Balance and Posture Control for Biped Robots
This work presents an overview of a new approach for balance and posture control by regulating simultaneously the center of mass position and trunk orientation of a biped robot. After an unknown external perturbation deviates the robot from a desired post
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Balance and Posture Control for Biped Robots Maximo A. Roa and Christian Ott
Abstract This work presents an overview of a new approach for balance and posture control by regulating simultaneously the center of mass position and trunk orientation of a biped robot. After an unknown external perturbation deviates the robot from a desired posture, the controller computes a wrench (force and torque) required to recover the desired position and orientation, according to a compliance control law. This wrench is distributed to predefined supporting contact points at the feet. The forces at these points are computed via a constrained optimization problem, adopted from the grasping literature, which minimizes the contact forces while including friction restrictions and torque limits at each joint.
8.1
Introduction
The goal of obtaining biped robots able to interact with humans in everyday tasks and environments, calls for a proper control system that allows the robot to balance (compliantly) in the presence of unknown external perturbations. Such balance, i.e. the control of the linear and angular momentum of the system, is achieved through the application of suitable contact forces to the ground, using the finite support area of the feet [12]. Traditional approaches use a dynamics based walking pattern generator that provides desired trajectories for the underlying position controllers. The execution of such trajectories requires the addition of force sensors in the feet for implementing a Zero Moment Point (ZMP) control loop. In this way, a large range of stepping and walking motions can be generated. Several position-based balance compensators have been developed, although in general they require the measurement of force at every expected point of interaction with the external environment, which increases the computational load and creates time delays in the controller [1, 7, 20, 22].
M.A. Roa (*) • C. Ott Institute of Robotics and Mechatronics, German Aerospace Center (DLR), Wessling, Germany e-mail: [email protected]; [email protected] H. Gattringer and J. Gerstmayr (eds.), Multibody System Dynamics, Robotics and Control, DOI 10.1007/978-3-7091-1289-2_8, # Springer-Verlag Wien 2013
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Fig. 8.1 DLR-Biped: a biped walking machine with torque controlled joints
Joint torque sensing and control allows sensitive compliance and impedance control [14], but requires additional instrumentation in the drive units. Torque sensing has been applied explicitly in the hydraulic humanoid robot CB [3] and implicitly via serial elastic actuators in [17]. At DLR, joint torque sensors are integrated in an electrically driven biped robot based on the torque controlled drive units of the DLR-KUKA Light-Weight Robot (Fig. 8.1), which can be position or torque controlled [15]. Passivity-based impedance and compliance controllers based on joint torque sensing have been traditionally applied to manipulation tasks [1, 14]. The application of such framework to biped balancing control was first proposed in [9].
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