JP2944002B2 - Method and apparatus for measuring thickness - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for measuring the thickness of an object to be measured such as a lens using ultrasonic waves.

[0002]

2. Description of the Related Art Generally, when a thickness of an object to be measured such as a lens is measured with a mechanical measuring device such as a micrometer, the surface of the object to be measured is scratched. A method of measuring the thickness of an object to be measured in a non-contact state has been studied. As an example of this, conventionally,
One ultrasonic element having a transmitting unit and a receiving unit is fixed at a fixed interval above a table serving as a reference, the distance between them is measured in advance, and in this state, transmission is performed from the transmitting unit of the ultrasonic element. The time until the reflected ultrasonic wave is reflected on the upper surface of the table and received by the receiving unit is measured. Next, the device under test is placed on the table, and the ultrasonic wave transmitted from the transmitting unit is measured by the ultrasonic device. A method of calculating the thickness of the object to be measured from the time difference between the two by measuring the time until the light is reflected and received by the receiving unit has been considered.

[0003]

However, the above-mentioned thickness measuring method has the following problems. That is, since one ultrasonic element is used, one-side measurement of the object to be measured is performed. Therefore, in the case of an object to be measured such as a lens having both curved surfaces, the position of the reference surface is not clear when the object is placed on the table. Therefore, the thickness cannot be measured. Further, since the speed at which the ultrasonic wave travels in the air varies depending on the temperature, an accurate measured value cannot be obtained unless the temperature is corrected for each measurement. In addition, since the amplitude of the ultrasonic wave transmitted from the transmitting section of the ultrasonic element gradually increases, it is difficult to accurately capture the same part of the ultrasonic wave at the time of transmission and reception, and the measurement time becomes inaccurate. An error occurs. SUMMARY OF THE INVENTION An object of the present invention is to provide a thickness measuring method capable of accurately measuring a thickness even when both surfaces of an object to be measured are curved surfaces and accurately correcting the temperature according to a temperature change, and transmitting an ultrasonic wave. It is an object of the present invention to provide a thickness measuring apparatus capable of accurately capturing a measurement time from time to reception and performing extremely accurate measurement.

[0004]

According to a thickness measuring method of the present invention, a pair of ultrasonic elements having a transmitting part and a receiving part are arranged opposite to each other at a predetermined interval so that their center lines coincide with each other, and one ultrasonic element is provided. The time until the ultrasonic wave transmitted from the transmitting part of the other ultrasonic element is received by the receiving part of the other ultrasonic element is measured, and in this state, the reference object is arranged between the pair of ultrasonic elements and transmitted from each transmitting part. A reference value setting step of measuring each time until the received ultrasonic wave is reflected by the front and back surfaces of the reference object and received by each receiving unit, and again, the ultrasonic wave transmitted from the transmitting unit of one ultrasonic element is The time until reception by the receiving unit of the other ultrasonic element is measured, and an object to be measured is placed between the pair of ultrasonic elements in this state, and the ultrasonic waves transmitted from each transmitting unit are transmitted to the object to be measured. Each time from when it is reflected on the front and back sides and received by each receiver A measurement step of measuring, and a data processing step of calculating the thickness of the measured object by performing an arithmetic process on each measured value and the thickness data of the reference object measured in the reference value setting step and the measurement step, respectively, in the arithmetic unit. It is characterized by consisting of. Further, the thickness measuring apparatus of the present invention has a transmitting section and a receiving section, respectively, and their center lines coincide with each other, are arranged at predetermined intervals, and a reference object or an object to be measured is arranged therebetween. A pair of ultrasonic elements and a drive signal for making the amplitude of the ultrasonic waves transmitted from each transmitting section of the pair of ultrasonic elements gradually increase to a constant amplitude are output based on a plurality of transmission pulses. Along with
A pair of transmission circuit sections that output a transmission pulse at a specific point where the amplitude of the ultrasonic wave suddenly changes as a start signal, and a waveform of the ultrasonic wave received by each receiving section of the pair of ultrasonic elements is processed to suddenly change the amplitude. A pair of receiving circuit units that output a shaped pulse at a specific point as a stop signal, and a time until a start signal from each transmitting circuit unit and a stop signal from each receiving circuit unit are input are determined by the transmission frequency of the ultrasonic wave. a pair of counters for counting and detecting with a clock having a frequency of n times, a time detected by each counter in a state where the reference object or the measured object is not arranged between the pair of ultrasonic elements, and Computes the time detected by each counter unit and the thickness data of the reference object in each state where the reference object or the measured object is placed between the ultrasonic elements of Characterized in that an arithmetic unit for calculating the thickness of the object to be measured by Rukoto.

