1、2011 IEEElRSJ International Conference on Intelligent Robots and Systems September 25-30, 2011. San Francisco, CA, USA Wrist and Forearm Rotation of the DLR Hand Arm System: Mechanical Design, Shape Analysis and Experimental Validation Werner Friedl, Hannes H6ppner, Florian Petit and Gerd Hirzinger
2、Institute of Robotics and Mechatronics, German Aerospace Center (DLR), Wessling, Germany E-mails:Werner.Friedl.Hannes.Hoeppner.Florian.Petitdlr.de Ahstract- The DLR Hand Arm System is based upon the variable stiffness concept which has been recently developed to improve impact robustness and energy
3、efficiency of modern robots. This paper continues the work on the bidirectional antagonistic variable stiffness (BAVS) joint concept which is an extension of antagonistic joints. Three mechanical setups utilizing different spring and cam disc combinations to implement a desired torque-stiffness char
4、acteristic are analyzed. Two BAVS joint solutions as used for the wrist and forearm rotation of the DLR Hand Arm System are presented. Furthermore in the experimental section torque-deflection calibration and drive redundancy are validated. I. INTRODUCTIONRecent research led to the development of th
5、e variable stiffness joint technology for robots. As reported in 1 DLR has developed the biologically motivated variable stiffness robot arm called the Hand Arm System (HASy) in the past. The robot provides 26 degrees of freedom (DOF), where 19 DOF are mounted in the hand and seven DoF in the fore-
6、and upper arm integrated with all electronic devices. Several Variable Stiffness Actuators (YSA) used to adjust the position and stiffness simultaneously have been analyzed by various researchers 2 3 4 5 6 7. Using YSA provides several benefits as e.g. the intrinsic compliance gives the possibility
7、to store mechanical energy in the joints similar to the human. The low pass force filter properties of elastic elements are especially relevant for robustness reasons in the hand. Furthermore, the energy storage property can be used for highly dynamic tasks as throwing a ball or during walking. Pass
8、ive compliance is also discussed in the context of human robot safety 8. While the YSA idea is similar for all the mentioned joint prototypes, the mechanical implementation varies widely and the evaluation of different VS joints is ongoing research 9. Therefore also multiple different VS joints have
9、 been implemented in the DLR Hand Arm system. For the 19 DoF of the hand 10 an antagonistic principle is used similar to the human hand with its elastic tendons. The arm joints 1-4, namely the elbow and the three shoulder joints, are implemented by Floating Spring Joints (FSJ) 11. A principle called
10、 the BidirectionalAntagonistic Variable Stiffness (BAYS) 12 concept has been used for both the forearm and the wrist joints. The objective of this paper is to introduce the developed BAYS joints used in the HASy. This paper is structured in the following way. We beginby evaluating the requirements a
11、nd the benefits of the BAYS design compared to other YSA principles in the context of the DLR Hand Arm System. Next we analyze the results of a desired torque-stiffness curve for the mechanism cam discs which are responsible for the VS properties of the joint. We will focus on different combinations
12、 of cam discs and linear springs for BAYS joints followed by the resulting mechanical design of the forearm and both wrist joints. Finally we will validate the capability of BAYS joints with first measurements and show results of a implemented automatic stiffness adaption. II. BAYS JOINTThe DLR Hand
13、 Arm system incorporates several different joint types. The BAYS joint principle was used for the implementation of the wrist and forearm joints. This choice follows from the requirements as presented in the following. 2） RequirementsDue to the location of the wrist joints and the forearm rotation j
14、oint, the requirements compared to other HASy joints are different: Wrist: In order to achieve the same size as the human wrist both wrist joint actuators can not be placed coincident to the joint axes, but are placed in the forearm close to the elbow. Thus the torque of the motors had to be transfe
15、red from the forearm to the wrist, similar to the power transfer implemented by tendons in the finger joints. Wrist: Furthermore the mechanical power transfer had to be as stiff as possible in order to achieve a direct coupling of the actuators to the wrist. This is important as the motion of the fi
16、ngers is coupled to the wrist to some extend. Thus rather flexible tendons can not be used. Forearm: A main challenge for the forearm rotation joint is to transfer the electronic power supply cable, water cooling tubes, and the communication bus cable to the forearm, while allowing a rotation range of 1800. On the other side the power to size ratio of the forearm and both wrist joints had to be optimized b
