Dynamic characterisation of Össur Flex-Run prosthetic feet for a more informed prescription

Background: The current method of prescribing composite Energy Storing and 6 Returning (ESR) feet is subjective and is based only on the amputee’s static body 7 weight/mass. 8 Objectives: The aim is to investigate their unique design features through identifying 9 and analysing their dynamic characteristics, utilising modal analysis, to determine 10 their mode shapes, natural damping and natural frequencies. Full understanding of 11 the dynamic characteristics can inform on how to tune a foot to match an amputee’s 12 gait and body condition. 13 Methods: This paper presents the modal analysis results of the full range of Össur 14 Flex-Run running feet that are commercially available (1LO-9LO). 15 Results: It is shown that both the undamped natural frequency and stiffness increase 16 linearly from the lowest to highest stiffness category of foot. The effect of over-load 17 and under-loading on natural frequencies is also presented. The damping factor for 18 each foot has been experimentally determined and it was found to be ranging 19 between 1.5-2.0%. An analysis of the mode shapes also showed a unique design 20 feature of these feet that is hypothesised to enhance their performance. 21 Conclusions: A better understanding of the feet dynamic characteristics can help to 22 tune the feet to the user’s requirements. 23 (194 words

Development of an economic wireless human motion analysis device for quantitative assessment of human body joint

In recent years, the study of human body dynamics has been attracting a significant amount of attention. Currently there are many camera or active sensor based motion analysis systems available on the market. They have been extensively adopted and used by the film and animation or entertainment industries such as film and video game producers. More recently their potential in studying human dynamics / motion for medical purposes has been realised to the extent that they are now used to study full body human biomechanics in the form of gait analysis systems. Most orthopaedic surgeries are usually about joint repair or implants. According health line, revision surgery is usually due to infection, continued pain, joint stiffness, wear, instability, loosening. Apart from infection, the rest can be linked to the operation itself. Currently, surgical planning and placing implants is performed in a subjective manner, relying on the surgeon’s experience and instinct, current systems to help the surgeon to place implant are also bulky, expensive, slow and not user friendly. The aim of this project is to develop an economic and portable motion assessment system which involves a wireless inertial measurement unit (IMU) dedicated to study and assess body joints. Through the data collected from the IMU, the system is capable real time measurement of relative position and orientation of the human joint. Several tests were conducted to validate the data extracted from gyroscope and accelerometer of the IMU. The joint motion results analysed using the device was compared with the results analysed using commercial video motion analysis software and it shows good correlation. It is found that the gyroscope of the IMU under DMP sensor fusion algorithm and calibration capability is able to give the angular velocity with less than 5% error. This has led to a more accurate orientation data which gives 7% error in average bending angle

Impact Force Identification using the Modal Transformation Method in Collocated and Non-Collocated Cases

Previous impact force identification has focused on collocated cases because noncollocated cases tend to be ill-posed. Considering the impact location is inaccessible, impact force identification using remote responses away from the impact location must be developed. This study initiates an effort to examine impact force identification for non-collocated case. A methodology utilizing operating deflection shape analysis, modal analysis and the modal transformation method (MTM) is presented to identify the unknown dynamic force. The performance of this approach is examined via experimental verification. The objective of this study is to examine the effectiveness of impact force identification by using MTM for both collocated and non-collocated cases. By measuring the response and frequency response function of the test rig, the time history of the unknown force is recovered by the force identification method where the impact location is known. The proposed method is examined at Points 1 and 15, which have satisfactory and poor curve fitting results respectively. It is found that force accuracy improves when the curve fitting result is enhanced. Experimental results show that impact force identification via MTM is applicable in both collocated and noncollocated cases, only if the curve fitting results satisfactory

Impact Force Identification using the Modal Transformation Method in Collocated and Non-Collocated Cases

