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Innovation in lightweight, low cost robotics

Justin Leonard, director at Igus UK, looks at the development of modular joints for robots and some of their applications.

With pressure across many industries to work more efficiently, there is increased demand for simple lightweight and cost-effective robotic systems. The challenge of developing strong, cost effective and lightweight joints for robotics and for integrating these with a central drive system has been achieved by Igus specialists, and is a real innovation in the field of low-cost robotics.

Igus has developed robolink, a multi-axis joint for humanoid robots and lightweight automation applications. A completely modular system, robolink combines enormous design freedom with simplicity and is particularly well-suited where mass, cost and complexity are to be kept as low as possible.

The initial concept came about during the company's involvement as sponsor to teams competing in the Robot football World Cup (RoboCup) from 2006-2008. RoboCup attracts teams of engineers and computer scientists from around the globe, where they pit their wits against each other in the football-field of robotics and artificial intelligence.

Igus' team of engineers set about creating a robotic joint design with good transferable torque characteristics between the articulated joint and rod, low cable friction and optional integrated magnetic sensors to measure and transfer the position of the articulated joints. Prior to launch, several Igus beta-testers were provided with robolink prototypes for use in a wide range of trial applications; these ranged from maritime robots for use with underwater vehicles, through to mobile robots on the ground, used for handling contaminated or explosive materials. Other examples include humanoid robots, camera guidance equipment and systems for facilitating interaction between man and machine. Further trials were carried out in the medical industry, as well as in the field of animatronics.

Then, with the feedback from these customers, the company continued to develop a full range of articulated joint modules and accessories for robotic applications.

Lightweight joints
At the heart of the robolink modular system are the lightweight, maintenance and corrosion-free joints with tribologically optimised plastic bearings that are driven via cables and can rotate and swivel freely. To articulate the multi-axis joints, Igus has developed flexible Bowden cables with high-performance polymer jackets that combine low friction values with a long service life. The cables have extremely small bending radii, making highly flexible movements possible and are suitable wherever frequent relative movements take place.

The robolink's core consists of lightweight plastic joints that are controlled via cable pulls that transfer tensile forces - similar to how tendons function in human muscle actuation. At the same time, cable sheaths hold steady while the inner cables move - similar to how a bicycle's brake cables operate. Cable pulls run through the joints and arm tubes, from one joint to the next, with just two cable loops necessary to enable each joint to rotate and swivel freely.

The robolink accessories include mounting plates, angular encoders, various drive wheels and pulleys. Also, the supplied arm tubes can be made of aluminium (standard), glass fibre or carbon fibre reinforced plastics to save weight and decrease operating power consumption. For design flexibility, drives and controls are compatible with pneumatics or electrics.

On the electro-mechanical side, Igus has developed space-saving drive units, available in different performance classes, with four or five drive motors provided in a housing. In addition, the drive wheel can be attached to a wide range of different motor or gear shafts and then connected quickly and easily to the wear-resistant cables. Tensioning of the cables can also be achieved simply using a split drive wheel with a torsioning tool. Simple control software is in early development to intuitively program and store all the movements of a 4-axis jointed arm.

Robolink is lightweight: one robolink including cables weighs just 380g and the aluminium tube is 270g/m. The transmitted torque for the rotational movement in continuous operation is 5Nm and transferable torque for the pivot movement is 10Nm, with a drive force of the cable tensile strength being 400N.

The Igus robolink humanoid robot joint is chemically resistant, corrosion resistant, low friction and virtually maintenance-free. With this new product range, Igus has met customer demands for an all-in-one modular joint for use in humanoid robots and lightweight handling applications. Robolink provides a simple, lightweight and economical solution in these, with a long service life.

Igus (UK) Ltd

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