MARCH 9--Production robots, which play a vital role in automotive manufacturing, require elaborate safety systems to ensure people who might accidentally get in their way are protected from injury. DaimlerChrysler is about to test a new concept at its Sindelfingen plant--SafetyEYE--designed to monitor a robot's radius of action. Group researchers in Ulm have provided the algorithms needed to process the images.
Robots can stack and pallet goods, weld, bolt, glue, drill, paint, and polish workpieces. These versatile pieces of production machinery can accomplish a vast range of operations faster, more precisely, and more consistently than the most conscientious workers. In fact, there's only one thing they lack: the ability to perceive workers in their midst. As soon as they are switched on, they will continue carrying out their programmed operation until someone presses the stop button or pulls the plug. That's why robot stations must be made safe for workers.
Optical devices such as light barriers and laser scanners can't monitor volumes. They erect a kind of optical barrier marking a danger zone's boundary. They can only be installed where there is an unobstructed view of the area under surveillance. In instances where this isn't possible, the workstation must be made safe with additional systems, such as pressure mats.
All of the safety systems currently in use are connected to the robot's emergency stop function. This means that as soon as the alarm is activated, the robot is immediately brought to a halt. Before production can be resumed, however, the robot must be returned to exactly the position it was in immediately before the emergency stop was activated. This consumes valuable time and drives up costs. Depending on the specific type of robot station used, the safety systems needed can also be very expensive--in some cases more costly than the robot itself.
For Anton Hirzle, head of process development for plant and control technology at the Sindelfingen plant, and Rainer Ott, former head of industrial image processing at DaimlerChrysler Research, these were good enough reasons to create a new concept. Their solution was to use a combination of cameras to produce a three-dimensional image of the protected area. This way, they reasoned, arithmetical methods could then be applied to the data to identify any objects penetrating this space.
SafetyEYE's sensor unit, which is currently undergoing tests at the Sindelfingen plant, features a total of three eyes. For humans and technical systems alike, two eyes are required to see in three dimensions. SafetyEYE, however, has been given three CMOS optical sensors to enable it to measure horizontal lines within a triangulated system and thereby precisely determine object distances along such a line. The sensors can produce a usable picture of every part of the monitored zone, even when the area encompasses extreme variations in brightness--a range of as much as 1 million to one. As a result, there is no danger of producing images that are overexposed or that have dark patches.
Unlike conventional robot stations, which are generally cordoned off with barriers and protected by other visible safety systems, the test bay for SafetyEYE is completely open, seemingly unsecure. Apart from the production robot, the only other piece of equipment to be seen is a metal mast slightly over 2.5 m high that supports an aluminum plate to which the three sensors have been fixed. The plate is positioned in such a way that the three sensors have an unobstructed view of the robot's complete radius of action.
Only a look at the corresponding monitor shows just how well the danger zone is protected. Superimposed on the black-and-white image of the area around the robot are colored cubes and squares. The latter represent the robot station's danger areas, which the computer program that controls SafetyEYE defines in terms of spatial coordinates. These correspond to all the space segments penetrated by the robot's moving parts during one complete working cycle. Taken together, these segments form a kind of "safety cocoon" around the robot. Objects outside of this zone are in no danger, but those within it are at risk.
And the new system offers many advantages. It only takes a couple of hours to create a safety cocoon in a workstation. By contrast, at least one full day is needed to position, set up, and check conventional safety systems. Likewise, the costs of SafetyEYE monitoring are highly competitive.
For more information go to www.daimlerchrysler.com.
