DE102012204638A1 - Ultrasonic sensor and method for measuring an object distance - Google Patents

Abstract

The invention relates to an ultrasonic sensor (10) for detecting a distance of an object, having a housing (20) and a damping mass (21). This fills the housing (20) at least partially. The ultrasonic sensor (10) further comprises a membrane (30), a piezoceramic (40) and an electrical contact (22). The electrical contact (22) comprises at least one electrode (23) and a ground electrode (25). Furthermore, the piezoceramic (40) is divided into at least three segments (41, 42, 43), wherein a first segment (41) is connected to the ground electrode (25) and a second (42) and third segment (43) each over separate electrodes (23, 24) are contacted. The invention further relates to a method for measuring an object distance by means of an ultrasonic sensor (10) having a piezoceramic (40) whose rear side (31) has a first segment (41), a second segment (42) and a third segment (43). The method comprises a method step in which a counter-vibration is introduced into the oscillating membrane (30) by means of the second segment (42).

Description

State of the art

The invention relates to an ultrasonic sensor for detecting a distance of an object and a method for measuring an object distance by means of an ultrasonic sensor.

DE 195 07 650 A1 discloses an ultrasonic sensor capable of transmitting and receiving ultrasonic signals. The ultrasonic sensor in this case has a sensor membrane, which is divided into a primary membrane and two or more secondary membranes. The primary and secondary membranes are adapted to the respective detection task. The segmentation of the sensor membrane determines the damping behavior of the sensor membrane, and thus the detection characteristic of the ultrasonic sensor.

Out US 3,698,051 is an ultrasonic sensor for material testing is known, which is disc-shaped and is provided with radial slots. Further, metallic polarizing layers are concentrically formed in the circumferential direction, which provide the arc segments of the polycrystalline material of the crystal surface with piezoelectric properties. The sensor according to US 3,698,051 is further operated at a resonant frequency of 10 kHz-500 kHz.

DE 196 05 502 C1 discloses an ultrasonic transducer for distance measurement, which he has attenuator, which may be formed as a piezoelectric element. The ultrasound transducer initially oscillates unattenuated during emission of ultrasound signals. After emitting the ultrasonic signals, the attenuator is brought to a membrane and brings them controlled to a halt.

A disadvantage of ultrasonic sensors according to the prior art is that they are designed to detect objects in a range of several meters and are not suitable to reliably and accurately detect small object distances, in particular those of less than 20 cm, with the same accuracy.

Disclosure of the invention

The ultrasonic sensor according to the invention for detecting a distance of an object has a housing which is partially filled with a damping mass. Furthermore, the ultrasonic sensor according to the invention has a membrane which is capable of generating an ultrasonic pulse by oscillation. Furthermore, the membrane is suitable for detecting the echo of an ultrasound pulse. The ultrasonic sensor according to the invention is equipped with a piezoceramic, which is in communication with the membrane, and is electrically contacted. The electrical contacting of the piezoceramic comprises at least one electrode and a ground electrode. The electrical connection with the piezoceramic can be produced by a conductive adhesive. The contacting extends through the damping mass, which at least partially fills the housing of the ultrasonic sensor. The piezoceramic of the ultrasonic sensor is divided into at least three segments, wherein a first segment is connected to the ground electrode. A second and a third segment are each electrically contacted via a separate electrode.

The second segment of the piezoceramic is designed to reduce a vibration of the membrane. Further, the third segment for detecting a vibration of the diaphragm is formed.

The piezoceramic may comprise at least one further segment, which is designed to detect a vibration and / or to reduce a vibration of the membrane. The first, the second and the third segments may each further surround concentrically.

In this case, the segments can be mechanically coupled to one another in such a way that they serve as measuring and control members of a control loop. The segments may be formed in the piezoceramic such that a lasered interruption is introduced in the surface of the piezoceramic. The interruption can also be produced by scratching the piezoceramic or by a screen printing process.

