Abstract:
A fluid delivery system includes a pump operably coupleable to a source of fluid. A reciprocating electromagnetic actuator is coupled to the pump and has a coil that when energized causes the actuator to drive the pump. Coil current sensing circuitry is configured to provide an indication of current flowing in the coil. A controller is coupled to the coil current sensing circuitry and is configured to calculate a coil drive parameter based upon a plurality of coil current indications from the coil current sensing circuitry. Coil drive circuitry is coupled to the controller and is configured to supply current to the coil based on the coil drive parameter.

Description:
The present disclosure relates to dynamic control of an electric drive, and more specifically, but not by limitation, to dynamic control of an electric drive in a fluid delivery system using current sensing circuitry. 
     BACKGROUND 
     Electric drives comprise devices that use electrical energy to produce mechanical energy (e.g., motion) and are used in a variety of applications. Some electric drives produce rotational forces while some electric drives are configured to produce linear forces. Electric drives can be configured to operate using alternating current (AC) and/or direct current (DC). 
     Examples of applications in which electric drives are utilized include, but are not limited to, manufacturing environments, automotive applications, robotic applications, consumer appliances and hardware, and construction equipment, to name a few. One particular application in which an electric drive can be used is a fluid delivery system. 
     One example of a fluid delivery system includes a device configured to atomize a material (e.g., paints, inks, varnishes, textures, herbicides, insecticides, food products, etc.) that is sprayed through the air. For example, a spray-coating system often includes a fluid source and, depending on the particular configuration or type of system, an electric drive for providing pressurized fluid to an output nozzle or tip that directs the fluid in a desired spray pattern. For example, some common types of paint spraying systems employ compressed gas, usually air compressed by an air compressor, to atomize and direct paint particles onto a surface. Other common types of paint spraying systems include airless systems that employ a pumping unit for pumping paint from a paint source, such as a paint can. Pressurized paint is pumped from the source through a hose, for example, to a spray gun having a tip with a particular nozzle shape for directing the paint in a desired pattern. 
     During use, internal and/or external factors, such as environmental changes, can affect operation of an electric drive. For example, some factors can affect the resonance characteristics of an electric drive system. For instance, in the fluid delivery system example discussed above it may be possible that factors such as changes in the fluid media (e.g., the material being sprayed), the level of fluid in the source, the mass of the user, and/or the position of the system (e.g., sitting on a table, being held by a user), to name a few, can affect the resonance and performance of the electric drive. 
     The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter. 
     SUMMARY 
     A fluid delivery system includes a pump operably coupleable to a source of fluid. A reciprocating electromagnetic actuator is coupled to the pump and has a coil that when energized causes the actuator to drive the pump. Coil current sensing circuitry is configured to provide an indication of current flowing in the coil. A controller is coupled to the coil current sensing circuitry and is configured to calculate a coil drive parameter based upon a plurality of coil current indications from the coil current sensing circuitry. Coil drive circuitry is coupled to the controller and is configured to supply current to the coil based on the coil drive parameter. 
     These and various other features and advantages will be apparent from a reading of the following Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the background. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an exemplary fluid delivery system. 
         FIG. 2  is a cross-sectional view of the system illustrated in  FIG. 1 . 
         FIG. 3  is a schematic block diagram of one embodiment of the fluid delivery system illustrated in  FIG. 1 . 
         FIG. 4  is a flow diagram illustrating a method for dynamically controlling operation of an electric drive, under one embodiment. 
         FIG. 5  is a flow diagram illustrating a method for dynamically controlling operation of an electric drive, under one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure relates to dynamic control of an electric drive, and more specifically, but not by limitation, to dynamic control of an electric drive in a fluid delivery system using current sensing circuitry. In accordance with one embodiment, a current sensing component is utilized to provide information pertaining to a coil current of the electric drive. The current information is provided to a controller comprising a microprocessor, for example, to facilitate adjustment of operating parameters of the electric drive. In one embodiment, the electric drive is power by a DC source and, using pulse width modulation (PWM), a duty cycle (i.e., pulse time) is adjusted to control an amount of current supplied to the coil such that the electric drive operates within a desired or optimum range to provide power to a pump mechanism. The electric drive is configured to be dynamically controlled based on the current information provided by the current sensing component to operate in the desired or optimum range over varying conditions, such as, but not limited to, varying battery voltage, changes in material volume, changes in material viscosity, and/or other factors that can affect resonance or frequency within the system. 
