Design of Powered Ankle-Foot Prosthesis Driven by Parallel Elastic Actuator (original) (raw)
Related papers
2012 IEEE International Conference on Robotics and Biomimetics (ROBIO), 2012
Peak power, peak torque and energy requirements are amongst the main issues for powered prosthetic ankles. Including series elastic actuators (SEA) can reduce peak power and energy requirements by reducing motor speed in comparison to a Direct Drive (DD). Parallel elastic actuation concept (PEA, the parallel spring can be compressed and elongated) can reduce the peak power even more by reducing required motor torque. However, the energy consumption increases in comparison to SEA. In this paper, we investigated if unidirectional parallel springs (UPS) that act only at special ankle angles could combine the positive features of both SEA and PEA concepts in terms of motor peak power and/or energy reductions. Therefore, the motor peak power and energy requirements are compared between active actuation concepts SEA, SEA+PS, SEA+UPS, DD+PS and DD+UPS. For the minimum motor peak power requirements, we found that the reduction was similar between PS and UPS. However, the corresponding energy requirements were less or similar in UPS for corresponding speeds. For the minimum energy requirements, it was found that the UPS reduced the energy requirements but increased the corresponding required peak power for the majority of speeds in comparison to PS. The ultimate goal of combining positive characteristics of SEA and PEA was identified mainly for lower walking and running speeds.
Concept of a Series-Parallel Elastic Actuator for a Powered Transtibial Prosthesis
Actuators, 2013
The majority of the commercial transtibial prostheses are purely passive devices. They store energy in an elastic element during the beginning of a step and release it at the end. A 75 kg human, however, produces on average 26 J of energy during one stride at the ankle joint when walking at normal cadence and stores/releases 9 J of energy, contributing to energy efficient locomotion. According to Winter, a subject produces on average of 250 W peak power at a maximum joint torque of 125 Nm. As a result, powering a prosthesis with traditional servomotors leads to excessive motors and gearboxes at the outer extremities of the legs. Therefore, research prototypes use series elastic actuation (SEA) concepts to reduce the power requirements of the motor. In the paper, it will be shown that SEAs are able to reduce the power of the electric motor, but not the torque. To further decrease the motor size, a novel human-centered actuator concept is developed, which is inspired by the variable recruitment of muscle fibers of a human muscle. We call this concept series-parallel elastic actuation (SPEA), and the actuator consists of multiple parallel springs, each connected to an intermittent mechanism with internal locking and a single motor. As a result, the motor torque requirements can be lowered and the efficiency drastically increased. In the paper, the novel actuation concept is explained, and a comparative study between a stiff motor, an SEA and an SPEA, which all aim at mimicking human ankle behavior, is performed.
Actuators, 2014
A monoarticular series elastic actuator (SEA) reduces energetic and peak power requirements compared to a direct drive (DD) in active prosthetic ankle-foot design. Simulation studies have shown that similar advantages are possible for the knee joint. The aims of this paper were to investigate the advantages of a monoarticular SEA driven hip joint and to quantify energetic benefit of an SEA driven leg (with monoarticular hip, knee and ankle SEAs) assuming that damping (negative power) is passively achieved. The hip SEA provided minor energetic advantages in walking (up to 29%) compared to the knee and the ankle SEA. Reductions in required peak power were observed only for speeds close to preferred walking speed (18 to 27%). No energetic advantages were found in running where a DD achieved the best performance when optimizing for energy. Using an SEA at each leg joint in the sagittal plane reduced positive work by 14 to 39% for walking and by 37 to 75% for running. When using an SEA instead of a DD, the contribution of the three leg joints to doing positive work changed: the knee contributed less, the hip contributed more positive work. For monoarticular SEAs the ankle joint motor did most of the positive work.
Advances in Powered Ankle-Foot Prostheses
Critical Reviews in Biomedical Engineering, 2018
We present a review of recent developments in powered ankle-foot prostheses (PAFPs), with emphasis on actuation, high-and low-level control strategies, and pneumatic, hydraulic, and electromechanical actuators. A high-level control strategy based on finite-state machines, combined with low-level control that drives the ankle torque, is the most common control strategy. On the other hand, brushless direct-current motors along with an energy storage and release mechanism are commonly used to reduce the overall size of the actuators and increase PAFP autonomy. Most designs have been evaluated experimentally, showing acceptable results in walking velocity and gait symmetry. Future research must focus on reducing weight, increasing energy efficiency, improving gait phase classification and/or intent of motion-prediction algorithms, updating low-level control of torque and position, and developing the ability of the patient to walk on sloped surfaces and negotiate stairs.
Biomechanical Design and Prototyping of a Powered Ankle-Foot Prosthesis
Materials, 2020
Powered ankle-foot prostheses for walking often have limitations in the range of motion and in push-off power, if compared to a lower limb of a healthy person. A new design of a powered ankle-foot prosthesis is proposed to obtain a wide range of motion and an adequate power for a push-off step. The design methodology for this prosthesis has three points. In the first one, a dimensionless kinematic model of the lower limb in the sagittal plane is built, through an experimental campaign with healthy subjects, to calculate the angles of lower limb during the gait. In the second point a multibody inverse dynamic model of the lower limb is constructed to calculate the foot-ground contact force, its point of application and the ankle torque too, entering as input data the calculated angles of the lower limb in the previous point. The third point requires, as input of the inverse dynamic model, the first dimensioning data of the ankle-foot prosthesis to obtain the load acting on the compon...
