IE42322B1 - Serial printer - Google Patents

Abstract

1469586 Printers INTERNATIONAL BUSINESS MACHINES CORP 11 Nov 1974 [26 Dec 1973] 48622/74 Heading G4H A serial printer comprises a movable print element mounted on a carrier itself movable past a plurality of print positions along a print line of a document, the print element having two or more arrays of type characters, each array containing all of a group of commonly used characters and part of a group of less frequently used characters, the print element and carrier being driven so that normally only one of the arrays is presented to a particular print position and other arrays are presented to successive adjacent print positions, there being a print hammer operable to effect impact of a selected type character with the document, and means responsive to the positions of the type characters in the arrays and to a character which is to be printed in a particular print position to inhibit drive of the carrier when the character to be printed is not in the next array to be presented to the print position. As disclosed, drive of the carrier is also inhibited if the distance between successive characters to be printed in their respective arrays is not large enough to allow time for hammer recovery. The print element is shown as a wheel of flexible radial tabs but may be a belt or drum instead. Index pulses from the wheel drive a type counter which indirectly drives an array counter, each character to be printed being used together with the array counter output (specifying the next array) to address a look-up table to determine if the character is in the next array and if so its position. The position of the previous character to be printed, stored in a register, is compared with the type counter output to control hammer firing. The positions of these two successive characters are subtracted, and added to the array length, the result being compared with the hammer recovery time. If there is not enough time, or the latter of the two characters is not in the next array, hammer firing is inhibited and the carrier is stopped, until printing can be resumed. Carrier velocity is always the same when the hammer is fired.

Description

The invention relates to a serial printer which has application in wheel, drum or belt printers.

Printers are known such as described in U.S.Patent No.3,461,225 entitled Data Transmission System and Printer, and relates to a continuously spinning print wheel moved at a constant speed along a print line; and U. S. Patent No.3,707,214 entitled “Serial Printing Device, wherein counters are used to control stepping motors in a start-stop sequence for driving the print wheel and the carriage of a printer to move the print wheel clockwise Or counter-clockwise to select the desired character, and move the carrier right or left to the desired print position.

According to the present invention there is provided a serial printer comprising a carrier moyable past a plurality of print positions along a print line of a document, a print element mounted on the carrier • I and having type bearing elements movable to print in different ones of the print positions on the document, the print element having two or more arrays of type characters, each array containing all of a group of commonly used characters and part of a group of less frequently used characters, means to drive the print element, driving means normally operable to drive the carrier at such a rate that only one of the arrays of characters is presented to a particular print position and other arrays are presented to successive adjacent print positions, a print hammer operable to effect impact of a selected type character with the document, and means responsive to the positions of the type characters in the arrays on the print element and to a character which is to be printed tn a particular print position operable to inhibit operation of the carrier driving means when the character to be printed is not in the next array to be presented to the print position. -242328 In order that the invention may be more readily understood, reference will now be made, by way of example, to the accompanying drawings, in which: FIG.1 is a schematic showing of a portion of a wheel printer.

FIG.2 is a schematic representation of a spoked print wheel utilizing a preferred character arrangement of the type characters.

FIG.3 is a schematic block diagram of a portion of the printer control system for controlling fhe operation of the type carrier in , accordance with the invention.

FIG.4 shows a set of timing curves illustrating fhe operation of the controls in FIG.3.

FIG.5 is a table showing a preferred arrangement of the type characters to be used on the print wheel.

Referring to FIG.1 a laterally sliding carrier I mounted on 15 guides la and lb carries a continuously rotating print wheel 2 driven by a bevel gear 3 which mates with a sliding bevel gear 4 on a spined drive shaft 5 driven by a constant speed electric motor 6. The carrier I is driven by a toothed belt'7 driven by a stepping motor 8. During the printing of any character the carrier I is moved from left to right, but it can be stopped and restarted by appropriate control of the stepping motor 8.

The print wheel 2 comprises a disk having a number of movable type elements such as the flexible spokes or type fingers 9A-Z, etc. Printing of any desired character, 9X for example as shown in FIG .2 is brought about by operating a print hammer 10 which may be actuated -343322 by σ solenoid II, both of which are mounted on the carrier I. When the appropriate type finger such as 9X approaches the printing position the solenoid II actuates the hammer 10 info contact with the type finger driving if info contact with the paper 12. An emitter wheel 13 rotating g with the print wheel 2 cooperates with a magnetic sensor 13a to produce a stream of emitter index pulses for controfling the operation of the printer, one for each character with a home pulse for each revolution of the print wheel, produced for example by having a missing tooth on the emitter 13. The printer controls can thus determine the angular position of the print wheel 2 at any time.

