Slip Detection Strategies for Automatic Grasping in Prosthetic Hands.

The detection of an object slipping within the grasp of a prosthetic hand enables the hand to react to ensure the grasp is stable. The computer controller of a prosthetic hand needs to be able to unambiguously detect the slide from other signals. Slip can be detected from the surface vibrations made as the contact between object and terminal device shifts. A second method measures the changes in the normal and tangential forces between the object and the digits. After a review of the principles of how the signals are generated and the detection technologies are employed, this paper details the acoustic and force sensors used in versions of the Southampton Hand. Attention is given to the techniques used in the field. The performance of the Southampton tube sensor is explored. Different surfaces are slid past a sensor and the signals analysed. The resulting signals have low-frequency content. The signals are low pass filtered and the resulting processing results in a consistent response across a range of surfaces. These techniques are fast and not computationally intensive, which makes them practical for a device that is to be used daily in the field.

A Strengthened and Sensorised Custom Silicone Glove for use with an Intelligent Prosthetic Hand.

External gloves for anthropomorphic prosthetic hands protect the mechanisms from damage and ingress of contaminants and can be used to create a pleasing, life-like appearance. The properties of the glove material are the result of a compromise between the resistance to damage and flexibility. Silicone gloves are easier to flex and keep clean, but also more easily damaged. This paper details the use of nanoclay fillers to enhance the properties of silicone, successfully increasing strength whilst maintaining flexibility. The performance of the enhanced silicone is as robust and resistant to tear and puncture as commercial gloves, while being more flexible. This flexibility makes the incorporation of a piezo-electric pressure sensor based on the EEonyx conductive fabric, practical. A sandwich of the cloth and copper fabric creates the sensor, which decreases in resistance with increasing pressure. The sensors are characterised and production variability within the silicone are tested. Three sensors are incorporated into a glove made to fit around a Southampton Intelligent Hand. The hand adapts its grip shape and force depending on the object held. The technology is adaptable and it can be incorporated in a glove produced to fit any prosthetic hand.

An investigation of proprioception illusion using a stimulator with feedback control.

It is possible to create illusions of limb movements using vibrations over the skin. If a muscle is vibrated it can feel as if the limb is moving while it remains still. These illusions have been studied for decades but it is not yet entirely clear how to create them effectively and repeatedly. In this study, three parameters were varied; the frequency of the vibration, the stimulation site and the arm position. A closed loop control of the vibration frequency was used to ensure a fixed frequency over the stimulation time and across the participants. The experiment included twenty-five able-bodied participants (mean age 32±7 years, 9 females). A hanging arm position was introduced with the aim to increase the success rate of illusions compared to other studies. Twenty-four participants felt an illusion across all scenarios. The results highlight that tactile feedback affects the illusion.

Chin tuck against resistance exercise with feedback to improve swallowing, eating and drinking in frail older people admitted to hospital with pneumonia: protocol for a feasibility randomised controlled study.

BACKGROUND: Swallowing difficulties (dysphagia) and community-acquired pneumonia are common in frail older people and maybe addressed through targeted training of the anterior neck musculature that affects the swallow. We have developed a swallowing exercise rehabilitation intervention (CTAR-SwiFt) by adapting a previously established swallowing exercise to ensure patient safety and ease of execution in the frail elderly population. The CTAR-SwiFt intervention consists of a feedback-enabled exercise ball that can be squeezed under the chin, with real-time feedback provided via a mobile application. The aim of this study is to evaluate the feasibility of assessing the effectiveness of the CTAR-SwiFt intervention in reducing dysphagia and community-acquired pneumonia, prior to a larger-scale multi-centre randomised controlled trial. METHODS: We will recruit 60 medically stable patients over the age of 75 years who have been admitted with a diagnosis of pneumonia to the acute frailty wards at two participating hospitals in the UK. Study participants will be randomised into one of three groups: standard care, low intensity (once daily) CTAR-SwiFt exercise or high intensity (twice daily) CTAR-SwiFt exercises. The intervention period will last for 12 weeks, the final follow-up assessment will be conducted at 24 weeks. We will assess the feasibility outcomes, including rates of participant recruitment and retention, compliance with the exercise regime and adverse incidents. Additionally, we will assess the usability and acceptability of the intervention device and the performance of different clinical outcome measures (e.g. chin tuck strength, Functional Oral Intake Scale, SWAL-QOL, EQ-5D and swallow speed). A sub-sample of study participants will complete videofluoroscopic assessments of swallowing function before and after the intervention to evaluate the physiological changes (e.g. bolus flow rates, laryngeal elevation, base-of-tongue retraction). CONCLUSIONS: By improving the ability to swallow, using our chin tuck exercise intervention, in frail older patients admitted to hospital with pneumonia, it is anticipated that patients' oral intake will improve. It is suggested that this will further impact clinical, patient and healthcare economic outcomes, i.e. reduce the need for supplemental feeding, improve patient satisfaction with oral intake and swallowing-related quality of life, decrease the occurrence of chest infections and reduce hospital admissions and related healthcare costs. TRIAL REGISTRATION: ISRCTN, ISRCTN12813363 . Registered on 20 January 2020.

