DE68921583T2 - Switch mechanism for a power tool. - Google Patents

Abstract

A switch mechanism for an electric power tool, comprising: a linear slider received in a switch case so as be moved manually in a first direction against the biasing force of a return spring; an actuating pin carried by the linear slider so as to be moveable along a second direction perpendicular to the first direction; a pair of direction converting levers crossed in the manner of a pair of scissors by a pivot pin mounted on the switch case, the actuating pin being located adjacent to first ends of the direction converting levers; a pair of lateral sliders engaged by second ends of the direction converting levers and allowed to move in the second direction; a first contact set including contacts carried by the linear slider and the wall surface of the switch case for mutual cooperation as the linear slider is moved in the first direction; and a second contact set including contacts carried by the lateral slides and the wall surface of the switch case for mutual cooperation as the lateral sliders are moved in the second direction; the actuating pins being moveable between the first ends of the direction converting levers so as to selectively actuate one of the direction converting levers and the associated one of the lateral sliders through movement of the liner slider along the first direction via an engagement between the actuating pin and the first end of the associated one of the direction converting levers.

Description

Description

The present invention relates to a switch for turning on and off and reversing the rotation direction of power tools such as electric screwdrivers and electric drills, and more particularly to a switch for power tools whose structure is simplified.

BACKGROUND OF THE INVENTION

Conventionally, a switch for power tools of this type is provided with a plurality of individual contact units for turning on and off, controlling the speed and reversing the direction of rotation of the motor by switching the polarity of the motor, as described, for example, in Japanese Patent Application No. 62-288228.

However, such contact units require each to be provided with a separate return spring for its movable contact part, and the resulting increase in the number of components represents a major difficulty in simplifying the design and assembly of the switch.

Furthermore, since the operation of the reversing switch lever was performed without generating any feeling, the operator had to have doubts about the accuracy of the operation, and there was a need to improve the tactile feeling of the operation in order to improve the operability and reliability of the switch.

A switch mechanism according to the preamble of patent claim 1 is known from US-A-3755640.

BRIEF SUMMARY OF THE INVENTION

A primary object of the present invention is to provide a switch mechanism for power tools which is simplified in construction and assembly by reducing the number of components.

A second object of the present invention is to provide a switch mechanism for a power tool in which the return spring for the linear slider is additionally used to provide the operation of the reversing switch lever with a tactile feel.

These and other objects of the present invention can be achieved by providing a switch mechanism for a power tool with a linear slide element which is accommodated in a switch housing so that it is displaceable in a first direction along a wall surface of the switch housing, a return spring for loading the linear slide element in the first direction, manual actuating means for manually moving the linear slide element against a spring force of the return spring, an actuating pin seated on the linear slide element so that it is displaceable along a second direction perpendicular to the first direction, characterized by a pair of direction reversing levers which are crossed by a pivot pin attached to the switch housing in the manner of scissors, the actuating pin being arranged adjacent to first ends of the direction reversing levers, a pair of lateral slide elements which are engaged by second ends of the direction reversing levers and can move in the second direction along a wall surface of the switch housing, a first contact set with contacts which are arranged for mutual cooperation in moving the linear slide element in the first direction on the linear sliding element and the wall surface of the switch housing, and a second contact set with contacts which are seated for mutual cooperation when the lateral sliding elements are moved in the second direction on the lateral sliding elements and the wall surface of the switch housing, the actuating pin being movable between the first ends of the direction reversing levers so that selected one of the direction reversing levers and the associated one of the lateral sliding elements are actuated with movement of the linear sliding element along the first direction via engagement between the actuating pin and the first end of the associated one of the direction reversing levers. Typically, the engagement between each of the lateral sliding elements and the second end of the associated one of the direction reversing levers from a capture between a slot and a pin.

According to the structure described above, the switching operation of the motor is carried out by pushing a linear slider, which may be provided with an operating shaft projecting forward from the switch housing under a loading force, so that the contact seated on the linear slider cooperates with a fixed contact for switching, and fine-tuning of the motor output can be carried out at an early stage of the pushing movement by moving one of the lateral sliders engaged with any one of a pair of direction reversing switches so that the contact seated on the applicable lateral slider cooperates with a fixed contact for power and direction control.

Since the lateral sliding elements can thus be displaced laterally synchronously with or at an early stage of the sliding or pushing movement of the lateral sliding element, and the switching of the two sliding elements can take place during the movement of the lateral sliding element in mutual synchronization, it is possible to avoid the need for a return spring for the lateral sliding elements. As a result, a significant reduction in the number of components, a simplification of the structure and an ease of assembly work can be achieved.

