Capacitance Free Length Gage User Manual
Contents
1. Figure 1 Calibration To determine the corresponding spring length from the output voltage the system must be calibrated with each use During calibration the user winds a spring but does not cut it off The user then uses the system interface to teach it three measurement points These three points are used in the calculation of spring length during production The probe s micrometer is used to simulate changes in spring length by changing the probe s distance from the spring During calibration the variables used in the length calculation are set These variables are Variable Example Nominal length desired length 45mm Tolerance imm Output voltage for nominal spring 0 065VDC 45mm spring Output voltage for nominal plus tolerance 4 56VDC 46mm spring Output voltage for nominal minus tolerance 3 84VDC 44mm spring The relationship between the output voltage and the spring length is nonlinear If actual length measurements are to be reported to the user then the spring length calculation will have to include a linearization algorithm The included software provides a function for doing this using a second order three point curve fitting algorithm parabolic If the voltage is only used to sort springs which exceed the tolerance then linearization is not necessary Length di Voltage 8 7 6 5 4 3 2 1 0 1 2 3 Spring lengths are reported as deviation from nominal For Figure 2 a2. V2 V2 V3 V3 V3 R2 3 L1 V1 L2 V2 L3 V3 R3 0 VI V1 V2 V2 V3 V3 R3 1 V1I V1 VI1 V2 V2 V2 V3 V3 V3 R3 2 V1 V1 V1 V1 V2 V2 V2 V2 V3 V3 V3 V3 R3 3 L1 V1 V1 L2 V2 V2 L3 V3 V3 divider R1 0 for i 0 i 4 i R1 i R1 i divider divider R2 0 for i 0 i lt 4 i R2 i R2 i divider R1 i divider R2 1 if divider return 1 for i20 i 4 i R2 i R2 i divider divider R3 0 for i 0 i 4 i R3 i R3 i divider R1 i divider R3 1 for i 0 i 4 i R3 i R3 i divider R2 i divider R3 2 if divider return 1 14 for i20 i lt 4 i R3 i R3 i divider R313 b Fe SS RBLZ p CORSI RTD RZS I A RAE RISI 337 Il Wo N Ww u N N u Ww Ww return 0 lp_find_horizontal_point Description Finds the horizontal point It uses the a b c coefficients calculated above and its output is used in the convert_volts_to_length function The derivative with respect to x of a x x b x 15 2 a x b To find the horizontal zero slope point you must solve for x when 2 a x b 0 This comes out to be x b 2 a Return If the values sent are invalid i e tolerance gt nominal a 1 is returned value otherwise the function will return 0 Parameters nominal Float The nominal desired length for the spring to be measured tolerance
3. ef Potentiometer Optional ten turn potentiometer for probe zeroing 1 J1 3 is automatically disabled when potentiometer is connected to J2 Data Acquisition System 5 0 5 VDC 0 7A J1 Connections Wire Colors Pin Signal Notes White 1 Power In 5 0 5VDC 0 7A max Brown 2 Probe Voltage Out 10VDC proportional to spring length more positive longer Black 3 Zero Voltage In 0 to 10VDC input voltage used to zero output voltage offset Negative voltage 0 1V input change yields approximately 5V output change Blue 4 Test Voltage Out lt 0 5VDC normal operation gt 0 5VDC when probe tip is grounded by contact with spring or other object Gray 5 Ground Common Software The floppy disk supplied with the Capacitance Free Length Gage contains several examples of C language functions that may be useful in the implementation of the driver None of these functions are required to use the driver They are provided as tested implementation examples They carry no warranty of functionality within any given system They are ANSI C compatible and should be useable in most systems using a C development environment All functions start with Ip_ to identify them as Larson Procedures The following procedure list gives detail on the provided functions to ease the understanding and implementation of them Ip_initialize Initializes 1 global vari
4. heating element that keeps the probe electronics at 130 F to prevent thermal drift This circuit is controlled by a very low speed integrator If power is interrupted to the probe the probe will require two minutes to stabilize Zeroing the Output Voltage Offset To provide a full voltage range during production the output voltage for a nominal spring must be near zero There are two ways to zero the output voltage useaten turn potentiometer accessible to the user provided optionally e or use a zeroing voltage into pin 3 of J1 When using the potentiometer the zeroing voltage input J1 3 is disabled The potentiometer provides a stable reference for the driver When using the zeroing voltage input the voltage must be stable and low in noise The zeroing voltage is amplified Gain 50 therefore any thermal drift or electrical noise can have a significant affect on the output voltage and the spring length measurement Zeroing Errors If the probe is too close to the spring the driver cannot be zeroed The output voltage will remain positive The probe must be moved farther away from the spring and re zeroed If the probe is too far away from the spring the driver cannot be zeroed The output voltage will remain negative The probe must be moved closer to the spring and re zeroed Probe Contact Errors Sometimes it is helpful to notify the operator if a spring makes contact with the probe tip This may indicate a broken cu
