RECORDING AND/OR REPRODUCING APPARATUS INCLUDING A SERVO CONTROL LOOP

Abstract: A recording and/or reproducing apparatus for recording/reproducing an information signal in a track on a longitudinal record carrier (2), comprises reel driving means including a motor (11) for driving a reel (9) to rotate to effect a feeding operation of the record carrier in its longitudinal direction. Record carrier speed detection means (20, 21, 56) are present for generating a first detection signal in relation to the speed of the record carrier during said feeding operation. Second detection means (18, 60) are present, adapted to generate a second detection signal having a relation to the radius of the amount of record carrier being wound on said reel. Further, signal combination means (58, 64) are present for combining said first and second detection signal and a predetermined signal which is representative of a predetermined speed of the record carrier so as to obtain a servo control signal, such that the feeding speed of the record carrier may be equal to the predetermined speed. The signal combination means are adapted to generate said servo control signal such that it is equivalent to calculating a deviation between said predetermined signal and said first detection signal, and non-linearly combining said deviation with said second detection signal.

Description: Recording and/or reproducing apparatus including a servo control loop. The invention relates to a recording and/or reproducing apparatus for recording/reproducing an information signal in a track on a longitudinal record carrier, comprising: - reel driving means including a motor for driving a reel to rotate to effect a feeding operation of the record carrier in its longitudinal direction, - record carrier speed detection means for generating a first detection signal in relation to the speed of the record carrier during said feeding operation, - second detection means for generating a second detection signal, - signal combination means for combining said first and second detection signal and a predetermined signal which is representative of a predetermined speed of the record carrier so as to obtain a servo control signal, such that the feeding speed of the record carrier may be equal to the predetermined speed. Such an apparatus is known from EP 570,956 A2. More specifically, the apparatus shown in figure 46 of this publication includes an outer (or first) servo control loop which serves as a speed control loop, in which the first detection signal, which relates to the actual speed of the record carrier, is compared to the predetermined signal, which relates to the required speed of the record carrier. Further, an inner (or second) servo control loop is present in which the rotational velocity is measured and used as a second feedback signal, so as to improve the speed control of the motor. The resultant servo control signal is used to supply the motor with a supply signal so as to rotate the take up reel. The known apparatus is however subject to irregularities in the record carrier speed that can not be suppressed sufficiently by the known servo system. The invention has for its object to provide an improved recording and/or reproducing apparatus with a better suppression capability for variations in the record carrier speed. The apparatus in accordance with the invention is characterized in that said second detection means is adapted to generate a second detection signal having a relation to the radius of the amount of record carrier being wound on said reel, and that said signal combination means is adapted to generate said servo control signal such that it is equivalen to calculating a deviation between said predetermined signal and said first detection signal, and non-linearly combining said deviation with said second detection signal. The invention is based on the recognition that during feeding the record carri onto the reel that is driven by the motor, the radius of the amount of record carrier wound on the said reel will change gradually from a low value to a higher value. Because of this, the servo gain changes. One would require a speed controller for the whole operating rang of the servo system. The varying gain however limits the achievable performance of the servo system. By proposing, in accordance with the invention, a non-linear compensation, which depends on the variation of the radius of the amount of record carrier wound on th reel, the servo system can be made substantially independent of this variation, resulting in better performance of the servo system. The second detection may be adapted to generate said second detection signal response to the rotational velocity of a reel. Said reel may be the take up reel, but may alternatively be the supply reel, as the radius on the take up reel may be determined from radius of the supply reel when knowing the total length of the record carrier. The apparatus may be further characterized in that, said second detection me is adapted to generate said second detection signal such that said second detection signal is proportional to 1 over said radius, and that said signal combination means is adapted to generate said servo control signal such that it is equivalent to calculating a