Nobuyuki Furuya

Motion control of parallel manipulator using pneumatic artificial actuators

In this paper, we describe the motion control of a parallel manipulator with two degrees of freedom. The parallel manipulator uses three pneumatic artificial actuators. We adopted the minimum number of pneumatic artificial actuators that are required to move a joint with two degrees of freedom because this manipulator is applied to the joint of a robot hand. It is known that the relationship between the inner pressure and contraction ratio of pneumatic artificial actuators is highly nonlinear and includes a hysteresis characteristic. Therefore, in this study, we perform motion control using a control system with integrated hysteresis compensation.

Easy calibration of camera-projector system using geometrical invariants

The projector is a projection equipment while the camera is a optical receiver. Hence, the camera can project three dimensional calibration points to an image, but it is difficult that the projector grabs the three dimensional calibration points. Therefore, it is necessary to devise obtaining the calibration points to calibrate the projector.

Control of pneumatic actuator in consideration of hysteresis characteristics

Recently, robots not only have been researched and developed actively but also have replaced humans in several fields such as medical treatment and nursing. For robots to coexist with humans and provide support, they must have human-like dexterity and should be very safe. Therefore, pneumatic actuators are used to develop safe and lightweight robot hands. However, the relationship between the internal pressure and contraction ratio of pneumatic actuators is nonlinear, with a hysteresis characteristic and a dead zone. Moreover, the nonlinear characteristics of pneumatic actuators change with the applied load. In this study, we proposed a hysteresis model that can express the change in these hysteresis characteristics, and we constructed a control system that integrated this hysteresis compensation by using the proposed hysteresis model.

Superquadrics model recognition from stereo image

This paper presents the process of recognition of the three-dimensional object and calculation of similarity. The object is recovered from stereo image and superquadrics function is used as the model. The superquadrics is a parametric and volumetric model. It is represented by an expanded ellipse function. And genetic algorithm is used for recovering of an object shape. A fitness function of genetic algorithm is defined using texture features of object on the stereo image. The features are shared area and difference of intensity among the left image and the right image. Parameters of superquadrics which are replaced by parameters of genetic algorithm are optimized and the superquadrics form fits to a solid body object. In the case of multiple body objects, the object is divided on the image, and each solid body is recovered. The objects used in the experiment are a cube, a cylinder and an elliptic column. The algorithm is useful for the recovery of the object under stereopsis. After recovery, the similarity between the recovered object and the model in the computer is calculated.

Study on Articulated type 3D Robot Teaching Machine (2nd Report)

An articulated type 3D robot teaching machine has been developed. This teaching machine has 6 degrees of freedom. It can produce the 3D coordinate data and orientation data of robot end effector. On the robot teaching task, easy operation and dexterity of the teaching machine is necessary to the teaching operator. The articulated type machine satisfies these requests but the accuracy is less than that of the Cartesian type machine, so the precise calibration is necessary to the articulated machine. On the 1st Report a calibration process was proposed but disregarded factor of error was found out. In this 2nd Report, we analyze the new factor of the measuring error and we have discovered the effect of the flexible coupling used in the teaching machine is very important. The measuring error of the teaching machine decreases about 1.0 mm to 1.3mm when the coupling is exchanged.

Study on Articulated type 3D Robot Teaching Machine. (1st Report). Basic Error Model Analysis and Development of Calibration Procedure.

This paper describes about the kinematic error model and calibration procedure of the 3D robot teaching instrument. 3D teaching operation, using a real robot is not efficient work. The 3D teaching instrument has been developed for the robot teaching tasks. Articulated type teaching instrument has high mobility, but it is necessary to calibrate precisely to realize high positioning accuracy. In this report a method to identify the base point of measuring coordinate system and offset angle of the joint, numerically by Powell method is proposed. A calibration method of link parameter errors, using the SVD (Singular Value Decomposition)is presented. By the experimental results, this calibration procedure is proved.

A Study on Stiffness Analysis of Parallel Mechanism-Stiffness Characteristics near the Singular Point.

Parallel manipulators have many useful characteristics, that is high speed motion as the inertia is light, rigid structure and full 6 degrees of freedom. There are many different type parallel manipulators. Stewart platform. is the most typical type which has 6 linear actuators called struts, A new type parallel manipulator named PSSP has been proposed, which is moved with three pentagon type SCARA robots. Parallel manipulators have many singular points in the working space, on the points the stiffness of the structure becomes zero. It is very important to study the location of singular points and characteristics. The standard approach of the study on singular points is to find the zero points of jacobian matrix determinant. In this study a new approach to analyze the singular configuration of parallel mechanism to resolve the eigenvalue and eigenvectors of stiffness matrix. PSSP robot is analyzed by the method.

Study on an Evaluation Process of Robot Control Accuracy. (2nd Report). Quantitative Estimation of Robot Tool Point Error on CP Control.

In the robot control, many factors such as the control accuracy of servo motors, stiffness of the arm mechanism and the performance of the control algorithm have influence to the total accuracy of robot motion. So it is necessary to evaluate quantitatively the total control accuracy under such influences. Especially, in the Continuous Path control the error of the tool point path becomes larger in proportion to the motion speed. In the previous first paper, Multivariate Root Mean Square criterion is proposed and applied to estimate quantitatively the control accuracy of the robot and examination of quantized velocity and sampling period is executed. In this report the method is applied to evaluate the control accuracy of tool point path in CP motion and an estimation formula to calculate the tool point error from the deviation of joint deviation is introduced. Experimental results of SCARA type robot in circular interpolation are shown.