Wrist posture affects hand and forearm muscle stress during tapping

Non-neutral wrist posture is a risk factor of the musculoskeletal disorders among computer users. This study aimed to assess internal loads on hand and forearm musculature while tapping in different wrist postures. Ten healthy subjects tapped on a key switch using their index finger in four wrist postures: straight, ulnar deviated, flexed and extended. Torque at the finger and wrist joints were calculated from measured joint postures and fingertip force. Muscle stresses of the six finger muscles and four wrist muscles that balanced the calculated joint torques were estimated using a musculoskeletal model and optimization algorithm minimizing the squared sum of muscle stress. Non-neutral wrist postures resulted in greater muscle stresses than the neutral (straight) wrist posture, and the stress in the extensor muscles were greater than the flexors in all conditions. Wrist extensors stress remained higher than 4.5 N/cm² and wrist flexor stress remained below 0.5 N/cm² during tapping. The sustained high motor unit recruitment of extensors suggests a greater risk than other muscles especially in flexed wrist posture. This study demonstrated from the perspective of internal tissue loading the importance of maintaining neutral wrist posture during keying activities.     

Operation of ternary chorded keys

Operation of the ternary chord keyboard (TCK) requires fast and finely controlled force and displacement by the fingertips in a horizontal plane—that is, rocking instead of the familiar tapping of keys. Associated human motoric abilities relate to finger movement directions, force capabilities, and responses to displayed stimuli. Underlying mental tasks are memorization of the chords for each character to be generated and control of simultaneous fingertip movements.

Experiments were performed: (1) on a TCK prototype to measure the time needed to learn its operation and to assess keying performance, and (2) on specially designed experimental apparatus to measure finger mobility, strength, and speed. The results indicate that finger mobility, strength, and tapping performance were not well correlated with keying performance and that the TCK principle is feasible.     

基于加速度计的手指运动姿态检测

针对动态测量手指关节角度的需要,设计了一种基于MEMS加速度计的手指运动姿态检测方法。在该方法中,通过固定于手指上的三轴加速度计ADXL330的各个敏感轴感受到的重力加速度分量的大小来检测手指的关节角度。为了验证该方法的可行性,设计了一步进电机控制的能在竖直平面内转动的装置,通过同步检测传感器的输出和电机转动的角度,评估传感器在动态条件下的测量精度,结果表明:在动态条件下,其绝对误差为1°～2.5°,相对误差为3%～6%。在此基础上,将传感器用于测量手指关节的运动姿态,采集手指敲击键盘时传感器的输出,通过数据处理获得食指MCP关节、PIP关节和DIP关节随时间的变化关系。实验结果表明:加速度计可以有效地检测手指的运动姿态。     

Design of an optical soft sensor for measuring fingertip force and contact recognition

Among the various ways to estimate user intention in hand exoskeletons, a contact force measurement is definitely the most straightforward and intuitive method. A force sensor, located at the center of a fingertip usually, hinders the tactile sensation of the user by blocking the contact between an object and the fingertip. To overcome this problem, a soft force sensor with horse shoe shape is utilized to measure the contact force and provide the tactile sensation to the user. This work presents the mechanical design, implementation and evaluation of a soft fingertip force sensor. To maximize tactile sensation of the user, we adopted a horse shoe shape structure to leave the finger pad exposed. An optical sensing mechanism was selected for its relatively fast response compared to other soft sensors. The whole sensor system has a soft exterior providing flexibility and a user-friendly interface. To evaluate the sensor’s performance, we carried out sensor optimization process and calibration experiment with a customized test bed. Then, we investigated both static and dynamic response and observed the mechanical behavior and light intensity changes caused by the cross sectional shape and base/agent ratio of PDMS. Lastly, we applied the proposed sensor to the glove type fingertip force monitoring system. The sensor estimates the index finger tip force with high accuracy (R ² = 0:96) within 5N range.     

