This research concerns the design of a new three-fingered anthropomorphic hand mechanism for prosthetic and robotic applications. Based on the configuration and flexion/extension features of human hands, we develop a three-jointed finger mechanism using a gear-constrained planar five-bar linkage with a single degree of freedom (DOF). From an operational study of human hands, we also propose a multi-functional palm mechanism using a cam-groove submechanism. The hand can perform grasping, holding and pinching operations. To achieve the automatic shape adaptability of a human hand, a selfadaptable submechanism was designed within the palm based on the lever principle. An automatically variable speed transmission with selfadaptability was developed for this hand to achieve optimal flexing speed and optimal fingertip forces. This paper describes the mechanical structure and operational principles of this new prosthetic device.

We treat the design of a three-jointed, anthropomorphic, finger mechanism for prostheses and robotic end-effectors. Based on the study of configurations for the human finger, we propose a six-bar linkage with one degree of freedom for the finger mechanism. A model of the fingertip displacement of the mechanism is derived by a vector analysis approach. We study the effects of joint friction on the transmission efficiency. By measuring the joint positions of a human finger, we develop a mathematical model of the pinching and holding configurations for the human finger. Optimal parameters for the finger mechanism are obtained by nonlinear programming based on motion posture, locus, transmission efficiency, and weight subject to geometric and bionic constraints. Simulations indicate that the mechanism is useful in a variety of prosthetic and robotic devices.

A new knee mechanism has been designed which is a significant improvement over existing designs used in knee disarticulation (K/D) prostheses. These are prostheses used when the amputation is performed through the knee joint as opposed to amputation performed above the knee. The new four-bar mechanism has a more desirable locus of instant centers thereby improving the gait for K/D amputees. In this paper, the design process involving the kinematics is discussed. A prototype has been made and is currently undergoing testing with a prosthetist.

This paper presents the design of a body powered voluntary closing prosthetic hand. It is argued that the motion of the fingers before establishing a grip is much less relevant for good control of the object held than the distribution of forces once the object has been contacted. Based on this notion, the configurations of forces on the fingers and the force transmission through the whole mechanism were taken as point of departure for the design, rather than motion characteristics. For a good distribution of pinching forces on the object and a natural behavior, the prosthesis is made adaptive and flexible. To achieve good force feedback, the disturbing influences of the cosmetic glove are strongly reduced by a compensation mechanism. To further improve the transmission of forces, friction is reduced by furnishing the whole mechanism with rolling links. This force directed design approach has led to a simple mechanism with low operating force and good feedback of the pinching force.

In biomechanical engineering, gravity balancers are often used in orthoses carrying the weight of paralyzed limbs. In these applications, simplicity is an insuperable demand. However, known gravity balancers do not combine simplicity with perfect balance. This paper describes several gravity equilibrators providing perfect static balance. As opposed to many known solutions, the proposed balancers incorporate normal off-the-shelf springs, rather than the zero-free-length springs (springs with a length equal to zero when not preloaded or loaded externally) usually employed. The conceptional synthesis is presented, dimensional design criteria are derived, and prototypes are shown. Based on the prototype’s working principle, an ankle prosthesis, which stabilizes the patient, will be developed.

By considering the coupling effect between the healthy lower-limb and the passive prosthesis, this paper builds a heterogeneous dynamic model for gait analysis, where the motions of the healthy limb and the prosthesis are driven by the central pattern generator (CPG) and the hip joint swing, respectively. The foot-ground contact is modelled as the process of unilateral force reaction rather than the constraint to get a refined representation of the gait motion. The response of the heterogeneous model, solved by numerical calculation, is then analyzed by comparison with a real gait test. Preliminary results show that the heterogeneous model not only describes the amputee’s gait well but also reveals a new gait feature of period-doubling. Parameter analysis further indicates that the period-doubling gait will return to the single-period pattern by amplifying the vertical motion of the hip joint at the amputated side. This dynamic bifurcation, which mimics the process of hip swing adaption, provides new insight into the compensatory mechanism for lamely walking.

