Power tool and method of operating a power tool

Abstract

A power tool (10) includes a motor (20) and a sensor assembly (100) configured to generate a differential voltage signal (102) indicative of a distance between an individual and a cutting tool (60) being less than a threshold distance. The sensor assembly is further configured to generate a sensor assembly output (104) based on the differential voltage signal. The power tool further includes an analysis circuit (300) configured to receive the sensor assembly output and generate a trigger signal (302) in response to the sensor assembly output being outside of a nominal sensor assembly output range. The power tool further includes a mechanical reaction mechanism (70) configured to isolate the individual from the cutting tool in response to receiving the trigger signal. A method for verifying operation of a sensor assembly.

Description

[0001] Related applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 046,975, filed July 1, 2020, the entire disclosure of which is hereby incorporated by reference. Technical Field

[0003] This disclosure generally relates to power tools and / or methods of operating power tools. Background Technology

[0004] Power tools utilize cutting tools to cut workpieces. These cutting tools are typically sharp and move rapidly during operation. Therefore, in some cases, the cutting tools can pose a safety hazard to the user. Some power tools include guards and / or other mechanisms to protect the user from contact with the cutting tools. However, it may still be desirable to have auxiliary and / or additional safety mechanisms in appropriate locations. Several such auxiliary and / or additional safety mechanisms have been developed for some power tools; however, they are often specific to certain types of power tools and / or are single-use safety mechanisms that may be destructive to at least one component of the cutting tool and / or the safety mechanism. Additionally or alternatively, known auxiliary and / or additional safety mechanisms may not be suitable for installation in a wide range of power tools. Therefore, there is a need for improved power tools and / or improved methods of operating power tools. Summary of the Invention

[0005] This document discloses power tools and methods of operating power tools. Power tools, which may include batteries and / or battery-powered and / or wireless power tools, include a motor comprising a motor shaft configured to rotate about an axis of rotation. The power tool also includes a sensor assembly configured to generate a differential voltage signal indicating that the distance between an individual and a cutting tool is less than a threshold distance. The sensor assembly is further configured to generate a sensor assembly output based on the differential voltage signal. The power tool also includes analysis circuitry configured to receive the sensor assembly output and generate a trigger signal in response to the sensor assembly output being outside a nominal sensor assembly output range. The power tool also includes a mechanical reaction mechanism configured to isolate the individual from the cutting tool in response to receiving the trigger signal.

[0006] The method includes blocking supply of electrical current to a motor of the power tool and verifying operation of a sensor assembly of the power tool. The sensor assembly is configured to generate a differential voltage signal indicative of a distance between an individual and a cutting tool of the power tool being less than a threshold distance. The method further includes allowing supply of electrical current to the motor in response to successful verification of the operation of the sensor assembly. BRIEF DESCRIPTION OF DRAWINGS

[0007] Figure 1 is a schematic diagram of an example of a power tool in accordance with the present disclosure.

[0008] Figure 2 is a schematic diagram of an example of a sensor assembly that can be used with a power tool in accordance with the present disclosure.

[0009] Figure 3 is a schematic diagram of an example of a sensor assembly that can be used with a power tool in accordance with the present disclosure.

[0010] Figure 4 is a schematic diagram of an example of a sensor assembly that can be used with a power tool in accordance with the present disclosure.

[0011] Figure 5 is a schematic diagram of an example of a sensor assembly that can be used with a power tool in accordance with the present disclosure.

[0012] Figure 6 is a schematic diagram of an example of a sensor assembly that can be used with a power tool in accordance with the present disclosure.

[0013] Figure 7 is a flowchart depicting an example of a method of operating a power tool in accordance with the present disclosure.

[0014] Figure 8 is a flowchart depicting an example of a method of operating a power tool in accordance with the present disclosure.

[0015] Figure 9 is a flowchart depicting an example of a method of operating a power tool in accordance with the present disclosure.

[0016] Figure 10 is a flowchart depicting an example of a method of operating a power tool in accordance with the present disclosure.

[0017] Figure 11 is a flowchart depicting an example of a method of operating a power tool in accordance with the present disclosure. DETAILED DESCRIPTION

[0018] Figures 1-11Examples of an electric power tool 10 according to the present disclosure, a sensor assembly 100 that can be used with the electric power tool 10, and / or methods 400 / 500 / 600 / 700 / 800 are provided. Elements for similar or at least substantially similar purposes are labeled with like reference numerals in each of the figures in Figures 1-11 and can not be discussed in detail herein without reference to each of the figures in Figures 1-11 . Similarly, all elements can not be labeled in each of the figures in Figures 1-11 , but for consistency, reference numerals associated therewith can be used herein. Elements, components, and / or features discussed with reference to one or more figures in Figures 1-11 may be included in any of the figures in Figures 1-11 and / or used with any of the figures in Figures 1-11 without departing from the scope of the present disclosure. Figure 1

[0019] Generally, elements that can be included in a particular embodiment are shown in solid lines while optional elements are shown in dashed lines. However, elements shown in solid lines can not be required and can be omitted in some embodiments without departing from the scope of the present disclosure.

[0020] Figure 1 is a schematic diagram of an example of an electric power tool 10 according to the present disclosure. As shown in solid lines in Figure 1 , the electric power tool 10 includes a motor 20, a mechanical reaction mechanism 70, a sensor assembly 100, and an analysis circuit 300. As shown in dashed lines in Figure 1 , the electric power tool 10 can include and / or be used with a cutting tool 60.

[0021] ​The motor 20 includes a motor shaft 22 configured to rotate about a shaft rotation axis 24. The cutting tool 60 (when present) can be configured to be actuated by the motor to act on and / or cut the workpiece 90. The sensor assembly 100 can be configured to generate and / or produce a differential voltage signal 102 that can be indicative of a distance between an individual (such as a user of the power tool) and the cutting tool being less than a threshold distance. In some examples, the threshold distance can include and / or be a limited distance between the individual and the cutting tool. Examples of limited distances include a limited distance of less than 10 millimeters (mm), less than 8 mm, less than 6 mm, less than 4 mm, less than 3 mm, less than 2 mm, less than 1 mm, less than 0.5 mm, less than 0.1 mm, at least 0.01 mm, at least 0.05 mm, at least 0.1 mm, at least 0.5 mm, and / or at least 1 mm. In some examples, the threshold distance can include and / or be contact or the beginning of contact between the user and the cutting tool. In other words, and in some such examples, the threshold distance can be negligible and / or can be zero.

[0022] The sensor assembly 100 can be configured to generate and / or produce a sensor assembly output 104 that can be based at least in part on the differential voltage signal. The analysis circuit 300 can be configured to receive the sensor assembly output 104 and generate a trigger signal 302 in response to the sensor assembly output being outside of a nominal sensor assembly output range and / or in response to the sensor assembly output being indicative of a distance between the individual and the cutting tool being less than the threshold distance. The mechanical reaction mechanism 70 can be configured to receive the trigger signal 302 and / or in response to receiving the trigger signal, isolate, separate, and / or protect the individual from the cutting tool.

[0023] During operation of the power tool 10, the motor 20 can be used to actuate the cutting tool 60 to cut the workpiece 90. Prior to and / or during actuation of the cutting tool 60, the sensor assembly 100 can generate and / or produce the differential voltage signal 102, and the sensor assembly 100 can generate the sensor assembly output 104 based on the differential voltage signal. If and / or when the differential voltage signal 102 is indicative of a distance between the individual and the cutting tool being less than the threshold distance, for example when there can be a potential for injury to the individual via contact with the cutting tool, the analysis circuit 300 can generate the trigger signal 302 that can be indicative of the mechanical reaction mechanism 70 isolating, separating, and / or protecting the individual from the cutting tool. Accordingly, the power tool 10 according to the present disclosure can include an electromechanical safety mechanism that includes at least the sensor assembly 100, the analysis circuit 300, and the mechanical reaction mechanism 70 that protects the individual from contact with the cutting tool.

[0024] Conventional electromechanical safety mechanisms exist for certain power tools, such as stationary table saws. Examples of such conventional electromechanical safety mechanisms are disclosed in U.S. Patent Nos. 7,536,238, 7,971,613, and 9,724,840, and also International Patent Application Publication No. WO 2017 / 0210091, the entire disclosures of which are hereby incorporated by reference herein. These conventional electromechanical safety mechanisms generally rely on a conventional sensor assembly that compares a single voltage signal to ground or earth to detect a condition in which the conventional electromechanical safety mechanism should actuate a conventional mechanical reaction mechanism.

