WO2008124770A1

WO2008124770A1 - Apparatus and methods for jetting amounts of a fluid material from a jet dispenser

Info

Publication number: WO2008124770A1
Application number: PCT/US2008/059756
Authority: WO
Inventors: Mani Ahmadi; Stephen Des Jardins; Don La; Thomas L. Ratledge; Floriana Suriawidjaja; Todd Weston
Original assignee: Nordson Corporation
Priority date: 2007-04-10
Filing date: 2008-04-09
Publication date: 2008-10-16

Abstract

Apparatus and method for jetting amounts of a fluid material from a jet dispenser. The dispensing apparatus (10, 10a) includes a valve body (122) assembly and a valve shaft (44) that is moveable relative to a valve seat (38) for opening and closing a fluid flow passage (25) to jet the amounts of the fluid material. A heating element (120, 130, 140, 150) may be provided within at least one of the valve body assembly (122) or the valve shaft (44). In addition, a temperature sensor (126, 132, 144) may be provided within at least one of the valve body assembly (122) or the valve shaft (44) and may be used supply temperature feedback to a temperature controller (124) for controlling the operation of the heating element (120, 130, 140, 150).

Description

APPARATUS AND METHODS FOR JETTING AMOUNTS OF A FLUID MATERIAL FROM A JET DISPENSER

Cross-Reference to Related Applications

[0001] The present application claims the benefit of U.S. Provisional Application Serial No. 60/910,869, filed April 10, 2007, the disclosure of which is hereby incorporated by reference herein in its entirety.

Technical Field

[0002] The invention relates to jet dispensing of fluid materials and, in particular, to apparatus and methods for controlling the temperature of the components of a jet dispenser.

Background

[0003] Conventional jet dispensers are operated at high cycle rates of 70 Hz to 1,000 Hz to dispense streams or dots of a fluid material. Dispensing is controlled by a motor that reciprocates a valve shaft to move a valve head relative to a valve seat. Typically, the jet dispenser is operated with a duty cycle in which a series of streams or dots is dispensed followed by a period of time during which the valve shaft is idle. These idle periods occur, for example, when the jet dispenser is moved among consecutive dispense locations. Inside the jet dispenser, the valve shaft moves relative to one or more fluid seals that control movement of the fluid material inside the jet dispenser and, in particular, isolate the motor against the infiltration of fluid material. Over the course of the duty cycle, heat is generated by friction when the valve shaft reciprocates in contact with the fluid seal(s). Heat is also generated within the motor itself. When the valve shaft and motor are idle, heat generation from these sources is reduced or ceases entirely. [0004] The body of the jet dispenser operates as a heat sink or thermal capacitor for the heat generated by the jet dispenser during operation. The body of the jet dispenser continuously dissipates the absorbed heat to the surrounding environment. However, when the valve shaft and motor are idle, the body of the jet dispenser cools. As a result, the temperature of the body of the jet dispenser fluctuates over time. These temperature fluctuations cause variations in the temperature of the fluid material inside the fluid chamber of the jet dispenser and awaiting ejection. As appreciated by a person having ordinary skill in the art, the viscosity of the fluid material exhibits a temperature dependency. As the viscosity changes, the weight or amount of fluid material in each individual dispensed droplet or stream changes. [0005] As the viscosity increases with decreasing temperature, less fluid material flows past the valve seat when the valve head is lifted and the amount of fluid material ejected from the jet dispenser in each individual droplet or stream decreases when the valve closes and the valve head impacts the valve seat. As the viscosity decreases with increasing temperature, more fluid material flows past the valve seat and the amount of fluid material jetted in each individual droplet or stream increases. Certain fluid materials may have a viscosity that is highly sensitivity to temperature variations. This may result in significant variations in the amount of jetted fluid material over time. [0006] In addition to its effect on fluid material viscosity, the operational temperature fluctuations induce dimensional variations by thermal expansion in the valve shaft and the body of the jet dispenser. These dimensional variations operate to alter the stroke length of the valve shaft, which changes the dimensions or size of the individual streams or dots ejected from the jet dispenser. Stroke lengths may be as short as 50 microns or so. For such short stroke lengths, the variations in the amount of jetted fluid material induced by stroke length variations may be significant.

