Abstract:
A hand-operated, double-action trigger switch is mounted in the handle area of a portable electric tool and comprises a thumb-actuated safety button protruding from the upper portion of the handle and a finger depressable trigger on the lower portion of the handle. The safety button must be pushed by the operator&#39;s thumb before the trigger can be depressed. Upon release of the pressure on the trigger, the safety button returns to its original position and effectively places the device in an inoperable or locked position.

Description:
This is a continuation, division, of application Ser. No. 714,911, filed Aug. 16, 1976 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to safety trigger switches adapted for use on portable electric tools. 
     2. Description of the Prior Art 
     The prior art in safety switches for hand held tools has generally provided relatively complicated switches with numerous molded pieces, springs and the like. Most such switches have separate lock and actuator elements that require a manual locking operation. One such switch is described in U.S. Pat. No. 3,780,246. This patent discloses a trigger actuator that is normally biased off and can be manually operated in the &#34;on&#34; position when the operator has his hand on the tool handle. Means is provided to automatically lock the trigger temporarily in the &#34;off&#34; position when the operator moves his hand from the tool handle, and requires intentional release to reactivate the tool. Other similar switches are described in U.S. Pat. Nos. 3,370,475; 3,646,298; 3,854,020 and 3,847,233. 
     A review of prior art practices shows that there is clearly a need for a double-acting safety switch that automatically assumes a locked position when released by the operator and that is simple to manufacture and compatible with a variety of tool handles. 
     SUMMARY OF THE INVENTION 
     The invention is directed to a hand-operated, double-acting trigger switch mounted in the handle area of a portable electric tool. The switch includes a pivotally-mounted trigger that protrudes from the handle and a safety button also mounted in the handle area. The safety button must first be pushed before the trigger can actuate the tool. The button is part of an integral molded piece that includes a resilient leaf for biasing the trigger to a non-depressed position. When the button is pressed, an abutment that locks the trigger in place is moved out of the way so that the trigger is clear to be depressed. The trigger carries a conductor strip that electrically connects the two electrical contacts on the switch. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevation view illustrating a portable electric grass shear with the invention trigger switch incorporated therein. 
     FIG. 2 is an enlarged, fragmentary, side elevation view of the shear of FIG. 1. 
     FIG. 3 is a view similar to that of FIG. 2 with the switch mechanism removed to illustrate the switch mounting guides. 
     FIG. 4 is an exploded, side elevation view of the button member and the trigger member which together comprises the device of the present invention. 
     FIG. 5 is an exploded, end elevation view of the device of FIG. 4. 
     FIG. 6 is a side elevation view of the assembled parts and illustrating the button member and trigger member in a non-actuated or locked position. 
     FIG. 7 is a view similar to that of FIG. 6 but with the safety button depressed to the unlocked position. 
     FIG. 8 is a view similar to that of FIGS. 6 and 7 with the safety button depressed and with the trigger also depressed to the operational position. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawings and particularly to FIGS. 1 and 2, there is illustrated a portable, battery pack powered electric grass shear 10 of a type which utilizes the hand-operated, double-action trigger switch 11 of the present invention. Trigger switch 11 is made up of two separately molded pieces, a button member 12 and a trigger member 13. 
     Button member 12 is an integral molded plastic piece including an upper resilient leaf spring member 14 which terminates at its remote end in a finger engageable button 20, a body portion 30, a lower resilient spring member 29, a solid pin member 17 and a hollow sleeve 16. Button member 12 is positively located within the tool housing at two points by pin 17 and sleeve 16. Pin 17 resides within a recess 18 in the trigger housing and sleeve 16 is positioned on a post 15 (FIG. 3). The button 20 resides within an opening 21 in the upper handle and, when depressed, bends upper leaf spring 14 downwardly. As explained in detail below, when leaf spring 14 is bent downwardly, a pair of abutments 36 move out of engagement with the trigger and clear the trigger so that it can be depressed. The movement of upper leaf spring 14 is guided by a small guide ledge formation 19 in the tool housing. The distance that button 20 may be pushed inwardly is limited by an abutment ledge 22 also formed in the housing. The lower leaf spring 29 engages the trigger 13 and biases it toward the locked position (FIG. 6). A pair of recesses 23, 24 are molded into button member 12 and serve to receive a pair of connectors 25, 26 which are retained by appropriate rivet contacts 27, 28. Connectors 25, 26 are electrically connected to the lead wires that operatively join the power source to the motor. 
