Tape Guide Arrangement for a Helical Scan Type Magnetic Record Reproduction Device

This invention relates to a magnetic record reproduction device, and in particular to a rotary head type digital audio tape recorder (hereinbelow abbreviated to R-DAT ), in which the tape is drawn out from the cassette at the recording/reproduction.

FIG. 6 is a scheme illustrating the track pattern on a magnetic tape, on which information is recorded/reproduced by an R-DAT, and FIG. 7 is a top view of a usual tape driving system of the R-DAT, in which the reference numeral 1 is an arrow indicating the movement direction of the tape; 2 is an arrow indicating the movement direction of the rotary head; 3 is a reference edge; 4, 4' are selection tracks; 5, 5' are track guards; 6.sub.1, 6.sub.2 are main tracks; 7 is a cassette; 8 is a drum; 9 is a capstan; and 10 represents the tape.

As indicated in the figures, two heads on the drum 8 record two tracks 6.sub.1, 6.sub.2 for every rotation of the drum 8 and inversely, at the reproduction, the two tracks 6.sub.1, 6.sub.2 are reproduced for every rotation of the drum 8. Although here it is supposed that the number of heads is 2, it is only the track pattern indicated in FIG. 6 that is determined by the standard. As indicated in FIG. 7, the tape 10 is wound around the drum 8 over 90.degree..

The diamater of the drum is determined to be d=30 mm, but when it is d=15 mm, which is a half thereof, the winding angle is changed from the prior art winding angle of 90.degree. to 180.degree., as indicated in FIG. 8, and thus the drum may be made more slender. In order to make the R-DAT more convenient for carrying it, it is necessary to make it smaller and inevitable to make it thinner. However, only if the diameter d is changed to 15 mm, as indicated in FIG. 8, although it can be made smaller in the direction perpendicular to the axis 11' of the motor 11, its thickness in the direction parallel to the axis 11' of the drum 8 and the motor 11 cannot be reduced.

The object of this invention is to provide a tape driving system for an R-DAT, for which the diameter of the drum holding the rotary head is reduced to a half of that according to the prior art techniques and in addition the thickness described above is reduced.

In order to achieve this object, a magnetic recording reproduction device, according to this invention, in which signals are recorded/reproduced by means of at least two rotary heads mounted on a drum rotated by a motor on a magnetic tape driven while being wound around the drum, comprises means for bending the tape approximately by 90.degree. and at the same time twisting it approximately by 90.degree. at the entrance side and at the exit side of the drum.

Since the diameter of the drum is reduced to a half and the rotation axis of the drum and the motor is disposed substantially parallelly to the base plate of the device, it is possible to realize a thin type R-DAT.

FIGS. 1 (a), (b) and (c) are schemes showing the basic construction of a tape driving system according to this invention; (a), (b) and (c) being a top view, a side view and a perspective view, respectively;

FIGS. 2 (a), (b) and (c) are schemes for explaining the movement of the tape;

FIG. 3 is a perspective view of a post guide and the tape;

FIGS. 4 (a) and (b) show the distribution of reproduced signals on the time axis;

FIG. 5 shows frequency characteristics;

FIG. 6 illustrates the track pattern of the R-DAT;

FIG. 7 illustrates the tape driving mechanism and the movement of the tape in a prior art R-DAT;

FIGS. 8 (a) and (b) are schemes for explaining the difference in the winding angle between the prior art system and the system according to this invention; and

FIGS. 9 (a) and (b) indicate the arrangement of a cassette, the drum and the motor in a prior art R-DAT.

FIGS. 1 (a), (b) and (c) are schemes showing the basic construction of a tape driving system according to this invention; (a), (b) and (c) being a top view, a side view and a perspective view, respectively, illustrating a tape 10 wound around the drum. in FIGS. 1 (a), (b) and (c), the axis 11' of the drum 8 and the motor 11 is disposed substantially parallelly to the base plate B such as a chassis of the R-DAT and the tape is wound around the drum after having been folded as stated later. With respect to the device indicated in FIG. 9, since the thickness T is determined by the diameter of the drum 8 or the motor 11, a slender motor 11 giving a required torque can be used without any influences on the thickness T.

FIGS. 2 (a), (b) and (c) are schemes for explaining the method for folding the tape 10 on the entrance side I and the exit side 0 of the drum 8, when the tape 10 is wound around the drum 8. As illustrated in FIG. 2 (a), the tape is folded once at a right angle. Then, as illustrated in FIG. 2 (b), the tape is bent again by 90.degree. so that the direction of the movement of the tape is perpendicular to the initial surface of the tape. FIG. 2 (c) shows the tape bent still again in order to wind it around the drum. It is possible to reduce the thickness T of the tape driving system in the reproduction device by winding the tape 10 around the drum 8 in this way, as indicated in FIG. 1 (c).

