Retroreflectometer giving direct reading

• US 4,373,819 A
• Filed: 12/22/1980
• Issued: 02/15/1983
• Est. Priority Date: 12/21/1979
• Status: Expired due to Fees

• Current Assignee: Autostrade
• Original Assignee: Stefano Pallotta
• Inventors: Pallotta, Stefano
• Primary Examiner(s): ARNOLD, BRUCE
• Application Number:
  US06/219,390
• Time in Patent Office: 785 Days
• Field of Search: 356/445-448, 356/429, 356/430, 356/369, 356/237, 356/238, 356/371, 250/571, 250/572, 250/559, 250/562
• US Class Current: 356/445
• CPC Class Codes: G01N 21/55 Specular reflectivity

Abstract

The invention concerns an improved retroreflectometer giving direct readings for measuring the value or degree of retroreflectivity, or visibility at night, of a paint applied to the surface of the road for marking ground signs, under conditions that simulate geometrically the real conditions of illumination and visibility of the sign from the driver of a vehicle. The value or degree of retroreflectivity is measured directly from the sample in question, making it unnecessary to have a sample for comparative purposes and, as a result, eliminating the need to zero the apparatus before each measurement is taken. Provision is made for varying the angle at which the light beam strikes the sample, so as to simulate the actual conditions produced by different heights and/or degrees of inclination of the headlights of different categories of vehicles, and to vary the degree of inclination of the detecting element in relation to the retroreflected beam, so as to simulate the visual angle of the driver, and thus alter the angle of divergence, or phase displacement angle, between the incident beam and the retroreflected beam. The detected data are processed, stored and transduced, so as to be readable on a known type of display.

Claims

1. A retroreflectometer giving direct readings, for measuring the value or degree of retroreflectivity of a paint applied to the road surface for marking road signs, and consisting essentially of a light-proof box or chamber (1), essentially prismatic in shape, and having in its under-side a rectangular opening or "window" (2) the perimeter of which has a frame (3) of lightproof, flexible material of a kind that will adhere to the surface to which it is placed, the retroreflectometer comprising:

a source of light, consisting of a parabolic reflector (12) and a light bulb (14) mounted on a rod (9) free to move in the vertical plane and attached, at one end, to the spindle of a hinge (10) fixed internally to the base of the chamber (1) near the "window" (2) which bounds the sample (20) to be measured, and a convergent lens (16) also mounted on the rod (9) for the purpose of directing on to the sample (20) the beam or ray (17) of light emitted by the source (12,

     14) so as to avoid dispersion, the rod (9) being inclinable in relation to the horizontal to at least 3 predetermined angles of inclination, suitable to be selected by means of a selector (18) that can be set from the outside;

at least one photo-electric cell (24) able to receive the retroreflected beam or ray of light (25) from the sample (20) under examination, such photo-electric cell (24) being mounted on a small plate (23) fixed to a rotating axle (22) mounted transversely in respect with the side walls of the chamber (1), and in a position such that the length of the retroreflected ray striking the photo-electric cell is about half the focal length of the lens (16)--so that the photo-electric cell (24) is struck by a cone of retroreflected light sufficiently small to obviate the need for optical focusing and/or return systems--, said plate being capable of being set at at least three predetermined angles of inclination, by means of an external knob (26) which turns the axle (22);

the value of degree of retroreflectivity of the sample measured by the photo-electric cell (24) being processed, stored and transduced PG,14 and so made available for reading on display (39).

2. A retroreflectometer according to claim 1, wherein the source of light, the incident ray and the retroreflected ray are arranged to simulate the real conditions of illumination and nocturnal visibility of road signs marked on a road'"'"'s surface from the driver of a motor vehicle;

and that the measurement of the value or degree of retroreflectivity is executed directly on the sample in question, eliminating the need for a comparative sample and, in consequence, the need for zeroing the apparatus before each measurement, being also possible to vary the angle of inclination of the incident ray (α

) and the angle of inclination of the photo-electric cell in relation to the retroreflected ray which simulates the driver'"'"'s angle of sight, and thus altering the value of the angle of divergence or phase displacement angle (β

-α

) between the incident ray and the retroreflected ray, the angle (β

) being the angle between the retroreflected ray and the horizontal.

3. A retroreflectometer in accordance with claims 1 or 2, wherein the optimum angles (α

), obtained experimentally, are 11°

, 13.5° and

16°

.

4. A retroreflectometer in accordance with claims 1 or 2, wherein the optimum time of the timer experimentally obtained in order to stabilize the reading of the retroreflectivity value is of 20 sec., and after this time the apparatus resets itself automatically.

5. A retroreflectometer in accordance with any one of claims 1 or 2, wherein the photosensitive measuring apparatus consists of a plurality of photo-electric cells (24) connected in series, each of which is provided to measure a portion of the intensity of the ray of retroreflected light, so as to ascertain a selective value for each single portion, such values being subsequently transduced into cumulative logical values, thus allowing a detailed survey to be made for the behavior of the sample.

6. A retroreflectometer in accordance with claim 1, characterized in that it is constructed in two separate sections or modules, one comprising the chamber with its photo-optical element and a battery of accumulators, and the other section, in the form of a portable control panel or console, comprising reading and control instruments.

7. An improved retroreflectometer in accordance with claim 1, which is fixed to a chassis that is open underneath and mounted telescopically on a trolley on roller or castors, so that it can be raised and lowered to enable the chamber to be in contact with the ground;

the chassis being raised and lowered by means of a rack and sector gear, or hydraulic devices, that can be operated by means of a bar used to tow and steer the trolley.