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.     

Surface myoelectric signal classification for prostheses control

This paper represents an ongoing investigation for surface myoelectric signal segmentation and classification. The classical moving average technique augmented with principal components analysis and time-frency analysis were used for segmentation. Multiresolution wavelet analysis was adopted as an effective feature extraction technique while artificial neural networks were used for classification. Results of classifying four elbow and wrist movement signals recorded from biceps and triceps gave 5.1% classification error when two channels were used.     

Tuning of myoelectric prostheses using fuzzy logic

This contribution concerns the use of a supervisory expert system based on fuzzy logic for the parameter adjusting of myoelectric prostheses. The prosthesis system is an artificial arm produced by INAIL in Vigorso (Bologna, Italy), which is equipped with an on-board actuation system. The expert system guides patients through an interactive session whose aim is to test the prosthesis functionality and, when necessary, to self-adjust the parameters.     

Control accuracy and response time in multiple-state myoelectric control of upper-limb prostheses. Initial results in nondisabled volunteers

In myoelectrically operated prosthetic systems control performance decreases with an increasing number of possible movements. A test has been designed that allows quantification of two related qualities of performance. A predefined amount of training was given to 40 nondisabled volunteers without previous prosthetic experience. After training they attempted the test. The two parameters measured were the response time and the control accuracy corresponding to the different movements. It is concluded that even with a very limited amount of training fairly complex control systems can be operated with acceptable performance.     

自制手部多功能外固定支具牵引修复伸指肌腱Ⅱ区损伤

背景：国内在手部支具的研究方面与国外相比明显落后,难以获得广泛推广。伸指肌腱Ⅱ区结构较为复杂,损伤后治疗恢复效果较差,目前国内外对伸指肌腱Ⅱ区损伤主要通过石膏托、夹板以及高分子材料等固定,还没有一种针对这一区域损伤修复术后较为理想的固定锻炼支具。 目的：评价自制手部多功能外固定牵引康复支具对伸指肌腱Ⅱ区损伤的修复作用。 方法：将筛选出的76例伸指肌腱Ⅱ区损伤患者随机分成试验组和对照组,每组38例。试验组在常规伸指肌腱Ⅱ区损伤手术治疗的基础之上,给予适宜的康复教育加自制多功能外固定牵引康复支具牵引治疗;对照组给予手外科常规治疗加指导功能训练。治疗后1,2,3 个月评价两组患者的指伸肌腱总主动活动度;治疗后2,3个月评价两组患者的手灵巧度及手的精细运动情况。 结果与结论：两组患者治疗后1,2,3个月时的肌腱总主动活动度相比差异有显著性意义(P < 0.05);两组患者治疗后2,3个月时明尼苏达手灵巧度及普渡手精细运动情况相比,差异均有显著性意义(P < 0.05)。成本-效果分析结果得出两组的总花费差异无显著性意义(P > 0.05);而在以上3个功能评分上的比较,无论哪个功能评分每改善1分试验组的花费都较对照组少(P < 0.05),实现了低成本高效果的治疗。提示该支具在伸指肌腱Ⅱ区损伤修复术后的辅助锻炼治疗中起到了预防粘连及防止关节僵硬的发生的作用,同时也有助于改善手在关节活动度、灵活性及精细动作方面的能力,并且具有较高的治疗性价比。 中国组织工程研究杂志出版内容重点：组织构建;骨细胞;软骨细胞;细胞培养;成纤维细胞;血管内皮细胞;骨质疏松;组织工程全文链接：     

Sensory-feedback system compatible with myoelectric control

Progress in the development of a system to provide sensory feedback of the pinch force of an artificial hand is described. Design criteria relating to electrocutaneous stimulation and compatibility with myoelectric control are discussed. Details of a practical system, presently in use by two amputees prior to full-scale clinical evaluation, are presented.     

Amplifier input impedances for myoelectric control

Normal requirements for differential and common-mode input impedance of amplifiers for biological signals are reviewed. It is shown that these are not sufficient for satisfactory performance of amplifiers in myoelectric control applications, where accidental opening of the input circuit through electrode movement must not make the system susceptible to external noise. The additional constraint imposed by this application is examined, and a circuit is presented illustrating its practical resolution.     

