Compact optical tracking system for magnetic tape

A compact optical tracking system for magnetic tape is disclosed which is independent of the magnetic format and head structure which can generate a position error signal without encoding on the servo track. A plurality of optical servo modules is arranged in a linear array. Each optical servo module contains an optical beam source, preferably a laser, an optical beam interference composite hologram for producing a predetermined pattern on a target and at least one detector for detecting an optical beam reflection. A position correction signal is generated by one or all of the optical servo modules for re-positioning a magnetic head, which reduces the error in the correction signal from tape degradation and dimensional changes. Reference grating may be added to provide further position calibration prior to the tape being positioned over the head. Refinements to the tracking system include outboard heads which are added for additional position references and which may include index marks for initial positioning in association with a desired servo track.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to the field of magnetic tape drives. More particularly, the present invention relates to positioning a magnetic head for proper pickup of information tracks on a magnetic tape or disk.

2. Description of Related Art

In magnetic tape drive technology, it is known to employ a tracking servo system to follow pre-written servo tracks on the magnetic tape to accurately position the magnetic heads. Typically, one or more read heads are dedicated to sensing the servo tracks and are added to or interleaved with the data read heads. For example, a combination head with 18 side-by-side data heads may include two or three servo read heads to assure accurate positioning. As the width and spacing of the data tracks is decreased to increase capacity, it becomes more difficult to maintain the necessary positional accuracy using a narrower magnetic servo track. If the width of the servo track is left wider to avoid this problem, some of the potential capacity increase is lost, and the head becomes more complex due to the unequal spacing of the elements. For the magnetic tracking method to work with an unstructured single-element read head, complex encoding of the track and signal processing is required to extract a position error signal.

Previously, optical tracking systems for magnetic tape drives have been proposed which use servo tracks on either the front (magnetic) side or back side of the tape. M. L. Leonhardt and S. D. Wilson disclose in “Optical Servo System For A Tape Drive” U.S. patent application Ser. No. 08/980,723, filed on Dec. 1, 1997, now U.S. Pat. No. 6,084,740 the use of conventional optics with servo tracks on the back of the tape, as well as reference marks on the sides of the magnetic head. This system enables accurate relative positioning of the tape and head without the need for rigid positioning of the optical system relative to the magnetic head. However, the large-scale optics required are difficult to implement in a small form factor drive, typically having limited space adjacent to the magnetic head.

Archibald Smith discloses in “Integrated Optical Tracking System For Magnetic Media”, U.S. patent application Ser. No. 09/203,784, filed on Dec. 2, 1998, now U.S. Pat. No. 6,275,349 an optical system which uses miniature opto-electronic modules with servo tracks on the front side of the tape. The opto-electronic modules are integrated into the magnetic head to achieve a compact structure. Both of these systems illuminate a region of the servo tracks with LED light sources and focus the tracks onto a segmented detector that senses their position. Accurate focusing is required, which places stringent dimensional tolerances on the system.

S. W. Farnsworth and S. D. Wilson disclose in “Optical Servo System For Magnetic Disk,” U.S. Pat. No. 5,121,371, Filed on Jun. 18, 1990 and again in “Diffractive Optical System For Tracking On FlopticalRDisks,”SPIE, vol 1960, pp 72–79 (1992), other prior art systems related to optical tracking for floppy magnetic disk drives. Using this system, the need for accurate focusing onto segmented detectors is avoided. This system uses two groups of small light spots. There are typically four to six strong spots in each group, having the same separation as the servo tracks. The two groups are offset in the transverse direction by one quarter of the servo track spacing, and separated in the longitudinal direction. Each group of spots is a fringe pattern produced by the interference of light from a double slit mask or hologram illuminated by a laser. Each group of spots is imaged onto a separate non-segmented detector, whose output varies depending on the position of the fringes relative to the servo tracks. The focal depth for the optical sensors described above is +/−100 um compared to +/−1 um for the previously referenced systems.

Problems associated with the prior art include the continued need for a separate encoding head in order to accurately judge the position of the magnetic head relative to the tape guiding structure. Other problems include inaccurate positioning of the tape head due to dirty or damaged servo tracks on the magnetic tape. Still other problems with the prior art include focusing problems associated with the segmented detectors and slow response or positioning overshoot due to configurations which actuate more than just the mass of the magnetic head. In an effort to solve the above-mentioned problems, the present invention is disclosed.

