JPS61112907A - Measuring apparatus of microscopic shape - Google Patents

Abstract

PURPOSE:To prevent a reject caused by inaccurate measurement by meter displaying by a photo-diode of light-reflecting rate from a specimen surface or issuing an alarm for unavailability of accurate measurement in case when an output is lower than the limit value set for the light-reflecting rate and stopping the measurement automatically. CONSTITUTION:A laser beam irradiated from a laser diode 7 through collimeter lens 8, polarized beam splitter 9, objective lens 11 is after reflection by the specimen measuring surface 1, converted to a voltage by photo-diodes 14, 16 and the sum of these outputs are introduced into a comparator 20 through an amplifier 19 and compared with the setting signal from a limit setting apparatus 21 of reflecting rate and only in case when an output of the photo-diode 1 is smaller, a signal is issued for driving alarm lamp 22, buzzer 23, etc. advising unavailability of an accurate measurement.A an output of the amplifier 19 and a reflecting rate of the surface 1 proportional, a value indicating the reflecting rate are shown on a meter 32. When situations demand, a measurement suspending command circuit is installed parallel with an alarm means to stop a motor for relative parallel travels of surface 1 and lens 11.

Description

[Detailed description of the invention] a0 Purpose of the invention (industrial application field) The micro-shape measuring instrument according to the present invention is suitable for various high-precision measurements such as surface roughness measurement of mirror-finished metal surfaces. used.

(Prior art) In order to perform various precision shape measurements such as the surface roughness of metal surfaces, optical screw type or electric type fine shape measuring instruments, or relatively less precise ones such as micrometers and dial gauges are used. is used.

Among these, an electric precision shape measuring instrument will be explained.

As shown in Fig. 1, the electric precision shape measuring instrument has an iron core 3 fixed in the middle of a contact 12 that moves up and down following the irregularities of the surface to be measured 1, and a structure surrounding the iron core 3. Coil 4 provided with
When the stylus 2 supported by a pair of upper and lower springs 5.5 parallel to each other rises and falls according to the unevenness of the surface to be measured l, the output voltage of the coil 4 changes changes in proportion to the amount of displacement. Therefore, the uneven shape of the surface to be measured 1 can be known from this voltage change. 6 is a spring for adjusting measurement pressure.

Such conventional micro-shape measuring instruments move the stylus while keeping it in contact with the surface of the object to be measured during measurement, thereby damaging the surface of the object to be measured. For this reason, various types of optical micro-shape measuring devices using laser light have been proposed, which can measure the shape of a surface to be measured without bringing a probe such as a stylus into contact with the surface to be measured. Next, the principle of this optical micro-shape measuring instrument will be briefly explained.

2 to 4 show a first example of the principle of an optical micro-shape measuring device. This principle was described in pages 391-392 of the Proceedings of the 1981 Autumn Conference of the Japan Precision Machinery Society, and pages 1-2 of Machine Price News 1983, Issue 9, published by the Institute of Mechanical Technology, Agency of Industrial Science and Technology. It is something. The laser beam sent out from the laser diode 7 is projected onto the surface to be measured 1 through the collimator lens 8, polarizing beam splitter 9, quarter wavelength plate 10, and objective lens 11 shown in FIG. The laser beam is reflected by the surface to be measured 1, passes through the objective lens 11 and quarter wavelength plate 10 again, is reflected by the polarizing beam splitter 9, and is sent to the half mirror 12. The laser beam reflected by this half mirror 12 passes through the first critical angle prism 13 and is sent to the first and second photodiodes 14.16, and the laser beam transmitted through the half mirror 12 passes through the second critical angle prism 13. 15 and is similarly sent to the first and second photodiodes 14 and 16.

When the distance between the objective lens 11 fixed to the measurement head and the surface to be measured l changes, the incident angle of the laser beam that is reflected from this surface to be measured and then enters the first and second critical angle prisms 13.15 changes. changes, and as a result, the intensity of the light reaching the first and second photodiodes 14.16 changes, so if a change in the output difference between the first and second photodiodes 14.16 is detected, the You can see the unevenness of the surface. To further explain the principle of the critical angle prism with reference to Figure 3, when the surface to be measured is at position B, the laser beam reflected from the surface to be measured passes through the first and second paths as shown by the solid line in the figure. The photodiodes 14 and 16 output the same amount of output from both photodiodes (potential difference 0). The surface to be measured is A
When it approaches the position, the reflected laser beam enters the critical angle prism 13.15 along a path as shown by the chain line in the figure. In this state, a part of the laser light passes through the prism without being reflected, so the laser light entering the first and second photodiodes 14 and 16 becomes weaker, but the degree of this weakening is Since the first photodiode 14 is larger than the second photodiode 16, there is a difference in the outputs of both diodes 14 and 16. On the other hand, when the surface to be measured moves away to position C, the reflected laser beam enters the critical angle prism 13.15 along the path shown by the broken line in the figure, and the potential difference opposite to that at position A described above becomes first, occurs between the second photodiode 14.16. Since there is a relationship as shown in FIG. 4 between the amount of displacement of the surface to be measured and the output potential difference V, the minute shape of the surface to be measured can be determined from this potential difference V. The reason why two critical angle prisms, first and second, and two sets of first and second photodiodes 14 and 16 are provided in FIG. 2 is based on the inclination of the surface to be measured l. This is to cancel the error.

