Command: Enter Pressure/Force Control (Rate) (46)

Supported Axes:

Pressure/Force Control Axes

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

Command Parameters

#	Parameter Description	Range
1	Requested Pressure/Force (Pr or Fr)	any
2	Pressure/Force Rate (Pr/sec or Fr/sec)	> 0
3	Pressure/Force Accel Rate (Pr/sec2or Fr/sec2)	≥ 0 (0=instantaneous) See Caution below.
4	Integrator Preload (%)	-100% to 100%

Description

This command enters pressure or force control and then ramps to the Target Pressure/Force to the Requested Pressure/Force at the rate specified by the Pressure/Force Rate parameter. It will accelerate to that rate as specified by the Pressure/Force Accel Rate.

Caution: Avoid overshoot!
This command starts with the Actual Pressure/Force Rate at the time the command is issued, and brings it to the requested Pressure/Force Rate as specified by the Accel Rate. Therefore, if the pressure/force is rising rapidly when this command is issued, the Target Pressure/Force may overshoot the Requested Pressure/Force by a large amount. To prevent overshoot, set the Requested Pressure/ForceAccel Rate to a very large value, or to zero for infinite acceleration. Or, use a different command for entering pressure/force control.

If the Pressure/Force Accel Rate is zero, the Pressure/Force will immediately begin changing at the specified Pressure/Force Rate.

Upon entering pressure or force control, the Target Pressure/Force will be set to the Actual Pressure/Force. The Target Pressure/Force will then be ramped to the Requested Pressure/Force at the specified Pressure/Force Rate.

The Integrator Preload specifies the value that the Integral Output Term should be set to when transitioning into pressure/force control. The Preload is specified as a percentage of the Output Scale (typically 10V), and is not affected by the pre-transition integrator state. Typically, this can be left at the default value of 0. If the pressure/force exhibits a drop upon entering pressure/force, increase this value to help smooth the transition.

Example

Consider a hydraulic press that must move toward the material to be pressed, transition to pressure control and hold a certain pressure.

The user program below shows a possible sequence of steps.

Step 0 issues a Move Absolute command to move the axis to a position beyond where it expects to encounter the material. The Step 0 Link Type waits for the Actual Pressure to exceed 1000, then it goes to Step 1 which issues an Enter Pressure/Force Control (Rate) command. The axis will transition to pressure control and go to the Requested Pressure/Force of 5000.

The plot below shows the transition:

At the beginning of the plot, the position is increasing. At approximately 0.55 seconds, the Actual Pressure starts increasing. When the Actual Pressure reaches 1000 at approximately 0.8 seconds, the Enter Pressure/Force Control command is issued, the axis transitions to pressure control, and then the Target Pressure ramps to 5000. Notice that the Target Pressure Rate decelerates to the specified rate and then decelerates to zero, stopping at the requested pressure.

Exiting Pressure/Force Control

To exit pressure/force control, send any open-loop command or closed-loop position command to the axis.

Status Bits

At Pressure/Force

When the axis is in Pressure or Force control and the Target Pressure or Force reaches the Requested Pressure/Force and the Actual Pressure or Actual 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.

Pressure/Force Control

The Pressure/Force Control Status bit indicates that the axis is in closed-loop pressure or force control.

Pressure/Force Target Generator Bits

The Pressure/Force Target Generator bits in the Status Bits register indicate which portion of the move the axis is currently in. These bits are useful when programming complex motion sequences.

Pressure/Force Target Generator Done bit

This bit indicates that the Target Pressure or Target Force has reached the Requested Pressure/Force. If the ramp is interrupted, e.g. due to a halt, the done bit will not be set because the commanded motion was not completed. Notice that this bit does not indicate whether the Actual Pressure or Actual Force has reached the Requested Pressure/Force.

Pressure/Force Target Generator State A and B bits

B	A	Description
0	0	Pressure/Force is stopped (done)
0	1	Pressure/Force is accelerating
1	0	Pressure/Force is changing at a constant rate
1	1	Pressure/Force is decelerating