Speed Control With MODBUS - AutomationDirect Technical Support
Contents
1. _FirstScan LD SPO 1 K5 OUT V4010 co C10 RST _1Second SP4 co 2 PD co LD 3 CTAO OUT Transactions s v4000 SP116 CNT 4 CTO co K9990 SP116 C1 C2 MRX 5 CPU DCM Slot CPU Port Number K2 Slave Address K2 Function Code 03 Read Holding Registers Start Slave Memory Address K40001 Start Master Memory Address V3000 Number of Elements K10 Modbus Data type 584 984 Mode Exception Response Buffer V10000 C1 SET If the content of V3011 is not equal to 5 and C1 is ON turn ON C2 C1 V3011 K5 C2 6 lt SET Continues on next page 1st Ed 6 09 13 Speed control with MODBUS EE Lines 2 to 4 are used for the determination of data transmission speed as explained on a previous page Rungs 5 6 and 7 were already explained Rung 8 turns OFF the bit C2 when the value in P2 30 is set to 5 Rung 9 executes the writing of 3 words to the PO 10 to PO 12 parameters Rungs 10 11 and 12 change the bits of the V2002 memory to cause that P4 07 gives the digital inputs servo enable and select one of the speeds If C2 is ON copy the value of 5 into P2 30 to allow only RAM writing C2 SP116 MWX 7 A CPU DCM Slot CPU Port Number K2 Slave Address K2 Function Code 06 Preset Single Register Start Slave Memory Address K40010 Start Master Memory Address V4010 Number of Elements n2. We can also read the status the current position the current torque the motor speed as a number directly expressed in rpm and not only through the single analog signal Use of MODBUS with Sureservo A characteristic of the Sureservo drive is the possibility of linking the registers of the servo as slave to a PLC as a master using MODBUS RTU The technical note AN SERV 004 available in the web site of Automation Direct in the area of Technical support gt Application Notes shows a simple example on how to implement a communication link through port 2 DirectSOFT software allows the programming of instructions MRX and MWX in a very simple way when the PLC DLO6 or the CPU D2 260 is used but not every command is done through MODBUS The DLO5 PLC and the CPU D2 250 1 have the instructions RX and WX or NETRX and NETWX New firmware 2 105 on the servo allows to command the digital inputs through MODBUS Previous versions allowed the transfer of some of the parameters only but not digital inputs Sometimes it is convenient to do so but there are certain inconveniences that we will not describe in detail in this document but as example the Home sensor should be wired directly to the servo drive to avoid delays on the detection of the Home position Other example is the wiring of overtravel limit switches that are safety switches and would be better to hardwire them Speed control with MODBUS es Introduction to communication
3. 09 11 Speed control with MODBUS ET 12 We will set each one of the bits according to the following table ee Bie Code Description Assigned value PLC bit order input 0 DI 101 Servo Enable 1 C100 1 DI2 0 Disabled input 1 2 DI3 114 VCSO 1 C101 3 D14 115 VCS1 1 C102 4 DI5 0 Disabled input 0 5 DI6 0 Disabled input 0 6 DI7 0 Disabled input 0 7 DI8 21 External fault stop 0 8 DI9 08 Trigger Predefined value 0 9 DI10 11 PCSO Predefined value 0 10 D111 12 PCS1 Predefined value 0 11 DI12 13 PCS2 Predefined value 0 12 D113 02 Alarm reset Predefined value 0 13 DI14 27 Home search trigger Predefined value 0 14 DI15 37 JOG Forward Predefined value 0 15 DI16 38 JOG Reverse Predefined value 0 In this case we must place P3 08 as OOOF Enter this value with the keypad The concept of speed control will be so that after enabling the servo drive output with DI1 will be able to be select the speed in P1 09 or a speed of 0 P4 07 is the parameter that contains the digital inputs on each one of the bits We will associate to P4 07 the following Therefore P3 08 has the first 4 bits set to 1 The first least significant bit of P4 07 must be turned ON so that the servo works third to select the speed P1 09 the quarter to select the speed in P1 10 that is zero so far but it can be any other speed in the operation ran
