Coaxial relay

A coaxial relay is build up from a contact block and an electromagnet block. The contact block carries a plurality of coaxial connectors each composed of a core conductor and a shield conductor surrounding the core conductor. The core conductors extend into a shield chamber to define thereat respective coaxial contacts. At least one movable blade is disposed within the shield chamber for closing and opening the two adjacent coaxial contacts. The movable blade is provided with a dielectric actuator which projects on the top of the contact block and is engaged with a return spring secured to the contact block for urging the movable blade in a direction of opening the coaxial contacts. The electromagnet block carries at least one electromagnet and an armature which is engageable with the actuator when the electromagnet block is assembled to the contact block. The armature moves about a pivot axis from a first position of opening the coaxial contacts to a second position of closing the same. The electromagnet includes a frame of a non-magnetic material which holds the electromagnet and has its lower end secured to the contact block. The frame has a retainer mechanism for pivotally supporting the armature. Thus, a magnetic gap distance between the electromagnet and the armature can be fixed and does not vary a the time of assembling the electromagnet block to the contact block, so that the relay can have a reliable armature movement in response to the excitation of the electromagnet.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a coaxial relay for switching high
 frequency signals, and more particular to such relay having a pivotable
 armature moving between two positions of switching the high frequency
 signals.
 2. Description of the Prior Art
 U.S. Pat. No. 4,496,919 discloses a coaxial relay with a pivotable armature
 for switching high frequency signals. The relay includes an electromagnet
 block and a contact block with a plurality of coaxial connectors each
 having a core conductor and a shield conductor. The contact block has a
 shield chamber into which the core conductors extend to define fixed
 contacts therein. Also mounted within the shield chamber is a movable
 blade for closing and opening the fixed contacts. The movable blade
 carries a dielectric actuator which projects on the contact block to be
 enageable with a pivotable armature and is driven thereby for opening and
 closing the fixed contacts. The armature is pivotally supported to a
 support plate fixed to the contact block for movement about a pivot axis
 between two positions of closing and opening the fixed contacts. The
 electromagnet block carries an electromagnet with a coil wound around a
 core and pole ends. The electromagnet block is assembled to the contact
 block by means of screws, while positioning the core and the pole ends in
 an opposed relation to the corresponding portions to the armature. In
 order to assure an accurate armature movement and the therefore the
 contacting operation in response to the eneraization of the electromagnet,
 it is required to give precise positioning of the core and the pole ends
 relative to the armature. However, since the armature is held on the
 contact block, while the core and the pole ends are held on the
 electromagnet block, the precise positioning is only made by adjusting the
 screws and therefore only at the time of assembling the electromagnet
 block to the contact block. That is, magnetic gap distances between the
 elements of the electromagnet and the armature is only determined at the
 time of screwing the electromagnet block to the contact block, so that the
 precise positioning of the electromagnet relative to the armature can not
 be always assured. This is inconvenient for manufacturing a number of the
 relay with reliability of the armature movement, and consequently reduces
 manufacturing efficiency and reliability.
 SUMMARY OF THE INVENTION
 In view of the above insufficiency, the present invention has been achieved
 to present a coaxial relay which is capable of assuring reliable
 operational characteristics and is easy to manufacture. The coaxial relay
 in accordance with the present invention is composed of two assemblies or
 blocks, namely, a contact block and an electromagnet block. The contact
 block is made of an electrically conductive metal to have a top surface
 and a shield chamber. The contact block carries a plurality of coaxial
 connectors each composed of a core conductor and a shield conductor
 surrounding the core conductor. The core conductors extend into the shield
 chamber to define thereat respective coaxial contacts. Also included in
 the contact block is at least one movable blade which is disposed within
 the shield chamber for closing and opening the two adjacent coaxial
 contacts. The movable blade is provided with a dielectric actuator which
 projects on the top surface of the contact block and is engaged with a
 return spring secured to the contact block for urging the movable blade in
 a direction of opening the coaxial contacts.
