Patent Publication Number: US-2022239241-A1

Title: Paint sprayer with dynamic pulse width modulation driven motor

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a continuation of U.S. application Ser. No. 16/476,955 filed Jul. 10, 2019 for “PAINT SPRAYER WITH DYNAMIC PULSE WIDTH MODULATION DRIVEN MOTOR,” which in turn is a 371 national phase filing of International PCT Application No. PCT/US2018/013711 filed Jan. 15, 2018 for “PAINT SPRAYER WITH DYNAMIC PULSE WIDTH MODULATION DRIVEN MOTOR,” which in turn claims the benefit of U.S. Provisional Application No. 62/446,487 filed Jan. 15, 2017 for “PAINT SPRAYER WITH DYNAMIC PULSE WIDTH MODULATION DRIVEN MOTOR”. 
    
    
     BACKGROUND 
     In most high voltage direct current brushed (HVDC) motor controllers in paint sprayer applications, use silicon controlled rectifiers (SCRs) or Triacs due to their simplistic and inexpensive control design. In a typical application circuit of a design using an AC to DC rectifying bridge and a Triac to drive a high voltage direct current (HVDC) brushed motor. This motor control strategy yields very high peak currents, for example, around 7.3 Arms (root mean square Amperes) that decay down to 0 Arms valleys every 8.3 ms in a 120 VAC 60 Hz power distribution system. As a result, motor brush life can be negatively affected or impacted, and operation of the sprayer can be affected by motor thermal trips caused by overheating. 
     SUMMARY 
     A fluid sprayer includes a housing, a pump, a nozzle, a high voltage direct current (HVDC) brushed electric motor that drives the pump, and a motor controller electrically connected to the motor. The motor controller drives the motor with a high speed pulse width modulated (PWM) drive signal that switches current through the motor on and off. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a perspective view of a handheld paint sprayer. 
         FIG. 1B  is a cross-sectional view of the handheld paint sprayer. 
         FIG. 2  is an electrical block diagram of the handheld paint sprayer. 
         FIG. 3  is a chart demonstrating different phases of operation of the electric motor of the handheld paint sprayer. 
     
    
    
     DETAILED DESCRIPTION 
     In this disclosure a variable output single phase high voltage (HVDC) brushed motor controller for paint sprayers (or other fluid sprayers) is described. This motor controller commutates a brushed motor that will drive a pump in a paint sprayer. The motor controller eliminates motor thermal trips, increases the existing motor&#39;s brush life, and provides high resolution variable output adjustment for the painter. The controller also increases motor efficiency to make it capable of driving three piston pump with low Arms. 
     Various embodiments of the present disclosure can be used to spray paint and/or other fluids and solutions. While paint will be used herein as an exemplar, it will be understood that this is merely one example and that other fluids (e.g., water, oil, stains, finishes, coatings, solvents, etc.) can be sprayed instead of paint. 
       FIG. 1A  is a perspective view, and  FIGS. 1B  is a cross-sectional view of sprayer  10 .  FIGS. 1A and 1B  will be discussed together. Sprayer  10  shown in  FIGS. 1A and 1B  is a handheld paint sprayer that can be supported and operated with just one hand during spraying. As shown in  FIGS. 1A and 1B , sprayer  10  includes housing  12  (which includes main body  14  and handle  16 ), fluid supply system  18 , spray tip assembly  20  (which includes nozzle  22 ), pump  24  (which includes pistons  26  and cylinders  28 ), valves  30 , motor  32 , wobble drive  34 , power cord  36 , motor controller  38 , spray setting input  40 , and trigger  42 . 
     It will be understood that this is but one type of sprayer within which the features of the present disclosure could be embodied. The features of the present disclosure could be practiced on larger, non-handheld sprayers. For example, the features of the present disclosure could be implemented in a professional-grade floor unit. 
     Fluid supply system  18  is a reservoir that can be used to hold the paint to be sprayed, such as by holding the paint in a flexible polymer container. The paint is sprayed out of nozzle  22  of spray tip assembly  20 . Nozzle  22  can be a carbide orifice at the end of the fluid pathway that atomizes paint into a fan spray pattern for painting surfaces. The mechanism (pump  24 , valves  30 , motor  32 , and wobble drive  34 ) for pumping the paint from the fluid supply system  18  and out nozzle  22  is contained within main body  14  of housing  12 . Housing  12  can be, for example, a molded polymer clamshell. 
