Patent Publication Number: US-9404491-B2

Title: Scroll pump having bellows providing angular synchronization and back-up system for bellows

Description:
BACKGROUND 
     1. Field of the Invention 
     The present invention relates to a scroll pump having a pump head assembly that includes a stationary plate scroll and an orbiting plate scroll having stationary and orbiting scroll blades, respectively, in particular, the present invention relates to the means used to angularly synchronize stationary and orbiting scroll blades in a scroll pump. 
     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 radial clearance and predetermined relative angular positioning such that a pocket (or pockets) is delimited by and between the 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 scroll plate 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 of 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 compressed. Thus, the fluid in the pocket is compressed and thereby discharged through the outlet of the pump. 
     In the case of a vacuum-type of scroll pump, the inlet of the pump is connected to a chamber that is to be evacuated. Conversely, in the case of a compressor-type of scroll pump, the outlet of the pump is connected to a chamber that is to be supplied with pressurized fluid by the pump. 
     In any case, the predetermined angular position of the orbiting scroll blade relative to the stationary scroll blade must be provided and maintained within certain tolerances if the above-described intake and discharge operations are to be executed satisfactorily by the scroll pump. More specifically, the orbiting plate scroll must maintain a certain angular synchronization with the stationary plate scroll if seals created by and between the stationary and orbiting scroll blades are to form the pocket(s) stably, cause the volume of the pocket(s) to vary appropriately, and effectively cause the pocket(s) to move through the pump head assembly with the timing required relative to the inlet and outlet of the pump. To this end, the orbiting plate scroll must not rotate in excess of a certain amount about its own central axis while it orbits about the longitudinal axis of the pump head assembly. 
     SUMMARY 
     It is an object of the present invention to provide a scroll pump having a primary means of angularly synchronizing the stationary and orbiting scroll blades of the pump, and a back-up system for the primary means, and neither of which have a tendency to create particles during normal operation of the pump and/or shorten the useful life of the pump. 
     It is another object of the present invention to provide a scroll pump having a primary means of angularly synchronizing the stationary and orbiting scroll blades of the pump, and a back-up system for the primary means, constituted by relatively simple and low cost structures that are easy to implement. 
     It is still another object of the present invention to provide a scroll pump having a primary means of angularly synchronizing the stationary and orbiting scroll blades of the pump, and a back-up system which maintains the angular synchronization in cases in which an excessive drive load is exerted on the orbiting scroll blade. 
     It is still another object of the present invention to provide a scroll pump having a primary means of angularly synchronizing the stationary and orbiting scroll blades of the pump, and a back-up system which can prevent the pump from being damaged should the primary means fail. 
     According to one aspect of the present invention, there is provided a scroll pump that includes a frame, a stationary plate scroll fixed to the frame and having a stationary scroll blade centered about a longitudinal axis of the pump, an orbiting scroll having an orbiting scroll blade juxtaposed with the stationary scroll blade in a radial direction of the pump such that the stationary and orbiting scroll blades are nested, an eccentric drive mechanism supported by the frame and operatively connected to the orbiting scroll blade so as to cause the orbiting scroll blade to orbit about the longitudinal axis, a metallic bellows that angularly synchronizes the orbiting and stationary scroll blades, and a non-contacting back-up system for the bellows. 
     The metallic bellows is fixed at a first end thereof to the orbiting plate scroll, and the frame is fixed to the metallic bellows at the second end of the metallic bellows such that the metallic bellows angularly synchronizes the orbiting and stationary scroll blades. The eccentric drive mechanism supports the orbiting scroll blade so as to be rotatable about a second axis that is parallel to the longitudinal axis. Thus, the orbiting plate scroll is an orbital part of the pump whereas the frame and the stationary plate scroll are a stationary part of the pump. 
     The non-contacting back-up system has a plurality of pins extending axially in directions parallel to the longitudinal axis of the pump from one of the stationary and orbital parts of the pump, and a guide part fixed relative to the other of the stationary and orbital parts of the pump. Several openings are defined in the guide part. The openings also extend axially in directions parallel to the longitudinal axis of the pump, and the pins extend axially into the openings, respectively. Furthermore, in normal operating conditions, each of the pins is spaced in its entirety from the stationary or orbital part of the pump to which the guide part is fixed and such that a radial clearance exists between each pin and the surface of the guide part that delimits the opening into which the pin extends. 