SUMMARY OF THE INVENTION

A compact optical tracking system for magnetic tape is disclosed which is independent of the magnetic format and head structure, and which can generate a position error signal without encoding on the servo track. A plurality of optical servo modules are arranged in a linear array. Each optical servo module contains an optical beam source, preferably a laser, an optical beam interference composite hologram for producing a predetermined pattern on a target and at least one detector for detecting an optical beam reflection. A position correction signal is generated by one or all of the optical servo modules for re-positioning a magnetic head which reduces the error from tape dimensional changes. Reference gratings may be added to provide further position calibration prior to the tape being positioned over the head. In other embodiments, outboard optical heads are added for use with additional position references, which may include index marks for initial positioning in association with a desired servo track.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1is a schematic illustrating an optical servo module structure in accordance with a preferred embodiment of the present invention. Optical servo module structure100comprises a plurality of servo modules in a linear array. Servo module101is typical of the servo modules contained in optical servo module structure100. Servo module101contains laser source106and detectors104A and104B, which are formed in or mounted on substrate160. Clear plastic block150is formed over laser source106, detectors104A and104B, and substrate160. Composite hologram108is formed in or added to clear plastic block150, approximately perpendicular to the direction of the optical beam projected from laser source106. The servo modules in optical servo module structure100may be independent modules mechanically assembled together to form a single optical servo module structure. However, in a preferred embodiment of the present invention, the individual servo modules are formed together on an single substrate using a semiconductor manufacturing process. Therefore, the alignment and positioning of each servo module is a function of the semiconductor manufacturing process rather than an assembly process.

Laser source106projects the optical beam through clear plastic block150to composite hologram108, which interferes with the optical beam and produces a group of spots in fringe pattern102on tape170. Alternatively, laser source106could illuminate a double slit mask and create a similar group of spots. Although not specifically detailed inFIG. 1, fringe patterns102,112,122and132actually consist of two groups of spots positioned laterally along the servo track (also not shown) of tape170. One group of spots in each of fringe patterns102,112,122and132are reflected on detectors104A,114A,124A and134A, respectively, while the second reflects on detectors104B,114B,124B and134B, respectively, as will be discussed in detail with respect toFIG. 2below. Detectors104A,104B,114A,114B,124A,124B,134A and134B use the reflected image from fringe patterns102,112,124and134to compute the relative position between optical servo module structure100and tape170, which is in turn used to adjust the alignment between tape170and the magnetic tape pickup head, which is affixed to optical servo module structure100.

Optical servo module structure100contains four identical servo modules, each having a laser source and two detectors on the substrate, and a composite hologram, all embedded within the clear plastic. Although optical servo module structure100shows four servo modules, any number may be employed in practicing the present invention.

The basic arrangement is shown for the case of a multi-track, combination write and read head with a width less than that of the tape. A linear array of servo modules may be embedded between the write and read head sections. The position of the light spots produced by the modules is referenced to the position of the magnetic head elements during assembly. The tape is positioned laterally by a guiding structure attached to the base of the head. The servo tracks typically have a spacing of 20 um and are written across the tape. When the head is moved or scanned to access a particular group of magnetic tracks, track crossing signals are produced by the A and B detectors. These can be counted to determine the distance moved. An index track (or tracks) with a unique modulation pattern can be used as a reference to the location of the magnetic tracks.

FIG. 2is a view of the tape as seen from optical servo module structure100. Tape200depicts eight groups of spots: fringe patterns202A and202B generated by laser source106inFIG. 1, fringe patterns212A and212B generated by laser source116, fringe patterns222A and222B generated by laser source126, and fringe patterns232A and232B generated by laser source136. Typically four to six strong spots are present in each group, having the same separation as the servo tracks. However, single spots in A and B suffice for the operation of the modules. The two groups (A and B groups of spots associated with each laser source) are offset in the transverse direction by one quarter of the servo track spacing. Further, the groups are separated in the longitudinal direction. As discussed above, each group of spots is a fringe pattern produced by the interference of light from hologram composites illuminated by a laser source. The reflected light from the tape for each group of spots is directed onto a separate non-segmented detector, whose output varies depending on the position of the fringes relative to the servo tracks.

