Patent Publication Number: US-10328449-B2

Title: Piezoelectric dispenser and method of calibrating stroke of the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Korean Patent Application No. 10-2014-0160691, filed on Nov. 18, 2014, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     1. Field 
     The present disclosure relates to a liquid dispenser for dispensing liquid by using a piezoelectric actuator, and a method of dispensing liquid using the same. 
     2. Description of the Related Technology 
     A liquid dispenser supplies a liquid solution such as water, oil, or resin of a predetermined amount and is used in diverse fields, for example, in a semiconductor process or in the medical field. 
     In particular, a liquid dispenser is frequently used in an underfill process of a semiconductor process, that is, to fill a package of a semiconductor device with a resin. In a process of manufacturing a light emitting diode (LED) device, a dispenser is used in a process of coating a LED chip with a phosphorescent solution which is a mixture of a phosphorescent material and a resin. 
     In liquid dispensers as described above, a pump receiving a viscous liquid and dispensing a fixed amount of the viscous liquid at an exact position is used as a core device. 
     Various pump structures such as a screw pump and a linear pump are available. Recently, a piezoelectric pump, in which a piezoelectric element is used as an actuator, has been developed and used to perform a fast dispensing operation in a semiconductor process or the like. Korean Patent No. KR 10-1301107 (published on Aug. 14, 2013) discloses a piezoelectric pump. 
     SUMMARY 
     One aspect of the invention provides a liquid dispenser apparatus, which may comprise: a valve assembly comprising a nozzle and a valve rod with a tip facing the nozzle, the valve rod configured to move along a first axis; at least one piezoelectric actuator configured to expand and shrink along a second axis in response to a voltage signal applied to the at least one piezoelectric actuator, the second axis being identical to or different from the first axis; a lever configured to move pivotally about a pivotal axis thereof and operably connected to the at least one piezoelectric actuator such that the lever pivotally moves as the at least one piezoelectric actuator expands and shrinks along the second axis; wherein the valve rod and the lever are operably connected such that, as the lever pivotally moves, the valve rod moves along the first axis and the tip reciprocates between a first position and a second position for dispensing liquid through the nozzle, wherein the second position changes over use of the liquid dispenser such that a stroke of the tip between the first position and the second position becomes longer or shorter; a lever-position detector connected to the lever and configured to detect the lever&#39;s position that is indicative of the tip&#39;s position; and at least one processor configured to process information from the lever-position detector to determine if the first position needs to be adjusted, and upon determining that the first position needs to be adjusted, to generate a control signal for changing the voltage signal applied to the at least one piezoelectric actuator to adjust a level of expansion and shrinkage thereof along the second axis, which causes to adjust pivotal movement of the lever, which to further change the first position. 
     In the foregoing apparatus, the at least one processor may be configured to determine if the first position needs to be adjusted by computing a distance of the stroke and then comparing the distance to the reference value. The at least one processor is configured to determine that the first position needs to be adjusted when the stroke has become longer than the reference value. The tip may contact the nozzle at the second position, wherein the stroke of the tip may become longer over use of the liquid dispenser as a valve seat of the nozzle wears out by repeated impacts of the tip. For determining if the first position needs to be adjusted, the at least one processor may be configured to determine if the stroke of the tip has become longer than a reference value based on information from the lever-position detector, wherein the at least one processor is configured to determine that the first position needs to be adjusted when the stroke has become longer than the reference value, wherein the change of the first position is to make the stroke shorter than the reference value. The at least one processor may be configured to determine if the stroke of the tip has become longer than the reference value by computing a distance of the stroke and then comparing the distance to the reference value. 
     Still in the foregoing apparatus, the at least one processor may be configured to determine if the first position needs to be adjusted by computing the second position of the tip based on the information from the lever-position detector and then comparing the second position of the tip to a reference position. The voltage signal may be configured to operate the at least one piezoelectric actuator such that the tip of the valve rod would move to a third position beyond the second position if the nozzle does not stop the valve rod&#39;s movement, wherein an over-stroke defined by a distance between the second position and the third position becomes shorter a reference distance when the stroke of the tip becomes longer than a reference value, wherein the at least one processor is configured to generate the control signal which is to change the third position such that the over-stroke is greater than the reference distance. 
     Further in the foregoing apparatus, the lever&#39;s position may be a displacement of the lever, which is a position of the lever relative to a reference position of the lever. The lever-position detector may be a displacement sensor configured to sense the lever&#39;s position indicative of the tip&#39;s position relative to the first position or the second position and further configured to provide the information indicative of the lever&#39;s position to the at least one processor. The at least one piezoelectric actuator may comprise a first piezoelectric actuator and a second piezoelectric actuator, wherein the first piezoelectric actuator is configured to expand and the second piezoelectric actuator is configured to shrink to place the tip of the valve rod to the first position, wherein when the stroke of the tip becomes longer than a reference value, the at least one processor is configured to generate the control signal to reduce the amount of the expansion of the first piezoelectric actuator and the amount of the shrinkage of the second piezoelectric actuator for changing the first position of the tip of the valve rod. 
     Another aspect of the invention provides a method of dispensing liquid, which may comprise: providing the foregoing liquid dispenser apparatus; applying a voltage signal to the at least one piezoelectric actuator for its expansion and shrinkage along the second axis, which causes pivotal movement of the lever, which then to cause movement of the valve rod along the first axis such that the valve assembly dispenses liquid through the nozzle as the tip reciprocates between the first position and the second position at which the tip contacts the nozzle; detecting the lever&#39;s position that is indicative of the tip&#39;s position; processing information from the lever-position detector to determine if the first position needs to be adjusted; and upon determining that the first position needs to be adjusted, generating a control signal for changing the voltage signal applied to the at least one piezoelectric actuator to adjust a level of expansion and shrinkage thereof along the second axis, which causes to adjust pivotal movement of the lever, which to further change the first position. 
