Sensor arrangement

Abstract

Sensor arrangement (1) with an optical distance sensor (2), by means of which distances of objects (11) in a detection area are determined, characterized in that the optical distance sensor (2) can be connected to an external computer unit (4) by means of a data connection (3), that in a calibration process with the optical distance sensor (2) against an object (11) at known, predetermined distances and with different reflectivities, distance measurements are carried out and distance measurement parameters determined in the process are transmitted to the external computer unit (4), that in the external computer unit (4) for the individual values ​​of the distance measurement parameters, correction values ​​(K) are determined by forming the difference between measured raw distance values ​​(D r ) and known, predetermined distances, that in the external computer unit (4) a correction value function (K F) is formed from the correction value function (K F ) a correction table is formed with a predeterminable number of support points, and that the correction table is transmitted via the data connection (3) from the external computer unit (4) to the optical distance sensor (2), wherein distance values ​​determined in a working mode with the optical distance sensor (2) are corrected with the correction table.

Description

[0001] The invention relates to a sensor arrangement.

[0002] Such a sensor arrangement comprises an optical distance sensor by means of which distances of objects in a detection area are determined.

[0003] The optical distance sensor comprises a transmitter that emits light rays, a receiver that receives light rays and an evaluation unit for evaluating received signals from the receiver.

[0004] Typically, distance measurements with the optical distance sensor are performed using a pulse-time-of-flight method. The transmitter of the optical distance sensor then emits light beams in the form of light pulses. The object distance is determined in the evaluation unit from the light pulses' time of flight from the transmitter to the object to be detected and back to the receiver.

[0005] Distance values ​​determined during distance measurements vary depending on the reflectivity of the surface of the objects to be detected. The resulting distance measurement errors are known as black-and-white errors.

[0006] To compensate for these measurement errors, it is known to measure an object with a light, white surface and an object with a dark, black surface and determine the respective distance measurement errors. Correction values ​​are then derived from this.

[0007] Since in subsequent operation a correction of distance values ​​is only possible by a linear interpolation between these two correction values, the compensation of the distance measurement errors is correspondingly inaccurate.

[0008] To correct such distance measurement errors, it is generally known to regulate the transmitter's transmission power depending on the amplitudes of the received signals registered in the receiver. This is not only circuit-complex but also time-consuming, resulting in an undesirably high dead time, defined as the time between the recording of the respective measurement data, i.e., received signals, and the output of an output signal.

[0009] The invention is based on the object of providing a sensor arrangement with an optical distance sensor by means of which distances of objects with different surface reflectivities can be reliably detected with short dead times.

[0010] To achieve this object, the features of claim 1 are provided. Advantageous embodiments and expedient developments of the invention are described in the dependent claims.

[0011] The invention relates to a sensor arrangement with an optical distance sensor, by means of which distances between objects in a detection area are determined. The optical distance sensor can be connected to an external computer unit via a data connection. In a calibration process, distance measurements are carried out with the optical distance sensor against an object at known, predetermined distances and with different reflectivities. The distance measurement parameters determined in this process are transmitted to the external computer unit. In the external computer unit, correction values ​​are determined for the individual values ​​of the distance measurement parameters by calculating the differences between measured raw distance values ​​and known, predetermined distances. In the external computer unit, a correction value function is created that is optimally adapted to the correction values. A correction table with a predeterminable number of support points is created from the correction value function.The correction table is transferred from the external computer unit to the optical distance sensor via the data connection, whereby distance values ​​determined during operation with the optical distance sensor are corrected using the correction table.

[0012] The basic idea of ​​the invention is to calculate a correction value function in a calibration process, by means of which distance measurement errors of the optical distance sensor due to different reflectivities of objects to be detected can be detected with high precision.

[0013] In this calibration process, an object is positioned at fixed, predetermined distances to the optical distance sensor, whereby in this measurement setup, distance values ​​for different reflectivities of the object are determined in the optical distance sensor.

