Ultrasonic proximity switch

Abstract

To provide an ultrasonic proximity switch.SOLUTION: What are shown and described are a device and a method for detecting an actuator by a sensor by irradiating the actuator with sound waves. The device is used in particular in safety applications. The sensor and the actuator may move relative to each other. The sensor includes a sound wave transmitter, a sound wave receiver, and a calculation unit. The sound wave transmitter is designed to transmit sound waves in the direction of the actuator. The sound wave receiver is designed to capture sound waves reflected by the actuator and convert the sound waves into an analog signal. The calculation unit detects the actuator by converting the analog signal into a digital signal and comparing the digital signal with a reference signal.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The invention relates to a device for detecting an actuator by means of a sensor according to the general terms of claim 1 and to a method for detecting an actuator by means of acoustic waves according to claim 18. [Background technology]

[0002] Ultrasonic sensors are used today, for example, to measure distances. Ultrasonic waves are emitted by a transmitting source, which strikes an obstacle and reflects a reflected wave in the form of an ultrasonic wave returning towards the sensor, where it is picked up by at least one receiver. The distance between the sensor and the obstacle is determined using the measurement time between transmitting and receiving the ultrasonic wave. The information given by the ultrasonic sensor is therefore limited to whether an obstacle is present or not, and at what distance this object is from the ultrasonic sensor. To increase the quality of the measurement, an ultrasonic sensor may have several transmitting sources and several receivers.

[0003] Ultrasonic sensors are currently used little or not at all in safety applications. One drawback of ultrasonic sensors is that they rely on reflected sound or waves, which are sensitive to external influences such as temperature. Another drawback is the increased complexity of the system to detect small three-dimensional structures.

[0004] Chinese patent application CN114758367 discloses a fingerprint identification device arranged under a printing plate. The identification device comprises an ultrasonic unit, a piezoelectric layer, a first electrode located on the piezoelectric layer and a second electrode located under the piezoelectric layer. The ultrasonic unit is used to transmit ultrasonic signals to the finger and to receive ultrasonic detection signals sent back from the finger. Under this ultrasonic unit is a silicon substrate with a thickness of about 50 μm, which has a switching unit used to generate ultrasonic signals and to process the ultrasonic detection signals. A piezoelectric layer with a thickness between 4 and 20 micrometers is applied to the silicon substrate and generates a resonant frequency between 8 and 26 MHz. A connection layer is advantageously provided between the ultrasonic unit and the pressure plate.

[0005] During fingerprint identification, the circuit unit generates an excitation signal to vibrate the piezoelectric layer. The resulting ultrasonic signal is transmitted to the finger and reflected. Based on the inverse piezoelectric effect, a potential difference is generated between the first electrode 112 and the second electrode 113, and a corresponding electrical signal is obtained. The electrical signal is processed to obtain the fingerprint pattern portion of the finger.

[0006] GB2529484 discloses an analysis device having an input section for receiving ultrasonic data related to a contact surface between a first element and a second element during frictional contact, and an output section for outputting data related to at least one of a contact stress at the first element and a contact load applied to the first element. In a processing section, the ultrasonic data is processed to determine ultrasonic travel time data and obtain output data. The propagation direction of the ultrasonic wave perpendicular to the contact surface has a maximum component. The process of determining the ultrasonic travel time data and the ultrasonic time of flight is independent of phase changes that depend on the contact conditions at the contact surface. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Chinese Patent Application No. CN114758367 [Patent Document 2] UK Patent Application No. GB2529484 Summary of the Invention [Problem to be solved by the invention]

[0008] It is therefore an object of the present invention to specify a device for detecting an actuator using acoustic waves, which is both inexpensive to manufacture and to use, and which is robust to external influences and the sensitivity of the acoustic wave sensor to changes in the detected actuator. [Means for solving the problem]

[0009] This problem is solved by a device for detecting an actuator by irradiating it with sound waves via a sensor having the features of claim 1.

[0010] The device is used in particular as an ultrasonic proximity switch in safety applications. The sensor can be moved relative to the actuator and comprises at least one sonic transmitter, at least one sonic receiver and at least one calculation unit. The sonic transmitter is designed to transmit sonic waves in the direction of the actuator, while the sonic receiver is designed to capture the sonic waves reflected by the actuator and convert them into an analog signal. The calculation unit detects the actuator by converting the analog signal into a digital signal and comparing the digital signal with a reference signal.