     According to another aspect of the present invention, there is provided a scroll pump that includes a scroll blade set including a stationary scroll blade fixed in the pump and an orbiting scroll blade juxtaposed with the stationary scroll blade in a radial direction of the pump such that the stationary and orbiting scroll blades are nested, an eccentric drive mechanism operatively connected to the orbiting scroll blade so as to cause the orbiting scroll blade to orbit about a longitudinal axis, a metallic bellows that angularly synchronizes the orbiting and stationary scroll blades, and angular synchronization back-up means for maintaining an angular synchronization between the orbiting and stationary scroll blades in the event that a load on the orbiting scroll blade exceeds a rated drive load of the scroll pump. 
     The metallic bellows has first and second ends. The second end of the bellows is fixed in the pump, and the orbiting scroll blade is fixed to the metallic bellows at the first end of the metallic bellows. The angular synchronization back-up means comprises a plurality of pins, and a guide part in which a plurality of openings open in directions parallel to the longitudinal axis of the pump are defined. The pins are fixed relative to one of the stationary and orbiting scroll blades in the pump, the guide part in which the openings are defined is fixed relative to the other of the stationary and orbiting scroll blades in the pump, and the pins extend axially in the directions parallel to the longitudinal axis into the openings, respectively. 
     According to still another aspect of the present invention, there is provided a scroll pump that includes a scroll blade set including a stationary scroll blade fixed in the pump and an orbiting scroll blade juxtaposed with the stationary scroll blade in a radial direction of the pump such that the stationary and orbiting scroll blades are nested, an eccentric drive mechanism operatively connected to the orbiting scroll blade so as to cause the orbiting scroll blade to orbit about a longitudinal axis, a metallic bellows as the only means of angularly synchronizing the orbiting and stationary scroll blades, and back-up means for preventing damage to the pump if the metallic bellows should fail. 
     The metallic bellows has first and second ends. The second end of the bellows is fixed in the pump, and the orbiting scroll blade is fixed to the metallic bellows at the first end of the metallic bellows. The back-up means comprises a plurality of pins, and a guide part in which a plurality of openings open in directions parallel to the longitudinal axis of the pump are defined. The pins are fixed relative to one of the stationary and orbiting scroll blades in the pump, the guide part in which the openings are defined is fixed relative to the other of the stationary and orbiting scroll blades in the pump, and the pins extend axially in the directions parallel to the longitudinal axis into the openings, respectively. 
    
    
     
       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 simplified version of a scroll pump according to the present invention; 
         FIG. 2  is a cross-sectional view of selected parts of the scroll pump taken along line II-II′ of FIG. 
         FIG. 3  is an enlarged view of a portion of the scroll pump shown in  FIG. 1 , again in a simplified form; 
         FIG. 4  is a schematic cross-sectional view, taken in the same direction as that of  FIG. 2 , of part of the back-up system of the scroll pump according to the present invention; 
         FIG. 5  is a schematic cross-sectional view similar to the of  FIG. 4  but of part of another example of the back-up system of the scroll pump according to the present invention; and 
         FIG. 6  is a schematic cross-sectional view similar to the of  FIG. 4  but of part of still another example of the back-up system of the scroll pump according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     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 ease of understanding. Also, like numerals and reference characters are used to designate like elements throughout the drawings. 
     Furthermore, spatially relative terms, such as “front” and “back” are used to describe an element&#39;s relationship to another element(s) as illustrated in the figures. Thus, the spatially relative terms may apply to orientations in use which differ from the orientation depicted in the figures. Obviously, though, all such spatially relative terms refer to the orientation shown in the drawings for ease of description and are not necessarily limiting as apparatus according to the invention can assume orientations different than those illustrated in the drawings when in use. 
