience PROJECT PLAN The goal of the project is to develop a reflow soldering oven for printed circuit boards suitable for use in small batch prototyping It will allow for an adjustable temperature profile via a graphical user interface on a connected computer The organizational customer for the reflow oven is the Biorobotics L
29. REFLOW SOLDER OVEN CHAPTER 3 SENSATIVITY TO PARAMETER CHANGES The sensitivity of the system to changes in the parameters and can be mathematically shown Sensitivity is defined in Equation 3 3 and the system transfer function in Equation 3 4 OT a a where a is one parameter and represents the system 3 3 T Ks Kj is Fle SER ITA 3 4 Since the calculations for the sensitivity ate very complex a Texas Instruments 11 89 Titanium calculator was used Equation 3 5 shows the sensitivity for K Equation 3 6 shows sensitivity for and Equation 3 7 shows sensitivity for 7 T s T s K Tos 2 3 5 s t s Ks ste ced oe gt se Ks K 9 p c 6 7 Ks 1 3 7 M SK k It appears that the system 18 most sensitive with an increased change in and to a lesser extent changes in either direction of K This makes the most sense because the rise time of the oven is most critical to its performance whereas delay time and the heating element constant are not HARDWARE AND SOFTWARE ARCHITECTURE All major hardware components are shown in Figure 3 5 Ultimately the PC will control the oven heating profile as the controller is to be digital and implemented in MATLAB The USB I O card setves as the intermediate between the PC and the oven and temperature sensor The temperature sensor requires 5 V power
30. ab of the Electrical Engineering Department at the University of Washington The points of contact are Professor Blake Hannaford Phil Roan and Jesse Dosher This project will develop a reflow soldering oven using a domestic toaster oven and professional grade temperature controller Further the required temperature cycle calls for accurate control and temperature changes in the range of 20 to 50 C per minute The oven must also be large enough to accommodate small PC boards and reach temperatures high enough to melt a range of solders Finally the oven must be able to cool with sufficient speed in order to avoid damage to the electronics on the board being soldered A graphical user interface will also be developed to aid the uset in the use of the oven The wotk breakdown for the design and construction of the reflow soldet oven 1s shown in Table 1 2 Task No 1 0 20 2l 3 0 2 4 02 4 0 4 1 4 2 5 0 2 6 0 6 1 7 0 nei Table 1 2 Reflow Solder Oven Work Breakdown Task Project Plan Research of Professional Solder Techniques Controller Specification Derivation Hardware Research Hardware Request Hardware Reception Plant Transfer Function Determination System Modeling Controller Design Hardware Assembly Computer Interface Control Software Development GUI Development System Testing System Revision Lead All All All Josh Keith Josh Keith N A Solomon Clement Solomon Clement S
31. alisacunubnk blook Diarani 11 Ramp Response of Realistic Simulink Simulation Litres tante 12 The Bode Diagram Used to Determine System Gain and Phase Margin 13 Step Response of the System Using 5ISO TOO tet roto Perito aro 13 Hardware Schematic of Reflow Soldering 15 software Pseudocode for Oven Temperature Conttol A ette e trt etre 15 Software Architecture for Oven Temperature COntt Ol e rto ei erts edis 16 Revised Project Plan Flow Chart and Critical Path in Green sss 17 Hardware Winne AO Ac qd qut ranu 18 Simplified MATLAB Code for Control of Reflow Oven lt 19 MAE GAB AG Reto Mb 20 Photograph of Reflow Oven Temperature Sensor and I O 22 Response Reflow Solder Oven to 150 516555 2 055 4 e ede er e 23 Temperature Profile of Combined Open Closed Loop Control 24 Temperature Profile without Fan and Tray in Lowest Position 24 Temperature Profile with Rack on Highest Position without 25 Temperature Profile with Board and Tray in Lowest Position and with Fan 25 Temperature Profile with Board and Tray in Lowest Position and Fan 26 Temperature Profile with Optimal Settings and Major Door Open Disturbance 26 Boards which have Successfully
32. an 30 seconds from the soak time the ramp changes slope Finally the oven turns to full on until when the temperature comes to within 15 C of the maximum temperature in which case it turns full off MATLAB GUI is illustrated in Figure 4 3 The GUI functions simply The user must enter the soak soldet and maximum temperatures and soak and dwell times if they so desire Otherwise the defaults shown below will be used Once all the desired values have been entered the user can begin the reflow solder process by pressing the start button in the oven panel Similarly the user presses the stop button when s he wants to stop the process in order to readjust gains the soak time target temperature or for emergencies The temperature of the oven will be displayed in the temperature panel and the actual profile will appear in the large plot on the upper left of the GUI A projected temperature profile will be shown in red and the actual temperature profile will appear in blue Once the target temperature is reached the oven will turn off and the user will be prompted to open the door The command will appear where the word ready does below the target temperature and soak time inputs EasySolder 0 1 0 2 0 3 0 4 0 6 U 0 9 Relay Temperature Soak Time Time Soak Temp Solder Temp Max Temp 456 150 1 E 183 C 3 400 Celsius 400 Fahrenheit Fi
33. cted computer PERFORMANCE CRITERIA The project team developed a reflow soldering oven using a domestically available toaster oven and temperature controller which was also designed and constructed Further the required temperature cycle calls for accurate control and temperature changes in the range of 20 to 50 C per minute The oven must also be large enough to accommodate small PC boards and reach temperatures high enough to melt a range of solders Finally the oven must be able to cool with sufficient speed in order to avoid damage to the electronics on the board being soldered A graphical user interface will also be developed to aid the user in the use of the oven A generic temperature profile of the oven with respect to time is shown in Figure 1 1 The profile was also customizable That is preheat flux activation reflow and cool times were to be adjustable EE 449 REFLOW SOLDER OVEN CHAPTER 1 300 i i Dwell Time 250 i 60 to 150 SeconHs Maximum Package Body Temperature 220 C PE PROC M OP RC i n 200 Melting Temperature of Solder 183 C Melting Temperature of Solder 183 C RT ua Temperature C 1 50 p NU Uo S S S o o o 1 4 to Two Minutes gt 1 to3 C Less than 6 C a per Second per Seco
