Industrial Motor Advice

[DukeTech]

Hello, i'm looking for some advice on a project i'm working on.

I am trying to design a system to push a heavy variable weight (maximum load 800lb) over a set of roller conveyors (Think assembly line setup) repeatable to a certain length programmed by a simple raspberry pie or arduino. The weight would be pushed an exact length, stop, drilled, then continued down. I would prefer not to run a servo motor as the cost would raise with encoders, and would prefer to use stepper motors. The weight would travel no faster than 2in/sec. The system would use a Rack and Pinion track to move, pushing the load, and I am looking to use a Nema 42 motor. i'm struggeling to figure out if the Nema 42 motor would be able to push max load without losing steps given the speed is fairly slow and i'm not quite sure where to start the calculations given i don't know the torque rating yet as this is mostly theoretical. To the experts in industrial machines, would this motor suffice? would it be overkill/underkill? Also as far as accuracy goes, i would like to be within a few mm for repeated movement of the load, repeatable results and reliability as well as cost reduction are a must. Any sources, info you guys could share would be hugely appreciated!

Thanks!

 

[waross]

I would use an induction motor.
Push your load up against a stop for repeatability.
Install a spring on the end of the push rod.
Use a limit switch to stop the motor when the work contacts the stop.
The spring will compress and allow the motor to coast down to a stop.
The spring will hold the work against the stop for best repeatability.
When drilling is complete, drop the stop and allow the work to be pushed ahead.
You will be able to sequence this with a couple of limit switches and a couple of relays.


Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[DukeTech]

Hey Bill, thanks for the response.

Sorry, I don't believe I was clear, the reason I'm discussing NEMA and encoder systems is because the system to push the load needs to be programmable through a user interface, depending on where the drilling needs to happen, user would input a length and the system would move the load to the inputted spec, drill, then continue moving the load to the next desired programmed length. The system is ideally an open loop configuration and the stop points as well as material length will always vary from process to process. I Don't believe i would have any trouble programming the system however i have never worked with Nema 42 motors or large weight movements before and am trying to get a ballpark or some sort of guidance on where to start if this motor would even be capable of moving a load on standard industrial rollers without losing steps. Load Weights can range from a few hundred to 800lbs and speed would always need to remain the same.

 

[MacGyverS2000]

If you can't afford to lose steps, include an encoder on the shaft... many motors can be had with the encoder pre-installed.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[waross]

You may get better accuracy and repeatability by adding to the system that I have suggested.
Use a movable stop, that may be programmed and locked in position.
That way you will always be moving a relatively small, constant mass.
Consider a closed loop system. You may use an encoder on the motor if the motor is a direct drive to the movable stop.
I have assembled, set up and commissioned a similar system.
This was a system for cutting rebar to length.
Bundles of re-bar, 60 feet long were dropped on a roll case.
The roll case led to an alligator shear.
On the far side of the shear was a second, movable roll case.
This second roll case had an air operated gate every three feet.
The table had three feet of end movement available.
The system was not completely under computer control.
A computer generated cur sheets that instructed the operator which gate to raise and where to set the movable table.
In operation, a ton or so of re-bar moved down the roll case quite rapidly.
The bundle would hit the gate and bounce and stop.
The shear would cut to length.
The cut bundle would be dumped off of the roll case and the remaining bundle would be advanced for the next cut.
The system worked well and repeatability was excellent.
With an open loop, you do not account for possible movement of the work piece on the conveyor.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!