[0025] While such conventional electromechanical safety mechanisms can be effective in certain situations, such as when used in conjunction with stationary power tools that include a direct ground, plug-in power tools, and / or power tools, they can be ineffective in other situations. As an example, wireless and / or battery-powered power tools can not include a direct ground, which can introduce additional signal noise and / or make it difficult or impossible to reliably utilize a conventional electromechanical safety mechanism.

[0026] As discussed, the power tool 10 according to the present disclosure utilizes a sensor assembly 100 that generates a differential voltage signal 102. The differential voltage signal 102 can include and / or be a voltage difference between two separate and / or distinct circuits, neither of which is directly connected to, directly shorted to, and / or directly shunted to ground. In other words, the differential voltage signal can be a voltage difference between two time-varying voltage signals, and / or can not include and / or be a difference between a single voltage and ground or earth. In other words, the differential voltage signal 102 can include and / or be a difference between a detected or sensed voltage and a reference voltage. Accordingly, the sensor assembly 100 according to the present disclosure can be reliably included in and / or used with wireless power tools 10, battery-powered power tools 10, and / or power tools 10 that do not include and / or utilize an electrical connection, direct electrical connection, and / or consistent electrical connection to earth. Additionally or alternatively, the sensor assembly 100 can be used to improve and / or increase the reliability of power tools 10 that include and / or utilize an electrical connection to earth.

[0027] As discussed in greater detail herein, the power tool 10 can include and / or utilize a sensor assembly 100 that utilizes capacitive coupling with an individual and / or with the cutting tool 60. To allow and / or facilitate such capacitive coupling, the power tool 10 can include a cutting tool isolation structure 62. The cutting tool isolation structure 62, when present, can be adapted, configured, designed, and / or constructed to electrically isolate the cutting tool from at least one other component of the power tool, or even from the remainder of the power tool. For example, the cutting tool can be electrically isolated from the power components of the power tool. As another example, the cutting tool 60 and the arbor 26 and / or the motor shaft 22 coupled with the cutting tool can be electrically isolated from the power components of the power tool, or even from the remainder of the power tool. Examples of the cutting tool isolation structure 62 include electrically insulating and / or dielectric materials.

[0028] The mechanical reaction mechanism 70 can include any suitable structure that, in response to receiving the trigger signal, can be adapted, configured, designed, and / or constructed to isolate, separate, and / or protect the individual from the cutting tool 60. Additionally, the mechanical reaction mechanism 70 can isolate, separate, and / or protect the individual from the cutting tool in any suitable manner.

[0029] As an example, the mechanical reaction mechanism 70 can be configured to stop actuation of the cutting tool in response to receiving the trigger signal 302. As used herein, actuation of the cutting tool refers to movement of the cutting tool, such as rotational movement, vibrational movement, and / or reciprocating movement. As a more particular example, the mechanical reaction mechanism 70 can include a braking assembly that can be configured to selectively apply and / or utilize a frictional force to stop actuation of the cutting tool. When present, the braking assembly can be configured to directly engage the cutting tool. Additionally or alternatively, the braking assembly, when present, can be configured to engage the arbor 26, the motor shaft 22, and / or another component of the power tool that moves in unison with the cutting tool, actuates with the cutting tool, and / or actuates the cutting tool.

[0030] As another example, the mechanical reaction mechanism 70 can be configured to selectively stop actuation of the cutting tool by the motor 20 in response to receiving the trigger signal. As a more particular example, the mechanical reaction mechanism 70 can include a decoupling mechanism and / or clutch that can be configured to disengage the motor 20 and / or the motor shaft 22 from the cutting tool. As another more particular example, the mechanical reaction mechanism 70 can include an electrical switch that can be configured to stop supplying current to the motor.

[0031] As yet another example, the mechanical reaction mechanism 70 can be configured to selectively retract the cutting tool into a remainder of the power tool and / or move the cutting tool away from the individual in response to receiving the trigger signal. As a more particular example, the mechanical reaction mechanism 70 can include a biasing mechanism, such as a spring, that biases the cutting tool into a recess or compartment that can be defined within the power tool, and a release mechanism that allows the biasing mechanism to move the cutting tool into the recess or compartment in response to receiving the trigger signal.

[0032] As another example, the mechanical reaction mechanism 70 can be configured to selectively sever the cutting tool in response to receiving the trigger signal. As a more particular example, the mechanical reaction mechanism 70 can include a cutting assembly that is configured to cut and / or sever at least one region of the cutting tool in order to reduce or remove tension, applied torque, and / or force applied to the cutting tool to actuate the cutting tool.

[0033] As yet another example, the mechanical reaction mechanism 70 can be configured to selectively position a protective structure between the individual and the cutting tool in response to receiving the trigger signal. As a more particular example, the mechanical reaction mechanism 70 can include a movable shield or barrier that can be deployed and / or extended to separate the individual from the cutting tool. As another example, the mechanical reaction mechanism 70 can include a wrapping material that is configured to wrap around the cutting tool to separate the individual from the cutting tool.

[0034] The motor 20 can include any suitable structure that can provide a motive force for rotation of the motor shaft 22, the arbor 26, and / or the cutting tool 60. Examples of the motor 20 include an electric motor, an AC electric motor, a DC electric motor, a variable speed motor, and / or a single speed motor.

[0035] As discussed in greater detail herein, the power tool 10 can include and / or be a battery-powered power tool 10, and / or can not include or can be without a ground or direct ground. Examples of the power tool 10 include a hand-held power tool and / or a portable power tool. Additional examples of the power tool 10 include a saw, a circular saw, a hand-held circular saw, a miter saw, a radial arm saw, a table saw, a chop saw, an insert saw, a track saw, a band saw, a vertical saw, an up-cut saw, a panel saw, a rotary cutting tool, a router, a drill bit, a sander, and / or a planer. Examples of the cutting tool 60 include a blade, a saw blade, a circular saw blade, a drill bit, a router bit, a drill bit, a rotary cutting bit, a sanding pad, a sanding belt, and / or a sanding drum.

[0036] Power tool 10 may include one or more structures and / or components common to conventional power tools. As an example, power tool 10 may include a spindle 26. Spindle 26 may include any suitable structure that can be operatively attached to motor shaft 22 and / or can or may be used to operatively attach cutting tool 60 to motor shaft 22, such that the motor shaft actuates the cutting tool. Typically, spindle 26 may be configured to allow and / or facilitate selective and repeated disengagement of the cutting tool from the remainder of the power tool to allow and / or facilitate sharpening and / or replacement of the cutting tool. Examples of spindle 26 include threaded spindle 26.

[0037] like Figure 1 As shown by the dashed lines, the power tool 10 may include a gripping area 30. The gripping area 30 (when present) may also be referred to herein as and / or may be a handle, and may be configured to be gripped by the user during use of the power tool.

[0038] For example Figure 1 As shown by the dashed lines, the power tool 10 may include a switch 35. The switch 35 (when present) may be configured to be selectively actuated by the user of the power tool and / or selectively apply current to the motor 20 to power the motor 20. Examples of the switch 35 include an electrical switch, a normally open electrical switch, a momentary electrical switch, and / or a locking momentary electrical switch.

[0039] For example Figures 2-6 As shown by the dashed lines, the power tool 10 may include a workpiece support 40. The workpiece support 40 (when present) may be configured to support the workpiece 90 and / or position the power tool relative to the workpiece when the workpiece is cut by a cutting tool or otherwise acted upon. For example, many power tools 10 in the form of a saw include a workpiece support 40 in the form of a base plate, table, shoe, frame, or pad.

[0040] The power tool 10 may include any suitable power source and corresponding power structure for powering the motor 20 and / or sensor assembly 100. Examples of power structures include power supply structure 50, such as power cord 52 and / or battery 54.

[0041] As discussed, sensor assembly 100 is configured to generate a differential voltage signal 102. The differential voltage signal may be based on and / or indicate that the distance between the individual and the cutting tool is less than a threshold distance. Also as discussed, in embodiments where detection is based on direct contact between the user and the cutting tool, the threshold distance is zero or may be zero, while in embodiments where detection is based at least in part on proximity between the user and the cutting tool, the threshold distance may be a non-zero value.

