DE102019115032A1 - Ultrasonic transducer - Google Patents

Abstract

An ultrasonic transducer (1) is described which has a container (2) with an opening, a base (3) and a wall (4). A piezoelectric disc (5) is arranged inside the container (2) on the base (3), which also serves as a membrane. The ultrasonic transducer (1) also has a cover (6) which closes the container (2). Electronics (7) which make electrical contact with the piezoelectric disk (5) and are designed to control and read out the piezoelectric disk (5) are integrated into the cover (6).

Description

The invention relates to an ultrasonic transducer.

Ultrasonic transducers are regularly used to measure distances in a wide variety of areas. In transmission mode, an ultrasound signal is sent out as a pulse from the ultrasound transducer when measuring the distance, which is partially reflected back after it hits an object or another obstacle. In the receiving mode, this reflected pulse is detected, whereby a transit time can be determined. Since the ultrasonic waves propagate in air but also in water with known speeds of sound, the distance to the reflected object can be calculated with the aid of the transit time.

This technology has long been known in shipping as sonar or echo sounder, for example. A distance measurement in a predominantly horizontal direction, for example to other ships, is referred to as sonar, and a distance measurement in a predominantly vertical direction, for example to measure the water depth or the seabed topography, as an echo sounder. Newer cars use ultrasound distance measurement, for example in parking assistance systems, which give the driver a warning signal when the distance to a nearby object is short. The ultrasonic transducers are usually housed in the bumpers, which offer a relatively large amount of space for the installation of an ultrasonic transducer including a housing and the required electronics.

New technological developments and applications, such as drones, robot vacuum cleaners, robotic lawn mowers and autonomous robots in general, pose new challenges for an ultrasonic transducer that is suitable for distance measurement.

An ultrasonic transducer that is more compact and robust is therefore desirable.

The object of the present invention is to provide an ultrasonic transducer which is more compact and robust.

The present object is achieved by the ultrasonic transducer according to claim 1. Further advantageous designs and potential arrangements can be found in the further claims.

An ultrasonic transducer is described which has a container with an opening, a base and walls. A piezoelectric disc is arranged inside the container on the floor, which also serves as a membrane. In addition, the ultrasonic transducer has a lid that closes the container. Electronics are integrated in the cover, which make electrical contact with the piezoelectric disk and are designed to control and read out the piezoelectric disk.

The integration of the electronics in the cover makes the ultrasonic transducer extremely compact, so that it can be used in applications that offer little space for the ultrasonic transducer. Robots that are becoming ever smaller, such as drones, vacuum cleaner robots, lawn mower robots or robots that are used, for example, in logistics or in industrial production, offer little space for individual components, which is why there is a strong need for smaller, more compact sensors and especially for ultrasonic converters. With the integration of the electronics in the cover, in contrast to conventional ultrasonic transducers, it is not necessary to build the ultrasonic transducer in an external housing in which the electronics are installed. By combining the function of a sound-emitting container with the function of a sensor housing, the ultrasonic transducer of the present invention can, contrary to conventional ultrasonic transducers, in which the sound-emitting container is built into the sensor housing, be made much more compact. In addition, production costs can be saved, since additional electrical and mechanical interfaces are not required and the assembly of the ultrasonic transducer and housing can be dispensed with.

In transmission mode, the piezoelectric disc can be excited to a pulse-like oscillation with a frequency of about 50 kHz to 100 kHz and a predetermined number of periods via an alternating voltage applied by the electronics. For example, it can be 8 periods. Since the piezoelectric disc can be fixed to the floor, the floor can vibrate as a membrane and can emit an ultrasonic cone. If the ultrasonic cone hits an object or another obstacle, it can partially be reflected back again. The reflected sound impulse can in turn hit the floor or membrane and can induce a mechanical deflection with the same frequency as the emitted sound impulse both in the floor and in the piezoelectric disc. The mechanical deflection of the piezoelectric disc can cause a voltage change on the applied electrodes, which in turn can be read out by the electronics. The distance to the reflecting object can be calculated from the determined transit time of the ultrasonic pulse and the known speed of sound.

