AU675734B2 - Apparatus for measuring roadway deflection - Google Patents

Description

1

AUSTRALIA

Patents Act 1990 Etat Francais as represented by LABORATOIRE CENTRAL DES PONTS ET CHAUSSEES

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT sc Invention Title: "Apparatus for measuring roadway deflection" The following statement is a full description of this invention including the best method of performing it known to us:- APPARATUS FOR MEASURING ROADWAY DEFLECTION The present invention relates to an apparatus for measuring the deflection of a roadway, the apparatus being associated with a vehicle comprising a chassis, front wheels, and a load-carrying back axle having two pairs of back wheels.

The apparatus is designed to measure the deflection of the roadway under the effect of the passage of said load-carrying back axle, and it comprises: a carriage resting on the roadway via two front support points and a back support point thereby defining a reference plane, the front support points being disposed on either side of the longitudinal axis of the carriage while the back support point is substantially S 15 situated on said axis; determining means for determining the deflection of coo• the roadway, the determining means comprising two feeler o arms pivotally mounted at their front ends to an intermediate portion of the carriage about an axis that 20 is perpendicular to the longitudinal axis of said eee• carriage, and resting on the roadway via their back ends that are provided with skids respectively placed on the paths over which the gaps between each pair of back wheels advance and capable of penetrating between said wheels of said pairs to behind a position vertically below said gaps, said determining means further comprising computer means for computing the deflection of the roadway as a function of the attitude of the feeler arms and associated with storage means for storing the computed values; and carriage displacement means associated with Q*ntrol means for releasing the carriage before each measurement cycle and, at the end of each measurement cycle, for returning said carriage forwards at a speed relative to the ground that is greater than the speed of the vehi e.

Such apparatuses, as known from French patent No. 1 552 070, suffer from the drawback of being relatively slow, given that their speed of advance while taking measurements is not greater than 3.5 kilometers per hour In .addition, it is generally assumed that the first measurement performed, which is taken as a reference value or a "deflection zero" value, is performed in a region of the road that has not yet been disturbed by the load-carrying axle. However, this is rarely the case since with all three support points of the carriage in front of the load-carrying back axle, the back support point being at a relatively short distance from said load-carrying axle. As a result, the measurements taken correspond to no better than values that approximate (by default) to the deflection.

Furthermore, although it is true that known S 15 apparatuses do have means for positioning the carriage relative to the load-carrying vehicle, thus making it possible during turning measurements to preposition the carriage as a function of the turning circle of the vehicle, nevertheless, if the turning circle is modified 20 while the measurement is being taken, due to some error, even a small error, on the part of the driver or due to the vehicle being offset by some external cause, then the feeder arms run the risk of being damaged or even crushed by the wheels on the load-carrying back axle. With existing apparatuses, such accidents are relatively frequent and give rise to significant losses. To avoid S them, it is necessary to limit the speed of the vehicle while turning, thereby further reducing the speed at which measurements are taken. Furthermore, it has been necessary to manufacture so-called "long-chassis" apparatuses having a wheel base of 6.8 meters for taking measurements on roadways such as motorways or main roads in non-mountainous regions, and handier so-called "short-chassis" apparatuses having a wheel base of 4.8 m for taking measurements on roads of the secondary type or on main roads in mountainous regions. Measurements taken using short-chassis apparatuses are naturally less accurate than those taken using long-chassis apparatuses.

In any event, any need to have two types of apparatuses clearly increases overall cost.

An object of the invention is to remedy the above drawbacks by proposing an apparatus that enables deflection zero to be determined quickly from the first measurement taken, that provides measurement accuracy that is at least equivalent to that of long-chassis apparatuses but on any type of road, that has a faster measurement displacement speed, e.g. about 10 km/h, and that is completely safe with respect to the danger of the feeler arms being crushed by the back wheels, thereby making it possible to use the same apparatus on any type of road.

