Questions about designing a safety mat

Most robotic industries use safety mats inside the physical barrier for safety purposes. I know there are commercial ones that you can
buy, but I was wondering can we design a safety mat in such a way that it can find -for instance-the distance from an obstacle to a robot depending on a grid map? Lets say if I have the workspace around the robot to be 5*5 m^2, we divide this area into cylinders and depending on the location of the cylinder on the grid map, the robot would behave differently, slow down or shut off. What are the requirement for such a mat? power supplies? and I want it to be synced digitally to a computer via a USB.
Thx
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Pardon me, but it sure sounds like a homework problem. What have power supplies to do with mats? What is your interest in such a system? Seems counter-intuitive that a safety region should be partially compromiseable. The safety region is exactly for one and only one purpose, to make the person safe by being sure it is not in the robots area, or that the robot stops when one is. To be reduced so a person could get closer to an unsafe area seems a horrible idea. Unless you have further justification, I don't get it.
-- Randy M. Dumse www.newmicros.com Caution: Objects in mirror are more confused than they appear.
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It is not a homework problem, this is part of a bigger project I'm working on. The idea is to retain the robot to be safe but also save some work area. This safety mat is mainly used as a pressure mat the same idea as a touch screen, just to basically find the distance between an obstacle and the robot (like the distance sensor). Instead of using IR sensor/capacitor sensor on the ceiling or any other type of sensor, the idea is to use the mat to find which area of the grid the obstacle is located. Depending on the location, there are appropriate messages sent to the robot. I guess I should've called it pressure mats.
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crazygrey wrote: the robot would

it has been done by Mr Pilz with a camera
http://www.pilz.com.au/safetyeye.htm
you could use a mat, but mats are usually a homogenous thing...you would need several zones instead...easy enough to do I guess with strips of matting wired up
instead of USB, wire it to the printer port and use a BASIC or VB program to read the inputs and creat some actions
to do it with a camera...webcam and directshow filters, unless you don't have the height for viewing angle!
then do it with a ring of cameras looking in
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Maybe I am just being Obtuse(like that is odd for me ;) ) but since you know about touch screens then you know that Palm/Handheld devices used a grid to pickup stylus position, just do the same thing but on a bigger scale withthe needed Grid points or resolution.
Place sheet of the size of the mat with one side of the contact points face up. Place another with holes in it where the contact should be. Place the thrid sheet withthe contact points on it face down, align all three. Place protect rubber over the top. Connect to Circuit...
Ever take a keyboard apart? Take a look. Chances are 50/50 it will be the kind you are looking for and just do that bigger. I have made such "mats" pads in the past and used the plastic sheets from the local hobby store and a punch for a tarp eyelet to create the "holes" contact points. the contacts and traces were drawn on by a trace repair pen and a straight edge.
The Hirudinea
wrote:

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As a side note, "Safety" mats are usually not monitored by the system they are protecting. Computers fail (bad software, poor sensing etc.). When it comes to a true safety mat things get a bit more basic or at least multiple redundent.Safety requires a more direct approach such as a removal of power when safety is breached. Nothing like a high speed/high energy system that does not stop because of a software glitch. Light curtains are used but are usually not as part of the system they are monitoring, they are seperate and closed systems that have been qualified before they can be used as safety devices. Safety doors use switches that again interupt power, not send a signal to the system to stop an action. The signal may still be sent but it is not the primary "stopping" source.
Using a grid system would be ok to a point, but the final boundry ( before human interaction with the danger source) must fall into the more direct approach.
We come compacent working with computers these days as computers control more and more but software is never perfect. Safety must be.
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Thanks everyone for the help. Appreciate all the information
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