Device for optically measuring the distance to a diffuse target object and a reflective target object

Abstract

The invention relates to a device (11) for optically measuring the distance to a target object, which is embodied as a scattering target object or a reflecting target object, the device comprising a distance measuring device (13) and an adjusting device (14). A laser beam is generated in the distance measuring device (13), and the laser beam is adapted to an external optical unit (12) by means of the adjusting device (14). The adjusting device (14) comprises a beam shaping optical unit (15) and a focus shifting device (16).

Description

Technical Field

[0001] The present invention relates to a system including an external optical unit and a device for optically measuring the distance to a target object. Background Art

[0002] In addition to hand-held measuring devices, known devices for optically measuring distances are provided for installation in, for example, total stations. During installation in a total station, the device is combined with additional optical elements, such as, for example, a telescope. For the sake of definition, the additional optical elements are referred to as external optical units.

[0003] The prior art has disclosed various solutions to allow the device to be used for optically measuring the distance to scattered target objects and reflective target objects. DE 198 40 049 A1 has disclosed a device for optically measuring distances that generates a first laser beam with a large beam divergence and a second laser beam with a low beam divergence, wherein the first laser beam is provided for optically measuring the distance to scattered target objects and the second laser beam is provided for optically measuring the distance to reflective target objects. Alternative solutions include generating a collimated laser beam in the distance measuring device, which can be shaped and adapted to the type of target object by an adjustment device arranged downstream of the distance measuring device.

[0004] EP 2 527 867 B1 has disclosed a distance measuring device with a coaxial arrangement that generates a collimated laser beam. The distance measuring device includes a laser beam source, a detector, a beam shaping optical unit having a laser beam shaping optical unit and a received beam shaping optical unit, and a beam splitting optical unit that separates the laser beam and the received beam from each other. The beam shaping optical unit is implemented as a collimating optical unit that shapes the laser beam into a collimated laser beam. The collimated laser beam leaving the distance measuring device is designed for optically measuring the distance to scattered target objects. The radiant flux of the laser beam source is too high for optical distance measurement to a reflective target object, which may cause detector overload. In the case where the reflective target object is implemented as a single retroreflector, it is disadvantageous to use a collimated laser beam. The collimated laser beam must be very precisely aligned with the center of the single retroreflector to prevent the situation where the received beam does not irradiate the detector. If the laser beam does not irradiate the center of the single retroreflector, a parallel offset of the received beam with respect to the optical axis of the laser beam will occur.

[0005] DE 10 2013 205 589 A1 has already disclosed a device for optically measuring the distance to scattering target objects and reflecting target objects. The device includes a distance measuring device, which includes a laser beam source, a detector, a beam splitting optical unit, a beam shaping optical unit, and an adjustment device. The beam shaping optical unit has a laser beam shaping optical unit and a received beam shaping optical unit. The adjustment device is arranged in the beam path of the laser beam, downstream of the distance measuring device. The adjustment device includes a second laser beam shaping optical unit and a second received beam shaping optical unit. The second laser beam shaping optical unit is implemented as a diverging optical unit, which shapes the collimated laser beam into an expanded laser beam. The second received beam shaping optical unit is implemented as a diffuser plate, which attenuates the laser beam reflected at the target object. In order to be able to adapt the laser beam to different target objects, the adjustment device can include a plurality of second laser beam shaping optical units and / or a plurality of second received beam shaping optical units. The plurality of second laser beam shaping optical units differ from each other in terms of their expansion characteristics. The plurality of second received beam shaping optical units are implemented as diffuser plates and differ from each other in terms of their light scattering characteristics.

[0006] The device for optically measuring distance known from DE 10 2013 205 589 A1 has a number of disadvantages: extraneous light (for example in the form of directly or indirectly incident sunlight) increases the measurement time required to measure the distance, or increases the measurement error in the case of a fixed measurement time. Different from the laser beam, the extraneous light is not directional but can be incident from different directions. The second received beam shaping optical unit implemented as a diffuser plate attenuates the extraneous light to a much greater extent than the directional received beam. In addition, the laser beam expanded by the diverging optical unit is not suitable for coupling into an external optical unit.

[0007] WO 2016 / 184735 A1 has already disclosed a further device for optically measuring the distance to scattering target objects and reflecting target objects. The device includes a laser beam source, a detector, and a laser beam shaping device, which has a first laser beam shaping optical unit and a second laser beam shaping optical unit. The second laser beam shaping optical unit is different from the first laser beam shaping optical unit and is arranged in the beam path of the laser beam, downstream of the first laser beam shaping optical unit.

[0008] The first laser beam shaping optical unit is implemented as a collimation optical unit and is designed to measure the distance to a scattering target object. The second laser beam shaping optical unit is implemented as a first array having a plurality of transmissive pixels and is designed to measure the distance to a reflective target object, which may be implemented as a single retroreflector or a surface retroreflector. By means of a first control unit, the transmittance of the transmissive pixels can be switched between three states, namely, a non-transmissive state with a transmittance of less than 10%, a partially transmissive state with a transmittance between 10% and 90%, and a fully transmissive state with a transmittance of greater than 90%. The laser beam can be adapted to the type of target object by the transmittance of the respective transmissive pixels of the first array. In order to prevent the detector from being overloaded when measuring the distance to a reflective target object, the radiant flux of the incident received beam must be significantly lower than the radiant flux of the emitted laser beam.

[0009] In the case of a single retroreflector, at least 50% of the transmissive pixels arranged in the beam path of the laser beam in the first array are switched to the non-transmissive state. The transmissive pixels arranged in the beam path of the laser beam and having a partially transmissive or fully transmissive embodiment form a transmissive aperture of the laser beam, which contributes to a significant expansion of the laser beam. This expansion allows reducing the accuracy required for aligning the laser beam on the single retroreflector. In the case of a partially transmissive pixel, the proportion of the transmitted radiant flux can be changed by the transmittance of the transmissive pixel; the smaller the transmittance, the more significant the attenuation of the laser beam.

