Laser Needle Controller/Sensor, Working Principles. - Page 1
Forum section: electronics / general

author: palpurul
author_rank: Regular Contributor
timestamp: March 01, 2022, 05:14:38 pm
content: Hello,Recently I visited a small knitting factory with about 20 circular knitting machines. They were pretty rudimentary. I talked to the owner of this factory to understand what they need to improve their manufacturing.He constantly talked about the needle controller/sensors, how useful it can be if they were to integrate them into each machine in the factory. There are a few companies selling them, but apparently the price is a bit prohibitive. I thought this can be a good opportunity for me because there are many small knitting factories in my city, and I decided to research more about it.Needle controllers/sensors are basically checks if there are any missing or bent needles in the knitting machine.I've found a video showing how it works, it's a very short video:How do you think it works? what kind of Lasers they are using to detect broken needles? It seems like they implement kind of a TOF algorithm, but I am not sure and came here to ask for opinions on how these devices work.The algorithm to detect broken needles must be kind of complicated, as of right now I can't wrap my head around it because knitting machines can rotate at not constant but variable speeds they are not very repeatable in terms of their operation. I just need to brainstorm more I guess.These are a few devices on the market:https://www.protechna.de/en/rundstrickmaschinen/needle_sensor_4022https://www.memminger-iro.de/en/ueberwachung/mnc2.php

author: MegaVolt
author_rank: Frequent Contributor
timestamp: March 02, 2022, 09:45:35 am
content: Camcorder / camera + digital processing. Comparing the pictures with the correct ones?

author: palpurul
author_rank: Regular Contributor
timestamp: March 02, 2022, 10:47:12 am
content: Quote from: MegaVolt on March 02, 2022, 09:45:35 amI don't think so. The video shows some type of laser is being used and I don't think it can be done with a camera becuase needles move pretty fast, well at least you can't do it affordably you'd need a pretty fast camera.

author: PlainName
author_rank: Super Contributor
timestamp: March 02, 2022, 11:28:02 am
content: Isn't it just a missing pulse detector? The laser bounce triggers the detector and then it's just checking the next one comes in at the expected time. Where you might have deliberately missing needles (don't know if they do, but I imagine there's a use case for that) the device knows when a gap should appear and it would be regular, so that's not a big problem. As for variable speed, either the needle transfer gubbins tells you what speed it's running at or you extrapolate from the timing between hits.Am I missing something?

author: palpurul
author_rank: Regular Contributor
timestamp: March 02, 2022, 12:42:34 pm
content: Quote from: dunkemhigh on March 02, 2022, 11:28:02 amI think it's just a more sophiticated version of a missing pulse detector. They have intentionally omit a few needles, so the device needs to be aware of this as well.Extrapolating part kind of confuses me, but I think we can easily measure the rpm of the needle spinner, that way we can roughly estimate the time between each needle.I am not too familiar with missing pulse detectors, do you have any resource that you can recommend about it?

author: PlainName
author_rank: Super Contributor
timestamp: March 02, 2022, 02:36:25 pm
content: QuoteNot specifically for this application, but a google search on 'missing pulse detector' will turn up far more info than a simple post here. The 555 timer has this as a classic scenario but I think you would want a MCU since the speed may vary and you'll have intentional holes.In principle you would measure the time between two pulses to determine when the next is due, but it's a bit more complicated in that you don't want to use the period in which the pulse is missing for adjustment. Of course, if you can determine the speed externally and feed that into the detector then that makes things easier.

author: palpurul
author_rank: Regular Contributor
timestamp: March 04, 2022, 07:23:09 am
content: Quote from: dunkemhigh on March 02, 2022, 02:36:25 pmI think I have a better understanding now, thanks for your comments.At the end of the day it's basically a laser with fancy TOF algorithm.I am little bit confused about how to pick laser for this type of application. I know that there are plenty of TOF laser ranging sensor likethis one, but in this application laser needs to be sharply concentrated on a very narrow point, most sensor have a good field of view, which I think is very bad for the application. For that reasons I think for this application we need something very specific (I am not really sure I am just brainstorming).How do I pick a laser for this type of applcation?

author: PlainName
author_rank: Super Contributor
timestamp: March 04, 2022, 10:59:58 am
content: QuoteI would have said it's a straight 'there/not there' thing, which would be the case with LEDs and a laser in this kind of application is essentially a fancy LED.However, having said that, if you did have a laser you could perhaps use it to determine doppler shift of the return signal and, hence, the speed of the needles passing (thus when a signal is expected to show up). The video you posted seems to show the sensor perpendicular to the needle travel, so I don't think that's doing anything like this.I shoulld reiterate that I have never had to find a missing needle (at least, not all lined up like this) so I might be completely wrong about this

author: palpurul
author_rank: Regular Contributor
timestamp: March 04, 2022, 11:18:22 am
content: Quote from: dunkemhigh on March 04, 2022, 10:59:58 amOne of the manufacturer says they use infrared light via fiber optic cable maybe that's where should be focusing on. I am still worried about how they achieve in concentrating the infrared light like that. I don'T know much about this stuff. Is it an intrinsic feature of infrared light or do they use a lense for concentrating to a small point?Quote from: dunkemhigh on March 04, 2022, 10:59:58 amI'm here to just brainstorm with who have built stuff

author: PlainName
author_rank: Super Contributor
timestamp: March 04, 2022, 02:21:44 pm
content: Infrared is probably used for the same reason security systems and TV remotes use it: you can filter out visible light easily so there is little interference.

author: palpurul
author_rank: Regular Contributor
timestamp: March 04, 2022, 02:23:51 pm
content: Quote from: dunkemhigh on March 04, 2022, 02:21:44 pmThanks! You helpmed me a lot