Laser projection system having a multiplicity of laser projectors

Abstract

A laser projection system comprises a multiplicity of laser projectors which each have a projection region into which it is possible to project using a laser beam, wherein the projection regions form intermeshable regions, in which spatial points belong to two projection regions, wherein at least one mobile target system with four or more markers is provided, the position of which relative to one of the laser projectors can be detected, wherein at least two laser projectors detect their spatial position relative to the mobile target system, and an overarching controller determines relative poses of the at least two laser projectors with respect to one another from the detected spatial positions, wherein the overarching controller is designed to repeat the determination of the relative poses in different spatial positions of the mobile target system until at least one relative pose with respect to another laser projector is determined for each of the laser projectors, wherein at least one spatially stationary target system is also provided, the latter being able to be detected by at least one laser projector, and the overarching controller is designed to convert the relative poses of all laser projectors into spatial poses using the reflection angles of the detected markers of the spatially stationary target system by way of the at least one laser projector.

Description

[0001] Laser projection system with a variety of laser projectors

[0002] The present invention relates to a laser projection system comprising a plurality of laser projectors. Each individual laser projector has a projection area in which points, lines, and geometric shapes can be projected using a laser beam. Typically, the laser projectors have a laser beam that is deflected by two mirrors. The axes of the motor-pivotable mirrors are positioned at a suitable angle to each other, allowing the laser beam to be deflected in any direction within the projection area.

[0003] US Pat. No. 9,879,983 B2 discloses a laser projection system in which a plurality of laser projectors project onto a large object, such as an aircraft. Reference targets are also provided on poles. The laser projectors determine their position relative to the stationary reference targets.

[0004] WO 2007 / 038740 A2 discloses an automation system in which a plurality of laser projectors are integrated into a lifting platform. The laser projectors project together onto an aircraft under construction.

[0005] DE 11 2016 001 118 T5 discloses a laser projection system that can position moving parts and assemblies using 3D laser projections and projected templates. The moving part is equipped with reflector marks that the laser projector follows. WO 2021 / 069079 A1 discloses a measuring system and a coordinate measuring machine for use in a smart factory environment. The measuring system has a defined arrangement of various measuring devices, which are configured so that the coordinate measurement data generated by the different measuring devices can be referenced to a common coordinate system.

[0006] WO 2021 / 033185 A2 discloses a surveying tool for determining position and orientation relative to a construction site. Using a laser projector, the desired construction plans are projected onto a target surface, for example, to improve the accuracy and efficiency with which a structure under construction is advanced.

[0007] With existing laser projection systems with multiple laser projectors, the technical challenge is to determine the position of the laser projectors as accurately as possible in space. This is a prerequisite for projecting accurately onto a workpiece using one or more laser projectors.

[0008] The invention is based on the object of providing a laser projection system with a plurality of laser projectors whose position in space with respect to a workpiece / coordinate system can be determined as accurately as possible.

[0009] According to the invention, the object is achieved by a laser projection system having the features of claim 1. Advantageous embodiments form the subject matter of the subclaims.

