Bidirectional printing device

Abstract: A printer mounted on an electronic cash register (ECR) performs prin­ ting on printing paper by moving a print head left to right and right to left, i.e. bidirectionally. The printer uses right (RR) and left reset signals (RL) to determine the print start position and printing direction of the print head, the right (RR) and left reset signals (RL) being fed alternately and regularly to the driving circuit (16) for the print head for performing bidirectional printing, thereby assuring correct bidirectional printing. The right (RR) and left re­ set signals (RL) are constantly monitored. If the reset signals (RR,RL) of the same kinds are successively detected, it is judged that trouble has occured, hampering correct bidirectional printing, and notice is issued accordingly.

Description: BACKGROUND OF THE INVENTION 1. Field of the invention The present invention relates to a bidirectional printing device which may be advantageously employed as a printing means mounted for example on an electronic cash register (ECR) or the like. 2. Description of the Prior Art Bidirectional printing devices for printing characters by moving the print head in one direction, then in the reverse direction thereof, i.e. bidirectionally, are used as printing means for electronic cash registers. With such printing devices, one line is printed as the print head is moved in one direction, and another line as it is moved in the reverse direction. That is, two lines are printed while the print head completes one bidirectional travel. When not performing printing operation, the print head is placed in a standby position where it stopped at the end of the preceding printing operation (i.e. at one end of the printing paper width). When printing operation is resumed, the print head starts to move toward the printing area on the printing paper. When the print head is detected having reached one end of the printing area width, a start signal described below is produced, in response to which the printing operation by the print head is started. The start signal is produced, for example, in response to a normal/reverse rotation instructing signal which instructs the rotating direction of a drive motor for driving the print head and the output signal from an optical detecting means which optically detects the print head positioning. The start signal is classified into two kinds, one being the right start signal which is given to start printing from the right end toward the left end of the printing area, and the other being the left start signal which is given to start printing from the left end toward the right end of the printing area. Both right and left start signals are used to determine the print start position and printing direction of the print head. In continuous printing operation, the right and left start signals are alternately produced. In such bidirectional printing device, either right or left start signal can be lost, for example, because of disconnection in a circuit within the printing device. In such a case, e.g., if the right start signal is lost when printing should be made by moving the print head from the right end toward the left end of the printing area, the printing operation may, for example, be suspended without issuing notice to the operator, or erroneous printing may be made because of erroneous response to the subsequently given left start signal. US-A-4, 179,223 shows a bidirectional printing device which performs line by line printing bidirectionally by printing means from a predetermined print start position to a predetermined print end position on printing paper, the bidirectional printing being performed in response to a left print start signal and a right print start signal produced for every line to be printed as the printing means reaches the respective print start positions. Three fixed optical sensing devices are positioned to sense the left and right margins as well as the center location of high speed printer carriage travel. Signals from the sensing devices are fed to programmed carriage logic control circuits which effect rapid carriage movements relative to the center location as well as the traditional left and right margin locations. Printing time of certain forms is greatly reduced by minimizing unnecessary carriage return to the left margin location. In such a bidirectional printing device, either right or left signals can be lost, for example, because of disconnection in a circuit within the printing device which leads to malfunction of the printing device. SUMMARY OF THE INVENTION Accordingly, it is an object of the invention to provide a bidirectional printing device wherein: when trouble has occurred to the signal for instructing the start of printing, the trouble status is detected and, on the basis of the detected result, prescribed corrective measures are taken. To achieve the above object, the invention provides a bidirectional printing device which is characterized by control means for determining if the current print start signal is of the same kind as the preceding print start signal, judging that trouble has occurred to the print start signal if the two signals are of the same kind, and thereafter performing a predetermined operation. When the bidirectional printing device is performing bidirectional printing operation in normal state, the left print start signal and the right print start signal are produced alternately. In this state, two successive signals are therefore of different kinds. On the other hand, if one of the print start signals is lost, for example, the subsequently issued signal will be of the same kind as the preceding signal, which makes it possible to detect a failure which has occurred