Patent Description:
Embodiments herein relate to the field of electric tools, and, more specifically, trigger systems, devices, and methods for providing variable power to an electric motor.

Many electric devices, such as hand operated tools, include a variable speed function. An electric hand tool, for example a chain saw or a hedge trimmer, has an electric motor whose speed may be variably controlled. This variable speed function is typically operated with a trigger position indicator, such as a potentiometer, that detects the relative position of the trigger and adjusts the power suppled to an electric motor accordingly. A tool according to the preamble of claim <NUM> is known from <CIT>.

Embodiments will be readily understood by the following detailed description in conjunction with the accompanying drawings and the appended claims.

In the following detailed description, reference is made to the accompanying drawings, which form a part hereof, and in which are shown by way of illustration embodiments that may be practiced. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope. Therefore, the following detailed description is not to be taken in a limiting sense, and the scope of embodiments is defined by the appended claims.

Various operations may be described as multiple discrete operations in turn, in a manner that may be helpful in understanding embodiments; however, the order of description should not be construed to imply that these operations are order dependent.

The description may use perspective-based descriptions such as up/down, back/front, and top/bottom. Such descriptions are merely used to facilitate the discussion and are not intended to restrict the application of disclosed embodiments.

The terms "coupled" and "connected," along with their derivatives, may be used. Rather, in particular embodiments, "connected" may be used to indicate that two or more elements are in direct physical contact with each other. "Coupled" may mean that two or more elements are in direct physical contact. However, "coupled" may also mean that two or more elements are not in direct contact with each other, but yet still cooperate or interact with each other.

The description may use the terms "embodiment" or "embodiments," which may each refer to one or more of the same or different embodiments. Furthermore, the terms "comprising," "including," "having," and the like, as used with respect to embodiments, are synonymous, and are generally intended as "open" terms (e.g., the term "including" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "includes but is not limited to," etc.).

With respect to the use of any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application.

Sensing the trigger position may implicate safety concerns with electrically powered tools. In variable speed tools, an electrical position indicator (such as a potentiometer, hall sensors, digital signal generator, or other like device) may be used to convert a physical position of a mechanical trigger into an electrical position signal, which may then be used to determine the speed at which the tool should operate. The further the trigger is advanced, the faster the tool may operate. In some embodiments, power may be routed directly through the electrical position indicator on route to an electric motor or other component of the tool. For example, the electrical position indicator may be used to indicate the trigger position to a control unit, which in turn translates the position to an electrical signal for driving the motor at the commanded speed. In other embodiments, such as where the electrical position indicator is a potentiometer, it may be sized to handle the maximum current the motor is expected to draw, and thereby control the speed of the motor by directly limiting the power delivered from the power supply.

Such electrical position indicators used in this manner have two common failure modes: fully open and fully short. While a failed indicator may be detected during quality control and testing during manufacturing, these failure modes can be difficult to detect during the useful life of the tool, as the position indicator may not provide any sign of an impending failure. When a tool that is subject to such a failure is subsequently powered, the failed electrical position indicator may cause unexpected behavior by the tool. For example, if the position indicator fails fully open, the tool may simply fail to power up regardless of trigger position, effectively resulting in a "dead" tool. Conversely, and potentially much more dangerous, is where the position indicator fails fully short. Powering up such a tool may result in the tool immediately and unexpectedly going to full power, unless the tool is equipped with other safety devices that prevent the motor from activating upon power-up.

A possible solution to address these failure modes is an electrical position indicator (for example, a potentiometer) that is configured to only operate in the middle or a predefined portion of its possible range. Because such an electrical position indicator never operates at the very top or bottom end of its possible range, a control system or unit that is configured to detect deviations in signal or indicated position from this middle range is able to determine if the signals received from the electrical position indicator are valid or, if out of the predefined range, indicative of a fault. The control unit can thus identify the two most common failure modes, namely, fully open and fully short. This ability to distinguish a fully shorted trigger (which could happen from wires being pinched during assembly, insulation breakdown, EMC noise, simple component failure, etc.) from a fully pulled trigger (or failure of the indicator) may allow more reliable indications that a tool can use to provide a reliable power-off state, and thus prevent unintended power-on safety risks.

Disclosed herein is an electric hand tool, such as a saw, hedge trimmer, pole saw, and the like. The electric hand tool may include an electric motor, an operating element such as a trigger or activation switch having an electrical position indicator (such as a sensor) for operation by a user, and a control unit for controlling the power delivered from a power supply to an electric motor based on signals received from the electrical position indicator. The electrical position indicator may be coupled to a trigger operable by a user, and the electrical position indicator may be configured to detect the relative position of the trigger, for example as it is moved by the user.

As mentioned above, in some embodiments, the electrical position indicator may directly modulate the flow of power to the motor, without need for a control unit. In other embodiments, a control unit may be separate from the electrical position indicator, and the position of the trigger determined by the electrical position indicator may be converted into an electrical control signal and passed to the control unit. In still other embodiments, the electrical position indicator may be integral with the control unit. In either case, the control unit may control the power hrough the electric motor on the basis of mechanical movement of the trigger as detected by the electrical position indicator. According to the invention, the electrical position indicator is configured to only operate in the middle of its possible range. For example, the electrical position indicator may be configured to only operate between <NUM>% to <NUM>% of its total operating range. In embodiments, the control unit may be configured to determine if the signals received from the electrical position indicator are out of the defined range of the electrical position indicator. For example, the range may be set to detect signals that are more than <NUM>% outside of the defined range. With reference to the diagram in <FIG>, this may equate to a signal indicating either below approximately <NUM> Ohms or above approximately <NUM> Ohms. In embodiments, if the signals received from the electrical position indicator are out of a defined range, the control unit may be configured to register a fault, such as a fully open and/or fully short fault. The fault may be communicated to the user, for example as an audio, visual, or other alert. In still other embodiments, the control unit may require that the electrical position indicator provide an out of range signal for greater than a predetermined amount of time, to prevent possible false positive fault detections that may be due to a transient out of range signal. For example, the control unit may not register a fault unless the out of range signal is detected for greater than <NUM>, or possibly longer ranges, such as up to <NUM> seconds, or even longer in other implementations.

<FIG> is a schematic of an electronic hand tool, in accordance with various embodiments. Electronic hand tool <NUM> may include a power supply <NUM>, an electric motor <NUM>, an operating element <NUM>, and a control unit <NUM>. Operating element <NUM> may include an electrical position indicator <NUM> and an actuation trigger <NUM>. Operation of the electric motor <NUM> may be controllable by the control unit <NUM>, which may control the power, as may be quantified by applied voltage or voltage duty cycle, from power supply <NUM> to the electric motor <NUM>. This control may depend on the position of the actuation trigger <NUM> as determined by the electrical position indicator <NUM>.

In embodiments, the power supply <NUM> may comprise an A/C power supply, such as a cord or other means to connect tool <NUM> to A/C power, such as a wall socket or generator. In other embodiments, the power supply <NUM> may comprise a D/C power supply, such as a NiMH or Li-Ion rechargeable battery pack. Such a battery pack may be permanently coupled or installed into tool <NUM>; in other embodiments, the battery pack may be removable and interchangeable with like-configured battery packs.

Electric motor <NUM> may be any motor suitable to operate within tool <NUM> for tool <NUM>'s intended use. Suitable motor types may include induction motors, universal motors, brushed motors, brushless motors, or any other type now known or later developed that is useful to the intended purposes of tool <NUM>. Electric motor <NUM> may be supplied power via an electronic speed control (ESC) <NUM>, which may be implemented using technology suitable for delivering and modulating power to electric motor <NUM> in a manner appropriate to the type of electric motor <NUM>. The ESC <NUM> may be integrated into, or be a part of, control unit <NUM>, as depicted in <FIG>, or may be a separate, discrete component in communication or under the direction of control unit <NUM>. In some embodiments, ESC <NUM> may be separate from control unit <NUM> while implementing at least a part of method <NUM>, with other actions of method <NUM> being implemented in whole or in part by control unit <NUM>. In various embodiments, electric motor <NUM> may be mechanically coupled to a driven element so as to supply power for tool <NUM> to perform work.

