JP2012030311A - Spherical surface grinding method and spherical surface grinding device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spherical surface grinding method and a spherical surface grinding device capable of shortening a processing time in following processes and further reducing the number of processes by improving a quality requirement, specifically the depth of crack without reducing a processing efficiency so as to reduce a load on a precise grinding and a polishing in the following processes.SOLUTION: This spherical surface grinding method includes a speed-controlled slitting step of grinding a workpiece only a predetermined depth of cut by a grinding wheel while controlling a slitting speed by mutually approaching a workpiece shaft at the distal end of which a lens base is attached and a grinding wheel shaft at the distal end of which the grinding wheel is attached while rotating these shafts, and a pressure-controlled slitting step of slitting the workpiece while controlling a pressure at which the workpiece is pressed against the grinding wheel after the speed-controlled slitting step.

Description

  The present invention relates to a spherical grinding method and a spherical grinding device, and more particularly to a spherical grinding method and a spherical grinding device for a workpiece such as an optical element such as a lens or a mold.

  Conventionally, as a spherical grinding method of an optical element such as a lens, there is a method disclosed in Patent Document 1. As shown in FIG. 7, the processing apparatus 18 used in this method has a work head 5 that rotatably supports a work holding portion 4 that holds a lens base 3 that is a work on a base 1 that supports each component. It is installed so that it can move back and forth. A pulley 6 is fixed to the shaft end of the work holding unit 4. The pulley 6 is connected via a belt 10 to a pulley 9 fixed to a drive shaft 8 of a motor 7 fixed to the work head 5. Reference numeral 11 denotes a cup-shaped grinding wheel for processing the lens base 3 into a spherical shape. The grinding wheel 11 is rotatably supported by a housing 13 via a grinding wheel shaft 12. The work head 5 is screwed with a ball screw 14 for moving the work head 5 in a direction for advancing and retreating the grinding head 11. The ball screw 14 is configured to be interlocked with a pulse motor 15 fixed to the base 1. Further, the rotation speed measuring unit 19 is configured such that the photoelectric sensor 21 detects a notch of the notch disk 20 fixed to the drive shaft 8 of the motor 7. The rotational speed measurement unit 19 transmits a detection result to the speed control device 17.

  When the lens is spherically ground using the processing device 18 having the above-described configuration, after the lens base 3 is held by the work holding unit 4, the motor 7 is rotated to rotate the work holding unit 4 and the grinding wheel 11. The notch disk 20 is rotated by the rotation of the motor 7, and the number of rotations of the lens base 3 can be measured by a signal sent to the speed control device 17. At the same time, the pulse motor 15 is driven by a command from the speed controller 17 to move the work head 5 forward in the direction of the grinding wheel 11 and press the lens base 3 against the grinding wheel 11. Further, when the pulse motor 15 is driven until a predetermined number of pulses are counted, the work head 5 is sent to a predetermined position and stops the cutting operation. When the pulse motor 15 is stopped, the speed control device 17 counts the signal sent from the photoelectric sensor 21, and when the signal corresponding to one rotation of the lens base 3 is counted, the speed control device 17 drives the pulse motor 15 in the reverse direction. To do. Due to the reverse rotation of the pulse motor 15, the work head 5 moves backward and the lens base 3 is separated from the grinding wheel 11. By the above operation, a spherical surface is created on the processing surface of the lens base 3.

  According to such a processing apparatus 18, after completing the lens cutting, the cutting operation of the lens base 3 is stopped at that position, and the number of rotations corresponding to one rotation (or more than one rotation) of the lens base 3 is further stopped. Can be reliably applied to the lens base 3 (so-called spark-out). Therefore, even if there is a grinding mark at the time of stopping the cutting of the lens base 3, the entire processed surface of the lens base 3 is rough-processed at the stop position by the spark out to obtain a spherical surface from which the grinding mark is removed. Can do.

Japanese Patent Publication No. 1-26821

  In general, the surface quality required for spherical grinding includes surface shape accuracy, surface roughness, crack depth, and the like. Although the above prior art can be expected to improve the surface shape accuracy, there is a problem that the crack depth needs to be improved. That is, cracks occurring in the lens base 3 occur when the grinding wheel 11 cuts the lens base 3, but the above spark-out is performed after the cut is stopped. For this reason, the crack generated during the cutting remains as it is.

  In an optical element such as a lens, a step of obtaining a mirror surface by rough grinding and polishing using a general-purpose grindstone in which the shape of the surface to be processed of the lens base 3 is substantially reversed after roughing (hereinafter referred to as a post-process) .)It is carried out. Here, when the above-mentioned crack is not removed, dot-like marks called pits or pits remain on the mirror surface and become defective. For this reason, it is necessary to remove these cracks over several steps in the fine grinding process, which is a subsequent process of roughing. Further, the demand for efficiency improvement is severe at the production site, and the crack depth is further increased because the cutting speed is increased to shorten the processing time. Therefore, there is a problem that the amount of processing in the subsequent process is further increased and the burden on the precision grinding wheel to be used is increased.

