The present invention relates to a lockable switch mechanism
which may be used in for example a machine guard to prevent the opening of a door
of the machine guard until predetermined conditions have been established.
A lockable switch mechanism is described in
US Patent No. 5,777,284
. That mechanism comprises a switch plunger which is mounted in a housing
and is displaceable relative to the housing along a predetermined axis between a
first unlocked position and a second locked position. A locking mechanism is provided
for locking the switch plunger in the second position and the switch plunger actuates
a switch mechanism as a result of movement of the switch plunger between the first
and second positions. The locking mechanism comprises two pivotally mounted latches
which are normally biased against the switch plunger so as to engage behind an axially
facing surface defined by the switch plunger when the plunger has been moved to
the second position. The latches can only be withdrawn so as to permit axial displacement
of the switch plunger if a plate extending transversely of the switch plunger is
displaced to a latch release position. Tzhe latch releasing plate is driven by a
lever mechanism the position of which is controlled by a solenoid arranged to one
side of the switch mechanism housing. This arrangement works well but is relatively
bulky and complex.
Documents
US-A-5 062 668
and
DE 2 040 046 A
disclose lockable switch mechanisms according to the preamble of claim
1.
It is an object of the present invention to provide an
improved lockable switch mechanism.
According to the present invention, there is provided a
lockable switch mechanism according to claim 1.
In contrast to the mechanism described in
US Patent 5,777,284
, the mechanism in accordance with the present invention relies upon a
first locking member which does not prevent axial displacement of the switch plunger
unless a second locking member is moved into a locked position. This means that
rather than providing a relatively complex mechanism to release a latch a relatively
simple and compact mechanism can be provided which is positionable either so as
to maintain the first locking member in a position in which axial displacement of
the switch plunger is not permitted or in a position in which the first locking
member can be simply displaced by axial movement of the switch plunger. All of the
necessary components can be arranged along a common axis with the switch plunger
axis in a compact and reliable assembly.
Preferably, the or each first locking member comprises
a locking pin extending transversely relative to the axis of displacement of the
switch plunger, the locking pin being spring biased towards the switch plunger in
a direction perpendicular to the switch plunger axis. Two locking pins may be provided
on opposite sides of the switch plunger. The locking pins may be mounted in a housing
assembly defining an aperture through which the switch plunger extends, the locking
pins being spring-biased towards each other from opposite sides of the aperture
by springs supported in the housing assembly. The housing assembly may comprise
a frame which receive the locking pins and springs and a cover plate which retains
the locking pins and springs within the assembly.
Preferably, the or each second locking member comprises
a locking arm which is displaceable in a direction parallel to the switch plunger
axis and, when in the locked position, extends on the side of the first locking
member remote from the switch plunger to prevent displacement of the first locking
member in a direction away from the switch plunger axis.
The profile may be defined by an annular shoulder extending
around the switch plunger. That shoulder may be tapered so as to readily lift the
locking pins away from the switch plunger if the mechanism is not in the locked
condition.
Two locking arms may be provided to lock respective locking
pins against displacement relative to the switch plunger axis. The locking arms
may extend from one end of a solenoid plunger which is arranged at one end of the
switch plunger and is displaceable along the switch plunger axis by a solenoid winding
within a solenoid housing. The solenoid may be arranged so that, when energised,
the locking arms are displaced from the locked position, or alternatively may be
arranged so that, when energised, the locking arms are displaced to the locked position.
A compression spring may be arranged between the switch
and solenoid plungers to bias the plungers apart, and a compression spring may also
be arranged between the solenoid plunger and the solenoid housing to bias the solenoid
plunger towards the switch plunger. The switch plunger may be axially displaced
by rotation of a cam from a datum position by insertion of an actuator into the
mechanism, withdrawal of the actuator being prevented unless the cam is rotated
back to the datum position, and such rotation being prevented by the locking mechanism
if the or each second locking member is in the locked position.
An embodiment of the present invention will now be described,
by way of example, with reference to the accompanying drawings, in which:
- Figure 1 is a schematic cut-away view of a locking switch mechanism in accordance
with the present invention with the switch in an unlocked condition;
- Figure 2 illustrates the mechanism of Figure 1 after the insertion of an actuator
to switch the mechanism and locking of the mechanism;
- Figure 3 is a partial perspective view of some of the components of the mechanism
of Figure 1 and 2 showing components in the positions adopted when the switch is
unlocked as shown in Figure 1;
- Figure 4 is a side view of the components of Figure 3;
- Figure 5 is a partial perspective view of the components shown in Figures 3and
4 with those components in the switch locked position corresponding to Figure 2;
- Figure 6 is a side view of the components shown in Figure 5;
- Figure 7 shows the mechanism of Figures 1 to 6 after insertion of an actuator
but before locking of the mechanism;
- Figure 8 illustrates the application of a force to withdraw the actuator when
the mechanism is locked;
- Figure 9 illustrates the mechanism after unlocking of the mechanism and partial
withdrawal of the actuator;
- Figure 10 is a perspective view of assembled components of the locking mechanism
and Figure 11 is an exploded view of the components making up the assembly of Figure
10;
- Figure 12 is a sectional view through a solenoid plunger incorporated in the
mechanism of Figures 1 to 11;
- Figure 13 is a perspective view of a solenoid locking fork incorporated in the
mechanism of Figures 1 to 12;
- Figure 14 is a sectional view through the solenoid locking fork of Figure 13;
- Figure 15 is a schematic cut-away view of a second locking switch mechanism
in accordance with the present invention with the switch in an unlocked condition;
- Figure 16 illustrates the mechanism of Figure 15 after the insertion of an actuator
and locking of the mechanism; and
- Figure 17 is a perspective view of a locking fork incorporated in the mechanism
of Figures 15 and 16.
Referring to Figure 1, the illustrated lockable switch
mechanism comprises a housing 1 in which a plunger 2 is slidable and which supports
a head assembly 3 supporting a rotatable cam 4, the cam 4 being rotatable about
a pin 5. The plunger 2 comprises a metal core supporting an outer casing 6 which
is slidably received in a sealing cap 7. The plunger 2 is symmetrical about its
longitudinal axis and is slidable relative to the housing 1 along that axis.
The end of the plunger 2 remote from the cam 4 is received
in a bore 8, a compression spring 9 being located within the bore 8 so as to bias
the plunger 2 in the direction indicated by arrow 10. The bore 8 is formed in the
end of a solenoid plunger 11 which is received within a solenoid housing 12. Energisation
of a solenoid winding (not shown) in the solenoid housing 12 drives the solenoid
plunger 11 to the right in Figure 1. Denergisation of the solenoid results in the
solenoid plunger 11 being moved to the left in Figure 1 by a compression spring
13 (Figure 2) which is located between the solenoid housing 12 and a locking fork
14 which is engaged in a groove extending around the end of the solenoid plunger
11 in which the bore 8 is formed.
Two locking pins 15 are positioned on either side of the
plunger 2, the locking pins 15 being biased by springs 16 against the plunger 2.
The locking pins 15 and springs 16 are retained within a housing assembly made up
from a frame 17 and a cover plate 18. It will be seen that with the plunger 2 in
the position shown in Figure 1 the pins 15 are held at a distance from the axis
of the plunger 2 such that they obstruct the passage of arms 19 supported by the
locking fork 14 in the direction of the arrow 10.
Figure 2 shows the assembly of Figure 1 after the insertion
of an actuator 20 into the head assembly 3 so as to cause rotation of the cam 4.
Such rotation of the cam 4 enables the plunger 2 to move towards the pin 5. As a
result a profile 21 in the form of an annular shoulder on the plunger 2 is moved
to the left of the locking pins 15. The locking pins 15 are biased towards each
other so as to remain in contact with the plunger 2, thereby enabling the arms 19
of the locking fork 14 to pass the locking pins 15.
The actuator 20 and cam 4 are shaped such that insertion
of the actuator into the head assembly 3 causes the cam to rotate from a datum position,
that is the position of the cam 4 as shown in Figure 1. In known manner, the actuator
defines projections (not shown) which engage in recesses defined by the cam 4 (as
shown in Figure 2) so that once the cam 4 has been rotated from the datum position
the actuator 20 cannot be withdrawn from the head assembly 3 unless the cam 4 has
been rotated back to the datum position. An actuator and cam mechanism of this general
type is described in the abovementioned
US Patent No. 5,777,284
.
Figures 3 and 4 show the assembly in the unlocked condition.
In Figure 3, the solenoid plunger 11 has been moved to the position it assumes when
the solenoid is energised and the plunger 2 is in the position in which it is displaced
by the cam 4 as far as possible towards the solenoid housing 12. As a result the
spacing between the pins 15 is such that even if the solenoid is then deenergised
the arms 19 cannot move past the pins 15. The pins 15 therefore impose no restraint
on the axial displacement of the plunger 2. In contrast, as shown in Figures 5 and
6, if the cam 4 is then rotated to displace the plunger 2 so that the pins 15 can
drop down the profiled shoulder 21 defined by the plunger 2, the springs 16 urge
the locking pins 15 towards each other so as to engage behind the shoulder 21. Deenergisation
of the solenoid then results in the arms 19 being extended past the pins 15, restraining
the pins 15 against movement away from each other. Any attempt therefore to drive
the plunger 2 towards the solenoid housing 12 will be resisted as a result of the
pins 15 jamming between the profile 21 and the arms 19.
Figure 7 shows the assembly after displacement of the plunger
2 towards the cam pin 5. Unless the solenoid is energised, the arms 19 of the locking
fork 14 will engage around the pins 15 as shown in Figures 5 and 6. In the configuration
shown in Figure 7 however the solenoid has been energised, displacing the arms 19
to the right. There is then nothing to stop the locking pins 15 being moved apart
against the biasing force provided by the springs 16. Thus if the actuator 20 was
to be withdrawn from the head assembly 3 this would result in the displacement of
the plunger 2 to the right in Figure 7, such movement being permitted as the tapered
surface of the shoulder 21 would push against and force apart the two locking pins
15.
Referring to Figure 8, this shows the assembly if an attempt
is made to withdraw the actuator 21 when the assembly is in the configuration shown
in Figure 2, that is with the pins 15 locked in position by the arms 19. Pulling
on the actuator 21 causes the cam 4 to rotate in the clockwise direction in Figure
8, thereby applying an axial force to the plunger 2 and causing the plunger to move
in the direction indicated by arrow 22. Such displacement is however resisted by
the locking pins 15 which bear against the profile 21. The arms 19 prevent the pins
15 moving apart and thus further axial displacement of the plunger 2 is prevented.
In contrast, if the solenoid is energised so as to displace
the arms 19 to the position shown in Figure 7, and the actuator 20 is pulled out
of the head assembly 3, rotation of the cam 4 is not resisted by contact between
the pins 15 and the profile 21 and as a result the plunger 2 can be displaced in
the direction of arrow 23 as shown in Figure 9.
Figure 10 illustrates the housing assembly for the locking
pins 15 and springs 16 and Figure 11 shows the components of the assembly of Figure
10 in exploded form.
Figure 12 is a sectional view through the solenoid plunger
11 showing the bore 8 and the groove extending around the end of the plunger 11
in which the bore 8 is provided, that groove being engaged by the locking fork 14
shown in Figures 13 and 14.
Referring to Figures 13 and 14, the locking fork which
supports the locking arms 19 has a C-shaped body defining an inwardly projecting
edge 24, that edge being received in the slot formed around the end of the solenoid
plunger 11 shown in Figure 12. The inner faces of the fork arms 19 are tapered such
that, on energisation of the solenoid, the arms 19 are released easily from engagement
with the pins 15.
Given the structure of the plunger and locking fork combination,
it is a relatively easy matter to assembly the combination. In an alternative arrangement
it would of course be possible to fabricate the plunger 11 and the locking fork
14 including the locking fork arms 19 as a single piece component.
In the embodiment of Figures 1 to 14, energisation of the
solenoid is necessary to release the locking mechanism. The solenoid is not energised
accept when it is desired to release the locking mechanism. In the event of a power
failure when the mechanism is locked, it is not possible to unlock the mechanism
and therefore it is not possible to release the actuator from the cam. The actuator
can only be released after the supply of power is restored. In some applications,
this can be a significant disadvantage. Figures 15 to 17 illustrate a second embodiment
of the invention in which this disadvantage is avoided by relying upon a solenoid
which is energised when the switch is locked and de-energised when the switch locking
mechanism is released.
Referring to Figures 15 to 17, components of the second
embodiment which are equivalent to components of the first embodiment shown in Figures
1 to 14 are identified by the same reference numerals. Thus, in the second embodiment
a plunger 2 is biased against a cam 4 by a compression spring 9. The plunger 2 is
located between a pair of locking pins 15 which are biased against the sides of
the plunger 2 by springs 16. The plunger 2 defines a shoulder 21 behind which the
locking pins 15 engage when the plunger 2 is displaced towards a pin 5 about which
the cam rotates. Figure 15 shows the locking mechanism before insertion of an actuator
into the assembly so as to rotate the cam. In this configuration the locking pins
15 cannot engage behind the shoulder 21. Figure 16 shows the mechanism after displacement
of the plunger 2 as a result of rotation of the cam 4. In this configuration the
pins 15 are biased inwards by the springs 16 so as to engage behind the shoulder
21. Figure 16 shows the locking pins 15 after displacement of a locking fork 14
so that locking arms 19 extend outside the locking pins 15, thereby preventing the
locking pins 15 from moving outwards. In the condition shown in Figure 16, the plunger
2 cannot therefore be moved to the right in Figure 16 as such movement would be
prevented by interengagement between the shoulder 21 and the locking pins 15.
The locking fork 14 is mounted on solenoid plunger 11 and
is biased towards the cam 4 by a compression spring 13. If the solenoid is de-energised,
the spring 13 ensures that the locking arms 19 are displaced away from the locking
pins 15. The mechanism is therefore unlocked in that axial movement of the plunger
2 is not obstructed. If the solenoid is energised, the plunger 11 is driven to the
right in Figure 16 such that, providing the plunger 2 is in the position shown in
Figure 16, the locking arms 19 can engage outside the locking pins 15, thereby locking
the mechanism.
With the arrangement illustrated in Figures 15 and 16,
the switch will remain locked only so long as the solenoid is energised. When it
is desired to unlock the mechanism, the solenoid is simply de-energised. With such
an arrangement it will be appreciated that, in the event of a power failure, the
mechanism is automatically unlocked. In some applications this is a significant
advantage. In contrast, with the mechanism illustrated in Figures 1 to 14, unlocking
of the mechanism requires energisation of the solenoid and therefore in the event
of a power failure it would not be possible to release the actuator 20 from the
cam 4.
Figure 17 illustrates the structure of the locking fork
14 of the embodiment of Figures 15 and 16 in greater detail. It will be noted that
the locking arms 19 are mounted on an L-shaped extension 25 of the locking fork
14, the locking fork 14 defining a C-shaped body defining an inwardly projecting
edge that is received in a slot formed around the end of the solenoid plunger 11.
