Optical distance sensor and method for closed-loop control thereof

Abstract

An optical distance sensor with closed-loop exposure control, comprising a light source, a detector, a measurement controller, an evaluation unit and a closed-loop controller. The light source generates and directs an illumination beam to an object under test. The detector detects a measurement beam which has been caused by a reflection of the illumination beam on the object under test. The measurement controller controls the detector during detection of the measurement beam and during readout of the measurement value. The evaluation unit is designed to evaluate the measurement value of the detector. The closed-loop controller drives the light source, the detector and / or the measurement controller such that the amount of received light detected by the detector or a part thereof during a shutter time lies within or close to a target range. The optical distance sensor is designed to emit the illumination beam and to detect the measurement beam and to evaluate the latter by means of the closed-loop controller both in phases of a measurement operation and in measurement pauses formed between the phases. A method for closed-loop control of an optical distance sensor is also disclosed.

Description

Technical Field

[0001] This invention relates to an optical distance sensor with closed-loop exposure control, and to a method for closed-loop control of an optical distance sensor. Background Technology

[0002] Optical distance sensors have been established as robust and widely available sensors in measurement technology. In this configuration, an illumination beam is generated by a light source and directed towards the object being measured. In many cases, the illumination beam generates a measurement beam at or within the object by reflecting off the surface of the object. The measurement beam is detected by a detector, and the distance between the sensor and the object is derived from the detector's measurement. Exemplary embodiments of such optical sensors include triangulation sensors, confocal chromaticity distance sensors, and interferometric distance sensors.

[0003] In the case of a triangulation sensor, the sensor, illumination beam, and measurement beam form a triangle. In this configuration, the detector is typically a line or surface detector. The measured distance is generated by the illumination point on the detector and the sensor geometry.

[0004] In the case of a confocal chromatic ranging sensor, chromatic aberration, typically longitudinal, is intentionally induced in a multicolor illumination beam. Its focal point is arranged close to the spectral portion of the reflective surface of the object being measured, generating a peak in the spectrum of the measurement beam. This peak can be used to infer the distance to the surface. In this case, the detector is a spectrometer.

[0005] In an interferometric sensor, the illumination beam and the measurement beam are superimposed, thus generating interference. Changes in the distance between the sensor and the object being measured cause changes in the interference pattern, and evaluation of the interference pattern allows for conclusions about these distance variations.

[0006] For consistently high measurement accuracy, it is crucial that the number of photons reaching the detector per unit time with the measurement beam remains within a relatively narrow tolerance range, such as between 75% and 85% of the detector's saturation limit, or between 60% and 80% of the saturation limit, or between 85% and 95% of the saturation limit. If the photon count per unit time is too high, the detector element may become saturated, making it impossible to clearly define the illumination point on the detector. If the photon count per unit time is too low, the generated measurement signal may approach the detection threshold and may be lost in noise. Therefore, a relatively narrow tolerance range ensures efficient utilization of the sensor's dynamic characteristics and a good signal-to-noise ratio (SNR).

[0007] The problem is that the number of photons reaching the detector depends on many boundary conditions. Besides the intensity of the illumination beam and its pulse duration, the reflectivity of the object under test, in particular, has a significant impact on the number of incident photons. For example, reflectivity depends on the surface characteristics of the object, the orientation of the surface relative to the illumination beam, and its color. Rough surfaces or object edges produce a significantly more dispersed measurement beam compared to smooth surfaces. Dark surfaces absorb part of the illumination beam and therefore generate a measurement beam with a lower intensity than that of a bright surface. These examples demonstrate that even with a constant illumination beam, the measurement beam can vary considerably. This necessitates closed-loop exposure control.

[0008] A particular challenge is measuring moving objects, such as those on assembly lines, where reflectivity changes rapidly. This necessitates exceptionally fast closed-loop exposure control. During the time before the steady-state control is restored, the variance of the measurements—and consequently the associated error—is very high, subsequently decreasing exponentially. In the case of real-time measurements, this results in a large number of measurements with high measurement errors being generated and output.

[0009] Adaptation of the detector's shutter time is known in practice to achieve optimal exposure for the detector. During the shutter time, the detector collects photons arriving from the measurement beam and other light sources (such as background light). Depending on the number of photons collected, detector properties change, such as the amount of charge stored in the detector elements. At the end of the shutter time, the detector is readout and reset. The sum of the shutter time and readout duration defines the maximum possible frame rate. The frame rate defines the number of individual frames generated per time interval.

