Ultrasonic sensor
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- SEIKO EPSON CORP
- Filing Date
- 2021-10-27
- Publication Date
- 2026-08-04
Smart Images
Figure 0007899525000001 
Figure 0007899525000002 
Figure 0007899525000003
Abstract
Description
Technical Field
[0001] The present invention relates to an ultrasonic sensor.
Background Art
[0002] Conventionally, an ultrasonic sensor that measures the distance to an object by transmitting ultrasonic waves and receiving the reflected waves reflected by the object is known (see, for example, Patent Document 1). In the conventional ultrasonic sensor of this Patent Document 1, ultrasonic waves are generated by the vibration of a piezoelectric vibrator, and the ultrasonic waves reflected by the object are received by the piezoelectric vibrator. A capacitor is connected in parallel to the piezoelectric vibrator, and the capacitor connected in parallel to the piezoelectric vibrator can be selected by a switch operation. In such an ultrasonic sensor, by changing the combination of capacitors connected to the piezoelectric vibrator, the reverberation time until the received signal output when the piezoelectric vibrator receives the reflected wave is attenuated is controlled.
Prior Art Documents
Patent Documents
[0003]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0004] However, in a so-called bulk-type ultrasonic vibrator that transmits ultrasonic waves by the vibration of the piezoelectric element itself and detects the reception of ultrasonic waves by the piezoelectric element itself receiving and vibrating ultrasonic waves as in Patent Document 1 above, it is difficult to miniaturize the ultrasonic element in terms of manufacturing, and there is a problem that it is difficult to measure at a short distance of, for example, 10 mm or less. In other words, when using ultrasound to detect objects placed at close range, it is necessary to use high-frequency ultrasound to reduce reverberation time. However, as mentioned above, miniaturization is difficult with bulk-type ultrasonic transducers, and there are limits to how high the ultrasonic frequency can be increased. Furthermore, when measuring objects at close range using ultrasound, it is desirable to detect the shape, such as irregularities, and the inclination of the object within a narrow area. However, with bulk-type ultrasonic transducers like the one described in Patent Document 1, miniaturization is difficult, which presents a challenge in reducing the ultrasonic spot diameter. [Means for solving the problem]
[0005] An ultrasonic sensor according to a first aspect of the present disclosure is an ultrasonic sensor that transmits ultrasonic waves to an object and receives ultrasonic waves reflected by the object, comprising an ultrasonic array chip in which ultrasonic elements for transmitting and receiving ultrasonic waves are arranged in an array, wherein the ultrasonic element comprises a vibrating part and a piezoelectric element provided on the vibrating part, the vibrating part is vibrated by applying a voltage to the piezoelectric element to transmit ultrasonic waves, the reception of ultrasonic waves is detected by a signal output from the piezoelectric element due to the vibration of the vibrating part, and the resonant frequency of the ultrasonic element is 2000 kHz or less.
[0006] In the ultrasonic sensor of this embodiment, when viewed from the direction of ultrasonic wave transmission, the ultrasonic array chip is rectangular in shape, with the length of one side being 5 mm or less.
[0007] In the ultrasonic sensor of this embodiment, the ultrasonic element has a resonant frequency of less than 1000 kHz, and the ultrasonic element is configured such that the reverberation time is defined as the time until the vibration amplitude of the vibrating part generated by transmitting ultrasonic waves from the ultrasonic element becomes 10% or less of the vibration amplitude of the vibrating part immediately after the transmission of ultrasonic waves, and the reverberation time is 60 μs or less.
[0008] In the ultrasonic sensor of this embodiment, the ultrasonic element has a resonant frequency of 1000 kHz or more and less than 1500 kHz, and the ultrasonic element is configured such that the reverberation time is defined as the time until the vibration amplitude of the vibrating part generated by transmitting ultrasonic waves from the ultrasonic element becomes 10% or less of the vibration amplitude of the vibrating part immediately after the transmission of ultrasonic waves, and the reverberation time is 50 μs or less.
