Abstract:
A flexure mount for economically producing pure translational motion with no arcuate or error motion in the vertical direction utilizing alignment pins and parts reducing structures including monolithic springs. A low profile embodiment utilizes a compound monolithic spring. The flexure mount may be used to translate a mirror or retroreflector in a purely linear direction of precisely controlled and known distance, useful in myriad interferometer applications including spectroscopy.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to provisional U.S. application Ser. No. 61/081,547, filed on Jul. 17, 2008, the entirety of which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention is in the field of mechanisms for economically producing pure translational motion with no arcuate or error motion in the vertical direction. Such pure translational motion is critical for precision instrumentation applications. One such application is the movement of optical assemblies such as retroreflectors in interferometer/spectroscopy applications. 
       BACKGROUND OF THE INVENTION 
       [0003]    Fourier transform infrared (“FTIR”) spectrometers are well known in the art. Michelson interferometers function by splitting a beam of electromagnetic radiation into two separate beams via a beam splitter. Each beam travels along its own path, e.g. a reference path of fixed length and a measurement path of variable length. A reflecting element, such as a retroreflector, is placed in the path of each beam and returns them both to the beam splitter. The beams are there recombined into a single exit beam. The variable path length causes the combined exit beam to be amplitude modulated due to interference between the fixed and variable length beams. By analyzing the exit beam, the spectrum or intensity of the input radiation can, after suitable calibration, be derived as a function of frequency. 
         [0004]    When the above interferometer is employed in a FTIR spectrometer, the exit beam is focused upon a detector. If a sample is placed such that the modulated beam passes through it prior to impinging upon the detector, the analysis performed can determine the absorption spectrum of the sample. The sample may also be placed otherwise in the arrangement to obtain other characteristics. 
         [0005]    Where the path length through the interferometer is varied by moving a retroreflecting element along the axis of the beam, the maximum resolution attainable with the instrument is proportional to the maximum path difference that can be produced. Because Michelson interferometers rely upon the interference from recombination of the two beams, a quality factor of such a device is the degree to which the optical elements remain aligned during path-length variation. Thus, translational displacement of the mirror must be extremely accurate. That is, the mirror must in most cases remain aligned to within a small fraction of the wavelength of incident light, over several centimeters of translation. Any deviation from pure translation may cause slight tilting of a plane mirror, leading to distortion in the detected beam. Substitution of cube-corner and cats-eye retroreflectors for plane mirrors can essentially eliminate such tilting distortion problems; but with certain inherent drawbacks. 
         [0006]    Precision bearings may be used to maintain alignment. In addition, monitoring and controlling alignment with analysis of feedback and subsequent repositioning has been utilized to maintain mirror alignment. Systems relying on either such solution are difficult to design, relatively large, expensive and present maintenance issues. 
         [0007]    Other efforts have been made to develop interferometers that do not require precision bearings or control systems. Tiltable assemblies consisting of a pair of parallel, confronting mirrors have been suggested as replacements to the longitudinally displaced retroreflector. U.S. Pat. No. 4,915,502, issued on Apr. 10, 1990, teaches a twin-arm interferometer spectrometer having a tiltable assembly by which the optical path lengths of the two beams are varied simultaneously. A much smaller rotation, relative to retroreflectors, of the paired mirrors results in the path difference. This design reduces sensitivity to linear movement of the optical element; moreover, rotating bearings are generally easier and less expensive to produce than are longitudinal or linear ones. 
         [0008]    U.S. Pat. No. 4,383,762, issued on May 17, 1983 and provides a two-beam interferometer for FTIR spectroscopy in which a pendulum arm holds moving cube corner retroreflectors. The movement, i.e. arcuate oscillation, results in accurate changes in path-length produced in a smooth motion. The retroreflectors render the system unaffected by the tilt and avoids the disadvantages for FTIR spectroscopy that are inherent in the deviation from strict linearity from the pendulous motion. 
         [0009]    So-called “porch swing” mounting arrangements are also known in the art. Here, structural elements are supported at four pivot points and form a parallelogram by which a mirror undergoes pure translation along an axis. The extremely high machining tolerances required of such an arrangement and related issue of assembling same, result in high costs of both manufacture and maintenance. In addition, such pure translation flexure mounts are not typically useful for the relatively large displacements necessary for high resolution applications. The need for greater displacement can be achieved, but primarily through great cost of highly engineered precision instrumentation. 
