GB2306400A - Micro-tooth carriage drive system for inkjet printhead - Google Patents

Description

2306400 1 MICRO-TOOTH CARRIAGE DRIVE SYSTEM FOR INME,T PRINTITEADS

Field of the Invention

The present invention relates generally to inkjet printing mechanisms, and more particularly to a quieter and more economical system for driving a carriage carrying an inkjet printhead.

Back2round of the Invention Inkjet printing mechanisms use inkjet cartridges, often called "pens," which shoot drops of liquid colorant, referred to generally herein as "ink," onto a page. Each pen has a printhead formed with very small nozzles through which the ink drops are fired. To print an image, the printhead is propelled back and forth across the page, shooting drops of ink in a desired pattern as it moves. The particular ink ejection mechanism within the printhead may take on a variety of different forms known to those skilled in the art, such as those using piezo-electric or thermal printhead technology. For instance, two earlier thermal ink ejection mechanisms are shown in U. S. Patent Nos. 5,278,584 and 4,683,48 1, both assigned to the present assignee, He,ilett-Packard Company. In a thermal system, a barrier layer containing ink channels and vaporization chambers is located between a nozzle orifice plate and a substrate layer. This substrate layer typically contains linear arrays of heater elements, such as resistors, which are energized to heat ink within the vaporization chambers. Upon heating, an ink droplet is ejected from a nozzle associated with the energized resistor. By selectively energizing the resistors as the printhead moves across the page, the ink is expelled in a pattern on the print media to form a desired image (e.g., picture, chart or text).

To clean and protect the printhead, typically a "service station" mechanism is mounted within the printer chassis so the printhead can be moved over the station for maintenance. For storage, or during nonprinting periods, the service stations usually include a capping system which hermetically seals the printhead nozzles from contaminants and drying. Some caps are also designed to facilitate priming, such as BP Docket No. 10950827 2 by being connected to a pumping unit or other mechanism that draws a vacuum on the printhead. During operation, clogs in the printhead are periodically cleared by firing a number of drops of ink through each of the nozzles in a process known as "spitting," with the waste ink being collected in a "spittoon" reservoir portion of the service station. After spitting, uncapping, or occasionally during printing, most service stations have an elastomeric wiper that wipes the printhead surface to remove ink residue, as well as any paper dust or other debris that has collected on the face of the printhead.

In the past, the inkjet printhead was carried back and forth across the page in a carriage attached to a belt that was driven by a drive pulley and carriage drive motor. Typically, the drive pulley was located at one end of the printzone, and an idler pulley was located at the opposite end of the printzone. Several different belt and drive pulley systems have been used. One the more popular systems employs a toothed belt, similar to a timing belt in automobiles, which is driven by a pulley having mating teeth formed in the pulley's drive surface. The pulley teeth engaged the belt teeth to provide a very reliable system that never slipped. This tooth arrangement had a high tension ratio across the drive pulley, which yielded a low belt tension requirement. The term belt tension refers to the static axial load or nominal tension in the belt to which the belt is stretched before use. Low belt tensions are preferred because higher belt tensions yield increased friction, higher motor heat, and wear. Moreover, with lower belt tensions both the motor and belt-tensioning pulley may be constructed without ball bearings, which reduces the overall system cost.

Unfortunately, the toothed belt drive suffered a variety of disadvantages. For example, the teeth do not transmit power smoothly when driving the carriage because the engagement and disengagement (cogging) of the teeth produces a non-uniform driving force. Additionally, the belt tooth cogging occurs at frequencies that induce undesirable carriage velocity ripple. Moreover, these tooth engagement disturbances excited numerous noise sources within the printer, due to resonance which was concentrated in narrow frequency bands. Thus, printers using a toothed belt carriage drive system were perceived as being noisy, and a source of annoyance to consumers.

