NC Implementing of the TwinCAT Position Correction

TwinCAT position correction is used for the backlash compensation.

The following table shows a description of TwinCAT position correction for drives in cyclic position and velocity interfaces.

	Implementation and effect of Position Correction resp. Backlash Compensation
Implementation	The backlash correction is subtracted from the set position which is transmitted to the drive. The backlash correction is added to the actual position which is transmitted from the encoder.
Effect in the Position Interface (position control in the Drive)	Description / Effect: By manipulating the set position which is transmitted to the drive the backlash will be driven (subtraction of position correction, see case 1). To realize that the monitored actual value is correct, this backlash correction is subtracted from the transmitted actual value (addition of the position correction, see case 2).
Effect in the Velocity Interface (position control in TwinCAT)	Description / Effect: In the velocity interface no set position is transmitted to the drive, so correcting the set position would have no effect. By correcting the actual position which is transmitted from the encoder to the drive a position difference is created. The closed loop position controller in TwinCAT controls, by means of this position difference (“lag error”) that the backlash is driven (addition of the position correction, see case 2).

Implementation and effect of Position Correction resp. Backlash Compensation

Implementation

The backlash correction is subtracted from the set position which is transmitted to the drive.
The backlash correction is added to the actual position which is transmitted from the encoder.

Effect in the Position Interface

(position control in the Drive)

Description / Effect:

By manipulating the set position which is transmitted to the drive the backlash will be driven (subtraction of position correction, see case 1).
To realize that the monitored actual value is correct, this backlash correction is subtracted from the transmitted actual value (addition of the position correction, see case 2).

Effect in the Velocity Interface

(position control in TwinCAT)

Description / Effect:

In the velocity interface no set position is transmitted to the drive, so correcting the set position would have no effect.

By correcting the actual position which is transmitted from the encoder to the drive a position difference is created. The closed loop position controller in TwinCAT controls, by means of this position difference (“lag error”) that the backlash is driven (addition of the position correction, see case 2).