GB2025725A - Multistyli recording systems - Google Patents

Abstract

A method of, and apparatus for, recording information in a recording area uses a plurality of recording styli distributed across, and reciprocating transversely of, the recording area, each stylus being reciprocated (for example, the path 20) across a band which is wider than a width obtained by dividing the width of the recording medium by the number of styli, but each stylus recording only in a band (0-15) which is less than the reciprocation band. <IMAGE>

Description

SPECIFICATION Multistyli recording systems The subject invention relates to information recording and, more specifically, to multistyli recording systems, printer-plotters and apparatus capable of printing gray tone graphical and picture information as well as line graphics and alphanumerical characters. The invention also relates to digital facsimile receivers.

Reciprocating facsimile apparatus have been known for a long time, as may, for instance, be seen from U.S. Patent 2,311,803, by R.J. Wise et al, employing a flying pen or stylus. Some systems have attempted to dispense with the need for a stylus drive by arranging a series of stationary styli across the recording medium or paper, as may, for instance, be seen in U.S. Patent 2,937,064, by D.A.

Walsh. In practice, stationary recording styli impose a severe limit to attainable resolution.

Some prior-art proposals have attempted to overcome such and other drawbacks by providing moving styli or stylus assemblies with the aid of endless bands, as may, for instance, be seen in U.S. Patent 3,166,752, by H.C. Waterman, U.S. Patent 3,369,250, by T.H. Gifft and French Patent 1,349,168, by A.

Hermet.

In an effort to overcome design and performance limitations of such endless belt systems, a multistyli system of the type shown, for instance, in U.K.

Patent Specification No. 943,011 has been developed. In particular, this British patent discloses an electrically controlled character printer which prints using a plurality of styli, each stylus printing one character in a line of characters. The styli are oscillated by an amplitude equal to the stylus spacing and equal to the width of characters to be printed. At the same time the record sheet is continuously moved in a direction at right angles to the line of styli so that each character is built up over a plurality of stylus oscillations with the styli being activated at proper points within the oscillation cycle to produce a character formed by a number of print dots resulting from the stylus striking an ink ribbon disposed between the styli and the record sheet or formed by such other known ways as Xerography.

As a matter of interest, recording systems in which the lateral deflections of styli are limited to interstylus spacing are disclosed in German Patent 936,582, by J. Dreyfus-Graf.

U.S. Patent 3,644,931, assigned to the sbject assignee and herewith incorporated by reference herein, discloses a multi-styli recorder where the styli are again oscillated transverse to the record sheet motion to effect marking by electric discharges through an electro-sensitive record sheet. Each stylus prints within an assigned band as the record sheet is continuously advanced. The multichannel recorder disclosed produces a record with information displayed as a print intensity mudulation which may vary down each band and between bands.

Variation in print intensity is achieved by varying the styli discharge pulse rate so that high print intensities are achieved with a high pulse rate and thus pulse density. The pulse rate of each stylus is varied in accordance with the usually analogue signal applied to each of the recorder channels.

Patterson, Ruffell, Walker and Schwartz in "A Digital Input Picture Printer System", a paper presented at the National Electronics and Geophysics Convention at the University of Auckland, August 1974, have described a printer capable of printing alpha-numerical characters and gray tone graphics and pictures which was developed from the multistyli recorder of the latter U.S. Patent 3,644,931. The printer disclosed by Patterson et al prints each line of information as a series of dots, the size-intensity of which are determined by the styli writing pulse length and each line is printed while the styli are oscillated in a left to right direction with an amplitude equal to the styli spacing.The styli printing information is accepted and stored for the subsequent line as the styli are oscillated in a right to left direction during which time the electro-sensitive record sheet is advanced by a predetermined line spacing distance. Timemark 14 electro-sensitive paper made by Fitchburg Coated Products, Inc., of Scranton, Pennsylvania 18501, is cited as an example.

In line with recommendations by manufacturers of electro-sensitive paper, a voltage of positive polarity has been applied to the styli.

During each stylus writing pulse, the potential of the stylus is made about +130 volts with respect to the platen and the discharge burns off the paper coating under the stylus tip. Each stylus has in series therewith an NPN switching transistor in emitter follower configuration with a series emitter resistor of between 1 and 2 Kohms to limit the current during the write pulse.

If the relative speed between styli and recording paper is increased for higher and higher writing speeds, and if the stylus diameter is decreased for better service, including higher resolution, the stylus lifetime eventually becomes unsatisfactory.

In practice, substantial stylus wear also degrades printout or gray tone quality.

It is an object of the present invention to obviate or mitigate the above mentioned disadvantages.

The present invention is in a method of recording information in a recording area with a plurality of recording styli distributed across, and reciprocated transversely of, said recording area, the improvement comprising in combination the steps of reciprocating each stylus across a reciprocation band wider than a width obtained by dividing the width of said recording area by the number of said styli; and recording information in said recording area with any stylus only within a recording band narrower than said reciprocation band.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 'shows a writing format of a multistyli recording system according to a preferred embodiment of the subject invention; Figure 2 is a graph of styli movement with respect to time, according to a preferred embodiment of the subject invention; Figure 3 diagrammatically indicates the writing method used in the preferred form of the invention which uses electro-sensitive paper; Figure 4 is a top view of a multistyli recording apparatus operated according to a preferred embodiment of the subject invention, with non-essential or conventional parts omitted for increased clarity; Figure 5 is an elevation of the mutistyli recording apparatus shown in Figure 4;; Figure 6 is a block diagram of the printer input and control circuits; Figure 7 is a plan view of an optical encoder disc used in the apparatus of Figures 4 and 5 for implementing the writing format of Figure 1 and styli movement of Figure 2; Figure 8 is a section through an eccentric drive assembly according to a further preferred embodiment of the subject invention; Figure 9 is a circuit diagram of a stylus driver, according to a further preferred embodiment of the subject invention; and Figure 10 is a diagrammatic showing of a dust and vapour extraction system employed in multistyli recoding systems according to preferred embodiments of the subject invention.

The writing format of the multistyli recording system or printer according to the illustrated preferred embodiment of the subject invention will presently be described with reference to Figure 1, which shows the formation of the character "A". Although the printing of an alphanumerical character is employed as an example, the same format is used in the printing of gray tone graphics or pictures.

In particular, the writing area is divided into a square grid of 1/8mm spaced points and printing is effected by the production of pixels (picture elements) having variable size-intensity on the point grid. The grid is 2048 pixels wide and any number of pixels in the paper feed direction. Printing is effected on a line by line bases and each line of pixels is divided into groups of 16, each group being assigned to one of the 128 styli. Figure 1 shows complete pixel groups for the first and last line styli (stylus 0 and stylus 127) and partial pixel groups for the second and penultimate styli (stylus 1 and stylus 126). The styli are reciprocated or oscillated in the line direction so that each stylus traverses each group of 16 pixels; e.g. stylus 0 in one oscillation direction (line 1) traverses pixels 0 - 15.

During the recording or printing of each line, the paper record sheet is held stationary, movement being effected between lines. In Figure 1, no printing is to be effected at the line 1 pixels shown in the diagram.

The styli are oscillated or reciprocated back and forth across their 16 pixels and, in Figure 1, line 1 is traversed buy a left to right oscillation portion, whereas line 2 is traversed by a right to left oscillation portion, the paper record sheet having been advanced 1/8mm during the change in oscillation direction. For the purpose of clarity, the styli paths indicated in Figure 1 show styli oscillation amplitude excursions beyond the 16 pixels writing lines by doted outlines 20. In practice, these deliberate extra amplitude excursions cover about 3 to 3.5 pixel spacings outside the assigned printing region of each stylus. The relevance of this "over oscillation" will more fully be described later.

In the formation of the character "A" illustrated in Figure 1 by stylus 0, at pixel locations or grid intersections 8 and 7, stylus 0 prints dots on the paper record sheet. The size-intensity of these printed dots could in fact be any one of 15 levels of gray tone, but for the purposes of illustration, the dot sizes in Figure 1 represent black or maximum intensity printing. The paper advance between lines is made equal to the line pixel spacings to produce a square grid.

Some aspects of the mutistyli printer according to the illustrated preferred embodiment of the subject invention may be further understood from a consideration of Figure 2. This figure shows a plot of styli displacement against time for two adjacent styli, for example, stylus 0 and stylus 1. Each stylus is responsible for printing within a longitudinal band on the record sheet and in the preferred embodiment, as there are 128 styli, each stylus is responsiblefor printing within a band 121 which is 1/128th of the width of the record sheet printing area; indicated at 110 in Figure 4 between dotted lines 112 and 113.

