MAGNETIC TONER TRANSFER METHOD AND APPARATUS

Abstract: Apparatus and method are provided for transferring toner particles (96) at a relatively high speed from a magnetically created latent image onto a toner-receiving medium (15) such as paper without sacrificing edge acuity or providing unwanted background, the latent image having been magnetically recorded on a magnetizeable web (13) such as magnetic tape. Generally, in both impact and electrostatic transfer systems, the record medium and/or paper are moved relative to each other prior to or during transfer. However, we have found that as the speeds of relative approaching motion between the toned medium (13) and the toner-receiving medium (15) are increased to meet higher print speed requirements, the associated velocities of escaping air (aerodynamic forces) in the transfer region proximate to the record medium (13) and the paper increase correspondingly, ultimately causing disruptive air currents (Figs. 4A and 4B) to form in the transfer region and the toner (96) present on either the medium (13) or paper (15) to disperse or spread. This toner disturbance produces poor character image edge acuity and unwanted background in, between, and around the character images. The invention provides close control of the velocity of the relative approaching (and separating) movement between the toned medium (13) (tone tape segment) and the toner-receiving medium (15) (paper) at the transfer station, maintaining such velocity at or below a predetermined maximum relatively high speed velocity which varies as a function of the instantaneous separation between the two media.

Description: MAGNETIC TONER TRANSFER METHOD AND APPARATUS Background of the Invention This invention relates to magnetographic print¬ ing generally, and more particularly to non-impact electrostatic toner transfer techniques for both improving print quality and increasing print speed. Often, when improvements are made in print quality, print speed (image transfer speed) is reduced, and when print speed is increased, print quality is reduced. For example, impact printing devices such as the electric typewriter or the so-called daisywheel type impact printer produce high quality print but are relatively slow. These devices print copy material by striking a preformed character against an inked ribbon onto paper. When using a carbon film type ribbon, these devices produce high quality print (i.e., letter-quality print as compared to print of lesser quality produced, for example, by dot matrix printers, thermal printers, computer line printers, and the like), but are generally noisy and print at the comparatively slow rate of 15-55 characters (symbols) per second. Certain other impact printers such as computer line printers are faster (e.g., they are capable of printing in excess of 900 lines per minute ) but produce poor quality (i.e., non-letter- quality) print. This print qualit /print speed trade-off problem is also reflected in magnetic or magnetographic printing systems. Of those magnetographic printing systems which transfer images by impact, contact of the record medium ( i.e., magnetic tape, drum, or other means carrying the toned magnetic image) with the paper introduces additional problems of contamination and degradation of the record medium. For example, in the system described in U.S. Patent 3,735,416 issued to Ott, the useful life of the magnetic belt is shortened significantly due to toner particles becoming embedded in or otherwise contaminating the belt surface as a result of pressure of the record medium against the paper. This contamination causes excess toner to accumulate on the tape surface, soiling the non-image areas (background areas) of the record medium and, hence, the paper, producing a smudged or dirty background effect on the paper. As in Ott's system, the system described in the U.S. Patent 3,740,265 issued to Springer transfers toner from a record medium (magnetic belt) to paper by means of pressure. This causes toner to become crushed into the surface of the belt, thus contami¬ nating the belt and causing toner background to build-up, . upon successive image transfers, in an unsightly manner on the paper. In U.S. Patent 3,254,646 issued to Umera, a toned magnetic belt is struck by a hammer causing the belt to impac the paper for transfer of the toned image from the belt to the paper. In U.S. Patent 3,749,833 issued to Rait, the transfer of toner particles to paper is accom¬ plished by means of pressure rollers. Again, in both Umera and Rait, toner background problems would be encoun¬ tered and belt or roller life would be shortened due to the toner particles becoming embedded in the surface of the magnetic medium. Other magnetic or magnetographic systems attempt to avoid this problem of contamination of the record medium by maintaining an air gap between the record medium and the paper, and transferring the toner image electro¬ statically rather than by impact or applied pressure. One such system is described in U.S. Patent 3,477,368 issued to Spaulding. Another such system is described in U.S. Patent 4,175,265 issued to Nelson et al. Generally, in both types of systems (impact and electrostatic transfer systems) the record medium and/or paper are moved relative to each other prior to or transfer. However, we have found that as the speeds of relative approaching motion between the toned medium and the toner-receiving medium are increased to meet higher print speed requirements, the associated velocities of escaping air (aerodynamic forces) in the transfer region proximate to the record medium and the paper increase cor¬ respondingly, ultimately causing disruptive air currents to form in the transfer region and the toner present on either the medium or paper to disperse or spread. This problem is amplified where it is intended that there be area contact between the media, as opposed to line contact systems such as are characteristically embodied in elec¬ trophotographic copying systems. The spread or loss of toner is most visible at the edges of the character images. This toner disturbance produces poor character image edge acuity and unwanted background in, between, and around the character images. Further, the air currents increase and are cumulative to a maximum level at or prox¬ imate to the physical edges of the toned medium. Thus, those characters or portions thereof which are present near the edges of the medium tend to experience dispropor¬ tionately greater disturbances than characters or portions thereof not so near the edges of the medium. In some systems that use electrostatic transfer, a high voltage (for example, a voltage greater than 1000 volts) is found to be necessary for transfer of toner from the record medium to paper. To reduce this high voltage necessary during the transfer process, some systems teach the application of a form of pretransfer or bias voltage. However, this pretransfer or bias voltage, which is applied just prior to transfer, is intended to facilitate transfer of toner to paper and tends to weaken the bond between record medium and toner. A system of this type is described, for example, in U.S. Patent 3,160,091 issued to Schwertz Unfortunately, in such systems the likelihood of toner spread is also substantial, because the effect of the air currents upon the toner particles (i.e., move ent of air occasioned by the relative movement of the paper and the record medium) tends to increase the spread of toner as a result of the binding force between toner and latent image being weakened due to the applied bias voltage. What is needed and would be useful, therefore, is a toner transfer method and system capable of providing high quality print without degrading image edge acuity or providing^unwanted background effects when printing at high speed, and such is a principal object of this invention. Summary of the Invention In accordance with the present invention, apparatus and method are provided for transferring toner particles at a relatively high speed from a magnetically created latent image onto a toner-receiving medium such as paper without sacrificing edge acuity or providing unwanted background, the latent image having been magneti¬ cally recorded by known means on a magnetizeable web such as magnetic tape. The invention provides close control of the velocity of the relative approaching (and separating) movement between the toned medium (toned tape segment) and the toner-receiving medium (paper) at the transfer station, maintaining such velocity at or below a predeter¬ mined maximum relatively high speed velocity which varies as a function of the instantaneous separation between the two media. The invention provides further for a carefully timed and controlled electrostatic transfer of electro¬ statically precharged toner particles from the tape medium to the paper. This comprises providing a bias electro¬ static field to the toner at the transfer station during relative movement of the two media which augments the toner-tape attracting forces and tends to prevent the premature- transfer of the toner to the paper ? and providing a transfer electrostatic field to the toner, when uniform contact has been established between the edia, for a sufficient time to ensure substantially complete transfer of the toner to the paper medium. This time includes the point of actual separation of the media and a period in which a predetermined separation distance is again reached between the media. According to a broader method and apparatus aspects of the invention, there is provided letter- quality, relatively high speed transfer operation - for exampe, 150 transfers per minute or greater, at one to six image lines per transfer involving the trans-fer of the toner particles being predeterminably arranged on a surface of a first medium to a toner-receiving