Preferably, the first contact set comprises contacts for selecting between full power and partial power of the electric motor, and the contact set comprises contacts for switching on the motor and for switching the direction of rotation of the motor.

According to a particularly preferred embodiment of the present invention, triggering means are arranged between the actuating pin and the linear sliding element for generating a tactile sensation when the actuating pin is operated. Preferably, the trigger means comprises a slot for receiving the actuating pin so as to permit its movement in the second direction, a trigger member received in a hole communicating with the slot so as to abut against the actuating pin at one end thereof and to receive a loading force from the linear slide return spring at the other end thereof, the actuating pin experiencing resilient resistance as it is moved along the slot and passes over the first end of the stop member.

When the reversing lever is operated, the cooperating operating pin is temporarily engaged by the load force sensing part, and the reversing lever is moved laterally against the pressure of the load force sensing part, thereby causing a sudden change in the load force and resistance on the lever and transmitting a distinct tactile feeling to the lever.

Since the operator of the reverse shift lever can clearly recognize the execution of the shifting by tactile feeling, the operability and reliability of the reverse shift lever can be improved.

Furthermore, in this tactile feeling generating structure, since the return spring for the linear slide member also serves as a load force tactile feeling part and a saving of components can be achieved without the need for an additional elastic member for producing such tactile feeling, the number of components can be reduced and at the same time the operability of the switch can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described with reference to the accompanying drawings.

Fig. 1 is an exploded perspective View of a first embodiment of the switch mechanism according to the invention for a DC power tool;

Fig. 2 is a longitudinal sectional view of the switch for a DC power tool;

Fig. 3 is an enlarged perspective view of the direction reversing levers;

Fig. 4 is a circuit diagram of the motor control circuit to which the present invention is applied; and

Fig. 5 is a perspective view of a portion of a second embodiment of the switch mechanism according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The drawings generally illustrate a switch for a DC power tool. Referring to Figs. 1 and 2, this switch for a DC power tool consists of a control circuit unit 11 for a DC motor, a switch housing 12 for receiving and supporting this control circuit unit 11, and an operating lever 13 for activating and controlling the motor, and is mounted, for example, in the handle of a power tool such as an electric screwdriver.

The control circuit unit 11 includes a power transistor 14, a dust cover 15 for covering the connection portion of the power transistor 14 from above, a transistor holder 16 for holding the power transistor 16, a circuit board 17 for mounting a control circuit thereon, a switch mechanism 18 for turning the motor on and off, a motor power fine control mechanism 19, and a motor rotation reversing switch mechanism 20.

The power transistor 14 has a rectangular shape and switches the voltage to the rotor of the DC motor on and off, with its three terminals 21, which protrude from one side surface, bent downwards and are connected to power or voltage and motor connections 22 which are injected into switch housing 12

The power transistor 14 is mounted and fixed on the upper surface of the transistor holder 16 by means of a pressed rivet. The lower end of the transistor holder 16 surrounds the outer edge of the circuit board 17, and is provided with engaging pawls which project downward from the four corners and engage with the switch housing 12.

The circuit board 17 is arranged between the transistor holder 16 and the switch housing 12, and protruding parts 26 of the dust cover 15 are engaged with engaging holes 25 provided on a side portion of the circuit board 17 for mounting the dust cover 15 on the circuit board 17. To the terminal connection holes 27 of the circuit board, the power and motor terminals 22 are connected.

The switch mechanism 18 consists of a linear sliding element 28, a linearly movable contact 29 mounted on its lower surface, and a front fixed contact 30, and is housed in the switch housing 12. The linear slider 28 is slidably received in the front/back direction in the upper opening 31 of the switch housing 12, and is normally urged to its front position by the spring force of a slider return spring 32 disposed between the inner surface of the linear slider 28 and the inner surface of the switch housing 12, with its pressing shaft 33 projecting from the front surface of the linear slider 28 projecting in the forward direction under a urging force from a front opening 35 of the switch housing 12 by means of a front sealing member 34 for dust prevention.

The lower surface of the linear slider 28 is provided with an inverted M-shaped linearly movable contact part 29 which is provided with a loading spring for generating a contact pressure, and this movable contact part can move linearly along the lower surface of the switch housing 12. A front fixed contact 30 for switching operation is molded into a front part of the lower surface of the switch housing so as to correspond to the linearly movable contact 29.

One end of the operating switch 13 faces the outer end of the push shaft 33, and a downward movement or stroke of the operating lever 13 causes the linear slide 28 to move linearly against the urging force of the slide return spring 32, so that a slide switch is formed. At the end of the movement or stroke of the operating lever 13, the linearly movable contact 29 comes into contact with the front fixed contact 30 and switches on the voltage to the motor.