[0042] Figures 2-6This may include, or be a schematic diagram of an example of a sensor assembly 100 or components thereof that may be included in and / or used with the power tool 10, as disclosed herein. With this in mind, reference is made herein to... Figure 1 Any structure, function, and / or feature disclosed in any sensor component 100 may include in Figure 1 In the power tool 10 and / or sensor assembly 100 and / or with Figure 1 The power tool 10 and / or sensor assembly 100 are used together. Similarly, without departing from the scope of this disclosure, references are made herein. Figures 2-6 Any structure, function, and / or feature disclosed in the power tool 10 and / or sensor assembly 100 may be included in Figures 2-6 In and / or with the sensor assembly 100 Figure 1 Used together with sensor assembly 100.

[0043] Sensor assembly 100 may include and / or may include any suitable structure that can be adapted, configured, designed, and / or constructed to generate and / or produce differential voltage signals. As an example, and as... Figures 2-4 The dashed lines in the middle and Figures 2-4 As shown by the solid line in the figure, the sensor assembly 100 may include a bridge circuit 110 that can be configured to generate a differential voltage signal 102. Figure 1 It may be included and / or may be included in and / or with the power tool 10 according to the invention (such as...) Figures 2-4 A schematic diagram of an example of a bridge circuit 110 or components of a bridge circuit 110 used with a power tool 10). With this in mind, reference is made herein to... Figures 2-4 Any structure, function, and / or feature disclosed in any bridge circuit 110 in any of the diagrams may include in Figures 2-4 In any other bridge circuit 110 of any other diagram in the circuit, it can be connected with Figures 2-4 It can be used with any other bridge circuit 110 in any other diagram, and / or can be replaced. Figure 3 Any other bridge circuit 110 in any other diagram. In other words, without departing from the scope of this disclosure, Figure 4 Bridge circuit 110 and / or Figure 2 The bridge circuit 110 can be replaced or substituted. Figures 2-4 Bridge circuit 110.

[0044] like Figures 2-4As shown in FIG. 1, the bridge circuit 110 can include a reference leg 120 and a sense leg 160. The reference leg 120 can be configured to produce a reference leg signal 122 at a reference leg voltage. Similarly, the sense leg 160 can be configured to produce a sense leg signal 162 at a sense leg voltage. The differential voltage signal 102 can include and / or be a difference between the reference leg voltage and the sense leg voltage.

[0045] Also as Figure 2 shown in FIG. 1, the sensor assembly 100 and / or its bridge circuit 110 can include at least one bridge circuit driver 112, which can be configured to provide a bridge circuit excitation voltage 114 to the bridge circuit 110. In some examples, and as Figure 4 and Figure 3 shown in FIG. 1, a single bridge circuit driver 112 can be used to provide respective bridge circuit excitation voltages 114 to both the reference leg 120 and the sense leg 160. In some such examples, a variable resistor 116 can be utilized to provide phase compensation between the reference leg 120 and the sense leg 160. In some examples, and as Figures 2-4 shown in FIG. 1, separate bridge circuit drivers 112 can be utilized to provide respective bridge circuit excitation voltages 114 to the reference leg 120 and the sense leg 160. In some such examples, the voltages, currents, and / or phases of the separate bridge circuit drivers 112 can be independently controlled and / or adjusted in order to allow for and / or facilitate tuning of the bridge circuit, as discussed in greater detail herein. Examples of bridge circuit drivers 112 include oscillators, voltage oscillators, and / or alternating current voltage sources.

[0046] As Figure 1 shown in FIG. 1, the reference leg 120 can include a first reference leg resistor 124 and a second reference leg resistor 126. The first reference leg resistor 124 can electrically interconnect the respective bridge circuit driver 112 with a reference leg output terminal 128 of the reference leg 120, and the second reference leg resistor 126 can electrically interconnect the reference leg output terminal 128 with the signal ground 106 of the sensor assembly.

[0047] As discussed in greater detail herein, the power tool 10 according to the present disclosure can not include a ground, or can not be in direct electrical communication with a ground. With this in mind, the signal ground 106 can not be or can not be equivalent to a ground, can be a floating ground, and / or can be a negative terminal of the bridge circuit driver 112, a negative terminal of a power structure of the power tool, and / or a negative terminal of a battery of the power tool, such as the battery 54 of the power tool 10 of FIG. 1. Figure 4

[0048] As Figures 2-4 ​As shown, the reference branch 120 may further include a tuning structure 200. The tuning structure 200 (when present) may be configured to tune the reference branch 120. This may include tuning the reference branch such that the amplitude of the reference branch voltage is within or set to a threshold voltage difference for detecting the amplitude of the branch voltage, and / or such that the phase of the reference branch voltage is within or set to a threshold phase difference for detecting the phase of the branch voltage. Examples of the tuning structure 200 include a potentiometer and / or a variable resistor.

[0049] like Figures 2-4 As shown, the detection branch 160 may include a first detection branch capacitor 164 and a second detection branch capacitor 166. The first detection branch capacitor 164 can electrically interconnect the corresponding bridge circuit driver 112 with the detection branch output terminal 168 of the detection branch 160, and the second detection branch capacitor 166 can electrically interconnect the detection branch output terminal 168 with the signal ground 106.

[0050] Continue to refer to Figures 3-4 The detection branch 160 may include a capacitive coupling structure 220. The capacitive coupling structure 220 may be electrically interconnected with the detection branch output terminal 168 and may be configured to be capacitively coupled to and / or capacitively coupled to an individual, such that the detection branch voltage is at least partially based on the distance between the individual and the cutting tool. Examples of the capacitive coupling structure 220 include current and / or capacitive coupling to and / or current and / or capacitive coupling to the cutting tool 60.

[0051] Go to Figures 2-4 As illustrated, the detection branch 160 may additionally include one or more additional structures, or the detection branch output terminal 168 may be electrically connected to one or more additional structures, which may be used to reduce noise and / or improve capacitive coupling to the user. As an example, a detection branch resistor 170 may electrically interconnect the detection branch output terminal 168 and the signal ground 106. The detection branch resistor 170 (when present) may be configured to prevent electrostatic charging or electrostatic discharge of the detection branch 160 and / or its detection branch output terminal 168.

[0052] As another example, the test switch 172 can be used to selectively electrically interconnect the detection branch output terminal 168 and the signal ground 106 to opposite terminals of a test capacitor 174. In this configuration, the test capacitor 174 can have a capacitance that is similar, analogous, and / or approximate to the capacitive coupling between the individual and the cutting tool when the individual is less than the threshold distance from the cutting tool. With this in mind, the power tool 10 and / or a user of the power tool 10, such as the individual, can selectively close the switch 172 to test the operation of the sensor assembly 100 and / or to determine whether the sensor assembly 100 is sensitive to the individual being less than the threshold distance from the cutting tool.

[0053] As another example, the calibration switch 175 can be used to selectively and electrically interconnect a first varactor diode 176, a second varactor diode 177, an inductor 178 (which can otherwise be referred to as a calibration inductor 178), and a variable DC source 179 between the detection branch output terminal 168 and the signal ground 106. An input of the first varactor diode 176 can be configured to receive current from the detection branch output terminal 168, and an output from the first varactor diode can be configured to provide current to a node that is electrically connected to an output from the second varactor diode 177. An input of the second varactor diode 177 can be electrically connected to the signal ground 106. The variable DC source 179 can be configured to provide a voltage to the node via the inductor 178. When the calibration switch 175 is closed, the variable DC source 179 can be used to selectively vary the capacitive load applied to the detection branch output terminal 168 in order to allow and / or facilitate calibration of the bridge circuit 110 and / or testing of the response of the bridge circuit 110 to certain and / or specified capacitive loads.

[0054] As discussed, Figures 2-4 A bridge circuit 110 that can be included in the sensor assembly 100 and / or that can be used to generate and / or produce the differential voltage signal 102 according to the present disclosure is shown. As Figure 2 As shown and discussed herein, the bridge circuit 110 generates a reference branch signal 122 at the reference branch output terminal 128 and also generates a detection branch signal 162 at the detection branch output terminal 168. As Figure 2 As shown in Figures 5-6 and Figure 2 Examples of additional circuitry that can receive the reference branch signal 122 and / or the detection branch signal 162 from the bridge circuit and from which the sensor assembly output 104 is produced are shown.