         [0010]    Over and above the issues raised above, the mirror-supporting structure must be isolated to the greatest possible degree from extraneous forces which would tend to produce distortions of the structure. Such forces and resultant distortions introduce inaccuracies into the optical measurements. The forces may arise from vibrational effects from the environment and can be rotational or translational in nature. A similarly pervasive issue concerns thermal and mechanical forces. Needless to say, considerations of weight, size, facility of use, efficiency, manufacturing cost and feasibility are also of primary importance. 
         [0011]    Accordingly, it would be desirable to provide an optical assembly comprising a flexure mount with pure translation over a sufficiently large displacement at a reasonable cost of manufacture and maintenance. It is also desirable that the optical assembly be isolated from extraneous forces tending to produce optical distortions. 
       SUMMARY OF THE INVENTION 
       [0012]    Accordingly, it is a broad object of the invention to provide a precision instrument flexure mount comprising a base, an actuator having a fixed relationship to the base and a frame mounted on the base. The flexure mount has two base monolithic springs and two carriage monolithic springs, each spring having a cross piece and two vertical pieces with bottom ends. A plurality of transverse members is also provided. Each transverse member is fastened to a top frame portion with at least a portion of one spring cross piece held therebetween. The bottom end of each vertical piece of the carriage springs is fastened between a connection member and a carriage member while the bottom end of each vertical piece of the base springs is fastened between a connection member and the base. A translation arm is attached adjacent a first end to the actuator and adjacent a second end to a precision instrument element. A central portion of the translation arm extends through the frame, the central portion attached to the carriage member. The actuator imparts a force on the arm, and the frame functions such that translation of the arm through the frame is constrained to one orthogonal axis. 
         [0013]    Stiffening members may be disposed over a central portion of the spring vertical pieces, dividing the spring vertical pieces into two spring elements. 
         [0014]    In a preferred embodiment of the present invention, an alignment system is provided. The alignment system includes a plurality of pin holes in one or more monolithic springs. A plurality of pin receptacles is provided in each one of either the transverse member or top frame portion; each one of either the carriage connection member or the carriage member; and each one of either the base connection member or the base. Finally, a plurality of alignment pins is provided on the other of either the transverse member or top frame portion; the other of either the carriage connection member or the carriage member; and the other of either the base connection member or the base. Each alignment pin is in registration with one pin hole and one pin receptacle, enabling precision assembly of the frame. 
         [0015]    The assembly alignment system may also be applied to the stiffening member structure with a plurality of alignment pins in the one of either the first stiffening member or second stiffening member, and a plurality of pin receptacles in the other stiffening member. Each alignment pin in registration with one pin hole and one pin receptacle, enabling precision assembly of the stiffening members. 
         [0016]    Another object of the invention is to provide a novel precision instrument flexure mount having a low profile. The low-profile frame having a base, an actuator having a fixed relationship to the base and a frame mounted on the base. The frame comprising two compound monolithic springs, each spring having a cross piece, two vertical pieces with bottom ends and a spring central piece with a bottom end. The frame further has a plurality of transverse members, each transverse member is fastened to a top frame portion with at least a portion of one spring cross piece held therebetween. The bottom end of the spring central piece is fastened between a carriage connection member and a carriage member while the bottom end of each vertical piece is fastened between a base connection member and the base. A translation arm is attached adjacent a first end to the actuator and adjacent a second end to a precision instrument element, a central portion of the translation arm extends through the frame and is attached to the carriage member, the actuator imparting a force on the arm, whereby translation of the arm through the frame is constrained to one orthogonal axis. The spring central piece may have a window through which the translation arm extends. 