[0014] This is advantageously achieved by positioning the optical distance sensor at different predefined distances from an object during the calibration process using a rail or similar device. A rotary wheel with different gray scales is installed between the optical distance sensor and the object. Different gray scales in the beam path of the optical distance sensor attenuate the light beams from the optical distance sensor to different degrees.

[0015] Advantageously, the optical distance sensor is connected to an external computer unit via a data connection only during the calibration process, whereby according to the invention the correction value function is determined in the external computer unit, not in the optical distance sensor.

[0016] This is advantageous because the required computing power is available in the external computing unit, which can be a PC, a microprocessor system, or even a cloud computing device. The optical distance sensor, in contrast, requires only comparatively little computing power.

[0017] During the calibration process, the optical distance sensor determines several distance measurement parameters for different object reflectivities. It is essential that several distance measurement parameters are determined that depend on the object reflectivities. The distance measurement parameters provide detailed information about the dependency of the distance measurements for different object reflectivities, with the distance measurement parameters preferably being determined for a large number of different object reflectivities. These distance measurement parameters are read into the external computer unit via the data connection.

[0018] In the external computer unit, discrete correction values ​​are determined for all distance measurement parameters, whereby a correction value is formed by the difference between the respective raw distance and the actual object distance.

[0019] According to the invention, a continuous correction value function is formed in the external computer unit from the discrete point cloud of the correction values ​​dependent on the distance measurement parameters, wherein the correction value function is optimally adapted to the correction values ​​by means of suitable mathematical methods.

[0020] For example, the optimization of the correction value function can be carried out using the least squares method.

[0021] The correction value function can be formed by n-th order polynomials.

[0022] 5th order polynomials are particularly suitable for this purpose.

[0023] Alternatively, the correction value function can be formed using a neural network.

[0024] From the correction value function thus generated, a correction table tailored to the application can be created with a specified number of support points. Each support point is assigned a correction value from the correction value function for defined values ​​of the distance measurement parameters.

[0025] It is advantageous that such support points can be defined at any point in the correction value function, whereby the number of support points in the external computer unit can be selected on an application-specific basis. In particular, the support points do not have to correspond to determined measured values.

[0026] This correction table is then read into the optical distance sensor, which preferably completes the calibration process. The data connection between the optical distance sensor and the external computer unit can then be terminated.

[0027] During subsequent operation, the optical distance sensor then corrects the currently recorded distance values ​​using the correction table, whereby distance measurement errors due to different object reflectivities can be compensated with high precision.

[0028] Since the correction table contains only a manageable number of values, the correction of the distance measurements can be carried out with little computing time.

[0029] During operation, a determined distance value is conveniently corrected by linear interpolation between two correction values.

[0030] These calculations require only a small amount of computing time.

[0031] Since the correction of the distance measurement values ​​using the correction table already provides a very reliable and precise compensation for distance measurement errors due to different object reflectivities, further error correction measures are not necessary.

[0032] In particular, the optical distance sensor can be operated with a constant transmission power, i.e. structurally complex and time-consuming transmission power controls are not required.

[0033] With the optical distance sensor according to the invention, output signals with short dead times can be generated.

[0034] According to an advantageous embodiment, the optical distance sensor has a transmitter that emits light beams in the form of light pulses and a receiver that is designed to receive the light pulses.

[0035] Advantageously, distance measurements are carried out with the optical distance sensor using a pulse-time-of-flight method.

[0036] In this case, the distance measurement parameters are advantageously formed from the raw distance values ​​measured during the calibration process and from the pulse widths of the light pulses registered at the receiver determined during the distance measurements.

[0037] In the distance measurements carried out with the optical distance sensor, not only the determined distance values ​​themselves but also the pulse widths of the light pulses registered at the receiving side depend on the reflectivity of the surfaces of the detected objects.

