US3660742A - Trigger operated speed control assembly for electrical motors - Google Patents

Abstract

A trigger operated switch includes three contact strips and a bypass contact button. The trigger carries three slides for respective sliding engagement with such strips. Two of the strips are adapted for connection with a speed control circuit, one strip cooperating with one slide to define a variable resistor of such circuit. When the trigger is fully depressed, one of the slides is in engagement with the contact button for bypassing the speed control circuit.

Description

United States Patent Gawron May 2, 1972 TRIGGER OPERATED SPEED [56] References Cited g ag gg g UNITED STATES PATENTS 3,327,196 6/1967 Sahrbacker ..318/345 [72] inventor: Alex F. Gawron, Chicago, 111. 3,328,613 6/1967 Gawron ..3l8/345 ,329, 42 7 1967 B ..3l8 45 [73] Assignee: Skil Corporation, Chicago, 111. 3 8 town /3 [22] Filed; June 24, 1970 Primary E.\'aminerBernard A. Gilheany Assistant E.raminerTh0mas Langer [21 App]. No; 49,217 AttorneyMcDougall, Hersh 84 Scott Related U.S. Application Data 57 1 S T Continuation of 19651 A trigger operated switch includes three contact strips and a fl n bypass contact button. The trigger carries three slides for respective sliding engagement with such strips. Two of the [52] U.S. Cl ..3l8/345 strips are adapted for connection with a speed control circuit, [51] Int. Cl. ..H02p 5/16 one strip cooperating with one slide to define a variable re- [58] Field of Search ..3 1 8/345 sister of h ir i When the gg is fully depressed. n

of the slides is in engagement with thecontact button for bypassing the speed control circuit.

2 Claims, 5 Drawing Figures Flinn ltd; May 2, 1972 1 JNVENTC ALEX BEAM/R05 This application is a continuation of application Ser. No. 438,627, filed Mar. 10, 1965, now abandoned.

This invention relates to controls for electric motors, and more particularly to a new and improved trigger operated speed control assembly for electric motors.

A primary object of the present invention is the provision of a speed control assembly of the type described, which assembly includes a trigger operated slide switch of unique construction.

A further object of the present invention is the provision of an assembly of the type described including a new and improved trigger operated slide switch in unique cooperation with a silicon controlled rectifier speed control circuit.

Another object of the present inventionis the provision of an assembly of the type described including a new and improved slide switch in cooperation with a silicon controlled rectifier circuit, which switch includes means for shunting the silicon controlled rectifier circuit when the trigger is in the full on or maximum speed position.

Even another object of the present invention is the provision of a trigger operated speed control assembly of the type described, which assembly lends itself to small and compact construction, thereby readily adapting it for incorporation in a hand manipulatable tool, as for example a power drill.

Still another object of the present invention is the provision of an assembly of the type described including a trigger operated slide switch including means forming a variable resistor for cooperation with an associated silicon controlled rectifier circuit.

These and other objects and advantages of the invention will become apparent from the following specification disclosing a preferred-embodiment of the invention which is illustrated in the accompanying drawing wherein:

2 housing thereby to mount the trigger for reciprocal movement longitudinally or axially, of housing 10. A coil spring 33 has one end thereof abutting the end of trigger bar 27 and the other end thereof abutting a closed end a of the trigger housing thereby to urge the trigger outwardly (to the left as seen in FIG. 1) of housing 10. Trigger bar 27 includes a stop 34 adapted to abut the front (not shown) of housing 10 thereby to limit outward movement of the trigger.

FIG. 1 is a side elevation of the assembly of this invention with the trigger housing being shown in phantom lines;

FIG. 2 is a section taken along line 2-2 of FIG. 1;

FIG. 3 is a bottom plan view of the slider and upper board of the slide switch of this invention;

FIG. 4 is a top plan view of the lower board forming a part of the switch of this invention; and

FIG. 5 is a diagrammatic view primarily showing the contact strips of the slide switch and an associated silicon controlled rectifier circuit.

Referring now to FIGS. 1 and 2, the trigger operated speed control assembly of this invention will be seen to include a generally elongated, box-like switch housing 10, which housing may be of any suitable construction. The housing is shown in phantom lines in FIG. 1 for better illustration of the slide switch mounted within the housing.

Suitably mounted in housing 10 is a board 12 formed of insulating or non-conducting material. As noted in FIG. 4, board 12 supports three parallel contact strips 14, 16 and 18, which strips are spaced from each other and extend lengthwise of board 12. It will be noted that strip 16 is shorter than strips 14 and 18. A contact 20 is mounted on board 12 adjacent the end of strip 16 which is offset or spaced from the corresponding ends of the adjacent strips. It will be understood that strips 14 and 16 are of suitable conductive material. Strip 18 is formed of conductive material having a relatively high resistance value, such as carbon for example, and as will be explained hereinbelow strip 18 forms one part of a variable resistor.

A board 22 is suitably mounted in housing 10 in parallel spaced relation above board 12. Board 22 includes a pair of parallel slots 24 and 25 which extend lengthwise of the board.

