Patent Publication Number: US-2023158658-A1

Title: Grinder including enhanced sensing and component detection

Description:
RELATED APPLICATIONS 
     This applications claims the benefit of U.S. Provisional Patent Application No. 63/282,964, filed Nov. 24, 2021, U.S. Provisional Patent Application No. 63/370,903, filed Aug. 9, 2022, and U.S. Provisional Patent Application No. 63/418,136, filed Oct. 21, 2022, the entire content of each of which is hereby incorporated by reference. 
    
    
     FIELD 
     Embodiments described herein provide battery pack powered power tools. 
     SUMMARY 
     Embodiments described herein provide various systems and methods for operating a device, such as a grinder. Operating machinery, such as a grinder, presents a multitude of safety hazards for both a user and the user&#39;s surrounding environment. A grinder that includes systems and methods for improved safety by preventing or mitigating hazardous events from occurring is advantageous for a user of the grinder. 
     Embodiments described herein provide a grinder that includes a guard presence sensor for detecting the presence of a grind wheel guard on the grinder. If the guard is determined to not be present based on the output of the guard presence sensor, the grinder is prevented from operating. If the guard is determined to be present based on the output of the guard presence sensor, the grinder is permitted to operate. This prevents operation of the grinder unless the protective guard is properly attached. 
     In some embodiments, a grinder requires an operator to use two hands to operate the grinder. The presence of two hands of the operator is detected using sensors (e.g., grip or pressure sensors, touch sensors, electromechanical sensors, etc.). For example, one sensor can be located in the main body handle of the grinder (e.g., above an attached battery pack) to detect the operator&#39;s first hand. A second sensor can be positioned on the forward stabilizing second handle. The grinder may only be permitted to operate when the presence of both operator hands is detected on the grinder. 
     In some embodiments, the grinder includes loss of control mitigation. The grinder includes a sensor configured to detect a motion (e.g., linear, rotational, etc.) of the grinder that is indicative of a loss of control of the grinder. If a predetermined threshold of the motion is exceeded, loss of control is determined and the motor of the grinder is braked so that the user can regain control of the stopped grinder. 
     In some embodiments, the grinder includes a grinder wheel that can be used to grind (e.g., cut) through a workpiece. The grinder is configured to detect when the grinder has completed a cut through of the workpiece using operational parameters of the grinder. Once the grinder has been determined to have cut through a workpiece, the motor is stopped. 
     In some embodiments, the grinder can detect a type of component (e.g., a particular type of disk guard, a particular type of dust hood, etc.) connected to the grinder. The detection of the particular type of component connected to the grinder can be achieved using a sensor (e.g., an induction coil sensor, a Hall effect sensor, an optical sensor, wireless communication, etc.) for detecting the type of the component. After the grinder determines the particular type of component connected to the grinder, the grinder can take a control action based on the detected type of component connected to the grinder. 
     In some embodiments, the grinder includes a main power tool housing that includes a handle for being gripped by a user. The grinder also includes an accessory device attachment portion on the main power tool housing. The accessory device attachment portion is configured to receive an accessory device (e.g., a second handle to provide a second grip for an operator). Having an additional grip stabilizes the grinder and improves task efficiency and safety. 
     Grinders described herein include a housing, a motor within the housing, a first handle, a second handle, and a controller. The first handle includes a first sensor configured to detect a presence of a user. The first handle is attached to the housing. The second handle is attached to a pivot arm. The pivot arm is attached to the housing and is configured to be pivoted around a circumference of the housing. The second handle includes a second sensor configured to detect the presence of the user. The controller is configured to control the motor based upon the detection of the presence of the user by the first sensor and the second sensor. The controller prevents the motor from operating when second sensor does not detect the presence of the user by the second sensor. 
     In some aspects, the pivot arm further includes a locking mechanism. The locking mechanism is configured to lock the pivot arm into one of a plurality of different positions around the circumference of the housing. 
     In some aspects, the plurality of different positions around the circumference of the housing includes a left-handed position and a right-handed position. 
     In some aspects, the pivot arm further includes a pivot mechanism configured to pivot the second handle into one of a plurality of different positions with respect to the pivot arm. 
     In some aspects, the plurality of different positions with respect to the pivot arm include at least two discrete positions. 
     In some aspects, the second handle includes a microswitch sensor connected to a printed circuit board, the microswitch sensor configured to detect the presence of a second hand of the user. 
     In some aspects, the first sensor is configured to detect a first hand of the user, and the controller is configured to prevent the motor from operating if the first sensor does not detect the first hand of the user and the second sensor does not detect the second hand of the user. 
     In some aspects, the pivot arm further includes a wire routing portion through which wires are routed from the second handle to the housing. 
     In some aspects, the wire routing portion includes a first channel within the pivot arm and a second channel that extends into the housing. 
     In some aspects, the grinder further includes a wireless transmitter inside the second handle, and a wireless receiver inside the first handle. The wireless transmitter is configured to transmit a signal when the second sensor detects the presence of the user. The wireless receiver is configured to receive the signal and communicate to the controller that that the second sensor has detected the presence of the user. 
     In some aspects, the second sensor is configured to detect a second hand of the user, and the controller is configured to prevent the motor from operating if the second sensor does not detect the second hand of the user. 
     Methods described herein for operating a grinder include prohibiting, by a controller, the operation of the grinder, detecting, by a first sensor, a presence of a user&#39;s first hand, detecting, by a second sensor, the presence of the user&#39;s second hand, and controlling, by the controller, a motor of the power tool based on the first sensor detecting the presence of the user&#39;s first hand and the second sensor detecting the presence of the user&#39;s second hand. 
     In some aspects, the method further includes determining, by the controller, whether the second sensor has detected the presence of the user&#39;s second hand within a period of time after the first sensor detected the presence of the user&#39;s first hand. 
     In some aspects, the method further includes prohibiting, by the controller, the operation of the grinder if the second sensor has not detected the presence of the user&#39;s second hand within the period of time. 
     Grinders described herein include a housing, a motor located within the housing, a first handle, a second handle, a pivot mechanism, and a controller. The first handle includes a first sensor configured to detect the presence of a first hand of a user. The second handle is attached to a pivot arm. The pivot arm is attached to the housing and is configured to be pivoted around a circumference of the housing. The second handle includes a second sensor configured to detect the presence of a second hand of the user. The pivot mechanism is attached to the pivot arm and is configured to pivot the second handle into one of a plurality of different positions with respect to the pivot arm. The controller is configured to control the motor based upon the detection of the presence of the first hand of the user by the first sensor and the second hand of the user by the second sensor. The controller prevents the motor from operating when the second sensor does not detect the presence of the second hand of the user. 
     In some aspects, the pivot arm further includes a locking mechanism. The locking mechanism is configured to lock the pivot arm into one of a plurality of different positions around the circumference of the housing. 
     In some aspects, the plurality of different positions around the circumference of the housing includes a left-handed position and a right-handed position. 
     In some aspects, the plurality of different positions with respect to the pivot arm include at least two discrete positions. 
     In some aspects, the pivot arm further includes a wire routing portion through which wires are routed from the second handle to the housing. 
     In some aspects, the wire routing portion includes a first channel within the pivot arm and a second channel that extends into the housing. 
     Power tools described herein include a housing, a motor located within the housing, a first handle, a second handle including a sensor configured to detect a user characteristic, and a controller. The controller is configured to control the motor based on a signal from the sensor related to the user characteristic. 
     In some aspects, the power tool further includes a pivot arm configured to be pivoted into a plurality of different positions around a circumference of the housing. 
     In some aspects, the plurality of different positions around the circumference of the housing include a left-handed position and a right-handed position. 
     In some aspects, the power tool further includes a locking mechanism configured to secure the pivot arm into one of the plurality of different positions around the circumference of the housing. 
     In some aspects, the locking mechanism includes a switch biased into a locked position. 
     In some aspects, the locking mechanism includes a pivot joint configured to connect the pivot arm to the locking mechanism. 
     In some aspects, the pivot joint includes an aperture configured to receive a projection of the locking mechanism to lock the pivot arm into one of the plurality of different positions around the circumference of the housing. 
     In some aspects, the power tool further includes a pivot mechanism configured to pivot the second handle through a plurality of positions relative to the pivot arm. 
     In some aspects, the power tool further includes a component presence sensor configured to detect whether a component is connected to the power tool. 
     In some aspects, the power tool includes a component type indicator configured to provide an indication of the type of component connected to the power tool. 
     In some aspects, the component is a guard and the component presence sensor is a guard presence sensor. 
     In some aspects, the first handle includes a first switch operable to electrically connect a power source to the motor. 
     In some aspects, the power tool further includes the first switch is configured to function as a detector for detecting presence of a user&#39;s hand on the first handle. 
     In some aspects, the power tool further includes a second sensor configured to detect presence of a user&#39;s hand on the second handle. 
     In some aspects, the second sensor is one selected from the group consisting of: a grip sensor, a pressure sensor, a touch sensor, and an electromechanical sensor. 
     In some aspects, the power tool further includes a battery pack interface. The battery pack interface is configured to receive a rechargeable battery pack. 
     In some aspects, the power tool further includes a user input module. The user input module includes a display and an input device. 
     In some aspects, the display is configured to display a speed setting for the power tool, and the input device is configured to set the speed setting for the power tool. 
     In some aspects, the power tool further includes a second sensor configured to detect a fault condition of the power tool. 
     In some aspects, the second sensor is one selected from the group consisting of: a current sensor, a speed sensor, a Hall effect sensor, a temperature sensor, an accelerometer, a gyroscope, an inertial measurement unit, a pressure sensor, and an object presence sensor. 
     In some aspects, the controller is configured to detect at least one of a linear motion of the power tool or a rotational motion of the power tool. 
     In some aspects, a loss of control of the power tool is detected based on the at least one of the linear motion of the power tool or the rotational motion of the power tool. 
     In some aspects, the second handle includes a printed circuit board, the printed circuit board including one or more microswitch sensors. 
     In some aspects, the microswitch sensor is configured to detect the user characteristic. 
     In some aspects, the user characteristic is a presence of a user&#39;s hand. 
     In some aspects, the user characteristic is a grip force greater than a threshold value. 
     In some aspects, the second handle includes a second microswitch sensor configured to detect the user characteristic. 
     In some aspects, the power tool further includes an internal wire routing portion configured to provide a wired electrical connection between the second handle and the housing. 
     In some aspects, the wire routing portion includes a includes a first channel within the second handle, a second channel within a pivot mechanism of the second handle, and a third channel within a pivot arm of the power tool. 
     In some aspects, the wire routing portion includes a fourth channel within the housing configured to route a wire to a connector for electrically connecting the wire to the controller. 
     In some aspects, the second handle includes a first electrical contact and a second electrical contact configured to electrically connect to electrical contacts on the housing. 
     In some aspects, the first electrical contact and the second electrical contact are spring-loaded electrical contacts. 
     In some aspects, the housing includes a plurality of rails configured to slidingly receive corresponding rails of the second handle. 
