Tape position detecting device that compares and selects between two modes of detecting the tape position
BACKGROUND OF THE INVENTION 
     This invention relates to a tape position detecting device which is suitable for detection of the position of a magnetic tape, for instance, in a cuing operation with a video tape recorder. 
     In the case where signals are to be recorded on a magnetic tape or reproduced therefrom with a video tape recorder, it is necessary to detect a magnetic tape position; that is, it is necessary to perform a so-called &#34;cuing operation&#34;. For this purpose, there are available a variety of tape position detecting devices employing various tape position detecting methods. 
     A first tape position detecting method is as follows: As shown in FIG. 1, a time code track TC is formed on a magnetic tape 1 in a longitudinal direction, and a time code LTC representing the absolute position of a record track TR on the magnetic tape 1 using, for instance, hours-minutes-seconds and frame number is recorded on the time code track TC. In the cuing operation, the time code LTC is reproduced from the track TC to detect the tape position. 
     A second tape position detecting method is as follows: A time code VITC including hours-minutes-seconds and a frame number is superposed on the vertical flyback time part of the video signal recorded on a record track TR of the magnetic tape 1, instead of the time code track TC. In the cuing opertion, the time code VITC is separated from the signal which is reproduced from the record track TR, to detect the tape position. 
     In a third tape position detecting method, the time code is not used, and instead means for mechanically detecting an amount of movement of a magnetic tape (hereinafter referred to as &#34;tape movement detecting means&#34;, when applicable) by utilizing a capstan for driving the magnetic tape, a reel frequency signal, or a timer roller provided for this purpose only is employed to detect a relative tape position of the magnetic tape 1. 
     In the third tape position detecting method, sometimes a so-called &#34;CTL timer&#34; is employed. That is, CTL pulse signals recorded regularly on the control track CT formed longitudinally on the magnetic tape 1 are utilized to increase the accuracy of detection of the tape movement detecting means. 
     In practice, as shown in FIG. 2, a magnetic tape 1 is supplied from a supply reel 2A in a tape cassette 2, and is wound on a drum 6 with the aid of first and second inclination guide after passing through a guide pin 3A, a tension regulator pin 4, and a guide pins 3B, 5A and 5B. Thereafter, the magnetic tape 1, while being abutted against a time code recording and reproducing TC head 7 and a control track recording and reproducing CTL head 8 and engaged by a capstan 9A and a pinch roller 9B, is moved on, so that it is wound on a take-up reel 2B while being guided by guide pins 3C and 3D. Thus, the magnetic tape 1 supplied from the tape cassette 2 has been loaded in the tape recorder. 
     Under this condition, in the first tape position detecting method, the time code LTC is recorded on and reproduced from the time code track TC of the magnetic taped 1 with the TC head 7. 
     In the second tape position detecting method, the time code VITC is recorded on and reproduced from the record track TR of the magnetic tape 1 with rotary heads 6A and 6B positioned over the drum 6. 
     In the third tape position detecting method, the CTL pulse signal is reproduced with the CTL head 8, and frequency signals obtained from the capstan 9A and the reels 2A and 2B are applied to the tape movement detecting means. 
     The first and second tape position detecting methods using the time codes LTC and VITC recorded on the magnetic tape 1 are advantageous in that the absolute position of the magnetic tape 1 can be detected with high accuracy. However, the methods are still disadvantageous in that, since the operator can specify the time code LTC or VITC, the continuity of the time code LTC/VITC is not assured, and sometimes it is impossible to detect the relative position of the magnetic tape 1. 
     In addition, the methods give rise to another problem that, during the ordinary operation in which reproducing signals can be positively obtained from the magnetic tape 1, the absolute position of the magnetic tape 1 can be detected with high accuracy, but in the case where the magnetic tape 1 is subject to high speed signal reproduction or low speed reproduction, the time code itself cannot be reproduced with the result that the tape position of the magnetic tape 1 cannot be detected. 
     The tape position detecting methods cannot be employed at all in the case where the time code LTC/VITC has not been recorded on the magnetic tape 1. 
