Patent Abstract:
A magnetic self-latching device for a gate has a main body with handles on either side for operation or has an arrangement to be remotely actuated, for example electrically. A latching body has a high strength magnet usually provided at the bottom of a cavity which defines a latching shoulder. The latching body is adapted to be fixed to a gate post. The main body, with its housing, can be mounted on the gate frame and incorporates a latch pin which, in the door-closed position, is displaced by magnetic attraction to an extended latching position and against the biasing of a return spring. The gate cannot be opened until actuation of the mechanism occurs, for example by rotating a handle to retract the pin against the magnetic force; the gate can then be swung open. When the handle is released, the biasing spring retains the latch pin in a retracted position. A lost motion arrangement is provided so that there is substantially no load on the pin when the handles are released and the pin is supported in the retracted position by the return spring. A carriage and an associated actuator or a flexible/semi flexible line connection is provided in the housing for incorporating the lost motion arrangement.

Full Description:
FIELD OF THE INVENTION 
   The present invention relates to magnetic latches suitable for use on gates or doors where automatic latching is required when the gate or door is displaced to a position at which it is to be latched. An actuator is provided for unlatching so that the gate or door can be opened, usually pivotally, away from its latching position. 
   The present invention in various embodiments offers new and useful alternatives to previously available options and indeed lends itself to embodiments which may incorporate security locks such as quality cylinder locks. 
   BACKGROUND OF THE INVENTION 
   A significant development in magnetic latching and devices is the subject of the PCT International Publication WO92/03631 on the basis of which U.S. Pat. No. 5,362,116 was issued to David Doyle and Neil Dunne. This invention has been assigned to the assignees of the present invention. The Doyle and Dunne invention relates to a vertically operating magnetic latch particularly for a swimming pool gate with a lost motion arrangement so that a latching pin, after manual retraction and after opening the gate, is retained in an elevated retracted position by spring biasing and the actuating mechanism does not apply downward load-imposing forces against the biasing spring. 
   While this device has been successfully exploited, the present invention has been conceived to offer novel inventive and alternative embodiments for different applications in a different form. Indeed the present invention may be applied to provide magnetic latching as an alternative to conventional striker plates with spring door latches and the invention may lend itself to versions incorporating locks. 
   Embodiments of the present invention are envisaged as extending both to manually actuatable versions (such as embodiments having rotatable rotary knobs or rotatable handles) but also extends to actuation by other means such as solenoids or electric motors permits actuation from a remote location. Of particular significance in these embodiments is the inherent characteristics of magnetic latching as demonstrated by the Doyle and Dunne prior patent whereby when a gate or door is swung to its closed position, in contrast to conventional gate latches where force is required to displace a spring biased latch pin initially away from a latching position prior to it entering into latching engagement, with Doyle and Dunne there is no such resistance. This is especially valuable in installations having an automatic door closing device. 
   SUMMARY OF THE INVENTION 
   The present invention is embodied in a self-latching device for latching, in a predetermined position, two members which are otherwise moveable relative to one another, the device comprising a latch arm and a retaining element which in use provides a latching shoulder for the latch arm to prevent relative movement of the members, at least one of the latch arm and the retaining element providing a magnetic field and the other having magnetic properties, the latch arm being arranged to be displaceably mounted on a first of said members and the retaining element being arranged to be associated with the second of said members, the latch arm and retaining element undergoing relative movement into a latching position under the influence of the magnetic field when the members are in the predetermined position, and then relative movement of the two members is substantially prevented by an engagement portion of the latch arm and latching shoulder interengaging, and the latch arm being displaceable under applied force away from the retaining element to a retracted position so that the members may be moved apart, the device further comprises: 
   (a) a resilient biasing element associated with the latch arm to bias it towards the retracted position, but with a biasing force on the latch arm which is less than the force imparted on the latch arm by the magnetic field when the members are located in the predetermined position; 
   (b) an actuator movably mounted on the housing and extending from the housing transversely to the path of displacement of the latch portion for receiving a displacement force to displace the latch arm from its latching position to its retracted position, whereby the two members may be moved apart away from the predetermined position; 
   (c) a connector for connecting the actuator and the latch arm to displace the latch arm from its latching position to its retracted position and to leave the actuator free to move relative to the connector; and 
   (d) a second biasing element for returning the actuator to its initial position on removal of the displacement force leaving the biasing element to maintain the latch arm and connector substantially in its retracted position, whereby when in the predetermined position the latch arm is displaceable under the magnetic forces against the biasing means to re-establish its latching position. 
