Patent Description:
Power tools such as a miter saw or an angle grinder have relatively high inertia. Therefore, the motor of this type of power tool coasts for a relatively long time after power-off. If a user turns on a switch and the power tool is powered again during the coast time of the motor after the power-off, the power tool may be caused to run again, thus causing a great security risk to an unprepared person near the power tool.

This part provides background information related to the present invention, which is not necessarily the existing art.

Document <CIT> discloses an electric tool according to the preamble of claim <NUM> and a driving control circuit thereof, and the tool comprises a power interface which is used for connecting a power supply; the motor is used for providing power for the electric tool; the controller is at least connected with the motor so as to control the working state of the motor; the multipath control circuit comprises a control switch triggered by a user and a switch element electrically connected with the control switch.

Document <CIT> discloses an electric tool, a motor assembly and a motor drive system. The motor drive system includes a trigger switch, an electronic switch, and a switch control circuit connected between the trigger switch and the electronic switch. The trigger switch is connected in series to a power supply. The electronic switch is configured to control a motor to be powered on or powered off.

Document <CIT> discloses an electric working machine comprising a motor, a switch, a drive device, a brake device, and a failure determiner.

Document <CIT> discloses a hand-portable garden, forestry and/or construction processing device has a cutting tool, an electric drive motor, a motor operating element, and a control device.

The present invention aims to solve or at least alleviate all or part of the preceding problems. Therefore, an object of the present invention is to provide a power tool and a power-off protection method thereof. The present invention is defined by the independent claim. Advantageous embodiments are described in the dependent claims, the following description and the drawings.

The present invention has the following benefit: the power-off protection method provided by the present invention improves the security performance of the power tool.

Before any examples of this invention are explained in detail, it is to be understood that this invention is not limited to its invention to the structural details and the arrangement of components set forth in the following description or illustrated in the above drawings.

In this invention, the terms "comprising", "including", "having" or any other variation thereof are intended to cover an inclusive inclusion such that a process, method, article or device comprising a series of elements includes not only those series of elements, but also other elements not expressly listed, or elements inherent in the process, method, article, or device.

In this invention, the term "and/or" is a kind of association relationship describing the relationship between associated objects, which means that there can be three kinds of relationships. In addition, the character "/" in this invention generally indicates that the contextual associated objects belong to an "and/or" relationship.

In this invention, the terms "connection", "combination", "coupling" and "installation" may be direct connection, combination, coupling or installation, and may also be indirect connection, combination, coupling or installation.

In this invention, it is to be understood by those skilled in the art that a relative term (such as "about", "approximately", and "substantially") used in conjunction with quantity or condition includes a stated value and has a meaning dictated by the context.

In this invention, those skilled in the art will understand that a function performed by an assembly may be performed by one assembly, multiple assemblies, one member, or multiple members.

In this invention, the terms "up", "down", "left", "right", "front", and "rear" " and other directional words are described based on the orientation or positional relationship shown in the drawings, and should not be understood as limitations to the examples of this invention. In addition, in this context, it also needs to be understood that when it is mentioned that an element is connected "above" or "under" another element, it can not only be directly connected "above" or "under" the other element, but can also be indirectly connected "above" or "under" the other element through an intermediate element. It should also be understood that orientation words such as upper side, lower side, left side, right side, front side, and rear side do not only represent perfect orientations, but can also be understood as lateral orientations. For example, lower side may include directly below, bottom left, bottom right, front bottom, and rear bottom.

In this invention, the terms "controller", "processor", "central processor", "CPU" and "MCU" are interchangeable. Where a unit "controller", "processor", "central processing", "CPU", or "MCU" is used to perform a specific function, the specific function may be implemented by a single aforementioned unit or a plurality of the aforementioned unit.

In this invention, the term "device", "module" or "unit" may be implemented in the form of hardware or software to achieve specific functions.

In this invention, the terms "computing", "judging", "controlling", "determining", "recognizing" and the like refer to the operations and processes of a computer system or similar electronic computing device (e.g., controller, processor, etc.).

<FIG> shows a power tool according to an example of the present invention, where the power tool is a miter saw. It is to be understood by those skilled in the art that the power tool provided by the present invention is not limited to the miter saw and may be a table saw, an angle grinder, an electric drill, a chain saw, a string trimmer, or the like.