[0005]

According to the present invention, a pair of ultrasonic elements having a transmitting section and a receiving section are arranged facing each other at predetermined intervals so that their center lines coincide with each other, and an object to be measured is arranged between the pair of ultrasonic elements. Since the thickness is measured by using the measuring method, it is not necessary to clarify the reference plane even if the object to be measured has a curved surface such as a lens, so that the measurement can be performed easily and accurately. Further, according to the thickness measuring method of the present invention, the time until the ultrasonic wave transmitted from the transmitting section of one ultrasonic element is received by the receiving section of the other ultrasonic element in the reference value setting step is measured. In the measuring step, the time until the ultrasonic wave transmitted from the transmitting section of one ultrasonic element is received again by the receiving section of the other ultrasonic element is measured. Even if the speed fluctuates due to temperature changes, the temperature can be corrected by the measured values of both, it is possible to accurately measure the thickness of the measured object, and once the reference value is set in the reference value setting step, The object to be measured can be measured sequentially only by repeating the measurement process. Further, according to the thickness measuring apparatus of the present invention, the transmission pulse at a specific point where the amplitude of the ultrasonic wave transmitted from the transmission section of the ultrasonic element changes suddenly is output as a start signal from the transmission circuit section to the counter section, The waveform of the ultrasonic wave received by the receiving unit of the acoustic wave element is processed by the receiving circuit unit, and a shaped pulse at a specific point where the amplitude changes suddenly is output as a stop signal from the receiving circuit unit to the counter unit. , The same location of the ultrasonic wave can be accurately detected, and the measurement time can be accurately determined. Moreover,
The counter unit counts the time until the start signal from the transmission circuit unit and the stop signal from the reception circuit unit are input using a clock having a frequency n times the transmission frequency of the ultrasonic wave. Measurement becomes possible.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows a thickness measuring device. In this figure, 1 is a base. A support column 2 is erected on the left side of the base 1. A vertically long attachment member 3 is fixed to the support column 2 at an appropriate upper and lower position. A table 4 is fixed horizontally in the middle of the right side surface of the mounting member 3, an upper support member 5 is fixed to an upper end portion so as to be vertically movable, and a lower support member 6 is fixed to a lower end portion. Has been fixed. The table 4 is for placing the reference object 7 or the device under test 8 at a predetermined position, and has a through hole 9 vertically penetrating the center thereof. A circuit board 10 is attached to the upper side of the upper support member 5 and the lower side of the lower support member 6 by screws 11.
First and second ultrasonic elements 12 and 13 are provided on the upper and lower circuit boards 10 so as to face each other with the table 4 interposed therebetween. That is, each of the ultrasonic elements 12 and 13 has a built-in transmitting unit and a receiving unit, and each of the center lines is provided so as to coincide with the center of the through hole 9 of the table 4. In this case, ultrasonic nozzles 14 for guiding ultrasonic waves are provided at the opposing distal ends of the ultrasonic elements 12 and 13 so as to protrude through the insertion holes 5a and 6a of the support members 5 and 6, respectively. Each circuit board 10 is electrically connected to a control device (not shown).

