Commissioning: Axis-Specific Machine Data; Dual Position Feedback - Siemens SINUMERIK 840D sl Function Manual

5.3.2.2

Commissioning: Axis-specific machine data

Compensation value
As precondition to commission the dynamic backlash compensation, the mechanical backlash
compensation must have already been commissioned. See Section "Commissioning: Axis-
specific machine data (Page 260)". To determine the compensation value for the dynamic
backlash compensation, the measurement described there should be repeated with low
traversing velocities. The compensation value determined in this way is entered in the machine
data for the corresponding measuring system:
MD32456 $MA_BACKLASH_DYN[ <active measuring system> ] = <compensation value for
dynamic backlash compensation>
Compensation value change
Using the machine data, the velocity with which the compensation value is traversed through
is set as a percentage of the maximum axis velocity (MD32000 $MA_MAX_AX_VELO):
MD32457 $MA_BACKLASH_DYN_MAX_VELO = <percentage of the maximum axis velocity>
5.3.3

Dual position feedback

For the "Dual position feedback" function, contrary to conventional (mechanical or dynamic)
backlash compensation, two measuring systems, which are mechanically coupled through a
gearbox without backlash, are used for the closed-loop position control. The advantages of a
direct measuring system are combined with the advantages of an indirect measuring system:
● Direct measuring system: The closed-loop position control with direct, i.e. encoder on the
load side, "automatically" corrects the backlash.
● Indirect measuring system: The closed-loop position control with indirect, i.e. encoder on
the motor side, is "rugged" and "stable" regarding discontinuous backlash.
Each time the setpoint changes, initially only the encoder data from the indirect measuring
system is used for rugged control without oscillation. With a parameterizable delay time, the
closed-loop control smoothly transitions to monitor the direct measuring system, therefore,
achieving the required accuracy on the load side. The control operations should, at this point
in time, only involve short distances. This is because in the meantime the tooth flanks are in
contact with one another, and the backlash has been moved through.
When using the "Dual position feedback" function, it is not necessary to measure and
mathematically compensate the backlash.
Extended Functions
Function Manual, 10/2015, 6FC5397-1BP40-5BA3
K3: Compensations
5.3 Backlash compensation
263