By sharing the printing area between a multiplicity of styli in this manner, the high effective writing speeds required for the printing of high resolution pictures can be achieved. In most applications it is desirable that each stylus writing band does not overlap with the writing bands of others. This means that the writing band of each stylus is equal in width to the styli spacing. According to a preferred embodiment, the paper used as the record sheet is about 11" in width and the printing area width is 256mm (10.1"). Thus the width of the styli printing bands and the styli spacing in the preferred embodiment is 2mm. It is obvious that each stylus must reciprocate or scan across its printing band with an amplitude at least equal to the width of the printing band, if continuous lines are to be printed.However, according to an aspect of the subject invention, the stylus reciprocation amplitude is made greater than the width of the printing band, each stylus being, however, controlled to print only as it scans within its assigned printing bands 121.

In the preferred embodiment, each stylus is made to over-oscillate it assigned printing band by about 0.41 5mm on each side of the assigned band to produce a reciprocation amplitude of 2.83mm peak to peak. As can be seen from Figure 2, stylus over-oscillation results in a time delay or gap between left to right and right to left scans of each stylus across its printing band.

According to a preferred embodiment of the present invention, this time delay or gap is utilized to load printing information into the styli stores to allow bi-directional writing, i.e. stylus writing in both left to right and right to left directions, and to advance the record sheet by a distance equal to the line spacing which is 1/8mm. Consecutive picture lines or pieces of information are therefore written in opposite directions in the course of styli reciprocation.

As is evident from Figure 2 the use of stylus over-oscillation means that the styli motion across their respective printing bands, and in particular while they are actually writing, is at a more constant velocity since the most non-linear portions of the stylus displacement curve occur outside the printing bands. This feature gives a very uniform print intensity across each printing band.

It is also evident from Figure 2 that for a line scan tobe printed faithfully independent of the direction of stylus head motion, the printing bands should occur symmetrically with respect to the centre of head motion. Provision therefore must be made to set the phase of the printing bands within a reciprocation cycle, as well as the angular separation. The printing of each pixel is initiated as the styli move into position on the pixel grid.

However, since the printing of a pixel may take almostthe whole time for the styli to move from one nominal pixel position to the next depending on the stylus head osciallation speed and the gray tone intensity required, the styli will transverse an elongated region during the printing of a pixel. Pixels will have a centroid or center of pixed area shifted from the nominal correct position by an amount depending on the pulse length. Since the intense gray pixels dominate the subjective appearance of the print it may be appropriate to advance the initiation of printing by an interval to compensate the centroid shift of the highest operating print intensities at the highest stylus head oscillation speed.This will ensure that intense pixels printed on succeeding lines occur in linear columns (see Figure 1) and the nominal centroid spacing of pixels is peserved across the assigned printing band. By using an electronic delay which increases appropriately as the stylus head oscillation speed decreases, the high intensity pixels are printed at the correct pixel grid position independently of stylus head oscillation speed.

With reference to Figure 2, it should be understood that such figure shows a time graph, rather than a printout of the preferred format. Also, since no printing takes place at the amplitude peaks, these may be distorted as shown in Figure 2 without any adverse effect on printout quality.

As has been mentioned with reference to Figure 1, each printed line is made up of 2,048 pixels of which each stylus is assigned the printing of 16 such pixels.

For this purpose, the styli printing bands as can be seen from Figure 2 are each divided into 16 seg nients scanned sequentially in time, with gray scale information determining each dot size being supplied to each stylus as it crosses from one print segment to the next. The flow of gray scale information and the stores for implementing this will be described later.

In the preferred embodiment, electrosensitive paper is used as the record sheet and the styli write by passing an electric current through the electrosensitive paper. The electro-sensitive paper employed may be of a conventional kind, wherein a white or reflecting top coating on the recording medium or paper acts as a dielectric coating until a threshold voltage is attained at an applied stylus and breakdown occurs. Upon such breakdown, electric energy supplied by the stylus removes some of the top coating, exposing a dense black underlayer on the recording medium or paper. Typical top coatings are cellular layers including, for instance, air or gas bubbles contained in electrically rupturable organic or inorganic cell structures.

The mechanics of the employed writing method and apparatus are diagrammatically illustrated in Figure 3, which may be considered incorporated in the stylus driver 153 shown in Figure 4. The electrosensitive paper 52 is passed around a metal roller or platen 50 which is maintained at earth or ground potential.

Each stylus indicated diagrammatically by the arrow heads 51 comprises a short length or tip of tungsten which is biased continuously against the electro-sensitive paper 52. When a stylus is to write (a dot), a potential is applied to it by a corresponding switching transitor 53, the stylus current being limited by a collector or emitter resistor 54. The stylus current path is completed between the stylus tip and the platen 50 through the electro-sensitive paper 52 with the electric energy burning off a portion of the white top layer or paper coating in the vicinity of the stylus tip. Gray tone or dot sizeintensity is achieved by varying the time duration of the stylus writing pulses, as more fully explained below.

Although the preferred embodiment of the invention uses electro-sensitive paper, the invention is not so limited and other methods of writing, provided they are compatible with the writing speed required to produce high quality gray tone pictures, line graphics and alpha numerics, could be used. For example, ink styli on plain paper where each dot written is produced by a controlled jet of ink discharged from the stylus, or a xerographictechni- que, could be employed.

Figures 4 and 5 jointly illustrate a multistyli recording apparatus or printer 60 constructed to operate, and operated, according to a preferred embodiment of the subject invention to implement the writing format illustrated in Figure 1 and writing mode illustrated with the time graph of Figure 2.

The printer 60 has a main frame assembly 61, including metal plate side walls 62 and 63.

It will be recalled in this respect from Figure 3, that the recording paper 52 passes over or around the grounded platen 50 at the electrically energized styli 51. The platen 50 may be part of the drive of the recording paper 52 which may also include supply and takeup rollers, pinch rollers and other paper drive equipment, which may be conventional and a showing of which has been omitted for the purpose of increased clarity.

For instance, the paper transport mechanism may include a metal plate deck (not shown) which stretches across most of the main frame between side walls 62 and 63 to support the recording paper 52 adjacent the platen 50 which drives the paper.

In practice, printing with the styli 51 occurs along a line extending on the surface of the paper 52 along, and parallel to the axis of rotation of, the platen 50.

An electric stepping motor 65 is coupled to the platen 50 via an internal reduction drive and effects paper advance pursuant to the above mentioned preferred embodiment of the subject invention.

The motion or advance of the paper 52 proceeds in discrete increments rather than continuously, with one incremental advance occuring between each adjacent pair of lines to be printed. The stepping motor 65 and associated drive are designed to produce one paper advance increment of 1/8mm for each angular step of the motor. Since the paper is required to be moved 1/8mm within, say, 4 milliseconds, without over-shoot or chatter, the motor must be carefully controlled. The motor winding control is preferably effected by a transistor switching system which uses unclamped constant current circuits, that is no feed back diodes, to enable more rapid switching.

Figures 4 and 5 also show the stylus head assembly 67 and stylus head wag drive 68. The stylus head assembly 67 comprises a head support 71 which is mounted on leaf springs 72 and 73 anchored to the main frame assembly by blocks 74 and 75, respectively, so that stylus head support is parallel to main frame 61 or main frame base plate.

The leaf springs 72 and 73 may be provided with corresponding cutouts (not shown), if it is desired to locate the platen 50 more toward the styli or otherwise to accommodate the curvature of platen 50.

Leaf springs 72 and 73 form a mounting system which enables the stylus head support 71 to be oscillated parallel to the axis of the platen 50 and thus transverse to the longitudinal direction of the paper to be printed.

Vertical motion is made negligible by making the leaf spring lengths much greater than the reciprocation amplitude. In place of leaf springs 72 and 73, it would be possible to use a slide arrangement to facilitate the oscillating or reciprocating motion of the head support; but the leaf spring mounting has been found superior for higher oscillation frequencies.

As seen in Figure 4, the stylus head per se comprises a bar 76 which carries a number of leaf springs 78 which, in turn, carry the tungsten tips or styli 51. The springs 78 with styli 51 are electrically insulated from each other and may be grouped into stylus modules which in a preferred prototype contain 16 styli per module. As indicated in Figure 4, each stylus consists of a tungsten tip mounted in the end of a leaf spring 78 cantilevered from the mounting bar 76 or module base. In use, the tungsten tips are held in continuous contact with the paper by the stored force in leaf springs 78. The styli diameter is preferably about 0.15mm and the length of the cantilevered leaf spring 78 is a compromise between torsional stability which is degraded with length, and predictable stylus pressure which is enhanced with increasing length.

The stylus head is mounted in the support 67 with fastenings passing preferably through head apertures into threaded bores (not shown) provided in the head support.

To permit high oscillation frequencies, the stylus head assembly is made as light as possible and for this reason, no provision is made in the preferred embodiment to hinge the styli away from the paper and paper transport mechanism. Separation of the two may be performed by sliding the paper transport mechanism rearwardly on lateral slides (not shown).

