Abstract:
A trigger switch for a portable electric tool providing substantial pretravel of the trigger before closing force is applied to the contacts. This is a safety measure to prevent the motor from starting if the trigger should be accidentally pressed in handling a circular saw or the like. The pretravel is provided by a telescopic joint between the trigger and contact carrier, each of which is biased independently by a return spring to insure immediate reopening of the contacts upon release of the trigger.

Description:
BACKGROUND OF THE INVENTION 
     Switches of the trigger type have been known heretofore. However, these switches have generally included a direct connection between the operating member and the movable contact causing actuation of the contacts toward closing immediately upon movement of the trigger. This subjects the switch to accidental closure when a portable tool is being handled. 
     Switches of the preloading, free play or lost motion type have also been known. Such preloading has been used in switches of the toggle lever or push-button type or the like for snap-action purposes. Thus, initial movement of the operating member causes compression or preloading of a spring while the movable contact is held by a spring-biased detent and, when the preloading overcomes the restraining action of detent, the switch snaps to its operating position. Free play has been used to impart an impact force or so-called &#34;hammer blow&#34; to aid in opening partially welded contacts, a very short free play being generally sufficient therefor. Lost motion has been used for overtravel purposes and the like when the thing that operates the switch must be allowed to keep moving after the switch has been operated thereby to avoid damaging the switch. 
     While these prior switches have been useful for their intended purposes, this invention has a different purpose, that is, to prevent accidental closure of the switch. 
     SUMMARY OF THE INVENTION 
     This invention relates to pretravel switches for portable tools. While not limited thereto, the invention is especially applicable to trigger switches to prevent accidental closure of the switch contacts while the tool is being handled. 
     An object of the invention is to provide an improved pretravel switch allowing substantial movement of the operating member before closing force is applied to the contacts. 
     A more specific object of the invention is to provide an improved pretravel structure allowing substantial switch operator movement before closing force is applied to the contact carrier on switch closing and insuring that on switch reopening the contact carrier moves first to open the contacts followed by restoration of the switch operator to its full off position. 
     Another object of the invention is to provide an improved pretravel trigger switch. 
     Another specific object of the invention is to provide such trigger switch with independent biasing means for the trigger and contact carrier for improved operation. 
     Other objects and advantages of the invention will hereinafter appear. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an enlarged vertical cross-sectional view of a pretravel trigger switch, this view being taken substantially along line 1--1 as indicated in FIG. 3; 
     FIG. 2 is a horizontal cross-sectional view taken substantially along line 2--2 of the switch of FIG. 1 to show a top view of the pretravel structure; 
     FIG. 3 is a vertical cross-sectional view taken along line 3--3 of the switch of FIG. 1 to show the pretravel structure and the stationary contacts; 
     FIG. 4 is a horizontal cross-sectional view taken along line 4--4 of the switch of FIG. 1 to show a top view of the switch contacts; and 
     FIG. 5 is a top view of the insulator plate located at the top of the base in FIGS. 1 and 3. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawing, there is shown a pretravel trigger switch constructed in accordance with the invention. This switch comprises an insulating base 2, an insulating switch operating member such as a trigger 4, an insulating contact carrier 6, and a frame 8 of metal or other suitable material for retaining the trigger and contact carrier slidably on top of the base. 
     The base is made of molded, electrically insulating material and is generally rectangular in shape as shown in FIGS. 1, 3 and 4. The base is provided with four compartments. These compartments include a pair of side-by-side forward compartments for housing a pair of terminal clips, the left one 2a of these compartments and the left and right terminal clips 10 and 11 being shown in FIGS. 1 and 4. These compartments and terminals clips are similar and are separated by a vertical dividing wall 2b integral with the base. 
     These compartments also include a contact compartment 2c overlying the aforementioned pair of terminal clip compartments and separated therefrom by an insulator plate 12 shown in top view in FIG. 4. This compartment houses stationary contacts 14 and 16 and movable bridging contact 18. 
     These compartments further comprise a rear compartment 2d for housing a bussing clip 20 as shown in FIGS. 1 and 4. 
     As shown in FIGS. 1, 3 and 4, stationary contact means including contacts 14 and 16 extend through holes in the folded-back stems of terminal clips 10 and 11, respectively, and are threaded into holes in the base to secure the terminal clips in their respective compartments. The spherical segments on the heads of the stationary contacts extend slightly above insulator plate 12 so that the movable bridging contact can be slid thereon to electrically bridge the stationary contacts. Two adjacent holes 2e, one of which is shown in FIG. 1, extend through the bottom of the base into each of the forward, terminal clip compartments so that one or two bare-ended conductors can be pushed in to connect to the corresponding stationary contact. 
     Three holes 2f, one of which is shown in FIG. 1, extend up through the bottom of the base into rear compartment 2d and bussing clip 20 is a wide clip as shown in FIG. 4 so that two or three stripped wires can be pushed thereinto to connect them to one another through the clip. 
