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Thread: Laser projector safety

  1. #1
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    Default Laser projector safety

    Goodmorning everyone
    thanks to this beautiful and very useful forum, unique in its kind. Sorry for my bad english. I'm Davide from Italy. Passionate about lasers since childhood. I was 13 when I saw this videoclip (https://www.youtube.com/watch?v=cgONWacjrT0) and fell in love with that "green ray".
    Years have passed, and only back in 1990 I managed to get my first red projector with a 650mW he/ne tube and two rather basic galvos that reproduced simple figures (circle, square, waves) at a reasonable price, around $ 2,500. I was thrilled.
    More recently, thanks to the diodes, I made some small projectors, 50mW green with a diode of a pointer, then an RGB of about 500mW and one of 1500mW. Considering that I am a hobbyist and I will hardly EVER recover all or part of the money invested. My laser shows will perhaps be used in 1/2 evenings in a year, with friends, and for pure passion. Struck by sudden madness, I decided to grow further.
    I purchased 2 empty used cases, (thanks to fb and Emile, a very nice French guy) 2 rgb modules from Optolaser and i'm building a pair of 6000mW rgb projectors. They will be driven by internal Fb4 and Quickshow.
    Perfectly aware of the danger of these tools, I state that they will be used exclusively by myself and any shows will be made with the basis of notions of safety: 2 meters min.lateral distance from the body of people and min.3 meters above the heads.
    The projectors have a remote safety system with E-stop which operates a solid-state relay that immediately cuts the driver's analogue voltage, completely obscuring the lasers. I wanted some advice if I need to implement another safety system for my projector (rotary actuator / mechanical shutter?)
    Sorry for the long post and thanks very much everyone.

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    Hello David;

    Thanks for sharing your experiences. Many people here followed a path similar to yours. I've been fascinated with lasers since the mid-to-late 1970's, but it wasn't until the early 1990's that I could afford to purchase one, and it's only been in the last 15 years or so that I've been able to enjoy scanned graphics at 30Kpps or higher with my own equipment.

    Regarding your question about adding a second attenuation method, this is always a good idea, and in fact it is a legal requirement for commercial projectors here in the USA. A shutter is one option, although another popular option is to crowbar the modulation input to ground on your laser drivers. It appears that the third most common option, disconnecting the DC power input to the drivers, is the one you are using as your primary attenuation method.

    I assume that your projector uses a relay to switch the power to the lasers on and off when the interlock circuit is either enabled or tripped. In that case, you could change that relay out for one with extra poles and use those extra poles to also switch the RGB modulation inputs on the drivers. The "on" position would connect the modulation input from the laser driver to the appropriate color signal on the ILDA connector, while the "off" position would connect the modulation input from the laser driver to ground. (Obviously this requires that all the poles on the relay be "doube-throw" so you have both an on and and off connection point for each pole.)

    Here is a link to a schematic I've used to implement this feature in previous projector builds. https://i.imgur.com/9yIXzM6.png

    Alternately, if you would rather use a shutter, then you might find this earlier schematic helpful: https://photonlexicon.com/gallery/bu...0Schematic.gif

    In both of these schematics the primary attenuation method is the interruption of DC power to the laser drivers. It's important to note that I specified interrupting the DC power supply: in the USA it is not legal to interrupt the AC power to the projector as a means of attenuation. The reason for this is that most AC-to-DC power supplies can continue to supply DC to a load for a few seconds after the AC input power is removed. But if you interrupt the DC power supply, it's off immediately.

    Note also that both of these schematics incorporate a "run" button. This prevents an un-commanded startup of the projector in cases where you have a momentary break in the interlock loop or the AC power supply. Once the projector shuts down, the main relay is left unlatched and thus can not be re-engergized until all interlocks are satisfied *and* the run button is pressed again. This is done to satisfy the USA requirement for a Class-IV reset mechanism. (All projector starts must be commanded by the operator.)

    There are lots of different ways to implement a shutter, but to be legal it must have a spring that forces it closed on a loss of power. (You can't just allow gravity to close the shutter.) Ledex rotary solenoids were often used in the early days of laser projectors for shutters, although they are noisy and can overheat if not driven properly. These days most people use something like a GM20 or a Vrad actuator, but I've also seen stepper motors used. Like I said, you have lots of options to choose from. Just be sure that the shutter flag is capable of withstanding the full output power of your projector for extended periods without causing any damage. (Black anodized aluminum works well.)

    Adam

    PS: Your English is just fine! For sure it's better than my Italian, which is non-existent...

