Recording and/or reproducing apparatus having rotary heads

Abstract: In the apparatus heads A, C, E and G having a first azimuth, and heads B, D, F and H having a second azimuth are alternately arranged, and heads A' and E' having a second azimuth are disposed adjacent to the heads A and E', respectively. The use of the heads A', C, E' and G permits recording and reproducing at 1/2 speed with the same track pitch. The positions of the heads A and E are deviated by predetermined amounts from the equal interval positions on the periphery of a rotating drum so that recording and reproducing can be performed with the same track pitch at least at 1/4 speed.

Description: The present invention relates to an apparatus for recording information on and/or reproducing information from a recording medium according to the preamble of claim 1 and to a method for recording information on and/or reproducing information from a tape-like recording medium according to the preamble of claim 8. As is generally known, an apparatus for recording and/or reproducing great amounts of digital signals such as video signals at a high speed must be equipped with many heads which simultaneously contact a tape for decreasing a bit rate per signal system by distributing signals to the many heads. Fig. 1 shows an example of the arrangement of rotary heads in a digital recording and/or reproducing apparatus equipped with eight heads on which a tape is wound for 180° + α for distributing signals to four systems. In Fig. 1, heads 2A to 2H provided on the periphery of a rotating drum 1 at equal intervals and the same height successively contact and separate from a magnetic tape 3 with the rotation of the rotating drum 1. Since at least four heads simultaneously contact the tape 3, four systems of signals can be recorded or reproduced. The track pattern shown in Fig. 2 is thus formed on the magnetic tape 3 at a track pitch T substantially proportional to the feed speed of the tape 3. In this example, the azimuth angles of adjacent heads are respectively set to +A° and -A° so that a high recording density can be obtained by a so-called azimuth overwrite technique, without using a guard band. In the arrangement of the rotary heads described above with reference to Figs. 1 and 2, there is demand for changing a bit rate of digital signals which can be recorded and/or reproduced. Namely, there is demand for recording and/or reproducing signals for a longer time by decreasing the information amount using the technique of band compression or the like, though deteriorating the image quality to some extent. In the above example, the demand can be satisfied by the following three possible methods: (1) A method of changing the tape speed alone. (2) A method of proportionally changing the tape speed and the rotational speed of the rotating drum. (3) A method of proportionally changing the tape speed and the number of the heads used. However, all of these methods have critical problems. The problems with these methods are described below with reference to a case where the bit rate is halved, and the recording time is doubled. In the first method, the track pitch is halved, as shown in Fig. 3, thereby decreasing the S/N (signal-to-noise) ratio by about 3 dB. Although an analog recording type apparatus generally employs this method, this method increases the error rate of data in recording of digital signals and thus has significant adverse effects on recording. In the second method, although the track pitch is constant, the rotational speed of the rotating drum 1 is halved, thereby causing mechanical troubles such as an increase in rotational unevenness, deterioration in head touch and the like. There is also an electrical problem that since the frequency of the signal handled by the heads is halved, a transmission system comprising a reproduction amplifier, an equalizer or the like cannot be optimized. In the third method, although two-system parallel recording is-performed by using the heads 2A, 2C, 2E and 2G (refer to Fig 4), crosstalk occurs due to the use of the four heads having the same azimuth angle. The use of the other heads causes trouble in that the track pitch varies. In consideration of the above points, the inventors have previously proposed a rotary head-type recording and/or reproducing apparatus which is arranged so that recording and/or reproducing can be realized with a constant track pitch in spite of a change in the tape speed. This apparatus is described below. Fig. 5 is a drawing illustrating the arrangement of rotary heads in a digital video tape recorder (DVTR) as an example of the above apparatus. In Fig. 5, reference numerals 2A, 2C, 2E and 2G each denote a head with a first azimuth angle, and reference numerals 2B, 2D, 2F and 2H each denote a head with a second azimuth angle. The heads 2A, 2C, 2E and 2G and the heads 2B, 2D, 2F and 2H are alternately arranged on the periphery of a rotating drum 1 at equal intervals. The heights of these heads in the direction of the rotational axis are adjusted to be the same. Reference numerals 2C' and 2G' denote heads with the second azimuth angle which are provided adjacent to the heads 2C and 2G, respectively, with the first azimuth angle, and being at a height having a predetermined difference X (not shown) in height therefrom. The heads 2C' and 2G' are arranged so as to have substantially the same trace locus as that of the heads 2C and 2G when a tape is moved at a predetermined speed of 1/2 V T , as shown in Fig. 6, which shows the case of the head 2C'. Reference numeral 3 denotes the magnetic tape which is wound around the rotating drum 1 for 180° + α. In this arrangement, when the magnetic tape 3 is moved at a speed of V T while the rotating drum 1 is rotated at a predetermined rotational speed using the eight heads 2A, 2B, 2C, 2D, 2E, 2F, 2G and 2H, and when four of the eight heads which simultaneously contact the tape are