CA1182063A - Printing complex characters - Google Patents

Abstract

PRINTING COMPLEX CHARACTERS

Abstract of the Disclosure There is disclosed an apparatus for and a method of printing complex characters using a high speed bidirectional on-the-fly printer. In accordance with the present method complex characters are printed in at least two steps. Once the first portion of a character has been printed and prior to the printing of the next character the carrier is turned around and again moved past the print position where the remaining portion of the first mentioned character is printed. This approach is termed "double turnaround".

Description

~8~063 PRINTING COMPLEX CHARACTERS

BACKGROUND

Technical Field The present invention relates to impact printers whexein the print member is moved relative to the printing medium and impact printing is carried out at a plurality of print positions along a lateral line on said printing medium by moving said print member so that a selected type character on said print mem~er 10 coincides with a particular print position and then impacting said character against said print medium through a suitable ink release ribbon or sheet.
More specifically, the present invention relates ko pr.inting complex characters; that is, those 15 r~quiriny at least one overstrike, using a bi~lrectional, high speed on-the-fly printer.

Description of the Prior Art U. S. patent 3,925,787 discloses operating an ink je~ type printer wherein turnaround of the printhead 20 on :lt.q carrier occurs so that the carrier is deliberately overshot at the end or at the beginning of a line for a distance such that the carrier will be at its on- he-fly print speed when it reaches the first character to be p.rinted after its direction 25 reversal. There is no teaching of double turnaround for printing a complex character before the next character is printed.
IBM Technical Disclosure Bulletin Vol. 18, No. 9, February 1~76, page 2825, describes the method for 30 ach.ieving high speed printing within the confines of a relatively slow character select system by printing only some of the characters in the first pass along~a ~8~63 given print line and then reversing the process and printing the remainder of the selected characters along the second pass. There is no teaching of on-the-fly printing of a single complex character in two passes carried out before the next character is printed~
U. S. patent 4,189,246 refers to printers which utilize a rotating disk with characters on the periphery thereof as being well kno-wn. Several such 10 printers are commercially available. Rotating disk printers can be divided in categories by either ~ocusing on how the disk rotates or by focusing on how thè carrier traverses.
Focusing on how the disk rotates, swch printers 15 can b~ divided into a first c:ategory where the disk c:onstantly rotates and into a second category where t}l~ motLon oE the disk is intermitterl-t. In printers w:ith a constantly rotating disk, printing takes place when the hammer strikes the rotating disk. Rotation 20 of the disk i9 not stopped each time a character is printed. In printers with a disk that intermittently rotateæ, the disk is rotated to the desired print position and then stopped. There is no disk rotation while printing takes place.
~5 An alternate division of disk printers can be made by focusing upon the motion of the carrier. In some printers, the traverse of the carrier is stopped each time printing takes place. In other printers the carrier is moving at the instant when printing occurs.
30 In both the type where the carrier is moving when printing occurs and in the type where the carrier is stopped when printing occurs, the disk may or may not be rotating at the time of printing. In some printers where the carrier is moving at a fixed speed when 35 printing takes place, the carrier is slowed down and ~3 82C)~3 stopped between print positions in order to give the rotating disk time to move to the desired character.
U. S. patent 4,178,108 discusses a number of issued patents which relate generally to printers of the type discussed above. That patent teaches moving a carrier from one print position to the next a fixed distance at a variable speed selected in order that the earrie.r reach the next print position in synehroniæAtion with the print disk reaching the next eharacter position. Upon such synchronization the print hammer is fired to print the character while the earriaye continues on-the-fly towarcl the next print pO.~ition.
U. S. patent 4,1~9,246 .relates to moving the J5 cA.rrier from one print positi.on to t:he next at a speed whieh is selected depending on the time required for the disk to rotate to the next character. Printing ta~es place with the carr.ier moving at one of the number of speeds and the force utilized to drive the hammer to print th~ eharaeters is varied dependent on whieh eharaeter is being prin-ted. ~lammer firing for eaeh eharaeter is timed dependent on print speed as well as the foree utilized to drive the hammer.
None of the prior art references are particular solutions to the problem of printing complex eharaeters whieh do not appear on the given printwheel petals. This problem arises often times in printing eharaeters for non-English languages and it is not always feasible to change printwheels. Thus, eharaeters may be eonstructecl from characters or symbols appeariny on inclividual petals of the printwheel~ For example, often times in eomputer related deseriptions, zeros are indieated by a slashed zero to avoid confusion with the letter "o". Another ~T9-79-013 example is an accented "e" when just one or two words will use such.
Also, a problem arises in optimiziny operation of a bidirectional printer where one line ends toward the rniddle of the page and the next line does not start until the middle of the paye so that allowiny the print carrier to go all the way to the riyht maryin may be inefficient.

