WO1995026025A1

WO1995026025A1 - Apparatus for and method of reducing head wear in magnetic recording devices

Info

Publication number: WO1995026025A1
Application number: PCT/US1995/003503
Authority: WO
Inventors: David Y. H. Pui; Da-Ren Chen; Keung-Shan Woo
Original assignee: University of Minnesota Twin Cities; University of Minnesota System
Current assignee: University of Minnesota Twin Cities; University of Minnesota System
Priority date: 1994-03-24
Filing date: 1995-03-22
Publication date: 1995-09-28
Anticipated expiration: 1996-09-24

Abstract

An apparatus (40, 68, 102, 113, 115) and method for reducing the wear on a surface of a rotating drum magnetic recording/reading head (12, 54, 82) by providing filtered air to an inlet region (34, 72, 90) formed where the in-feeding tape (26, 58, 84) contacts the rotating drum (12, 54, 82), to remove airborne particles and gaseous contaminants in the inlet region (34, 72, 90). The removal of particles and gaseous contaminants prevents them from abrading and chemically degrading the head (12, 54, 82) as the head (12, 54, 82) slides or scrubs against the tape (26, 58, 84) during use. The introduction of filtered air can be done by placing a filter (40) directly at the inlet (26), or by directing a filtered forced flow of air (110) into the inlet region (34).

Description

APPARATUS FOR AND METHOD OF REDUCING HEAD

WEAR IN MAGNETIC RECORDING DEVICES

BACKGROUND OF THE INVENTION The present invention relates to reducing head wear on magnetic read/record heads that are used with magnetic recording devices such as video recorders, that have a drum type head against which a tape is placed.

In the video cassette recorder the tape is moved from a cassette and is wrapped partially around the rotating drum head under a relatively high pressure. The head is generally canted or tilted relative to the center line of the tape, as well. The head surface moves at a lineal speed that is substantially higher than the speed of movement of the tape, so the head tends to scrub against the tape as it operates. After the heads have worn a certain amount they have to be replaced at a significant cost. Efforts to reduce head wear in the past have concentrated on the use of particular types of tapes, and head materials that would resist wear, but it was not recognized that part of the wear problem comes from airborne particles and gaseous contaminants that enter the tape-head interface and which adhere to the tape.

It has been discovered that there is an airflow at the inlet side of the tape feed between the rotating head and the tape, which tends to urge the air in the direction of rotation of the head. Airborne particles then will tend to get trapped between the head surface and the tape, and will adhere to the tape. The particles increase head wear as the surface of the head slides against the tape.

Experimentally it has been shown by introducing known particle sizes and concentrations, that head wear rate in micro inches per hour increases substantially linearly with changes in particle concentration and increase in particle size. Experiments using S0₂ as gaseous contaminant challenge 5 also show increased head wear with gaseous concentration. The present invention provides a direct filtration of the ambient air to remove both particulate and gaseous contaminants that enter the inlet or bight region between the rotating recording head and the tape

10. at the lead-in side of the tape-head interface.

SUMMARY OF THE INVENTION The present invention relates to an apparatus and method for reducing the head wear of magnetic recording devices by filtering the ambient air that is

15 introduced between the spinning drum type magnetic head and the much slower moving tape as the magnetic head operates. The filtering removes particles and gaseous contaminants from the ambient air to significantly reduce the abrasive wear that occurs, particularly where

20 the air carries high amounts of aerosols.

The term "recording head" will be used to means a rotating drum head used to record or play magnetic tape. Airborne particles come largely from two sources. Particles are produced within the magnetic 25. recording device itself, due to mechanical wear between the moving parts. These particles are then carried to the outlet location, that is, where the head and the tape separate after the tape has passed across the head. Particles generated from frictional wear between the

30 head and the tape interface are ejected at the outlet as the tape moves away from the recording head and at least some are carried in the air around to the tape inlet region. Wear caused particles also accumulate at the inlet region, that is the wedge shaped space where the tape is moving toward and engages the rotating drum, likely due to the detachment of particles from the tape as it moves around the guide reels, and the transport of expected wear particles with the rotating drum to the inlet.