[0009] In the ultrasonic sensor of this embodiment, the ultrasonic element has a resonant frequency of 1500 kHz or more and 2000 kHz or less, and the ultrasonic element is configured such that the reverberation time is defined as the time until the vibration amplitude of the vibrating part generated by transmitting ultrasonic waves from the ultrasonic element becomes 10% or less of the vibration amplitude of the vibrating part immediately after the transmission of ultrasonic waves, and the reverberation time is 25 μs or less. [Brief explanation of the drawing]
[0010] [Figure 1] A schematic diagram showing the general configuration of an ultrasonic sensor according to one embodiment of the present invention. [Figure 2] A cross-sectional view showing the schematic configuration of the ultrasonic array chip of this embodiment. [Figure 3] This figure shows an example of connecting ultrasonic transducers in the ultrasonic array chip of this embodiment. [Figure 4] This figure shows the relationship between the distance from the ultrasonic array tip and the spot diameter of the ultrasonic beam, when the resonant frequency of the ultrasonic transducer is set to 600 kHz. [Figure 5] This figure shows the relationship between the distance from the ultrasonic array tip and the spot diameter of the ultrasonic beam, when the resonant frequency of the ultrasonic transducer is set to 900 kHz. [Figure 6] This figure shows the relationship between the distance from the ultrasonic array tip and the spot diameter of the ultrasonic beam when the resonant frequencies of the ultrasonic transducer are set to 1000 kHz, 2000 kHz, and 3000 kHz. [Figure 7] This figure shows the change in vibration of the vibrating part after ultrasonic waves are transmitted from the ultrasonic sensor of this embodiment. [Figure 8]This diagram shows the change in vibration of an ultrasonic transducer after it transmits ultrasound from a bulk-type ultrasonic transducer. [Figure 9] This figure shows the relationship between the resonant frequency and the measurable distance in the ultrasonic sensor of this embodiment and a conventional bulk-type ultrasonic transducer. [Figure 10] A schematic diagram showing the general configuration of an ultrasonic sensor according to Modification 1. [Modes for carrying out the invention]
[0011] The following describes an ultrasonic sensor according to one embodiment. Figure 1 is a schematic diagram showing the general configuration of the ultrasonic sensor 10 of this embodiment. The ultrasonic sensor 10 comprises an ultrasonic array chip 20 placed on a substrate 11 or the like, and a control circuit 30 that controls the ultrasonic array chip 20. The ultrasonic sensor 10 performs ultrasonic transmission and reception processing, in which it transmits ultrasonic waves from the ultrasonic array chip 20 toward the object 1 under the control of the control circuit 30, and receives the ultrasonic waves reflected by the object 1 with the ultrasonic array chip 20. The control circuit 30 then calculates the distance from the ultrasonic array chip 20 to the object 1 based on the time from the timing of ultrasonic wave transmission in the ultrasonic transmission and reception processing by the ultrasonic array chip 20 to the timing of reception of the ultrasonic waves reflected by the object 1. In particular, the ultrasonic sensor 10 of this embodiment is advantageous as a short-range measuring device that requires limited installation space and is used when the distance to the object 1 is, for example, 10 mm or less. Such an ultrasonic sensor 10 can be applied to, for example, printers and image scanners, and can be suitably used to measure the distance to the paper surface (where the paper surface is the object 1), detect the unevenness of the paper surface, and detect the paper surface's transport state. Furthermore, by attaching it to a robot arm, it can be used to accurately detect the distance between the object 1 and the robot arm when the robot arm approaches the object 1, and to measure damage caused by collision between the robot arm and the object 1. When applied to printers or image scanners, it is preferable to simultaneously detect, for example, the tilt of the paper surface, wrinkles, and other irregularities. In addition, when an ultrasonic sensor 10 is mounted on a robot arm or the like, if there are protrusions or the like on the object 1 when the robot arm is brought close to the object 1, damage or scratches may occur on the object 1 due to an unintended contact between the robot arm and the object 1. Therefore, as the ultrasonic sensor 10, it is preferable not only to measure the distance to the object 1 but also to appropriately determine the surface shape of the object 1. For this reason, in the ultrasonic sensor 10 of the present embodiment, by performing measurement on a narrow range of the object 1, irregularities or the like of the object 1 are detected. Hereinafter, details of each configuration of such an ultrasonic sensor 10 will be described.
[0012] [Configuration of ultrasonic array chip 20] FIG. 2 is a cross-sectional view showing a schematic configuration of the ultrasonic array chip 20. The ultrasonic array chip 20 transmits ultrasonic waves to the object 1 and outputs a reception signal by receiving the ultrasonic waves reflected by the object 1. As shown in FIG. 2, the ultrasonic array chip 20 includes an element substrate 21, a diaphragm 22, and a piezoelectric element 23. Although not shown, the ultrasonic array chip 20 also includes a fixed substrate to which the element substrate 21 is fixed. In the following description, the transmission and reception direction of ultrasonic waves from the ultrasonic array chip 20 toward the object 1 is defined as the Z direction.
[0013] The element substrate 21 is a substrate that supports the diaphragm 22 and is formed of a semiconductor substrate such as Si. A plurality of openings 211 penetrating the element substrate 21 along the Z direction are provided in the element substrate 21.
[0014] The diaphragm 22 is composed of, for example, a laminate of SiO2 and ZrO2, etc., and is provided on the -Z side of the element substrate 21. This diaphragm 22 is supported by the element substrate 21 that constitutes the opening 211, and closes the -Z side of the opening 211. Among the diaphragm 22, the portion that overlaps with each opening 211 when viewed from the Z direction constitutes a vibrating portion 221 in the diaphragm 22 that transmits and receives ultrasonic waves by vibration. Also, the surface on the +Z side of the diaphragm 22, that is, the surface opposite to the element substrate 21 and formed by a plurality of vibrating portions 221 arranged in an array, constitutes an ultrasonic transmission / reception surface 22A (see FIG. 1).
