Magnetic Transducer Platforms With Protective Fairing

1. Field of the Invention

The present invention relates to a platform, i.e., a supporting structure, containing at least one transducer for reading from and/or writing on a data carrier. It is applicable in particular to the magnetic peripherals of data processing systems, such as disc memories.

2. Description of the Prior Art

In data processing systems, the application of magnetic disc memories is becoming increasingly frequent because of their storage capacity and of the relatively short access time. Access time is the period taken by a read and/or write transducer to gain access to data contained at a particular point on the discs from the instant in which the transducers receive the order from the said processing system to gain access to this data.

Magnetic discs conventionally carry data on circular and concentric recording tracks which have a radial width not exceeding several hundredths of a millimeter, and covering the major part of their two surfaces. If a memory of this kind comprises several discs, the discs are parallel, co-axial and most frequently of the sare diameter. Whether the memory comprises several discs or one only, the disc(s) is driven at a constant speed of revolution by an electric motor.

In current practice, each surface of a disc commonly has associated with it a single transducer. To make an appreciable reduction in the time spent to gain access to any data item contained on this surface, the latter may have associated with it several transducers, of which the number does not exceed one or two tens of units and remains considerably smaller than the number of tracks. In the remainder of the description, the term "disc surface" shall imply the association of the surface with one or more transducers.

The transducers associated with one surface of a disc are generally carried by one and the same principal member installed as part of a platform which also comprises a suspension device secured to this principal member. By extension, it is said that the principal member (and equally the platform) is associated with the said surface.

There are two conventional types of platforms, namely:

(1) platforms of the movable kind which are displaced radially above the disc surface associated with them. Radial orientation of the platform enables the transducer(s) carried by their (its) principal member to be positioned so as to be able to gain access to any information contained on the associated surface. In this case, the suspension device of the platform is installed on a carriage or slide which is displaced at the outside of the discs.

(2) platforms of the stationary kind which, during the read and/or record operations, remain permanently still above defined tracks on the disc surface with which the transducers of their principal member are associated, each of these remaining associated in time with one and the same track. In this case the platform suspension device is secured to the framework of the disc memory.

It is apparent that notwithstanding its nature of the platform, (stationary or movable) the platform is secured via its suspension device to supporting means which is a carriage for a platform of the movable kind, and a framework of the disc memory for a platform of the stationary kind. The platforms most frequently utilized in current practice, are of the movable kind.

Most often, the transducers form a magnetic circuit around which is arranged a winding, and which comprises an air gap. This winding is connected by electrical input and/or output conductors to the electronic read and/or record circuits of the disc memory which comprises the transducers.

The variation of the magnetic induction within the air gap of each transducer allows of reading and/or recording (writing) data on the surface of the disc associated with it. Because of this, the air gap consequently constitutes the transducer device for picking up (reading) and/or recording (writing) data.

As a rule, but not exclusively, the principal member of a platform has the form of a comparatively flat right angle parallelepiped of which a first "large surface" positioned opposite the surface of the disc contains the air gap or gaps of the transducer(s), the second "large surface" extending substantially parallel to the first, containing the ends of the input and/or output conductors attached to the transducer(s).

During the rotation of the disc, a cushion of compressed air is formed between the disc and the first "large surface" of the principal member, which prevents this member touching and consequently damaging the disc. It is then said that the principal member flies above the disc.

The distance between the air gap(s) of the transducer(s) and the disc surface is referred to as "flight altitude" or else "flying leight" of the principal member. It is usually of the order of several tens of microns. The air cushion exerts a pressure on all or part of the first "large surface" of the principal member at right angles to the same and directed towards its second large surface". The part of the "first large surface" which is exposed to the pressure of the air cushion is referred to as "flying surface". The resulting force is referred to as "lift of the principal member" which is a function of the flying surface.

The dynamic balance of the principal member in flight is obtained by opposing to the lift an equal and opposite force referred to as "loading force" which is commonly applied to the "second large surface".

Platforms known under the name of "Winchester" platforms are utilized ever more frequently in current practice. Platforms of this nature are produced in particular by the company "Applied Magnetic Corporation" (A.M.C.) under reference numbers 3304 and 3305.

A platform of the "Winchester" type is produced in the following manner.

One or more chemicals (which are often referred to as grooves) are formed on the lower surface of its principal member, their depth being greater than or equal to 30 microns, and being able to reach up to several tenths of a millimeter. The result thereof on this surface is the presence of several projecting parts which are referred to as skids. In common practice the skids are ski-shaped.

