Patent ID: 12220798

DETAILED DESCRIPTION

Before the disclosure is described in greater detail, it should be noted that where considered appropriate, reference numerals or terminal portions of reference numerals have been repeated among the figures to indicate corresponding or analogous elements, which may optionally have similar characteristics.

Referring toFIGS.1,3and4, 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 battery21, a power circuit22, a motor31, a driving module32, a switch module33, a lifter41configured to be driven by the motor31, a firing pin42configured to be driven by the lifter41, a piston44connected to the firing pin42, an electromagnet51, a driving circuit52, a joint61configured to be driven by the electromagnet51, a latch62configured to be driven by the joint61, and a controller7. The electric power tool further includes a housing10, and the piston44cooperates with the housing10to define a pressure chamber43.

The power circuit22is electrically connected to the battery21, and is configured to stabilize and transform electric energy provided by the battery21(e.g., DC 18V) for use by other internal circuits of the electric power tool. The power circuit22includes a direct-current to direct-current converter (DC-DC converter)221and, for example, two low-dropout regulators (LDOs)222. The LDOs222provide electric energy with different voltages (e.g., 5V and 12V) respectively for the controller7and the driving module32.

The motor31may be implemented using a brushless DC motor (BLDC). The driving module32is electrically connected to the switch circuit33, and the switch circuit33is electrically connected to the motor31. The driving module32is further electrically connected to the controller7, and is configured to receive a control signal in a form of a pulse-width modulation (PWM) signal outputted by the controller7, and to control the switch circuit33to drive the motor31to rotate at a desired rotational speed based on a duty cycle of the control signal thus received. The switch circuit33may be implemented using a metal-oxide-semiconductor field-effect transistor (MOSFET) switch.

The lifter41is connected to the motor31, and is configured to be driven by the motor31, where the lifter41then drives the firing pin42to move to perform a firing procedure. The lifter41includes a lifting wheel411that is configured to rotate (in a counter-clockwise direction inFIG.3) when being driven by the motor31, a plurality of posts412arranged along part of a circumference of the lifting wheel411, and a sliding surface413at the rest of the circumference. The firing pin42includes a shaft421, a plurality of teeth422that are positioned along the shaft421, and a block423disposed on the shaft421near a distal end of the shaft421that is opposite to the other end connected to the piston44.

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 pin42is originally located at a standby position where the firing pin42is ready to perform a firing action (seeFIG.3). The firing pin42is 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 pin42is located at the standby position, a first one of the posts412of the lifter41in the counter-clockwise direction is interlocked with a last one of the teeth422of the firing pin42in the firing direction, and the motor31drives the lifting wheel411to rotate, thus driving the firing pin42to 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 pin42is at the top dead center, the piston44compresses a volume of gas in the pressure chamber43to increase a pressure therein. When the lifting wheel411rotates to where the first one of the posts412is disengaged from the last one of the teeth422(i.e., when the teeth422reaches the sliding surface413), the firing pin42is driven by the pressure in the pressure chamber43to 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 pin42moving from the standby position to the top dead center by lifter41driven by the motor31, and then the firing pin42moving from the top dead center to the bottom dead center by the pressure in the pressure chamber43to fire a nail. The motor31continues to drive the lifting wheel411to rotate, and the posts412are interlocked with the teeth422again, thus driving the firing pin42to 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 pin42performing the firing action, and then the firing pin42moving from the bottom dead center back to the standby position. In this embodiment, the posts412of the lifter41are disengaged from the teeth422of the firing pin42at the top dead center.

Referring toFIG.2, the driving circuit52is electrically connected to the electromagnet51and the controller7, and is configured to provide an electric current to excite the electromagnet51. The driving circuit52includes a gate driver integrated circuit (IC)521, a semiconductor switch522(e.g., MOSFET switch), and a flywheel diode523that is electrically connected to the electromagnet51in parallel. The electric power tool further includes an electrical connector53that electrically connects the driving circuit52and the electromagnet51. The gate driver IC521is configured to receive a driving signal (as shown inFIGS.7-9) from the controller7, 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 switch522to drive the semiconductor switch522to be on or off. In some embodiments, the driving signal is designed to ensure that a channel of the semiconductor switch522may be fully opened when turned on, so as to reduce a resistance of the semiconductor switch522and thus reduce heat generated by the semiconductor switch522.

