Stepper Motor Control With a PC-Based Data Acquisition Toolkit
Contents
1. Figure 8 Front Panel and Block Diagram of the LABVIEW sub VI For the parallel Port Stepper Motor Control 4 0 Motion Control Using SCXI System National Instrument Signal Conditioning Extension for Instrumentation SCXI system with LabVIEW 5 0 was used to develop the program for running a wind tunnel experiment involving a stepper motor The sys tem consists of SCXI 1000 chassis which has 4 slots for data acquisition multiplexing and control modules Two modules are installed in the present system SCXI 1200 and SCXI 1121 The SCXI 1200 is the general purpose data acquisition board A D card It has 4 differential channels or 8 single end channels and three 8 bit digital I O ports The SCXI 1121 with SCXI 1321 accessory has 4 optically isolated channels differential and excitations The basic setup of the SCXI system is the same as the parallel motion control setup Since the SCXI system uses parallel port to communicate with a computer SCXI 1200 s digital I O port was used to control the stepper motor 4 1 Stepper Motor Connection SCXI 1200 SCXI 1200 s digital I O port PA O PA 7 and digital ground controls the stepper motor via translator circuit as shown in Figure 9 The detailed descriptions of the ports are provided in the SCXI 1200 man ual 3 The digital pulse combination described above and frequency of PA O and PA 7 control the direction and the speed of the motor The pin connection2. Input 3 Figure 7 CIN Icons with Terminals 6 Select Create C File from the pop up menu right click on the icon It will ask for the file name filename c format Type C source filename and save it The saved file contains following C code 12 CIN source file ii include extcode h CIN MgErr CINRun float64 Input_1 intl6 Input_2 ulnt16 Input_3 CIN MgErr CINRun float64 Input_l intl6 Input_2 ulntl6 Input_3 ENTER YOUR CODE HERE return noErr It should be noted that the labels 1 e Input 1 Output 1 etc and its data format i e double integer 16 etc on the controls and indica tors become the variable names and data format of the C code In addition include extcode h should be the first header file Addi tional header files such as math h and stdio h should follow extcode h header 7 Insert C code that you wrote into the LabVIEW generated C code where it says ENTER YOUR CODE HERE Make sure the variable names and types match with the declared variables For example for the present case C code for the stepper motor control CIN source file include extcode h include lt conio h gt include lt stdio h gt include lt stdlib h gt CIN MgErr CINRun int16 var1 CIN MgErr CINRun int16 var1 _outp 0x378 var1 _outp 0x378 0 return noEtr 8 Create a make file using text editor notepad
3. Computers Ordinateurs A ton Stepper Motor Control With a PC Based Data Acquisition Toolkit 1 0 Introduction requently data acquisition processes involve different types of device controls However most commonly used data acquisition software does not include general purpose device control drivers or optional add ons So the driver interface has to be developed by the user depending on the application This paper describes two methods developed at the Florida Institute of Technology to control a stepper motor utilizing the commonly used PC data acquisition toolkit LabVIEW 5 0 and parallel port or general pur pose digital I O port of a data acquisition board The first method uses digital I O port of SCXIJ 1200 data acquisition unit from National Instrument The second method uses the same software but compiling the external code C and controls the motor though a parallel port The source code used for the second method can be used as a stand alone motor control without using any data acquisition card or the data acquisition software With use of a translation module presented in this paper most of the general purpose stepper motor can be controlled using only two digital signal lines and a digital ground Any programming language such as BASIC or C or data acquisition software with digital I O can be used for the motor control 2 0 Motion Control System Figure shows the general schematic of motion control system It c
