The typical failure modes of a bolt-nut assembly subjected to static overload are breaking at the bolt shank (free thread portion) and stripping of the bolt or nut mating threads. Standard nuts specified in ISO 898-2 and ISO 898-6 are designed based on "Alexander Theory" to avoid stripping failure mode by controlling the nut height. However, the applicability of the Alexander Theory has not been confirmed for bolt and nut (or screw and tapped hole) assemblies whose specifications are not perfectly conforming to ISO standards. This study deals with the loadability for such types of bolt-nut assemblies. Experimental investigation for critical nut height using staircase method and elastic-plastic FEM analysis considering face-to-face contact at mating threads and bearing faces are performed to establish the design rules for predicting the failure mode and the failure load. The results show that the stripping strength can be predicted with good accuracy by using the load and the shear area of individual mating threads and the shear strength of the material, and the Alexander Theory can be applicable for bolt and non-standardized nut assemblies by modifying the factor for nut dilation.
This paper proposes a new geometric Newton-Raphson method for dealing with a rational polynomial curve. The algorithm is robust and at the same time locally unique. Although rational polynomial curves and surfaces have become standard forms in computer-aided design, they have many problems. For example, a Newton-Raphson algorithm for dealing with a rational polynomial curve tends to be unstable. This is a fatal problem. We propose to homogenize the coordinates of a rational curve when it is applied to the Newton-Raphson algorithm. Then it becomes very robust. Furthermore the solution point becomes locally unique with respect to an initial parameter range when the parameter is also homogenized in addition to the coordinates, because with this technique we have a freedom of controlling parameter values and we can adjust the increment of the parameter appropriately.
This paper deals with process planning system based on machining process model. So far, the taxonomy of machining features, for example, hole, pocket, slot, etc. are shape based classsifications and it is difficult to assign the machining process information without competition of assignment rule. To solve this problem, the machining process modeling is needed for mapping between machined shape element and machining process.However, only tool behaviors are derived from giving the tool and the cutting motion to the machine tool. Therefore, the behavior model of cutting tool, working tool, to connect the machining operation and machined shapes are introduced. The working tool consists of the swept macro tool, the envelope of the swept macro tool, and the working edge. The feature model of the machining process, operating step, is also proposed from the viewpoint of a macro cutting tool, controled table motion, and enveloping constraints. To capture the essential information, the dimension of operating step and working tool are also proposed as the parameric representation of them.
This paper is to present a method for tracking an object by processing the image from a camera, whose attitude is controlled in inertial space with inertial coordinate system. In order to recognize the object, an M-array pattern is attached on the object and it is observed by a camera which is controlled on inertial coordinate system by inertial stabilization unit. As the attitude of the camera is detected by gyroscope and servo accelerometer of inertial stabilization unit, the image of M-array is observed in inertial coordinate system. Standard M-array is made from the photographed image by using camera of inertial coordinate basis. Taking the cross-correlation function between the observed image and the standard M-array image, we can recognize the angle position of the object from the gap between the peaks of the correlation function. We can obtain the line of sight angle of object on inertial coordinate system by adding the attitude angle of the camera and the angle position of the object. This line of sight angle is used for controlling attitude of camera on inertial stabilization unit. Thus the camera can follow up the object without being affected by attitude of carrier on which the inertial stabilization unit is equipped.
For a multi-joint robot, desired operations can be realized by dexterously controlling its link postures. Especially for a stance robot with multiple joints, it is possible to select a trajectory that consists of many link postures, each of which makes the load torque of all the joints as low as possible even with the limitation of no turnover. In this paper, based on the idea above, firstly the trajectories of a stance robot(3 axes) in the sit-to-stand and the squat-to-stand movements are generated with the only consideration of their static influences. Then their dynamic performances, which are obtained by adding an adjustable time interval in any two consecutive link postures are analyzed.
A method is proposed for estimating density of active mites in the media by processing microscopic mite images taken in successive order. An estimated background image of the scene has an important role for constructing a robust detector of object regions from the image sequence. One of the difficulty comes from the fact of co-occurence of media motion with mite motion. Then a mathematical model for calculating mite density is described, which utilize the area obtained by the detector and an estimator of response area corresponding to mite motion. The experimental results show the effectivity of the proposed method.
The feasibility for fabricating a magneto-optical rotary encoder (MO encoder) has been shown in our previous paper. In this paper, an error corrected recording method to improve accuracy of the MO encoder is described. The recording method utilizes one feature of MO encoder, that is, ability for re-recording. First, an initial recording is made directly from referential encoder to MO encoder and angular errors of the MO encoder are measured. According to the errors, correcting values for canceling the errors are calculated based on Fourier components analysis. Finally, the MO encoder is re-recorded by the correcting values after erasing the initial recording. As the result of experiments, an accuracy of 1.3" for 2250 pulse/rev. and 1.7"for9000 pulse/rev. was achieved by using the error corrected recording method.
