JPS58172505A - Measuring method of configuration - Google Patents

Abstract

PURPOSE:To enable the measurement of the form of the surface of an object irrespective of the scale of the divergence thereof from a concave, convex or spherical surface and thereby to enable the high-speed measurement thereof, by moving the object round and straight so that a laser beam falls thereon constantly in the vertical direction thereto, and by finding the amounts of rotating and straight movements of the object at each point on the surface thereof. CONSTITUTION:The diameter of a laser beam L1 emitted from a laser 1 is decreased by a lens 2 and a lens 3, and the beam is transmitted through a beam splitter 4 and falls on the surface 5 of an object. Numeral 5 denotes the form of the surface of a section out of those obtained by cutting the object along a plane containing an axis of rotational symmetry, and mark (a) denotes the incident beam of the laser beam L1. Initially, the surface 5 of the object is arranged, as shown by a broken line, so that the laser beam L1 falls vertically onto the center O of the surface 5 of the object. A reflected beams (b) from the surface 5 of the object is reflected to be a laser beam L2 by the beam splitter 4, and falls on the detector 6 of the position of the beam. As the detector 6, a photoelectric detector divided into two parts consisting of two photoelectric detectors and differential amplifiers is employed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring the shape of rotationally symmetric objects having smooth, light-reflecting surfaces.

Conventionally, mechanical contact methods or methods using an interferometer have been known as methods for measuring the shape of an aspherical lens or an aspherical mirror. However, the mechanical contact method is not only troublesome to measure, but may also damage the surface to be measured. On the other hand, the method using an interferometer has very good relative accuracy and the measurement operation is relatively simple, but as the object surface shape deviates from a spherical surface, the interference fringes become more distorted, making analysis difficult.

The present invention eliminates the drawbacks of such conventional methods,
The present invention provides a shape measuring method that can easily measure the shape of an aspherical surface without making mechanical contact with the object to be measured (in C, a laser beam with a narrow beam diameter is used). The shape of the object surface is measured by making the reflected light incident on the surface of the object and detecting the position of the reflected light.In other words, the position of the reflected light is detected using a light positioning device placed at a predetermined position. The object is rotated and moved linearly so that the laser beam is always incident perpendicularly to the object surface, and the amount of rotational movement and linear movement of the object is determined for each point on the object surface. Based on these values, the object is The surface shape of is being calculated.

The present invention will be described in more detail below with reference to the drawings.

FIG. 1 is a schematic diagram showing the configuration of an optical system for explaining an embodiment of the present invention. In the figure, a laser beam L1 from a laser is narrowed down in beam diameter by lenses 2 and 3, passes through a beam splitter 4, and then enters a surface 5 of an object. Note that 6 is a cross section taken along the axis of rotational symmetry of the object at a-b f, in which the surface shape is omitted, and the cut a indicates the incident light of the laser beam L1.

As an initial arrangement, the object surface 5 is arranged so that the laser beam L1 is perpendicularly incident on the center 0 of the object surface 5, as shown by the broken line in the figure. The reflected light from the object surface 5 is reflected by the beam splitter 4:ll:1.

It becomes a laser beam L2 and enters a light position detector 6.

As the optical position detector 6, a two-part photoelectric detector consisting of two photoelectric detectors 7, 8 and a differential amplifier 9 is used, for example as shown in FIG. When the laser beam L2 enters the center of the two photoelectric detectors 1j as indicated by the diagonal lines in FIG. 2, the outputs of each photodetector become equal and the output of the differential amplifier 9 becomes zero. In this way, zero detection of the position of the laser beam can be performed with high precision.

Next, the object surface 6 is 0 as shown by the solid line 5' in FIG.
Cut the inside and close it, turn the angle α (b) in the above plane,
Further, when the laser beam L1 is moved straight by d in the X-axis direction perpendicular to the rotational symmetry axis y, the laser beam L1 force is again perpendicularly incident on the object surface 5'. This determination is made using the light detector 6. In this way, when the object surface 5 is rotated and moved linearly minute by minute and the laser beam is incident perpendicularly to the object surface, the object surface The amount of rotational movement α and the linear movement jtd at each point in 6 are found in 11 subsequent steps.

