A multi-view vision-based hand motion capturing system

Vision-based hand motion capturing approaches play a critical role in human computer interface owing to its non-invasiveness, cost effectiveness, and user friendliness. This work presents a multi-view vision-based method to capture hand motion. A 3-D hand model with structural and kinematical constraints is developed to ensure that the proposed hand model behaves similar to an ordinary human hand. Human hand motion in a high degree of freedom space is estimated by developing a separable state based particle filtering (SSBPF) method to track the finger motion. By integrating different features, including silhouette, Chamfer distance, and depth map in different view angles, the proposed motion tracking system can capture the hand motion parameter effectively and solve the self-occlusion problem of the finger motion. Experimental results indicate that the hand joint angle estimation generates an average error of 11°.     

Grip posture and forces during holding cylindrical objects with circular grips

Individual finger position and external grip forces were investigated while subjects held cylindrical objects from above using circular precision grips. Healthy females (n = 11) and males (n = 15) lifted cylindrical objects of various weights (05, 10 and 20kg), and varied diameters (50, 7-5 and 100cm) using the 5-finger grip mode. The effects of 4-, 3- and 2-finger grip modes in the circular grip were also investigated.

Individual finger position was nearly constant for all weights and for diameters of 5-0 and 7-5 cm. The mean angular positions for the index, middle, ring and little fingers relative to the thumb were 98°, 145°, 181°, and 236°, respectively. At the 10-cm diameter, the index and middle finger positions increased, while the ring and little finger positions decreased. There were no differences in individual finger position with regard to gender, hand dimension, or hand strength.

Total grip force increased with weight, and at diameters greater or lesser than 7-5 cm. Total grip force also increased as the number of fingers used for grasping decreased. Although the contribution of the individual fingers to the total grip force changed with weight and diameter, the thumb contribution always exceeded 38% followed by the ring and little fingers, which contributed approximately 18-23% for all weights and diameters. The contribution of the index finger was always smallest (>11%). There was no gender difference for any of the grip force variables. The effects of hand dimension and hand strength on the individual finger grip forces were subtle.     

Validity and reliability of a novel device for bilateral upper extremity functional measurements

Background and objective

This study was designed to establish the validity and reliability of a new device that measures bilateral shoulder and elbow range of motion (ROM) and grip force performance in vivo. A further aim was to investigate the control of inter-limb grip force coordination during isometric force-maintenance tasks. Validity of the ROM and grip force measurements was examined using a validated clinical goniometer and standard weights.

Subjects

Twenty-one healthy adults (six female, 15 male; mean ± standard deviation age = 23.05 ± 3.51) were recruited for this study.

Design

All subjects were asked to perform tests to evaluate the validity and reliability of ROM, grip force maximum voluntary contraction (MVC) and coordination control measurements.

Results

The ROM and grip force measurements were linearly correlated with criterion standards. For reliability testing, all of the intraclass correlation coefficient values were >0.99. The inter-limb grip force coordination control task showed that the force modulation timing during dominant-to-non-dominant hand transition was longer than the non-dominant-to-dominant hand transition (p < 0.05).

Conclusions

These results demonstrate that this device is valid and reliable when used to measure shoulder and elbow ROM and grip force of both hands. Isometric force-maintenance tasks also indicated changes in inter-limb grip force control.     

A new method for estimating hand internal loads from external force measurements

This study examines using force vectors measured using a directional strain gauge grip dynamometer for estimating finger flexor tendon tension. Fifty-three right-handed participants (25 males and 28 females) grasped varying-sized instrumented cylinders (2.54, 3.81, 5.08, 6.35 and 7.62 cm diameter) using a maximal voluntary power grip. The grip force vector magnitude and direction, referenced to the third metacarpal, was resolved by taking two orthogonal grip force measurements. A simple biomechanical model incorporating the flexor tendons was used to estimate long finger tendon tension during power grip. The flexor digitorum superficialis and the flexor digitorum profundus were assumed to create a moment about the metacarpal phalange (MCP) joint that equals and counteracts a moment around the MCP joint measured externally by the dynamometer. The model revealed that tendon tension increased by 130% from the smallest size handle to the largest, even though grip force magnitude decreased 36% for the same handles. The study demonstrates that grip force vectors may be useful for estimating internal hand forces.     