However, if the tape is moved in practice in the state indicated in FIG. 1, since the tape is folded and the radius of curvature of the tape is small, the life thereof is short and the torque of the capstan motor required for the movement of the tape should be consiserably great. In order to remove this difficulty, cylindrical post guide mechanisms 12.sub.1, 12.sub.2 and 12.sub.3 are located at the positions, where the tape is folded, i.e. at the entrance side I and at the exit side 0 of the drum 8 in FIG. 1 (c), as indicated in FIG. 3. These post guide mechanisms 12.sub.1, 12.sub.2 and 12.sub.3 can be either fixed or rotatable and they are disposed for realizing the folding of the tape as indicated in FIG. 2 (c). Owing to these mechanisms, the radius of curvature of the tape at the folding is made greater, the tape moves smoothly, a weak force may be sufficient for the movement of the tape, and the life of the tape may be elongated.

Owing to the tape movement system described above, an effect stated later can be obtained by reducing the diamater of the drum to 1/2, as indicated in FIG. 8 (b). It is supposed that the rotation number of the drum is 2000 rpm, which is identical to that according to the prior art techniques. FIGS. 4 (a) and (b) show the distribution of reproduced signals on the time axis. FIG. 4 (a) indicates variations of the signal obtained according to the prior art techniques, in the case where the track pattern indicated in FIG. 6 is read out by means of the two heads A and B mounted on the drum, the winding angle is 90.degree., and the heads A and B are located so as to be opposed to each other, i.e. at two angular positions which are separated by 180.degree.. As indicated in the upper portion of FIG. 4 (a), since the output of a reproduction head corresponds to 90.degree. which is the winding angle, in 180.degree. which is the rotation angle, the reproduced signal S.sub.1 is intermittent on the time axis. This intermittent signal is once recorded for 90.degree. in a memory, as indicated by arrows, and read out in a period of time correponding to 180.degree., i.e. with a clock frequency, which is 1/2 of the clock frequency at the recording in the memory. By this or another equivalent method the reproduced signal S.sub.2 is obtained, for which the time axis is stretched twice with respect to that for the reproduced signal S.sub.1. FIG. 4 (b) shows the reproduced signal according to the method of this invention, for which the stretch of the time axis is basically unnecessary. The output S.sub.3 of the reproduction heads is continuous, as indicated in the figure, and it is sufficient only to draw out the reproduced signal S.sub.3 after having stored it once in a memory, in order to absorb the time axis variation component (jitter) accompanied by the recording/reproduction to/from the magnetic tape.

FIG. 5 shows frequency characteristics of the transmission system for the reproduced signal. The full line indicates the characteristics of the transmission band for the reproduced signal according to the prior art techniques. To stretch these characteristics twice with respect to the time axis by means of a memory corresponds to the fact that the frequency axis is shortened to 1/2, as indicated by the broken line in FIG. 5. Since a reproduction system having the frequency characteristics indicated by the broken line is sufficient, the method of this invention is advantageous in the S/N ratio of the preamplifier in the reproduction system (generally the S/N ratio in an electro-magnetic transformation is lowered for the high frequency).

The construction according to this invention can be used also for the recording. Since the band of the recording system can be made narrower and the frequency region, where recording characteristics are good, in used, it is possible to ameliorate the whole S/N ratio of the signal.

As explained above, according to this invention, the following advantages can be obtained:

(i) The rotary drum can be made more slender and at the same time the device can be made thinner, because the tape is wound around the drum after having been folded at 90.degree.. A slender motor driving the drum is used, what doesn't increase the thickness.

(ii) Since the tape winding angle is increased from 90.degree. to 180.degree., the stretching of the time axis for the output of the reproduction heads is unnecessary. For this reason the memory for stretching the time axis is not required and thus the device is economical. Although a memory is necessary for absorbing the time axis variation component, this memory may have a small capacity with respect to the memory for stretching the time axis.

(iii) Since the band of the reproduced signal is narrow (1/2 of that according to the prior art techniques), it is possible to increase the S/N ratio of the preamplifier for the reproduction.

It is further understood by those skilled in the art that the foregoing description is a preferred embodiment of the disclosed device and that various changes and modifications may be made in the invention without departing from the spirit and scope thereof.