CA1084622A - Magnetic head drum configuration having a friction reducing helical step - Google Patents
Magnetic head drum configuration having a friction reducing helical stepInfo
- Publication number
- CA1084622A CA1084622A CA253,350A CA253350A CA1084622A CA 1084622 A CA1084622 A CA 1084622A CA 253350 A CA253350 A CA 253350A CA 1084622 A CA1084622 A CA 1084622A
- Authority
- CA
- Canada
- Prior art keywords
- tape
- section
- drum
- path
- head
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B15/00—Driving, starting or stopping record carriers of filamentary or web form; Driving both such record carriers and heads; Guiding such record carriers or containers therefor; Control thereof; Control of operating function
- G11B15/60—Guiding record carrier
- G11B15/61—Guiding record carrier on drum, e.g. drum containing rotating heads
Abstract
MAGNETIC HEAD DRUM CONFIGURATION
HAVING A FRICTION REDUCING HELICAL STEP
ABSTRACT OF THE DISCLOSURE
A magnetic head drum includes an upper section that carries a set of magnetic heads and rotates at a preselected head speed, and a stationary lower section that is character-ized by a reduced diameter step formed along the tape wrap path thereover (e.g., a helical path for a helical scan recorder). Because of the reduced diameter step, tape pres-sure is shifted from the lower drum section to the upper drum section which, by virtue of its rotation, produces a low fric-tion air bearing. The reduction in diameter to produce the above-described step, moreover, results in a shoulder or ledge along the lower edge of the tape wrap path, which shoulder serves as a guide for the tape, and promotes accurate tape tracking over the drum.
The amount of reduction in diameter for the lower drum section is not chosen arbitrarily, but is preferably within a range of 1 to 6 mils. In this range, a desirable balance is achieved between reduction in frictional drag and limiting of forces tending to distort the tape. Moreover, it appears that a reduction greater than around 6 mils tends to result in increased tape flutter.
HAVING A FRICTION REDUCING HELICAL STEP
ABSTRACT OF THE DISCLOSURE
A magnetic head drum includes an upper section that carries a set of magnetic heads and rotates at a preselected head speed, and a stationary lower section that is character-ized by a reduced diameter step formed along the tape wrap path thereover (e.g., a helical path for a helical scan recorder). Because of the reduced diameter step, tape pres-sure is shifted from the lower drum section to the upper drum section which, by virtue of its rotation, produces a low fric-tion air bearing. The reduction in diameter to produce the above-described step, moreover, results in a shoulder or ledge along the lower edge of the tape wrap path, which shoulder serves as a guide for the tape, and promotes accurate tape tracking over the drum.
The amount of reduction in diameter for the lower drum section is not chosen arbitrarily, but is preferably within a range of 1 to 6 mils. In this range, a desirable balance is achieved between reduction in frictional drag and limiting of forces tending to distort the tape. Moreover, it appears that a reduction greater than around 6 mils tends to result in increased tape flutter.
Description
10~
BACKGROUND OF THE INVENTION
Field o~ the Invention The present invention relates, in general, to head drums for use in magnetic tape units and, more particularly, to a low-frictional-drag head drum configuration suited to use in helical-scan-type magnetic tape units.
Description Relative to the Prior Art The movement of magnetic tape over a head drum is a critical aspect of the recording and the reading of magnetic records. As might be expected, there has been extensive development in the area o~ head drum design and ~arious approaches have been taken to achieve desired head drum characteri~tics.
United States Patent No. 3,~28,521~, issued February 18, 1969 to Wilcox et al, for example, shows a helical-scan-type head drum wherein air ports are provided for forcing air beneath the magnetic tape so as to form an air bearing. By so ~orcing air under the tape, resistance to longitudinal tape movement over the stationary drum is greatly reduced. Such an arrange-ment, however, is quite complex and expensive.
Another type of drum utilizes a cylindrical drum unit which rotates at high speed (the speed o~ the magnetic heads). Because the drum rotates at high ~peed, an air film is created between the drum and the tape. With such a design, however, accurate guiding of the tape past the heads become~
difficu~t because the tape tends to float on the drum.
United States Patent No. 3,510,60~, issued May 5, 1970 to Kell describe~ a configuration wherein a rotating drum is pecially tapered ~o as to cause air to be ~orced between the tape and the drum surface to produce an air bearing.
,. .
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:...... .. .. . .
. . .
,., ~ , , .
" , , , ~ , . , ~0~ 2 A spl:Lt drum configuration is described in United States Patent No. 3,436,~91, issued April 1, 1969 to J. E. Quinn et al, which configuration utilizes an inwardly tapered upper drum section having a diameter at its bottom face that is less than the diameter o~ an adjacent stationary lower drum section.
The taper is said to reduce ~rictional drag by reducing the buildup of oxides which are rubbed from the tape by the drum.
This arrangement, as described, is intended for a helical-scan apparatus having a tape wrap angle approaching 360 degrees.
- United States Patent No. 3,840,895, issued October 8, :i 1974 to Kubo, describes a split drum configuration having a rotating lower section which carries a set o~ heads and a coaxial, increased diameter upper section which is journaled so as to be rotated by the magnetic tape passing thereover. Because guide ridges are provided on the drum sections along the edges of the tape path, which ridges rotate with their respective sections, a circular, rather than helical, tape path must b~ utilized.
Moreover, it is noted that the torque required to rotate the upper section acts as a drag on longitudinal tape movement ~ with this arrangement.
I As will be appreciated, subtle changes in head drum design can result in significant differences in per~ormance characteri~ics. Consequently, various drum configurations have been developed and tho~e described above represent only a sampling. Each con~iguratlon has advantages and disadvan-tages which are related to a degree to the overall tape scan-ning system in which the configuration cooperates.
For u~e in a cartridge video apparatus, a simple helical-scan head drum which requirea no special air supply or elaborate tape guides would be desirable. An overall tape , scanning ~ystem which operate~ at low tensio~ to reduce head .. . .