second medium, which operation comprises the establishment of at least a first pretransfer force of attraction ( f ) between the toner and the first medium, and moving the first and second medium relative to one another such that the maximum force (f2) . exerted on the toner particles due to a high-speed movement of the first medium relative to a proximate toner-receiving second medium is less than force (fj) for any instantaneous separation between the first and second media. According to further broader method aspects of the invention, there is provided, in a process of high-speed transfer of toner particles from a toned first medium to a toner-receiving second medium at a given transfer station arrangement, which particles are predeterminably arranged on a surface of a first medium of preselected width and have associated therewith a preestablished toner holding force, the combination of steps which comprises the determination of the instanta¬ neous maximum velocity (v m ) of relative approaching movement of the first and second media as a function of: (1) the instantaneous separation distance therebetween, (2) the first medium's width, (3) the toner attracting force and (4) a preselected maxmium toner particle size, at and below which maximum velocity the toner particle arrangement on the first medium is maintained without substantial disruption; and effecting relative approaching movement between at least respective portions of facing surfaces of the first and second media until contact occurs therebetween, at a velocity (v) where v ■ < v m for any separation distance. Also according to the method aspects of this invention, there is provided a method of toned image transfer which comprises effecting, in succession, relative approaching movement, contact, and relative separating movement between at least respective portions of the facing surfaces of a toned first medium and a toner-receiving second medium substantially without disturbing the toner particle arrangement; subjecting the toner particles to a first electrostatic field, at least during the period of relative approaching movement begin- ning with a predetermined first separation distance being reached between said first and second medium portions, said first electrostatic field having a predetermined magnitude and a direction which urges the toner particles substantially toward the first medium and away from the second medium; and discontinuing the first electrostatic field and subjecting the toner particles to a second electrostatic field having a direction which urges the toner particles substantially toward the second medium and away from the first medium, for a predetermined time period following contact between said first and second medium portions, the close of which period is defined by a predetermined second minimum separation distance between the first and second medium portions being reached on relative separating movement thereof, said second electro- static field having a predetermined minimum magnitude at least when separation of the first and second medium portions is effected. According to the broader apparatus aspects of the invention, there is provided an apparatus for toned image transfer comprising a facing pair of media, the first of which is a toned endless medium (or fixed length medium) of pre-established width and having associated therewith a pre-established toner attracting force and the second- being: a toner-receiving medium; means for effecting high-speed relative approaching movement between the first and second media in accordance with a selected first velocity profile (acceleration) which includes an instan- taneous maximum relative approaching velocity which is proportional to. the width of and the toner attracting force associated with the first medium, at or below which instantaneous maximum velocity degradation of the toner particle arrangement is avoided; control means for effect- ing termination of the high-speed relative approaching movement upon a predetermined separation being achieved between the two media, which separation is proportional to the width of and the toner attracting force associated with the first medium; and means for generating relative approaching movement between the two media in accordance with a selected second velocity profile (deceleration), whereby the two media are brought into contact substantially without toner particle arrangement degrada¬ tion. The invention achieves the combined attributes of high speed, high quality and high reliability in a relatively simple and economic way. Relative movement between the media and ultimate contact therebetween is realized in the single-direction, reversable and closely controlled displacement of a single element. Transfer is accomplished with relatively low contact pressure between the media, with precharging of the toner, in deriving high efficiency (e.g., as high as 92%) of toner transfer, with high edge acuity and low background, over relatively long- term operation substantially without tape contamination. Yet, these accomplishments are achieved through the application of a relatively substantially low transfer field (as compared, for example, with conventional elec¬ trophotographic systems) and, consequent low applied voltage. Brief Description of Drawings The aobve- entioned objectives and features will become better .understood- with reference to the following deta-iled- description taken in conjunction with the accompanying drawings, in which: Fig. 1-is a combined schematic and block diagram of a system incorporating the present invention; Fig. 2- is a combined schematic and block diagram illustrating a preferred transfer station embodiment of the system of Fig. 1, in accordance with the invention; Fig. 3 is a combined schematic and block diagram illustrating a second embodiment of transfer station of the system of Fig. 1, in accordance with the invention; Figs 4A and 4B illustrate air currents generated by the relative approaching movement of the toned medium and paper and the tendency thereof to affect toner particle arrangement; Fig. 5A-5E are waveform diagrams illustrative of principal events occurring in connection with the transfer station of Figs. 2 and 3; Figs 6A and 6B are waveform diagrams illustrat¬ ing velocity profiles of relative approaching movement of the tape and paper as a function of respectively instan¬ taneous separation and time; and Fig. 7 is a graphic illustration of edge acuity, showing an ideal case, the case of transfer-station tape-to-paper relative velocity within the predetermined maximum of a given system and the case where said maximum for said system is exceeded. Description of Preferred Embodiments Referring now to Figure 1, there is shown a magnetographic printing apparatus or system 11 responsive, for example, to applied digital data, for recording data images on an endless magnetizeable medium or web such as a magnetic tape or band 13, for toning or developing the image, and for transferring the toned image to paper 15 to produce high quality printed output at relatively high- speed operation. The magnetizeable medium 13 is electri¬ cally conductive. The apparatus includes a magnetic recording head 17 for creating a magnetic latent image on tape 13, a- developer station 19 for developing the latent CMPI i age' by applying toner (dr -magnetically attractable ink particles contained in the developer station) to the latent image, and a transfer station 21 for transferring toner from the developed image to paper 15 or some other - medium. The latent image creation and development operations may be performed in much the same manner as described in U.S. Patent 4,110,758 issued to Nelson et al. As shown in Figure 1, tape 13 is operatively coupled to a shaft of motor 23 and is advanced by the motor as a closed loop through the various stations of the system. As the tape 13 passes recording station 18, recording head 17 records a magnetic latent image onto the tape. The tape is then advanced to developer station 19 where toner applicator brush or drum 27 develops the latent image by applying magnetic toner particles to the tape. The magnetized latent image areas on the tape attract the toner, thereby developing (toning) these image areas. Excess toner is removed from the tape by a scavenger brush or drum 29 and returned to toner reservoir 31.. As a further aid in cleaning the tape (i.e., removing unwanted toner from the tape), a first vacuum outlet 33 coupled to a vacuum source (not shown) provides a suction of air across the imaged (front) surface of the tape to remove background toner particles not tightly bound by the magnetic forces exerted by the image areas. Following developing and cleaning, the toner particles remaining on the tape are charged by a scorotron 35. The scorotron provides an ionizing source 37 and a bias screen 30 proximate to the tape surface to charge the toner particles on the tape prior to transfer of the toner .to the paper. The screen 39 of the scorotron 35 is maintained at a constant potential to ensure that the toner receives a uniform charge. After the recorded latent image is developed, the tape is cleaned, and the toner particles on the image areas are charged, the tape 13 is advanced to transfer station 21. In the example of embodiment here depicted, -the tape 13 is comprised of a predetermined nuώer (e.g., three) of segments for recording latent images. A hole (not shown) is formed through the tape preceding each such segment, a segment representing a length of tape used to print a line of characters (symbols). It will be appreci- ated that tape 13 could provide two or more lines of characters simultaneously to the transfer station. As a tape segment is moved into position in transfer station 21, light from a light source- of photosensor arrangement 41 passes through