A second source of airborne particles is the ambient environment in which the recording head is used. Atmospheric aerosols can enter the building through infiltration or through a ventilation system equipped with a coarse filter and consist of wind-blown dust, plant pollens, sea spray, combustion aerosols from automobiles and factory stacks. Other aerosols are added from cigarette smoke, cooking, skin flakes and the like. There are a number of gaseous contaminants in the atmosphere which also contribute to the increased head wear rate. These contaminants include S0₂, NOx, and gas phase organic compounds, among others. They are continuously produced in the atmosphere mostly from the combustion of fossil fuels. S0₂ and NO_x are known precursors for the formation of acid rain. Experiments have been performed by the present inventors showing increased head wear rate with increasing gaseous contaminant concentration. The head wear rate is shown to improve significantly when the gaseous contaminants are removed from the head-tape interface.

The problem involved with secondary head wear is reduced and solved by filtering the air that is introduced at the inlet region of the tape and head, by using a filter for filtering air and directing it toward the inlet to essentially exclude aerosols and gaseous contaminants which otherwise would enter the interface between the rotating drum type head and the tape. In one form of the invention, a low pressure drop, high efficiency filter made up of charged fibers that are available in the trade and which attract aerosol particles is used right at inlet region to filter passive airflow. Coating the filter with materials that will absorb gas components of the ambient air will tend to further reduce wear problems. For example, sulfur dioxide (S0₂) can be removed by a coating of a 2% Na₂C0₃/glycerin in deionized water/methanol mixtures that have been developed for denuders that were developed for the EPA. Also, NO_x can be removed with this same coating. Other coatings on the filter can be utilized for removing different materials such as organic compounds. Gaseous components also can be removed from the air by activated carbon filters treated with various coatings.

In other forms of the invention an active flow of air is established and filtered and then directed to the inlet region such that unfiltered ambient air is excluded from the rotary head-tape interface. Two devices for providing such active flow are disclosed.

The present invention thus provides a filter to remove particles and gaseous contaminants from air entering the inlet between a rotating drum magnetic recording head and the tape, to reduce head wear.

The passive airflow can be recirculated in a duct or chute from the outlet to the inlet, so the filter efficiency is increased, and disclosed a chute is placed adjacent the head and guides airflow through a filter to the inlet region.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a top plan schematic view of a typical video tape recorder/player, having a filter installed thereon according to the present invention; Figure 2 is a perspective view of the device in Figure 1;

Figure 3 is a front elevational view of the device of Figure 1; Figure 4 is a schematic top plan view of a modified form of the present invention;

Figure 5 is a further modified form of the present invention utilizing an air scoop for collecting and directing airflow; Figure 6 is a perspective schematic view of the air scoop used in Figure 5;

Figure 7 is a schematic top plan view of a further embodiment of the present invention; and

Figure 8 is a front elevational view of the embodiment of Figure 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 1, a schematically shown video cassette recorder (VCR) assembly indicated generally at 10 includes a base 11, and a rotating drum type recorder head 12 that is driven in a conventional manner with a motor indicated at 13, generally at high speed. It can be seen in Figure 3 that the axis of rotation 14 of the rotating recorder head 12 is at an angle other than perpendicular relative to the base 11. Cassette 18 is mounted in the cassette holder of the VCR in a conventional manner, and suitable guides indicated at 20 that are conventionally used guide the tape as it is moved out of the cassette 18 through the use of rollers 21, 21 mounted in movable arms so the rollers are moved along guide slots 23, 23 to hold a magnetic tape 26 tightly against the drum recording head 12. The tape is driven from one reel to another through a drive motor system 30 as shown schematically, at a lineal speed that is substantially slower than the lineal speed of the peripheral drum recording head 12 driven by the motor 13.

The tape 26 moves in the direction as indicated by the arrow 33. The rotational movement of the drum recording head 12 and the tape 26 will generate a passive flow of air into a wedge shaped inlet region indicated at 34 where the tape moves tangentially onto the surface of the drum. The air then is squeezed out but particles in the air are trapped between the surface of the drum recording head 12 and the tape 26, and since the drum recording head spins against the tape, the particles act as an abrasive to wear away the surface of the drum recording head 12. Some of the particles will be ejected out at the outlet region indicated at 36, which is where the tape separates from the drum recording head.

