LASER PROJECTOR WITH TWO LASER DIODES

Description

[0001] The present invention relates to a device for laser projection comprising two laser diodes.

[0002] Laser projectors are used in a wide variety of technical fields to project outlines and markings onto objects. Typically, their lines can be projected in red, green, or multicolored light onto a flat or curved surface, making them clearly visible. The projection is often based on CAD data, which is processed into projection data and transmitted to one or more projectors. Industrial laser projection systems create virtual, yet visible, stencils that do not touch or contaminate the surfaces. Technically, the projection is achieved using one or more galvanometers, each equipped with a mirror. The laser beam is deflected by the mirror, with the mirror's rotation angle determining the direction of the deflection. By combining two or more galvanometers, any accessible point in space can be illuminated.

[0003] German patent application DE 10 2019 217 801 A1 discloses a laser projection system for projecting a laser image onto a work surface, which provides optimized laser energy. The system includes a laser source and an electronic circuit for modulating an output power level. A control unit incorporates a scanning path input module for generating a simulation of the angular velocity of the scanning mirror along the scanning path, thus enabling the estimation of the laser energy concentration along the scanning path. The electronic circuit modulates the energy concentration of the laser beam depending on the laser energy and the angular velocity on the scanning mirror. The aim is to achieve a stable, flicker-free image even at high speeds.

[0004] A laser projector with two laser light sources is known from US patent 2019 / 0310539 A1. The laser sources are arranged opposite each other and are combined by two reflectors.

[0005] A compact laser projector with two laser diodes has been disclosed in US patent 2019 / 0237939 A1. The two laser diodes are combined to nearly double the laser's light intensity. The two laser beams are focused via a reflector using two collimator lenses and a λ / 2 plate. The key advantage lies in the compact design of this powerful laser.

[0006] From DE 10 2013 208 819 A1, a laser projection device and a laser projection method for projecting laser beams onto a projection plane are known. This device includes a controllable multi-beam laser diode array whose laser beams are deflected by means of deflection devices. A control unit actuates the deflection devices such that the deflected laser beams move along a scanning line on the projection plane, with differently deflected laser beams appearing as separate beams on the same scanning line in the projection plane.

[0007] US2016 / 0087393 A1 discloses a laser unit in an optical communication network. To compensate for aging processes in the laser diodes, their LI curves are recorded.

[0008] US2016 / 0073071 A1 describes a head-up display in which a laser beam is projected onto a windshield via a mirror.

[0009] The invention is based on the objective of providing a device for laser projection that provides a desired intensity of the laser beam using simple means.

[0010] According to the invention, the problem is solved by a device having the features of claim 1. Advantageous embodiments are the subject of the dependent claims.

[0011] The device according to the invention is designed and intended for laser projection. It is therefore a laser projector or a laser projector system. According to the invention, two laser diodes with the same wavelength are provided. The beams of the laser diodes are each linearly polarized, with the polarization axes or directions being perpendicular to each other in pairs. Furthermore, a polarization combiner is provided, which combines the incident beams of the laser diodes into a combined beam with circular or elliptical polarization. This utilizes the fact that the different polarizations of the incident beams can be combined into a circular or elliptical polarization. According to the invention, a measuring arrangement is also provided, which measures the intensity of the combined laser beam. The measured value of the measuring arrangement is therefore a measure of the intensity of the combined laser beam.The measured value for the intensity of the combined laser beam is preferably provided as an input signal to a control unit. The control unit adjusts the intensity of at least one of the LEDs. This adjustment can be performed manually or dependent on the input signal. This means that the device according to the invention combines two laser beams, identical except for their polarization, into a single combined laser beam and adjusts its intensity via the control unit.

[0012] This creates a number of important application possibilities for the laser projector, which result from adjusting the intensity.

