Apparatus for inspecting components of transparent material as to surface defects and inclusions

The present invention relates to a device according to the preamble of claim 1.

Components made of transparent material, for example, optical or ophthalmic lenses must be tested prior to use for errors, particularly surface defects such as scratches, wiper, cracks, dig, stains and inclusions such as bubbles or streaks. Such errors would reduce the usability of a lens if they exceed the specified in DIN 3140 limits.

Typically, the testing of optical components is carried out as a visual inspection by humans. Such an assessment must be carried out in a largely darkened room. It is expensive, not reliable enough not sufficiently objective and because of the high monotony of testing procedures.

It has therefore endeavored to develop methods and devices for automatic, objective testing of optical components.

From DE-OS 32 37 511 it is known to bring test optical components in the optical beam path of a television camera and through the component a test pattern imaged on the camera. The induced errors in the component faults lead to a video signal, which differs from the non-affected by the component desired signal. From the deviation from the desired and actual signal is Closed to the error en. An operating according to this method apparatus is quite complicated and can minor faults, not to recognize, for example, by scratches, wiper or hairline cracks.

In order to increase the sensitivity of the test procedure, it is proposed in DE-OS 30 11 014, the component to be tested to light as a whole, to produce a television image and to analyze the video signal line by line. This method is not sufficiently precise.

An even older proposal for a test method can be found in DE-OS 23 37 597. There, a light beam is focused onto the surface of the component to be tested and is point-like moves while maintaining its focus state on the surface. The light passing through the component light is reflected, passes again through the component, and then falls on a detector. Variations in the intensity of the receiver signal make it possible to infer a fault and to locate these also.

An operating according to this method is very expensive device. It only allows the examination of the surface of the workpiece to which the scanning beam is focused.

GB-A-2085579, it is assumed that the in the preamble of patent claim 1, allows the detection of defects in the upper and lower surfaces of transparent plates. In an apparatus described therein, a laser beam on one of the surfaces of the plates and is focused the scattered light as a result of errors is detected by a laser beam which is arranged inclined to the direction of the optical imaging device. This includes an aperture that is either as a mask for detecting the scattered light from defects in Plattenober- or plate underside. Thus it is possible with sufficiently thick plates to detect either the top or bottom fault, since the scattered light from defects of the other side of the plate is hidden by the pinhole. With very thin plates that isolation does not work anymore. To remedy this shortcoming and to simultaneously investigate both panel tops, is the use of two laser beams proposed in this document, each of which is focused on a disk surface, which is scanned with the beam. The purpose described arrangement, however, is quite expensive and also does not allow the detection of faults in other levels of the plate. The device is specifically designed for sheet-like transparencies.

It is the object of the present invention to provide an apparatus for testing components of transparent material for surface flaws and inclusions that enables reliable detection of such errors in one or more pre-selected planes or surfaces of the component.

This object is achieved by a device, whose structure is indicated in the characterizing part of claim 1.

The inventive device is characterized in that the component to be tested is rotatably disposed and is rotatively scanned about its axis in the diameter direction of a linear moving light beam. Furthermore, the inclination of an imaging device relative to the incident direction of the illumination beam can be preselected and the mask for separating the image of a plane of the test piece is interchangeable.

In the apparatus according to the invention, a light-section is generated by the component to be tested by the scanning light beam. This light-section is imaged by the serving for signal acquisition means, for illustration only, the light is used, which is deflected by error in the component. The angle formed by the optical axis of this device, with the rotational axis of the component is advantageously adjustable. It can be, depending on the deflection behavior of festzustellenden error between 10 and 60 °, with an angle of 40 ° has proved to be expedient. This allows scratches, hairline cracks and evidence of other, relatively sharp limited defects in the surface of the component.

In the apparatus according to the invention, provided in the image plane of the device for signal acquisition mask is used to separate the images from the back and front of the component to be tested. With an appropriate design of the masks also have a preferred inside the component level can be used for error detection.

The arrangement for evaluating the image signals generated can for example be designed as a monitor, practically a dark field image of the observed surface of the lens appear on the in which the errors are highlighted.