4. If Isb extension file is created correctly the status window displays the following status report Configuration Filename Win 32 Debug Microsoft R Program Maintenance Utility version 1 62 7022 Copyright C Microsoft Corp 1988 1997 All rights reserved filename c Microsoft R 32 Bit Incremental Linker Version 5 00 7022 Copyright C Microsoft Corp 1992 1997 All rights reserved LabVIEW resource file type CIN name filename sb created properly Filename exe 0 error s 0 warning s Where filename is the name of the C source code or the make file that you compiling The lsb extension file should be in the direc tory where the C source code and make files are in 12 From the LabVIEW vi diagram Step 3 right click on the CIN icon and choose Load Code Resources The dialog box indicates the path to the lsb extension files that you want to load Select the file and click Open 13 The source code is now loaded onto the CIN icon and ready to per form the task Once the code is loaded it will become a stand alone executable icon does not require c source code or make file When this vi is saved including CIN icon it can be called from other VI s A LabVIEW sub VI called Motor Control vi is developed to control the stepper motor through a parallel port The Front Panel diagram and the Block Diagram for which are shown below in Figure 8 NI DAQ Software
5. S Subramanian Florida Institute of Technology Melbourne Florida The use of LabVIEW is on the increase in universities and indus tries especially for data acquisition and process control Frequently there is a need to develop LabVIEW application soft ware to work with foreign hardware like a Slo Syn stepper motor Unfortunately simple and clear procedures to develop motion con trol routines are not easily available This paper describes a method developed to control a stepper motor using the LabVIEW 5 0 soft ware and the National Instrument SCXI data acquisition system LabVIEW est de plus en plus utilis dans les mondes universitaire et industriel particuli rement pour la saisie de donn es et le con tr le de proc d s R guli rement des applications LabVIEW doivent tre d velopp es pour travailler avec du mat riel tranger tel un moteur pas pas Slo Syn Malheureusement il n existe pas de proc dures simples et claires pour d velopper ces routines de gestion de mouvement Cet article d crit une m thode pour con tr ler un moteur pas pas en utilisant le logiciel LabVIEW version 5 0 et le syst me de saisie de donn es SCXI de National Instrument hex port was used to send the signals to the translation module The pin 2 controls the step and the pin 9 sets the rotational direction It should be noted that the any combination of 2 pins between 2 to 9 can be used to control the motor Table 2 shows an
6. word word pad etc and save it with the same file name as C source code with mak extension The make file should contain following 4 lines Name name of C file without extension Type CIN CINTOOLSDIR path to cintools directory linclude lt CINTOOLSDIR ntlvsb mak gt For example for the present case Make File for the stepper motor control name step type CIN cintoolsdir c labview cintools linclude lt cintoolsdir ntlvsb mak gt IEEE Canadian Review Autumn Automne 1999 The path to the cintools directory can be found for the Windows 95 system in C ProgramFiles National Instruments Lab VIEW Cin tools 9 Prior to compiling the source code make sure that the C source code and the make file are in the same directory or the compiler will not create lsb extension file it will create exe file instead 10 Open the make file in Microsoft Visual C When the file is opened the program displays two warning dialog boxes First it says This makefile was not generated by Developer Studio Answer Yes to Do you want to continue Then in the second dialog box shows the type of platform you wish to operate on default is Win32 Make sure the Win32 is checked and click OR 11 Select Build filename exe file from the build pull down menu in Microsoft Visual C The program follows the instruction in the make file and creates filename sb instead of filename exe
7. e The Microsoft Visual C compiler e Symantec C compiler e The Watcom C 386 compiler for Windows 3 1 The external code C loaded into the LabVIEW s CIN is simplified to minimize lockup of the program while the CIN code is executing The CIN code executes only one step at a time and returns to the motion control VI The one step is equivalent to 1 8 rotation To do multiple steps the CIN was called multiple times Inserting the loop delay in the motion control VI the speed of the subsequent steps can be controlled The drawback of this control configuration is that the stepping speed varies with the CPU speed This can be improved by placing the loop structure for the number of steps you want to execute in the C code 3 1 1 Description of Make File Compilers need instructions on how to build a project or a file These instructions come in the form of make files LabVIEW installs a make file in the LabVIEW cintools directory that has instructions for the com pilers to build a generic CIN ntlvsb mak but other compilers will need some additional instructions on how to build a CIN A specific make file combined with the LabVIEW generic make file will instruct the compiler to build a lsb file instead of a exe file The lsb file is used Stepper Motor Figure 4 Schematic of Stepper Motor Control Setup Using Computer Parallel Port IEEE Canadian Review Autumn Automne 1999 11 to interface the external code such