The method according to the invention for measuring an object distance is carried out by means of an ultrasound sensor comprising a membrane and a piezoceramic. In this case, the piezoceramic is divided into at least three segments, wherein a first segment serves as a carrier element for a second and third segment. Furthermore, an electric field is produced in the first segment for the second and third segments. The first segment is electrically connected via a ground electrode and the second and third segments each have a separate electrode. The method according to the invention comprises a first method step, according to which the second and / or third segment are electrically excited via the electrodes to a piezo-deformation and a vibration of the membrane is effected. The vibration of the membrane generates an ultrasonic pulse that is emitted. In a further method step, a vibration state of the membrane is detected by the third segment and the deflection of the membrane is measured. In a further method step, the second segment is excited, to create a counter-vibration that reduces the deflection of the diaphragm. An intensity of the vibration state is characterized by at least one physical parameter of a vibration, for example amplitude or frequency of deflection of the diaphragm. In a subsequent method step, the echo of the ultrasound pulse emitted in the above-described first method step is received over the membrane and detected by means of the second and / or third segment of the piezoceramic. In a subsequent method step, the transit time of the ultrasound pulse which elapsed between the emission of the ultrasound pulse and the detection of the ultrasound pulse is detected. Based on the determined running time, the object distance to be measured is determined.

In one embodiment of the invention, the method step, in which the deflection of the diaphragm is detected by the third segment, and the method step, in which a counter-vibration is generated by means of the second segment, can be carried out in a balancing loop. It is detected when the deflection of the membrane falls below a threshold value. If the threshold value is undershot, then the method step in which a countervibration is generated ends.

In a further embodiment of the invention, a further segment can be formed in the piezoceramic, which is coupled to the second and third segments. The further segment is in this case connected to the second and third segments such that these measuring and / or control elements in a control loop, which reduces the deflection of the membrane represent.

The ultrasonic sensor according to the invention can be used in particular in a driver assistance system of a motor vehicle for measuring an object distance.

Advantages of the invention

The ultrasonic sensor according to the invention has a piezoceramic, which is divided into at least three segments. Advantageously, the segments of the piezoceramic are functionally decoupled from each other and can fulfill a separate function regardless of the operating state of another segment. The segmented piezoceramic allows, immediately after emitting an ultrasonic pulse by excitation of the second and / or third segment, to detect the deflection of the membrane via the third segment. Furthermore, the second segment can be excited in a targeted manner in order to generate a countervibration which partially eliminates the already existing vibration of the diaphragm and thus reduces the deflection of the diaphragm. In the ultrasonic sensor according to the invention, a ringing of the membrane can be counteracted immediately after the emission of an ultrasonic pulse. Due to the functional separation of the second and third segments, a measurement of the deflection of the membrane and counteracting can be carried out continuously and simultaneously. The detection of the deflection of the membrane and the generation of countervibrations can hereby be permanently coordinated via a balancing loop. The second and third segments of the piezoceramic act as measuring and control elements of a control loop, which quickly minimizes ringing of the membrane.

The rapid minimization of the deflection of the membrane during ringing causes the membrane after a short time is again able to detect an arrival of an echo of an ultrasonic pulse to the membrane. As a result, it is also possible to use ultrasonic pulses which have only a short transit time reliably and accurately for a measurement of an object distance. The invention thus makes it possible to reduce the minimum range of an ultrasonic sensor. The ultrasonic sensor according to the invention can be used as a sensor for low object distances. As a result, in applications in which both high and low object distances must be measured, for example in a driver assistance system of a motor vehicle, separate proximity sensors are saved.

In one embodiment of the ultrasonic sensor according to the invention, a further segment may be provided in the piezoceramic, which is suitable for detecting a vibration and / or for reducing a vibration of the membrane. Further segmentation of the piezoceramic allows to form a plurality of measuring segments whose measuring signals can be compared with each other and thus increase the accuracy of the measurement of the deflection of the membrane. Furthermore, a further segmentation of the piezoceramic makes it possible to form uniformly distributed excitation segments which are capable of rapidly reducing reverberation of the membrane. As a result, the time until the membrane is again able to detect an echo of an ultrasonic pulse, further reduced.

Furthermore, the invention allows to reduce the damping of the membrane, whereby a higher deflection of the membrane is produced with constant excitation of the membrane. This allows the generation of high sound pressure, whereby high sensor ranges are possible. Furthermore, a reduced attenuation of the membrane allows to detect with this weak excitations and to detect them by means of the piezoceramic. The range of detection of distance sensors in motor vehicles, in particular those which are used for side-view Applications include improved by the invention.