     In the foregoing method, determining if the first position needs to be adjusted may comprise computing a distance of the stroke and then comparing the distance to the reference value. It may be determined that the first position needs to be adjusted when the stroke has become longer than the reference value. The tip may contact the nozzle at the second position, wherein the stroke of the tip becomes longer over use of the liquid dispenser as a valve seat of the nozzle wears out by repeated impacts of the tip. Determining if the first position needs to be adjusted may comprise determining if the stroke of the tip has become longer than a reference value based on information from the lever-position detector, wherein it is determined that the first position needs to be adjusted when the stroke has become longer than the reference value, wherein the change of the first position is to make the stroke shorter than the reference value. Determining if the stroke of the tip has become longer than the reference value may comprise computing a distance of the stroke and then comparing the distance to the reference value. 
     Still in the foregoing method, determining if the first position needs to be adjusted may comprise computing the second position of the tip based on the information from the lever-position detector and then comparing the second position of the tip to a reference position. The voltage signal may operate the at least one piezoelectric actuator such that the tip of the valve rod would move to a third position beyond the second position if the nozzle does not stop the valve rod&#39;s movement, wherein an over-stroke defined by a distance between the second position and the third position becomes shorter than a reference distance when the tip&#39;s stroke between the first position and the second position becomes longer than a reference value, wherein the control signal is to change the third position for increasing the over-stroke distance to be greater the reference distance. 
     Further in the foregoing method, the lever&#39;s position may be a displacement of the lever, which is a position of the lever relative to a reference position of the lever. The lever-position detector may be a displacement sensor which senses the lever&#39;s position indicative of the tip&#39;s position relative to the first position or the second position and provides the information indicative of the lever&#39;s position to the at least one processor. The at least one piezoelectric actuator may comprise a first piezoelectric actuator and a second piezoelectric actuator, wherein the first piezoelectric actuator expands and the second piezoelectric actuator shrinks to place the tip of the valve rod to the first position, wherein when the stroke of the tip becomes longer than a reference value, the control signal is to reduce the amount of the expansion of the first piezoelectric actuator and the amount of the shrinkage of the second piezoelectric actuator for changing the first position of the tip of the valve rod. 
     One or more embodiments include a piezoelectric dispenser capable of maintaining a uniform dispensing quality of a viscous liquid by calibrating an operation stroke of a valve rod discharging a viscous liquid (vertical operation displacement of the valve rod) by setting the operation stroke of the valve rod to an initial value when the operation stroke of the valve rod is changed during use due to factors such as assembly tolerance or abrasion of components. 
     Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented embodiments. 
     According to one or more embodiments, a piezoelectric dispenser includes: a pump body; a discharge instrument including a lever that is rotatably mounted with respect to a hinge axis mounted in the pump body and a valve rod that is liftably connected to the lever according to rotation of the lever; a piezoelectric actuator having an end that is mounted in the pump body and contactable to the lever, wherein when a voltage is applied to the piezoelectric actuator, a length of the piezoelectric actuator is increased and the piezoelectric actuator pressurizes the lever so as to rotate the lever with respect to the hinge axis; a valve body including a reservoir into which an end of the valve rod is inserted and in which a viscous liquid is stored, an inlet through which the viscous liquid flows into the reservoir, and a discharge outlet through which the viscous liquid of the reservoir is discharged according to advance and retreat of the valve rod in the reservoir; a displacement measurement sensor installed in the pump body and measuring an operation displacement of the lever of the discharge instrument; and a controller for calculating a difference between an operation stroke S_o of the valve rod of the discharge instrument (vertical operation displacement of the valve rod) calculated based on the measured operation displacement of the lever of the displacement measurement sensor and a preset initial operation stroke S_i of the valve rod and controlling a voltage to be applied to the piezoelectric actuator so as to calibrate the operation stroke of the valve rod by offsetting the operation stroke of the valve rod. 
     According to one or more embodiments, a method of calibrating an operation stroke of a piezoelectric dispenser, includes: (a) applying a voltage to a piezoelectric actuator of a piezoelectric pump of the piezoelectric dispenser and measuring an operation displacement of a lever of the piezoelectric pump generated by the piezoelectric actuator, wherein the piezoelectric pump comprises the lever that is rotatably mounted with respect to a hinge axis, a valve rod that is connected to the lever and lifted or lowered according to rotation of the lever, wherein when a voltage is applied to the piezoelectric actuator, a length of the piezoelectric actuator is increased and the piezoelectric actuator pressurizes the lever so as to rotate the lever with respect to the hinge axis, a reservoir into which an end of the valve rod is inserted and in which a viscous liquid is stored, an inlet through which the viscous liquid flows into the reservoir, and a discharge outlet through which the viscous liquid of the reservoir is discharged according to advance and retreat of the valve rod in the reservoir; (b) calculating an operation stroke S_o of the valve rod (vertical operation displacement of the valve rod) based on the operation displacement of the lever; (c) comparing the calculated operation stroke S_o and a preset initial operation stroke S_i of the valve rod; and (d) calibrating the operation stroke S_o of the valve rod by offsetting the operation stroke S_o of the valve rod by controlling a voltage to be applied to the piezoelectric actuator when there is a difference between the operation stroke S_o and the preset initial operation stroke S_i of the valve rod. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a front view of a piezoelectric dispenser according to an embodiment of the inventive concept; 
         FIG. 2  is a perspective view of a piezoelectric pump of the piezoelectric dispenser illustrated in  FIG. 1 ; 
         FIG. 3  is a cross-sectional view of a piezoelectric pump of the piezoelectric dispenser of  FIG. 1 ; 
         FIG. 4  is a cross-sectional view illustrating a nozzle of a piezoelectric dispenser and peripheral components therearound according to an embodiment of the inventive concept; 
         FIG. 5  is a flowchart of a method of calibrating a stroke of a piezoelectric dispenser according to an embodiment of the inventive concept, in an order; 
         FIG. 6  is a view for describing an example in which a stroke of a valve rod included in a piezoelectric dispenser according to an embodiment of the inventive concept is modified; 
         FIG. 7  is a view for describing a method of calibrating an operation stroke of a piezoelectric dispenser according to an embodiment of the inventive concept, by offsetting the operation stroke of the valve rod. 
