Patent Publication Number: US-8115122-B2

Title: Push button switch

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a push button switch which is attached to a control panel of a machine tool or the like, and used to give an emergency stop instruction etc. to the machine tool or similar instrument. 
     A push button switch for emergency stop is generally formed by combining and coupling a switch portion and an operation portion. The switch portion has a switching contact unit constituted by a fixed contact and a movable contact which is opened/closed against the fixed contact. The operation portion has a push button operation mechanism for performing an operation of opening/closing the switching contact unit. 
       FIGS. 28A-36  illustrate an example of a convention push button switch configuration.  FIGS. 28A and 28B  are perspective views showing the external appearance of the push button switch.  FIGS. 29A-32B  are sectional views of the push button switch shown in  FIGS. 28A and 28B , taken on different cutting lines respectively. 
     In the drawings, the reference numeral  1  represents an operation portion in which an operation mechanism is received in an operation portion case  11 . The operation mechanism includes a push button  12 , a push rod  13 , etc. The push button  12  can be operated to be pushed in. The push rod  13  is linked with the push button  12  so as to work together therewith. 
     The reference numeral  2  represents a switch portion which receives a switching contact unit  24   a  and a switching contact unit  24   b . The switching contact unit  24   a  has a normally open contact (“a” contact) configuration including a fixed contact  22   a  and a movable contact  23   a  which are normally open. The switching contact unit  24   b  has a normally closed contact (“b” contact) configuration including a fixed contact  22   b  and a movable contact  23   b  which are normally closed. Each switching contact unit has a movable frame  25   a ,  25   b  which slides supporting the movable contact  22   a ,  22   b.    
     The operation portion  1  and the switch portion  2  are formed separately as shown in  FIG. 29 . A fitting hole  21   a  is provided in a case  21  of the switch portion. A body portion  11   a  at a leading end of a cylindrical case  11  of the operation portion  1  is fitted into the fitting hole  21   a . A hook  21   c  provided in the inner circumference of the fitting hole  21   a  of the switch portion case  21  is engaged with an engagement recess  11   c  provided in the outer circumference of the body portion  11   a  so that the operation portion  1  and the switch portion  2  are coupled and combined integrally. To release the operation portion  1  and the switch portion  2  from the coupling, a slider  29  provided in the switch portion  2  is operated to release the hook  21   c  from the engagement with the engagement recess  11   c.    
       FIGS. 29A to 32B  show sectional views taken on cutting lines XIX and XXII in  FIG. 28B  respectively. Each  FIG. 29A-32A  shows a standby state in which the push button  12  of the push button switch has not been pushed in but is put in its initial reset position. Each  FIG. 29B-32B  shows an operating state in which the push button  12  has been pushed into an operating position in the lower side of the drawing. 
     The operation portion  1  is provided with a lock mechanism to keep the push button  12  pushed in. The lock mechanism is constituted by a protrusion  13   c  and a lock plate  11   c . The protrusion  13   c  is provided in the outer circumference of the push rod  13 . The lock plate  11   c  is provided in the inner circumference of the body portion  11   a  of the case  11 . When the push button  12  is pushed in at the standby position where the push button  12  has not been pushed in, the push rod  13  linked with the push button  12  moves down in connection therewith. When the protrusion  13   c  of the push rod  13  gets over the lock plate  11   c  and reaches a push-in position, the protrusion  13   c  engages with the lower end of the lock plate  11   c  so as to prevent the push button  12  from returning. Thus, the push button  12  is kept in the push-in position even after it is released from operation. To return the push button  12  to the standby position from the push-in position, the push button  12  is rotated at a predetermined angle to release the lock plate  11   c  and the protrusion  13   c  of the push rod  13  from engagement so as to release the push button  12  from the lock. Due to a return spring  14  consisting of a torsion coil spring, the rotated push button  12  is returned to the reset position where the push button  12  had been put before the rotation. 
     In the state where the operation portion  1  and the switch portion  2  have been coupled, as shown in  FIG. 29A , the movable frames  25   a  and  25   b  respectively supporting the movable contacts of the switching contact units of the switch portion  2  are pushed up by return springs  26   a  and  26   b  respectively. Thus, the upper end of each movable frame  25   a ,  25   b  is brought into contact with the lower end of the push rod  13  linked with the push button  12  of the operation portion  1 . When the push button  12  is in the standby position, the movable contact  23   a  leaves the fixed contact  22   a  as shown in  FIG. 31A . Thus, the switching contact unit  24   a  having the normally open contact (“a” contact) configuration is turned off. On the other hand, the movable contact  23   b  contacts with the fixed contact  22   b  as shown in  FIG. 32A . Thus, the switching contact unit  24   b  having the normally closed contact (“b” contact) configuration is turned on. 
     Here, when the push button  12  is operated to be pushed down against the return spring  14 , the movable frames  25   a  and  25   b  of the switch portion  2  are pushed down by the push rod  13  working with the push button  12 , so that the movable contacts  23   a  and  23   b  move down together with the movable frames  25   a  and  25   b . As a result, the movable contact  23   a  contacts with the fixed contact  22   a  as shown in  FIG. 31B . Thus, the switching contact unit  24   a  having the normally open contact configuration is turned on. On the other hand, the movable contact  23   b  leaves the fixed contact  22   b  as shown in  FIG. 32B . Thus, the switching contact unit  24   b  having the normally closed contact configuration is turned off. 
     The push button switch configured thus is in use attached to a panel such as a control panel. The process of attaching the push button switch will be described below. First, as shown in  FIG. 33 , a fixing nut  19  is detached from the operation portion  1  from which the switch portion  2  has been removed, and the body portion  11   a  is inserted into a mounting hole of the panel on the front side of the panel. Next, on the back side of the panel, the fixing nut  19  is screwed down to the inserted body portion  11   a  of the operation portion  1  so that the body portion  11   a  is fastened and fixed to the panel. The fitting hole  21   a  of the switch portion  2  is fitted to the body portion  11   a  of the operation portion  1  attached to the panel. Thus, the switch portion  2  is coupled and connected to the operation portion  1 . 
     In the push button switch attached to a control panel or the like in use in this manner, there may occur an accident in which the switch portion  2  drops off the operation portion  1  for some reason when the push button switch is in use. When there occurs such an accident in which the switch portion  2  drops off the operation portion  1  in the state where the push button switch is operated to be pushed in, the mode in which the switch portion  2  is pushed in by the push rod  13  of the operation portion  1  is canceled so that the movable frames  25   a  and  25   b  of the switch portion  2  are returned to their reset positions by the return springs  26   a  and  26   b . As shown in  FIGS. 36 and 37 , the normally open contact unit  24   a  is turned off again, while the normally closed contact unit  24   b  is turned on again. 
     Assume that the normally closed contact unit  24   b  is used for issuing an emergency stop instruction. When the normally closed contact unit is returned to be turned on due to an accident in which the switch portion  2  drops off the operation portion  1  in this case, the emergency stop instruction is cancelled so that there is a risk that a significant accident may be caused by resumed operation of an instrument which has been emergency-stopped. 
     In order to avoid such a risk, the opened movable contact of the switching contact unit having the normally closed contact configuration, which unit is used particularly as a switching contact unit for issuing an emergency stop instruction, has to be prevented from returning to the position where the movable contact will contact with the fixed contact, when the switch portion  2  of the push button switch drops off the operation portion. 
     As push button switches for solving such a problem, push button switches have been known in the background art as disclosed in Japanese Unexamined Patent Publication No. (Kokai) JP-A-2001-035302, Japanese Unexamined Patent Publication No. (Kokai) JP-A-2003-303527, Japanese Unexamined Patent Publication No. (Kokai) JP-A-2007-115703. 
       FIGS. 38-40  show the configuration of the conventional push button switch disclosed in JP-A-2001-035302. The conventional push button switch has an operation portion  1  and a switch portion  2 . The operation portion  1  includes a push button  12 , an operation portion case  11  and a push rod  13 . The operation portion case  11  supports the push button  12  slidably thereon. The push rod  13  is provided in the operation portion case  11  so as to work with the motion of the push button  12 . The switch portion  2  is removably attached to the lower portion of the operation portion case  11  of the operation portion  1 . 