[0010] A disadvantage of the device for optically measuring distance known from WO 2016 / 184735 A1 is that the transmissive aperture obscures most of the laser beam, which may lead to significant signal variations in the case of a highly structured and inhomogeneous laser beam. In addition, the device for optically measuring distance is not suitable for coupling with, for example, an external optical unit such as a zoom lens or a telescope. Summary of the Invention

[0011] The object of the present invention is to develop a device for optically measuring distance, which is suitable for optically measuring the distance to a scattering target object and a reflective target object, wherein the laser beam is coupled into an external optical unit. The device for optically measuring distance should exhibit stable operation over a temperature range between -20°C and +65°C.

[0012] In the case of a device for optically measuring the distance to a scattering target object or a reflective target object as set forth at the beginning, this object is achieved according to the invention by a system comprising an external optical unit and a device for optically measuring the distance to a target object.

[0013] According to the present invention, the device for optically measuring distance is characterized in that the second laser beam shaping optical unit is implemented as a focusing optical unit which shapes the collimated laser beam into a focused laser beam, and the adjusting device includes a focal shift device which can be moved into the beam path of the focused laser beam. The first laser beam shaping optical unit implemented as a collimating optical unit shapes the laser beam from the laser beam source into a collimated laser beam, which is then shaped into a focused laser beam by the second laser beam shaping optical unit implemented as a focusing optical unit.

[0014] The focal shift device that can be moved into the beam path of the focused laser beam is suitable for optically measuring the distance to a scattered target object and a retroreflective target object. Optically measuring the distance to a scattered target object is implemented by a focal shift device arranged outside the beam path of the focused laser beam, and optically measuring the distance to a retroreflective target object is implemented by a focal shift device arranged in the beam path of the focused laser beam, where these retroreflective target objects are implemented as single element retroreflectors.

[0015] Preferably, the collimating optical unit and the focusing optical unit are fastened to a common optical unit support. The common optical unit support for the collimating optical unit and the focusing optical unit helps to obtain a fixed position of the focus within the required temperature range. This ensures the maintenance of the adjusted state for measuring the distance to a scattered target object.

[0016] In a preferred variant, the focal shift device includes a focal shift element, wherein the focal shift device can be adjusted between a first state and a second state. In the first state, the focal shift element is arranged outside the beam path of the laser beam, and in the second state, the focal shift element is arranged in the beam path of the laser beam. The focal shift device that can be adjusted between two states is suitable for optically measuring the distance to a scattered target object and a retroreflective target object, where these scattered target objects and retroreflective target objects are implemented as single element retroreflectors or surface reflectors. The first state of the focal shift device is provided for optically measuring the distance to a scattered target object, in which the focal shift element is arranged outside the beam path of the laser beam; and the second state of the focal shift device is provided for optically measuring the distance to a single element retroreflector, in which the focal shift element is arranged in the beam path of the laser beam. The first state or the second state of the focal shift device can be used for measuring the distance to a surface reflector.

[0017] Preferably, the focus shifting element comprises two inclined planar glass plates, wherein, in the second state of the focus shifting device, a first glass plate of the two glass plates is inclined at a positive inclination angle α, and a second glass plate of the two glass plates is inclined at a corresponding negative inclination angle -α, in each case with respect to a propagation plane which is arranged perpendicular to the optical axis of the focused laser beam. By inclining the glass plates with respect to the propagation plane perpendicular to the optical axis of the collimated laser beam, back reflection of the laser beam in the direction of the laser beam source or in the direction of the detector can be prevented or at least reduced. The advantage of an embodiment of the focus shifting element consisting of planar glass plates inclined with respect to the propagation plane perpendicular to the optical axis of the focused laser beam is that the focal position of the focused laser beam can be changed. Here, the shift path can be set by the thickness of the glass plate.

[0018] In an alternative preferred variant, the focus shifting device comprises a first focus shifting element and a second focus shifting element, wherein the focus shifting device is adjustable between a first state, a second state and a third state, in which first state the first and second focus shifting elements are arranged outside the beam path of the laser beam, in the second state the first focus shifting element is arranged in the beam path of the laser beam, and in the third state the second focus shifting element is arranged in the beam path of the laser beam. A focus shifting device which is adjustable between these three states is suitable for optically measuring the distance to scattering target objects and retroreflective target objects, which scattering target objects and retroreflective target objects are embodied as single retroreflectors or surface retroreflectors. The first state of the focus shifting device is provided for optically measuring the distance to scattering target objects, in which first state the first focus shifting element and the second focus shifting element are arranged outside the beam path of the laser beam. The second state and the third state of the focus shifting device are provided for optically measuring the distance to single retroreflectors, in which second state and third state the first focus shifting element and the second focus shifting element are respectively arranged in the beam path of the laser beam. The first state, the second state or the third state of the focus shifting device can be used for measuring the distance to surface retroreflectors.

[0019] Preferably, the first focus shifting element comprises two inclined first glass plates, wherein, in the second state of the focus shifting device, a first one of the two first glass plates is inclined at a positive first inclination angle α 1 and a second one of the two first glass plates is inclined at a corresponding negative first inclination angle -α 1 in each case with respect to a propagation plane which is arranged perpendicular to the optical axis of the focused laser beam; and the second focus shifting element comprises two inclined second glass plates, wherein, in the third state of the focus shifting device, a first one of the two second glass plates is inclined at a positive second inclination angle α2 is inclined, and the second of the two second glass plates is inclined at a corresponding negative second inclination angle -α 2 is inclined, in each case with respect to this propagation plane. By inclining the glass plate with respect to the propagation plane perpendicular to the optical axis of the collimated laser beam, back-reflection of the laser beam in the direction of the laser beam source or in the direction of the detector can be prevented or at least reduced. In the case of a focus shifting device having a plurality of focus shifting elements, the focal position of the focused laser beam can be shifted to different extents. Here, the shifting path depends on the thickness of the glass plate used for the focus shifting element.

