On-off switch with off position locking actuator

[0002] The present invention relates to an on-off switch for use in an electric power hand tool.

[0003] The operation of an electric power hand tool is usually controlled by an on-off switch. As power hand tools would inevitably be subject to impact during arduous handling, care should be taken not to cause the switch to be turned on unintentionally, which may otherwise result in an accident. Most existing switches used in this field are not sufficiently robust.

[0004] The invention seeks to mitigate or at least alleviate such a problem by providing an improved on-off switch of this type.

[0005] According to the invention, there is provided an on-off switch for use in an electric power hand tool, which switch comprises a body, a switching mechanism provided within the body, an operator supported by the body for movement between a first position to turn on the switching mechanism and a second position to turn off the switching mechanism, a first spring resiliently biasing the operator towards the second position, and a movable locking device resiliently biased by a second spring for locking the operator in the second position against accidental switching on of the hand tool, the operator and locking device including respective first and second metal parts for abutment with each other to lock the operator in the second position.

[0006] Preferably, the first metal part is provided internally of the operator for reinforcement.

[0007] More preferably, the first metal part has a shape corresponding to the shape of the operator.

[0008] In a preferred embodiment, the locking device includes an actuator movable in opposite first and second directions, being resiliently biased by the second spring in the first direction, for moving the second metal part in the first direction into the path of movement of the first metal part for blocking the movement of the operator from the second position and in the second direction away from the path of movement to allow the operator to move to the first position.

[0009] More preferably, the actuator is movable in opposite directions past a central position to reach a side position on either side of the central position, and is resiliently biased by the second spring towards the central position.

[0010] Further, more preferably, the actuator has opposite ends to facilitate movement by a person using the hand tool on either side of the switch.

[0011] It is preferred that the body include a third metal part which is located behind the second metal part for providing reinforced support for the second metal part when the second metal part is abutted by the first metal part.

[0012] Advantageously, the locking device is releasably connected to the body for use and is removable such that the remainder of the switch may be used independently without the locking device.

[0013] More specifically, the body includes a pair of opposed hooks for connecting the locking device to the body between them through a snap-fit action.

[0014] The invention also provides an electric power hand tool incorporating the on-off switch, in that the hand tool has a body including a handle at which the switch is located for use.

[0015] The power hand tool may be an electric saw incorporating a motor-driven circular saw blade.

[0016] The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which:

[0017] FIG. 1 is a cross-sectional side view of an embodiment of an on-off switch in accordance with the invention;

[0018] FIG. 2 is a cross-sectional top plan view of the switch of FIG. 1, taken along line II—II, with the switch being in a locked-off condition;

[0019] FIG. 3 is a cross-sectional top plan view of the switch of FIG. 1, taken along line III—III, with the switch being in the same condition as shown in FIG. 2;

[0020] FIG. 4 is a cross-sectional top plan view of the switch of FIG. 1, taken along line II—II, with the switch being in an unlocked condition;

[0021] FIG. 5 is a cross-sectional top plan view of the switch of FIG. 1, taken along line III—III, with switch being in the same condition as shown in FIG. 4; and

[0022] FIG. 6 is a cross-sectional side view of an electric power hand tool incorporating the switch of FIG. 1.

[0023] Referring to the drawings, there is shown an on-off switch 100 embodying the invention for use in an electric power hand tool such as a hand-held electric saw 10, which switch 100 comprises a plastic switch body 200 and a plastic operator in the form of a trigger 300 slidably connected thereto. The switch body 200 has a lower part 210 housing a known switching mechanism (not shown), and an upper part 220 formed internally with a horizontal linear slideway 222 of a generally uniform rectangular cross-section. The slideway 222 has an open front end 224 and a closed rear end 226. The switching mechanism is typically formed by two fixed contacts and a movable contact for movement by the trigger 300 to make and break electrical connection between the fixed contacts, thereby switching on and off the electric saw 10.

[0024] The trigger 300 has a body 310 and a rearwardly extending integral shaft 320. The trigger body 310 is insert-molded internally with a one-piece central metal plate 330 for reinforcement, which has a shape corresponding to (and smaller than) the shape of the body 310. The plate 330 has a front part 332 extending into the adjacent end of the shaft 320. This part 332 includes a small corner 334 that protrudes from the upper side of the shaft 320 as a rib-like abutment 334.

[0025] The shaft 320 has a generally uniform rectangular cross-section and fits slidably into the slideway 222. At the front end 224, the upper wall of the slideway 222 includes an inverted rectangular flat recess 228 for accommodating, inter alia, the abutment 334 of the shaft 320. A laterally extending metal bar 229 is located against the innermost end or side of the recess 228.