         FIG. 8  illustrates a piezoelectric dispenser according to another embodiment of the inventive concept; and 
         FIG. 9  illustrates a piezoelectric dispenser according to another embodiment of the inventive concept. 
     
    
    
     DETAILED DESCRIPTION 
     The inventive concept will now be described more fully with reference to the accompanying drawings, in which embodiments of the inventive concept are shown. 
     In one embodiment, a liquid dispenser includes a pump body and a valve body that are separably coupled to each other. A hinge axis is mounted in the pump body, and a lever that extends horizontally is rotatably mounted with respect to the hinge axis. A valve rod that extends vertically is inserted into the valve body. The lever and the valve rod are connected to each other so that when the lever rotates with respect to the hinge axis, the valve rod is vertically lifted or lowered. A pair of piezoelectric actuators are installed in the pump body to rotate the lever with respect to the hinge axis. The pair of piezoelectric actuators are formed of piezoelectric elements whose length is increased or reduced according to an electrical potential of a voltage applied to the piezoelectric actuators. 
     In the foregoing liquid dispenser, when the valve body is separated from the pump body and then they are reassembled for maintenance, repair or cleaning of components of the piezoelectric pump, and then reassembling the same, a discharge amount of a viscous liquid may be different from the discharge amount thereof before reassembling. When the valve body is operated after reassembling, an operation stroke of the valve rod may be changed due to, for example, assembly tolerance. This may cause a difference in an actual discharge amount of the liquid from an initial discharge amount of viscous liquid. Such a difference between an actual discharge amount and a preset initial discharge amount of a viscous liquid may also be caused by abrasion of components such as a lever or a valve rod. For example, while using the dispenser, a valve seat of a nozzle in the valve body wears out by repeated impacts of the tip of a valve rod. This may cause changes in the dispensing amount of the liquid. 
       FIG. 1  is a front view of a piezoelectric dispenser  10  according to an embodiment of the inventive concept.  FIG. 2  is a perspective view of a piezoelectric pump  12  of the piezoelectric dispenser  10  illustrated in  FIG. 1 .  FIG. 3  is a cross-sectional view of the piezoelectric pump  12  of the piezoelectric dispenser  10  of  FIG. 1 . 
     As illustrated in  FIGS. 1 through 3 , the piezoelectric dispenser  10  according to the embodiment of the inventive concept includes the piezoelectric pump  12 , a displacement measurement sensor  40 , and a controller  44 . The piezoelectric pump  12  includes a pump body  15 , a valve body  20 , a discharge instrument  25 , first and second piezoelectric actuators  30  and  31 , and a pump control unit  33 . The pump control unit  33  applies a voltage to the first and second piezoelectric actuators  30  and  31  to control operations of the first and second piezoelectric actuators  30  and  31 . The pump body  15  and the valve body  20  are separably coupled to each other via a fixing member such as a bolt. The discharge instrument  25  includes a lever  26  mounted in the pump body  15  and a valve rod  28  that is mounted in the valve body  20  and is connectable to the lever  26 . 
     The valve body  20  includes a reservoir  21 , an inlet  22 , and a nozzle  23 . The reservoir  21  is in the form of a container that is opened upwardly, and the valve rod  28  is inserted into the reservoir  21  to tightly seal an upper portion of the reservoir  21 . The inlet  22  is connected to the reservoir  21 . A viscous liquid supplied from the outside through the inlet  22  is transmitted to the reservoir  21 . The viscous liquid of the reservoir  21  is discharged to the outside through a discharge outlet  24  of the nozzle  23 . 
     Referring to  FIG. 3 , a hinge axis  16  is mounted in the pump body  15 , and the lever  26  that extends horizontally is rotatably mounted with respect to the hinge axis  16 . The valve rod  28  that extends vertically is inserted into the valve body  20 . The lever  26  and the valve rod  28  are connected to each other so that when the lever  26  rotates with respect to the hinge axis  16 , the valve rod  28  is vertically lifted or lowered. 
     The valve rod  28  connected to the lever  26  is lifted or lowered with respect to the reservoir  21  according to rotation of the lever  26 . As the valve rod  28  is lifted up and then lowered down to approach the discharge outlet  24  located below the valve rod  28 , the valve rod  28  pressurizes the viscous liquid in the reservoir  21  to thereby dispense the viscous liquid to the outside through the discharge outlet  24 . 
