P H Chappell

University of Southampton, Southampton, England, United Kingdom

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Publications (120)73.19 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: One of the capability of a prosthetic hand device that is highly preferred is that it should be able to mimic the functionality of the lost arm, and that loss includes the tactile sensory system. A miniature DC motor has been identified to be the best haptic actuator to deliver the required sensory feedback. Experiments and simulations were carried out to predict the transient responses, driving frequencies as well as vibration amplitude of the motor. The results have shown that the motor is reliable in matching the optimum frequency response of the mechanoreceptors in the residual arm, which is important in providing an efficient supplementary sensation.
    2013 International Conference on Electronics, Computer and Computation (ICECCO); 11/2013
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    T Lister, P A Wright, P H Chappell
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    ABSTRACT: A new Monte Carlo program is presented for simulating light transport through clinically normal skin and skin containing Port Wine Stain (PWS) vessels. The program consists of an eight-layer mathematical skin model constructed from optical coefficients described previously. A simulation including diffuse illumination at the surface and subsequent light transport through the model is carried out using a radiative transfer theory ray-tracing technique. Total reflectance values over 39 wavelengths are scored by the addition of simulated light returning to the surface within a specified region and surface reflections (calculated using Fresnel's equations). These reflectance values are compared to measurements from individual participants, and characteristics of the model are adjusted until adequate agreement is produced between simulated and measured skin reflectance curves. The absorption and scattering coefficients of the epidermis are adjusted through changes in the simulated concentrations and mean diameters of epidermal melanosomes to reproduce non-lesional skin colour. Pseudo-cylindrical horizontal vessels are added to the skin model, and their simulated mean depths, diameters and number densities are adjusted to reproduce measured PWS skin colour. Accurate reproductions of colour measurement data are produced by the program, resulting in realistic predictions of melanin and PWS blood vessel parameters. Using a modest personal computer, the simulation currently requires an average of five and a half days to complete.
    Lasers in Medical Science 10/2013; · 2.42 Impact Factor
  • Tom Lister, Philip A Wright, Paul H Chappell
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    ABSTRACT: A survey of the literature is presented regarding the simulation of port wine stain (PWS) skin color. Knowledge of PWS features, such as the depths and diameters of affected vessels, is essential for informing laser treatment. These may be determined through the inverse application of a skin model. The techniques which have been applied to achieve this are analyzed in detail. Radiative transfer (RT) is found to be the preferred method of simulation. By far the most common approximations to RT are the diffusion approximations, which have been applied successfully in the past and Monte Carlo techniques, which are now the methods of choice. As the requirements for improvement of laser treatment on an individual basis continues, the needs for further work towards accurate estimations of individual optical coefficients and robust, flexible simulation techniques are identified.
    Journal of Biomedical Optics 11/2012; 17(11):110901. · 2.75 Impact Factor
  • Tom Lister, Philip A Wright, Paul H Chappell
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    ABSTRACT: A survey of the literature is presented that provides an analysis of the optical properties of human skin, with particular regard to their applications in medicine. Included is a description of the primary interactions of light with skin and how these are commonly estimated using radiative transfer theory (RTT). This is followed by analysis of measured RTT coefficients available in the literature. Orders of magnitude differences are found within published absorption and reduced-scattering coefficients. Causes for these discrepancies are discussed in detail, including contrasts between data acquired in vitro and in vivo. An analysis of the phase functions applied in skin optics, along with the remaining optical coefficients (anisotropy factors and refractive indices) is also included. The survey concludes that further work in the field is necessary to establish a definitive range of realistic coefficients for clinically normal skin.
    Journal of Biomedical Optics 09/2012; 17(9):90901-1. · 2.75 Impact Factor
  • M B Warner, P H Chappell, M J Stokes
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    ABSTRACT: The aim of the present study was to examine the acromion marker cluster (AMC) method of measuring scapular kinematics during the arm lowering, eccentric, phase. Twenty six participants completed arm elevation and lowering in the sagittal, frontal and scapular plane. The participants held their arm at 30° increments while the orientation of the scapula was recorded using an AMC and a scapular locator (SL). There were no significant differences between the AMC and SL during the lowering phase for sagittal and scapular plane arm movements. The AMC significantly underestimated upward rotation (max RMSE = 6.0°), and significantly overestimated posterior tilt (max RMSE = 7.2°) during arm lowering in the frontal plane. The reported root mean square errors, however, were within the ranges observed during the elevation phase and reported in previous literature. The AMC therefore provides a reasonable description of scapular kinematics during the arm lowering phase.
