DE102023200045A1 - Laser system calibration procedure, using an electronic paper as a calibration target and calibration target - Google Patents

Abstract

The invention is based on a laser system calibration method in which, in at least one calibration step (10), a laser signal (14) of a laser system (16) to be calibrated, reflected by a calibration target (12) is detected and evaluated. It is proposed that the calibration target (12) is formed at least partially by an electronic paper (20).

Description

State of the art

A laser system calibration method has already been proposed in which a laser signal reflected from a calibration target of a laser system to be calibrated is recorded and evaluated in at least one calibration step.

Known calibration targets based on masked diffuse light emitting surfaces or backlit LCD screens are less effective when used in conjunction with calibration of laser systems for distance measurement or in laser imaging systems where the imaging or distance measurement depends on the reflectivity of the object rather than its luminance. In addition, these systems usually use a coaxial optical configuration in which the optical paths for emission and detection overlap. In these cases, glass plate targets can be disadvantageous because their specular reflection does not return to the optical system. In the case of LCD screens, the absorption difference between bright and dark pixels can also be too small and also polarization dependent, which can also have adverse effects when used as a calibration target.

Disclosure of the invention

The invention is based on a laser system calibration method in which, in at least one calibration step, a laser signal of a laser system to be calibrated, which is returned by a calibration target, preferably reflected, is detected and evaluated.

It is proposed that the calibration target is at least partially formed by an electronic paper. This can provide advantageous properties for a calibration of laser imaging systems or laser distance measurement systems. Advantageously, charged particles with different absorption coefficients are used in the electronic paper to represent patterns on a flat surface. This can advantageously achieve a modulation of a degree of reflection of the calibration target, which is almost independent of the angle of incidence, wavelength and/or polarization of the laser light of the laser system to be calibrated. Advantageously, the electronic paper has a strong absorption contrast in a wide wavelength range, in particular at least substantially independent of the angle of incidence, wavelength and/or polarization of the laser light of the laser system to be calibrated. In particular, the calibration target is designed as an object that has or can represent a pattern, in particular a known calibration pattern, which is preferably used in a calibration process of a laser system. In particular, the laser system comprises a (laser system) control and/or regulating unit or is communicatively connected to at least one control and/or regulating unit, which is at least set up to evaluate the detected reflected laser signal. The term “intended” or “set up” should be understood in particular to mean specially programmed, designed and/or equipped. The fact that an object is intended for a specific function should be understood in particular to mean that the object fulfills and/or carries out this specific function in at least one application and/or operating state. A “control and/or regulating unit” should be understood in particular to mean a unit with at least one control electronics unit. A “control electronics unit” should be understood in particular to mean a unit with a processor and with a memory as well as with an operating program stored in the memory.

An “electronic paper” (also called e-paper, e-paper, ePaper, electronic ink, e-ink, reflective display or electrophoretic display) is to be understood in particular as a display technology by means of which the appearance of ink or color on a paper is to be reproduced as faithfully as possible. Preferably, an electronic paper reflects an incident light signal at least essentially like a normal paper. In particular, the electronic paper forms a passive display. In particular, the electronic paper forms a non-luminous display. It is conceivable that a display of the electronic paper is shown permanently without a maintenance voltage being required. However, this display can be changed at any time. The electronic paper can be flexible or rigid. Preferably, the electronic paper is designed as an electrophoretic display. However, alternative implementations of the electronic paper are also conceivable. In particular, a partial area of the calibration target used for carrying out the laser system calibration method is formed by the electronic paper, in particular the electrophoretic display.

If the laser system to be calibrated is designed as a laser imaging system, an efficient and/or precise calibration of the laser imaging system can advantageously be achieved. In particular, the laser imaging system is designed as a virtual current retinal display (retinal scan display) of data glasses. In particular, the laser imaging system is designed as an eye tracking system of data glasses, which is preferably based at least partially on an evaluation of back reflection signals of an eye to be monitored. For example, the laser imaging system designed as an eye tracking system of the data glasses can be based on signals from one or more laser feedback interferometry sensors.

