martinav (Customer) asked a question.
What encoder/sensor to use to measure small movements
I need to detect travel of a spool that would indicate a valve opening. I basically have full access to the end of a metal shaft/spool. This spool will move axially only 1/16 to 1/8" which will indicate the opening. I need to get a signal when this movement has occurred. I do not need to measure how much it moves, but just that it has moved. I would prefer not to have any contact with the spool. What would I use to do this? Thank you.
You could use a prox switch and set it up 1/16" from the end of the shaft oriented radially with the shaft. When the shaft then enters the prox switch "view" it would signaled on. The exact placement would have to be found at installation time. You could also use a laser signal with reflector to do same . You may be able to use a laser prox facing the axial end and set its sensitivity to trigger on when shaft has moved. If you could stand contacting the end of the shaft, AD sells linear position sensors that provide an output to the position.
automationdirect.com/adc/shopping/catalog/sensors_-z-_encoders/linear_position_sensors#
automation direct also sells precision limit switches that might work well for your application
https://www.automationdirect.com/adc/shopping/catalog/sensors_-z-_encoders/limit_switches/precision_limit_switches#
If you can put a small piece on the end of the shaft to make it stick out then you can detect it with an inductive proximity sensor. Those can detect small movements and are pretty sensitive, and are very repeatable. They also would not touch the shaft.
It looks like an ultrasonic prox sensor might work nicely. However, I do not see anything that gives me the resolution of the sensor. For instance, if the travel of the spool is between 1/16 and 1/8 of an inch, can the sensor provide a value? Also, learning mode I would only be able to teach it to the furthest point. I could not practically move the spool to teach it a minimum distance from the sensor. Is this a practical application for an ultrasonic?
Thanks.
Hmm, what about an FA series Laser? These are fairly inexpensive. But again, sensitivity is not indicated in the specs. It just says "variable". I like the look of the FALS-BN/BP-1E.
I would need to know if a NPN or PNP would be the right one. The normal condition of the sensed object will be the farthest distance from the sensor. As the spool moves, it will move 1/16" to 1/8" closer. If I had everything I wanted, I would like to not only indicate movement, but get a distance number too.
I will be wanting to connect to the BX-DM1E-18ER3.
Thanks!
From experience, it would be best to use an inductive prox, and a limit switch, second. The reason being photoeyes/laser sensors work best when the object detected is moving perpendicularly to the light source. Inductive proxes and limit switches work well with an object heading toward them. An ultrasonic sensor is a poor choice due to its field of view grows as the distance from the end of the sensor increases (this is also true of photoeyes). I think you'd be hard pressed to get it to detect just the spool and NOT anything else.
Good luck!
@Todd Dice (Customer) ,
I still dont know the resolution of any of these devices. I still dont know if a movement of as little as 1/16" toward any of these sensors would be noticed. All I have seen is mention that the laser ones are "high resolution". However, I have no reference to tell me if that will work either. I was thinking of the closest proximity laser in this case. I used the term "spool" just to communicate the operation of the device. It is in actuality the end of a 1/2" to 3/4" bolt depending on the particular product. I'll post an image to show you. It seems the laser is only a 1mm diameter beam. I dont think that would be a problem as far as it getting lost in some way. Also, the object is coming closer to the sensor, not going farther away. That also seemed to be a concern.
I'm not married to any sensor. I would just like to understand the resolution of any of them. I find it very odd that this detail is left off of all of the specifications. In fact, only ONE type I found a reference to resolution in the specs. It was the FA series. In the table, it only said "variable". I did not find that helpful at all.
What you are really concerned with is sensing distance. You'll want a sensor with a short sensing distance. I'd go with an inductive prox with a 1 or 2 mm sensing distance. This video from Automation Direct can also assist you in understanding how proximity sensors work.
https://www.youtube.com/watch?v=tpXW6qWoJGA
Please forgive me. I'm not sure I'm explaining myself well. If I have a sensor of any time end to end (axially) with a cylinder that is moving up to 1/8" (3mm), if the sensor needs to be 1-2mm from the end to sense it, how does the the cylinder not hit the sensor? This only works if I place the sensor 4mm away, and the spool moves into range of the sensor. That would leave only 1mm clearance, which is way too close. It may only move 1.5mm, so it wouldnt even be sensed at all with that close of a sensing range. I have watched videos, and have used prox sensors before. I do not believe I'm lacking any understanding of how they work. Just what the sensitivity of the gauges are, and if they can sense and measure a 1-3mm movement, and to what accuracy?
Maybe I'm not understanding your application.
I am assuming you wish to sense when the spool of the valve is in one position and not when it is in the other. So, you mount the sensor so it detects the valve spool (or whatever object) within the range of the sensor (0.5mm for a 1mm sensor, 1.5mm for a 2). And when your object is in the other position (moving away in a linear or otherwise direction) to a distance greater than the range of the sensor.