    Human movement science 08/2011; 31(2):386-96. · 2.15 Impact Factor
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    ABSTRACT: A new method for texture sensing, based on a calculation of the average standard deviation of the data from a thick film piezoelectric sensor, is presented. The repeating patterns in the surface texture of gratings as they move past the sensor are observable in the output signal. A comparison with a previous method has shown an improvement in the variability of the analyzed data. The method applied is not only able to distinguish two patterns of gratings, but also provides the dimension of each grating. The results have demonstrated the suitability of this approach as a fingertip texture sensor.
    04/2011;
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    ABSTRACT: User perceptions are critical, yet often ignored factors in the design and development of rehabilitation technologies. In this article, measures for collection of patient perceptions are developed and applied to a novel upper limb workstation that combines robotic therapy and electrical stimulation (ES). Five participants with chronic upper limb hemiplegia post-stroke used a robotic workstation to undertake supported tracking tasks augmented by precisely controlled ES to their triceps muscle. Following a 6 week trial, a purpose designed set of questions was developed and individual interviews were conducted by an independent health psychologist. The simple, quick to administer question set showed that participants had a positive response to the system, and contributed valuable feedback with regard to its usability and effectiveness. Participants want a home-based system targeting their whole arm. This article demonstrates the value in assessing user perceptions of a rehabilitation system via a simple question set. While the results of this study have implications for a wider audience, our recommendations are for a qualitative study to develop a generic evaluation tool which could be used across the growing number of devices to provide feedback to enhance future development of any new technology for rehabilitation.
    Disability and rehabilitation. Assistive technology 03/2011; 6(2):130-8.
  • P H Chappell
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    ABSTRACT: A review of sensors for artificial hands is presented in terms of their range, specifications and characteristics. There is a growing need for sensors due to the development of prosthetic hands that have multiple degrees of freedom requiring finger coordination into different postures. The sensing of force, position (angle), object-slip and temperature allows for the control of these hands automatically and frees the user from cognitive burden. To make the best possible use of individual sensing elements, future controllers will need to combine data from different types of sensor. They may also have an integral power supply using a small battery or harvest energy from their environment and transmit data wirelessly.
    Journal of Medical Engineering & Technology 01/2011; 35(1):1-18.
  • Tom Lister, Philip Wright, Paul Chappell
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    ABSTRACT: Reflectance spectrophotometry is the most established and widely used objective technique for the assessment of port-wine stain (PWS) skin, and has been applied extensively in other dermatological applications. To date, no review has been published regarding the different spectrophotometric devices used on PWS skin. This paper comprises such a review, introducing the reader to the relevant background material and then discussing scanning, narrow-band and tristimulus spectrophotometers in turn. Scanning spectrophotometry is the most versatile of the three methods but it is noted that considerable expertise is required to interpret the acquired data. Narrow-band and tristimulus devices are available at a much lower price and can be considerably simpler to use. They do, however, provide limited information that does not account for the complex effects of melanin and other chromophores within the skin. Although scanning spectrophotometers would be the preferred choice for most investigations, cheaper, simpler and equally reliable options are available and may better suit the needs of some research projects.
    Lasers in Medical Science 05/2010; 25(3):449-57. · 2.42 Impact Factor
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    ABSTRACT: The primary objective of the experiments was to investigate the wrist motion of a person while they were carrying out a prehensile task from a clinical hand function test. A sixcamera movement system was used to observe the wrist motion of 10 participants. A very light sphere and a heavy sphere were used in the experiments to study any mass effects. While seated at a table, a participant moved a sphere over a small obstacle using their dominant hand. The participants were observed to move their wrist at a constant angular velocity. This phenomenon has not been reported previously. Theoretically, the muscles of the wrist provide an impulse of force at the start of the rotation while the forearm maintains a constant vertical force on a sphere. Light–heavy mean differences for the velocities, absolute velocities, angles and times taken showed no significant differences (p¼0.05).
