# Patent

## Title
Actuation apparatus for power tool

## Abstract

When the mode change knob of a multi-mode hammer drill is moved to the hammer only position, an electronic sensor sends a signal to a control logic circuit. When the user then depresses the trigger mechanically closing the ON/OFF switch, the control logic circuit applies a voltage either to a holding relay or to the gate of a triac which enables the relay or triac to conduct, thus providing a parallel circuit by-passing the ON/OFF switch. Consequently, when the user releases the trigger and opens the ON/OFF switch, the parallel relay or triac maintains current flow to the motor. It can be seen that in hammer only mode the user can activate the hammer drill by simply tapping the trigger to depress it and does not need to hold down trigger during use of the hammer in operation.

## Background
REFERENCE TO RELATED CASES
This application is a continuation of U.S. patent application Ser. No. 11/359,167 filed in the U.S. on Feb. 22, 2006 now abandoned, the contents of which are incorporated herein in their entirety by reference, which claims priority from UK Application No. GB 05 035 58.9, filed in the United Kingdom on Feb. 22, 2005, the contents of which are incorporated herein in their entirety by reference.


FIELD OF THE INVENTION
The present invention relates to an actuation apparatus for a power tool. In particular, the invention relates to a hammer drill. The invention relates more particularly, but not exclusively to an actuation apparatus for the trigger of a power tool and to a power tool incorporating such an apparatus.
BACKGROUND OF THE INVENTION
Hammer drills are power tools that generally have three modes of operation, i.e. a hammer only mode, a drill only mode and a combined hammer and drilling mode. In general, the motor of a hammer drill is operated by the user depressing a spring-loaded trigger, and deactivated by the user releasing the trigger such that it is necessary to hold the trigger down during operation of the tool.
UK patent no. 2314288 describes an electric combination hammer having a drilling mode and a chiselling mode. The hammer comprises a housing with a handle and a trigger disposed on the handle for operating an electric on/off switch. The combination hammer has an operating knob for switching manually between the drilling mode and the chiselling mode, and the trigger has an associated detent which, when the operating knob is in the position corresponding to the chiselling mode, allows the on/off switch to be latched in a closed position such that even when the user releases their grip on the trigger the combination hammer remains in operation.
The electric combination hammer of GB2314288 suffers from the drawback that the components for the detent system are mechanical in nature, comprising cam surfaces and resilient springs, such that they are susceptible to wear and tear with repeated use. Also, the use of such mechanical components makes the hammer expensive to manufacture.
Preferred embodiments of the present invention seek to overcome the above disadvantage of the prior art.
BRIEF SUMMARY OF THE INVENTION
According to an aspect of the present invention, there is provided an actuation apparatus for a power tool having a housing, a motor with a rotary output shaft disposed in the housing, drive means for driving a working member of the tool in response to rotation of said rotary output shaft, and a trigger disposed on the housing to enable activation of said motor, the actuation apparatus comprising:
switching means for enabling a user to select between a hammer mode of said tool, a drilling mode of said tool and/or hammer and drilling mode of said tool;
detection means for providing at least one signal indicating which mode of operation of the tool has been selected; and
control means for controlling operation of the motor in response to at least one said signal, such that in at least one first predetermined mode of operation of said tool, said motor is operated by a first depression of the trigger and remains activated until deactivated by a second depression of the trigger, and in at least one second predetermined mode of operation of said tool, said motor is only activated while the trigger is depressed.
By providing control means for controlling operation of the motor in response to at least one said signal, such that in at least one first predetermined mode of operation of said tool, said motor is operated by a first depression of the trigger and remains activated until deactivated by a second depression of the trigger, and in at least one second predetermined mode of operation of said tool, said motor is only activated while the trigger is depressed, this provides the advantage that the need for a mechanical detent system to latch on the trigger mechanism when a predetermined mode of operation is selected is eliminated. This is advantageous because an electronic system is not subject to mechanical wear and tear to the same extent as a mechanical system and can also be made much more compact, thus reducing the dimensions of the tool. Also, the apparatus can be manufactured more cost-effectively than apparatus incorporating a purely mechanical actuator system.
in a preferred embodiment, at least one said first predetermined mode is a hammer mode of the tool.
This provides the advantage that the operator does not have to continuously grip the trigger during the hammer mode operation of the tool, and therefore can move their hands around the body of the tool whilst it is in operation to provide a better grip.
The apparatus may further comprise on/off switch means for actuating the motor and adapted to be actuated by the trigger of the tool.
The apparatus may further comprise override switch means adapted to be closed by said control means, in response to said first depression of the trigger of the tool, when at least one predetermined said first mode is selected, such that even when the trigger is released, the motor remains in operation.
In a preferred embodiment, when at least one said first predetermined mode is selected, said control means opens said override switch means in response to a second depression of said trigger.
Said override switch means may be connected in parallel with said on/off switch means.
Said override switch means may comprise at least one triac, thyristor, FET, transistor or relay.
In a preferred embodiment, said control means includes control logic which may include a microprocessor.
In a preferred embodiment, there I further provided a sensor for providing an electrical signal to the control logic or microprocessor indicative of the condition of said on/off switching means.
Said switching means may include a rotatable knob.
According to a further aspect of the present invention, there is provided a power tool comprising a control apparatus as defined above.
In a preferred embodiment, said power tool is a hammer drill.



