Device for the geometrical control of vehicles

0001The invention relates to a device for the geometric control of a vehicle, of the type comprising at least one element capable of being secured to a vehicle wheel rim by means of a fixing claw or the like.

0002There are many known geometric vehicle control devices, in which a measuring head fitted with appropriate sensors is fixed to a vehicle wheel rim and transmits by wire or wireless connection signals representative of physical parameters to a central unit programmable, able to calculate the geometry of the vehicle.

0003However, these known measuring heads comprising fragile sensors and electronic components sensitive to shocks present a risk of damage during geometrical control operations, in particular when fixing on the rim or when removing the rim.

0004To overcome this drawback, provision has been made to fix targets or mirrors on the rims of vehicle wheels, so as to illuminate these targets or these mirrors and to observe the reflected image by means of a camera or analogous observation. A laser transportable axis measuring device of this type is described in the document "KRAFTHAND", notebook 9, May 5, 1979, page 608. Another device of this type is described in the document WO 94/05969.

0005These target or mirror devices fixed on the rims of the wheels have the disadvantage of requiring a relatively complex image analysis and calculation device to determine the aiming angle by correlation of the image in perspective or in reflection. observed with the full-size image of each target or each mirror. In addition, due to the distance from the observation bench to targets or mirrors, the selectivity of the measurements is low, which requires the use of high-precision sensors or high-resolution matrix observation cameras.

0006The invention aims to remedy the drawbacks of the known technique, by creating a new device of high selectivity allowing the use of cameras of known type, in particular cameras with linear CCD, and avoiding the risk of damage to the heads. electronic measurement devices of the prior art.

0007The invention relates to a device for the geometric control of a vehicle, of the type comprising at least one element capable of being secured to a vehicle wheel rim by means of a fixing claw or the like, characterized in that the device comprises means capable of varying the appearance of the element as a function of the viewing angle from which it is seen, without constituting a perspective image of this element.

0008According to other characteristics:<ul id="ul0001" list-style="dash" compact="compact"><li>said means of variation of appearance are independent of the distance separating the point of sight from the device;</li><li>said means comprise at least one pair of moiré grids spaced from one another;</li><li>at least one moiré grid closest to the aiming point comprises a locating means defining a measurement origin;</li><li>in a pair of grids, two spaced moiré grids are substantially parallel to each other;</li><li>in a pair of grids, two spaced moiré grids are arranged on two surfaces at an angle to each other;</li><li>in a pair of grids, two spaced moiré grids each have a first grid for fine angular measurement and a second grid for absolute angular measurement;</li><li>a device element comprises at least two pairs of grids, which are not parallel to each other;</li><li>the device comprises at least one camera or observation means capable of observing the appearance of each element fixed to a vehicle wheel rim and of transmitting a signal representative of said observation to a programmable central unit, so as to calculate angles orienting said element and deducing therefrom physical parameters representative of the geometry of the vehicle;</li><li>the device comprises two cameras spaced a distance greater than the track of the vehicle to be checked.</li></ul>

0009A simple way to vary the appearance of an element according to the viewing angle from which it is seen is in fact the use of moiré measurement techniques. Numerous moiré measurement techniques are known: projected moiré, shadow moiré, superimposed moiré and other equivalent interference technique. However, these moiré measurement techniques have been used mainly up to now for the verification of the surface of an object to be tested and its conformity check with respect to a reference surface. Such surface control techniques are notably known from the documents FR 2,658,601, FR 2,614,691, FR 2,580,066 and FR 2,520,106. None of these documents indicates or suggests applying the moiré measurement technique to the geometric control of a wheeled vehicle.

0010The invention will be better understood thanks to the description which follows given by way of nonlimiting example with reference to the appended drawings in which:

0011FIG. 1 schematically represents the measuring principle implemented in the invention.

0012FIG. 2 schematically represents an explanatory arrangement of a pair of moiré grids spaced from one another for the implementation of the invention.

0013FIG. 3 schematically represents another explanatory arrangement of another pair of moiré grids spaced from one another for the implementation of the invention.

0014FIG. 4 schematically represents the appearance of a moiré observation corresponding to a normal incidence on an arrangement of two grids according to FIG. 2 or FIG. 3.

0015FIG. 5 schematically represents the appearance of a moiré observation under angular incidence of an arrangement of two moiré grids according to FIG. 2 or FIG. 3.

0016FIG. 6 schematically represents a first embodiment of a device element according to the invention fixed to a vehicle wheel.

0017FIG. 7 schematically represents a second embodiment of a device element according to the invention fixed to a vehicle wheel.

0018FIG. 8 schematically represents a third embodiment of a device element according to the invention fixed to a vehicle wheel rim.

0019FIG. 9 schematically represents a fourth embodiment of a device element according to the invention fixed to a vehicle wheel rim.

0020FIG. 10 schematically represents a top view of a device according to the invention.

0021FIG. 11 schematically represents a top view of another device according to the invention.

0022FIG. 12 schematically represents an operating flow diagram of a device according to the invention.

