METHOD AND APPARATUS FOR CHECKING THE SLACKS IN THE SUSPENSION AND STEERING OF A MOTOR VEHICLE

Abstract: The method for checking and measuring the slacks in the suspension and/or steering of motor vehicles comprises the steps of: associating a detecting videocamera, in a predetermined fixed position, with at least one wheel of the vehicle; identifying a reference point precisely determined on the wheel, detecting the coordinates thereof in the optical sensor plane of the respective videocamera; subjecting the wheel to stressing in the horizontal plane, so as to displace it from a rest position to a maximum stressed position; checking the displacement of said reference point in relation to said displacement of the wheel; and comparing the values of said displacement with predetermined reference values. Preferably said reference point is determined by identifying, for each wheel, the profile of a rim associated with the wheel and projected onto the optical sensor plane of the respective videocamera, as the locus of the points of greatest variation in luminous intensity, then calculating mathematically, using the least square fit mathematical method, the conic section which bests approximates the profile thus obtained; and finally calculating, from the equation of this conic section and from the known coordinates of the position of the videocamera, the point of intersection of the greater and smaller diameters of the said conic section, which forms said reference point.

Description: "METHOD AND APPARATUS FOR CHECKING THE SLACKS IN THE SUSPENSION AND STEERING OF A MOTOR VEHICLE" = 0 = 0 = 0 * = The present invention relates to a method and an apparatus for checking the slacks in the suspension and steering of a motor vehicle. It is known that, in order to ensure the safety of travel of a motor vehicle, it is necessary that the various mechanical components should be adeguately fastened together and that the wear in the parts which are subject to continuous movement should remain within limits defined during the design stage. The present invention concerns the provision of means for checking the correct mutual fastening in particular of the parts relating to the suspension and the steering which, owing to the continuous stress to which they are subjected, are particularly critical for ensuring adequate reliability of the vehicle. Checking of the correctness of said fastening, or of the slacks existing be- tween the various mechanical parts of the suspension and steering, is normally performed using an empirical manual method. In general, after positioning the vehicle with the directional wheels resting on a platform movable in the horizontal plane, oscillating movements in the horizontal plane, which are transmitted to the wheels, are imparted to this platform, for example by means of a pneumatic sys- tern. Since the vehicle is immobile, these movements result in lateral forces applied to the parts of the suspension. A mechanic checks the various parts of the suspension or steering in order to find those parts which, owing to the action of the oscillating force, move beyond that which is permitted, in particular on account of the presence of mechanical slacks. As can be easily understood, this verification procedure depends substantially on the evaluation of the mechanic who, although he may be very skilled in these types of operations, is nevertheless able to provide only a subjective assessment of a qualitative - but obviously not quantitative - nature as to the condition of the suspension and/or the steering. The object of the present invention is that of making this measurement objective, eliminating the human evaluation factor and replacing it with an objective evaluation, preferably based on operating parameters provided by the manufacturer. This object is achieved by means of the characteristic features indicated in Claim 1 . Further characteristic features and advantages of the invention will emerge, however, more clearly from the following detailed description of a preferred embodiment, provided purely by way of a non-limiting example and illustrated in the accompanying drawings, in which: Fig. 1 is a plan view diagram of the front axle of a motor vehicle, with the two wheels of which two respective detecting videocameras are associated; Fig. 2 is a diagram of the images viewed by a videocamera during the detecting operation. As shown, in order to perform an operation for detecting the slacks in the front suspension S of a vehicle (not shown), the front wheels R of the latter are rested on two respective platforms P1 and P2; these platforms are movable in the horizontal plane and are made to oscillate planwise, in the direction of the arrows F, by actuating means (not shown) which are known per se. Videocameras T 1 and T2 are arranged more or less facing each of the two wheels R, in order to record the profile of the respective rim. During measure- ment, when the platforms P are made to oscillate, the profile of a respective wheel, indicated by R in the rest condition, is displaced into the position R1 and R2, by an amount D1 or D2, following the oscillations of the platforms in a more or less intense manner depending on the elasticity of the suspension and/or the slacks in the respective linkages. Any point of the wheel, for example its centre 0, moves by the same amount D1 or D2, into the position 01 or 02. The process for measuring the displacements D1 and/or D2, according to the invention, comprises the following steps: 1 . Determination of a set of measuring points on the wheel A videocamera positioned approximately frontally, or at a certain angle with respect to the wheel, is used to