     In some aspects, the housing includes a second plurality of rails configured to sliding receive the corresponding rails of the second handle. 
     In some aspects, the second plurality of rails are located on an opposite side of the housing than the plurality of rails. 
     In some aspects, the second handle includes a threaded screw for fastening the second handle to the housing. 
     In some aspects, the power tool further includes a pivoting mechanism connected between the second handle and the housing. 
     In some aspects, the pivoting mechanism is configured to pivot the second handle through a plurality of positions relative to the housing. 
     In some aspects, the plurality positions includes at least two pivoting positions relative to the housing. 
     In some aspects, the power tool is a grinder. 
     Power tools described herein include a housing, a motor located within the housing, a handle, a component presence sensor configured to detect whether a component is connected to the power tool, and a controller. The controller is configured to control the motor based on a signal from the component presence sensor related to whether component is connected to the power tool. 
     In some aspects, the power tool includes a component type indicator configured to provide an indication of the type of component connected to the power tool. 
     In some aspects, the component is a guard and the component presence sensor is a guard presence sensor. 
     In some aspects, the component presence sensor is an inductive sensor. 
     In some aspects, the inductive sensor includes an inductor capacitor circuit connected to an inductance-to-digital converter. 
     In some aspects, the inductance-to-digital converter is configured to measure a proximity to metal based on changes in an alternative current magnetic field resulting from an interaction with a metal target. 
     In some aspects, the metal target is component connected to the power tool. 
     In some aspects, the component is a guard connected to the power tool. 
     In some aspects, the component presence sensor is an electromechanical sensor that is configured to be actuated when the component is coupled to the power tool. 
     In some aspects, the component present sensor is an optical sensor that is configured to detect light reflecting off of the component to detect presence. 
     Power tools described herein include a housing, a motor located within the housing, a wireless receiver, a first handle, a second handle including a wireless transmitter configured to communicate with the wireless receiver, and a controller. The controller is configured to control the motor based on the wireless communication between the wireless transmitter and the wireless receiver. 
     In some aspects, the second handle includes a battery configured to power the wireless transmitter. 
     In some aspects, the second handle is electrically isolated from the housing. 
     Methods described herein for operating a power tool include prohibiting operation of the power tool, detecting a first user hand on a first handle of the power tool, detecting a second user hand on a second handle of the power tool, and allowing operation of the power tool when both the first user hand is detected on the first handle and the second user hand is detected on the second user handle. Detecting the second user hand on the second handle of the power tool includes detecting a user characteristic using a sensor. 
     In some aspects, the method further includes pivoting a pivot arm into a plurality of different positions around a circumference of a housing of the power tool. 
     In some aspects, the plurality of different positions around the circumference of the housing include a left-handed position and a right-handed position. 
     In some aspects, the method further includes securing, using a locking mechanism, the pivot arm into one of the plurality of different positions around the circumference of the housing. 
     In some aspects, the method further includes the locking mechanism includes a switch biased into a locked position. 
     In some aspects, the locking mechanism includes a pivot joint configured to connect the pivot arm to the locking mechanism. 
     In some aspects, the method further includes receiving, at an aperture of the pivot joint, a projection of the locking mechanism to lock the pivot arm into one of the plurality of different positions around the circumference of the housing. 
     In some aspects, the method further includes pivoting, using a pivot mechanism, the second handle through a plurality of positions relative to the pivot arm. 
     In some aspects, the method further includes detecting, using a component presence sensor, whether a component is connected to the power tool. 
     In some aspects, the method further includes indicating, using a component type indicator, the type of component connected to the power tool. 
     In some aspects, the component is a guard and the component presence sensor is a guard presence sensor. 
     In some aspects, the first handle includes a first switch operable to electrically connect a power source to the motor. 
     In some aspects, the method further includes detecting, using the first switch, presence of a user&#39;s hand on the first handle. 
     In some aspects, the method further includes detecting, using a second sensor, presence of a user&#39;s hand on the second handle. 
     In some aspects, the second sensor is one selected from the group consisting of: a grip sensor, a pressure sensor, a touch sensor, and an electromechanical sensor. 
     In some aspects, the method further includes receiving, at a battery pack interface, a rechargeable battery pack. 
     In some aspects, the power tool includes a user input module, the user input module including a display and an input device. 
     In some aspects, the method further includes displaying, using the display, a speed setting for the power tool, and setting, using the input device, a speed setting for the power tool. 
     In some aspects, the method further includes detecting, using a second sensor, a fault condition of the power tool. 
     In some aspects, the second sensor is one selected from the group consisting of: a current sensor, a speed sensor, a Hall effect sensor, a temperature sensor, an accelerometer, a gyroscope, an inertial measurement unit, a pressure sensor, and an object presence sensor. 
     In some aspects, the method further includes detecting, using a controller, at least one of a linear motion of the power tool or a rotational motion of the power tool. 
     In some aspects, the method further includes detecting a loss of control of the power tool based on the at least one of the linear motion of the power tool or the rotational motion of the power tool. 
     In some aspects, the second handle includes a printed circuit board, the printed circuit board including a microswitch sensor. 
     In some aspects, the method further includes detecting, using the microswitch sensor, the user characteristic. 
     In some aspects, the user characteristic is a presence of a user&#39;s hand. 
     In some aspects, the user characteristic is a grip force greater than a threshold value. 
     In some aspects, the method further includes detecting, using a second microswitch sensor, the user characteristic. 
     In some aspects, the method further includes providing, via an internal wire routing portion, a wired electrical connection between the second handle and the housing. 
     In some aspects, the wire routing portion includes a includes a first channel within the second handle, a second channel within a pivot mechanism of the second handle, and a third channel within a pivot arm of the power tool. 
     In some aspects, the wire routing portion includes a fourth channel within the housing, and the method further includes routing, through the fourth channel, a wire to a connector for electrically connecting the wire to a controller. 
     In some aspects, the method further includes electrically connecting, using a first electrical contact and a second electrical contact of the second handle, the second handle to electrical contacts on the housing. 
     In some aspects, the first electrical contact and the second electrical contact are spring-loaded electrical contacts. 
     In some aspects, the method further includes slidingly receiving, at a plurality of rails of the housing, corresponding rails of the second handle. 
     In some aspects, the method further includes slidingly receiving, at a second plurality of rails of the housing, the corresponding rails of the second handle. 
     In some aspects, the second plurality of rails are located on an opposite side of the housing than the plurality of rails. 
     In some aspects, the method further includes fastening, using a threaded screw of the second handle, the second handle to the housing. 
     In some aspects, the power tool incudes a pivoting mechanism connected between the second handle and the housing. 
     In some aspects, the method further includes pivoting, using the pivoting mechanism, the second handle through a plurality of positions relative to the housing. 
     In some aspects, the plurality positions includes at least two pivoting positions relative to the housing. 
     In some aspects, the power tool is a grinder. 
     Methods described herein for detecting a presence of an accessory on a power tool include monitoring a parameter of the power tool, monitoring a motion of the power tool, detecting a change in the parameter of the power tool, comparing, using a controller, the change in the parameter of the power tool to a predetermined threshold, determining, using the controller, if the change in the parameter of the power tool is less than the predetermined threshold, determining, when the change in the parameter of the power tool is less than the predetermined threshold, whether the motion of the power tool is greater than a motion threshold, and controlling, using the controller, a motor of the power tool when the motion based on whether the motion of the power tool is greater than the motion threshold. 
     In some aspects, the method further includes stopping the motor when the motion of the power tool is greater than the motion threshold. 
     In some aspects, the motion of the power tool is monitored using a gyroscope. 
     In some aspects, the parameter of the power tool is a motor current. 
     In some aspects, the change in the parameter of the power tool is a decrease in the motor current. 
     Methods described herein for detecting a presence of a component on a power tool include sending a current through a coil to generate a magnetic field, inducing eddy currents in the component to generate an opposing magnetic field, detecting a change in inductance in a circuit based on the opposing magnetic field, generating an output signal indicative of the change in inductance, determining, using a controller, whether the component is present on the power tool based on the output signal indicative of the change in inductance, and controlling, using the controller, operation of a motor based on whether the component is present on the power tool. 
     Methods described herein for operating a power tool include detecting a linear motion of the power tool, comparing the linear motion of the power tool to a loss of control threshold, stopping operation of the power tool when the linear motion of the power tool is greater than the loss of control threshold, detecting a rotational motion of the power tool, comparing the rotational motion of the power tool to a loss of control rotation threshold, stopping operation of the power tool when the rotational motion of the power tool is greater than the loss of control rotation threshold. 
     Methods described herein for operating a power tool include detecting a linear motion of the power tool, detecting a rotational motion of the power tool, incrementing a linear and rotational motion accumulator when either the linear motion of the power tool is greater than a first threshold or the rotational motion of the power tool is greater than a second threshold, comparing the linear and rotational motion accumulator to a maximum value, and stopping operation of the power tool when the linear and rotational motion accumulator reaches the maximum value. 
     Methods described herein for operating a power tool include monitoring a parameter of a motor related to a cutting operation of the power tool, and comparing the parameter of the motor to a threshold value. The threshold value corresponds to a completion of the cutting operation of the power tool. The methods further include stopping the motor when the parameter of the motor is less than the threshold value. 
     In some aspects, the parameter of the motor is a motor current. 
     Before any embodiments are explained in detail, it is to be understood that the embodiments are not limited in application to the details of the configuration and arrangement of components set forth in the following description or illustrated in the accompanying drawings. The embodiments are capable of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof are meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. 
     In addition, it should be understood that embodiments may include hardware, software, and electronic components or modules that, for purposes of discussion, may be illustrated and described as if the majority of the components were implemented solely in hardware. However, one of ordinary skill in the art, and based on a reading of this detailed description, would recognize that, in at least one embodiment, the electronic-based aspects may be implemented in software (e.g., stored on non-transitory computer-readable medium) executable by one or more processing units, such as a microprocessor and/or application specific integrated circuits (“ASICs”). As such, it should be noted that a plurality of hardware and software based devices, as well as a plurality of different structural components, may be utilized to implement the embodiments. For example, “servers,” “computing devices,” “controllers,” “processors,” etc., described in the specification can include one or more processing units, one or more computer-readable medium modules, one or more input/output interfaces, and various connections (e.g., a system bus) connecting the components. 
     Relative terminology, such as, for example, “about,” “approximately,” “substantially,” etc., used in connection with a quantity or condition would be understood by those of ordinary skill to be inclusive of the stated value and has the meaning dictated by the context (e.g., the term includes at least the degree of error associated with the measurement accuracy, tolerances [e.g., manufacturing, assembly, use, etc.] associated with the particular value, etc.). Such terminology should also be considered as disclosing the range defined by the absolute values of the two endpoints. For example, the expression “from about 2 to about 4” also discloses the range “from 2 to 4”. The relative terminology may refer to plus or minus a percentage (e.g., 1%, 5%, 10%, or more) of an indicated value. 