     Trigger  42  is located at an upper end of handle  16 . When activated, trigger  42  causes sprayer  10  to spray paint, and when deactivated trigger  42  causes the sprayer  10  to stop spraying paint. While trigger  42  is shown in this embodiment, it will be appreciated that other types of inputs or activators can instead be used for commanding sprayer  10  to spray paint. 
     Sprayer  10  can develop different levels of pressure for expelling the paint from nozzle  22  depending on spray setting input  40 . Spray setting input  40  can be a potentiometer dial, a digital input, slider, one or more buttons, or other type of input. Generally, the user can turn the spray setting input  40  to a higher level for greater pressure and a lower level for lower pressure. The flow of paint, and in particular the pattern of the atomized spray fan, is dependent on the fluid pressure. 
     Sprayer  10  receives AC input power from power cord  36 , which connects to a conventional electrical wall outlet. The AC input power provides power to motor  32  and motor controller  38  of sprayer  10 . Motor controller  38  can be entirely or partially mounted on a circuit board. Motor controller  38  controls operation of sprayer  10 . In particular, motor controller  38  receives an on/off input from the trigger  42 , a spray setting from spray setting input  40 , and AC power from power cord  36 . Using these inputs, motor controller  38  controls operation of motor  32 , which drives pump  24  through wobble drive  34 . 
     Motor  32  is contained within main body  14  of housing  12 . Motor  32  can be, for example, a high voltage brushed DC electric motor. Rotational output from motor  32  operates wobble drive  34  which converts the rotational output into linear reciprocal motion. While a wobble drive  34  is shown to convert rotational motion into linear reciprocal motion, alternative mechanisms can instead be used, such as various yokes and/or cranks. 
     The reciprocal motion is used to operate pump  24 . Pump  24  includes a housing within which pistons  26  reciprocate. While only one piston is shown in the view of  FIG. 1B , in one embodiment two other pistons are located within pump  24  and operate similarly. However, different embodiments may only have two pistons or a single piston (e.g., non-handheld floor units can have a single, larger piston). Pistons  26  are located at least partially within cylinders  28  of pump  24 . Pistons  26  and cylinders  28  can be formed from carbide, amongst other options. 
     The reciprocating motion of each piston  26  pulls paint from fluid supply system  18  through the intake channel  44  and then into a chamber formed by cylinder  28  and piston  26  on an upstroke (or back stroke), and then expels the paint under pressure from the chamber on the downstroke (or forward stroke). The paint passes through one or more valves  30 . Under pressure from the pump  24 , the paint flows to nozzle  22  for release as an atomized spray fan. In floor units, the paint may travel through a flexible hose after being placed under pressure by the pump and released through a separate mechanical gun to which the flow fluidly connects. 
     Preferably, sprayer  10  is responsive, consistent, reliable, and lightweight. However, these can be competing considerations. When a user presses trigger  42  or otherwise activates motor  32 , a fine atomization of paint in an even fan pattern is expected to quickly be output (e.g., within 100 milliseconds) and maintained for the duration of trigger pull of trigger  42 . This requires that motor  32  accelerate very quickly. A smaller motor is also preferred to reduce weight, but is less capable of fast acceleration to high pressure. These competing demands risk several complications, such as ring fire and overheating, which are further discussed herein. 
       FIG. 2  shows a block diagram of some of the circuitry of sprayer  10 .  FIG. 2  shows high voltage direct current (HVDC) brushed motor  32 , power cord  36 , motor controller  38 , spray setting input  40 , trigger  42 , and trigger sense circuit  42 A. Motor controller  38  includes HVDC power supply  50  (which includes rectifier circuit  52  and filter circuit  54 ), switch mode power supply  56 , microcontroller  58 , pulse width modulation (PWM) driver  60 , semiconductor switch  62 , flyback diode  64 , current feedback circuit  66  (which includes current sense resistor  68 ), and pressure sensor  70 . 
