Patent Document

FIELD 
     The present disclosure relates generally to handheld power tools and more specifically to a handheld grinder with a brushless electric motor. 
     BACKGROUND 
     Some power tools include brushless electric motors. Power tools with brushless electric motors use a rectifier to convert an alternating current (AC) input into a direct current (DC) that is used to drive the brushless electric motor. Power tools with brushless electric motors also employ a capacitor to lessen ripple and to provide a current when the AC input voltage is unable to do so. Most power tools also include a power switch that directly controls the flow of current through the brushless electric motor. The capacitor and the power switch generate undesirable heat. 
     Most power tools include several circuit boards that reside inside a housing of the power tool. The circuit boards are used to support the capacitor, the power switch and circuitry that is used for controlling the brushless motor. The circuit boards undesirably increase the volume of the power tool. The connections between the circuit boards are susceptible to wearing out or breaking. This makes the power tool less reliable. Therefore, there is a need for a power tool that has a smaller volume, generates less heat and is more reliable. 
     This section provides background information related to the present disclosure which is not necessarily prior art. 
     SUMMARY 
     A handheld grinder is presented. The handheld grinder comprises an elongated housing having a grip portion that is shaped to be grasped by a user; a grinding disk; an electric motor having a drive shaft; an output shaft having a one end connected to the grinding disk and an opposing end drivably connected to the drive shaft of the motor to impart rotary motion thereto; and a circuit board residing in the housing, the circuit board having thereon a rectifier configured to receive power from an alternating current (AC) power source and operable to convert an alternating current to a direct current, a switching arrangement having a plurality of motor switches connected electrically between the rectifier and the electric motor and operates to deliver the direct current from the rectifier to the electric motor, a capacitor connected electrically between the rectifier and the switching arrangement, wherein the capacitor is coupled in parallel across the rectifier, a driver circuit interfaced with the motor switches and operable to control switching operation of the motor switches, and a power switch connected electrically between the rectifier and the driver circuit and operable by a tool operator to selectively energize the driver circuit and thereby power on the grinder disk. 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG. 1  is an illustration depicting a perspective view of an example power tool; 
         FIG. 2  is an illustration depicting a cross-sectional view of the example power tool having an example circuit board residing therein; 
         FIG. 3  is an illustration depicting a perspective view of the example circuit board illustrated in  FIG. 2 ; 
         FIG. 4  is an illustration depicting a perspective view of the example power tool having another example circuit board residing therein; 
         FIG. 5  is an illustration depicting a perspective view of the circuit board illustrated in  FIG. 4 ; 
         FIG. 6  is an illustration depicting a plan view of the circuit board illustrated in  FIG. 4  and  FIG. 5 ; 
         FIG. 7  is an illustration depicting a perspective view of yet another example circuit board; 
         FIG. 8  is an illustration depicting a plan view of the circuit board illustrated in  FIG. 7 ; 
         FIG. 9  is an illustration depicting a plan view of a back surface of an example circuit board; and 
         FIG. 10  is a schematic depicting an example embodiment of a motor control system having a power on/off switch that is positioned between a driver power supply and a driver circuit. 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     Example embodiments will now be described more fully with reference to the accompanying drawings. 
       FIG. 1  depicts an example power tool  10 . In this example embodiment, the power tool  10  comprises a housing  12  having an elongated shape. A user can grasp the power tool  10  by placing the palm of the user&#39;s hand over and around the housing  12 . An output member  18  is positioned at one end  12 - 1  of the housing  12  and comprises a right angle gearset  20  that drives a rotating disk  22 . In this example embodiment, the rotating disk  22  comprises a grinder disk. 
     The rotating disk  22  may be removed and replaced with a new rotating disk. For example, a user of the power tool  10  may replace the existing rotating disk  22  with a new rotating disk after the existing rotating disk  22  wears out. 
     An adjustable guard  24  may cover at least a portion of the rotating disk  22  to obstruct sparks and debris generated during operation of the power tool  10 . 