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    Quote Originally Posted by buffo View Post
    PS: Your English is just fine! For sure it's better than my Italian, which is non-existent...
    hello Adam
    thanks for the very comprehensive answer. Actually my english is scholastic, but I use a lot of google translator

    Your circuit is also very interesting, thanks. I have not yet implemented an ILDA card in my projector, I am using FB4 with its features. FB4 already has a PWM output to drive a transducer (this for example https://www.scannermax.com/pdf/VRAD0506.pdf).


    Using my projector for private use, and not being subject to USA regulations, I preferred to use an electronic rather than mechanical control for safety.

    My interlock works by cutting the 0/5v signal of the analog driver modulation, simultaneously acting on +/- and instantly darkening the laser output. I had also thought of interrupting the DC power supply of the laser driver, but in this way I would have also interrupted the cooling fans with the risk of damaging it.

    Do you think it is better to also connect the ILDA interlock signal? In this case, I will have to purchase dedicated cards for FB4 from Stanwax which are currently out of stock.
    Thanks for all

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    Quote Originally Posted by davidmaster View Post
    I am using FB4 with its features. FB4 already has a PWM output to drive a transducer (this for example https://www.scannermax.com/pdf/VRAD0506.pdf).
    I believe you are referring to the shutter output on the FB4. And yes, it will work with the Pangolin Vrad 506 actuator that you linked to. The Vrad is an *excellent* choice to drive a shutter, which is why I mentioned it in my previous post - along with the GM20.

    Using my projector for private use, and not being subject to USA regulations, I preferred to use an electronic rather than mechanical control for safety.
    I'm not sure what you mean by "mechanical control" compared to "electronic control".?. Could you clarify?

    Also, before we go any further, I want to say that I completely agree with your main point: Since you are using the projector for your own personal use you *don't* need to comply with the USA regulations (or the international IEC regulations, for that matter). However, if you want to improve the safety of your projector, it's always a good idea to follow the industry standards. After all, if it is safe enough for the rest of the laser light show industry, it should be safe enough for your home! So while I will discuss those standards below as an ideal to strive towards, I am not trying to imply that you are obligated to follow them.

    There are some small differences between the IEC and USA standards, but they are pretty much the same when it comes to the safety circuit. To summarize, those standards specify that you must have a dedicated emergency stop switch that will immediately halt all laser output from the projector when it is pressed. This circuit must use two separate attenuation methods to extinguish the laser output. You must also have a keyswitch that will lock the projector in the off or shutdown state when the key is in the off position, and the key must only be removable in the off position - when the key is in the on position it must be held captive by the switch so it can't be removed.

    Note that it is not permissible to use the "stop" control on your software (such as pressing the escape key on the keyboard or clicking your mouse on the "disable output" button on the screen) as your emergency stop circuit. Software can fail, computers can crash, and interrupting the data stream to the projector is not the same as physically shutting off the lasers inside the projector or blocking the output with a shutter flag. That's why the emergency stop system must be a separate, dedicated circuit.

    Again, this is the industry standard. You don't have to follow it if you don't want to. But this method is generally accepted to be both easy to use and very safe. When properly implemented, it will always fail in a safe (that is, no output) mode.

    My interlock works by cutting the 0/5v signal of the analog driver modulation, simultaneously acting on +/- and instantly darkening the laser output.
    Got it. So you are interrupting the modulation signal that is sent to the driver. This is one of the 3 most commonly used attenuation methods. (The other two being a mechanical shutter and interrupting the DC power supply to the laser drivers.)

    Do you leave the +/- leads to the driver disconnected (that is, an open circuit) when the interlock is triggered, or do you short them to ground? The best practice is to short them to ground, because a poorly designed laser driver can allow laser output if the positive modulation input is left to "float". Shorting it to ground (also called "crowbaring to ground") eliminates this possibility. (Again, I'm quoting the industry standards here, but you are under no obligation to follow those if you don't want to.)

    If you look at the schematic I posted above with the 5-pole, double-throw relay (the first schematic), you'll see that the top three poles connect to the positive modulation inputs for the red, green, and blue laser drivers. When the relay is energized, those inputs are connected to the ILDA connector to receive color signals from the controller, but when the relay is off the driver inputs are connected to ground. This is probably the easiest way to crowbar the positive modulation input to ground on the laser drivers.

