Patent Publication Number: US-9429020-B2

Title: Scroll pump having axially compliant spring element

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a scroll pump which includes plate scrolls having nested scroll blades, and a tip seal(s) that provides a seal between the tip of the scroll blade of one of the plate scrolls and the plate of the other plate scroll. 
     2. Description of the Related Art 
     A scroll pump is a type of pump that includes a stationary plate scroll having a spiral stationary scroll blade, and an orbiting plate scroll having a spiral orbiting scroll blade. The stationary and orbiting scroll blades are nested with a clearance and predetermined relative angular positioning such that a pocket (or pockets) is delimited by and between the scroll blades. The scroll pump also has a frame to which the stationary plate scroll is fixed and an eccentric drive mechanism supported by the frame. These parts generally make up an assembly that may be referred to as a pump head (assembly) of the scroll pump. 
     The orbiting plate scroll and hence, the orbiting scroll blade, is coupled to and driven by the eccentric driving mechanism so as to orbit about a longitudinal axis of the pump passing through the axial center of the stationary scroll blade. The volume of the pocket(s) delimited by the scroll blades of the pump is varied as the orbiting scroll blade moves relative to the stationary scroll blade. The orbiting motion of the orbiting scroll blade also causes the pocket(s) to move within the pump head assembly such that the pocket(s) is selectively placed in open communication with an inlet and outlet of the scroll pump. 
     In an example of such a scroll pump, the motion of the orbiting scroll blade relative to the stationary scroll blade causes a pocket sealed off from the outlet of the pump and in open communication with the inlet of the pump to expand. Accordingly, fluid is drawn into the pocket through the inlet. Then the pocket is moved to a position at which it is sealed off from the inlet of the pump and is in open communication with the outlet of the pump, and at the same time the pocket is collapsed. Thus, the fluid in the pocket is compressed and thereby discharged through the outlet of the pump. The sidewall surfaces of the stationary orbiting scroll blades need not contact each other to form a satisfactory pocket(s). Rather, a minute clearance may be maintained between the sidewall surfaces at the ends of the pocket(s). 
     A scroll pump as described above may be of a vacuum type, in which case the inlet of the pump is connected to a chamber that is to be evacuated. 
     Furthermore, oil may be used to create a seal between the stationary and orbiting plate scroll blades, i.e., to form a seal(s) that delimits the pocket(s) with the scroll blades. On the other hand, certain types of scroll pumps, referred to as “dry” scroll pumps, avoid the use of oil because oil may contaminate the fluid being worked by the pump. Instead of oil, dry scroll pumps employ a tip seal or seals each seated in a groove extending in and along the length of the tip (axial end) of a respective one of the scroll blades (the groove thus also having the form of a spiral). More specifically, each tip seal is provided between the tip of the scroll blade of a respective one of the plate scrolls and the plate of the other of the plate scrolls, to create a seal which maintains the pocket(s) between the stationary and orbiting scroll blades. Further in this respect, scroll pumps of the type described above typically require a certain degree of axial compliance among respective parts of the pump head assembly to maintain an effective seal between the opposing scroll blades and plates. 
     In general, there are two types of tip seal arrangements to meet these requirements: energized and non-energized. An energized type of tip seal arrangement includes a tip seal seated in the tip of the scroll blade of one of the plate scrolls, and a spring that biases the tip seal against the plate of the other of the plate scrolls. A typical non-energized type of tip seal arrangement has only a solid plastic tip seal seated in the tip of the scroll blade of one of the plate scrolls and the solid plastic tip seal directly confronts the plate of the other of the plate scrolls. 
     In the spring-biased tip seal arrangements, the friction produced by the engagement of the tip seal with the opposing scroll plate is limited in that it does not exceed a value corresponding to the maximum force that can be exerted by the spring on the tip seal. However, spring-biased tip seals are continuously worn because they are constantly biased into engagement with the opposing scroll plate. As a result, spring-biased tips seals must be replaced rather frequently. The solid plastic tip seals of the non-energized arrangements have a relatively longer useful life than the conventional spring-biased tip seals. However, the use of solid tip seals presents its own set of problems. 
