GB1596056A

GB1596056A - Magnetic tape apparatus

Info

Publication number: GB1596056A
Application number: GB1771378A
Authority: GB
Original assignee: Licentia Patent Verwaltungs GmbH
Current assignee: Licentia Patent Verwaltungs GmbH
Priority date: 1977-05-16
Filing date: 1978-05-04
Publication date: 1981-08-19
Also published as: JPS53142216A; DE2722126A1; DE2722126C2; JPS6057149B2

Description

(54) MAGNETIC TAPE APPARATUS (71) We, LICENTIA PATENT-VERWALTUNGS-GESELLSCHAFT MIT BES CHRANKTER HAFTUNG, a company organised under the laws of Germany, of Theodor-Stern-Kai 1, 6, Frankfurt/Main 70, Germany do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to magnetic tape apparatus.

In a magnetic tape apparatus there can be derived from a tape advancing means, e.g. a spool disc, so-called tape motion pulses which are counted in an electronic counter. The value counted is used for indicating the disposition or state of the tape. If the tape motion pulses are derived from one of the spool discs or from a part coupled to one of the spool discs, greatly varying values are given for the sections of tape associated with a counting step since the circumference of the roll of tape varies with the winding off or on of the magnetic tape.

For linearising the indication it is known (German Auslegeschrift 24 16 060.9) to provide a detector device on each of the spool discs, to derive tape motion pulses by them from both spool discs, and to feed the sum of the pulses to a counter. For compensating for the momentary fluctuations of the pulse spacings resulting from the formation of the sum, a pre-divider is connected in front of the counter and the number of tape motion pulses is selected so as to be higher, corresponding to the division ratio of the pre-divider, than would be necessary for indicating without the pre-divider. The linearity of the indication is greatly improved in this known arrangement. However, the known arrangement represents a higher expenditure in mass production since two detector devices have to be installed and adjusted.

According to the invention, there is provided magnetic tape apparatus having means for generating pulses at a first rate dependent on the rate of rotation of a spool of tape onto or from which magnetic tape is wound in operation of the apparatus, frequency divider means for producing further pulses in response to the said pulses at a second rate related to the first rate by a division ratio which is automatically variable in accordance with the variation of the diameter of the spool of tape as tape is wound thereon to or therefrom, and a counter for counting the further pulses to produce a representation of the amount of tape wound from or onto the spool.

In the following, the invention is explained with reference to practical examples illustrated in the drawings, in which Figure 1 shows a practical example of an electronic indicator of the disposition or state of the tape having the features of the invention.

Figures 2 and 3 show diagrams for making clear the operation of the circuit in Figure 1, Figure 4 shows a further practical example, and Figure 5 shows a diagram for the circuit according to Figure 4.

In Figure 1 are shown two tape spools 1 and 2 and a magnetic tape 3 of a cassette magnetic tape apparatus. From the spool disc of the left-hand spool disc, which is pulled during forward running, tape motion pulses are derived by means of a pulse receiver 4. It will be assumed that there are uniformly distributed on the circumference of the spool disc fifteen marks which are detected in any suitable manner, e.g. optically with the aid of a photo-resistor serving as the pulse receiver 4. The rotational speed of the spool disc is indicated by nO. A frequency nl = 15nO is thereby given for the pulses.

If these pulses were fed to a linear counter, then for the section of tape associated with one counting step of the counter considered in accordance with the spool diameter there would result a line as indicated at 18 in Figure 2. For the full spool, in the examples shown in Figure 2 and all further examples, a diameter of 51 mm is assumed and for the empty spool 2 a diameter of 22 mm. The tape section associated with a counting step of the counter is termed "length of tape/pulse fed to the counter" in the following. What is sought is a horizontal line for the "length of tape/pulse fed to the counter" related to the spool diameter; i.e. it is desired that the counter "integrating" the counting pulses may vary its counting state linearly with the shifted length of tape, i.e. with the playing time.

