# Light Curtain for Process



## MikeFL (Apr 16, 2016)

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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## splatz (May 23, 2015)

MikeFL said:


> 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. 



> 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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## CoolWill (Jan 5, 2019)

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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## 99cents (Aug 20, 2012)

CoolWill said:


> 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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## Cow (Jan 16, 2008)

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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## frenchelectrican (Mar 15, 2007)

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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## 99cents (Aug 20, 2012)

splatz said:


> 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.
> 
> 
> 
> ...


Phone the All England Club. Wimbledon’s over. They probably have time for a phone call.


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## frenchelectrican (Mar 15, 2007)

99cents said:


> 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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## 99cents (Aug 20, 2012)

frenchelectrican said:


> 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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## CoolWill (Jan 5, 2019)

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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## gpop (May 14, 2018)

CoolWill said:


> 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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## varmit (Apr 19, 2009)

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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## splatz (May 23, 2015)

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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## CoolWill (Jan 5, 2019)

splatz said:


> 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:vs_mad:

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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## splatz (May 23, 2015)

CoolWill said:


> If you would stop being so tight-lipped about it, maybe we could help you out:vs_mad:


 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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## gpop (May 14, 2018)

Laser, prism's, smoke and mirrors


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## paulengr (Oct 8, 2017)

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 


Sent from my iPhone using Tapatalk


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## Wardenclyffe (Jan 11, 2019)

Maybe a spinning mirror,...


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## gpop (May 14, 2018)

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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## CoolWill (Jan 5, 2019)

gpop said:


> 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)
> 
> ...


The code isn't the hard part. It's the actual hardware that will be difficult to implement. He will need some high-power IR LEDs and maybe some optics to reach the width he's trying to get to. Then he will need to make sure that the phototransistors are sufficiently immune to ambient radiation. 

Just for giggles I was able to get 40 cm between an LED and phototransistors on the work bench last night. I think with some optics it could be much more.

Also, I read that you can way overdrive those LEDs if you don't do it for too long. A paper I read said that you could blast up to 1 amp through a 50 mA LED as long as you didn't go over a few 10s of microseconds with a few 10s of microseconds rest period. So you could overdrive it and watch the interrupt, and then give it a rest and stop watching the interrupt, all within 100 microseconds.


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## splatz (May 23, 2015)

The Arduino - no doubt they are great for hobby / education I wouldn't use them for something that has to go into production. I can maybe see using them for prototyping but in this case that would be a poor choice since the performance is the critical thing in the proof of concept. 

If you're going to do it the hard way, build a circuit board, program a microprocessor in a low level language, etc. - you know just about anything will be doable but unless you're going to sell hundreds or thousands or millions you'll never pay for the development. 

I did not think it was necessary to resort to building a dedicated device and programming in a low level language to achieve 1ms scan time. I never used them but look at these 

https://www.controleng.com/articles/worlds-fastest-plc-based-on-cpu-scanning-speed/

100,000 instructions in 1ms! Maybe there's a catch. 

So I'd have to see if there's a PLC or other off the shelf brain capable of the necessary speed in my price range. 

I'd also have to verify that a series of photocell transistors is capable of going high to low fast enough to work. I assume the phototransistor needs enough light to saturate its sensor but I think this will work, I remember years ago seeing scope traces of a photoresistor picking up a high frequency signal. As mentioned before I don't know if noise would be a problem but that would be another consideration.


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## splatz (May 23, 2015)

Unless I am reading something wrong, the scan time of the AB Micro810 can go as low as .25ms - that ought to do it, right? 

https://literature.rockwellautomation.com/idc/groups/literature/documents/sg/2080-sg001_-en-p.pdf 

Some of the Clicks are in the 1-2 ms range, others are under 1ms with a decent sized program 

https://cdn.automationdirect.com/static/specs/clickspecs.pdf 

I know there are some functions that dramatically increase scan times, serial reads / writes etc., but for basic IO these look like they could check an IO that goes high / low for at least 1ms.


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## splatz (May 23, 2015)

CoolWill said:


> Also, I read that you can way overdrive those LEDs if you don't do it for too long. A paper I read said that you could blast up to 1 amp through a 50 mA LED as long as you didn't go over a few 10s of microseconds with a few 10s of microseconds rest period. So you could overdrive it and watch the interrupt, and then give it a rest and stop watching the interrupt, all within 100 microseconds.


What if you used the emitters in pairs, one with the bias reversed, on some AC with a square wave? Two emitters to the same phototransistor.


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## CoolWill (Jan 5, 2019)

splatz said:


> What if you used the emitters in pairs, one with the bias reversed, on some AC with a square wave? Two emitters to the same phototransistor.


I don't see why not, except you'd need a split power supply for the positive and negative halves of the square wave.


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## scotch (Oct 17, 2013)

There's certainly equipment used in the firearms industry for projectile velocities ....even some available for gun owner use....look it up ?


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## JRaef (Mar 23, 2009)

I used a color sensor from Sick to detect off colored dry beans falling in a stream, then acted on an air valve to shoot a puff of air to divert them from the stream. We had the time it took for the width of a kidney bean (worst case) to pass by at free fall to detect, decide and act. The sensors were plenty fast enough, we were able to spit out 1200 red beans per minute with 99% accuracy. You just need to engage a sensor mfr and tell them what you need. They have people who live for this sort of stuff.


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## splatz (May 23, 2015)

scotch said:


> There's certainly equipment used in the firearms industry for projectile velocities ....even some available for gun owner use....look it up ?


I have used those, chronographs for bullets, but they are very small windows, and you have to have the projectile pass through two windows. So it's related but really not applicable.


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## CoolWill (Jan 5, 2019)

JRaef said:


> I used a color sensor from Sick to detect off colored dry beans falling in a stream, then acted on an air valve to shoot a puff of air to divert them from the stream. We had the time it took for the width of a kidney bean (worst case) to pass by at free fall to detect, decide and act. The sensors were plenty fast enough, we were able to spit out 1200 red beans per minute with 99% accuracy. You just need to engage a sensor mfr and tell them what you need. They have people who live for this sort of stuff.


I agree that sensor people are the ones to see.... As an aside, falling beans are way, way slower than 170 mph.


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## splatz (May 23, 2015)

CoolWill said:


> I agree that sensor people are the ones to see.... As an aside, falling beans are way, way slower than 170 mph.


 Unless this is a really, really tall plant 



I'd think the challenge there would be getting that puff to fire off fast enough to hit the bean...


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## splatz (May 23, 2015)

As for the sensor manufacturers ... I am underwhelmed. They have people that are happy to read the spec sheet off the web site to me. Beyond that, not too helpful.


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## CoolWill (Jan 5, 2019)

splatz said:


> Unless this is a really, really tall plant
> 
> 
> 
> I'd think the challenge there would be getting that puff to fire off fast enough to hit the bean...


Term. In. Al. Vel...oc...ity. :vs_mad:


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