[0055] Turning to Figure 5 and Figure 2The sensor assembly 100 can include a reference leg buffer 140 that can be electrically connected to the reference leg output terminal 128. Figure 5 A reference leg buffer 140 electrically connected to the reference leg output terminal 128 of the reference leg 120 is shown, while Figure 2 Another example of a reference leg buffer 140 that can be electrically connected to the reference leg output terminal and / or can replace or can substitute the reference leg buffer 140 shown in Figure 2

[0056] The reference leg buffer 140 (when present) can be configured to buffer the reference leg signal 122 to produce and / or generate a buffered reference leg signal 142. In such a configuration, the sensor assembly output 104 can be based at least in part on the buffered reference leg signal 142. The reference leg buffer 140 can be configured or can function to convert a relatively higher output impedance of the bridge circuit 110 providing the reference leg signal 122 to a relatively lower output impedance of the reference leg buffer 140 to produce and / or generate the buffered reference leg signal. The relatively lower output impedance of the reference leg buffer 140 can allow the buffered reference leg signal 142 to act as a loadable voltage source for subsequent circuitry receiving the buffered reference leg signal, and / or can reduce the magnitude of the current of the buffered reference leg signal when compared to the reference leg signal 122. As Figure 5 and Figure 2 shown, an example of the reference leg buffer 140 includes a reference leg emitter follower circuit 144.

[0057] Turning to Figures 5-6 and Figure 2 The sensor assembly 100 can include a detection leg buffer 180 that can be electrically connected to the detection leg output terminal 168. Figures 5-6 A detection leg buffer 180 electrically connected to the detection leg output terminal 168 of the detection leg 160 is shown, while Figure 2 Other examples of a detection leg buffer 180 that can be electrically connected to the detection leg output terminal and / or can replace or can substitute the detection leg buffer 180 shown in Figure 2

[0058] ​​The detection leg buffer 180, when present, can be configured to buffer the detection leg signal 162 to produce and / or generate a buffered detection leg signal 182. In such a configuration, the sensor assembly output 104 can be based at least in part on the buffered detection leg signal 182. The detection leg buffer 180 can be configured to or can function to convert a relatively higher output impedance of the bridge circuit 110 providing the detection leg signal 162 to a relatively lower output impedance of the detection leg buffer 180 to produce and / or generate the buffered detection leg signal. The relatively lower output impedance of the detection leg buffer 180 can allow the buffered detection leg signal 162 to act as a loadable voltage source for subsequent circuitry receiving the buffered detection leg signal, and / or can reduce the magnitude of the current of the buffered detection leg signal when compared to the detection leg signal 162.

[0059] An example of the detection leg buffer 180 includes a detection leg emitter follower circuit 184, as shown in Figure 5 and Figure 6 An example of the detection leg buffer 180 includes a detection leg emitter follower circuit 184, as shown in Figure 2 and An example of the detection leg buffer 180 includes a detection leg emitter follower circuit 184, as shown in

[0060] and Figure 2 Within the scope of the present disclosure, the reference leg buffer 140 additionally or alternatively can include or alternatively can be a reference leg high pass filter, a reference leg low pass filter, and / or a reference leg high pass filter in series with a reference leg low pass filter. In other words, the general structure of the detection leg high pass filter 186 and / or the detection leg low pass filter 188 can be substituted or added to the reference leg buffer 140 shown in

[0061] With continued reference to Figures 5-6 and Figure 2The sensor assembly 100 can also include an amplifier circuit 240. The amplifier circuit 240 can also be referred to and / or can be a differential amplifier 240 herein. The amplifier circuit 240, when present, can be configured to amplify the differential voltage signal 102, such as via differential voltage of the amplified reference leg signal 122 or the buffered reference leg signal 142 and the detection leg signal 162 or the buffered detection leg signal 182. This can include amplifying to produce and / or generate an amplified differential voltage signal 242 that is based at least in part on the differential voltage signal. When the sensor assembly 100 includes the amplifier circuit 240, the sensor assembly output 104 can be based at least in part on the amplified differential voltage signal. Including the amplifier circuit 240 can increase the amplitude of the differential voltage signal 102 and / or increase or improve the signal-to-noise ratio of the differential voltage signal, thereby improving detection accuracy.

[0062] In some examples, the amplifier circuit 240 can be configured to receive or directly receive the reference leg signal 122 and / or the detection leg signal 162. In some examples, the amplifier circuit 240 can be configured to receive the buffered reference leg signal 142 and / or the buffered detection leg signal 182. Figure 5 and Figure 6 An example of the sensor assembly 100 is shown in which the amplifier circuit 240 receives the buffered reference leg signal 142 and the buffered detection leg signal 182. Figure 2 An example of the sensor assembly 100 is shown in which the amplifier circuit 240 receives the reference leg signal 122 and the buffered detection leg signal 182.

[0063] Figures 5-6 and Figures 5-6 An example of the amplifier circuit 240 is shown that is configured to produce a single amplified differential voltage signal 242. Some examples of the sensor assembly 100 can include and / or utilize an amplifier circuit 240 that can be configured to produce and / or generate a pair of outputs that together can define an amplified differential voltage signal (e.g., a voltage difference between the pair of outputs). Examples of such differential amplifiers include four-armed active bridge circuits and / or Wheatstone bridge circuits.

[0064] In some examples, the amplifier circuit 240 can be configured to produce and / or generate the amplified differential voltage signal 242 in the form of an amplifier output current that can be based on and / or proportional to the differential voltage signal. In some such examples, and as Figure 6As shown in FIG. 1, the sensor assembly 100 can include a transducer 260. The transducer 260, when present, can be configured to receive the amplifier output current and generate a transducer output voltage 262 therefrom. The transducer output voltage can be based at least in part on the amplifier output current, and the sensor assembly output 104 can be based at least in part on the transducer output voltage. Examples of the transducer 260 include a transimpedance transducer.

[0065] As Figure 7 As shown in FIG. 1, the sensor assembly 100 can also include a filter 280. The filter 280, when present, can be configured to receive the transducer output voltage 262 and generate and / or produce a filtered transducer output voltage 282 in order to reduce noise in the filtered transducer output voltage 282 relative to the transducer output voltage 262 and / or remove an undesired frequency range in the transducer output voltage from the filtered transducer output voltage. The filtered transducer output voltage 282 can be based at least in part on the transducer output voltage, and the sensor assembly output 104 can be based at least in part on the filtered transducer output voltage. Examples of the filter 280 include a second order multiple feedback bandpass filter.

[0066] The power tool 10 can be configured such that the sensor assembly 100 and / or its bridge circuit 110 is calibrated in order to allow and / or facilitate its operation. In some examples, a method of operating the power tool 10 can include blocking or beginning to block the supply of current to the motor assembly and calibrating the sensor assembly. These methods can also include allowing the supply of current to the motor in response to successful calibration of the sensor assembly. When the sensor assembly 100 includes the bridge circuit 110, the calibration can include balancing the bridge circuit such that the differential voltage signal has a threshold differential voltage of a predetermined voltage value or within a threshold differential voltage of a predetermined voltage value. In some examples, and as discussed in more detail herein, the calibration can utilize an iterative process in which the bridge circuit is adjusted until the differential voltage signal has the predetermined voltage value. Such a configuration can allow and / or facilitate system calibration of the bridge circuit and / or can allow the differential voltage signal to be set to the predetermined voltage value without needing to know the functional behavior of the differential voltage signal.

[0067] Figures 2-4 is a flowchart depicting an example of a method 400 of operating a power tool in accordance with the present disclosure. The method 400 can include initializing a first bridge circuit driver, such as the first bridge circuit driver 112 of FIG. 1, at 405, and balancing the bridge circuit, such as the bridge circuit 110 of FIG. 1, at 410. Figures 2-4 Figure 1 ​The bridge circuit 110. Then, method 400 may include determining at 415 whether the balancing at 410 has been performed a threshold number of times, and repeating the balancing at 410 until the threshold number of times is reached. Subsequently, method 400 includes calculating the signal amplitude of the signal generated by the cutting tool at 420, and determining at 425 whether the signal amplitude is valid and / or within a predetermined amplitude range. If the signal amplitude is invalid, an error state is generated as shown at 430. If the signal amplitude is valid, method 400 moves to optional driver amplitude adjustment at 435.

[0068] Subsequently, and as shown at 440, a bias can be set. This bias may include and / or be a specific target or desired value or range of the differential voltage signal generated by the sensor assembly, and can be selected based on any suitable criterion. As an example, the bias can be selected to improve, increase, and / or optimize the sensor assembly's sensitivity to distances between an individual and a cutting tool and / or distances less than a threshold distance. In some embodiments, the bias may be equal to, or at least substantially equal to, zero volts. In other examples, the bias may be non-zero and / or may have a non-zero voltage value. As a more specific example, the bias can be selected such that the sensor assembly is highly sensitive to capacitance changes in the capacitively coupled structure.