Referring toFIG.4, the joint61includes a pole611that partially extends into the electromagnet51, a connecting component612that connects the actuator611and the latch62, and a spring613that is connected between the electromagnet51and the pole611. The pole611is made of magnetic material and may be attracted to the electromagnet51when the electromagnet51is excited. Further referring toFIG.5, when the electromagnet51is in a non-excited state, the latch62is positioned at a blocking position in front of the block423to block the firing pin42from moving to the bottom dead center in the firing direction (i.e., disabling the firing pin42from performing the firing action), so as to avoid false firing. When the firing procedure is ready to be performed, the electromagnet51is excited by the driving circuit52to a fully excited state. The pole611is then attracted by the electromagnet51that is in the fully excited state to move in a first direction (i.e., the left direction inFIGS.5and6) so as to drive the connecting component612to rotate clockwise, and as shown inFIG.6, the latch62is driven by the connecting component612to rotate clockwise and move away from the block423to a non-blocking position where the latch62does not block the firing pin42from moving to the bottom dead center in the firing direction (i.e., enabling the firing pin42to perform the firing action). In addition, the spring613is compressed by the pole611when the pole611moves in the first direction. After performing the firing action, the electromagnet52may stop attracting the pole611by returning to the non-excited state, and the pole611is pushed by the spring613to move in a second direction (i.e., the right direction inFIGS.5and6) opposite to the first direction, so as to drive the connecting component612to rotate counter-clockwise, thus moving the latch62to the blocking position as shown inFIG.5.

Referring toFIGS.2and7, the controller7is electrically connected to the driving circuit52and is configured to output the driving signal to control the driving circuit52to turn on the semiconductor switch522during 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 controller7is configured to output the driving signal in a continuous manner to control the driving circuit52to continuously turn on the semiconductor switch522, thus providing a constant electric current to excite the electromagnet51for the first time period (t1) to excite the electromagnet51to the fully excited state. Then, the controller7is further configured to, immediately after the first time period (t1), output the driving signal in a pulsating manner to control the driving circuit52to periodically turn on the semiconductor switch522, thus providing a pulsating electric current to the electromagnet51for the second time period (t2) to keep the electromagnet51in 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 electromagnet51to 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 electromagnet51, and is usually between 20 to 100 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 circuit52is providing the pulsating electric current to the electromagnet51, the electromagnet51is already in the fully excited state.

The controller7may be implemented as a circuit (e.g., a microcontroller unit, MCU) with functions of analog-to-digital conversion (A/D conversion), input/output detection (I/O detection), and PWM output.

Referring toFIGS.1,3, and7, the controller7is further configured to, after a predetermined time period (T2) since the controller7started controlling the driving circuit52to provide the constant electric current, control the driving circuit52to operate the motor31to drive the lifter41, which then drives the firing pin42to 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 latch62blocking (or partially blocking) the firing pin42from 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 controller7is further configured to control the driving circuit52to stop providing the electric current to the electromagnet51when the second time period (t2) has elapsed, and control the driving circuit52to stop the motor31from operating when the controller7has determined that the firing pin42has 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 lifter41includes 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 controller7determines, based on the firing pin position switch, whether the magnet has moved to a predetermined position that corresponds to the firing pin42returning to the standby position. When the controller7determines that the magnet has moved to the predetermined position, the controller7controls the driving circuit52to stop the motor31from 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 pin42to 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 pin42to be moved by the lifter41from the bottom dead center to the top dead center. The excitement period (T1) (i.e., a total time that the electromagnet51is being excited) is equal to the first time period (t1) plus the second time period (t2). It should be noted that after the firing pin42is moved from the standby position to the top dead center and then to the bottom dead center (T2+Td), and before the firing pin42is moved from the bottom dead center back to the top dead center (T2+Td+Tu), the controller7controls the driving circuit52to stop providing the pulsating electric current to the electromagnet51. As such, the electromagnet51may be kept in the fully excited state when performing the firing action, thus keeping the latch62in the non-blocking position when the firing pin42is performing the firing action, and the electromagnet51may exit the fully excited state before the firing pin42is moved back to the top dead center, thus avoiding the firing pin42from accidently performing the firing action again when the lifting wheel411stops too slowly or fails to stop due to malfunction of the electric power tool.

Referring toFIGS.1,3,7, and10, a method of controlling the electric power tool includes: during the excitement period (T1), the controller7controlling the driving circuit52to provide the constant electric current to the electromagnet51for the first time period (t1) to excite the electromagnet51to the fully excited state; and immediately after the first time period (t1), the controller7controlling the driving circuit52to provide the pulsating electric current to the electromagnet51for the second time period (t2) to keep the electromagnet51in the fully excited state. To describe in further detail, the method of controlling the electric power tool includes steps80to89.

When the electric power tool is powered up, the flow of the method enters step80. In step80, the controller7determines 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 pin42is located at a correct position for performing the firing action (e.g., the standby position), etc. When the controller7determines that the firing procedure is ready to be performed, the flow proceeds to step81.

In step81, the controller7outputs the driving signal to the driving circuit52, and the driving circuit52provides the constant electric current to the electromagnet51based on the driving signal to excite the electromagnet51to the fully excited state, thus driving the latch62to move from the blocking position to the non-blocking position. Accordingly, the firing pin42is able to perform the firing action. The controller7starts timing a third time period (t1_i) and a fourth time period (T2_i), both starting from a time point when the driving circuit52starts to provide the constant electric current to the electromagnet51.

