EP0168485A1 - Rotary printer with off-carriage motor drive - Google Patents

Abstract

A serial impact printer of the type using a rotary printing element (36) is driven by a main drive motor (20) disposed outside the carriage (37) moving the printing element (36) along 'a print path. The motor housing (20) is mounted so that it can move, preferably be able to rotate, and is connected to the printing element (36) by an extendable shaft (21) and a flexible transmission element (24 ). Printing speed is improved by using the flexible transmission member (34) as a universal drive with a constant speed characteristic. Thus, a servo-mechanism regulating the angular orientation of the printing element (36) does not need to be unlocked when the drive angle is changed. A portion of the ribbon supply device (101) is at least partially disposed on the motor (20) and is pivotally coupled to the printing carriage (37). The ribbon supply device (101, 104, 105) acts as a motor guide adapting the pivoting orientation of the motor housing (20) to the changing location of the printing carriage (37). Thus, the bulk of the weight of the ribbon supply device (101) and of the motor (20) is carried by a structure located outside the printing carriage (37).

Description

ROTARY PRINTER WITH OFF-CARRIAGE MOTOR DRIVE

Relationship to Other Applications

This disclosure is related to, and incorporates by reference, the following applications:

Shift System for Multi-Row Print Element Serial Number .

System for Using Multiple Print Heads in Single

Printer, Serial Number .

Paper Transport System for Printer, Serial Number .

Changer Arrangement for Information-Bearing Elements,

Serial Number .

Printer Supplies Monitoring System,

Serial Number .

Ribbon Indicia System, Serial Number .

Vacuum Buffered Ribbon Transport System, Serial Number .

High Capacity Ribbon Supply Arrangement, Serial Number .

Splittable Keyboard for Word Processing,

Typing and Other Information Input Systems, Serial Number .

Rotary Print Element, Components thereof, and Drive Coupling Apparatus therefor, Serial Number.

Background of the Invention

This invention relates generally to serial impact printers which utilize multicharacter printing elements, such as ball heads, print wheels, or thimbles mounted on a printer carriage, and more particularly to a printer arrangement wherein a rotatable printing element is driven by a motor which is located off of the printer carriage.

As business generally increases its reliance upon electronic information systems, the need for enhanced throughput speed becomes evermore important. It is now well known that hard copy output systems, such as printers, of business information processing systems produce their output information at maximum speeds which are substantially lower than the speeds at which information is made available to them. For example, most word processing systems which are in common use in the business environment can produce processed information signals corresponding to repeatedly examined input information at a rate which exceeds the maximum printing speed of commercially available printers. The result of this situation is generally that after the information processing system has completed its task, it must remain idle while the printer produces the desired hard copy. More importantly, the word processing operator is also underutilized during this printing period. This situation is particularly distressing in word processing systems where a document having many pages may require only a few minor changes, but such changes will require the entire document to be reprinted for the sake of repagination and the production of a clean copy. The realization of this problem has resulted in substantial effort being devoted to increasing the overall system throughput by improving the operating speed of printers, and producing products, such as buffer memory systems, which are intended to compensate for the slow operating speed of printers by accepting the output information from the processing system at a much faster rate than the printer, thereby freeing the processing system to perform other work while a prior document is being printed. It is to be understood, however, that although such compensating systems improve the overall throughput, they do not correct the fundamental problem of the need for faster printers.

Some of the problems associated with increasing the speed of printers are generally known. The faster type of correspondence-quality printers which are commercially available are generally of the impact type and utilize a rotating print member which contains the fully-formed configuration of the characters or symbols to be printed as a raised figure arranged at a predetermined radial distance from an axis of rotation and on a radial segment thereof. Some known printing elements, such as rotatable rotably print thimbles, also have fully-formed characters at a predetermined radial distance from the axis of rotation, but axially displaced with respect to the point of communication between the print thimble and its drive shaft.

The rotatable printing element is conveyed on a carriage which delivers the print member to each location where a character or symbol is to be printed. Thus, persons skilled in the design and manufacture of printers know that the print member experiences at least two types of motion, rotating motion for bringing a selected character into a print position with respect to the carriage, and generally lateral motion for positioning the carriage at the appropriate location where the character or symbol is to be printed. It is also well known that the rate at which both such motions are performed must be increased if the productive output (i.e., net operating speed) of the printer is to be increased.

In most commercially available printing arrangements, two independent motors are provided, each for performing a respective one of the functions of rotating the rotatable print member and causing lateral translation of the print carriage. The rate at which one of a plurality of characters arranged circumferentially on the print member is brought into a predetermined print position is clearly a function of the rate at which the print member is rotated. It should be noted here, however, that since the rotation in question is generally only a fraction of one complete rotation of the print member, the important consideration is the rate at which the print member is accelerated and decelerated so that it can traverse the angular distance between an initial angular position and a desired angular position such that the selected character or symbol to be printed is in the print location. It is well known that an increase in such acceleration can be achieved only by the use of a motor having an increased power rating. Such a more powerful motor, however, would generally be heavier and larger than a motor used in a conventional printer.

In a manner similar to that discussed hereinabove with respect to the rate of rotation of a printing element, a carriage drive motor which moves the carriage to, and stops it at, each location where printing is desired is also required to be quite powerful to achieve the required accelerations and decelerations. However, as noted, the printing element drive motor is generally located on the carriage, and as its bulk and mass are increased to achieve the greater rotative accelerations of the printing member, the net mass of the carriage which must be accelerated to, and stopped at, each location where a character or symbol is to be printed is correspondingly increased. Elementary laws of physics pertaining to inertia and momentum indicate some of the problems associated with rapidly accelerating and decelerating substantial masses. There are, however, other problems with this approach to improving printer speed which are known to printer designers. For example, as the net mass of the carriage is increased, the wear on the drive components is increased, thereby reducing the useful life of the printer and increasing the frequency of maintenance and repair operations. It is a further problem with this approach of increasing the power of the print member drive motor that, as the relatively large mass of the carriage is accelerated and decelerated, the entire printer tends to move and vibrate. Moreover, the level of noise which is produced may be generally unacceptable in most business environments. It is therefore evident that, under the generally accepted design philosophies of commercially available printers, severe engineering compromises must be made to reconcile printer speed with acceptable printer noise, life, and frequency of repair. The obvious approach to correcting this problem is to improve the output power per unit weight characteristic of the printing element drive motor. In this manner, angular acceleration of the printing element is increased for only a modest gain in motor weight and overall net carriage mass. This approach to the problem, however, produces printing element drive motors which are complex and expensive in their use of rare earth magnets, expensive windings and difficult-to-machine materials for frames and other motor parts, and high manufacturing costs associated with the high precision and low tolerances of such motors. Even if the cost of such motors is deemed to be acceptable, such motors nevertheless, have substantial mass and therefore do not provide a satisfactory solution to the problems noted hereinabove. Moreover, such compact, high-technology motors would generally be operated in overdriven states, thereby generating excess heat and the problems associated with its dissipation, particularly in situations where heat sensitive ribbon supplies are also mounted on the carriage near the heated motor. Also, from the standpoint of safety, an operator can be burned upon contacting an exposed motor case. These considerations require additional weight on the carriage in the form of shielding.

Compounding the problem still further is the weight of the ribbon supply, since in known printing arrangements the ribbon supply box is located on the carriage. This additional weight typically includes not only the ribbon itself, but the ribbon supply box and internal mechanisms necessary to feed the ribbon as the printer operates. Even if it is assumed that a designer is able to reduce the weight of the ribbon supply box and its internal mechanisms to an acceptable minimum, he is still confronted with the weight of the ribbon itself, and once the weight per unit length is reduced to a minimum consistent with required strength, durability and performance, further weight reduction can only be achieved by reducing ribbon capacity. Thus, an extended period between ribbon changes must be sacrificed for higher printing speeds. An obvious dilemma arises from the fact that printing at higher speeds consumes ribbon more rapidly.

One prior art response to the problems associated with high carriage mass is embodied in an arrangement wherein the carriage and the printing element are driven by two motors arranged on the chassis of the printer. In the known arrangement, the print element and the carriage are coupled to the motors by taut cables in an integrated arrangement whereby both motors must be controlled to perform each function of print element rotation and its translation along a carriage path. For example, if it is desired to rotate the printing element without moving the carriage, both motors must be controlled so as to rotate in predetermined, compensating directions at precise speeds. This requires a complex control system wherein two motors, rather than one, are controlled differentially in a very precise manner. In addition, this known arrangement is plagued by the problems associated with all taut cable servo systems. More specifically, such cables tend to wear and stretch with time, thereby producing a loose coupling between the motors and the mechanisms to be driven, and exacerbating the problems of the servo control system which must not only control two motors differentially, but also accommodate for unequal degrees of coupling between the respective motors and the print member and carriage as loads. Such complexity which is inherent in the function which the control system is required to perform can produce excessive hunting which has the effect of reducing the net speed of the printer. It is a further problem with known printing arrangements that letter-quality printed results can be achieved only with fully-formed character impact printers, and such printers are generally not suitable for providing multicolor highlighting, graphs, or charts. Thus, in situations where high quality text is desired to be intermixed with charts, graphs, and/or background color, spaces must be left in the text and such additional information inserted later by a further operation utilizing printers having different ink deposition or ribbon characteristics such as dot matrix and ink jet printers. Alternatively, such non-text material must be inserted manually or with the aid of lithographic or xerographic equipment. There is a need, therefore, for a printer arrangement which can print several of the above types of material without the need of a multiplicity of specialized individual printers.