     While the present description is provided with reference to a grinder, it is readily understood that the broader aspects of the present disclosure are applicable to other types of power tools, including but not limited to sander, drill, impact driver, tapper, fastener driver, and saw. For example, the power tool  10  may include a chuck that is configured to receive a drill bit or a screw driver bit, thereby allowing the power tool  10  to be used as a power drill or a power screw driver. In another example embodiment, the output member  18  may be removed and replaced with another output member that may be more suitable for a drill, a screw driver, or any other power tool. 
     The housing  12  has a first portion  14  and a second portion  16 . The first portion  14  and second portion  16  may be secured together with screws  26 , illustratively six, and enclose an electric motor  28  and electronic circuit components, as further described below, that drive the output member  18 . While the present description is provided with reference to a brushless electric motor, the electric motor  28  may be any type of electrical motor capable of driving the output member  18 . A power cord  30  is connectable to an AC power source and is positioned at an opposite end  12 - 2  of the housing  12 . The power cord  30  provides power to the electric motor  28  and the electronic circuit components of the power tool  10 . 
     The first portion  14  further includes a power on/off switch  32  and a spindle lock switch  34 . Putting the power on/off switch  32  in on and off positions turns on and turns off the electric motor  28 , respectively. Pressing and holding the spindle lock switch  34  enables the user to change the rotating disk  22 . A plurality of narrow slot openings  36  of the first  14  and second  16  portions allow for venting of the electric motor  28  and the electronic circuit components. The one end  12 - 1  of the housing  12  also includes a threaded opening  38  for selectively attaching a side-handle (not shown) to enable two-handed operation. 
       FIG. 2  depicts a cross sectional view of the power tool  10  with the first portion  14  of the housing  12  removed. The power tool  10  includes a circuit board  40  that resides inside the housing  12 . In this embodiment, the circuit board  40  is fastened to the second portion  16  of the housing  12  with screws  42 . Other fasteners are also contemplated, for example bolts, clips, ties, latches, pegs, snap fasteners, or the like. 
     In this example embodiment, the circuit board  40  has a longitudinal axis that is aligned with the longitudinal axis of the housing  12 . In this embodiment, the circuit board  40  is rectangular. However, other shapes of the circuit board  40  are also contemplated. For example, the circuit board  40  may be a square. Alternatively, the circuit board  40  may be circular and the circuit board  40  may be positioned such that a planar surface of the circuit board  40  is perpendicular to the longitudinal axis of the housing  12 . 
     A plurality of electronic circuit components of the power tool  10  are attached to the circuit board  40  and are configured to control the electric motor  28 . The electronic circuit components may be attached to the circuit board  40  by soldering the electronic circuit components on the circuit board  40 . 
     The circuit board  40  includes a rectifier  44 . The rectifier  44  receives an alternating current and converts the alternating current into a direct current. The rectifier  44  may be a commercially-available full-wave bridge rectifier. 
     In this embodiment, the circuit board  40  includes AC input solder points  48 . The AC input solder points  48  are soldered at an end of the circuit board  40  that is proximate to the end  12 - 2  of the housing  12 . Wires can be connected from the power cord  30  to the AC input solder points  48  to deliver the alternating current to the rectifier  44 . 
     The circuit board  40  may include a heat sink  46  for diffusing heat away from the rectifier  44 . In this example embodiment, the heat sink  46  is placed adjacent to the rectifier  44  and is abutting the rectifier  44 . 
     DC bus capacitors  50  are soldered adjacent to the rectifier  44 . In this embodiment, there are two DC bus capacitors  50 , each having a capacitance of about 10 μF. In an alternate embodiment, the DC bus capacitors  50  may include just one 20 μF capacitor instead of two 10 μF capacitors. Other configurations of the DC bus capacitors  50  are also contemplated, for example the number of DC bus capacitors  50  may be three, four, six, eight, etc. In this embodiment, each DC bus capacitor  50  has a longitudinal axis that is perpendicular to the longitudinal axis of the housing  12 . In another embodiment, the longitudinal axes of the DC bus capacitors  50  may be aligned with the longitudinal axis of the housing  12 . 
