Haptic Interfaces with Wide Workspace and Gravity Compensation for Realistic Interaction = 실감 상호작용을 위한 넓은 작업공간 및 중력 보상형 햅틱 인터페이스

국문 초록 (Abstract)

햅틱 인터페이스는 가상 환경의 물리적 특성(무게, 강성 등)을 사용자에게 전달하여 실재감을 부여하는 핵심적인 상호작용 장치이다. 그러나 기존의 햅틱 장치들은 넓은 작업 공간 확보와 높은 동적 투명성 유지 사이에서 근본적인 기구학적 접근 문제에 직면해 있다. 직렬 기구는 넓은 작업 공간을 제공하지만 높은 관성으로 인해 투명성이 저하되며, 병렬 기구는 강성이 높고 관성이 낮으나 작업 공간이 협소하다는 한계가 있다. 또한, 기존의 중력 보상 기법들은 추가적인 질량으로 인한 관성 증가나 구동기 부하 증가를 초래하여 역감의 품질을 떨어뜨리는 요인이 되어왔다.

본 학위논문은 이러한 구조적 모순을 해결하고 고성능 햅틱 상호작용을 구현하기 위한 새로운 기구 설계 프레임워크를 제안한다. 본 연구는 (1) 구동기를 베이스에 고정하여 구동 질량을 최소화하면서도 인간 중심의 넓은 작업 공간을 확보하는 병렬 기구 설계, (2) 구조적 질량 또는 최적화된 스프링 메커니즘을 활용하여 관성 증가 없이 중력 부하를 제거하는 수동 중력 보상 기술, (3) 강체 접촉을 사실적으로 모사할 수 있는 고출력 구동 능력 확보라는 세 가지 핵심 설계 원칙에 중점을 둔다.

제안된 설계 방법론을 검증하기 위해 세 가지 햅틱 인터페이스 프로토타입을 개발하고 평가하였다. 첫째, VirtuaPower는 이중 5절 링크 병렬 기구를 채택하여 병렬 로봇의 작업 공간 한계를 극복하고, 1.0 ㎥의 넓은 작업 공간과 100N의 높은 출력 힘을 달성하였다. 둘째, Haptic B는 경량 카본 소재와 스프링-케이블 기반의 수동 중력 보상기를 결합하여 중력 토크를 54% 감소시키고 높은 역구동성을 확보하였다. 셋째, G-DHap은 수평형 4절 링크 구조를 기반으로 한 양팔형 햅틱 장치로, 구동기 자체의 질량을 평형추로 활용하는 구조적 밸런싱 기법을 도입하여 추가 질량 없이 효율적인 중력 보상을 실현하였다.

정적 힘 추종, 동적 응답 특성 분석, 가상 벽 렌더링 등을 포함한 실험적 검증을 통해, 제안된 장치들이 마찰과 관성이 최소화된 정밀한 힘 피드백을 제공함을 확인하였다. 또한, 사용자 평가를 통해 G-DHap이 상용 햅틱 장치 대비 우수한 사실감과 접촉 인식 능력을 제공함을 입증하였다. 본 연구는 투명하고, 높은 힘을 제공하며, 넓은 작업 공간을 갖는 햅틱 인터페이스를 위한 포괄적인 설계 방법론을 정립하였으며, 이는 원격 조작, 가상 훈련, 재활 로봇 등의 분야에 중요한 기여를 할 것으로 기대된다.

다국어 초록 (Multilingual Abstract)

Haptic interfaces are systems that provide a "sense of touch'' to a user to enable a virtual reality environment or remote robotic systems. They serve as a critical bridge between human operators and virtual environments, or remote robotic systems, enabling the perception of physical properties such as weight, stiffness, and texture. However, conventional haptic devices face a fundamental trade-off between achieving a large workspace and maintaining high dynamic transparency. Serial mechanisms offer wide workspaces but suffer from high effective inertia, while parallel mechanisms provide high stiffness and low inertia but are typically limited by restricted workspaces and complex mechanical interference. Furthermore, traditional gravity compensation methods often introduce significant parasitic inertia or excessive actuator burden, degrading the fidelity of force rendering.

This dissertation proposes a novel mechanical design framework to resolve these structural contradictions and achieve high-fidelity haptic interaction. The research focuses on three core design principles: (1) base-mounted parallel architectures to minimize moving mass while securing human-scale workspaces, (2) passive gravity compensation techniques utilizing structural mass or optimized spring mechanisms to eliminate gravitational loading without adding effective inertia, and (3) high-force actuation capabilities to realistically simulate rigid contacts.

To validate this framework, three distinct haptic interfaces were developed and evaluated. First, VirtuaPower utilizes a dual five-bar parallel mechanism to achieve a large workspace, 1.0 ㎥, and high force capability, 100N, effectively resolving the workspace limitation typically associated with parallel robots. Second, Haptic B incorporates a lightweight carbon-fiber structure and a passive spring-cable gravity compensator, reducing gravitational torque by 54% and ensuring high backdrivability. Finally, G-DHap features a dual-arm configuration with horizontally arranged four-bar linkages. It introduces a structural balancing method that utilizes the intrinsic mass of the actuators as counterweights, achieving effective gravity compensation without auxiliary mass.

Experimental validations, including static force tracking, dynamic response analysis, and virtual wall rendering, confirmed that the proposed devices provide precise force feedback with minimal friction and inertia. A comparative user study further demonstrated that G-DHap offers superior realism and contact perception compared to commercial haptic devices. This research establishes a comprehensive design methodology for transparent, high-force, and wide-workspace haptic interfaces, with significant implications for teleoperation, virtual training, and rehabilitation robotics.

