gwfami
Posts: 45
Joined: Thu Oct 25, 2018 4:04 am

Need help locating wire length sensor

Tue Nov 28, 2023 10:43 pm

Hi,
I'm building a project that requires me to roll a specific, but changing length of plastic cord from one reel to another reel. I can't simply calculate it from the number of turns of the reels as the length per rotation changes as the reels empty out or become fuller. I'm thinking of something that I can put inline that will turn a wheel sensor that will not be effected by reel issue. The problem is, I can't find anything like this, but I know they make them. Does anyone have any suggestions on what to use or where to find them?

The project will use a silicon cord that is about 0.84 mm in diameter, and the code will be ran on a RPi 4b. The lengths need to be measurable in inches.

Thanks,

GWFAMI

trejan
Posts: 7107
Joined: Tue Jul 02, 2019 2:28 pm

Re: Need help locating wire length sensor

Tue Nov 28, 2023 10:55 pm

They're called wire length counters. If you want to build it yourself then the 3D printing crowd have lots of designs of filament counter/meters e.g. https://www.instructables.com/Smart-3D- ... t-Counter/

gwfami
Posts: 45
Joined: Thu Oct 25, 2018 4:04 am

Re: Need help locating wire length sensor

Tue Nov 28, 2023 11:05 pm

Thanks. That is exactly what I'm looking for. Are the rotary encoders difficult to read with the Pi?

trejan
Posts: 7107
Joined: Tue Jul 02, 2019 2:28 pm

Re: Need help locating wire length sensor

Tue Nov 28, 2023 11:11 pm

I'd do it with a microcontroller such as a Raspberry Pi Pico to ensure no steps are lost e.g. https://github.com/GitJer/Some_RPI-Pico ... ry_encoder

ame
Posts: 8756
Joined: Sat Aug 18, 2012 1:21 am
Location: New Zealand

Re: Need help locating wire length sensor

Tue Nov 28, 2023 11:17 pm

gwfami wrote:
Tue Nov 28, 2023 11:05 pm
Thanks. That is exactly what I'm looking for. Are the rotary encoders difficult to read with the Pi?
No.
Oh no, not again.

ame
Posts: 8756
Joined: Sat Aug 18, 2012 1:21 am
Location: New Zealand

Re: Need help locating wire length sensor

Tue Nov 28, 2023 11:20 pm

trejan wrote:
Tue Nov 28, 2023 11:11 pm
I'd do it with a microcontroller such as a Raspberry Pi Pico to ensure no steps are lost e.g. https://github.com/GitJer/Some_RPI-Pico ... ry_encoder
That adds complication. And without knowing for sure I assert that the cord will not be moving very fast.

If it is, a micro could be used. In fact, a micro might be a better choice for this task instead of a Pi.
Oh no, not again.

gwfami
Posts: 45
Joined: Thu Oct 25, 2018 4:04 am

Re: Need help locating wire length sensor

Tue Nov 28, 2023 11:29 pm

Thanks. The pull motor will be doing about 20 rpm, and typically will pull between 1 and 24 inches of cord. I'm using this as part of a simple mechanical production system that is Pi 4B based, which is why I specified the Pi 4B. I'm looking at using this encoderhttps://www.amazon.com/Taiss-Incrementa ... =1-29&th=1, figured 600P would be high enough resolution, perhaps I'm wrong on that.

ame
Posts: 8756
Joined: Sat Aug 18, 2012 1:21 am
Location: New Zealand

Re: Need help locating wire length sensor

Tue Nov 28, 2023 11:33 pm

Here's a project that might give you some ideas:
https://hackaday.com/2020/12/09/this-au ... -the-wire/
Oh no, not again.

ame
Posts: 8756
Joined: Sat Aug 18, 2012 1:21 am
Location: New Zealand

Re: Need help locating wire length sensor

Tue Nov 28, 2023 11:41 pm

Are your feed reel and take-up reels motorised? How are you dealing with the additional length needed to wrap around the take-up reel?

You could have a powered drive for the cord, which draws from a freely rotating feed reel, then the take-up reel can have a slipping clutch so that it won't draw extra cord, but will take up the slack, unaffected by winding diameter.

The powered drive uses a stepper motor to feed a specific length, instead of a passive sensor that just measures the length.

Sort of based on this:
https://projecthub.arduino.cc/30percent ... ool-564f85
Oh no, not again.

gwfami
Posts: 45
Joined: Thu Oct 25, 2018 4:04 am

Re: Need help locating wire length sensor

Tue Nov 28, 2023 11:55 pm

The take-up reel will be motorized, 20 rpm. The feed reel will be freely rotating with a clutch mechanism to take up the slack. I thought about using a stepper for the take-up wheel, but as the cord winds onto the reel it will increase it's diameter causing unacceptable length changes as the process works, and due to the process it's very difficult to calculate the change, hence I'm looking at using a passive sensor that doesn't require complex calculations.

ame
Posts: 8756
Joined: Sat Aug 18, 2012 1:21 am
Location: New Zealand

Re: Need help locating wire length sensor

Wed Nov 29, 2023 12:03 am

gwfami wrote:
Tue Nov 28, 2023 11:55 pm
The take-up reel will be motorized, 20 rpm. The feed reel will be freely rotating with a clutch mechanism to take up the slack. I thought about using a stepper for the take-up wheel, but as the cord winds onto the reel it will increase it's diameter causing unacceptable length changes as the process works, and due to the process it's very difficult to calculate the change, hence I'm looking at using a passive sensor that doesn't require complex calculations.
Right, but if the take-up reel has a slipping clutch and the feed is controlled by the stepper motor driving two clamping wheels as shown in the second project link then the diameter change won't matter.
Oh no, not again.

gwfami
Posts: 45
Joined: Thu Oct 25, 2018 4:04 am

Re: Need help locating wire length sensor

Wed Nov 29, 2023 12:16 am

The second project is pretty nice, but the filament he is using is very stiff. I didn't describe the cord I'm using very well, apologies for that. The cord is 0.84mm silicon cord, which is very stretchy (up to 2x length), and is limp as a wet noodle. It will require something to physically pull it onto the take-up reel.

ame
Posts: 8756
Joined: Sat Aug 18, 2012 1:21 am
Location: New Zealand

Re: Need help locating wire length sensor

Wed Nov 29, 2023 12:18 am

gwfami wrote:
Wed Nov 29, 2023 12:16 am
The second project is pretty nice, but the filament he is using is very stiff. I didn't describe the cord I'm using very well, apologies for that. The cord is 0.84mm silicon cord, which is very stretchy (up to 2x length), and is limp as a wet noodle. It will require something to physically pull it onto the take-up reel.
Yes. The take up reel is driven with a slipping clutch, or just a light friction drive. Enough to pull the cord that comes through the wheels, but not enough to stretch the cord or pull more through the wheels.
Oh no, not again.

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