Mechanically Adjustable Compliance And Controllable Equilibrium Position Actuator Research Articles

Development of novel fish-inspired robot with variable stiffness

In nature, real fish can adjust stiffness to improve their swimming speed and efficiency, which prompted us to apply the variable stiffness mode to a fish-inspired robot. In this paper, we adopt a mechanically adjustable compliance and controllable equilibrium position actuator (MACCEPA) to achieve a wide range of rotational stiffness change of the robotic fish body. Fish-inspired robots with offline/online variable stiffness mechanisms are developed. Then, swimming experiments are carried out to study the effect of the rotational stiffness of robot body on the swimming performance. Experimental data are processed using the undulatory reconfiguration technique. The offline variable stiffness fish-inspired robot achieved a maximum stride length of 0.7 BL/cycle (body length per cycle), which is basically equal to that of real fish. Experimental results revealed that in addition to the rotational stiffness of caudal fin, the rotational stiffness of fish body is also important and should increase with the driving frequency to achieve a better swimming performance. The rotational stiffness of fish body is the key factor for keeping the stride length stable, which offers a new insight for performance improvement of the high-frequency fish-inspired robot. The findings of this study are beneficial to the design of variable-stiffness fish-inspired robots.

A Systematic Design Selection Methodology for System-Optimal Compliant Actuation

SummaryThis work presents a systematic design selection methodology that utilizes a co-design strategy for system-level optimization of compliantly actuated robots that are known for their advantages over robotic systems driven by rigid actuators. The introduced methodology facilitates a decision-making strategy that is instrumental in making selections among system-optimal robot designs actuated by various degrees of variable or fixed compliance. While the simultaneous co-design method that is utilized throughout guarantees systems performing at their full potential, a homotopy technique is used to maintain integrity via generation of a continuum of robot designs actuated with varying degrees of variable and fixed compliance. Fairness of the selection methodology is ensured via utilization of common underlying (variable) compliant actuation principle and dynamical task requirements throughout the generated system designs. The direct consequence of the developed methodology is that it allows robot designers make informed selections among a variety of systems which are guaranteed to perform at their best. Applicability of the introduced methodology has been validated using a case study for system-optimal design of an active knee prosthesis that is driven by a mechanically adjustable compliance and controllable equilibrium position actuator (MACCEPA) under a periodic/real-life dynamical task.

A Soft Robotic Fish with Variable-stiffness Decoupled Mechanisms

A Body and/or Caudal Fin (BCF) fish modulate its body stiffness by mechanisms consisting of antagonistic muscles. The mechanisms can be considered as Redundant Planar Rotational Parallel Mechanisms (RPRPM) with antagonistic flexible elements. For a typical RPRPM, its stiffness consists of the adjustable stiffness resulting from internal forces and the inherent stiffness caused by inherent compliances of flexible elements. In order to decouple the adjustable stiffness from the inherent stiffness and expand the range of stiffness variation, a variable-stiffness decoupled mechanism based on the Mechanically Adjustable Compliance and Controllable Equilibrium Position Actuator (MACCEPA) is presented and used to construct a soft robotic fish with large stiffness variation. According to the analysis of the evolution from RPRPM to MACCEPA, it can be found that MACCEPA is just a special type of RPRPM with only an adjustable stiffness. In addition, MACCEPA existed before RPRPM mechanism. The prototype of the soft robotic fish with variable-stiffness decoupled mechanisms is built to explore the relationships between the body stiffness and the swimming performance. It is validated experimentally that the stiffness variation multiple of the robotic fish is raised, the swimming performance of the robotic fish is improved when the stiffness is modulated to match the driving frequency.

Design and experimental evaluation of a lightweight, high-torque and compliant actuator for an active ankle foot orthosis.

The human ankle joint plays a crucial role during walking. At the push-off phase the ankle plantarflexors generate the highest torque among the lower limb joints during this activity. The potential of the ankle plantarflexors is affected by numerous pathologies and injuries, which cause a decrease in the ability of the subject to achieve a natural gait pattern. Active orthoses have shown to have potential in assisting these subjects. The design of such robots is very challenging due to the contrasting design requirements of wearability (light weight and compact) and high torques capacity. This paper presents the development of a high-torque ankle actuator to assist the ankle joint in both dorsiflexion and plantarflexion. The compliant actuator is a spindle-driven MACCEPA (Mechanically Adjustable Compliance and Controllable Equilibrium Position Actuator). The design of the actuator was made to keep its weight as low as possible, while being able to provide high torques. As a result of this novel design, the actuator weighs 1.18kg. Some static characterization tests were perfomed on the actuator and their results are shown in the paper.

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.

MACCEPA 2.0: compliant actuator used for energy efficient hopping robot Chobino1D

The MACCEPA (Mechanically Adjustable Compliance and Controllable Equilibrium Position Actuator) is an electric actuator of which the compliance and equilibrium position are fully independently controllable and both are set by two dedicated servomotor. In this paper an improvement of the actuator is proposed where the torque-angle curve and consequently the stiffness-angle curve can be modified by choosing an appropriate shape of a profile disk, which replaces the lever arm of the original design. The actuator has a large joint angle, torque and stiffness range and these properties can be made beneficial for safe human robot interaction and the construction of energy efficient walking, hopping and running robots. The benefit of the ability to store and release energy is shown by the 1DOF hopping robot Chobino1D. The achieved hopping height is much higher compared to a configuration in which the same motor is used without a series elastic element. The stiffness of the actuator increases with deflection, more closely resembling the properties shown by elastic tissue in humans.