Power tool having stamped brake resistor

Abstract

A system and method for braking a power tool using a stamped brake resistor. The power tool includes a motor, a trigger configured to be operated, and a brake switch coupled to the motor. A brake resistor assembly is selectively coupled to the motor via the brake switch and includes a stamped brake resistor. The stamped brake resistor includes a terminal portion and a resistive portion. The resistive portion includes a planar serpentine path. A controller including an electronic processor and memory is coupled to the trigger, motor, and brake switch and configured to control power delivered to the motor based on a position of the trigger, determine to brake the motor while the motor is operating, and actuate the brake switch in response to determining to brake the motor to connect the stamped brake resistor to the motor.

Description

[Technical field]

[0001] Related Applications This application claims the benefit of U.S. Provisional Patent Application No. 62 / 949,900, filed December 18, 2019, the entire contents of which are incorporated herein by reference.

[0002] SUMMARY OF THE DISCLOSURE The embodiments described herein relate to brake resistors. [Background technology]

[0003] In a permanent magnet brushless motor having a permanent magnet rotor and an associated stator with stator windings, the rotation of the rotor creates a variable magnetic field that induces a current in the windings of the stator. This current in turn generates a voltage in the stator windings, which is called the back EMF of the motor. Even when power is no longer supplied to the stator windings and the motor is no longer driven, the rotor continues to rotate for some time due to inertia during rotor deceleration. The rotor continues to rotate therefore continues to generate a back EMF, and in effect the motor becomes a generator. The back EMF also creates an opposing force that helps to decelerate the motor. However, if left unchecked, the back EMF can become excessive and damage components of the motor drive circuitry. To avoid excessive back EMF, a brake resistor can be used. The brake resistor is coupled to the stator windings during braking to dissipate the energy generated by the continuing to rotate rotor as heat.

[0004] Typically, barrel resistors with sufficient resistance to function as brake resistors are large, which may be undesirable in applications where space is limited. Additionally, dissipating heat from the brake resistor may require a large heat sink or other heat dissipation scheme, which is undesirable in applications where space is limited. Summary of the Invention [Means for solving the problem]

[0005] Some embodiments described herein provide power tools having stamped brake resistors, and methods of using the power tools. The stamped brake resistors may be coupled to one or more flat heat sinks to provide improved heat dissipation and a compact brake resistor assembly. Thus, in some embodiments, the power tools and methods of using the power tools described herein include improved braking and corresponding heat dissipation.

[0006] In some embodiments, a power tool is provided that includes a motor, a trigger configured to be operated, a brake switch coupled to the motor, and a brake resistor assembly. The brake resistor assembly is selectively connected to the motor via the brake switch and includes a stamped brake resistor, which includes a terminal portion and a resistor portion. The resistor portion includes a flat serpentine path. The power tool further includes a controller including an electronic processor and a memory. The controller is connected to the trigger, the motor, and the brake switch. The controller is configured to control power delivered to the motor based on a position of the trigger, determine to brake the motor during operation of the motor, and actuate the brake switch in response to determining to brake the motor to connect the stamped brake resistor to the motor.

[0007] In some embodiments, the brake resistor assembly further includes a first insulating pad and a second insulating pad that sandwich the stamped brake resistor. In some embodiments, the brake resistor assembly further includes a first heat sink and a second heat sink that sandwich the first insulating pad and the second insulating pad.

[0008] In some embodiments, the resistive portion and the terminal portion are coplanar. In some embodiments, the resistive portion includes a first leg, a second leg perpendicular to the first leg, a third leg, and a fourth leg perpendicular to the third leg. In some embodiments, the first leg and the third leg are separated via an opening in the resistive portion. In some embodiments, the second leg and the fourth leg are connected via a planar serpentine path. In some embodiments, the stamped resistor further includes an interlocking gap. In some embodiments, the stamped resistor is comprised of at least one selected from the group consisting of zinc, aluminum, chromium, iron, brass, bronze, stainless steel, carbon, metal oxides, phenol formaldehyde resins, tantalum, cermets, and metal alloys.

[0009] In some embodiments, a method of braking a motor of a power tool is provided. The method includes controlling, by a motor controller of the power tool, power delivered to the motor based on a position of a trigger. The method includes determining, with the motor controller, to brake the motor while the motor is in operation. In response to determining to brake the motor, the method includes activating, with the motor controller, a brake switch and connecting a stamped brake resistor to the motor. The stamped brake resistor includes a terminal portion and a resistive portion, the resistive portion including a planar serpentine path. In response to the brake switch being activated, the method includes receiving a motor current from the motor using the stamped brake resistor, thereby braking the motor.

[0010] In some embodiments, the method includes determining, with the motor controller, to brake the motor in response to detecting the release of the trigger. In some embodiments, the motor current received by the brake resistor is a current derived from the back EMF of the motor. In some embodiments, the method includes selectively activating, with the motor controller, switching elements coupled to phases of the motor to control power delivered to the motor based on a position of the trigger. Additionally, in some embodiments, selectively activating power switching elements coupled to phases of the motor includes selectively activating the power switching elements based on a rotor position when the brake switch is activated. In some embodiments, the method includes opening, with the motor controller, a switch coupled between a power source and the power switching elements in response to determining to brake the motor.

