forked from epics_driver_modules/motorBase
Ron Sluiter
62 lines
2.8 KiB
Plaintext
62 lines
2.8 KiB
Plaintext
Readme for PIasyn - EPICS support for PI GCS2 stages
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========================================================
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The PIasyn driver is written to support PI motion controllers which
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support GCS2 (General Command Set) as commanding language.
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Currently this is implemented with different C++ classes where the
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differences and specialties are handled. This can be implemented
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by querying the controller what features are supported. So in future
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developments these classes may disappear.
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Homing
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========
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a) stages with absolute sensors
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Some PI stages, mostly piezo stages, use an absolute position sensor.
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The correct absolute position is known to the controller immediately after power up.
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For these stages homing is not necessary and thus not supported.
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These stages will ignore HOMF and HOMR.
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The HOME flag of the MSTA field is meaningless for these stages
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and HOMED is always true,
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b) stages with incremental sensors
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Some PIStages needs to be referenced after controller power up. The state
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is reflected by the HOMED flag of MSTA. There are different ways to home
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a stage. The default is by using the reference switch. If a stage has
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a reference switch HOMF and HOMR will move to this switch. The direction is
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determined by the controller. The reference signal is edge based, so the controller
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can find out on which side of the reference the stage is and can move using
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the shortest path. HOMF and HOMR will trigger the same move. If the stage has
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no reference switch the built in limit switches can be used to determine the absolute
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position. In this case HOMF will send the stage to its positive limit switch and
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HOMR to its negative limit switch. As the reference is edge based or not present the
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HOME bit of the MSTA field is meaningless for these stages.
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c) setting the homing velocity
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Reducing the velocity used for homing is usually done to improve the accuracy.
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PI controllers reach the reference every time from the same "side". So only this
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last approach is performed with the homing velocity set with HVEL. The coarse move
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to the proximity of the reference is done with the a velocity limited by the current
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velocity (set with VELO) and the maximum possible velocity to decelerate in case of
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hitting a limit switch.
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"Motion Errors"
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=================
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If the controller detects a "motion error", i.e. the difference between target and
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current position is greater than some given limit (also known as "following error"),
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the driver will set the PROBLEM bit in MSTA. Servo control is also switched off.
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The EA_POSITION bit of MSTA will reflect the "servo control" state. To re-enable
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servo control use CNEN.
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C-702
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=======
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The C-702 controller uses an older "dialect" of GCS1.
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That's why at some points different parameter IDs are used and why there is no communication
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during homing. So the position cannot be updated during homing and will "jump" to the final
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position after homing is finished.
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