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  Free curved surface precision machining toolRelated Patent Categories: Abrading, Precision Device Or Process - Or With Condition Responsive Control, With IndicatingThe Patent Description & Claims data below is from USPTO Patent Application 20070004318. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a free curved surface precision machining tool for precision-machining a free curved surface (more specifically, for precision-removing the free curved surface with grinding or cutting), having a convex machining section in the form of an arcuate rotary body at the lower end. [0003] 2. Description of the Related Art [0004] Referring to FIG. 1, there is typically shown machining (removal machining) of a free curved surface with a conventional free curved surface machining tool. The conventional free curved surface machining tool 1 is, for example, a ball nose grindstone or a ball end mill, which has a spherical machining surface at the lower end and is configured to rotate around the axis z. A free curved surface 2 is a part of, for example, a molding die, an aspherical lens, or the like. With high-speed rotation around the axis z, the free curved surface machining tool 1 machines the free curved surface 2 while relatively moving the lower end along the free curved surface 2. A free curved surface of a die, an aspherical lens, or the like can be freely formed with repetition of the machining using the machining tool 1. [0005] Moreover, there has already been disclosed a free curved surface machining tool wherein the circumferential speed of the axis does not reach zero (0) in Patent Document 1. [0006] The "free curved surface machining tool" in Patent Document 1 is a tool for machining a surface to be machined with the lower end in contact therewith by rotation around an axis z, including a spherical tool having at least a spherical machining section on the lower side thereof and a support bearing for supporting the spherical tool on a rotation axis a, which is different from the axis z and passes through the center of the spherical surface. [Patent Document 1] [0007] Japanese Patent Laid-Open No. H10-156729 [0008] The free curved surface machining tool 1 shown in FIG. 1 rotates around the axis z and therefore the circumferential speed of the machining surface is zero (0) at the position of the axis (radius 0), by which the axis (radius 0) is the dead center of machining. Moreover, the radius of rotation significantly depends upon the position of the machining surface, and thus the circumferential speed and the rotation load largely fluctuate, which leads to a problem that the precision machining (high-precision and high-quality machining) cannot be performed. In addition, the free curved surface machining tool 1 has a problem that there is a need to maintain sharpness and an accurate spherical surface of the tool machining surface on a constant basis in order to achieve the machining function and precision. [0009] Accordingly, it has conventionally been necessary to prepare a multi-axis NC machining apparatus having four or five axes wherein the axis z of the free curved surface machining tool 1 can be arbitrarily inclined during machining and a program creation therefor. This kind of program creation, however, is complicated and difficult, and further the increase in the number of axes requires an advanced technique in manufacturing the machining apparatus. This leads to a problem that the multi-axis NC machining apparatus having four or more axes capable of precision machining becomes expensive and poor in versatility. [0010] The following gives more detailed description of the above problems in cases where precision machining is performed. [0011] Referring to FIGS. 2A to 2D, there are shown illustrations of machining portions, which are enlarged in some measure so as to be easy to understand. If the depth of the cut c (the depth of machining) is deep (FIG. 2A), the contact surface e is wide independently of the magnitude of feed d (a moving distance of the tool) unless the feed direction y (a direction of movement of the tool) is the vertical direction, and thus the main machining portion is far from the axis z. In this case, the roughness (concavity and convexity) of the surface to be machined is large (a plane roughness is large), but it does not become a problem since rough machining is mainly aimed for. [0012] If the depth of the cut c is shallow (FIG. 2B), in other words, in precision machining, the contact surface e is narrow, and as the main machining portion comes close to the axis z, the roughness of the surface to be machined becomes small. In this case, however, the above matters in question such as the precision machining (high-precision and high-quality machining) and the need for maintaining the sharpness and the accurate spherical surface of the tool machining surface are coming to the fore. [0013] Moreover, as well as the narrow contact surface e, the peripheral speed and the required driving torque undergo drastic changes according to the magnitude of the distance of the contact surface e from the axis (radius of rotation), thereby causing problems of irregularity in the roughness of the surface to be machined, a chatter mark (caused by vibration), or a decrease in machining accuracy. [0014] On the other hand, the narrowing of the contact surface e causes a local convergence of the contact position or frequency of the machining tool according to the feature of the free curved surface to be machined, which results in a local convergence of portions where the machining function (the sharpness) declines and of deformations caused by contact friction, by which the deformations are reverse-transferred to the surface to be machined or the surface is damaged. These are magnified by the interaction. [0015] In the NC grinding, it is essential to generate a new surface and to maintain an accurate spherical surface in the grinding section at all times in order to maintain the machining function and precision machining. [0016] Referring to FIG. 3, there is shown an illustration of a deformation in a spherical grindstone and correction thereof, which is enlarged so as to be easy to understand. The deformation occurs more easily as the contact frequency is higher and it is farther from the axis, and once the deformation begins to occur, a reverse transfer occurs and thereby the deformation is accelerated. Therefore, if so, rapid correction is required. It is necessary to fair the shape until there is nothing left of the deformation by removal machining from the radius m of an old spherical surface to the radius n of a new spherical surface. It is, however, generally hard to correct the deformation in a situation where the deformation from the spherical surface is significant. [0017] Therefore, there is a need to control a contact wear position and a contact frequency by inclining the axis z in such a way that the contact frequency of the grinding section is uniform over the entire surface thereof to reduce the need for the correction. Unless the axis z can be inclined arbitrarily, however, the grinding section is continuously and systematically corrected by using a setting value previously incorporated into the program, by which a large part of the spherical machining section is removed wastefully. [0018] Moreover, the correction of the spherical machining section of the spherical tool is made by decreasing the radius, in other words, by changing the curvature, and therefore there is a need for precision removal machining with an NC machining apparatus. [0019] Referring to FIG. 2C and FIG. 2D, there are shown cross sections perpendicular to a machining trajectory. It is necessary to minimize or remove a cusp amount h by decreasing a pick feed g or increasing the spherical radius of the machining tool. The spherical radius of the machining tool, however, need be equal to or larger than the curvature of the minimum negative (concave) curved surface in the free curved surface in order to prevent a damage to the machined curved surface, which may be caused by a tool interference. Therefore, it leads to a problem that there is no other choice but to select a measure to shift the pick feed g by a half pitch or decrease it, though the machining time thereby increases. [0020] Moreover, while the accuracy of machining position can be improved by decreasing the spherical radius of the machining tool, it leads to a problem that the machining time increases as described above. SUMMARY OF THE INVENTION [0021] The present invention has been provided to resolve the above various problems. Specifically, it is an object of the present invention to provide a free curved surface precision machining tool capable of efficiently precision-machining a free curved surface using a versatile 3-axis NC machining apparatus, by dispersing the moving trajectory of the contact surface of a tool machining section and achieving a constant moving speed and driving torque so as to maintain the sharpness of the tool machining section, to achieve uniform wear and a self-correction function thereof, and to decrease the wearing speed, whereby the accuracy of form of the tool machining section can be maintained continuously. Continue reading... Full patent description for Free curved surface precision machining tool Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Free curved surface precision machining tool patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. 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