Rene Jimenez-Fabian

Ankle-knee prosthesis with active ankle and energy transfer

This paper presents the development of the CYBERLEGs Alpha-Prototype prosthesis, a new transfemoral prosthesis incorporating a new variable stiffness ankle actuator based on the MACCEPA architecture, a passive knee with two locking mechanisms, and an energy transfer mechanism that harvests negative work from the knee and delivers it to the ankle to assist pushoff. The CYBERLEGs Alpha-Prosthesis is part of the CYBERLEGs FP7-ICT project, which combines a prosthesis system to replace a lost limb in parallel with an exoskeleton to assist the sound leg, and sensory array to control both systems. The prosthesis attempts to produce a natural level ground walking gait that approximates the joint torques and kinematics of a non-amputee while maintaining compliant joints, which has the potential to decrease impulsive losses, and ultimately reduce the end user energy consumption. This first prototype consists of a passive knee and an active ankle which are energetically coupled to reduce the total power consumption of the device. Here we present simulations of the actuation system of the ankle and the passive behavior of the knee module with and without the energy transfer effects, the mechanical design of the prosthesis, and empirical results from testing of the physical device with amputee subjects. We designed a new Knee-Ankle Prosthesis with energy transfer from knee to ankle.The ankle is a variable stiffness actuator based on the MACCEPA architecture.The prosthesis attempts to produce a natural level-ground gait.The behavior of the ankle joint and locking mechanisms is investigated.The energy transfer mechanism reduces the peak torque at the ankle joint.

Human-like compliant locomotion: state of the art of robotic implementations

This review paper provides a synthetic yet critical overview of the key biomechanical principles of human bipedal walking and their current implementation in robotic platforms. We describe the functional role of human joints, addressing in particular the relevance of the compliant properties of the different degrees of freedom throughout the gait cycle. We focused on three basic functional units involved in locomotion, i.e. the ankle-foot complex, the knee, and the hip-pelvis complex, and their relevance to whole-body performance. We present an extensive review of the current implementations of these mechanisms into robotic platforms, discussing their potentialities and limitations from the functional and energetic perspectives. We specifically targeted humanoid robots, but also revised evidence from the field of lower-limb prosthetics, which presents innovative solutions still unexploited in the current humanoids. Finally, we identified the main critical aspects of the process of translating human principles into actual machines, providing a number of relevant challenges that should be addressed in future research.

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.

Design and energetic evaluation of a prosthetic knee joint actuator with a lockable parallel spring

There are disadvantages to existing damping knee prostheses which cause an asymmetric gait and higher metabolic cost during level walking compared to non-amputees. Most existing active knee prostheses which could benefit the amputees use a significant amount of energy and require a considerable motor. In this work, a novel semi-active actuator with a lockable parallel spring for a prosthetic knee joint has been developed and tested. This actuator is able to provide an approximation of the behavior of a healthy knee during most of the gait cycle of level walking. This actuator is expanded with a series-elastic actuator to mimic the full gait cycle and enable its use in other functional tasks like stair climbing and sit-to-stance. The proposed novel actuator reduces the energy consumption for the same trajectory with respect to a compliant or directly-driven prosthetic active knee joint and improves the approximation of healthy knee behavior during level walking compared to passive or variable damping knee prostheses.

CYBERLEGS Beta-Prosthesis active knee system

The addition of active components to prostheses has the potential to extend the capabilities and reduce metabolic energy consumption of users when compared to current prosthetic technology. The CYBERLEGs Beta-Prosthesis is a new active transfemoral prosthesis that builds upon the passive principles of the CYBERLEGs Alpha-Prosthesis. The prosthesis has two active degrees of freedom, one in the ankle and one in the knee. The knee actuator is a totally new design consisting of a Weight Acceptance mechanism, Active knee drive that incorporates a primarily passive Baseline Spring system, and Energy Transfer mechanism. The use of low power motors in the knee has the potential to lead to a prosthesis that is electrically energy efficient for normal gait that is also capable of providing power for intensive actions such as stair climbing and sit-to-stand motions. Preliminary trials have shown basic walking functionality and results are described. Although this study focused on the usability of the prosthesis and general overall function, it is hoped that with better control the device will eventually be able to lead to an electrically efficient device which also can reduce user metabolic input during ambulation.

Reduction of the torque requirements of an active ankle prosthesis using a parallel spring

Abstract The present manuscript describes the combined effect of using a parallel spring in conjunction with a variable-stiffness actuator to reduce the torque and power requirements of an ankle–foot prosthesis during normal walking. The behavior of both elements is analyzed in terms of the reduction of the required motor peak power, energy and torque with respect to a conventional actuator. The proposed actuator is based on the Mechanically Adjustable Compliance and Controllable Equilibrium Position Actuator concept. The advantages and disadvantages of the referred actuation scheme are discussed and experimental results are used to illustrate the actual reduction of motor torque requirements.

Design, development and testing of a lightweight and compact locking mechanism for a passive knee prosthesis

In knee prosthetics and orthotics, there is the need to have a change in stiffness within the gait cycle. Doing this using a locking mechanism requires locking high forces using a small amount of energy. This paper presents a novel compact and light-weight locking mechanism which combines a ratchet-and-pawl and a singular position locking mechanism. It is used as a lock in a passive knee prosthesis and allows a change in compliance of the joint. The mechanism is transparent during the swing phase, allowing the joint to flex, and during the weight acceptance phase it provides the same stiffness as a natural knee joint. It is explained that this high stiffness characteristic can be approximated by a linear spring put in parallel with the knee joint. The mechanism uses a small servo motor to unlock the ratchet, other than this the operation is fully passive. The prosthesis has been tested during walking tests with amputee test subjects. The passive knee prosthesis is part of the CYBERLEGs-Project.

Energetic analysis and optimization of a MACCEPA actuator in an ankle prosthesis: Energetic evaluation of the CYBERLEGs alpha-prosthesis variable stiffness actuator during a realistic load cycle

The use of active prostheses for lower limb replacement brings new challenges like power optimization, energy efficiency and autonomy. The use of series and parallel elasticity is often explored to reduce the necessary motor power but this does not necessarily have a positive influence on the energy consumption of the prosthesis. This paper presents the experiments performed with the variable compliance actuator used in an active ankle prosthesis and the electromechanical model of this actuator. The results show that the measurements can be matched using the model, and this model can thus be used to optimize the energy efficiency of the actuator. Simulations show that the electrical efficiency can be increased by 10% compared to parameters selected by an optimization method that only takes mechanical properties into account.

Prototype design of a novel modular two-degree-of-freedom variable stiffness actuator

In bio-inspired robotic applications, multiple-degree-of-freedom actuators are often desired. The current state of the art of variable stiffness actuators consist mostly of different concepts for single-degree-of-freedom joints. An innovative Mechanically Adjustable Compliance and Controllable Equilibrium Position Actuator (MACCEPA) concept is presented to specifically accommodate implementation in two-degree-of-freedom joints. A prototype design, based on this concept, is furthermore presented. The working principle and relevant design choices are explained, a zero-dynamic model is derived for future design iterations, and the implementation in a first prototype is discussed.