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remove target_attr, keep target signal #535

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Oct 7, 2021
Merged

remove target_attr, keep target signal #535

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e58ebdf
MNT #530 remove target_attr, keep target signal
prjemian Sep 20, 2021
0241ba8
DOC #535
prjemian Sep 20, 2021
c760d6f
MNT #530 Should this class update target value?
prjemian Oct 5, 2021
a84b0ea
DOC #535
prjemian Oct 5, 2021
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53 changes: 38 additions & 15 deletions apstools/_devices/positioner_soft_done.py
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,7 @@
from ophyd import Signal
from ophyd import EpicsSignal
from ophyd import EpicsSignalRO
from ophyd.signal import EpicsSignalBase
import logging


Expand Down Expand Up @@ -37,10 +38,11 @@ class PVPositionerSoftDone(PVPositioner):

Defaults to ``10^(-1*precision)``,
where ``precision = setpoint.precision``.
target_attr : str, optional
Used if the setpoint is controlled incrementally by EPICS
(like with a ramp). Then a target attribute signal must be
defined, and its name passed in this variable.
update_target : bool
``True`` when this object update the ``target`` Component directly.
Use ``False`` if the ``target`` Component will be updated externally,
such as by the controller when ``target`` is an ``EpicsSignal``.
Defaults to ``True``.
kwargs :
Passed to `ophyd.PVPositioner`

Expand All @@ -59,8 +61,19 @@ class PVPositionerSoftDone(PVPositioner):
The stop PV to set when motion should be stopped
stop_value : any, optional
The value sent to stop_signal when a stop is requested
target : Signal
The target value of a move request.

(new in apstools 1.5.2)
Override (in subclass) with `EpicsSignal` to connect with a PV.

In some controllers (such as temperature controllers), the setpoint
may be changed incrementally towards this target value (such as a
ramp or controlled trajectory). In such cases, the ``target`` will
be final value while ``setpoint`` will be the current desired position.

Otherwise, both ``setpoint`` and ``target`` will be set to the same value.

(new in apstools 1.5.3)
"""

# positioner
Expand All @@ -76,15 +89,21 @@ class PVPositionerSoftDone(PVPositioner):
tolerance = Component(Signal, value=-1, kind="config")
report_dmov_changes = Component(Signal, value=False, kind="omitted")

target = Component(Signal, value=None, kind="config")

@property
def precision(self):
return self.setpoint.precision

def cb_readback(self, *args, **kwargs):
"""
Called when readback changes (EPICS CA monitor event).

Computes if the positioner is done moving::

done = |readback - setpoint| <= tolerance
"""
diff = self.readback.get() - self._target.get()
diff = self.readback.get() - self.setpoint.get()
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This won't work well for some devices in which the setpoint changes when a ramp is used. For example, this is the case for the lakeshore 340. So, it should be diff = self.readback.get() - self.target.get()

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The setpoint is the ultimate temperature where the controller is headed. The _target is the interim required value for the temperature control loop. (For example, a controller's PID loop will ramp _target as the immediate objective to calculate the following error: readback - _target.) This _target value may be changed incrementally (ramped) by the controller for a controlled transition from current to setpoint. We do not need to examine the controller's interim _target to determine if the controller has reached the requested temperature.

Definitely: done = |readback - setpoint| <= tolerance

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Currently, the Lakeshore 340 EPICS supports ramps the setpoint PV. Thus I think it's not great to call it setpoint in EPICS and target in Bluesky.

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You're saying the EPICS Lakeshore support uses setpoint for the interim setpoint of the ramp?
Doesn't the Lakeshore have a PV that reports where it is headed? That's the PV to be called setpoint in Bluesky to be consistent with how it is used in other positioners, such as EpicsMotor.

The PTC10 has both: a setpoint where the controller is headed (that is setpoint in bluesky) and a setpoint for the PID loop (that would target in bluesky but this interim goal is not interesting to the user).

An interesting case is when |target - setpoint| <= tolerance, that's when we expect to be close enough that |readback- setpoint| <= tolerance could become True.

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We would use this for more controllers than the Lakeshore?

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@gfabbris Can you review again?

_tolerance = (
self.tolerance.get()
if self.tolerance.get() >= 0
Expand All @@ -98,10 +117,12 @@ def cb_readback(self, *args, **kwargs):
def cb_setpoint(self, *args, **kwargs):
"""
Called when setpoint changes (EPICS CA monitor event).
When the setpoint is changed, force done=False. For any move,
done must go != done_value, then back to done_value (True).

When the setpoint is changed, force done=False. For any move, done
**must** transition to ``!= done_value``, then back to ``done_value``.

Without this response, a small move (within tolerance) will not return.
Next update of readback will compute self.done.
Next update of readback will compute ``self.done``.
"""
self.done.put(not self.done_value)

Expand All @@ -112,7 +133,7 @@ def __init__(
readback_pv="",
setpoint_pv="",
tolerance=None,
target_attr="setpoint",
update_target=True,
**kwargs,
):

Expand All @@ -121,11 +142,10 @@ def __init__(

super().__init__(prefix=prefix, **kwargs)

self._target = getattr(self, target_attr)

# Make the default alias for the readback the name of the
# positioner itself as in EpicsMotor.
self.readback.name = self.name
self.update_target = update_target

self.readback.subscribe(self.cb_readback)
self.setpoint.subscribe(self.cb_setpoint)
Expand All @@ -135,9 +155,12 @@ def __init__(
def _setup_move(self, position):
"""Move and do not wait until motion is complete (asynchronous)"""
self.log.debug("%s.setpoint = %s", self.name, position)
self._target.put(position, wait=True)
if self._target != self.setpoint:
self.setpoint.put(position, wait=True)
if self.update_target:
kwargs = {}
if issubclass(self.target.__class__, EpicsSignalBase):
kwargs["wait"] = True # Signal.put() warns if kwargs are given
self.target.put(position, **kwargs)
self.setpoint.put(position, wait=True)
if self.actuate is not None:
self.log.debug("%s.actuate = %s", self.name, self.actuate_value)
self.actuate.put(self.actuate_value, wait=False)
Expand Down