Geometrical instruments – Gauge – Screw thread
Reexamination Certificate
1999-01-22
2001-09-18
Bennett, G. Bradley (Department: 2859)
Geometrical instruments
Gauge
Screw thread
C033S701000
Reexamination Certificate
active
06289595
ABSTRACT:
This invention relates to determining a two-dimensional axial cross section of internal and external screw threads and similar workpieces, with a view to deriving therefrom screw thread quantities such as flank diameter.
There are methods known, in which such complete axial cross section can be determined in a single cycle with a single measuring instrument, or with which the flank diameter can be determined in a single cycle.
Such a method for determining geometric parameters of screw thread is known, for instance, from BP 0 589 500. The measuring results obtained by that method are highly accurate and hence suitable in particular for performing measurements on, for instance, reference screw threads or screw thread gauges.
A disadvantage of this known method, however, is that the required measuring device is complicated, sizeable and costly. Also, a measurement lasts relatively long. Owing to its large size, the known measuring device is not mobile, so that the object to be measured must be brought to the measuring device, which entails additional loss of time. further, the known measuring device is not suitable for the in situ measurement of objects, in particular products fixed in a processing machine. Consequently, it is not possible to perform a measurement during production without removing the object from the processing machine. When a form deficiency has been established, it is subsequently not possible anymore to remedy it by a supplementary processing operation, because the original fixture has been lost. In addition, for many applications, measurements of a calibration accuracy are not required, so that the application of a highly accurate but expensive measuring device is not economically feasible.
A method as described above is further known from DE 198 13 175. The method described there, too, has the above-mentioned associated disadvantages. In addition, this method is hardly applicable for measuring internal screw thread,
Accordingly, there is a need for a method for determining geometric parameters of internal and external screw thread, which, while maintaining a good accuracy, can yet be carried out fast, at low cost and in situ,
The object of the invention is to provide a method which meets this need. To that end, according to the invention, a method for determining a geometric parameter of screw thread is characterized in that separately two screw thread profiles which are located diametrically opposite each other and which are both located in a plane through the centerline of the screw thread are scanned, and the scanned profiles are subsequently linked with each other using at least one linked measurement of a suitable intermediate parameter such as, for instance, the core diameter in the case of internal thread or the outside diameter in the case of external thread.
Another object of the invention is to provide a measuring device that may be made of portable design, for measuring screw thread in situ. To that end, according to the invention, a scanning device is provided for scanning a screw thread profile, comprising a housing and a measuring arm at one end fitted with a scanning or probe element and at the other end pivotally connected with the housing, and further comprising detection means for determining a deflection of the probe element.
By splitting the known single measurement into a plurality of simpler measurements, the measuring equipment can likewise be split up into a compact profile depth measuring instrument or a profile scan measuring instrument and a measuring instrument for measuring the outside diameter of external screw thread, such as sliding calipers or an outside screw gauge, or a measuring instrument for measuring the core diameter of internal screw thread, such as sliding calipers or an inside screw gauge.
As a result of this split of the measuring process into subprocesses in conformity with the disclosure of this invention, the instrumentation can be made of highly compact and even portable construction, yielding the advantage that screw thread of products can be checked during production while the workpiece is still fixed on the processing machine and hence it is still possible, if necessary, to incorporate corrections into the screw thread machining process. Rejection can thus be prevented.
If the profiles are scanned, the actual dimension and geometry of the screw thread profile are determined and the actual values of the pitch, flank sub-angles and profile angle can be computed and a graphic presentation of the cross section can be presented even in combination with a graphic presentation of the minimum and maximum material tolerance zones.
The qualification of a complex screw thread geometry of a workpiece is thereby greatly simplified.
A further simplification of the invention can be obtained by performing, instead of a profile scan step, a profile depth measurement, for instance using the two-ball method, known per se, or (for external screw thread) the measuring wire method, known per se.
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Bennett G. Bradley
Kinney & Lange , P.A.
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