Patent Publication Number: US-2023147317-A1

Title: Voltage-based braking methodology for a power tool

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 17/342,879, filed Jun. 9, 2021, which claims the benefit of U.S. Provisional Patent Application No. 63/037,731, filed Jun. 11, 2020, the entire content of each of which is hereby incorporated by reference. 
    
    
     FIELD 
     Embodiments described herein provide systems and methods for braking a power tool based on a phase voltage of a motor. 
     SUMMARY 
     Power tools described herein include a motor and a power source configured to provide operating power to the motor. A power switching network is between the power source and the motor to drive the motor, the power switching network including a plurality of high side switching elements and a plurality of low side switching elements. An actuator is operable to provide an input. An electronic controller is connected to the actuator and the power switching network. The electronic controller is configured to receive, from the actuator, an indication related to initiating a braking operation of the motor, control the power switching network to allow the motor to coast, monitor a phase voltage of the motor, determine whether the phase voltage of the motor is equal to or less than a phase voltage threshold, and control, in response to determining the phase voltage of the motor is equal to or less than the phase voltage threshold, the power switching network to apply a braking force to the motor. 
     In some embodiments, controlling the power switching network to allow the motor to coast includes controlling the plurality of high side switching elements and the plurality of low side switching elements to a non-conductive state. In some embodiments, controlling the power switching network to apply the braking force to the motor includes controlling the plurality of low side switching elements to a conductive state. In some embodiments, the power tool further includes a position sensor configured to detect rotation of the motor. In some embodiments, the electronic controller is further configured to determine whether the motor has come to a stop, and control, in response to the motor being at a stopped, the plurality of low side switching elements to a non-conductive state. In some embodiments, the power switching network includes a plurality of pairs of high side switching elements and low side switching elements, and each pair of the plurality of pairs is connected by a phase node. In some embodiments, monitoring the phase voltage of the motor includes monitoring the phase voltage at each phase node. In some embodiments, monitoring the phase voltage of the motor includes monitoring the phase voltage at a single phase node. 
     Methods described herein for braking a motor in a power tool include receiving an indication at an electronic processor related to initiating a braking operation of the motor, controlling, with the electronic processor, a power switching network to allow the motor to coast, wherein the power switching network includes a plurality of high side switching elements and a plurality of low side switching elements, monitoring, with the electronic processor, a phase voltage of the motor, determining, with the electronic processor, that the phase voltage of the motor is equal to or less than a phase voltage threshold, and controlling, in response to determining that the phase voltage of the motor is equal to or less than the phase voltage threshold, the power switching network to apply a braking force to the motor. 
     In some embodiments, controlling, with the electronic processor, the power switching network to apply the braking force to the motor includes providing the braking force to the motor until the motor comes to a complete stop. In some embodiments, controlling, with the electronic processor, the power switching network to allow the motor to coast includes controlling the plurality of high side switching elements and the plurality of low side switching elements to a non-conductive state. In some embodiments, controlling the power switching network to apply the braking force to the motor includes controlling the plurality of low side switching elements to a conductive state. In some embodiments, the power switching network includes a plurality of pairs of high side switching elements and low side switching elements, and each pair of the plurality of pairs is connected by a phase node. In some embodiments, monitoring the phase voltage of the motor includes monitoring the phase voltage at each phase node. In some embodiments, monitoring the phase voltage of the motor includes monitoring the phase voltage at a single node. 
     Another power tool described herein includes a motor and a power source configured to provide operating power to the motor. A power switching network is between the power source and the motor for driving the motor, the power switching network including a plurality of high side switching elements and a plurality of low side switching elements. An actuator is operable to provide an input. An electronic controller is connected to the actuator and the power switching network. The electronic controller is configured to receive, from the actuator, an indication related to initiating a braking operation of the motor, monitor a phase voltage of the motor, and compare the phase voltage of the motor to a phase voltage threshold. The electronic controller is configured to control, in response to the phase voltage of the motor being greater than or equal to the phase voltage threshold, the power switching network to allow the motor to coast. The electronic controller is configured to control, in response to the phase voltage of the motor being less than the phase voltage threshold, the power switching network to apply a braking force to the motor. 