     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. The term “pump” may refer to apparatus that drives, or raises or decreases the pressure of a fluid, etc. The term “fixed” or “coupled” may be used to describe a direct connection of two parts to one another in such a way that the parts can not move relative to one another or a connection of the parts through the intermediary of one or more additional parts in such a way that the parts can not move relative to each other. The term “normal” operation of the pump or “normal” loads on the orbiting plate scroll will be understood by the those skilled in the art to refer to the rated conditions or rated loads, i.e., which constitute the design specifications of the pump, and which are readily ascertainable in the real world and may be found in the manual or the like accompanying a scroll pump when it is sold. 
     Referring now to  FIG. 1 , a scroll pump  1  to which the present invention may be applied includes a housing (not shown), and a pump head assembly  200  and a motor  300  having a rotary output disposed in the housing. The pump head assembly  200  includes a frame  210 , a stationary plate scroll  220 , an orbiting plate scroll  230 , an eccentric drive mechanism  240 , an annular metallic bellows  250  and fasteners (to be described in more detail later on) fixing the stationary plate scroll  220  to the frame  210  and the annular metallic bellows  250  to both the frame  210  and the orbiting plate scroll  230 . 
     The frame  210  may be of one unitary piece, as shown in the figure, or may comprise several integral parts that are fixed to one another. 
     The stationary plate scroll  220  is fixed to the frame  210 . The stationary plate scroll  220  has a front side  220 F and a back side  220 B, and comprises a stationary scroll blade  221  at its front side  220 F. The orbiting plate scroll  230  has a front side  230 F and a back side  230 B, and comprises an orbiting scroll blade  231 , at its front side. The stationary scroll blade  221  and the orbiting scroll blade  231  are nested with a clearance and predetermined relative angular positioning such that a pocket or pockets is/are delimited by and between the stationary and orbiting scroll blades  221  and  231 . In this respect, portions of the stationary scroll blade  221  and the orbiting scroll blade  231  need not contact each other to seal the pocket(s). Rather, minute radial clearances between portions of the stationary scroll blade  221  and the orbiting scroll blade  231  create a seal sufficient for forming a satisfactory pocket(s) and prevent excessive noise which would otherwise be produced if the stationary scroll blade  221  and orbiting scroll blade  231  were contacting each other. 
     The eccentric drive mechanism  240  includes a drive shaft  241  and bearings  246 . In this example, the drive shaft  241  is a crank shaft having a main portion  242  coupled to the motor  300  so as to be rotated by the motor about a longitudinal axis L of the scroll pump  1 , and a crank  243  whose central longitudinal axis is offset in a radial direction from the longitudinal axis L. Also, in this example, the main portion  242  of the crank shaft is supported by the frame  210  via one or more sets of the bearings  246  so as to be rotatable relative to the frame  210 . The orbiting plate scroll  230  is mounted to the crank  243  via another set or sets of the bearings  246 . Thus, the orbiting plate scroll  230  is carried by crank  243  so as to orbit about the longitudinal axis L of the scroll pump  1  when the main portion  242  is rotated by the motor  300 , and the orbiting plate scroll  230  is supported by the crank  243  so as to be rotatable about the central longitudinal axis of the crank  243 . 
     During a normal operation of the scroll pump  1 , loads on the orbiting scroll blade  231  tend to cause the orbiting plate scroll  230  to rotate about the central longitudinal axis of the crank  243 . However, the annular metallic bellows  250  restrains the orbiting plate scroll  230  in such a way as to allow it to orbit about the longitudinal axis L of the scroll pump  1  while inhibiting its rotation about the central longitudinal axis of the crank  243 . 
     More specifically, the annular metallic bellows  250  has a first end  251  at which the annular metallic bellows  250  is fixed to the back side  230 B of the orbiting plate scroll  230  and a second end  252  at which the annular metallic bellows  250  is fixed to the frame  210 . In this respect, the annular metallic bellows  250  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 annular metallic bellows  250  remains fixed to the frame  210 . On the other hand, the annular metallic bellows  250  has a torsional stiffness that prevents the first end  251  of the annular metallic bellows  250  from rotating significantly about the central longitudinal axis of the annular metallic bellows  250 , i.e., from rotating significantly in its circumferential direction, while the second end  252  of the annular metallic bellows  250  remains fixed to the frame  210 . 
