US 3884339 A
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United States Patent Castoldi et a1.
ASYNCHRONOUS SERIAL PRINTER Inventors: Fabrizio Castoldi, Milan; Serrio Cattaneo, Voghera; Adriano Niccolai, Cornaredo, all of Italy Honeywell Information Systems Italia, Milan, Italy Filed: Mar. 6, 1973 Appl. No; 338,499
Related US. Application Data Continuation of Ser, No. 108,787, Jan. 22, 1971, abandoned.
US. Cl 197/53; 101/93.19 Int. Cl B4lj l/32 Field of Search 101/93 C, 110; 197/16,
References Cited UNITED STATES PATENTS Masterson 101/93 C MacDonald et a1. 101/93 C May 20, 1975 3,215,985 11/1965 Marsh 101/93 C 3,356,199 12/1967 Robinson 101/93 C X 3,406,625 10/1968 Chamness et al 197/55 X 3,599,772 8/1971 Comstock 197/49 3,651,916 3/1972 Becchi 197/18 X Primary Examiner-Edgar S. Burr Assistant Examiner-R. T. Rader Attorney, Agent, or Firm-Fred Jacob  ABSTRACT In an asynchronous serial printer wherein a character bearing member is mounted on a carriage which is moved step-by-step along the print line and wherein the character bearing member is continuously rotating so as to move the characters thereon through a printing position with a velocity parallel to the print line, the striking hammer firing is subjected to a temporal correction to provide for printing in the proper printing position irrespective of the displacement of the carriage from such position and irrespective of the carriage speed.
7 Claims, 13 Drawing Figures PATENTEB HAY 20 I975 SHEET 10F 7 Fabrizio CASTOLDI $er i0 CA TTANEO dn'ano NICCOLAI INVENTORS.
SHEET PM 7 FIG. 2
Fa brizio CASTOLD/ Sergio CATTANEO Adriano NJCCOLAI INVENTORS BY I ATTORNEY I PATENTED 3,884,339
SHEET 3 OF 7 FIG. 9
Fagrl z lo CASTOLD/ Sergio CATTANEO Adriano NICCOLA/ INVEN TORS.
'TTORNEY Pmgmgmmoms 3,884,339
SHEET 50F 7 I 102, 7 IF U l I R E% m I 107i 110 I 106 I I 1m I I 114 I 103 I V I V III8\ I 104 v I I I 199 I II II I I 144 l I I J I I 747 I I 151 I I I I I I I I FIG. 10
CASTOLDI CA TT'ANEO NI CCOLAI INVENTORS.
PATEN'E'ED HAY 2 0 i975 SHEET 8 BF 7 FIG.
M NO 0 L E I T ON A E STOV ATCN C C N w 0 h a r.. F k M ATTORNEY.
Emm m 2 mm SHEET 7 OF 7 CAS'TOLDI CATTA NEO Serglo Adriano NI'CCOLAI INVENTORS.
ASYNCHRONOUS SERIAL PRINTER This is a continuation, of application Ser. No. 108,787, filed Jan. 22, 1971, now abandoned.
BACKGROUND OF THE INVENTION The present invention relates to impact type serial printers used in data processing systems and more particularly to printers which employ the on-the-fly principle of printing.
In on-the-fly serial printers, the characters to be printed are distributed along the outside surface of a wheel or drum which is maintained in continuous rotating and printing is accomplished when the character to be printed is in correspondence with a pre-established printing position. One type of such printer, known as back striking printer, provides an inking member and print receiving medium interposed between the character member and a printing hammer. Another type, known as a front striking or platen printer, provides that the printing hammer and character member act from the same side with respect to the print receiving medium to impress such medium against a resisting sur face. In the second type, the character member has the form of a flexible belt or of a cup or disc with cantilevered fingers on which the characters are located.
In serial printers, the character member and the printing hammer are mounted on a printing carriage, which is usually displaced with uniform motion, or in steps, along the entire print line so as to occupy all of the printing positions in succession. From the functional point of view, the distinction between synchro nous and asynchronous printers of this type is very important. Synchronous serial printers are characterized in that the character member and the printing hammer are displaced according to a predetermined synchronous relationship with the rotation of the character element. This synchronous relationship is imposed by positive mechanical couplings linking different movements. Synchronous printers are particularly suitable for constant speed printing, but are not suitable for the typewriting form of printing which conversely requires the capability of stopping the printing carriage after each character has been printed.
Thus, on-the-fly asynchronous serial printers are characterized by step-by-step displacement of the printing carriage from one printing position to the next and by the absence of any correlation between the motion of the printing carriage and the rotaion of the character element. Asynchronous printers are particularly suitable for the typewriting form of printing, i.e., wherein printing commands are issued from a keyboard. However, asynchronous printers are slower, because during the time of displacement of the carriage, it is not possible to accomplish printing and, therefore, such printers are less suitable to printing under control of an electronic computer. Moreover, asynchronous printers usually are more complex and costly than synchronous printers.
A proposed interim solution consists of altering a synchronous printer to make it asynchronous by equip ping it with a suitable mechanical carriage release. Such a solution requires solving serious problems of a mechanical nature, primarily those relating to the life and resistance to wear of such devices, and such solution reduces considerably the reliability of such devices.
Accordingly, it is the object of this invention to obviate the aforesaid disadvantages of prior art asynchro' nous printers.
Another object of this invention is to provide an improved asynchronous printer.