to the print start signal. The bidirectional printing device may be so constructed that when the failure as mentioned above is detected, the printing operation can be continued by using only the print start signal for the direction for which no failure has occurred. Also, the invention provides a bidirectional printing device which is provided with a print head for printing on printing paper, the print head being moved in a first direction relative to the printing paper, then in a second direction which is reverse of the first direction for printing on the printing paper by reading out the printing contents stored in memory when the print head is moved in the first and second directions, the bidirectional printing device including: start signal producing means for producing first and second start signals which instruct the start of printing by the print head when the print head is moved in the first and second directions respectively, said bidirectional printing device is characterized by judging means for judging, in response to the first and second start signals, if the first start signal is preceded by the second start signal, upon reception of the first start signal, and if the second start signal is preceded by the first start signal, upon reception of the second start signal; and means for enabling printing of the memory contents by the print head in response to the outputs from the judging means when it is judged that reception of the first start signal is preceded by reception of the second start signal and when it is judged that reception of the second start signal is preceded by reception of the first start signal. When the bidirectional printing device is performing continuous printing in normal state, reception of the first start signal is followed by reception of the second start signal, and reception of the second start signal is followed by reception of the first start signal. Accordingly, when it is judged that reception of the first start signal is preceded by reception of the second start signal, and when it is judged that the second start signal is preceded by reception of the first start signal, it is judged that each start signal produced by the signal producing means has been received in normal state, enabling printing of the memory contents by the print head. In a preferred embodiment of the invention, the bidirectional printing device includes means for stopping the printing by the print head and producing a signal indicating the trouble status in response to the outputs from the judging means when the first start signal is immediately followed by another first start signal or when the second start signal is immediately followed by another second start signal. In the bidirectional printing device, reception of the first start signal followed by another first start signal or reception of the second start signal followed by another second start signal means that each signal produced by the signal producing means has not been received in normal state, in which case a signal indicating the trouble state is produced, thereby making it possible to annunciate the trouble state. BRIEF DESCRIPTION OF THE DRAWINGS The above-mentioned and other objects as well as the features and advantages of the invention will become more apparent with reference to the following detailed description and the accompanying drawings. Fig.1 is a block diagram illustrating the electrical construction of the bidirectional printing device in a preferred embodiment of the invention. Fig.2 is a perspective view showing the construction of the area adjacent to a print head 1. Fig.3 is a diagram showing the locus of the print head 1 on printing paper 2 during printing operation. Fig.4 is a timing chart for a left start signal RL and a right start signal RR. Fig.5 is a timing chart showing the state when a failure has occurred to the left start signal RL. Fig.6 is a timing chart showing the state when a failure has occurred to the right start signal RR. Fig.7 is a flow chart explaining the operation of the bidirectional printing device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to the drawings, the preferred embodiments of the invention are hereinafter described in detail. Fig.1 is a block diagram illustrating the electrical construction of a preferred embodiment of the invention. Fig.2 is a perspective view showing the area adjacent to a print head 1. Printing paper 2 is loaded between the print head 1 and a platen 3, and is fed in the direction perpendicular to the axial direction of the platen 3 (in the direction of the arrow A shown in Fig.2). The print head 1 is movable bidirectionally along the axial direction of the platen 3 within the print head moving range P1, and performs bidirectional printing on the printable area set between a left print start position L and a right print start position R on the printing paper 2. A control section 11 for driving and controlling a printing device 10 includes a start signal producing circuit 12 for producing start signals to control the print head 1. The start signal producing circuit 12 produces a left start signal RL and a right start signal RR hereinafter described. These start signals RL and RR are fed through a filter 13 where noise is eliminated to a judging circuit 14 included in the printing device 10. The judging circuit 14 judges the kind of the start signal that has been input, the information of which is fed to a control circuit 15. The control circuit 15 controls a driving circuit 16 for driving the print head 1 bidirectionally, a driving circuit 17 for driving the platen 3 in an intermittent rotating motion, and a print driving circuit 18 for causing the print head 1 to print printing data stored in memory 