Operating element <NUM> may be configured to accept user actuations to control the electronic hand tool <NUM>. In various embodiments, operating element <NUM> may comprise a button or actuation trigger <NUM> that enables the user to engage tool <NUM> for use, and to control its speed. Actuation trigger <NUM> may be configured to be moveable by a user through a range of travel, where the range of travel may correspond to a range of variable speeds through which tool <NUM> may be operated. For example, operating element <NUM> may be a trigger on a tool <NUM>, where tool <NUM> may be a chainsaw, string trimmer, blower or similar implement. Initially depressing actuation trigger <NUM> into its range of travel may cause the electric motor <NUM> to power a driven element of tool <NUM> at a starting speed. Depressing actuation trigger <NUM> further into its range of travel may cause the electric motor <NUM> to operate at a faster speed and/or to provide additional power to an increasing load upon the driven element. Fully depressing actuation trigger <NUM> to the extent of its range of travel may cause the electric motor <NUM> to operate at full speed and/or full power. In other embodiments, actuation trigger <NUM> may comprise two controls, a power switch or button, and a second control for varying the power of electric motor <NUM>. In such embodiments, the power switch or button simply toggles power, while the level of power to be delivered is determined by the position or setting of the second control. Still other embodiments may use a plurality of buttons to increase or decrease power in a step-wise fashion. Operating element <NUM> may be implemented in any suitable form or fashion that allows a user to both toggle power to the tool <NUM> as well as vary the amount of power. In some embodiments, actuation trigger <NUM> may be spring-loaded to automatically bias actuation trigger <NUM> to a low or cut-off point unless a user of tool <NUM> is actively depressing and applying pressure to actuation trigger <NUM> against the spring bias.

To facilitate the variable delivery of power, the position of actuation trigger <NUM> (or a similar structure) of operating element <NUM> within its range of motion may be sensed by electrical position indicator <NUM>. Upon moving actuation trigger <NUM> of the operating element <NUM> by a user of the hand tool <NUM>, electrical position indicator <NUM> may read the displacement of the actuation trigger <NUM>. Depending upon its implementation in a given embodiment, actuation trigger <NUM> may be displaceable along one direction of movement or may be rotatable or pivotable about an axis of movement. In some embodiments, the electrical position indicator <NUM> may convert or encode the mechanical position of actuation trigger <NUM> into a control signal for input to control unit <NUM>, to facilitate control unit <NUM> in controlling the power delivered by electric motor <NUM>. In other embodiments, electrical position indicator <NUM> may directly modulate or control power delivery to the electric motor <NUM>. In such embodiments, control unit <NUM> may simply monitor electrical position indicator <NUM> for out of range positions (discussed further herein) to detect a possible failure of electrical position indicator <NUM>, and shut off power to electrical position indicator <NUM> in response.

The electrical position indicator <NUM> may be, for example, a microswitch, a spring contact, a sliding switch, a reed contact, a Hall sensor, a potentiometer, a photoelectric barrier, an encoder, or some other suitable device for reading the position of the actuation trigger <NUM> of the operating element <NUM>.

In embodiments, control unit <NUM> may be configured to receive a signal or other indication from electrical position indicator <NUM> that corresponds to a physical position of actuation trigger <NUM>. The nature of this signal may depend upon how electrical position indicator <NUM> is implemented, and the particular configuration of control unit <NUM>. For example, where electrical position indicator <NUM> is implemented using a potentiometer, control unit <NUM> may be configured to sense a current or voltage passed through electrical position indicator <NUM>. As the position of the potentiometer varies, the amount of current or voltage sensed by control unit <NUM> may vary, which control unit <NUM> may in turn use to determine a corresponding power level for electric motor <NUM>. In other embodiments, such as where electrical position indicator <NUM> is implemented as an encoder, control unit <NUM> may receive a binary or other type of code indicative of the position sensed by electrical position indicator <NUM>, which control unit <NUM> may correlate with a power level for electric motor <NUM>. In some such embodiments, control unit <NUM> may utilize a look-up table or similar data structure to map encoded positions sensed by electrical position indicator <NUM> to a corresponding power level. It will be appreciated by a person skilled in the art that the specifics of such embodiments will depend upon how control unit <NUM> and electrical position indicator <NUM> are implemented.

According to the invention, operating element <NUM> is arranged so that the full operational range of actuation trigger <NUM> is contained within and less than the full operable range of electrical position indicator <NUM>, such as about <NUM>% to <NUM>% of the full range. For example, in implementations where actuation trigger <NUM> is a linear-travel spring loaded trigger, when actuation trigger <NUM> is at its lowest or rest position (e.g. the trigger position if spring-biased and not depressed by a user), electrical position indicator <NUM> will signal or encode some amount above the bottom of its operable range. Similarly, when actuation trigger <NUM> is at its maximum or full position (e.g. the trigger position if fully depressed), electrical position indicator <NUM> will signal or encode some amount below the top of its operable range. These ranges are graphically depicted in <FIG>, which will be discussed in further detail herein.

