FR2499269A1 - Image data acquisition appts. for industrial quality control - uses laser scanning of sample surface with focussed image data provided by sensors for comparison with reference - Google Patents

Abstract

The arrangement utilises back lighting of the sample and focusses an image onto a scanning plane. The image is either in the form of a shadow where for example a mesh or photographic mask is being inspected or a diffraction pattern where a transparent object is being inspected. Digital information is generated by the analogue to digital conversion of the output from a light sensitive element which is moved systematically over the area of the image plane. Alternatively, a table of values can be obtained from an array of light sensitive elements fixed in the area of the image plane. A constant reference signal is obtained from the light source using a semi-silvered mirror. The light is provided by a laser.

Description

The invention relates to a set of high resolution image acquisition for exploitation
industrial by computer means, in particular for the automation of quality controls.

 This set was designed more particularly to 'transmit to a computer unit the details of the optical FOURIER transform of a given non-opaque object whose very high dynamics exclude the use of conventional acquisition systems such as cameras.

 The products to be analyzed in an industrial environment, for example at the end of the production line, appear more and more frequently at the level of quality control in the form of images due to the distance from the operating system, severe local conditions (temperature, chemically charged atmosphere, etc.) but also for reasons of convenience or any other.

 In order to be able to efficiently use the information contained in these images industrially, it is necessary to have upstream of the computer processing means a set of image acquisition which will convert a sufficient volume of purely optical information into digital data.

 Depending on the size of the volume of information supplied to the computer, it will be possible to develop more or less efficient chains of automation and thus solve, by automation, a multitude of industrial difficulties.

 The camera analysis systems currently in existence do not make it possible to acquire all the information contained in two-dimensional images due first of all to the limitations in dynamics and the lack of uniformity in the response curve but also in because of the aberrations and distortions brought by the video tube.

 By way of example, a television camera is limited to an accuracy of the order of 20 separable gray levels while the assembly according to the invention makes it possible to carry this pret '. i s i have at least up to # 000 levels in its mechanical scanning version.

 The object of the invention is to analyze and transmit to computer means with an entirely interesting degree of precision, the details of an image with a view to an industrial application, for example the quality control of a manufactured product.

 This control can be carried out either deferred on a fixed image or in real time on an image immobilized momentarily for the production of a chain allowing quality controls or automatic pattern recognition.

 One of the most important applications of the invention consists in analyzing and transmitting to computer means certain global transforms of a three-dimensional image by illuminating a non-opaque sample by a coherent monochromatic plane wave. The image thus formed represents with a good approximation the optical FOURIER transform and contains, in two-dimensional form, all the information relating to the structure of the object.

 The high resolution and the great dynamics of the acquisition assembly according to the invention give hope for multiple applications in the most varied fields.

 The following fields of application can already be cited with certainty: metrology, detection of surface defects, recognition of forms in robotic loop, uniformity control of light emitting systems such as video tubes, diode arrays, screens with plasma, lasers, as well as all applications for image processing essential in the following fields: ultrasound, thermography, radiography, astronomy, microscopy ...

 More specifically, the invention seems particularly well suited and will find an interesting industrial application in the automatic quality control of textiles, research and reproduction of microcircuits, in micro and macrolithography manufacturing.

General advantages specific to the set according to
the invention arise from the great geometric uniformity of response. They allow to practice an analysis and a treatment
high resolution images.

 The assembly according to the invention makes it possible to work on real or virtual images and in real time in its most elaborate embodiment. Its only limitation comes from the scanning and analysis time. I I could also extend automation in production lines to a level much higher than that currently existing.

Other characteristics and advantages of the invention are developed in the description which follows, given by way of example on an embodiment of the invention with reference to the accompanying drawings in which. Figure 1 is the general diagram of the acquisition set
images according to the invention in its basic version; Figure 2 is the general diagram of the acquisition set
images according to the invention in its elaborate version; league 3 is the detail diagram of the treatment unit
of the signal; . Figure 4 is the detailed diagram of a scanning system
with scanning head fitted with micrometric table sensors
and its associated control and processing circuits.

 We will first refer to Figures 1 and 2.

 A uniform beam 2 is formed from a photonic source 1 of coherent light by means of an optical system 3 followed by a diaphragm 4.

The beam is deflected using a semi-reflecting mirror 5 into a reflected beam 6 towards a reference sensor
CR to form a reference signal which will be used later in the signal processing unit to compensate for the fluctuations in intensity of the photonic source 1.