This paper describes a surface motor-driven XYθz stage equipped with a newly developed surface encoder as the position-detection sensor. The stage consists of a moving element, a stage base, a surface motor and a surface encoder. The surface motor is composed of four linear motors (two pairs in XY-axes). Translational motions in XY and the rotational motion θz around Z-axis of the moving element can be generated by the surface motor. The surface encoder consists of a two-dimensional angle sensor and a two-dimensional angle grid. The angle sensor is fixed on the stage base and the angle grid is mounted on the back of the moving element. The multi-axis position of the moving element can be obtained from the angle sensor output. The surface encoder is placed inside the stage and the stage system is very compact in size. The range of travel of the stage is designed to be 40mm x 40mm x 24deg. Experimental results in XY axes are reported.
The aim of the paper is to propose a magnetic abrasive finishing process that simultaneously finishes of all the surfaces of fine ceramic step features by the flexibility in the abrasive behavior. In a magnetic field, the magnetic abrasive is suspended by magnetic force along the lines of the magnetic force, making abrasive chains that have flexibility to general shape. Introducing a nonferrous, such as fine ceramic, step feature component into the abrasive chains causes the abrasive to be displaced aside the component. Using the flexibility of the abrasive behavior, the reconfigured chains acts against all the surfaces of the component and finishes all the surfaces of fine ceramic step features simultaneously. This study demonstrates the uniform roughness improvements, 8μmRy to 0.5μmRy, of all the surfaces of a Si3N4, ceramic step roller (20mm outer diameter, 5mm step of 10mm width).
An injection mold which has inside water cooling channels has been fabricated using selective laser sintering method.Box shape workpiece was chosen as a test piece in order to confirm the effect of the inside cooling channels. Cooling channels are constructed in the core to make the effective cooling and uniform temperature condition.The warp of the side surface of the product injected with high cooling core was copared with that molded in the low cooling core without inside water channels. The amount of the warp obtained with the high cooling core was the half of that with the low cooling core and constant from the initial shot numbers.The temperature difference between the top surface and the bottom part of the core was about 20°C in the high cooling core whereas it exceeds 50°C in the low cooling core.It was confirmed that the water cooling channel inside the core reduces the temperature difference in the core and improves the dimension accuracy of the workpiece. The fabrication of the inside cooling channels using selective sintering method is useful to obtain stable and accurate injection molding.
Robots may suffer from excessive internal force in contact tasks especially when they are position-controlled or executing complicated assemblies. Excessive internal force will lead to failure of the tasks, so it is important to predict and avoid such situations. This paper presents mechanical analysis of internal force applied to objects in robotic manipulation. A linear-programming-based algorithm that can judge the possibility of excessive internal force under Coulomb friction is proposed. Numerical examples including an internal force problem in graspless manipulation and a wedging problem in peg-in-hole are also showed. Our algorithm will help the planning of robotic contact tasks.
The purpose of this research is to develop a cavitation aided machining which positively makes use of cavitation occurring in fluid for machining phenomenon. In this paper, a fundamental ultraprecision machining phenomenon of glass surface is made clear and its machining characteristics is experimentally investigated by analyzing surface finish, stock removal and cavitation impact. Then an efficiency of applying the cavitation aided machining as an ultraprecision machining is proved by carrying out ultraprecision surface machining on glass surface based on the machining phenomenon. Main conclusions obtained in this paper are as follows; (1) Cavitation aided machining can be applied to an ultraprecision machining by which the surface finish of glass is improved down to the surface finish at about 5.0nmRy by using abrasives of WA 4000. (2) WA abrasive grains generate finer machined surface than GC abrasives which is harder or AZ abrasives which is heavier. (3)Ultraprecision machined glass surface with 60mm in length is generated by applying a fundamental machining phenomenon of cavitation aided machining along flowing direction of machining fluid continuously.
5-axis control machining centers are widely used for machining complicated shape pieces of work. Because the multi-axis machines such as 5-axis control machining center have not perpendicular coordinates of their driving axes, it is difficult to generate the tool path accurately according to interpolation of line and curve by the conventional NC controller. In this study, the new NC control method for 5-axis control machining center is proposed. In this method, that uses its jacobian matrix, V-F transformer and direct kinematics of 5-axis control machine, pulse series for driving 5-axis control machining center can be generated on real time with software for realizing a desired path of tool. The effectiveness of the proposed method is discussed by simulation as the case of machining a circle by using the new NC controller for 5-axis control machining center.
To improve the productivity of manufacturing systems, it is necessary to make best use of the capacities of manufacturing facilities. However, the facilities suffer from operational and environmental stress during operation, and their functions degrade due to deterioration of their components. Hence, if the aging process of facilities can be estimated, this will be useful for various purposes such as reliability design of the facility, operational planning, and maintenance planning. For this purpose, we have studied a life cycle simulation in which the aging process of facility under specified operating conditions is evaluated. In this paper, we have applied the life cycle simulation to industrial robots equipped with wave gears for their joints, and proposed a method for evaluating wear of tooth surface of the gear taking account of the Elasto-Hydrodynamic Lubrication of grease. As a result of the simulation, we find that deterioration process of the gears is divided into two patterns depending on the magnitude of operational load. The results of the experiments gave good agreement with the value obtained by the system.