0023With reference to FIG. 1, two grids of black lines regularly spaced apart by an interval corresponding to their width l are observed from an observation center 0. The grids formed by lines are separated from each other by a spacing e, so that the observation from the center 0 reveals a clear central fringe, substantially symmetrical with respect to the reference mark R forming the index located on the support of the grids, opposite the observation center 0, and alternately dark and light side fringes, symmetrical with respect to this central fringe.

0024When the pair of grids is rotated by an angle A, the observer placed at the observation center 0 has the sensation of a displacement of the clear central fringe relative to the image of the reference mark R forming an index, distance corresponding to an offset d (A) which is a trigonometric function of the angular displacement A.

0025This moire technique therefore makes it possible to link the angular inclination A to a displacement of the light (or dark) central fringe.

0026Referring to Figure 2, two grids 1 and 2 seen in section are substantially parallel to each other and are superimposed to allow observation of moiré. The grids 1 and 2 are preferably identical and include substantially trapezoidal lines, with progressive pitch. The grids are preferably produced on square or rectangular panels of predetermined dimensions depending on the desired angular resolution.

0027With reference to FIG. 3, two other grids 3 and 4 are shown and form between them an angle converging upwards. The grids 3 and 4 are preferably identical and constituted by lines of constant width, parallel to each other, and separated by transparent spaces of width corresponding to the width of the lines.

0028With reference to FIG. 4, an observation of moiré perpendicular to a pair of grids 1 and 2 or perpendicular to the bisector plane of a pair of grids 3 and 4 is shown. It can be seen that the shape of the moiré curves obtained is substantially symmetrical with respect to the axis Sr passing through the image of the reference index R corresponding to the reference R forming an index situated on the support of the grids.

0029When the reference frame R is located on the normal lowered from the observation center 0 on the support of the grids, the aspect of the moiré observation is symmetrical with respect to the axis Sr passing through the image of the reference frame R observed at observation center 0.

0030The interference of the lines of grids 1 and 2 in FIG. 2 (or grids 3 and 4 in FIG. 3) produces an aspect of curved fringes flaring downwards alternately dark and light.

0031The angular spacing of two adjacent dark (or light) fringes located on the same side of the image of the reference frame R is a trigonometric function f of the line width, the spacing of the line grids and the ordinal number of the fringe considered.

0032With reference to FIG. 5, when the pair of grids is turned by an angle A similar to the angle A in FIG. 1, the observation of moiré reveals a displacement of the fringes of an offset d (A) which is a trigonometric function of the tilt angle A.

0033In addition, the counting of the number of fringes corresponding to the offset d (A) is facilitated by recording the number of fringes along the line of intersection Sr passing through the image of the locating index R. Thus, as example, the number of fringes from the first line of moiré is three in the case of figure 5.

0034Thus, in the case where the central fringe of symmetry of axis S leaves the support of the grids as a result of a significant rotation, it suffices to count the number of fringes cut by the straight line Sr passing through the image of the index marking R to deduce the angular position of the grid support using the following formula:<maths id="math0001" num=""><img file="EP0806629A1_D0001.tif" /></maths>    where A is the angle of rotation of the support, a is the elementary angle of rotation from the fringe closest to the image of the frame of reference R, i is the fringe number and f (i) is the trigonometric function above associated with the fringe number i.

0035An important advantage of the invention is as follows: given that the observations are independent of the distance separating the observation point from the pair of grids observed, the angular field remains constant so that the appearance of a grid support panel is invariant when its distance from the observation center increases.

0036As a result, the angular measurement accuracy of the device is independent of the distance from the grid support panel to the observation center.

0037The invention thus overcomes the drawbacks of the known technique, in which the reflected image or the perspective image of a target decreased with distance and in which the accuracy of angular measurement consequently decreased sharply with distance.

0038The size and the spacing of the lines are defined as a function of the desired angular precision and of the number of visible fringes. For this purpose, it is preferred to use two pairs of moiré grids, the first of which is a pair of grids of the type of FIG. 1, called with uniform moiré, for carrying out a fine angular measurement, and the second of which is a pair of grids of the kind of FIGS. 2 and 3, called progressive moiré, to perform an absolute angular measurement to determine the numbers of the fringes seen on the uniform moiré. For example, the fine measurement corresponds to an angular precision of 30 arc seconds, while the absolute angular measurement with respect to a tracking index corresponds to an absolute precision of 30 arc minutes.

0039With reference to FIG. 6, a device element 6 in the form of a dihedral or an open book, the axis 7 of which is substantially vertical, has been mounted on a vehicle wheel 5. This element 6 carries four pairs 8 to 11 of grids, each pair of which comprises a pair of grids 8a to 11a of uniform moiré for precision and a pair of grids 8b to 11b of progressive moiré for absolute measurement. The index markers 8c to 11c are designated by arrows producing a contrast of light intensity and can be produced in the form of light-emitting diodes, or alternatively in the form of interruptions of a pair of grids revealing a black space or invariant white, or even in the form of a recess made through pairs 8 to 11 of grids. The pairs 8 to 11 of grids are produced for example on either side of a glass panel by mechanical or chemical etching or by depositing an ink, or even by bonding of wires, or other means of producing lines. black.

