Internet PLC Forum
General => Technical support => Topic started by: Tim_Law on June 06, 2003, 01:21:55 AM
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We are hoping to use an m series PLC to control a stepper motor for positioning and incorporate an analogue proximity switch to detect any failed steps or moves.
Ideally we need a 1.8degree stepper to move 50steps (90degrees) in 60 to 100milliseconds. Does this sound likely taking PLC scan times into account.
We are considering DPM or Sanyo steppers and Drives, any other cheap suggestions welcome.
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How many pulses will your analog proximity receive in relation to the rotation of the shart? Is it 1 pulse per step? You could feed the pulse back in the PLC's high speed counter to monitor the stepper motor actual rotation. So the PLC both generates the stepper pulses and monitor the encoder feedback.
50 steps in 60-100 milliseconds translate to 833 pulses or less per seconds. That is well within the PLC's capability to handle both pulse generation and encoder feedback.
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Thank you for your fast response.
The analogue proximity sensor we are considering has a 0 to 10v DC voltage output which we were hoping could be connected into the Analogue input of the PLC for position feedback, is this possible at our speed of operation.
If this is not possible the Digital encoder feedback you mention above would be an option.
could you let us have details of the following:-
- scan time
- time for one instruction
- sampling rate of analogue input
- time for one line of progam
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You can use two 10K resistors in series to divde the 0-10V input to 0-5V so that the ADC can read it. The ADC input are pretty fast response (less than 0.1ms). However, the PLC is really not designed to handle very high speed PID loop like in servo control.
PLC scan time is about 7 microsecond per word of ladder logic. TBASIC varies from 0.1ms to several ms depending on complexity of the function. It is not very meaningful to talk about "Scan Time" of TBASIC since you don't usually execute the TBASIC at every ladder scan. Instead you execute a custom function once when an event ocurrl or you could use a clock pulse to periodically execute a custom function written in TBASIC.
The smallest deterministic sampling time is using the 0.01s clock pulse, which means about 100 samples per second.