[0011] In some embodiments, a braking system for a power tool is provided. The system includes a stamped resistor having a terminal portion and a resistive portion. The resistive portion includes a planar serpentine path that defines a plurality of leaves with gaps between each of the leaves. The system further includes first and second insulating pads that sandwich the stamped resistor, and first and second heat sinks that sandwich the first and second insulating pads.

[0012] In some embodiments, the terminal portion includes a terminal connected to a voltage source, the terminal being coplanar with the stamped resistor. In some embodiments, each leaf of the plurality of leaves has a width of about 2.5 mm, and each gap of the plurality of gaps has a width of at least 1.5 mm. In some embodiments, the stamped resistor further includes an interlocking gap. In some embodiments, the serpentine path includes a filler material disposed within each gap formed between adjacent leaves.

[0013] Before any embodiment of the invention is described in detail, it is to be understood that the invention is not limited in its application to the details of construction and arrangement of components set forth in the following description or illustrated in the drawings, as follows. The invention is capable of other embodiments and of being practiced or carried out in various ways. The use of "including" and variations thereof, as used herein, is meant to include the subsequently listed items and equivalents thereof as well as additional items. The use of "consisting of" and variations thereof, as used herein, is meant to include only the subsequently listed items and equivalents thereof.

[0014] Also, functions described herein as being performed by one component may be performed in a distributed manner by multiple components. Similarly, functions performed by multiple components may be performed collectively by one component. Similarly, components described as performing a particular function may also perform other functions not described herein. For example, a device or structure "configured" in a particular way is configured in at least that way, but may also be configured in ways not recited.

[0015] Additionally, some embodiments described herein may include one or more electronic processors configured to perform the functions described herein by executing instructions stored on a non-transitory computer-readable medium. Similarly, embodiments described herein may be implemented as a non-transitory computer-readable medium having stored thereon instructions executable by one or more electronic processors to perform the functions described herein. As used herein, "non-transitory computer-readable medium" includes any computer-readable medium, but does not consist of a transitory propagating signal. Thus, non-transitory computer-readable medium may include, for example, a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a Read Only Memory (ROM), a Random Access Memory (RAM), a register memory, a processor cache, or any combination thereof.

[0016] Many of the modules and logical structures described herein may be implemented in software executable by a microprocessor or similar device, or in hardware using a variety of components including, for example, application specific integrated circuits ("ASICs"). Terms such as "controller" and "module" may include or refer to both hardware and / or software. Initial capitalization of terms conforms with common convention and aids in correlating the description with coding examples, equations, and / or drawings. However, no specific meaning is implied or should be inferred merely because capitalization is used. Thus, the claims should not be limited to specific examples or terms, or to any hardware or software implementations or combinations of software or hardware.

[0017] Other aspects of the embodiments will become apparent from the detailed description and accompanying drawings. [Brief description of the drawings]

[0018] [Figure 1]1 illustrates a power tool according to some embodiments. [Diagram 2] 2 illustrates a perspective view of the power tool shown in FIG. 1 with a housing top portion removed according to some embodiments. [Diagram 3] 3 illustrates an exploded view of the brake resistor assembly shown in FIG. 2 according to some embodiments. [Figure 4] 4 illustrates a partial side view of the brake resistor assembly shown in FIG. 3 according to some embodiments. [Figure 5A] 4 illustrates the stamped brake resistor shown in FIG. 3 according to some embodiments. [Figure 5B] 4 illustrates the stamped brake resistor shown in FIG. 3 according to some embodiments. [Figure 6] 2 illustrates a block diagram of the power tool shown in FIG. 1 according to some embodiments. [Figure 7] 2 illustrates a circuit diagram of the power tool shown in FIG. 1 according to some embodiments. [Figure 8] 2 shows a flowchart of a method that may be implemented by the power tool of FIG. 1 according to some embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] FIG. 1 shows an example of a power tool 100 with a battery pack 105. In the illustrated embodiment, the power tool 100 is a chop saw having a housing 110 with a handle 115. The housing 110 is coupled to a base 120, which includes a clamp 125 and a blade housing 130. The power tool 100 has a motor 630 (see FIG. 6) configured to rotate an arbor that holds a blade (not shown) in the blade housing 130. The rotating blade is configured to cut a workpiece secured by the clamp 125 on the base 120. Although the power tool 100 shown in FIG. 1 is a chop saw, the description applies to other power tools having motors, such as impact wrenches, AC grinders, hammer drills, impact hole saws, impact drivers, drills, reciprocating saws, nailers, staplers, and others. The description also applies to brushed and brushless motors and controls. In other words, in some embodiments, the power tool 100 includes a brushed motor instead of the brushless motor 630.

