JP2011121146A - Method for manufacturing fresnel lens, method for manufacturing die of fresnel lens, and cutting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique for cutting a fresnel lens or the die of the fresnel lens by relatively rotating a workpiece to the blade, which solves a problem that the degradation of smoothness and shape is caused at a processed surface of the workpiece while reducing revolving speed as a distance from a rotational center of a blade becomes larger during processing. <P>SOLUTION: A fresnel surface processing step of cutting one of fresnel surfaces 11 and a rising face processing step of cutting one of rising faces 12 are alternately repeated. While the fresnel surface is processed, revolving speed to the blade 27 of the workpiece is maintained constant, and while the rising face is processed, the revolving speed is changed. Alternatively, the blade 27 is separated from the workpiece between the fresnel surface processing process and the rising face processing process, and the revolving speed is changed while the blade 27 is separated from the workpiece. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a Fresnel lens manufacturing method, a Fresnel lens mold manufacturing method, and a cutting apparatus.

  Conventionally, a technique for cutting a Fresnel lens having a concentric groove or a mold of a Fresnel lens is known (see, for example, Patent Document 1). When machining, the workpiece is rotated relative to the bite. If the number of revolutions per unit time (hereinafter simply referred to as the number of revolutions) is constant, the bite is the center of rotation. As the distance from the workpiece increases, the relative speed between the bite and the workpiece increases. Therefore, if the relative speed is ideal at the center, the relative speed will be excessive at the outer periphery, and if the relative speed is ideal at the outer periphery, the relative speed will be insufficient at the inner periphery. End up. In addition, if the relative speed between the tool and the workpiece is greatly different between the vicinity of the rotation center and the outer peripheral portion, the surface roughness of the processed surface of the Fresnel lens (or its mold) is not stable.

  Therefore, a technique is adopted in which the rotational speed is reduced as the distance from the rotation center of the cutting tool increases so that the relative speed between the cutting tool and the workpiece does not change greatly depending on the distance from the rotation center. This technique is called a constant peripheral speed function.

JP 2004-42188 A

  However, as a result of the study of the inventors of the present invention, it has been found that adopting the conventional constant peripheral speed function has the following problems. In other words, if the rotation speed is changed as the distance from the rotation center of the tool changes, nano-level shaft shake occurs when the rotation speed changes, and rotation until the rotation speed stabilizes when the rotation speed changes. Unevenness occurs, and as a result, the surface roughness and shape of the processed surface of the workpiece are deteriorated.

  In view of the above points, the present invention is a technique for cutting a Fresnel lens or a mold of a Fresnel lens by rotating a workpiece relative to the cutting tool, so that the distance from the rotation center of the cutting tool becomes larger at the time of processing. An object of the present invention is to cope with a problem that surface roughness or shape deteriorates on a processed surface of a workpiece while reducing the number of rotations.

  In order to achieve the above object, according to the first aspect of the present invention, the workpiece (30) is rotated relative to the cutting tool (27), and the cutting tool (27) is rotated to the workpiece (30). The workpiece (30) is cut by the cutting tool (27) by moving the workpiece (30) relative to the thickness direction of the workpiece (30) and the radial direction of the workpiece (30). As a result, a Fresnel lens manufacturing method for manufacturing a Fresnel lens (1) in which a Fresnel surface (11) and a rise surface (12) are alternately formed concentrically, and one of the Fresnel surfaces (11). A Fresnel surface machining step for cutting a workpiece and a rise surface machining step for machining one of the rise surfaces (12) are alternately repeated. During the Fresnel surface machining step, the workpiece (30) For the byte (27) Keeping the rotational speed constant during the rise surface processing step, a method for manufacturing a Fresnel lens characterized by varying the rotational speed.

  In this way, during the cutting of the Fresnel surface (11), no nano-level axial run-out associated with the rotational speed change of the workpiece (30) relative to the cutting tool (27) occurs, Rotational unevenness until the rotational speed becomes stable due to the rotational speed change does not occur, and as a result, the surface roughness and shape are not deteriorated on the Fresnel surface (11). That is, a good finished surface can be obtained on the Fresnel surface (11) without being affected by rotational fluctuations.

  On the other hand, during the cutting process of the rise surface (12), there is a change in the rotational speed of the workpiece (30) with respect to the bite (27). Rotational unevenness until the rotational speed becomes stable due to the rotational change occurs, and as a result, the surface roughness and shape of the rise surface (12) may be deteriorated. However, since the rise surface (12) does not transmit light in actual use of the Fresnel lens, the adverse effect is much smaller than when the surface roughness or shape deteriorates on the Fresnel surface (11).

  According to the second aspect of the present invention, the workpiece (30) is rotated relative to the cutting tool (27), and the cutting tool (27) is rotated relative to the workpiece (30). The workpiece (30) is cut by the cutting tool (27) by relatively moving in the thickness direction of the workpiece (30) and the radial direction of the workpiece (30). A Fresnel lens manufacturing method for manufacturing a Fresnel lens (1) in which a Fresnel surface (11) and a rise surface (12) are alternately formed, wherein one of the Fresnel surfaces (11) is cut. Between the surface machining step, the rise surface machining step of cutting one of the rise surfaces (12), the Fresnel surface machining step, and the rise surface machining step, the tool (27) is placed on the workpiece (30). A step away from Repeatedly, during the Fresnel surface machining step and the rise surface machining step, the number of rotations of the workpiece (30) relative to the bite (27) is kept constant, and in the step of separating, the bite (27) The method of manufacturing a Fresnel lens, wherein the rotational speed is changed in a state of being separated from the workpiece (30).

  In this way, during the cutting of the Fresnel surface (11) and the rise surface (12), nano-level shaft runout accompanying the rotational speed change of the workpiece (30) with respect to the bite (27) occurs. It does not occur, and the rotation unevenness until the rotation speed is stabilized due to the change in the rotation speed does not occur. As a result, the surface roughness and shape of the Fresnel surface (11) and the rise surface (12) may be deteriorated. Disappear. That is, a good finished surface can be obtained on the Fresnel surface (11) and the rise surface (12) without being affected by rotational fluctuation.

  According to a third aspect of the present invention, the spindle (25) for rotating the workpiece (30) relative to the cutting tool (27) and the cutting tool (27) on the workpiece (30) are provided. In contrast, the scanning device (22, 23), the main shaft (25), and the operating device (22, 23) are moved relative to the thickness direction of the workpiece (30) and the radial direction of the workpiece (30). 23), the workpiece (30) is cut by the cutting tool (27), and as a result, the Fresnel surface (11) and the rise surface (12) are alternately formed concentrically. A control unit (28) for manufacturing the lens (1), and the control unit (28) includes a Fresnel surface processing step for cutting one of the Fresnel surfaces (11). , Cutting one of the rise surfaces (12) Rise surface machining step to be worked is alternately repeated. During the Fresnel surface machining step, the rotational speed of the workpiece (30) with respect to the bite (27) is kept constant, and during the rise surface machining step, A cutting apparatus characterized by changing the number of rotations. With this configuration, an effect equivalent to that of the invention described in claim 1 can be obtained.