[0010] In known variations of shutter speed adjustment, a fixed frame rate is set, and the shutter speed is adjusted within that frame rate as a function of the reflectivity of the object being measured. The advantage of this is that measurements are provided synchronously to the downstream system.

[0011] In another known variation, a flexible frame rate is employed, consisting of a flexible shutter speed as a function of the reflectivity of the object being measured and a constant readout duration. The advantage here is a very high frame rate, but the disadvantage is that the downstream system receives measurements asynchronously and is therefore unpredictable, especially in the case of moving objects, where spatial measurement references may be difficult to obtain.

[0012] The drawback of these two variations is that closed-loop control takes a long time to stabilize. This is because closed-loop control only becomes effective under time delays. In the first time window, the detector records measurements, and in the second time window, a new shutter time is calculated based on the read-out measurements. This means the new shutter time is only used in the third time window. Therefore, closed-loop exposure control always results in ideal shutter times for at least two time windows, which is particularly detrimental in cases of strong reflectivity variations. Poor SNR due to underexposure or overexposure of the detector element leads to a large scattering width, and consequently, measurement uncertainty in the measurement system.

[0013] Another approach is known from EP 3 165 874 A1. To avoid detector saturation, several saturation stages are introduced. The detector is illuminated with a predetermined detection sequence, which is divided into multiple subsequences. In each subsequence, a higher saturation limit is defined than that of the previous subsequence. In this case, the illumination duration and saturation limit are defined such that the charge at the end of the detection sequence is lower than the saturation in each pixel. The disadvantage of this approach is that it requires a special detector. Summary of the Invention

[0014] The object of this invention is to design and develop an optical distance sensor and a method of the type mentioned at the beginning in such a way that rapid closed-loop control of the detector exposure can be achieved with minimal possible impact on the quality of the generated distance measurements.

[0015] According to the present invention, the aforementioned objective is achieved through the features of the invention. Therefore, the distance sensor under discussion includes:

[0016] A light source is used to generate an illumination beam and guide it to the object being measured.

[0017] A detector is used to detect the measurement beam caused by the reflection of the illumination beam on the object being measured.

[0018] The measurement controller is used to control the detector when the measurement beam is detected and the measurement value is read.

[0019] The evaluation unit is designed to evaluate the detector's measurements during the measurement operation phase for the purpose of determining the distance between the distance sensor and the object being measured.

[0020] A closed-loop controller that drives the light source, detector, and / or measurement controller such that the amount of received light detected by the detector or a portion of the detector during the exposure duration is located in or near the target area.

[0021] The distance sensor is designed to emit an illumination beam and detect a measurement beam during both the phases of the measurement operation and the measurement intervals formed between the phases of the measurement operation, and to evaluate the latter by means of a closed-loop controller.

[0022] Regarding this method, the above-mentioned objective is achieved through the features of the present invention. Thereafter, the method uses a distance sensor comprising a light source and a detector, and determines the distance to the object being measured during a measurement operation phase by means of this distance sensor. The method includes the following steps:

[0023] It generates an illumination beam from a light source and directs the illumination beam onto the object being measured.

[0024] The measuring beam is detected by a detector, which detects the reflection of the illumination beam on the object being measured.

[0025] The detector's measured value is read out, and this reading is controlled by the measurement controller.

[0026] Determine the amount of received light detected by the detector or a portion of the detector during the exposure duration.

[0027] Specifically, during the measurement operation phase and the measurement intervals between phases, an illumination beam is generated and guided to the object being measured, and the measurement beam is detected and evaluated using a closed-loop controller.

[0028] The light source, detector, and / or measurement controller are driven in such a way that the received light quantity is located in or near the target area.

[0029] According to the present invention, it is first recognized that in practice, the maximum possible sampling rate of a distance sensor is rarely needed and / or used. Instead, in practice, distance sensors often operate at reduced sampling rates, resulting in more or less noticeable measurement intervals between the various stages of the measurement operation in each case. To accelerate closed-loop control, increasing the sampling rate and thus reducing measurement intervals could be considered. However, this leads to unnecessary work, wastes valuable resources, and negatively impacts energy consumption. If distance values ​​are not immediately rejected again, they will have to be stored, which will significantly load what is typically very limited storage space. However, it has been recognized that using measurement intervals is an effective means of accelerating closed-loop control.

