Abstract:
In holographic recording, it is important to form stably an interference fringe between a reference beam and a signal beam in a holographic storage medium. To suppress factors degrading stability of the interference fringe, such as fluctuation of atmospheric air, position displacement of optical components and the like during propagation of the reference and signal beams, an optical pickup and an optical information recording/reproducing apparatus adopt an optical system structure providing a higher proportion of optical components shared by the reference and signal beams optical path than conventional optical system structure. To increase the proportion of shared optical components, the signal beam and the reference beam pass through the PBS prism as parallel beams and a concave lens is placed on a reference beam path just before the objective lens.

Description:
INCORPORATION BY REFERENCE 
       [0001]    The present application claims priority from U.S. Provisional Application Ser. No. 60/905,838 filed on Mar. 9, 2007, the content of which is hereby incorporated by reference into this application. 
       CROSS-REFERENCE TO RELATED APPLICATION 
       [0002]    The present application relates to subject matter described in application Ser. No. 12/038,174 filed on Feb. 27, 2008, entitled “OPTICAL PICKUP, OPTICAL INFORMATION RECORDING AND REPRODUCING APPARATUS AND METHOD FOR OPTICALLY RECORDING AND REPRODUCING INFORMATION” by Tatsuro IDE, Kenichi SHIMADA, Masahiko TAKAHASI, Takeshi SHIMANO, Kevin R. CURTIS and Ken E. ANDERSON, claiming priority from U.S. provisional application Ser. No. 60/905,837, filed on Mar. 9, 2007. The entire content of the related application is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    The present invention relates to an optical pickup for recording/reproducing information by utilizing holography technologies, an optical information reproducing apparatus and an optical information recording/reproducing apparatus both utilizing the optical pickup. 
         [0004]    Optical discs having a recording density of about 50 GB are now commercially available even for public use, which discs use blue-violet semiconductor laser beams and rely upon Blu-Ray Disc (BD) specifications, High Definition Digital Versatile Disc (HD DVD) specifications and the like. Now, optical discs that will have a capacity as large as a Hard Disc Drive (HDD) having a capacity of e.g., 100 GB to 1 TB are desired. 
         [0005]    However, in order to realize such an ultra high density of an optical disc, high density techniques of a new scheme is required which are different from conventional high density techniques which resort to a shorter wavelength and a high objective lens NA. 
         [0006]    Researches of next generation storage techniques are under progress, and holographic recording techniques have been paid attention. The holographic recording techniques are techniques of superposing in a recording medium a signal beam having information on page data two-dimensionally modulated by a spatial light modulator and a reference beam and causing refraction index modulation in the recording medium in accordance with an interference fringe formed upon superposition to thereby record information in the recording medium. 
         [0007]    For information reproduction, upon application of the reference beam used for recording to the recording medium, a diffraction beam is generated because holograms recorded in the recording medium function as diffraction grating. This diffraction beam is reproduced as the same beam as the recorded signal beam including phase information. 
         [0008]    The reproduced signal beam is detected two-dimensionally at high speed with an optical detector such as CMOS and CCD. According to the holographic recording techniques, by using one hologram, two-dimensional information can be recorded in an optical recording medium at a time and this information can be reproduced. Since a plurality of sets of page data can be written in a superposed manner in an area of a recording medium, it is possible to realize recording/reproducing information of a large capacity at high speed. 
         [0009]    Hologram recording techniques are described, for example, in JP-A-2004-272268 (Patent Document 1). This publication describes a so-called angle multiplex recording method by which a signal beam is converged to an optical information recording medium via a lens, at the same time a reference beam as a parallel beam is applied to be interfered with the signal beam and record a hologram, and while an incidence angle of the reference beam upon the optical information recording medium is changed, different page data is displayed on a spatial light modulator to perform multiplex recording. This publication also describes the techniques that a space between adjacent holograms can be made short by disposing an aperture or opening (spatial filter) at a beam waist of the signal beam converged by a lens so that recording density/capacity can be increased more than a conventional angle multiplex recording method. 
         [0010]    Technical Digest ODS (2006), MA1 (Non-Patent Document 1) by Ian Redmond describes that in reproducing information recorded in an optical information recording medium, a phase conjugate beam of a reference beam is used to dispose a photodetector for signal detection on the same side as other optical components relative to the optical information recording medium so that the apparatus can be made compact. 
