Printer and method for controlling it

Abstract: Disclosed is a printer in which the driving time of its printer head (10) is determined based on a printer head driving mode selected as a result of control commands interpreted by a control command interpreter (45) and the actual driving voltage Vp used for driving the printer head, and printing is performed according to the determined driving time. The purpose is to set the driving time of the printer head (10) to a time suited to both the used type of recording paper and the actual head driving voltage.

Description: The invention relates to a printer that operates according to control commands sent from a host computer, and more particularly it relates to a printer that performs printing selectively on plural types of paper such as single sheet of paper and plural sheets of self-copying paper (referred to as copy paper in the following). The printer head driving voltage is normally supplied from an AC power source using a switching regulator, a series regulator or other type of DC stabilized power source. Such power sources have a tolerance of about ±10% from a rated voltage value so that the actual driving voltage may be different from printer to printer. Furthermore, these stabilized power sources still have an internal resistance, and the output voltage changes with changes in the load. Also, due to the impedance or resistance of the wiring from the power source to the printer head drive circuit, the printer head driving voltage supplied to the printer head drive circuit is not fixed and fluctuations occur in it. Therefore, assuming the driving time is constant, the energy supplied to the printer head is not always the same among various printers (static fluctuations) causing a print quality tolerance among the printers, and is not constant within the individual printers (dynamic fluctuations), resulting in uneven printing. In order to make this energy constant, control is performed that varies the driving time so that the driving time is made longer when the printer head driving voltage is low and the driving time is made shorter when the driving voltage is high. The term "driving time" as used herein means the duration of energization of a printer head actuator to cause printing of one dot. FIG. 8 is a graph showing the relationship between the printer head driving voltage and the suitable driving time. Both have a 1-to-1 relationship as indicated by T1 with respect to V1, and by controlling the printer head with a driving time suited to the printer head driving voltage, printing quality is stabilized. However, when the thickness and material of the recording paper vary in a printer that performs printing on plural types of recording paper, it is difficult to consistently obtain high print quality with the above method in which the driving voltage and driving time have a 1-to-1 relationship. That is, when the printing paper is one sheet, the driving time can be relatively short and in the case of copy paper, the driving time must be relatively long, but since the same driving time is used for the same driving voltage in the above method, the driving time could be longer than necessary, and in such case the printing noise becomes loud, the printer head overheats, etc., for one sheet, while for copy paper the driving time could be shorter than required for this type of paper, the ability to make copies is degraded. In order to solve this problem, printers are being developed with functions to control the driving time according to the thickness of the recording paper as disclosed in JP-A-53-113815, JP-A-03-23953 and JP-A-03-93549. The printer disclosed in JP-A-53-113815 is provided with a detector that detects a paper thickness indicator affixed to the recording paper and produces a magnet energizing time signal corresponding to the detected paper thickness in order to automatically detect the thickness of the recording paper and control the energizing current and driving time of the electro-magnetic actuators of the printing head according to the paper thickness. The printer disclosed in JP-A-03-23953 has a gap motor to adjust the gap between the platen and the printer head and a gap sensor, and by measuring the difference between when there is no recording paper on the platen and when there is recording paper, it detects the thickness of the recording paper. According to this, it sets the time current is sent to the printer head. As in the printer of JP-A-03-23953, the printer of JP-A-03-93549 has a motor to adjust the platen gap and a sensor that indicates the maximum gap, and by using the amount of feed of the motor from the maximum gap position to the position where the head comes in contact with the recording paper, it detects the thickness of the recording paper. According to this, it controls the driving time of the coils which drive the dot matrix pins of the printer head. However, the printers disclosed in these prior art documents require special means to detect the thickness of the recording paper. That is, in the printer of JP-A-53-113815, this is the paper thickness indicator affixed to the recording paper and the detector that detects this paper thickness indicator, and in the printers of JP-A-03-23953 and JP-A-03-93549 it is the platen gap adjustment motor and the sensor for the gap. By adding these special means, special recording paper is required, the reliability and