15 To this end, the two front support points are disposed at the front of the carriage and define a straight line perpendicular to the longitudinal axis of said carriage, while the back support point is placed, at the beginning of each measurement cycle, behind said back 20 axls. In addition the apparatus comprises carriage guide S" means designed to guide said carriage as a function of the turning circle radius of the vehicle to prevent the feeler arms being crushed by the back wheels.

Even if the first measurement is taken not outside the zone under the influence of the back axle, but already at the edge of the depression caused by the deflection, then by placing the back support point beyond the back axle from the beginning of each measurement cycle it is possible to ensure that benefit is obtained from the way the carriage tilts in the opposite direction to the pivoting of the feeler arms as the vehicle advances. This provides compensation for the initial deflection that is taken as the reference value.

Measurement accuracy is thus improved, and an apparatus having a short wheel base gives accuracy that is at least equivalent to that obtained using a conventional long chassis.

The guide means enable measurements to be taken at a higher speed while preventing any damage to the equipment. Should the turning circle radius of the vehicle be altered unacceptably while a measurement is being taken, then the guide means guide the carriage in such a manner as to ensure that the feeler arms are not crushed by the back wheels. If the carriage is offset too far laterally, then the measurements may be erroneous and the measurement cycles may need starting over, but at least the equipment has not been damaged. The same apparatus can thus be used on all of the road network without the accuracy or the speed of the measurements being affected.

Advantageously, the carriage guide means comprise 15 rolls projecting from the top face of the carriage and disposed in pairs on either side of the longitudinal axis of the carriage and in planes perpendicular to said axis.

These rolls comprise at least one front pair of rolls and one back pair of rolls. The guide means also include 20 elongate guide elements for said rolls, a fraction at least thereof being capable of pivoting as a function of the turning circle of the front wheels of the vehicle.

Preferably, the elongate guide elements comprise two fixed back guides and two mobile back guides extending outside the back rolls towards the back of the carriage.

The mobile back guides extend approximately longitudinally and are pivotable as a function of the turning circle of the front wheels, while the fixed back guides have back portions that are substantially parallel to the longitudinal axis of the carriage and front portions that diverge, determining the maximum angular displacement of the back rolls. The elongate guide elements further include front guides comprising approximately longitudinal guide surfaces extending between the front rolls and pivotable as a function of the radius of the turning circle of the vehicle.

To avoid the feeler arms being crushed, it is advantageous for the maximum distance between the guides and the rolls to be no greater than the spacing between the wheels in each pair of back wheels. This makes it possible to guide the carriage in such a manner that the back ends of the feeler arms are always situated between the pairs of back wheels, while nevertheless allowing the carriage a small amount of lateral freedom.

A stop assembly is advantageously provided, comprising front stop means for determining the foremost position of the carriage relative to the vehicle, and back stop means for determining the rearmost position of the carriage relative to the vehicle at the end of a *measurement cycle.

15 Known apparatuses suffer from problems of the carriage being set into vibration due to the rubbing of the support points against the roadway. These vibrations can give rise to measurement errors, so it is important to reduce them as much as possible and even to eliminate them. To this end, the carriage is advantageously made of composite material and possesses a resonant frequency of about 21 Hz. This frequency of 21 Hz is considerably 0greater than the frequencies of vibration on the road, which frequencies are generally about 5 Hz to 10 Hz.

This makes it possible to avoid putting the apparatus into resonance and also makes it possible to accelerate 00e 0 attenuation of vibrations due to the rubbing of the support points on the road. Furthermore, the composite material is both stiff and light in weight, thereby facilitating displacement of the carriage by the displacement means.

Also, still for the purpose of improving the speed of the apparatus, the stop assembly is advantageously associated with carriage shock absorbers. The front stop means advantageously comprise an energy-restoring system designed, when the carriage is released prior to a measurement cycle, to restore the energy stored during a shock against the front stop means. The energy-restoring system thus facilitates braking and holding the carriage stationary on the roadway as soon as the carriage is released prior to each measurement cycle being performed by said displacement means.