     The switch portion  2  has a fixed contact maker  22   c  and a fixed contact  22   b . The fixed contact maker  22   c  has a folded portion with vertical flexibility. The fixed contact maker  22   c  is displaceably fixed to a switch portion case  21 . The fixed contact  22   b  is disposed on the tip of the folded portion of the fixed contact maker  22   c . The switch portion  2  also has a movable contact maker  23   c  and a movable contact  23   b . The movable contact maker  23   c  is supported by a movable frame  25   b . The movable frame  25   b  is urged toward the fixed contact  22   b  by a first spring  27  and urged away from the fixed contact by a second spring  28 . The movable contact  23   b  is disposed on the tip of the movable contact maker  23   c.    
     When the operation portion  1  and the switch portion  2  configured thus are coupled with each other, the fixed contact  22   b  and the movable contact  23   b  of the switch portion  2  contact with each other to form an initial ON state (see  FIG. 38 ). 
     When the push button  12  is pushed in during the initial ON state, a pressing force from the push rod  13  held in the push-in position by a lock mechanism  18  is applied to the folded portion of the fixed contact maker  22   c  through a second movable frame  25   c . Thus, the fixed contact  22   b  is put away from the movable contact  23   b  to be brought into an OFF state (see  FIG. 39 ). 
     When the switch portion  2  is released from the coupling and separated from the operation portion  1 , the movable frame  25   b  supporting the movable contact  23   b  and the second movable frame  25   c  are pushed up by the effect of the elastic repulsion of the second spring  28 . Thus, the movable contact  23   b  can be put away from the fixed contact  22   b  to form an OFF state (see  FIG. 40 ). 
     The conventional push button switch disclosed in JP 2003-303527 is configured as shown in  FIGS. 41 and 42 , wherein an operation portion  1  has a push button  12 , a push rod  13 , a return spring  14 , a lock mechanism  18 , etc. The push button  12  is slidably supported by an operation portion case  11 . The push rod  13  is linked with the push button  12 . The return spring  14  serves to return the push button  12 . The lock mechanism  18  serves to hold the push button  12  in a push-in position. A switch portion  2  receives a switching contact mechanism in a switch portion case  21  removably coupled with the lower end portion of the operation portion case  11  of the operation portion  1 . The switching contact mechanism has a normally closed contact configuration constituted by a fixed contact  22   b  and a movable contact  23   b . A movable contact maker  23   c  to which the movable contact  23   b  is attached is supported by a movable frame  25   b . A spring  28  for urging the movable contact  23   b  away from the fixed contact  22   b  is provided between the movable frame  25   b  and the switch portion case  21 . 
     When the switch portion  2  is coupled with the operation portion  1 , the movable frame  25   b  is linked with the push rod  13  working with the push button  12  of the operation portion  1 . The spring force of the spring  28  urging the movable contact  23   b  of the switch portion  2  away from the fixed contact  22   b  is made smaller than the spring force of the return spring  14  pushing up the push button of the operation portion  1 . Thus, the spring forces of the respective springs are balanced to prevent the movable contact  23   b  from leaving the fixed contact  22   b  before the push button  12  is operated to be pushed in. 
     In the state where the push button is in the reset (initial) position where the push button has not been pushed in yet, the movable frame  25   b  of the switch portion  2  is lifted up by the push rod  13  of the operation portion  1  against the spring force of the opening spring  28  so that the movable contact  23   b  contacts with the fixed contact  22   b  to form an ON state, as shown in  FIG. 41 . As soon as the push button  12  is operated and pushed in as shown in  FIG. 42 , the push rod  13  is held in the push-in position by the lock mechanism  18 . The movable frame  25   b  is pushed down as the push rod  13  is pushed in. Thus, the movable contact  23   b  leaves the fixed contact  22   b  to form an OFF state. 
     Once the operation portion  1  and the switch portion  2  are released from coupling with each other so that the switch portion  2  is separated from the operation portion  1 , the movable frame  25   b  becomes free. Thus, the movable frame  25   b  is pushed down to put the movable contact  23   b  away from the fixed contact  22   b  by the spring force of the opening spring  28  so as to bring the switch portion  2  into an OFF state. 
     According to conventional push button switches disclosed in JP-A-2001-035302 or JP-A-2003-303527, an operation portion and a switch portion are removably coupled with each other. Once an accident occurs in which the switch portion drops off the operation portion in the push button switch, one of two closed contacts of a switching contact unit having a normally closed contact configuration is driven to be open to the other contact by an opening spring. Thus, the two contacts can be opened surely to form an OFF state. 
     However, according to the mechanism which opens the switching contacts of the switching contact unit having the normally closed contact configuration to form an OFF state as soon as the switch portion drops off the operation portion in the conventional push button switch, it is necessary to make both the contacts movable or to balance the spring force of the opening spring with the spring force of the return spring of the operation portion. Thus, there is a problem that the push button switch is too complicated in configuration to manufacture. 
     SUMMARY OF THE INVENTION 
     The invention provides a push button switch which is simple in configuration and easy to manufacture; which has an operation portion and a switch portion removably coupled with each other; and in which as soon as the switch portion drops off the operation portion, switching contacts of a switching contact unit having a normally closed contact configuration are surely opened to form an OFF state. 
     In order to solve the foregoing problem, the invention provides a push button switch including an operation portion and a switch portion which are removably coupled with each other, the operation portion having a push button to be subjected to a push-in operation, the switch portion having a switching contact unit whose contacts are opened/closed in connection with the push-in operation of the push button of the operation portion, wherein the switch portion includes a contact opening mechanism constituted by a lever which is rotatably supported and which has one end acting on a part of the operation portion coupled with the switch portion and the other end acting on a contact switching mechanism of the switching contact unit in the switch portion so as to operate to open/close contacts, and a spring which urges the lever in a fixed rotation direction, and the contact switching mechanism of the switching contact unit is urged to move a movable contact from a standby state position toward an operating state position by the contact opening mechanism as soon as the switch portion is separated from the operation portion, while the contact switching mechanism of the contact unit is released from the urging as soon as the switch portion is coupled with the operation portion. 
     In the invention, the lever in the contact opening mechanism may have a rotary fulcrum in an intermediate portion thereof. An urging force in one end of the lever acts on the operation portion while an urging force in the other end of the lever acts on a contact portion. When the switch portion is coupled with the operation portion, the urging force of the lever is borne by the operation portion so that the urging force can be prevented from acting on the switch portion. 
     In addition, a torsion coil spring or a compression coil spring may be used as the spring which urges the lever of the contact opening mechanism in the fixed rotation direction. 
     In addition, in the invention, it is preferable that, when the operation portion and the switch portion has been coupled with each other, a push rod working with the push button in the operation portion and a movable frame supporting the movable contact forming the switching mechanism of the contact unit in the switch portion are brought into contact with each other in their opposed end portions so as to transfer an operating force therebetween. 
     Further, in the invention, when the switch portion leaves the operation portion in the case where the switching contact unit has normally open contacts, a displacement of the normally open contacts caused by the switching mechanism of the contact unit urged to close the normally open contacts by the contact opening mechanism is limited not to allow the movable contact to contact with the fixed contact. 
     In the invention, one or plural switching contact units may be provided in the switch portion, and the contact opening mechanism may be provided for each switching contact unit. 
     In addition, the switching contact unit provided in the switch portion may have plural sets of switching contacts and a common movable frame collectively holding movable contacts of the respective sets of switching contacts, and the contact opening mechanism may be provided in connection to the switching contact unit. 
     Furthermore, the push button switch according to the invention may be received in a box which is divided into a base and a cover. The push button switch can be configured as a box-mounted push button switch. In this case, the operation portion and the switch portion may be coupled by fixing the switch portion to the base, attaching the operation portion to the cover, and placing the cover on the base for integration. 
     In addition, when the switch portion in the push button switch according to the invention is received in the box, the switch portion is fitted into the base to be temporarily retained in a predetermined reception position and the base is covered with the cover to be coupled integrally so that the switch portion is held and fixed by the cover and the base from above and below. Specifically, the push button switch according to the invention can be configured in the following modes: 
     (1) Relay terminal fittings with terminal screws are provided. One end of each relay terminal fitting is connected to a corresponding leading-out terminal provided in a switching contact unit of the switch portion while the other end thereof is led out to an upper surface side of the base of the box. The base is covered with the cover of the box to be coupled integrally. In this state, the relay terminal fittings are put between terminal bases formed in the base and press ribs formed on an inner side of the cover, so that the switch portion is held and fixed; 
     (2) The terminal fittings are pressed into grooves of the terminal bases formed in the base of the box so as to temporarily fix the switch portion to the base; 
     (3) A switch portion attachment frame is provided in a bottom portion of the base of the box and the switch portion is fitted into the attachment frame to be snap-fit connected thereto. 