ease of assembly are degraded due to the complex configuration of the printers, and the production cost of the printers is increased, thus hindering their general acceptance. Further, while these printers can accommodate various paper thicknesses, they do not readily accommodate various paper qualities; i.e., even though one sheet of paper and copy paper may have the same thickness, they require different driving times, and the prior printers cannot answer this need. Also, there is no example in the prior art of a printer that changes the driving time according to fluctuations in the above driving voltage while also optimizing the driving time to accommodate differences in paper thickness and paper quality, and the realization of such a printer is desired. This invention solves this problem and is intended to meet the above demands, and its purpose is to offer a printer that realizes optimum printer head drive control for a variety of types of paper without requiring special recording paper or complicated mechanisms. It is a further object of the invention to offer a printer that realizes optimum printer head drive control with respect to both the type of recording paper and the driving voltage by using the driving voltage and the type of recording paper as parameters to determine the driving time. These objects are achieved with a printer and a method for controlling it as claimed. When a driving mode selection command is input to the printer, the control command interpreter extracts the driving mode selection information and outputs it to the driving time determination section. Then the driving time determination section reads out the driving time from among the driving times corresponding to plural driving modes stored in the driving time memory and outputs it to the drive controller. The printer head drive controller uses this to control the printer head driver. By this means, it is possible to use the driving mode selection command to select the optimum printer head driving time for the recording paper to be printed on. Also, when a paper selection command is input to the printer, the control command interpreter extracts the recording paper selection information included therein and outputs it to the driving time determination section. The driving time determination section, then, converts the recording paper selection information to driving mode selection information using a converter and determines the driving time in the same manner as described above. By performing only selection of the recording paper in this manner, the optimum driving time for the selected recording paper can be selected. Further, the driving time determination section uses the driving time table in the driving time memory to determine the driving time from the measured value obtained by the voltage detector and the driving mode determined by interpretation of the control command. By this means, the optimum printer head driving time corresponding to both the type of recording paper and fluctuations in the driving voltage can be obtained. In this invention, a configuration is used in which the value measured by the voltage detector is converted to a digital value and digital processing is performed to reduce susceptibility of processing to power source voltage fluctuations and external disturbances. Also, the printer of the invention can select the driving mode by either the driving mode selection information included in the driving mode selection command or the driving mode selection information obtained from the recording paper selection information included in the paper selection command, and the driving mode selected by the command executed last becomes effective. Further, when a driving mode selection command is executed after execution of the paper selection command, the converter is updated so that the driving mode selection information included in the driving mode selection command and the driving mode selection information obtained from the recording paper selection information included in the recording paper selection command match. By this means, even if the driving mode corresponding to the recording paper is not initially the optimum mode, if it is corrected using the driving mode selection command once, a corrected optimum driving mode can be subsequently selected by merely selecting the recording paper. Preferred embodiments of the invention will be explained below with reference to the drawings, in which FIG. 1 is a block diagram illustrating an embodiment of the invention, FIG. 2 is a flowchart used for explaining an embodiment of the invention, FIG. 3 is a graph showing the relationship between the driving time, the driving mode and the driving voltage according to an embodiment of the invention, FIG. 4 is a memory map illustrating the contents of a driving time memory according to an embodiment of the invention, FIG. 5 is a flowchart used for explaining an embodiment of the invention, FIG. 6 is an explanatory diagram of an example of a driving mode selection command used in the invention, FIG. 7 is an explanatory diagram of an example of a paper selection command used in the invention, FIG. 8 is a graph showing the relationship between the printer head driving voltage and the suitable printer head driving time, FIG. 9 shows correlations between the selected recording paper and the driving mode set by it in an embodiment of the invention, FIG. 10 