THORLABS KBD101 User Manual page 50

Chapter 6
set default maximum, in the range 0% to 100%. When the accumulated energy exceeds
the value specified in the Energy Limit parameter, a 'current foldback' condition is said to
exist, and the commanded current is limited to the value specified in the Current Limit
parameter. When this occurs, the Current Foldback status bit (bit 25) is set in the Status
Register and the 'Current Limit' LED on the GUI panel is lit. When the accumulated energy
above the Current Limit value falls to 0, the limit is removed and the status bit is cleared.
Motor Signal Bias – When an axis is subject to a constant external force in one
direction (such as a vertical axis pulled downwards by gravity) the servo filter can
compensate by adding a constant DC bias to the output. This bias is set in the Motor
Bias parameter, which accepts values in the range -32768 to 32767. The default
value is 0. Once set, the motor bias is applied while the position loop is enabled.
Motor Signal Limit – This parameter sets a limit for the motor drive signal and accepts
values in the range 0 to 100% (32767). If the system produces a value greater than the
limit set, the motor command takes the limiting value. For example, if the Motor Limit is
set to 30000 (91.6%), then signals greater than 30000 will be output as 30000 and values
less than -30000 will be output as -30000.
Track Settle Settings
Moves are generated by an internal profile generator, and are based on either a
trapezoidal or s-curve trajectory (see Section 6.3.5.). A move is considered complete
when the profile generator has completed the calculated move and the axis has
'settled' at the demanded position.
The system incorporates a monitoring function, which continuously indicates whether
or not the axis has 'settled'. The 'Settled' indicator is bit 14 in the Status Register and
is set when the associated axis is settled. Note that the status bit is controlled by the
processor, and cannot be set or cleared manually.
The axis is considered to be 'settled' when the following conditions are met:
• the axis is at rest (i.e. not performing a move),
• the error between the demanded position and the actual motor position is less than or
equal to the specified number of encoder counts (0 to 65535) set in the Settle Window
field,
• the above two conditions have been met for a specified number of cycles
(1 cycle = 102.4 µs), set in the Settle Time field (range 0 to 32767).
The above settings are particularly important when performing a sequence of moves.
If the PID parameters (see Section 6.3.4.) are set such that the settle window cannot
be reached, the first move in the sequence will never complete, and the sequence will
stall. The Settle Window and Time parameter values should be specified carefully,
based on the required positional accuracy of the application. If positional accuracy is
not a major concern, the settle time should be set to '0'. In this case, a move will
complete when the motion calculated by the profile generator is completed,
irrespective of the actual position attained, and the settle parameters described above
will be ignored.
The processor also provides a 'tracking window' which is used to monitor servo
performance outside the context of motion error. The tracking window is a
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