The stylus head is oscillated by a servo-control)ed DC motor 80, the output shaft of which carries a double eccentric 81. The eccentric is formed in two halves 82 and 83, with the latter coupled to a stylus head connecting rod 85 which passes through apertures in the stylus head support 71 and is connected thereto by fasteners, one of which is seen at 86. Rotation of the eccentric 81 by the DC motor 80 thus causes the stylus head assembly 67 to execute a reciprocating motion on leaf springs 72 and 73, which in the preferred form is simple harmonic.

Other reciprocating drives could be employed and inevitable regions of changing velocity confined to the regions outside the assigned printing bands.

The movement of the stylus head may cause the printer to vibrate, notwithstanding a light head design. To overcome this vibration, a counter weight may be oscillated in counter movement to the head assembly.

According to Figures 4 and 5, this counter weight is made up by two weights or masses 91 and 92 clamped to a leaf spring 93 and coupled to the upper eccentric half 83. Adjustment of lower eccentric half 82 relative to the motor shaft axis determines the stylus head oscillation amplitude and relative angular orientation of the two eccentric halves permits vibration cancellation. A set screw 95 is shown in Figures 4 and 5 as a means for releasably retaining the eccenter parts in a set relative position.

The digital input and control circuits of the illustrated multistyli printer will now be briefly described.

It will be recalled that each printed line is built up from 2,048 pixels printed by 128 styli which each print 16 pixels. The present printer is a line-scan or raster-scan printer-plotter and, accordingly, the input circuits accept one line scan of data consisting of 2,048 bytes of four bit gray scale information prior to the printing of each line. This data is then sent in parallel to the 128 styli in appropriate time sequence during the over-oscillation time interval as described in relation to Figure 2 and shown therein. Control of gray scale in the print-out is accomplished by converting the four bit gray scale code (16 levels of gray tone) for each pixel into the width of the stylus write pulse for a particular pixel in the stylus printing band.

It will be recalled that the present printer will also print alpha-numeric characters as well as pictorial and graphical information, and accordingly, the input circuits will accept alpha-numeric text in ASCII code and overlay the characters on the gray scale picture as it is printed.

Referring to Figure 6, the essentials of the informationn processing will be briefly described, using terminology and a diagram which appeared in the above mentioned Patterson et al. article. As shown in Figure 6, one interface part includes a direct link to a PDP-11/05 Unibus wherein data and control signals are transferred from and to a CPU (central processing unit) via an Adapter.

As pointed out by Patterson et al, communication between the Adapter and the Interface can be either entirely serial in nature using only a single twisted wire pair- up to 300m in length, or it can be a combination of serial and parallel using a twisted pair and a 10-conductor cable of up to 5m in length.

In this latter mode, the twisted pair is used to transfer ASCII character data from the Adapter to the Interface and for returning "end of line" signals from the Interface to the Adapter. The 10-conductor cable is used to transfer gray-scale data from the Adapter to the Interface.

Gray-scale data are sent from the Adapter as a sequence of 1024 8-bit bytes in either bit-serial or bit-parallel with the lower order 4-bits of each byte corresponding to the right segment and the higher order four bits to the left segment of each pair of segments.

After completion of a line-scan the Interface will send and "end of line" signal back to the Adapter which will interrupt the PDP-1 1. The CPU responds by looking in location 274 for the address of the first word of the interrupting program and proceeds to that location for its next instruction.

In the serial transmission mode picture data is shifted out as a series of bits at a 140kHz clock rate.

The first bit is a "1" serving as a start bit. The second bit is also a "1" indicating that the data transmitted is gray-scale data while the next 8 bits are the grayscale byte ordered with the least significant bit first.

ASCII characters are always sent in serial mode with the first bit transmitted being the start bit as before. The second bit is now "0" identifying the succeeding seven data bits as character representation. Each text line consists of 128 characters (i.e.

one per stylus) and it is necessary to send out the full 128 characters (with blanks as necessary) to fill a line.

Completion of transmission of a byte in the serial mode results in the Adapter unterrupting the PDP11. The CPU looks in location 270 for the address of the first word of the interrupting program and proceeds to that address.

Central to the operation of the illustrated Interface are two memories, M1 and M2. M1 stores 1,024 eight bit bytes representing the 2,048 four bit gray scale data pixels required for one line scan, and with M2 storing 128 eight bit ASCII coded characters for a character line of text.

Once memory M1 is loaded with a line scan of gray scale information, any pixels forming part of characters to be printed in that line scan are read sequentially from memory M2 via an ASCII coded 7 x 9 point 128 character generator M3 and overlaid onto the appropriate points in memory M1 at maximum gray scale level (level 15). The line information stored in memory M1 is read into that memory in the over-oscillation region immediately prior to the styli scan for that particular line. Then prior to the styli crossing into their first printing segments, for gray scale code for each zero segment for each stylus is transferred from memory M1 to 128 four bit latches L0-1 27, one latch associated with each stylus.As has been previously mentioned, gray tone is produced by varying the width of the stylus write pulse. This write pulse may vary in duration from 0 to 1 ms. There are 15 preset pulse times plus the zero pulse to produce the 16 level graytone and the gray tone time intervals are preset in plug-in time scale memory 4. Since different papers require different time intervals, various ROMs may be switched, and the bit pattern may eve be scrambled if security is desired. Memory M5 sets the bit pattern corresponding to each particular analogue time interval for memory M4. Digital comparators C0-127 for each stylus compare the time interval bit pattern with the four bit gray code data in each of the stylus latches L0-127.When the two bit patterns match, a strobe pulse, which is generated at the end of each of the sixteen gray tone time intervals, is gated through to the appropriate stylus drive flip-flop F0-1 27 and resets it to the 0 state, it having been set to the 1 state at the time the writing means entered the particular printing segment.

The latches L0-1 27 are loaded 16 times during each wag to supply gray scale information for each of the 16 dots printed by each stylus. After the sixteenth loading, memory M1 is cleared and the paper record sheet is advanced 1/8mm during the over-oscillation time period. Memory M1 is reloaded with a further line scan of 2,048 points and if a new line of characters is to be started, memory M2 is cleared and loaded with the new character line.

These operations are all completed before the stylus head leaves the over-oscillation zone.

The timing of the information processing operations is dependent on the instantaneous physical position of the stylus head and the timing controller T1 receives position information from an encoder disc 100 coupled to the reciprocation drive motor 80 (see Figure 5). This disc (shown in piane view in Figure 7), which is fabricated from an optically transparent material, is provided with three concentric marked bands 101, 102 and 103, which are read by individual light source and sensor units, shown collectively at 105 in Figure 5. One rotation of the encoding disc 100 corresponds to one reciprocation cycle and the outer code band 101 comprises two diametrically opposed 90" arcs(l0la and 101b) of black code markings each corresponding to one of the 16 stylus printing segments.The stylus head reciprocation cycle comprises 90" of left to right oscillation through 16 printing segments; 90" of over-oscillation; 90" of right to left oscillation through 16 printing segments; and 90" of overoscillation.

The code markings in the outer code band of the disc are positioned at angular intervals which correspond to equal linear spacings of the stylus print segments and are located at the following angles: 48.48", 54.93", 60.910,66.560, 71.980,77.230,82.380, 87.470,92.530,97.620, 102.770, 108.020, 113.440, 119.09 ,125.07 and 131.52". Itwill be noted that the use of over-oscillation (in the present case a peak over-oscillation of 1.414 or the square root of two) provides for a linearization of the code mark segments which vary in spacings from 6.45 at the first and last segments to 5.063 between the eighth and ninth segments. The outer code band is read by a sensor at 105 and the timing pulses detected are fed to the timing controller T1 (Figure 6). The second coding band 102 is a solid black arc from 0" to 1800 which provides a means for detecting the direction of stylus head motion and is read buy a corresponding sensor unit. The inner code band 103 comprises 90 equally spaced markings which are read by a corresponding sensor unit to provide a tachometer feedback for the speed control of DC reciprocation drive motor 80 and to provide an electronic speed signal for the generation, if desired, of a printing delay as the stylus head oscillation speed decreases.

The use of an encoder of the type described allows the setting up of the 16 dot locations within each stylus band. The required "phase" adjustment referred to in the discussion of Figure 2 is made by simply rotating the position of the optical sensors in 105 (Figure 5) relative to the zero reference angle (0 REF.) of the disc 100.

The encoded transducer need not be optical in character; a possible alternative would be to use magnetic coupling or a magnetic time disc.

Considering the disclosure herein provided, it will be recognized that the subject invention, from a first aspect thereof, resides in a method and apparatus for recording information in a recording area 110 with a plurality of recording styli 51 distributed across, and reciprocated transversely of, the recording area 110 which, in Figure 4, is shown as extending between borders indicated by dotted lines 112 and 113. An eccentric drive 68 is coupled to the styli for reciprocating each stylus 51 across a reciprocation band which is wider than a width obtained by dividing the width of the recording area 110 by the number of styli 51 (see Figures 2 and 4).