         [0017]    The stiffening members and alignment systems described previously may also be associated with the compound monolithic spring, including the central spring portion thereof. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0018]      FIG. 1  is a diagram showing how radiation is reflected in a prior art Michelson interferometer; 
           [0019]      FIG. 2  is a perspective view of an interferometer having a monolithic optical assembly; 
           [0020]      FIG. 3  is a perspective view of flexure mount for producing pure translational motion; 
           [0021]      FIG. 4  is a side view of a flexure mount for producing pure translational motion; 
           [0022]      FIG. 5  is a side view of a monolithing spring used in a flexure mount of a preferred embodiment of the present invention; 
           [0023]      FIG. 6  is an exploded perspective view of a preferred embodiment of a flexure mount for producing pure translational motion; 
           [0024]      FIG. 7  is a perspective view of a low profile flexure mount for producing pure translational motion; 
           [0025]      FIG. 8  is an exploded perspective view of a low profile flexure mount for producing pure translational motion; 
           [0026]      FIG. 9  is a side view of a monolithic spring for use in a low profile flexure mount; 
           [0027]      FIG. 10  is a perspective view of a stressed monolithic spring for use in a low profile flexure mount; 
           [0028]      FIG. 11  is a perspective view of translation transmission structure used in a flexure mount for producing pure translational motion; 
           [0029]      FIG. 12  is an end view of a flexure mount for producing pure translational motion; 
           [0030]      FIG. 13  is a perspective exploded view of a preferred embodiment of a spring arrangement; 
           [0031]      FIG. 14  is a side view of a preferred embodiment of a spring arrangement; 
           [0032]      FIG. 14A  is a detail of  FIG. 14 ; and 
           [0033]      FIG. 15  is a perspective exploded view of a preferred embodiment of a spring arrangement. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0034]    Referring to  FIG. 1 , the general principals of a standard Michelson interferometer are shown. The Michelson interferometer has a radiation source  10  which sends a single radiation beam  20  towards beamsplitter  30  which is situated at an angle to two mirrors, a fixed mirror  40  and a movable mirror  50 . Radiation beam  20  is partially reflected toward fixed mirror  40  in the form of radiation beam  22 , and is partially translated through beamsplitter  30  towards movable mirror  50  as radiation beam  24 . Beam  22  is then reflected off of fixed mirror  40 , back towards beamsplitter  30 , where it is once again partially split, sending some radiation  25  back towards source  10 , and some radiation  26  toward detector  60 . Similarly, beam  24  reflects off of movable mirror  50  and is reflected back toward beamsplitter  30 . Here also, beam  24  is again split, sending some radiation back to source  10  and other radiation  26  toward detector  60 . 
         [0035]    Detector  60  measures the interference between the two radiation beams emanating from the single radiation source. These beams have, by design, traveled different distances (optical path lengths), which creates the fringe effect which is visible and measurable to detector  60 . 
         [0036]      FIG. 2  shows the lay out and component structure of a Michelson interferometer of the prior art, e.g. U.S. Pat. No. 6,141,101 to Bleier, herein incorporated by reference.  FIG. 2  shows interferometer  100 , and includes a radiation source  110 , a beamsplitter  130 , a movable reflecting assembly  150 , a fixed reflecting assembly  140  and a detector  142 . Radiation source  110  is mounted in a secure position by mounting assembly  112 . With radiation source  110  in mounting assembly  112 , radiation beam  120  is alignable along a path which will fix the direction of the beam at the appropriate angle to beamsplitter  130 . 
         [0037]    Radiation source  110  can be collimated white light for general interferometry applications, such as distance measurement calculation, or even a single collimated radiation intensity laser light source. 
         [0038]    Movable reflecting assembly  150  utilizes a hollow corner-cube retroreflector  152 . The hollow corner-cube retroreflector  152  could be made in accordance with the disclosure of U.S. Pat. No. 3,663,084 to Lipkins, herein incorporated by reference. 
         [0039]    Retroreflector  152  is mounted to a movable base assembly  144 , which assembly allows for adjustment of the location of retroreflector  152  in a line along the path of beam  120 . The displacement of assembly  144  is adjustable through use of adjusting knob  146 , but other means of moving assembly  144  are also anticipated by the invention, including such means that might allow for continuous, uniform movement of assembly  144 . It is also possible that the manor of mounting retroreflector  152  to assembly  144  might be made in accordance with the structure described in U.S. Pat. No. 5,335,111 to Bleier, herein incorporated by reference. 