.
~ ' : - -- .. .. . .........
,. .. . . . . . . .
. .
,.... . . . . . .
.
;, . . . .. .
4~ , wear would also be de~irableg but the tension should be uni-~orm along the tape wrap path to assure uni~orm head response.
It would ~urther be desirable, particularly i.n a cartridge-type tape scanning system~ to provide for protection of the heads and head drum in the event the tape supply jams.
. .SUMMARY OF THE INVENTION
While friction drag unavoidably occurs when mag-netic tape passes over a head drum, drum arrangements accord-ing to the invention provide desirably low levels of friction : 10 drag by virtue of a specially cut away stati.onary drum sec- -.
: tion. A split drum is utilized including a rotating upper . ~ . .
: ~ section which carri.es a set of magneti.c heads, and a sta-tionary lower section which steps down to a reduced diameter ~ along a predetermined tape wrap path (e.gO, a helical wrap : ~. path ~or a helical scan recorder).
It is believed that, by so reducing the diameter of ~ ... ..
: the lower drum section, tape pressure against that stationary . lower section is decreased while attendantly shifting tape ." , ~ .
. pressure to the upper section which is rotated at a high -~ 20 speed (the scanning speed of the magnetic heads). Because the upper section rotates at high speed, a thin air bearing . is created which offers low resistance to longitudinal tape ,- ... .
: ~ movement.
~; It is also signi~icant to note that, by reducing ,.~, ;
the diameter o~ the lower section only along the tape wrap : path, in accordance with the invention, a shoulder is formed ,~ ~
: : at the lower edge o~ the reduced-diameter step, which shoulder : :
., ~
is adapted to act as a guide for tape travel, In so providing for a reduced-diametér area or step~
it has been ~ound that ~riction drag decreases sharply as the , .. . .
~084~Z
reduction relative to the upper drum diameter increses -- but only until a di~ference in diameter of around 3 mils is achieved.
Since, on the other hand, a step which is deeply cut may result in distortion of the tape, the diameter reduction is pre~erably selected to be less than 6 mils. Within a range o~ 1 to 6 mils, a desirable balance is achieved between drag reduction and limiting of forces that might cause tape distortion. It should be noted that, while the above-mentioned diameter reductions are based upon a nominal drum diameter of around one inch, it appears that the diameter reduction~or reducing frictional drag is not significantly influenced by nominal drum diameter.
With the lower drum section reduced in diameter, as discussed above, it has furthermore been found that tolerances and surface finish specifications for that section can be relaxed to reduce fabrication costs.
, i .
-~ Thus, in accordance with the present teachings, an assembly for use in scanning a magnetic tape is provided which comprises a first drum section which has attached thereto at ~ least one magnetic head and is journaled for rotation about an -: 20 axis to define trajectory for the head(s) with the first drum ~ section having a predetermined diameter about the axis. A second I
drum section is provided which i8 adjacent to and coaxial with the first drum section and includes means for maintaining such section fixed relative to the axis and means for directing a tape along a prese~ected tape wrap path which extends over the first and second drum sections with the path extending over at least a i portion of the trajectory of the head(s), the second drum section has a reduced diameter relative to the first drum sec-tion along that portion of the pre~elected tape wrap path which extends over ~uch second drum section.
In accordance with a ~urther embodiment a drum head configuration is provided ~or use in scanning magnetic tape having ::
108~ Z
a longitudinal dimension, the configuration comprising a cylindrical upper drum section having a central axis and at least one mounting face which is substantially perpendicular to the axis with the upper drum section being mounted for rotation about the longitudinal axis and having attached to a mounting face thereof at least one magnetic head, and a lower drum section which is ixedly mounted to a support to be coaxial with the upper drum section and adjacent to the head(s) with the lower drum section having a reduced diameter relative to the upper drum section along a path preselected - 10 for longitudinal movement of a tape thereover.
In a presently preferred implementation, a helical-scan head drum according to the invention cooperates in a "pusher-type" tape advancing system wherein means such as a set of springs ; applies tension at both supply and takeup ends of the tape, causing the tape to be drawn against the head drum...a capstan on the supply side of the tape relative to the head drum then meters tape transport from supply to takeup. Because the head drum, with this arrangement, is not between the capstan and the tape if ~ supply, the excessive tape tensions which may be generated by ~
~,, . . . :
~;20 ~ the capstan as it attempts to meter tape in the event of a supply ; jam are isolated from the head drum. Hence, a significant source of possible damage to the head drum and magnetic heads is avoided with a "pusher-type" system.
1 .
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It should be noted, however, that in a "pusher-type" system, the takeup tension must be sufficient both to move the tape across the head drum and to pull against the capstan to establish a tape tension profile along the tape wrap path. Because~ with head drums according to the inven-tion, frictional drag is low~ there is little change in tape tension as the tape passes over the head drum. With only a low tension change, tape tension levels along the tape wrap path can be maintained within a narrow range slightly above 7. 10 the minimum tension for sustaining proper operation of the particular magnetic heads which are being utilized. By achieving a flat, low level tension profile along the tape ` wrap path, head response, which varies with tension, is ,~ :
caused to be substantially uniform and the rate of head wear is kept low. Moreover, only a low tension need be applied at the takeup end of the tape.
~ ....................................................................... . . .
Significantly, the above-described characteristics ~i~ are well suited to a cartridge-type video recording/repro-.. ,i . , ducing unit. By spring loading the reels of the cartridge, the supply and takeup tensions for a "pusher-type" system can be provided. Since snagging of the supply can prove to be more of a problem wlth a compact tape cartridge than~ for , . .
exarnple, with separate reels, it becomes partlcularly desir-;able to arrange the head drum on the takeup side of the cap-~ : .
i stan to avoid head damage as discussed above. With a flat ;' ~ low level tape tension profile, head wear is low, head response i ., is uniform~ and a light spring in the cartridge can suffice to apply adequate ten~ion-producing torque at the takeup reel.
