Arrangement for detection of rotary or linear motion

[VbDev100]

Hello everybody,

I am basically in computer & electronics field. In one of my project, I want to get the status of the motor of cnc machines (to detect whether it is running or not). Speed is not important. Presently I am using proximity sensor near the motor shaft. I get pulses when motor is running. Then I have to convert these pulses to a continuous signal.

I am looking for some simple mechanical arrangement to detect linear or rotary motion. So that a limit switch will operate when motor is running.

Thanks.

 

[tygerdawg]

Huh??? Don't you have this already for rotary motion?

IF input_PulsesDetected == TRUE THEN
output_ShaftIsRotating = TRUE
ELSE
output_ShaftIsRotating = FALSE
ENDIF

This would work for linear as well if you use a clever sensing target to give you pulses from linear motion (like a gear rack or similar).

Or are you seeking a tachometer / linear speed sensor?

TygerDawg
Blue Technik LLC
Virtuoso Robotics Engineering

http://www.bluetechnik.com

 

[VbDev100]

Thank you Posttygerdawg for your kind reply.

Basically I don't want to use software solution. I want to mechanically convert the rotary motion into say movement of a small lever. The lever should be on one side if shaft is rotating, & on other side when it is stopped.

I will attach a limit switch near the lever to get the signal. Thanks anyway.

 

[TheTick]

A CNC machine with motors that don't have encoders?

 

[BrianE22]

Centrifugal switches will do that. But the speed of rotation has to be above a certain value.

 

[btrueblood]

"A CNC machine with motors that don't have encoders? "

A CNC machine that doesn't know if it is pushing current to the motor?

 

[byrdj]

Using the design concepts of an hydrualic "rotor stopped" indication for older turbines

use a odd lobe cam, with dual rollers. Timing so that with rotor stopped, at least one roller is at minimun dwell. add damping cylinder to roller arms so roller leaves cam and slowly decays to minimun dwell. then add linkage from the two roller's in a "gate" so that if one roller is at minimun, you get stopped alarm.

this same concept would work much better if you replace the rollers with oil nozzle/reciever, with the reciever port oil lifting a piston

 

[MiketheEngineer]

Use a cam??

Tie a piece of string to it. IF its moving the rotor is moving??

 

[zekeman]

a slider crank compressing (basically a pump) a cylinder with leakage; piston overcomes spring loaded link.
While rotating the compressed air holds the link in "on" position.
Stopping causes pressure to fall and spring closure to "off" position

 

[VbDev100]

Thanks everybody.

Of course the CNC machines have encoder/resolver/tacho, but as my product is to be used with different types of CNC machines, every time I will have to use different method. In some machines I get 24V signal from the servo drive. I am searching a standard method which will work for any machine.

Thanks BrianE22, using centrifugal switch is really nice idea. I have not used it yet, I will search for it.

Methods suggested by byrdj & zekeman are also good. But for a guy like me it is difficult to understand & fabricate. Still I will certainly study these methods. R REALLY INTERESTING!!!

 

[1gibson]

A sensitive knock sensor to pickup on motor noise when running? An induction ring that produces a small current when shaft is turning?

 

[MintJulep]

Fan and sail switch.

 

[KENAT]

How about a magnet(s) on the shaft + a stationary reed switch. If the switch doesn't operate for greater than some appropriate time period you know the shaft isn't moving.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[VbDev100]

Thanks, I have learned a lot from you people. All the suggested methods are really interesting. But now I realized that the mechanical methods are not possible for me to implement, so I will stop thinking over them.

Going back to my original method, I was thinking to use some sort of proximity sensor & then use additional circuitry to flatten the pulse.

So now I have 3 options. Either use inductive proximity sensor or photoelectric proximity or 'magnet & reed switch' as suggested by KENAT. I will have to use additional circuitry to convert the pulses into a plain signal.

Using magnet & reed switch is the cheapest solution, but will it be reliable? Any thoughts? Thanks.

 

[Oldhydroman]

Years ago we used a rotation sensor based on an electronic timer: the timer would be counting down but would be repeatedly reset back to the start by a pulse from a magnetic pick up. If the timer ever managed to time out then it meant that the gap between the pulses had become so long that we could consider the shaft to have stopped.

I think the magnetic pick up would be a more reliable option (see attached) but it doesn't need a permanent magnet for its target. I believe some types will work if you just mount them close enough to the teeth of a spinning gear (ferrous material). The pulse output was triggered by the change from a magnetic to a non-magnetic environment near the tip of the pick-up. I don't think you had to try to extract a "pulse" from the rising edge of the signal (just in case the shaft stopped with the gear tooth in front of the tip) because the pulse was trigged simply by the change. You might already have a suitable gear on your shaft.

If you choose an encoder or proximity detector then you will have to put in a few extra lines of code to seek out the rising edge of the signal.

DOL

 

[VbDev100]

Thanks, I have decided to use a magnet attached to the shaft along with HALL EFFECT SENSOR IC. The hall effect sensor will be better than reed switch. I have made a small circuit with 74LS123 which is retriggerable monostable multivibrator to convert the pulses into plain signal.

I have one very interesting (& odd) idea. I can use pcb from an optical mouse & detect when the LED goes bright. Whenever a moving surface is in front of it, the LED goes bright, AND WILL WAIT FOR SOME TIME, THOUGH IT IS STATIONARY. DON'T KNOW, BUT MAY BE A PERFECT & CHEAP SOLUTION