Disclosure of the Invention lO lt is an object of the present invention to p.rovide an improved means of printiny complex characters, overstriking, underscoring in a bidi.r~ctional printer.
The present invention provides an improved means .15 O:e op~rcltin~ hi(3h speecl on-th~-fly bidi.rectional printers so as to print complex characters. The present inven-tion provides a hiyh speed on-the-fly disk printer which has one motor for controlling the disk and another for controlling carrier movement. As in all mechanical systems, mechanical characteristics of these motors and other related mechanica~
components impose physical limitations such as maximum speeds, maximum acceleration and maximum deceleration.
The present invention is directed to maximiziny the 5 performance of the printer by controlliny the carrier during the printing of complex characters which involve at least two passes at a given print position.
The present invention eliminates some of the problems mentioned with reference to the prior art 30 above discussed by controlliny the carrier to experience turnaround sequences at other than the left or right margins so as to more ef~iciently print complex characters or to underscore or overstrike a character or to end one 1ine and beyin another by 36;3 causing the carrier to pass a given print position more than once before reaching the margin.
The foregoing and other features and advantages will become apparent from the more particular description of the preferred embodiment of the invention is illustrated in the accompanying drawing.

Brief Descrl~tion of the Drawin~s Fig. 1 shows a printer apparatus adapted for use with the present invention.
Fig. 2 is a timing chart illustrative of the print cycle~ in the printer embodying the presenk inv~ntion.
Fig~ 3 illustrLlte~ a turnaround without overshoot ~equence.
Fig. 4 illustrates a turnaround with overshoot sequence.
Fig. 5 illustrates a loop sequence.
Fig. 6 illustrates a double loop sequence.
Fig. 7 is a more detailed block diagram of the 20 sequence of the logic for generating the sequence as shown in Figs. 3-6.
Fig. 8 is a more detailed diagram of turnaround without overshoot yenerator 784 from Fig. 7.
Fig. 9 is a more detailed diagram of turnaround 25 with overshoot generator 792 in Fig. 7.
Fig. 10 shows the details of the sequence with the loop generator sequence represented at 756 in Fig.
7.
Fig. 1 shows the main mechanical components of 30 the present printer. They are shown somewhat schematically since such components are well known and the present invention is directed to the control mechanism for the two stepper motors 3 and 8 and the AT9-7g-013 ~L~8;~63 prin-t hammer 10, and not to the mechanical components per se.
As shown in Fig. 1, a laterally sliding carrier 1 is mounted on a guide rod la and a lead screw 7 and carries a rotatable print wheel or disk 2 driven by a stepping motor 3. The carrier 1 is driven by lead screw 7 which is driven by a stepping motor 8.
~lternatively, motor 8 could drive a belt which in turn could drive carrier ].
A type disk 2 comprises a disk having a number of movable type elements such as the flexible spokes or petals or fingers 9A, 9B, 9C, etc. Printing of any ired character is brought about by operating a print hamrner L0, which is actuated by a solenoid 11, 15 both of which are mounted on carrier 1. When the appropriate type finyer approaches the print position, ~lolenoi.d 11 actuates hammer 10 into contact with the .~elecl:ed type finge~r, driviny it into contact with a paper 1~ or other printing meclium. An emitter wheel 13 attached to and rotating with type disk 2 cooperates with a magne-tic sensor FB2 to produce a stream of emitter index pulses for controlling the operation of the printer. The emitter has a series of teeth each of which correspond to one petal or finger 9A, 9B, 9C, etc. A homing pulse is generated for each revolution of the print wheel by a single tooth on another emitter (not shown). ~he printer controls can thus determine the angular position of type disk 2 at any time by counting the pulses received since the last homing pulse. A toothed emitter lS is mounted on the shaft of the motor 8 and in conjunction with a transducer FBl provides pulses which indicate the position of the carrier 1.
Stepper motors 3 and 8 are activated by conventional drive circuits 21 and 22. Examples of ~T9-79-013 the type of drive circuitry that could be used are shown in U. S. Patent 3,636,429. A hammer solenoid 11 is actuated by a hammer drlve circuit 23 which is also conventional.
The actions of positioning the carrier 1 and positioning the print wheel 2 are, in general, independent except that coordination is required at the instant printing occurs. Both type disk 2 and carrier 1 must be in a selected position (but they 10 need not be at rest) when hammer 10 strikes type disk