Total Knee Arthroplasty is one of the most commonly performed orthopedic procedures and it is expected to grow in the next future. In the last past years, computer-assisted procedures represent one of the trends that are transforming the way of practicing medicine. Cornering the Total Knee Arthroplasty, digital models of the joints have been used to carry out simulation of their kinematics and mechanical performance. Whilst for the 3D digital reconstruction of the patient geometry several studies have been conducted, an approximated geometry of the prosthesis has been several times employed, with undeniable consequences on the final results. This paper aims at comparing two non-contact reverse engineering technologies to acquire the shape of femoral components employed for total knee arthroplasty. A high-level device (Konika Minolta Vivid 9i) and a mid-low cost laser (NextEngine) has been compared. For the comparison, a systematic procedure of acquisition and elaboration of the results has been adopted in order to have as unbiased as possible results. The procedure involves the use of the proprietary software of the scanners for the elaboration of the raw data and the meshing procedure has been kept the same for all the models. Since the as-is acquired mesh is of high-resolution, a decimation procedure has been carried out in order to make the 3D models lighter and easier to be handled. Once the decimation procedure has been evaluated comparing the original and the simplified models to one another, the digitalized models have been compared with the measurements taken from a coordinate measuring machines. As a preliminary result, the two lasers seem to be adequate to accomplish the reverse engineering process as required by this application. Of course, the mid-low cost laser would be preferable whether the performance will be confirmed to be (statistically) equal.

A prosthesis is a replacement limb that must be functionally sound, comfortably fit, durable, and aesthetically pleasing. Difficulty in prescription is further amplified by each patient’s unique needs and the variability within patient data. The clinician’ s education and prior training is critical in effectively navigating the wealth of patient specific information needed to prescribe a prosthesis and rehabilitation plan that increases the likelihood of long-term patient success. Education and training significantly vary, however, from country to country, and in Lower Income Countries (LIC) a lack of formalized prosthetic training contributes to a lower quality of life for resident amputees. Prosthetists and technicians in LICs face further challenges due to a lack of material resources and formal medical infrastructure. This study was motivated to understand the types of patient information that influence decision-making strategies during prosthetic prescription and compare strategies across expert and novice groups. The results of this study suggest that salient factors are different between each clinician group and is influenced by the complexity of the patients’ case. Activity level of the amputee influenced novices’ prescription, whereas amputee’s motivation, insurance, and health history influenced experts’ prosthetic prescription. Future work exploring the utility of complimentary or supplemental prescription tools, particularly for prosthetists in LICs, is discussed.

Pelvic reconstruction is required to restore the functional activity after an internal hemipelvectomy. The available pelvic prosthesis has several complications and long terms issues (such as stability, dislocations etc.) due to non inclusion of the basic mechanics. In this study, a structural optimization based pelvic design is presented for an efficient pelvic prosthesis by including the effect of muscles under single leg stance. The single leg stance loading condition is divided into four categories, (a) all muscles, (b) lower muscles, (c) upper muscles and (d) average value of the muscles for entire stance phase. Thereafter, topology optimization is used to generate four prosthesis for pelvic reconstruction. Titanium alloy (Ti 6 Al 4 V) is used to design the pelvic prosthesis. The optimal designs are compared with the natural pelvic bone by measuring the shape similarity index. Results show that the stress and displacement produced by the optimal designs are less than the natural pelvic bone. The induced peak stresses in the optimal designs are low, within linear elastic zone and below the yield strength of the alloy. The moderate to good shape similarity values indicate less complications such as dislocations, stability and constraining the range of hip joint.

This paper proposes a redesign of a four-bar mechanism for an active transtibial prosthesis created by Bergelin 2010 and modified by Klein 2009. Bergelin utilized a four-bar mechanism, motor, and spring to match the prosthesis ankle moments to the ankle moments of a healthy ankle. Bergelin’s prosthesis did succeed in matching ankle moments closely, but with excessive motor energy expenditure when the prosthesis was in a neutral position. Klein proposed a redesign of the mechanism to change the motor-spring connection from parallel to series to eliminate the energy requirement when the device is in neutral position, which allowed for the application of impedance control of mechanism. This paper proposes a reoptimization of the series motor-spring mechanism configuration proposed by Klein, which further reduces the energy input configuration of the active prosthesis.

While using a prosthesis, transtibial amputees can experience pain and discomfort brought on by large pressure gradients, at the interface between the residual limb and prosthetic socket. Current prosthetic interface solutions attempt to alleviate these pressure gradients by using soft homogenous liners to reduce and distribute pressures. This research investigates an additively manufactured metamaterial inlay with adjustable mechanical response in order to reduce peak pressure gradients around the limb. The inlay uses a hyperelastic behaving metamaterial (US10244818) comprised of triangular pattern unit cells which can be 3D printed with walls of various thicknesses controlled by draft angles. The hyperelastic material properties are modeled using a third order representation based on Yeoh 3 rd order coefficients. The 3 rd order coefficients can be adjusted and optimized to represent a change in the unit cell wall thickness to create an inlay that can meet the unique offloading needs of an amputee. Finite element analyses evaluated the pressure gradient reduction from: 1) A common homogenous silicone liner, 2) A prosthetist’s inlay prescription that utilizes three variations of the metamaterial, and 3) A metamaterial solution with optimized Yeoh 3 rd order coefficients. When compared to a traditional homogenous silicone liner for two unique limb loading scenarios, the prosthetist prescribed inlay and optimized material inlay can achieve equal or greater pressure gradient reduction capabilities. These results show the potential feasibility of implementing this metamaterial as a method of personalized medicine for transtibial amputees by creating customizable interface solution to the meet unique performance needs of an individual patient.