[0015] The piezoelectric element 23 is provided on the diaphragm 22 and at a position that overlaps with each vibrating portion 221 when viewed from the Z direction. As shown in FIG. 2, this piezoelectric element 23 is constituted by sequentially laminating a lower electrode 231, a piezoelectric film 232, and an upper electrode 233 on the diaphragm 22.
[0016] In such an ultrasonic array chip 20, one ultrasonic transducer 24 (ultrasonic element) is constituted by one vibrating portion 221 and the piezoelectric element 23 arranged on the vibrating portion 221. Then, in this ultrasonic array chip 20, when a voltage is applied between the lower electrode 231 and the upper electrode 233, the piezoelectric film 232 expands and contracts, and the vibrating portion 221 vibrates at an oscillation frequency corresponding to the opening width of the opening 211, etc. Thereby, ultrasonic waves are transmitted from the vibrating portion 221 toward the +Z side. Also, in the ultrasonic array chip 20, when the ultrasonic waves reflected by the object 1 are input to the vibrating portion 221, the vibrating portion 221 vibrates with an amplitude corresponding to the sound pressure of the input ultrasonic waves, and a potential difference occurs between the lower electrode 231 side and the upper electrode 233 side of the piezoelectric film 232. Therefore, a reception signal corresponding to the potential difference is output from each piezoelectric element 23.
[0017] FIG. 3 is a diagram showing a connection example of the ultrasonic transducer 24 in the ultrasonic array chip 20. In this embodiment, multiple ultrasonic transducers 24 are arranged in an n x m matrix. The lower electrodes 231 of each ultrasonic array chip 20 are connected to each other by a first bypass wire 231A and connected to a first terminal 251 provided on a part of the element substrate 21. Similarly, the upper electrodes 233 of each ultrasonic array chip 20 are connected to each other by a second bypass wire 233A and connected to a second terminal 252 provided on a part of the element substrate 21. These first terminals 251 and second terminals 252 are each connected to a control circuit 30. In this configuration, all ultrasonic transducers 24 can be driven simultaneously by applying a voltage between the first terminal 251 and the second terminal 252. The example shown in Figure 3 is a configuration in which the lower electrodes 231 of all ultrasonic transducers 24 are connected to the first terminal 251. However, a predetermined number of ultrasonic transducers 24 may be used as one channel, and a first terminal 251 may be provided for each channel. In this case, by simultaneously inputting a drive signal between all first terminals 251 and second terminals 252, all ultrasonic transducers 24 can be driven simultaneously, similar to Figure 3. It is also possible to drive each first terminal 251 individually. In this case, the transmitted sound pressure can be adjusted by controlling the number of channels to be driven, and the direction of ultrasonic transmission can be controlled by delaying the drive timing of each channel. Furthermore, multiple channels may be used, divided into a transmitting channel for transmitting ultrasonic waves and a receiving channel for receiving ultrasonic waves.
[0018] In this embodiment, the ultrasonic array chip 20 has a rectangular shape when viewed from the Z direction in a plan view. Specifically, in the ultrasonic array chip 20, the ultrasonic transmission and reception area where the multiple ultrasonic transducers 24 are arranged, that is, the area constituting the ultrasonic transmission and reception surface 22A where ultrasonic waves are transmitted and received, is rectangular, and the length of the long side of this rectangular transmission and reception area (array aperture width) is formed to be 5 mm or less. In other words, in this embodiment, the length of one side of the ultrasonic array chip 20 being 5 mm or less indicates that the long side (array aperture width) of the rectangular transmission and reception area where the multiple ultrasonic transducers 24 are arranged is 5 mm or less.
[0019] Furthermore, the ultrasonic array chip 20 may have a vibration suppression layer having a predetermined Young's modulus placed on the diaphragm 22. For example, a resin material can be used as the vibration suppression layer, and the vibration suppression layer can further suppress the vibration of each vibrating part 221, thereby shortening the reverberation time. Here, the reverberation time in this embodiment refers to the time from when the ultrasonic transducer 24 transmits ultrasonic waves until the vibration amplitude of the vibrating part 221 generated at the time of ultrasonic wave transmission is attenuated to 10% or less.