       SUMMARY OF THE INVENTION 
       [0011]    In holographic recording, it is important to form stably an interference fringe, from the viewpoint of improving a recording quality. To this end, it is important to maintain constant an optical path length difference so as not to change the optical path length difference between a signal beam and a reference beam. If optical components shared by a signal beam optical path and a reference beam optical path have a large proportion, both the signal beam and reference beam have a similar change in an optical path length to be caused by fluctuation of atmospheric air, position displacement of optical components and the like during light propagation. It is therefore possible to cancel out the changes. However, as indicated by Non-Patent Document 1, in the structure of conventional optical system, a light beam emitted from a laser light source is split into a signal light beam and a reference light beam at an intermediate position of an optical path toward an optical information recording medium, and thereafter these light beams propagate a relatively long distance along different optical paths. This results in a large apparatus and a change in the optical path length difference between the signal beam and reference beam. 
         [0012]    The present invention aims to make compact the apparatus and improve a recording quality, and provides an optical system structure having a larger proportion of optical components shared by a signal light beam path and a reference light beam path than a conventional proportion, while a structure of adopting an angle multiplex recording method by applying a reference beam as a parallel beam to an information recording medium is adopted similarly to a conventional structure. 
         [0013]    The object of the present invention can be achieved, for example, by applying a reference beam and a signal beam to a PBS prism as generally parallel beams and disposing a concave lens in an optical path before an objective lens upon which the reference beam output from the PBS prism becomes incident. 
         [0014]    The proportion of optical components shared by a signal light beam path and a reference light beam path becomes larger than that of the conventional structure. This structure is effective for making compact the apparatus, and it is possible to mitigate a variation in an optical path length difference between a signal beam and a reference beam to be caused by fluctuation of atmospheric air, position displacement of optical components and the like during light propagation, resulting in an improved recording quality. 
         [0015]    These and other features, objects and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a schematic diagram showing a monocular system. 
           [0017]      FIG. 2  is a schematic diagram showing an optical system structure near an objective lens of an optical pickup. 
           [0018]      FIGS. 3A and 3B  are schematic diagrams showing an optical pickup according to an embodiment. 
           [0019]      FIGS. 4A and 4B  are schematic diagrams showing an optical pickup according to another embodiment. 
           [0020]      FIG. 5  is a schematic diagram showing the overall structure of an optical information recording/reproducing apparatus for recording/reproducing information. 
           [0021]      FIGS. 6A to 6C  are schematic diagrams illustrating recording/reproducing operation flows of the optical information recording/reproducing apparatus. 
           [0022]      FIG. 7  is a schematic diagram showing an optical pickup according to an embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0023]    Embodiments of the present invention will now be described with reference to the accompanying drawings. 
         [0024]    As shown in  FIG. 7 , for example, a structure that a signal beam and a reference beam are applied to the same objective lens is adopted. It is therefore possible to make the proportion of optical components shared by a signal light beam path and a reference light beam path larger than that of the conventional structure such as shown in Non-Patent Document 1. This structure is effective for making compact the apparatus, and it is possible to mitigate a variation in an optical path length difference between a signal beam and a reference beam to be caused by fluctuation of atmospheric air, position displacement of optical components and the like during light propagation. 
         [0025]    In this embodiment, as shown in  FIG. 7 , an optical beam emitted from a light source  201  transmits through a collimator lens  202  and becomes incident upon a shutter  203 . While the shutter  203  is open, the optical beam passes through the shutter  203 , and thereafter a polarization direction is controlled by a polarization direction conversion element  204  such as a half wavelength plate or a liquid crystal device to make the optical beam have a desired light amount ratio of a P polarized light beam and an S polarized light beam, and then the polarized light beams become incident upon a PBS prism  205 . 
         [0026]    The light beam passed through the PBS prism  205  becomes incident upon a spatial light modulator  208  via a PBS prism  207 . 
         [0027]    A signal optical beam  206  added with information by the spatial light modulator  208  is reflected by the PBS prism  207 , and propagates through an angle filter  209  which allows only an optical beam having a predetermined incidence angle to pass. Thereafter, the signal optical beam is converged upon an optical information recording medium  1  via an objective lens  210 . 
