Hello Guest it is November 16, 2019, 04:02:01 PM

Author Topic: Any one know how to build a cheap linear encoder?  (Read 7842 times)

0 Members and 2 Guests are viewing this topic.

Re: Any one know how to build a cheap linear encoder?
« Reply #10 on: March 11, 2008, 03:44:59 AM »
My CNC is stepper based. But that does not matter, I have play in the lead screws.  I can not attach the encoders to the lead screws as they will not pickup the play. So how about using encoders with a pulley on the far side of my CNC and a big cable loops that is mounted to the  cutting table? So when the table moves the mounted section goes with it, causing the loop to shift.  I just pick up the rotation count at one end.  I can use the brains out of a wheel mouse and a little bit of circuitry. What you think?

Offline jimpinder

*
  •  1,233 1,233
  • Wakefield, West Yorks, UK
    • View Profile
Re: Any one know how to build a cheap linear encoder?
« Reply #11 on: March 11, 2008, 04:11:34 AM »
I think that would do the trick - a couple of pulleys one at either end, with a belt. Fix your "mouse counter" to one of the pulleys.
If you could somehow "spring" the mouse counter so that was actually turned by friction off the belt, you would get very good resolution.

My first thought was to just attach the mouse wheel to the spindle of one of the pulleys, but you woud then need small pulleys to get anything like the resolution you are looking for.

Carrying one from that - why do we need the pulleys - mount the "mouse" on the table and have it sprung onto a small track on the frame of the lathe/mill - either use a friction contact, or a length of fine toothed rack material which is available at most engineering outlets. In my catalogue this goes down to 1mm teeth spacing, I dont know how many slots in a mouse wheel, but that should give you the resolution you are looking for.
« Last Edit: March 11, 2008, 04:18:42 AM by jimpinder »
Not me driving the engine - I'm better looking.
Re: Any one know how to build a cheap linear encoder?
« Reply #12 on: March 11, 2008, 04:20:51 AM »
Well, I think I am going to go with that, regardless of belt or friction, the device is the same.  What does mach 3 want for inputs from an encoder?
Re: Any one know how to build a cheap linear encoder?
« Reply #13 on: March 11, 2008, 05:35:15 AM »
1 - adjust out the play where you can
2 - If you're using mach3, use software backlash compensation.

Why not cut a spiral on an aluminium drum, fit a clock spring and a length of steel bowden cable to it and use linear motion to drive a rotary encoder? these can be had for comparatively little, compared to linear encoders at least.
Re: Any one know how to build a cheap linear encoder?
« Reply #14 on: March 13, 2008, 11:48:29 AM »
Why not some surplus rotary encoders with a rack & pinion configuration? Put a gear on the rotary encoder and mount it in a fixed position, attach a piece of gear rack to the table. SDP has anti backlash gears. Or you could simply put a pulley on the encoder, put a single loop of stainless fishing leader around the pulley and attach each end to the table. Think old radio dial. A sping in the system would keep tension on the wire to prevent slippage. The pulley diameter would determine your resolution. Elegantly simple.
Re: Any one know how to build a cheap linear encoder?
« Reply #15 on: March 13, 2008, 02:07:58 PM »
i had some thoughts about the wire - it would be prone to expansion and creep if the temperature changed. I saw a heater with a length of wire as a thermostat today, it's not a new idea but it got me thinking. Of course if your workshop is blessed with a steady temperature you may well be ok. Best way is to try it out :)

Offline Whacko

*
  •  239 239
  • Happy Days
    • View Profile
Re: Any one know how to build a cheap linear encoder?
« Reply #16 on: March 13, 2008, 06:53:12 PM »
If you are in the states, check out www.usdigital.com , they have cheap encoders and you can buy online. They used to call themselves the 10$ encoder company. If you mount a rack with a small pitch and have a small pinion on the encoder you should get better than 0.1 mm resolution. The encoders are good and is used by a well known Canadian CNC controller manufacturer (Linatrol) on the Lynx controllers. I have sold quite a few (Then Mach3 came along) of these controllers with the said encoders, and they have been working for years without a problem.

Whacko encoded
Nothing's impossible