JPH0571920A - Optical size-measuring apparatus - Google Patents

Abstract

PURPOSE:To measure the size of even a work smaller than the diameter of scanning beams with high accuracy by making the work agreed with the focal position of the scanning beams at all times in a scanning-type optical size measuring apparatus. CONSTITUTION:In this scanning-type optical size measuring apparatus, a predetermined measuring area is scanned with parallel beams, and the beams passing through the measuring area are detected by measuring photodetectors S1, S2. Accordingly, the size of a work 22 included in the measuring area is measured from the light and dark pattern in the scanning direction obtained by the photodetectors. The apparatus is provided with a position detecting means for detecting the position of the work in the advancing direction of beams to the focus of the beams and a servo means for moving the work 22 or a collimator lens 72 which determines the focus of the beams to make the position of the work 22 detected by the position detecting means agreed with the focus of the beams.

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 dimension measuring apparatus capable of highly accurately measuring the dimension of a work smaller than the scanning beam diameter.

[0002]

2. Description of the Related Art A scanning type optical measuring device which scans a laser beam in parallel and irradiates an object to be measured (workpiece), and measures the dimension of the work piece from a bright and dark pattern in the scanning direction detected on the rear side of the work piece. There is.

FIG. 4 is a block diagram showing an example of this type of optical measuring apparatus. In the figure, reference numeral 10 denotes 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 and further, a beam diameter is narrowed by an f-θ lens 18 so as to be parallel at a constant velocity. It is converted into a scanning beam 20. The parallel scanning beam 20 is irradiated so as to scan the measurement region including the work 22 as the polygon mirror 14 rotates, and enters the measurement light receiving element 26 through the condenser lens 24. 28 is a laser beam 1
A mirror that reflects 2 and enters the polygon mirror 14,
Reference numeral 30 is a motor for rotating the polygon mirror 14, and 32 is a reset light receiving element which is arranged outside the effective scanning range of the rotary scanning beam 16 and detects the start or end of one scanning.

The output of the measurement light receiving element 26 is amplified by an amplifier 48 and then input to an edge detection circuit 50. The edge detection circuit 50 waveform-shapes the output of the amplifier 48 and performs 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 outputs 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 rotation synchronization of the motor 30. Reference numeral 60 is a synchronizing signal generator for this purpose, and 62 is a motor drive circuit. The laser output adjusting circuit 64 keeps the output of the laser light source 10 constant. Reference numeral 40 is a CPU that performs various processes and controls, 42 is a keyboard display circuit, 44 is an input / output device, and 46 is 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, the entire scanning range becomes a bright part having a high level, and the work part therein is a dark part having a low level. Therefore, the dimension of the work can be measured from the width of the dark portion. 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 binarization is performed at the same threshold level when the dark portion is narrow and deep (sharp) as shown by the solid line and when it is wide and shallow as shown by the broken line.

[0007]

Generally, when the work is at the focal point of the beam, a sharp dark portion as shown by the solid line is obtained. On the other hand, when the work deviates from the focus position, a non-sharp dark portion such as a broken line is formed. In such a case, the slope of both ends of the scan signal (Gaussian distribution)
If changes, the measurement accuracy will decrease. This degree is shown in FIG.
This is remarkable in the case of a laser beam in which the beam waist is extremely thin as shown in FIG. For example, a laser beam having a diameter of 3 mm can be used with an f-θ lens having a focal length of 45 mm to have a diameter of 25 μ.
When the focus is set to m, even if the work is slightly away from the focus,
The beam diameter applied to the work becomes extremely thick. Therefore, the work is thinner than the beam waist, for example, the diameter 10
In the case of a thin line of about μm, the measurement accuracy is extremely reduced in the case of the broken line.

Therefore, the work may be installed within the range of the beam waist, but since the length of the beam waist in the beam traveling direction is as short as about 0.3 mm, it is extremely difficult to accurately perform this by manual operation. is there. An object of the present invention is to improve such a point and to make a workpiece always coincide with a beam focus so that a workpiece dimension smaller than the beam diameter can be measured with high measurement accuracy.