If the laser imaging system is designed as a virtual retinal display of data glasses, an efficient and/or precise calibration of the virtual retinal display, in particular the output of the data glasses, can advantageously be achieved. User comfort of the data glasses can advantageously be significantly increased. The virtual retinal display is in particular designed to scan an image content sequentially by deflecting at least one visible laser beam of at least one time-modulated light source, such as one or more (RGB) laser diodes of a laser projector, and to project it directly onto the retina of the user's eye using optical elements. The image source is in particular designed as an electronic image source, for example as a graphics output, in particular an (integrated) graphics card, of a computer or processor or the like. The (RGB) images to be displayed are in particular designed as color image data, e.g. RGB image data. In particular, the (RGB) images to be displayed can be designed as still or moving images, e.g. videos. In particular, the laser projector is designed to generate the (RGB) images to be displayed and to output them via a visible (RGB) laser beam.

If the virtual retinal display also has an integrated sensor, in particular the laser feedback interferometry sensor, with which the reflected laser signal is detected, a particularly simple and quick calibration of virtual retinal displays and/or data glasses can advantageously be enabled. The integrated sensor is in particular part of a ViP system (VCSEL with integrated photodiode).

It is also proposed that during the calibration step a display of the electronic paper is changed at least once, preferably several times, in particular by changing a representation and/or a resolution of the representation of the electronic paper. This can advantageously improve, accelerate and/or simplify a calibration process. This can advantageously enable an iterative calibration method based on the interaction with different displays and/or different resolutions of the electronic paper.

If a pattern displayed by the electronic paper and/or a resolution of the display of the electronic paper is changed at least once, preferably several times, during the calibration step, a calibration process can advantageously be improved, accelerated and/or simplified.

It is further proposed that the display of the electronic paper be inverted at least once during the calibration step. This can advantageously improve the immunity of the calibration method to external light, to ambient light, to parasitic and/or specular reflections, to so-called “fixed pattern noise” and/or to so-called “fixed pattern offset”. In particular, when the display of the electronic paper is inverted, all pixels of one color are switched to pixels of the complementary color associated with the color. In particular, when the display of the electronic paper is inverted, all black pixels of the display of the electronic paper are switched to white pixels of the display of the electronic paper and vice versa.

It is further proposed that in at least one further calibration step the recorded reflected laser signals from inverted but otherwise identical displays of the electronic paper are subtracted from one another. This advantageously makes it possible to achieve a particularly low signal-to-noise ratio. This advantageously makes it possible to "stacking" several frames, in particular sensor frames, without integrating the individual noise of the frames. This advantageously makes it possible to calibrate and/or characterize laser systems, in particular laser imaging systems, particularly precisely. In particular, the respective signals that the laser system receives from the two inverted displays can each be formed from many stacked frames.

In particular, to reduce speckle noise, it can be advantageous to adjust the distance to the calibration target by a length λ/2. Here, λ corresponds to a wavelength of the laser signal of the laser system used. This method is also referred to as interferometric modulation. In this case, a small actuator can be located in the display, in particular the calibration target, which preferably moves through at least 3 positions. In the known interferometric modulation, different colors can be scanned. In the present application, however, the distance to the calibration target is preferably adjusted so that slightly modified so that the (unwanted) speckle noise can be removed by simple averaging.

If the electronic paper has a resolution of at least 250 ppi, preferably at least 300 ppi, a particularly precise and particularly good calibration and/or characterization of laser systems, in particular laser imaging systems, can advantageously be enabled. The use of particularly complex test patterns/calibration patterns can advantageously be enabled.

Furthermore, the use of an electronic paper as a calibration target in the laser system calibration method, as well as the calibration target with the electronic paper, is proposed. This can provide advantageous properties for a calibration of laser imaging systems or laser distance measuring systems.