5. into the SPD 2 double high 0 0 low is the current lower limit of analog output voltage The desired voltage should be higher than this 10 volts is the smallest zeroing voltage you should put into the SPD 2 double low 10 0 in is the most recent voltage read double in 0 0 last in is the previous voltage read double last in 1 0 out is the voltage to be sent out to the probe driver double out Three conditions must be met for the loop to continue 1 i 100 If the loop has executed 100 times there s probably something wrong 2 fabs in last in 0 01 Once the voltage read back from the probe driver stops changing you know that you ve zeroed in on the appropriate output voltage 3 high low If high becomes less than low you have reached the zero volts point or something has gone wrong for i20 i 100 amp amp fabs in last in 0 01 amp amp high gt low i Output a voltage halfway between the upper and lower limits out high low 0 5 lp_volts_out out 11 Update last_in and read new voltage last_in in in lp get probe voltage Check whether new voltage is positive or negative and update high or low accordingly if in 0 low out else high out Check for errors if i 100 fabs in gt 1 0 return 1 return 0 get spring length
6. spring length and activates and sorting devices 4 System cuts off spring 5 System corrects for any length error Important Considerations Sensitivity Probe sensitivity is defined as the rate of change of the output voltage for a given change in spring length For example a change of 5V for a Imm change in length is more sensitive than a change of 1V for a Imm change The probe sensitivity is dependent on the size of the gap between the probe tip and the spring The smaller the gap the greater the sensitivity When calibrated the output voltage range should be at least 1V and not more than 8V If the probe is too sensitive more than 8V output change then the probe must be moved further away from the spring and recalibrated If the probe is not sensitive enough less than 1V output change then the probe must be moved closer to the spring and recalibrated These means that calibrations with smaller tolerances will have to be closer to the spring and larger tolerances may be farther away Multiple Sampling To reduce the affect of any electrical noise in the system probe voltage readings should be captured with multiple readings then averaged For example read and store ten readings of the probe voltage sum the readings and divide by ten The number of readings to be taken and averaged will depend on the running speed of the system and the amount of noise present in the signal Thermal Stability The probe features a
7. Description Reads the analog voltage from the probe and converts it to length setup probe must be completed before this function is used Return value Spring length Parameters none double lp get spring length return lp convert volts to length get probe voltage Ip_get_probe_voltage Description Acquires the output voltage from the spring probe Range is 10VDC Return value Voltage reading Parameters double lp get probe voltage double voltage put appropriate voltage reading code here return voltage 12 Ip_volts_out Description Puts a new analog voltage on the D to A converter output Range is 0 to 10VDC This is used to zero the output voltage fo the driver Return value voltage actually set Parameters double lp_volts_out double voltage if voltage gt 0 0 voltage 0 0 else if voltage lt 10 0 voltage 10 0 put appropriate voltage output code here return voltage Ip_convert_volts_to_length Description Converts a voltage to its associated length based on the specifications set in lp setup probe This function is called from within get spring length Return Value Spring length Parameters voltage The voltage to be converted to a length double lp convert volts to length double volts Check to see if the aforementioned horizontal point has been reached or exceeded if nominal voltage horizontal point nom
8. Float The tolerance for the springs being measured This determines the point at which springs are sorted and the point at which the probe will setup int lp find horizontal point double a double b double x 1 0 0 return 1 x b 2 0 a return 0 15 Gaging System TWO YEAR WARRANTY The Larson Systems Inc Gaging System parts and labor are warranted against defects in material and workmanship to the consumer for a period of twenty four months from the date of purchase The foregoing warranty is exclusive and in lieu of all other warranties whether written oral or implied including any warranty of fitness for purpose This warranty covers all parts except consumable items It applies only to gages and accessories which have been installed and operated in accordance with instructions in our reference manuals have not been tampered with in any way misused suffered damage through accident neglect or conditions beyond our control and have been serviced only by authorized personnel Larson Systems Incorporated is not responsible for loss in operating performance due to environmental conditions such as humidity dust corrosive chemicals deposition of oil or other foreign matter spillage or other conditions beyond our control There are no other warranties expressed or implied and Larson Systems Incorporated shall not be liable under any circumstances for incidental or consequential damage If it appears within t
