CH704286B1

CH704286B1 - Laser scanner and method for measuring target areas.

Info

Publication number: CH704286B1
Application number: CH01944/11A
Authority: CH
Inventors: Dr Johannes Riegl
Original assignee: Riegl Laser Measurement Sys
Priority date: 2010-12-21
Filing date: 2011-12-08
Publication date: 2016-02-29
Also published as: AT510579A4; CH704286A2; CH704286B9; DE102011121115A1; DE102011121115B4; AT510579B1

Abstract

The invention relates to a laser scanner which comprises a laser distance meter according to a signal propagation time method, a scanning device (6) deflecting the laser beams of the transmitting and receiving device, and an evaluating device from the propagation time of the received laser signals A 3D data set or a point cloud is generated by the target space, and the distance, the two deflection angles and the amplitude are recorded at each measuring point and are stored in a data memory. A control device (20) is provided which, in a first mode, operates the drive (33, 34) of the scanning device (6) with a high, constant angular velocity ω,

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a laser scanner for measuring target areas as well as to methods for measuring target areas using the laser scanners according to the invention. These laser scanners include laser distance meters according to a signal propagation process. Such distance meters have a transmitting device for emitting laser beams, in particular laser pulses, and a receiving device for receiving laser radiation which has been reflected by objects located in the target space. Both the transmitting and receiving devices are preceded by optical systems which each define an optical axis. The laser scanner also has a scanning device for deflecting the optical axes of the transmitting and receiving device into preferably two orthogonal directions, Wherein the average angular velocity com is adjustable in at least one of the two scanning directions (α, φ). Laser scanners with a variable angular velocity are known per se (cf. US patent application US 2005/0 195 459 A1, Eric Hoffman et al.). The laser scanner further comprises an evaluation device which consists of the running time of the laser scanner Is determined and preferably also the signal amplitude is detected. The evaluation device of the laser scanner also has a summation stage for summing the echo signals, the number of summing echo pulses being selectable. With the aid of such summation stages, the signal quality of the echo pulses,

[0004] In the case of large measuring distances or also in the case of targets which have highly reflective surfaces, the echo signals can have very small amplitudes so that the measurements are subject to relatively large uncertainties or an evaluation of the echo signals is no longer possible at all.

[0005] According to the invention, in order to enable a measurement with a corresponding measuring accuracy even under such extreme conditions, it is proposed according to the invention to provide a control device by means of which the laser scanner can be adjusted into at least two different modes, wherein in a first mode The drive of the scanning device operates at a high, constant angular velocity ω, and the individual echo signals can be evaluated directly, ie without summation, in the evaluation device. In another mode, the drive of the scanning device with reduced, average angular velocity ωΜ is operated. At the same time, echo signals are summed up in the summing stage and mean values are formed from the accumulated echo signals from which distance values can be calculated in the evaluation device.

In a first embodiment of the invention, the control device, by means of which the laser scanner can be adjusted in at least two different modes, operates in the second or further mode the drive of the scanning device at a reduced, constant angular velocity coM- [0007] According to another variant of the invention, the control device, by means of which the laser scanner can be adjusted in at least two different modes, operates the drive of the scanning device periodically, intermittently, with a low average angular velocity ωΜ in the second or further mode The scanning device adds up the echo signals to the summing stage and forms average values from the accumulated echo signals,From which distance values can be calculated in the evaluating device. Advantageously, a link between the speed controller of the scanning device and the summing stage is provided for the echo pulse signals, by means of which, in the case of a reduction in the average scanning speed, Calculation of the average value can be increased.

According to the method according to the invention for measuring target spaces, a target space is scanned in a first step by the laser scanner in a first mode in which the evaluation device of the laser scanner evaluates the echo pulse of each individual laser pulse and Thus creating a 3D data set or a corresponding point cloud. The result of this first survey is then examined for areas from which no usable echo pulses have been received. It is also possible to determine regions from photographs or from laser images of the laser scanner from which it is highly probable that no usable echo signals are to be expected, but which areas could be of considerable importance for the measurement of the target area. Such areas are measured in a second step and in a second mode of the laser scanner in which the average scanning speed coM, preferably at substantially the same pulse sequence frequency, is reduced and the echo pulses are used to improve the signal / Ratio are summed and averaged. The 3D data records or dot clouds determined in this way are linked in a third step to the results of a survey carried out in the first mode of the laser scanner.

