Imaging light measurement device

Abstract

The invention relates to an imaging light measuring device, comprising an image sensor (117), an optical spectrometer (120) and a data processing unit (118), wherein the image sensor (117) and the spectrometer (120) are configured to receive light emitted by a measuring object (110), and the data processing unit (118) is connected to the image sensor (117) and the spectrometer (120) and processes measurement signals output by the image sensor (117) and the spectrometer (120). The object of the invention is to provide a light measuring device which allows precise time control of a measuring process in a simple and cost-effective manner. To this end, the invention proposes that the image sensor (117) and the spectrometer (120) each have a trigger input (122, 123), wherein a trigger signal applied to the trigger input (122, 123) starts the measuring process.

Description

Technical Field

[0001] The present invention relates to an imaging light measuring device, which includes an image sensor and an optical spectrometer, and a data processing unit, wherein the image sensor and the spectrometer receive light emitted by a measurement object, and the data processing unit is connected to the image sensor and the spectrometer and processes measurement signals output by the image sensor and the spectrometer. Background Art

[0002] Devices of this type are known in the prior art. For example, EP 3054273 A1 describes a colorimetric system for measuring and checking matrix display devices (also called matrix displays, such as color matrix displays of smartphones, tablet computers, laptops, monitors, televisions, etc.) in quality assurance.

[0003] A key component of a known display testing environment is a light measuring device in the form of an imaging colorimeter, which makes it possible to accurately measure the visual performance of a single display, which corresponds to the human perception of brightness, color and spatial relationships. Powerful imaging light measuring equipment is able to accurately measure, for example, the color (i.e., the color coordinates in a suitable color space), the brightness (brightness) of a single pixel of a display and the overall uniformity of the display.

[0004] In a typical production process, the visual performance of each display is tested by an automated inspection system that includes this type of imaging light measurement device. This has several advantages. Quantitative evaluation of display errors is possible, as well as increased testing speed and especially simultaneous evaluation of the overall display quality, i.e. uniformity and color accuracy.

[0005] In known imaging colorimetric systems, a digital RGB camera is provided as an image sensor, which receives light emitted by the pixels of the display. In this way, the color distribution and the brightness distribution are measured in a simple manner with spatial resolution, i.e. in an imaging manner. In addition, the known colorimetric system includes an optical spectrometer, which receives light from a predetermined area ("spot") on the display without spatial resolution, i.e. in a non-imaging manner. A beam splitter is positioned between the measurement object and the image sensor or spectrometer, which separates the light from the measurement object for detection by means of the image sensor and the spectrometer. The known colorimetric system includes a data processing unit, which is data-connected to the image sensor and the spectrometer, which controls the measurement process and processes the measurement signals output by the image sensor and the spectrometer. In this case, the RGB measurement signal from the image sensor is converted into suitable colorimetric variables, radiometric variables and photometric variables (e.g., into X, Y, Z color coordinates), and the obtained variables detected in an imaging manner are corrected based on the accurate measurement signal from the spectrometer, so that a very fast and cost-effective imaging detection of the colorimetric variables and photometric variables required for evaluating the display quality is possible.

[0006] In modern automated inspection systems, the residence time of a single measurement object in the measuring device is intended to be minimal in order to maximize throughput.

[0007] Modern matrix displays based on arrays of micro-LEDs are almost ready for the market. When measuring LEDs, the problem arises that the LEDs heat up during operation. Temperature changes lead to changes in the spectrum of the emitted light. In this case, the aim is to switch on each LED in a single LED only for very short time intervals of a few milliseconds when testing a measurement object containing LEDs.

[0008] To make this possible, it is necessary to be able to precisely control the temporal sequence of the individual measurements.