read the profile of the wheel rim; this profile is determined on the basis of the difference in luminous contrast at the transition point from rim to tyre and, from this profile, the equation of the conic section which represents it is mathematically determined. In order to determine the wheel profile from the image of the rim shown in the optical sensor plane of the videocamera and consequently the conic section which represents it, a so-called "repeated approximation" method, consisting in the following steps, is used: a) the profile of the wheel rim is determined as the locus of the points of maximum difference in luminous contrast, occurring at the transition points from the rim to the tyre. The image recorded by the videocamera is digitalized and con- verted into a rectangular matrix of intensity values, one for each digitalized point. This matrix of values is equalized, namely multiplied by a special factor automatically calculated in relation to the average luminosity of the image. The purpose of the equalization is to reduce the effect of the variation in the lighting conditions of the object. A suitable mathematical operator (Laplace, Sobel) is applied to the equalized values in order to obtain a new matrix of values, one for each point sampled, where the values represent the gradient of variation in intensity. This gradient has a locally very high value at the points which, as mentioned, correspond to the rim-wheel interface. A threshold operator is then used in order to extract from the image, only those points for which the gradient is sufficiently high, and among these points there is certainly those corresponding to the rim-tyre interface. The binary matrix obtained is filtered using an erosion operator, in order to eliminate all the isolated points (noise) and leave only the points belonging to predetermined geometric groups (lines, circles, etc.). In order to improve the image quality and reduce the effect caused by the ambient lighting variable, the vehicle wheel is illuminated with infrared light using a set of emitting diodes, and an infrared filter having spectral characteristics coinciding exactly with the emission spectrum of the infrared diodes is placed in front of the optical system of the video- camera: the artificial ambient lighting is completely filtered and its negative effect on the quality of the measurement is thus eliminated. A small influence caused by the infrared fraction of the solar light which may pass through the filter remains, but normally this influence is not significant in the definition of the measurement. By way of further reduction of the effect of the ambient lighting it is also possible to obtain the image to be processed as the difference between the images detected with the infrared lighting switched on and with the infrared lighting switched off, respectively. b) Once a bundle of points sufficiently close to a conic line is obtained, the measuring method according to the invention must use the redundancy available in the data in order to be able to compensate for errors and imperfections in the image. The calculation of the reference conic section must namely use the greatest possible amount of information obtained from the image in order to reduce the effect of damage to the rim, imperfect detection of the image, imperfect lighting conditions, etc., and obtain the "best" conic section - i.e. the conic section which best approximates the true profile - using data analysis methods which extract this information, eliminating the imperfections as far as possible. One of the methods which can be used for this purpose is the least square fit method. More precisely, a pair of coordinates ( x, y ) corresponding to the position of the point in the image plane is assigned to each point determined in the preceding operation. The equation conic is identified as follows: an x 2 + 2*ai2 x y + a 2 2 y 2 + 2*a * i3 x + 2 *a 23 y + a 33 = 0 obtaining the coefficients an,ai2,a 2 2,ai3,a23,a33 which minimize the sum S (an x 2 + 2*ai2 x y + a22 y 2 + 2*ai3 x + 2 *a23 y + a33) 2 calculated using the coordinates x, y of the points obtained. In practice the system of linear equations is resolved with coefficients Sx 4 , Sx 3 y, Sx 2 y 2 , Sx 3 , Sx 2 y, Sx 2 Sx 3 y, Sx 2 y 2 , Sxy 3 , Sx 2 y, Sxy 2 , Sxy Sx 2 y 2 , Sxy 3 , Sx 2 y, Sy 4 , Sxy 2 , Sy 2 Sx 3 , Sx 2 y, Sxy 2 , Sx 2 , Sxy, Sx Sx 2 y, Sxy 2 , Sy 3 , Sxy, Sy 2 , Sy in relation to the variables aιι ,ai2,a22,a-i3,a23,a33. c) The points which are furthest from the conic section of first approximation are removed from the initial profile thus obtained, in order to eliminate erroneously inserted points, imperfections in the rim or the like from the calculation. The remaining points are then used to recalculate the conic section which best approximates them. d) From the equation of this conic section, the centre O of the conic section itself, which identifies a point on the wheel fixed to the wheel itself, is then obtained. The centre of the conic section has coordinates: xO = (ai2*a23-ai3*a 2 2) ( an *a22-ai2 2 ) yO = (ai2*ai3-*a-ιι *23)/(aιιa22-ai2 2 ) and the displacements D1 , D2 in the direction parallel to the horizontal plane are identified by the displacement of the coordinate xO. e) for conversion of this displacement into units of measurement which can be used subsequently (for example into mm), the radius of the rim must be known in the same units of measurement. In fact, using the relation: ra/rr = dxO/dxr where ra = apparent radius (measured in the image plane) rr = real radius dxO = displacement of xO measured in the image plane dxr = real displacement of the wheel it is possible to express the displacement in standards units of measurement. 