Device for measuring rotational test objects

Abstract

The invention relates to a device for measuring rotational test objects (1), in particular rims, comprising an image sensor unit for generating an image of the rotational test object (1), a support (4) for the rotational test object (1), said support defining a measurement region (3), and a control unit (5) for controlling the image sensor unit and the support (4). In order to facilitate a time-efficient and high-quality testing process of the rotational test objects (1), the invention proposes that the image sensor unit comprises two rotatably mounted 3D sensors (2) lying opposite each other with respect to the support (4) and that the support (4) can be moved between a release position and a fixing position for spatially fixing the rotational test object (1).

Description

[0001] Device for measuring rotating test objects

[0002] Technical field

[0003] The invention relates to a device for measuring rotating test objects, in particular rims, comprising an image sensor unit for generating an image of the rotating test object, a fixture for the rotating test object that spans a measuring range, and a control unit for controlling the image sensor unit and the fixture. Rotating test objects are defined as test objects that rotate during their intended use.

[0004] State of the art

[0005] From EP1830157A1, a device for measuring rims is known, comprising a receptacle for the rim arranged in a measuring area and an image sensor unit arranged opposite the receptacle for generating an image of the rim. To generate the image, the sensor unit can be aligned with the measuring area via linear guides. To generate an image of the rim, the receptacle is rotatably mounted, so that when the sensor unit is stationary during measurement, the surface of the rim facing the sensor unit can be imaged by rotating the rim. However, a disadvantage of this is that sufficient coverage of all safety-relevant test points, such as the bolt circle, the wheel hub bore, the screw holes, etc., is not possible.The rim must be positioned in different orientations within the camera, which necessitates a time-consuming measurement process due to both the realignment of the image sensor unit and the repositioning of the rim itself. Furthermore, the rotation of the rim introduces measurement inaccuracies, as tolerance-related irregularities in the rim introduce errors into the measurement during rotation. This necessitates extensive digital post-processing, particularly when inspecting safety-relevant test points.

[0006] The invention is therefore based on the objective of proposing a device for measuring rotational test objects, in particular rims, of the type described above, which enables time-efficient measurement of the rotational test objects despite high measuring accuracy.

[0007] Description of the invention

[0008] The invention solves the stated problem by providing an image sensor unit comprising two rotatably mounted 3D sensors positioned opposite each other with respect to the image capture area, and by allowing the image capture area to be moved between a release position and a fixation position for the purpose of fixing the rotating test object in a fixed position, particularly during measurement. According to the features of the invention, images, especially 3D images, can be simultaneously captured from both the top and bottom sides of the rotating test object during measurement, thus eliminating the need to turn or rearrange the rotating test object between multiple measurement cycles. A significant advantage is that both images are captured in the same fixed position of the rotating test object, so that digital post-processing to compensate for any alignment errors is unnecessary.Simultaneously, test points located on both sides, such as bores and the like, can be inspected from both the top and bottom sides of the rotating test object, further increasing the inspection quality. It has been found that the measurement accuracy can be increased primarily by statically fixing the rotating test object in a fixed position using the fixture located between the two 3D sensors (e.g., laser scanners or profile sensors operating on the principle of laser triangulation). This means that the rotating test object remains stationary during image acquisition by the 3D sensors, as the fixture is mounted without rotation. According to the invention, the scanning movement is achieved by rotating the 3D sensors, whose axis of rotation preferably runs parallel to the axis of rotation of the rotating test object.In a further preferred embodiment, the 3D sensors can be synchronized with respect to their rotation, so that the same image acquisition conditions prevail on both sides. It has been found that particularly accurate measurement results can be obtained when the 3D sensors are mounted around a common axis of rotation, preferably eccentrically rotatable around the axis of rotation. The common axis of rotation can be coaxial with the rotational axis of the test object.