[0009]

In order to achieve the above object, the present invention scans a predetermined measurement region with a parallel beam, receives the beam passing through this measurement region with a measuring light receiving element, and receives the beam. In the scanning type optical dimension measuring device for measuring the dimension of the work contained in the measurement region from the light-dark pattern in the scanning direction obtained in step 1, a position detecting means for detecting the beam traveling direction position of the work with respect to the focus of the beam And moving the workpiece, or moving the collimator lens that determines the focus of the beam,
And a servo unit for matching the position of the work detected by the position detection unit with the focus of the beam.

Further, in the present invention, the position detecting means includes a first light receiving element for directly receiving the beam and a second light receiving element for receiving the beam via a half mirror. It is characterized in that the positional relationship of the work with respect to the beam focus is detected from the phase relationship of the obtained signals.

[0011]

[Function] If a system configuration is adopted in which a beam traveling direction error between the beam focus and the work position is detected and a servo is applied so as to reduce this error to zero, the work is always placed at the beam focus. Even if the beam is extremely narrowed, the work can be positioned in the beam waist portion, and particularly, the work size smaller than the beam waist can be measured with high accuracy.

Further, when the position of the work is detected by disposing two light receiving elements in a distributed manner and using a half mirror, the central portion of the beam having the highest light receiving intensity can be surely received.
It enables highly accurate position detection.

[0013]

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, showing a position detecting means and a servo means added to the dimension measuring apparatus of FIG. Laser light source 10, polygon mirror 14,
The f-θ lens 18, the workpiece 22, the condenser lens 24, and the reflection mirror 28 have the same positional relationship as in FIG. However, the laser light source 10 of this embodiment includes a laser diode 70 and a collimator lens 72 that allows the laser beam to pass therethrough.
4 can move in the optical axis direction. This actuator 74 has a collimator lens 72 of several μm.
When moved, the focal position moves by several mm, so a micro-movement method using, for example, a piezoelectric vibrator or a voice coil motor is sufficient.

Two light receiving elements S1 and S2 for position detection are arranged behind the condenser lens 24, and one light receiving element S2.
The beam is directly incident on, and the beam reflected by the half mirror 76 is incident on the other light receiving element S1. The light receiving outputs of these light receiving elements S1 and S2 are amplified by amplifiers A1 and A2, respectively, and then converted into pulse waveforms D1 and D2 having edge information by a waveform shaping circuit 78.
The phase comparison circuit 80 compares the phases of the two pulse trains D1 and D2, has a pulse width corresponding to the phase difference, and generates a phase comparison output in which the polarities are opposite between the lead phase and the lag phase. The phase comparison output has a median value of, for example, 5 V, a peak value on the leading phase side of 10 V, and a peak value on the lagging phase side of 0.
It is V.

The integrator 82 integrates this phase comparison output,
The full-wave rectifier 84 full-wave rectifies the phase comparison output to generate a sample signal. The sample hold circuit 86 samples and holds the integrated output each time a sample signal is generated. This sample hold output is the adder 8
8 and the bias voltage supplied from the bias power source 90 is added to the actuator driver 92.
Will be input. This bias voltage is variable and is used to determine the desired initial focus position. Driver 92
Is for driving the actuator 74, and the servo system is configured by the above closed loop.

FIG. 2 is a signal waveform diagram of each part of FIG. 1. The left half shows the case where the phase of A1 output is advanced, and the right half shows the case where the phase of A1 is delayed. Both A1 output and A2 output are sharp level drop part (dark part) due to work 22
Have. By pulse-shaping such A1 and A2 outputs, pulse trains D1 and D2 having edge information can be obtained. The phase comparison output has opposite polarities in the lead phase and the lag phase, but the full-wave rectified sample signal becomes unipolar. In this example, the sampling of the sample hold circuit 86 is performed at the trailing edge (falling edge) of the sample signal.

The servo system of FIG. 1 can move the beam focus 94 as shown in FIG. That is, based on FIG. 3B, when the collimator lens 72 is moved away from the laser diode 70 by the actuator 74 as shown in FIG.
Approaching the θ lens 18. On the contrary, when the collimator lens 72 is brought close to the laser diode 70 as shown in FIG. 7C, the beam focus 94 moves away from the f-θ lens 18. How much the collimator lens 72 should be moved in which direction depends on the immediately preceding beam focus 94 and the workpiece 2.
2 (see FIG. 1).
Therefore, the position of the work 22 and the beam focal point 94 can be always kept in agreement by operating this servo system in the direction in which the amount of positional deviation is zero.
It is possible to measure with high accuracy even for work dimensions that are thinner than the beam waist.