     In some embodiments, controlling the power switching network to allow the motor to coast includes controlling the plurality of high side switching elements and the plurality of low side switching elements to a non-conductive state. In some embodiments, controlling the power switching network to apply the braking force to the motor includes controlling the plurality of low side switching elements to a conductive state. In some embodiments, the power tool further includes a position sensor configured to detect rotation of the motor. In some embodiments, the electronic controller is further configured to determine whether the motor has come to a stop, and control, in response to the motor being stopped, the plurality of low side switching elements to a non-conductive state. In some embodiments, the indication related to initiating braking of the motor is a transition of the actuator from a pulled position to a released position. In some embodiments, the power tool further includes a forward-reverse selector, and wherein, when the motor is driven in reverse, controlling the power switching network to apply the braking force to the motor includes controlling the plurality of high side switching elements to a conductive state. 
     Before any embodiments are explained in detail, it is to be understood that the embodiments are not limited in its 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 embodiments, 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” and “computing devices” 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. 
     Other features and aspects will become apparent by consideration of the following detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS.  1 A- 1 B  are perspective views of a power tool in accordance with embodiments described herein. 
         FIG.  1 C  is a cross-sectional view of the power tool of  FIGS.  1 A- 1 B  in accordance with embodiments described herein. 
         FIG.  2    illustrates a block circuit diagram for a controller of the power tool of  FIGS.  1 A- 1 C  in accordance with embodiments described herein. 
         FIG.  3    illustrates a block diagram of a power switching network and a braking circuit of the power tool of  FIGS.  1 A- 1 C  in accordance with embodiments described herein. 
         FIG.  4    illustrates a block diagram of a method performed by the controller of  FIG.  2    in accordance with an embodiment described herein. 
         FIG.  5    illustrates a graph of the method of  FIG.  4    in accordance with embodiments described herein. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS.  1 A- 1 C  illustrate a portable power tool  100 . One example of the power tool  100  is an angle grinder, as shown in  FIGS.  1 A- 1 C . The power tool  100  may include a motor housing  112  and a handle  114  that extends transversely from the motor housing  112 . The motor housing  112  extends along a first axis  116  (e.g., a motor axis), and the handle  114  extends along a second axis  118  that is transverse to the first axis  116 . A motor  110  (see  FIG.  1 C ) is located within the motor housing  112 . The first axis  116  is defined by a rotor shaft of the motor  110 , which extends longitudinally through the motor housing  112 . In some embodiments, the power tool  100  is an inline grinder, rather than an angle grinder, wherein the first axis  116  of the motor housing  112  is generally parallel or coaxial with the second axis  118  of the handle  114 . 
     The motor  110  also includes a rotor and a stator that surrounds the rotor. In some embodiments, the motor  110  is a brushless direct current (DC) motor in which the rotor is a permanent magnet motor and the stator includes coil windings that are selectively energized to drive the rotor. In other embodiments, the motor  110  is a brushed motor. The stator is supported within the motor housing  112  and remains stationary relative to the motor housing  112  during operation of the power tool  100 . The rotor is rotatably fixed to a rotor shaft and configured to co-rotate with the rotor shaft, relative to the stator, about the first axis  116 . A portion of the rotor shaft defines an output shaft  130  extending from the motor housing  112 . The output shaft  130  is coupleable to a tool holder (not shown) that may be configured to receive an accessory, 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, an accessory 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 power tool  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 torque depending on the characteristics of the accessory and the task at hand. During operation of the power tool  100 , the rotor shaft, and thus the output shaft  130 , may rotate at speeds above 20,000 rpm (e.g., 24,500 rpm). 
     In some embodiments, the handle  114  includes a power supply  150  (see  FIG.  1 B ). For example, the handle  114  may define a battery receptacle  154 , which is positioned on an end of the handle  114  opposite the motor housing  112 . The battery receptacle  154  is configured to selectively, mechanically, and electrically connect to the power supply  150  (e.g., a rechargeable battery pack  150 ) for powering the motor  110 . The battery pack  150  is insertable into the battery receptacle  154  such that, when inserted, the battery pack  150  is oriented along the second axis  118 . Alternatively, in another embodiment of the power tool  100 , the battery pack  150  may be slidably coupled to a battery receptacle  154  along an axis that is transverse to the second axis  118 . The battery pack  150  may include any of a number of different nominal voltages (e.g., 12V, 18V, etc.) and may be configured having any of a number of different chemistries (e.g., lithium-ion, nickel-cadmium, etc.). In alternative embodiments (not shown), the motor  110  may be powered by a remote power supply  150  (e.g., a household electrical outlet) through a power cord and a power interface  300  (as shown in  FIG.  3   ) of the power tool  100 . The handle  114  further contains control electronics  156  for the power tool  100 , which include controller  200  (see  FIG.  2   ). 