the hole and is detected by a detector of photosensor 41. In response to the detection of the hole, photosensor arrangement 41 applies a signal to controller 25 which brakes and stops the motor 23 (e.g., by applying a reverse polarity signal, then no signal to the motor) to position the tape segment within transfer station 21 in preparation for image transfer. With the tape segment having the toned image positioned thus for transfer, a moveable platen 43 of a tape positioner 49 is then actuated from the controller 25 via drive circuit 65 to press the tape segment with its toned image into gentle contact with the paper 15. A transfer voltage (pulse) is then applied to electrode 45 contained in hollow (vacuum) back plate 47 located adjacent to and above paper 15 which creates an electro¬ static force attracting the toner (the toned image) to the paper during the transfer period. While electrode 45 is shown in. Figures 2 and 3 somewhat apart from paper 15 for ease of illustration, the electrode is, in fact, in contact with the paper during transfer. Following image transfer, platen 43 is returned to an open (non-contact) position. The tape is then advanced by motor 23 as governed by controller 25 such that the tape segment cor¬ responding to the transferred developed image passes by a second vacuum outlet 75 which removes any residual toner particles from the tape's surface. Thereafter, the tape segment advances to a station 85 where the imaged portions are magnetically reoriented, thus preparing the tape segment for the next imaging operation. Fig. 2 shows a preferred embodiment of the transfer station 21. The segment of tape 13 carrying an imaged line of text is shown in position between the paper 15 and platen portion 43 of the transfer station 21. Platen 43 includes a horizontal portion 54 bearing a resilient covering 73 on its operative face. Situated behind the paper 15 is the transfer electrode 45 as contained in the hollow vacuum backplate 47. The paper 15 is maintained uniformly on the flat lower surface of backplate 47 by the presence of a controlled negative pressure thereon which communicates with the paper via a suitable arrangement of apertures (not shown) in the backplate's lower surface. As illustrated, an initial gap h (exaggerated for ease of understanding) exists between the tape medium 13 and the paper 15. Platen 43 is mounted upon a pair of rods housed in respective relatively long bearings 98 suitably affixed to the frame (not particularly shown) of the system. Movement of platen 43 is governed by a drive arrangement 78 which comprises an eccentrically mounted cam 76 having cam surfaces 80 and 82 in contact with the lower surface of platen 43. Cam 76 is secured to platen 43 via a spring 99, and the cam drive shaft is securely maintained in position relative to the system's frame. In operation, a drive signal is input- tα arrangement 78 (Figure 2) which actuates and governs continuous rotation of the cam whereby the cam surfaces 80 -and 82 thereof urge platen 43 upward at an instantaneously varying velocity (e.g., as depicted in Figs. 5C and 6B) such that the tape 13 controllably approaches the paper 15 situated on the lower surface of backplate 47, in accor¬ dance with the invention. Alternatively, arrangement 78 could comprise an eccentrically mounted cam having a less complex operating surface, which is driven by a stepping motor fed by an input control or drive signal of varying frequency corresponding to a selected velocity profile as shown in Fig. 6B. Design of a cam in accordance with the velocity profile may be made according to known methods reflected in the text "Cams" by H. Rothbart published by Wiley & Sons, New York, U.S.A. In another alternative arrangement (not particu¬ larly shown), unit 78 could be replaced by a spring-loaded bellows arrangement suitably coupled to a hydraulic system terminating in a cam-driven second bellows arrangement, the cam being contoured or configured so as to provide movement of the platen in accordance with a selected velocity profile. In this way, substantially all of the mechanical apparatus associated with the platen may be housed remotely from the transfer station, without sacrificing operation efficiency. Fig. 3 shows another embodiment of the transfer station 21. Tape positioner 49 (Fig. 1) comprises, as before, moveable platen 43, and in this embodiment a vertically moveable coil actuator-51. Platen 43 includes a vertical portion 53 and a horizontal or bar portion 54. Vertical portion 53 serves to rigidly coupie bar portion 54 to actuator 51. Actuator 51, in turn, includes a ring- shaped permanent magnet 55 and an armature 57. .The arma¬ ture 57 comprises a cylindrically shaped member 59 (illustrated in cross-section in Fig. 3) about which is wound a predetermined number of turns of conductor 61. Armature 57 and the vertical portion 53 of platen 43 are positioned for vertical motion within air gap 63 of ring magnet 55. Member 59 is constructed preferably of aluminum, which serves to damp the movement of the actuator to eliminate jitter. In response to a drive current signal applied by drive circuit 65 to armature 57 of actuator 51, a force proportional to the current in the conductor 61 in the magnetic field provided by ring magnet 55 serves to move platen 43, and in particular the horizontal bar 54, to bring the tape 13 rapidly into contact with the paper 15. Separation thereafter is achieved through the combination of the drive current and gravity. Fig. 4A illustrates the two-dimensional air currents 95 caused by the relative approaching movement of OMPI .. tape 13 and paper 15 at a velocity v for a relatively - - large separation distance between the tape and paper. Of course, similar air currents (though opposite in direction) are generated in reverse during relative 5 separating movement between the tape and paper. As shown, the air currents are directed outward and away from " the center of the tape, tending to influence (disturb) the toner particles 96. In Figs. 4A„and 4B particularly, the relative dimensions of tape 13, toner 96, paper 15, etc. 0 have been exaggerated for ease of illustration and under¬ standing. Fig. 4B shows the generated air currents 95 for the case of a relatively smaller tape-to-paper separation and how the toner particles 96 are then affected thereby. 5 As illustrated, the toner particles farther away from the center line of the tape (i.e., toward the edge of the tape) experience higher air currents than do particles nearer the center and are, therefore, more vulnerable to. the potentially disturbing forces caused by the air 0 currents. Thus, "w" in Figs. 4A and 4B is that width of the tape which accounts for the largest disturbing ' forces, i.e., those forces which are experienced by the toner particles near the edges of the tape. For the particular case of a narrow tape (narrow 5 in comparison to its length within the transfer station and to the dimensions of the paper), after repeated cal¬ culations and empirical tests, the instantaneous critical (maximum) velocity at which the tape may be allowed to approach paper, without creating a force (f2) that would 0 disturb the toner particles, has been found to be approximately according to the following equations: Vc = fl l/2 ( ^)- 2 .h2 r 2 .1/w (I) ■ f2 = v2 ( k/ . w 2 ) < £_ , and v < v c ( I I ) h 4 ~ where v c is the tape critical velocity, v is the actual or ins antaneous tape velocity, fl is the total force holding the toner particles to the tape, f2 is the disturbing or lift force exerted on a toner particle by the air currents generated between the tape and paper, __P is the density of the air (e.g., 1.3 x 10~3 gm/cc), h is the instantaneous separation distance between the tape and paper media, r is the radius of one of the largest sized toner particles , expected in signif icant proportion, w is the width of the tape , and k is a tape ge ometry factor or proportionality constant Λ*9U for tape conf igurations where the ratio of tape width (w ) to tape segment length {£) within the transfer region is << 1 (e . g . , where w _< 2.5 cm and = 25 cm in the examples depicted herein) . As this ratio approaches 1, k would become <9 " . Referring to equation I , it can be observed that the ins tantaneous tape-to-paper critical (maximum) velocity is directly proportional to the square of the instantaneous tape-to-paper distance (h ) and inversely proportional to the square of the radius (r ) of the toner particles and the width dimens ion (w ) of the tape medium. A direct relationship between the critical velocity (v c ) and the square root , of the air current forces [ 2 ) generated between tape and paper, is also shown. Equation I in particular predicts the relative sensitivity of the tape critical velocity (v c ), to the separation distance (h). To avoid disturbing the arrangement of the toner particles during relative approaching movement, and indeed relative separating movement as well, the instantaneous tape velocity (v) must not exceed the instantaneous critical velocity ( c UJ expressed by equation I in terms of instantaneous relative separation (h). In other words, as shown in equation II, the air current (aerodynamic) forces (f2) must remain less than the total toner- holding force (fi). Total toner-holding force (fl) is equal to the sum of the magnetic and electrostatic forces (f m + fe or alternatively f + f e + b' des¬ cribed hereinafter) holding the toner onto the tape. Fig. 5A illustrates the tape transport velocity profile of a toned segment of the tape in the vicinity of the transfer station. Fig. 5B shows a preferred drive current waveform (if employing the embodiment of Fig. 3) j applied by drive circuit 65 to coil 57 of actuator 51. Fig. 5C shows a platen velocity profile corresponding, for example, to the rotation of cam 76 (Fig. 2) or the drive