Rotary head type reproducing apparatus

Abstract: In a rotary head type reproducing apparatus, such as a digital audio tape recorder (DAT), display changeover operation, key scanning operation and/or a sensor scanning operation are inhibited during the periods TPB-A, TPB-B when a rotary head is contacted with a magnetic tape for reproducing signals, and the display changeover operation is performed during time periods TDS1 to TDS4 outside of these periods TPB-A, TPB-B, while the scanning operations are performed during a time period TSC. An error rate may be improved because noises due to display changeover or scanning may be eliminated during the time the magnetic head is contacted with the magnetic tape for signal reproduction. The result is that a shielding or the like may be eliminated and the display section or switches may be mounted in proximity to the rotary head to render it possible to reduce the size or weight of the apparatus.

Description: This invention relates to a rotary head type reproducing apparatus, such as a digital audio tape recorder (DAT), employing a rotary head device. Various apparatuses for recording and reproducing audio or video signals on or from a magnetic tape using a rotary head device are known, such as an apparatus described in US Patent Application Serial No.624,393, filed on December 7, 1990 published as US-A-5 517 370 on 14 May, 1996. With such a digital audio tape recorder employing a rotary head device as described in the pending application, if the voltage or current at an input or an output is changed while the rotating magnetic head is in contact with the magnetic tape for reproduction, there is a risk of noise being mixed into the playback signals, e.g. via the magnetic head or the playback RF amplifier. This can occur during switching of the operating states of a large number of light emitting diodes (LEDs), a liquid crystal device (LCD) or fluorescent segments (FL) or during scanning of a switch matrix, while the magnetic tape is in contact with the drum, as in the case when the switching or scanning operation is carried out in non- synchronism with the drum rotation. In particular, if the apparatus is of an ultra-small size, the magnetic head has to be mounted in close proximity to the display elements or switches which makes it difficult to inhibit noise intrusion. Although the problem is not felt so keenly during recording with a large recording signal current, during playback, because the signal current is low even the slightest noise intrusion tends to cause deterioration of the S/N ratio during reproduction. This noise is amplified and rendered more noticeable. EP-A-0,399,812 describes a magnetic tape recording/reproducing apparatus for selectively disabling the amplifier of the reproducing head which is not in contact with the tape. It is an object of the present invention to provide a rotary head type reproducing apparatus whereby the effect of noise generated by, for example, turning on or off of the display LEDs, LCD or FLs during signal reproduction by the rotary head or during scanning of sensors or a switch matrix may be reduced or eliminated. According to the present invention, a rotary head type reproducing apparatus for reproducing signals from a recording medium, using a head drum having one or more rotary heads intermittently contacted with said recording medium, comprising synchronizing means for synchronizing rotation of said rotary head with a timing generating operation by a timing generator, the apparatus including components the switching or scanning operations of which causes a change in current or voltage which generates a noise signal which is mixed into the reproduced signal and being characterised by control means for inhibiting said switching or scanning operations during the time interval when the or each rotary head is contacted with the area of the recording medium from which the recorded signals are reproduced. With the present rotary head type reproducing apparatus, display changeover operations at an input or an output or the operations of scanning the keys or sensors are inhibited by controlling means during the time when the rotary head is contacted with the magnetic tape as the recording medium for whereby noises generated by these changeover or scanning operations may be prevented from being intruded into the magnetic head or the amplifier. The invention will be further described by way of non-limitative example with reference to the accompanying drawings, in which:- Fig.1 is a block diagram showing a schematic arrangement of a digital audio tape recorder to which the present invention is applied; Fig.2 is a block diagram showing essential portions of the digital audio tape recorder shown in Fig.1; Fig.3 is a schematic view for explaining a rotary head applied to a digital audio tape recorder according to the present invention; Fig.4 is a timing chart for illustrating the operation of the digital audio tape recorder to which the present invention is applied; and Fig.5 is a schematic block diagram showing a modified embodiment of the rotary head type reproducing apparatus according to the present invention. Referring to Fig.1, a digital audio tape recorder, which is a reproducing apparatus constructed using a rotary head according to the present invention is explained in detail. With the present digital audio tape recorder, a rotary drum 1 of a rotary head device is rotationally driven at e.g. 50 Hz (at a