GB1600918A

GB1600918A - Airguide for recording tape transports

Info

Publication number: GB1600918A
Application number: GB1814278A
Authority: GB
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1977-05-09
Filing date: 1978-05-08
Publication date: 1981-10-21
Also published as: FR2390890A7; AT359300B; IT7835813V0; DE7813519U1; ATA331278A

Description

(54) AIR GUIDE FOR RECORDING TAPE TRANSPORTS (71) We, BASF AKTIENGESELL SCHAFT, a German Joint Stock Company of 6700 Ludwigshafen, Federal Republic of Germany, do hereby declare the invention for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following Statement: This invention relates to an air guide apparatus of the kind adapted to support and guide recording tape as it is transported to or from a stationary transducer head, said apparatus comprising a support surface curved in the length direction of the tape to define the path to be followed by said tape between first and second regions where the tape respectively enters and leaves the influence of said support surface, a pair of spaced apart bevelled flanges located on opposite sides of said path, for laterally guiding the tape and substantially sealing against airflow about the lateral edges of said tape as it is transported over said support surface between said first and second regions. The invention also relates to a method of supporting and guiding recording tape during transport to or from a stationary transducer head.

Although many variation of high speed recording tape guides, including air guides, are known and used in the magnetic recording industry, it has been found that a number of serious problems relating to friction and tape alignment have been associated with their use. These problems become particularly acute when processing video signals due to the high tape speeds involved and, consequently, the need to record on a multiplicity of parallel tracks, each of extremely narrow width, in order to provide record and/or playback capability for programs of reasonable duration on a tape of manageable length.

For example, in a video system which operates at a tape speed of 4 metres per second, approximately 11,000 metres of tape pass the transducing head each hour.

Due to physical and cost limitations in reel size, the data is generally recorded on a multiplicity of parallel tracks, and the shorter length of tape which results is passed repeatedly past the transducer head, each time reading information from a different track. In this manner a 550 m reel of tape having 30 tracks can be used to record or playback a 90 minute program utilizing the above-described system.

However, the requirement that the tape passes through the transport 30 times per program has resulted in serious wear considerations which it has been found may be greately overcome through utilization of an air guide type of tape transport. Such prior guides utilizing a film of air as a lubricant have had serious disadvantages associated therewith, for example the generation of an unequal air pressure distribution across the width of the tape resulting in an undesirable deformation of the tape and the requirement for relatively large quantities of air flow under high pressure for supporting the guided span of tape.

Likewise, due to the requirement that 30 different informational tracks be placed in parallel relation on a tape of reasonable and economical width for consumer use, typically 6,25 cm, a related problem concerning alignment of the extemely narrow tracks on the tape with a corresponding transducer head has arisen. This problem is compounded by the fact that commercially available magnetic tape is manufactured to width tolerances which approach the individual track width required (typically about 150 llm with 50 ijm spacing between tracks) for utilization of 30 tracks on a 6,25 mm tape format. Such alignment problems have been solved by the air guide described in U.K.

Patent Specification No. 1,523,385.

In U.K. Patent Specification No.

1,523,385 there is disclosed an air guide having bevelled flanges which extend along opposite sides of the path followed by the tape as it is transported over the guide. The bevelled flanges serve not only to self-center the tape with respect to the center line of the support surface which is curved in the length direction of the tape, but also provide an air seal which substantially impedes airflow about the lateral edges of the tape, thereby providing a supporting air film of substantially constant pressure along the entire span of the guide surface. However, in this known air guide undesirable amounts of scrape flutter and contamination build-up on the guide surfaces.

The present invention seeks to solve the above problem and according to one aspect of the present invention there is provided an air guide apparatus of the kind referred to which is characterized by means for feeding air under pressure between the tape and the surface only to. or adjacent to. each of said first and second regions whereby in use an air film of substantially constant local pressure is generated in an air chamber defined by said tape. said support surface and parts of said bevelled flanges to support said tape.

Suitably the air feed means comprise air jets at or adjacent to the first and second regions (i.e. the tangent points) to prevent the coated surface of the tape from touching any portion of the guide apparatus during the transport operation. In this manner, undesirabe amounts of scrape flutter and contamination build-up on the guide surfaces at these tangent points can be eliminated, thereby improving the overall performance of a system.

One important surprising result of the present invention is that air pressure and flow problems, which were expected to be created due to the fact that a perfect mechanical air seal is not maintained between the tape and guide at the tangent points, did not develop thereby permitting the continued use of portable and inexpensive low-capacity air pumps in the system.

For not fully understood reasons, locating the air feed means only at the first and second regions (i.e. at the tangent points) apparently did not substantially impair the formation of the required air chamber between the tape, support surface and bevelled flanges and thereby it has been found unnecessary to use high volumes of pressures of air.