SUMMARY OF THE INVENTION According to the instant invention, such disadvantages are eliminated with a converse system, which may be defined as synchronization of an asynchronous printer, such synchronization being realized by means of electronic devices and, therefore, not jeopardizing the printer reliability. With such synchronization the time required to move the printing carriage may also be employed for the printing operations, thus considerably increasing the overall operating speed. In addition, because it is no longer necessary to regularly halt the carriage in the various printing; positions to effect the printing, it is possible, in many instances during sequential character printing, to drive the carriage at a constant velocity, there by achieving a substantial reduction in the mechanical stresses and a subsequent increase in reliability.
BRIEF DESCRIPTION OF THE DRAWING The invention will be described with reference to the accompanying drawing, wherein: I
FIG. 1 is a perspective view of a state-of-the-art onthe-fly ansynchronous serial printer to which correction or electronic synchronization may be applied according to the invention;
FIG. 2 shows schematically and in part the character member of the printer of FIG. 1, and demonstrates the path of a character due to the superposition of two movements, that of the character member and that of the printing carriage;
FIG. 3 is a perspective view of a character member which can be used with a striking member having two distinct hammers and which can be selectively employed in the printer of the invention;
FIGS. 4, 5 and 6 are perspective views of other types of character members which can be employed in the printer of the invention;
FIG. 7 is a diagram of the curves of acceleration, speed and displacement of the printing carriage for a printer of the type of FIG. 1, and illustrates the correction made at the moment of printing according to the invention;
FIG. 8 is a diagram of approximate correction curves which can be used to apply the correction at the moment of printing in a discontinuous mode according to the invention;
FIG. 9 is a block diagram of one of the preferred forms of apparatus for realizing printing correction according to the invention;
FIG. 10 is a block diagram of a complete printing system with one of the preferred forms of apparatus for realizing printing correction;
FIG. 11 is a block diagram of an alternative form of the system shown in FIG. 10;,
FIG. 12 is a diagram of correction curves modified to take into account deviations in the behaviour of the printing carriage; and
FIG. 13 is a block diagram of one form of a counter circuit used in a preferred form of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT Before examining in detail the different embodiments, the invention will be considered generally. The mechanical structure of a printer of a type to be driven and synchronized electronically according to the invention is shown in FIG. 1, and includes a frame 1 in which are disposed the various parts that provide for movement of the print-receiving medium, the inking ribbon and the printing apparatus. For simplicity and clarity, only the essential parts are shown.
The different characters of the printing assembly are provided in relief, each one at the end of a flexible finger 2. Fingers 2 are distributed circumferentially to form a star or daisy shaped type carrying or character member 3, which is maintained in rotation at a constant velocity by a suitable motor means 4.
Character member 3 and motor means 4 are mounted on a carriage 5, which slides on guides 14 and is driven by positive transmissions 6 from a motor means 7 so as to occupy different positions in succession along guides 14, each such position corresponding to a printing position. Motor means 7 may comprise a low inertia motor, such as a printed circuit motor, coupled to a printing position detector 8, which identifies the different printing positions. Alternatively, motor means 7 may comprise a step motor, in which the rotor assumes a plurality of well-defined angular positions which correspond to the printing positions.
A printing hammer 9 is mounted on carriage in a suitable position. An electromagnet 10 drives hammer 9. The head of hammer 9 is disposed in close proximity to the periphery of character member 3 in a region where the direction of motion of the characters due to the rotation of the character member is substantially parallel to the print line. When electromagnet 10 is energized momentarily the end of the flexible finger 2 which at that moment is opposite the head of hammer 9 is driven against the inking ribbon 11, the printreceiving medium 12, and the rear resisting surface 13, whereby the particular character on the end of such driven flexible finger prints on-the-fly.
The sensing of the precise moment in which electromagnet 10 is to be energized is accomplished by a character position detector, which comprises, for example, a code or timing disc integral with the character member and a magnetic or optical pickup 16 rigidly affixed to carriage 5.
The mode of operation of a printer of the type shown in FIG. 1, according -to the present state of the art, provides for two distinct phases which do not overlap. In the first phase printing carriage 5 is displaced from one printing position to the next. In the second phase the printer must wait until the finger bearing the character to be printed is recognized by the character position detector as being in the proper printing position. Because there is no correlation between the movement of carriage 5 and the rotation of character member 3, this second phase waiting time, or latency time, is variable between a minimum value of virtually zero and a maximum value of the character repetition period, which is the interval between two consecutive passages of the same character through a printing position.
Without the teachings of the instant invention, overlapping of the two phases described is not possible. Thus, without the teachings of the instant invention,
printing during the carriage movement phase cannot be properly effected, even though during such movement the finger bearing the character to be printer might be recognized by the character position detector, because such printing would result in a printer image displaced laterally with respect to the correct printing position, i.e., in an offset position. According to the teachings of the instant invention, this disadvantage is eliminated and overlapping of the two phases is made possible by an appropriate correction in the moment of energization of electromagnet 10. The combined effect of such a correction and of .the peripheral velocity of the character member introduces a lateral displacement substantially equal and opposite to thatof the carriage from the correct printing position.
The criterion employed for determining the correction to be applied is shown in FIG. 2. The lines 20 and 21 represent the respective central vertical axes of two adjacent printing positions 22 and 23 denoted by respective rectangles. Points 24 and 25 represent the centers of rotation of the character member when the printing carriage is positioned properly for printing in respective positions 22 and 23.
