JPH04331345A - Measuring device of contact lens - Google Patents

Abstract

PURPOSE:To enable scattering of a measurement value depending on a measuring person to be eliminated and a measurement time to be reduced by performing measurement of a radius of curvature and a warpage of a center thickness and a base curve of a contact lens. CONSTITUTION:A title item is provided with a means 11 for detecting a focus- matching position automatically and a calculation means 12 for calculating a radius of curvature and a warpage of a center thickness/base curve from the focus-matching position information for an optical system based on the auto collimation method, thus enabling the center thickness, the radius of curvature of the base curve, and the warpage to be measured automatically without any contact with a single measuring equipment.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for measuring the center thickness, radius of curvature of a base curve, and warpage of a contact lens.

0002

2. Description of the Related Art Conventionally, the center thickness of a contact lens has been measured by applying a dial gauge to the center of the contact lens placed on the back.

Furthermore, the radius of curvature of the base curve is measured using an optical system based on the so-called autocollimation method.
A person detects the image point by forming a real or virtual image of the target at the center of curvature and the image point formed on the base curve surface using a microscope, and then measures the distance between the image points to determine the radius of curvature. was.

[0004] Furthermore, in warpage measurement, when measuring the radius of curvature of a base curve, the image point position of the target image formed at the center of curvature is partially different, and the deviation of the image point position is also measured by humans. It was measured by judgment and used as the value of the war page.

[0005]

[Problems to be Solved by the Invention] However, with the above-mentioned prior art, when measuring the center thickness, a measuring pressure of several tens of grams to more than 100 grams is applied to the center of the lens, which is very important for contact lenses, due to the tip of the gauge, resulting in damage. There is a high possibility that this will happen. Furthermore, in base curve measurement and warpage measurement, the in-focus position is judged by a person, so errors are likely to occur due to differences in skill level.

Furthermore, since the center thickness measurement and the base curve measurement are each performed using separate measuring instruments, the number of times the workpiece must be handled increases, the possibility of scratches increases, and the measurement time also increases.

The present invention is intended to solve these problems, and its purpose is to measure the center thickness, base curve, and warpage in a way that causes as little damage to the contact lens as possible, and to replace the values measured by humans. The aim is to eliminate variations in measurement and shorten measurement time.

[0008]

[Means for Solving the Problems] The contact lens measuring device of the present invention is a contact lens measuring device that is different from an optical system based on an autocollimation method in which the image point of a target objective lens coincides with the focal point position of a microscope. The distance between the objective lens and the objective lens is varied, and the focal point position when the target image is formed on the base curved surface of the contact lens and the focal focal point position when the target image is formed on the front curved surface of the contact lens are determined. The present invention is characterized by comprising a focal point detection means for automatically detecting the focal point and a calculation means for calculating the center thickness of the contact lens from the distance between the focal point positions.

[0009] Furthermore, by using the above-mentioned focused point detection means, the focused point position when the target image is formed at the center of curvature of the base curve is detected, and this position and the focused point position on the base curve surface are detected. The invention is characterized in that it has calculation means for calculating the radius of curvature of the base curve from.

[0010] Furthermore, when detecting the focused point position when the target image is formed at the center of curvature of the base curve and the focused point position on the base curve surface, the above two types of The present invention is characterized in that it has a focal point detection means for determining the focal point position of the base curve, and a warpage value is determined from the radius of curvature of the base curve at each location.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained in detail below with reference to the drawings. FIG. 1 is a diagram showing the configuration of an embodiment of the present invention.
Light emitted from a light source 5 passes through a radial slit-shaped target 6, is reflected by a half mirror 3, passes through a relay lens 4, and projects a target image onto a contact lens 1 via an objective lens 2. The projected image passes through the objective lens 2, relay lens 4, and half mirror 3, enters the TV camera 7, and is sent to the focal point detection means 11. When the target image seen by the TV camera 7 is focused, it becomes an image as shown in FIG. The focused point detection means 11 is composed of, for example, an image processing section, a motor control section, and a scale reading section. The contact lens 1 is placed on a support base 9 that can be moved vertically by a motor 8, and the distance from the objective lens 2 can be varied. The height of the support stand 9 is measured by a linear scale 10 and sent to a focused point detection means 11.