[0009] In known light measurement devices, the software of the data processing unit controls the entire measurement process. In this process, the command execution time is uncertain and varies between measurements, so that there may be measurement uncertainties in the range of 100ms or more. Therefore, it is necessary to operate with a measurement duration (only a few milliseconds) that exceeds the duration of the actual measurement process of the image sensor or spectrometer. This can only ensure that the measurement actually occurs within the available time window. This is exacerbated by the fact that the measurements of the image sensor and the spectrometer cannot be run accurately at the same time due to software control. Due to the different and varying command execution times, it is not possible to know exactly what time lag the measurement actually occurs. Here, the uncertainty also reaches 100ms. This leads to the following problem: when measuring LED-based measurement objects, as mentioned before, the spectral run-in behavior must be expected after the LED is turned on, so that, for example, the image sensor still measures the cold LED, while the spectrometer (a few milliseconds later) measures the red-shifted spectrum of the same LED. Then, the data from the image sensor and the spectrometer do not match. Summary of the invention

[0010] Against this background, the problem addressed by the present invention is to provide a light measuring device which allows a precise temporal control of the measuring process in a simple and cost-effective manner.

[0011] The invention solves this problem starting from a light measuring device of the type mentioned at the outset, wherein the image sensor and the spectrometer each have a trigger input, wherein a trigger signal applied to the trigger input starts the measuring process.

[0012] For the sake of clarity it should be noted that the measurement object is not part of the light measuring device according to the invention.

[0013] According to the invention, with regard to the start of the measuring process, the image sensor and the spectrometer are therefore not controlled by the software of the data processing unit as before, but by an external trigger signal. In this context, "external" means that the trigger signal comes from outside the optical measuring device, i.e., in particular from outside the data processing unit, i.e., the data processing unit is not involved in the start of the measurement. The trigger input is directly connected to the hardware, i.e., to the electronics of the image sensor or the spectrometer. The trigger signal can be transmitted as a voltage signal with digital logic levels via a simple electrical signal line. This leads to an instantaneous start of the conceivable measuring process, which is limited only by the electrical or electronic signal propagation time of the trigger signal. It is also conceivable to provide the trigger signal via a suitable data bus separated from the data processing unit.

[0014] The present invention makes it possible to start measurement by an image sensor and a spectrometer virtually simultaneously or at least almost simultaneously by means of a trigger signal. As a result, on the one hand, it is possible to ensure that the measurement is started accurately at the desired time point, wherein, in particular, the actual simultaneous measurement performed by the image sensor and the spectrometer is ensured. Therefore, problems caused by time delays of the measurement object based on LEDs are prevented. On the other hand, the measurement duration of the activation duration of the measurement object can be adjusted, and the measurement object is typically a matrix display or an LED array as described above. It is thus possible to shorten the measurement window and therefore shorten the dwell time of the measurement object. The measurement object can be replaced immediately after the (known) measurement duration of the image sensor and the spectrometer ends. This significantly increases the throughput.

[0015] In addition, the trigger signal can control the integration time of the image sensor and / or the spectrometer in various cases. For example, as long as the trigger signal has a "high" logic level, the image sensor and / or the spectrometer can perform a measurement. Therefore, an integration for reducing signal noise can be achieved. In addition, in this way, the measurement of the image sensor can continue, for example, when the light source (e.g., a separate LED group) of the measurement object is activated in sequence. Then, the image of the measurement object generated by the image sensor simultaneously shows all LED groups in an activated state. In parallel with the sequential activation of the LED groups, multiple individual measurements of the spectrometer can be started by means of corresponding synchronized sequential trigger signals. Then, a separate correction of the measurement signal of the image sensor can be obtained from the measurement signal of the spectrometer of each LED group. In this way, the entire measurement process can be performed within a minimum measurement cycle.

[0016] In a preferred configuration, the image sensor and / or the spectrometer each comprises at least one signal output and is configured to output a signal related to the operating state of the signal via the signal output. The signal output constitutes an external feedback channel corresponding to the trigger input. In this context, "external" again means that the signal output is separate from the data processing unit and is directly connected to the electronics of the image sensor or spectrometer.