     In this embodiment, the DC bus capacitors  50  are robust capacitors and not traditional electrolytic smoothening capacitors. Advantageously, the DC bus capacitors  50  have smaller physical dimensions than traditional electrolytic smoothening capacitors that typically have a capacitance of over 100 μF. The DC bus capacitors  50  generate less heat than typical smoothening capacitors that are 100 μF or greater. In this example embodiment, the DC bus capacitors  50  are film capacitors. The film capacitors can be made from polymer plastics metalized on both sides and may be rolled with additional suitable insulators. Advantageously, the smaller physical dimensions and the smaller footprint of the DC bus capacitors  50 , in comparison to traditional smoothening capacitors that are greater than 100 μF, allows placement of the DC bus capacitors  50  onto the circuit board  40  instead of a separate circuit board or placement within housing  12  as disjoint components connected to other components or circuit boards by means of wiring connections. 
     In this example embodiment, the circuit board  40  includes an integrated power module (IPM)  52 . The IPM  52  is soldered adjacent to the DC bus capacitors  50 . The IPM  52  includes a switching arrangement that has a plurality of motor switches, a driver circuit and a driver power supply. The motor switches may be connected electrically between the rectifier  44  and the electric motor  28 . The motor switches selectively deliver direct current from the rectifier  44  to electromagnets of the electric motor  28 . The driver circuit controls the state of the motor switches, for example between an ‘on’ state and an ‘off’ state. The driver power supply supplies power to the driver circuit. 
     The circuit board  40  may include a heat sink  54  that may be positioned on top of the IPM  52 . In this embodiment, the heat sink  54  is abutting a top surface of the IPM  52 . Additional or alternative cooling mechanisms are also contemplated for cooling the IPM  52 . For example, a fan may be mounted on the circuit board  40  to cool the IPM  52 . 
     The circuit board  40  includes a power switch for selectively turning the power tool  10  on and off. In this example embodiment, the power switch is shown as a switch contact  56  of the power on/off switch  32 . The switch contact  56  is soldered on the circuit board  40 . In this embodiment, the switch contact  56  is positioned at an end of the circuit board  40  that is proximate to the electric motor  28 . Other positions are also contemplated. For example, the switch contact  56  may be interposed between the IPM  52  and the DC bus capacitors  50 . 
     The switch contact  56  may be a mechanical switch that is mechanically coupled with the power on/off switch  32 . Example mechanical switches include a toggle switch, a rocker switch, a push-button switch, or the like. Alternatively, the switch contact  56  may be an electronic switch that is connected to the power on/off switch  32  with a wire. Examples of electronic switches include a relay, a transistor, or the like. 
     The switch contact  56  changes states when a user of the power tool  10  changes a position of the power on/off switch  32 . For example, if the power on/off switch  32  is moved to an ‘on’ position then the switch contact  56  moves to a corresponding ‘on’ state to power on the power tool  10 . Similarly, if the power on/off switch  32  is moved to an ‘off’ position then the switch contact  56  moves to a corresponding ‘off’ state to power down the power tool  10 . 
     The switch contact  56  operates at a voltage that is lower than the voltage at which the electric motor  28  operates. The switch contact  56  also operates at a current that is lower than the current at which the electric motor  28  operates. As an example, the electric motor  28  typically draws a current that is higher than one ampere (1 A) and can reach up to 15 A, whereas the current passing through the switch contact  56  is less than 1 A (e.g. 200 mA). 
     Advantageously, the switch contact  56  is physically smaller than a switch that operates at the same voltage and current levels as the electric motor  28 . The switch contact  56  also generates less heat than a switch that operates at the same voltage and current levels as the electric motor  28 . The smaller physical dimensions and smaller footprint allow placement of the switch contact  56  on the circuit board  40 . 
     If the switch contact  56  operated at the same voltage and current levels as the electric motor  28 , then the switch contact  56  might have greater physical dimensions and might generate more heat. Greater physical dimensions and larger heat generation may have required the switch contact  56  to be placed on a separate circuit board or placement within housing  12  as a disjoint component connected to other components or circuit boards by means of wiring connections. Using a separate circuit board for the switch contact  56  would increase the number of inter-board connections and may reduce the reliability of the power tool  10  by making the power tool  10  susceptible to more connection breakages. Using an additional circuit board for the switch contact  56  may undesirably increase the size of the power tool  10 . 
     Being able to place the switch contact  56  on the same circuit board  40  as the other electronic components reduces the need for a separate circuit board for the switch contact  56 . This reduces the number of inter-board connections and increases the reliability of the power tool  10  by making the power tool  10  less susceptible to connection breakages. 