     It should be understood that although certain drawings illustrate hardware and software located within particular devices, these depictions are for illustrative purposes only. Functionality described herein as being performed by one component may be performed by multiple components in a distributed manner. Likewise, functionality performed by multiple components may be consolidated and performed by a single component. In some embodiments, the illustrated components may be combined or divided into separate software, firmware and/or hardware. For example, instead of being located within and performed by a single electronic processor, logic and processing may be distributed among multiple electronic processors. Regardless of how they are combined or divided, hardware and software components may be located on the same computing device or may be distributed among different computing devices connected by one or more networks or other suitable communication links. Similarly, a component described as performing particular functionality may also perform additional functionality not described herein. For example, a device or structure that is “configured” in a certain way is configured in at least that way but may also be configured in ways that are not explicitly listed. 
     Other aspects of the embodiments will become apparent by consideration of the detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates a power tool according to some embodiments. 
         FIG.  2    illustrates a side section view of the power tool of  FIG.  1    according to some embodiments. 
         FIG.  3    illustrates a controller for the power tool of  FIG.  1    according to some embodiments. 
         FIG.  4    illustrates the adjustable second handle of the power tool of  FIG.  1    according to some embodiments. 
         FIG.  5    illustrates the adjustable second handle of  FIG.  4    according to some embodiments. 
         FIG.  6    illustrates the adjustable second handle of  FIG.  4    according to some embodiments. 
         FIG.  7    illustrates the adjustable second handle of  FIG.  4    according to some embodiments. 
         FIG.  8    illustrates the adjustable second handle of  FIG.  4    with an exterior housing removed according to some embodiments. 
         FIG.  9    illustrates a top section view of the adjustable side handle for the power tool of  FIG.  1    according to some embodiments. 
         FIG.  10    illustrates a top section view of the adjustable side handle for the power tool of  FIG.  1    according to some embodiments. 
         FIG.  11    illustrates a perspective view of an interior portion of the power tool including a side handle locking mechanism and a wire routing channel according to some embodiments. 
         FIG.  12    illustrates the side handle locking mechanism of the adjustable side handle for the power tool of  FIG.  1    according to some embodiments. 
         FIG.  13    illustrates the side handle locking mechanism of the adjustable side handle for the power tool of  FIG.  1    according to some embodiments. 
         FIG.  14    illustrates wire routing through the side handle locking mechanism of the adjustable side handle for the power tool of  FIG.  1    according to some embodiments. 
         FIG.  15    illustrates a perspective view of a power tool including two-hand control according to some embodiments. 
         FIG.  16 A  illustrates a side handle of a power tool of  FIG.  15    according to some embodiments. 
         FIG.  16 B  illustrates a method for detecting operator presence according to some embodiments. 
         FIGS.  17 A and  17 B  illustrate a perspective view of a side handle including an electrical connection to a power tool according to some embodiments. 
         FIG.  17 C  illustrates a circuit implemented in a power tool for detecting operator presence according to some embodiments. 
         FIG.  18    illustrates a flowchart for a detecting a type of attached component according to some embodiments. 
         FIG.  19 A  illustrates a side handle including a side handle electrical connection according to some embodiments. 
         FIG.  19 B  illustrates wire routing through the side handle of  FIG.  19 A  according to some embodiments. 
         FIG.  19 C  illustrates wire routing through the side handle of  FIG.  19 A  according to some embodiments. 
         FIG.  19 D  illustrates a power tool including a side handle electrical for connecting to the side handle of  FIG.  19 A  according to some embodiments. 
         FIG.  19 E  illustrates wire routing of the power tool of  FIG.  19 D  according to some embodiments. 
         FIG.  20    illustrates a power tool including an autostop function according to some embodiments. 
         FIGS.  21 A and  21 B  illustrates a perspective view of a power tool including loss of control detection according to some embodiments 
         FIG.  21 C  illustrates a flowchart for a power tool including loss of control detection according to some embodiments 
         FIG.  21 D  illustrates a flowchart for a power tool including loss of control detection according to some embodiments. 
         FIG.  22 A  illustrates a power tool including an adjustable side handle location according to some embodiments. 
         FIG.  22 B  illustrates a power tool including an adjustable side handle location according to some embodiments. 
         FIG.  22 C  illustrates a power tool including an adjustable side handle location according to some embodiments. 
         FIG.  22 D  illustrates a power tool including an adjustable side handle location according to some embodiments. 
         FIG.  22 E  illustrates a power tool including an adjustable side handle location according to some embodiments. 
         FIG.  22 F  illustrates a power tool including an adjustable side handle location according to some embodiments. 
         FIG.  23 A- 23 C  illustrate a power tool including component sensing according to some embodiments. 
         FIG.  23 D  illustrates a flowchart for the power tool of  FIGS.  23 A- 23 C  according to some embodiments. 
         FIG.  24    illustrates a flowchart for detecting loss of control for a power tool according to some embodiments. 
         FIG.  25    illustrates a fixed wheel guard according to some embodiments. 
         FIG.  26 A  illustrates a guard locking flange according to some embodiments. 
         FIG.  26 B  illustrates a roll pin according to some embodiments. 
         FIG.  27    illustrates a spindle locknut assembly according to some embodiments. 
         FIG.  28    illustrates a power tool including lanyard integration according to some embodiments. 
         FIG.  29    illustrates a power tool including battery isolation according to some embodiments. 
         FIG.  30    illustrates a power tool including an adjustable side handle in wireless communication with a power tool main housing according to some embodiments. 
         FIG.  31    illustrates a flowchart for detecting cut-through for a power tool according to some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  1    illustrates a power tool, such as a portable rotary power tool, that implements several different methods and systems to control the tool and a motor of the tool. In some embodiments, the portable power tool is a grinder  100 . The grinder  100  may include a main tool housing  120 , a first handle  140  that extends along the main tool housing  120 , and a second handle  105  that extends transversely in an outward direction from the main tool housing  120 . A motor  210  (shown in  FIG.  2   ) is located within the main tool housing  120 . An output shaft  125  is coupleable to a tool holder that may be configured to receive an accessory  150 , such as a cutting tool, a grinding disc, a rotary burr, a sanding disc, etc. Various types of accessories may be interchangeably attached to the tool holder and may be designed with different characteristics to perform different types of operations. For example, the accessory  150  may be made of a material and have dimensions suitable for performing a specific type of task. The characteristics of an accessory may affect the performance of the grinder  100  or may impose constraints on operation of the tool. For example, different accessory types may be configured to work at different rotational speeds or applied torques depending on the characteristics of the accessory and the task to be performed. During operation of the grinder  100 , the motor and the output shaft  125  may be controlled to rotate at a wide range of speeds. 
     Due to the wide range of speeds, in some embodiments, the grinder  100  may include a guard  130  to protect a user or another object in the surrounding environment from the different accessory types that may be attached to the tool holder. In some embodiments, the guard  130  prevents a user from contacting the accessory  150 . In some embodiments, the guard  130  provides protection against, for example, sparks. 
     In some embodiments, the first handle  140  may define a battery pack receptacle  145 , which is positioned on an end of the first handle  140  opposite the main tool housing  120 . The battery pack receptacle  145  is configured to selectively, mechanically, and electrically connect to a rechargeable battery pack (i.e., a power supply) for powering the motor  210 . The battery pack is insertable into or attachable to the battery pack receptacle  145 . The battery pack may include any of a number of different nominal voltages (e.g., 12V, 18V, 24V, 36V, 40V, 48V, etc.), and may be configured having any of a number of different chemistries (e.g., lithium-ion, nickel-cadmium, etc.). In some embodiments, the motor  210  may be powered by a remote power source (e.g., an AC electrical outlet) through a power cord and a power interface of the grinder  100 . The first handle  140  further contains control electronics for the grinder  100 . 
     The second handle  105  may allow a user to better control the operation of the grinder  100 . In some embodiments, the first handle  140  and/or the second handle  105  include a variety of sensors to detect different operational characteristics and/or user characteristics (e.g., operator presence, grip pressure, etc.). For example, the first handle  140  includes a first sensor  160  for detecting the presence of a user&#39;s hand on the first handle  140 , and the second handle  105  includes a second sensor  165  for detecting the presence of a user&#39;s second hand on the second handle  105 . In some embodiments, the sensors  160 ,  165  are pressure sensors that detect the presence of a minimum grip pressure on the handles  140 ,  105 . Various signals from the sensors located in the second handle  105  may be sent to the grinder  100 &#39;s main control system and the operation of the motor  210  may be controlled based on the signals (e.g., enabling or disabling the motor  210 , modifying a torque limit, etc.). 
     The second handle  105  includes a pivot mechanism  103 . The pivot mechanism  103  enables the second handle  105  to pivot with respect to a pivot arm  108 . The pivot mechanism  103  permits the second handle  105  to be pivoted through a plurality of different positions relative to the pivot arm  108 . For example, the second handle is positioned at a zero-degree angle, or parallel relative to the main tool housing  120  of the grinder  100  (e.g., substantially parallel to the main tool housing  120 ). The second handle  105  can also be moved to another position, such as substantially perpendicular to the main tool housing  120  (e.g., at a 90-degree angle). In some embodiments, the second handle  105  can be positioned at five discrete positions using the pivot mechanism  103 . In other embodiments, greater or fewer discrete positions are available for the second handle. 
     The pivot arm  108  allows the second handle  105  to be pivoted into a plurality of different positions around the circumference of the main tool housing  120 . For instance, the pivot arm  108  may rotate into a first pivot position, such as a left-handed position as illustrated in  FIG.  1   , or a second pivot position, such as a right-handed position. In some embodiments, the second handle  105  may be pivoted to be respectively above the main tool housing  120  and substantially perpendicular to left-handed and right-handed positions (e.g., perpendicular to a cutting plane of the grinder  100 ). Other embodiments may include additional pivot positions for the second handle  105 . Once the second handle  105  is rotated into one of the plurality of pivot positions, the pivot arm  108  can be secured in place by a locking mechanism  113 , as described in greater detail below. 
       FIG.  2    illustrates a side section view of the grinder  100 . In some embodiments, a controller  200  (e.g., located on a printed circuit board) is located within the first handle  140 . In some embodiments, various sensors  205  may also be located within the first handle  140 . The output shaft  125  protrudes downwards, towards a potential workpiece. In some embodiments, the accessory  150  (e.g., a grinder blade) may be attached to the output shaft  125 . Because an accessory  150 , such as a grinder blade, is potentially hazardous to the user and the area surrounding the grinder, the guard  130  is also attached to the output shaft  125  and protrudes downward towards a workpiece and extends around the blade  150 . This provides protection from the blade  150  and any potential debris that is produced during operation. 
     In some embodiments, the motor  210  is located between the output shaft  125  and the battery pack receptacle  145 , and beneath a trigger  155  within the main tool housing  120 . The trigger  155  is used to control the motor  210 , which receives control signals from the controller  200  to control the output shaft  125  and other aspects of the grinder  100 . 