[0020] [Ultrasonic beam frequency and spot diameter] Next, the frequency of the ultrasound emitted from the ultrasonic array chip 20 and the spot diameter of the ultrasonic beam formed by the ultrasound will be described. As described above, the main purpose of the ultrasonic sensor 10 of this embodiment is to properly measure the distance between the ultrasonic array chip 20 and an object 1 located at close range from the ultrasonic transmitting / receiving surface 22A of the ultrasonic array chip 20, and to properly detect the state of the object 1, such as unevenness, located at close range from the ultrasonic transmitting / receiving surface 22A of the ultrasonic array chip 20. In this case, the ultrasonic array chip 20 is required to transmit an ultrasonic beam with a small spot diameter from the ultrasonic transmitting / receiving surface 22A to a target distance range.
[0021] In this embodiment, the ultrasonic sensor 10 is configured such that, in a plan view from the Z direction, the array aperture width of the ultrasonic array chip 20 is 5 mm or less, and the resonant frequency of each ultrasonic transducer 24 is 2000 kHz or less. Such an ultrasonic sensor 10 makes it possible to transmit an ultrasonic beam with a spot diameter of 10 mm or less to a short distance of 50 mm or less from the ultrasonic transmitting / receiving surface 22A. The spot diameter is the maximum diameter of the ultrasonic beam in a plane perpendicular to the ultrasonic transmission direction (Z direction).
[0022] Figure 4 shows the relationship between the distance from the ultrasonic array tip 20 and the spot diameter of the ultrasonic beam. In Figure 4, the spot diameter of the ultrasonic beam is shown for each case where the resonance frequency of the ultrasonic transducer 24 is 600 kHz and the array aperture width is 10 mm, 5 mm, 3 mm, and 1 mm. Figure 5 shows the spot diameter of the ultrasonic beam for each case where the resonance frequency of the ultrasonic transducer 24 is 900 kHz and the array aperture width is 10 mm, 5 mm, 3 mm, and 1 mm. Figure 6 shows the spot diameter of the ultrasonic beam for each case where the resonance frequency of the ultrasonic transducer 24 is 2000 kHz and the array aperture width is 10 mm, 5 mm, 3 mm, and 1 mm. In Figures 4 to 6, the solid line shows the data for 5 mm, the dashed line for 3 mm, the double dashed line for 1 mm, and the dashed line for 10 mm.
[0023] As shown in Figures 4 to 6, if the resonance frequency of the ultrasonic transducer 24 is 2000 kHz or less, and the array aperture width is 5 mm or less, the spot diameter can be 10 mm or less within a distance range of 10 mm or less from the ultrasonic transmitting / receiving surface 22A. In particular, if the resonance frequency exceeds 1 MHz, an ultrasonic beam with a spot diameter of 10 mm or less can be transmitted to a short-range area of 50 mm or less. On the other hand, if the array aperture width exceeds 5 mm, the spot diameter may exceed 10 mm even within a range of 10 mm or less from the ultrasonic sensor 10. For example, as shown in Figures 4 and 5, if the array aperture width is 10 mm, the spot diameter exceeds 10 mm at a position approximately 10 mm from the ultrasonic sensor 10. Furthermore, the higher the resonant frequency of the ultrasonic transducer 24, the greater the attenuation of the ultrasound. In particular, when ultrasound is transmitted from the ultrasonic transducer 24 into the air, the attenuation rate becomes even greater, making it difficult to detect the ultrasound reflected by the object 1. Therefore, it is preferable to set the frequency of the ultrasound used, that is, the resonant frequency of the ultrasonic transducer 24, to 2000 kHz or less. Furthermore, Figures 4-6 show graphs where the spot diameter is 5 mm or less depending on the frequency band, even when the array aperture width is greater than 5 mm and 10 mm or less. However, when the array aperture width exceeds 5 mm, the effect of side lobes becomes significant, and it may not be possible to achieve a spot diameter of 10 mm or less. In contrast, by setting the array aperture width to 5 mm or less, it is possible to suppress the effect of side lobes while achieving a spot diameter of 10 mm or less for short-range areas, as shown in Figures 4-6.
[0024] Incidentally, when measuring the distance from the ultrasonic array chip 20 to an object located at a short distance, the so-called Time of Flight (ToF) method is used, in which the ultrasonic array chip 20 transmits ultrasound, receives the ultrasound reflected by the object, and measures the time from the timing of ultrasound transmission to the timing of reception of reflected ultrasound. In order to properly detect the timing of reflected ultrasound reception using the ToF method, it is necessary to ensure that the vibrations of the vibration unit 221 caused by the reception of reflected ultrasound are not masked by the reverberation vibrations of the vibration unit 221 generated during ultrasound transmission. In other words, at the time of reflected ultrasound reception, the vibration amplitude of the vibration unit 221 during ultrasound transmission must be attenuated to 10% or less. Here, the reverberation time from the time of ultrasonic transmission until the vibration amplitude of the vibrating section 221 falls below 10% is mainly determined by the frequency of the ultrasonic waves emitted from the ultrasonic transducer 24, that is, the resonant frequency of the ultrasonic transducer 24.