is a flowchart used for explaining another embodiment of the invention, FIG. 11 is a flowchart used for explaining another embodiment of the invention, and FIG. 12 is a flowchart used for explaining still another embodiment of the invention. First Embodiment FIG. 1 shows the configuration of the printer of a first embodiment of the invention. The printer of this embodiment is a wire dot matrix printer with a printer head 10 having plural dot wires (not shown) each driven by a respective electro-magnetic actuator including a head coil 11. The printer comprises a head driving voltage detector 30, which measures a voltage Vp supplied to the head coils 11, a control circuit 40, which performs printing control and communicates control commands, and a head driver 20, which controls powering of head coils 11 based on commands from control circuit 40. Head driver 20 includes for each head coil 11 a drive switch 21 which applies the driving voltage Vp to the respective head coil 11. The drive switches 21 are made up of transistors. Therefore, when a drive switch 21 is switched ON by the control signal from control circuit 40, the driving voltage Vp is applied to the associated head coil 11, and the corresponding dot wire is driven by its electromagnetic actuator, whereby dot matrix printing is performed. Voltage detector 30 comprises a reference resistor 31 and a reference resistor 32, and to one end of reference resistor 31 is applied the driving voltage Vp, while the other end is connected to one end of reference resistor 32. The other end of reference resistor 32 is connected to the ground. Therefore, a voltage divider circuit is formed by reference resistor 31 and reference resistor 32, and fluctuations of the driving voltage Vp are detected as voltage changes at voltage division point 33 and transferred to control circuit 40. In this embodiment, control circuit 40 uses a lower voltage power source which is separate from the power source that generates driving voltage Vp, and therefore this kind of voltage divider circuit is necessary. Also, by using this voltage divider circuit, the impedance seen from the input of the measurement circuit, the analog-digital converter 41 in this case, can be raised, which can be expected to have the effect of protecting the measurement circuit from being damaged for instance by a spike voltage that might occur superposed to the driving voltage Vp. Further, the integrating circuit made up of the input capacitance of analog-digital converter and the resistance of the voltage divider circuit has the effect of eliminating the effect of the radio-frequency noise contained in driving voltage Vp. Control circuit 40 includes a control command receiver 44 which receives control commands sent from the host computer, and a control command interpreter 45, which interprets the function of the received control command. A memory 50 includes a control command storage section 51 where the control commands received by control command receiver 44 are temporarily stored. When a control command is received, control command interpreter 45 fetches the already received control commands from control command storage section 51, interprets the function of each control command and determines the type of recording paper, the printer head driving mode (simply referred to as "driving mode" in the following), etc., according to the function. Further, control circuit 40 also has an analog-digital converter 41 which converts the analog value measured by voltage detector 30 to a digital measurement value corresponding to the divided voltage at voltage division point 33 and thereby representing the driving voltage Vp. Control circuit 40 also has a driving time determination section 43, which determines the driving time of printer head 10 from the driving mode determined by control command interpreter 45 and the digital measurement value, and a drive controller 42, which controls head driver 20 according to the time determined by driving time determination section 43. Memory 50 stores driving time tables including the correspondence of the driving voltage Vp and the driving time for each driving mode of the printer head. In this embodiment two tables (A and B in Fig. 4) are stored which correspond to respective driving modes. Driving time determination section 43 uses these tables to set in a timer 46 the driving time, i.e. the duration of energization of a head coil to cause the corresponding wire dot to print one dot, based on the digital measurement value and the driving mode determined by control command interpreter 45. FIG. 6 shows an example of the control command used by the invention to select the driving mode. Command code "GS E" 60 indicates that this command is a driving mode selection command, and when control command interpreter 45 reads this command code 60, it interprets it as a command for selecting the driving mode. The "GS" is the ASCII code group separator (GS); i.e., it indicates 1DH (H indicates that it is a hexadecimal number; same below), and "E" indicates the ASCII code 45H. The following parameter "n" 61 indicates the value that specifies the driving mode; e.g., when n = 0, mode A is selected and when n = 1, mode B is selected. In this embodiment, when the driving voltage is the same, mode A has a shorter driving time than mode B. That is, assuming that when driving voltage Vp is V1, the driving time of mode A with respect