Tokuji Okada

A three-wheeled self-adjusting vehicle in a pipe, FERRET-1

This paper describes three-wheeled vehicles that can move inside a pipe and adjust to the shape and size of the pipe. We propose two types of vehicles: tractive and nontractive. Both types are based on two hinged arms. The tractive vehicle has a driving wheel at a hinge and two sphere bearings at the ends of the arms. The driving wheel rotates about the axis perpendicular to the plane in which the two arms move. The wheel can freely move sideways. The sphere bearings can move in all directions like ball casters. Since the stretch force of the arm to the pipe wall is generated mechanically by pulleys and a spring, the vehicle rests in the pipe by pressing the two arms in opposite directions where the diameter is the biggest and it moves according to the action of the driving wheel. Three wheels of the nontractive vehicle are sphere bearings. We analyze the shape geometry of the pipe to obtain sta bility conditions under which the vehicle can move, and we consider friction and gravity bringing the vehicle to rest in the pipe. We also analyze the kinematics and dynamics of lo comotion, and we simulate locomotion of the vehicle in the plane in which the biggest diameter of the pipe is measured. The results of the simulation prove the self-adjustability of the vehicle to the shape and size of the pipe. Experimental results show that the vehicle can move and self-adjust in an inclined or twisted pipe with a deep angle.

An articulated multi-vehicle robot for inspection and testing of pipeline interiors

The authors describe the construction of an articulated multi-vehicle robot for inspection and testing of pipeline interiors. The robot is capable of traveling inside pipes of radius 520-800 mm diameter over a distance 150 m. Output pressure versus extension characteristics of the two-stage air cylinder, reduction of the wave reflection in a wheel-type ultrasonic probe, an umbilical cable assembly housing optical fibers, air tubes and electric cables are key elements of the robot. The articulated robot was tested in the laboratory to evaluate and the scanning performance. The results of the non-destructive test of a weld bead to the longitudinal direction show that the robot can pick up surrounding color images and transmit them to the ground stations monitor with high precision.

Development of a steerable, wheel-type, in-pipe robot and its path planning

This paper presents the development of a steerable, wheel-type, in-pipe robot and its path planning. First, we show the construction of the robot and demonstrate its locomotion inside a pipe. The robot is composed of two wheel frames and an extendable arm which links the centers of the two wheel frames. The arm presses the frames against the interior wall of a pipe to support the robot. The wheels of the frames are steered independently so that the robot can turn within a small radius of rotation. Experimental results of the locomotion show that the steering control is effective for autonomous navigation to avoid obstacles and to enter the joint spaces of L- and T-shaped pipes. Generally, autonomous navigation is difficult for wheel-type robots because the steering angles required to travel along a desired path are not easily determined. In our previous work, the relationship between the steering angles and locomotion trajectories in a pipe has already been analyzed. Using this analysis, we propose the path planning in pipes.

Development of an Optical Distance Sensor for Robots

A description is given of the development of an optical distance sensor for robots. The surface of an object is illuminated by light coming through a pinhole, and the light reffected on the surface is guided into a photosensor array by another pinhole. Based on the position of the photosensor unit that detects a magnitude greater than that detected by any other unit, the distance between the surface and the sensor head is determined geometrically, without influence from circumferential illumination or other conditions of an object such as irregularity, reflectivity, and orientation. This sensor is quite powerful and should have a wide variety of practical uses. Both analytic and experimental results are presented.

Motion Analysis with Experimental Verification of the Hybrid Robot PEOPLER-II for Reversible Switch between Walk and Roll on Demand

We propose a newly renovated mobile robot PEOPLER-II (Perpendicularly Oriented Planetary Legged Robot), and addresses its motion analysis for switching its locomotion from leg-type to wheel-type and vice versa. For the leg-type locomotion, particularly in a transitional state of sitting or standing, we propose a control method based on minimization of the total energy cost using the distribution of the motor power payload in the hip and knee joints, in addition to the method of keeping the same payload factor. Also, we discuss robot configurations for switching between the two locomotion types by considering environmental factors such as walking gaits, ground inclination angle and robot’s traveling direction. Knee joint position of a pivotal foot determines knee ahead and knee behind gaits. In each switch, we check such characteristics as the hip joint rotation direction, robot center trajectory, and necessary total power in a practical point of use. Then we build three beneficial switching cycles aiming for moderate use of a motor, rider’s comfort, and power saving. Finally, we demonstrate the switching by considering the aim and verify that the results of the analysis become useful for enabling switching on demand.

