Young-Bum Kim

Path tracking for a hydraulic excavator utilizing proportional-derivative and linear quadratic control

This paper presents a three-dimensional path tracking strategy for a hydraulic excavator. It mainly aims to design the controller for allowing the excavator to follow typical working motions of a skillful operator such as leveling and truck loading. The performance of the designed controller is verified through real-time experiments using a 21-ton class excavator in which displacement sensors, electro-proportional pressure reducing valves, and communication devices are incorporated. Basically, proportional-derivative (PD) controller with dead zone compensation is used to control the cylinder displacements and swing angle. In order to enhance the performance, a linear quadratic outer-loop is introduced for boom, arm, and bucket joints, which compensates reference inputs of the nonlinear PD controller. Experiments of individual joints show that the designed outer-loop can provide faster rise time than the nonlinear PD controller itself. Furthermore, experimental results demonstrate the feasibility of the proposed algorithm for achieving autonomous compliant motions of both leveling and truck loading.

A Study on the Durability Design of a Hydraulic Cylinder for an Excavator

A hydraulic cylinder is a primary component of an excavator and is used for activating attachments such as boom, arm, and bucket. Generally, the cylinder is prone to structural problems such as buckling and fatigue failure caused by cyclic high pressure. Therefore, the safety margin for fatigue, yield, and buckling during the design lifetime should be evaluated at the durability-design stage. The durability design includes basic and detailed stages. In the basic design, the principal dimensions of the rod and tube are determined by considering the working force, speed, and range with respect to yield and buckling. In the detailed design, the dimensions of the rod notch, welds, tube end, gland, orifice, and cushion ring are determined by considering the fatigue safety. We present and discuss the overall procedure for durability design and the related analysis techniques.

A Study on the Virtual Digging Simulation of a Hydraulic Excavator

The interest in unmanned excavator is growing more and more for the sake of work efficiency and safety of the operator. It is general understanding that an optimal working path planning and inverse dynamic control should be resolved first for the realization of the unmanned excavator. In this paper, the methods to determine the optimal working path based on minimum torque or time and to simulate digging works tracking on the designed working path are proposed. In case of the minimum torque, the optimal working path is determined to minimize the joint torques of attachments. On the other hand, in case of minimum time, the optimal working path is decided to minimize time duration for one-cycle working considering the hydraulic constraints such as oil flow rate and relief pressure etc. In order to verify the inverse dynamic code used in the optimization and the optimized path, field measurements were carried out for the various parameters such as swing angle, cylinder lengths, and pressures of a swing motor and hydraulic cylinders during digging works. The modified FEE(Fundamental Earthmoving Equation) is adopted for the modeling of soil-tool interaction in digging process and the inverse dynamics with external force such as constant and reducing lifting weights is used in lifting and dumping process. Finally, all the simulated data were compared with the measured data in order to examine the effectiveness of the proposed methods in view of the development of the unmanned excavator.

Degradation Assessment of Aluminum Alloy 6061-T6 Using Ultrasonic Attenuation Measurements

Abstract Ultrasonic methods are widely used to degradation assesment. Remaining-life cycle of metal can be estimated by ultrasonic parameters because ultrasonic velocity and attenuation are affected by change of material properties with accumulated fatigue in the metal. Therefore, in this study, we will estimate overall change of material properties by 2D C-scan image. Fatigued aluminum alloy 6061-T6 samples from 0 to 85% were prepared for evaluating fatigue life cycle. Also, degraded image of materials using attenuation is proposed to estimate degree of material degradation for determining degraded area of fatigued samples. Finally, we will predicts process pf degradation with measured attenuation of fatigued aluminum alloy 6061-T6 samples. Keywords: Al6061-T6, Attenuation, Ultrasonic, Degradation, Fatigue[접수일: 2012. 3. 14, 수정일: (1차: 2012. 12. 4, 2차: 2013. 2. 4) 게재확정일: 2013. 2. 7] *성균관대학교 기계공학부, **한국원자력안전기술원 ✝Corresponding Author: School of Mechanical Engineering, Sungkyunkwan University, Suwon 440-746, Korea (E-mail: sjsong@skku.edu)