Color image system for laser range finders has scanned fan beam illumination and receiver reduces power

The invention relates to a device for recording an object space with a measuring head, which comprises an opto-electronic range finder according to a signal processing method, with a transmitting device for transmitting optical, especially laser signals and a receiving device for receiving optical signals , especially from laser radiation that is reflected from objects located in the target area. The device further comprises a scanning device for deflecting the optical axes of the transmitting and receiving device, which has an oscillating mirror, a rotating prism or the like to deflect the beams in one direction, while the entire device is used to deflect the beams in the other direction The measuring head can be swiveled, the device being equipped with an evaluation device which is derived from the transit time or the phase position of the emitted optical signal determines distance values. In the new device, a brightness and / or color signal is derived from the area between the oscillating mirror, rotating prism or the like and transmitting and / or receiving device or from the latter, a distance value and solid angle being assigned to each picture element.

With the new device, so-called distance images are generated on the one hand, in which the distance assigned to each pixel is displayed, for example, in gray value levels or coded in false colors. On the other hand, the new device generates brightness or color images that are congruent with the distance images and can therefore be directly superimposed on them. This is important insofar as distance images are often difficult to interpret on their own. The distance image only shows structures staggered in depth, but cannot resolve colored structures in an area, so that important information such as inscriptions, skid marks, etc. can sometimes be lost. By superimposing a distance and a congruent brightness or color image, a resolution of the spatial structure is ensured on the one hand, even with the lowest contrast, and on the other hand it is ensured that colored structures in surfaces are also recognized and displayed.

In this context, it has been proposed to derive a brightness signal from the amplitudes of the received signals of the range finder. Since in this case the object is scanned selectively with the transmission beam, generally a laser beam, and thus also illuminated point by point, there is no need for special lighting and the device can therefore also work in complete darkness. Such distance measuring systems typically work with infra-red transmitters, so that infra-red images are generated according to this method. This is desirable for a number of applications, such as monitoring purposes, but it can be a disadvantage for other applications, such as the documentation of natural and art monuments. A color image to supplement the distance image is often required for such applications.

Since the natural lighting is generally not sufficient, especially when taking pictures of interiors, the scene must be illuminated as evenly as possible with spotlights. Since the scanning devices have a relatively large recording field on the order of up to 1.4 x 5.8 rad (80 ° x 330 °), this is extremely complex, both in terms of the devices and in terms of energy supply.

This problem is solved according to the invention in that a lamp is integrated into the swiveling measuring head of the scanning device or placed on it, which illuminates a field in the swiveling direction of the measuring head, the width of which essentially corresponds to that of a raster element of the scanning device.

In an advantageous embodiment of the invention, the lamp illuminates the object space to be scanned with a light fan whose dimensions in the pivoting direction of the measuring head correspond essentially to the width of a raster element, in the other direction to that of the maximum scanning angle of the oscillating mirror or the rotating prism.

With a typical size of a grid element of 3 mrad x 3 mrad corresponding to 10x10 minutes of arc and a recording field of 1.4 rad x 1.4 rad, the energy requirement for illuminating the object is reduced to less than 1%.

To generate such a fan of light, it is advantageous to use a light source with a longitudinally extending helix or gas discharge path, the axis of which runs essentially parallel to the pivot axis of the measuring head.

AT 409 195 B

The light source of the lamp is preferably preceded by aspherical optics which have a significantly longer focal length in the pivoting direction of the measuring head than in the scanning direction of the oscillating mirror or prism.

As an alternative to the solution described above, the light source of the lamp is preceded by a row of optics extending in the scanning direction of the oscillating mirror or prism.

In the interest of cost-effective production, the optics connected upstream of the light source of the lamp are made of plastic in a manner known per se.

The power requirement of the luminaire can be further drastically reduced by the fact that the light source of the luminaire is preceded by a deflection device of the same type, such as an oscillating mirror or rotating prism, as the scanning device has, the deflecting device of the luminaire with that of the scanning device , mechanically, for example, is coupled to a toothed belt or is preferably synchronized by electronic measures.

In order to ensure perfect illumination of the object field even at medium distances and in close proximity, an electronic control unit is provided according to the invention, which receives synchronous sensor signals from the deflection unit and distance values ​​from the data memory and uses these to calculate a synchronous control signal the deflection unit of the lamp is controllable, whereby, to compensate for the parallax between the measuring and illuminating beams, depending on the current deflection angle and the target distance, the measuring beam and the illuminating beam can be brought into congruence on the target surface by using a correction angle.

Typical scanning devices such as rotating prisms or oscillating mirrors have a so-called. Sampling gap on: for geometric reasons, only part of the deflection cycle can be used. In the case of prisms, the scanning gap is around 60% in a specific design. In the case of oscillating mirrors, the scanning gap is of the same order of magnitude. In an advantageous further development of the invention, a synchronization unit is proposed which can be controlled by the scanning device (8) and which controls the light source (21) of the lamp (10) in a pulse-like manner and which turns off or off the light source (21) during the scanning gaps of the scanning device (8) . switches to a reduced performance level.