Blood pressure lowering effects of a novel isometric exercise device following a 4-week isometric handgrip intervention.

Background: Hypertension is the leading risk factor for global mortality. Isometric resistance exercise training reduces blood pressure (BP). However, the protocols used are often limited by cost/immobility and the use of rigid exercise modalities. In response, a novel more versatile, isometric exercise (IE) device, the IsoBall (IB) was created. Purpose: The aim of this study was to test the BP-lowering effectiveness of this prototype. Methods: Twenty-three healthy participants (29.10±2.19 years old, 173.95±3.83 cm, 75.43±5.06 kg, SBP 127.10±10.37 mmHg, DBP 70.40±6.77 mmHg) were randomly allocated to either a control group (CON) or 2 isometric handgrip (IHG) training groups that used the Zona plus (ZON) and IB devices. The intervention groups completed 3 sessions each week of 4, 2 min IHG at 30% maximal voluntary contraction, with a 1-min rest, for 4 weeks. Resting BP, heart rate (HR) and IHG strength were measured in all groups at baseline and postintervention. Results: Postintervention systolic BP (SBP) was significantly lower in both ZON (114.5±8.2 mmHg, p = 0.000) and IB (119.9±7.0 mmHg, p = 0.000) compared to control (131.0±12.4 mmHg). Postintervention diastolic BP (DBP) was reduced in both intervention groups (ZON 66.6±7.4 mmHg, p = 0.004; IB 65.7±10.0 mmHg, p = 0.012) compared to CON (71.1±8.8 mmHg). Mean arterial pressure (MAP) was reduced in both groups (ZON 82.6±6.8 mmHg, p = 0.000; IB 84.3±9.1 mmHg, p = 0.000) compared to control (91.0±9.7 mmHg). No significant changes were seen in HR or strength (p > 0.05). Conclusion: The results of this study indicate that both the ZON and IB devices elicit significant SBP, DBP and MAP reductions. Despite the ZON group having larger reductions in BP, no significant differences were found between the two devices. Thus, this study indicates the IB device to be an effective alternative to the ZON that can also be used to perform other IE modalities.

Clinical evaluation of the refined clothespin relocation test: A pilot study.

BACKGROUND: The refined clothespin relocation test is a test used to evaluate the performance of a prosthesis user by analysing the compensatory motions and time to complete a grasping and placement exercise. The test has been studied previously with a motion capture laboratory and has now been adapted for a clinical setting. A comparison of prosthesis user to an able-bodied group is needed to determine efficacy as an assessment tool. OBJECTIVE: To modify the previous refined clothespin relocation test and assess whether it can distinguish between able-bodied and prosthesis users. STUDY DESIGN: Comparative analysis. METHODS: Forty-two able-bodied subjects and three prosthesis users completed the adapted refined clothespin relocation test protocol. Average refined clothespin relocation test scores describing the degree of compensatory movements and the time to complete the protocol were compared using a Mann-Whitney U-test. RESULTS: A significant difference was found in the refined clothespin relocation test score between the able-bodied (Md = 65.32, n = 42) and prosthesis users (Md = 23.07, n = 3) with a medium effect size (p < 0.001, r = 0.43). CONCLUSION: Prosthesis users demonstrated larger compensations and longer completion times, as reflected in the refined clothespin relocation test final score. The refined clothespin relocation test has the potential to be a useful clinical tool to assess user performance on a functional task. CLINICAL RELEVANCE: This preliminary study demonstrates that the adapted protocol can distinguish between the two groups based on refined clothespin relocation test score. A future multi-centre study is required using multiple raters and comparing it with the existing outcome measures to validate the refined clothespin relocation test and determine inter-rater reliability.

