The stage, using new mechanism called viscous-elastic unit, is proposed to improve accuracy and acting time of positioning, and the effects are examined experimentally. In this mechanism, a stage is supported by flexure hinges, and damping force is given by squeeze film of silicon oil instead of conventional sliding friction. When the stage moves for a long distance, a supporting part of the viscous-elastic unit slides along a guide, and maximum damping force is limited by sliding friction. In this paper, the viscous-elastic units have been added to a conventional one-axis stage mechanism driven by a ball screw. Positioning has been carried out with a closed-loop control system using a laser measurement system. The experimental results indicate that the viscous-elastic unit can reduce the peak more than 20dB on Bode diagram, and this system is capable of positioning the stage with an error less than 1Onm in 350ms acting time, when the mass of stage is 18kg and moving distance is 20mm.
A new guide mechanism called ' Viscous-Elastic Guide' is introduced in this paper. The viscous-elastic guide consists of flexure hinges and a squeeze damper, so the damping factor of the positioning mechanism using the introduced mechanism is adjustable. Single-axis positioning mechanism with the viscous-elastic guide, driven by a ball screw, has been constructed as experimental system, and its damping factor is optimized. Positioning experiments indicate that mechanical damping factor optimization improves the positioning control performance. The improved performance for a 20mm step input are as follows. (1) The average positioning time is 362ms. (2) The positioning accuracy is within 10nm.
The positioning mechanism can be regarded as a simple vibration system with one degree of freedom. Generally speaking, it is difficult to identify the physical parameters of this mechanism without decomposing. In this paper, an identification method of physical parameters for positioning mechanism is described. Firstly it is shown that the viscous damping of slide mechanism can be derived by measuring the frequency response from the collocated sensor to the non-collocated sensor. Moreover, the spring constant between the mechanisms also can be derived more accurately in comparison with the value based on the impulse response. Secondary the equivalent viscous damping is calculated by means of the constant velocity test or the frequency response. Then the viscous damping of rotational mechanism may easily be derived by subtracting the converted viscous damping, which is the value of slide mechanism at the position of motor axis, from the equivalent viscous damping. Finally, the proposed identification method is applied to an actual positioning mechanism.
Due to the difficulties of measuring technique for the whole spherical surface, a concrete three-dimensional verification is not yet developed. This article deals with calculation of the value of spherical form errors, that is sphericity. The iterative least squares method in which the problem is linearized, and the minimum zone method in which the downhill simplex method, one of the nonlinear optimization technique, is applied are considered. The data to be referred is not obtained by actual measurement of spherical surface but simulated by using surface harmonics (Laplace's spherical function) in a computer. Then, their application conditions are investigated. Furthermore, the roundness values of the spherical surface are compared with the sphericity by means of the present method of this article.
The aim of this research is to develop the air rotary bearing which has the following capability: (1) compensation of motion errors of the axis (high accuracy), (2) reduction of motion errors and residual vibrations which external disturbances cause (high stiffness and high vibration damping), (3) control of five degrees of freedom axis motion of the rotating axis (new function). To realize these, the authors propose an "Active Air Rotary Bearing" #(AARB). The AARB comprises an axis, two active air journal bearings which consist of four non-contact actuators and two non-contact sensors and an active air thrust bearing which consists of a non-contact actuator and a non-contact sensor. The AARB can support and drive the axis using the non-contact actuators. This paper describes the principle of the AARB and the identification of dynamic parameters. The models used for the identification are simple and the frequency responses of dynamic models agree well with those of an experimental mechanism.
An NC program simulator has been developed for evaluating productivity in NC lathe turning. Machining information about cutting parameters, tool paths and operating time are retrieved from an NC program by the simulator. These information are very useful in order to evaluate productivity in NC lathe turning. A total of 193 NC programs from 29 manufacturing companies are investigated their productivity by comparing the percentage of jog feeding time during turning operation. The result of the investigation shows that the jog feeding time occupies about 80% of total operation time on an average of 193 examples. The simulation of the revised NC programs using the touch and cut method which eliminates an air-cut travel during jog feeding shows that the operation time of the NC program can be reduced about 6% on an average. The cutting test for estimating tool life proved that the touch and cut method does not reduce the tool lifetime under the experimental cutting condition.