2.
Fig. 2 shows the timing required in a print cycle which is defined as those functi.ons required to print a character .including the activity required to move J.5 the carri.er f:rom a center line or print point of one cha.ract~r to the print point of t:he next character, ~ ect the chaYacter to be printcd and :eire the hamme.r .
As set out in U. S. Patent 4,030,591, the motion 20 of the carrier can be chosen to move at a plurality of different velocities depending upon the character selection of the print wheel and, thus, the time required for the print wheel to move between adjacent characters. In that patent, four different velocities 25 a.re utilized for the carriage and for purposes of illustrating this invention, the movement of carriage 1 will likewise be at a velocity chosen among four separate velocities, vl, v2, v3, and v4. For purposes of illustration of this invention, it is assumed that 30 velocity vl will be the slower of the velocities, velocity v2 faster than vl, velocity v3 faster than v2 and vl, and velocity v4 the faster velocity. Thus, by selecting the fastest velocity at which the carrier can move for any selected change i.n position of print 35 wheel 2 as it moves between successive charac-ters (or spaces if such are in the sequence of characters to be printed), then the printing speed of the printer can be maximized.
Refer now to Fiy. 2. At to escapement starts.
At tl, the hammer has completed its previous strike and issues a start command to character selection and index functions. At t~ character selection function is completed. At t3, indexing is completed. At t4 the escapement logic issues a synchronization pulse to 10 the hammer logic so that at t5 the hammer impacts the printwheel concurrently with the completion of e~capement.
The maximum time required for selection and indexing in a given system are known; however, the 15 carrier i3 capable of escapiny at a varying rate as ~rlicr discussed. Ilowever, the duration of these charact~r selecti.on and indexing is clependent upon the numher o~ positlorls that the selection device must be moved and/or the index device steppecl. To rnaximize 20 throughput it is desired that escapement occur at the highest possible rate while maintaining the relationship shown in Fig. 2. Escapement control sequences are designed under several constraints, one of which is that character selection must be completed 25 before the carrier reaches the print point. The other is the time re~uired to comple-te a verticle index. As shown in Fig. 2, verticle indexing requires more time.
As will be later described, the parameters are chosen to provide the highest print speeds. That is where no 30 indexing takes place. All escapement is completed by the end of character select time. Still further, escapement velocity should be constant prior to the carrier reaching its worst case hammer synchronization point, that point at which hammer fire must start.
35 E`urther, carrier motion may not stop in an on-the-fly l printer. This technique of velocity determination is disclosed in more detail in Canadian Patent ~lo. 1,128,446/ entitled 'IApparatus For Synchroniæing Carrier Speed And Print Charac-ter Selection In On-The-Fly Printing", issued July 27, 1982, and assigned to same assignee as the instant application.
Variations can occur in the standard print cycle shown in Fig. 2. These are occasioned by large escapement distances, a change in direction of escapement, or a very small escapement. When a large escapement occurs between two print points, it is more efficient to tab which involves accelerating the escapement to a velocity higher than that used for printing and then returning to print velocity before lS reaching the print point.
~he escapement control sequences which change the direction of carrier movement are of particular interest in printiny using the present invention.
These changes in direction are required when printing the next line of text in the opposite direction or when overstrilcing text on the current line, or when b~ ing a compl~x character. Once again, the constraints o~ a) selection complete, b) cbnstant velocity, and c) on-the-fly printing apply to escapement control sequences involving a change in escapement direction. Actually, at some point;
carrier velocity does momentarily reach zero, but this is the result of direction change only.
Figs. 3-6 illustrate four turnaround sequences by showing what happens to carrier velocities as a function of escapement distances. Escapement distances, for our purposes, are divided into three classifications: small, medium and large as a function of the turnaround and accumulated horizontal displacement. The small escapement is one between r~

Çi3 zero and 6/120's of an inch ~.127 cm). Similarly, medium displacements are those between 6/120's and 42/120's of an inch (.127 cm and .B89 cm~. Large displacements are those greater than 42/120's (.889 cm) of an inch. These dis-tances are dependent upon the instant implementation and can vary with implementation.
Referring now to Fig. 3, velocity is represented on the vertical axis and escapement distanc~ on the 10 horizontal axis in Fig. 3 which represents a turn around without overshoot with a vertical index. At the stclrt o the sequence the carrier is trav~lling at velocity vi and printing occurs at print point 1 indicated at 30. The distance 32 between print point 15 1 and print point 2 indi~ated at 34 is in the medium to lar~e ranye. 'rhe~ carrier velocity passes through z~ro in turnincJ around and even-tucllly reaches its E~ l v~:loc~ y v~ which is less than or equa] to its initial v~locity~ In this case, deceleration of the 20 carrier, or turnaround, may begin immedia-tely following the printing at position 30. To meet the aforement.ioned constraints on escapement control, the value of v~8 is varied. The lower this velocity, the longer the duration of the sequence, thus allowing a 25 longer selection rotation.
In Fig. 4, the turnaround sequence with verticle index including overshoot is illustrated. The need for overshoot occurs where print point 1 and print point 2 are quite close, that is, their escapement 30 range is small. Thus, from print point 1 indicated at 40, the carrier advances for the overshoot distance which is between print point 1 and the point indicated at 42 before slowing down to ~ero and reversing direction to build up again to its final fixed 35 velocity at pr:int point 2 indicated at 44. Variations ~82~)6~

