KR20000073479A - Apparatus and method of polishing aspherical surface lens - Google Patents

Abstract

PURPOSE: An apparatus for polishing non-spherical lens and method thereof are provided to polish a non-spherical lens or lens mould of rotational symmetric shape. CONSTITUTION: In an apparatus for polishing non-spherical lens and method thereof, the apparatus comprises a device for moving a work piece(2), a polishing tool(1), a device for rotating the work piece(2), and a computer for control. The method for polishing a non-spherical lens in the apparatus comprises the first step for measuring the shape and the surface roughness of a work piece(2); the second step for estimating shape tolerance by comparing the surface shape of the work piece(2) with a target surface shape; the third step for estimating polishing routes and duration times according to each of the polishing routes by applying the shape tolerance to an algorithm for polishing model and duration time; a fourth step for storing a value of horizontal position(X-axis) in a polishing position of the work piece(2), a value of tilting angle(theta), a revolution speed of a polishing tool, a revolution speed of the work piece, and a duration time at the very position as numerical control codes; and a fifth step for analyzing the numerical control codes and controlling the device for moving the work piece and the device for rotating the work piece.

Description

Apparatus and method of polishing aspherical surface lens

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for polishing a lens or a lens mold, and more particularly, to a method for polishing an aspheric lens having a rotationally symmetrical shape.

An aspherical lens is a lens that can replace a plurality of spherical lens combinations, and is a lens that can reduce the optical system weight, high precision, and low cost.

In order to manufacture such aspherical lenses, many precision cutting machines or grinding machines are currently used, but they have many constraints depending on the material and shape, and the surface roughness is improved since traces of the tool remain after the creation of the aspherical shape. In order to do this, a separate precision polishing must be performed. In addition, such a precision cutting machine or a precision grinding machine is a very expensive equipment, which also increases the manufacturing cost of aspherical lenses.

In order to solve this problem, an aspherical polishing apparatus using spherical surfaces has been developed and used. At this time, since the aspherical surface does not have the same radius of curvature unlike the spherical surface, a new polishing apparatus is required.

Therefore, the aspheric polishing apparatus is generally used a method of polishing while following the shape of the workpiece using a small grinding tool smaller than the size of the aspherical surface. At this time, the amount of grinding processing is mainly controlled by using the stay time control method. The stay time control method is a method of adjusting the tool stay time while maintaining a constant product of the pressure applied to the workpiece and the relative speed.

Either way, in order to control the amount of abrasive cut as desired, the amount of unit cut at any position on the workpiece must be known. This unit processing amount depends on the shape of the grinding tool, the shape of the rotational movement of the tool, the rotation of the workpiece, and the pressure distribution formed.

As a prior art of aspheric polishing apparatus, U.S. Patent No. 4,768,308, "Universal Lens Polishing Tool, Polishing Aparachus and Method of Polishing", POLISHING APPARATUS AND METHOD OF POLISHING, A method of polishing the surface of an aspherical lens while a tool is rotated and then reciprocates while attaching an elastic abrasive nonwoven fabric is described.

In general, when the tool is very small compared to the workpiece, the pressure distribution between the tool and the workpiece remains almost constant, but when the tool is very large compared to the workpiece, the change in pressure distribution is very severe. To solve this problem, the device divided the tool into three types of contact areas: 10%, 50% and 80%, depending on the size. In the case of an aspherical lens, a very small tool should be used for polishing, and when using the above-described annular grinding tool, it is difficult to polish a small aspherical lens having a diameter of 30 mm or less.

Meanwhile, US Patent No. 5,347,763, "POLISHING APPARATUS," describes a device for polishing a small aspherical lens by using a hydrodynamic method in which a tool is placed in a polishing liquid and rotated at high speed. This apparatus polishes a workpiece by the abrasive particles hitting and removing the unevenness of the workpiece between the abrasive tool and the workpiece by non-contact rotation of the abrasive tool and the workpiece. Such a non-contact polishing apparatus can more accurately predict the amount of processing due to processing conditions, but has a disadvantage of lower processing efficiency than the contact method.

Accordingly, the present invention has been made to solve the above problems of the prior art, and provides an aspherical lens polishing apparatus and method using a spherical polishing tool that increases the processing efficiency while accurately predicting the processing amount by the processing conditions. Its purpose is to.

1 is a block diagram showing an aspherical lens polishing apparatus according to an embodiment of the present invention,

2 is a configuration diagram showing in detail the transfer mechanism shown in FIG.

