TrackingActuator

class lsst.ts.simactuators.TrackingActuator(min_position: float, max_position: float, max_velocity: float, max_acceleration: float, dtmax_track: float, nsettle: int = 2, tai: Optional[float] = None, start_position: Optional[float] = None)

Bases: object

Simulate an actuator that slews to and tracks a path defined by regular calls to set_target.

Parameters

min_positionfloat

Minimum allowed position

max_positionfloat

Maximum allowed position

max_velocityfloat

Maximum allowed velocity (position units/second)

max_accelerationfloat

Maximum allowed acceleration (position units/second^2)

dtmax_trackfloat

Maximum allowed time interval (tai - time of last segment) for set_target to compute a tracking path (second). If this limit is not met then set_target computes a slewing path. This should be larger than the maximum expected time between calls to set_target, but not much more than that.

nsettleint, optional

Number of calls to set_target after a slew finishes (meaning self.path.kind is tracking) before self.kind(tai) reports tracking instead of slewing.

taifloat, optional

TAI time for self.target and self.path (unix seconds, e.g. from lsst.ts.utils.current_tai()). If None then use current TAI. This is primarily for unit tests; None is usually what you want.

start_positionfloat or None

Initial position. If None use 0 if 0 is in range [min_position, max_position] else use min_position.

Raises

ValueError

If min_position >= max_position, max_velocity <= 0, max_acceleration <= 0, start_position is not None and start_position < min_position, or start_position > max_position.

Notes

Attributes:

• target: target set by set_target (a PathSegment).

• path: actual actuator path (a Path).

Attributes Summary

path	Get or set the actuator path, a path.Path.

Methods Summary

abort([tai, position])	Stop motion immediately, with infinite acceleration.
kind([tai])	Kind of path at the specified time.
set_target(tai, position, velocity)	Set the target position, velocity and time.
stop([tai])	Stop the axis using maximum acceleration.

Attributes Documentation

path

Get or set the actuator path, a path.Path.

Methods Documentation

abort(tai: Optional[float] = None, position: Optional[float] = None) → None

Stop motion immediately, with infinite acceleration.

Do not change the commanded position.

Parameters

taifloat, optional

TAI time for self.target and self.path (unix seconds, e.g. from lsst.ts.utils.current_tai()). If None then use current TAI. This is primarily for unit tests; None is usually what you want.

positionfloat, optional

Position at which to stop (deg); if None then stop at position at time tai.

kind(tai: Optional[float] = None) → Kind

Kind of path at the specified time.

Parameters

taifloat, optional

TAI time at which to evaluate the kind of path (TAI unix seconds, e.g. from lsst.ts.utils.current_tai()). If None then use current TAI. Ignored unless stopping.

The result will always match ``self.path.kind`` except as follows:

- After a slew we report ``path.kind.Slewing`` until ``nsettle``

consecutive calls to set_target result in a path that is tracking.

- If self.path.kind is stopping and tai > start time of the

last segment, then the kind is reported as stopped.

set_target(tai: float, position: float, velocity: float) → None

Set the target position, velocity and time.

The actuator will track, if possible, else slew to match the specified path.

Parameters

taifloat

TAI time (unix seconds, e.g. from lsst.ts.utils.current_tai()).

positionfloat

Position (deg)

velocityfloat

Velocity (deg/sec)

Raises

ValueError

If tai <= self.target.tai, where self.target.tai is the time of the previous call to set_target.

Notes

The actuator will track if the following is true:

• tai - self.target.tai < self.dtmax_track where self.target.tai is the time of the previous call to set_target.

• The tracking segment path obeys the position, velocity and acceleration limits.

stop(tai: Optional[float] = None) → None

Stop the axis using maximum acceleration.

Update the commanded position to match the end point of the stop.

Parameters

taifloat, optional

TAI time for self.target and self.path (unix seconds, e.g. from lsst.ts.utils.current_tai()). If None then use current TAI. This is primarily for unit tests; None is usually what you want.