Command: Set Pressure/Force Limit Mode (40)

Supported Axes:	Pressure or Force Control Axes
Firmware Requirement:	1.00 or newer

See the Commands Overview topic for basic command information and how to issue commands from PLCs, HMIs, etc.

Command Parameters

Parameter Description

Range

Pressure/Force Limit

Disabled (0)
Positive (1)
Negative (2)1
Bidirectional (3)1

1Note: The Negative and Bidirectional options require firmware 3.44.0 or newer.

A valid integer as described

Description

This command enables or disables Pressure/Force Limit, and specifies the direction of the limiting. Pressure/Force Limit limits the Actual Pressure or Force during a position or velocity move. Pressure/Force Limit is useful in applications that require moving to a position while not exceeding a certain pressure or force during the move.

In Pressure/Force Limit, the Target Pressure/Force is the value at which the Actual Pressure or Force will be limited. The axis position or velocity can be controlled normally as long as the Actual Pressure or Force does not approach the limit. As the Actual Pressure or Force approaches the threshold, the RMC will limit the motion so that the pressure/force limit is not exceeded. For more details, see the Pressure/Force Limit Algorithm topic.

Direction

The direction of the force limiting is specified by choosing the Positive, Negative, or Bidirectional parameters.

Positive
The pressure/force will be limited to the Target Pressure/Force, in the direction of increasing pressure/force.
Negative
The pressure/force will be limited to the negative value of the Target Pressure/Force, in the direction of decreasing pressure/force. The Target Pressure/Force itself should be a positive value, but the limit will be applied to the negative value.
Bidirectional
The pressure/force will be limited in both directions of motion, to the positive Target Pressure/Force in the direction of increasing pressure/force, and to the negative Target Pressure/Force in the direction of decreasing pressure/force. The Target Pressure/Force itself should be a positive value. If different limit values are required in each direction, then the user must keep track of the direction of motion and set the Target Pressure/Force appropriately.

Limitations

Pressure Limit cannot be used in Direct Output. To issue the Set Pressure/Force Limit Mode command, the Direct Output Status bit must be off. To turn off the Direct Output Status bit, put the axis in Open Loop or Closed Loop control.

If the axis is in pressure/force control, then pressure/force limit will be ignored. However, the Set Pressure/Force Limit Mode (40) command will still set and clear the Pressure/Force Limit Enabled status bit. If the axis exits pressure/force control, pressure/force limit will be enabled if the Pressure/Force Limit Enabled status bit is set.

Note:
Pressure/force limit may affect motion even when the Actual Pressure/Force is well below the limit. In order to achieve precise motion when pressure/force is not important, do not set the pressure/force limit mode to Enabled. Enable pressure/force limit only after the pressure/force has increased close to the point where the pressure/force is to be limited.
Another option is to use pressure/force control, which will not affect the position motion.

Usage Details

Note:
See the Position-Pressure and Position-Force Control topic for information on setting up a position-pressure or position-force axis.

Entering Pressure or Force Limit Mode

This procedure is can be used to enter Pressure/Force Limit mode.

Make sure the Target Pressure/Force has been set to the desired value. For example, the Ramp Pressure/Force (Linear) (42) command can be used to set the Target Pressure/Force to the desired value.
Send the Set Pressure/Force Limit Mode (40) command to enable Pressure/Force Limit.
Move the axis as desired. When the motion begins to affect the pressure, the RMC will limit the motion such that the Actual Pressure/Force does not exceed the Target Pressure/Force.

Note:
Pressure/Force Limit mode may affect normal closed-loop motion even when the pressure is very low. Therefore, if possible, do not enter Pressure/Force Limit until you need to.

Changing the Target Pressure/Force

Once the axis is in pressure or force control, you can issue any of the following pressure/force commands to change the pressure/force. For example, you can ramp the pressure up or down, or perform a sinusoidal profile, or follow a spline. For details on each command, see the respective help topics.

DO NOT issue the pressure/force commands that enter pressure/force control, because this will exit pressure/force limit:

For more details, see the Pressure/Force Limit topic.

Status Bits

Pressure/Force Limit Enabled

This bit indicates that pressure/force limit is enabled. If an axis is in pressure or force control, pressure/force limit will not be active. If the axis exits pressure/force control to open loop or closed-loop position or velocity control, it will enter pressure/force limit if the Pressure/Force Limit Enabled bit is on.

Pressure/Force Limited

This bit indicates that pressure/force limit is enabled and the axis is limiting the pressure/force. If an axis is in pressure or force control, pressure/force limit will not be active and this bit will not be set.

At Pressure/Force

When the axis is in Pressure/Force control or Pressure/Force Limit and the Target Pressure/Force reaches the Requested Pressure/Force and the Actual Pressure/Force is within the At Pressure/Force Tolerance window from the Target Pressure/Force, the At Pressure/Force Status bit will be set. This bit indicates that the ramp is complete and the axis is at the pressure or force.