Patent Publication Number: US-11376623-B2

Title: Apparatuses for dispensing flowable materials

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 16/176,875, entitled: “APPARATUSES AND METHODS FOR DISPENSING FLOWABLE MATERIALS”, filed on 2018 Oct. 31, which is incorporated herein by reference in its entirety for all purposes. 
    
    
     TECHNICAL FIELD 
     The present disclosure generally relates to apparatuses and methods for dispensing flowable materials and, more specifically, to dispensing flowable materials using rotary actuators and hydraulic means. 
     BACKGROUND 
     Flowable materials are commonly dispensed using direct mechanical action. For example, a manual caulking gun has a trigger, configured to advance a plunger that extrudes material from a cartridge. However, manual activation of the trigger to extrude the flushable material, which often has a glutinous consistency, is physically demanding and, accordingly, difficult to control. Pneumatic action is readily available to supplement or replace direct mechanical action when force amplification is required. However, compressible nature of gases results in a loss of precision when pneumatic action is used for dispensing flowable materials. Overall, conventional devices and methods of dispensing flowable materials lack precision, needed in certain critical applications, such as aerospace. 
     SUMMARY 
     Accordingly, apparatuses and methods, intended to address at least the above-identified concerns, would find utility. 
     The following is a non-exhaustive list of examples, which may or may not be claimed, of the subject matter disclosed herein. 
     One example of the subject matter, disclosed herein, relates to an apparatus for dispensing a flowable material. The apparatus comprises a rotary actuator, a reservoir, containing a hydraulic fluid, a piston, movable inside the reservoir, a linear actuator, coupled to the piston, a gear train, coupling the rotary actuator with the linear actuator, and a flowable-material dispenser, hydraulically coupled with the reservoir. 
     Using the rotary actuator and direct mechanical or hydraulic coupling between various components of the apparatus provides high dispensing precision. Specifically, the linear movement of the piston inside the reservoir, containing the hydraulic fluid, is precisely controlled by the rotary actuator, such as a stepper motor. The rotary actuator is coupled to the linear actuator using the gear train, while the linear actuator is coupled to the piston. The linear movement of the piston transfers at least a portion of the hydraulic fluid between the reservoir and the flowable-material dispenser. The hydraulic fluid, once transferred to the flowable-material dispenser, displaces the flowable material from the flowable-material dispenser in a precise manner. It should be noted that the volume of the hydraulic fluid, displaced from the reservoir, is the same as the volume of the hydraulic fluid received in the flowable-material dispenser since hydraulic fluid is not compressible. As such, the dispensing of the flowable material is precisely controlled by the movement of the piston inside the reservoir, which in turn is precisely controlled by the rotary actuator. Overall, the rotary actuator controls precise dispensing of the flowable material through mechanical and hydraulic coupling between various components of the apparatus. Furthermore, the hydraulic coupling allows more flexible positioning of the flowable-material dispenser relative to the rotary actuator, thereby resulting in the apparatus being compact. 
     Another example of the subject matter, disclosed herein, relates to a method for dispensing a flowable material using an apparatus. The apparatus comprises a rotary actuator, a reservoir, containing a hydraulic fluid, a piston, movable inside the reservoir, a linear actuator, coupled to the piston, a gear train, coupling the rotary actuator with the linear actuator, a flowable-material dispenser, comprising a cartridge housing and a plunger and hydraulically coupled with the reservoir, an end-cap, movably coupled with the flowable-material dispenser, and an over-center mechanism, movably coupling the end-cap with the cartridge housing of the flowable-material dispenser. The method comprises holding the hydraulic fluid in the reservoir at a negative pressure, sufficient to generate a vacuum between the end-cap and the plunger, inserting a cartridge tube, having an interior, into the cartridge housing, wherein the flowable material is inside the cartridge tube, locking the over-center mechanism relative to the cartridge housing so that a hermetic seal is created between the plunger and the interior of the cartridge tube and between the end-cap and the interior of the cartridge tube, and turning the rotary actuator in a rotational direction so that the linear actuator advances the piston within the reservoir to transfer at least a portion of the hydraulic fluid from the reservoir to the flowable-material dispenser through the end-cap and into the interior of the cartridge tube, causing the plunger to advance within the cartridge tube in a forward plunger direction, away from the end-cap. 
     When the hydraulic fluid is held at the negative pressure in the reservoir, this negative pressure is also present in all other areas of the apparatus occupied by the hydraulic fluid. As a result, the plunger, which contacts the hydraulic fluid, is forced by the hydraulic fluid toward and against the end-cap. This force supports the plunger on the end-cap and allows positioning the plunger away from the cartridge housing when the end-cap is moved away from the cartridge housing. This position of the plunger and the end-cap, away from the cartridge housing, provides access to the cartridge housing, allowing insertion of the cartridge tube into the cartridge housing. 
     When the over-center mechanism is locked relative to the cartridge housing, the plunger is pressed by the end-cap into the interior of the cartridge tube and is hermetically sealed against the interior of the cartridge tube. The hermetic seal prevents the flowable material from flowing past the plunger. Furthermore, the hermetic seal prevents the hydraulic fluid from flowing past the plunger and reaching the flowable material while still allowing the plunger to advance within the cartridge tube. 
     Another hermetic seal is formed between the end-cap and the interior of the cartridge tube. This seal keeps the hydraulic fluid within the interior of the cartridge tube when the hydraulic fluid is transferred into the interior of the cartridge tube and maintained at a positive pressure or a negative pressure (e.g., to advance the plunger within the cartridge tube). This seal is maintained while the end-cap is positioned at a first end of the cartridge housing. 
     When the rotary actuator is turned in a rotational direction, the linear actuator advances the piston within the reservoir. The rotational speed and the degree of rotation (e.g., the number of rotations) of the rotary actuator are precisely controlled. This control translates into the precise linear motion of the piston. As the piston moves within the reservoir, at least a portion of the hydraulic fluid is transferred from the reservoir to the flowable-material dispenser. Specifically, the hydraulic fluid flows through the end-cap into the interior of the cartridge tube. This addition of the hydraulic fluid causes the plunger to advance within the cartridge tube in a forward plunger direction away from the end-cap. As a result, the flowable material is displaced by the plunger out of the cartridge tube. The precision of the rotary actuator results in the flowable material being dispensed in a controlled manner. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Having thus described one or more examples of the present disclosure in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein like reference characters designate the same or similar parts throughout the several views, and wherein: 
         FIGS. 1A and 1B , collectively, are a block diagram of an apparatus for dispensing flowable materials, according to one or more examples of the present disclosure; 
         FIG. 2  is a schematic perspective view of the apparatus of  FIGS. 1A and 1B , according to one or more examples of the present disclosure; 
         FIGS. 3A and 3B  are schematic cross-sectional views of a portion of the apparatus of  FIG. 2 , according to one or more examples of the present disclosure; 
         FIGS. 3C and 3D  are schematic cross-sectional views of an anti-rotation mechanism of the apparatus of  FIGS. 1A and 1B , according to one or more examples of the present disclosure; 
         FIGS. 3E and 3F  are schematic cross-sectional views of a piston and a reservoir of the apparatus of  FIGS. 1A and 1B , according to one or more examples of the present disclosure; 
         FIG. 4A  is a schematic cross-sectional view of a flowable-material dispenser of the apparatus of  FIG. 2 , illustrating a cartridge tube inserted into the cartridge housing, according to one or more examples of the present disclosure; 
         FIG. 4B  is a schematic cross-sectional view of the cartridge tube of  FIG. 4A , according to one or more examples of the present disclosure; 
         FIG. 4C  is a schematic cross-sectional view of a portion of the flowable-material dispenser in  FIG. 4A , illustrating a plunger positioned against an end-cap, according to one or more examples of the present disclosure; 
         FIG. 4D  is a schematic cross-sectional view of the portion of the flowable-material dispenser also shown in  FIG. 4B , illustrating the plunger moving away from the end-cap, according to one or more examples of the present disclosure; 
         FIG. 4E  is a schematic cross-sectional view of a portion of the flowable-material dispenser in  FIG. 4A , illustrating a cartridge tube sealed against a second end-cap, according to one or more examples of the present disclosure; 
         FIGS. 5A and 5B  are schematic side views of a portion of the apparatus in  FIG. 2 , illustrating operation of an over-center mechanism, according to one or more examples of the present disclosure; 
         FIGS. 6A and 6B  are schematic cross-sectional views of a portion of the flowable-material dispenser in  FIG. 4A , illustrating operation of a dispenser valve, according to one or more examples of the present disclosure; 
         FIGS. 7A and 7B , collectively, are a block diagram of a method of dispensing flowable material using the apparatus of  FIGS. 1A, 1B, and 2 , according to one or more examples of the present disclosure; 
         FIG. 8A  is a block diagram of aircraft production and service methodology; and 
         FIG. 8B  is a schematic illustration of an aircraft. 
     
    
    
     DETAILED DESCRIPTION 
     In  FIGS. 1A and 1B , referred to above, solid lines, if any, connecting various elements and/or components may represent mechanical, electrical, fluid, optical, electromagnetic and other couplings and/or combinations thereof. As used herein, “coupled” means associated directly as well as indirectly. For example, a member A may be directly associated with a member B, or may be indirectly associated therewith, e.g., via another member C. It will be understood that not all relationships among the various disclosed elements are necessarily represented. Accordingly, couplings other than those depicted in the block diagrams may also exist. Dashed lines, if any, connecting blocks designating the various elements and/or components represent couplings similar in function and purpose to those represented by solid lines; however, couplings represented by the dashed lines may either be selectively provided or may relate to alternative examples of the present disclosure. Likewise, elements and/or components, if any, represented with dashed lines, indicate alternative examples of the present disclosure. One or more elements shown in solid and/or dashed lines may be omitted from a particular example without departing from the scope of the present disclosure. Environmental elements, if any, are represented with dotted lines. Virtual (imaginary) elements may also be shown for clarity. Those skilled in the art will appreciate that some of the features illustrated in  FIGS. 1A, 1B, and 1C  may be combined in various ways without the need to include other features described in  FIGS. 1A, 1B, and 1C , other drawing figures, and/or the accompanying disclosure, even though such combination or combinations are not explicitly illustrated herein. Similarly, additional features not limited to the examples presented, may be combined with some or all of the features shown and described herein. 
     In  FIGS. 8A and 8B , referred to above, the blocks may represent operations and/or portions thereof and lines connecting the various blocks do not imply any particular order or dependency of the operations or portions thereof. Blocks represented by dashed lines indicate alternative operations and/or portions thereof. Dashed lines, if any, connecting the various blocks represent alternative dependencies of the operations or portions thereof. It will be understood that not all dependencies among the various disclosed operations are necessarily represented.  FIGS. 8A and 8B  and the accompanying disclosure describing the operations of the method(s) set forth herein should not be interpreted as necessarily determining a sequence in which the operations are to be performed. Rather, although one illustrative order is indicated, it is to be understood that the sequence of the operations may be modified when appropriate. Accordingly, certain operations may be performed in a different order or simultaneously. Additionally, those skilled in the art will appreciate that not all operations described need be performed. 
     In the following description, numerous specific details are set forth to provide a thorough understanding of the disclosed concepts, which may be practiced without some or all of these particulars. In other instances, details of known devices and/or processes have been omitted to avoid unnecessarily obscuring the disclosure. While some concepts will be described in conjunction with specific examples, it will be understood that these examples are not intended to be limiting. 