     In the pump head assembly  200  of the present invention, the specifications of the annular metallic bellows  250 , e.g., the wall thickness, etc., which impart the torsional stiffness to the annular metallic bellows  250  are designed such that the first end  251  of the annular metallic bellows  250  will not rotate more than a minimal amount in its circumferential direction under normal loads applied to the orbiting plate scroll  230 . 
     In this embodiment, the annular metallic bellows  250  is essentially the only means of providing the angular synchronization of the stationary scroll blade  221  and the orbiting scroll blade  231  during the normal operation of the scroll pump  1 . 
     Furthermore, not only does the annular metallic bellows  250  extend between the frame  210  and the back side  230 B of the orbiting plate scroll  230 , but the annular metallic bellows  250  also extends around a portion of the drive shaft  241  and the bearings  246  of the eccentric drive mechanism  240 . In this way, the annular metallic bellows  250  may also seal the bearings  246  and bearing surfaces from a space defined between the annular metallic bellows  250  and the frame  210  in the radial direction and which space may constitute a chamber C, e.g., a vacuum chamber of the scroll pump  1 , through which fluid worked by the scroll pump  1  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 annular metallic bellows  250 . 
     A back-up system for the annular metallic bellows  250  will now be described with reference to  FIGS. 1-4 . As is clear from the description above, the frame  210  and the stationary plate scroll  220  are a stationary part of the scroll pump  1 , and the orbiting plate scroll  230  is an orbiting part of the scroll pump  1 . 
     The back-up system consists of pins P integral with and fixed relative to one of the stationary and orbital parts, and a guide part  400  that is integral with and fixed relative to the other of the stationary and orbital parts. According to one aspect of the present invention, the back-up system is a non-contacting back-up system meaning that there is no contact between the pins P and the guide part  400  during normal operation of the scroll pump  1 . Therefore, no particles are created by a wearing away of such parts which would otherwise have the potential to contaminate the fluid being worked by the scroll pump  1 , and reduce the useful life of the backup system and hence the scroll pump  1  as well. 
     The pins P extend axially in directions parallel to the longitudinal axis L of the scroll pump  1 , and the guide part  400  defines openings  410  open in and also extending axially in directions parallel to the longitudinal axis L of the scroll pump  1 . The pins P, as best seen in  FIG. 3 , extend axially into the openings  410 , respectively, from locations outside the openings  410 . Also, as shown in the figures, the openings  410  may open radially inwardly toward the longitudinal axis L of the scroll pump  1 . 
     Also, in the example illustrated in  FIGS. 1-4 , the pins P extend from the orbital part of the scroll pump  1 , and the guide part  400  is integral with and fixed relative to the stationary part of the scroll pump  1 . More specifically, the pins P are integral with the orbiting plate scroll  230  and extend axially from the back side  230 B thereof in a direction away from the orbiting scroll blade  231 , and the guide part  400  is integral with the frame  210 . In this respect, the guide part  400  may be unitary with the frame  210  or may be a separate part that is integrated with the frame  210 . In this example, the guide part  400  is an annular member that is seated in a face of the frame  210  and fixed to the frame  210 . 
     In another example, the pins P extend axially from the orbiting plate scroll  230  at the front side  230 F thereof, and the guide part  400  is integral with and fixed relative to the stationary plate scroll  220 . 
       FIGS. 2 and 4  show the non-contacting state of the pins P and guide part  400 , which is the state that exists when the scroll pump  1  is operating normally or at rest. Note, in this state, the orbiting plate scroll  230  is in its eccentric (radially offset) position relative to the stationary plate scroll  220 . 
