Field of the invention

The present invention relates to a method for recording track marking information on flexible magnetical information carrier discs and to an appara¬ tus for fine adjustment of the position of a eading head _*

The method and apparatus according to the invention is generally applicable in mini-floppy and micro-floppy information recording systems, or in casette-systerns with flexible magnetical discs, in nhich the excentricity of the concentrical recording tracks is smaller than the permissible track adjusting error. The present invention facilitates the adjustment of ^" he reading head to the information carrying tracks.

Background of the Invention

In the field of floppy technique the position¬ ing and retrieval of circular infortnation reoording

tracks is solved in such a nay that concentrical and circular guiding tracks are recorded on the rear side of the circular information recording disc with an appropriate track density (e.g. 500 tracks per inch)• The information recording occurs in the first side of the disc during the reading of the corresponding rear guiding tracks, and a suitable servo-mechanical system controls the position of the reading-writing head in accordance with the guiding track. The guiding tracks are used in the same way when information is read out from the disc.

In this conventional head-adjusting system a first disadvantage lies in that a oomplete side of the disc is not used for record¬ ing useful information but only for track-guiding. A further drawback lies in that simultaneously at both sides of the disc respective writing- -reading heads should be moved. The two heads are separated by the rotating disc lying there¬ between, and a precisely adjustable mechanical link must be provided between the heads which must keep the relative position of the heads unchanged during adjustments. Such a double-sided access to the disc and the simultaneous precise adjustment of the heads raises increased difficulties in case of magnetical information recording discs placed in respective casette casings because the presence . of the closed casette renders the double-sided diso access to be difficult. Apart from a number of advantages such information recording magnetical casette disc systems have not gained wide acceptance, mostly due to the problems connected with track guiding.

It is an apparent advantage of the aforesaid conventional systems using guiding tracks that its track control can compensate the accuracy errors originating from the excentricity of the circular tracks and from the thermal deformation of the disc.

Object of the Invention

The object of the present invention is to provide a method and an apparatus that enables the solution of the task of track guiding in case of a single-sided disc access, in which there is no need of using two separate heads and in which both sides of the disc, can be used for recording useful information.

Summary of the Invention

The above object is attained by such a method in which conventional information recording occurs in information storage sectors o .circular tracks of flexible magnetical information carrier discs rotated with predetermined operational speed, in which the width of the information storage sectors is at least about 330°, and in the remaining track marking sectors of each of the tracks marking frequencies are recorded so that each marking frequency is distinguishable from the marking frequency recorded in the two adjacent tracks.

In a preferable embodiment of the method according to the invention in each even-numbered traok a first common marking frequency and in each odd- numbered track a second common marking frequency is recorded which latter is different from the first one.

According to a second aspect of the present invention the position of a reading head associated with a flexible magnetical information carrier disc is adjusted finely to the circular information recording tracks of the disc by means of an apparatus that comprises a circuit being selective to marking frequencies recorded in track marking sectors of the disc having an angular width of maximum about 30°, the circuit provides an out- put signal proportional to the amplitudes of the marking frequencies read out by the reading head, and a control unit which in response to the output signals of the selective circuit controls the out¬ put signal corresponding to a predetermined traok to reach a maximum by adjusting the radial position of the reading head.

The selective circuit of the apparatus according to the invention comprises a first selector that selects the first marking frequency component from the playback signal of the reading head and provides a direct current output signal proportional to the amplitude of this component, a second selector that selects the second marking frequency component from the playback signal of the reading head and provides a direct current out¬ put signal proportional to the amplitude of this second compon-nt, a first differential amplifier having a pair of inputs coupled to the outputs of the first and second selectors and provides an out- put voltage representing the difference of the two direct current input voltages.

The control unit of the apparatus accord¬ ing to the invention comprises preferably a second differential amplifier having a first input coupled to the output of the first differential amplifier,

a reference signal fortning unit having an output oonnected to the second input of the second differential amplifier and supplies a reference voltage associated with the predetermined track 5 to which adjustment should be made, and an adjust¬ ing means which, depending on the output signal of the second differential amplifier, adjusts the radial position of the reading head.

When using the method according to the

10 invention, the presence of the track marking sectors with an angular width falling between about 15° and 30° takes some percent of the useful information recording area, but the corresponding losses are compensated by the fact that the rear side of the

15 disc will be free for information recording and only a single head is required which substantially simplifies the constructional design.

The invention will now be described in connection with some preferable embodiments, in

20 which reference will be made to the accompanying drawings.

