A Double Diamond Design Process Framework for Improving Product Usability : A Case Study on Redesigning Cordless Vacuum Cleaner Handle

다국어 초록 (Multilingual Abstract)

In industry, designers and ergonomists often face situations when the design and ergonomics should be blended. Improving product usability and ergonomic factors is a representative case of interdisciplinary study on design and ergonomics. However, the ergonomic design process has been rarely studied despite the needs and necessity. With these motivations, this study aims to (1) propose an ergonomic design process by revising the double diamond design process (DDDP) with the ergonomic interventions and (2) test the performance and validity of the proposed framework through a case study on a cordless stick vacuum cleaner handle.

The current research consists of a case study and an ergonomic evaluation. The study suggests three ergonomic interventions in the DDDP: (1) Exploratory design study in the discover phase; (2) Defining the design scope and variables in the define phase; and (3) Hierarchical design modification using the 3D printing technology in the develop phase. A cordless vacuum cleaner handle was redesigned through the proposed framework as a case study. Then, ergonomic evaluations evaluated the original and redesigned handles’ usability qualitatively and quantitatively. A total of 18 participants performed two vacuuming tasks (floor and space vacuuming) and evaluated the following variables: subject discomfort in hand, grip satisfaction, preference, and perceived weight on each handle. Muscle activity and fatigue formation trends of four forearm muscles and the movements of the coordination of handle in hand and wrist were also studied. Results of measurements were compared and analyzed with a paired t-test.

In the case study, the redesigned handle was derived within 8 weeks, showing that the proposed framework can improve product usability in a timely- and cost-effective manner. Evaluation results revealed that the redesigned handle improved the usability of the handle, and there was no negative effect on the physical demand of users. Overall, hand discomfort was lower when using the redesigned handle. Grip satisfaction and preference for the redesigned handle were significantly higher (p<0.001 and p<0.005, respectively), and the perceived weight of the redesigned handle was significantly lighter (p<0.05) than the original handle. Meanwhile, there were no effects of type of handle on muscle activity, muscle fatigue formation, and movements of the coordination and of the wrist.

As in this study, research on ergonomic design processes where the perspectives of designers and human factor engineers can be synthesized is expected to accelerate efficient and effective product development. Research in methodology is a difficult, comprehensive, and lengthy study. Nevertheless, such attempts should be continued and encouraged to develop interdisciplinary research in design and ergonomics.

목차 (Table of Contents)

• ABSTRACT i
• CONTENTS ii
• LIST OF FIGURES v
• LIST OF TABLES viii
• EXPLANATION OF TERMS AND ABBREVIATIONS ix
• 1. INTRODUCTION 1
• 1.1. Research Background 1
• 1.1.1. Motivation 1
• 1.1.2. Importance of Ergonomics in Product Design 3
• 1.2. Research Aim and Method 5
• 2. LITERATURE REVIEW 6
• 2.1. Review on Double Diamond Design Process 6
• 2.1.1. The Double Diamond Design Process 6
• 2.1.2. Issues on the Conventional Double Diamond Design Process 7
• 2.2. Previous Studies 10
• 2.2.1. For an Effective Design Process 10
• 2.2.2. Additive Manufacturing 10
• 2.2.3. Design Ergonomics 11
• 2.3. A Proposed Framework with Ergonomic Interventions 12
• 2.3.1. Exploratory Design Study 14
• 2.3.2. Defining the Design Scope and Variables 14
• 2.3.3. Hierarchical Design Modification Using 3D Printing 14
• 3. A CASE STUDY: REDESIGNING A CORDLESS VACUUM CLEANER HANDLE 15
• 3.1. Background 15
• 3.2. Redesigning 17
• 3.2.1. Exploratory Design Study: An Experimental Study 17
• 3.2.2. Defining the Design Scope and Variables 20
• 3.2.3. Hierarchical Design Modification Using 3D Printing 24
• 3.3. Design Outcome 26
• 4. ERGONOMIC EVALUATIONS ON HANDLES 27
• 4.1. Participants 27
• 4.2. Instruments 29
• 4.2.1. Experimental Stimuli 29
• 4.2.2. Electromyography (EMG) measurement system 31
• 4.2.3. IMU Sensor 32
• 4.2.4. A Standard Discomfort Stimulus 33
• 4.3. Experimental Design 34
• 4.3.1. Experimental Variables 34
• 4.3.2. Overall Procedure of Experiment 35
• 4.3.3. Main Tasks 37
• 4.3.4. Discomfort Evaluation 40
• 4.3.5. Subjective Ratings 40
• 4.3.6. Perceived Weight Evaluation 40
• 4.4. Data Processing and Statistical Analysis 41
• 4.4.1. Discomfort Evaluation 41
• 4.4.2. Subjective Ratings 41
• 4.4.3. Perceived Weight Evaluation 41
• 4.4.4. Forearm Muscle Activities 41
• 4.4.5. Movements of Coordination and Wrist 44
• 5. EVALUATION RESULT 45
• 5.1. Discomfort Evaluation 45
• 5.1.1. Floor Vacuuming Task 45
• 5.1.2. Space Vacuuming Task 46
• 5.2. Subjective Ratings 47
• 5.3. Perceived Weight Evaluation 48
• 5.4. Forearm Muscle Activities 49
• 5.4.1. Muscle Activities 49
• 5.4.2. Joint Analysis of Spectra and Amplitude (JASA) 52
• 5.5. Movements of Coordination and Wrist 54
• 5.5.1. Floor Vacuuming Task 54
• 5.5.2. Space Vacuuming Task 56
• 6. DISCUSSION 58
• 6.1. Efficiency in the Design Process 58
• 6.1.1. Exploratory Design Study: An Experimental Study 58
• 6.1.2. Defining the Design Scope and Variables 61
• 6.1.3. Hierarchical Design Modification Using 3D Printing 62
• 6.2. Performance in Improving Usability 64
• 6.2.1. Discomfort Evaluation 64
• 6.2.2. Subjective Ratings and Perceived Weight Evaluation 65
• 6.2.3. Forearm Muscle Activities 65
• 6.2.4. Coordination of Handle and Hand 66
• 7. CONCLUSION 68
• 7.1. Summary 68
• 7.2. Limitations and Future Studies 70
• 7.2.1. In the Case Study 70
• 7.2.2. In the Ergonomic Evaluations 70
• REFERENCE 72
• APPENDICES 76
• Appendix A 76
• Appendix B 79
• ACKNOWLEDGEMENT 80
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