    Journal of Medical Engineering & Technology 03/2010;
  • R J Lowe, P H Chappell, S A Ahmad
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    ABSTRACT: A slip sensor, using accelerometers, has been investigated for use in prosthetic design. The basis of this report is the characterization of this sensor including how it performs in re-gripping a falling object. The possibility of using three-axis vibration control is investigated and the limitations of this method are reported. A controller was produced to determine how reliable the sensor is when using both open- and closed-loop control methods. The conclusion is that the sensor is robust, and in addition to basic vibration, it is possible to use the sensor to calculate a reliable value for the distance of slip. Using statistical measures, a minimum grip force is given for successful re-grip without knowledge of the tangential friction forces.
    Measurement Science and Technology 01/2010; 21(3):035203. · 1.35 Impact Factor
  • S. A. Ahmad, P. H. Chappell
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    ABSTRACT: An investigation of the fundamental operation of an artificial hand has been carried out with the aim to study the automatic control feedback for this system. The hand is modeled as a simple prehension system with three sensing elements; force, acceleration and slip. This prehension study focused on the object’s gripping and slippage processes. An automatic closed loop feedback control algorithm is developed to re-grip the object when it starts to slip which is similar in form to Hooke’s Law. The algorithm uses information from the distance of the object has slipped to re-grip the object and control the amount of force required. Also, a method called approximate entropy has been used to analyze and detect when the object begins to slip. This method can be used to prevent the object from slipping. KeywordsProsthesis control-prehension system-automatic feedback control-slip detection
    01/2010: pages 231-234;
  • N. Muridan, P H Chappell, A Cranny, N M White
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    ABSTRACT: This research has shown for the first time that the physical dimensions of small surface patterns in an object surface are detectable from sensors integrated into the fingertip and mechanical links of a prosthetic hand. A further novel aspect of this work is the use of the standard deviation of data used in the analysis. Charge amplifiers are used to extract the signal from the piezoelectric sensors when an object that has two grating surfaces moves past a fingertip. Similar signals have been observed from all the sensors. An analysis of the data has shown that the repeating pattern from the gratings is detectable from a calculation of the mean standard deviation. An estimate of the grating widths can also be made from this analysis. Approximately 32 and 58 grooves are in contact with fingertip (width 15mm) representing a resolution of 2 grooves and 4 grooves mm-1 respectively.
    Procedia Engineering 01/2010;
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    ABSTRACT: An inability to perform tasks involving reaching is a common problem for stroke patients. Knowledge of normal muscle activation patterns during these tasks is essential to the identification of abnormal patterns in post-stroke hemiplegia. Findings will provide insight into changes in muscle activation patterns associated with recovery of upper limb function. In this study with neurologically intact participants the co-ordination of shoulder and elbow muscle activity during two dimensional reaching tasks is explored. Eight participants undertook nine tracking tasks in which trajectory (orientation and length), duration, speed and resistance to movement were varied. The participants’ forearm was supported using a hinged arm-holder, which constrained their hand to move in a two dimensional plane. EMG signals were recorded from triceps, biceps, anterior deltoid, upper, middle and lower trapezius and pectoralis major. A wide variation in muscle activation patterns, in terms of timing and amplitude, was observed between participants performing the same task. EMG amplitude increased significantly with length, duration and resistance of the task for all muscles except anterior deltoid. Co-activation between biceps and triceps was significantly dependent on both task and trajectory orientation. Activation pattern of pectoralis major was dependent on trajectory. Neither trajectory orientation nor task condition affected the activation pattern of anterior deltoid. Normal ranges of timing of muscle activity during the tasks were identified.
    Journal of electromyography and kinesiology: official journal of the International Society of Electrophysiological Kinesiology 12/2009; · 2.00 Impact Factor
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    ABSTRACT: An inability to perform tasks involving reaching is a common problem for stroke patients. This paper provides an insight into mechanisms associated with recovery of upper limb function by examining how stroke participants’ upper limb muscle activation patterns differ from those of neurologically intact participants, and how they change in response to an intervention. In this study, five chronic stroke participants undertook nine tracking tasks in which trajectory (orientation and length), speed and resistance to movement were varied. During these tasks, EMG signals were recorded from triceps, biceps, anterior deltoid, upper, middle and lower trapezius and pectoralis major. Data collection was performed in sessions both before, and after, an intervention in which participants performed a similar range of tracking tasks with the addition of responsive electrical stimulation applied to their triceps muscle. The intervention consisted of eighteen one hour treatment sessions, with two participants attending an additional seven sessions. During all sessions, each participant’s arm was supported by a hinged arm-holder which constrained their hand to move in a two dimensional plane. Analysis of the pre intervention EMG data showed that timing and amplitude of peak EMG activity for all stroke participants differed from neurologically intact participants. Analysis of post intervention EMG data revealed that statistically significant changes in these quantities had occurred towards those of neurologically intact participants.
