Patent Publication Number: US-11638928-B2

Title: Dispenser with closed loop control

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 16/389,061, filed Apr. 19, 2019, which claims the benefit of U.S. Provisional Patent App. No. 62/667,696, filed May 7, 2018, the entire disclosures of both of which are hereby incorporated by reference as if set forth in their entirety herein. 
    
    
     TECHNICAL FIELD 
     This disclosure generally relates to fluid dispensing applicators, and more particularly relates to control loops for controlling the operation of a piezoelectric device within the fluid dispensing applicator. 
     BACKGROUND 
     Known applicators for dispensing fluid materials such as solder paste, conformal coatings, encapsulants, underfill material, and surface mount adhesives generally operate to dispense small volumes of fluid material onto a substrate by reciprocating a needle. One method of actuating the needle is through a piezoelectric device, which provides a high level of control and quick response to changes in operation. During jetting operation, for example, upon each down stroke, the needle contacts a valve seat to create a distinct, high pressure pulse that jets a small amount of a material from a nozzle of the applicator. The reciprocal movement of the needle must be precise to maintain a jetted dot of material having specific size and shape qualities that suit a particular purpose. However, the size and shape of a jetted dot of material may stray from the intended values over time. This may be in part to material wear, environmental changes, parts replacement, etc. Without accounting for these changes, undesirable fluid patterns may be applied, which can provide an unacceptable end product. 
     As a result, there is a need for a system that allows for dynamic, continuous, and automatic correction of needle motion to provide for a consistent jetted material dot size and shape. 
     SUMMARY 
     An embodiment of the present disclosure is a system for controlling needle motion of a material applicator. The system includes an actuator assembly that contains a piezoelectric device, wherein the actuator assembly is connected to a needle and configured to translate the needle along a vertical direction, and a sensor assembly comprising an emitter for emitting light, where a portion of the actuator assembly or a portion of the needle occludes a portion the light. The sensor assembly also includes a receiver for receiving a non-occluded portion of the light and a sensor holder configured to secure the emitter and the receiver. The system further includes a controller in electrical communication with the piezoelectric device, emitter, and receiver, where the controller is configured to adjust operation of the actuator assembly based on feedback received from the receiver. 
     Another embodiment of the present disclosure is a method of controlling needle motion of a material applicator that includes an actuator assembly coupled to a needle. The method includes actuating a piezoelectric device of the actuator assembly such that the needle translates along a vertical direction and emitting light from an emitter to a receiver such that a portion of the actuator assembly or a portion of the needle occludes a portion of the light and the receiver receives a non-occluded portion of the light. The method also includes adjusting operation of the piezoelectric device based on feedback received from the receiver. 
     A further embodiment of the present disclosure is a system for controlling a needle motion of a material applicator. The system includes an actuator assembly that contains a piezoelectric device, where the actuator assembly is connected to a needle and configured to translate the needle along a vertical direction between a first position where the needle is spaced from a valve seat of a nozzle and a second position where the needle contacts the valve seat. Transitioning the needle between the first and second positions jets an amount of the material from the nozzle. The system also includes a sensor assembly having an emitter for emitting light, where a portion of the actuator assembly or a portion of the needle occludes a portion of the light, and a receiver for receiving a non-occluded portion of the light, where the receiver is positioned on an opposite side of the actuator assembly from the emitter. The sensor assembly further has a sensor holder configured to secure the emitter and the receiver. The system also includes a controller in electrical communication with the piezoelectric device, emitter, and receiver, where the controller is configured to operate a feedback loop to adjust a voltage supplied to the piezoelectric device of the actuator assembly based on feedback received from the receiver to maintain a constant size and shape of the material jetted from the nozzle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing summary, as well as the following detailed description, will be better understood when read in conjunction with the appended drawings. The drawings show illustrative embodiments of the disclosure. It should be understood, however, that the application is not limited to the precise arrangements and instrumentalities shown. 
         FIG.  1    is a perspective view of an applicator; 
         FIG.  2    is an alternative perspective view of the applicator shown in  FIG.  1   ; 
         FIG.  3 A  is a cross-sectional view of the applicator shown in  FIG.  1   , taken along line  3 A- 3 A shown in  FIG.  2   ; 
         FIG.  3 B  is an enlarged view of the encircled region of the applicator shown in  FIG.  3 A ; 
         FIG.  4    is a cross-sectional view of the applicator shown in  FIG.  1   , taken along line  4 - 4  shown in  FIG.  2   ; 
         FIG.  5 A  is a diagram illustrating an embodiment of a control loop for controlling a piezoelectric device of an applicator; 
         FIG.  5 B  is a diagram illustrating another embodiment of a control loop for controlling a piezoelectric device of an applicator; 
         FIG.  5 C  is a diagram illustrating a further embodiment of a control loop for controlling a piezoelectric device of an applicator according to an embodiment of the present disclosure; 
         FIG.  6    is a plot of a voltage waveform provided to a piezoelectric device of the applicator shown in  FIG.  1    over time; and 
         FIG.  7    is a process flow diagram of a method of controlling needle motion of an applicator. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     An applicator  10  according to an embodiment of the present disclosure includes an actuator assembly  111  that includes a piezoelectric device  112 , where the actuator assembly  111  is connected to a needle  76 . The applicator  10  also includes a sensor assembly  138  that includes a sensor holder  140  that supports an emitter  154  and a receiver  156 , as well as a controller  166  for receiving feedback from the sensor assembly  138 . Certain terminology is used to describe the applicator  10  in the following description for convenience only and is not limiting. The words “right,” “left,” “lower,” and “upper” designate directions in the drawings to which reference is made. The words “inner” and “outer” refer to directions toward and away from, respectively, the geometric center of the description to describe the applicator  10  and related parts thereof. The words “forward” and “rearward” refer to directions in a longitudinal direction  2  and a direction opposite the longitudinal direction  2  along the applicator  10  and related parts thereof. The terminology includes the above-listed words, derivatives thereof, and words of similar import. 