[0038] Since, according to the invention, not only the raw distance values ​​but also the pulse widths of the light pulses registered at the receiving end are recorded as distance measurement parameters depending on the reflectivity of the objects, precise and comprehensive information is obtained about the influence of the reflectivities of the objects on the distance measurements carried out.

[0039] To increase measurement reliability, several light pulses are used in the calibration process to determine raw distance values ​​and pulse widths.

[0040] To determine raw distance values ​​and pulse widths, averages or histograms are created.

[0041] Accordingly, multiple evaluation of light pulses can also be provided during the operating mode of the optical distance sensor.

[0042] The invention is explained below with reference to the drawings. They show: Fig. 1: Schematic representation of an embodiment of the sensor arrangement according to the invention with an optical distance sensor and an external computer unit. Fig. 2: Time-dependent signal curves for object detection with the optical distance sensor according to Fig. 1. Fig. 3: Measurement setup for carrying out a calibration procedure with the sensor arrangement according to Fig. 1. Fig. 4: Example of a correction value function. Fig. 5: Time diagram for the distance measurements performed with the optical distance sensor.

[0043] Fig. 1 schematically shows an embodiment of the sensor arrangement 1 according to the invention.

[0044] The sensor arrangement 1 comprises an optical distance sensor 2, which can be connected to an external computer unit 4 via a data connection 3. In this case, the external computer unit 4 is a PC. The wired data connection 3, in this case, is connected to the optical distance sensor 2 and the external computer unit 4 via interfaces (not shown).

[0045] The sensor components of the optical distance sensor 2 are arranged in a housing 5, in the front wall of which there is a transparent pane 6.

[0046] The optical distance sensor 2 has a transmitter 8 emitting light beams 7, a receiver 9 receiving light beams 7 and an evaluation unit 10 for evaluating received signals from the receiver 9.

[0047] The transmitter 8 is formed by a laser diode, and the receiver 9 is formed by at least one SPAD (single-photon avalanche diode). The evaluation unit 10 can be formed by a microprocessor or the like.

[0048] The optical distance sensor 2 performs distance measurements using a pulse-time-of-flight method. For this purpose, the transmitter 8 emits light beams 7 in the form of light pulses. The evaluation unit 10 determines the light pulses' travel time to the object 11 and back to the receiver 9 as a measure of the distance to an object 11. Fig. 1 shows such an object detection, in which the light rays 7 of the transmitter 8 are guided through the disc 6 into a detection area, are reflected at the object 11 and from there are guided again through the disc 6 to the receiver 9.

[0049] During these object detections, the evaluation unit 10 generates an output signal that is output via an output (not shown). The output signal can be formed from the determined distance value. Alternatively, the output signal can output binary information indicating whether or not an object 11 is located within a specific distance range.

[0050] Distance values ​​determined during object detection depend on the reflectivity of the surfaces of the objects 11 to be detected.

[0051] This is in Fig. 2 illustrates. Fig. 2 shows the time course of the amplitude A of the received signal of the optical distance sensor 2 for a rectangular light pulse emitted by the transmitter 8, which was reflected back by an object 11. Fig. Figure 2 shows the time courses of the received signal pulse registered at the receiving end for a very bright surface a, a bright surface b and a dark surface c of the object 11.

[0052] The received signal pulse is evaluated with a trigger threshold S.

[0053] The time-of-flight measurement for distance determination is started with the emission of the light pulse and at time t r , when the amplitude A of the received signal exceeds the trigger threshold S. The pulse width t is also above the trigger threshold S p of the received signal pulse. In Fig. 2 these quantities are shown for the received signal pulse when a very bright object is detected.

[0054] How Fig. 2 shows, the shape of the received signal pulse deviates from the original shape of the light pulse more strongly, the darker the object surface is. The pulse width t p always smaller and the time tr shifts to larger values.

[0055] This dependence of the distance measurement on the reflectivity of the object surfaces results in distance measurement errors.