The means for controlling the carriage displacement means advantageously comprise means for automatically determining displacement sequences and for releasing the carriage on the road, associated with position sensors that enable the various stages to be controlled.

The apparatus advantageously includes at least one inclination indicator for determining the radius of curvature of the roadway.

The inclination indicator includes at least one 15 hinged arm provided with a skid mounted at the back end of one of the feeler arms, and pivotal about a horizontal eo..axis. The hinged arm can therefore follow slopes due to the deflection generated by passage of the back axle, with its skid remaining in contact with the roadway. The 20 inclination indicator also includes means for measuring the angular displacement of the arm hinged about its pivot axis, and means for computing the radius of curvature of the roadway on the basis of said angular displacement. It is also associated with means for storing computed values which retain the curvature or the radius of curvature at the bottom of the deflection S depression. It is thus preferable to store only one value per measurement cycle. The angular displacement of the hinged arm is measured over a plurality of points in front of and behind the back axle. The mean of the measurements performed at these points gives, by differentiation, the curvature at the bottom of the deflection depression. The radius of curvature is the reciprocal of said curvature.

The apparatus is advantageously associated with a computer system designed to eliminate calculated values that are deviant. Such values are considered as being deviant on the basis of predefined tests that take account of experience that has been acquired on this topic. Thus, any source of error due, for example, to the carriage sliding on the roadway can be eliminated.

The computer system may form part of a software package that also serves to collect and store the measurements performed, to calculate the deflection, and where appropriate, to calculate the radius of curvature.

Other characteristics and advantages of the apparatus appear more clearly on reading the following detailed description of embodiments given as non-limiting examples. The description refers to the accompanying drawings, in which: Figure 1 is a plan view of the apparatus associated with the vehicle; Figure 2 is a perspective view of the carriage on its own; Figure 3 is a perspective view of the apparatus associated with the vehicle in a turn; 20 Figure 4 is a plan view of the apparatus associated with the vehicle in a turn, with the carriage in its front stop position; Figure 5 is a view analogous to Figure 4, the vehicle having advanced so that the ends of the feeler arms lie vertically between the pairs of back wheels; o. Figure 6 shows the back end of a feeler arm fitted with a hinged arm; and Figures 7a and 7b are two block diagrams showing how the measurements are processed.

Figures i, 3, 4, and 5 show an apparatus for measuring the deflection of a roadway i, the apparatus being associated with a vehicle 2. The vehicle comprises a chassis 10, front wheels 12, and a load-carrying back axle 14 having two pairs of back wheels 14a and 14b. The apparatus is designed to measure the deflection of the roadway 1, i.e. the extent to which the level of the roadway sags as the load-carrying back axle 14 passes

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thereover, which back axle may be given a load of 13 (metric) tons, for example.

The apparatus for measuring deflection comprises a carriage 15 which is shown in perspective in ligure 2.

The carriage 15 rests on the roadway 1 via two front support points 16a and 16b and a back support point 16c.

These three support points define a reference plane. The front support points 16a and 16b are dispos-." on either side of the longitudinal axis A of the vi' l ciassis 10, while the back support point 16c lies ub't.- tially on said axis A. All three support points ar provided with skids (not referenced) that are required to provide a compromise between a good coefficient of friction on the roadway, a good high coefficient of sound and 15 vibration damping, and satisfactory resistance to .abrasion. Such a compromise can be achieved using skids .made of a plastics material or of a material based on rubber.

The apparatus is also provided with means for 20 determining the deflection of the roadway, which means comprise two feeler arms 18 and 20 pivotally mounted at their front ends 18a and 20a on an intermediate portion of the carriage 15 about an axis 22 extending across the carriage, the feeler arms rest on the roadway 1 via their back ends 18b and 20b which are provided with skids.