9. LTS QUT ineat eet e i e Ob Ue aane s 13 EP CONVERT VOLTS TO LENGTH iieri ie ee e EEG ETE DH TI RETRO REDE 13 EP FIT POINTS eee eie tette ro e e eb pie edat 14 EP EIND HORIZONTAL POINT ete vest ani eie m REED PEE EG PETENTE NE TERRE TIR NERO EFE QE ERE 15 Introduction The Larson Systems Capacitance Free Length Gage is a self contained probe driver assembly and probe for adding capacitance based spring free length measurement to OEM coilers and gages A disk with sample C code is included to assist in the implementation of the instrument An optional National Instruments data acquisition card can also be included The system is designed for use in CNC coilers and grinders enabling the CNC designer to incorporate internal gaging without the necessity of designing gaging hardware or interfaces to external gages This manual contains information on the basic concepts of spring measurement the included hardware and the included software Spring Measurement Basics Non contact spring measurement is accomplished with a probe containing a non contact sensor and an integral micrometer The probe is mounted to the coiler face and positioned so the spring approaches the probe tip as it is formed figure 1 DI The probe uses an electric field to measure the gap between the probe tip and end of the spring Changes in this gap create changes in output voltage which correspond to changes in spring length
10. Larson Systems Inc Capacitance Free Length Gage User Manual SPRING MEASUREMENT BASICS uuu ccsscsssssccseccscssccseccsccssscsccsessesseccscssscssecsssssscssecssessssssessssssessssecsoes 3 GALTBRATION T Bee 3 AC TYPICAE CALIBRATION CY CLES sie a aa ERGEBEN TRE E TED 4 A TYPICAL MEASUREMENT CYCLE i 4 IMPORTANT CONSIDERATIONS cri 5 AYANT EE 5 itae 5 ThermalStability sc de ces ass eae OC tete 5 Zeroing the Quiput Voltage Offset ae EPOR OR TORO OPENED ONERE 5 a tl 6 Probe CONLACENT ONS a UE aa MUT ETE casali ARE Aa 6 ls Wd DER 7 PROBE DIR D RE RIE ERRE RAEE ERG UE Na Cela Sua 7 CONNECTIONS ERR EORR ERO UU EUR ERAN ER SERI RU URINE EUN FUR EIU 8 SOFTWARE 9 EP INITIA LIZE avallare iba 9 EP SETUP PROBE enne ie ir HRS 9 ZERO PROBE 5 ener ipee oun 11 EP GET SPRING LENGTH carina eundi tene diee ien eniin 12 GET PROBE VOLTAGE connettersi bee beliebt 12 EP VO
11. ables All variables are normally set to valid values during normal operation however this function is provided to prevent any unexpected errors after start up Description void lp initialize void short_voltage 1 0 nominal_voltage 0 0 long_voltage 1 0 short_length 1 0017 nominal_length 0 0 long_length 1 0 fit points short voltage nominal voltage long voltage short length nominal length long length amp a coeff amp b coeff amp c coeff ys find horizontal point coeff b coeff amp horizontal point lp setup probe Description Goes through the steps necessary to zero the probe and set up a linearization curve These steps must be done every time the setup is changed Much of this code must be written by the user because it involves taking input from the operator which can be done many different ways This is simply a list of steps in the correct order Return value none Parameters none void lp setup probe instruct user to put a nominal length spring in front of the probe y lp zero probe obtain nominal spring length from user and store in nominal length X7 nominal length nominal voltage lp get probe voltage instruct user to adjust the micrometer probe to simulate a long maximum length spring obtain long spring length from user and store in long_length long_length long_voltage lp
12. ctual spring length the nominal length will have to be added Using our example values from above the length function may return a length deviation of 0 02mm The actual spring length would be 45 02mm A typical calibration cycle 1 Operator enters the nominal spring length Operator enters the tolerance Operator winds a spring but does not cut off Operator sets the probe gap see Important Considerations below Operator activates a Teach or Set Nominal button ues Ske RD System adjusts output voltage to near zero or the operator is instructed to zero the output with the potentiometer 7 System captures and stores the remaining offset voltage This voltage represents a nominal spring 8 Operator uses the micrometer to adjust the probe position to simulate a spring at the long tolerance point 9 System captures and stores the probe voltage for long tolerance 10 Operator uses the micrometer to adjust the probe position to simulate a spring at the short tolerance point 11 System captures and stores the probe voltage for short tolerance 12 System uses stored spring length specifications and captured voltages to generate linearization coefficients Ip fit points 13 Operator returns probe to nominal gap and starts production A typical measurement cycle 1 System coils a spring no cutoff System reads probe voltage an average of at least ten readings 2 3 System calculates