     Motor controller  38  is powered by standard line (or mains) power received from power cord  36  (e.g., a 120 volt 60 Hertz AC, or a 230 volt 50 Hertz AC, or other regionally standard line power). The AC power from power cord  36  is converted to a DC voltage of, for example, 165 volts, by HVDC power supply  50 . Rectifier circuit  52  receives the AC power from power cord  36  and full wave rectifies the power to produce rectified power. Filter circuit  54  conditions or smoothes the rectified power to create, the DC voltage (e.g. 165 volts) that is supplied to terminal M 1  of motor  32 . 
     Switch mode power supply  56  receives rectified power from HVDC power supply  50  and generates supply voltages V 1  and V 2 . All of the voltages share a common ground in the circuity shown in  FIG. 2 . Supply voltage V 1 , which in one embodiment is  15 VDC, is used by PWM driver  60  to produce a PWM drive signal that turns semiconductor switch  62  on and off. Supply voltage V 2 , which in one embodiment is 3.3 VDC, powers microcontroller  58 , spray setting input  40 , trigger sense circuit  42 A, PWM driver  60 , and current feedback circuit  66 . 
     Microcontroller  58  receives inputs from spray setting input  40 , trigger sense circuit  42 A, and current feedback circuit  66 . Based upon those inputs, microcontroller  58  outputs a PWM command signal to PWM driver  60 . In one embodiment, the PWM command signal has a frequency of 16 kHz for in rush current during a starting sequence and a frequency of 32 kHz for steady state current during a steady state phase of sprayer operation. Microcontroller  58  determines the duty cycle of the command signal, and thus the on and off time of the semiconductor switch  62  based upon the phase of operation, a spray setting input, and sensed current. 
     The PWM drive signal from PWM driver  60  is supplied to semiconductor switch  62 , which is shown in  FIG. 2  as an isolated gate bipolar transistor (IGBT). IGBT switch  62  has a control electrode (gate), a first main current carrying electrode (collector), and a second main current carrying electrode (emitter). IGBT switch  62  turns on and off in response to the PWM drive signal received at its gate. 
     Motor terminal M 2  is connected to the collector of IGBT switch  62 . The emitter of IGBT switch  62  is connected to current sense circuitry  66 . Flyback diode  64  is connected in parallel with motor  32 . The anode of flyback diode  64  is connected to motor terminal M 2 , and the cathode of flyback diode  64  is connected to motor terminal M 1 . 
     When IGBT switch  62  is turned on, a current path is established through motor  36 , IGBT switch  62 , and current sense resistor  68  to ground. The HVDC voltage at motor terminal M 1  causes current to flow through motor  32  to motor terminal M 2 , from collector to emitter of IGBT switch  62  and through current sense resistor  68 . When IGBT switch  62  is turned off, the HVDC voltage is still present at motor terminal M 1 , but current flow through, IGBT switch  62  is interrupted. Flyback diode  64  conducts motor current from terminal M 2  back to terminal M 1  when IGBT switch  62  turns off. 
     Microcontroller  58  can include, among other things, a digital processor and memory storing program instructions thereon which, when executed by the processor, perform the functions described herein. The microcontroller  58  calculates and outputs the high speed pulse width modulation (PWM) command signal to PWM driver  60  to set a duty cycle for powering motor  32 . More specifically, motor  32  is powered not by a continuous direct current but rather by a rapid series of voltage pulses (e.g., 165 volts DC). Each pulse is part of a cycle having an “on” portion and an “off” portion. The pulses are modulated in width (duration) over the cycle to deliver a greater or lesser amount of energy to motor  32  to increase or decrease the speed of motor  32 . For each cycle, the duty or “on” portion can be expressed as a percentage of the cycle. The duty cycle in this sense ranges from 0% (no on pulse) to 100% (pulse on fully throughout the cycle). Microcontroller  58  outputs the PWM command signal to PWM drive  60 , which provides the PWM drive signal to the gate of IGBT switch  62  to cause the IGBT  64  to turn on and off according to the frequency and duty cycle established by the PWM command signal. Specifically, IGBT Switch  64  turns on when the duty cycle is on (corresponding to pulse delivery to motor  32 ) and turns off when the duty cycle is off (corresponding to no pulse delivery to motor  16 ). Flyback diode  64  bridges the motor  16  to freewheel during the off portion of the duty cycle while blocking potentially damaging voltage generated by the motor  32 . 