Although the carrier I may be moving at the time of printing any character, .the firing of the hammer 10 is __________ -442322 timed so that the center line of the selected character is correctly aligned with the center line of the print column in which it has been printed.

The number of type fingers on the print wheel 2 js greater than the number of different characters to be printed. The type fingers are divided' into two or more arrays of about equal size as shown in FIG. 2. The most frequently used characters are duplicated in the arrays while the lesser used are placed in one array only. Within each array the most ^frequently^used characters are arranged in the middle with the lesser used characters at the ends. t During printing the motion of the carrier 1 is synchronized with the print wheel 2 so that the carrier 1 traverses exactly one column width as each array of, type fingers passes the printing position. That is to say two or more characters (as many characters as there are arrays on the print wheel) can be printed during each print wheel revolution.

However, this printing rate cannot be maintained continuously. There are two different circumstances in which the printing must be interrupted. (J.) the next character to be printed is found to be absent from the next array to pass the printing position, (2) two successive characters to.be printed are so close to each other on the print wheel that the hammer 10 does not have time to recover after printing the first one before the second character comes around. In either case the carrier 1 must be momentarily halted and then 3θ restarted when another array containing the required character approaches the printing position. One or more print cycles are lost every time this happens; the actual number in any instance depends upon the print wheel layout and on the mechanical characteristics of the carrier drive mechanism. This causes some degradation in the average printing speed. However, analysis of practical configurations shows that the actual printing speed will lie between 90% and 99% of the theoretical maximum; that is: at least 80% faster than it is possible without the use of fhis invention.

Referring to FIG. 3 logic circuitry is shown wherein a type counter 21 responsive to index pulses and reset by home pulses or array end 2 pulses through OR 21a, is connected to the emitter transducer 13a of FIG. 1 for providing a numerical indication of the print wheel type character in the printing position. The output of the type counter 21 is applied to a compare circuit 29 and to an AND circuit 25 for providing a hammer fire pulse for operating the print hammer solenoid 11 through a hammer driver 71. A decode circuit 16 is provided to identify a space designation in the character buffer 33. AND 17 and a position space latch 18 together with inverter 19 inhibit operation of the print hammer fire signal for a space.

The type counter 21 output also drives an.array counter 22 for providing through decode AND circuits 23, delay 24, and single shot 26, and delay 27 and single shot 28, array end 1 and array end 2 signals for each of the arrays of characters on the print wheel 2. These signals occur about 50 microseconds apart at the end of each array in the order designated, first 1 then 2. A lookup table 31 receives as inputs the output of a character buffer 33 (which is the code representation of the character to be printed) and the output of the array counter 22 (which is the binary value of the next array, that will pass in front of the print hammer). -642322 The lookup table 31 produces as outputs a character present signal indicating whether the character in the character buffer 32 is present in the next array, and a binary charI I acter position signal indicating the position of the charI acter in that array. One output from the lookup table 31, namely the next character position, is applied to an AND 33 for operating a register 37 which contains the next character position to be printed. The output of this register is applied to the compare circuit 29 to match with the print wheel position input for controlling hammer fire at AND 25.

An additional preset input quantity is provided by register 40 which is connected to a compare AND 42 together with an output from type counter 21 for determining the time at which the print wheel may be started to maintain synchronous operation. The start compare output from AND 42 is applied to an AND 44 together with an output from a buffer loaded latch 43 which is set fhroughAND 45 by a printer data ready from the system, a buffer not loaded signal, and an array end 2 signal from single shot 28, and is reset through AND 47 by array end 1 signal and carrier run from flip-flop 48. A print enable signal from triggered latch 46 is also applied to the AND 44 along with a character present or a space signal from OR 47.

The signal from AND 44 is applied to a carrier run flip-flop 48 for turning on the carrier drive control 70 to drive the carrier motor 8 as well as gate the hammer fire signal at AND 25 by means of the print enable signal from triggered latch 46.

An additional preset quantity is provided by register 5C and connected to a compare circuit 52 along with the output of the type counter 21 for providing a stop compare -748322 signal for stopping the carrier motor 8. The stop compare signal is applied to AND 54 along with the print enable signal from the triggered latch 46 and the output of an OR 56 for resetting the carrier run flip-flop 48. An inverter 58 is used to connect the character present or space signal input from OR 49 input to the OR 56 for resetting the carrier run flip-flop 48 whenever a character or a space is not present. Inverter 59 connects the buffer loaded latch to OR 56 for resetting the carrier run flipflop 48 whenever the latch is reset.

