Abstract:
A noise-free skip search apparatus utilizing a piezo-electric element wherein no noise appears on the screen at the high reproducing speed of a VCR. In the apparatus, a piezo-electric element is shifted according to a multiple angular speed for controlling the angle of reproducing head. The apparatus can remove a color crosstalk phenomenon thereby.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a noise-free skip search apparatus utilizing a piezo-electric element wherein no noise appears on the screen by performing a skip search at the high reproducing speed of a video cassette tape recorder (VCR). 
     Generally, at the high reproducing speed or low reproducing speed of a VCR, some noise bands appeared on a monitor. Accordingly, the prior art apparatus did not allow noise bands to appear on the monitor by using three heads at the low reproducing speed. However, such conventional apparatus was unable to obtain a clean image reproduction without any noise bands at the high reproducing speed. Specifically, at the high reproducing speed, as a head switching pulse signal as shown in (B) of FIG. 1 is applied, the reproducing heads A and B play across various tracks as shown in (A) of FIG. 1. Therefore, this caused noise bands to appear as shown in (C) of FIG. 1 in reproducing the adjacent tracks which are recorded at a different angle from the azimuth angle of heads. 
     Accordingly, in order to solve this by means of a simplified method, it was possible to reproduce the image on the screen without noise signals by simultaneously moving the heads whose azimuth angle is different from each other, during the difference of several horizontal scan lines H (1H is equal to 63.5 μsec); and then by combining the radio frequency (RF) signal which is read at each head along a time axis. Specifically, as a head switching pulse signal as shown in (B) of FIG. 1 is applied, two radio frequency waveforms reproduced at the advancing heads A and B&#39; and the retarding heads B, A&#39; are obtained as shown in (C) and (D) of FIG. 2 respectively; and then said two waveforms are combined as shown in (E) of FIG. 2, so that no noise bands occur on the screen. However, this method has a drawback in that a color crosstalk phenomenon due to the interference between said two signals in each portions in which two high frequency waveforms are crossed, occurs as shown in (E) of FIG. 2, so that a color stain appears on the screen. 
     OBJECT OF THE INVENTION 
     Accordingly, it is an object of the present invention, which is suggested in order to remove the above described drawback of the prior art, to provide a skip search apparatus wherein a piezo-electric element is shifted according to a multiple angular speed for controlling the angle of the reproducing head, so that noise bands and also color crosstalk phenomenon do not occur at the high reproducing speed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     This and other objects and features of the present invention will become more apparent as the detailed following explanation of an embodiment of this invention is considered with reference to the accompanying drawings wherein: 
     FIG. 1, (A)-(C), shows the track and waveform of a reproducing head with reference to the prior art track at the high speed reproducing speed, 
     FIG. 2, (A)-(E), shows the track and waveform of the prior art noise-free search according to a radio frequency envelope combining method, 
     FIG. 3 (A)-(C) shows the track and waveform of the noise-free search according to the present invention, 
     FIG. 4 is a block diagram of a noise-free skip search apparatus in accordance with the present invention, 
     FIG. 5 shows a graph of the target voltage dependent on the multiple speed in FIG. 3, and 
     FIG. 6, (A)-(C), shows an output waveform helpful in understand FIG. 3. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Generally, the angle (θ) of the playing head to the tape during normal operation is smaller than that in an advancing search mode. The former angle θ is expressed by the following equation: ##EQU1## in which W is a effective thickness of video tape; D is a diameter of drum; θ o  is an angle of the playing head with reference to the tape in the stop mode (it is about 5° 56&#39; 7&#34; for VHS system); V t  is a playing distance of tape per second; n is a constant number representive of multiple speed; and F v  is a vertical synchronization frequency. 
     Also, said angle θ is disclosed in the following table for a VHS system. 
     
                       TABLE I______________________________________     Magnitude of multiple speed       -9 multiple            9 multipleType        speed (SPN             speed (SPNof          -3 multiple                  One multi-  3 multipleMode        speed)     ple speed   speed)______________________________________SP (standard)       5.836°                  5.97°                              6.049°ModeEP (long per-       5.836°                  5.95°                              6.039°iod) Mode______________________________________ 
    
     As shown in equation (I) and table I, the angle θ becomes greater as the multiple speed becomes faster in a forward (+) direction. This means that the angle of the head is fixed according to each multiple speed. Accordingly, for the 9 multiple speed in a forward direction if the angle of head is increased by nine times, then the track of head is changed as shown in FIGS. 3 and 4 to permit a skip search without any noise on the screen. In this case, in order to correct the angle of head, the head itself must be shifted. In other words, in the prior art the shift of the head is impossible because the head is used by fixing it to the drum, while in the present invention the shift of head due to the movement of the piezo-electric element is permitted by adapting the technique of overlying the head on the piezo-electric element. 
     Hereinafter, the present invention as described above will be explained in further detail referring to FIG. 4. 