BP Docket No. 10950827 3 Another earlier carriage drive system employs a V-shaped belt driven by a pulley having a V-shaped groove around its periphery. While the V-belt drive systems exhibit improved acoustic properties and more consistent driving forces, unfortunately they have significant drawbacks. For instance, the V-belt.. drive system 5 is susceptible to slipping when oil or other lubricants inadvertently contact the belt. The V-belts are inherently thick, and must be wrapped around a large diameter pulley, which made it necessary to use larger motor, since the pulley diameter could not be chosen to optirnize motor performance. Moreover, the larger diameter pulley also increases the internal space required for the V-belt drive system within the printer. Another disadvantage of the V-belt drive is the low tension ratio across the drive pulley, which unfortunately induces high belt tension, leaving the belts susceptible to premature breakage. Thus, reliability of the V-belt drive systems is questionable. This high belt tension also increases friction in the V-belt system unless expensive ball bearings are used on the rotating components.

Another carriage drive system that has been proposed is a smooth belt which runs on a smooth pulley. Unfortunately, the smooth belt system is severely limited in the amount of power which it can transmit. In other words, as the driven load increases, for instance due to larger inkjet cartridges carrying greater supplies of ink, the smooth belts slip on the smooth pulleys. And, of course, this slippage increases if the smooth belt system is exposed to oil or other lubricating contaminants.

is Summary of the Invention

One aspect of the present invention addresses the noisy carriage drive problem by providing a friction drive system for driving a carriage that moves an inkjet printhead across a printzone in an inkjet printing mechanism. The friction drive system has a belt secured to the carriage, with the belt having a substantially flat drive surface. The friction drive system also has a carriage drive motor with an output shaft. A drive pulley is coupled to the motor output shaft. The drive pulley has a drive surface comprising a plurality of microteeth that engage the flat drive surface of the belt.

1P Docket No. 10950827 4 According to a further aspect of the invention, an inkjet printing mechanism is provided, including a media handling system that transports print media across a printzone, and a carriage that moves an inkjet printhead across the printzone. A belt is secured to the carriage, with the belt having a substantially flat drive surface. The printing mechanism also has a carriage drive motor with an output shaft. A drive pulley is coupled to the motor output shaft. The drive pulley has a drive surface comprising a plurality of microteeth that engage the flat drive surface of the belt.

According to another aspect of the invention, a method is provided of quieting inkjet printhead carriage motion in an inkjet printing mechanism. The method includes the step of coupling a belt having a substantially flat drive surface to a carriage that moves an inkjet printhead across a printzone in the inkjet printing mechanism. In an installing step, a drive pulley is installed on an output shaft of a carriage drive motor, with the drive pulley having a drive surface comprising a plurality of microteeth. In a driving step, the carriage is driven by engaging the flat drive surface of the belt with the plurality of microteeth and turning the drive pulley by operating the drive motor.

An overall goal of the present invention is to provide an inkjet printing mechanism which reliably produces clear crisp images while smoothly moving the ink-jet printhead across a page during printing.

A 'further goal of the present invention is to provide a method of quieting the printhead carriage motion to provide an inkjet printing mechanism which operates quieter than its predecessors.

Brief Description of the Drawings

FIS 1 is a fragmented, partially schematic, perspective view of one fonn of an inkjet printing mechanism employing one form of a microtooth carriage drive system of the present invention for propelling an inkjet printhead across a printzone for printing.

FIG. 2 is an enlarged perspective view of a portion of the microtooth carriage drive system of FIG. 1, BP Docket No. 10950827 FIG. 3 is an enlarged perspective view of a portion of an alternate embodiment of the n-ficrotooth carriage drive system of FIG. 1.

Detailed Description of the Preferred Embodiments

FIG. 1 illustrates an embodiment of an inkjet printing mechanism, here shown as an inkjet printer 20, constructed in accordance with the present invention, which may be used for printing for business reports, correspondence, desktop publishing, and the like, in an industrial, office, home or other environment. A variety of inkjet printing mechanisms are commercially available. For instance, some of the printing mechanisms that may embody the present invention include plotters, portable printing units, copiers, cameras, video printers, and facsimile machines, to name a few. For convenience the concepts of the present invention are illustrated in the environment of an inkjet printer 20.

