DE102022115020B3 - Depth scan measuring system, depth scan measuring device, calibration unit and method for calibrating a depth scan measuring device - Google Patents

Abstract

A depth scanning measuring system for examining a surface structure of a sample (3) is disclosed. The depth scan measuring system comprises a depth scan measuring device (1, 101) and a calibration unit (71). The depth scanning measuring device (1, 101) can be calibrated using the calibration unit (71), in particular if a liquid lens (19A) is used in an optical scanning device (17) to adjust an object plane (21) at a depth distance for measuring the surface structure. Furthermore, depth scanning measuring devices (1, 101) and a calibration unit (71) as well as a method for calibrating a depth scanning measuring device (1) are disclosed.

Description

The present invention relates to a depth scanning measuring system with a depth scanning measuring device and a calibration unit, which is designed in particular for measuring a surface structure of a sample. The invention further relates to a depth scan measuring device, a calibration unit and a method for calibrating a depth scan measuring device.

For an examination of a surface structure of a sample - e.g. B. as part of a quality control - an enlarged two-dimensional image capture of the surface of the sample can be carried out. In particular, light, hand-held or spaced devices allow the examination of pressure-sensitive samples extending in one plane with an image-capturing system placed on the sample, such systems being designed to be correspondingly compact and handy. For example, with flexographic plates, such as those used in the printing industry, grid areas with printing dots or lines can be captured two-dimensionally.

Systems for surface analysis are known from the prior art, which display surfaces of samples to be examined two-dimensionally or three-dimensionally using magnifying imaging systems. For transparent samples (media), a transmitted light unit can be used to illuminate the sample from below. One example is the “Sibress FlexoControl 3D Plus” measuring device, which simultaneously records the surface and deeper parts of the grid points of a flexo plate and its base from the side. For this purpose, two cameras record the surface and flanks of grid points, with a side camera allowing the entire viewing area to be scanned sharply. Another example of an optical inspection device is revealed by DE 10 2014 011 548 A1 . The inspection device has a recording means (sensor), imaging optics and a delay element coupled to the imaging optics for adjusting the focal plane of the optics. The delay element is e.g. B. a disk of stepped thickness, which is interposed between the recording means and an object to be examined. The position of the object plane is determined by the thickness of the delay element.

DE 102004047928 A1 discloses an optical 3D measuring method for measuring object surfaces with a camera. This has a focal plane that defines a very small depth of field. By moving the Z position of the focal plane and repeatedly recording images, an image stack consisting of individual images is created. The individual images only show sharp, ie high-contrast, areas where the object surface intersects the focal plane. Each individual image is assigned a Z value. The sharply imaged areas of the individual images are combined into a result image, the pixels of which are each assigned the X coordinate, the Y coordinate and the Z coordinate.

DE 102021108238 A1 discloses a computer-implemented method for generating a depth map of a region of a surface of a workpiece. A focal image stack has a plurality of images of the workpiece, the images imaging the area of the surface of the workpiece with defined focal plane positions that are different in a depth direction, and a focal plane position is assigned to each image of the focal image stack. Pixels of the images are each assigned to a corresponding object point on the surface of the workpiece; Based on certain depth values, a depth map of the area of the surface of the workpiece is determined.

EP 2598836 B1 discloses a method for compensating for illumination deficiencies in microscopic shape from focus (SFF), first estimating the reflectivity of the scene using a projector-camera system, and then microscopic shape from focus (SFF) onto a stack of reflectance cards instead of being applied to the original image data.

DE 10149357 A1 discloses a method for optically measuring a surface profile of an object. An image recording device is used to record a series of n images of the object in different planes in the z direction of a coordinate system. The image contents of all n images of the generated image stack are compared with each other at each coordinate point in the z direction in order to determine a level based on predetermined criteria and assign its level number to this coordinate point and save it in a mask image. The mask image contains all 3D information of the object surface.

DE 202019100530 U1 discloses a device for detecting a three-dimensional structure, which comprises an imaging device, in particular a camera, which can be adjusted in the z-direction, and a control device. The control device is designed to record an image of a first level and, after adjusting the imaging device in the z-direction, to record an image of a second level. The device further comprises an evaluation device which is designed to interpolate a sublevel between the first level and the second level.

US 9,629,552 B2 discloses a numerical aperture control unit and a variable optical probe containing the same. The NA control unit includes: an aperture adjustment unit that controls an aperture through which light is transmitted, and a focus control unit that focuses light that is transmitted through the aperture and has an adjustable focal length. The variable optical probe includes: a light transmission unit; a collimator that collimates the light transmitted by the light transmission unit into parallel light; an NA control unit that focuses the light on a sample to be examined, and a scanner that changes the path of the light transmitted through the light transmission unit so that a predetermined area of the sample is scanned by the light passing through the NA control unit .

Furthermore, from “Focus Variation - Robust Technology for High Resolution Optical 3D Surface Metrology, Danzl, R. et. al., Strojniski vestnik - Journal of Mechanical Engineering, Volume 57, No. 3, Pages 45-256, June 2011, a focus variation method in the context of an optical 3D measurement technique is known. In the focus variation method, precision optics are moved vertically along the optical axis.

It has generally been recognized that there is a need in the industry for a depth scanning measuring device, preferably lightweight and portable, which outputs calibrated measurement data relating to a depth direction of a sample. For example, a sample extends in a plane or has a curved surface, e.g. B. the shape of a cylindrical surface. A fine surface structure protrudes into the sample (i.e. in the depth direction perpendicular to the plane). The inventor has recognized that the calibration concepts proposed herein make it possible to image and measure a surface structure using simple means. Particularly in the area of analyzing flexographic plates, the inventor has recognized that information about the surface structure of a e.g. B. already used flexo plates are essential for a well-founded decision about re-use or further use and thus generally for the efficient use of flexo plates. A surface-friendly, rapid and reliable detection of surface structures of printing plates is essential for integrating such a surface measurement with a depth scanning measuring device into industrial workflows, for example in industrial workflows in flexo printing. With quick access to information about surface structure and surface quality, defective printed products and printing press downtime due to clamped defective flexographic plates can be avoided. Furthermore, the inventor has recognized that - with such a depth scanning measuring device - information can be obtained, for example, about PCBs (printed circuit boards) for quality analysis using optical surface measurement.

The depth scan measurement system concepts disclosed herein are directed at improving, at least in part, one or more aspects of known systems for examining surface structures. One aspect of this disclosure is based on the task of expanding the two-dimensional information content when examining a surface structure with a depth scanning measuring device by a third dimension, referred to herein as the depth direction. Another aspect of this disclosure is based on the task of enabling high-precision calibration of a depth scanning measuring device.

At least one of these tasks is solved by a depth scan measuring system according to claim 1, a depth scan measuring device according to claim 11, a calibration unit according to claim 17 and by a method for calibrating a depth scan measuring device according to claim 18. Further developments are specified in the subclaims.

In one aspect, a depth scan measurement system includes a depth scan measurement device and a calibration unit. The depth scanning measuring device comprises an image data acquisition unit, which has an image sensor unit with a two-dimensional pixel arrangement that defines an image plane, and an optical scanning device with a lens unit that defines an object plane at an adjustable depth distance from the image plane and which is designed to display a section of the object plane on the two-dimensional pixel arrangement. Furthermore, the depth scanning measuring device comprises a control unit which is connected to the image sensor unit for receiving image data and to the optical scanning device for adjusting the depth distance and which can be connected to an image evaluation unit for outputting the image data. The control unit is also set up to set a plurality of depth distances sequentially and to receive image data of the section of the object plane, whereby the depth distance can be changed step by step by a depth increment in a calibrated depth scan range of 0 mm to at least 0.5 mm. The calibration unit defines a reference plane for calibrating the depth scanning measuring device and comprises a support surface, which is arranged offset from the reference plane by at least the calibrated depth scanning range, and a calibration body, which is arranged on the support surface and forms at least part of a calibration structure which has an upper surface section and a lower surface section, wherein the upper surface section and the lower surface section are spaced apart from one another in a direction orthogonal to the reference plane by a calibration distance and the calibration distance is given with an accuracy of 0.005 mm or less.

