Abstract:
A recording apparatus is provided with detecting means for detecting any abnormality of a synchronizing signal included in an incoming signal; processing means for processing the incoming signal into a print recording signal; and print recording means for carrying out print recording in accordance with the print recording signal. Erroneous recording is prevented by inhibiting the print recording signal from being supplied to the print recording means when any abnormality is detected in the synchronizing signal.

Description:
This application is a continuation of appliation Ser. No. 248,317, filed 9/19/88, now abandoned; which is a continuation of application Ser. No. 141,510, filed 1/7/88, now abandoned; which is a continuation of application Ser. No. 907,843, filed 9/16/86, now abandoned. 
    
    
     Background of the Invention 
     1. Field of the Invention 
     This invention relates to a recording apparatus for print recording images, letters or the like and more particularly to an apparatus which is arranged to stop print recording when any abnormality is detected in a synchronizing signal which serves as the basis of timing for various control actions. 
     2. Description of the Related Art 
     Heretofore, the apparatus of the above-stated kind has been arranged as shown in FIG. 4 of accompanying drawings. Referring to this drawing, an A/D converter 1 is arranged to receive a video signal in the form of analog image signal and to convert it into a digital signal. An A/D (analog-to-digital) controller 2 is arranged to generate a clock signal A/DCK according to a horizontal synchronizing signal Sync. The A/D converter 1 is operated according to the timing of the clock signal A/DCK. A line memory 3 is arranged to store the digital image signal produced from the A/D converter 1. A D/A converter 4 is arranged to read out the signal stored at the line memory 3 under the control of a system controller 5 and to convert it into an analog signal. A head driver 6 is arranged to drive a head to perform print recording according to the analog signal. A reference numeral 7 denotes devices of varied kinds that are to be controlled by a control signal CTRL produced from the system controller 5. 
     The system controller 5 is arranged to supply a signal ADC to the A/D controller 2. This signal ADC causes the A/D controller 2 to begin to operate and to supply the signal A/DCK to the A/D converter 1 in synchronism with the horizontal synchronizing signal Sync. The A/D converter 1 converts the incoming video signal on the basis of the signal A/DCK. The digital data which is thus obtained is supplied to the line memory 3. The A/D converter 1 repeatedly performs sampling after the lapse of a given period of time from arrival of the horizontal synchronizing signal Sync for every period of 1-H (one horizontal scanning period). In other words, the converter 1 performs sampling in the vertical direction perpendicular to the video signal supplied. After one line portion of the video signal is A/D converted in the vertical direction, the A/D controller 2 produces a signal ADCE which informs the system controller 5 of completion of A/D conversion. Upon receipt of the signal ADCE, the system controller 5 judges the A/D conversion to have come to an end and produces the signal D/ACK to the D/A converter 4. Concurrently with this, the controller 5 produces the signal CTRL to cause thereby thee devices 7 of varied kinds to carry out printing operation on one line portion of the signal. With these processes repeatedly performed, a print of one image plane portion of the incoming video signal is obtained. 
     With the conventional circuit arranged in the above-stated manner, however, the A/D controller 2 comes to erroneously operate is a signal drop-out exists in the incoming synchronizing signal Sync or some noise mixes therein. In that event, the signal A/DCK which is produced from the conroller 2 becomes erroneous to disturb correct timing for the sampling action on the video signal. Then, the output of the A/D converter 1 becomes erroneous data to prevent a correct printing output from being produced. Accordingly, that results in a greatly deteriorated picture quality of print recording. 
     Summary of the Invention 
     A first object of this invention is to provide a recording apparatus which never performs recording when the picture quality of an incoming video signal deteriorates to an excessive degree in recording the video signal. 
     A second object of this invention is to provide a recording apparatus which never performs recording when an incoming video signal is in an inappropriate state in printing the video signal. 
     Under this object, a recording apparatus arranged as a preferred embodiment of this invention comprises: means for detecting any abnormality of a synchronizing signal included in an incoming signal; processing means for processing the incoming signal into a print recording signal; print recording means for carrying out print recording in accordance with the print recording signal; and inhibiting means for inhibiting the print recording signal from being supplied to the print recording means when an abnormality is detected in the synchronizing signal. 
     These and further objects and features of this invention will become apparent from the following detailed description of an embodiment thereof taken in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram showing an embodiment of this invention. 
     FIG. 2 is a flow chart showing by way of example control procedures employed in the same ebodiment. 
     FIG. 3 is a block diagram showing the details of a detecting circuit 8 included in FIG. 1. 
     FIG. 4 is a block diagram showing an example of the conventional circuit arrangement. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The details of this invention are a described below with reference to the accompanying drawings: 
     FIG. 1 shows in a block diagram the circuit arrangement of a recording apparatus as an embodiment of this invention. The parts which are similar to those shown in FIG. 4 are indicated by the same reference numerals and symbols. A synchronizing signal abnormality detecting circuit 8 is arranged to receive a horizontal synchronizing sigal Sync and to detect any abnormality of the signal Sync due to a signal drop-out or a noise mixed therein. More specifically, the detecting circuit 8 counts a time interval elapsing after receipt of a vertical synchronizing signal and before receipt of a horizontal synchronizing signal or a time interval between one horizontal synchronizing signal and another horizontal synchronizing signal. The circuit 8 judges the synchronizing signal to have a drop-out when the time interval becomes longer than a normal length of time and to have a noise mixed therein when the time interval becomes shorter. FIG. 3 shows the details of arrangement of the synchronizing signal abnormality detecting circuit 8. 