     In the third tape position detecting method using the so-called &#34;CTL timer&#34;, it is impossible to detect the absolute position of the magnetic tape 1 since no means for detecting an absolute position is provided. 
     On the other hand, the absolute position of the magnetic tape 1 may be erroneous because of the slip of the capstan 9A or the reel 2A or 2B or because of an error in reading the CTL pulse signal; however, it may be detected no matter when signals are not recorded on the magnetic tape or no matter how the operating condition is. 
     In view of the foregoing, a tape position detecting device employing a fourth tape position detecting method has been proposed in the art. In the fourth tape position detecting method, during the ordinary operation, tape position data is detected using the time code LTC/VITC recorded on the magnetic tape 1; and in the case where the time code LTC/VITC cannot be obtained because signals have not been recorded on the magnetic tape 1 or because the operating condition is not suitable, the time code LTC/VITC is interpolated with the output value of the CTL timer, thereby to detect the tape position data. 
     In the tape position detecting device thus constructed, the output value of the CTL timer is an auxiliary value as a general rule. Therefore, with the timing that the time code LTC/VITC is read, instead of the tape position data interpolated with the output value of the CTL timer, a value corresponding to the time code LTC/VITC thus read is outputted as correct tape position data. 
     As a result, in the case where, as shown in FIGS. 3A and 3B, a record region PRN of ten minutes in which no time code LTC/VITC is recorded is present between a record region PRA of ten minutes (from 10 minutes to 20 minutes) and a record region PRB of five minutes (from 50 minutes to 55 minutes) in which the time code LTC/VITC are recorded, two substantially different values of tape position data may be arrived at for the same position on the magnetic tape 1. This fact adversely affects the cuing operation. 
     As shown in FIG. 3C, the output value CTL FW  provided by the CTL timer when the cuing operation is carried out with the magnetic tape in the forward direction is a time of ten minutes (from 10 minutes to 20 minutes) in correspondence to the time code LTC/VITC when the record region PRA is subjected to reproduction; and then is a time of twenty minutes to twenty-nine minutes and fifty-nine seconds with the ten minutes interpolated when the record region PRN is subjected to reproduction. Thereafter, the output value is renewed with the timing that the reproduction of the record region PRB is started, so that it is a time of five minutes (from 50 minutes to 55 minutes) corresponding to the time code LTC/VITC. 
     In contrast, as shown in FIG. 3D, the output value CTL RW  provided by the CTL timer when the cuing operation is carried out with the magnetic tape in the reverse direction has a value of five minutes (from 55 minutes to 50 minutes) corresponding to the time code LTC/VITC when the record region PRB is subjected to reproduction; and then has a value of fifty minutes to forty minutes one second with the ten minutes interpolated when the record region PRN is subjected to reproduction. Thereafter, the output value is renewed with the timing that the record region PRA is subjected to reproduction, so that it has a value of ten minutes (from 20 minutes to 10 minutes) corresponding to the time code LTC/VITC. 
     As is apparent from the above description, the value of the CTL timer, which is provided by interpolation of the record region PRN of ten minutes in which no time code LTC/VITC is recorded, shows different values--twenty minutes to twenty-nine minutes and fifty-nine seconds, and fifty minutes to forty minutes and one second--depending on the cuing directions. Hence, it is impossible to correctly detect the tape position data for cuing. 
     Furthermore, even in the case where the time code LTC/VITC on the magnetic tape can be read without fail, the continuity of the time code LTC/VITC is not assured. Hence, in order to perform the cuing operation correctly at all times, it is essential that the time code LTC/VITC is provided on the magnetic tape 1 in correspondence to the aimed tape position, and with respect to the direction of movement of the magnetic tape 1 the time code LTC/VITC increase or decrease monotonously. Thus, the conventional tape position detecting device is still insufficient in practical use. 
     The above-described difficulties may be eliminated by employing the third tape position detecting method in which the value of the CTL timer is utilized for the cuing operation. However, since the CTL timer employs mechanical detecting means to detect tape position data, the error due to the expansion of the magnetic tape 1 or the slip of the magnetic tape 1 on the capstan 9A cannot be prevented. 