Previous impact force identification has focused on collocated cases because noncollocated cases tend to be ill-posed. Considering the impact location is inaccessible, impact force identification using remote responses away from the impact location must be developed. This study initiates an effort to examine impact force identification for non-collocated case. A methodology utilizing operating deflection shape analysis, modal analysis and the modal transformation method (MTM) is presented to identify the unknown dynamic force. The performance of this approach is examined via experimental verification. The objective of this study is to examine the effectiveness of impact force identification by using MTM for both collocated and non-collocated cases. By measuring the response and frequency response function of the test rig, the time history of the unknown force is recovered by the force identification method where the impact location is known. The proposed method is examined at Points 1 and 15, which have satisfactory and poor curve fitting results respectively. It is found that force accuracy improves when the curve fitting result is enhanced. Experimental results show that impact force identification via MTM is applicable in both collocated and noncollocated cases, only if the curve fitting results satisfactory

Simulation of gait asymmetry and energy transfer efficiency between unilateral and bilateral amputees

Efficient walking or running requires symmetrical gait. Gait symmetry is one of the key factors in efficient human dynamics, kinematics and kinetics. The desire of individuals with a lower-limb amputation to participate in sports has resulted in the development of energy-storing and-returning (ESR) feet. This paper analyses a case study to show the effect of symmetry and asymmetry as well as energy transfer efficiency during periodic jumping between simulated bilateral and unilateral runners. A custom gait analysis system is developed as part of this project to track the motion of the body of a physically active subject during a set of predefined motions. Stance and aerial times are accurately measured using a high speed camera. Gait frequency, the level of symmetry and the non-uniform displacement between left and right foot and their effects on the position of the Centre of Mass (CM) were used as criteria to calculate both peak energies and transformation efficiency. Gait asymmetry and discrepancy of energy transfer efficiency between the intact foot and the ESR are observed. It is concluded that unilateral runners require excessive effort to compensate for lack of symmetry as well as asymmetry in energy transfer, causing fatigue which could be a reason why bilateral amputee runners using ESR feet have a superior advantage over unilateral amputees

Artificial neural networks for vibration based inverse parametric identifications: A review

Vibration behavior of any solid structure reveals certain dynamic characteristics and property parameters of that structure. Inverse problems dealing with vibration response utilize the response signals to find out input factors and/or certain structural properties. Due to certain drawbacks of traditional solutions to inverse problems, ANNs have gained a major popularity in this field. This paper reviews some earlier researches where ANNs were applied to solve different vibration-based inverse parametric identification problems. The adoption of different ANN algorithms, input-output schemes and required signal processing were denoted in considerable detail. In addition, a number of issues have been reported, including the factors that affect ANNs’ prediction, as well as the advantage and disadvantage of ANN approaches with respect to general inverse methods Based on the critical analysis, suggestions to potential researchers have also been provided for future scopes

Enhancement of impact force determination with modal transformation method by using integration and data filtering /Khoo Shin Yee

Discovering the in-service dynamic forces, their location and their line of action regarding the structure are necessary during its design, development and modification stages. Additional information about the loads experienced by the structure will aid the development iterations resulting in a better outcome. However, direct measurement by using force transducer is not practical in some cases due to some difficulties in force sensor configuration. As an alternative, it would be more convenient to just measure the response and dynamic characteristic of a structure by using Operating Deflection Shape (ODS) analysis and Frequency Response Function (FRF) measurement. Hence, the analysis involved backtracking to determine the force causing the problem can be done. It is known that this inverse problem is ill-conditioned in most practical cases. In this study, a Perspex plate with 4 ground supports was used as test rig. Recovery of unknown impact force using Modal Transformation Method (MTM) is experimentally demonstrated. The transformation from high condition number of synthesised FRF matrix to a well-conditioned case is demonstrated by adding additional information of force location. The low quality of fitting a modal model by using modal parameters obtained from the polynomial curve fitting algorithm is highlighted. In this study, impact force determination with MTM is enhanced by using integration and data filtering approaches. The effectiveness of various types of responses (i.e. measured acceleration responses from sensors; velocity and displacement responses obtained from integration result) is studied, and the results of the impact force determination are examined in under-estimated, even-estimated and over-estimated cases of fixed analysis frequency range. The outcomes show the importance of selecting a suitable response unit and an appropriate analysis frequency range in impact force determination. When the excitation frequency of an impact force is unknown and time-variant, selection of an appropriate analysis frequency range by using Power Spectral Density (PSD) tool i