FIG. 2 shows a circuit configuration of the above-described thickness measuring apparatus. The thickness measuring device includes transmitting circuit units 20, 21, for each of the opposed first and second ultrasonic elements 12, 13, respectively.
It has receiving circuit units 22 and 23, counter units 24 and 25, and changeover switches 26 and 27, and these are controlled by a CPU (Central Processing Unit) 28. CP
U28 performs overall control of the apparatus, arithmetic processing of measurement data, and the like. A measurement start signal and thickness data of the reference object 7 are given from the operation switch unit 29, and first and second signals are given based on the measurement start signal. Changeover switches 26 and 27
Are simultaneously or selectively closed, and each of the transmission circuit units 20, 2
1 or both of them are instructed to start transmission. The first and second transmitting circuit units 20 and 21 are configured such that the amplitudes of the ultrasonic waves transmitted from the transmitting units of the respective ultrasonic elements 12 and 13 gradually increase and become constant as shown in FIG. A drive signal for obtaining an amplitude is output based on a plurality of (six in FIG. 3) transmission pulses, and a transmission pulse at a specific point A where the amplitude of the ultrasonic wave suddenly increases is used as a start signal. Counter unit 24, 2
5 is output. That is, the amplitude of the ultrasonic wave gradually increases according to the drive signal based on the transmission pulse shown in FIG.
It increases suddenly and becomes stable at the second to fourth emission pulses.
The point where the size suddenly increases and becomes stable is the specific point A.
Although the specific point A differs depending on the ultrasonic element, the third point of the transmission pulse is the specific point A in the ultrasonic elements 12 and 13 of this embodiment. In this case, the first transmitting circuit 20 operates the second ultrasonic element 13 when the reference object 7 or the device under test 8 is not arranged between the pair of ultrasonic elements 12 and 13.
The start signal is output to the counter 25 of the first ultrasonic element 12 and the start signal is output to the counter 24 of the first ultrasonic element 12 when the reference object 7 or the DUT 8 is disposed between the pair of ultrasonic elements 12 and 13. Output a signal. Similarly, the second transmission circuit 21 starts the counter 24 on the first ultrasonic element 12 side when the reference object 7 or the device under test 8 is not arranged between the pair of ultrasonic elements 12 and 13. A signal is output, and the reference object 7 is placed between the pair of ultrasonic elements 12 and 13.
Alternatively, a start signal is output to the counter 25 on the first ultrasonic element 12 side when the device under test 8 is arranged. The first and second receiving circuit units 22 and 23 shape the waveforms of the ultrasonic waves received by the respective receiving units of the ultrasonic elements 12 and 13, respectively, and the amplitude of the received ultrasonic waves suddenly increases. The shaped pulse corresponding to the specific point B is output to each of the counters 24 and 25 as a stop signal. That is, since the received ultrasonic wave is the same as the transmitted ultrasonic wave, it becomes large suddenly and becomes stable at the third generation of the shaping pulse.
This third shot is the specific point B. The first and second counter units 24 and 25 determine the time until the start signal from each of the transmission circuit units 20 and 21 and the stop signal from each of the reception circuit units 22 and 23 are input by the transmission frequency of the ultrasonic wave (for example, 400
KHz) of n times (for example, 50 times) frequency (for example, 20 times)
MHz), and outputs the count value (hereinafter referred to as a measured value) to the CPU 28. Note that C
The PU 28 calculates the thickness of the DUT 8 by performing arithmetic processing on the measurement values given from the respective counter units 24 and 25 and the thickness data of the reference object 7 input from the operation switch unit 29. The result is displayed on the display unit 30, and data is exchanged with an external device 31 such as a personal computer.

Next, a thickness measuring method will be described with reference to FIGS. 4 (a) to 4 (d). First, as shown in FIG. 4A, a state in which nothing is arranged between the first and second ultrasonic elements 12 and 13 which are vertically arranged at regular intervals, that is, the reference object 7 or A time T _R (or a second time) until the ultrasonic wave transmitted from the transmitting unit of the first ultrasonic element 12 is received by the receiving unit of the second ultrasonic element 13 in a state where the device under test 8 is not placed. ultrasonic wave transmitted from the transmitting portion of the ultrasonic element 13 measures the time T _R) to be received in the receiving portion of the first ultrasonic element 12. In this case, first, when the operation switch unit 29 is operated to give a measurement start command to the CPU 28, the CPU 28 closes the first switch 26, for example, and then starts transmission to the first transmission circuit unit 20. To instruct. Then, the first transmission circuit unit 20 outputs a drive signal based on the six transmission pulses, transmits an ultrasonic wave of 400 KHz from the transmission unit of the first ultrasonic element 12, and corresponds to the specific point A. The third transmission pulse to be output is output as a start signal, and the second counter 25 starts counting. Then, the first ultrasonic element 1
The ultrasonic wave transmitted from the transmitting unit 2 is the second ultrasonic element 13
Is received by the receiving unit, the waveform of the received ultrasonic wave is shaped by the second receiving circuit unit 23, and the receiving circuit unit 23 stops the third shaped pulse corresponding to the specific point B. It is output as a signal to stop counting in the second counter unit 25. At this time, the second counter 25 counts the clock of about 50 times the frequency (20 MHz) of the transmission frequency of the time T _R from the time the start signal is input to when the stop signal is inputted, the measured value Is output to the CPU 28.