Control unit <NUM> may be implemented as one or more electronic controllers, such as a microprocessor, a microcontroller, discrete circuitry, a combination of the foregoing, or some other device offering similar functionality. Some embodiments may implement some or all of control unit <NUM> using a field-programmable gate array (FPGA), application-specific integrated circuit (ASIC), or another similar technology. In some embodiments, control unit <NUM> may include a computer-readable medium such as a memory storage unit containing instructions capable of being executed by a processing unit that is part of control unit <NUM>. Control unit <NUM>, as depicted in <FIG>, should be understood as a logical block, and may, in various embodiments, may be implemented by one or more discrete modules.

Control unit <NUM> may implement one or more actions of the operational method <NUM> described below with respect to <FIG>. These actions may be implemented with respect to a given embodiment of control unit <NUM>. For example, where control unit <NUM> includes a microprocessor or microcontroller, method <NUM> may be implemented in whole or in part using instructions capable of being executed by the microprocessor or microcontroller. For another example, where control unit <NUM> is implemented using discrete components or using transistor-transistor logic (TTL), such components may be arranged to implement some or all actions of method <NUM>. For still another example, control unit <NUM> may use a combination of the foregoing, with some actions of method <NUM> implemented using a microcontroller and other actions implemented using discrete components.

Control unit <NUM> may be configured to accept as input a signal from electrical position indicator <NUM> that indicates a current position of actuation trigger <NUM>. Depending upon a particular implementation of control unit <NUM>, the position of actuation trigger <NUM> may be an analog or digital signal. Control unit <NUM> may accordingly be configured to convert from analog to digital, or vice versa. For example, where electrical position indicator <NUM> is a potentiometer (an analog device) and control unit <NUM> implements a digital microcontroller, control unit <NUM> may be equipped with an analog to digital converter to convert the sensed voltage or current from electrical position indicator <NUM> to a numerical value. Control unit <NUM> may use this numerical value to deliver to electric motor <NUM>, in some embodiments via ESC <NUM>, an appropriate voltage and current to drive electric motor <NUM> and any attached driven element to a power level corresponding to the sensed position of actuation trigger <NUM>.

In <FIG>, a method <NUM> of controlling the power of tool <NUM> that may be carried out in whole or in part by a control unit <NUM> is depicted. In block <NUM>, a position of an actuation trigger <NUM> may be sensed by an electrical position indicator <NUM>. As described above, both these components may be provided in an operating element <NUM>.

The sensed position may be provided to control unit <NUM>. In block <NUM>, the sensed position may be evaluated for whether it is within the working range of actuation trigger <NUM>. As discussed above, electrical position indicator <NUM> may be configured to have an operable range greater than the operable range of actuation trigger <NUM>, which may be defined by physical stops that limit the physical range of actuation trigger <NUM>. Control unit <NUM> may be configured to respond to the entire operable range of electrical position indicator <NUM>, and to further determine when a sensed position received from electrical position indicator <NUM> is within the operable range of actuation trigger <NUM>, or above or below the operable range of actuation trigger <NUM>.

In block <NUM>, if the sensed position is within the operable range of actuation trigger <NUM>, control unit <NUM> may command a power level to be provided to electric motor <NUM> that corresponds to the sensed position of actuation trigger <NUM>. In some embodiments, control unit <NUM> may either provide the appropriate power directly to electric motor <NUM>, e.g. by using a variable power supply, pulse-width modulation, or another known technique for controlling power to an electric motor, or may signal an associated ESC <NUM> to supply such power. In other embodiments such as where electrical position indicator <NUM> directly modulates the power (e.g. it is implemented as a potentiometer), control unit <NUM> may simply supply power to electrical position indicator <NUM>. The position of electrical position indicator <NUM> will directly control the power delivered to electric motor <NUM>.