While it is apparent that the printer components may vary from model to model, the typical inkjet printer 20 includes a chassis 22 surrounded by a housing or casing enclosure 24, typically of a plastic material. Sheets of print media are fed through a print zone 25 by a print media handling system 26. The print media may be any type of suitable sheet material, such as paper, card-stock, fabric, transparencies, mylar, and the like, but for convenience, the illustrated embodiment is described using paper as the print medium. The print media handling system 26 has a feed tray 28 for storing sheets of paper before printing. A series of conventional paper drive rollers (not shown), driven by a stepper motor 30 and a drive gear assembly 32, may be used to move the print media from tray 28 into the print zone 25 for printing, as shown for media sheet 34.

After printing, the motor 30 drives the printed sheet 34 onto a pair of retractable output drying wing members 36. The wings 36 momentarily hold the newly printed sheet above any previously printed sheets still drying in an output tray portion 38, after which the wings 36 retract to the sides to drop the newly printed sheet into the output tray 38. The media handling system 26 may include a series of 30 adjustment mechanisms for accommodating different sizes of print media, including BP Docket No. 10950827 6 letter, legal, A-4, envelopes, etc., such as a sliding length adjustment lever 40, a sliding width adjustment lever 42, and a sliding envelope feed plate 44.

The printer 20 also has a printer controller, illustrated schematically as a microprocessor 45, that receives instructions from a host device, typically a computer, such as a personal computer (not shown). The printer controller 45 may also operate in response to user inputs provided through a key pad 46 located on the exterior of the casing 24. A monitor coupled to the computer host may be used to display visual information to an operator, such as the printer status or a particular program being run on the host computer. Personal computers, their input devices, such as a keyboard and/or a mouse device, and monitors are all well known to those skilled in the art.

A carriage guide rod 48 is supported by the chassis 22 to slideably support an inkjet carriage 50 for travel back and forth, reciprocally, across the print zone 25 along a scanning axis 52. One suitable type of carriage support system is shown in U.S. Patent No. 5,366,305, assigned to Hewlett-Packard Company, the assignee of the present invention. The carriage 50 is also propelled along guide rod 48 into a servicing region housing a service station 54, located within the interior of casing 24. The service station 54 may be any type of servicing device, sized to service the particular printing cartridges used in a particular implementation. Service stations, such as those used in commercially available printers, typically include wiping, capping and priming devices, as well as a spittoon portion, as described above in the background portion. One suitable preferred service station is commercially available in the DeskJet(& 850C and 855C color inkjet printers, produced by the present assignee, Hewlett-Packard Company, of Palo Alto, California.

The printer 20 also has a DC carriage drive motor 56, coupled (as described in detail below) to the pen carriage 50 to incrementally advance the carriage along the guide rod 48. The motor 56 operates in response to control signals received from the printer controller 45. To provide carriage positional feedback information to printer controller 45, an encoder strip 58 extends along the length of the print zone 25 and over the service station 54. A conventional optical encoder reader may also be mounted on the back surface of printhead carTiage 50 to read positional information BP Docket No. 10950827 7 provided by the encoder strip 58. The manner of providing positional feedback information via the encoder strip reader, may be accomplished in a variety of different ways known to those skilled in the art.

In the print zone 25, the media sheet 34 receives ink from an inkjet cartridge, such as a monochrome black ink cartridge 60 and/or a color ink cartridge 62. The cartridges 60 and 62 are also often called "pens" by those in the art. The illustrated color pen 62 is a tri-compartment, tricolor pen, although in some embodiments, a set of discrete monochrome pens may be used. The illustrated pens 60, 62 each include reservoirs for storing a supply of ink, and printheads 64, 66 respectively, for selectively ejecting the ink. The monochrome black pen 60 has a single reservoir containing black ink, whereas the color pen 62 has three reservoirs for carrying cyan, magenta and yellow inks. While the color pen 62 may contain a pigment based ink, for the purposes of illustration, pen 62 is described as containing three dye based ink colors. The black ink pen 60 is illustrated herein as containing a pigment based ink.

It is apparent that other types of inks may also be used in pens 60, 62, such as paraffin based inks, as well as hybrid or composite inks having both dye and pigment characteristics.