BRIEF DESCRIPTION OF THE DRAWINGS
A preferred embodiment of the present invention will now be described, by way of example only and not in any limitative sense, with reference to the accompanying drawings in which:—
FIG. 1 is a side view of a hammer drill;
FIG. 2 is a circuit diagram of the control apparatus of the first embodiment of the present invention; and
FIG. 3 is a circuit diagram of the control apparatus of the second embodiment of the present invention.



DETAILED DESCRIPTION OF THE INVENTION
The first embodiment of the present invention will now be described with reference to FIGS. 1 and 2.
Referring to FIG. 1, a hammer drill shown generally by 2 comprises a housing 4 having a handle portion 6 for the user to grip. A motor 100 is disposed in the housing 4 which drives a drive mechanism 102 via a rotary output shaft 104, also disposed in the housing 4 and which is capable of driving a bit 8 in a drill mode, in which the bit is rotated, a hammer mode in which impacts are imparted to the bit 8, or a hammer and drill mode, in which both actions are combined. Bit 8 is held in a chuck 10 which is driveably connected to the drive mechanism 104. The operation of the drive mechanism will be familiar to persons skilled in the art and is not relevant to the understanding of the present invention, and will therefore not be described in greater detail herein.
A trigger 12 is disposed on the handle portion 6 to enable the user to activate the hammer drill 2. A mode change knob 14 is rotatably disposed on the housing 6. The mode change knob has three positions, one for hammer only mode, one for drill only mode and one for selecting combined hammer and drilling mode. When the mode change knob is rotated, it resiliently locks into one of the three positions indicating the selected mode. An electric cable 16 is attached to the housing 6 for providing electrical power to the motor. The electrical power is in the form of 230v A.C. electrical mains power supply. However, it will be obvious to a person skilled in the art that hammer drills powered by a 120v A.C. power supply or a D.C. power supply, such as a battery, could utilise the present invention in their construction.
Referring to FIG. 2, the cable16 provides a 230v A.C. voltage across contacts 18 and 20. The electric motor 22 is controlled by an on/off switch 24 which is directly coupled to the trigger 12 such that when trigger 12 is depressed the switch 24 closes. When the trigger 12 is released, the switch 24 opens. An electronic sensor 30 detects the position of the mode change knob 14 and hence is able to determine what mode of operation the mode change knob 14 is set to. When the mode change knob 14 is in the hammer only mode position, the electronic sensor 30 sends a signal to the control logic 26 indicative that the knob 14 is set to hammer only mode. The control logic 26 is utilised to control the operation of the hammer drill, including the control of the motor 22. The control logic 26 may include a microprocessor, depending on the complexity of the control required. The control logic 26 is connected to a first electrical switch 28, for example, an electrical relay, in order to control the electrical switch 28, which electrical switch 28 is electrically connected in parallel to the switch 24.
A second switch 34 is mechanically connected to the on/off switch 24 such that when the on/off switch 24 is closed, the second switch 34 closes, and when the on/off switch 24 is opened, the second switch opens. The second switch 34 is electrically connected to the control logic 26.
The operation of the control apparatus will now be described with reference to FIGS. 1 and 2.
The mode change knob 14 allows the user to select one of the three modes in which the hammer drill can operate. When the drill only or combined hammer and drilling mode is selected, the trigger 12 is used to open and close switch 24 such that when the trigger is pressed the motor activates and drives the bit either in a rotary drilling action (drill mode) or a rotating action in which impacts are imparted to the bit 8 (hammer and drill mode). When the trigger 12 is released, the switch 24 is opened which interrupts the connection between contacts 18 and 20 and deactivates the motor.
