Patent Description:
A conventional electric power tool disclosed in U. Patent No. <CIT> is configured to enable or disable a firing action based on whether an electromagnet of the electric power tool is excited or not. However, when the electromagnet is provided with electric current and is excited for a long time, an enameled wire and a core of the electromagnet may be burned due to high temperature generated by the electromagnet. One solution is to increase heat resistance of the enameled wire and the core by, for example, increasing a diameter of coil of the enameled wire or increasing the number of turns of the winding of the enameled wire. However, such solution not only increases the cost of the electric power tool, but also increases inner temperature of the electric power tool.

Therefore, an object of the disclosure is to provide an electric power tool and a method of controlling the electric power tool that can alleviate at least one of the drawbacks of the prior art.

According to an aspect of the disclosure, there is provided an electric power tool according to claim <NUM>.

According to an aspect of the disclosure, there is provided a method of controlling an electric power tool according to claim <NUM>.

Other features and advantages of the disclosure will become apparent in the following detailed description of the embodiment(s) with reference to the accompanying drawings. It is noted that various features may not be drawn to scale.

Referring to <FIG>, <FIG> and <FIG>, an electric power tool according to an embodiment of the disclosure is provided. In this embodiment, the electric power tool is a pneumatic electric nail gun, and includes a battery <NUM>, a power circuit <NUM>, a motor <NUM>, a driving module <NUM>, a switch module <NUM>, a lifter <NUM> configured to be driven by the motor <NUM>, a firing pin <NUM> configured to be driven by the lifter <NUM>, a piston <NUM> connected to the firing pin <NUM>, an electromagnet <NUM>, a driving circuit <NUM>, a joint <NUM> configured to be driven by the electromagnet <NUM>, a latch <NUM> configured to be driven by the joint <NUM>, and a controller <NUM>. The electric power tool further includes a housing <NUM>, and the piston <NUM> cooperates with the housing <NUM> to define a pressure chamber <NUM>.

The power circuit <NUM> is electrically connected to the battery <NUM>, and is configured to stabilize and transform electric energy provided by the battery <NUM> (e.g., DC 18V) for use by other internal circuits of the electric power tool. The power circuit <NUM> includes a direct-current to direct-current converter (DC-DC converter) <NUM> and, for example, two low-dropout regulators (LDOs) <NUM>. The LDOs <NUM> provide electric energy with different voltages (e.g., 5V and 12V) respectively for the controller <NUM> and the driving module <NUM>.

The motor <NUM> may be implemented using a brushless DC motor (BLDC). The driving module <NUM> is electrically connected to the switch circuit <NUM>, and the switch circuit <NUM> is electrically connected to the motor <NUM>. The driving module <NUM> is further electrically connected to the controller <NUM>, and is configured to receive a control signal in a form of a pulse-width modulation (PWM) signal outputted by the controller <NUM>, and to control the switch circuit <NUM> to drive the motor <NUM> to rotate at a desired rotational speed based on a duty cycle of the control signal thus received. The switch circuit <NUM> may be implemented using a metal-oxide-semiconductor field-effect transistor (MOSFET) switch.

The lifter <NUM> is connected to the motor <NUM>, and is configured to be driven by the motor <NUM>, where the lifter <NUM> then drives the firing pin <NUM> to move to perform a firing procedure. The lifter <NUM> includes a lifting wheel <NUM> that is configured to rotate (in a counter-clockwise direction in <FIG>) when being driven by the motor <NUM>, a plurality of posts <NUM> arranged along part of a circumference of the lifting wheel <NUM>, and a sliding surface <NUM> at the rest of the circumference. The firing pin <NUM> includes a shaft <NUM>, a plurality of teeth <NUM> that are positioned along the shaft <NUM>, and a block <NUM> disposed on the shaft <NUM> near a distal end of the shaft <NUM> that is opposite to the other end connected to the piston <NUM>.