Each printhead 64, 66 has an orifice plate with a plurality of nozzles formed therethrough in a manner well known to those skilled in the art. The illustrated printheads 64, 66 are thermal inkjet printheads, although other types of printheads may be used, such as piezoelectric printheads. The printheads 64, 66 typically include a substrate layer having a plurality of resistors which are associated with the nozzles. Upon energizing a selected resistor, a bubbl.e of gas is formed to eject a droplet of ink from an associated nozzle and onto sheet 34 in the print zone 25. Ink may also be ejected into a spittoon portion of the sen,ice station 54 during servicing, or to clear plugged nozzles. The printhead resistors are selectively energized in response to firing command control signals delivered by a multi-conductor strip 68 from the controller 45 to the printhead carriage 50.

BP Docket No. 10950827 8 Micro-Tooth Carriai!e Drive System FIG. 2 shows a detailed view of a flictional microtooth carriage drive system 70, constructed in accordance with the present invention, for propelling the printhead carriage 50 over the printzone 25 and service station 54. The drive system 70 may include one or more idler rollers or pulleys, such as idlers 72 and 74, supported by the chassis 22. At least one of the idler pulleys 72, 74 preferably is spring biased to aid in belt tensioning. The drive system 70 also has a drive pulley 75 which is coupled to an output shaft of the motor 56. The drive pulley 75 may be constructed of a metal, such as steel, brass or aluminum, or of a plastic material, such as nylon, polycarbonate, or a glass-filled polycarbonate.

The drive pulley 75 has a drive surface 76 with a plurality of microteeth formed thereon. In the illustrated embodiment, the drive surface 76 has a substantially regular pattern of rnicroteeth arranged in a knurled-type of diamond pattern. Preferably, the n-dcrotooth pattern is formed by defining lands surrounded by depressions in the drive surface, such as by machining a smooth surface, or by molding the teeth while molding the pulley 75. Other patterns are also possible, for instance, patterns having a combination of diamond shaped teeth and slanted ridged teeth. A group of slanted ridged microteeth may be easily formed by on- iitting one group of para'lel grooves of in a conventional diamond knurling pattern. In this way, each of the ridges lie along a plane that intersects a drive axis 77 of pulley 75 at an acute angle. Other microtooth patterns may also be used, such as a straight tooth knurl (not shown) comprising a plurality of rectangular-shaped teeth defined by grooves parallel to the pulley drive axis 77 which intersect grooves encircling the pulley axis 77.

The drive system 70 also includes a belt 78, which may be secured in a conventional manner to the pen carriage 50. Preferably, the drive belt 78 is a flat toothless belt of a material that is initially substantially flat along the drive surface which interfaces with the drive pulley surface 76. During use, the drive surface of belt 78 preferably conforms to the projections of the plurality of microteeth during use. For instance, a belt of a fiber-reinforced elastomeric material is suitable, and in testing, a belt of a polyurethane material reinforced with KevIarO fibers has 9 BP Docket No, 10950827 performed well. Other reinforcing fibers may also be used, such as fiberglass, Nomex@ brand fibers, or polyester fibers. Using belt 78 and the same carriage accelerations, belt tensions must be increased above that experienced when using the earlier toothed belts, described in the Background portion above. This increased belt tension is due to the reduced tension ratio across the drive pulley 75 at which slippage begins, as compared to that encountered in a conventional toothed belt drive system.

During studies of the drive system 70, an interesting attribute was discovered. During the life of drive system 70, the repeated impressions that the microtooth surface 76 leaves on the drive surface of belt 78 induces a memory in the belt material. This induced memory results from the diamond knurled points locally deforming the belt surface, which imparts a creep set to the belt 78. Advantageously, these local belt deformations reverse map directly to the knurl pitch, which creates a mechanical linkage between belt 78 and drive pulley 75 to allow the use of a higher applied motor torque. Moreover, due to this mechanical linkage between belt 78 and pulley 75, any inadvertent lubricant contamination, e.g., from oils and the like accidentally dripping onto the belt, have been found to have a small adverse belt slipping effect. Thus, these lubricating contaminants may slightly affect belt slip performance as verified through prototype testing.