Between the base on which the piezoelectric disc is arranged and the cover can a damping element can be arranged which fills the entire container. The damping element can primarily serve to dampen the ultrasonic vibrations from the piezoelectric disc in the direction of the lid, but it can also additionally stabilize the container. The most important material property for the damping element is the damping constant, which should be as large as possible at typical ultrasonic frequencies between 50 kHz and 100 kHz. Suitable materials are rubbers or foams. In particular foams made of plastics, such as silicone, which have gas inclusions, are suitable for the damping element. These can, for example, be added in liquid form to the container, where the silicone hardens and fills the container in a form-fitting manner.

The arrangement of an elastic ring, which can also be made of silicone, between the damping element and the lid can help prevent any possible transmission of vibrations from the container to the lid. In addition, the elastic ring can serve to seal between the lid and the container, so that no moisture or dust can get into the container.

The lid can be fixed in the container with a resealable fastening mechanism. It is thus possible to reach the underside of the cover at any time, for example to check or repair electrical components or contacts. If the lid is designed just opposite the cross-section of the container, it can be advantageous to position an elastic ring under the lid in order to gain a little space when the lid is opened. The fastening mechanism can expressly be a snap-in mechanism that can releasably fix the cover in at least one position.

The electronics can have a digital I / O interface on an outside of the cover. In a preferred embodiment, the digital I / O interface can also implement the electrical supply of the ultrasonic transducer. By placing the connector directly on the cover, the ultrasonic transducer can be kept compact. In addition, the ultrasonic transducer can be contacted immediately and does not need any further electrical connections. The digital I / O interface is particularly suitable for communication, for example to transmit measurement signals or warning signals to the outside world, as, in contrast to analog interfaces, it has a higher level of interference immunity and therefore functions without errors even in an environment loaded with interference signals.

Furthermore, the bottom can be thinner than 1 mm. The floor, which also serves as a membrane, must on the one hand be elastic enough to follow the deflection movements of the piezoelectric disc, and on the other hand it should be stable enough to withstand external influences, such as water jets for cleaning. A thickness from the floor of less than 1 mm and more than 0.2 mm have proven advantageous. The thickness of the bottom, together with the diameter, can also essentially determine the resonance frequency at which the component can advantageously be operated for emitting and receiving ultrasound.

The thickness of the walls can be more than 1.5 times the thickness of the floor and is preferably thicker than 3 times the thickness of the floor. It has been shown that such wall thicknesses are suitable for the transmission of vibrations of the floor or the membrane to a surface that runs parallel to the floor, such as the lid or a protrusion of the container that can be used to hold the ultrasonic transducer , to suppress. Vibrations that are transmitted via the bracket to an adjacent attachment that belongs to the application could then be reflected and thus incorrectly recorded as a phantom signal as a measurement signal in the ultrasonic transducer. If the wall thickness is chosen so that it is at least 1.5 times the thickness of the membrane, the transmission of vibrations from the floor to other parts of the container can be prevented. The soil has certain natural modes that vibrate with a natural frequency and are determined, among other things, by the strength of the soil. Since the wall can have at least 1.5 times the thickness of the base, transmission of the vibration modes to other areas of the container can be prevented. However, the wall thickness should not be more than 20 times, preferably not more than 10 times, the thickness of the floor, since otherwise the component can become too heavy and a small version of the component is more difficult to implement.

Furthermore, the container can be designed to give preference to a plane in the direction of sound propagation. By narrowing the propagating sound cone, the accuracy of the distance measurement can be increased, since the propagation of the sound wave in one spatial direction can be excluded. In the simplest case, the container is designed to be oval for this purpose. Other shapes of the container can also be designed to favor propagation of the sound in one plane.

The container can consist of an electrically conductive material. A container made of an electrically conductive material, which is connected to the electrical ground of the sensor, increases the electromagnetic compatibility, with which the Ultrasonic transducers cannot be unintentionally disturbed by other electrical devices in the vicinity. In an advantageous embodiment, the grounding of the container can be implemented via the optional digital I / O connection. In particular in smaller mobile applications such as drones or autonomous robots, for example, many electric motors can be installed that can emit electromagnetic interference signals. If the container is made of an electrically conductive material, the piezoelectric disk and electronics arranged inside the container can be shielded from external interference signals.

