Displacement measuring method

Abstract

To provide a technology capable of measuring displacement of a displacement device even when the displacement device is covered with a lid.SOLUTION: A displacement measuring method for measuring displacement of a measurement object includes steps of: (a) moving an infrared camera back and forth at a first frequency and by a first distance with respect to the measurement object while capturing the measurement object with the infrared camera, and obtaining a first signal intensity from infrared rays emitted by the measurement object; (b) driving the measurement object to repeatedly displace the measurement object at a second frequency while capturing the measurement object with the infrared camera, and obtaining a second signal intensity from infrared rays emitted by the measurement object; and (c) obtaining a second distance, which is the amount of displacement of the measurement object, using the first distance, the first signal intensity, and the second signal intensity.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a displacement measurement method. [Background technology]

[0002] Patent Document 1 discloses a technique for determining whether a nozzle in a liquid ejection head is malfunctioning. This technique involves irradiating the nozzle opening with a laser beam as measurement light, measuring the meniscus vibration of the ink liquid, and determining whether a malfunction exists based on the measurement results. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2023-176559 Summary of the Invention [Problem to be solved by the invention]

[0004] Liquid ejection heads are equipped with minute displacement devices such as piezoelectric elements to vibrate the ink liquid. When such displacement devices are covered with a sealing member made of silicon or the like, it is difficult to directly measure their displacement using laser light. [Means for solving the problem]

[0005] According to a first aspect of the present disclosure, there is provided a displacement measurement method for measuring the displacement of a measurement object using an infrared camera, the displacement measurement method including the steps of: (a) capturing an image of the measurement object with the infrared camera while reciprocating the infrared camera a first distance at a first frequency relative to the measurement object, and determining a first signal intensity from infrared rays emitted by the measurement object; (b) capturing an image of the measurement object with the infrared camera while driving the measurement object so that the measurement object is repeatedly displaced at a second frequency, and determining a second signal intensity from the infrared rays emitted by the measurement object; and (c) determining a second distance, which is a displacement of the measurement object, using the first distance, the first signal intensity, and the second signal intensity. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is an explanatory diagram showing a schematic configuration of a displacement measuring system according to a first embodiment. [Figure 2] 1A and 1B are explanatory diagrams showing two situations in which the distance between the displacement device and the infrared camera changes. [Figure 3] 10 is a flowchart of a displacement measurement process executed by the control device. [Figure 4] FIG. 4 is an explanatory diagram of a lock-in process for a first infrared signal. [Figure 5] FIG. 10 is a graph showing the relationship between the infrared intensity difference and the signal intensity after lock-in processing. [Figure 6] FIG. 10 is a diagram illustrating a lock-in process for a second infrared signal. [Figure 7] FIG. 10 is a diagram showing an example of displaying a second distance and a second signal strength. [Figure 8] 10 is a flowchart of a displacement measurement process in the second embodiment. [Figure 9] FIG. 10 is a diagram showing the correlation between the first distance and the first signal strength in the second embodiment. [Figure 10] 10A and 10B are diagrams illustrating other examples of setting the reference distance for displacing the displacement device. DETAILED DESCRIPTION OF THE INVENTION

[0007] A. First embodiment: 1 is an explanatory diagram showing a schematic configuration of a displacement measurement system 100 in a first embodiment. The displacement measurement system 100 is a system for measuring the displacement of a measurement object 200. The displacement measurement system 100 includes an infrared camera 10, a control device 20, a first driving device 30, and a second driving device 40.

[0008] The infrared camera 10 is a device that captures infrared light IR emitted from a measurement object 200. The infrared camera 10 outputs an infrared signal obtained by capturing the infrared light IR to the control device 20. The infrared camera 10 of this embodiment is configured to be movable back and forth between a direction moving away from the measurement object 200 and a direction moving toward the measurement object 200 by a first drive device 30. The first drive device 30 includes an actuator for moving the infrared camera 10 and a control circuit for controlling the actuator. The first drive device 30 is connected to the control device 20. Note that, hereinafter, the direction moving away from the measurement object 200 is considered to be an upward direction, and the direction moving toward the measurement object 200 is considered to be a downward direction.

[0009] The control device 20 is configured as a computer including a CPU 21 and a memory 22. The CPU 21 executes a program stored in the memory 22, causing the control device 20 to execute a displacement measurement process, which will be described later. A display device 50 is connected to the control device 20. The display device 50 displays the measurement results obtained by the displacement measurement process.

[0010] The second driving device 40 includes a circuit for driving the displacement device 201 provided on the measurement object 200. The second driving device 40 is connected to the control device 20.