deviation betwe said predetermined signal and said first detection signal, and multiplying said deviation wi said second detection signal and in that said signal combination means comprises - deviation calculation means for calculating said deviation, and - multiplying means for multiplying said deviation with said second detection signal. When it is assumed that the outer control loop may already be capable of keeping the spee of the record carrier substantially constant, the second detection signal can be derived fro detection means for detecting the rotational velocity of a reel alone. The apparatus may further be characterized in that, said signal combination means further comprises - combining means for non-linearly combining said third detection signal by said first detection signal so as to obtain said second detection signal. If, however, the outer loop is not capable of substantially keeping the record speed consta the first detection signal is also needed so as to obtain the second detection signal. More specifically, said reel rotational velocity detection means is adapted to generate the third detection signal which is proportional to the rotational velocity of said reel, and that the combining means is adapted to divide said third detection signal by said first detection signal. Various realisations of the record carrier speed detection means are possible. One such realisation is such that said speed detection means include a rotatable member for contacting the record carrier so as to be rotated thereby when the record carrier is fed. An embodiment of the rotating member can be as described in European patent application no. 94.201.618.9 (PHN 14,875). Another realisation of the speed detecting means makes use of an additional control track on the record carrier having pulses recorded in the track. Using a reading head, the pulses can be read out and used for obtaining the first detection signal. The invention is particularly applicable in an apparatus of the capstanless type as, without the servo control in accordance with the present invention, variations in the record carrier speed will be much larger in such apparatuses than in apparatuses provided with a capstan. These and other aspects of the invention will be further elucidated with reference to the embodiments in the figure description, in which figure 1 shows an embodiment of the apparatus, figure 2 shows an embodiment of the servo control circuit of figure 1 , figure 3 shows another embodiment of the servo control circuit, and figure 4 shows a further elaboration of the servo control circuit of figure 2. Figure 1 shows an embodiment of the apparatus for recording and/or reproducing an information signal on/from a record carrier 2. The record carrier is a tape¬ like record carrier that is transported from a supply reel 8 via guide rollers 13 and 14 to a take up reel 9 with a velocity v t . The direction of transport is indicated by the arrow in the figure. In the present embodiment, the tape transport is realized by means of a reel motor 11 that is coupled to the take up reel 9. The present embodiment is of the capstanless type. That means that no capstan and no pinch roller are available to realize the transport of the tape with the velocity v t . A magnetic head 1 is present for recording and/or reproducing the information signal, such as an audio signal, on/from a track on the record carrier 2. A signal processing unit 5 is available for processing the information signal applied to a terminal 6, so as to enable the recording of the information signal on the record carrier. When in a reproductio mode, the signal processing unit 5 processes the signal read from the record carrier by the head 1 so as to regenerate the information signal and to supply the regenerated information signal to the terminal 6. ~ A rotating member 21 is provided, which is in mechanical contact with the ta 2 and is rotated by the tape, as the tape is fed in one of its two longitudinal directions. A tacho generator 20 is coupled to the rotating member and supplies pulses with a pulse frequency dictated by the rotational velocity of the rotating member. The number of pulses per unit of time, supplied by the tacho generator 20 is thus a measure for the transport velocity of the tape 2. A tacho generator 18 is coupled to the take up reel 9 and supplies pulses wit pulse frequency dictated by the rotational velocity of the take up reel 9. The apparatus is further provided with a servo control unit 22. The servo control unit 22 has a first input 24 for receiving a predetermined signal v r . This predetermined signal relates to the required transport velocity of the record carrier 2. Further, the unit 22 has inputs 26 and 28 for receiving the pulses generated by the tacho generators 20 and 18 respectively. The unit has an output 32 for supplying a control signal so as to control the rotational velocity of the motor 11 such that the tape 2 is transported with the required velocity. A further elaboration of the servo control unit 22 is shown in figure 2. The u 22' of figure 2 comprises an outer loop 52 and an inner loop 54. The outer control loop 5 comprises a converter 56 which converts the pulses supplied by the tacho generator 20 int first detection signal