General automation question - re. start/stop motor vs motor wear

Hi all,

I have been toying with the idea of changing the philosophy on one of our lines to make the conveyors turn off if there has been no activity (i.e. no product past a photocell) on the previous conveyor for x seconds.

The goal of this mod is to reduce noise and carbon footprint.

I just wondered if this on/off switching would have any detrimental effect on the life of the componentry involved (i.e. inverters, contactors, conveyor slat, motor, bearings etc) and therefore whether the benefit would outweigh any detrimental effect??

Has anyone got any thoughts on this?

The system isn't going to be fast switching. But it will just mean that the lines will switch off when the operators go for their breaks, when the lines aren't being used, and if there is a breakdown on the line etc...

Thoughts / ideas / comments about this idea would be really welcome.

;-)

if you are using soft start or VFD they will protect your mechanical restart - this is good.
If the motors are DOL or Star/Delta then there is a high torque load on gearboxes and gears or sprocketc - not good.

the only trap that you need to look at is the Automatic restart.
someone could get caught in the conveyors on restart - be carefull

iant said:

the only trap that you need to look at is the Automatic restart.
someone could get caught in the conveyors on restart - be carefull

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Excellent point. I'll have to give this some thought as to how to protect from this. This could be an issue if an engineer thinks a conveyor is off (because it's not moving) and decided to start messing with the belt. They should always ensure it's isolated but to some people as long as it's not moving then it must be off!

Will have a think about this issue...

Thanks ;-)

uptown47 said:

and carbon footprint.

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That should sell.

would need info on ALL (i.e. inverters, contactors, conveyor slat, motor, bearings etc) and process. operator breaks are great time for pm. maybe if restart is time delayed for peak demand factors etc...why just one line? you could use the savings to buy trees

bce123 said:

why just one line? you could use the savings to buy trees

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I would be doing this on all the lines eventually but I would just trial it on one line first for a couple of weeks to see if there was any adverse effects. i.e. operators getting confused, damage to products caused by stop/starting etc...

I think it will be fine but best to be safe than sorry.

;-)

I've don this with all our conveyors and circular feeders, but as mentioned before, a softstarter or VFD is needed for most applications.
Look also for places were products change there direction, these place can give some jamming with start / stop movements.
Think also on switch off compressed air which is used for positioning of products, this is very expensive, and with a little valve and a PLC output very easy to save a lot of energy.

Jack

Did this in a system that had miles of conveyors to transport products. Most were across the line starters, but there were plenty of VFDs and softstarts. After running for 3-4 years that way, there was NO adverse effects and only good effects.

With the hundreds of motors, I calculated that the savings were in the thousands of dollars per year. Your contactors and inverters can handle hundreds of thousands of cycles. Bearings should have no effect and the conveyors, depending on the kind should be fine. We didn't see an increase in gear box replacement either (we wee running in the 150 ft/min range with 1800 rpm motors).

As for people thinking that they can work on it because it is off, then you have a much more serious problem there. That must be a lockout tagout task. If there are people who are witnessed doing that, then they must be removed from employment to protect themselves and the company.

brucechase said:

did this in a system that had miles of conveyors to transport products. Most were across the line starters, but there were plenty of vfds and softstarts. After running for 3-4 years that way, there was no adverse effects and only good effects.

With the hundreds of motors, i calculated that the savings were in the thousands of dollars per year. Your contactors and inverters can handle hundreds of thousands of cycles. Bearings should have no effect and the conveyors, depending on the kind should be fine. We didn't see an increase in gear box replacement either (we wee running in the 150 ft/min range with 1800 rpm motors).

As for people thinking that they can work on it because it is off, then you have a much more serious problem there. That must be a lockout tagout task. if there are people who are witnessed doing that, then they must be removed from employment to protect themselves and the company.

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+1

Some great points there. Jack, there aren't many 'jam points' but it's a good point and I'll certainly keep an eye out for that.

Bruce, thanks for your input. Good to know that it has worked well for you.

Thanks for everybodies help and input

;-)

brucechase said:

If there are people who are witnessed doing that, then they must be removed from employment to protect themselves and the company.

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I completely agree. I haven't witnessed this specifically but I've witnessed other folly. Enough to factor in this possibility into the equation.

We've done this on several systems before and the results are very well worth the effort--we call it "sleeping conveyors". We have used small alert buzzers in some locations that will alert anyone nearby that the conveyor is about to restart (after a small delay). We also make sure to place STOP and ESTOP switches in these locations, even if other scenarios don't dictate their need.

One thing to make sure of is a restart of the system that occurs after the "idle time" has passed. Most conveyor systems need to be started and restarted from the end of the line forward, where "waking a conveyor system up" more than likely means starting the conveyors in the opposite order--as product would flow.

Try it and you'll probably like it as well. Remember, though that carbon footprint can also mean a HUMAN BODY so safety first then the other carbon footprint.

This is fairly common. The thing to worry about is restart. I suggest at least a 5 second pulsing audible. Also some highly visable indicator that says the conveyor is in Auto Pause Mode. generally starting and stopping conveyors is not a bad thing when you have soft start and VFDs. Even with simple motor starters it is generally not an issue.

I think starting with one conveyor as a test is a very good idea. THis will allow you to get responces back from production on what they like and don't like.

Also give alot of thought to restart, mainly what is the trigger. THis can be an issue.

Good points there. Thank you.

Will definitely look into an indicator(s) of some sort to show that the system is in 'auto pause'. ;-)

The safety concerns are valid. However, I've noticed that the luggage carousel at our airport is off most of the time, and sounds a horn and flashes a strobe for a few seconds before restart. My personal experience is that there are a LOT of idiots going through the airport, so the safety issue may not be as bad as we think it might be.

On restart you might want to stagger starats as Rube suggests if for no other reason than to minimize current draw from simultaneous restarting. It's true that a VFD, and to a lesser extent a soft start, reduces this, but it still takes more torque to accellerate a load.