  According to a fourth aspect of the present invention, there is provided a spindle (25) for rotating the workpiece (30) relative to the cutting tool (27), and the cutting tool (27) to the workpiece (30). On the other hand, a scanning device (22, 23) for relatively moving in the thickness direction of the workpiece (30) and the radial direction of the workpiece (30), the spindle (25), and the operating device (22, 23), the workpiece (30) is cut by the cutting tool (27), and as a result, the Fresnel surface (11) and the rise surface (12) are alternately formed concentrically. A control unit (28) for manufacturing the lens (1), and the control unit (28) includes a Fresnel surface processing step for cutting one of the Fresnel surfaces (11). Cut one of the rise surfaces (12) Rise surface machining step to be processed, and the Fresnel surface machining step and the step of separating the cutting tool (27) from the workpiece (30) between the Rise surface machining step, the Fresnel surface machining step and During the rise surface machining step, the rotational speed of the workpiece (30) with respect to the cutting tool (27) is kept constant, and in the releasing step, the cutting tool (27) is separated from the workpiece (30). The cutting device is characterized in that the number of rotations is changed in a state of being cut. Thus, the same effect as that of the invention described in claim 2 can be obtained.

  In the invention according to claim 5, the workpiece (30) is rotated relative to the cutting tool (27), and the cutting tool (27) is moved relative to the workpiece (30). The workpiece (30) is cut by the cutting tool (27) by relatively moving in the thickness direction of the workpiece (30) and the radial direction of the workpiece (30). A mold manufacturing method for manufacturing a mold (40) of a Fresnel lens (1) in which a Fresnel surface (11) and a rise surface (12) are alternately formed, wherein the mold (40) A Fresnel mold surface machining step for cutting one of the Fresnel mold surfaces (41) to be a mold of the Fresnel surface (11), and a rise mold surface (to be a mold for the rise surface (12) in the mold (40)). 42) Rise die surface machining process for cutting one of The rotation number of the workpiece (30) with respect to the cutting tool (27) is kept constant during the Fresnel type surface processing step, and the rotation number is set during the rise type surface processing step. It is the manufacturing method of the metal mold | die characterized by making it change.

  In this way, during the cutting of the Fresnel type surface (41), no nano-level axial run-out due to the change in the rotational speed of the workpiece (30) relative to the cutting tool (27) occurs. In addition, the rotation unevenness until the rotation speed is stabilized due to the rotation speed change does not occur, and as a result, the surface roughness and the shape are not deteriorated on the Fresnel type surface (42). That is, a good finished surface can be obtained on the Fresnel type surface (41) without being affected by rotational fluctuation.

  On the other hand, during the cutting of the rise mold surface (42), there is a change in the rotational speed of the workpiece (30) with respect to the bite (27). Rotational unevenness until the rotational speed is stabilized due to the rotational change occurs, and as a result, there is a possibility that the surface roughness and shape of the rise type surface (42) may be deteriorated. However, since the rise mold surface (42) becomes a mold of the rise surface (12) that does not transmit light in actual use of the Fresnel lens, the surface roughness or shape of the Fresnel mold surface (11) deteriorates. Compared with, the adverse effects are much smaller.

  According to the sixth aspect of the present invention, the workpiece (30) is rotated relative to the bite (27), and the bite (27) is rotated relative to the workpiece (30). The workpiece (30) is cut by the cutting tool (27) by relatively moving in the thickness direction of the workpiece (30) and the radial direction of the workpiece (30). A mold manufacturing method for manufacturing a mold (40) of a Fresnel lens (1) in which a Fresnel surface (11) and a rise surface (12) are alternately formed, wherein the mold (40) A Fresnel mold surface machining step for cutting one of the Fresnel mold surfaces (41) to be a mold of the Fresnel surface (11), and a rise mold surface (to be a mold for the rise surface (12) in the mold (40)). 42) Rise die surface machining process for cutting one of A step of separating the cutting tool (27) from the workpiece (30) between the Fresnel mold surface machining step and the rise mold surface machining process, and repeating the Fresnel mold surface machining process and the rise mold surface. During the machining step, the rotational speed of the workpiece (30) with respect to the cutting tool (27) is kept constant, and in the releasing step, the cutting tool (27) is separated from the workpiece (30). A method for producing a mold for a Fresnel lens, wherein the rotational speed is changed.

  By doing so, during the cutting of the Fresnel mold surface (41) and the rise mold surface (42), the workpiece (30) as a material of the mold (40) with respect to the bite (27). There is no nano-level axial run-out associated with the change in the rotational speed, and there is no rotational unevenness until the rotational speed stabilizes with the rotational speed change. As a result, the Fresnel surface (41) and the rise-type surface (42) Therefore, the surface roughness and the shape are not deteriorated. That is, a good finished surface can be obtained on the Fresnel type surface (41) and the rise type surface (42) without being affected by rotational fluctuation.

  The invention according to claim 7 is directed to a spindle (25) for rotating the workpiece (30) relative to the cutting tool (27), and the cutting tool (27) to the workpiece (30). On the other hand, a scanning device (22, 23) for relatively moving in the thickness direction of the workpiece (30) and the radial direction of the workpiece (30), the spindle (25), and the operating device (22, 23), the workpiece (30) is cut by the cutting tool (27), and as a result, the Fresnel surface (11) and the rise surface (12) are alternately formed concentrically. And a control unit (28) for manufacturing a mold (40) of the lens (1), wherein the control unit (28) is arranged in the mold (40) with the Fresnel surface (11). 1) of the Fresnel type surface (41) to be the type of Alternately a Fresnel mold surface machining process for cutting the surface and a rise mold surface machining process for cutting one of the rise mold surfaces (42) which will be the mold of the rise surface (12) in the mold (40). Repeatedly, during the Fresnel mold surface machining step, the rotational speed of the workpiece (30) with respect to the cutting tool (27) is kept constant, and during the rise mold surface machining process, the rotational speed is changed. It is the cutting device characterized by these. With this configuration, an effect equivalent to that of the invention described in claim 5 can be obtained.

  In the invention according to claim 8, the spindle (25) for rotating the workpiece (30) relative to the cutting tool (27) and the cutting tool (27) on the workpiece (30). On the other hand, a scanning device (22, 23) for relatively moving in the thickness direction of the workpiece (30) and the radial direction of the workpiece (30), the spindle (25), and the operating device (22, 23), the workpiece (30) is cut by the cutting tool (27), and as a result, the Fresnel surface (11) and the rise surface (12) are alternately formed concentrically. And a control unit (28) for manufacturing a mold (40) of the lens (1), wherein the control unit (28) is arranged in the mold (40) with the Fresnel surface (11). 1) of the Fresnel type surface (41) to be the type of A fresnel mold surface machining process for cutting the mold, a rise mold surface machining process for cutting one of the rise mold surfaces (42) to be the mold of the rise surface (12) in the mold (40), and the fresnel Repeating the step of separating the cutting tool (27) from the workpiece (30) between the mold surface machining step and the rise die surface machining step, during the Fresnel mold surface machining step and during the rise die surface machining step. The rotation of the workpiece (30) with respect to the cutting tool (27) is kept constant, and in the step of releasing, the rotation of the cutting tool (27) is separated from the workpiece (30). It is a cutting device characterized by changing the number. Thus, the same effect as that of the invention described in claim 6 can be obtained.