In a further aspect, a, in particular portable, depth scanning measuring device for examining a surface structure of a sample that extends in a plane is disclosed. The depth scanning measuring device comprises a housing with a base plate which has a bottom side and a measuring opening, the underside being designed as a flat floor surface for placing the depth scanning measuring device on the sample to be examined. The depth scan measuring device further comprises an image data acquisition unit. The image data acquisition unit has an image sensor unit with a two-dimensional pixel arrangement that defines an image plane. Furthermore, the image data acquisition unit has an optical scanning device with a lens unit, wherein the lens unit defines an object plane at an adjustable depth distance from the image plane and is designed to image a section of the object plane onto the two-dimensional pixel arrangement. The image sensor unit and the lens unit are arranged and designed in the housing with respect to the base plate in such a way that the section of the object plane extends along the underside and outside of the measuring opening. The depth scanning measuring device further comprises a control unit which is connected to the image sensor unit for receiving image data and to the optical scanning device for adjusting the depth distance and which can be connected to an image evaluation unit for outputting the image data. The control unit is also set up to set a plurality of depth distances sequentially and to receive image data of the section of the object plane, wherein the depth distance can be changed step by step by a depth increment in a calibrated depth scan range of 0 mm to at least 0.5 mm.

In a further aspect, a depth scanning measuring device for examining a surface structure of a sample, which in particular has a curved surface, is disclosed. The depth scan measuring device includes an image data acquisition unit that has an image sensor unit with a two-dimensional pixel arrangement that defines an image plane. Furthermore, the image data acquisition unit has an optical scanning device with a lens unit which defines an object plane at an adjustable depth distance from the image plane and which is designed to image a section of the object plane onto the two-dimensional pixel arrangement. The depth scanning measuring device further comprises a positioning unit to which the image sensor unit is attached, wherein the positioning unit is designed to move the image sensor unit in space at least in a direction orthogonal to the image plane and, by positioning the image sensor unit in space, to move the object plane to a reference plane of a calibration unit or to to lay a surface section of the sample to be examined, in particular the curved surface. The depth scanning measuring device further comprises a control unit which is connected to the image sensor unit for receiving image data and to the optical scanning device for adjusting the depth distance and which can be connected to an image evaluation unit for outputting the image data. The control unit is also set up to set a plurality of depth distances sequentially and to receive image data of the section of the object plane, wherein the depth distance can be changed step by step by a depth increment in a calibrated depth scan range of 0 mm to at least 0.5 mm.

With respect to the depth scanning measurement system and depth scanning measurement devices disclosed herein, object planes located in a range of 0 mm to at least 0.5 mm (e.g., below the bottom of the bottom plate of a depth scanning measurement device with housing) can be applied to the pixel array of the image sensor unit using the optical scanning device be depicted. The depth scanning range is usually tailored to the sample to be examined, with a depth scanning range in the range of 1 mm to 1.5 mm, for example in the case of flexographic plates, enabling meaningful information about the quality condition of a flexographic plate.

As mentioned, an exemplary sample is a 3D flexo plate. Flexo plates are easily deformable, so - in order to avoid damage caused by a load on a depth scanning measuring device lying on it - a weight limit per square centimeter for a lying depth scanning measuring device must be taken into account. An alternative sample that can be examined with a portable depth scan measuring device is a PCB (printed circuit board). A PCB can also easily be damaged by an object lying on it.

• (insbesondere manuell oder automatisiert) Positionieren der Tiefenscanmessvorrichtung bezüglich der Auflageträgerstruktur der Kalibriereinheit derart, dass die Kalibrierstruktur in einem Ausschnitt einer Objektebene der Tiefenscanmessvorrichtung angeordnet ist, und in einem Prozessor der Tiefenscanmessvorrichtung:
  • Bereitstellen eines oberen Zielpunkts im oberen Oberflächenabschnitt der Kalibrierstruktur und eines unteren Zielpunkts im unteren Oberflächenabschnitt,
  • Ausführen eines Autofokusalgorithmus jeweils für den oberen Zielpunkt und den unteren Zielpunkt, wodurch die optische Scanvorrichtung jeweils für eine schrittweise Ein-stellung der Position der Objektebene in Tiefenrichtung angesteuert wird, bis die optische Scanvorrichtung bei einem oberen Schrittwert den oberen Oberflächenabschnitt im oberen Zielpunkt und bei einem unteren Schrittwert den unteren Oberflächenabschnitt im unteren Zielpunkt auf die Bildebene scharf abbildet,
  • Ausgeben des oberen Schrittwerts der schrittweisen Einstellung für den oberen Zielpunkt und des unteren Schrittwerts für den unteren Zielpunkt, und
  • Bestimmen einer Schrittwertedifferenz zwischen dem oberen Schrittwert und dem unteren Schrittwert,
  • Berechnen eines Tiefeninkrements, das einem Schritt der optischen Scanvorrichtung bei der schrittweisen Einstellung eines Tiefenabstandswerts zugeordnet ist, durch Vergleichen der Schrittwertedifferenz mit der Kalibrierdistanz, und
  • Ausgeben des Tiefeninkrements als Kalibrierparameter.

In a further aspect, a calibration unit is disclosed which comprises a support support structure, a support surface and a calibration body. The support support structure defines a support plane as a reference plane for the depth scanning measuring device. The support surface is offset from the support plane by at least the calibrated depth scanning range. The calibration body is arranged on the support surface and forms at least part of a calibration structure. The calibration structure includes an upper surface portion and a lower surface portion, the upper surface portion and the lower surface portion being spaced apart from each other in a direction orthogonal to the support plane by a calibration distance. The calibration distance is given with an accuracy of 0.005 mm or less. Another aspect includes a method for calibrating a depth scan measuring device using a calibration unit. The depth scan measurement device and the calibration unit may be designed in accordance with the depth scan measurement system disclosed herein. The calibration unit comprises a support support structure and a calibration body which forms at least a part of a calibration structure, wherein the calibration structure comprises an upper surface section and a lower surface section and the upper surface section and the lower surface section are spaced apart from one another in a direction orthogonal to the support plane by a calibration distance, wherein the calibration distance is given with an accuracy of 0.005 mm or less. The procedure includes the steps:

• (in particular manually or automatically) positioning the depth scanning measuring device with respect to the support support structure of the calibration unit in such a way that the calibration structure is arranged in a section of an object plane of the depth scanning measuring device, and in a processor of the depth scanning measuring device:
  • Providing an upper target point in the upper surface section of the calibration structure and a lower target point in the lower surface section,
  • Executing an autofocus algorithm for the upper target point and the lower target point, whereby the optical scanning device is controlled for a stepwise adjustment of the position of the object plane in the depth direction until the optical scanning device detects the upper surface section in the upper target point and at an upper step value lower step value sharply images the lower surface section in the lower target point on the image plane,
  • Outputting the upper step value of the step adjustment for the upper target point and the lower step value for the lower target point, and
  • determining a step value difference between the upper step value and the lower step value,
  • Calculating a depth increment associated with a step of the optical scanning device in stepping a depth distance value by comparing the step value difference with the calibration distance, and
  • Output the depth increment as a calibration parameter.

In some developments, the upper surface section of the calibration structure can be formed by a surface area of the calibration body that can be optically detected with the depth scanning measuring device and is preferably arranged no more than 0.1 mm away from the reference plane. Additionally or alternatively, the carrier surface can have an optically recognizable, in particular cross-shaped, marking, which forms the lower surface section of the calibration structure. Furthermore, the carrier surface can be formed by a partially transparent carrier plate at least in an area surrounding the calibration body, in particular as the top side of the carrier plate, and/or can run essentially parallel to the top side of the support plate and form the lower surface section of the calibration structure.

In some developments, the lens unit of the depth scanning measuring device can have a liquid lens with an adjustable focus length, the focus length being adjustable in a range of at least ±0.25 mm, in particular of at least ±0.5 mm or of at least ±1 mm, and in particular is in a range of 5 mm to 10 mm. The control unit can also be set up to supply the liquid lens with a supply voltage or a supply current for adjusting the focus length and to change the focus length step by step by changing the supply voltage or the supply current by a supply increment. Additionally or alternatively, the control unit can further comprise a memory in which a calibration parameter is stored, which assigns the depth increment to the supply increment. Additionally or alternatively, the pixel arrangement and the lens unit can be geometrically aligned with one another, in particular the image plane and the object plane can be aligned essentially parallel to one another in such a way that the autofocus algorithm can be carried out at four corners of a square flat measuring area of 1 mm by 1 mm in the Object plane depth distance values result from each other by less than 0.035 mm, in particular less than 0.025 mm or in particular less than 0.012 mm or in particular less than 0.005 mm.