     For instance, the tolerances of axial dimensions of various components of scroll pumps that employ non-energized tip seals must be maintained within narrow ranges to ensure that the tips seals are properly positioned in the pump head. More specifically, precise axial positioning ensures that any gap between a solid tip seal and the opposing scroll plate is minimal. If, the gap is too large, the tip seal will not produce an effective seal with the opposing scroll plate. However, if the tip seal is compressed too much between the scroll blade and the opposing scroll plate, the resulting friction and heat can overload and damage not only the seal itself but also parts of the pump such as the bearings of the drive mechanism. 
     SUMMARY OF THE INVENTION 
     The present invention is provided to overcome one or more of the problems, disadvantages and/or limitations presented by the use of a non-energized type of tip seal in a scroll pump. 
     One object of the present invention is to provide a scroll pump in which a tip seal(s) of the pump will be produce an effective seal with an opposing scroll plate without overloading and/or damaging components of the pump, at the time a pump head of the pump is assembled. 
     Another object of the present invention is to provide a scroll pump having pump head components whose axial dimensions may enjoy a wide range of tolerances and yet in which the tip seal(s) of the pump are ensured of producing an optimal seal with an opposing scroll pump at the time a pump head of the pump is assembled. 
     According to one aspect of the present invention there is provided a scroll pump including a frame, a stationary plate scroll fixed relative to the frame, an orbiting plate scroll, a tip seal(s) interposed between an axial end of the scroll blade of a respective one of the stationary and orbiting plate scrolls and the plate of the other of the stationary plate and orbiting plate scrolls, an eccentric drive mechanism supported by the frame, operative to drive the orbiting plate scroll in an orbit about the longitudinal axis, and including a crankshaft and bearings, and a flexure having compliance in an axial direction parallel to the longitudinal axis of the pump. The orbiting plate scroll is carried by the crank of the crankshaft, and the main portion of the crankshaft is supported by the frame via the bearings. Furthermore, the eccentric drive mechanism has an axially facing flexure-locating surface, one of the bearings is a flexure-locating bearing, the crankshaft of the eccentric drive mechanism is supported such that it is movable axially relative to the flexure-locating bearing, and the flexure is axially interposed between the axially facing flexure-locating surface and the flexure-locating bearing of the eccentric drive mechanism. 
     According to another aspect of the present invention, there is provided a scroll pump including a frame, a stationary plate scroll fixed relative to the frame, an orbiting plate scroll, a tip seal(s) interposed between an axial end of the scroll blade of a respective one of the stationary and orbiting plate scrolls and the plate of the other of the stationary plate and orbiting plate scrolls, an eccentric drive mechanism supported by the frame and operative to drive the orbiting plate scroll in an orbit about the longitudinal axis, and an axial compliance system including at least one spring and a flexure having compliance in the axial direction of the pump. The eccentric drive mechanism includes a drive shaft, and bearings each having an inner race, an outer race and rolling elements interposed between the inner and out races. The drive shaft comprises a crankshaft having a main shaft and a crank. Also, the eccentric drive mechanism has an axially facing flexure-locating surface, and the crankshaft is supported such that it is movable axially relative to the inner races of the bearings. The outer races of respective ones of the bearings are coupled to the frame and the orbiting plate scroll, the inner races of the respective ones of the bearings are disposed on the main shaft and the crank, the main shaft is supported by the frame, and the orbiting plate scroll is carried by the crank via the bearings. The at least one spring of the axial compliance system serves to clamp the inner races of the bearings axially, and the flexure is interposed in an axial direction, parallel to the longitudinal axis of the pump, between the inner race of one of the bearings and the axially facing flexure-locating surface of the eccentric drive mechanism. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects, features and advantages of the present invention will be better understood from the detailed description of the preferred embodiments thereof that follows with reference to the accompanying drawings, in which: 
