P H Chappell

University of Southampton, Southampton, ENG, United Kingdom

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Publications (70)28.84 Total impact

  • 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
  • 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.
  • 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. · 1.44 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.
    01/2010;
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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.
  • 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.
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    ABSTRACT: A model of the upper limb is developed in which the forearm is constrained to lie in a horizontal plane and electrical stimulation is applied to the triceps muscle. Identification procedures are described to estimate the unknown parameters using a small number of tests. Examples of identified parameters obtained experimentally are presented for both stroke patients and unimpaired subjects. The model has been used to derive controllers which have been applied during clinical trials to reduce the level of impairment of stroke patients.
    01/2009;
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    ABSTRACT: This paper presents a compact analogue circuit for the controlling of prosthetic hands. The circuit captures directly surface EMG signals as the input by which the user will be able to select different postures. The proposed circuit is able to work using only one EMG source targeting patients with different levels of amputation. It is also adaptable for different users with different EMG amplitude signals and the motion of each finger can be varied in the circuit even with the single EMG. Real captured EMG signals are applied to the design and simulation results demonstrate the capability of the circuit in processing EMG signals and controlling the prosthetic hand in an efficient way. The circuit is designed and implemented with 0.12 mum CMOS technology and consumes 4 mW power for a set of sample postures.
    Biomedical Circuits and Systems Conference, 2008. BioCAS 2008. IEEE; 12/2008
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    ABSTRACT: A kinematic model is presented based on surface marker placement generating wrist, metacarpal arch, fingers and thumb movements. Standard calculations are used throughout the model and then applied to the specified marker placement. A static trial involving eight unimpaired participants was carried out to assess inter-rater reliability. The standard deviations across the data were comparable to manual goniometers. In addition, a test-retest trial of ten unimpaired participants is also reported to illustrate the variability of movement at the wrist joint, metacarpal arch, and index finger as an example of model output when repeating the same task many times. Light and heavyweight versions of the tasks are assessed and characteristics of individual movement strategies presented. The participant trial showed moderate correlation in radial/ulnar deviation of the wrist (r = 0.65), and strong correlation in both metacarpal arch joints (r = 0.75 and r = 0.85), the MCP (r = 0.79), and PIP (r = 0.87) joints of the index finger. The results indicate that individuals use repeated strategies of movement when lifting light and heavyweight versions of the same object, but showed no obvious repeated pattern of movement across the population.
    IEEE Transactions on Biomedical Engineering 04/2008; 55(3):1199-210. · 2.35 Impact Factor
  • S.A. Ahmad, P.H. Chappell
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    ABSTRACT: Moving approximate entropy has been proposed as a new method to extract information from the surface electromyographic signal. Twenty subjects performed wrist flexion/extension, isometric contraction and co-contraction while electromyographic signals were recorded with surface electrodes. A moving data window of 200 values was applied to the data (moving approximate entropy). The results show that there is regularity in an EMG signal at the beginning and end of a muscle contraction with low regularity during the middle part.
    Intelligent and Advanced Systems, 2007. ICIAS 2007. International Conference on; 12/2007
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    ABSTRACT: The ability to mimic the tactile feedback exhibited by the human hand in an artificial limb is considered advantageous in the automatic control of new multifunctional prosthetic hands. The role of a slip sensor in this tactile feedback is to detect object slip and thus provide information to a controller, which automatically adjusts the grip force applied to a held object to prevent it from falling. This system reduces the cognitive load experienced by the user by not having to visually assess the stability of an object, as well as giving them the confidence not to apply unnecessarily excessive grip forces. A candidate for such a sensor is a thick-film piezoelectric sensor. The method of fabricating a thick-film piezoelectric slip sensor on a prototype fingertip is described. The construction of experimental apparatus to mimic slip has been designed and analyzed to allow the coefficient of friction between the fingertip and the material in contact with the fingertip to be calculated. Finally, results show that for a coefficient of friction between the fingertip and grade P100 sandpaper of approximately 0.3, an object velocity of 0.025plusmn0.008 ms<sup>-1</sup> was reached before a slip signal from the piezoelectric sensor was able to be used to detect slip. It is anticipated that this limiting velocity will be lowered (improved) in the intended application where the sensor electronics will be powered from a battery, connections will be appropriately screened, and if necessary a filter employed. This will remove mains interference and reduce other extraneous noise sources with the consequence of an improved signal-to-noise ratio, allowing lower threshold values to be used in the detection software