In some developments, the control unit can further comprise a processor that is set up to read in a target point in the section of the object plane as an input value, to execute an autofocus algorithm that uses the optical scanning device to set a tie distance value, in which the optical scanning device sharply images a surface section in the target point on the image plane, and to output the depth distance value as an output value.

In some developments, the depth scanning measuring device can further comprise a housing with a base plate, the base plate can have a bottom side and a measuring opening, and the underside can be designed as a flat floor surface for placing the depth scanning measuring device on the sample to be examined, the image sensor unit and the lens unit being in such a way with respect to the bottom plate can be arranged in the housing and designed so that the section of the object plane extends along the underside and outside of the measuring opening. The flat bottom surface of the base plate can have an extent of 30 mm to 100 mm in a first direction and an extent of 80 mm to 200 mm in a second direction orthogonal to the first direction and / or the support support structure can have at least three support points in the area of the base plate and in particular be designed as a support plate with an upper side, the upper side optionally being able to have at least the dimensions of the underside. Additionally or alternatively, the underside can be positioned on the support support structure in such a way that a surface area of the calibration body that can be optically detected with the depth scanning measuring device is arranged within the measuring opening and the calibration body is preferably arranged no more than 0.1 mm away from the underside.

Furthermore, the calibration unit can additionally have at least one stop to support the positioning of the depth scanning measuring device on the support support structure, the at least one stop being arranged at a distance from the calibration body in such a way that when the at least one stop comes into contact with the depth scanning measuring device, the calibration body is in the section of the object plane Depth scanning measuring device can be positioned.

In some developments of the depth scan measuring device, the image sensor unit can further comprise a mounting edge that surrounds the pixel arrangement. The optical scanning device may further comprise an outer tube and a spacer tube. The outer tube can be attached to the image sensor unit at a sensor-side end of the outer tube and can have an inner support surface directed into an interior of the outer tube at an object-side end. The spacer tube can comprise a sensor contact surface for resting on the mounting edge at a sensor-side end and an outer support surface directed in the direction of the inner support surface. The lens unit can be mounted between the inner support surface and the outer support surface and the outer tube can be placed over the lens unit and the spacer tube, so that the lens unit is positioned at a lens distance from the image plane that is predetermined by a length of the spacer tube.

In some developments of the depth scanning measuring device, the image sensor unit can be attached via a first holder at a fixed distance from the base plate and the lens unit can be held and positioned on the base plate at a predetermined lens distance from the image plane via a second holder.

In some developments, the depth scanning measuring device can further comprise at least one light source for illuminating the section of the object plane, wherein the at least one light source can be arranged in particular on the object side on the lens unit.

• Erfassen von Bilddaten des Kalibrierkörpers und der Trägerfläche neben dem Kalibrierkörper mit der Tiefenscanmessvorrichtung und optional Anzeigen der Bilddaten auf einer Anzeige,
• mithilfe einer Bedienschnittstelle der Tiefenscanmessvorrichtung oder automatisiert mithilfe eines Bildverarbeitungsalgorithmus, Auswählen eines ersten Pixels der angezeigten Bilddaten auf dem oberen Oberflächenabschnitt, und eines zweiten Pixels der angezeigten Bilddaten auf dem unteren Oberflächenabschnitt, und
• Einlesen des ersten Pixels als den oberen Zielpunkt und des zweiten Pixels als den unteren Zielpunkt in den Prozessor zum Ausführen des Autofokusalgorithmus jeweils für den oberen Zielpunkt und den unteren Zielpunkt.

In some developments of the method, the upper surface section can lie in the area of a top point of the calibration body and the lower surface section can lie in the area of a support surface on which the calibration body is arranged, and the method can further comprise the following steps:

• Capturing image data of the calibration body and the carrier surface next to the calibration body with the depth scan measuring device and optionally displaying the image data on a display,
• using an operating interface of the depth scanning measuring device or automated using an image processing algorithm, selecting a first pixel of the displayed image data on the upper surface portion, and a second pixel of the displayed image data on the lower surface portion, and
• Reading the first pixel as the upper target point and the second pixel as the lower target point into the processor to execute the autofocus algorithm for the upper target point and the lower target point, respectively.

• Einstellen der Fokuslänge die Flüssiglinse mit einer Versorgungsspannung oder einem Versorgungsstrom, und
• Ändern der Fokuslänge zur schrittweisen Einstellung der Position der Objektebene in Tiefenrichtung durch schrittweises Ändern der Versorgungsspannung oder des Versorgungsstroms um ein Versorgungsinkrement,

wobei der ausgegebene Kalibrierparameter das Tiefeninkrement dem Versorgungsinkrement zuordnet.In some developments of the method, the lens unit of the depth scanning measuring device can have a liquid lens with an adjustable focus length and the method can further comprise the following steps:

• Adjusting the focus length the liquid lens with a supply voltage or a supply current, and
• Changing the focus length to gradually adjust the position of the object plane in the depth direction by gradually changing the supply voltage or current by a supply increment,

where the output calibration parameter assigns the depth increment to the supply increment.

As part of the optical scanning device of the depth scanning measuring device disclosed herein, a volume that can be examined by imaging extends laterally in the area of the imaged section of the object plane and in the depth direction over a depth scanning area, as provided by the optical scanning device. The extent of the depth scanning area away from the underside results from the maximum scanning area of the optical scanning device, for example given by the adjustment range of a focus length of a lens unit. The extent of the deep scanning area is usually at least 0.5 mm for the analysis of flexographic plates, for example 1.5 mm or 2 mm.

The optical scanning device changes the position of the object plane step by step, the step size in the depth direction being given by the change in the focus length between two steps in the depth direction.

• 1 eine schematische Darstellung einer beispielhaften ersten Tiefenscanmessvorrichtung,
• 2 einen vergrößerten Ausschnitt der 1 zur Verdeutlichung eines ersten Ausführungsbeispiels einer optischen Scanvorrichtung,
• 3 eine Aufsicht auf die Unterseite einer Bodenplatte der beispielhaften ersten Tiefenscanmessvorrichtung im Bereich der Messöffnung,
• 4 eine perspektivische Ansicht der beispielhaften ersten Tiefenscanmessvorrichtung, die auf einer Flexoplatte abgelegt ist,
• 5 eine schematische Darstellung einer Tiefenscanmessvorrichtung zur Verdeutlichung eines zweiten Ausführungsbeispiels einer optischen Scanvorrichtung,
• 6 eine schematische Übersicht zur Verdeutlichung einer Verwendung einer Kalibriereinheit zur Kalibrierung einer Tiefenscanmessvorrichtung,
• 7 eine schematische perspektivische Darstellung einer Kalibriereinheit und
• 8 eine Sequenz von Abbildungen des Ausschnitts der Objektebene zur Verdeutlichung eines Verfahrens zur Kalibrierung einer Tiefenscanmessvorrichtung und
• 9A und 9B schematische Darstellungen einer zweiten beispielhaften Tiefenscanmessvorrichtung, die auf Abstand zu einer aufgespannten Flexoplatte gehalten wird.

Concepts are disclosed here that make it possible to at least partially improve aspects of the prior art. In particular, further features and their expediencies emerge from the following description of embodiments based on the figures. Of the figures show:

• 1 a schematic representation of an exemplary first depth scan measuring device,
• 2 an enlarged section of the 1 to illustrate a first exemplary embodiment of an optical scanning device,
• 3 a top view of the underside of a base plate of the exemplary first depth scanning measuring device in the area of the measuring opening,
• 4 a perspective view of the exemplary first depth scanning measuring device placed on a flexographic plate,
• 5 a schematic representation of a depth scanning measuring device to illustrate a second exemplary embodiment of an optical scanning device,
• 6 a schematic overview to illustrate the use of a calibration unit for calibrating a depth scan measuring device,
• 7 a schematic perspective view of a calibration unit and
• 8th a sequence of images of the section of the object plane to illustrate a method for calibrating a depth scanning measuring device and
• 9A and 9B schematic representations of a second exemplary depth scanning measuring device, which is kept at a distance from a clamped flexographic plate.

