Measuring and testing – Tire – tread or roadway
Reexamination Certificate
2002-06-13
2004-02-10
Lefkowitz, Edward (Department: 2855)
Measuring and testing
Tire, tread or roadway
C073S104000, C073S105000
Reexamination Certificate
active
06688167
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of measuring departures from planeness in the surfaces of road and highway pavements, and of all paths on which vehicles of any type travel, including runways.
BACKGROUND OF THE INVENTION
Departures from planeness in road or highway pavements, in traffic paths of all types, and in runways, give rise to significant drawbacks for users and also for the works themselves. For users, numerous studies have shown that the comfort, safety, and costs of using vehicles are influenced to a very great extent by the vibrations induced by departures from planeness. So far as the works themselves are concerned, these defects give rise to additional stresses which shorten their lifetime.
As a result, regulations require minimum quality standards to be satisfied when the works are constructed, both for satisfying users and for ensuring long life for the work. An evaluation of the planeness qualities of a work is also one of the major parameters used during periodic inspections thereof for maintenance purposes.
The advantage of having means for measuring departures from planeness is therefore manifest, both for contractors and for authorities.
In conventional road terminology, it is the practice to use the terms “profile” and “departures from profile” rather than “departures from planeness”, and apparatus capable of providing an image of the real profile of the road surface by sampling along one or more substantially parallel lines in a given direction, and capable of being included in ordinary traffic, is referred to as a “dynamic” profilometer, as contrasted with “static” profilometers which require the road under test to be closed to traffic.
It should be observed that all existing profilometers give an image that approximates to the real profile, firstly because they do not observe the entire surface but only a finite number of lines, and secondly because they filter the real profile, deforming it both in amplitude and in phase within wavelength bands where their response differs from unity, and generally in phase even in frequency bands where their amplitude response is indeed unity.
So far as roads are concerned, the following are generally distinguished:
microtexture for wavelengths shorter than 0.5 millimeters (mm);
macrotexture for wavelengths lying in the range 0.5 mm to 50 mm;
megatexture for wavelengths lying in the range 50 mm to 0.5 meters (m); and
smoothness (or conversely roughness) for wavelengths lying in the range 0.5 m to 50 m.
Present dynamic profilometers can be classified in two broad categories:
profilometers using an inertial reference making use of an inertial type artificial horizon as a reference plane, and measuring variations in height relative to said reference plane in order to estimate profile; by construction such devices are sensitive to measurement speed and to the quality of their reference plane; and
profilometers using a pure geometrical reference, which starting from a known position enable profile to be reconstructed by moving a ruler with precision; by construction, these devices are sensitive to the precision with which the ruler is moved and also to measurement errors, where the influence of such errors generally increases exponentially with distance.
The state of the art is illustrated by document WO 98/24977 published on Jun. 11, 1998 which shows a profilometer on board a vehicle, the profilometer having three contactless distance-measuring sensors mounted at the front of the vehicle chassis and aligned transversely in a direction perpendicular to the travel direction of the vehicle, together with a system for measuring the positions of the sensors relative to an artificial horizon, said system comprising in particular an accelerometer for measuring vertical acceleration and inclinometers for measuring the inclinations of the chassis relative to the artificial horizon, both in terms of roll and in terms of pitch. Each sensor provides a measurement of its height above the pavement. By using a computer that is connected to the various devices, that profilometer makes it possible to reconstruct the profile along three lines drawn along the pavement, one line to the right of the vehicle, one line to the left of the vehicle, and a central line.
U.S. Pat. No. 4,571,695 describes a device whose intended purpose is to measure the smoothness of a pavement, i.e. its deformation in the absence of any load relative to an ideal surface, and it also seeks to measure pavement deflection, i.e. deformation under the effect of a load relative to its state in the absence of load.
Given the principle on which it works, the device described in U.S. Pat. No. 4,571,695 requires four sensors referenced
10
,
20
,
30
, and
40
in its
FIGS. 1 and 2
. That document describes measuring smoothness with the help of a memory system, requiring extreme accuracy in the positioning of one measurement relative to another. The term “memory system” is used to designate a measurement system in which the value of measurement n depends on the value of measurement k where k<n. Such systems present at least two particular features: firstly, any error in measurement k induces an error in measurement n and entrains error propagation, and secondly it is generally necessary to make assumptions about the first measurement or to apply a posteriori corrections on the set of measurements, even if they do not include any error, in order to compensate for the lack of any antecedents for the first measurement. Thus, in the measurement method described in U.S. Pat. No. 4,571,695, the height of each measurement point is a function of previously measured points and the pitch at which measurement points are sampled is determined by the relative position of the various sensors along the beam which they use as a support.
The present invention thus seeks to provide a method of reconstituting the profile of a line drawn on a pavement that makes it possible to ignore the oscillations of the support for the measuring devices (body movements if the support is a road vehicle), variations in speed, speeds of the support, and problems of phase, of the influence of the shape of support beam on the sampling pitch, and of the need to use the preceding points in order to calculate the current point.
SUMMARY OF THE INVENTION
The method of the invention is characterized by:
moving over the pavement three contactless distance-measuring sensors that are equidistantly in horizontal alignment in the direction of motion;
simultaneously measuring the height of each of the three sensors above the pavement;
measuring the distance travelled by one of said sensors; and
substracting twice the height measured by the middle sensor from the sum of the heights measured by the end sensors.
It can be shown by calculation that the result of the subtraction is proportional to the function that represents the profile, and that it is independent of the position of the artificial horizon used in conventional methods of calculation. This is shown below in the present specification. In addition, the coefficient of proportionality does not include a phase term. As a result, if a direct Fourier transform is applied to the signal representative of the result of the subtraction, and if a simple multiplying coefficient is applied to the real and imaginary portions of the transform, then the initial profile can be obtained by performing the inverse Fourier transform.
The three contactless measurement sensors preferably pick up the distance between themselves and the pavement simultaneously. This operation is repeated each time the sensors have travelled through a selected distance. This distance is fixed for any one series of measurements.
The travel distance pitch is fixed for a series of measurements corresponding to a sample or to a portion of the pavement, but this travel distance pitch can be modified at will. It can be made longer when it is desired to measure the smoothness or the megastructure of the pavement, or shorter when it is desired to measure the microtexture or
Ellington Alandra
James Ray & Associates
Laboratoire Centrao des Ponts et Chaussees
Lefkowitz Edward
LandOfFree
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