According to another aspect of the present invention there is provided a method of supporting and guiding recording tape as it is transported to or from a stationary transducer head, the tape being supported and guided by a support surface curved in the length direction of the tape to define the path to be followed by said tape between first and second regions where the tape respectively enters and leaves the influence of said support surface, and a pair of bevelled flanges for laterally guiding the tape, which are formed along longitudinal sides of the support surface, and which are spaced apart at their base a distance less than the minimum width of the recording tape, said method comprising: transporting the recording tape along the support surface; tensioning the recording tape so as to maintain it in close proximity to said support surface; and providing air under pressure only at or adjacent each of said first and second regions so that an air film of substantially constant local pressure is generated in an air chamber defined by said tape, said support surface and parts of said bevelled flanges, the air film pressure being sufficient to lift said tape off said support surface to a point where its width substantially equals the distance, in the width direction of the tape, between said bevelled flanges, thereby maintaining said tape laterally centered along the length of said support surface and urging said tape away from frictional contact with said support surface, said bevelled flanges and said first and second regions.

This method provides certain advantages as pointed out below in the description of one embodiment of the invention.

It has been found that although a perfect mechanical air seal is not maintained between the tape and guide at the said first and second regions because of the supply of air thereto, e.g. by an air jet system, in operation significant air pressure and flow problems have not arisen and satisfactory tape fly over the guide assembly may be obtained utilizing inexpensive air pumps which produce only in the range of 0.5 Newton/cm2 of static air pressure and 0.7 Litre per minute of air flow.

Furthermore, it has been found that the mechanical design of the air guide assembly is significantly simplified by introducing air to the system, e.g. through air jets, only at the said first and second regions (i.e. the tangent points). In such circumstances, since the tape flys at only about 25 llm over the bottom surface of the guide, it is desirable to form an additional channel in this surface so as to allow better distribution of air over the entire guide assembly as it is carried along by the tape.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a top plan of tape guiding and supporting equipment comprising an air guide apparatus constructed in accordance with an embodiment of the present invention; Figure 2 is an enlarged top plan of a portion of the equipment shown in Figure 1; Figure 3 is an end elevational view of the equipment shown in Figure 2; and Figure 4 is a partial, enlarged side view of the equipment shown in Figure 3.

In the following one advantageous embodiment of the invention is described.

Figure 1 illustrates an embodiment of a self-centering air guide 10.

A pair of corresponding guides 20 define the path of a span of magnetic recording tape 30 as it is transported past a stationary transducer head 40 of video recording/ playback equipment. The positioning of guides 20 is symmetrical with respect to head 40, which is mounted therebetween, in order to permit bidirectional transport of the tape. In the shown embodiment the longitudinal dimension of each guide 20 is formed in the shape of a segment of a cylinder having a 2.54 cm radius and the guides are mounted in the apparatus with a 1.27 cm gap between their inner edges wherein head 40 is mounted.

Each guide 20 (see Figures 2 and 3) has a support surface 24 curved in the length direction of the tape. Air jets 22 are formed in the support surface 24 only at the tangent points 32,34, i.e. first and second regions where the tape respectively enters and departs from the influence of the support surface on its way to or from the take-up and supply reels (not shown) or across head 40. Although the air providing means is shown as multiple air jets 22 it is noted that it may also comprise either single or multiple slots, holes or even a porous material section.

Figures 2 and 3 show a single pair of air jets 22 located at the entry and departure tangent points 32,34 as being the sole means for providing air under pressure along the entire length of each guide 20. By supplying air only to the tangent points 32,34, the design of the preferred embodiment simplifies construction of the guide apparatus by reducing the complexity of the air delivery system. However, since such an arrangement requires that the supporting boundary layer of air of substantially constant local air pressure which forms on the underside of the tape be carried along by the tape from the entry tangent point air jet across the downstream guide surface, a channel 25 is formed in support surface 24 so as to aid in air distribution.

Channel 25, which is best shown in Figures 3 and 4, is formed in the preferred embodiment to a depth of 125 to 150 calm and extends substantially across the entire width of support surface 24 between the entry and departure sets of air jets 22.

A pair of bevelled flanges 26 are provided in the advantageous embodiment on opposite sides of the path followed by the tape as it is transported over support surface 24.

These flanges are spaced apart at their base 27 a distance less than the minimum width of the tape to be utilized in the system. It has been found that optimal results are obtained when bevelled flanges 26 of the configuration shown in Figures 3 and 4 are utilized as a means for both laterally guiding or centering the tape and sealing against airflow about the lateral edges of the tape.

