Danaher Motion
06/2005
Project
3.13.3. Velocity
Loop
For some applications, the motor must be under velocity loop control.
Maintaining a position is not important. The advantage is that the motor is
more responsive (typically 3 to 5 times faster in settling time). When you
configure an axis for velocity loop, you more or less fool the drive by setting
gains to disable the position loop. You need to set the position loop gain to
zero and the feed-forward gain to 100%. This produces the following servo
loop:
Since a lot of position error can accumulate in velocity loop, it is best to
configure the system to have such a large maximum position error that it
never realistically generates an error.
3. 14
S
IMULATED
A
XES
A simulated axis is an axis that exists only inside the MC. Simulated axes
have most of the functions of physical axes including profile generators,
units, position and velocity commands and feedback signals, and limits.
However, simulated axes do not include a drive, motor or feedback device.
An axis can only be configured as a simulated axis during Sercos.Phase 0 or
before SERCOS configuration takes place in CONFIG.PRG or
AUTOEXEC.PRG. To set up a simulated axis, set the axis property
SIMULATED
to ON:
A1.Simulated = ON
This step is inserted in the BASIC Moves auto setup program, in the
subroutine, SercosSetup, just after the phase is set to zero. See SERCOS
Setup Subroutine in Appendix A for additional details.
Simulated axes require about the same amount of resources from the MC,
as physical axes. As a result, simulated axes are part of the total axis count
of the controller. For example, a system with three physical axes and one
simulated axis requires a four-axis MC. Simulated axes are used in the MC
in the same way as physical axes. They are profiled with
JOG
and
MOVE
,
can be geared and cammed, and can act as masters for geared and
cammed axes. Variables from simulated axes such as position feedback can
be used to generate events. During operation, the feedback position and
velocity are set to their respective command values.
Although most commands and variables for axes work for simulated axes,
there are some exceptions. Simulated axes cannot receive SERCOS
commands. You cannot set drive variables such as position loop gains in
simulated axes.
M-SS-005-03 Rev
E
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