A new tactile sensor design based on suspension-shells

Requirements of sensors for dextrous fingers have been discussed and appropriate designs to satisfy these requirements have been proposed. Miniaturization of a tactile sensor element has also been considered. However, only a limited number of such sensors might be attached to the surface of a finger body. In addition, with present day tactile sensing technology, it is difficult to make all of the surfaces sensitive or efficiently handle all the signal lines. In order to solve these problems, a new tactile sensor devoid of blind sectors is proposed. The sensor uses a suspension shell covering the surface of the finger body. Tactile sense is obtained by detecting the relative displacement of the suspension-shell with respect to the finger body.

Optimization of mechanisms for force generation by using pulleys and spring

A link mechanism is proposed for force generation by using pulleys and springs (FGPS) based on a scissors structure having two arms, which are effective in energy saving, simpli fication, and miniaturization of a total system of force gener ation. The relationship between the motion of the mechanism and its output force is analyzed for optimization of structure and dimensions. For optimization of pulley shapes, analyti cal and approximate methods are discussed. Experimental results show that eccentric noncircular pulleys are more effective than circular pulleys in producing a force sufficiently accurate to satisfy conditional relations between the force and the displacement of the mechanism. The mechanism is useful in fulfilling various kinds offorce versus displacement characteristics requirements.

Proximity sensor using a spiral-shaped light-emitting mechanism

A proximity sensor is presented in which light is cast from a source point on an object through a slit cut in a rotating disk. The light passing through the slit is reflected onto the objects surface. Some of the reflected light is captured by a photodiode with the time period being recorded. The distance is determined from the function of the slits shape and the time period when the photodiode captures the reflected light. The light-emitting mechanism makes it possible to measure the distance of an object repetitively. The distance measurement is neither affected by environmental illumination nor by attributes of the object such as diffusibility or reflectivity as far as there is light to reach the photodiode. Two profiles of the slit are discussed. One allows for easy fabrication and the other simplifies signal processing. The validity of the measurement concerning the two profiles is shown by experimental results. >

Hip Joint Control of a Legged Robot for Walking Uniformly and the Self-lock Mechanism for Compensating Torque Caused by Weight

This paper describes hip joint control of the legged robot, PEOPLER (Perpendicularly Oriented Planetary Leg Robot) to make the robot walk uniformly. Equations are shown expressing robot speed while 4 legs change attitude patterns periodically as the hip joint rotates. With differentiation of each equation we can find angular velocity of the hip joint so that the robot can walk forward at a constant speed. Also, we show vertical displacements of the robot in connection with the angular velocity. Moreover, we devised a leg driving mechanism composed of worms and worm wheels for compensating torque caused by weight operating on the hip joint. Typical features for worm gearing such as generating lateral and axial forces are analyzed. In order to prevent the shaft from shifting toward the axial direction, we show how strong axial stoppers should be placed on a propeller shaft connecting the worms. These considerations are verified by experiments using PEOPLER Mk.2 and a miniature sized walker.

Measurement of Surface-Normal Using a Range Sensor with a Pair of Wedge-Prisms

We propose a method of measuring not only distance but also surface-normal of an object at several meters away with a single light source. Basically, one light beam source is enough to measure the distance, since the light beam is scanned toward wide area mechanically, however we use a pair of wedge-prisms for the purpose of collecting three distance data within a small surface of the object. That is, we make the light shift a little bit from the original laser beam axis by attaching a driving mechanism to rotate the pair of the wedge-prisms. There is no need to use optical lenses and mirrors for the light shift. This is beneficial to construct a simple device. Firstly we describe the measurement principle of the surface normal by using laser sensor with optical hood for beam shift. Then, we show the usefulness of the method by showing experimental data. It is applied to environmental recognition which is useful to mobile robots, e.g. a wall inclination or a stair layout