Geo Brick Drive User Manual
Motor Setup
172
Note
The Singleturn (ST) data bits for rotary encoders, as well as the serial
protocol bit-length for linear scales can be found in the encoder
manufacturer’s spec sheet.
Note
The Electrical Cycle Length (ECL) or pole-pair pitch (in user units)
can be found in the motor manufacturer’s spec sheet.
Ixx71 Saturation
High resolution encoders could saturate the Ixx71 register, which is a signed 24-bit register. Thus, the
maximum value writeable to it is 2
^24
-1
signbit
= 16,777,215.
But remember, the ratio of Ixx71/Ixx70 is what really matters. Dividing Ixx70 and Ixx71 by a common
integer divisor could alleviate settings which are out of range.
Example:
For an 8-pole brushless rotary motor, with a high resolution encoder (producing 33,554,432
counts/revolution), Ixx70 and Ixx71 are usually set to 4 (pole pairs), and 33554432 respectively. These
settings are not acceptable since Ixx71 exceeds the maximum permissible value in its 24-bit register,
dividing both Ixx70 and Ixx71 by 4 results in acceptable settings:
Ixx70= 4/4= 1
Ixx71= 33554432/4= 8388608
ADC Offsets: Ixx29, Ixx79
The ADC offsets importance may vary from one system to another, depending on the motor(s) type and
application requirements. They can be left at default of zero especially if a motor setup is to be
reproduced on multiple machines by copying the configuration file of the first time integration. However,
they should ultimately be set to minimize measurement offsets from the A and B-phase current feedback
circuits, respectively (read in Suggested M-variables Mxx05, Mxx06).
ADC offsets compensation can be done using the following procedure (starting from a killed motor).
This can be implemented in a one-time test PLC:
1.
Record the current loop tuning gains: Ixx61, Ixx62, and Ixx76. Then set them to zero, these will
be restored at the end of the test.
2.
Issue a #no0 (zero open loop output)
3.
Sample ADC phases A, and B. Using suggested M-Variables Mxx05, and Mxx06 respectively.
E.g. store snapshots in two separate arrays of P-Variable arrays.
4.
Average readings over the number of sampled points.
5.
Write the opposite value of the averaged ADCA readings in Ixx29
Write the opposite value of the averaged ADCB readings in Ixx79
6.
Issue a #nK (Kill motor)
7.
Restore the original current loop gains.
Summary of Contents for Geo Brick
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