The engine power fine control mechanism 19 includes an operating pin 37, first and second direction reversing levers 38 and 39, first and second lateral slide members 40 and 41, laterally slidable contacts 42 mounted on the lower surfaces of the lateral slide members 40 and 41, and fixed rear contacts 44, and is housed in the switch housing 12.

The operating pin 37 is provided with an upwardly directed pin 37a on its upper surface and an engaging projection 37b projecting downward from its lower surface and received in a receiving portion 45 which allows lateral movement of the engaging projection 37b. The engaging portion 45 is provided with an irregular shape for generating resistance to the lateral movement of the operating pin 37 to provide the operator with a tactile feeling for To make available.

First and second direction reversing levers 38 and 39 are crossed in a scissor-like manner, and a common pivot pin 47 extends through holes 46 at the mutually crossed parts so as to permit rotational movement of the direction reversing levers 38 and 39. As most clearly seen in Fig. 3, the inner peripheral surfaces of the holes 46 of the direction reversing levers 38 and 39 are provided with peripheral shoulder surfaces 38a and 38b to limit the possible range of mutual angular displacement between the two levers.

The two levers 38 and 39 are arranged above the linear slider 28 in such a manner that the pin 37a of the operating pin 37 is arranged between the front ends of the levers 38 and 39 so as to face them. Therefore, when the linear slider 28 is displaced, the front end of one lever 38 receives a pressure in the direction of movement of the operating pin 37 which moves as one part with the linear slider 28, and the rear end portion of the lever 38 is moved laterally as a result of its rotation about the pivot point. However, since the other lever 39 receives no pressure, it is not rotated and remains in its rest position.

First and second lateral sliding elements 40 and 41 are connected to the rear ends of the levers 38 and 39.

The lateral sliding elements 40 and 41 are provided with engagement pins 48 on their upper surfaces so that they can be moved synchronously with the movement of the levers via an engagement between the engagement pins 48 and in engagement slots 49 of the rear ends of the levers 38 and 39.

The lower surfaces of the lateral sliding elements 40 and 41 are provided with inverted M-shaped laterally movable contacts 42 and 43 by means of loading springs 50 to generate contact pressure so that these contacts are laterally displaceable along the inner bottom surface or the inner lower surface of the switch housing 12. A number of fixed rear contacts 44 for fine engine power control are molded in a rear part of the inner bottom surface of the switch housing 12.

In this case, the first linear slider is associated with normal rotation while the second lateral slider is associated with reverse rotation of the motor, and a small motor output can be achieved at an early stage of the movement or stroke of the linear slider 28 by making electrical contact with any of the laterally movable contacts 42.

The above-mentioned reversing switching mechanism 20 for the motor includes a reversing switching lever 51 in the switch housing 12 for switching between the normal rotation direction and the reverse rotation direction of the motor. This reversing switching lever 51 is rotatably supported by an upward pin 52 projecting from its upper surface and received in a pivot hole 53 provided in the circuit board 17, and the above-mentioned common pivot pin 47 projects downward from the lower surface of the reversing switching lever 51 in alignment with the upward pin 52. This common pivot pin 47 extends through the crossing holes 46 on the first and second direction reversing levers 38 and 39 for rotatably supporting the levers 38 and 39.

A pin receiving hole 54 provided in a continuation of this reversing switch lever 51 loosely receives the upward pin 37a of the operating pin 37 in a linearly movable manner so that the lateral movement of the operating pin 37 resulting from the rocking movement of the switch lever 51 can select either a normal or a reverse rotation direction of the motor.

A side lever 55 protrudes from a lateral side of this reversing lever, which protrudes from a side opening 57 of the switch housing 12 via a lateral sealing part 56 to prevent dust, so that the tilting operation of the side lever 55 is possible from the outside.

The switch housing 12 is formed as an open-top box, and fixed contacts 30 and 54 and other (power and motor) terminals are molded into the inner bottom surface of the housing, respectively. The switching mechanism 18, the motor power fine control mechanism 19, and the motor reversing switching mechanism are housed in the upper opening 31 of the switch housing 12, and the circuit board 17, the transistor holder 16, the power transistor 14, and the dust cover 15 are mounted thereon.

The switch for a DC power tool having the structure described above is housed in the handle of a power tool, and its operating lever 13 facing the linear slide member 28 is normally in its position rotated in the forward direction about the rotating portion of the operating lever and protrudes in an oblique manner, and is arranged to be pressed under the urging force of the internally installed slide member return spring 32.