Design of optimum grip and control area for one-handed manual control devices

The objective of this paper was to make a design specification of the control area in dual tasks of the hand grip and manual control. The grip postures were analyzed for three types of hand tools. An experiment was performed to measure the position of the fingers and the maximum finger forces at 4 different postures for nine subjects. It was found out that the finger forces were significantly affected by the subjects, the fingers, and the grip postures. The maximum force of women was 62% of men's. From the experiment, the primary control area was defined as 10–13cm and the secondary control area as 8–12cm from the wrist origin. The preferred hand posture of the index and the middle fingers was found to be 3045 degrees at metacarpophalangeal joint and 4050 degrees at proximal interphalangeal joint. It was also found out that the design of one-handed manual control devices should include the characteristics of the user, grip posture, finger force, and the control arrangement.     

Effects of the resting time associated with the number of trials on the total and individual finger forces in a maximum grasping task

The repetitive and excessive workload accompanying grip strength- or hand-intensive tasks are often considered to be common causes of work-related upper limb musculoskeletal disorders. For this reason, numerous experimental studies have been performed on maximum grip strength. However, due to an absence of standard guidelines, researchers have adopted different resting times and number of trials suited for their particular research purposes. The effects of resting time and the number of trials on the maximum total grip strength and individual finger forces of 24 participants over 20 trials were investigated. Results showed that the total grip strength and individual finger strengths differed significantly according to the resting time and the number of trials (p < 0.05). Overall, grip strength tended to increase with a reduction in resting time (% reduction: 7.8%, 9.1%, 11.1%, and 13.0% for 3 min, 2 min, 1 min, and 30 s resting time, respectively) as well as with an increase in the number of trials (% reduction: 8%, 10%, 13%, and 16% for 5th, 10th, 15th, and 20th trials). The effects of resting time and the number of trials also showed statistically significant effects on individual finger forces. Regression equations of total grip strength and finger forces with resting time and number of trials were established. These equations were then applied to formulate guidelines for appropriate resting times in experiments based on the number of trials and acceptable reductions in grip strength. Data from this and future studies regarding decreasing grip strength and the contribution of each finger are expected to form the groundwork for ergonomic hand tool design and development.     

EMG control of a pneumatic 5-fingered hand using a Petri net

This article presents the control method for a 5-fingered artificial hand using electromyography (EMG) signals. Our targeted artificial hand is driven by pneumatic actuators to reduce its weight, and we use ON/OFF solenoid valves instead of electro pneumatic regulators to simplify the control system. The pneumatic hand has 15 degrees of freedom, and it seems difficult to reproduce all the finger motions from the EMG signals only. Therefore, we describe typical hand motions using a Petri net, and control the finger motions efficiently based on this model. Each state of the Petri net indicates one step in the hand posture to complete the intended motion. Simultaneously, this state corresponds to the ON/OFF pattern of the 15 solenoid valves. This enables the operator to control the 5-fingered dexterous hand smoothly, transiting the state in the Petri net according to the EMG motion signals. We conducted an experiment to verify the validity of the proposed method. In the experiment, five typical motions (spherical grasp, power grip, hook grip, key grip, precision grip) were successfully performed using the 6-channel EMG signals measured from the operator’s forearm.     

Analysis of natural finger-press motions for design of trackball buttons

This study analysed natural press motions of the index, middle and ring fingers for ergonomic design of the positions and surface angles of the left, middle and right trackball buttons. Finger motions of 26 male participants for naturally pressing the trackball buttons were recorded after the participants adjusted the trackball buttons to their preferred locations for comfortable pressing. The natural positions of the finger pulps formed a symmetrically rainbow-shaped reach zone for the fingers. The natural press angles of the fingers’ motion trajectories to the vertical reference line ranged from 14.2° to 20.5°, suggesting an 18-degree surface from the horizontal line for the trackball buttons. Regression formulas (adjusted R²?=?0.90?±?0.07 and mean squared error?=?8.55?±?7.52?mm) were established to estimate the natural positions of finger pulps from hand segment lengths and joint angles for a population having different hand sizes from this study.