to V1 is TA and the driving time of mode B is TB, the relationship TA < TB becomes valid. The above parameter "n" was configured as one byte, but it may be two or more bytes as required. Also, two driving modes, A and B, were used in this embodiment, but the driving modes are not limited to two, and it is possible to use any number of required driving modes. FIG. 7 shows an example of the control command used by the invention for selecting recording paper. Command code "ESC c0" 70 indicates that this command is a paper selection command, and when control command interpreter 45 reads this command code, it interprets it as a paper selection command. The "ESC" indicates the ASCII code escape; it indicates 1BH, and the "c0" indicates the ASCII codes 63H and 30H, respectively. The following parameter "n" 71 indicates the value that specifies the type of recording paper; e.g., when n = 0, roll paper is selected, and when n = 1, cut-sheet paper is selected. The above parameter was configured as one byte, but it may be two or more bytes as required. Also, two types of paper, roll paper and cut-sheet paper, were used in this embodiment, but the types of paper are not limited to these, and it is possible to specify selection of recording paper according to the required number of paper types. Next is an explanation of the operation of the printer of this first embodiment of the invention. As already explained, the control command sent from the host computer is received by control command receiver 44 of the control circuit 40 and is stored in command storage section 51 of memory 50. The following operation is explained using a flowchart. FIG. 2 is a flowchart showing the operation when control command interpreter 45 processes a driving mode selection command or a paper selection command. First, the control command interpreter reads out the control command from control command storage section 51 in step ST1, and then in step ST2 it judges whether or not this control command is a driving mode selection command. If it is not a driving mode selection command, it judges whether or not it is a paper selection command in step ST7. If it is not a paper selection command, it is not a control command for driving mode selection and processing proceeds to step ST3 where commands other than selection of the driving mode are executed according to that control command. Examples of such other control commands include a line feed control command ("LF") and a printing data cancel control command ("CAN"). The explanation is continued from step ST2. If, at this time, the control command is a driving mode selection command, then judgment of the driving mode that should be set is done in step ST4. Then driving mode A or driving mode B is selected according to the setting of the control command (steps ST5 and ST6). If it is judged in step ST2 that the control command is not a driving mode selection command and then it is judged in step ST7 that it is a paper selection command, then judgment of the paper type specified by the command is performed in step ST8. If the paper specified by the control command is roll paper, then the printer is set to the roll paper printing mode in step ST9. More specifically, processing is performed in this step that switches the paper transport path to that for roll paper or sets the amount the paper is fed by the line feed command to a value corresponding to roll paper. In this embodiment, driving mode selection is not automatically performed following setting of the roll paper printing mode. This is because two types of paper, one sheet of roll paper and copy paper, are assumed to be used, and therefore selection of the driving mode is left to the driving mode selection command as far as roll paper is concerned. Also, if the paper specified by the control command is cut-sheet paper, then the printer is set to the cut-sheet paper printing mode in step ST10, after which driving mode B is automatically selected. This is because cut-sheet paper is often copy paper and driving mode B, which has a longer driving time, is selected to ensure sufficient copying capability. This automatic driving mode selection may be overrun by means of a driving mode selection command issued after the paper selection command. In other words, as can be seen from the flowchart, when the cut-sheet paper is one sheet, the cut-sheet paper mode and driving mode A can be selected by selecting driving mode A using the driving mode selection command after selecting cut-sheet paper. FIG. 9 (a) shows the relationship between the type of paper selected and the driving mode selected according to it in the sequence shown in this flowchart. In FIG. 9 "O" means "is automatically selected in response to the paper type selection" and "X" means "is not automatically selected". Next is an explanation of the sequence that determines the driving time for the printer head from the measured value of the driving voltage. The relationship between driving voltage Vp and the optimum driving time corresponding to each driving mode was found experimentally to be that indicated by the graph in FIG. 3. Driving voltage Vp is indicated on the horizontal axis, while the optimum driving time is indicated on the vertical axis. When driving voltage Vp is V1, the optimum driving time is TA if the driving mode is A and is TB if the driving mode is B. According to the graph in FIG. 3, the digital measurement