JP2857515B2 - Optical position measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning type optical position measuring apparatus capable of measuring a positional relationship between a focus position of a scanning beam and a workpiece with high accuracy.

[0002]

2. Description of the Related Art A scanning type optical dimension measurement for irradiating a measurement object (work) by scanning a laser beam in parallel and measuring the dimension of the work from a light-dark pattern in a scanning direction detected at a rear side of the work. There is a device.

FIG. 4 is a block diagram showing an example of this type of optical dimension measuring device. In the figure, 10 is a laser light source,
A laser beam 12 output from the laser light source 10 is converted into a rotary scanning beam 16 by a polygon mirror 14,
Further, the beam is converted into a parallel scanning beam 20 having a constant beam diameter and a constant speed by the f-θ lens 18. This parallel scanning beam 20
Is irradiated so as to scan the measurement area including the work 22 with the rotation of the polygon mirror 14, and enters the measurement light receiving element 26 through the condenser lens 24. 28 is a mirror for reflecting the laser beam 12 and entering the polygon mirror 14; 30 is a motor for rotating the polygon mirror 14;
2 is located outside the effective scanning range of the rotating scanning beam 16,
The reset light receiving element detects the start or end of one scan.

The output of the measuring light receiving element 26 is amplified by an amplifier 48 and then input to an edge detection circuit 50. The edge detection circuit 50 shapes an output of the amplifier 48 to perform edge detection. On the other hand, the output of the reset light receiving element 32 is input to the reset circuit 52. This reset circuit 5
2 generates a reset signal based on the output timing of the reset light receiving element 32.

The gate circuit 56 turns on and off at the timing of the edge signal output from the edge detection circuit 50 and the reset signal output from the reset circuit 52, and the counter 58 controls the clock input during the on period of the gate circuit 56. Count and measure the time between signals. This clock is generated by the clock generator 54, and is also used for synchronizing the rotation of the motor 30. Reference numeral 60 denotes a synchronization signal generator for this purpose, and reference numeral 62 denotes a motor drive circuit. The laser output adjustment circuit 64 keeps the output of the laser light source 10 constant. Reference numeral 40 denotes a CPU for performing various processes and controls; 42, a keyboard display circuit; 44, an input / output device; and 46, a storage device including a read-only memory (ROM) and a random access memory (RAM).

The output (scan signal) of the amplifier 48 is shown in FIG.
As shown in (1), the entire scanning range is a bright portion having a high level, and the work portion therein is a dark portion having a low level. Therefore, the size of the work can be measured from the width of the dark part. To realize this principle, the edge detection circuit 50 binarizes this scan signal at a predetermined threshold level and converts it into an edge signal. At this time, different edge signals are obtained when the dark portion is narrow and deep (sharp) as shown by a solid line, and when the dark portion is binarized at the same threshold level, as shown by a broken line.

Generally, when the workpiece is at the focal position of the beam, a sharp dark portion as shown by a solid line is obtained. In contrast,
If the work deviates from the focal position, an unsharp dark portion such as a broken line is formed. In such a case, if the inclination (having a Gaussian distribution) at both ends of the scan signal changes, the measurement accuracy decreases. This degree is remarkable in the case of a laser beam whose beam waist is extremely narrowed as shown in FIG. For example, a laser beam having a diameter of
In the case where the diameter is reduced to 25 μm with a 5 mm f-θ lens, even if the work is slightly away from the focal point, the diameter of the beam irradiated on the work becomes extremely large. For this reason, when the work is thinner than the beam waist, for example, a thin line having a diameter of about 10 μm, the measurement accuracy is extremely reduced in the case of the broken line.

In the case described above, if the positional relationship between the beam focal point and the work is known, a servo system that matches the work position with the focus position can be used. For this purpose, it is necessary to accurately measure the work position in the beam traveling direction. Japanese Utility Model Publication No. 58-26325 discloses a position detecting method of receiving light by arranging a joint of two light receiving elements S1 and S2 so as to coincide with a beam center as shown in FIG. According to this position detection method, whether the work 22 is located before or after the beam focal point 94 as shown in FIG.
When the phases of the light receiving outputs of the two light receiving elements S1 and S2 are compared, the polarity of the phase comparing output is inverted and the work 22
And the beam focal point 94 appear as a phase difference of the phase comparison output. Therefore, the position of the workpiece in the beam traveling direction with respect to the beam focal point can be calculated from the polarity and the phase difference.