Thereafter, the reference object 7 is quickly placed on the table 4. That is, as shown in FIG. 4B, the reference object 7 (thickness t _R ) is arranged between the pair of ultrasonic elements 12 and 13. In this state, the ultrasonic waves transmitted from the transmitting units of the ultrasonic elements 12 and 13 are reflected by the front and back surfaces of the reference object 7 and received by the receiving units of the ultrasonic elements 12 and 13 respectively. The time (2 × T _R1 , 2 × T _R2 ) is measured.
In this case, first, the reference object 7 is
After entering the thickness t _R in CPU 28, supplied from the operation switch unit 29 a measurement start instruction to the CPU 28. Then
The CPU 28 gives a transmission start instruction to the first and second transmission circuit units 20 and 21, respectively.
1 transmits an ultrasonic wave from each of the transmitting units of the first and second ultrasonic elements 12 and 13 in the same manner as described above, and outputs a start signal to the first and second counter units 24 and 25 to output each counter. The counting in the units 24 and 25 is started. Then, when the ultrasonic waves transmitted from the respective transmitting units are reflected on the front and back surfaces of the reference object 7 and received by the respective receiving units of the respective ultrasonic elements 12 and 13, from the respective receiving circuit units 22 and 23 as described above. A stop signal is provided to each of the counters 24 and 25. At this time, each of the counters 24 and 25 calculates each time (2 × T _R1 , 2 × T _R2 ) from the time when the start signal is input to the time when the stop signal is input to a frequency (20 MHz) which is about 50 times the transmission frequency. ), And outputs the measured value to the CPU 28. Thus, the reference value setting step is completed. Once the reference value setting step is set, there is no need to reset the reference value unless the interval between the first and second ultrasonic elements 12 and 13 is changed.

After setting the reference value, the thickness t _S of the object 8 is measured. In this case, nothing is placed on the table 4 again as described above. Status,
That is, as shown in FIG. 4C, in a state in which nothing is arranged between the ultrasonic elements 12 and 13 which are arranged at regular intervals and opposed to each other, the ultrasonic wave transmitted from the transmitting section of the first ultrasonic element 12 The second counter 25 counts the time T _S until it is received by the receiving unit of the second ultrasonic element 13, and outputs the measured value to the CPU 28. Thereafter, the device under test 8 is immediately placed on the table 4. That is, as shown in FIG. 4D, the device under test 8 is arranged between the ultrasonic elements 12 and 13. In this state, similarly to the above, each ultrasonic element 12,
Each time (2 × T _S1 , 2 ×) until the ultrasonic wave transmitted from each of the transmitting units 13 is reflected on the front and back surfaces of the DUT 8 and received by each of the receiving units of the ultrasonic elements 12 and 13. T _S2 )
Is counted by the counter units 24 and 25, and the measured value is output to the CPU 28. This ends the measurement process.

When the measurement process is completed, each measured value (T _R , 2 × 2) measured in the reference value setting process and the measurement process, respectively.
T _R1 , 2 × T _R2 , T _S , 2 × T _S1 , 2 × T _S2 ) and the thickness t _R of the reference object 7 are processed by the CPU 28 to calculate the thickness t _S of the DUT 8, The calculation result is displayed on the display unit 30 and is given to the external device 31 to exchange data with the external device 31. This ends the data processing step. In this case, the thickness t _S of the DUT 8 is calculated by the CPU 28 using the following equation.
That is, since the distance between the pair of ultrasonic elements 12 and 13 is constant in the reference value setting step and the measurement step, V ₁ × T _R = V ₂ × T _S (1) where V ₁ Is the speed of the ultrasonic wave in the reference value setting process,
V ₂ is the ultrasonic velocity in the measuring _{step, V 1 = t R / (} T R -T R1 -T R2) ............ (2) V 2 = t S / (T S -T S1 -T _S2 )... (3) When these equations (2) and (3) are substituted into equation (1),

(Equation 1) And if you organize this,

(Equation 2) Thus, the thickness t _S of the device under test 8 is obtained.