  The invention according to claim 9 is the cutting apparatus according to any one of claims 3, 4, 7, and 8, wherein the control unit (28) has a working diameter of the cutting tool (27). Is recorded, and when the rotation speed is changed, the processing diameter of the current bite (27) is calculated, and then, based on the recorded correspondence expression data The rotation speed corresponding to the calculated machining diameter is calculated, and the spindle 25 is controlled so as to realize the calculated rotation speed. By doing so, the cutting device automatically adjusts the number of rotations only by having the operator record the data of the corresponding relational expression in the cutting device.

  In addition, the code | symbol in the bracket | parenthesis in the said and the claim shows the correspondence of the term described in the claim, and the concrete thing etc. which illustrate the said term described in embodiment mentioned later. .

It is a figure which shows the head-up display 50 in which the Fresnel lens 1 which concerns on embodiment of this invention is used. 1 is a plan view of a Fresnel lens 1. FIG. It is AA sectional drawing of FIG. 2 is an enlarged view of a Fresnel surface 11 and a rise surface 12. FIG. 2 is a configuration diagram of an NC lathe 2. FIG. It is a flowchart which shows the detailed process of cutting. It is a schematic diagram which shows the positional relationship of the to-be-processed object 30 and the cutting tool 27 at the time of cutting. 5 are graphs 50 and 51 showing the relationship between the rotational speed and peripheral speed and the machining diameter. 6 is a schematic diagram showing a scanning process of the cutting tool 27. FIG. FIG. 6 is a schematic diagram showing a locus 52 of a bite 27. It is a flowchart which shows the detailed process of the cutting process in 2nd Embodiment. It is a schematic diagram which shows the scanning process of the byte | cutting-tool 27 in 2nd Embodiment. FIG. 5 is a schematic diagram showing a locus 53 of a bite 27. It is a flowchart which shows the detailed process of the cutting process in 3rd Embodiment. It is a flowchart which shows the detailed process of the cutting process in 3rd Embodiment. 2 is a cross-sectional view of a mold 4 for manufacturing the Fresnel lens 1. FIG.

(First embodiment)
The first embodiment of the present invention will be described below. The Fresnel lens manufactured in this embodiment is used for a head-up display 50 as shown in FIG. 1, for example. In the head-up display 50, the image projector 52 emits image light of a desired image in a case 51 installed on an instrument panel or the like, and the image light is reflected by the concave mirror 53 and the concave mirror 54. The reflected light exits from the upper surface of the case 51 indicated by hatching and is projected onto the image display unit 55 in the front windshield WS. The Fresnel lens 1 of the present embodiment is arranged on the upper surface of the case 51 through which the reflected light passes, so that the reflected light passes through the Fresnel lens 1, and as a result, the image is enlarged on the image display unit 55. By such an action of the Fresnel lens, it is possible to display a large image in the image display unit 55 while reducing the size of the case 51.

  2 and 3 are a perspective view and a side view of the Fresnel lens 1. As the material of the Fresnel lens 1, a resin such as a polycarbonate resin is employed. When attaching the Fresnel lens 1 to the case 51, the upper direction in FIG. 3 is attached to the case 51.

  In the Fresnel lens 1 manufactured in the present embodiment, the surface of the convex lens is divided by a plurality of concentric circles, and in order to make the height of each of the divided sections (Fresnel surface 11) substantially uniform, It is a lens with a step in between. Accordingly, the Fresnel lens 1 is formed with the fresnel surface 11 and the rise surface 12 for providing a step alternately in a concentric manner.

  2 and 3, the ratio between the size of the entire Fresnel lens 1 and the size of the Fresnel surface 11 and the rise surface 12 is exaggerated in order to clearly represent the shapes of the Fresnel surface 11 and the rise surface 12. ing. Actually, the diameter of the Fresnel lens 1 is about 180 mm, and the size of each Fresnel surface 11 and the rise surface 12 is such that the length of the Fresnel surface 11 in the lens radial direction is 0.3 mm as shown in FIG. The height of the rise surface 12 is 0.1 mm. Therefore, about 300 Fresnel surfaces 11 and rise surfaces 12 are formed on the Fresnel lens 1.

  Further, the Fresnel lens 1 of the present embodiment is desired to have high shape accuracy and stable surface roughness in order to project a clear image on the image display unit 55. Specifically, a shape accuracy of less than 500 nm and a surface roughness Rz of less than 50 nm are desirable, and the radius of curvature of the groove 13 between the Fresnel surface 11 and the rise surface 12 is desirably less than 5 μm.

  In the present embodiment, cutting is employed as a method for manufacturing such a Fresnel lens 1. FIG. 5 shows the configuration of the NC lathe 2 used for this cutting process. As this NC lathe 2, for example, an ultra-precision lathe ASP01 manufactured by Fujikoshi (drive control unit is 1 nm) may be used.

  As shown in this figure, the NC lathe 2 includes a bed 21, a Z moving table 22, an X moving table 23, a spindle stock 24, a spindle 25, and a tool rest 26.

  The Z moving table 22 and the X moving table 23 are respectively arranged on the upper surface of the bed portion 21 that serves as a base, and an X-axis direction and a Z-axis direction in the figure with respect to the bed portion 21 by a driving mechanism (motor or the like) not shown. It can move in the direction.

  The headstock 24 is a member that is fixed to the upper surface of the Z moving table 22 and incorporates a drive mechanism (such as a motor) for the spindle 25. The spindle 25 is supported by the spindle base 24 and is rotated with respect to the spindle base 24 by the drive mechanism described above. As will be described later, the rotational speed of the main shaft 25 can be controlled. A workpiece 30 that is a material of the Fresnel lens 1 can be fixed to the main shaft 25.

  The tool post 26 is disposed on the upper surface of the X moving table 23 so that various tools 27 can be attached thereto. The cutting tool 27 of the present embodiment is a diamond cutting tool having a fine tip curvature radius (for example, 5 μm) in order to realize high-precision processing.

  Further, the NC lathe 2 includes a control unit 28 that controls a drive mechanism for the Z movement table 22, the X movement table 23, and the main shaft 25. When the control unit 28 receives an input of the NC program 29 in which the operation content of the NC lathe 2 is described, the control unit 28 reads the received NC program 29 and records it on a storage medium, and further drives the NC lathe 2 according to the NC program 29. By controlling each of the mechanisms, the Z movement table 22 and the X movement table 23 are moved, and the operation of the spindle 25 is controlled. The NC program 29 includes data that defines the position and moving speed of the Z moving table 22 in the Z-axis direction and the position and moving speed of the X moving table 23 in the X-axis direction during cutting. Further, the rotation speed of the main shaft 25 can be controlled by the control unit 28 or can be directly controlled by the operator by operating the rotation speed setting unit (not shown).