     In operation, trigger  42  is activated (e.g., pulled), which causes trigger sense circuit  42 A to signal microcontroller  58  to output the PWM command signal to PWM driver  60  to cause IGBT switch  62  to turn on and off at the commanded frequency and duty cycle to cause current flow through motor  32 . 
     The duty cycle of the PWM command signal may be calculated by microprocessor  58  before or while being output based on various inputs. Microcontroller  58  receives a signal from the spray setting input  40  (such as a potentiometer) which is set to indicate a pressure, motor speed, or other parameter setting desired by the user. In some cases, the duty cycle of the PWM command signal is based on the signal received by microcontroller  58  from the spray setting input  40  indicating the parameter setting. For example, a higher setting of the spray setting input  40  can correspond to a user desire for greater fluid pressure output from pump  24  (which requires a correspondingly higher duty cycle to cause a higher motor  32  speed), while a lower setting of spray setting input  40  can correspond to a user desire for lesser fluid pressure output from pump  24  (which requires a correspondingly lower duty cycle to cause a lower motor  32  speed). 
     Additionally or alternatively to the trigger  42  and trigger sense circuit  42 A, the sprayer  10  can include a pressure sensor  70  which can be a pressure transducer or pressure switch (e.g., in non-handheld versions) that measures the pressure anywhere along the fluid line between the outputof the pump  24  and the nozzle  22 . Microcontroller  58  could start delivering the PWM command signal to PWM driver  60  to start motor  32  when the pressure within the fluid line, as indicated by the pressure sensor  70 , falls below a low pressure threshold. Likewise, microcontroller  58  could stop delivering the PWM command signal to PWM driver  60  to stop motor  32  when the pressure within the fluid line, as indicated by the pressure transducer, rises above a low pressure threshold. As alternatives to stopping and starting, microcontroller  58  could increase or decrease the duty cycle of the PWM command signal to increase or decrease pressure to maintain a preferred level corresponding to spray setting input  40 . Fluid may be released from the fluid line (e.g., as an atomized spray) when a mechanical valve in the fluid line opens, thereby lowering the pressure and triggering microcontroller  58  to turn on (or accelerate) motor  32  as described. The threshold(s) may be dynamically set based on the spray setting input signal to the microcontroller  58  from spray setting input  40 . 
     Current flowing through motor  32  can cause several problems. If the current and voltage are too high, then instances of ring fire can occur wherein current arcs between the trailing edge of the brush and the rotating commutator of motor  32 , which significantly reduces brush life or creates a short circuit around the commutator. Also, excessive current through motor  32  generates heat, particularly on startup when motor  32  is accelerating. Higher heat can raise the coefficient of friction of the brush, increasing wear. Heat rise can also trip internal thermal fuses of motor  32  or other components. Once a motor thermal trip occurs, the user has to wait until the motor cools down (which may be on the order of 30 minutes) before spraying can be resumed. Various features are provided to limit ring fire and heat rise, as further discussed herein. 
     Current feedback circuit  66  monitors current through current sense resistor  68  and provides a current feedback signal to microcontroller  58 . In steady state operation, microcomputer  58  uses the current feedback signal in conjunction with the spray setting input signal and a proportional and integral control loop algorithm to keep the peak and RMS current through the motor  32  at or below a predetermined current level. That current level can be at or just below the maximum continuous RMS current the motor  32  can handle without overheating (which due to the benefits achieved using the techniques of the present disclosure can be materially higher than the maximum continuous RMS current for which the motor  32  is rated). Current feedback circuit  66  includes current sense resistor  68 , which produces a current sense voltage as in function of current from IGBT switch  62  that flows through current sense resistor  68  to ground. The current feedback signal provided by current feedback circuit  66  to microcontroller  58  is based on the current sense voltage. Microprocessor  58  calculates the length of on time for each PWM cycle to maintain adequate RMS current at or below the predetermined current level. The microcontroller  58  may be programmed to increase or decrease the duty cycle (on time) to maintain the current through the motor  32  at or near the predetermined current level. In one embodiment, microcontroller  58  is programmed to maintain the current at a first Arms level during steady state operation such that the duty cycle is increased if the current falls below the first Arms level by a predetermined amount (e.g. 0.1 Arms) and the duty cycle is decreased if the current rises above the first Arms level by a predetermined amount (e.g. 0.1 Arms). In some cases, the predetermined current level may only function as upper limit so as to limit the duty cycle when the current exceeds the predetermined current limit but not otherwise increase the duty cycle based on a measured current. Alternatively, the set level can be, for example, in a range between a low Arms level and a high Arms level. Modulating the duty cycle to limit excessive current may be particularly useful when motor  32  is already accelerated to a functional speed for spraying, but a greater level of current is typically needed on startup to accelerate motor  32 . Mitigation of the previously mentioned issues during startup are further discussed herein. 