[0020] In a preferred development, the adjusting device includes an attenuation device, wherein the attenuation device is arranged in the beam path of the laser beam, between the first laser beam shaping optical unit and the second laser beam shaping optical unit. Arranging the attenuation device in the beam path of the laser beam between the first laser beam shaping optical unit and the second laser beam shaping optical unit is advantageous because the attenuation of the laser beam and, where applicable, the attenuation of the received beam are effected in the collimated laser beam. In the beam path of the collimated laser beam, the attenuation element can be inclined with respect to the propagation plane of the collimated laser beam in order to prevent or at least reduce back-reflection of the laser beam in the direction of the laser beam source or the detector.

[0021] In a preferred variant, the attenuation device includes an attenuation element, wherein the attenuation device can be adjusted between a first state and a second state, in the first state, the attenuation element is arranged outside the beam path of the laser beam, and in the second state, the attenuation element is arranged inside the beam path of the laser beam. An attenuation device that can be adjusted between these two states is suitable for optically measuring the distance to scattering target objects and reflecting target objects, which are implemented as single retroreflectors or surface retroreflectors. The first state of the attenuation device is provided for optically measuring the distance to scattering target objects, in which state the attenuation element is arranged outside the beam path of the laser beam; and the second state of the attenuation device is provided for optically measuring the distance to reflecting target objects, in which state the attenuation element is arranged in the beam path of the laser beam.

[0022] Particularly preferably, in the second state of the attenuation device, the attenuation element is inclined at an inclination angle β with respect to the propagation plane, which is arranged perpendicular to the optical axis of the collimated laser beam. By inclining the attenuation element with respect to the propagation plane perpendicular to the optical axis of the collimated laser beam, back-reflection of the laser beam in the direction of the laser beam source or the detector can be prevented or at least reduced.

[0023] In an alternative preferred variant, the attenuation device comprises a first attenuation element and a second attenuation element, wherein the attenuation device is adjustable between a first state, a second state and a third state. In the first state, the first and second attenuation elements are arranged outside the beam path of the laser beam. In the second state, the first attenuation element is arranged in the beam path of the laser beam. In the third state, the second attenuation element is arranged in the beam path of the laser beam. An attenuation device adjustable between these three states is suitable for optically measuring the distance to scattering target objects and reflecting target objects, which are embodied as corner reflectors or surface reflectors. The first state of the attenuation device is provided for optically measuring the distance to scattering target objects, in which the first attenuation element and the second attenuation element are arranged outside the beam path of the laser beam. The second state and the third state of the attenuation device are provided for optically measuring the distance to reflecting target objects, in which the first attenuation element and the second attenuation element are arranged in the beam path of the laser beam, respectively.

[0024] Particularly preferably, in the second state of the attenuation device, the first attenuation element is inclined at a first inclination angle β 1 and in the third state of the attenuation device, the second attenuation element is inclined at a second inclination angle β 2 in each case with respect to the propagation plane, which is arranged perpendicular to the optical axis of the collimated laser beam. By inclining the first attenuation element and the second attenuation element with respect to the propagation plane perpendicular to the optical axis of the collimated laser beam, back-reflection of the laser beam in the direction of the laser beam source or in the direction of the detector can be prevented or at least reduced.

[0025] In a development, the device comprises a first receiving beam shaping optical unit and the adjusting device comprises a second receiving beam shaping optical unit. The first receiving beam shaping optical unit is designed for measuring the distance to scattering target objects, and the second receiving beam shaping optical unit is for adapting the received beam to reflecting target objects, which can be embodied as corner reflectors or surface reflectors.

[0026] This application further relates to a system, which comprises an external optical unit and a device for optically measuring distances, the external optical unit being arranged in the beam path of the laser beam, downstream of the device. For example, the external optical unit is embodied as a zoom lens or a telescope.

[0027] Preferably, the rear focal plane of the external optical unit substantially coincides with the front focal plane of the focusing optical unit, wherein no focus shifting element is provided in the beam path of the laser beam. If the external optical unit is positioned such that the front focal plane of the second laser beam shaping optical unit coincides with the rear focal plane of the external optical unit, the focused laser beam is shaped by the external optical unit into a collimated laser beam, which is used to optically measure the distances to the scattered target object and the retroreflector. If the focused laser beam impinges on a focus shifting element that shifts the front focal plane of the second laser beam shaping optical unit relative to the rear focal plane of the external optical unit, the external optical unit cannot collimate the focused laser beam; instead, the focused laser beam is shaped into an expanded laser beam, which is used to optically measure the distance to the single reflector. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Exemplary embodiments of the present invention are described below with reference to the drawings. These are not necessarily intended to show the exemplary embodiments to scale; rather, the drawings are produced in a schematic and / or slightly distorted form where this aids illustration. It should be borne in mind that various modifications and changes can be made to the form and details associated with the embodiments without departing from the general concept of the present invention. The general concept of the present invention is not limited to the exact form or details of the preferred embodiments shown and described below, nor is it limited to a subject matter that would be restricted compared to the subject matter claimed in the claims. For a given design scope, values within the limits mentioned should also be disclosed as limiting values and should be available and claimable as required. For simplicity, the same reference numerals are used below to denote the same or similar one or more parts, which have the same or similar functions.