     The lever  26  and the valve rod  28  may be connected to each other using various methods. According to the present embodiment, the lever  26  and the valve rod  28  are connected via simple insertion coupling as illustrated in  FIG. 3 . An engaging groove  27  that is horizontally opened is formed in an end portion of the lever  26 . In embodiments, the engaging groove  27  of the lever  26  has a C-shape. An engaging rod  29  is provided at an upper end of the valve rod  28 . The engaging rod  29  is inserted into the engaging groove  27  of the lever  26  so as to be rotatably connected to the lever  26 . In embodiments, rotation of the lever  26  is converted to lifting movement of the valve rod  28 . 
     As the engaging groove  27  is formed to be horizontally opened, the engaging groove  27  and the engaging rod  29  may be detached from each other by moving the engaging rod  29  with respect to the engaging groove  27  in a horizontal direction. In addition, as the engaging groove  27  is formed in a horizontal direction, even when the engaging groove  27  is lifted or lowered due to rotation of the lever  26 , the engaging rod  29  is not deviated from the engaging groove  27 . When separating the lever  26  and the valve rod  28  from each other according to necessity, they may be easily separated by moving the engaging rod  29  with respect to the engaging groove  27  in a horizontal direction. 
     As illustrated in  FIG. 3 , the first and second piezoelectric actuators  30  and  31  are installed in the pump body  15 . Here, two piezoelectric actuators, in embodiments, the first and second piezoelectric actuators  30  and  31 , are provided and rotate the lever  26  with respect to the hinge axis  16 . The first piezoelectric actuator  30  and the second piezoelectric actuator  31  are each formed of a piezoelectric element. The first piezoelectric actuator  30  and the second piezoelectric actuator  31  are formed of piezoelectric elements whose length is increased or reduced according to an electrical potential of a voltage applied to the piezoelectric elements. In the present embodiment, description will focus on an example in which the first piezoelectric actuator  30  and the second piezoelectric actuator  31  are each formed of a multi-stack type piezoelectric actuator that is formed by stacking multiple piezoelectric elements. 
     The first piezoelectric actuator  30  and the second piezoelectric actuator  31  are arranged in the pump body  15  in parallel to each other in a vertical direction. The first piezoelectric actuator  30  and the second piezoelectric actuator  31  are arranged with the hinge axis  16  therebetween and such that lower ends thereof are each in contact with an upper surface of the lever  26 . When a voltage is applied to the first piezoelectric actuator  30  and a length of the first piezoelectric actuator  30  is increased, the lever  26  rotates counter-clockwise with respect to  FIG. 3 , and when a voltage is applied to the second piezoelectric actuator  31  and a length of the second piezoelectric actuator  31  is increased, the lever  26  rotates clockwise with respect to  FIG. 3 . 
     When voltages are alternately applied to the first piezoelectric actuator  30  and the second piezoelectric actuator  31 , the valve rod  28  is repeatedly lifted or lowered to continuously dispense the viscous liquid through the discharge outlet  24 . As a distance between the hinge axis  16  and the first piezoelectric actuator  30  and the second piezoelectric actuator  31  is far greater than a distance between the hinge axis  16  and the valve rod  28 , deformed lengths of the first piezoelectric actuator  30  and the second piezoelectric actuator  31  are sufficiently magnified by the lever  26 . Movement of the lever  26  according to deformation in the lengths of the first piezoelectric actuator  30  and the second piezoelectric actuator  31  may operate the valve rod  28  within a sufficient height range of the valve rod  28 . The pump control unit  33  controlling operations of the first piezoelectric actuator  30  and the second piezoelectric actuator  31  may apply a voltage having various pulse waveforms to the first piezoelectric actuator  30  and the second piezoelectric actuator  31  according to time, thereby controlling dynamic characteristics of the valve rod  28 . 
     Referring to  FIGS. 2 and 3 , a first position adjustor  35  and a second position adjustor  36  are respectively disposed at upper ends of the first piezoelectric actuator  30  and the second piezoelectric actuator  31 . The first position adjustor  35  and the second position adjustor  36  are screw-coupled to the pump body  15  while respective ends of the first position adjustor  35  and the second position adjustor  36  are in contact with respective ends of the first piezoelectric actuator  30  and the second piezoelectric actuator  31 . The first position adjustor  35  adjusts a position of the first piezoelectric actuator  30  with respect to the lever  26  and the pump body  15 , and the second position adjustor  36  adjusts a position of the second piezoelectric actuator  31  with respect to the lever  26  and the pump body  15 . In embodiments, when the first piezoelectric actuator  30  is pressurized by tightening the first position adjustor  35 , the first piezoelectric actuator  30  is lowered to approach or be closely adhered to the lever  26 . The second position adjustor  36  also operates in the same manner as the first position adjustor  35 . 
     The first and second piezoelectric actuators  30  and  31  are typically formed of a ceramic material. Expansion displacement of the first and second piezoelectric actuators  30  and  31  may be changed from an initial expansion displacement thereof according to an applied voltage after usage for a long period of time. In this case, dynamic characteristics of the discharge instrument  25  may be maintained by adjusting positions of the first piezoelectric actuator  30  and the second piezoelectric actuator  31  by using the first position adjustor  35  and the second position adjustor  36 . 
     A first returning instrument  38  and a second returning instrument  39  are respectively installed under the first piezoelectric actuator  30  and the second piezoelectric actuator  31 . The first returning instrument  38  is disposed in the pump body  15  to apply a force to the first piezoelectric actuator  30  in a direction in which the first piezoelectric actuator  30  is contracted. Likewise, the second returning instrument  39  is disposed in the pump body  15  to apply a force to the second piezoelectric actuator  31  in a direction in which the second piezoelectric actuator  31  is contracted. The first returning instrument  38  and the second returning instrument  39  may be, for example, springs that respectively provide an elastic force under the first piezoelectric actuator  30  and the second piezoelectric actuator  31  in a direction in which the first piezoelectric actuator  30  and the second piezoelectric actuator  31  are contracted, or may be fluid ducts. 