8. step 1 8 When the circuit is powered it sup plies the power to the windings even if it is not turning The translation module circuit diagram is shown in Figure 2 Stepper Motor 12V_ p m Supply Voltage 2 x x o 2 Gnd e PZE Sea e e L R o A a o 14 i 11 4 6 1 i 3 SET E Direction e D Q TS 2 14070 RRA 7 i i 14013 l PC Inputs 3 5 E O MCT 6 B i ii OptoCoupler l 1 2 1 7 eo Step e amp oe oe et tee a Ne f wa te 5 4 st 2 8 6 D Q iad 14070 239 o 14013 7 K CLR Q e 330 ces Power 1 Ground Screw Terminal 10 Figure 2 Translation Module Circuit Diagram IEEE Canadian Review Autumn Automne 1999 2 3 Stepper Motor A stepper motor is a device that positions loads by operating in discrete increments or steps The stepping is accomplished by switching the power to the motor windings so that the motor phases are energized in a specific sequence The Figure 3 shows the typical wiring diagram of the stepper motor 2 winding sets Figure 3 Schematic of Stepper Motor Windings Table 3 shows the switching sequence required to turn the motor through one step typical step size is 1 8 and 200 steps are used for one complete revolution 1 e 360 turn To step in the reverse direction the switching s
9. the sequence of following two statements move the motor in reverse direction counterclockwise one step The first statement reverses the direction of the rotation The second statement activates the flip flop circuit and sends a signal to the stepper motor _outp 0x378 255 _outp 0x378 0 binary representation of 255 11111111 binary representation of 0 00000000 These signals represent information of the Ist to 8th bits of parallel data respectively Each signal is at high level when data is logical 1 and low when logical 0 This signal indicates that the printer is in the selected state AUTO FEED XT _ This signal being at low level the paper is automatically fed one line after printing 1 STROBE STROBE pulse to read data in IN OUT ACKNLG A low indicates that data has been received amp printer is ready to accept other data BUSY A high signal indicates that the printer cannot receive data A high signal indicates that the printer is out of paper scr inter is i OUT C 2 2 Translation Module The translation module generates pulse signals as and when it receives the control data from the computer The pulse in from high to low state activates the circuit and sends signals to two sets of windings on the stepper motor The first set of signals changes the 1st winding polar ity and the 2nd set of signals changes the 2nd winding polarity causing the motor to rotate one
10. IN allows the motion control rou tine to be embedded as a part of the acquisition function The procedure is explained in detail here for the driver routine written in C The procedure can be applied to any motion control such as probe travers ing model rotation etc DIO Motor Control one step vi Front Panel Connector Panel Rotation digital device 1 digital channel Mode T Free Step Motor Speed 40 Angle task ID out Mecde T Free Step a ta eR a a a a a Or a or a a a a a a a rr a Or A A Sr a A A A a EE Moto Speed 40 raii Part H Write WEN Lz rc The authors are very grateful to Mr Dan Simpson for his assistance in the lab 1 Hall Douglas V Microprocessors and Interfacing Programming and Hardware McGraw Hill 2nd Ed 1991 2 National Instruments LabView Code Interface Reference Man ual National Instruments Jan 1998 Ed Part No 320539D 01 3 National Instruments LabView User Manual National Instru ments January 1998 Edition Part Number 320999D 01 4 National Instruments G Programming Reference Manual National Instruments Jan 1998 Ed Part Number 321296B 01 Part Write 1 aaien L Ue Figure 10 Front Panel and Block Diagram of the LABVIEW sub VI For the SCXI Stepper Motor Control Larry Buist a 13 year veteran Nagahiko Shinjo is a graduate research student pursuing of Flori