[0029] In the drawings:

[0030] Figure 1 A system according to the present invention is shown, which system includes an external optical unit and a device for optically measuring distances according to the present invention;

[0031] Figure 2 is shown in a cross-section along Figure 1 the section of Figure 1 a device for optically measuring distances according to the present invention;

[0032] Figure 3 Optical distance measurement of a scattered target object by means of a device for optically measuring distances according to the present invention is shown;

[0033] Figure 4 Optical distance measurement of a reflected target object, which is implemented as a retroreflector, by means of the device shown in Figure 3 is shown; and

[0034] Figure 5 shows an optical distance measurement of a reflective target object by means of Figure 3 the device shown, where the reflective target object is implemented as a retroreflector. DETAILED DESCRIPTION

[0035] Figure 1 shows a system 10 according to the invention, which system comprises an external optical unit 12 and a device 11 according to the invention for optically measuring the distance to a target object. The device 11 comprises a distance measurement device 13 and an adjustment device 14.

[0036] A laser beam is generated in the distance measurement device 13, and the laser beam is adapted to the external optical unit 12 by means of the adjustment device 14. The adjustment device 14 comprises a beam shaping optical unit 15 and a focus shifting device 16. Additionally, the adjustment device 14 may comprise an attenuation device 17, which is arranged between the distance measurement device 13 and the beam shaping optical unit 15.

[0037] Figure 2 along Figure 1 the cross-section of the Figure 1 system 10 according to the invention is shown. The system 10 comprises a distance measurement device 13, an adjustment device 14 and an external optical unit 12.

[0038] The distance measurement device 13 comprises: a laser beam source 21, which is implemented as a first electro-optical component and emits a laser beam along an optical axis; and a detector 22, which is implemented as a second electro-optical component and receives a received beam that has been scattered or reflected at the target object.

[0039] The distance measurement device 13 has a coaxial embodiment, i.e., the laser beam and the received beam extend coaxially with each other. In order to separate the laser beam and the received beam from each other, the distance measurement device 13 comprises a beam splitter optical unit, which can be implemented as a perforated mirror, a polarization beam splitter or a semi-transparent mirror. The distance measurement device 13 comprises a beam splitter optical unit 23, which is implemented as a perforated mirror. In an exemplary embodiment, the received beam is deflected by the beam splitter optical unit 23, and the laser beam passes through the beam splitter optical unit 23 without deflection.

[0040] The laser beam emitted by the laser beam source 21 along the optical axis is divergent and must be shaped by optical elements. The distance measuring device 13 includes a first beam shaping optical unit 24, which shapes the laser beam and the received beam. Since the beam splitter optical unit 23 is implemented as a perforated mirror, the inner region of the first beam shaping optical unit 24 is used for beam shaping of the laser beam and is referred to as the first laser beam shaping optical unit 25, and the outer region of the first beam shaping optical unit 24 is used for beam shaping of the received beam and is referred to as the first received beam shaping optical unit 26. In the case where the beam splitter optical unit is implemented as a polarization beam splitter or a semi-transparent mirror, the inner region of the first beam shaping optical unit 24 is used for beam shaping of the laser beam, and the entire first beam shaping optical unit 24 is used for beam shaping of the received beam. The aperture stop 27 can be arranged between the beam splitter optical unit 23 and the first beam shaping optical unit 24 in the beam path of the laser beam. The aperture stop 27 is used to prevent or at least reduce the back reflection of the laser beam in the direction of the detector 22.

[0041] The laser beam source 21, the detector 22, the beam splitter optical unit 23, and the first beam shaping optical unit 24 form the distance measuring device 13. The distance measuring device 13 further includes an optical unit holder 28, a circuit board 29, and a control and evaluation device 30. The laser beam source 21, the beam splitter optical unit 23, and the first beam shaping optical unit 24 are fastened to the optical unit holder 28, and the detector 22 is fastened to the circuit board 29. The control and evaluation device 30 is connected to the laser beam source 21 and the detector 22 and determines the distance to the scattering target object or the reflecting target object, for example, based on the time difference between the reference beam and the received beam.

[0042] The laser beam source 21 emits a divergent laser beam, which is directed towards the beam splitter optical unit 23. The largest possible part of the laser beam is transmitted through the beam splitter optical unit 23, and the transmitted part of the laser beam impinges on the first laser beam shaping optical unit 25, where the first beam shaping is completed. The first laser beam shaping optical unit 25 is implemented as a collimating optical unit, which collimates the divergent laser beam into a collimated laser beam. The optical properties of the collimating optical unit are adapted to measure the distance to a scattering target object at a large distance (infinity). In an exemplary embodiment, the first laser beam shaping optical unit 25 and the first received beam shaping optical unit 26 are implemented as collimating optical units and have the same optical properties. Alternatively, the first laser beam shaping optical unit and the first received beam shaping optical unit can differ in their optical properties.

[0043] The laser beam emitted from the distance measuring device 13 is adapted to the external optical unit 12 by means of the adjusting device 14. The adjusting device 14 includes a beam shaping optical unit 15 and a focus shifting device 16. The beam shaping optical unit is hereinafter referred to as the second beam shaping optical unit. The second beam shaping optical unit 15 shapes the laser beam and the received beam. Since the beam splitter optical unit 23 is implemented as a perforated mirror, the inner region of the second beam shaping optical unit 15 is used for beam shaping of the laser beam and is referred to as the second laser beam shaping optical unit 31, and the outer region of the second beam shaping optical unit 15 is used for beam shaping of the received beam and is referred to as the second received beam shaping optical unit 32. In the case where the beam splitter optical unit is implemented as a polarization beam splitter or a semi-transparent mirror, the inner region of the second beam shaping optical unit 15 is used for beam shaping of the laser beam, and the entire second beam shaping optical unit 15 is used for beam shaping of the received beam.

