Abstract:
A pressure switch includes a piston accommodated for sliding movement in a chamber formed in the interior of a casing and which communicates with an introduction port, a coil spring for elastically applying a force to one surface of the piston, an adjustment screw which is capable of variably adjusting an elastic force applied to the one surface, a swivel plate engaged with the adjustment screw and on which the coil spring is seated, and a pointer formed from a resin material integrally with the swivel plate for indicating a pressure of air detected by a switch unit. The adjustment screw variably stretches and compresses the coil spring by movement of the swivel plate, while also maintaining the coil spring at a position at which a predetermined elastic force is obtained. The swivel plate is colored together with the pointer in a high saturation color.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Patent Application No. 2009-180529 filed on Aug. 3, 2009, in the Japan Patent Office, of which the contents are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a pressure switch that measures the pressure of a fluid. 
     2. Description of the Related Art 
     Heretofore, as a means for ensuring that various types of machines can safely be driven automatically, pressure switches have widely been used. By setting beforehand a pressure threshold on the side of a pressure switch that is connected to various devices, excessive fluid pressures generated at a location where the pressure switch is disposed are detected mechanically and/or electrically, whereupon a detection signal can be issued immediately to notify the various devices. 
     For example, in the case that an air filter, a regulator, a lubricator, or the like, which make up types of air pressure auxiliary devices, are interconnected mutually via metal fittings, it is often the case that pressure switches are installed on such metal fittings. In this type of situation, a pressure switch that is small in size and lightweight preferably should be used. 
     In Japanese Laid-Open Patent Publication No. 10-208597, a technical concept is disclosed concerning a pressure switch, which comprises an adjustment screw for setting a pressure threshold value, a swivel plate screw-engaged with the adjustment screw and which slides under a linkage with rotary movement of the adjustment screw, a movable needle formed integrally with the swivel plate, and a display window, which is disposed on a part of a casing. In greater detail, in the vicinity of both sides of the display window provided on the casing, scale markings and a row of Arabic numbers are provided, together with a pointer consisting of a line colored in red or the like on an upper surface of the movable needle, which is applied by printing or the like. 
     As a result of being constructed in this manner, and by displaying in combination the needle, the scale markings and the row of Arabic numbers, the preset pressure threshold can be confirmed visually from an external area outside of the casing. Accordingly, while reading the numerical values of the scale markings pointed to and indicated by the needle, an operator turns the adjustment screw, whereby the threshold value of the pressure switch can easily be set. Naturally, when measurements are performed, measured pressures are capable of being confirmed visually as well by the numerical values of the scale markings which are indicated by the pointer. 
     However, in the pressure switch disclosed in Japanese Laid-Open Patent Publication No. 10-208597, since it is necessary that the plane in which the display window is formed be parallel to the displacement direction of the swivel plate, the planes in which the display window and the swivel plate are formed must be mutually perpendicular to each other. 
     Notwithstanding, in the case that the swivel plate in the aforementioned pressure switch is constructed from a metal plate, in order to form a separate movable needle, an L-shaped bending process must be carried out. Further, in order to display the pointer, which is made up of a red line or the like on the movable needle, it is necessary to perform a process step of engraving with respect to the metal plate, and a separate process step of applying color thereto. 
     In this manner, in the case that a pointer is to be provided on the movable needle after the swivel plate and the movable needle have been formed integrally using a metal plate, separate processing steps, together with an increase in the number of parts, are required. Consequently, a disadvantage results in that manufacturing costs for the pressure switch are increased. 
     SUMMARY OF THE INVENTION 
     The present invention has been devised as a solution to the aforementioned problems. An object of the present invention is to provide a pressure switch for which manufacturing costs are reduced, and which does not require an increase in the number of parts for the pressure switch. 
     The present invention is characterized by a pressure switch, including a casing equipped with an introduction port for enabling a fluid to be introduced therein, a piston accommodated for sliding movement in a chamber which is formed in the interior of the casing and which communicates with the introduction port, an elastic member for elastically applying a force to one surface of the piston, an elasticity adjusting means which is capable of variably adjusting an elastic force applied by the elastic member to the one surface, a swivel plate which is engaged with the elasticity adjusting means and on which the elastic member is seated, and a detecting means for detecting a pressure of the fluid based on displacement of the piston upon receiving the pressure from the fluid introduced and directed from the introduction port. The pressure switch further comprises a pointer formed from a resin material integrally with the swivel plate for indicating a threshold value of the pressure of the fluid detected by the detecting means. The elasticity adjusting means variably stretches and compresses the elastic member by movement of the swivel plate, while also maintaining the elastic member at a position at which a predetermined elastic force is obtained. The swivel plate is colored together with the pointer in a high saturation color. 