4. Speed control with MODBUS ies You can read V4000 in Data View and can M S see that the result is 55 or 56 counts every Jecb Hex word EII second Since there are 1000 milliseconds Elana Status in a second 1000 55 ms is approximately 18 ms on each transaction See the adjacent figure This it is a good method to determine the transmission speed When the comm link between the PLC and the servo has been tested we should code in the PLC something to be able to give the servo the value of speed setpoint Remember that we are still in the stage of creation of the program on the master PLC Also it is necessary to define how data is written to the servo drive We have said previously that we want to write the speed value in P1 09 The following logic can be written for MRX and MWX to avoid execution at the same time For that we do an interlock between reading and writing This is the fastest update possible A simple way to do this is the following SP116 C1 dani a EEE MRX At the beginning the CRUDOM Slot CPU closed contact SP116 Port Number K2 Slave Address K2 and C1 alow the Function Code 03 Read Holding Registers reading with MRX but Start Slave Memory Address k40001 3 K k Start Master Memory Address y3000 immediately will turn Number of Elements K8 ON C1 with the SET Modbus Data type 584 984 Mode inst ti d it Exception Response Buffer vioooo instrucuon and wait
5. a Modbus Data type 584 984 Mode Exception Response Buffer V10040 If the content of V3011 is 5 reset C2 V3011 K5 C2 8 RST SP116 Ci C2 MWX 9 a CPU DCM Slot CPU Port Number K2 Slave Address K2 Function Code 16 Preset Multiple Registers Start Slave Memory Address K40011 Start Master Memory Address V2000 Number of Elements K3 Modbus Data type 584 984 Mode Exception Response Buffer V10020 C1 RST Servo enable C100 B2002 0 10 OUT VCSso C101 B2002 2 11 OUT vcs1 C102 B2002 3 12 OUT 13 END 14 Speed control with MODBUS es The program is complete for this example Notice that the instruction MWX uses the data in 3 memories V2000 that goes into P1 09 the speed reference to be changed in some way on the PLC for example with an operator interface or by a calculation inside the PLC V2001 other possible speed that will go into P1 10 V2002 that is the word to be sent to P4 07 to define when the inputs are active In summary MODBUS RTU can transfer data in an operation of reading or writing one at the time the P2 30 parameter in the servo must be set as 5 and we can create virtual digital inputs using the parameters P3 08 and P4 07 Naturally it is necessary to emphasize the use of the PO 09 parameters to PO 16 for block transfer Take into account that initially we had 55 readings per second when a writing instruction is added the writing counts must also be consid
6. the overtravel limit switch is activated and this is true since of P2 15 default that corresponds to the DI6 input function it set as 22 P2 16 that corresponds to the DIZ input function is set as 23 and P2 17 that corresponds to the DI8 input function is set as 21 To make these errors disappear we must set P2 15 to P2 17 to a value O to disable the function of each input in DI6 DI7 and DI8 In order to clear the faults press the up and down arrow keys on the keypad simultaneously cleaning any error can be there or it is also possible to power cycle the servo drive to get the same function Also it is necessary to place some function in the parameters PO 03 to PO 08 to be able to visualize what it is desired to see in the PLC We will change the values in the parameters according to the following table IstEd 6 09 7 Speed control with MODBUS ET Parameter Value MODBUS address PLC memory Description PO 00 2105 40001 V3000 Software version PO 01 14 40002 V3001 Fault code PO 02 0 40003 V3002 Drive Status PO 03 1 40004 V3003 Analog monitor PO 04 1 40005 V3004 Current revolutions PO 05 0 40006 V3005 Current counts PO 06 6 40007 V3006 Current rpm PO 07 11 40008 V3007 Current torque PO 08 13 40009 V3010 DC Bus voltage The values in V3000 until V3007 are all signed decimal values When you have changed the parameter values you can move the shaft of the servomot
7. 2 inches therefore this can be a physical configuration whose cable distance between the drive and the PLC can have about 3 feet ONLY If more distance is needed it can be of up to 1000 meters with an additional RS 422 cable you can add in series 1st Ed 6 09 Speed control with MODBUS ET 3 Select the parameters Set P3 00 parameter to the desired slave address In this case we will use the value 2 that is just to say servo drive slave 2 Then set a value 3 in P3 01 that defines the transmission rate as 38 4 kBaud This value also must be set in the configuration of PLC port 2 P3 02 defines the protocol and the configuration In this case we select 8 as MODBUS RTU 8 data bits odd parity 1 stop bit Finally we set the P3 05 value with a value of 1 RS 422 This configuration is done with the keypad of the servo drive The communication para BST ween re meters in DLO6 PLC or D2 260 CPU are configured i AE E _ Chose with DirectSOFT5 software eens a mE or by ladder code This is DiectNET 800 ms Help explained in the manual V MODBUS 500 ms DO O6USER M or the D2 5 Non Sequence 3 Characters Remote 1 0 USER M respectively and ia we only show it here the Time out Base Timeout x 1 adopted values in the RTS on delay tenes O ms 5 adjacent figure RTS off delay time 0 ms v If you use another type of StationNumber 1 master device see how to Baud rate E Echo Suppression set these values in
