Patent Publication Number: US-6700083-B2

Title: Breaker apparatus

Description:
This application claims benefit of provisional application Serial No. 60/350,186 Filed Nov. 2, 2001 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to a breaker apparatus which fits a movable electrode with a pair of fixed electrodes and separates the movable electrode from the pair of fixed electrodes to thereby open and close a circuit. 
     2. Description of Related Art 
     In a breaker apparatus of this type, for example, there is known a breaker apparatus which is disclosed in JP-A-2000-235824. According to this breaker apparatus, a fixed-side housing, including a pair of mutually insulated fixed electrodes, is fitted with a movable-side housing including a movable electrode to thereby short-circuit a pair of fixed electrodes. By pulling a handle disposed on the movable-side housing, the movable-side housing is separated from the fixed-side housing to thereby remove the short-circuit between the pair of fixed electrodes. 
     However, in this breaker apparatus, when separating the movable-side housing, an operator holds the handle by hand and separates the movable-side housing at a stretch with all his or her strength. This means that, on the back surface side (on the opposite side to the fixed-side housing) of the movable-side housing, there is a relatively large operation space required in the fitting and separating direction of the two housings. Therefore, when sufficient operation space cannot be secured, for example, in a space within an engine room of an automobile, it is difficult to install the above-mentioned breaker apparatus. 
     SUMMARY OF THE INVENTION 
     To solve the above problem, the present applicants have proposed a breaker apparatus having the following structure. In this breaker apparatus, a driven pin is disposed in a fixed-side housing in a movable-side housing a drive member is disposed which is prevented from moving in the two-housing fitting direction but is allowed to move in a direction at right angles to the fitting direction. The drive member includes an inclined groove which is inclined with respect to the moving direction of the drive member. When the two housings are made to approach each other to thereby bring the driven pin into engagement with the entrance of the inclined groove and the drive member is moved from this engaged state, due to the engagement between the inclined groove and driven pin, the movable-side housing is pulled near to the fixed-side housing so that the two housings are fitted with each other. Also, when the drive member is moved from the fitted state in the opposite direction to the fitting direction, due to the engagement between the inclined groove and driven pin, the movable-side housing is separated from the fixed-side housing. In this manner, when removing the two housings from each other, by using a cam action due to the engagement between the inclined groove and driven pin, the movable-side housing can be separated from the fixed-side housing with a small operation force. 
     Further, in the present breaker apparatus, the fixed electrodes are disposed in an intermediate portion of a power circuit of an electric car and are used as a means to break the power circuit. In this structure,.when the movable electrode is suddenly removed from the fixed electrodes while the power circuit is electrically energized to thereby open the power circuit, there occurs an arc. In view of this, there can be expected the following structure: a relay circuit serving as switching means for opening and closing the power circuit, and a microswitch serving as a detect means which detects the movement of the drive member to thereby operate the relay circuit. 
     According to this structure, in a state where the two housings are fitted with each other and the fixed electrodes are fitted with the movable electrode (in a state where energization is permitted between the pair of fixed electrodes), the relay circuit executes its closing operation to thereby close the power circuit. When the movement of the drive member to separate the two housings from each other is started, just after the start of the movement of the drive member, the movement of the drive member is detected by the microswitch, and the relay circuit is allowed to execute its opening operation to thereby open the power circuit. When the movement of the drive member is moved further, the movable electrode is separated from the fixed electrodes and since the power circuit is already opened by the relay circuit, occurrence of the arc between the electrodes can be prevented. 
     However, between the start of the opening operation of the relay circuit and the time when the opening operation is completed and the energization of the power circuit stops, there exists a time lag (of the order of 150 msec.). Therefore, to prevent the occurrence of the arc, from the start of the opening operation of the relay circuit to the time when the fixed and movable electrodes are separated from each other, there is necessary the time that is longer than the above time lag. 
     Here, the moving operation of the drive member from the fitted state of the two housings (i.e., the closed state of the power circuit) to the time when the opening operation of the relay circuit is started and, after then, the fixed and movable electrodes are separated from each other is a linear-shaped one-action operation to be executed in a direction at right angles to the fitting direction of the two housings. Therefore, when the drive member is operated with great force, there is a fear that, although the opening operation of the relay circuit is not completed but the power circuit remains closed, the movable electrode can be removed from the fixed electrodes. 
