Servo motor application question

[tdent]

Hi, I am new to this forum and also very new to automation. I am a mechanical engineer but the plant I work at is small and we don't have any electrical engineers. Anyway, long story short, I am looking to replace an existing air-actuated rotary gate with a servo motor setup. The problem is that I don't know a whole heck of a lot about servo motors, controllers, etc.

The gate is basically a cylinder with 4 sets of cups located 90° apart around the circumference that take dough balls from a belt and load them onto an overhead proofer. The gate receives the balls, gets a signal from a proximity switch, rotates 90° and drops the balls into the proofer trays. Acceleration is moderate, torque requirements are very small, but the accuracy is important.

I guess what I am wondering is will a servo motor and controller be a decent solution for this application and if so, is the motor and controller basically all I need or are there other components that I am overlooking? In other words, can a servo motor with a controller be used as a stand-alone device or does it require other control/power components? (we have 3-phase, 480v at the plant)

The reason we want to change the setup for this operation is that the air actuator we are using right now has been failing on a monthly basis at $2500 a unit - primarily due to poor maintenance. We are hoping a servo motor setup would provide us with much better control and negligible maintenance. Any input is appreciated - thanks

 

[Marke]

If the power requirements are small and accuracy is important, then you may be better to consider a stepper motor.

Best regards,

Mark Empson

http://www.lmphotonics.com

 

[blacksea]

You may review servo controller with build-in amp and direct AC supply from Elmo (

http://www.elmomc.com)

also. But at first you must define main motor requirements - cont/peak torque, max speed, gear ratio, resolution...

 

[sreid]

For the moderate performance you are looking for a stepper system is probably the correct choice. Mitsubishi makes some nice ones. The system is turn-key with a controller/amplifier and a motor. There is encoder feedback to avoid mis-positioning.

You program canned moves and the moves are executed when a signal is asserted (usually from a PLC). For your application an inline gearbox should be used to decouple the motor from the load.

The Mitsubishi reps can basically recomend-design the system for you.

 

[jraef]

I agree that if the air cylindar was accurate enough, the stepper will be much more accurate and less expensive than a servo. However, there are several integrated servo motor / controller units on the market that make it very easy to implement them if you don't have another control system like a PLC in place already. If you did use a PLC for the air cylindar control, then stick with the stepper.

Here is a decent overview on stepper motor basics.

http://www.ams2000.com/pdf/step101.pdf

This company makes a decent all-in-one servo motor/controller, and in looking at their site again, it appears they may have a new version that is a stepper as well.

http://www.animatics.com/index.html

"Venditori de oleum-vipera non vigere excordis populi"

 

[tdent]

Hey, I really appreciate all the replies. I hadn't even thought about a stepper motor as the only ones I have ever worked with in my short career have been on some steam boilers for the purge air system. I will definately look into this closer. I just have some rough ideas on this project so I will look into the existing control system a little more and I may have a few more questions for you all. I am not positive, but I believe it is controlled by a remote PLC unit. I will certainly look over the articles/links that have been posted. Thanks Again

T. Dent

 

[mc5w]

Is your compressed air wet and dirty, particularly on humid or rainy days? If so, you need to spend something on fixing that problem.

If the air going into a rotary screw air compressor is more than 33% relative humidity, you are going to have problems with water emulsifying with the oil. Hooking up a set of household dehumidifiers to the pump intake filter comes to mind as a cheap solution.