In step82, the controller7determines whether the third time period (t1_i) has reached the first time period (t1) (e.g., 20 ms). If affirmative, the flow proceeds to step83; otherwise, the flow of the method goes back to step82.

In step83, the controller7controls the driving circuit52to provide the pulsating electric current to the electromagnet51, and the controller7starts timing a fifth time period (t2_i) starting from a time point when the driving circuit52starts to provide the pulsating electric current to the electromagnet51.

In step84, the controller7determines whether the fourth time period (T2_i) has reached the predetermined time period (T2) (e.g., 30 ms). If affirmative, the flow proceeds to step85; otherwise, the flow goes back to step84.

In step85, the controller7outputs the control signal to operate the motor31to drive the lifter41, which then drives the firing pin42to perform the firing action (i.e., driving the firing pin42to move from the standby position to the top dead center, where the firing pin42is then driven to the bottom dead center by the pressure in the pressure chamber43), and immediately after the firing action, drives the firing pin42back toward the standby position. After step85, the flow proceeds to step86and step87.

In step86, the controller7determines whether the fifth time period (t2_i) has reached the second time period (t2) (e.g., 100 ms). If affirmative, the flow proceeds to step88; otherwise, the flow goes back to step86.

In step87, the controller7determines whether the firing pin42is located at the standby location based on the firing pin position switch. If affirmative, the flow proceeds to step89; otherwise, the flow goes back to step87.

When the controller7determines that the fifth time period (T2_i) has reached the second time period (t2), in step88, the controller7controls the driving circuit52to stop providing the electric current to the electromagnet51, thus making the latch62move back to the blocking position to block the firing pin42from performing the firing action.

When the controller7determines that the firing pin42is located at the standby location, in step90, the controller7controls the driving circuit52to stop the motor31from operating, and the firing procedure ends. After steps88and89have 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 toFIGS.1and7, it should be noted that frequency of the pulsating electric current should not be too low during the second time period (t2), otherwise, the electromagnet51may switch alternately between the fully excited state and a partially excited state, where the electromagnet51in the partially excited state may not produce a magnetic force strong enough to attract the pole611for keeping the latch62in the non-blocking position. A higher frequency of the pulsating electric current could reduce occurrence of the partially excited state, but would cause the electromagnet51to generate more heat. A higher duty cycle of the pulsating electric current would also cause the electromagnet51to generate more heat. Since the heat generated by the electromagnet51depends on a wire diameter of wire wound into a coil of the electromagnet51and the number of turns of the winding, both of which are related to size of the electromagnet51, the frequency and the duty cycle of the pulsating electric current are set according to the size of the electromagnet51to avoid generating excess heat by the electromagnet51(i.e., reducing a time that the electromagnet51is provided with the electric current). The size of the electromagnet51depends on an available space in the electric power tool for placing the electromagnet51.

During the second time period (t2), the frequency of the pulsating electric current shown inFIG.7may be greater than 1 kHz, 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 50%). The off time period (t3) should be short enough to make the electromagnet51remain in the fully excited state. The pulsating electric current may, for example, have a higher frequency as shown inFIG.8, 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 ofFIG.8are both shorter than the off time period (t3) and the on time period (t4) of the pulsating electric current ofFIG.7. The pulsating electric current may also have a different duty cycle as shown inFIG.9, 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 ofFIG.9is greater than 50%). As such, if the voltage of the battery21is low, using a higher duty cycle may keep the electromagnet51in the fully excited state so as to produce a magnetic force strong enough to attract the pole611(as shown inFIG.4).

In summary, the controller7controls the driving circuit52to first provide the constant electric current to fully excite the electromagnet51, and then provide the pulsating electric current to keep the electromagnet51in the fully excited state during the firing action, thus reducing the heat generated by the electromagnet51. 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 electromagnet51, 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 electromagnet51remains in the fully excited state to keep the latch62in the non-blocking position when the firing pin42is performing the firing action, and that the electromagnet51exits the fully excited state before the firing pin42is moved back to the top dead center so that the latch62may 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 motor31only starts to operate after the electromagnet51has reached the fully excited state. In other words, when the motor31starts to operate for driving the firing pin42to perform the firing procedure, the latch62has already be driven by the electromagnet51to move to the non-blocking position, thus enabling the firing pin42to 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. In other words, in any described embodiment, when implementation of one or more features or specific details does not affect implementation of another one or more features or specific details, said one or more features may be singled out and practiced alone without said another one or more features or specific details. It should be further noted that one or more features or specific details from one embodiment may be practiced together with one or more features or specific details from another embodiment, where appropriate, in the practice of the disclosure.

While the disclosure has been described in connection with what is(are) considered the exemplary embodiment(s), it is understood that this disclosure is not limited to the disclosed embodiment(s) but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.