         [0028]    An optical beam reflected by the PBS prism  205  functions as a reference optical beam  212 , is made to have a polarization direction predetermined for recording/reproducing by a polarization conversion element  219 , and thereafter becomes incident upon a lens  215  via mirrors  213  and  214 . 
         [0029]    The lens  215  takes a role of converging the reference optical beam  212  upon a back focus plane of the objective lens  210 . The reference optical beam converged upon the back focus plane of the objective lens  210  is changed again to a parallel beam by the objective lens  210 , and becomes incident upon the optical information recording medium  1 . 
         [0030]    The objective lens  210  or an optical block  221  can be driven, for example, along a direction represented by reference number  220 . By displacing the position of the objective lens  210  or an optical block  221  along the drive direction  220 , a relative positional relation between the objective lens  210  and the convergence point on the back focus plane of the objective lens  210  changes. It is therefore possible to set an incidence angle of the reference optical beam incident upon the optical information recording medium  1  to a desired angle. 
         [0031]    As the signal optical beam and reference optical beam are made incident upon the optical information recording medium  1  in a superposed manner, an interference fringe pattern is formed in the recording medium. By writing this pattern in the recording medium, information can be recorded. By displacing the position of the objective lens  210  or optical block  221  along the drive direction  220 , an incidence angle of the reference optical beam incident upon the optical information recording medium  1  can be changed so that angle multiplex recording can be performed. 
         [0032]    The structure that the angle multiplex recording is realized by applying the signal beam and reference beam to the same objective lens and scanning the objective lens in a lateral direction, is referred to as a monocular system in the following embodiments. 
         [0033]    In reproducing recorded information, as described previously, the reference optical beam is applied to the optical information recording medium  1 , and the optical beam transmitted through the optical information recording medium  1  is reflected by a galvano mirror  216  to form its phase conjugate beam. 
         [0034]    A reproduction optical beam reproduced by the phase conjugate beam propagates through the objective lens  210  and angle filter  209 . Thereafter, the reproduction optical beam transmits through the PBS prism  207 , and becomes incident upon the photodetector  218  so that the recorded signal can be reproduced. 
         [0035]    As described above, as shown in  FIG. 1  the monocular system has a structure that the reference beam is once converged upon the back focus plane of the objective lens  210  so as to make the reference beam be applied to the optical information recording medium  1  as a parallel beam. Since a convergence point  235  of the reference beam is disposed on the back focus plane of the objective lens  210 , a lens  215  for the reference beam is additionally disposed to guide the reference light beam to the lens  215 . Therefore, it is necessary that, at an intermediate point in the optical path from the laser light source to the optical information recording medium  1 , the reference light beam is detoured to another optical path different from the signal beam optical path, to thereby guide the reference beam to the lens  215  for converging the reference beam upon the back focus plane of the objective lens.  FIG. 2  shows a structure that a detour quantity of the reference optical beam is improved so that the proportion of optical components shared by the signal optical beam and reference optical beam is further increased. The structure shown in  FIG. 2  is effective for further making compact the apparatus, and it is possible to further mitigate a variation in an optical path length difference between a signal beam and a reference beam to be caused by fluctuation of atmospheric air, position displacement of optical components and the like during light propagation. 
         [0036]    In this embodiment, as shown in  FIG. 2 , both the signal optical beam and reference optical beam are changed to parallel beams and incident to the PBS prism  207 . The reference optical beam is reflected by the PBS prism  207 , changed to a circularly polarized beam by a quarter wavelength plate  232 , and reflected by a reflection plate  233 . The beam reflected by the reflection plate  233  is changed to a P polarized beam by the quarter wavelength plate  232 , transmits through the PBS prism  207  and becomes incident upon a lens  231 . The lens  231  has a feature of a concave lens having a lens function of making the virtual convergence point  235  of the reference optical beam passed through the lens  231  be coincident with the back focus plane of the objective lens  210 . The reference optical beam passed through the concave lens  231  becomes incident upon the optical information recording medium  1  via the objective lens  210  as a parallel beam. 
