Sensor recommendation for spinning object

[Fuzzy67]

What type of sensor do I need to detect (not measure) the motion of a spinning cylinder at a fixed (<5cm) focal length under all lighting conditions? The cylinder cannot be altered in any way.

The purpose of this would be to drive a relay to wake up a gadget from a low power sleep state so it can operate when the cylinder starts moving, and then power it down to sleep mode when the cylinder stops. The less power the sensor draws the better. I think the device will be running 9v DC.

Thanks,
Gary

 

[Externet]

Is it possible to see a picture of the cylinder ?

 

[Boncuk]

Use a reflective IR-sensor such as CNY70. Its "focal length" is between 2 and 5mm.

Using the IR-chip with built in IR-filter you won't have to worry about ambient and artificial light.

Mark your cylinder with white color to detect motion.

Boncuk

 

[Fuzzy67]

Unfortunately I won't be able to put any marks on the cylinder, and in some cases they will be black, meaning very low reflectivity in a dark room, making motion detection that much harder. It would be possible, however, to have a white LED light the area the sensor will be measuring.

I don't have any cylinder photos. The sensor has to work on a range of cylinders on various machines. Generally the cylinders will be 8-15" in diameter, 2-10" high and will spin at 20-100 rpm. Materials will be various metals, typically aluminum or steel, and plastics such as acrylic or polycarbonate, and possible others.

My guess is it will be easy to detect motion when there are surface imperfections. I'm more concerned about exceptionally smooth surfaces that to the human eye might almost appear to not be moving at all if the cylinder's spinning fast enough, which I guess comes down to sensor sensitivity, and I don't have a good handle on that.

Most of what I've read about sensors points to infrared, which is what I'm most familiar with and will probably use for another aspect of this devise that detects motion of a part moving linearly past a fixed sensor at a similarly close range. This is what I had in mind:

GP2Y0D810Z0F Sharp Microelectronics Industrial Optical Sensors

But they call this a "distance measuring" sensor. With the cylinder at a fixed distance the distance to measure isn't changing. However, if there are surface imperfections those could minimally change the distance if the sensor's sensitive enough to detect them. And I guess the same could be said about a surface that visually appears to be very smooth. If you magnify a seemingly smooth surface enough there are imperfections.

Do you think an IR sensor the right choice? Is this one in particular going to be sensitive enough or should I look elsewhere?

 

[Vizier87]

Hi Hot Fuzz D) welcome here.

can you access the wiring which activates the cylinder motion? If you can, then the enabling signal to the cylinder's rotation (I assume it's just a motor) can be derived and made to be input to another activating circuitry.

 

[Fuzzy67]

Customers aren't going to allow me to tap into their motor's wiring. However, if there's some kind of simple, inexpensive, non-destructive sensor I can place around the wire lead to the motor that detect AC power in the line (meaning the motor is on and spinning), that would be work.

For obvious reasons all electricians carry a hand tool like that that activates an LED or beeps when current is detected. I believe this uses a Hall effect sensor. I haven't been able to find anything as cheap and simple as a little sensor inside my device that would do the job. For practicality and portability I'd really like the device to be as small and self contained as possible.

I think a sensor in the device is the way to go. The motion I want to detect isn't unusual.

Any other suggestions?

 

[cobra1]

maybe you could build a current sensor to wrap around the + lead of the motor, i know you can get hook on multimeters to detect current so it might not be that difficult to build one.

EDIT: what is the cylinder doing, whats its purpose??

 

[Fuzzy67]

I'm sure it's possible to build a current sensor, but if I can put a tiny $2 sensor on the device's pcb that does the job, there's no point. The only purpose of this sensor is to put the device into and get it out of low power sleep mode to save power when it's unattended. This is a minor part of the device. I really want to keep it simple and low cost. Some type of sensor is the way to go. I just don't know enough about the non-IR options.

Sorry, I can't provide any details about the purpose of the cylinders other than that they're parts of various customers' machinery that will need to be tested periodically.

 

[cobra1]

ok well with the information you have given, its hard to really give an idea on how to complete your objective.
as far as i can see you have 2 options

an inductive sensor, or a hall sensor, both of which are going to need electronics (signal conditioners) to give you an output to something that would then turn this device on/off or display its current state.

other than this you would have to mechanically interfere with the machine, i.e if its belt/gear driven you could use an optical sensor connected to one of these.

Without knowing what this machine is or what it does then its hard to make a good suggestion as to your approach

 

[ronv]

current sensor

Maybe something like this cheapie.

**broken link removed**

 

[dknguyen]

Personally, I don't think you'll be able to measure anything by using the cylinder itself with the conditions that have been placed. You can't stick an encoder on the motor or some measurement device on the motor (or any other part of the spinning system, doesn't really matter where). A single magnet on a spinning part in the system and a small hall sensor IC is all that's really needed. Of coures you can do the same thing with a reflective material or mark and a light sensor somewhere else in the system.

Of course, if it's a brushless motor you can measure the voltage on each winding to see how fast the the motor is commutating and figure out the speed that way. But this requires an or a DC brushless motor (or more precisely a electronically commutated brushless motor) and tapping into the motor line to measure the voltage. I don't think a contactless current method will work fast or accurately enough because of all the inductance and current flow in the motor. But my understanding is none of this will work with an AC or brushed motor. What counts as tapping into the motor wiring? A needle probe to pierce the insulation...does that count?

 

[Vizier87]

the next option which is cheap but will take time to master is to use image sensors, the detection will be similar to those USB mice. There are hacks using USB mice, but regarding a range of a few centimetres... I'm not sure.

 

[Boncuk]

the next option which is cheap but will take time to master is to use image sensors, the detection will be similar to those USB mice. There are hacks using USB mice, but regarding a range of a few centimetres... I'm not sure.

Hi Vizier87,

a USB mouse requires some kind of "pattern" to sense motion and count steps correctly.

Try your mouse on a white sheet of acrylic glass for prove. Even used on my PC table with a smooth white surface the mouse malfunctions badly.

If the cylinder's surface is polished the effect will be the same.

Regards

Hans

 

[Boncuk]

Hi Fuzzy67,

optical methods can't work since you can't mark a spot on the cylinder.

Hall sensors can't be used because you need to mount a tiny magnet to the cylinder.

I doubt that laser beam measuring will be successful if the "pits" on the cylinder are in the nanometer range.

Here might be another approach using temperature:

Have a rod of non abrasive (heat conducting) material touch the cylinder and attach a temperature probe to the rod.

Friction causes heat which will then be used to indicate a rotating cylinder.

Boncuk

 

[Vizier87]

Hi Vizier87,
a USB mouse requires some kind of "pattern" to sense motion and count steps correctly.
Try your mouse on a white sheet of acrylic glass for prove. Even used on my PC table with a smooth white surface the mouse malfunctions badly.
If the cylinder's surface is polished the effect will be the same.
Regards
Hans

Yup.. I'm afraid so, you're right. But if I'm not mistaken, how about the ones which also can move on glass? like this one: **broken link removed**

 

[Boncuk]

Yup.. I'm afraid so, you're right. But if I'm not mistaken, how about the ones which also can move on glass? like this one: **broken link removed**

That one should work alright.

 

[atferrari]

Please delete this post.

Moderator please delete this.

 

[Vizier87]

Several links on mouse hacking:
**broken link removed**
Sprites mods - Optical mouse-cam - Optical mouse cam

might get you started there. I too find these projects interesting, I think I'm gonna try out some things with these CMOS image sensors.