The guide shoulder on the lower sectlon o~ head drums accord-ing to the invention provides, moreover~ ~or accurate tape : .
~ tracking, for example, in a helical-scan video system.
'~ .
.~. , .
o~
The invention wil.l be described in detail with respect to the drawings~ wherein: -Figure 1 is a perspective view of a helical-scan head drum accordi.ng to the invention;
Figure 2 is a partial perspective view of such a . head drum;
Figure 3 is a parti.al cross-sectional view of such a head drum;
Figure 4 is a graphical illustration indicating the decoupling achieveable by use of a reduced-diameter step in accordance wlth the invention;
-~Figure 5 is a perspective view of such a head drum incorporated in a pusher-type tape scanning system;
Figure 6A is a simplified plan view ~or illustrating .
the tape wrap path;
.Figure 6B is a graph indicating a tape tension pro-. : file across a head drum; and Figure 6C is a graph indicating head response with .respect to tape tension.
. .
.: 20It should be noted that the step which is formed, according to the invention, in the lower drum section is i.~greatly exaggerated in the figures for purposes of emphasis and clarity. Without such exaggeration, the change from nominal drum diameter along the step would be scarcely ..
noticeable to the eye.
. ~Referring to Figure 1, a presently pre~erred head .drum 2, according to the invention, has a rotatable upper sec-tion 4 and a stationary lower section 6. The upper sectlon 1 ; carries a set o~ magnet;Lc heads 8 and is rotated at a pre-selected head speed by suitable means such as a motor (not shown), In ~orming the l.ol,ler section 6, a reduction ( ~) in . .
,' , .. .
~ ~ ~o~
diameter, relative to the diameter o~ the upper section, is provided along a predetermined tape wrap path, for example, the helical path shown~ to produce a step 10 ~see also Figure 2, where the radius reduction a is emphasized). By reducing the diameter of lower drum section 6 only along the tape wrap path3 a ledge or shoulder 12 results at the lower edge of such tape wrap path, which shoulder serves, advan- -. . tageously, as a tape guide and promotes accurate tape track-ing (see Figure 3)~ To assure that the tape does not slip over the shoulder 12, it is preferable to select a lower .. . ..
i drum section diameter that is somewhat oversized relative - -, to the upper drum section diameter3 thereby increasing the shoulder width. In other words, although the dimension ( ~) is of prime concern, the dimension (S ), Figure 2, is irrel-evant.
In reducing the diameter of the lower section 6 to produce the step 10, it has been found that frictional coup-ling between the tape and the lower section falls off sharply at first and continues to fall until a reduction (~) of about
BACKGROUND OF THE INVENTION
Field o~ the Invention The present invention relates, in general, to head drums for use in magnetic tape units and, more particularly, to a low-frictional-drag head drum configuration suited to use in helical-scan-type magnetic tape units.
Description Relative to the Prior Art The movement of magnetic tape over a head drum is a critical aspect of the recording and the reading of magnetic records. As might be expected, there has been extensive development in the area o~ head drum design and ~arious approaches have been taken to achieve desired head drum characteri~tics.
United States Patent No. 3,~28,521~, issued February 18, 1969 to Wilcox et al, for example, shows a helical-scan-type head drum wherein air ports are provided for forcing air beneath the magnetic tape so as to form an air bearing. By so ~orcing air under the tape, resistance to longitudinal tape movement over the stationary drum is greatly reduced. Such an arrange-ment, however, is quite complex and expensive.
Another type of drum utilizes a cylindrical drum unit which rotates at high speed (the speed o~ the magnetic heads). Because the drum rotates at high ~peed, an air film is created between the drum and the tape. With such a design, however, accurate guiding of the tape past the heads become~
difficu~t because the tape tends to float on the drum.
United States Patent No. 3,510,60~, issued May 5, 1970 to Kell describe~ a configuration wherein a rotating drum is pecially tapered ~o as to cause air to be ~orced between the tape and the drum surface to produce an air bearing.
,. .
, ~ ' ~ ~ -2- ~
~ ; ,........... .
:...... .. .. . .
. . .
,., ~ , , .
" , , , ~ , . , ~0~ 2 A spl:Lt drum configuration is described in United States Patent No. 3,436,~91, issued April 1, 1969 to J. E. Quinn et al, which configuration utilizes an inwardly tapered upper drum section having a diameter at its bottom face that is less than the diameter o~ an adjacent stationary lower drum section.
The taper is said to reduce ~rictional drag by reducing the buildup of oxides which are rubbed from the tape by the drum.
This arrangement, as described, is intended for a helical-scan apparatus having a tape wrap angle approaching 360 degrees.
- United States Patent No. 3,840,895, issued October 8, :i 1974 to Kubo, describes a split drum configuration having a rotating lower section which carries a set o~ heads and a coaxial, increased diameter upper section which is journaled so as to be rotated by the magnetic tape passing thereover. Because guide ridges are provided on the drum sections along the edges of the tape path, which ridges rotate with their respective sections, a circular, rather than helical, tape path must b~ utilized.
Moreover, it is noted that the torque required to rotate the upper section acts as a drag on longitudinal tape movement ~ with this arrangement.
I As will be appreciated, subtle changes in head drum design can result in significant differences in per~ormance characteri~ics. Consequently, various drum configurations have been developed and tho~e described above represent only a sampling. Each con~iguratlon has advantages and disadvan-tages which are related to a degree to the overall tape scan-ning system in which the configuration cooperates.
For u~e in a cartridge video apparatus, a simple helical-scan head drum which requirea no special air supply or elaborate tape guides would be desirable. An overall tape , scanning ~ystem which operate~ at low tensio~ to reduce head .. . .
.
~ ' : - -- .. .. . .........
,. .. . . . . . . .
. .
,.... . . . . . .
.
;, . . . .. .
4~ , wear would also be de~irableg but the tension should be uni-~orm along the tape wrap path to assure uni~orm head response.