People who have suffered a transtibial amputation show diminished ambulation and impaired quality of life. Powered ankle foot prostheses (AFP) are used to recover some mobility of transtibial amputees (TTAs). Powered AFP is an emerging technology that has great potential to improve the quality of life of TTAs with important avenues for research and development in different fields. This paper presents a survey on sensing systems and control strategies applied to powered AFPs. Sensing kinematic and kinetic information in powered AFPs is critical for control. Ankle angle position is commonly obtained via potentiometers and encoders directly installed on the joint, velocities can be estimated using numerical differentiators, and accelerations are normally obtained via inertial measurement units (IMUs). On the other hand, kinetic information is usually obtained via strain gauges and torque sensors. On the other hand, control strategies are classified as high- and low-level control. The high-level control sets the torque or position references based on pattern generators, user’s intent of motion recognition, or finite-state machine. The low-level control usually consists of linear controllers that drive the ankle’s joint position, velocity, or torque to follow an imposed reference signal. The most widely used control strategy is the one based on finite-state machines for the high-level control combined with a proportional-derivative torque control for low-level. Most designs have been experimentally assessed with acceptable results in terms of walking speed. However, some drawbacks related to powered AFP’s weight and autonomy remain to be overcome. Future research should be focused on reducing powered AFP size and weight, increasing energy efficiency, and improving both the high- and the low-level controllers in terms of efficiency and performance.

The Natural User Interface (NUI), which permits a simple and consistent user’s interaction, represents a meaningful challenge for developing virtual/augmented reality applications. This paper presents a set of guidelines to design optimal NUI as well as a software framework, named FrameworkVR, which encapsulates the rules of presented guidelines. FrameworkVR allows developing NUI for VR/AR reality applications based on Oculus Rift, Leap Motions device and on the VTK open source library. An example of VR application for prosthesis design developed using FrameworkVR, is also described. Tests have been carried to validate the approach and the designed NUI and results reached so far are presented and discussed.

Prosthetic limbs and assistive devices require customization to effectively meet the needs of users. Despite the expense and hassle involved in procuring a prosthetic, 56% of people with limb loss end up abandoning their devices [1]. Acceptance of these devices is contingent on the comfort of the user, which depends heavily on the size, weight, and overall aesthetic of the device. As seen in numerous applications, parametric modeling can be utilized to produce medical devices that are specific to the patient’s needs. However, current 3D printed upper limb prosthetics use uniform scaling to fit the prostheses to different users. In this paper, we propose a parametric modeling method for designing prosthetic fingers. We show that a prosthetic finger designed using parametric modeling has a range of motion (ROM) (path of the finger tip) that closely aligns with the digit’s natural path. We also show that the ROM produced by a uniformly scaled prosthetic poorly matches the natural ROM of the finger. To test this, finger width and length measurements were collected from 50 adults between the ages of 18–30. It was determined that there is negligible correlation between the length and width of the index (D2) digit among the participants. Using both the highest and the lowest length to width ratio found among the participants, a prosthetic finger was designed using a parametric model and fabricated using additive manufacturing. The mechanical design of the prosthetic finger utilized a crossed four bar linkage mechanism and its ROM was determined by Freudenstein’s equations. By simulating the different paths of the fingers, we demonstrate that parametrically modeled fingers outperform uniformly scaled fingers at matching a natural digit’s path.

Series Elastic Actuators (SEA) are one of the most widely studied compliant actuators in anthropomorphic robots and prostheses. However, due to the nature of its unique configuration, an unavoidable trade-off has to be made between compliance and bandwidth performance. In this paper, we show that by adopting a hypocycloid mechanism in rotary actuator designs, compliance and high force control bandwidth can be achieved at the same time, while reaping all the benefits of energy storage and shock absorption characteristics of mechanical springs.