     Referring to  FIG. 3 , the displacement measurement sensor  40  is installed in the pump body  15  to measure an operation displacement of the lever  26  of the discharge instrument  25  and to provide the controller  44  with the measured operation displacement of the lever  26 . The displacement measurement sensor  40  includes a probe  41  and a sensor body  42  to which the probe  41  is movably coupled. An end of the probe  41  is coupled to a middle of the lever  26  so that the probe  41  may be lifted or lowered in connection with rotation of the lever  26 . The sensor body  42  detects a movement displacement of the probe  41  when the probe  41  is lifted or lowered, thereby detecting an operation displacement of the lever  26 . In embodiments, the sensor body  42  measures an operation displacement of the lever  26  via the probe  41  and provides the controller  44  with the measured operation displacement of the lever  26 . The controller  44  may calculate an operation stroke S_o of the valve rod  28  (vertical operation displacement of the valve rod) based on the operation displacement of the lever  26 . 
     As the lever  26  rotates with respect to the hinge axis  16 , the probe  41  coupled to the lever  26  moves vertically while shaking to some extent in a horizontal direction. A rotation angle displacement of the lever  26  is very small, and thus a degree of horizontal shaking of the probe  41  is also relatively small. Thus, by appropriately designing an arrangement structure of internal components of the sensor body  42  and the probe  41 , the probe  41  may be moved vertically without interfering with the internal components of the sensor body  42 . Accordingly, an operation displacement of the lever  26  may be easily measured via the probe  41 . 
     Referring to  FIG. 4 , a stroke of the discharge instrument  25  may be classified as a free stroke S_f and an operation stroke S_o. The operation stroke S_o denotes an actual distance traveled by the valve rod  28  inside the reservoir  21 . The, and the free stroke S_f denotes a value obtained by adding a pressed value or over-stroke P to the operation stroke S_o. In embodiment, the nozzle  23  and the valve rod  28  are formed of a rigid material, such as a metal, which is sufficiently rigid to inhibit the valve rod  28  from digging into the valve seat portion  23   a  of the nozzle  23  by compressing the valve seat portion  23   a  of the nozzle  23 . The pressed value or over-stroke P denotes a virtual distance that the valve rod  28  would move or travel beyond the point of the valve seat portion  23   a  if the nozzle is not provided. The pressed value or over-stroke P may otherwise denote a virtual distance that the valve rod would further travel after contacting the valve seat portion  23   a  if the nozzle  23  travels along with the valve rod without any resistance against the valve rod&#39;s movement after the valve rod contacts the valve seat portion. The piezoelectric actuators is set to operate to provide the free stroke S_f of the valve rod. In the illustrated embodiments, since the nozzle is fixed to the pump body and is sufficiently rigid and the piezoelectric actuators is set to operate to provide the free stroke S_f of the valve rod, the valve rod reciprocates with the operation stroke S_o and the valve rod further pushes the valve seat portion after the valve rod contacts the valve seat portion. The force applied by the valve rod to the valve seat portion may depend upon the over-stroke P. Thus, when the pressing value P increases, the force applied by the valve rod  28  to the valve seat portion  23   a  is also increased. By including the pressing value P in a stroke of the discharge instrument  25 , the valve rod  28  may be compressed with respect to the valve seat portion  23   a  with a predetermined pressure, and leakage of the viscous liquid of the reservoir  21  through the discharge outlet  24  may be avoided or minimized when a dispensing operation of the viscous liquid is not performed. The pressing value P may be set to various values based on a type or viscosity of the viscous liquid. 
     A position of the probe  41  of the displacement measurement sensor  40  with respect to the lever  26  is not the same as a position of the valve rod  28  with respect to the lever  26 , and thus the movement displacement of the probe  41  and the operation displacement of the valve rod  28  are different. A distance from the hinge axis  16  to the probe  41  and a distance from the probe  41  to the engaging rod  29  of the valve rod  28  are each uniform, and thus, an operation stroke S_o of the valve rod  28  (vertical movement displacement of the valve rod) may be easily calculated based on the movement displacement of the probe  41 . The operation stroke S_o of the valve rod  28  may be measured while the valve rod  28  is connected to the lever  26 , and a free stroke S_f of the valve rod  28  may be measured while the valve rod  28  is separated from the lever  26 . 
     The controller  44  applies a voltage so as to operate the first and second piezoelectric actuators  30  and  31  via the pump control unit  33  that controls the first and second piezoelectric actuators  30  and  31  in the piezoelectric pump  12 . Also, the controller  44  receives an operation displacement of the lever  26  from the displacement measurement sensor  40  and calculates an operation stroke S_o of the valve rod  28  based on the operation displacement of the lever  26 . An input device  45  and a display  47  are integrally formed with the controller  44 . The input device  45  includes a plurality of operation buttons  46  used to input various types of input data. A user may input an offset value of the operation stroke S_o of the valve rod  28  or the like via the operation buttons  46  of the input device  45 . The controller  44  receives an offset value of the operation stroke S_o of the valve rod  28  of the user or the like via the input device  45 . The display  47  displays various information such as the operation stroke S_o of the valve rod  28  or input data input by the user. The input device  45  and the display  47  may also be installed outside the controller  44  so as to be electrically connected to the controller  44 . 