It is a further problem in printing arrangements which endeavor to increase the speed of rotation of a printing element in the form of a printing disc that the fragile structure of the printing disc, which is generally formed of a thermoplastic material, is stressed and vibrated in response to rapid accelerations and deceleration. This problem is compounded in some known systems wherein the control system which senses the angular position of the printing disc often requires a through aperture near each radial stem of the printing disc. Such an aperture weakens the stem, which is by its nature flexible, and limits the magnitude of acceleration to which the printing disc can be subjected. There is a need, therefore, for an improved sensing arrangement which does not weaken the printing disc.

It is also a problem with known printing arrangements that since the motor which rotates the print element is mounted directly on the laterally-translating print carriage, both vibratory arid magnetic disturbances arise. This results from the fact that since the print carriage moves laterally, the mounting bearings atop the lateral rails must allow side movement, but should resist movement in other directions. Lateral positioning is maintained by the lateral drive motor and its connecting cables or linkages which hold a position after an order for a new lateral movement step is carried out. Thus, when the motor is mounted directly upon the print carriage, the rapid acceleration, followed by rapid deceleration and then electrical clamping to maintain the desired stopping point, cause severe vibratory challenge to the mounts. If the lateral rail bearings are tight, then the vibration is propagated therethrough to a combination of the horizontal positioning system and through the rail mountings to the entire printer. If the normal practice of supporting the rails only at the two ends is followed, the difficulty in maintaining the desired position in space is greatest at the center of the rail span. As a result of the large component of the carriage weight contributed by the print disc drive motor, it is normal practice to tie or clamp the print carriage during shipment or movement of the printer. Otherwise, when if the print carriage is unrestrained by an electrical command, it may drift to the center portion of the support rails, and a sharp vertical movement of the printer may be sufficient to cause a permanent curvature in the rails. Thus, a known design response to this problem is to provide very robust support rails, resulting in an increase in printer weight and cost. Thus, the weight on the print carriage of the print disc drive motor and the vibrations it produces during operation generate problems which affect not only the positional accuracy of the carriage travel and the printer's weight and cost, but also the entire maintenance cycle. The frequency of repair is increased with respect to both alignment accuracy in printing and damage to other mechanical or electronic parts as a result of vibration-induced stress.

The strong magnetic field radiated by the print disc drive motor when responding to the rapid electronic comands wil not usually be a problem unless a designer intends to utilize a rotating print element printer in close proximity to magnetic field-sensitive devices, such as magnetic memory discs or cathode-ray tubes. Generally, memory discs and cathode-ray tubes are used with printers in a word processing terminal. However, the magnetic field produced by the motor can be a barrier to the use of design choices that would otherwise be preferable, such as the mounting of a floppy disc station within the printer volume to save desk space, or creating a terminal in which the printed page emerges from the case in the proximity of the cathode-ray tube to minimize eye travel from the cathode-ray screeen to observe whether the printout is occurring satisfactorily. Since this radiated magnetic field changes position during lateral carriage motion, it would be efficient to shield the print element drive motor itself, were it not that the shield would add substantial extra weight to an already very heavy load on the print carriage. Thus, current practice places very heavy magnetic shielding around the field-sensitive components, illustratively the magnetic storage unit or the cathode-ray tube. Of course, this is a costly addition to the word processing system due to the size of the component to be protected.

It is, therefore, an object of this invention to provide a high speed printing arrangement which can be manufactured simply and inexpensively.

It is a further object of this invention to provide a printing arrangement wherein a rotatable printing element is accelerated at rates which exceed those which can be achieved with conventional systems.

It is yet still another object of this invention to provide a tension-compensatory system which allows accurate coupling of rotary motion to a stationary pulley from a pulley which exhibits both a driving rotational motion around one axis and a second rotational motion around another axis.

It is also a further object of this invention to provide a printing arrangement wherein the printing element drive motor is removed from the carriage such that only the drive motor need be controlled by the printing element position servo control system, and such that the relocation of the motor off of the print carriage will substantially facilitate magnetic shielding of the motor or vibration isolation mounting.

It is another object of this invention to provide a printing arrangement wherein the mass of the carriage is reduced by removing the print element drive motor therefrom while requiring only one motor to perform the function of rotating the printing element. It is yet another object of this invention to provide a printing arrangement wherein at least a portion of the mass of the ribbon supply arrangement is removed from the carriage.

It is also another object of this invention to provide a printing arrangement which contains an enlarged supply of printing ribbon over known arrangements, thereby extending the interval between ribbon changes.

It is also an object of this invention to provide a printing arrangement which can allow supply of one type of ribbon to a rotating print element and yet another type of ribbon to a second printing element.

It is still a further object of this invention to provide a printing arrangement which can provide multicolor printing ribbon to highlight or augment letter-quality text which has been printed with a ribbon optimally designed for that printing task, without requiring removal and reinsertion of the output paper document.

It is still another object of this invention to provide an improved printing element which is not weakened by through apertures for sensing the angular position of the printing element, and without adding additional structure to the printing element which would increase its rotary movement.

Summary of the Invention

The foregoing and other objects are achieved by this invention which provides a printer of the type which utilizes a rotatable printing element which is rotated by a printing element drive motor. In accordance with the invention, the motor is arranged to be off of the carriage which conveys the printing element along a carriage path. The motor is coupled to the printing element through a rotatable drive shaft, which is preferably rigid and connected through a universal drive, but can be a flexible cable.

In a preferred embodiment of the invention, the drive shaft is rigid and the printing element drive motor is installed at a distance from the carriage in a pivoting arrangement whereby the case of the motor can be rotated such that the longitudinal axis of rotation of the motor shaft pivots in a substantially horizontal plane. Thus, as the carriage is translated along the carriage path, in a substantially horizontal direction, or any other direction selected by a designer in light of this disclosure, the motor housing is rotated such that the axis of the motor shaft aims continually in the general direction of the carriage. The variation in the distance between the motor and the carriage can be accommodated by slidably mounting the drive shaft in the motor shaft, which may be hollow. In a further embodiment, the drive shaft which couples the motor shaft to the printing element is itself of an elongatable type. This distance between the carriage and the pivoting drive motor mount serves mechanically to decouple the drive motor, which is a vibration source, from the carriage. Also, the placing of the drive motor on frame-mounted pivots allows for good vibration damping of the motor, as well as the ability to carry some magnetic shielding to the extent that the carriage-to-motor distance does not sufficiently isolate the magnetic field from sensitive components.

In accordance with the invention, as the carriage is translated along the carriage path, in a substantially horizontal direction, or any other direction selected by a designer in light of this disclosure, the motor is pivoted such that the axis of the motor shaft is maintained to aim essentially in the vicinity of the carriage. Pivoting of the motor is guided by an elongatable guide which couples the case of the motor to the carriage. Additionally, the motor drive shaft and the motor rotor are coupled in an elongatable fashion.

It is to be noted that a pivoting motor arrangement embodies only one of several schemes contemplated by the invention for removing weight from the carriage. The present invention includes within its scope embodiments where the motor is moved laterally along a separate path from the carriage path, but substantially parallel thereto. In such an arrangement, a drive arrangement may drive the motor assembly substantially laterally with respect to the axes of the drive shaft at a speed which corresponds, to a degree, with the speed of the carriage. In this laterally traveling motor system, it is desirable to provide at least a small measure of pivotal movability to the motor such that the pivotal motion will compensate for displacement differentials between the location of the carriage and the location of the laterally traveling motor; such a displacement differential resulting from speed differences.

Preferably, one or more slidable or elongatable guide bars are provided for coupling the case of the motor to the carriage. The use of such a guide arrangement to cause the printing element drive motor to pivot as the carriage is translated prevents the application of bending or side loads on the drive shaft.

The preferred drive arrangement can be visualized as having a center of arc located at the pivot of the corresponding circle, with the motor shaft and the drive shaft extending essentially radially therefrom to the carriage. The carriage path corresponds to a chord of the described arc. The slidably mounted or elongatable drive shaft accommodates the variation in distance between the motor and the carriage path as the carriage is translated along the chord. The slidably mounted or elongatable guide bars also traverse the distance between the carriage and the pivoting motor essentially along a radial direction from the pivot. As is the case with the elongatable drive shaft, the elongatable characteristic of the guide bars accommodates for the variation in distance between the motor and the carriage, as the carriage is translated along the carriage path.

It is evident from the foregoing that the drive shaft maintains a radial relationship with respect to the pivot of the motor, while in a particular illustrative embodiment of the invention, the carriage and rotating printing element maintain a fairly constant position with respect to the carriage path which, as noted, corresponds to a chord of an arc. Thus, as the carriage is translated, a varying drive angle is formed between the axes of rotation of the drive shaft and the print element, which requires the use of a universal coupling element. It is, however, a disadvantage of universal coupling elements which are in general use that they have a nonconstant velocity characteristic. In other words, if a rotation having a constant angular velocity is to be transmitted at an angle by a known universal coupling member, the angular velocity of the output end of the universal coupler will not be constant. Instead, the output angular velocity will increase and decrease during each cycle of rotation, while maintaining an overall average output velocity which corresponds to the input velocity. Such a nonconstant velocity characteristic is a function of the drive angle and has an adverse, displacing effect on the angular position of the rotatable printing element as the carriage is translated.