     In some embodiments, the grinder  100  incudes a guard presence sensor  215  for detecting the presence of the guard  130 . In some embodiments, the grinder  100  is prevented from operating (e.g., motor  305  is prevented from operating) when the guard presence sensor  215  does not detect the guard  130 . The grinder  100  also includes a component type indicator  220 . The component type indicator  220  is configured to provide an indication to the grinder  100  of the type of component (e.g., guard  130 ) that is connected to the grinder. For example, guards of different sizes may result in the grinder  100  operating differently. Although the component type indicator  220  is illustrated with respect to the guard  130 , the component type indicator can additionally or alternatively be associated with another component of the grinder  100 , such as the second handle  105 , a dust hood, the accessory  150 , etc. 
     The first handle  140  includes the switch or trigger  155  operable to electrically connect the power source (e.g., the battery pack) and the motor  210 . In some embodiments, the trigger  155  may be a “lock-off” trigger having a paddle member and a lock-off member  208  supported by the paddle member. The paddle member is operable to actuate a switch  203  electrically connected to the controller  200 . The switch  203  is configured to control selective activation and deactivation of the motor  210  during operation of the grinder  100 . The lock-off member  208  is configured to selectively prevent operation of the paddle member (e.g., prevent activation of the switch  203 ). In some embodiments, the paddle member acts as the detection for a user&#39;s first hand on the first handle  140 . In other embodiments, a user&#39;s hand is detected using other sensors (e.g., grip sensors, pressure sensors, touch sensors, electromechanical sensors, etc.). 
       FIG.  3    illustrates a control system for the grinder  100 . The control system includes a controller  300 . The controller  300  is electrically and/or communicatively connected to a variety of modules or components of the grinder  100 . For example, the illustrated controller  300  is electrically connected to a motor  305  (e.g., motor  210 ), a battery pack interface  310 , a trigger switch  315  (connected to a trigger  320 ), one or more sensors or sensing circuits  325 , one or more indicators  330 , a user input module  335 , a power input module  340 , and a FET switching module  350  (e.g., including a plurality of switching FETs). The controller  300  includes combinations of hardware and software that are operable to, among other things, control the operation of the grinder  100 , monitor the operation of the grinder  100 , activate the one or more indicators  330  (e.g., an LED), etc. 
     The controller  300  includes a plurality of electrical and electronic components that provide power, operational control, and protection to the components and modules within the controller  300  and/or the grinder  100 . For example, the controller  300  includes, among other things, a processing unit  355  (e.g., a microprocessor, a microcontroller, an electronic processor, an electronic controller, or another suitable programmable device), a memory  360 , input units  365 , and output units  370 . The processing unit  355  includes, among other things, a control unit  375 , an arithmetic logic unit (“ALU”)  380 , and a plurality of registers  385 , and is implemented using a known computer architecture (e.g., a modified Harvard architecture, a von Neumann architecture, etc.). The processing unit  355 , the memory  360 , the input units  365 , and the output units  370 , as well as the various modules or circuits connected to the controller  300  are connected by one or more control and/or data buses (e.g., common bus  390 ). The use of one or more control and/or data buses for the interconnection between and communication among the various modules, circuits, and components would be known to a person skilled in the art in view of the embodiments described herein. 
     The memory  360  is a non-transitory computer readable medium and includes, for example, a program storage area and a data storage area. The program storage area and the data storage area can include combinations of different types of memory, such as a ROM, a RAM (e.g., DRAM, SDRAM, etc.), EEPROM, flash memory, a hard disk, an SD card, or other suitable magnetic, optical, physical, or electronic memory devices. The processing unit  355  is connected to the memory  360  and executes software instructions that are capable of being stored in a RAM of the memory  360  (e.g., during execution), a ROM of the memory  360  (e.g., on a generally permanent basis), or another non-transitory computer readable medium such as another memory or a disc. Software included in the implementation of the grinder  100  can be stored in the memory  360  of the controller  300 . The software includes, for example, firmware, one or more applications, program data, filters, rules, one or more program modules, and other executable instructions. The controller  300  is configured to retrieve from the memory  360  and execute, among other things, instructions related to the control processes and methods described herein. In other constructions, the controller  300  includes additional, fewer, or different components. 
     The motor  305  includes a rotor and a stator that surrounds the rotor. In some embodiments, the motor  305  is a brushless direct current (“BLDC”) motor in which the rotor is a permanent magnet rotor and the stator includes coil windings that are selectively energized to drive the rotor. In other embodiments, the motor is a brushed motor. The stator is supported within the main tool housing  120  and remains stationary relative to the main tool housing  120  during operation of the grinder  100 . The rotor is rotatably fixed to a rotor shaft and configured to rotate with the rotor shaft, relative to the stator, about a motor axis. A portion of the rotor shaft is associated with or corresponds to the output shaft  125  extending from the main tool housing  120 . In some embodiments, the motor  305  is an outer rotor motor. 
     The battery pack interface  310  includes a combination of mechanical components (e.g., rails, grooves, latches, etc.) and electrical components (e.g., one or more terminals) configured to and operable for interfacing (e.g., mechanically, electrically, and communicatively connecting) the grinder  100  with a battery pack. For example, power provided by the battery pack to the grinder  100  is provided through the battery pack interface  310  to the power input module  340 . The power input module  340  includes combinations of active and passive components to regulate or control the power received from the battery pack prior to power being provided to the controller  300 . The battery pack interface  310  also supplies power to the FET switching module  350  to provide power to the motor  305 . The battery pack interface  310  also includes, for example, a communication line  395  for provided a communication line or link between the controller  300  and the battery pack. 
     The indicators  330  include, for example, one or more light-emitting diodes (“LEDs”). The indicators  330  can be configured to display conditions of, or information associated with, the grinder  100 . For example, the indicators  330  are configured to indicate measured electrical characteristics of the grinder  100 , the status of the grinder  100 , etc. The user input module  335  is operably coupled to the controller  300  to, for example, select a forward mode of operation or a reverse mode of operation, a torque and/or speed setting for the grinder  100  (e.g., using torque and/or speed switches), etc. In some embodiments, the user input module  335  includes a combination of digital and analog input or output devices required to achieve a desired level of operation for the grinder  100 , such as one or more knobs, one or more dials, one or more switches, one or more buttons, etc. 
     The controller  300  is configured to determine whether a fault condition of the grinder  100  is present and generate one or more control signals related to the fault condition. For example, the sensing circuits  325  include one or more current sensors, one or more speed sensors, one or more Hall Effect sensors, one or more temperature sensors, an accelerometer, a gyroscope, an inertial measurement unit [“IMU”], one or more pressure sensors, one or more object presence sensors, etc. The controller  300  calculates or includes, within memory  360 , predetermined operational threshold values and limits for operation of the grinder  100 . For example, when a potential thermal failure (e.g., of a FET, the motor  305 , etc.) is detected or predicted by the controller  300 , power to the motor  305  can be limited or interrupted until the potential for thermal failure is reduced. If the controller  300  detects one or more such fault conditions of the grinder  100  or determines that a fault condition of the grinder  100  no longer exists, the controller  300  is configured to provide information and/or control signals to another component of the grinder  100  (e.g. the battery pack interface  310 , the indicators  330 , etc.). 
       FIG.  4    and  FIG.  5    are illustrations of partial views of the second handle  105  of the grinder  100 , according to some embodiments. The second handle  105  incudes a first over-mold portion  403  positioned on the second handle  105  and configured to protect internal components of the second handle  105  from water, dust, or other unwanted foreign debris. The second handle  105  also includes a second over-mold portion, positioned opposite the first over-mold portion  405  (see  FIG.  8   ). The pivot arm  108  of the second handle  105  includes locking mechanism  408  configured to mechanically couple with the pivot mechanism  103 . 
       FIG.  6    and  FIG.  7    are illustrations of the second handle  105  of the grinder  100  with an outer housing removed. The second handle  105  includes an internal cavity  505 . The second handle  105  includes a printed circuit board (“PCB”)  603  (e.g., a flexible printed circuit board) which includes a microswitch sensor  608  positioned on the PCB. In some embodiments, the PCB  603  is folded or molded around the outer circumference  515  of the second handle  105 . The microswitch sensor  608  is configured to mechanically contact the first over-mold portion  403 . Additionally, the microswitch sensor  608  is configured to detect the presence of a hand. For example, when a user grips the second handle  105  with sufficient grip force (e.g., to overcome a spring force biasing the first over-mold portion  403  away from the microswitch sensor  608 ), the first over-mold portion  403  is depressed and the microswitch sensor  608  is activated. In some embodiments, a grip force above a threshold value is required for the grinder  100  to detect hand presence. In other embodiments, a user&#39;s hand is detected merely by detecting a user&#39;s hand touching the second handle  105 . The microswitch sensor  608  then sends a signal to the controller  200 . In some embodiments, the microswitch sensor  608  acts as a secondary trigger mechanism. For example, in some embodiments, the microswitch sensor  608  must be activated prior to the activation of the trigger  155  in order for the grinder to operate. In some embodiments, there is an activation time associated with the operation of the trigger  155  after a user grips the second handle  105 . For example, in some embodiments, the trigger  155  must be activated within a predetermined time period after a user&#39;s grip has been detected by the microswitch sensor  608 . 
     The internal cavity  505  includes wires  613  for connecting the microswitch sensor  608  to the controller  200 . In some embodiments, the wires  613  are routed around support structures  618  for the second handle  105 . The support structures  618  are configured to, for example, maintain the structural integrity of the internal cavity  505  during use of the second handle  105 . The wires  613  are configured to exit the second handle  105  through a first channel  623  through the locking mechanism  408 . 
     The locking mechanism  408  is configured to engage the pivot mechanism  103  to move the second handle  105  to a plurality of different position. The locking mechanism includes a spring  628  to bias the locking mechanism  408  toward the pivot mechanism  103 . In order to pivot the second handle  105  with respect to the pivot mechanism  103 , a user would have to pull the second handle  105  away from the pivot mechanism  103  and against the bias force of the spring  628 . A body portion  633  that forms the first channel  623  also includes ribs or projections  638 . The projections  638  prevent the second handle  105  from rotating with respect to the pivot mechanism  103 . When the locking mechanism  408  clears teeth  643  of the pivot mechanism  103  after being pulled away from the pivot mechanism  103 , the second handle  105  can be pivoted to a different position with respect to the pivot mechanism  103 . 
       FIG.  8    is an illustration of an interior portion of the second handle  105  of the grinder  100 . In this illustration, portions of the second handle  105  are removed in order to illustrate the first over-mold portion  403  and a second over-mold portion  803 . The second over-mold portion  803  is positioned opposite the first over-mold portion  403 . Either the first over-mold portion  403  or the second over-mold portion  803  can activate the microswitch sensor  608 . For example, depending on the position of the second handle (e.g., right or left side of the grinder  100 ), one of the first over-mold portion  403  and the second over-mold portion  803  would correspond to a top portion of the second handle  105 . In some embodiments, both the first and second over-mold portions  403 ,  803  need to be pressed to activate the microswitch sensor  608  and operate the grinder  100 . In some embodiments, the second handle includes a second microswitch sensor  608  for the second over-mold portion  803 . Wires  613  are routed around a screw  808  associated with the support structures  618  and into the first channel  623 . In some embodiments, the first over-mold portion  403  and the second over-mold portion  803  are mechanically connected to the microswitch sensor  608 . The second handle  105  additionally includes the projections  638  for rotationally locking the second handle  105  with respect to the pivot mechanism  103 . The projections  638  prevent twisting of the second handle  105  relative to pivot mechanism  103 . 