  The control unit 28 is provided with a display device 28a, and the control unit 28 displays the current control state of the Z movement table 22 and the X movement table 23 using the display device 28a. Yes. More specifically, the position coordinate value in the Z-axis direction (that is, the Z coordinate value) of the Z movement table 22 and the position coordinate value in the X-axis direction (that is, the X coordinate value) of the X movement table 23 are processed. It is displayed on the display device 28a as a position coordinate display. The time required for processing one rise surface 12 is about 30 seconds to 1 minute.

  Hereinafter, the cutting process of the Fresnel lens 1 using the NC lathe 2 will be described. In the cutting process, specifically, the workpiece 30 is profile-cut with the cutting tool 27 so that the surface of the workpiece 30 matches the surface of the Fresnel lens 1 with the desired shape accuracy.

  First, as a preparatory work, a workpiece 30 as a material of the Fresnel lens 1 is fixed to the main shaft 25 and a cutting tool 27 is attached to the tool rest 26.

  Next, actual cutting is performed. Specifically, the workpiece 30 is profile-cut with the cutting tool 27 so that the surface of the workpiece 30 matches the surface of the Fresnel lens 1 with the desired shape accuracy. FIG. 6 shows a flowchart of detailed steps of this cutting process.

  The outline of this cutting process is as follows. As shown in FIG. 7, the workpiece 30 is rotated relative to the cutting tool 27 by rotating the main shaft 25 to which the workpiece 30 is fixed. At that time, by moving the Z movement table 22 and the X movement table 23, the cutting tool 27 is moved with respect to the workpiece 30 in the thickness direction of the workpiece 30 (corresponding to the Z-axis direction) and the workpiece 30. Move relatively in the radial direction (corresponding to the X-axis direction). By adjusting the position change in the thickness direction and the radial direction, the nose of the cutting tool 27 is controlled to move in the radial direction while scraping the workpiece 30 along the desired surface shape of the Fresnel lens 1. Is possible. The Z movement table 22 and the X movement table 23 correspond to an example of a scanning device.

  Details of the cutting process will be described below. In the cutting process, first, the operator first confirms the number of steps to be provided on the workpiece 30 (that is, the number of rise surfaces 12), and determines the number of rotations of the main shaft 25 when the cutting tool 27 processes each Fresnel surface 11. Determine (step 100). In the present embodiment, the rotational speed is set to change between 400 rpm and 1000 rpm. However, while the cutting tool 27 is processing one Fresnel surface 11, the rotational speed is made constant.

  FIG. 8 schematically shows the relationship between the machining diameter and the rotational speed of the main shaft 25 as a graph 50. Here, the processing diameter refers to the distance from the center of rotation of the position on the workpiece 30 that the tool 27 is processing. As shown in this graph 50, in one Fresnel surface 11, the rotation speed is constant regardless of the machining diameter. However, between the adjacent Fresnel surfaces 11, the rotational speed is smaller on the side with the larger machining diameter. That is, as the Fresnel surface 11 is farther from the center of rotation, the number of rotations during processing is smaller.

  FIG. 8 also shows a graph 51 schematically showing the relationship between the machining diameter and the peripheral speed when the rotation speed is set as in the graph 50. Here, the circumferential speed refers to a component in the rotational direction (that is, the circumferential direction) of the relative speed between the position on the workpiece 30 where the cutting tool 27 is processing and the cutting tool 27. By making the rotation speed at the time of machining smaller as the Fresnel surface 11 is farther from the rotation center, as shown in this graph 51, the peripheral speed increases in proportion to the machining diameter in one Fresnel surface, There is not much difference in peripheral speed between adjacent Fresnel surfaces 11. As a result, when viewed as a whole of the workpiece 30, the peripheral speed slightly increases as the processing diameter increases, but the increase amount is much smaller than when the peripheral speed increases in proportion to the processing diameter, and the peripheral speed is substantially constant. It can be said that Therefore, the peripheral speed is not greatly different between the vicinity of the rotation center and the outer periphery of the workpiece 30, and for example, the surface roughness of the processing surface of the workpiece 30 can be made substantially constant.

  The characteristic point of the rotational speed determined in this way is that the rotational speed is changed between two adjacent Fresnel surfaces 11 and the rotational speed is kept constant within one Fresnel surface 11.

  Subsequently, the worker causes the control unit 28 to start executing a predetermined NC program 29 (step 110). Then, the control unit 28 rotates the spindle 25 and appropriately changes the positions of the Z moving table 22 and the X moving table 23 so that the nose of the bite 27 forms the desired shape of the Fresnel lens 1. The workpiece 30 starts to be cut with the cutting tool 27 while relatively moving the surface of the workpiece 30 in the thickness direction and the radial direction.

  Then, the control unit 28 executes a loop of steps 120 to 160 described below once to cut the pair of adjacent Fresnel surfaces 11 and the rise surface 12, and the loop is the same as the number of steps of the Fresnel lens 1. repeat. After the repetition of the loop, finally, the Fresnel surface 11 closest to the center is processed (this step is not shown) to obtain the completed Fresnel lens 1. Further, the operator adjusts the rotational speed of the main shaft 25 when the loop is repeated.

  More specifically, in each loop, first, the control unit 28 scans the Fresnel surface 11 on the cutting tool 27 according to the NC program 29 (relative movement in the thickness direction and the radial direction) as shown in FIG. This refers to cutting. The same applies hereinafter) (step 120).

  Then, the scanning of the Fresnel surface 11 proceeds in accordance with the NC program 29. After that, as shown in FIG. 9B, when the scanning of the Fresnel surface 11 is completed (step 130), the control unit 28 continues the NC program 29. Accordingly, as shown in FIG. 9C, the tool 27 is caused to start scanning the rise surface 12 (step 140).

  When the scanning on the rise surface 12 proceeds according to the NC program 29, the operator determines that the cutting tool 27 is scanning the rise surface 12, and changes the rotational speed of the spindle 25 (step 150). ). Specifically, the rotational speed of the main shaft 25 is adjusted so as to coincide with the rotational speed of the Fresnel surface 11 to be scanned next among the rotational speeds determined in step 100. Therefore, the rotational speed of the main shaft 25 changes while the cutting tool 27 is cutting the rise surface 12.

  The operator determines whether or not the cutting tool 27 is scanning the rise surface 12 by visually checking the processing position coordinate display of the control unit 28. Specifically, in the processing position coordinate display, when the Fresnel surface 11 is scanned, both the X coordinate value and the Z coordinate value change, but when the rise surface 12 is scanned, the Z coordinate value changes, but the X coordinate value is Since there is almost no change, the operator determines that the cutting tool 27 is scanning the rise surface 12 when the Z coordinate value changes greatly compared to the X coordinate value.