In the circuit illustrated, the pulses of frequency nl derived from the spool disc are fed via a programmable divider 5 and a predivider 6 to the actual counter which consists of three decadic counting stages 7, 8 and 9. As the programmable divider there may be used, for example, the known integrated circuit SN 7497. The result of counting by the counter 7, 8, 9 is transmitted via leads QO to Q11 to a visual indicating device 12. The division ratio of the programmable divider 5 is varied in steps in accordance with the diameter of the tape wound on the spool 1, so that pulses having an approximately constant spacing in time are produced by the divider in response to the pulses fed to the divider, which pulses have a variable spacing in time. Because the tape runs past the read head at a constant speed, there is a constant length of tape per pulse produced by the divider. Thus as constant a value as possible is given for the length of tape/pulse fed to the counter.

The change of the division ratio of the programmable divider 5 may be effected by means that detect the diameter of the tape spool. It is, however, particularly simple to control the programmable divider directly from the counter. In the circuit of Figure 1, the programmable divider 5 is controlled by the last decade 9 of the counter 7, 8, 9. In this way the division ratio of the programmable divider 5 changes at each hundreth counting pulse at the input of the counting stage 7. The said known programmable divider SN 7497, on which the example illustrated is based, has control inputs A to F. The division ratio is M/64. M is given from the logical levels at the control inputs A to F: M = A + 2B + 4C + 8D + 16E + 32F.

In Figure 1 the control inputs A and B are connected to the logical level "1". The levels at the other inputs C to F are fed via an inverting switch 10 from the outputs of the decade counter 9. The switch 10 can be programmed to act according to two settings C 120 and C 60 corresponding to the known cassettes "C 120" with the playing time of 120 minutes and "C 60" with a playing time of 60 minutes. The logical levels at the outputs of the counter decade 9 indicated by Q8 to Ql, are transmitted inverted, in the setting C 120 of a switch 11, by the switch 10 to the control inputs C to F of the programmable divider 5. In this way, Mc 120 is determined by the equation: Mc 120 = 1 + 2 + 4Q8 + 8Q9 + 16Q + 32Q1.

In the setting C 60 of the switch 11, the outputs Q8 to Qlo are connected to the control inputs D to F via the inverting switch 10, and C is at the level "1", so that in this setting Mc 6() = 1 + 2 + 4 + 8Q8 + 16Qg + 32Ql(,.

Since the switching over the programmable divider 5 occurs at each hundreth counting pulse, in one tape run the cassette C 60 runs through five different divider settings, the C 120 cassette ten in contrast. The change in diameter during one divider setting is therefore twice as large for the C 60 cassette as for the C 120 cassette. Hence the steps between the individual M values must be twice as large.

There are thus given for Mc 12() and My 60 in the various settings of the counter stage 9 the following values assembled in a table.

Setting in the counter stage 9 Q8 Qg Qlo Qn Mc 120 Me 60 0 0 0 0 0 63 63 1 1 0 0 0 59 55 2 0 1 0 0 55 47 3 1 1 0 0 51 39 4 0 0 1 0 47 31 5 1 0 1 0 43 6 0 1 1 0 39 7 1 1 1 0 35 8 0 0 0 1 31 9 1 0 0 1 27 In Figures 2 and 3 are entered the counting pulse spacings for the C 120 and C 60 cassettes respectively in relation to the spool diameter. There are 15 pulses per rotation of the spool disc and a counting range of 4 bits of the divider 6 is the basis.

The counting pulse spacing fluctuates in only a small range, so that the linearity of the indication is appreciably improved. The programmable frequency divider 5 supplies output pulses n2 of non-uniform spacing. These changes of spacing are compensated to a large extent by the 4 bit divider 6 in front of the actual counter 7, 8, 9. The number of pulses per rotation of the spool disc is selected to be 15 so that in the case of the C 120 cassette the three-place indication of the indicating device 12 is still sufficient.

By increasing the number of changes of the division ratio per run of the magnetic tape and a corresponding finer stepping of the M value the range in which the counting pulses spacing changes can be made still smaller.