         FIG. 1  is a schematic longitudinal sectional view of a scroll pump to which the present invention may be applied; 
         FIG. 2  is a longitudinal sectional view of part of a pump head of one embodiment of a scroll pump according to the present invention; 
         FIG. 3  is an enlarged sectional view of part of the pump head shown in  FIG. 2 , illustrating tip seals between the stationary plate scroll and the orbiting plate scroll; 
         FIG. 4  is a cross-sectional view, in a radial direction, of one version of a flexure employed by a scroll pump according to the present invention; 
         FIG. 5  is a cross-sectional view, in a radial direction, of another version of a flexure employed by a scroll pump according to the present invention; 
         FIGS. 6A, 6B and 6C  are each a conceptual diagram of a portion of the embodiment of the scroll pump of  FIG. 2  in section, with  FIG. 6A  showing a flexure in an essentially relaxed (non-deflected state),  FIG. 6B  showing the flexure in a deflected state, and  FIG. 6C  showing the flexure in a deflected hard-stopped state; and 
         FIGS. 7A, 7B and 7C  are each a conceptual diagram of a portion of another embodiment of a scroll pump according to the present invention in section, with  FIG. 7A  showing a flexure in an essentially relaxed (non-deflected state),  FIG. 7B  showing the flexure in a deflected state, and  FIG. 7C  showing the flexure in a deflected hard-stopped state. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Various embodiments and examples of embodiments of the inventive concept will be described more fully hereinafter with reference to the accompanying drawings. In the drawings, the sizes and relative sizes of elements may be exaggerated for clarity. Likewise, the shapes of elements may be exaggerated and/or simplified for clarity and elements may be shown schematically for ease of understanding. Also, like numerals and reference characters are used to designate like elements throughout the drawings. 
     Other terminology used herein for the purpose of describing particular examples or embodiments of the inventive concept is to be taken in context. For example, the terms “comprises” or “comprising” when used in this specification indicates the presence of stated features or processes but does not preclude the presence of additional features or processes. Terms such as “fixed” may be used to describe a direct connection of two parts/elements to one another in such a way that the parts/elements can not move relative to one another or an indirect connection of the parts/elements through the intermediary of one or more additional parts. Likewise, the term “coupled” may refer to a direct or indirect coupling of two parts/elements to one another. The term “spiral” as used to described a scroll blade is used in its most general sense and may refer to any of the various forms of scroll blades known in the art as having a number of turns or “wraps”. Finally, as would be readily apparent to those skilled in the art, the term “compliance” as an inherent characteristic of the flexure has a meaning similar to that of springs. That is, the term “compliance” is a vector quantity similar to the displacement vector of a spring. Thus, a phrase such as “the compliance of the flexure is in an axial direction” indicates that the axial direction is the direction along which a predetermined (designed for) relationship exists between the deflection of the flexure and the resulting force of the flexure. 
     Referring now to  FIG. 1 , a scroll vacuum pump  1  to which the present invention can be applied may include a cowling  100 , and a pump head assembly  200 , a pump motor  300 , and a cooling fan  400  disposed in the cowling  100 . Furthermore, the cowling  100  defines an air inlet  100 A and an air outlet  100 B at opposite ends thereof, respectively. The cowling  100  may also include a cover  110  that covers the pump head assembly  200  and pump motor  300 , and a base  120  that supports the pump head assembly  200  and pump motor  300 . The cover  110  may be of one or more parts and is detachably connected to the base  120  such that the cover  110  can be removed from the base  120  to access the pump head assembly  200 . Furthermore, the motor  300  is detachably connected to the pump head assembly  200  so that once the cover  110  is removed from the base  120 , for example, the motor  300  can be removed from the pump head assembly  200  to provide better access to the pump head assembly for maintenance and/or trouble shooting. 