[0025] Figure 7 shows the change in vibration of the vibrating section 221 after ultrasonic waves are transmitted from the ultrasonic sensor 10 of this embodiment. Figure 8 shows the change in vibration of the ultrasonic transducer after ultrasonic waves are transmitted from a bulk-type ultrasonic transducer. Note that Figure 7 shows the change in vibration when the ultrasonic frequency is 1.7 MHz, and Figure 8 shows the change in vibration when the ultrasonic frequency is 1.5 MHz. As shown in Figure 7, in the ultrasonic sensor 10 of this embodiment, the reverberation time T1 is approximately 20 μs. On the other hand, as shown in Figure 8, in the bulk-type ultrasonic transducer, the reverberation time T2 is approximately 30 μs. As shown in Figures 7 and 8, bulk-type ultrasonic transducers tend to have a longer reverberation time compared to thin-film type ultrasonic elements in which the vibrating part 221 is vibrated by a piezoelectric element 23, as in this embodiment.
[0026] Figure 9 shows the relationship between the resonant frequency and the measurable distance for the ultrasonic sensor 10 of this embodiment and a conventional bulk-type ultrasonic transducer. In Figure 9, the solid line represents the ultrasonic sensor 10 of this embodiment, and the dashed line represents the conventional bulk-type ultrasonic transducer. Conventional bulk-type ultrasonic transducers generally transmit ultrasonic waves by vibrating a piezoelectric material itself when a voltage is applied. The ultrasonic waves reflected by the target object are received by the piezoelectric material, causing the piezoelectric material itself to vibrate and thus detecting the reception of ultrasonic waves. In such bulk-type ultrasonic transducers, it is necessary to cut the piezoelectric material, such as a piezo element, to the desired size, making the formation of minute sizes extremely difficult from a manufacturing perspective and resulting in high manufacturing costs. For example, Figure 8 shows an example of a bulk-type ultrasonic transducer with a reverberation time T2 of approximately 30 μs. However, in reality, due to variations in the ultrasonic transducer, the reverberation time becomes even longer, making it difficult to form a bulk-type ultrasonic transducer with a reverberation time of 30 μs or less. Bulk-type ultrasonic transducers are typically formed by cutting piezoelectric material. However, when using cost-effective methods such as laser cutting, only frequencies below 1000 kHz, as shown in Figure 9, can be achieved. In such cases, the reverberation time also increases, and the detectable distance for bulk-type ultrasonic transducers exceeds 10 mm. Furthermore, bulk-type ultrasonic transducers are formed in a block shape, and their thickness is large, which limits the available space for installation.
[0027] On the other hand, in the ultrasonic sensor 10 of this embodiment, a thin-film vibrating portion 221 can be formed on an element substrate 21 such as Si by microfabrication such as etching, and a thin-film piezoelectric element 23 can also be easily formed into a desired pattern by etching. In this configuration, the resonance frequency of the ultrasonic transducer 24 can be set to any value from 500 kHz to 2000 kHz by controlling the opening width of the opening 211 and the thickness of the vibrating portion 221. In such an ultrasonic sensor 10, as shown in Figure 7, the reverberation time can be significantly shortened compared to a bulk-type ultrasonic transducer, and as a result, as shown in Figure 9, an object 1 placed at a distance of 10 mm or less from the ultrasonic sensor 10 in the range of 500 kHz to 2000 kHz can be properly detected.
[0028] As shown in Figures 4 to 6 and Figure 9, in this embodiment, the ultrasonic transducer 24 is configured such that the reverberation time is 60 μs or less when the resonant frequency of the ultrasonic transducer 24 (frequency of transmitted ultrasonic waves) is 600 kHz or more and less than 1000 kHz. This makes it possible to transmit an ultrasonic beam with a spot diameter of 10 mm or less to an object 1 located at a distance of approximately 10 mm from the ultrasonic sensor 10. Furthermore, when the resonant frequency of the ultrasonic transducer 24 is set to 1000 kHz or more and less than 1500 kHz, the ultrasonic transducer 24 is configured such that the reverberation time is 50 μs or less. This makes it possible to transmit an ultrasonic beam with a spot diameter of 10 mm or less to an object 1 located between 5 mm and 10 mm from the ultrasonic sensor 10. Furthermore, when the resonant frequency of the ultrasonic transducer 24 is set to 1500 kHz or higher and 2000 kHz or lower, the ultrasonic transducer 24 is configured such that the reverberation time is 25 μs or less. This makes it possible to transmit an ultrasonic beam with a spot diameter of 10 mm or less to an object 1 that is within 5 mm of the ultrasonic sensor 10. Furthermore, the ultrasonic sensor 10 of this embodiment has a configuration in which a thin film piezoelectric element 23 is arranged on a thin film vibrating part 221, and its thickness can be made extremely thin compared to a bulk-type ultrasonic transducer. Therefore, the degree of freedom in placement space is increased, and the ultrasonic sensor 10 can be placed even in narrow spaces with a gap dimension of about 5 mm.