Suitable materials can be metals such as Al, Cu, Sn, Fe, steel, but also alloys. Since the bottom of the container also acts as a membrane, it is advantageous to use a material that has a relatively high flexibility. Therefore, metals with a low elastic modulus such as Al or Sn are particularly preferred.

Furthermore, the inner surface of the container can be partially roughened and / or smoothed. Roughening the surface inside the container means that materials adhere better to this surface, but the ultrasound is also more strongly scattered on this surface. Smoothing the surface reduces adhesion to the surface, but does not scatter the ultrasound. For this reason it can be advantageous, for example, to roughen the surface of the floor adjacent to the piezoelectric disc so that it adheres better there. The rest of the area of the bottom inside the container can be smoothed, for example, in order to reduce the adhesion of a damping element at this point and thus to prevent a deflection of the piezoelectric disc less. In addition, the inside of the walls can also be roughened, which means that the sound is more strongly scattered on this surface. A sandblasting or etching process can be used for roughening, and a grinding or coating process for smoothing.

A part of the base or a surface of the container which runs parallel to the base can have a thicker thickness than the base surface adjoining the piezoelectric disc, which is used as a membrane. The reinforced surfaces stabilize the container and are suitable for use as support surfaces on a fastening, a frame or a supporting structure in an application.

The reinforced areas can have an adhesive material on an outer surface. This ensures that the ultrasonic transducer can be installed in an application without any problems. The ultrasonic transducer only needs to be positioned at the intended location so that the adhesive material adheres to the attachment. It is desirable that the adhesive material consists of a foam-like soft material with gas inclusions that dampens vibrations from the ultrasonic transducer to the attachment.

Sound-absorbing components can be arranged on an outer surface of the container. The sound-absorbing components dampen the ultrasound and vibrations with regard to an undesired direction of propagation. The sound-absorbing components are preferably made of a foam-like material. Execution as an electrically conductive material is desirable in order not to reduce the electromagnetic compatibility of the ultrasonic transducer but, on the contrary, to increase it.

In one embodiment, the cover is a printed circuit board. In this way, the electronics can be easily integrated into the cover and all required electrical components can easily be electrically contacted. In addition, since the conductor tracks can be modulated, the arrangement of electrical components on the conductor track can be changed, so that the electrical components can be arranged in a space-saving or geometrically advantageous manner.

If a circuit board is used as a cover, it can be flexible. Thus, ultrasound propagating from the piezoelectric disk to the cover can be dampened and both phantom signals and the transmission of vibrations can be suppressed. In addition, the installation of a flexible circuit board as a cover can be carried out more easily compared to a rigid circuit board.

The circuit board can have electrical ground planes on the outside, which are grounded. In this way, the electromagnetic compatibility of the ultrasonic transducer can be increased. At the same time, the electrical components arranged on the circuit board and the circuit board itself can be protected from dangerous voltage peaks.

Furthermore, the circuit board, which is used as a cover, can be cast in a plastic compound. The plastic mass is preferably also flexible after hardening in order to dampen vibrations. The plastic mass fills existing cracks or holes in the circuit board and gaps between the circuit board and the container. Accordingly, the container is sealed airtight and the propagation of the ultrasonic waves in this direction can be suppressed. In addition, a tight closure can be realized with a lid that has no point of contact with the walls of the container. This suppresses the transmission of vibrations between the cover and the walls. A silicone or a soft resin can be used as the plastic mass.

The circuit board can have electrical components which are arranged on a surface of the circuit board that faces the piezoelectric disc. The electrical components are thus protected against possible damage due to mechanical or chemical environmental influences as well as against external electromagnetic interference signals. In addition, the uneven surface of the lid caused by the electrical components can scatter the ultrasound and reduce undesired propagation of the ultrasound.

The ultrasonic transducer according to the present invention can be integrated in an arrangement which has a fastening for an associated application, wherein the ultrasonic sensor can be arranged directly on the fastening without further housing. Such an arrangement does not require an additional housing for the ultrasonic transducer, so that space is saved and the ultrasonic transducer can also be used in a crowded environment. This enables the use of the ultrasonic transducer in applications that conventional ultrasonic transducers cannot, such as small drones or autonomous robots.