IEEE Access
This paper introduces the analysis, design and preliminary evaluation of a self-integrated parallel elastic actuator (PEA) with an electric motor and a flat spiral spring in parallel to drive the hip joint of lower limb exoskeletons for power-efficient walking assistance. Firstly, we quantitatively analyze the reason why the parallel elasticity (PE) placed at the sagittal hip joint can reduce the motor power requirement during walking assistance, which contributes to the theory of PEA development and application. The design of the PEA is then introduced in detail. The novelty of the design is that the actuator is reduced in size by integrating the spring into the motor, and the requirement of spring stiffness is significantly reduced by placing the spring directly parallel to the motor shaft. Furthermore, both the simulation based on dynamic modeling and benchtop experiment are conducted preliminarily to evaluate the performance of the PEA with nine spring stiffnesses in a range from 0-5.29 mN•m/rad regarding two indexes including the average and maximum positive electrical power of the motor. Their results show that the two indexes become smaller when the PE is attached and decrease as the spring stiffness increases. When the PE with a stiffness of 5.29 mN•m/rad is attached, the actuator obtains the largest reduction rate of 11.99 and 16.84 % in the average and maximum positive electrical power of the motor in the simulation and 10.3 and 26.25 % in the experiment, respectively. Those results provide evidence for the applicability of the newly designed PEA in driving a lower limb exoskeleton with high power efficiency during walking assistance for paraplegic patients with complete loss in walking ability.
A low-power ankle-foot prosthesis for push-off enhancement
Wearable Technologies
Passive ankle-foot prostheses are light-weighted and reliable, but they cannot generate net positive power, which is essential in restoring the natural gait pattern of amputees. Recent robotic prostheses addressed the problem by actively controlling the storage and release of energy generated during the stance phase through the mechanical deformation of elastic elements housed in the device. This study proposes an innovative low-power active prosthetic module that fits on off-the-shelf passive ankle-foot energy-storage-and-release (ESAR) prostheses. The module is placed parallel to the ESAR foot, actively augmenting the energy stored in the foot and controlling the energy return for an enhanced push-off. The parallel elastic actuation takes advantage of the amputee’s natural loading action on the foot’s elastic structure, retaining its deformation. The actuation unit is designed to additionally deform the foot and command the return of the total stored energy. The control strategy o...
A powered prosthetic ankle joint for walking and running
BioMedical Engineering OnLine, 2016
Background The current standard for prosthetic ankle joints are passive SACH (solid ankle cushioned heel) or carbon fiber ESAR (energy storage and return) feet. In contrast to the stiff SACH feet, ESAR feet are able to store energy during the stance phase and release it later during push-off [1, 2]. Through this they are able to mimic the function of the Achilles tendon [3]. In contrast to human muscles, carbon feet are not able to create net positive work for ankle plantar-or dorsiflexion. Thus, actuation systems are required to achieve able-bodied ankle behavior. Different approaches with pneumatics [4] and electric motors [5-11] have been developed in recent years. In order to support amputees in common daily life activities like walking on flat terrain [10], stairs [12] or slopes [13],
Journal of Computational and Nonlinear Dynamics, 2023
Robotic leg prostheses and exoskeletons have traditionally been designed using highly-geared motor-transmission systems that minimally exploit the passive dynamics of human locomotion, resulting in inefficient actuators that require significant energy consumption and thus provide limited battery-powered operation or require large onboard batteries. Here we review two of the leading energy-efficient actuator design principles for legged and wearable robotic systems: series elasticity and backdrivability. As shown by inverse dynamic simulations of walking, there are periods of negative joint mechanical work that can be used to increase efficiency by recycling some of the otherwise dissipated energy using series elastic actuators and/or backdriveable actuators with energy regeneration. Series elastic actuators can improve shock tolerance during foot-ground impacts and reduce the peak power and energy consumption of the electric motor via mechanical energy storage and return. However, actuators with series elasticity tend to have lower output torque, increased mass and architecture complexity due to the added physical spring, and limited force and torque control bandwidth. High torque density motors with low-ratio transmissions, known as quasi-direct drives, can likewise achieve low output impedance and high backdrivability, allowing for safe and compliant human-robot physical interactions, in addition to energy regeneration. However, torque-dense motors tend to have higher Joule heating losses, greater motor mass and inertia, and require specialized motor drivers for real-time control. While each actuator design has advantages and drawbacks, designers should consider the energy-efficiency of robotic leg prostheses and exoskeletons beyond steady-state level-ground walking.
A Low Cost Design of Powered Ankle-Knee Prosthesis for Lower Limb Amputees - Preliminary Results
Proceedings of the International Conference on Biomedical Electronics and Devices, 2014
In this paper we described a new kind of a powered knee and powered ankle prosthesis for individuals who have suffered a complete or partial lower limb amputation. Our prototype prosthesis consist of two modules, the ankle module and the knee module. The first contains a unidirectional spring configured in parallel with a force-controlled actuator. This spring is intended to store energy in dorsiflexion, and then released it to assist power plantar flexion. The knee modules consist of a series of elastic clutch actuators and a unidirectional spring positioned in parallel to the motor. Preliminary results show two modules designs and ankle module prosthesis prototype almost complete. Two modules working together will enhance the performance of amputee individual, producing more natural gait and reducing the metabolic cost at walking in level-ground.