It can also automatically operating arrangement can be provided, detects the error by certain criteria and those classified according to size, burst and place in accordance with DIN 3140, Part 2 and 7. FIG. Such an arrangement is for example the subject of the patent application EP-A-0249798 entitled "Method of testing components of transparent material for surface defects and inclusions", which was filed by the applicant on the same day as the present application. Such automatically operating device allows serial testing of optical components.

The claims 2 and 3 indicate a suitable embodiment of the device according to the invention, which allows the front and rear of the component separated or to check simultaneously.

It has proved advantageous to the device according to claim 4 form.

Failure of the component that are not sharp limited, scatter the incident light is not isotropic but strongly anisotropic in a narrowly restricted solid angle which can assume very large values. Such, not sharp limited surface defects are, for example wiper. These errors can be with the device, as previously described, generally not demonstrate. It is therefore particularly advantageous to design the device according to claims 5 to 7, that is an additional system to provide for signal generation.

The invention is explained below with reference to Figures 1 to 5 of the accompanying drawings. In detail:<dl id="dl0001"><dt>Fig. 1</dt><dd>an embodiment of a device according to the invention in principle representation;</dd><dt>FIG. 2</dt><dd>the embodiment of Figure 1 in a position rotated by 90 °.</dd><dt>Fig. 3</dt><dd>an embodiment of a device for signal acquisition;</dd><dt>Fig. 4</dt><dd>another embodiment of the apparatus of the invention in schematic representation;</dd><dt>Fig. 5</dt><dd>an example arrangement for generating evaluation signals.</dd></dl>

In Fig. 1, (1) a lens made of transparent material designated to be tested for surface flaws. This lens is placed in a turntable (2), which is rotated by the stepping motor (3).

For the illumination of the lens (1) is a laser (4), the parallel light beam (7) is used by a mirror scanner (5) within a predetermined solid angle is deflected linear. A converging lens (6) is arranged so that it coincides with a focal point of the fulcrum of the mirror scanner (5). Accordingly, the deflected light beams are behind the lens (6) moved parallel to each other taken along a diameter of the lens (1) between the extreme positions (7a) and (7b). Such a lighting device is the subject of patent application EP-A-0249800 with the title "Apparatus for illuminating of components made of transparent material in the error check," which was filed on the same day as the present application by the Applicant.

The resulting light-section of the laser beam (7) with the lens (1) is observed by means of a device (8) which is arranged inclined to the axis of rotation of the lens (1). The tilt angle of the device (8) is chosen so that they, the surface defects of the lens (1) isotropic scattered light detects and maps via the imaging optical system (9), which is designed for example as a zoom lens, in the intermediate image plane (10) , In the intermediate image plane (10) a mask (11) is arranged which either the image of the front surface (12) or the image of the rear surface (13) of the lens (1) wegblendet. The mask (11) is arranged on a turntable in the housing (14). By means of a knob (15) the particular required mask (11) are pivoted into the beam path.

The mask (11) passing light is imaged by means of a relay lens (16) full-screen on a detector (17). The image signals generated by this be fed to an evaluation unit (18) shown schematically.

In bi-concave, bi-convex, plano-concave and plano-convex lenses (1) the mask (11) consists only of a straight edge. At concave-convex lenses in addition to a cutting mask still curved masks are required to both lens surfaces to be clearly separated.

With an appropriate design of the mask (11) between the surfaces (12) and (13) of the lens it is also possible to (1) select preferred level for signal acquisition. This level can then be checked for inclusions.

The detector (17) can also be designed as spatially resolving detector line. In this case, the mask (11) to be arranged displaceably in order to make a separation of the lens surfaces for evaluating a in the evaluation unit (18) used soft goods can.

Instead of the physical masks (11), it is also possible to use a mask whose optical transparency is controllable.

Instead of the means (8) for signal acquisition, such as shown and described in connection with FIGS. 1 and 2, a device can use, as shown for example in Fig. 3. This means (20) comprises a lens (21) which images the light section through the lens to be tested (1) in the intermediate image plane (22). Between the objective lens (21) and the intermediate image plane (22) is a beam splitter cube (23) is arranged, which deflects part of the light by 90 °. This redirected light is displayed in the second intermediate image plane (24). In the intermediate image plane (22) a replaceable mask (25) is arranged, which hides example the image of the front surface (12) of the lens (1). Also in the side branch of the device (20) a mask (26) is disposed in the intermediate image plane (24), which hides example the image of the back surface (13) of the lens (1). The to the masks (22) and (24) passing by light is imaged by relay lenses (26) and (27) shown schematically on detectors (28) and (29).