Upper- and lower-limb amputees show reduced levels of eeriness for images of prosthetic hands.

The "uncanny phenomenon" describes the feeling of unease associated with seeing an image that is close to appearing human. Prosthetic hands in particular are well known to induce this effect. Little is known, however, about this phenomenon from the viewpoint of prosthesis users. We studied perceptions of eeriness and human-likeness for images of different types of mechanical, cosmetic, and anatomic hands in upper-limb prosthesis users (n=9), lower-limb prosthesis users (n=10), prosthetists (n=16), control participants with no prosthetic training (n=20), and control participants who were trained to use a myoelectric prosthetic hand simulator (n=23). Both the upper- and lower-limb prosthesis user groups showed a reduced uncanny phenomenon (i.e., significantly lower levels of eeriness) for cosmetic prosthetic hands compared to the other groups, with no concomitant reduction in how these stimuli were rated in terms of human-likeness. However, a similar effect was found neither for prosthetists with prolonged visual experience of prosthetic hands nor for the group with short-term training with the simulator. These findings in the prosthesis users therefore seem likely to be related to limb absence or prolonged experience with prostheses.

Investigating the uncanny valley for prosthetic hands.

BACKGROUND: In 1970, Mori hypothesised the existence of an 'uncanny valley', whereby stimuli falling short of being fully human are found to be creepy or eerie. OBJECTIVES: To investigate how eerie people find different prosthetic hands and whether perceptions of eeriness can be accounted for by categorical ambiguity. STUDY DESIGN: Students participated in computerised experiments during which photographic images of hands were presented. METHODS: We compared photographs of prosthetic hands pre-selected as more (H+) or less human-like (H-), as well as mechanical and real hands. Participants rated the hands for eeriness and human-likeness, as well as performing a speeded classification (human/non-human) and location judgment (control) task. RESULTS: The H- prosthetic hands were rated as more eerie than the H+ prosthetic, mechanical and real hands, and this was unaffected by hand orientation. Participants were significantly slower to categorise the H+ prosthetic hands compared to the H- prosthetic and real hands, which was not due to generally slower responses to the H+ prosthetic hands (control task). CONCLUSION: People find prosthetic hands to be eerie, most consistently for less human-like prosthetic hands. This effect is not driven by ambiguity about whether to categorise the prosthetic hand as human or artificial. Clinical relevance More obviously artificial, less-realistic, prosthetic hands consistently generate a sense of eeriness, while more realistic prosthetic hands avoid the uncanny valley, at least on initial viewing. Thus, greater realism in prosthetic design may not always incur a cost, although the role of movement and cutaneous input requires further investigation.

Characterisation of the Clothespin Relocation Test as a functional assessment tool.

METHOD: The Clothespin Relocation Test has been adapted from an arm training tool to create an instrument to measure hand function. It is based on the time to move three clothespins from a horizontal to a vertical bar, and back. To be generally useful, the measures need to have their psychometric properties investigated. This paper measures the characteristics of an able-bodied population to gain an understanding of the underlying statistical properties of the test, in order that it can then be used to compare with different subject groups. Fifty adults (29 males, 21 females, mean age 31) were tested with five runs of three clothespins moved up and then down. Ten subjects returned twice more to observe repeatability. RESULTS: There was a non-Gaussian range of times, from 2.5 to 7.37 s. Mean time for Up was 4.1 s, and was 4.0 s for Down, with a skew towards the faster times of 0.57 for Up and 0.97 for Down. Over the three sessions there was a small (not significant) increase in speed 4.1 ± 0.5 s first run Down to 3.5 ± 0.4 s for third. CONCLUSION: These initial tests confirm that it has potential to be used as a measurement of the performance of arm movement.