In other words, assuming for example that a line of periods, or some other single character, is desired to be printed, the translation of the carriage along the carriage path will result in a change in the angle at which the universal coupler would transmit its rotative force, and consequently produce a slight angular displacement of the period or character from the preestablished print position. Such displacement is a result of the nonconstant velocity characteristic of the universal coupling element which translates into a rotation as the drive angle between the shaft axis and the carriage path Is varied. Moreover, such an undesired rotational displacement cannot be compensated simply in response to the drive angle because the undesired rotational displacement is also a function of the rotative orientation of the printing element. Thus, the magnitude of the resulting rotational displacement error of the printing element is different for the various characters. Of course, a servo control system which is intended to maintain a selected character fixed in the print position will cause the printing element drive motor to be rotated so as to compensate for the nonconstant velocity characteristic of the universal coupling element. Although such a system would yield operating speeds which exceed those of presently available printing arrangements, the printing system is nevertheless made more complex and may be slowed down as a result of the servo control adjustments required between each successive printing of the repeated character. In most systems, an impact hammer will not strike a character until a signal indicating achievement of the appropriate character position is received from the servo control system. In a preferred embodiment of the present invention, the need for such repetitive unlocking of the servo control system and compensating correction of the rotative orientation of the motor is obviated by use of a constant velocity universal coupling arrangement which eliminates the need for adjustments to the angular position of the motor as the carriage is translated. This results in substantially increased print speeds.

In a preferred embodiment of the invention, the desired constant velocity universal drive characteristic is achieved by the combination of drive and driven elements which are coupled to each other by a flexible drive or transmission member. For example, if the elongatable drive shaft is terminated at its end which is near the carriage with a drive pulley member, and the print element shaft, which is mounted on the carriage, is terminated at its end which is distal from the end where the print element is installed with a driven pulley member, and both such pulleys are rotatively coupled to each other by a flexible drive or transmission member element, such as a drive belt, a stranded metal cable, a flexible music wire, or a high strength fiber such as Kevlar (DuPont), a constant velocity universal coupling element is realized. In operation, as the carriage is translated along the carriage path, the driven pulley member rotates in a plane which remains parallel with the carriage path and, in one embodiment, is essentially vertical. The drive pulley member, however, though also substantially vertical, rotates in a plane which remains orthogonal to the pivoting drive shaft. A drive belt which couples such drive and driven pulley members is twisted equally on either side of the pulley members, thereby being selfcompensating insofar a rotational orientation is not affected by such twisting. However, such twisting stretches and increases the tension on the flexible drive member for a given distance between the pulley members. This variation is compensated for in accordance with one embodiment of the invention, by a novel drum head and coupling member compensator which varies the distance between the drive and driven elements in a manner which compensates for the stretching of the flexible drive member caused by the relative twisting of their axes of rotation. The extent of compensation is a function of drive angle.

This constant velocity universal drive or coupling arrangement permits the carriage to be translated, illustratively as a single character or symbol is repeatedly printed, without causing displacement of the angular position of the print member and without requiring the servo control system to be unlocked to make adjustments between such repeated printings.

The advantageous reductions in the mass of the carriage which result from the above-described removal of the motor and the shift mechanism from the carriage are useful to achieve increased printing speed in a relatively inexpensive manner. However, in a particularly advantageous embodiment of the invention, a large proportion of the mass associated with the ribbon supply box and the ribbon therein can also be removed from the carriage. Moreover, once the bulk of the mass of the ribbon supply arrangement is removed from the carriage, substantial additional ribbon can be provided thereby extending the period between ribbon changes. In accordance with the invention, a ribbon supply arrangement is installed on the motor guide. As such, therefore, a substantial portion of the weight of the ribbon supply arrangement is borne by the motor pivot, and not the carriage.

As previously indicated, the location of the motor, in accordance with the invention, need not be stationary with respect to the frame of the printer. Thus, the disposing of the ribbon supply arrangement over the motor in an arrangement where the motor travels laterally causes the ribbon supply arrangement to move laterally also. In such an embodiment, the ribbon supply arrangement would nevertheless maintain the pivotal coupling between the first and second ribbon portions to accommodate for the aforementioned displacement differential resulting from the differences in the speeds of translation of the motor and carriage.

In a particularly advantageous embodiment, the ribbon supply arrangement is divided into first and second portions which are pivotally coupled to one another. The first portion of the ribbon supply arrangement contains the reels of ribbon, which reels may preferably be enlarged as compared with known ribbon supply systems for printers, rests upon the motor guides so that most of the weight thereof is borne by the motor pivot. The second portion of the ribbon supply arrangement which is substantially lighter than the first portion, is pivotally coupled to the first portion and is situated on the carriage. As the carriage is translated along the carriage path, the second portion of the ribbon supply arrangement pivots with respect to the first portion, such that the second portion maintains a substantially fixed orientation with respect to the carriage. In this manner, the second portion of the ribbon supply arrangement, which holds the ribbon in a position intermediate of the printing element and the paper which is to be printed, does not change its orientation with respect to the carriage even though the first portion of the ribbon supply arrangement undergoes an angular displacement with respect to the carriage path as the carriage is translated.

This pivotally connected ribbon box may contain a second ribbon type, such as multicolor ribbon for use with the rotating print element, and arranged to substitute for, or in addition to, the primary ribbon type by mechanical interchange means. Usually, such a second ribbon supply is undesirable in known printer arrangements because of additional carriage weight. However, in accordance with the present invention, the bulk of the additional weight would be borne by the drive motor pivot assembly rather than the carriage.

In a yet further aspect of the invention, a second print head which is preferably of a different type from the rotating print element type described hereinabove, illustratively a dot matrix impact print head, is arranged to be translatable along the carriage path. The second print head may be arranged on a separate carriage. The pivotally-connected ribbon box may contain a second ribbon suitable for use with the second head. The second ribbon may bear several colors for highlighting or chart making, or may be of the single color type particularly suited for use with the second head.

Such a combination of print heads in a single printer permits the advantageous integration of charts, graphs and highlighting of the letter quality text, without requiring the substantial handling by an operator which reinserting and adjustment to relocate a desired printing point exactly for a second print pass normally entails. Moreover, such a multiple print head arrangement obviates the need for a plurality of additional printing, lithographic or laser-xerographic page making equipment.

Brief Description of the Drawings

Comprehension of the invention is facilitated by reading the following detailed description in conjunction with the annexed drawings, in which:

Fig. 1 is a simplified isometric and partially exploded representation of a printer drive arrangement constructed in accordance with the invention;

Figs. 2A, 2B, 2C, and 2D are isometric and fragmented representations of details of the transmission arrangement of the embodiment of Fig. 1;

Fig. 3A is a simplified isometric representation of a vibration-isolated drive motor mounting;

Fig. 3B is a front view of a vibration-isolated pulley mounting on a print carriage;

Fig. 4 is a simplified isometric representation of an off-carriage motor arrangement for driving a rotatable print element in accordance with the invention while providing magnetic isolation from a magnetic-field sensitive CRT;

Fig. 5 is a partially-sectioned side view of a CRT arranged with a printer having an off-carriage drive motor located so as to reduce the effects of an interfering magnetic field on the CRT;

Figs. 6A and 6B are plan and side cross-sectional views of a flexible transmission twist compensation arrangement;

Fig. 7A shows the embodiment of Figs. 6A and 6B in a position for compensating for a twist in a plane of a flexible transmission element;

Fig. 7B shows a detailed cross section of the compensation arrangement of Figs. 6A and 6B;

Figs. 8A and 8B show compensation embodiments for the printer drive arrangement of Fig. 1;

Fig. 9 is an isometric representation of a print disc having information encoded thereon and a sensor in the vicinity thereof;

Fig. 10 is an isometric representation of a ribbon system constructed in accordance with the invention and;

Fig. 11 is an isometric representation of a ribbon supply arrangement and an auxiliary print head.

Detailed Description

Fig. 1 is an isometric, simplified, and partially exploded representation of a printer embodiment of the invention. The printer is of the type having a rotatable print element 36 mounted on a movable print carriage 37. Unlike previously known printers of this type, however, a main drive motor 20 for the rotatable print element is not mounted on the print carriage, but is spaced apart therefrom. As shown, a main drive shaft 21 extends from main drive motor 20 to a lower pulley 22. Lower pulley 22 forms a part of a transmission system by connecting to an upper pulley 23 via a flexible belt 24. Upper pulley 23 is connected to an end of a print element drive shaft 35 which is coupled to rotate print disc 36. By such a rotation transmission arrangement, print disc 36 is rotated in response to the rotation of main drive motor 20.

Print element drive shaft 35 is mounted on print carriage 37 by means of a front journal bearing 38 and a rear journal bearing 39. The journal bearings are themselves installed on print carriage 37. Print carriage 37 is constrained to move only along a lateral direction by virtue of its being mounted on, and guided by, a front cross-shaft 50 and a rear cross-shaft 51. The print carriage is coupled to front cross-shaft 50 via a front linear bearing set 52 (not shown in detail), and to rear cross-shaft 51 by a linear bearing set 53

(not shown in detail). Either or both such cross-shafts can be driven rotationally by a drive (not shown) to drive print carriage 37 laterally therealong. Such driven shafts may be either threaded (e.g. a ball screw shaft) or smooth, and engage with a correspondingly threaded ball member (not shown) in the linear bearing sets, or drive the carriage by engaging angulated bearings (not shown), respectively.