[0010] In a first embodiment of the invention, the scanning device is operated at a constant, reduced speed in the second mode. In another variant of the method according to the invention, the scanning device is stopped during the transmission of pulses, and the measuring beam is swung stepwise through the scanning device into the following measuring positions.

It is expedient to summon and average the echo pulses over N pulse periods in the case of a reduction of the average scanning speed coM in the second mode to a value of ωΜ / berechnet, whereby a sliding average value is preferably calculated.

Advantageously, when the value N is less than a predetermined threshold value, the drive of the scanning device drives it at a constant speed, but the scan device operates step by step at N greater than or equal to the predetermined threshold value, so that during the measurement Of a point in the target area of the measuring beam remains substantially stationary.

If only the amplitude values are measured during the scanning of the target space in the first method step, then the regions which are to be scanned in further process steps with a reduced mean scanning speed ω werden are defined by the signal amplitudes. These ranges contain measuring points whose echo-signal amplitudes are below a predetermined level.

[0014] Further features of the invention will become apparent from the following description of an exemplary embodiment and with reference to the drawing. FIG. 1 shows in axial section and schematically the mechanical and optical construction of the laser scanner according to the invention. The diagrams according to FIG. 3 illustrate the pivoting movements of the scanning mirror in the different modes, as well as the associated "footprints". FIG. 2 schematically shows the electronic construction of the device in the form of a block diagram. FIG. 4 shows as a monitor image an exemplary target space to be measured.

FIG. 1 shows the optical design and the associated mechanics of the laser scanner. Reference numeral 1 denotes a semiconductor laser, the beam 7 of which is directed by a lens 2 onto a mirror 3. The beam 7 directs the beam 7 onto the oscillating mirror 6, passing through a bore 4 in the mirror 5. The oscillating mirror 6 is pivotable (angle a) about a horizontal shaft 8, which runs through the mirror surface. The shaft 8 is mounted in a bearing block 9 which is pivotally mounted about an axis 10 (angle φ). The axis 10 is identical to the optical axis of the beam 7. The corresponding bearings of the bearing block 9 are designated by 11 in the drawing, the drive motor by 12. The angular position φ of the bearing block is determined by means of an angle decoder 13. Analogously, the drive of the shaft 8 of the oscillating mirror 6 is equipped with a drive motor and an angle decoder (not shown in the drawing). By the oscillating movements of the oscillation mirror about the two axes, the laser beam 7 scans a corresponding solid angle. The beam 7 is reflected on objects in the target space, generally diffuse. A part of this reflected radiation impinges on the oscillation mirror 6 and is directed to the mirror 5 by the latter. This directs the radiation onto an optical system 14, which focuses it on a photodiode 15. Between the mirrors 5 and 6, the laser transmitting beam 7 and the beam reflected by the targets are coaxial, and the mirror 5 with its bore 4 functions as a beam splitter.

The laser scanner according to the invention and the method for measuring target areas using such a laser scanner are explained in more detail with reference to the block diagram according to FIG. The laser scanner according to the invention is controlled primarily by the processor 20. The processor 20 is clocked by a clock generator 21 and drives the laser 1, which periodically emits laser pulses of high power. The echo pulses reflected by the targets are converted by the photodiode 15 into electrical signals, amplified in the amplifier 22 and digitized in the A / D converter 23. The corresponding sampling values are summed up in stage 24. From these values, mean values, which are fed to the evaluation stage 25, are finally formed.

A small part is branched off from the edge region of the beam emitted by the laser 1 with an optical fiber 26 and is fed directly to the photodiode 15. The pulse obtained in this way is evaluated as a starting pulse. In the evaluation stage 25, the transit time between the emission of the laser pulse and the arrival of the echo signals is calculated and the distance between the laser scanner and the target is determined therefrom.

The processor 20 communicates with all components of the laser scanner via a data bus 26. Mit27 is the program memory of the processor 20, 28 and 29 are memories for the 3D data sets or point clouds determined in a first or second measurement. The point cloud resulting from the various measurements is stored in the memory 30.