Myoelectric control of prostheses

The development of myoelectric control systems for powered limb prostheses has advanced rapidly in recent years. The main thrusts in this development have been in realizing self-contained prostheses and in realizing better prostheses control through improvements in the myoelectric signal processing techniques. This review considers the latter of these two areas. It first presents an historical look at myoelectric signal processing and identifies the problems. It then presents a general look at the myoelectric signal and those characteristics which give rise to these problems. A review of the literature related to various control strategies and signal processing techniques to overcome these problems is given. Finally, future trends to be expected in this area are discussed.     

Conditioning and sampling issues of EMG signals in motion recognition of multifunctional myoelectric prostheses

Historically, the investigations of electromyography (EMG) pattern recognition-based classification of intentional movements for control of multifunctional prostheses have adopted the filter cut-off frequency and sampling rate that are commonly used in EMG research fields. In practical implementation of a multifunctional prosthesis control, it is desired to have a higher high-pass cut-off frequency to reduce more motion artifacts and to use a lower sampling rate to save the data processing time and memory of the prosthesis controller. However, it remains unclear whether a high high-pass cut-off frequency and a low-sampling rate still preserve sufficient neural control information for accurate classification of movements. In this study, we investigated the effects of high-pass cut-off frequency and sampling rate on accuracy in identifying 11 classes of arm and hand movements in both able-bodied subjects and arm amputees. Compared to a 5-Hz high-pass cut-off frequency, excluding the EMG components below 60 Hz decreased the average accuracy of 0.1% in classifying the 11 movements across able-bodied subjects and increased the average accuracy of 0.1 and 0.4% among the transradial (TR) and shoulder disarticulation (SD) amputees, respectively. Using a 500 Hz instead of a 1-kHz sampling rate, the average classification accuracy only dropped about 2.0% in arm amputees. The combination of sampling rate and high-pass cut-off frequency of 500 and 60 Hz only resulted in about 2.3% decrease in average accuracy for TR amputees and 0.4% decrease for SD amputees in comparison to the generally used values of 1 kHz and 5 Hz. These results suggest that the combination of sampling rate of 500 Hz and high-pass cut-off frequency of 60 Hz should be an optimal selection in EMG recordings for recognition of different arm movements without sacrificing too much of classification accuracy which can also remove most of motion artifacts and power-line interferences for improving the performance of myoelectric prosthesis control.     

Operator error in multistate myoelectric control systems

A myoelectric control system is one in which the operation of a device is controlled by the electric potential produced by voluntary contraction of a muscle. These systems have been used mainly for the control of artificial limbs. Early design of the control systems was empirical, but recent work has provided some theoretical basis for predicting their performance. This should lead to improvements in existing systems and make feasible the development of more complex prostheses.     

Error rate in five-state myoelectric control systems

A myoelectric control system is one in which the operation of a device is controlled by the electric potential produced by voluntary contraction of a muscle. The utilisation of a single muscle site for the 3-state control of a myoelectric prosthesis has proven beneficial for certain amputees. It has been proposed that a single muscle site could be used for 5-state control, perhaps for an elbow and hand. This paper presents a preliminary study of the error probability for 5-state control.     

Electric versus pneumatic power in hand prostheses for children

Most externally powered hand prostheses for children with a unilateral congenital below-elbow amputation are myoelectrically controlled. All of them are electrically powered. Despite the success of fitting children with this kind of prostheses, there are some disadvantages: prosthetic weight is high, operating speed is low, the system is vulnerable and its size prohibits fitting it to patients with a long fore-arm stump. It will be shown that pneumatic power can overcome most of these disadvantages.     

Electric versus pneumatic power in hand prostheses for children

Most externally powered hand prostheses for children with a unilateral congenital below-elbow amputation are myoelectrically controlled. All of them are electrically powered.

Despite the success of fitting children with this kind of prostheses, there are some disadvantages: prosthestic weight is high, operating speed is low, the system is vulnerable and its size prohibits fitting it to patients with a long fore-am stump.

It will be shown that pneumatic power can overcome most of these disadvantages.     

Neural control of canine small intestinal interdigestive myoelectric complexes

Our aim was to determine the role of the extrinsic and intrinsic nerves in the regulation of the small intestinal interdigestive myoelectric complex (IMC). In five dogs, the extrinsic nerves of the jejunoileum were divided, but the bowel was left in situ with its wall intact. After recovery, IMCs were detected in the duodenum (mean IMC period +/- SE = 188 +/- 19 min), from where most migrated distally into and through the jejunum (84%). In addition, extra IMCs appeared in the jejunum. Thus, the mean period of the IMCs in the jejunum (134 +/- 10 min) was shorter than in the duodenum (P less than 0.05). In contrast, after enteric transection and reanastomosis at the ligament of Treitz and at a site 75 cm distal to the ligament, fewer duodenal IMCs migrated into the jejunum (only 61%). However, extra IMCs still arose in the jejunum, so that the mean period of IMCs in the jejunum (111 +/- 5 min) was now similar to that in the duodenum (128 +/- 4 min, P greater than 0.05). Our data were consistent with the hypothesis that extrinsic nerves regulate the frequency of the small intestinal IMCs, while an intact enteric wall aids in their distal propagation.     