[0009] In principle, the inspection quality can be improved, in particular, by comparing the images of the 3D sensors positioned opposite each other with respect to the rotating test object (one 3D sensor is located above the rotating test object or the fixture, and one 3D sensor is located below the rotating test object or the fixture). For this purpose, it is advantageous to obtain a reliable and meaningful image comparison if the 3D sensors are precisely calibrated with respect to their orientation and movement patterns. To further reduce the measurement time, especially during the calibration of the 3D sensors and their alignment with the rotating test object, it is proposed that the 3D sensors be rotatably mounted on a common, preferably C-shaped, support.In this way, the 3D sensors do not need to be individually controlled and aligned with the rotating test object, as simultaneous repositioning via the common carrier can occur. For this purpose, the carrier can preferably be mounted horizontally and / or vertically adjustable via a linear guide. Particularly if the carrier itself is rigid, i.e., it contains no moving parts, the alignment and calibration of the 3D sensors can be performed very quickly, since the 3D sensors essentially only need to be calibrated once on the rigid carrier, and the alignment can be performed via the carrier in relation to the rotating test object without changing the relative position of the 3D sensors to each other.In order to perform the calibration and alignment largely independently of external influences such as ambient temperature or process heat generated, the support can be made of a material with a coefficient of thermal expansion at T = 293.15 K less than or equal to 5*10. A -6 / K, preferably less than or equal to 3*10 A -6 / K, especially preferred less than or equal to 2.2*10 A The support can be manufactured using -6 / K technology. For example, the support can be made of CFRP. Regardless of the material, the support can be C-shaped. In such an embodiment, the 3D sensors can be arranged on the facing sides of the end legs of the C-shaped support.

[0010] To automate the loading of the measuring device without compromising the measurement quality, particularly of the 3D sensor located below the fixture, a conveyor system can be used to transport the rotating test object into and out of the measuring area. This conveyor system must be free of any obstructions within the 3D sensors' field of view during measurement. The conveyor system should be designed so that no component of the conveyor system obstructs the 3D sensors' field of view of the rotating test object during measurement. However, it is only essential that the field of view remains unobstructed during measurement; therefore, components of the conveyor system may be present within the 3D sensors' field of view during transport or other process steps.For example, movable components of the conveyor can be temporarily moved into the field of view, as long as they are located outside the field of view during the measurement. A conveyor that remains free of obstructions in the field of view during measurement can be achieved by having the conveyor comprise two conveyor belts positioned opposite each other with respect to the measuring area. The spacing of the conveyor belts creates an unobstructed space within the conveyor, allowing the 3D sensors' field of view, aligned with the measuring area, to pass through it without hindrance. The conveyor belts run parallel to each other.The rotating test object can therefore rest with one edge section on the first conveyor belt and with the other edge section on the second conveyor belt, so that, due to the spacing or opposing position of the conveyor belts with respect to the measuring area, the underside of the rotating test object is also freely accessible and the relevant test points can be imaged by the lower 3D sensor. The conveyor belts are preferably driven synchronously. The normal distance between the conveyor belts can be 50 to 120 cm, preferably 70 to 100 cm, and more preferably 75 to 90 cm. The measuring area can be considered the area accessible to the field of view of the 3D sensors.

[0011] In principle, the scanning of the relevant rotating test object surface is achieved by a rotational movement of the 3D sensors, while the rotating test object itself remains stationary or fixed in space. Such fixation can be achieved by having a rotationally free-mounting fixture with two adjusting elements that can be positioned against the rotating test object. Specifically, the adjusting elements are designed to be positioned against the rotating test object's outer surface, thus allowing the measuring area to remain free of obstructions. This clamps the rotating test object, ensuring secure fixation. Particularly with rotating test objects, it has proven advantageous for the adjusting elements to include adjusting rollers. For example, two adjusting elements that can be moved relative to each other, each comprising two adjusting rollers, can be provided.