The use of two groups of spots for each optical servo module allows the direction of offset as well as the magnitude to be extracted. When one set of fringes is centered over a group of dark tracks on the medium, its reflected signal A will be at a minimum. The reflected signal B from the other fringe set will then be approximately 50 percent of the maximum, and in a linear response region. The sign and magnitude of deviations from its average are proportional to the position deviation between the fringes and the dark track center. If the head moves up the distance of a quarter track spacing, as shown inFIG. 2, the roles of the A and B signals are interchanged.

Tape200depicts a magnetic tape that is in less than perfect condition. Tape200contains a plurality of prewritten servo tracks, including pristine servo tracks272and eroded or damaged servo tracks274. Damaged servo tracks274contain small gaps and discontinuities. These defects reflect the projected fringe patterns differently than pristine servo tracks272, even when the fringe patterns are positioned identically across both the pristine track and the damaged track. Tape200also contains surface abnormalities, such as dirt and wear, depicted by flawed tape regions276.

As the tape moves under the fringe patterns, the effect of damaged servo tracks and surface contamination is averaged out by the multiplicity of fringes in the A and B groups, six fringes each in the example of FIG.2. Additional averaging is obtained by combining the signals from all A detectors and all B detectors, either in the analog domain or preferably in the digital domain. Averaging of this kind is particularly effective in the case where there is only one strong fringe or illuminated spot in each group. In the event that the servo tracks under one group of fringes are badly degraded, algorithms can be implemented in the digital domain to eliminate the signals from the corresponding A and B detectors from the averaging process. Averaging overall fringe groups also minimizes the effect of dimensional changes in the tape caused by changes in operating temperature and humidity, or by aging of the tape substrate.

FIG. 3is a quadrature signal display depicting one detector track crossing signal, plotted against the other detector track crossing signal produced by the optical servo module detectors in accordance with a preferred embodiment of the present invention. The position of the index track after loading the tape onto the head can be found by scanning the head. When the approximate position of the desired magnetic track has been reached by counting the track crossing signals, the head position can be accurately set using signal304A and signal304B.

Quadrature display300illustrates plotting an output signal from the B detector signal versus an output signal from the A detector signal in the optical servo module. In quadrature display300, signal304A and signal304B trace out circle302when the head moves a distance of one servo track spacing. Random motion of the tape within the lateral guiding system produces signal variations over an arc of the circle.

The servo system can be set to move the linear actuator to maintain a particular position on circle302corresponding to the center of the magnetic track. For example, operating point308is located at the 45-degree position in the upper right quadrant. Linear actuator adjustment indicator line310crosses circle302at two points, exactly one servo track of adjustment apart, one of which is operating point308. When the head, and therefore the groups of spots, is out of alignment, the plot of signal304B versus signal304A moves along the circle away from operating point308. By adjusting the linear actuator a scaled amount proportional to distance from operating point308, the servo tracks change their positions relative to the groups of spots on the tape. In response, the plots of signal304B versus signal304A move toward the position of operating point308.

The servo module closest to the desired track can be selected for optimum accuracy. If a group of tracks is accessed in parallel, interleaved with other tracks and spread across the tape, the multiple servo modules can be used to determine the optimum position for the desired track group by averaging procedures previously discussed.

FIG. 4is a schematic of a preferred embodiment of a servo position control system that may be employed in the present invention. Initially, in servo position control system400, module detectors404A and404B receive a reflection from groups of spots, such as fringe patterns202A and202B, respectively, as shown in FIG.2. The output signals from module detectors404A and404B vary depending on the position of the fringes relative to a group of servo tracks. The output signals from module detectors404A and404B are first fed into signal amplifiers476A and476B, where the signals are strengthened and passed to difference generator482. Difference generator482compares the output signal from module detector404B with the output signal from module detector404A. In a preferred embodiment, the comparison is in the form of an algorithmic position plot producing a quadrature signal display of one detector track crossing signal, plotted against the other detector track crossing signal, as shown inFIG. 3. As the current plot varies from operating point308inFIG. 3, a repositioning signal is generated in the form of a motor drive signal.