    I had also thought of interrupting the DC power supply of the laser driver, but in this way I would have also interrupted the cooling fans with the risk of damaging it.
    When you say this would also interrupt the power to the cooling fans, do you mean the cooling fans on the laser heads and/or the drivers? If so, then you do not need to worry. As soon as you remove the DC power, there will be no further heat generated. True, the head and the driver may still be warm, but with no further heat being generated they will begin to cool even without the fan running. There shouldn't be any danger of overheating. (To understand why, consider that in the event of a loss of AC power when the projector is operating you would have the exact same conditions.)

    If you are instead worried about the projector case fans losing power, it is easy enough to separate the DC power wires that feed the laser drivers from any other DC load in the projector (like fans) so that the case fans continue to run while only the DC power to the laser drivers is interrupted.

    Do you think it is better to also connect the ILDA interlock signal?
    If you are using the FB4 you probably don't have an ILDA connector on your projector. If you don't ever plan to connect a different controller to the projector, then there's no reason to ever install an ILDA connector, and thus no need for the ILDA interlock loop. (The ILDA interlock loop is designed to shut off the projector if the ILDA cable becomes unplugged.)

    A better question would be: What happens if the network cable to the FB4 becomes unplugged? According to the standard, this should trigger the emergency stop circuit, just as unplugging the ILDA cable would. But to be honest, I'm not sure how to implement this feature using the FB4. (I have several QM2000s and FB3s, but I do not own any FB4 controllers.) Perhaps someone else who is more familiar with the FB4 can comment on this.

    I would hope that the FB4 would have some sort of "connection enabled" signal output that confirms the FB4 is communicating with either Beyond or Quickshow. If it does have such an output, that could be used to open or close a relay in your safety circuit that would take the place of the ILDA interlock loop.

    A final point about the safety circuit: You'll notice that in both of the schematics I posted above the main relay is "latched" closed through one of it's own contacts. The "Run" button is a momentary-on switch that energizes the relay just long enough for the latching contacts to close. Thereafter the relay is only held closed through the latching contact. So any interruption in the circuit will cause the relay to open, and once that happens the relay can't re-energize until all the interlock conditions are cleared *and* the run button is pressed again.

    This is a crucial feature of a class-IV reset mechanism, and in my mind it is one of the most important safety features. Ideally any time the projector shuts down the first thing the operator should do is hit the emergency stop and turn the key off before approaching the projector to troubleshoot it. But if the operator forgets to do this, the class-IV reset ensures that the projector remains in a safe, shut down state. Without this protection, if you had a momentary interruption in the interlock circuit (a loose connection, for example) the projector could re-start on it's own if the connection was re-joined. This unexpected restart presents a hazard to the operator, who may have approached the projector and could now be in an unsafe position relative to the output aperture.

    Adam

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    Dear Adam
    I don't know how to thank you enough for your availability and completeness of information. Just today the cards dedicated to Fb4 are available again from Stanwax, I am attaching the manual, (http://www.stanwax.plus.com/lw/Ilda%...ons%20s4fb.pdf) so you can see their characteristics. Obviously I already have a remote E-stop with a security key. I'll just have to add the reset button. The safety devices on the projector are an additional key switch and a microswitch on the case cover which are also connected in order to short-circuit the laser output. I would be grateful if you gave me your opinion on the card that I point out to you and that I will buy shortly. Thanks again, best regards.
    David

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    Hi David;

    I'm enjoying the discussion. This sort of thing is exactly what PhotonLexicon is all about.

    Quote Originally Posted by davidmaster View Post
    Just today the cards dedicated to Fb4 are available again from Stanwax, I am attaching the manual
    Thanks for linking to the manual for the FB4 version of the Stanwax safety board. Reading through the manual, it appears that the board only supports a single attenuation method, which is to crowbar the laser driver modulation inputs to ground. This is a very good attenuation method, but it is only one. I don't see any other contact or output on the board that could be used to trigger a second attenuation method, such as a shutter or a relay that interrupts the DC power to the laser drivers.

    The original Stanwax board was similar, in that it had a single relay that would open or close based on the status of the safety circuit. It was left to the end user to integrate this single relay into the projector's internal wiring so that you had two separate attenuation methods that would activate when the relay opened. (Usually this required the use of a second relay or solid-state switch of some kind.)

    I remember that Rob was talking about upgrading the original design several years ago. He mentioned adding the solid-state switching circuitry to the board so that the modulation inputs would be grounded when the interlock was triggered, but I did not realize that he was also planning to do away with the relay. This is unfortunate. Had he kept the relay in place it would have been simple to use it to switch off the DC power to the lasers, or to interrupt the shutter signal going to the shutter, and thus you would still have two attenuation methods. But now I don't see how it's possible to implement a second method.

