CNC Safety Choice: Pressure Mat or Laser Sensors?
CNC owners weigh the pros and cons of various operator safety shutoff systems. January 4, 2014
Question
We are shopping for our first nested base router. I discussed the specifications of the machine with the worker that will operate it, and he told me that he has worked on two other machines, and the one with a safety mat gave him lots of problems, and the one with the safety laser (optic sensor) was fine. He felt strongly about this, and at this point he knows more than me. Can anybody else qualify the trouble (or lack of trouble) with a mat versus a laser?
Forum Responses
(CNC Forum)
From contributor L:
You don't want the mats - big waste of time and money; they will break constantly and some machines won't work properly without them.
Just paint some caution stripes down around the machine's movement area and maybe a couple of hand rails to keep onlookers from getting too close. Have multiple e-stops within reach at all times. Train your operators to stay out of the way when the machine is running and enforce it.
From the original questioner:
Will a mat-specific machine run without mat (e.g. can mats be disabled?). Has anyone ever changed a mat-machine to lasers?
From contributor L:
Depends on the machine. Some of the older machines require them to function properly and sometimes they're optional. Find out from the seller before you buy. Either way they're still more trouble than they're worth.
If they are not optional, you can sometimes bypass them with jumper wires. I wouldn't advise it unless the person doing the circuit bending knows what they're doing; as in a real machine tech and not some maintenance guy that knows a little about this and that.
If you have to replace the mats, they are not cheap, if you can even find a compatible replacement. I'm not sure about laser retrofitting, but I imagine it's a little pricey as well.
If you're using a true nesting router, I don't see a point in having either system. These systems are really only good for point to point style machines where you're constantly loading and unloading multiple zones within short cycle time; putting the operator in the direct path of the gantry.
Maybe the technology has improved with the times, but I haven't had good experiences with mats.
From contributor M:
I have used both as well. Problem with the lasers is that dust from the machine, especially cutting MDF, can easily interrupt the cycle. On the Fanuc control I used, it was an unrecoverable stop, meaning that you had to start the program from the beginning or rewrite it.
Also the lenses can just get dirty after a time, shutting the machine off.
If I had to have one, I prefer the mats. Mine are 10 years old and are running without a problem, although I admit I take a lot of care not to damage them. When one of the 3 does fail (which is inevitable and likely as not soon for me), it will be several thousand each to fix. If I had a choice I would have neither one.
If you must have a safety system, it's probably best for you overall to just get what the operator wants and be sure that you can restart a program from where the interrupt took place.
From contributor N:
Safety first. I agree with a lot that has been said. Curious on what machine your operator had problems with. When mats are installed correctly and maintained, they should last more than 10 years. There are a couple of reasons to go with the mats. First is the router dust will trigger the safety photo cells. Second is work flow. The beams will stick out at least 3 feet and there will be 3 of them. Plus you will have at least 6 photo cells to go bad versus 3 mats. True, safety mats are not cheap from the manufacturer, however these mats, when bad, can be replaced with a much better mat at a fraction of the cost.
From contributor F:
The Biesse I run is an older pod and rail with mats. I have had some false triggers from pieces of scrap that get pulled up on the piece I'm cutting, and then the router knocks it on the mat.
From contributor J:
The biggest problem with mats is where the cord attaches to the mats. This gets damaged very easily as this connection is very fragile. You will end up replacing mats every couple of years.
Lasers are a great upgrade and will last 10-15 years before needing replacing. The downside is cost and as previously stated, dust getting in the eyes and setting them off. But this can always be worked around.
I have done this switch before. Most machines that use safety mats or lasers have a safety relay that is tied in and shuts off control power to stop a machine. This is a necessary safety that is required. Just putting down tape and fencing will not stop a machine in an emergency.
From contributor O:
We have lasers on our Weeke. When we ordered it I had requested to have it changed over to the mats. Due to the cost of the changeover we left it with the lasers. This has worked out very well for us.
The lasers are on tubular steel frames that are about 18'' high and extend out from the router about 4'. Instead of bolting the frame to the floor at both ends, we only anchored the end closest to the machine. This lets us pivot the frame parallel to the machine when not in use and gains us almost the full 4' of space back for running the forklift through.
We have only had the laser tripped a couple of times over 4 years from any small parts of the frame that may get broken and pushed around when cutting. As for dust tripping them, never happened.
From the original questioner:
It seems that if we had a laser setup with the correct relay voltage, we could simply unplug the mat and plug in the laser? I'm picturing a garage door sensor across the front opening of the cage/fences.
From contributor J:
The laser has to be more than just a garage door type of safety light. You have to have a 4' range away from the machine and the grid has to be setup so that a person cannot stand inside of the beams and be able to reach the machine. Most laser eyes are now a full bar with about 1" between the safety lights. This way a person cannot reach from below and touch the machine or reach over the top. There is more required than what the older machines have. The older machines got away with just using 3-4 photo cells. This will not work today. If you modify the machine, you have to change it to current standards and use the more expensive light curtains. These are the safest.