An encoder including an encoder disc 100 shown in Figures 5 and 7, a control including a timing controller T1 as shown in Figure 6, and the transisto rized stylus drivers 53 shown in Figure 3, contitute a means connected to the styli 51 for recording information in the recording area 110 with any stylus onlywithin a recording band 121 narrower than the reciprocation band 122 as shown, for instance, in Figure 2.

The styli 51 are distributed at mutual interstylus spacings across the recording area 110 and, accord ing to another aspect of the subject invention, each stylus is reciprocated at a reciprocation amplitude 123 larger than an interstylus spacing (see Figure 2).

Information is recorded in the recording area 112 with any stylus 51 only within a recording band 121 narrowerthan the reciprocation amplitude 123.

The styli 51 are reciprocated by a drive 68 in alternating first and opposite second directions transversely of the recording area 110. According to a further aspect of the subject invention, information is recorded with the styli 51 in the recording area 110 in the course of movement in first directions 125, and information is also recorded with the styli 51 in the recording area 110 in the course of movement in second directions 126, as indicated in Figures 2 and 4.

The stylus drive 68 moves the styli 51 transversely of the recording area 110 at a velocity at least as substantially linear as a segment between -45 and +45 of a sine wave extending symmetrically to a 0 zero cross-over, and further moves the styli at a velocity less linear than the mentioned sine wave segment. As illustrated in Figure 2, the stylus movement amplitude has such a substantialy linear segment in both directions of stylus movement within the narrower recording band 121. Also, there is a less linear or non-linear velocity movement for each stylus at either side of the narrower recording band 121 (see 20 in Figure 1 and 123 in Figure 2).

The timing disc 100 shown in Figures 5 and 7 and the timing controller T1 with the remainder of the control shown in Figure 6 constitute a means connected to the styli 51 for recording information with such styli in the recording area 110 only during movement of the styli at the substantially linear velocity within the narrower recording band 121.

The subject invention also resides in methods and apparatus for recording information pixels on a recording medium sheet at intersections of a pixel grid shown in part in Figure 1,with a plurality of mutually spaced in-line recording styli 51 reciprocated transversely of the sheet 52. The control shown in Figure 6 assigns or allocates to each stylus 51 a number of pixel grid intersections for pixel recording. In this respect, sixteen pixels or pixel grid intersections are apparent to 0 to 15 in Figure 1 as to the Stylus 0.

The drive 68 constitutes a means coupled to the styli for reciprocating the styli 51 at an amplitude exceeding by a first distance spanning several pixel grid intersections a second distance spanning the number of pixel grid intersections assigned to any stylus. The mentioned first distance is apparent at 20 in Figure 1 or at the lateral excursions of the wave in Figure 2. On the other hand, the mentioned second distance is the distance spanning pixels or grid intersections 0 to 15 shown in Figure 1 orthe narrower recording band 121 shown in Figure 2. As mentioned above, the first distance may be equal to about 3 to 3.5 interstylus or pixel spacings. The mentioned second distance may be equal to sixteen interstylus or pixel spacings.

The time disc 100 shown in Figures 5 and 7, the control shown in Figure 6 and the stylus supply 120 with accompanying transistorized stylus driver, again constitute a means connected to the styli for recording information pixels with any stylus only at the assigned number of pixel grid intersections.

The paper drive 65 shown in Figures 4 and 5 and rotatable platen 50 constitute a means coupled to the sheet 52 for advancing the sheet incrementally relative to the styli 51 by a third distance spanning the space between two adjacent intersections of the pixel grid and being, by way of example, 1/8 of a millimeter.

As disclosed above, the reciprocation band 122 preferably in equal in width to the recording band 121 times the square root of two. In practice, this provides for the desired near linearity of stylus velocity within the recording band if the stylus drive is of a sinusoidal nature, as provided by the eccenter 81.

As seen in Figure 2, the reciprocation band 122 exceeds the recording band on both sides of that recording band 121.

By the same token, the reciprocation amplitude of the styli 51 preferably is equal to the interstylus spacing between two adjacent styli, times the square root of two. Again, the reciprocation amplitdue exceeds the recording band 121 preferably on both sides of that recording band.

The recording area 110 is located on a recording medium sheet 52 as shown in Figure 4, and the stepping motor drive 65 maintains the sheet stationary during any information recording within the recording band 121. On the other hand, the paper drive 65 incrementally advances the sheet 52 relative to the styii 51 while these styli are located outside of any recording band 121 in the course of their reciprocations in the outer excursions of the reciprocation amplitude 123.

Preferably, the sheet is incrementally advanced relative to the styli 51 while these styli are located at one side of the recording band 121 shown in Figure 2, and also while the styli are located at an opposite side of the recording band in the course of styli reciprocation.

In the illustrated bidirectional stylus drive, the recording sheet 52 is maintained stationary during any information recording in the course of styli movement in the mentioned first and second directions, and the sheet 52 is incrementally advanced relative to the styli 51 in intervals between movements in alternating first and second, and second and first, directions of stylus reciprocation.

In terms of stylus velocity, the incremental paper drive 65 maintains the recording sheet 52 stationary during any stylus movement at the above mentioned substantially linear velocity within the recording band 121 shown in Figure 2, but advances the sheet 52 incrementally relative to the styli 51 between styli movement at the above mentioned less linear or non-linear velocity illustrated by the peaks of the curve shown in Figure 2.

The styli 51 are reciprocated in unison, being located on the mounting bar 76 which is shuttled by the eccenter drive 68.

In order to further linearize gray scale across each information recording band 121, consecutive pieces of information or picture lines are recorded in opposite directions in the course of styii reciprocation.

In the illustrated preferred embodiment, the recording sheet 52 is advanced incrementally in intervals between pixel information recordings at the assigned number of pixel grid intersections 0 to 15.

In particular, the sheet is advanced incrementally in the course of excursions of the amplitude covering the above mentioned first distance indicated at 20 in Figure 1.

As mentioned above in connection with Figure 6, the control illustrated therein stores pixel information in the course of the excursions 20 of the latter amplitude covering the mentioned first distance 20.

This stored pixel information is released to the styli 51 for recording in the assigned number of pixel grid intersections 0 to 15 as to each stylus. As seen in Figures 1 and 2, information pixels are recorded as to each stylus within the assigned number of pixel grid intersection during travel of that stylus by the mentioned second distance 0 to 15 in a first direction and within the assigned number of pixel grid intersections during travel of the stylus by the second distance 15 to 0 in an opposite second direction.

Accordingly to a preferred embodiment, the invention may broadly be said to reside in a multistyli gray tone printer which prints on the intersections of a pixel grid covering the printing area (see Figures 1 and 2) and which comprises a record sheet transport mechanism 50, 65 which moves a record sheet 52 longitudinaliy, a plurality of in-line styli 51 carried by a head assembly 67 mounted transversely to the record sheet path, each stylus being assigned a number of pixels 0 to 15 to print on said grid.

The gray tone printer also includes means 68 which reciprocate said stylus head in a line of motion transverse to the record sheet path, the reciprocation amplitude being greater than the styli spacing to produce a stylus displacement 122 greater than the assigned printing region, a store shown in Figure 6 for receiving gray tone information for each pixel to be printed, a stylus activating means for each stylus which when triggered activates the corresponding stylus for a time duration determined by the gray scale information held in said store for the pixel to be printed by that stylus at the time of triggering, and control means, also shown in Figure 6, which load the store with gray scale information and move thee record sheet 52 forward by a distance equal to the grid spacing when the stylus head is in a region outside the assigned printing region and triggers said stylus activating means as each stylus passes over each pixel it is assigned to print when moving in the assigned printing region.

In the predecessor multistyli printer described in the above mentioned Patterson et al paper, the stylus assembly was very massive as compared to the stylus assembly 67 and, at the writing speed of that printer, provided tolerable overall vibration. On the other hand, a combination of highertransverse scan styli speed and much lower machine or stylus assembly mass brought about unacceptable vibration in experimental predecessors of the illustrated printer. This problem has been solved by the dynamic balancing methods and devices of an embodiment of the subject invention.

According to this embodiment, the mass or counterweight 90 is reciprocated in phase opposition to the reciprocating stylus assembly 67, which is dynamically balanced with the reciprocating mass or counterweight 90.

According to a preferred embodiment of the subject invention, the counterweight 90 is provided with a mass corresponding to the mass of the stylus assembly 67. In particular, the mass of the counterweight 90 may be equal to the mass of the stylus assembly.

As shown at 72 and 73 for the stylus assembly, and at 93 for the counterweight or mass 90, the stylus assembly 67 and the counterweight or mass 90 may each be spring suspended. In particular, the leaf spring suspension technique used to support the stylus assembly 67 is in effect employed to suspend the counterweight 90 for oscillatory motion.