         [0037]    Similarly, the signal optical beam is reflected by the PBS prism  207 , and added with signal information by the spatial light modulator  208 . After being reflected by the spatial light modulator  208 , the signal optical beam transmits through the PBS prism  207 , is changed to a desired polarization state by the polarization direction conversion elements  234 , and thereafter, becomes incident upon the optical information recording medium  1  via the objective lens  210  as a converged beam. 
         [0038]    Generally, a transmissivity and a reflection coefficient of a PBS prism have an incidence angle dependency. However, in this embodiment, with the structure that the reference optical beam is incident to the PBS prism as a parallel beam, an incidence angle at the PBS prism can be set uniquely to about 45 degrees so that there is no influence exerted by the incidence angle dependency. 
         [0039]      FIGS. 3A and 3B  show an optical system of a holographic recording/reproducing pickup having the structure shown in  FIG. 2 . In recording a hologram, as shown in  FIG. 3A  an optical beam emitted from the light source  201  transmits through the collimator lens  202 , and becomes incident upon the shutter  203 . While the shutter  203  is open, the optical beam passes through the shutter  203 , and thereafter becomes incident upon a shutter  240  for a signal optical beam. 
         [0040]    Portions of the optical beam incident upon the shutter  240  become the reference optical beam and signal optical beam through area division. The reference optical beam and signal optical beam become incident upon the PBS prism  207  as parallel beams. 
         [0041]    The reference optical beam is reflected by the PBS prism  207 , changed to a circularly polarized beam by the quarter wavelength plate  232 , and thereafter reflected by the reflection plate  233 . The beam reflected by the reflection plate  233  is changed to a P polarized beam by the quarter wavelength plate  232 , transmits through the PBS prism  207 , and becomes incident upon the lens  231 . The lens  231  has a feature of a concave lens having a lens function of making a virtual optical emission point  235  of the reference optical beam passed through the lens  231  be coincident with the back focus plane of the objective lens  210 . The reference optical beam passed through the concave lens  231  becomes incident upon the optical information recording medium  1  via the objective lens  210  as a parallel beam. 
         [0042]    Similarly, the signal optical beam is reflected by the PBS prism  207 , and added with signal information by the spatial light modulator  208 . After being reflected by the spatial light modulator  208 , the signal optical beam transmits through the PBS prism  207 , is changed to a desired polarization state by the polarization direction conversion elements  234 , and thereafter, becomes incident upon the optical information recording medium  1  via the objective lens  210  as a converged beam. 
         [0043]    The objective lens  210  can be driven, for example, along a direction represented by reference number  220 . By displacing the position of the objective lens  210  along the drive direction  220 , a relative positional relation between the objective lens  210  and the virtual optical emission points  235  on the back focus plane of the objective lens  210  changes. It is therefore possible to set an incidence angle of the reference optical beam incident upon the optical information recording medium  1  to a desired angle. 
         [0044]    As the signal optical beam and reference optical beam are made incident upon the optical information recording medium  1  in a superposed manner, an interference fringe pattern is formed in the recording medium. By writing this pattern in the recording medium, information can be recorded. By displacing the position of the objective lens  210  along the drive direction  220 , an incidence angle of the reference optical beam incident upon the optical information recording medium  1  can be changed so that angle multiplex recording can be performed. 
         [0045]    In reproducing recorded information, as shown in  FIG. 3B  only the reference optical beam is made to pass through the shutter  240 , and becomes incident upon the PBS prism  207  as a parallel beam. Similar to recording, the reference optical beam is incident to the optical information recording medium  1 , and the optical beam transmitted through the optical information recording medium  1  is reflected by a galvano mirror  216  to form its phase conjugate beam. A reproduction optical beam reproduced by the phase conjugate beam propagates through the objective lens  210 , is made to have a desired polarization state by the polarization direction conversion element  234 , and thereafter is reflected by the PBS prism  207 . The reproduction optical beam reflected by the PSB prism becomes incident upon the photodetector  218  so that the recorded signal can be reproduced. 
         [0046]    The lens  231  may be a reflection type lens, a diffraction type lens having diffraction grating or may be a combination of both. 
         [0047]    The optical system of the holographic recording/reproducing pickup may have the structure shown in  FIGS. 4A and 4B . 
