Combined on/off and reversing switch and electric device therewith

Abstract: A combined on/off and reversing switch (36), particularly for an electric screwdriver (10) having a reversible motor (M), has a switch plate (68) which can be rotatably mounted on an end of the motor. Terminals (50,52) of the motor (M) extend through the switch plate (68) and are selectively contacted by ends (80,82) of two resiliently flexible contact strips (74,76) carried by the switch plate (68). An actuating member (28) is moved along a selected path to rotate the switch plate (68) to select "forward" and "reverse", and then depressed inwardly to flex an end of the appropriate contact strip (74;76) to complete energization of the motor. The contact strips (74,76) resiliently bias the actuating member (28) outwardly to switch the motor "off" when the actuating member is released. Switching the motor "on" from a neutral "off" position of the switch (26) involves a two part movement of the actuating member (28). The switch is of simple and compact construction.

Description: FIELD OF THE INVENTION This invention relates to an electric switch combining on/off and reversing functions, particularly for operating an electric motor. This invention also relates to the incorporation of this switch into an electric device, for example a handheld electric tool. BACKGROUND OF THE INVENTION It is known to provide portable electric tools with reversing capability, e.g. handheld electric drills, power screwdrivers, etc. In general this has involved employing two switches, one for the reversing function and another for the on/off function. Both switches have separate actuating members which may be adjacent each other or spaced apart at different locations on the tool. Both these functions have been combined in a single switch with an actuating member which pivotally rocks, rocking in one direction selecting forward drive and simultaneously switching the motor "on", while rocking in the opposite direction selects reverse drive and simultaneously switches the motor "on". However, such switch which is known from US-A-4 678 871 or GB-A 2 137 821 has four stationary contacts with associated connecting strips as well as movable contacts, and a rotatable switch plate rotatably connected to a stationary switch plate; such an arrangement is somewhat expensive to manufacture, and is rather bulky. Further, when operating this switch by rocking the actuating member, the operator does not have any positive "feel" of the operating position of the switch. SUMMARY OF THE INVENTION This invention is concerned with providing an improved switch combining on/off and reversing functions. It is an object of the present invention to provide a combined switch in which the "forward" and "reverse" positions are selected by one movement of an actuating member, and then the on/off function is controlled by a different movement of the actuating member. In the preferred embodiment, this object is achieved by an electric device which is characterised by the features indicated in the second part of claim 1. Advantageous constructional characteristics of the electric device are defined by the features indicated in the subclaims. The switch means may be incorporated in its own housing as a separate unit, but is preferably incorporated in the housing of an electric device, for example an electric drill. The switch means may advantageously be incorporated in the handle of a palm held cordless screwdriver. It will be appreciated, therefore, that while there is provided by one aspect of the invention the switch means per se , there is also provided by another aspect of the invention an electric device equipped with the switch means. As will be understood from the detailed description subsequently, a preferred embodiment of the switch of the present invention offers convenience in manufacture and assembly, has a compact configuration, offers a reduction in manufacturing cost, allows a shorter tool handle in appropriate end uses, and provides fast operation between "forward" and "reverse" while providing the operator with operational "feel". Other objects, features and advantages of the present invention will become more fully apparent from the following detailed description of the preferred embodiment, the appended claims and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings: FIG. 1 is a top plan view of a cordless electric screwdriver according to the invention, with some of the tool's housing broken away to expose part of the interior; FIG. 2 is a longitudinal section on the line 2-2 of Fig. 1 with the batteries and wiring omitted for simplicity; FIG. 3 is a top plan view, in