The average value of the length of tape/pulse fed to the counter illustrated in Figures 2 and 3 has a slightly curved character. This is because the division ratio of the programmable divider 5 at the time influences the changeover of the programmable divider 5. The average value has a straight curve, if the changeover of the uniform steps of the programmable divider is controlled linearly with the change in diameter of the tape spool. For this purpose the pulses must, prior to the programmable divider 5, be given to an additional counter serving only for programming. Such a circuit is shown in Figure 4.

For controlling the programmable divider 5 there serves, in the circuit of Figure 4, a 4 bit counter 13 to which are fed the tape motion pulses from a detector, not illustrated, and via a pre-divider 14. The number of pulses that are derived from the spool disc per rotation is indicated by p. According to the thickness of tape in the cassette employed, which in the known cassettes is determined by the playing time of the cassette, the division of ratio 1:N of the predivider 14 is variable, by means of a stepping switch 15, between various values of N which are given in the lower part of Figure 4. The other parts of the circuit of Figure 4 correspond to parts of the circuit of Figure 1 and are provided with the same references.

For a selected value of p = 14 and N = 1136, for the cassette C 60 the curve of the counting pulse spacing is illustrated in Figure 5 in relation to the diameter of the unwound tape spool. It will be seen that the average length of tape/pulse fed to the counter is constant. When using other cassettes only the division ratio N of the pre-divider 14 needs to be changed by means of the steeping switch 15. This change may also be effected automatically when inserting the cassette, if the cassette is provided with a suitable identification mark and the apparatus is provided with a detector device. The numbers of steps of the division ratio of the programmable divider 5 for one run of the magnetic tape is the same for all cassettes in this case. The stepping may be made finer by using twice or four times the number of steps. In this case the counter 13 for the programming of the programmable divider 5 must be a 5 bit or 6 bit counter, and N must be reduced by the factor 2 or 4 respectively.

The counters and dividers 6 to 9 are constructed as forward/reverse counters and are changed over together via an input terminal 17 upon a change of direction of the movement of the tape. Similarly all the counters 6 to 9 are, via an input terminal 16, set back to their "zero" setting via resetting inputs at the start of the running of the tape. In order to enable a simple programmable divider 5 to be used it is possible in this case for changeover of the counting direction and resetting of the divider 5 to be dispensed with. The division ratio of the pre-divider 6 connected between the programmable divider 5 and the actual counter 7,8,9 must then be selected so that the error resulting from the missing changeover is negligible.

To enable the state-of-tape information with a cassette inserted to be reproduced it is advantageous for the tape motion pulses to be derived from the spool disc, the disc of which is- as described - unwound in forward running. The spool associated with this spool disc is wound up only in fast running with constant tape tension. In the use of different cassettes it is then important, for constancy of the counting pulse spacing, for the external diameter of the full spool to be the same.

If, in contrast, the spool disc that pulls during forward running is used for the generation of the tape motion pulses, the playing time of the cassette and the diameter of the full spool do not need to be taken into account. For the cassette, only the diameter of the spool core and the tape thickness then need to be known. In the event of standarization the diameter of the spool core and some different tape thicknesses may, for example, be firmly predetermined. Only the tape thickness would then be set by means of the selector switch 11 or 15. This may also take place automatically.

In the last described case, there may be provided for correction of the slight differences of spool thickness of the spool that is wound up during forward running, which results from the change between fast and slow running, a correcting circuit, e.g. a known circuit in accordance with German Offenlegungsschrift 24 49 565.6.

With a sufficiently fine stepping of the programmable divider 5 and with corresponding selection of the division ratio and the numbers of pulses the indication may also take place directly in a unit of time. The playing time of the cassette could then be read directly from the indicating device.

WHAT WE CLAIM IS: 1. Magnetic tape apparatus having means for generating pulses at a first rate dependent on the rate of rotation of a spool of tape onto or from which magnetic tape is wound in operation of the apparatus, frequency divider means for producing further pulses in response to the said pulses at a second rate related to the first rate by a division ratio which is automatically variable in accordance with the variation of the diameter of the spool of tape as tape is wound thereon to or therefrom, and a counter for counting the further pulses to produce a representation of the amount of tape wound from or onto the spool.

2. Apparatus according to Claim 1 having a visual display controlled by the counter for indicating the amount of tape wound from or onto the spool.