When a user presses a trigger switch (not shown) of the electric power tool, the firing procedure will be performed immediately. At the beginning of the firing procedure, the firing pin <NUM> is originally located at a standby position where the firing pin <NUM> is ready to perform a firing action (see <FIG>). The firing pin <NUM> is at a bottom dead center after finishing the firing action, and the bottom dead center is farthest from the standby position in a firing direction from the standby position to the bottom dead center (i.e., a direction in which an object, for example, a nail, is shot by the electric power tool). When the firing pin <NUM> is located at the standby position, a first one of the posts <NUM> of the lifter <NUM> in the counter-clockwise direction is interlocked with a last one of the teeth <NUM> of the firing pin <NUM> in the firing direction, and the motor <NUM> drives the lifting wheel <NUM> to rotate, thus driving the firing pin <NUM> to move from the standby position to a top dead center in an opposite direction that is opposite to the firing direction. The top dead center is farthest from the standby position in the opposite direction. When the firing pin <NUM> is at the top dead center, the piston <NUM> compresses a volume of gas in the pressure chamber <NUM> to increase a pressure therein. When the lifting wheel <NUM> rotates to where the first one of the posts <NUM> is disengaged from the last one of the teeth <NUM> (i.e., when the teeth <NUM> reaches the sliding surface <NUM>), the firing pin <NUM> is driven by the pressure in the pressure chamber <NUM> to move in the firing direction from the top dead center to the bottom dead center to complete the firing action (e.g., firing of a nail not shown in the drawings). That is to say, the firing action includes the firing pin <NUM> moving from the standby position to the top dead center by lifter <NUM> driven by the motor <NUM>, and then the firing pin <NUM> moving from the top dead center to the bottom dead center by the pressure in the pressure chamber <NUM> to fire a nail. The motor <NUM> continues to drive the lifting wheel <NUM> to rotate, and the posts <NUM> are interlocked with the teeth <NUM> again, thus driving the firing pin <NUM> to move from the bottom dead center toward the standby position for completing the firing procedure. That is to say, the firing procedure includes the firing pin <NUM> performing the firing action, and then the firing pin <NUM> moving from the bottom dead center back to the standby position. In this embodiment, the posts <NUM> of the lifter <NUM> are disengaged from the teeth <NUM> of the firing pin <NUM> at the top dead center.

Referring to <FIG>, the driving circuit <NUM> is electrically connected to the electromagnet <NUM> and the controller <NUM>, and is configured to provide an electric current to excite the electromagnet <NUM>. The driving circuit <NUM> includes a gate driver integrated circuit (IC) <NUM>, a semiconductor switch <NUM> (e.g., MOSFET switch), and a flywheel diode <NUM> that is electrically connected to the electromagnet <NUM> in parallel. The electric power tool further includes an electrical connector <NUM> that electrically connects the driving circuit <NUM> and the electromagnet <NUM>. The gate driver IC <NUM> is configured to receive a driving signal (as shown in <FIG>) from the controller <NUM>, convert a voltage of the driving signal (e.g., having a voltage of 5V) into a desired voltage (e.g., 12V), and output the driving signal with the desired voltage to the gate of the semiconductor switch <NUM> to drive the semiconductor switch <NUM> to be on or off. In some embodiments, the driving signal is designed to ensure that a channel of the semiconductor switch <NUM> may be fully opened when turned on, so as to reduce a resistance of the semiconductor switch <NUM> and thus reduce heat generated by the semiconductor switch <NUM>.