successively selected for recording four-system signals, the track pattern shown in Fig. 2 is obtained, as in the above-described conventional example. When the tape speed is then set to 1/2 V T , and when two of the four heads 2A, 2C', 2E and 2G', which simultaneously contact the tape, are successively selected for recording two-system signals, the track pattern shown in Fig. 6 is obtained. Namely, although the track angle is only slightly changed, the track pitch T is the same as that at the standard speed, and the S/N ratio of the recorded and reproduced signals is constant. The above arrangement permits recording and reproducing both in a standard speed mode using the heads 2A to 2H and a 1/2 speed mode using the heads 2A, 2C', 2E and 2G'. However, in the above arrangement, if recording and reproducing are performed at 1/4 speed by further decreasing the bit rate, further consideration must be made for keeping the track pitch constant. Namely, a track pattern with a substantially constant track pitch can be obtained when the heads 2C and 2G' or 2C' and 2G are used. However, since the difference X in height, which is provided to correspond with the phase interval between the heads 2C and 2C' and the heads 2G and 2G' is suitable for the 1/2 speed mode, the difference in height is too large by 1/2 X for the 1/4 speed mode achieved by decreasing the bit rate, thereby producing a track pitch increased by 1/2 X and a track pitch decreased by 1/2 x. When the recording density can be increased by improving the characteristics of the tape and heads, the track pitch is decreased by decreasing the tape speed so that the recording time can be increased. However, since an appropriate difference X in height is determined in proportion to the track pitch, nonuniformity significantly occurs in the track pitch in the above example. It is thus necessary to add a head for a long-term mode. From the document JP-A-1277301 on which the preambles of claims 1 and 8 are based, a generic apparatus is known. This apparatus comprises a rotating drum on which two groups of heads are mounted. Each group of heads consists of a first head with a head gap having a first azimuth angle, a second head with a head gap having a second azimuth angle, a third head with a head gap having the first azimuth angle and a fourth head with a head gap having the second azimuth angle. An additional fifth head with a head gap having the second azimuth angle is arranged adjacent to the first head. The positions of the first to fourth heads of each group are set such that these heads are used at a first speed VT of the information medium. Furthermore, since there is provided a head for ½VT (i.e. the fifth head), the first and fifth heads are to be used at ½VT, while the track pitch remains uniform at VT and ½ VT. From the document JP-A-59213002 it is known that a group of heads mounted on the rotary drum comprises first to fourth heads as well as a fifth head adjacent to one of the first to fourth heads. These first to fourth heads are not arranged such that a head with a gap having a first azimuth angle and a head with a gap having a second azimuth angle alternate on the periphery of the rotary drum. Another arrangement of heads on a rotary drum is known from the document JP-A-1277304, according to which the heads comprising a gap with a first azimuth angle, a second azimuth angle and a third azimuth angle. These heads are arranged such that recording/reproducing can be performed at VT and ½VT, while the track pitch remains uniform. Moreover, from the document EP-A-0 117 455 it is known to arrange a first pair of heads having different azimuth angles of gaps and being disposed with an angular spacing of 180° from each other. Additionally, there are provided a second pair of heads also having different azimuth angles of gaps and being disposed with an angular spacing of 180° from each other. The first and second pairs of heads are offset such that a pattern of record produced by a head of the first pair of heads is at least partly overlaid by a pattern of record produced by a head of the second pair of heads. From another document JP-A-1302518 a rotary drum is known comprising two groups of heads. Each group of heads has four heads. Regarding the arrangement of the heads in one group, the head of a width to be wider than a track pitch is arranged in the rotational direction downstream side of a rotary head, whose width is almost equal with the track pitch, and in a medium proceeding direction upstream side. Thus, in order to maintain the track pitch uniform at VT, ½VT and ¼VT, there has to be used heads which have different azimuth angles and different designs of the heads. The object of the present invention is to further improve the above apparatus and to provide a rotary head type recording and/or reproducing apparatus which permits a uniform track pitch to be obtained at both 1/2 speed and 1/4 speed. The above-stated object is achieved by means of the combination of the features defined in the independent apparatus claim 1. Preferred embodiments of the apparatus according to claim 1 are disclosed in the dependent claims 2 to 7 and 10 to 12, respectively. The object is also achieved by means of the combination of the features defined in the independent method claim 8. A preferred embodiment of the method according to claim 8 is disclosed in claim 9. According to an embodiment of the invention, a rotary head type recording and/or reproducing apparatus in accordance with an embodiment of the present invention comprises at least one group comprising two heads having a first azimuth, and two heads having a second azimuth, which are alternately arranged on the periphery of a rotating drum so as to be used for recording and/or reproducing at a tape speed V T . In the apparatus, another head having the second azimuth (referred to as the second azimuth head) is further arranged adjacent to one of the two