[0056] To systematically record these sources of error, the Fig. The measurement setup shown in Figure 3 is used during a calibration process.

[0057] Only during the calibration process is the optical distance sensor 2 connected to the external computer unit 4 via the data connection 3, as shown in Fig. 3 shown.

[0058] To carry out measurements during the calibration process, a measuring object 12 is positioned at predetermined distances relative to the optical distance sensor 2, these distances being referred to as target distances D wstored in the external computer unit 4. In the present case, the measuring object 12 can be moved on a rail (not shown), wherein a rail control 13 is provided for moving the measuring object 12, which is connected to the external computer unit 4.

[0059] For the individual target distances D w Different object reflectivities are simulated by placing a rotary wheel 14 with different gray wedges downstream of the optical distance sensor 2. Depending on which gray wedge is inserted into the beam path of the optical distance sensor 2, a specific value of the surface reflectivity of the measuring object 12 is obtained. The rotational position of the rotary wheel 14 is adjusted using a rotary wheel control 15.

[0060] During the calibration process, different target distances D w and different object reflectivities as distance measurement parameters Raw distance values ​​D r, ie measured object distances, and pulse widths t p determined.

[0061] For all pairs of raw distance values ​​D r and pulse widths t p a correction value K is calculated according to the relationship K=Dr−Dw determined.

[0062] These correction values ​​K are shown in the diagram according to Fig. 4 registered.

[0063] According to the invention, the discrete correction values ​​K are converted into a continuous correction value function K F ( Fig. 4). Determination of the correction value function K F is carried out by a mathematical optimization procedure with which the correction value function K F optimized to the correction values ​​K.

[0064] It is advantageous to optimize the correction value function K F carried out using the method of least squares.

[0065] The correction value function K Fformed by n-th order polynomials.

[0066] In particular, 5th order polynomials are used.

[0067] Alternatively, the correction value function K F formed using a neural network.

[0068] From this correction value function K F a discrete correction table is derived for the respective optical distance sensor 2. The correction table has a predeterminable number of support points of discrete correction values ​​K for certain pairs of raw distance values ​​D r and pulse widths t p on.

[0069] The support points can be freely selected and do not have to correspond to the measuring points determined during the calibration process.

[0070] The correction table is then loaded into the optical distance sensor 2. This completes the calibration process, and the data connection 3 is disconnected from the optical distance sensor 2, allowing the optical distance sensor 2 to begin operating.

[0071] During operation, the determined distance values ​​are corrected with correction values ​​K from the correction table, whereby a linear interpolation between two adjacent correction values ​​K is generally carried out to provide the appropriate correction value K.

[0072] While the determination of the correction value function K FWhile this requires a very high computational effort in the external computer unit 4, the correction of the distance values ​​can be carried out very quickly using the correction table during operation of the optical distance sensor 2. Furthermore, the optical distance sensor 2 can be operated with constant transmission power, since no transmission power control is required to compensate for distance measurement errors due to different object reflectivities.

[0073] Fig. 5 shows a flow chart for the optical distance sensor 2 in working mode.

[0074] In consecutive measurement sequences X1, X2, X3..., measurement data is first acquired Y1, Y2, Y3..., followed by a computing time Z1, Z2, Z3... for evaluating the measurement data. At the end of each evaluation, the output signal O1, O2, O3... is output. The computing time Z1, Z2, Z3... defines the dead time for generating the output signals O1, O2, O3....