The normal ambient room air carries particles of sufficient number and size to be a serious problem with magnetic tape drum type heads. Because the drum recording head is moving much faster than the tape there is a scrubbing or slipping action between the tape surface and the drum recording head surface, and this causes wear on the head. In the present invention a filter assembly 40 is mounted to filter substantially all air entering the inlet or bight region 34 to remove particulate contaminants from the air so that clean air moves between the tape 26 and the outer surface of the drum recording head 12. Filter 40 is made to have a low pressure drop, and can be sized so that it has a section 42 that has an edge closely adjacent the drum recording head peripheral surface, and an opposite edge which fits just outside the outer surface of the tape at a known location of the tape, such as where a guide arm or post 21 holds the tape. The filter, as shown, is extended partially over the top surface of the drum recording head with a filter portion 44 so that the portion 44 forms a scoop for any air carried along the top of the drum recording head as well. The VCR has a cover panel indicated at 48, and the filter 40 fits under this cover, but most of the air, if not all of the air, entering into the inlet region 34 is passed through the filter 42. The inlet filter is a planar, generally thin and made of fibers that can be formed in any desired manner. A peripheral frame can be used to support the fibers. The inlet filter 40 then removes particulate material in a wide size range from 0.01 to 10 μm from air flowing through the filter. The self pumping action as indicated by the arrows 50 and will cause sufficient differential in pressure so that the air will flow passively through the filter 40 for filtering before the air enters the inlet region 34.

A modified^' form of the invention is to place the drum recording head, the tape guide posts and the tape tensioning rollers in a walled enclosure. The wall used has three sides as shown to form a housing or enclosure 64. Some cassette recorders will have walls or shields built in. In Figure 4 a wall 52 is provided to partially surround or partially enclose the drum magnetic recording head 54 and the guide posts 56 which hold the tape 58 against the drum recording head 5 . The drum recording head rotates in the direction indicated by the arrow 60. The wall 52 forming the housing or enclosure extends between the base 11 and the top wall 48 of the video cassette recorder case, so that the drum recording head is within an enclosed space 64 except for the region indicated at 66 which is occupied by the video cassette- carrying the video tape. In this form of the invention a filter 68 is provided at a small inlet opening in the wall 52 aligned with an inlet region 72 between the tape and drum recording head. A small air pump or fan 70 is used to provide a flow of air sufficient to establish an air sheath at the inlet region 72 of the cassette recorder. The flow of air directed into the inlet region is filtered by filter 68, and the particulate contaminants are removed before the flow enters the housing 64. The air pump or fan 70 is a very low volume unit powered as desired and provides filtered air movement into the inlet region 72. The air is directly filtered prior to introduction into the inlet region 72, similar to the use of the filter 40 at the inlet region 34. The filter 68 can be of any desired construction as can the filter 40, and preferably the filter 68 is a very low pressure drop filter so that the fan 70 is small. A filter with charged fibers for picking up particles as the particles enter the filter is helpful.

Figures 5 and 6 illustrate a third preferred embodiment. A drum magnetic recording head 82 is powered in the same manner as before and as is conventionally done, and the tape 84 is guided by posts 86 so that it wraps partially around the drum recording head 82 under tension as the head rotates in direction as indicated by arrow 84. An air scoop 88 is positioned to extend between the inlet region 90 between the in- feeding tape and the drum recording head 82 and an outlet region 92 formed by the outlet feed length of the tape as it leaves the drum recording head 82. The air scoop 88 has a back wall 96 and top and bottom walls 98, but has an open side indicated at 100 that faces the drum recording head. A series of filters indicated generally at 102 can be provided in the interior passageway formed by the air scoop at the end portion of the air scoop near the inlet region 90. The filters 102 can include an activated carbon filter (or other treated filters) 104 for gaseous contaminant, and a particulate filter (fibrous filters with fine fibers or charged fibers, or membrane filters) 106, adjacent the inlet 90. The advantages of having the air scoop is that a portion of the passive airflow will be recirculated from the outlet 92 back through the scoop channel as indicated by arrow 108. The recirculated airflow will have been previously filtered, and thus become less and less contaminated as it passes through the air scoop filters. This means that the life of the filter will be greater and the filters will last a longer time without becoming partially plugged. The number of particles that will need to be filtered out will be reduced with each pass of air. There will be some make up air coming in through gaps and the open side of the air scoop, but recycling of at least a portion of the airflow will provide for a substantial reduction in particles that have to be filtered as the air circulates. In this form of the invention, a small fan could be utilized as well for urging the air to go through the air scoop and filters.