34. ds and overshoot of one percent From these performance specifications the natural frequency w has a value of 0 826 and the damping coefficient of 0 031 The transfer function of the new PI controller in series with the oven transfer function 18 shown in Equation 3 1 and the system in unity feedback 15 described by Equation 3 2 K s K G s 3 2 1 0 5 5 2005 mj Eventually the values of and K were found to be 0 06254 and 0 0591 respectively Howevet these were still not accurate and after even more trial and error the final values used in the actual control were 0 01 for and 0 0001 for K TIME DOMAIN SIMULATION With the estimated parameters the system 15 able to track a ramp input but with substantial delay error Please see Figure 3 2 The yellow line represents the input ramp function of one degree Celsius every second The blue line is the system The two lines are very nearly parallel but offset from each other by the time delay of five seconds This 18 due to the delay of five seconds S PPD i 100 120 140 160 180 Time offset 0 Figure 3 2 Ramp Response of Realistic Simulink Simulation 12 EE 449 REFLOW SOLDER OVEN CHAPTER 3 PERFORMANCE PREDICTION Based on the step response of our system the performance prediction for our system should be pretty good i e in terms of percent overshoot rise and settling time According to Figure 3
35. e comparable to those done in a professional shop La d r do Figure 5 10 Finished PCB Board To further improve the amount of data that can be gathered from the GUI additional plots for the PWM signal were added as seen in Figure 5 11 Open loop control consists of either all on or all off The PWM signal for such a case is green and appears between 100 and 0 on the y axis The PWM is a percentage with 100 indicating on and 0 meaning all off When the system enters closed loop mode the PWM plot turns black The default maximum temperature was changed from 220 C to 205 C EE 449 REFLOW SOLDER OVEN CHAPTER 5 EasySolder Projected Profile Actual Profile Open Loop PWM 96 Closed Loop PWM 96 300 400 600 700 900 Reflow Temperature Soak Time Dwell Time Soak Temp Solder Temp Max Temp 420 lsec 150 lsec 150 183 C 205 c 55 Celsius Status 131 Fahrenheit Ready Figure 5 11 Finalized GUI Showing Performance of Oven CUSTOMER RECEPTION To the best knowledge of the development group the customer appears to be satisfied with the final product Actually the word satisfied is an understatement the customer is ecstatic Not surprisingly other persons within the University of Washington s electrical engineering department are more excited about the reflow oven than even the intended customer and express a great desire to
36. e electrical engineering department for general use It now is located in Bill Lynes laboratory The physical construction of the toaster oven was key in the design process After all all the transfer functions and modeling would be based on the oven s physical properties Modifications included removing the dials and much of the internal circuitry Only three holes were made into the oven case Two of these holes accommodated the temperature sensor while the last allowed for connections to be made with the solid state power relay Later a protective box was bolted into the side of the toaster to house the relay circuit boards and provide for an attachment point of an I O catd Once the oven was ready testing was conducted to determine the various parameters in its mathematical model These measurements included the rise time of the oven the time delay in the heating elements and the oven s heating cooling rate At the same time modeling was done with estimated parameters in preparation for arrival of the actual Simulations were done on the step and ramp responses of the oven with these estimated parameters When the actual parameters were determined they were input into the pre existing models and simulated as well Overall the simulations showed that the oven was capable of accomplishing its performance criteria Actual tests on step inputs showed the oven s response to either be underdamped with large ring or overdamped with a lar
37. e estimated skill requirements for the tasks listed Table 1 2 are shown in Table 1 4 Available budget is limited to roughly 200 USD However private funds will be accessed if need be The development team will rely partly on sampled products in the construction of the reflow solder EE 449 REFLOW SOLDER OVEN CHAPTER 1 oven Such components will take several weeks to arrive However the oven itself can be procured in little time at a cost exceeding no more than 50 USD A trade study will be conducted by contractors to determine the best brand and model The development team will utilize laboratories in Sieg Hall and the Electrical Engineering Building on the University of Washington campus These facilities are believed to be ample in available space and no conflicts with other groups are expected Table 1 4 Skill Requirements for Development Tasks ros Computer Skill Electronics Skill MATLAB Skill Theoretical Skill 10 2 0 2 1 3 0 3 1 3 4 0 41 42 5 0 51 6 0 6 1 70 71 8 0 Oo O So A NW Oo elole Go Go M ol S l o SS o O SO DN O SO So SA S ho Go Go DM O NM olo o O NM All group members will be responsible for entering tasks in the online project management plan With regard to task status group members will update their own status Mr Johnson will be responsib
