Linear Multimodal Actuation Through Discrete Coupling

Abstract

Due to technological limitations, robot actuators are often designed for specific tasks with narrow performance goals, whereas a wide range of behaviors is necessary for autonomous robots in uncertain complex environments. In an effort to increase the versatility of actuators, we introduce a new concept of multimodal actuation (MMA) that employs dynamic coupling in the form of clutches and brakes to change its mode of operation. The dynamic coupling allows motors and passive elements such as springs to be engaged and disengaged within a single actuator. We apply the concept to a linear series elastic actuator which uses friction brakes controlled online for the dynamic coupling. With this prototype, we are able to demonstrate several modes of operation including stiff position control, series elastic actuation as well as the possibility to store and release energy in a controlled manner for explosive tasks such as jumping. In this paper, we model the proposed concept of actuation and show a systematic performance analysis of the physical prototype that we developed in our laboratory.Index Terms-Brake and clutch, discrete couplings, serieselastic actuator (SEA).

Relay-based hybrid control of minimal-order mechanical systems with applications

“…The transitions from stance to flight and from flight to stance correspond approximately to the spring being undeformed after having been compressed during the stance, and to the bottom end of the spring touching the ground after the flight, respectively. As in [28], the hopper is equipped with a motor that preloads the spring during the flight phase by a length θ (we assume that the duration of the flight phase allows for the spring to be shortened and preloaded). This storage of energy is then released via a clutch mechanism at the contact with the ground.…”

“…Paralleling the above mentioned research strand, several works such as [1] (see also [29, §18.1.8]) have testified the potential of reset control for sustaining oscillations, which then extends quite naturally to the problem of generating hybrid limit cycles via hybrid feedback for legged locomotion [27,28,37,48] and for the close setting of juggling systems [39]. The potential of applying hybrid dynamical systems techniques in the context of legged locomotion is pointed out in [19], and addressed in technical terms in [43].…”

“…Furthermore, in the same spirit of [15,16] (or [23] for a broader approach encompassing neurobiology and biomechanics), we use minimal order mechanical systems to provide a fundamental explanation to the phenomena of reset-sustained and reset-damped oscillations. Finally, our work is motivated by some newly devised actuators [28] for hopping locomotion [37,48], whose very fast action resembles the introduction of a "kick" of energy to the mechanical system and can be modeled by a controller reset (an alternative approach close to the nature of this work would be [38]). Similar types of actuation are used in [6,27] and in variable impedance actuators [46].…”

Clutched Elastic Actuators

“…The CEA type in Fig. 3h is used to obtain an actuator that mimics some aspects of biological muscles [46]. And finally, the CEA type in Fig.…”

The Energy Amplification Characteristic Research of a Multimodal Actuator

“…In recent years, different types of powered exoskeletons have been developed [1][2][3][4]. Although significant advances have been made in the exoskeleton robot design, all of these existing robots are actuated and controlled using conventional engineering techniques, realizing specific tasks with narrow performance goals, where what is required is a wide range of autonomous exoskeleton robot behaviours, capable of responding to uncertain, complex walking environments [5]. In an effort to increase the versatility of actuators, we present an actuator that combines motor, spring, brake and clutch elements, producing a multimodal actuation of the power-assisted knee exoskeleton.…”