     Unless otherwise specified herein, the terms “longitudinal,” “lateral,” and “vertical” are used to describe the orthogonal directional components of various components of the applicator  10 , as designated by the longitudinal direction  2 , lateral direction  4 , and vertical direction  6 . It should be appreciated that while the longitudinal and lateral directions  2 ,  4  are illustrated as extending along a horizontal plane, and the vertical direction  6  is illustrated as extending along a vertical plane, the planes that encompass the various directions may differ during use. 
     Embodiments of the invention include an applicator  10  for apply a material, such as a hot melt adhesive, to a substrate during manufacturing. In particular, the material may be a polyurethane reactive (PUR) hot melt. Referring to  FIGS.  1 - 2   , the applicator  10  includes a first connector  26  and a second connector  28 . The first connector  26  may define a male connection comprising a plurality of tines, and is configured to connect to a wire (not shown) that connects the first connector  26  to a power source, such that the applicator  10  receives a power input through the first connector  26 . The second connector  28  may define a female connection comprising a plurality of recesses, and can be configured to connect to a wire (not shown) that connects the second connector  28  to a controller, such as controller  166 , which will be discussed further below, such that information is transmitted to and from the applicator  10  through the second connector  28 . The controller may be a general purpose computer, tablet, laptop, smartphone, etc. However, the first and second connectors  26 ,  28  may be configured as other types of connectors as desired. In other embodiments, the applicator  10  may transmit information to a controller wirelessly via Bluetooth or Wi-Fi. The first and second connectors  26 ,  28  are configured to be mounted to a circuitry housing  32 , which can contain a circuit board (not shown). 
     The applicator  10  includes a cap  18  that is configured to cover an opening through which material is to be added to the applicator  10 . Though in the depicted embodiment the applicator  10  is configured to receive a syringe (not shown) that contains material, it is contemplated that the applicator  10  may receive material through alternative means, such as through filling material directly into the applicator  10  or providing the applicator  10  with an input to an external material source, such as a hopper or melter (not shown). The cap  18  can receive an input connector  22  that extends through the cap  18 . The input connector  22  can be configured to interface with an external pressurized air source, which functions to selectively move material through the applicator  10 . 
     The applicator  10  can further include a cap seat  19 , which is disposed between the cap  18  and a heater  36 . In addition to supporting the cap  18 , the cap seat  19  is configured to interact with the cap  18  such that the cap  18  is locked to the cap seat  19  during operation of the applicator  10 , in particular when pressurized air is received by the heater  36  through the input connector  22 . The cap seat  19  can be releasably coupled to the applicator  10 , such that the cap seat  19  secures the heater  36  within the applicator  10  when the cap seat  19  is attached to the applicator  10 , and provides an opening for removing the heater  36  from the applicator  10  when the cap seat  19  is detached from the applicator  10 . The cap seat  19  can define a channel that extends therethrough and is sized to allow a syringe to pass into the heater  36 . 
     Continuing with  FIGS.  1 - 2   , the heater  36  functions to provide heat to the material contained therein, which may be housed within with a syringe. This allows the material to be maintained at a desirable temperature for jetting and flowing through the applicator  10 , as well as allows an operator of the applicator  10  to monitor the temperature of the material within the heater  36  to avoid unintentional temperature peaks or dips in temperature of the material. The heater  36  can define a hollow, substantially cylindrical body that is open to the cap seat  19  for receiving the material, around which a heating element (not shown) is disposed. Portions of the heater  36  can be formed of a metal, such as aluminum, though other materials may be included that have sufficient conductivity to allow heat to pass through for heating the material within the heater  36 . The heater  36  can also include a temperature sensor (not shown) that is in communication with the controller  166  for monitoring temperature levels within the heater  36 . 
     At the bottom of the heater  36 , the heater  36  is supported by a connector  44 , which connects the heater  36  to the plate assembly  47 . The connector  44  defines a passageway that allows the heated material contained within heater  36  to flow out of the heater  36  and into the plate assembly  47 . The plate assembly  47 , which is located at the lower end of the applicator  10 , provides a pathway for material to flow from the heater  36  to the jetting dispenser assembly  54 , which will be described below. The plate assembly  47  can include a plurality of plates, such as a top plate  48  and a bottom plate  52  that are releasably coupled together to form the plate assembly  47 . However, the plate assembly  47  can include more than two plates, such as three, four, or more plates as desired. Alternatively, the plate assembly  47  can be replaced with a monolithic block (not shown) that similarly provides a pathway for material to flow from the heater  36  to the jetting dispenser assembly  54 . When two plates are included in the plate assembly  47 , the passageway through the plate assembly  47  can be defined at least partially by each of the top and bottom plates  48 ,  52 . The top and bottom plates  48 ,  52  can be configured to receive a seal  86  at their interface that surrounds the passageway through the plate assembly  47  and prevent material from exiting the passageway. 
