Geometrical instruments – Distance measuring – Of flexible material
Reexamination Certificate
1999-12-22
2003-04-08
Gutierrez, Diego (Department: 2859)
Geometrical instruments
Distance measuring
Of flexible material
C033S756000, C033SDIG001, C033S740000
Reexamination Certificate
active
06543152
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 braking device.
2. Discussion of the Background
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 point on the cable drum at which the cable runs tangentially on to 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.
However, measuring cable travel sensors of that kind suffer from two different difficulties which however are interrelated in terms of their origin, more specifically as follows:
In order to ensure measurement accuracy, the measuring cable has to be prestressed or biassed in the winding-on direction with a predetermined minimum force in any condition in terms of being wound on to or unwound from the cable drum and accordingly a suitably strong spring biassing effect is required to bias the cable drum in the winding-on direction.
The relatively strong spring biassing force applied to the cable drum serves inter alia to ensure that, even in the event of very fast movement on the part of the free end of the cable and the component to be measured, which is connected thereto, in a direction towards the cable drum, the measuring cable is wound on to the cable drum in a neat and tidy fashion by virtue of a sufficiently high biassing effect in the cable winding-on direction, independently of the speed with which the measuring cable is actually wound on to the drum.
Nonetheless, when the cable is wound on to the drum at very high speed, it can happen under some circumstances that the measuring cable can climb up or fly out, that is to say adopt a position at a spacing relative to the external peripheral surface of the cable winding drum, and in that case for example the measuring cable will jump over the first layer of turns already on the cable drum to form a second layer there over, being a phenomenon which is undesirable as it grossly falsifies the measurement result.
Attempts have already been made to prevent the measuring cable from climbing up over the previous turns already wound on the cable drum, for example by mechanical guide and tracking devices, distribution devices and so forth, but that tends to result in undesirable side effects such as wear, an increase in the winding force and the like, because of the mechanical friction involved.
Another detrimental effect of the high level of cable drum biassing is that, in the situation where the free end of the cable moves towards the cable drum more quickly than the cable drum can wind the measuring cable on to it or in the situation where the free end of the cable becomes detached from the component whose travel is to be measured so that the cable moves towards the cable entrance and into the travel sensor housing completely without any retardation force being applied to the cable, as a result the spring-biassed cable drum speeds up to very high speeds of rotation and at the end of the winding-on movement the free end of the cable which is usually of greater thickness and which is equipped with a fixing device for example using an eye strikes at very high speed against the cable entrance structure which is of smaller size in relation thereto. That can result in damage or even tearing of the measuring cable or can disrupt the connection between the measuring cable and its fixing device on the free end of the cable, and so forth.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a measuring cable travel sensor in which, in spite of a sufficiently strong biassing effect on the cable drum in the cable winding-on direction, excessive acceleration of the cable drum in a winding-on procedure can be reliably prevented.
Another object of the present invention is to provide a measuring cable travel sensor of such a structure as to prevent the cable from climbing up on to cable turns already on the drum in a winding-on movement of the drum.
Still another object of the present invention is to provide a measuring cable travel sensor which while being of a simple structural configuration can provide for satisfactory winding-on and unwinding of the cable under properly controlled conditions, thereby to contribute to an enhanced service life for the measuring cable travel sensor.
In accordance with the principles of the present invention the foregoing and other objects of the invention are attained in a first aspect by a measuring cable travel sensor including a measuring cable and a cable drum having a winding cylinder with an external winding surface, for the measuring cable to be wound on to the external winding surface of the cable drum. The cable drum is mounted in a housing. The travel sensor further includes at least one retardation or braking magnet which is so arranged at a point that is non-rotatable with the cable drum that it has a magnetic retardation or braking action
ASM Automation Sensorik Messtechnick & GmbH
Crowell & Moring LLP
Guadalupe Yaritza
Gutierrez Diego
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