On The Road To A Neuroprosthetic Hand: A Novel Hand Grasp Orthosis Based on Functional Electrical Stimulation

To patients who have lost the functionality of their hands as a result of a severe spinal cord injury or brain stroke, the development of new techniques for grasping is indispensable for reintegration and independency in daily life. Functional Electrical Stimulation (FES) of residual muscles can reproduce the most dominant grasping tasks and can be initialized by brain signals. However, due to the very complex hand anatomy and current limitations in FES-technology with surface electrodes, these grasp patterns cannot be smoothly executed. In this paper, we present an adaptable passive hand orthosis which is capable of producing natural and smooth movements when coupled with FES. It evenly synchronizes the grasping movements and applied forces on all fingers, allowing for naturalistic gestures and functional grasps of everyday objects. The orthosis is also equipped with a lock, which allows it to remain in the desired position without the need for long-term stimulation. Furthermore, we quantify improvements offered by the orthosis compare them with natural grasps on healthy subjects

Neural bases of hand synergies

abstract: The human hand has so many degrees of freedom that it may seem impossible to control. A potential solution to this problem is “synergy control” which combines dimensionality reduction with great flexibility. With applicability to a wide range of tasks, this has become a very popular concept. In this review, we describe the evolution of the modern concept using studies of kinematic and force synergies in human hand control, neurophysiology of cortical and spinal neurons, and electromyographic (EMG) activity of hand muscles. We go beyond the often purely descriptive usage of synergy by reviewing the organization of the underlying neuronal circuitry in order to propose mechanistic explanations for various observed synergy phenomena. Finally, we propose a theoretical framework to reconcile important and still debated concepts such as the definitions of “fixed” vs. “flexible” synergies and mechanisms underlying the combination of synergies for hand control.View the article as published at http://journal.frontiersin.org/article/10.3389/fncom.2013.00023/ful

Effect of kinetic degrees of freedom in multi-finger force and moment stabilizing synergies.

The purpose of the present study was to test the principle of motor abundance as compared to motor redundance, by investigating the changes in force stabilizing and moment stabilizing synergies for pressing tasks involving different number of fingers (IM, IR, IL, MR, ML, RL, IMR, IML, IRL, MRL, IMRL; where I=Index, M=Middle, R=Ring, L=Little). Twelve healthy right-handed subjects (6 males and 6 females, 27 4.3 years) participated in the experiment. Subjects were explicitly provided a visual feedback of forces for a constant multi finger force production task. Since subjects were explicitly given a visual feedback of their performance for the force production task, strong force stabilizing synergies were expected (Hypothesis 1). Based on the principle of abundance, we hypothesized that the force stabilizing synergies would increase with the number of fingers (Hypothesis 2). Assuming that the precise moment stabilizing synergies are conditioned by everyday prehension experiences, we hypothesized that moment stabilizing synergies, if existing, would increase with the number of fingers, since all the fingers are generally used for everyday prehension and manipulation tasks, and such tasks require a precise control of moments (Hypothesis 3). Also, if both the synergies existed simultaneously, we hypothesized that those synergies would be more prominent when more fingers are involved in the task (Hypothesis 4).It was found that strong force stabilizing synergies existed for all the finger combinations, thus confirming our first hypothesis. However, these force stabilizing synergies reduced with an increase in the number of task fingers, disproving our second hypothesis. Moment destabilizing synergies were found for the two finger combinations and no moment synergies were present for the three finger combinations. However, moment stabilizing synergies existed for the four finger combinations. This confirmed our third and fourth hypothesis. We interpret the findings an evidence for the principle of abundance for stabilization of moments during pressing tasks, regardless of the fact that only the visual feedback of forces was given to the subjects

MULTI-DIGIT HUMAN PREHENSION

The current dissertation addresses the central nervous system (CNS) strategies to solve kinetic redundancy in multi-digit static prehension under different geometries of hand-held objects and systematically varied mechanical constraints such as translation and rotation of the hand-held object. A series of experiments conducted for this dissertation tested the following hypotheses suggested in the current literatures for multi-digit human static prehension: Hierarchical organization hypothesis, principle of superposition hypothesis, proximity hypothesis, and mechanical advantage hypothesis. (1) Forces and moments produced by fingers during circular object prehension were grouped into two independent subsets: one subset related to grasping stability control and the other associated with rotational equilibrium control. This result supports the principle of superposition hypothesis. Individual fingers acted synergistically to compensate each other's errors. This result confirms the hierarchical organization hypothesis in circular object prehension. (2) During fixed object prehension of a rectangular object, the closer the non-task fingers positioned to the task finger, the greater the forces produced by the non-task fingers. However, during free object prehension, the non-task fingers with longer moment arms produced greater forces. The former and latter results support the proximity hypothesis and the mechanical advantage hypothesis, respectively. (3) The grasping stability control and rotational equilibrium control were decoupled during fixed object prehension as well as free object prehension. This result supports the principle of superposition hypothesis regardless of the mechanical constraints provided for these two prehension types. (4) During torque production, the fingers with longer moment arms produced greater forces when the fingers acted as agonists for the torque production. Therefore, the mechanical advantage hypothesis was supported for agonist fingers. (5) Coupling of thumb normal force and virtual finger normal force was not necessitated when horizontal translation of hand-held object was mechanically fixed. However, the coupling of two normal forces was always observed regardless of given translational constraints, and these two normal forces were independent to other mechanical variables such as tangential forces and moments. This result supports the principle of superposition hypothesis in static prehension under varied combinations of translational constraints

