Effects of progressive levels of industrial automation on force and repetitive movements of the wrist

The purpose of this research was to compare the repetition of wrist movements and force produced by workers when packing pencils in manual, semi-automated and automated industrial operations. The study was conducted in a multinational pencil company which had the three production systems operating simultaneously. Highly skilled workers were in a job rotation schedule between the systems. A portable electrogoniometer set was used for measuring the wrist movements. The software V.3.11 (Biometrics prototype design) was used to compute the number of repetitions of 5° or more motion of the wrist. Highly repetitive tasks were identified in all packaging operations involving the three different and progressive stages of production automation. The highest frequencies and most stereotyped movements were recorded in the semi-automated operations, followed by the manual and automated operations. The operations required force application between 9.1 and 12.3% of maximal voluntary contraction between three operations. These results were analysed using analysis of variance. The analysis showed significant differences in frequencies of wrist motion (p<0.05) between the production systems. However, force required by the three operations were not significantly different. The findings indicate that partial automation does not necessarily decrease or eliminate motions performed by human operators. Thus the goal of automation and its level must be carefully considerated prior to implementation.

Relevance to industry

The intensification of the industrial work seems to be influencing job contents, working movements and the rates of musculoskeletal disorders. The study of the relation between repetition and progressive levels of industrial automation may contribute to the understanding of this event.     

An optimal motion planning method for computer-assisted surgical training

This paper focuses on the development and validation of an optimal motion planning method for computer-assisted surgical training. The context of this work is the development of new-generation systems that combine artificial intelligence and computer vision techniques in order to adjust the learning process to specific needs of a trainee, while preventing a trainee from the memorization of particular task settings. The problem described in the paper is the generation of shortest, collision-free trajectories for laparoscopic instrument movements in the rigid block world used for hand–eye coordination tasks. Optimal trajectories are displayed on a monitor to provide continuous visual guidance for optimal navigation of instruments. The key result of the work is a framework for the transition from surgical training systems in which users are dependent on predefined task settings and lack guidance for optimal navigation of laparoscopic instruments, to the so called intelligent systems that can potentially deliver the utmost flexibility to the learning process. A preliminary empirical evaluation of the developed optimal motion planning method has demonstrated the increase of total scores measured by total time taken to complete the task, and the instrument movement economy ratio. Experimentation with different task settings and the technical enhancement of the visual guidance are subjects of future research.     

Off-road machine controls: investigating the risk of carpal tunnel syndrome

Occupationally induced hand and wrist repetitive strain injuries (RSI) such as carpal tunnel syndrome (CTS) are a growing problem in North America. The purpose of this investigation was to apply a modification of the wrist flexion/ extension models of Armstrong and Chaffin (1978, 1979) to determine if joystick controller use in off-road machines could contribute to the development of CTS. A construction equipment cab in the laboratory was instrumented to allow force, displacement and angle measurements from 10 operators while they completed an approximately 30-min joystick motion protocol. The investigation revealed that both the external fingertip and predicted internal wrist forces resulting from the use of these joysticks were very low, indicating that the CTS risk associated with this factor was slight. However, the results also indicated that, particularly for the 'forward' and 'left' right side motions and for all left side motions, force was exerted by other portions of the fingers and hand, thereby under-predicting the tendon tension and internal wrist forces. Wrist angles observed were highest for motions that moved the joysticks to the sides rather than front to back. Thus, the 'right' and 'left' motions for both hands posed a higher risk for CTS development. When the right hand moved into the 'right' position and the left hand moved into the 'left' position, the wrist went into extension in both cases. Results indicate that neither learning nor fatigue affected the results.     

Off-road machine controls: investigating the risk of carpal tunnel syndrome

Occupationally induced hand and wrist repetitive strain injuries (RSI) such as carpal tunnel syndrome (CTS) are a growing problem in North America. The purpose of this investigation was to apply a modification of the wrist flexion/extension models of Armstrong and Chaffin (1978, 1979) to determine if joystick controller use in oV-road machines could contribute to the development of CTS. A construction equipment cab in the laboratory was instrumented to allow force, displacement and angle measurements from 10 operators while they completed an ? 30-min joystick motion protocol. The investigation revealed that both the external fingertip and predicted internal wrist forces resulting from the use of these joysticks were very low, indicating that the CTS risk associated with this factor was slight. However, the results also indicated that, particularly for the ‘forward’ and ‘left’ right side motions and for all left side motions, force was exerted by other portions of the fingers and hand, thereby under-predicting the tendon tension and internal wrist forces. Wrist angles observed were highest for motions that moved the joysticks to the sides rather than front to back. Thus, the ‘right’ and ‘left’ motions for both hands posed a higher risk for CTS development. When the right hand moved into the ‘right’ position and the left hand moved into the ‘left’ position, the wrist went into extension in both cases. Results indicate that neither learning nor fatigue aVected the results.     