current (Fig. 5B) applied from drive circuit 65 to actuator 51 (Fig. 3). Fig. 5D shows platen displacement effected by cam 76 (Fig. 2), or effected by actuator 51 away from fixed stop 67 (Fig. 3). Fig. 5E illustrates the bias (e.g., -100 volts) and transfer (e.g., +600 volts) potentials which effect the electrostatic forces governing the transfer of the toner. It is to be noted that Figs. 5A-5E are exemplary and are somewhat exaggerated for ease of illustration. ^ Once the toned portion of tape 13 has arrived at the transfer station 21, the tape is brought to a halt as shown by curve 90 of Fig. 5A. A drive signal input to cam drive arrangement 78 (Fig. 2) causes the platen 43 and thus the toned web 13 to rapidly accelerate (e.g., at approximately 4 x lθ3 cm / S ec 2 ) toward the paper as indicated in Fig. 5C. Alternatively, current pulse 71 on Fig. 5B causes actuator 51 and thereby platen 43 and the toned web 13 to rapidly accelerate toward the paper 15. Thus, point "A" in Figs. 5A-5E is that point in time at which the relative movement between the magnetic tape 13 and the paper 15 begins. When the displacement is such that the distance between the two media becomes relatively small, the velocity of the tape has to be carefully limited so as to not exceed the critical tape velocity to minimize the effects of the air currents generated by the approach of the tape 13 to paper 15 (Figs. 5C and 5D). The combin¬ ation of the shape of the cam surface 80, 82 (Fig. 2) and the spring force acting between the platen 43 and the cam shaft result in slowing down the approach velocity of the tape (Fig. 5C) and ultimately establishing a first tape-paper contact at a point "B π in time. In the case of the arrangement of Fig. 3, when the platen 43 reaches a selected distance or displace- ment 44 from the paper (Fig. 5D) , the drive current 71 is reversed as shown in Fig. 5B to effect deceleration (e.g. at approximately 10 4 cm/sec 2 ) of the platen and tape or otherwise limit the tape velocity (v) to equal or less than the critical relative approaching velocity (v c ). This reverse current, i.e. pulse 71a, has a magnitude, as shown, greater than pulse 71 but with a duration consider¬ ably less than (e.g. <l/2) the duration of pulse 71. The absolute magnitude of the drive current is then reduced to a nominal reversed-direction value to allow the platen and tape to coast for a short while. This approac -movement segment of the drive current profile of Fig. 5B thus enables the platen to be initially accelerated at approxi¬ mately four gravities, the decelerated at approximately ten gravities and finally allowed to coast to effect a gental contact between the-tape and the paper at point "B". The coasting period is ended with a relatively gradual ramp pulse 71b (Fig. 5B) which again tends to urge the platen in the upward direction until contact is uni- O H formly established. The ramp pulse 71b thus ensures substantially uniform pressure between tape 13 and paper 15, and "B" is the point in time at which the toner partcles are evenly (uniformly) sandwiched between the tape 13 and paper 15 and the tape becomes fully at rest with the paper, ready for transfer. During the entire time period between points A and B, actually between points A and C and somewhat before A, as shown in (Fig. 5E), the toner particles are sub- jected to an electrostatic field force (ft,) generated by means of an applied bias voltage which augments the existing magnetic attractive force (f m ) between tape and toner and electrostatic attracting forces ( f_ ) between tape and toner provided by precharging the toner, such that the toner particles are urged to remain on the tape throughout the entirety of relative approaching movement between the tape and the paper and establishment of uniform contact between the two. This electrostatic field is generated between the aforementioned conductive portion of the magnetic tape being held at ground potential and a negative potential of predetermined magnitude, say 100 volts (for negatively charged toner), as a biasing voltage applied to electrode 45 (Fig. 1) under the control of controller 25. We have found that a preferred range of bias voltages for generating the bias field is from approximately -20 to -150 volts corresponding, for example, to widely varying humidity conditions, within given systems of commercially available toner and paper. The relationship between the conductive portion of the tape 13 and electrode 45 could be reversed, whereby electrode 45 is maintained at e.g., ground potential and the tape has applied thereto a potential of said prede¬ termined magnitude with a polarity that will effect the desired electrostatic field, to augment, as before, the pre-existing attracting forces on the toner particles which urge same to remain clinging to the tape. The former arrangement, i.e., having the conductive portion of tape at ground potential at all times, is preferred because this provides the dual advantage that the tape will not be allowed to asssu e the potential of the scorotron during precharging (thus preventing the tape frcm possibly becoming more negative than the transfer electrode 45 which would tend to urge the toner to transfer without application of the actual transfer pulse) and the tape will be unable to become charged to the same potential as the toner At a time "C" following uniform contact between the tape and paper (actually point π C may occur at "B" or any time during the period of uniform contact), the polarity and magnitude of the potential in Fig. 5E are changed to result in a reversal of the electrostatic forces on the toner and begin transfer of the toner particles from tape to paper. We have determined that for the within mentioned given systems a preferred range of transfer voltage is +400 to +800 volts (for negatively charged toner), and especially preferred magnitudes of the transfer potential between 600 to 800 volts. Below 400 volts experience has shown that the toner transfer. efficiency suffers, and above 800 volts edge acuity tends to degrade. To complete the transfer of toner to paper, the cam surface of the cam 76 (Fig. 2) is further rotated, or the drive current (Fig. 5B for the arrangement of Fig. 3) is such that at time "D" the platen 43 begins to reverse its travel as indicated in Fig. 5D. (For the embodiment of Fig. 3 this is due to the influence of gravitational forces). The tape, which will follow the platen, thus begins to separate from the paper, leaving behind the toner, under the influence of the electrostatic transfer forces. When separation between the tape and paper has progressed to a predetermined distance, i.e., at time "E" of Fig. 5E, the polarity of the transfer potential is again changed, with the magnitude again set to the bias potential (Λ? -100V). Subsequently, the tape segment is transported out of and away from the transfer zone as indicated via Fig. 5A. The period from time "A" to time "E" (Fig. 5A) constitutes a transfer cycle. Specifically for the separation segment of the preferred drive current profile illustrated in Fig. 5B, to achieve a total minimum transfer cycle time a current profile substantially mirroring the approach segment profile is utilized. Thus, the platen and tape are allowed to coast (at approximately one gravity) for a short time immediately following actual separation to achieve a selected small displacement (to avoid disruption of the toner particle arrangement on the paper due to the aerodynamic forces of the rushing air associated with th separation). Therefollowing, the platen is positively accelerated downward and the decelerated to zero velocity, in achieving full separation of tape and paper once again. Fig. 5E further illustrates, via dashed line 86, that the transfer potential need not be held completely constant. However, it is important that the potential be substantially maintained at least until actual transfer has occurred and for a time thereafter. The pretransfer (bias) and transfer potentials have been selected at least in part to also satisfy the following requirements.. The toner must remain on the paper throughout the period of relative separation of tape and paper and subsequent movement of the tape out of the transfer area. On the other hand, it is desired that no background toner be accumulated on the paper from residual toner which may be on the tape and/or from the next arriving toned segment. Thus, the bias field is applied preferably throughout operation at the transfer station except during the time the transfer field is to be generated. The latter field, then, is caused to be present and remain only so long as to permit transfer of toner to the paper, and to provide time for the tape and platen time to withdraw to a sufficient separation, i.e., a separation sufficiently large that the effect of the resumed bias field would not be strong enough to urge the toner particles now on the paper back, across the separation to the tape. It should be appreciated that as of this point in time, the toner has not yet been more permanently affixed to the paper surface such as by fusing. It is to be noted that it is well within the scope of this invention to provide the alternative considerations of precharging the toner positively, with corresponding bias and transfer potentials being accord- ingly reversed from the above-depicted example. Fig. 6A depicts a graph of computed critical (maximum) tape velocity as a function of instantaneous separation utilizing equation I for toner-to-substrate (tape) holding forces of 2 x 10~4 dyne per toner particles as an example. Here, it is assumed that r » 10 x 10-4 cm / θ ____ l 3 χ 10 -3 gm / C c, and w = 1.25 cm. This magnitude of toner-to-medium force is determined by experimental procedures for typical condi¬ tions, i.e., a given system. It should be noted that this