Method for setting tracking data of variable speed modes in a video tape recorder
FIELD OF THE INVENTION 
     The present invention relates to a method for setting variable speed tracking data in a magnetic reproducing apparatus, and more particularly to a method for setting variable speed tracking data in a magnetic reproducing apparatus having an automatic tracking circuit therein, which is capable of setting the tracking data at any speed reproducing mode. 
     BACKGROUND OF THE INVENTION 
     Recently, an automatic tracking circuit has been introduced for a magnetic recording and/or reproducing apparatus (hereinafter referred to as a VTR). Such a circuit makes accurate tracking possible while reproducing video signals. That is, in the VTR having an automatic tracking circuit, a microcomputer determines a data variation value between initial tracking data and current tracking data detected in the automatic tracking circuit, and controls a servo motor by use of the initial and current tracking data. However, the above automatic tracking method for a VTR is usually performed only in a normal speed reproducing mode, since an envelope form of the reproduced signal is not a shaped pattern in any speed reproducing mode except the normal speed reproducing mode. Therefore, the envelope form in automatic tracking is a problem. Accordingly, since the microcomputer controls the servo motor by using tracking data of the automatic tracking circuit only in the normal speed reproducing mode, automatic tracking can not be accurately performed in any other speed reproducing mode other than the normal speed reproducing mode. As a result, a tracking error of a reproducing screen is increased when reproduction occurs in any speed reproducing mode other than the normal speed reproducing mode. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide a method for setting tracking data for performing accurate tracking in any speed reproducing mode. 
     In accordance with the present invention accurate tracking can be performed by using a data variation value obtained from a variation between initial tracking data and current tracking data which is detected from an automatic tracking circuit during the normal speed reproducing mode. Since a tracking variation in the normal speed reproducing mode is related to a variation in any other speed reproducing mode, accurate tracking can be performed by determining the tracking data in any other speed reproducing mode by use of the tracking data in the normal speed reproducing mode. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The advantages and features of the present invention will be more apparent from the detailed description hereunder, with reference to the attached drawings, in which: 
     FIG. 1 shows a block diagram illustrating a system applied to the present invention; and 
     FIG. 2 shows a flow chart illustrating one preferred embodiment according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In FIG. 1, a microcomputer 20 controls a VTR, set by signals of a key 10 and a servo motor 30, by using tracking data from an automatic tracking circuit 40. Thus, the microcomputer 20 performs an automatic tracking operation both in a normal speed reproducing mode and in any other speed reproducing modes as outlined in FIG. 2. For example, the microcomputer 20 determines a tracking data variation value between current tracking data and initial tracking data after the automatic tracking at the normal speed reproducing mode is performed, and then determines tracking data at twice the normal and/or a slow speed reproducing modes by using the tracking data variation value. Thereafter, the microcomputer 20 transmits the tracking data at twice the normal and/or the slow speed reproducing modes to the servo motor 30. 
     Referring to FIG. 2, reproducing a normal speed mode or not is determined in step 51. If the reproducing normal speed is mode present, the method goes to step 53 to determine whether automatic tracking is present. If it is, the method advances to step 55 to determine a data variation value α by subtracting initial tracking data t in  from current tracking data T r1 . Thereafter, the current tracking data T r1  is transmitted to step 69. Then, the procedure returns to start to monitor whether two times the normal and/or the slow speed reproducing mode is present in step 57. Thus, in the normal speed reproducing mode, since the current tracking data T r1  is transmitted to the servo motor 30 after the automatic tracking operation is over, an accurate tracking operation can be performed and the tracking data variation value α which is determined by subtracting initial tracking data from current tracking data is used as a reference value for determining the tracking data at any other speed reproducing mode. Data variation functions f 1  (α), f 2  (α) at twice the normal and/or the slow speed reproducing modes are determined respectively by using the tracking data variation value α. If the speed reproducing mode is twice the normal speed mode in step 57, the initial tracking data is detected in step 59. If it is detected, the current tracking data T r2  is determined by adding initial tracking data t x2  at twice the normal speed reproducing mode to the data variation function f 1  (α) in step 61. This is followed by step 69 to transmit the current tracking data T r2 . In the same way, if the speed reproducing mode is determined in step 63, initial tracking data is detected in step 65. If detected, the current tracking data T r3  is determined by adding initial tracking data t sw  at the slow speed reproducing mode to the data variation function f 2  (α) in step 67, followed by step 69. If the automatic tracking operation is complete in the automatic tracking circuit 40, the data variation value α between the current tracking data and the initial tracking data is determined in the microcomputer 20. Then, the difference between the initial tracking data and an optimal data variation value at twice the normal and/or the slow speed modes can be determined by using the data variation value α. If the same tape of the VTR is used, since the tracking variation at the normal speed reproducing mode is related to the tracking variation at any other speed reproducing mode, setting optimal tracking data at any other speed reproducing mode is possible. For example, if an optimal tracking data variation value at the normal speed mode is α, in the case of the two times the normal speed mode, the data shifted by 1/2α compared with the initial tracking data becomes nearly optimal tracking data at twice the normal speed reproducing mode and, the data variation functions f 1  (α), f 2  (α) at twice the normal speed and/or the slow speed modes can be determined. 
     As described above, the tracking data variation value between the current tracking data and the initial tracking data is determined after the automatic tracking at the normal speed reproducing mode is performed, and the tracking data at twice the normal and/or the slow speed reproducing modes is determined by using the tracking data variation value. Therefore, even at twice the normal speed and/or the slow speed reproducing modes, tracking similar to the automatic tracking at the normal speed reproducing mode can be made. Therefore, the tracking correction effect of the automatic tracking at the normal speed reproducing mode is provided in the twice the normal and/or the slow speed reproducing modes, to decrease a tracking error. 
     While the present invention has been particularly shown and described with reference to the preferred embodiment thereof, it is understood by those skilled in the art that foregoing is merely exemplary and other embodiments may be made without departing from the spirit and scope of the invention. In particular, the preferred embodiment described herein can be expanded to provide tracking data at any speed reproducing mode.