     When the plate assembly  47  is fully assembled, the bottom surface of the top plate  48  may contact the top surface of the bottom plate  52 , such that the top plate  48  is disposed above the bottom plate  52  along the vertical direction  6 . The top plate  48  can be releasably coupled to a housing  58  through a plurality of threaded fasteners  57  that extend through the top plate  48  and engage the housing  58 . However, other methods of releasably coupling the top and bottom plates  48  and  52  are contemplated. For example, the top and bottom plates  48 ,  52  may be coupled by snap fit engagement, dovetail slot structure, etc. The plate assembly  47  may comprise a heating block, such that the top and bottom plates  48  and  52  are configured to heat material that passes through the plate assembly  47 , thus ensuring that the material maintains optimal qualities for flow and dispensing. 
     Now referring to  FIGS.  3 A- 3 B , the jetting dispenser assembly  54  will be described in greater detail. Components of the jetting dispenser assembly  54  can be received within a chamber  72  that is at least partially defined by each of the top and bottom plates  48 ,  52  of the plate assembly  47 . The jetting dispenser assembly  54  can include a nozzle  56  that defines a valve seat  80  and a discharge passageway  82  that extends from the chamber  72  to the to the exterior of the applicator  10 . The discharge passageway  82  is the conduit by which material exits the applicator  10  and is applied to a substrate. The jetting dispenser assembly  54  further includes a needle  76  that extends through and is movable within the chamber  72 . The needle  76  defines a needle tip  76   a  and a needle stem  76   b  that extends away from the needle tip  76   a  along the vertical direction  6 . The needle tip  76   a  can be configured to engage the valve seat  80  to form a seal, such that when the needle tip  76   a  engages the valve seat  80 , material is prevented from flowing through the discharge passageway  82 . As such, the needle  76  is moveable within the chamber  72  between a first position and a second position along the vertical direction  6 . In the first position, the needle tip  76   a  is spaced form the valve seat  80  along the vertical direction  6 , which allows the material to access the discharge passageway  82 . In the second position, the needle tip  76   a  engages the valve seat  80 , thus preventing material from entering the discharge passageway  82 . In a jetting dispenser assembly  54  such as the one depicted, actuation of the needle from the first position to the second position causes the needle tip  76   a  to jet an amount of material through the discharge passageway  82 . This jetting motion can be repeated rapidly, which allows for discrete dots of material having a predetermined size and shape to be applied to a substrate. The needle tip  76   a  and the valve seat  80  may be configured to have complementary shapes to prevent material leakage. In one embodiment, the needle tip  76   a  and the valve seat  80  may comprise complementary hemispherical shapes. Alternatively, the needle tip  76   a  and the valve seat  80  may comprise complementary flat shapes. The mechanism by which the needle  76  is actuated between the first and second positions will be described further below. 
     The jetting dispenser assembly  54  further includes a seal pack  90  that is configured to be received within the chamber  72 . Specifically, the seal pack  90  divides the chamber into two sections—a first section that is below the seal pack  90  along the vertical direction  6 , and a second section that is above the seal pack  90  along the vertical direction  6 . The seal pack  90  defines a ledge  94  that is configured to engage the top surface of the bottom plate  52 , which vertically positions the seal pack  90  within the chamber  72 . The seal pack  90  also defines a seal pack passageway  95  that extends through the seal pack  90  along the vertical direction  6 . The seal pack passageway  95  is configured to receive the needle stem  76   b , such that the needle  76  extends through the second section  72   b  of the chamber  72 , through the seal pack  90 , and into the first section  72   a  of the chamber  72 . The seal pack  90  may house a seal  96  within the seal pack passageway  95  that substantially surrounds the needle stem  76   b . The seal  96  may function to prevent material from flowing from the first section  72   a  of the chamber  72  into the second section  72   b  through the seal pack passageway  95 . Additionally, the jetting dispenser assembly  54  can include a seal  98  disposed around the seal pack  90  between the seal pack  90  and the top plate  48  of the plate assembly  47 . The seal  98  can prevent material from flowing from the top plate  48  to the gap between the top plate  48  and the housing  58 . Alternatively, the seal  98  can be disposed around the seal pack  90  between the seal pack  90  and the bottom plate  52 . As such, the seals  96  and  98  aid in keeping the material within the first section  72   a  of the chamber  72  after the material exits the passageway defined by the plate assembly  47 . 
     Further, the jetting dispenser assembly  54  includes a spring  104  disposed within the second section  72   b  of the chamber  72 . The spring  104  is disposed between a portion of the housing  58  that bounds the second section  72   b  of the chamber  72  and a ledge  100  defined by the needle  76 . The spring  104  may be placed within the jetting dispenser assembly  54  in a naturally compressed state, such that the spring  104  constantly applies a downward force to the ledge  100 . This downward force on the ledge  100  of the needle  76  biases the needle  76  downward along the vertical direction  6 . As such, the spring  104  naturally biases the needle  76  into the second position, such that an upward force on the needle  76  is required to displace the needle tip  76   a  from the valve seat  80 , and thus transition the needle  76  from the second position to the first position. 