in the overshoot distance are thus solely used to con-trol the duration of the escapement sequence and therefore allow the aforementioned contraint to be met.
Shown in Fig. 5 is a loop sequence in which there is no net direction change but print point 1 at 50 and print point 2 at 52 are separated by a distance in the previously defined small range. The loop is required as the lowest escapement velocity vi does not provide 10 a duration long enough to meet the aforementioned constraints. The initial velocity vi which the c~rrier is travelling is allowed to decrease to zero ~vO) and the carrier travels at a constant backward velocity vb in the opposite direction and accelerates 15 aEter once again changing direction to a final ve~locity vE10 which is, as shown, less than the lrlitialA velocity. For this sequence, the firlal and backwar~ velociti~s, ve10 and Vb, are fixed and are not determined as a funckion of the initial velocity, 20 vi. The distance travelled in -tl-e backward direction varies as a function of vi. It is the only variable in this example.
Fig. 6 illustrates a double turnaround sequence.
The double turnaround sequence is actually a composite 25 of the turnaround with and -turnaround without overshoot sequences illustrated in Figs. 4 and 3, respectively. This sequence is required when the distance between print point 1 at 60 and print point 2 at 64 are in the medium to large range. Print point 1 30 at 60 is first passed by the carrier travelling at its initial velocity vi. Carrier velocity decreases to zero over the distance indicated at 62; and as the direction changes, it accelerates to a constant veLocity vb in overshoo-ting tlle second print point 35 indicated at 64 by the distance indicated at 66 and then reverses direction passing through vOO lrhe carrier then accelerates to its final fixed velocity Vf which is equal to Vb in time to print at 64. Thu~, the only variable is the overshoot distance 66.
As has been shown, each escapement control sequence contains a variable parameter used to vary the time it takes to execute that particular sequence.
In addition, these variables are affected by the maximum time required for vertical indexing and 10 character selection in the printer.
In a bidirectional printer embodying our invention, the selection of the above described sequences i.5 made as a function of distance and direction the carrier must travel between the print 15 points, the initial direction in which the carrier is travelling, and the direction that carrier must be tr~vellirlg to reach the second print point and .Einally, the de~ire(l print direction at the second pr:Lnt point. When the type of sequence required has 20 be~n determined, which determination may be done as a straight forward table lookup function, as will later become more clear following a discussion of Table I, an appropriate sequence generator is called. The sequence generator logic will be discussed with 25 reference to Fiy. 7.
Of the four sequences illustrated in Figs. 3-6, each one is a function of a particular variable. In Figs. 3-6 the characteristics of these turnaround sequences were shown in terms of velocity as a 30 unction of carrier position. Obviously, within the specific sequence, control to meet given conditions can be done by varying these variables. For the sequence shown in Fig. 3, the turnaround without overshoot, the final escapement velocity is a function 35 of the initial velocity, the distance between print ~lB21063 points and the time required for a vertical index.
The sequence shown in Fig. 4, turnaround with overshoot, the overshoot distance chosen is chosen as a function of the initial velocity of the carrier and time required for a verticle index. In Fig. 5, the loop turnaround sequence, the backward escapement distance is a function of the initial velocity and index. Finally in Fig. 6, the double turnaround sequence varies as the variable in the turnaround with 10 overshoot sequence since it is, in fact, a combination O:e khis sequence and the turnaround without overshoot sequence.

~8;Z~ 3 Table I
Current Accumulated/ Desired Action Direction Required Print Required Direction Direction -5 Case 1 F F F No turn-Case 2 R R R around Case 3 F R R Single Case 4 R F F turn-around 0 Trailing*

Case 5 F F R Single CDse 6 R R F turn-around Leading**

.l5 C~IHe 7 F K F Double Ca~e 8 R F R turn--around *Si~gle turn~round trailing - a change ln escapement direction followed by an escape to the required 20 printpoint.

**Single turnaround leading = an escapement to the p.rintpoint followed by a change in escapement direction.

R = Reverse direction.
25 F = Forward direction.

AT9-79-013 ~18Z063 Similar sequences as described with re~erence -to Figs. 3-6 can also be characterized in other terms which are the current direction of the escapement at print point l, the accumulated or requi.red escapement direction from print point l to print point 2, and the desired print direction of print point 2. Table I
lists the actions required for these three var.iables.
No turnaround, single turnaround trailing, single turnaround leading, and double turnaround are the four lO po5sible actions. In the Table I r the forward print direction or escapement directi.on of left to right is indicated by "F", the reverse directi.on refers to right to left escapement direction and is indicated by "R".
~5 F~r cases l and 2, the carrier is required to l:ak~ no turnaround when all di.rections are the same wh~th0r ~orward or reverse. The loop se~uence d~crlbed below with reference to Fig. lO is a special case of this Table entry. Even though there is no net 20 direction change, the loop is used to gain the requ.ired time associated with the aforementioned escapement constraints.
When the desired print d.irection and required direction are the same but differ from the current 25 direction, as ir1 cases 3 and 4, a single turnaround trailing type sequence is required. That means that an escapement turnaround sequence is foll.owed by an escapement to the required print point.
When the desired print direction is opposite to 30 that of both of the current escapement direction and the required escapement direction, a single turnaround leading action is taken as in cases S and 6. This means that there is an escapement to the print point followed by the application of an escapement 35 turnaround sequence.

