Rockwell Automation 57C422B 2 Axis Servo Module - Manual (Page 37)

PROGRAMMING 4-9
4.10 Register 8: Maximum Position Error
Register 8 contains the maximum allowable position error
that is used to determine faults. Position error is defined as
the difference between commanded and actual position. The
value depends on the system configuration and performance
required. If this limit is exceeded, the feedback will be
disabled and the appropriate fault bits will be set in the fault
register (R73). Note that register 8 will be examined by the
module even when it is in velocity mode. The module may
respond to excessive position error while running in velocity
mode.
4.11 Register 9: Maximum Velocity Error
Register 9 contains the maximum allowable velocity error.
Velocity error is the difference between the commanded and
the actual velocity. Excessive velocity error usually indicates
excessive acceleration, excessive deceleration, or a
disconnected encoder. The maximum velocity error is
determined using the following equation.
Maximum
Velocity Error=(max acceptable velocity error in eng.
units/sec*encoder counts/eng units) (.00125)
The result of the equation is in counts/scan. If this limit is
exceeded, the feedback will be disabled and the appropriate
fault bits will be set in the fault register (R73).
Figure 4.9 – Maximum Position Error
Figure 4.10 – Maximum Velocity Error Register