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View Full Version : WANTED: Wanted Linear Scale/Encoder



gavztheouch
23-01-2013, 07:56 PM
Hi I am looking for a cheap linear encoder to experiment with, maybe something off an old manual mill? Preferable 5v and something that output a quadrature signal.

Cheers

Gav

Jonathan
23-01-2013, 08:24 PM
If the response time required is not very small, then a digital calliper might be suitable. What length and resolution do you need?

gavztheouch
24-01-2013, 12:11 AM
Hi Jonathan,

At the moment this is just for learning the ropes of a Kflop controler. Closed Loop Stepper (http://dynomotion.com/Help/ClosedLoopStep/ClosedLoopStepper.htm)

So anything that works would do, the plan was to use a stepper and a linear scale in a small test rig just to play about with the board to see what it can do.

I did think about the callipers, but im not sure they would be the easiest to implement as they do not have the A and B channels that I am used to with encoders?

Jonathan
24-01-2013, 12:27 AM
I did think about the callipers, but im not sure they would be the easiest to implement as they do not have the A and B channels that I am used to with encoders?

It would be easy enough to make something to convert the signal into something compatible, but the callipers response time is far too low to use for motor control, so forget that idea.

Linear encoders are generally very expensive. One cheap way to make one that should be plenty good enough to experiment with is to use a rotary encoder, put a timing pulley on it and have it run on a flat (open ended belt). Wrap the belt round the pulley with two idlers, so when the linear slide is moved it causes the pulley to rotate...I doubt it would be good enough to use in 'real life', due to small errors in the belt pitch and stretching, but worth a try I reckon.

Web Goblin
24-01-2013, 08:01 AM
Thats a pity. I have a couple of old Heidenhain rod420 or 426 encoders lying around somewhere. You could have one of them.

D.C.
24-01-2013, 09:08 AM
If you just want something to play with try this:

Digital Caliper With Data Output Port (http://www.bgmicro.com/digitalcaliperwithdataoutputport.aspx)

If you do a google search for arduino digital caliper there are loads of people that have hacked calipers. As already said, the response rate is far too slow to use for cnc positioning though.

gavztheouch
24-01-2013, 12:28 PM
Thats a pity. I have a couple of old Heidenhain rod420 or 426 encoders lying around somewhere. You could have one of them.

Thanks I would be intrested in buying one to play with if you have a price in mind?


Linear encoders are generally very expensive. One cheap way to make one that should be plenty good enough to experiment with is to use a rotary encoder, put a timing pulley on it and have it run on a flat (open ended belt). Wrap the belt round the pulley with two idlers, so when the linear slide is moved it causes the pulley to rotate...I doubt it would be good enough to use in 'real life', due to small errors in the belt pitch and stretching, but worth a try I reckon.

I haven't been able to get timing belts working well for me and liked the idea of a linear encoder as there would be very little possiblity for any sort of backlash. I also thought it would be a nice way of measuring the backlash in my marchant dice router. If I had a way of documenting the backlash or flex in the router I could see how different mods effected the backlash/flex and also determine how accurate the machine is when it is air cutting in comparision to cutting say hardwood or soft foam. This would show the limits of the machine and possibly help idendify where I would need to beef it up, although this would involve a lot of trial and error.

I think the Kflop has the possiblity to output positional error, if you could plot the error over time as you cut a certain program into varying materials you could hopefully compare. Could you take this one step further with an encoder on the motor to measure missed steps and linear encoder on the gantry to measure actual postion?

Web Goblin
24-01-2013, 02:50 PM
Well I was just about to order some more cutters which will be about 25 so cover that and its yours if you like. I have one here that hasnt been used.

gavztheouch
24-01-2013, 04:44 PM
Web Goblin, do you have a model number so I can check the specs.

Cheers

Web Goblin
24-01-2013, 05:32 PM
Here you go.
Heidenhain ROD 420 250 01 -03
ID no : 295 281-37