Backlash Compensation - Siemens SINUMERIK 808D Function Manual

Position display
The normal actual-value and setpoint position displays ignore the compensation values and show the position values of an
ideal machine. To view the compensation values, perform the following operations:
+ → →
Then navigate to the item "Abs. compens. value meas. system 1".
11.2

Backlash compensation

Effect
In the case of axes/spindle with indirect measuring systems, mechanical backlash results in corruption of the traverse path,
causing an axis, for example, to travel too much or too little by the amount of the backlash when the direction of movement
is reversed (see following figure).
Compensation
To compensate for backlash, the axis-specific actual value is corrected by the amount of backlash every time the
axis/spindle changes direction.
This quantity can be entered for each axis/spindle at the commissioning phase in MD32450 BACKLASH (backlash
compensation)
Effectiveness
Backlash compensation is always active in all operating modes after reference point approach.
Positive backlash
The encoder leads the machine part (e.g. table). Since the actual position acquired by the encoder also leads the real actual
position of the table, the table travels too short a distance (see diagram below). The backlash compensation value must be
entered as a positive value here (= normal case).
Positive backlash (normal case):
Negative backlash
The encoder lags behind the machine part (e.g. table); the table then travels too far. The correction value entered is negative.
High backlash compensation values
The user has the option of applying the backlash compensation value gradually in several increments when the relevant axis
reverses direction. This prevents an excessive setpoint step change from causing specific axis errors.
The contents of the axis-specific MD36500 ENC_CHANGE_TOL determine the increment with which the backlash
compensation value (MD32450 BACKLASH) is applied. Please note that the backlash compensation is fully calculated only
after n servo cycles (n=MD32450/MD36500). An excessive time span can cause the triggering of standstill monitoring
alarms. If MD36500 is greater than MD32450, the compensation is performed in a servo cycle.
Function Manual
104
01/2017