     With the pressure switch of the present invention, because the swivel plate is provided which is formed from a resin material integrally with the pointer thereof, after resin molding of the swivel plate, a separate forming process in order to provide a pointer is not needed. Therefore, the manufacturing costs for the pressure switch can be reduced, and the swivel plate and pointer can be completed without increasing the number of parts. Further, because the resin material is colored with a high saturation color, contrast with the casing, which is dark in the interior thereof, can be made more clear, so that visual confirmation by an operator of the value indicated by the pointer is made easier. 
     Further, a distal end of the pointer preferably extends from a seat of the swivel plate and is sharpened in a direction facing toward a display window disposed in the casing. 
     Because a pointer is provided having a distal end that extends from the seat of the swivel plate and which is sharpened in a direction facing toward the display window, the indicated portion by the pointer becomes clear and an operator can more easily read the indicated value. 
     The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front view of a pressure switch according to an embodiment of the present invention; 
         FIG. 2  is a left side view of the pressure switch according to the present embodiment; 
         FIG. 3  is a plan view of the pressure switch according to the present embodiment; 
         FIG. 4  is an enlarged cross sectional view, partially omitted, taken along line IV-IV of  FIG. 1 ; 
         FIG. 5A  is a front view showing a condition in which an attachment fitting is screw-connected with the pressure switch shown in  FIG. 1 ; and 
         FIG. 5B  is a left side view showing a condition in which an attachment fitting is screw-connected with the pressure switch shown in  FIG. 1 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  is a front view of a pressure switch according to an embodiment of the present invention,  FIG. 2  is a left side view, and  FIG. 3  is a plan view thereof.  FIG. 4  is an enlarged cross sectional view, partially omitted, taken along line IV-IV of  FIG. 1 . 
     As shown in  FIG. 4 , a pressure switch  10  includes a casing  12 , which is formed from a metal material substantially in the shape of a rectangular parallelepiped. A chamber  14  is formed in the interior of the casing  12 . 
     The casing  12  has a coupling  16  formed integrally on a lower part thereof. On an outer peripheral edge of the coupling  16 , a male screw  17  is formed, which is connectable with a later-described attachment fitting. A cylindrical introduction port  18  is disposed on a bottom surface part of the coupling  16 . The introduction port  18  communicates with one end of a communication passage  20 , which is gradually reduced in diameter via a stepped portion from a lower part to an upper part thereof. The introduction port  18  and the chamber  14  in the interior of the casing  12  communicate with each other via the communication passage  20 . The other end of the communication passage  20  terminates at an inner bottom wall surface  22  of the chamber  14 . 
     A cylinder main body  23  is formed integrally with the coupling  16  in the interior of the casing  12 . One part thereof extends upwardly as shown in  FIG. 4  and functions as a switch holder  66 , as will be described later. 
     A rectangular shaped cutout portion  24 , which extends longitudinally from an upper portion to a downward portion, is provided on a front surface of the casing  12 . A resin-manufactured faceplate  26  having predetermined printing thereon is adhered to the casing  12  so as to cover the cutout portion  24 . 
     On both sides thereof and on the rear of the casing  12 , a shield plate  28 , which is made from a rolled steel plate, is attached (see  FIG. 2 ). 
     The upper surface of the casing  12  includes a large rectangular shaped opening  30 . The opening  30  is covered and sealed by a flat plate shaped cover  32 , which has substantially the same area as the opening  30 . Two diagonally opposed stop screws  34 ,  36  are disposed in non-illustrated through holes on the cover  32  through which the stop screws  34 ,  36  are insertable (see  FIG. 3 ), whereby the casing  12  and the cover  32  are integrally assembled by means of the two stop screws  34 ,  36 . 