Maximum acceptable forces for repetitive wrist extension with a pinch grip

This study represents a continuation of a series of psychophysical studies on repetitive motions of the wrist conducted at the Liberty Mutual Research Center for Safety and Health. The purpose of the study was to quantify maximum acceptable forces for extension motions of the wrist performed with a pinch grip. Subjects grasped a handle with a pinch grip and moved it through a 1.57 rad (90°) extension wrist motion (similar to a light assembly operation). A psychophysical methodology was used in which the subject adjusted the resistance on the handle, and the experimenter manipulated or controlled all other variables. Twenty subjects performed the task at repetition rates of 15, 20 and 25 motions per minute. Subjects performed for 7 h per day, 5 days per week, for 4 weeks. The subjects were instructed to work as if they were on an incentive basis, getting paid for the amount of work they performed. Symptoms were recorded by the subjects during the last 5 min of each hour. The results are presented and compared with maximum acceptable forces for other types of wrist motion investigated in previous studies. Maximum acceptable force for wrist extension with a pinch grip is smaller than any of the other motions investigated so far.

Relevance to industry

Cumulative trauma disorders of the upper extremities continue to be a problem for industrial workers who perform repetitive tasks. Although a number of physical risk factors have been identified, there are very few data available for establishing acceptable levels of these risk factors. This study attempted to collect such data.     

Correlation between normal modes in the 20-200 cm-1 frequency range and localized torsion motions related to certain collective motions in proteins

In certain biologically relevant collective motions, such as protein domain motions and sub-domain motions, large amplitude movements are localized in one or a few flexible regions consisting of a small number of residues. This paper explores the possible use of normal mode analysis in probing localized vibrational torsion motions in these flexible regions that may be related to certain collective motions. The normal modes of 10 structures of five proteins in different conformation (TRP repressor, calmodulin, calbindin D(9k), HIV-1 protease and troponin C), known to have shear or hinge domain or sub-domain motion, respectively, are analyzed. Our study identifies, for each structure, unique normal modes in the 20-200 cm-1 frequency range, whose corresponding motions are primarily concentrated in the region where large amplitude torsion movements of a known domain or sub-domain motion occur. This suggests possible correlation between normal modes at 20-200 cm-1 frequency range and initial fluctuational motions leading to localized collective motions in proteins, and thus the potential application of normal mode analysis in facilitating the study of biologically important localized motions in biomolecules.     

Application of the differential transformation method to bifurcation and chaotic analysis of an AFM probe tip

The AFM (atomic force microscope) has become a popular and useful instrument for measuring intermolecular forces with atomic resolution, that can be applied in electronics, biological analysis, and studying materials, semiconductors etc. This paper conducts a systematic investigation into the bifurcation and chaotic behavior of the probe tip of an AFM using the differential transformation (DT) method. The validity of the analytical method is confirmed by comparing the DT solutions for the displacement and velocity of the probe tip at various values of the vibrational amplitude with those obtained using the Runge–Kutta (RK) method. The behavior of the probe tip is then characterized utilizing bifurcation diagrams, phase portraits, power spectra, Poincaré maps, and maximum Lyapunov exponent plots. The results indicate that the probe tip behavior is significantly dependent on the magnitude of the vibrational amplitude. Specifically, the tip motion changes first from subharmonic to chaotic motion, then from chaotic to multi-periodic motion, and finally from multi-periodic motion to subharmonic motion with windows of chaotic behavior as the non-dimensional vibrational amplitude is increased from 1.0 to 5.0.     

Psychophysical study of six hand movements.