heads having the first azimuth, in each group, so as to be used for recording and/or reproducing at a tape speed of 1/2V T, together with the other head having the first azimuth. The position of the head adjacent to the additional second head is deviated from an equal-interval arrangement position on the periphery of the rotating drum by a predetermined amount so that recording and/or reproducing can be performed at a tape speed of at least 1/4V T . In the above arrangement, the head for the 1/2 speed is provided adjacent to one of the four heads for the highest bit rate mode, and the positions of the two adjacent heads relative to the positions of the other heads, which are simultaneously used at the 1/2 speed, are offset from the positions at equal intervals so that a uniform track pitch can be obtained at both the 1/2 speed and the 1/4 speed. Moreover, the present invention shall further improve the above apparatus and provide a rotary head type recording and/or reproducing apparatus which permits a decrease in the offset between the track pitches in respective modes. Therefore, according to another embodiment of the present invention, a rotary head-type recording and/or reproducing apparatus comprises first and second heads having different azimuths and arranged adjacent to each other, a third head having the same azimuth as that of one of the first and second heads and arranged at a position offset from a position located 180° from the head having the same azimuth by a predetermined phase with a difference in height therefrom, and fourth and fifth heads having an azimuth different from that of the third azimuth and arranged at positions at substantially the same phase distance from one of the first and second heads with the same difference in height therefrom. This arrangement permits recording and/or reproducing with a substantially uniform track pitch of at least two kinds in any one of the following modes (1) to (3): (1) A lowest bit rate mode in which the first and second adjacent heads having different azimuth angles are alternately used for each rotation. (2) A double bit rate mode in which the third head arranged at a position offset, by a predetermined phase, from the position located 180° from one of the first and second heads, and the other head of the first and second heads are used. (3) A quadruple bit rate mode in which one of the first and second heads, the fourth and fifth heads arranged at positions offset, by a predetermined phase, from a position located 90° from the one of the first and second heads, and the third head are used. In one aspect, the present invention provides an apparatus for recording information on and/or reproducing information from a recording medium using a plurality of heads. The apparatus includes a rotating drum for mounting the plurality of heads, a first head with a head gap having a first azimuth angle, a second head with a head gap having a second azimuth angle, a third head with a head gap having the first azimuth angle, a fourth head with a head gap having the second azimuth angle, and a fifth head with a head gap having the second azimuth angle. The fifth head is arranged adjacent to the first head. The first to fourth heads are successively arranged on the periphery of the rotating drum at equal intervals, at least the first head is offset in position by a predetermined amount from the positions of equal interval of the first to fourth heads, and the heads record information on the recording medium in accordance with information signals and/or reproduce information from the recording medium. In another aspect, the present invention provides a method for recording information on and/or reproducing information from a tape-like recording medium using a rotating drum that mounts a plurality of heads including a first head with a head gap having a first azimuth angle, a second head with a head gap having a second azimuth angle, a third head with a head gap having the first azimuth angle, a fourth head with a head gap having the second azimuth angle, and a fifth head with a head gap having the second azimuth angle. The method includes the steps of arranging the first to fourth heads successively on the periphery of the rotating drum at equal intervals, with the fifth head being adjacent to the first head such that at least the first head is offset in position by a predetermined amount from the positions of equal interval of the first to fourth heads, and recording information on and/or reproducing information from the recording medium by using the first, second, third and fourth heads when the recording medium is moved at a first speed, and by using the third and fifth heads when the recording medium is moved at a speed of one-half of the first speed. In yet another aspect, the present invention provides an apparatus for recording information on and/or reproducing information from a recording medium using a plurality of heads, The apparatus includes a rotating drum for mounting the plurality of heads, a first head with a head gap having a first azimuth angle, a second head with a head gap having a second azimuth angle, a third head with a head gap having the first azimuth angle, a fourth head with a head gap having the second azimuth angle, and a fifth head with a head gap having the second azimuth angle. The fifth head is arranged adjacent to the first head, The first to fourth heads are successively arranged on the periphery of the rotating drum, the third head is arranged at a position offset by a predetermined amount from a position located 180° from the first head, the second and fourth heads are arranged at substantially equal distances from the first and third heads, respectively, and the heads record information on the recording medium in accordance with information signals and/or reproduce information from the recording medium. In the following the invention is further illustrated by embodiments