[0030] According to the invention, the illumination beam is emitted not only during a phase of the measurement operation, but also during one or more intermediate measurements in the case of measurement intervals formed between consecutive phases of the measurement operation. In the case of intermediate measurements, the illumination beam is emitted, the measurement beam is detected, and the detector is read out, as would also happen in the case of a phase of the measurement operation. However, the readout measurement value from the detector is only evaluated for closed-loop control, not for determining distance. This avoids unnecessary computational work by means of distance-related evaluation of the measurement value. As a result of the additional function of the additional measurement, additional measurement values ​​for control can be obtained, which also allows tracking of closed-loop control during measurement intervals, and still avoids wasting resources. Although there is still a time delay between generating and utilizing the measurement value, the closed-loop control achieves a stable closed-loop control state more quickly because the adjustment of the closed-loop control is performed at a higher rate without the need to calculate unnecessary distance values.

[0031] The distance sensor according to the present invention, realizing this basic concept, includes a light source, a detector, a measurement controller, an evaluation unit, and a closed-loop controller. The light source generates an illumination beam and guides it to the object being measured. The detector detects the measurement beam caused by the reflection of the illumination beam at the surface of the object being measured. When the measurement beam is detected, the detector generates a measurement value that can be read from the detector. The measurement value typically represents the number of photons arriving at the detector during the shutter time. Therefore, the measurement value represents the amount of received light that has been detected by the detector or a portion of the detector during the shutter time. The measurement value can be a scalar or a one-dimensional or multi-dimensional variable.

[0032] The evaluation unit is designed to determine distance by evaluating the detector's measurements during a phase of the measurement operation. This may include, for example, determining the maximum light intensity and assigning that maximum light intensity to the distance in the case of a triangulation sensor.

[0033] The measurement controller controls the detector, particularly during the detection of the measurement beam and during the reading of the measurement value. This may include, for example, activating the detector used to detect the beam and triggering the reading of the measurement value from the detector.

[0034] The closed-loop controller controls the components of the distance sensor in such a way that the amount of received light detected by the detector or a portion of the detector during the shutter time is within the target range, or if not within the target range, approaches the target range, and preferably reaches the target range. These controlled components may include a light source, a detector, and / or a measurement controller.

[0035] This invention can be used in conjunction with various optical distance measurement methods. Importantly, in optical distance measurement methods, an illumination beam is emitted and the measurement beam is received and evaluated. This requirement can be met in many optical distance measurement methods. In one embodiment, the distance sensor according to the invention operates based on the principle of a triangulation sensor, where point or line illumination of the object being measured can be used. In another embodiment, the distance sensor according to the invention operates based on the principle of a confocal chromatic distance sensor. In yet another embodiment, the distance sensor according to the invention operates based on the principle of an interferometric distance sensor.

[0036] The light source for a distance sensor can be formed in a variety of ways. As exemplary embodiments, references include LEDs (light-emitting diodes), SLEDs (superluminescent LEDs), lasers, particularly semiconductor lasers, supercontinuum lasers, or swept-frequency light sources, to name just a few conceivable light sources. Depending on the embodiment of the distance sensor, the illumination beam generated by the light source can be monochromatic or polychromatic. In addition to the actual light generator, the light source may also include optical devices that shape, guide, and / or influence the illumination beam in some other way. Examples include lenses, beam splitters, mirrors, and prisms.

[0037] Evaluation units, measurement controllers, and / or closed-loop controllers can be implemented in a variety of ways. In one embodiment, these units are implemented in hardware. In another embodiment, these units are implemented through a combination of software and hardware. In this case, the hardware can be formed, for example, a microprocessor, microcontroller, DSP (Digital Signal Processor), and / or FPGA (Field Programmable Gate Array), on which the software program is processed. For this purpose, RAM (Random Access Memory), ROM (Read-Only Memory), input and output interfaces, analog-to-digital converters, or other peripheral devices can be used.

[0038] The closed-loop controller and / or measurement controller can be designed to signal the evaluation unit to the stage or intermediate measurement of the measurement operation. In this way, the evaluation unit can be signaled whether to perform an evaluation of the measurement value relative to the distance. This information can be transmitted to the evaluation unit via a trigger input. Alternatively, it is conceivable to set a bit in a register, by which the evaluation unit signals the processing of the existing measurement value.

[0039] The "target range" within which the received light quantity falls can be defined in various ways. The objective of defining the target range is typically that the detector, or a portion of the detector, will not become saturated. The specific implementation is largely irrelevant. Normalizing the target range to a saturation limit can be advantageous. The target range can be specified as a percentage range, such as between 75% and 85% of the detector's saturation limit, or between 60% and 80% of the saturation limit, or between 85% and 95% of the saturation limit, to name just a few examples. However, the target range can also be defined using a target value and a scattering bandwidth, such as 80% ± 5%, or 70% ± 10%, or 90% ± 5%. The specific definition of the target range may depend on the specific embodiment of the detector and its behavior.