rate of 50 revolutions per second). A pair of magnetic heads 2A, 2B are mounted on the rotary drum 1 at an angular interval of e.g. 180°, and a magnetic tape 3 is wrapped obliquely around these magnetic heads through a wrapping angle of e.g. 90° so as to travel at a predetermined travelling velocity. These magnetic heads 2A, 2B alternately scan the magnetic tape 3 for forming inclined recording tracks on the tape. The magnetic gaps of the magnetic heads 2A, 2B are set at different angles from each other. The rotary drum 1 is rotationally driven by a drum motor 4, a rotary shaft of which is fitted with a frequency generator (FG) 5. The frequency generator (FG) 5 generates a signal SFG having a frequency corresponding to the rotational velocity of the drum to transmit the signal to a system controller 6. A pulse generator (PG) 8 generates a rotation detection pulse signal SPG at a predetermined rotational phase each time the rotary drum 1 completes one complete revolution. The rotation detection pulse signal SPG, which is a rotational phase detection pulse signal, or PG signal, is generated at a start timing of scanning of the magnetic tape 3. The PG signal SPG is also supplied to system controller 6. System controller 6 is responsive to these FG signal SFG and PG signal SPG to form a motor control signal which is supplied as a control signal to a drum motor 4 via an amplifier 10. The drum motor 4 is controlled to be rotationally driven at a rate of 50 revolutions per second so that the PG signal SPG is synchronized with a predetermined synchronization signal. The magnetic heads 2A, 2b are alternately switched by a head changeover switch 11 so that recording signals from a terminal r of a recording/play switch 12 is supplied via a rotary transformer, not shown, to the magnetic heads 2A, 2B, while playback signals from the magnetic heads 2A, 2B are taken out via another rotary transformer, not shown, at a terminal p of the recording/play switch 12. Analog/audio signals from an input terminal 13 are supplied via a low-pass filter (LPF) 14 to an A/D converter 15 so as to be converted into digital audio signals which are transmitted to a recording signal processing circuit 16. The recording signal processing circuit 16 processes the digital audio signals by, for example, error detection, appendage of codes for error correction or detection, interleaving and time base compression. Output signals from the processing circuit 16 are supplied to a modulating circuit 17 for being converted into signals suitable for recording. Recording signals from the modulating circuit 17 are supplied via a recording amplifier 18 and a terminal r of the recording/play switch 12 to the head changeover switch 11 whereby the recording signals are alternately supplied to the magnetic heads 2A, 2B. Signals reproduced by the magnetic heads 2A, 2B are transmitted via head changeover switch 11 and a terminal p of the recording/play switch 12 to a playback amplifier 19. Output signals from playback amplifier 19 are transmitted via an equalizer/PLL circuit 20 to a demodulation circuit 21 for demodulation before being transmitted to a playback signal processing circuit 22. The playback signal processing circuit 22 processes the demodulated output signals by, for example, time base expansion, deinterleaving, error correction or concealment. Output signals from the processing circuit 22 are transmitted to a D/A converter 23 for being converted into analog signals. Playback audio signals from D/A converter 23 are outputted via a low-pass filter (LPF) 24 at an output terminal 25. A variety of timing signals are generated by the system controller 6 comprised of a timing generator 7 and a microcomputer 8 for controlling switching timing of the head changeover switch 11, recording/play switch 12 or other circuitry. System controller 6 also takes charge of display control of a display device 26, key scanning of a set of switches or switch matrix, 28 or sensor scanning. A concrete embodiment of the present invention, as applied to a digital audio tape recorder having the arrangement as shown in Fig.1, is hereinafter explained. Fig.2 shows, as an embodiment of a rotary head type reproducing apparatus according to the present invention, a schematic arrangement of a small-sized rotary head type digital audio tape recorder (DAT). Fig.3 shows, in a schematic view, a rotary head applied to DAT shown in Fig.2. The details of these components may be constructed as shown in Fig.1 and are not shown herein for avoiding redundancy. Referring to Figs.2 and 3, the microcomputer 8 detects the time difference between the PG pulse signals SPG (rotational phase detection pulse signals) obtained upon detection of the rotational phase of the rotary drum 1 of DAT and an interrupt signal from timing generator 7 for transmitting a servo signal via a motor driving circuit 10 to a drum motor for applying a servo to the drum motor so as to maintain a constant phase relation between the rotational phase of the drum and the phase of the timing generator 7. Referring to Fig.4, which is a timing chart for illustrating the operations of various component parts during one complete revolution of a rotary head, the above-mentioned PG pulse signals (rotational phase detection pulse signals) SPG are generated at time points t0, t10, the time interval between time points t0 and t10 corresponding to one complete revolution of the rotary drum 1. The timing generator 7 generates