     Referring to FIG. 3, a counter 11 is arranged to count clock pulses produced from an oscillator 16 and to be reset for a latching action of a latch circuit 12 every time a synchronizing signal which has been delayed for a given period of time by a delay circuit 15 is supplied to the reset terminal R thereof. The latch circuit is arranged to latch the output of the counter 11. The output of the counter 11 is latched by the circuit 12 every time the synchronizing signal is supplied to the counter as mentioned above. A discriminating circuit 13 is arranged to determine whether the output of the counter 11 latched by the latch circuit 12 represents an appropriate time interval of the synchronizing signal. For example, the discriminating circuit 13 judges whether or not the time interval correctly corresponds to one horizontal scanning period. If not, a signal SE indicative of an abnormality is produced from the circuit 13. 
     An OR gate 9 (FIG. 1) is arranged to receive a signal ADCE from the A/D controller 2 and the synchronizing signal abnormality detection signal SE from the circuit 8 and to obtain a logical sum of these signals. A synchronizing signal separating circuit 10 is arranged to separate a synchronizing signal from an incoming video signal. The output of the OR gate 9 is supplied to the system controller 5 and, in the event of any abnormality of the synchronizing signal, the signal ADCE is not transmitted to the system controller 5. The signal ADCE is a pulse signal and its fall is arranged to indicate completion of the A/D conversion process. Meanwhile, the signal SE is arranged to be at a high level in the event of any abnormality in the synchronizing signal. Therefore, the output level of the OR gate 9 becomes high when the signal SE is at a high level and then does not become low even with the signal ADCE applied to the OR gate 9. As a result the signal ADCE is not transmitted to the system controller 5. At the system controller 5, it is determined whether the signal ADCE is received within a given period of time T after a signal ADC is sent out. If the signal ADCE is not received within the period of time T, the synchronizing signal is considered to have some abnormality. In that event, the controller 5 produces a signal CTRL to the devices 7 to bring a print recording operation to a stop; and to have a recording medium such as a recording paper sheet or the like to be discharged and removed from the devices 7. 
     When the signal ADC is supplied to the A/D controller 2 from the system controller 5, the A/D controller 2 begins to operate in response to the signal ADC. Then, the A/D controller 2 in turn causes the A/D converter 1 to perform A/D conversion. Upon completion of the A/D conversion, the A/D controller 2 produces the signal ADCE to the OR gate 9. 
     In case of any abnormality in the incoming synchronizing signal Sync in this instance, the synchronizing signal abnormality detecting circuit 8 produces the synchronizing signal abnormality signal SE to the OR gate 9. This causes the output of the OR gate 9 to remain at a high level. The output level of the OR gate 9 never becomes low even in the signal ADCE is suplied thereto. Thus, the signal ADCE is prevented from being supplied to the system controller 5. 
     The system controller 5 is arranged to detect an abnormality of the synchronizing signal through control steps which are, for example, as shown in FIG. 2. Referring to FIG. 2, the signal ADC is sent out to the A/D controller 2 at a step S1. After this, a counting action begins to count the given period of time T at a step S2. At a step S3, it is determined whether the period of time T has elapsed or not. If not, the control operation proceeds to steps S4 and S5, at which a check is made for the presence or absence of the signal ADCE. If the signal ADCE is found within the period of time T, the A/D conversion process is regarded as having been completed and the operation proceeds to a step S6. At the step S6, the signal D/ACK is supplied to the D/A converter 4. At the same time, the signal CTRL is supplied to the devices 7 to cause them to carry out printing action on one line portion of the signal. With these steps of control operation repeated, a print of one picture plane portion of the incoming video signal can be obtained. In case that the signal ADCE is not transmitted within the given period of time T on the other hand, the operation of the system controller proceeds to a step S7 from the step S3. At the step S7, a control signal CTRL is produced to bring the printing action to a stop. Then, at a next step S8, the recording medium is removed from the devices 7. 
     In the embodiment described, a signal indicative of an abnormality of the synchronizing signal is arranged to be superimposed on another signal, i.e. the signal ADCE produced from the A/D controller 2. This arrangement obviates the necessity of providing the system controller 5 with an additional input terminal for receiving a signal indicative of an abnormality of the synchronizing signal. Therefore, the embodiment can be arranged much simpler than the conventional apparatus. 
     This invention is not limited to the arrangement of the specific embodiment described. The arrangement to have the synchronizing signal abnormality indicating signal superimposed on another signal of course may be replaced wih some other suitable arrangement to have such a signal supplied to the system controller 5 as it is. 
     In the embodiment, the synchronizing signal abnormality is arranged to be detected from the horizontal synchronizing signal. However, the invention is of course not limited to that arrangement. The invented arrangement is applicable to the detection of abnormalities in a synchronizing signal for main or auxiliary scanning or to the detection of any abnormality in a clock signal defining a timing for control over the whole apparatus. 
     Further, in accordance with the arrangement of the embodiment, a recording operation is brought to a stop by inhibiting the recording signal from being supplied to head driver 6 in the event of some abnormality in the synchronizing signal. In accordance with this invention, however, this arrangement may be replaced with a different arrangement in which the recording operation is brought to a stop by driving the devices 7 to discharge and remove the recording medium such as a paper sheet or the like. 
     In accordance with this invention, as described in the foregoing, any abnormality in the synchronizing signal is detected. In the event of such abnormality, the recording operation is brought to a stop, so that recording can be effectively prevented from being performed to have a deteriorated picture quality.