학위논문 (석사)-- 서울대학교 대학원 농업생명과학대학 바이오시스템·소재학부, 2017. 8. 김학진.The most common solution to achieving automated steering in an agricultural tractor is the use of an electric motor in parallel with a conventional hydrostatic valve-based hydraulic steering system owing to its simplicity and low cost. However, the existing overlap, or dead band, of a hydrostatic valve has limited its potential benefit to automated tractor steering in terms of providing various agricultural operations, including planting and spraying, at higher speeds. The main objective of this study was to develop an electro hydraulic steering system applicable to an auto-guidance system, and to compare the performance of the developed system with a conventional automatic steering system. A proportional-feedforward control algorithm was implemented to effectively compensate the non-linear behaviors of the hydraulic cylinders used for changing the steered wheel angle of the tractor. A computer-controlled hardware-in-the-loop electro-hydraulic steering simulator consisting of two different types of valve sub-systems s, i.e., hydrostatic valve and EHPV sub-system, was designed and built for the development of the steering control algorithms and to verify the feasibility of the developed steering controller for accurate steering of the system with acceptable response times. A field test was conducted using a Real Time Kinematic GPS based autonomous tractor equipped with the developed EHPV-based steering system and an EPS-based steering system used as a control to compare and investigate their potential in enhancing the path tracking functionality of an auto-guided system. The use of the EHPV-based steering controller was shown to improve the tracking error by about 29% and 50% for straight and curved paths, respectively, as compared to the EPS-based steering system.Chapter 1. Introduction 1
1.1. Study Background 1
1.2. Description of Tractor Steering System 6
1.3. Automatic Steering System 10
1.3.1. Electric Power Steering System 10
1.3.2. Electro Hydraulic Steering System 12
1.4. Review of Literature 13
1.5. Research Purpose 16
Chapter 2. Materials and Methods 17
2.1. Preliminary Performance Test of Conventional Steering System 17
2.1.1. Purpose of Preliminary Test 17
2.1.2. Zero-Load Test 21
2.1.3. Tractor Traveling Test 22
2.2. Hardware-in-the Loop Simulator 24
2.2.1. Hydraulic Circuit 25
2.2.2. Hardware Description 27
2.3. ISO 11783 Network 37
2.3.1. ISO 11783 (ISOBUS) 37
2.4. Steering Control Algorithm 45
2.4.1. Dead Time 48
2.4.2. Dead Band 51
2.4.3. Static Friction 57
2.5. Virtual Terminal 61
2.6. Vehicle Traveling Test 66
2.6.1. Hardware Configurations 66
2.6.2. Trajectory Tracking Control 72
2.6.3. Zero-Load Test 74
2.6.4. Sinusoidal Tracking Test 75
2.6.5. Path-Tracking and Test Methods 76
2.6.6. Evaluation Method of Path Tracking Deviation 79
Chapter 3. Results and Discussion 81
3.1. Preliminary Test Results of EPS-based Hydrostatic Steering System 81
3.2. Experiment Results of Steering Behavior of Hydrostatic Steering System using HIL simulator 85
3.3. Experiment Results of Electrohydraulic Steering System using HIL simulator 81
3.3.1. Dead-Time Approximation 88
3.3.2. Dead-Band Compensation 90
3.3.3. Static Friction Compensation 92
3.3.4. Steering Controller Test under Load Conditions 94
3.4. Performance Evaluation of Tractor Steering System 96
3.4.1. Zero Load Test 96
3.4.2. Sinusoidal Steering Test 96
3.4.3. Path-Tracking Test 99
Chapter 4. Conclusions 107Maste
