Until the 1970s, hydraulic actuators were widely used in many mechanical systems; however, recently, electric motors have become mainstream by virtue of their improved performance, and hydraulic motors have largely been replaced by electric motors in many applications. Although this trend is expected to continue into the future, it is important to comprehensively evaluate which motor is most suitable when designing mechanical systems. This paper presents the results of a survey of the performance of electric and hydraulic servo motors and aims to provide quantitative data that can be used as a reference for selecting appropriate motors. We surveyed AC, AC direct, brushless DC, and brushed DC electric motors and swash plate-type axial piston, bent axis-type axial piston, crank-type radial piston, and multistroke-type radial piston hydraulic motors. Performance data were collected from catalogs and nonpublic data. We compared and evaluated the characteristics of these diverse servo motors using indexes such as torque, rotating speed, output power, power density, and power rate.

Small in-pipe robots are key to improving pipe inspection procedures, especially for narrow diameters. However, robotic locomotion in such spaces, namely achieving a high locomotion performance with a narrow and flexible mechanism, is difficult. The novel in-pipe locomotion mechanism proposed in this letter achieves rapid locomotion through narrow pipes by a unique duplex-chambered structure. The mechanism achieves smooth bi-directional inchworm locomotion by a combination of expandable silicone rubber and a coil spring and is fully controlled by only two air supply lines. The concept and locomotion technique, including a mathematical analysis and discussion from the viewpoint of operational pressure, are presented herein. Several experiments on the prototyped mechanism were performed to elucidate its characteristics. The results of locomotion tests through horizontal, vertical, and bent pipes showed that the mechanism can horizontally navigate through 25-mm pipes at 45.5 mm/s, which is the fastest yet reported for this size of bi-directional in-pipe robot.

Air bubbles in working oil affect the stiffness and efficiency of hydraulic systems; thus it is important for technical issues that air bubbles be actively eliminated from the hydraulic oil. A bubble eliminator is a device that uses a swirl flow to remove air bubbles. The shape of the device affects bubble elimination performance, so the selection of shape is the most important parameter in increasing the performance of the device. The purpose of this study is to design a bubble eliminator with an optimal shape. This paper discusses the validity of numerical simulation by comparing, using various diameters of the vent port, the numerical results with the results of the experimental flow visualization. Moreover, we focus on the length of the inlet tube and tapered tube of the bubble eliminator and establish a method of selecting them.

Micromouse contest is a competition which an autonomous micro-robot through a designated maze to compete for intelligence and speed. In this paper, a small soft mechanical braking device using electro-rheological fluid (ERF) for the micromouse was designed and fabricated. It was experimentally clarified that the prototype model of the ER braking device can provide a sufficient braking force.

Recently, observation by the THz wave implied the existence of the abundant oxygen near the Mars surface. It is required to observe the atmosphere around Mars. A project to launch a small THz Mars probe is in progress. The new simple and light landing mechanism is required for the probe. A method using aluminum foams as shock absorber is proposed, however, it requires a certain length of the aluminum foams. This makes the aluminum foams likely to buckle. In addition, it is difficult to load the aluminum foams for its length. Therefore, it is necessary to fold the legs filled with aluminum foams. This paper proposes the nested landing mechanism with shock absorber, and the landing legs with robustness for landing. In addition, the proposed leg was dropped and shock absorption performance was verified.