The motor drive signal is generated by difference generator482, for correcting the position of magnetic head486from its present position to a correctly adjusted position with respect to the servo tracks. The motor drive signal is then fed to power amplifier484, and the amplified motor drive signal is passed to motor474, which actuates linear slide472for magnetic head486.

Alternatively, the signals from the detectors may be digitized after amplification, and the motor drive signal generated in the digital domain. When a plurality of servo modules is used, their signals may be combined to optimize the head position in the analog domain, but preferably in the digital domain, as previously discussed.

Prior art embodiments disclose servo modules of 50×15×9 mm in size, too large to allow multiple units to be integrated with a magnetic tape head. A miniaturized version has been developed, about 2×2×2 mm in size (without a mounting pad). It is the purpose of the present invention to show how multiple units of these miniaturized modules can be integrated with a magnetic head to achieve a compact structure that generates stable track position signals. Such signals can be used by a servo system to accurately control the position of a magnetic head relative to the tracks on the tape.

FIGS. 5A,5B and5C depict a magnetic head assembly configured with the optical servo modules facing the magnetic side of a tape, having optical tracks in accordance with a preferred embodiment of the present invention.FIG. 5Adepicts a side view of assembly500, showing a cross section through the center of head504. Assembly500comprises a plurality of servo modules512emitting optical beams510onto tape570. Modules512are recessed within cavity513created between the read and write heads in head504. Head504is positioned relative to tape570by head actuator508. Head actuator508provides vertical linear movement in the depicted figure between magnetic head504and base506. Note that, in this configuration, only the positions of the head and servo modules are changed by actuator508, while base506remains stationary.

FIG. 5Bdepicts the face view of assembly500, including write head514and read head524, which are configured with a recessed area for servo modules512. Servo modules512are shown emitting optical beams510. Patterned traces530show the active head width, while trace520depicts the width and position of tape570when it is in position across the face of assembly500.

FIG. 5Cdepicts the top view of assembly500, including write head514and read head524, which are configured with a recessed area for placement of the servo modules. Servo module512is shown emitting optical beam510. Assembly500is shown with tape570in position across the face of write head514and read head524, and in contact with optical beam510.

In other embodiments of the present invention, other locations for front side servo module array are possible. For example, the modules can be mounted on the side of the head instead of in the middle. For side mounting of optical servo modules, the optical servo modules have to be mounted to the magnetic head at an angle equal to the tape wrap angle.

Assembly500depicts the basic arrangement of assembly100inFIG. 1, that is, the case of a multi-track combination write and read head with a width less than that of the tape. A linear array of servo modules (such as optical servo module structure100) may be embedded between the write and read head sections, as shown in assembly500. The position of the light spots produced by the modules is referenced to the position of the magnetic head elements during assembly. The tape is positioned laterally by a guiding structure attached to base506of the head. The servo tracks typically have a spacing of 20 um and are written across the full width of the tape. When the head is moved or scanned to access a particular magnetic track, track crossing signals are produced by the A and B detectors located in each optical servo module. These can be counted to determine the distance moved. An index track (or tracks) with a unique modulation pattern can be used on the tape as a reference for counting the track crossings. It should be mentioned that in cases where the servo modules are scanned across the tape with the magnetic head, there is only one index track and many servo tracks per head. For such cases, there are only a few index tracks and many servo tracks across the tape.

FIGS. 6A,6B and6C depict a magnetic head assembly configured with the optical servo modules facing the back side of a tape in accordance with a preferred embodiment of the present invention.FIG. 6Adepicts a side view of assembly600showing a cross section through the center of head604. Assembly600comprises a plurality of servo modules612emitting optical beams610onto the back side669of tape670. Note also that structure600is equipped with two outboard servo modules602that do not project spots onto tape670, instead servo modules602project spots onto reference gratings (not shown) located on reference grating plate616. Servo modules612and602are mounted on module structure609, in contrast to assembly500, where they are recessed within a cavity created between the read and write heads. Head604is positioned relative to tape670by head actuator608. In contrast to the previous embodiment, head actuator608provides vertical linear movement for yoke606and, in so doing, vertically repositions virtually all of structure600, including magnetic head604, module assembly609, and servo modules612.