[0013] According to the invention, the control unit is configured in one operating mode to increase the power of the at least one adjustable laser diode when the intensity of the combined beam decreases. In this operating mode, it is ensured that if one of the two laser diodes experiences a decrease in power or fails completely, the intensity of the other laser diode is increased, thereby also increasing the intensity of the combined laser beam. This operating mode is particularly advantageous for industrial applications of the laser projector. For example, if one of the laser diodes fails, the projection can continue with the other laser diode without interrupting operation. This allows for continuous operation without interruption for laser diode replacement.

[0014] In a preferred further development, the intensity of the combined laser beam is regulated. Its intensity is controlled to a setpoint, which can, for example, be predefined as constant over time. Intensity control offers several advantages for the practical use of the projector. For instance, a setpoint can be specified that is a certain value below the maximum permissible value for safety reasons. In this configuration, the laser projector operates at constant power.

[0015] According to the invention, a second operating mode is provided which increases or decreases the power of the combined beam for parts and / or sections of a figure to be projected. The figure to be projected can be a continuous figure in which parts of the figure are optically highlighted or receded, for example, by increasing or decreasing the power of the combined laser beam. This can also be used, for example, to indicate assembly steps in which parts or sections of the figure are highlighted step by step and sequentially. Furthermore, contours or contour sections to be projected can be displayed differently in the second operating mode. This is advantageous, for example, if a first contour and then a second contour are to be displayed for a specific process.

[0016] Preferably, a maximum permissible laser power is specified for the laser projector, which is not exceeded by a control unit for the combined laser beam. Conventionally, a maximum permissible laser power can result, for example, solely from the design of the laser diode without further measures. Therefore, when using two laser diodes that are combined and can thus operate with different laser powers for the combined laser beam, it is advantageous to specify the maximum permissible laser power.

[0017] Pulse width modulation (PWM) can be used to control the laser diodes. The PWM then determines the output power of the laser diode. Alternatively, or in combination with PWM, continuous drive of the laser diode can be used.

[0018] It has proven advantageous to provide an adjustable focus device for each laser diode. The focus device is generally not used during operation of the laser projector, but is initially set to a specific distance from the projection surface.

[0019] To achieve a particularly simple and effective alignment of the laser diodes with respect to the polarization combiner, each laser diode is mounted on a carrier plate, which is attached to a common base. This allows the laser beams of the laser diodes to be aligned relative to each other via the separate carrier plates.

[0020] To improve the alignment of the support plates relative to each other, the first support plate is equipped with a slotted hole that allows it to be aligned with a second support plate. The second support plate is, for example, already mounted directly onto the base plate, and the first support plate is aligned relative to the second using the slotted hole and is also attached to the base plate, for example, with a screw.

[0021] In the projector according to the invention, the projection is achieved via two galvanometer mirrors that can direct the combined laser beam in any direction.

[0022] In a preferred embodiment, the combined laser beam is deflected via two galvanometer mirrors. The rotation axes of the mirrors preferably form a right angle. This results in an X / Y alignment of the laser beam, which makes it possible to project contours, markings, and the like onto surfaces accessible to the laser beam using the laser light.

[0023] The invention will be explained in more detail using an exemplary embodiment.

[0024] They show: Fig. 1 shows a perspective view of the operation of two laser diodes that are combined to form a superposition beam, and Fig. 2 shows the principle of beam combination with polarization.

[0025] Figure 1Figure 1 shows the setup of a laser projector 10 with two laser diodes 12 and 14. The laser beams from the laser diodes 12 and 14 each pass through a focusing optic 16 and 18, respectively. The focusing optic 16 and 18 are each adjusted to a specific distance from the projection surface. The laser beam 20 from the laser diode 12 strikes a mirror 22 and is deflected to the polarization combiner 24. The laser beam 28, which passes through the focusing unit 18, also strikes the polarization combiner 24 and contributes to the combined laser beam 26. The measuring arrangement 25 for the intensity of the combined laser beam is arranged at the level of the polarization combiner 24 and measures the "fall-off" light of beam 20, which is not deflected to the combined laser beam 26, and the deflected light of beam 28, which is deflected in the polarization combiner 24. The measuring arrangement can be a photodiode that is sensitive to the wavelength of the laser light.

