Motors for Stacker System

[roshane87]

Hello,

I'm a mechanical engineer with limited electrical engineering knowledge so please excuse me if I sound naive.

I have a conveyor running with a variable speed drive and I have 3 stackers (as per picture) below them that need to extend based on a signal from a sensor independent of each other.

The stacker will have to move at the same surface speed as the conveyor belt but that's easy to control. This belt, in turn, changes speed based on the speed of the belt that feeds to it (not shown in pic).

I plan on using a toothed belt on a motor/gear motor to run the stacker back and forth.

My question is, what's the most cost-effective way to accomplish this task using the least amount of components?

Ideally, I'd like to do this with 1 PLC, 1 VFD (for the conveyor belt) and 3 independent controllers for the stackers.

I've seen a similar machine run with geared AC motors on the stackers but wouldn't each AC motor need a separate VFD?

Thanks,

RN

RN

 

[BrianPetersen]

So you need to use the motors for positioning?

What scale are we talking about here? I see a pretty picture, but no idea if one millimetre is a large dimension or one kilometre is a small dimension.

Servo motors would be common in that application. And yes, if they have to move separately, each one would need its own drive.

 

[roshane87]

Hi Brian,

The conveyor belt is about 1.5m long and the stacker needs to move (stroke) about 1.2m max but that depends on the length of the panel the conveyor feeds it.

Can I use a DC motor and control with a PWM instead? I don't need feedback from the stepper for position. Wouldn't that be a bit cheaper?

Thanks,

RN

RN

 

[BrianPetersen]

Questions that you need to ask, and answer, and calculate. How fast does it need to move ... how much mass does it need to move ... what sort of friction is involved ... what force will be needed to accelerate it and decelerate it ... figure out from that what sort of torque and speed are required of the motor/gearbox ... how many accelerations/decelerations per hour ... will the motor do it? (thermal ratings / start-stop limitations / duty-cycle limitations) ... and finally, how many of these things are you building. The answer to the latter question establishes how much time and effort it's worth putting into something that might be $3 cheaper if you are lucky but is uncertain as opposed to "get it done".

You need speed and synchronisation (position) control. A servo motor WILL do that - that's what they do. DC motors are terrible for that. Stepper motors in my experience are puny little things. Maybe the servo is overkill for the application. But it WILL do it (provided, of course, that you pick one which is appropriately sized).

AC induction motors with encoder feedback and the right VFD might do it if the system will put up with your frequent starts and stops.

http://www.seweurodrive.com/produkt/movidrive-b-drive-inverter.htm

In frequent start/stop operation, motor cooling can be an issue.

 

[roshane87]

Hi Brian,

I too was concerned about the frequent start-stop affecting the AC induction motor.

We have used an external fan in instances like that with success.

However, as you say, it seems like the servo is the best suited for the job.

Thanks for clarifying these for me.

RN

RN