Main drive motor 20 is pivotally mounted between a lower pivot 64 and an upper pivot 65. Such a mounting arrangement permits the motor to pivot about an axis which connects pivots 64 and 65. In this embodiment, lower pivot 64 is mounted directly on a frame base 63 which is arranged to be on a center line (not shown) orthogonal to the extent of lateral travel of print carriage 37 along the front and rear cross-shafts. Thus, in this specific illustrative embodiment, the motor is positioned with respect to the path of the print carriage such that main drive shaft 21 is substantially orthogonal to the cross-shafts when the print carriage is in the center of its lateral travel. Also in this embodiment, upper pivot 65 is coupled to frame base 63 by means of a vertical frame extension 66; the pivot arrangement being shown to have somewhat of a C-shape. Vertical frame extension 66 is arranged on frame base 63 such that upper pivot 65 is positioned directly and vertically above lower pivot 64. Thus, main drive motor 20 and main drive shaft 21 pivot in a substantially horizontal plane. In this regard, it is to be understood that the inventive concept herein is not limited to the drive arrangement of Fig. 1 where pivoting of the main drive motor and main drive shaft is essentially in a plane which is parallel to the translatory path of the print carriage or the general orientation of the driven shaft which is coupled to the printing element. As will be discussed below with respect to alternative embodiments of the invention, the main drive motor and main drive shaft can be arranged at various angles with respect to one another, including orthogonal thereto. Moreover, the main drive motor can be arranged on the other side of the cross-shafts from its location in Fig. 1. Finally, as will, described hereinbelow, the main drive motor and main drive shaft can be arranged to couple with the print element drive shaft from the rear of the printer and above the cross- shafts.

In addition to the foregoing, the motor may be arranged to move substantially in correspondence with the carriage, as indicated hereinbefore. Thus, only minimal pivotal motion would be required by the motor in such a system; the pivotal motion compensating for lateral speed and displacement differentials between the carriage and motor. Such a laterally moving motor embodiment would be particularly useful in wide-platen printers constructed in accordance with the invention. For sake of simplifying the disclosure, the description herein will focus on an embodiment of the invention wherein the motor undergoes essentially only pivotal motion in response to carriage motion.

Returning to the embodiment of Fig. 1, print carriage 37 moves laterally along front and rear cross-shafts 50 and 51, carrying print disc 37 in the same lateral movement. In response to such movement, main drive shaft 21 pivots about the axis defined by upper and lower pivots 65 and 64 to follow the center line (not shown) of print carriage 37. As noted, the lateral path travelled by print carriage 37 is constrained in this embodiment, to be horizontal and in a straight line. Such a path corresponds to the chord of an arc drawn about a center at pivots 64 and 65. The distance between the pivots and the chord representing the travel path of the print carriage is greatest at the lateral extremes of travel of the print carriage. Conversely, the distance is shortest when the print carriage is in the vicinity of the midpoint of the lateral travel.

It is apparent from the foregoing that main drive shaft 21 must be variable in effective length to accommodate for variations in the distance between the main drive motor and the print carriage, in response to the location of the print carriage. In this illustrative embodiment of the invention, as shown in Fig. 1, main drive motor 20 has a hollow central shaft 87 through which is arranged a frontmost portion of main drive shaft 21. When print carriage 37 is located at the midpoint of its permissible travel, the frontmost end of main drive shaft 21 protrudes slightly from the frontmost end of hollow central shaft 87. A sufficient length of main drive shaft 21 is provided so that when the print carriage moves to the extremes of its travel, the frontmost end of the main drive shaft moves rearward, but is nevertheless retained securely within hollow central shaft 87.

In a specific illustrative embodiment of the invention, the interior of hollow shaft 87 is provided with at least one spline groove 86. Main drive shaft 21, at least over the frontmost portion which engages within hollow shaft 87 of the main drive motor, is also provided with a spline groove which matches spline groove 86 of the hollow central shaft. Spline grooves 86 and 88 are maintained in registration with one another by a front spline quill 89 and a rear spline quill 90 (shown in phantom), each of which is equipped with ball bearings (not shown) to allow longitudinal movement of the main drive shaft within the hollow central shaft, while always coupling any rotation of the hollow central shaft to the main drive shaft. Alternatively, lower pulley 22 could be spline-coupled to main drive shaft 21. The lower pulley, however, could not house the main drive shaft to prevent substantial protrusion, as can hollow central shaft 87 in main drive motor 20.

In accordance with a further aspect of the invention, a ribbon supply box 101 is mounted above main drive motor 20, main drive shaft 21, and print carriage 37. Main drive motor 20 is provided with a left slide bar 102 and a right slide bar 103 which are fastened securely to the upper frame of the main drive motor. The front underside portion of ribbon supply box 101 is provided with a left slide guideway 104 and a right slide guideway 105. Left slide guideway 104 slidably engages with a left slide bar 102, and right slide guideway 105 slidably engages with a right slide bar 103. In this manner, the vertical weight component of the ribbon supply box is transmitted downward through the engagements between the slide guideways and the slide bars, through the frame of main drive motor 20, and to lower pivot 64 on frame base 63. Of course, persons skilled in the art can configure the slide guideways and slide bars to prevent the ribbon supply box from simply lifting off of the slide bars. Alternatively, any of several known slide coupling arrangements can be used.

A front end of ribbon supply box 101 is provided with a post receiver 116 which is shown schematically in Fig. 1 for clarity and which engages with print carriage 37. The print carriage is therefore fitted with a carriage pivot post 119 which is mounted in a pivot post bearing 120 which, in this embodiment, allows rotation in a horizontal plane. The lower face of post receiver 116 is provided with a receiver hole 117 which has a predetermined cross-sectional shape adapted to engage with a correspondingly shaped male portion 118 on the upper surface of carriage pivot post 119. In this particular embodiment, hole 117 and its corresponding mating member 118 each have substantially triangular cross-sectional configurations. However, any other suitable cross-sectional configuration can be utilized.

With this arrangement wherein the ribbon box is pivotally coupled to the print carriage and slidably coupled to the pivoting main drive motor, the ribbon supply box pivots about carriage pivot post 119 as print carriage 37 travels laterally. The pivoting motion of ribbon supply box 101 is conveyed to main drive motor 20 through the engagement between slide guideways 104 and 105, and guide bars 102 and 103. By this arrangement, therefore, main drive motor 20 would pivot about lower and upper pivots 64 and 65 as the print carriage is moved, even if main drive shaft 21 were to be removed. Thus, undesirable side-loading of the main drive shaft is prevented.

As will be described hereinbelow, lower pulley 22 rotates with respect to the plane of rotation of upper pulley 23 as the print carriage is moved laterally. Such an out-of-plane rotation is achieved by mechanism which will be described later. It is an advantage of the preferred embodiments of this invention that since the main drive motor is caused to pivot by virtue of its being coupled to the ribbon supply box, and since lower pulley 22 is also rotated as the print carriage is moved so that its plane of rotation remains essentially orthogonal to the axis of rotation of main drive shaft 21, no excessive side loads are placed on the main drive shaft. Thus, oscillations within the main drive shaft are prevented.

Figs. 2A, 2B, 2C, and 2D show several views of the transmission coupling arrangement at lower and upper pulleys 22 and 23, which serves as a constant velocity universal drive as hereinafter explained. Fig. 2A is a perspective view of the flexible transmission system. Referring for the moment to Fig. 1, pulleys 22 and 23 are coupled by flexible belt 24 which may be a known ladder-type belt. Alternatively, the belt may be a miniaturized box-link chain, and, in such embodiments, the pulleys would then be configured as sprockets which engage with the box-link chain. Either of these embodiments can provide excellent rotational coupling for an unlimited number of rotations of the pulleys, and would be useful in a unidirectional embodiment where the print element is rotated in only one direction. However, if the speed of the printer is desired to be maximized, it is desirable to rotate the print disc in a direction which requires minimum angular rotation. In a worst case situation where it is desired to select a prior adjacent character on the print disc, a unidirectional embodiment may require the print disc to be rotated for almost 360 degrees to select such a character. Clearly, it would be much faster simply to reverse the rotation of travel of the print disc to select the adjacent character. Thus, with such a bidirectional rotation selection system, the print disc is never required to be rotated over an angle which exceeds 180 degrees.

Returning to Fig. 2A, upper pulley 23 and lower pulley 22 are shown to be coupled by a flexible cable 127. In an advantageous embodiment, flexible cable 127 is formed of stranded steel wire, as a miniature aircraft control cable. Alternatively, the flexible cable may be solid wire, such as a music wire. However, in a preferred embodiment, the flexible cable may be formed of one of the newer plastics, such as Kevlar (a trademark of DuPont) or Aramid (a trademark of Goodyear). All of these metallic and plastic materials improve the linear strength of the pulley-to-pulley coupling, particularly the maximum dynamic and pulse load of the transmission. Moreover, coupling cables of this type exhibit increased twisting flexibility over that provided by a belt or a chain. The expanded view of the coupling arrangement shown in Fig. 2A illustrates upper pulley 23, which is connected to print element drive shaft 35, and shown to have an upper cableway 128 in which is arranged flexible cable 127. Lower pulley 22, which is coupled to main drive shaft 21, has arranged therearound a lower cableway 129 where flexible cable 127 engages with the lower pulley.

Fig. 2B shows a partially phantom plan view of a specific illustrative embodiment of upper pulley 23. Flexible cable 127 is shown to be connected to the upper pulley by clamp screws 135, only two of which are visible in this figure. The phantom plan view representation of Figs. 2B and 2D show the manner in which clamp screws 135 hold the ends of cable 127 securely. The inertial mass of clamp screws 135 is counterbalanced by balance weights 136 which are installed in upper pulley 23 to achieve dynamic and static balance of the pulley.

