Isaku Nagai

Noncontact position estimation device with optical sensor and laser sources for mobile robots traversing slippery terrains

This paper describes the development of a sensing device that can be used to estimate the position of mobile robots on slippery terrains. The device consists of an optical sensor designed for a computer mouse and dual laser light sources for generating a laser speckle pattern. It detects the motion of a moving surface at a large distance from the surface, from 80 mm to 300 mm, by tracking the laser speckle pattern. The use of dual laser light sources makes the tracking robust for both large distances from the ground and different surface materials. Some fundamental experiments validated the performance of the device, which tracked surfaces of different materials with high accuracy under various height conditions. Finally, the device was mounted on our mobile robot, and simple experiments were conducted on a slippery sandy terrain to evaluate the usefulness of the device as a noncontact odometry system.

Development of a visual odometry system for a wheeled robot on loose soil using a telecentric camera

In this paper, the development of a three-dimensional (3-D) odometry system for wheeled robots on loose soil in an application of planetary exploration is described. When a wheeled robot operates in a slippery environment, visual odometry, which is used to obtain flow images of the ground with a CCD camera, is effective for the measurement of motion because it is a non-contact method. However, in the target condition, a measurement result with a conventional camera is not reliable with this method because the viewing area of the ground varies as a result of the changing distance between the camera and the ground as a result of the wheels sinking in loose soil. To solve this problem, we used a telecentric camera for visual odometry. The lens of the camera robustly maintains the same field of view, regardless of the distance between the camera and the ground. Using the camera, we developed a (3-D) odometry system for our mobile robot to enable its positioning and navigation, and we validated the system with several experiments. In this paper, a structure and a performance test of the developed system is described. After that, the results of experiments in indoor (sandbox) and outdoor (seashore) environments are introduced.

A discontinuous exponential stabilization law for an underactuated X4-AUV

In this paper, stabilization of a class of second-order nonholonomic systems for an underactuated X4-AUV is investigated. We present a model of the underactuated X4-AUV with six degrees of freedom (DOF) and four control inputs. Then, the system is written in a control-affine form by applying a partial linearization technique, and a dynamic controller based on Astolfi’s discontinuous control is derived to stabilize all states of the system to the desired equilibrium point exponentially. The present approach does not necessitate the conversion of the system model into a “chained form”, and thus does not rely on any special transformation techniques to obtain a canonical form. A simulation is conducted to demonstrate the effectiveness of the proposed controller.

A study of tipping stability for omnidirectional mobile robot with active dual-wheel caster assemblies

A holonomic omnidirectional mobile robot with active dual-wheel caster assemblies is proposed as a robotic transport vehicle. With concern to the existence of sudden acceleration and other dynamical effects during maneuver, the tip-over instability monitoring is very important to prevent any unexpected injuries and property damage. This work presents the preventive method of the tip-over occurrence by estimating the tipping direction and stability metrics. The dynamical model of the omnidirectional mobile robot is derived to estimate the net force from the supporting reaction force at each wheel which is caused by the inertial and external forces. The direction of tipping and stability metric is estimated using moments stability measure. The performance of the tip-over prediction for an omnidirectional mobile robot with active dual-wheel assemblies is shown by the conducted simulations.

A nonholonomic control method for stabilizing an X4-AUV

A nonholonomic control method is considered for stabilizing all attitudes and positions (x, y, or z) of an underactuated X4 autonomous underwater vehicle (AUV) with four thrusters and six degrees of freedom (DOF), in which the positions are stabilized according to the Lyapunov stability theory. A dynamic model is first derived, and then a sequential nonlinear control strategy is implemented for the X4-AUV which is composed of translational and rotational subsystems. A controller for the translational subsystem stabilizes one position out of the x-, y-, and z-coordinates, whereas controllers for the rotational subsystems generate the desired roll, pitch, and yaw angles. Thus, the rotational controllers stabilize all the attitudes of the X4-AUV at the desired (x-, y-, or z-) position of the vehicle. Some numerical simulations are conducted to demonstrate the effectiveness of the proposed controllers.