values that represent driving voltages Vp (actually correspond to the value of the divided voltage in this embodiment) and the corresponding optimum driving times are stored in driving time table 52 in memory 50 for each driving mode as shown in FIG. 4. In the figure, table A corresponds to driving mode A and table B corresponds to driving mode B. Next is an explanation according to the flowchart in FIG. 5 of the operation when one dot is printed. In step ST11, the driving mode determined by control command interpreter 45 is judged, and if the driving mode is A, table A of driving time table 52 is selected (step ST12), while if the driving mode is B, then table B is selected (step ST13). Next, the digital measurement value is read (step ST14). The driving time corresponding to the digital value read in step ST14 from table A or table B in step ST12 or step ST13 is set in timer 46 (step ST16). Processing then waits for the operation timing of printer head 10 (step ST17). When the operation timing of the print head 10 is reached, driving controller 42 sends a driving signal to head driver 20 (step ST18), at which time timer 46 begins operation (step ST19). This switches drive switch 21 ON, driving voltage Vp is applied to head coil 11 and driving begins. Processing then waits for the driving time to pass (step ST20). When the driving time is completed, the drive signals to head driver 20 are stopped (step ST21) and timer 46 also stops (step ST22). This operation terminates the printing of one dot. Second Embodiment The second embodiment of the invention allows to preset for each type of paper a corresponding driving mode which will then be set automatically each time the selection of the paper type is changed by a paper selection command. The sequence for driving mode selection in a printer of the second embodiment of the invention is explained using FIGS. 9 and 10. FIG. 10 is a flowchart of the operation after step ST4 in which the driving mode is judged in the flowchart in FIG. 2 which explains operation of control command interpreter 45. After the driving mode is set in step ST5 and step ST6 based on the judgment of the driving mode in step ST4, the currently selected type of paper is judged in step ST51 and step ST61. If roll paper is selected, for example, then the driving mode set in step ST5 or step ST6 is stored as the driving mode corresponding to roll paper in step ST53 and step ST63. Also, when cut-sheet paper is selected, then the driving mode set in step ST5 or step ST6 is stored as the driving mode corresponding to cut-sheet paper. Therefore, when selection of driving mode A is performed by the driving mode selection command when roll paper has been selected, for example, then driving mode A is stored as the driving mode corresponding to roll paper. Also, if driving mode B is then selected by the driving mode selection command after cut-sheet paper has been selected, then driving mode B is stored as the driving mode corresponding to cutsheet paper. FIG. 9 (b) shows the correlation obtained for this specific example between the selected paper type and the driving mode selected according to it. FIG. 11 is a flowchart explaining the processing performed subsequent to step ST8 in the flowchart in FIG. 2 in which the type of paper is judged. Based on the judgment result of step ST8, the printer mode corresponding to the type of paper is set in step ST9 and step ST101. Also, following this, the driving mode corresponding to the selected paper is set in step ST91 and step ST102. In case of the example of the correlation in FIG. 9 (b), driving mode A is set when roll paper is selected and driving mode B is set when cut-sheet paper is selected. By means of this configuration, once the driving mode corresponding to the paper type has been set, the corresponding optimum driving mode can be selected by just selecting the paper type. Third Embodiment In the above embodiments the digital measurement value representing the driving voltage Vp is obtained (step ST14 in FIG. 5) prior to switching on the drive switch (actually one or more drive switches depending on what is to be printed) in step ST18 in FIG. 5. This processing allows to compensate for any static fluctuations of the driving voltage. In order to additionally take into account dynamic fluctuations when selecting the appropriate driving time a slight modification can be made as will be explained with reference to FIG. 12 showing a illustrating a third embodiment of the invention. In FIG. 12 operation steps corresponding to those in FIG. 5 are denoted in the way as in FIG. 5. As will be seen, step ST17 is performed next to the selection of table A or B, i.e. the printer is waiting for the head operation timing. When the head operation timing is reached, the required drive switches are switched on thereby powering of the respective electro-magnetic actuators and changing the load to the driving voltage source. Now the digital measurement value is read which represents the driving voltage under the current load condition, and the proper driving time is selected, the timer set and started (steps ST14, ST15, ST16, ST19). The steps ST20 to ST22 follow in the same order as in FIG. 5. Since in this embodiment the digital measurement value represents the actual driving voltage under the respective load condition the driving energy is maintained constant irrespective of how many printing wires