As described above, in the thickness measuring method described above,
Ultrasonic wave transmitted from the transmitting portion of the reference value setting step in the first ultrasonic element 12 measures the time T _R until it is received by the receiver of the second ultrasonic element 13, a first measurement step again By measuring the time T _S until the ultrasonic wave transmitted from the transmitting unit of the ultrasonic element 12 is received by the receiving unit of the second ultrasonic element 13, the ultrasonic wave can be measured in the reference value setting step and the measuring step. Even if the speed fluctuates due to a change in temperature, the temperature can be corrected based on the measured values of the two, so that the thickness t _S of the DUT 8 can be accurately measured without being affected by the change in temperature. Moreover, once the reference value is set in the reference value setting step, there is no need to reset it unless the interval between the first and second ultrasonic elements 12 and 13 is changed. Therefore, only the measurement step is repeated. The device under test 8 can be measured sequentially and accurately, and the measuring operation can be performed efficiently.

In the above-described thickness measuring apparatus, the first and second ultrasonic elements 12, 1 having a transmitting section and a receiving section are provided.
3 is arranged opposite to each other at a predetermined interval with its center line coincident, so that the reference surface of the object to be measured can be clearly defined even in the case of the object to be measured 8 having a curved surface such as a lens. Therefore, the thickness of the DUT 8 can be easily measured simply by disposing it between the ultrasonic elements 12 and 13. In this case, the object to be measured 8 can be sufficiently measured by using a lens having a radius of curvature equal to or larger than that of a pin ball.

Further, in this thickness measuring device, the amplitude of the ultrasonic wave transmitted from each transmitting section of each of the ultrasonic elements 12 and 13 is gradually increased by a drive signal based on the six transmitting pulses of each transmitting circuit section 20 and 21. The third transmission pulse corresponding to the specific point A, at which the amplitude suddenly increases and stabilizes as the amplitude increases, is output from each of the transmission circuit units 20 and 21 as a start signal to start counting in each of the counter units 24 and 25. In addition, the ultrasonic waves received by the respective receiving units of the respective ultrasonic elements 12 and 13 are subjected to waveform shaping processing by the respective receiving circuit units 22 and 23, and the amplitude of the received ultrasonic waves suddenly increases and becomes stable. Since the third reception pulse corresponding to the point B is output from each of the reception circuit units 22 and 23 as a stop signal for stopping the counting in each of the counter units 24 and 25, the reference value setting step and the measurement process are performed. In ultrasound same position when placing the at reception can catch accurately, the measurement time can be determined accurately. Moreover, each counter 25
Counts the measurement time until a start signal from the transmission circuit units 20 and 21 and a stop signal from the reception circuit units 22 and 23 are input by a clock having a frequency n times the transmission frequency, so that the accuracy is extremely high. The thickness can be measured. For example, if the transmitting frequency of the ultrasonic wave transmitted from each transmitting unit of the ultrasonic elements 12 and 13 is 400 KHz, the measuring time from the time of transmitting the ultrasonic wave to the time of receiving the ultrasonic wave is a clock having a frequency 50 times the transmitting frequency. For example, when counting with a clock of 20 MHz, a resolution of about 16 μm can be obtained, and measurement with extremely high accuracy can be performed.

[0015]

According to the present invention, a pair of ultrasonic elements having a transmitting part and a receiving part are arranged facing each other at predetermined intervals with their center lines coincident with each other, and an object to be measured is placed between the pair of ultrasonic elements. Since the thickness is measured by arranging, it is possible to measure easily and accurately even if the measurement target has a curved surface such as a lens, because there is no need to clarify the reference surface. . Further, according to the thickness measuring method of the present invention, the time until the ultrasonic wave transmitted from the transmitting section of one ultrasonic element is received by the receiving section of the other ultrasonic element in the reference value setting step is measured. In the measuring step, the time until the ultrasonic wave transmitted from the transmitting section of one ultrasonic element is received again by the receiving section of the other ultrasonic element is measured. Even if the speed changes due to temperature change, the temperature can be corrected by the measured values of both, the thickness of the object to be measured can be accurately measured without being affected by the temperature change, and the reference is set once in the reference value setting process. If the value is set, the object to be measured can be sequentially and accurately measured only by repeating the measurement process alone, and the measurement operation can be performed efficiently. Furthermore, according to the thickness measuring device of the present invention,
The transmission pulse at a specific point where the amplitude of the ultrasonic wave transmitted from the transmission unit of the ultrasonic element suddenly changes is output as a start signal from the transmission circuit unit to the counter unit, and the waveform of the received ultrasonic wave received by the reception unit of the ultrasonic element Is processed by the receiving circuit and the shaped pulse at a specific point where the amplitude changes suddenly is output as a stop signal from the receiving circuit unit to the counter unit, so that the same place of the ultrasonic wave at the time of transmission and at the time of reception can be accurately captured, The measurement time can be determined accurately. In addition, since the counter section counts the time until the start signal of the transmission circuit section and the stop signal of the reception circuit section are input using a clock having a frequency n times the transmission frequency, extremely accurate thickness measurement can be performed. .