Assume, now, that the alphabetic character A is to be printed in printing position 22, that character A is provided on finger 26, and that the printing carriage is properly positioned and halted so that the center of rotation of the character member is point 24. In this instance, when finger 26 is at the angle shown, a particular angle in advance of printing position 22 which is termed the advance angle a, the printing electromagnet is energized, whereby the actual printing occurs directly in printing position 22. This advance angle is necessary because the printing occurs on-the-fly, i.e., with a character having a peripheral velocity V, and because the printing hammer requires a finite time, approximately a millisecond, to complete the printing. The proper moment for energizing the electromagnet is sensed by a character position detector, the corresponding finger position, for simplicity, being represented in the Figure by a point 27. When the axis of finger 26, in rotating around point 24, passes through point 27 the electromagnet is energized. The pickup of the character position detector, meanwhile, is rigidly affixed to the printing carriage, so that its position relative to the center of rotation of the character member is invariant.
Assume, next, that the character A is to be printed in printing position 23, that the printing carriage is moving toward printing position 23, that the instantaneous position of the center of rotation of the character member is point 28, and that at this moment the axis of finger 26 passes through the point 27, where point 27 represents the finger position at which the character position detector identifies the character to be printed. If printing is initiated under these circumstances, without correction, the character is not printed in the cor rect position 23, but in a position whose center is denoted by the point 29. Point 29 does not lie precisely on the line perpendicular to the direction of. motion of the carriage which passes through point 28, the center of rotation of the character member when the character to be printed is sensed or identified, but is slightly displaced toward the right. This displacement occurs because the carriage, during the hammer delay time, moves with a velocity V,. The velocity V is not, in general, sufficient to eliminate the lateral offset of the printed image from the correct printing position.
However, if the moment of energizing the electromagnet is suitably delayed by a correction time, t the character image can be printed in the correction position 23, though with a very slight tilt. Using a mathematically exact expression the correction time is determined by the equation:
where t, is the correction time, V is the peripheral velocity of the character member, d is the distance by which the center of rotation of the character member is in advance at the correct printing position when a character to be printed is sensed, t is the time at which the character is sensed, and t,, is the hammer delay time.
Different approaches may be taken to determine the necessary correction time defined by the above equation. For example d and V may be expressed as a function of time, starting from the moment in which the carriage departs from a correct printing position. This requires a knowledge of the law of the motion of the carriage and an assumption of good repeatability of the printing carriage behaviour, which is permissible with a suitable choice of motor devices and control circuits. In such instance, the correction may be made as a function of the elapsed time from the moment of departure from the immediately preceding printing position. Thus, there will be provided in this instance a correction circuit which introduces a correction time, t based exclusively on a measure of time. However, if the repeatability of the printing carriage behaviour in its movement is not adequate, it is possible to make a correction based on an actual measurement of the spaces or a correction based on an actual measurement of the distance d, and the velocity V possibly combined with a time measurement. The preferred solutions for the realization of the correction will be described in detail hereinafter.
As a conclusion to the general information provided above, certain secondary implications of the proposed printing control system follow. First, the printing hammer must have a sufficient transverse dimension to provide for printing a character in either of two adjacent positions. Therefore, to avoid the simultaneous printing of two adjacent characters it is necessary that the characters be sufficiently spaced on their supporting character member.
Alternatively, however, for front printing, two hammers of suitable width may be employed, the two hammers being overlapped opposite a character member of the type shown in FIG. 3. In such character member, alternate fingers have near their extremities a projection cooperating exclusively with a respective one of the two hammers, thereby forming two different series of fingers. Second, when a character is printed while the printing carriage is'moving, the introduction of the printing time correction causes the character image to be slightly tilted. The amount of image tilt depends on the character member rotation angle necessary to correct for the displacement from the printing position. If the character member comprises an assemblage of more than 60 characters distributed along the circumference thereof, the amount of image tilt is not sufficient to substantially affect the printing quality. However, it is evident that such image tilt may be eliminated or reduced by the use of a cylindrical or cone shaped character member as, for example, shown in FIGS. 4 and 5 or bythe use of a belt or chain character membe shown in FIG. 6.
SYSTEM FOR CORRECTING THE TIME OF PRINTING AS A FUNCTION OF TIME This correction system assumes good repeatability in the behaviour of the printing carriage during its movement. As a first example of this hypothesis, it will be assumed that all steps of the carriage are completed in the same elapsed time, T,,, where T, 10 ms. During the first 5 ms of this T interval the carriage receives a uniform acceleration of a 0.1 ms 1 and during the remaining 5 ms it is braked with an equal and opposite deceleration. These values given by way of example are actual values or approximate those occurring in many serial printers of this type, whether the carriage movement is obtained by means of step motors or low inertia motors, such as printed circuit motors.
With these assumed values, the carriage completes its movement in steps of 2.5 mm, equal approximately to 1/10 inch, which is the most common spacing between adjacent printing positions in the typewriters and highspeed printers used in data processing systems. For this simple example, it is possible to obtain the space-time relationship of the carriage, and it is therefore simple to calculate the integral term in the preceding equation and its solution.
Thus, in the most general case, it will always be possible, at least experimentally, to define what correction must be made. FIG. 7 is a diagram of the acceleration (curve a), the velocity (curve b) and the distance (curve c) as a function of the time. The axis of abscissae and the horizontal line e identify, on the axis of ordinates, the distance between two adjacent printing positions. The curve d represents relative to line e the printing correction to be made, expressed dimensionally as a distance, i.e., the quantity denoted by r v.
FIG. 7 also demonstrates a simple graphical construction for obtaining curve d from the curve of the distance and from the other parameters involved. If t denotes any time at which a timing signal occurs identifying a character to be printed, the position occupied by the carriage at that instant corresponds to point A on the distance curve 0. Since I, is the delay time of the hammer, for example 1 msec., the position the carriage would occupy at the moment of printing would be point B, if no correction were applied. Through point B a perpendicular is drawn, to meet line e at point C and the axis of abscissae at point D. A segment DE is laid off corresponding to the correction time required foran entire printing position spacing. Point F, the intersection of the line connecting point C and point E with curve 6, defines the segment GF, which represents the correction time t necessary to correct for the distance CG. Therefore, correct printing occurs precisely when the position of the carriage is represented by point F and the correction time made at time t, is determined by the segment Il-I, where point H is the intersection of a horizontal line drawn through points G and F with the vertical line drawn through point 1,. Accordingly, correction curve d may be readily generated from points such as point H.