 The electromagnet block is separately formed from the contact block to be
 assembled thereto. The electromagnet block carries at least one
 electromagnet and an armature which is enageable with the actuator when
 the electromagnet block is assembled to the contact block. The
 electromagnet is composed of a coil wound around a core. The armature is
 responsive to an excitation of the coil to move about a pivot axis from a
 first position of opening the coaxial contacts to a second position of
 closing the same. The electromagnet includes a frame of a non-magnetic
 material which holds the electromagnet and has its one end secured to the
 contact block. The characterizing feature of the present invention resides
 in that the frame has a retainer mechanism for pivotally supporting the
 armature. With the provision of the retainer mechanism on the side of the
 electromagnet block, a magnetic gap distance between the electromagnet,
 i.e., the core and the armature can be fixed and does not vary at the time
 of assembling the electromagnet block to the contact block.
 Accordingly, the relay can have a reliable armature movement in response to
 the excitation of the electromagnet.
 Preferably, the frame is configured to have a top wall and a pair of
 opposed side walls extending from opposite sides of the tope wall. Each of
 the side walls is formed at its lower end with a pivot projection and with
 a stem. The armature is an elongated plate provided at its longitudinal
 center with a pair of transversely spaced brackets having respective
 bearing holes for loosely receiving therein the stems. The pivot
 projections, the stems, the brackets with the bearing holes are
 cooperative with a permanent magnet to define the retainer mechanism for
 pivotally supporting the armature. The permanent magnet is disposed
 between the side walls adjacent the lower ends thereof for attracting and
 holding the armature into a position where the stems loosely fit into the
 bearing holes and the pivot projections abut respectively against the
 brackets to define the pivot axis of the armature. Thus, the armature can
 be easily supported to the frame in an exact positional relation to the
 electromagnet for reliable armature movement without using a pivot pin and
 the associated fixture for the pivot pin.
 In a preferred embodiment, the contact block includes three coaxial
 connectors and first and second movable blades. The three coaxial
 connectors are arranged to define, within the shield chamber, a common
 fixed contact by the core conductor of one of the coaxial connectors and
 first and second fixed contacts by the conductors of the other coaxial
 connectors, respectively. The first movable blade is disposed within the
 shield chamber to close and open the first fixed contact to and from the
 common fixed contact, while the second movable blade is disposed within
 the shield chamber to close and open the second fixed contact to and from
 the common fixed contact. The armature is movable about the pivot axis
 between the first position where the first and second movable blades close
 and open the first and second fixed contacts respectively from and to the
 common fixed contact, and the second position where the first and second
 movable blades open and close the first and second fixed contacts
 respectively from and to common fixed contact.
 Preferably, the armature carries on its lower surface a spring plate having
 a length extending in parallel with the length of the armature. The spring
 plate includes an anchor section formed at the longitudinal center of the
 spring plate and a pair of first and second spring legs extending from the
 anchor section in opposite directions. The anchor sections are secured to
 the longitudinal center of the armature and are formed integral with the
 brackets extending transversely beyond width ends of the armature for
 pivotal connection with the lower ends of the frame. The first and second
 spring legs extend from the anchor section in a spaced relation with the
 armature to be engageable respectively with the actuators of the first and
 second movable blades for providing a contact pressure. Thus, the contact
 spring alone can combine the functions of supporting the armature to the
 frame and of giving the contact pressure to the first and second movable
 blades.
 The top surface of the contact block is rectangular in shape and is formed
 at its four corners respectively with recesses. The frame is configured to
 have the top wall and a pair of end walls extending from opposite ends of
 the top wall. The top wall is secured to the core, while the side walls is
 formed at its one end with legs which fit into the recesses of the contact
 block and are bonded thereto. Thus, the electromagnet block can be readily
 assembled to the contact block, while the core is held by the frame in an
 exact position relative to the armature supported at the lower end of the
 frame.
 Preferably, the contact block is composed of a base carrying the coaxial
 connectors and a cover plate secured to the base. The cover plate defines
 the top surface of the contact block and is cooperative with the base to
 define therebetween the shield chamber. The cover plate is formed with a
 hole through which the actuator of the movable blade extends for
 engagement with the armature.
 In another embodiment of the present invention, the electromagnet block
 includes a generally U-shaped members having a horizontal core and a pair
 of pole legs extending from the opposite ends of the horizontal core. The
 electromagnet block further includes at least one coil wound around the
 horizontal core at portions adjacent the pole legs, and a permanent magnet
 disposed between pole legs. The permanent magnet is magnetized to have
 opposite poles at its upper and lower ends and is arranged to have its
 upper end connected to the center of the horizontal core and to have its
 lower end opposed to the center of the armature. The pole legs define at
 the lower ends thereof pole ends which are opposed respectively to the
 longitudinal ends of said armature. This configuration in which the coils
 are wound around the horizontal cores is advantageous to reduce a height
 of the electromagnet and therefore the relay.
 The actuator is preferably made of a dielectric plastic material and is
 molded integrally at its lower end with the movable blade. With this
 insertion molding, the actuator is accurately positioned relative the
 movable blade so that, when the actuator is stably held by the contact
 block, the movable blade can be exactly positioned within the shield
 chamber to give a uniform high frequency characteristic to the contact
 block, i.e., a consistent impedance to a signal path of the contact block
 for reliable switching operation of the high frequency signals.
 Also, the present invention presents the return spring of unique
 configuration which is advantageous for stably holding the actuator to
 guide the actuator along its axis during the movement of the movable blade
 between the contact closing and opening positions. The return spring
 comprises a ring with a center spring strip bridging from opposite ends of
 the ring. The ring has seats which are spaced from connections between the
 ring and the center spring strip and are secured to the contact block. The
 connections are raised relative to the seats at which the ring is secured
 to the contact block. The center spring strip has a longitudinal center
 which is coupled to the actuator and is raised relative to the
 connections. With this arrangement, the return spring gives a biasing
 force to urge the actuator substantially along its vertical axis for
 guiding the same along the vertical axis against and by the biasing force.
 Thus, the actuator and the movable blade secured thereto can move exactly
 along the vertical axis for reliable relay operation. The ring may be
 rectangular, circular or of lozenge. These and still other advantageous
 features of the present invention will become more apparent from the
 following description of the embodiment when taken in conjunction with the
 attached drawings.

DETAILED DESCRIPTION OF THE EMBODIMENT
 Referring now to FIGS. 1 to 3, there is shown a coaxial relay in accordance
 with a preferred embodiment of the present invention. The coaxial relay is
 designed to switch a high frequency signal at a frequency of 5 to 30 GHz.
 The relay is composed of a contact block 10 and an electromagnet block 60
 which are separately formed from each other. The contact block 10 includes
 a rectangular base 11 and a rectangular cover plate 15 which are both made
 of an electrically conductive material and are secured to form
 therebetween a shield chamber 12. The base 11 mounts three spaced coaxial
 connectors 20 for connection with coaxial cables carrying a high frequency
 signal to and from a high frequency circuit. As shown in FIG. 4, each
 coaxial connector 20 is composed of a core conductor 21, a shield
 conductor 22, and a dielectric sleeve 23 interposed between the core
 conductor and the shield conductor. The shield conductor 22 is threaded
 into a vertical hole 13 of the base 11 to project the core conductor 21
 into the shield chamber 12, thereby defining a coaxial contact at the
 upper end of the core conductor 21. The three coaxial connectors 20 are
 spaced horizontally to define a common fixed contact 30 by the core
 conductor 21 of the center coaxial connector 20 and define first and
 second fixed contacts 31 and 32 by the core conductors of the other two
 coaxial connectors 20. The cover plate 15 fixed to the base 11 mounts
 first and second movable blades 41 and 42 which are disposed within the
 shield chamber 12 so that the first movable blade 41 extends over the
 first fixed contact 31 and the common fixed contact 30, while the second
 movable blade 42 extends over the second fixed contact 32 and the common
 fixed contact 30. Each of the first and second movable blades 41 and 42
 has at its center an actuator 44 which projects vertically through an
 aperture 16 of the cover plate 15 to have its upper end located above the
 cover plate 15. A return spring 50 is connected between the upper end of
 each actuator 44 and the cover plate 15 to urge the movable blade upwardly
 into a contact open position, while allowing the movable blade to move
 downwardly into a contact close position where the first movable blade 41
 establishes the connection between the common fixed contact 30 and the
 first fixed contact 31, and the second movable blade 42 establishes the
 connection between the common fixed contact 30 and the second fixed
 contact 32. The return spring 50 is fixed to the cover plate 15 by means
 of screws 17 which extend into the base 11 for securing the cover plate 15
 also to the base 42. Details of the return spring 50 will be discussed in
 later.
 Turning back to FIG. 3, the electromagnet block 60 includes a frame 70 made
 of non-magnetic metal, a chassis 80 of a magnetic metal, and an armature
 100 of a magnetic material. The frame 70 is shaped from a single plate to
 have a rectangular top wall 71, a pair of side walls 72 depending from
 opposite lateral ends at the longitudinal center of the top wall 71, and
 end walls 73 depending from opposite longitudinal ends of the top wall 71.
 The chassis 80 has a rectangular top plate 81 and a pair of yokes 82
 depending from the opposite lateral ends at the longitudinal center of the
 top plate 81. The top plate 81 is formed at the longitudinal ends thereof
 with a pair of holes 83 for securely holding the upper ends of individual
 cores 84 so that the cores 84 extend vertically in parallel with the yoke
 82. Disposed around the individual cores 84 are bobbins 85 which carry
 individual coils 86. Thus, two electromagnets are formed respectively
 around the individual cores 84. Each of the coil bobbins 85 mounts a pair
 of coil terminals 87 connected to the ends of the coil and projecting
 upwardly for connection with a control circuit. Held between the lower
 ends of the yokes 82 is a permanent magnet 90 which is magnetized to have
 opposite poles on the upper and lower surfaces of the permanent magnet 90.
 The permanent magnet 90 is secured to the lower ends of the yokes 82 by an
 adhesive with its longitudinal ends mated into notches at the lower ends
 of the yokes, as best shown in FIG. 2. The top plate 81 of the chassis 80
 is formed at its opposite longitudinal ends with studs 88 which fit into
 corresponding holes 74 in the frame 70 and are riveted thereto for
 securing the chassis 80 to the frame 70. Thus, the frame 70 fixedly
 supports the chassis 80 and therefore the electromagnets.
 As best shown in FIG. 6, the lower ends of the side walls 72 of the frame
 70 are bent inwardly at a right angle to form thereat individual flanges
 75 which are formed on the bottom thereof respectively with pivot
 projections 76. Depending from the inner ends of the flanges 75 are stem
 77 for loose connection to the armature 100. As shown in FIGS. 3 and 7,
 the armature 100 is an elongated plate made of a magnetic material and
 mounts on its bottom a spring plate 110. The spring plate 110 is also
 elongated to have a raised anchor section 111 at the longitudinal center
 of the spring plate 110 and to have a pair of opposed spring legs 112
 extending from the anchor section 111. The anchor section 111 has a pair
 of brackets 114 which extend transversely beyond the lateral ends of the
 armature for connection with the lower ends of the frame 70. It is the
 bracket 114 that has a bearing hole 115 into which the stem 77 at the
 lower end of the frame 70 engage loosely.
 Mounting of the armature 100 to the frame 70 is made simply by inserting
 the stems 77 into the bearing holes 115 in the brackets 114, after which
 the permanent magnet 90 attracts to hold the armature 100 in position
 where the pivot projections 76 on the lower end of the frame 70 abut
 against the brackets 114. Whereby, the armature 100 is pivotally supported
 to the frame 70 to be movable about a pivot axis defined by the
 transversely aligned pivot projections 76. It is noted here that since the
 frame 70 is a one-piece member shaped from the metal sheet to have
 dimensional stability and the chassis 80 mounting the electromagnets and
 the permanent magnet 90 is fixedly supported to the frame 70, the armature
 100 supported to the lower end of the frame 70 can be accurately
 positioned relative to the cores 84 and the permanent magnet 90, thereby
 giving a precise and reliable armature movement in response to the
 energization of the electromagnets.
 The armature 100 thus supported to the frame 70 is allowed to pivot about
 the pivot axis between first and second positions in response to the
 energization of the electromagnets. In the first position, as shown in
 FIG. 1, the armature 100 pushes the first movable blade 41 to connect the
 first fixed contact 31 to the common fixed contact 30 while the armature
 100 is disengaged from the second movable blade 42, allowing it to move
 upwardly for disconnection of the second fixed contact 32 from the common
 fixed contact 30. In the second position, on the other hand, the armature
 100 pushes the second movable blade 42 to connect the second fixed contact
 32 to the common fixed contact 30, while the armature 100 is disengaged
 from the first movable blade 41, allowing it to move upwardly for
 disconnection of the first fixed contact 31 from the common fixed contact
 30.
 The spring legs 112 are held engageable respectively with the actuators 44
 of the first and second movable blades 41 and 42 to give suitable contact
 pressure at which the movable blades are pressed against the coaxial
 contacts 30, 31, and 32. Formed at the free ends of the spring legs 112
 are adjustor tabs 113 which project laterally beyond the lateral ends of
 the armature 100 to be exposed into openings 78 in the lower ends of the
 frame 70. Thus, adjusting of the contact pressure after mounting the
 armature 100 can be made by holding the adjustor tab 113 with a suitable
 jig and deforming the spring legs 112.
 The armature 100 also carries a pair of residual plates 120 on opposite top
 ends thereof each of which has a pair of integral arms 121 for opening and
 closing a pair of indicator contacts 122 mounted on the coil bobbins 87.
 The indicator contacts 122 are provided for giving a signal indicative of
 the armature operation of closing and opening the coaxial contacts 30, 31,
 and 32 by the first and second movable blades 41 and 42. For this purpose,
 the indicator contacts 122 are connected to indicator terminal leads 124
 extending upwardly above the frame 70 for connection with an external
 circuit monitoring the operation of the relay.
 In the electromagnet block 60 thus mounting the electromagnets and the
 armature 100 to the frame 70, the permanent magnet 90 gives a first
 magnetic flux loop emanating from the magnet 90 through the yokes 82, the
 one core 84 and the one portion of the armature 100 back to the magnet, as
 well as to give a second magnetic flux loop emanating from the magnet 90
 through the yokes 82, the other core 84, and the other portion of the
 armature 100 back to the magnet 90 for latching the armature 100 in both
 of the first and second positions after deenergization of the
 electromagnets.
 Formed at the respective lower ends of the end walls 73 of the frame 70 are
 positioning legs 79 which fit respectively into recesses 14 formed at the
 four corners of the cover plate 15 and are welded thereto, thereby
 assembling the electromagnet block 60 to the contact block 10.
 Disposed above the frame 70 is a printed board 130 which mounts a plug 131
 for connection of the coil terminals 87 as well as the indicator terminal
 leads 124 to the external circuits. For this purpose, the printed board
 130 has through-holes 132 for connection with the terminals 87 and the
 terminal leads 124, and internal conductors for connection of the plug 131
 and the through-holes 132.
