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Project Help and Ideas » Using rotary encoders

September 26, 2011
by sask55
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I require an accurate means of measuring angular motion of slowly moving sets of gears. I would like to build a clock work type equatorial mount to be used to track celestial objects. I would like to have the angular position of several gears available to the micro and hence the PC to at accuracy of at least one degree for the entire 360 degree plain of rotation. A couple of year ago I accomplish this (for an automated gear cutter I made) by using a couple of arrays of IF reflective surface detectors. Using a script in a CAD I printed a 9 bit (360 resolution) and a 6 bit (64 resolution) ) graycode wheels on label paper. By affixing the graycode wheals to the 360 tooth worm gear and the worm drive I was able to get a theoretical angular resolution of 1/64 of a degree on the gear cutter head. Granted with gear lash and other issues the accrual precision is not nearly that good. A high degree of accuracy and small angular increments are essential to produce clock work type gears with 360,365 and 366 teeth. When the gear cutter advances to the next tooth I wanted a precise feedback to the computer to verify that the stepper motor has actually stopped at the correct spot. This all works “OK” there are a number of issues mechanical, not electronic in nature.

My question is does anyone have any sort of experience working with Ausriamicrosystems rotary encoders.

http://www.austriamicrosystems.com/eng/Products/Magnetic-Encoders/Rotary-Encoders

The data sheets are interesting the resolution is just about beyond belief. The prices are low, at least if I buy 1000 at time. None of my regular component suppliers seam to carry them. I could signup and possible get a few samples. The magnets seam even harder to locate. There are a number of kits available complete with a magnet and the chip mounted on a board, more expensive. I can see from the data sheet that I would have a number of obstacles to overcome just to try using these chips. I don’t have enough experience to know what would be involved with programming the chip itself. The physical tolerances for mounting the chip/board and the magnet a quite tight. I don’t have access to a guass-meter and don’t know how I could confirm that my magnets are good. I have never worked with surface mounted ICs, so starting with a kit may be the way to experiment with these chips. In short I am trying to determine if the there is a reasonable chance that the results produced by using these chips would be worth the steep learning curve and cash outlay that it will take to find out. What I don’t need is system that has a high precision (resolution) and low accuracy .

Any comments are welcome.

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