     Referring now to  FIG. 2 , the pump head assembly  200  includes a frame  210 , a stationary plate scroll  220 , an orbiting plate scroll  230 , and an eccentric drive mechanism  240 . 
     The frame  210  may be one unitary piece, or the frame  210  may comprise several integral parts that are fixed to one another. 
     The stationary plate scroll  220  in this example is detachably mounted to the frame  210  (by fasteners, not shown). The stationary plate scroll  220  includes a stationary plate  220 P, and a stationary scroll blade  220 B projecting axially from a front side of the plate  220 P. The stationary scroll blade  220 B is in the form of a spiral having a number of wraps as is known per se. The orbiting plate scroll  230  includes an orbiting plate  230 P, and an orbiting scroll blade  230 B projecting axially from a front side of the plate  230 P. The orbiting scroll blade  230 B has wraps that are complementary to those of the stationary scroll blade  220 B. 
     The stationary scroll blade  220 B and the orbiting scroll blade  230 B are nested, as shown in  FIG. 2 , with a clearance and predetermined relative angular and axial positioning such that pockets are delimited by and between the stationary and orbiting scroll blades  220 B and  230 B during operation of the pump to be described in detail below. In this respect, the sides of the scroll blades  220 B and  230 B may not actually contact each other to seal the pockets. Rather, minute clearances between sidewall surfaces of the scroll blades  220 B and  230 B along with tip seals  290  create seals sufficient for forming satisfactory pockets. 
     The eccentric drive mechanism  240  includes a drive shaft  241  and a number of bearings  246 . As shown in  FIG. 2 , each bearing  246  may have an inner race  246   a , an outer race  246   b  and rolling elements  246   c  interposed between the inner and outer races. Also, in the embodiment shown in  FIG. 2 , the drive shaft  241  includes a crankshaft having a main portion  242  and a crank  243 , and a counterbalance  244 . The counterbalance  244  may be unitary with the main portion  242  and crank  243  or may be fitted around an outer circumferential surface of the same. In any case, the main portion  242  of the crankshaft is coupled to the motor  300  so that the drive shaft  241  is rotated by the motor  300 . The central longitudinal axis of the crank  243  is offset in a radial direction from that of the main portion  242 . 
     The main portion  242  of the crankshaft is supported by the frame  210  via one or more of the bearings  246  so as to be rotatable relative to the frame  210  about central longitudinal axis L. In this example, the main portion  242  of the crankshaft is supported by the frame  210  via a pair of angular contact bearings  246 . The orbiting plate scroll  230  is mounted to the crank  243  via at least one other bearing  246 . In this example, as well, the orbiting plate scroll  230  is mounted to the crank  243  via a second pair of angular contact bearings  246 . Thus, the orbiting plate scroll  230  is carried by crank  243  via the angular contact bearings  246  so as to orbit about the longitudinal axis L of the pump when the main shaft  242  is rotated by the motor  300 , and so as to be rotatable about the central longitudinal axis of the crank  243 . 
     During a normal operation of the pump, a load applied to the orbiting scroll blade  230 B, due to the fluid being compressed in the pockets, tends to act in such a way as to cause the orbiting scroll plate  230  to rotate about the central longitudinal axis of the crank  243 . However, a tubular member  250  whose ends  251  and  252  are connected to the orbiting plate scroll  230  and frame  210 , respectively, and/or another mechanism such as an Oldham coupling restrains the orbiting plate scroll  230  in such a way as to allow it to orbit about the longitudinal axis L of the pump while inhibiting its rotation about the central longitudinal axis of the crank  243 . 
