Optical-electrical measuring method for determining cross-sectional dimensions

An optical-electrical measuring method for determining cross-sectional dimensions particularly of elongate articles with reference to at least one straight line, which is applied to the periphery of the cross-section and contacts the cross-section at, at least two points, and apparatuses for carrying out that method are presented. A light beam moved within a measuring field by a parallel displacement transverses at measurable locations in the measuring field boundaries of a region which is vignetted by the article disposed in the measuring field. The surface of the article is illuminated at a point by the same light beam when it has been deflected or by another light beam, and the distance from the axis of the light beam at the location of a predetermined boundary of the vignetted region to that illuminated point is determined in that an image of that point is formed at an angle which differs from the angle of the illumination and the location of the image is determined by triangulation. The entire measuring system is pivotally moved relative to the orientation of the cross-section of the article about an axis which is parallel to the longitudinal axis of the article. As a result, a detectable discontinuity of the change of the determined distance is detected, which discontinuity is characteristic of that angular position of the measuring system in which the axis of the light beam at the location of the predetermined boundary of the vignetted region contacts the periphery of the cross-section at at least two spaced apart points.

BACKGROUND OF THE INVENTION 
This invention relates to an optical-electrical measuring method, in which 
cross-sectional dimensions particularly of elongate articles are 
determined in geometric analogy to the known operation of mechanical depth 
indicators in that the distance from a point to be measured at the 
periphery of a cross-section to a straight reference line is determined, 
which contacts the periphery of the cross-section at at least two spaced 
apart points. By a pivotal movement of the entire measuring system a light 
beam, which is moved in the measuring field by a parallel displacement, is 
caused to contact in a measurable position assumed during that movement 
the periphery of the cross-section at said at least two points which 
determine the straight reference line when the measuring system is in a 
detectable angular position, and the distance from the point to be 
measured to the axis of the light beam in that contacting position is 
determined. 
A method of that kind has been proposed in Published German Application 32 
19 389, which is incorporated herein by reference and an apparatus for 
carrying out the method has also been described there. By means of that 
apparatus it is possible, e.g., to measure the movement of the light beam 
during its parallel displacement through the measuring field from its 
entrance into the region which is vignetted by the article disposed in the 
measuring field to its re-exit from that region when the entire measuring 
system is in such an angular position that the light beam exiting from the 
vignetted region contacts the periphery of the cross-section at at least 
two points, which determine a straight reference line. In that manner it 
is possible to measure at an angle section the width of each leg as the 
perpendicular distance from its terminal generatrix to the outside surface 
of the respective other leg or the height of a tee section. But that known 
measuring method cannot be used for measurements of the above-mentioned 
kind unless the point to be measured and those points on the periphery of 
the cross-section which determine the straight reference line constitute 
the boundaries of the vignetted region. 
But for a complete measurement of angle, tee, C or I sections or similar 
elongate products it is necessary also to measure leg thicknesses, flange 
thicknesses, web thicknesses and flange depths in cases in which terminal 
points of a distance to be measured or points of the straight reference 
line lie in all angular positions of the measuring system at such 
locations that they are covered by the shadow cast by other parts of the 
periphery of the cross-section in parallel or parallel-scanning light so 
that they do not constitute the boundaries of the vignetted region. For 
this reason such sections cannot completely be measured by means of the 
known method. 
SUMMARY OF THE INVENTION 
The above-discussed and the drawbacks and deficiencies of the prior art are 
overcome or alleviated by the optical-electrical measuring method for 
determining cross-sectional dimensions of the present invention. In 
accordance with the method of the present invention a measuring apparatus 
is provided in which a scanner for generating a light beam that is rapidly 
moved through the measuring field by a parallel displacement is mounted on 
one side of the measuring field on a motor-driven swivel mount. The swivel 
mount is pivotally movable about the article to be examined, and a 
receiver for receiving the light beam generated by the scanner and for 
generating electric signals in dependence on the vignetting of that light 
ray is mounted on the swivel mount on the other side of the measuring 
field. An optical-electrical distance sensor having a line of action that 
crosses in the measuring field the light beam generated by the scanner is 
also mounted on the swivel mount on the other side of the measuring field 
and comprises a light source for illuminating the article at a point in a 
predetermined direction. An optical system for forming an image of the 
illuminated point on a position-detecting optical-electrical receiving 
element is also mounted on said swivel mount on the other side of the 
measuring field. The spatial position of the distance sensor with respect 
to the scanner is invariable or is scanned by the scanner. 