     Continuing with  FIGS.  3 A- 3 B , the jetting dispenser assembly  54  also includes an actuator assembly  111  operatively coupled to the needle  76 . The actuator assembly  111  can include a piezoelectric device  112  and a pair of movable actuator arms  108 ,  110 . The actuator arms  108 ,  110  may extend diagonally from respective corners of the piezoelectric device  112  in a direction towards each other and the top end of the needle stem  76   b . A connector  109  is configured to connect the pair of actuator arms  108 ,  110  together, as well as secure the actuator arms  108 ,  110  to the upper end of the needle stem  76   b . The connector  109  can secure the needle stem  76   b  through a pair of locking tabs that project radially inwards towards each other, though other means of attachment are contemplated. For example, the connector  109  and the needle stem  76   b  can be releasably attached through a threaded engagement. 
     The piezoelectric device  112  is configured to translate the needle  76  between the first and second positions. The actuator assembly  111  is coupled to controller  166  external to the actuator that controls operation of the piezoelectric device  112 . The controller  166  will be described further below. The actuator assembly  111  is also coupled to a power source (not shown) that provides power to the piezoelectric device. As noted above, the needle  76  is in a neutral position in the second position, such that the needle tip  76   a  engages the valve seat  80 . To transition the needle  76  to the first position, the controller directs the power source to provide a positive charge to the piezoelectric device  112 . This positive charge causes the piezoelectric device  112 , which may include a piezoelectric stack, to expand, which pulls the actuator arms  108 ,  110  toward the piezoelectric device  112 . Thus, the actuator arms  108 ,  110  and the needle  76  are pulled toward the piezoelectric device  112 , causing the needle tip  76   a  to draw away from the valve seat  80 . When the controller  166  directs the power source to cease providing the positive charge to the piezoelectric device  112 , the piezoelectric device  112  retracts, which pushes the actuator arms  108 ,  110  away from the piezoelectric device  112 . This retraction of the piezoelectric device  112 , along with the force applied by the spring  104  to the ledge  100  of the needle  76 , forces the needle  76  downward such that the needle tip  76   a  impacts the valve seat  80 . When the needle tip  76   a  impacts the valve seat  80 , material is jetted through the discharge passageway  82  of the nozzle  56 . 
     Referring to  FIGS.  1 - 3 B , the piezoelectric device  112  can be connected to a lower block  114  through fasteners  113 , and the lower block  114  can be connected to an upper block  115  through fasteners  116 . Collectively, the piezoelectric device  112 , lower block  114 , and upper block  115  can comprise the actuator assembly  111 . The actuator assembly  111  can be disposed between first and second plates  60   a ,  60   b , which can be spaced apart along the lateral direction  4 . The first and second plates  60   a ,  60   b  may each define at least one slot that is configured to allow a fastener  64  to extend through. The fastener  64  can extend through the slot of the first plate  60   a , through the lower block  114 , through a corresponding slot of the second plate  60   b , and engage a nut  65 , which is disposed adjacent to plate  60   b . The fastener  64  can be threaded to engage the nut  65 , such that the fasteners  64  and nut  65  can be loosened from and tightened to the first and second plates  60   a ,  60   b , respectively. Loosening the fastener  64  and nut  65  from the plates  60   a ,  60   b  allows movement of the actuator assembly  111  along the vertical direction  6  relative to other components of the applicator  10 . Adjusting the position of the actuator assembly  111  adjusts the initial position of the needle  76 , thus changing the stroke length of the needle  76 , which is defined as the distance the needle  76  travels between the first position and the second position. The ability to adjust the initial position and the stroke length of the needle  76  allows the applicator  10  to have flexibility in types of material that can be jetted form the jetting dispenser assembly  54  and the types of jetting operations the applicator  10  can perform. Once the position of the actuator assembly  111  has been adjusted, the fastener  64  and nut  65  can be tightened to the plates  60   a ,  60   b , such that the actuator assembly  111  is locked in position. Though only one fastener  64  and nut  65  are shown, the applicator  10  can include a plurality of fasteners and corresponding nuts to further aid in adjustment of the actuator assembly  111 . 
     Continuing with  FIG.  3 A , the applicator  10  includes a stop  118  disposed above the upper block  115  along the vertical direction  6 . The stop  118 , which is positioned between the first and second plates  60   a ,  60   b , can be affixed to a plate  68  via fasteners  120 . The plate  68  can also be affixed to any combination of the plates  60   a ,  60   b  as well. The stop  118  can define a central channel  119  that is configured to receive a connector  124  that is attached to the upper block  115 . The connector  124  can receive pressurized air from an external source (not shown) for reducing heat buildup around the actuator assembly  111 . 
     Now referring to  FIGS.  1 ,  2 , and  4   , the applicator  10  includes a sensor assembly  138  for measure a position and/or velocity of a portion of the actuator assembly  111 . The sensor assembly  138  includes a sensor holder  140  that defines a vertically-extending central body portion  142   a  positioned adjacent the actuator assembly  111  along the longitudinal direction  2 . The sensor holder  140  can also define a first arm  142   b  that extends from the central body portion  142   a  along the longitudinal direction  2  and a second arm  142   c  that also extends from the central body portion  142   a  along the longitudinal direction  2 . The first and second arms  142   b ,  142   c  can be spaced apart along the lateral direction  4  on opposite sides of the actuator assembly  111 , and can be vertically aligned with at least a portion of the actuator assembly  111 . Though depicted as being located in a particular vertical position, the sensor assembly  138  can be adjusted upwards and downwards along the vertical direction  6  in relation to other components of the applicator  10 . To this end, the central body portion  142   a  of the sensor holder  140  defines a first slot  146   a  positioned at an upper end of the central body portion  142   a  and a second slot  146   b  positioned opposite the first slot  146   a  at a lower end of the central body portion  142   a . Each of the first and second slots  146   a ,  146   b  can be configured as substantially cylindrical slots, though other shapes are contemplated. Additionally, though only two slots are shown, the central body portion  142   a  can define more or less slots as desired. For example, the central body portion  142   a  can define only one slot, or can define three or more slots. 
