Background Art As well known to those skilled in the art, electromagnetic induction is a phenomenon wherein lines of magnetic force are changed according to variation in the strength of an electric current flowing through a circuit, resulting in the creation of an electromotive force. In addition, electromagnetic induction sensors are sensors for detecting an induced electromagnetic field, and consequently detecting the variation of the electric current, namely, induced electric current, flowing through the circuit.

The application and control fields of facilities, products, and electric circuits using such electromagnetic induction sensors are very wide. The electromagnetic

induction sensors are applicable in a wide range from their industrial purpose to home electronics and electric circuits.

Conventionally, these electromagnetic induction sensors have been manufactured by winding a coil around a core or a bobbin having a constant shape with a winding machine, and directly attaching the coil to a circuit or mounting the coil inside a sensor frame.

The conventional electromagnetic induction sensors, however, have a problem in that their shapes, sizes and characteristics have to be changed depending on their various uses. In order to manufacture an electromagnetic induction sensor having a particular shape and size, therefore, the core or bobbin should be conform to the particular shape and size of the electromagnetic induction sensor. This may require the change of a mold for forming the core or bobbin.

Another problem of the prior art is that a process for winding the coil around the core or bobbin is complicated.

For the winding of the coil, first, the coil should be wound around a circular auxiliary bobbin by making use of a winding machine. Then, after a main winding core or bobbin is assembled thereto, the winding machine is operated to rotate the core or bobbin by using a roller so that the coil previously wound around the auxiliary bobbin is rewound around the rotating main winding core or bobbin. Therefore, in order to wind the coil around the core or bobbin, the use of the

auxiliary bobbin is essential, and this makes the winding process complicated.

As still another problem of the prior art, there exists a need of a sensor frame, inside which a sensor unit, obtained by winding the coil around the core or bobbin, should be mounted. For the manufacture of such a sensor frame, there is a need for a separate mold. When the shape and size of the sensor unit to be mounted therein are changed, the mold for forming the sensor frame as well as the core or bobbin should be changed.

In addition to the above problems, there exists a need of a new winding machine for winding the coil around another core or bobbin having a changed shape and size. For example, when it is desired to wind the coil around a circular bobbin, there requires expensive equipment consisting of a complicated mechanism for inducing rotation of the bobbin, and an additional mechanism for winding the coil around the rotating bobbin at a high speed. Such expensive equipment, however, may be impossible or unsuitable to wind the coil around other different cores or bobbins for manufacturing new sensors having different shapes and sizes. Therefore, in order to manufacture the various electromagnetic induction sensors, the change of the winding machine is inevitable.

Especially, the winding of the coil around the core or bobbin have often showed a problem of cross winding. For

example, in case of a circular core or bobbin, since it is somewhat difficult for the winding machine to wind the coil conforming to a curvature of the core or bobbin, the coil may cross over itself rather than being uniformly wound. This increases a probability of producing poor sensors, which cannot show uniform sensing ability, and thus are unsuitable for use.

When it is desired to develop a particular sensor to be applied in a certain new product or to apply the sensor to products requiring an accurate sensor, the sensor should undergo repetitive tests in order to achieve a desired sensing ability thereof, resulting in consumption of a large amount of time for the manufacture thereof.

Disclosure of the Invention Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide an electromagnetic induction sensor, which can eliminate a need for the change of a winding machine even when the shape and size of the sensor have to be changed, and can save a time required for the change of a mold, thereby facilitating the manufacture thereof.

It is another object of the present invention to provide an electromagnetic induction sensor, which can eliminate a

cross winding problem of a coil around a bobbin, and can achieve uniform winding of the coil.

It is yet another object of the present invention to provide an electromagnetic induction sensor, which can ensure ease in the variation of the shape and size thereof.

In accordance with one aspect of the present invention, the above and other objects can be accomplished by the provision of an electromagnetic induction sensor comprising: a linear flexible tube; a coil which is wound around the tube while maintaining a constant tension thereof; a sensor frame having a fixed non-linear shape, into which the coil wound tube is mounted as it is deformed conforming to an interior space shape of the sensor frame, in a mounted state of the tube in the sensor frame, both ends of the coil being drawn out of the sensor frame; and an impregnant which is injected into the sensor frame, and seals it.

With the one aspect as stated above, since the coil is wound around the linear flexible tube, and the coil wound tube is mounted inside the sensor frame having the fixed non-linear shape, it is possible to eliminate necessity of plural winding machines corresponding to desired various shapes and sizes of the sensor, simplify a winding process of the coil by using a winding machine having a linear bobbin shaft, shorten the winding process of the coil through the elimination of a conventional auxiliary bobbin, reduce a probability of

producing poor products by solving a coil cross winding problem, and enable free change in the shape of the sensor by virtue of easy mounting of the shape-variable flexible tube into the sensor frame.