     Movable bridging contact 18 is shown in FIGS. 1, 3 and 4. This movable contact has a pair of upstanding arms 18a and 18b arranged forwardly-rearwardly as shown in FIGS. 1 and 4 that extend up into a slot in the bottom of contact carrier 6. This slot also accommodates a helical compression spring 22 that biases the movable contact down for proper contact pressure when the switch is closed. By the aforesaid upstanding arms, the movable contact is coupled to the contact carrier for rearward-forward sliding movement therewith. This movable contact also has a pair of lateral wings 18c and 18 d extending in opposite directions and having upturned rear edges as shown in FIG. 4 so that they will slide onto the stationary contacts when the trigger is pulled back. To assist in moving the movable contact, the contact carrier is provided with a downward projection 6a immediately in front of the movable contact, this projection sliding along insulator plate 12. Another short projection 6b extends down from the contact carrier directly behind the movable contact as shown in FIGS. 1 and 3. This projection serves with forward projection 6a not only to retain the movable contact on the contact carrier but also to limit the rearward movement of the contact carrier by stopping against the rear end of slot 24a in insulator plate 24. As will be apparent, this insulator plate shown in FIGS. 1, 3 and 5 closes the open top of the base except for this slot 24a that provides clearance for reciprocal movement of the movable contact. 
     Trigger 4 is provided with a forward finger-engaging portion 4a and a rearwardly extending slidable portion 4b as shown in FIGS. 1-3. This slidable portion is coupled to contact carrier 6 with allowance for pretravel as hereinafter described. The upper surface of the rear end of this slidable portion is provided with a pair of spaced short projections 4c and 4d extending up through rectangular holes in the frame as shown in FIGS. 1 and 3. These projections not only guide the trigger in its sliding movement but also limit its forward travel. 
     The aforesaid pretravel coupling between the trigger and contact carrier is provided by a telescopic connection therebetween. As shown in FIG. 2, the trigger is provided with a square recess 4e extending forward from its rear end and extending down from its upper surface. This recess snugly receives a complementary square projection 6c extending forward from the upper-rear portion of the contact carrier. A recess 4f extends from recess 4e forward slightly further into the trigger as shown in FIG. 2 to receive the forward end of trigger return spring 26. This spring is a helical compression spring and extends also through the contact carrier to abut at its rear end the rear inner wall of frame 8 as shown in FIG. 1. For this purpose, a round hole 6d extends through projection 6c and the upper rear part of the contact carrier freely to accommodate spring 26. 
     The aforesaid telescopic connection also includes sliding surfaces on the trigger and contact carrier. Thus, the lower surface of slidable rear portion 4b of the trigger slides on the upper surface of the forward-central portion of the contact carrier. 
     In addition, the rear end of the trigger is provided with a rearwardly extending flat tongue 4g that extends into a complementary flat hole 6e extending through the rear portion of the contact carrier directly below trigger return spring hole 6d as shown in FIGS. 1 and 2. This tongue and hole 6e provide added stability between the trigger and contact carrier after the trigger has been depressed enough to take up the pretravel thereby to insure easy gliding movement of the trigger and contact carrier in unison to close the contacts without any binding or sticking. 
     The contact carrier is provided with its independent return spring 28. For this purpose, a round hole 6f shown in FIGS. 1 and 3 extends from the rear end of the contact carrier forwardly partway thereinto. The forward end of helical compression spring 28 is held in this hole and its rear end abuts the inner rear wall of the frame below spring 26 as shown in FIG. 1. 
     The pretravel mechanism operates as follows. When the operator pulls back on the trigger, return spring 26 is compressed and the trigger slides on the contact carrier with tongue 4g sliding into hole 6e and projection 6c sliding into recess 4e. When the rear end of the trigger abuts the contact carrier, the pretravel has been taken up. Typically, this pretravel is of sufficient magnitude when added to the required movement of the contact carrier before the contacts touch of about a quarter inch (6.35 millimeters) to afford assurance under normal conditions of preventing turn-on of the portable saw when it is being handled. Further depression of the trigger causes movement of the contact carrier to slide the movable bridging contact across the stationary contacts. Trigger movement stops when downward projection 6b abut the rear end of slot 24a in insulator plate 24 as hereinbefore mentioned. 
     When the trigger is released, spring 26 pushes the trigger and spring 28 pushes the contact carrier which in turn pushes the trigger. Thus, the contact carrier and trigger move in unison forwardly to open the contacts. When downward projection 6a of the contact carrier abuts the front inner wall of the base, the contact carrier stops. However, return spring 26 continues to move the trigger forward until upper projections 4c and 4d of the trigger abut the front ends of the rectangular holes in the frame thereby to stop the trigger in its off position shown in FIG. 1. 
     While the apparatus hereinbefore described is effectively adapted to fulfill the objects stated, it is to be understood that the invention is not intended to be confined to the particular preferred embodiment of pretravel switch for portable tools disclosed, inasmuch as it is susceptible of various modifications without departing from the scope of the appended claims.