force could vary substantially for different systems. The vertical axis of Fig. 6A represents the tape critical (maximum) velocity in terms of cm/sec and the horizontal axis represents the instantaneous separation of the media (tape and paper) in units of 10 -4 cm. The point "A" indicates the initial separation distance between the media, corresponding to point "A" of Figs. 5A-5E. The dashed vertical line (identified as "B" to relate in time with point ~ " of Figs. 5A-5E) located at 20 x 10~4 cm indicates the separation distance at which toner particles normally first establish contact with the surface of the paper medium. In the case of a large toned area one could replace "h" with (h- £ ), where < ξ is the thickness of the toner layer; and for this case the paper surface is accordingly initially contacted by the toner at (h-<* ) = 0. As is illustrated by the graph of Fig. 6A, in order to not disturb the arrangement of the toner particles on either of the media and substantially pre- OMPI • serve- the. integrity of the- image quality, the approaching critical velocity near and at the point of contact between the substrates must be substantially smaller than the initial high velocities corresponding with the larger separation distances. Indeed, Fig. 6A illustrates the need for substantial reduction of tape velocity approach¬ ing the event of contact with the paper in order to prevent the disturbance of the toner particle arrange¬ ment. Fig. 6B illustrates the aforementioned computed critical (maximum) tape velocity as a function of time for an initial separation of 1250 x 10~ 4 cm anα - toner-to- substrate forces of 2 x 10~ 4 dyne per toner particle. In this example calculation, it is depicted that the platen 43 is accelerated from a rest position to a velocity of approximately 30 cm/sec with a corresponding acceleration of 3900 cm/sec" 2 (approximately four g's). The platen 43 is then allowed to travel approximately 940 x 10" 4 cm at this relatively high velocity. However, this velocity becomes critical at approximately the 310 x 10" 4 cm separation distance (point Q' of Fig. 6B, corresponding to point Q in Fig. 6A) and, as illustrated in Fig. 6B, the velocity must be reduced drastically in order to prevent disturbance of the toner particle arrangement. Furthermore, as shown in Fig. 6B the approaching velocity is reduced continuously over a period of time until the toner establishes contact (point B in time) with the surface of the paper medium. Thus, Fig. 6B shows the control of the velocity needed in the time domain to substantially preserve the integrity of the image quality. Fig. 7 is a graphic presentation of the optical density, D, of toner on a character image on tape versus the distance, s, in the vicinity of the edge of the toned character image. The dashed line curve 150 corresponds with an ideal density and depicts a very sharp transition of optical density, D, from a high value (e.g., D=1.8) to OMP zero within a. relatively immeasurabl short distance from the edge of the character image (s-»0) to the immediate surrounding background portion of the paper. The dot/dash line curve 152 depicts a condition of substantial toner spread at the edge of a toned character obtained from experiment in which the approach velocity of the tape has not been closely controlled, i.e. the tape approaching velocity has exceeded the critical (maximum) velocity for the system, and/or the tape has contacted the paper at an excessive velocity (e.g., five cm/second). Since the normal naked eye can sense optical densities as low as 0.002, it is clear from curve 152 that the gradual transition of optical density from the edge of the character image (s=0) to distances as large as one millimeter (i.e., s = 1000 x 10 -4 cm as depicted in Fig. 7 herein) corresponding to considerable toner spread, is readily detectable and is perceived as relatively poor edge sharpness or acuity. Further, the optical density of the character depicted in- curve 152 has suffered, having decreased from 1.8 '(chosen ideal case, corresponding to a dark black) to 0.7 (corresponding to a greyish appearance), which additionally degrades the image quality. The solid curve 151, on the other hand, illustrates a dramatic improvement over curve 152. Curve 151 depicts a typical relatively high speed test in which the instantaneous or approach velocity of the tape was controlled throughout the transfer operation to remain near but below the critical (maximum) velocity, while keeping all other parameters of the system the same. As shown by curve 151, there is no significant amount of toner spread detectable to the human eye within a relatively very small distance of approximately 75 x 10" 4 cm. Further, the optical density of the toned character image has been insignificantly affected, i.e., nominally reduced from 1.8 (corresponding to the ideal OMPI curve ) to 1.7. It is to be noted that at these high optical de ns ities the naked human eye will be unable to appreciate such a small difference . These illustrations and experimental results demonstrate that the present invention provides the dramatic improvement in edge acuity and image quali ty that is needed in high-speed printing for letter-quality applications . It is important to note also that a system in accordance with the invention thus provides real ad vantage in connection wi th computerized systems . OMPI

Claims: WHAT IS CLAIMED IS: 1. In a method of letter-quality, relatively high¬ speed transfer of toner particles predeterminably arranged on a surface of a first medium to a toner-receiving second medium, the steps of establishing at least a first pretransfer force of attraction (f^) between the toner and the first medium, and effecting relatively high speed relative approaching movement between the first and second media such that the maximum force (f2) exerted on the toner particles due to such movement is less than force (fl) for any instantaneous separation between the first and second media. 2. In a method of high-speed transfer of toner particles, which are predeterminably arranged on a surface of a first medium of preselected width and having associated therewith a pre-established toner attracting force, to a toner-receiving second medium, the combination - of steps comprising: determining instantaneous maximum velocity (v m ) of relative approaching movement of the first and second media as a function of: (1) the separation distance therebetween, (2) the first medium width, (3) the toner attracting force associated to the first medium and (4) a pre¬ selected maximum toner particle size, at and below which maximum velocity the toner particle arrangement on the first medium is maintained without substantial disruption; and effecting relative approaching movement between at least respective portions of the facing surfaces of the first and second media until contact occurs therebetween, at a velocity (v) where v <_ v m any separation distance. OMPI 3. The method of claim 2 further including the step of advancing the first medium relative to the second medium after contact to achieve uniform contact of the first and second media. 4. The method of claim 2 or 3 further including the step of subjecting the toner particles to a first electrostatic field force for facilitating retain ent of the toner on the first medium during relative approaching movement thereof with the second medium. 5. The method of claim 4 further including the steps of terminating the first electrostatic field force and subjecting the toner particles to a second electro¬ static field force during the period that the first medium is in uniform contact with the second medium to facilitate transfer of the toner particles from the first medium to the second medium. 6. The method of claim 5 further including separa¬ ting the first and second media during application of the second electrostatic field, and wherein the step of applying the second electrostatic field force includes the step of maintaining said force until the first and second media become separated by a predetermined distance. 7. Method of toned image transfer, comprising: a) effecting in succession relative approaching movement, contact and relative separating movement between at least respective portions of the facing surfaces of a toned first medium and a toner-receiving second medium substantially without disturbing the toner particle arrange¬ ment; OMPI b) subjecting the toner particles to a first electrostatic field, at least during the period of relative approaching movement beginning with a predetermined first separation distance being reached between said first and second medium portions, said first electrostatic field having a predetermined magnitude and a direction which urges the toner particles substantially toward the first medium and away from the second medium? and c) discontinuing the first electrostatic field and subjecting the toner particles to a second electrostatic field having a direction which urges the toner particles substantially toward the second medium and away from the first medium, for a predetermined time period following contact between said first and second medium portions, the close of which period.is defined by a predetermined second separation distance between the first and second medium portions being reached on relative separating movement thereof, said second electrostatic field having a predetermined minimum magnitude at least when separation of the first and second medium portions is effected. 8. Method according to claim 7, further including subjecting the first and second media to a third electro¬ static field of predetermined magnitude upon said second separation distance being reached. 