[0020] FIG. 2 shows a perspective view of the housing 110 with the housing top portion removed. The handle 115 of the housing 110 further includes a trigger 205. The trigger 205 is electronically coupled to an electronic processor (see FIG. 7). In operation, the trigger 205 is pulled to actuate the power tool 100 and rotate a motor 630 (see FIG. 6) of the power tool 100. Releasing the trigger 205 stops the flow of power to the motor 630, but the motor 630 may not immediately stop. The brake resistor assembly 200 (described in more detail below) is disposed in the top portion of the housing 110 and is coupled to a power switching network 700 and a brake switch 640 (see FIG. 7) via power terminals 215. In some embodiments, the power terminals 215 are coupled to the power switching network 700 and the brake switch 640 via terminal fasteners 225. In some embodiments, the power terminals 215 may be coupled to the electronic processor by a welding, fusion, or soldering process. The housing 110 is configured to receive the battery pack 105 (see FIG. 1) via a power interface 220.

[0021] In some embodiments, the power interface 220 is similar to a power interface of a set of devices selected from two or more of the following: power tools, fluid flow control devices, test and measurement devices, work site radios, and work lights, and is therefore compatible with the power tool battery pack 105. The battery pack 105 includes a battery housing in which there are one or more battery cells, which may be lithium ion ("Li-ion") batteries, nickel cadmium ("Ni-Cad") batteries, or other chemistry batteries. Collectively, the batteries may provide different nominal voltages depending on the pack. For example, the nominal output voltage of the battery pack 105 may be 4V, 12V, 18V, 28V, 36V, 40V, voltages between multiple levels, or other levels. In some embodiments, the power interface 220 is an alternating current (AC) power interface and is configured to be connected to a standard AC outlet that is further coupled to an AC power grid or an AC generator. For example, the AC power source may include an approximately 120V, 60 Hz power signal or an approximately 240V, 50 Hz power signal. In other words, in some embodiments, the power tool 100 includes an AC power cord that receives AC power (e.g., from a wall outlet) to drive the motor 630, rather than a battery interface for receiving a battery pack 105 that provides DC power.

[0022] 3 shows an exploded view of the brake resistor assembly 200. The brake resistor assembly 200 includes a stamped brake resistor 300, a first insulating pad 305a, a second insulating pad 305b, a first heat sink 310a, a second heat sink 310b, a number of fasteners 315, and a number of insulating sleeves 318. In the illustrated example, the stamped brake resistor 300, the first insulating pad 305a, the second insulating pad 305b, the first heat sink 310a, and the second heat sink 310b include four holes 320, one at each of the outer corners. The holes 320 at each respective corner are aligned such that a passage 325 is formed at each corner when the stamped brake resistor 300, the insulating pads 305a,b, and the heat sinks 310a,b are stacked (see, for example, FIG. 4). Each of the fasteners 315 passes through a respective aligned hole 320 (i.e., through one of the passages 325) in the stamped brake resistor 300, the insulating pads 305a,b, and the heat sink 310a,b to secure these elements together and attach the brake resistor assembly 200 to the power tool 100. In some embodiments, each of the passages 325 also receives one of the insulating sleeves 318. More specifically, as shown in FIG. 4 , each of the fasteners 315 passes through one of the passages 325 and one of the insulating sleeves 318 to engage a threaded hole 405 in the housing 110 of the power tool 100 and attach the brake resistor assembly 200 to the power tool 100. The insulating sleeve 318 restricts the current flowing through the stamped brake resistor 300 from entering the fasteners 315. Although the stamped brake resistor 300, the insulating pads 305a,b, and the heat sinks 310a,b are each depicted as including four holes 320, in some embodiments they may be provided with more or fewer holes 320, the holes 320 may be located in locations other than the corners, or a combination thereof.

[0023] When assembled, as shown in FIG. 4, the stamped brake resistor 300 is sandwiched between the first insulating pad 305a and the second insulating pad 305b, and the set of the first insulating pad 305a, the stamped brake resistor 300, and the second insulating pad 305b is sandwiched between the first heat sink 310a and the second heat sink 310b. As a result, the first insulating pad 305a is positioned on a first side of the stamped brake resistor 300, and the second insulating pad 305b is positioned on a second, opposite side of the stamped brake resistor 300. The planes formed by the first insulating pad 305a and the second insulating pad 305b are substantially parallel to each other. The first heat sink 310a is positioned on a first side of the first insulating pad 305a, and the second heat sink 310b is positioned on a second side of the second insulating pad 305b. The planes formed by the first heat sink 310a and the second heat sink 310b are substantially parallel to each other. Although Figure 4 illustrates a cross section of one corner of the brake resistor assembly 200, other corners of the brake resistor assembly 200 may include a similar configuration.