Amplitude values of the echo pulses which are supplied to the amplitude memory 31 and which contain a 2D data set of the target space at the end of a measurement are derived from the amplifier 22. The corresponding amplitude image can be displayed on the monitor 42 (in FIG. 4) of the computer 32 and serve as a basis for the decision concerning further measurements.

The stage 33 drives the drive motor 12 of the oscillation mirror 6 in accordance with the instructions received from the processor 20 and receives on the other side the actual angular values φ supplied by the angle decoder 13 with respect to the vertical axis of the oscillation mirror 6. In an analogous manner The mirror 6 is controlled by the stage 34 with respect to the horizontal axis (wave 8) of the scanning device and receives on the other hand the currently set angular values a. The angular values φ and α are available via the data bus 26 to all other stages of the system Are stored together with the distance values supplied by the evaluation device in the memories 28 to 30 and together with the amplitude values derived from the amplifier 22 results in the memory 31

Claims

Stored 2D amplitude image. Via the PC 33, the data sets stored in the memories 28 to 31 can be read out for further processing or storage. The sequence of a measurement is explained in more detail with the aid of the diagrams according to FIG. In the diagram (FIG. 3a), a sequence of transmit pulses with a constant pulse sequence frequency is plotted over time, the deflection angles α and φ over the same time axis being plotted in the diagram (FIG. 3b). The target space is sampled in a first step, wherein the adjustment speeds of the oscillation mirror 6 about its two pivot axes correspond to the maximum speeds and are essentially constant during the measurement. The corresponding line is indicated by 35 in FIG. 3b. The echo signals of each individual transmission pulse are evaluated together with the associated start pulse in the evaluation stage 25 and a distance value is determined, which is stored together with the associated angles α and φ in the memory 28. In this operating mode (mode 1), a summation of the pulses or of the sample values in stage 24 is omitted. Circles 36 in diagram FIG. 3c schematically illustrates the measurement spots or footprints in the target area. After completion of the measurement, the result thereof is displayed on the monitor of the PC 33, the distance values being displayed in false colors or grayscale. The corresponding echo signals can be so low that they can not be differentiated from the noise. This also applies to very distant objects. In a second method step, areas from which no useful signals have been received but which might be of interest are marked; in other areas such a marking is omitted. In general, the flash, from which no echoes are expected, will not be marked for further processing. In a third method step, the laser scanner from the above-described first mode is switched to a second mode in which the scanning speeds are reduced and the echo pulses or the summation values in the step 24 are added up and averaged become. The signal-to-noise ratio is improved in a known manner by the summation and averaging. The reduction factor for the scanning speeds can be adjusted as required on the PC 33, which also applies to the number of echo signals to be summed up. In an advantageous embodiment, the two values can be linked to one another so that, when one of the two values is input, the second value is set automatically in optimum size. The course of the scanning angles α or φ in the mode 2 is shown in the diagram FIG. 3 b as line 37, the associated footprint is designated by 38. The distance values originating from the marked regions of the target space are stored together with the scanning angles α or φ in the memory 29. By combining the 3D data sets or dot clouds stored in the memories 28 and 29, a resulting 3D data set or point cloud is generated, The regions which already provide sufficient echo signals in the first mode, as well as those regions from which no evaluable echo signals can be registered in the first mode, but which can be registered in the second mode by reducing the scan- Speed in conjunction with an average value formation of the echo signals have been determined. However, the increase in the number of echo signals to be summed for the average value formation is limited. As can be seen from FIG. 3c, the footprints 38 assume an elongated shape with a relatively large length, as a result of which the accuracy of the measurement is impaired. If an even larger number of echo signals are required for average value formation in order to achieve a useful signal quality, The oscillating mirror 6 is not adjusted continuously but in angular steps. The curve 40 in FIG. 3b shows the corresponding movement pattern in FIG 3. Mode. The oscillating mirror 6 performs a first step, then remains in this position and finally takes the next step. The footprints 41 which result during a stationary phase of the mirror 6 overlap and correspond essentially in shape and dimension to those of the 1st mode (item 36). The significantly improved quality of the measurement compared to the results of the second mode is, however, bought by a considerably longer measuring time. The determination of the regions which are scanned in mode 2 or 3 is determined by means of images which result as a result of the measurement in the first mode, from recordings with digital cameras (which may be integrated in the laser scanner if necessary) ) Or by means of amplitudes which are derived from the laser scanner. The images derived from the various systems can also be combined into a resulting image. In FIG. 4, which shows the screen 42 of the computer 32, such a combined image is shown. The foreground 43, which shows very high contrast values, comes from a measurement in mode 1, the background 44 with very low contrast has been recorded with a digital camera. However, this image part could also originate from a 2D amplitude image recorded by the laser scanner. The invention is not limited to the illustrated example but can be modified or supplemented in many ways. Reference is also made here to the patent claims 2-11, the objects of which contain a number of such modifications or configurations. claims Which shows the screen 42 of the computer 32, such a combined image is shown. The foreground 43, which shows very high contrast values, comes from a measurement in mode 1, the background 44 with very low contrast has been recorded with a digital camera. However, this image part could also originate from a 2D amplitude image recorded by the laser scanner. The invention is not limited to the illustrated example but can be modified or supplemented in many ways. Reference is also made here to the patent claims 2-11, the objects of which contain a number of such modifications. claims Which shows the screen 42 of the computer 32, such a combined image is shown. The foreground 43, which shows very high contrast values, comes from a measurement in mode 1, the background 44 with very low contrast has been recorded with a digital camera. However, this image part could also originate from a 2D amplitude image recorded by the laser scanner. The invention is not limited to the illustrated example but can be modified or supplemented in many ways. Reference is also made here to the patent claims 2-11, the objects of which contain a number of such modifications. claims The background 44 of very low contrast has been recorded with a digital camera. However, this image part could also originate from a 2D amplitude image recorded by the laser scanner. The invention is not limited to the illustrated example but can be modified or supplemented in many ways. Reference is also made here to the patent claims 2-11, the objects of which contain a number of such modifications. claims The background 44 of very low contrast has been recorded with a digital camera. However, this image part could also originate from a 2D amplitude image recorded by the laser scanner. The invention is not limited to the illustrated example but can be modified or supplemented in many ways. Reference is also made here to the patent claims 2-11, the objects of which contain a number of such modifications. claims Reference is also made here to the patent claims 2-11, the objects of which contain a number of such modifications. claims Reference is also made here to the patent claims 2-11, the objects of which contain a number of such modifications. claims