In regards to installation, the light curtains will come with their own safety relay. You will have to remove the existing safety relay for the mats and install this new relay. This could be complicated depending upon how it is tied in and how it is reset using the existing system. If you have someone who is not familiar with the machine, they will have extreme difficulties installing the new light curtain. I know a lot of electricians are not familiar with electrical controls to be able to make this change.
From contributor D:
I have the light beams on my Biesse. We built an edge off of the table to catch any sawdust spray off the router. We occasionally have alignment issues but never a big problem.
For those of you that think you don't need them and that you can disable them, you're crazy! To have a piece of equipment that travels at a high rate of speed, weighs hundreds of pounds running with people in the safety zone is a serious safety hazard. The liability of knowingly deactivating a safety device won't go over real well in court after an injury.
I had a non CNC injury that has cost me over $60k in elevated workers comp over the last 4 years.
From contributor Z:
Try looking at a machine with bumpers. With bumpers you can walk right up to the machine without breaking a light barrier or stepping on a mat. Bumpers are also immune to dust as light barriers are. SCM has a machine called a Pratix S15B that is 5 x 12 and uses light barriers. The machine can be loaded or accessed from three sided and will stop immediately if the bumper hits you.
From contributor A:
Agree with contributor Z. We have bumpers all around the gantry of our Multicam and they work great. I don't know about the price but in my opinion they are much easier to use than lasers or mats.
From contributor I:
I have spent a lot of time with both lasers and mats. I think mats are needed on machine centers where pendulum processing of parts is the norm, but nested machines are better off with lasers. I never ran a machine with bumpers but I like the sound of it. I suspect that is the best option. I would like to hear from Thermwood or other major nesting CNC manufacturers why they don't use bumpers. I assume they have a reason.
From contributor J:
There are some manufacturers who use bumpers on their machines. It is not a common use. With bumpers there are inherent problems. You would need a shroud around the machine to attach the bumpers to. When you are using the bigger iron machines, if the bumpers are attached directly to the machine, you will not be safe. When the machine comes around to bump into an operator, if you don't have the flex of the shroud, it can still send an operator flying. These machines cannot stop instantly, so once a bumper hits you, there would still be momentum.
To get a good bumper on the machine, there is some cost and mats are cheaper. Just like mats, bumpers can suffer problems and give you issues. Bumpers and mats are designed to have a certain amount of resistance. When you step on a mat, the resistance decreases until there is no resistance. The controller will recognize this and then send a signal. If there is too much resistance, the controller will also send a signal saying a mat is activated. That is why you have a limit of how many mats can be connected to one controller. This limited resistance is a safety factor, to make sure you don't have a broken wire and the mats are attached and working. Too much resistance and it senses a problem with the wiring or a mat not being recognized. Too little resistance and it thinks a weight is on the mat making the circuit.
To get the right bumper is not easy, as not many manufacturers make bumpers. There are plenty of thin profile bumpers, but not many bigger ones. This is one factor. The cost is a second factor for not using them. Then the weight of the bigger machines and the amount of time required to bring the machine to a complete stop is another factor.
From contributor Z:
I agree that the only way the bumpers work is if they strike something, which can be unnerving. With mats or light curtains, the machine will stop once anyone enters a determined area, and the operator will never be touched by the machine. However, "send the operator flying" is an extreme exaggeration. We have a 7000 series Multicam with bumpers. We test the bumpers every week by touching them at normal operating speed (800-1000ipm) and also at the rapid traverse speed (2400ipm). At the operating speed, the gantry comes to a complete stop 1-2" after the point of contact. At the rapid traverse speed it takes closer to 4" to come to a complete stop. The bumpers are covered with a foam rubber so that even if it did hit you unexpectedly, you would barely have a bruise. The bumpers also allow you to work on or around the machine, do maintenance, load/unload parts, or clean all while the machine is running. With mats or light curtains you have to wait until the machine is done cutting before you can do anything. I'm not saying mats and light curtains don't work, it all just depends on your application. We've had very good results with the bumpers and I would recommend them to anyone looking for a good safety option.
From contributor I:
As always great answers on this forum. I like the mats on our Biesse Rover. They are 13 years old and still work. I trip them every day, but it is a minor issue compared to the alternative.
From contributor M:
I know what you mean by using the mats every day. If I need to pause my machine I can just step on the mat (although I avoid doing so when the head is traveling at 1400 IPM buried in a sheet of plywood). Quicker and more easily recoverable than a Red Button stop.
From contributor I:
Exactly. I know the mats are not meant to be used as an emergency stop. But stomping on the mats has saved many pods, tools and materials. The funny thing is I seem to step on the darn mats every time I go through the startup sequence during the homing program. I also forget that you can't hit the green button to select a zone if you are standing on the mats. It is considered a fault. I wish I could clear error messages from the zone selection/program execute controls.
