Browsing by Author "Kyberd, Peter J."

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    A Totally Modular Arm Prosthesis
    (1999) Kyberd, Peter J.; Gow, David; Sperling, Lena; Boman, Andreas
    While some groups and centres have attempted to promote greater levels of sophistication in exo-prosthetics it is only in the past couple of year s that the ideas of computer control to be applied in prostheses has received a more widespread acceptance. It is probable that those at the clinical end have only recently become aware of the potentials within the electronics field. Now there are some systems that do incorporate some technology into their products. The latest trainer from Otto Bock is an example of the capabilities of such systems. The VASI systems with their reconfigurable set up has begun to show the extent to which the technology can progress. The TOMPAW project also aims explore this area more fully. TOMPAW stands for TOtally Modular Prosthetic Arm with high Workability. It is an EU project under the TIDE initiative (DE4210). The projects target is to produce a fully modular and functional prosthetic arm system that will enable the users and the clinical teams to customise the device to the user with the minimum of effort and time.
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    CANCELLATION OF FORCE INDUCED ARTIFACTS IN SURFACE EMG USING FSR MEASUREMENTS
    (2008) Fougner, Anders; Sæther, Marthe; Stavdahl, Øyvind; Kyberd, Peter J.; Blum, Jeremy
    As multifunction prostheses become increasingly common, there is a need for improved control signal quality in order to control all the functions. Most signals commonly used for prosthesis control are sensitive to sweat, motion and external forces [1], which impairs prosthesis control performance. We have developed a prototype surface electromyogram (sEMG) sensor with three built‐in force sensing resistors (FSRs) for measuring the external forces, which may be used to cancel artifacts caused by these forces. The performance of the sensor as an estimator of muscle force is presented in this paper. The sEMG and FSR signals have also been tested individually, as a reference for the performance using the combination of these signals.
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    Experience With Hierarchically Controlled Hand Prosthesis
    (1999) Kyberd, Peter J.
    The principles of hierarchical control ofhand prostheses have been described in previous MEC meetings. Simply put: It is possible to achieve easy use of a multi-axial artificial hand if the detailed control of the hand's grip posture and force is devolved to a microprocessor controller. Thus the controller is given simple instructions to open and close the hand and the controller decides on the grip posture based on the contact between hand and object and then adjusts the grip force depending on any motion of the object relative to the hand. Thus if the object slips the hand automatically grips tighter. This idea has been considered for many years. Now it is sufficiently well taken that similar methods are being applied by prosthesis producers. The detection of the slip is achieved using an acoustic method, where the sound of the start of the slide is detected. Although this may not mean that the entire object is moving relative to the hand, but only parts of the object, so called partial slip. A second method is that of measuring the change in the contact forces and inferring slip from those changes. This method can be confused by a change in orientation of the object or hand that occurs without slip. The concept has beenr ealised by a number of designs of prostheses in the past. They can be used with different numbers of degrees of fieedom, from one through to four (and most recently six). The basic control remains the same, the only difference is the number of different types of basic grip form can be achieved. For example: In the two degree of freedom hand, the controller can select from precision or power type prehension. Additional degrees of motion allow the controller to add, two or three jaw precision, lateral prehension and a more compact form of the power grip. The trigger between the different grips is the point of first contact between the hand and the target object during the reaching phase of a manipulation. The current generation of device that has been produced at the Oxford Orthopaedic Engineering Centre has been designed in order to be produced in small numbers and to be used extensively in the field. To that end a lightweight, robust, device was designed an tested and is now under going field assessment at Oxford.
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    Multimodal Input Device With SEMG And Contact Force Sensors
    (2011) Stavdahl, Øyvind; Kyberd, Peter J.; Magne, Tordis; Ottermo, Maria V.; Mugaas, Terje
    In myoelectric prostheses, movement artifacts are known to impair control performance. This study relates to a novel sensor which measures surface electromyograms (SEMG) as well as contact force at the electrode-skin interface. Its purpose is to explore the in-socket mechanical realities of movement artifacts in order to produce control algorithms that are more robust to said artifacts. The new sensor includes a commercial SEMG electrode and four surface-mounted force sensors, stacked within a plastic housing. Preliminary experiments in an experienced transradial user showed that sudden lack of control was often caused by electrode lift-off or re-connection. Future work will include algorithms for alleviating these problems.
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    The Use of Fuzzy Logic In the Processing Of Myoelectric Signals
    (1999) Taffler, Sean; Kyberd, Peter J.
    This paper describes the use of Fuzzy logic for the processing of EMG signals. This can increase the recognition rate and significantly reduce the number of computations required to generate an output. The initial placement of the Fuzzy sets was accomplished with the use of neural network techniques, these are not required for in the final system, only for setting up. The effectiveness of the features extracted from the EMG signals has been assessed using Principal Component Analysis (PCA) The developed system exhibits good generalisabilty but performs better when tuned to the intended user.
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    The use of the Hilbert transforra in EMG Analysis
    (1999) Taffler, Sean; Kyberd, Peter J.
    The Fourier transform has traditionally been used for the detailed analysis of EMG signals. This has yielded many useful results, none more so than the descriptions of the energy produced at differing frequencies. This has been invaluable in the development of robust EMG controllers and the analysis of active or diseased muscle. Recently, Wavelet analysis has been applied to the study of EMG signals and it has provided additional insight into the underlying structure of the signal. Both these methods have drawbacks, the Fourier transform relies on analysis of complete wavelengths to describe a signal Wavelet analysis cannot resolve any event less than the length of the fundamental Wavelet. These factors manifest themselves as a smudging or broadening of the spectrum and therefore they lead to inprecissions in the results. Empirical Mode Decomposition (EMD) and the Hilbert Transform (HT) have been applied to analyse the the EMG signal. This is a method that is used extensively in the fields of seismology and meteorology and is now being applied to biological data. It is particularly good a resolving signals that are not based on continuous sinusoids. It has been used on EMGs to show that the energy in the signal is significant at frequencies up to 2KHz. The paper will present the results of a study of signals derived from a range of prosthesis users and non-users. The results from the Hilbert transform will be compared with results obtained using conventional methods of analysis.
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    Using multiple outcome measures to determine skill level in myoelectric prosthesis use
    (2011) Bouwsema, Hanneke; Kyberd, Peter J.; Hill, Wendy; van der Sluis, Corry K.; Bongers, Raoul M.
    Most studies on prosthesis usage focus merely on one type of outcome measures, using questionnaires, functional tests, or kinematics. However, a combination of several outcome measures should provide a better picture on prosthesis use (Hill et al. 2009, Lindner et al. 2010, Wright 2009). Using both clinical and more fundamental measures (such as kinematics) would not only provide information about the skill level of a prosthesis user, but would also give insight in the processes from which the level of skill originates. To maximize the insight in the skill level of a prosthesis user the current study gauged a wide range of outcome measures. The aims of this study were 1) to describe prosthetic functioning at different levels of performance; 2) to relate the results of the clinical level to the more fundamental outcome measures; 3) to identify specific parameters in these measures that characterize the level of skill of a user.