  Thereafter, when scanning of the rise surface 12 is completed (step 160), one loop is completed and the next loop is started, and scanning of the next Fresnel surface 11 is started according to the NC program 29 (step 120).

  Thus, in the cutting process of the present embodiment, the rotational speed of the main shaft 25 is kept constant during the processing of the Fresnel surface 11, and the rotational speed is changed during the processing of the rise surface 12. That is, as shown in FIG. 10, when the scanning locus of the cutting tool 27 is represented by a broken line 52, the rotational speed of the main shaft 25 is changed only while the cutting tool 27 is moving from the point 52a to the point 52b.

  Therefore, during the cutting of the Fresnel surface 11, no nano-level shaft shake accompanying the change in the rotation speed of the main shaft 25 occurs and rotation unevenness until the rotation speed stabilizes due to the change in the rotation speed of the main shaft 25 does not occur. As a result, the surface roughness and shape of the Fresnel surface 11 are not deteriorated. That is, a good finished surface can be obtained on the Fresnel surface 11 without being affected by rotational fluctuation.

  On the other hand, since the rotational speed of the main shaft 25 is changed during the cutting process of the rise surface 12, nano-level shaft shake occurs due to the rotational speed change, and the rotational unevenness until the rotational speed is stabilized due to the rotational change. As a result, the rise surface 12 may be deteriorated in surface roughness and shape. However, since the rise surface 12 does not transmit light in actual use of the Fresnel lens 1, the adverse effect is much smaller than when the surface roughness or shape deteriorates on the Fresnel surface 11.

  Further, although the rise surface 12 may be deteriorated in surface roughness and shape, the rotational speed of the main shaft 25 can be changed without stopping the movement of the cutting tool 27 and without adversely affecting the Fresnel surface 11. There is also an advantage.

  In the present embodiment, the process of processing the final Fresnel surface 11 after the completion of the loops of Steps 120 to 130 and Steps 120 to 160 in FIG. 6 corresponds to the Fresnel surface processing process. To 160 corresponds to the rise surface processing step.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. This embodiment is different from the first embodiment in the position of the cutting tool 27 when the rotational speed of the main shaft 25 is changed. More specifically, in this embodiment, when the cutting tool 27 finishes the processing of the Fresnel surface 11 and moves away from the workpiece 30, the rotational speed of the main shaft 25 is changed.

  The NC lathe 2 used in the present embodiment is the same as that in the first embodiment. Further, regarding the processing of the workpiece 30, the roughing processing may be the same as that in the first embodiment.

  Below, the cutting of the workpiece 30 in this embodiment is demonstrated. FIG. 11 shows a flowchart of detailed steps of this cutting process.

  The NC program 29 of the present embodiment includes the Fresnel surface 11 in addition to the position and movement speed of the Z movement table 22 in the Z-axis direction and the position and movement speed of the X movement table 23 in the X-axis direction during cutting. Data that specifies that the nose of the cutting tool 27 is moved away from the workpiece 30 and the movement of the cutting tool 27 (more precisely, the movement of the workpiece 30 with respect to the center of rotation) is stopped when the scanning is completed is included. .

  In the cutting process, the operator first confirms the number of steps to be provided on the workpiece 30 in advance, similarly to step 100 of FIG. 6, and determines the number of rotations of the main shaft 25 during processing (step 200). The relationship between the machining diameter and the rotational speed of the main shaft 25 is also the same as in the first embodiment (see FIG. 8). As in the first embodiment, while the cutting tool 27 is processing one Fresnel surface 11, the rotational speed is made constant.

  Subsequently, the operator causes the control unit 28 to start executing the predetermined NC program 29 (step 210), similarly to step 110 of the first embodiment.

  The control unit 28 processes the pair of adjacent Fresnel surfaces 11 and the rise surfaces 12 by executing a loop of steps 220 to 290 described below once, and repeats the loop by the number of steps of the Fresnel lens 1. . After the repetition of the loop, finally, the Fresnel surface 11 closest to the center is processed (this step is not shown), whereby the cutting process is completed and the Fresnel lens 1 is completed. Further, the operator adjusts the rotational speed of the main shaft 25 when the loop is repeated.

  In each loop, the operations of steps 220 and 230 are the same as the operations of steps 120 and 130 in FIG. 6 (see FIGS. 12A and 12B). When the scanning of the Fresnel surface 11 is completed, the control unit 28 then moves the nose of the cutting tool 27 away from the workpiece 30 as shown in FIG. 12C according to the NC program 29 (step 240). In this state, the movement of the byte 27 (that is, the movement of the Z movement table 22 and the X movement table 23) is stopped according to the NC program 29 (step 250).

  Subsequently, when confirming that the movement of the cutting tool 27 has stopped, the operator changes the rotational speed of the spindle 25 in the same manner as in step 150 of the first embodiment (step 260). Therefore, the rotational speed of the main shaft 25 changes while the nose of the cutting tool 27 is away from the workpiece 30.

  After changing the rotation speed of the spindle 25, the operator subsequently operates the NC lathe 2 to resume the movement of the cutting tool 27 under the control of the control unit 28 (step 270).

  Then, the control unit 28 moves the cutting tool 27 in accordance with the NC program 29, and starts processing the rise surface 12 in the same manner as Step 140 in the first embodiment (Step 280). Thereafter, when the processing of the rise surface 12 is completed (step 290), one loop is completed and the next loop is started, and scanning of the next Fresnel surface 11 is started according to the NC program 29 (step 220).

  As described above, in the cutting process of the present embodiment, the rotational speed of the main shaft 25 is kept constant during the processing of the Fresnel surface 11 and the processing of the rise surface 12, and the rise is performed after the processing of the Fresnel surface 11 is completed. Before the machining of the surface 12 is started, the cutting tool 27 is moved away from the workpiece 30 and stopped, and the rotation speed of the spindle 25 is changed in a state where the cutting tool 27 is stopped moving away from the workpiece 30. That is, as shown in FIG. 13, when the scanning locus of the cutting tool 27 is represented by the broken line 53, the rotation speed of the main shaft 25 is changed while the cutting tool 27 is stopped at the position of the point 53a.

  Therefore, during the machining of the Fresnel surface 11 and the rise surface 12, no nano-level shaft shake accompanying the change in the rotation speed of the main shaft 25 occurs, and the rotation until the rotation speed stabilizes as the rotation speed of the main shaft 25 changes. Unevenness does not occur, and as a result, the surface roughness and the shape of the Fresnel surface 11 and the rise surface 12 are not deteriorated. That is, a good finished surface can be obtained on the Fresnel surface 11 and the rise surface 12 without being affected by rotational fluctuation.

  In the present embodiment, unlike the first embodiment, there is a step in which the cutting tool 27 is moved away from the workpiece 30 and stopped after the processing of the Fresnel surface 11 is finished, so that the processing time is shorter than that in the first embodiment. Although longer, the rise surface 12 has the advantage that the surface roughness and shape do not deteriorate.