[0069] As shown at 445, it can be done, for example, via to Figures 3-4 The motor 20 supplies current to turn on the power tool. Method 400 then includes verifying the operational status of the power tool at 450. If the power tool can be released for operation, or for user operation, without further testing, method 400 may proceed to step 455. For example, such release at 455 may be permitted if the operation of the sensor assembly has recently been verified. In other words, and as discussed in more detail herein, method 400 may include optionally verifying the operation of the sensor assembly to ensure that the sensor assembly is calibrated to ensure that the sensor assembly is configured to generate a differential voltage signal, and / or to ensure that the differential voltage signal actually indicates that the distance between the individual and the cutting tool is less than a threshold distance. With this in mind, and in some cases, the verification at 450 may include allowing the power tool to be released for operation if and / or when the operation of the cutting tool has recently been verified.

[0070] If the power tool cannot be released without further testing, such as when the operation of the sensor assembly has not been recently verified, method 400 can proceed to step 460, where the operation of the sensor assembly can be tested and / or verified. For example, a test capacitor connected in parallel with the cutting tool can be used. For example, it can be achieved through... Figure 2The test switch 172 and test capacitor 174 are used to apply a test capacitance. This test capacitance can be used to test the response of a power tool to a known and / or predefined capacitance (i.e., the test capacitance), which is similar to, analogous to, within a capacitance range similar to, and / or equal to, the capacitance experienced by the sensor assembly when the distance between the individual and the cutting tool is less than a threshold distance. The value of the differential voltage signal can then be recorded, and sensitivity and / or amplification / gain adjustment can be performed, such as by utilizing and / or adjusting... Figures 5-6 and Figure 3 Amplifier circuit 240.

[0071] Then, method 400 may include verifying the sensor component output from the sensor component at 465. If the sensor component output is valid, within a predetermined range, and / or exceeds a threshold, the verification of the sensor component can be completed, and method 400 may release the power tool for operation, as shown at 470. Alternatively, if the sensor component output is invalid, outside the predetermined range, and / or less than the threshold, method 400 may proceed to an error state, as shown at 475.

[0072] When the sensor assembly includes separate first bridge circuit driver 112 and second bridge circuit driver 112, and as Figure 8 As shown, it can be used Figure 7 Method 500 is used to perform balancing at 410. More specifically, balancing at 410 may include initializing the second bridge circuit driver at 505 and recording the value of the differential voltage signal at 510. If the differential voltage signal is within a target value range, for example, at or near its minimum value, and as shown at 515, balancing at 410 is complete, and method 400 moves to... Figure 7 Step 415. If the target value range of the differential voltage signal has not been reached, method 500 can verify at 520 that the value of the differential voltage signal is within a predetermined control range. If the value of the differential voltage signal is outside the predetermined control range, method 500 proceeds to error state 530. If the value of the differential voltage signal is within the predetermined control range, method 500 adjusts or iteratively adjusts the second bridge circuit driver at 525 and returns to the record at 510. The loop of steps 510, 515, 520, and 525 can be repeated until error state 530 is reached or until the target value range of the differential voltage signal is reached, thus returning to Figure 2 Method 400.

[0073] When the sensor assembly includes only a single bridge circuit driver 112, and as Figure 4 and Figure 9 As shown, Figure 10 Method 600 and / or Figure 9The method 700 can be used to perform balancing at 410. Figure 4 The method 600 can be used to balance the amplitudes of the reference branch signal and the detection branch signal. The method 600 can include initializing a first potentiometer at 605, such as the potentiometer 116 of the tuning structure 200, and recording a value of the differential voltage signal at 610. If a minimum value of the differential voltage signal is exceeded, and balancing at 410 is complete as indicated at 615, the method 600 returns to Figure 7 The method 600 can be used to balance the amplitudes of the reference branch signal and the detection branch signal. The method 600 can include initializing a first potentiometer at 605, such as the potentiometer 116 of the tuning structure 200, and recording a value of the differential voltage signal at 610. If a minimum value of the differential voltage signal is exceeded, and balancing at 410 is complete as indicated at 615, the method 600 returns to Figure 7 The method 600 can be used to balance the amplitudes of the reference branch signal and the detection branch signal. The method 600 can include initializing a first potentiometer at 605, such as the potentiometer 116 of the tuning structure 200, and recording a value of the differential voltage signal at 610. If a minimum value of the differential voltage signal is exceeded, and balancing at 410 is complete as indicated at 615, the method 600 returns to Figure 10 The method 400.

[0074] Figure 4 The method 700 can be used to balance the phases of the reference branch signal and the detection branch signal, and the method 700 can include initializing a second potentiometer at 705, such as the potentiometer 116 of the tuning structure 200, and recording a phase difference between the reference branch signal and the detection branch signal at 710. If a minimum value of the phase difference is exceeded, and balancing at 410 is complete as indicated at 715, the method 700 returns to Figure 7 The method 700 can be used to balance the phases of the reference branch signal and the detection branch signal, and the method 700 can include initializing a second potentiometer at 705, such as the potentiometer 116 of the tuning structure 200, and recording a phase difference between the reference branch signal and the detection branch signal at 710. If a minimum value of the phase difference is exceeded, and balancing at 410 is complete as indicated at 715, the method 700 returns to Figure 7 The method 700 can be used to balance the phases of the reference branch signal and the detection branch signal, and the method 700 can include initializing a second potentiometer at 705, such as the potentiometer 116 of the tuning structure 200, and recording a phase difference between the reference branch signal and the detection branch signal at 710. If a minimum value of the phase difference is exceeded, and balancing at 410 is complete as indicated at 715, the method 700 returns to Figure 11 The method 400.

[0075] Figures 1-6 is a flowchart depicting an example of a method 800 of operating a power tool in accordance with the present disclosure. Reference is made herein to the tuning structure 200 of FIG. 2.​ The power tool 10 of FIG. 1 discloses an example of such a power tool. The method 800 includes blocking a supply of current at 810 and verifying operation of a sensor assembly at 820. The method 800 can also include calibrating the sensor assembly at 830 and including allowing the supply of current at 840. The method 800 can also include detecting a distance at 850 and / or stopping movement of a cutting tool at 860.

[0076] Blocking the supply of current at 810 can include blocking the supply of current to a motor of the power tool. This can include blocking the supply of current in any suitable manner and / or with any suitable structure, examples of which include a switch, a solid state switch, a transistor, a relay, and / or a controller that can be adapted, configured, designed, constructed, and / or programmed to selectively allow and / or selectively restrict the supply of current to the motor of the power tool, even if a user actuates a switch and / or otherwise instructs the power tool to provide current to the motor.

[0077] The power tool includes a sensor assembly that can be configured to detect when a distance between an individual and a cutting tool of the power tool is less than a threshold distance. With this in mind, verifying operation of the sensor assembly at 820 can include verifying that the sensor assembly is or is currently adapted, configured, programmed, and / or capable of detecting when the distance between the individual and the cutting tool is less than the threshold distance and / or that the distance between the individual and the cutting tool is less than the threshold distance.

[0078] Calibrating the sensor assembly at 830 can include calibrating the sensor assembly in any suitable manner so as to enable the sensor assembly to detect when the distance between the individual and the cutting tool is less than the threshold distance and / or to detect that the distance between the individual and the cutting tool is less than the threshold distance. In some examples, the calibration at 830 can be or can be performed in response to the verification at 820 indicating that the sensor assembly is not, is not currently, or is not currently adapted, configured, programmed, and / or capable of detecting when the distance between the individual and the cutting tool is less than the threshold distance and / or that the distance between the individual and the cutting tool is less than the threshold distance.

[0079] As an example, the sensor assembly can include a bridge circuit, such as the bridge circuit 110 discussed herein. In some such examples, the calibration at 830 can include balancing the bridge circuit. In some examples, the balancing can include balancing a reference leg voltage of a reference leg of the bridge circuit and a detection leg voltage of a detection leg of the bridge circuit. In some examples, the balancing can include balancing a reference leg phase of the reference leg and a detection leg phase of the detection leg.

[0080] In some examples, the calibration can include setting the differential voltage signal of the sensor assembly to a target range. In some such examples, the target range can include 0 volts. In some such examples, the target range can not include 0 volts in order to increase sensitivity of the sensor assembly to distance between the individual and the cutting tool, as discussed in greater detail herein.

[0081] Allowing supply of current at 840 can include allowing supply of current to the motor of the power tool in response to verification or successful verification of operation of the sensor assembly. This can include allowing supply of current when the power tool does not have a direct ground. In other words, and as discussed in greater detail herein, the method 800 can be performed with a wireless or battery-powered power tool that does not include and / or utilize a connection, direct connection, and / or wired connection to ground.

[0082] Detecting distance at 850 can include detecting that the distance between the individual and the cutting tool is less than a threshold distance. In some examples, the detection at 850 can include capacitive detection, such as via a capacitive coupling structure of the power tool. Examples of capacitive coupling structures are disclosed herein with reference to the capacitive coupling structure 220. In some examples, the detection at 850 can be performed after the allowing at 840, and / or can be performed in response to the distance between the individual and the cutting tool being less than the threshold distance. In some examples, the detection at 850 can include generating a differential voltage signal that can be indicative of the distance between the individual and the cutting tool, and / or that can be indicative of the distance between the individual and the cutting tool being less than the threshold distance.

[0083] Stopping movement of the cutting tool at 860 can include stopping any suitable rotational, reciprocating, oscillating, and / or linear movement of the cutting tool in order to protect the individual from injury that can result from contact between the individual and the moving cutting tool. In some examples, the stopping at 860 can be in response to the detection at 850. In some examples, the stopping at 860 can be performed by, via, and / or with a mechanical reaction mechanism of the power tool. Examples of mechanical reaction mechanisms are disclosed herein with reference to the mechanical reaction mechanism 70.

[0084] In the present disclosure, several illustrative, non-exclusive examples have been discussed and / or presented in the context of flow diagrams or flow charts, in which methods are shown and described as a series of blocks or steps. Unless specifically set forth in the description, the order of the blocks can be varied from the order shown in the flowcharts, including two or more blocks (or steps) occurring in different orders and / or simultaneously. It is also within the scope of the present disclosure that a block or step can be implemented as logic, which can also be described as implementing a block or step as logic. In some applications, a block or step can represent expressions and / or actions to be taken by functional equivalent circuitry or other logic devices. The illustrated blocks can but are not required to represent executable instructions to cause a computer, processor, and / or other logic device to respond, perform an action, change a state, generate an output, and / or make a decision.

[0085] As used herein, the term "and / or," placed between the second and third recited items, means (1) the first recited item, (2) the second recited item, and (3) both of the first recited item and the second recited item. Multiple recited items

[0086] As used herein, the phrase “at least one of,” with respect to a listing of one or more entities, should be understood to mean at least one entity from among any one or more of the entities in the entity listing, but not necessarily including at least one of each and every entity specifically listed within the entity listing, or excluding any combinations of entities in the entity listing. This definition also allows that entities can optionally be present other than the entities specifically identified within the phrase “at least one of.” To the contrar, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and / or B”) can refer, in one embodiment, to at least one A, with no B present (and optionally including entities other than B); in another embodiment, to at least one B, with no A present (and optionally including entities other than A); in yet another embodiment, to at least one A, and at least one B (and optionally including other entities). In other words, the phrases “at least one of,” “one or more of,” and “and / or” are open-ended expressions that are both conjunctive and disjunctive in operation. For example, each of the expressions “at least one of A, B and C,” “at least one of A, B, or C,” “one or more of A, B, and C,” “one or more of A, B, or C,” and “A, B, and / or C” can mean A alone, B alone, C alone, A and B together, A and C together, B and C together, A, B and C together, and optionally any of these A, B, or C with any of the other entities mentioned.

[0087] In the event that any patent, patent application, or other reference that is incorporated by reference herein and (1) defines a term in a manner that is inconsistent with the unincorporated portion of the present disclosure or any other incorporated reference, or (2) defines a term in a manner that is inconsistent with the definition of term provided in the present disclosure, the definition of the term provided in the unincorporated portion of the present disclosure and / or the incorporated disclosure shall control.

[0088] As used herein, the terms "adapted" and "configured" mean that an element, component, or other aspect is designed and / or intended to perform a given function. Use of the terms "adapted" and "configured" should not be interpreted as implying that a given element, component, or other aspect is "capable of" performing the given function only as a result of being "adapted" and / or "configured" to perform the given function. It is further within the scope of the present disclosure that an element, component, and / or other recited subject matter that is recited as being adapted to perform a particular function can additionally or alternatively be described as being configured to perform that function, and vice versa.

[0089] As used herein, the phrase "for example," the phrase "as examples," and / or simply the term "example," when used with reference to a component, feature, detail, structure, embodiment and / or method according to the present disclosure, are intended to convey that the described component, feature, detail, structure, embodiment and / or method is a specific instance of a more general class of components, features, details, structures, embodiments and / or methods. Thus, the described component, feature, detail, structure, embodiment and / or method is not intended to be limiting, essential or exclusive / exhaustive; and other components, features, details, structures, embodiments and / or methods, including structural and / or functional analogous and / or equivalent components, features, details, structures, embodiments and / or methods, are within the scope of the present disclosure.

[0090] As used herein, when modifying a degree or relationship, "at least substantially" can include not only the recited "substantial" degree or relationship, but also the full degree of the recited degree or relationship. A substantial amount of the recited degree or relationship can include at least 75% of the recited degree or relationship. For example, an object formed at least substantially of a material includes an object in which at least 75% of the object is formed of the material, and also includes an object formed entirely of the material. As another example, a first length that is at least substantially as long as a second length includes a first length that is within 75% of the second length, and also includes a first length that is as long as the second length.

[0091] Illustrative, non-exclusive examples of electric power tools and methods according to the present disclosure are set forth in the following recited paragraphs. It is within the scope of the present disclosure that individual steps of the methods described herein, including in the following recited paragraphs, can additionally or alternatively be referred to as "steps" for performing the recited action.

[0092] A1. An electric power tool, comprising:

[0093] a motor including a motor shaft configured to rotate about a shaft rotation axis, wherein the motor is configured to actuate a cutting tool to cut a workpiece;

[0094] Optionally, a cutting tool configured to be actuated by the motor to cut a workpiece;

[0095] a sensor assembly configured to generate a differential voltage signal indicative of a distance between an individual and the cutting tool being less than a threshold distance, and to produce a sensor assembly output based on the differential voltage signal;

[0096] an analysis circuit configured to receive the sensor assembly output and to generate a trigger signal in response to the sensor assembly output being outside of a nominal sensor assembly output range; and

[0097] a mechanical reaction mechanism configured to isolate the individual from the cutting tool in response to receiving the trigger signal.

[0098] A2. The power tool of paragraph Al, wherein the sensor assembly includes a bridge circuit configured to generate the differential voltage signal.

[0099] A3. The power tool of paragraph A2, wherein the bridge circuit includes a reference leg configured to generate a reference leg signal at a reference leg voltage and a detection leg configured to generate a detection leg signal at a detection leg voltage, and further wherein the differential voltage signal includes or is a difference between the reference leg voltage and the detection leg voltage.

[0100] A4. The power tool of paragraph A3, wherein the bridge circuit includes a bridge circuit oscillator configured to provide a bridge circuit excitation voltage to the reference leg and also to the detection leg.

[0101] A5. The power tool of paragraph A3, wherein the bridge circuit includes a reference leg oscillator configured to provide a reference leg excitation voltage to the reference leg and a detection leg oscillator configured to provide a detection leg excitation voltage to the detection leg.

[0102] A6. The power tool of any of paragraphs A3-A5, wherein the reference leg includes a tuning structure configured for tuning the reference leg such that at least one of:

[0103] (i) a magnitude of the reference leg voltage is within a threshold voltage difference of a magnitude of the detection leg voltage; and

[0104] (ii) a phase of the reference leg voltage is within a threshold phase difference of a phase of the detection leg voltage.

[0105] A7. The power tool of any of paragraphs A3-A6, wherein the detection branch comprises a capacitive coupling structure configured to capacitively couple to the individual such that the detection branch voltage is based at least in part on a distance between the individual and the cutting tool.

[0106] A8. The power tool of any of paragraphs A3-A7, wherein the sensor assembly further comprises a reference branch buffer configured to buffer the reference branch signal to produce a buffered reference branch signal, wherein the sensor assembly output is based at least in part on the buffered reference branch signal, optionally wherein the reference branch buffer comprises at least one of a reference branch high pass filter, a reference branch low pass filter, and the reference branch high pass filter in series with the reference branch low pass filter.

[0107] A9. The power tool of paragraph A8, wherein the reference branch buffer has a lower output impedance relative to the bridge circuit.

[0108] A10. The power tool of any of paragraphs A8-A9, wherein reference branch buffer comprises a reference branch emitter follower circuit.

