JP5453459B2 - Grinding method of lens spherical surface using dish-shaped grinding wheel - Google Patents

Description

  The present invention relates to a spherical lens grinding method using a spherical core type lens grinding apparatus. More specifically, the present invention relates to a method for grinding a lens spherical surface, in which the rough grinding process and the fine grinding process are unified, and the rough grinding and the fine grinding of the lens material can be continuously performed using only the dish-shaped grindstone for fine grinding.

  In the spherical lens grinding process, rough grinding is performed on the lens material made of press-molded products or the cylindrical lens material obtained by cutting the round rod-shaped lens material (rough grinding process) A rough grinding lens having a roughly spherical lens surface is obtained. Next, fine grinding is performed on the spherical lens surface of the rough grinding lens (fine grinding step) to obtain a fine grinding lens having a spherical lens surface with a predetermined shape accuracy. The spherical lens surface obtained by the grinding process is polished to obtain a lens having a lens spherical surface with a target final shape accuracy.

  Thus, the conventional grinding process of the spherical lens includes a rough grinding process and a fine grinding process. In the rough grinding process, rough grinding is performed by a grinder using a cup-type grindstone, and in the fine grinding process, fine grinding is performed by a grinding apparatus using a dish-shaped grindstone. Such spherical lens grinding methods are disclosed in Patent Documents 1, 2, and 3. In Patent Documents 1 and 2, rough grinding and fine grinding are performed without using separate devices by exchanging the cup-type grindstone and the dish-shaped grindstone in the same grinding device. Patent Document 3 discloses a method of performing fine grinding using a cup-type grindstone used for rough grinding.

JP 2006-297520 A JP 2009-66724 A JP 2009-90414 A

  The spherical lens grinding method composed of the rough grinding process and the fine grinding process has the following problems to be solved. First, because it is difficult to maintain the processing accuracy of rough grinding, in the fine grinding process, there is a case where it is difficult to maintain the precision of precision grinding due to severe wear of the dish-shaped grindstone due to variations in the shape of the lens material. . In addition, rough grinding and fine grinding require different processing techniques, and engineers skilled in each processing technique are required.

  In view of these points, the object of the present invention is to unify the rough grinding process and the fine grinding process, and to grind the surface of the lens material using only the dish-shaped tool used for fine grinding, and to the polishing process. The object of the present invention is to propose a spherical lens grinding method capable of obtaining a precisely ground lens spherical surface that can be transferred.

In order to solve the above problems, the present invention provides:
A dish-shaped grindstone having a spherical grindstone surface provided with diamond abrasive grains is pressed against a surface to be ground of a lens material to be ground with a predetermined processing pressure, and in this state, the dish-shaped grindstone is rotated at a predetermined rotation speed. A method of grinding a lens spherical surface using a dish-shaped grindstone that grinds the surface to be ground into a spherical surface while rocking,
An initial grinding step in which the machining pressure is a first machining pressure, and the rotational speed is ground at a first rotational speed;
A medium-term grinding process in which the machining pressure is a second machining pressure, and the rotational speed is ground at a second rotational speed;
A second grinding step in which the machining pressure is a third machining pressure, and the rotational speed is ground at a third rotational speed;
The second processing pressure is a pressure at which the spherical grindstone surface can bite into the lens material, the hardness of the lens material, and the surface to be ground of the lens material and the spherical grindstone surface of the dish-shaped grindstone From the contact area, the amount of biting of the dish-shaped grindstone is obtained, and the second processing pressure is calculated based on the amount of biting,
The second rotational speed is set to a rotational speed at which the diamond abrasive grains of the dish-shaped grindstone can bite into the lens material when the processing pressure is set to the second processing pressure,
Setting the first processing pressure to a value lower than the second processing pressure, and setting the first rotational speed to a value lower than the second rotational speed;
The third processing pressure is set to a value lower than the first processing pressure, and the third rotational speed is set to a value lower than the second rotational speed and higher than the first rotational speed. .

  The above “number of revolutions that can bite into the lens material” is the maximum number of revolutions that substantially eliminates the change in machining time when the machining pressure is set to the second machining pressure and the revolution speed of the dish-shaped grindstone is changed. The number of rotations is less than the number. That is, when the rotational speed is higher than the maximum rotational speed, the processing time is not shortened, slip occurs between the spherical grinding wheel surface of the dish-shaped grinding wheel and the surface to be ground of the lens material, and the abrasive grains are formed on the surface of the lens material. It becomes a situation that can not be eaten.