These back ends are placed on the respective paths followed by the advancing gaps 24a and 24b of the pairs of back wheels 14a and 14b. To clarify the drawings, only the path Ta of the midpoint of the gap 24a is shown in Figure 3. Thus, the back ends of the feeler arms 18 and 20 are liable to penetrate between each pair of back wheels to a point beyond the point immediately below the corresponding midpoints of the gaps 24a and 24b. The determination means also include means for computing the deflection of the roadway as a function of the attitude of the feeler arms and they are associated with means for storing the computed values. To clarify the drawings, n, I-II -u these means are represented in highly diagrammatic form under the references MC and MS in Figures i, 4, and The apparatus also includes means 26 for displacing the carriage 15 and associated with control means 28.

These control means 28 include a motor that is shown very diagrammatically in the figures. They have the function of releasing the carriage 15 before each measurement cycle, and after each measurement cycle they have the function of returning the carriage towards the front of the vehicle at a speed relative to the ground that is greater than the speed of the vehicle. Depending on the desired measurement pitch, and thus on the length of the gaps between successive measurement cycles, the control means may also serve to hold the carriage 15 at the front S 15 of the vehicle between two measurement cycles. This may be achieved, for example, by powering the motor 28 to a small extent on a continuous basis.

The two front support points 16a and 16b are disposed at the front of the carriage 15 and they define 20 a straight line D perpendicular to the longitudinal axis ••it of said carriage. From the beginning of each measurement cycle, the back support point 16c is placed behind the back axle 14. This position of the back support point is particularly clearly visible in Figure 1 which shows the apparatus and the vehicle at the beginning of a measurement cycle on a straight line.

Figure 4 shows the position of the carriage relative to the vehicle before a measurement cycle or between two measurement cycles when performing measurements in a turn, this figure showing that the back support point 16c may be placed in front of the back axle during this period. In Figure 5, which shows the position of the carriage relative to the r-ehicle towards the end of a measurement cycle performed in a turn, the back support point 16c is situated well behind the back axle 14.

The apparatus includes carriage guide means for guiding the carriage as a function of the turning circle radius of the vehicle 2 to prevent any crushing of the feeler arms 18, 20 by the back wheels 14a, 14b. The effect of these guide means is particularly visible in Figures 4 and Advantageously, the guide means comprise rolls that project from the top face of the carriage 15 and, as can be seen more clearly in Figure 2, that are disposed in pairs on either side of the longitudinal axis A' of the carriage and in a plane perpendicular to said axis A' These rolls comprise at least one pair of front rolls and 30b and one pair of back rolls 32a and 32b. The guide means also include elongate guide elements for said rolls, which elements are particularly visible in Figures i, 4, and 5. At least a fraction of said S 15 elongate guide elements is capable of pivoting as a function of the steering applied to the fron, wheels of the vehicle. Naturally, as shown in Figure i, when the vehicle is on a straight line, the various guide means no longer act to guide the carriage, such that the longitudinal axis A' of the carriage coincides with the o longitudinal axis A of the chassis 10 of the vehicle.

In Figure 4, it can be seen that while turning, the longitudinal axis A' of the carriage 15 slopes relative to the longitudinal axis A of the chassis 10 when the carriage is against its front stop. Th:'.s is also true at the beginning of each measurement cycle, and it is only at the moment of passing under the back axle, as shown in Figure 5, that the axes A and A' are again superposed.

The elongate guide elements advantageously comprise two fixed back guides 34a and 34b and two mobile back guides 36a and 36b. These back guides extend outside the back rolls 32a and 32b towards the back of the carriage The mobile back guides 36a and 36b extend approximately longitudinally and are pivotal as a function of the steering applied to the front wheels 12.

The fixed back guides 34a and 34b have back portions that are substantially parallel to the longitudinal axis A' of the carriage 15 and diverging front portions which determine the maximum angular displacement of the back rolls 32a and 32b.