[0024] 3, each of the stamped brake resistor 300, the first insulating pad 305a, the second insulating pad 305b, the first heat sink 310a, and the second heat sink 310b includes one or more generally planar engagement surfaces 330 (individually designated 330a-j) that engage with an adjacent one of the engagement surfaces 330 of another one of the stamped brake resistor 300, the first insulating pad 305a, the second insulating pad 305b, the first heat sink 310a, and the second heat sink 310b. For example, the stamped brake resistor 300 includes engagement surface 330a that engages engagement surface 330c of the first insulating pad 305a, and the first heat sink 310a includes engagement surface 330e that engages engagement surface 330d of the first insulating pad 305a. Additionally, engagement surface 330a faces away from engagement surface 330b, engagement surface 330c faces away from engagement surface 330d, and engagement surface 330f faces away from engagement surface 330g. Further, first heat sink 310a includes outward facing surface 335a and second heat sink 310b includes outward facing surface 335b. Outward facing surface 335a faces away from engagement surface 330e, and outward facing surface 335b faces away from engagement surface 330h.

[0025] The insulating pads 305a,b are electrically insulating and limit the transfer of electrical current from the stamped brake resistor 300 to the heat sinks 310a,b. In some embodiments, the insulating pads 305a,b are made of a material that is also thermally conductive and transfers heat generated in the stamped brake resistor 300 to the heat sinks 310a,b, respectively. The heat sinks 310a,b dissipate the heat generated by the stamped brake resistor 300 away from the stamped brake resistor 300 and into the ambient environment within the housing 110. In some embodiments, the housing 110 further includes one or more vents into the ambient environment surrounding the power tool 100, such that heat dissipated by the heat sinks 310a,b is at least partially dissipated into the ambient environment surrounding the power tool 100 via the one or more vents.

[0026] In some embodiments, the stamped brake resistor 300 is made of zinc. In some embodiments, the stamped brake resistor 300 is made of other conductive materials, such as carbon, metal oxides, phenol formaldehyde resins, tantalum, cermets, metal alloys containing elements such as aluminum, copper, nickel, chromium, and / or iron, brass, bronze, stainless steel, or others. In some embodiments, the insulating pads 305a,b are made of silicon. In some embodiments, the insulating pads 305a,b are made of other insulating materials, such as glass, paper, Teflon, or porcelain.

[0027] 5A shows a perspective view of stamped brake resistor 300. Stamped brake resistor 300 includes a resistor portion 500 and a terminal portion 530. Resistor portion 500 includes a first leg 505, a second leg 510, a third leg 515, and a fourth leg 520. First leg 505 is coupled to terminal portion 530 at a first end and to second leg 510 at a second end, with first leg 505 being substantially perpendicular to second leg 510. Third leg 515 is coupled to terminal portion 530 at a first end and to fourth leg 520 at a second end, with third leg 515 being substantially perpendicular to fourth leg 520. First leg 505 and third leg 515 are separated by gap 540 in terminal portion 530.

[0028] The second leg 510 and the fourth leg 520 extend substantially parallel to each other and in opposite directions from the end of the stamped brake resistor 300 having the first leg 505 and the third leg 510. The second leg 510 has a first end connected to the first leg 505 and a second end coupled to a first end 525a of the planar serpentine path 525. The fourth leg 520 has a first end connected to the third leg 515 and a second end coupled to a second end 525b of the planar serpentine path 525.

[0029] The second leg 510 and the fourth leg 520 are connected via a flat serpentine path 525. In some embodiments, the flat serpentine path 525 is a flat, bent path that repeats multiple times. For example, as shown, the flat serpentine path 525 includes a plurality of leaves 526 and defines a plurality of gaps 527. Each leaf 526 includes a first member 528a that extends substantially parallel to a second member 528b, and the first and second members 528a,b are separated by one of the plurality of gaps 527 at one end 529a and joined at a bend point at the second end 529b. In the illustrated embodiment, the flat serpentine path 525 includes eight leaves 526, although in some embodiments, more or fewer leaves 526 are included in the flat serpentine path 525.

[0030] For clarity in the figures, only some of the leaves 526, gaps 527, members 528a,b, and ends 529a,b are labeled along the flat serpentine path 525. In some embodiments, the width of each leaf 526 of the flat serpentine path 525 is at least 2.5 mm. In some embodiments, the width of each gap of the plurality of gaps 527 is at least 1.5 mm. In some embodiments, the width of each of the legs 510 and 520 considered individually is greater than the width of each of the leaves 526 considered individually, but collectively, the width of the leaves 526 (i.e., the width of the flat serpentine path 525) is greater than the width of the legs 510 and 520 considered individually or collectively. In addition, the width of the gap 527 considered individually is less than the width of the leaves 526 considered individually and less than the width of the members 528a,b considered individually.

[0031] 5A, the boundaries of the planar serpentine path 525 are defined by the first leg 505, the second leg 510, the third leg 515, and the fourth leg 520. In some embodiments, the members 528a,b bend and then extend beyond the end of the stamped brake resistor 300 opposite the terminal portion 530 (i.e., the end where the planar serpentine path 525 joins the second leg 510 and the fourth leg 520). In other words, the second leg 510 and the fourth leg 520 extend distally as far as or farther than the members 528a,b of the leaf 526.