The surface of the skids opposite the surface of the disc forms the flying surface. The lift being proportional to this surface, it is apparent that the grooves made in the lower surface of the principal member make is possible to reduce the lift and consequently the loading force by reducing the flying surface (as compared to a principal member lacking grooves). Said loading force is provided, for example, by a preloaded spring associated with the platform suspension device. (In particular cases in current practice, the said spring forms all or part of the suspension device itself).

This loading force is comparatively small and of the order of ten to twenty grammes. Because of this, it is said that the "Winchester" type of platform is a low-load platform.

As a rule, flight of a principal platform member of the "Winchester" type above the surface of the disc associated with it, occurs in such manner that the surface of the skid is generally sloping with respect to the surface of the disc. This endows said skids with sufficient lift for the flight of the principal member to be comparatively stable.

The low-load platforms of the "Winchester" type which consequently have low flight altitude, make it possible:

(1) on the one hand, thanks to this low flight altitude, to obtain read signals delivered by its (their) transducer(s) which are of relatively great amplitude, which allows of satisfactory reading reliability,

(2) on the other hand, thanks to their low load, to prevent the principal member of the platform from striking the disc and consequently damaging this latter as well as the said principal member.

However, in view of the low loading force, these platforms have certain disadvantages. For example, the probability that the flight of their principal member above the disc surface associated with it is comparatively unstable, cannot be disregarded. Further, the principal member of the suspension device is exposed to other forces than the loading force such as "parasitic forces". These parasitic forces are caused, for example, by:

(1) vibrations generated by different elements of the disc memory, such as the disc driving motor, or the motor, or the motor for driving the carriage which carries the device for suspension of the platform;

(2) inherent oscillatory displacements of the principal member around a median position which causes the same to move away from or towards the dics; and

(3) air turbulence close to the surface of the disc associated with the transducer of the principal member of the platform.

If the disc memory comprises several discs, this turbulence is particularly large in the space present between two discs. The resultant forces act essentially on the suspension device. The forces caused by the turbulence are counted among the most substantial of the parasitic forces.

It can be readily appreciated that these parasitic forces cause the flying height of the principal member to vary appreciably which causes very appreciable variations in the amplitude of the read signals, which for their part may lead to faults in determing the value of the data recorded on the discs. It is of importance, therefore, to reduce the magnitude of the said force, either by suppressing all or part of these, or by restricting their effect.

In current practice, the parasitic forces caused by inherent vibrations of the principal member of the platform are reduced by placing its suspension device as close as possible to the disc surface with which the principal member is associated.

To this end, the suspension device is secured within a groove in the principal member, the groove for example being formed in the "second large surface" containing the extremities of the input and/or output conductors of the transducers of this member. The suspension device may equally be secured within a groove formed in the "first large surface" situated opposite the surface of the disc associated with the transducer of the principal member. This last solution is described in greater detail in the French patent application Ser. No. 78 15765 filed May 26th 1978, entitled "Platform Having At Least One Transducer For Reading From And/Or Writing On A Data Carrier", and corresponding U.S. application Ser. No. 37,725, filed May 16, 1979 now U.S. Pat. No. 4,261,024, both of which are assigned to the assignee of the present invention.

In accordance with the present invention, in order to eliminate the parasitic forces caused by the air turbulence, the platform is provided with a substantially U-shaped framework or protective fairing device which envelopes the principal member and all or part of the suspension device, so modifying the flow of air around these. This makes it possible to limit or even cancel the actions of the turbulent layers on the flying height of the principal member.

In accordance with the invention, the platform containing at least one transducer for reading from and/or writing on a data carrier, which comprises a principal member containing the said transducer and a suspension device connected on the one hand to the said member and on the other hand to platform supporting means, the "first large surface" of the principal member containing the means for reading and/or recording data is characterized in that is comprises means for modifying the air flow around all or part of the principal member and of the suspension device.