     According to the invention, in a push button switch in which an operation portion and a switch portion are removably coupled, a contact unit has normally closed contacts, and the normally closed contacts are automatically opened as soon as there occurs an accident in which the switch portion drops off the operation portion. It is therefore possible to prevent a danger that emergency stop operation may be canceled due to the accident in which the switch portion drops off the operation portion. Thus, the safety of the push button switch can be enhanced. 
     A contact opening mechanism used in the invention is designed independently of an operation mechanism of the operation portion. It is therefore possible to design and manufacture a spring system of the contact opening mechanism independently of a spring system of the operation portion. Thus, the push button switch can be designed and manufactured easily. 
     When the push button switch is in use received in a box divided into a base and a cover, the cover and the base of the box may be fastened so insufficiently as to cause an accident in which the cover may drop off the base. Even in such a case, the accident can be detected, and the normally closed contacts can be opened to make the push button switch safe. 
     Further, assume that a box-mounted push button switch to be connected to external wires is constructed by incorporating the push button switch into an operation box (optional component) which is divided into a base and a base. In this case, in accordance with the assembling structure of the invention, the operation portion having the aforementioned structure and mounted on a control panel etc. in use and the switch portion can be used as common components. Only if simple leading-out terminals are added to the switching contact unit of the switch portion, the switch portion can be fixed and supported in a predetermined position in the box without requiring a labor-consumed operation of screwing and fixing the switch portion to the base of the box, while an operation for connecting the push button switch to the external wires can be performed easily. Thus, serviceability to users and maintainability can be improved. 
     Other features, advantages, modifications, etc. of the invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to certain preferred embodiments thereof and the accompanying drawings, wherein: 
         FIG. 1A  is a perspective view showing the external appearance of a push button switch according to a first embodiment of the invention, and  FIG. 1B  is a plan view of the same; 
         FIG. 2A  is a sectional view taken on cutting line II-II in  FIG. 1B  and showing a standby state of the push button switch according to the first embodiment of the invention, and  FIG. 2B  is a sectional view likewise showing an operating state of the same; 
         FIG. 3A  is a sectional view taken on cutting line III-III in  FIG. 1B  and showing the standby state of the push button switch according to the first embodiment of the invention, and 
         FIG. 3B  is a sectional view likewise showing the operating state of the same; 
         FIG. 4A  is a sectional view taken on cutting line IV-IV in  FIG. 1B  and showing the standby state of the push button switch according to the first embodiment of the invention, and 
         FIG. 4B  is a sectional view likewise showing the operating state of the same; 
         FIG. 5A  is a sectional view taken on cutting line V-V in  FIG. 1B  and showing the standby state of the push button switch according to the first embodiment of the invention, and 
         FIG. 5B  is a sectional view likewise showing the operating state of the same; 
         FIG. 6  is a perspective view showing a state where an operation portion and a switch portion of the push button switch according to the first embodiment of the invention have been separated; 
         FIG. 7  is a sectional view taken on cutting line cutting II-II in  FIG. 1B  and showing the state where the operation portion and the switch portion of the push button switch according to the first embodiment of the invention have been separated; 
         FIG. 8  is a sectional view taken on cutting line III-III in  FIG. 1B  and showing the state where the operation portion and the switch portion of the push button switch according to the first embodiment of the invention have been separated; 
         FIG. 9  is a sectional view taken on cutting line IV-IV in  FIG. 1B  and showing the state where the operation portion and the switch portion of the push button switch according to the first embodiment of the invention have been separated; 
         FIG. 10  is a sectional view taken on cutting line V-V in  FIG. 1B  and showing the state where the operation portion and the switch portion of the push button switch according to the first embodiment of the invention have been separated; 
         FIG. 11  is a perspective view showing the external appearance of a switching contact unit having a contact opening mechanism for use in the invention; 
         FIG. 12  is an exploded perspective view showing the switching contact unit having the contact opening mechanism for use in the invention; 
       FIGS.  13 A 1 - 13 A 2  to  13 C 1 - 13 C 2  are sectional views taken on cutting lines a-a to c-c in  FIG. 11  respectively and showing an operating state of a switching contact unit with a normally open contact (“a” contact) configuration including the contact opening mechanism for use in the invention; 
       FIGS.  14 A 1 - 14 A 2  to  14 C 1 - 14 C 2  are sectional views taken on cutting lines a-a to c-c in  FIG. 11  respectively and showing an operating state of a switching contact unit with a normally closed contact (“b” contact) configuration including the contact opening mechanism for use in the invention; 
         FIG. 15  is a perspective view showing the external appearance of a switching contact unit having a contact opening mechanism for use in a second embodiment of the invention; 
         FIG. 16  is an exploded perspective view showing the switching contact unit having the contact opening mechanism for use in the second embodiment of the invention; 
       FIGS.  17 A 1 - 17 A 2  to  17 C 1 - 17 C 2  are sectional views taken on cutting lines a-a to c-c in  FIG. 15  respectively and showing an operating state of a switching contact unit with a normally closed contact (“b” contact) configuration including the contact opening mechanism for use in the second embodiment of the invention; 
         FIG. 18  is a perspective view showing a third embodiment of the invention; 
         FIG. 19  is a perspective view showing a fourth embodiment of the invention; 
         FIG. 20  is a partially cutaway perspective view of a switch portion for use in the fourth embodiment of the invention; 
         FIG. 21  is an exploded perspective view showing a main portion of the switch portion for use in the fourth embodiment of the invention; 
         FIG. 22  is an exploded perspective view showing a box-mounted push button switch according to a fifth embodiment of the invention; 
         FIG. 23A  is a perspective view showing a terminal base for use in the fifth embodiment of the invention, and  FIG. 23B  is a sectional view taken on cutting line b-b in  FIG. 23A ; 
         FIG. 24  is a side sectional view showing an assembling structure of a box-mounted push button switch according to a sixth embodiment of the invention; 
         FIGS. 25A to 25C  are exploded views showing the structure according to the sixth embodiment of the invention,  FIG. 25A  being a perspective view showing a state in which an operation portion of the push button switch is installed in a cover of a box,  FIG. 25B  being a perspective view showing an assembly of a switch portion, and  FIG. 25C  being a perspective view showing a temporarily assembled state in which the assembly of the switch portion shown in  FIG. 25B  is received in a base of the box; 
         FIGS. 26A and 26B  are detailed structure views showing the switch portion for use in the sixth embodiment of the invention,  FIG. 26A  being an exploded perspective view showing a leading-out terminal portion,  FIG. 26B  being a perspective view showing a relay terminal fitting shown in  FIG. 26A , and  FIG. 26C  being a sectional view showing a temporarily assembled state in which the switch portion is received in the base of the box; 
         FIGS. 27A to 27C  are exploded views showing a main part assembling structure of a box-mounted push button switch according to a seventh embodiment of the invention,  FIG. 27A  being a perspective view showing an assembly of a switch portion,  FIG. 27B  being a perspective view showing an attachment frame in which the assembly of the switch portion shown in  FIG. 27A  is retained and held in a bottom portion of a base of a box, and  FIG. 27C  being a perspective view showing the base of the box; 
         FIG. 28A  is a perspective view showing the configuration of a conventional push button switch, and  FIG. 28B  is a plan view of the same; 
         FIG. 29A  is a sectional view taken on cutting line XIX-XIX in  FIG. 28B  and showing a standby state of the conventional push button switch, and  FIG. 29B  is a sectional view likewise showing an operating state of the same; 
         FIG. 30A  is a sectional view taken on cutting line XX-XX in  FIG. 28B  and showing the standby state of the conventional push button switch, and  FIG. 30B  is a sectional view likewise showing the operating state of the same; 
         FIG. 31A  is a sectional view taken on cutting line XXI-XXI in  FIG. 28B  and showing the standby state of the conventional push button switch, and  FIG. 31B  is a sectional view likewise showing the operating state of the same; 
         FIG. 32A  is a sectional view taken on cutting line XXII-XXII in  FIG. 28B  and showing the standby state of the conventional push button switch, and  FIG. 32B  is a sectional view likewise showing the operating state of the same; 
         FIG. 33  is a perspective view showing a state where an operation portion and a switch portion of the conventional push button switch have been separated; 
         FIG. 34  is a sectional view taken on cutting line XIX-XIX in  FIG. 28B  and showing the state where the operation portion and the switch portion of the conventional push button switch have been separated; 
         FIG. 35  is a sectional view taken on cutting line XX-XX in  FIG. 28B  and showing the state where the operation portion and the switch portion of the conventional push button switch have been separated; 
         FIG. 36  is a sectional view taken on cutting line XXI-XXI in  FIG. 28B  and showing the state where the operation portion and the switch portion of the conventional push button switch have been separated; 
         FIG. 37  is a sectional view taken on cutting line XXII-XXII in  FIG. 28B  and showing the state where the operation portion and the switch portion of the conventional push button switch have been separated; 
         FIG. 38  is a longitudinally sectional view showing a standby state of another conventional push button switch; 
         FIG. 39  is a longitudinally sectional view showing an operating state of another conventional push button switch; 
         FIG. 40  is a longitudinally sectional view showing a switch portion which has dropped off an operation portion in another conventional push button switch; 
         FIG. 41  is a longitudinally sectional view showing a standby state of further another conventional push button switch; and 
         FIG. 42  is a longitudinally sectional view showing an operating state of further another conventional push button switch. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIGS. 1A-1B  to  5 A- 5 B,  FIGS. 6 to 12 , FIGS.  13 A 1 - 13 A 2  to  13 C 1 - 13 C 2  and FIGS.  14 A 1 - 14 A 2  to  14 C 1 - 14 C 2  show a first embodiment of the invention. 
