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Old 07-21-2019, 08:27 AM   #1
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Default Light Curtain for Process

I have seen light curtains used for safety, I am thinking about using one for a non-safety application. I'd like to set up a light curtain that could detect a tennis ball sized object passing through the curtain. The curtain would be about 4-5' tall by 30-35' wide.

These were the first ones I found, I don't know if they are the best choice, I just always had good luck with Omron:

https://assets.omron.com/m/5c05ac812...75IE05-pdf.pdf

I see the specs for distance between the beams, and for the range between the emitter and the receiver. The bigger ones look like they'd work - about an inch between beams and enough range.

I am wondering about the response time, not how long the device takes to react, but how long you have to break the beam to trigger the device. The object could be flung pretty fast, so I'd be looking for a 1ms beam break.

Maybe there's something better than a light curtain? Any ideas?
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Old 07-21-2019, 08:43 AM   #2
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Can't Omron answer those questions?

Something that comes to mind is UFO catcher software and a camera. Not sure though of the geometry of your target area. Those light beams may be better.
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Old 07-21-2019, 08:50 AM   #3
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Quote:
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Can't Omron answer those questions?
I haven't called Omron in a while but it's pretty hard to get to an engineer, the people answering the phones are just reading the spec sheet aloud to you.

Quote:
Something that comes to mind is UFO catcher software and a camera. Not sure though of the geometry of your target area. Those light beams may be better.
That is a good idea but I have used this kind of video analytics with surveillance systems and they are slow and not very precise / reliable.

Something like a radar gun that just alerts if it detects an object travelling at a speed over 5mph would probably work...
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Old 07-21-2019, 10:34 AM   #4
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What is the project? I can't find anything less than 15 ms response time. To move a tennis ball width in 1 ms is about 170 miles per hour, by my calculation... Are you sure your object is moving that fast?
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Old 07-21-2019, 11:09 AM   #5
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What is the project? I can't find anything less than 15 ms response time. To move a tennis ball width in 1 ms is about 170 miles per hour, by my calculation... Are you sure your object is moving that fast?
Milos Raonic can’t even hit one that hard.
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Old 07-21-2019, 11:16 AM   #6
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What's the project?!?!?!


We all want to know!!!


Are you trying to initiate a counter or audio device every time someone hits a tennis ball in the right spot???


This is making me think of electrical projects for my daughters softball team that I help coach....
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Old 07-21-2019, 01:09 PM   #7
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How fast the item are you talking about and what it is watching on what ??

I am try to come up with some answer what you are looking for but the most fastest light curtin I have see is about 10-15 Ms respond timing .

it have to do something with convoyer or hopper ?

we all like to know what kind gig we are looking at.
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Old 07-21-2019, 01:33 PM   #8
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Quote:
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I haven't called Omron in a while but it's pretty hard to get to an engineer, the people answering the phones are just reading the spec sheet aloud to you.



That is a good idea but I have used this kind of video analytics with surveillance systems and they are slow and not very precise / reliable.

Something like a radar gun that just alerts if it detects an object travelling at a speed over 5mph would probably work...
Phone the All England Club. Wimbledon’s over. They probably have time for a phone call.
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Old 07-21-2019, 01:39 PM   #9
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Phone the All England Club. Wimbledon’s over. They probably have time for a phone call.
I have to laugh for a second but seriously .,, you got me thinking it may be a good idea cuz they may have some equipment can able detect those pesky lime green balls moving that fast.
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Old 07-21-2019, 01:52 PM   #10
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I have to laugh for a second but seriously .,, you got me thinking it may be a good idea cuz they may have some equipment can able detect those pesky lime green balls moving that fast.
They have the sign that displays ball speed in MPH. The men are usually over 100. Federer will get in the 130’s, the heavy hitters higher.

I know, off topic...
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Old 07-21-2019, 02:23 PM   #11
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I can think of a simple DIY solution using some homebrew electronics, but that won't fly if the thing needs to be listed.
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Old 07-21-2019, 03:13 PM   #12
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What is the project? I can't find anything less than 15 ms response time. To move a tennis ball width in 1 ms is about 170 miles per hour, by my calculation... Are you sure your object is moving that fast?
Is the 15ms the time it takes to detect or the time between detection and response. the way im reading the manual it looks like a lag waiting on the relay to open and close which is why they list open to close and close to open.