11. as C to LabVIEW program The CIN only accepts the external code with Isb extension it does create c extension file but it does not accept c extension file as a CIN source code Additional information can be found on LabVIEW Code Inter face Reference Manual 2 3 1 2 Steps for Creating a CIN The procedures for creating a CIN differs with the platform and com piler used In this section the procedures for using Microsoft Windows 95 with Microsoft Visual C compiler are illustrated For more detail and other compiler s procedure refer to LabVIEW Code Interface Ref erence Manual 1 Prior to the CIN generation determine the data and the data format i e integer floating point strings etc to be passed to and received from the CIN 2 Write a C code and verify that there are no errors in the code 3 From the LabVIEW VI diagram select a code interface node icon Functions gt Advanced and place on the diagram It should look like in Figure 5 Figure 5 Code Interface Node Icon 4 Initially the CIN has one set of terminals a set of input and output terminals The additional terminals can be added by dragging the bottom left or right corner of the icon or by selecting Add Parame ters from the CIN terminal pop up menu right mouse click on the parameter terminals Figure 6 Figure 6 CIN Icon with Multiple Input and Output 5 Connect the terminals to control and indicator panels Figure 7
12. da Ph D degree in Tech has Ocean Engineering extensive pro at Florida Institute totyping Technology He experience with obtained his M S Harris GISD also in Ocean Engineering from the same University His general areas of research include bio fouling control autonomous underwater vehicle control system and underwater instrumentation Currently he is developing a memory alloy based bal last system for autonomous underwater vehicles and biologically based underwa ter vehicles Tech E mail shinjon winnie fit edu E mail Ibuist fit edu 14 Intersil MicroPac Industries and a variety of electronics start up compa nies in Nevada Texas and Florida He holds a patent in the video game industry and is involved in the design and construction of electronic and electro mechanical circuits on a vari ety of research projects at Florida Chelakara S Subramanian is an associate professor of Aerospace Engineering at Florida Institute of Technology He obtained his Ph D in Mechanical Engineering from University of Newcastle Australia and M E in Aerospace Engineer ing from the Indian Institute of Science India His research expertise is in experimental fluid mechanics and new instrumentation Currently he is involved in research projects on pressure sensitive temperature sensitive paint system particle imaging velocimetry low cost diode powered 2 component laser doppler velocimetry hurricane flow field measure
13. equence is reversed 1 e 4 3 2 1 Table 3 Winding Sequence 1 high state 0 low state The stepper motor is capable of operating in a half step 0 9 mode also However that would require additional switching sequence and a different translation module circuitry Further the half step reduces the holding torque of the motor For present application only the full step increment 1 8 is used 3 0 Motion Control Using Computer Parallel Port The schematic setup of the parallel port motor control is described in Section 2 1 With use of the translation module described in Section 2 2 the following lines of code executes one step in a specified direc tion The following code is written for Microsoft Visual C a SLL LL Ly Parallel Port Pin 2 Pin 9 GND Computer LabVIEW 5 0 Parallel Motor Control vi lt Translation Module command for parallel port communication varies with the language for example Borland C uses outp port address in hex binary code and the Visual Basic uses out port address in dec binary code By con trolling the loop execution time the speed of the stepping can be controlled For more accurate stepping time control a timer command wait statement can be used instead of a loop command do loop _outp 0x378 0 or 255 an empty loop to adjust the timing between the command _outp 0x378 0 an empty loop to adjust the timing between the command an empt
14. example of parallel port pin outs In the present case the following sequence is employed Table 1 Data Status Addresses Port Number Data hex Status hex Control hex LPT 1 378 319 37A LPT 2 278 279 27A e The pin states 1 and O pin 2 high state and pin 9 low state ini tialize the forward or clockwise step e The pin states and 1 both pin 2 and 9 are high initialize the backward or counterclockwise step e The pin states 0 and O both pin 2 and 9 are low followed by the state 1 1 or 1 0 executes the step Thus the following 2 statements send the signals to LPT1 and move the motor one step typically 1 8 Note that the command _outp only works for Microsoft Visual C The other compiler may use different command _outp 0x378 1 _outp 0x378 0 binary representation of 1 00000001 binary representation of 0 00000000 The first statement sets the Ist bit to high state rest of the bits are at low state Chas to gh bits The second statement sets all the bits to zero Table 2 Pin Connection and Description for Parallel interface to IBM PC Hall 1991 N z gt Uo S m gt N EAN SLCT O lt CHASIS GND Printer chassis GND 1 5 6 8 1 Q Z Zz JJ 10 1 12 13 14 1 1 17 1 19 20 2 22 23 24 N Q Z or The sequence of these two statements activate the flip flop gate to flip This causes the motor to move one step Similarly
