Simulation Model of the Automatic Planting Depth Control System for Rice Transplanter Using Proportional Valve

다국어 초록 (Multilingual Abstract)

Rice transplanter is an inevitable technology for rice farming. In Korea, rice transplanter is almost 99.9% mechanized. In recent year, rice transplanter is spreading out overseas with sophisticated facilities. However, the export of domestic rice transplanter has decreased compared to previous years due to the backdated technologies. This is why the mechanized rice transplanter should modify with advanced technology like a proportional valve to hold the global share market of the rice transplanter. Therefore, the goal of this study is to develop the simulation model of the automatic planting depth control system of a rice transplanter using proportional valve. In this study, the PID control law was also studied to control the hydraulic system of rice transplanter. Actually, two PID control algorithm was developed: i) to control the displacement of actuator ii) to compensate for the viscous effect on the hydraulic system of a rice transplanter. Ziegler-Nichols (Z-N) methods were used to determine the PID coefficients. The simulation was conducted for three ISO standard hydraulic oils. Validation test for both control laws was conducted by performing proportional valve test bench for the same hydraulic oils. The viscosity of the hydraulic oils was calculated at its reference temperature. The lowest overshoot and settling time were found at K_p: 5.24, K_i:4.39, and K_d:1.34 for the position control without considering viscosity, and K_p= 200 T_i=2.52 and T_d=0.63 for position control considering viscosity at the damping ratio 0.8. The simulation results of the position control without considering viscosity show that the pressure of the proportional valve is proportional to the decreasing rate of hydraulic oils viscosity. This result indicates that the position control without considering viscosity cannot able to control the viscosity effects. In case of position control considering viscosity, results were found that the maximum pressures of proportional valve for 1 A and 2A supplied current was the same for both simulation and experiment, calculated around 15.40 bar and 17.87 bar, respectively. The comparison of the settling time and steady-state error for both simulation and experiment were also the same. The settling time and steady-state error were 0.43 s and 0%, accordingly. Only, the overshoot of the experimental results was found higher than that of the simulation results. However, the overshoot of the experimental results was satisfied with the boundary condition, accounting for approximately 21.80% which is less than 25%. In conclusion, the validation test stated that the position control considering viscosity could be able to compensate for the viscous effects of hydraulic oils on the hydraulic system. This control law might also be able to control the movement of the hydraulic actuator. Because the movement of the actuator depends on the pressure supplied from the proportional valve. Therefore, it could be said that the position control considering viscosity could be feasible for the automatic planting depth control system of a rice transplanter that improve the rice transplanter planting accuracy with tilting of the planted seedlings. Ultimately, this control law could also be able to increase the comprehensive performance of the rice transplanter.

국문 초록 (Abstract)