     In the illustrated embodiment of the present invention, a tubular member  250  in the form of a metallic bellows restrains the orbiting plate scroll  230 . The metallic bellows is radially flexible enough to allow the first end  251  thereof to follow along with the orbiting plate scroll  230  while the second end  252  of the bellows remains fixed to the frame  210 . Furthermore, the tubular metallic bellows has some flexibility in the axial direction, i.e., in the direction of its central longitudinal axis. On the other hand, the metallic bellows may have a torsional stiffness that prevents the first end  251  of the bellows from rotating significantly about the central longitudinal axis of the bellows, i.e., from rotating significantly in its circumferential direction, while the second end  252  of the bellows remains fixed to the frame  210 . Accordingly, the metallic bellows may be essentially the only means of providing the angular synchronization between the stationary and orbiting scroll blades  220 B and  230 B, respectively, during the operation of the pump. 
     The tubular member  250  also extends around a portion of the crankshaft and the bearings  246  of the eccentric drive mechanism  240 . In this way, the tubular member  250  seals the bearings  246  and bearing surfaces from a space defined between the tubular member  250  and the frame  210  in the radial direction and which space may constitute the working chamber C, i.e., a vacuum chamber of the pump, through which fluid worked by the pump passes. Accordingly, lubricant employed by the bearings  246  and/or particulate matter generated by the bearings surfaces can be prevented from passing into the chamber C by the tubular member  250 . 
     Referring back to  FIG. 1 , the scroll vacuum pump  1  also has a pump inlet  140  and constituting a vacuum side of the pump where fluid is drawn into the pump, and a pump outlet  150  and constituting a compression side where fluid is discharged to atmosphere or under pressure from the pump. The pump head assembly  200  also has an inlet opening  270  connecting the inlet  140  of the pump to the vacuum chamber C, and an exhaust opening  280  leading to the pump outlet  150 . Also, in  FIG. 1 , reference numeral  260  designates a compression mechanism of the pump which is constituted by the pockets defined between the stationary and orbiting plate scrolls  220  and  230 . 
       FIGS. 2 and 3  show the tip seal(s)  290  of the pump head assembly  200  which creates an axial seal between the scroll blade of one of the orbiting and stationary plate scrolls and the plate (or floor) of the other of the orbiting and stationary plate scrolls. More specifically, the tip seal  290  is a solid plastic member seated in a groove in and running the length of the tip of the scroll blade  220 B,  230 B of one of the stationary and orbiting plate scrolls  220 ,  230  so as to be interposed between the tip of the scroll blade  220 B,  230 B and the plate of the other of the stationary and orbiting plate scrolls  220 ,  230 . In this embodiment, solid plastic tip seals  290  are associated with both of the scroll blades  220 B,  230 B, respectively. Also, in  FIG. 3 , reference character P designates an arbitrary one of the above-mentioned pockets. 
     A scroll vacuum pump  1  having the structure described above operates as follows. 
     The orbiting motion of the orbiting scroll blade  220 B relative to the stationary scroll blade  230 B causes the volume of a lead pocket P sealed off from the outlet  150  of the pump and in open communication with the inlet  140  of the pump to expand. Accordingly, fluid is drawn into the lead pocket P through the pump inlet  140  via the inlet opening  270  of the pump head assembly  200  and the vacuum chamber C. The orbiting motion also in effect moves the pocket P to a position at which it is sealed off from the chamber C and hence, from the inlet  140  of the pump, and is in open communication with the pump outlet  150  after one or more revolutions of the crank shaft  241 . Then the pocket P is in effect moved into open communication with the outlet opening  280  of the pump head assembly  200 . During this time, the volume of the pocket P is reduced. Thus, the fluid in the pocket P is compressed and thereby discharged from the pump through the outlet  150 . Also, during this time (which corresponds to one or more orbit(s) of the orbiting plate scroll  230 ), a number of successive or trailing pockets P may be formed between the stationary and orbiting scroll blades  220 B and  230 B and are in effect similarly and successively moved and have their volumes reduced. Thus, the compression mechanism  260  in this example is constituted by a series of pockets P. In any case, as shown schematically in  FIG. 1  by the arrow-headed lines, the fluid is forced through the pump due to the orbiting motion of the orbiting plate scroll  230  relative to the stationary plate scroll  220 . 