[0017] For example, the image sensor and / or the spectrometer can each be configured to output a signal via a signal output after receiving a trigger signal. In this case, the signal output is used to transmit a signal to confirm the receipt of the trigger signal, for example, at an external controller of the light measuring device integrated by automation technology. As a result, it can be recognized from the outside that a measurement process has actually been started.

[0018] In addition, the image sensor and / or the spectrometer can each be configured to output a signal via a signal output unit during the ongoing measurement process. Therefore, the external controller can recognize that the measurement is in progress. Particularly advantageously, the image sensor and / or the spectrometer are each configured to output a signal via a signal output unit after the measurement process is completed, and in this case, preferably before the measured signal is output to the data processing unit, but at least before the processing of the measured signal by the data processing unit is completed, the signal is output via the signal output unit. Once the measurement of the image sensor and the spectrometer is completed or once the entire measurement program is completed, the measurement object can be changed, in particular, there is no need to wait for a period of time until the data processing unit has completed the transmission, storage and evaluation of the measurement signal from the image sensor and the spectrometer. Therefore, the dwell time can be minimized without the risk of defective or incomplete measurement caused by, for example, premature changes in the measurement object. The processing duration of the measured signal by means of the data processing unit can be used to change the measurement object so that there is no unproductive waiting time.

[0019] Another option is that the image sensor and / or the spectrometer are each configured to output a signal via the signal output when ready for measurement. Thus, the external controller can recognize when a new measurement process can be started. This also helps to minimize the residence time of the measurement object at the light measurement device. As soon as the hardware is ready, the measurement can be started without taking into account safety margins due to uncertain and varying signal propagation times of the data processing unit.

[0020] In one possible configuration, in the image sensor and / or the spectrometer, a separate signal output is provided for each of at least two of the above signals (trigger confirmation, measurement in progress, measurement completed, ready to measure). In this way, each feedback signal can be transmitted as a simple electrical signal. Transmission via a data bus (separate from the data processing unit) is also conceivable.

[0021] In another preferred configuration of the light measuring device according to the invention, a control unit can be provided which is separate from the data processing unit and is connected to the trigger inputs of the image sensor and the spectrometer. The external control unit serves as an interface, so to speak, for actuating the light measuring device in an automated system, for example, in the industrial mass production of matrix displays. In the process, the device is actuated completely on an electrical / electronic level, i.e. without involving a data processing unit.

[0022] The control unit is also conveniently connected to the signal outputs of the image sensor and the spectrometer, wherein the control unit is configured to actuate the image sensor and the spectrometer via a trigger input and, in particular, based on a signal outputted via the signal outputs of the image sensor and the spectrometer. For example, by logically linking, starting a synchronized measurement by means of the image sensor and the spectrometer may depend on both the image sensor and the spectrometer indicating via their corresponding signal outputs that they are ready to measure. In the same way, the control unit may logically interconnect the signal outputs via which the completion of the measurement by both the image sensor and the spectrometer is indicated, so that once both modalities (i.e., the image sensor and the spectrometer) have completed their measurements, a change of the measurement object is triggered by an external automation technique.

[0023] In another preferred configuration, the control unit can be configured to actuate at least one peripheral element of the light measuring device, wherein the peripheral element is selected from:

[0024] - a beam deflecting device for deflecting light generated by the measurement object onto an image sensor or a spectrometer,

[0025] - an optical filter wheel arranged upstream of the image sensor or the spectrometer,

[0026] - a polarizer arranged upstream of the image sensor or the spectrometer, or