I may be totally wrong which is why i would contact the company and tell them the size and speed of the object then ask to borrow a demo unit.
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Old 07-21-2019, 09:55 PM   #13
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Keyence has some really good units. I don't recall the reaction times but Keyence has really good tech support. In larger cities, the local tech dude will come to the job site and give you help.
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Old 07-27-2019, 07:49 AM   #14
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The application is not tennis but maybe once I crack this I'll call Wimbledon with an idea and make the big bucks

After looking into it with the manufacturers, the light curtains specify the reaction time between the beam break / beam disruption and the output of the device, not the duration of the beam break required to register as a disruption.

I might be barking up the wrong tree, there may be something better than a beam break to detect this. If it's going to be a beam break type of device I might have to build rather than buy it.
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Old 07-27-2019, 08:06 AM   #15
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Quote:
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The application is not tennis but maybe once I crack this I'll call Wimbledon with an idea and make the big bucks

After looking into it with the manufacturers, the light curtains specify the reaction time between the beam break / beam disruption and the output of the device, not the duration of the beam break required to register as a disruption.

I might be barking up the wrong tree, there may be something better than a beam break to detect this. If it's going to be a beam break type of device I might have to build rather than buy it.
If you would stop being so tight-lipped about it, maybe we could help you out

As for break beam, infrared LEDs and phototransistors are dirt cheap. Wire the phototransistors in series and ground them through a 3300 ohm resistor. Your signal will come from the junction of the transistors and resistor. It will be high when the beams are unbroken and low when anything interrupts a beam. Black soda straws around each transistor will help keep the noise down.
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Old 07-27-2019, 09:27 AM   #16
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If you would stop being so tight-lipped about it, maybe we could help you out
I know, you're right, but I am afraid I am stuck with a NDA

I think I monkeyed with IR phototransistors years ago but only hobby / educational junk, I have a hard time picturing them working at bigger than benchtop distances with all kinds of ambient light.

Of course I guess if garage doors do it, can't be that hard...
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Last edited by splatz; 07-27-2019 at 09:36 AM.
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Old 07-27-2019, 12:48 PM   #17
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Laser, prism's, smoke and mirrors
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Old 07-27-2019, 04:23 PM   #18
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1 ms is really fast. It’s so fast that let’s take for instance the knife system for lollipop machines. This system uses a single high speed transmitter/receiver pair to trigger a high speed input on a timer or encoder card that fires the sealer/knife based on timing alone. The PLC is essentially administrative. They operate at around 10,090 pieces per minute which is still 6 times slower than you are looking for. Similarly motion systems are usually until recently written in compiled C code. Recently they have appeared in other programming systems but the control loops are still executable code, not interpreted. Execution times are about 1 ms with the inner servo controller running at around 0.1 ms in hardware such as FPGA code. The outer loop is making speed/torque decisions not full start/stop so it is operating far faster than your typical digital input or output.

So you are asking for beyond servo performance. Your best bet will be to write everything in Verilog and run it on say a Xilinx FPGA. Forget about off the shelf hardware. This will use phototransistors as direct inputs to the FPGA in push-pull (fast) FET pairs. Outputs will be 3.3 V, again FET outputs. Forget about relays on this one.

When it comes to camera systems at those speeds you need to talk to Cognex or Keyence. The surveillance systems of old are no comparison. Even the stuff in Microsoft Kinect is slow compared to high speed industrial systems. Cognex does a lot of hardware assist so it runs at 10,000 plus images per minute and given that it covers a much wider envelope it might work for you. Keyence is similar with some systems but they are more software oriented and just push the fastest Intel processors.

This is an instrumentation project. Forget UL. At best you might be able to List the custom system since this is close to working at the component level. This level of performance is not needed in almost all industrial applications


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Old 07-28-2019, 12:24 AM   #19
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Maybe a spinning mirror,...
Attached Thumbnails
Light Curtain for Process-spinning.jpg  

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Old 07-28-2019, 11:48 AM   #20
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After reading paul's post i think that you can write a basic code in C++ and put a sensor input on a interrupt pin using a cheap arduino. Once anything is sensed by the input the processor switches from its main code and runs what ever code you have written to deal with the input. (this makes it faster to respond as its not running the code in loop but it also means the code in loop that may be doing other things is delayed until the interrupt code is finished)

Arduino has a forum where a bunch of geeks hang out that will go supper nerdy for a project like this (most work on custom systems that are not arduino but will come play on the forum)

As you are only looking for sensing at 1ms not reacting with in 1ms it should be able to deal with that.
If you are looking at responding with in 1ms that is a different game as the processor would have to be able to run all the code between sense and response in well under 1ms which would require a fast processor and well written code.
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