Figure 3 is a schematic diagram showing an aspherical polishing method of the numerical control method according to an embodiment of the present invention,

4 is a flowchart illustrating a numerical control program generation method according to an embodiment of the present invention;

5 is a view for explaining the amount of processing according to the mutual rotation of the grinding tool and the workpiece.

※ Explanation of code about main part of drawing ※

1 grinding tool 2 workpiece

3: mixed liquid 4: feeder

5: transfer mechanism part 6: balance weight

7: Rotating Element 8: Vertical Line

9: rotating motor 10: vertical transfer mechanism

11: vertical guide portion 12: rotation element support

13 vertical support mechanism 14 horizontal support

15: vertical support 16: feeder support

17: linear transfer motor 18: linear transfer unit

19: motor 20: tilt moving mechanism support

21: tilt movement mechanism 22: motor

23: rotating shaft 24: housing

25: belt 31: computer

Aspheric lens polishing method according to the present invention for achieving the above object, by simultaneously performing the horizontal movement of the x-axis and the tilt rotation of the y-axis along the geometric surface shape of the workpiece, applied to the workpiece through the polishing tool A workpiece moving means for causing the load to always act in a constant direction;

A spherical polishing tool for rotating the workpiece by rotating while following the surface shape of the workpiece;

Workpiece rotating means for rotating the workpiece along the polishing path while the workpiece is polished by the polishing tool;

Non-powered grinding tool moving means for restraining only the movement in the vertical direction of the grinding tool so that the load applied to the workpiece through the grinding tool is always maintained; And

And a control computer for controlling the amount of movement of the workpiece and the rotational state of the workpiece and the grinding tool to form an aspherical lens of a desired shape.

More preferably, the non-powered grinding tool moving means,

A vertical transfer support guided to fix the grinding tool and move in the vertical direction;

A weight balance weight according to the load applied to the workpiece,

A row connecting the vertical transfer support and the counterweight;

Including a roller for supporting the string between the vertical transfer support and the counterweight,

When the grinding tool moves vertically along the surface of the workpiece, its movement force is transmitted to the counterweight through the string so that both sides of the string are balanced by the roller so that a constant load is always applied to the workpiece. It features.

In addition, in the polishing method of the aspherical lens according to the present invention, the workpiece moving means for simultaneously performing the horizontal movement of the x-axis and the tilt rotation of the y-axis along the geometric surface shape of the workpiece, while following the surface shape of the workpiece A spherical polishing tool for rotating the workpiece, a workpiece rotating means for rotating the workpiece along a polishing path while the workpiece is being polished by the polishing tool, and a movement amount of the workpiece and a rotation state of the workpiece and the polishing tool In the polishing method of the aspherical lens polishing apparatus comprising a control computer for controlling the to form an aspherical lens of the desired shape,

A first step of measuring the shape and surface roughness of the workpiece;

A second step of obtaining a shape error by comparing the surface shape of the workpiece with a target surface shape;

A third step of applying the shape error to the polishing processing model and the residence time algorithm to obtain the polishing path and the residence time according to each polishing path;

A fourth step of storing the horizontal position value (x-axis) of the workpiece polishing position, the tilted angle value (θ), the rotation speed of the polishing tool, the workpiece rotation speed, and the staying time at the position as numerical control codes; ; And

And a fifth step in which the control computer interprets the numerical control code to control the workpiece moving means, the grinding tool and the workpiece rotating means.

More preferably, the third step is

A first sub step of obtaining a contact area coefficient value of the workpiece;

A second sub step of obtaining an instant workpiece removal rate when an abrasive tool comes into contact with the workpiece using the contact area coefficient value of the workpiece, the pressure applied to the workpiece, and the relative speeds of the workpiece and the abrasive tool,

A third sub-step of obtaining a unit removal amount per unit time in the polishing path of the workpiece by using the instant workpiece removal rate; and

And a fourth sub-step of determining a stay time at each polishing position by using the total processing amount function and the unit removal amount per unit time for converging the shape error to '0'.

More preferably, the third step,

Stay time at each polishing position of the workpiece is characterized in that it is set to enable the integral rotation of the workpiece rotation period.