A compare circuit 60 is provided having as one input a quantity from a preset hammer recovery time register 62, and as the other input the difference between the sum of the output of a preset array length register 61 and the character position from lookup table 31, and the output of the next character position register 37 as determined by arithmetic logic 64. In the event that the output of 64 is less than the preset hammer recovery time.from the register 62 the output of the AND 60 resets the flip-flop 48 through OR 56 and AND 54 to stop the carrier drive motor 8 through carrier drive control 70. Registers 40, 50, 61 and 62 contain, for example seven bit binary coded numbers such as, 0010010, 0011110, 0100111 and 0001001 which are the decimal values 18, 30, 39 and 9, respectively.

Starting with a print wheel 2 rotating and the carrier 1 at rest, the logic shown in FIG. 3 initiates carrier motion at such time that the carrier 1 will just be up-to-speed when the array containing the first character to be printed approaches the printing position. Hereafter printing continues at maximum possible speed. Before printing each character the logic determines -842322 whether it will be possible to print the following character out of the next-but-one array. If not a carrier stop is initiated at the proper time during or just after traversing the last printable column, (depending on the mechanical characteristics of the system, the stop may have to be initiated before the hammer is fired to print the last character.) When the carrier 1 has come to rest the start up section of the logic takes over again and reinitiates carrier motion as described above.

Referring to FIG. 4 the group of curves b show the relationship of the emitter index pulses from the emitter 13 relative to the position of the print wheel 2 in the different print positions shown in a. Upon the occurrence of a carrier start compare signal from the AND 42 of FIG. 3 shown in curve c, the dotted line d shows the sequence for starting and printing two characters. As shown, the carrier run flip-flop 48 is turned on by AND 44 upon the concurrence of the carrier start compare signal from AND 42, a buffer loaded signal from latch 43 in curve h, and a not print enable signal from the carrier drive latch 46. A print data ready signal g from the system is used to turn on the buffer loaded latch 43 producing output h. The carrier run flip-flop 48 is turned on, producing carrier run signal m and activating the carrier drive control 70 to start the carrier drive motor 8. When the character to be printed is in position, the print enable signal n from the print enable latch 46 gates with a print compare signal in AND 25 and causes the print hammer to fire as shown in curve o.

At this time the carrier 1 is up to velocity as shown by' the carrier velocity curve n. -942322 When, the lookup table 31 determines what the next character position is, a character present output will also be produced if this character is in the next array as shown in the curve j. The lookup table 31 determines in this instance that the third character transmitted from the system is not present in the next array so that the OR 56 is activated through inverter 58 and in conjunction with a stop compare signal from AND 52, the AND 54 produces an output to reset the carrier run flip-flop 48 and stop the carrier drive motor 8. This is shown by the dotted line q where the character present signal curve j is turned off, producing a carrier stop compare signal curve e which turns off the carrier run signal from flipflop 48 upon the occurrence of the stop compare signal e as shown at m, so that we skip one cycle because of1 the next character being absent.

The next array does contain the character, so the character present signal is turned on by the lookup table Λ when the array counter 22 is indexed.

Upon the occurrence of the next carrier start compare signal c as shown by the dotted curve r and in . concurrence with a buffer loaded signal at curve h and a not print enable signal in curve n the carrier run flip-flop 48 will be turned.on by an output from the AND 44 to restart the carrier 1 and in this case effect the printing of two characters.

In the instance under consideration it will be assumed that the position of the fourth character printed is too close to the position of the fifth . character in the next array to permit immediately successive printing of the fifth character, so that the arithmetic logic 64 -1042322 produces an output which is compared in compare 60 with the hammer recovery time from register 62, producing an output when there is not enough time for hammer recovery, to energize OR 56, which upon the occurrence of a stop compare signal from curve e resets the carrier run flipflop 48 to stop the carrier motor 8. This sequence is shown by the dotted line s.

The carrier 1 is restarted as shown by the dotted line t upon the occurrence of the next carrier start compare signal from the AND 42, which with the concurrence with a buffer loaded signal from latch 43 and a character present signal from the lookup table 31, produces an output from the AND 44 to turn on the carrier run flip-flop 48.

As shown three characters are printed and then the carrier 1 is stopped upon the termination of the print data, ready signal represented by the curve g indicating the end of the data for printing. This is represented by the dotted line u, the inverter 59 producing an output when the buffer loaded signal drops. This output is applied to the OR 56, and through AND 54 upon the occurrence of a stop compare signal from AND 52, resets the carrier run flip-flop 48, thus stopping the carrier drive motor 8, through the carrier drive motor control 70.