[0044] The second laser beam shaping optical unit 31 is implemented as a focusing optical unit that shapes the collimated laser beam into a focused laser beam. The optical properties of the focusing optical unit are adapted to measure the distance to the scattered target object and the reflected target object. In an exemplary embodiment, the second laser beam shaping optical unit 31 and the second received beam shaping optical unit 32 are implemented as focusing optical units and have the same optical properties. Alternatively, the second laser beam shaping optical unit and the second received beam shaping optical unit may differ in their optical properties.

[0045] The focus shifting device 16 is arranged between the second laser beam shaping optical unit 15 and the external optical unit 12 and is used to adjust the position of the focal point when measuring the distance to the reflected target object. The focus shifting device 16 includes a focus shifting element 33, which includes two planar glass plates 34A, 34B.

[0046] The focus shifting device 16 can be adjusted between a first state and a second state. In the first state, the focus shifting element 33 is arranged outside the beam path of the laser beam. In the second state, the focus shifting element 33 is arranged inside the beam path of the laser beam. In an exemplary embodiment, the focus shifting device 16 is adjusted by a stepper motor 35, by means of which the focus shifting element 33 is implemented to be pivotable about a pivot axis 36. Figure 2 The focus shifting device 16 in the second state is shown.

[0047] The planar glass plates 34A, 34B are inclined with respect to the propagation plane 37 of the laser beam, wherein the propagation plane is set perpendicular to the optical axis 38 of the laser beam. The first glass plate 34A of the two glass plates is inclined with respect to the propagation plane 37 at a positive inclination angle α, and the second glass plate 34B of the two glass plates is inclined with respect to the propagation plane 37 at a corresponding negative inclination angle -α, so as to prevent or at least reduce the back reflection of the laser beam in the direction of the laser beam source 21 or in the direction of the detector 22. The inclination angle is measured between the surfaces of the glass plates 34A, 34B and the propagation plane 37.

[0048] The adjusting device 14 may additionally include an attenuation device 17, which is arranged between the first laser beam shaping optical unit 25 and the second laser beam shaping optical unit 31. The attenuation device 17 may include one attenuation element or a plurality of attenuation elements that are different from each other in terms of transmittance. Since the beam splitter optical unit 23 is implemented as a perforated mirror, the inner region of the attenuation element is used to attenuate the laser beam and is called the laser beam attenuation element, and the outer region of the attenuation element is used to attenuate the received beam and is called the received beam attenuation element. In the case where the beam splitter optical unit is implemented as a polarization beam splitter or a semi-transparent mirror, the inner region of the attenuation element is used to attenuate the laser beam, and the entire attenuation element is used to attenuate the received beam.

[0049] The attenuation device 17 includes an attenuation element 40, which is arranged in a rotating wheel 41. The rotating wheel is implemented to be rotatable about a rotation axis 43 by a stepping motor 42. The attenuation device 17 can be adjusted between a first state and a second state. In the first state, the attenuation element 40 is arranged outside the beam path of the laser beam. In the second state, the attenuation element is arranged inside the beam path of the laser beam. Figure 2 The attenuation device 17 in the first state is shown. By means of the attenuation device 17, the laser beam can be adapted to the target object. Within the scope of the present application, a distinction is made between a scattering target object and a reflecting target object.

[0050] A target object on which the laser beam is scattered is defined as a scattering target object, and a target object on which the laser beam is mainly reflected is defined as a reflecting target object. In the case of a reflecting target object, a distinction is made between a corner cube retroreflector and a surface retroreflector. A corner cube retroreflector is defined as a reflecting target object composed of one prism, wherein the size of the prism is larger than the typical laser beam diameter, and the incident laser beam captures the surface of the triangular prism. A surface retroreflector is defined as a reflecting target object composed of a plurality of prisms arranged adjacent to each other, wherein the size of these prisms is smaller than the typical laser beam diameter, and the incident laser beam captures a plurality of prisms; examples of surface retroreflectors are reflective films and cat's eyes.

[0051] In the second state of the attenuation device 17, the attenuation element 40 is inclined at an inclination angle β with respect to the propagation plane, which is arranged perpendicular to the optical axis of the collimated laser beam. By inclining the attenuation element 40 with respect to the propagation plane perpendicular to the optical axis of the collimated laser beam, back reflection of the laser beam in the direction of the laser beam source 21 or in the direction of the detector 22 can be prevented or at least reduced.

[0052] Figure 3 Optical distance measurement of a scattering target object by means of a system 50 according to the invention is shown, which system comprises an external optical unit 52 and a device 51 for optically measuring the distance to the target object according to the invention. The target object is embodied as a scattering target object 53.

[0053] The device 51 comprises a distance measurement device 13 and an adjustment device 54, which is different from the adjustment device 14 of the device 11. The adjustment device 54 comprises a second beam shaping optical unit 15 and a focus shifting device 55. The adjustment device 54 may additionally comprise an attenuation device 56, which is arranged between the first laser beam shaping optical unit 25 and the second laser beam shaping optical unit 31.

[0054] The distance measurement device 13 generates a laser beam 57 having an optical axis 58, which laser beam passes through a beam splitter optical unit 23 and is shaped into a collimated laser beam 59 by the first laser beam shaping optical unit 25. The collimated laser beam 59 has the same dimensions and properties for all target objects. After leaving the distance measurement device 13, the collimated laser beam 59 is shaped by the adjustment device 54 and adapted to the type of target object. In the case of target objects, a distinction is made between scattering target objects, single retroreflectors and surface retroreflectors.

[0055] In the case of optical distance measurement of a scattering target object, the laser beam is scattered at the target object over a large angular range, and only a small fraction of the radiant flux of the scattered laser beam impinges on the detector 22. The power of the laser beam source 21 is designed such that the radiant flux impinging on the detector 22 is sufficient for evaluation, even in the case of a scattering target object. In the case of optical distance measurement of a reflective target object, the laser beam is reflected at the target object and impinges on the detector 22 as a directionally received beam. The radiant flux of the reflected laser beam impinging on the detector 22 is much larger than the radiant flux of the scattered laser beam, which may cause the detector 22 to overload. To prevent the detector 22 from overloading, in the case of a reflective target object, the radiant flux is reduced by means of the attenuation device 56.