15. ments and wind engineering studies He is an associate fellow of AIAA member of ASME member of Society of Engineers U K licensed Professional Engineer in U K and a member of International Society of Professional Engineers in France E mail subraman winnie fit edu IEEE Canadian Review Autumn Automne 1999
16. on sists of an 8 bit digital communication port a driver or translation module and a stepper motor A parallel port or printer port or digital I O ports on the data acquisition board can be used to control the step per motor via translation module Two communication methods are provided since typical external data acquisition boards are interfaced to the computer via parallel port Digital Communication Port Digital I O or LPT port Translation Module Stepper Motor Figure 1 Schematic of Motion Control Setup Two digital lines and a digital ground are connected to the translation module One digital line controls the step and other controls the direc tion The translation module converts the signal from the communication port to a specific winding energizing sequence to step the motor The output signal from the translation module is sent to each winding typically 2 sets of winding on the stepper motor Details of the wiring signals and program code are described in the following sections 2 1 Parallel Port Communication An 8 bit data signal is sent to the translator module to move the stepper motor To send 8 bit data to a specified port port address and 8 bit hexadecimal code are required Table 1 shows the data status addresses for parallel port or LPT ports of a PC Pin 2 data 1 pin 9 data 8 and pin 20 ground of LPT1 378 IEEE Canadian Review Autumn Automne 1999 by N Shinjo L Buist and C
17. s between the SCXI 1200 unit 50 pin and the trans lation module terminal are described in the Table 4 For the connection from the translation modules to the stepper motor refer to the translator circuit diagram Figure 2 Table 4 Connector Pin outs SCXI 1200 Translation Circuit Terminal Number 3 Ground 11 Step Signal 12 Direction Signal A LabVIEW sub VI called DIO Motor Control one step vi is devel oped to control the stepper motor The Front Panel diagram and the Block Diagram of which are shown below in Figure 10 SCXI 1200 Pin Number 50 pin 13 Digital Ground 14 PA 0 21 PA 7 SUL LL Line DIO Port Computer SULLY LL PA 0 LabVIEW 5 0 Parallel Port SCXI 1200 e _ PA 7 Translation Module gt Stepper Motor DIO Motor Control vi DGND Figure 9 Schematic of Stepper Motor Control Setup Using SCXI 1200 IEEE Canadian Review Autumn Automne 1999 13 The methods to control a stepper motor using a parallel port and National Instrument s SCXI unit are described The use of the transla tion module described in this paper enables control of a stepper motor using conventional programming languages or data acquisition soft ware It is an inexpensive way of developing a prototype data acquisition control system In addition data acquisition software which has a capability of compiling conventional programming codes such as LabVIEW Code Interface Node C
18. y loop or timer to adjust loop execution time end loop The first _outp command sets the direction of the motor rotation and the second executes the step It should be noted that for a faster CPU it may require empty loops or timing command to create a delay between each command execution Rapid command execution can cause erratic stepper motor motion For the motor used in the present application the ideal timing between commands was 100 ms 3 1 Motion Control Using LabVIEW The basic setup for the parallel port motion control using LabVIEW Figure 4 is the same as the conventional setup described in Section 2 1 The exact same code described in the previous section can be used for the control The only difference is that instead of compiling the code as a stand alone executable program it is compiled as a LabVIEW exe cutable program In this way the motion control routine can be used along with data acquisition routines developed with the LabVIEW For this the LabVIEW function called the Code Interface Node CIN is used to link the external code written in a conventional programming language to LabVIEW 3 4 LabVIEW calls the executable code when the node executes passing input data from the block diagram to the exe cutable code and return the data from the executable code to the block diagram The code can be compiled as either single threaded or multi thread operations Only the following compilers can be used to create CIN
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