Optoelectronic scanning measurement instrument and method with temperature compensation

Abstract

The invention provides an optoelectronic scanning measurement instrument and method with temperature compensation. The invention relates to a method and an optoelectronic scanning measuring instrument (1) for online compensation of thermal effects on an optoelectronic scanning measuring instrument (1), which adapt a set of instrument parameters associated with a defined reference thermal state of the instrument (1) as a function of an actual measured thermal state of the instrument (1) sensed by a thermal sensor (6a-6d) of the instrument (1), and calculating corresponding object point coordinates based on the compensation parameter set.

Description

Technical Field

[0001] This invention relates to photoelectric scanning measurement instruments and methods. Background Technology

[0002] Point cloud generation is used to survey many different geodetic or industrial scenes. The resulting surveys can be used to obtain accurate three-dimensional (3D) models of the scene, which are composed of point clouds. This scanning is a highly efficient technique for generating millions of spatial measurement points on the surface of an object within a scan sphere in minutes or seconds. Terrestrial laser scanning technology is particularly useful for collecting static collaborative data on stationary, immobile natural or man-made structures or scenes of immobile man-made objects (e.g., collision sites). Typical surveying tasks include recording objects or their surfaces (such as industrial plants, building facades, or historic buildings), as well as accident scenes and crime scenes.

[0003] The points in this point cloud are stored by coordinates in a coordinate system, which can be defined by the surveying instrument recording the point cloud. Typically, the origin of the coordinate system is formed by the instrument's center (especially by the instrument's so-called nodal point). Points are usually surveyed by associating the distance measured with a laser beam with the alignment (i.e., aiming or measurement direction) used to measure that distance.

[0004] Common surveying instruments include at least one radiation source or emitter for generating optical measurement radiation (typically laser radiation), and an optical device including a deflector (such as a rotating mirror) through which the generated measurement radiation can be emitted into free space onto the target or object to be measured; therefore, these devices are also known as so-called free-beam sensors. In this context, optical measurement radiation is understood to be electromagnetic radiation not only in the visible range of the spectrum, but also in the ultraviolet, infrared, and terahertz ranges. Laser scanning instruments are known to use measurement radiation with wavelengths of 405 nm, 532 nm, 635 nm, 650–690 nm, 780 nm or 785 nm, 795 nm, 808–850 nm, 905 nm, 980 nm, 1064 nm, or 1500–1570 nm.

[0005] Typically, these surveying instruments also include a device for rotatably changing the direction of the free beam. Typically, a vertical rotation axis and a horizontal rotation axis are provided to change the measurement or aiming direction, wherein the actual rotational position of each axis is sensed by a corresponding angle sensor. Typically, the rotation of the vertical axis is measured by the azimuth angle, while the rotation of the horizontal axis is measured by the elevation angle. If the surveying instrument is specifically implemented as a laser scanner, one of the axes (usually the azimuth axis) can be a slow axis, while the other axis (the elevation axis) can be a fast axis.

[0006] More specifically, and in terms of its basic structure, such a laser scanner is therefore designed to deflect the measurement beam in one spatial direction by rotating the aforementioned deflector about one axis (pitch axis), and to independently deflect the measurement beam in another spatial direction by rotating the top portion or body that includes or supports the deflector about a second axis (azimuth axis). The body is, for example, rotatably mounted to a base including a tripod for securing the laser scanner in a known reference position.

[0007] Therefore, the spatial measurement area (scanning sphere) can be recorded. The horizontal scan width is often 360°, i.e., a complete circle around the azimuth axis, and in the vertical direction, it is, for example, 180°, i.e., a semicircle around the pitch axis. The result is a hemisphere that is covered, which, together with the maximum measurement distance, defines the measurement space or scanning sphere.

[0008] The distance to a point on the corresponding object surface can be calculated by observing the time between the transmission and reception of signals using time-of-flight measurement methods. Other methods, such as those using phase measurement, are also known in the art. Alignment angles are achieved using angle sensors arranged along the azimuth and pitch axes. Therefore, the measurement of point coordinates is typically achieved by determining distance and angle, that is, in spherical coordinates, such that the object point is characterized by the distance value, pitch angle, and azimuth angle from the origin of the reference coordinate system. However, other coordinate representations or transformations are also known, such as Cartesian coordinates, which are particularly advantageous for display and further processing.

[0009] For fast and accurate scanners, short measurement times and high accuracy of point coordinates are particularly important. For example, distance accuracy in the millimeter range or below and measurement times for individual points in the sub-microsecond to millisecond range are desirable, allowing the measurement range to vary from a few centimeters to several kilometers.

[0010] Regarding the accuracy of the measurement direction, an angular accuracy of a few seconds is desired. This requires highly precise assembly or highly accurate calibration to prevent measurement errors caused by assembly defects. High precision is particularly required between parts or components of the instrument that can rotate relative to each other. Methods for precise calibration to determine the measurement parameters of a scanning measuring instrument are known in the art.

[0011] However, internal or environmental influences, such as aging or thermal effects, can cause deviations in the size or position of instrument components after calibration. As a result, the calibration parameters no longer match the actual conditions of the instrument, thus reducing measurement accuracy. Therefore, recalibration is required to generate new calibration parameters. Although calibration methods are known and can be performed in the field, making meticulous factory calibration not mandatory, even such field calibrations require specific operator knowledge and significant time to perform.

[0012] It is also known in the art to reduce the impact on the internal or environmental aspects of an instrument, and thus on the accuracy of the resulting coordinate measurements. For example, US2013010307 A1 refers to a laser scanner equipped with cooling devices for dissipating heat generated by the motors used to rotate the measuring head and deflector, as well as heat generated by the current from the control and evaluation units and other electrical or electronic components.

[0013] However, the implementation of cooling equipment makes measuring instruments more complex and requires additional power. This is particularly disadvantageous for standalone devices (such as ground laser scanners or scanners mounted on mobile measuring platforms (UAVs / measuring drones or UGVs / robotic measuring vehicles)) with limited battery capacity used in the field (and which also constitute another heat source within the instrument itself), and cannot completely offset the thermal effects within the instrument, not to mention temperature changes caused by the environment. Summary of the Invention

[0014] Therefore, the object of the present invention is to provide an improved scanning measurement instrument and method thereof.