[0040] Another consideration is that the detector may not specifically detect the measurement beam. Therefore, it is conceivable that, in the case of a standalone measurement, background light would enter the detector, which exists in a space illuminated by the use of a distance sensor and cannot be adequately shielded.

[0041] For the purposes of this invention, the importance of the measurement interval is not critical. It is sufficient to achieve at least one intermediate measurement between the various stages of the measurement operation. Since conventional detectors typically have a maximum frame rate, this means that the actual frame rate used is lower than the maximum possible frame rate. The maximum possible frame rate can be determined by the sum of the shutter time and the readout duration. The actual frame rate used defines the frequency at which distance is determined per unit time. In one embodiment, the actual frame rate used is 50% or less relative to the maximum possible frame rate. For example, at a maximum possible frame rate of 10 kHz, this would mean that the actual frame rate used is 5 kHz or less. In another embodiment, the actual frame rate used is 10% or less relative to the maximum possible frame rate. At a maximum possible frame rate of 10 kHz, this would mean that the actual frame rate used is 1 kHz or less.

[0042] In one development, the measurement controller was designed to asynchronously read out the detector's measurements. This resulted in greater freedom of control over the distance sensor's components.

[0043] In another development, the measurement controller was designed to synchronously read out the detector's measurements. In this case, measurements could be read from the detector at constant time intervals.

[0044] In another development, synchronous and asynchronous readouts can be combined. In one embodiment, this could mean that the measurements evaluated by the evaluation unit for distance determination are synchronous at constant time intervals, while intermediate measurements occur asynchronously during the measurement intervals. This provides the advantage of having defined time intervals between distance values, particularly useful in downstream systems using the obtained distance values, and offers a high degree of freedom for closed-loop control via intermediate measurements.

[0045] In one embodiment, the measurement controller is designed to define the exposure start point for beginning to detect the measurement beam based on the shutter speed. This may mean selecting the exposure start point such that the sequence of shutter speeds and the readout of the measured values ​​occur at a defined readout time. This defined readout time can be defined, for example, by a timer that defines the synchronous readout of the measured values. The defined readout time can also be achieved using a variable shutter speed through this definition of the exposure start point.

[0046] In one embodiment, the closed-loop controller is designed to influence the intensity of the illumination beam to provide closed-loop control of the amount of light received. The intensity of the illumination beam can be an instantaneous value. In the case of a pulsed illumination beam, this value can define the intensity of the beam during the period the illumination beam is activated. In this case, the illumination beam can vary between this intensity value and zero intensity.

[0047] In one embodiment, the closed-loop controller is designed to influence the pulse duration of the illumination beam in order to provide closed-loop control of the amount of light received. The pulse duration defines the length of time the illumination beam is on. The longer the pulse duration, the longer the measurement beam caused by the illumination beam. In this way, the amount of light received can be influenced by simple means.

[0048] In one embodiment, the closed-loop controller is designed to influence the exposure start of the detector to provide closed-loop control of the amount of light received. Influencing the exposure start can optimize the accumulation of received photons. For example, in the case of a pulsed illumination beam, the exposure start can be synchronized with the pulse. In this way, it can be ensured that photons are collected in a defined manner.

[0049] In one embodiment, the closed-loop controller is designed to influence the detector's exposure initiation to provide closed-loop control of the amount of light received. Assuming the measurement beam arrives over the entire shutter time, the amount of light received can be increased by increasing the shutter time, or decreased by decreasing the shutter time. In this way, the amount of light received is easily influenced.

[0050] The aforementioned embodiments for closed-loop control of light reception can be combined as needed. An error detection device can also be installed, which terminates the test if there is no measurement beam to increase the received light intensity. In this case, there may be misplacement of the distance sensor and / or the object under test, causing the illumination beam to fail to produce a receivable measurement beam.

[0051] In one embodiment, the distance sensor includes a readout memory designed to store readout measurements from the detector. In this case, an analog-to-digital converter (ADC) can be positioned between the detector and the readout memory to convert the detector's analog measurements into digital values. The readout memory can serve as temporary storage for the measurements. As a result, the detector can perform the next measurement while other components, such as a closed-loop controller or evaluation unit, read out and / or process the temporarily stored measurements from the previous measurement. In this case, it is advantageous if the readout memory is large enough to store at least one set of measurements. However, depending on the type of evaluation, it may also be advantageous if multiple sets of measurements can be stored in the readout memory. This would make it possible to temporarily store measurements from several measurements.