Fig. 2C shows the embodiment of the invention in a position which indicates that the print carriage is located to the left of the midpoint. Thus, lower pulley 22 is rotated so that its plane of rotation is not parallel to that of upper pulley 23. As shown, the drive ratio between the lower and upper pulleys is approximately 1:1 since such a drive ratio will optimize a servomechanism system (not shown) which controls the angular orientation of the print disc. It is not essential, however, to use such a drive ratio, and with different drive ratios it may be desirable to increase the number of turns retained within cableway 128 of upper pulley 23. Lower pulley 22 would continue to use a single cableway 129. The amount of cable 127 which is wound on upper pulley 23 corresponds, in a preferred embodiment, to 540 degrees of total angular excursion. The 540 degree wrap provides a very high acceleration load capacity for only a small increase in running friction which results from the increased length of preformed cableway. It is, desirable to maintain the tension in flexible cable 127 so as to maintain the preload on the bearings within a reasonable limit. Thus, an engineering compromise must be reached between the tensile force in the flexible cable required to achieve a reliable engagement between the flexible cable and the lower pulley, and the wear on the bearings.

Fig. 2D shows a partially fragmented side view jof upper pulley 23 illustrating the guide grooves for the flexible cable. The circular cross-section of flexible cable 127 is shown interposed between clamp screws 135. Of course, upper pulley 23, which in this specific illustrative embodiment bears the clamping screws and balance weights 136, may be utilized by persons skilled in the art as the lower pulley. Alternatively, each of the pulleys may be of the clamping type.

As indicated hereinabove with respect to Fig. 1, print carriage 37 moves laterally and is guided by a front cross-shaft 50 and a rear cross-shaft 51. In the embodiment of Fig. 1, cross-shafts 50 and 51 define a plane which i3 transverse to the horizontal plane in which main drive motor 20 and main drive shaft 21 pivot. In fact, front cross-shaft 50 is arranged below print element drive shaft 35, while rear cross-shaft 51 is above the print element drive shaft.

It is evident from Fig. 1 that print element drive shaft 35 maintains a fixed relationship with respect to the cross-shafts 50 and 51. Moreover, the plane defined by cross-shafts is transverse to a plane defined by print element drive shaft 35 as the print carriage is moved arcuately, since print disc 36 has but a single outer row of characters emplaced thereon, and thus requires no vertical movement to access any character.

There are, however, dual-row print discs in commercial use wherein fully-formed characters to be printed are arranged concentrically on the print discs. Such dualrow discs require vertical shifting so that a selectable one of the rows is placed in registration with a print zone of the carriage where impact printing is to be performed. The combination of lateral movement to reach a desired printing position on the paper page, and vertical movement to access a particular character row on the periphery of the print disc 36, after which a rotation movement places the particular character in position to be printed, is described in my aforementioned copending U.S. Patent Application entitled "Shift System for Multi-Row Print Element."

Fig. 3A is a simplified isometric representation of a vibration-isolated drive motor mounting constructed in accordance with the invention wherein the print carriage may be further isolated from any drive-shaft-coupled vibration, thereby increasing the accuracy of printing. Vertical frame extension 66 holds drive motor 20 so that it may pivot about upper pivot 65 (not shown in Fig. 3A) and lower pivot 64. A vibration-isolating mount 515, herein shown as a lead-plastic laminate structure, serves to damp out any vibrations caused by rapid motion reversals or accelerations produced during operation of drive motor 20. Thus, these unwanted vibrations are absorbed, largely as frictionally-produced heat, before they are transmitted into base frame 63. In Fig. 3B, a front view of the mounting system for lower pulley 22 is shown. In this specific embodiment, flexible member 24 couples the rotation of lower pulley 22 to upper pulley 23. As previously noted, upper pulley 23 is then coupled directly to print element drive shaft 35 so as to rotate print disc 36 to select a chosen character for printing. Lower pulley 22 is rotated by drive shaft 21, and drive shaft 21 is in turn held in a lower trunnion plate 96. Lower trunnion plate 96 is coupled to a post shaft 115, which is held in the desired relationship to print carriage 37 by a carriage pivot bearing 120. Carriage pivot bearing 120 is vibration-isolated from print carriage 37 by a pair of vibration isolating pads 516 and 517. The isolation pads are preferentially constructed of a lead and plastic layer laminate wherein higher frequency vibrations are absorbed as frictional heat. Post shaft 115 is restrained vertically in post bearing 120 by post spring 97. Thus, between the vibration absorbing mounts for the drive motor and the post bearing, any residual vibration from drive motor 20 is prevented from causing positional inaccuracies in locating print carriage 37 at desired printing points. Additionally, the guide frame action for drive motor 20 eliminates side forces on drive shaft 21, as hereinbefore stated, so that essentially only rotational motions reach upper pulley 23. In Fig. 4, the off-carriage drive motor 21 which rotates print disc 36 to select characters has been located at an upper corner of an equipment case (not shown in this figure) in which a cathode ray tube (CRT) display is mounted. Since a CRT is often used to display input text for correction or reformatting before the output copy is made, a printer can be a natural adjunct component for a CRT. To help relate the CRT screen image of text to the final copy, the platen and printing mechanism may be mounted just above the top of the screen. If a conventional printer system were to be used in this arrangement, a drive motor would be located on the print carriage and in the immediate proximity of the CRT. However, since most cathode ray tubes are sensitive to external magnetic fiedls which deflect the beam of electrons, any such external magnetic disturbance will upset the clarity of the image. Moreover, since a drive motor mounted on a laterally-traversing print carriage would represent a varying disturbance field to a CRT, the image distortion would vary with the location of the motor along the carriage path; a particularly disturbing visual factor. Although the CRT can be shielded, the immediate proximity of the CRT to the motor would require the use of a substantial magnetic shield. Shielding of the motor would increase the traversing carriage weight, thereby slowing the action of the printer unless a much larger horizontal drive motor is used.

As shown in Fig. 4, drive motor 20 can be isolated from cathode ray tube 501 by mounting drive motor 20 well away from the CRT. Drive shaft 21 can extend downward at an angle so as to drive lower pulley 22. Flexible member 24 is routed around a pair of idler pulleys 508, 509 so as to couple rotational motion of drive shaft 21 into upper pulley 23 through an appropriate drive angle. Upper pulley 23 is attached to the rear end of print element drive shaft 35, so that print disc 36, which is attached at the front end in this embodiment, will rotate to the desired character as a result of rotary motion of drive motor 20. Print disc 36 is located at the upper edge of cathode ray tube 501, with the centerline of a platen 510 located at the center of the character row on the periphery of print disc 36.

In Fig. 5, a partial cutaway side view of the CRT printer equipment is shown. Drive motor 20 is at upper right, just inside a frame 63 which, in this embodiment, may be a corner-gusseted wire frame. A lower frame extension 525 allows lower pivot 64 mounting for drive motor 20, and upper frame extension 526 allows mounting of upper pivot 65. Ribbon case 101 is placed in a sliding mount (not shown) atop upper pivot 65, and is coupled at the pivoting axis of upper pulley 23, so that the frame of ribbon box 101 serves to cause drive motor 20 to pivot when print carriage 37 translates laterally along front guide rod 50 and rear guide rod 51 under platen 510. Film ribbon 99 passes out of ribbon box 101 and is conducted to the upper periphery of print disc 36 where impact printing occurs by a hammer (not shown), which rapidly presses fully-formed characters on print disc 36 into film ribbon 99 and subsequently onto a paper 19 which is to be printed and is located atop platen 510.

As hereinbefore mentioned, the off-board location of drive motor 20 minimizes the magnetic field disturbance of the CRT image. If any disturbance remains, even with this relatively remote positioning of the drive motor, it is possible to add magnetic shielding in the form of a surrounding jacket on drive motor 20. Such magnetic shields can be formed of "Netic" or "Co-Netic" materials, as supplied by Perfection Mica Company. The additional weight of such jacketing magnetic shields is almost entirely transferred to frame 63 through lower and upper pivots 64, 65, so that printing speeds are not degraded by adding translatory mass, as would occur if drive motor 20 were to be located directly on print carriage 37.

There is, however, a need for compensating for variations in tension within the flexible drive element which are responsive to the location of the print carriage along its path. More specifically, as described hereinabove, lower pulley 22 remains orthogonal to main drive shaft 21 and is thus rotated out of the plane of rotation of upper pulley 23 as the print carriage is translated. Such a rotation causes a twist in the plane of operation of the flexible transmission element, as can be visualized readily from the simplified structure of Fig. 2C. The effect of such a twist is to increase the tension in the flexible transmission element. In addition, the increasing tension produces a correspondingly increasing force component which tends to resist the rotation of the plane of rotation of the lower pulley, which force component translates into a greater force required to drive the print carriage along the cross-shafts. In other words, potential energy is stored in the arrangement as a function of carriage displacement on either side of the center point. Moreover, although such a twist in the flexible drive element is balanced insofar as it is equal on either side of the lower pulley so that the print disc is not rotated as the plane of rotation of the lower pulley is tilted with respect to the plane of rotation of the upper pulley, the resulting twist in the flexible drive element increases friction in the transmission thereby requiring a larger torque to be produced by the main drive motor for a given acceleration of the print disc. Thus, the forces required to drive the print carriage along its path, and the torque force required to rotate the print disc vary with the location of the print carriage along its print path.

Fig. 6 is a plan view of a mechanism for rotating the plane of rotation of lower pulley 22 such that it remains essentially orthogonal to the longitudinal axis of main drive shaft 21, while simultaneously compensating for the increased tensile force in the flexible drive element which would otherwise be produced.