[0027] - a positioning device for positioning the measurement object relative to the image sensor and the spectrometer. The control unit can conveniently be used to control optional peripherals of the light measuring device. Instead of a beam splitter (as in the prior art), a beam deflection device (e.g. a mirror that can be moved into the light path by an actuator) can be provided in order to deflect light from the measurement object onto the image sensor or the spectrometer. The control unit then controls the measurement sequence so that a measurement with the aid of the image sensor and a measurement with the aid of the spectrometer are performed in sequence, wherein the beam deflection device is actuated between the two measurements. An optical filter wheel can be provided, for example, in an imaging filter wheel colorimeter as an image sensor. This can also actuate the control unit in order to start sequential measurements in sequence by corresponding filtering. A so-called pixel shift can also be achieved by a beam deflection device (e.g. in the form of a glass plate that can be rotated in the light path), in particular to prevent moiré patterns during measurements with the aid of the image sensor. Other examples of peripheral elements are polarization filters in the optical path, or positioning devices (e.g., one-axis, two-axis, or three-axis positioning systems) in order to accurately orient the measurement object relative to the image sensor and / or spectrometer. When measuring matrix displays, accurate positioning is important to ensure the correct orientation of the image of the display matrix on the sensor matrix of the image sensor.

[0028] Furthermore, the control unit can conveniently be used to actuate a change device for automatically changing the measurement object. In this way, the control unit is also integrated into the automation environment of the light measuring device according to the invention. The control unit can advantageously directly coordinate and synchronize the change of the measurement object with the measurement being performed. In this way, the dwell time of the measurement object is minimized. In this case, the control unit also conveniently actuates an electric light source accommodated in the measurement object, such as an LED array on a wafer or the like as part of a display. In this way, the activation of the light-emitting element of the measurement object can be optimally synchronized with the measurement process.

[0029] The data processing unit is preferably configured to convert the measurement signals output by the image sensor and the spectrometer into radiometric variables and / or photometric variables (e.g. radiation power, radiation intensity, radiation flux density, radiation or color coordinates), preferably in an imaging manner, i.e. by assigning values ​​of the radiometric variables and / or photometric variables to individual positions detected by the image sensor on the measurement object. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Embodiments of the present invention will be explained in more detail below with reference to the accompanying drawings, in which:

[0031] Figure 1 is a schematic diagram of a light measuring device according to the invention in the form of a block diagram, which is integrated in a production line for matrix displays. DETAILED DESCRIPTION

[0032] exist Figure 1 In the embodiment, the measurement object (e.g., a micro LED matrix display) to be inspected for chromaticity, brightness, and uniformity is denoted by reference numeral 110. Light 111 emitted by the measurement object 110 is directed onto an imaging colorimetric device 112. The light 111 passes through an assembly 113 of optical elements (lens / screen) and a beam splitter 114. The beam splitter 114 splits the light 111 into a first partial beam 115 and a second partial beam 116.

[0033] An RGB camera 117 in the form of an image sensor receives the first partial beam 115, so that a two-dimensional image of the measurement object 110 is generated in an image plane on a sensor arrangement (e.g. a CCD sensor) of the RGB camera 117. The resulting (digital) camera image forms a two-dimensional matrix of RGB color values, which assigns a group of RGB color values ​​to each position on the measurement object 110.

[0034] The matrix of RGB color values ​​is transmitted as digital measurement signals to a data processing unit 118 which comprises a processor 119 which converts the RGB color values ​​into XYZ color coordinates such that a set of XYZ color coordinates is assigned to each position on the measurement object 110 .

[0035] The second partial beam 116 is directed onto an optical spectrometer 120. Within the meaning of the present invention, a spectrometer is understood in the most general sense as a device for detecting a spectrum (i.e. the wavelength dependence of the light intensity). This definition covers spectrally high-resolution spectrometers, for example of the Czerny-Turner design with dispersive spectral splitting and a CCD sensor, but also simple, compact and cost-effective optoelectronic three-filter colorimeters of the known type, in which the spectral resolution is low and corresponds to the filter characteristics of the X, Y, Z filters used (even sometimes with spectral overlap). The spectrometer 120 likewise generates XYZ color coordinates, but not in the form of an image like the image sensor 117, but instead without spatial resolution. The second partial beam 116 is emitted from a series of positions within an area (“spot”) on the measurement object 110. During the measurement performed by the spectrometer 120, the surface area of ​​the spot is averaged.