     The present invention aims at eliminating the drawbacks found in the above-mentioned conventional breaker apparatus. Accordingly, it is an object of the invention to provide a breaker apparatus which can prevent the movable electrode from being separated from the fixed electrodes while a main circuit remains closed. 
     In attaining the above object, according to a first aspect of the invention, there is provided a breaker apparatus having a pair of fixed electrodes disposed in series in a main circuit to be opened and closed by switching means. The breaker apparatus also includes a movable electrode disposed in a movable-side housing that is fitted with and separated from the pair of fixed electrodes to thereby allow or prevent energization between the pair of fixed electrodes independently of the opening and closing operation of the switching means. The breaker apparatus further comprises a guide means for guiding a fixed-side housing, with the pair of fixed electrodes disposed therein, and a movable-side housing, with the movable electrode disposed therein, in the fitting and separating direction of the movable electrode and fixed electrodes. A driven pin is disposed in the fixed-side housing and a drive member is disposed in the movable-side housing in such a manner that it is prevented from moving in the fitting and separating direction of the movable electrode and fixed electrodes and it is allowed to move in a direction at right angles to the electrode fitting and separating direction. An inclined groove formed in the drive member has a base end portion open on the side edge thereof opposed to the fixed-side housing, and inclined with respect to the moving direction of the drive member. A loose fit groove is formed in the drive member and, while the fixed-side electrodes and movable electrode are fitted with each other, extends in parallel to the moving direction of the drive member from a terminal end portion of the inclined groove where the driven pin is situated. A detect means which, when the drive member is present at an energization allowable position for positioning the driven pin in the loose fit groove, allows the switching means to execute its closing operation to thereby close the main circuit, and also which, in a process where the drive member moves from the energization allowable position to an energization preventive position for positioning the driven pin in the terminal end portion of the inclined groove, allows the switching means to execute its opening operation to thereby open the main circuit. 
     According to a second aspect of the invention, the drive member includes a protect portion which, while the fixed electrodes and movable electrode are fitted with each other, is situated to cover the detect means. 
     According to a third aspect of the invention, when the drive member moves from the energization allowable position to the energization preventive position, the detect means starts the opening operation of the switching means before the drive member reaches the energization preventive position, characterized by operation resistance increasing means which, as the drive member moves to the energization prevented position side after the switching means starts the opening operation, increases the operation resistance of the drive member. 
     According to the first aspect of the invention, when the drive member is moved with the driven pin engaged with the base end portion of the inclined groove, the two housings approach each other while they are guided by the guide means. When the drive member reaches the energization preventive position, not only the fitting engagement between the two housings but also the fitting engagement between the fixed and movable electrodes are completed and energization is allowed between the pair of fixed electrodes. When the drive member is moved to the energization allowable position, the switching means executes its closing operation to thereby close the main circuit, so that energization between the fixed electrodes is allowed. In a process where the drive member is moved in the opposite direction from this state, the driven pin moves within the loose fit groove during the movement of the drive member from the energization allowable position to the energization preventive position. Therefore, the opening operation of the switching means is executed while the fixed and movable electrodes remain unmovable with respect to each other in the separating direction (i.e., while maintaining their mutual fitting engagement), so that the main circuit is opened. 
     When the drive member is moved further, the movable electrode is separated from the fixed electrodes to thereby prevent energization between the pair of fixed electrodes. In this manner, according to the first aspect of the invention, due to provision of the loose fit groove, the opening operation of the switching means for opening the main circuit can be completed while maintaining the mutual fitting engagement between the fixed and movable electrodes. 
     According to the second aspect of the invention, since there is formed in the drive member the protect portion for covering the detect means, the detect means can be prevented from being operated unpreparedly due to interference by external foreign bodies. Thus, the unprepared execution of the opening operation of the switching means for opening the main circuit can be prevented. 
