Printer

Abstract: A printer comprises sheet feeding device (8) for starting to feed a printing sheet to the position of the next line immediately after data of one line is completely printed and deceleration of a carriage (7) from a predetermined printing speed is started, control table preparing device (4) for storing drive control information for the next line in a control table (4a) as soon as the data of the one line is completely printed and deceleration of the carriage (7) from the printing speed is started, first computing device (9) for computing a first period of time required until the printing speed is attained again after acceleration of the carriage (7) in a direction opposite to the direction of movement of the carriage (7) during printing the data of the one line so that data of the next line can now be printed, second computing device (10) for computing, after the carriage (7) is stopped, a second period of time required until the operation of the sheet feeding device (8) is completed from the time of stoppage of the carriage (7), the second computing device (10) continuing to compute the second period of time whenever the carriage (7) is stopped, and control device (2) comparing the result of computation by the second computing device (9) with the result of computation by the first computing device (10) whenever the carriage (7) is stopped, so that acceleration of the carriage (7) is started again each time the result of computation by the second computing device (10) becomes smaller than the result of computation by the first computing device (9).

Description: BACKGROUND OF THE INVENTION FIELD OF THE INVENTION This invention relates to a printer. DESCRIPTION OF THE RELATED ART With office automation, printers are now increasingly used in modern offices. These printers are characterised by low prices and excellent printing performance. It is now necessary to provide a printer which can print characters of high quality at a high printing speed and has multiple functions. In order to realise such a printer, preparation of software useful for controlling the operation of the printer is quite important. The operation of a prior art printer will be briefly described before describing the present invention in detail, so that the present invention can be more clearly understood. Fig. 8 is a timing chart showing the timing operation of an example of the prior art printer. First, in a period A-B, drive control information for controlling the operation of a carriage (not shown) carrying a printing unit so as to print data of one line on a printing sheet (now shown) is stored in a control table. Thus the control table for one line has been prepared. Then, in the next period B-C, the carriage is accelerated according to drive control information stored in the control table until the desired printing speed is attained. The operation of the carriage in the acceleration period is called "starting operation" below. In the next period C-D, a plurality of printing pins are selectively projected from a printing head (not shown) included in the printing unit while maintaining the printing speed, thereby printing characters on the printing sheet in a dot matrix pattern. Upon completion of printing of the characters of one line, the carriage is decelerated in the next period D-E, and, at the same time, the printing sheet is fed by an amount corresponding to one line by a line feed motor (not shown). The operation of the carriage in the deceleration period is called "stopping operation" below. In the succeeding period E-F, the line feed motor is maintained in a hold state for a predetermined period of time until the vibration of the printing sheet is completely settled. Then, drive control information corresponding to the next line is stored in the control table in the next period F-G. The carriage is then accelerated in the next period G-H until the printing speed is attained, and printing of characters of the next line at the printing speed is executed from time H. However, the prior art printer operating in the manner described above is disadvantageous in that, until characters of one line are completely printed, and the printing sheet is then fed to the position of the next line, preparation of the control table storing the drive control information for the next line as well as the starting operation of the carriage cannot be started. Thus, the prior art printer has the problem that a desired increase in the overall speed of printing operation is difficult to attain. Therefore, it has become necessary to provide a printer in which the line feed from one line to the next and preparation of the control table for storing drive information for the next line can be started simultaneously with the stopping operation of the carriage, so that characters of the next line can be printed as soon as possible. SUMMARY OF THE INVENTION It is an object of the present invention to provide a printer in which the period of time required from the end of printing data of one line to the start of printing data of the next line can be greatly shortened. Accordingly, the present invention provides a method of controlling printing of data by a printer, wherein the printer comprises : a carriage capable of reciprocating movement carrying printing means; sheet feeding means for feeding a printing sheet in a direction perpendicular to a direction of movement of the carriage, and a control table for storing drive control information for the carriage in respect of each line of data printing; said method including the steps of : printing data of one line whilst moving said carriage; preparing the control table for printing data of the next line after completion of printing of the data of the one line; the method being characterised by the steps of : computing, based on the control table, a first period of time (T1) required from a point of time when the carriage has stopped after the completion of printing the data of the one line to a point of time when the carriage is accelerated to printing speed, and computing a second period of time (T2) required from a point of time when the carriage has stopped to a point of time when the operation of said sheet feeding means for feeding the printing sheet to print the data of the next line is completed; comparing said first period of time (T1) with said second period of time (T2) and controlling the movement of said carriage and feeding of the printing sheet by said sheet feeding means so that acceleration of said carriage is started