       FIG. 1  illustrates an exemplary fluid delivery system configured to atomize a material (e.g., paints, varnishes, stains, inks, etc.) that is delivered through the air onto a surface. In the embodiment illustrated in  FIG. 1 , the fluid delivery system comprises a handheld paint sprayer  100  for spraying paint material. However, sprayer  100  can be configured to deliver other types of material. Sprayer  100  illustratively comprises an airless system and uses a pumping unit for pumping the paint material from a paint source. 
     Sprayer  100  includes a housing  102  containing electrical components for controlling operation of sprayer  100  and an electric drive operably coupled to a pumping mechanism. The pumping mechanism supplies paint from a paint container  104  to an output nozzle  106  having a particular size and shape for generating a desired spray pattern. Paint container  104  is removably attached to housing  102  by a threaded connection  108 . In one embodiment, the paint container  104  can be external to, and/or spaced apart from, sprayer  100 . For example, in one embodiment paint container  104  comprises a paint can that it position on a floor or table. System  100  includes a tube for supplying paint from the paint can to housing  102 . 
     Sprayer  100  also includes a handle  110  and a trigger  112  that allow a user to hold and control the operation of sprayer  100 . Sprayer  100  also includes a power source for supplying power to the electric drive in housing  102 . In the illustrated embodiment, the power source comprises a battery pack  114 . Battery pack  114  can include primary (e.g., non-rechargeable) batteries and/or secondary (e.g., rechargeable) batteries. In one embodiment, the power source can comprise a battery that is external to sprayer  100 . For example, power can be supplied to sprayer  100  from an external battery using a power cord. In one embodiment, the power source can comprise an AC power source, such as a wall outlet. 
     Sprayer  100  also includes a flow control knob  116  for controlling the flow of fluid, such as paint, through the pumping mechanism. Control knob  116  can be used to control the volume of the spray pattern out of nozzle  106 . 
     The electric drive of sprayer  100  comprises a device that uses electrical energy to produce mechanical energy that drives the pump mechanism.  FIG. 2  is a cross-sectional view of a portion of sprayer  100  illustrating one embodiment of the electric drive.  FIG. 2  illustrates some or all of the internal components of housing  102 . 
     In the embodiment illustrated in  FIG. 2 , the electric drive comprises a reciprocating electromagnetic actuator  222  that is configured to drive the pump mechanism  224 . In one embodiment, actuator  222  is referred to as an AC electromagnetic actuator that is configured to operate by applying an AC input to a coil of the actuator  222 . In another example, actuator  222  can comprise a DC electromagnetic actuator that is configured to operate by applying a DC input to a coil of the actuator  222 . 
     In the illustrated embodiment, power is supplied to the reciprocating electromagnetic actuator  222  from a DC power source (i.e., battery pack  114 ) using pulse width modulation (PWM) to provide a “simulated” AC power source. However, while actuator  222  is illustrated as receiving power from a DC power source (i.e., battery pack  114 ), it is noted that in other embodiments reciprocating electromagnetic actuator  222  can be configured to receive power from an AC power source. 
     Reciprocating electromagnetic actuator  222  includes a magnetic armature  242  and a coil  220  that is wrapped around at least a portion of a laminated stack (or “core”)  240 . The core/coil assembly is stationary or fixed within the housing  102  while the armature  242  is configured to move or pivot about a pivot assembly  244 , for example. Thus, the armature  242  moves in one or more directions with respect to the core/coil assembly based on the current applied to the coil  220 . In the illustrated embodiment, when current is applied to the coil  220  the armature  242  is magnetically attracted toward the core  240  (in a direction represented by arrow  243 ). The force at which the armature  242  is attracted toward the core  240  is proportional to (or otherwise related to) the amount of current applied to the coil  220 . 
     Armature  242  is configured to mechanically contact and drive a piston  246  of the pump mechanism  224 . Movement of piston  246  drives fluid through fluid path  250  toward output  106 . The fluid is supplied from a fluid source (i.e., fluid container  104 ) though a fluid tube  256 . A check valve  252  is provided in the fluid path  250  and allows fluid flow in a first direction  251 . The check value  252  is biased by a spring  254  to prevent, or otherwise limit, the flow of fluid in a second direction  253 . 