This study represents a continuation of a series of psychophysical studies on repetitive motions of the wrist and hand conducted at the Liberty Mutual Research Center for Safety and Health. The purpose of the study was to quantify maximum acceptable forces of six motions performed on separate days but within the context of the same experiment. The six motions were wrist flexion with a power grip, wrist extension with a power grip, wrist flexion with a pinch grip, wrist extension with a pinch grip, ulnar deviation with a power grip, and a handgrip task (with a power grip). A psychophysical methodology was used in which the subject adjusted the resistance on the handle and the experimenter manipulated or controlled all other variables. Thirty-one subjects performed the six tasks at repetition rates of 15, 20 and 25 motions/min. Subjects performed the tasks for 7 h per day, 5 days per week, for 4 weeks. The subjects were instructed to work as if they were on an incentive basis, getting paid for the amount of work performed. Symptoms were recorded by the subjects during the last 5 min of each hour. The results revealed that maximum acceptable torques ranged from 11 to 19% of maximum isometric torque depending on frequency and motion. Maximum acceptable torques for the tasks that could be compared with previous studies showed the same patterns of response. However, the selected forces were substantially lower using the mixed protocol. A table of maximum acceptable torques and forces is presented for application in the field.     

Psychophysical study of six hand movements

This study represents a continuation of a series of psychophysical studies on repetitive motions of the wrist and hand conducted at the Liberty Mutual Research Center for Safety and Health. The purpose of the study was to quantify maximum acceptable forces of six motions performed on separate days but within the context of the same experiment. The six motions were wrist flexion with a power grip, wrist extension with a power grip, wrist flexion with a pinch grip, wrist extension with a pinch grip, ulnar deviation with a power grip, and a handgrip task (with a power grip). A psychophysical methodology was used in which the subject adjusted the resistance on the handle and the experimenter manipulated or controlled all other variables. Thirty-one subjects performed the six tasks at repetition rates of 15, 20 and 25 motions/min. Subjects performed the tasks for 7 h per day, 5 days per week, for 4 weeks. The subjects were instructed to work as if they were on an incentive basis, getting paid for the amount of work performed. Symptoms were recorded by the subjects during the last 5 min of each hour. The results revealed that maximum acceptable torques ranged from 11 to 19% of maximum isometric torque depending on frequency and motion. Maximum acceptable torques for the tasks that could be compared with previous studies showed the same patterns of response. However, the selected forces were substantially lower using the mixed protocol. A table of maximum acceptable torques and forces is presented for application in the field.     

Psychophysical studies of repetitive wrist flexion and extension

Abstract

The purpose of this experiment was to investigate the feasibility of using psychophysical methods to determine maximum acceptable forces for various types and frequencies of repetitive wrist motion. Four adjustable work stations were built to simulate repetitive wrist flexion with a power grip, wrist flexion with a pinch grip, and wrist extension with a power grip. The study consisted of two separate experiments. Subjects worked for two days per week during the first experiment, and five days per week during the second experiment. Fifteen women completed the first experiment, working seven hours each day, two days per week, for 20 days. Repetition rates of 2, 5, 10, 15 and 20 motions per minute were used with each flexion and extension task. Maximum acceptable torques were determined for the various motions, grips, and repetition rates without dramatic changes in wrist strength, tactile sensitivity, or number of symptoms. Fourteen different women completed the second experiment, performing a wrist flexion motion (power grip) fifteen times per minute, seven hours per day, five days per week, for 23 days. There were no significant differences in maximum acceptable torque from day to day. However, the average maximum acceptable torque for a five days per week exposure was 36-3% lower than for the same task performed two days per week. Assuming that maximum acceptable torques decrease 36-3% for other repetition rates and motions, tables of maximum acceptable force were developed for female wrist flexion (power grip), female wrist flexion (pinch grip), and female wrist extension (power grip).     