[0036] The XYZ color coordinates of the spectrometer 120 are likewise transmitted in the form of digital measurement signals to the data processing unit 118. If this is a high-resolution spectrometer 120, it can instead transmit the measured optical spectrum (light intensity as a function of wavelength) directly to the data processing unit 118. Said unit then integrates across the spectrum according to the CIE standard system by weighting with the tristimulus curve stored in the data processing unit 118 to calculate the XYZ color coordinates. The processor 119 derives correction values ​​by comparing the XYZ color coordinates determined by the spectrometer 120 with a subset of the XYZ color coordinates determined from the RGB values ​​from the image sensor 117, wherein the color coordinates are assigned to positions within the light spot from which the second partial beam 116 is emitted. The processor 119 then applies the correction values ​​to the entire set of XYZ color coordinates generated from the RGB values, so as to thereby obtain a complete and accurate image of the XYZ coordinates of the light emitted by the measurement object.

[0037] The results of these calculations are finally output via the display device 121 in order to evaluate the color uniformity and various types of artifacts (line defects, pixel defects, black mura, yellow mura, etc.). Such artifacts can also be detected in an automatic manner by corresponding image processing software of the processor 119. If the measured object under consideration does not meet the applicable quality standards, a signal can be output via the display device 121.

[0038] According to the invention, the RGB camera 117 and the spectrometer 120 each comprise a trigger input, indicated by arrows 122, 123, respectively. An electrical trigger signal (e.g., a low / high edge of a logic signal) applied to the trigger input 122, 123 starts the measurement process in each case. The trigger input 122, 123 is directly connected to the hardware, i.e., to the electronics of the RGB camera 117 or the spectrometer 120.

[0039] According to the invention, the RGB camera 117 and the spectrometer 120 each comprise two signal outputs indicated by arrows 124, 125 and 126, 127, respectively. The RGB camera 117 and the spectrometer 120 output via the signal outputs 124, 126, respectively, a signal indicating that the associated measurement process has been completed. A signal indicating that the RGB camera 117 or the spectrometer 120 is ready and starts the next measurement is output via the signal outputs 125, 127, respectively (once the measured signal after the previous measurement process has been completely transmitted to the data processing unit 118).

[0040] The control unit 128 is connected to the trigger inputs 122, 123 and the signal outputs 124 to 127. The control unit 128 comprises two subunits 129, 130, wherein the subunit 129 is assigned to the light measuring device itself and the subunit 130 is assigned to the external automation technology. The subunit 129 serves as an interface for actuating the light measuring device in a superordinate automation system, for example, in the industrial mass production of matrix displays. For its part, the subunit 129 receives an input signal 131 from the subunit 130, by means of which the RGB camera 117 and the spectrometer 120 are started for synchronized measurement. In response to the input signal 131, the subunit 129 simultaneously outputs a trigger signal to the trigger inputs 122, 123. The subunit 129 performs a logical linking of the signal outputs 124 to 127, so that a first output signal 132 is generated when both the RGB camera 117 and the spectrometer 120 indicate that the relevant measurement process is completed. When both the RGB camera 117 and the spectrometer 120 indicate that they are ready for the next measurement process, a second output signal 133 is generated.

[0041] The subunit 130 is configured to start a change device 134 that changes the measurement object 110 in response to the first output signal 132 (i.e., each time the last measurement is completed). To this end, the current measurement object 110 is removed and returned to the schematically indicated production line 135. In each case, the next measurement object 110 is removed from the production line 135 and positioned on the test assembly towards the colorimetric device 112. In addition, the subunit 130 is configured to output an input signal 131 to the subunit 129 once the measurement object 110 has been changed and in response to the second output signal 133 (i.e., when the RGB camera 117 and the spectrometer 120 are ready for measurement), so that the next measurement process is started via the trigger inputs 122, 123 of the RGB camera 117 and the spectrometer, respectively. At the same time, the subunit 130 activates the light output from the measurement object 110 within the desired measurement cycle.

[0042] The control unit 128 can be implemented by simple logic elements (or FPGA). The signal propagation time is defined accordingly. The cost is very low.