Further, FIG. 5 shows another principle of the optical micro-shape measuring device. This principle is called the astigmatism method, and was described in the Proceedings of the 1981 Spring Conference of the Society of Fine Arts and Sciences, pages 393-394. Using the fact that the cross section of the light flux changes continuously into a straight line, a vertically elongated ellipse, a circle, and a horizontally elongated ellipse depending on the distance from the Measures the minute shape of the surface to be measured based on cross-sectional changes.

In addition to this, there are other principles of measuring instruments that use laser light.
There are those described on page 526, and those described on pages 413-414 of the academic lecture collection of the autumn conference of the same year. A fine shape measuring device manufactured based on either principle can measure the fine shape of a surface to be measured without bringing a contactor or the like into contact with the surface to be measured.

(Problems to be Solved by the Invention) However, in the conventional optical micro-shape measuring instrument as described above, the following disadvantages occur.

That is, no matter which measurement principle is used, in order to irradiate the surface to be measured, the laser light projected from the laser diode 7 is reflected by the surface to be measured 1 and then transmitted to the photodiode 14.1.
Enter 6 or 18. In this way, the intensity of the laser beam that enters the photodiode 14, 16 or 18 after being reflected by the surface to be measured 1 varies greatly depending on the reflectance of the surface to be measured 1, and even during one measurement operation. Changes sequentially. For this reason, fine shape measuring instruments that utilize reflection of laser light must be equipped with a mechanism to prevent changes in the amount of light incident on the photodiode due to the difference in reflectance as described above from affecting the measured value. Must be. Therefore, in the critical angle prism type micro-shape measuring instrument shown in Fig. 2, the total output value of the photodiode obtained by adding all the outputs of the four photodiodes 14 and 16 is By dividing the difference between the first and second photodiodes 14 and 16 by , the influence of the change in the amount of emitted light due to the difference in reflectance on the measured value is eliminated. That is, the output of the first photodiode 14 among the photodiodes on the right side of FIG. 2 is A,
If the output of the second photodiode 16 is B, the output of the first photodiode 14 among the left photodiodes is C1, and the output of the second photodiode 16 is D, then the objective lens 11 and the surface to be measured 1 The signal X indicating the distance is obtained as follows. In the case of a fine shape measuring instrument that applies the principle of the astigmatism method shown in FIG. Consideration should be given to ensuring that changes in reflectance do not affect the measured values.

By taking the above-mentioned measures, it is possible to prevent the measurement values from being affected even if the reflectance of the surface to be measured 1 changes, but it is possible to prevent the reflectance of the surface to be measured 1 from being, for example, 10% or less. If the value drops significantly, reliable measurements cannot be obtained. However, it is difficult to judge with the naked eye whether or not the reflectance of the surface to be measured is sufficient for measurement, and if small particles with low reflectance are attached during the measurement, etc. This cannot be detected with the naked eye. If a measurement operation is carried out in such a state that accurate measurements cannot be made and the next step is proceeded to based on the measurement results, it is not preferable because the desired performance of various products will not be obtained.

It is an object of the present invention to solve the above-mentioned disadvantages and to provide a micro-shape measuring instrument that does not produce unreliable measured values.

b1 Structure of the Invention The fine shape measuring device of the present invention can be used by amplifying the output of a photodiode that measures the amount of light reflected from a surface to be measured by an amplifier and indicating it with a meter, or by adjusting the above output and reflectance limit setting. If the output of the photodiode is lower than the set value, a warning will be issued that accurate measurement cannot be performed, and the measurement will be automatically stopped. are doing.

First, to explain the basic configuration with reference to FIG. 1 and enters the photodiode 14.16, and this photodiode 1
4.16, it is converted into voltage and output. The sum of the outputs of all photodiodes 14 and 16 is amplified by an amplifier 19 and then input to a comparator 20. This comparator 20
Now, the signal from the amplifier 19 and the reflectance limit setter 2
The output signals of the photodiodes 14 and 16 sent via the amplifier 19 are compared with the setting signal from the setting device 2.
1, outputs a signal and drives warning means such as a warning light 22 and a buzzer 23, only when the signal becomes smaller than the set signal from 1.
Issues a warning that accurate measurements cannot be made. In the example of FIG. 6, the reflectance limit setter 21 is shown so that the set value can be changed, but the reflectance set in this setter 21 may be fixed. Further, only one of the buzzer 23 and the warning light 22 may be provided as the warning means. The meter 32 is connected to the amplifier 19
Since this output is proportional to the reflectance of the surface to be measured 1, a numerical value indicating the reflectance is written on the indicator of the meter.