     Unless otherwise indicated, the terms “first,” “second,” etc. are used herein merely as labels, and are not intended to impose ordinal, positional, or hierarchical requirements on the items to which these terms refer. Moreover, reference to, e.g., a “second” item does not require or preclude the existence of, e.g., a “first” or lower-numbered item, and/or, e.g., a “third” or higher-numbered item. 
     Reference herein to “one example” means that one or more feature, structure, or characteristic described in connection with the example is included in at least one implementation. The phrase “one example” in various places in the specification may or may not be referring to the same example. 
     As used herein, a system, apparatus, structure, article, element, component, or hardware “configured to” perform a specified function is indeed capable of performing the specified function without any alteration, rather than merely having potential to perform the specified function after further modification. In other words, the system, apparatus, structure, article, element, component, or hardware “configured to” perform a specified function is specifically selected, created, implemented, utilized, programmed, and/or designed for the purpose of performing the specified function. As used herein, “configured to” denotes existing characteristics of a system, apparatus, structure, article, element, component, or hardware which enable the system, apparatus, structure, article, element, component, or hardware to perform the specified function without further modification. For purposes of this disclosure, a system, apparatus, structure, article, element, component, or hardware described as being “configured to” perform a particular function may additionally or alternatively be described as being “adapted to” and/or as being “operative to” perform that function. 
     Illustrative, non-exhaustive examples, which may or may not be claimed, of the subject matter according the present disclosure are provided below. 
     Referring generally to  FIGS. 1A and 1B , and particularly to, e.g.,  FIGS. 2, 3A, 3B , and  4 D, apparatus  100  for dispensing flowable material  308  is disclosed. Apparatus  100  comprises rotary actuator  120 , reservoir  140 , containing hydraulic fluid  155 , and piston  145 , movable inside reservoir  140 . Apparatus  100  also comprises linear actuator  130 , coupled to piston  145 , gear train  125 , coupling rotary actuator  120  with linear actuator  130 , and flowable-material dispenser  160 , hydraulically coupled with reservoir  140 . The preceding subject matter of this paragraph characterizes example 1 of the present disclosure. 
     Using rotary actuator  120  and direct mechanical or hydraulic coupling between various components of apparatus  100  provides high dispensing precision. Specifically, the linear movement of piston  145  inside reservoir  140 , containing hydraulic fluid  155 , is precisely controlled by rotary actuator  120 , such as a stepper motor. Rotary actuator  120  is coupled to linear actuator  130  using gear train  125 , while linear actuator  130  is coupled to piston  145 . The linear movement of piston  145  transfers at least a portion of hydraulic fluid  155  between reservoir  140  and flowable-material dispenser  160 . Hydraulic fluid  155 , transferred to flowable-material dispenser  160 , displaces flowable material  308  from flowable-material dispenser  160  in a precise manner. It should be noted that the volume of hydraulic fluid  155 , displaced from reservoir  140 , is the same as the volume of hydraulic fluid  155  received in flowable-material dispenser  160  since hydraulic fluid  155  is not compressible. As such, the dispensing of flowable material  308  is precisely controlled by the movement of piston  145  inside reservoir  140 , which in turn is precisely controlled by rotary actuator  120 . Overall, rotary actuator  120  controls precise dispensing of flowable material  308  through mechanical and hydraulic coupling between various components of apparatus  100 . Furthermore, the hydraulic coupling allows more flexible positioning of flowable-material dispenser  160  relative to rotary actuator  120 , thereby resulting in apparatus  100  being compact.  FIG. 2  illustrates an example of flowable-material dispenser  160  and rotary actuator  120  being positioned along two parallel axes. 
     Apparatus  100  is configured to dispense various types of flowable materials  308 . Some examples of flowable materials  308  include, but are not limited to, adhesives, sealants, lubricants, viscous materials, thixotropic materials, and the like. In some examples, the viscosity of flowable materials  308  is between about 10,000 cps and 1,000,000 cps or, more specifically, between about 50,000 cps and 250,000 cps. High viscosity and other flow characteristics of flowable materials  308  require high displacement forces, which interferes with precision of conventional methods. On the other hand, hydraulic coupling between different components of apparatus  100  allows generating high displacement forces without compromising displacement precision. 
     Some examples of rotary actuator  120  include, but are not limited to, stepper motors, servo motors, and the like. The rotational speed and degree of rotation (e.g., the rotational angle and/or the number of rotations) of rotary actuator  120  is precisely controlled. As further described below, various inputs, e.g., pressure inside reservoir  140 , are used for controlling rotary actuator  120 . The rotational speed controls the dispensing rate (e.g., the flow rate) of flowable material  308  from apparatus  100 . The degree of rotation controls the amount of flowable material  308  dispensed from apparatus  100 . 
     Precision of the dispensing rate and/or the dispensed amount of flowable material  308  is also enhanced by gear train  125  and/or linear actuator  130 . In some examples, gear train  125  provides a rotation speed reduction from rotary actuator  120  and linear actuator  130  thereby increasing the precision of linear actuator  130 . In these examples, the gear ratio is between about 1.5 and 30 and, more specifically, between about 2 and 10. The gear ratio is defined as a ratio of the number of teeth on an input gear, coupled to rotary actuator  120 , to the number of teeth on an output gear, coupled to linear actuator  130 . 
     Referring generally to  FIGS. 1A and 1B , and particularly to, e.g.,  FIGS. 4A-4E , flowable-material dispenser  160  comprises cartridge housing  173  and plunger  175 . Cartridge housing  173  has first end  176  and second end  177 , opposite first end  176 . Cartridge housing  173  is configured to receive cartridge tube  302 , having interior  303 , filled with flowable material  308 . Plunger  175  is selectively translatable within cartridge tube  302  once cartridge tube  302  is received in cartridge housing  173  and plunger  175  is received within cartridge tube  302 . The preceding subject matter of this paragraph characterizes example 2 of the present disclosure, wherein example 2 also includes the subject matter according to example 1, above. 
     Cartridge housing  173  receives and encloses cartridge tube  302 . Furthermore, cartridge housing  173  supports cartridge tube  302  while flowable material  308  is dispensed from cartridge tube  302 . During dispensing, plunger  175  is positioned within interior  303  of cartridge tube  302  and hydraulically forced to translate from first end  176  to second end  177 . As plunger  175  translates from first end  176  to second end  177 , plunger  175  displaces flowable material  308  from cartridge tube  302  at second end  177  of cartridge housing  173 . The controlled rotation of rotary actuator  120  causes plunger  175  to translate within cartridge tube  302  because of the hydraulic coupling between reservoir  140  and flowable-material dispenser  160 . The precision and control of rotary actuator  120  translates into precise and controlled dispensing of flowable material  308 . 
     In one or more examples, the length of cartridge housing  173 , between first end  176  and second end  177 , corresponds to the length of cartridge tube  302 . When cartridge tube  302  is inserted into cartridge housing  173 , the leading end of cartridge tube  302  is sealed against second end-cap  172  of apparatus  100 . Second end-cap  172  is positioned at second end  177  of cartridge housing  173 . In a similar manner, the lagging end of cartridge tube  302  is sealed against end-cap  171  of apparatus  100 , positioned at first end  176  of cartridge housing  173 . 
     In one or more examples, the inside diameter of cartridge housing  173  corresponds to the outside diameter of cartridge tube  302 . As a result, cartridge tube  302  snuggly fits inside cartridge housing  173 . In these examples, the wall of cartridge housing  173  supports the wall of cartridge tube  302  when the hydraulic pressure is applied to plunger  175  and also to the walls of cartridge tube  302 , either directly by hydraulic fluid  155  or by flowable material  308 . This feature allows using cartridge tube  302  with a thin wall and/or applying high hydraulic pressures (e.g., to dispense particularly viscous materials and/or dispense at high rates). 
     Referring generally to  FIGS. 1A and 1B , and particularly to, e.g.,  FIGS. 2, 3A, 3B , and  4 A- 4 D, plunger  175  is translatable within cartridge tube  302  responsive to motion of piston  145  inside reservoir  140 . The motion of piston  145  inside reservoir  140  transfers hydraulic fluid  155  between reservoir  140  and cartridge housing  173  of flowable-material dispenser  160 . The preceding subject matter of this paragraph characterizes example 3 of the present disclosure, wherein example 3 also includes the subject matter according to example 2, above. 
     The hydraulic coupling between reservoir  140  and cartridge tube  302  enables the position of plunger  175  in cartridge tube  302  to be controlled with piston  145  inside reservoir  140 , which in turn is controlled by rotary actuator  120 . Specifically, the volume of hydraulic fluid  155  displaced from reservoir  140  (due to the motion of piston  145  inside reservoir  140 ) is the same as the volume of hydraulic fluid  155  received in cartridge tube  302  since hydraulic fluid  155  is not compressible. This volume of hydraulic fluid  155  received in cartridge tube  302  pushes plunger  175  from first end  176  and second end  177 . 
     A process of retraction of plunger  175  from cartridge tube  302  is similar. The volume of hydraulic fluid  155  received into reservoir  140  due to the motion of piston  145  inside reservoir  140  is the same as the volume of hydraulic fluid  155  transferred from cartridge tube  302 . This removal of hydraulic fluid  155  from cartridge tube  302  between plunger  175  and first end  176  creates a negative pressure in hydraulic fluid  155 , which applies a force to plunger  175  toward first end  176 . As a result of this negative pressure, plunger  175  is pushed from second end  177  to first end  176 . 
     The translation distance of plunger  175  is proportional to the volume of hydraulic fluid  155 , transferred into or from cartridge tube  302 . Specifically, the translation distance of plunger  175  is equal to the ratio of the volume of hydraulic fluid  155 , transferred into or from cartridge tube  302 , to the cross-sectional area of interior  303  of cartridge tube  302 . As described above, the volume of hydraulic fluid  155  transferred to or from cartridge tube  302  is the same as the volume of hydraulic fluid  155  transferred from or to reservoir  140 . Furthermore, the volume of hydraulic fluid  155  transferred to from cartridge tube  302  is the same as the volume of flowable material  308  dispensed by apparatus  100 , assuming that flowable material  308  and plunger  175  are not compressible. This transferred volume is controlled by rotary actuator  120  via gear train  125  and linear actuator  130 . 
     In one or more examples, plunger  175  is translatable within cartridge tube  302  while being sealed against the interior surface of cartridge tube  302 . For example, plunger  175  is formed from an elastomeric material (e.g., rubber). A portion of plunger  175  is in direct contact with hydraulic fluid  155 . In one or more examples, this portion of plunger  175  is always in direct contact with hydraulic fluid  155 . 
     Referring generally to  FIGS. 1A and 1B , and particularly to, e.g.,  FIGS. 2, 4A, 4C, 4D, 5A, and 5B , apparatus  100  further comprises end-cap  171 , movably coupled with flowable-material dispenser  160  at first end  176  of cartridge housing  173 , hydraulically coupled with reservoir  140 , and configured to selectively sealingly engage interior  303  of cartridge tube  302  when cartridge tube  302  in received within cartridge housing  173  of flowable-material dispenser  160 . The preceding subject matter of this paragraph characterizes example 4 of the present disclosure, wherein example 4 also includes the subject matter according to example 2 or 3, above. 