The laser system calibration method according to the invention, the use of the electronic paper according to the invention and the calibration target according to the invention should not be limited to the application and embodiment described above. In particular, the laser system calibration method according to the invention, the use of the electronic paper according to the invention and the calibration target according to the invention can have a number of individual elements, components and units as well as method steps that differs from the number stated herein in order to fulfill a function described herein. In addition, in the value ranges specified in this disclosure, values within the stated limits should also be considered disclosed and can be used as desired.

drawing

Further advantages emerge from the following description of the drawing. The drawing shows an embodiment of the invention. The drawing, the description and the claims contain numerous features in combination. The person skilled in the art will also expediently consider the features individually and combine them into further useful combinations.

• 1 schematisch eine Kalibrationsvorrichtung für Lasersysteme,
• 2 schematisch eine Datenbrille mit einem Lasersystem,
• 3 schematisch einen vergrößerten Ausschnitt eines Kalibrationstargets zur Verwendung in der Kalibrationsvorrichtung und/oder in einem Lasersystem-Kalibrationsverfahren,
• 4a ein gestacktes Bild eines von einer Anzeige des Kalibrationstargets zurückgeworfenen Lasersignals des zu kalibrierenden Lasersystems,
• 4b ein gestacktes Bild eines von einer invertierten aber ansonsten zu der Anzeige der 4a identischen Anzeige des Kalibrationstargets zurückgeworfenen Lasersignals des zu kalibrierenden Lasersystems,
• 4c eine Subtraktion der Bilder der 4a und 4b und
• 5 ein schematisches Ablaufdiagramm des Lasersystem-Kalibrationsverfahrens.

Show it:

• 1 schematically a calibration device for laser systems,
• 2 schematic of a data glasses with a laser system,
• 3 schematically an enlarged section of a calibration target for use in the calibration device and/or in a laser system calibration method,
• 4a a stacked image of a laser signal of the laser system to be calibrated reflected from a display of the calibration target,
• 4b a stacked image of an inverted but otherwise to the display of the 4a identical display of the laser signal reflected from the calibration target of the laser system to be calibrated,
• 4c a subtraction of the images of the 4a and 4b and
• 5 a schematic flow diagram of the laser system calibration procedure.

Description of the embodiment

The 1 shows schematically a calibration device 36 for laser systems 16. The calibration device 36 is intended for carrying out a laser system calibration method. The calibration device 36 comprises a first holding device 34. The first holding device 34 is intended for fixing a calibration target 12. The calibration device 36 comprises a second holding device 38. The second holding device 38 is intended for fixing the laser system 16. The holding devices 34, 38 are intended to align the laser system 16 and the calibration target 12 with one another. The laser system 16 is aligned such that it emits laser beams 40 onto the calibration target 12. The laser system 16 is aligned such that it can detect a laser signal 14 reflected by the calibration target 12.

The calibration device 36 is intended for use in calibrating the laser system 16. The laser system 16 to be calibrated is designed as a laser imaging system. The laser imaging system can be designed, for example, as a virtual retinal display 22 of data glasses 18 (see. 2 ). In this case, the virtual retinal display 22 can have an integrated sensor 26. The integrated sensor 26 can be designed as a laser feedback interferometry sensor. The integrated sensor 26 is provided to detect the reflected laser signal 14. The laser system 16 comprises a control and/or regulating unit 42. The control and/or regulating unit 42 is provided to evaluate the detected reflected laser signals 14 and/or the sensor data of the integrated sensor 26.

The 3 shows an example of an enlarged section of the calibration target 12. The calibration target 12 is intended for use in the laser system calibration method. The calibration target 12 comprises an electronic paper 20. The calibration target 12 is at least partially formed by the electronic paper 20. The electronic paper 20 has a resolution of at least 250 ppi. The electronic paper 20 is intended for use as a calibration target 12 in the laser system calibration method. The electronic paper 20 is intended for displaying at least one pattern 32 forming a calibration pattern. In the 3 the pattern 32 is formed by evenly spaced straight strips 44, 44'. For example, the strips 44, 44' are each spaced approximately 3 mm apart from one another (see the additionally drawn scale 46). Other calibration patterns, in particular those with a different shape, are of course conceivable. The calibration target 12 has a display 28 whose output can be changed. The display 12 can have one or more small actuators (not shown). An interferometric modulation method for reducing speckle noise of the reflected laser signals 14 can be carried out using the actuator(s).