It should be emphasized here, however, that a significant advantage of this embodiment of the invention is that irrespective of whether compensation for the increased tensile force in the flexible drive element is provided, the upper pulley, and the print disc coupled thereto, are not rotationally displaced as the drive angle is varied in response to the translation of the print carriage, as would be the case if print element drive shaft 35 were to be coupled to the main drive motor by a conventional non-constant velocity universal coupling arrangement. In such conventional non-constant velocity universal coupling arrangements, variations in the transmission ratio throughout each cycle of rotation are responsive to the drive angle, which, in the present system, varies with carriage position. Thus, notwithstanding that a drive angle between the main drive shaft and the print element drive shaft is varied in correspondence with the location of the print carriage along its path, the transmission arrangement of the present invention maintains a constant velocity transmission characteristic whereby the transmission ratio remains constant throughout the entirety of each revolution of the main drive motor. Maximum operating speed of a printer is achieved with the use of such a constant velocity drive arrangement for several reasons. First, in a situation where a character or symbol is repeatedly printed along an excursion of the print carriage, a feedback-controlled servomechanism (not shown) which controls the angular position of the printed disc need not be unlocked to make corrections resulting from angular displacement of the print disc in response to the linear translation of the print carriage. Moreover, the use of a constant velocity transmission system such as the one described herein permits a character to be selected while the print carriage is moving to the next print location. The use of a transmission system having a non-constant velocity characteristic would require some adjustment to the angular orientation of the print disc to be performed after the carriage is stopped and the final drive angle determined. In contrast, in accordance with the preferred embodiments of the present invention, the print element can be prepared to perform a printing operation as soon as, or even a short time before, the print carriage has stopped.

Fig. 6A is a front view of a preferred compensator arrangement for achieving the foregoing advantage. In this figure, print carriage 37, of which only a fragmented portion thereof is illustrated, is located at the center of its lateral travel. Thus, main drive shaft 21, which is shown in cross section, is arranged essentially orthogonal, in this embodiment, to the cross-shafts (not shown in this figure). Consequently, lower pulley 22 is oriented so that its plane of rotation is parallel to the cross-shafts and the direction of lateral motion of the print carriage therealong. Main drive shaft 21 and lower pulley 22 are supported by a trunion plate 96 which is fastened to a lower drum head 94. Trunion plate 96 and lower drum head 94 are both secured to print carriage 37 by means of a post shaft 115. An upper drum head 93 is secured to the underside of print carriage 37. A plurality of leaves 95 are interposed between upper drum head 93 and lower drum head 94.

Fig. 6B is a cross-sectional side view of the embodiment of Fig. 6A showing in greater detail the communication between leaves 95 and the upper and lower drum heads. As shown in this drawing, post shaft 115 is arranged to pass through a carriage pivot bearing 120, and is secured at its top end by a post spring 97 and a spring washer 121.

Fig. 8 shows an expanded cross-sectional view of the engagement between upper drum head 93, lower drum head 94, and leaves 95. Each of leaves 95 is provided with a substantially U-shaped notch at each end thereof for engaging with respective substantially V-shaped rims on the upper and lower drum heads.

Upper drum head 93 is mechanically fastened to print carriage 37 and has a hole centrally arranged therethrough for accommodating post shaft 115. At its lower portion, post shaft 115 is pinned to lower drum head 94 which is itself affixed to trunion plate 96. Of course, any of several known affixation means may be utilized to couple the lower drum head to the post shaft. Lower drum head 94 is affixed to post shaft 115 by a locking pin 99 which is arranged in commonly registering holes.

Returning for the moment to Fig. 1, it was noted with respect thereto that carriage pivot post 119 is coupled to ribbon supply box 101 by the engagement between shaped hole 117 and post receiver 116. Since the engagement occurs by the mating of members 117 and 118 which have polygonal shapes, carriage pivot post 119 rotates as the print carriage is translated.

In Figs. 6A and 6B, carriage pivot post 119 is provided at its uppermost end with an engagement portion 118 having analogous correspondence to that shown in Fig. 1. Thus, in operation, the ribbon supply box couples to post shaft 115 so as to rotate the post shaft, lower drum head 94, trunion plate 96, and lower pulley 22 with shaft 21 as the print carriage is translated laterally along the cross-shafts.

A compression force is exerted to leaves 95 as lower drum head 94 is urged upward toward print carriage 37 by operation of a spring 97 which is held in compression between carriage pivot bearing 120 and a spring washer 121 which remains in engagement with post shaft 115 by application of a forced fit, notwithstanding the force applied by post spring 97.

Fig. 7 shows the compensation arrangement of Figs. 6A and 6B in a position corresponding to the print carriage being translated to the extreme right. Such translation causes post shaft 115 to be rotated clockwise (as viewed from the top), thereby rotating lower drum head 94, trunion plate 96, and lower pulley 22. Since upper drum head 93 is fixed to the print carriage, as shown in Fig. 6B, leaves 95 in Fig, 7 are shown to be angularly displaced. Such an angulation of the leaves permits the lower drum head and lower pulley 22 to rise closer to the lower surface of the print carriage, thereby decreasing slightly the overall length of the path of the flexible transmission element and compensating for the additional tensile force in the flexible drive member which is produced as a result of the twisting thereof, described hereinabove. It is a significant advantage of the present invention that the torque force applied through post shaft 115 to rotate the plane of rotation of lower pulley 22 is transmitted from ribbon supply box 101, and not main drive shaft 21. This avoids stressing main drive shaft 21 with side loads which would result in vibrations being transmitted through the main drive shaft.

In Fig. 8B, a specific illustrative compensator embodiment for the printer drive arrangement of Fig. 1 . is shown having upper drum head 93 supported above print carriage 37 and in the vicinity of upper pulley 23. For a driven pulley directly above a drive pulley, as shown in this embodiment, the approximate governing equation of height variation, for a constant flexible member length, would be: ( a) C = Co ( 1 -cos sin - 1 ( D sin 2 ) )

where: Co = initial shaft separation, inches

C = shaft rise needed to equalize tension, inches

D = effective flexible member diameter on pulleys, inches

= twist angle, degrees

and for a compensator of the design in Figs. 6A, 6B, and 7:

(b) Z = H2 - (Rupper-Rlower)2 0.5

1-COS (sin-1 (2Rlower sin 2 )

where:

H = drum head separation,

Rupper = upper drum head radius

Rlower = lower drum head surface, and

= twist angle

Thus, when the fr ee distance of the flexib le transmission member between the pulleys , L, is equal to Co at zero twist ang le , and the slant length of the leaf is made equal to Co, with the diameter of pulleys 22 and 23 equal to the diame ter Rlower of the lower drum head , there is a very close tracking, or compensation, of Z and C for angle variations between 0 and 30°.

A stamped plate embodiment of upper drum head 93 is shown, with a sleeve bearing 120 replacing the heavier plate needed in the embodiment previously described. Although the leaves are longer in the embodiment of Fig. 8B, this compensator embodiment functions essentially as described hereinbefore in conjunction with Figs. 6A, 6B, and 7, with the compensator also providing lateral support to lower drum head 94, as well as vertical motion during twisting of pulley 22 through an angle as print carriage 37 is translated laterally along front support shaft 50.

Fig. 9 is a front isometric view of a print disc 36 which is provided with a raised hub 133 having a reflective pattern 131 encoded thereon for use as a feedback control to the motor. Reflective pattern 131 is detected by a photosource/photosensor 130 which is arranged in the proximity of the reflective pattern. The reflective pattern may contain character index and angular information, which information is received by photosource/photosensor 130 and used to control main drive motor 20 in a known manner. The reflective pattern code is selected so that it can be detected during rotation in either direction of the print disc.

Fig. 10 is ah isometric and schematic rear view of an embodiment of the invention showing print carriage 37 and print disc 36 at an extreme lateral position. Thus, main drive motor 20 and main drive shaft 21 are shown pivoted to the midline of print carriage 37. Several elements of structure described hereinbefore have been eliminated in this drawing to preserve clarity. Ribbon supply box 101 is pivoted around post receiver 116 (shown in phantom), and, by means of coupling elements which are not shown in this figure, has caused the plane of rotation of lower pulley 22 to be rotated so that the lower pulley remains orthogonal to the main drive shaft without imparting a side load thereto.

Ribbon supply box 101 is shown to be coupled with a carriage ribbon box 100 which is held in a stationary position above print carriage 37. Thus, carriage ribbon box 100 maintains a fixed angular orientation with respect to print carriage 37 as it is translated laterally along cross-shafts 50 and 51. Ribbon supply box 101, as noted hereinabove, is engaged with main drive motor 20 at left and right slide bars 102 and 103, and slide bar guideways 104 and 105. Thus, ribbon supply box 101 assumes an angular orientation with respect to carriage supply box 100 which varies in correspondence with the position of print carriage 37 along the cross-shafts. When print carriage 37 is, in this embodiment, midway between the extremities of its lateral travel, carriage ribbon box 100 and ribbon supply box 101 are aligned axially with each other.

In accordance with the invention, carriage ribbon box 100 contains ribbon length compensators (not shown) and ribbon lift arrangements (not shown). In its rearmost area, carriage ribbon box 100 has a pair of print disc ribbon guides 109A and 109B which hold a film ribbon 99 on the other side of print disc 36 from upper pulley 23, such that the film ribbon is interposed between the print disc and a platen (not shown) which supports the paper to be printed. A conventional print hammer is accommodated in the opening between print disc ribbon guides 109A and 109B.

In accordance with the invention, a supply of film ribbon 99 is contained within ribbon supply box 101 on a ribbon supply reel 107. The film ribbon is passed out of ribbon supply box 101 and into carriage ribbon box 100, and is held in the vicinity of print disc 36 by guides 109A and 109B. After the ribbon has been used, the ribbon re-enters ribbon supply box 101 via a return path in carriage ribbon box 100, and is rewound on a ribbon take-up reel 108 which is arranged at the front of ribbon supply box 101. Since a substantial portion of the weight of supply reel 107 and take-up reel 108 is borne by lower pivot 64, reels 107 and 108 can be quite large because the bulk of their weight is conducted directly to frame base 63, bypassing the carriage.

