Doug Jones' Stepper Motor Tutorial University of Iowa Associate Professor of Computer Science Doug Jones' Stepper Basics , Control From the Computer Parallel port, & lots more.
Warner Electric manufacture the ubiquitous 'Slo-Syn' stepper motors and accessories. Warner Electric's excellent 'CAMAS' software for motor sizing is downloadable.
Parker Hannifin Corporation Compumotor Division An on-line version of the Compumotor Digiplan Catalog that includes their excellent downloadable tutorials on stepper motors and feedback devices including incremental and absolute encoders.
Stepper Motor Driving Application Notes fron SGS-Thomson including the popular L297/L298 chips. App Notes Index
Rotary optical encoders are often used for positional feedback in stepper motor and other systems. Rotary optical encoders typically use code wheels and sensors to generate a pair of pulse trains so direction can be sensed.
Incremental Encoder Wheel Nottingham University's picture of an experimental fibre-optic rotary optical encoder with the cover removed to show the code wheel. Don't try this at home.
BEI make a complete line of position encoders. Data and theory PDF files may be downloaded from their website.
Low resolution, low cost encoders have entered the market. We have had good results with a Clarostat 600-128-B66 which has 128 pulse per revolution quadrature outputs and cost around $50.00 Cdn. Clarostat Web Page
Some time ago one of our research associates came in packing a surplus residential gas meter that the gas company had declared surplus and given to him. We were working with liquid helium at the time, and one problem with transferring LHe from one dewar to another is that you are never quite sure whether you are transferring liquid or just boiling off gas. Most people just watch for a change in the plume of vented vapour, Kevin's more elegant idea was to run the 'boil-off' gas through the old residential gas meter and couple it to some sort of electronic counter that would indicate liquid helium transfer by a change in counter rate.
Some means of adding an encoder was required, ideally some sort of rotary optical encoder could be coupled to the 1/4 C.F. dial of the meter, and low cost was definitely an object.
A really cheap optical mouse will typically contain two code wheels good for about 40 pulses per each revolution of the code wheel . I bought a really cheap mouse at one of the local computer stores, opened it up and made a shaft coupling between one of the two optical encoder wheels and the 1/4 C.F. dial of the gas meter. It was then possible to use the diagnostic software that came with the mouse to track the rotation of that encoder on the computer crt. Later we accidentally damaged the mouse internal circuitry but salvaged the encoders by bringing their outputs out to a separate power supply & counter. The contraption put out about 20 pulses per liter of helium gas.
Compumotor have some excellent tutorials on stepper motors, encoders , etc. available in pdf format from their web site for those who need some background on such things.
