Automatic gear

Multi-robot systems provide the manufacturing industry with great flexibility, and the leading manufacturers have a range of solutions on offer.

At

, being held in Munich from 16-19 May, production and automation professionals can find out all about the latest developments in the field of 'co-operating robots' — those linked to work in synchrony — from companies such as ABB Motoman and Fanuc.

Manufacturers have developed many software and control functions for this concept. Multi-robot systems are the focus of much interest, because flexibility in terms of working hours and production processes is essential for the manufacturing industry. Such systems bring additional benefits to a range of sectors, because co-operating robots working together not only complete a task faster, but can also be used singly for other functions.

multiple robot systems are nothing new, having operated efficiently in a range of situations from small assembly cells to large spot welding production lines in the automotive sector for 35 years. What is new is the use of intelligent control to reduce tooling costs, cut set-up times and minimise time-to-market.

Fanuc Robotics' Intelligent Robots range offers Dualarm Control and Robotlink to allow multiple arms, and if required, work positioners, to be controlled by one programme. Typical applications include heavy handling and employing two arms to weld a single component while being moved continuously by the positioner. An increasing use for this multi-arm welding approach is for one robot arm to hold the work and position it relative to the other.

Fanuc sales and marketing manager Maurice Hanley said: 'Intelligent control gives robots true flexibility, and can dramatically reduce the cost of tooling and system set-up.

'This has all been made possible by integrating the intelligence into the robots' control system as opposed to costly use of external intelligent systems.

'Intelligent control of multi-robots can produce dramatic savings for businesses requiring specialist handling equipment. Using the intelligent Fanuc RJ3i controller offers the option to use Robotlink software to synchronise movements of several M-900iA 600-kg payload robots. This enables much more precise handling of heavier weights without risk of damage. For example, two robots could handle the manipulation of 1,200kg of fixtures and tooling on an inclined plane.'

Ten years ago, at the request of

and other car manufacturers looking to increase the versatility of their welding systems, Motoman was the first to introduce and patent the simultaneous control of two six-axis industrial robots.

Today, the company's NX100 controller can handle 36 axes simultaneously, allowing the movements of four industrial robots and peripheral equipment such as gantry systems, linear tracks and rotary indexers to be synchronised.

There are two main reasons for manufacturers wanting synchronous systems. First, having another robot hold and manipulate the part for other processes, such as welding, machining, painting or gluing, eliminates the need for expensive jigs. Second, productivity can be doubled, trebled or quadrupled by having two, three or four robots working on a part simultaneously.

What distinguishes robot programming via Motoman's NX100 hand-held pendant is that the motions of all robots are controlled as a single entity, rather than having to programme one first and subsequently the others to fit in with the motions of the first one, two or three. 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 Windows-based, colour controller incorporates ample digital I/O capability for switching welding power supplies, paint spraying units, machine tools or other equipment. There is flexibility in the way the external axes are configured, in groups of three so they can be switched off for repair while the other robots continue to operate.

The control incorporates refinements such as variable collision sensitivity, while advanced robotic motion control optimises acceleration, deceleration and speed for circular and corner movements.

Likewise, inertial compensation via the path control function maintains accuracy during high-speed movements. An ethernet card is built in as standard for good communication with the robots and peripherals. IP54 protection can be specified instead of the standard IP33.

Still in the automotive sector, where robots are most prevalent, ABB has supplied a global, tier one automotive supplier with 400 welding robots and state-of-the-art IRC5 control systems, destined for production plants in continental Europe and the

. The technology is being installed at the plants in

,

, the

,

and

, and in the

the robots will manufacture parts and components for DaimlerChrysler, GM, Fiat, Peugeot and Renault.

No less than 278 will operate in a MultiArc arrangement — an advanced system whereby multiple welding robots can be integrated with a part positioner, assisted by ABB's IRC5 controller.

With its MultiMove function embedded into the software, the IRC5 allows up to four robots, including part positioners and other devices, to work in fully co-ordinated operation. Such advanced functionality is made possible by the exceptional processing power of the control module computer that is capable of calculating paths for up to 36 servo axes, while directing up to four drive modules.

Robots can be programmed to carry out complex, co-ordinated activities — a typical configuration being three robots working together. One robot holds an object, while the other two work on it, thus eliminating the need for a positioner. Though the IRC5 can integrate as many as four robots at the same time, the optimum solution in the majority of industrial arc welding applications is based on a combination of two team-working robots and one positioner.

Multi robot solutions have significant advantages over single robot arc welding systems and/or conventional controllers. By using the control to co-ordinate two welding processes, synchronisation time between robots is eliminated, and cycle times are reduced.

As well as the advantages of cycle time reductions, conducting two welding processes at once improves heat distribution, thereby minimising the risk of deformations or cracks, and safeguarding quality. Using multi robot systems also reduces floor space, so it increases flexibility and minimises fixed production costs, while at the same time integrating two welding processes. This is said to be 70 per cent more efficient than a single robot solution, meaning increased output.