     An additional problem is that, since only the CTL pulse signal is employed, the absolute position data of the magnetic tape 1 cannot be detected, and the detection error of the CTL pulse signal is accumulated. Thus, the method is inferior in the accuracy of tape position data than the above-described tape position detecting methods. 
     Furthermore, in the case where the magnetic tape 1 is moved repeatedly in the forward direction and in the reverse direction, the detection of tape position data is lowered in accuracy. Thus, the conventional methods are not sufficiently effective in solving the above-described problems. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, an object of this invention is to provide a tape position detecting device in which the above-described difficulties have been eliminated. More specifically, an object of the invention is to provide a tape position detecting device which is capable of detecting tape position data with high accuracy at all times. 
     The foregoing object and other objects of the invention has been achieved by the provision of a tape position detecting device which comprises: relative position detecting means 8, 9A and 11 for detecting an amount of movement of a tape-shaped recording medium 1, and providing relative position data DT CTL  according to the result of detection; absolute position detecting means 7 and 12 for subjecting the tape-shaped recording medium 1 to reproduction, to provide absolute position data DT TC  ; reference position data storing means 13A through 19A and 13B through 19B for storing the relative position data DT CTL  and absolute position data DT TC  for predetermined reference points; and tape position data generating means 22 in which, with respect to an arbitrary point, first tape position data TT CTL1  is detected by using the relative position data DT CTL , tape movement data from each reference point to the arbitrary point which is obtained by using the absolute position data DT TC  is added to the absolute position data DT CTL  of the reference point to detect second tape position data TT CTL2 , and when the difference ΔTT between the first and second tape position data TT CTL1  and TT CTL2  is out of a predetermined range the first tape position data TT CTL1  is transmitted as an tape position data output P TAPE , whereas when the difference ΔTT is in the predetermined range, the second tape position data TT CTL2  is transmitted as the tape position data output P TAPE . 
     In the tape position detecting device of the invention, the relative position data DT CTL0  through DT CTL2  and absolute position data DT TC0  through DT TC2  of the reference points are stored, and with respect to the arbitrary point, the first tape position data TT CTL1  is detected by using the relative position data DT CTL , and the tape movement data from a reference point to the arbitrary point which is obtained using the absolute position data DT TC  is added to the absolute position data DT CTL  of the reference point to detect the second tape position data TT CTL2 , and depending on the difference ΔTT between the first and second tape position data TT CTL1  and TT CTL2 , the first or second tape position data TT CTL1  or TT CTL2  is transmitted as an tape position data output P TAPE . Hence, in this case, the tape position data P TAPE  can be detected much more accurately than in the case where it is detected by using the relative position data DT CTL  or absolute position data DT TC  only. 
     The nature, principle and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by like reference numerals or characters. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
     FIG. 1 is an explanatory diagram showing a track format on a magnetic tape; 
     FIG. 2 is an explanatory diagram showing a magnetic tape running path; 
     FIGS. 3A-3D are timing charts for a description of a conventional tape position detecting method; 
     FIG. 4 is a block diagram showing one example of a tape position detecting device according to this invention; 
     FIG. 5 is a flow chart for a description of a tape position data calculating procedure practice by the tape position detecting device of the invention; and 
     FIGS. 6A and 6B are timing charts for a description of a tape position detection carried out by the tape position detecting device of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Preferred embodiments of this invention will be described with reference to the accompanying drawings. 
     (1) First Embodiment 
     In FIG. 4, in which parts corresponding functionally to those which have been described with reference to FIG. 2 are designated by the same reference numerals or characters, reference numeral 10 designates a tape position detecting device according to the invention. A frequency signal FG CP  obtained by detection of the rotation of the capstan 9A adapted to drive the magnetic tape 1, and a CTL pulse signal S CTL  provided by the CTL head 8 are applied to a CTL timer detecting circuit 11. 