with reference to the enclosed figures. Fig. 1 is a drawing showing a typical example of a rotary head type recording and/or reproducing apparatus, in which eight heads are arranged on a rotating drum; Fig. 2 is a drawing showing a track pattern obtained when four of the rotary heads shown in Fig. 1 are used for recording on a tape which is moved at a tape feed speed V T by the rotary heads; Fig. 3 is a drawing showing a track pattern obtained when the tape feed speed V T is halved; Fig. 4 is a drawing showing a track pattern obtained when the tape feed speed V T is halved, and the number of the heads used is also halved; Fig. 5 is a drawing showing an arrangement of heads in a rotary head type recording and/or reproducing apparatus, which has previously been proposed by the inventors; Fig. 6 is a drawing corresponding to Fig. 4 and showing a track pattern obtained when the rotary heads shown in Fig. 5 are used for recording on a tape; Fig. 7 is a top view of rotary heads in a rotary head type recording and/or reproducing apparatus in accordance with a first embodiment of the present invention; Fig. 8 is a side development of the rotary heads in accordance with the first embodiment of the present invention; Fig. 9 is a top view of rotary heads in a rotary head type recording and/or reproducing apparatus in accordance with a second embodiment of the present invention; Fig. 10 is a side development of the rotary heads in accordance with the second embodiment of the present invention; Fig. 11 is a top view of rotary heads in a rotary head type recording and/or reproducing apparatus in accordance with a third embodiment of the present invention; Fig. 12 is a top view of rotary heads in a rotary head type recording and/or reproducing apparatus in accordance with a fourth embodiment of the present invention; Fig. 13 is a side development of the rotary heads in accordance with the fourth embodiment of the present invention; Fig. 14 is a drawing showing a track pattern obtained when a tape is moved at a speed V T in the fourth embodiment; and Fig. 15 is a drawing showing a track pattern obtained when a tape is moved at a speed V T ' higher than V T in the fourth embodiment. Like reference numerals have been used throughout the figures for like or corresponding elements. Figs. 7 and 8 are a top view and a side development, respectively, of rotary heads a rotary head type recording and/or reproducing apparatus, in accordance with a first embodiment of the present invention. In Fig. 7, reference characters A to H, A' and E' each denote a magnetic head, reference numeral 1 denotes a drum, and reference numeral 2 denotes a magnetic tape. The magnetic tape 2 is diagonally wound on the rotating drum 1 for about 180° and is moved at a constant speed V T in the direction shown in the drawing. On the other hand, the rotating drum 1 is rotated at a constant rotational speed of V H . The eight heads A to H are successively used for recording and/or reproduction by scanning the magnetic tape 2 at a constant track pitch t p . Referring to Fig. 8, of the heads A to H, the heads A, C, E and G have a first azimuth angle, and the heads B, D, F and H have a second azimuth angle. The heads B, C, D, F, G and H are arranged at the same height. The heads A and E are provided at positions deviated from arrangement positions O 1 and O 2 at equal intervals of 45° by amounts of  1 and  2 , respectively, and the lower ends thereof are at heights with differences X 1 and X 2 , respectively, in level from the height of the heads B, C, D, F, G and H so that recording can be made with a constant pitch. With a track pitch tp at the tape speed V T , a uniform pitch is obtained when the differences X 1 and X 2 in height have the following relations to the phases  1 and  2 , respectively: X 1 =  1 45° x t p X 2 =  2 45° x t p A mode of recording and/or reproducing at a 1/2 tape speed (1/2V T ) using four heads with the same track pitch t p is now considered. The two heads A' and E' having a second azimuth angle are arranged at positions deviated from the heads A and E by amounts  A and  E with differences X A and X E , respectively, in height therefrom so that recording and/or reproducing can be made with a uniform pitch by using the heads A', C, E' and G. At this time, the relations between the differences X A and X E in height and the deviations  A and  E are expressed as follows: X A = ( 1 +  A ) 90° x t p X E = ( 2 +  E ) 90° x t p A mode of recording and/or reproducing at a tape speed of 1/4V T using two heads is considered. Since two heads at about 180° having different azimuth angles may be used, the heads A' and E or A and E' may be used. In this embodiment, the heads A' and E are used. In order to obtain a uniform pitch, the differences X A and X 2 in height and the phases  1 ,  A and  2 may have the relations expressed by equation (5) below. When equations (2), (3) and (5) are solved as simultaneous equations, equation (5)' below is obtained. X A - X 2 = ( 1 +  A -  2 ) 90° x t p  A +  1 = 3 2 Since the phase difference  A between the heads A and A' cannot be set to zero, it is found from the equations that the differences  1 and  2 cannot be simultaneously set to zero. For example, if  1 = 0, and if the phase differences between the heads A an A', and E and E' are the same in consideration of equalization of parts, the following equations are derived from the above equations:  1 = 0,  2 = 1 3  A , X 1 = 0, X 2 =  A 135° x t p X A =  A 90° x t p , X E = 2 A 135° x t p In this embodiment, a uniform track pitch can be obtained even in a mode of recording and/or reproducing at a 1/8 speed (1/8V T ). Namely, in this mode, the heads A and A' or the heads E and E' are alternately used for each rotation for recording and/or reproducing. In this case, when the heads A and A' are used, a condition for obtaining a uniform track pitch is expressed by equation (6) below. Equation (6)' is obtained