Further features of the invention emerge from the following description of some exemplary embodiments and with reference to the drawing. Fig. 1 shows the measuring head of a scanning device with an attached lamp. FIG. 2 shows the lamp head according to FIG. 1 in axial section, FIG. 3 shows a section according to plane AA in FIG. 2. FIG. 4 also shows a variant of the lamp according to the invention in axial section. The fig. 5 illustrates the areas illuminated by the luminaire together with the measurement and recording fields . FIG. 6 shows a further variant of the device shown in FIG. 1. 7 shows a block diagram of the device according to FIGS. 4 and 6, respectively.

In FIG. 1, 1 denotes a measuring head of a laser scanner which is attached to a stand 2. The measuring head 1 consists of a first part 1 a, which is fixedly arranged opposite the stand 2. The upper part 1b of the measuring head 1 can be pivoted about an axis 9 with respect to the lower part 1a. The measuring head upper part 1 b comprises a mirror prism 8 which is arranged to be rotatable about an axis 7 which is normal with respect to the axis 9 of the measuring head 1. The mirror prism 8 is arranged in the beam path of the laser rangefinder and is driven at high speed by a motor (not shown). As a result, the measuring beams are deflected in the vertical direction (arrows α in FIG. 1). At the same time, the upper part of the measuring head 1a, driven by a further motor, also not shown, performs a comparatively slow reciprocating pivoting movement (arrows 6 in FIG. 1) about the axis 9. As a result, the object field is scanned by the measuring beams in the direction of the arrows φ. The object field is scanned line by line by the two orthogonal scanning systems, a distance value being assigned to each raster element. A known distance image is generated from the sum of these distance values ​​in an evaluation device.

In addition to the distance measuring system, the measuring head 1b contains a passive optical receiving system, for example for the three basic colors RGB, the beams of which are deflected by the same mirror prism 8 parallel to the distance measuring beams. As a result, a congruent color image is generated in addition to the distance image.

In order to be able to achieve a perfect color image even under unfavorable lighting conditions,

AT 409 195 B, a light 10 is placed on the measuring head 1, which lamp is aligned with the upper part 1b of the measuring head and generates a light beam 11 in which the measuring beam 12 of the measuring head lies. The lamp 10 is pivoted by the upper part 1b of the measuring head so that the light fan sweeps over the object field and illuminates a narrow band that is scanned by the rotating prism. Because only the band that is being scanned is illuminated, the energy required can be reduced to less than 1% compared to illuminating the entire object field. This low energy requirement enables operation with batteries, which results in the system being particularly mobile. Another advantage in certain applications is that the light fan indicates the zone that is currently being scanned. People who are in the recording field can adjust accordingly, preferably remaining motionless during the recording.

In Figures 2 and 3, the lamp head is shown in detail. The housing of the lamp 10 is in two parts and consists of two shells 10a and 10b, which are connected to one another in a manner not shown. An aspherical plastic lens 13 is inserted into the lamp housing. The focal length of this lens is substantially greater in the axial direction (FIG. 2) than the focal length in a plane normal to this (FIG. 3). The optics 13 therefore have no focal point but rather have a “focal line”. In this an incandescent lamp 15 is provided with an incandescent filament extending in the axial direction. In order to achieve the highest possible degree of efficiency, the light emitted to the rear and to the side is concentrated again on the filament by a cylindrical mirror 16. The light emitted forwards by the filament is strongly bundled in the horizontal direction by the optics 13, while only a slight bundling takes place in the vertical direction. In order to enable the system to operate independently, the lamp is powered by a battery 17, the lamp 10 is controlled by the measuring head 1, and the lamp is electrically connected to this by a plug connection. When the lamp 10 is installed, it is placed on top of the measuring head; a dowel pin 18 ensures the exact alignment of the lamp 10 to the measuring head 1. The lamp 10 is fastened to the measuring head 1 with a knurled screw 14.

4 shows a variant of the device described above. The structure of the lamp largely corresponds to the solution shown in FIG. Instead of an incandescent lamp, the luminaire has an array of high-performance LEDs. A plurality of LEDs 21 are arranged on a circuit board 20. The LEDs 21 are controlled in such a way that they each illuminate the area of ​​the recording field which is currently being scanned by the scanning device. In this case it can be useful to achieve bundling in the vertical direction as well. Instead of the aspherical lens 13 from FIG. 2, optics can be more favorable in this case, which consists of a large number of segments of spherical lenses. In this case, too, this optic is preferably made from clear plastic. The fig. 5 shows the luminous spot that scans the object field and, within the luminous spot, the raster element within which the distance measurement and the recording of a picture element takes place. The light 10 is synchronized with the measuring head via the plug connection 19. This arrangement results in multiple benefits in terms of energy savings: initially only the area in which the recording is made is illuminated. Compared to an embodiment with a light fan, as has been described in connection with FIGS. 1-3, this results in a further considerable energy saving. A further energy saving e is achieved in that the LEDs of the luminaire are not activated during the scanning gap of the scanning device. In typical scanning devices with rotating prisms or oscillating mirrors, the scanning gap exceeds the scanning phase by a factor of approximately 2. Instead of an array of LEDs, the light 10 can also be equipped with a large number of flash lamps arranged in a row, which sequentially illuminate the object field.