In accordance with another aspect of the present invention, there is provided an electromagnetic induction sensor comprising: a linear flexible tube; a coil which is wound around the tube while maintaining a constant tension thereof; an iron core having a fixed non-linear shape, the iron core being inserted into the coil wound tube; and an impregnant for allowing the tube, which is wound with the coil and contains the iron core inserted therein, to be immersed therein.

With the another aspect as stated above, since the coil is wound around the linear flexible tube, and the iron core, having the fixed non-linear shape, is inserted into the coil wound tube, it is possible to eliminate necessity of plural winding machines corresponding to desired various shapes and sizes of the sensor, simplify a winding process of the coil by using a winding machine having a linear bobbin shaft, shorten the winding process of the coil through the elimination of a conventional auxiliary bobbin, reduce a probability of producing poor products by solving a coil cross winding problem, enable free change in the shape of the sensor by virtue of simple insertion of the iron core into the shape

variable flexible tube without using a sensor frame, and control electric current capacity using the iron core inserted in the tube..

Preferably, the iron core may be a stacked core having a square sectional shape.

Through the use of the stacked core, which is mainly used in sensors, it is possible to improve a sensing ability of the sensor.

In accordance with yet another aspect of the present invention, there is provided a method for manufacturing an electromagnetic induction sensor comprising the steps of; a) fitting a linear flexible tube around a linear bobbin shaft of a winding machine; b) winding a coil around the tube while maintaining a constant tension thereof; c) separating the coil wound tube from the bobbin shaft; d) mounting the coil wound tube inside a sensor frame having a fixed non-linear shape, and drawing both ends of the coil out of the sensor frame; and e) injecting an impregnant into the sensor frame, and sealing the sensor frame.

As stated above, by virtue of the fact that the coil is wound around the linear flexible tube, and the flexible tube is easily mounted inside the sensor frame having the fixed non-linear shape as it is deformed, it is possible to eliminate necessity of plural winding machines corresponding to desired various shapes and sizes of the sensor, simplify a

winding process of the coil by using a winding machine having a linear bobbin shaft, shorten the winding process of the coil through the elimination of a conventional auxiliary bobbin, reduce a probability of producing poor products by solving a coil cross winding problem, and enable free change in the shape of the sensor.

Furthermore, since the coil is wound around the flexible tube while maintaining a constant tension thereof, there is no risk of causing the coil to be excessively embedded in the tube and causing irregularity in a winding radius of the coil.

As a result, it is possible to accurately control a sensing ability of the sensor.

Brief Description of the Drawings The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: Fig. 1 is a diagrammatic view illustrating one example of a winding machine for manufacturing an electromagnetic induction sensor; Fig. 2 is a perspective view illustrating a tube, around which a coil is wound by means of the winding machine shown in Fig. 1;

Fig. 3 is a perspective view illustrating an electromagnetic induction sensor in accordance with the present invention, wherein the tube shown in Fig. 2 is mounted inside a sensor frame having a fixed non-linear shape; and Fig. 4 is a flow chart illustrating sequential steps of a method for manufacturing the electromagnetic induction sensor in accordance with the present invention.

Best Mode for Carrying Out the Invention The above and other additional aspects of the present invention will be clearly understood by reading the following description related to preferred embodiments of the present invention with reference to the accompanying drawings.

Hereinafter, the present invention will be described in detail in order to allow those skilled in the art to easily understand and realize the present invention through the preferred embodiments.

Fig. 1 is a diagrammatic view illustrating one example of a winding machine for manufacturing an electromagnetic induction sensor. Fig. 2 is a perspective view illustrating a tube, around which a coil is wound by means of the winding machine shown in Fig. 1. Fig. 3 is a perspective view illustrating an electromagnetic induction sensor in accordance with the present invention, wherein the tube shown in Fig. 2

is mounted inside a sensor frame having a fixed non-linear shape. Now, the electromagnetic induction sensor of the present invention will be explained with reference to the above drawings.

The electromagnetic induction sensor of the present invention comprises a linear flexible tube 111, a coil 107 which is wound around the linear flexible tube 111 by means of a winding machine, a sensor frame 302, and an insulation impregnant.