Variable stiffness mechanisms have a wide range of applications in the field of human-robot interactions such as rehabilitation robotics, prosthesis and industrial robotics due to their ability to comply with the human limb stiffness in an unstructured environment. This paper presents the analysis of a single degree of freedom variable stiffness actuator based on nonlinear force interactions between permanent magnets and its effect on the natural frequency of the system. In the proposed mechanism, variable stiffness is achieved by modifying the separation between magnets. The main goal here is to achieve a desired cutoff frequency by varying the stiffness of the system to filter out the involuntary movement of upper limb during physical human-robot interactions. Moreover, due to the spring-like non-contact force interactions between magnets, this mechanism can prevent the exchange of high impact forces between the robot and human.

Active, transtibial prostheses typically use finite state control algorithms that struggle with cadence and gait variability of the amputee. Recent work in artificial neural networks (ANN) have shown the possibility to predict the users intent based on EMG activity and the current position of the ankle, which can be used as an input signal into an improved controller. This paper examines how to implement an ANN signal into a zero order impedance controller, i.e., a stiffness controller, on a specific active transtibial prosthesis. The prosthesis incorporates a linear spiral spring in parallel with a four-bar mechanism. In order to implement stiffness control, the spring was moved to being in series with the four-bar mechanism to establish a relationship between the torque of the spring and the position of the motor. To ensure stiffness control is feasible, a MATLAB Simulink model of the system was created to test the robustness of the controller and the effect of moving the spring from parallel to series. The robustness of the controller was verified as the ankle position and torque requirements are met in the simulation. The Simulink model accurately models the new system and can be used in the future to optimize the motor or the four-bar mechanism for this new type of control.

Alongside promising advances in biomechatronics, the following research presents the first documented investigation reviewing the electromechanical system designs of energetically-powered (i.e., robotic) prostheses for patients with transfemoral amputations. The technical review begins with examining the material and mechanical designs, and electrical batteries incorporated into robotic transfemoral prostheses. The actuation systems have encompassed electromagnetic actuators (i.e., occasionally featuring series elastic elements), pneumatic actuators (i.e., pneumatic cylinders and pneumatic artificial muscles), and hydraulic actuators. Various wearable sensors have been utilized to provide closed-loop feedback control, including electromechanical sensors, surface electromyography, and bioinspired machine vision systems. The Össur Power Knee (i.e., the only commercially-available powered transfemoral prosthesis) is additionally discussed. The technical review concludes with suggesting prospective future directions for innovation, specifically lower-limb prostheses capability of electrical energy regeneration.

The rise of affordable rapid non-contact digitizers and rapid prototyping tools, such as 3D printers, is enabling the seamless integration of geometric reverse engineering into the early phases of engineering design. Scanning technology has been widely adopted in bio-reverse engineering and the use of high fidelity non-contact scanners, such as Computed Tomography devices, allows designers, doctors, and researchers to digitally model boney structures, design orthotic and prosthetic devices, and preemptively plan complex surgeries. While the combination of 3D scanning and printing processes holds much promise for the fields of reverse engineering, biodesign, and new product development, problems with repeatability, accuracy, and precision have limited the wider spread adoption of 3D scan to print processes. While some studies have explored the errors inherent in higher fidelity scan to print (S2P) processes, no studies have explored the errors in S2P processes that leverage affordable rapid non-contact digitizers. The purpose of this study was to explore at which phases of the S2P process errors are introduced into the digital model. A controlled study was conducted using data from 27 scans using a common off-the-shelf non-contact optical digitizer and a relatively simple workpiece. Data from the digital thread was collected between each phase of the S2P process and compared against a truth model; the geometric and dimensional integrity of the data was calculated through a comparison between the digital model and the original truth model. Results indicate significant differences between digital models at the various steps of the S2P process.

Vibrotactile feedback may be able to compensate for the loss of sensory input in lower-limb prosthesis users. Designing an effective vibrotactile feedback system would require that users could perceive and correctly respond to vibrotactile stimuli applied by the tactors. Our study explored three key tactor configuration variables (i.e. vibratory intensity, prosthetic pressure, spacing between adjacent tactors) through two experiments. The vibration propagation experiment investigated the effects of tactor configurations on vibratory amplitude at the prosthesis-limb interface. Results revealed a positive relationship between vibratory amplitude and intensity, and a negative relationship between vibratory amplitude and prosthetic pressure. The vibrotactile perception experiment investigated the effects of tactor configurations on user response accuracy, and found that greater spacing between tactors, and higher prosthetic pressure resulted in more accurate responses from the subjects. These findings inform the design of a vibrotactile feedback system for use in lower-limb prostheses: 1) the tactors may be best placed in areas of slightly elevated pressure at the prosthesis-limb interface; 2) a higher vibratory intensity level should improve performance for vibrotactile feedback systems; and 3) more spacing between adjacent tactors improves user response accuracy.