A method is proposed for planning motion path of manipulators avoiding collisions with obstacles. Though configuration space (or c-space) of manipulator is widely used for planning collision-free path of manipulators, it does not respond adequately to the geometric configuration of the collision, which brings non-uniform precision of the path and increase of its calculation time. To resolve this problem, firstly, an approach is adopted to separate global path planning which generates candidate paths in the c-space of manipulator, and local path planning which generates local paths avoiding the collision. Secondly, a method for planning the local path is proposed ; It generates a path keeping contact with obstacle surface by utilizing local configuration space, called cc-space, which represents the geometric configuration composed from the link of manipulator and the face of obstacle in contact. Based on this strategy, a computer program is developed and a path is generated successfully for PUMA type manipulator using the program.
In order to make use of 5-axis control machining centers, the post-processor plays an important role, which converts collision-free CL data, generated by the main-processor, to actual NC data. The difficulty of developing the post-processor lies in the diversity of the structure of 5-axis control machining centers. The structure of 5-axis control machining centers can be classified into three types, that is, table-tilting type, spindle-tilting type and table/ spindle-tilting type. The study especially deals with the development of the post-processor concerning spindletilting type and table/spindle-tilting type 5-axis control machining centers, taking account of linearization, feed rate control and spindle rotation control. The validity of the post-processor developed in the study is experimentally confirmed.
The Clothoid is a curve which has linearly changing curvature in relation to the length of the curve. By choosing the curve as the interpolating curve between freely given 2-dimensional point series, we can obtain a smooth free curve. In this report a practical method of Clothoidal interpolation, called "tangent method", is mentioned. The algorithm of the method is derived and some examples are shown.
Drive units for robots and other automatic machines are generally composed of a motor and a reducing gear. Such units with inertia load show vibrational response to the reference change as well as to the load variation. In order to improve response speed and accuracy of the machines, these vibrations have to be suppressed. Many control methods successfully deal with the problem, but most of them are difficult to be practically realised or have a disadvantage of a needed high degree of knowledge for the controller design. An aim of the present research is a design of a simple but effective method for a vibration suppression. In this purpose a disturbance rejection control is used for motor and thus a dynamically decoupled motor and load system is obtained. The decoupling enables a simple design of a feedback loop for the vibration suppression. This paper discusses about the design of the feedback loop and its effect on the system's transient response.
A robot machining system for industrial art objects has been developed. The objective of the system is both to make good use of technical skill of artist or artisan, and to realize the automation of machining of industrial art objects. The developed system is composed of three units: (i) input unit to record the machining data of artist or artisan directly, or to measure the model of an industrial art object; (ii) data processing unit to generate and modify model from the input data, and to transform model data into machining data; (iii) machining unit to machine industrial art objects according to obtained machining data. In this paper, the general philosophy about the system is given, and the construction of developed system, design policy and functions of each unit are described. An example of machining experiments is given to show the practical availability of the system.
A study is presented of measurement for flatness by fitting partial shape deviations to large discrete flatness deviations calcurated by two-dimentional least square serial point method. In this paper, two methods are proposed. One is the method that uses the optical interferometer as the measuring head, and is applied with 2 DLS 3 PM. The other is the method which uses four displacement sensors as the measuring head, and is applied with 2 DLS 2 PM. The following fact is revealed by the experiment. The results of measurement by these two methods corresponded with accuracy of 0.05 μm (2σ). The accuracy is achieved to 1/20 movement errors of X-Y table used in this experiment.
This paper presents a new software datum method for roundness measurement, which is called the mixed method. In this method, 2-point displacement and a tangent angle of either point are simultaneously measured using 2 probes. A differential operation of them cancels the vibrational eccentric motions due to the rotational error and a deconvoluting operation of the differential data gives the correct roundness. In this paper, the mixed method is compared with the 3-point method, the traditional method of roundness measurement, by analyzing their transfer functions, resolutions and sensitivities to some factors of errors, such as the drift, positioning error, etc. Differing from the 3-point method, the mixed method can measure high frequency components regardless of the probe distance. The mixed method can also improve its resolution in the whole frequency domain by widening the probe distance. The effectiveness and limitations of the mixed method for roundness measurement have been verified by simulations and some important information for the sensor-design of roundness measurement have been gotten by theoretical analyses.
For the on-machine roughness measurement it is desirable that the sensor is not easily affected by circumferential noise and datum errors due to the scanning motion. An optical stylus with an optical skid made by a new design concept is proposed to satisfy these necessities. In the developed sensor, a set of an optical source and an adjusting lens is added simply to the optical system of the usual critical angle type optical stylus. The optical beam from the added source is arranged to make another diplacement-sensitive range which is known as the wide range in the stylus of this type. The spot at the wide range is so large that it can smooth the profile of high spatial frequency components to serve for the optical skid. Influence of the thermal drift and other circumferential noises in the optical stylus is reduced to about 1/10 in the difference between the stylus and the skid. Profiles of ground surfaces are smoothed to almost flat planes in the output of the optical skid. Thus the developed sensor is confirmed to be very promising for the application to roughness measurements under on-machine or in-process conditions.