[0052] In one embodiment, the detector comprises multiple detector elements. These detector elements can be formed in various ways. These detector elements should allow for a certain local resolution. This can be achieved, for example, by detector elements that are separated from each other and can detect incident light independently of each other. The multiple detector elements can be arranged differently. Preferably, the detector elements are arranged in a row or a region. In the case of a detector with multiple detector elements, the detector measurements can be one-dimensional or multi-dimensional, that is, they can be formed by, for example, vectors or matrices.

[0053] In this scenario, the portion determining the amount of light received can be formed by the detector element. When evaluating this portion, the closed-loop controller can identify the detector element that provides the maximum measurement value across all measurements. The amount of light received at the detector element with the maximum measurement value can then be controlled within the target range in a closed-loop manner by the closed-loop controller.

[0054] In one embodiment, at least one intermediate measurement is performed between two consecutive phases of the measurement operation, wherein an illumination beam is generated during the intermediate measurement and the measurement beam is detected in the event of an uncertain distance value.

[0055] If there may be several intermediate measurements during the measurement interval, the next possible intermediate measurement can be performed based on the anticipated need for further closed-loop control. If the control error determined by the closed-loop controller is higher than a first threshold, further intermediate measurements and further adaptation may be necessary or at least helpful. If the closed-loop control error determined by the closed-loop controller is lower than a second threshold, further intermediate measurements may be unnecessary and can therefore be skipped. The first threshold can be greater than or equal to the second threshold. In this way, the number of intermediate measurements can be kept low.

[0056] In a development process, the number of skipped intermediate measurements can be limited. If the maximum number of skipped intermediate measurements is reached or exceeded, the intermediate measurements can be forced to be performed. For example, it is conceivable to set this maximum number to 5 or 10 skipped intermediate measurements. In this way, timely readjustment can be achieved even when reflectivity changes.

[0057] In one development, intermediate measurements can be performed at least as one approaches the next stage of the measurement operation and cannot be skipped. The specific meaning of the term "approaching" depends on the particular application. If a large number of intermediate measurements are provided and / or reflectance changes frequently and abruptly, multiple time windows are available to perform further intermediate measurements immediately preceding a stage of the measurement operation. In one development, at least one final intermediate measurement within a timing window is performed immediately preceding a stage of the measurement operation, and this measurement is not skipped. In this way, possible deviations between the received light amount and the target range can be corrected.

[0058] In one development, measurement intervals can be used not only for closed-loop control of exposure but also for improving measured values. Therefore, information for improving measured values ​​can be detected between two consecutive phases of the measurement operation. In this case, the timing window actually used for intermediate measurements can be used to determine information for improving measured values. By skipping intermediate measurements, this timing window can also become idle under sufficiently low closed-loop control variance. Therefore, measurement intervals can still be used to improve measured values.

[0059] In this scenario, measurement improvement could include background masking to correct for the influence of background light. In this case, background light is understood to be light that does not originate from the measurement beam. This light could be formed, for example, by illuminating the space in which the distance sensor operates. In addition to the measurement beam, the detection of information for background masking would include detecting the background light illuminating the detector. To obtain this information, the illumination beam could be turned off, ensuring that the detector is illuminated only by the background light. In this scenario, exposure could initially be controlled in a closed-loop manner, and then the background light could be determined. Attached Figure Description

[0060] There are various possibilities for advantageously configuring and developing the teachings of the present invention. In this regard, the following explanation of preferred exemplary embodiments of the invention is given with reference to the accompanying drawings. The development of general preferred embodiments and teachings is also explained in conjunction with the explanation of preferred exemplary embodiments of the invention with reference to the accompanying drawings. The following are shown in the drawings:

[0061] Figure 1 A time-plot of the detector exposure profile is shown during the measurement operation phase.

[0062] Figure 2 A time plot of the detector's exposure curves is shown, illustrating two phases of the measurement operation and several intermediate measurements performed during the measurement intervals between the two phases of the measurement operation.

[0063] Figure 3 A block diagram of functional units according to an exemplary embodiment of the distance sensor of the present invention is shown.

[0064] Figure 4 A timeline of an embodiment of the method according to the present invention is shown.

[0065] Figure 5 The graph shows the intensity in the detector element with background light and without a measurement beam.

[0066] Figure 6 A graph showing the intensity of each detector element in a detector with background light and a measurement beam is presented, along with...

[0067] Figure 7 A graph showing the intensity of each detector element in a detector with a measuring beam corrected by background light is presented. Detailed Implementation

[0068] Regarding the fact that the maximum possible sampling rate (fmax) of a distance sensor is rarely needed and used in practice, in this invention, the measurement interval between the two phases of the measurement operation is explicitly used for adjusting the detector signal.