  Here, the initial grinding step is performed until a state in which the surface to be ground of the lens material is in contact with the spherical grindstone surface as a whole is formed. The process may be performed until a state thicker than the value by a preset dimension is formed.

  Further, at least in the medium-term grinding step, it is desirable to periodically change the region in which the surface to be ground of the lens material slides on the spherical grinding wheel surface of the dish-shaped grinding stone.

  In the present invention, when the hardness of the lens material is Knoop hardness 630, the second processing pressure is 10 kg / square cm, the second rotational speed is 1500 rpm, the first processing pressure is 2 kg / square cm, The first rotation speed can be set to 400 to 600 rpm, the third processing pressure can be set to 1.5 kg / square cm, and the third rotation speed can be set to 1000 rpm.

Next, the spherical core type lens grinding apparatus of the present invention,
A lens holder for holding the lens material;
A dish-shaped grindstone having a spherical grindstone surface against which the ground surface of the lens material held by the lens holder is pressed;
A pressurizing mechanism capable of selectively applying a first processing pressure, a second processing pressure and a third processing pressure as a processing pressure for pressing the lens material against the spherical grinding wheel surface;
A rotating mechanism for rotating the dish-shaped grindstone;
A swing mechanism for swinging the dish-shaped grindstone;
And a controller for controlling the driving of the pressurizing mechanism, the rotating mechanism, and the swinging mechanism to execute the above grinding method.

  According to the present invention, it is possible to simplify the processing technology, unify equipment, and unify management by processing only with the precision grinding processing technology of the lens. Quality can be improved.

It is a mechanism figure of the spherical-core-type lens grinding processing apparatus which grinds a lens spherical surface by the method of this invention. It is a schematic flowchart which shows the grinding operation of the apparatus of FIG. It is a graph which shows the relationship between the processing pressure and processing time in lens grinding. It is a graph which shows the relationship between the rotation speed of a grinding tool in lens grinding, and processing time.

  Embodiments of a method for grinding a lens spherical surface to which the present invention is applied will be described below with reference to the drawings.

(Spherical core lens grinding machine)
FIG. 1 is a mechanism diagram showing an example of a spherical core type lens grinding apparatus for grinding a spherical lens by the method of the present invention. The spherical core type lens grinding apparatus 1 includes an upper unit 2 and a lower unit 3. The upper unit 2 includes a lens holder 4 in a downward state. The lens holder 4 is attached to the lower end of the lens pressing shaft 5 and is pressed downward by the pressing cylinder 6 in the direction of the unit center axis 2a. It is possible. A lens material 7 to be processed can be held on the downward lens holding surface 4a of the lens holder 4 while being rotatable about the unit central axis 2a. Further, the upper unit 2 can move relative to the lower unit 3 in a direction approaching and leaving.

  The lower unit 3 includes a dish-shaped grindstone 8 in an upward state. The dish-shaped grindstone 8 has a concave spherical grindstone surface 8a including diamond abrasive grains. The upper unit 2 is provided on the spherical grindstone surface 8a. The to-be-ground surface 7a of the lens material 7 held on the side is pressed. The dish-type grindstone 8 is coaxially fixed to the upper end of the spindle shaft 9, and the spindle shaft 9 is rotationally driven around its central axis 9 a by a spindle motor 10. The dish-shaped grindstone 8 and its rotation mechanism (spindle shaft 9, spindle motor 10) are supported by a swing mechanism 11, which swings the dish-shaped grindstone 8 with its spherical grindstone surface 8a being the central axis. It is possible to oscillate in the set oscillating direction at the set oscillating angle R with the set oscillating angle θ around the oscillating center O located on 2a.

  Here, the pressure applied by the pressure cylinder 6 can be switched in three stages by the first regulator 12, the second regulator 13, and the third regulator 14. The working fluids whose pressures are set by the first to third regulators 12, 13, and 14 are supplied to the pressurizing cylinder 6 via first to third switching valves 15, 16, and 17 that can be switched on and off, respectively. It has come to be. The switching control of the applied pressure by the pressurizing mechanism (the lens pressurizing shaft 5, the pressurizing cylinder 6, the first to third regulators 12 to 14, the first to third switching valves 15 to 17) having this configuration is the first to the first. This can be done by switching the third switching valves 15-17.