from the above equations (1), (3) and (6). When equation (6)' is substituted in equation (5)', equation (7) below is obtained. X A - X 1 =  A 360° x t p  1 = 3 4  A  2 = 7 12  A Namely, since the differences  1 and  2 cannot both be set to zero, the following equations are obtained. Assuming that  E =  A , X E is also determined. X 1 =  A 60° x t p , X 2 = 7 A 540° x t p , X A = 7 A 360° x t p X E = 19 A 1080° x t p When the heads E and E' are used in the 1/8V t mode, equation (8) below is obtained. Equation (8)' is obtained from the above equations (2), (4) and (8). Assuming that  A =  E , when this equation is substituted in equation (5)', equation (9) below is obtained. Each of X 1 , X 2 , X A and X E is thus determined. X E - X 2 =  E 360° x t p  2 = 3 4  E  1 = 5 4  E X 1 =  E 36° x t p , X 2 =  E 60° x t p , X A =  E 40° x t p , X E = 7 E 360° x t p In any one of the cases, a uniform track pitch can be obtained in each of the 1, 1/2, 1/4 and 1/8 modes. This embodiment permits the realization of a uniform pitch in the modes at tape speeds up to 1/8V T . Although pitch error occurs in a mode at a lower tape speed,  A =  E is sometimes so small that the error can be allowed. For example, in the above embodiment, assuming that  A =  E = 12°,  2 = 9° and  1 = 15° are determined by equations (8)' and (9). Since X 1 = 1/3 t p , X 2 = 1/5 t p , X A = 3/10 t p and X E = 7/30 t p , and X E - X 2 = 1/30 t p . If the heads E and E' are used once each time the rotating drum is rotated twice in a 1/16V T mode, since the condition for obtaining a uniform pitch is X E - X 2 = ( E /720°) t p = 1/60 t p , the pitch error is 1/30 t p - 1/60 t p = 1/60 t p . Since this error corresponds to an output difference of ±20 log 10 (1 - 1/60) = ±0.15 dB, there is a great possibility that the error can be tolerated. The above embodiment concerns the case where  1 = 0. Although, in this case, pitch error occurs when the heads A and A' or the heads E and E' are used in the 1/8V T mode, the error can be tolerated if  A =  E is sufficiently small. For example, when  A =  E = 12°, since  1 = 0,  2 = 4°, X 1 = 0, X 2 = 4/45 t p , X A = 2/15 t p , and X E = 8/45 t p , X E - X 2 = 4/45 t p . On the other hand, since the condition for obtaining a uniform pitch at 1/8V T is X E - X 2 = ( E /360°) t p = 1/30 t p , the pitch error is 4/45 tp - 1/30 t p = 1/18 t p which corresponds to an output difference of ±20 log 10 (1 - 1/18) = ±0.5 dB. If this error can be tolerated, this state can be realized. A second embodiment of the present invention is shown in Figs. 9 and 10. In this embodiment, four heads are used in the highest bit rate mode, and the condition for obtaining a uniform track pitch at each of the tape speeds V T , 1/2V T and 1/4V T can be determined by the same method as that employed in the first embodiment. The condition when the heads A, B, C and D are used at the tape speed V T , the condition when the heads A' and C are used at the tape speed 1/2V T , and the condition when the heads A and A' are alternately used at the tape speed 1/4V T are expressed by the following equations (10), (11) and (12), respectively: X 1 =  1 90° x t p X A = ( 1 +  A ) 180° x t p X A - X 1 =  A 360° x t p With the substitution of equations (10) and (11), equation (12) is solved to give  1 = 1/2 A , X 1 = ( A /180°) t p and X A = ( A /120°) t p . If  A is determined, the mounting positions of the heads are thus determined. It is thus found that the use of either four or eight heads at the highest bit rate enables a uniform track pitch to be realized by application of the present invention. Fig. 11 shows a third embodiment of the present invention in which the positions of the heads B and D are deviated from the positions at 90° with respect to the head C. Since the heads B and D are used only in the highest bit rate mode, when the heads B and D are arranged at positions with differences of X B and X D in height, respectively, which are indicated by the equations X B = ( B /90°) t p and X D = ( D /90°) t p , a uniform pitch can be obtained. When the positions of the heads B and D are deviated from the position at 90°, as described above, since the differences X B and X D in height are increased, the positions of the heads B and D relative to the track are changed during reproduction at the 1/2 or 1/4 tape speed. For example, when  B = 90° -  A , and when the difference X B in height is close to the track pitch, the output from the track adjacent to the track reproduced by the head C is obtained from the head B. When the output of the head A' is decreased due to the clogging of the head or the like, the output of the head B is used. Since the data of adjacent tracks can be simultaneously obtained from the heads B and C during special reproduction such as search or the like, the image quality can possibly be improved. There is also the advantage that output can be checked by simultaneously reproducing during recording. As described above, in this embodiment, a head is added, for the speed of 1/2 of the speed at the highest bit rate, adjacent to one of the four heads. The two adjacent heads are arranged at positions deviated from positions at equal intervals relative to the other heads simultaneously used at the 1/2 speed so that a uniform track pitch can constantly be obtained not only at the 1/2 speed but also at the 1/4 speed and 1/8 speed. This embodiment thus has the effect of enabling a high recording density to be maintained in any one of the bit rate modes. This embodiment concerns the case when a track pattern is formed with the same track pitch in each of the bit rate modes including the 1/2 speed mode, 1/4 speed mode and 1/8 speed mode. The fourth embodiment described below concerns the case when the track pitch is decreased for long-term recording in the same bit rate mode, and the case when the track pitch (track width) is increased for improving the reliability of recording and