Technical Reference
Motion Programming
14
www.galilmc.com / Galil Motion Control, Inc.
Feedrate Override
In some cases it is desirable to give the machine operator the abili-
ty to adjust machine speed.This ability is called feed- rate override.
This feature may be useful, for example, when starting a machine
for the first time; the operator may wish to increase the speed
gradually.
The method of speed control is often accomplished by a poten-
tiometer with an output voltage between 0 and 10 V.When the
potentiometer output is at the full 10 V, the machine will run at full
speed. In all other cases, the speed should be proportional to the
potentiometer voltage.
To accomplish this function, motion controllers read the poten-
tiometer voltage and adjust the feedrate in proportions. For a spe-
cific implementation by the DMC, consider the example at right.
Tangent Motion
When two motors perform coordinated motion in a plane, it is
often desirable to control a third motor with its angle remaining
tangent to the direction of motion.This feature is useful in applica-
tions such as cutting cardboard with a knife. As the knife moves in
the plane, it is necessary to keep the blade angle tangent to the
motion trajectory.
The user must specify several parameters to generate the tan-
gent motion. First, the user must select the coordinated and tan-
gent axes. For the rest of this discussion, assume X and Y generate
the motion and Z is the tangent motor.
The second parameter is the resolution of the Z motor (or the
number of units of resolution that will turn the Z motor one
degree). For example: if the encoder resolution is 3600 counts per
revolution, the parameter is 10. Finally, the position of the Z
motor at which its angle is 0° in the XY plane must be given.
These parameters define the requirements for the tangent
motion completely.
To generate tangent motion by the DMC, first the axes must be
selected using the instruction VM. For example, the instruction VM
XYZ selects X and Y to form the motion in the plane, and Z to form
the tangent motion.The remaining two parameters are defined
with the instruction TN m,n. For example, the instruction TN 20,700
sets the resolution to 20 counts per degree.This command also
indicates that when the Z motor is at the absolute position of 700
counts, its angle in the XY plane is zero.
Repeat the motion of the previous example with feed- rate override.
The operator generates a voltage in the range between 0 and 10 V.This
voltage is applied to analog input #1 to set feedrate in proportion to
the voltage.
The motion is generated by two programs, #MOVE and #SPEED. Both
programs operate simultaneously in multitasking.The program #SPEED
reads the analog inputs and adjusts the vector speed continuously.The
second program #MOVE is the same as in the previous example with
the exception that the vector speed is not specified.The two programs
are listed below.
INSTRUCTION
INTERPRETATION
#MOVE
Label
VM XY
Specify XY plane
VP 6000,0
Move to Point B
CR 1000,270,180
Move to Point C
VP -6000,2000
Move to Point D
CR 1000,90,180
Move to Point E
VP 0,0
Return to Point A
VE
End of path
VA 100000
Vector acceleration
VD 100000
Vector deceleration
BGS
Start motion
XQ #SPEED,1
Run speed routine
AMS
Wait for motion complete
HX1
Kill thread 1
EN
End program
#SPEED
Label
A = @AN[1]
Read analog voltage
V = A*2000
Set feedrate
VS V
Update feedrate
JP #SPEED
Repeat the process
EN
End program
Example--Feedrate Override
