next topic »

[on:]

Hi there!

I'm currently building a lift for scientific purposes. It's driven by a stepper-motor with a high transmission.
As it is my first project with a stepper motor, i realized afterwards that it isn't all too accurate, i think it is loosing steps under high load.

So basically i have to measure the  distance between two panels, one of them is going up and down.

The distances the sensor would have to measure are between 5 and 30 cm and i aim for an accuracy around +- 0.2mm, the smaller the better.
I came across this one from sharp though i am not sure if it is the right one, because i didn't find any data on its accuracy.
http://www.sharpsma.com/webfm_send/1205

Does anyone have experiences with similar requirements?
Would be grateful for your suggestions.

Cheers

[Reply #1 on:]

Does anyone have experiences with similar requirements?
Would be grateful for your suggestions.

I don't have experience if close tolerance distance measurements using arduino but the sensor you linked to won't do 0.2mm accuracy for sure. What you probably need is an encoder on the stepper motor/drive chain to give movement/position feedback.

[Reply #2 on:]

measuring 0.2 mm deltas
speed of sound 340M/s    (but differs per temperature => drift is bigger than needed accuracy warnings apply)

0.2 * 10-3 / 340 => 0.588235 *10-6 sec. ~0.6 uSec

So to need this accuracy you need to switch in 0.6 uSec . This is about 9 clock cycli of the Arduino.
So you are operating at the edge what is feasable for an Arduino..

[Reply #3 on:]

hm, i see. for a few reasons i can't use an encoder on my stepper motor.

0.3 mm would be ok, too. So you say i should use a sonic sensor? any recommendations?
If my demands can't be met, i'll have to settle with the best thats possible. Ultrasonic vs. Infrared?

[Reply #4 on:]

think it comes down to comparing datasheets of diff sensors

[Reply #5 on:]

budget ?

- http://www.sick.com/group/en/home/products/product_portfolio/distance_sensors/pages/distance_sensors_short_range.aspx -

[Reply #6 on:]

- http://www.pololu.com/file/0J284/GP2Y0D805Z0F.pdf - 0.5..5cm,

[Reply #7 on:]

budget is 40€ max.
I couldn't find anything about the resolution of this sensor in its data sheep. have i overlooked something?
http://www.sharpsma.com/webfm_send/1205
neither in this one
http://www.parallax.com/Portals/0/Downloads/docs/prod/acc/28015-PING-Sensor-Product-Guide-v2.0.pdf

[Reply #8 on:]

can you explain why you need to measure distance?
what are you trying to reach?