that is representative of the actual velocity v t of the tape 2. This is indicated in figure 2 by the ' ÷ v t ' sign. This first detection signal is supplied to a first inp of a signal combination unit 58, which is in the present situation in the form of a subtracto circuit. The terminal 24 is coupled to a second input of the combination unit 58. The inner control loop 54 comprises a converter 60 which converts the pulses supplied by the tacho generator 18 into a detection signal which is representative of the rotational velocity of the take up reel. This is indicated in figure 2 by the ' ÷ ω' sign. This detection signal is supplied via a loop amplifier 62 to a first input 69 of a second signal combination unit 64, which is in the present situation in the form of a multiplier circuit. A output of the combination unit 58 is coupled to a second input 68 of the combination unit via a control unit 66 which may be a PH) controller. The control system is based on the following rules. Suppose that the control signal applied to the motor 11 has a value U Volts. Now the following relationship exists: U = C x . ω, (1) where ω is the rotational velocity of the motor 11 and C { a constant. Further, the following relationship is valid: v t = ω . R, (2) where R is the radius of the amount of tape that is wound on the take up reel 9. Combining both formulae results in v t = (- ! . U . R (3) Thus, the transfer function v^U, of the system to be controlled, that is the system formed by the apparatus between the terminal 32 and the output of the converter 56, equals C j .R. The actual value for R varies as a function of time. Therefore, the transfer function of the system varies as a function of time. Further, the actual value of R is not known. The invention is based on the measure to multiply the transfer function by another transfer function which is related to 1/R, so that the total transfer function of the system to be controlled by the outer control loop 52 becomes independent of R. This is realized by the multiplier circuit 64. This circuit multiplies the signal applied to its input 68 with the signal applied to its input 69. The signal applied to the input 69 has a relation to 1/R, such as C 2 /R, (4) where C 2 is a constant. As a result, the total transfer function from the input 68 to the output of the converter 56 becomes C^C^, and thus independent of R. Using equation (2), 1/R can be derived and leads to the formula 1/R = ω / v t . Assuming that the outer loop is capable of keeping v t substantially constant, t formula simplifies to 1/R ÷ ω. The output of the converter 60, which supplies a detection signal which relates to the rotational velocity of the take up reel can thus be applied to the input 69 of the multiplier circuit 64 as the second detection signal. Figure 3 shows a second embodiment. If the outer control loop 52 is not capable of keeping v t substantially constant, the formula (5) remains valid. In that case, the inner control loop 54' requires an additional signal combination unit 70 in the form of a divider. Outputs of both converters 56 and 60 are coupled to corresponding inputs of the divider 70. The divider realizes the division given by formula (5), so that the output signal the divider is related to 1/R. Figure 4 shows a further elaboration of the servo control circuit of figure 2. When the system is started from v t =0, ω will be zero also. Therefore, the input signal to t input 69 will be zero and start up will not come about. This problem can be solved by demanding a minimum value ω,,^ for ω. Therefore, the loop filter 62 comprises the unit 7 which gives a minimum output for small input signals and has an output signal proportion to the input signal for large input signals. Further, the assumption that the tape speed is controlled correctly by the oute loop, does not take into account small and relatively fast variations of ω. These (unwanted) variations can be filtered out by a lowpass filter 77, also included in the loop filter 62. The cutoff frequency of the filter 77 is such that it does not have a disturbing effect on the loop gain in the inner loop 54. The unit 62' in figure 3 comprises the filter 77 and the divider 70 must be reconditioned so as to avoid the problems explained above during start-up, so as to provide an output signal at the output of divider 70 when the input signals are zero. It should be noted that various modifications to the embodiments described ar possible without departing from the scope of the invention as defined by the claims. As an example, the tacho generator 18 described above is coupled to the take up reel so as to obtain the detection signal which is related to the rotational velocity of the take up reel. It may however be possible to couple the tacho generator 18 to the take up reel motor 11. Account should be taken in this situation for the ratio between the motor rotational velocity and the reel rotational velocity. Further, the tacho generator 18 may be coupled to the supply reel. This for the reason that when having information relating to the radius of the amount of record carrier on the supply reel, it is possible to derive therefrom information relating to the radius of the amount of record carrier on the take up reel, when knowing the