Patent Publication Number: US-2003226749-A1

Title: Limit switch

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to a limit switch which limits or controls a movement, and, in particular, to a constitution of a non-contact type microswitch extensively used for industrial purpose which comprises water resistance, corrosion resistance and abrasion resistance. It is to be noted that the limit switch is a switch to detect a position, a displacement, a movement, a passage and the like, and the microswitch is defined as a compact type switch designed and produced so that a switching operation to open and close an electrical current can be promptly and reliably performed with a small force.  
       [0003] 2. Description of the Related Art  
       [0004] A conventional limit switch generally has an actuator of a lever type rotatably supported by a hinge, and when a free end of the actuator is pushed and moved by a cam and a dog of an operational mechanism, the movement thereof is transmitted to a slide pin, and by a snap action of a toggle mechanism and the like, a contact thereof is switched to OFF from ON or ON from OFF, so that a signal is outputted and an operation of a moving mechanism is detected.  
       [0005] However, since an urging force which actuates the limit switch receives resistance due to a reaction accompanied with a snap action of the contact by moving the actuator lever, an urging force large enough to overcome the resistance is required. Therefore, in order to avoid an influence, which exerts a counteraction on the function, it is better that an operating force of the limit switch is as weak as possible. Further, in bad surroundings where the limit switch is used not only for industrial machines, but also for field equipment of civil engineering, building construction and the like, abrasion due to accumulation of dust and repeated operations is unavoidable for a spindle of the hinge which supports the lever to function as the actuator. A sealed microswitch of JIS C 4508 is a large type, and is difficult to use conveniently for the places, which require a compact construction.  
       SUMMARY OF THE INVENTION  
       [0006] Therefore, the object of the present invention is to provide a general type limit switch, which has abrasive resistance, corrosion resistance and water resistance, and is excellent in durability and, moreover, can function with a weak operating force.  
       [0007] In order to achieve the above-described object, the limit switch according to the present invention is a flat box type housing as a basic model with a cavity concavely provided, and an outer surface of the housing comprises: two surfaces backward and forward in a thickness direction where mounting holes are piercingly provided at standard positions (a center distance between two places of mounting holes according to JIS C 4505 is: 25.4 mm) and which function as mounting surfaces; an upper surface which defines upper edges of these two surfaces and supports an actuator lever; and an under surface which defines under edges of these two surfaces and where the cavity is open, wherein a non-contact type microswitch is provided inside the cavity with upper and lower positions adjustable; and the actuator lever is supported on the upper surface by a cantilever plate spring; and a piston connecting the actuator lever and the microswitch is insertably mounted between both of them; and an annular concave portion circumference on the upper surface, where a piercing hole to fittingly mount the piston by being connected with the cavity is open, is sealed at the outer edge of the elastic membrane which supports the piston by seal-connecting the piston with the center potion; and, moreover, the cavity which stores the microswitch is filled with a sealing agent.  
       [0008] In two surfaces which function as the mounting surfaces, low small protrusions are convexly provided on at least two places of one side, and in the corresponding position of the other side, hole portions to fit the small protrusions are concavely provided. Further, the plate spring is formed by polyimide, and the elastic membrane is formed by a disc bellows having an inclination along a flat conical surface with polyimide as a raw material. Further, the actuator lever is formed by stainless steel (SUS304) and the surface thereof is subjected to nitriding processing. In addition, a top end of the actuator lever is extended to the housing side, and a square hole which controls a moving range is piercingly provided at a position facing the housing side so as to idly fit to a protrusion of the housing side. On the other hand, a compression coil is insertably mounted between the piston and a mounting board of the microswitch and supports a weight of the piston and an urging force by the elastic membrane. Further, the mounting board of the microswitch is provided with an external thread on an outer periphery thereof and screwed into an internal thread provided on a piercing hole of the housing, and the mounting board of the microswitch is rotated so as to move a position relative to the actuator lever by a screw mechanism and a distance of an operating position by the actuator lever for a free position of the microswitch is made adjustable. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0009]FIG. 1 shows one embodiment of a limit switch according to the present invention. FIG. 1A is a plane view, and FIG. 1B is a cross sectional view cut along the line BB in FIG. 1A;  
     [0010]FIG. 2 is a bottom view cut along the line II-II in FIG. 1B; and  
     [0011]FIG. 3 is a side view of a part by a cross-sectional view cut along the line III-III in FIG. 1B. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
     [0012] Hereinafter, an embodiment of a limit switch according to the present invention will be described based on the drawings. FIG. 1 shows one embodiment of a limit switch  10  according to the invention, and FIG. 1A is a plane view and FIG. 1B is a sectional view cut along the line B-B in FIG. 1A. Further, FIG. 2 is a bottom view cut along the line II-II in FIG. 1B, and further FIG. 3 is a side view of a partial sectional view cut along the line III-III in FIG. 1B.  
