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Cable-driven robots can move heavy loads over long distances

14 July, 2014

German researchers have developed a novel robotic system in which a platform carrying end-effectors is suspended from an array of eight ropes, which are driven by winches to position the platform precisely in three dimensions with six degrees of freedom.

The researchers, from the Fraunhofer IPA institute, say that their cable robot – which they call IPAnema – is one or two orders of magnitude better than conventional robots in terms of its payload capacity and workspace area.

The lightweight robot – which operates in a similar way to the systems used to “fly” television cameras around sportsgrounds – is aimed at applications such as inspection, manipulation and assembly. It can also be used to create mobile robotic systems or to load and unload items on storage racks.

The lightweight platform appears to fly through the air. But when the winches are stationary, it stays firmly in position and, if touched, will not budge. The robot’s kinematics allow free and fully controllable motion in any direction. The forces exerted by the winches can be transmitted over long distances with almost no losses and minimal inertia.

“Cable robots can be used to automate production and handling tasks that cannot be performed by conventional robots for technical or economic reasons,” explains Andreas Pott from Fraunhofer IPA’s robot and assistive systems department. “Very short cycle times are possible in the case of small payloads. The cables can transmit the drive forces to the mobile platform almost without loss.”

“Our special focus is on system manufacturers and system integrators of robotics, automation and intralogistics,” he adds.

The cable robots can be adapted easily to meet the requirements of a particular application. Payload, workspace and cycle times can all be tailored to the task, allowing the robot to operate efficiently.

The German researchers say that their robot could improve on the pick-and-place performance of delta robots, carrying larger components or moving them through longer distances. If equipped with sufficiently powerful crane winches, the cable robots can even handle loads weighing several tonnes.

In manufacturing plants, such robots could be used to move large components, such as wind turbine blades, aircraft fuselages, ships’ hulls or large welded structures. They could also position and move tools used for applications such as laminating, grinding, polishing, cleaning or spray-painting.

The Fraunhofer cable-driven robots are controlled by eight winches which position the moving platform precisely

The German researchers have been working on the cable-driven technology since 2007 and have now reached their third generation of the technology using longer cables, higher-payload winches and integrated force-sensing.

The latest winches, powered by 0.5–7.5kW motors, can deliver forces up to 3kN and velocities up to 1om/s. The winches are controlled using Beckhoff’s TwinCat 3 control platform, while encoders are used to keep track of the cable lengths. One testbed, in Dortmund, covers an area of 10m by 17m.

Cable-driven robot technology is also being developed and applied in other parts of the world. For example, the Inria research institute in France has developed a portable rescue system that can be deployed within ten minutes and can lift loads of up to 2.5 tonnes. It operates with six degrees of freedom and encompasses a volume measuring 75 x 45 x 25m.

Other applications include a radio telescope (in China), a system to help rehabilitate injured patients by suspending them as they walk on a moving walkway, a system for suspending and moving objects in wind tunnels, a system for storing items in racks which is said to be 90% lighter than conventional storage/retrieval systems and to use less energy, and an amusement park ride (being developed in Korea).

At the recent Automatica show in Germany, Fraunhofer IPA demonstrated several potential applications for the new robot technology – including inspection, handling and assembly.  

The technology, which is said to be approaching the commercialisation phase, will be discussed at a conference in Germany in August.

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