Other features and advantages of the device of the invention will appear by way of non-limiting example and with reference to the accompanying drawings:

FIG. 1 illustrates a platform in accordance with the prior art, comprising at least one transducer of which the principal member is illustrated in flight above a magnetic disc D and comprises FIGS. 1a-1d; FIG. 1a being a sideview; FIG. 1b being a front view; FIG. 1c being a view from below; and FIG. 1d being a three-quarter perspective view, showing the suspension device and the first large surface of the principal member;

FIG. 2 shows how the turbulence act on two prior art platforms, when they are situated in a space present between two discs D.sub.1 and D.sub.2 ;

FIG. 3 shows a first embodiment of a platform in accordance with the invention, of which the principal member comprises two transducers, the platform being shown in flight opposite a disc D.sub.3 ;

FIG. 4 is an exploded three-quarter perspective view, showing two platforms according to the invention positioned opposite the two discs D.sub.4 and D.sub.5 and within the space present between these two discs, their protective fairing devices having a common partition;

FIG. 5 is a set of two FIGS. 5a and 5b showing the platform of FIG. 4 as seen from the rear and side in the form of simplified sketchas.

For a better understanding of the structural and operational principles of the platform comprising at least one transducer in accordance with the invention, it is useful to recall a number of features illustrated by FIG. 1 showing a platform PL.sub.a in accordance with the prior art.

Initially considering the side view of FIG. 1a, the front view of FIG. 1b and the bottom view of FIG. 1c, this platform comprises:

(1) on the one hand, a principal member CPL.sub.a of substantially parallelepiped shape, illustrated in the form of a catamaran comprising two skids PA.sub.1 and PA.sub.2 between which is situated a groove R; and

(2) on the other hand, a suspension device SUSP.sub.a.

Each of the two skids PA.sub.1 and PA.sub.2 comprises a transducer, the skid PA.sub.1 comprising the transducer TR.sub.1 and the skid PA.sub.2 comprising the transducer TR.sub.2. The transducers TR.sub.1 and TR.sub.2 have the corresponding read and/or record air gaps E.sub.1 and E.sub.2. The two skids comprise, respectively, on the one hand a principal flying surface SV.sub.1 and a chamfer CH.sub.1 having a sloped surface s.sub.1, and on the other hand a principal flying surface SV.sub.2 and a chamfer CH.sub.2 having a sloped surface s.sub.2. The flying surface of the skid PA.sub.1 is equal to SV.sub.1 +s.sub.1 and the flying surface of the skid PA.sub.2 is equal to SV.sub.2 +s.sub.2. The total flying surface of the principal member CPL.sub.a of the platform PL.sub.a is thus equal to SV=SV.sub.1 +s.sub.1 +SV.sub.2 +s.sub.2.

As is apparent from FIG. 1a, wherein is shown the principal member CPL.sub.a of the platform in flight above the magnetic disc D which travels past at a constant speed in the direction of the arrow f, the platform inclines slightly with respect to the disc surface in such a manner that the air gaps E.sub.1 and E.sub.2 are situated at a flight altitude a.sub.1 above the disc D which is smaller than the flight altitude a.sub.2 of the chamfer CH.sub.1 and of the chamfer CH.sub.2. The two flight surfaces SV.sub.1 and SV.sub.2 define a plane which intersects at an angle (not shown) with the disc surface. This angle is very small and of the order of a few milliradians. If a point P of the disc D is considered, it is apparent that the latter passes successively adjacent to the chamfer CH.sub.1 and, then, adjacent to the air gaps E.sub.1 and E.sub.2. It is then said that the chamfers CH.sub.1 and CH.sub.2 are situated to the front of the flying surface of the principal member CPL.sub.a and that the air gaps are situated to the rear of the flying surface.

One of the extremities EX.sub.1 of the susepnsion device SUSP.sub.a is secured by any appropriate means to platform carrying means which, when the lattar is movable, are formed by a carriage which makes it possible to displace the platform radially with respect to the tracks of the magnetic disc D (the carriage is not illustrated in FIG. 1 in order to simplify matters).

As best shown in FIG. 1d, the other extremity EX.sub.2 of the suspension device SUSP.sub.a is secured to the principal member CPL.sub.a, within a groove or channel R, for example formed in the upper surface of the same.

When the member CPL.sub.a flies above the disc D, an air cushion is formed between the flying surface SV and the disc surface, which exerts a thrust force F.sub.p on the principal member (F.sub.p is the lift) which is proportional to the flying surface and equal to k.times.SV (k being a proportionality factor).

To establish dynamic blance of the principal member of the platform in flight above the disc D, a force F.sub.c is applied on the second "large surface" of the same, for example by means of a pivot P. This force F.sub.c which is the loading force, or else the load, is of the order of ten to twenty grams and is provided by the blade LS illustrated in FIG. 1d, which blade acts as a spring.