[0011] The measurement object 200 of this embodiment includes a piezoelectric element as a displacement device 201. The displacement device 201 is attached to a vibration plate 202. The surface of the displacement device 201 opposite to the vibration plate 202 is covered with a sealing member 203. The sealing member 203 is made of a material that does not transmit visible light VR but transmits infrared light IR. The sealing member 203 in this embodiment is made of silicon (Si). The displacement device 201 is used, for example, as an actuator for ejecting ink from a liquid ejection head. The displacement device 201 is not limited to a piezoelectric element, and may be a quartz oscillator or the like.

[0012] FIG. 2 is an explanatory diagram showing two situations in which the distance between the displacement device 201 and the infrared camera 10 changes. The sealing member 203 and the diaphragm 202 are omitted from FIG. 2. The left side of FIG. 2 shows a state in which the lens 11 of the infrared camera 10 and the displacement device 201 are separated by a reference distance RD. The reference distance RD is, for example, the distance between the lens 11 and the displacement device 201 when the focus of the lens 11 is on the displacement device 201. The center of FIG. 2 shows a state in which the lens 11 is separated by a first distance D1 from the reference distance RD by moving the infrared camera 10 upward. The right side of FIG. 2 shows a state in which the distance between the displacement device 201 and the lens 11 is separated by a second distance D2 from the reference distance RD by displacing the displacement device 201 without moving the infrared camera 10. In this embodiment, the control device 20 calculates a second distance D2, which is the displacement amount of the displacement device 201, based on a first signal strength S1 measured using the infrared camera 10 when the infrared camera 10 is moved back and forth a first distance D1, and a second signal strength S2 measured using the infrared camera 10 when the displacement device 201 is repeatedly displaced. Note that in the present disclosure, moving the infrared camera 10 also includes moving the lens 11.

[0013] 3 is a flowchart of the displacement measurement process executed by the control device 20. This displacement measurement process is performed in an atmosphere where the environmental temperature around the measurement object 200 is constant. A constant environmental temperature means that the temperature change is less than 1°C.

[0014] In step S10, the control device 20 controls the first driving device 30 to focus the infrared camera 10 on the displacement device 201. The distance between the displacement device 201 and the infrared camera 10 at this time is the reference distance RD shown in FIG. 2. The control device 20 can dynamically set the reference distance RD by determining the position of the infrared camera 10 so that the intensity of the infrared light IR detected by the infrared camera 10 is maximized. Note that the reference distance RD may be determined in advance by conducting experiments or simulations.

[0015] In step S20, the control device 20 controls the first driving device 30 to reciprocate the infrared camera 10 a first distance D1 at a first frequency, while acquiring a first infrared signal from the infrared camera 10. The first frequency is, for example, 1 to 100 Hz. The first distance D1 over which the infrared camera 10 is reciprocated is, for example, several μm to several tens of μm. The first infrared signal is a signal that represents the intensity of infrared light emitted from the displacement device 201. In this embodiment, the value of the infrared signal acquired from the infrared camera 10 is an average value of signals in an area within the field of view of the infrared camera 10 where the displacement device 201 is photographed. Note that the value of the infrared signal acquired from the infrared camera 10 may be the maximum value of signals in an area within the field of view of the infrared camera 10 where the displacement device 201 is photographed.

[0016] In step S30, the control device 20 performs lock-in processing on the first infrared signal obtained in step S20 to obtain a first signal intensity S1.

[0017] FIG. 4 is an explanatory diagram of the lock-in process for the first infrared signal. The top of FIG. 4 shows a timing chart illustrating the reciprocating movement of the infrared camera 10 at a predetermined frequency in step S20. The center of FIG. 4 shows a timing chart illustrating the change in the intensity of the first infrared signal acquired from the infrared camera 10 in step S20. The intensity of the first infrared signal is strong when the distance between the infrared camera 10 and the displacement device 201 is the reference distance RD and weak when the distance is increased by a first distance D1 from the reference distance RD. Note that the signal representing the actual intensity of the first infrared signal has a waveform containing various frequency components due to the influence of noise. The bottom of FIG. 4 shows a waveform obtained by locking in the first infrared signal. The lock-in process is a process for extracting a specific frequency component from a time-varying AC signal. The control device 20 can obtain a waveform having an amplitude corresponding to the intensity of the first infrared signal by extracting from the first infrared signal a signal having the same frequency as the first frequency at which the infrared camera 10 is reciprocated. This waveform amplitude is hereinafter referred to as the first signal intensity S1.

