JPH0543366Y2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] The present invention is an optical displacement measuring device that uses light such as a laser beam to measure the displacement of a target. Particularly, the present invention relates to an improvement in a target sheet that is attached to a target.

[Conventional technology]

An example of this type of optical displacement measuring device is
A device as shown in FIG. 2 has been put into practical use. In the figure, TG is an object to be measured (target) that is displaced in two directions, X and Y, 1 is a light source that emits light such as a laser beam, 21 and 22 are half mirrors, 31,
32 is a lens, 4 is an aperture, 5 _X and 5 _Y are photodiode arrays and are image sensors having spatial filter characteristics, and 6 is an image sensor 5 _X and 5 _Y.
This is a signal processing circuit that generates an output signal according to the amount of displacement of the target TG from the output of the target TG. Furthermore, a retroreflective tape TS (hereinafter referred to as target sheet TS) with a checkered pattern is pasted on the surface of the target TG in order to facilitate the detection of the amount of displacement. The device shown in the figure is an image sensor 5
Image of target sheet TS on _X , 5 _Y (lattice image)
The movement of the image is detected by the image sensor ₅
5 _Y is used for direct detection.
The image sensors 5 _X and 5 _Y are arranged so as to be sensitive to the movement of the image in the X direction or the Y direction, respectively. That is, the light emitted from the light source 1 is irradiated onto the target TG via the half mirror 21, and the target TG (target sheet
The light reflected by the half mirror 21
After passing through the lens 31, the aperture 4, and the lens 32, the light is divided into two by the half mirror 22, and images (grid images) of the target sheet TS are focused on the image sensors _5X and _5Y , respectively.

Here, the target sheet TS attached to the target TG is generally a sheet on which glass beads with a diameter of several tens of micrometers are attached, but as shown in Fig. 3, a microcube with a side of just under 200 micrometers is used. A sheet covered with corner MCC is more advantageous in terms of retroreflection characteristics. In the target sheet TS using microcube corner MCCs, the microcube corners MCCs are regularly arranged, so the obtained lattice image has a certain spatial frequency.

However, such a target sheet
In TS, the accuracy of the pitch in the lattice image depends on the manufacturing accuracy of the microcube corner MCC, and it is not possible to obtain very high accuracy. Also, as shown in the figure, the pattern arrangement direction (hereinafter referred to as natural pattern Pn)
is along the 60° coordinate system, so it is not suitable for measuring the displacement of the target TG in Cartesian coordinates.

For this purpose, a target sheet TS with microcube corner MCC is used to set the orthogonal coordinates (X,
In order to measure the displacement along Y), a grid pattern Pm as shown in Fig. 4 is placed on the target sheet.
Must be formed on top of the TS. The grid pattern Pm is formed by printing the grid pattern Pm on the surface of the target sheet TS.

[Problem that the invention attempts to solve]

However, in this case, the image sensor ₅
5 The lattice image formed in _Y is a natural pattern
Since Pn and the lattice pattern Pm overlap, the unique spatial frequency in the natural pattern Pn causes a linearity error.
Furthermore, depending on the degree of overlapping of the patterns, the magnitude of the linearity error that appears differs in the X and Y coordinate directions, making it unsuitable for two-dimensional displacement measurement. Furthermore, it is impossible to estimate linearity errors.

The present invention eliminates the above-mentioned drawbacks of the conventional device, and makes it possible to estimate the magnitude of the linearity error that appears in the X and Y coordinate directions. It is an object of the present invention to realize a target sheet for an optical displacement measuring device that can accurately measure a quantity with a simple structure.

[Means for solving problems]

The target sheet for optical displacement measuring devices of the present invention is a target sheet for optical displacement measuring devices in which microcube corners are spread over one surface and a grating pattern according to orthogonal coordinates (X, Y) is formed on the surface. In the target sheet, arbitrarily select an axis of symmetry such that the natural pattern is symmetrical with respect to the natural pattern formed by the microcube corners, and
A straight line where X=Y is determined for the lattice pattern, and the lattice pattern is formed so that this straight line coincides with the axis of symmetry.