     Piston  246  includes a biasing mechanism (illustratively a spring  248 ) that biases the piston in a direction  245 , which is opposite the direction  243  in which piston  246  is driven by armature  242 . In this manner, armature  242  comprises a reciprocating member that moves or oscillates in response to forces applied by spring  248  and the magnetic field interaction between the coil  220  and armature  242 . In one embodiment, a surface  241  that contacts the piston  246  is configured to move in substantially linear directions along a length of the fluid path  250 . During a first action, a current is applied to coil  220  causing the armature  242  to contact piston  246  and drive paint through path  250  to output  106 . During a second action, the current in the coil  220  is removed (or otherwise reduced) causing the spring  248  to actuate the piston  246  toward the armature  242 . As the piston  246  is actuated by the spring  248 , spring  254  operates to close the check valve  252 . The closing of the check valve  252  and the actuation of spring  248  in direction  245  creates at least a partial vacuum in a portion  255  of fluid path  250 , thus causing additional fluid to travel from the fluid container through the fluid tube  256 . The additional fluid is then pumped through the fluid path  250  to the output  106  during a subsequent action of the pump mechanism. In one embodiment, the current applied to the coil  220  is pulsed between high and low values to cause reciprocation of armature  242  to drive piston  246 . 
       FIG. 3  illustrates a schematic block diagram  300  of sprayer  100 . As illustrated, DC power source  114  is configured to supply power to a coil  220  of reciprocating electromagnetic actuator  222 . In one embodiment, reciprocating electromagnetic actuator  222  is configured to operate at 120 Hz. In this manner, piston  246  is actuated by armature  242  once every 8.33 milliseconds (ms). However, it is noted that other types and configurations of the electric drive can be utilized in sprayer  100 . 
     Electromagnetic actuator  222  is operably coupled to pumping mechanism  224  to spray paint from output  106 . In the illustrated embodiment, the power from power source  114  is provided to the electromagnetic actuator  222  through a transistor  326  based on the status of mechanical trigger switch  112 . An overcurrent protection component  328 , such as a fuse, is also utilized. 
     In accordance with one embodiment, a controller  330  utilizes pulse width modulation (PWM) and modulates the duty cycle (i.e., the pulse widths) to control the amount of current supplied to, and thus the mechanical power generated by, electromagnetic actuator  222 . In one embodiment, a microprocessor  331  is provided in sprayer  100  to control the current supplied to the coil  220  of electromagnetic actuator  222 . 
     In accordance with one embodiment, electromagnetic actuator  222  is dynamically controlled using the microprocessor  331  based on a signal received from a current sensor  332 . Current sensor  332  provides current information to controller  330  indicative of the current in coil  220 . The input received from current sensor  332  is utilized by microprocessor  331  to control the pulses for the PWM. In one example, current sensor  332  comprises a resistor across which a voltage is measured, the voltage being proportional to the coil current. In another example, current sensor  332  comprises any suitable electrical component having a quantifiable resistance that can be used to measure the coil current. Examples of electrical components include, but are not limited to, resistors, capacitors, transistors, diodes, et cetera. 
     In the embodiment illustrated in  FIG. 3 , an alarm or visual indicator (such as LED  334 ) is provided to indicate a particular status of sprayer  100 . For example, LED  332  can be utilized to indicate a particular power condition such as low battery voltage, high battery voltage, high current draw, or any other condition of interest. 
       FIG. 4  is a flow diagram illustrating a method  400  for utilizing current sensed by current sensor  332  to dynamically control operation of electromagnetic actuator  222  in sprayer  100 . In one embodiment, some or all of method  400  is implemented by microprocessor  331 . 
     In the example illustrated in  FIG. 4 , the pulse cycle time for the pulse width modulation (PWM) is set for a frequency of 120 Hertz (Hz). However, it is noted that this is one example and is not intended to limit the scope of the concepts herein. In other embodiments, the pulse cycle time can be set for any desired frequency such as, but not limited to, 50 Hz, 60 Hz, 100 Hz, et cetera. 