     According to the third aspect of the invention, due to provision of the operation resistance increasing means, as the drive member moves to the energization preventive position side after the opening operation of the switching means starts, the operation resistance of the drive member can be increased. Thanks to this, as the time that is necessary from the start of the opening operation of the switching means to the separation of the movable electrode from the fixed electrodes, there can be secured sufficiently long time. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a section view of a breaker apparatus according to a first embodiment of the invention, showing a state in which two housings are separated from each other; 
     FIG. 2 is a section view of the breaker apparatus, showing the starting state of fitting of the two housings; 
     FIG. 3 is a side view of a drive member, showing a state in which it is present at an energization preventive position; 
     FIG. 4 is a side view of the drive member, showing a state in which it is present at an energization allowable position; 
     FIG. 5A is a back view of the drive member, showing a state in which it is present at an energization allowable position; 
     FIG. 5B is a back view of the drive member, showing a state in which it is present at an energization preventive position; 
     FIG. 6 is a section view taken along the line  6 — 6  shown in FIG. 1; and 
     FIG. 7 is a perspective view of the drive member. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A description will be given below of a first embodiment of a breaker apparatus according to the invention with reference to FIGS. 1 to  7 . 
     In a breaker apparatus according to the present embodiment, a pair of fixed electrodes  13  are disposed in a fixed-side housing  10  and arranged in series with a main circuit (not shown) to be opened and closed by a relay circuit (not shown) (switching means which is an element of the invention). Two movable electrodes  23  are disposed in a movable-side housing  20  and are fitted with and separated from the pair of fixed electrodes  13 , thereby permitting or preventing electric energization between the pair of fixed electrodes  13  independently of the opening and closing operations of the relay circuit. 
     The fixed-side housing  10  is formed in a box shape with the front side thereof corresponding to the left side in FIG.  1  and the side corresponding to the movable-side housing  20 . The fixed-side housing  10  comprises a base housing  11 , to be fixed to the body of a car, and a cover housing  12  fitted with the open surface of the housing  10 . In the base housing  11 , a pair of pin-type fixed electrodes  13  are arranged and fixed in upper and lower portions. The fixed electrodes  13  form part of the main circuit (not shown) and, in the case where the two movable electrodes  23  (to be discussed later) are fitted with the fixed electrodes  13 , the fixed electrodes  13  are short-circuited, i.e., energization is allowed between the fixed electrodes  13 . When the movable electrodes  23  are separated from the fixed electrodes  13 , the energization between the fixed electrodes  13  is prevented. 
     In the following description, the term “the vertical direction” is based on FIG. 1, whereas the term “the right and left direction” is the vertical direction of FIG.  6 . 
     In the cover housing  12 , there are formed insertion holes  14  into which the fixed electrodes  13  can be inserted respectively. The movable electrodes  23  can be stored in a cylindrical-shaped space between the insertion holes  14  and the outer peripheries of the fixed electrodes  13  (which will be discussed later). 
     The movable-side housing  20  comprises a cover  21  and two electrode mold bodies  22 . Each of the electrode mold bodies  22  includes a pair of movable electrodes  23  molded of resin. When the two housings  10  and  20  are fitted with each other, the movable electrodes  23  are respectively fitted with the pair of fixed electrodes  13 . The pair of movable electrodes  23  are connected to each other by a short-circuit piece  23 A. Therefore, when the movable electrodes  23  are fitted with the pair of fixed electrodes  13 , the movable electrodes  23  allow the fixed electrodes  13  to be short-circuited with respect to each other. 
     A connecting pin  24  penetrates through the electrode mold body  22  and cover  21  in the vertical direction, whereby the electrode mold body  22  can be mounted on the cover  21  in such a manner that it is prevented against removal. The inside diameter of the penetration hole of the electrode mold body  22  is set slightly larger than the outside diameter dimension of the connecting pin  24 . Thus, the electrode mold body  22  is allowed to shake in the vertical direction, as well as in the right and left directions, (in directions at right angles to the fitting and separating direction of the fixed electrode  13  and movable electrodes  23 ) within the cover  21 , so that the alignment of the movable electrodes  23  and fixed electrodes  13  can be adjusted automatically when they are fitted with each other. 
     In the cover housing  12  of the fixed-side housing  10 , there is formed a hood portion  12 A (guide means which is an element of the invention) which is open on the upper and front sides thereof (FIG. 1) and has a substantially U-like shape when it is viewed from the front surface side thereof Correspondingly, in the movable-side housing  20 , there is formed a substantially U-shaped slit  25  (guide means which is an element of the invention) into which the hood portion  12 A can be fitted. When the hood portion  12 A and slit  25  are fitted with each other, they fulfil the function of a guide rail. Due to this guide function, the movable-side housing  20  is guided with respect to the fixed-side housing  10  in a direction (in a back-and-forth direction) along the fitting direction of the movable electrodes  23  and fixed electrodes  13 . Thus, the movable-side housing  20  is moved in such a manner that the play thereof in the vertical direction as well as in the right and left direction, is restricted. 
