Surface Grinder Retrofit

I am currently retrofitting a small surface grinder. I would like to get rid of the mechanical side to side operation of the table
which uses limit switches to set the right & left distance the table will travel before it goes back the other way. Does anyone know where I may purchase a linear sensor (or device) that I will be able to set using a keypad that will send an input to the processor to tell the table to go the other way.Any input will be appreciated

One of the problems that your going to encounter is with the coolant, which will suspend and cary the grinding material, which in turn may foul electronic sensors like a liner encoder or proxcimity sensor. You might be able to use a prox switch, but it might have to be wiped often to prevent false firing.

http://web1.automationdirect.com/adc/Shopping/Catalog/Sensors_-z-_Encoders/Inductive_Proximity_Sensors

You might could mount an encoder on the screw that drives the table back and forth.

Try a magneitc encoder. I've used Dynapar mag encoders in similar applications where there are a lot of chips with good success. Unlike optical encoders, mag encoders are impervious to dust and chips.

I would recommend a mag unit or an untrasonic one. Both with a lot of math functions.

regards.....casey

Just another thought here:

Many surface grindering operations don't need super precision. If this is the case and if you already have an analog input, then you could probably have a dirt cheap implemention of your soft limits with an LVDT or a magnetostrictive transducer, a 12" LVDT with a 12 bit A/D will still give you .003 resolution, and both are absolute position devices, no homing operation required.

Thank you for all your input. since I don't need super precision

I would be interested in the inexpensive transducer. Could you lead me onto where I might find this.
Thanks Again
Wayne

Wayne,

If all you want to do is to replace the limit switches with a solid state device, then look here: http://web1.automationdirect.com/adc/Shopping/Catalog/Sensors_-z-_Encoders/Inductive_Proximity_Sensors


You'll need to choose the right one for the proper voltage and distance. You havent posted enough info for a reccomendation on a spicific part no.

Maybe I haven't given enough information so I will try & explain

The grinder table is about 3ft long. When they put a piece of steel on the table that is 1ft long they manually set two guide limits on a rail, one for the left distance travel & one for the right distance travel. When the left limit switch is hit it reverses the direction of travel until it hits the right limit switch which closes the right limit switch and the table goes side to side until you push the stop button. Since I am using a PLC to operate the grinder now. I would like to eliminate the mechanical limit switches and go with some kind of linear device that I can set the left & right limits with a Panelview key pad by the operator inputing say 12" then th table will travel 12" in each direction back and forth until I tell it to stop.Hope this is clearer now.
Wayne

Another option is a linear potentiometer, linear sensor or rotary transducer: http://www.spectrasymbol.com/linearposition.html

http://www.mtslinearsensors.com/Linear.htm

http://www.celesco.com/

I know exactly what is being refered to. This will be a fair sized heavy possibly cast iron type base with the grinder head that moves out to in while the table moves left to right, right to left. You place large flat metal pieces on the table, set the position and limits, then start it and it automatically grinds until it reaches the inner limit for the grinder head. Very dirty because of the metal dust, uses water for coolant so you get a sludge that sticks to things. I redid one a while back using a Horner plc/hmi combo using linear potentiometers, can not for the life remember the brand of the pots but I believe we got them thru NEWARK. The term inexpensive (or cheap) is relative because most reliable items that work in these grimy, slimy situations are going to be $300 or more.

I am curious, what are you going to use for the head travel?

Wayne,

What drives the table? Is it a rack & gear, or an screw & nut? What you choose for the measuring device will greatly depend on the type of drive (mechanical), and the resolution you looking for. Additionally I take it that this is going to get wet with coolant?

A while back we had some guy install a new nut & screw, and X Y Z readout on our Bridgeport mill. At the sales pitch he told me that it could be interfaced to a PLC or CNC through a serial port. So you might want to check with a machine tool builder/service shop.

Other then that I once mounted a rotary quad encoder on a lathe drive screw. The operator would have move the tool to the starting position then zero out the position, then provide the travel distance. Maybe you can do something like that, if your plc has a counter.

just a thought

These people make something you might could use. It`s a trainable analog sensor. We use these on 4 different machine they work good.
http://www.am.pepperl-fuchs.com/products/productfamily.asp?division=23&productfamily_id=13
These seem to be very accurate and cost about $300 us.

Thanks again.
The Head travels using a mechanical gear.You manual adjust the increments
from one thousants to ten thou.There are limit switches inside that operate a small motor that pushes a toothe gear something like on the old clock mechanisims .As far as expense $ 300 to $ 600 would be good. as long as I can control the length of th side to side movement

A surface grinder work table might also be driven by a hydraulic piston, or by a rack and gear. If its a piston, look at Temposonics transducers for hydraulic pistons. The ones I have worked with don't use screw drives because a screw drive is generally not fast enough unless it is very expensive.

wayne said:

Thanks again.
The Head travels using a mechanical gear.You manual adjust the increments
from one thousants to ten thou.There are limit switches inside that operate a small motor that pushes a toothe gear something like on the old clock mechanisims .As far as expense $ 300 to $ 600 would be good. as long as I can control the length of th side to side movement

Click to expand...

That sounds like a Chevalier surface grinder....