     When end-cap  171  seals against interior  303  of cartridge tube  302 , a combination of end-cap  171 , plunger  175 , and cartridge tube  302  defines the volume of hydraulic fluid  155  within interior  303  of cartridge tube  302 . As described above, when hydraulic fluid  155  is transferred into cartridge tube  302 , this volume increases. Specifically, hydraulic fluid  155  translates plunger  175  away from end-cap  171 . On the other hand, when hydraulic fluid  155  is transferred back in reservoir  140 , this volume decreases. During this operation, hydraulic fluid  155  is at a negative pressure and pulls plunger  175  within cartridge tube  302  toward end-cap  171 . 
     End-cap  171  is movably coupled to flowable-material dispenser  160 . In one position, shown in  FIGS. 4A, 4C, 4D, and 5B , end-cap  171  sealingly engages interior  303  of cartridge tube  302 . In this position, plunger  175  is disposed within cartridge tube  302  and is translatable within cartridge tube  302  by flowing hydraulic fluid  155  through end-cap  171 . In another position, shown in  FIG. 5A , end-cap  171  is positioned away from first end  176  of cartridge housing  173 . In this position, cartridge housing  173  is accessible to remove or install cartridge tube  302  inside cartridge housing  173 . 
     The seal between end-cap  171  and interior  303  of cartridge tube  302  ensures that hydraulic fluid  155  stays within interior  303  of cartridge tube  302  and does not leak from cartridge tube  302  into cartridge housing  173 . The seal is maintained while end-cap  171  is positioned at first end  176  of cartridge housing  173 . The seal is broken when end-cap  171  is moved away from first end  176  of cartridge housing  173  as shown, for example, in  FIG. 5A . 
     Referring generally to  FIGS. 1A and 1B , and particularly to, e.g.,  FIGS. 4A, 4C, and 4D , end-cap  171  comprises first gasket  421 , configured to selectively seal against interior  303  of cartridge tube  302  when cartridge tube  302  is received within cartridge housing  173 . The preceding subject matter of this paragraph characterizes example 5 of the present disclosure, wherein example 5 also includes the subject matter according to example 4, above. 
     First gasket  421  is sealed against interior  303  of cartridge tube  302  to ensure that hydraulic fluid  155  stays within cartridge tube  302  and does not leak out of cartridge tube  302 , e.g., into cartridge housing  173 . As hydraulic fluid  155  is supplied into cartridge tube  302 , plunger  175  translates from first end  176  to second end  177  of cartridge housing  173  and displaces flowable material  308  from cartridge tube  302 . Preventing loss of hydraulic fluid  155  from cartridge tube  302  ensures dispensing precision. 
     Referring to  FIGS. 4C and 4D , in one or more examples, first gasket  421  is an O-ring. In the same or other examples, first gasket  421  is positioned in a channel of end-cap  171 . The outer diameter of first gasket  421  is greater than the inner diameter of cartridge tube  302 , which provides interference fit and sealing. In one or more examples, first gasket  421  is formed from art elastomeric material (e.g., rubber). 
     Referring generally to  FIGS. 1A and 1B , and particularly to, e.g.,  FIGS. 4C and 4D , flowable-material dispenser  160  further comprises second gasket  422 , configured to seal end-cap  171  against plunger  175  when a sufficient amount of hydraulic fluid  155  is transferred from cartridge housing  173  to reservoir  140  to cause plunger  175  to abut end-cap  171  and an additional amount of hydraulic fluid  155  is subsequently transferred from cartridge housing  173  to reservoir  140 . The preceding subject matter of this paragraph characterizes example 6 of the present disclosure, wherein example 6 also includes the subject matter according to example 5, above. 
     Second gasket  422  forms a seal between plunger  175  and end-cap  171 , which in turn allows creating a negative pressure (relative to the atmosphere) in hydraulic fluid  155 . This negative pressure forces plunger  175  against end-cap  171  allowing, for example, removal of plunger  175  from cartridge tube  302 . Furthermore, this negative pressure supports plunger  175  on end-cap  171  after plunger  175  is removed from cartridge tube  302 . 
     In one or more examples, second gasket  422  is attached to end-cap  171 , as shown in  FIG. 4D . For example, second gasket  422  is glued to a surface of end-cap  171  or positioned in a groove formed in end-cap  171 . Second gasket  422  protrudes from the surface of end-cap  171  and, in one or more examples, directly contacts plunger  175  when plunger  175  is supported by end-cap  171 . Alternatively, second gasket  422  is a part of or is attached to plunger  175 . In one or more examples, second gasket  422 , shown in  FIG. 4D , is formed from an elastomeric material (e.g., rubber). 
     Referring generally to  FIGS. 1A and 1B , and particularly to, e.g.,  FIGS. 4C and 4D , end-cap  171  further comprises annular boss  427 . Plunger  175  comprises annular recess  429 . Annular boss  427  and annular recess  429  have complementary shapes. The preceding subject matter of this paragraph characterizes example 7 of the present disclosure, wherein example 7 also includes the subject matter according to example 5 or 6, above. 
     Inserting annular boss  427  of end-cap  171  into annular recess  429  of plunger  175  provides interference fit and/or frictional fit between end-cap  171  and plunger  175 . This fit provides support to plunger  175  relative to end-cap, in addition to or instead of support provided by the negative pressure of hydraulic fluid  155 , as described above. Furthermore, a combination of annular boss  427  of end-cap  171  and annular recess  429  of plunger  175  is used to control orientation of plunger  175  relative to end-cap  171  when plunger  175  is extracted from cartridge tube  302 . This orientation control allows removal of plunger  175  from end-cap  171  and reinstallation of plunger  175  onto end-cap  171 , e.g., during initial assembly of apparatus  100 , cleaning and maintenance of apparatus  100 , and other like tasks. 
     In one or more examples, annular boss  427  comprises a fillet or a chamfer for directing and/or centering annular recess  429  relative to annular boss  427 . Likewise, in one or more examples, annular recess  429  comprises a fillet or a chamfer for locating annular boss  427  relative to annular recess  429  and for guiding the rest of annular boss  427  into annular recess  429 . 
     Referring generally to  FIGS. 1A and 1B , and particularly to, e.g.,  FIGS. 4C and 4D , apparatus  100  further comprises second gasket  422  between annular boss  427  of end-cap  171  and annular recess  429  of plunger  175 . The preceding subject matter of this paragraph characterizes example 8 of the present disclosure, wherein example 8 also includes the subject matter according to example 7, above. 
     Second gasket  422  forms a seal between plunger  175  and end-cap  171 , which in turn allows creating a negative pressure (relative to the atmosphere) in hydraulic fluid  155 . This negative pressure creates a force, applied to plunger  175  against end-cap  171 , which in turn allows removing plunger  175  from cartridge tube  302 . The negative pressure is also used for supporting plunger  175  on end-cap  171 , after plunger  175  is removed from cartridge tube  302 . Annular boss  427  of end-cap  171  and annular recess  429  of plunger  175  have complementary shapes such that their mating surfaces contact each other when annular boss  427  is inserted into annular recess  429 . Second gasket  422  establishes a seal between these mating surfaces. 
     In one or more examples, shown in  FIG. 4D , second gasket  422  is attached to end-cap  171 . For example, second gasket  422  is glued to a surface of end-cap  171  or is positioned in a groove formed in end-cap  171 . Second gasket  422  protrudes from the surface of end-cap  171  and, in one or more examples, directly contacts plunger  175  when plunger  175  is supported by end-cap  171 . In one or more examples, second gasket  422 , shown in  FIG. 4D , is formed from an elastomenic material (e.g., rubber). 
     Referring generally to  FIGS. 1A and 1B , and particularly to, e.g.,  FIGS. 4C, 4D, 5A and 5B , apparatus  100  further comprises over-center mechanism  179 , movably coupling end-cap  171  with cartridge housing  173  of flowable-material dispenser  160  and configured to selectively retain end-cap  171  relative to cartridge housing  173  such that end-cap  171  sealingly engages interior  303  of cartridge tube  302 , received within cartridge housing  173 , and to selectively remove end-cap  171  from cartridge tube  302 , received within cartridge housing  173 . The preceding subject matter of this paragraph characterizes example 9 of the present disclosure, wherein example 9 also includes the subject matter according to any one of examples 4 to 8, above. 
     Over-center mechanism  179  is attached to end-cap  171  and is used to move end-cap  171  relative to cartridge housing  173  between at least two positions. In one position, end-cap  171  is positioned at first end  176  of cartridge housing  173  and sealingly engages interior  303  of cartridge tube  302  as shown, for example, in  FIG. 4C . In the other position, end-cap  171  is positioned away from cartridge housing  173  as shown, for example, in  FIG. 5B . In this other position, first end  176  of cartridge housing  173  is accessible, which allows removing, replacing, and/or installing cartridge tube  302 . 
     In some examples, over-center mechanism  179  is attached to and supported on cartridge housing  173 . End-cap  171  is movable by over-center mechanism  179  relative to cartridge housing  173  as shown, for example, in  FIGS. 5A and 5B . In some examples, over-center mechanism  179  comprises multiple arms pivotably coupled to each other. The number and the length of these arms establish the trajectory of end-cap  171  when end-cap  171  is moved by over-center mechanism  179  between at least the two positions of end-cap  171 . In one or more examples, the movement of end-cap  171  relative to cartridge housing  173  is substantially along the center axis of cartridge housing  173  when end-cap  171  approaches first end  176  of cartridge housing  173 . As described above, end-cap  171  supports plunger  175 , and plunger  175  is inserted into cartridge tube  302  when end-cap  171  approaches first end  176  of cartridge housing  173 . 
     Referring generally to  FIGS. 1A and 1B , and particularly to, e.g.,  FIGS. 5A and 5B , apparatus  100  further comprises first double-acting pneumatic cylinder  510 , operatively coupling over-center mechanism  179  with cartridge housing  173  of flowable-material dispenser  160 . The preceding subject matter of this paragraph characterizes example 10 of the present disclosure, wherein example 10 also includes the subject matter according to example 9, above. 
     First double-acting pneumatic cylinder  510  is connected to and is used to move one end of over-center mechanism  179 . The other end of over-center mechanism  179  is coupled to end-cap  171 . This movement of first double-acting pneumatic cylinder  510  causes the movement of end-cap  171  relative to cartridge housing  173  between at least two positions, described above. First double-acting pneumatic cylinder  510  enables automation of this operation. 
     The force applied by first double-acting pneumatic cylinder  510  to over-center mechanism  179  in one direction ensures that plunger  175  and a portion of end-cap  171  is inserted into cartridge tube  302  as shown, for example, in  FIG. 4C . The force applied by first double-acting pneumatic cylinder  510  to over-center mechanism  179  in the opposite direction ensures that plunger  175  is extracted from interior  303  of cartridge tube  302 . The travel length of first double-acting pneumatic cylinder  510  is such that end-cap  171  is positioned away from cartridge housing  173  as shown, for example, in  FIG. 5B . In this position, end-cap  171  and plunger  175  do not interfere with access to first end  176  of cartridge housing  173 , which allows removing, replacing, and/or installing cartridge tube  302 . 
     Referring generally to  FIGS. 1A and 1B , and particularly to, e.g.,  FIG. 4E , flowable-material dispenser  160  further comprises second end-cap  172 , located opposite end-cap  171  at second end  177  of cartridge housing  173  of flowable-material dispenser  160  and configured to seal against cartridge tube  302  when cartridge tube  302  is within cartridge housing  173  and end-cap  171  is retained relative to cartridge housing  173  such that end-cap  171  sealingly engages interior  303  of cartridge tube  302 . The preceding subject matter of this paragraph characterizes example 11 of the present disclosure, wherein example 11 also includes the subject matter according to any one of examples 4 to 10, above. 
