Acceleration Control

Acceleration Control is a High-Order Control option that adds high-order gains to the position control algorithm. These high-order gains operate on the higher-order derivatives of the controlled value. For example, on a position control axis, the Double Differential Gain operates on the second derivative of position.

Using acceleration control improves motion control in certain cases, such as for pneumatic systems.

The higher-order gains made available by Acceleration Control depends on the axis type:

Axis Type	Available High-Order Gains	Operates on:
Position Control	Double Differential Gain	Actual Acceleration based on the position input (2nd derivative of Actual Position)
Position-Acceleration Control	Double Differential Gain	Actual Acceleration from the secondary acceleration input
Position-Acceleration Control	Triple Differential Gain	Actual Jerk based on the secondary acceleration input (1st derivative of Actual Acceleration)
Velocity Control	Double Differential Gain	1st derivative of Actual Velocity
Velocity-Acceleration Control	Double Differential Gain	1st derivative of Actual Velocity

Effect on Control

Acceleration control can improve the motion control in certain cases because of the added terms.

For position only or velocity only control axes, the noise in the position or velocity measurement (mostly due to the conversion to digital values) requires the derived acceleration measurement to be filtered or smoothed quite a bit before it can be used. This introduces delays or other errors which diminish its effectiveness.

For position-acceleration or velocity-acceleration axes, the secondary input from an accelerometer provides very good acceleration measurements. However, this requires extra components and wiring out to the moving load where the accelerometer is mounted. It is also generally necessary to use two accelerometers, one on the stationary frame and one on the moving load. This is because the stationary frame is not usually truly stationary—its vibrations will impact the motion of the load.

Setting up Acceleration Control

Acceleration control uses a dual-loop axis. On the RMC75, this requires an AP2 module. On the RMC150, the CPU must have the pressure control option, designated as RMC151.

To enable Acceleration Control on a position or velocity control axis:

Set the High-Order Control parameter to Acceleration Control.

To enable Acceleration Control using accelerometers:

Define an axis with a secondary acceleration input. If you are using one accelerometer, choose Accel (single-input). If you are using two accelerometers, choose Accel (dual-input, diff.).
Set the High-Order Control parameter to Acceleration Control.

Note:
If you use the Tuning Wizard and choose a second-order model, the wizard will automatically set the High-Order Control parameter to Acceleration Control.

Tuning Acceleration Control

Manual Tuning

Acceleration Control adds the Double Differential Gain and Triple Differential Gain to the PID or I-PD control algorithm. See the Tuning Active Damping and Acceleration Control topic for details on tuning these gains.

Tuning Wizard

In the Tuning Wizard, on the Confirm Model page, uncheck Limit models to first order. If the wizard then selects a second-order model, it will automatically set the Double Differential Gain. It will not set the Triple Differential Gain.