24. The control circuit 15 has a memory 24 for storing data to be printed. The data input from a keyboard 25 undergoes prescribed arithmetic operation in an arithmetic circuit 26, and is stored as printing data in the memory 24. To print rightward (in the direction of the arrow B1 shown in Fig.2), the printing data is sequentially sent out by addressing the memory 24 in the order appropriate for rightward printing control, and to print leftward, the printing data is sent out by addressing the memory 24 in the reverse direction. The print head 1 is fixed to a wire 29 which is applied on a pair of pulleys 27 and 28. The rotating force of a drive motor 30 is transmitted to the pulley 27 to move the print head 1. The motor 30 is driven in the normal or reverse direction in response to the driving signal from the driving circuit 16. A control signal E from the control circuit 15 is given to the driving circuit 16. The control signal E contains the information for instructing the rotating direction of the motor 30. Adjacent to the ends of the travel path of the print head 1, are provided optical detecting means 31 and 32 for optically detecting the positioning of the print head 1. The left print start position L and the right print start position R are detected by the detecting means 31 and 32 respectively. The outputs from the optical detecting means 31 and 32 are fed to the start signal producing circuit 12 along with the control signal E from the control circuit 15. The start signal producing circuit 12 outputs a start signal in response to the control signal E and the output from either optical detecting means 31 or 32. The width of a printing area P which is set between the left print start position L and the right print start position R is set smaller than the travel of the print head set in the print head moving range P1. For bidirectional printing operation, the print head 1 is moved in one direction by the travel (= moving range P1) corresponding to the predetermined travelling time, and, after elapse of a given time, is moved in the reverse direction by the same time. Fig.3 is a diagram showing the locus of the print head 1 on the printing paper 2 during printing operation. In the bidirectional printing device, when not performing printing operation, the print head 1 is placed in a stationary state at the position where it stopped at the end of the preceding printing operation. Prior to initiation of printing operation, the print head 1 starts to move. After the print head 1 having reached the printing area P, characters to be printed are printed on the printing paper 2. The timing at which the printing operation starts when the print head 1 has reached the printing area P is determined by the start signal produced by the start signal producing circuit 12. For example, supposing the print head 1 stationary at the position indicated by the reference numeral 20 starts to move in the direction of the arrow B, when the print head 1 reaches the right print start position L indicated by the reference numeral 21 on the printing paper 2, the state is detected by the detecting means 31 to cause a left start signal RL1 to be produced by the start signal producing circuit 12. In response to the left start signal RL1, the print head 1 starts to print while being moved in the direction of the arrow B. When the print head 1 reaches the position indicated by the reference numeral 22, the state is detected by the detecting means 32 to end the printing for the line, the printing operation being suspended till the print head 1 reaches the position indicated by the reference numeral 23. When the print head 1 reaches the right print start position R, indicated by the reference numeral 23, on the printing paper 2, the state is detected by the detecting means 32 to cause a right start signal RR1 to be produced to resume the printing operation. The printing operation by the print head 1 is thus initiated in response to the left start signal RL and the right start signal RR to continuously perform bidirectional printing. When printing operation is performed in the normal state as described above, the left and right start signals RL and RR are produced alternately as shown in Fig.4. Accordingly, the control circuit 15 judges that printing operation is being performed in normal state when the left start signal RL and the right start signal RR are being input alternately. On the other hand, if two right start signals RR, for example, is input successively, it is judged that the left start signal RL which should be given between the right start signals RR has been lost. (Refer to Fig.5) Likewise, if two left start signals RL are input successively, it is judged that the right start signal RR which should be input between the left start signals RL has been lost. (Refer to Fig. 6) Trouble caused to the start signal is thus detected. The possible cause of omission of the start signal includes, for example, a disconnection between the control section 11 and the printing device 10. For performing such judgement, when the left start signal RL is input to the judging circuit 14, a data flag RLF is set in the control circuit 15, indicating that the left start signal RL has been given. Likewise, when the right start signal RR is input to the judging circuit 14, a data flag RRF is set, indicating that the right start signal RR has been given. Thus, in the control circuit 15, a flag is set to indicate the kind of the preceding start signal, thereby permitting comparison of the currently input start signal with the kind of the preceding start signal and judging that the other kind of start signal has been lost if the two successive start signals are of the same kind. Fig.7 is a flow chart explaining the