    IEEE Sensors Journal 06/2007; · 1.48 Impact Factor
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    P H Chappell, P N Taylor
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    ABSTRACT: 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.
    Computers in Biology and Medicine 01/2007; 36(12):1316-26. · 1.48 Impact Factor
  • D.P.J. Cotton, A Cranny, P H Chappell, N M White
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    ABSTRACT: INTRODUCTION Piezoelectric sensors produce a charge when mechanically deformed (for example through the action of an applied force). This charge decays with time dependant upon the connected electronics. This makes piezoelectric sensors an ideal candidate for detecting the vibrations (change in surface forces) associated with object slip from a prosthetic hand. Most previous work undertaken with piezoelectric sensors to detect object slip from upper limb prosthetics has used polyvinylidene fluoride strips (PVDF) (Dario 1996) (Howe 1989). This type of sensor has a low sensitivity of around 20-30 pCN-1 and comes in a sheet format so would have to be adhered manually to a hand. Thick-film piezoelectric sensors offer a superior alternative for this application with a much higher sensitivity than PVDF of around 130pCN-1 (Torah et al 2005) and the thick-film fabrication technique allows the sensors to be accurately printed onto the flat surface of a prosthesis finger or fingertip.
    01/2007;
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    ABSTRACT: The concept of ‘learned disuse’ is thought to be a significant barrier to recovery of sensory-motor function following a stroke. Unimpaired individuals learn new skills though practice, with feedback in various forms, but the problem facing the stroke patient is that they are unable to practice because of impaired motor control. Functional electrical stimulation (FES) can provide the experience for the patient of moving and consequently may limit the problem of learnt disuse and has been used with some success to improve recovery of upper limb motor control. Recent studies have shown that when stimulation is associated with a voluntary attempt to move the limb, improvement is enhanced but these techniques do not allow feedback that could be used to adjust stimulation parameters and thus provide more precise stimulation. This paper describes the design and construction of an experimental test facility that has been designed as part of a current project whose aim is to investigate the use of iterative learning control (ILC) and related strategies to mediate the electrical stimulation applied to a number of muscles of the shoulder and upper limb of stroke patients.
    01/2007;
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    ABSTRACT: This paper describes the experimental test facility that has been designed as part of a current project whose aim is to investigate the use of iterative learning control (ILC) and related strategies to mediate the electrical stimulation applied to a number of muscles of the shoulder and upper limb of stroke patients. ILC is a technique that has its origins in the area of industrial robotics and is especially targeted at systems operating in a repetitive mode with the additional requirement that a specified output trajectory over a finite interval (or trial) is followed to a specified level of precision. Motivated by human learning, the basic idea of ILC is to use information from previous executions of the task in order to improve performance from trial to trial. In the context of this work, ILC offers the opportunity of allowing the user to learn how to perfect a given task by controlling the amount of additional stimulation applied from one trial to the next. If this has been achieved, then further refinement is possible to reduce the stimulation effort supplied by the control scheme and thereby increase the effort necessary from the subject. In particular, ILC requires a basic representation of the underlying (dynamic) relationship between stimulation (or input) and response (or output) and also the specification of a target (or reference) trajectory to form the goal for the ILC scheme to achieve
    UKACC Control, 2006. Mini Symposia; 10/2006
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    D J Hart, P N Taylor, P H Chappell, D E Wood
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    ABSTRACT: 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.
    Medical Engineering & Physics 07/2006; 28(5):438-48. · 1.78 Impact Factor
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    ABSTRACT: Some of the traditional methods used to control a conventional prosthetic device are described alongside the current state of new control techniques and how they may progress. The review includes implantable myoelectric sensors and describes the potential of connecting directly to the peripheral nervous system. Control methods are then deduced for each technique, where the application is a six degrees of freedom hand having integral slip, force and temperature sensors.
    01/2006;
  • P H Chappell
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    ABSTRACT: Loss of a natural hand means that the neural connections between the brain and the palm, fingers and thumb are also lost, including any feedback paths e.g. sensing temperature. Equipping an artificial hand with sensors allows for the inclusion of automatic control loops, freeing the user from the cognitive burden of object holding which is similar to the natural low level spinal loops that automatically compensate for object movement. Force, object slip and finger positions are variables that need to be measured in a hand designed for the physically impaired person. A high specification is required for any sensor design.
    Journal of Physics Conference Series 08/2005; 15(1):7.
  • P J Kyberd, P H Chappell, D. Gow
    01/2005;