Delta RMC151 - Manual (Page 177)

3 Controller Features
• Hold Current Pressure/Force (19)
• Enter Pressure/Force Control (Auto) (44)
• Enter Pressure/Force Control (Time) (45)
For details on control issues to be aware of, see the Pressure/Force Limit Details topic.
Exiting Pressure/Force Limit
An axis will exit pressure/force limit mode if any of the following occurs:
• The Set Pressure/Force Limit Mode command is sent with the Pressure/Force
Limit command parameter set to 0 (Disabled).
• A Direct Output (9) command is sent to the axis.
• An Open Loop Halt or Direct Output Halt occurs on the axis.
• The Fault Controller (8) command is issued to the RMC.
Switching Between Pressure/Force Limit and Control
Pressure/force limit cannot be used simultaneously with pressure/force control. If the axis
is in pressure/force limit, and a command is issued that puts the axis in pressure/force
control, the pressure/force limit will no longer be active and the axis will start controlling
the pressure or force. However, the Pressure/Force Limit Enabled status bit will still be
set, and if the axis exits pressure/force control, it will resume pressure/force limit.
3.7.6. Pressure/Force Limit Details
This topic provides more in-depth information on the pressure/force limit. For general
information, and a step-by-step procedure, see the Pressure/Force Limit topic.
Pressure/Force Limit with Closed Loop Moves
When a closed-loop position move is made on the axis with pressure/force limit enabled,
the axis will move in position control until the Actual Pressure or Force comes close to the
Target Pressure/Force, at which point the position move will be limited such that the
pressure or force will be limited to the Target Pressure/Force.
The Limit algorithm works as follows:
1. Each loop time, for both the position and the pressure/force, the RMC calculates the
total of the Proportional, Differential, and Feed Forward terms and finds the smaller
total.
2. The appropriate integral term is added to the smaller total to calculate the Control
Output.
Therefore, the axis is performing both PIDs simultaneously and using the smaller one
such that the pressure or force will be limited to the Target Pressure/Force.
Position-Pressure Interplay
If the position of the axis varies a lot as the pressure or force changes, the closed loop
motion PID and the pressure PIDs may affect each other. That is, tuning the pressure
alone will not make the axis control better. Both the position and pressure PID must be
tuned to properly tune the combined motion.
Pressure Limit may affect position moves even though Actual Pressure is far from the
Target Pressure. If you wish to make position moves regardless of the pressure, verify
that the Pressure Limit mode is off, or the motion may be affected.
Pressure/Force Limit with Open Loop Moves
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