Method for synchronizing sensors on a data bus

Abstract

Method for synchronizing sensors (4, 5) with an independent timer (14, 15) for ultrasound-based environmental detection systems (1) in a vehicle (2), wherein the sensors (4, 5) communicate with a control unit (8) via a bus (7) using a bus protocol that includes at least one window (SYNC) of a predetermined time length (T), wherein the clock of the timer (14, 15) in the sensor (4, 5) is synchronized with the clock of a central timer (18) in the control unit (8) and a correction factor for the data of the sensor (4, 5) is calculated from the synchronization, and wherein the time length (T) of the window (SYNC) is measured by the timer (14, 15) of the sensor (4, 5) and the measured time is transmitted to the control unit (8), characterized in that the measured time of the window (SYNC) is compared with the time (T) of the window (SYNC) specified in the protocol. a comparison is made and a difference time is determined, which is used to correct the reading from the sensor (4,5) transmitted data is used.

Description

[0001] The invention relates to a method for synchronizing sensors with an independent timer, in particular for ultrasound-based environmental detection systems in a vehicle, in which the sensors communicate with a control unit via a bus system, according to the preamble of claim 1.

[0002] Ultrasound-based environmental sensing systems incorporate multiple ultrasonic sensors in a vehicle's bumper. Each sensor emits an ultrasonic signal, which is reflected by any object or obstacle and received by the same or another sensor. The travel times of the ultrasonic waves are then measured using a timer. By analyzing these travel times, the position of the detected object can be determined, allowing the environmental sensing system to function as a parking assistant.

[0003] From DE 10 2008 045 190 A1, a generic environmental detection system is known in which several sensors in a front and a rear bumper communicate with a central control unit via a bus. The bus is designed as a LIN bus, with trigger pulses being generated in the respective sensor by an independent timer to trigger the measurement sequence. To synchronize the sensors, the timers of the respective sensors are synchronized with each other.

[0004] The sensors use oscillators as timekeepers. While these oscillators are highly accurate, they are subject to drift during operation. The actual oscillator drift varies from sensor to sensor; for example, it can be ±3%. Because each oscillator in a timekeeper drifts to a different degree, the travel times measured by the sensors can be inaccurate. This leads to significant fluctuations when the travel times are used to calculate the distance to an object, resulting in an inaccurate calculation of the object's position.

[0005] The invention is based on the objective of synchronizing the sensors used in an ultrasound-based environment detection system in such a way that any oscillator drift of the timer has no significant impact on the distance calculation.

[0006] The invention relates to a method for synchronizing sensors with an independent timer, particularly for ultrasound-based environmental detection systems in a vehicle, in which the sensors communicate with a control unit via a bus using a predefined protocol that includes at least a window of predefined time length. According to the invention, the clock signal of the sensor is synchronized with the clock signal of a central timer in the control unit, and a correction factor for the sensor data is calculated from this synchronization to correct the transit times of the ultrasound waves detected by the sensor.

[0007] The advantageous adjustment of the sensor's timer is achieved by having the sensor's own timer measure the duration of a window in the bus protocol. The sensor then transmits this measured time, along with its data (i.e., the recorded transit times), to the control unit. Since the control unit has defined the window duration in the protocol, it can compare the sensor's measured time with this predefined window duration. This comparison allows the control unit to derive a correction factor, which is then used to correct the data transmitted by the sensor (i.e., the recorded transit times).

[0008] In this simple way, each data record sent by the sensor can be assigned the time of the time window measured by the sensor's timer in the protocol. The control unit, acting as the master, compares the specified time of the window measured by the sensor with the actual measured time and, if a difference occurs, calculates a correction factor that allows the transmitted data from the sensor to be immediately adjusted to the control unit's clock.

[0009] The comparison of the measured window time with the specified window time, as well as the correction of the data sent by the sensor itself, takes place in the central control unit as the master.

[0010] To synchronize the timing of the sensor's clock, a window in the message frame header can be selected; the synchronization window provided in the header is the most practical choice. Advantageously, any window of the message frame can be used, such as a data window, the checksum window, or even the break window or identifier. The only requirement for the selected window is that its duration is fixed, meaning the control unit, as the master, knows the window's duration.

[0011] Advantageously, the measured window time and the sensor data are transmitted within the same message frame, so that the current oscillator drift is transmitted together with the current sensor data. This enables an accurate calculation of the distance values ​​from the propagation times transmitted by the sensor and, if necessary, corrected.

[0012] It may be sufficient to transmit the measured time of a window and the sensor data set in successive message frames; if oscillator drift is low, it is also sufficient to measure the time of a given window at longer intervals, e.g., only every third or fifth message frame.