For the winding of the coil 107, the linear flexible tube 111 is configured to be fitted around a bobbin shaft 109 of the winding machine. Here, the coil 107 is guided from a position, designated as reference letter A, and is connected to a horizontal carrier member 105 of the winding machine and the linear flexible tube 111 fitted around the bobbin shaft 109. Although not shown in Fig. 1, the position (A) is connected to a coil supply source, and the bobbin shaft 109 and the horizontal carrier member 105 of the winding machine are adapted to be driven by a motor. According to the driving of the not-shown motor, the horizontal carrier member 105 serves to horizontally move the coil 107 connected thereto at a constant speed, and the bobbin shaft 109 rotates at a constant speed, so as to allow the coil 107 to be wound around the linear flexible tube 111 fitted therearound. The winding machine further has a tension adjustment unit 101, which

serves to control the tension of the coil 107 by receiving a tension control signal 113 inputted from a tension sensor 103.

The tension sensor 103 serves to sense the tension of the coil 107, and display a sensed value 115 on a tension display unit (not shown) for the configuration of the operator. From the sensed value 115 displayed on the not shown tension display unit, thereby, the operator can easily determine whether the tension of the coil 107 is appropriate or not. If the sensed value 115 is out of an appropriate range, in general, the tension control signal 113 is manually sent to the tension adjustment unit 101. Alternatively, the sending of the tension control signal 113 may be automatically performed by means of a tension controller (not shown).

After the winding of the coil 107 is completed, the coil wound tube 111 is separated from the bobbin shaft 109.

Referring to Fig. 2 illustrating such a separated state of the coil wound tube 111, one end of the coil 107, located at one end of the tube 111, penetrates through the interior space of the tube 111, and comes out of the other end of the tube 111, thereby being positioned near the other end thereof. In Fig.

2, both the ends of the coil 107 are designated as reference numeral 200. Then, as shown in Fig. 3, the coil wound flexible tube 111 is mounted inside the sensor frame 302 having a fixed non-linear shape, and both the ends of the coil 107 are drawn out of the sensor frame 302. Here, both the

drawn ends of the coil 107 constitute signal lines. After the flexible tube 111 is mounted therein, the sensor frame 302 is filled with an impregnant, and is sealed.

As the impregnant, there may be used epoxy, which is widely usable as an insulation material. In addition, the linear flexible tube 111 may be made of polyurethane.

With such a configuration, by virtue of the fact that the coil 107 is wound around the linear tube 111, a winding process of the coil 107 is simplified, and there is no risk of cross winding. This has an effect of reducing a probability of producing poor products. Further, through the use of the flexible tube 111, even after completing the winding of the coil 107, the linear flexible tube 111 is deformable according to a desired shape of the sensor frame 302. Furthermore, the present invention achieves an insulation effect through the use of the impregnant.

In order to achieve the above described effects, of course, the following prior conditions should be fulfilled.

First, in consideration of the fact that the coil 107 is wound around the flexible tube 111, the tension of the coil 107 should be held at a constant level. If the tension of the coil 107 is too high, it is difficult to separate the tube 111 from the bobbin shaft 109 after completing the winding of the coil 107. On the contrary, if the tension of the coil 107 is too low, the coil 107 tends to be excessively loosely wound

around the tube 111.

Second, the tube 111 and coil 107 should have a constant diameter and thickness, respectively. Even if the coil 107 is wound around the tube 111 while maintaining a constant tension thereof, when the diameter of the tube 11 is irregular throughout a full-length thereof, this affects characteristics of the sensor, thereby disabling accurate detection of an electric current. For example, if a diameter of the bobbin shaft 109 is 3.8 mm, the tube 111 should have an inner diameter of approximately 4 mm, an outer diameter of approximately 6 mm, and a thickness of approximately 1 mm, and these dimensions have to be uniformly maintained throughout a full-length thereof.

Similarly, the thickness of the coil 107 has to be uniformly maintained so as not to affect the characteristics of the sensor. For example, if the coil 107 has a thickness between 0.1 mm and 0.21 mm, it applies the tension of approximately 100 gram.

According to another aspect of the present invention, in a separated state from the bobbin shaft 109, an iron core, having a fixed non-linear shape, is inserted into the coil wound tube 111, and the tube 111, containing the iron core, is immersed in an impregnant.

Here, since the tube 111 is made of a flexible material, the iron core, having such a fixed non-linear shape, can be

inserted into the tube 111 after the coil 107 is wound around the tube 111. By making use of the fixed non-linear shaped iron core, it is possible to achieve an electromagnetic induction sensor having a desired shape without the above sensor frame. The use of the iron core, moreover, has an effect of achieving ease and convenience in the control of electric current capacity. In case that the iron core is twisted, especially, it is capable of offsetting the voltage phase of an excited electromagnetic field. As a result, it can cope with electromagnetic interference (EMI), which may be produced from the electromagnetic field.