     The controller  44  may receive a measured operation displacement of the lever  26  from the displacement measurement sensor  40  and display various information on the display  47 . The controller  44  may display, for example, an operation displacement of the lever  26 , an operation stroke S_o of the valve rod  28 , or a difference between a preset initial operation stroke S_i and a calculated operation stroke S_o of the valve rod  28 , on the display  47 . Also, the controller  44  may control a voltage to be applied to the first and second piezoelectric actuators  30  and  31  according to an offset value input by the user to thereby offset an operation stroke S_o of the valve rod  28 . Here, offsetting an operation stroke S_o of the valve rod  28  indicates increasing or decreasing each of an upper limit value and a lower limit value of movement of the valve rod  28  by an identical distance while maintaining a uniform amount of vertical operation displacement of the valve rod  28 . A method of offsetting an operation stroke of the discharge instrument  25  as described above will be described in detail later. 
     The piezoelectric dispenser  10  according to the present embodiment further includes cooling lines  48  and  49  to cool the first and second piezoelectric actuators  30  and  31 . The cooling lines  48  and  49  are installed in the pump body  15 . A cooling liquid flows to portions around the first and second piezoelectric actuators  30  and  31  through the cooling lines  48  and  49 . Due to characteristics of the first and second piezoelectric actuators  30  and  31 , a large amount of heat is generated in the first and second piezoelectric actuators  30  and  31  during use thereof. When temperatures of the first and second piezoelectric actuators  30  and  31  increase due to heat generated in the first and second piezoelectric actuators  30  and  31 , operating characteristics thereof may be degraded. The pump body  15  may be cooled by passing through the mounting space of the first and second piezoelectric actuators  30  and  31  by using the cooling lines  48  and  49  to thereby avoiding or minimizing an increase in temperatures of the first and second piezoelectric actuators  30  and  31 . 
     According to the piezoelectric dispenser  10  of the present embodiment, as the pump body  15  and the valve body  20  are detachably configured from each other, and the lever  26  and the valve rod  28  are also easily connectably and separably configured to and from each other, maintenance, repair and cleaning thereof is easy, and the piezoelectric pump  12  may be easily configured according to various characteristics of a viscous liquid. By unscrewing a screw coupling the pump body  15  and the valve body  20 , and detaching the engaging rod  29  of the valve rod  28  from the engaging groove  27  of the lever  26 , the valve body  20  and the valve rod  28  may be easily separated from the pump body  15 . When the valve body  20  is separated, it is easy to clean the same for next use. Also when the valve body  20  or the valve rod  28  is damaged, they may be separated using the above-described method, and a new valve body  20  or a new valve rod  28  may be easily replaced. 
     When the pump body  15  or the valve body  20  is separated and then reassembled, or when the lever  26  and the valve rod  28  are separated and reassembled, for maintenance, repair or cleaning of components as described above, an operation stroke S_o of the valve rod  28  may be changed due to, an assembly tolerance or the like. When the operation stroke S_o of the valve rod  28  is changed, a discharge amount of a viscous liquid according to an operation of the piezoelectric pump  12  is changed from an initial discharge amount of the viscous liquid, and a pressing value P of the valve rod  28  is changed. A change in the operation stroke S_o of the valve rod  28  may also be caused by abrasion of components such as the lever  26 , the valve rod  28 , and the valve seat portion  23   a.    
     Change in the operation stroke S_o of the valve rod  28  as described above may be adjusted by using a method of calibrating an operation stroke of a piezoelectric dispenser according to an embodiment of the inventive concept. Hereinafter, a method of calibrating an operation stroke of a piezoelectric dispenser according to an embodiment of the inventive concept will be described in detail. 
     As illustrated in  FIG. 5 , the method of calibrating an operation stroke of a piezoelectric dispenser according to the present embodiment includes measuring an operation displacement of the lever  26  (S 10 ), calculating an operation stroke S_o of the valve rod  28  (S 20 ), comparing the operation stroke S_o and an initial operation stroke S_i of the valve rod (S 30 ), and offsetting the operation stroke S_o of the valve rod  28  (S 40 ). 
     First, the controller  44  applies a voltage to the first and second piezoelectric actuators  30  and  31  to operate the discharge instrument  25  and measures an operation displacement of the lever  26  by using the displacement measurement sensor  40  (S 10 , step (a)). 
     The controller  44  calculates an operation stroke S_o of the valve rod  28  based on the measured operation displacement of the lever  26  measured in step (a) (S 20 , step (b)). 
     Next, the controller  44  compares the calculated operation stroke S_o of the valve rod  28  with a preset initial operation stroke S_i thereof (S 30 , step (c)). The initial operation stroke S_i is a value that is preset when the piezoelectric pump  12  is manufactured or according to a type of a viscous liquid or the like. As illustrated in  FIG. 6 , when the valve seat portion  23   a  of the nozzle  23  is worn out, for example, even though an uppermost position of the valve rod  28  that operates vertically is the same as an uppermost position thereof when the valve seat  23   a  is not worn out, a lowermost position of the valve rod  28  is further below from a normal lowermost position of the valve rod  28  by a height corresponding to a worn portion of the valve seat portion  23   a . Thus, the operation stroke S_o of the valve rod  28  is different from the initial operation stroke S_i thereof. During an operation of the piezoelectric pump  12 , as the valve rod  28  is continuously compressed with respect to the valve seat portion  23   a  of the nozzle  23 , the valve seat portion  23   a  may be worn away. In this case, even if a free stroke S_f of the valve rod  28  is not changed, the valve rod  28  is further moved towards the discharge outlet  24  by an amount corresponding to the worn portion of the valve seat portion  23   a  so that the operation stoke S_o of the valve rod  28  is greater than the initial operation stroke S_i thereof. A pressing value P′ of the valve rod  28  is smaller than an initial pressing value thereof. When the operation stroke S_o and the pressing value P of the valve rod  28  are changed as above, a dispensing amount of a viscous liquid may be changed or the viscous liquid may leak. 