     The CTL timer detecting circuit 11, according to the frequency signal FG CP  of the capstan 9A and the CTL pulse signal S CTL  reproduced from the control track CTL (FIG. 1) of the magnetic tape, produces CTL timer value data DT CTL  representing the relative position data of the magnetic tape 1. The CTL timer value data DT CTL   thus produced is applied to a first gate circuit 13A. 
     A time code signal S TC , which is reproduced from the time code track TC (FIG. 1) of the magnetic tape 1 with the TC head 7, is applied to a time code detecting circuit 12, which outputs time code data DT TC  representing the absolute position data of the magnetic tape 1. The time code data DT TC  is applied to a second gate circuit 13B. 
     The time code detecting circuit 12 monitors the time code signal S TC  for continuity at all times, and outputs a time code discontinuity detection signal E TC  upon detection of a discontinuous time code signal S TC . The time code discontinuity detection signal E TC  is applied to a reference point record control circuit 14. 
     In practice, the first and second gate circuits 13A and 13B, in response to a gate control signal C SW1  from the reference point record control circuit 14, gate the CTL timer value data DT CTL  and the time code data DT TC  with the timing of a desired reference point, so as to transmit these data to first and second memory select circuits 15A and 15B, respectively. 
     The reference point record control circuit 14 receives a record/reproduction signal C RP  (represents whether recorder is in a recording mode or a reproduction mode), a cuing aimed value signal C ENT  (represents a point designated by the user, e.g. end of movie, etc.), and a trigger pulse signal C TG   from a system control circuit 16 and the time code discontinuity detection signal E TC  from the time code detecting circuit 12, to produce the gate control signal C SW1  and a memory select signal C SW2 , which are applied to the gate circuits 13A and 13B and to the memory select circuits 15A and 15B, respectively. 
     In each of the first and second memory select circuits 15A and 15B, the armature is tripped over to three output terminals &#34;a&#34;, &#34;b&#34; and &#34;c&#34; one after another in response to the memory select signal C SW2  provided by the reference point record control circuit 14, so that the CTL timer value data DT CTL  and time code data DT TC  applied thereto are stored, as CTL timer value data DT CTL0  and DT TC0 , DT CTL1  and DT TC1 , and DT CTL2  and DT TC2 , in first, second and third memory pairs 17A and 17B, 18A and 18B, and 19A and 19B, respectively. In other words, the first, second and third memory pairs are selectively loaded one after another, as needed, to record timer value data DT CTL  and time code data DT TC  at certain reference points (e.g., at the point where the discontinuity signal E TC  indicates that the time code data has become unreadable, or when a cuing signal C ENT  is received from the system control circuit 16). 
     In practice, the CTL timer value data DT CTL0  and DT TC0 , DT CTL1  and DT TC1 , and DT CTL2  and DT TC2  stored in the first, second and third memory pairs 17A and 17B, 18A and 18B and 19A and 19B in correspondence to the first, second and third reference points are read out at predetermined time intervals, so that they are applied to the input terminals &#34;a&#34;, &#34;b&#34; and &#34;c&#34; of first and second reference point switch circuits 20A and 20B. More specifically, the CTL timer value data DT CTL0  through DT CTL2  are applied to the input terminals &#34;a&#34;, &#34;b&#34; and &#34;c&#34; of the first reference point switch circuit 20A, and the time code data DT TC0  through DT TC2  are applied to the input terminals &#34;a&#34;, &#34;b&#34; and &#34;c&#34; of the second reference point switch circuit 20B. 
     In each of the first and second reference point switch circuits 20A and 20B, the armature is tripped over to the input terminal &#34;a&#34;, &#34;b&#34; or &#34;c&#34; in response to a reference point select signal C SW3  provided by the reference point select circuit 21. As a result, the CTL timer value data DT CTL0 , DT CTL1  or DT CTL2  selected and the time code data DT CT0 , DT TC1  or DT TC2  selected are applied, as reference point CTL time value data DR CTL  and time code data DR TC , to a tape position calculating circuit 22 including a microcomputer with a CPU. 