       FIG. 3  shows a chart demonstrating different phases of operation for motor  32  driven by a pulse width modulated signal corresponding to the pulse width modulation command signal output by the microcontroller  58 . Duty cycle level  80  indicates the programmed duty cycle across various phases P 1 -P 5  of the pulse width modulation command signal. First-fourth phases P 1 -P 4  are different parts of a startup sequence while fifth phase P 5  is a steady state phase of indefinite duration (i.e. as long as trigger  42  is pulled). First-fourth phases P 1 -P 4  of the startup sequence are repeated for each trigger  42  pull or other activation of motor  32  from a dead stop. Specifically, first-fourth phases P 1 -P 4  of the startup sequence are intended to accelerate motor  32  from a stopped condition to a fully or nearly fully accelerated condition (e.g., accelerated to the speed corresponding to the setting of the spray setting input  40 ). 
     The first phase P 1  is a kick start phase in which a relatively high duty cycle pulse train is delivered to motor  32 . Motor  32  is typically not in motion during first phase P 1 , or at least at the start of phase P 1 , but the pulses during phase P 1  begin to establish the electromagnetic field that will drive motor  32 . The duty cycle may be constant at a first level throughout first phase P 1 . The first level may be greater than 85%. The first level may be greater than 90%. The first level may be greater than 92%. Moreover, the first level may be less than 100%, and in some cases may be less than or equal to 96%. The first level may be within the range 90-96%. The first level may be 95%. First phase P 1  may be less than 10, or 5, or 2 milliseconds (but greater than zero) in duration. In some cases, first phase P 1  is between 0.01-2.0 milliseconds. In some cases, first phase P 1  is 1.0 millisecond. 
     The current through motor  32  during first phase P rapidly increases, and may be 20 Arms or higher by the end of first phase P 1 . This trajectory for current level would be too high to continue, as higher current risks ring fire, excessive heat generation, and demagnetizing motor  32 . Therefore, the duty cycle is decreased by microcontroller  58  for second phase P 2 . Second phase P 2  may be considered a wave shaping phase because the decrease in duty cycle decreases the current level profile through motor  32 , transitioning from an increasing trajectory at the end of first phase P 1  to a leveling off or decaying trajectory soon after the start of second phase P 2 . 
     The duty cycle during the second phase P 2  is maintained below the duty cycle level of first phase P 1 . As shown, the duty cycle during second phase P 2  changes throughout phase P 2 . Specifically, the duty cycle ramps up, in this case linearly. The duty cycle during second phase P 2  may start out as less than 80%, 75%, or 70%, but greater than 50%, 55%, 60%, or 65%. The duty cycle during second phase P 2  may start out as between 60-70%. The duty cycle during second phase P 2  may start out as 66%. The duty cycle during second phase P 2  may end at less than 95%, 90%, or 85%, but greater than 70%, 75%, 80%, or 85%. The duty cycle during the second phase P 2  may end at between 85-95%. The duty cycle during second phase P 2  may end at 92%. Second phase P 2  may be longer than first phase P 1 . Second phase P 2  may be greater than 5 or 8 milliseconds but less than 20 or 15 milliseconds. In some cases, second phase P 2  is between 9-11 milliseconds. In some cases, the second phase P 2  is 10 milliseconds. 
