Technical Reference
Motion Programming
www.galilmc.com
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Galil Motion Control, Inc.
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The DMC can receive commands from both the host computer
and the stored program and execute these instructions simulta-
neously.
Control Variables
Many motion applications include variable parameters. For exam-
ple, a cut-to-length application often requires that the cut length
be variable.The motion process is the same, but the length is
changing.To accommodate these applications, advanced con-
trollers provide symbolic variables. A program can be written in
which certain parameters, such as position or speed, are defined as
variables.The variables can later be assigned by the operator or
determined by program calculations.Variables allow the motion
controller to perform certain mathematical functions and to make
decisions.This capability increases the intelligence of the motion
controller and allows it to perform some supervisory functions in
addition to the motion control.
A variable can be defined as a constant or can be equated to a
controller parameter. For example, the instruction V = 3 sets the
value of the variable V to 3.
The instruction P = _TPX reads the position of the X motor and
equates the variable P to that value.Variables can be defined in a
variety of ways. For example, the instruction YERROR = _TEY
equates the variable YERROR to the position error of the Y motor.
Once the variable is defined, it can be used in mathematical
operations.The DMC can perform mathematical functions which
typically include algebraic, trigonometric, and logical operations.
When the operation is completed, the controller can use the
computation result to adjust the system parameters. For example,
the results can be used to change the speed, set the distance, or
change the filter gain.The use of variables is best illustrated by the
following example.
To illustrate the concept, consider the move described in the point-
to-point example.To perform the same move from a stored program,
the host modifies the program by adding the label #A and the end
statement EN.The resulting program is as follows.
The host downloads this program to the controller memory,
where the program remains inactive.To execute the program, the
host sends the command XQ#A which causes the controller to exe-
cute the program labeled #A.
INSTRUCTION
INTERPRETATION
#A
Program label
PR 4000
Distance
SP 20000
Speed
AC 200000
Acceleration
DC 200000
Deceleration
BGX
Start X motion
EN
End of program
Example--Stored Programs
The following program shows an example where the X motor follows
the position of the Y motor.This is done by driving the X motor at a
speed proportional to the position difference.
INSTRUCTION
INTERPRETATION
#FOLLOW
Program name
DP 0,0
Define X,Y position as zero
JG 0
Set initial X speed to zero
BGX
Start X
#LOOP
Label
VE=_TPY-_TPX
Find the position difference
VEL=VE*10
Compute the speed
JG VEL
Modify the speed
JP #LOOP
Repeat the process
EN
End of program
Example--Position Follower