It would ~urther be desirable, particularly i.n a cartridge-type tape scanning system~ to provide for protection of the heads and head drum in the event the tape supply jams.
. .SUMMARY OF THE INVENTION
While friction drag unavoidably occurs when mag-netic tape passes over a head drum, drum arrangements accord-ing to the invention provide desirably low levels of friction : 10 drag by virtue of a specially cut away stati.onary drum sec- -.
: tion. A split drum is utilized including a rotating upper . ~ . .
: ~ section which carri.es a set of magneti.c heads, and a sta-tionary lower section which steps down to a reduced diameter ~ along a predetermined tape wrap path (e.gO, a helical wrap : ~. path ~or a helical scan recorder).
It is believed that, by so reducing the diameter of ~ ... ..
: the lower drum section, tape pressure against that stationary . lower section is decreased while attendantly shifting tape ." , ~ .
. pressure to the upper section which is rotated at a high -~ 20 speed (the scanning speed of the magnetic heads). Because the upper section rotates at high speed, a thin air bearing . is created which offers low resistance to longitudinal tape ,- ... .
: ~ movement.
~; It is also signi~icant to note that, by reducing ,.~, ;
the diameter o~ the lower section only along the tape wrap : path, in accordance with the invention, a shoulder is formed ,~ ~
: : at the lower edge o~ the reduced-diameter step, which shoulder : :
., ~
is adapted to act as a guide for tape travel, In so providing for a reduced-diametér area or step~
it has been ~ound that ~riction drag decreases sharply as the , .. . .
~084~Z
reduction relative to the upper drum diameter increses -- but only until a di~ference in diameter of around 3 mils is achieved.
Since, on the other hand, a step which is deeply cut may result in distortion of the tape, the diameter reduction is pre~erably selected to be less than 6 mils. Within a range o~ 1 to 6 mils, a desirable balance is achieved between drag reduction and limiting of forces that might cause tape distortion. It should be noted that, while the above-mentioned diameter reductions are based upon a nominal drum diameter of around one inch, it appears that the diameter reduction~or reducing frictional drag is not significantly influenced by nominal drum diameter.
With the lower drum section reduced in diameter, as discussed above, it has furthermore been found that tolerances and surface finish specifications for that section can be relaxed to reduce fabrication costs.
, i .
-~ Thus, in accordance with the present teachings, an assembly for use in scanning a magnetic tape is provided which comprises a first drum section which has attached thereto at ~ least one magnetic head and is journaled for rotation about an -: 20 axis to define trajectory for the head(s) with the first drum ~ section having a predetermined diameter about the axis. A second I
drum section is provided which i8 adjacent to and coaxial with the first drum section and includes means for maintaining such section fixed relative to the axis and means for directing a tape along a prese~ected tape wrap path which extends over the first and second drum sections with the path extending over at least a i portion of the trajectory of the head(s), the second drum section has a reduced diameter relative to the first drum sec-tion along that portion of the pre~elected tape wrap path which extends over ~uch second drum section.
In accordance with a ~urther embodiment a drum head configuration is provided ~or use in scanning magnetic tape having ::
108~ Z
a longitudinal dimension, the configuration comprising a cylindrical upper drum section having a central axis and at least one mounting face which is substantially perpendicular to the axis with the upper drum section being mounted for rotation about the longitudinal axis and having attached to a mounting face thereof at least one magnetic head, and a lower drum section which is ixedly mounted to a support to be coaxial with the upper drum section and adjacent to the head(s) with the lower drum section having a reduced diameter relative to the upper drum section along a path preselected - 10 for longitudinal movement of a tape thereover.
In a presently preferred implementation, a helical-scan head drum according to the invention cooperates in a "pusher-type" tape advancing system wherein means such as a set of springs ; applies tension at both supply and takeup ends of the tape, causing the tape to be drawn against the head drum...a capstan on the supply side of the tape relative to the head drum then meters tape transport from supply to takeup. Because the head drum, with this arrangement, is not between the capstan and the tape if ~ supply, the excessive tape tensions which may be generated by ~
~,, . . . :
~;20 ~ the capstan as it attempts to meter tape in the event of a supply ; jam are isolated from the head drum. Hence, a significant source of possible damage to the head drum and magnetic heads is avoided with a "pusher-type" system.
1 .
:
-5a-' . .:
. ~ .
. ~, . .
.
, .. .
~: ~L0~
It should be noted, however, that in a "pusher-type" system, the takeup tension must be sufficient both to move the tape across the head drum and to pull against the capstan to establish a tape tension profile along the tape wrap path. Because~ with head drums according to the inven-tion, frictional drag is low~ there is little change in tape tension as the tape passes over the head drum. With only a low tension change, tape tension levels along the tape wrap path can be maintained within a narrow range slightly above 7. 10 the minimum tension for sustaining proper operation of the particular magnetic heads which are being utilized. By achieving a flat, low level tension profile along the tape ` wrap path, head response, which varies with tension, is ,~ :
caused to be substantially uniform and the rate of head wear is kept low. Moreover, only a low tension need be applied at the takeup end of the tape.
~ ....................................................................... . . .
Significantly, the above-described characteristics ~i~ are well suited to a cartridge-type video recording/repro-.. ,i . , ducing unit. By spring loading the reels of the cartridge, the supply and takeup tensions for a "pusher-type" system can be provided. Since snagging of the supply can prove to be more of a problem wlth a compact tape cartridge than~ for , . .
exarnple, with separate reels, it becomes partlcularly desir-;able to arrange the head drum on the takeup side of the cap-~ : .
i stan to avoid head damage as discussed above. With a flat ;' ~ low level tape tension profile, head wear is low, head response i ., is uniform~ and a light spring in the cartridge can suffice to apply adequate ten~ion-producing torque at the takeup reel.
The guide shoulder on the lower sectlon o~ head drums accord-ing to the invention provides, moreover~ ~or accurate tape : .
~ tracking, for example, in a helical-scan video system.
'~ .