Referring to <FIG>, the joint <NUM> includes a pole <NUM> that partially extends into the electromagnet <NUM>, a connecting component <NUM> that connects the actuator <NUM> and the latch <NUM>, and a spring <NUM> that is connected between the electromagnet <NUM> and the pole <NUM>. The pole <NUM> is made of magnetic material and may be attracted to the electromagnet <NUM> when the electromagnet <NUM> is excited. Further referring to <FIG>, when the electromagnet <NUM> is in a non-excited state, the latch <NUM> is positioned at a blocking position in front of the block <NUM> to block the firing pin <NUM> from moving to the bottom dead center in the firing direction (i.e., disabling the firing pin <NUM> from performing the firing action), so as to avoid false firing. When the firing procedure is ready to be performed, the electromagnet <NUM> is excited by the driving circuit <NUM> to a fully excited state. The pole <NUM> is then attracted by the electromagnet <NUM> that is in the fully excited state to move in a first direction (i.e., the left direction in <FIG> and <FIG>) so as to drive the connecting component <NUM> to rotate clockwise, and as shown in <FIG>, the latch <NUM> is driven by the connecting component <NUM> to rotate clockwise and move away from the block <NUM> to a non-blocking position where the latch <NUM> does not block the firing pin <NUM> from moving to the bottom dead center in the firing direction (i.e., enabling the firing pin <NUM> to perform the firing action). In addition, the spring <NUM> is compressed by the pole <NUM> when the pole <NUM> moves in the first direction. After performing the firing action, the electromagnet <NUM> may stop attracting the pole <NUM> by returning to the non-excited state, and the pole <NUM> is pushed by the spring <NUM> to move in a second direction (i.e., the right direction in <FIG> and <FIG>) opposite to the first direction, so as to drive the connecting component <NUM> to rotate counter-clockwise, thus moving the latch <NUM> to the blocking position as shown in <FIG>.

Referring to <FIG> and <FIG>, the controller <NUM> is electrically connected to the driving circuit <NUM> and is configured to output the driving signal to control the driving circuit <NUM> to turn on the semiconductor switch <NUM> during an excitement period (T1) that includes a first time period (t1) and a second time period (t2) immediately after the first time period (t1). First, the controller <NUM> is configured to output the driving signal in a continuous manner to control the driving circuit <NUM> to continuously turn on the semiconductor switch <NUM>, thus providing a constant electric current to excite the electromagnet <NUM> for the first time period (t1) to excite the electromagnet <NUM> to the fully excited state. Then, the controller <NUM> is further configured to, immediately after the first time period (t1), output the driving signal in a pulsating manner to control the driving circuit <NUM> to periodically turn on the semiconductor switch <NUM>, thus providing a pulsating electric current to the electromagnet <NUM> for the second time period (t2) to keep the electromagnet <NUM> in the fully excited state.

In certain embodiments, the first time period (t1) is set to be not shorter than a fully excited time that is for the electromagnet <NUM> to reach the fully excited state from the non-excited state with the constant electric current. The fully excited time depends on the specifications of the electromagnet <NUM>, and is usually between <NUM> to <NUM> milliseconds (ms). In this embodiment, the first time period (t1) is set to be equal to the fully excited time, but should not be limited to the abovementioned example. Since the fully excited time may have slight offsets due to production uncertainties, the first time period (t1) may set to be longer than the fully excited time to ensure that when the driving circuit <NUM> is providing the pulsating electric current to the electromagnet <NUM>, the electromagnet <NUM> is already in the fully excited state.

The controller <NUM> may be implemented as a circuit (e.g., a microcontroller unit, MCU) with functions of analog-to-digital conversion (AID conversion), input/output detection (I/O detection), and PWM output.

Referring to <FIG>, <FIG>, and <FIG>, the controller <NUM> is further configured to, after a predetermined time period (T2) since the controller <NUM> started controlling the driving circuit <NUM> to provide the constant electric current, control the driving circuit <NUM> to operate the motor <NUM> to drive the lifter <NUM>, which then drives the firing pin <NUM> to perform the firing procedure. It should be noted that the predetermined time period (T2) should be at least longer than the first time period (t1) (i.e., longer than the fully excited time) to avoid the latch <NUM> blocking (or partially blocking) the firing pin <NUM> from performing the firing action. It should be further noted that the predetermined time period (T2) should not be too long, otherwise a time from the user pressing the trigger switch to completing the firing action would be too long. The controller <NUM> is further configured to control the driving circuit <NUM> to stop providing the electric current to the electromagnet <NUM> when the second time period (t2) has elapsed, and control the driving circuit <NUM> to stop the motor <NUM> from operating when the controller <NUM> has determined that the firing pin <NUM> has returned to the standby position based on a firing pin position switch (not shown) (i.e., the firing procedure has been completed). In this embodiment, the standby position is close to the top dead center so that the firing action may be performed quickly after the user presses the trigger switch. In this embodiment, the lifter <NUM> includes a magnet, the firing pin position switch may be implemented as a Hall sensor that is configured to detect a position of the magnet, and the controller <NUM> determines, based on the firing pin position switch, whether the magnet has moved to a predetermined position that corresponds to the firing pin <NUM> returning to the standby position. When the controller <NUM> determines that the magnet has moved to the predetermined position, the controller <NUM> controls the driving circuit <NUM> to stop the motor <NUM> from operating.