Fig. 11 is an isometric front view of the embodiment of Fig. 10 with the added provision of an auxiliary print head 150 mounted on an auxiliary carriage 151. In a specific illustrative embodiment, an auxiliary ribbon supply 154 is contained within ribbon supply box 101 for supplying a ribbon 153 to the auxiliary print head. Ribbon 153 is guided by a plurality of ribbon guides 152 such that auxiliary print head 150, which may be of a dot matrix impact type, can imprint upon the sheet (not shown) to be printed upon. As discussed hereinbefore, the provision of a relatively large ribbon supply, such as film ribbon 99 and ribbon 153 of auxiliary ribbon supply 154, is possible because the additional weight is substantially borne by drive motor pivots 64 and 65 (Fig. 1).

In embodiments of the invention where auxiliary print head 150 is of the known ink jet type, auxiliary print head ink supply 154 would supply several colors of pressurized ink (not shown) to the auxiliary print head. In a still further possible embodiment of the invention, if auxiliary print head 150 were to be of the electrostatic printing type, auxiliary ribbon supply 154 would be of the type which supplied either liquid or dry ink, as required. In such embodiments where the auxiliary print head is of the ink jet type or of the electrostatic printing type, the ink from auxiliary ribbon supply 154 may be provided in several colors. In other embodiments of the invention, the auxiliary ribbon supply could be mounted directly on auxiliary carriage 151, in a conventional manner.

In the dual-print head embodiment of the invention shown in Fig. 11, auxiliary print carriage 151 would be placed at one extreme lateral position along cross-shafts 50 and 51 when rotary print disc 36 on print carriage 37 is being used. Conversely, when auxiliary print head 150 is to be utilized, print carriage 37 would be placed at the extreme right of cross-shafts 50 and 51 and auxiliary print carriage 151 would then be movable to all print locations. In such an embodiment, cross-shafts 50 and 51 are longer than the desired printing width to accommodate the left and right storage positions of auxiliary print carriage 151 and print carriage 37, respectively.

Cross-shafts 50 and 51, in a dual-print head embodiment, are used to guide and drive both print heads. For example, cross-shaft 50 may be drivingly engaged with print carriage 37 so as to cause the print carriage to be translated laterally as cross-shaft 50 is rotated. Print carriage 37 would engage with cross-shaft 51 only for the purpose of guidance, and not drive. In such an embodiment, cross-shaft 51 would be drive-coupled with auxiliary carriage 151, while cross-shaft 50 would only guide the auxiliary carriage. Thus, each of auxiliary carriage 151 and print carriage 37 would be driven by a respectively associated one of cross-shafts 50 and 51. In a dual-print head embodiment of the type shown in Fig. 11 where both print heads are supplied with ink from a single ribbon supply box 101, the ribbon supply box can be made larger to accommodate both supplies for the two print heads. In such an embodiment, supply reel 107 and take-up reel 108 could be arranged on either side of the auxiliary ribbon supply, as shown. An auxiliary ink supply aperture 159 (not shown) is made in the periphery of ribbon supply box 101 at the left rear thereof to allow an ink supply, such as auxiliary ribbon 153, to pass out of ribbon supply box 101 to supply the auxiliary ribbon.

Although the invention has been disclosed in terms of specific embodiments and applications, persons skilled in the art, in light of this teaching, can generate additional embodiments without exceeding the scope or departing from the spirit of the claimed invention. Accordingly, it is to be understood that the drawings and descriptions in this disclosure are proffered to facilitate comprehension of the invention of the invention and should not be construed to limit the scope thereof.

Claims

WHAT IS CLAIMED IS:

1. A drive arrangement for transmitting rotary motion from a drive member having a predetermined drive circumference and rotating in a drive plane to a driven member having a predetermined driven circumference and rotatable in a driven plane, the drive arrangement comprising: flexible transmission means for rotatively coupling the drive member to the driven member, said flexible transmission means engaging respective portions of the predetermined drive and driven circumferences; displacement means for rotatively displacing the drive and driven planes with respect to one another as the drive and driven members are urged along a first predetermined path; and compensation means responsive to said displacement means whereby a tensile force in said flexible transmission means is maintained within a predetermined range essentially constant as said rotative displacement between the drive and driven planes is varied.

2. The drive arrangement of claim 1 wherein said displacement means comprises: support means for supporting a selectable one of the drive and driven members; and displacement actuation means for moving said support means such that the drive and driven planes are rotated with respect to one another as the drive and driven members move along said first predetermined path.

3. The drive arrangement of claim 2 wherein said compensation means comprises translation means connected to said support means means for translating a selectable one of the drive and driven members along a second predetermined path whereby a distance between the drive and driven members is varied in response to the location of the drive and driven members along said first predetermined path.

4. The drive arrangement of claim 3 wherein there is further provided carriage means for supporting the drive arrangement, said displacement actuation means moving said support means with respect to said carriage means, a one of the drive and driven members which is selected to be off of said support means being maintained in a substantially fixed position with respect to said carriage means as said one of the drive and driven members which is selected to be supported by said support means is moved along said first and second predetermined paths.

5. The drive arrangement of claim 4 wherein there are further provided: carriage drive means for moving said carriage means substantially along said first predetermined path; motor means for providing a rotary force, said motor means having an axis of rotation and being pivotally coupled with respect to said first predetermined path; and coupling means arranged substantially coaxially with said axis of rotation of said motor means for coupling said motor means to the drive member, the predetermined drive circumference of the drive member being arranged in the drive plane of rotation which is adapted to remain essentially orthogonal to said axis of rotation of said motor means as said carriage means is moved substantially along said first predetermined path.

6. The drive arrangement of claim 5 wherein the predetermined driven circumference is arranged on the driven plane of rotation which is adapted to retain a fixed orientation with respect to said carriage means.

7. The drive arrangement of claim 6 wherein the drive and driven planes of rotation have an angular orientation with respect to one another which varies as said carriage means is moved substantially along said first predetermined path.

8. In a printer of the type which utilizes a rotating print element containing symbols to be printed and arranged on a movable print carriage, a drive arrangement for the rotating print element, the drive arrangement comprising: a driven member rotatably fixed on the movable print carriage, said driven member being adapted to receive a rotative force; print element coupling means for coupling said driven member to the rotating print element to transmit said rotative force to the rotating print element; mo tor means arranged at a pr ede termi nab le location with respect to the movab le print carriage , said mo tor means havi ng an axi s of rotation ; pivot moun ting me ans fo r pivotal ly affixing said motor means at said predeterminab le location whereby said axi s of rotation is di rected general ly in the direction of the movab le print carriage ; shaft means arranged along said axis of rotation of said motor means, said shaft means being connected to said motor means for rotating with said motor means; a drive member connected to said shaft means and rotating therewith as said motor means rotates; and flexible transmission means for coupling said drive and driven members, said motor means being pivotally moved about said pivot mounting means as the moving print carriage moves.

9. The drive arrangement of claim 8 wherein the symbols to be printed are arranged at a predetermined radial distance from a central axis of rotation of the rotating print element, the rotating print element being rotated to select symbols to be printed as the moving print carriage is moved to a plurality of printing locations along a printing path, the drive arrangement further comprising compensation means responsive the printing locations for maintaining a tension force in said flexible transmission means within a predetermined tension force range as the movable print carriage is translated along the printing path.

10. The drive arrangement of claim 9 wherein said compensation means comprises: cam means for defining a distance between said drive and driven members, said distance being responsive to the printing locations; and cam follower means for communicating with said cam means, whereby said cam means and said cam follower means are rotated with respect to one another as the movable print carriage is moved.

11. The drive arrangement of claim 9 wherein said compensation means comprises: first and second annular members arranged parallel to one another and to rotate with respect to one another as the movable print carriage is moved; and a plurality of leaves interposed between said first and second annular members whereby a distance between said first and second annular members is varied as said first and second annular members rotate with respect to one another.

12. The drive arrangement of claim 9 wherein there is further provided carriage drive means for guiding the moving print carriage along the printing path and urging the movable print carriage therealong.

13. The drive arrangement of claim 12 wherein said carriage drive means comprises: drive shaft means having a substantially smooth external surface; and bearing means angularly engaged with said drive shaft means and coupled to the moving print carriage for moving the movable print carriage along an axis of said drive shaft means in response to rotation of said drive shaft means.

14. The drive arrangement of claim 13 wherein there are further provided: motor guide means connected at a first end thereof to said motor means and at a second end thereof to the movable print carriage for pivotally moving said motor means about said pivot mounting means as the movable print carriage moves along the printing path whereby said axis of rotation of said motor means is directed along said shaft means toward the movable print carriage; and elongatable coupling means for coupling said first end of said motor guide means to said motor means whereby variations in a distance between said motor means and the movable print carriage, along said axis of rotation of said motor means, are accommodated, as the movable print carriage is moved along the printing path.

15. The drive arrangement of claim 14 wherein there is further provided shaft coupling means for connecting said shaft means to said motor means, there being further provided elongation means adapted to accommodate for said variations in said distance between said motor means and the movable print carriage as the moyable print carriage is moved along the printing path.

16. The drive arrangement of claim 8 wherein there is further provided transmission engagement means for coupling with said flexible transmission means at a portion thereof intermediate of said coupling of said drive and driven members by transmitting said rotative force from said drive member to said driven member about a predetermined drive angle defined at the intersection of a plane of rotation of said drive member and a plane of rotation of said driven member.