[0018] Figure 5 shows the relationship between the infrared intensity difference and the signal strength after lock-in processing. A simulation was performed in which the intensity difference of the infrared signal shown in the central waveform of Figure 5 was changed in various ways and the corresponding signal strength was calculated using lock-in processing. As shown in Figure 5, the signal strength after lock-in processing increased as the infrared intensity difference increased. Therefore, the first signal strength S1 shown at the bottom of Figure 4 takes a value corresponding to the intensity difference of the first infrared signal.

[0019] 3, the control device 20 returns the distance between the infrared camera 10 and the displacement device 201 to the reference distance RD, and then controls the second driving device 40 to repeatedly displace the displacement device 201 by driving it at the second frequency, while acquiring a second infrared signal from the infrared camera 10. In this embodiment, the second frequency is the same as the first frequency. Note that the first frequency and the second frequency may be different frequencies.

[0020] In step S50, the control device 20 performs lock-in processing on the second infrared signal obtained in step S40 to obtain a second signal intensity S2.

[0021] FIG. 6 is an explanatory diagram of the lock-in process for the second infrared signal. The top of FIG. 6 shows a timing chart of the input voltage input to the displacement device 201 by the second drive unit 40. The second timing chart from the top of FIG. 6 shows the displacement of the displacement device 201 in response to the input voltage from the second drive unit 40. When the input voltage becomes an ON voltage, the displacement device 201 displaces downward by the second distance D2, as shown in FIG. 2. In other words, when the input voltage becomes an ON voltage, the distance between the infrared camera 10 and the displacement device 201 becomes the reference distance RD plus the second distance D2. The third timing chart from the top of FIG. 6 shows changes in the intensity of the second infrared signal acquired from the infrared camera 10 in step S40. The intensity of the second infrared signal is strong when the distance between the infrared camera 10 and the displacement device 201 is the reference distance RD, and is weak when the distance is the second distance D2 away from the reference distance RD. Note that the signal representing the actual intensity of the second infrared signal has a waveform containing various frequency components due to the influence of noise. The bottom of Fig. 6 shows a waveform obtained by locking-in processing the second infrared signal. The control device 20 can obtain a waveform having an amplitude corresponding to the intensity of the second infrared signal by extracting from the second infrared signal a signal having the same frequency as the second frequency, which is the drive frequency of the displacement device 201. The amplitude of this waveform will be referred to as the second signal intensity S2 below.

[0022] 3, the control device 20 calculates a second distance D2, which is the amount of displacement of the displacement device 201. In the first embodiment, it is assumed that the ratio between the first signal strength S1 and the second signal strength S2 is equal to the ratio between the first distance D1 and the second distance D2, and the control device 20 calculates the second distance D2 based on the following formula (1). D2=D1 (S2 / S1) (1)

[0023] The second distance D2 calculated in step S60 is, for example, 1 μm or less. More specifically, if the displacement device 201 is a thin-film piezoelectric element, the second distance D2 is, for example, several hundred nanometers. If the displacement device 201 is a quartz crystal oscillator, the second distance D2 is, for example, several tens of nanometers.

[0024] In step S70, the control device 20 displays on the display device 50 the correspondence between the second distance D2 calculated in step S60 and the second signal strength S2.

[0025] FIG. 7 is a diagram showing an example of displaying the second distance D2 and the second signal strength S2. As shown in FIG. 7, the control device 20 associates the value of the second distance D2 with an infrared image of the displacement device 201 corresponding to the second signal strength S2 and displays them on the display device 50. The image of the displacement device 201 is colored according to the second signal strength S2. More specifically, the lower the second signal strength S2, the darker the color displayed, such as blue or black, and the higher the second signal strength S2, the brighter the color displayed, such as yellow or white. The control device 20 may switch between the second distances D2 and the images shown in FIG. 7 over time. This allows changes in the second distance D2 and the second signal strength S2 to be displayed as changes in color over time.

[0026] The displacement measurement system 100 of the first embodiment described above has the following features: (a) While moving the infrared camera 10 back and forth at a first frequency by a first distance D1 relative to the displacement device 201, the infrared camera 10 captures an image of the displacement device 201, and determines a first signal strength S1 from the infrared rays emitted by the displacement device 201; (b) driving the displacement device 201 so that the displacement device 201 is repeatedly displaced at the second frequency, while capturing an image of the displacement device 201 with the infrared camera 10, and determining a second signal intensity S2 from the infrared rays emitted by the displacement device 201; (c) A second distance D2, which is the displacement amount of the displacement device 201, is calculated using the first distance D1, the first signal strength S1, and the second signal strength S2. Therefore, even when the displacement device 201 is sealed by the sealing member 203, the amount of displacement of the displacement device 201 can be measured by using the infrared camera 10.

