Head for measuring reflectance

• US 4,666,309 A
• Filed: 07/01/1983
• Issued: 05/19/1987
• Est. Priority Date: 07/14/1982
• Status: Expired due to Fees

• Current Assignee: Compur-Electronic GmbH
• Original Assignee: Compur-Electronic GmbH
• Inventors: Jansky, Karl P., Barry, Jurgen
• Primary Examiner(s): ROSENBERGER, RICHARD A
• Application Number:
  US06/510,461
• Time in Patent Office: 1,418 Days
• Field of Search: 356/445-448, 356/402, 356/375, 250/227, 350/96.24
• US Class Current: 356/446
• CPC Class Codes: G01N 2021/4742 comprising optical fibres
• CPC Class Codes: G01N 21/474 Details of optical heads therefor, e.g. using optical fibres

Abstract

The present invention is with respect to a reflectance measuring head that is designed for stopping the production of false readings by regular (as opposed to diffuse) reflection and shiny parts of the sample without using normal shine traps or diaphragms. False readings as produced by regular reflection, by surface grain or structure and by inhomogeneity of the surface of the sample are furthermore put an end to by having a number of transmitters placed at an equal distance from one receiver or having a number of receivers placed at an equal distance from a transmitter. A more specially useful effect is produced if a number of transmitters and a number of receivers are placed alternately in the form of a matrix.

Claims

1. A measuring head for measuring diffusely reflected light from the reflecting surface of a reflecting material while minimizing the measurement of regularly reflected light from the reflecting surface, the measuring head comprising:

a transmitter including a transmitter axis;

a receiver defining a receiver axis and a receiver aperture angle ε

, the receiver aperture angle ε

defining a light acceptance cone;

a first light guide having a first diameter;

a plurality of second light guides each having a second diameter;

the transmitter including a chosen one of the first and second light guides while the receiver includes the other of the first and second light guides;

the transmitter being adapted to create a conically diverging transmitted light beam to create an illuminated area on the reflecting surface, the transmitted light beam having a transmitter aperture angle u, the receiving being adapted to accept light reflected from the reflecting surface along the light acceptance cone;

the transmitter and receiver alternately positioned at an equal spacing from each other in the form of a matrix;

the receiver positioned substantially outside of a cone of regularly reflected light from the reflecting surface to minimize receipt of regularly reflected light;

the receiver aperture angle being substantially equal to the sum of a first angle α and

a second angle δ

, the second angle δ

being equal to or greater than the transmitter aperture angle u, wherein the first angle α

is an angle between reflected light rays coming to the receiver and a line normal to the reflecting surface and wherein the second angle δ

is an angle substantially equal to or greater than the transmitter aperture angle u; and

the receiver aperture angle ε

being sized and the receiver being positioned relative to the reflecting surface so that the light acceptance cone of the receiver encompasses substantially the entire illuminated surface to maximize receipt of diffusely reflected light.

2. The measuring head as claimed in claim 1 wherein the said angle α

has a value between 40° and

50°

.

3. The measuring head as claimed in claim 1 wherein the said angle α

is in substance equal to 45°

.

4. The measuring head as claimed in claim 1 wherein the distances between the transmitter and the reflecting surface and between the receiver and the reflecting surface are equal to each other, said head further comprising a transparent plate, including transmitting and receiving planes, with an index (n) of refraction generally equal to 1.5 between the transmitting plane and the receiving plane on one hand and the reflecting surface of the reflecting material on the other.

5. The measuring head as claimed in claim 4 wherein said angle α

has a value of 28°

.

6. The measuring head as claimed in claim 1 comprising at least two receivers each placed at a distance x from the transmitter in one plane.

7. The measuring head as claimed in claim 1 wherein the transmitter and receiver are oriented parallel to one another and perpendicular to the reflecting surface.