Min K. Chung

Upper body reach posture prediction for ergonomic evaluation models

Proper assessment of human reach posture is one of the essential functions for ergonomic workspace design and evaluation in computer-aided ergonomic evaluation models or any CAD system with a built-in man model. To predict reach posture, most existing models have been using heuristic methods, which provide only the range of feasible postures, not always ensuring the one that a person naturally takes. An analytic reach prediction algorithm was developed in this study by employing the inverse kinematics methods. Each upper limb is modelled as a four-link system, consisting of trunk, upper arm, lower arm, and hand, being regarded as a redundant manipulator with a total of eight degrees of freedom. Among several kinematic methods for solving human reach movement, the resolved motion method which is one of the redundant manipulator techniques in robotics was found to be effective. In this method, the joint range availability was used as a performance function to guarantee kinematic optimality and to simulate human reach closely. In addition, an approximate algorithm to generate the workspaces of human body was developed. Real reach postures taken from the subjects were analyzed by the motion analysis system and were statistically similar to those obtained from the prediction model.

Quantitative postural load assessment for whole body manual tasks based on perceived discomfort

Many Korean workers are exposed to repetitive manual tasks or prolonged poor working postures that are closely related to back pain or symptoms of musculoskeletal disorders. Workers engage in tasks that require not only handling of heavy materials, but also assuming prolonged or repetitive non-neutral work postures. Poor work postures that have been frequently observed in the workplaces of shipbuilding shops, manufacturing plants, automobile assembly lines and farms often require prolonged squatting, repetitive arm raising and wrist flexion and simultaneous trunk flexion and lateral bending. In most manufacturing industries, workers have to assume improper work postures repetitively, several hundreds of times per day depending on daily production rate. A series of psychophysical laboratory experiments were conducted to evaluate the postural load at various joints. A postural load assessment system was then developed based on a macro-postural classification scheme. The classification scheme was constructed based on perceived discomfort for various joint motions as well as previous research outcomes. On the basis of the perceived discomfort, postural stress levels for the postures at individual joints were also defined by a ratio scale to the standing neutral posture. Laboratory experiments simulating automobile assembly tasks were carried out to investigate the relationship between body-joint and whole-body discomfort. Results showed a linear relationship between the two types of discomfort, with the shoulder and low back postures being the dominant factor in determining the whole body postural stresses. The proposed method was implemented into a computer software program in order to automate the procedure of analysing postural load and to enhance usability and practical applicability.

Reach Posture Prediction of Upper Limb for Ergonomic Workspace Evaluation

Proper assessment of reach posture is one of the essential functions for ergonomic workspace evaluation in CAD systems with a built-in man-model. In this study, Each upper limb is modelled as a four-link system, consisting of trunk, upper arm, lower arm, and hand, being regarded as a redundant manipulator with a total of eight degrees of freedom. Inverse kinematics is introduced in this study to predict the trajectory of multi-link segmental movement. Among several kinematic methods for solving the multi-link system, the resolved motion method was found to be effective to solve this redundant manipulator model, and the joint range availability was used as a performance function in order to guarantee local optimality. Real reach postures taken from the subject were analyzed by Motion Analysis System and showed reasonable results when compared to those obtained from the model.

Development of an Object-oriented Anthropometric Database for an Ergonomic Man Model

An object-oriented anthropometric database was developed as a framework of integrating into an ergonomic interface model, data for workplace modelling, and ergonomic evaluation functions as well as basic anthropometric data required to construct a man model. In order to develop an ergonomic man model representing operators that interact with their working environments, not only anthropometric data but also efficient handling of such data and accurate representation of the workspace are needed as a prerequisite to proper ergonomic evaluation. In this research, these three sets of data with distinct characteristics were incorporated into a common integrated database needed for the manipulation of an ergonomic man model together with the generation of an anthropometric man itself. An object-oriented database scheme was used for designing the database to achieve flexibility and expandability, and to efficiently interface to any CAD system. UniSQL/X, an object-oriented database management system and the X-window system on a SPARC workstation were used for implementation. The ergonomic man model generated from the object-oriented database is found to possess great flexibility and performance compared with existing ergonomic interface models or ergonomic CAD systems.

