Stepper Position Feedback

[SK0480]

Hello

Iam working on a small project at my school, where Iam building a digital control system using a stepper motor. My buget for this project is between 50 to 80 dollars. THe equipment I have at school is NI Elvis II with a built in DAQ board, LABVIEW Software and it is not equipped with any motion control software anything.I have labview program that allows user to enter the position and direction of the stepper and it has  a vi that keeps track of the pulses being sent to the stepper. However  I need to know how can I measure the position of the stepper so that i can make sure that it is not missing any steps. Iam using a breadboard to build all the circuitry, I see that the quadrature encoders are expensive, so what other sensors I can possibly use to measure the actuall position of the stepper motor.

[SteveChandler]

You can put a reflective disk of some kind on the motor shaft with holes cut around it. Then you can use an LED on one side of the disk and photo diode on the other side. That will give you a pulse every time that the holes let the light through. In order to know where the shaft is at you will need some kind of "home position" sensor. You ca do that with one hole under the circle of holes that you use to measure position. In fact just one hole might be enough for you as you can correct any errors once per shaft revolution.

[SK0480]

Ok but could you please tell me where I can get this kind of disk, and How will I attach the photodiode and LED to the disk.

Thanks

[SteveChandler]

You can just make a disk or find something that works for you. I have seen CDs used for this - the small ones that device manufactureres sometimes use to ship drivers on. Chances are that the hole in the CD is bigger than the motor shaft. You could use a hole saw to cut a piece from another CD and use the drilled out piece as a washer. Just look around and use your imagination. You can do this for less than ten dollars.

As for mounting the LED and sensor you just need to build some kind of bracket. I can't help with that without seeing your setup.

[Matt_McLaughlin]

Hi SK0480,

You may also want to search online for "optical encoder template" to get some good ideas on how you want to setup the layout and spacing for this project.

[SteveChandler]

Good idea Matt. Here is a good one