       FIG.  9    and  FIG.  10    are illustrations of an internal wire routing portion of the second handle  105  and the grinder  100 . The wires  613  run from the internal cavity  505  of the second handle  105  into the first channel  623 , and then into a second channel  903  in the pivot mechanism  103 . The wires  613  run from the second channel  903  into a third channel  908  within the pivot arm  108 . The second channel  903  and the third channel  908  are configured to route the wires  613  such that the wires  613  do not interfere with the pivoting of the pivot mechanism  103  or the rotation of the pivot arm  108 . As a result, the second channel  903  and third channel  908  prevent the wires  613  from bundling/crimping when the second handle  105  is pivoted with respect to the pivot mechanism  103  or the pivot arm  108  is rotated with respect to the grinder  100 . A wire path  913  for routing the wires  613  from the second handle  105  to the main tool housing  120  is illustrated in  FIG.  14   . In the embodiment illustrated in  FIG.  10   , the second handle  105  is positioned at a 45-degree angle relative to the pivot arm  108 . 
       FIG.  11    illustrates an interior portion of the grinder  100  associated with the routing of the wires  613 . In some embodiments, the third channel  908  extends into and terminates in a main housing cavity  1103  of the main tool housing  120 . The main tool housing  120  houses the motor, controller, and other such components of the grinder  100  that are not illustrated in  FIG.  11   . In some embodiments, the main housing cavity  1103  includes a fourth channel  1108  configured proximate to, and extending orthogonally from, the third channel  908 . The fourth channel  1108  is configured to receive the wires  613  from the third channel  908  and route the wires  613  along the length of the fourth channel  1108  (e.g., around a gearcase of the grinder  100 ). The wires  613  terminate in or after the fourth channel  1108  at a first electrical connector (not illustrated). In some embodiments, the first connector is configured to electrically and mechanically connect with a main wire harness of the power tool to connect the wires  613  to the controller  200 . In some embodiments, the first connector is configured to connect to a second connector (not illustrated) that extends from the controller  200  of the grinder  100 . In some embodiments, the wires  613  extend all the way to the controller  200  without a first or second connector. In some embodiments, the grinder  100  includes additional channels or alternative wire routing paths. 
       FIG.  12    and  FIG.  13    illustrate the operation of the locking mechanism  113  for the pivot arm  108  of the grinder  100 , according to some embodiments. The locking mechanism  113  is configured to lock the pivot arm  108  into one of a plurality of pivot positions. In some embodiments, the locking mechanism  113  a button, a switch, a lever, or the like, that is biased into a locked position. Once locked by the locking mechanism  113 , the pivot arm  108  is secured in place and cannot be moved to another pivot position. In some embodiments, the pivot arm  108  includes a pivot joint  1203  in contact with the main tool housing  120  of the grinder  100 . A first bushing  1208  is mechanically connected to the pivot joint  1203 . The first bushing  1208  is configured to support the pivot joint  1203 . In some embodiments, a second bushing  1213  opposite the first bushing  1208  is also used to support the pivot joint  1203 . The pivot joint  1203  is configured to mechanically connect the pivot arm  108  with the locking mechanism  113 . The pivot joint  1203  includes a first aperture or first groove  1218  configured to mechanically couple with a tooth or projection  1223  of the locking mechanism  113 . When the projection  1223  is mechanically coupled to the first groove  1218 , the pivot arm  108  is locked into position by the locking mechanism  113 . In some embodiments, the first groove  1218  is associated with the first or left-handed pivot position. The pivot joint  1203  also includes a second aperture or second groove  1228  associated with a second or right-handed pivot position. The projection  1223  is configured to mechanically connect to the second groove  1228  to lock the pivot arm  108  into the second pivot position. The pivot joint  1203  further includes a third aperture or third groove  1233  associated with a third or middle position for the pivot arm  108 . The projection  1223  is configured to mechanically connect to the third groove  1233  to lock the pivot arm  108  into the third pivot position. In some embodiments, the pivot joint  1203  includes additional apertures or grooves associated with additional pivot positions. In some embodiments, the locking mechanism  113  includes one or more springs  1238  configured to bias the projection  1223  toward one of the first groove  1218 , the second groove  1228 , or the third groove  1233 . 
       FIG.  14    is an illustration of an internal wire routing portion of the second handle and the grinder  100 . The wire path  913  routes the wires  613  from the second handle  105  to the main tool housing  120 . The wires  613  run from the internal cavity  505  of the second handle  105  into the first channel  623 , and then into a second channel  903  in the pivot arm  108 . The wires  613  run from the second channel  903  into a third channel  908  within the pivot arm  108 . The second channel  903  and the third channel  908  are configured to route the wires  613  such that the wires  613  do not interfere with the pivoting of the pivot mechanism  103  or the rotation of the pivot arm  108 . As previously described, in some embodiments the wires may be configured to electrically and mechanically connect with a main wire harness of the power tool to connect the wires  613  to the controller  200 . In some embodiments, the wires  613  connect directly to the controller  200 . 
       FIG.  15    illustrates an embodiment of the grinder  100  including a two-handed control feature. The grinder  100  includes the first handle  140  for the user to grip with one hand, and a second handle  105  for the user to grip with another hand. In some embodiments, for the grinder  100  to operate, the first handle  140  and/or the second handle  105  include a variety of sensors to detect different operational characteristics and/or user characteristics (e.g., operator presence, grip pressure, etc.). For example, the first handle  140  includes a first sensor  160  for detecting the presence of a user&#39;s hand on the first handle  140 , and the second handle  105  includes a second sensor  165  for detecting the presence of a user&#39;s second hand on the second handle  105 . In some embodiments, the sensors  160 ,  165  are pressure sensors that detect the presence of a minimum grip pressure on the handles  140 ,  105 . Various signals from the sensors located in the second handle  105  may be sent to the grinder  100 &#39;s main control system, and the operation of the motor  210  may be controlled based on the signals (e.g., enabling or disabling the motor  210 , modifying a torque limit, etc.). 
     In another embodiment, the sensors  160 ,  165  are capacitive sensors that detect the presence of the user&#39;s hands on or near the handles  140 ,  105 . In other embodiments, the sensors  160 ,  165  are microswitches that detect the presence of the user&#39;s hands on the handles  140 ,  105 . In another embodiment, the sensors  160 ,  165  are photolight sensors that are configured to detect the adjustment of light based on the position of the users hand on the handles  140 ,  105  (e.g., no light detected indicates hand presence). 
     In some embodiments, the grinder  100  includes one sensor, such as second sensor  165 . The second sensor  165  (e.g., pressure sensor, capacitive sensor, microswitch, photolight sensor, etc.) is located in the second handle  105  to detect the presence of a user&#39;s second hand. The user uses the other hand to grip the first handle  140  and pull the main trigger  170  to operate the grinder  100 . The sensor  165  must detect the presence of one of the user&#39;s hands in addition to compressing the main trigger  170  in order for a signal to be sent to the grinder  100 &#39;s main control system, and the operation of the motor  210  may be controlled based on the signals (e.g., enabling or disabling the motor  210 , modifying a torque limit, etc.). 
       FIG.  16 A  illustrates a perspective view of the second handle  105 . In some embodiments, the grinder  100  will only operate if a user is operating the grinder  100  by gripping both the first handle  140  and the second handle  105 . In some embodiments, the first handle  140  may support a switch or trigger  155  operable to selectively electrically connect the power source (e.g., the battery pack) and the motor  305 . In some embodiments, the trigger  155  may be a “lock-off” trigger having a paddle member and a lock-off member supported by the paddle member. The paddle member is operable to actuate a microswitch to selectively activate and deactivate the motor during operation of the grinder  100 . The lock-off member selectively prevents operation of the paddle member. Specifically, the lock-off member is pivotable to selectively lock and unlock the paddle member. The speed of the motor may be controlled by varying the level of depression of the paddle member. In some embodiments, the paddle member acts as the detection for a user&#39;s first hand on the first handle  140 . In other embodiments, a first force sensitive resistor is located on the first handle  140  and is configured to detect pressure (e.g., from a user&#39;s first hand). In other embodiments, a user&#39;s hand is detected using other sensors (e.g., grip sensors, pressure sensors, touch sensors, electromechanical sensors, etc.). 
     The second handle  105  includes an internal surface which includes an internal cavity  505 . In some embodiments, the internal cavity  505  remains hollow throughout the length of the second handle  105 . In some embodiments, the second handle  105  includes a flexible printed circuit board (“PCB”)  510  which includes a force sensitive resistor printed on the PCB  510 . The PCB is folded or molded around an outer circumference  515  of the second handle  105 . The force sensitive resistor may be configured to detect a relatively light pressure (e.g., by a hand). In other embodiments, a grip force above a threshold value is required for the grinder to detect hand presence. In other embodiments, a user&#39;s hand is detected using other sensors (e.g., pressure sensors, touch sensors, electromechanical sensors, etc.). 
       FIG.  16 B  illustrates a method  600  for allowing use of the grinder  100 . When a user indicates an intention to use the grinder  100 , the grinder  100  detects a pick-up of the grinder  100  but the grinder  100  is prohibited from operating (STEP  605 ). The method  600  then includes checking if the user&#39;s first hand is detected on the first handle  140  (STEP  610 ). If the first hand is not detected on the first handle  140 , the user is prohibited from using the grinder  100 . If the user&#39;s first hand is detected, the method  600  then includes checking to see if the user&#39;s second hand is detected on the second handle  105  (STEP  615 ). If the second hand is not detected on the second handle  105 , the user is prohibited from using the grinder  100 . If the user&#39;s second hand is detected to be located on the second handle  105 , the controller  300  allows operation of the grinder  100  (STEP  620 ). As previously described, in some embodiments, there is an activation time associated with the operation of the trigger after a user grips the second handle. For example, in some embodiments, the trigger must be activated within a predetermined time period after a user&#39;s grip has been detected. In some embodiments, the controller  300  allows operation of the grinder  100  immediately. 
     In some embodiments, the grinder  100  includes an electrical connection to an accessory device (e.g., a second handle). The grinder  100  includes the main tool housing  120  that includes the first handle  140  for being gripped by a user. The grinder  100  also includes an accessory device attachment portion on the main tool housing  120 . The accessory device attachment portion includes, for example, a threaded hole that can receive an accessory (e.g., having a threaded stud). The accessory device attachment portion is configured to receive an accessory device such as the second handle  105  to provide a second hand grip for a user. When the accessory device is attached to the grinder  100 , an electrical connection is provided between the grinder  100  and the accessory device. As a result of this electrical connection, power is provided to the accessory device for powering one or more circuits (e.g., sensors, outputs, etc.) of the accessory device. 
