GB2117959A - Magnetic-tape cleaning head - Google Patents

Abstract

A magnetic-tape cleaner comprises a post or head including a body 10 having arcuate surfaces 12, 13 over which magnetic tape 14 is wrapped. The body 10 has an opening 16 formed therein shaped so as to form first and second knife edges 22, 24 at points where the arcuate surfaces 12, 13 are in contact with the magnetic-tape 14. These knife edges 22, 24 provide scraping surfaces for the tape 14 regardless of the direction of travel of the tape 14 thereby to remove any foreign particles from the tape surface to prevent signal disturbance and form an opening 16 or cavity to entrap these particles and remove them from the system. <IMAGE>

Description

SPECIFICATION Web cleaning apparatus This invention pertains to the field of cleaning and, more particularly, to means for cleaning the surface of a moving web.

In apparatus employing a moving web which is transported from one position in the apparatus to another position in the apparatus, in many instances it is desirable continuously to clean the surface of the web of foreign materials. This is particularly true in tape-drive systems, such as for magnetic tape recorders, wherein the tape is usually drawn from a supply roll, over a tape guide, over a transducing head, and hence passes onto a take-up roll. Since the magnetic tape is in repetitive contact with mechanical surfaces, the tape is stressed in such a manner that its oxide coating will shed particles. These small particles adhere to various surfaces, such as the surface of the head or the tape guide. These loose particles may then come in contact with the magnetic tape and become redeposited or accumulate on the recording surface.Successive passages of the tape over a sliding surface in contact with the recording surface of the tape, such as the head, may have the effect of impact-welding the oxide particles onto the tape-recording surface and/or the sliding contact surface.

In a tape transport system with a peripheral belt drive such as is disclosed in United States Patent 4 172 569 the oxide-recording surface faces outward on the tape roll and contacts the belt drive. Any loose particles caught between the belt and the tape will be embossed onto the taperecording surface.

The build-up of oxide on the tape surface may cause the tape to come out of contact with the head over such a large area that a signal drop-out will occur with respect to information recorded at that area. Particles accumulating on the magnetic transducing head surface may, upon impact, weld to the head surface resulting in build-up of oxide.

This oxide build-up will eventually lift the tape away from the head transducing gap, thus reducing the amplitude of the signal transduced from the recorded information because of the tape-to-head separation. Furthermore, the oxide build-up on the head surface will present a rough surface to the tape and accelerate tape wear.

Prior United States patents Nos. 3 683 445 and 3 745 602 disclose tape-cleaning heads which have a body portion with an arcuate surface around which tape is partially wrapped, with an opening formed in the body, a knife edge or knife edges being provided in the opening. The knife edges provide a scraping surface to clean the tape as the tape moves toward the knife edge, in either direction.

In United States Patent No. 3683445, the knife blade protrudes slightly out of the opening so that it presents a cleaning edge to the tape surface in either direction of tape travel. As particles are scraped from the tape they fall into the opening and are sucked out by means of a vacuum source.

In United States Patent No. 3745602 a similar structure is employed, the blade in the opening being movable so that it rocks back and forth as direction of tape travel changes, thereby to present a sharper angle to the tape surface.

The proposals of both these United States Specifications Nos. 3683445 and 3745602 have the disadvantage that the knife edges tend to dull rapidly with time, due to tape friction, and the geometries of the cleaning devices change.

Furthermore, when tape motion stops, particles have built up at the knife edge, and as tape direction reverses, any line of debris at the knife edge will be carried away by the tape. This debris will not be removed by the opening outer wall, and will be embossed onto the tape surface.

It is, therefore, a primary object of the present invention to provide a tape cleaner that will remove loose oxide particles from a tape surface.

It is a further object of the present invention to provide a tape cleaner that will remove loose oxide particles from magnetic recording tape and deposit the removed particles in a safe location so that they cannot be returned and redeposit themselves on the tape or other parts of the magnetic tape system.