Tip-over stability enhancement for omnidirectional mobile robot

Purpose – The purpose of this paper is to analyze the stability behavior of the omnidirectional mobile robot with active dual-wheel caster (ADWC) assemblies and provide a stable trajectory without any tip-over incident. The omnidirectional mobile robot to be developed is for transporting cuboid-shaped objects. Design/methodology/approach – The omnidirectional transport mobile robot is designed using an ADWC assemblies structure, the tip-over occurrence is estimated based on the support forces of an active footprint, the tip-over direction is predicted, the tip-over stability is enhanced to prevent the tip-over occurrence and a fast traveling motion is provided. Findings – The omnidirectional mobile robot tends to tip-over more on the sides with small ranges of tip-over angle. The proposed method for estimating the tip-over occurrence and enhancing the stability using the gyroscopic torque device was feasible as the tip-over prevention system of the omnidirectional mobile robot with ADWC assemblies. Origin...

Color Constancy Using the Inter-Reflection from a Reference Nose

This paper introduces a novel camera attachment for measuring the illumination color spatially in the scene. The illumination color is then used to transform color appearance in the image into that under white light.The main idea is that the scene inter-reflection through a reference camera-attached surface “Nose” can, under some conditions, represent the illumination color directly. The illumination measurement principle relies on the satisfaction of the gray world assumption in a local scene area or the appearance of highlights, from dielectric surfaces. Scene inter-reflections are strongly blurred due to optical dispersion on the nose surface and defocusing of the nose surface image. Blurring smoothes the intense highlights and it thus becomes possible to measure the nose inter-reflection under conditions in which intensity variation in the main image would exceed the sensor dynamic range.We designed a nose surface to reflect a blurred scene version into a small image section, which is interpreted as a spatial illumination image. The nose image is then mapped to the main image for adjusting every pixel color. Experimental results showed that the nose inter-reflection color is a good measure of illumination color when the model assumptions are satisfied. The nose method performance, operating on real images, is presented and compared with the Retinex and the scene-inserted white patch methods.

A pectoral fin analysis for diving rajiform-type fish robots by fluid dynamics

In this paper, we analyze a propulsive force generated from pectoral fins for a rajiform-type fish robot from fluid dynamic aspects. A pectoral fin of the rajiform-type fish robot is constructed by multiple fin rays, which move independently, and a film of pushing water. Then, the propulsive force of the fish robot is analyzed from the momentum of the fluid surrounding for every fin between fin rays. The total propulsive force for one pectoral fin is the sum of these momenta. The propulsive speed of a fish robot is determined from the difference of the propulsive force generated from pectoral fins, and the resistance force that the fish robot receives from the water when moving forward. The effectiveness of the proposed method is examined through numerical simulation and actual experimental results.

Underactuated control for an X4-AUV using partial linearization and attitude linearization

An autonomous underwater vehicle with four thrusters is reexamined from the viewpoints of derivation of a time-varying model. First, a bilinear model can be derived without depending on a chained form transformation, instead depending on partial linearization in inputs and on linearization of partial attitudes. Next, it can be transformed into a time-varying system that includes partially discontinuous states, and then an exponentially stabilizing method can be applied to its model to solve a stabilization problem. Some numerical simulations are conducted to demonstrate the effectiveness of the proposed method.

Tip-over stability control for a holonomic omnidirectional mobile robot with active dual-wheel caster assemblies using SGCMG

In this paper, we present the tip-over prevention technique using a control moment gyro for a holonomic omnidirectional mobile robot with active dual wheel caster assemblies. With concern to the sudden dynamic changes during maneuver, the dynamical model is derived and used together with the force-angle stability measure (FASM) to estimate the tip-over incident and the tipping direction. A single gimbal control moment gyro (SGCMG) is proposed to counter the instability by producing a precession torque in the opposite direction of the estimated tip-over direction. Simulation results are given to demonstrate the performance of this approach.