Institute for
Robotics and Process Control

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Multi-Sensor Integration

Playing Jenga

To demonstrate the potential of multi-sensor integration in industrial manipulation, a robot was programmed to play Jenga(External). The aim of this game is to find a loosen block in a tower of wooden cuboids, take it out and put it back onto the top of the tower. The manipulator is equipped with two cameras. One PC is dedicated for image processing and calculates the positions in space for all cuboids on-line. For tactile feedback, a six degree of freedom force/torque sensor and a six degree of freedom acceleration sensor are mounted between hand and gripper. For precise position measurements, an optical triangulation distance sensor is mounted on the gripper. Randomly, a block is chosen and the manipulator tries to push it out of the tower. If the counter force gets to high or if the cameras detect a dithering tower, the next cuboid will be chosen. Once a block could be pushed far enough, its contour is precisely surveyed by the distance sensor. Now the block can be gripped exactly centered, such that the tower will not move when closing the gripper. In order not to damage the tower, all transversal forces and torques are eliminated while pulling the brick out. To put a brick back onto the tower, a force guarded manipulation primitive is set up, which lets the manipulator stop, when a certain force is exceeded. The whole application is programmed on the base of manipulation primitives, which constitute atomic motion commands. Once the execution of a single primitive is finished, it depends on the sensor signals, which primitive will be executed next. This way a program can be summarized to a static manipulation primitive net. The path trough the net changes dynamically and depends on the situation in the work cell. At the end of each game, the tower collapses. The record height was 28 stages that means 10 additional stages consisting of 29 blocks were put onto the top of the tower. Video 1 (DivX [19.2 MB] or Windows Media [8.8 MB]) and Video 2 (DivX [16.2 MB] or Windows Media [22.6 MB]) show some sample sequences.

During the last years a hard- and software architecture for advanced control of industrial manipulators has been developed at the Institute for Robotic and Process Control. One major problem of the robotic community is, that there is huge number of publications containing highly sophisticated approaches for manipulation control (force/torque control, visual servoing, distance control, high level programming concepts etc.), but when eying onto today's industrial practice, manipulators are position controlled only and sensor integration can hardly be found. It should be one of the major aims of the national and international research community to bring research results into practice. As one contribution showing possibilities of multi-sensor integration, the Institute for Robotic and Process Control exhibited a standard manipulator, which is driven by a prototype of a new generation of manipulation controllers, at the Hannover Fair 2005. An motivating result of this exhibition was, that mainly users are interested in this kind of new technology. Robot manufacturers behaved more conservative. The exhibit was an industrial manipulator that played Jenga.

Further information may be found in our Publications. In case of any further questions please contact Daniel Kubus or Ingo Weidauer.

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