Plc an out as velocity to servo. Not much information.

[HJTRBO]

Hi all,
A customers rotary knife servo system is giving random cut length errors. Unfortuanetly i havent had the machine to look at what is wrong. All i know is its an old parker compumotor setup with a analoge servo drive, motion controller and a human interface unit.
We are pulling the machine down next monday to check all the mechanicals and that is when i will get to jot down the part numbers and the actual make up of the system.
It did have me thinking though, for such a simple system, can a plc be used instead? At least that way it is easy to configure. Just work out the accel rate etc. and model that with a simple 0-10V output to the existing servo drive.
The system is basically a conveyor with measuring encoder. A cut length is input into the parker compumotor interface unit, then at length the knife does one revolution. The web material is a sticky (easily torn by hand) sound deading type material 300mm wide with a thickness of around 6mm and the line speed is a mear 20m/min with cut lengths from 100mm to 500mm.
I apologies for the lack of information about the actual components of this (probably) 20 year old system, but with the info i have given would you use a plc to provide the velocity command for a simple system similar to this?
I do not have much motion experience, i am a maybe more than half a brain sparkie.

 

[James Mcquade]

HJTRBO,

not trying to slam you, but this reminds me of a similar project that went bad.

first off, you really need to know what you have and do your research first. then analyze the system. don't assume anything. don't say you will / can do this or that and everything will be ok.

you are setting yourself up for a fall. when you head down that path, you are designing a new system, not fixing whats wrong with the current system. you will get your head full of ideas which will clutter up your objective, what's wrong with the current system?

spending lots of time and money on a system the customer is thinking about replacing any way due to age may not be the best solution.

determine the problem first, then look at how to fix it, costs, downtime to repair/fix it. then get with the customer.

its a hard lesson to learn sometimes, but one you'll never forget.

parker makes several units in which they call servos. one unit is really a stepper motor with encoder feedback. is the stepper motor slipping, encoder going bad, wiring bad, dirty contacts, what changed in the plant recently, what changed on the machine recently? lots of questions to ask.

regards,
james

 

[HJTRBO]

Wise words James. Thankyou. My head does tend to lead off sometimes.
Waiting for monday...