[0007] What is needed, therefore, are apparatus and methods to more precisely control the temperature of the components of the jet dispenser that overcome these and other deficiencies of conventional jet dispensers and thereby provide the ability to more precisely exercise control over the size of the individual dots or streams of fluid material ejected from the jet dispenser.

Summary of the Invention

[0008] In one embodiment, an apparatus is provided for jetting droplets of a fluid material. The apparatus includes a valve body assembly with a fluid flow passage for the fluid material and a valve seat within the fluid flow passage, and a valve shaft inside the valve body assembly, an actuator coupled with the valve shaft. The valve shaft has an opened position in which a portion of the valve shaft has a non-contacting relationship with the valve seat to open the fluid passage and a closed position in which the portion of the valve shaft contacts the valve seat to close the fluid flow passage. The actuator is configured to move the valve shaft relative to the valve seat between the opened and closed positions to jet the droplets of the fluid material. A heating element, which is configured to transfer heat to the valve body assembly, may be provided within the valve body assembly. Alternatively, a heating element, which is configured to transfer heat to the valve shaft, may be provided within the valve shaft. [0009] In another embodiment, a method is provided for jetting droplets of a fluid material from a jet dispenser having a valve body assembly, a fluid flow passage for the fluid material, a valve seat in the fluid flow passage, and a valve shaft inside the valve body assembly. The method includes operating the jet dispenser by moving the valve shaft relative to the valve seat into and out of contact with the valve seat for jetting successive amounts of the fluid material as the droplets. The method further includes heating at least one of the valve shaft or the valve body assembly to compensate for temperature variations of the at least one of the valve shaft or the valve body assembly during operation of the jet dispenser.

[0010] These and other advantages will be apparent in light of the following figures and detailed description.

Brief Description of the Drawings

[0011] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above and the detailed description of the embodiments given below, serve to explain the principles of the invention.

[0012] FIG. 1 is a side cross-sectional view of a dispensing apparatus in accordance with an embodiment of the invention.

[0013] FIG. 2 is a side cross-sectional view similar to FIG. 1 of a dispensing apparatus in accordance with an alternative embodiment of the invention.

Detailed Description

[0014] With reference to FIG. 1, a dispensing apparatus 10 has the form of a jet dispenser used for dispensing small amounts of a fluid material from a syringe 12 onto a substrate 14, such as a printed circuit (PC) board. Dispensing apparatus 10 includes a dispenser housing 16 having an inlet 18 that is coupled with an outlet 20 of syringe 12. Extending laterally through the dispenser housing 16 is an inlet passage 22 that connects the inlet 18 of the dispenser housing 16 to a bore 24, which defines a flow passage 25 inside the dispenser housing 16.

[0015] The dispensing apparatus 10 includes an outlet tube 28 and a valve seat assembly 32 mounted by a threaded connection (not shown) to the outlet tube 28. The valve seat assembly 32 includes a bore 34, a flow passage 36 defined by the bore 34, and a valve seat 38 disposed in the flow passage 36. A valve seat component 42, which is disposed within the valve seat assembly 32, carries the valve seat 38. The outlet tube 28 includes a bore 26 with a flow passage 30 that is in flow communication with an inlet end - A -

of the flow passage 36 within the valve seat assembly 32. One end of the outlet tube 28 is secured to dispenser housing 16 by a mounting plate 41 so that flow passages 30, 36 are generally longitudinally aligned with each other. A nozzle 40 is coupled with an opposite outlet end of the flow passage 36. When the dispensing apparatus 10 is operating, amounts of fluid material are metered past the valve seat 38 from a fluid chamber 43 collectively defined by the flow passages 25, 30 and the portion of flow passage 36 upstream from the valve seat 38.