Evaluation of lifting tasks frequently performed during fire brick manufacturing processes using NIOSH lifting equations

Abstract A fire brick manufacturing company with a high prevalence of low back injuries was selected for analysis of lifting tasks using the 1991 revised NIOSH lifting equations. We analyzed several manufacturing processes: forming, heating and packing processes involving frequent lifting and lowering in asymmetric postures. A questionnaire survey showed that weight of the load significantly influenced the incidence of back injuries and that workers who reported to have experienced back injuries were older than those who did not experience them. Composite Lifting Indices (CLI) based on the 1991 revised NIOSH lifting equations were calculated for 14 tasks of the forming process and five tasks of the heating/packing processes. Calculated CLIs for the tasks ranged from 0.86 to 8.8 (average 2.73) in the forming process and from 3.7 to 18.9 (average 11.12) in the heating/packing processes. The majority of the lifting tasks in this company exceeded the recommended weight limit (RWL). The results suggest that the tasks should be redesigned ergonomically to eliminate the risk factors that may cause low back injuries. Most of the jobs under study could be redesigned to lessen the biomechanical stress simply by making horizontal locations closer to a worker or by reducing the asymmetric angles. Relevance to industry During fire brick manufacturing processes, asymmetric lifting activities are frequently performed in Korea. It is crucial and beneficial to both management and labor to evaluate such tasks ergonomically based on the 1991 revised NOISH lifting equations for identifying risk factors that may cause musculoskeletal disorders.

Isoresponse time regions for the evaluation of visual search performance in ergonomic interface models.

Computer-aided ergonomic evaluation models often provide a limited function of visual performance, usually in the form of visibility tests at any given location. It is, however, of great importance to complete a visual task in a predetermined time successfully or to predict the time to complete the task, e.g., a task of high-level control such as aircraft flight operations. In this study, isoresponse time regions which have an effect on visual performance in real-life situations are presented as an effort to complement aforementioned shortcomings of ergonomic interface models. A multiple regression was used to provide equal response time regions, being asymmetrical in shape. In addition, the fuzzy linear regression (FLR) model was introduced to provide a fuzzy set from which a decision-maker might select appropriately. It provided similar fitted values with having the advantage of utilizing the interval of those fitted values over the conventional regression model. The results can be applied effectively to the design of an interface for diverse visual tasks in real situations.

Effects of user age and target-expansion methods on target-acquisition tasks using a mouse

Target expansion, i.e., the increase of target size according to cursor movement, can be a practical scheme to improve the usability of target-selection tasks using a mouse. This study examined the effects of different user age groups and target-expansion methods on target-acquisition tasks with grouped icons. Twenty-eight subjects performed acquisition tasks under eight experimental conditions: combinations of four expansion areas (no, one-icon, fish-eye, and group expansion) and two expansion techniques (occlusion and push). Older users took longer to acquire targets than younger users; however, they showed no significant difference in accuracy. Target expansion did not substantially improve performance speed compared to the static condition. However, the error rate was lowest when group area was expanded with the push technique, and both age groups were most satisfied with one-icon area expansion with the occlusion technique. We suggest alternative guidelines in designing target-expansion schemes.

Towards successful user interaction with systems: Focusing on user-derived gestures for smart home systems

Various studies that derived gesture commands from users have used the frequency ratio to select popular gestures among the users. However, the users select only one gesture from a limited number of gestures that they could imagine during an experiment, and thus, the selected gesture may not always be the best gesture. Therefore, two experiments including the same participants were conducted to identify whether the participants maintain their own gestures after observing other gestures. As a result, 66% of the top gestures were different between the two experiments. Thus, to verify the changed gestures between the two experiments, a third experiment including another set of participants was conducted, which showed that the selected gestures were similar to those from the second experiment. This finding implies that the method of using the frequency in the first step does not necessarily guarantee the popularity of the gestures.

Selection and Classification of the Usability Attributes for Evaluating Consumer Electronic Products

Although the concept of usability has been well defined in the software usability engineering area, it is not appropriate to apply the same concept directly to the consumer electronic products. A new concept of usability appropriate for evaluating consumer electronic products was suggested in this study. It is characterized by integrating both the performance and impression factors. Based on the concept developed, specific usability attributes were defined and classified. In addition, the usability measures along with appropriate measurement techniques were also developed and classified to evaluate the usability attributes in an efficient and systematic manner. The results of this study can be used to evaluate the usability of consumer electronic products.

Comparison of prediction models for the compression force on the lumbosacral disc.

The main objective of this research was to compare three representative methods of predicting the compressive forces on the lumbosacral disc: LP-based model, double LP-based model, and EMG-assisted model. Two subjects simulated lifting tasks that are frequently performed in the refractories industry of Korea, in which vertical and lateral distances, and weight of load were varied. To calculate the L5/S1 compressive forces, EMG signals from six trunk muscles were measured, and postural data and locations of load were recorded using the Motion Analysis System. The EMG-assisted model was shown to reflect well all three factors considered here, whereas the compressive forces from the two LP-based models were only significantly affected by weight of load. In addition, low lifting index (LI) values were observed for relatively high L5/S1 compressive forces from the EMG-assisted model, suggesting that the 1991 NIOSH lifting equations may not fully evaluate the risk of dynamic asymmetric lifting tasks.