These elongate guide element. also include front guides which comprise approximately longitudinal guide surfaces 38a and 38b extending between the front rolls and 30b and pivotal as a function of the radius of the turning circle of the vehicle 2.

The means for controlling pivoting of the front guides as a function of the radius of the turning circle of the vehicle are shown in highly diagrammatic form under the references 31 and 33 in Figures 4 and Reference 33 designates means for determining the radius of the turning circle of the vehicle 2, which means may 15 be mechanical or otherwise, e.g. being constituted by 0 encoders, and serve to transmit the radius of the turning circle to a device 31 for actuating pivoting of the front guides. The device 31 may be constituted, for example, by an actuator. For clarity in the figures, it is shown between one of the chassis elements and the front guides.

The position of this actuator is merely illustrative, however it is clear that it pivots the front guides not only in the direction shown in Figures 4 and 5, but also in the opposite direction.

S 25 The steering is also transmitted to the mobile back guides 36a and 36b. To this end, upside-down U-shaped parts 35a and 35b shown in plan view in Figures i, 4, and serve to connect the guide surfaces 38a and 38b to said mobile back guides 36a and 36b. The upside-down U-shape makes it possible to leave a free passage for the rolls (see the cutaway portion of the part 34b in Figure 4) when the vehicle and the carriage move relative to each other. It would clearly be possible to use only one upside-down U-shaped part, situated between one of the mobile back gui:Ldes, e.g. 36a, and one of the guide surfaces, e.g. 38a.

-I It is also possible to use other means, e.g. nonmechanical means, for transmitting steering to the moving guide means.

The guide surfaces 38a and 38b of the front guides pivot about a pivot 29 placed towards their back portions. Similarly, the mobile back guides 36a and 36b pivot about a pivot 37 likewise situated towards their back portions.

The mobile back guides 36a and 36b advantageously have front portions spaced apart at substantially the spacing E between the back rolls 32a and 32b at an endof-stabilization point Da, Db. As from this end-ofstabilization point, and up to a load takeup point Fa or Fb, these mobile back guides have back portions whose 15 spacing increases and then decreases returning substantially to the spacing E between the back rolls at the load-takeup point. Similarly, the guide surfaces 38a and 38b of the front guides have front portions that are spaced apart substantially by the spacing F between the front rolls 30a and 30b at an end-of-stabilization point .Ga, Gb. From this end-of-stabilization point and up to a load takeup point Ha, Hb, these guide surfaces have back portions whose spacing decreases and then increases, returning substantially to the spacing F of the front rolls 30a and 30b at said load takeup point Ha, Hb.

This particular disposition makes it possible to adopt different stages when the carriage 15 is released by its displacement means. The carriage is released while in a position where its front rolls 30a, 30b are situated facing the front portions of the guide surfaces 38a, 38b of the front guides and/or its back rolls 32, 32b are situated facing the front portions of the back guides 34a, 34b, 36a, and 36b. Initially, when the carriage is released, the various guides come into contact with the rolls to stabilize the beam and to position it correctly. The position of the beam is correct when the rolls are level with the end-of- L _I 13 stabilization points. Thereafter, the measurement cycle begins and the rolls should no longer come into contact with their guides, That is why it is advantageous for the spacing between the front guide surfaces to decrease and for spacing between the mobile back guides to increase. Measurements begin to be taken in the position shown in Figure 1, i.e. when the rolls are situated substantially behind the end-of-stabilization points.