[0029] [Configuration of control circuit 30] Returning to Figure 1, the control circuit 30 will be described. As mentioned above, the control circuit 30 is connected to the first terminal 251 and the second terminal 252 of the ultrasonic array chip 20. As shown in Figure 1, the control circuit 30 includes a switching circuit 31, a signal ground 32, a transmission circuit section 33, a reception processing section 34, and a microcontroller 35. An example of the control circuit 30 is an integrated circuit such as a System-On-Chip (SoC) or Application Specific Standard Product (ASSP).
[0030] The switching circuit 31 is connected to the first terminal 251 of the ultrasonic array chip 20, the transmitting circuit section 33, and the receiving processing section 34. Based on the control of the microcontroller 35, the switching circuit 31 switches between a transmitting connection that connects the first terminal 251 and the transmitting circuit section 33, and a receiving connection that connects the first terminal 251 and the receiving processing section 34. The signal ground 32 is a ground connected to the second terminal 252, and maintains the second terminal 252 at a predetermined reference potential.
[0031] The transmitting circuit 33 is controlled, for example, by a microcontroller 35, and outputs a pulse drive signal of a predetermined voltage to the first terminal 251. This drives each ultrasonic transducer 24, and ultrasonic waves are output from the ultrasonic array chip 20 toward the object 1.
[0032] The receiving processing unit 34 is composed of, for example, a receiving amplifier, a comparator, etc., and processes the received signal output when the ultrasonic array chip 20 receives ultrasonic waves, and outputs the received signal to the microcontroller 35.
[0033] The microcontroller 35 includes a memory for storing various programs and data, and a processor for executing instruction sets written in the programs stored in the memory. The microcontroller 35 instructs the transmission circuit 33 to output a pulse drive signal, causing the ultrasonic array chip 20 to transmit ultrasound. The microcontroller 35 also measures the time from the ultrasound transmission timing until the reception processing unit 34 outputs a reception signal, and calculates the distance from the ultrasonic array chip 20 to the object 1 based on this time. In this embodiment, ultrasonic waves are transmitted to an object 1 over a narrow range of 10 mm or less, and the reflected ultrasonic waves are received. By continuously calculating the distance between the object 1 and the ultrasonic array chip 20 while moving the relative position of the ultrasonic array chip 20 with respect to the object 1, the surface condition of the object 1, such as the presence or absence of irregularities and the angle of inclination, can be measured.
[0034] [Effects of this embodiment] The ultrasonic sensor 10 of this embodiment transmits ultrasonic waves to an object and receives ultrasonic waves reflected by the object. This ultrasonic sensor 10 includes an ultrasonic array chip 20 in which ultrasonic transducers 24 that transmit and receive ultrasonic waves are arranged in an array. The ultrasonic transducer 24 includes a vibrating part 221 and a piezoelectric element 23 provided on the vibrating part 221. By applying a voltage to the piezoelectric element 23, the vibrating part 221 is vibrated and ultrasonic waves are transmitted, and the reception of ultrasonic waves is detected based on the signal output from the piezoelectric element due to the vibration of the vibrating part 221. In this embodiment, the resonant frequency of the ultrasonic transducer 24 is 2000 kHz or less. In an ultrasonic sensor 10 with this configuration, the reverberation time until the reverberation vibration of the vibrating section 221 attenuates when ultrasonic waves are transmitted by each ultrasonic transducer 24 is significantly shorter than that of a bulk-type ultrasonic transducer. Therefore, even when an object 1 is located 10 mm or less from the ultrasonic sensor 10, the reverberation vibration is suppressed when the ultrasonic waves reflected by the object 1 are received by the ultrasonic transducer 24, allowing for proper detection of the reflected ultrasonic waves. Furthermore, by setting the resonant frequency to 2000 kHz or less, ultrasonic attenuation in the air can be suppressed, allowing for proper detection of ultrasonic waves reflected by an object 1 located at close range.
[0035] In the ultrasonic sensor 10 of this embodiment, the ultrasonic array tip 20 is rectangular in shape when viewed from the direction of ultrasonic wave transmission, and the array aperture width is 5 mm or less. In this configuration, an ultrasonic beam is formed by ultrasonic waves transmitted from each ultrasonic transducer 24 located on the ultrasonic sensor 10. Within a distance range of 10 mm from the ultrasonic sensor 10, the spot diameter of the ultrasonic beam is 10 mm or less. Therefore, ultrasonic waves can be transmitted to a narrow area with a spot diameter of 10 mm or less relative to the object 1, and the distance between this narrow area of the object 1 and the ultrasonic sensor 10 can be measured. In this case, for example, by continuously changing the relative position between the narrow range from which the ultrasound is transmitted and the ultrasonic sensor 10, and monitoring the change in distance, the inclination of the object 1 and the surface shape of the object 1 can be measured.
