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Generally, manufacturing process of optical glass lenses, which are used for single lens reflex cameras, is classified into grinding and polishing for removing cracks generated by grinding. Thus, it is desired not to generate the cracks in grinding as much as possible. Because grinding condition with cracks differs depending on the material properties of the workpiece, suitable grinding condition needs to be selected based on a lot of experimental verifications. In addition, the controller’s gain of the tool spindle with grinding wheel may be intentionally set to low value in ultra-precision grinding. Thus, the spindle speed may decrease even under servo control because of grinding load. In this study, the influence of servo characteristics on crack generation is evaluated in ultra-precision grinding of optical glass lenses. Concretely, an optical glass lens was machined using an ultra-precision 5-axis grinding machine and servo information of tool spindle was monitored during the process. Comparison of the obtained servo information and the surface observation of the workpiece revealed that the spindle speed decreased and the number of the cracks increased at the outside of the workpiece. The experimental results suggested the possibility of estimating the grinding load and predicting the surface quality by monitoring the variation in the spindle speed.

Large aperture lenses with high surface quality are demanded for professional imaging products such as single-lens reflex cameras and astronomical telescopes. Large aperture optical lenses are shaped by ultra-precision grinding and finished by prolonged polishing. However, the prolonged polishing process leads to deterioration of the form accuracy. In order to reduce the amount of polishing, ductile-mode ultra-precision grinding is demanded. In this study, a rubber bonded wheel, which has a low elastic modulus, is used for grinding of spherical glass BK7, and influence of the hardness of the rubber bonded wheel and abrasive chip thickness on brittle fracture and surface roughness are experimentally investigated.

Large-aperture lens used for single-lens reflex cameras is generally produced by both ultra-precision grinding and polishing because a mass-produced lens by molding process can hardly achieve the required form accuracy and surface quality. Recently, grinding process of an optical glass should make surface quality as high as possible in order to reduce removal amount in polishing process. Accordingly, evaluation of subsurface damage induced under various grinding conditions has been required because subsurface damage leads to crack initiation or deterioration of the performance. However, evaluation method of subsurface damage on the spherical glass lens after grinding has not yet been established.In this study, the quantitative evaluation method by applying wet-etching of hydrofluoric acid (HF) is proposed, then its validity is verified. From the experimental results, we clarify to evaluate the subsurface damage by examining the surface transition according to etching time.

The demand for large aperture lenses with high surface quality and form accuracy used for single-lens reflex cameras has been increasing. Generally, large aperture glass lenses are produced by ultra-precision grinding. Considering the increasing global competition, the grinding process has to be improved. However, highly efficient grinding causes worse surface quality, which leads to much polishing and ultimately results in lower form accuracy. Thus in this study, aiming at the realization of highly efficient and precise grinding of glass lenses, cross grinding of optical glass BK7 is carried out. As a first step of the study, the influence of grinding conditions on the surface quality is investigated experimentally.

Recently, it has been required to improve qualities of aspherical lenses mounted on camera units. Optical lenses in highvolume production generally are applied with molding process using cemented carbide or Ni-P coated steel, which can be selected from lens material such as glass and plastic. Additionally it can be obtained high quality of the cut or ground surface on mold due to developments of different mold product technologies. As results, it can be less than 100nmPV as form-error and 1nmRa as surface roughness in molds. Furthermore it comes to need higher quality, not only formerror( PV) and surface roughness(Ra) but also other surface characteristics. For instance, it can be caused distorted shapes at imaging by middle spatial frequency undulations on the lens surface. In this study, we made focus on several types of sinuous structures, which can be classified into form errors for designed surface and deteriorate optical system performances. And it was obtained mold product processes minimalizing undulations on the surface. In the report, it was mentioned about the analyzing process by using PSD so as to evaluate micro undulations on the machined surface quantitatively. In addition, it was mentioned that the grinding process with circumferential velocity control was effective for large aperture lenses fabrication and could minimalize undulations appeared on outer area of the machined surface, and mentioned about the optical glass lens molding process by using the high precision press machine.