the direction of the arrow 3 in Fig. 2, of the handle portion of the screwdriver with the top clamshell half of the housing and the button removed to show the motor and batteries; FIG. 4 is a diagrammatic perspective view of the motor of the screwdriver; FIG. 5 is a section on the line 5-5 of Fig. 6 of a disc-like member of the combined on/off and reversing switch of the invention; FIG. 6 is a section on the line 6-6 of Fig. 3 with the combined on/off and reversing switch in a neutral position; FIG. 7 is a similar view to Fig. 6 with the combined switch "on" and in the position for forward drive as when inserting a screw; FIG. 8 is a circuit schematic of the screwdriver of Fig. 1 with the movable contacts of the combined switch of Fig. 6 in the "off" and reverse drive position; and FIG. 9 is the circuit schematic of Fig. 8 but with the movable contacts of the combined switch in the "on" and forward drive position of Fig. 7. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Figs. 1 to 3 illustrate a cordless electric screwdriver according to the invention, and Figs. 4 to 9 illustrate the construction and operation of the preferred embodiment of a combined on/off and reversing switch according to the invention and which is advantageously incorporated in the screwdriver, Fig. 4 showing a small D.C. motor with which this combined switch is particularly adapted to operate. Fig. 1 shows in plan view the screwdriver 10 having a main body and handle portion 12 comprising two clamshell type housing parts 14, 16. A gearbox compartment 18 is attached to the forward end of the handle portion 12 with a chuck 20, for holding a screwdriver bit (not shown), extending forwardly therefrom. Portions of clamshell housing part 14 are broken away to expose a rechargeable battery 22 and a wiring connection 24 between electrical components of the tool. The location of a switch 26 is indicated by an arrow. The switch 26 is a combined on/off and reversing switch, and has a manually operable button 28 exposed and accessible through a transverse arcuate opening 30 in the upper clamshell housing part 14 near the front thereof. In use, the handle portion 12 is grasped in one hand with a finger of that hand engaging the button 28 for operation thereof. Fig. 2 is a section on the line 2-2 of Fig. 1 and shows a battery compartment 32 (with the batteries removed ) in the handle portion 12. A small D.C. motor M, for example operating on 2.4 volts D.C., is housed forwardly of the battery compartment in a motor compartment 36 in the front of the handle portion 12. The switch 26 is disposed between the compartments 32, 36. Reduction gearing 38 of the planetary type is connected between the output shaft 40 of the motor M and the chuck 20 for drivingly rotating the latter. Fig. 3 is a view of the handle portion 12 in the direction of the arrow 3 in Fig. 2 with the upper clamshell housing part removed to show components inside the handle portion. Two rechargeable nickel/cadmium batteries 22, 42 in the compartment 32 are connected in series via a U-shaped metal contact strip 44. Wiring 46, 48 connects the end poles of the pair of batteries 22, 42 to terminals 84, 86 of the switch 26. Fig. 4 shows a perspective view of the motor M with the drive shaft 40 extending from the forward end and the two flat, spade-like terminals 50, 52 extending from the rear end. A cylindrical boss 54 protrudes from the center of the rear end wall 56 of the motor, a rear end 58 of the drive shaft being journalled in a bearing in the boss 54. The boss 54 is concentric with the drive shaft 40 and the terminals 50, 52 are disposed on diametrically opposite sides of the boss and adjacent the periphery of the rear end wall 56. The motor M is energized by connecting a 2.4 volt D.C. supply from the batteries 22, 42 across the terminals 50, 52. Fig. 6 is a cross-section on the line 6-6 of Fig. 3 and shows more details of the switch 26. The actuating button 28 has a serrated upper grip surface 59, and is integrally connected to an arcuate slide 60 which extends beyond the button 28 on each side thereof in the longitudinal direction of the screwdriver. Also, the slide 60 is arcuately longer than the slot 30 in the upper clamshell housing part 14. The button 28 extends upwardly through, and is movable along, the slot 30 with the slide 60 normally engaging and sliding around the inner surface 62 of the upper clamshell part 14. The extent of arcuate movement of the slide 60 is limited by the ends of the slot 30 by abutment thereagainst of the button 28. The button 28 is hollow and has a cylindrical recess or bore 64 therein opening downwards. An upwardly extending, cross-shaped peg 66 (see also Fig. 3), of an oscillatable disc-like switch plate 68 of electrically insulating material, is slidably engaged in the bore 64 and guides the button 28 and slide 60 during downward and upward movement thereof. Adjacent each arcuate end of the slide 60 is an integral, inwardly extending projection 70, 72 having a smoothly curved convex surface which functions as a cam. The two cam-like projections 70, 72 are located on the slide 60 nearer the rear edge thereof, that is the edge nearer the battery compartment 32 than the motor compartment 36 (Fig. 3). The projections 70, 72 engage respective upper free ends of a pair of resilient conductive strips 74, 76. The strips 74, 76 are made of electrically conductive sheet metal, such as steel or an alloy, and are resiliently deformable to also function as springs. The strips 74, 76 have a lower arcuate portion 77 (see Fig. 7) which is approximately concentric with the rotation axis of the motor shaft 40, which axis is also the central longitudinal axis 78 (see Figs. 3 and 7) of the screwdriver. The upper arcuate portion 79 of each strip is eccentric to the axis 78 and diverges upwardly and outwardly from the circle on which the lower arcuate portions 77 lie. At the extreme upper ends of the strips 74, 76 are contacts 80, 82 formed by inwardly extending convexly curved ends of the strips. The lower ends of the strips 74, 76 are of U-shape configuration with the outer leg of each U being formed with the rearwardly extending spade-like terminal 84, 86, respectively, and to which opposite end poles of the batteries are connected. Each strip 74, 76 is supported on the switch plate 68 by posts 90 and 94 extending axially from the plate 68. Each strip 74, 76 extends outside the post 90 and inside post 94. The posts 90 and 94 each have a small flange which engages over the axially rearward edge of the respective strip. Also, each strip has a pair of tabs 92, 96 which engage post 94 and prevents arcuate movement of the strips relative to the switch plate 68. The switch plate 68 has a lower arcuate wall 98 which prevents radially inward deflection of the U-shaped lower ends of the strips 74, 76; radially outwardly extending legs 100 on the wall 98 engage over the strips 74, 76. In this way, the strips 74, 76 are supported in position on the switch plate 68 for movement therewith, with the upper ends of the strips 74, 76 being free to be deflected inwardly towards the axis 78. The upper arcuate portions 79 of the strips 74, 76 resiliently bear against the cam-like projections 70, 72 and bias the button 28 upwardly until the slide 60 abuts firmly against the housing inner surface 62, as shown in Fig. 6. In this way, the contact strips 74, 76 jointly function as a spring for normally retaining the button 28 in an upward inoperative position. The switch plate 68 has upper and lower narrow arcuate apertures 102, 104 (see also Fig. 7) through which slidably extend, respectively, the spade-like terminals 52, 50 of the motor. The lower arcuate wall 98 supports the lower terminally 50 against radially inward deflection, and an upper arcuate wall 106 on the switch plate 68 supports the upper motor terminal 52 against such deflection. The switch plate has a central hub 107 defining a cylindrical hole therethrough concentric with the axis 78. The hub 107 is rotatably mounted on the boss 54 (see Fig. 4) of the motor. Arcuate movement of the actuating button 28 causes , via the peg 66, rotation of the switch plate 69 about the motor boss 54 within the limits imposed by the ends of the slot 30. In the position shown in Fig. 6, the motor terminal 50 is spaced from and midway between the lower U-shaped ends of the contact strips 74, 76, and the upper motor terminal 52 is disposed midway between the upper strip contacts 80, 82 with these contacts 80, 82 being spaced radially outwardly of the terminal 52. This is the neutral and "off" position of the switch 26 with no electrical connection between the contact strips 74, 76 and the motor terminals 50, 52. If the button 28 is manually depressed in this position, the cam-like projections 70, 72 will slide on and flex the resilient upper portions 79 of the strips 74, 76 inwards towards the axis 78, but the contacts 80, 82 will not contact the upper motor terminal 52. However, when the button is moved to the right in Fig. 6, the slide 60 rotates approximately 18 degrees clockwise through the angle x until the button reaches the right-hand end of the slot 30. In this new position, when the button 28 is depressed, the contacts 80, 82 are moved radially inward until the contact 80 engages the upper motor terminal 52 and presses it against the upper