When the mode change knob 14 is moved to the hammer only position, the electronic sensor 30 sends a signal to the control logic 26. The control logic 26 then waits for the user to depress trigger 12 closing switch 24. The control logic 26 knows the status of the on/off switch 24 due to the status of the second switch 34. When this happens, the control logic 26 applies a voltage to the second electrical switch 28 which switches the electrical switch 28 on and enables the electrical switch 28 to conduct, thus providing a parallel electrical connection bypassing the on/off switch 24. Consequently, when the user releases trigger 12 to open the switch 24, as the electrical switch 28 is in parallel with the on/off switch 24, a current continues to flow through the motor 22. It can be seen that in hammer only mode the user can activate the hammer drill by simply tapping the trigger 12 to depress it but then does not need to hold down trigger 12 to maintain operation of the motor 22 during use of the hammer in operation.
When the user depresses trigger 12 for the second time, causing the on/off switch 24 to be closed again, which in turn causes the second switch 34 to close again, which is then detected by the control logic 26, the electrical switch 28 is switched off by the control logic 26, so that no current is able to flow through the electrical switch 28, such that, when the trigger 12 is released, opening the on/off switch 24, the electrical connection between contacts 18 and 20 is interrupted and the motor 22 stops.
A second electrical switch 36 is shown in FIG. 2 in the electrical circuit between the contact 18 and the motor 22. During all modes of operation, the electrical switch 36 is normally switched on at all times by the control logic 26 to allow current to freely flow through it. However, in certain circumstances, due to safety or other operational reasons, the control logic 26 switches the second electrical switch 36 off, preventing the motor 22 from being activated by the trigger 12 when depressed.
It will be appreciated by persons skilled in the art that the above embodiment has been described by way of example only and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims.
In particular, the one press activation of the power drill has been described in connection with the hammer only mode. The power tool could be easily adapted such that this mode of operation is applied to any of the other modes of operation of the tool or any combination of the modes of operation.
In the embodiment described, the signals between electronic sensor 30, the electrical switch 24 and the control logic 26 are transmitted using electric cables or wires. However, a person skilled in the art will appreciate that the connections could be wireless e.g. the signals are transmitted using of a radio transmitter, or in the form of an optical cable or fibre.
A second embodiment of the present invention will now be described with reference to FIG. 3. The design of the second embodiment is substantially the same as that of the first embodiment. Where the same features are present in the second embodiment that are present in the first embodiment, the same reference numbers have been utilised in the drawings.
The difference between the first and second embodiments is that the electrical switches 28, 36 have been replaced by triacs 28′, 36′. This provides for a simpler design. Furthermore, the use of a triac 36′ to control the motor 22 not only enables it to be switched on or off, but also enables its speed to be controlled. Thus, during the operation of the hammer drill, by controlling the operation of the triac using the control logic 26, the speed of the motor is controlled.
In further embodiments of the present invention, other types of electrical or mechanical switching devices to those of relays or triacs can be used, such as transistors, thyristors and FETs in order to suite the type of power supply, the motor and control logic etc.