[0010] The laser projection system includes a plurality of laser projectors, each with a projection area. Within the projection area, a laser beam can be projected onto spatial points. Furthermore, the laser projector can determine the direction of the incident laser beam for a reflected laser beam. The plurality of laser projectors is arranged such that the projection areas can be meshed with one another. Two areas can be meshed with one another if there is at least one spatial point that belongs to both projection areas. In the meshable area, the projection areas of the laser projectors overlap at least partially. Furthermore, the laser projection system has at least one mobile target system, each with four or more markers, wherein the pose of the mobile target system can be determined relative to one of the laser projectors.The pose comprises a three-dimensional position and orientation with respect to the three spatial directions, i.e., 6-dimensional data that allows an extended object to be uniquely described in space. In the following, pose is always used in the sense of position and orientation, with a relative pose describing a position and orientation relative to a coordinate system with its position and orientation. Such a coordinate system, to which the relative pose refers, can be given by another laser projector or by a target system. Accordingly, spatial pose refers to the position and orientation relative to a space with its origin and orientation.According to the invention, at least two laser projectors detect their spatial pose relative to respective stationary positions of the mobile target system, and a higher-level controller determines their relative pose to one another from the detected spatial poses of the at least two laser projectors. Furthermore, the higher-level controller is designed to repeat the determination of the relative pose, with the mobile target system in a stationary position, in different spatial positions of the mobile target system until at least one relative pose to another laser projector has been determined for each of the laser projectors. A network of relative poses is created between the laser projectors, which describes how the position and orientation of a laser projector relates to one or more other laser projectors. The network preferably comprises all laser projectors.The laser projection system according to the invention is additionally equipped with a spatially fixed target system comprising four or more markers. Each marker of the spatially fixed target system is detected by at least one laser projector. The higher-level controller is configured to convert the relative poses of the plurality of laser projectors into spatial poses of all laser projectors from the markers of the spatially fixed target system detected by the at least one laser projector. When converting the relative poses into the spatial poses of the laser projectors using the markers of the spatially fixed target system, it is sufficient to only detect directional angles for the spatially fixed markers; a complete detection of a pose is not required. Of course, it is also possible to detect a relative pose of the spatially fixed markers, but this is not necessary.The laser projection system according to the invention therefore operates in a two-stage process: In a first process stage, the laser projectors are located relative to one another in terms of position and orientation. This is achieved by two or more laser projectors jointly looking at a mobile target system with four or more markers and thus determining their relative pose to one another. In a second step, one or more laser projectors detect markers of the spatially fixed target system in the second process stage, which then allows the position and orientation of all laser projectors in space to be determined by optimizing the relative poses and incorporating the spatially fixed markers. When detecting the spatially fixed target system, the at least one laser projector can determine its relative pose if four or more markers are within its projection range.However, it is also sufficient if a total of four or more angle pairs are recorded by one or more laser projectors at the stationary markers of the stationary target system. The angle pair consists of a pair of angle tuples at which the laser projector records the stationary marker. Thus, the angles of incidence to a marker of the stationary target system are recorded by the laser projector. The projection accuracy of the laser projection system achievable using this method depends on the dimensional accuracy of the stationary and mobile target systems and can be less than one millimeter per ten meters, making the laser projection system ideally suited for large-area applications.

[0011] In a particularly preferred design, the mobile target system is movable through the space to be measured and can thus be detected by the laser projectors in different spatial positions. For example, two laser projectors can track the movement in a specific spatial region and repeatedly calculate their respective relative poses to the target system and thus their relative poses to each other. This results in very high accuracy in determining the relative poses of the laser projectors to each other.

[0012] With regard to overall accuracy and free use of the surface, it has proven advantageous if several spatially fixed markers of the spatially fixed target system are positioned at least partially in an edge area of ​​the overall projection surface. By arranging them in the edge areas, the central area of ​​the overall projection surface also remains free for use. The overall projection surface is thereby created as the union of the individual projection surfaces, with overlaps of the projection surfaces to enable their meshability. By means of several spatially fixed markers positioned in an edge area of ​​the overall projection surface, the positions and orientations of the laser projectors located within the overall projection surface can be determined relatively precisely, since these are integrated as if in a network across several laser projectors from different directions with their relative positions and relative orientations.In a preferred embodiment, the higher-level controller is configured to perform a compensation calculation using the relative poses and the spatial poses of the laser projectors in order to determine the spatial poses of all laser projectors with minimal error. The compensation calculation can also include the case where, based on the detection of the spatially fixed target system, the calculation of the relative poses is repeated or at least corrected to minimize the errors.

[0013] In a preferred embodiment, a mobile target system comprising four or more retroreflective markers is provided as the mobile target system. The mobile target system can then be moved within the projection area.