arcuate wall 106 - as shown in Fig. 7. In reaching the position in Fig. 7, the lower U-shaped end of the righthand strip 76 rides over and in contact with the radially outer surface of the lower motor terminal 50, this terminal 50 being resiliently clamped between the lower arcuate wall 98 and the lower contact end of the strip 76. In the Fig. 7 position, the motor terminals 50, 52 are electrically connected across the end poles of the batteries via the contact strips 74, 76. Fig. 7 illustrates the forward position of the switch 26 with the switch "on", i.e. the motor M is energized to rotate in the forward direction of drive such as when inserting a screw with the screwdriver. In this forward position, if the button 28 is released, the resiliency of the deformed contact strips 74, 76 will urge the button 28 radially outwards so disconnecting the contact 80 from the motor terminal 52; this de-energizes the motor M even though the button 28 is in the forward position, i.e. the switch is then in a forward drive but "off" position. When the button 28 is manually slid counterclockwise to the lefthand end of the slot 30, i.e. through an angle 2x from the position in Fig. 7, the reverse position of the switch 28 is obtained. In the reverse position, the lower contact of the lefthand strip 74 engages over the lower motor terminal 50, and the upper contact 82 of the righthand strip 76 is positioned in register with the upper motor terminal 52. When the button 28 is inwardly depressed in this reverse position, the contact 82 engages the motor terminal 52 to energize the motor in the reverse direction of drive, for example for removing screws with the screwdriver. Again, in this reverse position, as soon as the button 28 is released, the button is moved radially outwardly by the "spring" formed by the upper strip portions 79 to de-energize the motor, i.e. the switch 26 occupies a reverse drive but "off" position. The lower portion of the switch plate 68 is provided with a downward extension having an arcuate opening 108 therein to provide a resiliently deformable arcuate member 110. A radially outwardly extending pip 112 is formed at the mid-point of the arcuate member 110. Three adjacent detent notches 114 are formed in the inside wall of the lower clamshell part 16. When the switch plate 68 is rotated by arcuate movement of the button 28, the pip 112 moves from engagement in one detent notch 114 to another due to the resilient inward flexing of the member 110. The pip 112 and the detents 114 function to releasably latch the switch plate in the forward, neutral and reverse positions of the switch 26. This has the advantage of providing a more positive feel of the position of the switch. Fig. 5 is a cross-section on a smaller scale of the switch plate 68 on the line 5-5 of Fig. 6, and shows further details thereof including the relative positions of the upper and lower arcuate walls 106, 98, the hub 107, the radially outward extending leg 100, and the pip 112. Figs. 8 and 9 are similar electrical schematic diagrams of the screwdriver, but with the switch 26 in different positions. The screwdriver is provided with a pair of battery recharging terminals 120 which are connected across the batteries 22, 42 via a diode 122. Opposite end poles of the batteries are connected via wires 48, 46 to terminals 84, 86, respectively, of the contact strips 74, 76. The motor M is illustrated diagrammatically with its terminals 50, 52. Fig. 8 represents the reverse position of the switch when the button 28 is moved counterclockwise in Fig. 6 and released. Although the lower contact end of strip 74 makes contact with the lower motor terminal 50, both upper contacts 80, 82 are spaced from the other motor terminal 52 so that the switch is "off". Fig. 9 represents the position of the switch 26 shown in Fig. 7, i.e. the forward "on" position; as can be seen, current is supplied to the motor M via the lower terminal 50 and leaves via the upper terminal 52. In operation, the operator grasps the handle portion 12 in one hand, and with a finger of that hand arcuately moves the button 28 to the right or left (Fig. 6) to move the switch 26 to the forward or reverse position, respectively. Then, in the selected position, the button 28 is depressed to energize the motor M in the selected direction. The motor only remains energized while the button 28 is manually held depressed; as soon as the finger releases the button 28, the motor is de-energized. If the button is depressed in the neutral position midway between the forward and reverse positions, the motor is not energized. It will be appreciated, therefore, that a combined on/off and reversing