[0012] Based on the design data of the workpiece, the height of the support stand 9 is moved so that the target image is projected onto the front curved surface of the contact lens 1, and the contrast of the target image near that height is adjusted by the support stand. 9 in detail (1
~2 microns) Measure while feeding. The height of the top of the front curved surface when the contact lens is placed face down is
There is a difference of about 0.5 mm to 1.5 mm depending on the lens specifications, and taking this into consideration, if the movement range of the support stand 9 for measuring the contrast at this time is made too wide, the processing time will increase accordingly. Therefore, if the lens outer diameter, base curve design value, and center thickness design value are given in advance, the distance from the top surface of the support base 9 to the apex of the front curve surface of the contact lens can be approximately calculated. Based on this, the moving range is set to be limited to a certain extent to reduce processing time. Contrast is defined as, for example, the difference in brightness between the radial portion of the target image captured by the TV camera 7 and its background, or the rate of change in brightness at the boundary between the two. As the target image moves closer to the focal position due to the movement of the support base 9, its contrast value increases, and as it moves away from it, the target image becomes blurred and its contrast value decreases. Therefore, if the contrast value is measured as the support base 9 moves, a mountain-shaped graph with a peak at the in-focus position can be drawn. From the contrast data and the positional information from the linear scale 10, the position where the contrast is greatest is determined and set as the focal point position (p1) on the front curve surface. The positional relationship between the contact lens and the objective lens at this time is shown in FIG. Next, the same method is used to reach the focal point position (p2) on the base curve surface. (See FIG. 4) Using the two determined focal point positions p1 and p2, the calculation means 12 calculates the center thickness. If the distance between p1 and p2 is s, and the refractive index of the contact lens 1 is n, then from Abbe's invariant, the center thickness t is t=n・s in the region where spherical aberration can be ignored.
・It can be approximated as r/(r+s(1-n)). Here, r is the radius of curvature of the base curve when the objective lens faces the base curve surface of the contact lens (in the case of FIG. 1). Therefore, as the value of r, a lens design value may be used, or a base curve measurement value, which will be described later, may be used. The refractive index n also needs to be given in advance. Furthermore, since the base curve value r is usually sufficiently large with respect to the center thickness, t=n·s may be used.

Next, an example of measuring the radius of curvature of the base curve will be described. The focal point position (p2) on the base curve surface has already been determined by the focal point detection means 11 used in the center thickness measurement. Therefore, when the target image is formed at the center of curvature of the base curve, the focal point position (
p3) is detected by the same method (see FIG. 5), and the difference between p2 and p3 is determined by the calculating means 12 and set as the radius of curvature r of the base curve. That is, if p3>p2, r=p
3-p2. Since a computer is usually used as the calculation means, the same configuration can be used for the center thickness measurement and the base curve radius of curvature measurement, making it possible to measure both with one measuring device.

Warpage is a condition in which the base curved surface of a manufactured contact lens does not form part of a perfect spherical surface, and the curvature differs depending on the direction in which the surface is cut, and the maximum value of this curvature The difference between the minimum value and the minimum value is calculated, and the quality is determined by comparing the difference with the inspection standard. For a workpiece with a large warpage value, even if an attempt is made to form a target image on the center of curvature of the base curve, only a portion of the image will be in focus, and the focused position will differ depending on the position of the image on the plane. Therefore, warpage can be evaluated by finding the focal point position for each line of the target image extending radially from the center. in particular,
A measurement line 14 may be provided to intersect the target image 13 shown in FIG. 2 at right angles, and each focal point position may be determined from a change in contrast on the line. In the case of FIG. 2, there are eight measurement lines, so the method for determining the radius of curvature of the base curve described above is applied to each of these eight measurement lines to obtain eight pieces of curvature data. The average value of this curvature data can be taken as the curvature radius of the base curve of this workpiece, and the difference between the maximum value and the minimum value can be determined and used as the warpage value.

Note that FIG. 1 shows one embodiment of the present invention, and the in-focus point detection means 11 and calculation means 12 do not have to be physically independent as long as they have their respective functions. That is, the calculation means 12 may be included as part of the focused point detection means 11.

Further, in the explanation, the support stand on which the contact lens is placed is moved, but the same measurement can be performed even if the support stand is fixed and the objective lens side is moved.

[0017]

As described above, the present invention has the advantage that center thickness, base curve curvature, and warpage can be automatically measured in a non-contact manner using a single measuring device.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a diagram showing the positional relationship between a target image obtained from the TV camera of the present invention and a measurement line.

FIG. 3 is a diagram showing the positional relationship between the contact lens and the objective lens when the focus position is adjusted to the front curved surface of the present invention.

FIG. 4 is a diagram showing the positional relationship between the contact lens and the objective lens when the focus position is adjusted to the base curve surface of the present invention.

FIG. 5 is a diagram showing the positional relationship between the contact lens and the objective lens when the focus position is aligned with the center of curvature of the base curved surface of the present invention.

[Explanation of symbols]

1 Contact lenses 2 Objective lens 3 Half mirror 4 Relay lens 5 Light source 6 Target 7 TV camera 8 Motor 9 Work support stand 10 Linear scale 11 Focused point detection means 12 Calculation means 13 Target image 14 Measurement line

Claims (3)

[Claims] Claim 1: For an optical system based on an autocollimation method in which the image point of a target objective lens is matched with the focused position of a microscope, the distance between the contact lens and the objective lens is varied, and the base curve of the contact lens is A focused point detection means for automatically detecting a focused point position when a target image is formed on a surface and a focused point position when the target image is formed on a front curved surface; A contact lens measuring device characterized by having calculation means for calculating the center thickness of a contact lens from the interval. 2. The focused point detection means according to claim 1 is further used to detect the focused point position when a target image is formed at the center of curvature of the base curve, and to detect the focused point position when the target image is formed at the center of curvature of the base curve. A contact lens measuring device characterized in that it has calculation means for calculating the radius of curvature of the base curve from the focal point position of the contact lens. 3. When detecting the focused point position when the target image is formed at the center of curvature of the base curve according to claim 2 and the focused point position on the base curve surface, A contact lens measuring device characterized in that it has a focal point detection means for determining the two types of focal point positions at a plurality of locations, and determines a warpage value from the radius of curvature of the base curve at each location.