[0011] The computation unit has a reference signal stored in the memory, which is usually assigned to a specific actuator. The sensor is designed to emit sound waves and in turn receive the reflected sound waves. By comparing the reflected sound waves with the reference signal already stored in the computation unit, the computation unit can determine whether the sound waves are reflected by the actuator associated with the reference signal. The device can use the sensor and the signal received by the sensor to detect the actuator illuminated by the sound waves and, if necessary, identify the actuator. The device allows to determine whether the actuator is in a specific position opposite the sensor. The actuator can be in contact with the sensor or at a specific distance from the sensor. When used in safety applications, the interaction between the sensor and the actuator has a safety-related function. Upon successfully detecting the actuator, the sensor can determine with the computation unit whether the taught actuator is in the intended location, which can be equated to ensuring the safety of the system. For example, the closed state of a door or window can be monitored using this device. The actuator can be placed in the door or window while the sensor is placed in the frame, or vice versa. Only when the door or window is fully closed and the distance between the door or window and the frame is minimal, will unambiguous detection of the actuator occur which equates to a door or window closed state.

[0012] The reference signal contains information to detect the actuator. A requirement of the reference signal is that it allows a comparison with the measurement signal. The reference signal may be stored in any form in the calculation unit, meaning that the type or form of the reference signal has no limiting effect on the subject matter of the present invention. It is conceivable that the reference signal may be in the form of a time function, a table or a graph, this being a non-exhaustive list of data representation options. The reference signal should ideally contain at least a correlation between time and amplitude.

[0013] The stored reference signal or one or more replicas of the reference signal may be adapted to changing ambient conditions, for which purpose the replica of the reference signal may be recognized, identified, updated at predefined intervals or based on other criteria in the actuators applied.

[0014] When the reflected sound wave coincides again, both the original and updated reference signals are used.

[0015] Preferably, the actuator has a three-dimensional pattern from which the sound waves are reflected and altered. This allows the realization of various actuators with similar structure, which only differ from each other by their three-dimensional pattern. At the same time, the three-dimensional pattern helps to more reliably determine the identity of the actuator, in that a first three-dimensional pattern shows a clear deviation from the three-dimensional pattern of the remaining actuators, thereby increasing the reliability and tamper protection of the actuator identification.

[0016] The sensor preferably comprises two calculation units, each of which has access to a reference signal. In principle, these calculation units may perform the conversion to a digital signal independently or may only be provided with an analog-to-digital transducer. The use of two calculation units may serve as a control, in that further steps are only performed if both calculation units show the same result for a coincidence of the measurement signal with the reference signal. The conversion by the two calculation units may also be performed in various ways independent of each other, for example by different analog-to-digital transducers (A / D transducers), integrated in a microcontroller (MCU) or externally as a dedicated component. These differences may also be achieved in the sampling frequency. This increases the safety of the conversion function to a digital signal during operation.

[0017] The sound waves emitted by the sensor reach the three-dimensional pattern via a forward path and, after being reflected by the pattern, travel the same path in the opposite direction. The forward path between the sensor and the pattern has a minimum length that is compatible with the sensor. A lower limit for the forward path is used to ensure that a certain time passes after the sound wave is emitted by the sensor until the reflected wave is received by the receiver. The duration also has a lower limit such that it must not degrade the effect if the transmitter and receiver are formed by the same component. In one such embodiment, the membrane used to generate the sound waves is also used to receive the reflected waves. The minimum time is defined by the time it takes for the membrane to return to its rest state after excitation.

[0018] The actuator preferably has a contact surface for the sensor, and the three-dimensional pattern portion is located in the actuator at a distance from the contact surface. The distance between the pattern portion (encryption portion) and the contact surface must be at least equal to the forward path. The actuator may be designed to contact the sensor. This contact should preferably be made via the contact surface of the actuator. This allows for convenient introduction of sound waves from the sensor to the actuator and from the actuator back to the sensor. The ultrasonic transducer of the sensor preferably contacts the actuator at the intended contact surface. In this case, the pattern portion of the actuator is located inside the actuator after the forward path, i.e. opposite the contact surface or at a distance from the contact surface. By locating the three-dimensional pattern portion on the opposite side of the contact surface, the distance between the pattern portion and the contact surface is maximized.