    I already have a remote E-stop with a security key. I'll just have to add the reset button. The safety devices on the projector are an additional key switch and a microswitch on the case cover which are also connected in order to short-circuit the laser output. I would be grateful if you gave me your opinion on the card that I point out to you and that I will buy shortly.
    If you purchase the FB4 version of the Stanwax safety board and connect it properly, you will have a very safe projector. The key switch on the projector should be connected to the key switch connector on the board, while the remote e-stop and remote key switch will connect to the remote connector. (The reset button also connects to the remote connector.) The microswitch on the case cover can be wired in series with the key switch on the projector.

    I should point out, however, that while this will make the projector very safe, it still will not fully comply with the regulations I've discussed above, because it will only have a single attenuation method. To be fully compliant, you need two separate methods, and I honestly don't see a way to implement that using the FB4 version of the Stanwax board. (If I am missing something, I hope someone will correct me on this!)

    But as I said, there is nothing forcing you to comply with these standards if you are using the projector in your home for your own personal use. So in your case, I agree that this is probably more than "good enough" for home use.

    Adam

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    Quote Originally Posted by buffo View Post
    I'm enjoying the discussion. This sort of thing is exactly what PhotonLexicon is all about.

    But as I said, there is nothing forcing you to comply with these standards if you are using the projector in your home for your own personal use. So in your case, I agree that this is probably more than "good enough" for home use.

    Adam
    hello Adam
    thanks again for this nice discussion. As I said, I'm a hobbyist (like so many here) and all the money invested ... well, it's gone.
    I would like to implement a mechanical shutter and I know the validity of the Scannermax but at the moment I cannot invest an additional $ 600 plus shipping and customs. If you know some other model (and a site where to buy it) a little cheaper would be appreciated. At this point I would use the Stanwax card to interrupt the analogue driver signal and the PWM output of the Fb4 to drive the shutter.
    As a second option, I could use the Stanwax card and in parallel to the E-stop a relay to interrupt the driver's DC power supply. In both cases, I would have the double security system according to standards.
    What do you think about it?
    Thanks

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    Quote Originally Posted by davidmaster View Post
    I'm a hobbyist (like so many here) and all the money invested ... well, it's gone.
    HAHA! Buddy, you can say that again! I don't even want to *think* about how much money I have spend on lasers in my life. Even though I have been doing commercial shows on a part time basis since 2012, I know that I still end up spending more than I earn.

    But, of course, we are all into lasers because we love them, so that takes some of the pain away from all the money we've lost. Or at least, that is what I keep telling myself!

    I would like to implement a mechanical shutter and I know the validity of the Scannermax but at the moment I cannot invest an additional $ 600 plus shipping and customs.
    Wow! I didn't know that Pangolin was charging $600 for a single Vrad actuator! That's really expensive. I thought they were only $150 or something... (Are you sure about that price?)

    Although now that I think about it, the last time I looked at the Vrad was back when they were using the larger laminated body that looked like a big padlock. The new design is based on the Compact 506 scanner design (which is why they now call it the Vrad 506) and this is a much smaller design. I agree that the 506 scanner is a superior design, but even so I'm shocked that they are charging $600 for a single actuator. That's just not reasonable.

    You may want to have a look on E-bay and see what you can find. Sometimes I see used GM20 actuators on E-bay for $75-$125. Those units are extremely robust and are probably the most common shutter actuator you'll find. I've also seen several E-bay listings for an over-built shutter called the LST400 that would probably work well if you have enough space to fit it inside your projector. There are also several designs that use spring-loaded rotary solenoids (like a Ledex), but those tend to be very loud when they actuate. Or you could post a new thread in the buy-sell area stating that you're looking for a shutter actuator and see what sort of replies you get...

    Here are a few E-bay links I found with just a quick search:
    https://www.ebay.com/itm/GSI-Lumonic...t/153877225093
    https://www.ebay.com/itm/NM-Laser-Pr...-/202609067650
    https://www.ebay.com/itm/LPL-Laser-S...0/401443392703

    I would use the Stanwax card to interrupt the analogue driver signal and the PWM output of the Fb4 to drive the shutter.
    Does the shutter signal from the FB4 pass through the Stanwax board before going to the shutter? I didn't see a connection for that on the Stanwax board. If the shutter signal does go through the Stanwax board, and if the Stanwax board will disconnect the shutter signal when the interlock circuit is triggered, then this would be an ideal safety solution.