The present study investigates the influence of three-dimensional tool geometry upon the cutting mechanism of a 18%Mn-5%Cr steel with a P 20 carbide tool, where the computer simulation method proposed in the previous paper has been employed. The three-dimensional simulation has revealed that the physical background of empirical knowledge such that a larger corner radius is recommended for difficult-to-cut materials for large work-hardening and low thermal conductivity; the increase of the radius causes a large chip-flow angle and small undeformed and deformed chip thicknesses at the corner, leading to the decrease in the deformation and the drop of temperature. As a result, not only wear at the corner but also the influence into the finished surface is lessened. Experiments have validated the simulation results: both predicted and measured cutting forces, chip geometry, tool temperature and tool wear accord well with each other.
For finding new in-process monitoring methods of tool function, the present paper treats about constraint effects of tool wear on transient vibration generated by calibrated force in turning operations. The definite impulse force in feed direction is made by hammering on the side face of the tool with a pendulum. The impulse is always calibrated with a piezoelectric force sensor located on the hammer. The tool vibration is detected with an acceleration sensor. The power-spectrum of the transient vibration is carefully examined for seeking correlation with flank wear. Similary, impulse in powerforce direction is also tested. Major findings of the study are as follows : 1) The first mode of resonance frequency f1 of the tool is mostly dominant in the power-spectrum, and the amplitude of f1 has fairly close correlation with flank wear. 2) Correlation between vibration in power-force direction and flank wear is also verified. 3) It is confirmed that the effect of the impulse on the machined surface is negligibly small.
Cutting conditions have an effect on machining efficiency, machining cost and machining time. Thus, a multitude of methods have been proposed to determine the optimum cutting conditions. But each in itself is specific and has limited applicability to the situation for which it was devised. Hence, it may be said that the cutting conditions which are led from those methods are only subconditions in the machining scene. On the other hand, the skilled machinist can continuously adjust operations in terms of machining efficiency, machinability and cost. This adjustment is done by means of cutting conditions. In this paper, the system is proposed to simulate the machinist's thinking process which set the appropriate cutting conditions based on evaluation of cutting state. The thinking process is constructed by fuzzy integral and hill-climbing. The accuracy of the system's output was examined by the experiments under various cutting conditions in turning, and the validity of the system was confirmed.
In order to enlarge industrial application of the ultra-precision metal cutting technique by single crystal natural diamond tools, a fundamental study to develop the ultra-precision machine tool with high cost performance is carried out. A newly developed air spindle unit is constructed compactly, and is driven by a built-in motor directly. In this paper, experimental results of rotational accuracy are presented. Vibration induced by magnetic attraction at the motor dominates the rotational accuracy. It is useful for reduction of the vibration to balance the magnetic attraction between the rotor and the stator. It is necessary to adopt a supplying voltage with an ideal sine wave for further improvement of rotational accuracy.
This paper deals with some theoretical and experimental investigations on a new forming of metallic corrugated diaphragms. In this method, both the blank and die are fixed to the end of the main spindle of a drilling machine, and the punch with several steel balls are set under them. When the blank revolves down and touches the punch, the steel balls are rolled and the blank are formed with the normal force P and the tangential force T. The principal force used for shaping corrugated diaphragm in this forming is the P. T is spent mainly for sending a circular blank and the deformation process of corrugated thin metallic plate for circumferential direction is caused by the bending and bending restoration of blank. Introducing the contact-coefficient m for evaluate the formability of corrugated diaphragm and analyzing the mechanism of forming process the theoretical value nearly coincides with the experimental one.
This paper presents a new generating method of an offset surface on which a milling tool path moves. It consists of three steps; 1. A workpiece and an end-milling tool are represented by 2.5 dimensional lattice space model, enhanced Z-map model. 2. The calculation of a center position of the tool is done through the detection of a nominal cutting point in the geometric simulation. Namely the sum of a height of the workpiece at a lattice point of the XY domain and that of the tool at the same point in scanned at all over the lattice point of the covering area of the tool. This successive locus of the tool center coincides with an offset surface. 3. If a geometric machining error due to a tool path generation is estimated to be over a tolerance, lattice pitches of the XY domain are binary subdivided hierarchically. Then Step 2 is carried out based on the new lattice pitch till the satisfaction of tolerance requirements. Through the comparative simulation with the inverse offset method, the proposed method performed the improvement of processing time and a small memory size. The conclusions are briefly mentioned too.