[0032] In some embodiments, the tortuous path, i.e., the planar serpentine path 525, includes a filler material disposed within each gap 527. For example, without the filler material, the leaves 526 may begin to deform from the desired shape over time or during construction of the stamped brake resistor 300. A polymethylmethacrylate (PMMA) filler material may be disposed within each gap 527 formed between each leaf 526 to maintain the correct shape of the stamped brake resistor 300. In addition, the stamped brake resistor 300 may include a number of interlocking gaps 550a-f, as shown in FIG. 5B, to help secure the stamped brake resistor 300 during processing. For example, the interlocking gaps 550a-g may engage corresponding features on a die, thereby maintaining the stamped brake resistor 300 while PMMA filler is injected into the die to fill the gaps 527.

[0033] The terminal portion 530 includes a first terminal 535a and a second terminal 535b that are configured to connect the stamped brake resistor 300 to the power terminal 215 (see FIGS. 2 and 7). The first terminal 535a and the second terminal 535b are separated by a gap 540. In some embodiments, the resistor portion 500 lies in a first plane. As shown in FIG. 5A, the terminal portion 530 can include a bent portion whereby the terminal portion 530 is bent such that the first terminal 535a and the second terminal 535b lie in a second plane that is a parallel plane different from the first plane. In other embodiments, the terminal portion 530 can be coplanar with the resistor portion 500 (e.g., the terminal portion 530 is flat with respect to the resistor portion 500), as shown in FIG. 5B.

[0034] 6 is a block diagram of the example power tool 100 of FIG. 1. The system 600 of the power tool 100 includes a power interface 605, field effect transistors (FETs) 620, a motor 630, an output unit 635, Hall sensors 625, a motor controller 615, a user input 610, a brake switch 640, and other components 650 (such as a battery pack fuel gauge, task lights (LEDs), current / voltage sensors, etc.). The power interface 605 may be, for example, the power interface 220 of FIG. 2. The motor controller 615 may also be referred to as an electronic motor controller or a motor microcontroller and includes an electronic processor and memory, etc. In some embodiments, the memory stores instructions that are executed by the electronic processor to perform the functions of the motor controller 615 described herein.

[0035] The Hall sensors 625 provide motor information feedback, such as motor rotational position information, that the motor controller 615 can use to determine the position, speed, and / or acceleration of the motor. The motor controller 615 receives user control from a user input 610, such as by pressing the trigger 205 or moving a forward / reverse switch of the power tool 100. In response to the motor information feedback and the user control, the motor controller 615 transmits control signals (e.g., pulse width modulated signals) to control the FETs 620 to drive the motor 630. For example, by periodically enabling and disabling the FETs 620, power from the power interface 605 is selectively applied to the stator windings of the motor 630 to rotate a rotor of the motor 630. The rotation of the rotor of the motor 630 drives the output unit 635. Upon receiving an instruction from a user input 610 to stop the motor 630, such as pressing the trigger 205, the electronic processor of the motor controller 615 may actuate a brake switch 640 to enable a braking mechanism of the motor 630. Although not shown, the motor controller 615 and other components of the power tool 100 are electrically coupled to the power interface 605 and receive power therefrom. The FETs 620 may also be referred to as power switching elements. The FETs 620, the motor 630, the Hall sensors 625, the motor controller 615, and the output unit 635 may be referred to as electromechanical components 660 of the power tool 100.

[0036] FIG. 7 illustrates a power switching network 700 of an electromechanical component 660. In the illustrated embodiment, the motor 630 is a brushless DC motor including three phases. For example, the motor 630 may include an outer stator with six stator windings arranged in three phases, and an inner rotor with four permanent magnets. However, in other embodiments, different types of motors may be used, such as those having different numbers of phases, windings, and magnets. As shown in FIG. 7, the power switching network 700 includes three high-side electronic switches 712, 716, 720 and three low-side electronic switches 710, 714, 718, which are examples of the FETs 620 shown in FIG. 6. In the illustrated embodiment, the electronic switches 710-720 include MOSFETs. In other embodiments, other types of electronic switches may be used, such as bipolar junction transistors (BJTs), insulated gate bipolar transistors (IGBTs), and other types of electronic switches. Additionally, each of the electronic switches 710-720 is connected in parallel with a body diode 730, 732, 734, 736, 738, 740, respectively. In the circuit diagram of FIG. 7, each phase of the motor 630 is represented by an inductor, a resistor, and a voltage source. Because the motor 630 is a three-phase motor, FIG. 7 shows three inductors 704a-c, three resistors 706a-c, and three voltage sources 702a-c. Each of the inductors 704a-c represents a motor winding for each phase of the motor 630. Each of the resistors 706a-c represents a motor winding for each phase of the motor 630. Each of the voltage sources 702a-c represents a back electromagnetic force (i.e., back electromotive force [EMF]) generated by each phase. The back EMF is generated by the rotor magnets rotating and inducing current in the stator windings. In addition, the power switching network 700 includes a brake switch 640 connected in series with the stamped brake resistor 300. The brake switch 640 and the stamped brake resistor 300 are connected in parallel with a first phase 750, a second phase 752, and a third phase 754 of the brushless DC motor 630.