[0014] Preferably, the higher-level controller is additionally designed to detect a single marker with two or more laser projectors during movement and to determine its spatial position. In doing so, the higher-level controller determines, for example, an angle pair, which is evaluated, for example, by triangulation, i.e. based on the relative poses of the laser projectors involved, and detects the spatial position of the individual marker. The individual marker can also be part of the mobile target system, so that this can also be used for this task. With this configuration, the subsurface can then be measured very precisely, for example, by moving or traversing the individual marker at a constant distance above the subsurface.In this way, for example, the mobile target system can measure the subsurface very precisely if sufficient relative poses of the laser projectors have been determined. The recorded values ​​are then subsequently evaluated for position determination, for example, through triangulation. If only a few relative poses are known, it is difficult to distinguish from the obtained data whether there is a deviation in the arrangement of the laser projectors or whether there is an unevenness in the floor. However, if the spatial poses of the laser projectors have been determined with sufficient precision, this allows conclusions to be drawn about the subsurface.

[0015] In a preferred embodiment, the spatially fixed target system has a code that can identify the maker of the spatially fixed target system. For example, the laser projection system can be equipped with a camera for this purpose. The higher-level controller can use the code to assign the spatial position to the target system. In this way, the spatially fixed target system can be used without having to previously define or determine its position in space or relative to the laser projectors. The higher-level controller then knows the position of the respective markers in the spatially fixed target system.

[0016] In a preferred embodiment, the mobile target systems comprise at least four markers arranged in a predetermined orientation relative to one another, allowing the laser projector to determine its pose relative to the markers. If the markers are positioned in a meshed projection area by at least two laser projectors, they allow the relative poses of the laser projectors to be determined based on their predetermined orientation relative to one another.

[0017] In a preferred embodiment, the laser projectors are mounted in a fixed location, for example, in a hall such as an exhibition center, market hall, or conference hall. The laser projectors can also be mounted in large halls such as concert halls, theaters, or other event halls. Meshable areas are formed by the projection areas or their sub-areas that contain spatial points belonging to two projection areas. Each projection area is meshed if at least one of its spatial points also falls within a second projection area.

[0018] The invention is explained in more detail below using an exemplary embodiment:

[0019] Figure 1 shows a schematic view of two laser projectors with different positions of the mobile target system,

[0020] Figure 2 shows a schematic view of laser projectors as they can be used in trade fair construction and

[0021] Figure 3 shows a mobile target system.

[0022] Figure 1 shows two laser projectors 10, 12, which are, for example, mounted in a fixed location. Furthermore, a mobile target system 14 is shown in six different positions 14a, 14b, 14c, 14d, 14e, 14f. The mobile target system has four markers 16a, 16b, 16c, 16d.

[0023] To determine the positions of the laser projectors 10, 12 in space, the mobile target system can move through positions 14a to 14f. In positions 14a and 14d, the laser projector 10 determines its relative pose to the mobile target system 14a, 14d. The laser projector 10 can determine its position because the mobile target system carries four markers 16a to 16d, which are arranged at a predefined distance and pattern from one another, so that the laser projector can triangulate its position relative to the markers by detecting multiple markers. If the mobile target system is located in positions 14b and 14e, the laser projector 10 and the laser projector 12 can determine their poses relative to the target system. This means that the difference between these determined poses describes the relative pose of the laser projectors 10 and 12 to one another, since they are directed at the same target system.In this way, even with more than two laser projectors, a network of relative poses can be established each time the mobile target system is located in a meshable area in which its position is detected by two or more laser projectors.

[0024] The relative poses of laser projectors 10 and 12 (or the resulting network of relative poses) are initially not spatially determined absolutely. The spatial assignment of the relative poses is only determined with the spatially fixed target positions 18a to 18d. For this purpose, laser projector 10 detects the position of targets 18a and 18b, and laser projector 12 detects the position of targets 18c and 18d. In a subsequent adjustment calculation, the relative pose (or the resulting network of relative poses) can be converted into a spatially fixed network of absolute poses with the positions of the spatially fixed targets, which only need to be detected by at least one projector each. When referring to a network of relative poses above, this also includes chains of relative poses as 1-to-1 connections. The more densely the targets in the spatially fixed target system are distributed across the entire projection area, the greater the achievable accuracy for the spatial poses.