When measurement is over, the carriage is brought back into guidance at the load-takeup points, where the rolls come back into contact with their guides. The last measurement point preferably corresponds to a position of the rolls slightly in front of said load-takeup points, so as to prevent measurement being perturbed by contact .I 15 between the rolls and their guides. The carriage 15 is then returned forwards and a new measurement cycle can begin again. Security against the feeler arms being crushed by the back wheels 14a and 14b is guaranteed by the fact that in a given position of the carriage 20 relative to the guide, the distance between the guides s er and the rolls is no more than the spacing K between the wheels in each pair of back wheels. This given position of the carriage corresponds to the position of the carriage at a given instant starting from the moment the S 25 carriage is released. Thus, at any moment, the maximum lateral displacement of the back ends of the feeler arms is no more than the spacing K between each pair of back wheels 14a and 14b, such that the ends of the feeler arms always lie on the paths of the gaps between the wheels.

This precaution makes it possible even to perform measurements behind a point vertically beneath the back axle 14.

Figures 4 and 5 show the vehicle at maximum steering lock, in which the front portion of the mobile back guide 36a overlies the front portion of the fixed back guide 34a.

The apparatus advantageously includes a stop assembly comprising front stop means for determining the foremost position of the carriage relative to the vehicle, as shown in Figure 4, and back stop means for determining the rearmost position of the carr-iage relative to the vehicle. This rearmost position is situated slightly behind the position shown in Figure which corresponds to the moment when the back ends of the feeler arms are vertically below the gaps between the pairs of back wheels.

In a preferred embodiment, the displacement means comprise a middle traction rail 26 extending longitudinally. In this case, as can be seen in the figures, the front guide may be constituted by lateral elements secured to the sides of said traction rail. The traction rail 26 is then likewise pivotally movable as a function of the radius of the turning circle of the front wheels about the pivot 29.

In this embodiment, the front stop means comprise at least one front stop element secured to the traction rail 26 and placed near its front portion. In the example shown, the front stop means comprise two front stop elements 40a and 40b extending on either side of the eeoc middle traction rail 26 and located towards its front 25 portion. The front stop means also comprise a front stop surface constituted by the front face of at least one of the front rolls 30a and 30b. Thus, at least one of these rolls is liable to come into contact with the front stop element to determine the foremost position of the carriage relative to the vehicle. It can thus be seen that the front rolls can perform simultaneously a function of guiding the carriage and a function of defining its foremost position.

They can also be used to contribute to defining the back stop position. The back stop means may comprise at least one back stop element 42a or 42b that is fixed relative to the front guides 38a and 38b, that is placed towards the back portions thereof, and that is designed to retain at least one of the front rolls 30a and 30b to define the rearmost position of the carriage. In the example shown, the two back stop elements 42a and 42b are identical.

In addition, or as an alternative, the back rolls may also contribute to defining the rearmost position of the carriage. To this end, the back stop means may comprise at least one back stop member 44a, 44b that is situated substantially level with the back axle 14 and that is designed to retain at least one of the back rolls 32a and 32b.

To facilitate braking of the carriage while it is being brought to rest, either against the front stop or S 15 against the back stop, the stop assembly may be associated with carriage shock absorbers. In the example shown, shock absorbers 46a and 46b are associated only with the front stop means, however it is possible to provide similar shock absorbers that are associated with the back stop means.

The front stop means 40a and 40b may comprise an S. energy-restoring system which, in the example shown, is directly associated with the shock ibsorbers 46a and 46b.

This energy-restoring system which is constituted by a ore S 25 spring, is so designed, that when the carriage 15 is released before the beginning of a measurement cycle, it restores the energy stored during the shock of the front stop means 40a, 40b, 30a, 30b. This energy-restoring system thus makes it possible to accelerate the positioning and stabilizing of the carriage once it has been released relative to the vehicle.

The means 28 for controlling the carriage displacement 26 advantageously comprise means for automatically determining displacement and release sequences for the carriage 15 on the roadway 1 and associated with position sensors 48. These position sensors 48 may be distributed along the chassis 10 of the vehicle and they serve to transmit the position of the carriage to the means for controlling its displacement, which means are actuated accordingly. A single computer system can serve simultaneously to handle measurement acquisition and to control the sequences of pulling, releasing, and recovering the carriage.