Particle concentrations of air at the inlet region are reduced significantly for all size particles, particularly for particles larger than 0.08 μm which have been shown to produce high wear on the device. Also, using a coated filter medium, or activated charcoal, the concentrations of S0₂ and other gasses that cause chemical, electrochemical and galvanic corrosion problems, which in turn cause degradation of the recording head, are reduced to a few parts per billion. The mechanical wear from such chemicals is also therefore significantly reduced.

Figures 7 and 8 illustrate a further embodiment of the present invention that is similar to the second embodiment. In this embodiment, the VCR assembly indicated generally at 10 includes base 11, a rotating drum recording head 12, as shown in the first form of the invention. A tape cassette 18 provides a tape 26 that is guided around suitable guide posts 20, and by the guide rollers 22 on the movable arms. The tape 26 is held tightly against the surface of the drum recording head as in the first form of the invention, and an inlet region 34 is formed where the tape is guided onto the drum, as previously explained. In this form of the invention, however, a miniature air pump 110 (a source of positive airflow) is operated from line power, and the power is turned on when the drum recording head starts to rotate. The air pump 110 has an intake, and has an outlet from the air pump case. A pair of filters including a gaseous filter 113, and a particulate filter 115 are supported in the air pump case and pumped air passes through the filters. The filter housing wall has a nipple outlet on which a tube 117 mounts. A flow distributor or plenum housing 119 at the outer end of the tube. The plenum housing is positioned at the opening to the inlet region 34, as can be seen, so that filtered air is provided through the plenum chamber or flow distributor 119 to the inlet region. To lengthen the filter life, a sampling scoop 128 can also be placed at the outlet of the head-tape interface to direct the outlet airflow to the inlet of the air pump 110 via a tube 130. this will allow recirculation of the relatively clean air between the inlet and outlet of the head-tape interface. The air pump 110 can be a pump that is conventionally used in aquariums, and it will push a small volume of air through the filters 113 and 115 and tube 117. The flow distributor 119 can be made of any size and can actually duplicate the size of the filter 40 shown in the first form of the invention if desired. The filters 113 and 115 can be formed as a cartridge so that it can be easily replaced by removing a cover. The filters 113 and 115 provide air that has been filtered to reduce the number or particulates in the air that is introduced into the inlet region of the VCR.

The active filtration thus occurs as in the second form of the invention, in that filtered air is introduced under a positive pressure creating a flow into the inlet region, and in this instance through a flow distributor which directs the air in the region desired.

The volume of the pump 110 can be adjusted as desired, and the flow distributor 119 can be made to be streamlined to fit into tight spaces. The use of tubing

117 makes it easy to connect the filtered air outlet to the flow distributor. The flow distributor can have small baffles to direct the air to get essentially a uniform flow across the vertical height and the width of the inlet region.

As can be seen in Figure 8, the pump can be of any desired form, and a divider such as a mesh divider indicated at 120 can be used for retaining the filters 113 and 115 in position. The wall 122 of the pump housing mounts the nipple or fitting for the tubing.

The flow distributor may comprise a small pipe 123 which could be used extending vertically with a number of perforations along its vertical length to evenly distribute the forced flow of filtered air through an outlet opening of the flow distributor indicated at 125.

Because the fan and filter can be located away from the rotating drum recording head, the assembly is easier to accommodate within the existing VCR housings.

The invention will work on other recording heads, other than rotatable drum type heads. A stationary head where the tape moves past the head also will benefit from the present invention. Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.

Claims

WHAT IS CLAIMED IS:

1. An apparatus for use with a reading/recording head having a tape held against an outer surface thereof at a head and tape interface, and wherein at least the tape moves relative to the head such that a surface of the head slides relative to an engaged surface of the tape, the tape and head defining an inlet region on a side of the head where the tape is moving toward the head, the apparatus comprising a filter mounted for filtering substantially all air flowing toward and moving into the inlet region and toward the head and tape interface.