Relevance to industry     

Three-dimensional finger joint angles by hand posture and object properties

The objective of this study was to identify three-dimensional finger joint angles for various hand postures and object properties. Finger joint angles were measured using a VICON system for 10 participants while they pinched objects with two, three, four and five fingers and grasped them with five fingers. The objects were cylinders and square pillars with diameters of 2, 4, 6 and 8 cm and weights of 400, 800, 1400 and 1800 g. Hand posture and object size more significantly affected the joint flexion angles than did object shape and weight. Object shape affected only the metacarpophalangeal (MCP) joint angle of the index finger and the flexion angle of the MCP joint of the little finger. Larger flexion angles resulted when the hand posture was grasping with five fingers. The joint angle increased linearly as the object size decreased. This report provides fundamental information about the specific joint angles of the thumb and fingers.

Practitioner Summary: Three-dimensional finger joint angles are of special interest in ergonomics because of their importance in handheld devices and musculoskeletal hand disorders. In this study, the finger joint angles corresponding to various hand postures and objects with different properties were determined.     

Primitive Object Grasping for Finger Motion Synthesis

We developed a new framework to generate hand and finger grasping motions. The proposed framework provides online adaptation to the position and orientation of objects and can generate grasping motions even when the object shape differs from that used during motion capture. This is achieved by using a mesh model, which we call primitive object grasping (POG), to represent the object grasping motion. The POG model uses a mesh deformation algorithm that keeps the original shape of the mesh while adapting to varying constraints. These characteristics are beneficial for finger grasping motion synthesis that satisfies constraints for mimicking the motion capture sequence and the grasping points reflecting the shape of the object. We verify the adaptability of the proposed motion synthesizer according to its position/orientation and shape variations of different objects by using motion capture sequences for grasping primitive objects, namely, a sphere, a cylinder, and a box. In addition, a different grasp strategy called a three‐finger grasp is synthesized to validate the generality of the POG‐based synthesis framework.     

The effect of sinusoidal rolling ground motion on lifting biomechanics

The objective of this study was to quantify the effects of ground surface motion on the biomechanical responses of a person performing a lifting task. A boat motion simulator (BMS) was built to provide a sinusoidal ground motion (simultaneous vertical linear translation and a roll angular displacement) that simulates the deck motion on a small fishing boat. Sixteen participants performed lifting, lowering and static holding tasks under conditions of two levels of mass (5 and 10 kg) and five ground moving conditions. Each ground moving condition was specified by its ground angular displacement and instantaneous vertical acceleration: A): +6°, −0.54 m/s²; B): +3°, −0.27 m/s²; C): 0°, 0 m/s²; D): −3°, 0.27 m/s²; and E): −6°, 0.54 m/s². As they performed these tasks, trunk kinematics were captured using the lumbar motion monitor and trunk muscle activities were evaluated through surface electromyography. The results showed that peak sagittal plane angular acceleration was significantly higher in Condition A than in Conditions C, D and E (698°/s² vs. 612-617°/s²) while peak sagittal plane angular deceleration during lowering was significantly higher in moving conditions (conditions A and E) than in the stationary condition C (538-542°/s² vs. 487°/s²). The EMG results indicate that the boat motions tend to amplify the effects of the slant of the lifting surface and the external oblique musculature plays an important role in stabilizing the torso during these dynamic lifting tasks.     

Development of a kinematic model to predict finger flexor tendon and subsynovial connective tissue displacement in the carpal tunnel

Finger flexor tendinopathies and carpal tunnel syndrome are histologically characterised by non-inflammatory fibrosis of the subsynovial connective tissue (SSCT) in the carpal tunnel, which is indicative of excessive and repetitive shear forces between the finger flexor tendons and SSCT. We assessed flexor digitorum superficialis (FDS) tendon and adjacent SSCT displacements with colour Doppler ultrasound as 16 healthy participants completed long finger flexion/extension movements captured by a motion capture system. FDS tendon displacements fit a second-order regression model based on metacarpophalangeal and proximal interphalangeal joint flexion angles (R² = 0.92 ± 0.01). SSCT displacements were 33.6 ± 1.7% smaller than FDS tendon displacements and also fit a second-order regression model (R² = 0.89 ± 0.01). FDS tendon and SSCT displacement both correlated with finger joint thickness, enabling participant-specific anthropometric scaling. We propose the current regression models as an ergonomic method to determine relative displacements between the finger flexor tendons and SSCT.     