A device can have an ultrasonic transducer according to the present invention, wherein the device can be configured to measure a distance of the device to an object on the basis of a signal determined by the ultrasonic transducer. The device can be, for example, autonomous robots, such as self-driving robots in warehouse logistics or in industrial production, vacuum cleaner robots, lawn mower robots or autonomous flying objects such as drones. The ultrasonic transducer can also be used in devices such as cars, charging stations in electromobility or laptops as well as control devices with monitors as an interface to the operator.

• 1 zeigt eine Explosionsansicht eines Ultraschall-Wandlers nach der vorliegenden Erfindung.
• 2 zeigt einen Querschnitt eines zusammengefügten Ultraschall-Wandler.

The invention is described in more detail below with the aid of schematic representations.

• 1 Figure 11 shows an exploded view of an ultrasonic transducer according to the present invention.
• 2 Figure 10 shows a cross-section of an assembled ultrasonic transducer.

In 1 Figure 11 is an exploded view of an ultrasonic transducer 1 shown according to the present invention. A container 2 which is an opening, a floor 3 and has circular walls, is composed of two cylindrical parts, a lower and an upper one. The lower part has a smaller radius than the upper part and is on a lower round base with the floor 3 closed, which also serves as a membrane. The lower part is open at the top. The entire container 2 is in one piece and the upper part is thus connected to the lower part via a connecting surface that is parallel to the floor 3 runs, connected. The upper part is also open at the top.

Inside the container 2 becomes a piezoelectric disc 5 with an adhesive layer 13th or an adhesive disc on the floor 3 fixed. Above it is a damping element 8th arranged that to the shape of the container 2 is adapted and fills this out completely. About wires 14th becomes the piezoelectric disc 5 with electronics 7th connected. This is on one side of a lid 6th arranged facing inwards. The lid 6th itself is a circuit board 12th and has a digital I / O interface on one side that faces outwards 9 on.

Via the digital I / O interface 9 Not only the communication to the outside is realized, but also the electronics 7th as well as the piezoelectric disc 5 supplied with electricity. The arrangement of the digital I / O interface 9 on the lid 6th enables a compact design of the ultrasonic transducer 1 and simple contacting, as no other connections have to be observed. In contrast to analog interfaces, it has a digital I / O interface 9 a high tolerance with regard to interference signals that can originate, for example, from nearby electric motors.

The lid 6th is a printed circuit board 12th that have ground planes on the outside and the electronics on the inside 7th in the form of electrical components. Preferably the lid is 6th shaped so that it covers the walls of the container 2 not touched. The conductor tracks on the circuit board 12th can be adapted to the electrical components, for example in a space-saving or geometrically advantageous manner with regard to the shape of the container 2 to arrange.

Through the arrangement of the electronics 7th on the inside of the lid 6th the electrical components, if the container 2 consists of an electrically conductive material, protected from external electromagnetic interference signals.

In addition, the uneven surface created by the electrical components encourages scattering of ultrasound emitted by the piezoelectric disc 5 to the lid 6th , and thus the wrong way round, propagated. Another advantage of the layout of the electronics 7th on the inside of the electronics 7th is that electronics 7th in front mechanical or chemical damage that can result from environmental influences is protected.

By the circuit board 12th is flexible and / or is cast in a plastic mass, ultrasound can be emitted by the piezoelectric disc 5 to the lid 6th propagated, damped and thus further spread of vibrations and associated phantom signals are suppressed. An installation of a flexible printed circuit board 12th as a lid 6th can opposite rigid lids 6th be easier to do. The plastic mass is used to fill up possible cracks and holes in the circuit board 12th and a possible gap between the lid 6th and container 2 used. So the container can do that 2 are sealed and the propagation of the ultrasonic waves can be suppressed even better. Will be a lid 6th used that is smaller than the container 2 is, a tight seal can still be realized with the plastic mass, which even transmits vibrations between the lid 6th and wall 4th diminishes. A silicone or a soft resin can be used as the plastic mass.

The lid 6th can with a resealable fastening mechanism in the container 2 be fixed. The fastening mechanism can for example be a snap-in mechanism that holds the lid 6th releasably fixed in one position. This allows the lid 6th are opened and the electrical components or contacts of the electronics 7th on the inside of the lid 6th be assessed. Corresponds to the cross section of the lid 6th the internal cross-section of the container 2 , it is advantageous to have an elastic ring, which can be made of silicone, for example, under the lid 6th to position. This allows a little clearance when opening the lid 6th be permitted, which facilitates opening.