In such a measuring apparatus the scanner preferably comprises a light 
source for generating a sharply defined light beam, which is caused to 
perform an angular movement by a motor-driven rotating mirror, and to 
perform a parallel displacement by collimating means. Distances covered by 
the movement are detected in that countable pulses are generated by a 
pulse generator at a frequency which by feedback control systems is caused 
to be proportional to the instantaneous velocity of the movement of the 
light beam in the measuring field. In that measuring apparatus the 
optical-electrical scanner receiver for receiving the parallel-displaced 
light beam emitted by the scanner preferably comprises optical focusing 
means and a detector for generating the electric signals, which depend on 
the received light beam or on its vignetting by the article. The scanner 
and the receiver of that measuring apparatus in an aligned arrangement are 
well known and are described, for example, in German Patent Specification 
28 49 252 which is incorporated herein by reference. In accordance with 
the present invention, the distance sensor which is scannable by the 
parallel-displaced light beam from the scanner is so arranged that the 
line of action of that sensor is oriented in the direction of movement of 
that light beam and at right angles to the latter. In a first embodiment 
the distance sensor comprises another light source for emitting a sharply 
defined light beam in the line of action of the distance sensor onto the 
article in the measuring field, an optical system for forming on a CCD 
line sensor at a certain angle to the line of action an image of that 
point of the article which is illuminated in the measuring field by the 
light beam, and an electronic system, which succeeds that line sensor and 
serves to generate electric signals in dependence on the position of the 
image of the point within the field of view. 
By means of such a measuring apparatus the distance between the point which 
is illuminated by the light beam of the distance sensor and the light beam 
of the scanner at a predetermined boundary of the region which is 
vignetted by the article, e.g., at the first bright-dark transition during 
a parallel movement through the measuring field, can be determined in 
consideration of the spatial distance, detected by the light beam of the 
scanner, from the distance sensor to the scanner in the measuring 
direction, also to detect the change of the distance thus determined in 
dependence on the angular position of the motor-driven swivel mount, and, 
in dependence on the angular position of the motor-driven swivel mount, 
and, in dependence on the discontinuity of the detected change of the 
distance, which discontinuity is characteristic of the orientation of the 
light when it is parallel to the straight reference line, e.g., at a 
certain minimum, to determine the measured distance as the magnitude of 
the straight segment which is to be measured at the cross-section of the 
article. 
In another embodiment of the measuring apparatus for carrying out the 
suggested measuring method, the axis of the optical system provided in the 
distance sensor and serving to form an image of the illuminated point is 
directed to coincide with the line of action of the distance sensor, the 
light beam for illuminating the point is moved over the surface of the 
article in the measuring field by means of another scanner by a parallel 
displacement at an angle which differs from that of the line of action, 
and a coincidence of the image of the illuminated point and of the axis of 
the image-forming optical system and a coincidence of the illuminating 
light beam and a predetermined reference position are detected by a method 
which is well known and described in from German Patent Specification 35 
03 086 which is incorporated herein by reference and comprises comparing 
the component signals of bipartite detectors, and virtual amount of the 
parallel displacement of the illuminating light beam between the two 
coincidences in the direction of the axis of the image-forming optical 
system is determined as the magnitude of the distance from the surface of 
the article. For that purpose, another pulse generator generates countable 
pulses at a frequency which by feedback control systems is caused to be 
proportional to the instantaneous velocity of the movement of the 
illuminating light ray, as is well known and described, e.g. in German 
Patent Specification 28 49 252 which is incorporated herein by reference. 