     When there is a difference between the operation stroke S_o and the preset initial operation stroke S_i of the valve rod  28 , the controller  44  calibrates the operation stroke S_o of the valve rod  28  by offsetting the operation stroke S_o of the valve rod  28  by a difference D between the operation stroke S_o of the valve rod  28  and the initial operation stroke S_i thereof (S 40 , step (d)). The operation stroke S_o of the valve rod  28  may be offset by controlling a voltage to be applied to the first and second piezoelectric actuators  30  and  31 . 
     Referring to  FIG. 6  and (a) of  FIG. 7 , when the valve seat portion  23   a  is worn away, the valve rod  28  that moves vertically is moved further below from an initial installation location of the valve rod  28  by an amount D of a worn portion of the valve seat portion  23   a  way. In this case, as illustrated in (b) of  FIG. 7 , the controller  44  controls a voltage to be applied to the first and second piezoelectric actuators  30  and  31  to offset the operation stroke S_o of the valve rod  28  downwards by the difference D between the initial operation stroke S_i and the operation stroke S_o of the valve rod  28 . In embodiments, the controller  44  lowers a lifting height of the valve rod  28  by the difference D between the initial operation stroke S_i and the operation stroke S_o of the valve rod  28  by reducing a voltage to be applied to the first piezoelectric actuator  30 . On the contrary, the controller  44  lowers a lowering height of the valve rod  28  also by the difference D by increasing a voltage to be applied to the second piezoelectric actuator  31 . By controlling voltages applied to the first and second piezoelectric actuators  30  and  31 , a uniform vertical operation displacement of the valve rod  28  may be maintained, and just an upper limit value and a lower limit value of the vertical operation displacement of the valve rod  28  may be varied by the same amount, and an initial pressing value P of the valve rod  28  may be maintained. 
     Calibration of an operation stroke S_o of the valve rod  28  by offsetting the operation stroke S_o of the valve rod  28  as above may be semi-automatically performed by the user. In this case, the controller  44  calculates an operation stroke S_o of the valve rod  28  based on an operation displacement of the lever  26 , and then displays the calculated operation stroke S_o of the valve rod  28  on the display  47  (step (e)). The user determines the operation stroke S_o of the valve rod  28  displayed on the display  47 , and inputs an offset value used to offset the operation stroke S_o of the valve rod  28 . Here, the controller  44  may calibrate the operation stroke S_o of the valve rod  28  by offsetting the operation stroke S_o of the valve rod  28  by controlling a voltage to be applied to the first and second piezoelectric actuators  30  and  31  according to the input offset value. 
     Calibration of an operation stroke S_o of the valve rod  28  may also be performed automatically, instead of by the user. In this case, the controller  44  calculates an operation stroke S_o of the valve rod  28  and calculates an offset value according to a set program, and controls a voltage to be applied to the first and second piezoelectric actuators  30  and  31  based on the calculated offset value, thereby automatically calibrating the operation stroke S_o of the valve rod  28 . 
     Calibration of an operation stroke S_o of the valve rod  28  by using the controller  44  may be performed in real time during a dispensing operation of a viscous liquid. In embodiments, the controller  44  may measure an operation displacement of the lever  26  in real time, and may calibrate the operation stroke S_o of the valve rod  28  in real time by offsetting the operation stroke S_o of the valve rod  28  by using the above-described method. During the dispensing operation of the viscous liquid, the operation stroke S_o of the valve rod  28  may be changed due to various factors such as expansion or contraction of components according to a temperature change. Thus, by calibrating the operation stroke S_o of the valve rod  28  in real time during dispensing of a viscous liquid, degradation of a dispensing quality due to a change in the operation stroke S_o of the valve rod  28  caused by peripheral factors or the like may be reduced. 
     As described above, according to the piezoelectric dispenser  10  of the present embodiment, the pump body  15  and the valve body  20  may be detachably configured from each other and the lever  26  and the valve rod  28  may also be easily connectably and separably configured to and from each other, and thus it is easy to maintain, repair, and clean the piezoelectric dispenser  10 , and to configure the piezoelectric pump  12  according to various characteristics of a viscous liquid. When separating the pump body  15  and the valve body  20  and reassembling the same for maintenance, repair, or cleaning of components, an operation stroke S_o of the valve rod  28  may be changed from an initial value thereof. In addition, an operation stroke S_o of the valve rod  28  may also be changed from an initial value thereof due to abrasion of components after usage for a long period of time. In this case, the operation stroke S_o of the valve rod  28  is calculated based on an operation displacement of the lever  26  that is measured using the displacement measurement sensor  40 , and the operation stroke S_o of the valve rod  28  is offset to thereby calibrate the operation stroke S_o of the valve rod  28  such that the operation stroke S_o of the valve rod is the same as the initial value, thereby maintaining the initial dispensing performance of the viscous liquid. 
     While it is described above that the operation stroke S_o of the valve rod  28  is calibrated when the pump body  15  and the valve body  20  are reassembled, the operation stroke S_o of the valve rod  28  may also be calibrated in various situations other than in the case of reassembly of the pump body  15  and the valve body  20 . For example, the operation stroke S_o of the valve rod  28  may be changed also due to abrasion of components, and thus, the operation stroke S_o of the valve rod  28  may be calibrated by setting the operation stroke S_o of the valve rod  28  to an initial value after the piezoelectric pump  12  is used for a predetermined period of time. 
