The RMC100 excels at smoothly transitioning from position to pressure (or force) control while in motion. This requires two axes: one for the position control and one for the pressure control. When set up for position/pressure control, the RMC100 effectively controls these two axes as one unit.
For information on only controlling pressure or force, see the Controlling Solely Pressure or Force topic.
For complete instruction on how to set up, tune and control a position/pressure system, read the following topics:
Required Equipment
To control position to pressure transitions, an RMC100 with the following options is required:
Pressure control option (the designation is RMC101)
An analog module (for the pressure transducer inputs). An H, G, or A module will work. For details on configuring the module for pressure control and for your particular transducer type refer to Using Analog Channels as Differential Force Inputs, Using Analog Channels as Pressure Inputs and Configuring the Analog Transducer Type.
A module for position inputs. This module must have an analog drive output (not a stepper output). This may be an MDT, SSI, QUAD, or even the same analog module in the previous item if it has a drive output. Most hydraulic systems use an MDT for position feedback.
Types of Pressure Control
The RMC100 offers two types of pressure control:
Set Pressure
This is the standard method of control. When the user issues a Set Pressure command with a certain value, the RMC attempts to change the pressure to that value. Note that if the pressure feedback is double-ended, this becomes force control.
Pressure Limit
This type of pressure control is only available upon request as it is intended for specific applications. It allows the user to do position moves while pressure is being limited to a given value.
Three Basic Modes of Operation
There are three basic modes that must be understood in order to control pressure or force:
Position Control Mode:
In this mode, the position axis is entirely controlling the drive output. The status fields of the pressure axis will still be updated, but the pressure axis will have no affect on the position drive output. Position axes which do not have assigned pressure axis will always operate in this mode.
Pressure Monitoring Mode:
In this mode, the position axis is controlling the drive output, but is monitoring the pressure (or force) during the move. As soon as the pressure reaches a minimum pressure threshold (given by the Pressure Set A field), the axis will enter Pressure Regulating Mode. To enter this mode, a move command (either Go (G) or Relative Move (J) ) with the Monitor Pressure bit set in the Mode word must be issued.
Pressure Regulating Mode:
In this mode, the pressure axis is controlling the pressure (or force). The position of the axis will have no effect on the control of the axis except in the following cases:
If the Actual Position of the axis moves outside the Extend or Retract limits, the axis goes into open loop mode with the Null Drive output. The axis does not return to pressure monitoring mode unless the pressure falls below another pressure threshold (given by the Pressure Set B field).
If the Actual Position reaches the commanded position, the Target Pressure will decrease in order to prevent the Actual Position from exceeding the Command Position. This assumes that the axis is compressing something that may spring back if the exerted force is decreased. To get the Target to increase, re-issue the Set Pressure Command.
The axis may leave pressure regulating mode and return to Position Control by giving a move command without the Monitor Pressure Mode bit set.
A typical position/pressure application uses the above modes in the following order:
A move is made in position control mode to the starting position.
A move is made in the direction of increasing pressure with the monitor pressure bit set (pressure monitoring mode).
When the pressure reaches Pressure Set A, the axis enters pressure regulating mode. Pressure can now be controlled.
To exit pressure control, a move is made with the Monitor Pressure bit cleared.
To perform position/pressure control on your system:
Set up the RMC100
See Position/Pressure Setup for a step-by-step illustrated procedure on how to set up the RMC100 for position/pressure control. Included are instructions for using the Step Table and the commands required for position/pressure control.
Tune the system
See Tuning a Position/Pressure System for a step-by-step procedure on how to tune your system.
Example
See Position/Pressure Example for a fully detailed, step-by-step, illustrated example of setting up and tuning position/pressure control.
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