Fine Motion Mechanism Research Articles

High-precision machining by measurement and compensation of motion error

This paper describes a systematic method to model and compensate geometric errors of machine tools. In order to separate geometric errors from other errors, measured errors are analyzed in the frequency domain by using the Fourier series. Then, the frequency components corresponding to geometric errors are selected based on the repeatability of their wavelength. Finally, the components are reconstructed and forwarded for the compensation by a fine motion drive. A CNC machine tool with a fine motion mechanism on the Z-axis was developed to compensate the error components in the Z direction on the XY plane. A flat surface machining with non-rotational cutting tools was tested to validate our approach. On the plane of 45 mm×70 mm, the fluctuation of the relative displacement was reduced from 1.3 to 0.5 μm P-V. Machining experiments with a single-crystal diamond tool were also carried out and the straightness of the profile curve was reduced from 1.0 to 0.4 μm. The result of the experiments showed that the geometric errors were compensated separately from the vibration due to the bending mode of the machine column.

High-precision Machining by Measurement and Compensation of Motion Error

Abstract This paper describes a systematic method to model and compensate geometric errors of machine tools. In order to separate geometric errors from other errors, measured errors are analyzed in the frequency domain by using the Fourier series. Then, the frequency components corresponding to geometric errors are selected based on the repeatability of their wavelength. Finally, the components are reconstructed and forwarded for the compensation by a fine motion drive. A CNC machine tool with a fine motion mechanism on the Z-axis was developed to compensate the error components in the Z direction on the XY plane. A flat surface machining with non-rotational cutting tools was tested to validate our approach. On the plane of 45 mm×70 mm, the fluctuation of the relative displacement was reduced from 1.3 to 0.5 μm P-V. Machining experiments with a single-crystal diamond tool were also carried out and the straightness of the profile curve was reduced from 1.0 to 0.4 μm. The result of the experiments showed that the geometric errors were compensated separately from the vibration due to the bending mode of the machine column.

Development of a High Precision Mounting Robot System With Fine Motion Mechanism(3rd Report). Positioning Experiments of SCARA Robot with Fine Mechanism.

In our previous work, robust control structure based on disturbance observer for a fast and precise fine motion mechanism has been proposed. The functionality of the controller was verified using one axis of precise X-Y table combined with-one axis fine motion mechanism. As a further step in this paper, the approach is extended to two-axes fine motion mechanism with a SCARA robot as a real system to realize the final purpose, that is, the development of high-precision mounting robot. First, the paper introduces a high performance robot system based on a SCARA robot coupled with a fine motion mechanism which was developed in our laboratory. Second, the paper presents a control scheme that enables correction of possible offsets of the end-effector relative to the target and compensation of the oscillations at the end-point. Finally, experimental results show significant improvements in end-point accuracy and settling time achieved by the novel configuration of the coarse/fine robotic system. As a result, a repeatability (3σ) less than 2 μm and the CP positioning error (3σ) less than 4.0 μm were achieved by the coarse/fine robotic system.

粗微動高精度実装ロボットの開発 １ ２軸微動機構の開発

A high precision mounting robot system consisting of SCARA robot and fine motion mechanism attached to the end effector of the robot is being developed by authors, This paper introduces basic concept and design specification of the system, and describes the design and capability of developed X-Y axes fine motion mechanism for this purpose in details. Developed fine motion mechanism is composed of piezo-electric actuator and displacement magnifying mechanism with elastic hinge. Detailed structure of the mechanism is designed by simulation based on FEM. Experimental results of positioning show the effectiveness of developed fine motion mechanism.

パラレルメカニズムを用いた６自由度精密運動機構 続報 試作機の性能評価

This study proposes a six-degree-of-freedom fine motion mechanism with isotropic stiffness and positioning resolution in XYZ directions. In the previous report, the optimum link layouts with the above characteristics have been designed by the singular value decomposition. In this paper, construction and experimental results have been described for the designed parallel mechanism. The stiffness values in translational directions and in aβ directions became equal. The stiffness value in γ direction, moreover, was two times those in γβ directions. The maximum movements of the stage were 10μm in XYZ directions. 200μrad in aβ directions and 100μrad in γ direction. The positioning errors and the motion errors were less than ±0.08βm and ±l.0μrad. The dynamic characteristics in six directions were equal under 1-50Hz frequency range.

Development of a High Precision Mounting Robot with Fine Motion Mechanism. (2nd Report). Control of the Fine Mechanism Considering Dynamic Response and Disturbance from Coarse Mechanism.

This paper presents a controller structure for a fast and precise fine positioner which can be attached to the end-effector of a classical industrial robot for assembly tasks. The overall control system consists of three elements: a position loop feedback controller, a feedforward controller, and a disturbance observer for the position loop. A useful method for compensating for the asymmetry and non-linearities of the piezoelectric based system is used as the first step in the design process. The robust feedback controller based on the disturbance observer compensates for external disturbances mainly from the coarse positioner. Precise tracking is achieved by the feedforward controller. Experimental results are presented to demonstrate performance improvement obtained by each element in the proposed robust structure.