  Next, the controller 18 performs drive control of each part, and the controller 18 performs switching control of the first to third switching valves 15 to 17 of the pressurizing mechanism. Further, the controller 18 monitors the grinding amount of the lens material 7 based on the measurement result by the length measuring device 19, and performs switching control of the switching valves 15 to 17 according to the grinding amount, so that the lens material 7 The processing pressure for pressing the surface to be ground 7a against the spherical grindstone surface 8a of the dish-shaped grindstone 8 is switched. Further, the controller 18 drives and controls the spindle motor 10 via the inverter 20 to control the rotational speed of the dish-shaped grindstone 8. Further, the controller 18 drives and controls the rocking mechanism 11 via the driver 21 to perform switching control of the rocking direction and rocking angle θ of the dish-shaped grindstone 8, change of the rocking position, and the like.

(Example of grinding operation)
FIG. 2 is a schematic flowchart showing the spherical lens grinding operation by the spherical core type lens grinding apparatus 1. 1 and 2, first, the lens material 7 is attached to the lens holding surface 4 a of the lens holder 4, and the surface 7 a to be ground of the lens material 7 is pushed against the spherical grinding wheel surface 8 a of the dish-shaped grindstone 8. The contact state is formed (lens material supply step ST1).

  In this state, rotation and swinging of the dish-shaped grindstone 8 is started, and grinding of the surface 7a to be ground of the lens material 7 is started. In the initial grinding step ST2 from when the grinding process starts until a predetermined time elapses, the grinding process is performed with the lens material 7 pressed against the dish-shaped grindstone 8 with the processing pressure set in the first regulator 12. Since the area where the lens material 7 is in contact with the dish-shaped grindstone 8 is small, it is desirable that the processing pressure be kept to a minimum so that the lens material 7 does not fall out between the lens holder 4 and the dish-shaped grindstone 8. It is smaller than the processing pressure in the next-stage medium-term grinding process. In addition, the rotational speed of the dish-shaped grindstone 8 in the initial grinding process is desirably a low rotational speed, but is preferably 400 to 600 rpm in consideration of the processing time. This number of rotations is also smaller than the number of rotations in the next medium-term grinding process.

  In the initial grinding step ST2, when the grinding of the grinding surface 7a of the lens material 7 proceeds and the grinding surface 7a is substantially in contact with the spherical grinding wheel surface 8a of the dish-shaped grinding stone 8, the processing pressure is set to the second. The machining pressure set in the regulator 13 is switched to. As a result, the grinding process shifts to the medium-term grinding step S3.

  The processing pressure in the medium-term grinding process ST3 is set to a pressure at which the abrasive grains (diamond bite) of the dish-shaped grindstone 8 can bite into the lens material 7. It is desirable to set the processing pressure to the minimum value of the pressure that can bite into the lens material 7 or a value in the vicinity thereof. The surface roughness usually required in spherical lens grinding is about 4 μm. Therefore, the processing pressure applied to the lens material 7 depends on the hardness of the lens material 7 and the contact area between the surface 7a to be ground of the lens material and the spherical grindstone surface 8a of the dish-shaped grindstone 8. Based on this, the processing pressure in the medium-term grinding process can be calculated.

  Further, the rotational speed of the dish-shaped grindstone 8 in the medium-term grinding process is set to a rotational speed at which the abrasive grains (diamond bite) of the dish-shaped grindstone 8 can bite into the lens material 7. The number of rotations that can bite into the lens material 7 is the number of rotations equal to or less than the maximum number of rotations at which the change in processing time is substantially eliminated when the number of rotations of the dish-shaped grindstone is changed at the processing pressure set as described above. I mean. That is, when the rotational speed is higher than the maximum rotational speed, the processing time is not shortened, slip occurs between the spherical grinding wheel surface of the dish-shaped grinding wheel and the surface to be ground of the lens material, and the abrasive grains are formed on the surface of the lens material. It becomes a situation that can not be eaten. The rotational speed is preferably set to the maximum value of the rotational speed that can bite into the lens material 7 or a value in the vicinity thereof.

  When the grinding in the medium-term grinding process proceeds and the center thickness of the lens material 7 reaches a value before the target thickness, the processing pressure is switched to the processing pressure set in the third regulator 14. As a result, the grinding process shifts to the late grinding step ST4.

