Geometrical instruments – Distance measuring – By flexible tape
Reexamination Certificate
1999-07-26
2002-05-07
Gutierrez, Diego (Department: 2859)
Geometrical instruments
Distance measuring
By flexible tape
C033S761000, C033S763000
Reexamination Certificate
active
06381863
ABSTRACT:
FIELD OF THE INVENTION
The invention concerns a measuring cable travel sensor.
BACKGROUND OF THE INVENTION
Measuring cable travel sensors are travel or distance-measuring sensors operating on the principle of a measuring cable, with a housing which is suitable for use in industrial situations. A typical travel sensor of that kind comprises a precisely defined and positioned cable drum on to which a measuring cable is wound, generally only in a single layer on the drum. One end of the measuring cable is suitably fixed to the cable drum. The other free end of the measuring cable is secured to the body or article, the variation in the position of which is to be precisely measured.
When the movable body or article moves away from or towards the cable drum of the measuring cable travel sensor, the resulting angular movements of the measuring cable drum about its axis are converted into a precise travel or distance length by means of a rotary angle sensor which is non-rotatably coupled to the cable drum. A rotary torsion spring which is operatively connected to the cable drum, generally in coaxial relationship therewith, ensures that the measuring cable is wound on to the cable drum when the movable body whose position is to be measured moves towards the cable drum, thereby to ensure that the measuring cable is properly wound on to the drum and is kept in a reasonably taut condition.
It will be noted that measuring cable travel sensors of such a kind are used in the most widely varying technical situations and assemblies, for example for determining the position of an elevator cabin in an elevator shaft, for continuously monitoring the angular positions of ailerons, control elevators and vertical rudders in aircraft and the like.
In order to achieve the desired level of measurement accuracy for such a measuring cable travel sensor, it is necessary on the one hand to ensure absolute angular truth as between the measuring cable drum and the rotary angle sensor. That inter alia requires free unimpeded rotary movement of the cable drum of the measuring cable travel sensor, under all operating conditions, as any impediment to the rotation of the cable drum could grossly falsify the measurement result. Accordingly on the one hand the cable drum must be reliably and dependably supported to permit it to rotate freely and accurately while on the other hand there is no way in which the measuring cable drum could be permitted to have its rotary movement adversely affected for example by the cable drum rubbing or the like against the housing or another component as a consequence of a mechanical loading, thermally induced distortion or the like of one of the components of the assembly.
For that reason the housings for measuring cable travel sensors were hitherto composed of a plurality of stable metal parts, more specifically on the one hand tube portions and on the other hand end plates which were respectively screwed together in the appropriate configuration.
The production of injection-molded parts of plastic material or die-cast parts of light metal or alloy has been less wide-spread both for reasons of the number of items involved and also because of the inadequate degree of accuracy, in comparison with the use of end plates and tube portions which are produced by a procedure which involves cutting machining.
In order to provide an arrangement in which the cable drum is reliably supported and free to rotate, the cable drum has hitherto generally been non-rotatably arranged on a separate shaft which is supported in the housing of the measuring cable travel sensor, and that shaft on which the cable drum is disposed is non-rotatably connected to a trunnion portion of the shaft of the rotary position sensor not directly but by way of a coupling which can compensate for angular displacement. In that case, the rotary angle sensor itself was generally fixed on the outside of the housing so that only the projecting trunnion portion of the sensor shaft extends into the housing.
Such designs of measuring cable travel sensors are cost-intensive because of the metal parts for the housing, which are expensive to machine, and they are also relatively large in the axial direction because of the separate support arrangement for the cable drum and the consequentially necessary angle coupling transmission to the rotary angle sensor.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a measuring cable travel sensor which can be of a compact structural size, more especially in its axial direction, and which is simple and inexpensive to produce.
Another object of the present invention is to provide a measuring cable travel sensor which will afford accurate and reliable measurement results while nonetheless being of a simple design configuration.
Still another object of the present invention is to provide a measuring cable travel sensor which is of a robust structure such as to be capable of withstanding severe operating conditions.
Yet another object of the present invention is to provide a measuring cable travel sensor which affords the possibility of adaptation to different dimensional aspects in consideration of the operational situations in which it is to be employed.
In accordance with the principles of the present invention the foregoing and other objects are attained by a measuring cable travel sensor comprising a housing in which a measuring cable drum and a rotary spring are disposed. A rotary angle sensor is connected to the housing. The sensor has a shaft including a trunnion portion which projects out of the sensor. The cable drum is non-rotatably fixed in concentrically aligned relationship on the trunnion portion of the sensor shaft, in the axial longitudinal region of the trunnion portion where it projects from the sensor.
As will be appreciated from a description hereinafter in greater detail of a preferred embodiment of the measuring cable travel sensor according to the invention, a reduction in the size thereof in the axial direction is achieved by virtue of the elimination of the coupling referred to hereinbefore in connection with the previous designs. That is made possible by the avoidance of angular displacement as between the shaft of the cable drum and the sensor shaft, insofar as the cable drum is fitted on to the trunnion portion of the sensor shaft. In that respect, the cable drum does not have to be non-rotatably fixed directly on the sensor shaft, but it is possible also to use a concentric adaptor which is disposed therebetween. That can afford the advantage that the adaptor can project in the axial direction beyond the free end of the trunnion portion of the sensor shaft and can serve as a central, for example slotted entrainment means for the rotary or torsion spring which is disposed in the housing and which is axially spaced in relation to the cable drum.
The basic point of departure in terms of all stability considerations relating to the housing is thus the location of the connection between the rotary angle sensor and the housing. In order to permit inexpensive manufacture of the housing in the form of a molded or cast component of plastic material or light metal or alloy, more especially for example aluminum or ZN-casting, with the additional weight advantage that this entails, while affording adequate stability and strength, the housing comprises first and second half-shell portions which are fitted to each other, namely a shell portion which accommodates the rotary spring and a shell portion which accommodates the sensor, both of those being of a substantially cup-shaped configuration.
While however the rotary spring shell portion has a closed bottom, the sensor shell portion has a bottom region with a sensor opening through which the trunnion portion of the sensor shaft can project into the housing. The sensor itself is fitted to and secured to the sensor shell portion on the outside thereof. In the housing, the assembly comprising the adaptor and the cable drum is non-rotatably disposed on the trunnion portion of the sensor shaft by suitable moun
ASM Automation Sensorik Messtechnik GmbH
Gonzalez Madeline
Gutierrez Diego
Jacobson & Holman PLLC
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