     The handle  114  supports a trigger or trigger assembly  160  (e.g., an actuator) operable to selectively electrically connect the power source  150  (e.g., the battery pack  150 ) and the motor  110 . The trigger assembly  160  may be a “lock-off” trigger assembly having a paddle member  162  and a lock-off member  164  supported by the paddle member  162 . The paddle member  162  is operable to actuate a trigger switch  158  (e.g., a microswitch) to selectively activate and deactivate the motor  110  during operation of the power tool  100 . The lock-off member  164  selectively prevents operation of the paddle member  162 . Specifically, the lock-off member  164  is pivotable to selectively lock and unlock the paddle member  162 . The speed of the motor  110  may be controlled by varying the level of depression of the paddle member  162 . 
     In some embodiments, the power tool  100  includes a vibration damping assembly  166  positioned between the motor housing  112  and the handle  114  to attenuate vibration from the motor housing  112 . The damping assembly may include a first coupling portion defined by the motor housing  112 , a second coupling portion defined by the handle  114 , and an elastomeric damper positioned between the first and second coupling portions. 
     The controller  200  for the power tool  100  is illustrated in  FIG.  2   . The controller  200  is electrically and/or communicatively connected to a variety of modules or components of the power tool  100 . For example, the illustrated controller  200  is connected to indicator(s)  245 , sensors  450  (which may include, for example, a speed sensor, a current sensor, a voltage sensor, a position sensor, etc.), the trigger  160  (via the trigger switch  158 ), a power switching network  255 , and a power input unit  260 . 
     The controller  200  includes a plurality of electrical and electronic components that provide power, operational control, and protection to the components and modules within the controller  200  and/or power tool  100 . For example, the controller  200  includes, among other things, a processing unit  205  (e.g., a microprocessor, an electronic processor, an electronic controller, a microcontroller, or another suitable programmable device), a memory  225 , input units  230 , and output units  235 . The processing unit  205  includes, among other things, a control unit  210 , an arithmetic logic unit (“ALU”)  215 , and a plurality of registers  220  (shown as a group of registers in  FIG.  2   ), and is implemented using a known computer architecture (e.g., a modified Harvard architecture, a von Neumann architecture, etc.). The processing unit  205 , the memory  225 , the input units  230 , and the output units  235 , as well as the various modules connected to the controller  200  are connected by one or more control and/or data buses (e.g., common bus  240 ). The control and/or data buses are shown generally in  FIG.  2    for illustrative purposes. The use of one or more control and/or data buses for the interconnection between and communication among the various modules and components would be known to a person skilled in the art in view of the embodiments described herein. 
     The memory  225  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  205  is connected to the memory  225  and executes software instruction that are capable of being stored in a RAM of the memory  225  (e.g., during execution), a ROM of the memory  225  (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 power tool  100  can be stored in the memory  225  of the controller  200 . 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  200  is configured to retrieve from the memory  225  and execute, among other things, instructions related to the control processes and methods described herein. In other embodiments, the controller  200  includes additional, fewer, or different components. 
     In some embodiments, as described above, the power tool  100  is an angle grinder. The controller  200  drives the motor  110  to rotate the output shaft  130  in response to a user&#39;s actuation of the trigger  160 . Depression of the trigger  160  actuates a trigger switch  158 , which outputs a signal to the controller  200  to drive the output shaft  130 . The controller  200  controls a power switching network  255  (e.g., a FET switching bridge) to drive the motor  110 . When the trigger  160  is released, the trigger switch  158  no longer outputs the actuation signal (or outputs a released signal) to the controller  200 . As detailed below with respect to  FIG.  4   , when the trigger  160  is released, the controller  200  controls the power switching network  255  to brake the motor  110  by allowing the motor  110  to freely coast prior to applying a braking force. 
     The indicators  245  are also connected to the controller  200  and receive control signals from the controller  200  to turn on and off or otherwise convey information based on different states of the power tool  100 . The indicators  245  include, for example, one or more light-emitting diodes (LEDs), or a display screen. The indicators  245  can be configured to display conditions of, or information associated with, the power tool  100 . For example, the indicators  245  can display information relating to the charging state of the power tool  100 , such as the charging capacity. The indicators  245  may also display information relating to a fault condition, or other abnormality, of the power tool  100 . In addition to or in place of visual indicators, the indicators  245  may also include a speaker or a tactile feedback mechanism to convey information to a user through audible or tactile outputs. 