In order to study the rolling behavior on rough surfaces, the rolling friction acting on a roller, which is rolling on model asperities, is measured preciously. The model asperities are cylindrical bars, which represent unidirectional asperities on a ground surface. It is clarified in our experiment that the rolling friction becomes small with the increase of the normal load acting on the roller, when the roller is pressed at the pressure close to the yield point. According to the assumption that the contact region between the roller and the cylindrical bar moves forward to generate the resisting moment, the above-mentioned rolling behavior can be explained qualitatively, moreover the reduction in the contact area is suggested. The reduction in the contact area is supported by the electrical contact resistance measurement. Thus, one aspect of the rolling contact mechanisms is confirmed.
In the machining centers as well as the turning centers, the herical feed is often used for boring and tapping so that it improves the cutting efficiency. In such machining, the radius of curvature of the herical feed is very small.Therefore, it is important to evaluate the accuracy of such small circles without actual cutting. Although the ISO standards and JIS specify several measurement methods of the circular trajectory, it is difficult to apply those methods to the small circles. In this paper, we newly developed a simple measuement system using two linear gauges and a square for small circles or other complicated tool pathes, and its effectiveness is confirmed through experimental works. Circlar motion tests are conducted on a machining center and an NC lathe by changing the radius from 0.1mm to 20mm using the developed instrument. In addition, the corner tracking trajectories are measured at various feed speeds. As the results, it is concluded that the developed measurement system is suitable for the measurement of the tool path for machining complicated two-dimensional parts.
It is known that Si(100) surfaces anisotropy etched in aqueous KOH exhibit the fractal characteristics. However, the basic mechanism leading to the fractal surface morphology by etching has not been explained. Therefore, the computer simulations using a model of surface formation that is based on the chemical dissolution reactions were carried out. As a result of analyzing the produced surfaces, it was found that the fractal characteristics of the produced surfaces were similar to those of the etched Si surfaces in their time, concentration and temperature-dependent fluctuations. From the fact, it can be concluded that the randomness in the dissolution of Si atom and/or the surface attachment of etch product forms the fractal surface morphology.
High quality diamond films have been synthesized on substrates of high-temperature high-pressure synthesized diamond by means of arc discharge plasma jet chemical vapor deposition. Diamond films have been deposited on diamond substrate at high growth rates up to approximately 130 μm/h when methane concentration was 3%. Properties of the diamond films were determined by optical microscopy, SEM, Raman spectroscopy, X-ray diffraction analysis and FT-IR. Diamond films synthesized at methane concentration of 3% have homoepitaxially grown on diamond substrates and have shown superior crystallinity similar to type IIa natural diamond. Nitrogen contaminant in the diamond films was less than in diamond substrates. Moreover, quality of diamond films has been improved by pre-treatment of the surface of diamond substrates. As a result, hydrogen plasma treatment of substrate surface has led to fewer defects in diamond films as compared with ion beam irradiation and thermochemical polishing using a hot iron plate.
This paper deals with the size decreasing and the power decreasing of rotating-head. The head is the most important part of the developed data-transmission system and is installed on the rotating spindle. The size decreasing is achieved by three methods; the adoption of one-way data-transmission from the rotating head toward the stationary head, the realization of function of nine electric-IC-parts by a one-chip micro-controller and the adoption of digital-filtering process after data transmission accompanying no RC-hardware filter in the rotating head. As a result of the three methods, also the power consumption at the electric circuit in the rotating head is decreased to 40mW, and the coin-type battery system and the non-contact power supply system are developed. Characteristics and composition know-how of the electric-circuit including thermo-couple in the rotating head are experimentally analyzed in detail.
This paper deals with a deposition method of lubricant during finishing electrical discharge machining (EDM) to produce parts for ultrahigh vacuum such as space environment. EDM with powder suspended in working oil has been widely used to smooth a surface and to deposit a hard layer. In this study, a solid lubricant, molybdenum disulfide (MoS2) powder is mixed in working oil instead of silicone, titanium or tungsten to deposit lubricant layer on carbon steel and stainless steel. Influence of electrical conditions in EDM and powder concentration on the deposition is investigated experimentally. MoS2 is observed on both steels. Electrical conditions to deposit MoS2 are similar to those with silicon powder, that is, a high open circuit voltage, a small discharge current, a short pulse duration and a medium pulse interval. Smoother surface can be obtained by adding aluminum powder to the mixture of MoS2 powder and working oil. In a friction test, a surface finished with a mixture of MoS2 and working oil has a smaller friction coefficient than that with normal working oil.