     The reference point select circuit 21 receives the CTL time value data DT CTL  which is outputted by the CTL timer detecting circuit 11 to represent the relative position data of the magnetic tape 1 at the present position, and the CTL time value data DT CTL0 , DT CTL1   and DT CTL2  corresponding to the first, second and third reference points which are stored in the first, second and third memory pairs 17A and 17B, 18A and 18B, and 19A and 19B. 
     As a result, the reference point select circuit 21 applies the reference point select signal C SW3  to the first and second reference point switch circuit 20A and 20B which selects the input terminal &#34;a&#34;, &#34;b&#34; or &#34;c&#34; to which, of the CTL time value data DT CTL0 , DT CTL1  and DT CTL2 , the closest to the CTL timer value data DT CTL  of the present position is applied. In other words, the circuit 21 will compare the reference points DT CTL0 , DT CTL1  and DT CTL2  stored in the first, second and third memory pairs, to the present relative position data DT CTL , and cause the switch circuits 20A and 20B to select the input terminal corresponding to the memory pair having data most closely matched to the present timer value data DT CTL . 
     In the embodiment, the tape position calculating circuit 22 receives the CTL timer value data DR CTL  and time code data DR TC  of the reference point, the CTL timer value data DT CTL  representing the relative position data of the magnetic tape 1 at the present position and the time code data DT TC  representing the absolute position data thereof, the time code discontinuity detection signal E TC  representing the detection of the discontinuous time code signal S TC , and the record/reproduction signal C RP  outputted by the system control circuit 16. 
     The tape position calculating circuit 22 utilizes these data and signals to practice a tape position data calculating procedure RTO as shown in FIG. 5, thereby to output the tape position data P TAPE  of the magnetic tape at the present position. 
     In the tape position calculating circuit 22, the CPU starts practicing the tape position data calculating procedure RTO, and operates as follows: In Step SP1, the tape movement data represented by the CTL timer value data DT CTL  of the present position is added to or subtracted from the previous tape position data P TAPE , so that a first CTL timer value TT CTL1  is calculated similarly as in the case of the third tape position detecting method. 
     In Step SP2, the difference between the time code data DT TC  of the present position and the time code data DR TC  of the reference point is added to or subtracted from the CTL timer value data DR CTL  of the reference point, to detect a second CTL timer value TT CTL2 . 
     In Step SP3, the difference ΔTT between the first and second CTL timer values TT CTL1  and TT CTL2  is calculated. 
     Thereafter, in Step SP4, it is determined whether or not the difference ΔTT is equal to or smaller than a predetermined value (five seconds in the embodiment). When the difference is smaller than the predetermined value (YES), then in Step SP5 it is determined from the time code discontinuity detection signal E TC  whether or not the time code DT TC  has been read correctly. 
     When it is determined that the time code DT TC  has been read correctly (YES), then in Step SP6 it is determined from the record/reproduction signal C RP  provided by the system control circuit 16 whether or not a recording operation is being carried out. When it is determined that the recording operation is not being carried out (NO), then in Step SP7 the second CTL timer value TT CTL2  is transmitted as the tape position data P TAPE  of the present position. And in Step SP8 the tape position data calculating procedure RTO is ended. 
     In the case where in Step SP4 or SP5 the result of determination is negative (NO), or in Step SP6 the result of determination is positive (YES), Step SP9 is effected so that the first CTL timer value TT CTL1  is transmitted as the tape position data P TAPE  of the present position. And In Step SP8 the tape position data calculating procedure RTO is ended. 
     It is assumed that, as shown in FIGS. 6A and 6B, in the case where the time code data DR TC  and CTL timer value data DR CTL  of a reference point t 0  are ten (10) minutes and three (3) minutes, respectively, fifteen (15) minutes and twelve (12) seconds, and eight (8) minutes and ten (10) seconds are detected as the time code date DR TC  and CTR timer value data DR CTL  of the present position t 1 , respectively. 