         [0040]    The use of retroreflector  152  as movable reflecting assembly  150  allows for any orientation of retroreflector  152 , as long as the reflecting surfaces of the retroreflector are maintained at the appropriate angle to the direction of incoming beam  120  after it passes through beamsplitter  130  and also as long as edge portions of the retroreflector mirrors do not clip a portion of beam  120 . 
         [0041]    From the foregoing, the length of the light path  22  is fixed and known while the length of light path  24  may be varied. The variation of the length of light path  24  is, of course, critical to the operation of the interferometer, as is knowing the length as precisely as possible. 
         [0042]      FIG. 3  illustrates a variable path length assembly  151  for displacing retroreflector  152  a precisely known distance in as perfectly linear a direction as possible, i.e. along a single straight-line axis. Retroreflector  152  is attached to a translation voice coil actuator  156  through translation arm  154  and translation bracket  158 . Voice coil actuator  156  contains standard means for causing translation bracket  158 , and thus translation arm  156  and retroreflector  152 , to move a precisely controlled and known distance. Translation arm  156  is also supported by bridge  180 . Bridge  180  is attached at its bottom end to carriage member  178 , further described below. Alternatively, carriage member  178  may be formed integrally with bridge  180 . 
         [0043]    Base  160  of variable path length assembly  151  supports frame  200  and translation voice coil actuator  156 . Attachment holes  162  are used to attach variable path length assembly  151  to other components of the device of which the assembly  151  is a component. Bottom frame member  164  may be formed integrally with base  160  or be attached thereto utilizing holes  166 . Bottom frame member  164  is provided with frame connection flange  168  to which the remainder of the frame  200  is attached by way of connection member  170 . 
         [0044]    Alignment and stability of the frame  200  are very important, as is ease of assembly from parts that may be formed with fewer machining steps. To the extent that the total number of parts of frame  200  may be reduced and that fabrication of these parts utilizing more mass production techniques is possible, significant economical savings are achieved. Frame  200  may be assembled using alignment pins  192  in cooperation with alignment pin holes  188  and alignment pin receptacles  196 . Assembly is completed with fasteners  198  which cooperate with fastener receptacles  196  and extend through fastener holes  190  in spring  182 . Alignment pins  192 , pin holes  188 , pin receptacles  194 , fasteners  198 , fastener receptacles  196 , fastener holes  190  and fastener tap holes  196 ′ are also used in attaching frame  200  to base  160  via frame connection flange  168 . These alignment and assembly elements may be utilized in each embodiment of the present invention and are best illustrated in  FIG. 6 . Such an arrangement of parts can enable looser tolerances of mass production to still result in a precision instrument. 
         [0045]    As seen in  FIG. 8 , it is possible to achieve many aspects of the present invention without the alignment pin structures of  FIG. 6 ; the fastener structures are primarily relied upon. Alignment assembly rods (not shown) may be used during assembly of a frame without alignment pins. One or more assembly rods are inserted through all structures that will be fastened together while a fastener  198  in attached through a still available set of structures. Once two or three fasteners are in place, alignment rods are not as necessary. 
         [0046]    Frame  200  is generally in the form of a parallelepiped with angles on two faces of the parallelepiped variable, i.e. the face shown in  FIG. 4  and its opposing face, while angles on the four remaining faces are invariant, e.g. 90°. This arrangement is enabled primarily through the placement of springs  182  which allow relative displacement of a top face  202  of frame  200  relative to the base  160 . Top face  202  of frame  200  is the square defined by top frame portions  176 ,  177  and transverse frame members  174 . The springs  182  may have their central portions clad in stiffening frame members  172 ,  184 . The stiffening frame members  172 ,  184  may have their alignment optimized using pin holes  188 , pins  192  and pin receptacles  194  and secured using fasteners  198 , fastener holes  190 , fastener receptacles  196  and fastener tap holes  196 ′. Stiffening frame member  172  receives the head of fastener  198  and stiffening frame member  184  comprises the tap holes for receiving the fastener  198 . 
         [0047]    In each embodiment described herein, spring stiffening members are optional. The entirety of the spring may be used as a single element instead of dividing it into two smaller elements by way of stiffeners. 