Skill assessment in upper limb myoelectric prosthesis users: Validation of a clinically feasible method for characterising upper limb temporal and amplitude variability during the performance of functional tasks.

Upper limb myoelectric prostheses remain challenging to use and are often abandoned. A proficient user must be able to plan/execute arm movements while activating the residual muscle(s), accounting for delays and unpredictability in prosthesis response. There is no validated, low cost measure of skill in performing such actions. Trial-trial variability of joint angle trajectories measured during functional task performance, linearly normalised by time, shows promise. However, linear normalisation of time introduces errors, and expensive camera systems are required for joint angle measurements. This study investigated whether trial-trial variability, assessed using dynamic time warping (DTW) of limb segment acceleration measured during functional task performance, is a valid measure of user skill. Temporal and amplitude variability of forearm accelerations were determined in (1) seven myoelectric prosthesis users and six anatomically-intact controls and (2) seven anatomically-intact subjects learning to use a prosthesis simulator over repeated sessions. (1): temporal variability showed clear group differences (p<0.05). (2): temporal variability considerably increased on first use of a prosthesis simulator, then declined with training (both p<0.05). Amplitude variability showed less obvious differences. Analysing forearm accelerations using DTW appears to be a valid low-cost method for quantifying movement quality of upper limb prosthesis use during goal-oriented task performance.

Use of Accelerometers in the Control of Practical Prosthetic Arms.

Accelerometers can be used to augment the control of powered prosthetic arms. They can detect the orientation of the joint and limb, and the controller can correct for the amount of torque required to move the limb. They can also be used to create a platform, with a fixed orientation relative to gravity for the object held in the hand. This paper describes three applications for this technology, in a powered wrist and powered arm. By adding sensors to the arm making these data available to the controller, the input from the user can be made simpler. The operator will not need to correct for changes in orientation of their body as they move. Two examples of the correction for orientation against gravity are described and an example of the system designed for use by a patient. The controller for all examples is a distributed set of microcontrollers, one node for each joint, linked with the control area network bus. The clinical arm uses a version of the Southampton adaptive manipulation scheme to control the arm and hand. In this control form, the user gives simpler input commands and leaves the detailed control of the arm to the controller.

High Cable Forces Deteriorate Pinch Force Control in Voluntary-Closing Body-Powered Prostheses.

BACKGROUND: It is generally asserted that reliable and intuitive control of upper-limb prostheses requires adequate feedback of prosthetic finger positions and pinch forces applied to objects. Body-powered prostheses (BPPs) provide the user with direct proprioceptive feedback. Currently available BPPs often require high cable operation forces, which complicates control of the forces at the terminal device. The aim of this study is to quantify the influence of high cable forces on object manipulation with voluntary-closing prostheses. METHOD: Able-bodied male subjects were fitted with a bypass-prosthesis with low and high cable force settings for the prehensor. Subjects were requested to grasp and transfer a collapsible object as fast as they could without dropping or breaking it. The object had a low and a high breaking force setting. RESULTS: Subjects conducted significantly more successful manipulations with the low cable force setting, both for the low (33% more) and high (50%) object's breaking force. The time to complete the task was not different between settings during successful manipulation trials. CONCLUSION: High cable forces lead to reduced pinch force control during object manipulation. This implies that low cable operation forces should be a key design requirement for voluntary-closing BPPs.

Refined clothespin relocation test and assessment of motion.

BACKGROUND: Advancements in upper limb prosthesis design have focused on providing increased degrees of freedom for the end effector through multiple articulations of a prosthetic hand, wrist and elbow. Measuring improvement in patient function with these devices requires development of appropriate assessment tools. OBJECTIVES: This study presents a refined clothespin relocation test for measuring performance and assessing compensatory motion between able-bodied subjects and subjects with upper limb impairments. STUDY DESIGN: Comparative analysis. METHODS: Trunk and head motions of 13 able-bodied subjects who performed the refined clothespin relocation test were compared to the motion of a transradial prosthesis user with a single degree of freedom hand. RESULTS: There were observable differences between the prosthesis user and the able-bodied group. The assessment used provided a clear indication of the differences in motion through analysis of compensatory motion. CONCLUSION: The refined clothespin relocation test provides additional benefits over the standard clothespin assessment and makes identification of compensatory motions easily identifiable to the researcher. While this article establishes the method for the new assessment, further validation will need to be performed with more users. Clinical relevance The refined test provides a more defined structure for the trajectory of the hand/terminal device than the standard protocol for the clothespin relocation test. This will help researchers interested in motion studies of limb segments to efficiently compare and analyse motion between able-bodied and prosthesis user groups.

