Geometrical instruments – Miscellaneous – Light direction
Reexamination Certificate
2002-08-20
2004-09-07
Gutierrez, Diego (Department: 2859)
Geometrical instruments
Miscellaneous
Light direction
C033S756000, C033S763000
Reexamination Certificate
active
06785973
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The invention relates to a measuring device comprising a movable measuring probe and sensors coupled to the measuring probe for providing position data of the measuring probe.
(2) Description of Related Art
A measuring device of this kind is known from U.S. patent application Ser. No. 4,703,443, and can be used for measuring the shape or contour of a two-dimensional or three-dimensional object, such as machine components or the like that are placed on a measuring table.
This prior art measuring device comprises an arm that is rotatably mounted on the measuring table, the length of which arm can be varied. The arm consists of a number of separate, pivotally interconnected elements. Disposed on the free end of the arm is a measuring probe, which is likewise pivotally connected thereto.
Angular displacement sensors, such as potentiometers, for measuring the angle between elements disposed adjacently to each other are present at all pivot points of the arm for the purpose of determining the effective length of the arm, that is, from the pivot point to the point where the measuring probe is in contact with the object to be measured. On the basis of the lengths of the individual elements, which are known per se, and the measured angle between said elements it is then possible to determine the effective length of the arm by means of a simple mathematical computation. Subsequently the two-dimensional or three-dimensional contour of an object to be measured can be determined from the length and the angular displacement of the arm by means of well-known mathematical formulas based on a Cartesian, spherical or cylindrical coordinate system.
The presence of a relatively large number of sensors at the pivot points of the arm for determining the length thereof makes the arm relatively vulnerable and liable to malfunction, in particular when potentiometers are used. Furthermore it will be apparent that the maximum length of the arm is inevitably limited for constructional reasons, so that this prior art device is only suitable for measuring relatively small objects, which can be placed on a measuring table.
Consequently it is an object of the invention to provide an improved measuring device, which has been designed for measuring small objects to be placed on a measuring table, as well as relatively large objects disposed in a room.
BRIEF SUMMARY OF THE INVENTION
According to the invention this object has been accomplished in that the measuring probe is coupled, via a cord or a wire, to a first sensor for measuring the length or change in length of the cord or the wire, and to a second sensor for measuring an angle or angular displacement of the cord or the wire.
Instead of using a pivotable arm the device according to the invention uses a cord or a wire, so that a single sensor will suffice for determining the length or change in length of the cord or the wire, and a measuring device that is much less liable to malfunction can be provided. By using a cord or a wire also the inherent limitation as regards the length of the prior art pivotable arm has been overcome, as a result of which it is also possible to measure relatively large objects that are disposed in a room. By way of illustration, in a practical embodiment of the measuring device according to the invention, measurement is carried out with a cord or wire having a length of 6 meters or more.
In an embodiment of the device according to the invention, in order to enable accurate determination of the angle or angular displacement of the cord caused by a change in position of the measuring probe, the second sensor is coupled to an elongate, rotatably supported arm, in the longitudinal direction of which the cord or the wire engages the arm.
In a preferred embodiment of the measuring device according to the invention, the arm is coupled to the second sensor at a first end, and is provided at a second free end with an opening precisely adapted to the thickness of the cord or the wire, through which opening the cord or the wire can be moved. The clearance between the wire and the opening must be minimal in order to keep the arm in line with the cord or the wire as accurately as possible.
In an embodiment of the measuring device according to the invention the arm is supported in such a manner that it is rotatable in an imaginary plane, in particular for measuring two-dimensional objects. On the basis of the measured angle or angular displacement of the arm and the measured length or change in length of the cord or the wire, the contour of an object scanned by means of the measuring probe can be accurately determined by means of mathematic computations based on a polar coordinate system.
Since the accuracy of such a measurement is determined, among other things, by the accurate rotation of the arm in said imaginary plane, the arm of another embodiment of the measuring device according to the invention is rotatably supported at a point some distance away from its first end, in such a manner that the first end of the arm extending beyond the point of support is suitably shaped for balancing the arm, or that said end can be provided with adjusting means for balancing the arm in said imaginary plane with the desired accuracy.
In yet another embodiment of the measuring device according to the invention the arm is spatially rotatably supported, for example by means of a ball joint mounted on the first end of the arm for swingably supporting the arm. An arm which is spatially rotatable or swingable in this manner is suitable for measuring contours of three-dimensional objects, for example based on the well-known spherical coordinate system.
The speed at which the measurement can be carried out depends, among other things, on the speed at which the arm is capable of following the changes in position of the cord or the wire.
In the preferred embodiment of the invention the arm is supported in a precision bearing having the smallest possible starting moment, that is, the moment that is required for causing the bearing to rotate from standstill.
In yet another embodiment of the invention the arm is made of a material having a low specific weight, such as aluminium or a plastic, wherein the arm is furthermore designed to comprise as little material as possible whilst retaining sufficient mechanical strength, however.
For an accurate measurement of the length or change in length of the cord or the wire caused by a change in position of the measuring probe, the cord or the wire needs to be sufficiently taut when the position of the probe is being determined.
According to an embodiment of the invention, again in order to enhance the speed of the measuring operation, the first sensor is coupled to a tensioning and roll-up mechanism for keeping the cord or wire tensioned under the influence of spring tension and for automatically rolling up said cord or wire. Thus it is achieved that the cord or the wire is sufficiently tensioned for carrying out the measurement at all times so as to be able to accurately determine the length or change in length of the cord or the wire.
In a preferred embodiment of the measuring device according to the invention the tensioning and roll-up mechanism comprises a rotatably supported reel, whose outer surface is provided with a spiral groove that has a depth adapted to the diameter of the cord or the wire, and movably supported guide wheels for guiding the cord or the wire in such a manner that it will follow said spiral groove of the reel.
This embodiment of the tensioning and roll-up mechanism prevents the cord or the wire from heaping up upon being wound onto the reel, which would introduce an error into the measurement. After all, the length of the cord or the wire is determined by the diameter of the reel, wherein the heaping up of layers of cord or the wire in fact corresponds to unknown changes in the diameter of the reel. Furthermore, the cord or the wire is prevented from being flattened upon being wound up as a result of several layers of cord or the wire being w
E. Knip & Co.
Gonzalez Madeline
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