[0015] In particular, the aim is to provide a scanning measurement instrument and method that compensates for thermal effects.

[0016] Another object of the present invention is to provide a scanning measurement instrument and method that thus accurately and very precisely compensates for the thermal effects on the accuracy of the coordinates of the measured object points.

[0017] Another objective is to provide a scanning measurement instrument and method that can compensate for thermally induced measurement errors online or in real time during scanning.

[0018] This invention relates to a method for online or real-time compensation of the thermal effects on photoelectric scanning measuring instruments, which can be performed by the control and processing unit of the claimed scanning measuring instrument.

[0019] The method includes an automated step of rotating the optical free beam of the instrument on the surface of the object to be scanned to measure the corresponding coordinates of multiple surface points (based on the distance to the corresponding object point sensed by the free beam in a known measurement direction), preferably for geodetic and / or industrial measurements of stationary objects.

[0020] The method also includes providing a set of instrument parameters associated with a defined reference thermal state (such as a reference temperature field) of the instrument. This set of parameters may include instrument parameters calibrated or measured under the reference thermal state, for example, using calibration standards or metrologies or other calibration methods known in the art during factory or field calibration. In addition to or as an alternative to calibration parameters, parameters are conventionally defined simply, for example, set to defined values, such as zero, under the reference thermal state (e.g., at a temperature of 20°C).

[0021] The method also includes measuring the current or actual thermal state of the instrument and determining the difference between the current thermal state (especially the current temperature field) and the reference thermal state.

[0022] The method further includes: using a compensation model that may include a compensation coefficient matrix, starting from a provided initial parameter set and estimating a compensation parameter set based on differences in thermal states; and calculating the corresponding object point coordinates based on the determined compensation parameter set.

[0023] Alternatively, a thermal state history of the instrument including at least one previous thermal state is provided, and the estimation of the compensation parameter set is based on the thermal state history as input to the compensation model.

[0024] Therefore, when the instrument is in off mode, at least one previous thermal state can be automatically measured and the thermal state history calculated before the measurement object point. Alternatively or additionally, the thermal state measurement is performed at a lower measurement rate before the measurement object point or before the scan, compared to a higher measurement rate during the measurement at the object point or during the scan.

[0025] Therefore, previous thermal states and reference or actual thermal states can differ in their characteristics or definitions. For example, the temperature field of a thermal state in the state history can have a different, preferably lower, degree or density, or can include fewer temperature sensing locations or areas as a reference or actual thermal state. For example, it may include only a reduced number of temperature sensing points for the instrument's measuring components, i.e., sparse or weakened thermal monitoring of the instrument's components, such as skipping some installed thermal sensors or components. A more streamlined or reduced thermal state history compared to a reference or actual thermal state allows for a reduced workload in thermal data acquisition, processing, and storage, which is particularly advantageous in the optional case of automated measurements in the instrument's off-mode.

[0026] As another option, methods for coordinating scans include providing at least two different compensation models and / or sets of calibration parameters applicable to different operating phases of the instrument and / or different ranges of the current thermal state (such as the warm-up phase).

[0027] As another option, the compensation model is based on a machine learning correlation between the compensation parameters and the thermal state. This allows the compensation model to be configured to be trainable when operating the measuring instrument in the field, which enables the compensation model to be adapted or optimized for the specific measuring instrument.

[0028] The present invention also relates to a photoelectric scanning measuring instrument for scanning the surface of a stationary (preferably geodetic and / or industrial) object by measuring the corresponding coordinates of multiple surface points.

[0029] The instrument includes: a base; a radiation source configured to generate optical measurement radiation; a deflector, such as a rotatable mirror, configured to emit measurement radiation in the form of a free beam onto a corresponding surface point in the measurement direction; at least one driver for rotating the deflector relative to the base about at least one axis to rotate the free beam on the object surface, the rotation being based on one or more stored scanning patterns; and at least one angle meter for determining the current rotational position of the deflector relative to the base about at least one axis, indicating the current measurement direction.

[0030] The instrument also includes: a receiver configured to detect reflected measurement radiation reflected from a corresponding surface point and deflected onto the receiver by a deflector; and a control and processing unit configured to calculate the coordinates of the corresponding point based on the distance derived from the detected measurement radiation (e.g., using the time-of-flight principle) and based on the current measurement direction measured by the angle meter.

[0031] Furthermore, the measuring instrument includes a set of sensors for sensing the temperature of at least one corresponding temperature of a plurality of components of the measuring instrument that affect the measurement of the coordinates of a surface point. Such measuring components include instrument parts that influence the determination of the measurement direction and / or the current measurement direction and / or the distance to the object point. Examples of such instrument parts are units of a radiation source or optical measurement path (such as lenses or mirrors), a frame structure, or mechanical supports for measuring units (or portions thereof) (such as angle meters / encoders or optical receivers).

[0032] The instrument also has a memory that stores a compensation model and a set of particularly calibrated measurement parameters associated with the defined reference temperature of the corresponding components.

[0033] In addition, the control and processing unit is configured to feed the temperature sensed by the sensor during the scanning process to the compensation model, and to estimate a set of compensation parameters starting from the stored set of parameters based on the difference between the sensed temperature and the corresponding or associated reference temperature, and finally to calculate the corresponding object point coordinates based on the set of compensation parameters.

[0034] The temperature sensors can be distributed within the instrument as needed, enabling them to measure the distributed thermal state and, in particular, the thermal gradient at locations / components within the instrument and / or in relation to point coordinate measurements (specifically, locations / components related to the final beam direction of the emitted measurement radiation). The set of sensors may include non-contact temperature sensors, particularly self-calibrating point infrared sensors, especially for sensing the temperature of movable components such as the beam deflector.