[0043] The control unit 128 is combined with the trigger inputs 122, 123 and the signal outputs 124 to 127, so that an automated measurement sequence can be realized without the data processing unit 118 being involved in the control. The residence time of the measurement object 110 at the test assembly can thus be minimized without the risk of errors due to fluctuating command execution times in the software of the data processing unit 118. In addition, the precise time synchronization of the measurements is ensured by means of the RGB camera 117 and the spectrometer 120.

Claims

1. An imaging light measuring device, comprising an image sensor (117), an optical spectrometer (120), and a data processing unit (118), wherein: The image sensor (117) and the spectrometer (120) are configured to receive light emitted by the measurement object (110), the data processing unit (118) is connected to the image sensor (117) and the spectrometer (120), and processes measurement signals output by the image sensor (117) and the spectrometer (120), The image sensor (117) and the spectrometer (120) each have a trigger input (122, 123), wherein a trigger signal applied to the trigger input (122, 123) starts a measurement process; The image sensor (117) and / or the spectrometer (120) each comprises at least one signal output unit (124 to 127) and is configured to output a signal related to a relevant operating state of the signal via the signal output unit (124 to 127), Thereby, a control unit (128) is separated from the data processing unit (118) and is connected to the trigger inputs (122, 123) of the image sensor (117) and the spectrometer (120), whereby the control unit (128) is connected to the signal outputs (124 to 127) of the image sensor (117) and the spectrometer (120), and wherein the control unit (128) is configured to control the image sensor (117) and the spectrometer (120) via the trigger inputs (122, 123) and, in practice, to control the image sensor (117) and the spectrometer (120) based on the signals output via the signal outputs (124 to 127) of the image sensor (117) and the spectrometer (120).

2. The optical measuring device according to claim 1, characterized in that The image sensor (117) and / or the spectrometer (120) are each configured to output a signal via the signal output section (124 to 127) after receiving the trigger signal.

3. The optical measuring device according to claim 1 or 2, characterized in that The image sensor (117) and / or the spectrometer (120) are each configured to output a signal via the signal outputs (124 to 127) during an ongoing measurement process.

4. The optical measuring device according to claim 1 or 2, characterized in that The image sensor (117) and / or the spectrometer (120) are each configured to output a signal via the signal output section (124 to 127) after the measurement process is completed, and to output a signal via the signal output section (124 to 127) before the measured signal is transmitted to the data processing unit (118).

5. The optical measuring device according to claim 1 or 2, characterized in that: The image sensor (117) and / or the spectrometer (120) are each configured to output a signal via the signal output section (124 to 127) when ready to perform a measurement.

6. The optical measuring device according to claim 1 or 2, characterized in that: The trigger signal controls in each case an integration time of the image sensor (117) and / or of the spectrometer (120).

7. The optical measuring device according to claim 1, characterized in that The control unit (128) is configured to actuate at least one peripheral element in the light measuring device, wherein the peripheral element is selected from: a beam deflecting device for deflecting light emitted by the measurement object (110) onto the image sensor (117) or the spectrometer (120), - an optical filter wheel arranged upstream of the image sensor (117) or the spectrometer (120), a polarizer arranged upstream of the image sensor (117) or the spectrometer (120), or - positioning means for positioning the measurement object (110) relative to the image sensor (117) and the spectrometer (120).

8. The optical measuring device according to claim 7, characterized in that The control unit (128) actuates a changing device (134) for automatically changing the measurement object (110).

9. The optical measuring device according to claim 7, characterized in that The control unit (128) actuates an electric light source accommodated in the measurement object (110).

10. The optical measuring device according to claim 9, characterized in that The measurement object (110) is a matrix display device.

11. The optical measuring device according to claim 1 or 2, characterized in that: The data processing unit (118) is configured to convert the measurement signals output by the image sensor (117) and the spectrometer (120) into radiometric variables and / or photometric variables.

12. The optical measuring device according to claim 11, characterized in that The data processing unit (118) is configured to convert the measurement signals output by the image sensor (117) and the spectrometer (120) into color coordinates.

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