[0013] Further features of the invention will become apparent from the further claims, the description, and the drawing, in which a detailed embodiment of the invention is shown below. The drawing shows:

[0014] Fig. 1. A schematic view of an environment detection system in a vehicle,

[0015] Fig. 2. In schematic representation, a “Message Frame” on a bus line,

[0016] Fig. 3 A schematic flowchart illustrating the operation of a synchronization of the timer in a sensor with a central timer in a control unit.

[0017] In Fig. 1 is an ultrasound-based environmental detection system 1 depicted, which is shown in a schematically indicated vehicle 2 is arranged. This allows for the following in a bumper 3 of the vehicle 2 one or more sensors 4 , 5 e.g. ultrasonic sensors are arranged to detect an object 6 in the immediate vicinity of the sensors 4 and 5 are provided. In the illustrated embodiment, two sensors are provided. 4 and 5 shown; further sensors may be provided, as shown in Fig. 1 is indicated by a dashed line.

[0018] The sensors shown 4 and 5 are via a bus 7 with a control unit8 connected, which serves as the central control unit 8 in the vehicle 2 is arranged and the master of the bus 7 educates.

[0019] The bus 7 It can be a CAN bus, a LIN bus, or a suitably appropriate bus.

[0020] The ultrasonic waves emitted by the sensor are detected by an object 6 reflected, whereby the transit times of the ultrasonic waves in the sensor 4 , 5 can be determined independently. This is done in each individual sensor. 4 or 5 a timepiece 14 or 15 provided for, which is designed, for example, as an oscillator in a known manner. The sensors 4 and 5 The transmitted data consists of the transit times of the ultrasonic waves as recorded by the sensor, for which the internal timer of the individual sensor is used. Since the oscillator of the timer 14 , 15Due to design limitations or factors such as aging, temperature influences, etc., the transit times output by the sensor are dependent on the oscillator drift present at the time of measurement; due to this oscillator drift, the measured transit times can be inaccurate, so that the object being detected 6 with an incorrect distance A from the bumper 3 of the vehicle 2 is calculated.

[0021] Becoming – as in Fig. 1 shown – two sensors 4 and 5 If used, then the intersection point of the two recorded distance values ​​corresponds to 11 and 12 exactly the position of the real object 6 .

[0022] For example, the timepiece indicates 15 If an oscillator drift of, for example, +3% occurs, a distance value results. 12' with the consequence that the intersection point S shifts to the intersection point S', i.e. the position of the object. 6The coordinates Δx and Δy are calculated incorrectly.

[0023] To synchronize the timepieces 14 and 15 the sensors 4 and 5 To achieve this, it is planned to use the timepieces 14 and 15 in the sensors 4 and 5 with the beat of the central timepiece 18 in the control unit 8 to calibrate. Each calibration results in a correction factor for the data of each individual sensor. 4 and 5 calculated.

[0024] For comparison, information from the control unit is required. 8 (Master) to the sensor 4 or 5 (Slave) of the timepiece 14 or 15 the sensor 4 or 5 measured, whereby the length of the information from the control unit 8 (Master) must be known. Long pieces of information consisting of several bits are advantageously suited for this purpose.

[0025] In Fig. Figure 2 is a schematic example of a protocol on the bus. 7 reproduced. Each message frame 10 It consists of a header H and a data section D. The header H includes, for example, a break window B, a synchronization window SYNC, and an identifier ID; the data section D includes one or more data windows DATA and a CHECK window for the checksum, which concludes the data section D. Each window B, SYNC, ID, DATA, and CHECK has a predefined, fixed time, e.g., the SYNC window has a time T.

[0026] On a header H of the control unit 8 The respective sensor is identified using the identifier ID. 4 or 5 addressed, which then outputs its data – e.g., the transit times of the ultrasound waves – which are displayed as a data window by the central control unit. 8 be received.

[0027] In the exemplary embodiment, the timepieces are synchronized. 14 , 15 in the sensors 4 , 5 the SYNC window with the time T of the control unit 8 (Master) of the timekeepers 14 and 15 the sensors 4 and 5 (Slave) measured and in the sensor 4 or 5 The measured time of the SYNC window is kept available. This data is stored along with the sensor data. 4 or 5 , i.e., the transit times of the ultrasound waves to the control unit 8 (Master) transmitted.

[0028] The control unit 8 (Master) knows the time T of the SYNC window and compares it with that of a timer. 14 or 15 a sensor 4 or 5 measured time. From the difference in the control unit 8 known time T at which the sensors 4 and 5A time difference is calculated from the measured time, which is used to correct the transit time data of the ultrasonic waves transmitted by the sensor. The timers 14 and 15 The measured time is thus used to correct the sensor's timer and its transmitted data.

