Evaluation of a dynamic armrest for hydraulic-actuation controller use

The efficacy of a newly designed dynamic armrest was evaluated during joystick operation of a typical North American hydraulic-actuation joystick. The dynamic design was evaluated against a stationary armrest condition as well as no armrest condition. Electromyography (EMG) and subjective measurements were used to make the evaluation. The dynamic armrest, which mimics the natural pendulation of a joystick operator's arm in the forward and backward directions, was shown to significantly decrease the muscular activation in the upper trapezius, posterior deltoid, and anterior deltoid (p ≤ 0.01) over a stationary armrest. A questionnaire revealed that subjects significantly (p = 0.01) preferred the dynamic armrest design over either a standard armrest or no armrest with 17 of 21 operators preferring the dynamic armrest. Ratings from the questionnaire indicated that subjects felt that the dynamic armrest required less effort, was more comfortable, and was more effective than either of the other two armrest conditions.     

Trunk posture: reliability, accuracy, and risk estimates for low back pain from a video based assessment method

It has been recently reported that both dynamic movement characteristics, as well as the duration of postures adopted during work, are important in the development of low back pain (LBP). This paper presents a video-based posture assessment method capable of measuring trunk angles and angular velocities in industrial workplaces. The inter-observer reliability, system accuracy, and the relationship of the measured exposures to the reporting of low back pain are reported. The video analysis workstation consisted of a desktop computer equipped with digital video capture and playback technology, a VCR, and a computer game type joystick. The operator could then use a joystick to track trunk flexion and lateral bending during computer-controlled video playback. The joystick buttons were used for binary input of twisting. The inter-observer reliability for peak flexion and percentage of time spent in posture category variables were excellent (ICC>0.8). Lower reliability levels were observed for peak and average velocity and movement related variables. The video analysis system time series data showed very high correlation to the criterion optoelectronic imaging system (r=0.92). Root mean square errors averaged 5.8° for the amplitude probability distribution function data. Trunk flexion variables including peak level, peak velocity, average velocity indicators, and percent time in flexion category indicators all showed significant differences between cases and controls in the epidemiological study. A model consisting of the measures peak trunk flexion, percent time in lateral bend and average lateral bending velocity emerged after multivariable analysis for relationship to low back pain.

Relevance to industry

Risk of injury for the low back is multifactorial. The trunk position and movement velocity are emerging as important parameters. This analysis confirms the importance of these factors and demonstrates the utility of a video-based method to measure them in industrial settings.     

Vision for Performance in Virtual Environments: The Role of Feedback Timing

This work explores how people use visual feedback when performing simple reach-to-grasp movements in a tabletop virtual environment. In particular we investigated whether visual feedback is required for the entire reach or whether minimal feedback can be effectively used. Twelve participants performed reach-to-grasp movements toward targets at two locations. Visual feedback about the index finger and thumb was provided in four conditions: vision available throughout the movement, vision available up to peak wrist velocity, vision available until movement initiation, or vision absent throughout the movement. It was hypothesized that vision available until movement onset would be an advantage over a no vision situation yet not attain the performance observed when vision was available up to peak velocity. Results indicated that movement time was longest in the no vision condition but similar for the three conditions where vision was available. However, deceleration time and peak aperture measures suggest grasping is more difficult when vision is not available for at least the first third of the movement. These results suggest that designers of virtual environments can manipulate the availability of visual feedback of one's hand without compromising interactivity. This may be applied, for example, when detailed rendering of other aspects of the environmental layout is more important, when motion lag is a problem or when hand/object concealment is an issue.     

Isokinetic strength characteristics in wrist flexion and extension

A laboratory experiment was conducted to measure strength characteristics in dynamic (isokinetic) wrist flexion and extension. Twenty four college-age males exerted their maximum torque in both concentric flexion and extension at 60, 120, and 180°/s of angular velocity through a ±60° range of deviation from wrist neutral. Results show that velocity and motion direction significantly effected both peak torque as well as the postural displacement of peak torque. The value of peak torque decreased with an increase in velocity and the wrist angle at peak torque generally moved to a more deviated, flexed posture (from neutral) with increasing velocity as well. Peak torque for all velocity and motion-type conditions tested occurred in a flexed posture relative to neutral. It is anticipated that these results may be of use as biomechanically based considerations in the evaluation and design of upper extremity tasks involving wrist flexion/extension as well as to perhaps give insight into functional characteristics of the wrist. Finally, regression equations were developed to aid in the prediction of peak torque based upon task, individual and/or population parameters.