2. The apparatus of claim 1 wherein the filter is positioned to span the space between the tape and the head at the inlet region and positioned to filter ambient air immediately prior to entering the inlet region.

3. The apparatus of claim 1 and an airflow source providing forced airflow passing through the filter, the airflow being directed from the filter directly into the inlet region.

4. The apparatus of claim 3 and a wall forming at least a partial enclosure adjacent the inlet region, the airflow source and filter directing air through an opening in the wall forming the partial enclosure.

5. The apparatus of claim 3 wherein the airflow source is mounted in a separate housing, and the filter is adjacent the airflow source, and the apparatus further comprises a tube carrying the filtered air to the inlet region.

6. The apparatus of claim 5 and an air distributor positioned at the inlet region and connected to the tube to distribute filtered air across an area of the inlet region.

7. The apparatus of claim 1 wherein said head is a rotatable drum head and said filter is a generally planar member spanning the inlet region between a portion of the tape and a surface of the rotary head, whereby passive flow of air into said inlet region must pass through said filter.

8. An airborne particle and gaseous contaminant reduction apparatus for use with a head having a tape held against an outer surface thereof, the tape moving in a tape path from a tape guide to the head, the space between the head and the tape where the tape path approaches the head defining a tape inlet region, a surface of the head slipping relative to an engaged surface of the tape in use, the apparatus comprising a filter positioned to filter substantially all air directed to the inlet region to remove airborne particles and thereby to reduce contaminants in the air entering the inlet region.

9. The apparatus of claim 8 wherein the source of filtered air comprises a filter member spanning a portion of the inlet region between the tape moving in the tape path and the head to filter ambient air immediately prior to entering the inlet region.

10. The apparatus of claim 8 wherein the flow of air directed to the inlet region comprises a flow of forced air passing through the filter and directed toward the inlet region.

11. The apparatus of claim 10 and a wall forming at least a partial enclosure adjacent the inlet region, and an air pump moving air into said inlet region through a filter positioned in an opening in the wall forming the partial enclosure.

12. The apparatus of claim 8 and a scoop forming an airflow channel leading from an outlet region where the tape separates from the head, to the inlet region, and the filter being mounted in the airflow channel of the scoop.

13. The apparatus of claim 12 wherein said filter in the scoop comprises a multistage filter including an activated carbon filter and a fiber filter for removing particulate matter.

14. The apparatus of claim 8 wherein said filter comprises a fiber filter having a coating capable of removing gaseous contaminants from air that passes through the filter.

15. The apparatus of claim 11 wherein the air pump is mounted in a separate housing, and the filter is adjacent the air pump, and a tube carrying the filtered air to the inlet region.

16. The apparatus of claim 15 and an air distributor positioned at the inlet region and connected to the tube to distribute filtered air across an area of the inlet region.

17. The apparatus of claim 8 wherein the head comprises a rotating drum having an end surface transverse to an axis of rotation, and said filter comprises a generally planar filter member spanning a portion of the inlet region defined between the tape moving in the tape path at a position where the tape is spaced from the head, and including a filter portion closely overlying the end surface of the drum and being at a level above the tape adjacent the inlet region, whereby a substantial portion of air moving into said inlet region passes through said filter.

18. A method of reducing wear on an exterior surface of a reading/recording head having a tape engaging the exterior surface, said tape being held against the head and moving in a path having a portion spaced from the head, and the tape moving along the portion of the path to engage the head at a position to form an inlet region between the head and the tape moving in the path, the method comprising the step of filtering ambient air that enters the inlet region and flows toward the location where the tape engages the head.

19. The method of claim 18 wherein the step of filtering includes passing a substantial portion of the ambient air through a filter.

20. The method of claim 18 including the steps of forming a flow of air by an air pump, and the step including directing the flow of filtered air into the inlet region.

21. The method of claim 18 wherein the head rotates and is moved at a speed such that the head slips relative to the tape, and the method includes recirculating air caused by the movement of the head through a filter adjacent the inlet region.