Furthermore, the segments are advantageously mechanically coupled together and are designed as measuring and control elements of a control loop. The segments are parts of the same piezoceramic and are based on the same physical principle as sensors and actuators If an ultrasonic echo is detected during the ringing of the membrane, the ringing from the detected deflection of the membrane after the arrival of the ultrasonic echo can be calculated by the sensing by means of the third segment be filtered out. As a result, the measurement accuracy of the ultrasonic sensor is improved. The ultrasonic sensor according to the invention further allows a simple control technology implementation. Furthermore, the integration of the second and third segments in a control loop allows the control behavior of the segments to be easily adapted to different application requirements. The invention thus improves the range of use of ultrasonic sensors for distance measurement.

Furthermore, the segments on a surface of the piezoceramic can be prepared by lasered interruptions. Laser processing can be performed at high speed and can easily be incorporated into a manufacturing chain. Alternatively, the breaks may be made by scribing or screen printing. Cracks and screen printing processes are production steps that can be easily integrated into a production chain. The ultrasonic sensor according to the invention thus makes it possible to achieve a reduction of the minimum range with relatively simple means. Similarly, the ultrasonic sensor according to the invention requires that each segment is driven by a separate electrode. Electrodes can be easily incorporated in a manufacturing process.

Further, by actively introducing counter vibrations of the membrane, the invention allows to reduce the electrical stresses on the membrane during operation. As a result, the life of the ultrasonic sensor is increased. Furthermore, in the case of an ultrasonic sensor according to the invention, a transformer can be dispensed with as a result of the low attenuation of the diaphragm. In this case, the number of components of the ultrasonic sensor is reduced, simplifies its manufacture and saves installation space.

Brief description of the drawings

1 : Top view of a piezoceramic according to the prior art

2 : Schematic representation of an ultrasonic sensor in cross section

3 : Schematic representation of a piezoceramic of an inventive

ultrasonic sensor

4 : Schematic representation of an embodiment of a piezoceramic of an ultrasonic sensor according to the invention

5 : Schematic representation of a piezoceramic of an ultrasonic sensor according to the invention

6 : Schematic representation of a piezoceramic of an ultrasonic sensor according to the invention

7 : Schematic representation of the method according to the invention for measuring an object distance

In 1 is a piezoceramic 40 imaged according to the prior art. The piezoceramic 40 has a surface 60 on that by the edge 70 is limited. The piezoceramic 40 is on her surface 60 in a first segment 41 and a second segment 42 assigned. This encloses the first segment 41 the second segment 42 like a ring. The first segment 41 is electrically via a ground electrode 25 that part of the electrical contact 22 is electrically connected. The second segment 42 is via a separate electrode 23 electrically contacted.

Embodiments of the invention

In 2 an ultrasonic sensor is shown in cross-section. The ultrasonic sensor 10 includes a housing 20 , which partially with a damping mass 21 is filled. At one end of the housing 20 is a membrane 30 formed, which is capable of generating ultrasonic pulses by vibration. Further, the membrane 30 suitable to record and detect echoes of ultrasound pulses. On a back 31 the membrane 30 is a piezoceramic 40 attached, which is capable of by electrical excitation of the membrane 30 to stimulate vibrations. Furthermore, the piezoceramic is 40 suitable, vibrations of the membrane 30 to detect and convert into an electrical signal. The damping mass 21 that the case 20 partially fills, here closes the piezoceramic 40 one. The piezoceramic 40 is via an electrical contact 22 connected, which allows the ultrasonic sensor 10 electrically connect and drive. The electrical contact 22 extends through the damping mass 21 ,

In 3 is a plan view of a piezoelectric ceramic of an advantageous embodiment of the ultrasonic sensor according to the invention shown. The surface 60 the piezoceramic 40 is by a border 70 limited. The first segment 41 on the surface 60 the piezoceramic 40 encloses the second 42 and third segment 43 like a ring. The second segment 42 and the third segment 43 are arranged adjacent and each serve to reduce a vibration of the membrane 30 of the ultrasonic sensor 10 or for detecting a vibration of the membrane 30 , These are the second segment 42 and the third segment 43 each via separate electrodes 23 . 24 electrically contacted. The ground connection of the piezoceramic 40 via a ground electrode 25 that in a ground connection area 45 with the piezoceramic 40 connected is. The first segment 41 , the second segment 42 and the third segment 43 are each by lasered breaks 50 separated from each other, which on the surface 60 the piezoceramic 40 are formed.

