GB2169433A

GB2169433A - Tape scanner guide structure

Info

Publication number: GB2169433A
Application number: GB08432585A
Authority: GB
Inventors: Roger Wakefield Fenton; Denis Geoffrey Lofts
Original assignee: Mcmichael Ltd
Current assignee: Mcmichael Ltd
Priority date: 1984-12-22
Filing date: 1984-12-22
Publication date: 1986-07-09
Also published as: GB2169433B; GB8432585D0

Abstract

A tape scanner arrangement for a video tape uses a guide structure 12 which is wear resistant, but which accurately guides the tape along a helical path. A helical recess is formed in the body of the scanner, which is formed of aluminium or the like, and a band of stainless steel is held in the recess so that it projects therefrom to constitute a hard tape bearing surface. <IMAGE>

Description

SPECIFICATION Improvements in or relating to Tape Scanners This invention relates to tape scanners and their associated mechanisms. By tape scanner is meant a recording or play back device which records information on a storage medium in the form of an elongate tape or which retrieves information therefrom. As the packing density of stored information increases, it becomes more necessary to guide the tape very accurately over a tape scanner, so that particular elements of information are precisely placed upon the tape thereby enabling the information to be faithfully reproduced. In certain kinds of tape scanner, notably those used for the recording and retrieving of video information, the tape is passed around a rotatable drum in a helical manner so that portions of it pass over a video record/play head in the correct manner.The precise shape of the helical path and the position of the tape are of great importance, but it has proved difficult to provide means which guide the tape along the required helical path, as previously used guide arrangements have relatively short lives before their bearing surfaces are worn by continual contact with the tape, or else it has proved difficult to accurately and economically mount a suitable guide with hard-wearing properties.

The present invention seeks to provide in a particularly simple manner a tape scanner having improved guide means.

According to this invention a tape scanner arrangement having a rotatable drum mounted above a tape guide stator includes a band formed of a wear resistant material retained with a bearing surface in abutting relationship with a helical disposed recess formed in the stator such that the bearing surface partially protrudes from the stator so as to be capable of engaging with the edge of a tape which passes around said drum. It is customary for the stator to be formed of a light material such as aluminium or a similar alloy, but such a material is soft and is easily cut or worn by the cutting action of the edge of a moving tape held in contact with it.Preferably the recess is provided with a continuous edge surface which extends for at least a major portion of the circumference of a circular portion of the stator, such that the outer rim of the edge surface is aligned with the cylindrical surface of the rotatable drum which carries the record/play head.

Preferably again, the band has a flat bearing surface which is disposed perpencidularly to the axis of rotation of the drum. It will be appreciated that a perfect conformity between the inner surface of the band and the surface of the recess is not required, as the edge of the tape contacts the middle regions of the bearing surface of the band. However, the accuracy of the helical profile of the bearing surface can be easily attained by correct formation of the edge of the recess which is formed in the stator by, e.g. a simple machining operation. The resulting tape scanner is of very simple construction, yet possesses the necessary very high degreee of accuracy and is able to maintain this accuracy for a very long time due to the use of a band material which can be chosen primarily for its wear resistant properties.

The invention is further described by way of example with reference to the accompanying drawings, in which: Figure 1 is a schematic and diagrammatic representation of a tape scanner carrying a helically disposed tape, and Figure 2 is a part sectional view of a tape scanner in accordance with the invention.

Referring to Fig. 1, there is shown therein a rotatable drum 1 which is mounted above and coaxial with, a cylindrical stator 2, both the drum and the stator being of similar diameters. The rotatable drum 1 carries an electromagnetic transducer more commonly termed a record/play head. Video information can be recorded, and retrieved from an elongate tape 3 which is passed around the tape scanner arrangement in a helical manner. As the rotatable drum 1 is rotated in a clockwise manner in the direction of the arrow 4, the tape is caused to move in the direction of the arrow 5. The drum rotates at a very much higher speed than that at which the tape passes over the stator so that the head traces out a series of diagonal stripes of recorded information as the tape passes over it.Appropriate tension on the tape 3 ensures that it is in close contact with the drum 1 and the stator 2 as it passes around the tape scanner arrangement between a pair of guide pins 6 and 7. In order to produce the correct scanning pattern across the surface of the tape 3 it is essential that the tape is guided precisely along a predetermined helical path. For electrical and weight reasons the rotatable drum and the stator are manufactured of aluminium or a similar alloy. Whilst such material is eminently suitable for such a purpose, it suffers from the disadvantage that it is relatively soft and is easily worn by the action of the tape passing over it. Whilst the degree of wear caused by the flat major surface of the tape is minimal, the edge of the tape can produce a serious cutting effect as the tape itself is extremely thin.Thus, edge guides formed as a part of the aluminium stator have a very short life. As thinner tapes are likely to be introduced in the future, this problem will become more serious.

An improved helical guide arrangement is illustrated in Fig. 2 in which similar reference numerals are used for like parts. The play/record head 16 is shown on this figure. In this case, the circular stator 2 is provided with a helical recess 10 which extends almost com pletely around the circumference of the stator 2. The upper helical edge 11 of this recess can be very accurately defined by a suitable machining process without any real difficulty.

A stainless steel band 12 fits into the recess 10 and abutts the surface 11. The band 12 is held in place by a series of screws 17 positioned around the circumference of the stator.

It is relatively thick so that it protrudes by a significant amount from the surface 13 of the stator 2. This ensures that the bearing surface 14 of the band 12 fully supports the lower edge of the tape 3, so that in fact, the edge of the tape 3 bears upon middle regions of the bearing surface 14. The actual shape of the band 12 is of secondary importance since it can be held firmly in contact with the helical surface 11 and it is not necessary for the underside of the band 12 to completely conform to the cylindrical base of the recess 10.

Thus, by a relatively simple expedient, the tape 3 can be very accurately guided along its helical path by means of a band 12 typically formed of stainless steel which is very wear resistant, yet which itself does not have a complex profile requiring any difficult machining operation.

Claims

1. A tape scanner arrangement having a rotatable drum mounted above a tape guide stator including a band formed of a wear resistant material retained with a bearing surface in abutting relationship with a helical disposed recess formed in the stator such that the bearing surface partially protrudes from the stator so as to be capable of engaging with the edge of a tape which passes around said drum.

2. An arrangement as claimed in claim 1 and wherein the recess is provided with a continuous edge surface which extends for at least a major portion of the circumference of a circular portion of the stator, such that the outer rim of the edge surface is aligned with the cylindrical surface of the rotatable drum which carries the record/play head.

3. An arrangement as claimed in claim 1 or 2 and wherein the band has a flat bearing surface which is disposed perpendicularly to the axis of rotation of the drum.

4. An arrangement as claimed in claim 1, 2 or 3 and wherein the stator is of a generally drum shape, with the portion of it which is adjacent to the rotatable drum being of a similar diameter as the rotatable drum, the remaining portion of the stator having a smaller cross section and a curved surface which is inset from that of the first mentioned portions, the two portions having a common helical shaped boundary.

5. A tape scanner arrangement substantially as illustrated in and described with reference to Fig. 2 of the accompanying drawing.