[0019] In a preferred embodiment of the device, the actuator is placed opposite the sensor, such that the sonic transmitter of the sensor is directed towards the pattern of the actuator when the actuator and the sensor are in contact or when the sensor and the actuator are at a minimum required distance from each other. The sensor is used to detect the actuator and the three-dimensional pattern of the actuator. In some applications, it may be sufficient to realize detection of the actuator only when the sensor is in contact with the actuator or when the distance between the sensor and the actuator is minimal. This makes it possible to reduce the window in which the actuator can be detected by the sensor, thus bringing about a higher safety hurdle when using the device in safety applications. Detection of the actuator is only possible when the sensor and the actuator are as close together as possible.

[0020] In a further preferred embodiment, the sonic transmitter and receiver must be in contact with the contact surface of the actuator in order to detect the actuator. This means that the sensor must be in contact with the actuator in order to successfully detect the actuator. In use, this feature ensures that the door is closed without any gaps. As soon as the door is opened, there is a slight gap and the safety of the system is no longer guaranteed, which can be detected by the sensor, for example.

[0021] The sonic receiver prefers to capture the entire reflected sound wave. Recording the entire reflected sound wave means that the sonic receiver receives the reflected sound wave locally at one point and converts it into a single signal. This allows the device to function with just one sensor, simplifying manufacturing, reducing space requirements and minimizing costs.

[0022] The calculation unit has the task of effecting a comparison between the received signal and a reference signal. The processing speed of the processing unit effecting this adjustment is fastest if the processing unit has the most direct access to the reference signal. Preferably, the reference signal is stored in the calculation unit. This gives the calculation unit the most direct access to the reference signal. A fast processing speed of the calculation unit may be particularly important in safety applications.

[0023] Ideally, the pattern of the actuator has a three-dimensional structure, which has the advantage that it undergoes specific changes when the sound wave is reflected, making it easier to infer the actuator from the reflected sound wave, and at the same time, the three-dimensional structure provides a wide variety of modification options to generate different three-dimensional pattern parts.

[0024] In a further preferred embodiment, the pattern portion comprises two faces facing the contact surface of the actuator, each of the two faces having a different distance from the contact surface. Splitting the pattern portion into two faces, each with a different distance from the contact surface, forms a three-dimensional structure. At the same time, splitting into two faces with different distances to the contact surface results in a simple structure with a large number of possible variations by changing the distance of one or both faces to the contact surface.

[0025] As already mentioned above, the reflected sound waves reflected by the two faces of the pattern are preferably received and evaluated in their entirety. The evaluation of the entire sound waves also brings advantages when designing the pattern. This means that the difference between the distances between the two faces and the contact face can be made quite small. Preferably, the difference between the distances of these two faces is less than 1 mm, preferably less than 0.5 mm, even more preferably less than 0.3 mm, but more than 0.01 mm, preferably more than 0.05 mm.

[0026] Advantageously, the calculation unit recognises the actuator pattern portion by comparing the actuator pattern portion with a reference signal, the calculation unit being responsible for effecting the comparison between the measurement signal and the reference signal.

[0027] The calculation unit is responsible for the recognition of the actuator. Preferably, the calculation unit generates a binary signal based on the detection of the actuator. The binary signal makes it possible to state for example whether the actuator is present at the transmitter / receiver or not. This can be of great importance in safety-related applications, since the device states a clear state of the device. For example, such a state can be a door safely closed.

[0028] In a further preferred embodiment, the calculation unit generates a switch-off signal if the actuator is not successfully detected. The generation of the switch-off signal is usually of considerable importance in safety applications. The detection of the actuator is the basic state in which safety is guaranteed. As long as the actuator is detected, the safety of the system is guaranteed. The need to detect a dangerous situation as quickly as possible and to transfer this situation to the control unit can be met by generating a switch-off signal as quickly as possible. The generation of the switch-off signal by the calculation unit provides a fairly fast reaction to any change in the allocation between transmitters and actuators.

