Abstract:
In the method and apparatus for controlling an intermittent recording state, an operating mode is received from a user. The operating mode indicates an operation period and a pause period, wherein operations are performed on a tape medium during the operation period and no operation is performed on the tape medium during the pause period. The pause period is compared with a predetermined period of time, and if the pause period exceeds the predetermined period of time, the tape medium is disengaged from the recording/reproducing head of the recording/reproducing apparatus during the pause period and/or the rotation of the recording/reproducing head is stopped during the pause period.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a method and apparatus for intermittent recording in a time-lapse video tape recorder, and in particular, to a control method for intermittent recording in a time-lapse video tape recorder that is capable of calculating a recording pause period based on a time-lapse recording mode, and capable of ( 1 ) stopping the rotation of the head drum temporarily and/or ( 2 ) unloading the magnetic tape that has been loaded for recording when the calculated recording pause period is longer than a predetermined period of time. 
     2. Brief Description of the Prior Art 
     Unlike ordinary continuous video tape recorders, which record every frame of video signals, the time-lapse video tape recorder intermittently records video signals from several video cameras or the like on a magnetic tape at a pre-selected regular interval while the recorder repeatedly runs and stops. Time-lapse video tape recorders have been used in various areas requiring long-time recording, such as security monitoring systems in banks and museums. As shown in FIG. 8, a time-lapse video tape recorder comprises switching unit  10 , which selects a signal among video signals received from several video cameras; control unit  20 , which extracts one frame intermittently from the continuous video signal received from the switching unit  10 ; and recording unit  30  which records the video signal as a frame is received from the control unit  20  on a frame basis in each video track of a magnetic tape. 
     The recording unit  30  comprises a signal processing unit, which processes the video signal for recording, and mechanical elements. The mechanical elements include a loading motor which moves a loading post into a loading/unloading state of the magnetic tape; a drum motor which rotates a head drum on which video heads are mounted to record/reproduce the video signal on/from the magnetic tape; and a capstan motor which rotates a capstan shaft to drive the magnetic tape at a predetermined tape running speed. 
     For example, in a conventional time-lapse video tape recorder configured as above, if a magnetic tape of 2 hours running time is used for recording during 48 hours, then the switching unit  10  switches to the next video camera at intervals of time corresponding to 24 video frames (48 hours/2 hours=24). The switching unit  10  receives a video signal from the video camera selected, and sends the received video signal to the control unit  20 . Then, the control unit  20  extracts one frame out of the video signal received from the switching unit  10  and records the extracted frame on the magnetic tape while moving a single video track of the magnetic tape by driving the capstan motor in the recording unit  30 . 
     In case of the prior art above, while the video signal is recorded on the magnetic tape intermittently, the magnetic tape is loaded in the recording unit  30  even when no video signal is recorded. The rotation of the capstan motor is stopped temporarily when recording is paused, but the head drum always rotates. Therefore, high-precision control of the capstan motor is required to perform repeated run-and-stop of the magnetic tape by one video track. In addition, because the magnetic tape is always in contact with the head drum, even when no video signal is recorded on the magnetic tape, friction between the magnetic tape and the head drum lowers the quality of the video signal recorded on the magnetic tape and shortens the life of the magnetic tape and head drum. 
     SUMMARY OF THE INVENTION 
     One objective of the present invention is to solve the above mentioned problems in the conventional method, and a further objective is to provide a control method and apparatus for intermittent recording in time-lapse video tape recorder that is capable of unloading the magnetic tape or temporarily stopping the rotation of the head drum when recording is stopped. 
     Another objective of this invention is to provide a control method and apparatus for intermittent recording in a time-lapse video tape recorder that selectively performs unloading of the magnetic tape or temporary stopping of the rotation of the head drum depending on whether or not a recording pause period is longer than a predetermined period of time. 
     The present invention is characterized as a method for the intermittent recording in the time-lapse video tape recorder, which comprises the steps of: confirming whether the recording is stopped temporarily in the intermittent recording mode; and either unloading the magnetic tape or temporarily stopping the rotation of the head drum during the recording pause period. 