.~. , .
o~
The invention wil.l be described in detail with respect to the drawings~ wherein: -Figure 1 is a perspective view of a helical-scan head drum accordi.ng to the invention;
Figure 2 is a partial perspective view of such a . head drum;
Figure 3 is a parti.al cross-sectional view of such a head drum;
Figure 4 is a graphical illustration indicating the decoupling achieveable by use of a reduced-diameter step in accordance wlth the invention;
-~Figure 5 is a perspective view of such a head drum incorporated in a pusher-type tape scanning system;
Figure 6A is a simplified plan view ~or illustrating .
the tape wrap path;
.Figure 6B is a graph indicating a tape tension pro-. : file across a head drum; and Figure 6C is a graph indicating head response with .respect to tape tension.
. .
.: 20It should be noted that the step which is formed, according to the invention, in the lower drum section is i.~greatly exaggerated in the figures for purposes of emphasis and clarity. Without such exaggeration, the change from nominal drum diameter along the step would be scarcely ..
noticeable to the eye.
. ~Referring to Figure 1, a presently pre~erred head .drum 2, according to the invention, has a rotatable upper sec-tion 4 and a stationary lower section 6. The upper sectlon 1 ; carries a set o~ magnet;Lc heads 8 and is rotated at a pre-selected head speed by suitable means such as a motor (not shown), In ~orming the l.ol,ler section 6, a reduction ( ~) in . .
,' , .. .
~ ~ ~o~
diameter, relative to the diameter o~ the upper section, is provided along a predetermined tape wrap path, for example, the helical path shown~ to produce a step 10 ~see also Figure 2, where the radius reduction a is emphasized). By reducing the diameter of lower drum section 6 only along the tape wrap path3 a ledge or shoulder 12 results at the lower edge of such tape wrap path, which shoulder serves, advan- -. . tageously, as a tape guide and promotes accurate tape track-ing (see Figure 3)~ To assure that the tape does not slip over the shoulder 12, it is preferable to select a lower .. . ..
i drum section diameter that is somewhat oversized relative - -, to the upper drum section diameter3 thereby increasing the shoulder width. In other words, although the dimension ( ~) is of prime concern, the dimension (S ), Figure 2, is irrel-evant.
In reducing the diameter of the lower section 6 to produce the step 10, it has been found that frictional coup-ling between the tape and the lower section falls off sharply at first and continues to fall until a reduction (~) of about
2 mils is achieved. While some decoupling occurs with further dlarneter reduction, the rate of decoupllng is reduced and at around 3 mils the tape and lower drum section are essentially decoupled (the decoupling characteristic~ are illustrated graphically in Figure 4) Since distortion of the tape may occur as the diarneter difference (4 ) between drurn sections 4 and 6 increases, it is pre~erable to select the difference (Q ) ~ , ~ ~ :
~ to be less than 6 mils.
. ~
The above-discussed diameter differences were deter-mined for a dr~n of around one~inch cliameter and for Estar and --~30 ~ylar base magnetic tapes of one-quarter inch in width~ It ~ ~ , ~ ~ has been found, ho~,Jever, that the decoupling characteristlcs : , ::
: ' ~ , .
, : ~
, :
, .. . .
are not strongly in~luenced by drum diameter. Tape character-istics, such as width and stiffness, do influence the decoup-ling, however, satis~actory decoupling appears to be achieve-able with the commonly encountered types of magnetic tape.
The magnetic tape preferably contacts the drum 2 over a wrap angle of around 190 degrees and extends in part onto the upper section 4 over the entire tape wrap path. If the tape is caused to be entirely on the lower section 6 for a ; portion of the tape wrap path as, for example, would generally be the case for drums having wrap angles approaching or exceed-ing 360 degrees, the decoupling effect provided according to the invention would be diminished~
Referring to ~igure 5, a presently preferred imple-mentation of the invention incorporates a head drum 2 of the type described with respect to Figure 1 in a helical-type tape ?1, ~. scanning apparatus~
The preferred scanning apparatus is adapted to receive tape stored in cartridges, for example~ a cartridge ~ ~ 22. The cartridge 22 has tape supply and takeup ports 24 and ;~¦; 20~ 26, respectively, and includes means such as a set of springs (not shown) for applying tension at supply and takeup ends of ~; ~ the tape (the tension forces are indicated as FS and FTU, respectively, in Figure 5) From the supply port 24, the tape pa8ses along a tape path to a capstan assembly 28 which meters tape advance. The tape then proceeds to a roller 30 whlch, in cooperation with a roller 32, causes the tape to wrap around a head drum 2. (Note that a wrap angle of around 190 degrees is preferred as discussed above.) After passing around the roller 32, the tape returns to the cartridge at ~30 takeup port 26.
::~ . ~ , ~,~ ~
, ,' . : g ~, ~'~ : ` _ _ : , V " ' .
,' : ', . ,.... ...
; ,' ' ' ', ' ' ' , ~ , . , , : , With this arrangemerlt~ the takeup tension force serves to pull the tape past the head drum, after the tape has been metered, through the capstan assernbly 28. In so . pulling the tape, the takeup tension force establishes a pro- .
file of tape tension al.ong the tape path across the head drum -2. It is this tension which urges the tape against a set of magnetic heads 8. As menti.oned above, the head drurn 2 is, . with this arrangement, isolated ~rom the extreme tape tensions which may be generated by the relativel.y powerful capstan : 10 assembly 28 in trying to meter the tape in the event of a .. :
... supply jam~
It is significant to note that a low frictional drag .~. head drum, of the type proposed according to the invention, :. complements the operation of a "pusher-type" system (capstan ~.
ahead of the head drwn in the forward tape direction), as des-cribed above, by permitting low and yet uniform tension levels : .
to be established between the capstan 28 and the takeup port :
.. 26. Referring to Figure 6A, the tape wrap path around the `
~ head drurn 2 is illustrated in simplified form, and a wrap :
.~ 20 angle (~) along the tape wrap path is indicated. Figure 6B
,~ then indicates the tension profi.le along the tape wrap path, Tl being the supply side tension and T2 being the takeup side tension, The difference between supply and takeup tensions the integrated ~rictional drag denoted Td.