The inventive concepts are explained below by way of example in connection with the figures.

1 shows a schematic overview of a depth scanning measuring device 1 using the example of an examination of a flexographic plate 3 (flexographic printing form). For example, the flexographic plate 3 is examined for renewed use with regard to the quality of the surface with the depth scanning device 1. The flexographic plate 3 forms a relief structure with higher-lying flat printing elements 3A (e.g. grid dots or grid lines) for a flexographic printing process. The surface areas of the printing elements 3A lie in one plane and are wetted with ink for the flexo printing process. Due to damage or wear, the surface areas 3 can deviate locally from the plane, which can influence the quality of a printing process carried out with the flexographic plate 3. Accordingly, for example, a remaining depth of the relief structure represents a decision criterion for the further usability of the flexographic plate 3. Likewise, a depth-resolved optical examination can be used, for example, in the quality control of PCBs.

In the 1 Depth scanning measuring device 1 shown comprises a housing 5 with a base plate 7. By way of example, the base plate 7 extends in the XY plane. An underside 7A of the base plate 7 is designed as a flat floor surface for placing the depth scanning measuring device 1 on the sample to be examined. Accordingly, the underside 7A rests on the pressure elements 3A.

A measuring opening 9 is provided in the base plate 7. An image data acquisition unit 11 allows the underlying surface structure to be recorded through the measuring opening 9. The image data acquisition unit 11 includes an image sensor unit 13 with a two-dimensional (sensor) pixel arrangement 13A (in the XY plane). The pixel arrangement 13A defines an image plane 14 of the image data acquisition unit 11. The image data acquisition unit 11 further comprises an optical scanning device 17 with a lens unit 19. The lens unit 19 defines an object plane 21, with a depth distance between the object plane 21 and the underside 7 of the base plate 7 being adjustable. The depth distance is defined in a depth direction that is orthogonal to the bottom 7A (in the Z-axis direction in the figures).

In the example of 1 For example, the lens unit 19 can have a liquid lens 19A with an adjustable focus length, in which the focus length can be adjusted in a range of at least ±0.25 mm. In some embodiments, a liquid lens is a mechanically or electrically controlled device filled with an optical liquid medium. As soon as a current or voltage is applied, the lens takes on a certain shape. If you change the current/voltage, the shape and thus the refractive power and focal length of the lens change, so that a different focus length can be set within milliseconds. For example, the liquid lens changes its radius of curvature depending on the applied voltage, whereby the object plane can be shifted or, in the case of several liquid lenses used together, a focal length of the lens unit 19 can generally be adjusted. Accordingly, the distance of the object plane 21 from the underside 7A can be varied/adjusted at least within a range of 0.5 mm using the liquid lens 19A. The adjustment of the focus length or scanning through a plurality of focus lengths can be effected step by step with corresponding incremental current/voltage changes. The focus length can preferably be adjusted in a range of at least ±0.5 mm or at least ±1 mm. Typically the focus length is in a range of 5 mm to 10 mm.

The optical scanning device 17 is designed to image a section of the object plane 21 onto the two-dimensional pixel arrangement 13A. The image sensor unit 13 and the lens unit 19 are arranged and designed in the housing 5 with respect to the base plate 7, in particular with respect to the underside 7A of the base plate 7, in such a way that the section of the object plane 21 extends along the underside 7A and outside the measuring opening 9. The object plane 21 preferably runs as parallel as possible to the underside 7A within the tolerance, so that the underside 7A can be viewed as the reference plane of a measuring process. In 1 A holder 22 is indicated by way of example, to which the image sensor unit 13 is attached. In particular, the image sensor unit 13 is attached in such a way that the pixel arrangement 13A runs as parallel as possible to the underside 7A within the tolerance. The f number of the lens unit 19 is, for example, in the range from 2.5 to 3.5. The optical arrangement of the components is such that a depth of field can be, for example, in the range of 2 µm to 50 µm, in particular in the range of 5 µm to 30 µm, for example in the range of 10 µm. The depth of field is assigned to the object plane 21 in the depth direction. “To focus” is understood here to mean that structures in the area of the depth of field around the object plane are imaged “sharply” on the image plane 14. A sharp image of a target point can be set, for example, by an autofocus algorithm that causes the target point to fall within the depth of field range.

The image data acquisition unit 11 further comprises a control unit 23, which is connected to the image sensor unit 13 for receiving image data and to the optical scanning device 17 for adjusting the depth distance (wired or wireless). The control unit 23 includes, for example, a memory 23A and a processor 23B. It is designed, for example, as a computer or a programmable computing unit. For example, the adjustment of the depth distance can be done by adjusting the focus length of the liquid lens 19A. In general, the control unit can be set up to supply the liquid lens 19A with a supply voltage or a supply current, thereby determining the focus length. By changing the supply voltage or current by one supply increment, the focus length can be gradually changed/adjusted.

Furthermore, the control unit 23 can be set up to control the image data acquisition with regard to possible recording parameters and can be connected to the image sensor unit 13. Furthermore, the control unit 23 is connected to an image evaluation unit 25 for outputting image data (wired or wireless). The image evaluation unit 25 can display the image data in combination with evaluated data on a display 27. Furthermore, the image evaluation unit 25 can receive parameters or input data using an input device 29 (keyboard, mouse, ...). Examples are in 1 several lines 24 for data exchange and/or control between the various components are shown.

In general, the control unit 23 can be designed to deliver control signals to the image sensor unit 13 and the optical scanning device in order to gradually shift the object plane by the depth increment through the depth scanning area and to capture image data for the (preferably equally spaced) object planes. The object planes are preferably equally spaced and are scanned with the same step size (equal supply increments).

With regard to the setting of the depth distance, the control unit 23 is also set up to sequentially set a plurality of depth distances and to receive image data of the section of the object plane in each case. The image data belongs to image recording of the sample, in which the optical scanning device 17 is at different depth distances from the underside 7A is in focus. 2 shows the optical scanning device 17 in an enlarged view 1 according to a first exemplary embodiment.

Referring again to the examination of the flexo plate 3, in order to rule out, for example, that the flexo plate 3 is damaged, the surface of the flexo plate 3 can be examined visually with the depth scanning measuring device 1. In a first examination step, the depth scanning measuring device 1 can be sharply adjusted to the higher-lying flat printing elements 3A. In other words, the object plane 21 set by the depth scanning measuring device 1 and imaged by the optical scanning device 17 is set to the plane of the printing elements 3A. If the depth scanning measuring device 1 is moved over the flexographic plate 3, it can be recognized on the display 27 by an operator or automatically using image processing when the expected surface structure is no longer in the plane of the printing elements 3A. This is illustrated by an example 1 in the illustration shown on the display 27, a line structure 31 is no longer sharply displayed in the central area.

For such a first examination step (assessment of large areas), a depth of field of the depth scanning measuring device 1 is preferably in a range of, for example, 10 µm to 30 µm for flexographic plates and generally in a range that differentiates an “upper” area from a “lower” area surface structure of a sample to be examined.

1 further illustrates in the illustration shown on the display 27 a depth measurement process in the “blurred area” using a measuring point 33A (in the removed area of the pressure element 3A) and a measuring point 33B (in the area of the bottom of the relief). For the example measurement, an actual value T_i of 42 µm and a target value T_s of 60 µm are displayed for the surface variation of the relief. The depth measurement process as a second examination step is subsequently used in combination with 2 as well as in combination with the procedure for calibrating the depth measuring device 1 explained in more detail.

2 shows the optical scanning device 17 in an enlarged view 1 . According to a first exemplary embodiment, the lens unit 19 is attached to the image sensor unit 13 at a lens distance using a spacer tube 41 and an outer tube 43 (as part of the optical scanning device 17). The lens distance from the image sensor unit 13 is selected for a desired magnification. For example, with a focus length in the range of 5 mm to 10 mm and a magnification factor in the range of 4 to 6, the lens unit 19 (for example the mentioned liquid lens or its lens plane) is at a lens distance from the image sensor unit 13 in a range of 10 mm to 40 mm arranged.

In the example shown, the outer tube 43 is placed over the lens unit 19 and the spacer tube 41, so that the lens unit 19 is held away from the image plane 14 at a lens distance predetermined by a length of the spacer tube 41.