The damping element 8th that between the lid 6th and the ground 3 is arranged and the entire container 2 fills, serves primarily to dampen the ultrasound and the vibrations emitted by the piezoelectric disc 5 come. Hence the most important property of the damping element 8th the damping constant especially for typical ultrasonic frequencies between 50 kHz and 100 kHz, whereby the damping constant should be as large as possible. Rubbers or foams have suitable damping properties. Foams made of plastics, such as silicone, which have gas inclusions, are expressly used as the material for the damping element 8th suitable. These can be put into the container as a solid 2 be positioned or as a liquid in the container 2 be poured where the liquid mass, such as two-component silicone, hardens and the container 2 fills form-fitting. In addition to damping the ultrasonic waves, the damping element stabilizes 8th the container 2 also mechanically, so that the container 2 withstands greater external pressure.

On an outer surface of the interface between the upper and lower parts of the container 2 , is an adhesive material 10 arranged. The adhesive material is preferred 10 made of a foam-like, soft material that dampens vibrations. By using the adhesive material 10 installation of the ultrasonic transducer 1 simplified as the ultrasonic transducer 1 only needs to be placed at a target position, so that the adhesive material 10 adheres to a fastening. A foam-like material reduces the transmission of vibrations from the ultrasonic transducer 1 to the attachment. It can be a double adhesive tape that has a foam-like core. This adhesive tape can already be attached to the intended surface with one side of the adhesive tape, with a second adhesive side of the adhesive tape still up until the final assembly of the ultrasonic transducer 1 can remain covered with a protective film in an application.

Along an outer surface of the wall 5 the lower part of the container 2 is a vibration dampening component 11 arranged. The vibration dampening component 11 dampens the ultrasound and vibrations with respect to an undesired direction of propagation perpendicular to the ground 3 . The vibration dampening component 11 is preferably made of a foam-like material, which is preferably also electrically conductive, in order to ensure the electromagnetic compatibility of the ultrasonic transducer 1 to increase. However, it is also possible to use a non-conductive material such as silicone.

In 2 becomes the cross section of an assembled ultrasonic transducer 1 shown. The wall 5 the lower part of the container 2 comes with a vibration dampening component 11 clad from the outside and the interface between the lower and upper part of the container 2 is externally with adhesive material 10 Mistake. On the ground 3 inside the container 2 is a piezoelectric disc 5 arranged by the damping element 8th that is the entire container 2 fills in, with the electronics 7th over wires 14th is electrically contacted.

The interface between the top and bottom of the container 2 is thicker than the rest of the container 2 . These reinforced connection surfaces are designed to be used as support surfaces on a fastening, a frame or a supporting structure in an application. The floor 3 , which is also used as a membrane, is thinner than 1 mm. On the one hand there must be the floor 3 be elastic enough to withstand the deflection movements of the piezoelectric disc 5 not to hinder much. On the other hand, the floor must be 3 have a certain stability so that it is not damaged by an external force, such as irradiation with water for cleaning. A favorable compromise was made on strength from the ground 3 of less than 1 mm and more than 0.2 mm were found. The walls are at least 1.5 times as thick as the floor 3 , but should be thicker than 3 times the thickness of the floor if possible 3 his. Such a thick wall is suitable for the transmission of vibrations from the floor 3 or the membrane to the connecting surface between the upper and lower part of the container 2 to reduce. As the connecting surface is a support surface of the ultrasonic transducer 1 can be to a fastening, vibrations and deflections should be avoided especially at these connection surfaces. Otherwise, vibrations can be transmitted to an adjacent attachment belonging to the application. The transmitted vibrations can in turn be reflected and therefore in the ultrasonic transducer 1 falsely detected as a measurement signal as a phantom signal. A wall thickness that is at least 1.5 times the thickness of the membrane reduces the transmission of vibrations from the floor 3 to other parts of the container 2 and thus prevents the problem.

