In connection with the cam automat features “Cam automat ACOPOS” and “Common cam automat” the parameter “Relative master start position” is provided as an advanced parameter below “Common parameters → Advanced parameters”.
Working on several support cases it got noticed, that many times the parameter “Relative master start position” is not defined properly according the intended application and its desired movement behaviour of the cam automat coupling. For example, it can be, that the entire compensation movement at the beginning of the start state gets skipped.
IMPORTANT FACT:
When having a cam automat start state unequal state 0 and it is intended that the compensation movement is executed, the “Relative master start position” must be set to “-1 axis unit” (not measurement units) of the master axis.
Example: Measurement resolution of the master = 0.01, so the “Relative master start position” must be set to -0.01.
ParID Info:
If the “Relative master start position” is “0” (default), no compensation is executed with cam automat start states unequal 0!
Use case + AS Help section (ACP10)
One specific use case, where using start state 0 will not work, would be having a moving slave axis and the goal to couple it via the cam automat command to a master which is currently in standstill.
The slave velocity always jumps directly to 0, if the cam automat is started with state 0. So, state 0 is unsuitable for a moving slave at the cam automat start. Here a start state unequal 0 in combination with a proper velocity compensation must be used. For doing so and having the compensation enabled, the parameter “Relative master start position” (AUT_CAM_MA_S_REL) must be set correctly to -1 axis units.
AS Help section (ACP10):
Motion control → ACP10/ARNC0 → Reference manual → ACOPOS Drive Functions → Cam automat → Direct start → Start from a movement with speed compensation ncV_COMP_A_CYC
Traces which show the different behaviour
Trace from active compensation in start state with “Relative master start position” = -1 axis units (-0.01 measurement units):
Trace from skipped compensation in start state unqual 0 due to “Relative master start position” =0:
Situation with mapp Motion V6
With mapp Motion Version 6.x.x the cam automat configuration slightly looks different related to the “Relative master start position” configuration. Here the user directly can select “Start type = Compensation” which would internal automatically uses the configuration “Relative master start position” = -1 axis units (-0.01 measurement units).