From the above description and the accompanying draw25 ing it will be apparent that 0 simple and effective printer contiol is provided. By utilizing the arrangement shown increased throughput is possible. By utilizing a preferred arrangement of characters and having the print wheel traverse two or more print positions in one revolution in a normal uninterrupted sequence higher printing speeds are obtainable. By providing for carrier -1142322 stop and restart whenever a character to be printed is not in the next array or whenever there is not enough time for hammer reset between characters this arrangement is rendered most effective.

Although the embodiment of the invention described uses a 5 print wheel, the invention may boused with other forms of print mechanism such as drum printers or belt printers. ·

Claims (5)

1. A serial printer comprising a carrier movable past a plurality of print positions along a print line of a document, a print element mounted on the carrier and having type bearing elements movable to print in different ones of the print positions on the document, the print element having two or more arrays of type characters, each array containing all of a group of commonly used characters and part of a group of less frequently used characters, means to drive the print element, driving means normally operable to drive the carrier at such a rate that only one of the arrays of characters is presented to a particular print position and other arrays are presented to successive adjacent print positions, a print hammer operable to effect impact of a selected type character with the document, and means responsive to the positions of the type characters in the arrays on the print element and to a character which is to be printed in a particular print position operable to inhibit operation of the carrier driving means when the character to be printed is not in the next array to be presented to the print position.

2. A printer as claimed in claim I in which said inhibit means comprises means for determining the position in the array of the next character-but-one to be printed, means providing a predetermined count representative of the recovery time of the print hammer, and means effective to inhibit the print hammer actuating and the carrier driving means if the present hammer recovery count of said print hammer is greater than the difference between the next and the next-buf-one character positions of the print wheel. -1342322

3. A printer as claimed in claim I or claim 2 comprising a lookup table containing the position in the next usable array of characters of the next character to print, and means for comparing the output of the lookup table with the output of a counter recording the position of the. 5 print element at the print position.

4. A printer as claimed in claim 3 comprising an array counter connected to said lookup table for determining whether the character for the next character position is in the next usable array of characters on the print element. 10 5* A printer as claimed in claim 3 or claim 4 comprising said lookup table including data for determining whether the next-but-one . character to be printed is in the next usable array of characters on said print wheel, and gate means responsive to the absence of the next-but-one character from the next usable array of characters to inhibit the 15 carrier drive means. 6. A.printer as claimed in any one of the preceding claims 2 to 5 in which said driving is activated by a bistable switch connected thereto and operable to one position in response to the presence of a next character to be printed and operable to another .position in response to an output 20 from the lookup table indicating that the next character is not present in the next usable array. 7. A printer as claimed in any one of the preceding claims comprising -1442322 logic means for determining the difference between the sum of the next character position and a preset array length register output, and the next character position, means providing a predetermined print hammer recovery time quantity, and means to inhibit the carrier driving means if the difference is not greater than the hammer recovery time. 8. A serial printer comprising a carrier movable past a plurality of print positions along a print line of a document, a print element mounted oh the carrier and having type bearing elements movable to print in different ones of the print positions on the document, means to drive the print element and a print hammer operable to effect impact of a selected type character with the document, in which the print positions are uniformly spaced along the print line, the type characters are in a predetermined fixed arrangement on the print element and a carrier driving means is operable to move the carrier along the print Tine at a constant first velocity when the separation of successive type characters to be printed is such that the time required for the print element drive means to present the successive selected type characters to be printed is within the traverse time of the carrier between adjacent print positions and at a modified second velocity between adjacent print positions when said separation is such that said time required exceeds said traverse time, the modified second velocity comprising deceleration from said first velocity at one print position to zero and acceleration to said first velocity at the next adjacent print position. 9. A printer according to Claim 8, in which the print element is a type wheel. 10. A printer according to Claim 9, in which the type wheel is constantly rotatable. 11. A printer according to any of Claims 8 to 10, including means for determining the times required for the print element drive means to present successive selected type characters and means responsive to the determining means to operate the carrier driving means at said first velocity or at said modified second velocity during relative movement of the print element on the carrier. 12. A printer according to Claim 11 in which the determining means includes means for ascertaining during printing the relative positions on the print - 15 42322 element of successive characters to be printed at successive adjacent print positions, and means responsive to the ascertaining means to operate the carrier driving means at said constant first velocity or said modified second velocity. 13. A printer substantially as described herein with reference to

5. Figures 1 to 4 of the accompanying drawings. Dated this 30th day of December, 1974. BY:— TOMKINS & CO.,