Relevance to industry

Results from this study should enhance the overall understanding of wrist functioning. Specifically, motion type, velocity of movement and wrist posture are important ergonomic design considerations. These results can also be used to modify existing biomechanical models that do not consider wrist variables.     

A force reflected exoskeleton-type masterarm for human-robot interaction

Two human-robot interactions, including a haptic interaction and a teleoperated interaction, are explored with a new exoskeleton-type masterarm, in which the electric brakes with the torque sensor beams are used for force reflection. In the haptic interaction with virtual environment, the masterarm is used as a haptic device and tested to examine how the resistant torque of the electric brake for the force reflection is implemented in contact regime prior to conducting the teleoperated interaction. Two types of virtual environments, a rigid wall with high stiffness (hard contact with 10 [KN/m]) and a soft wall with low stiffness (soft contact with 0.1 [N/m]), are integrated with the masterarm for the haptic interaction. In hard contact, large force is fed back to the human operator, and makes the human operator hardly move. The electric brake with the torque sensor beam can detect the torque and its direction so that it allows free motion as well as contact motion by releasing or holding the movement of the operator. The experimental results show how the electric brake is switched from contact to free regime to allow the operator to move freely, especially when the operator intends to move toward the free regime in contact. In soft contact, the force applied to the human operator can be increased or decreased proportionally to the torque amount sensed by the torque sensor beam, thus the operator can feel the contact force proportional to the amount of the deformation during the contact. Finally, the masterarm is integrated with the humanoid robot, CENTAUR developed at Korea Institute of Science and Technology to conduct a pick-and-place task through the teleoperated interaction. It is examined that the CENTAUR as a slave robot can follow the movement of the operator.     

Dynamic characteristic analysis of TBM tunnelling in mixed-face conditions

In this paper, by taking into account the periodically varying mesh stiffness in multiple pinions transmission and the speed–torque characteristics of variable frequency motor drives, the dynamic model for the revolving system of tunnel boring machine (TBM) has been established. Based on the soft ground/hard rock assumption of mixed-face conditions and the analysis of cutting force on each disc cutter and each drag bit, the time-varying excavation torque on the TBM cutterhead in mixed-face tunnelling is obtained. The dynamic excavation torque and cutterhead rotation speed are discussed and compared for TBM tunnelling in several typical mixed-face conditions, which are characterized by the area percentage of soft ground on the excavation face and the uniaxial compressive strength (UCS) of rock. The results show that the excavation torque may run up to a critical value and fluctuate greatly in extremely adverse excavation environments, which may lead to an unexpected TBM stoppage and even a catastrophic failure of the drive motor. To decrease the penetration per revolution in time through applying a lower advance velocity and a higher cutterhead revolution will significantly reduce the excavation torque and effectively avoid such situations.     

An optimal control model of a neuromuscular system in human arm movements and its control characteristics

The joint torque which sets human limbs into motion is generated by a separate group of muscles provided for each joint. As the activation of each muscle is determined by a neural input, a neuromuscular system controlling all muscles has to be considered in order to understand human movements. In this study, an optimal control model of a neuromuscular system is investigated, and its control characteristics are examined. First, the dynamic and mechanical properties of a muscle are examined, and a neuromuscular system is formulated mathematically. Second, a performance criterion for the optimal control model is defined in order to characterize the dynamic behavior of the neuromuscular system, and a mathematical procedure for producing optimal trajectories is represented. Third, optimal trajectories in human arm movements are produced under various conditions of movement, and these trajectories are compared with experimentally observed ones. It is then verified that the optimal trajectories demonstrate human arm movements well. Finally, the behavior of individual muscles in various movements is examined quantitatively by means of simulation results, and the control characteristics of the human neuromuscular system are investigated. This work was presented in part at the Sixth International Symposium on Artificial Life and Robotics, Tokyo, January 15–17, 2001.     

Torque reaction in angled nutrunners

In the process of tightening a joint, the angled nutrunner acts on the operator with a torque reaction in the final stages of the tightening sequence. In the following series of experiments, the torque reaction of a machine acting on various joints is studied. A distinctive feature of the torque reaction is that the handle of the angled nutrunner causes a rapid displacement. The amplitude and time aspect of this displacement depend on the stiffness of the joint (whether it is hard or soft), and the movement of the handle depends on how the operator is holding it. How the operator responds to the torque reaction depends upon, among other things, the displacement amplitude as well as the torque level of the machine. Because of this, the displacement amplitude can be used as a measure of the operator's discomfort.     