[0035] In some embodiments of scanning measurement instruments or methods, the calculation of the coordinates of the corresponding object point includes correction of the corresponding raw point scan data based on a determined set of compensation parameters, whereby the "raw" object point scan data also includes preprocessed scan data, such as sensor data that has undergone typical data cleaning or improvement steps (such as filtering, smoothing, or amplification).

[0036] Alternatively, the set of measurement component-related parameters associated with the defined reference temperature of the corresponding component includes calibration parameters calibrated at the reference temperature. Furthermore, calibration can further refine the parameter set, and this calibration will continue to be applied until another calibration (e.g., in the field) updates these calibrations again.

[0037] In another embodiment, the instrument is designed to rotate the beam about an azimuth axis, which is the first axis, and about a pitch axis, which is the second axis. Therefore, the set of sensors includes at least one sensor for sensing temperature affecting the measurement directions about the azimuth and pitch axes, and the parameter set includes parameters for compensation based on the sensed temperature about the azimuth and pitch axes. Preferably, the instrument includes at least a first sensor for sensing a first temperature (of a component of the instrument) affecting the measurement direction about the azimuth axis and at least a second sensor for sensing a second temperature affecting the measurement direction about the pitch axis, and the parameter set includes a first parameter for first compensation based on the first temperature about the azimuth axis and a second parameter for second compensation based on the second temperature about the pitch axis.

[0038] Additionally or alternatively, the control and processing unit is configured to estimate a set of compensation parameters separately for isolated or individual regions or areas (e.g., a single scan line or a specific number of adjacent scan lines) of the scan surface points based on the temperature sensed and / or interpolated when measuring the corresponding scan area.

[0039] In other embodiments, the compensation model includes a kinematic model of the instrument that models at least the kinematic chain from the base to the deflector, and the parameter set includes the kinematic parameters of the kinematic model. The kinematic parameters may include, for example, angular parameters, and may be based on nominal construction data of the instrument and / or numerical simulations.

[0040] Additionally or alternatively, the control and processing unit is configured to compensate for temperature hysteresis effects on the parameters, whereby the compensation model includes a function representing past or previous temperatures sensed by at least some of the sensors in a set of sensors. Alternatively, only temperatures above a defined temperature difference threshold are considered past temperatures (no consideration or recording of any temperature changes within the threshold interval).

[0041] In some implementations, the control and processing unit is configured to automatically determine a confidence value for the compensation parameter set, and if the confidence value is below a threshold, trigger a new calibration parameter set associated with the new reference thermal state through manual and / or automatic field calibration. Therefore, the confidence value may take into account at least one of the following: sensed temperature, hysteresis of sensed temperature, difference between sensed temperatures of different sensors (temperature gradient) and / or difference between sensed temperature and reference temperature, or statistical evaluation over time and / or with the location of sensed temperature.

[0042] The present invention also relates to a computer program product comprising program code stored on a machine-readable medium or embodied by an electromagnetic wave including the program code, and having computer-executable instructions for performing the claimed method for online temperature compensation, particularly when running on the control and processing unit of the claimed photoelectric scanning measuring instrument.

[0043] The method, measuring instrument, and computer program of this invention improve the scanning of object surfaces, particularly for geodetic or metrological applications, where improved accuracy in point coordinate determination is crucial. This invention provides high scanning or point cloud accuracy regardless of changes in the temperature or thermal state of the measuring instrument, by applying compensation or correction based on the degree of temperature or thermal state variation, using a compensation parameter set determined accordingly, and performing calculations using a reference parameter set and a compensation model. Attached Figure Description

[0044] In the following, the invention will be described in detail with reference to exemplary embodiments, which are accompanied by accompanying drawings, wherein:

[0045] Figures 1a to 1c An exemplary photoelectric scanning measurement instrument is schematically shown, specifically implemented as a laser scanner in this example;

[0046] Figure 2 This schematically illustrates the changes in the measurement parameters of a photoelectric scanning measuring instrument caused by temperature variations.

[0047] Figure 3 This illustrates a set of thermal sensors arranged within an exemplary photoelectric scanning measurement instrument;

[0048] Figure 4 The method for calculating scan points using temperature compensation is illustrated in the form of a flowchart.

[0049] Figure 5 This schematically illustrates another example of scan point compensation based on sensed instrument thermal state;

[0050] Figure 6a , Figure 6b The diagram schematically illustrates the results of the above compensation for the effect of temperature using a set of compensation parameters; and

[0051] Figure 7 This schematically illustrates consideration of the instrument's thermal history. Detailed Implementation

[0052] Figure 1a , Figure 1b , Figure 1c An exemplary photoelectric scanning measuring instrument is schematically shown, specifically implemented as a laser scanner 1 in the example, for generating a point cloud representing objects within a scanning space, which in the example is an outdoor scene. Figure 1a Scanner 1 is shown in the scene, while Figure 1b A more detailed view of scanner 1 is shown, while Figure 1c A thermal image of scanner 1 is shown.

[0053] An exemplary fixed laser scanner includes a body or upper part or top 2 and a base 3. As shown, the base 3 can be mounted on a tripod 9 for positioning this ground scanner 1 at position L. The body 2 includes a distance measuring unit having a transmitting unit 4, a receiving unit 5, and a beam guiding unit or deflector 7, wherein the transmitting unit 4 and the receiving unit 5 are combined as a single unit in this example; however, they can be implemented as separate components, for example, in combination with a beam splitter.

[0054] Using a first driver or motor M1, a first change in the measurement direction is achieved by a controlled relative rotation between the main body 2 and the base 3 about a first azimuth axis or vertical axis V, as a first rotation (indicated by arrow r1 in the figure). In this example, a second rotation (indicated by arrow r2 in the figure) is achieved by a deflector 7 (e.g., a reflector) mounted in the main body 2, allowing it to rotate about a second pitch axis H via a second driver or motor M2. During rotation, the guide unit 7 deflects the radiation beam from the transmitting unit 4 as a free beam B along the alignment or line of sight or measurement direction A toward the object surface point to be scanned into the measurement space. The corresponding angular positions about each, or simply referred to as the current aiming or scanning direction A, azimuth axis and pitch axis can be determined by a corresponding angle encoder (not shown). By rotating the reflector 7 about the transverse axis H by r2, the elevation scanning direction can be changed, and the measurement beam can be guided vertically on the surface of the object. Simultaneously, the azimuth direction can be changed, and the beam can be rotated horizontally on the surface by rotating the entire upper part 2 about the azimuth axis V by r1. Therefore, the scanning direction can be continuously changed, for example, according to a known or defined scanning pattern of multiple parallel scanning lines S. Figure 1a As shown in the figure.

