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Biomedical subjects

P H Chappell

Publications and source records attributed to P H Chappell.

15 recordsLinked to original sources
PubMed2005

The functional form of the lognormal distribution as a sum of decaying exponential and sinusoidal terms applied to the isometric pinch force of human fingers.

The transient data of the pinch force produced between the human forefinger and thumb have been shown to fit the functional form of the well-known lognormal density function. Isometeric force generation is achieved by the stochastic recruitment of individual motor units, which sum together. Evidence from animal and human experiments demonstrates that the force generation can be modelled by underdamped terms. It is shown that a lognormal time series (distribution) can be fitted to a sum of exponential decaying sinusoidal terms.

Electric Stimulation↗
PubMed2005

A microcontroller system for investigating the catch effect: functional electrical stimulation of the common peroneal nerve.

Correction of drop foot in hemiplegic gait is achieved by electrical stimulation of the common peroneal nerve with a series of pulses at a fixed frequency. However, during normal gait, the electromyographic signals from the tibialis anterior muscle indicate that muscle force is not constant but varies during the swing phase. The application of double pulses for the correction of drop foot may enhance the gait by generating greater torque at the ankle and thereby increase the efficiency of the stimulation with reduced fatigue. A flexible controller has been designed around the Odstock Drop Foot Stimulator to deliver different profiles of pulses implementing doublets and optimum series. A peripheral interface controller (PIC) microcontroller with some external circuits has been designed and tested to accommodate six profiles. Preliminary results of the measurements from a normal subject seated in a multi-moment chair (an isometric torque measurement device) indicate that profiles containing doublets and optimum spaced pulses look favourable for clinical use.

Ankle Joint↗
PubMed2000

Development of a lightweight and adaptable multiple-axis hand prosthesis.

The last few decades have produced significant improvements in the design of upper limb prostheses through the increasing use of technology. However the limited function exhibited by these devices remains rooted in their single degree of freedom format. Commercial myoelectric hand prostheses warrant high grip forces to ensure stable prehension due to a planar pincer movement. Hence precise and conscious effort is required on the part of the user to ensure optimum grip. Consumers have shown dissatisfaction with the status quo due to the excessive weight and poor function of existing artificial hands. Increasing the number of grasping patterns and improving the visual feedback from an object in the hand are cited as key objectives. This paper outlines the development of the six-axis Southampton-Remedi hand prosthesis that addresses these design issues by maintaining stable prehension with minimal grip force. Constraints such as modularity, anthropomorphism, and low weight and power consumption are factors that have been adhered to throughout the design process.

Artificial Limbs↗
PubMed1999

Hand and arm injuries associated with repetitive manual work in industry: a review of disorders, risk factors and preventive measures.

Musculoskeletal disorders are the most common self-reported, work-related illness in the UK, with upper limb disorders ranking second only to back complaints. The rapid increase in disablement cases, the reduced productivity resulting from the disorders, and, perhaps, the threat of litigation which is on the increase, has led to an increased awareness of the problems and an increasing desire to reduce the incidence of such disorders. This paper reviews the problem of upper limb disorders and focuses on those disorders that could be associated with repetitive manual work in industry. The disorders are described and categorized, and potential occupational risk factors are discussed and related to the injuries. In addition, a number of preventive measures, in the form of ergonomics design changes and changes in workplace practice are reviewed. There are frequent calls for well-designed epidemiological studies, so that meaningful dose-response relationships can be drawn up. A significant part of good study design is associated with measurement and analysis of the user-tool interface and the working environment. With this in mind, a variety of measurement techniques are described. Furthermore, this paper highlights the need for study designs to be founded on a better understanding of the potential damage mechanisms, and points the way towards which areas should be investigated.

Arm Injuries↗
PubMed1998

A portable system for closed loop control of the paralysed hand using functional electrical stimulation.

A portable and closed-loop system is described for the paralysed hand using transcutaneous electrical stimulation. It is implemented using a modest microprocessor which receives data from force sensors mounted in a glove on the users hand. A display shows parameter values and a menu for the user to sequentially select controller states. For the grip state, the control loop is basically proportional plus a two stage integral response (gain adaptation). Eight channels can be accommodated in the stimulator. The system was evaluated with the help of a tetraplegic who managed to hold everyday objects in a stable grip.

Biomedical Engineering↗
PubMed1996

A method for the extraction of an object from a noisy background.

The removal of the background from a noisy image to leave the object of interest, with well defined edges, is a difficult task. Images obtained using radioisotopes have low signal-to-noise ratios due to scattered photons, as well as emitted radiation from the background. Moreover, noise is, also, a consequence of the low number of detected photons. A scan of a row or column of such an image demonstrates that the pixels do not change value rapidly near the edge of the object. In addition, clusters of pixels, which can be found outside the edges of the object and in the background, can have higher values than those in the object. This effect is worse in abnormal images, where the abnormal clusters may have values as low as those of the noisy clusters. An image processing technique has been developed to determine the object edges. It is part of a research project in the field of the computer aided diagnosis, which involves artificial neural networks. It makes use of the so-called 'moving window operations' which are very common in digital image processing. The technique was tested using male lung images that were taken by a gamma camera.

Algorithms↗
PubMed1995

Real time microcontroller implementation of an adaptive myoelectric filter.