     The first slot  146   a  of the sensor holder  140  can align with a bore  132  that extends into the stop  118  along the longitudinal direction, while the second slot  146   b  can align with a bore  128  that extends into the housing  58  along the longitudinal direction  2 . Each of the bores  128 ,  132  can be configured to receive a corresponding fastener  136 . For example, a fastener  136  can extend through the first slot  146   a  and into the bore  132 , while another fastener  136  can extend through the second slot  146   b  and engage the bore  128 . Each of the fasteners  136 , as well as the bores  128 ,  132 , can be at least partially threaded to permit threaded engagement between each of the fasteners  136  and the corresponding one of the bores  128 ,  132 . Though each of the fasteners  136  is depicted as being the same, the fasteners  136 , and likewise the first and second slots  146   a ,  146   b  can be differently configured as desired. 
     In operation, the sensor holder  140  can be attached to the other components of the applicator  10  by aligning the first slot  146   a  with the bore  132  and the second slot  146   b  with the bore  128 . Then, a fastener  136  can be inserted through the first slot  146   a  and engaged with the bore  132 , while another fastener  136  can be inserted through the second slot  146   b  and engaged with the bore  128 . Each of the fasteners  136  can then be sufficiently tightened such that the compressive force imparted on the sensor holder  140  by the fasteners  136 , stop  118 , and housing  58  locks the sensor assembly  138  relative to the other components of the applicator  10 . To adjust the position of the sensor assembly  138  along the vertical direction  6 , the upper fastener  136  can be sufficiently loosened from the bore  132  and the lower fastener  136  can be sufficiently loosened from the bore  128  such that the fasteners still extend through the first and second slots  146   a ,  146   b , and engage the bores  132  and  128 , respectively, but the sensor holder  140  is capable of moving along the vertical direction  6 . The sensor holder  140  can thus be moved along the vertical direction  6  to a desired position. However, the fasteners  136  still extending through the first and second slots  146   a ,  146   b  limits the range of motion the sensor holder  140  is capable of, such as only along the vertical direction  6 . Once the sensor holder  140  is in the desired position, the fasteners  136  can again be sufficiently tightened against the sensor holder  140  so that the sensor holder  140  is again affixed relative to the other components of the applicator  10 . 
     Now referring to  FIG.  4   , the first arm  142   b  of the sensor holder  142  defines a first bore  148   a , while the second arm  142   c  of the sensor holder  142  defines a second bore  148   b . The first and second bores  148   a ,  148   b , are thus positioned on opposite sides of the actuator assembly  111 , but can be oriented such that they are aligned and face each other along a direction D. As depicted, the direction D lies along a plane defined by the longitudinal and lateral directions  2 ,  4  and is normal to the vertical direction  6 , which further results in the direction D being perpendicular to the direction of motion of the needle  76  as it transitions between the first and second positions. Additionally, the direction D is depicted as angularly offset from both the longitudinal and lateral directions  2 ,  4 . However, the direction D can be alternatively configured as extending in any direction within the plane defined by the longitudinal and lateral directions  2 ,  4 , or even angularly offset from this plane such that the direction D defines a component along the vertical direction  6 . 
     The first bore  148   a  can be sized so as to receive one of an emitter  154  or a receiver  156 , while the second bore  148   b  can also be sized so as to receive one of an emitter  154  or a receiver  156 . In the depicted embodiment, the emitter  154  is shown as secured to the sensor holder  140  within the first bore  148   a , while the receiver  156  is shown as secured to the sensor holder  140  within the second bore  148   b , though it is contemplated that this arrangement can be reversed. Regardless of which of the first and second bores  148   a ,  148   b  the emitter  154  and receiver  156  are respectively received in, in the depicted embodiment the emitter  154  and receiver  156  are shown as being positioned on opposite sides of the actuator assembly  111 . In operation, the emitter  154  can be configured to emit light L, and the receiver  156  can be configured to receive at least a portion of the light L emitted by the emitter  154 . The emitter  154  can be any emitter capable of emitting light, such as an LED, or more specifically can be an emitter capable of emitting light in the infrared spectrum. The receiver  156  can be any type of receiver that can be tuned to receive light having the wavelength emitted by the corresponding emitter  154 . As the emitter  154  and receiver  156  are aligned along the direction D, light L emitted by the emitter  154  can be at least partially occluded by a portion of the actuator assembly  111  at any particular time, depending on the position of the actuator assembly  111  and the given position of the needle  76  within a jetting cycle. The receiver  156  then receives the non-occluded portion of the light. Alternatively, the light L emitted by the emitter  154  can be at least partially occluded by a portion of the needle  76 . 