FIG. 8 illustrates how the correction curve for the above-mentioned example may be closely approximated by the broken line curve LMNOP. In this curve the slope of segment LM is equal to that of segment NO, and segment OP is horizontal. The broken line curve LMNOP may be replaced, in turn, to a good approximation by a broken line curve having steps of equal height and varying widths. Therefore, without substantial error, the correction may be provided in a discontinuous manner, leading to the possibility of using preferred digital type techniques and circuits instead of analog circuits. Digital technology is preferred for reasons of providing uniformity with the other logic circuits that drive the printer. In the curve of FIG. 8, by way of example, the height of the individual steps has been chosen to represent one thirty-second of the printing position spacing, corresponding to about 0.08 mm. The width of the steps represents about 210 ts in the curve portion with the greater slope and 420 as in the portions with less slope. The maximum difference between the broken line curve of correction and the corresponding exact curve does not exceed one-tenth of a millimeter, which is completely irrelevant in practical effects.
A block diagram of a logic arrangement representing a preferred embodiment for providing the necessary correction is shown in FIG. 9. The signals arriving from the timing device, or character position detector associated with the character member are transmitted on an input lead 50 to a logic circuit comparator 52. A code corresponding to the character to be printed is applied to comparator 52 on an input lead 51. When the code represented by the signals arriving from the timing device is the same as the code of the character to be printed, comparator 52 transmits a coincidence signal on output lead 53, which signal is used to control the correction circuits and subsequently the printing.
These correction circuits comprise an oscillator 54, a counter 55 and decoding networks 56 and 57. Oscillator 54 is designed for operating at different and suitable frequencies, according to conditions imposed by decoding network 57 and the coincidence signal on lead 53.
Oscillator 54 is started by a starting signal which is received on input lead 58 simultaneously with the start of the printing carriage, whereby oscillator 54 produces a train of pulses which steps counter 55 from a predetermined initial state. For the example of FIG. 8,
counter 55 is initially in a state representing the decimal 2, and counts to a state representing the decimal 5. When the counter output reaches a state representing a value equal to or exceeding the decimal 5, decoding network 57 applies to oscillator 54 a signal which doubles its frequency of oscillation. The counter now is stepped at a doubled rate to a state representing the decimal 27. At this point decoding network 57 no longer supplies the signal which doubled the frequency, and oscillator 54 resumes oscillating at the initial frequency until counter 55 reaches the state representing the decimal 32 or 00. A stop signal is then transmitted by decoding network 56 to halt oscillator 54.
If the coincidence signal from comparator 52 is received by oscillator 54 when counter 55 has reached a representation of the decimal 32, which denotes that the printing carriage has reached or nearly reached the printing position, no printing correction is necessary. The coincidence signal, arriving on output lead 53, is
thereupontransferred through decoding network 57 to an output lead 59 and initiates energizing of the printing electromagnet. However, if the coincidence signal is received while the oscillator is in operation, its frequency is appropriately modified so that counter 55 is stepped at a suitable speed until it reaches the state corresponding to the decimal 32. Only then does decoding network 57 issue a printing signal to energize the printing electromagnet.
The counter introduces a delay in delivering the printing signal of I (32 N)/f, where N is the state of the counter at the instant in which the coincidence signal is applied to oscillator 54 and f is the modified oscillation frequency. For example, if the peripheral speed of the character member is V 4 m/sec, the required counting frequency, f, must be such as to introduce a correction of 2.5 mm while counting from 0 to 32; i.e.
4 32 4 51,000 pulses/sec.
Therefore, in this instance the corresponding pulse repetition period must be 19.6 [.LS. By employing a peripheral speed of V 3.80 m/sec. this pulse repetition period may be made 21 ,us, i.e., one-tenth of the period of variation of the correction time (FIG. 8). This peripheral speed adjustment of the character member is easily obtainable, and permits the use of a constant frequency pulse generator followed by suitable digital type frequency dividers, i.e., counters. This arrangement may also be employed when the character member peripheral speed must be higher, for example V 5 m/sec.; it being sufficient that the pulse generator period be a submultiple of the period of variation of the correction time. This solution is adopted in the complete printing system of FIG. 10.
FIG. 10 represents the entire printing system by the reference numeral 101. Printing system 101 is controlled by an electronic control unit 100, which is known in the art and which may consist of an electronic central computer unit or a particular control unit for the printing system. Connection between the control unit and the printing system is provided by a set of wires for exchanging signals, commands and information, which in its entirely is termed the interface. The division shown between control unit and printer peripheral device is manifestly exemplary, inasmuch as the particular electronic circuits shown in the peripheral device may be incorporated in the control unit.
The interface between control unit and printing system 101 of FIG. 10 includes a command lead 102 on which space command pulse signals are transmitted, i.e., pulses which start the printing carriage moving along the print line, and a set of leads or data channel 103 on which are transmitted continuous signals representing in binary code the character required to be printed. Associated with data channel 103 is a lead 104 for enabling recognition of the character to be printed. Accordingly, the character code on channel 103 is acknowledged by printing system 101 only when the code is accompanied by a suitable signal on lead 104. Two leads 105 and 107 complete the interface. Lead 105 transmits a pulse signal from printing system 101 to control unit 100 for providing notification that a printing operation has been initiated. This signal on lead 105 is used by the printing system to control the printing through a lead 106, and by control unit 100 tostart subsequent operations. Lead 107 transmits a pulse signal to control unit 100 to provide notification that a spacing operation has been completed. The signal on lead 107 is generated by a position detector T, associated with a motor unit M which provides for the displacement of the printing carriage 108.