[0109] A11. The power tool of any of paragraphs A3-A10, wherein the sensor assembly further comprises a detection branch buffer configured to buffer the detection branch signal to produce a buffered detection branch signal, wherein the sensor assembly output is based at least in part on the buffered detection branch signal, optionally wherein the detection branch buffer comprises at least one of a detection branch emitter follower circuit, a detection branch high pass filter, a detection branch low pass filter, and the detection branch high pass filter in series with the detection branch low pass filter.

[0110] A12. The power tool of paragraph A11, wherein the detection branch buffer has a lower output impedance relative to the bridge circuit.

[0111] A13. The power tool of any of paragraphs A11-A12, wherein the detection branch buffer comprises a detection branch emitter follower circuit.

[0112] A14. The power tool of any of paragraphs A1-A13, wherein the sensor assembly further comprises an amplifier circuit configured to amplify the differential voltage signal to produce an amplified differential voltage signal, wherein the sensor assembly output is based at least in part on the amplified differential voltage signal.

[0113] A15. The power tool of paragraph A14, wherein the amplifier circuit is configured to generate the amplified differential voltage signal based at least in part on at least one of the buffered reference leg signal and the buffered sense leg signal.

[0114] A16. The power tool of any of paragraphs A14-A15, wherein the amplifier circuit is configured to generate an amplifier output current, and further wherein the sensor assembly includes a transducer configured to receive the amplifier output current and generate a transducer output voltage, wherein the transducer output voltage is based at least in part on the amplifier output current, and further wherein the sensor assembly output is based at least in part on the transducer output voltage.

[0115] A17. The power tool of paragraph A16, wherein the amplifier circuit further includes a filter configured to receive the transducer output voltage and generate a filtered transducer output voltage, wherein the filtered transducer output voltage is based at least in part on the transducer output voltage, and further wherein the sensor assembly output is based at least in part on the filtered transducer output voltage.

[0116] A18. The power tool of any of paragraphs A1-A17, wherein the power tool further includes a cutting tool isolation structure configured to electrically isolate the cutting tool from at least one other component of the power tool.

[0117] A19. The power tool of any of paragraphs A1-A18, wherein the mechanical reaction mechanism is configured to at least one of:

[0118] (i) selectively stop actuation of the cutting tool in response to receiving a trigger signal;

[0119] (ii) selectively stop actuation of the cutting tool by the motor in response to receiving the trigger signal;

[0120] (iii) selectively retract the cutting tool into the power tool in response to receiving a trigger signal;

[0121] (iv) selectively shut off the cutting tool in response to receiving the trigger signal; and

[0122] (v) selectively position a protective structure between the individual and the cutting tool in response to receiving the trigger signal.

[0123] A20. The power tool of any of paragraphs A1-A19, wherein the motor includes at least one of: (i) an electric motor;

[0124] (ii) an alternating current electric motor;

[0125] (iii) a direct current electric motor;

[0126] (iv) a single speed electric motor; and

[0127] (v) a variable speed motor.

[0128] A21. The power tool of any of paragraphs A1-A20, wherein the power tool is a battery- powered power tool.

[0129] A22. The power tool of any of paragraphs A1-A21, wherein the power tool is not directly grounded.

[0130] A23. The power tool of any of paragraphs A21-A22, wherein the power tool further comprises at least one of:

[0131] (i) a power cord configured to provide electrical current to the power tool; and

[0132] (ii) a battery configured to provide electrical current to the power tool.

[0133] A24. The power tool of any of paragraphs A1-A23, wherein the power tool comprises at least one of:

[0134] (i) a hand-held power tool; and

[0135] (ii) a portable power tool.

[0136] A25. The power tool of any of paragraphs A1-A23, wherein the power tool comprises at least one of:

[0137] (i) a saw;

[0138] (ii) a circular saw;

[0139] (iii) a hand-held circular saw;

[0140] (iv) a miter saw;

[0141] (v) a radial arm saw;

[0142] (vi) a table saw;

[0143] (vii) a chop saw;

[0144] (viii) a plunge saw;

[0145] (ix) a track saw;

[0146] (x) band saw;

[0147] (xi) jigsaw;

[0148] (xii) up-cut saw;

[0149] (xiii) panel saw;

[0150] (xiv) rotary cutting tool;

[0151] (xv) router;

[0152] (xvi) drill bit; and

[0153] (xvii) chisel.

[0154] A26. The power tool of any of paragraphs A1-A25, wherein the cutting tool comprises at least one of:

[0155] (i) a blade;

[0156] (ii) a saw blade;

[0157] (iii) a circular saw blade;

[0158] (iv) a drill bit;

[0159] (v) a router bit;

[0160] (vi) a drill bit point; and

[0161] (vii) a rotary cutting drill bit.

[0162] A27. The power tool of any of paragraphs A1-A26, wherein the power tool comprises a mandrel operably attached to the motor shaft.

[0163] A28. The power tool of paragraph A27, wherein the mandrel is configured to facilitate selective and repeated detachment of the cutting tool from the remainder of the power tool.

[0164] A29. The power tool of any of paragraphs A27-A28, wherein the mandrel comprises a threaded mandrel.

[0165] A30. The power tool of any of paragraphs A1-A29, wherein the power tool further comprises a gripping region configured to be grasped by a user of the power tool.

[0166] A31. The power tool of any of paragraphs A1-A30, wherein the power tool further comprises a switch configured to selectively apply an electrical current to the motor to provide power for rotation of the motor shaft.

[0167] A32. The power tool of any of paragraphs A1-A31, wherein the power tool further comprises a workpiece support configured to support a workpiece when being cut by the power tool.

[0168] B1. A method of operating a power tool, the method comprising:

[0169] blocking supply of electrical current to a motor of the power tool;

[0170] verifying operation of a sensor assembly of the power tool, wherein the sensor assembly is configured to generate a differential voltage signal indicative of a distance between an individual and a cutting tool of the power tool being less than a threshold distance; and

[0171] in response to successful verification of the operation of the sensor assembly, allowing supply of electrical current to the motor.

[0172] B2. The method of paragraph B1, wherein the method further comprises calibrating the sensor assembly.

[0173] B3. The method of paragraph B2, wherein the sensor assembly comprises a bridge circuit, and further wherein calibrating comprises balancing the bridge circuit.

[0174] B4. The method of paragraph B3, wherein balancing the bridge circuit comprises balancing a reference leg voltage of a reference leg of the bridge circuit and a sense leg voltage of a sense leg of the bridge circuit.

[0175] B5. The method of any of paragraphs B3-B4, wherein balancing the bridge circuit comprises balancing a reference leg phase of a reference leg of the bridge circuit and a sense leg phase of a sense leg of the bridge circuit.

[0176] B6. The method of any of paragraphs B2-B5, wherein the calibrating comprises setting the differential voltage signal to a target range.

[0177] B7. The method of paragraph B6, wherein the target range comprises 0 volts.

[0178] B8. The method of paragraph B7, wherein the target range does not comprise 0 volts.

[0179] B9. The method of any of paragraphs B2-B8, wherein the calibrating is in response to the verifying indicating that the sensor assembly is not configured to detect when the distance between the individual and the cutting tool is less than the threshold distance.

[0180] B10. The method of any of paragraphs B1-B9, wherein after the allowing, the method further comprises detecting that the individual is less than the threshold distance from the cutting tool.

[0181] B11. The method of paragraph B10, wherein the verifying comprises verifying that the sensor assembly is configured to detect that the individual is less than the threshold distance from the cutting tool.

[0182] B12. The method of any of paragraphs B10-B11, wherein the detecting comprises capacitive detection with a capacitive coupling structure of the power tool.

[0183] B13. The method of any of paragraphs B10-B12, wherein the detecting further comprises generating the differential voltage signal indicative of the individual being less than the threshold distance from the cutting tool.

[0184] B14. The method of any of paragraphs B10-B13, wherein in response to the detecting, the method further comprises stopping movement of the cutting tool.

[0185] B15. The method of any of paragraphs B1-B14, wherein allowing supply of current comprises allowing supply of current when the power tool does not have a direct ground.

[0186] B16. The method of any of paragraphs B1-B15, wherein the power tool is or comprises any of the power tools of any of paragraphs A1-A32.

[0187] C1. Use of a sensor assembly in a power tool, the sensor assembly configured to generate a differential voltage signal indicative of an individual being less than a threshold distance from a cutting tool.

[0188] C2. Use of a mechanical reaction mechanism in a power tool, the mechanical reaction mechanism for isolating an individual from a cutting tool in response to a differential voltage signal indicative of the individual being less than a threshold distance from the cutting tool.