[0056] The attenuation device 56 includes a first attenuation element and a second attenuation element, and is implemented to be adjustable between three different states. The attenuation device 56 can be adjusted between a first state, a second state, and a third state. In the first state, the first attenuation element and the second attenuation element are arranged outside the beam path of the laser beam. In the second state, the first attenuation element is arranged within the beam path of the laser beam. In the third state, the second attenuation element is arranged within the beam path of the laser beam. Generally applicable is that an attenuation device having M different attenuation elements can be adjusted between M + 1 different states. In the first state of the attenuation device, no attenuation element is located in the beam path. In the second state of the attenuation device, the first attenuation element is located in the beam path. And in the (M + 1)-th state of the attenuation device, the M-th attenuation element is located in the beam path.

[0057] In the case of a scattered target object, the beam cross-section of the laser beam scattered at the target object should be as small as possible. Therefore, a collimated laser beam is used to measure the distance to the scattered target object. In the case where the reflective target object is implemented as a corner cube retroreflector, the incident laser beam should irradiate the centers of these corner cube retroreflectors. If the laser beam does not irradiate the centers of the corner cube retroreflectors, due to parallel offset, the reflected laser beam or the received beam may miss the distance measuring device 13 and thus miss the detector 22. To reduce the accuracy requirement for the laser beam to have to point to the centers of the corner cube retroreflectors, the laser beam is expanded, and a laser beam with a larger beam cross-section is directed at the corner cube retroreflectors. To optically measure the distance to the corner cube retroreflectors, the laser beam is expanded by the focus shifting device 55.

[0058] The focus shifting device 55 includes a first focus shifting element and a second focus shifting element, and is implemented to be adjustable between three different states. The focus shifting device 55 can be adjusted between a first state, a second state, and a third state. In the first state, the first focus shifting element and the second focus shifting element are arranged outside the beam path of the laser beam. In the second state, the first focus shifting element is arranged within the beam path of the laser beam. In the third state, the second focus shifting element is arranged within the beam path of the laser beam. Generally applicable is that a focus shifting device having N different focus shifting elements can be adjusted between N + 1 different states. In the first state of the focus shifting device, no focus shifting element is located in the beam path. In the second state of the focus shifting device, the first focus shifting element is located in the beam path. And in the (N + 1)-th state of the focus shifting device, the N-th focus shifting element is located in the beam path.

[0059] In Figure 3In the case of optically measuring the distance to the scattering target object 53 as shown, the laser beam is not attenuated, the received beam is not attenuated, and the laser beam is not expanded. The focus shifting device 55 and the attenuation device 56 are in their first states. In the first state of the focus shifting device 55, the first focus shifting element and the second focus shifting element are arranged outside the beam path of the laser beam, and in the first state of the attenuation device 56, the first attenuation element and the second attenuation element are arranged outside the beam path of the laser beam.

[0060] The collimated laser beam 59 is incident on the second laser beam shaping optical unit 31, which is implemented as a focusing optical unit having a front focal plane 61. The focusing optical unit 15 shapes the collimated laser beam 59 into a focused laser beam 62. In order to generate a collimated laser beam downstream of the external optical unit 52, the second beam shaping optical unit 15 and the external optical unit 52 must be positioned relative to each other such that the front focal plane 61 of the second beam shaping optical unit 15 coincides with the rear focal plane 63 of the external optical unit 52. The focused laser beam 62 is shaped by the external optical unit 52 into a collimated laser beam 64 and is directed towards the scattering target object 53.

[0061] The collimated laser beam 64 is scattered at the scattering target object 53 and impinges on the detector 22 as a scattered received beam 65. Along the path from the scattering target object 53 to the detector 22, the scattered received beam 65 passes through the external optical unit 52, the second received beam shaping optical unit 32, the first received beam shaping optical unit 26, and the beam splitter optical unit 23.

[0062] Figure 4 Optical distance measurement of a retroreflective target object by means of the device 51 and the external optical unit 52 is shown, which is implemented as a surface retroreflector 71. Here, Figure 4 The structure is different with respect to the state of the attenuation device 56 from Figure 3 the structure.

[0063] In Figure 3 the case of optically measuring the distance to the scattering target object 53 as shown, the attenuation device 56 is in the first state, and in Figure 4 the case of optically measuring the distance to the surface retroreflector 71 as shown in

[0064] The attenuation device 56 includes a first attenuation element 72 and a second attenuation element 73, which are different from each other in terms of their attenuation characteristics, where these attenuation characteristics are set by the transmittance. The attenuation device 56 can be adjusted between a first state, a second state, and a third state. In the first state, the first attenuation element 72 and the second attenuation element 73 are arranged outside the beam path of the laser beam. In the second state, the first attenuation element 72 is arranged within the beam path of the laser beam. In the third state, the second attenuation element 73 is arranged within the beam path of the laser beam.

[0065] Since the beam splitter optical unit 23 is implemented as a perforated mirror, the inner region 72A of the first attenuation element 72 is used to attenuate the laser beam and is referred to as the first laser beam attenuation element 72A, and the outer region 72B of the first attenuation element 72 is used to attenuate the received beam and is referred to as the first received beam attenuation element 72B. The inner region 73A of the second attenuation element 73 is used to attenuate the laser beam and is referred to as the second laser beam attenuation element 73A, and the outer region 73B of the second attenuation element 73 is used to attenuate the received beam and is referred to as the second received beam attenuation element 73B. In the case where the beam splitter optical unit is implemented as a polarization beam splitter or a semi-transparent mirror, the inner region of the attenuation element is used to attenuate the laser beam, and the entire attenuation element is used to attenuate the received beam.