[0069] Figure 1 Display each stage of the measurement operation as "F". i “F” i+1 "and "F i+2 ", where i is the exponent, and is typically an integer or a natural number. To provide the technical advantage of synchronous distance measurement, in this embodiment, the detector exposure and distance value calculation are implemented in a common mode. For each falling edge, the detector is read out such that each falling edge is within a time interval T. F At this location, the sampling rate f thus achieved F Significantly smaller than the maximum sampling rate f maxCorresponding to a given illumination duration (the distance between the rising and falling edges), the exposure start (i.e., the time of the rising edge) is selected. For objects moving at a constant speed, this selection is equivalent to the advantage of equidistant measurement.

[0070] During the measurement intervals between the various stages of the measurement operation, the optimal shutter speed is determined and readjusted through several ideal asynchronous intermediate measurements (subframes). Figure 2 In the middle, in "F i "and "F i+1 The figure shows multiple intermediate measurements 1 (i.e., a total of 16 intermediate measurements), of which only some are labeled for clarity. If the reflective properties of the object being measured change drastically, such as due to hard edge contrast, the shutter time readjustment will not initially affect the distance sensor's output distance measurement, because the closed-loop control has multiple (intermediate) measurement times to adjust.

[0071] In the illustrated scenario, it can be seen that the shutter speed is assumed to be constant after only a few intermediate measurements. This means that more intermediate measurements can be skipped starting from the fourth. In this case, intermediate measurements can be forced after at least five intermediate measurements have been skipped. Furthermore, it is conceivable to perform the 16th or 15th and 16th intermediate measurements in any case. As a result, even a hard contrast before the actual measurement would only result in a single erroneous distance measurement.

[0072] This results in an advantage over known static measurement methods that only have a reduced measurement frequency and methods with asynchronous measurements, namely, the exposure used to determine the distance value has a near-ideal signal-to-noise ratio (SNR). This advantageously and significantly narrows the confidence interval of the output measurement because statistical outliers in the output distance measurement due to overexposure or underexposure of the detector can be significantly reduced.

[0073] Figure 3A block diagram illustrating an exemplary embodiment of a distance sensor 2 according to the present invention is shown, which operates based on the principle of triangulation. The distance sensor 2 includes a light source 3, a detector 4, a measurement controller 5, an evaluation unit 6, and a closed-loop controller 7. The light source 3 generates an illumination beam 8, which is guided onto the surface 9 of the object 10 being measured. A measurement beam 11 is caused by the reflection of the illumination beam 8 on the surface 9. The measurement beam 11 illuminates one or more detector elements (not shown) of the detector 4. The detector 4 detects the measurement beam 11 and generates a measurement value, wherein the measurement value is a vector (in the case of a linear detector) / matrix (in the case of a zone detector) of several values, and each entry of the vector / matrix corresponds to a measurement value of the detector element. In this case, the detector is controlled by the measurement controller 5, particularly regarding the exposure start and shutter time. Ideally, the measurement controller takes over the entire measurement timing of the detector 4.

[0074] If detector 4 has generated a measurement value, it is stored in readout memory 12. Evaluation unit 6 and closed-loop controller 7 can access the measurement value stored in readout memory 12. Evaluation unit 6 uses these measurement values ​​during a phase of the measurement operation to determine the distance 'a' between distance sensor 2 and the object 10 being measured. Closed-loop controller 7 determines the amount of light received that has been detected by detector 4 during the shutter speed. Closed-loop controller 7 influences light source 3 and measurement controller 5 in such a way that the amount of light received is within or near the target range. For this purpose, closed-loop controller 7 can influence the intensity and pulse duration of illumination beam 8 via light source 3, and can influence exposure initiation and shutter speed via measurement controller 5.

[0075] Figure 4 A timing diagram detailing an embodiment of the method according to the invention is shown. Two intermediate measurements 1 and 1', measurement 13 for improving measurement values, and stage 14 of the measurement operation are illustrated. In the sub- Figure 4 Figure a shows the exposure of detector 4, in the sub- Figure 4 b shows the readout of detector 4, in the sub- Figure 4 c illustrates the use of the read memory 12, in the sub- Figure 4 The activity of light source 3 is shown in d, while in the sub- Figure 4 The output of the determined distance value a is shown in e.