Optimal design of fluid dynamic bearings to develop a robust disk-spindle system in a hard disk drive utilizing modal analysis

This research proposes an optimal design methodology for fluid dynamic bearings (FDBs) in a hard disk drive to improve the dynamic performance of the disk-spindle system. We solved equations of motion for the rigid rotor supported by FDBs with five degrees of freedom. Five modal damping ratios were selected as multi-objective functions. The constraint equations were the friction torque of the FDBs and the stiffness and damping coefficients related to under-damped vibration modes. Ten major design variables of the FDBs were chosen for this optimization problem. The steady-state whirl radius and the shock response at half-speed whirl of the rotating rigid spindle-bearing system were evaluated as RRO and NRRO, respectively. The RRO and NRRO of the optimal design were compared with those of the conventional design. Our results show that the proposed method effectively reduces RRO and NRRO.     

Experimental study on torque control using Harmonic Drive built-in torque sensors

We have proposed the practical torque sensor which utilizes elasticity of harmonic drives. The sensing technique provides joint torque sensing without reducing stiffness of the robot and changing the mechanical structure of the joints. In this article, we examine experimentally the characteristics of joint torque control using this torque sensor. Three types of torque control laws are implemented with a one-link arm to find a control method which provides excellent friction reduction and dynamic response in joint torque. The experimental results of joint torque control show that the torque sensor is very useful to compensate the nonlinear friction. Furthermore the torque control is effective to improve the accuracy of the motion control at low velocity and to suppress the vibration caused by the joint flexibility. © 1998 John Wiley & Sons, Inc.     

Verification of models for ballistic movement time and endpoint variability

A hand control movement is composed of several ballistic movements. The time required in performing a ballistic movement and its endpoint variability are two important properties in developing movement models. The purpose of this study was to test potential models for predicting these two properties. Twelve participants conducted ballistic movements of specific amplitudes using a drawing tablet. The measured data of movement time and endpoint variability were then used to verify the models. This study was successful with Hoffmann and Gan's movement time model (Hoffmann, 1981; Gan and Hoffmann 1988) predicting more than 90.7% data variance for 84 individual measurements. A new theoretically developed ballistic movement variability model, proved to be better than Howarth, Beggs, and Bowden's (1971) model, predicting on average 84.8% of stopping-variable error and 88.3% of aiming-variable errors. These two validated models will help build solid theoretical movement models and evaluate input devices.

Practitioner summary: This article provides better models for predicting end accuracy and movement time of ballistic movements that are desirable in rapid aiming tasks, such as keying in numbers on a smart phone. The models allow better design of aiming tasks, for example button sizes on mobile phones for different user populations.     

Effects of load and speed on lumbar vertebral kinematics during lifting motions

This experimental study investigated the effects of load magnitude and movement speed on lumbar vertebral kinematics during lifting task performance. Ten participants performed sagittally symmetric lifting movements with systematically varied load using either a normal or a faster-than-normal speed. Skin-surface markers were strategically placed over the participants' spinous processes and other landmarks representing major body joints and were recorded during the movements by a motion capture system. The center of rotation (COR) locations and segmental movement profiles for lumbar vertebrae L2 to L5 were derived and analyzed. Results suggested that (a) the COR locations and vertebral angular displacement were not significantly affected by the speed or load variation; (b) a faster speed tended to shorten the time to complete the acceleration for all the lumbar vertebrae considered; and (c) the load increase incurred a tendency for the L5 to complete the primary displacement in a briefer time while enduring greater peak acceleration and velocity. The findings lead to a better understanding of the relation between lifting dynamics and spinal motion. Potential applications of this research include the development of more accurate biomechanical models and software tools for depicting spinal motions and quantifying low-back stress.     

基于Linux的游戏杆控制的实现方法

游戏杆作为一种输入设备,往往被人们用来玩电脑游戏。但是,在科学研究领域,游戏杆可以被用作人机交互的接口。一般来说,游戏杆具有三个自由度,因此可以用它来操 控被控对象在三雏空间中的运动。所以,如果实现对游戏杆的控制,那么就可以用游戏杆来控制被控对象的运动。本文主要介绍了两种游戏杆控制的实现方法。     

Computerized control system and interface for flexible micromanipulator control

Micro- and nanomanipulators are essential for a broad range of applications requiring precise micro- and nanoscopic spatial control such as those in micromanufacturing and single cell analysis. These manipulators are often manually controlled using an attached joystick and can be difficult for operators to use efficiently. This paper describes a system developed in MATLAB to control a well-known, commercial micromanipulator in a user friendly and versatile manner through a graphical user interface (GUI). The control system and interface allows several types of flexible movement controls in three-axis, Cartesian space, including single movements, multiple queued movements, and mouse-following continuous movements. The system uses image processing for closed loop feedback to ensure precise and accurate control over the movement of the manipulator’s end effector. The system can be used on any electronic device capable of running the free MATLAB Runtime Environment (MRE) and the system is extensible to simultaneously control other instruments capable of serial communication.     