     On the inner bottom wall surface  22  on the front face side of the chamber  14  formed in the casing  12 , a cylindrical column shaped piston  38  that extends in the longitudinal direction of the casing  12  is slidably accommodated. The piston  38  preferably is constructed from a lightweight polyacetal resin having a low coefficient of friction. An annular groove  40  is disposed centrally around the side surface of the piston  38 , and an annular shaped Y-packing  42  is fitted into the groove  40 . Further, on an upper surface of the piston  38 , a cylindrical columnar shaped projection  44  is disposed coaxially with the piston  38 . An annular magnet  46  is fitted over the projection  44 . 
     A lower end of a coil spring  48 , which serves as an elastic member, is affixed coaxially on an upper surface of the magnet  46 . The coil spring  48  has an annular form and is of substantially the same diameter as that of an annular form of the magnet  46 . 
     A swivel plate  50 , which is substantially tubular shaped in outline, is mounted at the upper end of the coil spring  48 . The swivel plate  50  is constructed from a resin material, which is colored in red. A cylindrical bulging portion  51  is formed on a lower part of the swivel plate  50 , and the periphery of the bulging portion  51  constitutes a seat  53  for the coil spring  48 . 
     Together with the swivel plate  50  constructed in this manner, a pointer  52  is formed integrally therewith. The distal end of the pointer  52  is formed by a thin sharpened flat plate, which extends from the seat  53  in a direction perpendicular to the longitudinal direction of the casing  12 . The distal end of the pointer  52  faces toward the opening of the faceplate  26 . 
     A round hole  54 , which is narrow in diameter along the axial direction, is disposed on a lower part of the swivel plate  50 . The round hole  54  communicates with a hexagonal recess  56 , the opening area of which is larger than the round hole  54 , and which is provided on an upper part of the swivel plate  50 . 
     On the other hand, a screw hole  58  is provided roughly in the center of the cover  32 . An adjustment screw (elasticity adjusting means)  60  is inserted through the screw hole  58 , being directed into the chamber  14 . The upper end face of the adjustment screw  60  is exposed through the screw hole  58 , with cross-shaped grooves  62  (see  FIG. 3 ) being engraved into the upper end face thereof. 
     Further, the adjustment screw  60  is screw-engaged with a hexagonal nut  64 , which is seated in the recess  56 . 
     Also, the adjustment screw  60  penetrates into the inner side of the coil spring  48 , such that the end portion of the adjustment screw  60  confronts, with a given distance therebetween, the projection  44  of the piston  38 . 
     On the back surface side of the chamber  14  formed in the casing  12 , the cylindrical switch holder  66  is disposed in the casing  12 , and more specifically, is disposed integrally with the cylinder main body  23 . A columnar shaped switch unit (detecting means)  68  is accommodated in a hole that extends in the axial direction of the casing  12  of the switch holder  66 . The switch unit  68  is affixed to the switch holder  66  by a stop screw  70 , which is inserted through the shield plate  28  and the casing  12 . In this case, a non-illustrated reed switch is mounted inside the switch unit  68 , and two ferromagnetic reeds, which make up the reed switch, normally are in a switched OFF state with a predetermined contact spacing therebetween (i.e., the contacts thereof are in an open state). 
     Lead lines  72  are electrically connected to the switch unit  68  for the purpose of externally outputting detection signals therefrom. The lead lines  72  are drawn out externally from the pressure switch  10  via a through hole  74 , which is formed in the cover  32 . 
     Opposite from the location where the switch unit  68  is attached inside the casing  12 , the faceplate  26  (and a later-described display window  80 ) are disposed. 
     As shown in  FIG. 1 , in au upper central region of the faceplate  26 , which is disposed roughly over the entire surface of the front of the pressure switch  10 , there are provided the display window  80  having a vertical rectangular shape with rounded corners, scale markings  82 ,  84  on both left and right sides of the display window  80 , two rows of Arabic numbers  86 ,  88  that correspond to positions of the scale markings  82 ,  84 , and an alphabet row  90  that reads “MPa” at a lower side position of the display window  80 . 
     The display window  80  is light permeable, being either transparent or semitransparent, whereas the pointer  52 , which is disposed inside the chamber  14  of the casing  12 , is arranged at a position to enable visual confirmation thereof from the exterior front surface of the pressure switch  10 . 
     Further, the scale markings  82 ,  84  are made up of four long lines disposed at positions corresponding to the rows of Arabic numbers  86 ,  88 , and four short lines disposed at positions that divide the intervals between adjacent long lines into five equal intervals. 