A minimally invasive surgery robotic assistant for HALS–SILS techniques

This paper is focused in the design and implementation of a robotic surgical motion controller. The proposed control scheme addresses the issues related to the application of a robot assistant in novel surgical scenario, which combines hand assisted laparoscopic surgery (HALS) with the single incision laparoscopic surgery (SILS) techniques. It is designed for collaborating with the surgeon in a natural way, by performing autonomous movements, in order to assist the surgeon during a surgical maneuver. In this way, it is implemented a hierarchical architecture which includes an upper auto-guide velocity planner connected to a low-level force feedback controller. The first one, based on a behavior approach, computes a collision free trajectory of the surgical instrument tip, held by the robot, for reaching a goal location inside of the abdominal cavity. On the other hand, the force feedback controller uses this trajectory for performing the instrument displacement by taking into account the holonomic movement constraints introduced by the fulcrum point. The aim of this controller is positioning the surgical instrument by minimizing the forces exerted over the abdominal wall due to the fulcrum location uncertainty. The overall system has been integrated in the control architecture of the surgical assistant CISOBOT, designed and developed at the University of Malaga. The whole architecture performance has been tested by means of in vitro trials.     

On the motion of oblique bevel geared robot wrists

In this article, we show that the principle of superposition can be applied for analyzing the spatial motion of a bevel geared three-roll wrist with nonzero oblique angle. The total motion of the wrist is decomposed into three independent component motions, which are easier to analyze. A superposition tabulation is then constructed to derive the relations among the three wrist joint variables and three coaxial actuation variables. The displacement solution for the wrist joint variables is found by using the zero reference position method.     

Comparison of abdominal‐wall stretching between basic and enhanced laparoscopic instruments

In laparoscopic surgery, access to the patient's abdomen is gained by using an instrument, consisting of a 300–400 mm long stem with attached tool, inserted through a cannula mounted in the patient's abdominal wall. Sliding of the stem relative to the cannula and rotation of the stem about its longitudinal axis are the only motions not constrained by the abdominal wall. These limited‐motion capabilities necessitate abdominal‐wall stretching for full‐spatial tool displacements. Abdominal‐wall stretching is potentially damaging to the patient and fatiguing to the surgeon. Minimization of stretching is shown to be possible by the addition of a single revolute joint to the basic instrument. The motions allowed by the stem and cannula, the additional joint, and the abdominal wall result in a kinematically redundant system; i.e., an infinite number of joint displacements exist to achieve a desired tool position and orientation (desired tool pose). An optimization technique is applied to determine the minimum stretching for desired tool poses. Elimination of stretching is shown to be possible by the addition of two revolute joints to the basic instrument. Displacement models for the basic and enhanced instruments are found using concepts of manipulator kinematics. Forward and inverse displacement solutions for the instruments are found. The inverse displacement solutions are used to compare the amount of stretching required by each instrument. The stretching is highest for the basic instrument. The instrument with one additional joint produces stretching that is always less than or equal to that of the basic instrument. The instrument with two additional joints eliminates the need for stretching. © 2001 John Wiley & Sons, Inc.     

Wrist postures in the general population of computer users during a computer task

Computer activities have commonly been linked to the development of musculoskeletal disorders (MSDs) in the upper limbs. However, to understand the effects computer use has on such disorders, it is necessary to identify and classify the movements involved in performing common computer tasks, one of these being typing. Motion analysis techniques were adopted to determine the movements involved during a typing task. This involved markers being placed on the knuckles, wrists and forearms of participants. This marker configuration allowed for the flexion, extension, radial deviation, ulnar deviation and a combination of these movements to be calculated. The results in one plane of motion show a mean extension|flexion and radial|ulnar deviation of 18.825°?±?10.013° and 5.228°?±?11.703° respectively. The most common position in two planes of motion was 20° extension with a simultaneous 20° ulnar deviation (10.72%). The results depict an alternative method of categorizing wrist positions in two planes during computer use. Coincident wrist postures should be addressed as opposed to motion in a single plane as these postures may result in different ergonomic risk factors developing.     

Reconstructing whole-body motions with wrist trajectories

Reconstructing whole-body motions using only a low-dimensional input reduces the cost of and efforts for performance capture significantly, and yet remains a challenging problem. We introduce a novel technique that synthesizes whole-body motion using the two wrist trajectories. Given the wrist trajectories, we first determine the optimal ankle trajectories from a large number of candidate ankle paths obtained from example poses in the motion database. The optimal trajectory is efficiently achieved by solving for the shortest path problem in a directed acyclic graph. Next, we use both the wrist and ankle trajectories as the low-dimensional control signals to achieve the whole-body pose at each time step. We show that our method can reconstruct various whole-body motions that can be recognized by arm motions, such as walking, stepping, and in-place upper-body motions. Comparisons with ground truth motions and with other methods are provided.     