are driven at a time. The time delay between switching on the one or more drive switches and the start of the timer which is caused by the processing of steps ST14 - ST16 and ST19 in FIG. 12 is much shorter than the driving time. Since this time delay has a constant value, if necessary, it may be easily compensated for, for instance by storing correspondingly shorter driving times in driving time table 52 (FIG. 1). In the case of this embodiment, the settings shown in FIG. 9 (c) are initially set in the initialization sequence of the printer as the relationship between the selected paper and the driving mode set by it. By this means, the driving mode with the longer driving time is selected even when no specific driving mode has been set, thus ensuring reliable printing. As described above, by means of the invention, in addition to being able to change the driving time of the head coil depending on the actual driving voltage, the driving time of the head coil can also be changed by switching the driving mode via a control command, thus making it possible to lower printing noise and suppress the generation of heat by the printer head by using a control command to select a driving mode with a shorter driving time when the printing noise is loud or the printer head generates heat because the driving time is longer than necessary. Also, when the copy capability drops because the driving time is shorter than the required driving time, the necessary copy capability can be obtained by selecting a driving mode with a longer driving time. Also, when the paper requires a copy capability, the necessary copy capability can be obtained by using the recording paper information to select a driving mode with a longer driving time. Therefore, the invention makes it possible to perform the optimum printing on various types of recording paper without sacrificing print quality.

Claims: A printer adapted to print on a selected one of at least two types of recording paper, comprising: a control command receiver (44) for receiving control commands sent from a host computer, a control command interpreter (45) for interpreting said control commands, said control command interpreter (45) being capable of distinguishing between a paper selection command and a driving mode selection command, and including converting means for deriving, from a paper selection command, a driving mode selection information, a printer head (10) for dot matrix printing, a head driver (20) for driving said printer head, a driving time determination means (43) for determining the driving time of the printer head (10) based on a driving mode selected by said control command interpreter after interpreting either a driving mode selection command or a paper selection command, and a drive controller (42) for controlling said head driver (20) based on the driving time determined by said driving time determination means (43). The printer of claim 1 further comprising a driving time memory (50, 52) that stores respective driving times for plural driving modes, said driving time determination means (43) being configured such that it determines the driving mode from the driving mode selection information that is included in said control command and reads from said driving time memory the driving time that corresponds to the driving mode determined. The printer of claim 1 or 2 further comprising a voltage detector (30) that measures the value of the voltage used to drive the printer head (10), wherein said driving time determination means (43) is configured such that it determines the driving time from both the driving mode determined by interpretation of the control command by said control command interpreter (45) and the voltage measurement value measured by said voltage detector (30). The printer of claim 3 wherein said driving time memory (50, 52) stores a driving time table (52) including the driving times corresponding to plural driving modes and the driving times corresponding to said measurement values. The printer of claim 3 or 4 further comprising an analog-digital converter (41) that converts said measurement value to a digital value. A control method for controlling a printer as defined in any of claims 1 to 5 wherein the driving mode selection is performed after getting said driving mode selection information from said paper selection command using said converting means when said paper selection command is interpreted. The method of claim 6 wherein said driving mode can be selected by either the driving mode selection information included in the driving mode selection command or the driving mode selection information obtained from said paper selection command, and the driving mode is determined by the one of these control commands executed later. The method of claim 7 wherein when said driving mode selection command is executed after execution of said paper selection command, said converting means is updated so that the driving mode selection information included in said driving mode selection command and driving mode selection information obtained from paper selection command match. The method of claim 8 wherein initialization of said converting means is performed in the initialization process of the printer.

Inventors: KAZUHISA ARUGA, KAZUHISA, ARUGA
Applicants: SEIKO EPSON CORP, SEIKO EPSON CORPORATION
Application year: 1993
Main classification: B41J2
IPC codes: B41J11, B41J2, B41J29