GB2188154A - Improvements in or relating to a method of and an apparatus for detecting the abrasive quality of a floppy disc - Google Patents

Abstract

A method of and an apparatus for measuring the abrasiveness of a floppy disc are disclosed. The apparatus comprises a head 7 adapted to be urged into contact with a floppy disc whilst the head and the disc move relative to each other. The surface 2 of the head which is urged into contact with the floppy disc is provided with a thin film of electrically conductive material e.g. of nickel-chrome alloy 100 to 400 A thick. Means are provided for measuring the electrical resistance of the thin film on the head and thus change in the film's electrical resistance can be monitored. Such change is related to the abrasiveness of the disc and calculations can be undertaken to determine the abrasiveness from the change in resistance measured. As described the head comprises an alumina ceramic substrate 1 with a flat upper surface 2 bounding a recess 3. Leads 6 are soldered to nickel-coated regions 5 connected to the alloy film. Temperature variations are compensated by supplying the head 7 and a resistor 13 at the same temperature in series from a constant current source 8. <IMAGE>

Description

SPECIFICATION Improvements in or relating to a method of and an apparatus for detecting the abrasive quality of a floppy disc The present invention relates to a method of and apparatus for measuring the abrasive quality of a floppy disc.

Atthe present tim e floppy discs a re used frequently in connection with word processors and computers. Information stored magnetically on a floppy disc is read by means of a head which is in contact with the floppy disc. The floppy disc rotates past the head, and the head is also moved relatively to the floppy disc. Thefloppydiscthus tends to abrade orwearthe reading head, and if the material from which thefloppy disc isfabricated is unduly abrasive the head that reads the floppy disc becomes worn very rapidly.

There is thus a need for an apparatuswhich can measure and determine the abrasiveness of a floppy disc. The present invention seeks to provide such a method and apparatus.

According to one aspect of this invention there is provided an apparatus for measuring the abrasiveness of a floppy disc, said apparatus comprising a head adapted to be urged into contact with a floppy disc whilst effecting relative movement between the head and the floppy disc, the part of the head being urged intocontactwiththefloppydisc being provided with a thin film of electrically conductive material which is mounted on an insulating substrate, means being provided for measuring the electrical resistance ofthe said thin film.

Thefilm may consistofa film of nickel/chromium alloy, the alloy may comprise 80% nickel and 20% chromium.

Preferably the nickel/chromium alloy has parts thereof coated with nickel, electric leads being bonded to said nickel-coated regions of the alloy.

The thin film may be less than 500 angstrom units thick, such as between 100 and 400 angstrom units thick.

Conveniently said sensor is associated with a constant current source passing said constant cu rrent th roug h the sensor, the means to measure the resistance ofthethin film comprising a voltageto frequency or analog to digital converter adapted to measure the voltage drop across the sensor.

Preferably the output of the said converter or analog to digital is fed to a microprocessororthe like adapted to control a display and/or printer two provide an output indicative of the abrasive quality ofthe floppy disc.

Preferably said sensor is associated with a compensating resistor such that the temperature of the compensating resistor is substantially the same as the temperature of the sensor, the compensating resistor being adaptedtocompensateforany variation in the resistance of the thin film with temperature.

Conveniently the compensating resistor is associated with said constant current source which passes constant current through the resistor, a voltage to frequency or analog to digital converter being provided to convert the voltage drop across the resistor into a freq uency sig nal .

According to another aspect ofthis invention there is provided a method of measuring the abrasiveness of a floppy disc comprising the steps of urging a sensor head into contact with the disc, said sensor head comprising an insulating substrate carrying, or at least the part thereof in contact with the disc, athin film of electrically conductive material, effecting relative movement between the head and the disc, and measuring anychange in the electric resistance ofthe thin film.

Conveniently the disc is rotated relative to said head.

Preferably the resistance ofthefilm is measured by passing a constant current th rough thefilm and measuring the voltage drop across the film with a voltage to frequency or analog to digital converter.