  In the present embodiment, the process of processing the final Fresnel surface 11 from Steps 220 to 230 in FIG. 11 and the repetition of the loop of Steps 220 to 290 corresponds to the Fresnel surface processing process, and Step 280 is performed. To 290 correspond to the rise surface processing step, and step 240 corresponds to the separation step.

(Third embodiment)
Next, a third embodiment of the present invention will be described. This embodiment is different from the first embodiment in that the control unit 28 automatically executes the rotation speed change in step 150 of FIG.

  In FIG. 14, the flowchart of the detailed process of the cutting process in this embodiment is shown. In addition, the operation | movement content of the step to which the same code | symbol is attached | subjected in the flowchart of FIG. 6 and FIG. 14 is mutually the same.

  In the NC program 29, in addition to the data defining the position and moving speed of the Z moving table 22 in the Z axis direction and the position and moving speed of the X moving table 23 in the X axis direction during cutting, the machining of the cutting tool 27 is performed. Data of a relational expression between the diameter and the rotational speed of the main shaft 25 is also included. As the data of the corresponding relational expression, for example, an expression in which the rotational speed decreases linearly as the machining diameter increases or an expression in which the rotational speed decreases in inverse proportion to the machining diameter may be used.

  Hereinafter, the cutting process will be described. In the cutting process of the present embodiment, first, the operator causes the control unit 28 to start executing a predetermined NC program 29 (step 110), whereby the loops of steps 120 to 160 are repeated. First, the Fresnel surface 11 is scanned by the control of the unit 28 (steps 120 and 130), and then the processing of the rise surface 12 is started (step 140).

  When machining of the rise surface 12 starts, the control unit 28 calculates the machining diameter of the current cutting tool 27 on the basis of the current X coordinate value and Z coordinate value (step 345), and subsequently records it in the NC program 29. Based on the data of the corresponding relational expression, the number of rotations corresponding to the calculated machining diameter is calculated (step 350). Subsequently, the rotational speed of the main shaft 25 is changed so as to realize the calculated rotational speed (step 355).

  Whether the control unit 28 is currently processing the Fresnel surface 11 or the rise surface 12 is based on the fact that the Z coordinate value changes greatly compared to the X coordinate value. It may be determined that 27 is scanning the rise surface 12. Alternatively, the X-coordinate and Z-coordinate values when machining the rise surface 12 are recorded in advance in the NC program 29 as the X-coordinate and Z-coordinate values when changing the rotation speed, and the control unit 28 Determines that the rise surface 12 is scanned when the X-coordinate and Z-coordinate values for changing the rotation speed in the NC program 29 are realized, and steps 345 to 355 are executed. It may be.

  After the rotation speed is changed, when the scanning of the rise surface 12 is completed (step 160), one loop is completed and the next loop is started. In this way, the control unit 28 reads the data of the correspondence expression between the machining diameter and the rotation speed in advance, and at a certain temporary point during the processing of the rise surface 12, the rotation speed corresponding to the machining diameter at that time is represented by the relational expression. The rotation speed of the spindle 25 is changed so as to realize the determined rotation speed calculated based on the data.

  By doing so, as in the first embodiment, the surface roughness and shape of the Fresnel surface 11 are not deteriorated. That is, a good finished surface can be obtained on the Fresnel surface 11 without being affected by rotational fluctuation. Further, since the control unit 28 automatically changes the rotation speed in accordance with the machining diameter, the labor of the operator can be saved. Further, the NC lathe 2 automatically adjusts the number of revolutions only by having the operator record the data of the corresponding relation formula on the NC lathe 2.

  In the present embodiment, the processing process of the last Fresnel surface 11 after the completion of the loop of Steps 120 to 130 in FIG. 14 and Steps 120 to 160 corresponds to the Fresnel surface processing process, and Step 140 To 160 corresponds to the rise surface processing step.

(Fourth embodiment)
Next, a fourth embodiment of the present invention will be described. This embodiment is different from the second embodiment in that the control unit 28 automatically executes the operations of changing the rotation speed and resuming the movement in steps 260 and 270 of FIG.

  FIG. 15 shows a flowchart of detailed steps of the cutting process in the present embodiment. In addition, the operation | movement content of the step to which the same code | symbol is attached | subjected in the flowchart of FIG. 11 and FIG. 15 is mutually the same.

  The NC program 29 includes, in addition to data defining the position and movement speed in the Z-axis direction of the Z movement table 22 and the position and movement speed in the X-axis direction of the X movement table 23 during cutting, the third embodiment. The data of the correspondence relation between the machining diameter of the cutting tool 27 and the rotational speed of the main shaft 25, which is created in the same manner as described above, is also included.

  Hereinafter, the cutting process will be described. In the cutting process of the present embodiment, first, the operator causes the control unit 28 to start executing a predetermined NC program 29 (step 210), whereby the loop of steps 220 to 290 is repeated, and in each loop, the control is performed. The Fresnel surface 11 is first scanned by the control of the unit 28 (steps 220 and 230), and then the nose of the cutting tool 27 is moved away from the workpiece 30 and stopped (steps 240 and 250).

  With the movement of the cutting tool 27 stopped, the control unit 28 calculates the machining diameter of the current cutting tool 27 based on the current X coordinate value and Z coordinate value (step 455). Based on the recorded data of the corresponding relational expression, the rotation speed corresponding to the calculated machining diameter is calculated (step 460). Subsequently, the rotational speed of the main shaft 25 is changed so as to realize the calculated rotational speed (step 465). After that, the control unit 28 restarts the movement of the cutting tool 27 after changing the rotational speed (step 470), and processes the rise surface 12 (steps 280, 290).

  By doing so, as in the second embodiment, the surface roughness and shape of the Fresnel surface 11 and the rise surface 12 are not deteriorated. That is, a good finished surface can be obtained on the Fresnel surface 11 and the rise surface 12 without being affected by rotational fluctuation. Further, since the control unit 28 automatically changes the rotation speed in accordance with the machining diameter, the labor of the operator can be saved. Further, the NC lathe 2 automatically adjusts the number of revolutions only by having the operator record the data of the corresponding relation formula on the NC lathe 2.

  In the present embodiment, the process of processing the final Fresnel surface 11 from Steps 220 to 230 in FIG. 15 and the repetition of the loop of Steps 220 to 290 corresponds to the Fresnel surface processing process, and Step 280 is performed. To 290 correspond to the rise surface processing step, and step 240 corresponds to the separation step.

(Other embodiments)
As mentioned above, although embodiment of this invention was described, the scope of the present invention is not limited only to the said embodiment, The various form which can implement | achieve the function of each invention specific matter of this invention is included. It is.