[Effect]

In this way, if we find a straight line where X=Y in a lattice pattern arranged based on orthogonal coordinates (X, Y) and form a lattice pattern so that this straight line coincides with the axis of symmetry in the natural pattern, , the spatial frequency patterns generated by the natural pattern that interfere with the lattice pattern and cause linearity errors are exactly the same on the The size can be estimated and the amount of two-dimensional displacement in the target can be accurately measured.

〔Example〕

FIG. 1 is a structural diagram showing an embodiment of a target sheet for an optical displacement measuring device according to the present invention. The figure shows the positional relationship between the natural pattern Pn generated by the microcube corner MCC on the target sheet TS and the lattice pattern Pm formed on the target sheet TS. If Po is the origin, natural pattern
In Pn, there are several possible symmetry axes such as x, y, and w for which the pattern (dot position) is line symmetrical, but the y-axis is selected here. In addition, in the grid pattern Pm, if the straight line indicating X=Y is I, the grid pattern Pm is the straight line I
is formed on the natural pattern Pn so that it coincides with the y-axis of the natural pattern Pn.
The target sheet TS thus created is attached to the target TG so that its orthogonal coordinates (X, Y) coincide with the coordinates to be measured.

If the relationship between the natural pattern Pn and the lattice pattern Pm is determined in this way, the natural pattern Pn will also be line symmetrical with respect to the straight line I, so the linearity error generated by this natural pattern Pn will interfere with the lattice pattern Pm The pattern of spatial frequencies that give rise to is exactly the same on the X and Y axes. In this way, if the magnitude of the linearity error included in the X-axis and Y-axis measurement outputs becomes equal and the magnitude can be estimated, then
It becomes easy to correct linearity errors,
It is possible to accurately measure the amount of two-dimensional displacement in the target TG.

Further, by specifying the formation conditions of the grating pattern Pm in this way, it is possible to always create the target sheet TS with the same pattern, and the linearity of the optical displacement measuring device can be guaranteed.

In addition, in the above description, the case where the y-axis was selected as the symmetry axis of the natural pattern Pn was exemplified, but the reference symmetry axis is not limited to this.

[Effect of idea]

As explained above, in the target sheet for an optical displacement measuring device of the present invention, microcube corners are spread over the entire surface, and a lattice pattern corresponding to orthogonal coordinates (X, Y) is formed on the surface. In the target sheet for an optical displacement measuring device, an axis of symmetry is arbitrarily selected such that the natural pattern is symmetrical with respect to the natural pattern formed by the microcube corners, and an axis of symmetry with respect to the lattice pattern is = Y is found, and the lattice pattern is formed so that this straight line coincides with the axis of symmetry, so the spatial frequency pattern is generated by the natural pattern and interferes with the lattice pattern, causing a linearity error. are exactly equal for the X and Y axes, and the magnitude of the linearity error appearing in the X and Y coordinate directions is the same, and the magnitude can be estimated, and the amount of two-dimensional displacement in the target can be accurately calculated. It is possible to realize a target sheet for an optical displacement measuring device that can perform measurements with a simple structure.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing an embodiment of the target sheet for an optical displacement measuring device of the present invention, and Fig. 2 is an example of an optical displacement measuring device in which the target sheet for an optical displacement measuring device of the present invention is used. FIG. 3 is a diagram showing the state of the natural pattern Pn on the target sheet TS, and FIG. 4 is a diagram showing the state of the lattice pattern Pm formed on the target sheet TS. 1...Light source, 21, 22...Half mirror, 3
1, 32...Lens, 4...Aperture, 5 _X , 5 _Y ...
Image sensor, 6... Signal processing circuit, TG...
Object to be measured (target), TS...Target sheet, MCC...Microcube corner, Pn...
...Natural pattern, Pm...Lattice pattern.

Claims (1)

[Scope of utility model registration request] In a target sheet for an optical displacement measuring device, which is covered with microcube corners and forms a grating pattern according to orthogonal coordinates (X, Y) on the surface thereof, the target sheet is formed by the microcube corners. At the same time, arbitrarily select an axis of symmetry such that this natural pattern has line symmetry with respect to the natural pattern, find a straight line such that X=Y with respect to the lattice pattern, and A target sheet for optical displacement measuring devices formed with a lattice pattern.