Joonho Chang

Determination of Optimal Grip Span between a Bicycle Handlebar and a Brake Lever by Using a Two-Dimensional Biomechanical Hand Model

In this study, optimal grip span between a bicycle handlebar and a brake lever was determined by a two- dimensional biomechanical hand model. A three-step process was applied: (1) develop a two- dimensional biomechanical hand model, (2) determine input data for hand model simulation, and (3) conduct mathematical simulation. In the first step, in order to estimate tendon forces, joint constraint forces and total gripping support force at the metacarpal, a mathematical static hand model was developed based upon the hand anatomy and static equilibrium conditions. In the second step, US 50%ile hand length was selected as target population from the 1988 US Army data, and grip postures for five participants(average hand length = 18.2 cm and SD = 0.8) were measured to get joint angles(θ 1, θ 2, and θ 3) which are required for the hand model simulation, by using a dynamometer having adjustable grip spans such as 4, 5.2, 6.4, 7.6, and 8.8 cm. In the third and final step, mathematical simulation was conducted to determine an optimal grip span. Consequently, on given external load(grip force), 100 N, both total tendon forces and total gripping support force of the metacarpal showed monotonically increasing trend while grip span broadening from 4 to 8.8 cm. Also, minimum of both total tendon force and total gripping support force at the metacarpal was achieved at 4 cm grip span.

Cost-effectiveness Analysis for Clothing Design Improvement Using Ergonomic Methods: Evaluation of Flame-proof Clothing and Design Optimization

Ergonomic techniques have been required to analyze the effectiveness of functional clothing design improvement in a systematic and analytic manner. The goals of the present study are to: (1) comprehensively and analytically examine the effectiveness of clothing improvement by using the relationship analysis between clothing design components (D) and ergonomic evaluation measures (E) and (2) prove the usefulness of cost-effectiveness analysis for clothing design optimization. The cost effectiveness analysis is comprised of the preliminary evaluation based on expertise and the in-depth evaluation where the D-E relationship analysis is applied. As a result of the cost effectiveness analysis applied to flame-proof clothing, an optimal design was identified by analyzing costs and qualitative/quantitative effects. In the preliminary evaluation, the expected effectiveness of each design alternative on wear efficiency and wear comfort was estimated. In the in-depth evaluation, however, the effectiveness of each design alternative was analyzed by quantitative evaluation in a wearing test using a questionnaire prepared based on the D-E relationship analysis. It was concluded that the D-E relationship analysis and the cost-effectiveness analysis are useful for comprehensive evaluation and optimization of functional clothing design.

Development and Application of an Ergonomic Evaluation System for Functional Clothing: Evaluation of Flame-proof Clothing and Identification of Design Problems

Ergonomic methods have been effectively applied to design and evaluation of functional clothing. The goals of the present study are to: (1) develop an ergonomic evaluation system for the systematic analysis of functional clothing and (2) examine the usefulness of the proposed evaluation system by applying to flame-proof clothing. Based on the survey of literature and the brainstorming of experts in clothing design and ergonomics, factors considered for clothing evaluation were selected, classified, and complemented, resulting in an ergonomic clothing evaluation system consisting of four factor categories (clothing construction, user, work and environment, and user response). Using the proposed system, a field survey and a laboratory experiment were conducted for flame-proof clothing to identify its design problems. The field survey to workers found a comprehensive set of problems on the flame-proof clothing design in terms of pattern, textile, and color. The laboratory experiment identified additional design problems using a questionnaire that was developed based on an analysis on the relationship between clothing design components and ergonomic evaluation measures. The present study showed the ergonomic evaluation system and the relationship analysis of clothing design components and ergonomic evaluation measures are of use to identify design problems of functional clothing in a comprehensive and analytic manner.

Development of a usability evaluation method using natural product-use motion

The present study developed and tested a new usability evaluation method which considers natural product-use motions. The proposed method measures both natural product-use motions (NMs) and actual product-use motions (AMs) for a product using an optical motion capture system and examines the usability of the product based on motion similarity (MS; %) between NMs and AMs. The proposed method was applied to a usability test of four vacuum cleaners (A, B, C, and D) with 15 participants and their MSs were compared with EMG measurements and subjective discomfort ratings. Cleaners A (44.6%) and C (44.2%) showed higher MSs than cleaners B (42.9%) and D (41.7%); the MSs mostly corresponded to the EMG measurements, which could indicate that AMs deviated from NMs may increase muscular efforts. However, the MSs were slightly different from the corresponding discomfort ratings. The proposed method demonstrated its usefulness in usability testing, but further research is needed with various products to generalize its effectiveness.

Development of the Two-Dimensional Biomechanical Hand Model for a Guitar Player

In this study, a two-dimensional biomechanical hand model predicting tendon loads in the fingers during guitar playing was developed. To estimate tendon forces, joint reaction forces, and force reactions against a given fingertip pressure (external force), a static hand model was developed based on the hand anatomy and static equilibrium conditions. Model inputs included 1) adopted existing anthropometry data, 2) fingertip pressures measured while playing the guitar, and 3) measured joint angles on the fingers. The hand model evaluated four chords: C, E, G7, and Am. G7 required the highest internal tendon force (41.0N), and Am (32.8N), E (30.3N), and C (26.6N) followed it. The index finger was mainly recruited for all four chords while the ring finger showed the worst efficiency, using the external force to internal tendon force ratio. Finally, the quick-and-dirty test showed the simulation result had strong correlation (R2= 65.1 %) with EMG result (C: 22.9%MVC, E: 22.1%, G7: 34.8%, and Am: 34.3%) on the FDP muscle, a main flexor of the finger.