     Referring to  FIG. 4 , in this example, each of the pins P fixed relative to the orbital part of the scroll pump  1  is spaced from the stationary part of the scroll pump  1  and in this respect, a radial clearance C r  exists between each pin P and the surface of the guide part  400  that delimits the opening  410  into which the pin P extends. Furthermore, the geometric axial center C p  of each of the pins P is offset from the geometric axial center C o  of the opening  410  into which the pin P extends. Therefore, the geometric axial center C p  of the pin P traverses an orbit (shown by the dashed lines) about the geometric axial center C o  of the opening  410  as the orbiting scroll blade  231  is being driven by the eccentric drive mechanism  240 . The clearance C r  between the pins P and the surfaces of the guide part  400  that delimit the openings  410  is critical for reasons that follow. 
     When an abnormal operation of the scroll pump  1  occurs, the pins P will contact the surfaces delimiting the openings  410  of the guide part  400  into which the pins P extend. The abnormal condition of the scroll pump  1  may be a case in which the annular metallic bellows  250  fails. In this case, the guide part  400  keeps the orbiting plate scroll  230  from rotating excessively about the central axis of the crank  243  as it continues to orbit about the central longitudinal axis L of the scroll pump  1 . This means that the clearance C r  at a minimum prevents the orbiting scroll blade  231  from colliding so violently with the stationary scroll blade  221  as to damage the scroll blade(s)  221 ,  231  before the scroll pump  1  can be shut down. 
     However, an abnormal operation may also refer to a situation in which a load exerted on the orbiting scroll blade  231  is so great (e.g., greater than a rated load of the scroll pump  1 ) as to overcome the torsional resistance offered by the annular metallic bellows  250  at the first end  251  thereof but without the annular metallic bellows  250  failing. In this case, the contours of the pins P, the surfaces of the guide part  400  delimiting the openings  410 , and the clearance C r  are such that the surfaces of the guide part  400  guide the pins P therealong and keep the orbiting plate scroll  230  from rotating excessively about the central axis of the crank  243  as it continues to orbit about the central longitudinal axis L of the scroll pump  1 . Moreover, in this case, the clearance C r  is small enough to prevent overloading the annular metallic bellows  250  and radial contact between the stationary scroll blade  221  and orbiting scroll blade  231 . 
     In these respects, it should be noted that radial contact between the stationary and orbiting scroll blades  221  and  231  can occur at less than the rated load of the scroll pump  1  as a result of differential thermal expansion and manufacturing errors. Furthermore, the loads produced by radial contact between the stationary and orbiting scroll blades  221  and  231  are cyclic by nature, the contact occurring at least once per revolution. Therefore, these loads have the potential to fatigue the annular metallic bellows  250 . 
     According to an aspect of the present invention, the clearance C r  is designed to allow for a rotation of the orbiting plate scroll  230  (about its central axis) relative to the stationary plate scroll  220  but prevent the scroll blades  221  and  231  of the stationary and orbiting plate scrolls  220  and  230  from contacting each other and additionally limit the torsion induced stress in the annular metallic bellows  250  in order to prevent fatigue or other damage to the annular metallic bellows  250 . 
     Generally speaking, to provide the proper clearance C r , the width W o  of the opening  410  is set to be the sum of the width WP of the pin P plus the width W of the orbit of the geometric axial center C P  of the pin P plus a predetermined value, 2*C r  (all widths being in the circumferential direction of the guide part  400  in this case). 
     In an example of this embodiment, the clearance C r  is preferably in the range of 0.006″ to 0.070″ and more preferably, is substantially equal to 0.006″. 
     This range was arrived at based on the following considerations. As should be clear from the explanation above, the geometry of the pins P and openings  410  in the guide part  400  should allow for some rotation of the orbiting plate scroll  230  relative to the stationary plate scroll  220  during normal operation. Also, the geometry must prevent excessive rotation of the orbiting plate scroll  230  during an abnormal operation. 
