In order to employ service robots in domestic environments, it is necessary to adapt these robots to the human’s living space in the best possible way. Legged walking machines allow the climbing of stairs and stepping over small obstacles without the need of circumnavigating them.
Fig. 1: The DLR-Biped. An experimental
system for studyind biped walking.
The biped walking machine developed at DLR is based on the reliable technology of the torque controlled DLR lightweight arms. Based on the modular drive technology with integrated joint sensing and electronics, the design of a biped experimental system was possible with a minimum development time of about 10 month. The developed system utilizes link side joint torque sensors in combination with electrical actuators and harmonic drive gears. In addition to position and force controlled approaches, this system therefore allows for a detailed study of joint torque based control concepts for biped balancing and walking. In particular, the applicability of compliant impedance control, as developed for manipulation tasks with the DLR lightweight arms, to biped locomotion shall be analyzed.
Fig. 2 shows the overall kinematic structure. Each leg has six degrees of freedom. For the kinematic structure from the hip to the knee, the link segments of the DLR lightweight arm have been used, while a new lower leg was designed. The ankle pitch axis is driven by a rod mechanism by a motor located just below the knee. For the roll axis a small motor unit could be used. For the feet, the robot currently is equipped with simple plates with a minimum damping layer and a (compared to other biped robots) narrow foot size of less than 10 cm. The overall weight of the system is about 50 kg, with a mass of 18 kg in the trunk.
| Fig. 2: Kinematic structure|
Sensors and Computer system
Besides motor position and joint torque sensors, the robot is equipped with two six axis force torque sensors in the feet and an inertial measurement unit in the trunk. The robot is controlled from an onboard computer in the trunk and provides a wireless network communication with a host PC. For testing of the realtime control algorithms, dynamic simulations using OpenHRP3 and Simpack were performed.
This video shows our first experimental results on dynamic walking at the Automatica fair in June 2010.
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Development of a Biped Robot with Torque Controlled Joints, Ch. Ott, Ch. Baumgärtner, J. Mayr, M. Fuchs, R. Burger, D. Lee, O. Eiberger, A. Albu-Schäffer, M. Grebenstein, and G. Hirzinger, IEEE/RAS International Conference on Humanoid Robots 2010.