OT But Urgently Need Help

[Sergei Troizky 26]

I am having a problem after adding a light curtain to the machine driven by Omron R88D-WT15H servo drive. The light curtain driven contactors cut power supply for the drive output circuits. The problem is that the drive falls into A74 error (inrush current overload) after about 10 power-up cycles of 5-6 sec period each. If the drive control power is cut along with the motor power, the error does not appear but the drive cannot move ~2 sec after power up. This cuts the machine throughput and will not be accepted by the customer. Did anybody face such problem and what may be a solution? Any suggestions will be highly appreciated. Also, will it be a legitimate solution just to cut the drive RUN signal? Edited 17 Apr 2008 by Sergei Troizky

[ParaffinPower 13]

If the drive is stopped, you can break the circuit between drive and motor. You also want to short the motor windings through resistors, too. I stress - ONLY if the drive is stopped! Pp

[BITS N BYTES 66]

How about moving the contactor from the output to the input of the drive? Unfortunately this drive does NOT have an input with "Safe Stop" function according to EN954-1. If it did you could get rid of the contactor completely.

[ParaffinPower 13]

Have I misunderstood? Where are the contactors now?

[BITS N BYTES 66]

Quote:- The light curtain driven contactors cut power supply for the drive output circuits.

[ParaffinPower 13]

Thank you for posting that, BnB; however, the problem is inrush current, so the contactors are already in front of the drive... More than 10 times per 2 second intervals, IIRC Edited 17 Apr 2008 by ParaffinPower

[Sergei Troizky 26]

Did not catch this. Explain, please. Thank you for replies. Made some tests for cutting the motor itself. May be a solution. It does not matter though, whether it is disconnected when stopped or moving- arcing is the same if the drive is in Run (enabled). Will use a software signal from the light curtain to disable the drive in attempt to reduce arcing. Edited 17 Apr 2008 by Sergei Troizky

[ParaffinPower 13]

Hi Sergei A74 is detected if the main circuit power has been cycled 10 times in 2 seconds. In my original post, I should have said the drive needs to be stopped AND disabled before opening the contactor. I still think you'll have to stop and disable the drives with software, then open the contactor some time later (from light curtain). Edited 18 Apr 2008 by ParaffinPower

[Sergei Troizky 26]

OK, this is exactly what I meant.

[Mark The Spark 0]

As with any machine - check the level of protection required by the light curtain / drive interlock is correct to suit the application. In many instances because the curtain is being interrupted frequently and the safety system 'checked' each time just a 'Run hold' MAY suffice. This could be further interlocked by a movement detector that pulls the drive power if for some reason the curtain system fails. Also - if a frequent drive interruption is required due to the dangers involved then use a drive that's circuitry does comply with the relevant safety standards in that region. Or - fit a clutch / brake system - again that meets relevant standards, I like a drive that complies AND a clutch! - (cos it might be my paws wot get squished!). EN 954-1, Machine directive etc all give good pointers as to how to design a reliable safety system - but at the end of the day it must be workable else someone will disable it to make working the machine easier! I'm a tad long in the tooth - used to always fit monitored loop contactors to DC drives etc and did not like the early 3 phase drives because a lot of 'em did not like having open output circuits - hence I have fitted a few clutches or supplementary 'movement / kill' devices to machines where the risks were great. As for drives with 'built in' safety circuits - well if it's got a micro doing it would you put your head under it? Saw a chap demonstrate a laser light guard the other day by putting his hand where it would be crushed if the device failed - brave? - nope foolhardy and stupid I'd say, ALWAYS use a test rod / sacrificial part when testing safety circuits, they are not guaranteed NOT to fail - just not LIKELY to fail unsafe. Edited 17 May 2008 by Mark The Spark

[beegee 7]

we do this all the time, but the system yo use depends on the application possibility 1: just cut the power supply to the drive. This will cause an error but this is easily recovered. possibility 2 : signal the servo to stop (baseblock) and open the contactors with a delayed safety relay (G9SX like). Be carefull to calculate your safety distances. Never open the contactors in between during run this can blow the IGBT's easily cheers