Lastly for cases 7 and 8, wh~n the current carrier escapement direction and desired pîint direction are the same with the required direction beiny different, a douhle turnar~und sequence is required. This sequence i.s a composite of two single turnaround sequences.
E'ig. 7 is a block diagram illustrating the actions taken in the controls of the printer embodying our invention. More particularly, Fig. 7 shows the :lO turnaround sequence generating logic for those sequences il].ustrated in Figs. 3-6. Referring now to r~i.g. 7, escapement parameters :input to the sys-tem in a conventional way b~ the user and including such information as represented at hlock 700. Those par~meters are passed over line 702 to sequence g~nerator loyic 704. The detailed view of that logic .if) w.ith.in ~he dotted lines 706. Output from the ~ec~u~nc~ gen~rator is passed along li.ne 708 to ~scapement control loyic 710 which sends the necessary signal over line 712 to the escapement mechanism indicated generally at 714. The signals represented in lines 702, 708, and 712 are, in fact, a plurality o:E signals to be described below.
Included in the e.scapement parameters 700 are specific values such as escapement distance, current escapement distance direction, the required escapement direction, and the desired print direction. The distance to be escaped is on line 740. The current escape direction (CED) is on line 720, the required direction (RED) on line 722, and the desired print direct.ion (DPD) on line 724. These three lines are input to comparator 726 for determining whether a sequence has the characteristics above defined for cases 1 and 2 in Table I. That is, current 3S escapement direction, required direction and desired AT9-79-013 ~1 ~Z063 print direction must be in the same direction for cases 1 and 2.
Similarly, these three signals are input to other comparators for determining the other cases. Current escapement direction on line 720 is inverted by lnverter 728 and the inverted signal placed along line 729 is input with signals on lines 722 and 724 to comparator 730 for determining whether this sequence will have the characteristics of case 3 or 4. That is ~or cases 3 and 4 CED must be opposite to the direction of RE'D and DPD.
In a like manner, the required escapement direction on line 722 is inverted by inverter 732 and the output placed on line 733 which, along with the ~5 ~ignals on lines 720 and 724, is input to comparator 73~ wh:Lch determines whether the particular sequence deEin~d by the escapement parameters has the characteristics ascribed -to cases 7 or 8. Again, for cases 7 and 8, RED must be opposite to CED and DPD.
The required print direction on line 724 is inverted in inverter 736 with the output placed on line 737 which together with the required escapement direction on line 722 and the current escapement direction on line 720 are input to comparator 738 for determining whether case 5 or 6 has been defined.
Again, here DPD must be in the opposite direction of RED.
The other escapement parameter is the distance to be escaped on line 740 which is decoded in distance decoder 742. Distance decoder 742 has three outputs on lines 744, 746, and 748, representing small, medium, and large escapement distances, respectively.
These signals on lines 744, 746, and 748 are gating signals used with the output from the comparators 726, 730, 734, and 738. The small distance signal on line 2~6~

744 and the output from comparator 726 on line 7~7 representing no turnaround are input to AND gate 750 whose output on line 752 activates loop generator 756. Loop yenerator 756, shown in detail in Fig. 10, outputs signals to escapement control on line 758 to cause the turnaround sequence illustrated in Fig. 5. Line 758 is actually a plurality of lines which dictate the velocity, direction, and distance of a given escapement and vary in accordance with the parameter values of the sequence as depicted in Fig. 5-Line 727 is also an input to AND gate 760. The other input to AND gate 760 is the medium distance signal on line 746.
Output from AND gate 760 on line 762 is passed to the velocity determination logic which is disclosed in CA Patent No. 1,128,446 entitled "~pparatus For Synchronizing Carrier Speed ~nd Print Character Selection In On-The-Fly Printing", hav~.nc~ C.W. Evans, Jr., et al. as inventors. Line 727 is al~o ~n input to AND gate 768. The other input which is ~long line 748, the large distance signal, output from AND
gat~ 768 on line 770 i5 pa~sed along t:o logic for generating tabulation commands, a description of which is given since it does not constitute part of the present invention.

Output from comparator 730 on line 731 representing single turnaround trailing is input to AND gate 780. The other input to AND gate 780 is the inverted small distance signal.
The small distance signal on line 744 is inverted in inverter 774. The inverted small distance signal on line 776 is applied to AND gate 780. Output from AND gate 780 on line 782 B

without overshoot generator 784, described in detail in Fig. 8, on line 802 whose output siynals on line 786 are passed to the escapement control logic to cause an action as illustrated in Fig. 3. Line 786 is S actually a plurality of lines which dictate the velocity, direction, and distance of a given escapement and vary in accordance with the values of the sequence depicted in Fig. 3.
The turnaround without overshoot generator 784 10 has another output. The function complete signal on line 795 indicates that the sequence has been carried ou~ .
Output from comparator 734 on line 735 representing double turnarourld is input to the double turnaround gencrator 796 which has an output on line 797 which is another input signal to OR gate 801 which ln turn activates the turnaround without overshoot yen~rator 78~ on line 802. Line 797 is also input to ~ND gate 798 which has the function complet~ signal on line 795 as its other inputO AND gate 798 develops its output signal along line 799 which forms an input to the turnaround with overshoot generator 792, described in detail in Fig. 9, through OR gate 803 alony line 804. Thus double turnaround generates a 25 turnaround without overshoot followed by a turnaround with overshoot. This is the sequence of Fig. 6.
Output from comparator 738 on line 739 representing single turnaround leading is another input to the turnaround with overshoot generator 792 30 through OR gate 803 along line 804.
The small distance signal on line 744 along with the signal on line 731 representing single turnaround trailing are input to AND gate 788. The output of AND
gate 788 on line 790 forms an additional input to the 35 turnaround with overshoot generator 792 through QR

