WEBBED SCANNER WINDOW

Abstract: A head assembly (10) which provides in the rotary scanner body (18) a tape support structure including a scanner opening (26), a pair of magnetic heads (16) mounted in the scanner opening for the reading and writing of data on a mag­ netic tape medium, a support member (28) disposed on the scanner body at the scanner opening and extending between the two magentic heads to support the tape as it moves across the scanner opening, said tape support structure producing dramatic improvement in signal output across the length of the head scan.

Description: The present invention relates to a recording and reproducing apparatus for magnetic recording tape and in particular to a tape support structure associated with the scanning function of the apparatus. BACKGROUND OF THE INVENTION A known record/reproduce apparatus for magnetic recording tape includes a two piece, cylindrical scanner assembly. A lower stationary guide drum includes a tape guide element positioned at the entrance of the tape to an upper rotary scanner body mounted on the stationary guide drum so as to be freely rotatable. Magnetic tape is driven around the upper scanner body by the record/reproduce apparatus along a tape path defined by the tape guide and one or more entrance and/or exit guides mounted adjacent the upper scanner body. Depending on the data format and the apparatus configuration, the upper scanner body rotates either counter to or in the direction of tape movement and contains one or more read/write heads which scan the tape at a rate which is normally much higher than the rate of linear tape movement. The apparatus moves the tape medium along a helical path for scanning; in such format the data tracks are positioned obliquely to the longitudinal axis of the tape, to maximize the width of the individual data tracks per width of tape. To align the data tracks of the tape for movement across the heads in the scanning drum the tape must follow a helical path around the scanning drum. With respect to both component and composite digital formats the read/write transducers mounted in the scanning drum are mounted in pairs to substantially reduce the cost and complexity of such mechanism. Typically the head pairs are disposed at a scanning window provided in the upper scanner body. Moreover, with respect to the recording or transmission of television signals, with substantially high multiples of tracks required for each television field, particularly in variable speed playback applications, each head pair sharing a common window experiences Automatic Scan Tracking (AST) deflections in rapid reciprocal movement (dithering) across the entire width of the scanning window to satisfy AST deflection requirements. Those AST deflections are large and necessitate a relatively wide scanner opening for the record/ playback head pair. Moreover, typical scanner opening/head structure requirements which produce satisfactory head to tape contact using older and thicker magnetic tapes produce less predictable results when a thinner tape, such as normally used for digital applications, is used, particularly when a head pair is deflected to one side of the scanner opening. There are known structures which place obstacles between the head and the scanner body to modify the head-to-tape interface; for example, in the Japanese publication 56-94539, "Cylindrical Body For Fitting Of Rotating Magnetic Head". There is, however, no known structure which provides a means for supporting the tape between a pair of separated AST scanner heads. SUMMARY OF THE INVENTION US-A-3778560 describes a head assembly for a tape transport, having the features recited in the precharacterising part of claim 1. The document also discloses two magnetic transducing heads, each having a tip end, each head being so mounted that the tip slightly protrudes from the scanner body to contact the tape as it is guided across the scanner body. Each head is mounted in a body which is a close fit in a respective slot in the scanner body. The slots are spaced apart along the helical tape path. There is, however, no window in the assembled scanner body that can diminish the air bearing and so the head to tape contact problem does not arise. The invention provides a head assembly for a tape transport including a guide drum, a scanner body mounted on the guide drum so as to be rotatable relative thereto, said scanner body having an outer diameter which is generally equivalent to that of said guide drum, and guide means defining a path which extends around the scanner body helically relative to the axis of rotation of the scanner body, characterised by a window in the scanner body, disposed adjacent the tape path, a pair of deflectable magnetic transducing heads, each having a tip end, each head being so mounted in the window that the tip slightly protrudes from the window to contact the tape as it is guided across the scanner body, the tip of each head being deflectable back and forth in a direction transverse to the tape path across a width of the said window and each head being substantially narrower than the width of the window across which it moves, and a member attached to the body of the scanner and extending across the window between the two head tips and serving to support the tape between the two head tips as the tape moves around the said path. Having described the preferred