13. get probe voltage instruct user to adjust the micrometer probe to simulate a short minimum length spring xy obtain short spring length from user and store in short length xy short_length short voltage lp get probe voltage if 1 lp fit points short voltage nominal voltage long voltage short length nominal length long length amp c coeff amp b coeff amp a coeff If there is a problem with the numbers input to fit points code within these brackets will be run if lp_find_horizontal_point a_coeff b_coeff amp horizontal_point If there is a problem with finding the horizontal point code within these brackets will be run 10 Ip_zero_probe Description This function will zero the output voltage of the probe driver by adjusting the zeroing voltage put out by a D to A converter When using a potentiometer for zeroing this function is substituted by instructions and feedback to the user to adjust the potentiometer Return If there is an error in acquiring the voltage or the probe cannot be zeroed value a 1 is returned otherwise the function will return 0 Parameters none int lp zero probe i is a counter to show how many times the loop has been executed The ae high is the current upper limit of analog output voltage The desired voltage should be less than this 0 volts is the largest zeroing voltage you should put
14. inal voltage horizontal point amp amp volts horizontal point nominal voltage horizontal point amp amp volts horizontal point return a coeff horizontal point horizontal point b coeff horizontal point c coeff This point in the program should be reached under normal operating conditions return a coeff volts volts b coeff volts c coeff 13 Ip_fit_points Description Calculates the coefficients of a quadratic curve that fits the three points given Return If the values sent are invalid a 1 is returned otherwise the function will value return 0 Parameters V1 V2 V3 Doubles The measured probe output voltage at the short nominal and long spring lengths L1 L2 L3 Doubles Short nominal and long spring lengths Be sure they are in the same order as the voltages a b c Double pointers The three quadratic coefficients that determine the curve that fits the three points V1 L1 V2 L2 V3 L3 Length a Voltage Voltage b Voltage c int lp fit points double V1 double V2 double V3 double L1 double L2 double L3 double a double b double c irit 15 double R1 4 R2 4 R3 4 divider R1 0 3 R1 1 VI V2 V3 R1 2 V1 V1 V2 V2 V3 V3 R1 3 L1 L2 L3 R2 0 V1 V2 V3 R2 1 VI V1 V2 V2 V3 V3 R2 2 VI FVI VI V2
15. toff tool The Test Voltage from J1 4 indicates this condition Under normal operation conditions the voltage on this pin is less than 0 2VDC If something contacts the tip the Test Voltage will rise to over 0 7VDC Using a routine to verify that this voltage is below 0 5VDC will monitor and report any probe contact Hardware Probe Driver The Capacitance Free Length Driver is a self contained system for driving the non contact probe The driver electronics produce an output voltage which is proportional to the length of the spring at the probe Longer springs closer to the probe produce more positive output voltages The output voltage offset must be adjusted to near zero for a nominal length spring Probe Zero adjustments can be made by a DAC output voltage from the users data acquisition system or by a ten turn potentiometer that can be purchased with the system Figure 3 The probe driver is mounted with two screws M3 0 5 Do not loosen or remove the probe connector nut See Figure 3 for panel cutout specifications The maximum depth of the threaded mounting holes is 9 5mm 3 8 inch Connections Probe The probe voltage must be adjusted to zero when measuring a nominal length spring This zero adjustment can be accomplished two ways A potentiometer connected to J2 or An adjustable DC voltage to J1 3 This voltage must be VERY stable and noise free for reliable operation vam
16. wo years from the date of shipment by Larson Systems Inc that the equipment as delivered does not meet the warranties specified above and the Purchaser so notifies the Larson Systems Inc promptly Larson Systems Inc at its Mpls MN facility shall correct any defect including non conformance with the specifications at it s option either by repairing any defective part s or by making available a replacement or required part Warranty service is conducted at LSI s facilities in Minneapolis MN Return the tester freight prepaid during the warranty period and Larson Systems Incorporated will make a warranty determination repair and return the tester freight collect Shipments sent collect will be rejected The foregoing shall constitute the sole remedy of the Purchaser and the sole liability of Larson Systems Inc 16 LSE Larson Systems Inc 10073 Baltimore Street NE Minneapolis MN 55449 4425 www larsonsystems com 17 763 780 2131 VISA 1 877 780 2131 Fax 763 780 2182 ara info larsonsystems com 060 1000 0075 00A
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