  The present invention has been made in view of the above, and it is possible to improve the required quality, in particular, the crack depth without reducing the processing efficiency, and reduce the burden of fine grinding and polishing processing, which are subsequent processes, thereby reducing the subsequent process. It is an object of the present invention to provide a spherical grinding method and a spherical grinding machine capable of reducing the machining time of the process and further reducing the process.

  In order to achieve the above object, the spherical grinding method according to the present invention includes a work shaft having a work piece attached to the tip and a grindstone shaft having a grindstone attached to the tip while being brought close to each other to make a cut. The workpiece is ground by a predetermined amount with a grinding wheel while controlling the speed, and after the grinding, cutting is performed by pressure control.

  In addition, the spherical grinding apparatus according to the present invention includes a work holding unit configured to be rotatable, a work side rotation driving unit coupled to the work holding unit, a grindstone shaft on which a grindstone is mounted at the tip, and the grindstone shaft The grindstone-side rotation driving unit connected to the grindstone, the advancing / retreating driving unit that moves the workpiece held in the workpiece holding unit in a direction to advance and retreat with respect to the grinding wheel mounted on the grindstone shaft, and the workpiece holding unit. A pressure drive unit that pressurizes the workpiece toward the grinding wheel side mounted on the grindstone shaft, a speed control device that controls the drive speed, advance / retreat direction, and stop position of the advance / retreat drive unit, and the workpiece and the grinding wheel by the pressure drive unit And a pressure control device for controlling the processing pressure during the grinding process. After the rotating workpiece is moved at a predetermined speed relative to the rotating grinding wheel and the workpiece is cut by a predetermined amount, the workpiece is cut by a predetermined pressure. It is characterized in.

  According to the present invention, when a workpiece is subjected to spherical grinding, a machined surface with a small crack depth can be obtained without extending the machining time, the burden on subsequent processes from fine grinding to polishing can be reduced, and the number of processes can be reduced. Is also possible.

FIG. 1 is a plan view showing a spherical grinding apparatus according to an embodiment of the present invention. FIG. 2 is a flowchart showing a case where the polishing process is performed including the process using the spherical grinding method according to the embodiment of the present invention. FIG. 3 is a flowchart showing the spherical grinding process. FIG. 4 is a diagram showing set values of an example using the spherical grinding method according to the embodiment of the present invention. FIG. 5 is a diagram illustrating setting values of the comparative example. FIG. 6 is a flowchart of the comparative example. FIG. 7 is a plan view showing a conventional spherical grinding apparatus.

  Hereinafter, details of a spherical grinding method and a spherical grinding device according to embodiments of the present invention will be described with reference to the drawings. First, a spherical grinding apparatus according to an embodiment of the present invention will be described with reference to FIG. In the following description, the same members as those of the conventional apparatus member shown in FIG.

  As shown in FIG. 1, a ball screw 14 is screwed on a work shaft base 2 that supports a work head 5 so as to be movable back and forth, and is linked to a pulse motor 15 as an advancing / retreating drive unit fixed on the base 1 side. ing. The cylinder 35 is fixed to the work shaft base 2 and is connected to the work head 5. The cylinder 35 serves as a pressure drive unit for pressing the lens base 3 against the grinding wheel 11 on the grinding wheel shaft 12 in a contact state so that the pressure can be adjusted. On the work shaft base 2, there is provided a stopper 36 that can be adjusted in the front-rear direction to define the forward movement position of the work head 5 that is driven forward and backward by the cylinder 35. The cylinder 35 is connected to a pressure control device 37 that controls the pressure of the cylinder 35.

  The grinding wheel 11 is a cup-shaped grinding wheel that processes the lens base 3 into a spherical shape, and is rotatably supported by the housing 13 via a grinding wheel shaft 12. The housing 13 is provided on the grindstone shaft base 30. The grindstone shaft 12 is rotated by a motor 31 via a pulley 32, a belt 33, and the like.

  Hereinafter, a spherical grinding method using the spherical grinding device according to this embodiment, and its operation and operation will be described. In the spherical grinding method according to this embodiment, a workpiece holding portion (work shaft) having a lens base 3 attached to the tip and a grinding wheel shaft 12 having a grinding wheel 11 attached to the tip are brought close to each other while rotating. A speed control cutting process for grinding the lens base 3 by a predetermined cutting amount with the grinding wheel 11 while controlling the cutting speed, and a pressure for pressing the lens base (workpiece) 3 against the grinding wheel 11 after the speed control cutting process. And a pressure control cutting process for cutting while controlling the pressure.