In block <NUM>, however, if the sensed position is outside of the operable range of actuation trigger <NUM>, viz. above or below the operable range of actuation trigger <NUM>, then power may be cut off or otherwise prevented from being supplied to electric motor <NUM>. A sensed position outside of the operable range of actuation trigger <NUM> may indicate a likely component failure. For example, electrical position indicator <NUM> may have failed in a fully open or shorted condition. Alternatively, actuation trigger <NUM> or any associated physical stops may have failed or broken, allowing electrical position indicator <NUM> to move into a position outside of the operable range of actuation trigger <NUM>. In either event, a potentially unsafe operating condition can be detected and avoided. The control unit <NUM> may be configured to require that the electrical position indicator <NUM> provide an out of range signal for greater than a predetermined amount of time, to prevent possible false positive fault detections that may be due to a transient out of range signal. For example, control unit <NUM> may not register a fault unless the out of range signal is detected for greater than <NUM>, or possibly longer ranges, such as up to <NUM> seconds, or even longer in other implementations.

In block <NUM>, control unit <NUM> or some other component may provide an alert to a user of the malfunction. For example, a warning buzzer or sound and/or visual display may be provided to the user, combined with the tool <NUM> being rendered inoperable. In some embodiments, control unit <NUM> may be configured to indicate the nature of the failure to the user to facilitate proper repairs.

Referring to <FIG>, a graph of the resistance curve of an electrical position indicator <NUM> showing both the maximum operable range of the electrical position indicator <NUM> as well as the operable range of an actuation trigger <NUM>, according to one possible embodiment, is shown. In the depicted embodiment, electrical position indicator <NUM> may be a potentiometer, where the resistance of the device can vary depending upon the position of the device. This variable resistance may be sensed by control unit <NUM> and thereby be translated into a corresponding power level to be delivered to electric motor <NUM>. The maximum operable range of electrical position indicator <NUM> may be defined by a maximum resistance <NUM>, shown as a possible range of <NUM> to <NUM> Ohms, and a minimum resistance <NUM>, shown as a possible range of <NUM>-<NUM> Ohms. Within this maximum operable range is the operable range of actuation trigger <NUM>, defined by a maximum operable resistance <NUM> and a minimum operable resistance <NUM>. As can be seen, the maximum operable resistance <NUM> is less than the maximum resistance <NUM>, and the minimum operable resistance <NUM> is greater than the minimum resistance <NUM>.

The maximum operable resistance <NUM> and minimum operable resistance <NUM> may be set depending upon the nature of electrical position indicator <NUM>, the desired range of operation of the tool <NUM>, the potential travel of actuation trigger <NUM>, the desired amount of fine control over tool <NUM>, and/or the capabilities of control unit <NUM> of detecting variations of resistance within the operable range of actuation trigger <NUM>, among other potential factors. It should be understood that the particular resistance values need not correlate to any specific power level, but rather may be defined according to the particular configuration of control unit <NUM> as well as the nature and intended use of tool <NUM>.

In operation, any operation of actuation trigger <NUM> may produce a resistance that falls within maximum operable resistance <NUM> and minimum operable resistance <NUM>, subject to some deviation within predefined tolerance limits. A resistance that is between maximum resistance <NUM> and maximum operable resistance <NUM>, or is between minimum resistance <NUM> and minimum operable resistance <NUM>, indicates a failure somewhere within tool <NUM>, likely either with electrical position indicator <NUM> or with actuation trigger <NUM>.

It should be understood that the embodiment depicted in <FIG> reflects an implementation of electrical position indicator <NUM> using a potentiometer, or similar device. While other embodiments may implement the electrical position indicator <NUM> using a different technology or type of device, the general principles of operable ranges depicted in <FIG> may still apply.

Claim 1:
An electric hand tool (<NUM>), comprising:
an electrical motor (<NUM>);
an operating element (<NUM>) comprising an actuation trigger (<NUM>) and an electrical position indicator (<NUM>) that is configured to read
a position of the actuation trigger (<NUM>); and
a control unit (<NUM>) for controlling power delivery to the electrical motor (<NUM>) on the basis of the position of the actuation trigger (<NUM>), wherein:
the electrical position indicator (<NUM>) is configured to sense the position of the actuation trigger (<NUM>) and provide a signal of the position of the actuation trigger (<NUM>) to the control unit (<NUM>), and
the control unit (<NUM>) is configured to detect when the position signal from the electrical position indicator (<NUM>) is outside of a working range,
characterised in that the actuation trigger (<NUM>) is configured to move within the working range of the electrical position indicator (<NUM>) that is confined within and less than the possible range that may be sensed by the electrical position indicator (<NUM>).