[0037] The power switching network 700 receives power from a power interface 605. In the illustrated embodiment, the power interface 605 receives power from a battery pack 105. The battery pack 105 is represented by a power source 701 connected in series with a resistor 722 and an inductor 724, which represent the internal resistance and inductance of the power interface 605, the battery pack 105, or both. Additionally, the power source 701 is connected in series with a parallel combination of a diode 726 and a switch 727. The diode 726 and the switch 727 control the flow of current from the power source 701. For example, the switch 727 can be switched between a conductive state and a non-conductive state. The switch 727 can be controlled based on the trigger 205. For example, in some embodiments, the electronic processor of the motor controller 615 controls the state of the switch 727 based on the state of the trigger 205. For example, in some embodiments, the switch 727 is closed by the motor controller 615 when the trigger 205 is pressed, and the switch 727 is opened when the trigger 205 is released. In some embodiments, the switch 727 and trigger 205 are electromechanical devices such that the switch 727 is closed by the trigger 205 when the trigger 205 is pressed (e.g., when a contact is rotated to establish an electrical connection) and the switch 727 is opened when the trigger 205 is released.

[0038] When switch 727 is in a conducting state, current can flow bidirectionally to and from power supply 701. However, when switch 727 is in a non-conducting state, current (e.g., regenerative current) can only flow to power supply 701 through diode 726. In some embodiments, diode 726 is not provided. Capacitor 728 is connected in parallel with power supply 701 as shown in FIG. 7. Capacitor 728 smoothes the voltage from (and to) power supply 701. Additionally, the electronic processor of motor controller 615 controls the state of each of electronic switches 710-720 in power switching network 700.

[0039] To drive the motor 630 forward, the electronic processor sets the switch 727 to a conductive state and activates the high-side electronic switch 712 and the low-side electronic switch 714. As shown in FIG. 7, the high-side electronic switch 712 is on a first side of the first phase 750 of the motor 630, and the low-side electronic switch 714 is on a second side of the first phase 750. In such a configuration, the first phase 750 of the motor 630 is connected such that the back EMF has an opposite polarity with respect to the power source 701. Thus, the electronic processor keeps the first high-side electronic switch 712 and the first low-side electronic switch 714 in a conductive state, but the back EMF is subtracted from the overall power provided to the motor 630. In other words, the motor current is set by dividing the difference between the voltage from the power source 701 and the back EMF by the resistance of the motor 630. That is, the motor current is set according to the following equation:

number

[0040] The electronic processor of the motor controller 615 determines which of the high-side electronic switches 712, 716, 720 and the low-side electronic switches 710, 714, 718 to energize based on the position of the rotor relative to the stator of the motor 630. In particular, actuating one pair of the high-side electronic switches 712, 716, 720 and the low-side electronic switches 710, 714, 718 once rotates the motor 630 approximately 120 degrees. After the motor 630 has rotated approximately 60 degrees, the electronic processor deactivates one pair of electronic switches and actuates another pair of electronic switches to energize another phase of the motor 630. In particular, the electronic processor actuates a first high-side electronic switch 712 and actuates a first low-side electronic switch 714 to drive the first phase 750 of the motor to advance. The electronic processor actuates a second high side electronic switch 716 and a second low side electronic switch 718 to drive a second phase 752 of the motor 630 to advance, and the electronic processor actuates a third high side electronic switch 720 and a third low side switch 710 to drive a third phase 754 of the motor 630 to advance. The switches 710-720 may be driven by the motor controller 615 using pulse width modulated (PWM) control signals. During each phase, the motor controller 615 can set the current (and thus the speed and torque) provided to the motor 630 by adjusting the duty cycle of the PWM control signal to one or both of the energized switches.

[0041] In the illustrated embodiment, the electronic processor of the motor controller 615 also performs electronic braking of the motor 630. FIG. 8 is a flow chart illustrating a method 800 for electronically braking the motor 630. In block 801, the motor controller 615 controls the motor 630 (e.g., delivers power to the motor 630) based on the position of the trigger 205. For example, referring to FIG. 6, a trigger signal is received via the user input 610, which indicates to the motor controller 615 that the trigger 205 has been pressed. In some embodiments, the trigger signal is binary, indicating whether the trigger 205 has been pressed or not. In some embodiments, rather than a binary indication of whether the trigger 205 has been pressed or not, a trigger sensor (e.g., an electrometer, hall sensor, or other) is provided as part of the user input 610 to indicate the amount the trigger has been pressed (e.g., 0-100%). In response to detecting that the trigger 205 has been pressed, the motor controller 615 drives the motor 630 by providing control signals to the switches 710-720, as described above with respect to FIG. 7.