17. The drive arrangement of claim 16 wherein said transmission engagement means further comprises: first and second transmission members coupled to the movable print carriage by respective rotative couplings, said first and second transmission members being arranged essentially orthogonally with respect to said driven member, said flexible transmission means communicating with each of said first and second transmission members over an angle of arc which corresponds essentially to said predetermined drive angle.

18. An arrangement for driving and controlling a print head mounted on a carriage which is translatable along a predetermined path, the print head being of the type wherein symbols to be printed are arranged thereon, the symbols being selected for printing by rotating the print head such that a selected symbol is rotatively positioned at a predetermined print location with respect to the carriage, the arrangement further comprising: controllable rotary drive means disposed at a predetermined distance from the predetermined path of the carriage, said controllable rotary drive means having an axis of rotation which is arranged to be essentially transverse to the predetermined path; elongatable shaft means engaged with said controllable rotary drive means for transmitting a rotative force, said elongatable shaft means having an axis of rotation arranged to be substantially coaxial with said axis of rotation of said controllable rotary drive means; constant velocity universal coupling means for coupling said elongatable shaft means to the print head; and feedback control means responsive to the rotative position of the print head for controlling said controllable rotary drive means.

19. The arrangement of claim 18 wherein said constant velocity universal coupling means comprises: a drive member connected to said elongated shaft means at a portion thereof distal from said controllable rotary drive means; a driven member coupled to the print head for transmitting rotary motion thereto; and drive coupling means for rotatively coupling the drive and driven members.

20. The arrangement of claim 19 wherein said drive and driven members have respective axes of rotation and planes of rotation, said axis of rotation of each of said drive and driven members being orthogonal to its respectively associated plane of rotation, said respectively associated planes of rotation forming a drive transmission angle therebetween which varies as the carriage is translated along the predetermined path, said drive coupling means being adapted to maintain a substantially linear correspondence between the respective rotations of said drive and driven members as said drive transmission angle is varied.

21. The arrangement of claim 20 wherein said drive coupling means is formed of a flexible material and engages said drive and driven members along respective portions thereof.

22. The arrangement of claim 21 wherein said drive and driven members are laterally translatable so as to have a variable distance therebetween, there being further provided compensation means for maintaining a tensile force in said drive coupling means within a predetermined range of forces.

23. The arrangement of claim 22 wherein said compensation means comprises distance control means arranged to control a distance between said drive and driven members, said distance between said drive and driven members being varied as said drive and driven members are translated in response to the translation of the carriage.

24. The arrangement of claim 18 wherein said feedback control means comprises: sensor means in the vicinity of the print head for determining whether a symbol is positioned at the predetermined print location; and controller means responsive to signals from said sensor means and connected to said controllable rotary drive means for controlling the rotation of said controllable rotary drive means in response to said signals from said sensor means.

25. The arrangement of claim 24 wherein said sensor means comprises: a plurality of reflectors arranged on the print head, each reflector being positioned to correspond at least to an associated one of the symbols; light emitter means adapted to produce a light for illuminating said reflectors; and light receiver means arranged to receive said light from said light emitter means after said light has been reflected by any of said reflectors which is located at a reflector location corresponding to its associated symbol being at the predetermined print location.

26. A printing arrangement of the type wherein a plurality of symbols to be printed are arranged on radial elements of a rotatable print element at a predetermined radial distance from a center of rotation thereof, the print element being mounted on a carriage for translating the print element along a substantially straight carriage path, the arrangement further comprising print element drive means for rotating the rotatable print element, said print element drive means being provided with a motor having a motor axis of rotation and for supplying a rotative force to the rotatable print element, said motor having a motor axis of rotation and being disposed at a predetermined distance from the carriage path, and a shaft for rotatively coupling said motor to the print element.

27. The printing arrangement of claim 26 wherein there is further provided guide means for coupling the carriage and said print element drive means whereby said motor axis of rotation is directed toward the carriage as the carriage is translated along the carriage path.

28. The printing arrangement of claim 28 wherein said guide means is further provided with: pivotal coupling means aranged at a respective first end of said guide means for pivotally coupling said guide means at said respective first end thereof to the carriage; and bidirectional slide means having first and second slide members for slidably communicating with one another, said first slide member being coupled to a respective second end of said guide means and said second slide member being coupled to said print element drive means.

29. The printing arrangement of claim 28 wherein there is further provided pivoting drive mounting means for pivotally supporting said print element drive means whereby said print element drive means is urged into pivotal motion by said guide means in respoonse to the translation of the carriage along the carriage path.

30. The printing arrangement of claim 29 wherein said shaft is provided with means for accommodating variations in a length between said motor and the print element as said print element drive means is pivoted.

31. The printing arrangement of claim 26 wherein there is further provided a ribbon supply for providing a length of printing ribbon in the vicinity of the rotatable print element.

32. The printing arrangement of claim 31 wherein there is further provided carriage mounting means for holding said ribbon supply on the carriage.

33. The printing arrangement of claim 31 wherein there are further provided: pivot means for pivotally holding said motor at said predetermined distance from the carriage path; and ribbon supply holding means for holding said ribbon supply and coupling said motor and the carriage to one another and pivoting said motor about said pivot means as the carriage is translated along the carriage path.

34. The printing arrangement of claim 33 wherein there is further provided ribbon alignment means for holding at least a portion of said ribbon from said ribbon supply on the carriage and near the rotatable print element in a predetermined alignment for printing.

35. The printing arrangement of claim 34 wherein said ribbon supply holding means is pivotally coupled to said ribbon alignment means, and said ribbon alignment means is arranged to maintain a substantially fixed orientation with respect to the carriage as the carriage is translated along the carriage path.

36. The printing arrangement of claim 26 wherein there is further provided auxiliary printer means having a respective auxiliary carriage arranged to be translated along the carriage path.

37. The printing arrangement of claim 36 wherein there is further provided ribbon supply means for providing printing ribbon to said auxiliary printer means and the rotatable print element.

38. A twist compensator arrangement for a constant velocity drive arrangement, the twist compensator arrangement engaging a selectable one of first and second rotating members which are rotatively coupled by a flexible transmission element and arranged at a predetermined nominal distance from one another, each rotating member being rotatable in a respective reference plane so that, when the twist compensator arrangement is at a rest position corresponding to parallel reference planes, said nominal distance is at a maximum, the twist compensator arrangement further comprising means for reducing the predetermined distance between the rotating members as the angle between the respective reference planes is varied from said rest position.

39. The twist compensator arrangement of claim 38 wherein said means for reducing the predetermined distance comprises: first engagement means fixedly arranged with respect to said first rotating member; second engagement means arranged to face said first engagement means and fixedly arranged with respect to said second rotating member, said first and second engagement means rotating with respect to one another in correspondence with the variations in the angle between the respective reference planes; and a plurality of coupling members for coupling said first and second engagement means, said coupling members being angularly displaceable as said first and second engagement means rotate with respect to one another, thereby reducing a distance betweeen said first and second engagement means.

40. The twist compensator arrangement of claim 39 wherein there are further provided resilient means for urging said second engagement means toward said first engagement means for applying a compression force to said coupling members.

41. The twist compensator arrangement of claim 40 wherein said first and second engagement means are each provided with V-shaped rims facing each other, and said coupling members are provided with a U- shaped notch on each end thereof for engaging respective ones of said V-shaped rims.

42. The twist coupling arrangement of claim 38 wherein the first and second rotating members each comprise respective pulley means rotatably coupled with the flexible transmission element.

43. A serial impact printer comprising a movable print carriage, a rotatable print element mounted on the carriage, a print element drive motor mounted off said movable print carriage, and a rotatable drive shaft extending between said print element drive motor and said print carriage.

44. A serial impact printer in accordance with claim 43 further comprising a ribbon supply mounted off the carriage.

45. A serial impact printer in accordance with claim 43 wherein said print element drive motor is pivotably mounted in a fixed location and said rotatable drive shaft is adapted to pivot with said print element drive motor such that an axis of rotation thereof remains aimed in a direction from said print element drive motor toward said movable print carriage as said movable print carriage is moved.

46. A serial impact printer in accordance with claim 44 further comprising a pivoting guide bar extending from said print element drive motor to said movable print carriage, said guide bar being spaced apart from said rotable drive shaft, such that said print element drive motor is pivoted in response to translational movement of said movable print carriage substantially without exerting lateral loads on said rotatable drive shaft.

47. A serial impact printer in accordance with claim 45 wherein said rotatable drive shaft is slidably connected to said print element drive motor to compensate for variations in a distance between said print element drive motor and said movable print carriage.

48. A serial impact printer in accordance with claim 45 wherein said rotatable drive shaft is extendable to compensate for variations in a distance between said print element drive motor and said movable print carriage.

49. A serial impact printer in accordance with claim 44 wherein further including a constant velocity universal drive disposed between said rotatable drive shaft and said rotatable print element.

50. A serial impact printer in accordance with claim 49 wherein said constant velocity universal drive comprises a first drive wheel connected to said rotatable print element and having an axis of rotation aligned with an axis of rotation of said rotatable print element, a second drive wheel connected to said rotatable drive shaft and having a pivoting axis of rotation aligned with an axis of rotation of said rotatable drive shaft, and a flexible drive member engaging said first and second drive wheels, whereby a given angular velocity of said rotatable drive shaft will cause a corresponding angular velocity of said rotatable print element irrespective of variations in a drive angle between said axes of rotation of said rotatable drive shaft and said print element caused by translational movement of said movable carriage.

51. A serial impact printer in accordance with claim 49 further comprising means for maintaining substantially constant tension in said flexible drive member during variations in said drive angle between said axes of rotation of said rotatable drive shaft and said rotatable print element.