圧電素子駆動レーザトラッキングステーションを用いた高精度空間座標測定システムの開発 （第１報） 微動トラッキングステーションの開発と性能評価

Recently, it is required to improve the production efficiency and accuracy in the manufacturing factories, where many robots and manipulators are used. Therefore, it is required that the development of measuring method for position and attitude of moving objects with high accuracy. The main purpose of this study is to establish spatial coordinate measuring method using laser tracking station. In this method, spatial coordinates are calculated by the principle of triangulation from rotational mirror angles. However, the measuring accuracy of this method depends greatly on the mirror angle resolution. Thus, the laser tracking stations are combined with coarse and fine rotational mechanisms to achieve high accuracy spatial coordinate measurement over the wide range and dynamic measurement by using rapid-controlled-mirrors. The aim of this report is to realize the measurement error within 10μm in l×l×1m3 working space which is a common requirement in manufacturing industry. As the first step, the fine motion mechanism with a two degree-of-freedom was developed. In order to track laser beams to the targets attached on the moving object, the three piezoelectric actuators control mirror angles with high speed and high accuracy. Operating the fine motion unit, the measurement error was less than 10μm for both one- and two-dimensional coordinates measurement with the distance of 1000mm between tracking station and target or more. It was confirmed that the measuring system was applicable for the manufacturing industries.

Characteristics of Motional-Mode-Based Positioning for a Fine-Motion Mechanism.

In order to realize high-speed positioning, we previously proposed acceleration feedback for a three-degrees-of-freedom fine-motion mechanism with piezo elements. Its superior performance was illustrated by the experimental results. In this experiment, a motional-mode-based decoupling control scheme was adopted. As is well known, the motional-mode selector and motional-mode distributor matrices, which are calculated using the displacement of both sensors and actuators, are inserted in to the decoupling control loop. However, it is difficult to determine these matrices uniquely. Thus, in this paper, a method to derive these matrices is presented which coincides with the initial condition of the compensator gain of an individual control system for comparison. In addition, the characteristics of motional-mode based positioning are shown in the experimental results.

圧電素子を用いた高剛性多自由度微動機構 (第2報)

圧電素子を用いた高剛性多自由度微動機構 (第2報)

A robotically assisted munition loading system

AbstractDue to the reliance upon manual operations, conventional loading of munitions on tactical arcraft has several deficiencies including inefficient manpower and time utilization; accident potential; exposure of crew members to chemical, biological, and nuclear agents; and visual obstruction. This article reports on the research and development of a full‐scale prototype robotic system called Robotically Assisted Munition Loading System (RAMLS) comprising a fine motion mechanism (FIMOM), a pose acquisition device (PAD), a manual controller, and a data acquisition and computing system. The FIMOM is a six‐degree‐of‐freedom (DOF) parallel mechanism driven by six hydraulic actuators and the PAD is a passive open kinematic chain mechanism having 6 DOF. The article describes the design and functions of the RAMLS components and presents results of experiments conducted to evaluate the RAMLS's performance. © 3995 John Wiley & Sons, Inc.

Modeling of Three-Degree-of-Freedom Fine Motion Mechanism and Improvement of Control Performance.

As miniaturization of exposure patterns progresses, high positioning accuracy of submicron order is necessary for the semiconductor components. Moreover, in order to transcribe the circuit pattern to multiple positions on an IC wafer, a positioning mechanism with long stroke also must be developed. This paper focuses on the former. By driving the piezo actuators mounted under the flat plate, this mechanism has a positioning function with 3 degrees of freedom. This paper first describes a mathematical model of a fine motion mechanism with 3 d. o. f., and we confirm the adequacy of the control model by comparison with the measured frequency response. Secondly, both static and dynamic decoupling conditions for the controlled object itself are derived, and we show that this conditions are equivalent to that of the center of percussion. In the case of control for the positioning mechanism with multi-d. o. f., the matrix inversions are generally inserted into the control loop to cancel the interference based on the space assignment of both the position sensors and actuators. However, if the controlled object can be kinematically decoupled by the mechanical design, it is unnecessary to construct the complex control loop. Finally, we propose acceleration feedback in order to improve the control performance, and its superior performance is illustrated by the numerical simulation.

圧電素子を用いた高剛性多自由度微動機構

In this paper, a new five-degrees-of-freedom fine motion mechanism whose rigidity is high is proposed, and the construction and the experimental results are also described for the characteristics of newly developed three-degrees-of-freedom mechanism. This mechanism comprises three wedge-shaped plates and six multi-layered piezoelectric actuators. The mechanism which requires neither guide plane nor lubrication enables it to move without any friction, wear and badklash. The maximum movements of the stage were 3 μm in X-direction, 12μm in Z-direction and 12 second of arc in β-direction. The positioning resolutions in the translational and rotational directions were less than 0.01μm and 0.01 second of arc, respectively. The loading capacity was 400N. The positioning errors and the motion error were less than ±0.01μm and ±0.03 second of arc. 1 μm step positioning in X-direction interfered with other directions transiently because of difference of the contraction and expansion velocities of the piezoelectric actuators.

6自由度微動機構の研究 (第3報)

6自由度微動機構の研究 (第3報)

６自由度微動機構の研究

６自由度微動機構の研究

The ultraviolet microscope.

A form of ultraviolet microscope of the refracting type is described in which the source of radiation is a spark gap between fixed or rotating electrodes and the objectives are normally monochromats. The microscope is horizontal, thus avoiding the use of a mirror, and the fine motion mechanism responds to movements of 0.10 micron. Phase contrast may be used for visual scanning of the object and also for photography in the ultraviolet.The source of radiation can be supplied as a separate unit and used in conjunction with metallurgical microscopes of normal type to enable photographs of opaque objects to be taken in the ultraviolet.Some examples of microphotographs taken with the equipment described are appended, together with particulars.