 As shown in FIG. 8, the return spring 50 is a one-piece structure having a
 rectangular ring with opposed end segments 51, opposed side segments 53,
 and a center spring strip 57 extending between the opposed side segments
 51. Each of the opposed side segments 53 is formed at its center with a
 seat 54 with a mount hole 55 for receiving a screw 17. The screw 17
 extends further through the cover plate 15 into a threaded hole 19 in the
 base 11 for securing the cover plate to the base and at the same time to
 fasten the return spring 50 to the cover plate, i.e., the contact block
 10. Each of the opposed end segments 51 is raised relative to the seats 54
 in the absence of an external force and has connections 52 at the center
 of thereof with the center spring strip 57. The center spring strip 57 is
 formed at its center with a piece 58 having a square hole 59 for
 engagement with the upper end of the actuator 44. In a neutral position
 where no external force is applied to the piece 58, the piece 58 is kept
 raised relative to the opposed end segments 51 which are also kept raised
 relative to the seats 54. When the piece 58 is depressed as a consequence
 of the actuator 44 being depressed by the armature 100, the center spring
 strip 57 are resiliently deformed and at the same time the opposed end
 legs 51 are also resiliently deformed 51, thereby give a spring bias for
 urging the actuator 44 and therefore the associated movable blade 41, 42
 upwardly in a direction of the contact open position. Since the center
 spring strip 57 and the opposed end legs 51 are resiliently deformed in
 mutually perpendicular vertical planes respectively including the lengths
 of the center spring strip 57 and the opposed end legs 51, the actuator 44
 can move substantially only along a vertical axis without being tilted, so
 that the actuator 44 gives no interference with the aperture 16 through
 which the actuator extends, while the actuator moves vertically.
 The actuator 44 is made of a liquid crystal polymer (LCP) and is integrally
 molded at its lower end with the metal-made movable blade 41 (42), so that
 the actuator 44 can have an accurate dimensional relationship with the
 movable blade, i.e., the actuator 44 can extend integrally from the
 movable blade without causing any slack therebetween. For example, as
 shown in FIG. 4, a projection amount (a) of the dielectric actuator 44
 from the lower surface of movable blade 41 (42) into the shield chamber 12
 can be accurately controlled with the integral molding, and also the
 movable blade can be held close to the bottom of the cover plate 15
 without leaving any substantial gap therebetween in the contact opening
 position. This is particularly advantageous to design the contact block 10
 having stable high frequency characteristic such as uniform impedance
 along a signal path extending within the shield chamber 12. In this
 connection, the base 11 is formed at portions corresponding to the lower
 end of the actuator 44 with a circular dent 18 of which depth (.beta.) is
 accurately determined by drilling to give the uniform impedance along the
 signal path. As shown in FIG. 5, the connection of the actuator 44 to the
 movable blade 41 (42) is shaped to have a square configuration for
 avoiding undesired rotation of the actuator 44 about its vertical axis
 relative to the movable blade. Connection of the actuator 44 to the piece
 58 of the return spring 50 is made by inserting the upper end of the
 actuator into the hole 59 of the piece 58 and heat-welding it around the
 hole 59. Thus, the actuator 44 can be securely connected to the return
 spring 50 without giving any undesired distortion or deformation to the
 return spring 50, and to give an accurate projection amount of the
 actuator 44 from the top surface of the cover plate 15 for reliable
 contact closing and opening operation in response to the pivotal movement
 of the armature 100.
 A cover 150 of a dielectric material is fitted over the electromagnet block
 60 and is secured thereto by engagement of hooks 89 on the coil bobbins 85
 into notches 151 in the lower end of the cover. The cover 150 has an array
 of openings 152 through which pins of the plug 131 extend.
 Turning back to FIG. 4, each coaxial connector 20 includes a dielectric
 bush 24 held in the upper end of the shield conductor 22. The bush 24 is
 made of polychlorotrifluoroethylene (PCTFE) and is press-fitted around a
 reduced-in-diameter section of the core conductor 21 and is also
 press-fitted in the upper end of the shield conductor 22. When the coaxial
 connector 20 is threaded into a hole of the base 11, the bush 24 abuts
 against a seat in the hole. After being threaded into the base 11, the
 coaxial connector 20 is secured to the base 11 by an adhesive filled in a
 slit formed in the upper end of the shield conductor 22.
