Delta RMC151 User Manual
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RMC70/150 and RMCTools User Manual
Control Mode status register. The Current Control Mode register indicates the mode
currently in use.
See the Closed Loop Control topic for details on which commands are supported in
Position I-PD control.
Special Notes
Decreasing Jerk at Start of Motion
When using the Move Absolute (I-PD)(28) and Move Relative (I-PD)(29) commands, the
system will start moving with a sudden jerk. This is because the Target Position is set to
the Command Position immediately. In many systems this is acceptable. If it is not
acceptable for your system, you can instead use the Move Absolute (20) or Move Relative
(21) commands in I-PD mode. With these commands, the Target Position is ramped
toward the Command Position at the speed you specify (set the Accel and Decel to a high
value, such as 1000). This will essentially eliminate the sudden jerk. This may increase
the time it takes to get into position at the end of the move.
Fast Moves (Saturating the Output)
If the Control Output saturates, the I-PD is not disrupted like the PID is (with the PID, the
Integrator doesn't handle it very well). Therefore, the I-PD can be used to move the
system at it's maximum speed (typically the speed at 10V Control Output). To achieve
this, with the Move Absolute (I-PD)(28) and Move Relative (I-PD)(29) commands, set the
Maximum Speed command parameter to a value greater than you system's maximum
speed. The moves will then saturate the Control Output during the move, indicating that
it is moving at it's maximum speed. You will, of course, need to set the Output Saturated
Auto Stop to Status Only.
Saturating the output can be very useful with non-linear valves where the gain "rolls off"
at the upper end. With a PID, it is especially difficult to get close to maximum speed,
because a small increase in speed can suddenly saturate the output. The I-PD makes it
easy to get to maximum speed.
Position I-PD Algorithm
Each closed loop motion command issued to the RMC specifies a target profile, which
defines where the axis should be at any given moment. For each loop time when the axis
is in closed loop control, the Position I-PD algorithm calculates the values from each gain,
as described below. Then, the terms from the Proportional and Differential gains are
subtracted from the Integral Gain term. The resulting value (in percent) is multiplied by
the maximum output (typically 10V), to come up with the Control Output voltage for that
loop time.
Gains and Feed Forwards
The Position I-PD uses the gains listed below. It does not use any Feed Forwards.
•
The Integral Gain is multiplied by the accumulated Position Error.
•
In this control mode, the Proportional Gain multiplied by the change in the Actual
Position is subtracted from the Control Output each control loop.
•
In this control mode, the Differential Gain multiplied by the change in the Actual
Velocity is subtracted from the Control Output each control loop.
In addition, higher-order gains may be used if Acceleration Control or Active Damping are
selected.
Tuning Position I-PD
The tuned position I-PD gains are typically the same values as the tuned position PID
gains. Therefore, you can use the same tuning procedures for as for position PID. See the
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