     At step  402 , the trigger (i.e., trigger  112 ) of sprayer  100  is activated. For example, a user initially depresses and holds the trigger  112 . In one embodiment, upon activation of the trigger the voltage level of the battery  114  is checked. Based on the battery voltage level, the indicator LED  334  can be illuminated and/or operation of sprayer  100  can either be allowed or disabled. 
     At step  404 , the current in coil  220  of electromagnetic actuator  222  is sensed using current sensor  332 . Current information is provided to microprocessor  331 , which analyzes the current information at step  406 . For example, microprocessor  331  can access a lookup table to determine if the coil current is within a predetermined range. In one embodiment, the predetermined range for the coil current is based on the design and characteristics of sprayer  100  and is indicative of a desired, acceptable operation of electromagnetic actuator  222 . 
     Based on the current analysis at step  406 , the microprocessor  331  can adjust the duty cycle (i.e., pulse times) for the PWM at step  408 . For example, the on and off times for each pulse cycle can be adjusted based on the current information feedback such that the coil current for subsequent pulse cycles is within the predetermined range. In one embodiment, the microprocessor  331  sets a “target” pulse time for one or more subsequent pulse cycles. At step  410 , if the trigger  112  remains activated (i.e., depressed), the electromagnetic actuator  222  is operated using the adjusted duty cycle (i.e., the “target” pulse time). 
     In accordance with one embodiment, the “target” pulse time can be further adjusted during subsequent iterations in which steps  404 - 410  are repeated. For example, steps  404 - 410  can be repeated for the first M pulse cycles. In one instance, steps  404 - 410  are repeated for the first  9  pulse cycles. In another embodiment, the number of pulse cycles for which steps of method  400  are repeated can be greater than, or less than, 9 pulse cycles. Moreover, in one embodiment one or more steps of method  400  are implemented periodically. For example, if the trigger remains depressed, the method  400  can be repeated after every N seconds (e.g., 0.5 seconds, 1 second, 2 seconds, et cetera). It is noted that each iteration of method  400  can utilize different coil current and/or pulse time thresholds for determining the “target” pulse time. 
     During use of sprayer  100 , internal and/or external factors (such as environmental changes) can affect operation of electromagnetic actuator  222 . For example, some factors can affect the resonance characteristics of the sprayer  100 . For instance, changes in the paint material (such as the consistency, viscosity, et cetera), the level of fluid in container  104 , the size of and grip of the user operating sprayer  100 , and/or the position of the sprayer  100  (e.g., sitting on a table, being held by the user), can affect the resonance of sprayer  100 . Potentially, these changes can have undesired effects on the performance of sprayer  100 . By utilizing the input from current sensor  332 , microprocessor  331  is able to dynamically control electromagnetic actuator  222  to compensate for such changes and enable electromagnetic actuator  222  to operate with optimum performance over varying conditions, for example. 
       FIG. 5  illustrates one particular embodiment of a method  500  for dynamically controlling electromagnetic actuator  222 . At step  502 , if the trigger is activated the method proceeds to block  504  in which the pulse cycle time is set to an initial value based on the frequency for operation of electromagnetic actuator  222 . For example, in one embodiment the pulse cycle time for the pulse width modulation (PWM) is set for a frequency of 120 Hz. In one example, the period for each cycle is approximately 8.33 milliseconds (ms). 
     At step  506 , the battery voltage can be checked. In one embodiment, the method determines the minimum battery voltage during a period of time (e.g., one or more cycles) after the trigger is activated. The battery voltage may fluctuate during the period of time as a result of the current draw, for instance. For example, the battery voltage may be at a maximum level when the sprayer  100  is not being operated. The battery voltage may drop to the minimum battery voltage level when the trigger is activated and current is being supplied to electromagnetic actuator  222 . 
     If the minimum battery voltage is at or below a first voltage threshold (e.g., 15.5 volts (V)), the indicator LED  334  is illuminated and operation of the sprayer is disabled. If the minimum battery voltage is between the first voltage threshold and a second voltage threshold (e.g., 17.5V), the LED  334  is flashed and operation of the sprayer is allowed. If the battery voltage is above the second voltage threshold, the LED  334  is not illuminated and operation of the sprayer is allowed. 