The present invention uses a spherical abrasive tool as a contact method. While applying or adding abrasive particles on the rotating workpiece, the spherical polishing tool of high speed rotation is brought into close contact to remove the irregularities on the surface of the workpiece. In order to obtain the desired throughput for the entire surface, the workpiece is moved by simultaneous control of two axes, and the grinding tool is free to move only vertically to counteract the vibration of the workpiece. All movements and rotations are controlled by a computer with numerical control, and the contact time of the grinding tool and the workpiece is made to be a positive integer multiple of the workpiece rotation period.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

As described above, the adjustment of the amount of polishing processing is mainly used for the stay time control method of adjusting the stay time of the polishing tool while adding a constant pressure and relative speed to the workpiece, and in the present invention, the stay time control method is a small rotational symmetry method. Applies to aspherical surface.

1 is a block diagram showing an aspherical lens polishing apparatus according to an embodiment of the present invention. Between the polishing tool 1 and the work piece 2, a mixed liquid 3 of abrasive particles and lubricating oil is supplied from the feeder 4. The grinding tool 1 is mounted on the rotary motor mechanism 9 by air supply and rotated. The work piece 2 is mounted and rotated on the conveying mechanism part 5, which is shown in detail in FIG. 2. Here, the unevenness of the work piece 2 is removed by the rotational movement of the polishing tool 1 and the work piece 2.

The conveying mechanism part 5 is mounted on the horizontal support 14, and in consideration of the geometric curve of the aspherical lens which is the work piece 2, the load applied in the normal direction in the region where the work piece 2 and the grinding tool 1 come into contact with each other is applied. The workpiece 2 is biaxially controlled so as to remain constant. In other words, the work piece 2 is horizontally moved on the x-axis and at the same time tilted on the y-axis. The vertical support 15 is mounted on the horizontal support 14, the vertical transport mechanism support 13 is connected to the vertical support 15, and the vertical guide 11 is formed on the vertical movement support 13.

When the workpiece 2 is controlled in two axes and moves, the grinding tool 1 is not restrained in the vertical direction, so that the grinding tool 1 moves in the vertical direction, and the rotary motor mechanism 9 fixed to the vertical transfer mechanism portion 10 is carried out. ) Is guided by the vertical guide 11 and moves in the vertical direction. The grinding tool 1 is rotated by the rotary motor mechanism 9 in contact with the surface of the work piece 2. The vertical line 8 fixed to the vertical transport mechanism 10 is fitted to the rotating element 7 supported by the rotating element support 12, and balances the force with the counterweight 6 along the rotating element 7. Move to achieve. In other words, the vertical tool (8) and the balance weight (6), the polishing tool 1 can polish the workpiece while always applying a constant load on the surface of the workpiece. When the transfer mechanism part 5 moves, the grinding tool 1 automatically moves by the vertical transfer mechanism part 10 which is a non-binding mechanism in a vertical direction.

2 is a configuration diagram showing in detail the transfer mechanism 5 shown in FIG. The transfer mechanism part 5 is mounted on the horizontal support 14, and the vertical support 15 is also mounted on the horizontal support 14. The linear feed motor 17 moves the linear feed part 18 in the horizontal direction on the feed part support 16 using a mechanism such as a feed screw. The tilt movement mechanism 21 is rotated by the motor 19 so that a constant normal force is applied to the workpiece. The motor 19 is supported by the tilt movement mechanism support 20. The rotating shaft 23 is supported by the housing 24 by a bearing or the like, and the workpiece is mounted on the rotating shaft 23 to receive the rotational force of the motor 22 through the belt 25.

Figure 3 is a schematic diagram showing an aspheric polishing method of the numerical control method according to an embodiment of the present invention.

Referring to Fig. 3, an aspheric polishing apparatus controlled by a numerical control method is controlled by a computer 31. The computer 31 controls four rotary axes of the polishing apparatus 32. Of these, horizontal movement in the x-axis direction and tilt rotation in the y-axis direction of the workpiece are controlled by linear interpolation which simultaneously moves in consideration of the geometric surface of the aspherical lens by the respective motors 17 and 19. . Workpiece rotation control is on / off control and can be controlled at a constant speed. The grinding tool rotation control is on / off control and the grinding tool is rotated by the rotary motor 9.

In order to make an aspherical lens having precise shape and surface roughness, first, the surface shape of the aspherical lens is measured using a measuring device, and the shape error is obtained by comparing with the target surface shape. Next, a numerical control (NC) code is generated to correct the shape error. The numerical control code is generated through the grinding model and the calculation of the residence time distribution, and the computer uses the numerical control code to control the polishing device.

