Louis Flynn

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.

CYBERLEGs: A User-Oriented Robotic Transfemoral Prosthesis with Whole-Body Awareness Control

Restoring the mobility of transfemoral dysvascular amputees is essential to their rehabilitation process. Impeding the restoration of mobility, exhaustion is often the cause of noneffective deambulation of elderly lowerlimb amputees using a prosthesis as they use more energy for locomotion than younger amputees do. This article presents finite-state control of a novel powered prosthesis prototype for transfemoral amputees based on whole-body awareness. Intention detection was implemented through a noninvasive, distributed wireless wearable sensory system. The cybernetic lower-limb cognitive orthoprosthesis (CYBERLEGs) system was evaluated in a study involving three amputees. The subjects were able to walk with the prosthesis without training, showing accurate performance of the intention detection. The functionality of the CYBERLEGs approach was confirmed by gait pattern analysis and intention detection statistics.

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.

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.

Whole Body Awareness for Controlling a Robotic Transfemoral Prosthesis

Restoring locomotion functionality of transfemoral amputees is essential for early rehabilitation treatment and for preserving mobility and independence in daily life. Research in wearable robotics fostered the development of innovative active mechatronic lower-limb prostheses designed with the goal to reduce the cognitive and physical effort of lower-limb amputees in rehabilitation and daily life activities. To ensure benefits to the users, active mechatronic prostheses are expected to be aware of the user intention and properly interact in a closed human-in-the-loop paradigm. In the state of the art various cognitive interfaces have been proposed to online decode the users intention. Electromyography in combination with mechanical sensing such as inertial or pressure sensors is a widely adopted solution for driving active mechatronic prostheses. In this framework, researchers also explored targeted muscles re-innervation for an objective-oriented surgical amputation promoting wider usability of active prostheses. However, information kept by the neural component of the cognitive interface deteriorates in a prolonged use scenario due to electrodes-related issues, thereby undermining the correct functionality of the active prosthesis. The objective of this work is to present a novel controller for an active transfemoral prosthesis based on whole body awareness relying on a wireless distributed non-invasive sensory apparatus acting as cognitive interface. A finite-state machine controller based on signals monitored from the wearable interface performs subject-independent intention detection of functional tasks such as ground level walking, stair ascent, and sit-to-stand maneuvres and their main sub-phases. Experimental activities carried out with four transfemoral amputees (among them one dysvascular) demonstrated high reliability of the controller capable of providing 100% accuracy rate in treadmill walking even for weak subjects and low walking speeds. The minimum success rate was of 94.8% in performing sit-to-stand tasks. All the participants showed high confidence in using the transfemoral active prosthesis even without training period thanks to intuitiveness of the whole body awareness controller.

VUB-CYBERLEGs CYBATHLON 2016 Beta-Prosthesis: Case study in control of an active two degree of freedom transfemoral prosthesis

BackgroundHere we present how the CYBERLEGs Beta-Prosthesis was modified with a new control system to participate in the Powered Leg Prosthesis event, and to report on our experience at the CYBATHLON 2016 which was held in Zurich, Switzerland in October 2016. The prosthesis has two active degrees of freedom which assist the user with extra joint power at the knee and ankle to complete tasks. The CYBATHLON is a championship for people with disabilities competing in six disciplines, using advanced assistive devices. Tasks for CYBATHLON 2016 were chosen to reflect everyday normal task such as sitting and standing from a chair, obstacle avoidance, stepping stones, slope walking and descent, and stair climbing and descent.MethodsThe control schemata were presented along with the description of each of the six tasks. The participant of the competition, the pilot, ran through each of the trials under lab conditions and representative behaviors were recorded.ResultsThe VUB CYBERLEGs prosthesis was able to accomplish, to some degree, five of the six tasks and here the torque and angle behaviors of the device while accomplishing these tasks are presented. The relatively simple control methods were able to provide assistive torque during many of the events, particularly sit to stand and stair climbing. For example, the prosthesis was able to consistently provide over 30 Nm in arresting knee torque in the sitting task, and over 20 Nm while standing. Peak torque of the device was not sufficient for unassisted stair climbing, but was able to provide around 60 Nm of assistance in both ascent and descent. Use of the passive behaviors of the device were shown to be able to trigger state machine events reliably for certain tasks.ConclusionsAlthough the performance of the CYBERLEGs prosthesis during CYBATHLON 2016 did not compare to the other top of the market designs with regards to speed, the device performed all of the tasks that were deemed possible by the start of the competition. Moreover, the Pilot was able to accomplish tasks in ways the Pilot’s personal microcontrolled prosthesis could not, with limited powered prosthesis training. Future studies will focus on decreasing weight, increasing reliability, incorporating better control, and increasing the velocity of the device. This is only a case study and actual benefits to clinical outcomes are not yet understood and need to be further investigated. This competition was a unique experience to illuminate problems that future versions of the device will be able to solve.

On the Importance of a Motor Model for the Optimization of SEA-driven Prosthetic Ankles

Several examples in literature demonstrate the potential impact of motor inertia on the electrical energy consumption of actuators. Nevertheless, optimizations of actuated prosthetics are often based on the mechanical energy consumption, disregarding the potential effects of motor inertia. In this short abstract, we simulate the electrical energy consumption of a powered prosthetic ankle actuated by a Series Elastic Actuator. Its compliant element is optimized for mechanical energy consumption, a typical strategy in state-of-the-art prosthetics. Our results confirm the importance of motor inertia. Due to the resulting changes in the operating points of the motor, the average motor efficiency is lowered by 17 %.