## Claims

1. A power impact tool comprising: a motor, a tool bit driven by the motor, the tool bit having at least a driven mode to perform a predetermined operation on a workpiece by a striking movement in an axial direction of the tool bit, a trigger manually operated by a user of the power impact tool to control energization and non-energization of current to drive the motor, wherein the motor is energized when the user operates the trigger to turn on and the energized state of the motor is maintained until the trigger is again operated in a same manner with the turning-on operation, wherein the trigger has a operating position and an initial position, wherein the trigger is biased from the operating position toward the initial position and is normally held in the initial position, the trigger being operated by a user of the power impact tool between the initial position and the operating position to control energization and non-energization of current to the motor, the power impact tool further comprising a mode changing member manually switched by the user between a first mode in which the tool bit performs a striking movement and a second mode in which the tool bit performs a rotating movement around the axis of the tool bit in addition to or instead of the striking movement wherein, when the mode changing member is located in the first mode position, the motor is energized by depressing the trigger from the initial position to the operating position and the energized state of the motor is maintained until the trigger is operated again after the trigger is released and returned again to the initial position and when the mode changing member is located in the second mode position, the motor is energized by depressing the trigger from the initial position to the operating position and the energization of the motor is disabled when the trigger is released and returned to the initial position.

2. The power impact tool as defined in claim 1 further comprising a driving circuit for the motor, wherein the motor is energized by the driving circuit when the user operates the trigger to turn on and the driving circuit maintains the energized state of the motor until the trigger is again operated in a same manner with the turning-on operation, while allowing the trigger being returned to an initial position during maintaining the energized state of the motor.

3. The power impact tool as defined in claim 1 further comprising a driving circuit for the motor wherein: when the mode changing member is located in the first mode position, the driving circuit energizes the motor according to the user depressing the trigger from the initial position to the operating position and the driving circuit maintains the energized state of the motor until the trigger is operated again after the trigger is released and returned again to the initial position and, when the mode changing member is located in the second mode position, the driving circuit energizes the motor according to the user depressing the trigger from the initial position to the operating position and the driving circuit disables the energization of the motor when the trigger is released and returned to the initial position.

4. The power impact tool as defined in claim 1 further comprising: a first switch that outputs a detection signal in the form of an electric signal to detect whether the trigger is in the initial position or in the operating position, a second switch that outputs a detection signal in the form of an electric signal to detect whether the mode changing member is in the first mode position or in the second mode position, a third switch that is provided in a driving circuit of the motor and is turned on and off to energize and non-energize the driving circuit and a controller which receives the electric signals from the first and the second switches and controls the on-off operation of the third switch according to the received electric signals, wherein: when the second switch outputs a signal that the mode changing member is located in the first mode position and the first switch outputs a signal that the trigger is in the operating position, the controller turns on the third switch and energizes the driving circuit of the motor, and the controller keeps the third switch in the on state until the first switch changes to a signal that the trigger is located in the initial position and to the operating position and again to the initial position and when the electric signal of the second switch outputs a signal that the mode changing member is located in the second mode position and the first switch outputs a signal that the trigger is located in the operating position, the controller turns on the third switch and energizes the driving circuit of the motor, and when the first switch thereafter outputs a signal that the trigger is located in the initial position, the controller turns off the third switch and non-energizes the driving circuit of the motor.

5. The power impact tool as defined in claim 1 further comprising a controller of the motor: wherein, when the mode changing member is located in the first mode position, the controller respectively counts the number of times of depressing operations of the trigger and the number of times of releasing operations of the trigger, the controller energizes the motor when odd-numbered depressing operations of the trigger are counted and the controller keeps the energized state when even-numbered depressing operations of the trigger are counted, while the controller keeps energized state of the motor when odd-numbered releasing operations of the trigger are counted and turns off the energized state of the motor when even-numbered releasing operations of the trigger are counted.

6. The power impact tool as defined in claim 1 further comprising: a body that houses the motor, a grip which the user of the power impact tool holds, an elastic element provided between the body and an upper end region of the grip, the elastic element elastically coupling the grip to the body, wherein the trigger is located in the upper region of the grip or in the vicinity of the upper region of the grip.