    Journal of electromyography and kinesiology: official journal of the International Society of Electrophysiological Kinesiology 10/2009; · 2.00 Impact Factor
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    ABSTRACT: In the April 2008 issue of Progress,we featured an article describing a new technique for improving arm movement following stroke developed at the University of Southampton.The technique involves the use of a robotic workstation delivering precisely controlled electrical stimulation mediated by iterative learning control to improve task performance.Here,the scientists who developed the system discuss the promising results of their pilot clinical study using this technique. Copyright © 2009 Wiley Interface Ltd
    Progress in Neurology and Psychiatry 08/2009; 13(5):16 - 20.
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    ABSTRACT: A Piezoelectric thick-film sensor is a good candidate for the extraction of information from object slip in hand prosthesis. Five slip sensors were fabricated on different linkages of an artificial hand. The signals from each sensor were compared to the output from the sensor mounted on the fingertip. An analysis of the output signals from all the sensors indicates that the linkage sensors also produce similar output signals to the fingertip sensor. In the next phase of the research, velocity and acceleration of the slipped object will be considered in the analysis.
    Journal of Physics Conference Series 07/2009; 178(1):012022.
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    ABSTRACT: An overview is provided of the design, operation and performance of an experimental test facility that has been developed for stroke rehabilitation. The aim of the system is to improve sensory-motor function of the impaired upper limb, and it has recently been used in clinical trials with stroke participants. During treatment subjects were seated at the workstation and their impaired arm strapped to the robotic end-effector. Their task was to follow elliptical trajectories that were projected onto a target above their arm, using voluntary control with the addition of electrical stimulation mediated by advanced control schemes. The design of the experimental system is first summarised, and then details are presented of the modelling, identification and control techniques used by the workstation over the course of treatment.
    Rehabilitation Robotics, 2009. ICORR 2009. IEEE International Conference on; 07/2009
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    ABSTRACT: A summary is presented of the tracking and surface electromyographic (EMG) results obtained using a robotic workstation that was designed and built for use by stroke participants in order to improve voluntary control of their impaired arm. The intervention consisted of eighteen sessions in which five chronic stroke participants performed a range of tracking tasks using their remaining voluntary effort, with the addition of responsive electrical stimulation (ES) applied to their triceps muscles. Unassisted error tracking was measured during each intervention session. EMG, which may be related to impaired performance and function, was recorded in separate sessions before and after the intervention, in order to investigate changes in muscle activation patterns resulting from treatment. In these sessions, participants tracked similar trajectories without ES, and their muscle activity has been compared against that of eight neurologically intact subjects. Results are presented which describe changes in tracking ability and EMG, and their inter-relationship.
    Rehabilitation Robotics, 2009. ICORR 2009. IEEE International Conference on; 07/2009
  • S A Ahmad, P H Chappell
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    ABSTRACT: The aim of this study is to investigate the characteristics of surface electromyographic signals, particularly in pattern analysis. The data were collected from the wrist muscles (flexor carpi ulnaris and extensor carpi radialis) of 20 healthy participants. The study focuses on the movement of the wrist muscles at different frequencies. Participants were asked to contract their muscles at four different speeds (60, 90 and 120 cycles a minute and maximum speed) during wrist flexion and extension, co-contraction and isometric contraction. In this work, moving approximate entropy, mean absolute value and kurtosis are evaluated from the surface electromyographic signals at the four speeds. Moving approximate entropy and kurtosis analysis show that there are significant differences at three states of contraction; start, middle and end. It is shown that there are more regular data in a surface electromyographic signal at the beginning and end of a muscle contraction with low regularity during the middle part.
    Journal of Medical Engineering & Technology 05/2009; 33(5):376-85.