According to the subject invention, the double eccentric 81 jointly reciprocates the stylus assembly 67 and the counterweight or mass 90 in phase opposition to each other.

The double eccentric 81 shown in section in Figure 8 has been found that effective in practice, that multistyli printers have been retrofitted therewith to reduce vibration, increase writing speed and enhance printout quality.

In particular, a first eccentric drive 82 is located on the shaft 84 which is rotated by the servo motor 80.

The first eccentric drive 82 is coupled to the stylus assembly 67 via a bearing 88, flange 89 and connecting rod 85 for reciprocating the stylus assembly 67 relative to the recording area 110 or paper 52 during rotation of the shaft 84.

In addition to the counterweight or mass 90, the means according to the illustrated preferred embodiment for dynamically balancing the reciprocating stylus assembly 67 include a second eccentric drive 83 located on the shaft 84 and coupled to the first eccentric drive at an extreme angular displacement relative to the first eccentric drive. This extreme angular displacement may be a displacement by 180 . In other words, the phase angles of the first and second eccentric drives 82 a 83 may be diametrically opposed so that the oscillations or reciprocations of the stylus assembly 67 and counterweight or mass 90 are 180 out of phase.

According to the illustrated preferred embodiment of the subject invention, the first and second drives 82 and 83 are mounted on a common shaft 84, and are arranged as closely together as possible in order to coincide their lines of action and to minimize the force couple between them which, if substantial, would in itself produce vibration.

The upper or first eccentric drive 83 is coupled to the counterweight or mass 90 via a bearing 97, flange 98 and rod 87. The rod 87 is attached to the counterweight assembly 90, and preferrably to the leaf spring 93 thereof. The counterweight or mass part 91, located on the side of the leaf spring 93 facing the eccentric 81, may have an aperture or bore 99 so that the part 91 clears the connecting rod 87 and thereby prevents objectionable forces from interfering with the operation of, and from imposing excessive wear, on the eccentric drive assembly.

The eccentric drives 82 and 83 are coupled to each other by one or more screws or bolts 131 which releasably clamp the drives 82 and 83 to each other.

In this respect, it should be noted that the bolt 131 does not extend through the shaft 84. Rather, this bolt extends behind the shaft 84 as seen in Figure 8, and a similar or coresponding bolt may, if desired, be provided on the side of the shaft 84 facing the observer of Figure 8. In this respect, reference is made to Figure 1 which shows a similar set screw extending parallel to, but being spaced from the shaft 84. The bolt 131 has a shaft 132 which extends through a bore 133 in the eccenter drive 83. The shaft 132 of the bolt 131 has a threaded end 134 engaging the thread of an internally threaded bore 135. In this manner, the bolt 131 releasably clamps the first and second eccentric drives or eccenter halves 82 and 83 together.

In principle, either of the first and second eccentric drives 82 and 83 could be connected to the shaft 84, with the other of these eccentric drives being connected to that one eccentric drive and including means for adjusting the position of the other eccentric drive relative to that one eccentric drive. According to the preferred embodiment illustrated in Figure 8, the second eccentric drive or upper eccenter half 83 is connected to the shaft 84. In particular, the upper half 83 may be attached to the shaft 84 by a press fit or, preferably, by a set screw (not shown).

Further radial set screws 137 and 138 act on the first eccentric drive 82 relative to the shaft 84 for radially adjusting and setting the first eccentric drive 82 relative to the second eccentric drive 83. To this end, the upper and lower eccenter halves 82 and 83 jointly define radial bores 139 and 140 for accommodating the set screws 137 and 138. To permit relative adjustment of the first half 82 relative to the second half 83, the upper half 141 of the bore 139 and the upper half 143 of the bore 140 are smooth, whereas the lower half 144 of the bore 139 and the lower half 145 of the bore 140 are internally threaded for meshing engagement by the screws 137 and 138, respectively.

Among several possible alternatives, the preferred embodiment shown in Figure 8 elects to design and dimension the upper or second eccentric drive 83 for reciprocation of the counterweight or mass 90 at an amplitude equal to the maximum reciprocation amplitude of the stylus assembly 67. The preferred embodiment of Figure 8 thus allocates reciprocation amplitude adjustment to the stylus head drive. In Figure 8, the eccenter 81 is shown as set for minimum amplitude of the reciprocating stylus assembly 67. It may be noted in this respect that the largest clearance between the shaft 84 and the cylindrical wall of the axial bore 146 of the lower eccenter half 82 is at the left side of the shaft 84 as seen in Figure 8.

The optimum reciprocation amplitude for the stylus assembly 67 may be set by either using a dial gauge or by observing printing in a test mode. In this respect, there should be no detectable gaps or overlaps between the adjacent bands printed by the reciprocating styli 91 in the recording area 110.

For gross adjustment, the clamp bolt or bolts 131 are slackened and axial adjustment is effected with the set screws, the angular position of the eccenter 81 relative to the connecting rods 85 and 87 then being such as to render the set screws 137 and 138 accessible by a screwdriver or suitable wrench.

Since progressing tightening of the set screws 137 and 138 tends to jack the upper and lower eccenter halves 82 and 83 apart, it is important that the finial adjustment, such as the last 5 to 10 mils be done with the clanip bolt or bolts 131 in tight position.

Final adjustment is thus done by just breaking the tightness of the set screw 137 or 138 which is paying out, tightening thy makeup set screw 138 or 137, and then re-tightening the paying out set screw 137 or 138.

Practicai tests have confirmed the preferred embo dimentofthe invention shown in Figure 8 to present a compact, economical design which satisfies requirements for high precision. In any set position, the eccenter drive 81 is solid, free from backlash, and the amplitude can be adjusted while the angular relationship between the eccentric and the motor shaft 84 is preserved. This is important for the maintenance of a correct phase relationship between the writing encoder and the actual stylus movement.

.Reverting now to Figure 3 and its description set forth above, it will be recalled that information is recorded on paper 52 with an electrically biased stylus by selectively breaking down and removing, with electric energy supplied through that stylus and a corresponding electrode forming part of the recording paper 52, portions of the mentioned dielectric top coating to expose corresponding portions of a contrasting underlayer of the recording medium 52. According to a preferred embodiment of the subject invention, there is applied to any stylus 51 and corresponding paper roller platen 50 an electric direct current having at the stylus 51 a negative potential relative to the electrode 50 of sufficient magnitude to breakdown a portion of the dielectric top coating.To record a dot or similar information element, a portion of the dielectric top coating is broken down with the negative potential at the stylus 51 relative to the common electrode 50, and such broken-down portion is removed with electric direct current supplied via stylus 51 and corresponding electrode 50.

Apparatus according to the subject invention include a source 120 of electric direct current having a positive terminal connected to the paper roller 50 and a negative terminal 50 connected to the switching transistors 53 as shown in Figure 3. The source 55 includes an electric power supply for providing at the negative terminal a negative potential relative to the positive terminal or paper roller 50 of sufficient magnitude, if applied via a stylus 51, to break down a portion of the dielectric top coating of the recording paper 52.

The choice of stylus polarity was made on considerations of stylus ablation during use. It was discovered that if the stylus potential was made negative with respect to the platen potential, stylus life was considerably enhanced, i.e. with this particu lar polarity ablatement of wear at the stylus tip occurred more slowly than was the case when the stylus potential was made positive with respect to the platen potential. It is believed that the energy in the arc between the stylus and the platen is driven into the positive polarity component and accordingly it is that component which will suffer most wear during the arcing process. The use of a negative stylus potential results in a finer paper residure which is more readily removed by an airflow, such as more fully described below, to further reduce cleaning and maintenance of the writing head.

The stylus drive circuit will now be described. An important feature of this is the mode of energy transfer which has been selected. One preferred electro-sensitive paper is the above mentioned Timemark 14 recording paper manufactured by Fitchburg Coated Products, Inc., and experiments with this paper have indicated that a stylus voltage in excess of 150 volts is required to obtain the position resolution and gray tone fidelity required.

The voltage used in the preferred embodiment is -180 volts. Experiments were also undertaken to determine whether the stylus drive should be constant voltage, constant current or constant power.

These experiments indicated that a more satisfactory writing result was achieved when the energy transfer was by a constant power mode, i.e. the output resistance of the stylus drive should be approximately equal to the "through resistance" of the paper when writing from stylus to platen. This through resistance varies due to the grainyness of the paper, but after breakdown has occurred, i.e.

when conduction is taking place, the through resistance averages at about 7 Kohms. In brief, the direct current having the negative potential is proved at a source resistance being of the same order of magnitude as a conduction resistance through the top coating and contrasting underlayer of the recording paper 52.

In Figure 9, the drive circuits are shown for four styli 51, with NPN transistors 53, designated as Q3, Q6, Q9, and Q12 swtiching the -180 volt supply applied from the negative terminal via lead 65.