  Specifically, the lens base 3 is cut by a predetermined amount e1 at a predetermined speed by speed control in the same manner as in the conventional processing, and then the predetermined amount e2 equal to or substantially equal to the depth of the crack generated by the cutting by this speed control. Incision is performed at a predetermined pressure by pressure control. At this time, if an appropriate pressure is set, the depth of the crack generated in the lens base 3 is one-tenth to one-tenth of the depth of the crack generated by the speed control cut. The speed control cutting process may be the same as or higher than the conventional machining, and a good machined surface can be obtained in almost the same machining time.

  First, after holding the lens base 3 on the work holding part 4, the motor 7 is rotated to rotate the work holding part 4. Further, the pulse motor 15 is driven by a command from the speed control device 17. Then, the work head 5 is moved forward in a direction approaching the grinding wheel 11 that is rotationally driven by the motor 31, and the lens base 3 is pressed against the grinding wheel 11. Further, the speed control device 17 drives the pulse motor 15 until a predetermined number of pulses are counted, and stops the work head 5 by a distance e1 by the ball screw 14 at a predetermined position. As a result, a speed control cutting process is performed in which the grinding wheel 11 grinds the lens base 3 by a predetermined cutting amount while controlling the cutting speed. As a result, the lens base 3 can be cut by moving the rotating lens base 3 relative to the rotating grinding wheel 11 at a constant speed.

  When the pulse motor 15 stops, the speed control device 17 continues to instruct the pressure control device 37, and the pressure control device 37 drives the cylinder 35 so that the pressure becomes a predetermined value. When the cylinder 35 is pressurized in this way, the work head 5 moves forward by a distance e2 and stops until it abuts against the stopper 36. Thus, a pressure control cutting process is performed in which cutting is performed while controlling the pressure with which the lens base 3 is pressed by the grinding wheel 11. As a result, the lens base 3 can be cut with a constant pressure.

  In a state of moving forward and stopping, after rotating the lens base 3 one or more times (sparking out), the speed controller 17 drives the pulse motor 15 in reverse. Due to the reverse rotation of the pulse motor 15, the work head 5 moves backward and the lens base 3 is separated from the grinding wheel 11. By the above operation, a spherical surface is created on the processing surface of the lens base 3.

  According to the spherical grinding method and the spherical grinding apparatus according to this embodiment, when the lens base 3 is spherically ground, the speed control device 17 performs the speed control cutting so that the processing time is not extended. By performing pressure control cutting with the pressure control device 37, a processed surface having a small crack depth can be obtained. That is, according to this spherical grinding apparatus, it is possible to accurately perform the cutting (cutting amount e2) by pressure control after the cutting (moving amount e1) by speed control, and to reduce the crack depth. Therefore, by using this spherical grinding apparatus, it is possible to reduce the burden on subsequent processes from fine grinding to polishing, and to reduce the number of processes.

(Example)
The case where the spherical grinding method according to this embodiment is applied to the optical element manufacturing method up to the lens substrate polishing step is shown in the flowchart of FIG. FIG. 2 is a flowchart showing a case where the polishing process is performed after the spherical grinding is performed using the spherical grinding method according to this embodiment. As shown in FIG. 2, the optical element is manufactured by sequentially grinding the surface ground in the spherical grinding process (step S1) including the speed controlled cutting process and the pressure controlled cutting process, and the spherical grinding process. Polishing process (step S3), polishing the surface of the lens substrate that has been finished to some extent in the fine grinding 2 process (step S2), and finishing with high precision so as to have a predetermined surface roughness, curvature, and thickness (step S3) To finish.

  FIG. 3 is a flowchart showing the contents of the spherical grinding process (step S1). As shown in FIG. 3, in the spherical grinding process, first, a speed control cutting process for cutting the lens base by speed control is performed (step S11). Then, it is determined whether or not the predetermined amount e1 has been cut in the speed control cutting step (step S12). If the cutting length is less than the predetermined amount e1, the speed control cutting is continued and reaches the predetermined amount e1. In that case, cutting is performed by pressure control (step S13). Then, it is determined whether or not the predetermined amount e2 has been cut in the pressure control cutting step (step S14). If the predetermined amount e2 is not reached, the pressure control cutting step is continued, and if the predetermined amount e2 is reached, End the pressure control cut. In this pressure control cutting step (step S13), the pressure control cutting is performed by a predetermined amount e2 substantially equal to the depth of the crack generated by the speed control cutting. Thereafter, the lens base is fixed and rotated one or more times to perform spark out (step S15), and then the lens base is moved backward (step S16) to complete the spherical grinding process. To do.