[0016] A valve shaft 44 extends through the flow passages 25, 30 into the flow passage 36 inside the valve seat assembly 32. One end of the valve shaft 44 carries a valve head 46 that contacts the valve seat 38 to close flow passage 36. An opposite end of the valve shaft 44 is engaged with an actuator or control mechanism generally indicated by reference numeral 48, which is configured to reciprocate the valve shaft 44 into and out of a seating engagement with the valve seat 38. A seal ring 52, which is disposed in sealing relation about valve shaft 44, is located above flow passage 25. The seal ring 52 ensures that the fluid material in the fluid chamber 43 does not leak past valve shaft 44 and into the control mechanism 48. Seal ring 52 is secured in place by a ring 54, which in turn is held in place by the bottom surface of a housing block 56. [0017] The valve seat assembly 32 and nozzle 40 are mounted by a mounting body 58 to an opposite outlet end of the flow passage 36. A heating element 50 is disposed about, and secured to, a mounting body 58 in the area of and adjacent to the valve seat assembly 32 and nozzle 40. Heating element 50 is used to selectively and locally heat valve seat assembly 32 and nozzle 40. A temperature controller 60, which is connected by wire leads 62, 64 to the heating element 50, is operated to power the heating element 50. An air tube 66 connected to a pressure regulator 68 and a source of low-pressure air (not shown) is coupled to the inlet of syringe 12. The air pressure is used to force the liquid or viscous material through the inlet passage and into flow passages 25, 30 at a substantially constant pressure.

[0018] During operation, the control mechanism 48 reciprocates the valve shaft 44 along a longitudinal axis 70 between a first open position in which the valve head 46 is spaced from valve seat 38 and a second closed position in which the valve head 46 contacts the valve seat 38 with a seating engagement. In the closed position, the fluid material collects in the valve seat component 42 to await ejection and is heated to a preset temperature established by heat transferred from the heating element 50. The control mechanism 48 includes the housing block 56, which has a centrally disposed longitudinal bore 72, and an air chamber block 74. A portion of the valve shaft 44 extends through bore 72 and another portion of the valve shaft 44 projects from an upper end of the bore 72 into the air chamber block 74. An air seal ring 76 provides an air seal about valve shaft 44 at the junction of the housing block 56 and air chamber block 74. [0019] The control mechanism 48 includes a piston 78 situated between air chambers 82, 84 defined inside the air chamber block 74 and a seal element 86 carried by the piston 78. Air chamber 82 is defined below seal 80 and air chamber 84 is defined above seal 80. Valve shaft 44 extends through with a central bore in the piston 78 and the seal element 86 isolates the air chambers 82, 84 from each other. Air inlets 88, 90 to the respective air chambers 82, 84 are connected by a supply line 92 with a source of pressurized air (not shown). A solenoid valve 95, located between supply line 92 and inlets 88, 90, regulates the application and removal of air pressure within the air chambers 82, 84. The solenoid valve 95 is electrically actuated by a controller 96. Solenoid valve 95 may be actuated by the controller 96 to exhaust air chamber 82 while concurrently pressurizing air chamber 84, when closing the valve, and conversely, to exhaust air chamber 84 while concurrently pressurizing air chamber 82, when opening the valve.

[0020] A spring housing 98 is mounted against the top surface of air chamber block 74. A spring retainer 100, which is securely mounted onto the upper end of valve shaft 44, abuts against the piston 78. A spring adjustment component 102, which is secured by a threaded engagement with the spring housing 98, is movable relative to the spring retainer 100. A compression spring 104 is captured between spring retainer 100 and a bottom surface of the spring adjustment component 102. A lock nut 106 is secured with a threaded engagement to an exterior of the spring adjustment component 102 by threads. The force applied by the compression spring 104 to the spring retainer 100 increases as the spring adjustment component 102 is moved towards spring retainer 100 and decreases as the spring adjustment component 102 is moved away from spring retainer 100. The compression spring 104 exerts this closure force on the spring retainer 100 and ultimately, on the valve head 46 of valve shaft 44. The lock nut 106 is used to lock the spring adjustment component 102 in an adjusted position relative to the spring retainer 100 so that the adjusted position is retained.