In such an embodiment of the measuring apparatus, influences which would be 
due to the limited resolution of a CCD line sensor are precluded and the 
distance measurement is substantially independent of the reflection 
characteristics of the surface of the article. But it has been found in 
practice that in the two embodiments just described in case of an 
undesirable angular position of the measuring system and in case of an 
undesirable reflecting behavior of the surface of the article the light 
beam of that partial system which determines the straight reference line 
or the light beam of the distance-detecting partial system will be 
deflected to the detector of the respective other partial system and will 
interfere with the measurement. That interference is avoided in that the 
two scanning operations are synchronized by means of known phase control 
circuits at such a phase angle that they will be performed in alternation 
and without an overlap. 
In a preferred embodiment of the measuring apparatus the offset operation 
of the partial systems is achieved by optical means and in conjunction 
with a substantial simplification of the overall system in that only one 
scanner is used and the light beam emitted by that scanner is deflected 
during at least part of its parallel displacement by an optical deflector 
and, to detect the distance in the described manner during the remaining 
part of the displacement, the contour of the shade of the article is 
caused to perform a scanning movement through the measuring field for the 
determination of the straight reference line, wherein such an optical 
deflector, e.g., an anamorphotic lens system, is used that the point of 
intersection of the line of action of the distance sensor and the axis of 
the illuminating light beam is moved at the same velocity as the light 
beam for scanning the contour of the shade or the pulse generator for 
generating countable pulses is succeeded by a switchable frequency 
divider, which in response to the transition of the moving light beam from 
the region in which the distance is detected into the region in which the 
contour of the shade is scanned is so switched that pulses equal in number 
appear at the output of the frequency divider for each path length unit of 
the movement of the above-mentioned point of intersection and of the 
movement of the light beam for scanning the contour of the shade. 
In the use of that preferred embodiment of the measuring apparatus it is 
possible during the time from the coincidence of the image of the 
illuminated point and the axis of the image-forming optical system to the 
arrival of the light beam at a predetermined boundary of the region which 
is vignetted by the article to deliver the pulses from the pulse generator 
or frequency divider to a single counter and to evaluate the count 
resulting there, in consideration of an offset value, as the distance, 
measured in the line of action of the distance sensor, from the 
illuminated point on the surface of the article to the axis of the light 
beam at the boundry of the shaded area. 
It is an object of the invention to measure the cross-sectional dimensions 
also of elongate products in which the end points of a straight segment to 
be measured and those points on the periphery of the cross-section which 
define a straight reference line that is at right angles to that segment 
cannot be represented by a shadow projection in parallel light at the same 
time. 
That object is accomplished in accordance with the invention in that those 
points on the periphery of the cross-section which lie on the straight 
reference line are scanned by means of a light beam, which is moved 
through the measuring field by a parallel displacement, when that light 
beam is parallel to the straight reference line and the cross-sectional 
dimension which is to be determined in measuring by a triangulating 
incident-light method, in which the light paths are substantially 
transverse to the light beam passing through the points of the straight 
reference line. 
The above discussed and other features and advantages of the present 
invention will be appreciated and understood by those skilled in the art 
from the following detailed description and drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The scanner designated 1 in FIG. 1 emits a sharply defined light beam 2, 
which moves through a measuring field by a parallel displacement. This is 
indicated in the drawing by the arrow 3. The measuring field is defined in 
the direction of the beam by the exit window 4 of the scanner 1 and by the 
entrance window (4', which is concealed in the perspective view of FIG. 1) 
of an optical-electrical receiver 5 and in the direction of movement of 
the light beam by the edges of the openings of said two windows. The light 
beam 2 scans the spatial position of a distance sensor 6 at that housing 
edge 7 thereof which protrudes into the measuring field. In dependence on 
the mode of operation of the distance sensor 6, one of the two optical 
paths 8 and 9, which are shown as connected to the distance sensor 6 is 
identical to the axis of an illuminating system contained in the distance 
sensor 6 and the other path 9 or 8, is identical to the axis of an 
image-forming system, which is also contained in the distance sensor 6. 