[0029] Ideally, the acoustic transmitter and the acoustic receiver are co-located, in particular using the same membrane for transmitting and receiving the acoustic waves. This means that the origin of the acoustic wave coincides with the reception point of the reflected acoustic wave. Generally, the reflected acoustic wave is received from the direction from which the acoustic wave is emitted. By co-locating the transmitter and the receiver, the sensor can have a compact design. Furthermore, if the transmitter and the receiver use the same membrane, elements such as a transducer comprising the transmitter and the receiver can also be used. Using the same membrane for the transmitter and the receiver makes the sensor, and therefore the whole device, less expensive to manufacture. Preferably, a piezoelectric ultrasonic transducer is used, which can be used as both a transmitter and a receiver.

[0030] Preferably, the sonic transmitter generates sonic waves at frequencies between 300 kHz and 20 MHz, preferably between 350 kHz and 8 MHz, particularly preferably between 1 and 4 MHz. Ultrasound is exclusively within this range. The use of this frequency range does not cause any undesirable environmental pollution.

[0031] The actuator is preferably made of plastic. Preferably, plastics with a low sound speed that remains constant with temperature, such as POM (polyoxymethylene), are used. Preferably, plastics are used in which sound propagation is less than 2500 m / s and the effect of temperature changes is less than 2 m / s per degree Celsius. The advantage of plastics is that they are convenient for the manufacture of complex shapes and structures, such as those that can occur in the pattern of the actuator. At the same time, plastics have the necessary properties for the reflection of sound waves, so that they can be well received and evaluated in their entirety.

[0032] A further aspect of the invention relates to a method for detecting an actuator using acoustic waves. The acoustic waves are emitted by an acoustic transmitter and captured by an acoustic receiver. The method comprises transmitting acoustic waves to a pattern of the actuator and receiving the acoustic waves reflected by the pattern of the actuator by the acoustic receiver. The received acoustic waves are converted into an electrical signal. It is further provided in the method according to the invention that this signal is compared by a calculation unit with a reference signal stored in the calculation unit, a binary signal is generated by the calculation unit as a result of the comparison, and the detection of the actuator is determined based on the binary signal. The comparison of the measurement signal and the reference signal makes it possible to determine a match between the two signals. If the match shows a predefined similarity, the sonicated actuator is unambiguously recognized as a taught reference actuator. This means, for example, that it can be stated whether or not a taught (reference) actuator is present in the sensor. Advantageously, the reflected acoustic waves are captured in their entirety by the acoustic receiver. This means that a single acoustic receiver captures the reflected acoustic waves and generates a single measurement signal based on the received and reflected acoustic waves. This allows the sensor to be designed as simply as possible, since it only needs to comprise an acoustic transmitter and an acoustic receiver.

[0033] Preferably, the reference signal is generated in a first step by teaching the actuator. Teaching the actuator refers to performing a reference measurement. For this purpose, the actuator is placed at a target position and is sounded by a sensor. A receiver in the sensor captures the reflected sound waves and generates a signal based on the measured sound waves, thus generating the reference signal. The reference signal can therefore be understood as a template for the taught actuator.

[0034] The method is preferably used in safety applications, where a warning or switch-off signal or a safety cancellation is generated if the actuator is not successfully detected. The method can be used to check whether the actuator is in the intended location and whether it is the taught actuator, making it ideal for use in safety applications. The state of a door or window can be reliably monitored using such a method, and a warning or shut-off signal can be generated immediately when the door or window is opened. Another advantage in this respect is the high sensitivity of the method according to the invention. For example, if the actuator is only slightly displaced from its original state, i.e. in the range of 0.1 to 1 mm, the reflected sound wave deviates from the reference signal quite quickly. The high sensitivity of the method allows only small tolerances to be introduced into the monitored device, resulting in accurate inspection or monitoring of the monitored device.

[0035] Advantageously, the actuator has a contact surface with which the sonic transmitter detects the actuator. When the sonic transmitter contacts the contact surface of the actuator, the sonic waves propagate only within the housing of the actuator. This means that there are no disturbing influences from the environment on the sound waves and their measurement, such as different distances between the actuator and the sensor or air conditions between the actuator and the sensor. Provided that there is perfect contact between the sensor and the actuator, the provision of a contact surface allows for interference-free measurement.

[0036] Preferably, the acoustic wave transmitter emits acoustic waves orthogonal to the contact surface, which makes the most efficient use of the actuator volume and allows better discrimination between reflected acoustic waves.

[0037] Any of the above features may be combined in any combination, unless the features are mutually exclusive. In particular, where preferred ranges are specified, further preferred ranges result from the combination of the minimum and maximum specified within the range.

[0038] The invention will be explained in more detail below with reference to the drawings in schematic form, in which: The drawings show schematic views that are not to scale. [Brief description of the drawings]

[0039] [Figure 1] 1 is a cross-sectional view of a device with a sensor according to the present invention, the device comprising an acoustic wave sensor, an acoustic wave receiver and an actuator. [Diagram 2] FIG. [Diagram 3] 1 shows six graphs comparing measurement signals from six actuators with a reference signal. [Figure 4] 1 is a graph with correlation curves for various actuators. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] Hereinafter, the same reference numbers represent identical or functionally identical elements (in the various figures). Additional apostrophe symbols may be used to distinguish between similar elements or functionally identical or functionally similar elements in further versions.

[0041] FIG. 1 shows a diagram of a device 11 composed of two separate components. The first component is the sensor 13. The sensor 13 comprises an acoustic transmitter 17 and an acoustic receiver 19, which are connected to an analog front end 21. Two passages 23, 25 lead from the analog front end 21 to the outside. The passages 23, 25 each have a calculation unit 24, 26. The acoustic transmitter 17, also called transmitter for short, and the acoustic receiver 19, also called receiver for short, are mounted on the front side of the sensor 13 in approximately the same position. The transmitter and the receiver may be the same component, in which case the only difference between the transmitter and the receiver is the function of transmitting and receiving acoustic waves. Preferably, as acoustic transducers, piezoelectric sensors are used that operate at frequencies between 300 kHz and 20 MHz.

[0042] The second component is formed by the actuator 27. In Fig. 1, the actuator 27 is in contact with the transmitter 17 and the receiver 19. The side of the actuator 27 in contact with the transmitter 17 and the receiver 19 is the contact surface 29 of the actuator. The pattern section 31 is provided on the actuator 27 on the side opposite the contact surface 29 at a distance from the contact surface 29. In the example shown in Fig. 1, the pattern section 31 is formed by a gradation section. The pattern section 31 thus has two faces 33, 33', which are directed towards the contact surface 29 and are parallel to each other and to the contact surface. The two faces 33, 33' differ in distance from the contact surface 29. The difference may be between 0.05 and 3 mm, preferably between 0.1 and 2 mm, particularly preferably between 0.5 and 1.5 mm.

[0043] The transmitter 17 is intended to emit an acoustic wave 35 in the direction of the actuator 27. When the actuator 27 comes into contact with the transmitter 17, the acoustic wave 35 emitted by the transmitter propagates through the actuator to the pattern 31. The pattern 31 of the actuator limits the propagation of the acoustic wave in the actuator. The acoustic wave 35 strikes the pattern 31 and is reflected by it. The reflected acoustic wave 35 travels the same path in the opposite direction and reaches the receiver 19. The receiver 19 has a membrane that is set to vibrate due to the reflected acoustic wave. The vibration of the receiver membrane is recorded as an analog signal. The analog signal may be further processed in an analog receiver circuit (front end) 21, for example by amplifying or filtering the analog signal. After processing in the front end 21, the analog signal is transferred to the respective calculation units 24, 26 in the two evaluation paths 23, 25.

[0044] Each of the two calculation units 24, 26 has a memory in which a reference signal is stored. After receiving an electrical signal from the receiver, each calculation unit 24, 26 compares the electrical signal with the stored reference signal and determines the degree of similarity or match between the two signals. If the match exceeds a certain degree or value, this means that the previously taught actuator 27 is present in the sensor.

[0045] The reference signal can be generated in various ways. One option is to perform a reference measurement and generate a reference signal before empowering the device. For this purpose, the actuator 27 is guided to the sensor so that the transmitter 17 and the receiver 19 of the sensor rest on the contact surface 29 of the actuator. Irradiating the actuator 27 with sound waves gives rise to a signal in the receiver 19, which is transferred to the calculation units 24, 26 and, after any signal processing, is stored by the calculation units 24, 26 as a reference signal. This actuator 27 is thus read by the sensor 13 with this reference measurement.

[0046] 2 shows a possible configuration of an actuator 27 suitable for a device according to the invention. According to the illustrated exemplary embodiment, the actuator comprises a housing 28 in which the three-dimensional pattern 33, 33' is integrated. In principle, however, it is also possible to manufacture the actuator from a solid material in which the three-dimensional pattern is embedded. In the present case, the housing of the actuator is designed as a cylinder with a stepped base surface 33, 33', which may be designed as a hollow or solid cylinder.

[0047] One side of the actuator serves as the contact surface 29. The opposite side of the contact surface 29 serves as the pattern portion 31. The distance between the contact surface 29 and the pattern portion 31 is divided into two paths, the so-called forward path 39 and the variable path 40. The forward path 39 is adjacent to the contact surface 29 and has the same length for all actuators 27. The variable path 40 forms the portion from the forward path 39 to the pattern portion 31. The forward path 39 is of smallest dimension due to the distance between the contact surface 29 and the pattern portion 31.

[0048] It is possible to manufacture further actuators 27, each having a different distance, i.e., variable path 40, between the pattern surface 33 and the contact surface 29, and accordingly each will produce a different reflection of the acoustic wave 35, resulting in a different signal.

[0049] The sound wave 35 is captured in its entirety by the receiver and transmitted as an analog signal. The analog signal can be processed in the analog front end 21 to simplify the comparison between the signals. The amplitude of the signal is plotted as a function of the measurement time, thus forming the time function of the signal. The actuator 27 is detected by the coincidence of the signal functions thus generated. The adjustment is generally performed by comparison of the measurement signal 41 with a reference signal 43. The reference signal can be generated in various ways.

[0050] The first way to generate the reference signal 43 is to calculate an average value, for which each data point of a measurement series is averaged over several measurement series. The choice of the measurement value for calculating the average value may remain undefined, so that the measurements obtained as the measurements are performed are continuously included in the calculation of the average value. The format of the measurement signal 41 and the reference signal 43 must match so that both signals can be compared. To ensure this, the signals may undergo digital signal processing. The reference signal 43 may then be compared with the measurement signal 41, for example, by correlation or cross-correlation. The cross-correlation is used to calculate a number indicating the deviation between the two signal functions. If this number is close to zero, the actuators are in agreement. To generate a binary output, a limit value may be defined for the cross-correlation result, below which the actuator is considered to be correctly recognized. An alternative to cross-correlation is to use the mean squared error method, which forms a sum of the mean squared deviations. The smaller this sum is, the more similar the functions or signal curves being compared are. To detect the actuator 27, a limit value for the sum of the squared deviations must now be defined. If the result is below this limit, there is a similarity and the actuator is recognized as distinct.The reference and measurement signals are usually available in a normalized state before any adjustments are performed.

[0051] An alternative approach to the first method of providing a comparison with a reference signal described above is the use of artificial intelligence. To recognize the actuators, training data is fed into the neural network. This training data must first be generated. For this purpose, several different actuators 27 are manufactured, read by the sensor 13 and the signals of the actuators 27 are stored in a database. The measurements of the actuators 27 read by the sensor 13 can be performed under different boundary conditions so that, for example, the influence of the contact surface 29 and the contact between the sensor 13 and the actuator 27 can be included in the training data. The data is divided into several classes, the number of classes being equal to the number of different actuators plus one. The additional class is the class to which all signals that do not fit into one of the actuator classes are assigned. This means that each signal recorded by the sensor is assigned to a class. The calculation unit 24 is responsible for assigning the received signals 41 to the respective classes. The calculation unit 24 uses an artificial neural network or other AI methods that have been trained on the training data and have developed a classification mechanism. The assignment of the received signal 41 to each class is under comparison of the received signal 41 with a reference signal 43 .