1. A laser scanner for measuring target areas by means of a laser range finder according to a signal propagation time method, having a transmitting device for emitting laser pulses and a receiving device for receiving laser pulses which have been reflected by objects located in the target space as Echo pulses in echo signals, wherein optical systems are connected to both the transmitting and the receiving device, a scanning device for deflecting the laser pulses of the transmitting device in two scanning directions which are preferably orthogonal to one another, wherein the angular speed ωΜ of the scanning device is arranged in at least one Of the two scanning directions (α, φ), an evaluation device which determines distance measurement values from the propagation time of the received laser pulses and preferably also detects the signal amplitude,Wherein the evaluation device has a summation stage for summing the echo signals and the number of such echoed signals is selectable, a distance angle being assigned to each distance measurement value so that a 3D data set and / or a corresponding point cloud can be generated by the target space (20) is provided, by means of which the laser scanner can be divided into at least two different measuring positions, wherein the control unit (20) is provided with at least one control unit (20) (33, 34) of the scanning device (6) is configured with a first,Constant angular velocity co and to evaluate the individual echo signals directly, ie, without accumulation, in the evaluation device (25), and in a further mode the drive (33, 34) of the scanning device (6) A second, reduced averaged angular velocity ω und and summing the echo signals in the summing stage (24), and from the summated echo signals form mean values from which the distance measurement values can be calculated in the evaluation device (25).Reduced mean angular velocity ω und and to summon the echo signals in the summing stage (24) and to form mean values from the accumulated echo signals, from which the distance measurement values can be calculated in the evaluation device (25).Reduced mean angular velocity ω und and to summon the echo signals in the summing stage (24) and to form mean values from the accumulated echo signals, from which the distance measurement values can be calculated in the evaluation device (25).

2. The laser scanner as claimed in claim 1, characterized in that the control device (20), by means of which the laser scanner can be adjusted in at least two different modes, is configured to drive the drive (33, 34) (6) at a reduced, constant angular velocity ω und and summing the echo signals in the summing stage (24) and from the summated echo signals to form average values from which distance measurement values can be calculated in the evaluation device (25).

