This invention relates to apparatus for analysing graph cal in ormation on a planar carrier. The inven- tion is particularly, but not exclusively, applicable to the analysis of graphical data such as the traces on a tachograph chart- In many countries tachographs are now compulsory on certain classes of vehicle. These devices have various benefits in improving road safety and regulating transport operations. However, analysis of tachograph charts has hitherto been carried out in practice by eye, which is time consuming and inaccurate.

An ob ect of the present invention is to provide an apparatus for the automatic analysis of tachograph charts, or similar data, which will enhance the practical useful- ness of such charts.

Accordingly, the invention. provides apparatus for analysing graphical informartion on a planar carrier, compri s ng: means for illuminating said carrier; imaging means operable to provide an accurate representation of the graphical information by means of a digitised video signal or a numerical array; and means defining a datum point within the area viewed by the imaging means. From another aspect, the invention provides a method of analysing a tachograph or like chart, including illu¬ minating the chart from behind, and imaging the front of the chart to provide a digitized video signal or numerical array. An embodiment of the invention will now be des¬ cribed, by way of example, with reference to the drawings, in which:-

Fig. 1 is a block diagram of an apparatus embodying the invention; Fig. 2 is a schematic cross-sectional view of a chart

platen and associated parts used in the apparatus of Fig. 1;

Fig. 3 is a plan view of a lens member σf Fig. 2; and

Fig. 4 is a cross-sectional side view of a boss used in Fig. 2.

Referring to Fig. 1, tachograph charts are loaded into a hopper 100 from which they are removed one at a time by a pick/feed mechanism 102 and loaded by a loader mechanism 104 onto a chart platen assembly 106 for analysis. After analysis, the charts are discharged to an analysed chart hopper 108. Suitable mechanisms for handling the charts will be apparent to those skilled in the art, and thus the parts 100, 102, 104, 108 are not described in detail herein. Alternat vely, charts could be loaded in and removed from the platen assembly 106 by hand.

The analysis of the chart is performed by imaging the chart by a video camera 110 to provide an analog video signal which is converted to digital format in A/D converter 112 and suppl ed to a microcomputer 114. The microcomputer 114 is programmed to extract the desired information from the video signal and to provide a desired analysis on a printer 116. Data can also be transferred to a mainframe computer or other data handling devices.

The apparatus also includes a video monitor 118 driven by the microcomputer 114 via a D/A converter 120. Preferably, the video image can also be displayed on the monitor 118 via the D/A converter 120, and can be multiplexed with text resulting from the analysis. This allows areas of the chart image which are unusual or anomalous to be drawn to the operator's attention on a real-time basi s .

In the preferred embodiment shown, the whole chart

area is imaged by video camera 110, and the record traces are identified and quantized by examination of the digitized video signal. Suitably, a datum point is established, e.g. by a fixed central l- ^' ght spot as in Fig. 4 below, or by means of a special marking on the chart .

Alternative imaging methods are possible; for example, the chart could be rotated past a camera or an array of light sensitive elements to provide a video signal or a numerical array.

Figs. 2 to 4 illustrate a preferred form of the platen assembly 106. We have found that there can be difficulties in obtaining a good video signal arising from (a) the fact that charts in common use are of a variety of colours and (b) the presence of smudges or fingermarks on the surface of the chart. The preferred embodiment to be described has two features which over¬ come or itigate these problems, namely (1) illu ination of the chart from the rear, and (2) the use of a special lens men.ber .

Referring to Fig. 2, a tachograph chart 10 is mounted on a transparent holder 12, which may suitably be in the form of a slide or drawer. The central aper¬ ture of the chart 10 is engaged by a boss 40. A lens 16 images the chart 10 in the video camera.

The chart 10 is illuminated from below by a toro dal lamp 18, which is provided with a toroidal reflector 20 and a plane circular reflector 22. The geometrical relationship of the lens 16, lamps 18, and plane reflec- tor 22 is such that the i age in the latter of the lamp 18 ⁽ as indicated at 18') fills the field of view of the lens 16, indicated at 24. Thus maximum utilisation of the available light is achieyed.

Tachograph charts, and certain other charts, are recorded by means of styli which form substantially

V-shaped grooves in a coating. We have found that rear illumination gives a sharper and hence more accurate image; it causes the grooves to be illuminated in a distinct manner which can be readily imaged regardless of the body colour of the chart, whilst surface marks such as finger marks are not illuminated and thus do not give rise to spurious images. It is useful in certain cases to interpose a colour filter between the chart 10 and the lamp 18. This may be used to remove from view printed matter on the underside of the chart. The imaging is further improved by the lens member 26.

This may conveniently be formed from 'Perspex' or other transparent plastics material by machining or moulding. The member 26 comprises a plane base 28 from which project two toroidal segments 30,32 of semi-circular cross-section. In use, the segments 30, 32 overlie inner and outer tracks of a conventional tachograph chart 10 and enhance their i aging by providing both magnification (approx mately x 3) and a condenser lens effect.

The circular area 34 between the segments 30,32 s plane. This area 34 registers with a bar-type trace found on certain forms of tachograph chart which can be easily read without magnification.

The lens member 26 as shown has a segmental opening 36 to allow the chart 10 and means carrying it, such as boss 40, to be sl d into place. Alternatively, the lens member 26 could be vertically displaceable in which case the parts 30,32 could extend through 360°C.

The boss 40 is provided (Fig. 4) with a central aperture 38 which passes illumination from the lamp 18 to produce a bright light spot in the centre of the field of view of the lens 16, the remainder of the central area being dark because of, the member 42. This light

spot is imaged by the video camera to provide a datum for establishing coordinates of the chart indicia, thus reducing the mechanical accuracy required in positioning the chart . '

Tachograoh charts in current use may have either of two forms of central aperture, one relatively small and circular, the other larger and elongate or pear- shaped. As shown in Fig. 3, in a further modification the boss 40 is adapted for the first type of chart and a cap 44 may be press-fitted thereon to receive the second type. The cap 44 is provided with an aperture 46 to reveal the aperture 38.