This paper presents the dynamic response of an air-bearing displacement sensor for on-machine surface form measurement of micro structures. The on-machine measurement system has some merits in terms of measurement efficiency and re-machining for error compensation after measurement. On the other hand, the performance of the contact type measurement system based on stylus methods is dominated by the dynamic characteristics of the system because the system is subject to random vibrations of the machine tool including the spindle during measurement. Therefore, the dynamic response of the system is useful for analyzing the mechanical vibrations of the practical on-machine measurement system. In this paper, the equation of motion for the air-bearing displacement sensor to the excited input displacement is derived and the displacement behavior of the system by using a PZT actuator is investigated within certain frequency ranges experimentally for identifying the dynamics of the system.

This paper presents the experimental results of investigating the performances of an air-bearing displacement sensor for surface form measurement of micro-structures, such as micro-lenses, on an ultra-precision machine tool. The sensor consists of a stylus for contacting the surface, a shaft for mounting the stylus, an air-bearing for suspending the shaft and a blade spring for applying the measuring force against the surface. At first, experiments were conducted on a vibration isolated table to identify the basic performance of the sensor for displacement measurement. Then, the sensor was mounted on a diamond turning machine for evaluating the performance of the sensor for on-machine surface form measurement of micro-lenses. A roll workpiece, on which a micro-lens array was fabricated by using a fast tool servo on the diamond turning machine, was employed as the specimen for the on-machine experiment of surface profile measurement.

The requirement of the ultra-precision machine tools for ductile cutting of hard brittle materials was examined experimentally. One of the essential factors of achieving ductile mode cutting was not only high-resolution feedback control but also the dynamic performance of the machine tool in forming solid immersion lens of monocrystalline silicon. We also proposed newly developed method for ultra-precision machine tools, which does not have enough high dynamic performance in order to achieve ductile mode cutting of the hard brittle materials. An additional device consisted of air slider on the machine tool was applied to cutting of glass in order to keep stable ductile mode cutting. We fabricated high-value added structure, which are designed a diffraction grating, consisted of micro groove on a borosilicate crown glass surface with the developed device.

A new contact type of on-machine measuring system is developed in order to measure aspherical optical parts with steep surface angle for large numerical aperture (NA). A ceramic air slider made of SIALON is adopted for the measurement probe because of its low thermal expansion coefficient, high rigidity and light weight. A high accuracy glass scale is employed to reduce the thermal drift of the displacement gauge. The air slider or the measuring probe is tilted for 45° against the aspherical workpiece axis, and the probe is scanned over the workpiece surface, so as to keep the contact angle between the probe axis and the contact surface constant in order to reduce the change in the probe friction force.

The study proposes a non-contact adjustment method of grinding wheel alignment in ultra-precision grinder by using electric capacitance between grinding wheel and master ball. Cemented carbide with almost no binder is used for die material as molding glass lens. The carbide is one of the most difficult-to-cut materials because of its high hardness. Diamond wheel therefore is generally used for grinding the material under quite light grinding conditions such as less than 1 micrometer of depth of cut. In such ultraprecision grinding, an alignment and a radius of the grinding wheel must be settled precisely to achieve high efficient grinding. In ultra-precision grinding, grinding and measuring are repeated several times, that is, after grinding the work form is measured, and the result is used to correct a grinding program for next grinding. The method proposed in this study is based on an electric capacitance between grinding wheel having conductivity and the master ball, this means that the method is carried out without any contact between the wheel and the master. The capacitance is in inverse proportion to the gap, and that can be measured precisely. Using the method, the alignment and the radius of the wheel can be adjusted within short time.