[0026] Figure 2 This illustrates the basic operating principle of the polarization combiner. The incoming beam 20 is linearly polarized with a so-called S-polarization. The incoming beam 28 also has a linear polarization with a P-polarization. The S- and P-polarizations are perpendicular to each other. The combined light beam 26 has a superimposed polarization, which manifests as a circular or elliptical polarization.

[0027] The polarization combiner is preferably equipped with a measuring device that detects the intensity of the combined laser beam 26. The detected intensity is transmitted to a control unit. The control unit controls the laser diodes 12 and 14. Various operating modes can be distinguished: Both laser diodes 12 and 14 have the same wavelength and can replace each other. If the laser projector is operating with one of the laser diodes, for example, laser diode 14, the brightness of the first laser diode can be manually switched to the other laser diode 12 at the control unit when the brightness of the second laser diode decreases for the projected figure. In this configuration, the control unit performs the manual switching. In an automatic configuration, the control unit switches to the other laser diode automatically, depending on the input signal, as the intensity of the combined laser beam decreases.In this case, the user does not need to intervene and the laser projector continues to operate automatically.

[0028] The control unit can be equipped with a second operating mode. This second mode does not necessarily exclude the first. The second mode allows the brightness of the projection to be increased at specific points and in specific areas. This is achieved by increasing the intensity of the combined laser beam. A particular advantage of this is that it allows a user, for example, who is guided through their work by the projection, to highlight individual steps within the workflow. Other features, such as highlighting individual contours when projecting more than one outline, can also be used. This improves clarity when using the laser projector. Reference symbol list

[0029] 10 Laser projector 12 Laser diode 14 Laser diode 16 Focusing optics 18 Focusing optics 20 Laser beam 22 Mirror 24 Polarizing combiner 25 Measuring setup 26 Combined laser beam 28 Laser beam

Claims

1. Device for laser projection of outlines and markings on objects, wherein a laser beam is deflected through a mirror via one or more galvanometers, comprising the following: • two laser diodes (12, 14) with the same wavelength, whose beam is linearly polarized and whose polarization axes are perpendicular to each other, wherein each laser diode (12, 14) is mounted on a support plate, which is attached in each case to a common base support, • a polarization combiner (24), which combines the beams of the laser diodes (12, 14) into a combined beam (26) with circular or elliptical polarization, • a measuring arrangement (25), which measures an intensity of the combined laser beam (26) and • a control unit, to which the measured intensity of the combined laser beam (26) is applied as an input signal and which adjusts an intensity of at least one of the laser diodes (12, 14), • wherein the control unit in a first operating mode increases the power of the at least one adjustable laser diode (12, 14) at an attenuating intensity of the combined beam (26), and • a second operating mode is provided, which provides an elevated or reduced power of the combined beam (26) for the projection for parts and / or sections of a figure to be projected, wherein the second operating mode is configured to display contours or contour sections to be projected with differing brightness.

2. Device according to claim 1, characterized in that the control unit adjusts the intensity of at least one of the laser diodes (12, 14) depending on the applied input signal.

3. Device according to one of claims 1 to 2, characterized in that the control unit regulates the intensity of the combined beam (26) to a setpoint.

4. Device according to one of claims 1 to 3, characterized in that a maximum permissible laser power is predetermined, which is not exceeded by the control unit.

5. Device according to one of claims 1 to 4, characterized in that a controlling of the laser diodes (12, 14) occurs via a pulse width modulation.

6. Device according to one of claims 1 to 5, characterized in that a controlling of the laser diodes (12, 14) occurs via a continuous controlling.

7. Device according to one of claims 1 to 6, characterized in that an adjustable focusing apparatus (16, 18) is provided for each laser diode (12, 14),8. Device according to claim 1, characterized in that a first support plate is equipped with a slot that permits an alignment of the first support plate relative to a second support plate.

9. Device according to one of claims 1 to 8, characterized in that the combined laser beam (26) are redirected via two galvanometer mirrors.