again each time said second period of time (T2) is less than said first period of time (T1). BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a functional block diagram of a printer utilizing a method according to the present invention, Fig. 2 is a system block diagram showing the structure of the printer shown in Fig. 1, Figs. 3A, 3B and 3C are graphs showing the operating characteristic of a CR motor, in which Fig. 3A shows how the speed of the CR motor changes in a normal starting operation pattern, Fig. 3B shows how the speed of the CR motor changes in a high-speed starting operation pattern, and Fig. 3C shows how the speed of the CR motor changes in an inverted starting operation pattern, Fig. 4 is a schematic plan view showing the contents of the control table shown in Fig. 1, Fig. 5 is a system block diagram showing how an interrupt signal is applied to the CPU shown in Fig. 2, Fig. 6 is a timing chart showing the timing of the printing operation of the printer shown in Fig. 1, Fig. 7 is a flow chart showing the steps of a subroutine executed during the printing operation of the printer shown in Fig. 1, and Fig. 8 is a timing chart showing the timing of the printing operation of a prior art printer. DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 is a functional block diagram of a printer utilising a method according to the present invention. Referring to Fig. 1, data receiving device 1 receives character data to be printed from, for example, a computer (not shown). Printing data storage device 3 includes a line buffer 3a storing character information to be printed on one line on a printing sheet (not shown), and character information received by the data receiving device 1 is stored in the line buffer 3a. Control table preparing device 4 prepares control information for driving a carriage (not shown) on the basis of the information stored in the line buffer 3a, and the control information thus prepared is stored in a control table 4a. Printing position shifting device 5 includes a carriage motor (not shown and abbreviated hereinafter as a CR motor) for moving the carriage, and the CR motor is driven according to data stored in the control table 4a thereby causing movement of the carriage. Printing pulse data storage device 6 produces printing pulse data or information for driving a plurality of pins of a printing head (not shown), and the printing pulse data thus produced is stored in a printing pulse data memory (not shown). Printing device 7 includes the printing head to execute printing by selectively projecting the pins from the printing head according to the printing pulse data stored in the printing pulse data memory. Sheet feeding device 8 includes a line feed motor (not shown and abbreviated hereinafter as an LF motor) to feed the printing sheet so as to change the line on which characters are to be printed. Second computing device 10 computes the period of time from the operation starting time to the operation stopping time of the LF motor. First computing means 9 computes the period of time required until, after the operation starting time of the CR motor according to the control table 4a is started, a first printing pulse can be applied from the printing pulse data storage device 6 to the printing device 7. Control device 2 controls the printing data storage device 3, printing pulse data storage device 6, sheet feeding device 8 and first and second computing devices 9 and 10 according to data received by the data receiving device 1 can be printed. Fig. 2 is a system block diagram for the printer shown in Fig. 1. Referring to Fig. 2, a read-only memory 12 (abbreviated hereinafter as a ROM) and a random access memory 13 (abbreviated hereinafter as a RAM) are connected to a central processor unit 11 (abbreviated hereinafter as a CPU), to which the data receiving device 1, printing position shifting device 5, printing device 7 and sheet feeding device 8 shown in Fig. 1 are connected. The control device 2, printing data storage device 3, control table preparing device 4, printing pulse data storage device 6 and first and second computing devices 9 and 10 shown in Fig. 1 are embodied by the combination of the CPU 11, ROM 12 and RAM 13 shown in Fig. 2. The operation of the carriage in the embodiment of the printer shown in Fig. 1 will now be described with reference to Fig. 3. Fig. 3A is a graph showing a normal pattern of driving the carriage (which pattern will be referred to hereinafter as a normal starting operation pattern). Up to time a , the CR motor is held in a preparatory state in which the CR motor is ready to be accelerated (which state will be referred to hereinafter as a preparatory hold state). In a period a-b, the CR motor is accelerated until the carriage is moved at a speed V p (which will be referred to hereinafter as a predetermined printing speed) suitable for printing character data. Such acceleration will be referred to hereinafter as normal acceleration. In the next period b-c, the CR motor is rotating at a constant speed, and the carriage is also moving at the predetermined printing speed V p . Upon completion of one-line printing operation, the carriage is decelerated in the next period c-d until the carriage is stopped at time d . Such deceleration will be referred to hereinafter as stopping operation. Fig. 3B is a graph showing a pattern of driving the carriage at a high speed (which pattern will be referred to hereinafter as a high-speed starting operation pattern). The carriage is driven according to such a pattern when the position of the carriage is remote from the next printing position on the printing sheet. The carriage is moved once at a high speed and is then decelerated to carry out printing by the printing head. Up to time e , the CR motor is placed in the preparatory hold state, and, in a period e-f, the CR motor is accelerated until the carriage is driven at a high speed V SK . In the next period f-g, the carriage moves at the constant speed V SK . Then, in the next period g-h, the carriage is decelerated down to the printing speed V p , and printing by the printing head is carried out in the succeeding period h-i. Then, the carriage is deenergized in the next period i-j until it is stopped at time j . Fig: 3C is a graph showing a pattern of driving the carriage when the carriage located at a position inside a printing zone is first moved to the outside of the printing zone at a constant speed and is then controlled to operate according to the normal starting operation pattern. The pattern