Fig. 4 is a block diagram of the switching circuit of a power tool, and in Fig. 4, a motor M is connected to a power source E through a main circuit 110 having a normal rotation control switch unit 111 and a reverse rotation switch unit 112 so that power is supplied to the motor M and the motor is driven in the desired direction by turning on either of the switch units 111 and 112.

The main circuit 110 further includes an output device 114 which is part of a low-speed control circuit 113 and a short-circuit switch unit 115 constituting a high-speed control circuit, which are connected in parallel with each other, and the torque output of the motor M is carried out by performing switching control on the power device 114, while the short-circuit switch unit 115, when turned on, directly connects the motor M to the power source E so that the motor M is driven at high speed.

The low speed control circuit 113 consists of a triangular wave generating circuit 116, a switching circuit 117 and the above-mentioned power device 114. The triangular wave generating circuit 116 is connected to both sides of the above-mentioned motor M via diodes D1 and D2 which are connected in the normal direction.

Normally, since the short-circuit switch unit 115 is open and the low-speed control circuit 113 is in an operable state, the motor M is driven at a low speed in a desired direction by rotating either the normal rotation control switch unit 111 or the reverse rotation control switch unit 112.

When no load is applied to the motor M, the triangular wave generating circuit 116 generates a basic triangular wave, and the switching circuit 117 is activated by the control signal at ON intervals of a time T1, so that the motor is accordingly driven via the output device 114.

When a load is applied to the motor M, since the current flowing through the motor increases, the increased current is detected by a motor current detection circuit 119 consisting of a resistor R6 and an amplifier circuit 120, and accordingly the time duration of each ON interval of the triangular wave generating circuit 116 is increased, with the result that the time period T2 or T3 of each ON interval of the control signal "a" is increased to achieve a high duty ratio state, and the torque output of the motor M is increased.

Thus, the switching circuit 117 drives the output device 114 with an increased duty ratio in response to the increase in the time duration of the ON interval. Therefore, when the load of the motor is increased from the state of low-speed rotation, the control current of the motor M is automatically increased and its torque output is increased, so that a control state equivalent to a continuously variable speed control can be obtained.

When the high-speed condition is selected, the short-circuit switch unit 115 is turned on, and the motor M is directly driven by the power source E, with the result that the high-speed state is created. Since such switching takes place when the motor torque is high, the shock resulting from the switching is reduced, and smooth operation is enabled.

It is to be understood that switch 115 in Fig. 4 corresponds to the contact set consisting of contact 29 and contact 30 in Fig. 1. For a more detailed description of the motor control circuit, reference is made to the pending U.S. patent application based on Japanese patent applications Nos. 63-326438 and 01-140110.

If this actuating lever is now pressed against the sliding element return spring, the linear sliding element 28 cooperating with the lever 13 is moved backwards, and this causes the linearly movable contact 29 to come into contact with the front fixed contact 30, whereby the motor voltage is switched on and the motor is rotated in the normal direction is rotated.

In this connection, it should be mentioned that by adjusting the pressing stroke of the operating lever 13, one of the direction reversing levers 38 is pressed by the operating pin 37 at an early stage of the pressing stroke, and the lateral sliding member 40 cooperating with this lever 38 is moved laterally, with the result that one of the laterally movable contacts 44 comes into contact with the rear fixed contact 44 for output control to generate a small power which can improve the working efficiency, for example, when threading a screw.

When the operating lever is fully depressed, the maximum torque of the engine is obtained and high power can be easily obtained.

When the operating lever 13 is released, the linear slide 28 returns to its forward position by the loading force of the slide return spring 32 and switches off the voltage supply to the motor.

When the polarity of the motor is to be reversed, the side lever 55 of the reversing switch lever 51 is moved to another position and the resulting lateral movement of the operating pin 37 is transmitted to the front portion of the other direction reversing lever and switches the polarity of the motor. When the operating lever is pressed after this switching is made, the operating pin 37 faces the front portion of the other direction reversing lever by means of the linear slider 28, thereby causing the associated lateral slider to be moved and the associated rotational direction of the motor to be achieved, while the lateral slider associated with one direction reversing lever would not be moved.

As described above, by moving the lateral slider laterally in synchronism with an early portion of the stroke of the linear slider, it becomes possible to switch between the contacts of the two lateral sliders in synchronism with the movement of the linear slider, and the return spring for the lateral sliders can be omitted, so that the number of components can be reduced, the structure can be simplified, and the assembly work can be facilitated.

Referring to Fig. 5, which shows a second embodiment of the present invention, a load force sensing piece F is arranged between the opposite surfaces of the linear slide 28 and the slide return spring 32. The load force sensing piece F is provided with a circular spring seat F1 in its rear end and a small projection F2 in its front end, and its front end is received in a loose hole 28a provided in the opposite surface of the linear slide 28 by the spring force of the slide return spring 32 in such a manner that a tactile feeling is given to the operating pin 37 when a lower pin 37b of the operating pin is caught by the free end of the small projection F2, as described below.

The operating pin 37 is provided with an upward pin 37a on its upper surface and a lower pin 37b projecting downward from its lower surface, and the operating pin 37 is received in a lateral sliding slot 45 provided in the upper surface of the linear slide member 28, while the lower pin 37b is received in a lateral movement permitting slot 45 which communicates with a lower part of the lateral sliding slot 45. Further, the lower pin 37b and the small projection F2 are provided on an intersection point of the vertically recessed lateral movement permitting slot 45 and the horizontally recessed loose hole 28a in such a manner that the operating pin 37 is subjected to a resistance change so as to produce a tactile feeling when it is moved laterally against the loading force acting between the lower pin 37b and the small projection F2.

When the reversing lever 51 is operated, since the operating pin 37 cooperating therewith by means of one of the direction reversing levers is temporarily engaged with the tactile piece F by the loading force, and the lower pin 37b passes over the free end of the small projection F2, thereby producing a sudden change in the loading force and hence also in the resistance to which the reversing lever 51 is subjected, the operator of this reversing lever 51 can obtain a clear tactile feeling.

As described above, according to this embodiment, since a clear tactile feeling is provided when the lever is switched so that the operability and reliability of the reversing shift lever are improved, and the return spring for the linear slider is used to generate this tactile feeling so that a saving of components is achieved without the need for special elastic parts for generating the tactile feeling, it is possible to simultaneously achieve both a saving of components and an improvement in the operability of the reversing shift lever.

Claims (6)

1. Switch mechanism for a power tool with a linear sliding element (28) which is accommodated in a switch housing (12) such that it can be displaced in a first direction along a wall surface of the switch housing, a return spring (32) for loading the linear sliding element (28) in the first direction, Manual actuating means (13) for manually moving the linear sliding element against a spring force of the return spring, an actuating pin (37) seated on the linear sliding element so that it can be displaced along a second direction perpendicular to the first direction, characterized by a pair of direction reversing levers (38, 39) crossed by a pivot pin (47) mounted on the switch housing (12) in the manner of scissors, the actuating pin (37) being arranged adjacent to first ends of the direction reversing levers, a pair of lateral sliding elements (40, 41) which are engaged by second ends of the direction reversing levers and can move in the second direction along a wall surface of the switch housing, a first contact set with contacts (29, 30) which are seated on the linear sliding element (28) and the wall surface of the switch housing for mutual interaction when moving the linear sliding element in the first direction, and a second contact set with contacts (42, 43, 44) which are arranged for mutual interaction when moving the lateral sliding elements in the second direction on the lateral sliding elements (40, 41) and the wall surface of the switch housing (12) sit, wherein the actuating pin (37) is movable between the first ends of the direction reversing levers (38, 39) such that selectively one of the direction reversing levers and the associated one of the lateral sliding elements (40, 41) is actuated with movement of the linear sliding element (28) along the first direction via an engagement between the actuating pin and the first end of the associated one of the direction reversing levers. 2. A switch mechanism for a power tool according to claim 1, wherein the engagement between each of the lateral sliding members (40, 41) and the second end of the associated one of the direction reversing levers (38, 39) consists of engagement between a slot (49) and a pin (48). 3. A switch mechanism for a power tool according to claim 1, wherein the first contact set comprises contacts for selecting between full power and partial power of an electric motor (M) and the contact set comprises contacts for turning on the motor and switching the direction of rotation of the motor. 4. A switch mechanism for a power tool according to claim 1, wherein the direction reversing levers (38, 39) are provided with means for restricting a range of mutual angular displacement. 5. Switch mechanism for a power tool according to Claim 1, wherein trigger means are provided between the actuating pin (37) and the linear sliding element (28) for generating a tactile feeling when the actuating pin is actuated, 6. Switch mechanism for a power tool according to claim 5, wherein the trigger means comprises a slot (45) for receiving the actuating pin so as to permit its movement in the second direction, a trigger element (F) received in a hole (28a) communicating with the slot so as to abut against the actuating pin (37) at one end (F2) thereof and to receive a loading force from the return spring (32) for the linear slide element (28) at its other end (F1), the actuating pin experiencing elastic resistance when it is moved along the slot and passes over the first end of the stop element.