As in 2 shown, the image sensor unit 13 includes a mounting edge 13B that surrounds the pixel array 13A. The spacer tube 41 has a sensor contact surface 41A for resting on the mounting edge 13A at a sensor-side end. The outer tube 43 is attached to a sensor-side end on the image sensor unit 13 outside the mounting edge 13B, usually in at least two positions. Shows as an example 2 , how the outer tube 43 is attached to the image sensor unit 13 on two webs 45 by means of screws 47.

At an object-side end, the outer tube 43 has an inner support surface 43A directed into the interior of the outer tube 43. At an object-side end, the spacer tube 41 has an outer support surface 41B directed in the direction of the object plane and thus in the direction of the inner support surface 43A. The lens unit 19 is mounted between the inner support surface 43A and the outer support surface 41B. It can be seen that the outer tube 43 clamps the lens unit 19 and the spacer tube 41 against the mounting edge 13B. In addition to the in 2 In the embodiment shown, in which the outer support surface 41B forms a cylindrical end surface of the spacer tube 41, the outer support surface 41B can also be provided offset inside the spacer tube 41. This enables the lens unit 19 to be guided in an end section of the spacer tube 41.

2 further illustrates how the optical scanning device 17 is designed to scan a depth scanning area 51 in the depth measuring process. The depth scanning area 51 includes depth distances from 0 mm to at least 0.5 mm or preferably up to at least 1 mm or up to at least 1.5 mm. For clarification, a number of object planes 21 (running parallel to one another) are shown schematically in section. Adjacent object levels 21 differ by a depth increment ΔT in their distance from the underside 7 of the base plate 7. For example, the depth increment ΔT can be set to a value in the range from 0.001 mm to 0.01 mm.

The control unit 23 can further include a processor 23B, which is set up to execute an autofocus algorithm as part of a depth measurement process. For example, the autofocus algorithm is read out from the memory 23A together with input parameters. A calibration parameter can also be stored in the memory 23A, for example, which assigns the depth increment ΔT to a (voltage/current) supply increment of the liquid lens 19A. The autofocus algorithm evaluates image data from the flexographic plate 3, which were obtained with the image data acquisition unit 11 for a section 49 of the object plane 21 and forwarded to the control unit 23. The control unit 23 sets a specific depth distance for the object plane 21 by controlling the optical scanning device 17. The aim is to set a depth distance value such that the optical scanning device 17 sharply images a surface section of the sample, here the flexographic plate 3, in the area of a target point on the image plane 14. For example, if the measuring point 33A is used as the target point in the display 27 of the 1 shown image selected by an operator or in an automated program sequence and read by the autofocus algorithm, the autofocus algorithm carries out, for example, a pixel contrast analysis of the pixels in the area of the measuring point 33A and varies the depth distance of the object plane 21 by the depth increment ΔT until - as in 2 shown - the optical scanning device 17 focuses a point 53A on the surface of the flexographic plate 3 onto the pixel arrangement 13A and images it sharply as an image point 53B.

In particular, in some embodiments, the optical scanning device 17 can image the object plane 21 sharply onto the image plane within a tolerance range of 0.025 mm or less. The focus length of the lens unit 19, the distance between the image sensor unit 13 and the lens unit 19 (lens distance) and the aperture of the lens unit 19 can be selected such that the object plane 21 has a depth of field in the range of 0.002 mm to 0.05 mm, in particular in Range from 0.01 mm to 0.03 mm is assigned. In particular, the object plane can be assigned a depth of field in the range from 0.2% to 5%, for example in the range around 1%, of the depth scan area 51.

The autofocus algorithm then outputs the depth distance value to which the optical scanning device 17 was set as the output value of the depth measurement process.

For example, using the holder 22, the outer tube 43 and the spacer tube 41 - geometrically designed with appropriate precision - the pixel arrangement 13A, the lens unit 19 and the underside 7A can be geometrically aligned with one another in such a way that an autofocus algorithm can be carried out on four corners of a square plan Measuring range of 1 mm by 1 mm in the object plane 21 leads to comparable depth distance values. Depth distance values output as part of a depth measurement process differ, for example. B. from each other less than 0.035 mm, in particular less than 0.025 mm or in particular less than 0.012 mm or in particular less than 0.005 mm. With appropriate alignment, an area is sharply imaged that extends parallel to the underside 7A. In other words - within the tolerance and over the entire depth scanning area 51 - the image plane 14 and the object plane 21 are essentially aligned parallel to one another. This makes it possible for the image data acquisition unit 11 to - through an existing depth of field - focus on an area in the depth direction (Z direction in 1 ) limited - sharp recording is produced.

Furthermore, they show 1 and 2 Light sources 55 (e.g. LEDs), which are designed and aligned to illuminate the imaged section of the object plane 21. Four light sources 55 can, for example, be integrated in an azimuthally distributed manner into an end flange of the outer tube 43. The light sources 55 can z. B. can be supplied with power via lines along the outer tube 43. The light sources 55 can be used in particular for the method described below, which is based on a non-transparent calibration body, for calibrating a depth scanning measuring device or for examining a surface structure of a non-transparent (or only slightly) transparent sample.

3 shows a top view of the underside 7A in the area of the measuring opening 9. You can see the liquid lens 19A centrally in the measuring opening 9, which is held in a lens holder 19B. Furthermore, one can see the outer tube 43 with the four light sources 55. In addition, one can see an adjustment mandrel 57, which points to the center of the depicted section of the object plane 21 and facilitates the alignment of an area to be examined on the depicted section of the object plane 21 (see also 4 ). Alternatively or in addition to the adjustment mandrel 57, a laser beam/intersecting laser beams could be directed onto the area to be examined.

Referring to the schematic representation of a portable embodiment of the depth scanning measuring device 1 in 4 The flat bottom surface of the base plate 7 can be z. B. in a first direction a dimension of 30 mm to 100 mm (width B in 4 ) and in a second direction orthogonal to the first direction an extent of 80 mm to 200 mm (length L in 4 ) exhibit. Furthermore, the housing 5 - particularly in the case of a portable depth scanning measuring device - can extend to a height in the range of 80 mm to 200 mm above the base plate 7 (height H in 4 ) to enable manual handling and positioning of the depth scanning measuring device 1. Designed as a portable depth scanning measuring device, the depth scanning measuring device 1 can have a total weight, for example, in the range of 200 g to 800 g. Further clarified 4 a wireless connection (with a transmitter 59) of the depth scan measuring device 1 with z. B. the image evaluation unit 25.

5 shows a further embodiment for mounting the lens unit 19 at a lens distance from the sensor unit 13. As in the embodiment of 1 the image sensor unit 13 is arranged via a first holder 22A at a fixed distance from the base plate 7 for protection in the housing 5 and is fastened to the base plate 7, for example. In contrast to the embodiment of 1 the lens unit 19 is held by a second holder 61 on the base plate 7 at a predetermined lens distance from the image plane 14. Shows as an example 4 schematically a thread 61A in the holder 61, into which the lens unit 19 is screwed. The light sources 55 can be arranged on the holder 61.

Essential for the use of the depth scanning measuring device 1 is a high level of accuracy in measuring a surface structure in the depth direction. In connection with the 6 until 8D The calibration of the depth scanning measuring device 1 using a calibration unit 71 is explained.

6 shows the image data acquisition unit 11 in a sectional view 1 stored on the calibration unit 71, as shown in 7 is shown in perspective. The calibration unit 71 includes a support support structure that defines a support plane for the depth scanning measuring device 1. The support support structure generally provides at least three support points that define the support plane. In the exemplary embodiment of the calibration unit 71, the support support structure is designed as a support plate 73, for example an aluminum plate, the top side 73A of which forms the support plane as a reference plane for calibrating a depth scanning measuring device. As in 6 shown, the base plate 7 rests on the top 73A. The support plate 73 preferably has at least the dimensions of the flat bottom surface of the depth scanning measuring device 1.

The calibration unit 71 further comprises a support surface 75A, which is arranged offset/lowered from the support plane/reference plane by at least the depth scanning area 51 to be calibrated, and a calibration body 77, which is arranged on the support surface 75A. The calibration body 77 forms at least part of a calibration structure that includes an upper surface section and a lower surface section. The surface sections are preferably designed in such a way that they can be localized in a recording of the depth scanning measuring device 1 by an operator or automatically using image processing in order to be able to determine a target point in the respective surface section for an autofocus algorithm.