This paper proposes a newly developed monitoring system for grinding ultra-precision small size casting die having asphericl surface. Small size aspheric glass lenses are widely used for IT industry. The lenses are cast in cemented carbide die because of its high melting temperature and the die is usually ground by small size diamond grinding wheels. The wheel can not be changed or dressed in finish grinding, because changing or dressing the wheel brings deterioration of die accuracy, therefore, very light grinding conditions must be adopted, such as less than one micrometer of depth of cut. In such conditions, monitoring of grinding state, such as that of grinding force, is indispensable to achieve high quality and high efficient grinding. However sensing of very low grinding force is quite difficult, because of the system stability and Signal/Noise ratio in the sensing. In the system developed, an induced current was applied to a closed circuit, which was consisted from die, diamond wheel, spindle, air bearing and machine tool, by a ring coil coupling with the circuit and the current was detected by an another ring coil. The current was depended on an impedance of the circuit, and the impedance was influenced by the conditions between die and grinding wheel, Stable or unstable grinding conditions was detected, so that high efficiency ultra-precision grinding was achieved by using the system.

In order to develop high efficiency finishing for guide ways of machine tools, hardened and ground die steel SKD61 was lapped by using a robot or a milling machine. Lapping, in general, is carried out on a machined surface to obtain fully flat surface, this means that the machined surface is lapped away completely. In this study, however, the purpose of the lapping is to make a surface having a superior wear characteristics without damage of the geometrical accuracy obtained by grinding. Gray cast iron and a layered soft disk made by a rubber, a sponge and an acrylic resin were used for the lap. It was found that lapping by the robot with gray cast iron lap was difficult because of many scratches and geometrical damage on the lapped surface, while lapping by the milling machine with the iron lap could get a fairly good surface finish without any geometrical damage except some scratches. The best surface finish was obtained by using the layered soft disk lap.

This paper presents the experimental investigations for performance evaluation of an air-bearing displacement sensor as a measurement system for nanometrology of surface forms by using it. The experimental configuration and some considerations for the air-bearing displacement sensor are described. Then, in order to identify the basic performance of the sensor, a measuring force and displacement output of the sensor are evaluated on a vibration isolated table. The sensor is also mounted on a diamond turning machine to evaluate the surface form of micro structures. A roll workpiece with Ni-P plating surface, on which micro-lens array are fabricated by using a FS-FTS (Force sensor fast tool servo) on the machine tool, is employed as a specimen for measurement.

In order to eliminate the difficulty in machining a tungsten carbide glass lens mould by using a fine diamond wheel, a new type of coolant supply method - the megasonic coolant supply method - is introduced. Using the megasonic coolant supply method, a substantial reduction in the error factor presently associated with the grinding wheel can be achieved, thus making it possible to achieve the target accuracy without using any compensation parameters. Increased wheel life and increased depth of cut have also been achieved along with an improvement in the machined surface quality.

It is strongly wished that hard and brittle materials could be used in a wide variety of fields because of their great material characteristics. For now, however, minute profiling or high-efficiency cutting of these materials has not yet been put into practice due to their hardness. At the same time, there have been numerous reports available on ductile mode cutting for hard and brittle materials in response to the increasing demand. Very smoothly finished surfaces can reportedly be generated through the work of a material removal mechanism similar to plastic deformation, done by microminiaturizing cutting units with the sharp cutting edges of tools. Because of the extremely narrow ductile mode regions, however, forced cutting processing, which includes cutting work, demands extremely high motion performance or rigidity of machine tools, and this makes it difficult to realize stable ductile mode cutting. On the other hand, pressure cutting processing similar to polishing is known to be capable of producing extremely smooth finished surfaces on hard and brittle materials; this suggests that we could realize stable ductile mode cutting that will always create the same depths of cut by controlling the insertion forces on the tools. In this paper, in order to realize stable ductile mode cutting, we have devised and prototyped a constant pressure cutting device which can regulate cutting forces by regulating supply pressure with air static pressure bearings. We have investigated the relationships between the pressure supplied in the cutting direction and the cutting forces in order to get static pressure characteristics of the prototype device. We have also carried out experiments to cut hard and brittle materials with the prototype constant pressure cutting device mounted on the tool post of an ultraprecision machine tool to prove the effectiveness of the constant pressure cutting device for the ductile mode cutting of hard and brittle materials.