As the impregnant, used for the purpose of insulation, epoxy may be used. For example, the tube, which is wound with the coil, and contains the iron core inserted therein, is immersed in an epoxy liquid for 24 hours at room temperature.

According to an additional aspect of the present invention, the iron core, to be inserted into the tube, is a stacked core having a square sectional shape.

Conventionally, in relation with the manufacture of the electromagnetic induction sensor, such a stacked core having a square sectional shape has been effectively used in order to improve a sensing ability of the sensor. That is, when the electromagnetic induction sensor is manufactured by making use of a tube, the stacked core is inserted into the tube, resulting in improvement in sensing efficiency of the sensor.

Fig. 4 is a flow chart explaining sequential steps of a method for manufacturing the electromagnetic induction sensor.

Now, referring to Figs. 1 to 4, the manufacturing method of the electromagnetic induction sensor will be explained.

In accordance with the manufacturing method of the present invention, first, the linear flexible tube 111 is fitted around the bobbin shaft 109 (Step 401). Then, the coil 107 is connected to the winding machine (Step 403). In a connected state of the coil 107, a not-shown motor is driven to operate the horizontal carrier member 105 and the bobbin shaft 109 of the winding machine (Step 405). During the operation of the winding machine, the tension adjustment unit 101 is operated to maintain a constant tension of the coil 107 depending on the tension control signal 113 inputted from the tension sensor 103. In addition, the tension sensor 103 is operated to sense the tension of the coil 107, and display the sensed value 115 on a not-shown tension display unit, so as to allow the operator to confirm whether the tension of the coil 107 is appropriate or not (Step 407). If the sensed tension value 115 is out of an appropriate range, the tension control signal 113 is manually submitted to the tension adjustment unit 101 in order to maintain a constant tension of the coil (Step 409). Alternatively, in case that a tension controller (not shown) is provided, the transmission of the tension control signal 113 may be automatically performed. In this

way, in a state wherein a constant tension is applied to the coil 107, the coil 107 is wound around the linear flexible tube 111 (Step 411). After completing the winding of the coil 107, the coil wound tube 111 is separated from the bobbin shaft 109 (Step 415). Then, the coil wound tube 111 is mounted inside the sensor frame 302 having a fixed non-linear shape (Step 417). In a mounted state, both ends of the coil 107, wound around the tube 111, are drawn out of the sensor frame 302, so as to constitute signal lines (Step 419).

Finally, for the purpose of insulation, the sensor frame 302, in which the tube 111 is mounted, is filled with the impregnant, and is sealed (Step 421).

When the coil 107 is wound around the tube 111 made of a flexible material as stated above, the tension of the coil 107 is very important. According to the present invention, since the tension adjustment unit 101 of the winding machine can maintain a constant tension of the coil 107, and furthermore can adjust the tension of the coil 107 through the use of the sensed value 115 from the tension sensor 103, it is possible to apply a constant tension to the coil 107.

Industrial Applicability As apparent from the above description, the present invention provides an electromagnetic induction sensor wherein

a coil is wound around a linear flexible tube, and the coil wound tube is mounted inside a sensor frame having a fixed non-linear shape, which is capable of eliminating necessity of plural winding machines corresponding to desired various shapes and sizes of the sensor, simplifying a winding process of the coil by using a winding machine having a linear bobbin shaft, shortening the winding process of the coil through the elimination of a conventional auxiliary bobbin, reducing a probability of producing poor products by eliminating a coil cross winding problem, and enabling free change in the shape thereof by virtue of easy mounting of the shape-variable flexible tube into the sensor frame.

Further, according to the present invention, the present invention provides an electromagnetic induction sensor wherein a coil is wound around a linear flexible tube, and an iron core, having a fixed non-linear shape, is inserted into the coil wound tube, which is capable of eliminating necessity of plural winding machines corresponding to desired various shapes and sizes of the sensor, simplifying a winding process of the coil by using a winding machine having a linear bobbin shaft, shortening the winding process of the coil through the elimination of a conventional auxiliary bobbin, reducing a probability of producing poor products by eliminating a coil cross winding problem, enabling free change in the shape thereof by virtue of simple insertion of the iron core into

the shape variable flexible tube without using a sensor frame, and controlling electric current capacity using the iron core inserted in the tube.

Furthermore, the iron core is a stacked core, which is mainly used in sensors using a tube, resulting in improvement in sensing efficiency of the sensor.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.