Common patterns of voluntary grasp types according to object shape,size, and direction

This study aimed to investigate commonly used voluntary grasp types according to object shape, size, and direction, with the participation of 50 students. The grasp type classifications consisted of grasping (G) and pinching (P) and were further subdivided based on the number and use of fingers (T, thumb; I, index finger; M, middle finger; R, ring finger; or L, little finger) and palm (P). Seven grasp types were commonly used by the participants: 5P (TIMRL), 5G (TIMRL), 3P (TIM), 4P (TIMR), 2P (TI), 4G (TIMR), and 3G (TIM). Participants most frequently held cylindrical and square pillar objects using 5G (TIMRL) and 5P (TIMRL), respectively. 3P (TIM) was commonly used to hold 1- to 4-cm objects, whereas 5G (TIMRL) and 5P (TIMRL) were commonly used to hold 8- to 12-cm objects. The up-down direction-oriented objects were commonly held with 5G (TIMRL), and the left-right direction-oriented objects were held with 2P (TI), 3P (TIM), and 5G (TIMRL). These results provide basic information regarding common patterns of human grasp types.Relevance to industryThis paper provides a guideline on the selection of hand tools in industry in terms of their shapes and sizes, so that workers can use appropriate hand postures to reduce hand stresses.     

Coupled dynamical system based arm–hand grasping model for learning fast adaptation strategies

Performing manipulation tasks interactively in real environments requires a high degree of accuracy and stability. At the same time, when one cannot assume a fully deterministic and static environment, one must endow the robot with the ability to react rapidly to sudden changes in the environment. These considerations make the task of reach and grasp difficult to deal with. We follow a Programming by Demonstration (PbD) approach to the problem and take inspiration from the way humans adapt their reach and grasp motions when perturbed. This is in sharp contrast to previous work in PbD that uses unperturbed motions for training the system and then applies perturbation solely during the testing phase. In this work, we record the kinematics of arm and fingers of human subjects during unperturbed and perturbed reach and grasp motions. In the perturbed demonstrations, the target’s location is changed suddenly after the onset of the motion. Data show a strong coupling between the hand transport and finger motions. We hypothesize that this coupling enables the subject to seamlessly and rapidly adapt the finger motion in coordination with the hand posture. To endow our robot with this competence, we develop a coupled dynamical system based controller, whereby two dynamical systems driving the hand and finger motions are coupled. This offers a compact encoding for reach-to-grasp motions that ensures fast adaptation with zero latency for re-planning. We show in simulation and on the real iCub robot that this coupling ensures smooth and “human-like” motions. We demonstrate the performance of our model under spatial, temporal and grasp type perturbations which show that reaching the target with coordinated hand–arm motion is necessary for the success of the task.     

虚拟手抓握动作的Petri网模型及其仿真实现

虚拟手的运动建模是三维人机交互研究中的一个关键问题.虚拟人在执行维修作业的过程中,不可避免地需要徒手抓握操作对象或维修工具.为此,该文提出了一种基于位置/变迁Petri网的虚拟人手抓握动作模型.该方法以关节化虚拟手的几何建模和关节约束分析为基础,描述了抓握动作的Petri网模型,通过仿真循环叠代和关节插值计算,实现关节链上各个关节的运动控制,并基于面向对象的技术设计实现了典型抓握动作.最后,基于人体建模与仿真软件Jack,设计并实现了一个虚拟手抓握动作的Petri网,仿真和实验结果表明所述方法简便易行,能够满足虚拟维修作业的要求.     

The effects of vibration-reducing gloves on finger vibration

Vibration-reducing (VR) gloves have been used to reduce the hand-transmitted vibration exposures from machines and powered hand tools but their effectiveness remains unclear, especially for finger protection. The objectives of this study are to determine whether VR gloves can attenuate the vibration transmitted to the fingers and to enhance the understanding of the mechanisms of how these gloves work. Seven adult male subjects participated in the experiment. The fixed factors evaluated include hand force (four levels), glove condition (gel-filled, air bladder, no gloves), and location of the finger vibration measurement. A 3-D laser vibrometer was used to measure the vibrations on the fingers with and without wearing a glove on a 3-D hand-arm vibration test system. This study finds that the effect of VR gloves on the finger vibration depends on not only the gloves but also their influence on the distribution of the finger contact stiffness and the grip effort. As a result, the gloves increase the vibration in the fingertip area but marginally reduce the vibration in the proximal area at some frequencies below 100 Hz. On average, the gloves reduce the vibration of the entire fingers by less than 3% at frequencies below 80 Hz but increase at frequencies from 80 to 400 Hz. At higher frequencies, the gel-filled glove is more effective at reducing the finger vibration than the air bladder-filled glove. The implications of these findings are discussed.     