  In the latter grinding step, the surface roughness of the surface to be ground 7a is reduced in a state where the center wall thickness of the lens material 7 does not vary by slowing the progress of the grinding process (by reducing the rotational speed of the dish-shaped grindstone 8). Grind to achieve the desired surface roughness. In the late grinding process, the working pressure is set to a pressure lower than the working pressure in the initial grinding process, and the rotational speed of the dish-shaped grindstone 8 is lower than the rotational speed in the medium grinding process, and more than the rotational speed in the initial grinding process. Is also set to a high value.

  Here, spherical grinding using a dish-shaped grindstone is a cutting process using a diamond cutting tool having a plurality of cutting edges. Therefore, the processing pressure as the grinding processing condition and the rotational speed of the dish-shaped grindstone can be set according to the hardness of the lens material. That is, the processing pressure may be proportional to the hardness of the lens material, and the rotation speed may be inversely proportional thereto. Since the hardness data of the lens material can be easily obtained from a material catalog or the like, the optimum processing pressure and rotation speed can be obtained based on this data.

  Next, if the portion of the spherical grinding wheel surface 8a of the dish-shaped grinding wheel 8 that grinds the surface 7a to be ground of the lens material 7 is always the same, uneven wear occurs on the grinding wheel surface and the grinding shape changes. Therefore, periodically, the position of the spherical grindstone surface 8a (the sliding area of the grindstone surface 7a on the spherical grindstone surface 8a) on which the ground surface 7a of the lens material 7 abuts is changed, and uneven wear of the spherical grindstone surface 8a is caused. It is desirable to keep the grinding accuracy constant so that the whole is worn uniformly. It is desirable to change at least in the medium-term grinding process.

  As described above, in the present embodiment, in spherical grinding, it is possible to prevent chipping and cracking of the lens material to be processed by setting the processing pressure at the initial stage of processing to a low pressure and the rotational speed to a low speed. In the middle of machining, the machining time can be shortened by switching the machining pressure to a higher pressure and the rotation speed faster than in the early stage of machining. At the end of processing, the center pressure of the lens material is accurate by lowering the processing pressure compared to the beginning of processing and setting the rotation speed to a medium speed that is faster than the initial processing and slower than the middle processing. Can be secured. In this way, by changing the grinding conditions in multiple stages in accordance with the progress of grinding, it is possible to form a highly accurate precision grinding surface on the lens material using only a dish-shaped grindstone.

(Experimental example)
The present inventors performed processing as follows using the grinding method of the present invention.
The processing data of this example is as follows.
Lens Material TAFD25
Degree of wear of lens material 90
Knoop hardness of lens material 630
Processing spherical radius R 108mm
Lens outer diameter 37.5mm
Plate-shaped whetstone diamond pellet SP60B # 800

  First, a test for determining the processing pressure was performed. The test conditions are as follows, and the test results are shown in the table and graph of FIG.

Sphere type lens grinding machine NC polisher PM50 type
(Manufacturer: Kojima Engineering Co., Ltd.)
Number of revolutions of dish-shaped grinding wheel 1000rpm
Lens contact area of dish-shaped grinding wheel 4.52 square cm
Processing amount 0.1mm

  From this test result, it is understood that when the processing pressure is 10 kg / square cm or more, the wear amount of the lens material hardly changes, and this pressure is the maximum point of the grinding processing efficiency.

  Next, using the same spherical core type lens grinding apparatus, a test for determining the number of revolutions of the dish-shaped grindstone was performed. Processing pressure 1 (15 kg / square cm) and processing pressure 2 (10 kg / square cm) In this case, the processing time when the rotation speed was changed was examined. The test conditions are the same as in the above case except for the processing pressure. The test results are shown in the graph of FIG.

  From this test result, it can be seen that this point is the maximum processing efficiency since the wear amount hardly changes from about 1500 rpm. That is, when the processing pressure is kept constant and the rotational speed is increased, the rotational speed at which the machining time hardly changes is the maximum value of the “rotating speed that can bite in”. As a result, slipping occurs on the dish-shaped grindstone, and the abrasive grains of the dish-shaped grindstone cannot penetrate the surface of the lens material. The maximum value of the “number of revolutions that can be bite in” is the maximum processing efficiency. This maximum value varies depending on the hardness of the lens material, the grain size of the dish-shaped grindstone, the performance of the cutting fluid, and the like, and may be set by performing a test.

  Based on these test results, it is understood that the processing pressure in the medium-term grinding step ST3 is optimal when the processing pressure is 10 kg / square cm and the rotational speed of the dish-shaped grindstone is 1500 rpm. Based on this, the processing conditions in the initial grinding step ST2 and the late grinding step ST4 are set.

