Good day! I’m new here and hoping to get some guidance on selecting the right component for a project I’m working on. I want to automate the standoff distance between a handheld pulsed laser cleaning head and the workpiece. Typically, the operator adjusts the distance manually to maintain the focal point, but my plan is to mount the cleaning head on a linear actuator and use a sensor to automatically keep it at the correct focus distance.
The challenge is that the cleaning laser runs at 1064 nm, which could interfere with any distance sensors that rely on their own laser sources. I need to measure distances from about 0.5 mm up to 300 mm, with at least 0.5 mm accuracy across that range.
Does anyone have suggestions on a suitable type of sensor or a specific model that could handle these conditions? Thanks heaps
What is the wave length of your laser?
Visible?
My prediction is that microwave distance lasers should be suitably out of band width and so you will avoid undesirable de-constructive interference.
Maybe CE sells something MW that is short range?
Hi Heinrich
I think the 0.5mm minimum measuring distance and 0.5mm accuracy might be the game changer.
Also what sort of material are you cleaning. It would have to be reflective to radio waves for a pulse echo radar to work. Doppler radar would be no good as the target has to be moving toward or away for this type work.Also the radiated beam width would be too wide I think for this resolution and accuracy so the visible light types might have to be the way to go.
Your resolution and accuracy specs are going to be hard to meed I think
Cheers Bob
PS: Could you edit the title to read “Piece” instead of “Peace”.
It sounds like you want to send this device off to somewhere to clean up a couple of wars.
Hi Heinrich
Just had another few thoughts about your minimum distance and accuracy requirement.
If you use “Timo of Flight” type measurement, that is transmit a pulse and measure the time for the return to arrive I don’t think is feasible for your requirements.
At 0.5mm the round trip will be 1.0mm.
Light (and radio waves) travel at about 300,000,000 m/Sec. or 300,000,000,000 mm/sec so the 1mm return trip will be 0.003333 nSec or 3.333 pSec (Pico Sec). Pico being one millionth part of one millionth (1 / 10^12)
Very good luck with that. Particularly at this hobby level.
Cheers Bob
I think my math is right.
Bob, and everyone thanks for your input. First, I’ve corrected the war issue . Secondly, to answer your question regarding material type: in most cases the material will be metal, often with contaminants or paint on the surface.
To explain my design in terms of distance from the workpiece, the laser beam is typically focused at around 300 mm from the workpiece. My plan was to connect the sensor and the linear actuator so that it has a 150 mm tolerance on either side of that focal point, giving a total of 300 mm of travel. This would allow the system to maintain the 300 mm standoff distance while compensating for any variations, such as humps or dents in the material surface.
The speed at which the focus needs to be adjusted would depend on the travel speed of the beam across the workpiece in order to keep up with these surface irregularities. At this stage, I’m assuming the travel speed will not exceed 10 seconds per meter.
With that in mind, my question is: do your previous calculations still indicate that this setup would be unworkable, or does this updated explanation change the outcome?
Now you indicate that is actually 150mm to 450mm. That makes a difference to the original minimum of 0.5mm.
BUT it makes no difference to your required accuracy. 0.5mm still equates to 1.0mm round trip so if your required accuracy is +/- 0.5mm you still have to measure time to within =/- 3.333 pSec.
As for that DFRobot device. The description tells us nothing except the target has to be moving.
The description says 5.8GHz and the specifications say 24GHz. I will leave the imagination bit up to you. Just what can you believe. The beam width is also 120º which I think would be pretty unsuitable anyway.
This sort of beam width is what you are going to get with any of this type of radar device. Far too broad for your application I think. That is why I mentioned a visible light system as it can be reduced to a spot measurement.
I think my previous math is correct so your time measurement resolution will have to be in the pSec range which I am not sure the currently available crop of devices is capable of doing. To put it into perspective 1.0pSec resolution would require a clock of 1000GHz presuming i clock pulse per tick. Frightening.
Cheers Bob
Someone else might chip in here who is familiar with this sort of thing
Someone might care to check my math too. I might have got the number of zeros wrong but I don’t think so
Thanks for your insight and clarification Bob. That makes sense the beam width on radar or microwave systems is definitely too broad for the level of precision and spot-specific measurement I need. Your point about using a visible light system is well taken. Since a visible-light laser or triangulation setup can be focused down to a very tight spot, it seems much better suited for accurately tracking the standoff distance in my application.
I’ll shift the focus toward evaluating visible-light options that allow for a narrow, precise spot measurement. Any specific sensor types or configurations you’d recommend.
Sorry can’t help with that problem as I have no experience in this particular field. I have used reflective type Laser sensors but did not measure distance The target was either there or not
Cheers Bob
However would a simpler approach be better?
Could you manufacture jigs that allow the head to be mounted, kind of like a router?
Then that can be measured so its always focused on the sheet?
Hi Liam, Henrich
Lia, that is a “run out” usually called a “Dial Run Out” gauge but in this case it is digital output.
That should work with the sensor mounted on the linear actuator with the laser cleaner and a roller on the moving part of the rod to track the work piece.
In practice you could focus he laser, reset the sensor to zero then arrange everything (coding, actuator drive etc) to keep the sensor reading zero. I think this could be a far more reliable way o achieve the 0.5mm accuracy spec than any other electronic method.
Cheers Bob
Liam
I think that is for pictorial purposes, he has actually used what used to be called a “dial tun out” caliber with a digital scale instead of a mechanical scale. A handy digital output I noticed too. Will research that little device as it could be handy.
Thank you very much all for the suggestions, I really appreciate the thought and detail you’ve put into them. It’s a good idea, and I have actually tried a similar method before, but the arm with the roller still tends to get stuck and struggles to navigate around tighter or more complex corners.
. Secondly, to answer your question regarding material type: in most cases the material will be metal, often with contaminants or paint on the surface.