Evaluation of upper-limb function by the sensor pegboard test method

Man moves his hands and arms to create things. These movements may be constructed as activities to change the environment favourably. Such movements result from co-ordinated control of the musculoskeletal system, by the hierarchical central nervous system. Man develops his working ability through learning, evaluation of the co-ordinated working ability of the highly advanced motor and sensory central nervous systems in addition to the ability to conduct a series of simple movements may produce valuable results which could be helpful in evaluating finger working ability.

The sensor pegboard test method was developed in this study. The upper-limb motions of the subjects as they perform various specified tasks are measured and evaluated at the micromotion level (micromotion is defined here as the smallest motion element that can be distinguished with the sensor pegboard). This method can produce immediate results, which are not obtainable by conventional time and motion study methods, and can evaluate many aspects of the capability of the upper-limb of workers. Using this method, the change in the upper-limb capability as a result of ageing was quantitatively determined, and its overall picture was clarified.     

Strength and range of motion of females with carpal tunnel syndrome

An experimental study was conducted to evaluate the grip and fingertip pinch strength, and range of motion of females with carpal tunnel syndrome (CTS). The range of motion of the wrist was measured in the sagittal, frontal, and transverse planes. Strength and range of motion measurements were also conducted on a control group. Results indicate that some strength and range of motion measures of the females with CTS were significantly different from that of the control group. Also, measurements in different planes caused significant differences in some range of motions of the wrist for both the CTS and the control groups.     

A sensor-aided self coaching model for uncocking improvement in golf swing

This paper describes an autonomous kinematic analysis platform for wrist angle measurement that is capable of evaluating a user’s uncocking motion in his or her golf swing and providing instructional multimodal feedback to improve his or her skills. This uncocking motion, which is a characteristic movement of the wrist during the golf swing, is an important factor in achieving accurate ball hitting and long driving distances, but is difficult to measure. In order to efficiently compute the wrist angle for uncocking evaluation, we present a sensor-based intelligent Inertial Measurement Unit (IMU) agent that collects three-dimensional orientation data during the golf swing from two IMU sensors placed on the forearm and on the golf club. It accurately analyzes changes in wrist angle to detect uncocking throughout the sequence of golf swing motions. In this paper, we first introduce the design considerations based on the concept of the uncocking motion and explain the system architecture with the sensors used for quantitative measurement and qualitative feedback generation. Then, we illustrate the detailed algorithms for wrist angle computation, golf swing motion segmentation based on key pose detection, and uncocking evaluation. A multimodal feedback-based user interface for our system is also presented. Experimental results show that the proposed system has the ability to accurately calculate the wrist angle in real time and also that it can be applied to a practical self-coaching system to improve the uncocking motion.     

Surface exploration using laparoscopic surgical instruments: the perception of surface roughness

During laparoscopic surgery video images are used to guide the movements of the hand and instruments, and objects in the operating field often obscure these images. Thus, surgeons often rely heavily on tactile information (sense of touch) to help guide their movements. It is important to understand how tactile perception is affected when using laparoscopic instruments, since many surgical judgements are based on how a tissue 'feels' to the surgeon, particularly in situations where visual inputs are degraded. Twelve na?ve participants used either their index finger or a laparoscopic instrument to explore sandpaper surfaces of various grits (60, 100, 150 and 220). These movements were generated with either vision or no vision. Participants were asked to estimate the roughness of the surfaces they explored. The normal and tangential forces of either the finger or instrument on the sandpaper surfaces were measured. Results showed that participants were able to judge the roughness of the sandpaper surfaces when using both the finger and the instrument. However, post hoc comparisons showed that perceptual judgements of surface texture were altered in the no vision condition compared to the vision condition. This was also the case when using the instrument, compared to the judgements provided when exploring with the finger. This highlights the importance of the completeness of the video images during laparoscopic surgery. More normal and tangential force was used when exploring the surfaces with the finger as opposed to the instrument. This was probably an attempt to increase the contact area of the fingertip to maximize tactile input. With the instrument, texture was probably sensed through vibrations of the instrument in the hand. Applications of the findings lie in the field of laparoscopic surgery simulation techniques and tactile perception.