M O T I O N C O N T R O L P R O G R A M M I N G
FEEDRATE
OVERRIDE
Motion Control Programming
109
The second step defines the motion path, which consists
of a collection of straight lines and circular arcs. Straight lines
are defined with the instruction
VP m,n
where (m,n) are the coordinates of the endpoint with respect
to the start of the move sequence. Circular arcs are defined
with the instruction
CR R, q, d
where R indicates the radius, q defines the starting angle, and
d defines the width of the arc.
The complete path may consist of a collection of many
such motion segments, as illustrated by the following exam-
ple. There is no limit to the number of segments that can be
specified and additional segments can be sent during motion.
This allows the DMC to control motion along very long
paths without stopping.
In addition to the motion path, the user can specify
the vector speed (feedrate). In most applications, the feed-
rate is set to a constant value. However, the velocity can
also be reduced around corners, for example. A specific
feedrate may also be prescribed for an individual segment.
For example, VP 1000,2000 < 5000 sets the vector speed to
5000 counts/sec for the segment VP 1000,2000.
Similarly, the acceleration and deceleration rates along
the motion can be specified. The instructions for the vector
velocity, acceleration, and deceleration are VS, VA, and VD
respectively.
The generation of a coordinated move is illustrated by
the following example.
Consider the motion path described by the figure on
page 109 and write a program to generate it. The motion is
in the XY plane, the radius of the corners is 1000 counts, the
vector speed is 20,000 count/sec, and the vector acceleration
and deceleration rates are both 100,000 ct/sec
2
.
The instructions and their interpretations are shown
below.
Instruction
Interpretation
#M 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
VS 20000 Vector speed
VA 100000 Vector acceleration
VD 100000 Vector deceleration
BGS Start motion
EN End program
Feedrate Override
In some cases it is desirable to give the machine operator the
ability to adjust the 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
potentiometer with an output voltage between 0 and 10 V.
When the potentiometer output is at the full 10 V, the
machine is supposed to run at the full speed. In all other
cases, the speed should be proportional to the potentiometer
voltage.
Motion Path for XY
C (6000,2000)
D (-6000,2000)
B (6000,0)
E (-6000,0)
A (0,0)