[0009]

However, according to the position detecting method disclosed in the publication, as shown in FIG. 8, two light receiving elements S1 and S2 are brought close to each other and ideally brought into close contact with each other so that the optical axis of the lens is set to both light receiving elements. In the contact area.
However, even when the two light receiving elements S1 and S2 are actually brought close to each other, it is difficult to make them completely adhere to each other, and a gap 96 of several tens of μm is generated between them. This gap 96
Since this corresponds to the portion 98 having the highest received light intensity at the center of the beam, this portion includes a defect that this portion cannot be received. An object of the present invention is to improve such a point and to measure the positional relationship between the beam focal point and the workpiece in the beam traveling direction with high accuracy.

[0010]

In order to achieve the above object, according to the present invention, a predetermined measurement area is scanned by a main scanning beam, and the main scanning beam passing through the measurement area is received by a main scanning light receiving element. Main scanning means for scanning the measurement area with a sub-scanning beam inclined at a predetermined angle (θ) with respect to the main scanning beam, and receiving the sub-scanning beam passing through the measurement area with a sub-scanning light receiving element. Sub-scanning means for detecting a position (a) of a work included in the measurement area from the center of the main scanning beam from a light-dark pattern in the main scanning direction obtained by the main scanning light-receiving element; Means for detecting the position (b) of the work included in the measurement area from the center of the sub-scanning beam from the light-dark pattern in the sub-scanning direction obtained by the light receiving element for the main scanning beam; It is characterized by comprising an arithmetic unit for calculating from the main scanning direction of beam advance position (e) the position of the workpiece (a) and (b) and the angle (theta).

[0011]

When the work is scanned by the main scanning beam, the work position in the main scanning direction can be detected. At this time, if the same work is scanned with the sub-scanning beam inclined with respect to the main scanning beam,
The work position in the sub-scanning direction can be detected. Since the sub-scanning direction is inclined at an angle θ with respect to the main scanning direction, the focal position of the main scanning beam is geometrically determined from the work position in the main scanning direction, the work position in the sub-scanning direction, and the inclination angle of the sub-scanning beam. Can be calculated in the main scanning beam advancing direction. At this time, since the scanning speed of the sub-scanning beam is 1 / cos θ of the scanning speed of the main scanning beam, the scanning speed is corrected and accurate work position measurement is performed. However, since ^{cos 2 θ ≒ 1, cos 2} θ in the arithmetic expression
Can be omitted.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention, and shows a position measuring device added to the dimension measuring device of FIG. In the figure, P is the main scanning beam B from the parallel scanning beam 20 in FIG.
1 and a prism which simultaneously generates the sub-scanning beam B2, L
Reference numerals 1 and L2 denote lenses for condensing the beams B1 and B2, respectively, and reference numerals S1 and S2 denote light receiving elements for receiving the beams condensed by the lenses L1 and L2 at the center. The outputs of these light receiving elements are combined on a time axis and input to a processing circuit (not shown).

The sub-scanning beam B2 is set at an angle θ with respect to the main scanning beam B1, so that the sub-scanning beam center C2 (see FIG. 3) passes through the focal position of the main scanning beam B1. Accordingly, when the workpiece 22 is arranged and scanned near the beam focal point, when a scan signal like the output S1 in FIG. 2 is obtained by the main scanning beam B1, another scan like the output S2 in FIG. Is obtained. That is, when the workpiece 22 is located at each of the points B, C, and A in FIG. 1, dark areas corresponding to the S2 output by the sub-scanning are generated. In this example, it is assumed that point C is the focal position of the main scanning beam. Therefore, point B is ahead of the focal position, and a dark portion occurs before point C in the S2 output. On the other hand, point A is behind the focal position, and S2
In the output, a dark part occurs after the point C. The advance or delay time b from the point C corresponds to the work center position in the sub scanning direction from the sub scanning beam center C2 in FIG.