[0025] Figure 2 shows a schematic view of three laser projectors 20, 22, and 24 mounted in a hall. For example, roof rails 25 and 27 are provided in the hall, on which the projectors 20, 22, and 24 are mounted. The projectors have projection areas 26 to 32 directed toward the floor. Projectors 20 and 22 create an overlapping projection area 28. Projector 24 also has two projection areas, with projection area 32, for example, overlapping with a projection area of ​​another laser projector (not shown).

[0026] The laser projectors are used to support, for example, trade fair construction, stage construction, or the erection of other installations and structures by projecting individual objects. For example, the position of partition walls 34 can be marked out on the floor using the laser projectors. By accurately measuring the surface, the projection can be carried out with high precision, allowing designs for the partition walls to be erected to be implemented with great accuracy. The positions of tables 36, 40, and a chair 38 can also be specified very precisely using the laser projectors.

[0027] Because the invention allows an exhibition hall, concert hall, conference hall, theater stage, or other space to be precisely measured, the laser projectors can be used to very precisely specify any necessary construction or modifications. This can significantly shorten construction and setup times.

[0028] Figure 3 shows a perspective view of a mobile target system 40 constructed as a rolling table. A total of six retroreflective markers 42a to 42f with known relative positions are provided on the tabletop. This illustrates the case where a retroreflective marker 42c is detected by the laser beams 44 and 46 of two projectors. From this double detection of at least four markers, the relative positions of the two projectors can be calculated. The mobile target system 40 can be moved through the hall to be measured, whereby the relative pose of the two projectors 22 and 20 can then be determined in the overlapping projection areas, such as 28 in Figure 2.

Claims

Claims 1. Laser projection system with a plurality of laser projectors, each having a projection area into which a laser beam can project onto points in space, wherein the projection areas form meshable regions in which points in space belong to two or more projection areas, wherein at least one mobile target system with four or more markers is provided, the pose of which can be determined relative to one of the laser projectors, wherein at least two laser projectors detect their spatial pose relative to the mobile target system, and a higher-level control system determines the relative pose of the at least two laser projectors to each other from the detected spatial poses, wherein the higher-level control system is configured to repeat the determination of the relative pose in different positions of the mobile target system in space until at least one relative pose to another laser projector has been determined for each of the laser projectors.wherein a stationary target system equipped with four or more markers is provided, each of whose markers can be detected by at least one laser projector, and the higher-level control system is configured to convert the relative pose of all laser projectors into spatial poses from the markers of the stationary target system detected by the at least one laser projector.

2. Laser projection system according to claim 1, characterized in that the mobile target system is movable through space and can be detected in different positions. A laser projection system according to claim 1 or 2, characterized in that the four or more markers of the stationary target system are positioned at least partially in a boundary region of the total projection area. A laser projection system according to claim 3, characterized in that the total projection area is at least simply covered by the combination of the projection areas of the laser projectors. A laser projection system according to any one of claims 1 to 4, characterized in that the higher-level control system is configured to perform a least-squares adjustment calculation with the relative poses and the spatial poses of the laser projectors in order to determine the spatial poses of all laser projectors with minimal error. A laser projection system according to any one of claims 1 to 5, characterized in that a mobile target system is provided which has at least four retrospectively effective markers.A laser projection system according to any one of claims 1 to 6, characterized in that the higher-level control system is configured such that, during the movement of a single marker, one or more laser projectors detect the marker and determine its spatial pose. A laser projection system according to any one of claims 1 to 7, characterized in that the mobile target systems have at least four markers arranged in a predetermined orientation relative to one another, so that the laser projector can determine its relative pose relative to the markers of the mobile target system. A laser projection system according to any one of claims 1 to 8, characterized in that the laser projectors are mounted in a fixed position. A laser projection system according to any one of the preceding claims, characterized in that the markers of the target systems are designed as retroreflective markers.

Images