Junji Oaki

A collaborative multi-site teleoperation over an ISDN

Abstract We have developed an advanced infrastructure and technologies for collaborative remote operations, enabling multiple operators with large physical separation to control multiple slave robots in a common environment over the network. Human operators’ delayed visual perception arising from communication time delays seriously affects the performance of collaborative multi-site operations and accordingly requires supplementary information locally available to operators irrespective of time delays. Few facilities exist to investigate remote multi-site operations, thus we have built an experimental test bed connecting Tsukuba and Kawasaki in Japan via an integrated services digital network. In particular, an on-line predictive graphics simulator is incorporated to cope with image feedback delays from the remote site. Specifically, exploiting audio-visual features of the simulator, operators can detect a priori the possibility of collision between robots and guide them towards task goal through time delays. To verify the validity of the simulator assisted approach, we have performed a demonstration of prototype plant maintenance in April 2000 between Tsukuba and Kawasaki.

High-speed object tracking in ordinary surroundings based on temporally evaluated optical flow

This paper describes an active camera system for high-speed object tracking. Under ordinary illumination, such as fluorescent lights, our system is capable of tracking an object in a typical indoor environment that contains a cluttered background. In order to accomplish this task, we developed a high-sensitivity high-frame-rate visual sensor system and a real-time object tracking algorithm that makes use of our previously proposed motion estimation technique, which is capable of robustly estimating optical flow in a high-frame-rate image sequence. The experimental results for our active camera system show the effectiveness and robustness of our visual sensor system and tracking algorithm.

Robot control strategy for in-orbit assembly of a micro satellite

We have developed novel heuristic control strategies for fitting parts with almost no clearance and also dealing with flexible objects using visual and force feedback. We have applied these control strategies for micro satellite assembly tasks of a ground research model of an in-orbit maintenance robot system. For the in-orbit maintenance system, micro satellites should be modularized as much as possible. The in-orbit maintenance system needs to assemble the modularized parts into micro satellites. We have developed a ground research model including a two-armed robotic platform and modularized micro satellite models. To assemble a micro satellite model, two problems arise: one is to engage two parts into a tight fit and the other is to handle flexible parts. We use a heuristic approach to solve the first problem — to grope one part to find the entrance of engagement of the other and to wobble this part to make a tight fit. For the second problem, visual measurement of the parts is used to position the end-effector of a robot arm and also active limp control is extensively used to adjust any misalignment that arises from the visual measurement error. With the combination of the heuristic, visual and active limp control, the system can successfully assemble a micro satellite.

Decoupling Identification for Serial Two-link Robot Arm with Elastic Joints

Abstract The objective of our study is to build a precise model by applying the technique of system identification for the model-based control of a nonlinear robot arm, taking joint-elasticity into consideration. This paper proposes a systematic identification method, called “decoupling identification”, for a serial two-link robot arm with elastic joints caused by the Harmonic drive® reduction gears. The proposed method serves as an extension of the conventional rigid-joint-model-based identification. The robot arm is treated as a serial two-link two-inertia system with nonlinearity. The decoupling identification method using link-accelerometer signals enables the serial two-link two-inertia system to be divided into two linear one-link two-inertia systems. The MATLAB®s commands for state-space model estimation are utilized in the proposed method. Physical parameters such as motor inertias, link inertias, joint-friction coefficients and joint-spring coefficients are estimated through the identified one-link two-inertia systems. Experimental results using a SCARA-type planar two-link robot arm with elastic reduction gears showed an accuracy of the proposed identification method.

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.

Stable force controller design based on frequency response identification

Proposes a method of stable force controller design for robotic manipulators based on frequency response identification. The force controller described falls into the hybrid controller category. Force control loops are added to a popular position controller, enabling position control loops and force control loops to be designed independently. The proposed method does not require a detailed model of manipulator and environment dynamics. It is, therefore, robust enough for unmodeled dynamics, and easily analyzes stability in the high frequency region using the phase and gain margin method. The frequency response is identified by an accurate method called multi-decimation (MD), using motor input and contact-force output data. The MD method was previously developed by the author. The force control parameters (i.e. PID feedback parameters) are calculated by a stable design method called partial-model-matching (PMM), using the identified frequency response. The effectiveness of the proposed design method is demonstrated, through some experimental results, including a tracing task along a stiff environment, carried out using a planar two-link manipulator with harmonic drive gears.<<ETX>>

Grey-box Modeling of Elastic-joint Robot with Harmonic Drive and Timing Belt

Abstract We previously proposed a multivariable identification method, called the “decoupling identification method”, for a horizontal two-link robot arm with elastic harmonic drive gears. This paper extends the identification method to a vertical two-link robot arm with the harmonic drive gears and timing belts, under gravity. The mechanical resonance effects of the timing belts in the high-frequency range are decimated in advance, to apply the decoupling method. The characteristics of the timing belts are independently estimated as perturbations in the high-frequency range for robust controller design. The effectiveness of the extended identification method was experimentally verified using the vertical two-link robot with the elastic elements.