A relation of various time periods that are mentioned above are as following: T2+Td < t1+t2 < T2+Td+Tu, where Td represents a time taken for the firing pin <NUM> to move from the standby position to the top dead center and then to the bottom dead center (i.e., the time for performing the firing action), and Tu represents a time taken for the firing pin <NUM> to be moved by the lifter <NUM> from the bottom dead center to the top dead center. The excitement period (T1) (i.e., a total time that the electromagnet <NUM> is being excited) is equal to the first time period (t1) plus the second time period (t2). It should be noted that after the firing pin <NUM> is moved from the standby position to the top dead center and then to the bottom dead center (T2+Td), and before the firing pin <NUM> is moved from the bottom dead center back to the top dead center (T2+Td+Tu), the controller <NUM> controls the driving circuit <NUM> to stop providing the pulsating electric current to the electromagnet <NUM>. As such, the electromagnet <NUM> may be kept in the fully excited state when performing the firing action, thus keeping the latch <NUM> in the non-blocking position when the firing pin <NUM> is performing the firing action, and the electromagnet <NUM> may exit the fully excited state before the firing pin <NUM> is moved back to the top dead center, thus avoiding the firing pin <NUM> from accidently performing the firing action again when the lifting wheel <NUM> stops too slowly or fails to stop due to malfunction of the electric power tool.

Referring to <FIG>, <FIG>, <FIG>, and <FIG>, a method of controlling the electric power tool includes: during the excitement period (T1), the controller <NUM> controlling the driving circuit <NUM> to provide the constant electric current to the electromagnet <NUM> for the first time period (t1) to excite the electromagnet <NUM> to the fully excited state; and immediately after the first time period (t1), the controller <NUM> controlling the driving circuit <NUM> to provide the pulsating electric current to the electromagnet <NUM> for the second time period (t2) to keep the electromagnet <NUM> in the fully excited state. To describe in further detail, the method of controlling the electric power tool includes steps <NUM> to <NUM>.

When the electric power tool is powered up, the flow of the method enters step <NUM>. In step <NUM>, the controller <NUM> determines whether the firing procedure is ready to be performed, for example, by determining a condition of a safety switch (not shown), the trigger switch, and the firing pin position switch. The condition may be, for example, the safety switch and the trigger switch are both being pressed, and the firing pin position switch is indicating that the firing pin <NUM> is located at a correct position for performing the firing action (e.g., the standby position), etc. When the controller <NUM> determines that the firing procedure is ready to be performed, the flow proceeds to step <NUM>.

In step <NUM>, the controller <NUM> outputs the driving signal to the driving circuit <NUM>, and the driving circuit <NUM> provides the constant electric current to the electromagnet <NUM> based on the driving signal to excite the electromagnet <NUM> to the fully excited state, thus driving the latch <NUM> to move from the blocking position to the non-blocking position. Accordingly, the firing pin <NUM> is able to perform the firing action. The controller <NUM> starts timing a third time period (t1_i) and a fourth time period (T2_i), both starting from a time point when the driving circuit <NUM> starts to provide the constant electric current to the electromagnet <NUM>.

In step <NUM>, the controller <NUM> determines whether the third time period (t1_i) has reached the first time period (t1) (e.g., <NUM>). If affirmative, the flow proceeds to step <NUM>; otherwise, the flow of the method goes back to step <NUM>.