Determination of Bicycle Handle Diameters considering Hand Anthropometric Data and User Satisfaction

Ergonomic product design considering both anthropometric variability and user preference is required for harmonizing the target users and products. In this study, bicycle handle diameters for three size categories were determined by considering anthropometric variability and preference. To design the bicycle handles, a four-step process was applied: (1) define anthropometric data, (2) develop size chart, (3) define a design equation, and (4) determine design values. In the first step, the 1988 US Army data was chosen as anthropometric data for the design target population. In the second step, to develop a size chart of bicycle handle, hand length and circumference were selected as key dimensions by principal component analysis on six representative hand dimensions. Next, a size chart of three categories (small: 175.5 mm, medium: 186.7 mm, and large: 196.2 mm) were derived by K-means clustering analysis for hand length and circumference. In the third step, the design equation accounting geometrical relationship between the sizes of two key dimensions and diameters of bicycle handle was adopted from a relevant existing research. In the last step, design values (40.9 mm, 43.5mm, and 45.7 mm) for each size category were calculated by inputting the sizes of the key dimensions to the design equation. To evaluate user satisfaction level of the bicycle handles, a user testing of three handle prototypes was conducted for 17 participants with various hand sizes. The test results showed that satisfaction scores for each hand group were significantly higher at the corresponding size category.

Design and Assessment of Ergonomics of Hand-Powered Pruning Shears Based On Gender-Specific Operating Strategy

The present study investigated the biomechanical and physiological loads when working with pruning shears of varying design. The objective of this study was to find usability issues on conventional pruning shears and integrate ergonomics into the design process to improve users’ safety and health as well as performance. Effects of pruning shear design, gender, and hand size on muscle activities, grip force distribution, wrist deviations, and gender-specific operating strategy were studied in six male and six female participants while cutting wooden dowels with pruning shears. Three types of pruning shears were used, one conventional and two modified, either with a rubber grip-padded, or with a thumb grip attached to the upper handle. The results showed that (1) the two redesigned pruning shears minimized pressures on some critical hand regions and improved muscle activities, grip force distribution, and wrist deviations and (2) a large degree of wrist extension, greater use of the extensor digitorum (ED) muscle, and excessive squeezing force were women’s operating strategies to overcome their biomechanical disadvantages due to small hand size and less muscle strength during pruning work. Based on this finding, it was concluded that conventional pruning shears have potential design problems related to musculoskeletal disorders (MSDs), and therefore ergonomic interventions should focus more on variations in user anthropometry and physiological responses.

Evaluation of Driving Posture Prediction in Digital Human Simulation Using RAMSIS

For proper ergonomic evaluation using a digital human model simulation (DHMS) system such as RAMSIS®, postures of a humanoid for designated tasks need to be predicted accurately. The present study (1) evaluated the accuracy of driving postures of humanoids predicted by RAMSIS, (2) proposed methods to improve its accuracy, and (3) examined the effectiveness of the proposed methods. Driving postures of 12 participants in a seating buck were measured by a motion capture system and compared with those predicted by RAMSIS. Significant discrepancies (8.7° to 74.9°) between predicted and measured postures were observed for different body parts and driving tasks. Constraint addition and user-defined posture methods were proposed and their performance was assessed in terms of prediction accuracy. Of the two proposed methods, the user-defined posture method was found preferred by improving the accuracy of posture prediction by 11.5% to 84.9%. Both the posture prediction accuracy assessment protocol and user-defined posture method introduced in the study would be of use for practitioners to improve the accuracy of predicted postures of humanoids in virtual environments.

Evaluation of Information Presentation Methods for a Wearable Braille Display

Objective: The present study evaluated information presentation methods applicable to a wearable Braille display in terms of performance and satisfaction measures. Background: A Braille display wearable at a finger can improve accessibility of information for the blind by presenting information in real time. Method: A Braille display with six pins operated by DC servomotors was developed to simulate four information presentation methods(active, stationary, simultaneous, and sequential methods). An evaluation experiment was conducted with 16 participants(8 normal and 8 blind participants) by using three objective measures(reaction time, RT, unit: sec; recognition time, CT, unit: sec; correct response percentage, CP) and two subjective measures(overall satisfaction, OS; perception easiness, PE) with a 7-point scale. Results: The average RTs and CTs of the active and stationary methods were significantly shorter than those of the simultaneous and sequential methods for the blind participants. Also, the average CPs, OSs, and PEs of the active and sequential methods were significantly higher than those of the stationary and simultaneous methods. Conclusion: The active and sequential methods were preferred to the other methods for the blind. Application: The performance characteristics identified in the present study for the four braille display methods can be utilized to develop an effective wearable Braille display system.

Glasses-type wearable computer displays: usability considerations examined with a 3D glasses case study

Abstract This study presents usability considerations and solutions for the design of glasses-type wearable computer displays and examines their effectiveness in a case study. Design countermeasures were investigated by a four-step design process: (1) preliminary design analysis; (2) design idea generation; (3) final design selection; and (4) virtual fitting trial. Three design interventions were devised from the design process: (1) weight balance to reduce pressure concentrated on the nose, (2) compliant temples to accommodate diverse head sizes and (3) a hanger mechanism to help spectacle users hang their wearable display on their eye glasses. To investigate their effectiveness, in the case study, the novel 3D glasses adopting the three interventions were compared with two existing 3D glasses in terms of neck muscle fatigue and subjective discomfort rating. While neck muscle fatigue was not significantly different among the three glasses (p = 0.467), the novel glasses had significantly smaller discomfort ratings (p = 0.009). Relevance to Industry: A four-step design process identified usability considerations and solutions for the design of glasses-type wearable computer displays. A novel 3D glasses was proposed through the process and its effectiveness was validated. The results identify design considerations and opportunities relevant to the emerging wearable display industry.