CompAct Arm: a Compliant Manipulator with Intrinsic Variable Physical Damping

Abstract

Abstract-Humans exploit compliance in their biomechanical muscle-tendon-bone actuation structure to enable robust and safe interaction with the environment and utilize the elastic energy stored into muscles and tendons to obtain large energy efficiency or high output mechanical power peaks at their limbs. From the robotic/mechatronic point of view it is clear that emulating such a property in robotic actuation systems enables the achievement of performance which is not possible with classical stiff designs. In contrast to this, transmission compliance introduces some disadvantages as e.g. typically underdamped modes which reduce the achievable control bandwidth, stability margin and accuracy of the controlled system. These limitations are solved in mammalians by means of physical damping which clarifies why these biological systems are able of performing fast and smooth yet accurate motions in their limbs. This motivates this work which consists in the analysis and development of the CompAct™ Arm, a novel compliant manipulator with intrinsic variable damping. This is probably the first robotic system to exhibit these diverse bio inspired characteristics. A motivation analysis is initially presented to show how the drawbacks introduced by compliance can be overcome by means of physical damping. The second part of the paper presents the mechatronic development of the robotic manipulator and preliminary experimental results.

A novel curve fitting based discrete velocity estimator for high performance motion control

“…All simulated input position signals ( ) were quantized with the same resolution, i.e. 12 bit/rev to emulate the output signal of the encoder employed in the CompAct™ actuation units developed at IIT, [18][19][20][21][22][23]. All the initial conditions were set to zero.…”

“…the VPDA, [18][19][20]23]. In such a device it is expected that the advantages of the FCFVE estimator will be further exploited to improve physical damping feedforward/feedback control.…”

A model-free approach to vibration suppression for intrinsically elastic robots

“…Historically, the stiffness adaptation idea can be allocated to the efforts of the robotics community to embed more functionality into hardware mechanisms themself, called task embodiment. Some examples for elastic systems are the multi joint robots DLR Hand Arm System [8] or the CompAct TM arm [9]. These robots are high end prototype systems, built with substantial monetary effort.…”

Control of Adjustable Compliant Actuators

“…In order to overcome the drawback of limited bandwidth, more advanced compliant actuator approaches consider, for example, nonlinear or adjustable compliant elements. Most recent approaches mimic the biological musculoskeletal system and impedance modulation by the antagonist co-activation of muscles [13,14] or by introducing an additional variable damping term [15,16], leading to additional degrees of freedom in physical impedance transfer function shaping. These new devices, although not limited in bandwidth, are often heavy and require two actuators, one for force/torque generation and one for the adjustment of the stiffness of the compliant element.…”

“…The advantage of this new approach is twofold: The use of a norm optimal convex controller procedure minimizing the load impedance function guarantees the best achievable performance in terms of the H 2 -norm, yet guarantees stability for varying passive load by a strictly positive-real port transfer function. Furthermore, the procedure is not only limited to interaction variable stiffness, but also can be easily extended by variable damping [15,16]. This paper is organized as follows.…”