38. elay is situated and secured by bolts within the box Note that the terminals are not protected and therefore there 15 a risk of shock and electrocution should any part of the body come in contact The next step in preparing the oven was to prepare a series of holes to accommodate the thermocouple temperature sensor From Figure 5 1 it is seen that the holes were drilled in the left side through both the outer case and inner wall of the oven and just about the highest rack slot Dimensionally the hole has a diameter of 3 16 inches The thermocouple s wire was run behind the oven and securely attached by three eye clips Within the black box a protoboard is situated which accepts wires from the I O card and thermocouple For wiring schematics please see the previous chapter The box itself was originally patt of a HAMM radio set and converted in a protected covering for the power relay Four holes were drilled into the wings allowing for the box to be screwed to the side of the oven In order to allow for additional cooling spacers were added to create one inch gap for air flow Moreover a series of holes were drilled in the other end of the box to create the potential for air flow over the heat sink The I O card is also set on top of the box and secured by Velcro Tubing was used to protect wires from contact with the oven case on the route from the protoboard to the I O card The risk of heat damage to the wires however is very low as the
39. elp with cooling The plot will display the desired profile in red the actual temperature in blue and the control signal in green black open loop closed loop The current temperature readings in degrees C and F are found in the lower right cornet Modification to the Ma ab file can be made to change how the oven operate and how the GUI wotks It is tecommended to make a backup file before changing anything Also the files are currently set to read only to prevent accidental modification Turn off the fan when done Caring for Your Reflow Solder Oven The Reflow Solder Oven needs love to function properly Taking proper care of your oven will help work reliably for many years To clean the oven use soap and water on a towel This will get those nasty finger prints off the glass When picking up the oven DO NOT pick it up by the thermocouple or the control box The thermocouple it somewhat fragile and may bend or break The control box is head on by some small headed bolts that may rip out of the side of the oven if too much weight is being supported To pick up the oven put your hands on the oven Be careful that the oven is not hot Bend at the knees and all 1s good Hopefully you will have many good years ot reflow fun with your new oven 45 ACKNOWLEDGEMENTS EE 449 DESIGN OF AUTOMATIC CONTROL SYSTEMS Dr Blake Hannaford Professor of Electrical Engineering Mr Phil Roan Electrical Engineering Teaching Assistant Mr Eric
40. ent of the reflow soldering oven and its primary purpose The board was placed in the metal tray on the rack in the lowest position The convection fan was left on Figure 5 6 shows the projected temperature profile in red and the actual in blue The overall profile was good and the resulting board was not burned The solder joints were also nicely done and the components that were mounted still functioned after the process This is the optimal configuration and the one used for the extraction of model parameters and simulation EasySolder 250 200 150 100 50 0 0 100 200 300 400 900 Temperature Soak Time Dwell Time Soak Temp Solder Temp Max Temp 120 sec 120 sec 150 c 183 c 220 c 70 Celsius 158 Fahrenheit Ready Figure 5 6 Temperature Profile with Board and Tray in Lowest position and with Fan However if the optimal conditions are not used as in Figure 5 5 the result is a grilled board with non working parts though the joints remain good Figure 5 7 shows another successful solder job with a different maximum temperature of 205 C instead of 220 C The boards used for these two successful tests were obtained from Sandy Chan Eric Carlson and Sharon Cheung 25 EE 449 REFLOW SOLDER OVEN CHAPTER 5 EasySolder 200 300 400 500 600 700 900 Reflow Temperature Soak Time Dwell Time Soak Temp Solder Temp Max Temp 120 12 46 le as Stet 49 Celsius
41. er Temp Max Temp 120 150 sec 150 e 185 205 55 Celsius A 131 Fahrenheit Ready Figure 2 The Easy Solder GUI The GUI will allow you to set profile characteristics such as Soak Time Dwell Time Soak Temp Solder Temp and Max Temp It will start with default values that have been tested and work There are no limits to the values so some values will create a messed up looking profile If you change the 44 profile settings first hit start then stop to view the profile you created If it looks like the profile that you desire then proceed otherwise enter new values and try again You can always restart the program to get the defaults back Once you have a profile you are ready to put your PCB and pasted components on the tray and insert the tray into the oven Turn the oven convection fan using the switch on the front of the oven This will help to create an even temperature in the oven and help with cooling during the ramp down cycle The fan 1s loud so you have an audible clue that the oven 1s working The GUI will display Ready in the lower text box Clicking the Start button will start the reflow process Clicking Stop at anytime will stop the process While the process is running Running will appear in the lower text box Once the profile reaches the end of the solder cycle you will be prompted to Open Door lower text box At this time open the oven door to h
42. ge settling time Ramp inputs did not perform well either Both inputs also never fully utilized the limits of the oven so the control was split between open and closed loop During the rising of the temperature open loop would be used to turn the oven on such that the minimal rise time could be reached In between rises during areas of relative plateaus a closed loop controller was used to careful control the temperature At the end of the process the open loop control was shutdown the heating elements Cooling proved to be a concern with the oven While a convection fan distributed heat equally throughout the oven it did not expedite cooling when the heating elements were turned off Therefore it was decided that a small level of user input would be needed Through a graphical user interface GUI the user would be told to open the oven door to help cool the interior of the oven and any parts therein Programming was done to create the controllers in MATLAB In addition the GUI was also done in MATLAB small amount of circuit design was also done to integrate all the hardware together Ultimately the results of the oven were vety good The oven was used to solder the boards of another development team in charge of a shaker table Though slightly overcooked their boards worked perfectly Upon further refinement of the temperature profile another board belonging to Professor Eric Klavin s Self Organizing Systems Lab was also do