With these objects in view, the present invention provides apparatus for cleaning the recording surface of a magnetic tape and guiding the tape as it travels either forward or backward through an arcuate path, the apparatus comprising: a post body having a peripheral opening therein; a a pair of walls that diverge inwardly of the post body to define opposite sides of the opening; a pair of arcuate surfaces on the periphery of the post body, one said arcuate surface being located adjacent one side of the opening and the other said arcuate surface being located adjacent the other side of the opening, for supporting the tape; and a pair of knife edges, one at one side of the opening and the other at the other side of the opening, each formed by the intersection of a respective wall with an adjacent said arcuate surface for cleaning the tape in forward and backward directions of tape travel; said post body being located with the peripheral opening facing the recording surface of the magnetic tape and centred between the arcuate surfaces contacted by the tape; whereby tape tension forces the tape against the knife edges and the recording surface is scraped regardless of reversal of the direction of tape travel.

Accordingly, the apparatus of the invention has a specially contoured tape-cleaning post or head around which the tape is wrapped during transit, e.g. from a supply roll to a take-up roll in such a manner that the oxide surface may be passed over cleaning edges with a very controlled pressure. The shape of the cleaning post or head is such that spurious particles are removed upon the first pass of tape over the edge before embossing or welding can occur but with a low enough scraping action that no oxide bonding within the coating binder on the tape is removed.

In accordance with a preferred aspect of the invention, the tape cleaning post or head is symmetrical with respect to tape direction so that the cleaning activity is identical regardless of the direction of travel of the tape over the cleaning surface.

In the invention, the cleaning post or head is provided with an opening or cavity into which scraped-off particles drop and collect, thereby effectively insulating the removed particles from redeposit on other parts of the tape drive system.

in accordance with a still further aspect of the invention, grooves are provided before and after the cleaning edges to thereby spill entrapped air to thus ensure adequate cleaning activity at all tape speeds and to maintain a high enough pressure against the cleaning surface so that no oxide build-up occurs on the cleaning edges.

The cleaning post or head in the apparatus of the invention has the advantage that its unique shape allows it to be used for the dual purpose of providing a turn-around post or a friction post in a tape guide system in addition to being used as a tape cleaning head.

The post or head as aforesaid has the further advantages that it is symmetrical in shape thus providing identical cleaning activity in both the forward and backward direction of tape travel, and that when tape is travelling in a direction opposite to the cleaning direction, the tape acts as a strop to the knife edge not engaged in cleaning action, tending to sharpen the edge.

The arrangement of the invention has yet a further advantage in that it provides an opening or cavity through which particles that has been scaped off are pulled back into the opening or cavity, and do not build up on the edges of the cleaning post or head as for example might occur as the tape changes direction. The loose particles can be removed by means of a vacuum or by providing an aperture outside of the tape cartridge in those cases where the apparatus of the invention is embodied in an enclosed tape cartridge.

The foregoing and other objects, features, and advantages of the invention will be apparent from the following detailed description of a preferred embodiment of the invention, as illustrated in the accompanying drawing wherein:~ Fig. 1 is a perspective view of a web-cleaning device of the invention; and Fig. 2 is a cross-sectional view of the web cleaning device shown in Fig. 1.

Referring firstly to Fig. 1, a preferred embodiment of the apparatus of the invention comprises a tape cleaning post or head which is composed of a body portion 10 having arcuate surfaces 12 and 13 adapted to be contacted by a web, such as a magnetic recording tape 14 (Fig.

2) wrapped partially around the post 10. An opening 1 5 is formed in the body 10. This opening is disposed between two locations where the tape 14 contacts the arcuate surfaces 12, 13 of the post when the tape 14 is trained around the post.

As shown more clearly in Fig. 2, the opening 16 is formed by machining away or forming the material at an angle 6 to a radial plane that passes through the midpoint between the surface areas 1 2, 1 3 contacted by the tape 14. At one side of the opening, the body forms a wall 18 that intersects with the arcuate surface 12 to form a knife edge 22 where the arcuate surface 12 is in contact with the magnetic tape 14.

A A similar wall 20 is formed by machining away or forming the body portion 10 at a similar angle 61 to form another knife edge 24 between the wall 20 and the arcuate surface 13. The two knife edges 22 and 24 form identical mirror images of each other and thus provide symmetrical cleaning surfaces to clean the tape 14 in both the forward and the backward direction of tape travel. As can be seen from Fig. 2, the knife edge 22 provides a scraping surface to clean the magnetic recording tape 14 when the tape 14 is drawn from right to left in a direction toward the knife edge 22.

Conversely, the knife edge 24 provides a scraping surface to clean the tape 14 when the tape 14 is drawn from left to right in a direction toward the knife edge 24.