[0021] The control mechanism 48 also includes a knob 108 attached to a rod 110. The rod 110 has a threaded engagement with a tapped opening in the spring adjustment component 102. The rod 110 extends longitudinally through the coils of the compression spring 104 and bears against the top end of valve shaft 44, which projects above the spring retainer 100. By turning the knob 108 either clockwise or counterclockwise, the position of the rod 110 is adjusted relative to the spring adjustment component 102, which adjusts the stroke of the valve shaft 44 with respect to the valve seat 38. [0022] In alternative embodiments, other types of actuators, such as piezoelectric actuators or piezoelectric torque motors, may be coupled with the valve shaft 44 for the purpose of moving the valve shaft 44 relative to the valve seat 38. These actuator types are recognized by a person having ordinary skill in the art of fluid material dispensing and jetting. For example, an exemplary piezoelectric torque motor is disclosed in commonly- owned Application Serial No. 11/ 931,397, filed October 31, 2007 and entitled "Fluid Dispensers and Methods for Dispensing Viscous Fluids With Improved Edge Definition," the disclosure of which is hereby incorporated by reference herein in its entirety. [0023] In use, the syringe 12 of liquid or viscous material is mounted to the inlet opening 18 of the dispenser housing 16 and air tube 66 is coupled to the inlet of syringe 12 to force the liquid or viscous material into the inlet passage 22 and flow passage 25 circumscribing the valve shaft 44. In the closed position, the valve head 46 is seated against valve seat 38 and the valve seat component 42 is filled with a small amount of the liquid or viscous material. Heating element 50 transfers heat to the liquid or viscous material in valve seat component 42 in the local vicinity of the valve seat 38. [0024] When the valve head 46 is lifted by the control mechanism 48 from contact with the valve seat 38 to an opened position, the viscous material is pushed through and out from an outlet in nozzle 40 as a thin stream. Then, after valve head 46 impacts and closes against valve seat 38 to establish a closed position, the sudden deceleration of the flowing material overcomes the adhesive's yield stress and breaks the stream. The solid nature of the heated viscous material causes the viscous material to break off from the outlet of nozzle 40 and form a droplet of material. When the solenoid valve 95 is switched to exhaust air pressure from air chamber 82, the compression spring 104 rapidly moves valve head 46 to a seated position contacting valve seat 38 to close the valve, which pushes the heated liquid or viscous material out of the nozzle 40. The streams or droplets of liquid or viscous material ejected from nozzle 40 can be dispensed at a rate of 70 Hz to 1,000 Hz. The streams or droplets are deposited on the surface of a substrate 14, such as a printed circuit board.

[0025] With continued reference to FIG. 1 and in accordance with an embodiment of the invention, an auxiliary heater in the representative form of a heating element 120 is embedded in the housing block 56 of the control mechanism 48. The dispenser housing 16, the outlet tube 28, and the housing block 56 may be collectively considered to constitute a primary valve body, which is generally indicated by reference numeral 122, of the dispensing apparatus 10. The valve body assembly 122 depicted in FIG. 1, which is representative, includes multiple separable pieces joined together to form an assembly that contains the entire fluid chamber 43 defined by the flow passages 25, 30 and the portion of flow passage 36 upstream from the valve seat 38. In an alternative embodiment, the valve body assembly 122 may be a unitary housing containing the fluid chamber 43. In this regard, the dispenser housing 16, outlet tube 28, and housing block 56 may be united to define an integral structure lacking distinguishable multiple pieces exclusive of the control mechanism 48. The dispenser housing 16, outlet tube 28, and housing block 56 are formed from a material that has a relatively high thermal conductivity, which is typically a metal or metal alloy.

[0026] The heating element 120 is connected by a set of conductors 123 with a temperature controller 124. The construction and operation of the heating element 120 and temperature controller 124 are understood by a person having ordinary skill in the art. In one embodiment, the temperature controller 124 includes a power supply that is used to electrically power the heating element 120. In one embodiment, the heating element 120 may be an electrically-operated, resistance-type cartridge heater and the housing block 56 may be drilled with a port that is occupied by the cartridge heater. [0027] A temperature sensor 126 is also embedded in the housing block 56 of the control mechanism 48 at a location near the heating element 120. The temperature sensor 126, which is in good thermal contact with the housing block 56, is configured to measure the temperature of the housing block 56. The temperature sensor 126, which is electrically coupled by another set of conductors 128 with the temperature controller 124, is configured to communicate output signals representative of the temperature of the housing block 56 to the temperature controller 124. In one embodiment, the temperature sensor 126 may be a resistance temperature detector that changes resistance as the temperature of the housing block 56 varies from heat supplied by the temperature controller.

