JPS61286701A - Method for measuring curvature of mirror - Google Patents

Abstract

PURPOSE:To rapidly and easily measure the curvature of a mirror with high accuracy, by contacting the respective lower ends of three measuring levers with the surface of the mirror in a vertical state under their own wt. and relatively moving said levers on the mirror. CONSTITUTION:The displacement meters 8a, 8b, 8c are mounted to an arm 7 and respectively vertically support lever shaped measuring elements 9a, 9b, 9c in a freely slidable manner while the slide table 10 on a base 5 has a structure capable of horizontally and reciprocally driving to the directions shown by a double arrow X-X' and a mirror 4 is mounted on said table 10 and three lever shaped measuring elements are contacted with the mirror 4 under their own wt. When the table 10 is moved to an X-axis direction, the measuring elements 9a, 9b, 9c are displaced in the up-and-down direction corresponding to the surface state of the mirror and, therefore, the displacement meters 8a, 8b, 8c respectively electrically measure the displacement quantities of said measuring elements to output the same. The output signals are inputted to a computer and radii at a large number of points are calculated to be displayed on CRT display.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method of measuring the curvature of a mirror surface.

[Background of the invention]

In the prior art, the curvature of a mirror surface is generally measured using a spherometer using a dial gauge or a similar measuring instrument.

Figure 6 shows one of the instruments used in the measurement method according to the prior art.
As an example, two fixed contacts 2 are fixed to a pedestal l, and a dial gauge 3 is attached.

The conventional measuring method is to press the two fixed contacts 2 against the surface of the mirror 4, bring the movable contact 3a of the dial gauge 3 into contact with the surface of the mirror 4, read the finger strength of the dial gauge 3, and then press the movable contact 3a of the dial gauge 3 against the surface of the mirror 4. Calculate the curvature of.

In measuring the mirror curvature using the conventional method described above, it is possible to theoretically calculate an accurate curvature if the mirror has sufficient rigidity, but in actual measurement, the fixed contact 2 must be (If it is pressed against the mirror 4, the mirror 4 will be distorted and the measurement results will be inaccurate. Also, if the above pressing force is insufficient, the contact rod state of the contact will become unstable and the measurement will be inaccurate. Becomes stable and produces errors.

Also, according to JIS regulations, the force with which the movable contact of a dial gauge is pressed against the surface of the object to be measured is 150 grams or less, but if the mirror is thin, the pressing force of 150 grams can be ignored. This will cause distortion to an extent that is impossible to obtain.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned circumstances, and it is possible to quickly and easily measure the curvature of a mirror with high precision, without the risk of causing harmful distortion, even for mirrors with low rigidity. We are trying to provide a way to obtain it.

[Summary of the invention]

In order to achieve the above object, the measuring method of the present invention supports three measuring rods vertically and slidably in the vertical direction at regular intervals, and the lower ends of each of the three measuring rods are supported vertically and slidably in the vertical direction. is brought into contact with the mirror surface by its own weight, and the vertical position of each of the three measuring rods is electrically detected,
The detection signal is inputted to a computer, and the curvature of the mirror is calculated by the computer while the three measuring rods and the mirror are moved relative to each other while keeping the distance between the three measuring rods constant. Features.

[Embodiments of the invention]

FIG. 1 is a schematic front view showing an example of a curvature measuring device configured to carry out the measuring method of the present invention.

An arm 7 is horizontally and fixedly supported on the base member 5 via a stand 6.

The above arm 7 has three displacement meters 3a and 3b.

8C is installed. Each of these displacement gauges supports rod-shaped measuring elements 9a, 9b, and 9c in a slidable manner vertically (in the X-axis direction).

The distance between the rod-shaped measuring tip 9a and the same 9b is L+, and the rod-shaped measuring tip 9
The distance between b and 9c is Lt, the above distance dimension L+, Lx
is constant. In this example, L t =L t, but these spacing dimensions do not necessarily have to be equal.

On the other hand, a slide table 10 is provided on the base 5. This slide table 10 is indicated by the arrow x-x'
It has a structure that can be horizontally reciprocated like this, and a mirror 4 is mounted on it.
It is designed to be installed.

Since the three rod-shaped measuring elements are slidable in the X-axis direction, they abut against the mirror 4 due to their own weight.

The displacement meters 8a, 8b, and 8c have a function of electrically measuring the amount of vertical displacement of the rod-shaped measuring elements 9a, 9b, and 9c, respectively.

FIG. 2 is a block diagram showing the connections of the three displacement meters 8a, 8b, and 8c. The output signal of each displacement meter is input manually to the computer 11, and the calculation results are displayed on the CRT display 12.
．． Or it is displayed by the printer (which may also be a block) 13.