[0189] C3. Use of any power tool of any of paragraphs A1-A32 with any method of any of paragraphs B1-B16.

[0190] C4. Use of any method of any of paragraphs B1-B16 with any power tool of any of paragraphs A1-A32.

[0191] INDUSTRIAL APPLICABILITY

[0192] The power tools and methods disclosed herein are applicable to the power tool industry.

[0193] It is believed that the disclosure set forth above encompasses multiple independent inventions. Although each of these inventions has been disclosed in its preferred form, the specific embodiments thereof as disclosed and explained herein are not to be considered in a limiting sense as numerous modifications are possible. The subject matter of the inventions includes all novel and nonobvious combinations and subcombinations of the various elements, features, functions and / or properties disclosed herein. Similarly, where the claims recite "a" or "a first" element or the equivalent thereof, such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements.

[0194] It is believed that the following claims particularly point out certain combinations and subcombinations of the disclosed inventions and are novel and nonobvious. Applicational or related applications incorporating by reference the disclosure of the present application in their entirety are also directed to each of the individual embodiments as can be represented by this claims. The inventors may also be entitled to protection under 35 U.S.C. § 122 (now 37 C.F.R. § 1.78) for any inventions disclosed in this application that he did not also originally invent.

Claims

1. A power tool comprising: a motor including a motor shaft configured to rotate about a shaft rotation axis, wherein the motor is configured to actuate a cutting tool to cut a workpiece; a sensor assembly configured to generate a differential voltage signal indicative of a distance between an individual and the cutting tool being less than a threshold distance, and to produce a sensor assembly output based on the differential voltage signal; an analysis circuit configured to receive the sensor assembly output and to generate a trigger signal in response to the sensor assembly output being outside of a nominal sensor assembly output range; and a mechanical reaction mechanism configured to isolate the individual from the cutting tool in response to receiving the trigger signal, wherein the sensor assembly includes a bridge circuit configured to generate the differential voltage signal, the bridge circuit including a reference leg and a detection leg, the reference leg configured to generate a reference leg signal under a reference leg voltage condition, the detection leg configured to generate a detection leg signal under a detection leg voltage condition, and further wherein the differential voltage signal includes a difference between the reference leg voltage and the detection leg voltage.

2. The power tool of claim 1, wherein, the bridge circuit includes a bridge circuit oscillator configured to provide a bridge circuit excitation voltage to the reference leg and also to the detection leg.

3. The power tool of claim 1, wherein, the bridge circuit includes a reference leg oscillator configured to provide a reference leg excitation voltage to the reference leg and a detection leg oscillator configured to provide a detection leg excitation voltage to the detection leg.

4. The power tool of any one of claims 1-3, wherein, the reference leg includes a tuning structure configured for tuning the reference leg such that at least one of: (i) a magnitude of the reference leg voltage is within a threshold voltage difference of a magnitude of the detection leg voltage; and (ii) a phase of the reference leg voltage is within a threshold phase difference of a phase of the detection leg voltage.

5. The power tool of any one of claims 1-3, wherein, the detection leg includes a capacitive coupling structure configured to be capacitively coupled to the individual such that the detection leg voltage is based at least in part on the distance between the individual and the cutting tool.

6. The power tool of any one of claims 1-3, wherein, the sensor assembly further includes a reference leg buffer configured to buffer the reference leg signal to produce a buffered reference leg signal, wherein the sensor assembly output is based at least in part on the buffered reference leg signal.

7. The power tool of any one of claims 1-3, wherein, the sensor assembly further includes a detection leg buffer configured to buffer the detection leg signal to produce a buffered detection leg signal, wherein the sensor assembly output is based at least in part on the buffered detection leg signal.

8. The power tool of any one of claims 1-3, wherein, the sensor assembly further includes an amplifier circuit configured to amplify the differential voltage signal to produce an amplified differential voltage signal, wherein the sensor assembly output is based at least in part on the amplified differential voltage signal.

9. The power tool of claim 8, wherein, The amplifier circuit is configured to generate an amplifier output current, and further wherein the sensor assembly includes a transducer configured to receive the amplifier output current and generate a transducer output voltage, wherein the transducer output voltage is based at least in part on the amplifier output current, and further wherein the sensor assembly output is based at least in part on the transducer output voltage.

10. The power tool of claim 9, wherein, The amplifier circuit further includes a filter configured to receive the transducer output voltage and generate a filtered transducer output voltage, wherein the filtered transducer output voltage is based at least in part on the transducer output voltage, and further wherein the sensor assembly output is based at least in part on the filtered transducer output voltage.

11. The power tool of any one of claims 1-3, wherein, The power tool further includes a cutting tool isolation structure configured to electrically isolate the cutting tool from at least one other component of the power tool.

12. The power tool of any one of claims 1-3, wherein, The mechanical reaction mechanism is configured to at least one of: (i) selectively stop actuation of a cutting tool in response to receiving a trigger signal; (ii) selectively stop actuation of the cutting tool by the motor in response to receiving a trigger signal; (iii) selectively retract a cutting tool into the power tool in response to receiving a trigger signal; (iv) selectively shut off the cutting tool in response to receiving a trigger signal; and (v) selectively position a protective structure between the individual and the cutting tool in response to receiving a trigger signal. The power tool is a battery-powered power tool.

13. The power tool of any one of claims 1-3, wherein, The power tool is not directly grounded.

14. The power tool of any one of claims 1-3, wherein, The power tool includes at least one of:

15. The power tool of any one of claims 1-3, wherein, (i) a saw; (ii) a circular saw; (iii) a hand-held circular saw; (iv) a miter saw; (v) a radial arm saw; (vi) a table saw; (vii) a chop saw; (viii) an insert saw; (ix) a track saw; (x) a band saw; (xi) a rip saw; (xii) an up-cut saw; (xiii) a panel saw; (xiv) a rotary cutting tool; (xv) a router; (xvi) a drill bit; and (xvii) a router bit. The power tool includes at least one of:

16. The power tool of any one of claims 1-3, wherein, (i) a hand-held power tool; and (ii) a portable power tool. The cutting tool includes at least one of:

17. The power tool of any one of claims 1-3, wherein, (i) a blade; (ii) a saw blade; (iii) a circular saw blade; (iv) a drill bit; (v) a router bit; (vi) a drill bit; and (vii) a rotary cutting drill bit.

18. A method of operating a power tool, the method comprising: blocking supply of current to a motor of the power tool; verifying operation of a sensor assembly of the power tool, wherein the sensor assembly is configured to generate a differential voltage signal indicative of a distance between an individual and a cutting tool of the power tool being less than a threshold distance; and in response to successful verification of the operation of the sensor assembly, allowing supply of current to the motor, ​ wherein the method further comprises calibrating the sensor assembly, the sensor assembly comprising a bridge circuit, and further wherein the calibrating comprises balancing the bridge circuit, balancing the bridge circuit comprising balancing a reference leg voltage of a reference leg of the bridge circuit and a sense leg voltage of a sense leg of the bridge circuit.

19. The method of claim 18, wherein, Balancing the bridge circuit comprises balancing a reference leg phase of the reference leg of the bridge circuit and a sense leg phase of the sense leg of the bridge circuit.

20. The method of claim 18 or 19, wherein, The calibrating comprises setting the differential voltage signal to a target range.

21. The method of claim 20, wherein, The target range comprises 0 volts.

22. The method of claim 20, wherein, The target range does not comprise 0 volts.

23. The method of claim 18 or 19, wherein, The calibrating is in response to the verifying indicating that the sensor assembly is not configured to detect when a distance between the individual and the cutting tool is less than the threshold distance.

24. The method of claim 18 or 19, wherein, After the allowing, the method further comprises detecting that the distance between the individual and the cutting tool is less than the threshold distance.

25. The method of claim 24, wherein, The verifying comprises verifying that the sensor assembly is configured to detect that the distance between the individual and the cutting tool is less than the threshold distance.

26. The method of claim 24, wherein, The detecting comprises capacitive detection with a capacitive coupling structure of the power tool.

27. The method of claim 24, wherein, The detecting further comprises generating the differential voltage signal indicating that the distance between the individual and the cutting tool is less than the threshold distance.

28. The method of claim 24, wherein, In response to the detecting, the method further comprises stopping movement of the cutting tool.

29. The method of claim 18 or 19, wherein, The allowing supply of current comprises allowing supply of current when the power tool does not have a direct ground.

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