shown in Fig. 3C will be referred to hereinafter as an inverted starting operation pattern. Up to time k , the CR motor is placed in the preparatory hold state, and, in a period k-ℓ, the carriage is energized to move in the negative direction. Then, in the next period ℓ-m, the carriage is moved at the constant speed V p , and, in the next period m-n, the carriage is deenergized. Then, in the next period n-o, the CR motor is placed in the preparatory hold state so as to energize the carriage to move it in the positive direction. In the next period o-p, the carriage is energized to move in the positive direction, and, in the next period p-q, the carriage is moved at the predetermined printing speed V p . Finally, in the period q-r, the carriage is deenergized until it is stopped at time r . In the aforementioned printer, the control device 2 decides the range of data to be printed on one line on a printing sheet when a data input is applied from the data receiving device 1, and the data to be printed on one line is stored in the line buffer 3a of the printing data storage device 3. On the basis of the information stored in the line buffer 3a of the printing data storage device 3, the control table preparing device 4 selects one of the three drive patterns described above and decides that the carriage is to be moved according to the selected pattern. Thus, the control table 4a stores a sequence of the drive patterns according to which the carriage is to be moved. As shown in Fig. 4, the address numbers in the ROM 12 are actually stored in the control table 4a, and, at each of the corresponding addresses of the ROM 12, control information for executing one of the drive patterns is stored. The CR motor is connected to a carriage control counter 5a. The control information stored in the ROM 12 is read out in the sequential order of the address numbers stored in the control table 4a, and the initial values are successively set in the carriage control counter 5a so as to drive the CR motor. Referring to Fig. 5, a timer 15 counts pulses generated from an oscillator 14. When the timer 15 counts a pre-set number of pulses, the timer 15 applies an interrupt pulse to the CPU 11, and, in response to the application of the interrupt pulse, the CPU 11 executes a subroutine of interrupt processing for deciding the pattern of the movement of the carriage. The second computing device 10 computes the period of time required until a line feed operation is completed, and the first computing device 9 computes the period of time required until the CR motor is energized to permit printing by the printing head. The operation of the printer having the above structure will now be described with reference to Fig. 6 which is a timing chart showing the timing of the printing operation and Fig. 7 which is a flow chart of the subroutine executed during the printing operation. When now the data receiving device 1 receives information of character data to be printed from an external apparatus such as a computer, the control device 2 decides the range of data to be printed on one line on a printing sheet. Such printing data is temporarily stored in the line buffer 3a in the RAM 13, and a flag demanding printing the data is registered. In a step 50 in Fig. 7, the CPU 11 fetches from the line buffer 3a the information to be printed on one line, and, on the basis of this information, prepares control information to be stored in the control table 4a for controlling the movement of the carriage. (This step 50 corresponds to a period I-J in Fig. 6.) In the next step 51, energization of the CR motor is started according to the control information stored in the control table 4a, and, in the next step 52, whether or not the carriage has reached the printing starting point is decided. (The steps 51 and 52 correspond to a period J-K in Fig. 6.) When the result of decision in the step 52 is "YES", printing is executed in a step 53, and, in the next step 54, whether or not the printing of the data has been completed is decided. When the result of decision in the step 54 is "NO", printing is continued until all the data is completely printed. (These steps 53 and 54 correspond to a period k-L in Fig. 6.) Immediately after the printing of the data is completed, rotation of the LF motor is started in a step 55 to feed the printing sheet until the printing position reaches the next line. At the same time, decision is made in a step 56 as to whether or not data to be printed on the next line has already been stored in the line buffer 3a and a flag demanding printing the data has been registered. When the result of decision in the step 56 proves that the flag has not been registered yet, the step 56 jumps to a step 62 where the series of printing operation comes to an end after both the CR motor and the LF motor are stopped. On the other hand, when the result of decision in the step 56 proves that the flag has been already registered, control information for printing data on the next line is prepared and stored in the control table 4a in a step 57 on the basis of the information stored in the line buffer 3a. Then, in the next step 58, the CR motor is deenergized until it is completely stopped. (The steps 57 and 58 correspond to a period L-M in Fig. 6.) Then, in a step 59, the first computing device 9 computes, according to the control information stored in the control table 4a, the period of time T1 required until the carriage reaches the printing starting position after energization of the carriage is started, and the computed value of T1 is supplied to the control device 2. In a step 60, the second computing device 10 computes the period of time T2 required, from the present time, until the line feed by the LF motor is completed, and the vibration of the printing sheet caused by the line feed operation is completely attenuated, and the computed value of T2 is supplied to the control device 2. At the time of applying a first printing pulse for printing the data on the next line, it is necessary that the line feed operation has already been completed, and the vibration of the printing sheet caused by the operation of the LF motor has been completely attenuated to place the printing sheet in a stable state. Therefore, the control device 2 compares the value of T2 with the value of T1 in a step 61, and the steps 60 and 61 are repeated until the relation T1 > T2 is satisfied. At the time where the relation T1 > T2 is satisfied, energization of the CR motor is started again in the step 51 under control