Hello All,

i need to select a incremental encoder to rotate a round specimen attached to an experimental rig. The experimental rig i am designing will be used to scan the surface of a specimen using a laser scanner. i have the scanner already setup and runing.

Now I need to rotate the specimen at say 1 deg increments and trigger the scanner using the encoder at 1 deg rotation.

I know that i can program a PCI board and control the system via a PC, but idealy i want to have a stand-alone (mobile)system capable of working independently of a PC. So my question is, is this possible and what is the cheapest and easiest way of dealing with this. Should i use a microcontroller and perhaps a counter/timer?

Your help and recommendations are appreciated

Thank you,
Beks
[email protected]

 

Hi

I don't know if you got your problem solved, but the best "affordable" thing to do is implement a stepper motor with high resolution. I have one that has 300 steps/rotation. I just had to buy 2 wheels one with half size the other and made a "1/2deg"/impulse system. Steppers aren't that easy to implement, but once you do the first, all the others are simple. And with stepper you can send a pulse so the raising edge puts the stepper in position and put laser "on" on the falling edge of the pulse, if your hardware allows it.

Encoders with that precision are expensive.

I would go for the stepper in your case. (Take a look at the LM297 and LM298 chips, easy to implement and easy to control, even a PIC can do it.)

If your scanner sent a signal when it was "over" with the current section you could put that signal controlling the next step for the motor/stepper.
With encoder you would also have to buy a decent somehow strong DC motor so it could start and stop in such a short time and that is very battery consuming (if applicable) or have a very high frequency square wave...

electronics... world of possibilities!

Hope I helped.

 

The stepper motor is a good open loop type solution if you are not worried about missing steps. You will probably be ok if there is no physical loading, and you don't attempt to rotate or stop too quickly.

If you want to be sure of the position, you can use a 360 LC encoder and and use each of the pulses to trigger the scanner. A microcontroller would work and may be the best choice depending the complexities of your application, but it may be just as suitable to build dedicated electronics that advance the motor until it sees a rising edge, or a positive pulse from the encoder, stop rotation, trigger the scanner, after the scan has completed, start rotation. As long as you have a method for homing to it first, you could use the encoder index (Z) pulse as a marker for one complete rotation and end the process.

I work as an Application Engineer for a company that manufactures optical incremental encoders. We have 360 line count resolutions as part of our standard offering. Below is a link to the spec. sheet for an encoder that I think might be a good affordable match for what you are trying to accomplish.

http://www.quantumdev.com/products/optical_encoders/qr12.html

Jim Miller
Application Engineer
Quantum Devices Inc.
jmiller at quantumdev. com
www.quantumdev.com