Simulation of Performance Enhancement of Bi-Lateral Lower-Limb Amputees Through Impulse Synchronisation with Self Selected Running Step Frequency

Current method of enhancing the performance of a bilateral amputee runners using energy return prosthesis is rarely linked to the system dynamics. In this paper a simple simulation is used to show that if a self selected running step frequency could be synchronized with dynamic elastic response of a mass spring system extra gain in height or faster take off velocity can be achieved which results is higher state of energy equilibrium that is more favourable to running activity. Current method often relies on physiological methodology, making the differentiation between the contributions from the biological and the prosthetic element of the below-knee amputee athlete difficult. In this paper a series of mass and composite foot system are modelled based on a combination of mass, spring and damper arrangement to study the effect of gravity, mass, stiffness, damping and inertia on the dynamics characteristics of prosthesis and how human can instinctively detect the natural elastic response of such system both to cyclic excitation and impulse through self selection of frequency or impulse.It will be demonstrated that if the natural characteristics of a system are identified and synchronised with the physiological gait behaviour of a runner, performance enhancement could occur that can be stored and controlled at will by the user. In the case of a bi-lateral amputee athlete with near symmetrical gaitit can result in steady state running which can be beneficial over longer distances. Keywords: Amputee, Prosthesis, Lower-Limb, Foot, Energ

A Simplified Technique to Distinguish Unbalance and Misalignment Using Frequency Domain Operating Deflection Shape

Machinery fault can be identified by performing Condition-Based Monitoring (CBM) program which rely on the machinery vibration data. However, the data which represented by the time wave and vibration spectrum requires technically trained personnel to understand and diagnose. In this research, a simplified technique through visualization of the Operating Deflection Shape (ODS) is proposed. The technique combines both the data of vibration amplitude and phase measurement. An ODS of a general machinery arrangement can be visualized from 4 measurement points. The technique is performed and tested in laboratory condition. Future CBM program should implement this technique because it helps untrained personnel to be able to distinguish primary machinery fault such as unbalance and misalignment easily by visualizing the machine motion

A Performance Study of Controlled Impact Timing on Harmonics Reduction in Operational Modal Testing

As an alternative to operational modal analysis and classical experimental modal analysis (EMA), a novel method was introduced previously, namely impact-synchronous modal analysis (ISMA). The effectiveness ISMA on rotor and structural dynamic systems has been proven in previous literature. More recently, an automated impact device (AID) was introduced which utilized tachometer pulse as initiation signal and its effectiveness on ISMA was proven. An attempt to further enhance this device in term of equipment and cost is then proposed by replacing the tachometer with the in-use tri-axial accelerometer through utilizing the filtered response of cyclic load component as an initiation signal to control the impact device, which is also the primary aim for this study. Prior to modal testing, accuracy of this device is illustrated at desired phase angles of 0 deg, 90 deg, 180 deg, and 270 deg. Subsequently, frequency response function (FRF) estimations obtained for ISMA using enhanced AID has demonstrated the suppression capabilities of this device on disturbances, i.e., reduction of 93.58% at 30 Hz and 57.78% at 60 Hz, resulting in a high correlation for signature assurance criterion (SAC) and cross signature assurance criterion (CSAC). Modal parameters extracted from the EMA and ISMA using impact device are presented and compared, for the first three natural modes of the test rig. It is found that natural frequencies are deviating by less than 6%, whereas modal assurance criterion (MAC) values between the mode shapes of the two tests are found to be above 0.9