   Implementation of the invention may be by including a lost motion interconnection between the actuator and the latch arm whereby no significant load is applied to the latching arm and its biasing element when in the retracted position. 
   In the subject invention, the actuator may be designed so as to be movable in a rectilinear, arcuate or rotary manner either in or transverse to a plane in which the latch arm is to be displaced. 
   A particular embodiment is one wherein the latch arm is mounted for reciprocation in a housing and the housing also mounts the actuator in the form of a rotary actuator which may include a conventional rotatable handle, with the option of providing one handle on either side of the device, for example to be disposed on either sides of a gate. Each handle might incorporate a locking mechanism such as a wafer lock or cylinder lock for security reasons. The housing might incorporate an alternative locking mechanism. 
   One embodiment provides a carriage with spaced guides along which mounting elements of the latch arm can slide, the latch arm incorporating a pin around which a helical compression biasing spring is mounted as the biasing means. In such an embodiment a torsion spring can be provided as the restoring means for the rotary actuating means (such as the handles). 
   As described with reference to an illustrated embodiment, the latch arm can take the form of a generally C-shaped carriage which moves in guides in the housing and the C-shaped carriage has lobes at its open ends for engagement with corresponding projecting elements associated with a barrel connected to a rotatable handle. 
   An alternative approach, however, is to provide the latch arm with a drum-like structure around which a flexible connection element extends. The arrangement is such that the element is extended and perhaps tensioned when the latch arm is in the latching position and rotation of the drum by the actuator causes the latch arm to be retracted. The arrangement is such that after movement of a gate (or door) to an open position, the biasing means retains the latch arm in its retracted position and tension previously applied to the flexible element is relieved so that no or only negligible load is applied against the biasing means. 
   The device may include an actuator for displacing the latch arm by remote actuation for remote gate opening control. However, larger markets are thought to be for directly operated gate latches having handles. 
   Embodiments of the invention can be formed into a volume, shape and configuration consistent with conventional cylinder lock door locks, i.e. within an envelope of about 15 cm×10 cm×5 cm. 
   Embodiments may have the magnet material provided by a permanent magnet having a remanence (residual flux density) of about 12 kilogauss and the latch arm has a pin having magnetic properties and of transverse dimension of about 8 mm, preferably sealed within the body of the retaining element and the latch arm then has a steel pin providing the latching portion and of a suitable grade of steel having magnetic properties. 
   In place of a rotatable knob or rotatable handle for actuating means, the invention lends itself to embodiments which are remotely actuated, for example electrically by the use of a solenoid arrangement or motor to cause rotation of the actuator for retraction of the latching arm. 
   Generally arrangements incorporate a lost motion interconnection between the actuator and the latch arm such that little or preferably no load is applied to the latching arm and its biasing means when in the retracted position. 
   Although significant markets for embodiments of the invention are perceived to be for gate locks incorporating key actuated mechanisms such as wafer locks or cylinder locks, embodiments may be simply no-lock latch mechanisms, or embodiments having an egress button on one handle and a lock on the other. 
   Embodiments can provide a lost motion effect by having an eccentric drive pin to be displaced upon lock actuation to displace an internal element from a retracted position (where it rotates freely upon handle rotation) to an extended position in which it engages with a collar to rotate the collar and the collar in turn displaces a carriage to retract the latch arm. 
   The term “comprising” (and its grammatical variations) as used herein are used in the inclusive sense of “having” or “including” and not in the sense of “consisting only of.” Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the features of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be further exemplified with reference to the accompanying drawings of which: 
       FIGS. 1A ,  1 B and  1 C are respectively a plan view, a front elevation and an end elevation (in the direction of arrow A in  FIG. 1A ) of an embodiment of the invention suitable for fitting to a gate; 
       FIG. 2  is an exploded view of the device of the embodiment of  FIGS. 1A to 1C ; 
       FIG. 3  is an end view of an actuating barrel of the device on an enlarged scale; 
       FIG. 4  is an isometric view of the actuating barrel on an enlarged scale; 
       FIG. 5  is an end elevation of a sliding carriage of the latch arm on an enlarged scale; 
       FIG. 6  is an elevation of the sliding carriage of  FIG. 5 ; 
       FIG. 7  is an elevation with the front housing removed and showing the latching configuration with a latch pin of the latch arm extended into latching engagement in a cavity of a latch block; 
       FIG. 8  corresponds to  FIG. 7  but after rotation of an actuating handle to retract the latch pin to permit the associated gate to be swung open; 
       FIG. 9  is a view corresponding to  FIG. 8  but after release of the handle to return to its normal position and with the latch pin retained in a retracted position; 
       FIG. 10  is a partly exploded isometric view of a second embodiment; 
       FIG. 11  is an isometric cross-sectional view of the embodiment of  FIG. 10  when in the locked configuration and latch pin engaged by magnetic force into the receiving latch block; 
       FIG. 12  is an isometric view on an enlarged scale of the rotary actuating a mechanism of the second embodiment shown on an enlarged scale and in a locked configuration; 
       FIG. 13  is a view corresponding to  FIG. 12  and showing an unlocked configuration; 
       FIG. 14  is an exploded view of a third embodiment; 
       FIG. 15  is an exploded view of a fourth embodiment; 
       FIG. 16  is a view of a fifth embodiment of the invention utilizing a flexible line to provide a lost motion system; 
       FIG. 17  is a view of the embodiment of  FIG. 16  in which the handle has been depressed; 
       FIG. 18  is a view of the embodiment of  FIGS. 16 and 17  in which the handle has returned to its neutral position after depression; and 
       FIG. 19  is a schematic view of the sixth embodiment modified for remote actuation. 
       FIG. 20  is a front part-sectional view of a seventh embodiment when actuated to retract a latch pin; and 
       FIG. 21  is a view of the embodiment of  FIG. 20  when the actuator is released and the gate-closing position has been achieved and the latch pin magnetically displaced to a latching portion. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The gate latch generally shown in  FIGS. 1A to 1C  is shown in assembled form and prior to installation. The latch  10  comprises a lockable latch module  11  to be mounted on a post of a gate and a receiving latch block  12  which is adapted to be mounted to a fixed gate post. 
   The latch module has a front casing  13  and a rear casing  14  adapted to be mounted on opposite sides of gate post. Front and rear handles  15  and  16  are provided and a security cylinder lock  17  is provided for each handle for independent locking purposes. 
   The components are shown in more detail in  FIG. 2 . A mounting structure  20  is provided for attachment to a gate post of rectangular cross-section and to mount the components within the casings  13  and  14  and to mount the handles  15  and  16 . The mounting structure  20  includes a back plate  21  having spaced parallel grooves  22  to guide a latch pin assembly, and an integral end wall  23  having a small collar  24  around an aperture (not shown) through which a latching pin  25  can move. A helical compression spring  26  is mounted on the latching pin and the right hand end of the latching pin  25  upon assembly is attached by engagement in a cylindrical projection  30  of a generally C-shaped carriage  31 . The carriage  31  has integral parallel guide strips  32  extending from its rear face provided for sliding engagement in the grooves  22  in the back plate  21 . 
   An actuating barrel  33  (as shown in more detail in  FIGS. 3 and 4 ) is to be rotated by the handles and displace the carriage axially relative to the latching pin  25 . The barrel engages with an end portion  34  of a front handle  15  after the end portion is assembled by passing through an aperture in the front casing  13 . An arcuate tab  40  projects from the end portion  34  to engage a slot in the barrel  33  so as to transmit rotation. The barrel  33  extends through an aperture in the back plate  21  to be connected to an end portion  35  of the rear handle  16 . An arcuate tab  40  also engages with a slot on the rear of the barrel  33  to transmit rotation. 
   As best seen in  FIG. 3 , the actuating barrel  33  has a rectangular shaped through-aperture  38  for receiving a conventional actuating bar which extends from the rear of a cylinder lock  17 . The barrel has a structure which permits rotation of the barrel only when the key has been turned to unlock the lock  17 , as now described with reference to  FIGS. 3 and 4 . 
   The rear end of the barrel  33  has a groove  33 B for accommodating the corresponding arcuate tab  40  from the rear handle so that rotary motion is transmitted to the barrel  33  when the latch is assembled and either handle is rotated. A similar groove  39 A is provided on the front of the barrel for the arcuate tab  40  of the front handle. The barrel assembly includes upper and lower ears  41  at the ends of pivotal arms  34  which are mounted on pivot pin  35  with a C-shaped spring clip  36  fitted over the arms  34  to bias them radially inwardly so that recess  37  in the inner periphery of each arm rest on lobes  39 A of a rotor  39 . The recess provides a detent function to define positively the position shown. 
   A middle portion of the barrel has an L-shaped bracket  43  for retaining end pins  64  of a torsion spring  66  (not shown in  FIGS. 3 and 4  but shown in  FIGS. 2 and 7 ). The L-shaped bracket has a mounting leg  44  and an arcuate base  45  with a groove  46  for accommodating the body of the torsion spring  66 . 
     FIGS. 5 and 6  show detail of the carriage  31  which has a central wall  31  A and the part cylindrical projection  30  accommodating a spring locking tag  31 B into which a groove  25 A near the rear of latching pin  25  is snap-fitted. The carriage  31  has inwardly directed lobes  63  for receiving a displacement force when either is engaged by an ear  41  of an arm  42  as described below. 
     FIG. 3  shows the configuration when the lock  17  has been unlocked so that the ears  41  project and upon rotation of the handle, as shown in  FIG. 8 , upper ear  63  is engaged and the carriage moved rectilinearly to the right. 
   Referring now to  FIG. 7 , the latching block  12  is shown mounted to a fixed gate post  60  and the latching module I 1  is shown mounted to an end post  61  of a gate. The latching block  12  is shown in part-sectional view and the latching module is shown with the front casing removed for clarity. In the configuration shown in  FIG. 7 , the handles have been released and are arranged horizontally by the effect of a torsion spring  66  (shown in  FIG. 2 ) and mounted on the barrel  33 .  FIG. 7  shows the device in the predetermined position, i.e. the latching position at which the latch pin  25  has been magnetically attracted to extend so that the tip of the latch pin engages in the aperture  56 . The spring  26  is compressed between the interior of the end wall  23  and the carriage  31 . The carriage is thus drawn to the left and the lobes  63  of the carriage are adjacent to or engage with the ears  41  of the actuating barrel  33 , since in this configuration the lock is unlocked. 
   However, when the lock is locked, the rotor  39  is rotated and the lobes  39 A disengage the arms  34  which displace inwardly under the pressure of the spring clip  36 . If the handle  15  is displaced, the ears  41  do not engaged the lobes  63  of the carriage and the carriage does not move. 
     FIG. 7  also shows the end pins  64  of the torsion spring which engage of a location pin  65  which extends from the back plate  21 . 
   The components of the latching block  12  are more clearly shown in exploded view in  FIG. 2 . 
   The components comprise an L-shaped mounting plate  50  adapted to be secured to a post by screws passing through apertures  51  on an end face. The mounting plate has dovetail section tracks  52  for engaging slidingly with complimentary shaped grooves on the rear of a latch body  53 . The latch body has a central cavity for accommodating a high strength magnet  54  which is held in position and the cavity sealed with suitable sealant when a cover element  55  is secured in place. The element  55  has a suitable shaped aperture  56  having a latching function when engaged with the tip of latching pin  25 . 
   Main fixing screws  67  (shown more clearly in  FIG. 8 ) extend through the end wall  23  of the mounting structure  20  and into tapped receiving arms  68  of the rear housing  14 . 
   Although not shown in the drawing, the rear of the front housing  11  is provided with spaced mounting lugs having cylindrical bores through which the mounting screws  67  also extend to achieve assembly.  FIG. 8  shows downward rotation of the handle  15 , typically after manual unlocking and depression of the handle. The actuating barrel  33  retracts the carriage  31  by virtue of engagement of the upper ear  41  with the upper lobe  63  of the carriage thereby displacing it to the right as shown in  FIG. 8 . The pin  25  is thus retracted to the position shown in  FIG. 8  and is removed from engagement with the cavity  56  of the receiving block. The gate can then be swung open and, when the handle is released, because there is no magnetic field influence, the carriage  31  remains in its position under biasing of the spring  26  and leaving the latch pin  25  retracted. 
     FIG. 9  shows the handle returned to its original position under influence of the torsion spring  66  with the carriage  32  in its right hand displaced position. 
   As and when the gate is returned to its closed position, the latch pin  25  again becomes aligned with the receiving cavity  56  and is then attracted under the strong magnetic field to move to the left thereby compressing the biasing spring  26  and sliding the carriage  32  to the left so that the configuration of  FIG. 7  is attained. 
   Reference will now be made to  FIG. 10  which shows a second embodiment of the disclosure which is similar to but a more practical version of the first embodiment. Like reference numerals have been used for like parts and only differences will be highlighted. 
   This embodiment shows the detail for mounting a conventional six pin cylinder lock  17  in each handle. The lock is inserted into the handle barrel with a lateral projection from each cylinder engaging in a corresponding cavity. A retaining plate  19  is inserted to close the cavity and secured by fixing screws  19 A. Each cylinder lock has a projecting tab  18  being of rectangular cross-sectional shape for conventional purposes and of a length to suit engagement in respective rotor elements  27  and  28  to be associated with the actuating barrel  33  as described in more detail below. 
   Each handle is secured to the respective casing by a spring clip  69 . 
   In this embodiment, the form of the mounting plate  20  is slightly different form, as illustrated, and the end wall  23  incorporates an integral security housing projection  28 . 
   In this embodiment, the barrel  33 , in place of the pivotal spring arms  34  of the first embodiment, has a moulded collar  29 . Within the collar is mounted a tongue  57  which is secured in cooperating relationship to the front and rear rotors  27  and  28  which are secured, as described below, by two plain roll pins  59 . 
     FIG. 10  shows in this embodiment that the handles have a pair of arcuate projecting tabs  40  for transmitting rotation. The front handle  40  has its tabs, on assembly, engaged in grooves  66  in a front portion of the barrel  33  whereas the rear handle  16  has its tabs  40  engaged in grooves  67  on the rear of the barrel  33 . Thus rotation of either handle will rotate the barrel. However the collar  29  does not rotate unless the tongue  57  has engaged in a recess  29 A in the collar. Engagement is achieved by unlocking. Unlocking the front lock turns the rotor  27  by virtue of engagement of the rectangular bar  18  in a central aperture in the rotor and, because of eccentric positioning of the pins  59 , the tongue is displaced to the left as shown in  FIG. 10  so its leading end engages in the cavity  29 A in the collar. Thereafter rotation of the handle causes rotation of the collar  29  and upper or lower ear  41  then engages a lobe  63  of the C-shaped carriage to retract the latching pin. 
   Referring now to  FIG. 11 , which is an oblique view through a vertical central plane of the assembled device in a locked configuration, the configuration of the tongue  57  will be better appreciated. The collar  29  is mounted on and freely rotatable on the barrel  33  with the torsion spring  66 , not shown in the drawing, located behind the collar  29 . This biases the barrel to its normal or rest position. The tongue  57  has a slightly elongate aperture  58  elongated in the vertical direction and receiving from each side thereof cylindrical projections, each having a through bore, from the respective rotors  27  and  28 . A first of the pins  59 A is inserted through rotor  27  through its cylindrical projection and into the complimentary cylindrical protection of the rotor  28  lying behind the tongue. The second pin  59 B is inserted through an aperture in the rotor  27 , through an arcuate slot  57 A in the tongue and into a corresponding aperture in the other rotor  28 . 
   The collar  29  is rotatably mounted around the barrel and in the position shown in  FIG. 11  the tongue  57  is in a retracted position so that rotation of the barrel and tongue by a handle does not transmit any rotation to the collar  41 . The ears  41  lay adjacent the lobes  63  of the carriage. When the key mechanism is actuated to unlock the handle rotation of the rotor  27  occurs and the eccentrically disposed upper roll pin  59  occurs relative to the central pin  59 B in an anti-clockwise direction thereby displacing the tongue to the left is shown in  FIG. 11 . This then causes the leading edge of the tongue to engage in the cavity  29 A whereby any rotation of the handle thereafter rotates the barrel, the tongue and the collar thereby retracting the carriage  31  and the latch pin  25 . 
     FIGS. 12 and 13  show an enlarged scale in isometric view the assembled components in the locked and unlocked configurations. 
   In place of the cylinder lock shown in  FIG. 10  a wafer lock, which is less expensive and simpler, may be used.  FIG. 14  is an exploded view of such an embodiment. A cylinder lock has an inherent lost motion effect but a wafer lock does not. Therefore when a wafer lock  117  is used, an adapter barrel  117 A or  117 B is utilised. Each adapter barrel has an eccentrically disposed arcuate slot facing the end of the wafer lock and accommodating and providing lost-motion for an eccentrically disposed cylindrical projection from the tip  117 C on the rear end of the wafer lock (see rear wafer lock  117  in  FIG. 14 ). In the case of the front adapter barrel  117 A, it contains a short rectangular bar  117 D for engaging in and rotating the front rotor  27  and in the case of the rear adapter barrel  117 B there is a rectangular slot  117 E in the adapter barrel for accommodating the end of an elongate rectangular drive bar  18  which has the effect of driving the rear rotor  29 . 
     FIG. 15  is an exploded view of a third embodiment being a no-lock version wherein like parts have been given like reference numerals. Equivalent functionality applies without the complexity of locking options. In this embodiment an alternative form of non-adjustable latch block  112  is illustrated incorporating a cavity for the high performance magnet  54  which is retained by a cover plate  113 . 
   The barrel  33  is simplified as an integral moulding incorporating ears  41  and at a forward end region a pair of grooves  33 A for engaging with the projecting tabs  40  from the rear of the front handle for rotating the barrel. The rear portion of the barrel has further grooves  33 B for similar engagement with the projecting tabs  40  from the rear handle  16 . Upon assembly the barrel is located with the ears  41  located behind the lobes  63  of the carriage  31  and the embodiment operates by direct actuation of the carriage. 
     FIG. 15  also illustrates a square aperture  33 C extending through the barrel for accommodating a conventional square drive bar of a rotary door knob which is an alternative to the use of the handles shown. 
   Referring now to the fifth embodiment of  FIGS. 16-18 , the drawings show an alternative connection system between the locking pin  25  and handle  15  to replace the actuating barrel  33  and the associated upper ear  41  and upper lobe  63  of the first embodiment. In this embodiment, there is provided a drum (not shown) around which is mounted a flexible line  70 . The line  70  is connected to a right hand end portion of the pin  25 .  FIG. 16  shows the device in the same predetermined position as shown in  FIG. 7 . The locking pin  25  is drawn to the left and the flexible line  70  is drawn off the drum and becomes taut. In this configuration the handles  15  and  16  are released and arranged horizontally by the effect of the torsion spring  66 . 
   Referring now to  FIG. 17 , downward rotation of the handle  15  has occurred, typically after manual unlocking and depression of the handle  15 , causing the flexible line  70  to retract the locking pin  25 , displacing it to the right against the force of the magnet  54 . The pin  25  is thus retracted to the position shown in  FIG. 17  and is removed from engagement with the cavity  56  of the receiving block. The gate can then be swung open, and when the handle is released, there is no magnetic field influence on the locking pin  25 . The pin  25  which is biased to the right by the biasing spring  26 .  FIG. 18  shows the sagging of the flexible line  70  when the handle  15  is released and returns to its original position under the influence of the torsion spring  66 . 
   In a similar way to previous embodiments, when the door or gate is returned to its closed position, the configuration of  FIG. 16  is attained once again. 
   Referring now to the adaptation of  FIG. 19 , the parts are shown schematically with provision for a remote actuator  72  including an electrical actuator  72  having a set of connections  73  when it is to be hardwired to a circuit closing device or an aerial  74  where a wireless signal is to be received and interpreted to actuate the device. The circuit includes a source of electrical power such as a transistor radio battery sufficient to drive either a solenoid or a small motor  75  which drives the drum  70 A. Thus remote actuation can occur to remotely actuate the gate lock. 
   Referring now to the seventh embodiment of  FIGS. 20 and 21 , like reference numerals have been used for like parts. This embodiment differs from the first embodiment by responding to rectilinear push-button operation which rotates a modified barrel  33  which otherwise functions as in the first embodiment. 
   Push button  118  has a gear rack  119  engaging a pinion  122  having a horizontal axis aligned with the axis of the latch pin  25 . The button  118  is slidably mounted in the housing of the device and is biased by a spring (not shown) to its outward or projecting position. When the button is depressed, rack  119  rotates pinion  122  which carries a crown gear  120  in constant mesh with a gear  121  on the barrel  33  so that the barrel rotates. Upper ear  41  engages the upper lobe  63  of the carriage  31  to retract it and the latch pin  25  to the position shown in  FIG. 20 . 
   After opening of the gate on which the device is mounted, and upon release of the button, the barrel and button return to an initial position, corresponding to that shown in  FIG. 21 , but with the carriage  31  and latch pins remaining in the displaced position shown in  FIG. 20 . 
   When the gate is re-positioned to its closing position, the magnet in the receiving unit (not shown) attracts the latch pin to the latching position shown in  FIG. 21 .

Technology Classification (CPC): 8