     For example,  FIG.  17 A  illustrates an embodiment of the electrical connection of the accessory device. In this embodiment, the accessory device is illustrated as second handle  105 . The second handle  105  includes a first electrical contact  1710  located on a threaded stem  1725 , and a second contact  1705 . In some embodiments, the second contact  1705  is a metal annular ring positioned on the second handle  105 , and is configured to contact a corresponding electrical contact located on the main tool housing  120 . Once the first electrical contact  1710  and the second contact  1705  have made proper connections with their counterparts on the main tool housing  120  (e.g., the second handle  105  is fully screwed down), a sensor (e.g., the force sensitive resistor) will be able to begin sensing on the second handle  105 . 
       FIG.  17 B  illustrates another embodiment of the electrical connection of the accessory device. In this embodiment, the accessory device is illustrated as the second handle  105 . The second handle  105  includes a first electrical contact  1715  and a second contact  1720 , which are metal annular rings positioned on the second handle  105 . Once the first electrical contact  1715  and the second contact  1720  have made proper connections with their counterparts on the main tool housing  120  (e.g., the second handle  105  is fully screwed down), a sensor (e.g., the force sensitive resistor) will be able to begin sensing on the second handle  105 . In some embodiments, the electrical connection of the accessory device would be a wireless connection between the main tool housing  120  and the accessory device. For example, an inductive or capacitive coupling can be used to wirelessly transmit power to the accessory device. Such a configuration enables a water-tight seal between the grinder  100  and the accessory device. 
       FIG.  17 C  illustrates a schematic  1750  for the electrical connection of the accessory device to the grinder  100 . The schematic  1750  includes a sensor  1755  (e.g., a force sensitive resistor), a gearcase  1760 , and the controller  300 . An electrical connection  1765  is made between the grinder  100  and the second handle  105  using, for example, the connection techniques described above with respect to  FIGS.  17 A and  17 B . The controller  300  monitors the resistance of the force sensitive resistor to detect, for example, the presence or absence of a user&#39;s hand. 
       FIG.  18    illustrates a method  1800  for the grinder  100  that detects a type of component connected to the grinder  100  (STEP  1805 ). For example, the grinder  100  can detect a particular type of disk guard, a particular type of dust hood, etc. The detection of the particular type of component connected to the grinder  100  can be achieved using a sensor (e.g., an induction coil sensor, a Hall effect sensor, an optical sensor, wireless communication, etc.). In some embodiments, the sensor is configured to detect a passive characteristic of the component (e.g., read a bar code, serial number, QR code, etc.). In other embodiments, the component can provide information to the grinder (e.g., using the component type indicator  220 ). In some embodiments, the component type indicator  220  is an RFID tag. In other embodiments, the component type indicator  220  includes a power source and is configured to communicate with the grinder  100  (e.g., using a short-range communication protocol, such as Bluetooth). 
     The sensor provides an output to the controller  300  of the grinder  100  (STEP  1810 ). The controller  300  can then determine the type of attached component based on the output of the sensor (STEP  1815 ). In some embodiments, the controller  300  looks up a characteristic of the component (e.g., a bar code, serial number, QR code, etc.) to determine the type of component. In other embodiments, information received from the component includes an indication of the type of component attached to the grinder  100 . After the grinder  100  determines the particular type of component connected to the grinder  100 , the grinder  100  can take a control action based on the detected type of component connected to the grinder (e.g., adjust a torque or speed setting) (STEP  1820 ). 
       FIG.  19 A  illustrates an embodiment of an electrical connection of an accessory device  1945 . In this embodiment, the accessory device  1945  is illustrated as the second handle  105 . The second handle  105  includes spring loaded contacts  1905 . The spring loaded contacts  1905  are used to form the electrical connection from the second handle  105  to the main tool housing  120 . The spring loaded contacts  1905  are mounted, for example, on a printed circuit board (“PCB”)  1940  located within an accessory device  1945  of the second handle  105 . The accessory device  1945  includes an aperture or hole  1950  on a surface of the accessory device  1945 . The PCB  1940  is mounted on the surface of the accessory device  1945  that includes the hole  1950 . The spring loaded contacts  1905  are positioned on the PCB  1940  to be accessible through the hole  1950 . 
     In some embodiments, the grinder  100  includes a plurality of rails  1955  (see  FIG.  19 D ) located on the side of the main tool housing  120  (as shown in  FIG.  19 D ). The plurality of rails  1955  of the grinder  100  are used to attach to a plurality of rails  1910  of the second handle  105 . The rails  1910  slide directly on the rails of the grinder  100 , mechanically connecting the grinder  100  and the second handle  105 . 
     When the grinder  100  and the second handle  105  are connected to one another, the spring loaded contacts  1905  are then coupled to a corresponding electrical contact  1935  located on the main tool housing  120 . Once the spring loaded contacts  1905  have made electrical connection with their counterparts on the main tool housing  120  (e.g., the second handle  105  has attached rails  1910  with the corresponding rails of the main tool housing  120 ), a sensor (e.g., pressure sensor, capacitive sensor, microswitch, photolight sensor, etc.) will be able to be used to sense the second handle  105  and a user&#39;s hand. 
       FIG.  19 B  illustrates an interior of the accessory device  1945 . The accessory device  1945  is illustrated as the second handle  105 . The second handle  105  includes the spring loaded contacts  1905 . In some embodiments, the accessory device  1945  includes a pivoting mechanism  1930 . The pivoting mechanism  1930  allows the second handle  105  to rotate with respect to the grinder  100 , while the accessory device  1945  remains securely attached and electrically connected to the main tool housing  120 . In some embodiments, the accessory device  1945  includes extra space extending from the second handle  105  to the PCB  1940 . This extra space allows wire to coil as the second handle  105  is adjusted. In some embodiments, the extra space includes a channel  1915  for the extra wire to travel to. For example, as the second handle  105  rotates with respect to the accessory device  1945  via the pivoting mechanism  1930 , the extra wire extends and retracts based on the positioning of the second handle  105 . 
       FIG.  19 C  illustrates another view of the electrical connection of the accessory device  1945 . In some embodiments, the accessory device  1945  includes the pivoting mechanism  1930 . To allow the wires  1960  to move with the pivoting mechanism  1930 , the extra space includes the channel  1915  for the wire to extend from the second handle  105  to the PCB  1940 . The channel  1915  is curved around the pivoting mechanism  1930 , allowing for the extra wire to travel around the pivoting mechanism  1930  and not interfere with the rotation of the pivoting mechanism  1930 . 
       FIG.  19 D  illustrates the electrical connection of the grinder  100  to the second handle  105 . As previously noted, the main tool housing  120  includes an accessory device interface. The accessory device interface includes a plurality of rails  1955  that are attached to the plurality of rails  1910 . Once the second handle  105  is attached to the main tool housing  120 , a plurality of electrical contacts  1935  are configured to come into contact with the corresponding spring loaded contacts  1905 . When the plurality of electrical contacts  135  and the spring loaded contacts  1905  have made electrical connection, a sensor (e.g., pressure sensor, capacitive sensor, microswitch, photolight sensor, etc.) will be able to begin sensing on the second handle  105  and a user&#39;s hand. 
       FIG.  19 E  illustrates electrical connections of the grinder  100  to the second handle  105 . In some embodiments, the second handle  105  may be electrically and mechanically connected to either side of the grinder  100 . Furthermore, because the second handle  105  can be connected to either side of the grinder  100 , there is a set of mechanical components on either side of the grinder  100 . For example, the mechanical components include rails  1955  for the rails  1910  of the second handle  105  to firmly attach to. In addition to the mechanical components, there are also electrical contacts  1935  on either side of the grinder so that an electrical connection may be made from the second handle  105  and the grinder  100 . In some embodiments, a plurality of wires  1970  extend from the grinder  100 &#39;s main control system to the plurality of electrical contacts  1935  of the grinder  100 . Two sets of the plurality of wires  1970  extend from the main control system, one set of the plurality of wires  1970  extend to one side of the grinder  100  and the other set of the plurality of wires  1970  extend to the other side of the grinder  100 . When the second handle  105  is attached to either or both sides of the grinder  100 , the plurality of electrical contacts  1935  on either side of the grinder  100  are configured to come into contact with the corresponding spring loaded contacts  1905  of the handle  105 . When the plurality of electrical contacts  1935  and the spring loaded contacts  1905  have made electrical connection, a sensor (e.g., pressure sensor, capacitive sensor, photolight sensor, etc.) will be able to begin sensing on the second handle  105  and a user&#39;s hand. 
       FIG.  20    illustrates a grinder  2000  that includes a loss of control mitigation system. In some embodiments, the grinder  2000  includes some or all of the previously described features of the grinder  100 . The grinder  2000  includes a loss of control module. The loss of control module includes a sensor (e.g., an accelerometer, a gyroscope, an inertial measurement unit [“IMU”]) and is configured to detect linear and/or rotational motion of the grinder  2000 . In some embodiments, the loss of control module is located in a first position  2005 . The first position  2005  couples the loss of control module to the main control system. The main control system is located within the first handle  140  between the main tool housing  120  and the battery pack interface  310 . In some embodiments, by coupling the loss of control module with the main control system of the grinder  2000 , the loss of control module will be slightly tilted relative to a longitudinal axis of the grinder  2000  (i.e., the cutting plane of the blade  150 ). 
     In another embodiment, the loss of control module is located in a second position  2010 . The second position  2010  locates the loss of control module in the area of the guard presence sensor  215  described above. The guard presence sensor  215  is located near the front of the grinder  2000 , above the disk guard  130  so that, when the guard presence sensor  215  is coupled to the loss of control module, the loss of control module will be close to the front of the grinder  2000 . In the second position, the loss of control module is parallel to the longitudinal axis of the grinder  2000  (i.e., the cutting plane of the blade  150 ). 
       FIGS.  21 A and  21 B  illustrate a grinder that includes a loss of control mitigation system. The grinder  100  includes at least one sensor located, for example, within the main tool housing  120 . The at least one sensor is configured to detect a motion of the grinder  100  indicative of a loss of control of the grinder  100 . 
     In some embodiments, as illustrated in  FIG.  21 A , a sensor (e.g., an accelerometer, a gyroscope, an inertial measurement unit [“IMU”]) is configured to detect linear motion of the grinder  100 . The linear motion may be described as a forward motion or a reverse motion with respect to a workpiece  199 . In other embodiments, the linear motion may be described as lateral to the workpiece  199 . If the linear motion, as detected by the sensor, exceeds a predetermined threshold, a loss of control is determined. In some embodiments, when the loss of control is determined, the grinder  100  is configured to brake the motor  305 . 
     In other embodiments, as illustrated in  FIG.  21 B , a sensor (e.g., an accelerometer, a gyroscope, an inertial measurement unit [“IMU”]) is configured to detect a rotation of the grinder  100 . The rotation of the grinder  100  may be described as an upward or vertical motion with respect to a workpiece  199 . In another embodiment, the rotation of the grinder  100  may be described as a rotation about the battery pack receptacle  145 . If the rotational motion, as detected by the sensor, exceeds a predetermined threshold, a loss of control is determined. In some embodiments, when the loss of control is determined, the grinder  100  is configured to brake the motor  305 . 
