Ramazan Ünal

Modeling and design of energy efficient variable stiffness actuators

In this paper, we provide a port-based mathematical framework for analyzing and modeling variable stiffness actuators. The framework provides important insights in the energy requirements and, therefore, it is an important tool for the design of energy efficient variable stiffness actuators. Based on new insights gained from this approach, a novel conceptual actuator is presented. Simulations show that the apparent output stiffness of this actuator can be dynamically changed in an energy efficient way.

Prototype design and realization of an innovative energy efficient transfemoral prosthesis

In this paper, we present the prototype realization of the conceptual design of a fully-passive transfemoral prosthesis. The working principle has been inspired by the power flow in human gait so to achieve an energy efficient device. The main goal of this paper is to validate the concept by implementing in a real prototype. The prototype, in scale 1 ∶ 2 with respect to the average dimensions of an adult human, is based on two storage elements, which are responsible for the energetic coupling between the knee and ankle joints during the swing phase and for the energy storage during the stance phase. The design parameters of the prototype are determined according to the human body and the energetic characteristics of the gait. The construction of the prototype is explained in details together with a test setup that has been built to evaluate the prototype.

A Multi-criteria Design Optimization Framework for Haptic Interfaces

This paper presents a general framework for optimization of haptic interfaces, in particular for haptic interfaces with closed kinematic chains, with respect to multiple design objectives, namely kinematic and dynamic criteria. Both performance measures are discussed and optimization problems for a haptic interface with best worst-case kinematic and dynamic performance are formulated. Non-convex single objective optimization problems are solved with a branch-and-bound type (culling) algorithm. Pareto methods characterizing the trade-off between multiple design criteria are advocated for multi-criteria optimization over widely used scalarization approaches and Normal Boundary Intersection method is applied to efficiently obtain the Pareto-front hyper-surface. The framework is applied to a sample parallel mechanism (five-bar mechanism) and the results are compared with the results of previously published methods in the literature. Finally, dimensional synthesis of a high performance haptic interface utilizing its Pareto-front curve is demonstrated.

Multi-criteria Design Optimization of Parallel Robots

This paper presents a framework for multi-criteria design optimization of parallel mechanisms. Pareto methods characterizing the trade-off between multiple design criteria are advocated for multi-criteria optimization over widely used scalarization approaches and Normal Boundary Intersection method is applied to efficiently obtain the Pareto-front hyper-surface. The proposed framework is compared against sequential optimization and weighted sum approaches. Dimensional synthesis of a sample parallel mechanism (five-bar mechanism) is demonstrated through estimation of the relative weights of performance indices that are implicit in the Pareto plot. The framework is computational efficient, applicable to any set of performance indices, and extendable to include any number of design criteria that is required by the application.

Optimal dimensional synthesis of force feedback lower arm exoskeletons

This paper presents multi-criteria design optimization of parallel mechanism based force feedback exoskeletons for human forearm and wrist. The optimized devices are aimed to be employed as a high fidelity haptic interfaces. Multiple design objectives are discussed and classified for the devices and the optimization problem to study the trade-offs between these criteria is formulated. Dimensional syntheses are performed for optimal global kinematic and dynamic performance, utilizing a Pareto front based framework, for two spherical parallel mechanisms that satisfy the ergonomic necessities of a human forearm and wrist. Two optimized mechanisms are compared and discussed in the light of multiple design criteria. Finally, kinematic structure and dimensions of an optimal exoskeleton are decided.

Design of a fully-passive transfemoral prosthesis prototype

In this study, we present the mechanical design of a prototype of a fully-passive transfemoral prosthesis for normal walking. The conceptual working principle at the basis of the design is inspired by the power flow in human gait, with the main purpose of realizing an energy efficient device. The mechanism is based on three elements, which are responsible of the energetic coupling between the knee and ankle joints. The design parameters of the prototype are determined according to the human body and the natural gait characteristics, in order to mimic the dynamic behavior of a healthy leg. Hereby, we present the construction details of the prototype, which realizes the working principle of the conceptual mechanism.

Modeling of WalkMECH: A fully-passive energy-efficient transfemoral prosthesis prototype

In this paper we present the port-based model of WalkMECH, a fully-passive transfemoral prosthesis prototype that has been designed and realized for normal walking. The model has been implemented in a simulation environment so to analyze the performance of the prosthetic leg in walking experiments and so to enhance the mechanics of the system. The accuracy of the model has been validated by experimental tests with a unilateral amputee participant.

Biomechanical conceptual design of a passive transfemoral prosthesis

In this study, we present the conceptual design of a fully-passive transfemoral prosthesis. The proposed design is inspired by the analysis of the musculo-skeletal activity of the healthy human leg. In order to realize an energy efficient device, we introduce three storage elements, which are responsible of the energetic coupling between the knee and the ankle joints. Simulation results show that the power storage of the designed conceptual prosthesis is comparable with the human gait.

The control of recycling energy strorage capacity for WalkMECHadapt

In this study, we present the implementation of the controller for adapting the energy storage capacity of the WalkMECH according to the different walking speeds and gait characteristics of an amputee. Since the main aim is to keep the design both mechanically and metabolically energy-efficient, the actuation system is designed based on the minimal actuation principle. The overall system, called WalkMECHadapt, is evaluated with the experimental test set-up with a healthy subject. Test results show that the system is working sufficiently for adapting the energy storage capacity of the WalkMECHadapt thanks to the simple nature of the controller architecture.

WalkMECH: design and control of an energy recycling transfemoral prosthesis

This study presents the design and realization of an energy-efficient trans-femoral prosthesis called WalkMECH. Trans-femoral amputees consume significant amount of extra metabolic energy (more than 65% extra) during walking compared to the ablebodied person. Therefore, we mainly focused on the design possibilities for reducing the metabolic cost of an amputee during walking. Both clinical and bio-mechanical research studies have shown that the lack of energetic relations between the hip, knee and ankle joints that take place with the muscles and tendons of the natural leg is one of the main reasons for the extra metabolic energy consumption of a trans-femoral amputee during walking by means of a prosthetic device. In particular, the lack of ankle push-off generation in the current trans-femoral prostheses is considered to be the main limitation, since this generation requires more than 80% of the energy that is recycling between the joints in healthy human gait. nIn this study, a research has been conducted that led to the design of a trans-femoral prosthesis that reduces the metabolic energy cost by providing an ankle push-off generation. The design is inspired by the power exchange between the hip, knee and ankle joints of the natural human leg. The working principle of the prosthetic device is based on elastic storage elements, which are responsible for the energetic recycling between the knee and ankle joints. nIn conclusion, the evaluation studies on the performance and validation of the working principle show that the prosthesis prototype is working as hypothesized. Also the feedback from the amputee partic- ipants are promising for the realization of WalkMECH as a prosthetic device. The patent application of the design was published under the Patent Cooperation Treaty (PCT) with the international publication number: WO 2012/177125 A1 on 27 December 2012.