BASIC STEPPER MOTOR CONTROL USING A PLC

PURPOSE:  The purpose of this laboratory exercise is to control the direction and speed of
a stepper motor using a PLC.  Data Bytes will be used to define the sequence bit pattern
for each respective step.   Speed of the motor will be controlled using a timer for delaying
between pulse output.   Counters will be used to keep track of the number of bit patterns produced
and the total steps generated in both the forward and reverse direction.

OBJECTIVE:  Write a PLC program to drive the pointer on the simplified measuring device
to 10 mm greater than the starting location, and then return to the original starting point.

PROCEDURE:  The following steps should be taken to carry out this laboratory exercise:

    1.  Define 4 data bytes corresponding to the required step sequence bit pattern;
    2.  Use Q Byte  (QB0) as the output BYTE for controlling the motor;
    3.  Program an on delay timer to create a one shot "clock pulse" from a counter at a time interval
         of 20 milliseconds;
    4.  Use one counter to count step sequences and a second counter to count total sequences;
    5.  Use the Move Byte function to move the required data byte to QB0 depending on the
         counter value being used to count step sequences. 

Note:  An improvment in your program can be made by following the following method.
By using Memory Bytes (MB....i.e. MB10) rather than QB0, extra output bits can be reserved for
controlling outputs rather than the four field coils for the stepper motor.. Remember a BYTE = 8 bits, and
QB0 will consume all 8  bits of the output  byte for addresses Q0.0 through Q0.7.  Since only 4 bits
are actually required for controlling the stepper motor, 4 bits of QB0 would be "wasted".  Therefore
to avoid this,  simply MOVE the DATA BYTES (i.e. VB10 to MB10), then use discrete individual
bytes of MB10 to control the field coils of the stepper motor. A conceptual diagram and example
PLC Networks are shown below:

    6.  Write the program to generate the pulse train required for the distance to be moved.
         (Note: You will have to determine the total number of revolutions required to equate to 10 mm).
         The leadscrew attached to the stepper motor is 1/4-20 UNC, and is a single thread.
         Therefore, the lead is equal to the pitch = 1/20 inch per revolution. !/20 in. X 25.4 mm/in. = 1.27 mm/rev.

    7.  Complete your PLC program and download to the simplified measuring station; run the PLC program.
    8.  Compare the finish point to the original starting point on the motor shaft and determine
         if any error occurs (e.g. too few or to many steps generated).
    9.  Modify your program to compensate for any error (if required) and be prepared to
         explain why any modification was necessary.
    10.Submit a written laboratory report, following the usual format.
 
 
SUPPLEMENTAL INFORMATION 

The following four step in put sequence provides CW rotation as viewed from then nameplate end
of the motor.  To reverse the direction, step sequence is 1,4,3,2,1.

STEP        SWITCH 1        SWITCH 2        SWITCH 3        SWITCH 4
   1                  ON                   OFF                    ON                  OFF
   2                  ON                   OFF                    OFF                 ON
   3                  OFF                  ON                     OFF                 ON
   4                  OFF                  ON                     ON                   OFF
   1                  ON                   OFF                    ON                   OFF
 

SUPPLEMENTAL SUPPORTING DIAGRAMS AND EXAMPLES
 

                    WIRING DIAGRAM
 
 

MOVE FUNCTIONS

EXAMPLE OF USING COUNTER WITH IF CONDITION  (----| = = I |-----) TO MOVE DATA
FROM A VARIABLE BYTE (VB10) TO OUTPUT BYTE (QB0).
NOTE:  IF COUNTER 0  (C0) IS EQUAL TO 3,  THEN THE CONTENTS OF VB10 WILL BE
MOVED TO OUTPUT BYTE (QB0) AS SHOWN IN NETWORK 1 BELOW.

Description of operation:  MOV_B

The Move Byte (MOV_B) box moves the input byte (IN) to the output byte (OUT). The input byte is not altered by the move.
 

Operands:

IN (byte): VB, IB, QB, MB, SMB, SB, AC, Constant, *VD, *AC
OUT (byte): VB, IB, QB, MB, SMB, SB, AC, *VD, *AC
Description of operation:
 
 

DATA BLOCKS:   YOU WILL NEED TO CREATE DATA BLOCKS TO STORE THE CONTENTS OF
THE BIT PATTERNS REQUIRED TO INDEX THE STEPPER MOTOR.  ONE BLOCK WILL BE REQUIRED
FOR EACH BIT PATTERN AS SHOWN BELOW:

//
//DATA BLOCK TITLE COMMENTS
//
//Press F1 for help and example data block
//
VB10 10 // DATA FOR FIRST STEP SEQUENCE  (BINARY 1010)
VB20 9 // DATA FOR SECOND STEP SEQUENCE (BINARY 1001)
VB30 5 // DATA FOR THIRD STEP SEQUENCE  (BINARY 0101)
VB40 6 // DATA FOR FOURTH STEP SEQUENCE (BINARY 0110)