[Brief description of the drawings]

FIG. 1 is a schematic side view of a thickness measuring device.

FIG. 2 is a block diagram showing a circuit configuration of the thickness measuring device.

FIG. 3 is a timing chart of waveforms of ultrasonic waves and pulses on a transmitting side and a receiving side.

FIG. 4 is a process chart showing a thickness measuring method.

[Explanation of symbols]

 7 Reference object 8 Device under test 12, 13 Ultrasonic element 20, 21 Transmitting circuit unit 22, 23 Receiving circuit unit 24, 25 Counter unit 28 CPU A, B Specific point

Continuation of the front page (56) References JP-A-61-104211 (JP, A) JP-A-55-59311 (JP, U) JP-A-49-79260 (JP, U) JP-B-49-16830 (JP) , B1) (58) Fields surveyed (Int. Cl. ⁶ , DB name) G01B 17/00-17/04 G01M 11/00

Claims (2)

(57) [Claims] 1. A pair of ultrasonic elements having a transmitting part and a receiving part are arranged facing each other at predetermined intervals with their center lines coincident with each other, and the ultrasonic wave transmitted from the transmitting part of said one ultrasonic element is transmitted to said other ultrasonic element. While measuring the time until it is received by the receiving unit of the ultrasonic element, the reference object is arranged between the pair of ultrasonic elements in this state, and the ultrasonic waves transmitted from each of the transmitting units are the ultrasonic waves of the reference object. A reference value setting step of measuring each time until each of the ultrasonic elements is reflected by the front and back surfaces and received by each of the receiving units, and again, the ultrasonic wave transmitted from the transmitting unit of the one ultrasonic element is the other ultrasonic element. While measuring the time until it is received by the receiving unit, an object to be measured is arranged between the pair of ultrasonic elements in this state, and the ultrasonic waves transmitted from each of the transmitting units are displayed on the surface of the object to be measured. The light is reflected by the back side and received by each receiver. The measurement step of measuring each time until it is transmitted, and the reference value setting step and the measurement data measured in the measurement step and the thickness data of the reference object are processed by a calculation unit in the calculation unit. A data processing step of calculating the thickness of the object to be measured. 2. A pair of ultrasonic elements each having a transmitting section and a receiving section, which are arranged opposite to each other at predetermined intervals so that their center lines coincide with each other, and between which a reference object or an object to be measured is arranged. Based on a plurality of transmission pulses, a drive signal is provided corresponding to the pair of ultrasonic elements, so that the amplitude of the ultrasonic waves transmitted from each of the transmission units gradually increases and becomes a constant amplitude. A pair of transmitting circuit units that output and output the transmitting pulse as a start signal at a specific point where the amplitude of the ultrasonic wave suddenly changes, and are provided corresponding to the pair of ultrasonic elements and received by the receiving units. A pair of receiving circuit units that process the waveform of the ultrasound waves and output a shaped pulse at a specific point where the amplitude changes suddenly as a stop signal, and are provided in correspondence with the pair of ultrasound elements, A pair of counter units for counting and detecting the time until the start signal from the transmission circuit unit and the stop signal from each of the reception circuit units are input with a clock having a frequency n times the transmission frequency of the ultrasonic wave, The time detected by each counter unit in a state where the reference object or the device under test is not arranged between the pair of ultrasonic elements, and the reference object or the device under test between the pair of ultrasonic devices. A calculation unit for calculating the thickness of the object to be measured by performing arithmetic processing on the time detected by each of the counter units in each state where the arrangement is arranged, and the thickness data of the reference object. A thickness measuring device, characterized in that: