METHOD AND DEVICE FOR PROVIDING A DIGITAL SENSOR SIGNAL FROM AN ULTRASONIC SENSOR

Description

[0001] The present invention relates to a method for providing a digital sensor signal of an ultrasonic sensor for signal transmission to a signal receiver, in which a -preferably digital- output signal of the ultrasonic sensor is processed into the digital sensor signal for signal transmission.

[0002] The invention further relates to a corresponding device for providing a digital sensor signal of an ultrasonic sensor for signal transmission to a signal receiver, a corresponding ultrasonic sensor device with an ultrasonic sensor and such a device, and a corresponding ultrasonic sensor system.

[0003] Document DE 10 2017 108348 deals with the configuration of ultrasonic sensor systems. During sensor configuration, the analog-to-digital converter parameter settings are optimized to achieve, for example, optimal detection results or a reduction in the amount of data to be transmitted. To achieve this, the analog-to-digital converters of the ultrasonic sensors must have adjustable converter parameters. Different bit rates or delta coding are described.

[0004] Document DE 10 2008 044 058 B4 describes a method and a system for providing a digital sensor signal from an ultrasonic sensor for signal transmission via LIN communication (LIN: Local Interconnect Network) to a control unit of this sensor. The system processes an output signal from the sensor into the digital sensor signal for signal transmission via LIN communication.

[0005] The terms "signal transmission" and "signal transmission" generally refer to information and data transmission. Data transmission between an ultrasonic sensor and the electronic control unit (ECU) responsible for that sensor in motor vehicles currently takes place using standardized transmission protocols, such as the LIN bus protocol.

[0006] The transmission systems used for this purpose are limited in their data rate. While the ultrasonic sensor itself, with the help of an analog-to-digital converter with a high sampling rate and high quantization, provides detailed information about the membrane vibrations when receiving an ultrasonic signal as a measurement signal, in today's systems, only highly lossy images of the actual measurement data are available in the control unit.

[0007] The data rate of the transmission between the ultrasonic sensor and the control unit always results from the sampling rate and quantization used. If the sampling rate of the measurement signal, referred to below as the output signal of the ultrasonic sensor or raw signal, is too low (whereby a reduction in the sampling rate also results in a reduction in the necessary data rate), errors such as aliasing or a significantly reduced resolution arise due to the loss of information. Conventional quantization with a low number of bits, usually less than 5, generates high quantization noise, which in the worst case can prevent meaningful use of the data. An improvement in quantization noise can sometimes be achieved through nonlinear characteristics. However, this approach is also severely limited by the number of possible quantization states resulting from the quantization bits.

[0008] Based on the above-mentioned prior art, the invention is therefore based on the object of specifying measures that enable the sensor signal to be transmitted as accurately as possible, even with a limited transmission bandwidth.

[0009] The object is achieved according to the invention by the features of the independent claims. Advantageous embodiments of the invention are specified in the subclaims.

[0010] In the method according to the invention for providing a digital sensor signal from an ultrasonic sensor for signal transmission to a signal receiver, in which a - preferably digital - output signal of the ultrasonic sensor is processed into the digital sensor signal for signal transmission, it is provided that the processing comprises the following steps: (i) determining a signal change from successive values ​​of the output signal, (ii) scaling this signal change using a variable scaling factor that is specified by a scaling scheme known to the ultrasonic sensor and the signal receiver, and (iii) outputting the scaled signal change as the digital sensor signal. In other words, instead of (re-)scaling the values ​​of the output signal, i.e., the signal amplitude, a signal change from successive values ​​of the output signal is determined and scaled.

[0011] If a sufficiently high bandwidth is available for signal transmission and the dynamic range of the resulting signal change is known in advance, the scaling only needs to be specified once. However, this situation generally does not exist.

[0012] According to a preferred embodiment of the invention, the signal transmission to the signal receiver has a predetermined bandwidth (number of bits), with the scaling scheme adapting the size of the scaling factor to this predetermined bandwidth. The need for repeated (re-)scaling is generally necessary because the bandwidth during transmission is significantly too small for the dynamic range of the signal change. As mentioned above, the number of bits is generally less than 5. With a number of bits of 3, only a resolution of 1 / 8 of the bandwidth can be achieved. The fact that the signal change to be transmitted here has a relatively high dynamic range must be taken into account by changing the scaling factor, i.e., rescaling.

[0013] To avoid having to transmit the scaling factor to the signal receiver during signal transmission, the variable scaling factor is defined according to a scaling scheme that is known to both the ultrasonic sensor and the signal receiver.

[0014] In particular, the scaling factor is adjusted such that the signal change can be accurately transmitted within the given bandwidth. Two factors are of particular interest: (i) the criterion for determining when an adjustment is necessary and (ii) the "step size" of the adjustment.

[0015] According to a further preferred embodiment of the invention, it is provided that, according to the scaling scheme, the size of the scaling factor for two consecutive values ​​of a continuous sequence of values ​​is adapted to the predetermined bandwidth if the scaled signal change of the last two previously considered values ​​of the continuous sequence utilizes the bandwidth to a proportion that lies in at least one predetermined range. As a rule, two such ranges are provided. If the scaled signal change lies in the first range, it is scaled up, i.e. a higher scaling factor than previously is used; if the scaled signal change lies in the second range, it is scaled down, i.e. a lower scaling factor than previously is used. The first range is a range from 0 to x times the bandwidth, and the second range is a range from y to 1 times the bandwidth, where 0.1 < x < 0.33 and 0.66 < y < 0.9 apply for x.For example, it is intended that scaling up occurs by increasing the scaling factor if the bandwidth is used to less than 20% (x = 0.2) and scaling down occurs by decreasing the scaling factor if the bandwidth is used to more than 80% (y = 0.8).

[0016] The adjustment of the scaling factor according to the scaling scheme now depends only on the last scaled signal change SC, i.e., the last signal change determined and subsequently scaled according to the scheme. Since the scaling scheme is known to both the device for generating a digital sensor signal and the signal receiver, no further information is required for either of them—besides the scheme itself—to encode / decode the signal.

[0017] The scaling scheme is therefore a scaling scheme in which the scaling factor results solely from the last previously processed scaled signal change value.

[0018] In particular, it is intended that the size of the scaling factor be increased or decreased by at least a factor of two during the adjustment. Preferably, the size of the scaling factor is increased or decreased during the adjustment by a whole order of magnitude, i.e., by a factor of 10. In other words, the adjustment is highly dynamic, so that the output signal of the ultrasonic sensor can be transmitted correctly even at very low bandwidths.

[0019] According to a further preferred embodiment of the invention, the signal change of the output signal is determined by means of subtraction. Such subtraction can be performed easily using a subtractor module.

[0020] According to yet another preferred embodiment of the invention, the signal transmission is data transmission via a BUS system, in particular a LIN bus system. The Local Interconnect Network (LIN), also called a LIN bus, is a serial communication system for networking sensors and actuators, i.e., a fieldbus. The LIN bus is used particularly where the bandwidth and versatility of a CAN bus system (CAN: Controller Area Network) is not required. Typical application examples include networking within a motor vehicle sector.

[0021] The data transmission is advantageously based on the DSI3 bus protocol. The Distributed Systems Interface (DSI) is a bus protocol used to connect multiple distributed systems, sensors, and actuators to a central control unit. It is therefore one of, if not the, predestined protocols for this application.

[0022] In the device according to the invention for providing a digital sensor signal from an ultrasonic sensor for signal transmission to a signal receiver, which is designed to process a - preferably digital - output signal of the ultrasonic sensor into the digital sensor signal for signal transmission, it is provided that the device is designed to: (i) determine a signal change from successive values ​​of the output signal, (ii) scale this signal change by means of a variable scaling factor which is predetermined by a scaling scheme known to the ultrasonic sensor and the signal receiver, and (iii) output the scaled signal change as the digital sensor signal.

[0023] The embodiments of the invention mentioned above in the description of the method also apply accordingly to the device.

[0024] According to a preferred embodiment of the device according to the invention, it is provided that it is set up to carry out the above-mentioned method.

[0025] In the ultrasonic sensor device according to the invention with an ultrasonic sensor, it is provided that it further comprises an aforementioned device for generating a digital sensor signal of the ultrasonic sensor, which is connected downstream of the ultrasonic sensor in terms of signal technology.

[0026] In the ultrasonic sensor system according to the invention for a motor vehicle, with at least one ultrasonic sensor and a signal receiver, in particular a control unit, it is provided that this ultrasonic sensor system further comprises at least one aforementioned device for generating a digital sensor signal of the ultrasonic sensor.

[0027] The invention is explained in more detail below with reference to the attached drawings using preferred embodiments.

[0028] It shows Fig. 1 shows a motor vehicle having a driver assistance system with an ultrasonic sensor device according to an embodiment of the invention, Fig. 2 shows an equivalent circuit diagram of a device for generating a digital sensor signal of an ultrasonic sensor according to an embodiment of the invention, and Fig. 3 shows a comparison of an original sensor output signal and a signal reconstructed after transmission in a time-dependent representation.

[0029] Fig. 1shows a top view of a motor vehicle 10, in the present case designed as a passenger car. The motor vehicle 10 includes a driver assistance system 12, which serves to assist a driver in driving the motor vehicle 10. In particular, the driver assistance system 12 can be designed as a parking aid system, by means of which the driver can be assisted when parking the motor vehicle 10 into a parking space and / or when exiting the parking space.

[0030] The driver assistance system 12 in turn comprises an ultrasonic sensor system 14. The ultrasonic sensor system 14 has at least one ultrasonic sensor 16. In the present exemplary embodiment, the ultrasonic sensor device 14 comprises twelve ultrasonic sensors 16. Six ultrasonic sensors 16 are arranged in a front region 18 of the motor vehicle 10 and six ultrasonic sensors 16 in a rear region 20 of the motor vehicle 10. The ultrasonic sensors 16 can be mounted in particular on the bumper of the motor vehicle 10. The ultrasonic sensors 16 can be arranged, at least in certain regions, in corresponding recesses or through-openings in the bumper. It can also be provided that the ultrasonic sensors 16 are arranged concealed behind the bumper. In principle, the ultrasonic sensors 16 can also be arranged on other trim parts of the motor vehicle 10.For example, the ultrasonic sensors 10 can be arranged on or concealed behind the doors of the motor vehicle 10.

[0031] With the aid of the respective ultrasonic sensors 16, sensor signals can be provided which describe at least one object 22 in an environmental region 24 of the motor vehicle 1. In the present case, an object 22 is shown schematically in the environmental region 24. To determine the sensor signal, an ultrasonic signal can be emitted using each of the ultrasonic sensors 16. The ultrasonic signal reflected by the object 22 can then be received again. Based on the propagation time between the emission of the ultrasonic signal and the reception of the ultrasonic signal reflected by the object 22, a distance between the ultrasonic sensor 16 and the object 22 can then be determined. It can also be provided that the respective distances determined with different ultrasonic sensors 16 are taken into account. Thus, the relative position between the motor vehicle 10 and the object 22 can be determined by means of trilateration.It may also be provided that the ultrasonic signal emitted by one of the ultrasonic sensors 16 is received by another of the ultrasonic sensors 16. This is also referred to as cross-measurement.

[0032] Furthermore, the ultrasonic sensor system 14 comprises an electronic control unit 26 as a signal receiver 28, which is connected to the ultrasonic sensors 16 for data transmission via a data line 30 or a bus system (the line 30 is in Fig. 2shown). The sensor signals determined by the respective ultrasonic sensors 16 can be transmitted via the data line 30 to the control unit 26 as a signal receiver 28. Based on the sensor signals, the control unit 26 can check whether the object 22 is located in the surrounding area 24 and the position of the object 22 in the surrounding area 24. This information can then be used by the driver assistance system 12 to provide an output to the driver of the motor vehicle 10. In addition, it can be provided that the driver assistance system 12 intervenes in a steering system, a braking system, and / or a drive motor in order to maneuver the motor vehicle 10 autonomously or at least semi-autonomously depending on the at least one detected object 22.

[0033] Fig. 2shows a device 32 for providing a digital sensor signal DS of an ultrasonic sensor 16 from the original measurement signal of the sensor 16, referred to below as the output signal (or raw signal) OS. The digital sensor signal DS is then transmitted, for example, via a LIN bus (LIN: Local Interconnect Network) data line 30 to the control unit 26 as a signal receiver 28. For this purpose, the device 32 processes the output signal OS of the ultrasonic sensor 16 into a digital sensor signal DS for signal transmission with a limited transmission rate.A signal change SC of successive values ​​(or amplitudes) of the output signal OS is determined by means of a subtractor 34 and a holding element (not shown here) that retains the previous value of the output signal OS, so that the difference between the previous and current value of the output signal OS, i.e., the signal change SC of the output signal OS, is determined by means of the subtractor 34. This signal change SC is then scaled accordingly by means of a scaler 36 and made available for transmission as the digital sensor signal DS. The scaler 36 is a type of quantizer in which the quantization step size is scalable / adjustable.

[0034] Scaling of amplitude values ​​of the signal OS (instead of the scaling of the signal changes SC performed here) has the disadvantage, especially in the case of ultrasonic echoes, that high amplitude deflections are generated by the reverberation of the membranes during transmission, while the output signals RS of ambient echoes are usually significantly lower.

[0035] The scaling of the signal change SC is performed via a variable scaling factor SF, which is specified by a scaling scheme known to the ultrasonic sensor 16 and the signal receiver 28. This scaling scheme is stored as a scaling adaptation protocol both in a data memory 38 of the device 32 for generating the digital sensor signal DS and in a data memory 40 of the control unit 26.

[0036] According to the scaling scheme, the size of the scaling factor SF is adjusted to the specified bandwidth for two consecutive values ​​of a continuous sequence of values ​​if the scaled signal change of the last two previously considered values ​​of the continuous sequence utilizes the bandwidth to a degree that lies at the upper or lower end of the bandwidth in at least one specified range. If the bandwidth is currently only utilized to a small extent, for example, below 20%, the bandwidth is scaled up; if the bandwidth is currently utilized to a high extent, for example, above 80%, the bandwidth is scaled down.

[0037] The Fig. 3shows a comparison of the original sensor output signal OS and a signal RS reconstructed from the transmitted digital sensor signal DS in a time-dependent representation. In other words, the original sensor output signal OS and a signal RS reconstructed from the transmitted digital sensor signal DS are each shown as a graph, with the respective signal amplitude A plotted against time t. The reconstructed signal RS shown here results from a digital sensor signal DS that was transmitted via DSI bus operation, with the sampling frequency first divided by two, then encoded and decoded with DSI3 according to the described method.

[0038] This comparison shows how well the reconstructed signal RS follows the original sensor output signal OS even with only 3 bits.

[0039] In the following, the properties and the advantageous effects of the procedure described here will be briefly outlined again in other words: The sensor electronics provides a sample of the vibration amplitude with a certain frequency (Graph OS in Fig. 3 ). Instead of the sampled values ​​of the vibration amplitude, the differences between two consecutive sampled values ​​of the vibration amplitude, i.e. the signal change SC (as a digital sensor signal DS), are transmitted.

[0040] Each difference value, i.e. each signal change SC, is coded to a fixed number of bits (in the example: 3 bits).

[0041] However, the scaling of the difference values ​​(signal change SC) to the 3 bits is flexible and follows a protocol known to each side (the ultrasonic sensor device 16, 32 as transmitter and the control unit 26 as receiver), the scaling scheme.

[0042] The adaptation according to the scaling adaptation protocol or scaling scheme depends only on the last transmitted 3-bit scaled signal change SC. Since the receiver also knows the scaling adaptation protocol or scaling scheme, no further information needs to be transmitted.

[0043] The scaling adjustment protocol takes as input the last 3-bit difference value and the last so-called scaling factor SF ("scaling level", referred to simply as n below, where the scaling adjustment protocol or scaling scheme is stored locally at the transmitter and receiver) and produces as output a new, adjusted scaling factor SF. For example, with these 3 bits, this results in: Values ​​0 and 7 (strongest increase / strongest decrease): n = n + step_up (e.g. step_up = 4); values ​​3, 4 and 5 (small to no increase / small to no decrease): n = n - step_down (e.g. step_down = 2); n is limited between 1 and max_scaling_level (e.g. max_scaling_level = 12); each scaling level has an amplitude value, referred to here as f(n) (where n is the scaling factor). A linear conversion from difference value to 3 bits is used, with principal factor f(n), for example: value 3 on 3 bits (011) gives a difference value between -f(n) / 2 and +f(n) / 2 (so more or less no difference at all); A value of 7 gives a difference value greater than 4*f(n) - f(n) / 2 (largest representable difference, value reaches saturation on 3 bits); a value of 0 gives a difference value less than -3*f(n) + f(n) / 2 (smallest representable difference, value reaches saturation on 3 bits); and so on. Example for f: f(n) = scaling_factor*n3 / 2 (e.g.scaling_factor = 4).