     The circuit board  40  may include motor connections  58 . The motor connections  58  may be solder points that are similar to the AC input solder points  48 . Wires may be connected from the motor connections  58  to the electric motor  28  to supply current to the electric motor  28 . 
     Advantageously, by soldering the rectifier  44 , the DC bus capacitors  50 , the motor switches, the driver circuit and the switch contact  56  onto the single circuit board  40 , as opposed to multiple circuit boards, the number of inter-circuit board connections are minimized. Inter-circuit board connections tend to loosen or break due to vibratory motion of the power tool when the power tool is operated. By minimizing the number of connections between circuit boards and disjoint components, the reliability of the power tool  10  may have increased. 
     Another advantage of soldering the rectifier  44 , the DC bus capacitors  50 , the motor switches, the driver circuit and the switch contact  56  onto the single circuit board  40 , as opposed to multiple circuit boards, is that the power tool  10  is more compact. For example, the housing  12  of the power tool  10  has a diameter of about 54 mm and the housing  12  has a girth (i.e. circumference) of about 170 mm. 
       FIG. 3  is a perspective view of the circuit board  40 . The circuit board  40  has a first end  40 - 1  and an opposing second end  40 - 2 . 
     In this example embodiment, the rectifier  44  is soldered on the circuit  40  at the first end  40 - 1  and the switch contact  56  is soldered at the second end  40 - 2  of the circuit board  40 . 
     In this example embodiment, the heat sink  46  is interposed between the rectifier  44  and one of the DC bus capacitors  50 - 1 . As illustrated, the heat sink  46  has a first portion  46 - 1  and a second portion  46 - 2 . The first portion  46 - 1  is perpendicular to a soldering surface of the circuit board  40  on which the rectifier  44  and other components are soldered. The first portion  46 - 1  extends downwardly towards the soldering surface of the circuit board  40  along a wall of the rectifier  44 . The first portion  46 - 1  is abutting the wall of the rectifier  44 . The second portion  46 - 2  is folded over the top of the DC bus capacitor  50 - 1  to increase its mass and surface area within the confines of the housing  12 , but does not abut the DC bus capacitor  50 - 1 . Advantageously, by abutting the walls of the rectifier  44 , the heat sink  46  is able to dissipate some of the heat generated by the rectifier  44 . 
     The second portion  46 - 2  of the heat sink  46  is perpendicular to the first portion  46 - 1  of the heat sink  46 . The second portion  46 - 2  extends parallel to the soldering surface of the circuit board  40 . The second portion  46 - 2  extends along but does not abut a top surface of the DC bus capacitor  50 - 1 . In this embodiment, the second portion  46 - 2  partially covers the top surface of the DC bus capacitor  50 - 1 . In other embodiments, the second portion  46 - 2  may cover the entire top surface of the DC bus capacitor  50 - 1  and may further cover a top surface of the DC bus capacitor  50 - 2 . Other configurations of the heat sink  46  are also contemplated. 
     In this example embodiment, the IPM  52  is interposed between the DC bus capacitors  50  and the switch contact  56 . The IPM  52  contains the switching arrangement and the driver circuit. The switching arrangement includes motor switches. The motor switches may be transistors, such as insulated gate bipolar transistors (IGBTs). The motor switches may be switched on and off at a very high rate when the power tool  10  is being operated. Switches, especially transistors such as IGBTs, generate heat when they are rapidly switched on and off. Similarly, the driver circuit that is driving the motor switches may also generate heat when the power tool  10  is being operated. The driver power supply that is regulating the power to the driver circuit may also generate heat. In sum, the IPM  52  may generate heat while the power tool  10  is being operated. 
     In this example embodiment, the heat sink  54  dissipates the heat generated by the IPM  52 . The heat sink  54  has a plurality of fins, for example  54 - 1 ,  54 - 2 ,  54 - 3 , etc. The fins  54 - 1 ,  54 - 2 ,  54 - 3  increase the surface area of the heat sink  54  thereby facilitating faster heat dissipation. In another embodiment, a coolant may be passed through the fins  54 - 1 ,  54 - 2 ,  54 - 3  of the heat sink  54  to accelerate the heat dissipation. Other cooling mechanisms are also contemplated for cooling the IPM  52 , for example a fan may be used to dissipate heat generated by the IPM  52 . 
