One control synchronises three 6-axis robot paths

The Swedish headquarters of robot company, Motoman, has been granted a European patent for the synchronous control of twin- and triple-robot systems.

The Swedish headquarters of robot company, Motoman, has been granted a European patent for the synchronous control of twin- and triple-robot systems.

Central to the application is the unique ability of the company's XRC robot controller to co-ordinate the movements of up to 27 separate axes simultaneously.

Its introduction in 1999 marked a major advance in technology in that it was, and still is, the only control capable of synchronising the movement of three 6-axis robots plus peripheral equipment such as gantry systems, linear tracks and rotary indexers.

Only two robots could be handled synchronously by the previous Motoman controller, although when introduced in the mid 1990s at the request of Toyota and other car manufacturers who wanted to increase the versatility of their welding systems, it was the most powerful then available.

Prime reasons for manufacturers wanting synchronous systems are twofold.

First, having another robot hold and manipulate the part for welding, or indeed machining, painting, gluing or any other process, eliminates the need for expensive jigs; and secondly, productivity can be doubled or trebled by having two or three robots working on a part simultaneously.

What distinguishes robot programming via the Motoman XRC hand-held pendant is that the motions of all robots are controlled as a single entity, rather than having to program one first and subsequently the other robot(s) to fit in with the motions of the first one or two.

Fully synchronous programming results in no cross-talk between separate robot controllers and hence no time lag between their relative movements.

In practice, savings of up to 25 per cent in cycle times can be achieved.

Moreover quality is normally enhanced.

For example, a weld bead may be laid more accurately in the absence of hysterisis in the system and there is no risk of burning through the metal if the arc-off command is received slightly later than the instruction to stop the torch.

The XRC controller incorporates ample digital I/O capability for switching welding power supplies, paint spraying units, machine tools or other equipment.

Multi-tasking capability allows up to six separate operations to be executed at once.

As well as having increased functionality, the control incorporates refinements such as variable collision sensitivity, whilst advanced robotic motion control optimises acceleration, deceleration and speed for circular and corner movements.

Likewise, inertial compensation via the path control function maintains path accuracy during high speed movements.

The unit is designed for ease of installation and has minimal space requirements.

Plug-in cable connections are used, while additional expansion units can be added and docked into the main controller using ports on the top and sides.

Compatibility with Ethernet, Profibus, Interbus-S, Device-NET and other factory networks allows the system to be controlled and monitored remotely.

At Motoman Robotics (UK)'s open house in April 2002, both twin- and triple-robot systems were demonstrated welding automotive components, the triple system being deployed on vehicle exhaust manufacture with the added assistance of Motoman's new servo-powered torch, SAWK-350.

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