Double Actuator Unit with Planetary Gear Train for a Safe Manipulator

Abstract

Control of a robot manipulator in contact with the environment is usually conducted by the direct feedback control system using a force-torque sensor or the indirect impedance control scheme. Although these methods have been successfully applied to many applications, simultaneous control of force and position cannot be achieved. Furthermore, collision safety has been of primary concern in recent years with emergence of service robots in direct contact with humans. To cope with such problems, redundant actuation has been used to enhance the performance of a position/force controller. In this paper, the novel design of a double actuator unit (DAU) composed of double actuators and a planetary gear train is proposed to provide the capability of simultaneous control of position and force as well as the improved collision safety. Since one actuator controls position and the other actuator modulates stiffness, DAU can control the position and stiffness simultaneously at the same joint. The torque exerted on the joint can be estimated without an expensive torque/force sensor. DAU is capable of detecting dynamic collision by monitoring the speed of the stiffness modulator. Upon detection of dynamic collision, DAU immediately reduces its joint stiffness according to the collision magnitude, thus providing the optimum collision safety. It is shown from various experiments that DAU can provide good performance of position tracking, force estimation and collision safety.

On the Design of Human-Safe Robot Manipulators

“…Programmable Passive Compliance Choi et al (2008); Kim et al (2007); Tonietti et al (2005); Wolf & Hirzinger (2008) consists in using a compliant joint for each axis of the robot and a second set of actuators that allow the adjustment of each joint stiffness. This is obtained either by using two antagonistic actuators or by having a second actuator that adjusts the stiffness via a mechanism.…”

“…to detect a collision by monitoring joint torques or a robot skin and quickly react to maintain the contact forces under a certain levelDe Luca et al (2006); 3. to design robots that are intrinsically safe, i.e., that are physically unable to hurt a personChoi et al (2008); Kim et al (2007); Park et al (2009;; Sardellitti et al (2007); Tonietti et al (2005); Zinn, Khatib & Roth (2004).…”

Design, Development and Scaling Analysis of a Variable Stiffness Magnetic Torsion Spring

“…Examples include robotic hands, where the elastic elements are used to perform a stable grasp [1][2][3], flying robots, in order to estimate the pitch torques generated by wings during flapping [4] and robotic snakes, for estimating ground contact forces [5]. Furthermore elastic elements are key components of Series Elastic Actuators (SEAs) [6][7][8][9], Variable Stiffness Actuators (VSAs) [10][11][12][13][14][15][16][17][18] and, more generally, of Variable Impedance Actuators (VIAs) [19], where damping can also be adjusted by properly controlling the device. In this field, a seminal work is that of Fasse et al [20], where an electromagnetic variable impedance actuator is demonstrated, capable of exerting a torque much higher than that of the prototype described in this paper.…”

Human–robot collision model with effective mass and manipulability for design of a spatial manipulator

“…Previous researches on collision safety focused on minimizing the collision force by the use of additional devices or control strategies [1][2][3][4]. However, these additional devices or control strategies may affect the performance of the manipulators, and can only be used in limited circumstances.…”