6 shows a further variant of the invention: The lamp 10 fixed on the measuring head 1 has an essentially point-shaped light source 25, the light of which is bundled by a collimator lens 26, the light source being imaged essentially into infinity. Downstream of the optics is a mirror prism 27, which is designed analogously to the prism 8 of the measuring head. The optical quality of this prism can, however, be considerably more modest compared to that of prism 8: in many cases a plastic prism will also suffice. The prisms 8 and 27 are driven synchronously, for example with a toothed belt 28 that the

AT 409 195 B connects both systems The parallax correction ensures that the illuminating beam and the measuring and recording beam meet at the target, so that optimal illumination is achieved despite greatly changing object distances.

Instead of the mechanical coupling, electrical synchronization can also be provided. If the scanning device is used not only for recording objects that are far away, but also in a medium distance range or in a close range at all, a parallax error results when the illuminating beam and the recording beam are aligned in parallel. To avoid this error, a phase correction can be built into the drive of the mirror prism on the luminaire side in the case of electrical synchronization. This phase correction can take place automatically as a function of the distance measured with respect to the respective area of ​​the recording field.

In an analogous manner, an automatic parallax correction can also be carried out in the device according to FIG. 4.

FIG. 7 shows, in the form of a block diagram, the structure of the control device of the laser scanner, only the systems downstream of the deflection units being shown in this diagram. A laser transmitter is designated by 50, which controls the laser diode 51, which is preceded by the optics 52, which preferably images the emitter zone of the laser into infinity. In addition to the transmission optics 52, a receiver optics 53 is provided, the optical axis of which is aligned parallel to that of the transmission optics 52. A beam splitting prism 54 is provided in the beam path of the receiver optics 53. The receiver optics 53, on the one hand, concentrate the radiation, which is generally diffusely reflected from a target located in the beam path of the transmitter optics, onto the receiver diode 55. An avalanche diode is advantageously used as the receiver diode 55. Transmission and reception diodes are preferably matched to one another in terms of their spectral characteristics, the reception diode having its maximum spectral sensitivity in the region in which the transmission diode emits at a maximum. Since the receiving diode 55 receives a lot of interfering radiation in the form of daylight or light from various artificial light sources in addition to the radiation emitted by the transmitting diode and reflected by the target, it can be advantageous to place an optical filter as narrow-band as possible in front of the receiving diode, which has its maximum transmission in the spectral band in which the laser emits.

A part of the light emitted from the object space is concentrated onto a receiving diode 57 by the beam splitter prism 54. The beam splitting prism 54 preferably has a dichroic mirror coating 56 which allows radiation of the wavelength of the laser diode 51 to pass essentially undisturbed, while shorter-wave radiation, in particular visible light, is predominantly reflected onto the diode 57. Instead of a single receiving diode 57, a diode triple can also be provided, the diodes of which are matched in their spectral sensitivity to the 3 basic colors. With such a variant, a black-and-white or color image of the object field can therefore be recorded parallel to the distance image (active channel) via the second, passive channel.

The laser transmitter 50 comprises a pulse generator which controls the laser diode 51. The laser transmitter emits a sequence of laser pulses when it is appropriately controlled by the processor 58.

The signals received by the diode 55 are amplified and processed in an amplifier and analog signal processor stage 59. The signals processed in this way are digitized in an analog / digital converter 60 and stored in a memory 61.

In an alternative embodiment, the running interval between the transmission and reception pulses is digitized by means of a time interval digitizing device 60, and the results are stored in a memory 61.

The entire device is clocked by a clock generator 62. The processor 58 and the data memory 61 are connected to one another by a data bus, which is indicated schematically and denoted by 63. A program memory 64 for the processor 58 is also connected to this data bus 63, as well as an intermediate data memory 65 in which, after a first evaluation by the processor 58, raw data are stored which are read out at the end of the measurement cycle. A distance value for each individual raster element is determined from this raw data using algorithms stored in the program memory.

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The signal supplied by the diode (or the diode triple) 57 is amplified in the video processor stage 66 and processed further. This video processor is in connection with the processor 58 and the other blocks of the system, especially with the digital image memory 67 and the video interface 68, via the bus 63. The image coordinates belonging to the individual raster elements are fed into the system by the two deflection electronics units 69 and 70 via the data bus 63.

The synchronization unit for the lamp in an embodiment according to FIG. 4 or 6 is denoted by 71. This unit is activated directly by the control of the drive of the mirror prism 8. This unit communicates via the data bus 63 with the measured value memories and the processor 58, so that an automatic parallax correction can also be carried out.

The invention is not restricted to the exemplary embodiments described above.