     [0013] A housing  12  of the limit switch  10  is an aluminum die cast molded article piercingly provided with mounting holes  16 ,  17  which pass through two surfaces (surface parallel to the paper surface of FIG. 1B)  14 ,  15  frontward and backward in a thickness direction at two places. A center distance between the mounting holes  16 ,  17  is preferably set to 25.4 mm based on JIS C 4505 standard. Front surface  14  side opening of the mounting holes  16 ,  17  is concavely provided with counter sinking holes  18 ,  19  which sink heads of mounting bolts (not shown), and low small protrusions  20 ,  21  loosely fittable to the counter sinking holes  18 ,  19  are convexly provided on the periphery of the rear surface  15  of the mounting holes  16 ,  17 .  
     [0014] Hence, for example, by providing a concave portion, to which the small protrusions  20 ,  21  are fittable, on a mounting member (not shown), the position of the limit switch can be easily and precisely decided.  
     [0015] In FIG. 1B, screw holes  23   a  are carved at two places of a seat  23  provided at right side in the drawing of the upper surface  22  which defines the upper edges of the frontward and backward two surfaces  14 ,  15 , and bolt holes  24   b  are piercingly provided at two places at positions aligned with the holes  23   a  in the plate spring  25  of polyimide and a clamp  24 , respectively. A plate spring  25  is piercingly provided between the seat  23  and the clamp  24 , and s bolt  26  inserted into the bolt hole  24   b  is screwed into the screw hole  23   a  and clamped, and the plate spring  25  is compressed and fixed to the seat  23  by the clamp  24 . In the clamp  24  is concavely provided a counter sinking hole  24   a  which sinks a head  26   a  of the bold  26 . The plate spring  25  is detachable by this bolt connection so that, when dust is accumulated in a gap  22   a  between the upper surface  22  and the plate spring  25 , it is possible to remove and clean the plate spring  25 . In the case where the plate spring  25  suffers an accidental damage from an external force, the plate spring  25  has advantages of being exchanged.  
     [0016] Reference numeral  28  denotes an actuator lever, which is connected with a free end of the plate spring  25  by a rivet  29 . The actuator lever  28  is formed by a plate of stainless steel (SUS304) and is subjected to nitriding processing, and therefore, is excellent in corrosion resistance and abrasion resistance, and has little friction. Hence, there is a considerable degree of freedom in an operating direction by an operating member such as a dog, a cam and the like, and an exact vertical degree for an edge line of a sliding portion  28   b  is not necessarily required. Since the actuator lever  28  is supported by the plate spring  25  having a cantilever constitution, an axis or a bearing that wears by receiving rotation does not exist. Accordingly, the actuator lever  28  does not require lubrication, and abrasion is not expedited by insertion of dust and rust.  
     [0017] A free end  28   a  of the actuator lever  28  is provided with a sliding portion  28   b  with the dog and the cam not shown which receives operation and which is greatly bent upward in the drawing from an extension of the plate spring  25  at an angle of 45° and is further bent at the sliding portion  28   b  at about 90°. Further, a top end portion  28   c  is bent along the side  30  of the housing  21  and hangs down almost in parallel. On upper portion of the housing side  30  is concavely provided a notched portion  30   a , which movably stores the top end portion  28   c.    
