How robots avoid collisions and do more work

To remove the risks of collisions between robots, and increase robots' versatility, Fanuc Robotics Europe has developed two important program functions.

To remove the risks of collisions between robots, and increase robots' versatility, Fanuc Robotics Europe has developed two important program functions.

These developments are particularly important for tasks in automotive body assembly shops where robots are concentrated in a confined area of operation.

The first function is the Approach Deterrence Function software, which prevents any crash from taking place between robots and between robots, tooling and other assembly system components.

The Approach Deterrence Function (ADF) uses Fast Ethernet links to continually monitor the distance between robots, end-effectors, and tooling.

When the distance becomes less than a preset value, the robots decelerate quickly to a stop, thereby preventing a crash from occurring.

The second function is the Robot Link function, which allows a group of robots to work together to share the effort required to move large payloads.

The robots can work independently or with synchronous motion.

The real-time synchronous motion is achieved using the high speed Ethernet and separate communications processor.

The first major production application of ADF is in one of the Nissan bodyshops in Japan.

Robot collisions are most likely to take place during setting-up and re-configuration of cycles.

ADF prevents such collisions.

ADF is a development of Fanuc Robotics' High-Sensitivity Collision Detection (HSCD), now installed on over 4000 robots throughout Europe.

The Robot Link Function will allow, for example, two or more robots to carry and manipulate a large sub-assembly, or a complete car body, thus replacing a conventional conveyor system.

Robot Link allowed four Fanuc S430iW robots to carry a complete 'Smart' car during a recent in-house demonstration.

The first installations of this new function in Europe are due to start production at a Honda plant, in mid- 2001.

Fanuc Robotics is tendering to Europe1s leading automotive producers for robotic systems employing ADF and Robot Link functions.

Approach Deterrence Function: Robot collisions have been a major R and D project of Fanuc from the very onset of robot control systems.

In 1995, Fanuc Robotics introduced High-Sensitivity Collision Detection (HSCD) into the European Bodyshop market for the Opel Astra project.

This function has replaced the traditional safety-clutch devices, used to protect welding guns and end-of -arm tooling, with smart software.

The results were significant reductions in hardware costs and effectively increased robot payloads.

Recently, HSCD has been further refined.

It was first introduced on the R-J2 controller, and on the new R-J3i controller, which features significantly increased processor capacity and, therefore, increased sensitivity.

HSCD works by predicting and measuring motor currents.

A spin-off has been the "Payload Identification" Function.

The function allows the robot to measure the mass, moment and inertia of its payload, that is, of the combined end-effector and part.

The robot is therefore able to automatically adjust its motion parameters to give optimum motion performance.

Very importantly, it allows the user to be sure that the robot is not overloaded.

The arrival of high-speed Ethernet communication systems opened up new applications in robot systems monitoring and control.

The systems made possible the continuous monitoring of the distance between robots.

To do this, the robots have be in continuous high-speed communication with one another.

The Fanuc R-J3i controller achieves the continuous monitoring objective using two basic functions: * A high speed (100BaseT) Ethernet connection as standard on all robots, and * A separate communications processor to make sure that the communications processing does not affect robot motion performance.

The robots, end-effectors and tooling are all modelled as 3-D objects.

All interferences between these objects are monitored.

So the system prevents crashes between all parts of the robots, that is, the Oback end1 of the robot as well as the Tool Centre Point (TCP).

"It represents a significant step forward from earlier functions, which merely monitored the position of the TCP and ignored the rest of the robot arm," said Fanuc Robotics Europe1s engineering manager, Nigel Ramsden.

The robot computer models are dynamic and reflect the actual positions of the robots.

The tooling models can also have dynamic features, so that the model of a clamp can reflect it's actual status, whether open or closed.

The advantage of ADF over standard robot interlocking is that it is always active, during manual operation as well as automatic operation.

It protects against operator error during set-up and production.

Robot Link Function: The "Robot Link" function allows a group of robots to work together to share the effort required to move large payloads.

The robots can work independently or with synchronous motion.

The real-time synchronous motion is achieved using the high speed Ethernet and separate communications processor.

The Robot Link Function considerably increases the mechanical dexterity of robotic systems.

Instead of the robots standing idle after performing, say, spot-welding tasks, they can be used to transfer say, a floor pan assembly, to the next operation.

Another example is where it may be more advantageous to for two robots to manipulate a large assembly under a pedestal spot welder, rather than invest in expensive manipulation jigs to present the assembly in the right attitude for robot access.

A number of robots could perform welding, riveting and other functions as well as manipulating the assembly.

The advantage here would be in low-volume production, where normally, the investment in manipulatory jigs and fixtures would not be economic.

The robots, on the other hand, could benefit from the Robotic Link Function to perform the handling tasks as well as joining, welding, buffing and so on.

To-date, Fanuc Robotics has installed over 16,000 robots in Europe, most of which have the HSCD function.

The company is also quoting for on-going European projects, for which the ADF, as well as the HSDC options are available.

ADF and HSDC options are also available to users of Comau robots equipped with Fanuc R-J3i robot controllers.

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