Cable robot

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A parallel cable robot (English: cable-driven parallel robot or wire robot) is a special type of parallel robot in which cables are used as motion-transmitting components.

definition

A cable robot is a parallel manipulator in which flexible transmission elements such as plastic or wire ropes are used instead of rigid rods. The mobile platform of the cable robot guides the tool, the goods to be handled or a sensor and is braced by the cables against a supporting structure. The platform is firmly clamped in one place by the ropes so that it withstands forces and moments without pendulum or swinging. If the effective length of the ropes is changed, for example by windings , the movable platform can be moved in up to three translational and three rotational degrees of freedom . A robot controller calculates the individual rope lengths and synchronizes the movement of the winches so that the platform can be moved in a well-defined manner both in terms of time and space.

Essential properties

The main limiting factor in the development of faster and larger robots is the dead weight of the robot structure. The potential for optimization through lightweight construction and new materials has already been largely exhausted. The comparatively large dead weight of industrial robots is due to the fact that the support elements have to be designed against bending, which leads to large cross-sections and thus a high weight. With parallel robots, slimmer and thus lighter components are used, because here the more favorable load case of a compression rod is used as a basis, which must be designed against kinking. Furthermore, with a parallel robot, the moving mass can be significantly reduced, since the heavy motors can be installed in such a way that they do not have to be moved, or only slightly, by the robot. A parallel cable robot uses taut ropes instead of rigid rods for the transmission of motion. As a result, the motion-transmitting ropes must be designed exclusively for tensile forces. Steel cables are very well suited for this type of load and are very well understood as machine elements. With synthetic fiber ropes , a particularly favorable ratio between the payload and the moving weight of the robot is achieved. In a typical industrial robot, the ratio of payload to moving dead weight is around 1:10. In contrast, a typical cable robot has a ratio greater than 10: 1, so that it outperforms industrial robots by a factor of 100.

advantages

The kinematic concept of the cable robot has a number of conceptual advantages over conventional robot technology:

  • Enlargement of the possible working area by a factor of more than 10. Industrial robots are limited in their ranges to the lengths of their arms of a few meters. The working area can be expanded in one direction with expensive linear axes . With cable robots, on the other hand, it is possible to expand the working area in height, width and length. In this way, a robot system can be built that encompasses an entire hall.
  • Enlargement of the possible payloads by a factor of more than 10: The winches of cable robots are related to the well-established crane winches and enable extremely large loads to be carried. With reduced dynamics, payloads of several tons are possible.
  • Higher speeds and accelerations due to lower moving mass: If a higher acceleration is necessary for the process, this can be achieved with more powerful motors. While the structure of industrial robots has to be completely redesigned, the greater force of the cable robot benefits the end effector without significant adjustments to the winches and thus allows greater accelerations and consequently shorter cycle times .
  • Extremely high energy efficiency : Due to the drastic reduction in the moving mass, only the energy required to move the products needs to be used. The loss for the acceleration and deceleration of the robot structures is largely eliminated.
  • Simple and modular structure of the robot's mechanics. The cable winches form simple, universal drive devices that can be configured for a variety of applications. The modern control technology with its field bus systems supports the decentralized control of the cable winches and enables a plug-and-produce system. Furthermore, many variants can be configured from fewer basic designs of cable winches.
  • Freely configurable: The size of the cable robot can be selected continuously without changing the hardware, as the cable winches can be positioned at any distance from one another.
  • Reconfiguration: The modular structure also benefits the flexibility of the systems that have been set up. The working area can be varied when the positions of the winches are changed. By exchanging the gear stage on the IPAnema demonstrator, it was proven that the cable robot can be efficiently adapted to a new task with regard to the parameters workspace, payload and dynamics. The workspace volume and the payload were increased by a factor of 10, while the speed was reduced to 2 m / s.

disadvantage

  • The transmission of movement through ropes is less accurate compared to other types of robots. Therefore, cable robots are not suitable for applications that place the highest demands on positioning accuracy.
  • Since the platform is guyed with ropes from several sides, accessibility problems can arise. Such restrictions arise especially when the movable platform has to be immersed in other structures.

Well-known cable robot systems

The following cable robot systems are typical examples

  • The cable robots of the IPAnema family, Fraunhofer IPA, Stuttgart
  • CableRobot Simulator from the Max Planck Institute for Biological Cybernetics , Tübingen
  • The NIST's Robocrane robotic crane
  • Five hundred meter Aperture Spherical Telescope (FAST), a radio telescope in China
  • The rope camera Spidercam or the Skycam system
  • The SEGESTA prototype at the University of Duisburg-Essen, Chair of Mechatronics
  • The CoGiRo prototype was built in a cooperation between the French institute LIRMM and the Spanish institute TECNALIA

Initial studies show a wide range of possible applications:

  • At the University of Duisburg-Essen, Chair of Mechatronics, a storage and retrieval system based on cable robot technology was tested
  • The TU Hamburg-Harburg and the University of Duisburg-Essen jointly developed an active suspension system for a wind tunnel
  • In the EU project CableBOT, applications in the field of aircraft maintenance and the manufacture of large components were examined.

literature

Web links

Individual evidence

  1. ↑ Parallel cable robots. on: ipa.fraunhofer.de
  2. ↑ see YouTube video about the robot (2015) at https://www.youtube.com/watch?v=cJCsomGwdk0 , accessed May 11, 2020, YouTube channel MaxPlanckSociety