Brief description of the drawings

25 Fig. 1 shows the schematical top view of a flexible magnetical information recording disc with tracks of enlarged width; Fig. 2 shows the block diagram of a preferred embodiment of the apparatus according to the

30. invention with schematically illustrated enlarged tracks in front of the reading hβad| Fig. 3 shows the output voltage of the first differential amplifier of Fig. 2 as a func¬ tion of the radial displacement of the head|

Fig. 4 shows the sectional elevational view of a hub disc for.centrally fixing the flexible magnetical disc.

Description of the preferred embodiments

Fig. 1 shows an information recording disc 1 of magnetical material, which is similar to the discs used in mini-floppy systems. The accurate central mounting of the disc 1 is provided by means of its central bore 2. There are circular informa¬ tion recording tracks on the disc 1, and of these four neighbouring tracks 00, 01, 02 and 03 are illustrated in an enlarged scale in Fig. 1. In eaoh track there is provided a track marking sector 3 having an angular width c for recording a suitable marking frequency signal as it will be explained later. Within certain constructional limits the value of the angle can be chosen optionally, and this value falls preferably between 15° and 30°. The remaining information caπying sectors 4 of the tracks (shown with dashed lines in Fig. 1) comprise useful information recorded in the form of binary ones and zeros. The role of the marking frequencies recorded in the track marking sectors is to distinguish any particular track from the adjacent ones. If a respective common marking frequency is recorded in the track marking sectors 3 of every second track, then the above condition is satisfied because it will be valid for any track that the marking frequency recorded on the two neighbouring tracks will be different from that of the particular track in question. Taking into account that in the informa- tion carrying sectors the recorded information is a

^■ JΪU ζ _j

OMPI

^ τi'

sequence of frequency signals representing the bitu "l ⁿ and "0", respectively, it will be pre¬ ferable to use the same frequency signals as marking frequency signals. For example, in that case the marking frequency recorded on each track with even track number (counted from the peri¬ meter towards the center) can correspond to the frequency of the bits "0", and that which is re¬ corded on each track with odd track number can correspond to the frequency o£ the bits "1", or vice-versa.

Referring now to Fig. 2 showing a reading head 10 which is located in front (or above) of the tracks 00, 01, 02 and 03 shown in an enlarged scale, and the head 10 is precisely adjustable along arrow 11 designating the radial direction of the disc 1. The reading head 10 is generally a combined reading-writing head. A precise position adjusting means 12 is shown that adjusts the radial position of the head 10. It has not been illustrated but it iβ widely known that the coarse position adjustment of the head iβ provided by a separate head positioning assembly (with an adjusting accuracy of about 0.5 - 0.75 track width), and the precise position adjusting means 12 is capable of adjusting the posi¬ tion of the head relative to that assembly.

The output of the reading head 10 iβ coupled to a reading amplifier 13 and the output of this latter is connected to the input of a selective circuit consisting of a first frequency selector 14 and of a second frequency selector 15- The first frequency selector 14 is selective to the first narking frequency component of the read out signal and it provides an output direct current signal hav- ing a voltage corresponding to the amplitude of the

first marking frequency component. The second frequency selector 15 has a similar design, but it is selective to the second marking frequency components. The outputs of the first and second frequency selectors 14 and 15 are coupled to respective inputs of a first differential amplifier 16, the output of which being connected to a first input of a second differential amplifier 17. The second differential amplifier 17 has a second in- put and it is connected to a reference signal form¬ ing circuit 18 that supplies a direct current reference level to the second differential amplifier 18 associated with the actual marking frequency of the particular track to which adjustment should be made.

The output of the second differential amplifier 18 is coupled to a control amplifier 19 _» which in response to its input signal provides a sufficiently amplified driving signal with appropriate sign for the precise position adjusting means 12. The operation of the apparatus shown in Fig. 2 is as follows. In the position shown in the drawing the reading head 10 permanently receives the first and second marking frequencies when it is opposite to the track marking sector 3 of the diso 1. Supposing that the reading head 10 is closer to the track 01 than to the adjacent track 00, the signals recorded with the second marking frequency f ₂ generate a higher voltage in the head than the signals of the second marking frequency f ₂ » The first and second frequency selectors 14 and 15, comprising both a tuned band amplifier and a rectifier, provide direct current voltage signals at their out¬ puts that correspond to the respective marking frequency components. The two inputs of the first

differential amplifier 16 are driven by voltages

^~ tύ ^mΛ \ ^v a wherein

Ufl designates the absolute value of the first marking frequency component f,, and

uf2 designates the absolute value of the second marking frequency component f«.