 FIGS. 9 and 10 show modified return springs which can be equally utilized
 in the above relay. The return sprig 50A of FIG. 9 comprises a circular
 ring 51A with a center spring strip 57A extending between diametrically
 spaced connection points 52. Formed in the ring 51A at portions angularly
 spaced from the connection points 52 by 90.degree. are seats 54A each
 provided with a mount hole 55A for receiving a screw which fastens the
 return spring 50A to the cover plate and at the same time fasten the cover
 plate 15 to the base 11. The center spring strip 57A is formed at its
 longitudinal center with a piece 58A having a hole for connection with the
 upper end of the actuator 44. In a condition where no eternal force is
 applied to the return spring 50A, the piece 58B is raised relative to the
 connection points 52 which are in turn raised relative to the seats 54A.
 Thus, when the piece 58A is subject to the downward force, the return
 spring can develop a spring bias of urging the actuator upwardly by
 resilient deformation of the center spring strip and the portions of the
 ring between the seats 54A.
 The return spring 50B of FIG. 10 comprises a lozenge-shaped ring 51B and a
 center spring strip 57B extending between two opposed corners of the ring
 51B. Formed at the other two corners of the ring are seats 54B with mount
 holes 55B, respectively for receiving screws which fasten the return
 spring to the cover plate as well as the cover plate to the base. The
 center spring strip 57B is formed at its longitudinal center with a piece
 58B having a hole 59B for connection with the upper end of the actuator
 44. In a condition where no eternal force is applied to the return spring,
 the piece 58B is raised relative to the connection ends of the spring
 strip, which are in turn raised relative to the seats 54B. Thus, when the
 piece 58B is lowered, the return spring 50B can develop a spring bias of
 urging the actuator upwardly by resilient deformation of the center spring
 strip 57B and the portions of the ring between the seats 54B. With the use
 the return springs 50A and 50B, it is also possible to guide the actuator
 44 upwardly along its axis without tilting the actuator. It is noted in
 this connection that the return springs 50, 50A, and SOB of the unique
 configurations as disclosed in above can be utilized in other relays in
 which the armature may be mounted either on the contact block or on the
 electromagnet block.
 In the electromagnet block as discussed in the above, the permanent magnet
 90 has a horizontal length of which center is vertically aligned with a
 pivot axis of the armature 100 to give the bi-stable relay operation.
 However, if is possible to give a mono-stable relay operation when, as
 shown in FIG. 11, a permanent magnet 90C of reduced width is secured to
 the bottom of the yokes 82 with the longitudinal center of the permanent
 magnet 90C is offset horizontally with respect to the pivot axis X. With
 this structure, the armature 100 is held stable at one of the first and
 second positions where the armature 100 is attracted by a greater magnetic
 force than at the other position. Thus, the relay can be made bi-stable or
 mono-stable simply by changing the permanent magnet.
 FIG. 12 shows a modification of the above relay which is identical to the
 above embodiment except for detailed structures of electromagnets. Like
 parts are designated by like numerals with a suffix letter of "D". The
 electromagnets utilize a common magnetic member which is a generally
 U-shaped to have a horizontal core 141 and a pair of pole legs 142
 depending from opposite ends of the horizontal core 141. A permanent
 magnet 190, which is secured to the center of the horizontal core 141, is
 magnetized to have opposite poles at the upper and lower ends thereof.
 Coils 144 are wound around the horizontal core 141 on opposite sides of
 the permanent magnet 190 to constitute the electromagnet. The lower end of
 the permanent magnet 190 is positioned to oppose the center of the
 armature 100D, i.e., the pivot axis thereof, while the pole legs 142
 define at their respective lower ends pole ends which are opposed to the
 opposite ends of the armature 100. Thus, the relay is given the bi-stable
 operation of holding the armature both at the first and second positions.