     The amount of allowable rotation may be determined by the minimum radial clearance, MRC, between the stationary scroll blade  221  and the orbiting scroll blade  231  and the pitch P of the scroll blades  221  and  231  (distance between successive sections or so-called “wraps” of a blade that traverse 360°). The maximum allowable rotation, measured in degrees (dO), is given by the equation: dO&lt;MRC/(P/360). Typical values for dO are on the order of a couple of degrees depending on the MRC, pitch P, differential thermal expansion, and manufacturing tolerances. A maximum allowable rotation, dO, less than MRC/(P/360) can prevent contact of the stationary and orbiting scroll blades  221  and  231 . An even smaller value for dO may be required to prevent excessive rotation of the orbiting end  251  of the annular metallic bellows  250  relative to the fixed end  252  that will lead to excessive stress and failure within the annular metallic bellows  250 . 
     Once the maximum allowable rotation is determined, a window for clearances C r  between the pin P and (the surface defining opening  410  of) the guide part  400  can be estimated. 
     The maximum clearance C r  between the pin P and the guide part  400  should be no greater than Tan(dO) multiplied by one half of the bolt circle diameter (BCD) of the pins. For dO of 1 degree and a bolt circle diameter of 8″ for the pins P, the clearance between each pin P and the associated surface of the guide part  400  defining opening  410  should be no greater than 0.070″=4″ *Tan (1 degree). That is, the clearance will need to be less than 0.070″ to prevent contact between the stationary scroll blade  221  and the orbiting scroll blade  221  when abnormal operation that brings the pins P into contact with the guide part  400  occurs. 
     On the other hand, as mentioned above, there is a minimum clearance that keeps the pins P from contacting the guide part  400  during normal operation when the maximum allowable rotation of the orbiting plate scroll  230  relative to the stationary plate scroll  220  occurs. The effects of differential temperature, thermal expansion rates of the pins P and material of the guide part  400 , bolt circle diameter of the pins P, and manufacturing tolerances, will determine the minimum clearance. 
     On these bases, and again with reference to  FIG. 4 , the width W o  of the opening  410  is set to be the sum of the width W p  of the pin P, plus the width W of the orbit of the geometric center C p  of the pin P, plus a predetermined value 2*C r , the predetermined value being less than BCD*Tan (MRC/(Pitch/360)). 
     In an example of a scroll pump  1  according to the present invention, using the equations above, a window of values which will provide an acceptable clearance C r  was calculated to be in the range of approximately 0.006″ to approximately 0.070″. It should be clear, though, it is best to select a value close to the minimum value, i.e., to a value substantially equal to approximately 0.006″ in this example to prevent the annular metallic bellows  250  from being over rotated and hence over stressed especially in a cyclic pattern leading to fatigue failure. 
     Referring still to the example shown in  FIG. 4 , the pins P and openings  410  each have a generally rectangular cross section (in a plane perpendicular to the longitudinal axis L). However, the pins P and openings  410  may have other polygonal cross-sectional shapes, such as trapezoidal. 
       FIG. 5  schematically shows another example of the back-up system of the scroll pump  1  according to the present invention. In this example, the pins P and the surfaces of the guide part  400  that define the openings  410  have corresponding profiles of gear teeth, e.g., each has an involute type of gear tooth profile. 
       FIG. 6  schematically shows another example of the back-up system of the scroll pump  1  according to the present invention. In this example, the guide part  400  is integral with and fixed relative to the orbiting plate scroll  230  at the back side  230 B thereof, whereas the pins P extend from the frame  210  into the openings  410 , respectively. Alternatively, the guide part  400  may be integral with and fixed relative to the orbiting plate scroll  230  at the front side  230 F thereof, whereas the pins P extend axially from the stationary plate scroll  220  into the openings  410 , respectively. 
     Also, in the example shown in  FIG. 6 , the pins P and the openings  410  have round cross sections in a plane perpendicular to the longitudinal axis L. Further, in this respect, as shown in the figure, the cross-sections of the openings  410  are closed unlike the openings  410  in the example shown in  FIG. 4 . It is also clear that other examples of a scroll pump  1  in accordance with the present invention can employ other combinations of individual features described above with reference to  FIGS. 4-6 . For example, the back-up system may have round pins P as shown in and described with reference to  FIG. 6  extending from the frame  210  as described with reference to  FIG. 4 , and the openings  410  in the guide part  400  may have semi-circular cross-sectional shapes which open radially inwardly. 
     That is, 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.