A trigger 26 includes an integral bar-like extension 27 which extends into an opening (not shown) in the forward end of housing 10. Trigger bar 27 includes longitudinally extending, oppositely facing grooves 28, 29 in the side faces thereof, which grooves slidably receive respective ribs 30, 31 formed integrally with the side walls of housing 10. It will be appreciated that trigger bar 27 is slidably associated with the Trigger 26 carries a slider 35 for reciprocal movement along with the trigger. Slider 35, which is disposed between boards 12 and 22, is secured to trigger bar 27 by means of a pair of fasteners 36, 37, which fasteners extend through respective slots 24, 25 in board 22. Fasteners 36, 37 extend through a spacer or spacers 38 (FIG. 1) and are suitably secured to trigger bar 27. It will be understood that spacer 38 is adapted to slide along the upper surface of board 22 and that slider 35 is adapted to slide along the underside of board 22. Fasteners 36, 37 of course slide in respective grooves'24, 25 in the upper board 22. i

As best seen in FIG. 3, slider 35 includes three integral slides or fingers 40, 41, and 42. The slider, which is madeof resilient or spring-like conductive material, is so constructed that the arcuate slides are biased into sliding engagement with lower board 12. As the slider is reciprocated, slides 40, 41 and 42 come into respective sliding engagement with contact strips 14, 16 and 18, respectively.

FIG. 5 diagrammatically illustrates the contact strips of the slide switch in association with a circuit including a silicon controlled rectifier circuit. In FIG. 5, the numerals 44 and 45 represent the lines or conductors from a suitable source of alternating current operating at a frequency of 60 cycles and a voltage of 117 volts, for example. A line or conductor 44 representing one side of the alternating current source is connected to contact strip 14 at a terminal 47. Line 45 is in series circuit relation with a load device in the form of a universal or series type motor 48. A line 49 connects the motor with a terminal 50.

In order to cause the silicon controlled rectifier 52 to become conducting in the half cycle of the alternating current that it is adaptedto conduct, a circuit is associated with the gate of the silicon controlled rectifier. This circuit includes a neon bulb 60 connected to gate 55 of the silicon controlled rectifier. The neon bulb is interposed between the control electrode of the silicon controlled rectifier and a common connection 62 between the capacitor 58 and a fixed resistor 63. The resistor 63 is provided to limit the current which passes through the variable resistor formed by resistance strip 18 and slide 42. It will be realized that resistor 63 could be a part of resistance strip 18. It will also be realized that a diode of a type such as a trigger or zener may be substituted for neon bulb 60.

It will be noted that contact strip 18 of the slide switch is connected to the fixed resistor 63 of the silicon controlled rectifier circuit. It will also be noted that contact 20'is connected with terminal'50.

' When trigger26 is in its position illustrated in FIG. 1 with the stop 34 being urged into engagement with the front of the housing by means of spring 33, slides 40, 41 and 42 are 7 separated or spaced from respective contact strips l4, l6 and 18. In other words, trigger 26 is illustrated in its off position in FIG. 1. When trigger 26 is initially moved to the right as viewed in FIG. 1, the slides come into respective sliding engagement with the contact strips on board 12. When this occurs, it will be apparent that strip 14 is placed in electrical duct a half cycle of alternating current. As trigger 26 is moved from left to right as viewed in FIG. 1 thereby imparting corresponding movement to slide 42 along contact strip 18 for reducing the resistance of the variable resistor defined by slide 42 and strip 18, the voltage applied to capacitor 58 is increased with the result that the silicon controlled rectifier 52 is rendered conducting at an earlier point in the half cycle of alternating current that it is adapted to conduct with the further result that the voltage and current applied to motor 48 are correspondingly increased for increasing the speed of the latter. Accordingly, as the trigger is moved from left to right as viewed in FIG. 1, the speed of motor 48 is increased. It will be apparent that when trigger 26 is moved from right to left there is a corresponding reduction in the voltage and current applied to motor 48 for reducing the speed of the latter.

When trigger 26 is moved to the right or pulled inwardly to a position wherein slide 41 passes from the end of strip 16 and comes into contact with contact 20, the silicon controlled rectifier circuit is shunted and both half cycles of alternating current at the voltage existing between the lines or conductors 44 and 45 are applied to the load device, thereby to operate the same at maximum speed. When slide 41 engages contact 20, the circuit for motor 28 is as follows: line 44, terminal 47, strip 14, slider 35 (slides 40 and 41), contact 20, terminal 50, line 49, motor 48 and line 45. When trigger 26 is in the position just mentioned, slide 41 no longer engages strip 16 and therefore the circuit to the anode of the silicon controlled rectifier is opened so that the latter is not activated.