2. Determination of the displacement The position of the centre 0, with the wheel positioned, but not stressed, is taken as the zero point or basic reference point for subsequent evaluation of the displacement. The wheel is stressed so as to move in the horizontal plane; for this purpose a special oscillating platform system is used, the wheel, as mentioned, resting on said platform. The oscillation may be imparted using a pneumatic, hydraulic or mechanical actuating system, able to produce forces F with components in different directions. When the stress occurs in the direction where the slacks is pre- sent, the displacement is clearly detectable as displacement of the zero point. 3. Determination of the value of the displacement The displacement D1 , D2 of the measuring points, and in particular the zero point, is then compared with values contained in a special data base of limit values provided for example by the vehicle manufacturer themselves. In this way it is possible to determine precisely whether the displacement is greater than the threshold values associated with a given motor vehicle and consequently generate alarm signals. Preferably, the displacement of the wheel is recorded as a Euclidean distance (this being the classic method of measuring the distance between two points with coordinates x0,y0 and x1 ,y1 defined by the square root of (xO- x1 ) 2 + (y0-t1 ) 2 ) between the position of the centre of the wheel at rest and the position of the centre of the wheel when stressed. The stress is then zeroed and the difference in the position between the position of the wheel before and after stressing, as another qualitative indication of the suspension/steering system, is recorded. The determination of the "slacks" or any other movement which may be the cause of problems of safety or stability of the vehicle is performed, as mentioned, by a comparison with data stored in a special data base. In fact, even when there is no slack, a suspension may be designed so as to move also signifi- cantly in the presence of stress, owing to the elastic deformation of the parts forming it. The presence of slacks may be detected also from a difference between the position of the wheel before stressing and during maximum stressing: each displacement caused by elastic effects, is in fact recovered, so that non-elastic dis- placements, such as slacks in the fastening systems of the movable parts, are placed in evidence. It is understood, however, that the invention must not be regarded as limited to the particular embodiment illustrated above which constitutes only a non- limiting example of the scope of the invention, but that various variants are possi- ble, all of which within the scope of a person skilled in the art, without thereby departing from the scope of protection of the invention itself, as defined by the claims which follow. In particular, it is obviously possible to refer, as the zero point, not only to the centre of the conic section representing the rim of the wheel, but also to any other point which is fixed to the wheel and may be easily and precisely determined as such in the optical sensor plane of the videocamera.

Claims: CLAIMS 1 ) Method for checking and measuring the slacks in the suspension and/or steering of motor vehicles, characterized in that it comprises the steps of : - associating a detecting videocamera, in a predetermined fixed position, with at least one wheel of the vehicle; - identifying a reference point precisely determined on the wheel by detecting the coordinates thereof in the optical sensor plane of the respective videocamera; - subjecting the wheel to stressing in the horizontal plane, by maintaining the suspension and steering in a fixed position and by pushing the wheel from a rest position towards a maximum stressed position; - checking the displacement of said reference point in relation to said stressing of the wheel; and - comparing the values of said displacement with predetermined reference values. 2) Method for checking and measuring the slacks in the suspension and/or steering of motor vehicles, characterized in that it comprises the steps of: - identifying, for each wheel, the profile of a rim associated with the wheel and projected onto the optical sensor plane of the respective videocamera, as the locus of the points of greatest variation in luminous intensity; - calculating mathematically, using a repeated approximation method, the conic section which bests approximates the profile thus obtained; - calculating, from the equation of this conic section and from the known coordinates of the position of the videocamera, the point of intersection of the greater and smaller diameters of the said conic section, said point of intersection forming said precisely determined reference point. 3) Method for checking and measuring the slacks in the suspension and/or steering of motor vehicles according to Claim 2, characterized in that said repeated approximation method consists in the least square fit mathematical method. 4) Method according to Claim 1 or 2, in which said predetermined reference values are those provided by the manufacturers for the type of vehicle being checked. 5) Method according to Claims 1 , 2 or 4, in which said predetermined reference values are stored in an electronic data base.

Inventors: COLOMBO FLAVIO, RATTI ALESSANDRO, COLOMBO, FLAVIO, RATTI, ALESSANDRO
Applicants: COLOMBO FLAVIO, GIEFFE IMMOBILIARE S N C DI GI, RATTI ALESSANDRO, COLOMBO, FLAVIO, GIEFFE IMMOBILIARE S.N.C. DI GIANFRANCO CROSTA & C., RATTI, ALESSANDRO
Application year: 2001
Main classification: G01M17
IPC codes: G01B11, G01M17