reproduction. In order to realize both cases, the arrangement of the heads is determined as described below. In contrast with the description of the above embodiment, the lowest bit rate mode is first described for the sake of simplicity. Figs. 12 and 13 show the arrangement of the heads in the fourth embodiment. Figs. 14 and 15 show the track patterns obtained when the tape is moved at tape feed speeds V T and V T ', respectively, which have the relation, V T < V T '. In a mode (referred to as "V T mode") which alternately uses heads A and A' for each rotation for recording at a tape speed V T and an average track pitch of t p , the difference d 1 between the average track pitch t p and the track pitch determined by the mounting phase  A ' of the head A', the difference X A ' in height thereof relative to the head A and the overwrite by the lower end of the head A' is shown in Fig. 14 and indicated by the following equation: d 1 =  A ' 360° x t p - X A ' Similarly, in a mode (V T ' mode) using the heads A and A' for recording at an average track pitch t p ' and a tape speed V T ' (= a x V T ) slightly higher than that of the V T mode, the difference d 1 ' from the average track pitch t p ' is shown in Fig. 15 and is indicated by the following equation: d 1 ' =  A ' 360° x t p ' - X A ' =  A ' 360° x a x t p - X A ' Since  A ' cannot be decreased to 0, it is apparent that d 1 and d 1 ' cannot simultaneously be decreased to 0. It is thus thought to minimize the effects of the differences d 1 and d 1 ' of the track pitches in both modes. The possible conditions for minimizing the effects include the following three conditions: (A) The pitch errors produced in both modes are uniform. d 1 + d 1 ' = 0 (B) The output differences produced in both modes are uniform. d 1 x a + d 1 ' = 0 (C) The pitch error in the mode with a smaller average track pitch is zero. d 1 = 0 The condition (A) is the optimum condition for the case when although the output difference in the V T mode is greater than that in the V T ' mode, the mechanical tracking margin during compatible reproduction is given priority. The condition (B) is the optimum condition for the case when both modes are averaged. The condition (C) is the optimum condition for the case when the output margin in the V T ' mode is sufficiently large. The medium condition of the conditions (A), (B) and (C), i.e., the condition below, may actually be satisfied in accordance with the apparatus used. d 1 x a' + d 1 ' = 0 wherein a' > 1. Although a case when the condition (B) is performed is described below, the same as that described below can, of course, be applied to any of the cases. With the substitution of the equations (21) and (22)' the equation (24) is rearranged to give the following equations: X A ' =  A ' 180° x a a + 1 x t p d 1 t p = d 1 ' t p ' =  A ' 360° x 1 - a 1 + a The track pitch deviations d 2 and d 2 ' determined by the lower end of the head A' in the double speed modes, i.e., the 2V T mode and 2V T ' mode, in which the heads A' and C are used, are then determined. Since the head C is arranged at a position deviated by  C from the position at 180° with respect to the head A, the head A' is deviated by  C +  A ' from the position at 180° with respect to the head C. The head C also has the difference X C in height from the head A. Therefore the deviations d 2 and d 2 ' are as follows: d 2 =  C +  A ' 180° x t p - X C - X A ' d 2 ' =  C +  A ' 180° x t p ' - X C - X A ' =  C +  A ' 180° x a x t p -X C - X A ' The condition (B) is expressed by the following equation: d 2 x a + d 2 ' = 0 With the substitution of equations (26), (28) and (29)', equation (30) is rearranged to give the following equations: X C = 2 C +  A ' 180° x a a + 1 x t p d 2 t p = d 2 ' t p ' =  C +  A ' 180° x 1 - a 1 + a In the quadruple speed modes, i.e., the 4V T mode and the 4V T' mode, which use the heads A, B, C and D, the track pitch deviations d 3 and d 3 ', d 4 and d 4 ', d 5 and d 5 ', and d 6 and d 6 ' which are determined by the lower ends of the heads B, C, D and A, respectively, are determined. Since the head B is arranged at a position deviated by  A from the position at 90° with respect to the head A at a height X B from the head A, and the head C is arranged at a position deviated by  C at a height X C from the head A, the following equations are obtained: d 3 = -  B 90° x t p + X B d 3 ' = -  B 90° x t p ' + X B = -  B 90° x a x t p + X B d 4 = -  C 90° x t p + X C - d 3 d 4 ' = -  C 90° x t p ' + X C - d 3' = -  C 90° x a x t p + X C - d 3 ' As seen from equations (35) and (36)', since d 3 + d 4 , and d 3 ' + d 4 ' are determined by  C and X C alone, the absolute value of each of d 3 , d 3 ', d 4 and d 4 ' can be minimized by determining  B and X B so that d 3 = d 4 , and d 3 '= d 4 '. Equations (37) and (38) below are thus obtained from the equations (35) and (36)', respectively. The equations (33) and (34)' and the equations (37) and (38) are solved to give the equations (39) and (40) below, respectively. d 3 = d 4 = d 3 + d 4 2 = -  C 180° x t p + X C 2 d 3 ' = d 4 ' = d 3 ' + d 4 ' 2 = -  C 180° x a x t p + X C 2  B = 1 2  C X B = 1 2 X C On the other hand, since the head D is arranged at a position deviated by  D from the position at 90° with respect to the head A at a height X D therefrom, d 5 , d 5 ', d 6 and d 6 ' are indicated by the equations below. Since equation (45) below is obtained from equations (41) and (43), and equation (46) below is obtained from equations (42)' and (44)', equations (47) and (48) below are established by the same method as that applied to d 3 and d 4 . Therefore, equations (49) and (50) below are obtained from equations (43) and (44)' and equations (47) and (48), respectively. d 5 = -  D -  C 90° x t p + X D - X C d 5 ' = -  D -  C 90° x t p ' + X D - X C = -  D -  C 90° x a x t p + X D - X C d 6 =  D 90° x t p - X D d 6 ' =  D 90° x t p ' - X D =  D 90° x a x t p - X D d 5 + d 