~: Figure 6C indicates the variation in head response ., , :: :: whlch occurR with variations in tape tension. To provide for . ~ a low rate of head wear, it i8 desirable to have low levels ., 1~ of tape tension. But at low tensions, head response tends to vary more sharply with changes i.n tape tension, and hence the , ~30 uniforrnity o~ tape tensi.on across the head drurn becomes o~
increased importance~ Accordingly, ln order to utilixe low .- .
~ - 10 -;''' ~ , , , --- 10~
tensions, it is desirable to minimize tension changes along the tape path. By reducing ~rictional drag, head drums according to the invention cause the tension range between Tl -and T2 to be small ahd, hence, keep the range of head response ; narrow (see Figures 6B and 6C).
It is noted that, if the upper section of the head drum were to rotate in the direction of forward tape travel, ~-the upper and lower section drag forces would be opposed, rather than additive. In fact, it is possible to form grooves in the upper section to increase coupling thereto and cause a total cancellation of drag force&. Such an approach, however, leads to increased flutter as is discussed in United States Patent No. 3,840,895, issued October 8, 1974 to Kubo. Hence, , .
even for such systems, where the upper drum rotates in the direction of tape travel, a low level of frictional drag for the lower drum section appears nonetheless desirable.
- As discussed above, the pre~ently preferred tape scanning system, by allowing uniform head response to be achieved at low tension levels, which have the advantage of reduced head wear, is well suited to a cartridge video tape unit. Such low tension levels may be achieved by a light spring which can be conveniently built into a tape cartridge , i (see United States Patent No. 2,996,264, issued August 15, 1961 to Bygdne~. Moreover, the guide shoulder of the pre-ferred head drum allows accurate tape tracking to be achieved while utilizing a helical tape wrap path.
The lnvention has been described in detail with ~ ~ particular reference to a presently preferred implementation ; thereof; however, it will be appreciated that altera~ions and modifications within the spirit and ~cope of the invention will be suggested to those ~killed in the art. For example, a tape path which is circular rather than hellcal mi~ht be ~' .
, ~ -11-, .. , ., , , , ,:
,~,. . . .
.. .. .
Z
. ' .: . . , employed, and head drums accorcling to the invention might be incorporated in a conventional tape scanning system having the capstan locatecl on the takeup side of the head drum. . -~
. , -.
~:
.' , , . :.
~ .~ .' .
'."','' ' . ,~ , :. : - ' ,,, 1~ .
1: :
;- i-: ~
J ~
.. ,, : ~ .
.
. , 5' `' . ,j ; ,{ __-~.S~
' ' ` `
;: :
, , . ..
~' ,~ ,,
~ to be less than 6 mils.
. ~
The above-discussed diameter differences were deter-mined for a dr~n of around one~inch cliameter and for Estar and --~30 ~ylar base magnetic tapes of one-quarter inch in width~ It ~ ~ , ~ ~ has been found, ho~,Jever, that the decoupling characteristlcs : , ::
: ' ~ , .
, : ~
, :
, .. . .
are not strongly in~luenced by drum diameter. Tape character-istics, such as width and stiffness, do influence the decoup-ling, however, satis~actory decoupling appears to be achieve-able with the commonly encountered types of magnetic tape.
The magnetic tape preferably contacts the drum 2 over a wrap angle of around 190 degrees and extends in part onto the upper section 4 over the entire tape wrap path. If the tape is caused to be entirely on the lower section 6 for a ; portion of the tape wrap path as, for example, would generally be the case for drums having wrap angles approaching or exceed-ing 360 degrees, the decoupling effect provided according to the invention would be diminished~
Referring to ~igure 5, a presently preferred imple-mentation of the invention incorporates a head drum 2 of the type described with respect to Figure 1 in a helical-type tape ?1, ~. scanning apparatus~
The preferred scanning apparatus is adapted to receive tape stored in cartridges, for example~ a cartridge ~ ~ 22. The cartridge 22 has tape supply and takeup ports 24 and ;~¦; 20~ 26, respectively, and includes means such as a set of springs (not shown) for applying tension at supply and takeup ends of ~; ~ the tape (the tension forces are indicated as FS and FTU, respectively, in Figure 5) From the supply port 24, the tape pa8ses along a tape path to a capstan assembly 28 which meters tape advance. The tape then proceeds to a roller 30 whlch, in cooperation with a roller 32, causes the tape to wrap around a head drum 2. (Note that a wrap angle of around 190 degrees is preferred as discussed above.) After passing around the roller 32, the tape returns to the cartridge at ~30 takeup port 26.
::~ . ~ , ~,~ ~
, ,' . : g ~, ~'~ : ` _ _ : , V " ' .
,' : ', . ,.... ...
; ,' ' ' ', ' ' ' , ~ , . , , : , With this arrangemerlt~ the takeup tension force serves to pull the tape past the head drum, after the tape has been metered, through the capstan assernbly 28. In so . pulling the tape, the takeup tension force establishes a pro- .
file of tape tension al.ong the tape path across the head drum -2. It is this tension which urges the tape against a set of magnetic heads 8. As menti.oned above, the head drurn 2 is, . with this arrangement, isolated ~rom the extreme tape tensions which may be generated by the relativel.y powerful capstan : 10 assembly 28 in trying to meter the tape in the event of a .. :
... supply jam~
It is significant to note that a low frictional drag .~. head drum, of the type proposed according to the invention, :. complements the operation of a "pusher-type" system (capstan ~.
ahead of the head drwn in the forward tape direction), as des-cribed above, by permitting low and yet uniform tension levels : .
to be established between the capstan 28 and the takeup port :
.. 26. Referring to Figure 6A, the tape wrap path around the `
~ head drurn 2 is illustrated in simplified form, and a wrap :
.~ 20 angle (~) along the tape wrap path is indicated. Figure 6B
,~ then indicates the tension profi.le along the tape wrap path, Tl being the supply side tension and T2 being the takeup side tension, The difference between supply and takeup tensions the integrated ~rictional drag denoted Td.
