Servo or cylinder positioning?

Hello all- I have a project coming up where we need to raise a small part (size of a 3/4 x 2" bolt) approx 4" so a gripper can grab it and move to the next location. The parts will vary in size so they may have to raise anywhere from 2-4". The going plan was to use a small servo and a linear slide w/lead screw to run the part up into position. I'm struggling to figure out why we don't use a pneumatic cylinder with some type of position feedback or LVDT instead. It seems like it's servo/linear slide/servo motor vs. air cylinder/feedback device?? speed isn't any issue ans accuracy could be +/- 1/8". Any thoughts?

Air seems cheaper but......

By the time you add the servo controls to the air system the price difference narrows and the performance of the air system will never come close to that of the linear motor. Plus tuning an pneumatic system is tricky. Tuning a linear slide is a no brainer.

Unless you already have the air and can't use a motor/electricity for some reason I would stick with the linear electric motor.

Peter Nachtwey said:

By the time you add the servo controls to the air system the price difference narrows and the performance of the air system will never come close to that of the linear motor. Plus tuning an pneumatic system is tricky. Tuning a linear slide is a no brainer.

Unless you already have the air and can't use a motor/electricity for some reason I would stick with the linear electric motor.

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I agree with that.

Is it something that perhaps would not need to be positioned too accurately? could an air cylinder just sorta jam the part up into the gripper without having to actually position it? the gripper (or some sorta plate) just wouldn't allow the air cylinder to push it up any farther?

I used to have a flat bed plotter, (which I thought was the coolest thing ever).
The pens were held by little springy clips that were made in such a way that the outside of the empty clip would fit inside the inside of the clip that held the pen.

All the empty clip had to do was push inside the clip with the pen and back out and then IT had the pen. I always admired how simple, effective and clever that was. It had eight colored pens... the arm would come get the pen, use it, and return it.... It never missed one time

perhaps a cogged belt on two pullies with some sorta fixture(s) to hold the part.. that'd be fast

You might be able to get the pneumatic thing to work, but it's not easy

I'm not the biggest fan of lead screws either.

Thanks for the feedback to both of you.
It may be possible to jam the part up into the grippers-there's a shoulder on them so if it hit the bottom of the gripper it would stop which would probably be "in position". I think they were looking for more feedback that it actually raised a part up. It seemed just to raise the part up 2-4" in about 10 seconds could be done fairly accurately with a cylinder, flow control and position feedback. I'm sure more accurate with the servo.

dginbuffalo said:

Thanks for the feedback to both of you.
It may be possible to jam the part up into the grippers-there's a shoulder on them so if it hit the bottom of the gripper it would stop which would probably be "in position". I think they were looking for more feedback that it actually raised a part up. It seemed just to raise the part up 2-4" in about 10 seconds could be done fairly accurately with a cylinder, flow control and position feedback. I'm sure more accurate with the servo.

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I'm not saying you can't do it ... it's just a pain that you can probably avoid with other methods... right off the bat you pretty much have to use two solenoids, because if you just exhaust the cylinder, the pressure changes and the cylinder moves. The cylinder's characteristics change with age and lubrication. The pot inside the cylinder wears out at points where the cylinder frequently oscillates (end points) .

Reading the pot just to tell if it has raised the part up wouldn't be nearly as difficult though

happy trails to you

additional info only,

Is this something you are going to have to build?

If so then take time to look at a small robot instead. Robots are commodities now, and they have become inexpensive. You can probably get a pick and place to do what you want for far less money than it will cost to roll you own.

TConnolly said:

Is this something you are going to have to build?

If so then take time to look at a small robot instead. Robots are commodities now, and they have become inexpensive. You can probably get a pick and place to do what you want for far less money than it will cost to roll you own.

Click to expand...

have you any links to suppliers?
or brand names?

Johnny 5

somethings like this,

http://www.crustcrawler.com/index.php

dginbuffalo said:

It seemed just to raise the part up 2-4" in about 10 seconds could be done fairly accurately with a cylinder, flow control and position feedback. I'm sure more accurate with the servo.

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I've got a roof full of pneumatic controlled I/P rotary cylinders that you are more than welcome to take. Not a single one is working reliably, mind you.

I can't tell you how many times Maintenance has had to get up on the roof, rain or shine, freezing or not and deal with these stupid things.

They will soon all be replaced with Becks actuators that use a inverter to drive them to their failsafe positions should we lose power (the only reason why we went with pneumatic in the first place was loss of power concerns)

They will never be as accurate as the servo, and nor will it be as repeatable & reliable. And they are a bear to deal with when tuning them. And you will have to tune them, over, and over, and over...

Stick with Peter's suggestion, you won't be sorry.