~z~

gate 803 along line 804. Its output on line 794 is passed through escapement control logic to cause the carrie.r to experience the turnaround sequence shown in Fig. 4. Line 794 is actually a plurality of lines which d.i.ctate the velocity, direction, and distance of a given escapement and vary in accordance with the values of the sequence depicted in Fig. 4.
Finally, the outputs from the loop generator 756, the turnaround with overshoot generator 792, and the turnaround without overshoot gerlerator 784 along lines 758, 79~, and 786, respectively, are OR'd together by yate 707 to form the input to the escapement control logic 710 along line 708.
Fig. 8 shows details of the turnaround without ov~rshoot sequence generator 784. The sequence is :~l.lu~t.rated in Fig. 3. The escapemerlt distance 740, Lg. 7, :is one input to ~ND gate 810. The other is i.nput :Line 802, Fig. 7, which is the activation line for this sequence generation. Therefore, when this sequence generator is activated, the escapement distance is passed along l.ine 811 to the output 786 of this sequence generator 784, which is also shown in Fig. 7. The desired print direction signal 724, Fig.
7, is applied as one input to AND gate 812. The other 25 input to AND gate 812 is line 802, which is the activation line for the sequence generator.
Therefore, when the sequence generator 784 is activated, the escapement direction is passed along line 813 to the output line 786.
Line 802 is also applied to one input of AND-gate 81~.~. The other input along 818 is the velocity vi of the escapement device when print point 1 at 30 is reached in Fig. 3. When this sequence generator is activated, vi is passed along line 816 to the velocity look up table 815 which yields a value of the final ~T9-79-013 C36~

velocity vf8 which will be attained at print point 2 at 34 in Fig. 3. This value is passed along line 817 to the output of the sequence generator 786. Vf8 is also input to clock 820. The escape distance on line 740 is also input to the clock 820. The clock is set to timeout and places a signal at its output when the escapement dictated by the distance and velocity has been complete. This output along line 795 is also shown in Fig. 7 as the function complete line used as 10 input to AND gate 798. When output 786 is applied to t:he escapemen-t control 710, E'ig. 7, the escapement u~nce of Fig, 3 results.
It should be noted that the selection duration and index duration could also be usecl as vectors in lS khe lookup table which would provide a finer degree of final velocity determination.
Fig. 9 depictx the cletails oi the turnaround with ov~rshoot sequence generator shown at, 792 in Fig. l.
I,ine 809, Fig. 7, is the ac-tivation signal for this 20 sequence generator. It is input to AND gates 901, 902, and 903.
rrhe other input to gate 901 is the current escapement direction signal on line 720 which is also the direction of the overshoot to be generated by this 25 circuit.
The output of gate 901 runs along line 905 to AND
gate 906. The other input to gate 906 is from clock 907 via inverter 908 along line 909. Line 909 is active during the overshoot stage of the sequence and 30 is also input to AND gates 910 and 911.
Returning now to AND gate 906, its output which represents the current print direction is passed along line 912 through OR gate 913 to line 914. This, in turn, foxms the output 794 of the sequence generator 35 which also appears in Fig. 7.