In 4 is an advantageous embodiment of the piezoceramic 40 of the ultrasonic sensor according to the invention 10 shown. This indicates the surface 60 the piezoceramic 40 a first segment 41 , a second segment 42 and a third segment 43 on. This encloses the first segment 41 the third segment 43 annular, which in turn is the second segment 42 encloses annularly. The segments 41 . 42 . 43 are arranged substantially concentric. The second segment 42 is essentially in the center of the piezoceramic 40 arranged where the vibration of the membrane 30 has the largest amplitude. Backlash caused by the second segment 42 are initiated, reduce the deflection of the membrane 30 strongly. The third segment 43 is an area of the surface 60 the piezoceramic attached, in which the vibration of the membrane 30 has a mean amplitude. At a mean amplitude are from the third segment 43 recorded such high measurement rashes, which ensure a high accuracy, but not the entire work area of the third segment 43 exploit. The first segment 41 serves as a ground connection of the piezoceramic 40 , which has a ground electrode 25 ensures that in a ground connection area 45 with the piezoceramic 40 connected is.

In 5 is a further advantageous embodiment of the piezoceramic 40 an ultrasonic sensor according to the invention 20 shown. The surface 60 the piezoceramic 40 is in a first segment 41 , a second segment 42 , a third segment 43 and another segment 44 divided, the further segment 44 is via an additional electrode 26 electrically connected. The second segment 42 and the other segment 44 are essentially congruent and extend from the center of the piezoceramic 40 in a border area 70 passing through the first segment 41 is defined. This allows the second segment 42 and the other segment 44 the membrane 30 sense or excite in a wide radial range. Become both the second segment 42 as well as the further segment 44 for detecting a vibration of the membrane 30 used, allows the congruent shape of the second segment 42 and the other segment 44 , a direct comparison of these measurement signals.

6 schematically shows a plan view of another advantageous embodiment of the piezoceramic 40 of the ultrasonic sensor according to the invention. Therein is the surface 60 a piezoceramic 40 in a first segment 41 , a second segment 42 , a third segment 43 and another segment 44 assigned. The segments 41 . 42 . 43 . 44 are by lasered interruptions 50 on the surface 60 the piezoceramic 40 educated. The first segment 41 surrounds the third segment annularly 43 , which in turn ring the second segment 42 and the other segment 44 encloses. The second segment 42 and the other segment 44 are essentially congruent. Further, the first segment 41 with a ground electrode 25 electrically contacted, and the second segment 42 , the third segment 43 and the other segment 44 each via separate electrodes 23 . 24 . 26 electrically connected. The second segment 42 which is essentially in the center of the piezoceramic 40 is capable of being in the range of the largest vibration amplitude of the membrane 30 to initiate a counter-vibration, and thereby the vibration of the membrane 30 to pay off quickly. The third segment 43 encloses substantially annularly the center of the piezoceramic 40 and extends to a border area 70 the piezoceramic 40 passing through the first segment 41 is defined. The third segment 43 allowed the vibration of the membrane 30 to sense in an area where the vibration amplitude of the membrane 30 achieved an order of magnitude in which a high accuracy of measurement is ensured, but not the entire working range of the third segment 43 is exhausted. Will the other segment 44 used as a measuring element, so the deflection of the membrane 30 be detected more accurately than with a single measuring element. Will the other segment 44 used as a control element, so in interaction with the second segment 42 efficiently counter vibrations in the membrane 30 be introduced. This will determine the time in which the deflection of the membrane 30 is minimized, reduced.

In 7 is schematically illustrated the sequence of an advantageous embodiment of the method according to the invention for measuring an object distance by means of an ultrasonic sensor. In a first process step 110 becomes the membrane 30 by stimulating the second 42 and / or third segment 43 excited to a vibration and generates an ultrasonic pulse. This is in a second step 120 the deflection of the membrane 30 through the third segment 43 the piezoceramic 40 detected. In a further process step 130 becomes the second segment 42 for generating a counter-vibration, which determines the vibration of the membrane 30 blotted out. Here, the deflection of the membrane 30 reduced. The second process step 120 and the third process step 130 are through a balance loop 160 coupled together. In the adjustment loop 160 it checks if the deflection of the membrane 30 falls below a threshold. If the threshold is undershot, then the vibration of the membrane 30 so low that it is able to register an echo of an ultrasonic pulse. The second process step 120 and the third process step 130 are repeated by the adjustment loop until the threshold is undershot. The second 120 and the third process step 130 make up together with the matching loop 160 a control loop 170 , After discharging the third process step 130 is in a fourth process step 140 the echo of the emitted in the first step ultrasonic pulse 110 over the membrane 30 detected.