The angles 6 and 61 are chosen to provide just enough cleaning activity to remove the spurious particles without removing virgin oxide. An angle of 31 was found to be optimum for the configuration shown in Fig. 1 and Fig. 2. At the knife edges 22 and 24, the included angle between the adjacent walls 18 and 20 and the knife edges would be 900 plus 6 or 61. With an angle of 31 for 6 or 61 this included angle would be 121 #.

It should be understood that with the configuration shown, the angle between the wall 1 8, 20 and the respective arcuate surface 12, 13 remains substantially the same as the arcuate surface 12 or 13 wears due to tape friction. Thus the knife edges 22, 24 do not become dull in a short period of time. Further, the tape actually tends to sharpen the knife edges 22, 24 by a stropping effect.

Grooves 26 and 28 may be cut into the surface of the body 10 in order to spill entrapped air, thereby to ensure adequate cleaning activity at all tape speeds, and to maintain a high enough unit pressure so that no oxide build-up occurs on the cleaning knife edges 22 and 24.

Ideally, two of the illustrated cleaning posts would be employed, one at each side of a magnetic recording head (not shown), these being located respectively between a take-up hub and the recording head and a supply hub and the recording head in order to ensure that loose oxide particles are removed prior to the tape being passed over any sliding surface and prior to being wound upon the one or the other of the hubs, according to whether it is moving in the forward or the backward direction.

In our copending patent application No.

82 08218 (Seriai No. ) entitled "Apparatus for Reducing Tape Tension Variations in a Peripheral Belt Drive Tape Transport System" there is described a tape cartridge wherein a tape is drawn from a supply hub over a first post located so as to be in constant contact with the tape as it runs off of the supply roll. The tape is then drawn past a first turn-around idler, past a transducing head, over a second turn-around idler, over a second post, and then onto the takeup hub. The first and second fixed posts are incorporated into this system to apply a drag to the tape thus to compensate for differences in tape tension due to the particular characteristics of the cartridge as more fully described in the said patent application.The fixed friction posts are located so as to be in constant contact with the tape as it spools off of the appropriate hub, the tape describing a minimum angle of wrap around each of the posts when a minimum amount of tape is wound upon the hub, and a maximum angle of wrap around the post when a maximum amount of tape is wound upon the hub. The tape cleaning post of the apparatus of the present application can be substituted for each of the first and second friction guide-posts in our aforesaid application when they will perform the dual functions of cleaning and applying a frictional drag to the tape. When so utilized, the minimum angle of wrap around the post can be chosen to provide sufficient cleaning activity, as the particular contour of the cleaning head is such that a maximum angle of wrap will not increase the angle at which the knife edges 22, 24 contact the tape 14. Thus, no damage to the tape will occur if the wrap angle varies, as is the case in the cartridge described in the above-identified application.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention, as defined by the following claims.

Claims (4)

Claims

1. Apparatus for cleaning the recording surface of a magnetic tape guiding the tape as it travels either forward or backward through an arcuate path, the apparatus comprising: a post body having a peripheral opening therein; a pair of walls that diverge inwardly of the post body to define opposite sides of the opening; a pair of arcuate surfaces on the periphery of the post body, one said arcuate surface being located adjacent one side of the opening and the other said arcuate surface being located adjacent the other side of the opening, for supporting the tape; and a pair of knife edges, one at one side of the opening and the other at the other side of the opening, each formed by the intersection of a respective wall with an adjacent said arcuate surface for cleaning the tape in forward and backward directions of tape travel; said post body being located with the peripheral opening facing the recording surface of the magnetic tape and centred between the arcuate surfaces contacted by the tape; whereby tape tension forces the tape against the knife edges and the recording surface is scraped regardless of reversal of the direction of tape travel.

2. Apparatus as claimed in claim 1 wherein at each knife edge the included angle between the respective wall and a chord between opposed knife edges is 1210.

3. Apparatus as claimed in claim 1 or 2 wherein said post body has a pair of grooves on its periphery, at opposite sides of the arcuate surfaces from the opening, to spill entrapped air as the tape is drawn over the arcuate surfaces, thereby ensuring adequate cleaning activity at all tape speeds and maintaining a high enough unit pressure to prevent oxide build-up on the knife edges.

4. Apparatus for cleaning the recording surface of a magnetic tape substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.