43. get hObject String returns contents of dwellTime as text str2double get hObject String returns contents of dwellTime as a double Executes during object creation after setting all properties function dwellTime CreateFcn hObject eventdata handles hObject handle to dwellTime see GCBO eventdata reserved to be defined in a future version of MATLAB handles empty handles not created until after all CreateFcns called oO Hint edit controls usually have a white background on Windows See ISPC and COMPUTER if ispc amp amp isegual get hObject BackgroundColor 0 defaultUicontrolBackgroundColor set hObject BackgroundColor white end function soakTemp Callback hObject eventdata handles hObject handle to soakTemp see GCBO eventdata reserved to be defined in a future version of MATLAB handles Structure with handles and user data see GUIDATA oe Hints get hObject String returns contents of soakTemp text str2double get hObject String returns contents of soakTemp as a double oO Executes during object creation after setting all properties function soakTemp CreateFcn hObject eventdata handles hObject handle to soakTemp see GCBO 40 eventdata reserved to be defined in a future version of MATLAB handles empty handles not created until after all CreateFcns called Hint edit controls u
44. gure 4 3 MATLAB GUI for Reflow Oven MECHANICAL DESIGN Mechanically the project consists of a toaster oven with a box attached to the side that houses the control components The box is offset from the side of the toaster oven to reduce the chances heat will affect the circuit The box is also vented and a fan may be attached later if cooling becomes an issue The I O card is attached by Velcro to the top of the box for easy removal A set screw is used to prevent the thermocouple from being pulled out of the oven Also great care was taken to 20 EE 449 REFLOW SOLDER OVEN CHAPTER 4 protect the wires running out of the oven and control box from being frayed Edges are sharp so the protective sleeves provide protection SAFETY REVIEW AND PROTECTION SYSTEM DESIGN The major safety concern was the 120V A C voltage required to power the oven The relay is housed inside the box to prevent people from inadvertently touching the power posts It is not advised to place fingers or other body parts into the box as doing so may result in severe shock electrocution The oven case gets hot so it is advised not to touch the hot oven when it is in operation TECHNICAL OBSTACLES There are no technical obstacles which obstructed the progress of the reflow toaster oven during the two weeks leading up to the fourth milestone MANAGEMENT REPORT Work was conducted diligently and with full participation of all group members All tasks were completed
45. joys sailing flying motorcycles wind surfing and a plethora of other pastimes in his limited free time and acts as Commodore for the Washington Yacht Club His specialty is in controls engineering and he possesses a minor in mathematics Josh has big guns CLEMENT SUN Clement Sung Jay Sun is the son of Lionel Lo Jung Sun PE and grandson of Hsiang Pei Sun He is descended from Tien Shu Duke of Lo An but 1s a native of Washington State A senior in Electrical Engineering at the University of Washington Clement will continue his attendance at the University in pursuit of a Masters degree His specialization is in controls and digital signal processing and he has a strong interest in chemistry and biology
46. le for updating the wiki twice per week on Tuesdays and Fridays by 5 00 pm Mr Sun will provide web space for the reports TECHNICAL OBSTACLES No technical obstacles were faced in the first two weeks of the project TEAM MANAGEMENT The development team members were on speaking terms Work was equally distributed and communication between individuals was civil and most polite CHAPTER 2 SYSTEM MODELING INTRODUCTION The most critical component of any control design is to obtain approximated linear models of the vatious parts of the equipment This chapter deals with the modeling of the system For the reflow solder oven the system is composed of the oven heating element which also serves as the actuator the controller the sensor and the computer interface input output catd SYSTEM MODEL The system model is not overly complicated It is shown below in Figure 2 1 Desired Temperature C Plant and Actuator Sakot gt PID Controller Oven Heating Output Temperature C Thermocouple T Element Figure 2 1 Reflow Solder Oven High Level System Model PLANT ACTUATOR MODEL The toaster oven that will be given the new task of soldering circuit boards has not yet been acquired However it is expected to be a forced air convection oven to distribute the heat uniformly through out the PCB The transfer function of the heating element is expected to be similar to tha
47. lot time 2 time 1 temperature 2 temperature 1 plot time l 100 4 drawnow Splot data it arrives stop get handles stopButton Userdata sreflow done open cool down cycle while stop false more then 50 degrees putvalue dio 0 Sall off if startDwell 0 amp time 1 gt startDwellt dwellTime if past dwell time openDoor 1 door set handles status String Open end time 2 time 1 s lt double buffer time time 1 toc delta time 1 time 2 temperature 2 temperature 1 double buffer input voltage round 1000 getsample ai Slookup temperature 1 while voltage gt 1ookup 2 i itl end rounded lookup i 2 lookup i 1 2 2 if voltage lookup i 2 rounded temperature 1 lookup i 1 else temperature 1 lookup i 4 1 1 end end set handles tempC String num2str temperature 1 Display temp farenheit round 9 5 temperature 1 32 Convert C to F set handles tempF String num2str farenheit SDisplay temp F plot time 2 time 1 temperature 2 temperature 1 plot time 1 0 g drawnow plot data as it arrives Stop get handles stopButton Userdata 39 s Executes on button press in stopButton function stopButton Callback hObject eventdata handles hObject handle to stopButton see GCBO eventdata reserved to be defined in a