Both systems are not shown in FIG. 1 because the mode of operation of the 
distance sensor can arbitrarily be chosen. Regardless of the mode of 
operation of the distance sensor, that optical path 8 which is at right 
angles to the moving (scanning) light beam 2 is identical to the line of 
action of the distance sensor 6. In that line of action, the distance 
sensor 6 detects changes of the distance from the distance sensor to a 
point 10 on a plane, which is at a predetermined distance from a surface 
of an article 13 disposed in the measuring field; that surface is scanned 
by the moving light beam 2 at further points 11 and 12. The moving light 
beam 2 is shown in certain phases of movement, in which its propagation is 
changed. Specifically, this refers in the position a designated to the 
entrance of the light beam 2 into the measuring field during the movement 
in the direction of the arrow 3, in the position b designated to the 
termination, detectable by the receiver 5, of a vignetting by the distance 
sensor 6 at its housing edge 7, in the position c designated to the 
renewed vignetting of the light beam at the points 11 and/or 12 of the 
article 13, in the position d designated to the termination of the 
vignetting by the article 13, and in the position e designated to the last 
vignetting of the light beam in its cycle of motion as the light beam 
leaves the measuring field. The receiver 5 can also detect the changes 
taking place at positions c, d, and e. The scanner 1, the 
optical-electrical receiver 5, and the distance sensor 6 are jointly 
mounted on a swivel mount 14, which is pivotally mounted by means now 
shown and is driven by a motor 15 so that the means 1, 5 and 6 are 
pivotally moved in unison continuously or intermittently and in a changing 
or consistent sense of rotation around the article to be examined, which 
is disposed in the measuring field. That movement is indicated in the 
drawing by the arrow n. 
FIG. 2 shows details of a preferred embodiment of the measuring apparatus 
of FIG. 1. The sharply defined light beam 2 is generated by a light source 
16 and is incident on a rotating mirror 18, which is driven by a motor 17 
to impart an angular movement to the light beam 2 when it has been 
reflected. During its angular movement, the light beam 2 is deflected by a 
collimator 19 to move through the measuring field by a parallel 
displacement, which is indicated in the drawing by the arrow 3. Those 
phases of the movement of the light beam 2 are shown in which the latter 
is at positions a, b, c, d and e and in which the propagation of the light 
beam 2 is changed as described hereinbefore. During those phases of the 
movement in which the light beam 2 is not vignetted the light beam 2 is 
deflected onto a detector 21 by focusing means 20, contained in the 
receiver 5. In dependence on said changes the signals generated by the 
detector 21 are subjected to changes, which by known means, not shown, are 
utilized, e.g., during the movement of the light beam 2 from position b to 
position c, to supply a pulse counter with pulses at a frequency which is 
proportional to the velocity of the movement of the light beam 2. The 
distance sensor 6 comprises a scanning illuminating system which 
illuminates the article from a first direction and, which comprises a 
light source 16', a motor 17', a rotating mirror 18', and a collimator 
19', which cooperate in the same manner as the corresponding parts of the 
scanner 1. The light beam 2' which is moved by that illuminating system is 
shown in three positions A, B and C assumed during its movement through 
the measuring field. The light beam 2' enters the measuring field in 
position A, coincides in position B on the surface of the article to be 
examined with the axis of an image-forming system to be explained 
hereinafter, and leaves the measuring field in position C. The illustrated 
coincidence of the beam in position B and of the optical path 9, which is 
identical here to the axis of the illuminating system, is incidental and 
has no significance. The distance sensor 6 comprises also an image-forming 
system that consists of an image-forming optical system 22, the axis of 
which is oriented in a second direction. In the mode of operation of the 
distance sensor 6 chosen here the axis of that image-forming system or 
optical system is identical to the line of action of the distance sensor 6 
in the optical path 8. That image-forming optical system 22 forms on a 
detector in a said direction an image of the surface of the article 13 to 
be examined. Owing to the movement of the illuminating light beam 2' a 
light flux which has been scattered by the surface is collected at a 
point, which is moved across the detector 23. That detector comprises two 
light-sensitive partial surfaces 23a and 23b, which in response to the 
light flux generate electric signals, which can separately be conducted. 