[0012] While the shared support structure can reduce the need for recalibration of the 3D sensors, recalibration may still be desirable, especially during long measurement cycles with a large number of rotating test objects. To make calibration more time-efficient, it is proposed that the device include a reference object that can be moved into and out of the 3D sensors' field of view, with its reference dimensions stored on the control unit. If necessary, the reference object can be moved into the field of view between measurement cycles and scanned by the 3D sensors. If there is a discrepancy between the dimensions recorded by the 3D sensors and the reference dimensions stored on the control unit, recalibration can be performed. This can be initiated by the control unit, for example, using the least squares method or the ICP algorithm.The reference object can, for example, be positioned so that it can be moved between the conveyor and thus into the field of view. A plate with integrated reference structures has proven to be a suitable reference object. Advantageously, the reference object has a coefficient of thermal expansion at T = 293.15 K of less than or equal to 5*10. A -6 / K, preferably less than or equal to 3*10 A -6 / K, especially preferred less than or equal to 2.2*10 A -6 / K. The reference object can be made of CFRP, for example.

[0013] Regular cleaning steps are required on the rotating test object before measurement. This can leave liquid residues on the rotating test object, which in turn can contaminate the 3D sensors. To prevent these liquid residues and other contaminants that may arise during the production process from negatively impacting the measurement quality, a preferred embodiment of the device according to the invention recommends that the device include a cleaning unit for cleaning the rotating test object and / or at least one of the 3D sensors. The cleaning unit can be a blow-off device, particularly one equipped with compressed air. The cleaning unit is preferably assigned to and directed towards one or both of the 3D sensors.

[0014] A device according to the invention can be used in a method for measuring rotating test objects, in particular rims. In this process, a rotating test object is arranged in a measuring area, fixed by a fixture within the measuring area, and, with the rotating test object stationary, a top and bottom image of the rotating test object is captured by rotating 3D sensors positioned opposite each other with respect to the fixture. The rotating test object is then released from the fixture and removed from the measuring area. After a predefined number of measurement cycles, a reference object with known reference dimensions can be moved into the field of view of the 3D sensors. The 3D sensors then capture the image of the reference object, compare the image with the stored reference dimensions, and calibrate the 3D sensors based on the detected deviations. The comparison and calibration can be performed by a control unit.The known reference dimensions may be stored on the control unit. Calibration can be performed using the "least squares method" or the "ICP algorithm".

[0015] Brief description of the invention

[0016] The invention is illustrated in the drawing as an example. It shows

[0017] Fig. 1 is a perspective view of the device according to the invention and Fig. 2 is a side view of the device according to the invention.

[0018] Ways to implement the invention

[0019] As can be seen in Figures 1 and 2, a device according to the invention for measuring rotating test objects 1 has an image sensor unit comprising two 3D sensors 2, which are mounted opposite each other and rotatably relative to a receptacle 4 that defines a measuring area 3 for the rotating test object 1. This means that the receptacle 4 is arranged between the 3D sensors 2, such that one 3D sensor 2 is located above the receptacle 4 and the rotating test object 1 arranged in the receptacle 4, and one 3D sensor 2 is located below, which enables imaging of the top and bottom sides of the rotating test object. The receptacle 4 can be moved between a fixed position, in which the rotating test object 1 is statically held, and a release position, in which the rotating test object can be removed from the measuring area 3. A control unit 5 is provided for controlling the 3D sensors 2, the recording device 4 and for any necessary calculation steps.During the measurement process, the 3D sensors 2 rotate, but not the rotational test object 1 or the recording device 3, which allows for a more accurate measurement.

[0020] The 3D sensors 2 can be rotatably mounted on a common, C-shaped support 6, preferably made of CFRP, which is height-adjustable via a linear guide 7. The linear guide 7 can be arranged on an I-beam 8. A safety device, designed as a light barrier 9, can be provided on the support 6 accommodating the 3D sensors 2. This safety device can be used to detect the presence of a rotating test object 1 and can be signal-connected to the control unit 5. Preferably, the 3D sensors 2 are rotatably mounted eccentrically about a common axis of rotation 10.

