Optical dimension measuring device employing an elongated focused beam

United States Patent m

Taylor

[li] 4,074,938 [45] Feb. 21, 1978

[54] OPTICAL DIMENSION MEASURING

DEVICE EMPLOYING AN ELONGATED
FOCUSED BEAM

[75] Inventor: Francis M. Taylor, Xenia, Ohio

[73] Assignee: Systems Research Laboratories, Inc.,

Dayton, Ohio

[21] Appl. No.: 726,991

[22] Filed: Sept. 27,1976

[51] Int. C1.2 G01B 11/10

[52] U.S. CI 356/160; 250/560

[58] Field of Search 356/160, 167; 250/548,

250/560, 571

[56] References Cited

U.S. PATENT DOCUMENTS

3,804,529 4/1974 Hansler 356/167

4,007,992 2/1977 Petrohilos et al 356/160

Primary Examiner—John K. Corbin
Assistant Examiner—Wm. H. Punter
Attorney, Agent, or Firm—Biebel, French & Nauman

[57] ABSTRACT

In an optical dimension gauging instrument, commonly referred to as a laser micrometer, particularly for use in

measuring the outside dimension of elongated cylindrical objects, such as coated wires of steel tubes, in hostile optical environments, including a laser for generating a beam of collimated light, means for directing the light through a measurement zone, photodetector means responsive to the light passing through the measurement zone, and a mirror mounted for rotation by a motor to cause the beam to be scanned repeatedly across the measurement zone, a beam expander is employed to enlarge the output of the laser to a diameter substantially greater than the maximum dimension of normally anticipated foreign objects which might intercept the beam outside the measurement zone, an anamorphic lens further expands the beam in one plane to a size greater than the size of normally anticipated foreign objects both within and without the measurement zone, and a lens system causes the beam to be focused in the other plane ia the measurement zone while the expanded beam is projected through the measurement zone with the long dimension of the beam parallel to the cylindrical axis of the article whose outer dimension is being measured.

3 Claims, 11 Drawing Figures

OPTICAL DIMENSION MEASURING DEVICE EMPLOYING AN ELONGATED FOCUSED BEAM

BACKGROUND OF THE INVENTION 5

This invention relates to improved optical dimension gauging instruments now commonly referred to as laser micrometers.

Examples of optical or laser micrometers are shown in the following U.S. Pat. Nos. : 2,812,685, 3,856,411 10 3,765,774, 3,856,412, 3,592,545, 3,686,437, 3,743,428, 3,870,890, 3,853,406, 3,905,705.

Laser micrometers are effective in measuring certain products by non-contact methods, and the resulting measurement signal may be used to control the process 15 by which that product is manufactured. The accuracy and tolerance to which the end product can be made depends upon whether the laser micrometer can see the article and the nature of the disturbing influences which are present. 20

In certain maufacturing processes, the atmosphere surrounding the object being measured may be hostile due to dust or vapor, and in those processes where the measurement must be inside of a closed container, dirt, dust, water and other foreign objects may collect on the 25 viewing windows.

For example, in the manufacture of insulated wires wherein material extruded on the wire is vulcanized in what is known as the continuous vulcanization process, the coated wire is enclosed in a steam tube hundreds of 30 feet long. Attempts have been made to measure the hot diameter of the wire while in the steam tube using conventional laser micrometers positioned on either side of sight glass windows. Such attempts have only met with partial success because of the variable and optically 35 hostile atmosphere within the tube, water droplets on the wire, in the air and on the sight glass, and occasional momentary irregularities resulting from the extruding process prevent accurate continuous diameter measurements. 40

Another example is in the manufacture of precision steel tubing where it is important to have an accurate measurement of the hot outside diameter of the tubing after it passes through rollers which control its dimensions. Since the tubing is frequently red hot at the de- 45 sired point of measurement, a non-contacting type gauge is normally used, such as a laser micrometer. However, the optical atmosphere in a steel mill is generally poor, especially since the hot tubing is frequently surrounded by vapor, dust and dirt. 50

SUMMARY OF THE INVENTION

This invention relates to an optical or laser micrometer which is so constructed as to reduce the sensitivity of the dimension measurements to all objects in the 55 ambient environment which may intercept the optical beam except those objects having a specific geometry and which occupy a specified position in space.

Specifically, the improved optical or laser micrometer of this invention may be used to measure the hot 60 diameter of elongated cylindrical objects, such as a horizontally moving coated wire or steel tube, having a total outside diameter of one-quarter inch, for example, but it would be insensitive to a one inch diameter round or cubically shaped object or even a vertically posi- 65 tioned one-quarter inch diameter cylinder. Similarly, the instrument would be insensitive to a horizontally positioned one-quarter inch diameter cylindrical object

located outside the measurement zone, as for example on the sight glass.

The above result is accomplished by focusing a laser beam to a thin, elongated line of light within a measurement zone, and defocusing the laser beam outside the measurement zone. Therefore, only a portion of the non-focused beam would be intercepted by an object which is not of the proper configuration (cylindrical) or which is located outside the measurement zone. For example, an object such as water or dirt on a sight glass assembly through which the laser beam is directed would be in the areas where the beam is non-focused, and therefore a substantially larger object is needed to intercept the beam at that location than would be necessary if the object were located in the measurement zone.

In a preferred embodiment of the invention, a laser beam is first expanded from approximately 0.025 inch to approximately 0.750 inch in diameter. The laser beam then passes through an anamorphic lens which focuses the beam in a first plane (horizontal, for example) onto a scanning mirror while leaving the beam in a second, orthogonal (vertical), plane collimated. A first scan lens having a focus un one side thereof on the scanning mirror, and the beam will have a horizontal length of approximately three inches at the scan lens. The elongated dimension of the beam is parallel to the cylindrical axis of the cylindrical article moving through the zone of measurement, and the scanning mirror causes the beam to be scanned vertically through the measurement zone. Since the anamorphic lens does not effect the dimension of the beam in the second or vertical plane, that beam is essentially collimated until it passes through the first scan lens which then focuses the beam to a fine line approximately 0.010 inch in thickness and three inches in length within the measurement zone. After the beam passes through the measurement zone it again expands in its vertical dimension, passes through a second scan lens and is projected onto a photodetector element.

Thus, in the region of the sight glass on either side of the measurement zone, the beam is approximately 0.750 inch thick and three inches long. Within the measurement zone, the beam is 0.010 inch thick and 3 inches long.

The vertical dimension of the beam outside the zone of measurement is made greater than any anticipated foreign object located outside the zone of measurement, and the horizontal expansion of the beam is made greater than any foreign object anticipated both within and without the zone of measurement. Also, the length of the beam in the measurement zone is longer than the momentary discontinuity or irregularity which might be introduced onto the object being measured. This insensitivity to momentary irregularities allows an optical micrometer constructed according to this invention to be used effectively in a system for the accurate control of the outside dimension of an object or the outside diameter of a coating placed on an object.

Accordingly, it is an object of this invention to provide an optical micrometer of the type described wherein the scanning beam is focused and elongated in a zone of measurement to provide accurate dimension information of cylindrical objects and defocused outside the zone of measurement to render the micrometer insensitive to objects in the ambient environment.

These and other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.