다중손가락 과제 수행 시 인간의 감각 및 인지 처리 과정의 정량화

학위논문 (박사) -- 서울대학교 대학원 : 사범대학 체육교육과, 2021. 2. 박재범.The continuously varied states of human body and surrounding environment require instantaneous motor adaptations and the understanding of motor goal to achieve desired actions. These sensory and cognitive processes have been investigated as elements in motor control during last five decades. Specially, the task dependency on sensory and cognitive processes suggest the effects of movement properties in terms of environment situation and motor goal. However, these effects were mostly empirically summarized with the measurements of either neural activity or simple motor accomplishment unilaterally. The current thesis addresses the quantification of sensory and cognitive processes based on simultaneous measurements of brain activity and synergic motor performance during multi-digit actions with different movement properties. Multi-digit action as a representation of synergic movements has developed into a widespread agency to quantify the efficacy of motor control, as the reason applied in this thesis. In this thesis, multi-digit rotation and pressing tasks were performed with different movement directions, frequencies, feedback modalities, or task complexities. (Chapter 3) The changes of movement direction induced a decrease in motor synergy but regardless of which direction. (Chapter 4 and 5) Increased frequency of rhythmic movement reduced synergic motor performance associate with decreased sensory process and less efficient cognitive process. (Chapter 6) More comprehensive feedback modality improved synergic performance with increased sensory process. (Chapter 7) Increased movement complexity had a consistent but stronger effect as increased frequency on synergic performance and efficiency of cognitive process. These observations suggest that several movement properties affect the contributions of sensory and cognitive processes to motor control which can be quantified through either neural activity or synergic motor performance. Accordingly, those movement properties may be applied in the rehabilitation of motor dysfunction by developing new training programs or assistant devices. Additionally, it may be possible to develop a simplified while efficient method to estimate the contribution of sensory or cognitive process to motor control.시시각각으로 변화하는 신체 상태와 주변 환경의 상호작용 속에서 알맞은 움직임을 수행하기 위해서는 그에 따른 즉각적인 운동 적응(motor adaptation) 과정와 과제 목표에 대한 이해가 필요하다. 이를 위해 인간의 감각 및 인지 처리과정은 운동 제어 분야의 중요한 요소로 여겨졌다. 선행연구에 따르면, 운동 과제에 따라 변화하는 감각 및 인지 처리과정은 주변 환경과 과제의 목표에 따라 움직임의 특성에 영향을 미친다고 보고되어왔다. 그러나 이러한 영향은 대부분 단순한 운동과제 수행 결과 또는 측정된 신경 활동에 의해 경험적으로 요약된 결과에 국한되어 있다. 따라서 본 논문은 다양한 움직임 특성을 가진 다중 손가락 과제 수행 시, 뇌 활동 (Brain activity)과 더불어 손가락들 간의 협응적인 움직임의 수행 결과를 동시 측정하여 과제의 특성에 따른 감각 및 인지 처리과정의 변화를 분석했다. 다중 손가락 과제는 운동 제어의 성능 효율성을 정량화하기 위해 사용되는 대표적인 과제다. 본 논문에서는 다양한 조건의 움직임 방향, 움직임의 주기빈도, 감각 피드백 양식 또는 과제 난이도에 따른 다중 손가락 회전 동작 및 힘 생성 과제를 사용했다. 연구 결과로는, (문단 3) 움직임 방향이 변화하기 전에 변화할 방향에 상관없이 협응적인 움직임이 악화되었다. (문단 4와 5) 움직임의 주기빈도가 증가할수록 협응적인 움직임이 악화됐으며, 이와 관련된 감각 및 인지 처리과정의 효율성도 감소되었다. (문단 6) 단일 감각 피드백 제공조건에 비해 종합적인 감각 피드백은 증가된 감각 처리과정과 함께 협응적인 움직임을 향상시켰다. (문단 7) 과제의 난이도가 증가할수록 협응적인 움직임과 인지 처리과정의 효율성은 감소되었으며, 움직임의 주기빈도 조건에 비해 과제의 난이도에 따라 협응적인 움직임과 인지 처리과정에 미치는 영향은 상대적으로 더 크게 나타났다. 이러한 결과는 움직임 특성에 따른 뇌 활동과 협응적인 과제 수해 결과를 통해 운동 제어 과정에서 감각 및 인지 처리과정의 기여정도를 정량화할 수 있다는 점을 시사한다. 따라서 움직임 특성에 따른 감각 및 인지 처리 과정의 기여정도의 변화는 운동 기능 장애를 가진 사람들의 새로운 재활 훈련 프로그램 및 움직임 보조 장치를 개발하기 위한 실험적인 근거로 적용될 수 있다. 