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jbjarnson
Starting Member
USA
2 Posts |
 Posted - 14 Jul 2008 : 18:58:09
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I'm looking for some examples of how to control a servo motor with encoder. I have a V120 PLC and a servo drive that has CANopen or ±10V input. Any help would be appreciated.
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Sremac
Senior Member
125 Posts |
Posted - 15 Jul 2008 : 01:11:49
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| For that purpose you will need a dedicated motion or position controller (i.e. Trio Motion MC202 or MC206) if you want some performance level. But, on a certain types of servo drivers, there is also a possibility to input pulses in "position control mode". In this mode, the driver itself performs servo algorithm, and turns itself into a step motor's driver, so you "just" have to input an exact number of pulses, which is not easy with Unitronics hard/software. The main problem in motion control mode (true servo algorithm, where you can actually control speed and position of the axis in real time by calculating the demanded position and comparing the measured position with it, amplifying the error counter and feeding it back to the velocity reference whether analog or digital) is the speed of the PLC system which is not designed for that purpose. Typical servo loop has a cycle of at least 1 microsecond (1.000.000 calculations per second), which is far beyond the limits of a general purpose PLC (you will not be able to go beyond a few milliseconds with V120, in the best case, which is more than 1000 times slower). In other words, the mechanical system will make a "runout" or will oscillate heavily if your control system is too slow as it is. I hope that this will help. Greetings. |
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Nacho
Moderator
Spain
575 Posts |
Posted - 15 Jul 2008 : 02:59:03
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Well, it depends of the accuracy of the application. A customer of mine did a X-Y robot with a V280 and Two servos with +/-10V and it had good precision and repeatibility.
There are servos with profiles of position. You can send the order to do some profile through CanOPEN and the servo will do all the work. |
There are 10 types of people in the world: those who understand binary, and those who don't. |
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Sremac
Senior Member
125 Posts |
Posted - 15 Jul 2008 : 03:12:36
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Of course, I also use Yaskawa Sigma II servo drivers with snap-in NS600 position control module, so it is possible to control the application just by a few digital outputs, but this is just the choice of the preprogrammed steps, and the whole algorithm is up to the dedicated controller again.
But it is very interesting to hear that someone did it successfully with +/-10V and V280. I would really like to take a look at the application! Thank you, Nacho, for that information. |
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Nacho
Moderator
Spain
575 Posts |
Posted - 15 Jul 2008 : 04:39:07
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quote:
Originally posted by Sremac
But it is very interesting to hear that someone did it successfully with +/-10V and V280. I would really like to take a look at the application! Thank you, Nacho, for that information.
In that application times was not important.
Some customers use the V280 and V570 with a inverter with 0-10V for positioning a screw of a Bolt clipper. The time is not important again. |
There are 10 types of people in the world: those who understand binary, and those who don't. |
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Sremac
Senior Member
125 Posts |
Posted - 15 Jul 2008 : 04:54:27
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| Hey, I use it all the time (but with 4-20mA), but this is not servo. The guy is trying to control servo driver with analog voltage. Can you imagine how hard is to eliminate just a DC offset value (small +/- DC voltage that corresponds with the zero speed of the drive AND IS NOT ZERO) by counting pulses from the encoder? In other words just to maintain the current position with the full torque, without moving anything! I am afraid that the oscillations would occur. |
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Emil
tech support manager
Israel
978 Posts |
Posted - 15 Jul 2008 : 06:03:27
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No doubts that communication is the up to date way to drive such systems. It has a lot of advantages. In general - it divides the "duty" between the controller, which is designed to drive the whole machine and the driver, which is made especially for driving preciselly the movements.
There are few ways to communicate between drivers and Unitronics OPLC - RS232/484 - Modbus RTU or implementing driver's protocol in Unitronics, TCP/IP or UDP - in general Modbus IP and now CANoppen. All these ways were used in differnt parts of the world with success.
Each way you will choose, you can receive help from Unitronics Support team on support@unitronics.com |
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Sremac
Senior Member
125 Posts |
Posted - 15 Jul 2008 : 06:09:10
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Nice to know that, thanks a lot, Emil. The Big U team has proven its efficiency in years behind!
Greetings |
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jbjarnson
Starting Member
USA
2 Posts |
Posted - 15 Jul 2008 : 16:46:32
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Thanks everyone for the the input.
For this application I'm using a Servo to drive a linear actuator coupled to a cylinder being used as a pressure amplifier. Motor position accuracy is not so important but feedback from a Pressure transducer for motor speed is important. The motor will be required to move in one direction at a speed as to provide a specific pressure ramp rate. At the same time collecting the data from the transducer. |
Edited by - jbjarnson on 15 Jul 2008 19:45:19 |
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Sremac
Senior Member
125 Posts |
Posted - 16 Jul 2008 : 00:09:28
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Well, at first, your question was >>I'm looking for some examples of how to control a servo motor with encoder. I have a V120 PLC and a servo drive that has CANopen or ±10V input. Any help would be appreciated.<< And now, it seems that you want to use feedback from the pressure transducer. For that purpose I recommend some inverter with built-in PID controller (Yaskawa V1000 or V7, for instance) and classical induction motor. In that case you don't need any additional hardware - just inverter, motor and pressure transducer. Good luck.
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plclatin
Starting Member
6 Posts |
Posted - 27 Jan 2009 : 22:07:55
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I have already finish the integration of a Canopen servo drive and a vision series plc. I consider Canopen a very powerful network, but unless you have very good documentation, you are gonna find a lot of problems.
I recommend to use a "sniffer" o similar tool. It is very easy misunderstand the data.
There are several tutorials all over the place, but will need the standard itself, and honestly very little advice, because it is complex.
Best regards |
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Nacho
Moderator
Spain
575 Posts |
Posted - 29 Jan 2009 : 03:13:36
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| Hello plclatin, Could you send me an example of your visilogic application with Canopen?. We are starting to use the canopen with Sanyo Denki servos. |
There are 10 types of people in the world: those who understand binary, and those who don't. |
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Servo motor with HSC
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