       FIGS. 1A and 1B  are a perspective view and a plan view showing the external appearance of a push button switch according to the first embodiment of the invention.  FIGS. 2A-2B  to  5 A- 5 B are sectional views taken on lines II-II to V-V in  FIG. 1B  respectively and showing working states of the invention. Each  FIG. 2A-5A  shows a standby state where a push button has not been pushed in yet, while each  FIG. 2B-5B  shows an operating state where the push button has been pushed into a push-in position. 
       FIG. 6  is a perspective view showing a state where an operation portion and a switch portion of the push button switch according to the invention have been separated.  FIGS. 7-10  are sectional views of the push button switch shown in  FIG. 6 , cut on the same lines as the cutting lines shown in  FIG. 1B . 
       FIGS. 11 and 12 , FIGS.  13 A 1 - 13 A 2  to  13 C 1 - 13 C 2  and FIGS.  14 A 1 - 14 A 2  to  14 C 1 - 14 C 2  show a configuration example of a switching contact unit of the switch portion for use in the invention.  FIG. 11  is a perspective view showing the configuration of the external appearance of the contact unit.  FIG. 12  is an exploded perspective view showing the configuration of the contact unit. FIGS.  13 A 1 - 13 A 2  to  13 C 1 - 13 C 2  are sectional views taken on lines a-a to c-c in  FIG. 11  respectively and showing a working state of a switching contact unit with a normally open contact configuration. FIGS.  14 A 1 - 14 A 2  to  14 C 1 - 14 C 2  are sectional views taken on lines a-a to c-c in  FIG. 11  respectively and showing a working state of a switching contact unit with a normally closed contact configuration. 
     The principal configuration of the push button switch according to the embodiment of the invention shown in these drawings is the same as the configuration of the conventional push button switch shown in  FIGS. 24A-24B  to  28 A- 28 B and  FIGS. 29 to 33 . Constituent parts the same as those in the conventional are referred to by the same numerals correspondingly, and will be described briefly. Different constituent parts from those in the background art will be described in detail. 
     In the same manner as the conventional push button switch, the push button switch according to the invention is used in the state where an operation portion  1  and a switch portion  2  formed separately as shown in  FIG. 6  have been coupled and connected as shown in  FIGS. 1A and 1B . The operation portion  1  has a push button  12  which is vertically movably inserted into and supported on an operation portion case  11 . The switch portion  2  is designed so that a switching contact unit  24   a  having a normally open contact (“a” contact) configuration and a switching contact unit  24   b  having a normally closed contact (“b” contact) configuration are received in a switch portion case  21 . 
       FIGS. 2A-5A  show the standby state in which the push button  12  of the push button switch configured thus is in a standby position where the push button  12  has not been pushed in yet. In this state, movable frames  25   a  and  25   b  supporting movable contact makers  27   a  and  27   b  to which movable contacts  23   a  and  23   b  of the switching contact units  24   a  and  24   b  of the switch portion  2  have been fixedly attached are pushed up by return springs  26   a  and  26   b  respectively so that the leading ends of the movable frames  25   a  and  25   b  are linked with the push button  12  of the operation portion  1  and brought into contact with the lower end of the push rod  13  working with the push button  12 . In this state, as shown in  FIG. 4A , the switching contact unit  24   a  with the normally open contact (“a” contact) configuration has been turned off because the movable contact  23   a  has left the fixed contact  22   a . On the other hand, as shown in  FIG. 5A , the switching contact unit  24   b  with the normally closed contact (“b” contact) configuration has been turned on because the movable contact  23   b  has contacted with the fixed contact  22   b.    
     When the push button  12  is pushed into the push-in position here, the push rod  13  moves down in conjunction therewith and is held in the push-in position by a lock mechanism  18 . When the push rod  13  moves down, the movable frames  25   a  and  25   b  of the switching contact units  24   a  and  24   b  of the switch portion  2  are pushed down. Thus, the movable contact  23   a  contacts with the fixed contact  22   a  to turn on the switching contact unit  24   a , while the movable contact  23   b  leaves the fixed contact  22   b  to turn off the switching contact unit  24   b.    
     When the push button  12  is rotated at a predetermined angle in the state where the push button  12  has been pushed in, the push rod  13  is released from being locked by the lock mechanism  18 . Then, the push button  12  and the push rod  13  are pushed up by a return spring  14  consisting of a torsion coil spring, while the both are returned to the positions where they had been before they were rotated. Thus, the push button  12  and the push rod  13  are returned to their initial reset positions to stand by there. As a result, the open/close conditions of the contacts in the switching contact units  24   a  and  24   b  of the switch portion  2  are resumed to their initial conditions. 
     Such an operation for opening/closing the contacts in the switching contact units  24   a  and  24   b  of the switch portion  2  by the push-in operation and the return operation of the push button  12  of the operation portion  1  is the same as that in the aforementioned conventional push button switch. 
     As apparent from  FIGS. 2A-2B  to  FIG. 5A-5B  showing the sectional views of the push button switch, in the push button switch according to the invention, a contact opening mechanism  3  (shown in  FIG. 11 ) constituted by a lever  31  and an opening spring  32 , which is not shown here, is provided in each switching contact unit  24   a ,  24   b  of the switch portion  2 . The lever  31  and the opening spring  32  are formed rotatably, and the opening spring  32  urges the lever  31  in a predetermined direction. The contact opening mechanism  3  is a mechanism which is absent from the conventional push button switch. 
     The detailed configuration of a switching contact unit  24  provided with the contact opening mechanism  3  will be described with reference to  FIGS. 11 and 12 , FIGS.  13 A 1 - 13 A 2  to  13 C 1 - 13 C 2  and FIGS.  14 A 1 - 14 A 2  to  14 C 1 - 14 C 2 . The switching contact unit  24  can have one of a normally open contact (“a” contact) configuration and a normally closed contact (“b” contact) configuration if a switching contact mechanism to be received therein is selected. 
     The switching contact unit  24  is constituted by a unit frame  24   f , a switching contact mechanism  24   c  and the contact opening mechanism  3  as shown in  FIG. 12 . The unit frame  24   f  supports the unit as a whole. The switching contact mechanism  24   c  and the contact opening mechanism  3  are received in the unit frame  24   f.    
     The above-mentioned switching contact mechanism  24   c  has a movable frame  25  which is vertically movably supported on a case  24   d . The case  24   d  is provided with a leading-out terminal  24   t  which is led out from a fixed contact  22  (see  FIGS. 4A and 4B  and  FIGS. 5A and 5B ) received in the switching contact mechanism  24   c . A spring bearing piece  25   c  is provided to protrude from a side surface of the movable frame  25 . The spring bearing piece  25   c  bears a return spring force applied upward by the upper end of a return spring  26 . The lower end of the return spring  26  is supported by the case  24   d . Thus, the movable frame  25  is urged upward by the return spring  26 . The movable frame  25  supports a movable contact maker piece  27   a  or  27   b  including a movable contact  23   a  or  23   b , which is not shown here. In the case  24   d , a fixed contact  22   a  or  22   b  is disposed oppositely to the movable contact  23   a  or  23   b . The two contacts form a switching contact pair. The switching contact pair can be formed as a contact pair with a normally open contact (“a” contact) configuration as shown in FIG.  13 A 1  or a normally closed contact (“b” contact) configuration as shown in FIG.  14 A 1  if the kind of movable contact is selected. 
