In addition, the double loop control secondary feedback device can be AB quadrature, BiSS-C
interface or EnDat2.2.
For a stable dual loop control, the effective resolution of the motor encoder must be higher
than the effective resolution of the load feedback device. The low resolution of the motor encoder
will cause the position loop to issue VCMD (its resolution is too high), and it cannot be executed by
the velocity loop. If the load encoder servos closed position and velocity control loop and the motor
encoder servos current control loop, a load encoder with high resolution can be used.
6.6.3 Secondary feedback bus
In EtherCAT and CANopen, the drive reports position feedback (object 6064h), velocity
feedback (object 606Ch) and position error (object 60F4h).
In PROFINET, the drive reports position feedback (PZD G1_XIST1 and XIST_A), velocity feedback
(PZD NSOLL_A and NSOLL_B)
⚫ When dual loop is activated, the above objects will be reported based on the load
feedback.
⚫ When dual loop is not activated (default), the above objects will be reported based
on the motor feedback.
6.6.4 Secondary feedback unit
User unit
Secondary feedback uses the same parameters as motor feedback.
⚫ If the load feedback is a rotary encoder: SFB and SFBVEL are expressed in rotation
units: UNITSROTPOS, UNITSROTACC and UNITSROTVEL.
⚫ If the load feedback is a linear encoder: SFB and SFBVEL are expressed in linear units:
UNITSLINACC, UNITSLINVEL, UNITSLINPOS.
Secondary feedback motor to load ratio
[LMUNITSNUM/LMUNITSDEN] is the mechanical ratio, defined as follows:
⚫ For a rotating system: the motor rotates once for every n turns of the load.
⚫ For a linear system: the motor rotates once per n millimeter of linear motion.
Load rotating motor and linear encoder - example
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