embodiment of the invention and its advantages, additional advantages should be readily apparent to the reader upon consideration of the detailed description of the invention taken in conjunction with the drawings as described below. BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a perspective view of a scanner assembly incorporating the tape support structure of the present invention; FIGURE 2A is a partial elevational view of a prior art scanner window taken from a prior art scanner assembly similar to the assembly of FIGURE 1; FIGURE 2B is an alternative embodiment of the prior art scanner window; FIGURE 3A is a partial view taken from the scanner assembly of FIGURE 1 of the tape support structure of the present invention; FIGURE 3B is an alternate embodiment of the tape support structure of the present invention; FIGURE 4A is a graphical representation of the signal output produced by a scanner assembly using the prior art structure; FIGURE 4B is a graphical representation of the signal output produced by a scanner assembly using the present invention. FIGURE 5 is a schematic representation of an edge view of the tape path across a scanner window of the prior art; FIGURE 6 is a schematic representation of an edge view of a tape path across a scanner window and a tape support member of the present invention; FIGURE 7 is a view taken along the lines 7-7 of FIGURE 6; and FIGURE 8 is an enlargement of a portion of the view shown in FIGURE 7; DETAILED DESCRIPTION OF THE INVENTION In FIGURE 1 is shown a head assembly 10 for a record/reproduce apparatus (not shown), the head assembly 10 incorporating the present invention. The head assembly 10 includes a stationary guide drum 17 and a rotary scanner body 18 mounted on the guide drum 17 for free rotary movement. Magnetic recording tape 14, used with the assembly 10 for the input/output of data, moves from a guide element 19 mounted on the outer surface of the guide drum 17 and travels in a helical path around the rotary scanner body 18 to permit read/write heads 16 contained within the scanning drum 18 of the assembly 10 to scan the tape 14, and thereby either read data from or write data on the tape 14. In the head assembly 10, the rotary scanner body 18 rotates counter to the direction of the tape movement. The rate and direction of the scanner movement can vary from the rate and direction of tape movement, depending on the apparatus and the tape format. To maximize the width of the data tracks per width of the tape 14, data tracks 20 on the tape 14 are disposed obliquely to a longitudinal axis 22 of the tape 14. Accordingly, to align the data tracks 20 on the tape 14 with the scanning heads 16 on the scanner body 18, it is necessary that the tape 14 traverse the drum 18 along a helical path. The tape guide element 19, provided on the stationary drum 17, directs the tape 14 into its helical path around the scanner body 18. The read/write heads 16 which read from or write on the tape 14 are positioned as shown in the accompanying drawings FIGURES 2 and 3. In a prior art configuration as shown in FIGURE 2A, a pair of transducing heads 16 are disposed at a common opening or window 26 in the scanner body 18. The window 26 and the heads 16 are disposed adjacent to the stationary drum 17 in FIGURE 2A but the window 26 could be located at any relative position on the scanner body 18. In an alternate construction shown in FIGURE 2B, the transducing heads 16 are mounted in a window 26a which includes a bottom wall 27. Although it is theoretically possible to use only a single pair of heads 16 at a single scanner window 26 to read from or read on the tape 14, most applications use more than one pair of magnetic read/write heads 16, which are mounted on the scanner body 18, equispaced at the periphery thereof. Thus, two sets of heads are spaced 180° apart, four sets of heads are spaced 90° apart, etc. The use of equispaced pairs of heads 16 reduces the speed of rotation for both the scanner body 18 and the heads 16, thus increasing and improving tolerances for head rotation speeds. In FIGURE 3A one embodiment of the present invention is seen as a support member or web 28 in the window 26 and between the transducer heads 16. A second embodiment of the present invention, shown in FIGURE 3B, includes a web 28a which is inserted in the window 26a to extend between the heads 16a and engage a bottom wall 27a. The function of the support member 28 is better understood when preceded by a brief description of the scanning process. Transducing heads 16 having a generally tapered upper body portion (not shown) terminate in head tips 16a which are also at the approximate mid-point thereof. The head tips 16a contact the tape 14 to read or write thereon. Although the head tips 16a appear to be in parallel alignment in FIGURE 3A, because the tape 14 moves obliquely across the face of the scanner body 18, each of the head tips 16a read or write on different tracks 20 on the tape 14. Moreover, in a video format the head tips 16a move along a transverse axis 30 in a rapid back and forth traverse across the width of the scanner window 26 (referred to as a dithering motion in the video art) as depicted by the arrow 31. In the first embodiment disclosed, the width of each scanner window is approximately 2 millimeters (mm). In FIGURE 3A, the direction of tape movement around the scanner body 18 is approximated