Radiant energy – Photocells; circuits and apparatus – With circuit for evaluating a web – strand – strip – or sheet
Reexamination Certificate
1999-11-05
2001-11-13
Allen, Stephone B. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
With circuit for evaluating a web, strand, strip, or sheet
C360S077030
Reexamination Certificate
active
06316779
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to the field of optical measurement, and more particularly to accurately detecting positional characteristics of a fixed or moving measurement target. It is anticipated that primary applications of the present invention will be in manufacturing of highly precise assemblies and in industrial and laboratory processes requiring high precision position detection and control.
BACKGROUND ART
Many present industries and fields of research are encountering a need for faster and more accurate position and movement determination. For example, in semiconductor fabrication and disk drive assembly the capacity of the ultimate end product depends highly on the of accuracy of the measurement systems used, while the economy of the product often depends highly on the speed of the measurement systems used.
Many different measurement systems exist and are in wide use today. Of present interest are optical measurement systems, since they often permit non-contact measurement and have many other desirable characteristics. Present optical systems range from simple triangulation systems which use light beam reflection and geometric principles known since ancient times, to complex laser systems which use interferometric principles to achieve accuracy to within fractions of one light wavelength. However, particularly as modern applications become increasingly complex, the often conflicting goals of measurement accuracy and manufacturing speed remain ones where many seek further improvement.
FIG. 1
(background art) stylistically depicts a measurement system
10
for determining positional information about a movement stage
12
As
FIG. 1
illustrates with linear and circular arrowed lines, the movement stage
12
can have its position defined with respect to numerous coordinate systems. For example, positional information about the movement stage
12
can be with respect to each of x, y, and z linear axes, as well as with respect to each of rotational axes for pitch, yaw, and roll. The movement stage
12
thus can be viewed as having as many as has six degrees of freedom. Of course, and as often is the case, movement may be limited to only some of or may not be of interest in only some of these degrees of freedom, but accurate and fast measurement is still often a daunting task.
FIG. 1
includes a first detector
14
, a second detector
16
, a third detector
18
, a controller
20
, and an external system
22
. The first detector
14
can detect position relative to the x-axis, and provide positional information with respect to this to the controller
20
. The second detector
16
can detect position or displacement relative to the y-axis, and provide further positional information about this to the controller
20
. The third detector
18
can detect position or displacement relative to the z-axis and provide information about this to the controller
20
.
Practitioners of the optical measurement arts will recall that many common detectors today are only be able to detect positional change. For example, interferometers can only detect target displacement, a relative position measurement, and not initial or absolute position. Further, if displacement occurs too slow or too fast even these techniques will fail. Herein we generally discuss absolute and relative measurement techniques collectively unless particular differences are important.
Returning to
FIG. 1
, the controller
20
there provides the positional information it receives, perhaps after appropriate processing and format conversion, to the external system
22
. The external system
22
may simply be a display unit that a human user reads, or it may be a servo feedback system precisely controlling various movements of the movement stage
12
in a complex manufacturing process. The external system
22
is thus “external” with respect to the measurement process used; it is merely a recipient of and an ultimate user of the results of the measurement system for some higher purpose.
Unfortunately, the simple position determining system of
FIG. 1
can only provide positional information about three degrees of freedom for the movement stage
12
. It cannot, for example, tell us anything about roll as depicted by the rotational arrowed line
24
. Using detectors of the sort depicted here, adding roll detection would require adding at least a fourth detector
26
(depicted in ghost form) in parallel with the second detector
16
. Doing this would thus entail the expenses of more detector hardware, increased controller capability to handle the additional burden of this and the attendant set-up and maintenance of the more complex position determining system which would result. If the detectors which are used are laser interferometers, as might very well be the case today in a manufacturing or laboratory scenario where high accuracy is necessary, the expense of another detector could be quite appreciable. The costs of additional set-up and maintenance would also likely be appreciable. However, and worth noting for later in this discussion, the added cost for increased controller capability might be quite negligible.
Accordingly, what is needed is a position determining system which employs relatively simple detection hardware yet provides positional information for a measurement target with respect to multiple axes.
DISCLOSURE OF INVENTION
Accordingly, it is an object of the present invention to provide a position determining system which provides information about a measurement target with respect to multiple axes or degrees of freedom.
Another object of the invention is to provide a position determining system which provides information on absolute or initial position, as contrasted with merely relative position based on measurement target displacement.
Another object of the invention is to provide a position determining system which concurrently provides both rotation and translation of positional information.
And, another object of the invention is to provide a position determining system which is fast in operation yet provides positional information which is highly accurate.
Briefly, one preferred embodiment of the present invention is a measuring apparatus for providing positional information about a stage to an external system. The apparatus includes a light source which produces a light beam that is modulated with a particular characteristic. The light beam is directed at the stage substantially perpendicular to the stage. A multi-cell sensor receives the light beam and each cell produces a raw signal which is representative of the respective total illumination received by that cell. Movement of the stage accordingly produces changing illumination of the individual sensor cells. A processing system including a differentiator receives the raw signals and produces a differential signal from a pair of the raw signals, this differential signal being representative of the illumination received by the respective cells which produced the pair raw signals. The processing system further includes a demodulator which receives and demodulates the differential signal with respect to the particular characteristic initially used for modulation. A demodulated signal is thus produced which is representative of only the illumination actually attributable to the light beam. The processing system still further includes a logic unit which receives the demodulated signal and determines position data from it about the location. The processing system finally further includes a communications link which it uses to communicate the position data to the external system.
An advantage of the present invention is that it provides highly desirable non-contact position determination, based on its use of optical principles. Further, due to its ability to employ lasers as a light source, the invention may be used for measurement targets ranging from small to quite large and at distances ranging from near to quite remote.
Another advantage of the invention is that it permits measurement of combinations of positional character
Allen Stephone B.
Excel Precision Corp.
Oppenheimer Wolff & Donnelly LLP
Roberts Raymond E.
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