The partial surfaces 23a and 23b adjoin at a line, which is substantially 
transverse to the path of motion of the point which moves across the 
detector 23. The detector 23 is so mounted that the line and the 
above-mentioned path of movement cross in the axis of the image-forming 
optical system 22. The electric signals coming from the partial surfaces 
23a and 23b are compared in an electronic circuit, not shown, and the 
light beam 2' is detected at its position B when the two partial surfaces 
are equally illuminated by the light flux scattered from the surface of 
the article 13. At that position B the light beam 2' crosses on the 
surface the axis of the image-forming optical system 22. Another 
bi-partite detector 24 is disposed in a predetermined spatial reference 
position and is similarly used to detect the arrival of the light beam 2' 
at the reference position. The signals generated in response to the 
comparison of the signals from the detectors 23 and 24, respectively, 
during the movement of the light beam 2' from the reference position at 
the detector 24 to the position B are converted by known means, not shown, 
to pulses at a frequency which is proportional to the velocity of the 
movement of the light beam 2' and said pulses are delivered to a pulse 
counter. 
FIG. 3 shows an embodiment in which a single light beam 2 is used at 
different times and in different positions for the distance measurement 
and for defining the straight reference line, respectively. During a part 
of the parallel displacement imparted to the light beam 2 by the scanner 
1, the light beam 2 which has been deflected by an optical deflector 25 is 
propagated in such a direction and moved in such a direction that the 
light beam at an angle that differs from the axis of the image-forming 
optical system 22 transverses the point 10 which is disposed on the 
surface of the article and the distance of which from the straight 
reference line is to be measured. Owing to the strict coordination with 
respect to position and time of the resulting phases of the movement of 
the light beam 2 it is possible in this embodiment during the movement of 
the light beam 2 from position B to position c to supply a single pulse 
counter with pulses for determining the distance from the point 10 to the 
axis of the light beam 2 in position c. Necessarily it is ensured that the 
number of pulses to be counted per unit of the path length covered by the 
movement of the light beam 2 in the direction of the optical path 8 from 
position A to position C after the light beam has been deflected by the 
deflector 25 equals the number of pulses to be counted per unit of the 
path length covered by the movement through the positions a to e, when the 
light beam is not influenced by the deflector 25. In the embodiment shown 
in FIG. 3 this is accomplished in that the pulse frequency of the pulses 
to be counted is switched, e.g., by a frequency divider, not shown, when 
the light beam 2 arrives at the reference position detected by the 
detector 24. In an arrangement which differs from that shown in FIG. 3 
such a switching will not be required because the optical deflector 25 
consists of a pair of Littrow prisms in such an anamorphotic arrangement 
that before and after the deflection of the light beam 2 by the deflector 
25 the light beam 2 moves at the same velocity along the line of action of 
the distance sensor 6, which line is identical to the optical path 8. 
The embodiment of the measuring apparatus shown in FIG. 4 comprises a 
further distance sensor 6' that has the same mode of operation as the 
distance sensor 6. Because the two distance sensors 6 and 6' are 
diametrically opposite to each other it is possible to measure further 
points on the surface of the article which is to be examined. For 
instance, when the swivel mount 14 is in the illustrated position relative 
to the orientation of the cross-section of the article consisting of an I 
section, it is possible to measure also its web thickness at the point 10 
at right angles to the straight line of reference which contacts the 
points 11 and 12. The large number of measurements which can be performed 
also on other sectional shapes owing to the arrangement in accordance with 
the invention is made particularly clear in FIG. 4 because all signal 
changes at the detectors 21, 23 and/or 23' which are caused by the article 
to be examined in dependence on its spatial position and dimensions and 
the relations of said signal changes to each other or to the signal 
changes at the detectors 23 and/or 24' can be utilized to determine the 
position and/or spacing of the instantaneously scanned points on the 
surface of the article. 
While preferred embodiments have been shown and described, various 
modifications and substitutions may be made thereto without departing from 
the spirit and scope of the invention. Accordingly, it is to be understood 
that the present invention has been described by way of illustrations and 
not limitation.