0040With reference to FIG. 7, another embodiment of an element 12 of the device according to the invention is in the form of a dihedral or an open book, the axis 13 of which is substantially horizontal. This element is substantially similar to the element of Figure 6 on which is performed a rotation of 90 ° in a vertical plane and a translation to make the axis of the dihedral coincide with the axis of the wheel.

0041With reference to FIG. 8, another embodiment of element 14 of the device according to the invention is in the form of a cube comprising three observable faces: two vertical faces 15 and 16 each carrying a pair of grids, and a horizontal face 17 located on the upper side.

0042With reference to FIG. 9, another embodiment of element 18 of the device according to the invention is in the form of a projecting dihedron produced in the form of a trihedron formed from three planes 18a to 18c forming for example an angle of 120 ° two to two, and oriented so that the bisector plane 19 of the two planes 18a, 18b is parallel to the plane of the wheel 5.

0043The embodiments of FIGS. 6 to 9 are particularly advantageous for measuring the deflection of the steering wheels of a vehicle, thus avoiding the use of rotary plates for measuring the deflection.

0044With reference to FIG. 10, a general arrangement of the device according to the invention is shown with four elements 20 to 23 of devices attached to the four wheels of the vehicle to be checked and lit by light projectors 24 and 25. The elements 20 to 23 of the device fixed to the wheels of the vehicle are observed by a pair of cameras 26, 27, each consisting for example of a linear CCD camera and an oscillating mirror mounted on a galvanometer or other drive member. in rotation to cover the entire useful field of observation. The cameras 26 and 27 are connected to a programmable central unit 28 allowing viewing on a screen 30 and connected on the one hand to a mobile display remote control 29 making it possible to repeat the indications on the screen 30 and on the other hand to an external network 31 allowing direct connection to a vehicle database or to a CD ROM integrated in the programmable central unit 28.

0045As can be seen, the cameras with linear CCD, for example of the type described in document FR 2,711,238, can be placed in pairs on the side of the rear wheels of the vehicle, or alternatively between the front wheels and the rear wheels, or else of the side of the front wheels of the vehicle to be checked.

0046With reference to FIG. 11, another device arrangement is shown with four elements 20 to 23 of devices, among which a pair 20, 21 of device elements is intended for transverse measurements relating to the front axle, a third element 22 is intended for measurements on the left longitudinal side and a fourth element 23 is intended for measurements on the right longitudinal side.

0047In this exemplary embodiment, the cameras 26 and 27 mounted on the steering front axle each have a longitudinal field of observation, in the direction of the elements 22 and 23 respectively, and a transverse field of observation, in the direction of the elements 20 and 21 respectively.

0048The cameras 26 and 27 are advantageously linear CCD and oscillating mirror cameras; the invention also covers any other variant embodiment, in which the measurements in the transverse direction are carried out using transverse observation slots (technique of the apparatus 8675 manufactured by the applicant of the present application) or using potentiometric sensors (device technique 8670 manufactured by the applicant of this application).

0049Inclinometers can be provided to acquire the parameters necessary for the change of coordinates, in order to express the measurements in an absolute coordinate system (defined benchmark of two vertical planes and a horizontal plane).

0050The invention also covers the variant not shown in which the cameras 26 and 27 are mounted integral with the rear axle, on the axis or else in front or even behind the rear wheels. In this case, the transverse measurements are made relative to the rear axle.

0051The reference numbers identical to the figures in Figure 10 denote elements identical or functionally equivalent to the elements of Figure 10 which have been described with reference to this figure.

0052With reference to FIG. 12, a device operating program according to the invention comprises the following steps: an initialization step during which the lighting conditions are established by switching on projectors 24, 25 if necessary; a step of capturing images and shots making it possible to verify the general operation of the system; a step of finding and locating the elements 20 to 23 fixed to the wheels of the vehicle; a step of searching for the index mark R of each element 20 to 23 and focusing on this index mark; a moiré observation analysis step making it possible to determine offset values ​​which are trigonometric functions of angular inclination along a desired geometric axis; a step of calculating the independent angles making it possible to define the position of each element 20 to 23 on each vehicle wheel; a vehicle pushing step for measuring the sail of each wheel and storing measurement correction parameters; a step of calculating the overall geometry of the vehicle; a step of consistency check and storage of the geometry check carried out in connection with a vehicle database accessible by means of a telephone or wireless network or resident on a permanent memory contained in the programmable central unit of the device.

0053The geometric control results of the vehicle are displayed on the screen, printed, or possibly archived.

0054The invention described with reference to particular embodiments is in no way limited thereto, but covers all modifications of form and technique of moiré and all variant embodiments in which the device comprises means capable of varying the appearance of the element fixed to a wheel of the vehicle as a function of the viewing angle from which it is seen.

0055Thus, the invention also covers the variants according to which a moiré grid is projected onto a grid of an element fixed to a wheel of the vehicle; or another variant in which the two grids are projected onto a panel with a uniform bottom fixed to the vehicle, said panel not necessarily being plane.