~: Figure 6C indicates the variation in head response ., , :: :: whlch occurR with variations in tape tension. To provide for . ~ a low rate of head wear, it i8 desirable to have low levels ., 1~ of tape tension. But at low tensions, head response tends to vary more sharply with changes i.n tape tension, and hence the , ~30 uniforrnity o~ tape tensi.on across the head drurn becomes o~
increased importance~ Accordingly, ln order to utilixe low .- .
~ - 10 -;''' ~ , , , --- 10~
tensions, it is desirable to minimize tension changes along the tape path. By reducing ~rictional drag, head drums according to the invention cause the tension range between Tl -and T2 to be small ahd, hence, keep the range of head response ; narrow (see Figures 6B and 6C).
It is noted that, if the upper section of the head drum were to rotate in the direction of forward tape travel, ~-the upper and lower section drag forces would be opposed, rather than additive. In fact, it is possible to form grooves in the upper section to increase coupling thereto and cause a total cancellation of drag force&. Such an approach, however, leads to increased flutter as is discussed in United States Patent No. 3,840,895, issued October 8, 1974 to Kubo. Hence, , .
even for such systems, where the upper drum rotates in the direction of tape travel, a low level of frictional drag for the lower drum section appears nonetheless desirable.
- As discussed above, the pre~ently preferred tape scanning system, by allowing uniform head response to be achieved at low tension levels, which have the advantage of reduced head wear, is well suited to a cartridge video tape unit. Such low tension levels may be achieved by a light spring which can be conveniently built into a tape cartridge , i (see United States Patent No. 2,996,264, issued August 15, 1961 to Bygdne~. Moreover, the guide shoulder of the pre-ferred head drum allows accurate tape tracking to be achieved while utilizing a helical tape wrap path.
The lnvention has been described in detail with ~ ~ particular reference to a presently preferred implementation ; thereof; however, it will be appreciated that altera~ions and modifications within the spirit and ~cope of the invention will be suggested to those ~killed in the art. For example, a tape path which is circular rather than hellcal mi~ht be ~' .
, ~ -11-, .. , ., , , , ,:
,~,. . . .
.. .. .
Z
. ' .: . . , employed, and head drums accorcling to the invention might be incorporated in a conventional tape scanning system having the capstan locatecl on the takeup side of the head drum. . -~
. , -.
~:
.' , , . :.
~ .~ .' .
'."','' ' . ,~ , :. : - ' ,,, 1~ .
1: :
;- i-: ~
J ~
.. ,, : ~ .
.
. , 5' `' . ,j ; ,{ __-~.S~
' ' ` `
;: :
, , . ..
~' ,~ ,,
Claims (9)
1. An assembly for use in scanning a magnetic tape comprising:
a first drum section having attached thereto at least one magnetic head and being journaled for rotation about an axis to define trajectory for said head(s), said first drum section having a predetermined diameter about said axis;
a second drum section which is adjacent to and coaxial with the first drum section and includes means for main-taining such section fixed relative to said axis; and means for directing such a tape along a preselected tape wrap path which extends over said first and second drum sections, said path extending over at least a portion of the trajectory of said head(s), said second drum section having a reduced diameter relative to said first drum section along that portion of the preselected tape wrap path which extends over such second drum section.
a first drum section having attached thereto at least one magnetic head and being journaled for rotation about an axis to define trajectory for said head(s), said first drum section having a predetermined diameter about said axis;
a second drum section which is adjacent to and coaxial with the first drum section and includes means for main-taining such section fixed relative to said axis; and means for directing such a tape along a preselected tape wrap path which extends over said first and second drum sections, said path extending over at least a portion of the trajectory of said head(s), said second drum section having a reduced diameter relative to said first drum section along that portion of the preselected tape wrap path which extends over such second drum section.
2. An assembly according to claim 1 wherein said tape wrap path is helical and wherein said second section has a nominal diameter which is at least as great at the diameter of the upper section, whereby a helical guide shoulder is pro-vided along an edge of the tape wrap path.
3. An assembly according to claim 2 wherein said tape wrap path is selected to extend transversely onto both first and second drum sections over the entire length of such path.
4. A head drum configuration for use in scanning magnetic tape which wraps thereover alone a preselected path, said configuration comprising:
a first drum section having a longitudinal axis and being, of preselected diameter over at least tape supporting portions thereof, which section includes journal means for rotatable mounting thereof relative to sais axis;
a second drum section including means for rigid mounting thereof coaxially to said first drum section, said second drum section having a reduced diameter relative to said first drum section along a preselected tape wrap path thereover;
and at least one magnetic head mounted to said first drum section at a location adjacent to said second drum section and at a distance from said longitudinal axis .
generally corresponding to the diameter of such first drum section.
.
a first drum section having a longitudinal axis and being, of preselected diameter over at least tape supporting portions thereof, which section includes journal means for rotatable mounting thereof relative to sais axis;
a second drum section including means for rigid mounting thereof coaxially to said first drum section, said second drum section having a reduced diameter relative to said first drum section along a preselected tape wrap path thereover;
and at least one magnetic head mounted to said first drum section at a location adjacent to said second drum section and at a distance from said longitudinal axis .
generally corresponding to the diameter of such first drum section.
.
5. A head drum configuration for use in scanning magnetic tape having a longitudinal dimension, said configura-tion comprising:
a cylindrical upper drum section having a central axis and at least one mounting face which is substantially perpendicular to such axis, such upper drum section being mounted for rotation about such longitudinal axis and having attached to a mounting face thereof at least one magnetic head, and a lower drum section which is fixedly mounted to a support to be coaxial with said upper drum section and adjacent to said head(s), said lower drum section having a reduced diameter relative to said upper drum section along a path preselected for longitudinal move-ment of such a tape thereover.
a cylindrical upper drum section having a central axis and at least one mounting face which is substantially perpendicular to such axis, such upper drum section being mounted for rotation about such longitudinal axis and having attached to a mounting face thereof at least one magnetic head, and a lower drum section which is fixedly mounted to a support to be coaxial with said upper drum section and adjacent to said head(s), said lower drum section having a reduced diameter relative to said upper drum section along a path preselected for longitudinal move-ment of such a tape thereover.