i3 The second input of gate 902 is the velocity of the escapement at the time the first print point is reached vi on line 818 which represents the carrier velocity as print point 1 in Fig. 4O This is also the velocity of the carrier during overshoo-t to print 42 in Fig. 4. This velocity is passed along line 915 to AND gate 910 which has been activated by line 907.
The çarrier velocity vi on line 818 is therefore passed to the output of gate 910 on line 916 through OR gate 917 to line 918 and finally to the output 794 of this sequence generator.
The initial velocity on line 818 is also passed' along line 920 to table look up mechanism 921. This mechani~m yields a unique overshoot distance on line lS 922 which is dependent upon the input 920. This overshoot distance is passed to AND ga-te 911 which is act.ivated hy line 909. The overshoot distance is the~'or~ applied -to the output of 911 along 923, throuyh or~ gate 924 to lille 925 ~ncl Einally to the output 794 of the sequence generator.
The output of the table look up mechanism 921 along 922 and the initial velocity along 920 are applied to the clock 907 which yields a signal at its output when the time to escape the overshoot distance ~40 42 in Fig. 4) at vi the initial velocity has expired. This signal is applied through inverter 908 to AND gates 906, 910, and 911, these gates are deactivated, thus degating the overshoot distance, direction, and velocity from the output of the se~uence generator 794.
At the same time, the output of clock 907 is applied along line 930 to AND gates 940, 941, and 942.
The other input to 940 is line 950 from inverter 951.
The input to this inverter is along line 905 which is the current or overshoot direction. Therefore, the ~8~(~63 opposite direction is applied to AND gate 940 which, being so conditioned, passes this direction information along line 952, through OR gate 913, along line 914 to sequence control output 794. Similarly, Vfg, the fixed final velocity for a -turnaround with overshoot sequence, is applied as the second input to AND gate 941, and, being thusly conditioned, is passed along line 953, through OR gate 917, along line 918 to sequence control output 794.
The second input to AND gate 942 is the return d.istance for this sequence and is applied along line 960. Being so conditioned, the return distance is passed through AND gate 942, along line 961, through OR gate 924, along line 325, to sequence control output 794. The return distance is generated as a result o~ adding in ADDER 963 the ove:rshoot distance ~long 922 and the distance between the two print ~oints (40 and 44 in Fig. 4) which is applied on line 740 to AND gate 903 and finRlly along line 962. This addition is required since the distance between the two print points has been increased by the amount of the overshoot and must be accounted for when the turnaround is accomplished. This circuit, when activated, applies at the output 794 the distance, direction, and velocity of the overshoot, followed by the distance, direction, and velocity of the return escapement. When this information is applied to ~scapement control 710, Fig. 7, the escapement sequence depicted in Fig. 4 results~
It should be noted that the selection duration and index duration can also be used as vectors in the look up table which would provide a finer degree of overshoot distance determination.
Fig. 10 depicts the loop generator circuit 756 in 35 Fig. 7. This circuit is similar to that used for the 3L~8Z0~3 2~
turnaround with overshoot sequence génerator 792 shown in FigO 9. One major difference is that the variable used to control the sequence is a fwlction of the escape distance rather than the initial velocity.
The loop generator 756 activation line 752, Fig.
7, is also seen in Fig. 10 as input to AND gates 1001, 1002, 1003, 1004, and 1005. The other input to gate 1001 is the current escape direction along line 720.
Therefore, when the loop generator is activated, the current escape direction is passed through gate 1001 to line 1010. This signal is inverted by inverter 1006 and passes along line 1011 to AND gate 1007. The other input to gate 1007 is along line 1012 which is the inverted output of the clock 1008 along line 1013 throuyh inverter 1009. The clock 1008 will become actlve following the time t takes to travel the cli~3~Anc~ ~rom print point 1 at 50 to print point 2 at 52 on Fiy. 5. Since the clock 1008 is not active initially, the inverted clock signal along line 1012 is up and activates AND gate 1007 and allows the inverse of the current escapemen~ direction to pass to line :L014, through OR gate 1020, along line 1015 to t~he output 758 of the loop generator.
Now, when the clock 1008 becomes active, line 1012 becomes inactive and the inverse escape direction no longer passes to the output 758. However, line 1013 is active and is presented as input to AND gate 1021. The other input to this gate is the current escapement direction along line 1010. Being so conditioned, the current escapement direction passes through gate 1021, along line 1016 through OR gate 1020, and long line 1015 to the output 758 of the loop generator as shown in Fig. 5.
Examining the inputs to AND gate 1003, one input, 3S along line 1030, is the fixed velocity vb used in the ~ ~82~63 reverse direction of the l.oop escapement sequence, the second input is along 75~ and has been described earlier as the activation signal, the third is along line 10].2 and has been shown to be the inverted outpu of the clock which is active during the reverse p~rtion of the loop sequence fxom point 50 to point 54 of E'ig. 5. Being so conditioned, the velocity, Vb, is passed through gate 1003 along line 1031 through OR
yate 1022 and along line 1033 to loop generator output 758. When the clock 1008 becomes active, line 1012 b~com~s inacti.ve, thus deactlvati.ng gate 1003 and Vh .is no longer pas.sfd to the output 758.
However, :line 1013 is act:ive and is presented as an .input to ~ND C.Jclte 1002. ~ second input alorlg line :lS 752 :is t.h~ activat.i~n signa:l previously di.scussed. A
kllircl :in~ut to Jate 'I.0()2 :is along .l..i.ne 1034 and l~l3t3~r)~rltc; til~ l..ix(~d f:in.l.l vc1.c?c.Lty v~ tc) bc o~t~ clcl .in t:~le .I.oop ~:eclucnte showrl in l':ig. 5. I3ei.ncJ so cc~nd.itioned, the final. ve].ocity is pas-ed through gal:e 20 1002, along line 1035, through OR gate 1022, and along line 1033 to loop genera-tor output 758. Therefore, the circuit shown in Fig. 10 presents th~ velocities Vb and v~ to the output of the loop generator in a sequence required to support the loop shown in Fiy. 5.
Now, -the escape distance, -the distance be-tween points 50 and 52, Fig. 5, is present along line 740 which also appears on Fig. 7. This signal is presented to table ].oolc up 1040. This tablc yields the escapement distance to be travelled betwcen points 30 50 and 54 of Fig. 5. This value is present on line ].041. Line 1041 i5 input to -thc clock which conditions the clock to time out (act:ivate~ when the time to travel this distance has expired. Li.ne 1041 is also on input to AN~ gate 1004. A second input to 3s CJate 1004 is the act.ivat.ion siynal along line 752 A~rs-7s-0l3 2~
which has been previously discussed. A third input to gate 1004 is the inverted clock outpu~ ~long line 1012. Being so conditioned, the dist~nce ob-tained from look up table 1040 is passed through gate 1004, along line 1042, through OR gate 1043 and alony line 1044 to loop generator output 758. When the clock becomes active, line 1012 becomes inactive, thus blocking the transfer of the table generated escape distance from passing to the outpu-t 758.
However, line 1013 is active and is present as one input to AND gate 1005. A second input to gate 1005 is the p.reviously discussed activate signal along line 752. ~ third input to gate 1005 is along 1045.
Thi9 line is the output of ADDER 1046. 'rhis ADDER
15 yields the sum of the escape distance (50 to 52, Fig.
5) presented along line 740, and the tab].e generated ~sc~pe d.istance (50 to ~4, r~ig. 5) along line 1041.
I'hat .i~.~, the distance 54 to 52, Fi.g. 5, is present at klla output of the~ ~DD~I~ al.ony l.ine L0~5. 'rhereEore, ~0 thi.s cl.istance :is pas3e(3 tllrough ANI) CJ~te 10~5, along linê 1046, throuyh OR yate 10~3, and along line 1044 to loop generator 758. The escapement dis,tances required to support the loop sequence sllown in Yig. 5 are presented to the output 758.
In summary, the above described means will generate a loop escapement sequence along line 758 when the distance between two print points is small yet there is no required change in print direction.
Additionally, a turnaround without overshoot 30 escapement sequence will be generated when the distance between the two print points is medium or large, a change in print direction is required, and the direction Erom print point 1 to print point 2 is opposite to the direction of escapement when print 35 point 1. is reached.