Collector resistors 54 designated as R6, R12, R18, and R24 respectively ensure approximately constant power drive. The common emitter configuration of the switching transistors was selected for reasons of efficiency. In practice it was found that by reducing the value of the series resistors, R6, R12, R18 and R24 from the theoretical optimum of 7 Kohms to 3.3 Kohms little was lost in terms of writing quality.

Such a reduction allows the use of a power supply of lower capacity. It will be appreciated that with about 100 styli writing, currents of around 3 amps may be passing into the paper and accordingly overall printer power consumption can be reduced significantly by lowering the value of the stylus seeries resistors from the optimum for constant power drive. A preferred source resistance range thus extends from 3 to 7 Kohms.

The output switching transistors are driven by transitor pairs Q1, Q2; Q4, Q5; Q7, Q8; Q10, Q1 1 in cascode configuration, the input or stylus switching signals being supplied to the base resistors R2, R8, R14 and R20 which with base resistors R1, R7, R13 and R19 result in an AND gate configuration to allow the alternative application of a common test input.

Suitable bias voltages are applied via leads 67 and 68.

The negative potential stylus driving methods and apparatus of the subject invention increase the lifetime of the styli 51 by a factor of from three to five relative to positively biased styli. Such driving methods and apparatus also enable substantial writing speed increases, and material improvements in gray scale rendition and in resolution through use of finer styli.

The use of an electrosensitive writing method means that there is dust and odor production as the electrosensitive paper coating is removed during writing. At high writing speeds, this problem increases and in a preferred embodiment, a dust and vapor extraction system is incorporated.

According to Figure 10 the extraction system takes the form of a motor driven fan 156 coupled by a duct 157 to a manifold 158 which surrounds the paper 52 as it passes around platen 50 and draws air 159 in at high velocity between the styli 51 to remove the dust and vapor in a rearward direction through a duct where they are collected in a filter. A sliding duct joint using a sealing gasket 160 ensures coupling between the fan circuit of the dust extraction circuit and the manifold 158 which is mounted on the moving stylus head.

The air flow past the styli eliminates or reduces the accumulation of paper residue on the styli resulting in prints of much improved position and gray tone precision than obtained without airflow. In addition the print is produced free of dust and smudges.

The position of the stylus head relative to platen 50 is such that the styli make contact with the paper about 30 back from the horizontal tangent to the platen. This means the styli make contact with the paper while it is still completely in contact with the platen to secure the advantages of uniform stylus pressure, uniform paper contact with the platen and better visibility of the printing process than would be the case if the line of contact were made at the horizontal tangent to the platen where the paper leaves the platen surface.

Each stylus 51 preferably has a shaped tungsten tip 171 mounted at the free extremity of a cantilevered leaf spring 172 which, in turn, is mounted on a stylus head bar 173.

Claims (96)

1. In a method of recording information in a recording area with a plurality of recording styli distributed across, and reciprocated transversely of, said recording area, the improvement comprising in combination the steps of reciprocating each stylus across a reciprocation band wider than a width obtained by dividing the width of said recording area by the number of said styli, and recording information in said recording area with any stylus only within a recording band narrower than said reciprocation band.

2. A method as claimed in claim 1, wherein said reciprocation band is equal in width to said recording band times the square root of two.

3. A method as claimed in claim 1 or claim 2, wherein said reciprocation band exceeds said recording band on both sides of said recording band.

4. In a method of recording information with a plurality of recording styli distributed at mutual interstylus spacings across, and reciprocated transversely of, a recording area, the improvement comprising in combination the steps of reciprocating each stylus at a reciprocation amplitude larger than an interstylus spacing, and recording information in said recording area with said stylus only within a recording band narrower than said reciprocation amplitude.

5. A method as claimed in claim 4, wherein said reciprocation amplitude is equal to said interstylus spacing times the square root of two.

6. A method as claim 4 or claim 5, wherein said amplitude exceeds said recording band on both sides of said recording band.

7. A method as claimed in claim 1,2,3,4,5 or 6, wherein said recording area is located on a recording medium sheet, said sheet is maintained stationary during any information recording within a recording band, and said sheet is incrementaly advanced relative to said styli while said styli are located outside of any recording band in the course of styli reciprocation.

8. A method as claimed in claim 1,2,4 or 5, wherein said reciprocation exceeds said recording band on both sides of said recording band, said recording area is located on a recording medium sheet, said sheet is maintained stationary during any information recording within a recording medium band, and said sheet is incrementally advanced relative to said styli while said styli are located to one side of any recording band and also while said styli are located at an opposite side of any recording band in the course of styli reciprocation.

9. In a method of recording information with a plurality of recording styli distributed across, and reciprocated in alternating first and second directions transversely of, a recording area, the improvement comprising in combination the steps of recording information with said styli in said recording area in the course of movement in said first directions and recording information with said styli in said recording area in the course of movement in said second directions.

10. A method as claimed in claim 9, wherein each stylus is reciprocated in said alternating first and second directions across a reciprocation band wider than a width obtained by dividing the width of said recording area by the number of said styli, and said recording of information with any stylus in the course of movement in said first and second directions is limited to a recording band narrowerthan said reciprocation band.

11. A method as claimed in claim 10, wherein said reciprocation band is equal in width to said recording band times the square root of two.

12. A method as claimed in claim 10 or 11, wherein said reciprocation band exceeds said recording band on both sides recording band.

13. A method as claimed in claim 9,10, 11 or 12, wherein said styli are distributed at mutual interstylus spacings across said recording area, each stylus is reciprocated in said alternating first and second directions at a reciprocation amplitude larger than an interstylus spacing, and said recording of information with any stylus in the course of movement in said first and second directions is limited to a recording band narrower than said reciprocation amplitude.

14. A method as claimed in claim 13, wherein said reciprocation amplitude is equal to said interstylus spacing times the square root of two.

15. A method as claimed in claim 13 or 14, wherein said amplitude exceeds said recording band on both sides of said recording band.

16. A method as claimed in any of claims 9 to 15, wherein said recording area is located on a recording medium sheet, said sheet is maintained stationary during any information recording in the course of styli movement in said first and second directions, and said sheet is incrementally advanced relative to said styli in intervals between movement in alternating first and second, and second and first, directions.

j7. In a method of recording information with a plurality of recording styli distributed across a recording area, the improvement comprising in combination the steps of moving said styli transversely of said recording area at a velocity at least as substantially linear as a segment between -45" and +45 of a sine wave extending symmetrically to a 0 zero crossover, further moving said styli at a velocity less linear than said segment, and recording information with said styli in said recording area only during movement of said styli at said substantially linear velocity.

18. A method as claimed in claim 17, wherein said styli are reciprocated in alternating first and second directions transversely of said recording area, said styli moving includes the steps of moving said styli in said first directions at said substantially linear velocity and further at said less linear velocity, and moving said styli in said second directions at said substantially linear velocity and further at said less linear velocity, and said information recording includes the step of recording information with said styli in said recording area only during movement of said styli at said substantial linear velocity in said first direction and at said substantially linear velocity second direction.

19. A method as claimed in claim 17 or 18, wherein said recording area is located on a recording medium sheet, said sheet is maintained stationary during any stylus movement at said substantially linear velocity, and said sheet is incrementally advanced relative to said styli between styli movements at said less linear velocity.

20. A method as claimed in any of claims 1 to 19, wherein said styli are reciprocated in unison.

21. A method as claimed in any of claims 1 to 20, wherein consecutive pieces of information are recorded in opposite directions in the course of styli reciprocation.

22. In a method of recording information pixels on a recording medium sheet at intersections of a pixel grid, with a plurality of mutually spaced in-line recording styli reciprocated transversely of said sheet, the improvement comprising in combination the steps of assigning to each stylus a number of pixel grid intersections for pixel recording, reciprocating said styli at an amplitude exceeding by a first distance spanning several pixel grid intersections a second distance spanning said number of pixel grid intersections assigned to any stylus, recording information pixels with any stylus only at said assigned number of pixel grid intersections, and advancing said sheet incrementally relative to said styli by a third distance spanning the space between two adjacent intersections of said pixel grid.

23. A method as claimed in claim 22, wherein said sheet is advanced incrementally in intervals between pixel information recordings at said assigned number of pixel grid intersections.

24. A method as claimed in claim 22, wherein said sheet is advanced incrementally in the course of excursions of said amplitude covering said first distance.

25. A method as claimed in claim 22,23 or 24, wherein pixel information is stored in the course of excursions of said amplitude covering said first distance and is released to said styli for recording in the assigned number of pixel grid intersections as to each stylus.

26. A method as claimed in claim 22,23,24 or 25, wherein information pixels are recorded as to each stylus within the assigned number of pixel grid intersections during travel of that stylus by said second distance in a first direction and within the assigned number of pixel grid intersections during travel of said stylus by said second distance in an opposite second direction.