Next, FIG. 7 shows that a memory device 24 is provided between the comparator 20 and warning means such as a warning light 22 and a buzzer 23, and indicates whether accurate measurement has been performed at the end of a series of measurement operations. It is configured as follows. 25 is a comparator 20 and a memory 24
27 is a reset command circuit. At the start of measurement, the contact 26 is closed based on a signal from the measurement start command circuit 25, and the measurement work is started. If the reflectance of the surface to be measured becomes smaller than the set value even once during the measurement process, the comparator 20 outputs a signal, this signal is stored in the memory 24, and the series of measurement processes ends. At that stage, warning light 22,
A warning means such as a buzzer 23 is activated. When the warning is confirmed, the memory 2 is reset by a signal from the reset command circuit 27.
4 is erased and the contact 26 is opened via the measurement start command circuit 25.

Furthermore, in order to stop the measurement operation even once when the reflectance of the surface to be measured falls below a set value, a configuration as shown in FIG. 8 is used. In Fig. 8, 28 is a measurement stop command circuit;
Reference numeral 29 is a motor for driving the sample stage or laser head during measurement work to relatively move the surface to be measured 1 and the objective lens 11 in parallel; 30 is a contact provided in the middle of a conductive wire 31 that supplies electricity to the motor 29; It is. When the contact point 30 is closed to determine the shape of the surface to be measured l and the sample stage (or laser head) is moved horizontally by the motor 29 while the measurement work is performed, the reflectance of the surface to be measured l is less than the set value even by one degree. When this happens, the measurement stop command circuit 2 is activated based on the signal from the comparator 20.
8 opens contact 30.

As a result, the motor 29 is stopped, the horizontal movement of the sample stage or the laser head is stopped, and the measurement operation is stopped. The circuit for automatically stopping the measurement operation as shown in FIG. 8 may be combined with a circuit for driving a warning means as shown in FIGS. 6 and 7.

C8 Effects of the Invention The fine shape measuring device of the present invention is configured as described above,
Since it is possible to prevent unintentionally performing inaccurate measurements, it is possible to prevent the production of defective products due to inaccurate measurements, and it is possible to improve the yield and reliability of various products.

[Brief explanation of the drawing]

Fig. 1 is a schematic vertical side view showing an example of a contact type micro-shape measuring device, Fig. 2 is a schematic side view showing a first example of the principle of an optical displacement detector, and Fig. 3 is a critical angle prism. 4 is a diagram showing the relationship between the potential difference generated by the critical angle prism and the amount of displacement. FIG. 5 is a schematic side view showing the second example of the principle of the optical displacement detector. FIG. 6 is a circuit diagram showing the first invention, and FIGS. 7 and 8 are circuit diagrams corresponding to section X in FIG. 6 showing the second and third inventions, respectively. 1: Surface to be measured, 2: Stylus, 3: Iron core, 4: Coil, 5.
6: Spring, 7: Laser diode, 8: Collimator lens, 9: Polarizing beam splitter, 10: Quarter wavelength plate, 11: Objective lens, 12: Half mirror, 13: First critical angle prism, 14: first photodiode, 1
5: Second critical angle prism, 16: Second photodiode, 17: Cylindrical lens, 18: Photodiode, 19: Amplifier, 20: Comparator, 21: Reflectance limit setter, 22: Warning light, 23 : Buzzer, 24: Memory device, 25: Measurement start command circuit, 26: Contact, 27: Reset command circuit, 28: Measurement stop command circuit, 29: Motor,
30: Contact, 31: Conductor, 32: Meter.

Claims (1)

[Scope of Claims] 1) In a micro-shape measuring instrument that measures the reflected light of a laser beam projected onto a surface to be measured using a photodiode, and determines the change in distance from the output of the photodiode to the surface to be measured. . A fine shape measuring instrument, characterized in that it is provided with a meter that is driven by the output of the photodiode and that indicates the reflectance of the surface to be measured. 2) In a micro-shape measuring instrument that measures the reflected light of the laser beam projected onto the surface to be measured with a photodiode and calculates the change in distance from the output of this photodiode to the surface to be measured, the output of the photodiode and a set value of the reflectance limit setter, and a comparator that outputs a signal only when the output is lower than the set value, and a warning means that issues a warning based on the signal from the comparator. A fine shape measuring instrument characterized by: 3) In a micro-shape measuring instrument that measures the reflected light of the laser beam projected onto the surface to be measured with a photodiode and calculates the change in distance from the output of this photodiode to the surface to be measured, the output of the photodiode and the set value of the reflectance limit setter, and a comparator that outputs the first signal only when the above output is lower than the set value, and a comparator that memorizes the signal from this comparator and outputs the first signal once during measurement work. However, when the first signal is received, a memory device that outputs a second signal after the measurement operation is completed, and a warning means that issues a warning based on the second signal are provided. . 4) In a micro-shape measuring instrument that measures the reflected light of the laser beam projected onto the surface to be measured with a photodiode and calculates the change in distance from the output of this photodiode to the surface to be measured, the output of the photodiode A comparator that compares the output with the set value of the reflectance limit setter and outputs a signal only when the above output is lower than the set value, and a comparator that parallels the surface to be measured and the measurement head based on the signal from this comparator. A micro-shape measuring instrument characterized by being provided with a measurement stop command circuit that opens a contact point provided in the middle of a conductive wire that energizes a motor for movement.