[0042] In block 802, the motor controller 615 determines to brake the motor 630. For example, the motor controller 615 may detect that the trigger 205 has been released, may detect a fault in the system 600 of the power tool 100, may detect a low charge state of the battery pack 105 (e.g., using a voltage sensor that detects when the battery voltage drops to a level below a low voltage threshold), or otherwise.

[0043] In block 803, in response to determining to brake the motor 630, the motor controller 615 actuates the brake switch 640 to connect the stamped brake resistor 300 to the motor 630. As shown in FIG 7, the brake switch 640 is connected in series with the stamped brake resistor 300, and the series connection of the stamped brake resistor 300 and the brake switch 640 is connected to a power supply line that provides power to the high side switches 712, 716, and 720.

[0044] At block 804, the motor controller 615 selectively activates power switching elements (e.g., high side electronic switches 712, 716, 720 and low side electronic switches 710, 714, 718) based on the position of the rotor relative to the stator of the motor 630. In some embodiments, the motor controller 615 activates a pair of power switching elements (including one high side electronic switch and one low side electronic switch) that provides the lowest impedance path from the motor to the brake resistor 300 from the current position of the rotor of the motor 630. In other words, each possible pair of selectively actuable power switching elements has an impedance associated with it at a given moment in time, and the possible pair that provides the lowest impedance path is activated. For example, the motor controller 615 may operate high side electronic switch 712 and low side electronic switch 714 to provide a path from a first phase 750 when the rotor is in a first position, high side electronic switch 716 and low side electronic switch 718 to provide a path from a second phase 752 when the rotor is in a second position, and high side electronic switch 720 and low side electronic switch 710 to provide a path from a third phase 754 when the rotor is in a third position. In one example of a three-phase, six stator coil brushless motor, the selected pair of power switching elements operated by the motor controller 615 may be changed approximately every 60 degrees of motor rotation. Activation may be performed by the motor controller 615 providing a respective PWM signal to each of the power switching elements of the pair. In at least some embodiments, the expected impedance of a selectable pair of power switching elements for a given rotor position is known (e.g., from empirical testing), and the motor controller 615 has thereby mapped (in memory) various rotor positions for which pairs of power switching elements should be activated at a particular time to result in connecting the path with the lowest impedance. By providing the lowest impedance for the excitation phase, maximum motor current can flow from the excitation phase of the motor 630 to the stamped brake resistor 300.

[0045] At block 805, the stamped brake resistor 300 receives a motor current from the motor 630 in response to the brake switch 640 being actuated, thereby braking the motor 630. The motor current may be a current derived from the back EMF of the motor 630, for example.

[0046] In some embodiments, the power tool 100 loops back from block 805 to block 803 to actuate the brake switch 640 during braking of the motor to selectively conduct pairs of power switching elements to steer motor current to the stamped brake resistor 300. Thus, as the rotor rotates during braking, the motor controller 615 continues to selectively actuate the pair of power switching elements that provides the path of lowest impedance based on the rotor position. Thus, the selected pair of power switching elements changes as the rotor rotates during braking of the motor.

[0047] In some embodiments, such as with a brushed motor in power tool 100, block 804 may be omitted since there is no power switching element shown in FIG 7. For example, in some embodiments of tools having a brushed motor, one power switching element in series with the brushed motor is controlled by the motor controller via a PWM signal to regulate motor speed or torque. In such embodiments, this power switching element may be held closed (e.g., by a 100% duty cycle PWM signal) while brake switch 640 is closed in blocks 803 and 805.

[0048] In some embodiments, the motor controller 615 may be coupled to a solid state disconnect (SSD) PCB assembly (not shown). The SSD PCB assembly includes a solid state disconnect switch between the power interface 605 and the motor 630. The solid state disconnect switch may be semiconductor based and include, for example, a field effect transistor (FET). When the solid state disconnect switch is closed, the solid state disconnect switch allows current to flow from the power interface 605 to the motor 630, and when the solid state disconnect switch is open, the solid state disconnect switch prevents power from flowing to or from the power interface 605. In some embodiments, the motor controller 615 is configured to close the solid state disconnect switch in response to determining to drive the motor 630 (e.g., in block 801). In some embodiments, the motor controller 615 is configured to open the solid state disconnect switch in response to determining to brake the motor 630 (e.g., in block 803 prior to actuating the brake switch 640). By opening the solid-state disconnect switch in this manner, no current resulting from the motor's back EMF flows to the power interface 605 (e.g., power supply 701). In some embodiments, switch 727 in Figure 7 represents a solid-state disconnect switch.

[0049] In some embodiments, the motor controller 615 may be configured to deactivate the brake switch 640 in response to determining that the motor 630 has stopped rotating or has slowed below a low speed threshold. The electronic processor may determine that the motor 630 has stopped or slowed below a threshold based on motor position information from the Hall sensors 625. For example, each Hall sensor 625 may output a pulse when a rotor magnet of the motor 630 rotates across the face of the Hall sensor 625. Thus, the frequency of the pulses is proportional to and indicative of the rotational speed of the motor 630, and the absence of pulses for a particular length of time indicates that the motor 630 is not rotating.