     The lever  31  of the contact opening mechanism  3  is formed into a U-shape by a pair of parallel rotary arms  31   a  and  31   a  and a connector arm  31   b  connecting the tips of the rotary arms  31   a  and  31   a  with each other. A rotary shaft  31   c  is formed in an intermediate portion of each rotary arm  31   a . A pressure piece  31   d  is provided in an intermediate portion of the connector arm  31   b  so as to protrude downward. The rotary shafts  31   c  protruding outward are inserted into grooves of bearing pieces  24   e  formed to protrude from the upper surface of the case  24   d  of the switching contact mechanism  24   c , respectively. Thus, the lever  31  configured thus is supported rotatably by the case  24   d . Another rotary shaft  31   g  on the inner side of one of the rotary arms and a support shaft  24   g  provided in the switching contact mechanism  24   c  are connected to each other through an opening spring  32  consisting of a torsion coil spring (torsion spring). The pressure piece  31   d  of the lever  31  is inserted into a groove  24   h  of the case  24   d  of the switching contact mechanism  24   c . The spring bearing piece  25   c  of the movable frame  25  is guided by the groove  24   h . Therefore, the pressure piece  31   d  can detachably contact with the spring bearing piece  25   c  in accordance with the rotation of the lever  31 . 
     In this manner, the contact opening mechanism  3  is built in the switching contact mechanism  24   c . Fitting protrusions  24   p  of the switching contact mechanism  24   c  are fitted into fitting grooves  24   q  of the unit frame  24   f  so that the switching contact mechanism  24   c  is mounted on the frame  24   f . Thus, the switching contact unit  24  as shown in  FIG. 11  is formed. 
     The switching contact unit  24  configured thus is built in the switch portion case  21  as the switching contact unit  24   a  with a normally open contact configuration or the switching contact unit  24   b  with a normally closed contact configuration. Thus, the switch portion  2  is arranged. When the switch portion  2  and the operation portion  1  are coupled and connected, the push button switch is completed. 
     The opening spring  32  of the contact opening mechanism  3  built in the switching contact unit  24  has one end fixed to the case  24   d  of the switching contact mechanism and the other end fixed to the rotary arm  31   a  of the lever  31 . Thus, a counterclockwise urging force is always applied to the lever  31  by the opening spring  32 . 
     However, the switching contact unit  24  is designed as follows. That is, as soon as the switch portion  2  is coupled with the operation portion  1  having the push button  12 , the lower end of the body portion  11   a  at the leading end of the case  11  of the operation portion  1  inserted into the switch portion  2  is brought into abutment against the base-side (opposite to the connector arm) end portion of the lever  31  so as to push down the base-side end portion of the lever  31  slightly against the urging force of the opening spring  32  as well shown in  FIGS. 3A and 3B . Thus, in the state where the switch portion  2  has been coupled with the operation portion  1 , the lever  31  is rotated clockwise with its rotary shaft  31   c  as a fulcrum. As a result, the pressure piece  31   d  on the leading end side (connector arm  31   b  side) of the lever  31  moves upward to leave the spring bearing piece  25   c  of the movable frame  25  of the switching contact mechanism. Thus, the urging force applied to the movable frame  25  by the opening spring  32  is canceled. 
     Accordingly, in the state where the switch portion  2  has been perfectly coupled with and connected to the operation portion  1 , the movable contact  23   a  leaves the fixed contact  22   a  to turn off the switching contact mechanism of the switching contact unit  24   a  with the normally open contact (“a” contact) configuration as shown in FIGS.  13 A 1 - 13 C 1  and  FIG. 4A . On the other hand, the movable contact  23   b  contacts with the fixed contact  22   b  to turn on the switching contact mechanism of the switching contact unit  24   b  with the normally closed contact (“b” contact) configuration as shown in FIGS.  14 A 1 - 14 C 1  and  FIG. 5A . 
     When the push button  12  is pushed in here to set an operating state, the movable frame  25   a ,  25   b  of the switching contact unit  24   a ,  24   b  is pushed down by the push rod  13  working with the push button  12 . Thus, the movable contact  23   a  contacts with the fixed contact  22   a  to turn on the switching contact unit  24   a  having the normally open contact (“a” contact) configuration as shown in  FIG. 4B . On the other hand, the movable contact  23   b  leaves the fixed contact  22   b  to turn off the switching contact unit  24   b  having the normally closed contact (“b” contact) configuration as shown in  FIG. 5B . 
     In the state where the switch portion  2  has been perfectly coupled with the operation portion  1 , in the lever  31  of the contact opening mechanism  3 , the urging force of the opening spring  32  is borne by the base side end portion of the lever  31  joined to the body portion  11   a  of the operation portion  1 . Thus, the urging force of the opening spring  32  is not transmitted to the movable frame  25  of the switching contact mechanism through the pressure piece  31   d  on the leading end side of the lever  31 . Thus, the switching operation by the push button  12  in this state can be performed smoothly without any influence of the spring force of the opening spring  32  of the contact opening mechanism  3 . 
     Next, description will be made in the case where the operation portion  1  and the switch portion  2  in the push button switch configured thus are released from coupling with each other for some reason so that the switch portion  2  drops off the operation portion  1  and the operation portion  1  and the switch portion  2  are imperfectly coupled with each other. 
     When the switch portion  2  is detached from the operation portion, the leading end of the body portion  11   a  of the operation portion case  11 , which has contacted with the base side end portion of the lever  31  and applied pressure thereto till then, leaves the base side end portion of the lever  31 . Thus, the lever  31  is released from restriction on its base side end portion so that the lever  31  becomes free. 
     FIGS.  13 A 2 - 13 C 2  and FIGS.  14 A 2 - 14 C 2  show the conditions of the switching contact units  24   a  and  24   b  with the normally open contact (“a” contact) configuration and the normally closed contact (“b” contact) configuration in this state. 
     As is apparent from these drawings, when the switch portion  2  is detached from the operation portion  1 , the leading end of the body portion  11   a  of the operation portion case  11  leaves the base side end portion of the lever  31  so as to make the lever  31  free. Thus, the lever  31  is rotated counterclockwise by the urging force of the opening spring  32 . With the rotation of the lever  31 , the pressure piece  31   d  of the leading end portion of the lever  31  moves downward to abut against the spring bearing piece  25   c  of the movable frame  25  of the switching contact mechanism  24   c  so as to push down the spring bearing piece  25   c . As a result, the movable frame  25  moves down against the return spring  26 . Together with the movable frame  25 , the movable contact maker  27   a ,  27   b  supporting the movable contact also move down. Thus, in the switching contact unit  24   b  with the normally closed contact (“b” contact) configuration, the movable contact  23   b  leaves the fixed contact  22   b  to form an OFF state (FIGS.  14 A 2  and  10 ). On the other hand, in the switching contact unit  24   a  with the normally open contact (“a” contact) configuration, the movable contact  23   a  moves down to approach the fixed contact  22   a . However, the push-down distance of the lever  31  is limited not to reach the position where the movable contact  23   a  contacts with the fixed contact  22   a . Thus, the OFF state is kept while the movable contact  23   a  cannot contact with the fixed contact  22   a  (FIGS.  13 A 2  and  9 ). 
     Assume that the push button switch formed by coupling the switch portion with the operation portion in the state in which the switching contact unit configured thus and particularly having the normally closed contact (“b” contact) configuration has been built in the switch portion is used as a push button switch S for emergency stop of an instrument. Then, assume that there occurs an abnormal (incomplete coupling) condition where the switch portion  2  drops off the operation portion  1  in the state where the push button has been operated to be pushed in to turn off the contacts to issue an instruction of emergency stop. Even in this case, the movable contact which should be returned to contact with the fixed contact can be forcedly separated from the fixed contact and turned off by the contact opening mechanism  3 . Thus, it is possible to prevent a risk that the emergency stop instruction may be canceled. 
     This embodiment has shown switching contact units each having a set of switching contacts. However, the invention is not limited to such a configuration. A switching contact unit having plural sets of switching contacts may be used as a switching contact unit in the switch portion. An embodiment thereof will be described later. 