    Assuming that the Stanwax board operates this way, then adding the shutter as you are planning to do would satisfy the US requirement for having two separate attenuation methods that are triggered upon an interlock condition. (The second attenuation method would be the Stanwax board disconnecting the color modulation signals and crowbarring the modulation inputs on the laser drivers to ground.)

    I could use the Stanwax card and in parallel to the E-stop a relay to interrupt the driver's DC power supply.
    The relay coil would need to be powered by the Stanwax board when it is in the "run" mode, and the relay coil would have to be de-energized whenever the Stanwax interlock was active. I don't see any connections on the FB4 version of the Stanwax board where you could connect such a relay though. (The older version of the Stanwax board actually had a single relay mounted right on the board that would allow for this, but the FB4 version doesn't have this relay.)

    I have reached out to Stanwax (Rob) again. Hopefully he will join this discussion thread soon and comment about the FB4 version of the Stanwax board. There *should* be a way to do this, but as I read through the manual I just can't see how. (Then too, it may be that your proposed solution with the shutter as explained above will be sufficient.) But before we go further I think we need to bring Rob into this discussion to be sure I'm not missing something obvious with the new FB4 version of the Stanwax board.

    Adam

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    Hi Adam And David.
    Adam is right that the FB4 version of the S4 board does only have a single method of attenuation, whereas the standard versions of the board (S4i and S4p) that use the same solid state shutter circuitry, do still have the relay for mains power control, on board. There is good reason for this and itís in no way an oversight! As the S4FB is designed to piggy back onto an FB4 I didnít want to be putting mains in such close proximity to the FB4 as the clearances would have been a bit too close for comfort. The idea was that if required an additional satellite board could be used, to be switched from the Emission LED output to flip a relay in as required, this could control the power to the laser drivers in much the same way as all other versions of the ILDA interface board.
    However when the board was first made, in April 2016, it was introduced without this optional add on and in four years I have only been asked about this once and we came to a solution. That lack of demand has led me not to waste time and effort in producing something with little or no no take up.
    That said if you did want to add a relay for this task it would be really simple to do and David if you you need this please let me know and I will either make something for you or give you simple instruction as to how it can be achieved.
    If you have any other questions relating to this or any other stuff I make just ask.

    Rob
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    Quote Originally Posted by stanwax View Post
    Adam is right that the FB4 version of the S4 board does only have a single method of attenuation
    Hi Rob! Thanks for chiming in here, and thanks for confirming that my interpretation of the new FB4 version was correct.

    As the FB is designed to piggy back onto an FB4 I didnít want to be putting mains in such close proximity to the FB4 as the clearances would have been a bit too close for comfort.
    I agree that putting mains power that close to the FB4 would be a bad idea!

    However, I should point out that using a relay to interrupt the main AC power is, in fact, *not* an acceptable attenuation method - at least according to the USA regulations. I mentioned this in the discussion above, but the idea is that if you drop mains power you will still have some lingering DC power to the lasers for a short time period after the shutdown because of the large filter capacitors on the output of the DC power supply.

    Instead, the standard is to use the relay to interrupt the DC power going to the lasers. That will extinguish the lasers more or less instantly. However, these days it's common to have two DC power supplies for the lasers: 5 volts for red and 12 volts for green and blue. So you would need a double-pole relay.

    if required an additional satellite board could be used, to be switched from the Emission LED output to flip a relay in as required
    I was wondering about using the emission LED circuit, but I had two concerns: First, how much current could one safely draw from this LED circuit? (This would place limits on the coil resistance used for the relay.) And second, I thought that the emission LED was a bi-directional circuit... Isn't that how you achieved the two different colors on the LED? If so, then you would need to add a diode in series with the relay coil to prevent operation except when the LED was solid red. Also, isn't there a "flashing" mode for the LED during the startup delay where it switches between green and red? If so, that would cause the relay to pulse on and off during the startup delay, right?

    in four years I have only been asked about this once and we came to a solution. That lack of demand has led me not to waste time and effort in producing something with little or no no take up.
    Yeah, I agree that it doesn't make sense to modify the entire board just to comply with the USA requirement, especially since you've only had a single inquiry about it. I know that everyone I've spoken to here in the USA who use the Stanwax board for their interlock are using the original design (like I have), so this isn't an issue. It would only be an issue if someone in the USA wanted to use the FB4 version...

    I do have another question, and that relates to the shutter signal from the FB4. Does the shutter signal pass through the FB4 version of the Stanwax board? And if so, is that signal interrupted when the interlock is triggered just like the color signals are?

    Adam

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