switch is provided having only a single actuating button. Movement of the button along one path changing the switch between forward and reverse positions through a neutral position, and movement in a direction transverse to said one path switching "on" and "off" when in either the forward or reverse position. This provides simple one finger control of the combined switch and the feature of automatically switching "off" the instant downward pressure of the finger on the button is released. Further, when the button is depressed by the finger to switch "on", this finger action tends to increase the user's single handed grip of the screwdriver for surer use. It will also be appreciated that the illustrated switch is of simple construction with a minimum of parts, particularly moving parts, and is relatively easy to assemble. Both these features help reduce production cost. Further, mounting the oscillatable switch plate directly on an end face of the motor, via the motor boss 54, enables a very compact switch construction to be obtained. In the illustrated preferred embodiment, the switch 26 extends the overall axial length of the motor M only a short distance, approximately 4 mm. The economy of occupied space enables the length of the main body and handle portion of the tool to be reduced. Further, it enables the actuating button 26 of the switch to be readily located at the commencement of the handle portion for convenient finger operation. As mentioned above, the detent arrangement between the switch plate and the housing enables the switch to be positively located in the neutral, forward and reverse positions in a manner which gives a "feel" to the user of positive switching. This is advantageous when manipulating the actuating button to different positions with one finger, particularly when the finger remains continuously on the actuating button or other suitable actuating member. It should be noted that in the preferred embodiment, the contacts engage the motor terminals with a sliding action. The sliding action is more pronounced with engagement of the lower motor terminal. With the upper motor terminal there is first a direct contact action, but then as the upper portions of the contact strips are further flexed downwards, a sliding action occurs. This is advantageous as the sliding action tends to clean the contacting surfaces of the contacts and the terminals, and inhibits build-up of any corrosion; it also minimizes the effect of any pitting. Advantageously, the actuating button can be arranged to have an extent of travel during full depression which results in a definite amount of "over travel". This will cause additional flattening of the upper curved portion of each contact strip after the upper contact thereof has engaged the upper motor terminal; thus, additional sliding motion will occur between the contact and the terminal. Further, the contact will be held more firmly against the terminal.

Claims: An electric device, comprising: a housing (14, 16); a reversible electric motor (M) mounted in said housing; switch means (26) for selecting a direction of drive of said motor between forward and reverse directions of drive, and for switching said motor "on" and "off"; said switch means (26) having an actuating member (28) accessible from externally of said housing for manual actuation of said switch means, said actuating member being manually displaceable relative to said housing along a path between "neutral", "forward" and "reverse" positions which are spaced apart with said "neutral" position being intermediate and distinctly spaced from said "forward" and "reverse" positions, said motor normally being switch "off" when said actuating member is in said "neutral", "forward" and "reverse" positions; characterized in that: said actuating member is manually depressible inwardly relative to said housing in said "forward" and "reverse" positions to effect switching "on" of said motor and effect drive thereof in said forward and reverse directions of drive, respectively; and said switch means is incapable of switching "on" said motor by any depression of said actuating member when said actuating member in said "neutral" position. The device of Claim 1, characterized by resilient means (74, 76) for resiliently biasing said actuating member (28) to switch said motor "off" in said "forward" and "reverse" positions. The device of Claim 1 or 2, characterized in that said path is defined by a slot (30) in said housing (14, 16) through which said actuating member (28) extends and is movable along, and said actuating member (28) is depressible inwardly through said slot (30) to switch said motor "on". The device of