48. nd Flux Activation 100 Temperature 50 1 to 3 Second 1 1 Preheat Flux Activation o Reflow 3J3 4 Cool Jd 0 0 50 100 150 200 250 Time Seconds Figure 1 1 Temperature Profile for Convection Reflow PLANT AND CONTROLLER IDENTIFICATION AND DESCRIPTION For the reflow soldering oven the heating elements will be the primary plant as this project involves controlling the heat of the system If the oven 1s unable to cool relatively quickly then the added fans will be the secondary plants In place of fans simply opening the door may suffice for cooling For both of these systems controllers may necessary and the systems will be placed in unity feedback creating a closed loop system A temperature sensor also makes an appearance in the overall system and is integral in the control process Lastly an analog to digital converter will be used to convert the sensor readings into digital data for a computer to process COST AND SCHEDULE CONSTRAINTS Available budget was limited to roughly 200 USD The oven was to be delivered by the beginning of June 2006 No real schedule constraints were foreseen Time in the magnitude of one to two weeks was all that was required for parts to arrive The oven itself was procured in relatively little time once a quick trade study was completed The bill of materials is shown in Table 1 1 Table 1 1 Bill of
49. ne this time with no sign of board discoloration In all cases the solder joints were comparable to those done in a professional setting and no difference between the two was observed TABLE OF CONTENTS Page EXeCUttye SUMA 222 221542552 00 2 busta ot etu I olka oba sh 1 Table E 1 Lisbot 2 NI Ad ose iv LESE DiC UE CS A V Chapter 1 Problemi Chartac tenza HOP T 1 OO ee MU O O EA DUE SUPE SP 1 01 01 11 O as 1 EIGHT de oe uen 1 Plantand Controller Identitieationand 2 Costand schedule C NRN 2 oystern Inputs and IntebPA6 eS peti itu 5 P 3 ODS 5 5 Chapter 29V SLC VIO SAG i PR A E ASR R OTO S R NR A PO 6 Eee mentee ene E 6 121 55185 epp EE CE 6 Contoler Mode NT T 8 Debsor S
50. ner it is possible to correct the incompatibility of the T and K type devices through a series of output voltage conversions A table was constructed which will allow a person or program to look up the correct temperature when provided an output from the conditioner it can be seen in its truncated form in Table 2 3 The model for the temperature sensor is shown in Figure 2 5 s T Type gt gt Thermocouple Output mV Conditioner Digital Output Range 0 20 64 Range 3 5160 Figure 2 5 Temperature Sensor Model EE 449 REFLOW SOLDER OVEN CHAPTER 2 Table 2 3 Temperature at Thermocouple Based on Conditioner Output Temp Conditioner Temp Conditioner Temp Conditioner Temp Conditioner Temp Conditioner Temp Conditioner Temp Conditioner C Output C Output C Output C Output C Output C Output C Output 20 3197 21 2650 26713212 22 2664 26813220 23 2130 228 2677 26913240 24 3254 25 3268 26 3282 27 3296 28 2745 27413310 29 2208 23412759 27513324 30 2221 235 3338 31 3352 32 2247 25712800 278 3367 33 3381 34 2274 239 3398 35 3412 36 3426 37 3440 38 3455 39 2339 24412892 28513469 40 2352 24512905 286 3483 41 3497 42 2378 2472033 28813512 43 3526 44 3540 45 3555 46 2988 292 3569 47 3002 203 3583 48 3016 204 3598 49 2471 254 3029 29513612 50 2484 255 3626 51 3640 52 3071 298 3655 53 3670 54 2000 218 2538 259 3679 55 3197 56 2026 220 3212 5
51. olomon Clement Josh Keith Keith Josh Josh All All Start Date 3 8 11 11 13 14 29 Apr 3 May 6 May 22 Apt 26 Apr 13 May 13 May 20 May 24 May End Date 7 Apt 11 Apr 14 13 Apr 14 21 Apr 2 May 5 May 12 May 25 Apr 28 Apr 19 May 19 May 23 30 Dependant Tasks All 241 3 0 4 2 6 1 3 1 3 2 4 0 5 0 41 4 2 6 0 5 1 7 0 7 0 7 0 Zd 9 0 Prerequisite Tasks N A N A 2 0 2 0 24 3 0 3 1 32 4 0 2d 4 D2 5 0 4 2 2 1 5 1 6 0 6 1 7 0 EE 449 REFLOW SOLDER OVEN CHAPTER 1 8 0 Report Compilation Clement 25 May 1 Jun N A All The task descriptions are discussed below 1 0 Project Plan Determine objective tasks and path of completion for the project 2 0 Research of Professional Solder Techniques Determine necessary hardware components and techniques for reflow soldering 2 1 Controller Specification Derivation Determine rise time overshoot system order etc 3 0 Hardware Research Find hardware capable of achieving specifications 3 1 Hardware Request Place order for delivery of all necessary hardware 3 2 Hardware Reception Final procurement of all necessary hardware 4 0 Plant Transfer Function Determination Run tests to determine the transfer function of the toaster oven 4 1 System Modeling Use MATLAB to build a realistic model of the sys
52. otection against electrical fire and possibly electrocution All group members possess cell phones and are capable of using them to request medical assistance and or other emergency pertinent authorities In addition to power management users must be aware of heat damage and burns resulting from exceedingly close contact with the heating element and or interior of the oven itself These injuties can be avoided by removing the power supply and allowing the oven and heating elements to cool to a maximum temperature of 140 F The temperature sensor can be used to determine the temperature or a quick wave of the hand through the air enclosed within the oven 16 EE 449 REFLOW SOLDER OVEN REVISED PROJECT PLAN CHAPTER 3 The project plan has been revised concerning tasks remaining to be done beginning May 5 2006 and appears below in Table 3 1 Table 3 1 Revised Reflow Solder Oven Work Breakdown Task No 4 0 4 1 5 0 MI 6 0 6 1 7 0 9 0 Plant Transfer Function Task Determination Controller Design Hardware Assembly Computer Interface Control Software Development GUI Development System Testing System Revision Report Compilation Lead Clement Solomon Josh Keith Josh Josh Keith Clement Clement Start Date 5 May 6 May 4 May 6 May 6 May 16 May 20 May 24 May 25 May End Date 7 May 12 May 12 May 12 May 20 May 20 May 23 May 30 May 1 J
53. ovide the 120V AC required Figure 1 shows all connections that need to be made USB to PC Thermocouple Conditioner Out AO DO m uw cnm A1 stripe Ground AG nd USB 1208FS I O CARD DGnd white wire 5 DGnd DGnd Ground Figure 1 USB Connections 43 Software Setup To use the reflow oven you need to have InstaCal and Matlab software installed on your PC Once these are installed you must also make sure you have the most up to date mwmcec ini file installed in you C Program_Files Matlab Toolbox DAQ DAQ Private directory We have included the mwmcc ini we used for this project Copy the files for the oven GUI to the PC The files are called EasySolder fig EasySolder m InstaCal If your Plug and Play board has been properly detected by the system InstaCal will display a Board Detection dialog box listing the board you are installing and any boards that have been detected in the system Once installed the properties configuration of the board may be changed by double clicking on the board name Test to make sure the I O card is working properly by flashing the LED Matlab You can start the oven GUI by double clicking on the EasySolder m file EasySolder GUI EasySolder Projected Profile Actual Profile Loop 90 Closed Loop PWM 50 300 400 rug 900 Relay Temperature Soak Time Dell Time Soak Temp Sold