The starting' signal for the spacing operation is received from lead 102 by regulation circuit R. Circuit R is coupled to motor unit M through supply leads 109 to provide for starting motor unit M and for controlling its operation according to a predetermined rule, for example, with constant acceleration and deceleration.
On printing carriage 108 is mounted a character position detector or pickup 110 proximate to the character member which is maintained in continuous rotation. For every character which reaches registration with the printing hammer, pickup 110 generates a pulse. The series of character pulses delivered by pickup 110 is transmitted on a lead 111 to a code counter 112, the state of which progresses according to a predetermined rule. Counter 112 produces on its output leads 113 signals representing a binary code corresponding to the different characters on,the character member. The character position detector also produces a zero or reset signal which identifies the first character of the character member, or a well-defined position of the character member. The reset signal is transmitted on a lead 114 to reset counter 112.
Data channel 103 and output leads 113 apply to a comparator 115 the respective binary codes corresponding to the character required to be printed and the character which is in registration with the printing hammer. Comparator 115 compares the two codes received thereby and, delivers a coincidence-pulse on output lead 116 when the two received codes are alike, or match. l
The portion of the apparatus of FIG. thusfar described, being conventional and well known in the art, is, accordingly, described only briefly herein. In the conventional printers the coincidence pulse is used in fact, to control the printing electromagnet. However, in accordance with the instant invention such pulse is suitably delayed by means of circuit elements described hibiting an AND-gate 123 so that on the signal on the output lead 124 thereof cannot be at the logic level representing a binary ONE. Lead 124 is connected to the respective reset input terminals 125 and 126 of flip-flop 120 and counter 121.
Accordingly, whenthe starting pulse signal initiates a spacing operation, flip-flop 120 is transferred to the set condition by virtue ofthe starting pulse applied to input terminal 127 thereof and the absence of a signal on reset input terminal 125. At the same time, counter 121 is transferred to a predetermined preset state by virtue of the starting pulse applied to a preset input terminal 128 of counter 121 and the absence of a signal on reset input terminal 126. As a consequence output lead 129 of flip-flop 120 delivers a steady signal at the logic level representing a binary ONE, and output channel 130 of counter 121 delivers a pattern of steady signals corresponding to the preset binary code and representing, for example, the decimal digit 2.
The signal on lead 129 is applied to the control input terminal of a pulse generator 131, which responds to such signal to'commence operation. The pulses produced by generator 131 are applied to the input terminal of a frequency divider 132, which provides for the division; for example by 10 of the frequency of the pulses received thereby. The pulses delivered by generator 131 are also applied to one input terminal of an AND-gate 133.
The pulses delivered by frequency divider 132 are applied to the input terminal of another frequency divider 134, which provides for a further division by two, and to one input terminal of an AND-gate 135. The pulsed delivered by divider 134 are applied to one input terminal of an AND-gate 136.
The group of logic elements comprising AND-gates 133, 135, and 136, NOT circuits 137 and 138, and OR- gate 139 forms a network which responds to the occurrence of certain conditions to selectively apply to input terminal 140 of counter 121 a train of pulses which has the frequency of the pulses produced by generator 131,
one-tenth of such frequency, or one-twentieth of such frequency. This pulse train controls counter 121 to count at a variable rate. The: conditions for modifying this counting rate are represented by signals supplied on respective leads 141 and 142.
A binary ONE signal is delivered on lead 141 after a match occurs between the code of the character required to be printed and the code of the-character effectively in the printing position provided that the enabling signal on lead 104 is present. If these two conditions are satisfied, an AND-gate 143 applies a signal to the set input terminal of flip-flop 144, thereby setting flip-flop 144, which was, initially in the reset state. With flip-flop 144 in the set state, the output signal thereof provides a steady level on lead 141, thereby enabling AND-gate 133, so that the original pulse train produced by generator 131 is transferred through the OR- gate 139 to counter 121. At the same time, this output signal of flip-flop 144 is inverted through NOT circuit 137 and applied toinhibit AND-gates 135 and 136.
A binary ONE signal is delivered on lead 142 only for certain states of counter 121, as recognized by a decoding network 145. In the instant example, these states correspond to the decimal numbers 2, 3, 4, 5 and 27, 28, 29, 30, 31. For these states, the binary ONE signal on lead 142 enables AND-gate 136 andinhibits AND- gate 135. The converse operation of AND-gates 135 to the decimal numbers 6-26.
When the state of counter 121 corresponds to the decimal 00 a decoding network 146 delivers an output signal, which is transmitted on leads 149 and 150 to AND-gates 123and 147. If there isno space command signal on lead 102, the output signal of network 146 is transferred through AND-gate 123 to halt counter 121, by acting on its reset input terminal 126, and to halt pulse generator 131, by resetting flip-flop 120. The output signal of flip-flop 144 enables the output signal of network 146 also to be transferred through AND-gate 147 to provide a control signal for the printing electromagnet on lead 106 and to denote in execution to control unit 100 on interface lead 105. The output signal of AND-gate 147 is of the pulse type, as a consequence of its delivery on lead 151 to a delay circuit 148, which may comprise a one-shot, whose output signal, in turn, is applied to reset flip-flop 144.