[0044] The values ​​f(n) for all n between 1 and max_scaling_level are calculated in advance (e.g., during initialization) to save runtime during encoding / decoding. This example variant for f also allows for rapid scaling increases as n increases. During encoding, the value that the receiver 28 would decode is calculated in parallel, and the difference is then calculated with the next sample. This improves the overall accuracy of the entire encoding / decoding process and ensures possible slow drift during decoding. During decoding, it is assumed that the first value is 0. This assumption is realistic in most cases. This means that no starting value needs to be sent at the beginning. Even the first transmitted value of the transmitted digital signal DS can be a first difference value, namely the difference between 0 and the second sample of the amplitude. List of reference symbols

[0045] motor vehicle 10 Driver assistance system 12 Ultrasonic sensor system 14 Ultrasonic sensor 16 Front area 18 Rear area 20 object 22 surrounding area 24 control unit 26 signal receiver 28 data line 30 Device for generating a digital sensor signal 32 Subtractor 34 Scaler 36 Data storage 38 Data storage 40 amplitude A Digital sensor signal for transmission DS Sensor output signal OS Reconstructed signal at the signal receiver RS Signal change (output signal) SC Scaling factor SF Time t

Claims

1. Method for providing a digital sensor signal (DS) from an ultrasonic sensor (16) for signal transmission to a signal receiver (28), in which a - preferably digital - output signal (OS) from the ultrasonic sensor (16) is processed to form the digital sensor signal for signal transmission, characterized in that the processing comprises the following steps: - determining a signal change (SC) of successive values of the output signal (OS), - scaling this signal change (SC) by means of a variable scaling factor (SF) which is specified by a scaling scheme known to the ultrasonic sensor (16) and the signal receiver (28), and - outputting the scaled signal change (SC) as the digital sensor signal (DS).

2. Method according to Claim 1, characterized in that the signal transmission to the signal receiver (28) has a predefined bandwidth and the size of the scaling factor (SF) is adapted to this predefined bandwidth by means of the scaling scheme.

3. Method according to Claim 2, characterized in that the size of the scaling factor (SF) for two successive values in a continuous sequence of values of the output signal (OS) is adapted to the predefined bandwidth according to the scaling scheme if the scaled signal change of the last two previously considered values in the continuous sequence uses a portion of the bandwidth that is in at least a predefined range.

4. Method according to one of Claims 1 to 3, characterized in that the size of the scaling factor (SF) is increased or decreased at least by a factor of two during the adaptation.

5. Method according to one of Claims 1 to 4, characterized in that the signal change (SC) of the output signal (OS) is determined by means of a subtraction.

6. Method according to one of Claims 1 to 5, characterized in that the signal transmission is a data transmission via a BUS system, in particular a LIN bus system.

7. Method according to Claim 6, characterized in that the data transmission is a data transmission according to the DSI3 bus protocol.

8. Apparatus (32) for providing a digital sensor signal (DS) from an ultrasonic sensor (16) for signal transmission to a signal receiver (28), the apparatus (32) being configured to process a - preferably digital - output signal (OS) from the ultrasonic sensor (16) to form the digital sensor signal (DS) for signal transmission, characterized in that the apparatus (32) is configured to determine a signal change (SC) of successive values of the output signal (RS), to scale this signal change (SC) by means of a variable scaling factor (SF) which is specified by a scaling scheme known to the ultrasonic sensor (16) and the signal receiver (26), and to output the scaled signal change (SC) as the digital sensor signal (DS).

9. Ultrasonic sensor device with an ultrasonic sensor (16) and an apparatus (32) according to Claim 8 connected downstream of the ultrasonic sensor (16) in terms of signalling.

10. Ultrasonic sensor system (14) for a motor vehicle (10), with at least one ultrasonic sensor (16), a signal receiver (28), in particular a control unit (26), and at least one apparatus (32) according to Claim 8.