         [0048]    In recording a hologram, as shown in  FIG. 4A  an optical beam emitted from the light source  201  transmits thorough the collimator lens  202 , and becomes incident upon the shutter  203 . While the shutter  203  is open, the optical beam passes through the shutter  203 , thereafter is made to have a desired polarization state by the polarization direction conversion element  204 . An optical beam transmitted through a PBS prism  250  is the reference optical beam, and an optical beam reflected twice in the PBS prism  250  is the signal optical beam. 
         [0049]    The reference optical beam transmitted through the PBS prism  250  is changed from a P polarized beam to an S polarized beam by a half wavelength plate  251 , and becomes incident upon the PBS prism  207  as a parallel beam. Similarly, the signal optical beam reflected by the PBS prism  250  becomes incident upon the PBS prism  207  as a parallel beam. Propagation after incidence upon the PBS prism  207  is similar to that described with reference to  FIGS. 3A and 3B , and so the description thereof is omitted. 
         [0050]    In reproducing recorded information, as shown in  FIG. 4B  a polarization state of the incident optical beam is changed to a P polarized beam by the polarization direction conversion element  204  so that almost all the incident optical beam transmits through the PBS prism  250  and can be used as the reference optical beam. The reference optical beam passed through the PBS prism  250  is changed from a P polarized beam to an S polarized beam by a half wavelength plate  251 , and becomes incident upon the PBS prism  207  as a parallel beam. Propagation after incidence upon the PBS prism  207  is similar to that described with reference to  FIGS. 3A and 3B , and so the description thereof is omitted. 
         [0051]    In the embodiment shown in  FIGS. 3A and 3B , the reference optical beam and signal optical beam are generated by area division of an optical beam emitted from the light source  201 . In the structure shown in  FIGS. 4A and 4B , the reference optical beam and signal optical beam are generated from the optical beam of the same area, by utilizing the polarization direction conversion element  204  and PBS prism  250 . With this structure, for example, the optical beam emitted from the light source  201  can be used efficiently as the reference optical beam during reproduction, and the light usage efficiency can be improved. 
         [0052]      FIG. 5  shows the overall structure of an optical information recording/reproducing apparatus for recording and/or reproducing digital information by utilizing holography. 
         [0053]    An optical information recording/reproducing apparatus  10  is constituted of a pickup  11  shown in  FIGS. 3A and 3B  or  FIGS. 4A and 4B , a phase conjugate optical system  12 , a disc curing optical system  13 , a disc rotation angle detecting optical system  14  and a rotation (spindle) motor  50 . The optical information recording medium  1  is structured being able to be rotated by the rotation motor  50 . 
         [0054]    The pickup  11  has a role of recording digital information by applying a reference beam and a signal beam to the optical information recording medium  1  by utilizing photography. In performing this, a controller  89  operates to send an information signal to be recorded to a spatial light modulator in the pickup  11  to be described later via a signal generator circuit  86 , and the signal beam is modulated by the spatial light modulator. 
         [0055]    In reproducing information recorded in the optical information recording medium  1 , a phase conjugate optical system  12  generates a phase conjugate beam of the reference beam emitted from the pickup  11 . A phase conjugate beam is an optical beam having the same wavefront as that of the input beam and propagating in a direction opposite to that of the input beam. A reproduction beam reproduced by the phase conjugate beam is detected with a photodetector in the pickup  1  to be described later, and reproduced by a signal processing circuit  85 . 
         [0056]    An application time of the reference beam and signal beam applied to the optical information recording medium  1  can be adjusted in such a manner that the controller  89  controls an open/close time of a shutter in the pickup  11  to be described later via a shutter control circuit  87 . 
         [0057]    A disc curing optical system  13  has a role of generating an optical beam to be used for pre-cure and post-cure of the optical information recording medium  1 . Pre-cure is a pre-process of, when information is to be recorded in the optical information recording medium  1  at a desired position, applying a predetermined optical beam before the reference beam and signal beam are applied to the desired position. Post-cure is a post-process of, after information is recorded in the optical information recording medium  1  at a desired position, applying a predetermined optical beam to the desired position in order to make unable to overwrite information at the desired position. 
         [0058]    A disc rotation angle detecting optical system  14  is used for detecting a rotation angle of the optical information recording medium  1 . In adjusting the optical information recording medium  1  to have a predetermined rotation angle, the disc rotation angle detecting optical system  14  detects a signal corresponding to a rotation angle, and by using the detected signal, the controller  89  can control a rotation angle of the optical information recording medium  1  via a spindle motor control circuit  88 . 