Conveniently the method also comprises the step of measuring the resistance of a compensating register exposed to the same temperature as the sensor head.

In orderthatthe invention may be more readily understood and so that furtherfeatures thereof may be appreciated, the invention will now be described by way of example with reference to the accompanying drawings in which: Figure lisa plan view of a sensor head forming part of an apparatus in accordance with the invention; Figure2 is a side elevational view of the sensor head shown in Figure 1, and Figure3 is a blockdiagramofanapparaus incorporating the sensor head shown in Figure 1.

Referring to Figures 1 and 2 ofthe accompanying drawings a sensor head for use in accordance with the present invention comprises a substrate 1 preferablyformed of a ceramic material such as, for example, alumina. The substrate has the configuration of a conventional floppy disc reading head, and thus presents a flat upper surface 2 which is divided into two regions by a central recessed channel 3.

At leastone partofthe uppersurface 2 ofthe substrate illustrated in Figures 1 and 2 is coated with a thin film of an electrically conductive material. The preferred electrically conductive material is a nickel/chromium alloy comprising 80% nickel and 20% chromium. However, other materials may be utilised. The preferred thickness forthe film of alloy is less than 500 angstrom units, such as 100 to 400 angstrom units.

It is to be noted that the substrate shown in Figures 1 and 2 has end regions 4, which slope away from the surface 2. The thin coating of conductive material film extends on to the sloping regions 4. These parts of the coating are coated with nickel, in the regions 5, to enablewires or leads 6to be soldered to the nickel coated regions 5. When the wires 6 have been soldered in position the substrate 1 may be located in position with the surface 2 in contact with a floppy disc, and the wires 6 will not touch the floppy disc.

The nickel/chromium alloy may be deposited by means of a vacuum evaporation technique, and the nickel coating applied to the said selected regions of the nickel/chromium alloy may also be deposited by a similartechnique.

Itisto be noted thatthe nickel/chromium alloy has a lowtemperature coefficient of resistance.

When the described head is to be used it may be mounted in position in the place of a normal recording head in a conventional floppy disc drive unit. Such units are now conventional and thus it is not necessary for such a unit to be described here.

Referring now to Figure 3 ofthe accompanying drawings it can be seen that the sensor 7, corresponding to the head described with reference to Figures 1 and 2 is connected in series with a compensating resistor 13 between a constant currentsource8and earth 9. Avoltage drop is created across the sensor 7, and the resistor 13, the voltage drop depending upon the electrical resistance ofthe thin coating.

A voltage to frequency converter 10 is connected across the sensor7 so thatthe voltage drop existing across the sensor is converted to a frequency signal, this frequency signal being fed by the lead 11 to a microprocessor 12.

The resistor 13 is a compensating resistor which is located adjacentthe sensor 7, so thatthe temperature of the compensating resistor 13 is always substantially the same as the temperature of the sensor. The compensating resistor is connected in series with the sensor 7 between the constant current source 8 and earth 9. The voltage drop across the resistor, which varies with temperature, is converted to a frequency signal by means of a voltage to frequency converter 14 connected across the resistor 13. The frequency signal from the voltage to frequency converter 14 is fed by a lead 15 to the microprocessor 12. This enables accurate compensation to be made for any variation in the resistance ofthe nickel/chromium coating ofthe sensor with temperature.The voltage drop across thesensor7 is thus determined bythe microprocessor and the electrical resistance ofthe thin coating ofthe sensor is thus measured.

Associated with the microprocessor 12 is a keyboard 16 and a display or printer unit 17.

In utilising the described apparatus a floppy disc, the abrasive quality ofthesurface of which iso be measured, is located in the disc drive, and the disc drive is actuated with the described sensor pressed against the floppy disc. As the floppy disc rotates, so the surface ofthe floppy disc will tend to abradethe thin coating film. Part of the coating will thus be worn away and the electrical resistance ofthe coating will alter. The described apparatus senses any change in the resistance ofthe coating, and by performing the appropriate calculations can determine the abrasiveness of a disc.The microprocessor may be programmed to provide a direct display or printout in terms ofthe abrasive quqlity of the disc present in the drive unit.