     According to the embodiments of the inventive concept, a specific structure of a displacement measurement sensor used to measure an operation displacement of the lever  26  or a connection structure between the displacement measurement sensor and the discharge instrument  25  may be modified in various manners. For example,  FIGS. 8 and 9  illustrate various modified examples of a piezoelectric dispenser including a displacement measurement sensor having a modified structure. 
     First, a piezoelectric dispenser  50  according to another embodiment of the inventive concept includes a piezoelectric pump  12 , a displacement measurement sensor  52 , and a controller  44 . The piezoelectric pump  12  and the controller  44  are the same as those described above. 
     The displacement measurement sensor  52  is installed in the pump body  15  to detect an operation displacement of the lever  26  and provide the controller  44  with a detection signal corresponding to the operation displacement of the lever  26 . The displacement measurement sensor  52  includes a probe  53  and a sensor body  55  to which the probe  53  is movably coupled. An end of the probe  53  is rotatably coupled to a pivot pin  57  located in a middle of the lever  26  so that the probe  53  may be lifted or lowered in connection with rotation of the lever  26 . A coupling groove  54  is formed at the end of the probe  53  so as to be coupled to the pivot pin  57 , thereby inserting the pivot pin  57  into the coupling groove  54 . 
     When the lever  26  rotates with respect to the hinge axis  16  due to operations of the first and second piezoelectric actuators  30  and  31 , the probe  53  rotates with respect to the pivot pin  57  in connection with rotation of the lever  26 , and is vertically moved at the same time. A guide instrument that guides the probe  53  such that the probe  53  moves vertically and linearly without horizontally shaking is included in the sensor body  55 . 
     Meanwhile, a piezoelectric dispenser  60  according to another embodiment of the inventive concept illustrated in  FIG. 9  includes a piezoelectric pump  12 , a displacement measurement sensor  62 , and a controller  44 . The piezoelectric pump  12  and the controller  44  are the same as those described above. 
     The displacement measurement sensor  62  is coupled to an external surface of the pump body  15  so as to detect an operation displacement of the lever  26  and provide the controller  44  with a detection signal corresponding to the operation displacement of the lever  26 . The displacement measurement sensor  62  includes a probe  63  and a sensor body  65  to which the probe  63  is movably coupled. An end of the probe  63  is in contact with an external surface of an extension portion  67  extending to an end of the lever  26  so that the probe  63  may be lifted or lowered in connection with rotation of the lever  26 . A curved contact surface  64  that is in sliding contact with a surface of the lever  26  is formed on the end of the probe  53 . 
     While the piezoelectric dispenser and the method of calibrating operation stroke of the piezoelectric dispenser according to the embodiments of the inventive concept have been described above, the scope of the inventive concept is not limited to the described and illustrated embodiments. 
     For example, the lever  26  and the valve rod  28  may be connected to each other also using other methods than a method of using the engaging groove  27  of the lever  26  and the engaging rod  29  of the valve rod  28 . The discharge instrument  25  may be modified to another structure than the structure including the lever  26  and the valve rod  28 , and the pump body  15  and the valve body  20  may be integrally formed with each other instead of being detachably coupled to each other. 
     In addition, besides the so-called probe sensor implemented and illustrated above as the displacement measurement sensor for detecting an operation displacement of the lever  26 , a displacement measurement sensor having various structures to detect an operation displacement of the lever  26  in a contact or non-contact manner and provide the controller  44  with a detection signal corresponding to the detected operation displacement of the lever  26  may be used. 
     In embodiments, to adjust changes of dispensing amount back to the preset value, a liquid dispenser apparatus includes a lever&#39;s position detector for detecting the lever&#39;s position which is indicative the valve rod&#39;s position. In one embodiment, the lever&#39;s position may be a relative position of the lever relative to a reference position of the lever. This relative position may indicate a displacement from the reference position. This displacement of the lever may be indicative of the displacement of the valve rod (or the tip of the valve rod which contacts a valve seat of the nozzle) which may be a stroke of the valve rod. This displacement may be a linear displacement or an angular displacement. In another embodiment, the lever&#39;s position may be a relative position of any other reference point, for example, an axis of the hinge of the lever. 
     In the illustrated embodiments, the dispensing apparatus includes one or more control circuits which include one or more processors and a memory which contain a program for controlling the operation of the piezoelectric actuators. The one or more processors may process the information of the lever&#39;s position, for example, the displacement of the lever, from the lever-position sensor to generate a control signal. The control signal is to change the voltage signal applied to the piezoelectric actuators to adjust a level of expansion and shrinkage of the piezoelectric actuators. Such change of the voltage signal may change the valve rod position without change of the stroke. In alternative embodiments, the stroke may be slightly changed. 
     According to the piezoelectric dispenser according to the inventive concept, when an operation stroke of a valve rod is changed from an initial value due to various factors during use of the piezoelectric dispenser, the operation stroke of the valve rod is calibrated by setting the same to an initial value by offsetting the operation stroke of the valve rod by controlling a voltage to be applied to the piezoelectric actuator. Accordingly, uniform dispensing performance of a viscous liquid may be maintained, and poor dispensing quality of a viscous liquid due to abrasion of components or the like may be reduced. 
     In addition, the operation stroke of the valve rod may be calibrated in real time during dispensing of a viscous liquid, thereby maintaining an optimum state of the dispensing quality of the viscous liquid. 
     It should be understood that embodiments described herein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each embodiment should typically be considered as available for other similar features or aspects in other embodiments. 
     While one or more embodiments have been described with reference to the figures, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the inventive concept as defined by the following claims.