Installation guide

Mint™ v4 Advanced Programming Guide
40 MN1270 02.2002
In order to smoothly take up backlash, the compensation is applied over a number of servo loop cycles.
The time it takes to compensate also depends on the servo loop frequency set with the
LOOPTIME
keyword. The default servo loop interval is 1 milli-second so a backlash interval of 1000 would imply a
1000 servo cycles and therefore a compensation time of 1 second. If the servo loop interval was 500
micro-seconds, then the compensation time would be 500 micro-seconds.
Example:
BACKLASH.0 = 0.02
BACKLASHINTERVAL.0 = 200
The backlash size of 0.02 will be taken up over 200 servo cycles. The axis must be IDLE in order to
change the backlash interval. Backlash is only taken up whilst the axis is motion.
See Also:
BACKLASH, BACKLASHMODE, LOOPTIME
BACKLASHMODE/BLM
Purpose:
Controls the use of backlash compensation.
Controllers Supported:
NextMove PCI NextMove PC NextMove BX MintDrive ServoNode 51
  
Format:
BACKLASHMODE[axes] = <expression> {,<expression> ...}
v = BACKLASHMODE[axis]
Dot Parameters:
Axis - Axis No.
Attributes:
Controller Read Write Command Multi-
Axis
Scaled Default Range
NextMove
  
0
0 ≤ x ≤ 1
Description:
Backlash compensation can be turned on and off with the
BACKLASHMODE keyword. 0 is off, 1 turns
compensation on. When compensation is turned on, the sign of the backlash compensation size is used
to determine the direction in which backlash was taken up.
It is assumed that if a positive size is given, then the motor is at the negative extent of the backlash area,
as if the axis had been homed in an initial positive direction. This implies that for a negative
movement, no compensation would need to be applied and for a positive movement, the backlash size
would have to compensate in order to move the physical axis. If the backlash size was negative then the
opposite assumption applies.
When the axis changes direction, the compensation size is taken up over the number of servo cycles
specified with the
BACKLASHINTERVAL keyword. The compensation method is known as constant
since once a change in direction has occurred, the compensation value is applied constantly.
Compensation is only applied whilst an axis is in motion. Therefore if a large number of servo cycles
are specified but the change in direction is achieved with a small move distance, then it is possible that
the whole compensation distance will not be taken up with the move. When the next movement is
given, the remaining compensation will be taken up.
Reading the axis position will return the compensated position, i.e., the physical axis position and not
the motor encoder position. Axis velocity does show the effect of the compensation distance being
taken up.
Backlash compensation only has affect whilst the axis is configured as a servo axis. It also has no
affect if the axis is performing a
TORQUE move.