     Though the sensor assembly  138  is depicted such that the sensor holder  140  defines two arms  142   b ,  142   c , where the first arm  142   b  supports the emitter  154  and the second arm  142   c  supports the receiver  156 , alternative embodiments are contemplated. In one embodiment, both the emitter  154  and receiver  156  can be secured to one of the first and second arms  142   b ,  142   c , such that both the emitter  154  and the receiver  156  face the same side of the actuator assembly  111 . As a result, the sensor holder  140  may only include one of the first and second arms  142   b ,  142   c  in this embodiment (not shown). In operation, in this embodiment the emitter  154  can emit light L, which can interact with a portion of the actuator assembly  111  or needle  76  and received at least in part by the receiver  156 . However, rather than receiving the portion of the light L not occluded by the actuator assembly  111  or the needle  76 , in this embodiment the receiver  156  will receive the portion of the light L reflected by the component with which it interacts. 
     Now referring to  FIGS.  4 - 5 C , the applicator  10  includes a controller  166  coupled to the emitter  154  and the receiver  156  through connections  160 ,  162 , respectively. The controller  166  can comprise any suitable computing device configured to host a software application for monitoring and controlling various operations of the applicator  10  as described herein. It will be understood that the controller  166  can include any appropriate computing device, examples of which include a processor, a desktop computing device, a server computing device, or a portable computing device, such as a laptop, tablet, or smart phone. Specifically, the controller can include a memory  170  and an HMI device  174 . The memory  170  can be volatile (such as some types of RAM), non-volatile (such as ROM, flash memory, etc.), or a combination thereof. The controller  166  can include additional storage (e.g., removable storage and/or non-removable storage) including, but not limited to, tape, flash memory, smart cards, CD-ROM, digital versatile disks (DVD) or other optical storage, magnetic tape, magnetic disk storage or other magnetic storage devices, universal serial bus (USB) compatible memory, or any other medium which can be used to store information and which can be accessed by the controller  166 . The HMI device  174  can include inputs that provide the ability to control the controller  166 , via, for example, buttons, soft keys, a mouse, voice actuated controls, a touch screen, movement of the controller  166 , visual cues (e.g., moving a hand in front of a camera on the controller  166 ), or the like. The HMI device  174  can provide outputs, via a graphical user interface, including visual information, such as the visual indication of the current position and velocity values of the needle  76 , as well as acceptable ranges for these parameters via a display. Other outputs can include audio information (e.g., via speaker), mechanically (e.g., via a vibrating mechanism), or a combination thereof. In various configurations, the HMI device  174  can include a display, a touch screen, a keyboard, a mouse, a motion detector, a speaker, a microphone, a camera, or any combination thereof. The HMI device  174  can further include any suitable device for inputting biometric information, such as, for example, fingerprint information, retinal information, voice information, and/or facial characteristic information, for instance, so as to require specific biometric information for access the controller  166 . 
     The controller  166  can control the emission of light L from the emitter  154  by transmitting instructions to the emitter  154  through the connection  160 , as well as receive a signal from the receiver  156  indicative of the portion of the light L received by the receiver  156  through the connection  162 . Each of the connections  160 ,  162  can be a wired connection or wireless connection. Examples of suitable wireless connections include ZigBee, Z-wave, Bluetooth, Wi-Fi, or radio wave. The portion of the light L received by the receiver  156  can comprise feedback into a control loop implemented by the controller  166 , which will be discussed further below. The controller  166  can use the information about the light L received from the receiver  156 , which can also be referred to as feedback, to determine a position of the needle  76  at a discrete moment in time. The controller  166  can also use the information about the light L received from the receiver  156  to determine a velocity of the needle  76  at a discrete moment in time. The controller  166 , in addition to being in signal communication with the emitter  154  and the receiver  156 , can also be in signal communication with the piezoelectric device  112  of the actuator assembly  111 . In response to receiving the feedback from the receiver  156 , the controller  166  can adjust the operation of the actuator assembly  111  using one of the control loops  200   a - 200   c  described below to maintain a desired jetted material dot size and shape. 
     The controller  166  is configured to implement a control loop to control the operation of the actuator assembly  111 , and thus the movement of the needle  76  between the first and second positions. To achieve this, the control loop can comprise one of the control loops  200   a - 200   c  ( FIGS.  5 A- 5 C ). The input into the control loops  200   a - 200   c  can be a desired voltage waveform provided to the piezoelectric device  112  of the actuator assembly  111 . The memory  170  can be configured to store a variety of voltage waveforms, each of which has a predetermined relation to a particular motion pattern or velocity of the needle  76  and a particular dot size and/or shape. The particular voltage waveform provided to a particular one of the control loops  200   a - 200   c  can be recalled from the memory  170  in response to a particular input into the HMI device  174 . The input provided to the HMI device  174  can be a desired jetting motion of the needle  76 , a specific jetting operation, a particular fluid or substrate to be utilized, a particular jetted dot size and shape, initial voltage values to provide to the piezoelectric device  112 , a voltage rate at which to apply voltage to the piezoelectric device  112 , etc. Each of these inputs, as well as others, can be correlated to a specific voltage waveform stored in the memory  170 , which can be automatically recalled and inputted into one of the control loops  200   a - 200   c  upon receiving the corresponding input. Likewise, the outputs of each of the control loops  200   a - 200   c  is an adjustment to the voltage or voltage rate provided to the piezoelectric device  112  in order to achieve the desired needle motion, which is in part determined from the feedback received from the sensor assembly  138 . 