     The seal between second end-cap  172  and cartridge tube  302  ensures that flowable material  308  is directed from cartridge tube  302  through second end-cap  172  and toward the dispensing tip of flowable-material dispenser  160 . Furthermore, this seal ensures that flowable material  308  does not flow into the space between cartridge tube  302  and cartridge housing  173 , thereby preventing contamination of cartridge housing  173 . The seal is established when cartridge tube  302  is inserted into cartridge housing  173  and maintained until cartridge tube  302  is removed from cartridge housing  173 . 
     In some examples, as shown in  FIG. 4E , second end-cap  172  comprises gasket  163  for sealing against cartridge tube  302 . When cartridge tube  302  is inserted into cartridge housing  173 , the leading end of cartridge tube  302  is pressed against gasket  163 , establishing the seal. Gasket  163  is formed from an elastomeric material (e.g., rubber). As shown in  FIG. 4E , a sealing portion of second end-cap  172  overlaps with cartridge tube  302  or, more specifically, with the leading end of cartridge tube  302 , for additional sealing and/or maintaining orientation of cartridge tube  302 . For example, this sealing portion of second end-cap  172  protrudes into cartridge tube  302 . 
     Referring generally to  FIGS. 1A and 1B , and particularly to, e.g.,  FIG. 4E , flowable-material dispenser  160  further comprises cartridge-ejection inlet  530 , pneumatically coupled with second end-cap  172  to selectively supply compressed fluid inside cartridge housing  173  of flowable-material dispenser  160  for ejecting cartridge tube  302  from cartridge housing  173  when end-cap  171  is removed from cartridge tube  302 , received within cartridge housing  173 . The preceding subject matter of this paragraph characterizes example 12 of the present disclosure, wherein example 12 also includes the subject matter according to example 11, above. 
     Cartridge-ejection inlet  530  is used to break the seal between second end-cap  172  and cartridge tube  302  and remove cartridge tube  302  from cartridge housing  173 . In one or more examples, access to cartridge tube  302  from first end  176  of cartridge housing  173  is limited. For instance,  FIGS. 4C and 4D  illustrate only a small portion of cartridge tube  302  protruding from cartridge housing  173  at first end  176  of cartridge housing  173 . Specifically, the flow of the compressed fluid (e.g., compressed air) through cartridge-ejection inlet  530  into cartridge housing  173 , at a location close to second end-cap  172 , increases the pressure inside cartridge housing  173  at second end  177 . This pressure forces plunger  175  away from second end-cap  172 . The gap between cartridge housing  173  and cartridge tube  302  is minimal (e.g., less than 1 millimeter) to pressurize an area inside cartridge housing  173 , at least near second end-cap  172 . 
     In one or more examples, the outer diameter of cartridge tube  302  is substantially the same as the inner diameter of cartridge housing  173  (e.g., within 10% or within 5%). As such, the compressed fluid cannot easily escape between cartridge tube  302  and cartridge housing  173  when compressed gas is supplied into cartridge housing  173  at a location close to second end-cap  172 . In one or more examples, cartridge-ejection inlet  530  comprises a valve and a coupling to a source of the compressed fluid, such as compressed air. More specifically, the operation of cartridge-ejection inlet  530  is synchronized with operation of other components of apparatus  100 , such as over-center mechanism  179 . For example, cartridge-ejection inlet  530  supplies the compressed fluid inside cartridge housing  173  only after over-center mechanism  179  moves end-cap  171  away from second end  177  of cartridge housing  173 , thereby allowing cartridge tube  302  to be removed from cartridge housing  173 . 
     Referring generally to  FIGS. 1A and 1B , and particularly to, e.g.,  FIG. 4E , flowable-material dispenser  160  further comprises vent  162 , located at second end  177  of cartridge housing  173 . Vent  162  is configured to admit atmosphere into cartridge tube  302 , received inside cartridge housing  173 , as plunger  175  is retracted within cartridge tube  302  from second end  177  of cartridge housing  173  toward first end  176  of cartridge housing  173 . The preceding subject matter of this paragraph characterizes example 13 of the present disclosure, wherein example 13 also includes the subject matter according to example 11 or 12, above. 
     When plunger  175  is moved within cartridge tube  302  from first end  176  to second end  177  of cartridge housing  173 , flowable material  308  is dispensed from cartridge tube  302 . Vent  162  is closed during this operation to prevent flowable material  308  from escaping through vent  162 . On the other hand, when plunger  175  is retracted within cartridge tube  302  from second end  177  to first end  176 , the volume inside cartridge tube  302 , previously occupied by flowable material  308 , needs to be backfilled. If the volume is not backfilled, the excessive negative pressure within cartridge tube  302 , between plunger  175  and the dispensing nozzle, will prevent plunger  175  from being moved within cartridge tube  302 . Furthermore, this negative pressure can pull a portion of flowable material  308 , remaining in apparatus  100  (e.g., in the dispensing nozzle), back into cartridge tube  302 . During this plunger extraction operation, vent  162  is open and admits the atmosphere into cartridge tube  302 . Cartridge tube  302  is effectively backfilled, which allows effortless movement of plunger  175  within cartridge tube  302  from second end  177  toward first end  176  of cartridge housing  173 . 
     In one or more examples, vent  162  comprises a valve, one end of which is in fluid communication with interior  303  of cartridge tube  302  (when cartridge tube  302  is positioned inside cartridge housing  173 ). The other end of this valve is open to the atmosphere. In one or more examples, the operation of vent  162  is synchronized with the operation of other components of apparatus  100 , such as rotary actuator  120 . Specifically, vent  162  allows the atmosphere into cartridge tube  302  when rotary actuator  120  is turning in second rotational direction  122 , resulting in hydraulic fluid  155  being transferred from flowable-material dispenser  160  to reservoir  140 . 
     Referring generally to  FIGS. 1A and 1B , and particularly to, e.g.,  FIG. 4E , vent  162  is further configured to admit atmosphere into cartridge tube  302 , received inside cartridge housing  173 , as plunger  175  is extracted from cartridge tube  302  by end-cap  171 . The preceding subject matter of this paragraph characterizes example 14 of the present disclosure, wherein example 14 also includes the subject matter according to example 13, above. 
     When plunger  175  is retracted within cartridge tube  302  from second end  177  to first end  176  and later extracted from cartridge tube  302 , the volume inside cartridge tube  302 , previously occupied by flowable material  308 , needs to be backfilled to avoid excessive negative pressure within cartridge tube  302 . If the volume is not backfilled, the excessive negative pressure will prevent plunger  175  from being extracted from cartridge tube  302 . 
     In one or more examples, the backfill continues as plunger  175  is completely; extracted from cartridge tube  302  by end-cap  171 . Overall, the force acting on plunger  175  and created by the negative pressure of hydraulic fluid  155 , should be greater than the friction force between plunger  175  and cartridge tube  302  and should also exceed any negative pressure within cartridge tube  302  between plunger  175  and the dispensing nozzle. Backfilling through vent  162  allows reducing this negative pressure within cartridge tube  302  between plunger  175  and the dispensing nozzle. 
     In one or more examples, the operation of vent  162  is synchronized with operation of other components of apparatus  100 , such as over-center mechanism  179  or, more specifically, first double-acting pneumatic cylinder  510 , operatively coupled to over-center mechanism  179 . Specifically, vent  162  allows the atmosphere into cartridge tube  302  when over-center mechanism  179  moves end-cap  171  away from first end  176  of cartridge housing  173 , thereby extracting plunger  175  from cartridge tube  302 . It should be noted that plunger  175  is supported on end-cap  171  during this operation by the negative pressure of hydraulic fluid  155 . 
     Referring generally to  FIGS. 1A and 1B , and particularly to, e.g.,  FIGS. 4C and 4D , piston  145  comprises third gasket  423 , configured to seal against cartridge tube  302 . The preceding subject matter of this paragraph characterizes example 15 of the present disclosure, wherein example 15 also includes the subject matter according to any one of examples 2 to 14, above. 
     Sealing third gasket  423  of piston  145  against cartridge tube  302  allows pressurizing hydraulic fluid  155 , particularly in a volume between piston  145  and end-cap  171 , as shown in  FIG. 4D . This seal prevents hydraulic fluid  155  from leaking past piston  145  and from contacting flowable material  308  inside cartridge tube  302 . At the same time, the pressure is needed to advance piston  145  from first end  176  to second end  177  of cartridge housing  173  and displace flowable material  308  from cartridge tube  302 . Furthermore, this seal prevents air being introduced into the pool of hydraulic fluid  155 , which is positioned between piston  145  and end-cap  171  when piston  145  is extracted from cartridge tube  302  (e.g., pulled by the negative pressure of hydraulic fluid  155  from second end  177  to first end  176  of cartridge housing  173 ). Third gasket  423  allows piston  145  to move within cartridge tube  302  while maintaining the seal against cartridge tube  302 . 
     In one or more examples, third gasket  423  is formed from an elastomeric material (e.g., rubber). In the same or other examples, third gasket  423  is positioned in an annular groove of piston  145  and protrudes past the surface of piston  145 , adjacent to the annular groove, to form interference fit with interior  303  of cartridge tube  302 . 
     Referring generally to  FIGS. 1A and 1B , and particularly to, e.g.,  FIGS. 4B and 4C , cartridge tube  302  comprises cartridge plunger  304 , comprising rear surface  305  and front surface  301 , opposite rear surface  305 . Plunger  175  comprises thrust surface  178 , complementary in shape to rear surface  305  of cartridge plunger  304 . The preceding subject matter of this paragraph characterizes example 16 of the present disclosure, wherein example 16 also includes the subject matter according to any one of examples 2 to 15, above. 
     Cartridge plunger  304  seals flowable material  308  within interior  303  of cartridge tube  302  prior to installation of cartridge tube  302  into cartridge housing  173 . Once cartridge tube  302  is installed in cartridge housing  173  and plunger  175  is inserted into cartridge tube  302 , cartridge plunger  304  separates plunger  175  from flowable material  308 , thereby preventing any direct contact between plunger  175  and flowable material  308  and contamination of plunger  175 . Cartridge plunger  304  is advanced by plunger  175  from one end of cartridge tube  302 , proximate to first end  176  of cartridge housing  173 , to another end of cartridge tube  302 , proximate to second end  177  of cartridge housing  173 . During this operation, thrust surface  178  of plunger  175  is pressed against rear surface  305  of cartridge plunger  304 . The complementary shapes of rear surface  305  of cartridge plunger  304  and thrust surface  178  of plunger  175  ensure that the original or working shape of cartridge plunger  304  is preserved and that cartridge plunger  304  continues to separate plunger  175  from flowable material  308 . 
     In one or more examples, cartridge plunger  304  is flexible or, more specifically, deformable. In these examples, rear surface  305  of cartridge plunger  304  becomes complementary in shape to thrust surface  178  of plunger  175  when rear surface  305  of cartridge plunger  304  is contacted by thrust surface  178  of plunger  175  and while plunger  175  advances cartridge plunger  304  within cartridge tube  302 . In one or more examples, both rear surface  305  of cartridge plunger  304  and thrust surface  178  of plunger  175  have a dome shape. 
     Referring generally to  FIGS. 1A and 1B , and particularly to, e.g.,  FIGS. 6A and 6B , flowable-material dispenser  160  further comprises dispenser valve  600 , located at second end  177  of cartridge housing  173 , and second double-acting pneumatic cylinder  520 , configured to selectively open or close dispenser valve  600 . The preceding subject matter of this paragraph characterizes example 17 of the present disclosure, wherein example 17 also includes the subject matter according to any one of examples 2 to 16, above. 
