Opinion trawling; Servo E-Stopping; Omron

I'm putting a shopping list together for a two-axis system using the Omron CJ1 plc and a Sigma-2 drive/motor. The machine operator will be working via a light guard. When using Rockwell servos, I've had the luxury of their resistive brake module to place between the drive and the motor. (When used in anger, the axis stops like it's hit a wall!) However, Omron don't seem to supply an aquivalent and I'm all too aware of the burden placed on a drive's charging circuit when frequently cycling the line power. So... With a legitimate light guard breach every 20 seconds or so, and the health & safety requirement to ensure that the motor is isolated from its power source during the loading/unloading phase, does anyone have any ideas as to what my options might be?

Thanks,
Steve.

Omron do make a braked servo motor, I had them on a high speed punching machine. I can't remember the part number and I have moved companies now. Alternatively fit an external electromagnetic brake. You don't have any other choice with a light curtain, if you had interlocked guarding you could use a run-down timer and solenoid unlocking.

Steven,

Omron does not actually make servo's they are brand labled by Yaskawa, therefore Omron has a very limited line of servo choices. You may want to look at someone like Mitsubishi who can offer you a complete package of servo's and PLC.

Even if you go with Yaskawa on the servo's you still have the problem of commonality.

Mike

There are dynamic brakes available for Sigma II drives; as it was said before, you have to go to Yaskawa - they have it all. It should not be a problem to use Yaskawa drive with CJ1 - Omron just offers the limited choice of the same product line under their name.

All Sigma IIs have exactly the same interface and are controlled in exactly the same way. In the whole range from 100W to 5kW.

For fairness sake, Yaskawa can offer the complete package, including their own PLC - and it eats CJ1 for lunch! However, I would advise caution as the learning curve would not be easy.

Have a look here

http://oeiweb.omron.com/Products-WServoMotors.shtm

About time I replied...

Well, thanks for all the information. I looked at braked motors, but whilst the brakes are generally good for 120% rated motor torque, they are not intended as safety devices as the motors can generate up to 300% for starting and I don't want to compromise that facility. However... I think I have a solution: A contactor between the drive and the motor, enabled by the light guard monitor, with a light guard status signal fed directly into the drive enable. The rationale is that the drive will shut down the outputs (just) before the contactor physically drops out, so the drive won't "see" the opening contacts whilst sourcing motor current.

I may yet use a Rockwell brake unit.

Anyway, my "personal drive" is shutting down now for the weekend.

Steve.

We don't use Omron servos so this mat not work. We use a timed off safety relay that opens contactors between the servo amp and the motors. The timing is set for enough time to allow the servo controller to stop the load. The safety relay opens, usually within two seconds, preventing the servo amp from running the motor after that time. Nothing, except maybe a mechanical brake, can stop that servo motor faster than a (working) servo controller. If the controller loses its mind, after two seconds, the contactor provides hardwired safety. Your conditions may prevent the use of a timed off safety circuit, so disregard this if your application is classified as a high risk.

I've used the exact setup OkiePc discribed and it works great.

Steve Kemp said:

The rationale is that the drive will shut down the outputs (just) before the contactor physically drops out, so the drive won't "see" the opening contacts whilst sourcing motor current.

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Click to expand...

This works OK with VSDs so it should work OK with a servo motor, if there is any sort of overrun on the motor, you will still need the brake. All motion has to cease within the stop time used to calculate the safe distance of the light curtain. You also need some system to periodically measure the stopping time. I suggest you have a look at the machinery safety legislation. As from last year you were personally responsible for your designs with regard to machinery safety.