Frequent Motor Starting

[ConveyorMan]

I'm looking at a project where a cleated conveyor (chains on either side connected by a metal cleat with product between the chains being pushed by the cleat) will be sliding cardboard boxes across a steel surface and positioning them for filling. This will have to index forward approximately 20 times per minute with 2 boxes each weighing approximately 40lbs. We were planning to drive this with a 480v 3 phase motor and VFD. I'm concerned about starting the motor that frequently. Does anybody have suggestions for motor or drive specs?

Thanks

 

[Binaural]

I'm looking at a project where a cleated conveyor (chains on either side connected by a metal cleat with product between the chains being pushed by the cleat) will be sliding cardboard boxes across a steel surface and positioning them for filling. This will have to index forward approximately 20 times per m
inute with 2 boxes each weighing approximately 40lbs. We were planning to drive this with a 480v 3 phase motor and VFD. I'm concerned about starting the motor that frequently. Does anybody have suggestions for motor or drive specs?

Thanks

The main problems you will have are with cooling. Choose a motor which has a cooling fan which is run by a separate piggyback fan motor that is not mechanically connected to the drive motor shaft. Run this separate fan continuously whenever there is need to ensure that the cooling air flow is efficient.

Other things you may do to maximise reliability here:
- Use a positioning VSD with encoder or resolver feedback, and profile the index acceleration profile to minimise stopping and starting forces (and give yourself much more accurate location). I've used this approach successfully for a very similar sounding application in the past.
- Oversize the motor a bit more than usual to cope with the rough treatment
- Run the drive motor constantly, and use a clutch/brake unit (Lenze and others make these) controlled by a simple relay to achieve very accurate albeit harsh stopping and starting. These units can withstand near-constant cycling and are mechanically much simpler and more robust than a conventional AC motor.

 

[brucechase]

Sounds like this might be an opportunity for a servo motor. It all depends on how accurate you want everything to position.

 

[Clay B.]

Will the motor need to reverse to start position? Also will the motor need to change speeds and stop at a specific point?

You may need to look at your VFD also. Something like this I would expect the VFD to be derated also.

 

[dmargineau]

If installing an electro-mechanical clutch between the permanently running motor and the conveyor drive is not an option, you could use a Vector VFD/Vector Duty AC squirrel cage motor if the system is sized up properly.
Since a x000:1 rated Vector Duty AC motor is rated to permanently run at nameplate full load current at zero speed you should be able to size up to a system which doesn't exceed the full load current when accelerating or deccelerating the driven load.

 

[ConveyorMan]

We had considered the Clutch/Brake option, but were concerned that the instant acceleration could upset the product. I'll have to look into the vector duty motor and drive.

Acuracy is not important enough to warrant a servo system but would it get rid of the starting overheating issues?

Thanks for your input guys.

 

[OkiePC]

Acuracy is not important enough to warrant a servo system but would it get rid of the starting overheating issues?

Yes, if sized right. Duty cycle is another area where servo motors trump regular old VFDs and squirrel cage motors.

 

[Clay B.]

Acuracy is not important enough to warrant a servo system but would it get rid of the starting overheating issues?

Yes the servo would be less likely to overheat. Servos are built for rapid start stop where as a standard motor is not.

Either way with the cycling you are looking at you are going to up the motor size. IE if you need a 5 hp for your load you will probably need to use a 7.5 or a 10 hp.

Servo systems have come down in cost over the years so I would shop around. You may find that the servo is about equal in cost with what you would need to use using a VFD and rated motor.

 

[DickDV]

This really is a servo application. An induction motor regardless of rating is not suitable for 20 start/run/stop cycles per minute

if you absolutely have to use an induction motor, look for one that is auxiliary-cooled and has an ultra low inertia rotor. A Baldor/Reliance RPM AC motor would be the best candidate that I can think of.

Still, a servo system would be more appropriate.

 

[Binaural]

We had considered the Clutch/Brake option, but were concerned that the instant acceleration could upset the product. I'll have to look into the vector duty motor and drive.

Acuracy is not important enough to warrant a servo system but would it get rid of the starting overheating issues?

Thanks for your input guys.

It really sounds like a clear-cut servo drive application (and good experience for you if you've not had it before). If you can tell us what PLC architecture you are using perhaps we could recommend some well-liked servo systems. Allen Bradley, for example, have some very simple to use servo drives. SEW also make some excellent stuff in my experience.

 

[Tom Jenkins]

Most motors have optional temperature sensors in the windings available. On small motors this may be a Klixon or similar temperature switch. On larger motors this can be thermistors or RTDs in each winding. This may be good, inexpensive insurance for protecting the motor to consider.

 

[ConveyorMan]

It really sounds like a clear-cut servo drive application (and good experience for you if you've not had it before). If you can tell us what PLC architecture you are using perhaps we could recommend some well-liked servo systems. Allen Bradley, for example, have some very simple to use servo drives. SEW also make some excellent stuff in my experience.

It will definitely be Allen Bradley PLC. I haven't decided yet if I'll use a ML1400 or a Compactlogix L32E. Some guidance on some simple to set up Servo systems would be great thanks.

 

[Binaural]

It will definitely be Allen Bradley PLC. I haven't decided yet if I'll use a ML1400 or a Compactlogix L32E. Some guidance on some simple to set up Servo systems would be great thanks.

Go for CompactLogix for sure - micrologix is out of date. Much easier to use the motion control instructions to control a servo axis in RS5000.

The sort of thing you'd be looking at: http://www.controleng.com/new-produ...s-servo-drive-uses-ethernetip/f3021a8404.html

 

[shooter]

Move the boxes in constant and use the filler head to move in a circle.
If you can fill a 40lb box in three seconds you are very fast.
The stopping/starting of empty boxes is not very handy.

 

[iant]

go to http://www.sew-eurodrive.com/ this is one supplier
worth talking to. there are others


you can program the servo to accept digital inputs.
it will be very price competitive -