       FIG.  5 A  shows one embodiment of a control loop  200   a  that can be implemented by the controller  166 . Control loop  200   a  embodies a typical feedback controller. The control loop  200   a  receives an input that can take the form of a desired voltage waveform, as described above. However, this input only partially comprises the complete input provided to the control loop  200   a . In addition to the desired voltage waveform, the control loop  200   a  incorporates the feedback received from the sensor assembly  138 , particularly the receiver  156 , into the input. This complete input is then provided to a feedback controller  204 , which compares the feedback received from the receiver  156  and the intended position or velocity of the needle  76  based on the input embodying the desired waveform, and produces an output that is an adjustment to the voltage or voltage rate provided to the piezoelectric device  112  to achieve the desired voltage waveform, and thus the desired motion of the needle  76 . This feedback controller  204  can calculate this adjustment with reference to a variety of predetermined relations between voltage provided to the piezoelectric device  112  and velocity or position of the needle  76  that are stored in the memory  170 . 
       FIG.  5 B  shows another embodiment of a control loop  200   b  that can be implemented by the controller  166 . Control loop  200   b  embodies a combination of feedback and feedforward control. The control loop  200   a  receives an input that can take the form of a desired waveform, which is subsequently incorporated with feedback received from the receiver  156  of the sensor assembly  138  and provided to the feedback controller  204 . Like the control loop  200   a , the feedback controller  204  compares the feedback received from the receiver  156  and the intended position or velocity of the needle  76  based on the input embodying the desired waveform, and produces an output that is an adjustment to the voltage or voltage rate provided to the piezoelectric device  112  to achieve the desired voltage waveform, and thus the desired motion of the needle  76 . This feedback controller  204  can calculate this adjustment with reference to a variety of predetermined relations between voltage provided to the piezoelectric device  112  and velocity or position of the needle  76  that are stored in the memory  170 . However, the control loop  200   b  also includes a feedforward controller  208  that can receive the input of the desired waveform, and produce an output that is an adjustment to the voltage or voltage rate provided to the piezoelectric device  112  that bypasses the feedback controller  204  and is combined with the output of the feedback controller  204 . This use of the feedforward controller  208  can aid in anticipating and minimizing disturbances in the movement of the needle  76  due to the adjustment output produced by the feedback controller  204 . 
       FIG.  5 C  shows a third embodiment of a control loop  200   c  that can be implemented by the controller  166 . Control loop  200   c  embodies an alternative combination of feedback and feedforward control. The control loop  200   b  receives an input that can take the form of a desired waveform, which is subsequently provided as an input to the feedforward controller  208 . The feedforward controller  208  then provides an output, which is combined with the feedback received from the receiver  156  of the sensor assembly  138  to form an input provided to the feedback controller  204 . The feedback controller  204  then compares the feedback received from the receiver  156  and the output from the feedforward controller  208 , and produces an output that is an adjustment to the voltage or voltage rate provided to the piezoelectric device  112  to achieve the desired voltage waveform, and thus the desired motion of the needle  76 . This feedback controller  204  can calculate this adjustment with reference to a variety of predetermined relations between voltage provided to the piezoelectric device  112  and velocity or position of the needle  76  that are stored in the memory  170 . This use of the feedforward controller  208  provides an alternative method for anticipating and minimizing disturbances in the movement of the needle  76  due to the adjustments caused by the feedback controller  204 . 
     This control loop  200   a  can be implemented on a continuous basis to continuously monitor and adjust the movement of the needle  76  throughout a jetting cycle. With respect to a velocity of the needle  76 , the controller  166  can be programmed such that any of the control loops  200   a - 200   c  decreases the voltage or voltage rate supplied to the piezoelectric device  112  when the velocity of the needle  76  is above a predetermined threshold, or alternatively increase the voltage or voltage rate supplied to the piezoelectric device  112  when the velocity of the needle  76  is below a predetermined threshold. The controller  166  can be programmed such that there is an acceptable range of needle velocities, and that the voltage rate supplied to the piezoelectric device  112  is maintained when the velocity of the needle  76  is within the acceptable range. The acceptable ranges and/or predetermined thresholds can be provided to the controller  166  by a user through the HMI device  174  or recalled from the memory  170 . 
     Now referring to  FIG.  6   , a plot of an exemplary voltage waveform  250  provided to the piezoelectric device  112  of the actuator assembly  111  to transition the needle  76  from the second position, to the first position, and back to the second position over a period of time is depicted. As shown, the voltage waveform  250  may not be sinusoidal, but may rather take on a somewhat sawtooth shape. This is because a sharp drop in the needle  76  is required when transitioning the needle  76  from the first position to the second position so that a discrete amount of material having a desired shape and size is jetted from the nozzle  56 . As depicted, the voltage waveform  250  has several discrete sections. In baseline portion  254 , no voltage is being supplied to the piezoelectric device  112  between 0 and 500 microseconds. At 500 microseconds, an increasing portion  258   a  of the voltage waveform  250  begins. This increasing portion  258  of the voltage waveform  250  continues from 500 microseconds to about 2700 microseconds, and defines a portion of the voltage waveform  250  during with the voltage supplied to the piezoelectric device  112  continuously increases. This increase in voltage causes the piezoelectric device  112  to expand, thus drawing the needle  76  away from the nozzle  56 . As depicted, the increasing portion  258  includes first and second portions  258   a ,  258   b . During the first portion  258   a , the voltage level increases quicker than in in the second portion  258   b . As a result, the needle  76  is drawn away from the nozzle  56  quicker during the beginning of the piezoelectric device  112  receiving the increasing portion  258  of the voltage waveform  250  than at the end. Though the increasing portion  258  of the voltage waveform  250  is shown as having two sections of differing voltage increase speed, more or less sections are contemplated. 