[0027] Furthermore, in the first embodiment, the first signal strength S1 is a value obtained by performing lock-in processing to extract a signal having a first frequency from the infrared signal captured by the infrared camera 10. The second signal strength S2 is a value obtained by performing lock-in processing to extract a signal having a second frequency from the infrared signal captured by the infrared camera 10. Therefore, even in a situation where noises of various frequencies are superimposed on the infrared signal acquired by the infrared camera 10, the first signal strength S1 and the second signal strength S2 can be accurately determined.

[0028] In the first embodiment, the control device 20 displays the correspondence between the second distance D2 and the second signal strength on the display device 50, thereby improving user convenience. In the first embodiment, the control device 20 displays the change in the second distance D2 as a change in color over time, allowing the user to observe the internal movement of the measurement object 200.

[0029] B. Second embodiment: The configuration of the displacement measurement system 100 in the second embodiment is the same as that in the first embodiment. In the second embodiment, the processing content of the displacement measurement processing shown in Fig. 3 is different from that in the first embodiment.

[0030] Fig. 8 is a flowchart of the displacement measurement process in the second embodiment. In Fig. 8, the same step numbers are used for steps having the same processing content as in the displacement measurement process shown in Fig. 3. In the second embodiment, step S35 is added to the displacement measurement process of the first embodiment shown in Fig. 3.

[0031] In the second embodiment, the control device 20 calculates a first signal strength S1 corresponding to a first distance D1 by performing the processes of steps S10 to S30 in the same manner as in the first embodiment. In step S35, the control device 20 repeatedly performs the processes of steps S20 and S30 multiple times to determine the correlation between the first distance D1 and the first signal strength S1. More specifically, the control device 20 varies the first distance D1 shown in FIG. 2 and determines the first signal strength S1 corresponding to that first distance D1. The control device 20 varies the first distance D1 at least twice, and preferably three or more times, to determine the correlation between the first distance D1 and the first signal strength S1.

[0032] FIG. 9 is a diagram showing an example of the correlation between the first distance D1 and the first signal strength S1 in the second embodiment. FIG. 9 shows the correlation obtained by changing the first distance D1 in two stages. In the example shown in FIG. 9, the relationship between the first distance D1 and the first signal strength S1 is nonlinear. The control device 20 derives a mathematical formula representing the correlation by finding an approximation curve that passes through the black circles shown in FIG. 9.

[0033] The control device 20 calculates the second signal strength S2 by executing the processes of steps S40 to S50 in Fig. 8 in the same manner as in the first embodiment, and then calculates the second distance D2, which is the amount of displacement of the displacement device 201, in step S60. In step S60 of the second embodiment, the control device 20 calculates the second distance D2 corresponding to the second signal strength S2 using the correlation obtained in step S35, rather than using the above-mentioned formula (1). By calculating the second distance D2 using the correlation obtained in step S35, the control device 20 can accurately calculate the second distance D2, which is the amount of displacement of the displacement device 201.

[0034] C. Other Embodiments: (C1) In the above embodiment, the control device 20 determines the signal intensities S1 and S2 by performing lock-in processing on the waveform of the infrared signal. On the other hand, if the infrared signal does not contain noise and the amplitude can be clearly measured, the amplitude of the infrared signal may be used as the signal intensities S1 and S2 without performing lock-in processing.

[0035] (C2) In the above embodiment, the control device 20 sets the reference distance RD between the displacement device 201 and the infrared camera 10 to the distance at which the infrared camera 10 is in focus. However, the reference distance RD does not have to be the distance at which the infrared camera 10 is in focus. The reference distance RD may be any distance set as long as it is within the range of distances at which the intensity of the infrared signal changes due to the reciprocating movement of the infrared camera 10 or the displacement of the displacement device 201.

[0036] (C3) In the above embodiment, in step S70 shown in Figures 3 and 8, the correspondence relationship between the second distance D2 and the second signal strength is displayed on the display device 50. However, the process of displaying the correspondence relationship between the second distance D2 and the second signal strength on the display device 50 may be omitted.

[0037] (C4) As shown in FIG. 2, in the above embodiment, the reference distance RD when the infrared camera 10 is reciprocated and the reference distance RD when the displacement device 201 is displaced are the same. However, these reference distances may be different. For example, when displacing the displacement device 201, as shown in FIG. 10, the displacement device 201 may be displaced at a distance RD2 that is farther away than the reference distance RD when the infrared camera 10 is reciprocated. In this case, in order to accurately determine the displacement amount of the displacement device 201, it is preferable to set the distance RD2 so that the distance obtained by adding the second distance D2, which is the displacement amount of the displacement device 201, to the distance RD2 is smaller than the distance obtained by adding the first distance D1 to the reference distance RD.

