Adjustable compliance soft gripper system

This article proposes a novel, innovative, soft gripper system developed for the manipulation of objects of unknown or unspecified shape and consistence. This could be achieved by the utilization of a linear pneumatic muscle benefitting from an inherently compliant behaviour. A gripper system of this type does not require the presence of sensors or complex controllers, as it is the mechanical system itself that provides the required adaptive behaviour. The compliance of the system is ensured by the variations of the air pressure fed to the pneumatic muscle, monitored and controlled in a closed loop by means of proportional pressure regulator.

Design of a Novel Variable Stiffness Series Elastic Actuator for Extended Linearity

Recently, Series Elastic Actuator (SEA) has been popularly used as a torque sensor thanks to its notable ability to calibrate the relation between torque and displacement. It has been applied to many robotic applications and used in a various industrial automation fields. However, most of the current SEAs have nonlinear torque-displacement characteristics which could not be easily alleviated. In order to be utilized as a feasible torque sensor, the wide linearity of a SEA in torque-displacement relationship is not an option. Also, adjustable compliance is needed to implement a mechanism with different stiffness, depending on the various cases where SEA can be applied. In this paper, we designed a Variable Stiffness Linear Series Elastic Actuator (VLSEA) mechanism that can achieve variable stiffness with a linear relationship between torque and displacement. At first, a design with a four-bar link was proposed for linear relations, but it was difficult to implement variable stiffness. We modified the design using the Scotch Yoke mechanisms for the model to have variable stiffness. Simulation of the designed model then verifies that the model can properly implement linearity and variable stiffness.

Mechanical Simplification of Variable-Stiffness Actuators Using Dielectric Elastomer Transducers

Legged and gait-assistance robots can walk more efficiently if their actuators are compliant. The adjustable compliance of variable-stiffness actuators (VSAs) can enhance this benefit. However, this functionality requires additional mechanical components making VSAs impractical for some uses due to increased weight, volume, and cost. VSAs would be more practical if they could modulate the stiffness of their springs without additional components, which usually include moving parts and an additional motor. Therefore, we designed a VSA that uses dielectric elastomer transducers (DETs) for springs. It does not need mechanical stiffness-adjusting components because DETs soften due to electrostatic forces. This paper presents details and performance of our design. Our DET VSA demonstrated independent modulation of its equilibrium position and stiffness. Our design approach could make it practical to obtain the benefits of variable-stiffness actuation with less weight, volume, and cost than normally accompanies them, once weaknesses of DET technology are addressed.

Sliding-Bar MACCEPA for a Powered Ankle Prosthesis

This paper describes a new design that improves several aspects of the mechanically adjustable compliance and controllable equilibrium position actuator (MACCEPA). The proposed design avoids premature wear and attachment issues found in the cable transmission used in previous MACCEPA designs and allows the use of high-performance compact compression springs. The mechanical configuration of the actuator provides an adjustable stiffness with a nonlinear stiffening output torque. The output position of the actuator and its global stiffness are independent from each other. In this work, we provide a mathematical description of the actuation principle along with an experimental verification of its performance in a powered ankle–foot prosthesis. This work is part of the CYBERLEGs project funded by the European Commissions 7th Framework Programme.

Planar Manipulator with Mechanically Adjustable Joint Compliance

A novel robot joint with mechanically adjustable compliance is presented. It utilizes a leaf spring and the joint compliance can be adjusted by rotating this spring, i.e., changing its bending direction. A joint actuatormoves an armlink via a connection that consists of a hollow cylinder and a leaf spring. This mechanism is compact to be installed in a joint and it can change the joint stiffness rapidly and stably. A planar manipulator using this joint mechanism is proposed for the contact or constraint tasks. Since four joints are necessary to obtain arbitrary stiffnesses and an arbitrary position of the end-effector in plane motion, a four DOF (degrees of freedom) manipulator with mechanically adjustable joint compliance is developed.