Servos - simple question

I have spent some time in a lab playing around with a ControlLogix, which had a SERCOS card running to an Ultra3000 which controlled an AB servo.

It was a very nice setup and I didn't have much trouble programming the servo to do some pretty cool things.

Are those four components always required when dealing with servos?

PLC -> Motion controller card -> Drive -> Servo

If you had an SLC 500, would you need a SERCOS card for it? I ask because I haven't seen any SERCOS cards for the SLC 500.

Assuming that a motion controller card is required in the PLC rack, are there cards like this for SLC 500's?

Or can you just go direct from the PLC to the drive? ie:

PLC -> Drive -> Servo

I am looking at just using two small servos to control a couple of small tables which must be able to be positioned very precisely, but they don't have to get there very fast.

Another question: Is a high speed counter card used for motors which have encoders, but which are not servos?

Your best option for the SLC500 is probably to use Ultra 3000 I drives and a device net interface. The drive has its own motion controller built it and the SLC simply sends commands over the DN.

If you are already familiar with Logix 5000, why are you using a SLC500? The CompactLogix family of processors costs less money.

PLCBox said:

Are those four components always required when dealing with servos?

PLC -> Motion controller card -> Drive -> Servo

Click to expand...

Not always. Some motion controllers don't need a PLC and are much more powerful than the PLC. They are programmable and can be stand alone if there isn't too much I/O.

If you had an SLC 500, would you need a SERCOS card for it? I ask because I haven't seen any SERCOS cards for the SLC 500.

Click to expand...

Most modern motion controllers are 32 bit. I think it is best if you stick with a 32 bit PLC if you must use one.

Or can you just go direct from the PLC to the drive? ie:

PLC -> Drive -> Servo

Click to expand...

Yes.

Another question: Is a high speed counter card used for motors which have encoders, but which are not servos?

Click to expand...

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If you use a motion controller it should have the encoder interface, otherwise it will be the drive that has the encoder interface. These are much faster/better than the so called high speed counters that PLCs have. Many of the motion controller interfaces can count 8-12 millions counts per second.

Heed Alaric's advice about using a Compactlogix if you must save money.

http://automationnotebook.com/2005_Issue_4/featurestory_Issue4_2005.html

Really confused by the names people use for servo, controller or driver. Generally u can use two controllers motion controller or CPU to control. Most of the servo drives today require a train pulse and direction signals or CW/CCW and I think even some DC levels as a command.

I am doing my bachelor on High counter unit - servo driver- motor.

Counter sends a pulse, difrent freq or a number of pulses= speed/distance, servo driver takes care of PI/P control and motor does the job. Feedback is fed into servo driver, so CPU gets only confirmation that motor is in position. It works fine, the only flow is, that when I force stop of the motor, my counter unit knows how many impulses it managed to send, because it can continue and finished the command if I start it again, bit library does not list any pointer to the actual value. It might be that it does not count, only compares with the defined number. Who knows.

But back to the encoder to high counter unit. It can be done and there are units that can do A/B/Z encoder signals. They are much cheaper than motion controller. Motion controller is really only for most complicated task that needs tracking or synchronising. The special path of few axis.
Otherwice u don't need it.
For better presition of your homing procedure u can use Z signal. Try to search this boards for "origin search" or " homing", it was really nicely explained here.
It's not a complicated procedure, and that is something motion controller has predifined inputs for, but it's not worth the money. If your system is slow, I would definetly drop the motion controller. Servo driver is optimum, but u can also close the loop in the high counter if u feel like playing with PID control.