[0028] The temperature controller 124 uses the feedback information from the temperature sensor 126 to control the power supplied to the heating element 120 and, thereby, maintain the temperature of the housing block 56 at a control temperature. The temperature controller 124 may employ, for example, a proportional integral derivative (PID) algorithm based on feedback from the temperature sensor 126 to determine the power supplied to the heating element 120 based upon the error between the measured temperature and the control temperature. Power is supplied over the conductors 123 from the temperature controller 124 to the heating element 120.

[0029] Based upon the feedback temperature measured by the temperature sensor 126, the temperature controller 124 increases or reduces the amount of heat generated by heating element 120 to maintain the valve shaft 44, the valve body assembly 122, and the fluid material in the fluid chamber 43 at a substantially constant temperature. The functions of the temperature controller 60 can be combined into temperature controller 124 to better achieve uniform temperature control of the fluid material residing within the fluid chamber 43.

[0030] Using the heating element 120, temperature sensor 126, and temperature controller 124, the temperature of the valve body assembly 122 is maintained approximately at the control temperature. If the heat generated by the operation of the dispensing apparatus 10 increases, the temperature sensor 126 detects the increased temperature and the temperature controller 124 notes the increase in the sampled temperature signals communicated from the temperature sensor. To maintain the control temperature, the temperature controller 124 determines the error and reduces the power supplied to the heating element 120 so that the temperature of the valve body assembly 122 is maintained approximately at the control temperature. Conversely, if the heat generated by the operation of the dispensing apparatus 10 decreases, the temperature sensor 126 detects the decreased temperature and the temperature controller 124 notes the decrease in the sampled temperature signals communicated from the temperature sensor. To maintain the control temperature in this situation, the temperature controller 124 determines the error and increases the power supplied to the heating element 120 so that the temperature of the valve body assembly 122 is maintained approximately at the control temperature. The temperature control also maintains the valve shaft 44 at an approximately constant temperature, which prevents significant changes in the dimensions of the valve shaft 44 and maintains a constant stroke length. The fluid material inside the fluid chamber 43 is also maintained at an approximately constant temperature such that the quantity of fluid material ejected in each individual droplet or stream is constant despite the presence of fluctuating heat sources. The temperature regulation is continuous while the dispensing apparatus 10 is in operation. [0031] The heating element 120, temperature sensor 126, and temperature controller 124 cooperate to compensate for fluctuations in the fluid temperature and in the temperature of the valve shaft 44 produced by heat generated by the reciprocation of the valve shaft 44 by the motor. Consequently, the valve shaft 44, the valve body assembly 122, and the fluid material in the fluid chamber 43 are more precisely controlled at respective approximately steady state temperatures, which more closely controls the size of the dots or streams ejected from the dispensing apparatus 10. [0032] In an alternative embodiment, another heating element 130 substantially identical to heating element 120 may be embedded in, for example, the dispenser housing 16. This alternative embodiment may be used, for example, if the valve body assembly 122 is constructed multiple pieces to ensure that the entire valve body assembly 122 is uniformly heated. In addition, an additional temperature sensor 132, which is substantially identical to temperature sensor 126, may be embedded in the dispenser housing 16. Similar to heating element 120 and temperature sensor 126, the heating element 130 and temperature sensor 132 are electrically coupled with the temperature controller 124, or with another temperature controller (not shown), for use in heating the dispenser housing 16 to a control temperature. In yet another alternative embodiment, heating element 120 may be omitted in its entirety from the construction of the dispensing apparatus 10 so that heating element 130 supplies the requisite temperature control in conjunction with the temperature sensor 132 and the temperature controller 124. [0033] With reference to FIG. 2 in which like reference numerals refer to like features in FIG. 1 and in accordance with an alternative embodiment, a dispensing apparatus 10a includes an auxiliary heater in the representative form of a heating element 140 embedded in the valve shaft 44, rather than heating element 120 (FIG. 1). The heating element 140 is located longitudinally along the length of the valve shaft 44 such that the heating element 140 is located within the bore 24 of the dispenser housing 16. However, the invention is not so limited as the location of the heating element 140 along the length of the valve shaft 44. Dispensing apparatus 10a is otherwise identical in construction to dispensing apparatus 10 (FIG. 1).