A turnaround with overshoot sequence is also generated when 1) the distance between the two prlnt points is small, a change in p:rin-t direction is required, ancl the direction froln print poin-t 1 to print point ~ is opposite to the direction of escapement when print point 1 is reached, and 2) a change in print direction is required and the direction from print point 1 to print point 2 is in the same direction ~s the dire~ction of escapement when .1.0 pr.int point 1 :is re~ached. Finally, a complex double turncl.rollnd se~querlce, consistinc3 of, first a turnaround without overshoo-t and, second, a turnaround with overshoot, is ~enerated when -there is to be no chanc3e .i.n tho ~lirt3ctiorl ot' print. ~lowev~r, -the direction ~rom pr:int point 1 to print pO.ill-t 2 :i.s opposi-te to the ~lirt;~ction of pri.rlt.
Whi..le l.he lnvo~lt.:ion h~5 beetl pa:rt.Lculclll.y showr alld descri~t.~d w:Lth re~e:rerlce to one embodittlell~, i-t will be understood by those skilled in the ar-t that various changes in implementati.on, form, and detail may be made without departinc~ from the spirit and scope oE the invention.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
Claim 1 A method of forming complex characters in an on-the-fly printer, said printer comprising:
carrier means movable past a plurality of print positions on a print medium, and printing means mounted on said carrier for printing selected characters or portions thereof at a plurality of said print positions while said carrier is moving, said method comprising:
printing a portion of a complex character while said carrier is moving past a selected print position, moving said carrier again past said selected print position prior to printing the next character, and printing another portion of said complex character while said carrier is again moving past said selected position.

Claim 2 A process for printing complex characters such as overstrikes, underscores, and accented symbols in a preformatted text stream using a high speed, bidirectional printer including a print element carrier characterized in:
printing a first portion of a complex character at a given print location;
reversing the direction of the print element carrier;
varying the velocity of the print element carrier during the direction reversing to provide sufficient time for the selection of the remaining portion of the complex character;
moving the print element carrier again past the given print location; and printing another portion of the complex character while the print element carrier is moving and before printing at another print location.
Claim 3 The process of Claim 2 wherein said moving step includes twice reversing the direction of the print element carrier.
Claim 4 The process of Claims 2 or 3 further including determing the velocity profile of said moving step as a function of initial carrier velocity.

Claim 5 The method as defined in claim 1 wherein said carrier is moved past a print position and a portion of a character is printed; the direction of motion of the carrier is then twice reversed and the carrier is moved again past the same print position to print another portion of the character.
Claim 6 The method as defined in claim 5 wherein the step of twice reversing the carrier motion includes:
(a) decreasing carrier velocity over a first distance;
(b) reversing carrier direction;
(c) increasing carrier velocity to a constant value;
(d) decreasing carrier velocity over a second distance;
(e) reversing carrier direction; and (f) increasing carrier velocity to a final velocity.