Positioning a rotating basket precisely to the same position each time

[AndyBethea]

I need to align a very large round basket lid precisly at the same spot within 0.25 inches every time. This is in an industrial environment with water, chemcials, heat, fiber, ...etc. Lids presently may be cocked in the top of the basket as much as 1.5 inches therefore elevation is not the same all the way around the outer perimeter. The baskets sit on a turntable and rotate until correct position is found. I presently use a proximity device looking for a raised sensing block that is very unreliable.

What type of non-contact sensor may be employed to sense when the lid is properly aligned?

 

[dydt]

hi..
is there a mechanical or electrical brake that stops (whichever is rotating)it on the desired spot? you might be able to get away with the existing proximity by slowing down the speed as it approaches the target point...thereby it won't overshoot....

a use of stepper motor is a possibility but it will be quite an investment...

dydt

 

[ve7brz]

I'm not certain of the precise problem here. If you're only looking for a 'cocked' basket, why not use a light beam/photo eye across the top of the pot. There is no position in which a 'cocked' lid would not be detected.

If you need more accuracy both Honeywell and Allen-Bradly had linear CCD sensors which could be used in conjunction with a fluourescent tube for this type of application. (I'm uncertain if they still market them.)

 

[usaidit]

Your discription of the task leaves me guessing.
Is the lid hinged and you simply need to stop the basket accuratly?
Is the lid unatached and not relivent to the basket location?
If you will provide more information we will be glad to help.

 

[Glueguy]

I think ve7brz may be on the right path. The problem that I have had w/ photo sensors has been with refining accuracy. The photo eyes that I have used are good to within 12" for a large target. You can compensate for this by going to the fiber optic accessory. You would have to designate a point where a series of these would surround the lid. I am assuming that it can be cocked in any position. The fiber optics will be approx. 1/4" and would tell if the lid is cocked that high and are easily routed. Hopefully, someone with more background in design can help you more.

Good luck,
John Schrock

http://www.glubie.com

 

[SERVOCAM]

You should be able to use a photo-eye looking down on it. When looking down, the cocked part could be an various places, assuming this is why you use a turn table. You can get PEs that you can set a range to trigger an output or just have a set point. Look up Banner Engineering,

http://www.bannerengineering.com.

They will have a sensor for you. I'm a Motion Control guy, so not super knowledgable on sensors.

Cameron Anderson
Sales & Applications Engineer
Aerotech, Inc
St. Paul, MN

http://www.aerotech.com

"Dedicated to the Science of Motion"

 

[AndyBethea]

Thanks for the thoughts so far. I will clarify about the system. The lid is inserted down into the top of the basket and locked with spring loaded latches into slots that are cut into the side of the basket. These slots and the spring loaded locks that protrude from the lid don't always lock into the same place for each basket causing elevation changes when trying to sense the lid and often they don't always stop the lid at the same elevation around the perimeter therefore producing a cocked postion of the lid inside the basket.

There is a VFD driven brake motor on this system that does slow down when approaching the sensor.

 

[ve7brz]

Now it becomes clearer. The 'lid' is actually an insert with outward protruding 'dogs' which latch into slots in the side of the basket. One would assume that there are stops to keep the lid from dropping too far into the basket.

Several questions arise. How do you align the dogs with the slots, or as I suspect do you simply lower the lid into the basket and rotate the basket through 360+ degrees so that somewhere the dogs will be in allignment with the slots?

If this is the case can you not use two or three (or more) air cylinders to press the lid into its horizontal position and hold it there until the rotation is complete? I'm not sure about air cylinders but I do know that Parker made hydraulic cylinders with integral encoders which could be used for position sensing. This approach could also be used here for confirmation that the lid was fully inserted into the pot.

 

[dydt]

hi..
....a proximity switch, inductive or capacitive can survive harsh environment...from dust, grease, powder, ink, etc....imagine an operator running a machine....called an electrician at 2 AM because a simple machine won't run because somebody blocked a photoeye accidentaly....

...everytime we have to design or modify a system in our plant...we always try to "idiot proof" it....sorry for the word but it is true.....

dydt

 

[IRstuff]

A Hall sensor with a magnet as the index could work reasonably well. TTFN

 

[steamboat444]

I'm sure that this is much too late to do you any good, but.....

I think you mentioned using an inductive proximity switch on the lid which indicates that it is metallic.

Inductive proximity switches are also available in analog output types and are very accurate in measuring distance to a ferrous part. They have been used in saw mills to monitor blade sharpness. A dull blade has a slight side to side excursion not seen in a sharper blade.

Your total range of possible lid position may be outside the range of the sensor and thus cause a possible problem with the lid hitting the sensor, but might be worth a look.

Good Luck