     Third phase P 3  is a speed control phase in which the duty cycle is constant at a predetermined level. The current through motor  32  is self limited to some degree because motor  32  has accelerated, although not to full speed, and motor  32  continues to accelerate through third phase P 3 . The current through motor  32  is used more efficiently for acceleration work in this phase and results in less heat generation. The duty cycle in the third phase P 3  is constant through third phase P 3 . The duty cycle during third phase P 3  may be less than the duty cycle of first phase P 1 . The duty cycle during third phase P 3  may be greater than 90%, or 85%. The duty cycle in third phase P 3  may be greater than 90% and less than 100%. The duty cycle during third phase P 3  may be 92%. Third phase P 3  may be longer than first phase P 1 . Third phase P 3  may be the same duration as second phase P 2 . Third phase P 3  may be greater than 5 or 8 milliseconds but less than 20 or 15 milliseconds. In some cases, third phase P 3  is between 9-11 milliseconds. In some cases, third phase P 3  is 10 milliseconds. It is noted that second and third phases P 2 , P 3  could be combined (or third phase P 3  eliminated) such that the duty cycle increases (e.g., linearly) through both phases with the starting and ending duty cycle levels discussed in connection with second phase P 2 . 
     The duty cycle through fourth phase P 4  is based on the spray setting input  40 . For example, if the user has input a setting that corresponds with 50% duty cycle (i.e. 50% power), then microcontroller  58  causes the duty cycle to be 50% throughout fourth phase P 4 . As such, the duty cycle through fourth phase P 4  is variable based on user input. However, ring fire and overheating are still concerns at this phase, and therefore the duty cycle has an upper limit regardless of the current spray setting input  40  setting. The upper limit can be 95%, or 92%. As such, if the user set the current spray setting input  40  setting to a level which would correspond to 97% duty cycle, then the duty cycle for fourth phase P 4  would be the upper limit (e.g., 92%), not 97%. Fourth phase P 4  may be longer than any of the first, second, or third phases P 1 , P 2 , P 3  (individually or collectively). Fourth phase P 4  may be greater than 20, 30, or 50 milliseconds but less than 85, 90, or 100 milliseconds. In some cases, Fourth phase P 4  is between 75-85 milliseconds. In some cases, fourth phase P 4  is 82 milliseconds. It is expected that motor  32  may not be spinning at a speed which corresponds to the steady state speed for the setting provide by spray setting input  40  at the beginning of fourth phase P 4 , but it is expected that motor  32  will be spinning at that speed by the end of fourth phase P 4 . In some embodiments, the duration of fourth phase P 4  may be dependent on the acceleration of motor  32  or a feedback parameter. For example, microprocessor  58  may only transition from fourth phase P 4  to fifth phase P 5  when motor  32  speed reaches a level that corresponds with the setting from current spray setting input  40  or when the current through motor  32  is at or crosses a threshold level. 
     Phase P 4  could be longer than 100 ms in other embodiments, such as embodiments using a slightly larger motor or a motor that cannot handle as much current, or a drive and pump system with more mass. In those embodiments, it could take longer to fully accelerate the motor &amp; drive system to sprayable pressures. 
     Fifth phase P 5  corresponds to a steady state phase in which the PWM command signal is modulated based on the setting from current spray setting input  40  and the predetermined current level. In some cases, the current duty cycle will be set at whichever of the current spray setting input  40  setting and the predetermined current level dictates a lower duty cycle at the particular moment. In some cases, the duty cycle will be maintained at the current spray setting input  40  as long as the predetermined current level is within acceptable limit(s), but if the sensed current is beyond the predetermined current level (e.g., over a threshold, such as the first Arms level or outside a Arms range), then microcontroller  58  will reduce or otherwise change the duty cycle to restore the level of the current through motor  32  to the predetermined current level. If the current level through motor  32  is within the predetermined current level, then microcontroller  58  bases the duty cycle on the current spray setting input  40  setting until there is a change in the current level that deviates from the predetermined current level. Limiting the duty cycle based on comparing the sensed current through motor  32  (as represented by the current feedback signal from current feedback circuit  66 ) to the predetermined current level may only be implemented by microcontroller  58  in fifth phase P 5 , and accordingly may not be performed in the first-fourth phases P 1 -P 4 . This is because the current will likely rise well above the predetermined current level during the startup sequence but should decay to, or below, the predetermined current level by the end of the startup sequence. 
     Steady state phase P 5  may extend indefinitely, until the trigger  42  or other activator is deactivated, at which point microcontroller  58  discontinues the PWM command signal, which causes IGBT switch  62  to remain open and current through motor  32  to cease. 