It is preferred thatthe voltage to frequency converters aretemperature compensated so that they are matched, and it is also preferred that the microprocessor is programmed to monitorthe voltage drop across the sensor every half second.

The abrasiveness value is calculated by means of a technique involving the linear least squares value overa half minute interval,thustaking into account sixty readings of voltage, in other words sixty readings of resistance.

It is to be appreciated that the preferred arrangement provides a sensitivity for resistance measurementto enable a detection of changes in resistance of one part in 106 persecond.

Whilst the invention has been described with reference to one embodiment it is to be understood that many modifications may be made without department from the scope of the invention.

Claims (19)

1. An apparatus for measuring the abrasiveness of a floppy disc, said apparatus comprising ahead adapted to be urged into contact with a floppy disc whilst effecting relative movement between the head and the floppy disc, the part of the head being urged into contact with the floppy disc being provided with a thin film of electrically conductive material which is mounted on an insulating substrate, means being provided for measuring the electrical resistance of the said thin film.

2. An apparatus according to claim 1 whereinthe film consists of a film of nickel/chromium alloy.

3. An apparatus according to claim 2 wherein the alloy comprises 80% nickel and 20% chromium.

4. An apparatus according to claim 2 or 3 wherein the nickel/chromium alloy has parts thereof coated with nickel, electric leads being bonded to said nickel-coated regions ofthe alloy.

5. An apparatus according to any one ofthe preceding claims wherein the thin film is lessthan 500 angstrom units thick.

6. An apparatus according to claim 5whereinthe thin film is between 100 and 400 angstrom units thick.

7. An apparatus according to any one ofthe preceding claims wherein the head comprises a substrate formed of ceramic.

8. An apparatus according to claim 7wherein said ceramic substrate is formed of alumina.

9. An apparatus according to any one ofthe preceding claims wherein said sensor is associated with a constant current source passing said constant cu rrent th rough the sensor, the means to measu re the resistance of the thin film comprising a voltage to frequency oranalog to digital converter adapted to measure the voltage drop across the sensor.

10. An apparatus according to claim 9wherein the output of the said converter or analog to digital is fed to a microprocessor orthe like adapted to control a display and/or printer to provide an output indicative ofthe abrasive quality of the floppy disc.

11. An apparatus according to any one ofthe preceding claims wherein said sensor is associated with a compensating resistor such thatthe temperature of the compensating resistor is substantially the same as the temperature ofthe sensor, the compensating resistor being adapted to compensate for any variation in the resistance of the thin film with temperature.

12. An apparatus according to claim 9 or 10 as dependent on claim 10 wherein the compensating resistor is associated with said constant current source which passes constant current through the resistor, a voltage to frequency or analog to digital converter being provided to convert the voltage drop across the resistor into a frequency signal.

13. A method of measuring the abrasiveness of a floppy disc comprising the steps of surging a sensor head into contact with the disc, said sensor head comprising an insulating substrate carrying, or at least the part thereof in contact with the disc, a thin film of electrically conductive material, effecting relative movement between the head and the disc, and measuring any change in the electric resistance ofthethinfilm.

14. Amethod accordingto claim 13whereinthe disc is rotated relative to said head.

15. A method according to claim 13 or 14wherein the resistance of the film is measured by passing a constantcurrentthroughthefilm and measuringthe voltage drop across the film with a voltage to frequency or analog to ditigal converter.

16. A method according to claim 13, 14or 15 wherein the method also comprises the step of measuring the resistance of a compensating register exposed to the sametemperature as the sensor head.

17. An apparatus substantially as herein described with reference to and as shown in the accompanying drawings.

18. A method substantially as herein described with reference to the accompanying drawings.

19. Any novel feature or combination offeatures disclosed herein.