[0021] A conveyor 11 can be used to feed the device. To avoid obstructing the field of view 12, particularly that of the 3D sensor 2 located below the mount 4, the conveyor 11 can be free of any components obstructing the field of view 12 of the 3D sensor 2 during measurement. For this purpose, the conveyor 11 can be equipped with two conveyor belts 13 opposite each other with respect to the measuring area 3. These belts are preferably parallel to each other, spaced apart, and synchronized by their drives. The spacing of the conveyor belts is transverse to the conveying direction.

[0022] According to the embodiment shown in Figures 1 and 2, the receptacle 3 can comprise two adjusting elements 14 that can be moved towards and away from each other, so that they can be positioned against the rotating test object 1 on their outer surface. Preferably, the adjusting elements 14 each have two adjusting rollers 15 whose axis of rotation is parallel to the axis of rotation of the rotating test object 1. For calibrating the 3D sensors 2, a reference object 16 can be provided that can be moved into and out of the field of view 12 of the 3D sensors 2 and is preferably arranged to be movable between the conveyor belts 13. If necessary, this reference object 16, which may be designed as a plate, for example, can be moved into the field of view 12 and then moved out of the field of view 12 again before the actual measurement of the rotating test object 1, in order to allow free access to the 3D sensors 2.The reference object 16 can comprise reference structures R whose reference dimensions are known and, for example, stored on the control unit 5. To clean the 3D sensors 2, in particular the lower 3D sensor 2, a cleaning unit 17 can be used, as can be seen particularly in Fig. 2. This unit is directed at the 3D sensor 2 and can remove any residues and contaminants from it. This is preferably done using compressed air.

Claims

Patent claims 1. Device for measuring rotational test objects (1), in particular rims, comprising an image sensor unit for generating an image of the rotational test object (1), a receptacle (4) for the rotational test object (1) that spans a measuring area (3), and a control unit (5) for controlling the image sensor unit and the receptacle (4), characterized in that the image sensor unit comprises two rotatably mounted 3D sensors (2) opposite each other with respect to the receptacle (4), and that the receptacle (4) is movable between a release position and a fixation position for fixing the rotational test object (1) in space.

2. Device according to claim 1, characterized in that the 3D sensors (2) are rotatably mounted on a common, in particular c-shaped, carrier (6).

3. Device according to claim 2, characterized in that the carrier (6) is mounted horizontally and / or vertically adjustable over a linear guide (7).

4. Device according to one of claims 1 to 3, characterized in that a conveyor (11) which is free of installations during measurement in the field of view (12) of the 3D sensors (2) is provided for transporting the rotational test object (1 ) into and out of the measuring area (3).

5. Device according to one of claims 1 to 4, characterized in that a conveyor (11) with two conveyor belts (13) opposite each other with respect to the measuring area (3) is provided for transporting the rotational test object (1) into and out of the measuring area (3).

6. Device according to one of claims 1 to 5, characterized in that the receptacle (4) has two adjusting elements (14) which can be adjusted against the rotational test object (1).

7. Device according to one of claims 1 to 6, characterized by a reference object (16) that can be moved into and out of the field of view (12) of the 3D sensors (2), the reference dimensions of which are stored on the control unit (5).

8. Device according to one of claims 1 to 7, characterized by a cleaning unit (17) for cleaning the rotational test object (1) and / or at least one of the 3D sensors (2).

9. Method for measuring rotational test objects (1), in particular rims, characterized in that a rotational test object (1) is arranged in a measuring area (3), fixed by a receptacle (4) in the measuring area (3) and, with the rotational test object (1) stationary, a top and bottom image of the rotational test object (1) is captured by rotating 3D sensors (2) opposite each other with respect to the receptacle (4), after which the rotational test object (1) is released from the receptacle (4) and removed from the measuring area (3).

10. Method according to claim 9, characterized in that after a predefinable number of measurement cycles a reference object (16) with known reference dimensions is moved into the field of view (12) of the 3D sensors (2), after which the 3D sensors (2) capture the image of the reference object (16), the image is compared with the stored reference dimensions and the 3D sensors (2) are calibrated depending on the detected deviations.

Images