8. Speed control with MODBUS es THIS INFORMATION PROVIDED BY AUTOMATIONDIRECT COM TECHNICAL SUPPORT IS SUPPLIED AS IS WITHOUT ANY GUARANTEE OF ANY KIND These documents are provided by our technical support department to assist others We do not guarantee that the data is suitable for your particular application nor do we assume any responsibility for them in your application PRODUCT FAMILY SureServo Number AN SERV 008 Subject Speed contro with MODBUS Date issued Jun 30 2009 Revision First edition This example shows how to use a Sureservo with MODBUS to control the speed using a MODBUS RTU master PLC Here is shown a procedure on how to program a DirectLOGIC PLC but the concept is the same for other PLCs Rotary table Servomotor hy yy Rca Willi Gearbox ratio 8 1 In a given situation we could create a displacement on a rotary table shown on the adjacent figure to 1 4 of a revolution from the original position or 2 revolutions in the servo motor with a gearbox of 8 1 ratio or any other angle by programming the parameters of P1 15 and P1 16 to 2 revolutions and 0O counts P1 17 and P1 18 to may be 4 revolutions and 0 counts and so on for up to 8 target preset positions What if we desire to change this desired position by an angle changed by an operator In a given application we may wish to place the rotary table in any angle that we wish of course we can program 8 positions with respect to absolute Home posi
9. co Exception Response Buffer 10000 SET V3011 content is compared with C1 V3011 K5 C2 5 l l x set 5 Ifis not so turn ON C2 6 Paa If C2 is ON and SP116 is OFF it 6 F V DCN Slot CPU is written the value in V4010 Port Number K2 i i e ka That is 5 forced by the first line Function Code 16 Preset Multiple Registers j Start Slave Memory Address K40010 not shown here in P2 30 Start Master Memory Address v4010 through PO 09 Number of Elements K1 Modbus Data type 584 984 Mode Exception Response Buffer Y10040 When the content of V3011 is 5 V3011 K5 C2 i RST C2 is turned OFF S8P116 c1 C2 or A i e ho E unei cpu This is the writing instruction that Aditi Gi ka Writes the value of V2000 in P1 Function Code 06 Preset Single Register j j j Start Slave Memory Address 40268 09 Enabling this function turns Start Master Memory Address v2000 OFF C1 and now it is possible Number of Elements nia Modbus Data type 584984 Mode tO read the 10 data again Exception Response Buffer Y10020 This it is the interlock between reading and writing Speed control with MODBUS ies Now we have the complete communication defined but we cannot command the servo to be moved through MODBUS We need to be able to enable the servo with a virtual digital input and to define acceleration and deceleration the operation mode and other constants that are listed below Other para
10. e the control of a servo using a speed reference given by the control though Modbus We will explain this with an example that uses speed set point and PLC port 2 1 Control concept In this example we will need to run a motor with a speed reference with a value given in memory V2000 directly in rpm in binary format that can be written by example from a calculation on the PLC or from a tachogenerator or read with an analog input module or from the determination of speed from encoder The acceleration and deceleration can be fixed for now but also it can be written to the servo drive through MODBUS communication The speed reference will be written in the servo drive to the P1 09 parameter and the servo will be enabled with one of the virtual inputs defined in P4 07 with help of P3 08 as is explained on page 11 in this document The values will be chosen either O rpm or the value in P1 09 2 Network design One possibility is to link them with RS 422 as in the following figure Configuration for RS 422 Use a cable such E D as the Belden 8102 ae a k Jooj z dJa a F 3 l0 FD TX Yellow RX Red RX Red Black TX Yellow Black SG Brown SVC MDCOM CBL c mea XN C C4394 VE 3 H AN j For RS 422 configuration only Af VU The SVC MDCOM CBL is a cable of 3 feet length and the ZL CMA15L module only measures about