3. Apparatus according to Claim 1 or 2, wherein the apparatus is so arranged that said amount is length of tape.

4. Apparatus according to Claim 1 or 2. wherein the apparatus is so arranged that said amount is tape playing time.

5. Apparatus according to Claim 1, 2, 3 or 4, wherein the said counter is arranged to vary the division ratio of the divider means in dependence upon the count made thereby.

6. Apparatus according to Claim 1, 2, 3 or 4, having an additional counter arranged to count the first-mentioned pulses and to vary the division ratio of the divider means in dependence on the count made thereby.

7. Apparatus according to any of Claims 1 to 5 wherein the divider means has a plurality of control inputs for receiving signals for varying its division ration, and the counter has a plurality of count outputs, and there are provided means for connecting the count outputs to the control inputs.

8. Apparatus according to claim 6 wherein the divider means has a plurality of control inputs for receiving signals for varying its division ration, and the additional counter has a plurality of count outputs, and there are provided means for connecting the count outputs to the control inputs.

9. Apparatus according to any of claims 1 to 5 and 7, comprising a frequency divider for feeding the further pulser to the counter.

10. Apparatus according to claim 6 or 8 comprising a frequency divider for feeding the further pulses to the first-mentioned counter.

11. Apparatus according to claim 6,8 or 10 comprising a further frequency divider for feeding the first-mentioned pulses to the said additional counter.

12. Apparatus according to claim 11 comprising means for varying the division ratio of the further divider.

13. Apparatus according to any preceding claim, wherein all the said counters and dividers (but not the said frequency divider means) are constructed as forward/reverse counters, and including means for setting the counts of the forward/reverse counters to zero together.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. simple programmable divider 5 to be used it is possible in this case for changeover of the counting direction and resetting of the divider 5 to be dispensed with. The division ratio of the pre-divider 6 connected between the programmable divider 5 and the actual counter 7,8,9 must then be selected so that the error resulting from the missing changeover is negligible. To enable the state-of-tape information with a cassette inserted to be reproduced it is advantageous for the tape motion pulses to be derived from the spool disc, the disc of which is- as described - unwound in forward running. The spool associated with this spool disc is wound up only in fast running with constant tape tension. In the use of different cassettes it is then important, for constancy of the counting pulse spacing, for the external diameter of the full spool to be the same. If, in contrast, the spool disc that pulls during forward running is used for the generation of the tape motion pulses, the playing time of the cassette and the diameter of the full spool do not need to be taken into account. For the cassette, only the diameter of the spool core and the tape thickness then need to be known. In the event of standarization the diameter of the spool core and some different tape thicknesses may, for example, be firmly predetermined. Only the tape thickness would then be set by means of the selector switch 11 or 15. This may also take place automatically. In the last described case, there may be provided for correction of the slight differences of spool thickness of the spool that is wound up during forward running, which results from the change between fast and slow running, a correcting circuit, e.g. a known circuit in accordance with German Offenlegungsschrift 24 49 565.6. With a sufficiently fine stepping of the programmable divider 5 and with corresponding selection of the division ratio and the numbers of pulses the indication may also take place directly in a unit of time. The playing time of the cassette could then be read directly from the indicating device. WHAT WE CLAIM IS:

1. Magnetic tape apparatus having means for generating pulses at a first rate dependent on the rate of rotation of a spool of tape onto or from which magnetic tape is wound in operation of the apparatus, frequency divider means for producing further pulses in response to the said pulses at a second rate related to the first rate by a division ratio which is automatically variable in accordance with the variation of the diameter of the spool of tape as tape is wound thereon to or therefrom, and a counter for counting the further pulses to produce a representation of the amount of tape wound from or onto the spool.

14. Apparatus according to claim 13 wherein the apparatus is arranged to move the tape

in two directions and comprising means for changing the direction of counting of the forward/reverse counters together upon change of direction of movement of the tape.

15. Magnetic tape apparatus substantially as hereinbefore described with reference to Figures 1, 2 and 3, or to Figures 4 and 5 of the accompanying drawings.