[0075] Since the calculation times Z1, Z2, Z3... can be kept short by using the correction table according to the invention, short dead times are obtained when generating the output signals O1, O2, O3... List of reference symbols 1 Sensor arrangement 2 optical distance sensor 3 Data connection 4 external computer unit 5 housings 6 slices 7 light beam 8 channels 9 recipients 10 Evaluation unit 11 objects 12 Measuring object 13 Rail control 14 Rotary wheel 15 Rotary wheel control A Amplitude a very bright surface b bright surface c dark surface D r Raw distance value D w Target distance K Correction value K F Correction value function O1, O2, O3 output signal S trigger threshold t time t r time t p Pulse width X1, X2, X3... measurement sequence Y1, Y2, Y3... Measurement data recording Z1, Z2, Z3... computing time

Claims

[1] Sensor arrangement (1) with an optical distance sensor (2), by means of which distances of objects (11) in a detection area are determined, characterized by that the optical distance sensor (2) can be connected to an external computer unit (4) by means of a data connection (3), that in a calibration process with the optical distance sensor (2) against an object (11) at known, predetermined distances and with different reflectivities, distance measurements are carried out and distance measurement parameters determined in the process are transmitted to the external computer unit (4), that in the external computer unit (4) for the individual values ​​of the distance measurement parameters, correction values ​​(K) are determined by forming the difference between measured raw distance values ​​(D r ) and known, predetermined distances, that in the external computer unit (4) a correction value function (K F) is formed from the correction value function (K F ) a correction table is formed with a predeterminable number of support points, and that the correction table is transmitted via the data connection (3) from the external computer unit (4) to the optical distance sensor (2), wherein distance values ​​determined in a working mode with the optical distance sensor (2) are corrected with the correction table. [2] Sensor arrangement (1) according to claim 1, characterized by that the optical distance sensor (2) has a transmitter (8) which emits light beams (7) in the form of light pulses, and a receiver (9) which is designed to receive the light pulses. [3] Sensor arrangement (1) according to claim 2, characterized by that distance measurements are carried out using the optical distance sensor (2) using a pulse transit time method. [4] Sensor arrangement (1) according to one of claims 2 or 3, characterized bythat the distance measurement parameters differ from the raw distance values ​​measured during the calibration process (D r ) and pulse widths determined during the distance measurements (t p ) of the light pulses registered at the receiver (9). [5] Sensor arrangement (1) according to claim 4, characterized by that to determine raw distance values ​​(D r ) and pulse widths (t p ) several light pulses can be used. [6] Sensor arrangement (1) according to claim 5, characterized by that to determine raw distance values ​​(D r ) and pulse widths (t p ) Averages or histograms are calculated. [7] Sensor arrangement (1) according to one of claims 1 to 6, characterized bythat during the calibration process the optical distance sensor (2) is arranged at a fixed predetermined distance from an object (11), and that between the optical distance sensor (2) and the object (11) a rotary wheel (14) with different gray wedges is installed, wherein different gray wedges in the beam path of the optical distance sensor (2) attenuate the light beams (7) emitted by the latter to different degrees. [8] Sensor arrangement (1) according to claim 7, characterized by that the calibration process is terminated after the correction table has been transferred to the optical distance sensor (2). [9] Sensor arrangement (1) according to one of claims 1 to 8, characterized by that the external computer unit (4) is only connected to the optical distance sensor (2) via the data connection (3) during the calibration process. [10] Sensor arrangement (1) according to one of claims 1 to 9, characterized by that the optimization of the correction value function (K F) is carried out using the least squares method. [11] Sensor arrangement (1) according to one of claims 1 to 10, characterized by that the correction value function (K F ) is formed by n-th order polynomials. [12] Sensor arrangement (1) according to one of claims 1 to 9, characterized by that the correction value function (K F ) is formed by means of a neural network. [13] Sensor arrangement (1) according to one of claims 1 to 12, characterized by that a correction value (K) is specified for each support point in the correction table. [14] Sensor arrangement (1) according to claim 13, characterized by that the number of support points in the correction table can be specified on an application-specific basis. [15] Sensor arrangement (1) according to one of claims 1 to 14, characterized bythat during operation a correction of a determined distance value is carried out by a linear interpolation between two correction values ​​(K). [16] Sensor arrangement (1) according to one of claims 2 to 15, characterized by that the transmission power of the transmitter (8) is constant.

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