11. ered and therefore the number of readings decreases Evidently it is possible to create counters for readings and writings Another possibility is to only write when necessary The reader can consider to do this if it is important in the process 5 Operate the network by activating the master program to initiate the communications Use Data View in DirectSOFT for the next actions 5 1 Set a value of rpm in V2000 for example 300 rpm 5 2 Turn ON C100 to enable the servo The motor will be powered and you will hear the typical noise of motor windings excited The shaft should be locked in position 5 3 Turn ON C101 and the servo will rotate at the speed defined in V2000 You can change the speed at any time 5 4 The servo can be stopped by turning off the bit C101 or you can disable the servo IstEd 6 09 15 Speed control with MODBUS ET
12. ge of the servo Notice in the figure of the following page that we added line 1 to cause that CO to C10 always be OFF in the beginning of the program when powering up the PLC and that the V4010 memory has value 5 to be able to pass this value to P2 30 at the right moment What is a value of memory V to send the data of the digital inputs and the value in P1 102 The answer is given by the following We can define the 3 consecutive parameters beginning in PO 10 and consecutive in such way than they are the values of speed in P1 09 PO 10 P1 10 PO 12 and the digital input word in P4 07 PO 12 Therefore it is necessary to change the code of line 9 so that 3 consecutive registers could be written and the function will be 16 instead of 6 We must write with the keypad the following PO 10 will be desired speed 1 with the value 109hex equivalent to P1 09 PO 11 will be desired speed 2 with the value 10Ap equivalent to P1 10 PO 12 will be the word with the digital inputs with the value 407 equivalent to P4 07 Speed control with MODBUS ies Since we had defined that V2000 is the value of speed reference it is logical that we will have the V2001 values as the second speed that is zero so far and V2002 must be equal to what goes in P4 07 This allows to write in those memories and the only thing that is missing is to relate the bits of V2002 to C100 C101 and C192 See the ladder code in the next pages
13. meters are left by default P1 01 Operation mode that by default is 0 set as 4 P1 32 Selection of the stop mode changed to 1 from value 0 P1 34 Acceleration time Let us define 1000 ms P1 35 Deceleration time 500 ms to arrive at 0 P1 55 left as 5000 P2 10 DI1 set as 101 P2 11 DI2 set as 0 P2 12 DI3 setas 114 P2 13 DI4 set as 115 P2 14 until P2 17 set as O Disabled inputs The values of digital inputs are defined by the content in the P3 08 parameters and the P4 07 P3 08 is a parameter that allows control of digital inputs with MODBUS Each one of the parameter bits has a predefined function or defined with other parameters If any one of the eight less significant bits is a 1 digital inputs DI1 until DI8 are used with MODBUS The 8 most significant bits have predefined functions ae ee Code Description Pree 0 DI1 101 Servo Enable 1 1 DI2 0 Disabled 1 2 DI3 114 VCSO 1 3 DI4 115 VCS1 1 4 DI5 0 Disabled 0 5 DI6 0 Disabled 0 6 DI7 0 Disabled 0 7 DI8 121 External fault stop 0 8 DI9 08 Trigger Predefined value 0 9 DI10 11 PCSO Predefined value 0 10 DI11 T2 PCS1 Predefined value 0 11 DI12 13 PCS2 Predefined value 0 12 DI13 02 Alarm reset Predefined value 0 13 DI14 27 Home search trigger Predefined value 0 14 DI15 37 JOG Forward Predefined value 0 15 DI16 38 JOG Reverse Predefined value 0 IstEd 6
14. or and it will be possible to observe that the V3005 memory shows the same number that the display on the servo and can be seen that the speed changes when the shaft of the motor moves The DC voltage in PO 08 should be of the order of 305 to 315 Volt DC as it is in V3010 as decimal value This allows us to check that the communication has been established Sa How can we measure the PLC scan time and how many transactions are happening per second With the Current Scan Time following method Maximum Scan Time Minimum Scan Time The scan can be seen using menu PLC gt Diagnostics in DirectSOFT and then select scan Time the dialogue of the adjacent figure will appear He Roane As we know when a communication transaction begins SP116 will turn ON and then we can count how many times the SP116 contact closes in 1 second for example with a simple counter Remember that a counter counts whenever there is a transition of the input from OFF to ON See the diagram below with the ladder code corresponding and the explanations in Setup Time Over Counter 10 each line _1Second CO closes one scan every second a SP4 co 4 A PD very time CO closes the current count is copied to V4000 a CTAO H OUT v4000 my Here the counter CTO counts the closing of SP116 i ot 16 Pt cTo F e L CO resets the counter every one second K2990 E 16 MRX CPUIDCM Slot CPU Port Number K2 Slave Address K2