     In this embodiment, the switch contact  56  is positioned at the second end  40 - 2  of the circuit board  40 . However, in other embodiments, the switch contact  56  may be positioned at other portions of the circuit board  40 . For example, in an alternate embodiment, the IPM  52  may be soldered at the second end  40 - 2  of the circuit board  40  and the switch contact  56  may be interposed between the IPM  52  and the DC bus capacitor  50 - 2 . 
       FIG. 4  depicts a power tool  10 ′ with another example circuit board  40 ′. The power tool  10 ′ receives AC power through the power cord  30 . The AC power passes through a fuse  60  before reaching an input of the rectifier  44 . AC power often experiences sudden unexpected current and/or voltage surges. Such sudden surges can damage the electronic components on the circuit board  40 ′ because most electronic components are designed to operate at steady current and voltage values. 
     The fuse  60  may turn off the power tool  10 ′ when the current being supplied by the power cord  30  exceeds a current rating of the fuse  60 . The fuse  60  may be reset either manually by a user of the power tool  10 ′ or automatically by an electronic controller of the power tool  10 ′. The fuse  60  may also be removed and replaced with a new fuse  60 . Advantageously, the fuse  60  protects the rectifier  44  and other electronic components on the circuit board  40 ′ from current surges in the AC power being supplied by the power cord  30 . 
     In this example embodiment, the circuit board  40 ′ includes four DC bus capacitors  50 - 1 ,  50 - 2 ,  50 - 3 ,  50 - 4  that are arranged on the circuit board in a two-by-two (2×2) array. Each capacitor has a capacitance of about 4.7 μF which brings the total capacitance of the DC bus capacitors  50  to about 18.8 μF. In an alternate embodiment, each DC bus capacitor  50 - 1 ,  50 - 2 ,  50 - 3 ,  50 - 4  may have a capacitance ranging from about 4 μF to 5 μF, summing the total capacitance to about 16 μF to 20 μF. Other configurations, arrangements and capacitance values are also contemplated, for example the total capacitance may be as low as 10 μF. 
     In this example embodiment, the power tool  10 ′ includes a fan  62  that is connected to a drive shaft of the electric motor  28  and is driven by the electric motor  28 . The fan  62  is positioned between the electric motor  28  and the output member  18 . The fan  62  is driven by the electric motor  28  when the power tool  10 ′ is being operated. The fan  62  circulates air through the power tool  10 ′. 
     In this example embodiment, the fan  62  draws air into the housing  12  of the power tool  10 ′. The air that the fan  62  draws into the housing  12  makes contact with the heat sinks  46 ,  54  and facilitates further cooling of the rectifier  44 , the DC bus capacitors  50  and the IPM  52 . 
     In an alternate embodiment, the fan  62  forces air out of the housing  12  of the power tool  10 ′. The fan  62  removes hot air surrounding the heat sinks  46 ,  54  to facilitate further cooling of the rectifier  44 , the DC bus capacitors  50  and the IPM  52 . 
     The power tool  10 ′ includes a second printed circuit board (PCB)  64 . A position sensor, such as a Hall effect sensor, is mounted on the second PCB  64 . The Hall effect sensor may be connected to the controller. The Hall effect sensor includes a transducer that varies its output voltage in response to a magnetic field generated by electromagnets of the electric motor  28 . As the electric motor  28  rotates, the magnetic field sensed by the Hall effect sensor changes. The Hall effect sensor is used to determine a position and/or a speed of the electric motor  28 . Other position and/or speed sensors for detecting the position and/or the speed of the electric motor  28  are also contemplated, for example an infrared (IR) sensor. Alternatively, the power tool  10 ′ may operate without the aid of any Hall effect sensor and without printed circuit board  64 . 
     Referring to  FIG. 5  and  FIG. 6 , the circuit board  40 ′ has a first end  40 ′- 1  and an opposing second end  40 ′- 2 . 
     In this example embodiment, the fuse  60  is soldered at the first end  40 ′- 1  of the circuit board  40 ′ and the switch contact  56  is soldered at the second end  40 ′- 2  of the circuit board  40 ′. The rectifier  44  is soldered adjacent to the fuse  60 . 