Claim 3, characterized in that said actuating member (28) is located at opposite ends of said slot (30) in said "forward" and "reverse" positions. The device of any preceding claim, characterized in that said switch means (26) comprises a rotatably mounted switch means (26) comprises a rotatably mounted switch plate (68) carrying two resilient contact strips (74, 76), said contact strips (74, 76) resiliently biasing said actuating member (28) to switch said motor "off" in both said "forward" and "reverse" positions. The device of Claim 5, characterized in that said motor (M) has an end wall (56) with a boss (54) extending centrally therefrom, said switch plate 968) engages over and is rotatably mounted on said boss (54), and terminals (50, 52) of said motor (M) extend through arcuate openings (102, 104) in said switch plate (68) for selective engagement with said contact strips (74, 76) by actuation of said actuating member (28). The device of Claim 5 characterized in that: (a) each said contact strip (74, 76) is curved and has contacts (80, 84; 82, 86) at opposite ends thereof, (b) rotation of said switch plate (68) to said "forward" and "reverse" positions connects a first contact (86) of one contact strip (76) with one (50) of said terminals and places a second contact (80) of the other contact strip (74) in register with but spaced from the other (52) of said terminals, and (c) depression of said actuating member (28) effects connecting of said second contact (80) with said other (52) of said terminals (FIG. 7). The device of Claim 5, characterized in that: (a) said switch plate (68) is rotatable about a rotational axis (78) of said motor (M), (b) each contact strip (74, 76) has a curved portion 977) which is concentric to said axis (78) and another curved portion (79) which is eccentric to said axis (78) and (c) depression of said actuating member (28) flexes said eccentric portion (79) towards said axis (78). The electric device of claim 1 wherein: the actuating member (28) has a slide (60) slidably engaged with an inner wall (62) of said housing (14, 16), and a manually operable button (28) extending outwardly from said slide (60) through a slot (30) in said housing (14, 16), said button (28) being movable along said slot (30) between "forward" and "reverse" positions; said button (28) also is depressible through said slot (30) to space said slide (60) away from and inwardly of said inner wall (62); a switch plate (68) is rotatably mounted in said housing and carries two resilient contact strips (74, 76) having first and second contacts (84, 80; 86, 82) at opposite ends; two terminals (50, 52) are connected to said motor (M); one (50) of said terminals is slidably engaged by the first contact (84; 86) of a respective one of said contact strips (74; 76) upon rotation o said switch plate (68) to a respective one of said "forward" and "reverse" positions but the second contact strips (76; 74) is spaced from the other 952) of said terminals; and depression of said button (28) in said "forward" and "reverse" positions causes said slide (60) to flex portions (79) of said contact strips (74, 76) and bring said second contact strips (76; 74) into engagement with said other (52) of said terminals to energize said motor (M) in the selected forward or reverse direction. The device of Claim 9, characterized in that said contact strips (74, 76) remain in engagement with said slide (60) and resiliently bias said slide towards engagement with said inner wall (62) to de-energize said motor (M) when said button (28) is released by an operator in said "forward" and "reverse" positions. The device of Claim 10, characterized in that each contact strip (74, 76) has a portion (77) adjacent one end which is concentric with an axis (78) about which said switch plate (68) is rotatable and a portion (79) adjacent the other end which is eccentric to said axis (78), said concentric portion (77) being restrained against flexing by posts (90, 94) extending from said switch plate (68) but said eccentric portion being free to flex, depression of said button (28) flexing said eccentric portion (79) towards a concentric configuration. The device of any preceding claim wherein: the device is a portable power tool; the housing is generally cylindrical and has a handle portion (12); and the switch means 26 is located adjacent one end of the handle whereby the actuating member is depressible with a finger of a hand gripping the handle portion.

Inventors: MARKLE STANLEY A, MOORE KEITH, MARKLE, STANLEY A., MOORE, KEITH
Applicants: BLACK & DECKER INC, BLACK & DECKER INC.
Application year: 1988
Main classification: H01H9
IPC codes: H01H9, H01H25