     Under this condition, the first CTL timer value TT CTL1  obtained in Step SP1 is eight (8) minutes and ten (10) seconds similarly as in the case of the CTL timer value data DT CTL , while the second CTL timer value TT CTL2  obtained in Step SP2 is as follows: ##EQU1## Hence, the difference ΔTT between the first and second CTL timer values TT CTL1  and TT CTL2  is two (2) seconds. 
     Therefore, in the case where the time code data DT TC  is read correctly and no recording operation is being carried out, it is determined that the difference ΔTT of two (2) seconds is the error of the CTL timer value data, and the second CTL timer value TT CTL2 , or eight (8) minutes and twelve (12) seconds, is transmitted as the tape position data P TAPE  of the present position t 1 . 
     On the other hand, in the case where fifteen (15) minutes and twelve (12) seconds, and eight (8) minutes and twenty (20) seconds are detected as the time code data DT TC  and CTL timer value data DT CTL  of the present position t 1 , respectively, the first CTL timer value TT CTL1  is eight (8) minutes and twenty (20) seconds, while the second CTL timer value TT TCL2  is eight (8) minutes and twelve (12) seconds similarly as in the above-described case. 
     Therefore, the difference ΔTT between the first and second CTL timer values TT CTL1  and TT CTL2  is eight (8) seconds. In this case, it is determined that the time code data DT TC  is discontinuous. As a result, the first CTL timer value TT CTL1 , or eight (8) minutes and twenty (20) seconds, is outputted as the tape position data P TAPE  of the present position t 1 . 
     Thus, in the tape position detecting device, first the CTL timer value data DR CTL  and time code data DR TC  of a predetermined reference point are stored; and the first CTL timer value of the present position represented by the CTL timer value data DT CTL , and the second CTL timer value TT CTL2  are detected. The second CTL timer value TT CTL  is obtained by adding the tape movement data, which is obtained by subtracting the time code data DR TC  of the reference point from the time code data DT TC  of the present position, to the CTL timer value data DR CTL  of the reference point. When the difference ΔTT between the first and second CTL timer values TT CTL1  and TT CTL2  is longer than five (5) seconds, the first CTL timer value TT CTL1  is outputted as the tape position data P TAPE . When the difference ΔTT is equal to or shorter than five (5) seconds, the second CTL timer value TT CTL2  is outputted as the tape position data P TAPE . Thus, in this case, the tape position data P TAPE  of the present position can be detected with higher accuracy than in the case where the tape position data is obtained by using only the CTL timer value data DT CTL  or time code data DT TC . 
     That is, in the tape position detecting device 10 of the invention, the CTL timer value data DT CTL  representing the relative position data is interpolated with the time code data DT TC  representing the absolute position data, to obtain the tape position data P TAPE . Hence, the tape position detecting device 10 thus designed is higher both in stability and in accuracy than the prior art. 
     Thus, by utilizing the tape position data P TAPE  provided by the tape position detecting device 10, a video tape recorder can be realized which can achieve the cuing operation with higher accuracy than a conventional one. 
     (2) Other Embodiments 
     (2-1) In the above-described embodiment, the CTL timer value data DT CTL  and the time code data DT TC  are stored with the record/reproduction starting timing, the cuing aimed value setting timing, the time code discontinuity detecting timing, or the timing occurring at predetermined time intervals as a reference point; however, the reference point setting timing is not limited thereto or thereby; that is, it may be selected in various manners as the case may be. 
     (2-2) Furthermore, in the above-described embodiment, the data on three reference points are stored, and the reference point closest to the present position is selected. However, it should be noted that the number of reference points is not limited to three; that is, it can be determined freely, for instance, according to the capacity of memory. 
     (2-3) In the above-described embodiment, the tape position data in the video tape recorder is detected; however, the invention is not limited thereto or thereby. That is, the tape position detecting device of the invention can be applied effectively to a variety of tape recorders having a tape-shaped recording medium on which absolute position data is recorded. 
     While there has been described in connection with the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is aimed, therefore, to cover in the appended claims all such changes and modifications as fall within the true spirit and scope of the invention.