<FIG> is a block diagram of a power-off protection circuit of a power tool according to an example of the present invention. Referring to <FIG>, a power tool <NUM> includes a power terminal <NUM>, a detection module <NUM>, a controller <NUM>, and a motor <NUM>. The motor <NUM> may be a brushless motor. The power terminal <NUM> is configured to be electrically connected to a battery pack <NUM> to access a power supply of the battery pack <NUM>. A circuit between the power terminal <NUM> and the battery pack <NUM> is a first circuit <NUM>, and a circuit between the power terminal <NUM> and the motor <NUM> is a second circuit <NUM>. The detection module <NUM> can detect that the first circuit <NUM> and the second circuit <NUM> are in a power-on mode or a power-off mode. The controller <NUM> can control the second circuit <NUM> to be in the power-on mode or the power-off mode.

When the first circuit <NUM> is in the power-on mode, the power supply of the battery pack <NUM> can be supplied to the power tool <NUM>, that is, the battery pack <NUM> is in good contact with an electrical connection structure of the power tool <NUM>. When the first circuit <NUM> is in the power-off mode, that is, the battery pack <NUM> is not electrically connected to the power tool <NUM>, for example, the battery pack <NUM> is separated from the power tool <NUM>, the power supply of the battery pack <NUM> cannot be supplied to the power tool <NUM>. In some examples, the battery pack <NUM> is plugged into the power tool <NUM>, where the first circuit <NUM> is in the power-on mode when the battery pack <NUM> is plugged into the power tool <NUM>, and the first circuit <NUM> is in the power-off mode when the battery pack <NUM> is pulled out of the power tool <NUM>.

When the second circuit <NUM> is in the power-on mode, a power supply received by the power terminal <NUM> from the battery pack <NUM> can be delivered to the motor <NUM> so that the motor <NUM> can rotate. When the second circuit <NUM> is in the power-off mode, the power supply received by the power terminal <NUM> from the battery pack <NUM> cannot be delivered to the motor <NUM> so that the motor <NUM> stops rotating or keeps still.

The power tool <NUM> further includes an operation switch <NUM> disposed between the power terminal <NUM> and the motor <NUM>. The operation switch <NUM> can control the second circuit <NUM> to be in the power-off mode or control, through the controller <NUM>, the second circuit <NUM> to be in the power-on mode. In some examples, the operation switch <NUM> can be moved between a first position and a second position. When the operation switch <NUM> is at the first position, the operation switch <NUM> is in the off state, and when the operation switch <NUM> is at the second position, the operation switch <NUM> is in the on state. When the operation switch <NUM> is in the off state, the second circuit <NUM> is in the power-off mode. When the operation switch <NUM> is in the on state, the controller <NUM> can control the second circuit <NUM> to be in the power-on mode.

In some examples, if the operation switch <NUM> can directly control whether the second circuit <NUM> is in the power-on mode, a relatively high security risk is caused. For example, the operation of safely replacing the battery pack <NUM> should be as follows: the operation switch <NUM> is turned off so that the second circuit <NUM> is in the power-off mode, next, the battery pack <NUM> is pulled out so that the first circuit <NUM> is in the power-off mode, then another battery pack <NUM> is plugged so that the first circuit <NUM> is restored to the power-on mode but the operation switch <NUM> is kept in the off state so that the second circuit <NUM> is in the power-off mode, and when a user needs to work by using the power tool <NUM>, the operation switch <NUM> is turned on so that the second circuit <NUM> is switched from the power-off mode to the power-on mode. In some scenarios, the user may replace the battery pack <NUM> in violation of regulations: when the operation switch <NUM> is in the on state, the battery pack <NUM> is directly pulled out and then another battery pack <NUM> is plugged. In the replacement process, the second circuit <NUM> is always in the power-on mode, and when the first circuit <NUM> is restored to the power-on mode, the power supply of the battery pack <NUM> can be quickly delivered to the motor <NUM> through the first circuit <NUM> and the second circuit <NUM> so that the motor <NUM> in a coast state is driven to rotate again (after the power supply is stopped, the motor <NUM> does not stop rotating immediately but coasts for a period of time under the action of inertia). Power tools such as the miter saw or the angle grinder have relatively high inertia. Therefore, the motor <NUM> of this type of power tool <NUM> coasts for a relatively long time after the power-off. If the operation switch <NUM> is kept in the on state when the user replaces the battery pack <NUM> of the miter saw, the motor <NUM> of the miter saw into which the battery pack <NUM> is plugged again is started in the coast state, and a saw blade is driven to rotate quickly and may hurt an unprepared person near the miter saw.

