Michihiro Uenohara

Vision-Based Object Registration for Real-Time Image Overlay

This paper presents computer vision based techniques for object registration, real-time tracking, and image overlay. The capability can be used to superimpose registered images such as those from CT or MRI onto a video image of a patient’s body. Real-time object registration enables an image to be overlaid consistently onto objects even while the object or the viewer is moving. The video image of a patient’s body is used as input for object registration. Reliable real-time object registration at frame rate (30 Hz) is realized by a combination of techniques, including template matching based feature detection, feature correspondence by geometric constraints, and pose calculation of objects from feature positions in the image. Two types of image overlay systems are presented. The first one registers objects in the image and projects preoperative model data onto a raw camera image. The other computes the position of image overlay directly from 2D feature positions without any prior models. With the techniques developed in this paper, interactive video, which transmits images of a patient to the expert and sends them back with some image overlay, can be realized.

Use of Fourier and Karhunen-Loeve decomposition for fast pattern matching with a large set of templates

We present a fast pattern matching algorithm with a large set of templates. The algorithm is based on the typical template matching speeded up by the dual decomposition; the Fourier transform and the Karhunen-Loeve transform. The proposed algorithm is appropriate for the search of an object with unknown distortion within a short period. Patterns with different distortion differ slightly from each other and are highly correlated. The image vector subspace required for effective representation can be defined by a small number of eigenvectors derived by the Karhunen-Loeve transform. A vector subspace spanned by the eigenvectors is generated, and any image vector in the subspace is considered as a pattern to be recognized. The pattern matching of objects with unknown distortion is formulated as the process to extract the portion of the input image, find the pattern most similar to the extracted portion in the subspace, compute normalized correlation between them at each location in the input image, and find the location with the best score. Searching for objects with unknown distortion requires vast computation. The formulation above makes it possible to decompose highly correlated reference images into eigenvectors, as well as to decompose images in frequency domain, and to speed up the process significantly.

Optimal approximation of uniformly rotated images: relationship between Karhunen-Loeve expansion and discrete cosine transform

We present the concept that for uniformly rotated images, the optimal approximation of the images can be obtained by computing the basis vectors for the discrete cosine transform (DCT) of the original image in polar coordinates, and that the images can be represented as linear combinations of the basis vectors.

Development of an advanced master-slave manipulator using a pantograph master arm and a redundant slave arm

A new master-slave manipulator (MSM) with different configurations and different degrees of freedom (DOF) has been developed. It consists of a general master arm using pantograph mechanisms and a seven degree of freedom slave arm with a redundant joint. Symmetric bilateral control using a virtual internal model and redundant arm control with a singular configuration are used to improve the maneuverability of the MSM. The developed MSM has been confirmed to have good maneuverability from basic experiments. This paper describes the mechanisms, control methods, and experimental results of the MSM.

Teaching-less robot system for finishing workpieces of various shapes using force control and computer vision

In the case of conventional industrial robot systems, operators have to write robot-language programs for each type of workpiece. This is an onerous task, especially when each workpiece has a different shape. We propose a teaching-less robot system for the finishing of two-dimensional workpieces of various shapes and thicknesses using force control and computer vision. The robot system does not require shape information for the workpiece to be included in the CAD data or to be input by the operator. Each workpiece shape is acquired by segmenting edges into straight lines and circular arcs from the image data of the workpiece. The robot-language program for each workpiece is generated automatically from the workpiece shape data and finishing condition data. The effectiveness of the proposed method is verified by experiments using a newly developed robot system. In the system, the robot picks up a workpiece whose shape is not previously known on the workpiece stand by itself and carries out the finishing tasks using the automatically generated robot-language program. This method provides a compact and inexpensive finishing robot system which reduces the programming and workpiece-setting burden on the operators.

The development of an autonomous space robot operation testbed: ASROT

We have developed a two-dimensional operation testbed for an autonomous free-flying space robot such as an orbital manoeuvring vehicle. This system has been named ASROT (autonomous space robot operation testbed). Basically, ASROT consists of a satellite robot, a target, a host computer, and a planar base. The host computer is used only for observation and data gathering of the system. The satellite robot is a satellite which can accomplish various tasks with a manipulator. The satellite is 620 mm (W) x 805 mm (H) x 620 mm (L), and weighs 120 kg. This system floats on a planar base using air pads, and is able to fly around using thrusters for position control and a control moment gyro for attitude control. The manipulator is a 1.4 m long flexible arm. This paper proposes an operating system needed for real-time autonomous control. The satellite robot contains hardware systems such as vision systems, board computers, and image processing units, and software systems such as algorithms for path planning.

Active vibration control of a multi-link space flexible manipulator with torque feedback

In this article, a new vibration control method for a space flexible manipulator is proposed from the viewpoint of practicability. An N-link SCARA flexible manipulator is considered. The features of the proposed method are as follows: (1) The control system basically consists of simple local feedback of the joint angle and joint torque. Therefore, it is easy to adapt this method for the construction of a controller with a sensor system in a practical system. (2) The asymptotic stability of this feedback scheme has been proved for a distributed system. (3) On the other hand, the proposed method is not an optimal control method because a dynamic compensator is not used. Therefore, this is a low authority control method. First the dynamics of a manipulator are derived by Hamiltons principle. Then the control method is derived based on an artificial potential. The stability of the proposed method has also been proved by the Lyapunov method for stability analysis. The validity of this method has been proved b...

Experimental Study on Autonomous Retrieval/Release of a Moving Payload by a Free-Flying Space Robot*

Abstract We proposed the strategy and control system of an autonomous satellite retrieval/release mission of a free-flying space robot with an attitude-controlled base. This mission consists of tasks of retrieving a moving payload, equipping parts with the payload, and releasing it on an orbit again. Our control system consists of position/attitude control of both a spacecraft and manipulators, reaction torque compensation for a spacecraft, and impedance control of a space manipulator. The effectiveness of this system was shown by the simulation experiment of performing this mission with a two dimensional operation testbed of a space robot equipped with thrusters and a control moment gyro. The complete mission was implemented successfully.

Vibration control for two-link flexible manipulator using a wrist force sensor.

This paper reports on the vibration control of a flexible space manipulator in which the tip deflection of each flexible link is fed back in a closed control system. A simple dynamic model is derived using the static deflection model to derive the system dynamics equations of a flexible manipulator. A force/torque sensor incorporated in the manipulators wrist is proposed as a new type of sensors to estimate the deflection. To investigate the effectiveness of this control method, a two-link flexible SCARA manipulator system was constructed. This manipulator was 1.5 m long and was floating on a base-plate using air bearings capable of handling a 40kg payload. The experimental results showed that the deflection feedback realized the same effect on the vibration control as the general method of strain gauge output feedback.