[0055] The range of rotation about one or more axes H and / or V, as well as the (maximum) measurement distance, defines the range of the setup. Typically, a so-called full dome scan is performed, meaning a scanning sphere that rotates fully in the horizontal direction, with an angular range of, for example, 270° in the vertical direction, and a maximum distance of tens, hundreds, or even hundreds of meters, thus providing a spherical range that depicts almost the entire surrounding environment up to the maximum range in all spatial directions. However, any other angular range is also possible.

[0056] After the free beam B is reflected off the surface of the target object, the received beam R is guided in the beam path toward the receiving unit 5 by the rotatable beam deflection unit 7, and then guided by additional optical devices such as lenses or mirrors (not shown) to an optical sensor or receiver such as an APD diode (not shown) for time-resolved detection, for example, measuring radiation. The distance to the target point O can be determined by measuring the time of flight of the (pulse) light or by other methods known in principle in the art (such as phase measurement).

[0057] The control and evaluation unit 8 is data-connected to the sensor or to the radiation emitter 4 and radiation receiver 5 of the scanner 1, as well as the aforementioned angle encoder. In the illustrated example, this data processing and device control computer 8 is included within the instrument housing 2, and is particularly connected to a permanent data storage device or storage unit (not shown). However, the computer and storage unit can also be external to the laser scanner 1, for example, implemented by a cloud computer with a permanent wireless connection to the laser scanner 1. The computer 8 is configured to control the aforementioned components of the laser scanner 1 and perform the steps of the method according to the invention. The control and evaluation unit 8 is specifically implemented to determine the distance between the laser scanner 1 and the corresponding scan point O on the surface O of the object being measured for multiple measurement points. In this case, together with the determined scanning / measurement direction or angle axis value, the three-dimensional coordinates of the corresponding scan point O can be accurately determined, and these three-dimensional coordinates can be stored as a point cloud in the storage unit.

[0058] In addition to the determined distance associated with the direction or 3D coordinates from the laser scanner 1 (or from the origin of the reference frame relative to the station L), each scan point may also have a brightness or intensity value, which is also determined by the control and evaluation unit 8. The brightness is a grayscale value, which is determined, for example, by integrating the bandpass-filtered and amplified signal of the radiation receiver over a measurement period assigned to the measurement point P. These values ​​can form an intensity image of the scan.

[0059] Therefore, the measurement involves a set of points for each object or scan point O, determining their respective spatial coordinates, including the corresponding distances to the scan points and the corresponding alignment of the scan direction with respect to the two measurement axes H, V (the current horizontal and vertical beam emission directions) or two angles. Thus, the scanning process produces a set of points containing three-dimensional information about the surface of the scanned object (such as building O). All the measurement points in this process are called a scan, and a 3D point cloud can be generated. Point-by-point 3D data or 3D information (e.g., Cartesian coordinates or a point distance grid (e.g., derived from such 3D coordinates or generated directly from the original measurement data), which maps the measured point distances according to the corresponding scan direction) can be stored as a depth layer of the point cloud. Similarly, intensity data associated with the measured object points can be stored as an intensity layer of the point cloud.

[0060] A display device (not shown here) can be connected to the control and evaluation unit 8 for displaying the acquired point cloud to a user. This display device can be configured as a screen directly on the operable laser scanner 1, or as a display of a networked computer (e.g., a handheld device or desktop computer). Furthermore, a color camera (not shown), particularly a wide-angle camera, panoramic camera, spherical camera, etc., can be arranged in the housing 2. The color camera allows additional color values ​​to be assigned to the measurement point O to provide textured or colored point clouds.

[0061] When instrument 1 is operated, electrical or electronic units such as motors M1 and M2, computer 8, laser source 4, display, camera, and PCB (not shown) become heat sources. In addition, external or ambient heat flux (e.g., general ambient temperature or impact solar radiation) affects the temperature of instrument 1 or its components.

[0062] As in Figure 1c The different shades of gray indicate that the scanner 1 is heated during operation, resulting in different temperatures for different parts or components of the scanner 1. For illustrative purposes, three such different temperature zones 10a-10c are marked in the figure with different shades of gray: the middle scanner portion 10b has a higher temperature than the upper left region 10a, and the upper left region 10a has a higher temperature than the scanner portion 10c on the right side of the housing.

[0063] Any heat or thermocurrent generated by an internal or external heat source or radiator alters the thermal state of instrument 1, and particularly affects the structural dimensions and / or position or orientation of components such as mirror 7, beam source 4, or detection unit 5. For example, Figure 1b As shown, the distance D or length of the beam path between the deflector 7 and the laser source 4 / optical sensor 5 is changed. Furthermore, the initial angular position or alignment of measuring components or structures, such as the entire top 2, undergoes thermal expansion, resulting in, for example, a displacement of the azimuth axis V relative to the pitch axis H (or a displacement of components placed and oriented according to axes V and H), such as a deviation from the nominal 90° (or more precisely, a value different from or a deviation from the nominal value derived and stored through calibration).

[0064] Finally, changing the size or alignment of the measuring components affects the measurement results in the form of surface point coordinates. In other words, the accuracy of the object point measurement decreases because the components or parameters of the scanner 1 related to the measurement deviate from the actual situation or conditions of the instrument 1.

[0065] The instrument parameters are calibrated under a certain thermal state of instrument 1, which is rarely equivalent to but more often different from its current thermal state. Therefore, the calibrated and usable parameter values ​​are mismatched with the actual true state of measuring device 1. (As already...) Figure 1c As mentioned and indicated, this problem is exacerbated because any temperature change is not equal for different parts of scanner 1, and one component may have a different temperature change than other components.