The upper surface section and/or the lower surface section can preferably be designed as flat surface areas. A single depth distance is assigned to such a flat surface area if the surface area extends essentially parallel to the support plane/top side 73A and is therefore aligned parallel to the underside 7A of the depth scanning measuring device 1 placed on it. A spherical surface in the area around the uppermost point of the sphere is also to be viewed as essentially parallel to the support plane/top side 73A.

Furthermore, in a surface section, a position to be measured in the depth direction can be determined, for example, by a top (bottom) point of a curved or tapering surface profile. This can be used as a target point for an autofocus algorithm in a recording of the depth scan measuring device 1 by an operator or can be localized automatically using image processing.

In the exemplary embodiment, the carrier surface 75A is a surface of a carrier plate 75 and represents a lower surface section of the calibration structure. The carrier plate 75 is arranged recessed in a recess 73B of the support plate 73. The carrier plate 75 rests, for example, on a projection in the recess 73B (can also be designed as a through opening, especially when used with a transmitted light unit) and is optionally attached to the support plate 73. The support surface 75A preferably runs essentially parallel to the support plane/reference plane (and thus the top side 73A) and is therefore also aligned parallel to the underside 7A of the depth scanning measuring device 1 placed on it. The carrier plate 75 can be designed to be partially transparent - at least in the vicinity of the calibration body 77 - so that in addition to the illumination of the calibration body 77 by the light sources 55 from the side from above (arrow 81A), illumination from below (arrow 81B) can be provided. The illumination from below can be generated, for example, using a transmitted light unit on which the calibration unit 71 rests Increase the contrast in imaging. The carrier plate 75 can, for example, be made of glass and have a thickness in the range of 0.05 mm to 2 mm, for example a thickness of 100 μm. The carrier plate 75 is preferably a precision glass that has small fluctuations in thickness and can therefore be viewed as essentially “flat”.

In general, the calibration unit 71, in particular the calibration body 77, optionally in combination with the support surface 75A, structurally provides a precisely calibrated height difference in the depth direction between two surface sections, which can be detected with the depth scanning measuring device 1 at two different depth distances and whose height difference can be evaluated with an autofocus algorithm. In the example of 6 and 7 The calibration body 77, together with the carrier plate 25, forms a calibration structure which extends orthogonally to the support plane over a calibration distance D; for example, the calibration distance D is 0.5 mm, 1 mm or 1.5 mm. The calibration distance D is preferably given with an accuracy of 0.005 mm or less. Several exemplary geometric shapes of the calibration body 77 are shown in 7 indicated: a calibration ball 77A, a calibration cube 77B and a calibration cylinder 77C. Furthermore, in alternative embodiments, the calibration body 77 can have two surface sections, the distance between which is defined in the depth direction and which form the calibration structure and. For example, a step-shaped calibration body can form the upper surface section and the lower surface section, with a step height corresponding to the calibration distance D.

An upper surface section of the calibration body 77 that can be optically detected with the depth scanning measuring device 1 preferably has a minimum distance from the carrier surface 75A and is preferably arranged not more than 0.1 mm away from the carrier surface 75A (below), whereby contact of the calibration body 77 with the depth scanning measuring device is possible 1 can be avoided during calibration.

As in 7 shown, the carrier surface 75A can optionally have an optically recognizable marking 79. The marking 79 is provided and designed on the carrier surface 75A in such a way that when the object plane 21 is correctly adjusted in the area of the carrier surface 75A in the receptacle of the depth scanning measuring device 1, it can be recognized and can thus be used as a target point by the autofocus algorithm. In the example of 7 the marking 79 is cross-shaped, with the calibration ball 77A and the calibration cuboid 77B each being arranged in the center of the cross-shaped marking 79.

In general, the depth scanning measuring device 1, in particular the bottom surface of the support support structure, can be positioned on the calibration unit 71 in such a way that a surface area of the calibration body 77 that can be optically detected with the depth scanning measuring device 1 is arranged within the measuring opening 9. To support the positioning of the depth scanning measuring device 1, the calibration unit can also have at least one stop 83 on the support support structure. The at least one stop 82 is preferably arranged at a distance from the calibration body 77 in such a way that when the at least one stop 83 comes into contact with the depth scanning measuring device 1, the calibration body 77 can be positioned in the depicted section of the object plane 21 of the depth scanning measuring device 1. As in 7 shown, the stop 83 can preferably determine the position of the depth scanning measuring device 1 in two directions if only one calibration body 77, for example the calibration ball 77A, is used for calibration.

In a method for calibrating the depth scanning measuring device 1 using the calibration unit 71, the depth scanning measuring device is arranged according to the arrangement as shown in 6 is shown positioned on the calibration unit 71. The operator can move the object plane 21 step by step through the depth scanning area 51 in the depth direction - for example by incrementally adjusting a supply voltage or a supply current of the liquid lens 19A and thus the focus length. Accordingly, the operator can create images in which he can clearly see the upper surface section or the lower surface section of the calibration structure. In these images, the operator or an automated process can select corresponding pixels and use them as target points in autofocus adjustment using an autofocus algorithm.

In 6 the calibration structure is formed by the calibration body 77 and the areas of the support surface 75A adjacent to the calibration body 77. The calibration distance D is given by the distance of the uppermost point of the spherical calibration body 77 from the support surface 75A (in the depth direction). The distance corresponds to the diameter of the spherical calibration body 77, which can be known, for example, to an accuracy of 5 μm when using a precision ball. 6 shows the selected target point 91A on the top of the spherical calibration body 77 (upper surface section of the calibration structure) and the selected target point 93A next to the calibration body 77 on the support surface 75A (lower surface section of the calibration structure). If the object plane 21 is positioned accordingly, either the target point 91A or the target point 93A sharply imaged in the image plane 14 at the point 91B or the point 93B. The sharper the image, the more contrasting a pixel analysis of the corresponding images is. The latter can be used, for example, by an autofocus algorithm to focus the optical scanning device 17 on the corresponding target point.

As schematically in 8A is shown, an image 90A of the section 49 of the object plane 21, which was recorded with the object plane 21 above the calibration body 77, is blurred due to the high depth of field.

An operator or an image processing routine can select the target points 91A and 93A and set them as an upper target point in the upper surface portion of the calibration structure and a lower target point in the lower surface portion in a processor 23B (see 1 ) of the depth scan measuring device 1 for calibration. An autofocus algorithm can then be carried out by the processor for the upper target point and the lower target point. As part of the autofocus algorithm, the optical scanning device 17 is controlled for a step-by-step adjustment of the position of the object plane 21 in the depth direction until the optical scanning device 17 detects the upper surface section in the upper target point at an upper step value and the lower surface section in the lower target point at a lower step value sharply depicted on the image plane 14.

8B Figure 90B schematically illustrates a photograph of the calibration body 77 at the upper step value. A sharp image of the target point 91A as well as four light reflections of the illumination from the light sources 55 can be seen centrally. Furthermore, in 8B a vaguely recognizable spherical shape of the calibration body 77 is indicated by dashed lines.

8C clarifies in an image 90C an image of the calibration body 77 in the area of the largest circumference during the scanning process in the direction of the carrier surface 75A. Due to the shallow depth of field, only the edge area of the calibration body 77 is imaged sharply.

8D Figure 90D schematically illustrates a photograph of the support surface 75A at the lower step value. The cross-shaped marking 79 can be seen, with the central area of the marking 79 being covered by the calibration body 77. For clarification, in 8D The spherical shape of the calibration body 77 is indicated schematically.

The upper step value of the step adjustment for the upper target point and the lower step value for the lower target point are output by the autofocus algorithm, so that a step value difference between the upper step value and the lower step value can be determined by the processor. The step value difference represents the number of steps that the optical scanning device 17 must move between the upper target point 91A and the lower target point 93A for a sharp image of the same.

The number of steps corresponds to the calibration distance D. By comparing the step value difference with the calibration distance D, the depth increment ΔT, which is assigned to a (single) step of the optical scanning device when setting a depth distance value step by step, can be determined by the processor. With a number of 250 steps for a calibration distance D of 0.5 mm, this results in a depth increment ΔT of 2 µm.