         [0048]    Transverse frame members  174  and top frame end portions  176  are similarly aligned adjacent one end of spring  182  using pin holes  188 , pins  192  and pin receptacles  194  and secured using fasteners  198 , fastener holes  190 , fastener receptacles  196  and fastener through bores  196 ″. Fastener through bores  196 ″ are provided in top frame end portion  176 , such that fastener  198  passes through top frame end portion  176  and is tightened to tap hole  196 ′ in top frame central portion  177 . A bottom end of spring  182  is secured to frame connection flange  168  or carriage member  178  via connection member  170 . Fasteners  198  may be of varying length, including a sufficient length to connect transverse frame members  174  to multiple top frame portions  176  and  177  while passing through more than one spring  182 . No mechanical connection exists between the carriage member  178  and the bottom frame  164  except through the other elements of frame  200 . 
         [0049]    Thus, frame  200  is attached to base  160  upon which resides voice coil actuator  156 . As seen in  FIGS. 11 and 12 , voice coil actuator  156  imparts a force through the driven voice coil  322  upon translation bracket  158 , translation arm  154  and retroreflector  152 . Each carriage member  178  is connected to translation bracket  158  and translation arm  154  by bridge  180 . Each carriage member  178  is attached by carriage attachment point  179  to bridge attachment point  181  by a fastener  198 . 
         [0050]    In accordance with known principles of flexure design, the compound spring of frame  200  will offset any reduction in height of frame  200 , i.e. the distance between top face  202  and base  160 , by an equal and opposite ‘lifting’ of carriage member  178  and, thus, translation arm  154 . Thus, translation arm  154  and retroreflector  152  can only move parallel to base  160  and the change in height relative to base  160  is zero. Put another way, curvilinear motion between retroreflector  152  and  160  is eliminated as completely as possible. 
         [0051]    Obviously, the portions of spring  182  that are clamped between frame elements, e.g.  178 / 184  or  174 / 176 , do not act as springs. Only the exposed portions of spring  182  function as springs, e.g. between stiffening frame members  172 ,  184  and the transverse frame member  174  or connection member  170 . This exposed portion of spring  182  can be referred to as the flexure gap  148 . In the arrangement presented herein, the spring constant for each spring element must be as close to equal as possible. Any inequality or deviation from a desired constant value could adversely affect the precise planar relationship desired between top frame face  202  and base  160  and/or the equal ‘lifting’ of retroreflector  152 . In the arrangements of  FIGS. 3 ,  4  and  6 , there are sixteen spring elements and thirty-two flexure gaps, i.e. one on each side of each spring element. Control over the size of the thirty-two flexure gaps  148  is a key tolerance issue. Deviations in the size of the flexure gap  148  can cause a reduction in the purity of the translational motion enabled by the frame  200 . Connection members  170  cause particularly difficult tolerance control issues because eight such members are used in  FIG. 3  each influencing the size of two flexure gaps  148 . 
         [0052]      FIG. 6  is an exploded view of a preferred embodiment of frame  200 . Frame  201  utilizes monolithic springs  183  having at least one spring cross piece  185  and two vertical pieces  186 . Cross pieces  185  may be utilized across the top and bottom of spring  183 . The eight independent connection members  170  are replaced by four cross connection members  171 . Besides the general reduction in necessary parts, the monolithic springs  183  and cross connection members  171  greatly reduce the tolerance concerns of the connection members. Combined with the alignment pin arrangements, among other factors, tight control of the size of the flexure gaps  148  is achieved in an economical manner. 
         [0053]    A single carriage member  178  is also enabled in the preferred embodiment, further aiding in the size control of flexure gaps  148  as well as the all-around reduced number of parts. In addition, bridge  180  may be replaced by the simpler post  314 , as shown in  FIG. 8 , connecting the carriage member  178  to translation arm  154  and/or translation bracket  158 . 
         [0054]    An alternative embodiment of the present invention is disclosed in  FIGS. 7-10 . Low profile frame  300  brings carriage member and the associated spring portions and stiffener elements to an interior portion of the frame and permits significant reduction in the overall size of the assembly  151 . Low profile frame  300  is enabled through the use of compound monolithic spring  312  having a spring central piece  304  with a window  306 . Central piece stiffening member  302  is also provided with a window  308  and performs the same function as stiffening member  172 . A single carriage member  178  is centered in the frame  300  and attached to the lower end of spring central piece by connection member  310 . 