또한 감각 또는 인지 과정이 운동 제어에 미치는 영향을 추정하기 위한 효율적인 방법을 개발하는데 도움이 될 것이다.Chapter 1. Introduction 1 1.1 Problem statement 1 1.2 Study objective 2 1.3 Organization of dissertation 3 Chapter 2. Background 6 2.1 Motor system 6 2.1.1 Ascending pathway 6 2.1.2 Descending pathway 8 2.1.3 Brain networks 9 2.2 Motor synergy 11 2.2.1 Synergy in performance 12 2.2.2 Synergy in muscles 13 2.2.3 Synergy in neurons 14 2.3 Motor control 15 2.1.1 Sensory process 16 2.1.2 Cognitive process 19 Chapter 3. Effect of movement direction: Multi-Finger Interaction and Synergies in Finger Flexion and Extension Force Production 23 3.1 Abstract 23 3.2 Introduction 24 3.3 Method 28 3.4 Results 35 3.4.1 Maximal voluntary contraction (MVC) force and finger independency 36 3.4.2 Timing indices 37 3.4.3 Multi-finger synergy indices in mode space 39 3.4.4 Multi-finger synergy indices in force space 43 3.5 Discussion 44 3.5.1 Finger independency during finger flexion and extension 44 3.5.2 Multi-finger synergies in force and mode spaces 46 3.5.3 Anticipatory synergy adjustment 48 Chapter 4. Effect of Frequency: Brain Oxygenation Magnitude and Mechanical Outcomes during Multi-Digit Rhythmic Rotation Task 51 4.1 Abstract 51 4.2 Introduction 51 4.3 Methods 55 4.4 Results 61 4.4.1 PET imaging 61 4.4.2 Finger forces 62 4.4.3 UCM analysis 64 4.4.4 Correlation between neural activation and mechanics 65 4.5 Discussion 66 4.5.1 Regions involved in feedback 67 4.5.2 Regions involved in feedforward 69 4.5.3 Corporation of feedforward and feedback 71 4.6 Conclusions 72 Chapter 5. Effect of frequency: Prefrontal Cortex Oxygenation during Multi-Digit Rhythmic Pressing Actions using fNIRS 74 5.1 Abstract 74 5.2 Introduction 74 5.3 Method 77 5.4 Results 84 5.4.1 Performance 84 5.4.2 Multi-digit coordination indices 84 5.4.3 Functional connectivity (FC) 87 5.5 Discussion 88 5.6 Conclusion 91 Chapter 6. Effect of Sensory Modality: Multi-Sensory Integration during Multi-Digit Rotation Task with Different Frequency 92 6.1 Abstract 92 6.2 Introduction 92 6.3 Method 94 6.4 Results 100 6.4.1 Performance 100 6.4.2 Multi-digit coordination indices 101 6.5 Discussion 101 6.6 Conclusion 103 Chapter 7. Effect of Task Complexity: Prefrontal Cortex Oxygenation during Multi-Digit Pressing Actions with Different Frequency Components 104 7.1 Abstract 104 7.2 Introduction 104 7.3 Method 106 7.4 Results 112 7.4.1 Performance 112 7.4.2 Multi-finger coordination indices 113 7.4.3 Functional connectivity (FC) 114 7.5 Discussion 115 7.5.1 Relation between Frequency and task complexity 115 7.5.2 Cognitive process in motor control 116 7.5.3 Relation between motor coordination and cognitive process 118 7.6 Conclusion 119 Chapter 8. Conclusions and Future Work 120 8.1 Summary of conclusions 120 8.2 Future work 121 Bibliography 122 Abstract in Korean 160Docto

Parallel Manipulators

In recent years, parallel kinematics mechanisms have attracted a lot of attention from the academic and industrial communities due to potential applications not only as robot manipulators but also as machine tools. Generally, the criteria used to compare the performance of traditional serial robots and parallel robots are the workspace, the ratio between the payload and the robot mass, accuracy, and dynamic behaviour. In addition to the reduced coupling effect between joints, parallel robots bring the benefits of much higher payload-robot mass ratios, superior accuracy and greater stiffness; qualities which lead to better dynamic performance. The main drawback with parallel robots is the relatively small workspace. A great deal of research on parallel robots has been carried out worldwide, and a large number of parallel mechanism systems have been built for various applications, such as remote handling, machine tools, medical robots, simulators, micro-robots, and humanoid robots. This book opens a window to exceptional research and development work on parallel mechanisms contributed by authors from around the world. Through this window the reader can get a good view of current parallel robot research and applications