Proportional myoelectric control of a virtual object to investigate human efferent control

We used proportional myoelectric control of a one-dimensional virtual object to investigate differences in efferent control between the proximal and distal muscles of the upper limbs. Eleven subjects placed one of their upper limbs in a brace that restricted movement while we recorded electromyography (EMG) signals from elbow flexors/extensors or wrist flexors/extensors during isometric contractions. By activating their muscles, subjects applied virtual forces to a virtual object using a real-time computer interface. The magnitudes of these forces were proportional to EMG amplitudes. Subjects used this proportional EMG control to move the virtual object through two tracking tasks, one with a static target and one with a moving target (i.e., a sine wave). We hypothesized that subjects would have better control over the virtual object using their distal muscles rather than using their proximal muscles because humans typically use more distal joints to perform fine motor tasks. The results indicated that there was no difference in subjects ability to control virtual object movements when using either upper arm muscles or forearm muscles. These results suggest that differences in control accuracy between elbow joint movements and wrist joint movements are more likely to be a result of motor practice, proprioceptive feedback or joint mechanics rather than inherent differences in efferent control.     

Comparative study of wavelet denoising in myoelectric control applications

Here, the wavelet analysis has been investigated to improve the quality of myoelectric signal before use in prosthetic design. Effective Surface Electromyogram (SEMG) signals were estimated by first decomposing the obtained signal using wavelet transform and then analysing the decomposed coefficients by threshold methods. With the appropriate choice of wavelet, it is possible to reduce interference noise effectively in the SEMG signal. However, the most effective wavelet for SEMG denoising is chosen by calculating the root mean square value and signal power values. The combined results of root mean square value and signal power shows that wavelet db4 performs the best denoising among the wavelets. Furthermore, time domain and frequency domain methods were applied for SEMG signal analysis to investigate the effect of muscle-force contraction on the signal. It was found that, during sustained contractions, the mean frequency (MNF) and median frequency (MDF) increase as muscle force levels increase.     

Neuroplasticity in amputees: Main implications on bidirectional interfacing of cybernetic hand prostheses

The development of a new generation of hand prostheses that can ideally approximate the human ‘physiological’ performance in terms of movement dexterity and sensory feedback for amputees still poses many open research challenges. The most promising approaches aim at establishing a direct connection with either the central or the peripheral human nervous system by means of invasive or non-invasive neural interfaces. This paper starts from the assumption that a major contribution to derive functional and technical specifications for such interfaces, and even for the whole prosthetic system, can stem from in-depth analysis of the nervous system reorganization following limb amputation. Neuroplasticity can be modulated by the use of hand prostheses both in the acute phase and in the long-term. We hereby critically review the literature concerning neuroplastic phenomena in amputees, in terms of changes at different CNS levels, particularly for their implications on the development of bidirectional neural interfaces for cybernetic hand prostheses. Our analysis of the literature demonstrates that: (1) the level of CNS reorganization could be used as a parameter of the effectiveness achieved by the prosthetic device and its interfaces, in restoring the hand physiological functionality, (2) the prosthetic system could be seen as a neurorehabilitation tool, as it could induce reduction in aberrant plasticity and promote ‘good’ plasticity and (3) new generations of ‘natural’ interfaces can be developed by fully exploiting neuroplastic phenomena to restore neural connections originally governing the lost limb and linking them to the prosthetic system.     

Adaptable myoelectric prosthetic control with functional visual feedback using microprocessor techniques

A microprocessor-based system for the myoelectric control of one, two or three degrees of freedom has been designed. The electromyographic (EMG) activity is picked up by one or two sets of surface electrodes, depending on the number of degrees of freedom to be controlled. The system described makes it possible to control the movements in either an on/off or a proportional mode. A graphic display provides feedback information to the operator and the person in charge of the evaluation/training session. The system is designed as an evaluation and training equipment for use in the laboratory. It is applicable to both above-elbow and below-elbow amputees.