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