Ideally the container is 2 made of an electrically conductive material, as so the electromagnetic compatibility of the ultrasonic transducer 1 is increased. In particular the piezoelectric disc 5 and the one on the inside of the lid 6th arranged electronics 7th can through the use of conductive materials in the container 2 shielded from external electromagnetic interference signals. In small and narrow applications, such as drones or autonomous robots, a large number of electric motors are often built into the ultrasonic transducers 1 can affect. Metals such as Al, Cu, Sn, Fe, steel but also alloys are suitable conductive materials for the container 2 . The function of the soil 3 as a membrane requires a relatively high flexibility. Because of this, conductive materials with a low elastic modulus such as Al and Sn are excellent.

The container 2 can also be optimized by partially roughening and / or smoothing the inner surface. Roughening a surface causes materials to adhere more strongly to it. However, ultrasound is also scattered more strongly on a rough, uneven surface. Smoothing the surface reduces adhesion to the surface, but it scatters less ultrasound. Hence it is favorable to the surface of the soil 3 adjacent to the piezoelectric disc 5 roughen this up so that this is over the adhesive layer 13th holds better. Furthermore, the remaining area is the floor 3 inside the container 2 smoothed to make a damping element 8th does not adhere to these surfaces and the deflection of the piezoelectric disc 5 through the damping element 8th is not hindered too much. Optionally, the inside of the walls can also be roughened in order to spread the ultrasound more strongly on this surface. Suitable methods for roughening are, for example, a sandblasting or etching process, as well as grinding or coating processes for smoothing the surface.

List of reference symbols

1

Ultrasonic transducer

2

container

3

ground

4th

wall

5

piezoelectric disc

6th

cover

7th

electronics

8th

Damping element

9

digital I / O interface

10

adhesive material

11

vibration damping component

12

Circuit board

13th

Adhesive layer

14th

wire

Claims (16)

An ultrasonic transducer (1) comprising: - A container (2) with an opening, a bottom (3) and a wall (5); - a piezoelectric disc (5), wherein the piezoelectric disc (5) is arranged inside the container (2) on the floor (3); - a lid (6), wherein the lid (6) closes the container (2); - Electronics (7) which are integrated in the cover (6), the electronics (7) making electrical contact with the piezoelectric disc (5) and being designed to control and read out the piezoelectric disc (5). An ultrasonic transducer (1) according to the preceding claim, wherein a damping element (8) is arranged between the base (3) and the cover (6), and wherein the damping element (8) fills the container (2). An ultrasonic transducer (1) according to one of the preceding claims, wherein the lid (6) is fixed with a reclosable fastening mechanism. An ultrasonic transducer (1) according to one of the preceding claims, wherein the electronics (7) have a digital I / O interface (9) on the outside of the cover (6). An ultrasonic transducer (1) according to one of the preceding claims, wherein the base (3) is thinner than 1 mm. An ultrasonic transducer (1) according to one of the preceding claims, wherein a thickness of the walls is at least 1.5 times the thickness of the base (3). An ultrasonic transducer (1) according to one of the preceding claims, wherein the container (2) consists of an electrically conductive material. An ultrasonic transducer (1) according to one of the preceding claims, wherein an inner surface of the container (2) is partially roughened and / or smoothed. An ultrasonic transducer (1) according to one of the preceding claims, wherein a part of the base (3) or a surface of the container (2) which runs parallel to the base (3) has a thicker wall thickness than that of the piezoelectric disc (5) ) adjacent floor area. An ultrasonic transducer (1) according to the preceding claim, wherein the container (2) has an adhesive material (10) on an outer surface of the surfaces which have a thicker wall thickness. An ultrasonic transducer (1) according to one of the preceding claims, wherein vibration-damping components (11) are arranged on an outer surface of the container (2). An ultrasonic transducer (1) according to one of the preceding claims, wherein the cover (6) is a printed circuit board (12). An ultrasonic transducer (1) according to the preceding claim, wherein the circuit board (12) is flexible. An ultrasonic transducer (1) according to Claim 12 or 13th , wherein the circuit board (12) is cast in a plastic mass. An ultrasonic transducer (1) according to one of the Claims 12 to 14th wherein the circuit board (12) has electrical components, and wherein the electrical components are arranged on a surface of the circuit board (12) which faces the piezoelectric disc (5). Device comprising an ultrasonic transducer (1) according to one of the Claims 1 to 15th , wherein the device is designed to measure a distance of the device to an object on the basis of a signal determined by the ultrasonic transducer (1).

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