Set gear ratio

Notice

Gear unit parameters affect scaling

Changes to the gear unit parameters affect the scaling of position and speed values.

After changing the gear unit parameters, take the new scaling into account.
See chapter The effect of CoE parameters on scaling

The drive controller can account for a gear unit connected to the motor. In this process, all setpoints and actual values for positions and speeds are scaled as if the encoder were mounted on the load side of the gear unit.

Gear ratio

Set the gear ratio between the motor side and the load side in the following parameters:

0x6091:01/0x6891:01 (Channel 1/2) Motor shaft revolutions
0x6091:02/0x6891:02 (Channel 1/2) Driving shaft revolutions

“Motor shaft revolutions” describes the number of motor revolutions required to achieve the number of load revolutions configured in “Driving shaft revolutions”.

The gear ratio is represented as an unsigned fraction. A possible reversal of the direction of rotation caused by the gear unit cannot be taken into account at this point.

Example: For a reduction gear unit in which 5 motor revolutions result in 3 load revolutions, set the parameters as follows:

Motor shaft revolutions = 5
Driving shaft revolutions = 3

Modulo position

You can use the modulo position parameters to limit the value range of the target position and the actual position. If the value range exceeds or falls below the specified range, it overflows to the other end of the range. This function ensures that the target and actual positions are always uniquely assigned to a load position.

Example: The connected load completes one full revolution for every seven revolutions of the motor. In the drive controller's default configuration, one motor revolution corresponds to 2²⁰ increments, i.e., the value range 0x00000000 … 0x000FFFFF. To account for an overflow after seven revolutions, configure a value range of 7 × 2²⁰ increments. Please note that both value range limits are included in the configured range. In addition, when using TwinCAT NC, the Min Position range limit must always be configured to 0x0000000.

0x607B:01/0x687B:01 (Channel 1/2) Min Position range limit: 0x0000000 = 0
0x607B:02/0x687B:02 (Channel 1/2) Max Position range limit: 0x006FFFFF = 7 × 2²⁰ – 1

Special considerations when using a gear unit

Speed limitation: If a gear ratio other than 1:1 is configured, the speed limitation specified in the Amplifier Settings > Velocity limitation parameter applies to the load side of the gear unit.
Position offset: The Position offset is subtracted from the position in process data scaling, just as it would be during operation without a modulo/gear unit.
Note: To prevent loss of a calibrated zero position, the drive position offset is rescaled when the gear ratio and/or the single-turn bits/multi-turn bits of the process data representation are changed.

High gear ratios

For high gear ratios, the position resolution in the process data representation is low: the higher the gear ratio, the fewer position increments per motor revolution.

This results in higher noise levels due to the internal interpolators and feedforward controls. Therefore, for high gear ratios, it is recommended to adjust the process data representation (Feedback Settings: Singleturn bits and Multiturn bits) so that the setpoint resolution becomes finer again.

When working with a modulo position, it is advisable to scale the position representation using single-turn bits or multi-turn bits so that the process data value is fully utilized.