[0038] D. Other forms: The present disclosure is not limited to the above-described embodiments and can be realized in various configurations without departing from the spirit thereof. For example, the technical features of the embodiments corresponding to the technical features in each aspect described below can be appropriately replaced or combined to solve some or all of the above-described problems or achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately deleted.

[0039] (1) According to a first aspect of the present disclosure, there is provided a displacement measurement method for measuring the displacement of a measurement object, the displacement measurement method including the steps of: (a) capturing an image of the measurement object with the infrared camera while reciprocating the infrared camera a first distance at a first frequency relative to the measurement object, and determining a first signal intensity from infrared rays emitted by the measurement object; (b) capturing an image of the measurement object with the infrared camera while driving the measurement object so that the measurement object is repeatedly displaced at a second frequency, and determining a second signal intensity from infrared rays emitted by the measurement object; and (c) determining a second distance, which is a displacement amount of the measurement object, using the first distance, the first signal intensity, and the second signal intensity. According to this aspect, by using an infrared camera, it is possible to measure the displacement of the measurement object even if the measurement object is covered with a sealing member or the like.

[0040] (2) In the above embodiment, the first signal strength may be a value obtained by performing a lock-in process to extract a signal having the first frequency from the infrared signal captured by the infrared camera, and the second signal strength may be a value obtained by performing a lock-in process to extract a signal having the second frequency from the infrared signal captured by the infrared camera. According to this embodiment, even in a situation where noise of various frequencies is superimposed on the intensity signal of the infrared light captured by the infrared camera, the first signal strength and the second signal strength can be accurately determined.

[0041] (3) In the above aspect, the method may further include the step of changing the first distance a plurality of times and determining a correlation between the first distance and the first signal strength. According to this aspect, the second distance can be determined with high accuracy.

[0042] (4) In the above aspect, in the step (c), the second distance may be calculated from the second signal strength based on the correlation. According to this aspect, the second distance can be calculated with high accuracy.

[0043] (5) In the above embodiment, the second distance may be 1 μm or less.

[0044] (6) In the above aspect, the method may further include the step of: (d) displaying the correspondence relationship between the second distance and the second signal strength calculated in the step (c). With this aspect, it is possible to improve user convenience.

[0045] (7) In the above embodiment, in the step (d), the change in the second distance may be displayed as a change in color over time. In this embodiment, the internal movement of the object to be measured can be observed.

[0046] The present disclosure is not limited to the displacement measurement method described above, but can be realized in various forms, such as a displacement measurement system, a computer program for displacement measurement, and a non-transitory tangible recording medium on which the computer program is recorded in a computer-readable manner. [Explanation of symbols]

[0047] 10...infrared camera, 11...lens, 20...control device, 21...CPU, 22...memory, 30...first driving device, 40...second driving device, 50...display device, 100...displacement measurement system, 200...measurement object, 201...displacement device, 202...diaphragm, 203...sealing member

Claims

1. A displacement measurement method for measuring a displacement of a measurement object, comprising: (a) capturing an image of the object to be measured using an infrared camera while reciprocating the infrared camera a first distance at a first frequency relative to the object to be measured, and determining a first signal intensity from infrared light emitted by the object to be measured; (b) taking an image of the measurement object with the infrared camera while driving the measurement object so that the measurement object is repeatedly displaced at a second frequency, and determining a second signal intensity from infrared rays emitted by the measurement object; (c) calculating a second distance, which is a displacement amount of the object to be measured, using the first distance, the first signal strength, and the second signal strength; A displacement measurement method comprising:

2. 2. The displacement measuring method according to claim 1, the first signal intensity is a value obtained by performing a lock-in process to extract a signal having the first frequency from the infrared signal captured by the infrared camera, A displacement measurement method, wherein the second signal intensity is a value obtained by performing a lock-in process to extract a signal having the second frequency from the infrared signal captured by the infrared camera.

3. 2. The displacement measuring method according to claim 1, A method of measuring displacement, comprising the steps of varying the first distance a plurality of times and determining a correlation between the first distance and the first signal strength.

4. 4. The displacement measuring method according to claim 3, In the step (c), the second distance is calculated from the second signal intensity based on the correlation.

5. 2. The displacement measuring method according to claim 1, The displacement measurement method, wherein the second distance is 1 μm or less.

6. 2. The displacement measuring method according to claim 1, (d) displaying the correspondence between the second distance and the second signal strength obtained in step (c).

7. 7. The displacement measuring method according to claim 6, In the step (d), the change in the second distance is displayed as a change in color over time.

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