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Speed adjustment with external position feedback

Valid for S300, S400, S600, S700

Situation

Usually the position controller operates with the primary feedback (FBTYPE). In this setting the gain factor for the position controller is evaluated.

Now the actual position value is switched over to an external (secondary) feedback, that, for example due to a gearing,rotates slower (e.g. factor 3) than the motor feedback. Now the position controller refers to the external encoder.

General procedure

It must be ensured, that one turn of the position set point (S_SETL) generates one turn of the position actual value (PFB0).

  • This means for S300/S700, that one turn of S_SETL generates one external encoder turn 232(Counts) in PFB0.
  • This means for S400/S600, that one turn of S_SETL generates one external encoder turn 2PRBASE(Counts) in PFB0

This can be ensured by the procedures described below:

Procedure I (valid for S300, S700)

The velocity controller setpoint must be factorized with 3 by EGEARO=3 & EGEARI =1, because the external encoder turns factor 3 slower than the feedback in the motor.

If the position controller generates e.g. a set point of 60 rpm, this value is multiplied with 3 and transmitted to the velocity controller. The motor therefore rotates with 180 rpm, due to the gearing the external encoder rotates with 60 rpm. So the gearing has been compensated.

Procedure II (valid for S400, S600)

The velocity controller setpoint must be factorized with 3, because the external encoder turns factor 3 slower than the feedback in the motor. Two setting are required:

  1. VEXTRES modifies the speed feed forward value GPFFV. GPFFVmust be increased by factor 3. VEXTRES is located in the denominator during calculation, therefore VEXTRES must be set to 1/3 = 0.333.
  2. GP must be increased by factor 3

The position controller now generates a velocity controller set point with factor 3 higher, the external encoder however rotates with 0.333 of the motor speed due to the gearing. The gearing is therefore compensated.

Procedure III (valid for S400, S600, S300, S700)

It is possible to manipulate the evaluation of the external encoder. If the external encoder turns 3 times slower than the motor encoder, you can adjust the external encoder so that 0.333 rotation of the encoder results in one turn in PFB0 (see ENCLINES, ENCIN, EXTMUL etc). The garing is therefore compensated.

Procedure IV (valid for S400, S600, S300, S700)

You can change the gain factor and feed forward factor of the position controller (like EGEARI&EGEARO with S300/S700). This procedure is very similar with S400/S600 to procedure II, but GPFFV instead ov VEXTRES must be changed.

If the external encoder turns factor 3 slower than the motor feedback, you must increase GP and GPFFV by factor 3. Now a 3 times higher velocity controller set point is generated at identical control difference. This 3 times higher velocity controller set point forces the motor to turn 3 times faster and therefore compensates the encoder gearing.

Setting of PGEARI & PGEARO

PGEARI & PGEARO refer to the internal parameters (PFB, PFB0 and S_SETL). That means, with procedures I, II and IV PGEARI & PGEARO represent one turn of the external encoder. In procedure II however PGEARI & PGEARO represent 0.333 turn of the external encoder.

Remarks

The position controller gain factors have been evaluated with the primary feedback (motor feedback FBTYPE) as position controller actual value. The external encoder however may have higher or lower resolution. It may occur, that the gain factor GP must be adapted after operating one of the described procdures.

If the external encoder has a lower resolution than the motor feedback FBTYPE, it is possible that the gain factor GP of the position controller must be decreased to get a stably behavior.

If the external encoder has a higher resolution than the motor feedback FBTYPE, it is possible that the gain factor GP of the position controller must be increased to get a higher performance.