In operation, a compressed air supply (not shown) is connected to air jets 22 in guides 20 and a film of pressurized air of substantially constant local air pressure is generated along the air chamber formed by tape 30, support surface 24, flanges 26 and the tangent points 32,34 where the tape enters and exits from the guide in close proximity to the support surface as the boundary layer of air is carried along channel 25 to lift the tape off of the support surface to a point where its width substantially equals the horizontal distance between the bevelled flanges. In practice it has been found that pressure in the range of from about 356 to 508 mm (millimetres) of water is sufficient to lift the tape, under 56.7 pound of tension, to the above-described level. This operation is best illustrated in Figure 4 where tape 30 is shown supported on a film of pressurized air 50 between the bevelled flanges 26. When supported in this manner, tape 30 will rise or drop along the surface of flanges 26 as variations in tape width are experienced during the transport operation, thereby maintaining the Iontu- dinal centerline of the tape in a precise centered relationship with respect to the longitudinal centerline of support surface 24 and guide 20. Hence, lateral movement of the tape is eliminated irrespective of manufacturing variations in tape width and precision alignment of the playback head with the individual track recorded on the tape is maintained at all times.

In addition, since sufficient air pressure may be provided so as to allow for a pressure drop between the edges of the tape and the adjacent surface of the flanges so as to ensure that the tape will seek the proper level between the flanges, and since the air jets are provided at the tape entry and departure tangent points of the support surface, scrape flutter and contamination are virtually eliminated since the tape tends to be pushed away from all surfaces of the air guide thereby minimizing physical contact and resulting friction therebetween.

WHAT WE CLAIM IS: 1. An air guide apparatus adapted to support and guide recording tape as it is transported to or from a stationary transducer head, said apparatus including a support surface curved in the length direc

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Figure 2 is an enlarged top plan of a portion of the equipment shown in Figure 1; Figure 3 is an end elevational view of the equipment shown in Figure 2; and Figure 4 is a partial, enlarged side view of the equipment shown in Figure 3. In the following one advantageous embodiment of the invention is described. Figure 1 illustrates an embodiment of a self-centering air guide 10. A pair of corresponding guides 20 define the path of a span of magnetic recording tape 30 as it is transported past a stationary transducer head 40 of video recording/ playback equipment. The positioning of guides 20 is symmetrical with respect to head 40, which is mounted therebetween, in order to permit bidirectional transport of the tape. In the shown embodiment the longitudinal dimension of each guide 20 is formed in the shape of a segment of a cylinder having a 2.54 cm radius and the guides are mounted in the apparatus with a 1.27 cm gap between their inner edges wherein head 40 is mounted. Each guide 20 (see Figures 2 and 3) has a support surface 24 curved in the length direction of the tape. Air jets 22 are formed in the support surface 24 only at the tangent points 32,34, i.e. first and second regions where the tape respectively enters and departs from the influence of the support surface on its way to or from the take-up and supply reels (not shown) or across head 40. Although the air providing means is shown as multiple air jets 22 it is noted that it may also comprise either single or multiple slots, holes or even a porous material section. Figures 2 and 3 show a single pair of air jets 22 located at the entry and departure tangent points 32,34 as being the sole means for providing air under pressure along the entire length of each guide 20. By supplying air only to the tangent points 32,34, the design of the preferred embodiment simplifies construction of the guide apparatus by reducing the complexity of the air delivery system. However, since such an arrangement requires that the supporting boundary layer of air of substantially constant local air pressure which forms on the underside of the tape be carried along by the tape from the entry tangent point air jet across the downstream guide surface, a channel 25 is formed in support surface 24 so as to aid in air distribution. Channel 25, which is best shown in Figures 3 and 4, is formed in the preferred embodiment to a depth of 125 to 150 calm and extends substantially across the entire width of support surface 24 between the entry and departure sets of air jets 22. A pair of bevelled flanges 26 are provided in the advantageous embodiment on opposite sides of the path followed by the tape as it is transported over support surface 24. These flanges are spaced apart at their base 27 a distance less than the minimum width of the tape to be utilized in the system. It has been found that optimal results are obtained when bevelled flanges 26 of the configuration shown in Figures 3 and 4 are utilized as a means for both laterally guiding or centering the tape and sealing against airflow about the lateral edges of the tape. In operation, a compressed air supply (not shown) is connected to air jets 22 in guides 20 and a film of pressurized air of substantially constant local air pressure is generated along the air chamber formed by tape 30, support surface 24, flanges 26 and the tangent points 32,34 where the tape enters and exits from the guide in close proximity to the support surface as the boundary layer of air is carried along channel 25 to lift the tape off of the support surface to a point where its width substantially equals the horizontal distance between the bevelled flanges. In practice it has been found that pressure in the range of from about 356 to 508 mm (millimetres) of water is sufficient to lift the tape, under 56.7 pound of tension, to the above-described level. This operation is best illustrated in Figure 4 where tape 30 is shown supported on a film of pressurized air 50 between the bevelled flanges 26. When supported in this manner, tape 30 will rise or drop along the surface of flanges 26 as variations in tape width are experienced during the transport operation, thereby maintaining the Iontu- dinal centerline of the tape in a precise centered relationship with respect to the longitudinal centerline of support surface 24 and guide 20. Hence, lateral movement of the tape is eliminated irrespective of manufacturing variations in tape width and precision alignment of the playback head with the individual track recorded on the tape is maintained at all times. In addition, since sufficient air pressure may be provided so as to allow for a pressure drop between the edges of the tape and the adjacent surface of the flanges so as to ensure that the tape will seek the proper level between the flanges, and since the air jets are provided at the tape entry and departure tangent points of the support surface, scrape flutter and contamination are virtually eliminated since the tape tends to be pushed away from all surfaces of the air guide thereby minimizing physical contact and resulting friction therebetween. WHAT WE CLAIM IS:

1. An air guide apparatus adapted to support and guide recording tape as it is transported to or from a stationary transducer head, said apparatus including a support surface curved in the length direc

tion of the tape to define the path to be followed by the tape between first and second regions where the tape respectively enters and leaves the influence of said support surface, a pair of spaced-apart bevelled flanges located on opposite sides of said path, for laterally guiding the tape and substantially sealing against airflow about the lateral edges of said tape as it is transported over said surface between the said first and second regions, said apparatus being characterised by means for feeding air under pressure between the tape and the support surface only to, or adjacent to, each of said first and second regions whereby in use an air film of substantially constant local pressure is generated in an air chamber defined by said tape, said support surface and parts of said bevelled flanges to support said tape.

2. An apparatus according to claim 1, in which the support surface is linear in the width direction of the tape between the spaced-apart bevelled flanges at each of said first and second regions.

3. An apparatus according to claim 1 or 2, further comprising a channel formed in the support surface for enlarging the air chamber and for facilitating the distribution of air between said first and second regions.

4. An apparatus according to claim 3, wherein said channel substantilly extends across substantially the entire width of said support surface.

5. An apparatus according to claim 3 or claim 4, wherein said channel extends between the said first and second regions.

t. An apparatus according to any of the preceding claims, in which said air feed means comprises at least one jet at each of said first and second regions.

7. An apparatus according to any of the preceding claims, wherein said pair of bevelled flanges are spaced-apart at their base a distance less than the minimum width of the recording tape.

8. An apparatus according to any of the preceding claims, further comprising a compressed air supply connected to the air feeding means whereby as said recording tape travels over said support surface a film of pressurised air is generated between said tape, support surface and bevelled flanges sufficient to lift said tape off said support surface to a point where its width substantially equals the distance, in the width direction of the tape, between said pair of bevelled flanges, thereby maintaining said tape laterally centered along the length of said support surface and providing a substantial air seal between the edges of said tape and said flanges while urging said tape away from frictional contact with said support surface, said bevelled flanges and said first and second regions.

9. A method of supporting and guiding recording tape as it is transported to or from a stationary transducer head, the tape being supported and guided by a support surface curved in the length direction of the tape to define the path to be followed by said tape between first and second regions where the tape respectively enters and leaves the influence of said support surface, and a pair of bevelled flanges, for laterally guiding the tape, which are formed along longitudinal sides of the support surface and which are spaced-apart at their base a distance less than the minimum width of the recording tape, the method comprising transporting the recording tape along the support surface, tensioning the recording tape so as to maintain it in close proximity to said support surface, and providing air under pressure only at, or adjacent, each of said first and second regions so that an air film of substantially constant local pressure is generated in an air chamber defined by said tape, said support surface and parts of said bevelled flanges, the air film pressure being sufficient to lift said tape off said support surface to a point where its width substantially equals the distance, in the width direction of the tape, between said bevelled flanges, thereby maintaining said tape laterally centered along the length of said support surface and urging said tape away from frictional contact with said support surface, said bevelled flanges and said first and second regions.

10. An air guide apparatus substantially as herein before described with reference to, and as illustrated in, the accompanying drawings.

11. An air guide equipment comprising a stationary transducer head and a pair of guide apparatuses, each as claimed in any of claims 1 to 8 or 10, disposed on opposite sides of the transducer head for guiding and supporting recording tape as it is transported to or from the transducer head.

12. Magnetic tape video-recording/playback equipment incorporating the air guide equipment claimed in claim 11.