[0076] In intermediate measurement 1, 1', the emitted illumination beam (sub-) Figure 4 d), and exposure detector (sub) Figure 4 a) At the end of the shutter speed, the illumination beam is deactivated, and the detector's exposure ends. The detector is read out (sub-detection). Figure 4b). After reading, the contents of the read memory 12 are updated. As a result, in the case of intermediate measurement 1, the memory contents are updated from "t1" to "t2", while in the case of intermediate measurement 1', the memory contents are updated from "t2" to "t3". Specific memory contents are used during intermediate measurements 1 and 1', and during the phase of measurement operation 14 for closed-loop control of exposure, which is determined by the slave... Figure 4 c to child Figure 4 The arrow pointing to 'a'.

[0077] exist Figure 4 In the exemplary embodiment shown, measurement 13 for measurement value correction is inserted immediately before the stage immediately following measurement operation 14. During this measurement 13, the illumination beam is stopped, and the amount of light reaching the detector is detected in the absence of a measurement beam. This means that the detector detects only background light. The background light detected in this way can be used to correct the measurement value, such as in conjunction with... Figures 5 to 7 To explain in more detail: The detected measurements are not sent to the readout memory, but are instead fed directly to the brightness calibration.

[0078] After measurement 13 for measurement value correction, the actual distance measurement is performed in the measurement operation 14 phase. For this purpose, the illumination beam is emitted again, and the detector is illuminated with the measurement beam. After the measurement value is read from the detector, the contents of the read memory are updated from "t3" to "t4". The evaluation unit 6 uses the measurement value to calculate the distance value a. This calculated distance value a is finally output from the distance sensor (sub-). Figure 4 e). At the same time, the new intermediate measurement 1” begins.

[0079] Figures 5 to 7 The following are exemplary curves representing brightness calibration. All graphs show intensity values ​​plotted on a pixel index. It is assumed here that the detector is a linear detector with 500 detector elements (pixels) in the example shown.

[0080] Figure 5 Intensity curve 15 of the background light without a measurement beam is shown. Figure 6 The intensity curves 16 for the background light and the measurement beam are shown. A threshold 17, which helps detect the incident point of the measurement beam on the detector, is also shown in both graphs. It can be seen that peaks 18 above this threshold 17 appear in the background light, and peaks 19 appear in the measurement beam. Therefore, measurement correction is helpful.

[0081] During measurement 13, used to obtain measurement correction information, intensity distribution 15 can be obtained. Because the illumination beam is stopped during measurement 13, the collected light must originate from the background light. Therefore, the intensity distribution 16, which has already been detected with the activated illumination beam, can be corrected by subtracting the intensity curve 15. This results in... Figure 7 The intensity curve 20 is shown. With the corrected intensity distribution 20, only the peak 19 exceeds the threshold 17, and therefore the incident point of the measurement beam on the detector can be clearly identified. Thus, brightness calibration is achieved.

[0082] Finally, it should be clearly stated that the above exemplary embodiments are only used to explain the claimed teachings, and not to limit the teachings to the exemplary embodiments.