54. p Time Variables Temperature vs Time Controller Code Start Stop Outputs GUI Plot Button Tode Temperature PWM anos Temperature Digital Input Lookup Table Figure 3 7 Software Architecture for Oven Temperature Control Notice that no pause feature is present as such an option would complicate the reflow solder process Reflow soldering should be continuously and any discontinuity in the process might produce an undesired product Within the start method code will exist to initialize channels and prepare the temperature profile as defined by the user Once everything is set up an infinite loop will begin in which code will be run control calculations will be done and the desired PWM output will be sent to the I O card The loop will continue until told to stop when the user presses the stop button on the GUI A temperature display will also be implemented in the GUI for the convenience of the user The user will be given five hard coded inputs for which three are allocated toward temperature and two towatd time RISK AND HAZARD ANALYSIS Two hazatds involve dealing with high output voltage from wall outlets and the temperature of the heating elements All due diligence will be made toward propetly connecting the power source with various elements in the oven such as the power relay Testers and users will be adequately shielded from live high voltage wires through proper insulation solutions Along with this goes pr
55. possible Here there is no control of temperature The temperature is raised to a set preheat value Since this is hardcode it must be changed in the code itself and no option to do so will be given in the GUI The third part is the actual controller When the temperature is not rising rapidly the controller will be allowed to take control of the temperature Using a discretized set of equations for the integrator and differentiator the gains are used to calculate the necessary output in the form of a PWM It must also be mentioned that the software corrects for the error between the conditioner and the thermocouple A lookup table was created which translates a given voltage to a specific temperature This array must be loaded before any temperature measurements take place targetTemp 0 Stemperature step size temperature 1 lookup i 1 PWMsamples 1000 number of sapmles in PWM frame else startSoak 0 temperature 1 lookup i 1 1 Kp 01 SProportional gain end Ki 0001 integration gain plot time 2 time 1 temperature 2 temperature 1 Kd 0 drawnow Splot data as it arrives dio digitalio mcc 0 initiate digital output end dline addline dio 0 Out add channel to output ai analoginput mcc 0 initiate analog input putvalue dio 0
56. r of gain candidates into a relatively narrow range With the acquisition of a well tuned controller the product would be well on its way to completion CONTROL GAIN CALCULATION Unfortunately no known method has yet been devised for calculating the variables of K and K such that the system meets performance specifications of any kind let alone no overshoot Hence they must be chosen intuitively in other words at random in a way that results in the most favorable response This can be done through guessing the values and simulating the system in a program such as Simulink The gains for the PID controller have been determined to be in the ratio of K 1 K70 5 K 0 025 These numbers were obtained through simulation using Simulink in MATLAB A realistic block diagram is shown below in Figure 3 1 Figure 3 1 Realistic Simulink Block Diagram While the rest of this chapter concerns findings with estimated model parameters something must be said about the gain calculations used for the actual system After many hours of testing with the EE 449 REFLOW SOLDER OVEN CHAPTER 3 hardware it was determined that the differential term was unnecessary for successful control of the oven s temperature In addition the average K value for the oven determined in the last chapter was not used in favor of 4 3794 which is the K value at high temperatures While the system should track a ramp a step response was considered with a rise time of 180 secon
57. s not suggested to disable the convection fan even for the sake of peace and quiet while the oven 15 in operation and a board is being soldered EasySolder 100 200 300 400 900 Temperature Soak Time Dwell Time Soak Temp Solder Temp Max Temp 120 sec 150 sec 150 C 183 220 70 Celsius 158 Fahrenheit Ready Figute 5 4 Temperature Profile without Fan and Tray in Lowest Position 24 EE 449 REFLOW SOLDER OVEN CHAPTER 5 Figure 5 5 shows the temperature profile that 1s obtained from the oven when the rack 18 moved to the highest position in the oven and the tray 18 removed The convention fan was operational From the plot the temperature changes very quickly without the tray as a barrier to rising heat This makes sense because the thermocouple is located high up in the oven and therefore registers the change in temperature much more rapidly than it would otherwise Removing the tray however is also not recommended for reasons to become apparent latet EasySolder 0 100 200 300 400 600 900 Temperature Soak Time Dwell Time Soak Temp Solder Temp Max Temp 120 sec 150 sec 150 c 183 220 c 81 Celsius 178 Fahrenheit Ready Figure 5 5 Temperature Profile with Rack on Highest Position without Tray One of the most important tests that were conducted was for the soldering of an actual board with surface mounted components This of course is the int
