Hey everyone!

I'm currently working on a little project that has to count the number of teeth of a gear inside a gearbox.
I'd like to use a opto reflection sensor like this one:

Here are some requirements:
The gear itself has around 18 teeth, it's not fully covered with them only one side like this:

https://www.google.be/search?q=aeg+...AUICigB&biw=1560&bih=800#imgrc=EgfBEc3qR_pYBM:

It's not very big around 30mm in diameter and has a teeth depth of around 2mm.
The circuitry has to be placed inside the gearbox with minimal space, that's why i'd like to use a optic reflection sensor to count when a gear teeth passes the sensor.

I've been looking on Mouser and found this sensor:

VCNT2020
https://www.google.be/url?sa=t&rct=...oduct-84285/&usg=AOvVaw2mniwY9pVi0eGWjdRQAK4S

I can place it close to the gear but I wonder if it will detect the 2mm gap between two teeth of the gear.

Does anyone have any expierence with this?

I know that their are other types of opto detectors like a slotted detector but I don't have enough space for those types.


Regards

Alex Deb

 

I think a hall effect gear tooth sensor would be a better solution. This is an example of one type. The first two examples on this web page are using hall effect gear tooth sensors.

Les.

 

I've been looking on Mouser and found this sensor:

VCNT2020
https://www.google.be/url?sa=t&rct=...oduct-84285/&usg=AOvVaw2mniwY9pVi0eGWjdRQAK4S

I can place it close to the gear but I wonder if it will detect the 2mm gap between two teeth of the gear.

Judging from the dimensions of the device and from its specifications, I expect it should be able to detect the passage of the gear teeth without much difficulty. The gear color might have an influence, however; black might not be optimal.

It will probably take some experimentation to arrive at the best physical arrangement of the sensor relative to the gear, and the best combination of circuit values (LED forward current and phototransistor load resistor). I expect quite a bit of fiddling will be necessary before achieving optimal results.

 

I'm skeptical about this sensor because it isn't focused, as far as I can tell. That means you'd need to be sure that the gear teeth are big enough to give you a consistent change in output, per tooth. What about a focused sensor like this one? It's optimized for objects at 3mm range.
https://octopart.com/gp2s700hcp-sharp-39642811

Also, you haven't said whether this gear rotates both ways, or if it's always going in the same direction. If it can go either way, a single sensor won't tell you which way the sensed teeth are going.

 

If you want one that is similar to the one cited https://www.vishay.com/optical-sensors/list/product-84285/
There is the leaded type QRE1113
Max.

 

If it is possible to use a Proximity sensor, there is a threaded barrel type By Omron, the E2E series goes down to 3mm dia.
Max.

 

I think a hall effect gear tooth sensor would be a better solution. This is an example of one type. The first two examples on this web page are using hall effect gear tooth sensors.

Les.

Don't You need a magnetic for the hall sensor? I'm tought you needed a magnetic field to use those kind of sensors?

 

As for the VCNT2020 , one of the reasons I like to take this is because it's Relative Collector Current vs. Distance curve is very good.
at 2mm distance it's collector output is dropped by 40%

However like John P says it might not be focused.

If I look at the Sharp product that John P suggested the Relative Collector Current vs. Distance curve is not as good as the VCNT2020.

But like OBW0549 said, the dark surface can be a big of a problem.

The hall effect sensor that LesJones suggest looks promising...
But I've never used them.

 

Don't You need a magnetic for the hall sensor? I'm tought you needed a magnetic field to use those kind of sensors?

There are many hall sensors that just require a ferrite target.
As in the Omron versions also.
Max.

 

The hall sensor in the Ebay advert and the first example on the web page have a built in magnet. The second one is a small surface mount sensor which I mounted with a very small disk magnet behind it. (3mm dia 2mm thick)

This is a picture of this type of sensor against 1mm divisions on a ruler. For an idea of scale the one in the picture is mounted on the end of 1/4" diameter rod with holes drilled throuh it for the wires.

Les.
Hall sensors only work with feromagnetic gears so they will not work with brass or aluminium

 

Hall sensors only work with feromagnetic gears so they will not work with brass or aluminium

Although there are some versions available that detect non-ferrous metal, brass etc.
Max.

 

My point about the focused sensor was that I don't think the real issue is detecting an object that may or may not be present. What's needed is to detect the gear teeth, versus the gaps between the teeth. For that purpose, I'd have thought that the sensor ought to look at one small volume of space, and tell you whether that is occupied or not. With a diffuse sensor, I'd be worried that if the field of view covers multiple teeth, there might not be much change as the gear rotates.

 

Hey everyone!

I'm currently working on a little project that has to count the number of teeth of a gear inside a gearbox.
I'd like to use a opto reflection sensor like this one:

Here are some requirements:
The gear itself has around 18 teeth, it's not fully covered with them only one side like this:

https://www.google.be/search?q=aeg+...AUICigB&biw=1560&bih=800#imgrc=EgfBEc3qR_pYBM:

It's not very big around 30mm in diameter and has a teeth depth of around 2mm.
The circuitry has to be placed inside the gearbox with minimal space, that's why i'd like to use a optic reflection sensor to count when a gear teeth passes the sensor.

I've been looking on Mouser and found this sensor:

VCNT2020
https://www.google.be/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=0ahUKEwid85myrOnYAhVHPFAKHRRFC2QQFggxMAE&url=https://www.vishay.com/optical-sensors/list/product-84285/&usg=AOvVaw2mniwY9pVi0eGWjdRQAK4S

I can place it close to the gear but I wonder if it will detect the 2mm gap between two teeth of the gear.

Does anyone have any expierence with this?

I know that their are other types of opto detectors like a slotted detector but I don't have enough space for those types.


Regards

Alex Deb

Given that the sensor you pointed out is 2.5mm (approximately square), and you said the inter-tooth gap is 2mm, I think it's a safe bet it can do what you need. Buy one, make a small circuit and see what signal it outputs when you turn the gear teeth across it.

 

My point about the focused sensor was that I don't think the real issue is detecting an object that may or may not be present. What's needed is to detect the gear teeth, versus the gaps between the teeth. For that purpose, I'd have thought that the sensor ought to look at one small volume of space, and tell you whether that is occupied or not. With a diffuse sensor, I'd be worried that if the field of view covers multiple teeth, there might not be much change as the gear rotates.

Whether you detect a tooth or a gap is a matter of hi or low signal. As long as it's reliable, you can tell the difference.