3. The laser scanner as claimed in claim 1, wherein the control device, by means of which the laser scanner can be adjusted in at least two different modes, is configured to drive, in the further mode, the drive (33, (6) to periodically intermittently operate with a reduced average angular velocity (coM) and to sum up the echo signals in the summing stage (24) into the standstill phases of the scanning device and to form mean values from the summated echo signals from which in the evaluations (25) the distance measurement values can be calculated.

4. The laser scanner as claimed in claim 1, wherein a speed regulator is connected to the summing stage for the echo signals, by means of which a connection is made in the case of an echo signal Reduction of the averaged scanning speed ωΜ, the number of distance measurement values used for calculating the mean value can be increased.

5. The laser scanner as claimed in claim 1, wherein a device is provided for evaluating the quality of the echo signals, for example on the basis of the signal amplitudes and / or the signal-to-noise ratios (20, 33, 34) for the scanning speed and the number of echo signals to be summed for the purpose of average-value formation can be supplied.

6. A method for measuring a target area with a laser scanner as claimed in claim 1, wherein the target area is scanned in a first step by the laser scanner in a first mode in which the evaluation device (25) of the laser scanner evaluates the echo pulse of each individual laser pulse emitted and thus generates an SD data set and / or a corresponding point cloud, and the result of this first measurement is examined for areas (44) from which no usable Echo pulses, or - if the laser scanner comprises a camera for this purpose - areas from which photographic signals and / or image images of the laser scanner are highly likely not to be expected,Which ranges are important for the measurement of the target space and that such areas are measured in a second step and in a further mode of the laser scanner in which the averaged scanning speed ωΜ, preferably at substantially the same pulse sequence frequency, First step is reduced and the echo signals are summed and averaged to improve the signal-to-noise ratio and thus determined 3D data sets and / or point clouds are performed in a third step with the results of a measurement performed in the first mode of the laser scanner Be linked.Preferably at substantially the same pulse sequence frequency, is reduced compared to the first step, and the echo signals are summed and averaged to improve the signal-to-noise ratio and thus determined 3D data sets and / or point clouds are recorded in a third step with the results of a In the first mode of the laser scanner.Preferably at substantially the same pulse sequence frequency, is reduced compared to the first step, and the echo signals are summed and averaged to improve the signal-to-noise ratio and thus determined 3D data sets and / or point clouds are recorded in a third step with the results of a In the first mode of the laser scanner.

7. A method for measuring a target space according to claim 6, characterized in that the scanning device (6) is stopped in the further mode during the emission of laser pulses, and then is step-wise pivoted into the following measuring positions.

8. The method for measuring a target space according to claim 6, wherein the quality of the echo signals is evaluated in a corresponding device and the results of this evaluation are used, for example, in a 2D image in gray scale and / or false colors - for an additional scanning operation of the control device (20) for the scanning speed and the number of echo signals to be summed for the average value formation, the control device (20, 33, 34) automatically or semi-automatically scanning the scanning device 6) in such a way that those regions of the target space (44) from which echo signals are received or received, the quality of which is below a fixed threshold value,Can be scanned in a further scanning process with a reduced scanning speed and an increased number of echo signals to be summed for the average value formation.

9. The method according to claim 8, wherein the control device determines the scanning speed and the number of echo signals to be summed for the further scanning processes as a function of the quality of the received echo signals.

10. A method for measuring a target space according to claim 6, characterized in that in the case of a reduction of the averaged scanning speed ωΜ in the further mode to a value of com / N, the echo signals are summed up and averaged over N pulse periods Mean value is calculated.

11. The method according to claim 10, characterized in that the drive (20, 33, 34) of the scanning device (6) is operated at a constant speed at a value N less than a predetermined threshold value (6) is operated stepwise in such a way that the laser beam (7) remains essentially stationary during the measurement of a point in the target area.

12. The method for measuring a target space according to claim 6, wherein the signal amplitude is detected in the first method step, characterized in that the areas which scan in further process steps at a reduced average scanning speed .omega..sub.0 Are defined by the signal amplitudes and the said regions (44) contain measuring points whose echo signal amplitudes are below a predetermined level.