It will be understood that switch housing may be readily mounted in the handgrip portion of a hand manipulatable tool, such as an electric drill. In such a case, housing 10 is mounted within the handgrip portion of the drill so that the trigger 26 may be manipulated by the finger of a persons hand gripping the handgrip portion of the drill. In this respect, it should be mentioned that the length of the switch has been extended in the drawings for purposes of better illustration. Actually, the switch housing can be constructed with a length of between one inch and l /zinches, with a trigger stroke of approximately one-half inch. The silicon controlled rectifier circuit may be readily incorporated in a small electronic package represented by block 65 in FIGS. 1 and 5, and suitably connected with the trigger housing. of course, the trigger housing itself could be enlarged for enclosing the entire silicon controlled rectifier circuit thereby to provide a unitary trigger operated speed control assembly for incorporation in the handle of a hand manipulatable tool, such as a drill. It will be understood that housing 10, or electronic package 65 if desired, mounts terminals 47, 50 for connecting the trigger operated speed control assembly of this invention in one side of the alternating current line providing the source of current for energizing the motor 48, which in the case of a drill would be the motor for the same. Preferably, the trigger and the entire slide switch with the exception of contact strips 14, 16 and 18, contact 20, slider 35 and spring 33, are made of suitable non-conducting material, such as plastic.

It should now be apparent that the trigger operated speed control of this invention provides a new and improved slide switch in unique cooperation with a silicon controlled rectifier circuit for activating the latter to provide motor speed control at an infinite number of speeds and for shunting the silicon controlled rectifier when maximum speed is desired.

While the invention has been shown in but one form, it will be obvious to those skilled in the art that it is not to be so We claim: l l. A trigger operated control unit for use in controlling the speed of an electric motor in a hand manipulatable tool, said unit comprising, a base mounting first, second and third contact strips in spaced, parallel and insulated relation, a contact mounted on said baseadjacent one end of said first strip and in insulated relation with the same, a conductive slider mounted for reciprocal movement axially of said strips, a trigger associated with said slider for reciprocating the same, said slider having first, second and third slides adapted for respective sliding engagement with said first, second and third strips for placing each strip in electrical communication with the other strips, said slides being arranged with respect to said strips so that as said slider is moved by said trigger in a direction toward said contact said slides slidably engage respective strips simultaneously until said first slide passes beyond said one end of said first strip whereby upon continued movement of said slider in said direction said second slide remains in sliding engagement with said second strip and said first slide comes into engagement with said contact, said third strip third strip having a resistance value and forming, with said third slide, a variable resistor, a speed control circuit including a thyristor, two of said contact strips being adapted for connection with said speed control circuit, said contact being adapted for connection with a bypass line for shunting said circuit.

2. A trigger operated speed control assembly for an electric motor comprising, a switch housing including a base mounting first, second and third contact strips in parallel, spaced and insulated relation, a contact mounted on said base in insulated relation with the latter and in adjacent relation with one end of said first strip, a trigger mounted in said housing for reciprocating movement axially of said strip between first and second positions, a conductive slider carried by said trigger, which slider includes first, second and third slides adapted for respective sliding engagement with said first, second and third strips, said slides being arranged so that when said trigger is in said first position at least one of said slides is separated from the associated strip, so that when said trigger is in said second position said first and second slides are in respective contact with said contact and said second strip, and so that during movement of said trigger between said first an second positions said slides slidably engage respective strips simultaneously, said third strip having a resistance value and forming, with said third slide, a variable resistor, a speed control circuit including a thyristor, two of said contact strips being adapted for connection with said speed control circuit, said contact being adapted for communication with a bypass line for shunting said circuit when said trigger is in said second position.

Claims (2)

1. A trigger operated control unit for use in controlling the speed of an electric motor in a hand manipulatable tool, said unit comprising, a base mounting first, second and third contact strips in spaced, parallel and insulated relation, a contact mounted on said base adjacent one end of said first strip and in insulated relation with the same, a conductive slider mounted for reciprocal movement axially of said strips, a trigger associated with said slider for reciprocating the same, said slider having first, second and third slides adapted for respective sliding engagement with said first, second and third strips for placing each strip in electrical communication with the other strips, said slides being arranged with respect to said strips so that as said slider is moved by said trigger in a direction toward said contact said slides slidably engage respective strips simultaneously until said first slide passes beyond said one end of said first strip whereby upon continued movement of said slider in said direction said second slide remains in sliding engagement with said second strip and said first slide comes into engagement with said contact, said third strip third strip having a resistance value and forming, with said third slide, a variable resistor, a speed control circuit including a thyristor, two of said contact strips being adapted for connection with said speed control circuit, said contact being adapted for connection with a bypass line for shunting said circuit.

2. A trigger operated speed control assembly for an electric motor comprising, a switch housing including a base mounting first, second and third contact strips in parallel, spaced and insulated relation, a contact mounted on said base in insulated relation with the latter and in adjacent relation with one end of said first strip, a trigger mounted in said housing for reciprocating movement axially of said strip between first and second positions, a conductive slider carried by said trigger, which slider includes first, second and third slides adapted for respective sliding engagement with said first, second and third strips, said slides being arranged so thaT when said trigger is in said first position at least one of said slides is separated from the associated strip, so that when said trigger is in said second position said first and second slides are in respective contact with said contact and said second strip, and so that during movement of said trigger between said first an second positions said slides slidably engage respective strips simultaneously, said third strip having a resistance value and forming, with said third slide, a variable resistor, a speed control circuit including a thyristor, two of said contact strips being adapted for connection with said speed control circuit, said contact being adapted for communication with a bypass line for shunting said circuit when said trigger is in said second position.

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