This paper describes the development of the electromagnetic force sensor which can be used to measure both the displacement of its probe end from the measured surface and the normal direction of the surface. The inclination of the sensor axis from the normal direction can be obtained by measuring the three components of the magnetic attraction force which is applied to the magnet at the end of the probe, based on the fact that the force is perpendicular to the surface. In the preceding report, one of the authors proposed a magnetic force sensor with a permanent magnet. In this case, however, the diameter of the magnet should be large enough to get a sufficient force. Therefore, there are some problems as follows: (1) It is difficult to measure intricate configurations of the surface because of collision of the magliet to the surface. (2) The error of measurement is large at a point where the radius of curvature is small. (3) The weight of the magnet affects the measurement of the magnetic force. In the present work, the permanent magnet is replaced by an electromagnet, and the probe end is made sharp. Moreover, it is found that the preciseness of measurement can be improved by comparing the sensor outputs when the coil current is switched on and off, because the influence of the self-weight of the probe and the drift noise can be eliminated.
Micro-cracks were mechanically induced in the CVD coating layers on a cemented carbide tool. With decreasing mean value of distance between cracks from 200 μm to 20 μm, tensile residual stress in the coating decreased from 0.55 GPa to 0.05 GPa, the initiation time of thermal fatigue cracks in face milling became longer, and the chipping resistance in interrupted cutting tripled. It seems that the improvement of tool performance is closely related to the relief of tensile residual stress in the coating.
To supply low-cost and high-precision ground gears, the CNC gear form-grinding machine with the truing attachment was developed. The grinding machine can finish spur and helical gears with an arbitrary profile and with a three-dimensionally modified tooth surface by using the supporting software developed at the same time. The structure of the grinding machine was determined so that positioning errors between the grinding wheel and work gear do not affect profile errors of ground gears, and that number of control axes becomes as small as possible. The grinding wheel is trued accurately on the machine by a single-point diamond dresser, of which the direction is controlled corresponding to the normal direction of the grinding-wheel profile. The accuracy of the gears finished on the grinding machine were better than 0 class of JIS and the surface roughness of the ground gears were lower than 1 μmRmax.
Amorphous silicon/amorphous silicon carbide (a-Si/a-SiC) multilayer films are prepared by a dual rf magnetron sputtering method. The multilayer structure is confirmed by a depth profile of Auger electron spectroscopy (AES). Difference in the etch rate of amorphous silicon and amorphous silicon carbide in a mixture of HF, HNO3 and CH3COOH creates series of concentric steps in multilayer films, that show up clearly in the observation by an optical microscope. Furthermore, a small angle X-ray diffraction is carried out in order to be clarified the periodic structure. In the [a-Si (14.1 nm)/ a-SiC(7.5 nm)]30 film with its superstructure period Λ =21.6 nm, from 1st to 23rd Bragg reflections caused by the regular periodicity can be observed. The diffraction profile has been well explained by a l-dimensional step model, which takes into account a random distribution of the superstructure period, varying according to a Gaussian distribution with the width ΔΛ/Λ =0.3 % (ΔΛ =0.064 nm).
Grit sprinkling is important for the effective working process of a product with a diamond wheel. However, to date this working process is still carried out manually. Hence, development of a mechanical method is expected. In the present paper, sprinkling method utilizing a jet issuing from a nozzle is proposed and studied. Influences of diameter of diamond grits, jet velocity at the nozzle exit, depth of liquid in an electrodepositing bath and the distance between a nozzle and wall of a bath on the grit distribution are experimentally investigated. Dimensionless variables determining the mean position and standard deviation of the distribution are obtained by a method of dimensional analysis, and the empirical formulas for these values are presented. The uniformity of grit distribution on a nozzle sprinkle method are examined, and superiority of this method with the uniformity of distribution is confirmed.
This paper deals with the ultrasonic screw vibration tapping for natural rubber. For the machining of elastic material such as natural rubber, it is necessary to heighten apparent rigidity of work material by decreasing the cutting torque by means of ultrasonic vibration. The following results were obtained. Female screw formed by ultrasonic vibration tapping with kerosene showed good geometry, especially in the case of rake angle 20°. Chip formation was mainly ribbon type for vibration tapping and powder type for conventional tapping. Cutting torque in vibration tapping was below half of that in conventional tapping and the value was about 30 Nmm. For very flexible natural rubber of the hardness 50 IRHD, female screw can be obtained with liquid nitrogen cooling by conventional tapping.