VSA-CubeBot: A modular variable stiffness platform for multiple degrees of freedom robots

Abstract

We propose a prototype of a Variable Stiffness Actuator (VSA) conceived with low cost as its first goal. This approach was scarcely covered in past literature. Many recent works introduced a large number of actuators with adjustable stiffness, optimized for a wide set of applications. They cover a broad range of design possibilities, but their availability is still limited to small quantities. This work presents the design and implementation of a modular servo-VSA multi-unit system, called VSA-CubeBot. It offers a customizable platform for the realization and test of variable stiffness robotic structures with many degrees of freedom. We present solutions relative to the variable stiffness mechanism, embedded electronics, mechanical and electrical interconnections. Characteristics, both theoretic and experimental, of the single actuator are reported and, finally, five units are interconnected to form a single arm, to give an example of the many possible applications of this modular VSA actuation unit.

CompAct Arm: a Compliant Manipulator with Intrinsic Variable Physical Damping

“…To satisfy the lightweight property of the overall arm a carbon fibre frame was used in this design. The mentioned structure is used not only as frame but also as a cover preventing the human/environment to enter in contact with the mechatronics of the manipulator 4 The use of semi-active damping systems placed between the actuator and the load is not a new concept in robotics, see e.g. [12,19]; however these works do not make use of mechanical compliance.…”

“…2a, the rotor velocity v θ required to produce certain link motion can be computed using (2), while the required actuator force F in is obtained using (1). The corresponding mechanical power input P in required to provide a desired link velocity can therefore be computed in the frequency domain as: (4) Considering a required velocity output of amplitude 0.1 rad/s, the required RMS power input as a function of the frequency is shown in Fig. 3 for different physical viscous damping levels.…”

“…The employed actuation system is a series elastic actuator which presents the ability of regulating the physical damping in parallel to the joint compliance and is therefore suited for the development of this manipulator [8]. The adjustment of the damping is realized by a semi-active friction damper actuated by light and compact piezoelectric stack actuators ( 4 ) , Fig. 5b.…”

“…humans' biological structures can exploit this property to improve the mentioned characteristics. These bio-inspired drives motivate scientists to attempt to replicate compliance within robots with a variety of solutions [1,[4][5]. Although compliance can effectively make the difference, from the engineering point of view it introduces also some side effects.…”

Variable impedance actuators: Moving the robots of tomorrow

“…To have the sum of the two motor torques available, bi-directional antagonistic arrangements were made [16] [17]. The VSA-cube is a hobby servomotor style of VIA actuator [18] and is currently commercialised so that as wide public audience can explore the possibilities of VIAs. The Pleated Pneumatic Artificial Muscles are in an antagonistic setup adaptably compliant and can generate higher forces at lower pressures compared to McKibben muscles [19].…”