[0066] Furthermore, since environmental scanning takes time, the thermal state of Instrument 1 may be unstable and change during this period. Therefore, the actual instrument values ​​at different time points during scanning may differ not only from the calibrated parameters but also from another instrument value. For example, the size or position of the measured component may change from the start to the end of the scan, due to factors such as the instrument's heating phase, changes in processing activities, or unstable environmental conditions. Consequently, the deviation between the stored parameters and the actual parameter values ​​(which form the basis for calculating the object point coordinates) may fluctuate during the scanning process or from one scan point or area to another.

[0067] Figure 2 The diagram schematically illustrates the aforementioned changes in the measurement parameters of the scanning measuring instrument caused by temperature variations. Black dots 11' and 11" indicate discrete parameter values, while line 11 indicates the overall trend.

[0068] As can be seen from trend line 11, the parameter generally increases with increasing temperature or changes in the thermal state of the scanning instrument, and therefore decreases with decreasing temperature. Thus, trend line 11 illustrates a general problem of instability in measurement parameters due to thermal effects.

[0069] More specifically, points 11' and 11" illustrate a further problem: the occurrence of hysteresis. That is, as indicated by spot 11', the parameter changes as the temperature increases differ from those as the temperature decreases (spot 11"). Therefore, at the same temperature T, different values ​​P' or P" exist depending on the temperature process (heating or cooling phase). Thus, the difference between the true and calibrated values ​​depends not only on the actual thermal state or different temperatures, but also on the temperature progression.

[0070] Figure 3 based on Figure 1b A scanner measuring instrument 1 is shown, now equipped with a set of thermal sensors 6a-6d. In the example, the sensors 6a-6d are distributed inside or on the housing of the instrument 1, attached to or near the measurement-related components.

[0071] like Figure 3 As shown, the first temperature sensor 6a is located at the distance measurement unit or near the transmitting unit 4 and the receiving unit 5, the second sensor 6b is located at the frame of the instrument, in this example near the processing unit 8 (or processor board or PCB), and the third sensor 6c is located at the motor M2.

[0072] The fourth sensor 6d is located near the deflector 7, preferably as close as possible to it structurally. In this example, this sensor is specifically implemented as an infrared (IR) sensor, such as a self-calibrating point infrared sensor. This non-contact temperature sensor is particularly advantageous for detecting the temperature of moving or rotating parts (such as the exemplary rotating mirror 7). Self-calibration is applied because the calorific value is indirectly derived from the emissivity coefficient depending on the surface being inspected. This self-calibration must be based on the known thermal state of the rotor, or more generally on the known thermal state of a component / part of the target instrument (at least compared to other states within the instrument). Preferably, the surface being inspected (here, the mirror surface) is designed to exhibit minimized infrared reflections, for example, through an optical coating.

[0073] In any case, thermal sensors 6a-6d with absolute accuracy in the range of 0.1K are distributed on or within the structure of the laser scanner 1 to determine the temperature distribution within the laser scanner 1. Therefore, the actual temperature field or current thermal state of the instrument 1 can be sensed. In other words, accurate thermal sensors are distributed, for example, on the PCB within the instrument, and directly near locations on the instrument (e.g., structural parts, housing) where the thermal state affects the accuracy of the measurement points / point clouds used to sense the actual temperature, especially during scanning with the instrument 1.

[0074] Therefore, the number of sensors 6a-d used may differ from the exemplary number of four; for example, it may be in the range of up to twenty sensors, such as ten or sixteen sensors, such as three sensors arranged to monitor the temperature of the component related to the pitch axis, two sensors arranged to monitor the temperature related to the azimuth axis, three additional sensors for sensing the temperature of the laser / range measuring component, and four additional sensors for monitoring the temperature of the central frame of the scanner 1.

[0075] Figure 4 The method for calculating scan points with temperature compensation or compensation for changes in thermal state is shown in the form of a flowchart.

[0076] As described at the beginning, the current thermal state T of the instrument is derived. mes (Figure reference 20), which is made by using the instrument's thermal sensors 6a-6d (see Figure 20). Figure 3 The measured temperatures Ta, Tb, Tc, and Td are described. This current thermal state 20 is compared with the stored reference thermal state T provided by the instrument's memory. cal (Figure 21) compares the values ​​to produce the difference Δ(T) mes ,T cal (See attached figure, reference numeral 23).

[0077] The difference 23, Δ(T) between the reference thermal state 21 sensed by a set of thermal sensors of the instrument and the actual thermal state 20 mes ,T cal The parameters 22 are used as inputs to the compensation model 24. Additionally, calibrated parameters P1-P3 (reference numeral 22) are input to the model (the number of these three instrument parameters is for illustrative purposes only). These values ​​22 are associated with a reference thermal state 21 and are specifically calibrated to a well-defined reference temperature that can be compared to the actual temperature of the measured component.

[0078] Based on reference parameter 22 and thermal difference 23, compensation parameters P1'-P3' (reference numeral 25) are determined using compensation model 24.

[0079] The compensation model 24 can be, for example, a numerical or analog model of the scanning instrument, such as a digital twin (e.g., based on CAE-models and / or FEM-technology), which can be parameterized (e.g., in the form of a coefficient matrix) to directly adjust the kinematic parameters of the instrument, or using a regression algorithm.

[0080] Model 24 is based on thermal surveys of several real instruments. Alternatively or additionally, multiple datasets covering real instruments for different use cases can be generated, and the model can be trained directly on this measurement data. For example, compensation model 24 can be trained on mapping measurements using one (for a single) or several instruments in well-defined thermal environments to obtain instrument-wide compensation (based on factory calibration), field calibration in several thermal environments on one or several instruments (collecting or continuously performing field calibration information over a specific time period, including raw measurements, reference thermal states, and estimated kinematic parameters, using instrument-specific data for updating, training, and parameterizing compensation model 24), and / or data synthesized through numerical simulations applied to instruments in several well-defined thermal environments, where the numerical simulations match measurements to reality.