interruption signals IR1, IR3 at time points t1, t3 of turning on of a playback amplifier 9, while generating interruption signals IR3, IR4 at time points t2, t4 of turning off of the playback amplifier 9. Within the time intervals of t1 to t2 and t3 to t4, there are provided a time period TPB-A during which signals are actually reproduced by the magnetic head 2A (Fig.3) and a time period TPB-B during which signals are actually reproduced by the magnetic head 2B (Fig.3), respectively. That is, a magnetic tape 3 is wrapped around the rotary drum 1 through an angle slightly larger than 90°, such that the above-mentioned playback time intervals TPB-A, TPB-B represent the time intervals during which the magnetic heads 2A, 2B are actually contacted with the magnetic tape 3 and which correspond to rotation by one-fourth of a full revolution through 360°, or by 90°, of drum 1. During display changeover periods TDS1, TDS2, TDS3, TDS4, directly after these interrupt signals IR1, IR2, IR3, IR4, display contents or dynamic illumination of display device 26 are changed over by microcomputer 8. It is noted that the display changeover periods TDS1, TDS3 are terminated before the start periods of the playback time periods TPB-A, TPB-B without being overlapped with these playback time periods. It is also noted that a key scanning period TSC is provided after the display changeover period TDS2 directly following interrupt signal IR2 so that the key scanning for the switch matrix 28 or the sensor scanning is carried out during this key scan period TSC by microcomputer 8 for reading the contents of the switches and sensors. The display contents or dynamic illumination need not be changed over for each of the four display changeover periods TDS1, TDS2, TDS3, TDS4 per each complete revolution, so that it suffices to carry out display changeover once each complete revolution or once for several complete revolutions. These time periods TDS1 to TDS4 may also be used for key scanning or sensor scanning operations. The time period directly following the ends of the playback time periods TPB-A, TPB-B, or the time periods when the playback amplifier 9 is turned off, that is the time period since t2 until t3 or the time period since t4 until the time point of start of the next period of revolution t1, may naturally be employed as the permitted time for carrying out the above-mentioned display changeover operation or the scanning operation. In this manner, there is no risk of noise generation from the display device 26 or a line connected thereto due to changes in display or from the switch matrix 28 or a line connected thereto due to the key scanning or sensor scanning operation during the time periods TPB-A, TPB-B when the magnetic heads 2A, 2B are actually contacted with the magnetic tape 3. Consequently, noise intrusion into the magnetic heads 2A, 2B, playback amplifier 9 or playback signal line may be prevented to eliminate S/N deterioration for improving an error rate. The result is that a shielding for noise elimination may be dispensed with, while it becomes possible to mount the display device 26 or the switch matrix 28 in proximity to the rotary head for reducing the size or weight of the reproducing apparatus. It is also desirable that operations possibly leading to fluctuations in voltage or current to affect the playback signals, besides the above-mentioned display changeover operations or scanning operations, above all, various input and output operations, be carried out during time periods other than the reproducing periods TPB-A, TPB-B. During recording, it is also desirable that input and output operations possibly leading to voltage or current fluctuations be inhibited during the time periods when the magnetic head is contacted with the magnetic tape for carrying out actual recording operations, although the recording signals are affected to a lesser extent by these input or output operations. In the above embodiment, the rotary drum (driving motor) is servo-controlled as a method for maintaining a constant relation between the rotational phase of the drum and the phase of the timing generator. As a modification, it is also possible to effect timing control of a timing generator responsive to the rotational phase or the rotational velocity of the drum (rotary head) for locking the timing signal from the timing generator itself with respect to drum rotation. Fig.5 shows an embodiment of a concrete constitution in which the period of timing generation is controlled responsive to the rotational velocity of the drum (rotary head). With the present embodiment, the timing generator is controlled not only by the phase information but also by the velocity information of the rotary head. For example, the phase of the signal TG indicating the start point of timing generation with respect to PG pulse signals SPG (target phase) is corrected, while the period of the timing generation is rendered to be variable (programmable) and controlled depending on the velocity information. That is, in the embodiment shown in Fig.5, the above- mentioned programmable timing generator is built into a one-chip microcomputer system. The timing generator includes, as main components, a time base counter 31 having the count number for one period of the rotary head as its maximum countable bits, a timing pattern memory 32 having stored therein data for generating various timing patterns, and a programmable frequency divider 41 for