A system for evaluating the effect of keyboard design on force,posture, comfort,and productivity

The purpose of this study was to develop a system to determine the effectiveness of an alternative keyboard design which aimed to reduce fingertip force and awkward wrist postures. A prototype alphanumeric keyboard, adjustable in four ways, was developed for this study. Four measurements were chosen to determine the effectiveness of each keyboard configuration: fingertip impact force; wrist position; productivity; and comfort and ease of use. Fingertip force was measured using instrumented keys that had strain gauges located between the key cap and the key switch. Wrist position was measured using electronic goniometers attached to the forearms and hands of the test subjects. A computer program was developed to measure productivity, and a questionnaire based on the Borg rating scale was developed to measure comfort and ease of use. The system was tested to ensure its accuracy. Linearity, repeatability, strike position sensitivity, and natural frequency of the instrumented keycap assembly were assessed. Output of the electric goniometers was compared with readings on a manual goniometer to ensure the former's accuracy over the range of wrist angles expected during keyboard operations. Results of the validation indicated that the system is capable of measuring fingertip force and wrist angle accurately and repeatably. The system described in this paper is the first one that measures fingertip force, wrist position, productivity, and comfort and ease of use simultaneously.     

Effect of horizontal position of the computer keyboard on upper extremity posture and muscular load during computer work

The distance of the keyboard from the edge of a work surface has been associated with hand and arm pain; however, the variation in postural and muscular effects with the horizontal position have not been explicitly explored in previous studies. It was hypothesized that the wrist approaches more of a neutral posture as the keyboard distance from the edge of table increases. In a laboratory setting, 20 adults completed computer tasks using four workstation configurations: with the keyboard at the edge of the work surface (NEAR), 8 cm from the edge and 15 cm from the edge, the latter condition also with a pad that raised the work surface proximal to the keyboard (FWP). Electrogoniometers and an electromagnetic motion analysis system measured wrist and upper arm postures and surface electromyography measured muscle activity of two forearm and two shoulder muscles. Wrist ulnar deviation decreased by 50% (4 degrees ) as the keyboard position moved away from the user. Without a pad, wrist extension increased by 20% (4 degrees ) as the keyboard moved away but when the pad was added, wrist extension did not differ from that in the NEAR configuration. Median values of wrist extensor muscle activity decreased by 4% maximum voluntary contraction for the farthest position with a pad (FWP). The upper arm followed suit: flexion increased while abduction and internal rotation decreased as the keyboard was positioned further away from the edge of the table. In order to achieve neutral postures of the upper extremity, the keyboard position in the horizontal plane has an important role and needs to be considered within the context of workstation designs and interventions.     

Effect of horizontal position of the computer keyboard on upper extremity posture and muscular load during computer work

The distance of the keyboard from the edge of a work surface has been associated with hand and arm pain; however, the variation in postural and muscular effects with the horizontal position have not been explicitly explored in previous studies. It was hypothesized that the wrist approaches more of a neutral posture as the keyboard distance from the edge of table increases. In a laboratory setting, 20 adults completed computer tasks using four workstation configurations: with the keyboard at the edge of the work surface (NEAR), 8 cm from the edge and 15 cm from the edge, the latter condition also with a pad that raised the work surface proximal to the keyboard (FWP). Electrogoniometers and an electromagnetic motion analysis system measured wrist and upper arm postures and surface electromyography measured muscle activity of two forearm and two shoulder muscles. Wrist ulnar deviation decreased by 50% (4°) as the keyboard position moved away from the user. Without a pad, wrist extension increased by 20% (4°) as the keyboard moved away but when the pad was added, wrist extension did not differ from that in the NEAR configuration. Median values of wrist extensor muscle activity decreased by 4% maximum voluntary contraction for the farthest position with a pad (FWP). The upper arm followed suit: flexion increased while abduction and internal rotation decreased as the keyboard was positioned further away from the edge of the table. In order to achieve neutral postures of the upper extremity, the keyboard position in the horizontal plane has an important role and needs to be considered within the context of workstation designs and interventions.     