     Next, an embodiment of application about the contact opening mechanism  3  provided in the switching contact unit  24  (see  FIGS. 11 and 12 ) according to the first embodiment will be described with reference to  FIGS. 15-17 . In the embodiment of application, the opening spring (torsion coil spring)  32  additionally provided in the lever  31  of the contact opening mechanism  3  is replaced by opening springs each consisting of a compression coil spring. 
       FIG. 15  is a perspective view showing the external appearance of the switching contact unit which has been assembled.  FIG. 16  is an exploded perspective view of  FIG. 15 . FIGS.  17 A 1 - 17 A 2  to  17 C 1 - 17 C 2  are views showing the operation of a normally closed contact (“b” contact) configuration mounted on the switching contact unit. Members corresponding to those in  FIGS. 11 and 12  and FIGS.  14 A 1 - 14 A 2  to  14 C 1 - 14 C 2  are referred to by the same numerals correspondingly. 
     That is, in this embodiment, an opening spring  33  consisting of a compression coil spring is put between an end portion  31   e  on the opposite side to the connector arm  31   b  with respect to the rotary shaft  31   c  in each rotary arm  31   a  of the lever  31  and the case  24   d  of the switching contact mechanism  24   c . The opening spring  33  is inserted into a recess portion  24   i  (see  FIG. 16 ) formed in the case  24   d  and retained in a predetermined position. 
     Due to the aforementioned configuration, a counterclockwise urging force is always applied from the opening spring (compression coil spring)  33  to the lever  31  with the rotary shaft  31   c  as a fulcrum. In the state where the switch portion  2  has been coupled with the operation portion  1 , the lower end of the body portion  11   a  (see  FIGS. 3A and 3B ) on the leading end side of the case  11  of the operation portion  1  inserted into the switch portion  2  is brought into abutment onto the end portion  31   e  of the lever  31  so as to push down the end portion  31   e  slightly against the urging force of the opening spring  33  in the same manner as in the first embodiment. Thus, in the state where the switch portion  2  has been coupled with the operation portion  1 , the lever  31  is rotated clockwise with its rotary shaft  31   c  as a fulcrum. As a result, the pressure piece  31   d  provided on the connector arm  31   b  of the lever  31  moves upward to leave the spring bearing piece  25   c  of the movable frame  25  built in the switching contact mechanism  24   c . Thus, the urging force applied to the movable frame  25  by the opening spring  33  is canceled. 
     Accordingly, in the state where the switch portion  2  has been coupled with the operation portion  1 , the movable contact  23   b  contacts with the fixed contact  22   b  to form an ON state in the switching contact mechanism  24   b  having the normally closed contact (“b” contact) configuration, as shown in FIGS.  17 A 1 - 17 C 1 . 
     When the push button  12  of the operation portion  1  is pushed in here to set an operating state, the movable frame  25  of the switching contact unit is pushed down by the push rod  13  working with the push button  12 . Thus, the movable contact  23   b  leaves the fixed contact  22   b  to form an OFF state in the switching contact unit  24   b  having the normally closed contact (“b” contact) configuration as shown in FIGS.  17 A 2 - 17 C 2 . 
     That is, in the state where the switch portion  2  has been perfectly coupled with the operation portion  1 , in the lever  31  of the contact opening mechanism  3 , the urging force of the opening spring  33  is borne by the end portion of the lever  31  joined to the body portion  11   a  (see  FIGS. 3A and 3B ) of the operation portion  1  so as to rotate the lever  31  counterclockwise. Thus, the urging force of the opening spring (compression coil spring)  33  is not transmitted to the movable frame  25  of the switching contact mechanism through the pressure piece  31   d  of the lever  31 . Thus, the switching operation by the push button  12  in this state can be performed smoothly without any influence of the spring force of the opening spring  33  of the contact opening mechanism  3  in the same manner as in the first embodiment. 
     On the contrary, when the operation portion  1  and the switch portion  2  are released from coupling with each other for some reason so that the switch portion  2  drops off the operation portion  1 , the leading end of the body portion  11   a  of the operation portion case  11 , which has contacted with the base side end portion  31   e  of the lever  31  and pushed in the base side end portion  31   e  till then, leaves the base side end portion  31   e . Thus, the lever  31  is released from restriction so that the lever  31  becomes free. As a result, the movable contact  23   b  in the normally closed contact (“b” contact) configuration is forced to leave the fixed contact  22   b  as shown in FIGS.  17 A 2 - 17 C 2 , so as to form an OFF state. Thus, the same safety function as in the first embodiment can be exerted. 
     In addition, the compression coil spring as an opening spring of the lever  31  is put between the rear end portion  31   e  of the lever  31  and the case  24   d  of the switching contact mechanism, so that the opening spring can be installed more easily than in the configuration of the first embodiment where a torsion coil spring as an opening spring is additionally provided in the rotary shaft  31   c  of the lever  31 . Even a mechanical assembling system using a robot can be therefore applied easily to the installation of the opening spring. 
     Next, a third embodiment of the invention shown in  FIG. 18  will be described.  FIG. 18  is a perspective view showing the external appearance of this embodiment. A switch portion  2  coupled with an operation portion  1  in this embodiment has four switching contact units  24 - 1  to  24 - 4 . The switching contact unit  24   a  with the normally open contact (“a” contact) configuration or the switching contact unit  24   b  with the normally closed contact (“b” contact) configuration shown in the first embodiment is used selectively as each switching contact unit. The switching contact units are coupled and connected in parallel and in series to each other and supported on a common switch portion case  21 . In the switching contact units coupled in two stages and in series, movable frames supporting internal movable contacts and working with a push rod inside the operation portion  1  are connected to be able to work together. Thus, the push button switch can be allowed to operate a large number of switching contact circuits, and can be used, for example, when a plurality of emergency stop instructions have to be issued. The switching contact units  24  may be coupled in two or more plural stages. 
     Next, a fourth embodiment of the invention in which the assembling structure of the switch portion has been improved to make the push button switch small and compact will be described with reference to  FIGS. 19-21 . 
     The third embodiment showed a push button switch in which the plurality of switching contact units  24 - 1  to  24 - 4  having independent structures are provided in combination in the switch portion  2 , the movable frame  25  of the contact switching mechanism and the contact opening mechanism  3  are provided in each switching contact unit and linked with the operation portion  1 . In the fourth embodiment, however, plural sets of switching contacts (contact pairs with a normally open contact (“a” contact) configuration and/or contact pairs with a normally closed contact (“b” contact) configuration) are built in a switching contact unit with a single structure. At the same time, all the movable contacts of the respective switching contact sets are held collectively by a common movable frame, and a contact opening mechanism is combined with the common movable frame and linked with the operation portion. 
     That is, in this embodiment, a total of six sets of switching contacts, three of which are arranged in the front rank and the other three of which are arranged in the rear rank, are built in a box-like switch portion case  21 . In the illustrated structure, three normally closed contact pairs (“b” contacts) are disposed laterally in the front rank of the switch portion case  21 , and three normally open contact pairs (“a” contacts) are disposed likewise in the rear rank. Here, each set of switching contacts consists of a combination of two fixed contact makers  22   c  and a movable contact maker  27   a . That is, for each set of switching contacts, adjacent two of fixed contact makers  22   c  with leading-out terminals  24   t  arranged laterally and fitted to and retained in the switch portion case  21  are paired, and a movable contact maker  27   a  of a bridging type is disposed perpendicularly to the adjacent fixed contact makers  22   c . In addition, the movable contact makers  27  of the respective sets are combined with contact springs and fitted into and retained in contact maker holders  25 - 1  which are formed to protrude in front and at the rear of a common movable frame  25 . 
     In addition, the common movable frame  25  has a cylindrical convex portion which protrudes upward from its central portion. The cylindrical convex portion is disposed to face a fitting hole  21   a  opened in the upper surface of the switch portion case  21 . Further, on the opposite, left and right sides of the movable frame  25 , two seesaw levers  31  serving as contact opening mechanisms are provided in combination with opening springs  33  which are compression coil springs. 