In step <NUM>, the controller <NUM> controls the driving circuit <NUM> to provide the pulsating electric current to the electromagnet <NUM>, and the controller <NUM> starts timing a fifth time period (t2_i) starting from a time point when the driving circuit <NUM> starts to provide the pulsating electric current to the electromagnet <NUM>.

In step <NUM>, the controller <NUM> determines whether the fourth time period (T2_i) has reached the predetermined time period (T2) (e.g., <NUM>). If affirmative, the flow proceeds to step <NUM>; otherwise, the flow goes back to step <NUM>.

In step <NUM>, the controller <NUM> outputs the control signal to operate the motor <NUM> to drive the lifter <NUM>, which then drives the firing pin <NUM> to perform the firing action (i.e., driving the firing pin <NUM> to move from the standby position to the top dead center, where the firing pin <NUM> is then driven to the bottom dead center by the pressure in the pressure chamber <NUM>), and immediately after the firing action, drives the firing pin <NUM> back toward the standby position. After step <NUM>, the flow proceeds to step <NUM> and step <NUM>.

In step <NUM>, the controller <NUM> determines whether the fifth time period (t2_i) has reached the second time period (t2) (e.g., <NUM>). If affirmative, the flow proceeds to step <NUM>; otherwise, the flow goes back to step <NUM>.

In step <NUM>, the controller <NUM> determines whether the firing pin <NUM> is located at the standby location based on the firing pin position switch. If affirmative, the flow proceeds to step <NUM>; otherwise, the flow goes back to step <NUM>.

When the controller <NUM> determines that the fifth time period (T2_i) has reached the second time period (t2), in step <NUM>, the controller <NUM> controls the driving circuit <NUM> to stop providing the electric current to the electromagnet <NUM>, thus making the latch <NUM> move back to the blocking position to block the firing pin <NUM> from performing the firing action.

When the controller <NUM> determines that the firing pin <NUM> is located at the standby location, in step <NUM>, the controller <NUM> controls the driving circuit <NUM> to stop the motor <NUM> from operating, and the firing procedure ends. After steps <NUM> and <NUM> have being implemented, the method terminates and the electric power tool may be in a standby mode ready for the user to perform the firing procedure again (i.e., the method is implemented again) or enter a sleep mode when not being used for a standby time period.

Referring to <FIG> and <FIG>, it should be noted that frequency of the pulsating electric current should not be too low during the second time period (t2), otherwise, the electromagnet <NUM> may switch alternately between the fully excited state and a partially excited state, where the electromagnet <NUM> in the partially excited state may not produce a magnetic force strong enough to attract the pole <NUM> for keeping the latch <NUM> in the non-blocking position. A higher frequency of the pulsating electric current could reduce occurrence of the partially excited state, but would cause the electromagnet <NUM> to generate more heat. A higher duty cycle of the pulsating electric current would also cause the electromagnet <NUM> to generate more heat. Since the heat generated by the electromagnet <NUM> depends on a wire diameter of wire wound into a coil of the electromagnet <NUM> and the number of turns of the winding, both of which are related to size of the electromagnet <NUM>, the frequency and the duty cycle of the pulsating electric current are set according to the size of the electromagnet <NUM> to avoid generating excess heat by the electromagnet <NUM> (i.e., reducing a time that the electromagnet <NUM> is provided with the electric current). The size of the electromagnet <NUM> depends on an available space in the electric power tool for placing the electromagnet <NUM>.

During the second time period (t2), the frequency of the pulsating electric current shown in <FIG> may be greater than <NUM>, and an off time period (t3) during which the pulsating electric current is in an off state is equal to an on time period (t4) during which the pulsating electric current is in an on state (i.e., the duty cycle of the pulsating electric current is <NUM>%). The off time period (t3) should be short enough to make the electromagnet <NUM> remain in the fully excited state. The pulsating electric current may, for example, have a higher frequency as shown in <FIG>, where the pulsating electric current has an off time period (t5) also equal to an on time period (t6) while the off time period (t5) and the on time period (t6) of the pulsating electric current of <FIG> are both shorter than the off time period (t3) and the on time period (t4) of the pulsating electric current of <FIG>. The pulsating electric current may also have a different duty cycle as shown in <FIG>, where the pulsating electric current has an off time period (t7) shorter than an on time period (t8) (i.e., the duty cycle of the pulsating electric current of <FIG> is greater than <NUM>%). As such, if the voltage of the battery <NUM> is low, using a higher duty cycle may keep the electromagnet <NUM> in the fully excited state so as to produce a magnetic force strong enough to attract the pole <NUM> (as shown in <FIG>).