[0081] Then, the raw scan data O raw (Ref. 26) is fed into a measurement or kinematic model 27, preferably modeling the complete kinematic chain or line from the base to the end of the beam path or all aiming-direction related components, which uses the compensation parameter 25 to calculate the final compensated scan data O. comp (Ref. 28). Therefore, when processing the raw measurement data 26 of the object point to calculate the compensated point coordinates 28, compensation is applied, whereby this processing may include basic data refinement known in the art, such as filtering, compressing, or removing outliers. The compensation parameter set 25 replaces or corrects the initial calibration parameter set 22 for calculating point coordinates or calculating point clouds. In other words, a pair of scanner calibration parameters is continuously compensated or corrected (at a specific rate) based on environmental sensor data to maintain accuracy in the field.

[0082] Therefore, in Figure 4 The compensation model 24 and measurement model 27 of the optoelectronic instrument shown as separate entities in the purely exemplary embodiment can be specifically implemented as a combination or a single model, such as a kinematic model for compensating for the angle between the azimuth axis and the pitch axis, the distance between the azimuth axis and the pitch axis, the angle between the laser and the pitch axis, the translation of the laser in the pitch frame, the pitch axis angle offset, the angle between the parabola vertex and the pitch axis, and the translation of the reflector along the pitch axis.

[0083] Figure 5 Another example of scan point compensation based on sensed instrument thermal state is illustrated schematically.

[0084] In this example, the kinematic parameters of the instrument and its thermal state / temperature over time are depicted. It can be seen that, starting from the first reference parameter (or parameter set) 22a, the first compensation parameter 25' is calculated based on the actual difference 23 of the sensed thermal state.

[0085] Based on the current thermal state 20 (or the current difference 23 from the reference state 21), the above compensation model is used to determine the corresponding compensation parameters 25.

[0086] Therefore, the temperature of the relevant components is repeatedly sensed at a certain measurement rate, which allows the actual thermal state 20 of the instrument to be determined over a period of time, starting from the calibration parameter 22, and the corresponding compensation parameter 25 adapted to it to be derived.

[0087] For example, starting from the (first) reference parameter 22a and the reference thermal state 21a, at a first time, a first difference 23' (shown as "Δ" in the figure) in the thermal state is determined, and based on this, a first correction value 25' is determined.

[0088] Then, at a second time and a different current thermal state (a further increase in temperature), starting again from the same first reference parameter 22a, but this time determining and using the second thermal state difference 23""", the second compensation parameter 25"" is calculated. Further, or given the further increase in temperature, parameter 25"' is updated again based on the first calibration value 22a, but this time again based on the third "updated" thermal state difference (not shown in the figure for better clarity). Combinations of reference values ​​can also be used, for example by considering calibration parameters generated from more than one recent field calibration.

[0089] Therefore, by using a set of internal temperature sensors of the instrument and cyclically sensing the actual thermal state of the instrument based on reference parameter 22a, cyclic compensation parameters 25', 25”, and 25”' are calculated, each of which is adapted to the actual thermal state.

[0090] like Figure 5 As shown, the reference parameter (set) 22 on which the calculation is based can be updated or changed. For example, different reference values ​​can be applied for different temperature ranges. That is, a first set of calibration parameters 22a referencing a first reference thermal state 21a is used for a first actual thermal state range, and another set of calibration parameters 22b referencing a different reference thermal state 21B is used for a second thermal state range.

[0091] Similarly, this adaptation to different instrument conditions can also be achieved, as multiple compensation models are provided, for example, for different ranges of thermal conditions or temperatures. Adaptation in the form of selection among multiple references or compensation tools can also be based on other variables (such as time). For example, a second calibration model is used to determine compensation parameters 25, since a first calibration model is used after the start of instrument operation (e.g., the heating phase) and for a period of time after a defined time (which may be a fixed value or itself may be coupled to the sensed temperature). Predictions covering thermal state changes within a scan can use a specifically defined thermal state as a reference (e.g., the start, end, or average of the scan); the reference thermal value can be defined as the average value over a scan, at least at the beginning or end of the scan at the measurement point. Furthermore, compensation can be applied not only individually within a scan (window or all), but also from one scan to another by defining a reference thermal state for each scan. The correction within a scan is calculated using the difference between the reference thermal state and the thermal state at at least one measurement point, and the correction between the relevant scan and the well-defined scan is estimated using the difference between the reference thermal state of a scan and the thermal state of a well-defined scan. This well-defined scan can be a factory-calibrated scan within a specific calibration test bench or field calibration prior to shipment to the customer or any other field calibration. Different prediction concepts or models can cover any changes between scans and factory / field calibration.

[0092] As another example of providing different or new reference values, calibrations known in principle in the art are performed in the field (e.g., during scan pauses). Based on such calibration, updated reference parameters 22b are provided associated with a certain reference thermal state 21b. These new references are then used as the basis for any further compensation, i.e., any subsequent compensation parameters 25b used to compensate for current changes in the thermal state are calculated starting from the new calibration values ​​22b of the new reference thermal state 21b. Therefore, in-field calibration may not necessarily be completely replaced by compensation methods, but is performed only rather infrequently compared to known instruments, while maintaining or even improving measurement accuracy.

[0093] Therefore, defining the concept of compensation parameters can be used to monitor whether calibration should be performed, as predictions of compensation parameters may become inadequate over a certain period or after large changes in thermal state (or due to instrument impacts and shocks). New reference values ​​for kinematic parameters can then be generated in-situ through the calibration process.

[0094] Therefore, a confidence level indicating the quality or reliability of the current thermal compensation can be derived based on indicators such as the instrument's actual thermal state, parameter hysteresis, temperature gradient, and / or statistical temperature data (e.g., standard deviation, average value, and their variation). Once this confidence level falls below a certain threshold (i.e., indicating low robustness of the compensation), the generation of a new reference value can be triggered. For example, the scanner's control unit then notifies the user, who can then initiate calibration and / or, if available, trigger an automatic calibration process for the scanning device.