[0036] In the ultrasonic sensor 10 of this embodiment, the ultrasonic transducer 24 is configured such that when the resonant frequency of the ultrasonic transducer 24 is less than 1000 kHz, the reverberation time is 60 μs or less. This makes it possible to transmit an ultrasonic beam with a spot diameter of 10 mm or less to an object 1 at a short distance of approximately 10 mm from the ultrasonic sensor 10.
[0037] In the ultrasonic sensor 10 of this embodiment, the ultrasonic transducer 24 is configured such that when the resonance frequency of the ultrasonic transducer 24 is set to 1000 kHz or more and less than 1500 kHz, the reverberation time is 50 μs or less. This makes it possible to transmit an ultrasonic beam with a spot diameter of 10 mm or less to an object 1 located between 5 mm and 10 mm away from the ultrasonic sensor 10.
[0038] In the ultrasonic sensor 10 of this embodiment, the ultrasonic transducer 24 is configured such that when the resonant frequency of the ultrasonic transducer 24 is set to 1500 kHz or more and 2000 kHz or less, the reverberation time is 25 μs or less. This makes it possible to transmit an ultrasonic beam with a spot diameter of 10 mm or less to an object 1 within 5 mm of the ultrasonic sensor 10.
[0039] [Differentiation] It should be noted that the present invention is not limited to the embodiments described above, and any configurations obtained by modifying, improving, or appropriately combining the embodiments to the extent that the objectives of the present invention can be achieved are included in the present invention.
[0040] [Example 1] In the above embodiment, as shown in Figure 1, the space between the ultrasonic array chip 20 placed on the substrate 11 and the object 1 is a space where other components are placed, but the embodiment is not limited to this. Figure 10 is a schematic diagram showing another example of the configuration of the ultrasonic sensor 10. For example, as shown in Figure 10, a partition plate 12 may be provided between the ultrasonic array chip 20 and the object 1 so as to cover it, and the partition plate 12 may be provided with a through hole 121 through which the ultrasonic beam passes.
[0041] [Differentiation 2] As described above, in this disclosure, "the length of one side of the ultrasonic array chip 20 being 5 mm or less" refers to the length of one side of the rectangular transmitting and receiving area in the ultrasonic array chip 20 where the ultrasonic transducers 24, which transmit and receive ultrasonic waves, are arranged in an array. Therefore, if there is a wiring area outside the transmitting and receiving area, for example, where wiring is formed, the size of the wiring area is not particularly limited. In the above embodiment, an example was shown in which the ultrasonic array tip 20 is rectangular and the shape of the transmission / reception area of the ultrasonic transmission / reception surface 22A is also rectangular, but the invention is not limited to this. For example, a square transmission / reception area with a side length of 5 mm or less may be provided, a circular transmission / reception area with a diameter of 5 mm or less may be provided, or an elliptical transmission / reception area with a major axis length of 5 mm or less may be provided.
[0042] [Summary of this disclosure] An ultrasonic sensor according to a first aspect of the present disclosure is an ultrasonic sensor that transmits ultrasonic waves to an object and receives ultrasonic waves reflected by the object, comprising an ultrasonic array chip in which ultrasonic elements for transmitting and receiving ultrasonic waves are arranged in an array, wherein the ultrasonic element comprises a vibrating part and a piezoelectric element provided on the vibrating part, the vibrating part is vibrated by applying a voltage to the piezoelectric element to transmit ultrasonic waves, the reception of ultrasonic waves is detected by a signal output from the piezoelectric element due to the vibration of the vibrating part, and the resonant frequency of the ultrasonic element is 2000 kHz or less.
[0043] This allows the reverberation time—the time it takes for reverberant vibrations to decay when ultrasound is transmitted—in the ultrasonic element of the ultrasonic sensor to be significantly reduced compared to bulk-type ultrasonic transducers. Therefore, even when an object is located less than 10 mm from the ultrasonic sensor, reverberant vibrations are suppressed when the ultrasonic element receives ultrasound reflected from the object, enabling proper detection of the reflected ultrasound.
[0044] In the ultrasonic sensor of this embodiment, when viewed from the direction of ultrasonic wave transmission, the ultrasonic array chip is rectangular in shape, with the length of one side being 5 mm or less. This allows the spot diameter of the ultrasonic beam formed within a 10mm distance from the ultrasonic sensor to be reduced to 10mm or less, enabling the measurement of the tilt and surface shape of the object.