  In the experiments by the present inventors, in the initial grinding step, the grinding pressure was 2 kg / square cm, the rotation speed was 500 rpm, and grinding was performed for 10 seconds. Next, a transition to the medium-term grinding process was performed, the grinding pressure was set to 10 kg / square cm, the rotational speed was set to 1500 rpm, and the lens material was ground until the target thickness became 0.1 mm before the target thickness. Then, the process was shifted to the late grinding step, the working pressure was 1.5 kg / square cm, the rotational speed was 1000 rpm, and grinding was performed until the lens material reached the target thickness.

  As a result, it was confirmed that the thickness accuracy was within ± 0.005 μm. Further, when the curvature of the ground surface was measured, ΔH changed by −0.001 μm after 150 times of machining. When the rocking position was shifted by 10% and further machining was performed 150 times, ΔH returned to the reference value, so the rocking position was restored. With these continuations, it was confirmed that the curvature of the ground surface was within a range of 0 to 0.001 μm in ΔH.

DESCRIPTION OF SYMBOLS 1 Sphere-core type lens grinding apparatus 2 Upper unit 2a Center axis 3 Lower unit 4 Lens holder 4a Lens holding surface 5 Lens pressing shaft 6 Pressing cylinder 7 Lens material 7a Surface to be ground 8 Plate-shaped grindstone 8a Spherical grinding wheel surface 9 Spindle shaft 9a Center axis 10 Spindle motor 11 Swing mechanism 12, 13, 14 Regulator 15, 16, 17 Switching valve 18 Controller 19 Measuring device 20 Inverter 21 Driver O Swing center θ Swing angle R Machining spherical radius

Claims (5)

A dish-shaped grindstone having a spherical grindstone surface with diamond abrasive grains is pressed against a surface to be ground of a lens material to be ground with a predetermined processing pressure, and in this state, the dish-shaped grindstone is rotated at a predetermined rotation speed. A method of grinding a spherical surface of a lens using a dish-shaped grindstone that grinds the surface to be ground into a spherical surface while rocking with
An initial grinding step in which the machining pressure is a first machining pressure, and the rotational speed is ground at a first rotational speed;
A medium-term grinding process in which the machining pressure is a second machining pressure, and the rotational speed is ground at a second rotational speed;
A second grinding step in which the machining pressure is a third machining pressure, and the rotational speed is ground at a third rotational speed;
The second processing pressure is a pressure at which the spherical grindstone surface can bite into the lens material, the hardness of the lens material, and the surface to be ground of the lens material and the spherical grindstone surface of the dish-shaped grindstone From the contact area, the amount of biting of the dish-shaped grindstone is obtained, and the second processing pressure is calculated based on the amount of biting,
The second rotational speed is set to a rotational speed at which the diamond abrasive grains of the dish-shaped grindstone can bite into the lens material,
Setting the first processing pressure to a value lower than the second processing pressure, and setting the first rotational speed to a value lower than the second rotational speed;
The third processing pressure is set to a value lower than the first processing pressure, and the third rotational speed is set to a value lower than the second rotational speed and higher than the first rotational speed. A method of grinding a lens spherical surface using a dish-shaped grindstone. In claim 1,
The second processing pressure is set to a minimum value at which the diamond abrasive grains of the dish-shaped grindstone can bite into the lens material,
A method of grinding a lens spherical surface using a dish-shaped grindstone, wherein the second rotational speed is set to a maximum value at which the diamond abrasive grains of the dish-shaped grindstone can bite into the lens material. In claim 1 or 2,
The initial grinding step is performed until the surface of the lens material to be ground is in contact with the spherical grinding wheel surface as a whole,
The intermediate grinding step is carried out until a state in which the center thickness of the lens material is thicker than a target value by a preset dimension is formed. In any one of claims 1 to 3,
At least in the medium-term grinding step, the lens spherical surface using the dish-shaped grindstone is characterized by periodically changing a region in which the ground surface of the lens material slides on the spherical grindstone surface of the dish-shaped grindstone. Grinding method. In any one of claims 1 to 4,
The lens material has a Knoop hardness of 630,
The second processing pressure is 10 kg / square cm, and the second rotational speed is 1500 rpm,
The first processing pressure is 2 kg / square cm, and the first rotational speed is 400 to 600 rpm,
A lens spherical grinding method using a dish-shaped grindstone, wherein the third machining pressure is 1.5 kg / square cm and the third rotation speed is 1000 rpm.

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