15. ration SP116 is a bit in the PLC that turns ON when there is communication on port 2 It is called Busy and indicates when the PLC is transmitting data through the communication in port 2 and turns OFF when the data transmission is completed Therefore on the first scan instruction MRX is executed and reads 9 consecutive registers from the servo See more details in the PLC manual Let us say that the PLC scan takes 2 ms when beginning the transmission the contact of bit SP116 closes and makes the rung true to allow the transmission to be executed When establishing the transmission SP116 turns ON when the transaction completes SP116 contact is closed again and then another transaction begins and thus it follows continuously Typically the transmission takes more than the PLC scan time In this case it is approximately 18 ms The values in the selected range go to the memories of the PLC V3000 to V3010 according to the following table Parameter Value MODBUS address PLC memory Description PO 00 2105 40001 V3000 Software version PO 01 14 40002 V3001 Fault code PO 02 0 40003 V3002 Display code PO 03 1 40004 V3003 Analog monitor PO 04 1 40005 V3004 Status monitor 1 PO 05 0 40006 V3005 Status monitor 2 PO 06 0 40007 V3006 Status monitor 3 PO 07 0 40008 V3007 Status monitor 4 PO 08 0 40009 V3010 Status monitor 5 The fault ALE 14 and others in the servo drive display indicates that
16. rs or 3280 feet Standard RS 422 does not specify a topology of the network but actually a topology of multiple connections in series with the master on one end is the only way to make the communication reliable daisy chain The cable Belden 8102 or equivalent is recommended for networks RS 422 Use a termination resistor of equal value to the characteristic impedance of the cable that is used 100 for Ohm Belden 8102 at both ends of the network RS 485 is a standard of wiring of multiple nodes with a practical distance of maximum wiring of 4000 feet Standard RS 485 does not specify a network topology but actually a topology of multiple connections in series with the master on one end daisy chain is the only way to make the communication reliable The cable Belden 9841or equivalent is recommended for networks RS 485 Use a termination resistance of equal value to the characteristic impedance of the cable that is used 120 Ohm for Belden 9841 at both ends of the network The data transmission uses digital asynchronous serial data transmission The characters are sent codified in bits one bit every time in signal levels such as the ones in RS 232C The detail of this transmission is outside the intention of this document and more will not be explained here The reader can look for information on this subject in Internet or specialized books From the point of view of the user this is not important and it is mentioned here only for be
17. s of for SP116 to be turned SET OFF SP116 c1 MAX C1 will close but SP116 5 lt CPU DCM Slot cpu will be ON busy Port Number K2 i Slave Address K2 when the reading Function Code 06 Preset Single Register transaction IS Start Slave Memory Address K40266 completed the writing Start Master Memory Address 2000 bedi ith i 5 Number of Elements nia begins with instruction Modbus Data type 584 984 Mode MVWX C1 is turned OFF Exception Response Buffer 10020 with the Reset instruction Notice that only one transaction at a time is possible The PLC will be reading or writing in sequence Nevertheless it is necessary to consider the following The servo drive has two types of memory RAM and EEPROM In RAM memory data can be written at any time but the memory EEPROM can be written a limited number if times the order of 100 000 times The fixed parameters are written typically in EEPROM memory and with this memory it is not necessary to maintain drive power When powering the servo drive these values will be still stored in the memory Ist Ed 6 09 9 Speed control with MODBUS ET 10 In RAM memory this is not possible and the data only stays if the drive stays powered If we want to write continuously to the drive memory we should set the value of P2 30 parameter as 5 but this value is not retained in memory EEPROM Clearly it is not possible that the setting of this value be done by the operator of