The points B, C, and A of the work 22 in FIG. 1 assume that the work 22 moves in the horizontal direction (the traveling direction of the main scanning beam B1). Therefore, the main scanning beam B1
Output to the horizontal position B, C,
A dark portion is generated at the same position regardless of A. The advance or delay time a of the dark portion from the center of the scan signal waveform corresponds to the work center position in the main scanning direction from the main scanning beam center C1 shown in FIG. The horizontal position e of the workpiece 22 with respect to the focal point of the main scanning beam to be measured in the present invention can be calculated from the times a and b and the angle θ by the following equation (1).

[0015]

E = (ab / cos ² θ) / tan θ

FIG. 9 is an explanatory diagram for deriving the above equation (1). The work position a in the main scanning direction can be divided into a distance c from the center of the work 22 to the sub-scanning beam center C2 and a distance d from the sub-scanning beam center C2 to the main scanning beam center C1. Sub-scanning beam center C2 from work center
The distance b in the sub-scanning direction is obtained by multiplying the distance c by cos θ. Here, when the correction based on the sub-scanning speed is added, the distance c is expressed as the following Expression 2.

[0017]

## EQU2 ## c = b / cos ² θ

The work position e in the horizontal direction is e = d / tan
It can be obtained by substituting Equation 2 into the relational expression of θ = (ac) / tan θ. Equation 1 is the work position calculation expression of the present invention obtained in this way. Note that cos ² θ ≒
Since it is 1, Equation 1 can be simplified as Equation 3 below.

[0019]

## EQU3 ## e = (ab) / tan θ

In the above-described method of detecting a workpiece position by using both the main and sub scanning beams according to the present invention, since the beam center is not lost as shown in FIG. 8, a scan signal can be obtained with a sufficient amount of received light. . Therefore, the work position can be measured with high accuracy. This work position detection method can be used alone, but when combined with a dimension measuring device as shown in FIG. 4, a servo system for moving a movable work table (not shown) that supports the work 22 is configured. If the servo system is operated with the work position obtained by the apparatus of the present invention as an error signal, the work 22 can be made to coincide with the beam focus, so that the dimension measurement accuracy of the work 22 can be significantly improved.

[0021]

As described above, according to the present invention, the positional relationship between the work to be measured and the focal point of the scanning beam can be measured with high accuracy in the scanning type optical position measuring device.

[Brief description of the drawings]

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

FIG. 2 is a scan signal waveform diagram of FIG.

FIG. 3 is a diagram illustrating the principle of position measurement according to the present invention.

FIG. 4 is a configuration diagram of a scanning optical dimension measuring device.

FIG. 5 is a waveform diagram of a work scanning signal.

FIG. 6 is an explanatory diagram of a scanning beam.

FIG. 7 is an explanatory diagram of a conventional work position detection method.

FIG. 8 is a layout view of a conventional work position detecting light receiving element.

FIG. 9 is an enlarged explanatory view of a main part of FIG. 3;

[Explanation of symbols]

P: prism, L1, L2: condenser lens, S1, S2 ...
Light receiving element, 20: parallel scanning beam, 22: work.

Continuation of the front page (56) References JP-A-2-112706 (JP, A) JP-A-3-71003 (JP, A) JP-A-49-97645 (JP, A) JP-A-3-52608 (JP) , U) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01B 11/00-11/30

Claims (1)

(57) [Claims] A main scanning means for scanning a predetermined measurement area with a main scanning beam and receiving the main scanning beam having passed through the measurement area with a main scanning light receiving element; Scanning means for scanning with a sub-scanning beam tilted at a predetermined angle (θ), and receiving the sub-scanning beam passing through the measurement area by a sub-scanning light receiving element; Means for detecting the position (a) of the work included in the measurement area from the center of the main scanning beam from the obtained light / dark pattern in the main scanning direction, and detecting the position (a) of the work in the sub-scanning direction obtained by the sub-scanning light receiving element. Means for detecting a position (b) of the work included in the measurement region from the center of the sub-scanning beam; and a position (e) of the work in the main scanning beam traveling direction with respect to the focal position of the main scanning beam. ) From the positions (a) and (b) and the angle (θ).