How Do I Configure RMC75E Position, Velocity, and Force?

RMC75E control should use one dual-loop axis: position as the primary feedback and force as the secondary feedback. Velocity can be calculated from position for closed-loop control, while a separate velocity input remains informational. Look at the trend first. Tuning does not fix wiring, scaling, or an incorrect Axis Definition.

Which axis architecture matches the required control?

Configure Axis 0 as a dual-loop axis and assign force as its secondary input. Remove the separate Axis 2 definition if it was created only to represent force. This places position control and force limiting inside the same commanded axis rather than splitting related signals across independent axes.

The signal chain is position setpoint to position controller to analog output to actuator, with measured position closing the primary loop. Measured force closes the secondary loop and constrains the primary loop's action. The controller can derive velocity from the change in position, so a dedicated velocity transducer is not required for either position PID or velocity PID control.

The application calls the 5 lb value a torque limit, but pounds are units of force, not torque. Treat it as a force limit unless the mechanism definition supplies a moment arm and converts measured force into torque. Do not label a force-feedback loop as torque control without that conversion.

Does the position reading prove the primary loop is correct?

Start with the actuator disabled or otherwise prevented from producing hazardous motion. Read the raw position input, the scaled position, the target position, and the analog output while moving the mechanism through a controlled portion of its travel.

1. At the physical low end, verify that scaled position approaches 0 in.
2. At the physical high end, verify that it approaches 30 in.
3. Move in the defined positive direction. The position reading must increase.
4. Compare a known physical displacement with the displayed displacement. Correct input scaling before changing PID gains.
5. Apply a small command and confirm that the AA1 output polarity moves the mechanism in the direction that reduces position error.

If position is noisy, reversed, or incorrectly scaled, stop on this branch. Derived velocity inherits those defects and can make a velocity limit appear unreliable. If position follows physical travel correctly, proceed to the force channel.

Does the force channel represent the limiting variable?

Read the raw force input, scaled force, force setpoint, and controller output together. With no applied load, establish whether the scaled value has a zero offset. Then apply a known load within the transducer and input range and verify both magnitude and polarity.

If increasing load produces decreasing force, correct the signal polarity or configured direction before enabling the secondary loop. If 5 lb in the controller does not represent 5 lb at the mechanism, correct scaling or the mechanical conversion. PID tuning cannot repair either defect.

Once the measurement is valid, configure force as the secondary feedback of the dual-loop axis and select the pressure/force limit behavior. A force limit changes what the final element may command when measured load reaches the specified boundary; it is not merely an alarm. Confirm that the intended positive and negative limiting directions match the mechanics.

Is a separate velocity feedback channel required?

No separate velocity feedback is required for this control arrangement. The RMC75E can perform position PID or velocity PID control from position feedback, because velocity is obtained from position change. The AP2 velocity input may still be scaled to ±10 in/sec, trended, displayed, or compared with calculated velocity, but it does not need to occupy the secondary-feedback position.

Do not replace force with velocity as the secondary input when the required behavior is velocity control with a force limit. That choice removes the measured limiting variable from the dual loop. Use velocity PID mode for a commanded velocity and retain force as the secondary feedback so the controller can constrain both velocity and force.

If the independent velocity measurement disagrees with calculated velocity, compare polarity, engineering-unit scaling, sensor mounting, and signal noise. Diagnose that discrepancy as a measurement problem unless the channel has explicitly been assigned to the control loop.

How should the commands and Modbus values be applied?

Configure and deploy the axis definition in RMCTools first. The controller can then execute the deployed control sequence independently while supervisory equipment supplies setpoints and limits through Modbus/TCP.

1. Define Axis 0 as dual loop with position primary and force secondary.
2. Scale position to 0–30 in, the retained velocity input to ±10 in/sec, and force to 0–1000 lb.
3. Configure the AA1 analog output as the axis command output.
4. Use Set pos/vel control mode to select the required position or velocity PID behavior.
5. Use Ramp prs/frc and Set prs/frc limit mode to establish the force-limiting behavior.
6. Use Move velocity when commanding velocity. For the stated operating request, write the 5 in position setpoint, 1 in/sec velocity limit, and 5 lb force limit to the mapped Modbus/TCP variables used by the deployed program.

Modbus/TCP and Modbus/RTU are different transports. Ethernet connectivity directly matches Modbus/TCP; Modbus/RTU uses serial framing and is not interchangeable with Modbus/TCP merely because an Ethernet cable or network path exists. If a supervisory device only supports RTU, use a documented serial interface or protocol gateway and verify the resulting register mapping rather than configuring the Ethernet connection as RTU.

What readings verify the resolving branch?

Trend target position or target velocity, actual position, calculated velocity, independent velocity input, measured force, and analog output during a low-risk test. Begin below the intended production demand and increase the command only after the signal directions and scales agree.

1. Command motion toward 5 in and confirm that actual position approaches the target without the output driving in the wrong direction.
2. Verify that calculated velocity remains within the commanded 1 in/sec boundary during the applicable control mode.
3. Compare the AP2 velocity measurement with calculated velocity as an independent diagnostic, allowing only the difference justified by sensor response and measurement noise.
4. Apply load progressively and confirm that controller action is constrained when measured force reaches 5 lb.
5. Confirm that removing load permits normal controller action again and that the output does not remain saturated.
6. Interrupt Modbus updates in a controlled test and verify that the deployed program follows the plant's required behavior for stale supervisory data.

If a limit fails, return to the signal that defines it: position for calculated velocity and the force input for force limiting. Change gains only after feedback, command values, operating mode, and output polarity have passed these checks.

FAQ