     In this example embodiment, the heat sink  46  is interposed between the rectifier  44  and two DC bus capacitors  50 - 1 ,  50 - 2 . The first portion  46 - 1  of the heat sink  46  is abutting the wall of the rectifier  44 . Advantageously, by abutting the walls of the rectifier  44 , the heat sink  46  is able to dissipate some of the heat generated by the rectifier  44 . 
     The second portion  46 - 2  of the heat sink  46  extends along and does not abut the top surfaces of the DC bus capacitors  50 - 1 ,  50 - 2 . In this embodiment, the second portion  46 - 2  partially covers the top surfaces of the DC bus capacitors  50 - 1 ,  50 - 2 . In other embodiments, the second portion  46 - 2  may cover the entire top surfaces of the DC bus capacitors  50 - 1 ,  50 - 2  and may further cover top surfaces of the DC bus capacitors  50 - 3 ,  50 - 4 . Other configurations of the heat sink  46  are also contemplated. 
     In this example embodiment, the IPM  52  is interposed between the DC bus capacitors  50 - 3 ,  50 - 4  and the switch contact  56 . The heat sink  54  is positioned on a top surface of the IPM  52  to dissipate the heat generated by the IPM  52 . Other cooling mechanisms for cooling the IPM  52  are also contemplated. 
     In this example embodiment, the switch contact  56  is positioned at the second end  40 ′- 2  of the circuit board  40 ′. However, in other embodiments, the switch contact  56  may be positioned at other portions of the circuit board  40 ′. For example, in an alternate embodiment, the IPM  52  may be soldered at the second end  40 ′- 2  of the circuit board  40 ′ and the switch contact  56  may be interposed between the IPM  52  and the DC bus capacitors  50 - 3 ,  50 - 4 . 
     Referring to  FIG. 7  and  FIG. 8 , a circuit board  40 ″ is presented. The circuit board  40 ″ includes six IGBTs  66  that operate as motor switches as part of the switching arrangement. The circuit board  40 ″ includes six heat sinks  68  that are positioned adjacent to the IGBTs  66  to dissipate the heat generated by the IGBTs. Each heat sink  68  is abutting a wall of a corresponding IGBT  66 . Each heat sink  68  includes fins that extend towards the center of the circuit board  40 ″. 
     In this example embodiment, three IGBTs  66  are placed at one edge of the circuit board  40 ″ and another three IGBTs  66  are placed at another opposing edge of the circuit board  40 ″. By placing sets of three IGBTs  66  at opposing edges of the circuit board  40 ″, the heat generated by the IGBTs  66  is distributed over a greater surface area of the circuit board  40 ″. 
     However, in an alternate embodiment, the heat sinks  68  may be placed at the edges of the circuit board  40 ″ and the IGBTs  66  may be placed more towards the center of the circuit board  40 ″. In another alternate embodiment, only two heat sinks  68  may be provided and each heat sink  68  may abut walls of three IGBTs  66 . 
     In this example embodiment, the circuit board  40 ″ includes a driver circuit  70  that drives the IGBTs  66 . The driver circuit  70  may supply pulse width modulated (PWM) signals to each of the IGBTs  66  in order to control the states of the IGBTs  66  by switching the IGBTs  66  between ‘on’ and ‘off’ states. In this embodiment, the circuit board  40 ″ further includes capacitors  72 , an inductor  74  and a resistor  76 . 
     In this example embodiment, the circuit board  40 ″ includes four DC bus capacitors  50 - 1 ,  50 - 2 ,  50 - 3 ,  50 - 4 , each having a longitudinal axis. Three DC bus capacitors  50 - 1 ,  50 - 2 ,  50 - 3  have longitudinal axis&#39; that are aligned with the longitudinal axis of the circuit board  40 ″. The fourth DC bus capacitor  50 - 4  has a longitudinal axis that is perpendicular to the longitudinal axis of the circuit board  40 ″. 
       FIG. 9  depicts a back surface of the circuit board  40 . Various connections for the electronic components soldered to the circuit board  40  can be seen. In particular, a controller  78  is shown. The controller  78  may be a microcontroller. 