     [0018] On the other hand, in the actuator lever top end portion  28   c  is piercingly provided a square hole  32  (see FIG. 3), and the notched portion  30   a  notches a position corresponding to almost a center of the square hole  32  and forms a control portion  30   b , which is idly fitted to the square hole  32 . Accordingly, the movement of the actuator lever  28  by a compelling force from the outside is controlled within a range where an inner edge of the square hole  32  abuts against the control portion  30   b . Further, the left and right peripheral walls  30   c  remained on the outer periphery of the notched portion  30   a  and a counter surface  30   d  at the lower end of the top end portion  28   c  control excessive movement and function as a safety stopper.  
     [0019] Against the vicinity of the connecting portion with the plate spring  25  of the actuator lever  28 , a spherically formed apex face of a head  36   a  of a piston  36 , which transmits the movement of the actuator lever  28  to a non-contact type microswitch  34 , abuts. A base  36   b  of the piston  36  is cylindrical, and on the upper end thereof, a seat  36   d  having a diameter slightly larger than the base  36   b  extends from an upper portion of a flange  36   c  expanded in diameter, and a center hole of the head  36   a  fits to a small diameter boss  36   e  protruding from a center of the seat  36   d . A central portion of the disc bellows  38  of the elastic membrane formed by polyimide is insertingly mounted between the under surface of the head  36   a  and the upper surface of the boss  36   d , and the joined surface thereof is completely sealed by polyimide. The disc bellows  38  has a coaxial wavelike convex-concave formed along a flat conical surface, and the same size diameter see-through hole as the boss  36   a  passes through the center.  
     [0020] As shown in FIG. 1B, in the housing  12  is formed a cavity  42  opened to an under surface  40  in the drawing at the side opposing to the upper surface  22 , and is shown in FIG. 2 as a bottom view. From the upper surface  22  to the cavity  42  is passed a piercing hole  44  having steps. On the upper surface  22  to which the piercing hole  44  is opened is formed an inclined plane annular concave portion  46  expanded upward in diameter, where a peripheral wall  46   a  expands upward, and a circumference where a peripheral wall  46   a  contacts a under surface  46   b  is allowed to abut against an outer periphery of the disc bellows  38  so as to be sealed by s bonding agent. In the under surface  46  is concavely provided a step portion  46   c  having a diameter slightly larger than an outer shape of the flange  36   b  which overhangs from the piston  36 , and the step portion  46   c  controls a downward moving area of the flange  36   b  and functions as a safety stopper for an excessive external force in a vertical direction.  
     [0021] In the under portion of a reduced diameter cylindrical hole  46   d  communicating with the cavity  42  from the step portion  46   c  is carved an internal thread  48 , and in the cavity  42 , an opening expanded in diameter functions as a linear line guide portion  52  of a microswitch mounting board  50 . The microswitch mounting board  50  is cylindrical, and in the top end portion thereof is provided an external thread  54  which is screwed into an internal thread  48  of a lower portion of the cylindrical hole  46   d , and a base  56  is slidably fits to the linear line guide portion  52 . The under portion in the drawing of the base  56  is expanded in diameter and forms a microswitch mounting seat  58 , and is carved with a counter sinking hole  62  adapted to the outer shape of the ready-made non-contact type microswitch  34 , and the ready-made non-contact type microswitch is fixed inside the hole  62  by adequate means. Note that a hole IC is utilized for the non-contact type microswitch  64 .  