     The fixed-side housing  10  and movable-side housing  20  can be fitted with and separated from each other by the following cam means. That is, a pair of driven pins  15  are provided on and projected from each of the upper and lower portions of the right and left outer surfaces of the hood portion  12 A of the fixed-side housing  10 . On the movable-side housing  20 , there is disposed a drive member  30  which can cooperate with the driven pins  15  in fulfilling the function of a cam. 
     The drive member  30  includes a right and a left movable plate  31 ,  31  each having a rectangular-plate shape long in the vertical direction, a plate-shaped connecting portion  32  (a protect portion which is an element of the invention) for connecting together the upper end portions of the two movable plates  31 , and a handle portion  33  extending upwardly from the connecting portion  32 . The components of the drive member  30  can be formed by press working a sheet of steel plate. 
     The movable plate  31  is stored in a vertically-extending slit  26  formed in the movable-side housing  20  in communication with the slit  25 . It is movable in the interior of the slit  26 . The movable plate  31  is allowed to move with respect to the movable-side housing  20  only in the vertical direction (a direction at right angles to the fitting and separating direction of the fixed electrodes  13  and movable electrodes  23 ) which is the longitudinal direction of the slit  26 . However, the relative movements of the movable plate  31  to the movable-side housing  20  in the back-and-forth direction (a direction parallel to the fitting and separating direction of the fixed electrodes  13  and movable electrodes  23 ) at right angles to the vertical direction, as well as in the right and left direction, are restricted. 
     Also in the movable plate  31 , there are formed two mutually parallel linear-shaped inclined grooves  34  each having a base end portion  34 A which is open on the side edge  31  A of the movable plate  31  opposed to the fixed-side housing  10 . Each of the inclined grooves  34  is formed such that, as it goes upwardly, it parts away from the side edge  31  A toward the back surface side of the movable plate  31  (in FIG. 2, toward the left side). In other words, it extends in an inclined direction to the relatively moving direction (the vertical direction) of the drive member  30  with respect to the movable-side housing  20 . The driven pin  15  of the fixed-side housing  10  can be engaged into the inclined groove  34 . When the movable plate  31  is moved in the downward direction (FIG. 1) while the driven pin  15  is introduced into the base end portion  34 A of the inclined groove  34 , the movable plate  31  and thus the movable-side housing  20  is moved in such a manner that it is drawn close to the fixed-side housing  10  due to the cam action caused by the engagement between the inclined groove  34  and driven pin  15 . When the driven pin  15  reaches the terminal end portion  34 B of the inclined groove  34 , the fitting of the two housings  10  and  20  is completed, as well as the fitting of the movable electrodes  23  and fixed electrodes  13  is completed. Also, when the drive member  30  is lifted up from this position, the movable-side housing  20  is separated from the fixed-side housing  10  and also the movable electrodes  23  are separated from the fixed electrodes  13  due to the cam action caused by the engagement between the inclined groove  34  and driven pin  15 . 
     Further, there is formed in the movable plate  31 , a loose fit groove  35  which extends upwardly from the terminal end portion  34 B of each of the inclined grooves  34  in parallel to the moving direction of the drive member  30 . When the drive member  30  is moved further downwardly from the fit completed position, i.e., where the driven pin  15  is situated in the terminal end portion  34 B of the inclined groove  34 , the driven pin  15  is moved within the loose fit groove  35  but the cam action is not fulfilled. Therefore, the two housings  10  and  20  are not shifted with respect to each other in the fitting and separating direction. Furthermore, the electrodes  13  and  23  are not shifted with respect to each other in the fitting and separating direction. 
     On the outer surface of the upper end portion of the cover housing  12  of the fixed-side housing  10 , a microswitch  36  is disposed (detect means which is an element of the invention) for detecting the position of the drive member  30  to thereby allow the relay circuit to execute its operation for opening and closing the main circuit. The microswitch  36  is stored in a storage portion  17  which is formed in a cylinder-like shape. The microswitch  36  includes a probe  36 A and a movable piece  36 B which is disposed upwardly of the probe  36 A and can be elastically shifted in the vertical direction. 