In a preferred embodiment, the means for computing the deflection of the roadway comprise rotary encoders 19a and 19b for measuring the pivot angle of the feeler arms 18 and 20 and means MC for determining the displacement of the skids on said feeler arms as a function of the measured degree of pivoting. These rotary encoders 19a and 19b are represented highly diagrammatically in the figures and they make it possible 15 to avoid any need for the operators to calibrate the measurements. They serve to measure pivoting of the feeler arms between two given instants, and therefore they do not need zeroing. This further improves the speed with which measurements can be taken.

The apparatus may include at least one inclination indicator designed to determine the radius of curvature of the roadway. The state of the roadway can be defined not only by the depth of the deflection depression as given by the aoove-specified means for determining S 25 deflection, but also by the curvature at the bottom of said deflection depression. It is also possible to take account of the temperature of the roadway when processing the measurements, in which case it is necessary to dispose temperature sensors beneath the vehicle.

As shown in Figure 6, which shows a detail of the end 18b of a feeler arm, the inclination indicator includes at least one hinged arm 51 provided with a skid 52. The arm 51 is mounted to pivot about a horizontal axis P at the back end 18b of a feeler arm 18. The end 18b is already provided with a skid 50, which is used for measuring deflection, and the skid 52 of the hinged arm 51 is placed at a determined distance L from the skid

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17 of the feeler arm. Clearly the two skids are preferably in alignment in the longitudinal direction. The inclination indicator also includes measurement means MD shown diagrammatically in Figures i, 4, and 5 for measuring the angular displacement of the skid hinged about its pivot axis P, and computation means MCI for computing the radius of curvature of the roadway 1 on the basis of said angular displacement. The inclination indicator is also associated with means MS for storing the computed values and that serve to store, for each measurement cycle, the value of the radius of curvature at the bottom of the deflection depression. The vertical positions of the skid 50 and of the skid 52 are measured, thereafter, as a function of the distance L between these S 15 two skids, it is possible by differentiation to calculate the curvature of the deflection depression. The calculation is performed on the basis of a few measurement points situated on either side c4 ue tically below the back axle, and on the basis therecur curvature at the bottom is determined. The radius of curvature is given by the reciprocal of said curvature.

Clearly the means MCI for computing the radius of curvature and the means MS for storing the calculated values can form portions of the computer system mentioned 25 above.

Figure 6 shows the beginning of a cable 54 which connects the hinged skid 52 to the remainder of the apparatus. To avoid cluttering the drawings, the other cables that interconnect the various component elements of the apparatus are not shown. Naturally, there are cables connecting the ends of the feeler arms to the rotary encoders, cables connecting the rotary encoders to the deflection computing means, and where appropriate, cables connecting the means for automatically determining displacement and release sequences of the carriage to the position sensors 48 and to the means 28 for controlling the carriage displacement reans. Specifically for the purpose of facilitating displacement of the carriage, the various cables are displaced by the carriage traction system, thereby making it possible substantially to cancel any forces transmitted by said cables and applied to the carriage. This thus makes it possible to avoid the traction cables and the data transmission cables interfering with the measurements.

Still with reference to Figure 6, it can be seen that the hinged arm 51 may be removable. Thus, it is possible at will either to measure only the depth of the deflection depression, or else also to measure the radius of curvature thereof. Naturally, it is possible to implement means for determining the deflection and the inclination indicator either simultaneously or else 15 separately from each other.

As can be seen from Figure 6, the hinged skid 52 may be mounted at the back end of a hinged arm 51 itself mounted to the end 18b of the feeler arm 18, e.g. by means of a fork 53 and a screw on the axis P. As already mentioned, the hinged skid, or more particularly the hinged arm 51, may be removable and may be withdrawn merely by unscrewing the screw on the axis P, with the cable 54 being connected or disconnected by means of a *connector 60. Reference 62 designates a cell on the 25 hinged arm 51 and serving to measure inclination.