A real-time strategy for dexterous manipulation: Fingertips motion planning,force sensing and grasp stability

This paper presents a global strategy for object manipulation with the fingertips with an anthropomorphic dexterous hand: the LMS Hand of the ROBIOSS team from PPRIME Institute in Poitiers (France). Fine manipulation with the fingertips requires to compute on one hand, finger motions able to produce the desired object motion and on the other hand, it is necessary to ensure object stability with a real time scheme for the fingertip force computation. In the literature, lot of works propose to solve the stability problem, but most of these works are grasp oriented; it means that the use of the proposed methods are not easy to implement for online computation while the grasped object is moving inside the hand. Also simple real time schemes and experimental results with full-actuated mechanical hands using three fingers were not proposed or are extremely rare. Thus we wish to propose in a same strategy, a robust and simple way to solve the fingertip path planning and the fingertip force computation. First, finger path planning is based on a geometric approach, and on a contact modelling between the grasped object and the finger. And as force sensing is required for force control, a new original approach based on neural networks and on the use of tendon-driven joints is also used to evaluate the normal force acting on the finger distal phalanx. And an efficient algorithm that computes fingertip forces involved is presented in the case of three dimensional object grasps. Based on previous works, those forces are computed by using a robust optimization scheme.In order to validate this strategy, different grasps and different manipulation tasks are presented and detailed with a simulation software, SMAR, developed by the PPRIME Institute. And finally experimental results with the real hand illustrate the efficiency of the whole approach.     

A fingerprint pointing device utilizing the deformation of the fingertip during the incipient slip

In this paper, a novel pointing device is proposed that utilizes the deformation of the fingertip. When a fingertip is pressed and slightly slid on a rigid plate, a partial slip, called an "incipient slip", occurs on the contact surface. While the deformation around the center of the contact area is small during the incipient slip, the boundary region moves to the sliding direction of the fingertip. The deformation changes depending on the sliding distance of the fingertip and the exerted force on the contact surface. The velocity of the pointer can be determined by the estimated distance and force based on the measurement of the deformation. In this study, the correlation between the sliding distance of the fingertip and the deformation and between the exerted force and the deformation are investigated. The degree of the deformation due to the sliding motion can be estimated based on the detected fingerprint center. The group delay spectrum tracking method is proposed for the detection of the fingerprint center. A prototype pointing device is developed to evaluate the operationality of the proposed device. Comparative experiments with conventional pointing devices are conducted. The validity of the proposed device is confirmed by the experiments.     

Artificial neural network dexterous robotics hand optimal control methodology: grasping and manipulation forces optimization

Optimal fingertip forces can always be computed through the well-known optimization algorithms. However, computation time has always remained a real-time constraint. This article presents an efficient scheme to compute optimal grasping and manipulation forces for dexterous robotics hands. This is expressed as a quadratic optimization problem, and an artificial neural network (ANN) is used to learn such quadratic optimization formulations. Computation has been based on a nonlinear model of fingertip contacts and slips. In achieving object grasping while in motion, the hand Jacobian is considered an important matrix to be computed, but it is also highly intensive for real-time computed applications. Consequently, we investigated an efficient approach using artificial neural networks to learn optimal grasping forces. An ANN is used here to learn the optimal contact forces relating hand joint-space torques to the resulting object force. The results have indicated that the ANN has reduced computation times to reasonable values owing to its ability to map nonlinear force relations. Furthermore, the results have revealed that ANNs are capable of learning highly nonlinear relations relating to distributed fingertip forces and joint torques. The technique developed has also proved to be suitable for off-line learning of computed fingertip forces, even with large training samples.     

Development of a 2-d.o.f. finger using load-sensitive continuously variable transmissions and ultrasonic motors

This paper presents a 2-d.o.f. finger using ultrasonic motors and load-sensitive continuously variable transmissions (CVTs) we proposed previously, which consist of a five-bar linkage and a torsion coil spring. The proposed CVT is remarkably simple and enables a finger joint to exert a large fingertip force and to move quickly. For the two joints of the 2-d.o.f. finger, we designed five-bar linkage CVTs which are more compact than the previous ones so that they can be installed on its base. Taking advantage of the geometric feature that ultrasonic motors are thin, we can arrange the drive systems for the two joints, including the two CVTs and the two ultrasonic motors, in a parallel configuration. The experimental results verify that the maximum fingertip force of the finger is as large as 30 N and the maximum angular velocity of its joints is more than 400°/s. These performance results would be impossible without the CVTs. We also verify that the finger can lift up a 1.5-kg load.     

