Winding – tensioning – or guiding – Unwinding – With detector – indicator – or control
Reexamination Certificate
1999-12-22
2003-05-13
Noland, Thomas P. (Department: 2856)
Winding, tensioning, or guiding
Unwinding
With detector, indicator, or control
C242S396000, C242S397000, C242S397200, C033S700000, C033S754000
Reexamination Certificate
active
06561451
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
1. Field of the Invention
The invention concerns a measuring cable travel sensor and more particularly a measuring cable travel sensor having a longitudinal drive for displacement of the cable drum.
2. Background of the Invention
Measuring cable travel sensors occur in many different configurations for example for determining the precise position of a given component which in particular can move over considerable travel distances, for example the cabin of an elevator. A typical measuring cable travel sensor of that kind and for that purpose has a pull element such as a measuring cable which is wound on a cable drum which is biassed in the cable winding-on direction. The free end of the measuring cable is connected to that component whose position is to be determined, for example as mentioned above an elevator cabin. The prestressing force for urging the cable drum in the winding-on direction is produced for example by way of a flat spiral spring which for example is arranged coaxially with respect to the cable drum and is non-rotatably connected thereto.
The cable drum is also typically coupled to a detection unit for recording the revolutions or angular distances through which the cable drum passes in the winding-on or unwinding direction, and which in addition by way of a suitable electronic evaluation system determines the length of the pull element or measuring cable which has been drawn off the cable drum.
In order to simplify that operation of determining the drawn-off length of the measuring cable and to ensure an accurate measurement result, the measuring cable is wound in only a single layer on the periphery of the cable drum, with the turns of the wound cable on the cable drum being disposed in axially juxtaposed relationship. As a result, one revolution of the cable drum will always correspond to exactly the same length of the pull element or measuring cable.
In order to ensure that the measuring cable is wound on to the drum in only a single layer and in order to prevent the measuring cable from jumping over on to the first layer to start to form a second layer there over when winding the measuring cable on to the cable drum, it is generally necessary to take suitable mechanical steps involving appropriate structure on the travel sensor to obviate this occurrence.
In that respect there is an additional difficulty insofar as such measuring cable travel sensors often have to be used in an adverse environment, for example involving a high level of fouling and contamination. For that reason the measuring cable travel sensor has to be disposed in a housing which affords sealing integrity, and the measuring cable which is passed out of the housing also has to be taken out of the housing by way of a cable guide passing through the wall of the housing, which also offers the greatest possible level of sealing integrity in relation to the cable.
In order to ensure that the measuring cable is wound on the cable drum in a neat and tidy fashion in a single layer, one possible way of achieving that is for the cable drum to be very short in its axial direction. If in addition the cable entrance is at a sufficient distance from the cable drum, then the measuring cable, on moving from the cable entrance to the cable drum, runs only at such a slight degree of angular deflection as to still be acceptable, and such an arrangement automatically causes the cable drum which is biassed in the winding-on direction to have the measuring cable wrap there around in only a single layer.
Even if the diameter of the cable drum is selected to be relatively large to provide a compensatory effect, that nonetheless entails a limitation in terms of the maximum possible length of the measuring cable. In addition, that affords a structural configuration which is very large in the radial direction, and a single revolution of the cable drum corresponds in that case to a relatively long peripheral length and thus a relatively long length of cable, so that the level of resolution of the measuring cable travel sensor is restricted in consequence.
If the above-indicated limitations give rise to the need for the cable drum to be of a substantially greater axial extent, then the cable entrance must be moved relative to the cable drum when the measuring cable is being wound on to or unwound from the cable drum, so that the cable entrance is disposed always substantially at the radial plane at which the measuring cable is being wound on to or unwound from the cable drum at that time. In that respect, and for that purpose, while it is possible for the cable entrance to be displaced relative to the cable drum which is arranged in axially fixed relationship in the housing, it is also possible to adopt the reverse arrangement.
At first view, it may admittedly be an easier course of action for the relatively small and light cable entrance to be adapted to be axially displaceable, rather than the rotatably mounted cable drum, but from the point of view of affording good sealing integrity for the measuring cable travel sensor with respect to its ambient conditions, a preferred arrangement is for cable guide means to be arranged fixedly on the housing, so that the measuring cable drum is axially displaceable relative thereto.
In that respect attention may be directed for example to U.S. Pat. No. 4,443,888 in which the measuring cable drum is rotatably mounted directly on a central screwthreaded spindle. The pitch of the screwthread on the spindle establishes the relationship between rotary movement and longitudinal displacement of the cable drum. The rotary movement of the cable drum is transmitted by way of an eccentric entrainment means to the return unit of the cable drum for urging it on the winding-on direction.
Reference may also be made to European patent No. 0 778 239 disclosing a screwthreaded spindle of a hollow configuration, wherein disposed in the interior of the hollow screwthreaded spindle in coaxial relationship therewith is a shaft, for example a splined shaft, on which the cable drum is arranged longitudinally displaceably but non-rotatably by way of one of its end plate portions, while the other end plate portion of the cable drum is in screwthreaded engagement with the male screwthread on the screwthreaded spindle. The longitudinal drive means in the form of the screwthreaded spindle on the one hand and transmission of the rotary movement of the cable drum to the rotary angle sensor and/or the return drive by means of the splined shaft on the other hand are thus disposed in the center of the cable.drum in mutually coaxial relationship.
A disadvantage with those structures however is that the degree of longitudinal displacement depends on the pitch of the screwthread on the screwthreaded spindle and the spindle nut co-operating therewith. If for example the travel sensor uses a measuring cable of relatively great thickness, for example because the tensile loading acting on the measuring cable is relatively high, then when the cable drum rotates, a greater degree of longitudinal displacement thereof is required than when using a thinner measuring cable.
In the above-mentioned conventional structures, in order to solve this problem the screwthreaded spindle and the spindle nut co-operating therewith must to be, exchanged, which entails complete dismantling of the measuring cable sensor, including fitting and thus, in the fitting operation the return device which in general is a flat shaped spring in the form of a spiral spring, must be again prestressed. This can scarcely be effected on site even by a specialized fitter, quite apart from the large amount of time that this necessarily entails.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a measuring cable travel sensor adapted to provide for longitudinal displacement of the cable drum within its housing using a simple structure, wherein the relationship between rotary movement of the cable drum and longitudinal displacement thereof can be repeated and easily altered.
Another object of
ASM Automation Sensorik Messtechnik GmbH
Noland Thomas P.
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