     Trigger member 13 is also molded from plastic as an integral substantially hollow piece and includes a body portion 32, a finger engageable surface 33, and a pair of aligned holes 35 which mate with the sleeve 16 of button member 12 to secure member 13 to member 12 for pivoting about sleeve 16. The hollow interior portion of trigger member 13 encloses lower leaf spring 29 and body portion 30 of button member 12. Once button member 12 and trigger member 13 are secured together and mounted within the handle (see FIG. 2), lower leaf spring 29 rests against the inside wall surface of trigger member 13 so as to bias trigger 13 to a non-depressed &#34;off&#34; position. Trigger member 13 also includes a conductor strip 38 mounted on an inside wall thereof by a rivet 39. As explained below, strip 38 is adapted to electrically connect connectors 25, 26 by contacting rivets 27, 28 whose heads 27&#39;, 28&#39; make contact with strip 38 when the trigger switch is in the &#34;on&#34; position as illustrated by FIGS. 5 and 8. 
     The sequence of operating the trigger switch 11 will now be described in detail with reference to FIGS. 6, 7 and 8. FIG. 6 depicts the switch 11 in its normal locked position. As noted previously, the aligned holes 35 of trigger member 13 are mounted on sleeve 16 so that the trigger may pivot about the sleeve. The sleeve 16 is, in turn, mounted on the inner walls of the handle housing as is locating pin 17. In the locked position, trigger member 13 is biased downwardly by lower leaf spring 29. The trigger may not be depressed while in the locked position because abutments 36 on upper leaf spring 14 engage the mating trigger wall surfaces 37 to prevent the trigger from pivoting about sleeve 16. Connectors 25, 26 are not engaged with conductor strip 38 since the heads 27&#39;, 28&#39; of rivets 27, 28 are out of contact therewith. FIG. 7 illustrates the unlocked position that the switch 11 assumes after button 20 is pushed downwardly, but before the trigger 13 is depressed. In the unlocked position, upper leaf spring 14 is bent downwardly by the force on button 20 until the lower portion of button 20 engages ledge 22 (FIG. 2). At this point, abutments 36 have moved out of contact with trigger walls 37 so that walls 37 may clear the abutments when the trigger is depressed. FIG. 8 depicts the &#34;on&#34; position which the switch assumes after trigger is depressed. Rivets 27, 28 are now brought into engagement with conductor strip 38 and connectors 25, 26 are thereby electrically connected. 
     Once the switch is placed in the &#34;on&#34; position, the operator&#39;s thumb may be removed from the button 20 so long as the trigger 13 remains depressed since abutments 36 are held by walls 37 as in FIG. 8. However, it has been found in practice that the operator&#39;s thumb will most conveniently remain on the button 20 throughout the operation. Once the button 20 and trigger 13 are released, lower leaf spring 29 biases trigger member 13 back to the non-depressed position and upper leaf spring 14 returns button 20 to its original position so that the switch is once again in the locked position. 
     Although the switch 11 has been illustrated as embodied in a grass shear, it will be appreciated and from the foregoing that the switch may be utilized with numerous other hand-held tools. The switch of the present invention provides a simple and effective automatic lock mechanism for preventing the accidental actuation of a hand-held electric tool. By first pushing the safety button and then depressing the trigger, the operator may easily place the tool in operation. The switch is compatible with various hand-held tool handles and may be actuated without impairing the ability of the operator to support and manipulate the tool.