     At step  508 , the coil  220  is charged during the first two pulse cycles. The pulse during each of the first two pulse cycles is terminated if a particular termination condition is met. For example, the pulse can be terminated if the coil current is greater than a current threshold and/or a maximum pulse time is reached. The coil current threshold and/or maximum pulse time threshold can be obtained by accessing a lookup table, in one embodiment. In one example, the coil current threshold at step  508  is approximately 25 amps (A) and the maximum pulse time threshold is approximately 7.8 ms. After the pulses have been terminated, the off time for the remaining portion of the pulse cycles is calculated based on 120 Hz (or other frequency, based on the system). 
     At step  510 , during the third pulse cycle, the pulse is terminated if a termination condition is met. For example, the third pulse is terminated if the coil current is greater than a current threshold, a “dip and rise” in the coil current is detected, and/or a maximum pulse time is reached. As used herein, a “dip and rise” means the coil current reaches a local minima following a coil current decrease. In one embodiment, at step  510  the current threshold is approximately 18.5 A and the maximum pulse time is approximately 6.5 ms. 
     When the pulse is terminated at step  510 , the duration of the pulse during the third pulse cycle is saved as the “target” pulse time at step  512 . If the “target” pulse time is determined to be too short (e.g., less than 5 ms), the “target” pulse time can be set to a default (i.e., 5 ms). The off time for the remaining portion of the pulse cycle is calculated based on 120 Hz. As illustrated, in one embodiment the first two pulse cycles are disregarded and are not used to calculate the “target” pulse time. 
     At step  514 , during the next pulse cycle (in this case the fourth pulse cycle), the pulse is terminated if a termination condition is met. For example, the pulse can be terminated at step  514  if the coil current is greater than a current threshold, a “dip and rise” in the coil current is detected, and/or the pulse time equals the “target” pulse time set at step  512 . 
     If the pulse is terminated due to the current threshold, at step  516  the new, adjusted “target” pulse time is set to be equal to the current “target” pulse time (set at step  512 ) minus a margin. In one embodiment, the margin is 277 microseconds (μs), for example. 
     If the termination of the pulse at step  514  is due to a detected “dip and rise” in the coil current, at step  518  the new, adjusted “target” pulse time is set to be the average of the pulse time recorded at step  514  and the current “target” pulse time (set at step  512 ). 
     After the pulse is terminated at step  514 , the off time for the remaining portion of the cycle is calculated based on 120 Hz. 
     At step  520 , method  500  determines whether to repeat steps  514 - 518  for additional pulse cycles. In one embodiment, steps  514 - 518  are repeated for the next N pulse cycles. In one example, steps  514 - 518  are repeated for the next 5 pulse cycles (i.e., pulse cycles  5 - 9 ). In other examples, steps  514 - 518  are repeated for more than, or less than, the next 5 pulse cycles. 
     At step  522 , the current “target” pulse time is used for any remaining pulse cycles. In one example, the pulse cycles continue for as long as the trigger remains activated. For each of the remaining pulse cycles, the pulses are terminated based on a termination condition. For example, as illustrated in step  524  the pulses are terminated based on a current threshold and/or the current “target” pulse time. 
     In accordance with one embodiment, some or all of the steps of establishing a “target” pulse time illustrated in steps  504 - 518  can be repeated periodically. For example, the “target” pulse time can be recalculated periodically, such as every N seconds (e.g., 0.5 seconds, 1 second, 2 seconds, et cetera). It is noted that this is one example, and is not intended to limit the scope of the concepts described herein. 
     In method  500 , for each step where the pulse is terminated based on coil current thresholds and/or maximum pulse time thresholds (e.g., steps  508 ,  510 ,  514 , etc.), it is noted that different thresholds can be utilized for one or more of the steps, for example by accessing a lookup table stored in controller  330 . 
     While various embodiments of the invention have been set forth in the foregoing description, together with details of the structure and function of various embodiments of the disclosure, this disclosure is illustrative only, and changes may be made in detail, especially in matters of structure and arrangement of parts within the principles of the present disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. For example, the particular elements may vary depending on the particular application for the system or method while maintaining substantially the same functionality without departing from the scope and spirit of the present disclosure and/or the appended claims.