This paper describes a real time digital adaptive filter for processing myoelectric signals. The filter time constant is automatically selected by the adaptation algorithm, giving a significant improvement over linear filters for estimating the muscle force and controlling a prosthetic device. Interference from mains sources often produces problems for myoelectric processing, and so 50 Hz and all harmonic frequencies are reduced by an averaging filter and differential process. This makes practical electrode placement and contact less critical and time consuming. An economic real time implementation is essential for a prosthetic controller, and this is achieved using an Intel 80C196KC microcontroller.

Artificial Limbs↗
PubMed1995

A new approach in artificial neuron theory for use in computer aided diagnosis.

An artificial neuron, which has an original training process, has been developed as part of a project in the field of computer aided diagnosis. The aim of this work is to analyse medical images to recognise an abnormal region of an organ. In contrast to other methods, generating information of the abnormality's level is part of the recognition stage. Moreover, the whole process is independent of the particular disease. The neuron was tested using lung images taken by a gamma camera.

Diagnosis, Computer-Assisted↗
PubMed1994

The Southampton Hand: an intelligent myoelectric prosthesis.

The form of the control and structure of the mechanism of an artificial hand are important factors which tend to dictate the prosthesis' level of use. Conventional prostheses are simple devices with limited functional range and a control format that requires high levels of user concentration for successful operation. The Southampton Adaptive Manipulation Scheme (SAMS) is a hierarchical control format that allows a larger number of independent motions to be controlled while requiring a smaller degree of user input. The SAMS control has been applied to different hand mechanisms, both custom-made and modified commercial systems. Their application with users shows them to have a performance on a par with, or superior to, other conventional devices. The form of prosthesis control is reviewed and the development of, and clinical experiments with, the Southampton Hand are outlined.

Artificial Limbs↗
PubMed1993

A clinical experience with a hierarchically controlled myoelectric hand prosthesis with vibro-tactile feedback.

UNLABELLED: Improved performance of externally powered myoelectric hands is possible when the direct control of the digit flexion and grip force are given over to an electronic controller which frees the operator to concentrate on other demands. DESIGN: A commercial myoelectric hand was modified to take the new touch and slip sensors and novel control method. SUBJECT: An adult male with a traumatic mid-forearm amputation. OUTCOME MEASURE: The range and ease of use of the prosthetics system. RESULT: The hand was easily and usefully operated in the home and work environment. CONCLUSION: Hierarchical control of a hand is possible using sensory feedback to a sophisticated electronic controller. Such a control method reduces the demands on the user's concentration and enhances the hand's range.

Adult↗
PubMed1991

Prehensile control of a hand prosthesis by a microcontroller.

The functional replacement of a natural hand and wrist is usually achieved by a split hook or an electrically powered and myoelectrically controlled artificial hand with one degree of freedom. In contrast to the commercial devices, this paper describes an experimental hand with four electric motors, nineteen sensors, and control algorithms which are written for a microcontroller. The hand significantly improves the prehension capabilities of an artificial device and leads to a design which is easily controlled by a user as it mimics the control system of the natural hand.

Algorithms↗
PubMed1987

Control of a single degree of freedom artificial hand.

A commercial single degree of freedom artificial hand has been fitted with touch, slip and position sensors, which permit low-level control tasks to be performed by a microprocessor; little conscious effort is required by the wearer. Hardware and software for the microprocessor system are described.

Biomedical Engineering↗
PubMedDate not supplied

Sensory control of a multifunction hand prosthesis.

The current generation of prostheses that are fitted to limb deficient individuals have only a single degree of freedom which limits their functional range. Furthermore, electrically powered prostheses have a limited user input. Electrical signals generated by the contraction of muscles in the user's stump open and close the hand in an 'on and off' fashion. Since the only feedback is visual, the prostheses tend to be used less dexterously than body powered devices. A different approach has been adopted by the Control Engineering Group at Southampton University. They have retained a single electromyographic input channel, but added sensory feedback to an electronic controller, which decides on the grip posture and tension. Satisfactory operation of the hand depends on the sensors employed. A review of transducers used on previous prostheses at Southampton is followed by a description of recent sensor developments. Finally the intentions for a new generation of prostheses are outlined. These include combining sensory input with an integrated circuit microcontroller to provide a more reliable system.

Biomedical Engineering↗
PubMedDate not supplied

Intelligent multifunction myoelectric control of hand prostheses.

Intuitive myoelectric prosthesis control is difficult to achieve due to the absence of proprioceptive feedback, which forces the user to monitor grip pressure by visual information. Existing myoelectric hand prostheses form a single degree of freedom pincer motion that inhibits the stable prehension of a range of objects. Multi-axis hands may address this lack of functionality, but as with multifunction devices in general, serve to increase the cognitive burden on the user. Intelligent hierarchical control of multiple degree-of-freedom hand prostheses has been used to reduce the need for visual feedback by automating the grasping process. This paper presents a hybrid controller that has been developed to enable different prehensile functions to be initiated directly from the user's myoelectric signal. A digital signal processor (DSP) regulates the grip pressure of a new six-degree-of-freedom hand prosthesis thereby ensuring secure prehension without continuous visual feedback.

Algorithms↗