4 is a flowchart illustrating a method of generating a numerical control program according to an embodiment of the present invention. The residence time control requires calculation of the position movement time and residence time at each discrete discretized radial grid position.

When the measured surface shape of the aspherical lens is input (S41) and the target surface shape is given (S42), the surface shape of the measured aspherical lens and the target surface shape are compared (S43) to obtain an error surface shape (S44). In addition, various processing variables (speed, load, abrasive particles, etc.) (S45) and the target surface shape is applied to the unit removal function model to model the unit removal function (S46).

The relationship between the abrasive machining variable and the material removal rate has been expressed by Equation 1 by Preston.

The rate of material removal when the abrasive tool is in contact with the aspherical surface at a radial position is called the unit removal function (dh (x, y) / dt), which is the pressure (P) and relative velocity (V) and the preston coefficient ( Kwear). This Preston coefficient (Kwear) can be obtained by measuring the area polishing size and depth after polishing a flat specimen for a certain time.

When the unit removal function is obtained as described above, the residence time distribution is obtained by applying the same to the stay time algorithm (S47). Details of the stay time algorithm will be described later. The stay time distribution thus obtained is stored as a numerical control code (S48).

When the stay time at the polishing position 1 is T1 and the stay time at the polishing position 2 is T2 in the numerical control code obtained as described above, FIG. 5 illustrates the processing amount according to the mutual rotation of the polishing tool and the workpiece. It is shown for the sake of simplicity.

A process of setting a stay time will be described with reference to FIG. 5.

The residence times T1 and T2 are set to integer multiples of the rotation period of the workpiece, respectively. Therefore, the amount of polishing in the contact region determined by any one polishing position is a processing amount depending on time. In addition, since the workpiece is rotated when the polishing tool stays in any polishing position 1 for a time T1, the polishing tool crosses the contact area 1 of the closed curve. At this time, when the rotational angular velocity of the workpiece is Ω, the abrasive tool passes through the contact area 1 by the number of times T1 / (2π / Ω), and T1 is set so that this number becomes an integer.

If the removal amount per unit time in the unit contact region 1 is R1, the machining amount H1 of the contact region 1 around the radial position x1 of the workpiece is obtained as in Equation (2).

Where R1 is the amount of processing per unit revolution in contact area 1, and N1 is the number of times the abrasive tool passes through contact area 1.

Even in contact area 2 Equation is established, and the total processing amount H is the result of adding together the processing amounts H1, H2, ... in each contact area.

As shown in FIG. 5, the throughput matrix R in all the contact regions becomes a sum matrix of the matrix extending the throughput matrix R1, R2,..., Per unit rotation in each contact region.

For example, when polishing with a spherical polishing tool in one contact area, the center portion of the contact area is polished in a larger amount than the peripheral part. Therefore, the polishing positions are set so that adjacent contact regions overlap each other. In this case, the staying time should be set so that a uniform polishing amount can be obtained even in all the polishing regions, particularly in the overlapping portions of the two polishing positions. That is, when the machining amount matrix R1 per unit rotation in the contact region 1 and the machining amount matrix R2 per unit rotation in the contact region 2 are given by Equation 4, the machining amounts of the contact region 1 and the contact region 2 are given. The matrix R is shown in Equation 5.

here, The number of elements of is equal to the number of elements of the matrix R1 subtracted from the number of elements (3) or the number of elements (3) of the matrix R2 from the number of extractions (m = 5) of the throughput function H to be extracted.

The total number of extraction of the processing amount function (H) is expressed as in Equation 6.

That is, if the total machining amount H is given as a value at m arbitrary positions extracted in the radial direction (m = 5 in the example above), the residence time at all n polishing positions (n in the example above) = 2). At this time, the rotation speed N (N1, N2, ..., Nn) at n polishing positions The ritual must be satisfied.

Given the machining function (H) and the machining function per unit revolution (R) determined by the shape error between the surface shape of the aspherical lens and the target surface shape as shown in Equation 6, the solution is solved by the least-squares method. Find the function. In this case, the throughput function is expressed as in Equation (7).

E is an error function. The obtained rotation speed function N is replaced with a positive integer by rounding off, and finally, the rotation speed function N at the n lattice positions and the stay times T1, T2, ... are obtained.