CONTROLLER DESIGN: INTERACTIONS OF CONTROLLING LIMBS,TIME-LAGS AND GAINS IN POSITIONAL AND VELOCITY SYSTEMS

The effectiveness of the thumb, hand and forearm were compared in operating joystick controls of both a positional servo-mechanism and a velocity system. The angular displacement sensitivity (gain) and exponential time constant (lag) of the systems were systematically varied. The operator's task was to manipulate a joystick in order to move a display marker a constant distance to a specified degree of accuracy. The times taken to do this were used to compare performances in the different control conditions.

Two experiments were conducted. In the first, in which a positional system was used, optimal angular gain changed through a range- from 0-15 to 0 50 as lags increased from 0 to 2 sec. Curve-fitting to the results enabled formulae to be derived to estimate the times required to complete accurate movements if control gain and lag arc known, and to determine the optimum control gain if the lag is known.

In the second experiment, in which a velocity system was used, optimal angular gain was about 1-3 radians/sec of display movement to 1 radian of joystick movement in all conditions of control and for all controlling limbs.     

Passive joint stiffness in the hip and knee increases the energy efficiency of leg swinging

In the field of minimally-actuated robots, energy efficiency and stability are two of the fundamental criteria that can increase autonomy and improve task-performance capabilities. In this paper, we demonstrate that the energetic cost of leg swinging in dynamic robots can be reduced without significantly affecting stability by emulating the physiological use of passive joint stiffness, and we suggest that similar efficiency improvements could be realized in dynamic walking robots. Our experimental model consists of a two-segment dynamically swinging robotic leg with hip and knee joints. Closed-loop control is provided to the hip using neurally inspired, nonlinear oscillators that do not override the leg’s natural dynamics. We examined both linear and nonlinear, physiologically based stiffness profiles at the hip and knee and a hyperextension-preventing hard stop at the knee. Our results indicate that passive joint stiffness applied at one or both joints can improve the energy efficiency of leg swinging by reducing the actuator work required to counter gravitational torque and by promoting kinetic energy transfer between the shank and thigh. Energetic cost reductions (relative to the no-stiffness case) of approximately 25% can be achieved using hip stiffness, provided that the hip actuation bias angle is not coincident with gravity, and cost reductions of approximately 66% can be achieved using knee stiffness. We also found that constant stiffness combined with a limit on knee hyperextension produces comparable results to the physiological stiffness model without requiring complex implementation techniques. Although this study focused on the task of leg swinging, our results suggest that passive-stiffness properties could also increase the energy efficiency of walking by reducing the cost of forward leg swing by up to 66%. We also expect that the energetic cost of walking could be further reduced by adding stiffness to the ankle to assist in the propulsive portion of stance phase.     

Different predictions by the minimum variance and minimum torque-change models on the skewness of movement velocity profiles

We investigated the differences between two well-known optimization principles for understanding movement planning: the minimum variance (MV) model of Harris and Wolpert (1998) and the minimum torque change (MTC) model of Uno, Kawato, and Suzuki (1989). Both models accurately describe the properties of human reaching movements in ordinary situations (e.g., nearly straight paths and bell-shaped velocity profiles). However, we found that the two models can make very different predictions when external forces are applied or when the movement duration is increased. We considered a second-order linear system for the motor plant that has been used previously to simulate eye movements and single-joint arm movements and were able to derive analytical solutions based on the MV and MTC assumptions. With the linear plant, the MTC model predicts that the movement velocity profile should always be symmetrical, independent of the external forces and movement duration. In contrast, the MV model strongly depends on the movement duration and the system's degree of stability; the latter in turn depends on the total forces. The MV model thus predicts a skewed velocity profile under many circumstances. For example, it predicts that the peak location should be skewed toward the end of the movement when the movement duration is increased in the absence of any elastic force. It also predicts that with appropriate viscous and elastic forces applied to increase system stability, the velocity profile should be skewed toward the beginning of the movement. The velocity profiles predicted by the MV model can even show oscillations when the plant becomes highly oscillatory. Our analytical and simulation results suggest specific experiments for testing the validity of the two models.