operation of the bidirectional printing device. In step n1, the motor 30 for moving the print head 1 bidirectionally is started to initiate a series of printing operations. In step n2, it is checked if the right start signal RR is input to the judging circuit 14, and if yes, the operation proceeds to step n3. In step n3, it is checked if the data flag RRF is set to indicate generation of a right start signal RR preceding the current reset signal. If yes, since it is judged that two successive right start signals have been input to the judging circuit 14, the operation proceeds to step n4 to process the error. If it is judged in step n3 that the data flag RLF is set, since it is judged that the start signal have been input to the judging circuit 14 in normal state, setting the data flag RRF in step n5, and the operation proceeds to step n9. If it is checked in step n2 that the right start signal RR is not input, it is checked in step n6 if the left start signal RL is input. If yes, the operation proceeds to step n7, and if no, the operation returns to n2. In step n7, it is checked if the data flag RLF is set to indicate generation of a left signal preceding the current start signal. If yes, since it is judged that two successive left start signals have been input to the judging circuit 14, the operation proceeds to step n4 to process the error. When the data flag RRF is set in step n7, the operation proceeds to step n8 to set the data flag RLF, and in step n9, printing operation for one cycle is performed. After step n9 the flag RLF or RRF is reset. In step n10, it is judged if the printing operation should be terminated, and if no, the operation returns to step n2. If yes, the operation proceeds to step n11 to stop the motor and to terminate the printing operation. The error processing in step n4 may include, for example, annunciation of the absence of the start signal by means of a display or a buzzer. Also, in the case of the absence of the start signal, the printing operation thereafter may be performed by using only the start signal for the direction for which no failure has occurred. Thus, it is possible to continue the printing operation in normal state without stopping the printing operation or without performing erroneous printing, although the printing speed is reduced to half. The bidirectional printing device may also be constructed in such a way that the motor runs only in one direction to feed the print head 1 bidirectionally over the moving range P1, or other alternative construction may be conceived. Also, it may be so constructed that instead of moving the print head 1, the platen is moved bidirectionally. Furthermore, bidirectional printing may be performed dot by dot instead of line by line.

Claims: A bidirectional printing device (10) which performs line by line printing bidirectionally by printing means (1) from a predetermined print start position (L, R) to a predetermined print end position (R, L) on printing paper (2), the bidirectional printing being performed in response to a left print start signal (RL1,2...) and a right print start signal (RR1,2...) produced for every line to be printed as the printing means (1) reaches the respective print start positions (L, R), characterized by control means (15) for determining if the current print start signal (RL, RR) is of the same kind as the preceding print start signal (RR, RL), judging that trouble has occured to the print start signal (RL, RR) if the two signals are of the same kind, and thereafter performing a predetermined operation. A bidirectional printing device (10) which is provided with a print head (1) for printing on printing paper (2), the print head (1) being moved in a first direction (B1) relative to the printing paper (2), then in a second direction (B2) which is reverse of the first direction (B1) for printing on the printing paper (2) by reading out the printing contents stored in memory (24) when the print head (1) is moved in the first (B1) and second directions (B2), the bidirectional printing device (10) including: start signal producing means (12) for producing first (RL) and second start signals (RR) which instruct the start of printing by the print head (1) when the print head (1) is moved in the first (B1) and second directions (B2) respectively, characterized by judging means (14) for judging, in response to the first (RL) and second start signals (RR), if the first start signal (RL) is preceded by the second start signal (RR), upon reception of the first start signal (RL), and if the second start signal (RR) is preceded by the first start signal, (RL), upon reception of the second start signal (RR); and means (16,17,18) for enabling printing of the memory (24) contents by the print head (1) in response to the outputs from the judging means (14) when it is judged that reception of the first start signal (RL) is preceded by reception of the second start signal (RR) and when it is judged that reception of the second start signal (RR) is preceded by reception of the first start signal (RL). A bidirectional printing device (10) claimed in Claim 2, including: means (15) for stopping the printing by the print head (1) and producing a signal (RLF, RRF) indicating the trouble status in response to the outputs from the judging means (14) when the first start signal (RL) is immediately followed by another first start signal (RL) or when the second start signal (RR) is immediately followed by another second start signal (RR).

Inventors: IKOMA KEIICHI, MIWA KENJI, NAKAI SHIZUO, OBATA TOMOKAZU, IKOMA, KEIICHI, MIWA, KENJI, NAKAI, SHIZUO, OBATA, TOMOKAZU
Applicants: SHARP KK, SHARP KABUSHIKI KAISHA
Application year: 1989
Main classification: B41J19
IPC codes: G07G5, B41J19, B41J29