electric motor position application

[merv1234]

I have an application where I have four electric cylinders pressing down on the lid of a cart to press a laminate material together before the cart goes into an oven. There are many different carts so I cannot run the cylinders to a position, I am using the current pulled by the motor.

When the cycle is started the cylinders will extend until they touchoff on the lid of the cart. (which will never be level or in the same position). Then I will start running the cylinders very slow until each one senses that is bottomed out on the cart. My issue is that I want the four cylinders to bottom out on the cart at the same time.

My first thought is to use position to calculate velocity. that way if one cylinder is ahead of the others it will be running at a slower speed, therefore allowing the lagging cylinders to catch up. By the end of the stroke they should all be pretty close to the same position.
Does anyone else have any thoughts or suggestions? Any help is greatly appreciated.

 

[itsmoked]

Yeah! Get it all for free.. Use hydraulic cylinders.

You can achieve what you want, you just have to spend way more $$$ than if you did it hydraulically. You need to get electric cylinders with linear encoders. Then have your controller do the math.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[PNachtwey]

This can be done with electric cylinders too. What is needed is an accurate torque measurement when using EMAs. When using hydraulic cylinders one needs to know the pressure on both ends of the cylinders.

Getting to a position at the same time is easy as long there is force to over come the obstructions.

Four corner presses are easy if the mechanics are right.

 

[merv1234]

We thought about using Hydraulics, but the material being pressed in the cart must remain free of contaminants. We didnt want Hydraulic Oil in the Area. Like I said I am not going to be driving to a particular position, but a particular torque. i will just use position to ramp down velocity. This should get my four cylinders reaching their final torque at about the same time. Do you agree?

 

[itsmoked]

From your description.. No. I don't think you will like the results.

Here's what I'd do:

Make a four armed device, essentially a cross with feet on the ends to bear on your material. At the center of your cross on the top put a universal joint. Use one cylinder that bears down on the universal joint.

This causes all the feet to apply pretty much the same force regardless of the material being pressed. It jettisons all sorts of control hassles and expense.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[PNachtwey]

Synchronizing the four axes is not a problem.
Since this is a reactive system there would be a few thousands of error between the axes.

Then I will start running the cylinders very slow until each one senses that is bottomed out on the cart. My issue is that I want the four cylinders to bottom out on the cart at the same time.

After reading the original post I find there are conflicting goals or statements.
If the crate isn't level then some axis will need to travel farther to reach the desired torque. There can be no guarantee this will happen at the same time.
One can control position or force but not both at the same time. One can limit position and force at the same time but limiting doesn't guarantee position synchronization. If the synchronization can be ignored after contact is made the all the EMAs can move till an intermediate torque is achieved and then the torque can be ramped up so the desired torque is achieved.