58. sually have white background on Windows See ISPC and COMPUTER if ispc amp amp isegual get hObject BackgroundColor 0 defaultUicontrolBackgroundColor set hObject BackgroundColor white end oe function solderTemp Callback hObject eventdata handles hObject handle to solderTemp see GCBO 5 eventdata reserved to be defined in a future version of MATLAB handles Structure with handles and user data see GUIDATA Hints get hObject String returns contents of solderTemp as text str2double get hObject String returns contents of solderTemp as a double Executes during object creation after setting all properties function solderTemp CreateFcn hObject eventdata handles hObject handle to solderTemp see GCBO eventdata reserved to be defined in a future version of MATLAB handles empty handles not created until after all CreateFcns called Hint edit controls usually have a white background on Windows See ISPC and COMPUTER if ispc amp amp isegual get hObject BackgroundColor 0 defaultUicontrolBackgroundColor set hObject BackgroundColor white end oe function maxTemp Callback hObject eventdata handles hObject handle to maxTemp see GCBO eventdata reserved to be defined in a future version of MATLAB handles structure with handles and user data see GUIDATA Hints get hObject String returns contents of
59. supply to be provided by the I O card It outputs an analog signal in the range of 0 0 to 5 0 V The I O card will feed the input from the temperature sensor to the PC which will take the appropriate action in controlling the temperature of the oven The MATLAB program will send a signal to the I O which determines the duty factor of the PWM signal When the duty cycle is high 5 V will be placed across the relay allowing the AC current from the wall outlet to flow through the heating element When the duty cycle is low no voltage will be placed across the relay input and it will switch off the heating element by breaking the circuit 14 EE 449 REFLOW SOLDER OVEN CHAPTER 3 To Windows PC Heating Element Temperature Sensor we o SAN US EE Output 0 5V 4 USB K Type Conditionet TUN 1208FS a CO 7 Ground 1 e AD595 Analog 0 5V e Board i Ground I Type Thermocouple Figure 3 5 Hardware Schematic of Reflow Soldering Oven Software is to be implemented in MATLAB which is to all be encapsulated within the automatically generated Graphical User Interface file Included within the code will be the PID controller in addition to the anti windup subsystem Invariably the next step would be to convert the controller into a form which can be used to test the actual physical hardware This 15 done by taking the inverse transform of the transfer function in
60. t of the Temperature Control Laboratory TCL board from EE 448 Actuators and Sensors That model assumes the plant transfer function to be linear and have the form of Equation 2 1 Since the toaster oven deals with the dispersion and introduction of heat to a system a simple yet effective model would follow Newton s Law of Cooling a first order differential equation Modified for purposes of this project Equation 2 1 represents the system with additional constants and vatiables T X x 2 1 The variable in Equation 2 1 represents the duty factor of the pulse width modulated PWM input signal The variable x represents temperature where x Toven temperatures By taking the Laplace Transform of Equation 2 1 the result is Equation 2 2 EE 449 REFLOW SOLDER OVEN CHAPTER 2 TSX s X s KU s 2 2 The frequency domain transfer function derived from Equation 2 2 is shown in Equation 2 3 2 3 ZST x ZPF Hence the toaster oven 15 modeled by the transfer function in Equation 2 3 To complete system model the values for K 7 and 7 must be determined In the future the oven can be controlled by using Equation 2 3 as the model for the system In out case we will assume K will be dependent on the power output of the oven and the temperature at full blast If we assume the rated power output of the oven being around 1500 W and at full blast the oven temperature can reach 30
61. tem 4 2 Controller Design Use MATLAB and associated tools to build a controller for the toaster oven 5 0 Hardware Assembly Make necessary modifications to toaster and implement a sensor 5 1 Computer Interface Connect toaster oven to computer via an interface so that software can run from the computer to control temperature 6 0 Control Software Development Build the controller in MATLAB 6 1 GUI Development Build a GUI to interface with the toaster oven so that a user does not need to deal directly with code Eventually there should be an executable 7 0 System Testing Test the hardware and software for functionality 7 1 System Revision Troubleshoot and debug problems in the system 8 0 Report Compilation Compiling the report from previous milestone reports detailing the specifics and development of the final product For task dependencies see Table 1 2 The development group consists of four senior undergraduates in Electrical Engineering Their skills are rated below in Table 1 2 They are rated on a scale from 0 to 3 Zero having absolutely no ability in that area whatsoever and three having achieved complete and utter mastery Table 1 3 Rated Skills of Reflow Solder Oven Personnel Electromechanical Theoretical Computer Skill Electronics Skill MATLAB Skill Hardware Skills Ability S Gebre 2 2 2 3 3 K Johnson 2 2 2 1 1 W Russell 3 3 2 2 1 C Sun 1 2 2 2 2 In addition to the personnel skills th
62. tem however is set to zero thus effectively removing it from the transfer function and all control calculations SISOTOOL was used to determine the gains of the PID controller for the approximated parameters of the plant model The result of the step response is as shown in Figure 2 4 The SISOTOOL result has a nice rise time of 0 567 s and settling time of 4 01 s with a slight overshoot of 1 46 It should be noted that extremely high gains were used and that future experiments had gains reduced while maintaining the ratios between them and have the luxury of better model parameters Step Response 155 EF System Closed Loop rtoy 150 VO r to y e Peak amplitude 152 System Closed Loop r to y Overshoot 1 46 VO rto y stem Closed Loop r to y At time sec 1 54 Settling Time sec 4 01 VO rto y Rise Time sec 0 567 140 7 135 130 0 0 5 1 1 5 2 2 5 3 3 5 4 4 5 Time sec Figure 2 4 Step Response of Toaster Oven Using SISOTOOL SENSOR MODEL Based on the specifications the voltage of the device changes in relation with temperature and 18 extremely linear over a large range of temperatures Unfortunately the voltage output is extremely small An AD595 conditioner integrated circuit allows the thermocouple to be used From the datasheets provided by the manufacturers of the thermocouple and conditio