Figure 3 shows how the mirror 4 is measured based on the detected values of the three displacement meters.
FIG. 2 is an explanatory diagram of calculation for calculating the curvature of

4 indicated by a solid line is a mirror as an object to be measured, and 4' indicated by a broken line indicates the designed shape of the mirror.

The three displacement meters 3a, 3b, F3c measure the three points P on the mirror 4 via the three rod-shaped measuring elements 9a, 9b, 9c.
+, Pz, P: When the x and y coordinates of t' are measured, the coordinate values of each point are P+(X+, Xz), P
i(X2, )'z), P3'(X+'+ y+
') into the general circle formula % formula % (1) The radius r can be calculated by the computer 11 from the above formula (2).

If the radius r of a large number of points is calculated by the above calculation while moving the slide table 10 shown in FIG. 1 in the X-axis direction, for example, FIG. 4 is obtained. The horizontal axis of this figure 4 represents the measurement location on the mirror 4, the left side of the diagram is the center of the mirror, the right side is the peripheral area of the mirror, and the point Edg on the horizontal axis
indicates the periphery of the mirror 4.

In the example shown in Fig. 4, the radius of curvature is constant in the area M at the center of the mirror, and the radius of curvature changes within a range of distance from the periphery, decreasing as it approaches the periphery. I understand that there is.

The dimension Δy shown in Figure 3 is the design point P and the actual measurement point P3.
′ represents the difference in y-coordinate value.

FIG. 5 is a chart showing the results of measuring the above-mentioned Δy for five examples, and the horizontal axis in FIG. 5 represents the measurement position on the mirror 4, as in FIG. 4.

As shown by the curve C1 shown by the solid line, when Δy and the measured value are approximately zero, it means that both the central portion and the peripheral portion of the mirror have the curvature as designed.

As shown by the curve Ct shown by the broken line, when Δy and the measured value are positive over the entire area, it means that the mirror curvature of both the central portion 9 and the peripheral portion is larger than the designed value. On the contrary,
If the measured value of Δy is negative over the entire region, as shown by the curve C1 indicated by a dashed-dotted line, it means that the mirror curvature is smaller than the design value in both the central and peripheral parts of the mirror.

A curve C4 drawn with a two-dot chain line means that the mirror curvature is almost the same as the design value at the center and is excessive at the periphery.

Further, the curve CS drawn by a dotted line means that the central part is as designed, but the peripheral part is too small.

In the measurement value of the mirror curvature described above, as can be easily understood from FIG.
, 9c only have their lower ends in contact with the surface of the mirror 4 due to their own weight, and the contact pressure is small.
Moreover, it is constant.

Therefore, even if the rigidity of the mirror that is the object to be measured is not large, the distortion imparted to it is so small that it can be ignored in practice. In addition, since the calculation of the curvature is performed by the computer 11 (Fig. 2), there is no need for the operator to have separate calculation ability.
Measurements can be taken quickly, there is no risk of human calculation errors, and high accuracy and reliability can always be obtained.

〔Effect of the invention〕

As detailed above, according to the measurement method of the present invention, even if the rigidity of the mirror to be measured is small, the curvature of the mirror can be measured quickly, easily, and with high precision without the risk of causing harmful distortion. Can measure automatically 1.

[Brief explanation of drawings]

1 and 2 show an example of a curvature measuring device configured to carry out the curvature measuring method of the present invention, FIG. 1 is a schematic front view, and FIG. 2 is a block diagram near the calculation section. It is a diagram. FIG. 3 is an explanatory diagram of calculations in one embodiment of the curvature measuring method of the present invention, and FIGS. 4 and 5 are charts showing measurement results in the above embodiment, respectively. FIG. 6 is an external view of a measuring instrument used for conventional curvature measurement. 4...Mirror, 5...Base, 6...Stand,
7... Arm, 8a, 8b, 8cm displacement meter, 9a, 9
b. 9C...rod-shaped probe, 10...slide table,
12...CRT display, 13...Printer.

Claims (1)

[Claims] Three measuring rods are supported vertically and slidably in the vertical direction at regular intervals, and the lower ends of each of the three measuring rods are brought into contact with the mirror surface by their own weight. The vertical positions of the three measuring rods are electrically detected, the detected signals are input to the computer, and the three measuring rods and the mirror are moved relative to each other while keeping the distance between the three measuring rods constant. A method for measuring the curvature of a mirror, characterized in that the curvature of the mirror is calculated by the computer while moving the mirror.