Decoupling Identification Method of Serial Two-Link Two-Inertia System for Robot Motion Control

Abstract The goal of our study is to obtain a precise dynamic model by applying the technique of system identification for the model-based control of a nonlinear robot arm, taking joint-elasticity into consideration. We previously proposed “decoupling identification method” for a planar serial two-link robot arm with elastic-joints caused by the Harmonic-drive reduction gears. First, this paper reviews the decoupling effectiveness of the proposed identification method. This method serves as an extension of the conventional rigid-joint-model-based identification, and treats the robot arm as a serial two-link two-inertia system with nonlinearity. The main idea of the decoupling method is nonlinear interaction torques between two links are utilized as identification inputs besides motor inputs. The torques can be computed using the rigid-joint-model parameters and link-accelerometer signals, and enable the serial two-link two-inertia system to be divided into two linear one-link systems. Typical multi-input multi-output linear model estimation algorithms can be applied for the identification method. Physical parameters such as motor inertias, link inertias, joint-friction coefficients and joint-spring coefficients of the dynamic model are estimated by applying the coefficient comparison method to the transfer functions of the one-link two-inertia systems. This is a gray-box modeling approach. Second, this paper extends the proposed method to closed-loop identification from open-loop identification. Thus the method is applicable for not only a SCARA (Selective Compliant Assembly Robot Arm) but also a PUMA (Programmable Universal Manipulation Arm) under gravity. Third, this paper unveils the robustness of the decoupling method against estimation errors of coupling-inertia parameters for computing nonlinear interaction torques; these parameters are obtained by the conventional rigid-joint-model-based identification. Several experiments using the planar serial two-link robot arm with elastic-joints are conducted to demonstrate the effectiveness and robustness of the decoupling identification method.

Plug-in feedback using physically parameterized observer for vibration-suppression control of elastic-joint robot

This paper proposes a plug-in feedback scheme for vibration-suppression control of a serial two-link robot arm with joint elasticity due to the Harmonic-drive gear. The serial two-link arm simulates the 1st and 2nd joints of the SCARA (Selective Compliance Assembly Robot Arm)-type robot or the 2nd and 3rd joints of the PUMA (Programmable Universal Manipulator Arm)-type robot. In order to suppress the arm-tip vibration of both robot types, it is important to control the basic two-link arm. We propose a torsion-angular velocity feedback (TVFB) scheme, which can be plugged into existing joint servos (PI velocity controllers), using a nonlinear state-observer based on a physically parameterized dynamic model of the serial two-link robot arm. Physical parameters of the elastic-joint model are accurately estimated by the “decoupling identification method” previously proposed by the authors. The feedback gains of the observer are set identical to the PI gains tuned for the existing joint servos. Thus the nonlinear observer, which estimates the torsion-angular velocity, is designless. Also, simple gain-scheduling scheme with few hand-tuned state-feedback gains is implemented for the TVFB, taking the arm-posture and payload changes into consideration. We just have to manually tune the few state-feedback gains. Several experiments are conducted to demonstrate the effectiveness of the TVFB using the serial two-link robot arm.

Advanced mask inspection optical system (AMOS) using 198.5-nm wavelength for 65-nm (hp) node and beyond: system development and initial state D/D inspection performance

A novel high-resolution mask inspection platform using DUV wavelength has been developed. This platform is designed to enable the defect inspection of high quality masks for 65nm node used in 193nm lithography. In this paper, newly developed optical system and its performance are reported. The system is operated at wavelength of 198.5nm, which wavelength is nearly equal to 193nm-ArF laser exposure tool. Some defect image data and defect inspection sensitivity due to simulation-base die-to-die (D/D) inspection are shown on standard programmed defect test mask. As an initial state D/D inspection performance, 20-60 nm defects are certified. System capabilities for 65nm node inspection and beyond are also discussed.