[0026] Inter-engageable snap-fitting means are provided between the outer surface of the trigger shaft 320 and the inner surface of the switch body slideway 222 such that, upon insertion, the shaft 320 engages internally the slideway 222 and cannot subsequently be removed. An internal compression coil spring 340 co-acts between the rearmost end of the shaft 320 and the rear end 226 of the slideway 222 for resiliently biassing the trigger 300 outwards. Under the action of the spring 340, the trigger 300, normally projects outwards and switches off the said switching mechanism. Upon pressing, the trigger 300 moves inward and switches on the switching mechanism for as long as the pressing force lasts.

[0027] The on-off switch 100 includes a locking device 400 for locking the switch 100 off against unintended or accidental switching on, by obstructing the inward movement of the trigger 300.

[0028] Upstanding from the upper part 220, the switch body 200 is integrally, includes a pair of confronting front and rear hooks 230 and 232 at opposite ends and a generally rectangular block 240 between them. The block 240 has, at its upper end, a transversely extending channel 242 having opposite restricted open ends 244. The portion of the upper wall of the body part 220 between the front hook 230 and the block 240 is void, thereby forming a vertical aperture 234 in communication with the recess 228 below.

[0029] The locking device 400 incorporates a elongate plastic actuator 410 which has opposite left and right ends 420 having an oval cross-section and an integral middle section 430. The middle section 430 has front and rear edges 432 and 434 and includes a downwardly facing rectangular recess 436. The recess 436 contains a metal bar 438 extending centrally across its opposite left and right sides and a compression coil spring 439 disposed on the bar 438. The spring 439 is fixed at mid-length centrally on the bar 438, but its opposite ends remain free to extend and retract.

[0030] The actuator 410 is supported to extend transversely atop the switch body 200 by having its middle section 430 snap-fitted between the hooks 230 and 232 and, more specifically, the front and rear section edges 432 and 434 retained by the hooks 230 and 232 respectively. The front side (edge) 432 of the middle section 430 extends downwards through the vertical aperture 234 to reach the recess 228 and includes a bottom hole 433 having a rectangular cross-section. The section recess 436 encloses the upper end of the block 240, with the bar 438 extending within the channel 242 and the spring 439 held captive between the channel ends 244.

[0031] Taking in the longitudinal direction of the actuator 410, the dimension of the recess 436 is greater than that of the block 240. This allows the actuator 410 to slide lengthwise in opposite directions, to a limited extent, relative to the switch body 200. The spring 439 acts symmetrically in opposite directions to resiliently bias the actuator 410 into a normal central position (FIG. 2). The actuator 410 is slidable in either opposite direction, against the action of the spring 439, into a respective side position (FIG. 4).

[0032] The locking device 400 includes a flat metal locking member 440, located immediately below the front side 432 of the actuator section 430 and contained within the recess 228. The locking member 440 extends parallel to the abutment 334 and perpendicular to the bar 229 inside the recess 228. The locking member 440 has an upstanding pin 442 which has a rectangular cross-section and is engaged with the bottom hole 433 of the section side 432 for lateral movement by the actuator 410.

[0033] In operation, while the actuator 410 stays normally in the central position (FIG. 2), the locking member 440 extends in line with and close between the abutment 334 and the bar 229 (FIG. 3), thereby lying in the path of movement of the abutment 334 and blocking it and hence the overall trigger 300 against any inward movement. The bar 229 serves to provide reinforced support for the locking member 440 from behind. When the actuator 410 is slid to reach either opposite side position (FIG. 4), the locking member 440 moves laterally away from the path of movement of the abutment 334 (FIG. 5), thereby allowing the trigger 300 to be pressed inwards.

[0034] The locking device 400 is designed to lock the switch 100 off against any unintended or accidental switching on of the electric saw 10, which can withstand a minimum impact force up to

[0035] 300N. In order to switch on the electric saw 10, the actuator 410 should initially be slid sideways before the trigger 300 can be pressed.

[0036] As shown in FIG. 6, the electric saw 10 has a body 9 including a handle 8 at which the on-off switch 100 is located for controlling the operation of a motor-driven circular saw blade 7. The left and right ends 420 of the actuator 410 protrude from opposite sides of the handle 8 to facilitate the movement of the actuator 410 by a person using the electric saw 10 on either side.

[0037] It should be noted that the snap-fit connection of the actuator 410 to the switch body 200 is releasable by deforming either of hooks, 230 and 232 outwards, such that the actuator 410 may be removed. The remainder of the on-off switch 100 may then be used independently as a normal switch without the locking-off function.

[0038] It is envisaged that the subject on-off switch may be used in any other electric power hand tools, such as a drill or a grinder and that its operator may take any form other than a trigger, such as a pushbutton, a sliding knob or a lever.

[0039] The invention has been given by way of example only, and various modifications of and/or alterations to the described embodiment may be made by persons skilled in the art without departing from the scope of the invention as specified in the appended claims.