The operation of the system of FIG. 10 may be described briefly as follows:
Case A Printing when the spacing operation has been completed. In this instance, the spacing operation is initiated by a pulse signal on lead 102. This signal causes 7 simultaneously the setting of flip-flop 120, the presetting of counter 121, and the starting of pulse generator 131. Counter 121 thereupon counts at the minimum rate from the state representing the number 2 to that representing the number 5. At this point AND-gate 136 becomes inhibited and AND-gate 135 becomes enabled, whereupon counter 121 counts at twice its initial rate until the state representing the number 27 is reached. At this point once again AND-gate 135 is inhibited and AND-gate 136 enabled, whereupon counter 121 again counts at the minimum rate, halting at the rest state 00. A steady signal now appears on lead 149.
Simultaneously with the stepping of counter 121, the spacing operation is being accomplished under control of regulation circuit R, and printing carriage 108 halts in the position at which a character is to be printed. When the desired character reaches the printing position, due to the rotation of the character member, comparator 115 delivers a signal which is transferred through AND-gate 143 and sets flip-flop 144, which in turn delivers a signal through AND-gate 147 as the printing control signal on lead 105, all substantially without delay.
Case B Printing when the spacing operation is being performed. In this instance, comparator 115 delivers a coincidence pulse while counter 121 is still counting. This pulse sets flip-flop 144, whose output signal then changes the counting rate of counter 121 to the maximum rate imposed directly by the frequency of pulse generator 131. Counter 121 continues to count at this maximum rate until it reaches the rest state 00. The delay before the rest state is reached depends on the intermediate state from which the fast counting starts. Only when the state is reached is the character printing commanded.
The previous description relative to the printing system of FIG. 10 has illustrated the use of the spacing execution time for accomplishing correct character printing. However, the performance of the system may be further enhanced by additional improvements. Thus, if the printing of a character in a predetermined printing position is completed before the printing carriage reaches such position and while it is still in the acceleration phase, braking the carriage to stop it in the printing position and then starting it immediately thereafter is unnecessary. Instead, it is preferable for the carriage to continue at a constant velocity until it reaches the It is possible to verify after the construction of the correction diagram, that this correction time may be provided by the same circuit described above, provided that at the beginning of the next spacing operation counter 121 starts from a different preset state, for example, representing the decimal 0.
FIG. 11 represents a printing system provided for this improved form of operation. The system of FIG. 11 comprises all of the logic circuits and elements shown and described with reference to FIG. 10, and includes the following additions:
Interface: Leads 200, 201 and 202 are added between control unit and printing system 101. A signal on lead 200 controls the continuous movement of printing carriage 108. Lead 201 transmits a pulse signal to notify control unit 100 that a character is being printed during the acceleration phase, so that printing carriage braking is not necessary. Lead 202 transmits a braking beginning signal, concurrent with which control unit 100 either applies a signal to lead 200 to control the printing carriage to continue in motion at a constant velocity, or removes such signal to brake the carriage.
Correction network: Decoding network 203, for recognizing the counter state corresponding to the number 22, and AND-gate 204 are added. Although not shown, counter 121 is modified internally to accept an additional signal on input terminal 205, which additional signal together with the signal applied to preset input terminal 128 presets counter 121 to a state corresponding to the number 10.
Lead 200 applies a signal to regulation circuit R of motor unit M for controlling the displacement of the printing carriage at' a constant velocity for the entire spacing between the central axes of two adjacent printing positions, and in the limit, if such signal is applied continuously, the carriage is continuously displaced at constant velocity. The signal supplied by lead 200 is also applied to input terminal 205 of counter 121.
Decoding network 203 delivers a pulse on lead 206 each time counter 121 reaches a predetermined state, corresponding for example to the decimal number 22. Such pulse is transferred through AND-gate 204 to lead 201 only if a second input signal is received by AND-gate 204 from flip-flop 144. Thus, a pulse is deliverd on lead 201 only when the printing operation .is initiated during the acceleration phase of the printing carriage.
Until the output signal of flip-flop 144 intervenes to change the counting rate of counter 121, there is precise correspondence between the states of counter 121 and the instantaneous positions occupied by the printing carriage, and the counter state corresponding to the decimal number 22 is close to the moment in which, normally, the braking phase starts. However, if the output signal from flip-flop 144 appears on lead 141 before counter 121 reaches state 22, the braking phase has not yet been reached, and counter 121 is stepped very rapidly to state 22 to provide the pulse on lead 201. Conversely, if the output signal from flip-flop 144 appears on lead 141 after counter 121 has reached state 22, no pulse is provided on lead 201.
The operation of the system of FIG. 11 may be described as follows: The control unit 100 transmits a space command signal on lead 102. The printing carriage starts to move, counter 121 is preset to state 3,
and pulse generator 131 is started. Control unit 100 transmits on channel 103 signals representing the code of the character required to be printed. If a match occurs between the code representing the character in the printing position and the code representing the character required to be printed before counter 121 progresses to state 22, a pulse signal is delivered on lead 201 and, after appropriate delay, the printing is initiated.
Control unit 100 receives the signal on lead 201 and responds thereto to select one of the following opera-.
tions to be accomplished:
If another character is not to be printed, no further signal is transmitted to system 101, whereupon regulation circuit R provides for stopping motor unit M and printing carriage 108.
If another character is to be printed, control unit 100 transmits as soon as possible, but not after the reception of a braking beginning signal on lead 202, a continuous movement control signal on lead 200. In this manner, the printing carriage proceeds at constant velocity. As the printing position in which printing already has been accomplished is reached, position detector T delivers a signal on lead 107. Control unit 100 responds to the signal on lead 107 to transmit a new space command signal on lead 102, which presets counter 121 to state 10. Control unit 100 also transmits on channel 103 a new character code.
