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United States Patent [w]
Boege et al.
US005979238A [ii] Patent Number:  Date of Patent:
 STRIP-SHAPED RESILIENTLY FLEXIBLE MEASURING TAPE FOR LENGTH—OR ANGLE-MEASURING DEVICES
 Inventors: Ludwig Boege; Hans-Joachim Freitag,
both of Jena, Germany
 Assignee: Carl Zeiss Jena GmbH, Jena, Germany
 Appl. No.: 08/945,833
 PCT Filed: Mar. 20, 1997
 PCT No.: PCT/EP97/01421
§ 371 Date: Nov. 5, 1997
§ 102(e) Date: Nov. 5, 1997  PCT Pub. No.: W097/36149
PCT Pub. Date: Oct. 2, 1997
 Foreign Application Priority Data
Mar. 26, 1996 [DE] Germany 196 11 983
 Int. CI.6 G01P 15/00; G01B 3/10
 U.S. CI 73/490; 33/755; 33/758
 Field of Search 73/490; 33/700,
33/732, 755, 758
 References Cited
U.S. PATENT DOCUMENTS
3,603,929 9/1971 Drysdale 73/490
3,724,083 4/1973 Mehl 33/755
4,546,650 10/1985 Cameron 73/490
5,258,861 11/1993 Tsuchiya .
5,732,475 3/1998 Sacks et al 33/512
FOREIGN PATENT DOCUMENTS
1176382 of 1959 Germany .
7908975 of 1979 Germany .
3226132 of 1982 Germany .
4204878 of 1992 Germany .
9526518 of 1995 Germany .
9526517 of 1996 Germany .
Primary Examiner—Max Noori
Attorney, Agent, or Firm—McAulay Nissen Goldberg Kiel & Hand, LLP
A strip-shaped, elastically flexible measurement strip for length measuring devices or angle measuring devices having a measurement scale is formed of two elastically flexible stripes which adhere to one another via a viscous intermediate film, the measurement scale being applied to one of these stripes.
22 Claims, 2 Drawing Sheets
STRIP-SHAPED RESILIENTLY FLEXIBLE
MEASURING TAPE FOR LENGTH— OR
BACKGROUND OF THE INVENTION 5
a) . Field of the Invention
The invention is directed to a strip-shaped, elastically flexible measurement strip for length measuring devices or angle measuring devices which is provided with a graduated measurement scale. 10
b) . Description of the Related Art
Such measurement strips are used industrially for length measurements and angle measurements, e.g., for machine tools or the like, wherein a measurement strip is fastened in 15 a suitable manner, for example, at the machine bed of the machine tool or at its clamping table, and its scale is sensed by a measurement head which is suitably connected with the other part. In order to fasten the measurement strips, the measurement strip is either glued directly to its associated 20 receiving base by means of a suitable glue or is fastened, via a measurement scale body in which the measurement strip is held, e.g., also by means of gluing, to this measurement scale body.
When the measurement strip is glued on, mechanically 25 induced internal stresses inevitably build up therein, either because of the required contact pressure forces when gluing on, since there can never be contact pressure without longitudinal forces, or because of internal stresses resulting from the hardening or ageing of the glue, or because of 30 thermal stresses due to different thermal expansion coefficients of the measurement strip and measurement scale carrier or receiving base. Because of this, substantial errors can result when measuring which considerably impair the accuracy of such a measuring system. A further possible 35 source of error in measurement strips is the occurrence of bending in the measurement strip because the surface of the measurement strip which generally carries the measurement scale changes in length when the measurement strip bends. Local tensile stresses and compressive stresses, which also 40 cause longitudinal errors, occur in the measurement strip depending in each case on the local position in relation to the neutral grain or fiber. This longitudinal error increases as the distance increases from the neutral fiber and therefore as the thickness of the measurement strip increases so that, to 45 minimize this error, it is desirable to use the thinnest possible measurement strips. However, with decreasing thickness of the measurement strip the inherent strength or inherent stability of the measurement strip drops sharply, as a result of which minor mechanical stresses such as inevitably occur 50 in the gluing process lead to the occurrence of noticeable errors, for which reason the use of thicker and accordingly more inherently stable measurement strips is desirable from this point of view.
An article in "F & M Feinwerktechnik und Me(3technik", 55 Vol. 80, No. 7, pages 333ff, describes a measurement strip in which a groove is machined into a stainless steel measurement scale body to receive a thin steel strip with the measurement scale which is cemented therein. For the purpose of reinforcing the cement connection, the steel strip 60 is connected laterally via welds with the associated carrier body. In this solution, although the carrier body and measurement strip are produced separately and the measurement strip can accordingly be produced with the desired length in an economical manner, the attainable accuracy of the mea- 65 suring system is limited because the relatively low longitudinal stiffness of the thin steel strip, the unevenness in the
strip, the inhomogeneity of the glue layer, and the scale errors caused by the bending of the scale body lead to errors which can no longer be overlooked.
A measurement device in which a scale is fastened in a flat manner on a metallic carrier by means of a silicone rubber glue layer is known from DE-PS 25 05 587. In this type of elastic fastening of the measurement scale on a stable base body, there are still extensive constraining forces which cannot be ignored and which can result in turn in deformations of the measurement scale, because the elastic adhesive forces of the glue layer can still be unacceptably large especially when the scales are relatively thin.
In another type of measurement system described, for example, in PCT-WO19/02919, a self-adhesive steel-strip measurement scale is aligned via an applicator to the operating sequence of the slide and is glued onto the machine bed or onto a base body. This known measurement system is very complicated to assemble and the attainable accuracy of the measurement system is only relatively limited, since the inherent stability of the measurement strip is rather low and even very slight mechanical stresses or differences in tension lead to corresponding errors. The linearity error of such glued measurement strips amounts to as much as approximately 40 fim/m of the measurement strip. The attainable accuracy is accordingly sharply restricted and the scale errors must be corrected electronically by calibrating measurements, e.g., by means of a laser interferometer, which additionally complicates measurement and requires an electronic correction device.
OBJECT AND SUMMARY OF THE INVENTION
On this basis, the primary object of the invention is to further develop a measurement strip of the type mentioned above in such a way that it has an adequate longitudinal stability in spite of a limited thickness and the errors occurring during assembly and during bending movements are particularly minor.
This object is met, according to the invention, in a measurement strip of the generic type in that it is formed of two elastically flexible stripes which adhere to one another via a viscous intermediate film, the measurement scale being applied to one of these stripes.
In the measurement strip according to the invention, the coupling is produced by the capillary action of the viscous intermediate layer so that the strips are extensively uncoupled from one another with respect to the occurring mechanical stresses. At low displacement speeds of the strips relative to one another, no adhesive friction occurs between them; however, the strips are held together firmly and form a stable composite action on the whole due to the relatively extensive capillary action of the viscous intermediate film, that is, of a thin viscous intermediate layer. In this respect, the capillary action also effectively prevents the viscous intermediate film from flowing out. When faster displacement speeds occur between the two strips, the viscous frictional force generated by the viscous intermediate film sharply increases between these strips so that high stability is also achieved in the longitudinal direction of the bond. As a result of this type of coupling, the occurring tension in the elastically flexible stripe which does not have the measurement scale is uncoupled from the other stripe carrying the measurement scale, and the deformation component connected with the former is not transmitted to the other stripe. However, even when bending movements proceed gradually, the use of the stripes which are connected with one another in a viscous manner makes it possible to