In summary, the controller <NUM> controls the driving circuit <NUM> to first provide the constant electric current to fully excite the electromagnet <NUM>, and then provide the pulsating electric current to keep the electromagnet <NUM> in the fully excited state during the firing action, thus reducing the heat generated by the electromagnet <NUM>. Accordingly, there is no need to increase the wire diameter or the number of turns of the winding to reduce the heat generated by the electromagnet <NUM>, and thus the electric power tool may be designed with a relatively smaller size and a lighter weight.

The relation of T2+Td < t1+t2 < T2+Td+Tu for the various time periods that are mentioned above are designed to ensure that the electromagnet <NUM> remains in the fully excited state to keep the latch <NUM> in the non-blocking position when the firing pin <NUM> is performing the firing action, and that the electromagnet <NUM> exits the fully excited state before the firing pin <NUM> is moved back to the top dead center so that the latch <NUM> may be moved to the blocking position to avoid false firing.

The predetermined time period (T2) is set to be longer than the fully excited time to ensure that the motor <NUM> only starts to operate after the electromagnet <NUM> has reached the fully excited state. In other words, when the motor <NUM> starts to operate for driving the firing pin <NUM> to perform the firing procedure, the latch <NUM> has already be driven by the electromagnet <NUM> to move to the non-blocking position, thus enabling the firing pin <NUM> to perform the firing action.

In the description above, for the purposes of explanation, numerous specific details have been set forth in order to provide a thorough understanding of the embodiment(s). It will be apparent, however, to one skilled in the art, that one or more other embodiments may be practiced without some of these specific details. It should also be appreciated that reference throughout this specification to "one embodiment," "an embodiment," an embodiment with an indication of an ordinal number and so forth means that a particular feature, structure, or characteristic may be included in the practice of the disclosure. It should be further appreciated that in the description, various features are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of various inventive aspects; such does not mean that every one of these features needs to be practiced with the presence of all the other features.

Claim 1:
An electric power tool comprising:
a motor (<NUM>);
a lifter (<NUM>) configured to be driven by said motor (<NUM>);
a firing pin (<NUM>) configured to be driven by said lifter (<NUM>) to move from a bottom dead center to a standby position where said firing pin (<NUM>) is ready to perform a firing action, the bottom dead center being farthest from the standby position in a firing direction from the standby position to the bottom dead center, said firing pin (<NUM>) being at the bottom dead center after finishing the firing action;
an electromagnet (<NUM>);
a driving circuit (<NUM>) electrically connected to said electromagnet (<NUM>) and configured to provide an electric current to excite said electromagnet (<NUM>); and
a latch (<NUM>) configured to be moved by said electromagnet (<NUM>) from a blocking position where said latch (<NUM>) blocks the firing pin (<NUM>) from moving to the bottom dead center to a non-blocking position where said latch (<NUM>) does not block the firing pin (<NUM>) from moving to the bottom dead center when said electromagnet (<NUM>) is in a fully excited state, and be in the blocking position when said electromagnet (<NUM>) is in a non-excited state;
the electric power tool being characterized by a controller (<NUM>) that is electrically connected to said driving circuit (<NUM>) and that is configured to, during an excitement period (T1),
control said driving circuit (<NUM>) to provide a constant electric current to said electromagnet (<NUM>) for a first time period (t1) to excite said electromagnet (<NUM>) to the fully excited state, and
immediately after the first time period (t1), control said driving circuit (<NUM>) to provide a pulsating electric current to said electromagnet (<NUM>) for a second time period (t2) to keep said electromagnet (<NUM>) in the fully excited state.