     Dispenser valve  600  controls the flow of flowable material  308  from apparatus  100 . This control is used in addition to control provided by rotary actuator  120 . Furthermore, when dispenser valve  600  is closed, flowable material  308 , which remains in flowable-material dispenser  160 , is isolated from the environment (e.g., to prevent curing of the remaining portion of flowable material  308  that is still inside flowable-material dispenser  160 ). When dispenser valve  600  is open, flowable material  308  passes through dispenser valve  600  and is dispensed from apparatus  100 . In one or more examples, a combination of dispenser valve  600  and rotary actuator  120  is used to control the pressure of hydraulic fluid  155 , which in turn controls the flow rate of flowable material  308 . 
     In one or more examples, dispenser valve  600  comprises stem  612 , protruding through pass-through  614  and supporting plug  610 , as shown, for instance, in  FIGS. 6A and 6B . When plug  610  is pressed against pass-through  614  as shown, for example, in  FIG. 6A , dispenser valve  600  is closed and flowable material  308  cannot pass through dispenser valve  600 . On the other hand, when plug  610  is positioned away from pass-through  614  as shown, for example, in  FIG. 6B , dispenser valve  600  is open and flowable material  308  is able to pass through dispenser valve  600 . In one or more examples, dispenser valve  600  has one or more partially open positions. 
     Referring generally to  FIGS. 1A and 1B , and particularly to, e.g.,  FIGS. 3A and 3B , linear actuator  130  comprises screw  135 , ball nut  134 , and plurality of balls  133 , threadably coupling screw  135  and ball nut  134 . Screw  135  has central axis  131  and is coupled to piston  145 . Ball nut  134  is coupled to one of gears in gear train  125 . The preceding subject matter of this paragraph characterizes example 18 of the present disclosure, wherein example 18 also includes the subject matter according to any one of examples 1 to 17, above. 
     A combination of screw  135 , ball nut  134 , and plurality of balls  133  in linear actuator  130  translates the rotation of ball nut  134 , which is driven by gear train  125 , into the linear motion of screw  135 , which is coupled to piston  145 . As such, the precise rotation of rotary actuator  120 , through gear train  125  to ball nut  134 , is translated in the precise linear motion of screw  135  and, more specifically, of piston  145 . The linear motion of piston  145  within reservoir  140  results in the precise transfer of hydraulic fluid  155  between reservoir  140  and flowable-material dispenser  160 , which in turn results in the precise dispensing of flowable material  308 . 
     In one or more examples, screw  135  is a threaded shaft, which provides a helical raceway for a plurality of balls  133 . Linear actuator  130  is able to apply or withstand high thrust loads (e.g., for dispensing flowable materials  308  that have high viscosities) with minimum internal friction. Close tolerances screw  135 , ball nut  134 , and plurality of balls  133  provide high precision with minimal friction. 
     Referring generally to  FIGS. 1A and 1B , and particularly to, e.g.,  FIGS. 3B-3D , linear actuator  130  comprises housing  138  and anti-rotation mechanism  139 , coupled to housing  138  and slidably coupled to screw  135 . Anti-rotation mechanism prevents screw  135  from rotating around central axis  131  of screw  135  relative to housing  138 . Housing is stationary relative to rotary actuator  120 . The preceding subject matter of this paragraph characterizes example 19 of the present disclosure, wherein example 19 also includes the subject matter according to example 18, above. 
     Anti-rotation mechanism  139  ensures that screw  135  does not rotate relative to housing  138  around central axis  131  of screw  135 . As such, anti-rotation mechanism  139  ensures the exact relationship between the rotation of ball nut  134  and the linear motion of screw  135 . This relationship is provided by the thread pitch of ball nut  134  and screw  135 , which is fixed, and the rotation of ball nut  134  relative to screw  135  around central axis  131  of screw  135 . Thus, by preventing screw  135  from rotating, the rotation of ball nut  134  provides the exclusive control of this linear motion, thereby ensuring the precise dispensing of flowable material  308 . 
     The thread pitch of ball nut  134  and screw  135  is, for example, between 0.1 millimeters and 10 millimeters or, more specifically, between 0.5 millimeters and 3 millimeters. For example, a thread pitch of 1 millimeter results in a 1 millimeter linear motion of screw  135  for each rotation of ball nut  134  relative to screw  135 . Since ball nut  134  does not rotate around central axis  131 , the rotation of ball nut  134  controls this linear motion. 
     Referring generally to  FIGS. 1A and 1B , and particularly to, e.g.,  FIGS. 3B and 3C , screw  135  comprises slot  192 . Anti-rotation mechanism  139  comprises protrusion  191 , extending into slot  192  of screw  135 . Slot  192  extends along central axis  131  of screw  135 . The preceding subject matter of this paragraph characterizes example 20 of the present disclosure, wherein example 20 also includes the subject matter according to example 19, above. 
     Protrusion  191  is coupled to housing  138  and extends into slot  192  of screw  135 . As such, screw  135  is not able to rotate around central axis  131  relative to housing  138 . Preventing the rotation of screw  135 , provided by protrusion  191  and slot  192 , ensures the exclusive control of the linear translation of screw  135  by the rotation of ball nut  134 . Slot  192 , extending along central axis  131  of screw  135 , enables screw  135  to linearly move relative to protrusion  191  and relative to housing  138 , so that piston  145  is linearly advanced inside reservoir  140 . 
     In some examples, protrusion  191  is a set screw, threaded into housing  138 . In these examples, protrusion  191  is adjustable relative to screw  135  (e.g., to extend into slot  192  during operation of apparatus  100  or to retract from slot  192  during disassembly of apparatus  100 ). In one or more examples, slot  192  has two parallel walls, extending along central axis  131 , as shown, for example, in  FIG. 3C . 
     Referring generally to  FIGS. 1A and 1B , and particularly to, e.g.,  FIGS. 3B and 3D , screw  135  comprises first surface  193 . Anti-rotation mechanism  139  comprises second surface  194 , slidably contacting first surface  193  of screw  135  at at least two points of first surface  193  that lie on opposite sides of orthogonal projection  132  of central axis  131  onto first surface  193 . The preceding subject matter of this paragraph characterizes example 21 of the present disclosure, wherein example 21 also includes the subject matter according to example 19, above. 
     The slidable contact between second surface  194  and first surface  193  enable screw  135  to linearly translate relative to housing  138  along central axis  131 . At the same time, since contact exists between second surface  194  and first surface  193  at at least two points that lie on opposite sides of orthogonal projection  132  of central axis  131  onto first surface  193 , rotation of screw  135  relative to second surface  194  and relative to housing  138  is prevented, ensuring exclusive control of the linear translation of screw  135  by the rotation of ball nut  134 . 
     In one or more examples, first surface  193  and second surface  194  are conformal surfaces or, more specifically, planar surfaces as shown, for example, in  FIG. 3D . However, other types of surfaces that contact each other at at least two points that lie on opposite sides of orthogonal projection  132  of central axis  131  are also within the scope of the present disclosure. 
     Referring generally to  FIGS. 1A and 1B , and particularly to, e.g.,  FIGS. 3E and 3F  piston  145  and reservoir  140  have complementary, non-circular cross-sections. The preceding subject matter of this paragraph characterizes example 22 of the present disclosure, wherein example 22 also includes the subject matter according to any one of examples 1 to 18, above. 
     The non-circular aspect of the complementary non-circular cross-sections of piston  145  and reservoir  140  prevents rotation of piston  145  around central axis  131  relative to reservoir  140 . Piston  145  is also coupled to screw  135 , which, as a result of this coupling, also does not rotate around central axis  131  relative to reservoir  140  or, more specifically, relative to housing  138 . Preventing the rotation of screw  135  ensures the exclusive control of the linear translation of screw  135  by the rotation of ball nut  134 . However, piston  145  is allowed to linearly translate relative to reservoir  140  along central axis  131 . Furthermore, the complementary aspect of the non-circular cross-sections establishes a seal between piston  145  and reservoir  140  such that hydraulic fluid  155  does not leak past piston  145  during operation of apparatus  100 . 
     The complementary non-circular cross-sections of piston  145  and reservoir  140  have any shape that is different from that of a circle. Any such shape will prevent rotation of piston  145  relative to reservoir  140 .  FIG. 3E  illustrates an example of an oval shape, while  FIG. 3F  illustrates an example of a rectangular shape. In one or more examples, at least one gasket is positioned at the interface of piston  145  and reservoir  140 . 
     Referring generally to  FIGS. 1A and 1B , and particularly to, e.g.,  FIG. 3E , the complementary non-circular cross-sections are oval. The preceding subject matter of this paragraph characterizes example 23 of the present disclosure, wherein example 23 also includes the subject matter according to example 22, above. 
     The oval shapes of the complementary non-circular cross-sections of piston  145  and reservoir  140  prevent rotation of piston  145  around central axis  131  relative to reservoir  140 . Piston  145  is also coupled to screw  135 , which, as a result of this coupling, also does not rotate around central axis  131  relative to reservoir  140  or, more specifically, relative to housing  138 . Preventing the rotation of screw  135  ensures the exclusive control of the linear translation of screw  135  by the rotation of ball nut  134 . However, piston  145  is allowed to linearly translate relative to reservoir  140  along central axis  131 . Furthermore, the complementary aspect of the oval cross-sections establishes a seal between piston  145  and reservoir  140  such that hydraulic fluid  155  does not leak past piston  145  during operation of apparatus  100 . 
     The oval shape, or any other shape without sharp corners, allows using a continuous seal, thereby sealing the interface between piston  145  and reservoir  140 . Furthermore, fabrication of pistons and reservoirs having oval shapes is generally simpler than that of parts having shapes with sharp corners. 
     Referring generally to  FIGS. 1A and 1B  and particularly to, e.g.,  FIG. 3F , the complementary non-circular cross-sections are rectangular. The preceding subject matter of this paragraph characterizes example 24 of the present disclosure, wherein example 24 also includes the subject matter according to example 22, above. 
     The rectangular shape of complementary non-circular cross-sections of piston  145  and reservoir  140  prevents rotation of piston  145  around central axis  131  relative to reservoir  140 . Piston  145  is also coupled to screw  135 , which, as a result of this coupling, also does not rotate around central axis  131  relative to reservoir  140  or, more specifically, relative to housing  138 . Preventing the rotation of screw  135  ensures the exclusive control of the linear translation of screw  135  by the rotation of ball nut  134 . However, piston  145  is allowed to linearly translate relative to reservoir  140  along central axis  131 . Furthermore, the complementary aspect of the rectangular cross-sections establishes a seal between piston  145  and reservoir  140  such that hydraulic fluid  155  does not leak past piston  145  during operation of apparatus  100 . 
     The rectangular shape, or any other shape with sharp corners, is able to withstand large torques applied to piston  145 , e.g., when linear actuator  130  experiences friction or when piston  145  reaches an end point and further motion is not possible. For example, rotary actuator  120  is automatically shut down when experiencing a torque spike (e.g., when piston  145  reaches the end of its travel). However, other components of apparatus  100  should be able to withstand this torque as well. 
     Referring generally to  FIGS. 1A and 1B , and particularly to, e.g.,  FIG. 2 , apparatus  100  further comprises conduit  150 , hydraulically coupling flowable-material dispenser  160  with reservoir  140 . The preceding subject matter of this paragraph characterizes example 25 of the present disclosure, wherein example 25 also includes the subject matter according to any one of examples 1 to 24, above. 