  FIG. 6 is a flowchart showing a comparative example in which the lens substrate is subjected to the polishing process with respect to the above embodiment. FIG. 5 shows the set values of crack depth and machining allowance that occur in a comparative example similar to the conventional method (see the flowchart of FIG. 6). In the comparative example shown in FIG. 5, the average crack depth generated by spherical grinding in the speed control cut is 35 μm. For this reason, in the fine grinding 1 process which is a subsequent process, it is necessary to set a machining allowance of 45 μm in consideration of the variation in crack depth in order to remove cracks generated in the spherical grinding. In the fine grinding 1 step, even if the crack generated in the spherical grinding is removed, a new crack of 8 μm is generated. Therefore, in the fine grinding 2 step, a machining allowance of 12 μm is further set, and cracks newly generated in the fine grinding 1 step are removed. In the polishing process as the final process, a crack of about 1 μm newly generated in the two precision grinding processes is removed to obtain a mirror surface. Thus, in the process of obtaining the mirror surface of the optical element, the surface roughness is reduced while removing the cracks generated in the previous process in the subsequent process. As shown in FIG. 5, the total machining allowance at this time is 60 μm.

  In this comparative example, as shown in FIG. 6, precision grinding is performed in order to accurately grind the surface ground in the speed control cutting process (spherical grinding process: step S21) and the spherical grinding process in the same manner as in the prior art. 1 step (step S22), a fine grinding 2 step (step S23) for grinding the surface ground in the fine grinding 1 step with higher accuracy, and polishing the surface of the lens substrate that has been finished to some extent in the fine grinding 2 step. The process is finished through a polishing step (step S24) in which the surface is finished with high accuracy so as to have surface roughness, curvature, and thickness.

  FIG. 4 shows an example when the lens base 3 is subjected to the polishing process by applying the spherical grinding method according to the above embodiment (see the flowchart of FIG. 2), and the crack depth generated is set as a allowance. Indicates the value. As shown in FIG. 4, in the embodiment, the speed control cut is initially performed in the same manner as the conventional machining, but the speed control cut is stopped about 45 μm before the stop position of the conventional machining performed in the comparative example, and then Change to the notch by pressure control and machine to a predetermined stop position. According to this embodiment, the crack depth generated in the spherical grinding is reduced to about 15 μm, and it is not necessary to perform one fine grinding step required in the comparative example as a post process, and two fine grinding steps and polishing. Two steps may be performed. At this time, when the crack is removed, the total machining allowance is about 23 μm.

  As described above, in the embodiment, by performing the spherical grinding by pressure control after the speed control, the cracks generated by the spherical grinding are reduced, and the fine grinding 1 which is a subsequent process can be reduced.

  Although the spherical grinding method and the spherical grinding machine according to the embodiment of the present invention have been described above, the description and the drawings that constitute a part of the disclosure of the above embodiment do not limit the present invention. For example, in the above embodiment, the lens base 3 (work) side is moved back and forth by the pulse motor 15 and the cylinder 35, but the grinding wheel 11 side or both may be moved back and forth. The cylinder 35 may be pneumatic, hydraulic, spring, or the like as long as the pressure can be controlled.

  In the above embodiment, the lens base 3 is applied as a work. However, in addition to the work of other optical elements, the present invention is applied to various objects to be subjected to spherical grinding such as molds and decorations. Is possible.

3 Lens base (work)
4 Workpiece holding part (workpiece axis)
7 Motor (work side rotation drive part)
8 Drive shaft 11 Grinding wheel 12 Grinding wheel shaft 14 Ball screw 15 Pulse motor (advance / retreat drive)
17 Speed control device 31 Motor (grinding wheel side rotation drive part)
35 cylinders (pressurization drive)
37 Pressure control device

Claims (2)

Each of the workpiece shaft with the workpiece attached to the tip and the grinding wheel shaft with the grinding wheel attached to the tip is brought close to each other,
Grinding the workpiece with the grinding wheel while controlling the cutting speed;
And a step of performing cutting by pressure control. A workpiece holder configured to be freely rotatable;
A workpiece-side rotation driving unit coupled to the workpiece holding unit;
A grinding wheel shaft with a grinding wheel attached to the tip;
A grindstone-side rotation drive unit connected to the grindstone shaft,
An advancing / retreating drive unit that moves the workpiece held by the workpiece holding unit in a direction of advancing / retreating with respect to the grinding wheel mounted on the grindstone shaft;
A pressure drive unit that pressurizes the workpiece held by the workpiece holding unit toward the grinding wheel mounted on the wheel shaft;
A speed control device for controlling the driving speed, the advancing / retreating direction and the stop position of the advancing / retreating drive unit;
A pressure control device for controlling a processing pressure during grinding of the workpiece and the grinding wheel by the pressure driving unit;
With
A spherical grinding machine characterized in that, after the rotating workpiece is moved at a predetermined speed with respect to the rotating grinding wheel, the workpiece is cut, and then the cutting is performed with a predetermined pressure.

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