The skids 52 and 50 are parts that are subject to wear, and it is therefore clearly preferable for those parts to be capable of being changed. To this end, the skid 52 can be fixed to the end of the hinged arm 51 by means of a screw 58, while the skid 50 is fixed to the end 18b of the feeler arm 18 by means of a screw 56.

This method of fixing the skids 50 and 52 can clearly be seen in the figure which is a section view showing the hinged arm 52 and the end 18b of the feeler arm.

Figure 7 comprises a first portion 7a which is a flow chart for measuring deflection, and a second portion 7b which is a flow chart for measuring the radii of 19 curvature of the deflection depression. Measurements are taken while the vehicle 2 is travelling at constant speed. Initially, the carriage displacement means re4lease the carriage onto the roadway. The vehicle then advances relative to the carriage so as to give the carriage time to stabilize and damp vibrations.

Measurements begin at a measurement starting point, and they end at a measurement finishing point. After the measurement finishing point, the carriage is recovered at its back stop and is then returned by its displacement means towards ihe front of the vehicle until it reaches its front stop position. As explained above, the displacement means may be controlled by a computer system which receives data from position sensors 48. For S 15 example, during a measurement cycle, a measurement may be taken about once every 2 centimeters. The measurement :i cycle pitch may be 10 meters, i.e. measurements are repeated every LC meters, with the vehicle moving forwards at a speed of 10 kilometers per hour. It is also possible to take measurements at a pitch of 5 meters for a constant speed of advance of 3.5 km/h.

During the measurement cycle, deflection is determined in the following manner as shown by the flow *fl.

chart of Figure 7a. The rotary encoders 19a and 19b observe the attitude of the feeler arms 18 and 20 about every 2 centimeters. These rotary encoders 19a and 19b ;thus determine the degree of pivoting of the feeler arms

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•once every 2 centimeters. The computer means MC then determine the displacement of the skids 50 as a function of the degree of pivoting. This gives the deflection of the roadway once every 2 centimeters. At each measurement point, the ccmputer system SI can be used as a filter to eliminate values that are deemed to be deviant on the basis of predefined tests. Values tha are deemed to be acceptable are then stored by the storage means MS and the set of these values gives the depth of the deflection depression once every 2 centimeters.

With reference to the flow chart of Figure 7b, there follows a description of how the radius of curvature at the bottom of the deflection depression is determined.

The measurement means MD determine the angular attitude of the hinged arm 51 provided with the skid 52 at a few points situated on either side of vertically below the back axle. These measurement means MD may be associated with the above-mentioned rotary encoders and they determine the angular displacement of the hinged arm 51.

The computer means MCI are then implemented to calculate the curvature at these few points, to average the results obtained and thus deduce the curvature at the bottom, and 15 then to take the reciprocal of the curvature in order to "obtain the radius of curvature at the bottom. As S. mentioned above, the computer means determine the curvature on the basis of the inclination of the hinged arm 51 and on the basis of the distance L between the skid 50 at the end 18b of the feeler arm from the skid 52 at the back end of the hinged arm 51. The curvature *results at the various measurement points may be passed through a filter constituted by the computer system SI which serves to eliminate values that are deemed to be 25 deviant on the basis of predefined tests. Values that are deemed acceptable are then taken into account for calculating the curvature at the bottom of the deflection depression. The storage means MS store a value for the radius of curvature for each measurement cycle.

Clearly the various computer means MC and MCI, the computer system SI, and the storage means MS may all form portions of overall computer management software. In addition, as mentioned over, the computer management software may also manage the sequences of depositing and repositioning the carriage on the roadway as a function of data transmitted by the position sensors 48. The various computer means are preferably mounted on board the vehicle.

Naturally, numerous modifications can be made to the apparatus as described above without going beyond the ambit of the invention.

*Oe ae.