Regarding the pitch of the knurling on surface 76, a large knurling pitch (the number of points in a unit circumference, typically in inches or millimeters) may result in lower local contact forces on the belt 78, may advantageously reduce the tension ratio property across the pulley 75. On the other hand, a small knurling pitch may induce inconsistent driving forces into the carriage 50, resulting in velocity ripple, or an increase in the acoustic volume behavior of the system, which were both unfortunate situations experienced in the earlier toothed belt drive systems. In a preferred embodiment, a diamond pattern with knurled pitches on the order of 0.5-1.2 pitch (here, in points per rnillimeter, which is equivalent to 12- 30 pitch in points per inch), or even more preferably 0.7-1.0 pitch in millimeters (18-26 pitch in 3 0 inches), or even more preferably 0.83-0.91 pitch in rnillimeters (about 22 pitch in inches) is believed to provide an adequate contact area with the belt 78. Moreover, BY Docket No. 10950827 this preferred pitch also yields an adequate stress for local belt deformation, while also yielding excellent low velocity ripple characteristics. Furthermore, the preferred pitch yielded good acoustic performance. For instance, during testing, the knurled drive system 70 was found to reduce sound levels by as much as 12 decibels (dB) when compared to that experienced using the earlier toothed belt drive system. It was also found that the level of acoustic reduction was dependent upon the printing mechanism architecture and its resonant frequency.

FIG. 3 shows an alternate embodiment of a flictional microtooth carriage drive system 80 constructed in accordance with the present invention. The system 80 may include one or more idler pulleys, such as pulleys 72, 74 and a drive pulley 85 coupled to an output shaft of the drive motor 56. Here, the drive pulley 85 has a drive surface 86 coated with a random arrangement of microteeth, here, of an abrasive granular material or medium. Preferably this abrasive material is a coating similar to the silica grit material used in sandpaper, although is apparent that other grit materials may also be used, such as diamond, silicon carbide, gamet, or tungsten carbide. Preferably, the abrasive material may be sized between 80 and 200 grit, or more preferably around 100 grit. The drive system 80 also includes an endless flat belt 88, which may be of the same material as described above for belt 78.

This random arrangement of abrasive or grit microteeth 86 significantly decreases printer noise, as well as providing a smooth ripple-free drive motion. The random nature of abrasive microteeth 86 advantageously decreases the amplitude of disturbances induced during belt engagement because the random pattern is less likely to excite resonances within the other components of the printer 20. Moreover, the randomness of the grit teeth 86 disperses the engagement energy from that previously concentrated in very narrow frequency bands, such as when using the earlier toothed belt drives.

As a further advantage, the drive system 80 is able to use a flat belt 88 with a smaller average thickness than required for the earlier tooth belts. This thinner dimension of belt 88 allows use of a smaller diameter for pulley 85 than that required for the earlier toothed belt configurations. Using a smaller diameter pulley 85 advantageously lets motor 56 have a lower rating than required for motors in the 11 BP Docket No. 10950827 earlier toothed belt systems. Use of a smaller motor 56 not only decreases the initial manufacturing costs, but it also decreases the operating costs experienced by a consumer.

When comparing the excellent acoustic properties and consistent driving force of system 80 with the advantages of system 70 described above, it is believed that the knurled drive system 70 may have some advantages over the grit drive system 80. For example, additional labor costs are required to apply the random grit surface 86 to pulley 85, whereas the knurled pattern 76 may be easily molded into a plastic pulley or machined into a metal pulley. Thus, the knurled design of pulley 75 is believed to be more easily manufactured than the grit concept of pulley 85.

In implementing the concepts of the microtooth drive systems 70, 80 illustrated herein, it is apparent that a method of quieting inkjet printer operation may be realized. In this method, the drive belt 78, 88 is coupled to the printhead carriage 50. In a surfacing step, a microtoothed drive surface is applied to the drive pulley 75, 85. The belt 78, 88 is then driven by motor 56 and pulley 75, 85 to engage and reciprocally drive the carriage 50 back and forth (as shown by the double-headed arrows) to propel the printheads 64, 66 across the printzo-l-e 25 and the service station 54. In a driving step, the drive pulley 75, 85 is rotated by motor 56, in response to carriage travel signals received from the printer controller 45. In the illustrated embodiments, the surfacing step may be accomplished by imparting a repeating pattern to the pulley drive surface, such as the diamond knurled pattern 76 of FIG. 2. In an alternate embodiment, the microtooth pattern may be randomly ar:anged on the pulley drive surface, such as illustrated by the silica grit surface 86 formed on pulley 85.

