Takayoshi Muto

Development of a Hydraulic Tele-Operated Construction Robot using Virtual Reality

Abstract In this study, we have developed a bilateral telerobotics system for a construction robot using virtual reality. The system consists of a servo-controlled construction robot, two joysticks for operation of the robot from a remote place, and a three degrees of freedom motion base. The operator of the robot sits on the motion base and controls the robot bilaterally from a remote place. The role of the motion base is to realistically simulate the motion of the construction robot. In this study, firstly, we propose a new method of master-slave control in order to make better feedback feeling of the reaction force to the joystick for the tele-operated construction robot. Secondly, we tested the visual feedback system for the construction robot using CCD video camera and computer graphics. For tele-operations, a video image of the operation field is normally projected onto a screen to assist the operator. In this study, an additional computer graphics (CG) was generated as a virtual robot to the real video image in order to present the end condition of the robot arm. The usefulness of the system is confirmed by the experiments in this study.

Construction tele-robotic system with virtual reality (CG presentation of virtual robot and task object using stereo vision system)

In this study, we investigated a tele-robotics system for a construction machine. The system consists of a servo-controlled construction robot, two joysticks for controlling the robot from a remote place, and a 3-degrees-of-freedom motion base. The operator of the robot sits on the motion base and controls the robot bilaterally from a remote place. The role of the motion base is to realistically simulate the motion of the construction robot. As a tool for assisting the operator, a stereo video of the operation field is projected on a screen. If, in addition to the video, computer graphics (CG) of the robot were to be presented to the operator, the task efficiency could be expected to increase. To confirm this, a CG of a virtual robot was created, and its effectiveness for a task involving carrying an object was determined in this study. This system can present the position and shape of the task object by means of a stereo vision system. The results of the experiment clarified that tasking time was shortened effectively even for amateur operators. Thus, the usefulness of the developed CG system was confirmed.

Using virtual reality to assess factors affecting shipboard accessibility for wheelchair users

In order to improve the usability and safety of public transportation for wheelchair users such as the aged and people with disabilities, designers need to assess the usability of facilities in the design stage based on the available data. This studys objective is to develop a wheelchair simulator and control method suitable for barrier-free transportation. By controlling the hand-rims of the wheelchair, the operator can re-create traveling and turning motion in a virtual reality (VR) space. The position and attitude of the wheelchair are presented to the operator as the motion of a six-axis motion base. Through a head-mounted display, a computer graphics system provides the operator with scenery that changes in accordance with the wheelchairs operation. To study barrier-free transportation onboard a ship, the ships motion was re-created in VR space, and the operational ability of the wheelchair was compared for cases including and not including the ships simulated motion. The experimental results demonstrate the feasibility of the developed system.

A Precision Driving System Composed of a Hydraulic Cylinder and High-Speed on/off Valves

Abstract In manufacturing technology, the predominant tendency in recent years has been for machine tools, for example, turning-, milling-, and drilling-machines, to employ electrically operated actuators such as a servo-motor equipped with a ball screw. There are, however, various problems with these electric driving systems; they are excessively large-sized with complex machinery, and their application is expensive, as seen, for example, in the case of the NC-machine. In order to solve these problems, this study aims to develop a precision driving system actuated by a hydraulic cylinder. The hydraulic driving system consists of a cylinder and four ON/OFF solenoid valves. The valves are the same as those used in a fuel injector of an automobile, which are capable of high speed switching, as fast as 1.5 ms. It was confirmed in experiments that the developed system had a moving resolution of 1.2 μm and, as a result, was applicable to a precision driving table for micro-processing.

Development of a High-Speed on/off Digital Valve for Hydraulic Control Systems using a Multilayered PZT Actuator

Abstract In this study, a high-speed on/off digital valve was developed for use in a hydraulic control system. The device basically consists of a poppet valve acting as the main valve, and a multilayered piezoelectric (PZT) actuator for driving the poppet valve. A hydraulic amplifier was adopted to increase the actuation of the PZT actuator to the poppet valve. A compensation mechanism was set up to reduce this temperature effect in the hydraulic actuation of the PZT actuator. This problem arises when the oil temperature increases and causes the valve displacement to fluctuate slightly. The static and dynamic characteristics of the device were investigated by experiment and computer simulation. As a result, it was found that the switching time of the valve is less than 0.7 ms. Moreover, the valve can be driven by a PWM carrier wave using frequencies of up to 500 Hz. Additionally, the validity of the temperature compensation mechanism was confirmed. Hence, this valve may be determined as feasible device to be used in hydraulic systems.

