CLOSER QUARTERS

Today?s industrial robots are fairly well behaved creatures, doing only what they are programmed to do ? as long as nobody gets in their way.

Since robots move at astonishingly high speeds and often carry loads weighing up to hundreds of kilograms, humans need to keep their distance. As such, humans and robots are usually separated by specially designed safety fences, like visitors and tigers in the zoo. However, because the cost of this kind of safety equipment can be very high, it is actually slowing the advancement of robot-based automation in industrialized countries.

Of course, where humans and robots are working together, the need for safety is paramount. According to European and North American regulations for occupational health and safety, even a potential malfunction of a robot?s controller hardware or software ? however unlikely ? is considered a serious risk and must be anticipated. This means that if the door to a robot cell is opened, for whatever reason, a contact must be tripped and the machine shut down immediately.

To avoid even a theoretical failure of this safety device, dual channel switches and circuits are required, as are fitted in all safety circuits of conventional robot controllers. In addition, to avoid accidents caused by robot collisions, mechanical cams are used to activate position switches mounted on the robot axes, thereby limiting the robot?s range of motion. Unfortunately, these expensive, hard automation methods actually curb the efficiency of a machine that was originally intended to provide flexible and affordable automation.

WORKER SAFETY: A COMPETITIVE DISADVANTAGE?

The fact that accidents with robots are extremely rare suggests that adequate safety measures are already in place. Indeed, some argue that modern safety requirements have been taken too far, and that the strict regulations imposed on European and North American factories make them less competitive than rivals who are working under less exacting safety standards.

Others question why robots should have higher safety requirements than overhead cranes, for example. After all, not only do cranes carry substantially heavier loads than robots, but their manual operation makes them subject to human error. Robots, on the other hand, perform repetitive, pre-programmed tasks and generally make no mistakes.

The answer is not to compromise on the safety of robotic applications ? but to provide users with more cost-effective safety installations by utilizing the latest technological advances. By replacing expensive mechanical safeguarding equipment with more efficient and re-configurable electronic motion safety for robots, the SafeMove concept can enhance the flexibility of robotic products.

NEXT GENERATION ROBOT SAFETY

SafeMove builds on the latest developments in redundant software, electronics-based safety technology, and the most up-to-date safety regulations (ISO 10218). It allows the reliable, fault-tolerant monitoring of robot speed and position, as well as the detection of any unwanted or suspicious deviation from the norm. If a safety hazard is detected, the controller executes an emergency stop, halting the robot within a fraction of a second.

SafeMove also offers a host of new functions, such as electronic position switches, programmable safe zones, safe speed limits, safe standstill positions and an automatic brake test, which allows more flexible safety setups. Programmable safe zones can be used to ensure that the robot stays out of protected, three-dimensional
zones. These zones can have complex shapes, and can be adapted to specific installations.

Alternatively, the robot can be confined within three-dimensional geometric spaces, allowing significant reductions in the size of robot installations. In addition, these 'fences' can now be moved much closer to the robot, thereby saving valuable floor space.

Of course, it is also possible to limit axis ranges by mimicking conventional electromechanical position switches using software, but this is no longer restricted to the three principal axes of the robot: instead, all six axes can be safely limited. Axis limits can be combined logically, and work-piece positioners, linear tracks, and other external axes can be restricted without any additional effort.

In "safe standstill" mode, robot movement is inhibited completely, yet all drives are powered and the motors can still be actively controlled. The purpose of this operating mode is to allow the worker to approach the robot in safety, and even to load a work piece into the gripper or carry out maintenance on the tooling without the need to shut the robot down. This not only saves cycle time when operation is resumed, it also reduces wear on the brakes and contacts needed to shut the unit down.

In "safe speed" mode, the robot is allowed to move ? completely or partially ? at a speed that is slow enough to pose no threat to the worker, eliminating the need for a separating fence altogether. In combination with other controls ? such as confined space ? workers and robots can now perform manufacturing tasks together, something that has not previously been allowed.

The safety of a robot ultimately relies on its ability to stop, or to be stopped, when a hazardous situation arises. This stopping capability is made possible by the function of mechanical brakes on the robot motors. For this reason, SafeMove? contains an automatic brake test procedure that periodically checks the mechanical brakes of the robot ? something that would be very useful in a car!

The system uses motion-control sensors to monitor the position of the motor, and then computes the robot position in a safety-rated computer that works independently from the robot controller. A separate model of the robot mechanics, as well as extra reasoning about the nominal behavior of the servo control loop, further enhance the safety level (patent pending).