18. s with MODBUS RTU protocol Before explaining the example we will develop an introduction to serial communications with Sureservo using MODBUS RTU protocol A communication protocol is a language used by devices in a network to communicate with each another All the devices in the network must use the same communication protocol to be able to communicate among them The MODBUS RTU serial protocol is a standard protocol very common in the industry and it is used to communicate with an ample variety of industrial devices that support this protocol In this case it is needed a Master device to command the servo which is acting as slave There are three standards of wiring that can be used with the Sureservo actuators RS 232C is a wiring standard point to point with a practical distance of wiring of 15 meters or 50 feet maximum Only two devices can communicate in a RS 232C network only a master device and one slave device and the total cable length can not exceed 50 feet A cable Belden 8102 or equivalent is recommended for networks RS 232C A cable Belden 9729 also will work RS 422 is a standard of multiple nodes with a practical distance of wiring of 1000 meters or 3280 feet length overall maximum This means that a master can communicate with up to 247 slaves theoretically but in practice about 10 slaves is the maximum practical limit and the total distance of all the network between all the devices cannot exceed 1000 mete
19. the G RS 422 485 4 wire manual of the master pas bes RS 232C 2 wire device Any master that Parity M au follows the MODBUS RTU specifications can be used Next leave the other values Port2 15 Pin as factory default Then we must connect the PLC to the servo drive 4 Creation of the program In order to be able to read the data from the servo drive and at the same time to verify that the connections are correct suggest to run the program shown in the following diagram Set a value 10 in the P2 08 parameter with the keyboard to configure all the values of the servo as default values Errors ALE14 ALE15 and ALE13 will appear on the display and this is normal Next be sure that the value of the motor code is set in the P1 32 parameter When the servo is powered up but not enabled and the axis of the motor turns freely the data that is contained in the parameters PO 00 to PO 08 can be read These parameters have memory addresses 40001 up to 40009 as shown in the table on the following page and described in the user manual in chapter 6 Speed control with MODBUS ees MRX Busy CPU DCM Slot CPU 4 pe Port Number K2 8 AA Slave Address K2 Function Code 03 Read Holding Registers Start Slave Memory Address K40001 Start Master Memory Address 3000 Number of Elements K9 Modbus Data type 584 984 Mode Exception Response Buffer Y10000 2 E END This is the explanation of the ope
20. the machine when the servo powers on Therefore it is necessary to write a value 5 to this memory when the drive powers ON or otherwise the servo will reach the limit of writings and the device will not be functional anymore One of several ways is to use a comparison function reading the content of P2 30 parameter and on the basis of that value execute a writing of that parameter It can be created an interlock such that this function is not executed anymore when P2 30 MODBUS address 40543 or 21E in hexadecimal format has a 5 in its content Here it is advisable the use of the block transfer parameters PO 09 up to PO 16 that are configurable parameters allowing to read or write data in consecutive servo addresses which is better than to read data in random addresses not consecutive For that we will configure PO 09 with the keyboard By default with value 407 as 21E that causes this parameter to be defined as P2 30 Then we will increase the reading of 9 registers in MRX to 10 to have included PO 09 For example 5P116 c1 C2 MRX eS ee cae a Instruction MRX reads 10 Port Number x2 Consecutive registers up to PO Slave Address K2 Function Code 03 Read Holding Registers Start Slave Memory Address K40001 09 PO 09 is the value contained in P2 30 that corresponds to Start Master Memory Address 3000 Number of Elements K10 C1 turn ON with th il Modbus Data type 584 984 Mode v3011 C u O e