FIG. 6Bdepicts the face view of assembly600, including write head614and read head624, which are configured with a recessed area for reference grating plate616. On reference grating plate616are fashioned reference grates628, which are associated with servo modules612and outboard reference grates618, which are associated with outboard servos602.

Patterned traces630show the active head width, while trace620depicts the width and position of tape670when in position across the face of assembly600. Reference grates628are only exposed to the optical beams from servo modules612prior to tape670being positioned across write head614and read head624, while outboard reference grates618remain uncovered even when tape670is in position.

FIG. 6Cdepicts the top view of assembly600, including write head614and read head624, which are configured with a recessed area for placement of the servo modules. Outboard servo module602is shown emitting optical beam610across tape670because the width of the magnetic tape does not extend to the outboard servo modules.

As can be seen inFIGS. 6A–6C, yoke606is used to fix optical servo modules612to magnetic head604. As before, assembly600is moved with actuator608to access various parts of tape670and to compensate for random lateral tape motion. In this case, the relative position of servo modules612and the index servo track will be sensitive to temperature changes, aging effects, and vibration in assembly600, including the component attached to yoke606.

Various reference marks are provided to calibrate and compensate for changes in relative position within the control range of modules612(one servo track spacing decreased by the effect of noise). Reference gratings628are placed under each optical module in the body of magnetic head604, aligned with the magnetic tracks. These are used to set the operating position on the quadrature circle before loading tape. The number of lines in each grating is equal to the number of strong fringes produced by the module, typically four or five.

Additional outboard optical modules602and outboard reference gratings618are provided outboard of tape670to monitor changes when the tape is loaded and running, for example, due to temperature variations. If assembly600is sufficiently stable, one set of reference marks may be adequate, either inboard optical servo modules612or outboard servo modules602. For the previously mentioned example of 20 um servo track spacing, the total variations must be less than +/−10 um for the system to remain in control without additional alignment methods.

FIG. 7depicts a magnetic head assembly configured with the back side configuration, including a fine actuator, in accordance with a preferred embodiment of the present invention. Assembly700is a side view showing a cross section through the center of the head. Assembly700is similar to assembly600, including a plurality of servo modules712emitting optical beams710onto the back of tape770, and two outboard servo modules702projecting onto reference gratings (not shown) located on reference grating plate716. As in assembly600, virtually all of structure700, including magnetic head704, module assembly709, and servo modules712, are moved by head actuator708. However, assembly700further includes fine actuator730between yoke706and module assembly709.

In the event that servo modules712go out of alignment long term with the magnetic servo tracks by more than one servo track spacing, for example, after several days of operation, the position of the index tracks can be recalibrated by scanning magnetic head704and comparing the magnetic and optical signals. If it is desired to set the index servo tracks to a particular position relative to the magnetic tracks to optimize servo accuracy, fine actuator730can be used for adjusting the alignment of servo modules712relative to magnetic head704. A compact piezoelectric translator (not shown) can provide a range of a few servo tracks spacing for this purpose.

Two ways of mounting the servo modules in the back side configuration exist. The first way is with the servo modules attached to the magnetic head via the yoke so that they move together. Assembly600shown inFIG. 6illustrates this method. The other way of mounting is with the modules fixed to a stationary base so that they are stationary and only the head moves. Assembly800shown below inFIG. 8illustrates this method.

FIGS. 8A,8B and8C depict a magnetic head assembly in a back side configuration utilizing outboard reference grates, including an index reference, in accordance with a preferred embodiment of the present invention. InFIG. 8A, assembly800is similar to assembly600, illustrating a side view of assembly800showing a cross section through the center of the head. Assembly800comprises a plurality of servo modules812emitting optical beams810onto the back of tape870. Structure800is also equipped with two outboard servo modules802, which project optical beams that do not project onto tape870but, instead, project onto reference grates (not shown) located on reference grating plate816, as described above in assembly600.

FIG. 8Bdepicts the face view of assembly800, including write head814and read head824. The reference grating plate (shown as reference grates818) provides two outboard reference grates818, which are associated with the outboard servos rather than reference gratings under tape870. Note also that reference grates818are positioned adjacent to read head824rather than between the read and write heads as depicted by assembly600inFIGS. 6B and 6C. Patterned traces830show the active head width, while trace820depicts the width and position of tape870when in position across the face of assembly800. Outboard reference grates818remain uncovered while tape870is in position.