A match can occur again between the code of the character required to be printed and the code of the character in the printing position during the constant velocity phase, so that the printing carriage continues to advance at constant velocity. If this match occurs late, i.e., after the position detector T has issued on lead 202 a signal denoting the midposition of the spacing between two printing positions, or if there are no futher characters to be printed, the continuous movement control signal on lead 200 is terminated and the printing carriage is braked. In this manner, a two-fold advantage is provided; obtaining a further increase in the average speed of printing and obtaining a carriage movement subject to only a small number of stresses of acceleration and deceleration.
OTHER CORRECTION SYSTEMS In the preferred embodiment, described previously herein, the correction is based exclusively on a measure of time. However, as has been mentioned previously, the correction may be based on other parameters, or possibly combinations thereof, according as different circuit embodiments are adopted.
In particular, it is evident that position detector T may generate, in addition to pulses identifying the position of the printing carriage upon the completion of each spacing operation, other pulses which identify a suitable number of intermediate positions. For each of there intermediate positions there is a corresponding correction time. For example, the pulses generated by position detector T may control a counting circuit, such as counter 121, to progress according to an appropriate rule, the pulse generator being left the task of stepping the counter at a rapid rate to subsequent states so as to produce a variable delay.
In solutions intermediate the last-mentioned embodiment and the embodiment described previously, intermediate position pulses provided by position detector T may be employed to set pre-established states into the counter, which is caused to progress at variable rates by the pulse generator. In this manner, possible errors may be corrected which are the result of variations in velocity, acceleration and distance relative to the corresponding values for which representations are established by the counter states. Similarly possible deviations may be corrected which are caused by variations in the operating frequency of the pulse generator. Such a correction system is described with reference to FIGS. 12 and 13.
FIG. 12 is a diagram of distance as a function of time and illustrates the corresponding printing corrections to be made, expressed in terms of distance, and is similar to the diagrams of FIGS. 7 and 8. The curve c represents the distance-time relationship under normal conditions, i.e., the predicted average behaviour of the printing carriage. For example, if the time requires to complete a spacing operation is 10 ms, curve d represents the corresponding approximated curve of the corrections to be made.
Assume, now, that for some reason (excessive acceleration or deceleration torque, decrease in the passive resistance, etc.) the printing carriage movement is more rapid and is completed, for example, in 9 ms. In this instance, the distance-time relationship representing the carriage movement is illustrated by the cruve c. The corresponding curve of the corrections to be made is represented by the curve d, from which it is seen there are substantial deviations from correction curve d based exclusively on the time measures.
Modification of correction curve d to have it approximate as close as possible the exact curve d is effected by a direct inspection of the distance covered by the printing carriage. FIG. 12 shows that in the normal or average operation (execution time of a spacing operation is 10 ms), for a distance equal to 7.5 percent of the character spacing the state assumed by the counter used for the correction corresponds to the decimal digit 6. Similarly, for distances equal to 30 percent, 50 percent and percent of the character spacing, the state of the counter corresponds to the respective decimal numbers 16, 20, 25.
When the movement of the carriage occurs in a time less than the average, in the instant example 9 ms, a counter state of 5, instead of 6, corresponds to the 7.5 percent fractional spacing.
To correct the counter a signal can be sent from position detector T to counter 121, FIGS. 10 and 11, and when the 7.5 percent fractional spacing is reached, for setting counter 121 to state 6. Similarly, for the fractional spacings of 30 percent, 50 percent and 70 percent other signals can be sent from position detector T to set counter 141 to a state corresponding to the respective numbers 16, 20, 25 and this setting is independent of the actual state of the counter, which may correspond to a higher or lower number than the correct number. In this manner, curve a is modified to become curve d", which approximates more closely the exact correction curve d of the example. It is evident that by such technique it is possible to correct deviating both above and below the predicted average behaviour, as well as possible frequency errors of the pulse generator.
FIG. 13 illustrates a counter circuit provided with input terminals for receiving the above-mentioned state-setting signals, showing details of counter 121 of FIGS. 10 and 11. Counter 121' comprises six flip-flops 304, 305, 306, 307, 308 and 309, connected in cascade in a conventional manner. The pulses which step counter 121 are applied to the timing or clock input terminal of the first flip-flop 304 on counter input terminal 140, which is preceded by the above-described logic network.
The counter is completed by a plurality of OR-gates 310-318, which permit the application of signals arriving at input terminals 126, 128, 205, 300, 301, 302, and 303 to various set and reset input terminals of the flip-flops. The output terminals of the flip-flops are connected to a group of six leads comprising output channel 130.
Input terminal 126 is provided for resetting the counter. A signal arriving at input terminal 126 is transferred through OR-gates 310-315 to the reset input terminal of each flip-flop of the counter.
Input terminal 128 is provided for setting the counter to a state representing the decimal number 2. Thus, a signal arriving at input terminal 128 (following a reset signal at terminal 126) is transferred through OR-gate 316 to set flip-flop 305. Following such occurrence, the signals present on output channel 130 represent the binary code 000010, which corresponds to the decimal digit 2.
A signal arriving at the input terminal 205 is transferred through OR-gate 316 to set flip-flop 305 and is coupled directly to set flip-flop 307. Following such occurrence, the signals present on output channel 130 represent the binary code 001010, which corresponds to the decimal digit 10.
The function of the three input terminals 126, 128, and 205 has been described previously herein with reference to FIGS. 10 and 11. However, for the purpose of modifying the counter state to correct for possible deviations in the behaviour of the printing carriage relative to the predicted or normal behaviour, input terminals 300, 301, 302-and 303 are provided.