by the arrow 32. The length of the scanner window is typically in the range of six to seven mm. The distance between the transducing gaps of the head tips 16a is typically three to four mm. The tape 14 (FIGURE 1) moves along the guide element 19 (FIGURE 1) on the guide drum 17 and onto the scanning drum 18 along a helical path as shown by the directional arrows 32 in FIGURES 1 and 3A. To encourage contact between the tape 14 and the edge guiding element 19 of the stationary guide drum 17, the diameter of the scanner body 18 is slightly larger than the diameter of the guide drum 17. Although it has been found that the elimination of a bottom wall, such as the wall 27 in FIGURE 2B, serves to better establish the air bearing between the tape 14 and the scanner assembly 10 to facilitate the movement of tape 14 around the scanner body 18, the use of a bottom wall 27 better insulates the tape 14 from crosstalk. The support member 28, according to the present invention, in the scanning window 26 also produces a substantially improved and unexpected result in signal output. That substantial improvement in signal output can be readily seen in a comparison of FIGURES 4A and 4B. Graph 4A, which represents the prior art structure of FIGURE 2, shows a substantial drop-off (-4.5dB) in signal output from the start 32a to the end 32b of the head scan 32, while the present invention produces a substantially clean and uniform signal output from the start 34a to the end 34b of the head scan 34 as shown in FIGURE 4B. While the addition of the support member 28 to the window 26 could be expected to better support the tape 14 as it moves across the window 26, the magnitude of the dramatic and substantial improvement in signal output (+4.5dB) is an unexpected but welcome result developing from structural changes made. An examination of the structural relationship occurring at the head-to-tape interface is discussed below in conjunction with FIGURES 5-8. FIGURE 5 is a top plan view of the tape 14 moving across the scanner opening 26 in the prior art structure. Note that a substantial dip (at least 0.005 in) occurs on the opposite sides of the transducer heads 16 as the tape 14 moves across the scanner opening 26. As shown in FIGURE 6, the addition of the web member 28 results in a substantial reduction (<<<0.005 in.) of tape dip. A complementary problem is shown in FIGURES 7 and 8 which relate to the amount of tape dip along the width of the window 26. The addition of the web 28 between the heads 16 produces a substantial decrease in the tape dip at the side of the heads 16 as shown by comparing the solid line 30 of the present invention with the dotted line 32 of the prior art construction in FIGURES 7 and 8. The above structural analysis suggests several reasons for the improvement in signal output noted, but may not completely explain it. A more meaningful measurement might result from monitoring the distance X between the head tip 16a and the tape 14 (FIGURE 8) from beginning to end of head scan. At present, we only know that a specific physical modification to a scanning window structure produces a dramatic and unexpected improvement in signal output during a typical head scan.

Claims: A head assembly for a tape transport including a guide drum (17), a scanner body (18) mounted on the guide drum so as to be rotatable relative thereto, said scanner body (18) having an outer diameter which is generally equivalent to that of said guide drum, and guide means (19) defining a path which extends around the scanner body helically relative to the axis of rotation of the scanner body, characterized by a window (26) in the scanner body, disposed adjacent the tape path, a pair of deflectable magnetic transducing heads (16), each having a tip end, each head being so mounted in the window that the tip slightly protrudes from the window to contact the tape as it is guided across the scanner body, the tip of each head (16) being deflectable back and forth in a direction transverse to the tape path across a width of the said window (16) and each head being substantially narrower than the width of the window across which it moves, and a member (28) attached to the body of the scanner and extending across the window between the two head tips and serving to support the tape between the two head tips as the tape moves around the said path. A head assembly as claimed in claim 1 wherein the window (26) in the scanner body is disposed near the interface between the scanner body and the guide drum. A head assembly as claimed in claim 2 wherein the window (26) includes a bottom wall (27a) adjacent the interface between the scanner body (18) and the guide drum (17). A head assembly as claimed in claim 2 wherein the said window (26) is located on the scanner body at the interface between the scanner body and the guide drum so that it is open at its bottom margin. A head assembly as claimed in any of claims 2 to 4 wherein the magnetic heads (16) are mounted in the said window (26) so that the distance between the transducing gaps of each respective head tip is in the range of two to five millimeters, the length of the said window (26) is in the range of six to seven millimeters, and the width of the window (26) is approximately two millimeters.

Inventors: MAGNUSSON, STEVEN, L.
Applicants: AMPEX CORPORATION
Application year: 1988
Main classification: G11B15
IPC codes: G11B15