This controller is actually an independent computer that sits in the cabinet of a fifth-generation industrial robot controller, the IRC5. However, from a user perspective, it is seamlessly integrated. Events, alarms and changes of state are logged on the robot controller?s flash disk. The state of the safe inputs and outputs can be read just like normal robot I/Os and used in the robot program, even though there is no physical wiring between the I/O systems. Instead, SafeMove and IRC5 communicate over an internal network link.

Finally, synchronization between the safety computer and the robot controller must be checked after a power outage and at the beginning of each shift. This is achieved by a simple switch mounted in the cell, where it is easily accessible by the robot. The switch is visited and regularly activated by the robot ? typically every 24 hours. Since this procedure can be easily combined with regular automatic tool service operations like cleaning, dressing or wire cutting, it does not normally add to the cycle time of the installation.

PROCESS SAFETY

Robots often handle dangerous process equipment ? such as weld guns, laser heads, waterjet guns, or even radioactive materials. Such equipment needs special attention in case a fault develops, which means that it may be necessary to provide a protective enclosure around the complete robot cell that can withstand the process energy in case of a robot malfunction.

Imagine, for example, the consequences if a robot were to point an ultra-high-pressure water jet horizontally, rather than downwards, and then the jet is accidentally turned on. This is the kind of scenario that must be considered when planning a water jet cutting cell.

SafeMove performs a series of safety checks to ensure that the orientation and position of the robot tool are within a defined tolerance before the tool can be activated. Likewise, the robot is monitored continuously during operation, to ensure that the tool orientation stays within the tolerance band. As soon as this tolerance is exceeded, a safe shutdown of both the robot and the process equipment is initiated. This approach can offer drastic reductions in the cost of protective enclosures.

Most accidents with machine installations occur as a result of disabled safety equipment. Unfortunately, safety is often seen as an obstacle to productivity, and workers will sometimes take calculated risks if they feel that time can be saved. It is therefore in the best interest of both worker and employer ? especially now that safety functions can be moved from hardware to software ? to limit access to configuration data. This can be achieved by providing password-access to specially trained, authorized personnel only.

Industrial practice has shown, however, that it is difficult to keep passwords secret on the shop floor, which means that the system is often left open to abuse. To address this important issue, scientists and engineers have developed and patented a mechanism that protects the safety set-up of the system through a combination of an access-restricted configuration tools and a public activation code. This mechanism makes the safety configuration as secure as a bank account, and yet also very convenient to use.

With the features that this controller can provide, it is possible to reduce significantly the number of safety devices employed, including light curtains, safety relays, mechanical position switches, protective barriers, and so on. Plus, by replacing mechanical position switches for robots and additional axes, there is no longer any need to maintain these devices, which are often exposed to severe environmental conditions and therefore have a limited lifetime.

This approach also allows robot cells to become more compact, and flexibility is increased as safety configurations can be reset easily using software. Replacing broken-down robots which are equipped with dedicated cams and position switches used to be a lengthy procedure. Today, the time required for such repairs is significantly reduced, since the safety parameters are handled by the controller, and limit switches no longer exist.

As a result of these advances in technology, it is possible to make robots that are even more compact, since the cam rings of the past required a significant amount of space. Robots without position switches will therefore provide reductions in cost.

In addition to SafeMove, RobotStudio? is an on- and off-line programming tool that allows the visualization, programming and testing of a robot installation on an office PC. SafetyBuilder? is a secure tool for setting the parameters of, and activating, the SafeMove controller. The combination of these powerful tools allows engineers to design and test the safety zones in a virtual environment during the planning phase, and later to use the data for engineering and commissioning.

All of these advantages can be fully exploited by implementing them into the initial cell concept. Of course, it is also possible to retrofit IRC5 with SafeMove, so that new functions can be introduced into existing IRC5 installations.

This system will allow robots to realize completely new manufacturing concepts. Since humans and robots are now able to work closely together, they can now team up to become real colleagues. The powerful robot can lift and present heavy work pieces to the worker, and the worker can perform tasks that are harder to automate.

Likewise, in another scenario, a worker can load small parts from a container box directly into the robot gripper, without the need for separating turntables, receiving fixtures or roll doors, and the robot can then do the work ? perhaps even in cooperation with another robot or another worker.

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Soenke Kock works in Corporate Research at ABB AB in Västerås, Sweden; Jan Bredahl, Peter J. Eriksson and Mats Myhr work at ABB Automation Technologies AB in Västerås, Sweden; and Kevin Behnisch works for ABB Automation GmbH in Friedberg, Germany.

The ABB Group of companies operates in approximately 100 countries and employs about 120,000 people. ABB Robotics (www.abb.com/robotics) has installed more than 160,000 industrial robots worldwide.