[0066] Figure 4 The attenuation device 56 in the second state is shown, in which the first attenuation element 72 is arranged in the beam path of the collimated laser beam. It is advantageous to arrange the attenuation device 56 in the beam path of the collimated laser beam because the first attenuation element 72 can be tilted to prevent or at least reduce the back reflection of the laser beam in the direction of the laser beam source 21 or in the direction of the detector 22. In the second state of the attenuation device 56, the first attenuation element 72 is tilted at a first inclination angle β 1 with respect to the propagation plane 74, where the propagation plane 74 is arranged perpendicular to the optical axis 75 of the collimated laser beam.

[0067] The collimated laser beam 59 is attenuated by the first attenuation element 72 and irradiated onto the second laser beam shaping optical unit 31, which shapes the attenuated collimated laser beam 59 into a focused laser beam 62. The external optical unit 52 is positioned such that the front focal plane 61 of the second laser beam shaping optical unit 31 coincides with the rear focal plane 63 of the external optical unit 52. The focused laser beam 62 is shaped into a collimated laser beam 64 by the external optical unit 52 and directed towards the retroreflector 71.

[0068] The collimated laser beam 64 is reflected at the surface retroreflector 71 and impinges as a reflected received beam 76 on the detector 22. Along the path from the surface retroreflector 71 to the detector 22, the reflected received beam 76 passes through the external optical unit 52, the second received beam shaping optical unit 32, the first attenuation element 72, the first received beam shaping optical unit 26, and the beam splitter optical unit 23.

[0069] Figure 5 Optical distance measurement of a reflected target object by means of the device 51 and the external optical unit 52 is shown, where the reflected target object is embodied as a corner cube retroreflector 81. Here, Figure 5 The structure is different with respect to the state of the focus shifting device 55 and the state of the attenuation device 56 from Figure 3 and Figure 4 the structure.

[0070] In Figure 3 the case of optical distance measurement of the scattered target object 53 shown, the focus shifting device 55 and the attenuation device 56 are in a first state; in Figure 4 the case of optical distance measurement of the surface retroreflector 71 shown, the focus shifting device 55 is in the first state and the attenuation device 56 is in a second state; and in Figure 5 the case of optical distance measurement of the corner cube retroreflector 81 shown, the focus shifting device 55 is in a second state and the attenuation device 56 is in a third state.

[0071] Figure 5 The attenuation device 56 in the third state is shown, in which the second attenuation element 73 is arranged in the beam path of the laser beam. By arranging the attenuation device 56 in the beam path of the collimated laser beam, the second attenuation element 73 can be tilted in order to prevent or at least reduce the back reflection of the laser beam in the direction of the laser beam source 21 or in the direction of the detector 22. In the third state of the attenuation device 56, the second attenuation element 73 is tilted relative to the propagation plane 74 by a second tilt angle β 2 which is arranged perpendicular to the optical axis 75 of the collimated laser beam. The second tilt angle β 2 of the second attenuation element 73 and the first tilt angle β 1 of the first attenuation element 72 preferably correspond to each other, but they can also be different from each other.

[0072] The focus shifting device 55 includes a first focus shifting element 82 and a second focus shifting element 83, which are different from each other in terms of their optical characteristics. The focus shifting device 55 can be adjusted between a first state, a second state, and a third state. In the first state, the first focus shifting element 82 and the second focus shifting element 83 are arranged outside the beam path of the laser beam. In the second state, the first focus shifting element 82 is arranged within the beam path of the laser beam. In the third state, the second focus shifting element 83 is arranged within the beam path of the laser beam.

[0073] The first focus shifting element 82 includes two inclined first glass plates 84A, 84B, and the second focus shifting element 83 includes two inclined second glass plates 85A, 85B. The first glass plates 84A, 84B and the second glass plates 85A, 85B are inclined with respect to a propagation plane 86, which is arranged perpendicular to the optical axis 87 of the focused laser beam 62. The first of the two first glass plates 84A is inclined at a positive first inclination angle α 1 and the second of the two first glass plates 84B is inclined at a corresponding negative first inclination angle -α 1 both with respect to the propagation plane 86 in each case. The first of the two second glass plates 85A is inclined at a positive second inclination angle α 2 and the second of the two second glass plates 85B is inclined at a corresponding negative second inclination angle -α 2 both with respect to the propagation plane 86 in each case. Due to the inclination of the glass plates, back reflection of the laser beam in the direction of the laser beam source 21 or in the direction of the detector 22 is prevented or at least reduced.

[0074] The collimated laser beam 59 impinges on a second attenuation element 73, where the collimated laser beam is attenuated. The collimated laser beam 59 impinges on a second laser beam shaping optical unit 31, which shapes the collimated laser beam 59 into a focused laser beam 62. The focused laser beam 62 impinges on the first focus shifting element 82, which shifts the front focal plane 61 of the second laser beam shaping optical unit 31 relative to the rear focal plane 63 of the external optical unit 52. Due to the shift, the external optical unit 52 does not collimate the focused laser beam 62 but expands it. The focused laser beam 62 is shaped by the external optical unit 52 into an expanded laser beam 88.

[0075] The expanded laser beam 88 is reflected at the single retroreflector 81 and impinges as a reflected received beam 89 onto the detector 22. Along the path from the single retroreflector 81 to the detector 22, the reflected received beam 89 passes through the external optical unit 52, the first focal shift element 82, the second received beam shaping optical unit 32, the second attenuation element 73, the first received beam shaping optical unit 26, and the beam splitter optical unit 23.