In order to perform the polishing, the computer must process the numerical control code that is written. The numerical control code is analyzed by one paragraph and executed. The coordinates of the polishing position in the geometric relationship of the aspherical lens as the work piece are obtained as (x1, θ1), (x2, θ2), ..., and the residence time at that position is given by T1, T2 ... Given that the polishing tool rotational speed is P and the workpiece rotational speed is Q, for example, the numerical control code is given as follows.

N10 G01 x1 θ1 P200 Q300 ...

N20 G04 T40

N30 G01 x2 θ2

Where N is a command number, G01 is a position shift command by linear interpolation, and P and Q are rotational speeds of the abrasive tool and the workpiece, respectively, initially given.

In this numerical control code, the command N10 stays at position 1 given by the coordinate value of (x1, θ1) for T40, and then moves to the position 2 given by the coordinate value of (x2, θ2) at the command N30.

As described above, according to the present invention, since the spherical abrasive tool of high speed rotation is polished while the abrasive particles are applied or added to the workpiece to grind irregularities on the surface of the workpiece, the processing efficiency is increased, and the contact time between the abrasive tool and the workpiece is rotated. It is suitable for rotationally symmetric lenses because it is set to be an integer multiple of the period, and the machining variables such as the movement amount and rotation state of the workpiece are created by numerical control code and adjusted by computer, so that the processing amount under various processing conditions can be precisely adjusted. It has a predictable effect.

Claims (5)

Workpiece moving means for simultaneously performing horizontal movement of the x-axis and tilt rotation of the y-axis along the geometric surface shape of the workpiece so that the load applied to the workpiece through the grinding tool always acts in a constant direction; A spherical polishing tool for rotating the workpiece by rotating while following the surface shape of the workpiece; Workpiece rotating means for rotating the workpiece along the polishing path while the workpiece is polished by the polishing tool; Non-powered grinding tool moving means for restraining only the movement in the vertical direction of the grinding tool so that the load applied to the workpiece through the grinding tool is always maintained; And And a control computer for controlling the amount of movement of the workpiece and the rotational state of the workpiece and the polishing tool to form an aspherical lens of a desired shape. The method of claim 1, wherein the non-powered grinding tool moving means, A vertical transfer support guided to fix the grinding tool and move in the vertical direction; A weight balance weight according to the load applied to the workpiece, A row connecting the vertical transfer support and the counterweight; Including a roller for supporting the string between the vertical transfer support and the counterweight, When the grinding tool moves vertically along the surface of the workpiece, its movement force is transmitted to the counterweight through the string so that both sides of the string are balanced by the roller so that a constant load is always applied to the workpiece. Aspherical lens polishing apparatus characterized in that. Workpiece movement means for simultaneously performing horizontal movement of the x-axis and tilt rotation of the y-axis along the geometric surface shape of the workpiece, and the spherical polishing tool for rotating the workpiece by rotating while following the surface shape of the workpiece, the A control computer for rotating the workpiece along the polishing path while the workpiece is being polished by an abrasive tool, and a control computer for controlling the amount of movement of the workpiece and the rotational state of the workpiece and the abrasive tool to form an aspherical lens of a desired shape. In the polishing method of an aspherical lens polishing apparatus comprising: A first step of measuring the shape and surface roughness of the workpiece; A second step of obtaining a shape error by comparing the surface shape of the workpiece with a target surface shape; A third step of applying the shape error to the polishing processing model and the residence time algorithm to obtain the polishing path and the residence time according to each polishing path; A fourth step of storing the horizontal position value (x-axis) of the workpiece polishing position, the tilted angle value (θ), the rotation speed of the polishing tool, the workpiece rotation speed, and the staying time at the position as numerical control codes; ; And And a fifth step of the control computer interpreting the numerical control code to control the work moving means, the polishing tool, and the work rotating means. The method of claim 3, wherein the third step is A first sub step of obtaining a contact area coefficient value of the workpiece; A second sub step of obtaining an instant workpiece removal rate when an abrasive tool comes into contact with the workpiece using the contact area coefficient value of the workpiece, the pressure applied to the workpiece, and the relative speeds of the workpiece and the abrasive tool, A third sub-step of obtaining a unit removal amount per unit time in the polishing path of the workpiece by using the instant workpiece removal rate; and And a fourth sub-step of obtaining a stay time at each polishing position by using the total processing amount function and the unit removal amount per unit time for converging the shape error to '0'. . The method of claim 3, wherein the third step, The stay time at each polishing position of the workpiece is set so that the integral rotation of the workpiece rotation period is possible.