To resolve the preceding security risk, the present invention provides an example. In this example, when the detection module <NUM> detects that the first circuit <NUM> is switched from the power-on mode to the power-off mode, the controller <NUM> controls the second circuit <NUM> to be in the power-off mode within a first preset time. The first preset time is greater than or equal to a coast time of the motor <NUM>. Specifically, the first preset time may be <NUM> seconds, <NUM> seconds, or <NUM> seconds.

In this example, after the battery pack <NUM> is pulled out of the power tool <NUM>, the controller <NUM> controls the second circuit <NUM> to be in the power-off mode within the first preset time so that the case is avoided where the motor <NUM> is powered on again immediately after the power-off so as to drive a working accessory to rotate quickly. Thus, the security risk of the power tool <NUM> is reduced.

In this example, even if the detection module <NUM> detects, within the first preset time, that the first circuit <NUM> is switched from the power-off mode to the power-on mode, the controller <NUM> still controls the second circuit <NUM> to be in the power-off mode within the first preset time. The controller <NUM> controls the second circuit <NUM> to be in the power-on mode only when the detection module <NUM> detects, outside the first preset time, that the first circuit <NUM> is in the power-on mode.

In some examples, the operation switch <NUM> is configured to be incapable of directly controlling the second circuit <NUM> to be switched from the power-off mode to the power-on mode, and the operation switch <NUM> needs to control, through the controller <NUM>, the second circuit <NUM> to be switched to the power-on mode. For example, after the battery pack <NUM> is pulled out of the power tool <NUM>, the controller <NUM> controls the second circuit <NUM> to be in the power-off mode within the first preset time. Even if the operation switch <NUM> is always in the on state within the first preset time or is switched from the off state to the on state, the controller <NUM> still controls the second circuit <NUM> to be in the power-off mode within the first preset time. The controller <NUM> controls the second circuit <NUM> to be in the power-on mode only when the detection module <NUM> detects, outside the first preset time, that the first circuit <NUM> is in the power-on mode and the operation switch <NUM> is in the on state outside the first preset time.

The power tool <NUM> further includes a communication terminal <NUM>, and the communication terminal <NUM> performs data communication with the battery pack <NUM>. When the battery pack <NUM> is pulled out of the power tool <NUM>, the first circuit <NUM> is switched from the power-on mode to the power-off mode, no data communication occurs between the communication terminal <NUM> and the battery pack <NUM>, and a level of the communication terminal <NUM> keeps stable. Therefore, the detection module <NUM> can assist in determining, by detecting whether the level of the communication terminal <NUM> varies, whether the battery pack <NUM> is not electrically connected to the power tool <NUM>, that is, the detection module <NUM> can determine, based on whether the level of the communication terminal <NUM> varies, that the first circuit <NUM> is in the power-on mode or the power-off mode.

After the battery pack <NUM> is pulled out of the power tool <NUM>, the first circuit <NUM> is switched from the power-on mode to the power-off mode. However, the motor <NUM> does not immediately stop rotating. Instead, the motor <NUM> coasts for a period of time under the action of the inertia. The motor <NUM> generates a back electromotive force in the coast state. Therefore, a small current is generated. Therefore, the detection module <NUM> can assist in determining, by detecting the magnitude of the phase current of the motor, whether the battery pack <NUM> is not electrically connected to the power tool <NUM>, that is, the detection module <NUM> can determine, based on the magnitude of the phase current of the motor <NUM>, that the first circuit <NUM> is in the power-on mode or the power-off mode.

In summary, the present invention provides an example in which it can be determined, in a relatively accurate manner, whether the first circuit <NUM> is switched from the power-on mode to the power-off mode. In this example, the detection module <NUM> can detect whether the level of the communication terminal <NUM> varies, and the detection module <NUM> can further detect the phase current of the motor <NUM>. When the absolute value of the phase current of the motor <NUM> is less than a preset current threshold and the level of the communication terminal <NUM> does not vary within a second preset time, the detection module <NUM> determines that the first circuit <NUM> is in the power-off mode.