Under these conditions, the transducers TR.sub.1 and TR.sub.2 then have a flight altitude a.sub.1 substantially equal to 0.4 to 0.5 microns.

Considering now FIG. 2, this illustrates two prior art platforms namely PL.sub.a and PL'.sub.a in flight above the surfaces of two discs D.sub.1 and D.sub.2 of a disc memory comprising a plurality of discs (the other discs not being illustrated to simplify matters). These platforms are located within the space E situated between the two discs D.sub.1 and D.sub.2.

In current practice, for the purpose of eliminating dust and all other kinds of impurities found in the space E, the disc memory comprises a ventilation system (not shown in FIG. 2 to simplify matters), which causes air to circulate along the surface of the two discs D.sub.1 and D.sub.2, latter up to their peripheries. This air, which will be referred to as "ventilated air" flows tangentially to the surface of the discs in the directions denoted by the arrows f.sub.1 and f.sub.2.

Because of the rotation of the discs, the ventilated air tends to be drawn along in the direction of this rotation, tangentially to the circular tracks of the disc. Its speed close to one of the tracks (that is to say at a distance of several microns) which is equal to the linear tangential speed of any point of the track in question is greater close to a track at the periphery than close to a track nearer to the center. Conversely, the pressure of the ventilated air is lower close to the periphery than close to the center.

The following consequences result: for any point situated between a track having a particular serial number P.sub.O and a track at the periphery of the disc, the pressure of the air outside the space E situated between the discs D.sub.1 and D.sub.2, which pressure is equal for example, to atmospheric pressure. This has the result that a part of the external air penetrates into the space E, which is denoted in FIG. 2 by the arrow F.sub.1 and F.sub.2. The encounter between the ventilated air flowing in accordance with the arrows f.sub.1 and f.sub.2 and the external air flowing in accordance with the arrows F.sub.1 and F.sub.2 gives rise to turbulence or turbulence layers V.sub.1, V.sub.2, V.sub.3, V.sub.4, etc... These turbulence layers or turbulence act on the platforms PL.sub.a and PL'.sub.a in the following manner: whether the platform PL.sub.a (or PL'.sub.a) be exposed to very small displacements (smaller than the width of a track) or to more substantial displacements, it is exposed successively to forces FT.sub.1, FT.sub.2, (FT'.sub.1, FT'.sub.2) which are producing turbulence, as shown in FIG. 2. This causes variations either in the flight altitude a(a') of the tranducers TR.sub.1 and TR.sub.2 (TR'.sub.1 and TR'.sub.2) of the platform PL.sub.a (PL'.sub.a), or vibrations of the suspension device SUSP.sub.a (SUSP'.sub.a) which equally cause variation of the said flight altitude. This leads to appreciable variations of the amplitude of the signals delivered by each of the transducers TR.sub.1 and TR.sub.2 (TR'.sub.1 and TR'.sub.2). Thus, if the signal delivered by each of the transducers TR.sub.1 and TR.sub.2 has a mean amplitude equal to U.sub.m for a mean flight altitude a.sub.m, the amplitude of the signals delivered varies in practice between two values U.sub.min and U.sub.max which are equal, respectively, to (U.sub.m -50% U.sub.m) and (U.sub.m +50% U.sub.m).

In order to reduce the risk of errors in establishing the value of the data corresponding to each of these signals, it is thus necessary to reduce or even eliminate either the said turbulence layers or their effects at the level of the principal member as well as of the suspension device of these platforms.

The platform in accordance with the invention, illustrated in FIGS. 3, 4 and 5, makes it possible to obtain the desired result. As is apparent from FIG. 3, the platform PL.sub.i1 which is a first embodiment of the invention, comprises a protective fairing device PROTECT.sub.i1 which surrounds the suspension device SUSP.sub.i1 and the principal member CPL.sub.i1 except for parts of these which are opposite the disc D.sub.3 associated with the transducers TR.sub.3 and TR.sub.4 of the principal member CPL.sub.i1. As apparent from the lower part of FIG. 3, the protective device PROTECT.sub.i1 comprises a wall CLOIS.sub.i1 situated at the side of the second "large surface" of the principal member CPL.sub.i1 and which has a surface substantially perpendicular to the surface of the disc D.sub.3. The device PROTECT.sub.i1 is fastened by appropriate means, for example by rivoting or by welding, to a plate PLAQ.sub.i1 secured by means which are not shown to the carriage which carries the said platform PL.sub.i1.