     FIG. 4 is a detailed block diagram of the skip search apparatus according to the present invention, in which the output terminal of a 1/N frequency divider 1 for dividing a clock pulse signal fsc (which is 3.58 or 4.43 MHz) is connected to the count input of a counter 2, and a capstan pulse generating signal CFG generated according to the rotation of capstan motor is connected to the reset terminal RS of said counter 2. The count output of said counter 2 is connected via a latch circuit 3 to the comparison input terminal b of a subtractor 5, and the count output of a preset counter 4 which applies a mode selection signal MS to said count input, is connected to the reference input terminal a of said subtractor 5. Also, the output terminal of said subtractor 5 is connected via a digital to analog converter 6 and a linear d.c. amplifier 7 to the comparison voltage terminal CV of a piezo-electric element driver 10, and the sign bit output terminal SB thereof is connected to the forward/reverse selection terminal F/R of said piezo-electric element driver 10. The output terminal of said preset counter 4 is connected via another digital to analog converter 8 and a reference voltage generator 9 to the reference voltage terminal RV of said piezo-electric element driver 10, and the enable terminal EN and reset terminal RS of said piezo-electric element driver 10 are connected to apply a reproducing button signal PB and a head switching pulse signal HS, respectively, and the output terminal of said piezo-electric element driver 10 is connected to a piezo-electric element with the head attached. 
     Hereinafter, the operation and effect of the present invention as described above will be explained in detail. Generally, at the performance of search the transfer speed of tape becomes rapid by rotating the capstan motor at a high speed to obtain a desired multiple speed. When the capstan motor is rotated, a capstan pulse generation signal CFG is generated and output in response to the rotation of said motor, and this capstan pulse generation signal CFG is applied to the reset terminal RS of counter 2 as a reset signal, which is irrespective of whether the time period when the capstan pulse generation signal CFG is changed from a high level to a low level or the time period when the capstan pulse generation signal CFG is changed from a low level to a high level conversely is used. Further, said capstan pulse generation signal is applied to the latch circuit 3 as a latch pulse signal. 
     In the meantime, a clock pulse signal fsc is frequency divided by the 1/N frequency divider 1 and then applied to the count input terminal of counter 2 for counting it upwardly. In this manner, the counter 2 counts upwardly the frequency divided signal of 1/N frequency divider 1 and output the same and is reset by a capstan pulse generation signal CFG. The count signal output from the counter 2 is latched at latch circuit 3 by a latch pulse signal from the capstan pulse generation signal and thereafter applied to the comparison input terminal b of subtractor 5 as comparison data. 
     Further, a constant count value is output at the preset counter 4 by a mode selection signal MS according to the reproducing state, i.e., SP, LP or EP and applied to the reference input terminal a of subtractor 5 as reference data. 
     Accordingly, the subtraction operation is performed at the subtractor 5, which in turn outputs a high level signal at the high reproducing speed while a low level signal at the low reproducing speed at its sign bit output terminal. The output signal at said sign bit output terminal SB is applied to the forward/reverse selection terminal F/R of piezo-electric element driver 10 to become the reference of whether the changing direction of piezo-electric element must be moved a plus (+) direction or a minus (-) direction with reference to the X axis. 
     Meanwhile, a digital signal which is subtracted and output at the subtractor 5 is converted to an analog signal at the digital to analog converter 6 and output as a d.c. voltage, and this d.c. voltage is amplified at the linear d.c. amplifier 7 to apply to the comparison voltage terminal CV. The characteristic of the voltage applied at this comparison voltage terminal CV (which is referred to as a target voltage) is varied in proportion to each multiple speed as shown in FIG. 5. 
     Further, the output data signal of said preset counter 4 is converted to an analog signal at the digital to analog converter 8 and output as a d.c. voltage, and this d.c. voltage is applied via the reference voltage generator 9 to the reference voltage terminal RV of piezo-electric driver 10 as a reference voltage. 
     The piezo-electric element driver 10 in the reproducing mode is driven by being enabled only in such a state that the reproducing push button signal PB is applied. 
     Accordingly, the reference voltage applied to the reference voltage terminal CV of piezo-electric element driver 10 at the normal reproducing speed operation is set to be equal to a target voltage applied to the comparison voltage terminal CV thereof, so that the piezo-electric element (11) is not moved to the central position. 
     On the other hand, for a multiple speed reproducing operation the target voltage according to each multiple speed is applied to the comparison voltage terminal CV of piezo-electric element driver 10 as described above and compared with the reference voltage, so that a drive voltage as shown in (A) of FIG. 6 is output from the piezo-electric element driver 10 and applied to the piezo-electric element 11, and therefore the piezo-electric element 11 is moved in the plus (+) direction or the minus (-) direction in proportion to said drive voltage. Herein, the movement variation of piezo-electric element 11 is determined by the time period of the variation of head (from A to B or from B or A). That is, the reference of variation point is determined by a head switching pulse signal as shown in (B) of FIG. 6. 
     Further, during a recording operation a reproducing button signal PB is not applied and thus the piezo-electric element driven 10 is not drived, so that the piezo-electric element 11 is disposed in the central position, thereby allowing compatability between the tapes at the recording. 
     According to the present invention as described above, noise bands and a color crosstalk phenomenon does not occur since the angle of reproducing head is controlled by shifting the piezo-electric element in proportion to each multiple speed reproducing operation, thereby providing a clean, noise-free screen in any multiple speed corresponding to the search.