     Also, by virtue of the above-described operation, the fluid flows behind the tip seals  290  and in effect “energizes” the tips seals  290 , meaning that the fluid forces the tip seals against the plates of the opposing plates scrolls. The pump  1  may be assembled with less axial clearance than the axial height of the tip seal also forcing the tip seal against the plate of the opposing plate scroll. One problem with a solid tip seal, as was described earlier, is that it does not provide sufficient axial compliance because such a tip seal is relatively incompressible. Thus, normally, when the pump is built and, in particular, when the pump head is assembled, the orbiting plate scroll must be set at a precise axial position in the pump to ensure that each tip seal produces an effective seal. Typically, this axial position must be within ˜0.001 inches of a reference position. Also, as is clear from the background section of this disclosure, an effective seal means one that produces a sufficient seal of the pocket P without generating excessive friction and heat. 
     The present invention, in one respect, obviates the need for such a precise assembly process of the pump head. In particular, according to one aspect of the invention, an axial compliance system comprising a flexure is provided. 
     The flexure is interposed between a flexure-locating surface and a flexure-locating bearing of the eccentric drive mechanism  240  as disposed in contact with the flexure-locating surface. The flexure-locating surface is a surface of the drive shaft  241  that extends outwardly from an outer circumferential surface of the drive shaft  241 . One version of the flexure  500  is shown in  FIG. 4  and another version of the flexure  500 ′ is shown in  FIG. 5 . The flexures  500  and  500 ′, and the overall axial compliance system comprising the flexure  500  or  500 ′, will now be described in more detail below. 
     The axial compliance system may also include a set of springs  247  such as Belleville springs or Belleville washers. The springs  247  serve to pre-load the bearings  246 . The flexure-locating bearing  246  is biased by and between at least one of the disk springs  247  and the flexure  500  (or  500 ′). Also, in the embodiment of  FIG. 2 , for reasons that will become clear, at least the flexure-locating bearing  246  is disposed on the drive shaft  241  such that the drive shaft  241  is axially movable relative to (the inner race of) the flexure-locating bearing  246 . To this end, the coefficient of thermal expansion of the material of the drive shaft  241  should match that of the bearing(s)  246  or there should be an appropriate level of radial clearance between the shaft  241  and the bearing(s). Note, in the illustrated embodiment of  FIG. 2 , all of the bearings  246  are disposed on the drive shaft  241  such that the drive shaft  241  is axially movable relative to (the inner races of) the bearings  246 , and six disk springs  247  are employed, for example, to pre-load the bearings  246 . 
     Also, the embodiment of  FIG. 2  is shown as employing the flexure  500  of  FIG. 4 , as an example, but other types of flexures such as that later shown in and described with respect to  FIG. 5  may be employed instead. 
     Referring still to the embodiment of  FIG. 2 , the flexure-locating surface is a surface  244   a  of the counterbalance  244  of the eccentric drive mechanism  240 . The flexure-locating surface  244   a  extends outwardly in a radial direction relative to an outer circumferential surface of the main portion  242  of the drive shaft  241 . The flexure-locating bearing in this embodiment is a bearing  246  which mounts the drive shaft  241  to the frame  210  (the left-most one of the angular contact bearings disposed on the main shaft  242  in the figure). The flexure  500  is disposed in contact with the flexure-locating surface  244   a  and may contact the flexure-locating bearing  246 . Also, in this example, the flexure-locating bearing  246  is biased by and between a set of four of the disk springs  247  (right hand side of the figure) and the flexure  500 . 
     Moreover, the flexure  500  has compliance in an axial direction parallel to the longitudinal axis L of the pump. 