[0052] Figures 3 and 4 show graphs with which the above mentioned correlations can be made and actuators 27 can be detected. Figure 3 shows six graphs, in each of which the measurement signal 41 from a particular actuator is plotted together with the reference signal 43. The reference signal 43 is shown by a thick line, while the measurement signal 41 is formed by a thin line. In this example, the reference signal 43 is formed by an actuator 27 with a single encryption depth of 18 mm. The six graphs show the reflected sound waves for actuators 27 with encryption depths of 17.5 mm, 17.8 mm, 18 mm, 18.1 mm and 19 mm, the reflected sound waves being recorded by the receiver 19 and transferred in normalized form to the calculation unit 24. Two series of measurements were tested for an encryption depth of 18 mm. Figure 4 shows the maximum and minimum correlation values ​​between the measurement signal 41 and the reference signal 43 for various actuators 27. On the X-axis of the graph in Figure 4, actuators 27 are plotted with increasing encryption depths, while the Y-axis shows the correlation values. Upper and lower limits are defined for the correlation values, represented in the graph by two horizontal lines. The results in Figure 4 show that the correlation for those actuators with encryption depths from 17.8mm to 18.1mm is within the limits. In comparison, the reference signal 43 is formed by the actuator 27 with an encryption depth of 18mm.

[0053] Another possible way in this or similar embodiment to match the measurement signal 41 with the reference signal 43 is to generate a difference signal between these two signals. In contrast to previous approaches, which assigned some actuators to different classes, we try to obtain a binary classification by generating a difference signal or other methods. This means that the result is a binary statement as to whether the measurement signal 41 matches the reference signal 43 sufficiently or not. In case of perfect match, the measurement signal 41 is equal to the reference signal 43 and the difference between the two signals is zero. When the reference actuator is sonicated, the difference between the two signals may deviate from zero. For this reason, a tolerance is defined in the form of a threshold for the difference, within which the detection of the reference actuator is still considered unambiguous. The binary classification is used only for the detection of a single actuator, since it makes it possible to state whether this single actuator is in exactly the same position at the time of the measurement as it was during the reference measurement. In safety applications, for example, the binary classification may be used to check the closed state of a door.

[0054] The proximity switch works as follows: sound waves are emitted for a first predefined time period between 0.25 μs and 5 μs depending on the operating frequency of the ultrasonic transducer by exciting the ultrasonic transducer with two pulses. The reflected sound waves are then detected for a second predefined time period between 0 μs and 200 μs. Preferably, the detection of the reflected sound waves starts only between 30 μs and 60 μs after transmission so that the attenuation of the ultrasonic transducer after excitation by the control pulse is not included in the measurement. The current measurement window of the received reflected waves is between 55 μs and 95 μs.

[0055] Although specific embodiments have been described above, it will be apparent that various combinations of the disclosed embodiments may be used, unless the embodiments are mutually exclusive. [Explanation of symbols]

[0056] 11 Devices 13 Sensors 17 Sonic Transmitter 19 Sonic Receiver 21 Analog Front End 23 First Passage 24 First Calculation Unit 25 Second Passage 26 Second Computation Unit 27 Actuator 28 Case 29 Contact surface 31 Pattern section 33 Reflective surface of pattern 35 Sound Waves 39 Forward Route 40 Variable Path 41 Measurement Signal 43 Reference Signal

Claims

1. A device (11) for detecting an actuator (27) by a sensor (13) by subjecting said actuator (27) to sound waves (35), in particular for safety applications, comprising: - said sensor (13) and said actuator (27) are movable relative to each other; said sensor (13) comprises an acoustic transmitter (17), an acoustic receiver (19) and a calculation unit (24), said acoustic transmitter (17) and said acoustic receiver (19) being realizable as a single component; a device (11) in which the acoustic wave transmitter (17) is intended to transmit the acoustic waves (35) in the direction of the actuator (27) and the acoustic wave receiver (19) is intended to capture the acoustic waves reflected by the actuator (27) and to convert them into an analog signal, A device (11), characterized in that the calculation unit (24) converts the analog signal into a digital signal and performs the detection of the actuator (27) by comparison with a reference signal (43).