     According to the present invention, in the control method of the head drum or tape unloading of the time-lapse video tape recorder, a frame extraction ratio of a video signal, or a ratio of the number of fields to be skipped and the number of field to be recorded, is calculated from a recording time in a time-lapse recording mode that is set by a user. Based on a frame extraction ratio and the size of a memory in which the selected input video frames are temporarily stored before recording, a recording pause period or the time during which no video signal is recorded is calculated. 
     If the recording pause period is longer than a predetermined reference period of time, the magnetic tape is unloaded or the rotation of the head drum is stopped temporarily during the recording pause period. If the recording pause period is not longer than a predetermined reference period of time, the head drum keeps rotating and contacting with the magnetic tape during the recording pause period as in conventional time-lapse video tape recorders. 
     In the case where a recording pause period is long, the intermittent recording method of the present invention can prolong the life of the head drum and the magnetic tape through reduction of friction between the magnetic tape and the head drum and reduce the power consumption by the rotation of the head drum. 
    
    
     The above objectives, features, and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof to read in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are included to provide a further understanding of the invention, illustrate a preferred embodiment of this invention, and together with the description, serve to explain the principles of the present invention. 
     In the drawings: 
     FIG. 1 shows a schematic block diagram of an embodiment of a time-lapse video tape recorder according to the present invention; 
     FIG. 2 shows a diagrammatic view of the recording unit when a magnetic tape is loaded for recording; 
     FIG. 3 shows a diagrammatic view of the recording unit when a magnetic tape is unloaded; 
     FIG. 4 is a diagram describing schematically the principle of the intermittent recording of a time-lapse video tape recorder; 
     FIG. 5 is a flow chart of the magnetic tape unloading method for the intermittent recording according to the first embodiment of the present invention; 
     FIG. 6 is a flow chart of the head drum stopping method for the intermittent recording according to the second embodiment of the present invention; 
     FIG. 7 is a table showing illustrative values of the recording pause period according to recording time in the time-lapse recording mode and a decision boundary of tape unloading or drum rotation stopping based on the calculated recording pause period; and 
     FIG. 8 shows a general block diagram of a conventional time-lapse video tape recorder. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The intermittent recording method in a time-lapse video tape recorder according to the present invention is described below in detail with reference to schematic diagrams shown in FIG. 1, FIG. 2, and FIG.  3  and the flow chart of FIG.  5 . 
     FIG.1 shows the block diagram of the time-lapse video tape recorder to which the method for controlling the intermittent recording state is applied. The time-lapse video tape recorder in FIG. 1 comprises an A/D converter  100  which converts analog video signals from a external video camera into digital data streams, a buffer memory  201  which temporarily stores the converted digital video data, a field memory  202  which transfers the video data filled in the buffer memory  201  into itself, a D/A converter  300  which converts the digital data in the field memory  202  into analog video signal, a recording unit  400  which records the converted analog video signal, and a controller  500  which controls writing/reading intervals to/from the memories  201  and  202  and the recording operation of the recording unit  400  according to commands received by an input unit  600  from a user. 
     Referring to FIG. 5, when a recording time is set by a user (S 11 ), the controller  500  calculates a recording pause period during which recording is stopped (S 13 ). For an illustration of the calculation of the recording pause period, suppose that the running time of the magnetic tape is 2 hours and a maximum number of frames of video signal that can be stored in the field memory  202  is  150 , which corresponds to 5 seconds in a normal reproduction time. 
     In the case of continuous recording with no time lapse, video signals from external video cameras are digitized by the A/D converter  100  and are then stored in the field memory  202  via buffer memory  201  without skipping any field. 
