(a) Characteristics of an ankle joint for a 75 kg subject walking at normal cadence: ankle angle, torque, and power versus percentage of stride during one step. Data taken from [6]. (b) Torque-angle characteristics of an intact ankle joint for a 75 kg subject walking at normal cadence. Data taken from [6]. The main phases of gait are highlighted as initial contact (IC), foot flat (FF), heel off (HO), and toe off (TO).

(a) Characteristics of an ankle joint for a 75 kg subject walking at normal cadence: ankle angle, torque, and power versus percentage of stride during one step. Data taken from [6]. (b) Torque-angle characteristics of an intact ankle joint for a 75 kg subject walking at normal cadence. Data taken from [6]. The main phases of gait are highlighted as initial contact (IC), foot flat (FF), heel off (HO), and toe off (TO).

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In the past decades, researchers have deeply studied pathological and nonpathological gait to understand the human ankle function during walking. These efforts resulted in the development of new lower limb prosthetic devices aiming at raising the 3C-level (control, comfort, and cosmetics) of amputees. Thanks to the technological advances in enginee...

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... Therefore, we analyzed the motor model and design the prosthesis parameters with biomechanical data as the target load. A situation can be seen in [14], where the maximum power of the ankle was 552 W, but it cannot provide enough torque compared with the biomechanical data. The load profiles were also not matched in comparable active EHA prostheses [22,23]. ...
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Several studies have shown that actuation concepts such as Serial elastic actuator (SEA) can reduce peak power and energy consumption in ankle prostheses. Proper selection and design of the actuation concepts is important to unlock the power source potential. In this work, the optimization design, mechanical design, control scheme, and bench experiments of a new powered ankle–foot prosthesis is proposed. The actuation concept of this prosthesis is parallel elastic actuator (PEA) composed of electro-hydrostatic actuator (EHA) as the power kernel and a unidirectional parallel spring as the auxiliary energy storage element. After the appropriate motor and transmission ratio was selected, a dynamic model of the PEA prosthesis was built to obtain the appropriate spring parameters driven by biological data. The design of the hydraulic and mechanical system and the controller were provided for the implementation of the designed system. Bench experiments were performed to verify the performance. The results showed that the designed prosthesis meets the biomechanical dynamics requirements. This result emphasizes the feasibility of the EHA as a power source and actuator and provides new ideas for the design of ankle–foot prostheses.
... Despite several mechanical innovations and a slew of novel environmental sensing modalities [8] [9], current powered ankle prostheses have not been shown to achieve direct volitional controllability to the same degree as intact physiology [10]. However, one class of physiological lowerextremity signals, surface electromyography (sEMG), has demonstrated utility for control of both powered ankle prostheses and powered ankle orthoses [11] [12][13] [14][15] [16]. ...
... The most common type of prosthetic feet on the market are conventional feet (CF), and Energy Storage and Return (ESR) feet (Cherelle et al., 2014). ESR feet are claimed to be more beneficial for amputees due to a flexible keel that possibly aids with push-off during walking (Versluys et al., 2008). ...
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Transfemoral amputees are currently forced to utilize energetically passive prostheses that provide little to no propulsive work. Among the several joints and muscles required for healthy walking, the ones most vital for push-off assistance include the knee, ankle, and metatarsophalangeal (MTP) joints. There are only a handful of powered knee-ankle prostheses (also called powered transfemoral prostheses) in literature and few of them comprise a toe-joint. However, no one has researched the impact of toe-joint stiffness on walking with a power transfemoral prosthesis. This study is aimed at filling this gap in knowledge. We conducted a study with an amputee and a powered transfemoral prosthesis consisting of a spring loaded toe-joint. The prosthesis's toe-joint stiffness was varied between three values: 0.83 Nm/deg, 1.25 Nm/deg, and infinite (rigid). This study found that 0.83 Nm/deg stiffness reduced push-off assistance and resulted in compensatory movements that could lead to issues over time. While the joint angles and moments did not considerably vary across 1.25 Nm/deg and rigid stiffness, the latter led to greater power generation on the prosthesis side. However, the 1.25 Nm/deg joint stiffness resulted in the least power production from the intact side. We, thus, concluded that the use of a stiff toe-joint with a powered transfemoral prosthesis can reduce the cost of transport of the intact limb.
... 6 Because the "powered" device is doing some of the work necessary for movement, there may be reduced compensatory motion at the sound limb. 92 "Powered" prosthetic devices may be able to redistribute and handle loads in a more biomimetic way and prevent dermatological issues on the residual limb. Without the ability to be comfortable, those with LLA will be unable to achieve physical function. ...
... 6 Since the "powered" device is doing some of the work necessary for movement there may be reduced compensatory motion at the sound limb. 92 "Powered" prosthetic devices may be able to redistribute an handle loads in a more biomimetic way and prevent dermatological issues on the residual limb. Without the ability to be comfortable those with LLA will be unable to achieve physical function. ...
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... Hence, the additional active power is needed for the prosthetic foot to better mimic the dynamics of the human ankle. In past few years, more and more studies are focused on the design and validation of novel powered ankle-foot prostheses [5][6][7][8][9][10][11][12][13][14]. ...