[0029] Since the control unit 8 (Master) both the measured times of the SYNC window and the transit times of the ultrasonic waves of the sensors 4 and 5 via the bus 7 receives, can be received in the control unit 8 the correction of the transit times of the ultrasonic waves of the sensors 4 and 5 from the difference between time T and that measured by the timepieces 14 and 15 measured time.

[0030] Any window of the message frame can be used as a window to correct runtimes. 10 can be used if the window is controlled by the master (control unit).8 ) has a fixed, predetermined duration. A synchronization window in the header H is appropriate, e.g., the break window B, the synchronization window SYNC, or the identifier ID; it can also be advantageous to use the data window DATA or the CHECK window for the checksum via the timer. 14 , 15 in a sensor 4 , 5 to record in order to synchronize the timepiece 14 , 15 in the sensor 4 , 5 with the timepiece 18 in the control unit 8 to be performed. Any time difference resulting from the comparison is converted into a correction value, which is used to correct the runtime data of the sensors. 4 and 5 is used.

[0031] The measured time of the selected window, e.g., the SYNC window, and a transmitted data set from the sensor. 4 or 5e.g., the travel times of the ultrasound waves, are advantageously placed within the same message frame. 10 transmitted. It can also be useful to include the measured time of a window and the queried data set from the sensor. 4 , 5 in successive message frames 10 to transmit.

[0032] As in Fig. 3 is shown in the starting field 20 from the control unit 8 (Master) on the bus 7 a header H of a message frame 10 sent; the sensor 4 , 5 (Slave) measures in the field 21 The time of the SYNC window in header H. The sensor 4 , 5 (Slave) sends in the field 22 both the measured time of the SYNC window and the time from the sensor 4 , 5 Data captured in one or more data fields DATA. The control unit 8 (Master) compares in the field 23The known time T of the SYNC window is compared to the time measured by the slave; if the times are the same, no correction is necessary, and the object distance can be determined in the field. 25 directly from the data transmitted by the sensor 4 , 5 The decision diamond is calculated. If the measured time is longer, the decision diamond is... 19 about determining a correction value in the field 24b exit and use the correction value from field 24b in the field 25 The object distance is calculated. A correction value is then entered in the field. 24a determined if the measured time is less than the time T of the SYNC window and then using the correction value from field 24a the object distance in the field 25 calculated. QUOTES INCLUDED IN THE DESCRIPTION

[0033] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0034] DE 102008045190 A1

[0003]

Claims

[1] Methods for synchronizing sensors ( 4 , 5 ) with an independent timepiece ( 14 , 15 ), especially for ultrasound-based environmental detection systems ( 1 ) in a vehicle ( 2 ), in which the sensors ( 4 , 5 ) with a control unit ( 8 ) via a bus ( 7 ) communicate using a bus protocol that includes at least one window (SYNC) of a predefined time length (T), characterized by that the beat of the timepiece ( 14 , 15 ) in the sensor ( 4 , 5 ) with the beat of a central timepiece ( 18 ) in the control unit ( 8 ) is compared and a correction factor for the sensor data is derived from the comparison ( 4 , 5 ) is calculated. [2] Method according to claim 1, characterized by that the time length (T) of the window (SYNC) is determined by the timer ( 14 , 15 ) of the sensor (4 , 5 ) is measured and the measured time is sent to the control unit ( 8 ) is transmitted. [3] Method according to claim 1 or 2, characterized by that the measured time together with the sensor data ( 4 , 5 ) the control unit ( 8 ) is transmitted. [4] Method according to claim 2 or 3, characterized by that the measured time is used to correct the timer ( 14 , 15 ) of the sensor ( 4 , 5 ) and whose transmitted data is used. [5] Method according to any one of claims 2 to 4, characterized by that the measured window time (SYNC) is compared with the window time (T) specified in the protocol and a difference time is determined, which is used to correct the sensor reading ( 4 , 5 ) transmitted data is used. [6] Method according to any one of claims 1 to 5, characterized bythat the correction of the data in the central control unit ( 8 ). [7] Method according to any one of claims 1 to 6, characterized by that the window (SYNC) is the synchronization window in the header (H). [8] Method according to any one of claims 1 to 6, characterized by that the window is a data window or the checksum window. [9] Method according to any one of claims 1 to 8, characterized by that the measured time of the window and a data set from the sensor ( 4 , 5 ) within the same message frame ( 10 ) are transmitted. [10] Method according to any one of claims 1 to 8, characterized by that the measured time of the window (SYNC) and a data set from the sensor ( 4 , 5 ) in successive message frames ( 10 ) will be transmitted.

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