21. tion or find a combination of incremental positions to move the table in certain discrete positions What options do we have if we wish to define the revolutions and the pulses only some moments before the movement This is possible writing data to registers of the Sureservo through the CN3 port of the drive that allows the data transfer in a transmission rate of up to 115 2 kbps kilobit per second IstEd 6 09 1 Speed control with MODBUS EEE DirectLOGIC PLC s can be master and use port 2 with up to 38 4 kBaud namely CPU s D2 250 1 D2 260 DLO5 and DLO6 PLCs or up to 115 2 kbps using the port 2 of DO DCM module Any other system that could transmit commands as a master with MODBUS can also make this exchange of information In this example we will show only the velocity mode control Speed control with Sureservo can be done in several ways Using an analog input with a signal 10 Volt in terminal V REF Using up to 3 preset values stored inside the servo drive and selecting then with the combination of 2 digital inputs Using an external pulse train Using a master PLC with MODBUS protocol to write the value of speed This is the purpose of this application note The speed writing to the servo is one of many possibilities it has of course the possibility to write the target positions we can change other parameters such as the acceleration and deceleration speed torque and speed and torque limits etc
22. tter understanding of the basic concepts Ist Ed 6 09 3 Speed control with MODBUS It does not matter what wiring protocol is used there are several communication parameters that must be selected for each device before they can establish the communication These parameters include Transmission rate in kilobits s kbps Baud rate Flow control Data bits Echo Suppression Parity Timeouts Stop bits Delay times Node address Format All these parameters may not be necessary or not be available The used parameters depend on the device that is used and if the device is a master or a slave NOTE The point to remember is that when the same parameters are available in the master and the slave that is baud rate parity stop bits etc the values of these must be equal The serial transmission can be of the type half duplex or full duplex A transmission half duplex can transmit in both directions but in a single direction every time One full duplex can transmit data in two way traffic simultaneously For example it is possible to be said that a walkie talkie is half duplex because it can only transmit the voice in a single direction In contrast a telephone is full duplex since both parties can talk simultaneously The servo drive only can be half duplex A serial network can be the one as shown one in the following figure The network is controlled by a master station that typically is a PLC with capacity to e
23. xecute these orders which commands the data interchange to each one of the slaves in a sequence one at a time The slave responds to the orders of the master The slave cannot initiate communications Generates orders or instructions to transfer data for example read the data in the slave register whose address is 40002 The servo drive that is the slave in this case has registers with parameters whose content causes the servo to work the way that the designer of the control system wishes it to work These registers have location addresses you select shown in the chapter 6 of the servo drive user manual For example if you want to read if the servo is with or without fault or want to know the type of fault in case there is an alarm you can read the register 40002 that corresponds to the PO 02 parameter Speed control with MODBUS es How can we control the servo through a network You can easily create a control system with a servo using a serial MODBUS network following the six steps below 1 Define the control concept 2 Design the network according to your application select the master who will communicate with the slave or slaves 3 Select the cables and communication parameters 4 Create the program in the master PLC and set up the slave 5 Run the start up of the network setting up the port and activate the program of the master to initiate the communications 6 Test that the actuator works as desired Let us se
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