     As shown in  FIG. 3 , substantially in the center of the cover  32 , the upper surface part of the adjustment screw  60  (having a round shape in planar view) is exposed. On the upper surface  100  of the cover  32 , with respect to the position of the adjustment screw  60 , there are engraved, respectively, a curved arrow  102  that runs along the outer circumference of the adjustment screw  60  on an upper portion thereof, with a plus (“+”) sign  104  on the righthand side, and a minus (“−”) sign  106  on the lefthand side thereof. 
     Next, and explanation shall be made of a configuration in which an attachment fitting is screw-connected with the pressure switch  10  according to the present embodiment.  FIG. 5A  is a front view showing a condition in which the attachment fitting is screw-connected with the pressure switch  10  shown in  FIG. 1 , whereas  FIG. 5B  is a left side view showing a condition in which the attachment fitting is screw-connected with the pressure switch  10  shown in  FIG. 1 . 
     Female screw threads  112  are provided in an upper side inner wall of an attachment fitting  110 . The female screw threads  112  are screw-engaged with the male screw  17  on the side of the pressure switch  10 . A hollow fluid passage  114  is disposed in the center of the attachment fitting  110 . The fluid passage  114  communicates with the communication passage  20  via the introduction port  18 , which is disposed in the coupling  16 . 
     The pressure switch  10  according to the present embodiment is basically constructed as described above. Next, operations and advantages of the pressure switch  10  shall be explained with reference primarily to  FIG. 4 . 
     First, an operator performs an operation to set the pressure threshold for the fluid in the pressure switch  10 . In this case, the operator engages a non-illustrated plus-driver (i.e., a screw driver having a “+” shape) in the cross-shaped grooves  62  on the upper end surface of the adjustment screw  60  that is inserted through the cover  32 , and performs a turning operation to rotate the adjustment screw  60 . 
     When the adjustment screw  60  is rotated clockwise (toward the side of the plus sign  104 ) in the direction of the arrow  102  (see  FIG. 3 ), the swivel plate  50 , which is screw-engaged with the adjustment screw  60  and is integral with the nut  64  engaged in the recess  56  of the swivel plate  50 , is caused to move downward, thereby compressing the coil spring  48  against the elasticity thereof, whereby the distance between the piston  38  and the swivel plate  50  is made shorter. In this manner, because the coil spring  48  is caused to contract, the elastic force imposed on the piston  38  increases. 
     On the other hand, when the adjustment screw  60  is rotated counterclockwise (toward the side of the minus sign  106 ) in the direction of the arrow  102  (see  FIG. 3 ), the swivel plate  50 , which is screw-engaged with the adjustment screw  60  and is integral with the nut  64  engaged in the recess  56  of the swivel plate  50 , is caused to move upward, thereby gradually releasing the pressing force on the coil spring  48 , so that the distance between the piston  38  and the swivel plate  50  is made longer. In this manner, because the coil spring  48  is made to expand, the elastic force imposed on the piston  38  decreases. 
     As shown in  FIG. 1 , the display window  80  of the faceplate  26  is transparent. The region of the display window  80  is contained within a region of the cutout portion  24  (see  FIG. 4 ) at the front of the casing  12 . Accordingly, when an operator views the front surface from the exterior of the pressure switch  10 , the pointer  52 , which is disposed in the interior of the casing  12 , can be perceived visually. The pointer  52  is formed integrally with the swivel plate  50 , which is made of a resin material, and has a sharpened flat plate shape. Therefore, a fluid pressure threshold value (set value) which corresponds to the displacement amount of the coil spring  48  is displayed in an analog manner through the display window  80 . 
     More specifically, an operator is capable of reading, through a combination of the scale markings  82 ,  84 , the rows of Arabic numbers  86 ,  88  and the alphabet row  90 , a range of 0.1 to 0.4 MPa, at intervals of 0.02 MPa (megapascals). 
     After resin molding of the swivel plate  50  is completed, a separate forming process in order to provide the pointer  52  is not needed. Therefore, the manufacturing costs for the pressure switch  10  can be reduced, and the swivel plate  50  and pointer  52  can be completed without increasing the number of parts. 
     Further, because the swivel plate  50  is colored with a high saturation color, for example in red, contrast with the casing  12 , which is dark in the interior thereof, can be made more clear, so that confirmation by an operator of the value indicated by the pointer  52  is made easier. Saturation is defined as a scale or measure of brightness exhibited by a mixing ratio of white, black, and a primary color. Colors having high saturation (high saturation colors) are defined as colors for which the mixing ratio of the primary color therein is high, and are not limited to the aforementioned red. It goes without saying that colors of green and blue, etc., may also be used. 