6. A head drum configuration according to claim 5 wherein the tape path is helical and the diameter of the lower drum is relatively reduced an amount less than 6 mils.
7. A head drum configuration according to claim 6 wherein the tape path is selected to extend over both upper and lower drum sections for the entire length of such path.
8. In a tape scanning apparatus of the type having a tape supply, a tape takeup, a head drum, and a capstan for metering tape, and wherein the tape passes along a predetermined path from the supply to the capstan, wraps around the head drum to define a helical wrap path, and wherein said apparatus includes means for applying a takeup tension to the tape, the improve-ment comprising:
a low-frictional-drag head drum having a first section which is cylindrical and has mounted thereto at least one magnetic head, said first section being (1) supported by means for permitting rotation about a central axis thereof and (2) coupled to drive means for causing rotation at a preselected speed about such central axis; and a second section which is coaxial with said first section and has a reduced diameter, relative to said first section, along the tape wrap path thereover, whereby tape pressure against the stationary second section is reduced, said second section including means for maintaining such section in fixed relation-ship to said central axis.
a low-frictional-drag head drum having a first section which is cylindrical and has mounted thereto at least one magnetic head, said first section being (1) supported by means for permitting rotation about a central axis thereof and (2) coupled to drive means for causing rotation at a preselected speed about such central axis; and a second section which is coaxial with said first section and has a reduced diameter, relative to said first section, along the tape wrap path thereover, whereby tape pressure against the stationary second section is reduced, said second section including means for maintaining such section in fixed relation-ship to said central axis.
9. A tape scanning apparatus according to claim 8 wherein said second section has a nominal diameter which is greater than the diameter of said first section, whereby a shoulder is provided on said lower section at an edge of the tape path and wherein the relative reduction in diameter for said second drum section is in the range of 1 to 6 mils.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US05/603,557 US4012792A (en) | 1975-08-11 | 1975-08-11 | Magnetic head drum configuration having a friction reducing helical step |
| US603,557 | 1975-08-11 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1084622A true CA1084622A (en) | 1980-08-26 |
Family
ID=24415946
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA253,350A Expired CA1084622A (en) | 1975-08-11 | 1976-05-26 | Magnetic head drum configuration having a friction reducing helical step |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US4012792A (en) |
| JP (1) | JPS5223315A (en) |
| CA (1) | CA1084622A (en) |
| DE (1) | DE2635844A1 (en) |
| FR (1) | FR2321166A1 (en) |
| GB (1) | GB1562619A (en) |
| NL (1) | NL7608914A (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0019825B1 (en) * | 1979-05-18 | 1985-04-24 | Matsushita Electric Industrial Co., Ltd. | Tape guide device of rotary head type video tape recorder |
| NL7905278A (en) * | 1979-07-06 | 1981-01-08 | Philips Nv | APPARATUS FOR RECORDING AND READING SIGNALS IN TRACKS ON A MAGNETIC TAPE. |
| DE3127340C2 (en) * | 1980-07-17 | 1985-01-31 | Hitachi, Ltd., Tokio/Tokyo | Guide roller for a tape movement system of a magnetic recording and reproducing device |
| DE3381911D1 (en) * | 1982-07-06 | 1990-10-31 | Matsushita Electric Ind Co Ltd | ASSEMBLING A ROTATING HEAD. |
| NL8304156A (en) * | 1982-12-08 | 1984-07-02 | Sony Corp | TIRE GUIDING DEVICE. |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3333753A (en) * | 1965-06-17 | 1967-08-01 | Ampex | Helical scan magnetic tape apparatus with a squeeze film bearing |
| US3436491A (en) * | 1966-12-27 | 1969-04-01 | Ampex | Helical scan recorder with tapered drum to prevent oxide build-up |
| NL6803410A (en) * | 1968-03-09 | 1969-09-11 | ||
| DE6753560U (en) * | 1968-09-02 | 1969-05-22 | Blaupunkt Werke Gmbh | DEVICE FOR INSERTING A MAGNETIC TAPE |
| US3840895A (en) * | 1972-04-20 | 1974-10-08 | Sony Corp | Head drum assembly with grooves perpendicular to axis of rotation |
| JPS518004B2 (en) * | 1972-08-18 | 1976-03-12 | ||
| US3930270A (en) * | 1973-07-12 | 1975-12-30 | Matsushita Electric Ind Co Ltd | Tape guiding drums of the magnetic recording and reproducing apparatus |
| JPS5087906U (en) * | 1973-12-14 | 1975-07-25 |
-
1975
- 1975-08-11 US US05/603,557 patent/US4012792A/en not_active Expired - Lifetime
-
1976
- 1976-05-26 CA CA253,350A patent/CA1084622A/en not_active Expired
- 1976-08-05 GB GB32691/76A patent/GB1562619A/en not_active Expired
- 1976-08-10 FR FR7624356A patent/FR2321166A1/en not_active Withdrawn
- 1976-08-10 DE DE19762635844 patent/DE2635844A1/en not_active Withdrawn
- 1976-08-11 NL NL7608914A patent/NL7608914A/en not_active Application Discontinuation
- 1976-08-11 JP JP51095920A patent/JPS5223315A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| US4012792A (en) | 1977-03-15 |
| JPS5223315A (en) | 1977-02-22 |
| NL7608914A (en) | 1977-02-15 |
| GB1562619A (en) | 1980-03-12 |
| DE2635844A1 (en) | 1977-02-24 |
| FR2321166A1 (en) | 1977-03-11 |
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