     The battery pack interface  265  is connected to the controller  200  and is configured to couple to a battery pack  150  (e.g., using the battery receptacle  154 ). The battery pack interface  265  includes a combination of mechanical (e.g., a battery pack receiving portion) and electrical components configured to and operable for interfacing (e.g., mechanically, electrically, and communicatively connecting) the power tool  100  with the battery pack  150 . The battery pack interface  265  is coupled to the power input unit  260 . The battery pack interface  265  transmits the power received from the battery pack  150  to the power input unit  260 . The power input unit  260  includes active and/or passive components (e.g., voltage step-down controllers, voltage converters, rectifiers, filters, etc.) to regulate or control the power received through the battery pack interface  265  and to the controller  200 . In some embodiments, the battery pack interface  265  is also coupled to the power switching network  255 . The operation of the power switching network  255 , as controlled by the controller  200 , determines how power is supplied to the motor  110 . 
       FIG.  3    illustrates a circuit diagram of the power switching network  255  according to some embodiments. The power switching network  255  includes a plurality of high side switching elements  310  (e.g., field effect transistors [FETs]) and a plurality of low side switching elements  315  (e.g., FETs). Each high side FET  310  and low side FET  315  pair is connected by a phase node  320 . The controller  200  provides the control signals to control the high side FETs  310  and the low side FETs  315  to drive the motor  110  based on user controls, as described above. For example, in response to detecting a pull of the trigger  160 , the controller  200  provides the control signals to selectively enable and disable the high side FETs  310  and the low side FETs  315  (e.g., sequentially, in pairs) resulting in power from the battery pack  150  to be selectively applied to stator coils of the motor  110  to cause rotation of a rotor. The rotor may be driven in a first direction (e.g., a clockwise direction) or a second direction (e.g., a counter-clockwise direction) based on an additional input, such as a forward/reverse selector. More particularly, to drive the motor  110 , the controller  200  enables a first high side FET  310  and a first low side FET  315  pair (e.g., by providing a voltage at a gate terminal of the FETs) for a first period of time. As the rotor of the motor  110  rotates, a position sensor may detect rotation of the motor  110 , such as detecting the position of a specific phase, causing the controller  200  to disable the first FET pair, and enable a second high side FET  310  and a second low side FET  315 . In response to detecting further rotation, the controller  200  disables the second FET pair and enables a third high side FET  310  and a third low side FET  315 . This sequence of cyclically enabling pairs of high side FET  310  and low side FET  315  repeats to drive the motor  110 . 
     In the example illustrated in  FIG.  3   , the power tool  100  includes a straight connect power interface  300 , or a connection between the battery pack  150  and the power switching network  255 . In some embodiments, the straight connect power interface  300  includes a mechanical on/off switch that is controlled by the trigger  160  of the power tool  100 . The mechanical switch may be, for example, a relay or a solid state drive switch coupled on the current path between the battery pack  150  and the power switching network  255 . The mechanical switch is used to enable or disable power from the battery pack  150  to the power switching network  255  and is controlled mechanically by the trigger  160 . In some embodiments, rather than using a mechanical switch mechanically controlled by the trigger  160 , the straight connect power interface  300  may include a power FET controlled by the controller  200  to selectively connect and disconnect the battery pack  150  to the power switching network  255  (e.g., based on a trigger pull). 
     To stop the motor  110 , the controller  200  controls the power switching network  255  to first allow the motor  110  to freely coast before applying a braking force. For example,  FIG.  4    is a flowchart of an example method  400  for braking the motor  110  of the power tool  100 . The method  400  may be performed by the controller  200 . At block  405 , the method  400  includes detecting, using the controller  200 , a trigger pull. When the trigger  160  is pulled (e.g., pressed, pushed, or the like), the controller  200  receives an input from the trigger switch  158  indicating that the trigger  160  is pulled. In some embodiments, a trigger sensor (e.g., a push button switch, a Hall effect sensor, a potentiometer, a force sensor, etc.) may detect depression of trigger  160  and output a signal indicative of the pull state (e.g., pulled or not pulled) to the controller  200 .  FIG.  5   , for example, illustrates a graph of the operation of controller  200 . At time t 0 , the controller  200  detects a pull (or actuation) of the trigger  160  (shown by value V 1 ). In some embodiments, the controller  200  receives an input indicating the distance to which the trigger  160  is pulled. The distance the trigger  160  is pulled may indicate a desired speed for variable speed control of the motor  110 . 
