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Coupled Tendon-Driven Arm "CT Arm" BACK TO SNAKE ROBOT

CT Arm

(1990-1993) In order to conduct operations by reaching an arm into an environment complicated with machinery such as a nuclear reactor, etc., it is necessary to have an arm that can freely change shapes like the trunk of an elephant. However, this kind of multi-segmented manipulator must be equipped with an actuator that produces as large a movement as possible on the base segment, and this is difficult to be made light in weight.

The CT Arm uses the soft grip mechanism that connects links with rotationally free pulleys as indicated in Fig. 1, and is designed to be made light weight. As indicated in Fig. 2, these mechanisms of the CT Arm are arranged in parallel. When the wires of the soft grip mechanism are pulled, torque proportional to the radius of the pulley is produced on each segment. Specifically, the tension of the wire that drives the tip segment of the CT Arm produces torque on every segment of the base side. Because this torque is accumulated, the CT Arm manifests the remarkable characteristic that even as the posture where the load is the largest with the arm extended horizontally, the tensile force of the arm wires of the base side is nearly the same as at the tip.

The CT Arm-I in the photograph has a total length of 1.2 m, and an arm weight of 21 kg. The gripper and the seven segments are driven by wires that are pulled using a 100 W DC motor. A smooth, strong movement is realized with multiple degrees of freedom.

The same structure which allows coupling of the wire tension in this CT Arm can also be observed in the tendons of the finger indicated in Fig. 3. From this fact it is clear that the mechanism by which the finger can produce a large grasping force is the effect of the coupled drive of the drive tendons.

Fig.1 Soft Gripper mechanism

Fig.2 Basic structure of the CT Arm

Photo.1a Operation of the CT Arm

Photo.1b Operation of the CT Arm

Fig.3 Bone and tendon system of the finger

References:
  1. Shigeo Hirose; Biologically Inspired Robots (Snake-like Locomotor and Manipulator), Oxford University Press ,, , pp. (1993)
  2. Shigeo Hirose, Shugen Ma; Redundancy Decomposition Control for Multi- Joint Manipulator, Proc. IEEE Int. Conf. on Robotics and Automation, Scottsdale, Arizona ,, , pp.119-124 (1989)
  3. Shigeo Hirose, Shugen Ma; Coupled Tendon-Driven Multijoint Manipulator, Proc. IEEE Int. Conf. Robotics & Automation,Sacramento, California ,, , pp.1268-1275 (1991)
  4. Shugen Ma, Shigeo Hirose, Hiroshi Yoshinada, Taku Yamazaki; Development of Coupled Tendon-Driven Multijoint Manipulator, Proc. IEEE/RSJ Int. Workshop on Intelligent Robots and Systems, Osaka ,, , pp.725-730 (1991)
  5. Shugen Ma, Shigeo Hirose, Hiroshi Yoshinada; CT ARM-I: Coupled Tendon-Driven Manipulator Model I -Design and Basic Experiments-, Proc. IEEE Int. Conf. on Robotics and Automation ,, , pp.2094- 2100 (1992)
  6. Shugen Ma, Shigeo Hirose, Hiroshi Yoshinada; Design and Experiments for a Coupled Tendon-Driven Manipulator, IEEE Control Systems ,13, 1, pp.30-36 (1993)
  7. Shugen Ma, Shigeo Hirose; Development of a Super-redundant Multijoint Manipulator for Maintenance of Nuclear Reactors, Proc. of 2nd Specialist Meeting on Application of Artificial Intelligence and Ronotics to Nuclear Plants ,, , pp.1-10 (1994)
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