The 4a to 4c show exemplary representations of the reflected laser signals 14 detected by the integrated sensor 26. The 4a and 4b each show a representation of 600 stacked recording frames from displays 28, 28' of the calibration target 12. The 4a and 4b show the stacked recording frames of two inverted images. The 4c shows the result of subtracting the image from 4b from the image of 4a A significantly increased contrast and significantly minimized noise is noticeable.

The 5 shows a schematic flow diagram of the laser system calibration method. In at least one method step 48, the calibration target 12 and the laser system 16 are clamped into the calibration device 36. In at least one calibration step 50, a laser beam 40 is emitted by the laser system 16 in the direction of the calibration target 12. In at least one further calibration step 10, the laser beam 40 is at least partially reflected by the calibration target 12. The calibration target 12 is formed by the electronic paper 20. In the calibration step 10, the laser signal 14 of the laser system 16 to be calibrated, which is reflected by a calibration target 12, is detected. In the calibration step 10, the detected reflected laser signal 14 is evaluated by means of the control and/or regulating unit 42. During the calibration step 10, a display 28 of the electronic paper 20 is changed at least once. In doing so, a pattern 32 displayed by the electronic paper 20 is changed at least once. Alternatively or additionally, the resolution of the display 28 of the electronic paper 20 can be changed at least once during the calibration step 10. When the displayed pattern 32 is changed, the display 28 of the electronic paper 20 is inverted at least once during the calibration step 10 (see. 4a and 4b) . In at least one further calibration step 30, the detected reflected laser signals 14 of the inverted but otherwise identical displays 28, 28' of the electronic paper 20 are subtracted from one another (cf. 4c ). In at least one further calibration step 24, parameters of the laser system 16 are adapted and/or set based on the calibration data determined using the calibration target 12, in particular by means of one or more of the previously described calibration steps 10, 30, 50.

Claims (12)

Laser system calibration method in which, in at least one calibration step (10), a laser signal (14) of a laser system (16) to be calibrated, reflected by a calibration target (12) is detected and evaluated, characterized in that the calibration target (12) is at least partially formed by an electronic paper (20). Laser system calibration procedure according to Claim 1 , characterized in that the laser system (16) to be calibrated is designed as a laser imaging system. Laser system calibration procedure according to Claim 2 , characterized in that the laser imaging system is designed as a virtual retinal display (22) of data glasses (18). Laser system calibration procedure according to Claim 3 , characterized in that the virtual retinal display (22) has an integrated sensor (26), in particular a laser feedback interferometry sensor, with which the reflected laser signal (14) is detected. Laser system calibration method according to one of the preceding claims, characterized in that during the calibration step (10) a display (28) of the electronic paper (20) is changed at least once, preferably several times. Laser system calibration procedure according to Claim 5 , characterized in that during during the calibration step (10) a pattern (32) displayed by the electronic paper (20) is changed at least once, preferably several times. Laser system calibration procedure according to Claim 5 or 6 , characterized in that during the calibration step (10) the resolution of the display (28) of the electronic paper (20) is changed at least once, preferably several times. Laser system calibration procedure according to one of the Claims 5 until 7 , characterized in that during the calibration step (10) the display (28) of the electronic paper (20) is inverted at least once. Laser system calibration procedure according to Claim 8 , characterized in that in at least one further calibration step (30) the detected reflected laser signals (14) from inverted but otherwise identical displays (28, 28`) of the electronic paper (20) are subtracted from one another. Laser system calibration method according to one of the preceding claims, characterized in that the electronic paper (20) has a resolution of at least 250 ppi, preferably of at least 300 ppi. Use of an electronic paper (20) as a calibration target (12) in a laser system calibration method, in particular according to one of the Claims 1 until 10 in which, in at least one calibration step (10), a laser signal (14) of a laser system (16) to be calibrated, reflected by the calibration target (12) is detected and evaluated. Calibration target (12), in particular for carrying out a laser system calibration method according to one of the Claims 1 until 10 , characterized by an electronic paper (20).

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