GB2093987A

GB2093987A - Photo-electric determination of dimensions and surface quality

Info

Publication number: GB2093987A
Application number: GB8200187A
Authority: GB
Original assignee: VE WISSENSCHAFTLICH TECH BETRI; VE WISSENSCHAFTLICH TECHNISCHER BETRIEB KERAMIK
Current assignee: VE WISSENSCHAFTLICH TECH BETRI; VE WISSENSCHAFTLICH TECHNISCHER BETRIEB KERAMIK
Priority date: 1981-01-29
Filing date: 1982-01-05
Publication date: 1982-09-08
Also published as: DE3146834A1; DD157828A1; IT8247672A0; IT1150371B; GB2093987B

Abstract

To obtain reproducible values relating to the geometry and surface quality of objects 2 such as fine ceramics, are transported between vertical and horizontal optical scanning devices 4.2 and 4.1, the data obtained being compared with preselected values in order that the objects can be allocated to appropriate quality categories. Different views of the objects are focussed onto line sensors 4.1 and 4.2 as the objects are moved past by a driving system 9. A pulse transmitter is connected to the driving system to synchronise the scanned signals with the movement of the objects. A microprocessor calculates the actual dimensions of the objects from the geometry of the system and compares these with ideal values. Surface flaws of different reflectivity are also distinguished and their positions calculated. <IMAGE>

Description

SPECIFICATION Measuring apparatus and process for contactless geometry and surface quality testing The invention relates to a measuring device and a process for contactless testing of geometry and surface of bodies having a light coloured surface, particularly of white fine ceramic products. The measuring device and the process enable characteristic values of geometry and surface quality to be determined without contact during the passage of the body through the apparatus. The values thus found are evaluated mathematically by mechanical means, so that the body tested can be ailocated to the appropriate quality category by comparing it with preselected qualitative criteria.

Geometrical measurements on bodies have generally been- iimited to a certain product and are usually evaluated by analog measurements.

Pneumatic or mechanical rolling or scanning devices are generally used for this purpose.

Optical-mechanical methods are known which carry out measurements on bodies by scanning them with a beam. These processes all require precision mechanical apparatus.

Measuring devices and methods are also known for simultaneously determining, without contact, the height and parallelism of bodies passing through them.

In further apparatus rotating or oscillating mirrors are employed which supply receivers with light impulses from the object to be measured.

In the fine ceramics industry all products have to be classified in terms of quality. The quality category determines the price group to which the product is allocated.

All tests required for determining the quality have so far been carried out visually and manually. These testing methods frequently lead to subjective errors, and the measuring operation can be easily manipulated.

The purpose of the invention is to eliminate the visual test and consequent strain on the operators involved and not only to render the task easier but also to ensure increased efficiency and to eliminate errors in subjective testing procedures.

It is of particular interest for fine ceramic products such as plates, bowls and cups to be tested. Any other desired products can similarly be tested, provided their geometrical shape is simple to describe mathematically and flaws in the surface can be clearly seen against its light colour.

The criteria adopted to classify quality of fine ceramic products are the deformations present in the edges and the number and size of any spots on either side of the surface.

According to one aspect of this invention there is provided a measuring apparatus for contactless testing of the geometry and surface quality of bodies such as fine ceramic products comprising a horizontally positioned projection device and a vertically positioned projection device, the optical axes of which intersect on or above a product transport plane to form a measuring plane, the projection devices being positioned such that the centres of specimen products can pass continuously through the centre of the measuring plane.

The body to be tested, which must stand out distinctly against the background, is transported at a defined speed along the transport plane and through the measuring plane.

Each projection device contains a lens system and by means of which, on the image side, an image is produced of the view presented by the specimen in each case on the receiving side of photo-electric converter, which is capable of effecting raster definition of the content of the image and also conversion proportional to the brightness.

According to a second aspect of this invention there is provided an apparatus incorporating two horizontally positioned projection devices located symmetrically about a common optical axis which is parallel to the product transport plane and/or coincides therewith, and two vertically positioned projection devices located on a common optical axis which is perpendicular to the horizontal optical axis, the said optical axes intersecting on or above the product transport plane.

The linear image situated in the measuring plane in each case is recalled cyclically and in synchronism with the relative movement of the sample existing in respect of the measuring plane, as an electrical pulse telegram of constant length, by all the converters mounted in the measuring plane, and conveyed to a central evaluation device, where the individual projections are combined in such a way that the true magnitudes of the specimen in the horizontal and vertical direction are determined and, after the passage of the specimen through the measuring plane, conveyed to an over-all evaluation unit, the specimen being qualitatively classifiable after it has been identified and also compared with preselected limit values.