         [0055]    The compound monolithic spring  312  eliminates the need for two monolithic springs  183 . The typical result of part reduction and elimination of degrees of freedom to tolerance factors is achieved by this elimination. In addition, each set of two spring elements is merged into a single spring element, i.e. along the top of spring central piece  304 . This single spring element is exactly twice the width of the single spring elements along the top of each spring vertical piece  186  of spring  183 . Thus, the spring constants are the same for the monolithic spring  183  and the compound monolithic spring  312 . 
         [0056]    Windows  306  and  308  may be sized to accommodate only translation arm  154 . Alternatively, windows  306  and  308  may be sized to accommodate some or all of translation bracket  154  and/or some or all of retroreflector  152  to further reduce the profile offered by frame  300 . In addition, the low profile frame  300  requires only twelve springs and twenty four flexure gaps  148 . Some of these flexure gaps share a single element defining one side thereof, i.e. two transverse frame member  174  and top frame member  316  define one side of half of the flexure gaps  148 . 
         [0057]    Bridge  180  may be replaced by the simpler post  314  connecting the carriage member  178  to translation arm  154  and/or translation bracket  158 . 
         [0058]    The alignment pin  192  arrangement may also be used in conjunction with some or all assembly of the low profile frame  300 . Though the drastic reduction in the number of parts may completely obviate the need for using alignment pins  192 . 
         [0059]      FIG. 13  is an exploded view of an alternative embodiment utilizing multiple monolithic springs  183 . Compound monolithic spring  312  could also be utilized in this manner. A plurality of monolithic springs  183  are separated by spacers  320 ,  322  spanning the non-flexing areas of the monolithic springs  183 . Stiffening frame members  172 ,  184 ,  302  and other elements of the frame, e.g. transverse frame member  174  and top frame member  316 , retain the spacers  320 ,  322  in place in the same way that the monolithic springs  283 ,  312  are typically held in place. Once assembled in the full frame, as best seen in detail  FIG. 14A , flexure gap  148  is preferably coextensive with the areas not occupied by spacers  320 ,  322 . 
         [0060]    In a further alternative embodiment, as illustrated in  FIG. 15 , spacers  320  remains but spacer  322  is replaced with a viscoelastic damping material  328 . As shown, there are three monolithic springs  183 . No stiffening members  172 ,  184  are utilized in this alternative embodiment, as discussed previously. Thus, the entire vertical piece  186  of monolithic springs  183  act as flexural elements. When they are present, viscoelastic damping material  328 , which may be affixed adhesively, or by casting in place a viscoelastic compound material  328 , act to damp the motion of the flexural springs through shear or other damping, with either an unimportant or compensated-in-design effect on the stiffness characteristics of the flexural springs. 
         [0061]    When material  328  is absent, the resulting air space causes the monolithic springs to flex semi-independently. These flexings will be substantially identical if the assembly, facilitated by proper tolerances of the parts and self-fixturing enabled by the monolithic springs, is done accurately. When the flexings are identical, the stiffness of the individual springs add, and the accurate translational properties of the variable path length assembly  151  are preserved. By this method, it is possible to choose thicknesses of multiple monolithic springs  183  replicating the stiffness properties of designs with a single spring but with much reduced stress in the individual springs, and with increased stiffness of the assembly in directions orthogonal to the desired translation direction. 
         [0062]    When viscoelastic damping material  328  is provided, an advantage in control system stability is obtained, permitting more accurate linear trajectory of the mount and lower noise operation. Finally, it will be appreciated that a compound non-stiffened spring, with a viscoelastic damping embodiment option exists for the side-by-side flexure mount embodiment shown in  FIG. 7  by similar compounding of springs  312  therein, and other elements, with or without the inclusion of clamping and viscoelastic damping materials, in a manner similar to the method shown in  FIGS. 13-15 . 
         [0063]    It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the invention has been described with reference to various embodiments, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitations. Further, although the invention has been described herein with reference to particular means, materials and embodiments, the invention is not intended to be limited to the particulars disclosed herein; rather, the invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims. Those skilled in the art, having the benefit of the teachings of this specification, may achieve numerous modifications thereto and changes may be made without departing from the scope and spirit of the invention in its aspects.