     In the state where the switch portion  2  has been coupled with the operation portion  1  (see  FIG. 19 ), the body portion  11   a  of the operation portion  1  abuts against end portions  31   e  of the levers  31  from above so as to push in the end portions of the two levers  31  concurrently against the opening springs  33 . As a result, the levers  31  rotate with their rotary shafts  31   c  as fulcrums. Pressure pieces  31   d  of the levers  31  leave spring bearing pieces  25   c  protruding from the opposite, left and right ends of the movable frame  25  so as to cancel the spring urging forces of the opening springs  33  acting on the movable frame  25 . As a result, the movable frame  25  and the movable contact makers  22   c  of the respective sets retained in the movable frame  25  are pushed up by spring urging forces of return springs  26  applied thereto. Thus, the normally open switching contacts (“a” contacts) are turned on, while the normally closed switching contacts (“b” contacts) are turned off. When the push button  12  of the operation portion  1  is pushed in during this state, the push rod linked with the push button  12  pushes in the movable frame  25  directly to change over the respective sets of switching contacts. 
     On the other hand, when the operation portion  1  and the switch portion  2  are released from coupling with each other so that the switch portion  2  drops off the operation portion  1 , the spring urging forces of the opening springs  33  are applied to the levers  31  so that the levers  31  swing and return with the result that the pressure pieces  31   d  at the leading ends of the levers  31  push in the spring bearing pieces  25   c  of the movable frame. As a result, the movable frame  25  moves down against the return springs  26  and turns off all the sets of switching contacts. This operation and function are the same as that described in the first and second embodiments. 
     That is, when the push button  12  has not been pushed in the state where the switch portion  2  has been coupled with the operation portion  1 , the normally closed contacts (“b” contacts) are ON, and the normally open contacts (“a” contacts) are OFF. When the push button  12  is pushed in, the normally closed contacts are turned off, and the normally open contacts are turned on. When the operation portion  1  and the switch portion  2  are accidentally released from coupling with each other so that the switch portion drops off the operation portion, both the normally open contacts and the normally closed contacts are turned off as described in FIGS.  13 A 1 - 13 A 2  to  13 C 1 - 13 C 2  and FIGS.  14 A 1 - 14 A 2  to  14 C 1 - 14 C 2 . Thus, the coupling state and the dropping-off state between the operation portion  1  and the switch portion  2  can be identified and detected from on/off signals of the plural sets of switching contacts (normally open contacts and normally closed contacts) mounted on the switch portion  2 . 
     The switch portion according to this embodiment is designed so that plural sets of switching contacts and a movable frame shared by the respective sets of switching contacts are mounted on one switching contact unit. Accordingly, the switch portion can be made small and compact in comparison with that in the third embodiment where a plurality of independent switching contact units are combined and coupled in the switch portion. 
     Although three sets of normally closed contacts and three sets of normally open contacts are arrayed in the front and rear ranks respectively in the switch portion case  21  in the illustrated embodiment, the number of installed sets of switching contacts and the combination of normally open and normally closed contacts are not limited thereto but may be selected desirably. 
     In each push button switch according to the first to fourth embodiments, the operation portion of the push button is attached to a panel such as a control panel and the switch portion is connected to the back of the operation portion so that the push button switch in use is connected to wires (lead wires) of the panel. Besides the push button switch, there is also known a box-mounted push button switch which is configured as follows. That is, an operation portion and a switch portion of a push button switch are incorporated into an independent operation box. This operation box is attached to a panel front surface etc. of a control panel. Then, electric wires connected to the switch portion are led out from the operation box, and connected externally. 
     This box-mounted push button switch is configured in the following manner. The operation box (this operation box is provided as an optional component to a user) is consisted of a resin molding which has a split structure of a base and a cover. The operation portion is attached to the cover of the box, and an assembly of the switch portion is incorporated into the base. Then, external wires connected to terminals of the switch portion are led sideways from the base. 
     Next,  FIG. 22  and  FIGS. 23A and 23B  show a fifth embodiment of the invention applied to the box-mounted push button switch. In the fifth embodiment, the box-mounted push button switch is formed as follows. That is, an operation portion  1  and a switch portion  2  of a push button switch are received in an operation box  4  made of a resin molding. Here, the operation box  4  is divided into a cover  41  and a base  42  as shown in  FIG. 22 . The cover  41  and the base  42  are put on top of each other, and fastening screws  41   a  inserted into the cover  41  are screwed down into threaded holes  42   a  of the base  42  so as to couple the cover  41  and the base  42  integrally. 
     The operation portion  1  of the push button switch is provided with the push button  12  and attached to the cover  41 . The switch portion  2  is attached to the base  42 . Since the switch portion  2  according to the first embodiment cannot be attached as it is, a terminal base  43  is used in the embodiment. 
     The terminal base  43  is fixed to the base  42  by a mounting screw  43   a  which is screwed down into a threaded hole  42   b . As shown in detail in  FIGS. 23A and 23B , screw connection terminals  43   d  are provided in four corners of the terminal base  43 , and a cavity to mount the switching contact unit  24  therein is provided in the middle portion of the terminal base  43 . Each connection terminal portion is provided with a contact piece  43   e  consisting of an L-shaped elastic conductive plate which is electrically connected to corresponding one of the screw connection terminals  43   d , as shown in  FIG. 23B . When the switching contact unit  24  is mounted on the terminal base  43  as shown in  FIG. 22 , the contact pieces  43   e  contact with the leading-out terminals  24   t  (see  FIG. 11 ) of the switching contact unit  24  so as to conductively connect the leading-out terminals  24   t  of the switching contact unit  24  to the screw connection terminals  43   d . Incidentally, in the state in which the cover  41  has been removed, the electric wires connected externally are led into the inside of the base through a lead hole  42   c  opened in a side wall of the base  42 , and connected to the screw connection terminals  43   d.    
     The switching contact unit  24  used in the switch portion  2  shown in the first embodiment can be used directly as the switching contact unit  24  here. Each engagement hook  43   f  provided in a side surface of the terminal base  43  is engaged with a fitting recess  24   a  provided in a side surface of the switching contact unit  24 . Thus, the switching contact unit  24  mounted on the terminal bases  43  is fixed to the terminal bases  43 . In the configuration of this embodiment, two switching contact units  24  can be mounted. However, the embodiment may be arranged so that two or more switching contact units  24  are mounted. Moreover, a switching contact unit having plural sets of switching contacts in one switching contact unit may be used as described in the fourth embodiment. 
     The switch portion  2  formed by mounting a required number of switching contact units  24  on terminal bases  43  is attached and fixed into the base  42  of the operation box  4 . The base  42  is covered with the cover  41  to which the operation portion  1  is attached. The cover  41  is fastened and coupled with the base  42  by the fastening screws  41   a . Thus, the operation box  4  is completed. At the same time that the base  42  is covered with and coupled with the cover  41 , the operation portion  1  and the switch portion  2  of the push button switch can be also coupled. 
     For this reason, when the cover  41  and the base  42  of the operation box  4  are fastened insufficiently or when the cover  41  is put off carelessly because of maintenance or the like during the operation of emergency stop, coupling between the operation portion  1  and the switch portion  2  of the push button switch becomes imperfect. Assume that coupling between the operation portion  1  and the switch portion  2  of the push button switch becomes imperfect in this manner. Then, because the contact opening mechanism  3  is provided in the switching contact unit  24  in the switch portion  2  in the same manner as in the first embodiment, the contact opening mechanism  3  can detect the incomplete coupling between the operation portion  1  and the switch portion  2  and forcedly open the normally closed contacts of the switching contact unit having a normally closed contact (“b” contact) configuration. Accordingly, when the push button switch received in the operation box is used as a switch for emergency stop, there is no fear that an emergency stop instruction is canceled carelessly even if there occurs an accident in which the switch portion drops off the operation portion. Thus, safety can be secured. 
     Next,  FIG. 24 ,  FIGS. 25A to 25C , and  FIGS. 26A to 26C  show a sixth embodiment of the invention in which the assembling structure of the box-mounted push button switch according to the fifth embodiment is further improved. 
     That is, in the configuration of the fifth embodiment (see  FIG. 22  and  FIGS. 23A and 23B ), the terminal base  43  as an independent component is placed in the base  42  of the operation box  4  and the terminal base  43  is screwed down to the bottom portion of the base  42  by the mounting screw  43   a . In addition, the screw connection terminals  43   d  used for connection to external wires and the contact pieces  43   e  electrically connected to the leading-out terminals  24   t  of the switching contact units  24  are provided in the terminal base  43 . Then, the assembly of the switch portion  2  is fitted and fixed into the cavity in the middle portion of the terminal base  43 . For this reason, in the assembling structure according to the fifth embodiment, the structure of the terminal base  43  used for incorporating the switch portion  2  into the operation box  4  is so complicated that there remains a problem that the number of components and the assembling man-hours are increased. 