Categorization of compensatory motions in transradial myoelectric prosthesis users.

BACKGROUND: Prosthesis users perform various compensatory motions to accommodate for the loss of the hand and wrist as well as the reduced functionality of a prosthetic hand. OBJECTIVES: Investigate different compensation strategies that are performed by prosthesis users. STUDY DESIGN: Comparative analysis. METHODS: A total of 20 able-bodied subjects and 4 prosthesis users performed a set of bimanual activities. Movements of the trunk and head were recorded using a motion capture system and a digital video recorder. Clinical motion angles were calculated to assess the compensatory motions made by the prosthesis users. The video recording also assisted in visually identifying the compensations. RESULTS: Compensatory motions by the prosthesis users were evident in the tasks performed (slicing and stirring activities) as compared to the benchmark of able-bodied subjects. Compensations took the form of a measured increase in range of motion, an observed adoption of a new posture during task execution, and prepositioning of items in the workspace prior to initiating a given task. CONCLUSION: Compensatory motions were performed by prosthesis users during the selected tasks. These can be categorized into three different types of compensations. Clinical relevance Proper identification and classification of compensatory motions performed by prosthesis users into three distinct forms allows clinicians and researchers to accurately identify and quantify movement. It will assist in evaluating new prosthetic interventions by providing distinct terminology that is easily understood and can be shared between research institutions.

System training and assessment in simultaneous proportional myoelectric prosthesis control.

BACKGROUND: Pattern recognition control of prosthetic hands take inputs from one or more myoelectric sensors and controls one or more degrees of freedom. However, most systems created allow only sequential control of one motion class at a time. Additionally, only recently have researchers demonstrated proportional myoelectric control in such systems, an option that is believed to make fine control easier for the user. Recent developments suggest improved reliability if the user follows a so-called prosthesis guided training (PGT) scheme. METHODS: In this study, a system for simultaneous proportional myoelectric control has been developed for a hand prosthesis with two motor functions (hand open/close, and wrist pro-/supination). The prosthesis has been used with a prosthesis socket equivalent designed for normally-limbed subjects. An extended version of PGT was developed for use with proportional control. The control system's performance was tested for two subjects in the Clothespin Relocation Task and the Southampton Hand Assessment Procedure (SHAP). Simultaneous proportional control was compared with three other control strategies implemented on the same prosthesis: mutex proportional control (the same system but with simultaneous control disabled), mutex on-off control, and a more traditional, sequential proportional control system with co-contractions for state switching. RESULTS: The practical tests indicate that the simultaneous proportional control strategy and the two mutex-based pattern recognition strategies performed equally well, and superiorly to the more traditional sequential strategy according to the chosen outcome measures. CONCLUSIONS: This is the first simultaneous proportional myoelectric control system demonstrated on a prosthesis affixed to the forearm of a subject. The study illustrates that PGT is a promising system training method for proportional control. Due to the limited number of subjects in this study, no definite conclusions can be drawn.

Visuomotor behaviours when using a myoelectric prosthesis.