A pulse applied to input terminal 300 is transferred through OR-gate 316 to set flip-flop 305, is transferred through OR-gate 317 to set flip-flop 306 and is transferred through OR-gates 310, 313, 314, and 315 to reset the respective flip-flops 304, 307, 308 and 309. Following such occurrence, the counter assumes a state which provides on output channel 130 a set of signals representing the binary code 0001 10, which corresponds to the decimal digit 6. Similarly, pulses applied to input terminals 301, 302, and 303 transfer the counter to respective states which provide output signal sets representing the corresponding decimal digits 16, and 25. Pulses arrive at input terminals 300-303 from the position detector associated with the motor unit which drives the printing carriage movement.
It is evident that the number of input terminals used to set states into the counter may be modified or increased, according to the particular requirement or to obtain better precision. In the limiting case, as has been mentioned previously herein, the counter may be stepped directly by pulses from the position detector, provided that the resolution of the position detector becomes sufficiently high to accomplish such fine adjustment. Clearly, however, the counter always will be conditioned to count at a rapid rate under control of an independent oscillator during the correction phase of the printing operation. During such correction phase, any pulses possibly generated by the position detector must be prevented from reaching the counter.
Accordingly, with the solution last described, correction is provided based on an actual measure of the printing carriage displacement. However, it is possible to adopt more sophisticated solutions, through the sampling of the displacement speed and acceleration of the carriage and the use of circuits of correction based on such samples, without departing from the spirit and the purpose of the invention. Moreover, although in the example described, the character motion on the character member proximates the printing positions was assumed to be in the same direction as the displacement of the carriage, i.e., from one printing position to the next in printing sequence, the character motion may be chosen to be opposite without the consideration set forth herein losing their validity. Again in this case, the offset corrections may be made by introducing suitable delays in the moment of printing.
1. In a serial on-the-fly printer for serially printing characters at a plurality of printing positions to form a print line, wherein a type-carrying member is maintained in continuous motion to present in sequence different characters at a printing position with the direction of motion of said characters proximate to the printing position being substantially parallel to the print line, and wherein said type-carrying member is mounted on a printing carriage which is moved between adjacent printing positions with a movement independent of the motion of said type-carrying member, the improvement comprising: detecting means for detecting the position of said type-carrying member relative to said detecting means and for delivering coded signals representing said position of the type-carrying member, comparing means for comparing said coded signals with a code representing a character required to be printed to generate signals representing the results of said comparison, and means for timing at a variable rate responsive to the movement of said carriage and coupled to said comparing means, said timing means being effective for controlling printing at suitable moments in said printing positions, independently of the actual position of said printing carriage.
2. The printer of claim 1, wherein said variable rate timing means includes a timing pulse generator and a pulse counter, means for starting said pulse generator and said counter at the beginning of every printing carriage movement operation from one printing position to the next, and circuit means responsive to signals generated by said comparing means for varying the counting frequency of said counter.
3. In a printer wherein a carriage moves parallel to a print line comprising spaced apart character image receiving locations, wherein a character member mounted on said carriage comprises a moveable typecarrying member which presents characters sequentially and cyclically proximate to said print line and moving substantially parallel to said print line independent of the motion of said carriage, and wherein a printing member mounted on said carriage responds to a control signal to cooperate with one. of said characters to form an image of said character on said print line, the improvement comprising:
character position indicating means for delivering a first signal when one of said characters reaches a predetermined position relative to said carriage, offset correction representing means responsive to at least one second signal and controlled by a third signal representing information relating to said carriage movement for generating a representation of the offset correction relativeto one of a plurality of predetermined carriage positions spaced apart along the path of travel of said carriage,
delay providing means responsive to said first signal and controlled by said representation for generating said second signal, and
means responsive to said first signal and to said'representation for generating said control signal after the expiration of a delay interval initiated by said first signal, the duration of said delay interval being controlled by said representation to provide for the formation of a character image by said printing member in one of said image receiving locations.
4. The printer of claim 3 wherein said offset correc tion representing means comprises a counter.
5. The printer of claim 4 wherein said delay providing means comprises a pulse generator, wherein the pulses provided by said pulse generator are coupled to said counter to stop said counter following the occurrence of said first signal, and wherein said control signal is generated when said counter reaches a predetermined value.
6. In a serial on-the-fly printer for serially printing characters at a plurality of printing positions to form a print line, wherein a type-carrying member is maintained in continuous motion to present in sequence different characters at a printing position with the direction of motion of said characters proximate to the printing position being substantially parallel to the print line, and wherein said type-carrying member is mounted on a printing carriage which is moved between adjacent printing positions with a movement independent of the motion of said type-carrying member, the improvement comprising:
detecting means for detecting the position of said type-carrying member relative to said detecting means and for delivering coded signals representing said position of the type-carrying member, comparing means for comparing said coded signals with a code representing a character required to be printed to generate comparison signals representing the result of said comparison, clocking means for indicating with a clock signal when said carriage leaves a printing position and initiates its travel toward a next printing position, and means for timing at a variable rate responsive to said clocking means and to said comparing means for controlling printing at suitable moments in said printing position with a delay in respect to said comparison signals representing the result of the comparison, which depends on the interval between said clock signal and said comparison signals. 7. A serial on-the-fly printer as claimed in claim 6 further comprising:
auxiliary clocking means for indicating with auxiliary clock signals when said carriage passes through preestablished positions intermediate to said printing positions, said means for timing at a variable rate, also being responsive to said auxiliary clock signals.