一种单电机驱动多指多关节机械手的设计

为了使机械手灵巧、稳妥地抓取物体,设计了一种新型结构的单电机驱动4 指12 关节机械手爪．该手 爪由电机驱动一根十字连杆,其端部分别连接4 个手指的第1 动力连杆;每个手指有3 个指节,由2 个平行四边形 的指节结构确保手指末端做平移运动;每个手指的第2 动力连杆具有延伸滑槽,当第2 动力连杆运动时,经过特别 设计的滑槽在固定支点滑动,可使手指末端匀速运动．该新型的单电机驱动手爪设计方案实现了机械手控制简单、 抓握可靠的目的．     

Nonlinear viscoelastic contact and deformation of freeform virtual surfaces

This article is concerned with the haptic deformation display of discrete viscoelastic surfaces by means of a human fingertip. The virtual surface of a deformable quadrilateral mesh is interactively deformed by a Kelvin–Voigt soft fingertip model attached to the end-effector of a haptic interface device. In achieving this task, a nonlinear constitutive model approximating experimental data from literature is developed for determining the contact point deformations. By employing a new kernel weighting function, the deformations are distributed dependently on the discrete surface topology based on a nonlinear spring–damper net around the contact location. For illustration and evaluation of the proposed approach, a parallel robotic device with a constraint-based controller is adopted. The grip of the device is moved by the user to feel a sense of touch as the soft fingertip deforms the mesh surface of an ex vivo porcine liver tissue. Experimental data indicates stable realistic interactions thorough mechanical coupling between the soft fingertip and the deforming liver tissue. Dynamic response data of liver show rate-dependent hysteretic deformations and match closely with experimental indentation data from literature. A thorough analysis of mesh node count on the sample rate and the rendering quality is also presented.     

Ladder Climbing Method for the Limb Mechanism Robot ASTERISK

A ladder climbing method for the limb mechanism robot ASTERISK is proposed. This robot has six legs. The upper three legs hold on to the upper rung from both sides alternately, just like pinching it. The lower three legs hold on to the lower rung in the same way. Hence, the robot can take hold of the ladder stably. First, the robot releases the left upper and lower legs from the current rungs, and hangs them on the next rungs while supporting itself with the other four legs. Then, the mid two legs and the right two legs are moved to the next rungs in sequence. Finally, the robot lifts up its body using the six legs. Depending on the relative pose of the robot to the ladder, the robot automatically selects the legs that can support vertical and/or horizontal forces applied by the rungs. The robot then distributes its weight to the legs supporting the vertical force based on their force margins. The legs that cannot support forces are controlled to always touch the rungs slightly in order to pinch the rungs with the other legs. The advantages of the proposed gait and control method are verified by analysis of the leg workspace for generating the ladder climb gait, analysis of the range of force direction that the legs can support, analysis of the joint torques required for ladder climbing and an experiment on force distribution. Finally, the range of ladder pitch variation that ASTERISK can climb is clarified.     

视频虚拟键盘中的按键自定义问题研究

目前,电子数码产品的功能越来越强大,功能的复杂直接导致了操作的繁琐.为此,对视频虚拟键盘中的按键自定义问题进行了细致的研究,提出一种基于视频图像处理技术的用户自定义标示符方法,以求针对不同用户提供不同的操作方式.该方法利用电子数码设备附加的摄像设备,记录用户手指移动轨迹,由此识别出用户标识区域,并为该区域赋予相关信息的功能,即用户对于该区域的点击被识别为指定的按键操作,从而实现用户自定义虚拟键盘的功能.最后对该方法进行了实验验证与分析,证明该方法具有技术可行性,并在操作简单方便和成本控制方面有较好表现.