[0095] Figure 5 Also shown (on the right) is how the determined compensation parameter 25 is used to calculate the object point coordinates. The vertical line 29 indicates the time interval of a single scan line.

[0096] Because the rate at which the actual thermal state 20 and / or compensation parameter 25 is determined is lower than the scan (line) rate shown in the figure, the compensation parameter 25 is only available for certain time intervals / certain scan lines 29, and the compensation parameter is determined for that specific time. For example, thermal sensor values ​​are measured during a scan with an update rate of a few seconds. This stream of thermal sensor values ​​serves as the input to the compensation model. The sensor values ​​include timestamps, each used to allow synchronization with scan lines 29 and to calculate the coordinates of points on the corresponding scan lines (in exemplary lines 29a, 29b, 29c) using these parameters 25 fitted with respect to time.

[0097] For other scan lines or scan points between lines 29a-29c, the parameter values ​​are interpolated based on the "true" values ​​derived from the actual measurement time, for example, through linear fitting as shown by interpolation line 30. Two interpolation lines 30 are shown in the figure. Scan lines 29 within the interpolation lines are compensated for with corresponding interpolation compensation values ​​for the corresponding time intervals.

[0098] Therefore, based on the timestamp stored for each scan line (e.g., a separate temperature value), and based on this, the compensation parameters can be interpolated for each scan line 29 based on the temperature measurement 20 recorded during scanning. Using the temperature values ​​corresponding to scan lines 29a, 29b, and 29c, a separate set of parameters can be interpolated for every other scan line 29 in between.

[0099] More generally, based on matching timestamps and based on "real" sensor values ​​or considering timely interpolated values ​​calculated based on such actual measurements, different compensation parameters are applied to individual regions or multiple sets of scan points in the point cloud. Thus, compared to other scan lines 29, individual "sensing" or interpolation compensation parameters are used to correct measurement points belonging to a single scan line 29 or a single pitch axis rotation (fast axis, second axis), and / or timely fitting compensation values ​​are used to calculate the coordinates of scan points within a specific range of azimuth axis rotations (first axis, slow axis). This concept can be applied to more or fewer extended scan areas (e.g., a set of scan lines), or even decomposed into individual scan points by determining the corresponding high rate of thermal state or by a high rate and / or fine interpolation of the compensation parameters based on sensor compensation parameters.

[0100] Figure 6a , Figure 6b The above schematically illustrates the results of compensating for the effects of temperature by using a set of compensation parameters.

[0101] Figure 6a The diagram illustrates the angular error of surface point coordinates based on uncompensated thermal state changes or temperature drift of the scanning instrument. Figure 6b This illustrates such angular error (with arbitrary units but the same scale) based on the thermal state change or temperature drift of the instrument with the aforementioned compensation.

[0102] It can be seen that when the compensation method of the present invention is applied, or when the measuring instrument of the present invention with compensation function is used, the error range of the scanning point coordinates is significantly reduced, and the scanning accuracy is significantly improved. As described below, the scanning accuracy can even be further improved.

[0103] Figure 7 The historical consideration of the instrument's thermal state is illustrated schematically.

[0104] Graph 31 shows the temperature values ​​of the scanning measuring instrument sensed over time. Thus, in this example, even at the time T when scanning begins using the scanning instrument... s Temperature is sensed previously or in the instrument's off mode. Therefore, when the instrument is operating or scanning, the sensing rate can be reduced compared to the rate of temperature measurement or thermal state derivation; for example, the sensing interval can be in the range of minutes rather than seconds. Furthermore, the number of temperature sensors actually measuring may be limited; for example, only a subgroup of thermal sensors in a whole set of sensors may register values, while other sensors are "sleep," or only some parts of the temperature monitoring instrument may be measured. This results in a thermal state with less detail compared to the thermal state acquired during the actual scanning phase. However, this is sufficient for many applications (such as hysteresis compensation described below) while saving resources, particularly relevant to mobile devices.

[0105] This permanent temperature monitoring before (and after) the scan is crucial for compensating for the aforementioned hysteresis effect (see...). Figure 2 This is advantageous (but not mandatory) because the history of thermal states is available, and thus the direction of change in thermal states is known. That is, at least one previous thermal state of the instrument is known and can be fed into the compensation model before the current thermal state, on which the compensation parameters are primarily based, is determined. In other words, the history of thermal values ​​from the last reference point in the past until it reached its thermal state at the time of scan is considered for parameter compensation. As mentioned above, historical thermal states retrieved from less detailed temperature monitoring can have a smaller cardinality than the current thermal state, for example, in the instrument's off-mode or by eliminating some details during permanent storage (e.g., data from some defined sensors are irrelevant to or have low correlation with hysteresis compensation).

[0106] This hysteresis thermal state, or temperature value, can be pre-calculated continuously and then fed as input to the compensation model. This can be accomplished, for example, by introducing a "generated virtual thermal sensor," which represents a specific history of past thermal state changes, for instance, through a defined function of the selected thermal sensor and its past states. In the case of machine learning models, this can also be used to train the model using such a virtual sensor.

[0107] Therefore, as shown by line 32 in the figure, the hysteresis value or previous thermal state can be updated with some delay or buffer. For example, and as indicated at positions 33a and 33b in the figure, a new hysteresis temperature is generated only when the sensed temperature change (line 31) or the thermal state is sufficiently different (e.g., above a defined range or threshold). For example, an update to the hysteresis temperature or a new log entry for the thermal state is applied only when the temperature difference is greater than 5°C.

[0108] Although the invention has been described above with reference to some preferred embodiments, it should be understood that many modifications and combinations of different features of the embodiments can be made. All such modifications are within the scope of the appended claims.