27. In apparatus for recording information in a recording area with a plurality of recoding styli distributed across, and reciprocated transversely of, said recording area, the improvement comprising in combination means coupled to said styli for reciprocating each stylus across a reciprocation band wider than a width obtained by dividing the width of said recording area by the number of said styli, and means connected to said styli for recording information in said recording area with any stylus only within a recording band narrower than said reciprocation band.

28. Apparatus as claimed in claim 27, wherein said reciprocation band is equal in width to said recording band times the square root of two.

29. Apparatus as claimed in claim 27 or 28, wherein said reciprocation band exceeds said recording band on both sides of said recording band.

30. In apparatus for recording information with a plurality of recording styli distributed at mutual interstylus spacings across, and reciprocated transversely of, a recording area, the improvement comprising in combination means coupled to said styli for reciprocating each stylus at a reciprocation amplitude larger than an interstylus spacing, and means connected to said styli for recording information in said recording area with said stylus only within a recording band narrower than said reciprocation amplitude.

31. Apparatus as claimed in claim 30, wherein said reciprocation amplitude is equal to said interstylus spacing times the square root of two.

32. Apparatus as claimed in claim 30 or 31, wherein said amplitude exceeds said recording band on both sides of said recording band.

33. Apparatus as claimed in claim 27, 28, 29,30, 31 or 32, wherein said recording area is located on a recording medium sheet, and said apparatus includes means coupled to said sheet for maintaining said sheet stationary during any information recording within a recording band and for incrementally advancing said sheet relative to said styli while said styli are located outside of any recording band in the course of styli reciprocation.

34. Apparatus as claimed in claim 27,28,30 or 31, wherein said stylus reciprocation exceeds said recording band on both sides of said recording band, said recording are is located on a recording medium sheet, and said apparatus includes means coupled to said sheet for maintaining said sheet stationary during any information recording within a recording medium band and for advancing said sheet incrementally relative to said styli while said styli are located to one side of any recording band and also while said styli are located at an opposite side of any recording band in the course of styli reciprocation.

35. In apparatus for recording information with a plurality of recording styli distributed across a recording area, the improvement comprising in combination means coupled to said styli for reciprocating said styli in alternating first and second directions transversely of said recording area, and means connected to said styli for recording information with said styli in said recording area in the course of movement in said first directions and for recording information with said styli in said recording area in the course of movement in said second directions.

36. Apparatus as claimed in claim 35, wherein said reciprocating means include means for reciprocating each stylus in said alternating first and second directions across a reciprocation band wider than a width obtained by dividing the width of said recording area by the number of said styli, and said recording means include means for recording information with any stylus in the course of movement in said first and second directions only in a recording band narrower than said reciprocation band.

37. Apparatus as claimed in claim 36, wherein said reciprocation band is equal in width to said recording band times the square root of two.

38. Apparatus as claimed in claim 36 or 37, wherein said reciprocation band exceeds said recording band on both sides of said recording band.

39. Apparatus as claimed in claim 35, wherein said styli are distributed at mutual interstylus spacings across said recording area, said reciprocating means include means for reciprocating each stylus in said alternating first and second directions at a reciprocation amplitude larger than an interstylus spacing, and said recording means include means for recording information with any stylus in the course of movement in said first and second directions only in a recording band narrower than said reciprocation amplitude.

40. Apparatus as claimed in claim 39, wherein said reciprocation amplitude is equal to said interstylus spacing times the square root of two.

41. Apparatus as claimed in claim 39 or 40, wherein said amplitude exceeds said recording band on both sides of said recording band.

42. Apparatus as claimed in any of claims 35 to 41, wherein said recording area is located on a recording medium sheet, and said apparatus includes means for maintaining said sheet stationary during any information recording in the course of styli movement in said first and second directions and for incrementally advancing said sheet relative to said styli in intervals between movements in alternating first and second, and second and first, directions.

43. In apparatus for recording information with a plurality of recording styli distributed across a recording area, the improvement comprising in combination means coupled to said styli for moving said styli transversely of said recording area at a velocity at least as substantially linear as a segment between -45 and +45 of a sine wave extending symmetrically to a 0 zero crossover and for further moving said styli at a velocity less linear than said segment, and means connected to said styli for recording information with said styli in said recording area only during movement of said styli at said substantially linear velocity.

44. Apparatus as claimed in claim 43, wherein said styli moving means include means for reciprocating said styli in alternating first and second directions transversely of said recording area and for thus moving said styli in said first directions at said substantially linear velocity and further at said less linear velocity, and for moving said styli in said second directions at said substantially linear velocity and further at said less linear velocity, and said recording means include means for recording information with said styli in said recording area only during movement of said styli at said substantial linear velocity in said first direction and at said substantially linear velocity in said second direction.

45. Apparatus as claimed in claim 43 or 44, wherein said recording area is located on a recording medium sheet, said apparatus includes means for maintaining said sheet stationary during any stylus movement at said substantially linear velocity and for incrementally advancing said sheet relative to said styli between styli movements at said substantially linear velocity.

46. Apparatus as claimed in any one of claims 27 to 45, wherein said apparatus includes means for mounting said styli in-line transversely across said recording area, and said reciprocating means include means coupled to said mounting means for reciprocating said styli in unison.

47. Apparatus as claimed in any of claims 27 to 46, wherein said recording means include means for recording consecutive pieces of information in opposite directions in the course of styli reciprocation.

48. In apparatus for recording information pixels on a recording medium sheet at intersections of a pixel grid, with a plurality of mutually spaced in-line recording styli reciprocated transversely of said sheet, the improvement comprising in combination means connected to said styli for assigning to each stylus a number of pixel grid intersections for pixel recording, means coupled to said styli for reciprocating said styli at an amplitude exceeding by a first distance spanning several pixel grid intersections a second distance spanning said number of pixel grid intersections assigned to any stylus, means connected to said styli for recording information pixels with any stylus only at said assigned number of pixel grid intersections,

and means coupled to said sheet for advancing said sheet incrementally relative to said styli by a third distance spanning the space between two adjacent intersections of said pixel grid.

49. Apparatus as claimed in claim 48, wherein said sheet advancing means include means for advancing said sheet incrementally in intervals between pixel information recordings at said assigned number of pixel grid intersections.

50. Apparatus as claimed in claim 48, wherein said sheet advancing means include means for advancing said sheet incrementally in the course of excursions of said amplitude covering said first distance.

51. Apparatus as claimed in claim 48, including means for storing pixel information in the course of excursions of said amplitude covering said first distance, and means connected to said storing means for releasing stored information to said styli for recordation in the assigned number of pixel grid intersections as to each stylus.

52. Apparatus as claimed in claim 48,49,50 or 51, wherein said recording means include means for recording information pixels as to each stylus within the assigned number of pixel grid intersections during travel of that stylus by said second distance in a first direction and within the assigned number of pixel grid intersections during travel of said stylus by said second distance in an opposite second direction.

53. A method as claimed in any of claims 1 to 26, including the steps of providing said styli in a stylus assembly, providing a mass, reciprocating the stylus assembly relative to the recording area, reciprocating said mass in phase opposition to the reciprocating stylus assembly, and dynamically balancing the reciprocating stylus assembly with the reciprocating mass.

54. A method as claimed in any of claims 1 to 26, including the steps of providing said styli in a stylus assembly, providing a counterweight of a mass corresponding to the mass of the stylus assembly, reciprocating the stylus assembly relative to the recording area, reciprocating the counterweight in phase opposition to the reciprocating stylus assembly, and dynamically balancing the reciprocating stylus assembly with the reciprocating counterweight.

55. A method as claimed in any of claims 1 to 26, including the steps of recording information with said styli by selectively breaking down and removing, with electric energy supplied through said styli and a corresponding electrode forming part of a recording medium, portions of a dielectric top coating to expose corresponding portions of a contrasting underlayer of said recording medium, applying to said stylus and corresponding electrode an electric direct current having at said stylus a negative potential relative to said electrode of sufficient magnitude to break down a portion of said dielectric top coating, breaking down a portion of said dielectric top coating with said negative potential at said stylus relative to said electrode, and removing said broken-down portion with said electric direct current supplied via said stylus and corresponding electrode.

56. Apparatus as claimed in any of claims 27 to 52, including said styli in a stylus assembly movable relative to a recording area, a first eccentric drive coupled to the stylus assembly for reciprocating the stylus assembly relative to the recording area, and means for dynamically balancing the reciprocating stylus assembly including a counterweight and a second eccentric drive coupled to the first eccentric drive at an extreme angular displacement relative to the first eccentric drive and coupled to the counterweight for reciprocating the counterweight in phase opposition to the reciprocating stylus assembly.

57. Apparatus as claimed in any of claims 27 to 52, including said styli in a stylus assembly movable relative to a recording area, a shaft, means for rotating said shaft, a first eccentric drive located on said shaft and coupled to the stylus assembly for reciprocating the stylus assembly relative to the recording area during rotation of the shaft, and means for dynamically balancing the reciprocating stylus assembly including a counterweight and a second eccentric drive located on said shaft and coupled to the first eccentric drive at an extreme angular displacement relative to the first eccentric drive and coupled to the counterweight for reciprocating the counterweight in phase opposition to the reciprocating stylus assembly during rotation of the shaft.