       FIG. 10  depicts a schematic that illustrates an embodiment of a motor control system  80  that may be employed by the power tool  10 . The motor control system  80  is comprised generally of the controller  78 , a switching arrangement  82  and a driver circuit  84 . The motor control system  80  may further include position sensors  86 ,  88 ,  90  (e.g. the Hall effect sensors on the second PCB  64 ) that are configured to detect rotational motion of the electric motor  28  and generate a signal indicative of the rotational motion. The signal may have a periodic waveform whose magnitude may vary in accordance with the rotational position of the electric motor  28 . In other embodiments the position sensors  86 ,  88 ,  90  may connect to controller  78 . 
     An AC power supply  92  delivers an alternating current to the rectifier  44 , for example through the power cord  30 . The rectifier  44  converts the alternating current into a direct current. The output of the rectifier  44  may be a pulsating DC signal and not a pure DC signal. 
     In this example embodiment, the DC bus capacitors  50  are electrically connected in parallel with the rectifier  44 . In an example embodiment, the DC bus capacitors  50  may smoothen the output of the rectifier  44  by converting the pulsating DC signal outputted by the rectifier  44  into a pure DC signal or a substantially pure DC signal or a somewhat smoothened DC signal or a slightly smoothened DC signal. 
     In this example embodiment, the switching arrangement  82  is electrically connected with the DC bus capacitors  50  and may receive the pure DC signal or the substantially pure DC signal from the DC bus capacitors  50 . The switching arrangement  82  includes a plurality of motor switches that, when switched on, deliver the DC current to the electric motor  28 . Example motor switches are the IGBTs  66 . In an example embodiment, the switching arrangement  82  may be further defined as a three-phase inverter bridge although other arrangements are contemplated by this disclosure. 
     The driver circuit  84  is interfaced with the motor switches of switching arrangement  82 . The driver circuit  84  controls the state of the motor switches. In this embodiment, the driver circuit  84  is shown as being separate from the switching arrangement  82 . In other embodiments, the driver circuit  84  and the switching arrangement  82  may be a single integrated circuit which may be commercially available from various manufactures. For example, the switching arrangement  82 , which may include the IGBTs  66 , and the driver circuit  84  may be a part of the IPM  52 . 
     The controller  78  is interfaced with the driver circuit  84  and may generate PWM signals to control the electric motor  28 . In this embodiment, the controller  78  receives power from a driver power supply  94 . In an alternate embodiment, the controller  78  may receive power directly from the rectifier  44 . 
     The driver power supply  94  is electrically connected in series with the rectifier  44  and operates to power the driver circuit  84  via the power on/off switch  32 . The power on/off switch  32  is positioned between the driver power supply  94  and the driver circuit  84 . In an example embodiment, the switch contact  56  of the power on/off switch  32  is positioned between the driver power supply  94  and the driver circuit  84 . 
     When the power on/off switch  32  is switched to the on position, the driver circuit  84  receives power from the driver power supply  94 . When the driver circuit  84  receives power, the driver circuit  84  is able to control the state of the motor switches and the electric motor  28  is on. 
     Conversely, when the power on/off switch  32  is switched to the off position, the driver circuit  84  does not receive power from the driver power supply  94 . When the driver circuit  84  does not receive power, the driver circuit  84  is not able to control the state of the motor switches and the electric motor  28  is off. 
     As illustrated, the power on/off switch  32  is electrically connected between the rectifier  44  and the driver circuit  84 . The power on/off switch  32  is positioned such that the power, conveyed from the AC power supply  92  through the switching arrangement  82 , does not pass through the power on/off switch  32 . Furthermore, the current being drawn by the electric motor  28  does not pass through the power on/off switch  32 . The current passing through the power on/off switch  32  is the current being drawn by the driver circuit  84  and the current being drawn by the driver circuit  84  is lower than the current being drawn by the electric motor  28 . 
     The power on/off switch  32  has a current rating that is approximately equal to the lower current being drawn by the driver circuit  84  and not the higher current being drawn by the electric motor  28 . Similarly, the power on/off switch  32  has a voltage rating that is approximately equal to the lower voltage at which the driver circuit  84  operates and not the higher voltage at which the electric motor  28  operates. The power on/off switch  32  is a low current and low voltage switch. Advantageously, the power on/off switch  32  has smaller physical dimensions and generates less heat than a switch that would be required to withstand the higher current and higher voltage at which the electric motor  28  operates. 