     Conduit  150  allows separation and different orientations of flowable-material dispenser  160  and reservoir  140  relative to each other. As a result, apparatus  100  is more compact than it would have been if, for instance, flowable-material dispenser  160  were directly coupled to reservoir  140 . For example,  FIG. 2  illustrates flowable-material dispenser  160  and reservoir  140  positioned along different axes. 
     In one or more examples, conduit  150  is flexible, which allows movement of flowable-material dispenser  160  relative to reservoir  140 . For example, reservoir  140  is a part of stationary components of apparatus  100 , while flowable-material dispenser  160  is a movable component. 
     Referring generally to  FIGS. 7A and 7B  and particularly to, e.g.,  FIGS. 3A-3B, 4A-4D, 5A, 5B , method  700  for dispensing flowable material  308  using apparatus  100  is disclosed. Apparatus  100  comprises rotary actuator  120 , reservoir  140 , containing hydraulic fluid  155 , and piston  145 , movable inside reservoir  140 . Apparatus  100  also comprises linear actuator  130 , coupled to piston  145 , and gear train  125 , coupling rotary actuator  120  with linear actuator  130 . Apparatus  100  additionally comprises flowable-material dispenser  160 , comprising cartridge housing  173  and plunger  175  and hydraulically coupled with reservoir  140 . Apparatus  100  further comprises end-cap  171 , movably coupled with flow/able-material dispenser  160 , and over-center mechanism  179 , movably coupling end-cap  171  with cartridge housing  173  of flowable-material dispenser  160 . Method  700  comprises (block  710 ) holding hydraulic fluid  155  in reservoir  140  at a negative pressure, sufficient to generate a vacuum between end-cap  171  and plunger  175 , (block  720 ) inserting cartridge tube  302 , having interior  303 , into cartridge housing  173 , wherein flowable material  308  is inside cartridge tube  302 , (block  730 ) locking over-center mechanism  179  relative to cartridge housing  173  so that a hermetic seal is created between plunger  175  and interior  303  of cartridge tube  302  and between end-cap  171  and interior  303  of cartridge tube  302 , and (block  740 ) turning rotary actuator  120  in rotational direction  121  so that linear actuator  130  advances piston  145  within reservoir  140  to transfer at least a portion of hydraulic fluid  155  from reservoir  140  to flowable-material dispenser  160  through end-cap  171  and into interior  303  of cartridge tube  302 , causing plunger  175  to advance within cartridge tube  302  in forward plunger direction  181 , away from end-cap  171 . The preceding subject matter of this paragraph characterizes example 26 of the present disclosure. 
     When hydraulic fluid  155  is held at a negative pressure in reservoir  140 , this negative pressure is also present in all other areas of apparatus  100  occupied by hydraulic fluid  155 . As a result, plunger  175 , which contacts hydraulic fluid  155 , is forced by hydraulic fluid  155  toward and against end-cap  171 . This force supports plunger  175  on end-cap  171  and allows positioning plunger  175  away front cartridge housing  173  when end-cap  171  is moved away from cartridge housing  173 . This position of plunger  175  and end-cap  171 , away from cartridge housing  173 , provides access to cartridge housing  173  allowing to insert cartridge tube  302  into cartridge housing  173  (block  720 ). 
     Referring to  FIGS. 5A and 5B , one end of over-center mechanism  179  is attached to end-cap  171 . When over-center mechanism  179  is locked relative to cartridge housing  173  as shown in  FIG. 5B , plunger  175  is pressed by end-cap  171  into interior  303  and is hermetically sealed against interior  303  as shown in  FIG. 4C . The hermetic seal prevents flowable material  308  from flowing past plunger  175 . Furthermore, the hermetic seal prevents hydraulic fluid  155  from flowing past plunger  175  and reaching flowable material  308 . However, the seal allows plunger  175  to advance within cartridge tube  302 . 
     The other hermetic seal is formed between end-cap  171  and interior  303  of cartridge tube  302 . This other seal keeps hydraulic fluid  155  within interior  303  when hydraulic fluid  155  is transferred into interior  303  and maintained at a positive pressure or at a negative pressure (e.g., to advance plunger  175  within cartridge tube  302 ). This seal is maintained while end-cap  171  is positioned at first end  176  of cartridge housing  173 . 
     When rotary actuator  120  is turned in rotational direction  121 , linear actuator  130  advances piston  145  within reservoir  140 , as schematically shown in  FIG. 3B . The rotational speed and the degree of rotation of rotary actuator  120  are precisely controlled. This control translates into the precise linear motion of piston  145 . As piston  145  moves within reservoir  140 , at least a portion of hydraulic fluid  155  is transferred from reservoir  140  to flowable-material dispenser  160 . Specifically, hydraulic fluid  155  flows through end-cap  171  into interior  303  of cartridge tube  302 . This addition of hydraulic fluid  155  causes plunger  175  to advance within cartridge tube  302  in forward plunger direction  181  and away from end-cap  171 . As a result, flowable material  308  is displaced by plunger  175  out of cartridge tube  302 . The precision of rotary actuator  120  results in flowable material  308  being dispensed in a precisely controlled manner. 
     Some examples of hydraulic fluid  155  include mineral oils, glycols (e.g., propylene glycol), esters, organophosphate esters, polyalphaolefins, and silicone oils. Hydraulic fluid  155  is non-compressible. As a result, the volume of hydraulic fluid  155  displaced from reservoir  140  is the same as the volume of hydraulic fluid  155  received in flowable-material dispenser  160 . 
     The negative pressure of hydraulic fluid  155  is generated in reservoir  140  by advancing piston  145  inside reservoir  140  away from the hydraulic fluid outlet (e.g., a coupling to conduit  150 ). The negative pressure of hydraulic fluid  155  is determined by the contact area between piston  145  and hydraulic fluid  155  and by the sealing and supporting force needed between piston  145  and end-cap  171 . 
     Over-center mechanism  179  is attached to end-cap  171  and configured to move end-cap  171  with piston  145 , supported on end-cap  171 , between two positions. In one position, end-cap  171  and piston  145  are spaced away from cartridge housing  173  or, more specifically, from first end  176  of cartridge housing  173 . This position allows inserting cartridge tube  302  into cartridge housing  173 . In another position, plunger  175  is inserted into interior  303  and hermetically sealed against interior  303 . In this portion, end-cap  171  is also sealed against interior  303 . Furthermore, plunger  175  is now movable within interior  303 . 
     Rotary actuator  120  is turned in one of rotational direction  121  and second rotational direction  122 , which causes the transfer of hydraulic fluid  155  between reservoir  140  and flowable-material dispenser  160 . Some examples of rotary actuator  120  include, but are not limited to, stepper motors, servo motors, and the like. These examples provide very precise control of the rotation speed and the degree of rotation, which in turn enables flowable material  308  to be dispensed in precise quantities. 
     Referring generally to  FIGS. 7A-7B  and particularly to, e.g.,  FIG. 4E , according to method  700 , (block  722 ) inserting cartridge tube  302  into cartridge housing  173  comprises hermetically sealing cartridge tube  302  against second end-cap  172  of flowable-material dispenser  160 , attached to cartridge housing  173  opposite of end-cap  171 . The preceding subject matter of this paragraph characterizes example 27 of the present disclosure, wherein example 27 also includes the subject matter according to example 26, above. 
     When second end-cap  172  is sealed against cartridge tube  302 , flowable material  308  is directed from cartridge tube  302  through second end-cap  172  and toward the dispensing tip of flowable-material dispenser  160 . This seal ensures that flowable material  308  does not flow into space between cartridge tube  302  and cartridge housing  173 , thereby preventing contamination of cartridge housing  173 . The seal is established when cartridge tube  302  is inserted into cartridge housing  173  and is maintained until cartridge tube  302  is removed from cartridge housing  173 . 
     In some examples, as shown in  FIG. 4E , second end-cap  172  comprises gasket  163  for sealing against cartridge tube  302 . Gasket  163  is formed of an elastomeric material (e.g., rubber). As shown in  FIG. 4E , a portion of second end-cap  172  overlaps with cartridge tube  302  for additional sealing and/or maintaining orientation of cartridge tube  302 . For example, this portion of second end-cap  172  protrudes into cartridge tube  302 . 
     Referring generally to  FIGS. 7A and 7B , and particularly to, e.g.,  FIGS. 4A, 4B, 4C, 5A, 5B , according to method  700 , (block  730 ) locking over-center mechanism  179  relative to cartridge housing  173  is performed while plunger  175  is coupled to end-cap  171  and comprises inserting plunger  175  into interior  303  of cartridge tube  302 . The preceding subject matter of this paragraph characterizes example 28 of the present disclosure, wherein example 28 also includes the subject matter according to example 26 or 27, above. 
     Over-center mechanism  179  is used to move end-cap  171  and plunger  175  relative to cartridge housing  173 . In one position, plunger  175  and end-cap  171  are positioned away from cartridge housing  173  or, more specifically, away from first end  176  of cartridge housing  173 . In another position, end-cap  171  is positioned at first end  176  of cartridge housing  173  and plunger  175  is inserted into cartridge tube  302 . At this position, over-center mechanism  179  is locked. 
     End-cap  171  is pivotable by over-center mechanism  179  relative to cartridge housing  173  as shown, for example, in  FIGS. 5A and 5B . In some examples, over-center mechanism  179  comprises multiple arms pivotably coupled to each other. The number and the length of these arms establish the trajectory of end-cap  171  when end-cap  171  is moved by over-center mechanism  179 . In one or more examples, the movement of end-cap  171  relative to cartridge housing  173  is substantially along the center axis of cartridge housing  173  when end-cap  171  approaches first end  176  of cartridge housing  173 . As described above, end-cap  171  supports plunger  175 , and plunger  175  is inserted into cartridge tube  302 , when end-cap  171  approaches first end  176  of cartridge housing  173 . 
     Referring. e.g., to  FIGS. 7A and 7B , method  700  further comprises (block  750 ) monitoring pressure inside reservoir  140 . The preceding subject matter of this paragraph characterizes example 29 of the present disclosure, wherein example 29 also includes the subject matter according to any one of examples 26 to 28, above. 
     The pressure inside reservoir  140  is monitored to control the dispensing rate of flowable material  308 . Furthermore, the pressure inside reservoir  140  is monitored to ensure support to plunger  175  by end-cap  171 , e.g., when plunger  175  is extracted from cartridge tube  302  and moved away from of cartridge housing  173 . When this pressure, inside reservoir  140 , exceeds atmospheric pressure, which is referred to as a positive pressure, plunger  175  is forced from first end  176  to second end  177  of cartridge housing  173 . At some point, the positive pressure overcomes the frictional resistance of plunger  175 , relative to cartridge tube  302 , and also the flow resistance of flowable material  308 , and plunger  175  starts moving from first end  176  to second end  177 . The speed of this movement depends on the level of this positive pressure (relative to the frictional forces and flow resistance). As plunger  175  moves from first end  176  to second end  177 , plunger  175  displaces flowable material  308  from cartridge tube  302 . As such, the positive pressure controls the plunger speed, which, in turn, determines the dispensing rate of flowable material  308 . 
     When this pressure is a negative pressure (i.e., is below atmospheric pressure), plunger  175  is forced from second end  177  to first end  176  of cartridge housing  173  and against end-cap  171 . When end-cap  171  is moved away from cartridge housing  173 , end-cap  171  pulls plunger  175  out of cartridge tube  302  and supports plunger  175  until plunger  175  is reinserted into a new cartridge tube. 