     Cycle frequency of the duty cycle as output by the microcontroller  58  and/or the operational switching frequency of the IGBT switch  62  may change between the startup first-fourth phases P 1 -P 4  and the steady state fifth phase P 5 . For example, the cycle frequency may be at a first frequency during startup first-fourth phases P 1 -P 4  and at a second frequency during steady state fifth phase P 5 . The first frequency may be greater than the second frequency. The first frequency may be at least 10 kHz greater than the second frequency. The first frequency may be less than 20 kHz while the second frequency may be greater than 20 kHz. The first frequency may be 16 kHz while the second frequency may be 32 kHz. The change in cycle frequency balances the heat production and responsiveness of the algorithm for limiting current within motor  32 . For example, a higher switching frequency is more responsive to counteract increases in current through motor  32  but results in higher heat production within the switching components as they cycle at the higher rate. Therefore, switching frequency is lower at the startup phases P 1 -P 4  because higher current is needed through first-fourth phases P 1 -P 4  (which generates greater heat) until motor  32  is accelerated, at which point current through IGBT switch  62  is less and a higher switching frequency in the steady state fifth phase  90  can be tolerated despite increased heat production associated with higher switching frequency. 
     The algorithm demonstrated in  FIG. 3  for motor  32  startup and steady state operation is particularly efficient at accelerating and maintaining motor  32  speed while avoiding ring fire and overheating. This increase in efficiency allows motor  32  to be smaller, which is particularly beneficial for a handheld unit that must be entirely supported by the user. 
     The disclosed controller offers a number of advantages, including increased HVDC motor brush life, increased motor efficiency, elimination of motor thermal trips, reduced motor heat rise, and variable spray output. 
     The peak and RMS current can be controlled to a range below  4 Arms and 7.3 Apeak as would otherwise be typical in prior controllers using triac or SCR communication. This reduction in peak current and RMS current has two significant impacts that affect brush life. The first positive effect is reduced commutation arcing on the trailing edge of the brush between the brush and the rotating commutator bars. This effectively reduces the electrical brush wear rate from that trailing arc causing the brushes to last longer in this application. High peak and RMS currents can cause excessively fast brush wear. The current feedback coupled with the PI loop used by microcontroller  58  helps prevent excessive brush wear. The second effect is a reduction in brush heat rise and steady state operating temperature. Generally, with a temperature decrease, brushes have a lower coefficient of friction during operation which reduces the mechanical ware rate of the brush. Controller  38  can increase the amount of paint a user can spray before replacing the motor from 50 gallons of paint to more than 150 gallons, an increase of 200%. 
     With the addition of high voltage direct current power supply  50 , current feedback circuit  66  and the PI loop used by microcontroller  58 , the sprayer  10  is able to do the same amount of mechanical work but with lower RMS and peak current. With motor  32  operating at higher efficiency, less power is being wasted as heat and more is being used for work. This means paint sprayer  10  can utilize a smaller, lighter weight fractional horsepower motor taking up less space, reducing product weight and cost. 
     One significant issue with many paint spraying products is motor thermal trips. A user will be spraying and the motor will overheat causing an internal thermal fuse to open. A user then needs to wait 30 minutes for the motor to cool down before the user can finish the painting job. This happens because different materials can cause the sprayer to work harder due to their fluid properties. Some fluids increase the load on the motor and thus increase the peak and RMS currents the motor draws. Since controller  38  increases the efficiency of the motor, less power is wasted as heat and more is used to do work. This allows for greater loads to be applied the motor without significant variations in motor current. With the addition of the current feedback loop and PI algorithm, microcontroller  58  keeps the current below the maximum continuous current rating of motor  32 . This means that no matter what materials the user places in sprayer  10 , controller  38  will adapt and limit the power applied to motor  32  to ensure that motor is operating within its designed limits. 
     The ability to provide a variable spray setting with spray setting input  40  significantly enhances the spray performance for the user, reducing paint waste due to overspray and limiting fluid flow dramatically for an improved finish in a wide range of materials and tip sizes. This variable setting provides can provide a large number of different flow reduction operating points for the user. 
     The present disclosure is made using an embodiment to highlight various inventive aspects. Modifications can be made to the embodiment presented herein without departing from the scope of the invention. As such, the scope of the invention is not limited to the embodiment disclosed herein. 
     While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.