63. the frequency domain and bringing it into the time domain Equations 3 8 and 3 9 show this process U s K H s K B Ks E s 3 8 7 AZ u t K e t eZ Ki K K eZ 24 K 3 9 The anti windup would be included within the integral term Even now however the function cannot be used due to the fact that it is continuous Computers are digital creatures and the previous equations must therefore be digested in order for them to be able to be simulated This process happens to be called discretization and the product is discrete rather than continuous in nature The software pseudo code and architecture is shown below in Figures 3 6 and 3 7 respectively INPUT METHOD Allow users to input values into static boxes GUI provides for value recall MATLAB GUI M FILE START METHOD nitiate channels User input for temp profile Load user input values Begin reflow solder process Create temperature profile arrays Abort reflow solder process While the program is not stopped Display temperature Run the temperature profile and controller STOP METHOD Stop value is true or false initiated as false Pressing the button changes the value to true Start method constantly checks stop value Figure 3 6 Software Pseudocode for Oven Temperature Control 15 EE 449 REFLOW SOLDER CHAPTER 3 MATLAB GUI EasySolder Uset 1111 Load Tem
64. ture 1 plot time 2 time l uold u l0 k drawnow Splot data as it arrives stop gert bandles stopBuLton Userdata uold 417102 end startSoak targetTemp solderMeltTemp ramp up to solder melt temp while toc lt startSoak soakTime 60 5 stop false for thirty seconds less then soakTime time 2 time 1 Sdouble buffer time time 1 toc delta time 1 time 2 temperature 2 temperature 1 double buffer input voltage round 1000 getsample ai look up temperature 1 while voltage gt lookup i 2 i i l end rounded lookup ip 2 lookupli 1 2 2 if voltage lookup i 2 lt rounded temperature 1 lookup i 1 else temperature 1 lookup i 4 1 1 end set handles tempC String num2str temperature 1 Display temp farenheit round 9 5 temperature 1 32 Convert C to F set handles tempF String num2str farenheit Display temp error targetTemp temperature 1 compute error Z Zz Ki error ctrlOut u PWMsamples delta Sintegrate error ctrlOur Kp error z 4 compute output oO Fh perlou gt 1 u PWMsamples elseif ctrlOut O if duty factor too large make duty factor 1005 11 duty too small oO oO Fh u 0 make duty 05 else Sotherwise u round ctrlOut PWMsamples duty stays same end for count Stor first part of PWM putvalue dio 1
65. un Dependant Prerequisite Tasks Tasks 6 0 4 1 5 0 6 0 N A 5 1 N A 6 0 7 0 5 0 6 1 5 0 5 1 7 0 6 0 141 6 1 8 0 7 0 N A All A flow chart has been created to illustrate the critical path of the project It can be seen below in Figure 3 8 May 4 5 0 4 0 f sa May 6 4 7 May 8 6 0 6 1 May 16 May 12 May 20 7 0 23 7 1 May 30 May 25 8 0 Figure 3 8 Revised Project Plan Flow Chart and Critical Path in Green TECHNICAL OBSTACLES There are no technical obstacles which obstructed the progress of the reflow toaster oven MANAGEMENT REPORT Work was conducted diligently and with full participation of all group members All tasks were completed on time 17 CHAPTER 4 DETAILED DESIGN INTRODUCTION Detailed design of the hardware and software is discussed in this chapter The software used to control the temperature of the oven using a digital PI controller also appears within the chapter ELECTRICAL HARDWARE AND WIRING DESIGN The electrical hardware wiring diagram appears below in Figure 4 1 20 VAL 3 VIL Digital ut Thermocouple E a Figure 4 1 Hardware Wiring Diagram The reflow oven utilizes several components in its control The most important of which and most expensive is a USB 1208FS I O card This device provides a digital output in the range of 0 and 5 V to the solid state relay When no voltage 15 placed o
66. ut was still better than a step and so it was decided to use a combination of open and closed loop control The open loop system was used to cause a rapid climb in temperature and closed loop to carefully control the temperature between the use of open loop Figure 5 3 shows the results of this combined open closed loop controller Temperature Profile of Reflow Solder Oven 225 200 175 150 FP 100 75 50 25 Temperature C 0 0 60 120 180 240 300 360 420 480 540 600 660 720 780 840 900 960000 Time seconds Figure 5 3 Temperature Profile of Combined Open Closed Loop Control Portions of the graph in Figure 5 3 which are smooth and narrow indicate the use of closed loop control approximately between 150 and 400 seconds The remainder of the plot consists of thick blue line indicating open loop control either all on or all off PERFORMANCE AND STABILITY TESTING With the initial testing complete and a finalized controller the limits of the system can be tested Several tests were done on the oven to determine the optimal setup of oven internally This involved different configurations with the rack and oven tray and convection fan Figure 5 4 illustrates the results of turning off the convention fan While it may seem that the absence of the fan does not affect the profile what 18 not shown 18 the inconsistency and unequal distribution of heat within the oven It i
67. ver the relay the switch 15 turned off and current from the wall 1s allowed to pass through the heating elements of the oven Likewise when 5 V is placed across the relay the switch is turned on allowing current to flow A manual switch allows the user to turn on and off the convection fan For the purposes of reflow soldering the fan should never be turned off during the reflow soldering process The next component to note is the T Type thermocouple interfaced with a K Type conditioner Because of the incompatibility between these two parts software will need to be written to correct for this The thermocouple and condition work together as a unit to provide analog temperature data to the I O card The I O card provides a power supply of 5 V to the unit The thermocouple conditioner set sends its data to the analog input of the I O through a buffer The buffer is EE 449 REFLOW SOLDER OVEN CHAPTER 4 necessary to block outgoing current from the I O as such current would interfere with the functionality of the conditionet SOFTWARE PROGRAMMING Control software programming was performed in MATLAB and can be seen in Figure 4 2 The code consists of three major parts The first part is the initialization ot input and output channels in addition to the various variables needed for calculations The second and third parts occur with a loop which terminates on command of the user The second part involves ramping up the temperature as fast as

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