     When the drive member  30  is at an energization allowable position, (see FIG. 4) i.e., where it sets the driven pin  15  at the upper end portion of the loose fit groove  35 , the connecting portion  32  presses down the movable piece  36 B to bring it into contact with the probe  36 A to thereby allow the microswitch  36  to detect that the drive member  30  is at the energization allowable position. Due to this detection, the relay circuit is allowed to execute its closing operation for closing the main circuit. When the drive member  30  moves from the energization allowable position to an energization preventive position (see FIG. 3) in which the driven pin  15  is situated at the terminal end portion  34 B of the inclined groove  34 , the connecting portion  32  retreats upwardly to separate the movable piece  36 B from the probe  36 A, just after the start of the movement of the drive member  30 , and the microswitch  36  detects the movement of the drive member  30  toward the energization preventive position to thereby allow the relay circuit to start its opening operation for opening the main circuit. After approximately 150 msec. from the start of the opening operation of the relay circuit, the opening operation of the relay circuit is completed so that the main circuit is opened. 
     Two upper and lower notches  38  and  37  are formed in the side edge of the movable plate  31  on the opposite side to the side edge  31 A thereof where the base end portion  34 A of the inclined groove  34  is open. When the drive member  30  is in the upper-most end, i.e., where the driven pin  15  is situated at the base end portion  34 A of the inclined groove  34  (FIG.  2 ), the lower notch  37  is fitted with a plate spring  27  (operation resistance increasing means which is an element of the invention) of the movable-side housing  20 , so that the drive member  30  is held at the same height. When the drive member  30  is at the energization allowable position (FIG.  4 ), the upper notch  38  and plate spring  27  are fitted with each other, so that the drive member  30  is held at the energization allowable position. Additionally, when the drive member  30  is at the energization allowable position, the plate spring  27  is contacted with the inclined portion  38 A (operation resistance increasing means which is an element of the invention) of the upper notch  38  and is thereby flexed elastically, not only due to the elastic recovery of the plate spring  27  but also due to the inclination of the inclined portion  38 A. Therefore, an energization force going toward the energization allowable position side is applied to the drive member  30 . 
     Next, a description will be given below of the operation of the present embodiment. 
     To bring the movable-side housing  20  into fitting engagement with the fixed-side housing  10 , the movable electrodes  23  are moved into the hood portion  12 A and are moved laterally until the driven pins  15  move into the base end portions  34 A of the inclined grooves  34  of the movable plate  31 . In this operation, because the hood portion  12 A is open on the upper side thereof, the movable electrodes  23  may be moved down straight from the position shown in FIG.  1  and thereafter, may be moved laterally. As a result, the movable electrodes  23  and fixed electrodes  13  are brought into slight fit with each other. 
     Next, the drive member  30  is pressed down to the energization preventive position. During this operation, due to the engagement between the driven pins  15  and inclined grooves  34 , the two housings  10  and  20  are brought into their mutual fit completed state and the two kinds of electrodes  13  and  23  are brought into their mutual fit completed state to allow energization between the fixed electrodes  13 . The main circuit is not closed yet at the time. 
     Next, the drive member  30  is pressed further down to the energization allowable position. This operation is detected by the microswitch  36  and the relay circuit carries out its closing operation. Thus, the main circuit is turned into its closed state not only due to the closing operation of the relay circuit but also due to the energization allowed state between the fixed electrodes  13 , (a state in which energization is allowed). In this state, owing to the engagement between the upper notch  38  and plate spring  27 , the drive member  30  is held at the energization allowed position, while the main circuit is held in the closed state. 
     Additionally, while the drive member  30  remains at the energization prevented position, the further pressing-down operation is not executed (FIG.  3 ), since the plate spring  27  is elastically contacted with the inclined portion  38 A of the upper notch  38 . Thus, due to the elasticity and inclination of the plate spring  27 , the drive member  30  is automatically moved to the energization allowed position side. 
     Next, description will be given below of the operation to remove the two housings  10  and  20  from each other. 