Figure 3 shows the amount of rotational movement α determined by this measurement method.
The linear movement amount d and the surface shape of the object can be calculated by simple calculation using the rotational movement amount α and the linear movement amount d.For example, two adjacent points on the object surface are approximated by a quadratic equation. The method for determining the surface shape of an object in this case will be explained with reference to FIG.

In FIG. 4, the (x, y) coordinates are a coordinate system in which the center 0 of the object surface 6 is the origin, the axis of rotational symmetry is the y axis, and the direction perpendicular to this is the x axis. Also ( x / , y l
) coordinate is a coordinate system parallel to the ('' + V ) coordinate with point A as the origin, and the following '' is (x'
, y′) represents the value in the coordinate thread.

Calculation is based on regression method VC. (x) of the nth measurement point A.

y) If the coordinate values are determined as xn and yn, then the distance penalty XT' between point A and point 0 is calculated as follows.

Also, if the object surface shape near point A is approximated by a quadratic equation, it can be expressed as y = a (x') + bx, so X7' =: XB' + tanαn+, + (a(XB
) +bXB'""" (2) is also calculated.

Note that the slope of the surface shape of the object at both points A and B is 30αtanα n l n+1, respectively, so the unknown coefficients a and b in the above equation are -α = b... ・(3
)1α −2a XB′ ” b −
・It has the following relationship: -(')n+1.

Above, from the four equations (1), (2), (3), and (4), the three unknowns a', b, and XB' are found, and the (x, y) coordinate value of point B ("n+i + )'n
+1) is calculated as 1+□. According to this recurrence formula, the shape of the object surface is calculated sequentially.

In addition, in the above explanation, an example of quadratic approximation was shown, but
It is clear that the shape of the object surface can be similarly calculated using other n-th approximations (n is a natural number).

As is clear from the above description, according to the present invention, if a rotationally symmetrical object has a smooth light-reflective surface,
The shape of the object's surface can be measured regardless of whether it is concave, convex, or deviated from a spherical surface. Furthermore, since the method of the present invention is a non-contact measurement method, it does not damage the surface of the object.

Furthermore, if necessary, (b) it is also possible to use a computer to control axial movement and linear movement, and to determine whether or not the laser beam is incident perpendicularly to the object surface.
J enables high-speed measurement

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the configuration of an optical system for explaining an embodiment of the present invention, FIG. 2 is a configuration diagram of an example of an optical position detector used in the present invention, and FIG. A diagram showing the relationship between the measured quantities ((b) rotational displacement, linear displacement) obtained by the method and the surface shape of the object, Figure 4 shows the calculation of the surface shape of the object from the measured quantities obtained by the method of the present invention It is an auxiliary explanatory diagram explaining a process of 1... Laser jt = relation, 2+ 3...
Lens, 4...Beam splitter, 5...
...Object surface, 6...Light position detector, 7,8
...Photoelectric detector, 9...Differential amplifier. Name of agent: Patent attorney Toshio Nakao and 1 other person
1 Figure 2m

Claims (1)

[Claims] When measuring the shape of a rotationally symmetrical object having a smooth light-reflecting surface, a laser beam is irradiated within a plane that includes the axis of rotational symmetry of the object, and the reflected light of the laser beam from the surface of the object is measured. By detecting the position of the object with a light position detector placed at a predetermined position, the rotational symmetry axis of the object is set so that the reflected light from any point on the object's surface always returns to the same position. This operation is performed for each point in the plane containing the rotational symmetry axis of the surface of the object, and the surface shape of the object is calculated from the amount of rotational movement and the amount of linear movement at each point. A shape measuring method characterized by: