The present invention relates to switches and, more particularly to electrical switches with a safety mechanism against inadvertent actuation.

Switches are essential for operation of many electrical devices or appliances. In many such electrical devices, for example, power tools especially power cutting tools, inadvertent actuation of the device can be dangerous. Therefore, it is desirable to provide electrical switches with safety means to mitigate risks of inadvertent actuation.

JP 57 007029 discloses a switch having a safety mechanism that requires a user to press a lever before the lever can be switched between first and second positions.

JP 2005-112163 discloses a selector switch for a motor car that allows users to select between various electrical devices in the vehicle. The selector switch includes a piston that is depressed and then turned to positions to activate different electrical devices.

US3604868 discloses a safety switch for preventing inadvertent activation of an electrical device. The lever of the switch can be locked to prevent operation and unlocked to allow operation. Locking and unlocking of the lever is achieved by pushing the lever into the device and by rotating the lever through 90 degrees. When the switch is locked the lever is locked in position and when unlocked, the lever can be freely switched between the on and off positions.

DE 10 2005 053955 discloses a switch for activating a sunroof in a motor vehicle. The switch is a rocker switch that has a locking mechanism to prevent tilting of the switch unless the switch is depressed.

According to the present invention, there is provided an electrical switch in accordance with claim 1.

A switch requiring a two-stage actuation movement alleviates the risks of inadvertent actuation.

A one-way barrier means provides a simple means to devise a switch which requires a two-stage movement to actuate the switch. In addition, its non-symmetrical barrier resistance means only a single stage movement is required to deactivate the switch.

Since the actuation member will be urged out of engagement from the guide means at the off-position, a user has to move the actuation member along a first direction to engage with the guide means, and then along a second, different, direction to move the actuation member into the on-position. This requires a clear intention of the user and mitigates the risks of inadvertent actuation.

A switch with a guide means which requires a user to perform a two-stage movement in two different directions in order to move an actuator member into the on-state would alleviate the risks of inadvertent actuation since a clear actuation intention of a user is required before a switch is actuated.

Preferred embodiments of the present invention will be explained in further detail below by way of example and with reference to the accompanying drawings, in which:-

• Figure 1 shows a first side view of a switch comprising a safety mechanism of this invention,
• Figure 2 is a second side view of the switch of Figure 1 from another, opposite, side of Figure 1,
• Figure 3 shows an end view of the switch of Figure 1,
• Figure 4 is a longitudinal cross-sectional view along the section line A-A' of Figure 3 of a first embodiment of the switch of Figure 1 with the actuation member in the off-position,
• Figure 4A shows the lower portion of the switch housing of Figure 4, with the actuation member, the upper housing portion removed and the switching mechanism,
• Figure 4B is a transverse cross-sectional view of the lower housing portion of Figure 4A along the line B-B',
• Figure 4C shows the switch of Figure 4A, with the actuation member at the on-position;
• Figure 5 shows the longitudinal cross-sectional view of a second embodiment of the switch of Figure 1 in the off-position along the section line A-A' of Figure 3,
• Figure 5A shows the lower portion of the switch housing of Figure 5, with the actuation member, the upper housing portion and the switching mechanism removed,
• Figure 5B is a transverse cross-sectional view of the lower housing portion of Figure 5A along the line C-C',
• Figure 5C shows the switch of Figure 5A with the actuation member at the on-position;
• Figures 6A and 6B show respectively a first and second side view of the actuation member of the embodiments of Figures 4 and 5;
• Figure 6C is a longitudinal cross-sectional view of the actuation member of the switch of Figure 1 along the line D-D';

Referring to Figures 1 to 4C, a first exemplary embodiment of a switch 100 of this invention comprising a switching mechanism, an actuation mechanism and a safety mechanism installed on an insulated housing is shown.

The switching mechanism comprises a first contact terminal 120 and a second contact terminal 122 which are connectable by a moveable conductive member 124. When the first and second contact terminals are connected by the conductive member, the switching mechanism will be in its "make" condition and a closed circuit is formed so that electrical power can flow from a power source to a load, corresponding to an "on" state of the switch. On the other hand, when the conduction path between the first and second contact terminals is broken, the switching mechanism will be in its "break" condition, thereby isolating a load from a power source, and correspond to the "off" state of the switch. The first and second contact terminals are fixedly mounted on the bottom portion of the housing and are connected respectively to a first 130 and a second 132 switch terminal provided for making external connection.

The conductive member 124 comprises a bridge-like member permanently connected electrically to the first contact terminal and having a length covering at least the span between the first and second contact terminals. The conductive member may be made of steel, for example, stainless steel, a rigid copper alloy, or other rigid alloys to give good rigidity and durability for repeated operations. One end of the conductive member is moveable between a make position when it is in electrical contact with the second terminal and a break position when it is lifted clear of the second contact terminal, thereby insulated from the second contact terminal. By moving the conductive member between the contact and no-contact positions, the switching mechanism will be toggled between the make- and break-conditions respectively.

As shown more particularly in Figures 4 & 4C, the conductive member is arranged as a conductive cantilever extending from the first contact terminal as a base and supported on a conductive fulcrum 126 at a location intermediate its longitudinal ends. The conductive fulcrum is an electrical extension of the first contact terminal and comprises a transversely extending knife or sharp edge which is elevated from a base level to permit pivotal movement of the conductive member about the conductive fulcrum. The knife edge is adapted to ensure good electrical contact with the conductive member, as well as to facilitate more efficient toggling of the conductive member during switching operations. The end of the conductive member distal from the cantilever base comprises a contact head 128 which is moveable between the contact (Figure 4C) and no-contact (Figure 4) positions when driven by an actuation member as explained below. The lower side of the conductive fulcrum is permanently connected, again electrically, to the first contact terminal so that the conductive member will always be in electrical contact with the first terminal, irrespective of the position of the free end. When the switching mechanism is in its off-state, as shown in Figure 4, the contact head 128 of the conductive member will be lifted clear of the second contact terminal, leaving an air-gap sufficient to isolate the second terminal from the bridge member. Alternatively, when the switching mechanism is in its on-state, the contact head will be pushed into compressive contact to form a contact engagement with the second contact terminal to complete electrical connection between the first and second contact terminals.

The switching mechanism can be switched or toggled between the on- and off- states by operation of an actuation mechanism, which comprises an actuation member 140 moveably mounted on the housing. More specifically, the operation state of the switching mechanism is toggled in response to actuation and de-actuation movements of the actuation member 140 relative to the housing.

The housing is made of hard plastics and comprises an upper housing portion 160 and a lower housing portion 162, which are snap fitted together by means of a snap-fit arrangement. As shown in Figure 4B, the snap-fit arrangement comprises a pair of tapered protruding wings 156 formed on opposite external walls of the lower housing. The pair of wings is adapted for detachable engagement with a pair of corresponding windows 158 formed on the upper housing. The switching mechanism is mounted on the bottom of the lower housing portion with the switch terminals 130, 132 protruding downwardly from the floor of the lower housing portion.

The actuation member 140 is arranged to drive the switching mechanism to operate between on- and off-states. As such, the actuation member is required to drive the conductive bridge to move or toggle between make- and break-positions. As shown more particularly in Figures 6A to 6C, the actuation member 140 comprises an actuation lever 142 having an elongate body which defines at its lower end an axially extending bore 144 for receiving the actuation tongue 146. The dimension of the bore is adapted to permit slidable movement of the actuation tongue axially along the bore and relative to the elongate body so as to vary the length or extent of the actuation tongue protruding from the elongate body under spring urge. For this purpose, the length of the bore is shorter than that of the actuation tongue while its cross-sectional dimension is slightly larger that of the actuation tongue. A helical spring which is substantially coaxial with the bore is disposed intermediate the actuation tongue and the top end of the bore to provide spring urge to urge the actuation tongue to protrude away from the elongate body. To provide a better and guided mechanical coupling between the helical spring and the actuation tongue, the actuation tongue further comprises a thinner neck portion which protrudes inside the helical spring. The upper end of the elongate body distal from the bore is adapted and dimensioned to provide an operation interface for a user.

A partially spherical portion 150 is formed on the actuation lever immediate the upper and lower portions of the elongate body. This partially spherical portion 150 is adapted to be received within a neck portion 164 of the housing formed on the top part of the upper housing. Upon coupling with a sealing ring 170 or a sealing collar disposed on the inner periphery of the neck portion, this partially spherical portion enhances the water-tightness of the switch while permitting pivotal movement of the actuation lever 142 relative to the switch housing.

To facilitate guided pivotal movements of the actuation member 140 relative to the switch housing, a pair of transversal protrusions 152 is formed diametrically on the partial spherical portion, as depicted more particularly in Figure 6B. This pair of transversal protrusions 152 is arranged to cooperate with a pair of axially extending channels formed inside the neck portion (no shown) so as to restrict the transversal protrusions 152 to be slidable axially along the pair of channels while making pivotal or swivel movements to move between the on- and off positions. Another pair of diametrically extending guide protrusions 154 is formed on the lower portion of the actuation lever. This pair of guide protrusions is adapted to engage with a guide means to facilitate guided sliding movements of the actuation member along a guide means formed on the housing as explained below. The axes of the two pairs of protrusions 152 154 formed on the actuation lever are parallel to each other and both are orthogonal to the longitudinal axis x-x' of the actuation lever. The guide channels are parallel to the longitudinal axis x-x'.

A guide track 166 is formed on the housing as a form of guide means to facilitate guided pivotal movement of the actuation member along a guided movement path to operate the switch. The guide track comprises a pair of arcuate recesses formed, for example, by moulding on opposite walls on the upper portion of the housing (as shown more clearly in Figures 4A and 4B) for cooperative engagement with the pair of guide protrusions 154 formed on the lower portion of the actuation lever. The guide track, defined by an upper flange and a lower flange on a side wall of the housing, defines a movement path along which the actuation lever is guided to move between a first position when the switching mechanism is actuated, as depicted in Figure 4C, and a second position when the switching mechanism is de-actuated, as depicted in Figure 4.

To provide safety measures to mitigate the risks of inadvertent actuation of the switch, a two-stage actuation movement is required to actuate the switch. An exemplary implementation of such safety measures thorough cooperative operation of the actuation member and the guide track is described below with reference to Figures 4-4C.

When the switch is at its on-state as depicted in Figure 4C, the actuation member will be pivoted with the actuation tongue proximal the contact head 128. At this switching state, the pair of transversal protrusions on the upper part of the actuation lever is received by the pair of channels formed on the neck portion of the switch housing, the pair of guide protrusions 154 is in coupling engagement with the guide track, and the contact head 128 is firmly pressed into electrical contact engagement with the second contact terminal by the actuation tongue. To ensure a good electrical contact, the spring bias is devised so that it is sufficiently strong to bring about a firm compressive contact between the contact head 128 and the second contact terminal 122. It will be appreciated that when the when the actuation member is at this state, the spring urge due to the helical spring will tend to push the elongate body axially upwards. However, due to coupling engagement between the pair of transversal protrusions 154 and the guide track 166, the upper portion of the guide track, or more specifically the upper flange, prevents upward movement of the elongate body. As a result, the spring urge operates to urge the actuation tongue to press downwards to close the contact head and the second terminal.

On the other hand, when the switch is at its off-state as depicted in Figure 4, the actuation tongue is moved away from the contact head 128 and is now adjacent the first contact terminal 120. At this state, the pair of transversal protrusions on the upper part of the actuation lever is still received by the pair of channels formed on the neck portion, but the pair of guide protrusions 154 is now out of engagement with the guide track as shown in Figure 4A. Due to the spring urge on the actuation tongue 146, the actuation tongue will gradually sweep across the conductive member when it moves from the on-state to the off-state and will maintain contact with the conductive member throughout the sweeping. When at this off-state, the actuation tongue acts on the end of the conductive member, which is distal from the contact head 128, thereby lifting the contact head 128 out of contact with the second terminal 122. Furthermore, since the transversal protrusions 154 are no longer in engagement with the guide track, the spring urge due to the helical spring will now push the elongate body axially upwards. The end of the axial channels on the next portion of the housing will then limit the maximum upward displacement of the elongate body.

The guide track 166 is devised to provide a guided movement path for the actuation member to pivotally movable between the on- and off states. When moving between the on- and off-states, the actuation tongue will gradually retract axially when it approaches the conductive fulcrum, and then extend to depress the contact head 128 or the distal end of the conductive member 124 after it has passed the knife edge of the fulcrum. More particularly, the actuation tongue is fully extended when it is at the stable on- or off states.

As shown more particularly in Figure 4A, the guide track is discontinued at one end corresponding to the end at which the actuation member has completed its journey to lift the contact head 128 clear of the second contact terminal. At this location of discontinuity, the pair of guide protrusions 154 on the actuation member is no longer engaged by the guide track, but is released and is slidably movable along its longitudinal axis and along a pair of longitudinal recesses formed on the neck portion of the upper housing. Since the actuation tongue is now resting on the conductive member, spring bias on the actuation tongue will operate to push the actuation member axially upwards and abruptly away from the locus of the guide track. Once the actuation member has reached this state, it will be prevented from moving back to the on-state by a simple pivotal movement in reversal, since the pair of guide protrusions is now blocked by a portion of the housing which defines the guide track, in particular the entry to the guide track.

To turn off the switch, a user only needs to move the actuation member pivotally, in order to drive the actuation member from the state of Figure 4C into the state of Figure 4. Upon reaching the state of Figure 4, the actuation member will be out of engagement with the guide track.

To move the actuation member from the off- position to the on- position, it will be necessary to first move the actuation member axially downwards towards the entry of the guide track, or the location of discontinuity of the guide track, by depressing the actuation lever relative to the actuation tongue so that the pair of transversal protrusions is aligned with the guide track entry. After the pair of guide protrusions has been aligned with the guide track entry, the next step will be to pivotally move the actuation member along the guide track and then into the on-position to actuate the switching mechanism as described above.

Stated simply, when moving the actuation member from the off- state to the on- state, a user will have to move the actuation member firstly in a first, axial, direction towards the location of discontinuity in order to gain entry into engagement with a guide means, and then a second movement along the guide means to bring the actuation member fully into the on-state. On the other hand, a single step action is required to turn the switch off. Thus, by devising the guide track so that a discontinuity, especially an abrupt discontinuity, is formed at a location corresponding to the off-location of the switching mechanism, so that the actuation member is driven out of engagement from a guiding means, safety measures are provided.

In the second embodiment as shown in Figures 5 to 5C, the components of the switch 200 are substantially identical to that of the first embodiment shown above except with a modified guide track on the housing. Parts of the first embodiment are incorporated herein by reference, and parts which are common or equivalent to the parts of the first embodiment are designated by the same numerals increased by 100.

In this embodiment, the guide track 266 is also discontinued at a location corresponding to the position at which the actuation lever is in the off- position. Differing from the first embodiment, the guide tracks 266 is joined by an extension guide track, which extends axially upwards and joins the guide track 266 with an abrupt junction at the discontinuity as an upward extension of the guide track. As a result of the extension track, a user will have to depress the actuation member in an axial direction to bring the guide protrusions 254 into alignment with the guide track 266 and gain entry into the guide track 266, and then abruptly change the direction of movement to move along the guide track in order to bring the actuation member into the on- state.