목차 (Table of Contents)

• Abstract i
• Contents iii
• List of Tables viii
• List of Figures ix
• 1 Introduction 1
• 1.1 Motivation: The Need for Realistic Physical Interaction 1
• 1.2 Structural Limitations of Conventional Kinematic Architectures 2
• 1.2.1 The Inertia Problem of Serial Mechanisms 3
• 1.2.2 The Workspace Limitation of Parallel Mechanisms 3
• 1.3 Structural Constraints of Existing Compensation Methods 3
• 1.4 Thesis Objective and Contributions 4
• 2 Background and Related Work 6
• 2.1 Overview of Haptic Interfaces 6
• 2.2 Kinematic Architectures in Haptics 7
• 2.2.1 Serial Mechanisms (Open-Chain) 7
• 2.2.2 Parallel Mechanisms (Closed-Chain) 9
• 2.2.3 Comparative Analysis 10
• 2.3 Dynamics and Gravity Compensation 10
• 2.3.1 Impact of Inertia on Haptic Fidelity 11
• 2.3.2 Conventional Gravity Compensation Methods 11
• 2.3.3 Active Compensation (Motor-Driven) 11
• 2.3.4 Passive Compensation (Mechanical) 12
• 2.4 Conclusion on Related Work 13
• 3 Development of High-Force Display and Wide-Workspace Haptic Interface: VirtuaPower 14
• 3.1 Design Purpose and Structural Overview 14
• 3.2 Mechanism and Structural Configuration 15
• 3.2.1 Geometric Parameters 19
• 3.2.2 Force Display Principle 20
• 3.2.3 Prototype of VirtuaPower 21
• 3.3 Kinematics and Dynamics 24
• 3.3.1 Forward Kinematics 24
• 3.3.2 Constraint Jacobian of VirtuaPower 30
• 3.3.3 Jacobian 34
• 3.3.4 Dynamic Model 37
• 3.4 Experiment and Results 38
• 3.4.1 Reachable and Constant Orientation Workspaces 38
• 3.4.2 Force-Display Capability 40
• 3.4.3 Static, Step, and Frequency Responses 42
• 3.4.4 Virtual Sphere Wall 46
• 3.4.5 Virtual Reality Environment 47
• 3.5 Conclusion 49
• 4 Haptic B: Parallel Five-bar Mechanism with a Spring Gravity Compensator 51
• 4.1 Introduction and Overview of Haptic B 51
• 4.2 Mechanism Design 53
• 4.2.1 Conceptual Design 53
• 4.2.2 Geometric Parameters 54
• 4.2.3 Prototype Implementation 55
• 4.3 Standard of Parameter Design 58
• 4.3.1 Five-Bar Mechanism Optimization 58
• 4.3.2 Gimbal Mechanism Configuration 59
• 4.4 Gravity Compensator Design and Analysis 61
• 4.4.1 Mechanism Design and Implementation 61
• 4.4.2 Compensating Torque Analysis 62
• 4.5 Kinematic and Dynamic Modeling 67
• 4.5.1 Forward Kinematics 67
• 4.5.2 Constraint Jacobian and Passive Joint Mapping 69
• 4.5.3 Forward Jacobian 70
• 4.5.4 Dynamic Equations of Motion 72
• 4.6 Kinematic and Dynamic Performance Analysis 73
• 4.6.1 Performance Verification of Spring-based Gravity Compensation 73
• 4.6.2 Kinematic Constraints and Reachable Workspace 75
• 4.7 Evaluation 76
• 4.7.1 Force Display Performance Evaluation 76
• 4.7.2 Virtual Wall Interaction Experiment 78
• 4.8 Conclusion 80
• 5 G-DHap: Dual-Arm Device with Gravity Compensation via Structural Mass 82
• 5.1 Design Purpose and Structural Overview 82
• 5.2 Mechanical Implementation 86
• 5.2.1 Mechanical Architecture and Actuation 86
• 5.2.2 Geometric Parameters 87
• 5.2.3 Force Display Principle 88
• 5.3 Kinematic and Dynamic Modeling 89
• 5.3.1 Forward Kinematics 89
• 5.3.2 Constraint Jacobian 90
• 5.3.3 Manipulator Jacobian 91
• 5.3.4 Dynamic Equations of Motion 91
• 5.4 Design Analysis and Simulation 92
• 5.4.1 Gravity Compensation Analysis (Concept A vs. Concept B) 92
• 5.4.2 Workspace Analysis 94
• 5.5 Experimental Performance Evaluation 95
• 5.5.1 Six-DoF Force Rendering 95
• 5.5.2 Gravity Compensation Verification 96
• 5.5.3 Virtual Environment Interaction 97
• 5.6 User Evaluation Study 99
• 5.6.1 Workload and Realism Analysis 101
• 5.6.2 Qualitative Feedback 102
• 5.7 Chapter Summary 103
• 6 Conclusions 105
• 6.1 Summary of Research 105
• 6.2 Key Contributions 106
• 6.2.1 Inertia Minimization via Functional Mass Redistribution 107
• 6.2.2 Overcoming Kinematic Trade-offs 108
• 6.2.3 Innovative Passive Gravity Compensation 108
• 6.2.4 Validation of High-Fidelity Interaction 109
• 6.3 Limitations and Future Work 109
• 6.3.1 Control Strategy Enhancement for User Fatigue Reduction 109
• 6.3.2 Impedance Control Strategy for Rotational Dynamics 110
• 6.3.3 Establishment of Design References for Haptic Wrist Modules 111
• 6.3.4 Expansion to Multi-Modal Interaction 111
• 6.4 Concluding Remarks 112
• Abstract (In Korean) 123