     At block  410 , the method  400  includes controlling, using the controller  200 , the power switching network  255  to drive the motor  110 . For example, as described above, the controller  200  selects high side FET  310  and low side FET  315  pairs to drive the motor  110 . At block  415 , the method  400  includes determining, with the controller  200 , whether the trigger  160  is released. If the trigger  160  is not released, the method  400  returns to block  410 . If the trigger  160  is released, the method  400  determines to initiate braking of the motor  110  and continues to block  420 . In some embodiments, when the trigger  160  is released, the controller  200  receives, from the trigger  160 , an indication to initiate braking of the motor  110 , such as a signal from the trigger switch  158 . For example,  FIG.  5    shows the trigger  160  being released at time t 1 . 
     At block  420 , the method  400  includes monitoring (or measuring), with the controller  200 , the phase voltage supplied to the motor  110 . For example, in  FIG.  5   , at time t 1 , the controller  200  measures a phase voltage of V 2  supplied to the motor  110 . The controller  200  may monitor the phase voltage at each phase node  320 . In some embodiments, the controller  200  measures only a single phase node  320  of the power switching network  255 . In other embodiments, the controller  200  measures the voltage of each phase node  320  (e.g., three phase nodes) of the power switching network  255 . In some embodiments, the controller  200  continuously monitors the phase voltage supplied to the motor  110 . For example, the controller  200  may monitor the phase voltage supplied to the motor  110  while the trigger  160  is pulled (at time t 0 ). 
     At block  425 , the method  400  includes comparing, in response to the trigger  160  being released, the measured phase voltage at the phase node  320  to a phase voltage threshold. For example, in  FIG.  5   , the trigger  160  is released at time t 1 . The phase voltage at time t 1  is V 2 , which is greater than the phase voltage threshold (V 0 ). If the phase voltage of the motor  110  is above the phase voltage threshold, the method  400  proceeds to block  430 . If the phase voltage of the motor  110  is below the phase voltage threshold, the method  400  proceeds to block  440 . 
     At block  430 , the method  400  includes controlling, with the controller  200 , the power switching network  255  to coast the motor  110 . For example, the controller  200  may control the high side FETs  310  and the low side FETs  315  to a non-conductive state such that no current is supplied to the motor  110 . While coasting, the motor  110  may experience a resistive force due to friction. For example, in  FIG.  5   , the phase voltage, which is related to the back emf generated by the motor  110  as it coasts, decreases between t 1  to t 2 . The reduction in phase voltage is associated with the speed of the motor  110  being reduced due to frictional forces. The phase voltage of the motor  110  is continuously compared to the phase threshold, as shown at block  435 . Accordingly, the controller  200  continues to allow the motor  110  to freely coast for the duration of time that the phase voltage of the motor  110  remains above the phase threshold. 
     If, at block  435 , the phase voltage of the motor  110  is equal to or below the phase threshold, the method  400  proceeds to block  440 , which includes controlling, with the controller  200 , the power switching network  255  to provide a braking force (e.g., a hard braking force) to the motor  110 . For example, if the motor  110  is rotating in the first direction (e.g., clockwise), the controller  200  may control the low side FETs  315  to a conductive state, providing a back-emf current to the motor  110 . The controller  200  may place the low side FETs  315  in the conductive state until the motor  110  comes to a stop, as detected by the position sensor. In some embodiments, if the motor  110  is rotating in the second direction (e.g., counter-clockwise), the controller  200  may control the high side FETs  310  to a conductive state.  FIG.  5   , for example, illustrates the controller  200  initiating the low side FETs  315  to a conductive state at time t 2 . The low side FETs  315  remain in the conductive state until time t 3 . During this time, the motor  110  brakes much more quickly than when the motor  110  was simply coasting, due to the provided braking force. 
     Once braking is complete, the controller  200  may place the low side FETs  315  (or the high side FETs  310 ) back in the non-conductive state. Should the trigger  160  be pulled again, the method  400  returns to block  405 . In some embodiments, the trigger  160  may be pulled while the controller  200  performs the braking action. For example, at block  430 , while the motor  110  is coasting, the controller  200  may receive an input indicative of a trigger pull. When the controller  200  receives the input, it returns to block  405 , and the method  400  starts over. Although block  430  is provided as an example, this may occur at any point during the method  400 . In some embodiments, the trigger  160  being pulled during coasting or hard braking is ignored by the controller  200  until the motor  110  has come to a complete stop. 
     Thus, embodiments provided herein describe, among other things, systems and methods for braking a power tool based on the phase voltage. Various features and advantages are set forth in the following claims.