The present invention further provides an example in which it can be determined whether the first circuit <NUM> is switched from the power-on mode to the power-off mode. The detection module <NUM> can detect the back electromotive force of the motor <NUM> and the bus voltage of the motor <NUM>. When the difference between the back electromotive force of the motor <NUM> and the bus voltage of the motor <NUM> is less than a preset voltage threshold within a third preset time, the detection module <NUM> determines that the first circuit <NUM> is in the power-off mode. In some examples, the product of a current of the unloaded motor <NUM> and an internal resistance of the motor <NUM> may be calculated and used as a basis for a value range of the preset voltage threshold.

To resolve the security risk mentioned above, the present invention further provides another example. In this example, when the detection module <NUM> detects that the first circuit <NUM> is switched from the power-off mode to the power-on mode, the controller <NUM> controls the second circuit <NUM> based on a time when the first circuit <NUM> is in the power-off mode before the mode switchover. If the time when the first circuit <NUM> is in the power-off mode before the mode switchover does not exceed the first preset time, the second circuit <NUM> is controlled to be in the power-off mode. Optionally, the first preset time may be greater than or equal to <NUM> seconds and less than or equal to <NUM> seconds.

In some examples, if the time when the first circuit <NUM> is in the power-off mode before the mode switchover has exceeded the first preset time, the controller <NUM> may control the second circuit <NUM> to be in the power-on mode.

In some examples, the operation switch <NUM> is configured to be incapable of directly controlling the second circuit <NUM> to be switched from the power-off mode to the power-on mode, and the operation switch <NUM> needs to control, through the controller <NUM>, the second circuit <NUM> to be switched to the power-on mode. When the detection module <NUM> detects that the first circuit <NUM> is switched from the power-off mode to the power-on mode, the controller <NUM> controls the second circuit <NUM> to be in the power-off mode if the operation switch <NUM> is in the on mode and the time when the first circuit <NUM> is in the power-off mode before the mode switchover does not exceed the first preset time.

As shown in <FIG>, the present invention further provides a power-off protection method applicable to the power tool <NUM> such as the miter saw. The power tool <NUM> includes the motor <NUM>, the power terminal <NUM>, the detection module <NUM>, the controller <NUM>, and the operation switch <NUM> as mentioned in the preceding example. The power-off protection method includes the steps below.

In S110, the detection module <NUM> detects that the first circuit <NUM> is in the power-on mode or the power-off mode.

In S120, it is determined whether the first circuit <NUM> is switched from the power-on mode to the power-off mode. If yes, step S130 is performed. If not, the detection is continued.

In S130, the controller <NUM> controls the second circuit <NUM> to be in the power-off mode within the first preset time.

In S140, the detection module <NUM> detects whether the first circuit <NUM> is switched from the power-off mode to the power-on mode. If yes, step S150 is performed. If not, step S130 is performed.

In S150, it is determined whether the operation switch is in the on state. If yes, step S160 is performed. If not, it is continuously detected whether the operation switch is in the on state.

In S160, it is determined whether the first preset time is exceeded. If yes, step S170 is performed. If not, it is continuously detected whether the first preset time is exceeded.

In S170, the controller <NUM> controls the second circuit <NUM> to be in the power-on mode.

The preceding power-off protection method improves the security performance of the power tool <NUM>.

Claim 1:
A power tool (<NUM>), comprising:
a motor (<NUM>);
a power terminal (<NUM>) configured to access a power supply of a battery pack (<NUM>);
a detection module (<NUM>) capable of detecting that a first circuit (<NUM>) between the power terminal and the battery pack is in a power-on mode or a power-off mode; and
a controller (<NUM>) capable of controlling a second circuit (<NUM>) between the power terminal and the motor to be in a power-on mode or a power-off mode;
wherein the controller is configured to, when the detection module detects that the first circuit is switched from the power-on mode to the power-off mode, control the second circuit to be in the power-off mode within a first preset time,
characterized in that,
the first preset time is greater than or equal to a coast time of the motor, wherein the coast time is the period of time for which the motor does not stop rotating immediately but coasts under the action of inertia after the power supply is stopped.