[0083] List of reference numerals

[0084] 1,1',1” Intermediate Measurement

[0085] 2 Distance Sensor

[0086] 3. Light source

[0087] 4 Detectors

[0088] 5. Measurement Controller

[0089] 6. Evaluation Unit

[0090] 7. Closed-loop controller

[0091] 8 lighting beams

[0092] 9 Surface

[0093] 10 Test Subjects

[0094] 11 lighting beam

[0095] 12 Reading out memory

[0096] 13 Measurements used for measurement value correction

[0097] 14. Stages of Measurement Operation

[0098] 15. Background light intensity curve

[0099] 16. Measurement of the intensity curve of the light beam

[0100] 17 Threshold

[0101] 18 Peak value of background light

[0102] 19. Measuring the peak value of the beam

[0103] 20 Corrected intensity distribution

Claims

1. An optical distance sensor having closed-loop exposure control, comprising: A light source (3) is used to generate an illumination beam (8) and to guide the illumination beam (8) to the object under test (10). Detector (4) for detecting the measurement beam (11) caused by the reflection of the illumination beam (8) on the object under test (10). A measurement controller (5) is used to control the detector (4) when the measurement beam (11) is detected and when the measurement value is read. The evaluation unit (6) is designed to evaluate the measurements of the detector (4) during a phase of the measurement operation (14) for the purpose of determining the distance (a) between the optical distance sensor (2) and the object under test (10), and A closed-loop controller (7) drives the light source (3), the detector (4), and / or the measurement controller (5) such that the amount of received light detected by the detector (4) or a portion of the detector (4) during the shutter time is within or near the target range. The optical distance sensor (2) is designed to emit the illumination beam (8) during each stage of the measurement operation (14) and during the measurement intervals formed between each stage of the measurement operation (14), and to detect the measurement beam (11), and to evaluate the latter by means of the closed-loop controller (7). The optical distance sensor (2) is further configured to perform at least one intermediate measurement (1, 1', 1") between two consecutive phases of the measurement operation (14), wherein the illumination beam (8) is generated during the intermediate measurement (1, 1', 1") and the measurement beam (11) is detected without determining the distance (a), wherein the measurement value of the detector read during the intermediate measurement is evaluated only for controlling the amount of light received and not for determining the distance, and in the case of multiple intermediate measurements (1, 1', 1"), before performing a possible intermediate measurement (1, 1', 1"), it is checked whether the control difference determined by the closed-loop controller (7) is higher than a first threshold and therefore requires another intermediate measurement (1, 1', 1") or whether the control difference determined by the closed-loop controller (7) is lower than a second threshold and therefore does not require another intermediate measurement (1, 1', 1").

2. The optical distance sensor according to claim 1, characterized in that, The measurement controller (5) is designed to operate at a constant time interval (T). Frame This prompts the reader to read the measured value of the detector (4).

3. The optical distance sensor according to claim 1 or 2, characterized in that, The measurement controller (5) is designed to define the exposure start of the measurement beam (11) at which it begins to detect the exposure based on the shutter time.

4. The optical distance sensor according to claim 1, characterized in that, The closed-loop controller (7) for closed-loop control of the amount of light received is designed to influence the intensity of the illumination beam (8), the pulse duration of the illumination beam (8), the exposure start of the detector (4), and / or the shutter time of the detector (4).

5. The optical distance sensor according to claim 1, characterized in that, The optical distance sensor (2) includes a readout memory (12) designed to store readout measurements of the detector (4), wherein an analog-to-digital converter can be arranged between the detector (4) and the readout memory (12).

6. The optical distance sensor according to claim 1, characterized in that, The detector (4) includes a plurality of detector elements, wherein the detector elements are arranged in a row or in a region, and wherein a portion for determining the amount of light received can be formed by the detector elements.

7. A method for closed-loop control of an optical distance sensor, wherein the optical distance sensor (2) includes a light source (3) and a detector (4), and wherein the distance to a measured object (10) is determined by means of the optical distance sensor (2) at various stages of a measurement operation, the method comprising the following steps: An illumination beam (8) is generated from the light source (3) and guided onto the object under test (10). The measurement beam (11) caused by the reflection of the illumination beam (8) onto the object under test (10) is detected by the detector (4). The measured value of the detector (4) is read out, wherein the reading is controlled by the measurement controller (5). Determine the amount of received light detected by the detector (4) or a portion of the detector (4) during the shutter time. The illumination beam (8) is generated and guided to the object under test (10) during both the phases of the measurement operation (14) and the measurement intervals formed between the phases of the measurement operation (14), and the measurement beam (11) is detected and evaluated by means of a closed-loop controller (7). The light source (3), the detector (4), and / or the measurement controller (5) are driven by the closed-loop controller (7) in such a way that the amount of light received is within or close to the target range. Between two consecutive phases of the measurement operation (14), at least one intermediate measurement (1, 1', 1") is performed, wherein the illumination beam (8) is generated during the intermediate measurement (1, 1', 1") and the measurement beam (11) is detected without determining the distance (a), wherein the measurement value of the detector read during the intermediate measurement is used only to evaluate the control of the amount of light received and not to determine the distance, and in the case of multiple intermediate measurements (1, 1', 1"), before performing a possible intermediate measurement (1, 1', 1"), it is checked whether the control difference determined by the closed-loop controller (7) is higher than a first threshold and therefore requires another intermediate measurement (1, 1', 1") or whether the control difference determined by the closed-loop controller (7) is lower than a second threshold and therefore does not require another intermediate measurement (1, 1', 1").

8. The method according to claim 7, characterized in that, The intermediate measurement (1, 1', 1") is performed in a timing window immediately preceding the measurement operation (14) in order to correct for any possible deviation between the received light amount and the target range.

9. The method according to claim 7 or 8, characterized in that, Information for improving the measurement value is detected between two consecutive stages of the measurement operation (14).

10. The method according to claim 9, characterized in that, The measurement improvement includes background occlusion for correcting the effects of background light, wherein the detector is exposed to background light to obtain information for background occlusion.

11. The method according to claim 9, characterized in that, The measurement improvement includes background occlusion for correcting the influence of background light, wherein the detector is exposed to background light to acquire information for background occlusion without an activated illumination beam.

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