BACKGROUND: A recent study showed that the gaze patterns of amputee users of myoelectric prostheses differ markedly from those seen in anatomically intact subjects. Gaze behaviour is a promising outcome measures for prosthesis designers, as it appears to reflect the strategies adopted by amputees to compensate for the absence of proprioceptive feedback and uncertainty/delays in the control system, factors believed to be central to the difficulty in using prostheses. The primary aim of our study was to characterise visuomotor behaviours over learning to use a trans-radial myoelectric prosthesis. Secondly, as there are logistical advantages to using anatomically intact subjects in prosthesis evaluation studies, we investigated similarities in visuomotor behaviours between anatomically intact users of a trans-radial prosthesis simulator and experienced trans-radial myoelectric prosthesis users. METHODS: In part 1 of the study, we investigated visuomotor behaviours during performance of a functional task (reaching, grasping and manipulating a carton) in a group of seven anatomically intact subjects over learning to use a trans-radial myoelectric prosthesis simulator (Dataset 1). Secondly, we compared their patterns of visuomotor behaviour with those of four experienced trans-radial myoelectric prosthesis users (Dataset 2). We recorded task movement time, performance on the SHAP test of hand function and gaze behaviour. RESULTS: Dataset 1 showed that while reaching and grasping the object, anatomically intact subjects using the prosthesis simulator devoted around 90% of their visual attention to either the hand or the area of the object to be grasped. This pattern of behaviour did not change with training, and similar patterns were seen in Dataset 2. Anatomically intact subjects exhibited significant increases in task duration at their first attempts to use the prosthesis simulator. At the end of training, the values had decreased and were similar to those seen in Dataset 2. CONCLUSIONS: The study provides the first functional description of the gaze behaviours seen during use of a myoelectric prosthesis. Gaze behaviours were found to be relatively insensitive to practice. In addition, encouraging similarities were seen between the amputee group and the prosthesis simulator group.

Design and development of ankle-foot prosthesis with delayed release of plantarflexion.

A computer-controlled mechanism that fits a standard ankle-foot prosthesis was designed to capture the absorbed energy in the ankle and delay its release until specific times in the gait cycle. This mechanism used a direct current motor to take up and hold the compression of a carbon-fiber ankle joint. Based on the timing of the contact forces between the foot and the ground, a microprocessor released the spring at preset times later in the gait cycle. This mechanism was added to a Talux prosthetic foot and was employed by a user of a conventional energy-storage ankle-foot prosthesis. His gait was recorded using a motion analysis system. Five settings: 0, 55, 65, 75, and 85 ms delay were tested on separate days, and the standard kinematic and kinetic gait data were recorded. The user reported some settings were more comfortable than others. When these preferences were tested with a randomized double-blind trial, the preferences were not consistent. A second user showed a preference for the 55 ms delay. The modifications to the device resulted in changes to the gait of the subjects, including increased cadence and kinematics of the unaffected joints and a longer, slower push from the ankle, which was noticed by both of the subjects.

Control of upper limb prostheses: terminology and proportional myoelectric control-a review.

The recent introduction of novel multifunction hands as well as new control paradigms increase the demand for advanced prosthetic control systems. In this context, an unambiguous terminology and a good understanding of the nature of the control problem is important for efficient research and communication concerning the subject. Thus, one purpose of this paper is to suggest an unambiguous taxonomy, applicable to control systems for upper limb prostheses and also to prostheses in general. A functionally partitioned model of the prosthesis control problem is also presented along with the taxonomy. In the second half of the paper, the suggested taxonomy has been exploited in a comprehensive literature review on proportional myoelectric control of upper limb prostheses. The review revealed that the methods for system training have not matured at the same pace as the novel multifunction prostheses and more advanced intent interpretation methods. Few publications exist regarding the choice of training method and the composition of the training data set. In this context, the notion of outcome measures is essential. By definition, system training involves optimization, and the quality of the results depends heavily on the choice of appropriate optimization criteria. In order to further promote the development of proportional myoelectric control, these topics need to be addressed.

Determining skill level in myoelectric prosthesis use with multiple outcome measures.

To obtain more insight into how the skill level of an upper-limb myoelectric prosthesis user is composed, the current study aimed to (1) portray prosthetic handling at different levels of description, (2) relate results of the clinical level to kinematic measures, and (3) identify specific parameters in these measures that characterize the skill level of a prosthesis user. Six experienced transradial myoelectric prosthesis users performed a clinical test (Southampton Hand Assessment Procedure [SHAP]) and two grasping tasks. Kinematic measures were end point kinematics, joint angles, grasp force control, and gaze behavior. The results of the clinical and kinematic measures were in broad agreement with each other. Participants who scored higher on the SHAP showed overall better performance on the kinematic measures. They had smaller movement times, had better grip force control, and needed less visual attention on the hand. The results showed that time was a key parameter in prosthesis use and should be one of the main focus aspects of rehabilitation. The insights from this study are useful in rehabilitation practice because they allow therapists to specifically focus on certain parameters that may result in a higher level of skill for the prosthesis user.