         [0059]    A light source drive circuit  82  supplies a predetermined light source drive current to light sources in the pickup  11 , disc curing optical system  13  and disc rotation angle detecting optical system  14 , and each of the light sources can emit an optical beam having a predetermined light quantity. 
         [0060]    The pickup  11 , phase conjugate optical system  12  and disc curing optical system  13  have each a mechanism for sliding a position of the optical information recording medium  1  in a radial direction, to perform position control via an access control circuit  81 . 
         [0061]    Recording techniques utilizing holography are techniques capable of recording ultra high density information. There is therefore a tendency that an error allowance for a shift of inclination and dislocation of the optical information recording medium  1  becomes extremely small. The pickup  11  may have a mechanism for detecting a shift quantity of, e.g., a shift quantity having a small error allowance such as inclination and dislocation of the optical information recording medium  1 , and the optical information recording/reproducing apparatus  10  may have a servo mechanism in which a servo signal generator circuit  83  generates a servo control signal and a servo control circuit  84  corrects the shift quantity. 
         [0062]    The pickup  11 , phase conjugate optical system  12 , disc curing optical system  13 , and disc rotation angle detecting circuit  14  may be constituted of several optical system structures or may be constituted of one optical structure integrating all optical systems to simplify the structure. 
         [0063]      FIGS. 6A to 6C  show recording/reproducing operation flows of the optical information recording/reproducing apparatus  10 . Description will be made on the recording/reproducing operation flows utilizing, in particular, holography. 
         [0064]      FIG. 6A  shows an operation flow from insertion of the optical information recording medium  1  into the optical information recording/reproducing apparatus  10  to completion of preparation for recording or reproducing,  FIG. 6B  shows an operation flow from the preparation completion state to recording information in the optical information recording medium optical information recording medium  1 , and  FIG. 6C  shows an operation flow from the preparation completion state to reproducing information recorded in the optical information recording medium  1 . 
         [0065]    As shown in  FIG. 6A , as a medium is inserted, the optical information recording/reproducing apparatus  10  judges whether the inserted medium is, for example, a medium for recording or reproducing digital information by utilizing holography. If the disc judgment result indicates an optical information recording medium for recording or reproducing digital information by utilizing holography, then the optical information recording/reproducing apparatus  10  reads control data provided in the optical information recording medium, to acquire, for example, information on the optical information recording medium and information on various setting conditions during recording and reproducing. After the control data is read, various adjustments corresponding to the control data and learning processes for the pickup  11  are performed so that the optical information recording/reproducing apparatus  10  completes preparation for recording or reproducing. 
         [0066]    In the operation flow from the preparation completion state to recording information, as shown in  FIG. 6B  data to be recorded is first received, and information corresponding to the received data is sent to the spatial light modulator in the pickup  11 . Thereafter, various learning processes are executed beforehand if necessary in order to allow high quality information to be recorded in the optical information recording medium, and while a seek operation and an address reproduction operation are repetitively performed, the pickup  11  and disc curing optical system  13  are disposed at predetermined positions of the optical information recording medium. Thereafter, by using an optical beam emitted from the disc curing optical system  13 , a predetermined area is pre-cured, and data is recorded by using a reference beam and a signal beam emitted from the pickup  11 . After the data is recorded, data is verified if necessary, and post-cure is performed by using an optical beam emitted from the disc curing optical system  13 . 
         [0067]    In the operation flow from the preparation completion state to reproducing information, as shown in  FIG. 6C  various learning processes are executed beforehand if necessary in order to allow high quality information to be reproduced from the optical information recording medium. Thereafter, while a seek operation and an address reproduction operation are repetitively performed, the pickup  11  and phase conjugate optical system  12  are disposed at predetermined positions of the optical information recording medium. Thereafter, by making the pickup  11  emit a reference beam, information recorded in the optical information recording medium is read. 
         [0068]    While we have shown and described several embodiments in accordance with our invention, it should be understood that disclosed embodiments are susceptible of changes and modifications without departing from the scope of the invention. Therefore, we do not intend to be bound by the details shown and described herein but intend to cover all such changes and modifications which fall within the ambit of the appended claims.