     Accordingly, the sixth embodiment is to improve the problem. In this embodiment, the terminal base  43  attached as a separate component (see  FIG. 22 ) to the base  42  according to the fifth embodiment is not used. The assembly of the switch portion  2  is incorporated into the operation box  4 . The external wires led into the operation box  4  are connected to the terminals of the switch portion  2 . Incidentally, in the embodiment, the switch portion  2  is formed by combining two switching contact units  24  in the same manner as in the first embodiment. 
     That is, in the sixth embodiment, a recess cavity into which the assembly of the switch portion  2  is fitted in a drop-in manner is formed in the inside of the base  42  of the operation box  4 . Terminal base portions  42   d  for holding relay terminal fittings which will be described later are formed integrally on left and right sides of the base  42  with the cavity being interposed therebetween. In addition, Z-shaped relay terminal fittings  44  (see  FIG. 26 ) are attached to the switching contact units  24  constructing the assembly of the switch portion  2 . One end of each relay terminal fitting  44  is connected to a corresponding leading-out terminal  24   t  disposed on a lower surface side of a corresponding switching contact unit  24 , while the other end thereof is led to an upper surface side of the base  42 . Terminal screws  45  used for connection to external wires are provided at the tips of the relay terminal fittings  44 . Incidentally, each relay terminal fitting  44  is made of a copper plate which is punched out by press working and bent into L-shapes in its opposite ends respectively so as to be formed into a Z-shape. The relay terminal fitting  44  includes a threaded hole  44   a  into which the terminal screw  45  is screwed down, and a screw insertion hole  44   b  into which the leading-out terminal  24   t  (terminal screw) of the switching contact unit  24  is inserted. 
     When the assembly of the switch portion  2  is dropped in from above and fitted into the center of the base  42  of the operation box  4  in the condition that the relay terminal fittings  44  are attached to the switching contact units  24  as shown in  FIGS. 26A to 26C , front end portions of the relay terminal fittings  44  are held on the terminal bases  42   d  formed in the inside of the base  42  so that the switch portion  2  is temporarily retained in a predetermined position in the base (see  FIG. 26C ). On the other hand, the operation portion  1  provided with the push button  12  is attached to the cover  41  of the operation box  4  in the same manner as in the fifth embodiment. Moreover, in the embodiment, wall-shaped press ribs  41   b  are molded integrally with an inner side of the cover  41  so as to be opposed to the terminal bases  42   d  of the base  42 . 
     When the base  42  of the operation box  4  is covered with the cover  41  in the temporarily assembled state and the fastening screws  41   a  inserted into the cover  41  are screwed down into the threaded holes  42   a  of the base  42  so as to couple the cover  41  and the base  42  integrally, the top portions of the relay terminal fittings  44  are interposed between the press ribs  41   b  of the cover  41  and the terminal bases  42   d  of the base  42  from above and below so as to be held and fixed in these positions. At the same time, the operation portion  1  and the switch portion  2  are set to be coupled. Thus, the box-mounted push button switch is completed. In addition, to externally connect electric wires to the push button switch, the electric wires are led into the inside of the base through the lead hole  42   c  opened in the side wall of the base  42 , and connected to the terminal screws  45  in the state in which the cover  41  has been removed in the same manner as in the fifth embodiment. In this case, the terminal screws  45  are disposed on the upper surface side of the base  42  so that the operation of wiring can be performed easily. 
     According to the configuration of the sixth embodiment, the terminal base  43  (see  FIG. 22 ) as an independent component does not have to be additionally installed on the base  42  side of the operation box  4  as described in the fifth embodiment. Nevertheless the operation portion  1  and the switching contact units  24  of the switch portion  2  can be used as common components and incorporated into the operation box  4  in a screwless manner. On this occasion, the operation portion  1  and the switching contact units  24  have the same structures as those in the push button switch according to the first embodiment, which is attached to the control panel in use. Thus, the number of components and the assembling man-hours can be reduced. For example, assume that a user wants to combine an additionally purchased operation box (optional component) with the existing operation portion and the existing switch portion to thereby construct a box-mounted push button switch. Even in such a case, the box-mounted push button switch can be constructed with a simple operation. 
     In this embodiment, the following structure is used for the purpose of enhancing convenience of an assembling operation for incorporating the switch portion  2  into the base  42  of the operation box  4 . That is, sawtooth-like engagement protrusions  44   c  (see  FIG. 26B ) are formed on left and right edges in an upstand portion of each relay terminal fitting  44  and vertical grooves into which the engagement protrusions  44   c  are pressed are formed in the terminal base  42   d  of the base  42 . Thus, when the assembly of the switch portion  2  is incorporated into the base  42  of the operation box  4 , the engagement protrusions  44   c  of the relay terminal fittings  44  are pressed into the grooves of the terminal bases  42   d . Thus, the switch portion  2  can be retained and held in the temporary assembling position easily. 
     In addition, in the push button switch according to the fifth embodiment, two switching contact units  24  are used to form the switch portion  2 . However, three or more switching contact units  24  may be used in combination to form one switch portion  2 . In addition, as described in the fourth embodiment, a switching contact unit provided with plural sets of switching contacts may be used as one switching contact unit. Moreover, the contact opening mechanism  3  described in the first embodiment is installed in each switching contact unit  24  of the switch portion  2 . When the box-mounted push button switch is used as an emergency stop switch, even if a situation occurs that the cover  42  of the operation box  4  is loosened or removed unexpectedly to thereby release the operation portion  1  and the switch portion  2  from coupling with each other, there is no fear that an emergency stop instruction is cancelled carelessly. Thus, high safety can be ensured. 
     Incidentally, the contact opening mechanism  3  is internally incorporated into the switch portion  2  in the first embodiment, however, the box-mounted push button switch in which the switch portion  2  is received in the operation box  4  may be configured so that the contact opening mechanism is provided outside the switch portion  2  by use of an internal space of the operation box  4 . 
       FIGS. 27A to 27C  show a seventh embodiment of the invention in which the structure according to the fifth embodiment is partially changed. 
     According to the sixth embodiment, the engagement protrusions  44   c  are formed in the relay terminal fittings  44  provided in the switching contact units  24  of the switch portion  2 , and when the switch portion  2  is incorporated into the base  42  of the operation box  4 , the engagement protrusions  44   c  are pressed into the grooves of the terminal bases  42   d  of the base so as to retain and hold the switching contact units  24  in the temporary assembling positions. On the other hand, in the seventh embodiment, a switch portion attachment frame (resin molding)  46  having a simple structure is placed in the bottom portion of the base  42 , and the switching contact units  24  fitted into the attachment frame  46  are snap-fit connected to the attachment frame  46  so as to be retained and fixed to the assembling positions. 
     That is, retaining fitting cavities  24   v  are provided in left and right side surfaces of an outer frame in each switching contact unit  24  of the switch portion  2  as shown in the first embodiment (see  FIGS. 1A and 1B ) and the fifth embodiment (see  FIG. 22 ). Accordingly, in the seventh embodiment, screw bases  46   a  are formed in the attachment frame  46  as shown in  FIG. 27B . The attachment frame  46  is fixed to the center of the bottom portion of the base  42  through attachment screws  46   b  inserted into the screw bases  46   a . In addition, the terminal bases  42   d  for supporting the front end portions of the relay terminal fittings  44  provided in the switching contact units  24  are formed integrally in the inside of the base  42  with the attachment frame  46  interposed therebetween, in the same manner as in the fifth embodiment. The relay terminal fittings  44  are fitted into vertical grooves  42   d - 1 . Engagement protrusions  46   c  corresponding to fitting cavities  24   v  (see  FIG. 27A ) provided in the switching contact units  24  are formed in the left and right edges of the attachment frame  46 . 
     When the assembly of the switch portion  2  is pressed into the attachment frame  46  from above in the aforementioned configuration, the retaining fitting cavities  24   v  provided in the switching contact units  24  are fitted into the engagement protrusions  46   c  of the attachment frame  46  respectively to thereby snap-fit connect the switching contact units  24  and the attachment frame  46  to each other. In this manner, the switch portion  2  is retained and fixed to the predetermined position. In addition, the attachment frame  46  is simple in structure and can be produced inexpensively in comparison with the terminal base  43  according to the fifth embodiment. 
     The invention has been described with reference to certain preferred embodiments thereof. It will be understood, however, that modifications and variations are possible within the scope of the appended claims.