Referring to FIG. 4, which illustrates a preferred embodiment of two platforms or magnetic transducer supporting structures; PL.sub.i2 and PL.sub.i3 constructed in accordance with the present invention, which associate with two discs D.sub.4 and D.sub.5, respectively. The platform PL.sub.i2 comprises a principal member CPL.sub.i2 containing two transducers TR.sub.5 and TR.sub.6. The platform PL.sub.i3 comprises a principal member CPL.sub.i3 containing the two transducers TR.sub.7 and TR.sub.8. The suspension devices SUSP.sub.i2 and SUSP.sub.i3 of the platforms PL.sub.i2 and PL.sub.i3 are identical to the suspension device SUSP.sub.i1 of the platform PL.sub.i1 in accordance with the invention illustrated in FIG. 3, which suspension device itself is identical to the device SUSP.sub.a of the platform PL.sub.a. The suspension devices SUSP.sub.i2 and SUSP.sub.i3 are integral, respectively with the plates PLAQ.sub.i2 and PLAQ.sub.i3 which are themselves attached to the same carriage which supports the said platforms PL.sub.i2 and PL.sub.i3. The device for protection of the platform PL.sub.i2 is referred PROTECT.sub.i2, whereas that for the platform PL.sub.i3 is referenced PROTECT.sub.i3. These two protective devices comprise substantially U-shaped frameworks which; have a common partition or center wall CLOIS.sub.i23 and which envelope three sides of the platforms remote from the data surfaces, as best shown, for example, in FIG. 5a. As apparent more clearly from FIG. 4, the protective fairing devices PROTECT.sub.i2 and PROTECT.sub.i3 form a one-piece protective combination ENSPROTECT.sub.i23. The lower part (see FIG. 4) of this protective combination which relates to the protective device PROTECT.sub.i2 is fastened by appropriate means (for example by rivoting or by welding) to the plate PLAQ.sub.i2, whereas the upper part of the said combination which relates to the protective device PROTECT.sub.i3 is secured by appropriate means identical to the former to the plate PLAQ.sub.i3.

Experience demonstrates, with the platform PL.sub.i1 as well as with the platforms PL.sub.i2 and PL.sub.i3, that the actions of the turbulence or turbulent layers on the amplitude variations of the signals delivered by the transducers of the said platforms are much weaker than for the platforms in accordance with the prior art. As a matter of fact, the air coming from the outside passes above or over the different protective devices PROTECT.sub.1 and ENSPROTECT.sub.i23 without passing through the immediate surroundings of the different principal members (and consequently of the transducers) CPL.sub.i1, CPL.sub.i2 and CPL.sub.i3, as well as of the suspension devices SUSP.sub.i1, SUSP.sub.i2 and SUSP.sub.i3. PROTECT.sub.i1 and ENSPROTECT.sub.i23 thus shield against turbulence by blocking airflow parallel to the data surfaces of discs D.sub.3, D.sub.4 and D.sub.5. It is then shown that the amplitude variations of these signals around the means value U.sub.m are on the order of approximately 10 to 15% of the same. It may thus be stated that the protective device PROTECT.sub.i1 of the platform PL.sub.i1 as well as the protective devices PROTECT.sub.i2 and PROTEDT.sub.i3 of the platforms PL.sub.i2 and PL.sub.i3 constitute means for modifying the flow of air around the principal member and the suspension device of the corresponding platforms, in such a manner as to limit or even eliminate the actions of the turbulent layers on the flight conditions of this same principal member opposite the disc with which it is associated. This has the results of reducing the amplitude variations of the signals delivered by the transducers around their mean value.

The protective function of ENSPROTECT.sub.i23 is further evident from the simplified drawings of FIGS. 5a and 5b showing different view of the platform of FIG. 4. FIG. 5a shows the view from the carriage or rear end of the platform, whereas FIG. 5b shows a side view of the platform. The sidewalls PROTECT.sub.i2 and PROTECT.sub.i3 are perpendicular to centerwall CLOIS.sub.i23 and the data surfaces of discs D.sub.4 and D.sub.5, as shown.

Although specific embodiments have been disclosed, it is to be understood that these are for illustrative purposes only. Accordingly, the scope of the present invention should be determined with reference to the appended claims.