     Furthermore, since the distal end of the pointer  52  that confronts the faceplate  26  on the casing  12  is tapered or sharpened, an operator can easily read the numerical value indicated by the pointer  52 . In particular, if a sharp-pointed flat plate is used, as is preferable, the indicated value can be confirmed more assuredly. 
     Still further, since the pointer  52  consists of a sharpened flat plate, the pointer  52  possesses depth perspective with respect to the direction in which the operator visually perceives the pointer  52 . Consequently, even if the display window  80  is visualized from the front of the casing  12  at an angle in the vertical direction (i.e., in the longitudinal direction of the casing  12 ), deterioration of visual perception of the pointer  52  can be prevented. 
     In this manner, after the fluid pressure threshold has been set, the attachment fitting  110  is connected to a non-illustrated device. Upon doing so, for example, compressed air, which is blown out from an air filter, a regulator, a lubricator or the like, which make up types of air pressure auxiliary devices, is enabled to flow through the fluid passage  114  of the attachment fitting  110 . 
     A portion of the air, which forms the fluid that flows through the fluid passage  114 , is introduced into the interior of the chamber  14  of the pressure switch  10  through the introduction port  18  and the communication passage  20 . Because the end of the communication passage  20  communicates with the inner bottom wall surface  22  of the chamber  14 , the lower surface of the piston  38  receives the pressure of the air. 
     When air having a pressure that exceeds the set value set by the adjustment screw  60  is introduced into the chamber  14 , because the piston  38  is made to slide and is displaced upwardly against the elasticity of the coil spring  48 , the magnet  46 , which is fitted onto the projection  44  of the piston  38 , also is displaced upwardly in unison with the piston  38 . When this happens, accompanying the magnet  46  coming into proximity thereof, the two ferromagnetic reeds (not shown) of the switch unit  68  are made to contact each other (i.e., the contacts thereof are placed in a closed state), and the non-illustrated reed switch is switched ON. Thereafter, a detection signal is transmitted externally through the lead lines  72  from the switch unit  68 . As shown in  FIG. 2 , both side surfaces as well as the back surface of the casing  12 , that is, in the vicinity of the disposed position of the switch unit  68 , the shield plate  28  is provided. Consequently, the influence of external electromagnetic waves can be reduced and faulty operation of the pressure switch  10  can be prevented. 
     In the event that the pressure threshold set by the adjustment screw  60  is high, the elastic force from the coil spring  48  increases, and therefore the air pressure required to displace the piston  38  is made larger. Conversely, in the event that the pressure threshold set by the adjustment screw  60  is low, the elastic force from the coil spring  48  decreases, and therefore the air pressure required to displace the piston  38  is made smaller. 
     In this manner, with the pressure switch  10  according to the present embodiment, excessive fluid pressure, such as air pressure or the like, can be detected, whereupon a detection signal can be issued immediately as a notification to the exterior (i.e., to the side of various devices). 
     The pressure switch  10  according to the present invention is not limited to the above-described embodiment, and it is a matter of course that various modified or additional structures could be adopted without deviating from the essence and gist of the invention. 
     For example, if a structure is adopted in which the casing  12  and the coupling  16  are formed as an integral unit, the number of parts and assembly steps can be reduced, thus lowering the rate of assembly defects. Consequently, the manufacturing costs for the pressure switch  10  can be even further reduced. 
     Further, if a structure is adopted in which the internal parts can be accommodated in an integral manner from the opening  30  of the casing  12  upon removing the cover  32  of the pressure switch  10 , the number of assembly steps also can be reduced. As a result, the manufacturing costs for the pressure switch  10  can be further reduced. In this case, the concerned internal parts are made up, for example, of the magnet  46 , the coil spring  48 , the swivel plate  50 , the adjustment screw  60  and the nut  64 . 
     Moreover, although in the present embodiment, a case has been described in which the fluid was air, the invention is not limited by this feature, and the invention is applicable for use with various types of liquids and gases. 
     Furthermore, in the present embodiment, although for the switch unit  68 , a kind of contact type cylinder switch was used, the switching technique is not limited solely to this type. For example, a non-contact type of piston sensor could also be used.