     In one or more examples, the pressure inside reservoir  140  is monitored using a gauge attached to reservoir  140  or to conduit  150 . It should be noted that the pressure inside reservoir  140  is the same as in any other volume of apparatus  100  containing hydraulic fluid  155 . 
     Referring generally to  FIGS. 7A and 7B , and particularly to, e.g.,  FIGS. 3A and 3B , according to method  700 , (block  740 ) turning rotary actuator  120  in rotational direction  121  is terminated once the pressure inside reservoir  140  reaches a predetermined level. The preceding subject matter of this paragraph characterizes example 30 of the present disclosure, wherein example 30 also includes the subject matter according to example 29, above. 
     The pressure inside reservoir  140  is monitored to control the dispensing rate of flowable material  308 . Specifically, the positive pressure of hydraulic fluid  155  applies a force to plunger  175  from first end  176  to second end  177  of cartridge housing  173 , thereby displacing flowable material  308  from cartridge housing  173 . The plunger  175  stops once plunger  175  reaches second end  177 . At this point, supplying an additional portion of hydraulic fluid  155  from reservoir  140  to cartridge housing  173  will increase the pressure of hydraulic fluid  155 . To ensure safety and to prevent damage of various components of apparatus  100  from excessive pressure of hydraulic fluid  155 , turning rotary actuator  120  in rotational direction  121  is terminated once the pressure inside reservoir  140  reaches the predetermined level. In one or more examples, even before plunger  175  reaches second end  177 , the pressure inside reservoir  140  is controlled for the same reasons and also to prevent excessive dispensing rates of flowable material  308 . 
     In one or more examples, the pressure inside reservoir  140  is monitored using a gauge, attached to reservoir  140  or conduit  150 . In these examples, the gauge is coupled to the switch, which controls rotary actuator  120 , e.g., either directly or through a central controller. 
     Referring generally to  FIGS. 7A and 7B , and particularly to, e.g.,  FIGS. 3A and 3B , method  700  further comprises (block  760 ) turning rotary actuator  120  in second rotational direction  122 , opposite of rotational direction  121 , so that linear actuator  130  retracts piston  145  within reservoir  140  and at least a portion of hydraulic fluid  155  is transferred from flowable-material dispenser  160  to reservoir  140 , causing plunger  175  to retract within cartridge tube  302  in reverse plunger direction  182 , opposite of forward plunger direction  181 . The preceding subject matter of this paragraph characterizes example 31 of the present disclosure, wherein example 31 also includes the subject matter according to any one of examples 26 to 30, above. 
     Turning rotary actuator  120  in second rotational direction  122  results in piston  145  moving away from the hydraulic fluid exit in reservoir  140 . As a result, hydraulic fluid  155  is being transferred from flowable-material dispenser  160  to reservoir  140  during this operation. This transfer of hydraulic fluid  155  creates a negative pressure in hydraulic fluid  155 . This negative pressure causes plunger  175  to retract within cartridge tube  302  in reverse plunger direction  182 , opposite of forward plunger direction  181 . Specifically, plunger  175  moves from second end  177  to first end  176  of cartridge housing  173 . 
     In general, rotary actuator  120  is configured to turn in rotational direction  121  or second rotational direction  122  at different times. Some examples of rotary actuator  120  having this functionality, include, but are not limited to, stepper motors, servo motors, and the like. Furthermore, these examples ensure precise control of the rotation speed and the degree of rotation, which in turn translates into precise dispensing of flowable material  308 . 
     Referring generally to  FIGS. 7A and 7B , and particularly to, e.g.,  FIGS. 3A and 3B , according to method  700 , (block  760 ) turning rotary actuator  120  in second rotational direction  122  comprises (block  762 ) monitoring pressure inside reservoir  140 . The preceding subject matter of this paragraph characterizes example 32 of the present disclosure, wherein example 32 also includes the subject matter according to example 31, above. 
     The pressure inside reservoir  140  is monitored to determine when plunger  175  reaches end-cap  171 . Specifically, as rotary actuator  120  is turned in second rotational direction  122  and hydraulic fluid  155  is transferred from interior  303  of cartridge tube  302  to reservoir  140 , plunger  175  moves toward end-cap  171 . Once plunger  175  reaches end-cap  171 , plunger  175  stops. At this point, transferring an additional portion of hydraulic fluid  155  from interior  303  of cartridge tube  302  to reservoir  140  simply decreases the pressure of hydraulic fluid  155 . To ensure safety and to prevent damage of various components of apparatus  100  from excessive negative pressure of hydraulic fluid  155 , the pressure of hydraulic fluid  155  inside reservoir  140  is monitored. 
     In one or more examples, the pressure inside reservoir  140  is monitored using a gauge attached to reservoir  140  or to conduit  150 . 
     Referring generally to  FIGS. 7A and 7B , and particularly to, e.g.,  FIGS. 3A and 3B , according to method  700 , (block  760 ) turning rotary actuator  120  in second rotational direction  122  is terminated once pressure inside reservoir  140  reaches a predetermined level. The preceding subject matter of this paragraph characterizes example 33 of the present disclosure, wherein example 33 also includes the subject matter according to example 32, above. 
     The pressure inside reservoir  140  is monitored to determine when plunger  175  reaches end-cap  171 . Specifically, as rotary actuator  120  is turned in second rotational direction  122  and hydraulic fluid  155  is transferred from interior  303  of cartridge tube  302  to reservoir  140 , plunger  175  moves toward end-cap  171 . Once plunger  175  reaches end-cap  171 , plunger  175  stops. At this point, transferring an additional portion of hydraulic fluid  155  from interior  303  of cartridge tube  302  to reservoir  140  simply decreases the pressure of hydraulic fluid  155 . To ensure safety and to prevent damage of various components of apparatus  100  from excessive negative pressure of hydraulic fluid  155 , the pressure of hydraulic fluid  155  inside reservoir  140  is monitored. Once the pressure reaches the predetermined level, turning rotary actuator  120  in second rotational direction  122  is terminated. 
     In one or more examples, the pressure inside reservoir  140  is monitored using a gauge attached to reservoir  140  or to conduit  150 . In these examples, the gauge is coupled to the switch, which controls rotary actuator  120 , e.g., either directly or through a central controller. In one or more examples, the predetermined level of the pressure is determined to ensure support of plunger  175  on end-cap  171 . 
     Referring generally to  FIGS. 7A and 7B , and particularly to, e.g.,  FIG. 3A, 3B, 4C , according to method  700 , (block  760 ) turning rotary actuator  120  in second rotational direction  122  comprises (block  764 ) hermetically sealing plunger  175  against end-cap  171 . The preceding subject matter of this paragraph characterizes example 34 of the present disclosure, wherein example 34 also includes the subject matter according to any one of examples 31 to 33, above. 
     Plunger  175  stops once plunger  175  reaches end-cap  171 . At this point, transferring an additional amount of hydraulic fluid  155  from interior  303  of cartridge tube  302  to reservoir  140  decreases the pressure of hydraulic fluid  155 , thereby creating negative pressure. This negative pressure forces plunger  175  against end-cap  171  and forms a hermetic seal between plunger  175  and end-cap  171 . As such, this hermetic seal ensures support of plunger  175  in end-cap  171 . Furthermore, the hermetic seal ensures that the negative pressure is maintained and that air is not introduced into hydraulic fluid  155 . 
     Referring to  FIG. 4C , plunger  175  is shown directly contacting end-cap  171 . The hermetic seal is provided by direct contact between plunger  175  and end-cap  171 . Furthermore, in one or more examples, second gasket  422 , disposed between plunger  175  and end-cap  171 , is used to form the hermetic seal. 
     Referring generally to  FIGS. 7A and 7B , and particularly to, e.g.,  FIG. 4E , according to method  700 , (block  760 ) turning rotary actuator  120  in second rotational direction  122  comprises (block  766 ) admitting atmosphere into cartridge tube  302  through vent  162 , located in cartridge housing  173 . The preceding subject matter of this paragraph characterizes example 35 of the present disclosure, wherein example 35 also includes the subject matter according to any one of examples 31 to 34, above. 
     As described above, turning rotary actuator  120  in a second rotational direction  122  causes movement of plunger  175  away from second end  177  of cartridge housing  173 . Vent  162  admits the atmosphere into cartridge tube  302  during this operation, effectively backfilling cartridge tube  302 , e.g., with atmosphere. This backfill prevents flow/able material  308  from being pulled back into cartridge tube  302 . Furthermore, the backfill prevents the negative pressure from building up inside cartridge tube  302  (e.g., between plunger  175  away from second end  177  of cartridge housing  173 ). 
     In one or more examples, vent  162  comprises a valve, one end of which is in fluid communication with interior  303  of cartridge tube  302  (when cartridge tube  302  is positioned inside cartridge housing  173 ). The other end of this valve is open to the atmosphere. In one or more examples, the operation of vent  162  is synchronized with operation of other components of apparatus  100 , such as rotary actuator  120 . Specifically, vent  162  allows the atmosphere to enter cartridge tube  302  when rotary actuator  120  is turning in second rotational direction  122 , resulting in the transfer of hydraulic fluid  155  from flowable-material dispenser  160  to reservoir  140 . 
     Referring generally to  FIGS. 7A and 7B , and particularly to, e.g.,  FIG. 4C , according to method  700 , plunger  175  is retracted within cartridge tube  302  until annular boss  427  of end-cap  171  protrudes into annular recess  429  of plunger  175 . The preceding subject matter of this paragraph characterizes example 36 of the present disclosure, wherein example 36 also includes the subject matter according to any one of examples 31 to 35, above. 
     When annular boss  427  of end-cap  171  protrudes into annular recess  429  of plunger  175 , a geometric coupling is formed between end-cap  171  and plunger  175 . This geometric coupling is used in addition to or instead of the vacuum coupling between end-cap  171  and plunger  175  caused by the negative pressure of hydraulic fluid  155 . 
     In one or more examples, annular boss  427  of end-cap  171  and annular recess  429  of plunger  175  have interference fit. In these examples, plunger  175  is formed from a flexible material (e.g., elastomer). 
     Referring generally to  FIGS. 7A and 7B , and particularly to, e.g.,  FIG. 5A , method  700  further comprises (block  770 ) unlocking over-center mechanism  179  relative to cartridge housing  173  to move plunger  175  and end-cap  171  away from cartridge tube  302  and cartridge housing  173 . The preceding subject matter of this paragraph characterizes example 37 of the present disclosure, wherein example 37 also includes the subject matter according to any one of examples 26 to 36, above. 
     Plunger  175  and end-cap  171  are moved away from cartridge tube  302  and cartridge housing  173  to provide access to cartridge tube  302 . This position of plunger  175  and end-cap  171  allows removal of cartridge tube  302  from cartridge housing  173  (e.g., to replace cartridge tube  302  with new cartridge tube when flowable material  308  is dispensed from cartridge tube  302 ). 
     End-cap  171  is pivotable by over-center mechanism  179  relative to cartridge housing  173  as shown, for example, in  FIGS. 5A and 5B . In some examples, over-center mechanism  179  comprises multiple arms pivotably coupled to each other. The number and the length of these arms establish the trajectory of end-cap  171  when end-cap  171  is moved by over-center mechanism  179 . 