In a preferred embodiment, extended outboard reference grates818are required to accommodate the movement of the magnetic head relative to the servo modules. Index mark819is included in one or each of reference grates818. Index mark819is referenced to the magnetic tracks. On the back side of the tape, only a few tracks are required under each servo module, a few more than the number of strong fringes. Two advantages are provided by this configuration over the embodiment shown inFIG. 7, the first one, namely, outboard gratings818act as a position encoder for the linear head actuator, eliminating the need for a separate encoder; and the moving mass of the magnetic head is lower. If the variation in the position of magnetic tape after loading exceeds one servo track spacing, then additional means are necessary to determine the correct head position. An initial portion of the servo tracks can be encoded or patterned so that the integral track offset can be determined from the optical signals. The precise position can then be determined by scanning the magnetic head over one servo track spacing and comparing the magnetic and optical signals.

FIG. 8Cdepicts the top view of assembly800, including write head814and read head824. Outboard servo module802is shown emitting optical beam810across tape870in a position adjacent to read head824.

As can be seen inFIGS. 8A–8C, in the back side configuration, the tape must be inserted between the magnetic head and the servo modules. This separation is typically 2 to 3 mm. Once the tape is inserted, the head assembly can be moved to wrap the tape over the head. The separation can be increased for loading by placing an actuator in the yoke structure, as shown in assembly900inFIGS. 9A and 9Bfor a linear actuator, and as assembly1000inFIGS. 10A and 10Bfor a rotary actuator. This arrangement is feasible for the servo modules fixed to the base, where the additional mass of the opening actuator is not added to the magnetic head.

FIGS. 9A and 9Bdepict a magnetic head assembly in a back side configuration and in the open and closed positions, utilizing a linear actuator. InFIG. 9A, assembly900appears in a side view, showing a cross section through the center of head904. Assembly900comprises a plurality of servo modules912emitting optical beams910onto the back of tape970. Structure900is also equipped with two outboard servo modules902, which project optical beams that do not project onto tape970but, instead, project onto reference gratings (not shown) located on reference grating plate916. Assembly900is shown in the closed position, as described above in assembly600. In a preferred embodiment of the present invention, the yoke is configured as two cooperating yoke assemblies, head yoke906A and module yoke906B. Head yoke906A and module yoke906B meet at servo module actuator930, where module yoke906B can be opened away from head yoke906B by activating module actuator930, as shown inFIG. 9B. Note that the additional mass of the opening actuator is not added to magnetic head904but, instead, is affixed between head yoke906A and module yoke906B.

FIGS. 10A and 10Bdepict a magnetic head assembly in a back side configuration and in the open and closed positions, utilizing a rotary actuator in accordance with a preferred embodiment of the present invention.FIG. 10Ais a side view of assembly1000, showing a cross section through the center of head1004. Assembly1000comprises a plurality of servo modules1012emitting optical beams1010onto the back of tape1070. Assembly1000may also be equipped with two outboard servo modules (not shown), which project optical beams that do not project onto tape1070but, instead, project onto reference grates (not shown) located on the reference grate plate. Assembly1000is shown in the closed position, as described above in assembly600. In a preferred embodiment of the present invention, the yoke is configured as two cooperating yoke assemblies, head yoke1006A and module yoke1006B. Head yoke1006A and module yoke1006B meet at rotary actuator1030, where module yoke1006B can be suitably opened away from head yoke1006A by activating rotary actuator1030, as shown inFIG. 10B. The positional accuracy of the module assembly may be lessened by the insertion of the actuator, but alignment features can be included to overcome this. Assembly1000also includes alignment pins1040for aligning module yoke1006B with head yoke1006A in the closed position. InFIG. 10, the outboard gratings and modules have been omitted for simplicity, but in practice, they remain a part of assembly1000. Note again that the additional mass of the opening actuator is not added to magnetic head1004but, instead, is affixed between head yoke1006A and module yoke1006B.

The description of the present invention has been presented for purposes of illustration and description but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. For example, the tracking method described here is independent of the magnetic format and head structure, and can generate a position error signal without encoding on the servo track. However, modulation and encoding can be added to increase function and reliability if desired.

The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.