9. In a method of high-speed transfer of toner particles which are predeterminbly arranged on a surface of a sub¬ stantially endless first medium of pre-selected width and having associated therewith a preestablished toner attracting force, to a toner-receiving second medium, the combination of steps comprising: a) selecting a maximum variable first rate- and a maximum variable second rate of relative approaching movement between the first and second media, which rates are defined at least in part by the instantaneous separation between the first and second media and the width of and toner attracting force associated with the first medium, said second rate being substantially less than the first rate; b) selecting a first separation distance between the first and second media; c) effecting relative approaching movement between the first and second media at or below the maximum of said variable first rate until said first separation distance is reached; and d) therefollowing, effecting-relative approach¬ ing movement between the first and second media at or below the maximum of said second rate such that the media are non-disruptively brought into contact, said first separation distance and the maxi ums of said variable first and second rates being selected such that relative approaching movement between the media is achieved substantially without degradation of the toner particle arrangement on the first medium. 10. The method of claim 9 further including the step of advancing the first medium relative to the second medium after contact is effected therebetween to achieve uniform contact of the first medium with the second medium. 11. The method of claim 9 or claim 10 further including the step of subjecting the toner particles to a first electrostatic field force for facilitating retain- ment of the toner on the first medium during relative approaching movement thereof with the second medium. 12. The method of claim 11 further including the steps of terminating the first electrostatic field force and subjecting the toner particles to a second electro¬ static field force during the period that the first medium is in uniform contact with the second medium to facilitate transfer of the toner particles from the first medium to the second medium. 13. The method of claim 12 further including separating the first and second media during application of the second electrostatic field, and wherein the step of applyi.ng the second electrostatic field force includes the stey of maintaining said force until the first and second media become, separated by a predetermined distance. 14. A method of effecting rapid relative approaching movement between a toned substantially endless first medium and a toner-receiving second medium substantially without spread or loss of toner .particles from the first medium, in which such movement is controlled by a signal of predeterminably varying waveform applied to moving means, comprising the steps of: 1) a first portion thereof representative of a predetermined, relatively high-speed, variable maximum first rate of said relative approaching movement, 2) a second portion thereof representative of selected variable maximum second rate of said relative approaching movement, and 3) a third portion thereof representative of a selected separation between the first and second media; b) applying said first portion of said signal to said moving means for a selected time during which the arrangement of toner particles on the first medium remains substantially undisturbed; c) applying said second and third portions of said signal to said moving means, whereby the relative approaching movement between the first and second media at the second rate commences when said separation between said selected first and second media is reached and continues until substantially non-disruptive contact is effected between the first and second media. 15. Method of effecting high-speed relative movement between a toner-receiving first medium, such as paper, and a toner-bearing substantially endless second medium having a selected width and providing a preestablished attracting force to the toner particles arranged thereon, comprising of the steps of: effecting relative approaching movement between the first and second media at a high-speed variable first rate until a selected separation therebetween is reached; effecting relative approaching movement between the first and second media at a variable second rate such that the media are nondisruptively brought into contact, said second rate being substantially less than the first rate, said selected separation and said first and second rates being proportional to the instantaneous separation between the first and second media, the width of the second medium and the strength of said attracting force and being selected such that maximum relative approaching movement between the media is effected substantially without degradation of the toner particle arrangement on the first medium. 16. Method of effecting relative moveϊhent between a toned substantially endless web and a toner-receiving medium at high-speed and subsequent contact between the web the medium substantially without spread or loss of toner particles from the web, in which such movement and contact are controlled by a signal of predetermined varying magnitude applied to a moving means, comprising the steps of: effecting relative acceleration between the web and the medium which defines a varying first rate of high-speed relative approaching movement in accordance with the signal, the signal further comprising portions representative of a maximum of said first velocity rate of relative approaching movement, a selected varying deceleration, and a selected time between accel¬ eration and commencement of deceleration corres¬ ponding to a selected separation between the web and the medium? and effecting in accordance with the signal relative deceleration between the web and the medium which defines a varying second rate of relative approaching movement commencing when said selected separation is reached and continuing until non-disruptive contact is made between the web and the medium, the first rate corresponding -to a first magnitude and polarity of the signal. OMPI the second magnitude being substantially less than the first magnitude. 17. Method of toned image transfer comprising: a) predetermining for a facing pair of media, the first of which is a toned substantially endless medium of pre-established width and having associated thereto a pre-established toner-attracting force and the second being a toner-receiving medium, a first velocity profile of high-speed relative approaching movement between the two media which profile includes a maximum relative approaching velocity as a function of the instantaneous separation distance between the two media which is proportional to the width of and the toner attracting force associated to the first medium, at or below which maximum degradation of the toner particle arrangement on the toned medium . is substanti-ally avoided; b) predetermining a separation between the two media which is proportional to the width of and the toner attracting force associated to the first medium by which the relative approaching velocity of the two media of said first velocity profile should be discontinued to avoid toner arrangement degradation; c) predeterming a second velocity profile of relative approaching movement between the two media which has a maximum velocity substantially less than the maximum velocity of the first velocity profile and by which the media are brought into nondisruptive contact substantial¬ ly without toner particle arrangement degrada- OI/ΪPI " " ion, -said.-second velocity profile being a function of the instantaneous separation distance between the two media and the width of and the toner attracting force associated with the first medium? and d) effecting relative approaching movement between the two media in accordance said first velocity profile until said separation is reached and therefollowing, effecting relative approaching movement between the two media in accordance with said second velocity profile. 18. In a method of toned image transfer the combina¬ tion of steps comprising: a) Effecting high-speed relative approaching movement between a toner-bearing substantially endless first medium and a toner-receiving second medium, substantially without degradation of the toner particle arrangement on said first medium, within a maximum relative approaching velocity profile where velocity varies as a function of the separation distance between the two media, and which maximum velocity is defined at least in part by the width of the first medium and the toner attracting force associated thereto; b) discontinuing said high-speed relative approaching movement by or prior to a predeter¬ mined separation distance between the two media being reached? and c ) effecting relative approaching movement between the two media over a range of separation distances- less than said predetermined separa¬ tion distance within said maximum relative approaching velocity profile, wherein said maximum velocity profile is further defined at least in part by the minimum force required to materially disturb the toner particle arrange¬ ment on the first medium and the maximum force of contact between the two media in which the toner particle arrangement is maintained sub- stantially undisturbed. 19. In a relatively high speed printer providing letter quality transfer of toner particles predeterminably arranged on a surface of a first medium to a toner- receiving second medium, the combination comprising means for establishing at least a first pretransfer force of attraction (fl) between the toner and .the first medium and means for effecting relatively high speed relative approaching movement between the first and second media according to the relationship that the maximum force (f2) exerted on the toner particles due to such movement is less than the force (f^) for any instantaneous separation between the first and second media. 