Single-Axis Motion
06/2005
Danaher Motion
98 Rev
E
M-SS-005-03l
4.1.9. Velocity
Override
The MC can speed up or slow down all motion commands. This can be
applied to the entire machine at once, or to individual axes, independently.
This capability is used extensively in machine development as it enables you
to adjust the entire machine speed in a single command. Since the
command can be issued from the terminal, you can observe the operation of
the machine at a variety of speeds without modifying your program.
All axes on an MC are controlled with
SYSTEM.VELOCITYOVERRIDE
(
SYSTEM.VORD
). For example:
System.VelocityOverride = 25
immediately reduces the velocity commands of all currently executing
MOVE
s and
JOG
s and any subsequent commands to 25% of the current
values. Since the velocities are controlled by
VORD
, the acceleration rates of
all axes are proportionally adjusted. The final positions of
MOVE
s are not
affected.
If you want to override the velocity of a single axis rather than the entire
machine, you can use
<axis>.VORD.VELOCITYOVERRIDE
(
<axis>.VORD
). It is used in the same way as
SYSTEM.VORD
except it
applies only to one axis.
<axis>.VORD
can be applied to as many or as few
axes as desired and the amount of override specified for one axis is
independent of the others. If you use
SYSTEM.VORD
and
<axis>.VORD
simultaneously, the axis speed is reduced by the product of both override
properties as shown below:
System.VOrd = 66 ‘Reduce entire system to 2/3 speed
MainAxis.VOrd = 50 ‘Reduce MainAxis to 1/3 speed
In this example, the entire system is reduced to 66% and the MainAxis is
reduced to 50% of the system speed which is 33%. There is a delay of 5
samples until the velocity start to change that to insure a smoothness
velocity exchange.
4. 2
M
OTION
E
XAMPLES
This section provides a few examples that apply the motion control
techniques discussed in this chapter to common machine functions.
4.2.1. Position
Capture
Many drives (including all current SERVO
STAR
drives) implement the
position capture functionality, commonly used in homing and registration
procedures. Starting with version 3.0, the MC uses the SERCOS procedure
mechanism to accomplish positioning.
While position capture is a drive-based function, the MC provides various
commands to control the capture procedure. SERVO
STAR
drives provide
three digital inputs (IN_1, IN_2, and IN_3), any one of which can be
designated for the capture trigger signal. The command properties provided
in the MC are:
<axis>.Capture
Position capture is executed once the SERCOS relevant
procedure (IDN 170) has been started.
<axis>.Capture
encapsulates this
process and starts and stops the capture procedure. It takes the value 1 to
start or 0 to stop the procedure, respectively.