     Referring generally to  FIGS. 7A and 7B , and particularly to, e.g.,  FIG. 5A , according to method  700 , (block  770 ) unlocking over-center mechanism  179  relative to cartridge housing  173  comprises (block  772 ) coupling plunger  175  to end-cap  171 . The preceding subject matter of this paragraph characterizes example 38 of the present disclosure, wherein example 38 also includes the subject matter according to example 37, above. 
     This coupling supports plunger  175  relative to end-cap  171  when plunger  175  is extracted from cartridge tube  302 . Furthermore, this coupling supports plunger  175  relative to end-cap  171  when plunger  175  and end-cap  171  are moved away from cartridge tube  302 . 
     Plunger  175  is coupled to end-cap  171 , for example, using the negative pressure of hydraulic fluid  155 . The negative pressure is created when plunger  175  is positioned against end-cap  171  and rotary actuator  120  continues to turn in second rotational direction  122 . 
     Referring generally to  FIGS. 7A and 7B , and particularly to, e.g.,  FIG. 5A , according to method  700 , (block  772 ) coupling plunger  175  to end-cap  171  comprises (block  774 ) maintaining negative pressure of hydraulic fluid  155  at least in reservoir  140 . The preceding subject matter of this paragraph characterizes example 39 of the present disclosure, wherein example 39 also includes the subject matter according to example 38, above. 
     Maintaining the negative pressure of hydraulic fluid  155  at least in reservoir  140  also maintains the negative pressure of hydraulic fluid  155  in other portions of apparatus  100  due to hydraulic coupling and flow of hydraulic fluid  155  between reservoir  140  and other portions. Specifically, the negative pressure of hydraulic fluid  155  forces plunger  175  against end-cap  171 . 
     Referring generally to, e.g.,  FIG. 7B , method  700  further comprises (block  780 ) removing cartridge tube  302  from cartridge housing  173 . The preceding subject matter of this paragraph characterizes example 40 of the present disclosure, wherein example 40 also includes the subject matter according to any one of examples 26 to 39, above. 
     Cartridge tube  302  is removed from cartridge housing  173  when flowable material  308  is dispensed from cartridge tube  302 . For example, a new cartridge tube is later placed inside cartridge housing  173  to replace cartridge tube  302 . To remove cartridge tube  302 , end-cap  171  is positioned away from cartridge housing  173  providing access to cartridge housing  173 . In one or more examples, end-cap  171  supports plunger  175 . 
     Referring generally to  FIGS. 7A and 7B , and particularly to, e.g.,  FIGS. 6A and 6B , method  700  further comprises (block  756 ) opening dispenser valve  600  of flowable-material dispenser  160 , fluidically coupled to interior  303  of cartridge tube  302 , to enable flowable material  308  to flow from apparatus  100 . The preceding subject matter of this paragraph characterizes example 41 of the present disclosure, wherein example 41 also includes the subject matter according to any one of examples 26 to 40, above. 
     Dispenser valve  600  controls the flow of flowable material  308  from apparatus  100 . In one or more examples, when flowable material  308  is not dispensed, dispenser valve  600  is kept closed. As such, flowable material  308  is isolated from the environment (e.g., to prevent curing of flowable material  308  remaining in apparatus  100 ). 
     In one or more examples, dispenser valve  600  is coupled to second double-acting pneumatic cylinder  520 , which opens and closes dispenser valve  600 , as shown in  FIGS. 6A and 6B . 
     Referring generally to  FIGS. 7A and 7B , and particularly to, e.g.,  FIGS. 6A and 6B , according to method  700 , (block  756 ) opening dispenser valve  600  is synchronized with turning rotary actuator  120  in rotational direction  121 . The preceding subject matter of this paragraph characterizes example 42 of the present disclosure, wherein example 42 also includes the subject matter according to example 41, above. 
     Both dispenser valve  600  and rotary actuator  120  control the flow of flowable material  308  from apparatus  100 . Specifically, when rotary actuator  120  turns in rotational direction  121 , hydraulic fluid  155  is transferred from reservoir  140  to interior  303  of cartridge tube  302 , thereby causing movement of plunger  175  and dispensing of flowable material  308 . Dispenser valve  600  controls the flow path of flowable material  308  from cartridge tube  302 . Therefore, flowable material  308  is dispensed only when dispenser valve  600  is open and rotary actuator  120  is turning in a rotational direction. Flowable material  308  is not dispensed when either dispenser valve  600  is closed or rotary actuator  120  does not turn in the rotational direction. 
     In one or more examples, dispenser valve  600  is immediately open when rotary actuator  120  begins turning in the rotational direction. This synchronization prevents building up an excessive hydraulic pressure in apparatus  100 , which is otherwise possible when dispenser valve  600  remains closed while rotary actuator  120  continues turning in the rotational direction. In the same or other examples, dispenser valve  600  is closed as soon as rotary actuator  120  stops turning in the rotational direction. This feature prevents exposure of a portion of flowable material  308 , remaining in apparatus  100 , to the environment. In one or more examples, dispenser valve  600  remains closed even when rotary actuator  120  starts turning in second rotational direction  122 , opposite of rotational direction  121 . 
     Referring generally to  FIGS. 7A and 7B , and particularly to, e.g.,  FIGS. 3B and 3C-3F , according to method  700 , piston  145  is coupled to rotary actuator  120  by screw  135  and ball nut  134 . Piston  145  does not rotate relative to reservoir  140  as piston  145  advances or retracts within reservoir  140 . The preceding subject matter of this paragraph characterizes example 43 of the present disclosure, wherein example 43 also includes the subject matter according to any one of examples 26 to 42, above. 
     Screw  135  is non-rotatably coupled to piston  145  and is linearly advanced along central axis  131  by rotating ball nut  134  relative to screw  135  as schematically shown, for example, in  FIG. 3B . As such, the rotation of ball nut  134  relative to screw  135  determines the linear motion of screw  135  and piston  145  and also determines the transfer of hydraulic fluid  155  to and from reservoir  140 . When piston  145  does not rotate relative to reservoir  140 , screw  135  also does not rotate relative to reservoir  140  and other stationary components of apparatus  100 . As such, the rotation of ball nut  134  relative to screw  135  is precisely controllable by rotary actuator  120 , which is coupled to ball nut  134  by gear train  125 . In other words, the rotation of ball nut  134  relative to screw  135  is only controlled by the rotation of rotary actuator  120 , since screw  135  and piston  145  do not rotate. 
       FIGS. 3C-3F  illustrate various examples of features and mechanisms used to ensure that piston  145  does not rotate relative to reservoir  140  yet is able to advance and/or retract within reservoir  140  along central axis  131 . Specifically,  FIG. 3C  illustrates anti-rotation mechanism  139 , which comprises slot  192  and protrusion  191  protruding into slot  192 . Slot  192  is formed in screw  135 , while protrusion  191  is attached to housing  138  of linear actuator  130 . However, other arrangements are also within the scope of the present disclosure, e.g., a slot in housing  138  and a protrusion in screw  135 , a slot in piston  145  and a protrusion in reservoir  140 , a slot in reservoir  140  and a protrusion in piston  145 , and the like. Both slot  192  and protrusion  191  extend along central axis  131  of screw  135 , which allows piston  145  to advance and/or retract within reservoir  140  along central axis  131 . 
       FIG. 3C  illustrates another example of anti-rotation mechanism  139 , which comprises first surface  193 , and second surface  194  slidably contacting first surface  193  at least two points of first surface  193  that lie on opposite sides of orthogonal projection  132  of central axis  131  onto first surface  193 . In this example, first surface  193  is on screw  135 , while second surface  194  is on protrusion  191  attached to housing  138 . However, other arrangements are also within the scope of the present disclosure. 
       FIGS. 5E and 5F  illustrate two examples of cross-sections of piston  145  and reservoir  140  in a plane perpendicular to central axis  131 . These examples show piston  145  and reservoir  140  having complementary non-circular cross-sections. These non-circular cross-sections provide a seal between piston  145  and reservoir  140  and allow piston  145  to advance and/or retract within reservoir  140  along central axis  131 .  FIG. 3E  illustrates a specific example where these complementary non-circular cross-sections are oval.  FIG. 3E  illustrates another example where these complementary non-circular cross-sections are rectangular. 
     Examples of the present disclosure may be described in the context of method  1100  for aircraft manufacturing and service as shown in  FIG. 8A  and aircraft  1102  as shown in  FIG. 8B . During pre-production, method  1100  may include specification and design (block  1104 ) of aircraft  1102  and material procurement (block  1106 ). During production, component and subassembly manufacturing (block  1108 ) and system integration (block  1110 ) of aircraft  1102  may take place. Thereafter, aircraft  1102  may go through certification and delivery (block  1112 ) to be placed in service (block  1114 ). While in service, aircraft  1102  may be scheduled for routine maintenance and service (block  1116 ). Routine maintenance and service may include modification, reconfiguration, refurbishment, etc. of one or more systems of aircraft  1102 . 
     Each of the processes of method  1100  may be performed or carried out by a system integrator, a third party, and/or an operator (e.g., a customer). For the purposes of this description, a system integrator may include, without limitation, any number of aircraft manufacturers and major-system subcontractors; a third party may include, without limitation, any number of vendors, subcontractors, and suppliers; and an operator may be an airline, leasing company, military entity, service organization, and so on. 
     As shown in  FIG. 8B , aircraft  1102  produced by method  1100  may include airframe  1118  with a plurality of high-level systems  1120  and interior  1122 . Examples of high-level systems  1120  include one or more of propulsion system  1124 , electrical system  1126 , hydraulic system  1128 , and environmental system  1130 . Any number of other systems may be included. Although an aerospace example is shown, the principles disclosed herein may be applied to other industries, such as the automotive industry. Accordingly, in addition to aircraft  1102 , the principles disclosed herein may apply to other vehicles, e.g., land vehicles, marine vehicles, space vehicles, etc. 
     Apparatus(es) and method(s) shown or described herein may be employed during any one or more of the stages of method  1100 . For example, components or subassemblies corresponding to component and subassembly manufacturing (block  1108 ) may be fabricated or manufactured in a manner similar to components or subassemblies produced while aircraft  1102  is in service (block  1114 ). Also, one or more examples of the apparatus(es), method(s), or combination thereof may be utilized during production stages (shown as block  1108  and block  1110 ), for example, by substantially expediting assembly of or reducing the cost of aircraft  1102 . Similarly, one or more examples of the apparatus or method realizations, or a combination thereof, may be utilized, for example and without limitation, while aircraft  1102  is in service (block  1114 ) and/or during maintenance and service (block  1116 ). 
     Different examples of the apparatus(es) and method(s) disclosed herein include a variety of components, features, and functionalities. It should be understood that the various examples of the apparatus(es) and method(s) disclosed herein may include any of the components, features, and functionalities of any of the other examples of the apparatus(es) and method(s) disclosed herein in any combination, and all of such possibilities are intended to be within the scope of the present disclosure. 
     Many modifications of examples set forth herein will come to mind to one skilled in the art to which the present disclosure pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. 
     Therefore, it is to be understood that the present disclosure is not to be limited to the specific examples illustrated and that modifications and other examples are intended to be included within the scope of the appended claims. Moreover, although the foregoing description and the associated drawings describe examples of the present disclosure in the context of certain illustrative combinations of elements and/or functions, it should be appreciated that different combinations of elements and/or functions may be provided by alternative implementations without departing from the scope of the appended claims. Accordingly, parenthetical reference numerals in the appended claims are presented for illustrative purposes only and are not intended to limit the scope of the claimed subject matter to the specific examples provided in the present disclosure.