High precision proximity sensor for auto-zeroing stopmotion rig?  - Page 1
Forum section: electronics / projects

author: miceuz
author_rank: Frequent Contributor
timestamp: May 10, 2016, 05:41:09 am
content: Hi all,At our hackerspace we are building/improving this rig for stop motion animationIn this iteration we want to add an auto-zeroing option and I'm looking for a highly repeatable proximity sensor to do that. I was browsing Farnell catalogue, but almost all of the inductive sensors available there that seem to be designed for the job do not even have precision/repeatability data in their datasheets.Can anybody help me to choose the suitable sensor/strategy? The expected precision at the camera end is around 10micron, at least our mechanical system gives us this repeatability.We had good results by using pogo pins as homing switches in a CNC machine before, but we want a more robust solution this time.Please help!A bit more about the system:http://blog.technariumas.lt/post/137778940366/camera-crane-steppers-and-assemblyhttp://blog.technariumas.lt/post/137701336211/assembling-the-electronics-for-the-camera-cranehttp://blog.technariumas.lt/post/137343528611/developing-electronics-for-the-camera-crane-motionhttp://blog.technariumas.lt/post/138662097001/camera-motion-control-system-in-action

author: Dubbie
author_rank: Unknown
timestamp: May 11, 2016, 01:57:30 am
content: Just glancing at that thing, there is no way in a million years you will get 10 micron repeatability.Sent from my phone using Tapatalk

author: Marco
author_rank: Super Contributor
timestamp: May 11, 2016, 02:59:36 am
content: Your application allows you to take multiple measurements at multiple known distances with an unknown offset ... I think this in theory makes it an easier problem than instantaneous non contact distance measurement.Lets say you used aslide-by configurationwith a Hall effect sensor and a magnet, I think you could then very accurately determine when the magnet crossed the sensor (band pass the output vs distance function and look for the zero crossing for instance).

author: miceuz
author_rank: Frequent Contributor
timestamp: May 11, 2016, 06:57:26 am
content: Quote from: Dubbie on May 11, 2016, 01:57:30 amWell, but it is...It's very slow, it has zillions of resolution and backlashes are kept in check.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: May 11, 2016, 09:08:18 am
content: How about a pair of tape heads, in a drive-by configuration. Gap size is of the order of 1 micron, so as long as you can get them close enough you should get good resolution.Or maybe a force sensor combined with a spring-buffer endstop.

author: H.O
author_rank: Frequent Contributor
timestamp: May 11, 2016, 01:48:58 pm
content: If you can live with a mechanical switch then BaumerMy-Comseries might be suitable.

author: Cerebus
author_rank: Super Contributor
timestamp: May 11, 2016, 03:18:23 pm
content: How about a slotted opto switch? You can make it as arbitrarily high resolution as you like by using an opaque tab with a hole in it - size of the hole determines resolution along with the noise floor of the system. Two comparators on the opto output would give you three states {lots of light - open, little light - hole in tab detected, no light - just tab}. So as your moving part slid towards the end stop you'd see the sequence {open, tab detected, hole detected}. You can even use the {tab detected} state to reduce your stepping speed.

author: Marco
author_rank: Super Contributor
timestamp: May 11, 2016, 04:49:41 pm
content: Also an option.If you really want a micron range repeatability instantaneous distance measurement I think you're going to want a triangulation based laser displacement sensor, a lot more expensive than a slotted opto or hall effect switch and some signal processing ... if the time you will need for the little R&D to get it to work is free.

author: ynfo
author_rank: Contributor
timestamp: May 11, 2016, 04:51:03 pm
content: Rigol make Champagne now?

author: miceuz
author_rank: Frequent Contributor
timestamp: May 12, 2016, 10:56:26 am
content: Quote from: ynfo on May 11, 2016, 04:51:03 pmYeah, we bought this bottle to celebrate 100MHz hack to our DS1054Z

author: miceuz
author_rank: Frequent Contributor
timestamp: May 12, 2016, 11:08:02 am
content: We don't need distance measurement, we just want to know if the end for the crane is there or not.Quote from: mikeselectricstuff on May 11, 2016, 09:08:18 amThis is interesting do you have a force sensor to suggest? I have never worked with force sensors before, no idea how repeatable they are. Probably drift a lot with temperature, but we can assume that to be stable enough.Quote from: Cerebus on May 11, 2016, 03:18:23 pmThis is a very interesting idea also, thank you.Quote from: H.O on May 11, 2016, 01:48:58 pmIdeally we would like to have an off the shelf solution. These switches are the top schmick stuff! Unfortunately not available in common distributors also, no distributor network in Europe. Still this gives me another track of search - I have never knew there are mechanical switches that precise!

author: nali
author_rank: Frequent Contributor
timestamp: May 12, 2016, 11:54:07 am
content: Quote from: miceuz on May 12, 2016, 11:08:02 amRS components in the UK sell them - just type My-Com in the search box.