이앙기는 벼 재배에 필수적이다. 한국은 벼 이식 작업이 거의 99.9% 기계화가 되어있다. 최근 몇 년간, 전세계적으로 이앙기 기술은 진보되었다. 그러나 국내의 이앙기의 수출은 전년도 대비 감소하였다. 이에, 이앙기에 비례 제어 밸브를 적용하여 세계 시장에서 경쟁력을 갖춰야한다. 따라서, 본 연구의 목적은 비례 제어 밸브를 이용한 이앙기의 자동 식부 깊이 제어 시스템의 시뮬레이션 모델을 개발하는 것이다. 본 연구에서, PID 제어기는 이앙기의 유압 시스템을 제어하기 위해 연구되었다. 두가지의 PID 제어 알고리즘을 개발하였으며 Ziegler-Nichols (Z-N) 방법을 사용하여 PID 계수를 결정했다. 시뮬레이션은 ISO 표준을 만족하는 유압 오일 3가지에 대해 수행하였다. 두개의 컨트롤러의 검증 테스트는 동일한 유압 오일에 대한 비례 제어 밸브 테스트 벤치를 수행하였다. 작동유의 점도는 기준 온도에서 계산되었다. K_p: 5.24, K_i:4.39, K_d:1.34, K_p= 200, T_i=2.52, T_d=0.63으로 감쇠비 0.8에서 압력 제어가 가능하다. 위치 제어기의 시뮬레이션 결과는 비례 제어 밸브의 압력이 작동유 점도의 감소율에 반비례로 나타났다. 이는 위치 컨트롤러가 점도 영향을 제어 할 수 없음을 나타냈다. 압력 제어기의 경우 1A 및 2A 공급 전류에 대한 비례 제어 밸브의 최대 압력은 시뮬레이션 및 실험 모두 동일하며, 각각 약 15.40 bar 및 17.87 bar로 계산되었다. 시뮬레이션과 실험 모두에 대한 안정 시간과 정상 상태 오차의 비교도 동일하게 나타났다. 따라서, 정착 시간과 정상 상태 오차는 0.43 초 및 0 % 였다. 실험 결과는 시뮬레이션 결과보다 높았다. 그러나 실험 결과의 오버 슈트는 경계 조건에 만족하여 약 21.80 %를 차지하는데 이는 25 % 미만이다. 결론적으로 검증 테스트에서는 압력 제어기가 유압 시스템의 유압 오일의 점성 영향을 보상 할 수 있다고 판단된다. 이 컨트롤러는 유압 액츄에이터의 움직임을 제어 할 수 있다. 액츄에이터의 움직임은 비례 제어 밸브에서 공급 된 압력에 의존한다. 따라서 모종이 기울어져 이앙기의 식부의 정밀도를 향상시키는 이앙기의 자동 식부 깊이 제어 시스템에 있어서 압력 제어기가 가능할 수 있다고 할 수 있다. 궁극적으로, 이 컨트롤러는 이앙기의 종합 성능을 향상시킬 수 있을 것으로 판단된다.

목차 (Table of Contents)

• LIST OF FIGURES IV
• LIST OF TABLES VI
• Chapter 1. INTRODUCTION 1
• Chapter 2. REVIEW OF LITERATURE 6
• 2.1 Global market of rice transplanter 6
• 2.2 Characteristics of hydraulic oils 8
• 2.3. Hydraulic control system 9
• Chapter 3. MATERIALS AND METHODS 12
• 3.1 Rice Transplanter 12
• 3.2 Simulation model of the automatic planting depth control system 13
• 3.2.1 Rice transplanter power flow 13
• 3.2.2 Simulation model 14
• 3.3 Design of PID control law 18
• 3.3.1 Actuator model 19
• 3.3.2 PID control law for position control without considering viscosity 21
• 3.3.3 PID control law for position control considering viscosity 23
• 3.4 Initial PID coefficients 25
• 3.4.1 PID coefficients for the position control without considering viscosity 25
• 3.4.2 PID coefficients for position control considering viscosity 26
• 3.4.3 Performance evaluation method of PID coefficients 28
• 3.5 Determination of PID coefficients 29
• 3.5.1 Determination of PID coefficients for position control without considering viscosity 29
• 3.5.2 Determination of PID coefficients for position control considering viscosity 29
• 3.5.3 Input signal to the proportional valve 31
• 3.6 Experimental method 32
• 3.6.1 Test bench 32
• 3.6.2 Specifications of hydraulic oils 33
• 3.7.3 Data acquisition system 35
• Chapter 4. RERSULTS AND DISCUSION 36
• 4.1 Initial PID coefficients for position control without considering viscosity 36
• 4.2 Determination of PID coefficients for position control without considering viscosity 38
• 4.3 Determination of PID coefficients for position control considering viscosity 40
• 4.4 Validation test for the position control without considering viscosity 41
• 4.5 Validation test for control law considering viscosity 42
• 4.5.1 Simulation results using the input signal 42
• 4.5.2 Experimental results 43
• 4.5.3 Comparison of response characteristics 45
• Chapter 5. CONCLUSION 48
• REFERENCES 51
• List of Nomenclatures 60
• ABSTRACT 62
• 국문초록 64