Abstract:
A switch mechanism for use in for example a rope switch. The mechanism comprises a switch which is actuable to switch between first and second conditions, for example to turn on and off kinetic machinery. A cam follower actuates the switch, the cam follower bearing against the surface of a rotatably mounted cam. An actuator member is displaceable relative the cam and a linkage is provided between the actuator member and the cam such that displacement of the actuator member from a predetermined position causes the cam to rotate and actuate the switch. The linkage comprises a lever mounted on a pivot that is displaced with the actuator member, the lever co-operating with a surface of a stationary cam such that displacement of the actuator member causes the lever to pivot and rotate the rotatable cam.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to switch assemblies and more particularly, but not exclusively, to rope operated switch assemblies used to control the power supply to kinetic machinery. 
     Known rope operated switch assemblies comprise a safety switch adapted to be fitted in proximity to a machine. and an actuator connected to the switch and operable by a rope to turn off the electrical power supply when the rope is pulled or slackened. 
     2. Discussion of the Related Art 
     Safety switches of this type have a housing in which are situated normally-open contacts, one set fixed, the other movable and carried by an axially-movable plunger spring-loaded to maintain the sets of contacts closed and the power supply consequently on. 
     The axially-movable plunger bears against a rotatable cam of a cam arrangement normally disposed to maintain the cam in a position such that the plunger is in a power supply ON position but which is operable by the rope to cause cam rotation and axial movement of the plunger to a power supply OFF position. 
     In one particular example the rope is connected in axial alignment to a shaft extending into the housing. The rope is connected to the shaft in tension so that the shaft is held against a biasing force provided by a shaft spring. If the rope tension is relaxed (e.g. by cutting it) the biasing force moves the shaft in a first axial direction and if the rope tension is increased (e.g. by pulling it) the shaft moves in a second axial direction with the rope. The shaft has a circumferential latch adjacent an undercut at a certain position along its length. The latch is biased in a direction perpendicular to the longitudinal axis of the shaft. The shaft carries a loop that engages a pin on the cam so that axial movement of the shaft in either direction will drive the cam and operate the plunger to a power supply OFF position. If the rope is cut, the shaft spring maintains the shaft in a switch OFF position. If the rope is pulled but subsequently released, the shaft is maintained in a switch OFF position by the latch which has engaged with the undercut. This prevents the power supply being turned on again unless the switch is reset. 
     These known switch assemblies operate satisfactorily if the rope is cut, but suffer from the disadvantage that if the rope tension is increased slightly it may be sufficient to turn the power supply off but not sufficient for the latch to operate so as to prevent a subsequent slight reduction in rope tension turning the power on again. Similarly, if the rope tension is decreased slightly it may be sufficient to turn the power supply off but a subsequent slight increase in tension could turn the power supply on again. Thus dangerous conditions can arise if for example a machine operator has been injured and has pulled the rope to switch off the machinery but it too weak or is otherwise unable to pull on the rope with sufficient force to engage the latch. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a switch assembly in which such disadvantages are obviated or mitigated. 
     According to the present invention there is provided a switch mechanism comprising a switch which is actuable to switch between first and second conditions, a cam follower movement of which actuates the switch, a rotatably mounted cam against a surface of which the cam follower bears, an actuator member which is displaceable relative to the cam, and a linkage between the actuator member and cam arranged such that displacement of the actuator member from a predetermined position causes the cam to rotate and actuate the switch, wherein the linkage comprises a lever mounted on a pivot that is displaced with the actuator member, the lever co-operating with a surface of a stationary cam such that displacement of the actuator member causes the lever to pivot and rotate the rotatable cam. 
     The lever arrangement in accordance with the present invention makes it possible for a relatively small movement of an actuator shaft or the like to cause a relatively large angular movement of the rotatable cam. Thus the device is particularly sensitive which is of real importance in the case of a rope-operated switch. 
     The actuator member may be a shaft that extends into a housing, the lever being pivotally supported on a body connected to the shaft and the stationary cam being defined by an internal wall of the housing. 
     Preferably the rotatable cam is rotatable from a datum position in which the switch assumes the first condition to at least one displaced position in which the switch assumes the second condition. and means are provided to bias the cam away from the datum position once the cam has been rotated by the lever. The biasing means preferably comprises a first latch member pivotally supported adjacent the rotatable cam, a second latch member bearing against the cam, and a spring arranged to bias the first and second latch members apart, the spring biasing force being directed in a direction which intersects the axis of rotation of the rotatable cam when the cam is in the datum position. The actuator member may extend through an aperture in at least one of the latch members, and the first latch member may be pivoted about an arcuate surface against which it is biased by the spring. Means may be provided to push the first latch member to a position in which the spring biasing force is directed in a direction to one side of the axis of rotation of the rotatable cam and thereby to cause the cam to rotate. 
     Preferably the lever defines a recess on one side which receives the stationary cam and a pair of arms on the opposite side to the recess which arms project on opposite sides of an abutment member forming part of the rotatable cam when the actuator member is in the predetermined position, one arm being displaced into contact with the abutment member when the actuator member is displaced in a first direction from the predetermined position, and the other arm being displaced into contact with the abutment member when the actuator member is displaced in the opposite direction to the first direction. The lever arms may be disposed such that rotation of the cam to actuate the switch between the first and second conditions is obstructed unless the actuator member is in the predetermined position. 
     In an alternative arrangement, the lever may define a recess on one side which receives the stationary cam and a single arm on the opposite side to the recess, the arm projecting to one side of an abutment member forming part of the rotatable cam when the actuator is in the predetermined position, and being displaced into contact with the abutment member so as to rotate the cam when the actuator member is displaced in a first direction from the predetermined position. And the actuator member supporting an abutment member which is displaced into contact with the biasing means so as to rotate the cam when the actuator member is displaced in a second direction from the predetermined position. Displacement of the actuator member in the first or the second direction may rotate the cam in the same direction. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A specific embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
     FIG. 1 is an exploded view of a switch assembly in accordance with the present invention; 
     FIG. 2 is a part-sectional view through the switch assembly of FIG. 1; 
     FIG. 3 is a section on the line  3 — 3  of FIG.  2  and indicates the section of FIG. 2 by the lines  2 — 2 : 
     FIG. 4 is a view similar to that of FIG. 3 showing the switch assembly after an actuator shaft has been displaced in a first direction; 
     FIG. 5 is a similar view to that of FIG. 3 showing the actuator shaft displaced in a second direction; 
     FIGS. 6,  7  and  8  show an actuator cam incorporated in the switch assembly of FIG.  1 . FIGS. 7 and 8 being sections on the lines  7 — 7  and  8 — 8  as shown in FIG. 6; 
     FIGS. 9 to  13  illustrate an outer spring support incorporated in the switch assembly of FIG. 1, FIGS. 10 and 13 being views on the lines  10 — 10  and  13 — 13  of FIG.  9  and FIGS. 11 and 12 being sections on the lines  11 — 11  and  12 — 12  of FIG. 10; 
     FIGS. 14 to  16  illustrate an inner spring support incorporated in the switch assembly of FIG. 1, FIGS. 15 and 16 being views on the lines  15 — 15  and  16 — 16  of FIG. 14; 
     FIG. 17 is a plan view of one end of a box casting incorporated in the switch assembly of FIG. 1; 
     FIG. 18 is a section on the lines  18 — 18  of FIG. 17; 
     FIGS. 19 and 20 respectively illustrate the relative positions of the actuator cam and inner and outer spring supports for a first and second switching condition of the assembly of FIG. 1; 
     FIGS. 21 to  24  illustrate a lever support incorporated in the switch assembly of FIG. 1, FIGS. 22,  23  and  24  being views on the lines  22 — 22 ,  23 — 23  and  24 — 24  of FIG. 21; 
     FIGS. 25 to  27  illustrate a lid cam incorporated in the assembly of FIG. 1, FIGS. 26 and 27 being sections on the lines  26 — 26  and  27 — 27  of FIG.  25 . 