controlling clocks of the counter 31 responsive to the above-mentioned velocity information. An output of counter 31 and an output from timing pattern memory 32 are compared to each other in a comparator 33. A comparison output of comparator 33 is supplied to a timing controller 34, an output of which is supplied to an event counter 35 and a selector 36. An output of event counter is supplied via a selector 36 to timing pattern memory 32. A static RAM (random access memory) is usually employed as timing pattern memory 32 and has for example a storage capacity of 64 bytes or 32 words, each word consisting of 6 bits of output data and 10 bits of time base data. The time base data correspond to the count value of time base counter 31. When the time (phase and position) indicated by counter 31 coincides with the time base data, the respective 6 bits of the output data become respective timing output signals STG0 to STG5. That is, six timing patterns when the timing from counter 31 becomes the above-mentioned time base data are stored as respective bits of the above-mentioned 6-bit output data. The velocity information obtained upon detecting the rotational velocity of the rotary drum 1 of Fig.2 is processed by e.g. a microcomputer to generate variable or programmable velocity information for frequency division, which programmable velocity information is supplied over data bus 46 to a velocity register 41. The above-mentioned programmable velocity information from velocity register 41 is in the form of 2's complement data in an 8-bit configuration (-128 to +127) which is transmitted to an adder 42 after, if necessary, bit expansion. An output from adder 42 is returned to adder 42 via a frequency dividing register 43. The register 43 is fed via an input terminal 44 with master clocks CKMS which are frequency divided at a frequency division ratio r which is changed depending on the above-mentioned velocity information to generate count clocks CKT for time base counter 31. If the above-mentioned velocity information for programmable frequency division is NSP, the frequency division ratio r is given by r = (NSP + 512)/2048 so that the value r may be changed in a range of from 384/2048 to 639/2048, with 512/2048 = 1/4 as a centre. The time base counter 31 is a 10-bit binary counter, as an example, counting the count clocks CKT outputted from programmable frequency divider 40. The count value of the counter is incremented each time the counter is triggered by output CKT. The counter 31 continues its binary counting operation as long as it is fed with the master clocks CKMS. 1024 counts of the frequency-divided clocks CKT make up a complete cycle of the time base counter 31 which constitutes a cycle of an output pattern of the ultimate timing output signal STG. In operation, the microcomputer previously loads, responsive to the states (recording, playback or stop states) of a DAT, which is a rotary head type reproducing apparatus, 10-bit time- base data or 6-bit timing pattern data, for example, in the timing pattern memory 32, from data bus 46 via data buffer 47 or from address bus 48 via address buffer 49 and selector 36. On the other hand, master clocks CKMS, supplied to input terminal 44, are frequency-divided by programmable frequency divider 40 to generate count clocks CKT which are transmitted to time base counter 31, which then effects a counting operation. In case of an overflow of counter 31, a reset signal is supplied via timing controller to event counter 35 which is thereby reset or cleared to zero. The output "0" from event counter 35 is supplied via selector 36 to timing pattern memory 32 for pointing out the first word (address "0" word) among the 32 words with address 0 to address 31 stored in timing pattern memory 32. The 10-bit time base data of the 16-bit word having the address 0 in the timing pattern memory 32 are latched as an input to comparator 33, while 6-bit output data of the address 0 word are outputted at an output port via timing output buffer 37. The 6 bits of the 6-bit output represent six timing output signals STG0 to STG5. The time base data latched as an input to comparator 33 are compared to an output of time base counter 31. At a time point when the output of the counter 31 performing the counting operation is coincident with the above-mentioned time base data, comparator 33 outputs a coincidence output which is transmitted via timing controller 34 to event counter 35 to increment the count value of the event counter 35. That is, directly following resetting, the output of event counter 35 is changed from "0" to "1" to point out the second word (address 1 word) of timing pattern memory 32, which second word is read out. In general, the word of the timing pattern memory 32 pointed out by the output of the incremented event counter 35 is read out and its 10-bit time base data is latched as an input to comparator 33, while its 6-bit output data is outputted at an output port via timing output buffer 37. By repetition of the above described sequence of operations, outputs for each time base data stored in the timing pattern memory 32 for the six timing output signals STG0 to STG5 are produced. When the time base counter 31 counts 1024 count clocks CKT corresponding to the upper limit of counting capacity of the timing pattern memory 32 to cause its overflow, event counter 35 is reset, so that the above-described sequence of operations is repeated from the first word, that