     To this end, and referring to  FIGS. 2 and 4 , the flexure  500  is an annular member having first and second opposite sides  500   a  and  500   b  and radially innermost and outermost portions  500   i  and  500   o . Referring particularly to  FIG. 4 , the first side  500   a  of the annular member has an annular first surface  501  extending substantially perpendicular to a central axis of the annular member, and a cylindrical projection  500   p  that projects, at the radially outermost portion  500   o  of the annular member, axially from the first surface  501  in a direction parallel to the central axis of the annular member. The second side  500   b  of the annular member has a frustum-shaped second surface  502  extending obliquely relative to the central axis of the annular member towards the first side  500   a  of the annular member. The second side  500   b  may also have an annular third surface  503  at the radially innermost portion of the flexure  500  and extending substantially perpendicular to the central axis of the annular member. Thus, the second surface  503  subtends an acute angle θ with a plane perpendicular to the central axis of the annular member. 
     In the embodiment of  FIG. 2 , the projection  500   p  of the flexure contacts the inner race of the flexure-locating bearing  246 , and the radially innermost portion  500   i  of the second side  500   b  of the flexure contacts the flexure-locating surface  244   a . Specifically, the third surface  503  of the flexure  500  contacts the flexure-locating surface  244   a . Accordingly, the compliance of the flexure  500  is in a region between the inner race of the flexure-locating bearing  246  and the locating surface  244   a.    
     In the version of the flexure  500 ′ shown in  FIG. 5 , the flexure  500 ′ is also an annular member having first and second opposite sides  500   a ′ and  500   b ′ and radially innermost and outermost portions  500   i ′ and  500   o ′. The first side  500   a ′ of the annular member has an annular first surface  501 ′ extending substantially perpendicular to a central axis of the annular member, and a cylindrical first projection  500   p   1  that projects axially at the radially outermost portion  500   o ′ of the annular member from the first surface  501 ′ in a first direction parallel to the central axis of the annular member. On the other hand, the second side  500   b ′ of the annular member has an annular second surface  502 ′ extending substantially perpendicular to the central axis of the annular member, and a cylindrical second projection  500   p   2  that projects axially at the radially innermost portion  500   i ′ of the annular member from the second surface  502 ′ in a second direction opposite to the first direction. 
     Thus, in the case in which the flexure  500 ′ is employed instead of the flexure  500  in the embodiment of  FIG. 2  (refer to  FIGS. 6A, 6B and 6C  and the description thereof that follows), the first projection  500   p   1  of the flexure contacts the inner race of the flexure-locating bearing  246 , and the second projection  500   p   2  of the flexure  500 ′ contacts the flexure-locating surface  244   a . Thus, in this case as well, the compliance of the flexure  500 ′ would be in a region between the inner race of the flexure-locating bearing  246  and the flexure-locating surface  244   a.    
     Also, in the embodiment of  FIG. 2 , the angular contact bearings  246  by which the orbiting plate scroll  230  is mounted to the crank  243  are set against a radially extending surface of the counterbalance  244 . Those angular contact bearings  246  are urged against that surface by a set of two of the disk springs  247  (held in place on the crank  243  by a clip, for example) to thereby pre-load the bearings. 
     Basically, the flexure  500  (or  500 ′) is engineered so that its spring rate satisfies two conditions. First, the pre-load exerted on the bearings  246  (by the disk springs  247 ) should deflect the flexure  500  (or  500 ′) by only a relatively small amount (for instance, 0.001″ in the case in which the pre-load is 350 lbf) so that when there is a vacuum in the stage  260  of the pump axial loads will not result in the orbiting plate scroll moving towards the stationary plate scroll  220  by an excessive amount. The second condition is that the spring rate of the flexure  500  (or  500 ′) should be low enough so that a relatively small spring force will urge the orbiting plate scroll  230  away from the stationary plate scroll  220  when the axial clearance between the tip seal(s)  290  and the opposing plate is too small. With respect to the latter condition, the flexure  500  (or  500 ′) allows the orbiting plate scroll  230  to move away from the stationary plate scroll  220  in the event that an excessively small gap is provided between the tip seal(s)  290  and the plate of the opposing plate scroll when the pump head of the pump is assembled such as at the time the pump is built. This is shown in  FIGS. 6A, 6B and 6C . 