     FIG. 28 is a plan view of internal components of a further embodiment of the present invention; 
     FIG. 29 is a plan view of a lever support incorporated in the embodiment of FIG. 28; 
     FIG. 30 is a view on lines  30 — 30  of FIG. 29, 
     FIG. 31 is a view on lines  31 — 31  of FIG. 30, and 
     FIG. 32 is a view on lines  32 — 32  of FIG. 30; 
     FIG. 33 is a plan view of a lever incorporated in the embodiment of FIG. 28; 
     FIG. 34 is a top view of a cam incorporated in the embodiment of FIG. 28; 
     FIG. 35 is a section through FIG. 34 on line  35 — 35 ; 
     FIG. 36 is a top view of an outer spring support incorporated in the embodiment of FIG. 28; and 
     FIG. 37 is a view on the lines  37 — 37  of FIG.  36  and 
     FIG. 38 is a view on the lines  38 — 38  of FIG.  37 . 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, the illustrated switch assembly comprises a box casting  1  having an open top that is normally closed by a lid  2 . A resilient seal is received between the box  1  and lid  2 , the lid being secured by bolts  4 . The box defines a window  5  closed by a transparent lens  6 , a first bore  7  which receives a shaft  8  connected to a reset lever  9 . And a second bore which receives a shaft  10  coupled to a stop button  11 . 
     A three hole circuit breaker assembly  12  is secured within the box  1  by bolts  13 . Wires (not shown) may be fed into the box through one of the illustrated ports to the circuit breaker assembly  12  and the circuit breaker assembly may be earthed by connecting a wire to a formation  14  within the box by means of a screw  15  and an associated washer. 
     An actuator cam  16  is secured by a pin  17  adjacent one end of the circuit breaker assembly  12 . The actuator cam  16  carries two drive pins  18  which extend into a lid cam  19 . The lid cam  19  is fixed to rotate with the shaft  8  of the reset lever  9 . A lever support  20  is positioned between the actuator cam  16  and the lid cam  19  and between the drive pins  18 . A lever  21  is mounted by a pin  22  on the lever support  20 , the lever co-operating with a cam surface (not shown in FIG. 1) defined by a formation cast into the inside wall of the box  1 . The lever  21  defines a recess  21   a  and two arms  21   b.    
     The actuator cam  16  defines a slot  23  which receives a short pin  24  extending upwards from the body of an inner spring support  25 . The inner spring support  25  is slidably received in a lower portion of an outer spring support  26 , a spring  27  being compressed between the spring supports  25  and  26  so as to bias them apart. The outer spring support  26  bears against an arcuate rib  28  defined on the inside of one of the walls of the box  1 . 
     The outer spring support  26  defines an aperture  29  through which an actuator shaft  30  extends. The actuator shaft  30  extends through a spring housing  31  defining a flange  32  which is mounted on the end wall of the box  1  by bolts  33 . A spring  34  is arranged around the shaft  30  between a sleeve  35  which abuts the spring housing  31  and a circlip  36  and circlip cover  37  which are fixed in position along the length of the shaft  30 . The spring  36  thus biases the shaft  30  into the box  1 . The end of the shaft  30  inside the box  1  extends through a bore in the lever support  20  and is retained against withdrawal from that bore by a circlip  38 . Appropriate O-ring and bellow seals are provided around the shafts  8 ,  10  and  30  to ensure that the circuit breaker  12  is located within a sealed enclosure. 
     Referring to FIGS. 2 and 3, it will be seen that the circuit breaker assembly  12  supports a cam follower in the form of a plunger  39  which faces a recess  40  defined in the actuator cam  16 . For the purposes of illustration the plunger  39  is shown spaced from the actuator cam but in practice the plunger will be biased towards the right in FIG. 3 so as to bear against the cam. In FIGS. 2 and 3, the components are shown in the positions they adopt when a ring  41  attached to the shaft  30  has been connected to a rope that has been appropriately tensioned to hold the shaft  30  and the lever support  20  in an intermediate position. In that intermediate position. The W-shaped lever  21  is symmetrical about a plane through the axis of the pins  18 . With the lever  21  in that position, the actuator cam  16  can be rotated in either direction without the movement of the lower pin  18  (in FIG. 3) being obstructed. If the rope tension is increased however the shaft  30  is displaced to the right. As a result the lever support  20  is also displaced to the right, carrying with it the pin  22  and the lever  21 . Such a displacement is shown in FIG.  4 . The side of the lever  21  remote from the actuator cam bears against a vertically extending rib  42  moulded into the wall of the box  1 . The rib  42  acts as a cam against which the lever  21  bears and as a result as the pin  22  moves to the right the lever  21  is turned around the pin  22  in a clockwise direction until it bears against the adjacent pin  18 . If the shaft  30  is moved further to the right than the position shown in FIG. 4 the lever  21  forces the pin  18  to the right, causing the actuator cam  16  to rotate in the anticlockwise direction in FIG.  4 . As a result the plunger  39  is pushed into the body of the circuit breaker  12 , switching the contacts within the circuit breaker  12   
     If the tension of the rope controlling the position of the shaft  30  reduces, the shaft  30  will move to the left in FIG.  3 . As a result the lever  21  will pivot in the anticlockwise direction as shown in FIG. 5 until it bears on the pin  18 . Further relaxation of the tension applied to the shaft  30  will cause further rotation of the lever  21 , forcing the pin  18  to the left in FIG.  5  and the consequential clockwise rotation of the actuator cam  16 . This is turn once again causes the plunger  39  to be pushed into the body of the circuit breaker  12 . 
     Once the actuator cam  16  has been displaced from the position shown in FIG. 3, the spring  27  and the inner and outer spring supports  25  and  26  cause the actuator cam  16  to move rapidly with a snap-action. This can best be appreciated by reference to FIGS. 17 to  20 . 
     FIGS. 17 and 18 are respectively plan and sectional views through the end of the box  1  which receives the outer spring support  26 . These Figures show the vertically extending rib  28  which is of semi-circular section and extends above and below an opening in the box through which the shaft  30  extends. In addition, an arcuate upstanding rib  43  is formed in the base of the box, the rib  43  retaining a lower portion  44  of the outer spring support  26  as best seen from FIG.  2 . The outer spring support  26  is thus rotatable along an arcuate path defined between the rib  28  and the rib  43 . 
     Referring to FIGS. 19 and 20, the outer lines of the actuator cam  16 , inner spring support  25  and outer sprint support  26  are shown in the configuration corresponding to FIG. 2 (FIG. 19) and the configuration corresponding to displacement of the actuator cam as a result of the shaft  30  being pulled out of the box  1  (an even more extreme condition than that illustrated in FIG.  4 ). The point  45  represents the fixed axis about which the actuator cam  16  is rotatable. The point  46  represents the position of the axis about which the outer spring support  26  can turn, and the point  47  represents the position of the axis about which the inner spring support  25  can turn relative to the actuator cam  16 . In the relative position shown in FIG. 19, the points  45 ,  46  and  47  are aligned. Hence the spring force tending to push the spring supports  25  and  26  apart does not apply any torque to the actuator cam  16 . As soon as the actuator cam  16  is displaced from the position shown in FIG. 19 however the point  47  is no longer aligned with the points  45  and  46  and as a result the lever supports  25  and  26  will move apart, thereby causing the actuator cam  16  to rotate away from its initial position as represented in FIG.  19 . The required snap-action is thus obtained. 
     Referring to FIGS. 4 and 5, it will be seen that once the lever  21  has been displaced from the position shown in FIG. 3, one or other of the two arms  21   b  defined by the lever  21  extends across the arcuate path which must be followed by the adjacent pin  18  if the actuator cam  16  is to be returned to the position shown in FIG.  3 . Accordingly if for example the rope controlling the axial position of the shaft  30  is severed and the shaft therefore moves to the left in FIG. 2, the lever  21  will push the actuator cam  16  in the clockwise direction and will prevent the return of the actuator camn  16  to the position shown in FIG. 2 until the lever  21  has been returned to its starting position as shown in FIG.  2 . Thus any equipment energised via the circuit breaker  12  will be disabled when the rope is severed and cannot be re-enabled until the shaft  30  has been returned to the position shown in FIG.  3 . Once the shaft  30  has been returned to the position shown in FIG. 3, an operator can simply rotate the reset lever  9  to thereby rotate the lid cam  19 . The lid cam is engaged by the pins  18  and accordingly rotation of that cam also causes rotation of the actuator cam  16 . 
     The position of the lever support  20  can be inspected through the lens  6  and to make this easier the lever support  20  may support an appropriate pattern  48  on a surface extending beneath the lens  6 . Therefore the condition of the circuit breaker can be inspected readily. 
     The stop button  11  may be depressed to move the actuator cam  16  from the position shown in FIG.  3 . The stop button shaft  10  has a pointed tip  49  (FIG. 2) which is located immediately above a ramp  50  defined in the outer spring support  26 . Pushing down on the button  11  drives the pin  10  against the ramp  50 , causing the outer spring support  26  to turn about the vertical rib  28 . As soon as a turning movement has been initiated the snap action mechanism ensures a rapid and substantial rotation of the actuator cam  16 . 
     In the embodiment of FIGS. 1 to  27 , the cam is rotated in one direction when the tension in the rope exceeds a predetermined limit and is rotated in the opposite direction when the tension in the rope is less than a predetermined limit. Alternative arrangements are possible however and one such alternative arrangement will now be described with reference to FIGS. 28 to  38 . 
     Referring to FIG. 28, it will be noted that this embodiment bears striking resemblances to the embodiment of FIGS. 1 to  27 . In particular, the illustrated rope switch comprises a casing  51  defining a cam  52  against which a lever  53  bears. The lever is pivotally mounted on a pin extending downwards from a lever support  54  which is mounted on one end of a shaft  55 . The lever support  54  is mounted above a cam  56  from which two pins  57  extend. An outer spring support  58  bears against and can rotate about a cam  59  defined by an inside wall of the casing. The outer spring support  58  receives an inner spring support  60  which engages in a recess in the cam  56 . The inner spring support  60  is identical in shape and function to that illustrated in FIG. 14, but only portions of it are visible in FIG. 28 as it is largely covered by the outer spring support  58  and the lever support  54 . A spring (not shown) biases supports  58  and  60  apart. 
     In the case of the embodiment of FIGS. 1 to  27 , if the shaft  30  is displaced in either direction from the position shown in FIG.  28 . the cam is caused to rotate in the corresponding direction so as to actuate the switch into an OFF condition. In the case of the embodiments of FIGS. 28 to  38  however regardless of the direction of displacement of the shaft  55  the cam  56  will always rotate in the same direction, that is the clockwise direction as shown in FIG.  28 . 
     If the shaft  55  is displaced to the right in FIG. 28, the lever  53  will be caused to rotate in an anticlockwise direction as a result of engagement between a recess  53   a  defined by the lever  53  and with the cam  52 . 
     An arm  3   b  defined by the lever  53  will engage the uppermost pin  5 , pushing the cam  56  in the clockwise direction. A very small displacement of the cam  56  will cause the over centre mechanism defined by the interengagement between the inner and outer spring supports and the cam  56  to apply a clockwise torque to the cam  56  which will as a result rapidly rotate to a contacts OFF position. 
     If the shaft  55  is displaced to the left in FIG.  28 . an abutment surface  61  will bear against a surface  62  defined by the outer spring support  58 . As a result the outer spring support will rotate in an anticlockwise direction and the inner spring support  60  will rotate with it, causing thereby a clockwise rotation of the cam  56 . Again, as soon as a displacement of the cam  56  has been initiated the over centre mechanism will rapidly rotate the cam to a contacts OFF position. 
     Thus if a rope attached to the switch becomes too slack or too tight the switch will automatically assume a safe position. In an emergency, the switch can be turned off by pressing against a button (not shown) similar to the button  11  of the embodiment of FIGS. 1 to  27 . Pressing the button drives a pointed shaft (not shown) into contact with a ramp  63  defined in an upper portion of the outer spring support  58 . This causes the outer spring support to turn in an anticlockwise direction, again forcing the cam  56  to turn in a clockwise direction towards a contacts OFF position. 
     Although the components of the embodiment illustrated in figs. 28 to  38  have not been described in such great detail as those of the embodiment of FIG. 1 to  27 , it is believed that the description provided is sufficient given the similarities between the method of the two embodiments.