The depth increment ΔT can be calculated by the processor as a calibration parameter and stored in memory 23A. In general, the processor can prepare/determine a plurality of depth increments ΔT for different supply increments (i.e. different step sizes) with a view to different surface structures to be examined for setting the focus length and stored in the memory 23A.

When using the depth scanning measuring device 1, a surface structure of a sample can be measured in the depth direction, taking into account the depth increment ΔT. After manually/automatically selecting a target point and determining the step value for the target point using the autofocus algorithm, the step value for the object plane 21 “focused on the target point” can be multiplied by the depth increment ΔT and output by the processor as a depth distance value and displayed on the display 27, for example . This allows, for example, the measurement of the height/depth of pressure points or pressure lines.

In the exemplary embodiments described herein, the spacer tube 41 and the outer tube 43 as well as the holder 22 ( 1 ) and brackets 22A and 61 ( 5 ) for example, 3D printed with a resin (liquid synthetic resin), injection molded or made from metal. In particular, this enables the sensor contact surface 41A, the outer support surface 41B, the inner support surface 43A, the thread 61A and the lens spacing (length of the spacer tube 41) to be designed with a precision that brings about the necessary parallelism of the image plane 14, the object plane 21 and the underside 7A.

Alternatively, to use the concepts disclosed herein in a portable depth context scan measuring device ( 4 ), the depth scanning measuring device can be guided over a sample to be examined using an optionally robotically guided positioning unit. This is shown schematically in the 9A and 9B shown using the example of a depth scanning measuring device 101 for checking a flexographic plate 103 clamped on a printing cylinder. The flexographic plate 103 comprises a plurality of printing elements 103A, for example in the 9A and 9B a pressure element 103A' was shown reduced in height.

The depth scanning measuring device 101 includes an image data acquisition unit 111, which includes an image sensor unit 113 and an optical scanning device 117, which are exemplary formed according to the first embodiment. Regarding the structure and function, please refer to the previous description e.g. B. in connection with the 1 and 2 referred.

Furthermore, the depth scanning measuring device 101 includes a positioning unit 104 to which the image sensor unit 113 is attached. The positioning unit 104 is designed to position the image sensor unit 113 in space at least in a direction orthogonal to the image plane 14 (in 9A in the Z direction). Further degrees of freedom (for example at least a lateral positioning along a cylinder axis of the printing cylinder; alternatively a positioning in a tangential plane and one or more axes of rotation) can be provided by the positioning unit 104.

By positioning the image sensor unit 113 in space, the object plane 21 can be placed on a reference plane of a calibration unit (not shown). Alternatively, a calibration can be carried out before mounting the image data acquisition unit 111. Regarding calibration, please refer to the previous description in connection with 6 until 8A referred.

To examine the flexo plate 103, the “top” object level 21 of the scanning area 51 can be placed on a surface of the higher-lying printing elements 103A of the flexo plate 103 as a sample to be examined.

The printing cylinder is rotatably mounted (illustrated by arrow 102), so that faulty printing elements can easily be identified in a first examination step due to the limited depth of field by rotating the printing cylinder. Located - as in 9B shown - e.g. B. the printing element 103 A 'in the depicted section of the object plane 21, the surface of the printing element 103A' is not imaged sharply. This can be detected by an operator or automatically using image processing. Incorrect locations on the flexographic plate 103 clamped on the printing cylinder can be stored in the memory as cylinder coordinates. For the first examination step (assessment of large areas), a depth of field of the depth scanning measuring device 101 is preferably in a range of, for example, 10 μm to 30 μm for flexographic plates and generally in a range that allows a differentiation of an “upper” area from a “lower” area surface structure of a sample to be examined.

As part of a second examination step (depth measurement process), the flexographic plate 103 is examined using the depth scanning measuring device 101 in the area of the defective printing elements with the printing cylinder stationary. As in 9B shown, the surface of the pressure element 103A' lies in the scanning area 51, so that, for example, a current height (reduced due to wear/damage) of the surface of the pressure element 103A' can be measured. Regarding the depth measurement process, please refer to the previous description in connection with 1 and 2 referred.

It is expressly emphasized that all features disclosed in the description and/or the claims are considered to be separate and independent from each other for the purpose of the original disclosure as well as for the purpose of limiting the claimed invention, regardless of the combinations of features in the embodiments and/or the claims should. It is explicitly stated that all range statements or statements of groups of units disclose every possible intermediate value or subgroup of units for the purpose of the original disclosure as well as for the purpose of limiting the claimed invention, in particular also as a limit of a range statement.

Claims (20)

