Measuring and testing – With fluid pressure – Dimension – shape – or size
Reexamination Certificate
1999-03-26
2001-11-20
Noland, Thomas P. (Department: 2856)
Measuring and testing
With fluid pressure
Dimension, shape, or size
C073S159000
Reexamination Certificate
active
06318153
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a sensor for noncontacting thickness gauging on films, in particular blown films, with a sensor head and a mount for the sensor head, the sensor head comprising at least one noncontacting sensor element for gauging the thickness in accordance with the physical properties of the film.
Large varieties of sensors for noncontacting thickness gauging are known from practice. For example, the thickness of film tapes is monitored during production with two oppositely arranged displacement measuring sensors with the film tape advancing between the displacement measuring sensors. In practice, this sensor arrangement is problematic, since displacement measuring sensors normally display a nonlinear behavior. Fluttering of the film tape being monitored, different tape thicknesses, or the movement of the tapes toward or away from the displacement measuring sensors will cause measuring errors that are due to the nonlinear behavior of the displacement measuring sensors in the measuring range.
For thickness measurements on blown films the known sensor arrangement is totally unsuited, since a blown film cannot be guided between the two displacement measuring sensors. For this reason, it has until now been common practice to use sensing sensor arrangements for gauging the thickness of blown films. However, since thickness gauging should not occur during a stage of the production process, when the film material is still soft and deformable, a sensing thickness measurement will always leave sliding marks of the sensor head, unless it even leads to damage to the film tape and to tearing of same in the extreme case.
It is therefore the object of the invention to provide a sensor for gauging the thickness on films, which makes it possible to perform on the one hand a noncontacting thickness measurement, in particular also on blown films, and which largely prevents on the other hand measuring errors that are caused by the movement of film during the production process.
SUMMARY OF THE INVENTION
The above and other objects and advantages of the present invention are achieved by the provision of a sensor which comprises a sensor head which includes a bottom plate, and at least one non-contacting sensor element mounted on the bottom plate and which is capable of gauging the thickness of the film from the physical properties of the film when the film is located adjacent and spaced below the bottom plate. A plurality of gas outlets extend through the bottom plate and are directed toward the film, with the outlets arranged to encircle the sensor element. A mount is provided for mounting the sensor head for movement toward and away from the film, and means is provided for adjusting the position of the sensor head in the mount. The adjusting means comprises a gas supply connected to the gas outlets so that a gas flow is directed toward the film, and thus a fine adjustment of the spacing between the sensor head and the film occurs automatically by means of the gas flow. Also, the gas flow generates a vacuum about the sensor element which acts to lift the film without contacting the bottom plate so that during the measuring procedure a predeterminable and essentially constant relative position is maintained between the bottom plate and the film in spite of any random movement of the film toward and away from the bottom plate.
It has been recognized by the present invention that in particular for gauging films during the production process it is desirable to prefer noncontacting sensor elements, since same are by no means able to influence the deforming process of the film material. It has further been recognized that the selection of the sensor element or of a suitable measuring method depends essentially on the physical properties of the film material. Finally, it has also been recognized that in the case of all noncontacting sensor elements a defined distance between the sensor element and the measuring object, in this instance the film, is prerequisite for an as reliable acquisition as possible of measuring data. Proceeding from this prerequisite, it has been recognized that a defined distance between the sensor head or sensor element and the film does not necessarily require that the film be secured in position relative to the sensor head, but that it is necessary to maintain only a defined relative position between the film and the sensor head. The present invention therefore suggests that the position of the sensor head be dynamically adapted to the position of the film. Thus, the position of the sensor head is to be adjusted to the expected position of the film not only one time, but is to be adjustable such that the sensor head maintains during the entire measuring process a predeterminable, at least largely constant distance from the film. This means that the present invention is directed to securing not only exclusively the position of the film, but also to adjusting the position of the sensor head to the movement of the film.
In a particularly advantageous embodiment of the sensor according to the invention, the sensor element furnishes distance-independent measuring results in a small distance range between the sensor head and the film. In this manner, it is possible to neglect minor inaccuracies in the position adjustment of the sensor head. Likewise, a certain time shift between the movement of the film and the movement of the sensor head will not negatively affect the measuring accuracy of the sensor even when the spacing between the sensor head and the film lies within the distance range of the distance-independent measuring results.
In particular for gauging the thickness on blown films, sensor elements operating by capacitance have been successful. Blown films are normally made of a plastic material that influences as a dielectric the capacitance of a capacitor arrangement. Contrary thereto, inductive sensor elements offer themselves in the case of an electrically conductive film material. Such materials interact with the field of a measuring coil and thereby influence the inductance of the measuring coil. Noncontacting thickness measurements may also be made with the use of optical sensor elements, which will require a corresponding measuring arrangement and a suitable film material.
In an advantageous embodiment of the sensor according to the invention, the sensor head is supported for displacement in a mount. This is especially advantageous, inasmuch as the position of the sensor head must be adjusted substantially only perpendicularly to the direction of transportation of the film. With a corresponding orientation of the mount, only a one-dimensional mobility of the sensor head is necessary, which can be realized in the simplest way in a linear displacement.
Basically, quite different drive means are possible for adjusting the position of the sensor head.
Especially advantageous is an adjustment of the position with the aid of a gas supply in the sensor head and with at least one outlet opening arranged on the measuring side. Via the gas supply and the outlet opening, a gas is directed under a predetermined pressure to the measuring object, namely the film. In this process, two effects overlie each other, so that an air cushion forms between the sensor head and the film. On the one hand, the gas pressure pushes the film away from the sensor head. On the other hand, however, the gas escaping laterally between the sensor head and the film and a thereby developing vacuum pulls up the film. If the gas pressure is adjusted to the arrangement and geometric configuration of the outlet opening as well as to the counterpressure of the film, an air cushion will form between the sensor head and the film. The thickness of this air cushion will determine the distance between the sensor head and the film. Especially advantageous with this procedure is that with a suitable selection of the operating parameters, an approximately constant distance adjusts itself between the sensor head and the film after a short buildup process. This distance adjusts it
Dumberger Martin
Seikowsky Axel
Sellen Martin
Wisspeintner Karl
Alston & Bird LLP
Micro-Epsilon Messtechnik GmbH & Co. KG
Noland Thomas P.
Politzer Jay L.
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