THORLABS BBD301, Руководство пользователя

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BBD30x Series Brushless DC Servo Controllers
Page 57
30000 (91.6%), then signals greater than 30000 will be output as 30000 and values less
than -30000 will be output as -30000.
Motor 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.
Tracking & Settling Settings
Moves are generated by an internal profile generator, and are based on either a
trapezoidal or s-curve trajectory (see Section 6.3.3.). 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 6.3.3.) 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 settle time 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
programmable position error limit within which the axis must remain, but unlike the
Position Err Limit parameter set in the Advanced - Control Loop Settings tab, the axis
is not stopped if it moves outside the specified tracking window.
This function is useful for processes that rely on the motor's correct tracking of a set
trajectory within a specific range. The tracking window may also be used as an early
warning for performance problems that do not yet qualify as motion error.
The size of the tracking window (i.e. the maximum allowable position error while
remaining within the tracking window) is specified in the
Tracking Window field, in the
range 0 to 65535. If the position error of the axis exceeds this value, the Tracking