2. 2. The device (11) according to claim 1, characterized in that the actuator (27) has a patterned portion (31) from which the sound waves (35) are reflected and modified.

3. 3. The device (11) according to claim 1 or 2, characterized in that the sensor (13) comprises two calculation units (24, 26) each having a reference signal (43).

4. 4. The device (11) according to claim 2 or 3, characterized in that the actuator (27) has a contact surface (29) for the sensor (13), and the pattern portion (31) is arranged at a distance from the contact surface (29).

5. The device (11) according to any one of claims 2 to 4, characterized in that the actuator (27) is arranged opposite the sensor (13) so that when there is contact or a minimum possible distance between the sensor (13) and the actuator (27), the acoustic transmitter (17) of the sensor (13) is directed towards the pattern portion (31) of the actuator (27).

6. The device (11) according to any one of claims 2 to 5, characterized in that the ultrasonic transmitter (17) and the ultrasonic receiver (19) for detecting the actuator (27) are mounted on the contact surface (29) of the actuator (27).

7. 7. The device (11) according to any one of the preceding claims, characterized in that the acoustic receiver (19) captures the reflected acoustic waves in their entirety.

8. The device (11) according to any one of the preceding claims, characterized in that the reference signal (43) is stored in the calculation unit (24).

9. The device (11) according to any one of claims 2 to 8, characterized in that the pattern portion (31) of the actuator (27) has a three-dimensional structure.

10. A device (11) according to any one of claims 4 to 8, characterized in that the pattern portion (31) has two faces (33) directed towards the contact surface (29) of the actuator, each of the two faces (33) having a different distance from the contact surface (29).

11. 11. The device (11) according to claim 10, characterized in that the difference between the distances of the two faces (33) is less than 1 mm, preferably less than 0.5 mm, and even more preferably less than 0.3 mm.

12. 12. The device (11) according to any one of claims 2 to 11, characterized in that the calculation unit (24) infers the pattern portion (31) of the actuator (27) by comparison with the reference signal (43).

13. The device (11) according to any one of the preceding claims, characterized in that the calculation unit (24) generates a binary signal based on the detection of the actuator (27).

14. The device (11) according to any one of the preceding claims, characterized in that the computing unit (24) generates a switch-off signal if the actuator (27) is not successfully detected.

15. 15. The device (11) according to any one of claims 1 to 14, characterized in that the acoustic transmitter (17) and the acoustic receiver (19) are arranged at the same location, in particular using the same membrane for transmitting and receiving acoustic waves.

16. 16. The device (11) according to any one of claims 1 to 15, characterized in that the acoustic wave transmitter (17) generates the acoustic waves (35) at a frequency between 300 kHz and 20 MHz, preferably between 350 kHz and 8 MHz, particularly preferably between 1 and 4 MHz.

17. 17. The device (11) according to any one of the preceding claims, characterized in that the actuator (27) is made from a plastic material characterized by a low sound speed and a low temperature dependence of said sound speed.

18. A method for recognizing an actuator (27) using sound waves (35) transmitted by a sound wave transmitter (17) and received by a sound wave receiver (19), the method comprising: - transmitting said acoustic waves (35) to a pattern portion (31) of said actuator (27); - receiving, by the acoustic wave receiver (19), the acoustic waves reflected by the pattern portion (31) of the actuator (27); - converting said sound waves into an electrical signal (41); - comparing said signal by a calculation unit (24) with a reference signal (43) stored in said calculation unit (24); - generating a binary signal as a result of said comparison by said calculation unit (24) and determining the detection of said actuator (27) based on said binary signal; A method comprising:

19. 19. A method according to claim 18, characterized in that in a first step, the reference signal (43) is generated by teaching the actuator (27).

20. 20. The method according to claim 18 or 19, characterized in that the method is used in safety applications and a warning signal or a safety cancel is generated if the actuator (27) is not successfully detected.

21. 21. The method according to any one of claims 18 to 20, characterized in that the actuator (27) has a contact surface (29) and the acoustic transmitter (17) is in contact with the contact surface (29) so as to detect the actuator (27).

22. 22. The method according to claim 21, characterized in that the acoustic wave transmitter (17) transmits acoustic waves directed essentially orthogonally to the contact surface (29).

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