  For example, in the above embodiment, the shape accuracy of less than 500 nm and the surface roughness Rz of less than 50 nm are desirable for the Fresnel lens 1, and the radius of curvature of the groove 13 between the Fresnel surface 11 and the rise surface 12 is less than 5 μm. However, the manufactured Fresnel lens 1 is not necessarily limited to such a condition.

  In the first and second embodiments, the operations in steps 150, 260, and 270 may be realized by automatic control of the control unit 28 instead of a person. In that case, the NC program 29 includes data on the timing of changing the rotational speed of the spindle 25 and data on the rotational speed after the change at each timing. In that case, the control unit 28 determines in step 150 whether the Fresnel surface 11 is being scanned or the rise surface 12 is being scanned by the same method as in the third embodiment.

  In the third and fourth embodiments, the control unit 28 calculates the number of rotations corresponding to the current machining diameter based on the correspondence relation recorded in advance in the NC program 29. From the beginning, the correspondence table between the machining diameter and the rotational speed may be recorded in the NC program 29 in advance.

  In this case, the NC program 29 includes, in addition to data defining the position and moving speed of the Z moving table 22 in the Z axis direction and the position and moving speed of the X moving table 23 in the X axis direction during cutting, Data on the number of rotations of the spindle 25 at each machining diameter (that is, a correspondence table) is also included. In steps 350 and 450, the control unit 28 calculates the rotation speed corresponding to the current machining diameter based on the correspondence table.

  Further, in the first embodiment, the cutting tool 27 is scanned from the outer periphery of the workpiece 30 toward the rotation center, but conversely, the tool 27 is scanned from the rotation center of the workpiece 30 toward the outer periphery. It may be. Even in such a case, it is sufficient that the rotational speed of the main shaft 25 is increased during the cutting of the rise surface 12.

  Also in the second embodiment, the cutting tool 27 is scanned from the outer periphery of the workpiece 30 toward the rotation center, but conversely, the tool 27 is scanned from the rotation center of the workpiece 30 toward the outer periphery. It may be. In that case, contrary to the second embodiment, after the cutting of one rise surface 12 is finished, the cutting tool 27 is separated from the workpiece 30 and stopped before the next rise surface 12 is cut. It is only necessary to increase the rotational speed of the main shaft 25 in the stopped state. That is, the tool 27 is separated from the workpiece 30 and stopped, and the rotational speed of the main shaft 25 is increased in the stopped state in the boundary between the Fresnel surface 11 and the rising surface 12 (see FIG. 4), but immediately after processing the protruding apex portion 14.

  Moreover, in the said embodiment, although the lens for expansion projection of the head-up display 50 is illustrated as an application of the cut Fresnel lens 1, as an application of the Fresnel lens 1, it is not restricted to such a thing. For example, it can be used for a lens of a high-detail overhead projector, a high-detail loupe, and the like.

  Further, in the above embodiment, as the Fresnel lens, the surface of the convex lens is divided by a plurality of concentric circles, and in order to make the height of each divided section (Fresnel surface) substantially uniform, between the adjacent sections. A convex Fresnel lens with a step is illustrated. However, even if this convex Fresnel lens is replaced with a concave Fresnel lens, the same effect can be obtained by using the same cutting process. A concave Fresnel lens means that the surface of a concave lens is divided into a plurality of concentric circles, and in order to make the height of each divided section (Fresnel surface) substantially uniform, there is a step between adjacent sections. This is a Fresnel lens.

  Moreover, in the said embodiment, although the Fresnel lens 1 is manufactured using the NC lathe 2, the NC lathe 2 is not the Fresnel lens 1, but the Fresnel lens 1 by resin molding (for example, injection molding). It can also be used for cutting a mold for manufacturing. FIG. 16 shows a cross-sectional view of such a mold 40.

  In this case as well, the workpiece that is the material of the mold 40 can be cut by the same method as in the above embodiment. In that case, in each of the above-described embodiments, the workpiece 30 is read as a workpiece to be a material of the mold 40 of the Fresnel lens (for example, a plate mainly made of iron-based material plated with nickel). The Fresnel surface 11 is read as “Fresnel mold surface 41 which becomes the mold of the Fresnel surface 11 of the Fresnel lens 1 when molded in the mold”, and the rise surface 12 is “the mold of the rise surface 12 of the Fresnel lens 1 when molded in the mold”. Rise mold surface 42 ", the Fresnel surface machining process is read as a Fresnel mold surface machining process, and the rise surface machining process is read as a rise surface machining process.

  If read as such, the cutting method of the present invention can be understood as a mold 40 of a Fresnel lens. In the mold 40 manufactured in this way, the Fresnel lens 1 manufactured using such a mold 40 also faces the Fresnel surface (or the surface on the mold forming the Fresnel surface). The roughness and shape are not deteriorated.

  In the above embodiment, the NC lathe 2 is used as an apparatus for cutting the Fresnel lens 1 or the mold 40. However, if the cutting apparatus is capable of realizing the machining function as in the above embodiment, the NC lathe 2 A device other than the lathe 2 (for example, a machining center) may be used.

DESCRIPTION OF SYMBOLS 1 Fresnel lens 2 NC lathe 11 Fresnel surface 12 Rise surface 22 Z movement table 23 X movement table 25 Spindle 27 Bit 28 Control unit 28a Display device 29 NC program 30 Work piece 40 Mold 41 Fresnel type surface 42 Rise type surface 50 Machining Graph 51 showing relationship between diameter and rotation speed Graph 52 showing relationship between machining diameter and peripheral speed, 53 Machining locus of byte 27

Claims (9)