20. Apparatus for effecting rapid relative movement between a toned first medium and a toner-receiving second medium substantially without disturbing the arrangement of toner particles on the first medium, comprising: means for generating a control signal, and medium positioning means responsive to said signal for effecting relative approaching movement between the first medium and the second medium at or below a selected first maximum variable rate until a selected separation is reached between the two media. then, effecting a second relative approaching movement between the two media at or below a selected second maximum variable rate until contact occurs between the two media, said first and second variable rates being a function of the toner first medium attracting force, the instantaneous separation distance between the two mediums and at least the width dimension of the first medium. 21. The apparatus of claim 20 wherein the medium positioning means includes platen means disposed for engaging one of said media for effecting relative motion thereof toward the other medium. 22. The apparatus of claim 21 wherein the medium positioning means further includes actuator means operatively coupled to the platen means for moving the platen means and said one medium in response to said signal. 23. The apparatus of claim 22 wherein the actuator means includes cam means having at least one cam surface in operative engagement with the platen means. 24. The apparatus of claim 22 wherein the actuator means includes coil means and permanent magnet means, the coil means being fixedly attached to the platen means for movement of the coil and platen means relative to the magnet means upon application of said signal to the coil means. 25. The apparatus of claim 20 including first electric field generating means for facilitating retain- ent of the toner particles on the first medium during relative movement between the media. OMPI 26. The apparatus -of claim 25 wherein said generat¬ ing means includes an electrode disposed proximate to the second medium for generating the electric field, the second medium being positioned between the electrode and the medium positioning means. 27. The apparatus of claim 26 further including second electric field generating means coupled to the electrode for effecting letter quality transfer of the toner particles from the first medium to the second medium. 28. Apparatus for relatively high-speed transfer of toner particles predeterminably arranged on the surface of a substantially endless first medium of preselected width and having associated thereto a preestablished toner attracting force, to a toner-receiving second medium, comprising: a) means for effecting a high-speed variable first rate and a variable second rate of relative approaching movement between the first and second media which rates are respectively proportional to the width and toner attracting force of the first medium, said second rate having a maximum substantially less than the first rate; and means for controlling said means for effecting said first rate of relative approaching movement until a preselected separa¬ tion distance is achieved between the first and second media, which separation is proportional to the width of and the toner attracting force associated to the first medium, and thereafter controlling relative approaching movement of said media at the second variable rate to bring the first and second media into non-disruptive contact, said separation and said first and second variable rates being controlled by said coπtroi- eans, such- that said, relative movements between the media are achieved substantially without degradation of said toner particle arrangement. 29. Apparatus for toned image transfer comprising: a) a facing pair of media, the first of which is a toned endless medium of preestablished width and having associated thereto a preestablished toner attracting force and the second being a toner-receiving medium; b) means for effecting high-speed relative approaching movement between the first and second media in accordance with a first velocity profile which includes an instantaneous maximum relative approaching velocity which is propor¬ tional to the width of and the toner attracting force associated to the first medium, at or below which instantaneous "maximum velocity degradation of the toner particle arrangement is avoided? c) control means for effecting termination of the high-speed relative approaching movement upon a predetermined separation being achieved between the two media, which separation is proportional to the width of and the toner attracting force associated to the first medium; and d) means for generating relative approaching -movement between the two media in accordance with a second velocity profile, which profile has an instantaneous maximum velocity substan¬ tially less than the instantaneous maximum OMPI velocity of the first velocity profile, whereby the two media are brought into contact substan¬ tially without toner particle arrangement degradation. 30. Apparatus for toned image transfer comprising: a) means for effecting high-speed relative approaching movement between a toner-bearing first medium and a toner-receiving second medium substantially without degradation of the toner particle arranagement on said first medium within a variable maximum value of relative approaching velocity as a function of separation between the two media, which high-speed variable velocity is defined at least in part by the width of toned first medium and the toner attracting force associated thereto; b) control means for discontinuing said high¬ speed relative approaching movement by or prior to a predetermined separation being achieved between the two approaching media; and c) means for effecting relative approaching movement between the two media over a range of separation distances less than said predetermined separation within a variable maximum of relative approaching velocity as a function of separation between the two media, which latter variable velocity is defined at least in part by the force required to mater- ially disrupt the toner particle arrangement on the toned medium and the maximum force of contact of the two media under which said toner arrangement is substantially maintained. 31. Method of .moving a- toned web relative to a toner-rece iving medium at a selected rapid rate substantially -without spread or loss of toner particles from the web, the toner particles being attracted to the web by a binding force of predetermined strength, the method compris ing the steps of : moving the web non-disruptively into contact with the toner-receiving medium, and applying a firs t electros tatic f ield force to the toner for facilitating the binding of the toner to the web during movement of the web toward the toner- receiving medium, thereby substantially preve nting spread or loss of toner from the web . 32. The method of claim 31 further including the steps of terminating the first electrostatic field force and applying a second electros tatic field force to the toner during the period that the web is in contact with the toner-rece iving medium to ef fect letter quality trans¬ fer of the toner from the web to the toner-rece iving medium. 33. Apparatus for moving a toned web relative to a toner-receiving medium at a rapid rate substantially without spread or loss of toner particles from the web , the toner particles being attracted to the web by a binding force of predetermined strength, the web having a selected width , the apparatus comprising: web positioning means disposed for engaging and moving the web toward the toner-rece iving medium, and drive means coupled to the web positioning means and respons ive to an applied signal of varying frequency for effecting movement of the web toward the toner-receiving medium at a first maximum rate in accordance with the instanta- neous separation distance of the web from the toner-receiving medium, and then moving the web toward the toner-receiving medium at a second rate in accordance with a selected frequency of the signal such that the web nondisruptively contacts the toner-receiving medium, the second rate being substantially less than the first rate, said first and second rates being pro¬ portional to the web width and the strength of the binding force and selected such that the toned web may be rapidly moved toward the toner- receiving medium substantially without spread or loss of toner from the web. 34. The apparatus of claim 33 wherein the web positioning means includes a platen and a cam, the cam being coupled to the drive means for rotary motion thereof and for translating the platen to said toner-receiving means. 35. The apparatus as in claim 34 wherein the drive means is a stepper motor, and the signal represents discrete pulses applied to said motor. 36. Method of transferring prearranged toner particles from a surface of a f irst medium to a surface of second medium, comprising: a) non-distruptively pre-charging the toner particles on the first medium by subjecting the toner particles to a first electrostatic force of selected first polarity and magnitude thereby creating an attracting field force between the toner particles and the first medium? OMPI b) effecting relative movement between the first and second media subs antially without degrada¬ tion of the arrangement of toner particles on the first medium and such that substantially nondisruptive contact is effected between the first and second media? and c) effecting transfer of the toner particles from the first medium to the second medium sub¬ stantially without degradation of the arrange¬ ment of the toner particles by subjecting the toner particles to a second electrostatic force of selected second polarity and magnitude, the polarity of said second electrostatic force being opposite to that of the first electrosta¬ tic force. 