[0050] Thus, the present disclosure provides systems and methods for braking a motor in a power tool.

Claims

1. A power tool, A motor; a trigger configured to be operated; A brake switch connected to the motor; a brake resistor assembly selectively connected to the motor via the brake switch, the brake resistor assembly including a stamped brake resistor, the stamped brake resistor including a terminal portion and a resistor portion, the resistor portion including a planar serpentine path forming a plurality of leaves and gaps between each leaf, the resistor portion including a first leg connected to the terminal portion, a second leg perpendicular to the first leg and connected to a first end of the planar serpentine path, a third leg connected to the terminal portion, and a fourth leg perpendicular to the third leg and connected to a second end of the planar serpentine path, the planar serpentine path including a filler material disposed within each gap formed between adjacent leaves, the filler material configured to retain a shape of the stamped brake resistor; a controller including an electronic processor and memory, the controller being connected to the trigger, the motor, and the brake switch, the controller comprising: controlling power delivered to the motor based on a position of the trigger; determining to brake the motor while the motor is in operation; in response to determining to brake the motor, actuating the brake switch to connect the stamped brake resistor to the motor. It is configured as follows: Power tools.

2. The power tool of claim 1 , wherein the brake resistor assembly further comprises first and second insulating pads sandwiching the stamped brake resistor.

3. The power tool of claim 2 , wherein the brake resistor assembly further comprises a first heat sink and a second heat sink sandwiching the first insulating pad and the second insulating pad.

4. The power tool of claim 1 , wherein the resistor portion and the terminal portion are coplanar.

5. The power tool of claim 1 , wherein the first leg and the third leg are separated by an opening in the resistor portion.

6. The power tool of claim 1 , wherein the second leg and the fourth leg are connected by the flat serpentine path.

7. The power tool of claim 1 , wherein the stamped brake resistor further comprises a meshing gap.

8. 10. The power tool of claim 1, wherein the stamped brake resistor is comprised of at least one selected from the group consisting of zinc, carbon, metal oxides, phenol formaldehyde resins, tantalum, cermets, and metal alloys.

9. A method for braking a motor of a power tool, comprising: controlling, with a motor controller of the power tool, power delivered to the motor based on a position of a trigger; determining, with the motor controller, to brake the motor while the motor is in operation; in response to determining to brake the motor, actuating a brake switch with the motor controller to connect a stamped brake resistor to the motor, the stamped brake resistor including a terminal portion and a resistor portion, the resistor portion including a planar serpentine path forming a plurality of leaves and gaps between each leaf, the resistor portion including a first leg connected to the terminal portion, a second leg perpendicular to the first leg, a third leg connected to the terminal portion, and a fourth leg perpendicular to the third leg, the planar serpentine path including a filler material disposed in each gap formed between adjacent leaves, the filler material configured to retain a shape of the stamped brake resistor; and in response to the brake switch being actuated, receiving a motor current from the motor with the stamped brake resistor, thereby braking the motor. method.

10. 10. The method of claim 9, further comprising: determining, with the motor controller, to brake the motor in response to detecting a release of the trigger.

11. 10. The method of claim 9, wherein the motor current received by the stamped brake resistor is a current derived from the back EMF of the motor.

12. 10. The method of claim 9, further comprising the step of selectively actuating, with the motor controller, power switching elements connected to phases of the motor to control power delivered to the motor based on a position of a trigger.

13. 13. The method of claim 12, wherein selectively activating the power switching elements connected to phases of the motor includes selectively activating the power switching elements based on a rotor position while the brake switch is activated.

14. 13. The method of claim 12, further comprising the step of opening a switch connected between a power source and the power switching element in response to determining, with the motor controller, to brake the motor.

15. 1. A braking system for a motor of a power tool, comprising: a stamped brake resistor selectively connected to the motor via a brake switch, the stamped brake resistor having a terminal portion and a resistor portion, the resistor portion including a planar serpentine path forming a plurality of leaves and gaps between each leaf, the resistor portion including a first leg connected to the terminal portion, a second leg perpendicular to the first leg, a third leg connected to the terminal portion, and a fourth leg perpendicular to the third leg, the planar serpentine path including a filler material disposed in each gap formed between adjacent leaves, the filler material configured to retain a shape of the stamped brake resistor; a first insulating pad and a second insulating pad sandwiching the stamped brake resistor; a first heat sink and a second heat sink sandwiching the first insulating pad and the second insulating pad, Braking system.

16. 16. The braking system of claim 15, wherein the terminal portion includes a terminal connected to a voltage source, the terminal being coplanar with the stamped brake resistor.

17. 16. The braking system of claim 15, wherein each leaf of the plurality of leaves has a width of approximately 2.5 millimeters and each gap of the plurality of gaps has a width of at least 1.5 millimeters.

18. The braking system of claim 15 , wherein the stamped brake resistor further includes a meshing gap.

Images