of the control device 2. (This time corresponds to time M in Fig. 6.) In the manner described above, the data is printed on the next line on the printing sheet. The printer as aforementioned is distinguished from the prior art printer in that the operation of the CR motor can be started without waiting for complete stoppage of the LF motor. Therefore, the overall printing speed of the printer is not affected at all by the period of time required for the line feed operation when this period of time required for the line feed is shorter than the period of time required for the starting and stopping operations of the carriage. Further, even when the period of time required for the line feed is longer than the period of time required for the starting and stopping operations of the carriage, an undesirable decrease in the overall speed of printing operation due to the operation required for the line feed can be minimised. The present invention provides a method for controlling a printer comprising sheet feeding means for starting to feed a printing sheet to the position of the next line immediately after data of one line is completely printed and deceleration of a carriage from a predetermined printing speed is started, control table preparing device for storing drive control information for the next line in a control table as soon as the data of the one line is completely printed and deceleration of the carriage from the printing speed is started, first computing device for computing a first period of time required a point of time when the carriage has stopped after completion of printing of the data of the one line until the printing speed is attained again after acceleration of the carriage in a direction opposite to the direction of movement of the carriage during printing the data of the one line so that data of the next line can now be printed, second computing device for computing, after the carriage is stopped, a second period of time required until the operation of the sheet feeding device is completed from the time of stoppage of the carriage, the second computing device continuing to compute the second period of time whenever the carriage is stopped, and control device comparing the result of computation by the second computing device with the result of computation by the first computing device whenever the carriage is stopped, so that acceleration of the carriage is started again each time the result of computation by the second computing device becomes smaller than the result of computation by the first computing device. It will be understood from the feature of the present invention described above that, whenever the carriage is stopped after printing of data of one line, the period of time required for the starting operation of the carriage for printing data of the next line is compared with the period of time required until the line feed operation is completed, and the starting operation of the carriage is started at the time where the former period of time becomes longer than the latter period of time. Therefore, the overall speed of printing operation is not affected at all by the period of time required for the line feed operation when this period of time require for the line feed is shorter than the period of time required for the starting and stopping operations of the carriage. Further, even when the period of required for the line feed is longer than the period of time required for the starting and stopping operations of the carriage, an undesirable decrease in the overall printing speed due to the operation required for the line feed can be minimized.

Claims: A method of controlling printing of data by a printer, wherein the printer comprises : a carriage capable of reciprocating movement carrying printing means (7); sheet feeding means (8) for feeding a printing sheet in a direction perpendicular to a direction of movement of the carriage, and a control table (4a) for storing drive control information for the carriage in respect of each line of data printing; said method including the steps of : printing data of one line whilst moving said carriage; preparing the control table (4a) for printing data of the next line after completion of printing of the data of the one line; the method being characterised by the steps of : computing, based on the control table (4a), a first period of time (T1) required from a point of time when the carriage has stopped after the completion of printing the data of the one line to a point of time when the carriage is accelerated to printing speed, and computing a second period of time (T2) required from a point of time when the carriage has stopped to a point of time when the operation of said sheet feeding means (8) for feeding the printing sheet to print the data of the next line is completed; comparing said first period of time (T1) with said second period of time (T2) and controlling the movement of said carriage and feeding of the printing sheet by said sheet feeding means (8) so that acceleration of said carriage is started again each time said second period of time (T2) is less than said first period of time (T1). A method according to claim 1, characterised by including the steps of : comparing, based on the control table (4a), a remaining time of said first period of time (T1) with a remaining time of said second period of time (T2), sequentially at discrete time points after said carriage has stopped after the completion of printing of the data of the one line; and starting acceleration of said carriage each time it is decided that the remaining time of said second period of time (T2) is less than the remaining time of said first period of time (T1). A method according to claims 1 or 2, characterised in that preparation of the control table (4a) for printing data of the next line is initiated prior to completion of printing sheet feeding by the feeding means (8). A method according to claims 1 or 2, characterised in that preparation of the control table (4a) for printing data of the next line is initiated prior to the carriage stopping after completion of printing of the data of said one line. A method according to claim 1, characterised in that preparation of the control table (4a) for printing data of the next line and feeding of the printing sheet by the sheet feeding means are initiated simultaneously on stopping of the carriage.

Inventors: YAMASAKI KEIICHI, YAMASAKI, KEIICHI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1988
Main classification: B41J19
IPC codes: B41J19, B41J11