The pulse telegrams are also used for the purpose of detecting and localizing deviations of the colour in the surface from the basic colour of the specimens and conveying these deviations, after passage of the specimen through the measuring plane, to an over-all evaluation unit in which the dimensional ratios of the colour deviations detected, mainly consisting of visible spots, are evaluated and taken into account in the qualitative classification.

On the basis of the electronic evaluation the qualitative classification of the specimens can be rendered more precise by taking account of results obtained in other tests, such as additionally scanned mechanical magnitudes of deformed bases and/or sound-emission or infrared measurements for detecting cracks or surface flaws of the "relief" type.

By way of example only references will now be made to the accompanying drawings, illustrating an embodiment and in which: Figure 1 is a schematic section from the front view of the measuring and transport device with horizontally and vertically positioned projection systems, Figure 2 is a plan view of the measuring and transport device, Figure 3 is a view in perspective of the measuring and transport device with horizontally and vertically positioned projection systems in the measuring plane, and Figure 4 is a diagram indicating the magnitudes required for the calcuiation of the actual dimensions.

Referring to Figured 1 to 3, the specimen 2, a fine ceramic flat dish, is moved on the transport system 1 through the measuring plane 6. The measuring plane 6 contains two horizontal projection systems consisting of optical units 3.1 and photo-sensitive line sensors 4.1, the common optical axis 5.1 of which is on a level with the supporting surface of the specimen 2. Two vertical projection systems are also provided with the optical units 3.2 and the photo-sensitive line sensors 4.2, of which the common optical axis 5.2, off-set in respect of the optical axis 5.1 by an angle of 900, passes through the median line of the transport plane 7 and intersects the optical axis 5.1 at the same point.

The projection systems, which in the simplest embodiments are constructed on the principle of the pin hole camera but are nevertheless equipped with optical lens systems and diaphragming devices for greater light efficiency, contain photo-sensitive electronic sensors in the image plane with raster elements arranged in lines being in the form of known electronic camera tubes or equivalent semi-conductor components which are capable of converting the brightness of a line of the projected image into electrical voltages proportional thereto.

When the electrical voltages of each line of the photo-sensitive line sensors 4.1 and 4.2 are recalled in synchronisation, under the control of an interval pulse transmitter 8, an electrical pulse diagram of constant length is produced which reflects the scaled geometrical proportions of the specimen 2, which are shown in the projection perspective, and from which diagram, by means of known mathematical inter-relationships, the actual geometrical dimensions of the specimen 2, required for mechanical evaluation by electronic arithmetic circuits can be calculated, preferably by the use of micro processor technique.

The synchronism, required for the measurement, between the acquisition of pulses for the brightness values and the speed at which the specimen 2 passes through the system is ensured by the pulses supplied by the interval pulse transmitter 8, while the drive of the transport system 1 and thus the further transport of the specimen 2 are effected by a driving system 9 of which the rotation speed is regulated.

Figure 4 shows the magnitudes required for the mathematical evaluation. The meanings of the symbols are as follows: E, and E2=distance of central point of optical unit from the intersection point of all optical axes.

e1 and e2=distance of central point of optical unit from image plane.

A, B = actual dimensions of the specimen.

a, b = the dimensions A and B shown in the image plane.

The intersections of the two extrerne measuring lines, i.e. the points at which a transition from dark to bright or vice versa takes place on the edge of the specimen, from the two projections off-set in relation to each other by an angle of 900, contain the two magnitudes required in the horizontal and vertical directions.

From the two basic equations a(E1-B) A= e, and bE(2-A) B= e2 it is possible to determine the dimensions of the specimen. These equations, however, only apply to the pin-hole camera and to so-called "thin lenses". If "thick lenses" are used the result has to be corrected with constants appropriate to the lens system employed.

These mathematical inter-relationships are processed, after each scanned iine, by known computer technique, but preferably by electronic micro-processor technique, in order to obtain, in the result, the actual values of the dimensions of the specimen 2. The lines scanned and the dimensions A and B calculated are evaluated on the basis of a continuous transport of the specimen 2 through the measuring plane 6. After the entire specimen 2 has passed through the apparatus all the absolute dimensions are available and a comparison can be made with the preselected ideal demensions of a comparison specimen, in order to allocate the test specimens to preselected quality categories.