[0034] The heating element 140 is connected by a set of conductors 142 with the temperature controller 124. A temperature sensor 144 is also embedded in the valve shaft 44 proximate to the heating element 140. The construction and operation of the heating element 140 and the temperature sensor 144 are substantially identical to the construction and operation of the heating element 120 and temperature sensor 126 (FIG. 1). The temperature sensor 144, which is in good thermal contact with the valve shaft 44, is configured to measure the temperature of the valve shaft 44. The temperature sensor 144, which is electrically coupled by a set of conductors 146 with the temperature controller 124, is configured to communicate output signals representative of the valve shaft 44 to the temperature controller 124.

[0035] The temperature controller 124 uses the feedback information from the temperature sensor 144 to control the power supplied to the heating element 140 and thereby maintain the temperature at a control temperature. Based upon the feedback temperature measured by the temperature sensor 144, the temperature controller 124 increases or reduces the amount of heat generated by heating element 140 by adjusting the power supplied to the heating element 140. These adjustments maintain the valve shaft 44, the valve body assembly 122, and the fluid material in the fluid chamber 43 at a substantially constant temperature. Using the heating element 140, temperature sensor 144, and temperature controller 124, the temperature of the valve body assembly 122 is maintained approximately at the control temperature, which supplies benefits as outlined hereinabove.

[0036] In an alternative embodiment, the dispensing apparatus 10a may incorporate heating element 120 (FIG. 1) and/or heating element 130 (FIG. 1), heating element 140 (FIG. 2), and at least one of the temperature sensors 126, 132, 144 that participate in regulating the temperature of the valve shaft 44, the valve body assembly 122, and the fluid material in the fluid chamber 43 when the dispensing apparatus 10a is operating. [0037] In yet another alternative embodiment, the dispensing apparatus 10a may include an auxiliary heater in the representative form of a thermoelectric device 150 coupled with the valve body assembly 122, rather than heating element 130 (FIG. 1) or in addition to heating element 130. The thermoelectric device 150 is coupled with the temperature controller 124 by a set of conductors 152. When the dispensing apparatus 10a is operating, the thermoelectric device 150 is operated by the temperature controller 124 as a heating element in a manner similar to heating element 120 to regulate the temperature of the valve shaft 44, the valve body assembly 122, and the fluid material in the fluid chamber 43.

[0038] The thermoelectric device 150 includes multiple thermoelectric elements that extend between support plates. The thermoelectric elements consist of an array of up to several hundred dissimilar n-type and p-type semiconductors, which may be formed from p-doped and n-doped bismuth- telluride, thermally joined in parallel and electrically joined in series at both ends to form couples. The power supplied to the thermoelectric device 150 over conductors 152 is normally direct current (DC) power. The thermoelectric device 150, which operates by the Peltier effect as understood by a person having ordinary skill in the art, converts electrical energy from the temperature controller 124 to heat pumping energy. In particular, DC power applied between the support plates induces pumped heat flow from one of the plates through the thermoelectric elements to the opposite plate as the thermoelectric elements of the thermoelectric device 150 convert electrical energy to heat pumping energy. Normally, the support plate of the thermoelectric device 150 coupled with the valve body assembly 122 defines a hot side of the thermoelectric device 150 that transfers heat to the valve body assembly 122. Alternatively, the DC power may be reversed biased so that the support plate of thermoelectric device 150 contacting the valve body assembly 122 absorbs heat from the valve body assembly 122, which is subsequently rejected by the opposite support plate of the thermoelectric device 150 after conduction through the thermoelectric elements. [0039] While the present invention has been illustrated by a description of the various embodiments and examples, and while these embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Thus, the invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and illustrative example shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicants' general inventive concept.

