Difference between revisions of "Gantry Issues"
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= Re-ordering the master-slave sequence. = | = Re-ordering the master-slave sequence. = | ||
In softMC the sequence of calling different RTKs is assured by giving them different priorities (starting from 20). By default the first axis (the one with lowest ID) has the starting priority (20), the next has 21, and so on. IF the group's RTK is activated, it gets the priority number of it's first axis. In this way we assure that no RTK interrupts execution of the other one. | In softMC the sequence of calling different RTKs is assured by giving them different priorities (starting from 20). By default the first axis (the one with lowest ID) has the starting priority (20), the next has 21, and so on. IF the group's RTK is activated, it gets the priority number of it's first axis. In this way we assure that no RTK interrupts execution of the other one. | ||
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{{Bugzilla|1003}} B/F: Master-Slave order affects PCMD synchronization | {{Bugzilla|1003}} B/F: Master-Slave order affects PCMD synchronization | ||
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Revision as of 11:01, 9 April 2014
In some applications, gantry systems (pair of parallel axes) are implemented as master slave pairs. Where master is a part of a bigger (XYZ) group and each of the group's axis can be a master to a different slave axis. The whole issue can be extended to any group of geared axes that are moving together one physical object.
Problems:
Problems occur when due to asymmetrical engagement of the system either by different stopping starting or mechanical non-symmetries.
1.) Motors are directly working against mechanic and possible mechanical breakage/damage can occur.
2.) The systems forms a mechanical feedback loop and instability in form of axis runway can occur.
3.) Load is distributed not equally, therefore dynamic behavior of one axis differs from the other.
Prevention features:
- Slave deviation: difference in position between master's and slave's feedback is monitored if it exceeds certain threshold an error is generated and the system stopped. MC-Basic: <slave>.SlaveDeviation .
- Slave disconnect: when slave is disabled either due to explicit user command or as a result of an error it's master is automatically disabled. MC-Basic: <slave>.SlaveDisconnect .
- The master is "aware" of its slaves. Keeping slave in enabled state when master is disabled can introduce a feedback loop (mechanical linkage between slave and master) resulting is a system that is not always stable i.e. we have a runaway. This can be prevented using SlaveDisable flag, each time a master is disabled due to whatever reason all its slaves will be disabled too. MC-Basic: <master>.SlaveDisable .
- In order to keep the delay between master and slave minimal it is imporrtant to take care about the order of calling of axis RTK. Connecting slave to a master automaticaly re-orders their RTK by changing their priorities.
Table of Actions
We define General Axis Deviation (GAD) is as one of the following events:
- position follwing error (Pe > PeMax)
- velocity overspeed (Vfb > Vospd)
- excessive acceleration (over Sys.MotionMargin*Amax)
- excessive torque (over Tmax)
- slave deviation (SlaveDeviation > SlaveMaxDeviation)
| Action: | (or master is PEXT) |
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| Slave GAD | Stopping master axis Stopping slave axis |
else disabling the master |
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| Slave GAD (when slave is stopped) |
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| Slave GAD (when master is stopped) |
Disabling slave | |||
| Master GAD | | |||
| Master GAD (wnen master is stopped) |
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| Error on slave axis | Stopping slave axis |
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| Error on master axis | | |||
| Disabling master: (max.en: 1→0) |
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| Disabling slave: (sax.en: 1→0) |
No disconnection. |
Disable all master axes connected directly or indirectly. |
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