58. Apparatus as claimed in any of claims 27 to 52, including means for recording information with said styli by selectively breaking down and removing, with electric energy supplied through said stylus and a corresponding electrode forming part of a recording medium, portions of a dielectric top coating to expose corresponding portions of a contrasting underlayer of said recording medium, including a source of electric direct current having a positive terminal and a negative terminal and includng means for providing at said negative terminal a negative potential relative to said electrode of sufficient magnitude to break down a portion of said dielectric top coating, means for connecting said corresponding electrode to said positive terminal, and means for selectively connecting said stylus to said negative terminal to break down a portion of said dielectric top coating with said negative potential at said stylus relative to said electrode and to remove said broken-down portion with said electric direct current from said source.

59. In a method of recording information with a stylus assembly in a recording area, the improvement comprising in combination the steps of providing a mass, reciprocating the stylus assembly relative to the recording area, reciprocating said mass in phase opposition to the reciprocating stylus assembly, and dynamically balancing the reciprocating stylus assembly with the reciprocating mass.

60. In a method of recording information with a stylus assembly in a recording area, the improvement comprising in combination the steps of providing a counterweight of a mass corresponding to the mass of the stylus assembly, reciprocating the stylus assembly relative to the recording area, reciprocating the counterweight in phase opposition to the reciprocating stylus assembly, and dynamically balancing the reciprocating stylus assembly with the reciprocating counterweight.

61. In a method of recording information with a stylus assembly, the improvement comprising in combination the steps of providing a mass, and jointly reciprocating the stylus assembly and said mass in phase opposition to each other.

62. A method as claimed in claim 59 or 61, wherein said mass is reciprocated at an amplitude equal to a maximum reciprocation amplitude of the stylus assembly.

63. A method as claimed in claim 59 or 61, wherein said mass and the stylus assembly each are spring suspended.

64. A method as claimed in claim 63, wherein said mass is reciprocated at an amplitude equal to a maximum reciprocation amplitude of the stylus assembly.

65. In a method of recording information with a stylus assembly, the improvement comprisng in combination the steps of providing a counterweight of a mass corresponding to the mass of the stylus assembly, and jointly reciprocating the stylus assembly and the counterweight in phase opposition to each other.

66. A method as claimed in claim 60 or 65, wherein said counterweight is reciprocated at an amplitude equal to a maximum reciprocation amplitude of the stylus assembly.

67. A method as claimed in claim 60 or 65, wherein said counterweight and the stylus assembly each are spring suspended.

68. A method as claimed in claim 67, wherein said counterweight is reciprocated at an amplitude equal to a maximum reciprocation amplitude of the stylus assembly.

69. In apparatus for recording information with a stylus assembly in a recording area, the improvement comprising in combination first means for reciprocating the stylus assembly relative to the recording area, and means for dynamically balancing the reciprocating stylus assembly including a counterweight and means coupled to said first means for reciprocating the counterweight in phase opposition to the reciprocating stylus assembly.

70. In apparatus for recording information with a stylus assembly, the improvement comprising in combination a counterweight, means coupled to the stylus assembly and to the counterweightfor jointly reciprocating the stylus assembly and the counterweight in phase opposition to each other.

71. Apparatus as claimed in claim 69 or 70, including a spring suspension for said stylus assembly, and a corresponding spring suspension for said counterweight.

72. Apparatus as claimed in claim 69 or 70, wherein said counterweight has a mass corresponding to the mass of the stylus assembly.

73. Apparatus as claimed in claim 69 or 70, wherein said counterweight reciprocating means include means for reciprocating the counterweight at an amplitude equal to a maximum reciprocation amplitude of the stylus assembly.

74. Apparatus as claimed in claim 73, wherein said counterweight has a mass corresponding to the mass of the stylus assembly.

75. In apparatus for recording information with a stylus assembly in a recording area, the improvement comprising in combination a first eccentric drive coupled to the stylus assembly for reciprocating the stylus assembly relative to the recording area, and means for dynamically balancing the reciprocating stylus assembly including a counterweight and a second eccentric drive coupled to the first eccentric drive at an extreme angular displacement relative to the first eccentric drive and coupled to the counterweight for reciprocating the counterweight in phase opposition to the reciprocating stylus assembly.

76. Apparatus as claimed in claim 75, wherein said first and second eccentric drives are adjustable relative to each other

77. Apparatus as claimed in claim 75, wherein said first and second eccentric drives are radially adjustable relative to each other.

78. Apparatus as claimed in claim 75, wherein said first drive includes means for radially adjusting the first eccentric drive relative to the second eccentric drive to vary the reciprocation amplitude of the stylus assembly.

79. In apparatus for recording information with a stylus assembly in a recording area, the improvement comprising in combination a shaft, means for - rotating said shaft, a first eccentric drive located on said shaft and coupled to the stylus assembly for reciprocating the stylus assembly relative to the recording area during rotation of the shaft, and means for dynamically balancing the reciprocating stylus assembly including a counterweight and a second eccentric drive located on said shaft and coupled to the first eccentric drive at an extreme angular displacement relative to the first eccentric drive and coupled to the counterweight for reciprocating the counterweight in phase opposition to the reciprocating stylus assembly during rotation of the shaft.

80. Apparatus as claimed in claim 79, wherein one of said first and second eccentric drives is connected to said shaft, and the other of said eccentric drives is connected to said one eccentric drive and includes means for adjusting the position of said other eccentric drive relative to said one eccentric drive.

81. Apparatus as claimed in claim 79, wherein said second eccentric drive is connected to said shaft, and said first eccentric drive is connected to said second eccentric drive and includes means for radially adjusting the first eccentric drive relative to the second eccentric drive.

82. Apparatus as claimed in claim 75 or 79, wherein said counterweight has a mass corresponding to the mass of the stylus assembly.

83. Apparatus as claimed in claim 75 or 79, including a spring suspension for the stylus assembly, and a spring suspension for the counterweight.

84. Apparatus as claimed in claim 83, wherein said counterweight has a mass corresponding to the mass of the stylus assembly.

85. In a method of recording information with an electrically biased stylus by selectively breaking down and removing, with electric energy supplied through said stylus and a corresponding electrode forming part of a recording medium, portions of a dielectric top coating to expose corresponding portions of a contrasting underlayer of said recording medium, the improvement comprising the steps of applying to said stylus and corresponding electrode an electric direct current having at said stylus a negative potential relative to said electrode of sufficient magnitude to break down a portion of said dielectric top coating, breaking down a portion of said dielectric top coating with said negative potential at said stylus relative to said electrode, and removing said b,roken-down portion with said electric direct current supplied via said stylus and corresponding electrode.

86. A method as claimed in claim 85, wherein said negative potential at said stylus relative to ground has a magnitude of more than 150 volts.

87. A method as claimed in claim 85, wherein said electric direct current is applied to said stylus in a constant power mode.

88. A method as claimed in claim 85 or 86, wherein said direct current having said negative potential is provided at a source resistance of from 3 Kohms to 7 Kohms.

89. In apparatus for recording information with an electrically biased stylus by selectively breaking down and removing, with electric energy supplied through said stylus and a corresponding electrode forming part of a recording medium, portions of a dielectric top coating to expose corresponding portions of a contrasting underlayer of said recording medium, the improvement comprising in combination a source of electric direct current having a positive terminal and a negative terminal and including means for providing at said negative terminal a negative potential relative to said electrode of sufficient magnitude to break down a portion of said dielectric top coating, means for connecting said corresponding electrode to said positive terminal, and means for selectively connecting said stylus to said negative terminal to break down a portion of said dielectric top coating with said negative potential at said stylus relative to said electrode and to remove said broken-down portion with said electric direct current from said source.

90. Apparatus as claimed in claim 89, wherein said negative potential providing means include means for providing a negative potential of more than 150 volts.

91. Apparatus as claimed in claim 90, including means for applying said electric direct current to said stylus in a constant power mode.

92. Apparatus as claimed in claim 89, including means for providing said direct current having said negative potential at a source resistance being of the same order of magnitude as a conduction resistance through said top coating and underlayer.

93. Apparatus as claimed in claim 89, including means for providing said direct current having said negative potential at a source resistance of from 3 Kohms to 7 Kohms.

94. Apparatus as claimed in claim 89, wherein said stylus has a tungsten tip.

95. A method of recording information in a recording area with a plurality of styli distributed across, and reciprocated transversely of, said recording area substantially as hereinbefore described with reference to the accompanying drawings.

96. Apparatus for recording information in a recording area with a plurality of styli distributed across, and reciprocated transversely of, said recording area substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.