Here, a method for detecting the position of the work 22 will be described. According to the position detection method described in Japanese Utility Model Publication No. 58-26325, the polarity of the phase comparison output in FIG. 2 is inverted depending on whether the work 22 is before or after the beam focus 94,
Moreover, the amount of positional deviation between the work and the beam focus is reflected in the pulse width of the phase-phase comparison output. Therefore, this position detection method can be applied to FIG.

However, in the position detection method according to the above publication, as shown in FIG. 8, the 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 lens optical axis is located at the contact portion of both light receiving elements. I am trying. However, even if the two light receiving elements S1 and S2 are actually brought close to each other, it is difficult to bring them into close contact with each other, and a gap 96 of several tens of μm is formed between them. Since this gap 96 coincides with the portion 98 having the highest received light intensity at the center of the beam, it contains a defect that this portion cannot be received.

On the other hand, as shown in FIG.
S2 is separated, one light receiving element directly receives the beam,
The other light-receiving element has the following advantages when the system configuration is such that the beam is received at another position via the half mirror. For example, as shown in the figure, the beam reflected by the half mirror 76 is made incident on the central portion of one light receiving element S1. In this way, even if the lower end of the other light receiving element S2 that directly receives the beam is arranged so as to coincide with the beam center, the light receiving element S1 can receive the light receiving intensity strongest portion 98 as shown in FIG. There is no omission as described in the figure.

If this system is further advanced, the light receiving element S1,
Even if S2 is an edge and the beam center is received, the loss as shown in FIG. 8 does not occur. Because half mirror 76
This is because, when is used, the optical positions of the light receiving elements S1 and S2 can be individually arranged so that the edges of both elements are in close contact with each other.

By using the half mirror 76, the amount of light incident on the light receiving element S1 is halved, but this does not cause any problem since it can be amplified by the amplifier A1 in the subsequent stage. In the configuration of FIG. 1, since the output of the light receiving element S1 is a sum signal, the output can be input to the amplifier 48 of FIG. 4 for measuring the work size.

[0023]

As described above, according to the present invention, in the scanning type optical dimension measuring device, the work to be measured can be always aligned with the focal position of the scanning beam, so that it is smaller than the beam diameter. It is possible to measure the workpiece size with high accuracy.

[Brief description of drawings]

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

FIG. 2 is an operation waveform diagram of FIG.

FIG. 3 is an operation explanatory diagram of a servo system of the present invention.

FIG. 4 is a configuration diagram of a scanning optical size 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 work position detection method.

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

[Explanation of symbols]

S1, S2 ... Light receiving element, 10 ... Laser light source, 14 ... Polygon mirror, 18 ... f-θ mirror, 22 ... Workpiece, 24
... condenser lens, 70 ... laser diode, 72 ... collimator lens, 74 ... actuator, 76 ... half mirror, 78 ... waveform shaping circuit, 80 ... phase comparison circuit, 82 ...
Integrator, 84 ... Full wave rectifier, 86 ... Sample and hold circuit, 92 ... Actuator driver.

Claims (2)

[Claims] 1. A predetermined measurement area is scanned with a parallel beam, and a beam passing through this measurement area is received by a measurement light receiving element, and a light-dark pattern in the scanning direction obtained by this light receiving element is transferred to the measurement area. In a scanning type optical dimension measuring device for measuring the dimension of a work included therein, a position detecting means for detecting a beam traveling direction position of the work with respect to a focus of the beam, and moving the work, or a focus of the beam. A scanning type optical dimension measuring apparatus comprising: a servo unit that moves a collimator lens that determines the position of the workpiece to match the focus of the beam with the position of the workpiece detected by the position detecting unit. 2. The position detecting means includes a first light receiving element for directly receiving the beam and a second light receiving element for receiving the beam via a half mirror, and a signal obtained by both the light receiving elements. 2. The optical dimension measuring apparatus according to claim 1, wherein the positional relationship of the work with respect to the beam focus is detected from the phase relationship of 1.