The effects of tool handle shape on hand performance,usability and discomfort using masons' trowels

The effects of five new different handle shapes on hand performance capabilities, usability and discomfort, and also the relationship between these variables were evaluated in the context of masonry work and using masons’ trowels as an exemplar hand tool. The prototype handles were designed to provide different patterns of grip so that they could be suited to the hand/tool interaction in particular hand areas. The results showed significant effect of tool handle shape on the hand grip effort, usability, and hand and finger discomfort assessments, but not on the time to complete the masonry task. The hand grip effort and usability were negatively correlated with subjective assessment of hand and finger discomfort, so that a lower level of hand and finger discomfort corresponded to higher hand grip exertion and usability. These findings provide a better insight into the performance and usability issues when using hand tools which can be applied by tool manufacturers to improve industrial hand tool design.Relevance to industryThese findings present a unique insight into the handle design for industrial hand tool use and support the general conclusion that objective measurements should be supplemented by qualitative subjective assessments to provide a more holistic approach where specific and additional details about the hand tool design characteristics are incorporated from the workers' perspective.     

Effect of object width on precision grip force and finger posture

This study aimed to define the effect of object width on spontaneous grasp. Participants held objects of various masses (0.75 to 2.25 kg) and widths (3.5 to 9.5 cm) between thumb and index finger. Grip force, maximal grip force and corresponding finger postures were recorded using an embedded force sensor and an optoelectronic system, respectively. Results showed that index finger joints varied to accommodate the object width, whereas thumb posture remained constant across conditions. For a given object mass, grip force increased as a function of object width, although this result is not dictated by the laws of mechanics. Because maximal grip force also increased with object width, we hypothesise that participants maintain a constant ratio between grip force and their maximal grip force at each given width. Altogether we conclude that when the task consists in manipulating objects/tools, the optimal width is different than when maximal force exertions are required.     

Effect of object width on precision grip force and finger posture

This study aimed to define the effect of object width on spontaneous grasp. Participants held objects of various masses (0.75 to 2.25 kg) and widths (3.5 to 9.5 cm) between thumb and index finger. Grip force, maximal grip force and corresponding finger postures were recorded using an embedded force sensor and an optoelectronic system, respectively. Results showed that index finger joints varied to accommodate the object width, whereas thumb posture remained constant across conditions. For a given object mass, grip force increased as a function of object width, although this result is not dictated by the laws of mechanics. Because maximal grip force also increased with object width, we hypothesise that participants maintain a constant ratio between grip force and their maximal grip force at each given width. Altogether we conclude that when the task consists in manipulating objects/tools, the optimal width is different than when maximal force exertions are required.     

Wireless Face Interface: Using voluntary gaze direction and facial muscle activations for human-computer interaction

The present aim was to investigate the functionality of a new wireless prototype called Face Interface. The prototype combines the use of voluntary gaze direction and facial muscle activations, for pointing and selecting objects on a computer screen, respectively. The subjective and objective functionality of the prototype was evaluated with a series of pointing tasks using either frowning (i.e., frowning technique) or raising the eyebrows (i.e., raising technique) as the selection technique. Pointing task times and accuracies were measured using three target diameters (i.e., 25, 30, 40 mm), seven pointing distances (i.e., 60, 120, 180, 240, 260, 450, and 520 mm), and eight pointing angles (0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315°). The results showed that the raising technique was faster selection technique than the frowning technique for the objects that were presented in the pointing distances from 60 mm to 260 mm. For those pointing distances the overall pointing task times were 2.4 s for the frowning technique, and 1.6 s for the raising technique. Fitts’ law computations showed that the correlations for the Fitts’ law model were r = 0.77 for the frowning technique and r = 0.51 for the raising technique. Further, the index of performance (IP) value was 1.9 bits/s for the frowning technique and 5.4 bits/s for raising the eyebrows technique. Based on the results, the prototype functioned well and was adjustable so that two different facial activations can be used in combination with gaze direction for pointing and selecting objects on a computer screen.