Claims

1. A system (10; 50) comprising an external optical unit (12) and a device (11; 51) for optically measuring the distance to a target object (53; 71; 81), which target object is embodied as a scattering target object (53) or a reflecting target object (71; 81), said external optical unit being arranged in the beam path of a laser beam, downstream of the device (11; 51), the device (11; 51) comprising: - a laser beam source (21), which is embodied as a first electro-optical component and emits a laser beam (57) along an optical axis (58), - a detector (22), which is embodied as a second electro-optical component and receives a received beam (65) that has been scattered at the target object or a received beam (76; 89）， - a first laser beam shaping optical unit (25), which is embodied as a collimating optical unit and shapes the laser beam (57) into a collimated laser beam (59), - an adjusting device (14; 54), which has a second laser beam shaping optical unit (31) and a focus shifting device (16; 55), the second laser beam shaping optical unit (31) being arranged in the beam path of the laser beam, downstream of the first laser beam shaping optical unit (25) and being embodied as a focusing optical unit, which focusing optical unit shapes the collimated laser beam (59) into a focused laser beam (62), and - a beam splitting optical unit (23), which separates the laser beam and the received beam from each other and is arranged in the beam path of the laser beam, upstream of the first laser beam shaping optical unit (25), characterized in that the focus shifting device (16; 55) has N focus shifting elements and is adjustable between N + 1 different states, where N ≥ 1, in a first state, the N focus shifting elements are located outside the beam path of the laser beam, and in a second state, one focus shifting element (33; 82) is located in the beam path of the laser beam.

2. The system according to claim 1, characterized in that the first laser beam shaping optical unit (25) and the second laser beam shaping optical unit (31) are fastened to a common optical unit support (28).

3. The system according to either claim 1 or 2, characterized in that the focus shifting device (16) comprises a focus shifting element (33), wherein the focus shifting device (16) is adjustable between a first state and a second state, in the first state, the focus shifting element (33) is arranged outside the beam path of the laser beam, and in the second state, the focus shifting element (33) is arranged in the beam path of the laser beam.

4. The system according to claim 3, characterized in that The focus shift element (33) includes two glass plates (34A, 34B) with inclined planes, wherein, in the second state of the focus shift device (16), a first glass plate (34A) of the two glass plates is inclined at a positive inclination angle (α), and a second glass plate (34B) of the two glass plates is inclined at a corresponding negative inclination angle (-α), in each case with respect to a propagation plane (37) which is arranged perpendicular to the optical axis (38) of the laser beam.

5. The system according to one of claims 1 and 2, characterized in that the N focus shift elements (82, 83) of the focus shift device (55) include a first focus shift element (82) and a second focus shift element (83), wherein the focus shift device (55) is adjustable between a first state, a second state and a third state, in the first state, the first focus shift element and the second focus shift element (82, 83) are arranged outside the beam path of the laser beam, in the second state, the first focus shift element (82) is arranged in the beam path of the laser beam, and in the third state, the second focus shift element (83) is arranged in the beam path of the laser beam.

6. The system according to claim 5, characterized in that The first focus shifting element (82) includes two first glass plates (84A, 84B) that are inclined, wherein, in the second state of the focus shifting device (55), the first of the two first glass plates (84A) is inclined at a positive first inclination angle (α 1 ), and the second of the two first glass plates (84B) is inclined at a corresponding negative first inclination angle (-α 1 ), in each case with respect to the propagation plane (86), which is arranged perpendicular to the optical axis (87) of the laser beam; and the second focus shifting element (83) includes two second glass plates (85A, 85B) that are inclined, wherein, in the third state of the focus shifting device (55), the first of the two second glass plates (85A) is inclined at a positive second inclination angle (α 2 ), and the second of the two second glass plates (85B) is inclined at a corresponding negative second inclination angle (-α 2 ), in each case with respect to the propagation plane (86).

7. The system according to claim 1 or 2, characterized in that the adjustment device (14; 54) includes an attenuation device (17; 56), wherein the attenuation device (17; 56) is arranged in the beam path of the laser beam, between the first laser beam shaping optical unit (25) and the second laser beam shaping optical unit (31).

8. The system according to claim 7, characterized in that the attenuation device (17) includes an attenuation element (40), wherein the attenuation device (17) is adjustable between a first state and a second state, in the first state, the attenuation element (40) is arranged outside the beam path of the laser beam, and in the second state, the attenuation element (40) is arranged in the beam path of the laser beam.

9. The system according to claim 8, characterized in that in the second state of the attenuation device (17), the attenuation element (40) is inclined at an inclination angle (β) with respect to the propagation plane (37) which is arranged perpendicular to the optical axis (38) of the collimated laser beam (59).

10. The system according to claim 7, characterized in that the attenuation device (56) includes a first attenuation element (72) and a second attenuation element (73), wherein the attenuation device (56) is adjustable between a first state, a second state and a third state, in the first state, the first attenuation element and the second attenuation element (72, 73) are arranged outside the beam path of the laser beam, in the second state, the first attenuation element (72) is arranged in the beam path of the laser beam, and in the third state, the second attenuation element (73) is arranged in the beam path of the laser beam.

11. The system according to claim 10, characterized in that In the second state of the attenuation device (56), the first attenuation element (72) is tilted at a first inclination angle (β 1 ), and in the third state of the attenuation device (56), the second attenuation element (73) is tilted at a second inclination angle (β 2 ), in each case with respect to the propagation plane (74), which is arranged perpendicular to the optical axis (75) of the collimated laser beam.

12. The system according to claim 1 or 2, characterized in that, the device (11; 51) comprises a first received beam shaping optical unit (26) and the adjustment device (14; 54) comprises a second received beam shaping optical unit (32).

13. The system according to claim 1 or 2, characterized in that, when the N focus shift elements (33; 82, 83) are located outside the beam path of the laser beam, the rear focal plane (63) of the external optical unit (52) coincides with the front focal plane (61) of the second laser beam shaping optical unit (31).

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