       FIG.  21 C  shows a method  2100  for detecting a loss of control condition of the grinder  100 . When a user initiate use of the grinder  100  (STEP  2105 ), work on a workpiece begins. The method  2100  includes detecting linear motion (STEP  2110 ) as detected from a sensor (e.g., an accelerometer, a gyroscope, an inertial measurement unit [“IMU”]). If the linear motion detected by the sensor exceeds a linear loss of control threshold (STEP  2115 ), the motor  305  of the grinder  100  is stopped (e.g., braked). If the linear motion detected does not exceed the linear loss of control threshold, the method  2100  then includes detecting rotational motion of the grinder  100  (STEP  2125 ). If the rotational motion of the grinder  100  exceeds a rotational loss of control threshold (STEP  2130 ), the motor  305  of the grinder  100  is stopped (e.g., braked). If the rotational motion of the grinder  100  does not exceed the rotational loss of control threshold, the method  2100  restarts, providing a constant monitoring of a loss of control mitigation method. In some embodiments, both linear and rotational motion are detected and monitored for the loss of control condition simultaneously. In some embodiments, rotational motion is monitored prior to linear motion of the grinder  100 . 
       FIG.  21 D  shows a method  2150  for detecting a loss of control condition of the grinder  100 . When a user initiates use of the grinder  100  (STEP  2155 ), work on a workpiece begins. The method  2150  includes detecting linear motion (STEP  2160 ) as detected from a sensor (e.g., an accelerometer, a gyroscope, an inertial measurement unit [“IMU”]). The method  2150  includes detecting rotational motion (STEP  2165 ) as detected from a sensor (e.g., an accelerometer, a gyroscope, one or more Hall effect sensors, or the like). The method  2150  further includes incrementing a linear and rotation accumulator (STEP  2170 ) based upon a threshold level. For example, if the linear motion detected in STEP  2160  exceeds a first threshold and/or the rotational motion detected in STEP  2165  exceeds a second threshold, the accumulator will increment. In some examples, the accumulator increments based upon both a linear motion threshold and a rotational motion threshold. In some examples, the linear motion and the rotational motion have separate accumulators that increment independently. If the accumulator has reached a predetermined maximum value at STEP  2175 , the motor  305  of the grinder  100  is stopped (e.g. braked) (STEP  2180 ). On the other hand, if the accumulator has not reached a predetermined maximum value, the method  2150  returns to STEP  2160  to again detect motion, and thus providing a constant monitoring for a loss of control mitigation method. In some embodiments, rotational motion is monitored prior to linear motion of the grinder  100 . 
       FIGS.  22 A,  22 B,  22 C,  22 D,  22 E, and  22 F  illustrate embodiments of a grinder including a connected second handle  105 . In some examples, the grinder includes some or all of the previously described features of the grinder  100 . The second handle  105  includes several different embodiments regarding the movement and placement of the second handle  105 , making the second handle  105  adjustable to suit the user&#39;s needs. 
     As illustrated in  FIG.  22 A , an embodiment  2200  of the grinder  100  includes the second handle  105 . The second handle  105  includes, for example a threaded screw for fastening the second handle to the grinder  2200 . The grinder  2200  includes corresponding threaded holes  2205  for receiving the threaded screw of the second handle  105  on either side of the grinder  2200 .  FIG.  22 A  illustrates the second handle  105  in a standard position on a left-hand side of the grinder  2200  with the second handle  105  configured at a 90-degree angle to the grinder  2200 . The second handle  105  can alternatively or additionally be positioned on the right-hand side of the grinder  2200 . 
     In some embodiments, if the 90-degree angle for the user is not conducive to the operation that the user is performing, an embodiment  2210  of the grinder  100  can include the second handle  105  having a pivoting mechanism  2215  for pivoting the second handle  105  from a position perpendicular to the grinder  2210  to a position parallel to the grinder  2210  (not shown), as illustrated in  FIG.  22 B . The pivoting mechanism  2215  allows for the second handle  105  to pivot towards the grinder  2210 . In some embodiments, the second handle  105  can attach to the grinder  2210  using rails as described above with respect to  FIGS.  19 A- 19 D . The second handle  105  can alternatively or additionally be positioned on the right-hand side of the grinder  2210 . In some embodiments, the pivoting mechanism includes a button to release the second handle  105  for movement of the second handle  105 . 
       FIG.  22 C  illustrates an embodiment  2220  of the grinder  100  that includes a two-position pivoting handle. When the second handle  105  has pivoted away the grinder  2220  to a primary position, the second handle  105  is an approximately 90 degree angle (i.e., perpendicular) with respect to the grinder  2220 . In some embodiments, when the second handle is pivoted toward a secondary position, the second handle  105  is in an approximately 45 degree angle with respect to the grinder  100 . In other embodiments, the secondary position can be at another angle (e.g., 40-degrees, 60-degrees, etc.) with respect to the grinder  2220 . A pivoting mechanism  2225  is connected between the handle  105  and the grinder  2220  such that the second handle includes two (or possible more) discrete locked mechanical positions for securing the orientation of the second handle  105 . The pivoting mechanism  2225  can then include a threaded screw or hole for securing the second handle  105  to a complementary interface  2230  on the left and/or right side of the grinder  2220 . 
     In another embodiment  2240  of the grinder  100 , the second handle  105  can be secured to the grinder  2240  by a strap  2245 , as illustrated in  FIG.  22 D . A tightening mechanism  2250  can be rotated to slacken or tighten the strap  2245  around the housing of the grinder  2240 . Because the strap  2245  secures the second handle  105  to the grinder  2240  by friction and not a dedicated mechanical interface of the grinder  2240 , the second handle can be rotated to any desirable orientation of the second handle  105  perpendicular to the grinder  2240 . 
       FIG.  22 E  illustrates in another embodiment  2260  of the grinder  100  that includes a pivoting mechanism  2265 , similar to the pivoting mechanisms described previously. The pivoting mechanism  2265  enables the second handle  105  to be pivoted closer to the grinder  2260  in a secondary position other than perpendicularly to the grinder  100 . In some embodiments, the secondary position is in a 45 degree angle from the grinder  2260 . In other embodiments, the secondary position can be at another angle (e.g., zero degrees, 20 degrees, 40 degrees, 60 degrees, etc.) with respect to the grinder  100 . The pivoting mechanism is also attached to a pivot arm  2270  that permits the second handle  105  to be rotated from the right side of the grinder  2260  to the left side of the grinder  2260  about a pivot axis  2275 . The grinder  2260  includes a channel  2280  for receiving the pivot arm  2270  on either side of the grinder  2260 . Once the second handle  105  is rotated to either side of the grinder, the pivot arm  2270  can be secured in place (e.g., by a button and a retention mechanism, a lever, etc.) to secure the pivot arm  2270  in place. 
       FIG.  22 F  illustrates the embodiment  2260  of the grinder  100  with the second handle  105  pivoted to be directly adjacent to the grinder at a 0-degree angle in a fold-away position. By pivoting the second handle  105  to be adjacent to the grinder  100 , it allows for a more compact and efficient method of storage. In some embodiments, the fold-away position prevents an opportunity for damage to occur to the second handle  105  when the second handle  105  is secured against the main tool housing  120 . The second handle  105  could be similarly stowed on the left side of the grinder  2260 . 
       FIGS.  23 A,  23 B, and  23 C  illustrate the grinder  100  including a guard presence lockout system. The grinder that includes the guard presence sensor  215  for detecting the presence of the guard  130  on the grinder  100 . In some embodiments, the guard presence sensor  215  is an electromechanical sensor (e.g., a pressure sensor) that is actuated when the guard  130  is coupled to the grinder  100  (e.g., a switch is closed when the guard  130  is attached to the grinder  100 ). In other embodiments, the guard presence sensor  215  is an optical sensor that, for example, detects light reflected off of the guard  130  to detect presence. In other embodiments, an inductive sensor, such as inductive sensor  400  illustrated in  FIGS.  23 B and  23 C  is used to detect the guard  130 . For example, the grinder  100  may only function if the inductive sensor  400  is at a certain distance from the guard  130 , depending on the material of the guard  130 . For example, the inductive sensor  400  must be within a minimum to maximum distance range to allow the grinder  100  to operate. In some embodiments, the inductive sensor  400  detects the inductive response of the metal blade  150  placed in proximity to the inductive sensor. In other embodiments, the guard presence sensor  215  detects the inductive response of the guard  130  based on material type (e.g., zinc, steel, zinc-plated steel, copper, aluminum, bronze, plastic with metal film, glass with metal film, etc.), material thickness, or material geometry. In some embodiments if the guard presence sensor  215  detects that the inductive response of the guard  130  is outside a desired range, the controller  300  will halt the operation of the grinder  100 . 
     In some embodiments, the smaller the distance from the guard presence sensor  215  and the guard  130  itself, the greater the detected inductance change will be. The reduced range between the guard presence sensor  215  and the guard  130  provides a more accurate reading of an inductance value, allowing for a more accurate reading. 
     In some embodiments, the grinder  100  detects the type of component connected to the grinder  100 . In this embodiment, the component is the guard  130 . The detection of the particular type of component connected to the grinder  100  is achieved using a sensor (e.g., an induction coil, a Hall effect sensor, an optical sensor, wireless communication, etc.) for detecting the type of component. For example, an induction coil detects if the guard  130  is coupled to the grinder  100  or if it is disconnected from the grinder  100 . In one embodiment, the induction coil and a reference coil are inputs to a differential switch, which returns a binary “yes/no” or “I/O” output. The coil and reference coil can be tuned such that metal guards are detected at varying distances from the sensor input. 
     As illustrated in  FIG.  23 B , the inductive sensor  2300  includes an inductor capacitor (“LC”) circuit formed by an inductor L and a capacitor C. The LC circuit is connected to an inductance-to-digital converter (“LDC”)  2305 , which is used to measure proximity to metal by detecting subtle changes in an alternating current (“AC”) magnetic field resulting from the interaction with a metal target  2315  (e.g., the metal guard). The LDC  2305  generates an AC magnetic field by supplying an AC current into the LC circuit. 
     If a conductive target is brought into the vicinity of the AC magnetic field, small circulating currents (i.e., eddy currents  2310 ), will be induced by the magnetic field onto the surface of the conductor (shown in  FIG.  23 C ). The eddy currents  2310  produce their own magnetic fields that oppose the magnetic field generated by the LC circuit. A resulting inductance shift is measured by the LDC  2305  and is used to provide information about the position of a metal target  2315  over a sensor coil (e.g., a distance to the metal target  2315 , whether the metal target  2315  is present or not, a characteristic of the metal target  2315 , etc.). In some embodiments, the inductor L is a spiral or coil inductor, as illustrated in  FIG.  23 C . In some embodiments, the LC circuit is located on a printed circuit board (“PCB”) that is positioned within housing of the grinder  100 , as illustrated in  FIG.  23 A . 