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... To reduce aforementioned difficulties, improving prosthetic alignment and the development of novel devices are required [10]. The further optimization of prosthetic devices (greater range of motion, stabilizing and powering joints [11]) would positively influence functional independency and prevent further pathology along the body segments [12]. Preceding a market-proof product, a lower-limb prosthetic device (LLPD) undergoes an iterative process of design, development and construction. ...
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INTRODUCTION Evaluating the efficacy of a lower-limb prosthetic device (LLPD) is a crucial step in the iterative process of redesigning and product development of new generation prostheses. To date, no standardized experimental methodology for the evaluation of LLPDs is available which complicates the comparison of results. OBJECTIVE This systematic review provides an overview of study designs, tests and outcome measures to evaluate a LLPD. Ultimately, guidelines and recommendations are formulated. METHODS Two databases were screened on studies evaluating a LLPD, published between 2009 and 2019. RESULTS 109 articles were eventually included. We identified 43 outcome measures in four main categories: 53% were biomechanical, 26% physiological, 14% physical performance and 7% psychological. Mainly walking tests were included (78%), of which 31% were performed on a slope, followed by stair climbing (15%) and other functional tasks (15%). CONCLUSION An overview of currently used study designs and experimental protocols is presented, which led to guidelines and recommendations for the evaluation of a LLPD. The main recommendation is to include daily activities in a case-report and in a later stage in a randomized controlled study design. Biomechanical, physiological, physical performance and psychological outcome measures are key for the evaluation of a LLPD.
... World-wide, engineers strive at improving prosthetics' design and functionalities with the aim of optimising comfort and dexterity during daily activities. Although most of these advances are still on a research level, their results show a preview of the upwards potential future prosthetics hold for amputees [1]. Recently, a novel bionic foot, the Ankle Mimicking Prosthetic-foot or AMPfoot 4.0, has been developed at the Vrije Universiteit Brussel (Belgium). ...
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... A very good review article was written by Lefeber's group outlining the progress of prosthetic feet from passive systems to active systems. 3,7 New prosthetic feet include the ProFlex by Ossur which uses a four-bar linkage and a passive foot. The foot has greater peak power and range of motion as compared to standard feet, see Fig. 9. ...
... The AMP 2 device used a locking clutch to store energy in the PO (push-off) spring. 7,51,52 The AMP 3 device used a resettable, overrunning clutch at the ankle axis to adjust the starting angle of the device. 53 Figure 15. ...
... This concept was first mentioned by Lefeber. 3,7 Wang developed a powered ankle prosthesis that can create a moment about the ankle joint and the toe, 7 see Fig. 18. ...
Chapter
Great strides have been made over the last two decades to develop powered, active, ankle–foot orthoses and prostheses. Lightweight, powerful systems return gait movements and torques (kinematics and kinetics) to the user. An explosion of research in the areas of biomechanics, control, and mechanical design has allowed systems to assist and enhance the user’s ambulatory pattern. This review will discuss the trends in the development of wearable robotic systems enhancing ankle gait. Trends in passive systems include the development of lightweight carbon fiber systems for drop foot. Trends in active systems include the development of lightweight, battery-powered, motorized ankle–foot orthoses to aid in rehabilitation of stroke survivors. Similar systems are being built to assist transtibial and transfemoral amputees. Many new systems are quasi-passive and use minimal control techniques to tune the device during the gait cycle. Lastly, there has been a trend to develop soft-actuation techniques that do not rely on rigid exoskeletal structures. The trend is for smarter, more lightweight, powerful systems that return better gait kinematics and kinetics reducing metabolic cost.
... These prostheses join the use of the elastic foot, for the passive energy recovery, to the use of mechanical systems for the ankle rotation, electronically controlled. The most widespread mechanical systems are made of leverages with one or more coil springs or pneumatic muscle actuators [9][10], acting like human tendons, joined to the ankle hinge [11][12][13][14][15]. These solutions enhance the mobility of the foot, the restoring of the kinematics of the ankle. ...
... Some of them, commercially available as the Proprio Foot (Össur), the Elan foot (Endolite) and Motion and Raize Foot (Fillauer), provide for stabilization of the ankle-foot system by means of hydraulic and electric actuators. These devices allow a natural kinematics of the ankle and the adaptability to different ground conditions [9]. Nevertheless, the power amount provided to the user by these devices cannot be more than the power stored during gait. ...
Conference Paper
This paper describes a model of a prosthesis of ankle able to control the pitch and the release of energy recovered during the gait; moreover, the model is able to provide to the user more power than the one recovered during the gait, in order to ensure a natural gait. The development of the model has been articulated in 3 steps: the study of the gait of able body people; the design of a mechanical system able to adjust the pitch of the ankle and at the same time able to store the mechanical energy; the development of an active control of the foot and of the energy recovery system. The conceived model is made of a four-bar linkage with a further fifth element. Two of those elements can modify the length: one is an active shock absorber for damping and for the energy recovery; the other is a linear actuator for the pitch adjusting. The first is equipped with two control flow valves; the second is made of a screw nut mechanism. The control system is based on a central control unit that detects signals from three sensors to determine the gait phase, to control the shock absorber and to adapt the actuator to the correct position.