37. The method of claim 36 further including main¬ taining the first electric potential during the period between said precharging and .said transfer. 38. The method of claim 36 wherein said toner particles are arranged on the surface of the first medium in accordance with a latent magnetic image associated to -said surface. 39. The method according to claim 37 wherein the tape surface bearing the toner is maintained at a constant ground potential between pre-charging and transfer. 40. The method of claim 36 wherein the toner particles are subjected to a third electrostatic force of selected polarity and magnitude which facilitates the retainment of the toner particles on the surface of the first medium during relative movement between the first - - and second media, by augmenting the attracting force field between the toner particles and the first medium and simultaneously tending to repel the toner particles away from the second medium and in the direction of the toned 10 medium surface. 41. The method of claim 39 wherein said third electrostatic force together with the attracting force existing between the toner particles and the first medium are greater than or equal to forces on the toner particles 5 which are generated by the relative movement between the two media. 42. Apparatus for transferring prearranged toner particles from a first medium to a second medium comprising: a) means for non-disruptively pre-charging the 5 toner particles on the first medium, including means for subjecting the toner particles to a first electrostatic force of selected first polarity- and magnitude? b) means for effecting relative movement between 0 the first and second media substantially without degradation of the arrangement of toner particles on the first medium and for effecting substantially non-disruptive contact between the first and second media? and c) means for effecting transfer of the toner particles from the first medium to the second medium substantially without degradation of the arrangement of the toner particles, including means for subjecting the toner particles to a second electrostatic force of selected second OMPI polarity and magnitude , the polarity of such second electrostatic force being oppos ite to that of the first electrostatic force . 43. A method of transfer of toner from a toned first medium having a toner attracting first force associated thereto to a toner-receiving second medium, comprising: a) effecting high-speed variable-velocity relative approaching movement of the two media substantially without degradation of the arrangement of the toner particles on the first medium prior to and during contact with the second medium, b) during said relative approaching movement, subjecting at least the toner particles on the first medium to a first electrostatic field of predetermined magnitude and having a direction which augments the toner attracting first force? and c) when said contact between the media is achieved, subjecting the toner particles to a second electrostatic field of predetermined magnitude and having a direction which effects transfer of the toner particles to the second medium. 44. The method of claim 43 wherein second electro¬ static field is maintained until a predetermined separa¬ tion is effected between the two media. 45. The method of claim 43 wherein said toner attracting first force comprises an electrostatic field force. OMP * 46. The method of claim 45 wherein said toner attracting first force includes a magnetic force. 47. Method of toned image transfer of toner particles prearranged on the first medium to a toner- receiving second medium comprising: a) precharging the toner on the first medium via subjecting the toner particles to a first electrostatic field of selected polarity and magnitude which imparts to the toner particles a uniform charge of first polarity and to the first medium a corresponding charge of and opposite polarity thus effecting a force field between the toner particles and the first medium such that the toner particles are attracted to the. surface of the first medium? b) at a transfer station, subjecting the toner particles to a second electrostatic field of selected polarity c) effecting relative movement between the first and second media substantially without degrada¬ tion of the arrangement of toner particles on the first medium and such that substantially non-disruptive contact is effected between the first and second media? and d) when contact has been achieved between the two media, discontinuing the second electrostatic field and subjecting the toner particles to a third electrostatic field of selected magnitude and polarity which is maintained at least until the two media are reseparated and thereby causing the toner particles to transfer from the first medium to the second medium. 48. In the method of claim 47 further including the step of maintaining the- surface of the first medium at a preselected potential. 49. The method of claim 47 wherein said third electrostatic field is maintained until the two media are again separated following transfer by a preselected distance. 50. The method of claim 49 wherein said third electrostatic field is opposite in direction to the second electrostatic field. 51. The method of claim 50 wherein said first electrostatic field is of the same direction as the second electrostatic field. 52. The method of claim 48 wherein the surface of the first medium is maintained at ground potential. 53. The method of claim 52 wherein said pre-charging imparts a negative charge to the toner particles. 54. The method of claim 47 wherein said second and third electrostatic fields are created between the surface of the first medium and an electrode disposed behind the second medium wherein one or the other of the electrode and the surface of the first medium is maintained at a constant potential and the other has applied thereto potentials to effect said second and third electrostatic fields respectively. 55. Method of moving a toned web toward a toner- receiving medium at a selected high velocity for a selected period of time substantially without disruption of toner particles on the web, the toner particles being attracted to the web by a binding force of predetermined -magnitude-,-the method comprising the step of: varying the velocity of the web relative to the distance of the web from the medium such that the magnitude of the binding force is not exceeded by forces exerted on the toner particles as a result of movement of the web. 56. The method of claim 55 where the step of varying the velocity includes the steps of: increasing the velocity of the web to a selected maximum velocity for a selected period of time? then decreasing the velocity of the web relative to the distance of the web from the medium, the increasing and decreasing being performed at rates such that the magnitude of the binding force remains greater than forces exerted on the toner particles due to movement of the web relative to the medium. 57. Method of moving a toned web toward a toner- receiving medium at a rapid rate substantially without disruption of toner particles from the web, the method utilizing a web-positioning means for moving the web, and a drive means for driving the web-positioning means in accordance with a predetermined signal waveform, the toner particles being attracted to the web by a binding force of predetermined strength, the web having a selected width, the method comprising the steps of: moving the web toward the toner-receiving medium at an accelerating rapid rate, the waveform representing the rapid rate, a decelerating slow rate, and a time at which movement may be OMPI ^ ~ WIPO ~ v changed fro -the ra id to the slow rate to effect gentle contact of the web with the toner- receiving- medium, the time corresponding to a selected distance of the web from the toner- receiving medium? and moving the web toward the toner-receiving medium at the decelerating slow rate upon the web reaching the distance, enabling the web to gently contact the toner-receiving medium sub¬ stantially without toner disruption, the rapid and slow rates and the distance being proportional to the web width and to the strength of said binding force. 58. Method of moving a toned web toward a toner- receiving medium at a rapid rate substantially without disruption of toner particles on the web, the method utilizing a web-positioning means for moving .and position- ing the web proximate to and contiguous with the .medium, and a drive means for driving the web-positioning means, the toner particles being attracted to the web by the action of a binding force of predetermined magnitude, the method comprising the steps of: moving the web toward the toner-receiving medium at an accelerating rapid rate for a first selected period of time? moving the web toward the toner-receiving medium at a decelerating rapid rate for a second selected period of time? and reducing the rate of deceleration until the web makes gentle contact with the medium by varying the velocity of the web in accordance with the distance of the web from the medium, the 20 velocity being reduced progressively as the distance between the web and medium decreases such that a resultant magnitude of forces exerted on the toner particles as a result of movement of the web does not exceed the 25 magnitude of the binding force, thereby substan¬ tially preventing disruption of the toner particles on the web during movement of the web toward the medium.

Inventors: NELSON ALFRED MAGNUS, RASEKHI HOUSHANG
Applicants: AM INT, AM INTERNATIONAL INC
Application year: 1982
Main classification: G03G13
IPC codes: G03G13, G03G15, G03G19