Depth scanning measuring system for examining a surface structure of a sample (3) with: a depth scanning measuring device (1) comprising a housing (5) with a base plate (7) which has a bottom (7A) and a measuring opening (9), the bottom (7A) is designed as a flat floor surface for placing the depth scanning measuring device (1) on the sample (3) to be examined, an image data acquisition unit (11) which has an image sensor unit (13) with a two-dimensional pixel arrangement (13A) which defines an image plane (14), and an optical scanning device (17) with a lens unit (19) which defines an object plane (21) at an adjustable depth distance from the image plane (14) and which is designed to display a section (49) of the object plane (21) on the two dimensional pixel arrangement (13A), wherein the image sensor unit (13) and the lens unit (17) are arranged and designed in the housing (5) with respect to the base plate (7) in such a way that the cutout (49) of the object plane (21) is along the Underside (7A) and extends outside the measuring opening (9), and a control unit (23) which is connected to the image sensor unit (13) for receiving image data and to the optical scanning device (17) for adjusting the depth distance and which is connected to an image evaluation unit (25) can be connected to output the image data, wherein the control unit (23) is further set up to set a plurality of depth distances sequentially and to receive image data of the section (49) of the object plane (21), the depth distance being in a calibrated depth scanning range (51) can be changed step by step from 0 mm to at least 0.5 mm by a depth increment (ΔT), and a calibration unit (71), which defines a reference plane for the calibration of the depth scanning measuring device (1), comprising a support surface (75A), which is arranged offset from the reference plane by at least the calibrated depth scanning area (51), and a calibration body (77) which is arranged on the support surface (170A) and forms at least part of a calibration structure which comprises an upper surface section and a lower surface section, wherein the upper surface portion and the lower surface portion are spaced apart from each other in a direction orthogonal to the reference plane by a calibration distance (D), and the calibration distance (D) is given with an accuracy of 0.005 mm or less. Depth scanning measurement system Claim 1 , wherein the upper surface section of the calibration structure is formed by a surface area of the calibration body (77) that can be optically detected with the depth scanning measuring device (1), which is preferably arranged not more than 0.1 mm away from the reference plane, and / or the support surface (A) has an optically recognizable, in particular cross-shaped, marking (79) which forms the lower surface section of the calibration structure. Depth scanning measurement system Claim 1 or 2 , wherein the carrier surface (75A) is formed by a partially transparent carrier plate (75) at least in one area of the calibration body (77), in particular as the top side of the carrier plate (75), and / or wherein the carrier surface (75A) is essentially parallel to the top side the support plate (73) and forms the lower surface section of the calibration structure. Depth scan measurement system according to one of the Claims 1 until 3 , wherein the lens unit (19) of the depth scanning measuring device (1) has a liquid lens (19A) with an adjustable focus length, the focus length being in a range of at least ±0.25 mm, in particular at least ±0.5 mm or at least ±1 mm, is adjustable, and in particular is in a range of 5 mm to 10 mm and the control unit (23) is further designed to - supply the liquid lens (19A) with a supply voltage or a supply current for adjusting the focus length and - the focus length by changing the supply voltage or the supply current by a supply increment step by step, and/or wherein the control unit (23) further comprises a memory (23A) in which a calibration parameter is stored which assigns the depth increment (ΔT) to the supply increment. Depth scan measurement system according to one of the Claims 1 until 4 , wherein the control unit (23) further comprises a processor (23B) which is set up to - read in a target point in the section (49) of the object plane (21) as an input value, - execute an autofocus algorithm that uses the optical scanning device (17). Setting a depth distance value controls, in which the optical scanning device (17) sharply images a surface section in the target point on the image plane (14), and - to output the depth distance value as an output value. Depth scan measurement system according to one of the Claims 1 until 5 , wherein the pixel arrangement (13A) and the lens unit (19) are geometrically aligned with one another, in particular the image plane (14) and the object plane (21) are aligned essentially parallel to one another in such a way that the autofocus algorithm can be carried out at four corners of a square plan Measuring range of 1 mm by 1 mm in the object plane (21) results in depth distance values that differ from each other by less than 0.035 mm, in particular less than 0.025 mm or in particular less than 0.012 mm or in particular less than 0.005 mm. Depth scan measurement system according to one of the Claims 1 until 6 , wherein the flat bottom surface of the base plate (7) has an extent of 30 mm to 100 mm in a first direction (Y) and an extent of 80 mm to 200 mm in a second direction (Y) orthogonal to the first direction (X). Depth scan measurement system according to one of the Claims 1 until 7 , where the support support structure has at least three support points in the area of the base plate (7) and is in particular designed as a support plate (73) with an upper side (73A), the upper side (73A) optionally having at least the dimensions of the underside (7A). Depth scan measurement system according to one of the Claims 1 until 8th , wherein the underside (7A) can be positioned on the support support structure in such a way that a surface area of the calibration body (77) which can be optically detected with the depth scanning measuring device (1) is arranged within the measuring opening (9) and the calibration body (77) is preferably no more than 0, 1 mm away from the bottom (7A). Depth scan measurement system according to one of the Claims 1 until 9 , wherein the calibration unit (71) has at least one stop (83) to support the positioning of the depth scanning measuring device (1) on the support support structure, the at least one stop (83) being arranged at a distance from the calibration body (77) in such a way that when Contacting the at least one stop (83) with the depth scanning measuring device (1), the calibration body (70) can be positioned in the cutout (49) of the object plane (41) of the depth scanning measuring device (1). Depth scanning measuring device (1) for examining a surface structure of a sample extending in a plane, comprising: a housing (5) with a base plate (7) which has a bottom (7A) and a measuring opening (9), the bottom (7A) serving as a flat bottom surface for placing the depth scanning measuring device (1) on the sample (3) to be examined. is trained, an image data acquisition unit (11), which has an image sensor unit (13) with a two-dimensional pixel arrangement (13A) that defines an image plane (14), and an optical scanning device (17) with a lens unit (19) that defines an object plane (21). an adjustable depth distance to the image plane (14) and which is designed to image a section (49) of the object plane (21) onto the two-dimensional pixel arrangement (13A), wherein the image sensor unit (13) and the lens unit (17) are arranged and designed in the housing (5) with respect to the base plate (7) in such a way that the cutout (49) of the object plane (21) is along the underside (7A) and outside of the Measuring opening (9) extends, and a control unit (23) which is connected to the image sensor unit (13) for receiving image data and to the optical scanning device (17) for adjusting the depth distance and which can be connected to an image evaluation unit (25) for outputting the image data, wherein the control unit (23) is further set up to set a plurality of depth distances sequentially and to receive image data of the section (49) of the object plane (21), the depth distance in a calibrated depth scanning range (51) from 0 mm to at least 0, 5 mm can be changed step by step by a depth increment (ΔT). Depth scanning measuring device (1). Claim 11 , wherein the lens unit (19) has a liquid lens (19A) with an adjustable focus length, the focus length being adjustable in a range of at least ±0.25 mm, in particular at least ±0.5 mm or at least ±1 mm, and wherein the adjustable focus length is in particular in a range of 5 mm to 10 mm. Depth scanning measuring device (1). Claim 11 or 12 , wherein the control unit (23) is further set up to - supply the liquid lens (19A) with a supply voltage or a supply current for adjusting the focus length and - to change the focus length step by step by changing the supply voltage or the supply current by a supply increment, and /or wherein the control unit (23) further comprises a memory (23A) in which a calibration parameter is stored, which assigns the depth increment (ΔT) to the supply increment. Depth scanning measuring device (1) according to one of the Claims 11 until 13 , wherein the image sensor unit (13) further comprises a mounting edge (13B) which surrounds the pixel arrangement (13A), and wherein the optical scanning device (17) further comprises - an outer tube (43) which is attached to a sensor-side end of the outer tube (43). is attached to the image sensor unit (13) and has an inner support surface (43A) directed into the interior of the outer tube at an object-side end, and - a spacer tube (41) with a sensor contact surface (41A) for resting on the mounting edge (13B) on a sensor-side End and an outer support surface (41B) directed towards the inner support surface (43A), and wherein the lens unit (19) is mounted between the inner support surface (43A) and the outer support surface (41B) and the outer tube (43) over the lens unit (19) and the spacer tube (41) is placed so that the lens unit (19) is positioned at a lens distance from the image plane (14) predetermined by a length of the spacer tube (41). Depth scanning measuring device (1) according to one of the Claims 11 until 14 , wherein the image sensor unit (13) is attached via a first holder (22A) at a fixed distance from the base plate (7) and the lens unit (19) is attached to the base plate (7) via a second holder (61) at a predetermined distance Lens distance from the image plane (14) is held and positioned. Depth scanning measuring device (1) according to one of the Claims 11 until 16 , further with at least one light source (55) for illuminating the section (49) of the object plane (21), the at least one light source (55) being arranged in particular on the object side on the lens unit (19). Calibration unit (71) comprising a support support structure that defines a support plane as a reference plane for the depth scanning measuring device (1), a support surface (75A) which is offset from the support plane by at least the calibrated depth scanning area (51), and a calibration body (77) which is arranged on the support surface (170A) and forms at least part of a calibration structure which comprises an upper surface section and a lower surface section, the upper surface section and the lower surface section being in a direction orthogonal to the support plane by a calibration distance (D) are spaced apart from each other, with the calibration distance (D) being given with an accuracy of 0.005 mm or less. Method for calibrating a depth scan measuring device (1) using a calibration unit (71), wherein the depth scan measuring device (1) and the calibration unit (71) according to a depth scan measuring system according to one of Claims 1 until 10 are formed, wherein the calibration unit (71) comprises a support support structure and a calibration body (77) which forms at least part of a calibration structure, the calibration structure comprising an upper surface section and a lower surface section and the upper surface section and the lower surface section are orthogonal in a direction are spaced apart from each other from the support plane by a calibration distance (D), the calibration distance (D) being given with an accuracy of 0.005 mm or less, with the steps: positioning the depth scanning measuring device (1) with respect to the support support structure of the calibration unit (71) in such a way that the calibration structure is arranged in a section (49) of an object plane (21) of the depth scanning measuring device (1), in a processor (23B) of the depth scanning measuring device (1): providing an upper target point in the upper surface section of the calibration structure and a lower target point in the lower surface section, Executing an autofocus algorithm for the upper target point and the lower target point, whereby the optical scanning device (17) is controlled for a stepwise adjustment of the position of the object plane (21) in the depth direction until the optical scanning device (17) reaches the upper one at an upper step value Surface section in the upper target point and at a lower step value the lower surface section in the lower target point is sharply imaged on the image plane (14), outputting the upper step value of the step setting for the upper target point and the lower step value for the lower target point, and determining a step value difference between the upper step value and the lower step value, calculating a depth increment (ΔT) associated with a step of the optical scanning device in stepwise adjustment of a depth distance value by comparing the step value difference with the calibration distance (D), and outputting the depth increment (ΔT) as a calibration parameter. Procedure according to Claim 18 , wherein the upper surface section is in the area of a top point of the calibration body (77) and the lower surface section is in the area of a support surface (75A) on which the calibration body (77) is arranged, further comprising the steps: acquiring image data of the calibration body ( 77) and the support surface (75A) next to the calibration body (77) with the depth scanning measuring device (1) and optionally displaying the image data on a display (27), using an operating interface (29) of the depth scanning measuring device (1) or automatically using an image processing algorithm, selecting a first pixel of the displayed image data on the upper surface portion, and a second pixel of the displayed image data on the lower surface portion, and reading the first pixel as the upper target point and the second pixel as the lower target point into the processor (23B) for executing the autofocus algorithm each for the upper target point and the lower target point. Procedure according to Claim 18 or 19 , wherein the lens unit (19) of the depth scanning measuring device (1) has a liquid lens (19A) with an adjustable focus length, further comprising the steps: adjusting the focus length, the liquid lens (19A) with a supply voltage or a supply current, and changing the focus length for gradual adjustment the position of the object plane (21) in the depth direction by gradually changing the supply voltage or the supply current by a supply increment, whereby the output Calibration parameter assigns the depth increment (ΔT) to the supply increment.

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