S. Sujatha

Design of controller for single axis knee using hydraulic damper

A prosthetic swing-phase control mechanism simulates the action of the upper leg musculature to aid in increased gait function. More specifically, swing-phase control mechanisms limit the maximum knee flexion and allow the shank to smoothly decelerate into full knee extension without excessive impact. In this work, a hydraulic damper is designed with the objective of controlling swing-phase damping in an above-knee prosthesis. A linear spring and damper model is used to represent the dynamic properties of the damper. Based on this model, three control parameters that govern the damping force and displacement of the damper have been identified. The parameters of the damper are determined through optimization of the prosthesis knee angle with a desired knee angle trajectory obtained from experimental data in normal level walking. Experimental data of thigh and hip motions are introduced as inputs into a dynamic system to find out a set of control parameters. A computer simulation is carried out. Comparison of the desired knee angle with that of the knee angle obtained from control parameters shows the effectiveness of the present design. Moreover, conditions of knee angle and shank velocity at the end of swing phase have been checked. The results obtained show a satisfactory performance of the system.

A method for performance comparison of polycentric knees and its application to the design of a knee for developing countries.

Background: Polycentric knees for transfemoral prostheses have a variety of geometries, but a survey of literature shows that there are few ways of comparing their performance. Objectives: Our objective was to present a method for performance comparison of polycentric knee geometries and design a new geometry. Study design: In this work, we define parameters to compare various commercially available prosthetic knees in terms of their stability, toe clearance, maximum flexion, and so on and optimize the parameters to obtain a new knee design. Methods: We use the defined parameters and optimization to design a new knee geometry that provides the greater stability and toe clearance necessary to navigate uneven terrain which is typically encountered in developing countries. Results: Several commercial knees were compared based on the defined parameters to determine their suitability for uneven terrain. A new knee was designed based on optimization of these parameters. Preliminary user testing indicates that the new knee is very stable and easy to use. Conclusion: The methodology can be used for better knee selection and design of more customized knee geometries. Clinical relevance The method provides a tool to aid in the selection and design of polycentric knees for transfemoral prostheses.

A Method for Optimal Synthesis of a Biomimetic Four-Bar Linkage Knee Joint for a Knee-Ankle-Foot Orthosis

A Knee-Ankle-Foot orthosis (KAFO) is used as a supportive device by individuals with lower limb disability. A type of KAFO that allows knee flexion-extension is prescribed for people who need knee stability in the transverse and frontal planes. In such an orthosis, mimicking the human knee motion is vital to avoid relative motion (called pistoning) between the limb and the orthosis. A four-bar mechanism, owing to its polycentric nature, simplicity and ease of fabrication can provide a customizable, biomimetic solution. This paper presents an improved and robust optimization approach to synthesize a four-bar mechanism to closely mimic the anatomical knee motion. The reference human knee centrode is obtained from literature. A genetic algorithm is used for optimal synthesis of the fourbar mechanism. Results show that the average error between the reference centrode and the centrode of the synthesized four-bar mechanism is very small (0.2 mm). Thus, the synthesized crossed four-bar linkage can reproduce better anthropomorphic characteristics of the knee joint. The methodology can be used for the design of customized orthotic knee joints for KAFOs and knee braces.

Identification and analysis of knee–ankle–foot orthosis design requirements based on a feedback survey of orthosis users in India

Abstract Purpose: The world is advancing towards a technological revolution in various fields, yet the assistive devices available for people with disability, especially in developing countries, are in the most primitive stage. For many years, lower limb orthotics has been a neglected area of research and there is an urgent need to address the problems faced by lower limb orthosis users to enable them to lead an independent life. This work is a first step in this direction and aims to identify and analyse the needs of knee–ankle–foot orthosis (KAFO) users in India. Method: A structured feedback survey of 29 KAFO users was conducted at three rehabilitation centres located in South India. A feedback questionnaire and a novel outcome measure tool (trigger cards) were used as means to assess user satisfaction about their existing KAFOs. The results of the survey were analysed to obtain quantitative and qualitative outcomes. Results: The survey identifies various biomechanical and functional issues associated with lower limb orthosis design. The results of the survey imply that there is an urgent need to solve issues, especially related to locked orthotic knee joint design. Additionally, it sheds light on the lifestyle and socio-economic issues of KAFO users that are likely prevalent in many other low- and middle-income countries. Conclusions: The outcomes of this survey can motivate and guide researchers to design improved orthotic solutions to meet the needs of lower limb orthosis users all over the world. Implications for Rehabilitation  • This is a first of its kind survey that brings forth the needs of lower limb orthosis users in India, and is an important step towards rehabilitation and empowerment of people with lower limb disability.  • The pilot survey helps to identify critical areas for design improvements in a knee–ankle–foot orthosis.  • The outcomes of this survey can help researchers to design functionally improved assistive devices that better meet the needs of users than currently available technology in developing countries such as India.

Minimal Kinematic Model for Inverse Dynamic Analysis of Gait

The objective of this work is to develop an inverse dynamics model that uses minimal kinematic inputs to estimate the ground reaction force (GRF). The human body is modeled with 14 rigid segments and a circular ankle-foot-roll-over shape (AFROS) for the foot-ground interaction. The input kinematic data and body segment parameter estimates are obtained from literature. Optimization is used to ensure that the kinematic data satisfy the constraint that the swing leg clears the ground in the single support (SS) phase. For the SS phase, using the segment angles as the generalized degrees of freedom (DOF), the kinematic component of the GRF is expressed analytically as the summation of weighted kinematics of individual segments. The weighting functions are constants that are functions of the segment masses and center of mass distances. Using this form of the equation for GRF, it is seen that the kinematics of the upper body segments do not contribute to the vertical component GRFy in SS phase enabling the reduction of a 16-DOF 14-segment model to a 10-DOF 7-segment model. It is seen that the model can be further reduced to a 3-DOF model for GRFy estimation in the SS phase of gait. The horizontal component GRFx is computed assuming that the net GRF vector passes through the center of mass (CoM). The GRF in double support phase is assumed to change linearly from one foot to the other. The sagittal plane internal joint forces and moments acting at the ankle, knee and hip are computed using the 3-DOF model and the 10-DOF model and compared with the results from literature. An AFROS and measurements of the stance shank and thigh rotations in the sagittal plane, and of the lower trunk (or pelvis) in the frontal plane provide sufficient kinematics in an inverse dynamics model to estimate the GRF and joint reaction forces and moments. Such a model has the potential to simplify gait analysis.© 2014 ASME