I need an encoder of the wire-draw type for a particular application. It's main advantage is that it's not as expensive as a long, magnetic (or optical) linear encoder, although it's not as precise either.
Anyway, I don't need that much precision. About 0.1 mm will do, which is something I believe can be attained with a wire draw encoder. But the big objection here, is that those encoders are being sold on the market for far too much I'm willing to pay. I have resources, and I can easily design and fabricate all the components needed for this small project.
I'm planning on using one of these as the encoding component. It's of the optical type, can easily work at up to 100 kHz, and it's got 5,000 divisions per revolution. Working the numbers, I'd need to wind the wire (never mind its gauge at this moment) around a drum measuring about 6-1/4" in diameter to get what I want.
To round things down a bit, I think I'll go for a 4.7" drum instead. The material would be easy to find and rectify to its desired diameter, and I'd be getting a resolution of about 0.075 mm per encoder pulse.
At this stage, my question is mechanical (and I'm a mechanical engineer... as embarrassing as it is to admit ... but I'm no fool, and I'd rather ask for help in matters on which I have no experience and try to save myself some painfully spent time and money).
The drum must travel back and forth along its axis, so as to properly wind and unwind the wire without it wrapping around itself. For this to happen, I plan to install a fine-pitch nut on the drum's axis, and the axis will have a matching screw (which will be of a special design and fabrication). I do not plan to use the screw as the axis, of course, but the axis will be a split shaft at which ends will be installed a couple of ball bearings.
I promise I'll post the final design when it's done, and also share whatever circuitry is needed to properly adapt and transmit the encoder signal over a given wire length.... maybe this will even qualify in the completed projects collection forum.
This encoder will be working on a machine with a length of about 6.5m (a little over 21'), and I plan to use a pitch of about 40 TPI for the screw and nut responsible for moving the drum back and forth along its axis. So, for 6,500 mm of thin-gauge wire to be wrapped around a 119 mm drum, around 18 turns would be needed. And 18 turns of a nut on a threaded rod with 40 TPI would result in travel of 0.450". That's pretty neat and compact... just the way I like it. Of course, the wire would have to have a maximum diameter of 0.025" (1/40th of an inch) for this to work, but I think that that thickness will be more than enough for my purposes.
Now, back to the original question, which is this:
I was thinking about using D2 steel for the 40 TPI threaded rod, which will have an o.d. of 0.750". And bronze for the nut, which will have a width of at least 1/2".
@MaxHeadRoom, I think this question is right up your alley, what do you think?
Anyway, I don't need that much precision. About 0.1 mm will do, which is something I believe can be attained with a wire draw encoder. But the big objection here, is that those encoders are being sold on the market for far too much I'm willing to pay. I have resources, and I can easily design and fabricate all the components needed for this small project.
I'm planning on using one of these as the encoding component. It's of the optical type, can easily work at up to 100 kHz, and it's got 5,000 divisions per revolution. Working the numbers, I'd need to wind the wire (never mind its gauge at this moment) around a drum measuring about 6-1/4" in diameter to get what I want.
To round things down a bit, I think I'll go for a 4.7" drum instead. The material would be easy to find and rectify to its desired diameter, and I'd be getting a resolution of about 0.075 mm per encoder pulse.
At this stage, my question is mechanical (and I'm a mechanical engineer... as embarrassing as it is to admit ... but I'm no fool, and I'd rather ask for help in matters on which I have no experience and try to save myself some painfully spent time and money).
The drum must travel back and forth along its axis, so as to properly wind and unwind the wire without it wrapping around itself. For this to happen, I plan to install a fine-pitch nut on the drum's axis, and the axis will have a matching screw (which will be of a special design and fabrication). I do not plan to use the screw as the axis, of course, but the axis will be a split shaft at which ends will be installed a couple of ball bearings.
I promise I'll post the final design when it's done, and also share whatever circuitry is needed to properly adapt and transmit the encoder signal over a given wire length.... maybe this will even qualify in the completed projects collection forum.
This encoder will be working on a machine with a length of about 6.5m (a little over 21'), and I plan to use a pitch of about 40 TPI for the screw and nut responsible for moving the drum back and forth along its axis. So, for 6,500 mm of thin-gauge wire to be wrapped around a 119 mm drum, around 18 turns would be needed. And 18 turns of a nut on a threaded rod with 40 TPI would result in travel of 0.450". That's pretty neat and compact... just the way I like it. Of course, the wire would have to have a maximum diameter of 0.025" (1/40th of an inch) for this to work, but I think that that thickness will be more than enough for my purposes.
Now, back to the original question, which is this:
- The machine will be performing a couple of hundred of cycles back and forth its total length per day. Of what material should I fabricate the threaded rod and the matching nut that will make the drum travel back and forth along its axis?
I was thinking about using D2 steel for the 40 TPI threaded rod, which will have an o.d. of 0.750". And bronze for the nut, which will have a width of at least 1/2".
@MaxHeadRoom, I think this question is right up your alley, what do you think?