6 =  C 90° x t p - X C d 5 ' + d 6 ' =  C 90° x a x t p - X C d 5 = d 6 = d 5 + d 6 2 =  C 180° x t p - X C 2 d 5 ' = d 6 ' = d 5 ' + d 6 ' 2 =  C 180° x a x t p - X C 2  D = 1 2  C X D = 1 2 X C If the condition (B) is applied to d 4 and d 4' , equations (51) and (52) below are obtained, and equation (53) below is obtained from equations (51) and (52). Equation (54) below is thus obtained. d 4 x a + d 4 ' = 0 -  C 90° x a x t p x X C = 0, X C =  C 90° x a x t p  C =  A ' 2a X C =  A ' 180° x t p From these equations, the position and the pitch deviation of each of the heads is determined by  A ', a and t p , as shown below. X A ' =  A ' 180° x a a + 1 x t p  B =  D =  A ' 4a ,  C =  A ' 2a X B = X D =  A ' 360° x t p , X C =  A ' 180° x t p d 1 t p = - d 1 ' t p ' =  A ' 360° x 1 - a 1 + a d 2 t p = - d 2 ' t p ' =  A ' 360° x (1 + 2a)(1 - a) a(1 + a) d 3 t p = d 4 t p = - d 5 t p = - d 6 t p = - d 3 ' t p ' = - d 4 ' t p ' = d 5 ' t p ' = d 6 ' t p ' =  A ' 360° x a - 1 a For example, when  A ' = 15° and a = 1.5, X A '= 1/20tp,  B =  D = 2.5°, X B = X D = 1/24t p ,  C = 5° and X C = 1/12t p . The right sides of the equations (27), (57) and (58) are thus -1/120, -1/45 and 1/120, respectively. Therefore, the increase in the output variation caused by the pitch error produced due to the addition of the 2V T , 2V T ', 4V T and 4V T ' modes is + 20 log 10 (1 - 1/45) = ± 0.20 dB. This causes no practical problem. Since the above-described results are obtained by applying the condition (B) to each of the modes, the pitch deviations in the 2V T and 2V T ' modes are maximum. However, since the pitch deviations in the 4V T and 4V T ' modes, and the pitch deviations in the 2V T and 2V T ' modes are determined by  C , the pitch deviation in the 2V T or 2V T ' mode and the deviation in the 4V T or 4V T ' mode is used in place of the application of the condition (B) to the 4V T and 4V T ' modes so that the output variation can be further decreased. Namely, the following equation (59) or (60) is used in place of equation (51): d 2 + d 4 = 0 d 2 ' + d 4 ' = 0  C +  A ' 180° x 1 - a 1 + a -  C 180° + 2 C +  A ' 360° x a a + 1 = 0  C = 2 - a 2a  A '  C = (a - 1 2 )  A ' Examination of equation (62) shows that when  C is greater than -  A ', the pitch deviation in the 2V T mode decreases as  C decreases. Comparison between equations (61) and (62) shows that when a > 1,  C shown by equation (61) is smaller than that shown by equation (62). The required condition is the equation (59) with  C shown by equation (61). Under the condition, the positions of the heads, and the pitch deviations are given by the following:  B =  D = 2 - a 4a  A ',  C = 2 - a 2a  A ' X B = X D =  A ' 180° x 1 a + 1 x t p X C =  A ' 90° x 1 a + 1 x t p d 2 t p = - d 2 ' t p ' =  A ' 360° x (2 + a)(1 - a) a(1 + a) d 3 t p = d 4 t p = - d 5 t p = - d 6 t p =  A ' 360° x (a + 2)(a - 1) a(1 + a) d 3 ' t p ' = d 4 ' t p ' = - d 5 ' t p ' = - d 6 ' t p ' =  A ' 360° x a(a - 1) a + 1 For example, when  A ' = 15° and a = 1.5, X A = 1/20t p ,  B =  D = 1.2°, X B = X D = 1/30t p ,  C = 2.4° and X C = 1/15t p . The right sides of the equations (65), (66) and (67) are thus -7/360, 7/360 and 1/80, respectively. Therefore, the increase in the output variation is ± 20 log 10 (1 - 7/360) = ± 0.17 dB. This is slightly different from that in the above-described case. As described above, although an optimum point is present, substantially the same result can be obtained in the vicinity of the optimum point. In practice,  C is set to a value close to this optimum point from the viewpoint of the ease of formation of a head switch timing pulse, the ease of mounting and adjustment of the heads, and the ease of balancing of rotation, and X C ,  B ,  D , X B , and X D may then be determined using the condition (B). As described above, in this embodiment, since the case at the lowest bit rate is considered as a reference in contrast with the previous embodiment, the tape feed speed is the double speed or the quadruple speed. However, since the bit rate is considered as a reference, the tape speed is a relative speed. On the highest bit rate basis, the tape speed is 1/2 speed or 1/4 speed, and on the medium bit rate basis, the tape speed is 1/2 speed or double speed. Furthermore, in this embodiment, the head A' is arranged at a position so as to contact the tape after the head A contacts it. However, even if the head A' is arranged so as to contact the tape before the head A contacts it, the position of each of the heads is determined by the same method as that described above to produce the same results. In addition, although the embodiment concerns the case when the feed direction of the tape is the same as the rotation direction of the heads, the feed direction of the tape may be different from the rotation direction of the heads. The contact angle of the tape is not limited to 180°. As described above, in this embodiment, the mounting positions of the heads used in the V T and V T ' (> V T ) modes are slightly deviated from the equal interval positions so that the track pitch deviation in each of the modes can be decreased. The embodiment also has the effect of providing an apparatus which can comply with long-term recording and/or reproduction without an increase in the number of the heads used. In a recording/reproducing apparatus having rotary heads, heads A, C, E and G having a first azimuth, and heads B, D, F and H having a second azimuth are alternately arranged, and heads A' and E' having a second azimuth are disposed adjacent to the heads A and E', respectively. The use of the heads A', C, E' and G permits recording and reproducing at 1/2 speed with the same track pitch. The positions of the heads A and E are deviated by predetermined amounts from the equal interval positions on the periphery of a rotating drum so that recording and reproducing can be performed with the same track pitch at least at 1/4 speed.