The work piece (30) is rotated relative to the cutting tool (27), and the cutting tool (27) is moved relative to the work piece (30) in the thickness direction of the work piece (30) and the work piece. The workpiece (30) is cut with the cutting tool (27) by relatively moving in the radial direction of the workpiece (30). As a result, the Fresnel surface (11) and the rise are alternately formed concentrically. A method for manufacturing a Fresnel lens (1) having a surface (12) formed thereon, comprising:
Alternately repeating a Fresnel surface machining step of cutting one of the Fresnel surfaces (11) and a rise surface machining step of cutting one of the rise surfaces (12),
During the Fresnel surface machining step, the number of rotations of the workpiece (30) relative to the bite (27) is kept constant,
The method of manufacturing a Fresnel lens, wherein the rotation speed is changed during the rise surface processing step. The work piece (30) is rotated relative to the cutting tool (27), and the cutting tool (27) is moved relative to the work piece (30) in the thickness direction of the work piece (30) and the work piece. The workpiece (30) is cut with the cutting tool (27) by relatively moving in the radial direction of the workpiece (30). As a result, the Fresnel surface (11) and the rise are alternately formed concentrically. A method for manufacturing a Fresnel lens (1) having a surface (12) formed thereon, comprising:
A Fresnel surface processing step of cutting one of the Fresnel surfaces (11), a rise surface processing step of cutting one of the rise surfaces (12), the Fresnel surface processing step, and the rise surface processing steps. Repeating the step of separating the bite (27) from the workpiece (30) in between,
During the Fresnel surface processing step and the rise surface processing step, the number of rotations of the workpiece (30) relative to the cutting tool (27) is kept constant,
In the separating step, the rotational speed is changed in a state where the cutting tool (27) is separated from the workpiece (30). A spindle (25) for rotating the workpiece (30) relative to the bite (27);
Scanning device (22, 23) for moving the cutting tool (27) relative to the workpiece (30) in the thickness direction of the workpiece (30) and the radial direction of the workpiece (30) When,
The workpiece (30) is cut by the cutting tool (27) by controlling the main shaft (25) and the operating device (22, 23). As a result, the Fresnel surface (11) is alternately formed concentrically. And a control unit (28) for manufacturing the Fresnel lens (1) on which the rise surface (12) is formed,
The control unit (28) alternately repeats a Fresnel surface processing step of cutting one of the Fresnel surfaces (11) and a rise surface processing step of cutting one of the rise surfaces (12), During the Fresnel surface processing step, the rotational speed of the workpiece (30) with respect to the bite (27) is kept constant, and during the rise surface processing step, the rotational speed is changed. Cutting device. A spindle (25) for rotating the workpiece (30) relative to the bite (27);
Scanning device (22, 23) for moving the cutting tool (27) relative to the workpiece (30) in the thickness direction of the workpiece (30) and the radial direction of the workpiece (30) When,
The workpiece (30) is cut by the cutting tool (27) by controlling the main shaft (25) and the operating device (22, 23). As a result, the Fresnel surface (11) is alternately formed concentrically. And a control unit (28) for manufacturing the Fresnel lens (1) on which the rise surface (12) is formed,
The control unit (28) includes: a Fresnel surface machining step for cutting one of the Fresnel surfaces (11); a rise surface machining step for cutting one of the rise surfaces (12); and the Fresnel surface machining. And the step of separating the cutting tool (27) from the workpiece (30) between the step and the rise surface processing step, and the workpiece is processed during the Fresnel surface processing step and the rise surface processing step. Keeping the rotational speed of the object (30) relative to the cutting tool (27) constant, and in the step of releasing, changing the rotating speed in a state in which the cutting tool (27) is separated from the workpiece (30). A cutting device characterized. The work piece (30) is rotated relative to the cutting tool (27), and the cutting tool (27) is moved relative to the work piece (30) in the thickness direction of the work piece (30) and the work piece. The workpiece (30) is cut with the cutting tool (27) by relatively moving in the radial direction of the workpiece (30). As a result, the Fresnel surface (11) and the rise are alternately formed concentrically. A mold manufacturing method for manufacturing a mold (40) of a Fresnel lens (1) having a surface (12) formed thereon,
A Fresnel mold surface machining step for cutting one of the Fresnel mold surfaces (41) to be a mold of the Fresnel surface (11) in the mold (40); and the rise surface (12) in the mold (40). Alternately repeating the rise mold surface machining step of cutting one of the rise mold surfaces (42) to be the mold of
During the Fresnel mold surface machining step, the rotational speed of the workpiece (30) relative to the bite (27) is kept constant,
The mold manufacturing method, wherein the number of rotations is changed during the rise mold surface machining step. The work piece (30) is rotated relative to the cutting tool (27), and the cutting tool (27) is moved relative to the work piece (30) in the thickness direction of the work piece (30) and the work piece. The workpiece (30) is cut with the cutting tool (27) by relatively moving in the radial direction of the workpiece (30). As a result, the Fresnel surface (11) and the rise are alternately formed concentrically. A mold manufacturing method for manufacturing a mold (40) of a Fresnel lens (1) having a surface (12) formed thereon,
A Fresnel mold surface machining step for cutting one of the Fresnel mold surfaces (41) to be a mold of the Fresnel surface (11) in the mold (40); and the rise surface (12) in the mold (40). The cutting tool (27) is placed between the rise die surface machining step for cutting one of the rise die surfaces (42) to be the mold, the Fresnel die surface machining step, and the rise die surface machining step. Repeating the step of separating from (30),
During the Fresnel type surface processing step and the rise type surface processing step, the number of rotations of the workpiece (30) relative to the cutting tool (27) is kept constant,
The Fresnel lens mold manufacturing method, wherein, in the separating step, the rotational speed is changed in a state where the cutting tool (27) is separated from the workpiece (30). A spindle (25) for rotating the workpiece (30) relative to the bite (27);
Scanning device (22, 23) for moving the cutting tool (27) relative to the workpiece (30) in the thickness direction of the workpiece (30) and the radial direction of the workpiece (30) When,
The workpiece (30) is cut by the cutting tool (27) by controlling the main shaft (25) and the operating device (22, 23). As a result, the Fresnel surface (11) is alternately formed concentrically. And a control unit (28) for producing a mold (40) of the Fresnel lens (1) on which the rise surface (12) is formed,
The control unit (28) includes a Fresnel mold surface machining step for cutting one of the Fresnel mold surfaces (41) to be the mold of the Fresnel surface (11) in the mold (40), and the mold (40 ) And a rise mold surface machining step for cutting one of the rise mold surfaces (42) to be a mold of the rise surface (12) are alternately repeated. During the Fresnel mold surface machining process, the workpiece A cutting apparatus characterized in that the number of rotations of (30) with respect to the cutting tool (27) is kept constant, and the number of rotations is changed during the rise die surface machining step. A spindle (25) for rotating the workpiece (30) relative to the bite (27);
Scanning device (22, 23) for moving the cutting tool (27) relative to the workpiece (30) in the thickness direction of the workpiece (30) and the radial direction of the workpiece (30) When,
The workpiece (30) is cut by the cutting tool (27) by controlling the main shaft (25) and the operating device (22, 23). As a result, the Fresnel surface (11) is alternately formed concentrically. And a control unit (28) for producing a mold (40) of the Fresnel lens (1) on which the rise surface (12) is formed,
The control unit (28) includes a Fresnel mold surface machining step for cutting one of the Fresnel mold surfaces (41) to be the mold of the Fresnel surface (11) in the mold (40), and the mold (40 ) Between the rise die surface machining step for cutting one of the rise die surfaces (42) to be the mold of the rise surface (12), and between the Fresnel die surface machining step and the rise die surface machining step. The step of separating (27) from the workpiece (30) is repeated, and during the Fresnel type surface processing step and the rise type surface processing step, the bit (27) of the workpiece (30). The cutting device is characterized in that, in the step of keeping the rotational speed with respect to the constant and releasing, the rotational speed is changed in a state where the cutting tool (27) is separated from the workpiece (30). The control unit (28) records data of a relational expression between the machining diameter of the cutting tool (27) and the rotational speed,
When changing the rotation speed, the machining diameter of the current bite (27) is calculated, and then the rotation speed corresponding to the calculated machining diameter is calculated based on the recorded data of the corresponding relational expression. The cutting apparatus according to any one of claims 3, 4, 7, and 8, wherein the main shaft 25 is controlled so as to realize the rotational speed.

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