As each point to be measured is taken up by two images 900 apart and defined in the evaluation, displacements of the specimen 2 from the median line of the transport plane 7 are automatically compensated. The pulse diagrams formed by the projected images contain not only the dimensions of the outer edges of the specimen 2 but also information on the quality of the surface, particularly details on brightness differences which occur in the form of spots. The position and size of the spots are determined by known electronic evaluation processes in which each scanned line of which the pulse telegram contains the brightness value of each point in the scanned line, is examined in the zone of the surface of the specimen 2, as regards brightness differences and their length.The position of the spot in each line is stored by means of suitable known electronic storage processes until the entire specimen 2 has been scanned, after which the entire faulty surface and its geometrical position on the specimen 2 are determined by known electronic evaluation methods.

In the subsequent over-all evaluation all the criteria measured and calculated and any which do not originate from this invention are compared with required values which correspond to the ideal values for the specimen 2, with their permissible tolerances, and evaluated by known methods, preferably the electronic micro processing technique, and indicated in the form of a control signal for an automatic qualitative classification.

The device is suitable, without mechanical conversion, for testing a wide variety of products, provided they remain within dimensional ranges which do not go beyond the imaging plane and their surface shows a distinct contrast against the background. All that is required is data and materials specific to the product in question. The change-overfrom one type of specimen to another requires very little time in comparison with the testing time obtainable.

The testing time and, on this basis, the efficiency of the process covered by the invention is governed first and foremost by the operating speed of a micro processor used and also by the required number of raster elements per line. If the clock frequency of the micro processor is 2.5 MHz for the logic part, in accordance with the present state of technical progress, this being at the same time used for recalling the brightness values of the line rasters, it is found that with specimens of 250 mm in diameter and 125 mm in height, and with a resolution of up to 0.5 mm, corresponding to 500 raster elements per line in the vertical projection systems and 250 raster elements in the horizontal projection systems, totalling 1 500 brightness values to be recalled, the scanning time per line is 0.6 ms, plus 0.2 ms required for the line evaluation. Provided the ratio of the length to the width of the specimen is 1:1, e.g.

with a concentrically shaped fine ceramic flat dish, the total testing time amounts to 400 ms per specimen. If it is also assumed that the clear distances between the specimens continuously conveyed to the measuring device by means of a conveyor belt correspond to the diameters of the specimens, 4500 such specimens can be tested per hour.

Claims

1. A measuring apparatus for contactless testing of the geometry and surface quality of bodies such as fine ceramic products comprising a horizontally positioned projection device and a vertically positioned projection device, the optical axes of which intersect on or above a product transport plane to form a measuring plane, the projection devices being positioned such that the centres of specimen products can pass continuously through the centre of the measuring plane.

2. An apparatus according to Claim 1, incorporating two horizontally positioned projection devices located symmetrically about a common optical axis which is parallel to the product transport plane and/or coincides therewith, and two vertically positioned projection devices located on a common optical axis which is perpendicular to the horizontal optical axis, the said optical axes intersecting on or above the product transport plane.

3. A process for contactless testing of the geometry of bodies such as fine ceramic products by electronic and data processing means by using conversion processes for converting the projections in the form of lines into electrical voltage images, which images are recalled in the form of constant length impulse telegrams directly related and dependant upon the image resolution and thereby the transport speed, said telegrams being conveyed to a central electronic evaluation unit, the individual projections being combined together such that the true magnitudes of the specimen in the horizontal and vertical directions are determined in the relevant measuring plane and after passage of the specimen through the measuring plane the true magnitudes are subjected to an over-all evaluation and are used after identification and comparison of the specimen with preselected limit values to allocate the specimens to appropriate quality categories.

4. Process according to Claim 3, wherein surface quality of the specimens is tested by using the impulse telegrams to determine local deviations in the colour of the specimen from the basic colour, localising these deviations and after passage of the specimen through the measuring plane, subjecting said deviations to an over-all evaluation process in which the dimensional ratios of the observed colour deviations which are mainly in the form of spots, are evaluated and used after comparison with preselected limit values to allocate the specimens to appropriate quality categories.

5. Process according to Claim 3 or 4, wherein after passage of the specimen through the measuring plane, the over-all evaluation can be effected in conjunction with other measuring values or signals such as additionally scanned mechanical magnitudes of deformed bases and/or sound emission or infra-red measurement for detecting cracks or surface flaws of "relief" type when such measurements are suitable for a complex assessment of the specimen.

6. A process for contactless testing of the geometry or surface quality of bodies substantially as herein described and illustrated in any of the accompanying drawings.

7. A measuring apparatus for contactless testing of the geometry and surface quality of bodies substantially as herein described with reference to and as illustrated in the accompanying drawings.