     In a working example of the embodiment of  FIG. 2 , in the case in which the spring rate of the flexure  500  (or  500 ′ is engineered so that a relatively modest force of ˜350 lbf will deflect the flexure  500  (or  500 ′) by 0.001″ in the axial direction, the spring rate of the flexure  500  (or  500 ′) is approximately 350,000 lbf/in, which is relatively small compared to the “spring rate” of a solid plastic tip seal (considering that the tip seal is essentially incompressible).  FIG. 6A  shows an ideal state of assembly in which an optimal seal(s) is established by the tip seal(s). In this case, a gap g between the radially outermost portion of the flexure  500  (or  500 ′) and the flexure-locating surface  244   a  is 0.006″ and there is minimal deflection of the flexure  500  (or  500 ′). 
       FIG. 6B  shows the state in which the flexure  500  (or  500 ′) has allowed the orbiting plate scroll  230  to move away from the stationary plate scroll  220  in the case in which the assembly of the pump head would otherwise result in the tip seal(s) being fitted too tightly against the opposing plate. In this case, the maximum allowable tolerance of the pump head in the axial direction was off by 0.003″ whereby deflection of the flexure  500  (or  500 ′) reduced the axial gap g between the radially outermost portion of the flexure  500  (or  500 ) and the flexure-locating surface  244   a  to 0.003″. At this time, the reaction force of the flexure  500  (or  500 ′) in the axial direction as transmitted to the tip seal(s) is only approximately 1050 lbs. Without the flexure  500  (or  500 ′, the reaction force could easily be an order of magnitude higher. Note, also, the reaction force of 1050 lbs., which would be transmitted to the angular contact bearings  246  disposed on the crank  243 , is sufficient to keep the bearings  243  from separating from each other in the axial direction. 
       FIG. 6C  shows a state in which the flexure  500  (or  500 ′) has limited the movement of the orbiting scroll plate  230  away from the stationary scroll plate  220 . That is, the flexure  500  (or  500 ′) is configured to provide a hard stop for the axial compliance system. 
       FIGS. 7A, 7B and 7C  show another embodiment according to the present invention. In this embodiment, the flexure  500  (or  500 ′) is interposed between the pair of angular contact bearings  246  by which the orbiting plate scroll  230  is mounted to the crank  243  and a flexure-locating surface. The flexure-locating surface in this embodiment may be a surface  244   b  of the counterbalance  244  (refer to  FIG. 2 ). More specifically, the flexure  500  (or  500 ′) contacts the inner race of the angular contact bearing  246  remote from the orbiting plate scroll  230  and the pair of disk springs  247  that pre-load the angular contact bearings  246 . Furthermore, the flexure  500  (or  500 ) may contact the flexure-locating surface  244   b . In any case, the compliance of the flexure  500  (or  500 ′) is in a region between the inner race of the angular contact bearing  246  and the flexure-locating surface  244   b.    
       FIGS. 7A, 7B and 7C  show states corresponding to those shown in  FIGS. 6A, 6B and 6C , respectively. Thus,  FIGS. 7A, 7B and 7C  show that the same results and advantages can be achieved when the flexure  500  ( 500 ′) is interposed between the angular contact bearings  246  on which the orbiting plate scroll  230  is disposed and a flexure-locating surface of the drive shaft  241 . 
     Finally, embodiments of the inventive concept and examples thereof have been described above in detail. The inventive concept may, however, be embodied in many different forms and should not be construed as being limited to the embodiments described above. Rather, these embodiments were described so that this disclosure is thorough and complete, and fully conveys the inventive concept to those skilled in the art. Thus, the true spirit and scope of the inventive concept is not limited by the embodiment and examples described above but by the following claims.