[0045] In the ultrasonic sensor of this embodiment, the ultrasonic element has a resonant frequency of less than 1000 kHz, and the ultrasonic element is configured such that the reverberation time is defined as the time until the vibration amplitude of the vibrating part generated by transmitting ultrasonic waves from the ultrasonic element becomes 10% or less of the vibration amplitude of the vibrating part immediately after the transmission of ultrasonic waves, and the reverberation time is 60 μs or less. This allows for the transmission of an ultrasonic beam with a spot diameter of 10 mm or less to objects at close range, approximately 10 mm from the ultrasonic sensor.
[0046] In the ultrasonic sensor of this embodiment, the ultrasonic element has a resonant frequency of 1000 kHz or more and less than 1500 kHz, and the ultrasonic element is configured such that the reverberation time is defined as the time until the vibration amplitude of the vibrating part generated by transmitting ultrasonic waves from the ultrasonic element becomes 10% or less of the vibration amplitude of the vibrating part immediately after the transmission of ultrasonic waves, and the reverberation time is 50 μs or less. This allows for the transmission of an ultrasonic beam with a spot diameter of 10 mm or less to objects located between 5 mm and 10 mm away from the ultrasonic sensor.
[0047] In the ultrasonic sensor of this embodiment, the ultrasonic element has a resonant frequency of 1500 kHz or more and 2000 kHz or less, and the ultrasonic element is configured such that the reverberation time is defined as the time until the vibration amplitude of the vibrating part generated by transmitting ultrasonic waves from the ultrasonic element becomes 10% or less of the vibration amplitude of the vibrating part immediately after the transmission of ultrasonic waves, and the reverberation time is 25 μs or less. This allows the transmission of an ultrasonic beam with a spot diameter of 10 mm or less to an object within 5 mm of the ultrasonic sensor. [Explanation of Symbols]
[0048] 1...Object, 10...Ultrasonic sensor, 20...Ultrasonic array chip, 21...Element substrate, 22...Diaphragm, 22A...Ultrasonic transmitting / receiving surface, 23...Piezoelectric element, 24...Ultrasonic transducer, 30...Control circuit, 31...Switching circuit, 32...Signal ground, 33...Transmitting circuit section, 34...Receiving processing section, 35...Microcontroller, 211...Opening, 221...Vibrating section, 231...Lower electrode.
Claims
1. An ultrasonic sensor that transmits ultrasonic waves to an object and receives ultrasonic waves reflected by the object, It is equipped with an ultrasonic array chip in which ultrasonic elements that transmit and receive ultrasonic waves are arranged in an array, The ultrasonic element comprises an element substrate, a thin film diaphragm that closes an opening formed in the element substrate, and a thin film piezoelectric element provided on the vibrating portion of the diaphragm that closes the opening. By applying a voltage to the piezoelectric element, the vibrating portion is vibrated to transmit ultrasonic waves, and the reception of ultrasonic waves is detected by a signal output from the piezoelectric element due to the vibration of the vibrating portion. The aforementioned element substrate is made of a semiconductor substrate, The diaphragm is made of SiO ２ and ZrO ２ It is composed of a laminate containing, The resonant frequency of the ultrasonic element is between 500 kHz and 2000 kHz. When viewed from the direction of ultrasonic wave transmission, the ultrasonic array tip is rectangular in shape, with a side length of 5 mm or less. The ultrasonic array tip transmits an ultrasonic beam with a spot diameter of 10 mm or less to an object placed at a predetermined distance from the vibrating unit. When the predetermined distance is y (mm) and the resonant frequency of the ultrasonic element is x (kHz), -0.0076x+15.745x≦y<-0.0076x+20.241 An ultrasonic sensor that satisfies the requirements.
2. The resonant frequency of the ultrasonic element is 500 kHz or more and less than 1000 kHz. The reverberation time is defined as the time it takes for the vibration amplitude of the vibrating part, generated by transmitting the ultrasonic waves from the ultrasonic element, to become 10% or less of the vibration amplitude of the vibrating part immediately after the transmission of the ultrasonic waves, and the reverberation time is 60 μs or less. The ultrasonic sensor according to claim 1.
3. The resonant frequency of the ultrasonic element is 1000 kHz or more and less than 1500 kHz. The reverberation time is defined as the time it takes for the vibration amplitude of the vibrating part generated by transmitting the ultrasonic waves from the ultrasonic element to become 10% or less of the vibration amplitude of the vibrating part immediately after the transmission of the ultrasonic waves, and the reverberation time is 50 μs or less. The ultrasonic sensor according to claim 1.
4. The resonant frequency of the ultrasonic element is 1500 kHz or more and 2000 kHz or less. The time it takes for the vibration amplitude of the vibrating part generated by transmitting the ultrasonic waves from the ultrasonic element to become 10% or less of the vibration amplitude of the vibrating part immediately after the transmission of the ultrasonic waves is 25 μs or less. The ultrasonic sensor according to claim 1.