The voltage U on the output of the differential amplifier 16 is the difference of the above two signals:

Fig. 3 shows the curve of the voltage U as a function of the radial displacement d of the reading head 10. It oan be seen that when the reading head 10 is in position opposite to the even-numbered tracks 00 and 02, then the value of the voltage U is at a positive maximum + „. When the reading head is in positions opposite to the odd-numbered tracks 01 and 03, then the voltage U will be at negative maximums -U«.

Depending on the particular track to which the adjustment of the reading head 10 should be made, the reference signal forming unit 18 supplies a reference signal of +U _M or -U^ to the second input of the second differential amplifier 17. In the example illustrated in Fig. 2 the position of the reading head 10 should be adjusted to the second track 01. For such an adjustment a reference voltage of -U _™ should be provided for the second differential amplifier 17. Depending on the difference between the actual voltage U and the preset reference value -ϋ _j ,, the control amplifier

- lo -

19 will provide a driving voltage to the precise position adjusting means 12. Obviously, this- latter will change the radial position of the reading head 10 until it will be just opposite to the centre of 5 the track 01. In this position the control voltage will be Bβro. The control amplifier 19 comprises an appropriate differentiating member which senseβ the sign (i.e. direction) of the control process. When the control occurs with a correct sign, the

10 oontrol voltage should be of decreasing character in time. When the differentiating member senses a sign that would move the reading head 10 away from the correct position instead of towards to it, then it activates an appropriate switch for changing the

If βiøa αf "fee output voltage of the control amplifier 19.

The control process according to the invention is sufficiently effective to bring the reading head 10 into the correct position relative 0 to the required track during the period in which the reading head 10 reads the track marking sector 3.

The above described arrangement iβ there¬ fore capable of positioning the reading head follow¬ ing a preliminary coarse adjustment. 5 Now the technical limits of the proposed way of head adjustment will be analyzed from which the track density can be determined.

The above described control system can¬ not offer protection against the deviations of the 0 . information carrying tracks on the diso 1 from the idealistic geometrically circular path, because the control is carried out only in a small sector of the whole path. Any excentrici y of the tracks results in an inaccurate positioning (offset) of 5 the reading head relative to the centra of the

track. Such excentrioity error may ariβet a) from the excentricity of the driving shaft (not shown in the drawing) that drives the disc 1; b) from the excentricity of the central bore 2 of the disc 1; and c) from the excentricity caused by the non-even thermical dilatation of the disc when unevenly distributed heat is applied to the disc.

When the maximum permitted excentrioity is arbitrarily chosed to a value corresponding to about 15 % of the radial distance (spacing) between adjacent tracks, then this amount of excentricity cannot cause noticeable playback or recording errors. Practical tests have shown that with accuracies or tolerance ranges used widely in the field of mini- -floppy technique the maximum value of the expectable excentricity is about 12.6 yum if the corresponding diameter of the disc is 120 mm and that of the bore 2 is 28 mm.

With such conditions the maximum track denβity is 302 tracks per inch.

The excentricity can be reduced substantial- ly by using discs provided with solid centering hubs.. Fig. 4 shows such a disc construction. The disc comprises a central disc-shaped hub 5 made of a firm plastic material in which a central guiding bore 6 is tooled with very small tolerances. The bore 6 communicates at its first side with a conical inlet opening 7 and at its other side with a bore 8 of larger diameter. A cylindrical outer surface 9 of the central hub 5 coaxially guides the mounting bore 2 of the disc 1. A clamping ring 5a closely fits to the cylindrical outer surface 9, whereby it

keeps the diso 1 in engagement with the central hub 5.

The tests for excentrioity have shown that in case of the construction shown in Fig. 4 with an outer disc diameter of 68 mm and with a central bore 2 diameter of 2 mm, the exoentricity was better than 6.8 yum. With this excentricity the realizable track density reaches the value of 560 tracks per inch. By using the present invention the mark¬ ing information and the useful information can be recorded in one side of the disc, which results in an information storage loss ranging between about 4 % and 8 % _t but it enables the usage of an inexpensive system with a single head in combination with a cheaper only on one side recordable disc-type. In case of using a double-sided information recording system, the present invention provides almost a double information storage capacity compared to conventional systems. The above desoribed realizable tracking density values show that the usual tracking densities used in mini-floppy technique can be used with the present invention, too.