That of the membrane 30 recorded echo of the emitted in the first step ultrasonic pulse is by the second 42 and / or third segment 43 the piezoceramic 40 converted into a measured value. In a subsequent fifth process step 150 becomes the elapsed time between the emission of the ultrasonic pulse in the first process step 110 and recording the echo of the ultrasonic pulse in the fourth method step 140 determined. From the elapsed time results in a duration of the ultrasonic pulse, based on the distance of an object can be determined.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 19507650 A1 [0002]
• US 3698051 [0003, 0003]
• DE 19605502 C1 [0004]

Claims (11)

Ultrasonic sensor ( 10 ) for detecting a distance of an object, with a housing ( 20 ) and a damping mass ( 21 ), the housing ( 20 ) at least partially filled with a membrane ( 30 ) and a piezoceramic ( 40 ) and an electrical contact ( 22 ) with at least one electrode ( 23 ) and a ground electrode ( 25 ), characterized in that the piezoceramic ( 40 ) into at least three segments ( 41 . 42 . 43 ), where a first segment ( 41 ) with the ground electrode ( 25 ) and a second ( 42 ) and third segment ( 43 ) in each case via separate electrodes ( 23 . 24 ) are contacted. Ultrasonic sensor ( 10 ) according to claim 1, characterized in that the second segment ( 42 ) for reducing a vibration of the membrane ( 30 ) is trained. Ultrasonic sensor ( 10 ) according to claim 1 or 2, characterized in that the third segment ( 43 ) for detecting a vibration of the membrane ( 30 ) is trained. Ultrasonic sensor ( 10 ) according to one of claims 1 to 3, characterized in that at least one further segment ( 44 ) for detecting a vibration and / or for reducing a vibration of the membrane ( 30 ) in the piezoceramic ( 40 ) is trained. Ultrasonic sensor according to one of claims 1 to 4, characterized in that the first ( 41 ) Segment, the second segment ( 42 ) and the third segment ( 43 ) enclose concentrically. Ultrasonic sensor ( 10 ) according to one of claims 1 to 5, characterized in that the segments ( 41 . 42 . 43 . 44 ) mechanically coupled to each other as measuring and control elements of a control loop ( 170 ) are formed. Ultrasonic sensor ( 10 ) according to one of claims 1 to 6, characterized in that the segments ( 41 . 42 . 43 ) by a lasered interruption ( 50 ) on a surface ( 60 ) of the piezoceramic ( 40 ) are formed. Method for measuring an object distance by means of an ultrasonic sensor ( 10 ), which has a membrane ( 30 ) and a piezoceramic ( 40 ), wherein the piezoceramic ( 40 ) into at least three segments ( 41 . 42 . 43 ), where a first segment ( 41 ), which is a second ( 42 ) and a third segment ( 43 ), with a ground electrode ( 25 ) and the second ( 42 ) and the third segment ( 43 ) each via a separate electrode ( 23 . 24 ), with the following method steps: a) generating a vibration of the membrane ( 30 ) for emitting an ultrasonic pulse by exciting the second ( 42 ) and / or third segment ( 43 b) detecting a deflection of the membrane ( 30 ) through the third segment ( 43 ), c) exciting the second segment ( 42 ) for generating a counter-vibration, which is suitable, the deflection of the membrane ( 30 ), d) detecting the echo of the ultrasound pulse emitted in step a) via the membrane ( 30 ) by means of the second ( 42 ) and / or third segment ( 43 ) of the piezoceramic ( 40 ), and e) detecting a running between the step a) and step d) running time of the ultrasonic pulse and determining the object distance based on the determined transit time. Method for measuring an object distance by means of an ultrasonic sensor ( 10 ) according to claim 8, characterized in that the steps b) and c) in a balancing loop ( 160 ), wherein step c) is ended when in step b) falls below a threshold value of the deflection of the membrane ( 30 ) is detected. Method for measuring an object distance by means of an ultrasonic sensor ( 10 ) according to one of claims 8 or 9, characterized in that at least one further segment ( 44 ) in the piezoceramic ( 40 ), wherein the further segment ( 44 ) with the second ( 42 ) and third segment ( 43 ) as measuring and / or control elements in a control loop ( 170 ), which controls the deflection of the membrane ( 30 ) in step c). Use of an ultrasonic sensor ( 10 ) according to one of claims 1 to 7 for measuring an object distance in a driving assistance system of a motor vehicle.

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