 The emerging beam 7 is projected onto the sample 8 to be analyzed or onto its photographic image. This transparent, translucent or mesh texture sample, or its image, diffracts the incident beam according to its own structural characteristics.

 The part analyzed can be constituted by a sample of a production or by its photographic image placed on a fixed frame. The total surface of the sample corresponds to the scanning area or part of it.

We consider, in os the ace of the elt alorét 'version,
to perform constant control during continuous production. This control presupposes a momentary immobilization of the product in front of the analysis zone and, consequently, a jerky advance using an appropriate device.

 The diffracted beam passes through an optical system 9 which forms an image of the sample 8 or of its photographic representation in its focal plane 10 coinciding perfectly with the exploration surface of an analysis assembly 11 of the mechanical scanning type 12 or electronically scanned 13.

The implementation version of the analysis set
It with mechanical scanning 12 comprises an exploration head 14, for example with four sensors 15 each exploring a quarter of the scanning surface animated by a micrometric table TM.

 This version is more particularly adapted to the analysis and the acquisition of samples and photographic reproductions in deferred time.

 The embodiment of the electronic scanning analysis unit 13 includes a matrix of diodes viewed successively at high speed or any equivalent.

The signals supplied by its sensors or by the diode array are processed in a TS processing block before their exploitation by a computer means MI with a view to presenting the results in the most appropriate forms that currently allow computer techniques or # dt
their subsequent use in an automation chain 16 in industrial production of the type, for example, robotic loop
BR which can act on certain organs of the production chain 17 such as, for example, the extruder of an extrusion head, the control of a textile machine, etc.

 The IT means include dialogue peripherals, for example a control console and display members represented by the PF block allowing the operator to intervene at any time.

 The block for processing the signal TS and its associated circuits will be detailed below by referring to FIGS. 3 and 4.

The signal processing module is broken down into an analog processing block A which receives directly
the signal from the sensors 15 mounted on the exploration head or
of the static analysis system of the image pi'evti as a whole
electronically scanned 13.

 This analog processing block consists of several chains in parallel leading to a multiplexing unit MX. Each chain includes an integrator 18 followed by a blocking sampler I '). The signals are adapted and compared successively to the reference signal given by the reference sensor CR. They are transformed into digital information by the CAD converter and transmitted to the computer means MI after adaptation in the computer interface IT.

CM control of mechanical scanning is given by the CAD converter through logic control cards
CCL to the micrometric table TM for mechanical movement of the exploration head.

 Electronic scanning does not require any particular commando of this type, for example of "stepping" motors for linear displacements in two orthogonal directions but a time-based and offset command for the rows and columns of the photosensitive element matrix .

 A suitable analog output SA can be used for graphic displays such as a TT plotter, SC scope or other.

 The main advantage of the acquisition assembly according to the invention lies in its high precision. Its use is only justified in cases where the precision that one wants to obtain lies outside the limits of faster acquisition systems.

 it is understood that various simple modifications and the field of equivalents made to the invention cannot go beyond the scope of this protection.

Claims (5)

KEVEND I CATI ONS  1. High resolution image acquisition assembly for industrial exploitation by computer means characterized in that it comprises in combination a photonic source LS of the coherent urri er whose beam illuminates a sample (X) or its photographic representation and a reference sensor CR for the formation of the image of the sample in the focal plane (10) of an optical system (9) coinciding with the exploration surface of an analysis assembly (11) with mechanical scanning ( 12) or electronic (13), the signal of which is processed with that of the sensor CK in a TS unit for its exploitation by a computer means MI with a view to industrial automation application, for example by robotic loop BR.  2. The assembly as claimed in claim 1, characterized in that the analysis assembly (11) consists of an exploration unit (14) with four sensors animated by a micrometric table TM.  3. The assembly of claim 1 as activated in that the processing unit consists of an analog processing block A followed by a converter into digital information CAf).  4. The assembly of claim 1 characterized in that the analog processing block A comprises for each sensor a chain formed of an integrator (luts) and a sample  neur blocker (19) leading to a multiplexing unit MX, block A also comprising a separate channel for the reference voltage given by the CR sensor.  5. The assembly as claimed in claim 1, characterized in that the voltage levels supplied by the sensors are constantly compared with the levels supplied by the reference sensor CR.