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Manual Pulse Generator?


chuber
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Has anyone used a manual pulse generator (mpg) to "step" through a motion program? If anyone has any experience on this and would want to share that would be great. This would be similar to what happens with a CNC machine tool as you increment the mpg the controller "steps" through the program.

 

Thank You

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What do you mean by "step through a motion program"? As the term is usually used, with a "step" meaning one full programmed move, Sina's suggestion is correct -- you would probably have a PLC program issue an step command after N pulses have been received.

 

If what you want is to increment through the trajectory of moves proportionate to the number of pulses from the MPG, you would use a completely different strategy. Here you would probably want to use our "external time base" functionality, where the "time" elapsed in the trajectory is proportional to the number of pulses received. (It is more common that the pulses come from an encoder on a spindle or web encoder, but the algorithm doesn't care where they come from.)

 

This simple technique works well for moving forward through the program, but it is not reversible. Bi-directional techniques are possible, but tricky to implement.

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What do you mean by "step through a motion program"? As the term is usually used, with a "step" meaning one full programmed move, Sina's suggestion is correct -- you would probably have a PLC program issue an step command after N pulses have been received.

 

If what you want is to increment through the trajectory of moves proportionate to the number of pulses from the MPG, you would use a completely different strategy. Here you would probably want to use our "external time base" functionality, where the "time" elapsed in the trajectory is proportional to the number of pulses received. (It is more common that the pulses come from an encoder on a spindle or web encoder, but the algorithm doesn't care where they come from.)

 

This simple technique works well for moving forward through the program, but it is not reversible. Bi-directional techniques are possible, but tricky to implement.

 

In the past we have used the step command as Sina suggested. What we would like in the future is what Curt suggested. At this point we would not want bi-directional capability. When using the external time base would this also control setting of Outputs and reading in inputs in sync with the motion?

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What do you mean by "step through a motion program"? As the term is usually used, with a "step" meaning one full programmed move, Sina's suggestion is correct -- you would probably have a PLC program issue an step command after N pulses have been received.

 

If what you want is to increment through the trajectory of moves proportionate to the number of pulses from the MPG, you would use a completely different strategy. Here you would probably want to use our "external time base" functionality, where the "time" elapsed in the trajectory is proportional to the number of pulses received. (It is more common that the pulses come from an encoder on a spindle or web encoder, but the algorithm doesn't care where they come from.)

 

This simple technique works well for moving forward through the program, but it is not reversible. Bi-directional techniques are possible, but tricky to implement.

 

In the past we have used the step command as Sina suggested. What we would like in the future is what Curt suggested. At this point we would not want bi-directional capability. When using the external time base would this also control setting of Outputs and reading in inputs in sync with the motion?

 

In reading the section on external time base control. I have one further question. What would happen if the end user of the machine rotated the manual pulse generator in the negative direction a large amount? Would the PPMAC simply not move (hopefully for me this is correct) or would some instability arise?

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In external time base mode, the relationship of setting outputs and reading inputs relative to the motion is not changed. You can think of the mode as compressing and stretching time in proportion to the input frequency.

 

You will have to do something special to protect against significant negative motion of the MPG. External time base can pass through a negative time increment in any given servo cycle. This is valuable in the more common use of slaving the motion sequence to a true master position -- if the master stops and oscillates a little positive and negative, the slave position is maintained in proper relationship to the master.

 

However, this reversibility is only maintained in the present motion section's equations of motion. PMAC does not check to see that it has gone back past the beginning of this section and load the previous section (which may be gone). Of course, in the forward direction, it checks to see that it has gone past the end of the section and loads the equations for the next section.

 

People who create this functionality generally just check in a PLC program to see if the master position is going negative, and if it is, they set the output scale factor of the encoder conversion table entry that processes the MPG position to 0.

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