     By picking up the handle portion  33 , the drive member  30  situated at the energization allowed position is lifted up. When the drive member  30  is moved toward the energization prevented position, i.e., just after the start of the movement of the drive member  30 , the relay circuit begins its opening operation and, after approximately 150 msec., the opening operation of the relay circuit is completed. Accordingly, the main circuit opens to stop the energization between the fixed electrodes. 
     Here, the distance from the position of the drive member  30  where the relay circuit begins the opening operation to the energization preventive position is set in such a manner that, when the lifting operation of the drive member  30  is carried out at the normal speed, it takes the time longer than about 150 msec. (which is the time lag between the start of the opening operation of the relay circuit and the opening operation of the main circuit) for the drive member  30  to move between the energization allowable and preventive positions. Therefore, when the drive member  30  reaches the energization preventive position, the main circuit is opened. Also, during the time while the drive member  30  starts from the energization allowable position and reaches the energization preventive position, the two housings  10  and  20  are not shifted in the separating direction with respect to each other since the driven pins  15  only move within the loose fit groove  35 . Therefore, the electrodes  13  and  23  are also not shifted in the separating direction with respect to each other, thereby maintaining the state where the movable electrodes  23  are removed from the fixed electrodes  13 . 
     After the drive member  30  reaches the energization preventive position, if the drive member  30  is further lifted, the driven pins  15  are engaged with the inclined grooves  34 , thereby starting the movements of the movable electrodes  13  in the separating direction from the fixed electrodes  23 . When the driven pins  15  reach the base end portions  34 A of the inclined grooves  34 , the movable and fixed electrodes  13  and  23  are completely separated from each other. When the movable and fixed electrodes  13  and  23  are separated from each other, there is no possibility that there can occur any arc between the movable and fixed electrodes  13  and  23  because the main circuit is already opened due to the opening operation of the relay circuit. 
     As described above, since the loose fit groove  35  is formed, even in case where there is a time lag between the start and completion of the opening operation of the relay circuit for opening the main circuit, the opening operation of the relay circuit for opening the main circuit can be completed while maintaining the movable and fixed electrodes  13  and  23  in the mutually fitted state. 
     Also, when the drive member  30  moves from the energization allowable position to the energization preventive position, i.e., during the time when the opening operation of the relay circuit for opening the main circuit starts and the drive member  30  reaches the energization preventive position, the elastic flexion amount of the plate spring  27  increases due to the inclination of the inclined portion  38 A of the upper notch  38  and the operation force (operation resistance) to be applied to the drive member also increases gradually. Therefore, a sufficient amount of time may be secured for the start of the opening operation of the relay circuit to the removal of the movable electrodes  23  from the fixed electrodes  13 . 
     When the movable and fixed electrodes  23  and  13  are fitted with each other, the microswitch  36  is covered from above by the connecting portion  32  of the drive member  30 . This can prevent the microswitch  36  from being mistakenly operated due to interference by external foreign bodies and thus can prevent the opening operation of the relay circuit for opening the main circuit from being carried out in error. 
     The invention is not limited to the embodiment explained by the above description and drawings but, for example, the following embodiments also fall within the technical scope of the invention and, further, other various modifications are also possible without departing from the subject matter of the invention. 
     (1) In the above embodiment, there is employed a structure in which two short-circuited movable electrodes are fitted with the two pin-shaped fixed electrodes. However, this is not limitative but there can also be employed a structure in which a pair of tongue-shaped fixed electrodes are respectively disposed on the two sides of an insulated support pillar, and a U-shaped movable electrode is fitted with the two fixed electrodes to thereby short-circuit the two fixed electrodes. 
     (2) A fuse device may be attached to the breaker apparatus according to the above embodiment, or there may be disposed a switch which can detect that the movable-side housing is fitted with the fixed-side housing. 
     (3) In the above embodiment, as the detect means which detects the movement of the drive member to thereby operate the relay circuit, there is used a microswitch. However, according to the invention, alternatively, there may be used a pair of terminal metal members in the fixed-side housing and there may be disposed a short-circuit terminal in the drive member, whereby the short-circuiting of the pair of metal members and the removal of such short-circuiting may be may be carried out using the short-circuit terminal. 
     (4) In the above embodiment, the microswitch is disposed in the fixed-side housing. However, according to the invention, the microswitch may also be disposed in the movable-side housing. 
     (5) In the above embodiment, as the switching means, there is used a relay circuit. However, according to the invention, there can also be used other means such as a transistor.