Jog-while-pause changes to motion

what it is

An enhancement to the motion pause handling to:

• enable jog moves during auto pause (in coordinated mode, that is axes, not joints)
• un-pausing will return to the position where 'pause' was hit, then continue the auto run
• hitting 'step' will just return to the pause position and stop
• otherwise, 'pause' and 'step' should behave as before
• inputting jog offsets and feeds happens through HAL pins
• feed override keeps working during jog moves in pause mode as usual.
• automatic return moves cane be paused or 'feed held' just alike.
• provide the primitives to record a jog history during pause, and replay it for return (could be done in HAL or Python)

the intent is to provide a stopgap solution to the 'pause, jog away, clean swarf, continue' issue to provide the basis for other scenarios

what it doesnt provide:

• a complete 'jog solution' including keyboard jog, MPG support, your daughter's kinect etc. All it does is provide the HAL hooks to provide these features, but it doesnt do so by itself. This is experimental, and needs some shakeout. Until then, some HAL plumbing is needed, it isnt yet clear to me how jogging in coordinated mode fits in the overall picture.

• touchoff during pause. This is a fundamental restriction in current linuxcnc and forcing the issue would have some serious side effects.

• MDI during pause. As far as the rest of linuxcnc is concerned, jog-while-paused is not visible - it all looks like a loooong pause. This modification assures that at resume happens at the point where where 'pause' was hit.

• jog moves during spindle-synced moves. These changes rely on the current 'pause' capabilities.

How to try it out

Pull

 http://git.mah.priv.at/gitweb?p=emc2-dev.git;a=shortlog;h=refs/heads/jog-while-paused-preview2-rebase-onto-master

and build

 cd configs/sim/axis 
 linuxcnc jog-while-pause9.ini

execute, hit pause somewhere

set feed to some realistic value in the glade panel

press 'pause-offset-enable'

change some offset

press 'pause-offset-enable' again

press 'step' to return to pause point

press 'pause' again to continue

Integration notes

I assume here you want to build a jog-while-paused support component, for instance for an MPG. I use 'IPP' to mean the 'inital pause position', which is the pose where the pause request was honored and state changed from running to paused.

Status pins:

• motion.pause-state, s32, one of:
  • 0 = running - 'not paused'
  • 1 = pausing - looking for the first pausable motion (e.g. not spindle-synced)
  • 2 = paused in initial pause position
  • 3 = paused, but in offset to IPP (return move needed on resume)
  • 4 = jogging - currently executing a move due to a valid offset applied
  • 5 = returning - currently executing a return move to initial pause position
  • 6 = pausing for step - short temporary state while executing a step
• motion.pause-at-motion, s32: the motion type at which the pause request was honored.
  • 0 = invalid (not paused/paused in offset)
  • 1 = traverse linear move
  • 2 = feed linear move
  • 3 = arc
  • 4 = toolchange move
  • 5 = probing
  • 6 = indexrotary
• motion.pause-offset-in-range: bit - the value of the pause-offset-* pins would result in a move not violating machineconstraints. Updated during states 1 and 2.
• motion.in-position: existing motion pin signifying the end of a coordinated motion has been reached and no further motions are pending.

Control pins:

• motion.pause-jog-feed: feed for jog moves
• motion.pause-offset-x..motion.pause-offset-w: offset value to be
• applied to the IPP as long as pause-offset-enable is true
• motion.pause-offset-enable: apply pause-offset-* to generate a move
• to the target position. when the move completes, motion.in-position
• becomes true. Deasserting pause-offset-enable before the target is
• reached causes an immediate stop of motion.

Pause, Resume and Step:

• the Axis 'Pause' button causes transition to the paused state at next chance (EMC_TASK_PLAN_PAUSE NML message).
• The Axis 'Resume from pause' (clicking pause button in paused state) causes transition to the running state (EMC_TASK_PLAN_RESUME NML message).
• The Axis 'Step' button resumes the pause for the current motion if paused in the initial pause position. If not in the initial pause position, it triggers a return move. (EMC_TASK_PLAN_STEP NML message).
• The joint jog requests (EMC_AXIS_JOG NML message) are currently ignored.

HAL flows:

• apply an offset:
  • apply desired offset values to pause-offset*
  • In state = 1 or 2:
    • if pause-offset-in-range is true, enable pause-offset-enable -> move starts, state changes to 4 (jogging)
    • stop current jog: disable pause-offset-enable, curent jog move inprogress stops immediately.
  • end of jog move reached: keep pause-offset-enable applied until motion.in-position becomes true.
  • continuous jogging: keep pause-offset-enabled - any change to pause-offset-* will be honored by a corresponding linear move immediately.
• for pause, step, resume from HAL use halui.program.pause, halui.program.resume, halui.program.step

Python notes:

for recording/replaying jog history: to determine the current pause point, use the linuxcnc module and query linuxcnc.stat.position when state is 1 or 2. Some example supporting code can be found in configs/sim/axis/gladevcp-jwp.py .

Changes in behaviour:

The DRO values for velocity, and distance-to-go are set to zero during a pause, and thereafter reflect velocity and DTG of the jog moves. On resume the velocity and DTG values of the initial paused move are restored.

Deficiencies and surprises

• There's currently no support for spindle, mist, flood handling etc during pause. Some HAL plumbing required for now.
• I dont know how to handle a rotary indexer during jog.

Programming notes

The basic approach is to employ an alternate motion queue - on pause, motion control is switched to the alternate queue, and arbitrary moves can be executed. Switchback to the primary motion queue happens on 'resume'; if the current pose doesnt match where execution was paused, a linear move to the pause point is executed. Then primary motion queue execution continues as before.

WRT pause, the externally significant change is that 'paused' isnt just an emcmotStatus flag anymore, but the state of the pause FSM (see enum pause_state in mot_priv.h). Any state other than 'not paused' is nonzero which is compatible with current task assumptions.

The semantics of 'step' are now such that if paused on the inital pause position, a return move to the initial pause position is executed. That seemed the most logical step to me.

While this implementation relies on the current pause behavior, the underlying mechanism could be used to for more advanced backout strategies, like retracting during a threading move.

--

Updated to master on Aug 7,2012; added missing retract.hal file.