Conclusion

Thus, a variety of advantages are realized by implementing either the knurled drive system 70 or the grit drive system 80, as illustrated. For example, the belt drive torque margin is believed to be improved over the life of the printer product 20.

Additionally, by replacing the earlier toothed belt and pulley systems with a smooth belt 78 and a knurled pulley 75, the perception of sound and acoustic levels being 12 BP Docket No. 10950827 emitted from the carriage drive system is significantly reduced. Moreover, less carriage velocity ripple is experienced using the knurled drive system 70 or the grit drive system 80 than in the earlier toothed belt systems.

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Claims (10)

1. We claim:

   HP Docket No. 10950827 1. A ffiction drive system (70; 80) for driving a carriage (50) that moves an inkjet printhead (60, 62) across a printzone (25) in an inkjet printing mechanism (20), the fliction drive system (7080) comprising: a belt (78; 88) secured to the carriage (50), with the belt (78; 88) having a substantially flat drive surface; a carriage drive motor (56) having an output shaft; and a drive pulley (75; 85) coupled to the motor output shaft, with the drive pulley (75; 85) having a drive surface (76; 86) comprising a plurality of microteeth that engage the flat drive surface of the belt (78; 88).
2. 2. A friction drive system according to claim 1, wherein the plurality of microteeth are arranged randon-dy on the drive surface (86) of the drive pulley (85).
3. 3. A friction drive system according to claim 2, wherein the plurality of microteeth are of a granular material (86) selected from the group comprising silica grit, diamond, silicon carbide, garnet, or tungsten carbide.
4. 4. A fliction drive system according to claim 1, wherein the plurality of microteeth are arranged in a pattern on the drive surface (76) of the drive pulley (75).
5. 5. A friction drive system according to claim 4, wherein the plurality of microteeth are arranged in a knurled diamond pattern on the drive surface (76) of the drive pulley (75).
6. 6. A friction drive system according to any of the preceding claims, wherein the plurality of microteeth are formed by defining lands surrounded by depressions in the drive surface (76, 86) of the drive pulley(75, 85).

   14 BP Docket No. 10950827
7. 7. A friction drive system according to any of the preceding claims, wherein the belt (78; 88) is of a material which is initially substantially flat, and which conforms to the plurality of microteeth during use.
8. 8. A friction drive system according to any of the preceding claims, wherein the belt (78, 88) is of a polyurethane material reinforced with fibers selected from the group comprising Keviar@ fibers, fiberglass, Nomex@ brand fibers, or polyester fibers.
9. 9. An inkjet printing mechanism, comprising: a media handling system (26) that transports print media (34) across a printzone (25); a carriage (50) that moves an inkjet printhead (60, 62) across the printzone (25); and a friction drive system (70; 80) for driving the carriage (50) that moves the inkjet printhead (60, 62) across the printzone (25) according to any of the preceding claims.
10. 10. A method of quieting inkjet printhead carriage motion in an inkjet printing mechanism (20), comprising the steps of. coupling a belt (78; 88) having a substantially flat drive surface to a carriage (50) that moves an inkjet printhead (60, 62) across a printzone (25) in the inkjet printing mechanism (20); installing a drive pulley (75; 85) on an output shaft of a carriage drive motor (56), with the drive pulley (75; 85) having a drive surface (76; 86) comprising a plurality of microteeth; driving the carriage (50) by engaging the flat drive surface of the belt (78, 88) with the plurality of nroteeth and turning the drive pulley (75; 85) by operating the drive motor (56); and confom-dng the belt drive surface (78, 88) to the plurality of microteeth (76, 86) during the driving step.