       FIG.  23 D  illustrates a method  2350  to detect the presence of the guard  130  and to ensure that the guard  130  is properly attached to the grinder  100 . When a user indicates an intention to use the grinder  100 , a current is sent through the coil (i.e., LC circuit in  FIG.  24 B ) (STEP  2355 ) to attempt to detect the presence of metal in proximity to the grinder  100 . The current through the coil generates a magnetic field (STEP  2360 ). As described above, if a metal object is in proximity to the inductive sensor  2300 , eddy currents  2310  will be induced in the metal object. These eddy currents  2310  generate their own magnetic field that opposes the magnetic field generated by the LC circuit. The magnetic field from the eddy currents  2310  causes a change in the inductance of the LC circuit. The LDC  2305  monitors for this change in inductance (STEP  2365 ). If no change in inductance is detected at STEP  2370 , the grinder  100  will continue to monitor for a change in inductance. If a change in inductance is detected at STEP  2370 , the LDC  2305  generates an output signal indicative of the change in inductance (STEP  2375 ). In some embodiments, the LDC  2305  continuously outputs an output signal related to the inductance of the LC circuit. A value associated with that continuous output signal then change when the inductance of the LC circuit changes. The output signal is then sent or provided to the controller  300  (STEP  2380 ). Based on the output signal from the LDC  2305 , the controller  300  then determines whether the guard  130  is present (STEP  2385 ). If the guard  130  is not present (e.g., no change in inductance or not a significant enough change in inductance), the controller  300  prevents the motor  305  and grinder  100  from operating (STEP  2390 ). If the guard  130  is determined to be present, the controller  300  allows operation of motor  305  and grinder  100  (STEP  2395 ). 
       FIG.  24    illustrates a method  2400  for the grinder  100  which includes an accessory  150  (e.g., a grinder wheel) that can be used to grind (e.g., cut) through a workpiece (STEP  2405 ). The grinder  100  is configured to detect when the grinder  100  has completed a cut through a workpiece. The grinder  100  includes a sensor (e.g., a current sensor) and is configured to monitor a parameter (e.g., motor current) of the grinder  100  (STEP  2410 ). In some embodiments, the parameter includes the motor current of the grinder  100 . For example, a high current can be indicative of the grinder being used to cut a workpiece. When the grinder cuts through the workpiece, the amount of current drawn by the motor  305  decreases. This decrease in current can be used to detect when cut through has occurred. In some embodiments, an additional sensor (e.g., a gyroscope) monitors a motion of the grinder  100  (STEP  2415 ). The grinder  100  detects a change in the parameter (e.g., motor current), such as a reduction in motor current or loading of the grinder  100  (STEP  2420 ). The controller  300  of the grinder  100  then compares the change in the parameter to a predetermined threshold (STEP  2425 ). If the detected parameter is greater than the predetermined threshold, the grinder continues to monitor the parameter. If the detected parameter falls to or below the predetermined threshold for the parameter, the grinder  100  determines whether the motion of the grinder  100  is greater than a motion threshold (STEP  2430 ). For example, the motion of the grinder below the motion threshold (e.g., a velocity, and acceleration, etc.) indicates a user may be slowly pulling the grinder  100  away from a workpiece. In such an instance, it may be undesirable to stop the motor  305 . If the motion of the grinder  100  is greater than the motion threshold, the motor  305  is stopped (e.g. braked) (STEP  2435 ). 
       FIG.  25    illustrates an embodiment  2500  of the grinder  100  which includes a fixed guard  2515 . The fixed guard  2515  is coupled to, for example, the main tool housing  120  of the grinder  100 , and is unable to be removed from the main tool housing  120  of the grinder  100  by a user. The fixed guard  2515  is used to protect a user or another object in the surrounding environment from the different accessory types that may be attached to the tool holder (e.g., a blade). In some embodiments, the fixed guard  2515  prevents a user from contacting the accessory. In some embodiments, the fixed guard  2515  provides protection against, for example, sparks. 
     In some embodiments, the fixed guard  2515  is permanently affixed to a gearcase  2505  including gearcase cover  2510  via a guard locking flange  2520 . The gearcase cover  2510  is an outer portion of the main tool housing  120  which protects the gearcase  2505 . Below both the gearcase cover  2510  and the gearcase  2505  are the fixed guard  2515  and the guard locking flange  2520 . 
       FIG.  26 A  illustrates an embodiment  2600  of the grinder  100  to attach the fixed guard  2515  to the gearcase cover  2510  via the guard locking flange  2520 . In some embodiments, a left handle thread and various torque driving features are used to attach the fixed guard  2615  to the gearcase cover  2510 . In other embodiments, the guard locking flange  2520  attaches the fixed guard  2515  to the gearcase cover  2510  via a press fit into the gearcase cover  2510 .  FIG.  26 B  illustrates an additional retention feature for securing the fixed guard  2515  to the gearcase cover  2510 . In some embodiments, a blind roll pin  2610  is inserted through the gearcase cover  2510  as well as the guard locking flange  2520  to further secure the gearcase cover  2510  and the guard locking flange  2520  together. In some embodiments, the blind roll pin  2610  is perpendicular to the output shaft  125  of the grinder  100 . 
       FIG.  27    illustrates a spindle locknut design  2700 . In some embodiments, the spindle locknut design  2700  includes a spacer  2745 . The spacer  2745  includes a reduced thickness relative to conventional designs of a spindle locknut assembly. This reduced thickness allows the spindle locknut design  2700  to position a ball bearing  2725  close to the blade  150  when it is secured to a spindle shaft  2705 . The ball bearing  2725  then supports the spindle shaft  2705  to reduce vibrations imparted to the spindle shaft  2705  by the blade  150  during a user&#39;s operation of the grinder  100 . In some embodiments, the ball bearing  2725  supporting the spindle shaft  2705  also protects the grinder  100 &#39;s components, allowing the grinder  100  to function for a longer period of time and reducing the chances that the grinder  100  will frequently require repairs. 
     The spindle locknut design  2700  further includes at least one disc spring  2730  positioned between the ball bearing  2725  and a spindle flange  2740  to bias the spacer  2745  into engagement with the ball bearing  2725 . In some embodiments, the spacer  2745  and the ball bearing  2725  are coupled due to the disc spring  2730  being positioned between the ball bearing  2725  and the spindle flange  2740 . Furthermore, another spacer  2715  is positioned between a bevel gear  2710  and the ball bearing  2725  to account for the ball bearing  2725  being positioned closer to an outboard end of the spindle shaft  2705 , the bevel gear  2710  being directly above the spacer  2715 . The spindle shaft  2705  is driven about a longitudinal axis by the bevel gear  2710 . In some embodiments, the spindle locknut design  2700  further includes a locking flange  2735 . The blade  150  is positioned between the spindle flange  2740  and the locking flange  2735 , and is secured to the spindle shaft  2705  by tightening the locking flange  2735  on the spindle shaft  2705  (e.g., using threads). The locking flange  2735  firmly secures spindle flange  2740  against the spacer  2745 , which ensures that the ball bearing  2725  fixed against the other spacer  2715  allowing the spacer  2715  to properly be positioned against the bevel gear  2710 . This embodiment reduces unnecessary and unwanted vibrations or movement that could cause damage to the components of the grinder  100  and allows for smoother operation of the grinder  100 . 
       FIG.  28    illustrates an embodiment for the main tool housing  120 . The main tool housing  120  includes a lanyard integration assembly. The lanyard integration assembly includes a lanyard interface  2800  affixed to or built into the surface of the main tool housing  120 . In some embodiments, the lanyard interface  2800  is located by the rear of the grinder  100 , directly above a battery pack interface  2805 . The lanyard interface  2800  includes a component (e.g., a loop, a hook, etc.) that is operable to attach a lanyard to the lanyard interface  2800 . By attaching a lanyard to the grinder  100 , the grinder  100  is less susceptible to dropping or damage because the lanyard can secure the grinder  100  to a user (e.g., a belt). 
       FIG.  29    illustrates an embodiment  2900  of a battery pack interface that includes battery pack isolation features. During operation, the grinder  100  may generate aggressive vibrational forces, so it is advantageous to isolate the vibrational forces within the grinder  100  so that the vibrational forces do not propagate to an attached battery pack. Excess vibrational forces exerted on the battery pack can limit the life cycle of the battery pack (e.g., loosen electrical connections, etc.). The battery pack interface  310  of the grinder  100  includes a plurality of front isolators  2905  (e.g., cylindrical isolators) and rear isolators  2910  (e.g., cylindrical isolators). The front isolators  2905  are positioned on a front end of the battery pack interface  310 , and the rear isolators  2910  are positioned on a rear end of the battery pack interface  310 . By having both the front isolators  2905  and the rear isolators  2910 , the battery pack experiences vibrational isolation on either side of the battery pack. The battery pack interface  310  further includes a rear ramp  2915 . The rear ramp  2915  is used to secure the battery pack to the battery pack interface  310  and press the battery pack against the isolators  2905 ,  2910 . 
       FIG.  30    illustrates an embodiment of the grinder  100  including the second handle  105  and a wireless communication system  3000 . The wireless communication system  3000  includes a wireless receiver  3005  within the main tool housing  120 . In some embodiments, the wireless receiver  3005  is part of the controller  300 . In some embodiments, the wireless receiver  3005  is separate from the controller  300 . The second handle  105  includes a wireless transmitter  3010 . The wireless transmitter is configured to wirelessly communicate with the wireless receiver  3005 . The wireless transmitter  3010  is electrically connected to the microswitch sensor  608  which is configured to mechanically contact the first over-mold portion  403 , as previously described. In some embodiments, when the microswitch sensor  608  detects the presence of a hand, the wireless transmitter  3010  transmits a signal to the wireless receiver  3005 . In this embodiment, the wireless transmitter  3010  and wireless receiver  3005  perform the same functions as the previously described second handle  105  without the need for a wired connection. In some embodiments, the second handle  105  includes a power source (e.g., a battery, a coin cell battery, etc.) for powering the transmitter  3010 . 
       FIG.  31    illustrates a method  3100  for the grinder  100 . In some embodiments, the method  3100  is referred to as cut-through breaking. For example, the method  3100  may include monitoring operation of the grinder  100  such that when the controller  300  detects that the accessory  150  has completed a cutting operation, the controller  300  stops driving the motor  210 . The method  3100  begins at step  3105 , where the grinder  100  is being operated by a user and the motor  210  is being driven. The method  3100  includes step  3110  where a parameter of the grinder  100  is monitored. For instance, in some embodiments, a current sensor monitors a current of the motor  305 . The current sensor generates data associated with the current of the motor  305 , and transmits the data to the controller  300 . If, at step  3115 , the motor parameter is less than a threshold value (e.g., motor current is less than a threshold value), the motor is stopped at step  3120  (e.g., indicating that cut-through has occurred). If the motor parameter is greater than or equal to the threshold, the controller  300  continues to monitor the motor parameter at step  3110 . 
     Thus, embodiments described herein provide, among other things, systems and methods for a grinder with enhanced sensing and component detection. Various features and advantages are set forth in the following claims.