     The performance of the power tool  10  may be measured using numerous performance metrics. In some countries, there may be laws or regulations that require certain metrics to be printed on a nameplate that is attached to the housing  12  of the power tool  10 . For example, a law may require that the nameplate state that the power tool  10  draws up to a certain current, of 15 A for example, at a voltage of 120 V. In the United States, the law presently requires the nameplate to state an amount of current drawn by the power tool  10  (i.e. Amperes in or Amps-in). In Europe, the law presently requires the nameplate to state an amount of Watts that are input into the power tool  10  (i.e. Watts-in). It may be beneficial to state certain other performance metrics on the nameplate, for example to assist a potential user in deciding whether the power tool  10  is adequate for a particular task. One such other performance metric on the nameplate may be rotational speed. 
     In an example embodiment, the power tool  10  is configured to receive a maximum steady-state current of 15 Amperes from the AC power source, at a voltage of 120 Volts. In this example embodiment, the power tool  10  is configured to generate an output such that a quotient obtained by dividing the output, measured in Watts (Wout), by an input, measured in Volt-Amps (VAin), and further dividing by a capacitance of the capacitor, measured in Farads (Fd), is greater than 10,000 Wout/VAin/Fd. 
     In another example embodiment, the power tool  10  is configured to generate an output such that a quotient obtained by dividing the output, measured in Watts (Wout), by an input, measured in Volt-Amps (VAin), and further dividing by a capacitance of the capacitor, measured in Farads (Fd), is greater than 5,000 Wout/VAin/Fd. 
     A power factor (PF) of the power tool  10  may be computed by dividing an input of the power tool  10 , measured in Watts (Watts-in), by a product of the amount of voltage (Volts-in) at which the power tool  10  is drawing current (Amps-in). An efficiency (Eff) of the power tool  10  may be computed by dividing the output of the power tool  10 , measured in Watts (Wout), by the input of the power tool  10 , measured in Watts (Win). 
     In an example embodiment, the power tool  10  is configured to generate an output such that a quotient obtained by dividing a product of the power factor (PF) and the efficiency (Eff) by a capacitance of the DC bus capacitors  50 , measured in Farads (Fd), is greater than 5,000 PF*Eff/Fd. 
     In another example embodiment, the power tool  10  is configured to generate an output such that a quotient obtained by dividing the output, measured in Watts (Wout), by an input, measured in Volt-Amperes (VAin), and further dividing by a diameter of the electric motor  28 , measured in meters (m), is greater than 10 Wout/VAin/m. 
     In another example embodiment, the power tool  10  is configured to generate an output that is greater than 1,200 continuous hot Watts out when the power tool  10  is being supplied by a 15 Ampere AC power source at 120 V. 
     A grip diameter of the power tool  10  may be measured in meters (m). The grip diameter for non-circular cross-sections may be the girth or circumference of the housing  12  divided by the quantity Pi, approximately 3.14159265. In an example embodiment, the power tool  10  is configured to generate an output such that a quotient obtained by dividing the output, measured in Watts (Wout), by an input, measured in Volt-Amps (VAin), and further dividing by the grip diameter, measured in meters, is greater than 10 Wout/VAin/m. In an alternate embodiment, the quotient may be greater than 8.3 Wout/VAin/m. 
     The grip diameter of the power tool  10  may also be measured in millimeters (mm). In an example embodiment, the power tool  10  may be configured such that a quotient obtained by dividing an input, measured in Watts (Win), by the grip diameter, measured in millimeters, is greater than 18 Win/mm. In this example embodiment, the quotient may be less than 179 Win/mm. 
     A volume of the power tool  10  may be measured in cubic centimeters (cc). In an example embodiment, the power tool  10  may be configured to generate an output such that a quotient obtained by dividing the output measured in Watts (Wout) by an input measured in Volt-Amps (VAin) and further dividing by the volume of the power tool  10  measured in cubic centimeters is greater than 600 Wout/VAin/cc. 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure. 
     The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
     When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.

Technology Category: 7