The device (20) can also be formed by provision of a further beam splitter cube so that it enables the reception of three evaluation signals from three different surfaces or planes of the lens (1) simultaneously.

In the embodiment of the novel apparatus shown in Fig. 4, two means (30) and (31) for signal acquisition are provided which are arranged symmetrically to the axis of rotation of the lens (1). The two bodies (30) and (31) may be formed 3 example of FIG.. By this means it is possible to detect surface defects of the front and back of the lens (1), which are relatively sharp limits and the isotropic scatter light. Such errors are, for example, scratches and crazing. As problematic cases surface defects have been found, in which the surface is only lightly pressed. Such errors are known as wiper. It has been found that wipers can scatter light strongly anisotropic namely accept only in a narrow solid angle, the large values. In order to detect these surface flaws, a so-called integral optics is provided, which consists of a hemisphere (32). this hemisphere plurality of bores (33) are distributed into each of which a small imaging lens and a downstream detector are used. Each detector has an associated adjustable pre-amplifier and the signals from all detectors of an array (34) supplied, which forms therefrom a signal that is comparable in strength to the signals which provide the means (30) and (31). All signals, that the signals of the means (30) and (31) as well as signals of the array (34) are together fed to an assembly (35), which is used for electronic signal processing.

It is also possible to arrange in each case only one imaging lens which supplies the incident light an incoherent light beam (36) in the bores (33) of the half-shell (32). All these light beams lead together to a detector, which, instead of the arrangement (34) of FIG. 4 is provided.

The means (30) and (31) can distinguish between the signals which are associated with the front or back of the lens (1). This may not be the integral appearance of the hemisphere (32). It is therefore necessary to make a signal combination of all signals fed to the evaluation arrangement (35). Since at all times the outputs of the receiver can be queried on coincident events by the pointwise scanning, an assignment of the recorded in the integral receiver information on the individual lens sides can take place as long as at least some of the pixels are detected in the bodies (30) and (31) ,

In the embodiment of Fig. 5 is a plan view of the evaluated lens (1) is shown, which is rotated in the arrow direction and which is to scan by the laser light beam (7) in direction of a diameter. The resulting light section is observed by means of a device (8), as shown in FIG. 1. For reasons of clarity only one such device for signal extraction is illustrated.

The turntable (2), in which the lens (1) is centered, is provided with a mark (40), which is detected by a receiver (41). The signal from the receiver (41) marks the beginning of the image and, after actuation of the switch (42) for switching of the rotation motor (3) via an AND-gate an arrangement (44) is supplied, which starts the image recording. Of the assembly (44) the signals pass to a line counter (45), at the output line (46) of the row clock is applied. The line counter (45) is controlled by a motor-pulse generator (47) and a divider (48).

With the turntable (2), a further receiver (49) cooperates, which generates a signal at the beginning of a line, which is supplied to an AND gate (50). This AND-gate, a further signal which is controlled by the pixel clock (52) fed via a pixel counter (51). At the starting line (53) of the AND gate (50) then lies on a pixel clock signal.

The pixel counter (51) controls a generator (54) for the scanner function, ie for the movement of the scanner mirror (5). Over the assembly (54), the scanner controller (55) is actuated which moves the scanner (5).

At the output (56) of the device (8), the video signal is present. The signals on the lines (46, 53, 56) to be a receiver (57) supplied showing a monitor image of the selected area of ​​the lens (1). On this monitor screen surface error of the lens (1) are light, while the non-faulty areas remain dark.

Instead of the pictorial evaluation on the monitor (57) can also be an arrangement for electronic image evaluation can be provided as described in the patent application EP-A-0249798 with the title "A method for testing of parts made of transparent material for surface defects and inclusions", and is shown, which has the same filing date as the present application.