Claims

What is claimed is:

1. An apparatus for jetting amounts of a fluid material, the apparatus comprising: a valve body assembly including a fluid flow passage for the fluid material and a valve seat within the fluid flow passage; a valve shaft inside the valve body assembly, the valve shaft having an opened position in which a portion of the valve shaft has a non-contacting relationship with the valve seat to open the fluid passage and a closed position in which the portion of the valve shaft contacts the valve seat to close the fluid flow passage; an actuator coupled with the valve shaft, the actuator configured to move the valve shaft relative to the valve seat between the opened position and the closed position to jet the amounts of the fluid material; and a heating element provided within the valve body assembly, the heating element configured to transfer heat to the valve body assembly.

2. The apparatus of claim 1 further comprising: a sensor for sensing the temperature of the valve body assembly.

3. The apparatus of claim 2 further comprising: a controller connected to the sensor and the heating element, the controller to operate the heating element to maintain the fluid material within the fluid flow passage at a substantially constant temperature based upon the temperature sensed by the sensor.

4. The apparatus of claim 1 wherein the valve body assembly is an integral structure containing the fluid flow passage.

5. The apparatus of claim 1 wherein the actuator is a pneumatic actuator.

6. The apparatus of claim 1 wherein the heating element is a thermoelectric device or a resistance-type cartridge heater.

7. An apparatus for jetting amounts of a fluid material, the apparatus comprising: a valve body assembly including a fluid flow passage for the fluid material and a valve seat within the fluid flow passage; a valve shaft inside the valve body assembly, the valve shaft having an opened position in which a portion of the valve shaft has a non-contacting relationship with the valve seat to open the fluid passage and a closed position in which the portion of the valve shaft contacts the valve seat to close the fluid flow passage; an actuator coupled with the valve shaft, the actuator configured to move the valve shaft relative to the valve seat between the opened position and the closed position to jet the amounts of the fluid material; and a heating element provided within the valve shaft, the heating element configured to transfer heat to the valve shaft.

8. The apparatus of claim 7 further comprising: a sensor for sensing the temperature of the valve body assembly.

9. The apparatus of claim 8 further comprising: a controller electrically connected to the sensor and the heating element, the controller to operate the heating element to maintain the fluid material within the fluid flow passage at a substantially constant temperature based upon the temperature sensed by the sensor.

10. The apparatus of claim 7 wherein the valve body assembly is an integral structure containing the fluid flow passage.

11. The apparatus of claim 7 wherein the actuator is a pneumatic actuator.

12. The apparatus of claim 1 wherein the heating element is a thermoelectric device or a resistance-type cartridge heater.

13. A method of jetting amounts of a fluid material from a jet dispenser having a valve body assembly, a fluid flow passage for the fluid material, a valve seat in the fluid flow passage, and a valve shaft inside the valve body assembly, the method comprising: operating the jet dispenser by moving the valve shaft relative to the valve seat into and out of contact with the valve seat for jetting successive amounts of the fluid material as the amounts; and heating at least one of the valve shaft or the valve body assembly to compensate for temperature variations of the at least one of the valve shaft or the valve body assembly during operation of the jet dispenser.

14. The method of claim 13 further comprising: sensing a temperature of the valve body assembly; and using the sensed temperature as feedback to detect the temperature variations.

15. The method of claim 14 further comprising: operating a heating element in the valve body assembly based upon the feedback to regulate the temperature of at least one of the valve shaft or the valve body assembly.

16. The method of claim 13 further comprising: sensing a temperature of the valve shaft; and using the temperature as feedback to detect the temperature variations.

17. The method of claim 16 further comprising: operating a heating element in the valve shaft based upon the feedback to regulate the temperature of at least one of the valve shaft or the valve body assembly.

18. The method of claim 13 wherein heating the at least one of the valve shaft or the valve body assembly further comprises: heating the valve body assembly to compensate for the temperature variations.

19. The method of claim 13 wherein heating the at least one of the valve shaft or the valve body assembly further comprises: heating the valve shaft to compensate for the temperature variations.

20. The method of claim 13 wherein heating the at least one of the valve shaft or the valve body assembly further comprises: temporally controlling the heating so that the fluid material in the fluid chamber is maintained at a substantially constant temperature.