     [0022] In the center of the microswitch mounting board  50  is provided a through hole  50   a  so that a base  36   b  of the piston  36  is slidably fittingly mounted. The lower end portion of the through hole  50   a  is a sliding portion  50   b  which has little gap with the piston base  36   b , and in the upper portion other than this is provided an escape way expanded in diameter. Between the under surface of the flange  36   c  of the piston and the upper surface of the external thread  54  of the microswitch mounting board is insertably mounted a compression coil  64 , which energizes the piston  36  upward so that the apex surface of the piston head  36   a  is allowed to always abut against the under surface of the actuator lever  28 . On the other hand, the lower end in the drawing of the piston  36  abuts against a top end of an operating pin (actuator)  34   a , which is located at a free position of the ready-made microswitch  34 . Since the microswitch  34  is a non-contact type, a return spring is weak, and in contrast to a contact which operates by a snap action of the conventional general industry limit switch, the microswitch  34  can be sufficiently functioned by an extremely slight operating force.  
     [0023] In order that the operating position of the contact is not largely affected by tares of the actuator lever  28  and the piston  36  depending on a mounting direction of the limit switch  10 , elasticity of the plate spring  25 , the disc bellows  38  and the compression coil spring  64  is comprehensively set. By rotation of the microswitch mounting board  50 , the piston  36  and the compression coil spring  64  moves together upward and downward, and can adjust a distance of an operating position (shown by two-dot chain line) relative to the free position of the actuator lever  28  shown in FIG. 1A by a solid line. After performing a prescribed operating position adjustment in a plant and drawing out a cable (not shown) wired in the non-contact type microswitch  34  from a distribution port  66  of the housing  12 , the cavity  42  is sealed by silicon rubber or an epoxy filler.  
     [0024] As described above, while one embodiment of the limit switch according to the present invention is described based on the drawings, the invention is not limited to the illustrated embodiment, and it is expected that a variety of changes and modifications with respect to the details and alternation such as reconstitution of parts and the like can be performed in a range not deviating from the constituent features of the present invention. For example, as an operating indicator light, a light emitting diode  68  may be mounted.  
     [0025] As evidenced by the above-described explanation, according to the limit switch according to the present invention, since a micro-shaped non-contact type microswitch requiring a delicate attention in handling is sealed into a basic model limit switch, the microswitch can be handled as a sensor also for an extremely sensitive positioning, a displacement, a movement or a passage with a sense for usual machine parts, and moreover, the same operating sensitivity as the microswitch is guaranteed. By the convex portion and the concave portion which are provided on the mounting surface and fit to each other, mutual precise positioning can be easily performed in using the lamination layers of a plurality of microswitches.  
     [0026] Further, since the non-contact type microswitch is installed with the upper and lower positions adjustable, an appropriate operating position can be set. Furthermore, the actuator lever is supported by a cantilever plate spring, and the piston, which transmits the movement of the actuator lever to the non-contact type microswitch, is supported by a bellows-shaped elastic membrane. Since there exist no frictional portions, lubrication is not required, and since there exist no frictional components, durability is improved. Further, since the connecting portion between the bellows-shaped piston and the housing is sealed air tight and the non-contact type microswitch is sealed inside the cavity of the housing by the filler, the electrical contact is completely isolated from the external world, and the limit switch becomes completely a waterproof and dustproof type, so that use in water and oil and in bad surroundings where a lot of dusts abound is possible.  
     [0027] Further, since the actuator lever is formed by stainless steel (SUS304), and the surface thereof is subjected to nitriding processing, and the plate spring and the bellows-shaped elastic membrane are formed by polyimide, the actuator lever is excellent in erosion resistance and abrasion resistance. In addition, a moving range of the actuator lever is controlled by the protrusion of the housing side which idly fits inside the square hole of the top end, and moreover, the notched portion of the housing which stores the top end of the actuator lever can be allowed to function as a safety stopper. Further, for the downward movement in an excessive vertical direction, which acts on the actuator lever, since the lower step of the disc bellows elastic membrane prevents the downward movement of the piston flange, the non-contact type microswitch can be prevented from being affected by unreasonable external force.  
     [0028] On the other hand, since the compression coil spring insertably mounted between the piston and the microswitch mounting board supports the urging force by the tare of the piston and the wavelike elastic membrane, regardless of a mounting posture of the limit switch, a stable constant operating position can be secured, and the microswitch mounting board can precisely set the operating position for the free position of the microswitch by the actuator by a slight adjustment by a screw mechanism.