     When the number of fields of a video signal that has been successively stored in the field memory  202  equals the capacity of the field memory  202  i.e., 150 frames, the video signal in the field memory  202  is converted into an analog signal and is then recorded on the magnetic tape. While the video signal is recorded, the video signal received from the external video camera is stored temporarily in the buffer memory  201 . Therefore, when the recording of video signal of 150 frames in the field memory is completed, the buffer memory  201  becomes full with the video signal of 150 frames. Then, the video signal is recorded as soon as it is transferred to the field memory  202 . Thus, the video signal that is received in real time from the external video camera is recorded with some delay, but a recording pause does not occur. 
     On the other hand, if the time-lapse recording time of 72 hours is set by a user, or if the user intends to record the video signal received from an external video camera during 72 hours with the magnetic tape of 2 hours running time, the video signal should be recorded at a ratio of one frame to every 36 frames. In other words, one frame out of every  36  frames that have been stored in the buffer memory  201  in the digital form is transferred to the field memory  202 , as shown in A of FIG.  4 . 
     When the field memory  202  is filled with the video signal of 150 frames, the video signal begins to be recorded on the magnetic tape by the controller  500 , as shown in B of FIG.  4 . Three minutes corresponding to the amount of 150×36 frames is required to fill the field memory  202 , and it takes 5 seconds to record the 150 frames. Thus, the time during which no video signal is recorded or the recording pause period. is 2 min. and 55 seconds. The recording pause period (Tw) is given by 
     
       
           Tw=Tm ×( N− 1) 
       
     
     where Tm is the storage capacity of the field memory expressed in seconds and N is the compression ratio of video frames. The compression ratio in the above example is 36. 
     Returning to FIG. 5, after calculating the recording pause period (S 13 ), the controller  500  checks whether or not the pause period is longer than a predetermined value e.g., 3 minutes (S 15 ). If it is longer than 3 min., the controller  500  makes the recording unit  400  operate in an alternating recording mode where the magnetic tape is unloaded in the recording pause period as shown in FIG. 3, and then reloaded in the recording period as shown in FIG. 2 (S 17 ). If the recording pause period is not longer than 3 min., the recording unit  400  is set to the mode where the tape is loaded all the time regardless of recording or non-recording period (S 19 ). The recording unit  400  records the video frames intermittently in the set mode. 
     FIG. 6 shows a flow chart of the head drum stopping method for the intermittent recording according to another embodiment of the present invention. With the same procedures as shown in FIG. 5, the recording pause period is calculated based on the time-lapse recording time set by a user and is then compared against the predetermined reference period e.g., 3 minutes (S 31 ˜S 35 ). If the calculated recording pause period is longer than the 3 minutes, an alternating recording mode is set and the rotation of the head drum is stopped during the recording pause period and the head drum rotates only when the video signal is recorded (S 37 ). Otherwise, the recording mode is maintained where the head drum keeps rotating all the time (S 39 ). 
     Given that the capacity of the field memory is 5 seconds, FIG. 7 shows different values of the recording pause period according to the various recording times in the time-lapse recording mode and a decision boundary of the tape unloading or the drum rotation stopping based on the calculated recording pause period. 
     Even though 4 seconds or so is a sufficient time to rotate the head drum that was stopped during the recording pause period at the normal rotation speed, the length of 3 minutes in FIG. 5 is used for a reference period of time by which a decision is made as to whether the magnetic tape is unloaded. This is because if a reference period shorter than 3 min. is used, frequent alternation between tape loading and unloading state may cause unstable driving of the recording deck or damage the recording unit. Likewise, whether or not the rotation of the head drum should be stopped is determined by using a reference period of 3 min. because it is desirable to allow a sufficient amount of time so as to stabilize the rotation speed of the head drum. 
     Unlike the above embodiments, a reference period of time other than 3 min. can be used for the two methods for the intermittent recording. For example, a reference period of time shorter than 3 min. can be used in the head drum stopping method for the intermittent recording. 
     The foregoing is provided only for the purpose of illustration and explanation of the preferred embodiment of the present invention, so changes, variations and modifications may be made without departing from the spirit and scope of the invention.