Claims

1. A method for online compensation of thermal effects on a photoelectric scanning measuring instrument (1), the method comprising the following automated steps: • The instrument's free-beam optical system (B) rotates on the surface of the object to be scanned, used to measure the corresponding coordinates of multiple surface points (O), particularly for geodetic and / or industrial measurements of stationary objects. • Provides a set of instrument parameters (22) associated with the defined reference thermal state (21) and, in particular, the reference temperature field of the photoelectric scanning measuring instrument (1), especially a calibrated set of instrument parameters. • Measure the actual thermal state (20) of the photoelectric scanning measuring instrument (1). • Determine the difference between the actual thermal state (20), and in particular the actual temperature field, and the reference thermal state (21). • The compensation parameter set (25) is estimated using the compensation model (24) based on the following: The provided instrument parameter set (22), and The difference in thermal state mentioned in □ (23), • Calculate the corresponding object point coordinates (28) based on the compensation parameter set (25).

2. The method according to claim 1, Its features • Provides the thermal state history of the photoelectric scanning measuring instrument (1), including at least one previous thermal state, and • Make the estimation of the compensation parameter set (25) based on the thermal state history.

3. The method according to claim 2, Its features When the photoelectric scanning measuring instrument (1) is in the off mode, it automatically measures at least one previous thermal state before the measurement object point and calculates the thermal state history.

4. The method according to claim 2 or 3, Its features The thermal state is measured at a lower measurement rate when the object point is not being measured, compared to a higher measurement rate during the measurement of the object point.

5. The method according to any one of the preceding claims, Its features Provide at least two different compensation models (24) and / or • Calibrated parameter set (22) For different operating stages of the photoelectric scanning measuring instrument (1), particularly the heating stage, and / or for different ranges of the current thermal state.

6. The method according to any one of the preceding claims, Its features The compensation model (24) is based on a machine learning association between compensation parameters and thermal state, and is specifically trained by this method when operating the photoelectric scanning measuring instrument (1) in the field.

7. A photoelectric scanning measuring instrument (1), said photoelectric scanning measuring instrument for scanning the surface of a stationary object, particularly a geodetic and / or industrial object, by measuring the corresponding coordinates of multiple surface points, said photoelectric scanning measuring instrument (1) comprising: ·Base (3), • Radiation source (4), which is configured to generate optical measurement radiation, • Deflector (7), which is configured to emit the measurement radiation in the form of a free beam (B) onto a corresponding surface point (O) in the measurement direction (A). • At least one driver (M1, M2) for rotating the deflector (7) relative to the base (3) about at least one axis to cause the free beam (B) to rotate on the object surface. • At least one angle gauge, said angle gauge being used to determine the current rotational position of the deflector (7) relative to the base about said at least one axis (V, H), indicating the current measurement direction, • Receiver (5), which is configured to detect reflected measurement radiation (R) reflected from a corresponding surface point (O), • Control and processing unit (8), which is configured to calculate the coordinates of the corresponding point based on: □ The distance derived from the detected measured radiation, and The current measurement direction (A) determined by □ Its features The photoelectric scanning measuring instrument (1) includes A set of sensors (6a-6d) is used to sense the corresponding temperatures of multiple components of the photoelectric scanning measuring instrument (1) that affect the measurement of surface point coordinates, and □ Memory, which stores a compensation model (24) and a set of measurement component-related parameters (22) associated with the defined reference temperature (21) of the corresponding component, and The control and processing unit (8) is configured for... The compensation model is fed with the current temperature (20) sensed during the scanning process using the sensors (6a-6d), and the compensation model (24) is used to estimate a compensation parameter set (25) starting from the stored parameter set based on the difference (23) between the sensed temperature and the associated reference temperature. □ Calculate the corresponding object point coordinates (28) based on the compensation parameter set (25).

8. The photoelectric scanning measuring instrument (1) according to claim 7, Its features The calculation of the corresponding object point coordinates (28) includes correction of the corresponding original object point scan data (26) based on the compensation parameter set (25), and / or • The set of measurement component-related parameters (22) associated with the definition reference temperature (21) of the corresponding component includes calibration parameters calibrated at the reference temperature.

9. The photoelectric scanning measuring instrument (1) according to any one of claims 7 to 8, Its features The photoelectric scanning measuring instrument (1) is designed to rotate the light beam (B) about the following: □ The azimuth axis (V) as the first axis, and □ The pitch axis (H) as the second axis, and The set of sensors includes at least one sensor for sensing the temperature affecting the measurement directions with respect to the azimuth axis (V) and the pitch axis (H), and The parameter set (22) includes parameters for compensation based on the sensed temperature with respect to the azimuth axis (V) and the pitch axis (H).

10. The photoelectric scanning measuring instrument (1) according to any one of claims 7 to 9, Its features The control and processing unit (8) is configured to estimate a set of compensation parameters (25) individually for individual regions of the scanned surface points, particularly for individual scan lines, based on the temperature sensed and / or interpolated when measuring the corresponding scanned area.

11. The photoelectric scanning measuring instrument (1) according to any one of claims 7 to 10, Its features The compensation model (24) includes a kinematic model (27) of the photoelectric scanning measuring instrument (1) that models the motion chain from at least the base (3) to the deflector (7), and the parameter set (22) includes the kinematic parameters of the kinematic model.

12. The photoelectric scanning measuring instrument (1) according to any one of claims 7 to 11, Its features The control and processing unit (8) is configured to compensate for hysteresis effects (11', 11"), whereby the compensation model (24) includes a function representing past temperatures sensed by at least some of the sensors (6a-6d) in the set of sensors.

13. The photoelectric scanning measuring instrument (1) according to any one of claims 7 to 12, Its features The control and processing unit (8) is configured to automatically determine the confidence value of the compensation parameter set (25), and if the confidence value is lower than a threshold, trigger the acquisition of a new parameter set (22) associated with the new reference thermal state through field calibration.

14. The photoelectric scanning measuring instrument (1) according to claim 13, Its features The confidence level value considers at least one of the following: • Sensing temperature, • Hysteresis in temperature sensing • Differences in sensing temperature between different sensors and / or differences between the sensing temperature and the reference temperature, • Statistical evaluation over time and / or at the location of the sensed temperature.

15. A computer program product comprising program code stored on a machine-readable medium or embodied by an electromagnetic wave including the program code, and having computer-executable instructions for executing the method according to any one of claims 1 to 6, particularly when operated on a control and processing unit of the photoelectric scanning measuring instrument (1) according to claim 7.

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