ACTIVE SUSPENSION SYSTEM WITH HIGH-SPEED ON/OFF VALVE (APPLICATION OF PREVIEW CONTROL WITH ADAPTIVE DIGITAL FILTER)

ABSTRACT The aim of this study is to propose an active control hydro-pneumatic suspension system composed of high speed on/off solenoid valves. In order to realize a robust control system, we adopted preview control method utilizing an ADF (Adaptive Digital Filter). The experiment was performed on a bench system which physically simulates induced vibrations from the road. These results confirmed that in the case of the preview control method, the damping efficiency is higher than in the case using the conventional sky-hook control method. Furthermore, the control performance of preview control using an ADF is superior to the conventional preview control system. Therefore, it is expected that the active suspension system, which is developed in this study, could produced at low cost and achieve a high level of reliability.

Development of a Pneumatic Force-Display (Application to a Master-Slave System)

Abstract In this study we deal with a bilateral master-slave system composed of a pneumatic force-display as the master and a hydraulic servo system as the slave. In such systems the force-display must play two roles as master: first as a reference input device to the slave and second as a force-display device. The first purpose of this study is to develop a pneumatic force-display that consists of a pneumatic servo system. To achieve this, it is necessary to solve a problem called back-drivability, a characteristic of pneumatic servo systems. The second purpose is to investigate the compatibility of our thusly developed force-display with some representative methods of bilateral master-slave control systems in conventional use. In experiments to confirm such compatibility, the sensibility of load forces is estimated based on a master-slave system equipped with a spring to serve as a load. The experiments confirm that the developed force-display would be applicable to conventional methods of bilateral master-slave systems.

The Dynamic Characteristics of Tapered Fluid Lines with Viscoelastic Pipe Walls

Abstract For convenience in investigating the dynamic responses of a liquid-filled tapered line with a viscoelastic pipe wall, a transfer matrix equation, relating pressure to volumetric flow, is derived. In this derivation, it was assumed that the rate of divergence (or convergence) of the line is comparatively small. The fluid line model employed in the analysis is one of an unsteady viscous flow; that is, the frequency-dependent effect of viscosity is taken into consideration. The visco-elastic pipe wall model is a modified version of the Voigt mechanical model, and it is distributed along the pipeline. The frequency response curves are calculated from the matrix, and the accuracy of the curves is evaluated by comparing them with the response curves obtained without assuming the small taper angle. The results verify that the transfer matrix is accurate enough for practical applications.

A Fast and Convenient Method for Simulating a Transient Response of Fluid Viscoelastic Lines.

The purpose of this study is to find a faster and more convenient method for simulating a transient response of viscoelastic transmission lines. Another objective of this study is to formulate and evaluate rational polynomial approximations for an exact model for viscoelastic transmission lines. If an approximation by rational polynomials is carried out using precision accuracy, we can adopt conventional methods of numerical integration for ordinary differential equations, and thus, we obtain a faster and more convenient method for simulation. It could be confirmed that the results of simulation agreed well with the experimental results, and thus, the usefulness of the proposed method could be verified.

Fundamental Study of Power Match Control of Hydraulic Power Systems.

Power match control of hydraulic power systems involves continuous control of the output power of the hydraulic pump so as to agree with the power of the load actuator. In a previous report, we investigated the dynamic performance of pressure match control, employing an electrohydraulic power match system driven by the differential-PWM method. The result showed that the system had good control performance. The feature of this system is different from that of a conventional type ; that is, pressure, flow rate or power of the load actuator can be controlled without the need for any control valves such as a load-sensing valve and a flow control valve. In this report, the performance of flow rate match control is evaluated by experiment and computer simulation. It is verified that the system has good control performance.