is the address 0 word, in the timing pattern memory 32. Meanwhile, the overflow output from time base counter 31 is transmitted to a waveform shaping section 38, from which an interrupt signal is transmitted via output terminal 39 to the microcomputer. This interrupt signal causes an interrupt to the operation of the microcomputer to initiate execution of a predetermined interrupt program, such as a program of rewriting the storage contents of the timing pattern memory 32 for each revolution of the rotary head. In this manner, when the operation of timing generation itself is controlled depending on the rotational velocity of the rotary head, it is possible, by employing control means, such as the microcomputer 8 shown in Fig.2, or by properly setting the timing pattern, that is by previously setting a pattern directly controlling the display changeover operation or a variety of scanning operations as the above-mentioned timing pattern, to inhibit the display changeover operation of display devices, key-scanning operation or the sensor scanning operations during the time when the magnetic head is actually contacting the magnetic tape for actually reproducing the signals to prevent noise intrusion into the magnetic head or the amplifier. It is to be noted that the present invention is not limited to the above-described embodiments. For example, the present invention may be applied to equipment other than the ultra-small sized DAT, such as a reproducing apparatus employing a video tape recorder (VTR) or a variety of rotary heads. Besides, the functions of the microcomputer 8 or the timing generator 7 may be changed arbitrarily. For example, the display changeover operations or the key or sensor scanning operations may be controlled directly from timing generator 7. From the foregoing it is seen that the present invention provides a rotary head type reproducing apparatus in which the rotation of the rotary head is synchronized with the operation of timing generation of the timing generator and the operation of the input or the output changing the voltage or the current is inhibited during the time when the rotary head is contacted with the recording medium for reproducing the signals, so that it becomes possible to prevent the noise generated by the operation of changing the voltage or current from being intruded into the magnetic head or amplifier to deteriorate the playback signals for improving the error rate. The result is that shielding may be eliminated and the display section, switches or sensors may be mounted in close proximity to the rotary head for reducing the size or the weight of the apparatus.

Claims: A rotary head type reproducing apparatus for reproducing signals from a recording medium (3), using a head drum having one or more rotary heads (2A, 2B) intermittently contacted with said recording medium, comprising synchronizing means (5, 6, 8) for synchronizing rotation of said rotary head with a timing generating operation by a timing generator (7), the apparatus including components (26, 28), the switching or scanning operations of which causes a change in current or voltage which generates a noise signal which is mixed into the reproduced signal and being characterised by control means for inhibiting said switching or scanning operations during the time interval (TPB-A, TPB-B) when the or each rotary head is contacted with the area of the recording medium from which the recorded signals are reproduced. The rotary head type reproducing apparatus as defined in claim 1 wherein an operation inhibited by the control means is a display changeover operation (26). The rotary head type reproducing apparatus as defined in claim 1 or 2 wherein the operation is inhibited by the control means is an operating-key scanning or sensor scanning operation (28). The rotary head type reproducing apparatus as defined in any one of claims 1 to 3 and further comprising detection means (5) for detecting rotation of a drum around which, in use, said medium passes, and control means for controlling said timing generator responsive to output information (SFG) of said detection means. The rotary head type reproducing apparatus as defined in any one of claims 1 to 4 wherein said control means comprises frequency dividing means (40) fed with clock signals (44) and having its frequency dividing ratio changed depending on the output information of said detection means, a time base counter (31) fed with an output of said frequency dividing means and adapted for outputting time base data, a timing pattern memory (32) for storing plural time base data and timing output data, a comparator (33) for comparing time base data from said time base counter with time base data from said timing pattern memory, and an event counter (35) responsive to an output of said comparator, one of said time base data and the timing output data of said timing pattern memory being selected (36) by an output of said event counter for outputting timing output data. The rotary head type reproducing apparatus according to any one of the preceding claims, wherein said input or output is in a path for the signals reproduced from the recording medium.

Inventors: TANAKA MASATO, WATANABE NOBUHIKO, TANAKA, MASATO, WATANABE, NOBUHIKO, TANAKA, MASATO, C/O SONY CORPORATION, WATANABE, NOBUHIKO, C/O SONY CORPORATION
Applicants: SONY CORP, SONY CORPORATION
Application year: 1993
Main classification: G11B15
IPC codes: G11B33, G11B15, G11B5, G11B27