Claims: An apparatus for recording information on and/or reproducing information from a recording medium (2) using a plurality of heads, said apparatus comprising: a rotating drum (1) on which at least one group of heads (A, B, C, D, A'; E, F, G, H, E') is mounted, each group including a first head (A; E) with a head gap having a first azimuth angle, a second head (B; F) with a head gap having a second azimuth angle, a third head (C; G) with a head gap having the first azimuth angle, a fourth head (D; H) with a head gap having the second azimuth angle, and a fifth head (A'; E') with a head gap having the second azimuth angle, said fifth head (A; E') being arranged adjacent to said first head (A; E), wherein said heads (A, B, C, D, A'; E, F, G, H, E') record information on the recording medium (2) in accordance with information signals and/or reproduce information from the recording medium (2), on the periphery of said rotating drum (1), first to fourth arrangement positions are successively defined at equal intervals, said first to fourth heads (A, B, C, D; E, F, G, H) being associated with said first to fourth arrangement positions, respectively, so as to be used for the recording and/or reproducing at a first speed (VT), said fifth head (A'; E') being used, together with the third head (C; G), for the recording and/or reproducing at a speed of ½ of the first speed (VT), while maintaining a track pitch (t p ) of the first speed (VT), characterized in that at least said first head (A; E) is offset in position by a predetermined amount ( 1 ;  2 ) from the associated arrangement position (O 1 ; O 2 ) in a direction of rotation and along the rotational axis of the rotating drum (1) such that the first and fifth heads (A, A'; E, E') are to be used for recording and/or reproducing at a speed of ¼ of the first speed, while maintaining the track pitch (t p ) of the first speed (VT). An apparatus according to claim 1, characterized in that said second, third and fourth heads (B, C, D; F, G, H) are respectively arranged at the second, third and fourth arrangement positions of equal interval. An apparatus according to claim 2, characterized in that said second, third and fourth heads (B, C, D; F, G, H) are arranged at the same position in a direction along a rotation axis of said rotating drum (1), and said first and fifth heads (A, A'; E, E') are offset in position from that position by an amount (X 1 , X A ; X 2 , X E ) corresponding to the offset ( 1 ,  A ;  2 ,  E ) from the first arrangement positions (O 1 ; O 2 ) of equal interval. An apparatus according to claim 1, characterized in that said second and fourth heads (B, D) are arranged at positions offset by a predetermined amount ( B ,  D ) from the second and fourth arrangement positions of equal interval in a direction of rotation of said rotating drum (1) and in a direction opposite to the direction of rotation of said rotating drum (1), respectively. An apparatus according to claim 4, characterized in that said first, second, fourth and fifth heads (A, B, D, A') are offset from the position of said third head (C) in a direction along a rotation axis of said rotating drum (2) by an amount (X 1 , X B , X D , X A ) corresponding to the offsets ( 1 ,  B ,  D ,  A ) from the first, second and fourth arrangement positions of equal interval. An apparatus according to claim 5, characterized in that the amount of offset ( 1 ) of said first head (A) from the first arrangement position of equal interval is A 0 , the offset ( B ) of said second head (B) from the second arrangement position of equal interval is (90 - A) 0 , and the offset (X B ) of said second head (B) in a direction along a rotation axis of said rotating drum (1) is approximately equal to the track pitch (tp) formed on the recording medium (2). An apparatus according to claim 4, characterized in that said second and fourth heads (B, D) are arranged at substantially equal distances from said first and third heads (A, C), respectively. A method for recording information on and/or reproducing information from a tape-like recording medium (2) using a rotating drum (1) on which at least a group of heads is mounted, each group including a first head (A; E) with a head gap having a first azimuth angle, a second head (B; F) with a head gap having a second azimuth angle, a third head (C; G) with a head gap having the first azimuth angle, a fourth head (D; H) with a head gap having the second azimuth angle, and a fifth head (A'; E') with a head gap having the second azimuth angle, wherein information on/from the recording medium are recorded/reproduced by using the first, second, third and fourth heads (A, B, C, D; E, F, G, H) when the recording medium (2) is moved at a first speed (V T ), and by using the third and fifth heads (C, A'; G, E') when the recording medium (2) is moved at a speed of 1/2 of the first speed (V T ), while permitting that a uniform track pitch (t p ) is obtained at a first speed (VT) and at a speed of ½ of the first speed (V T ), said method comprising the steps of: subdividing the periphery of the rotating drum (1) into first to fourth arrangement positions which are successively defined at equal intervals; associating the first to fourth heads (A, B, C, D; E, F, G, H) with the first to fourth arrangement positions, respectively, and arranging the fifth head (A'; E') adjacent to the first head (A; E); characterized in that at least the first head (A; E) is offset by a predetermined amount ( 1 ;  2 ) from the associated arrangement position (O 1 ; O 2 ) in a direction of rotation and along the rotational axis of the rotating drum (1) such that the first and fifth heads (A, A'; E, E') are to be used for recording and/or reproducing at a speed of ¼ of the first speed, while maintaining the track pitch (t p ) of the first speed (VT). A method according to claim 8, characterized in that the first and fifth heads (A, A'; E, E') are alternately used for each 2 n-2 rotation of the rotating drum (1) when the recording medium (2) is moved at a speed of 1/2 n (n > 2) of the first speed (V T ). An apparatus according to claim 1, characterized in that said first to fourth heads (A, B, C, D) are successively arranged on the periphery of said rotating drum (1), said third head (C) is arranged at a position offset by a predetermined amount from a position located 180° from said first head (A), said second and fourth heads (B, D) are arranged at substantially equal distances from said first and third heads (A, C), respectively, and said heads (A, B, C, D, A') record information on the recording medium in accordance with information signals and/or reproduce information from the recording medium (2). An apparatus according to claim 10, characterized in that said second and fourth heads (B, D) are arranged at positions slighty offset in a direction of rotation of said rotating drum (1). An apparatus according to claim 11, characterized in that said second, third, fourth and fifth heads (B, C, D, A') are offset from the position of said first head (A) in a direction along a rotation axis of said rotating drum (1) by an amount (X B , X C , X D , X A' ) corresponding to the offsets ( B ,  C ,  D ,  A' ) from the respective arrangement positions of the heads (B, C, D, A') in a direction of rotation of said rotary drum (1).

Inventors: HASEGAWA MASAHIDE, HASEGAWA, MASAHIDE, Hasegawa, Masahide, c/o Canon Kabushiki Kaisha
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1993
Main classification: G11B5
IPC codes: G11B5, H04N5