     After the increasing portion  258  of the voltage waveform  250 , voltage is supplied to the piezoelectric device  112  at a constant voltage from about 2700 to about 2800 microseconds. This constant portion  262  of the voltage waveform represents the time that the needle  76  is retracted completely into the first position, and is referred to as the dwell. Adjusting the dwell position of the needle  76  by adjusting the voltage applied to the piezoelectric device  112  during the constant portion  262  of the waveform using one of the control loops  200   a - 200   c  can aid in controlling the shape and size of the dot of material jetted from the nozzle  56 . After the constant portion  262 , the voltage applied to the piezoelectric device  112  quickly drops to zero during the decreasing portion  264 . This quick drop in voltage supplied to the piezoelectric device  112  during the decreasing portion  264  of the voltage waveform  250  causes a quick contraction of the piezoelectric device  112 , thus quickly driving the needle  76  towards the nozzle  56  until the needle  76  strikes the valve seat  80 . This causes a dot of material having a predetermined size and shape to be jetted from the nozzle  56  of the applicator  10  onto a substrate. By altering the speed at which the voltage decreases during the decreasing portion  264  of the voltage waveform  250  using one of the control loops  200   a - 200   c , the dot size and shape of the material jetted from the applicator  10  can be further controlled. 
     Continuing with  FIG.  7   , a method  300  for controlling the motion of the needle  76  using the sensor assembly  138  and connected controller  166  to maintain a predetermined material dot size and shape will be discussed. The method  300  includes first actuating the piezoelectric device  112  of the actuator assembly  111  in step  302 . By actuating the piezoelectric device  112 , the needle  76  translates along the vertical direction  6  between the first and second position, as described above. This reciprocal movement functions to jet an amount of material from the nozzle  56 . In step  306 , which can be initiated before, during, or after performing step  302 , the controller  166  can initiate the emitting of light L from the emitter  154  to the receiver  156 , such that a portion of the actuator assembly  111  or the needle  76  interacts with the light L. As noted above, the light L can be emitted along a direction D that is perpendicular to the vertical direction  6 , and can be emitted such that a portion of the actuator assembly  111  or the needle  76  partially occludes the light L. Alternatively, the light L can be emitted such that a portion of the actuator assembly  111  or the needle  76  reflects the light L. After steps  302  and  306 , the method  300  includes determining a position of the needle  76  at a discrete point in time based upon the feedback received by the controller  166  from the receiver  156  in step  310 . After or concurrently with step  310 , in step  314  the controller  166  can determine the velocity of the needle  76  at a discrete moment in time based upon the feedback received by the controller  166  from the receiver  156 . 
     After the position and/or velocity of the needle is determined in steps  310  and  314 , the controller  166  can adjust the operation of the piezoelectric device  112  in step  318  based upon feedback received by the controller  166  from the receiver  156 . This adjustment can be accomplished by adjusting the voltage supplied to the piezoelectric device  112  according to a predetermined relationship between voltage and needle velocity or position that is stored in the memory  170 . The adjustment can be determined using any of one or combination of the control loops  200   a - 200   c  shown in  FIGS.  5 A- 5 C , each of which incorporates an input provided by a user of the applicator  10  to the HMI device  174 . The adjusting step  318  can include decreasing the voltage supplied to the piezoelectric device  112  when the velocity of the needle  76  is above a predetermined threshold, increasing the voltage supplied to the piezoelectric device  112  when the velocity of the needle  76  is below a predetermined threshold, or maintaining the voltage supplied to the piezoelectric device  112  when the velocity of the needle  76  is within a predetermined range. 
     By continuously obtaining feedback on the position and velocity of the needle  76 , and using this information to control the voltage waveform provided to the piezoelectric device  112 , a material dot size and shape jetted from the applicator  10  can be kept consistent over time. The use of the emitter  154  and receiver  156  of the sensor assembly  138  provides a highly accurate system for obtaining this feedback, such that accurate determinations of instantaneous needle  76  position and velocity can be easily obtained. Further, the control loops  200   a - 200   c  can use the information obtained by the controller  166  from the sensor assembly  138  to help adjust the voltage provided by the piezoelectric device  112 , while minimizing negative consequences that can come from taking such corrective action. 
     While various inventive aspects, concepts and features of the inventions may be described and illustrated herein as embodied in combination in the exemplary embodiments, these various aspects, concepts and features may be used in many alternative embodiments, either individually or in various combinations and sub-combinations thereof. Unless expressly excluded herein all such combinations and sub-combinations are intended to be within the scope of the present inventions. Even though some features, concepts or aspects of the inventions may be described herein as being a preferred arrangement or method, such description is not intended to suggest that such feature is required or necessary unless expressly so stated. Still further, exemplary or representative values and ranges may be included to assist in understanding the present disclosure; however, such values and ranges are not to be construed in a limiting sense and are intended to be critical values or ranges only if so expressly stated. Descriptions of exemplary methods or processes are not limited to inclusion of all steps as being required in all cases, nor is the order that the steps are presented to be construed as required or necessary unless expressly so stated.