total length of the record carrier. As another example, the divider 70 in figure 3 realizes the division ω / v t . One could have decided to carry out the inverse division in the divider 70, that is: v t / ω. In such a situation, the multiplier 64 should be replaced by a divider so as to realize the multiplication by 1/R. Further, in the embodiments described, the second detection signal applied to the input 69 of the combination unit 64 has been obtained from a measurement of the rotational velocity of the reel 9. It may however be possible to measure the radius R of the amount of tape wound on the reel 9 in another way, such as directly by optical means. Moreover, the signal combination unit 64 in the embodiments described can be moved from the position where it is shown in the figures to a position between the terminal 24 and the combination unit 58. This further requires an additional combination unit, such as the unit 64, in the outer loop 52, before the combination unit 58. In this situation, the total signal combination circuit of the combination units present, that is the units 58 and 64 and the additional unit 64, to generate said servo control signal such that it is equivalent to calculating a deviation between said predetermined signal v r and said first detection signal (which is the signal applied to the minus-input of the unit 58 in figure 2), and non-linearly combining said deviation with said second detection signal (which is the signal applied to the input 69 of unit 64 in figure 2). Further, it should be noted that the invention is applicable to recording/reproducing apparatuses of the helical scan type and the linear recording/reproducing type.

Claims: CLAIMS 1. A recording and or reproducing apparatus for recording/reproducing an information signal in a track on a longitudinal record carrier, comprising: - reel driving means including a motor for driving a reel to rotate to effect a feeding operation of the record carrier in its longitudinal direction, - record carrier speed detection means for generating a first detection signal in relation to t speed of the record carrier during said feeding operation, - second detection means for generating a second detection signal, - signal combination means for combining said first and second detection signal and a predetermined signal which is representative of a predetermined speed of the record carrie so as to obtain a servo control signal, such that the feeding speed of the record carrier ma be equal to the predetermined speed, characterized in that said second detection means is adapted to generate a second detection signal having a relation to the radius of the amount of record carrier being wound on said reel, and that said signal combination means is adapted to generate said servo control sign such that it is equivalent to calculating a deviation between said predetermined signal and said first detection signal, and non-linearly combining said deviation with said second detection signal. 2. Apparatus as claimed in claim 1, characterized in that said second detection means is adapted to generate said second detection signal in response to the rotational velocity of a reel. 3. Apparatus as claimed in claim 2, characterized in that said second detection means is adapted to generate said second detection signal such that said second detection signal is proportional to 1 over said radius, and that said signal combination means is adap to generate said servo control signal such that it is equivalent to calculating a deviation between said predetermined signal and said first detection signal, and multiplying said deviation with said second detection signal. 4. Apparatus as claimed in claim 3, characterized in that said signal combinatio means comprises - deviation calculation means for calculating said deviation, and - multiplying means for multiplying said deviation with said second detection signal. 5. Apparatus as claimed in claim 4, further comprising - reel rotational velocity detection means for generating a third detection signal in relation to the rotational velocity of said reel, characterized in that said signal combination means further comprises - combining means for non-linearly combining said third detection signal by said first detection signal so as to obtain said second detection signal. 6. Apparatus as claimed in claim 5, characterized in that said reel rotational velocity detection means is adapted to generate the third detection signal which is proportional to the rotational velocity of said reel, and that the combining means is adapted to divide said third detection signal by said first detection signal. 7. Apparatus as claimed in anyone of the preceding claims, characterized in that, said speed detection means include a rotatable member for contacting the record carrier so as to be rotated thereby when the record carrier is fed. 8. Apparatus as claimed in anyone of the preceding claims, characterized in that the apparatus is devoid of a pinch roller and a capstan.

Inventors: NORG MEINDERT LAMBERTUS, STEINBUCH MAARTEN, NORG, MEINDERT, LAMBERTUS, STEINBUCH, MAARTEN
Applicants: PHILIPS ELECTRONICS NV, PHILIPS NORDEN AB, PHILIPS ELECTRONICS N.V.
Application year: 1995
Main classification: G11B15
IPC codes: G11B15