Balanced line printer

Abstract: A dot matrix printer having a plurality of hammers on a hammerbank (22) with a counterbalance (130) for the hammerbank (22) in adjacent parallel relationship to the hammerbank (22). The hammerbank (22) and counterbalance (130) are driven by a first crank arm (172) connected to the hammerbank (22) and a second crank arm (200) connected to the counterbalance (130) with looped circular portions (180) having bearing surfaces for moving the crank arms (172,200) in opposite relationship to each other. A single shaft (230) with two eccentrics (232,234), each respectively in the bearing surfaces turns the two crank arms. The crank arms are in close parallel relationship to each other and close proximity to the hammerbank (22) and counterbalance (130). The single shaft is connected to a motor for driving the hammerbank (22) and counterbalance (130), and is formed with a stator (356) having coils (358) with a magnetic ring (360) formed as a rotor portion Surrounding the stator (356), and a flywheel (364) surrounding and connected to the magnetic rotor ring (360).

Description: The invention relates to printers, in particular, a printer comprising a hammerbank having a plurality of hammers; means for driving said hammerbank and releasing said hammers for printing on a print medium; and a counterbalance mechanically linked to said hammerbank. The prior art with regard to dot matrix printers encompasses multiple printers of various configurations. Such configurations use wheels and hammers of various types to impress a dot on a print media. One particular type of printer which is known in the art is a line printer. Line printers generally have a series of hammers. The series of hammers are on a hammerbank which moves reciprocally across a print media. The print media is advanced across the hammers and is printed thereon by an inked ribbon. Such hammers are supported on a hammerbank. The hammers are often held in place by a permanent magnet until released or fired. The release or firing takes place by the permanent magnetism holding the print hammers being overcome. The permanent magnetism is overcome by means of coils which receive a drive current to overcome the magnetism of the permanent magnets. The foregoing action releases the hammers at a given time and causes them to move toward a print ribbon moving across their face. When the print ribbon is impressed by the hammers, it is pressed on an underlying print media which has the dots printed thereon. The hammers are released and controlled by electronic drivers which cause the coils to function. The drivers are provided with logic consistent with the particular configuration of the print to be impressed on the print media. The logic can be in the form of local logic control in conjunction with a host and a central and data processing, unit integral to the printer. In prior art printers a drive motor is placed at an offset location from the hammers of a hammerbank and drives the hammerbank reciprocally by a crank or a connector. The crank or connector must move the hammerbank in a reciprocal manner rapidly to provide high speed printing. To accomplish this, a sufficiently strong and reliable connection is provided between the drive means, such as the motor, and the hammerbank. During reciprocal movement of the hammerbank, it moves in such a manner as to reciprocate and terminate this movement at various positions with regard to the desired effect on the print media. During its course of movement, when considering the mass of the hammerbank and the speed, it is known to counterbalance the hammerbank. The foregoing counterbalances have been placed in a manner so that they can offset the movement of the hammerbank at different portions of its stroke or movement. Such offset relationships have not always been desirable because of the fact that they were offset and not in a compact and tightly oriented relationship to the hammerbank. In effect, the counterbalance although helping to balance the hammerbank was offset to a degree wherein it created forces which caused the printer to vibrate. Various methods have been used to dampen such vibrational forces. However, in most cases, the vibrational forces could only be dampened and not significantly offset in a consistent and balanced manner. Another problem of the prior art is that the motor's flywheel is not consistent and balanced with regard to a configuration to provide for smooth and compact mechanical movement. Prior art flywheels have not provided for a smooth balanced operation between the connecting rod and the hammerbank and counterbalance. Another drawback of the prior art was that the capability of driving the hammerbank in a reciprocal manner was not accomplished to the extent where the various forces of movement could be readily dampened. Examples of prior art printers are to be found in the following patent documents, GB 2132561, EP 0357251 and US 4543884. We have appreciated that prior art printers such as described above are deficient in that they produce considerable vibration which cannot be adequately dampened. In a first aspect, the invention provides an improved printer which has reduced vibration. More specifically, the printer of the invention is characterised in that the counterbalance is adjacent and parallel to said hammerbank; and in that the means for driving said hammerbank comprises a shaft dynamically balanced having regard to the hammerbank and counterbalance, first and second crank arms, connected to the counterbalance and means for rotating said first and second crank arms 180° apart in substantially parallel relationship to each other. In a preferred embodiment of the invention the motor is connected directly to the connecting rods of the hammerbank and the counterbalance. This connection is through an integrated motor shaft connected to the flywheel. This relationship thereby transmits the inertia of the flywheel directly to the shaft and the connectors. The connectors are each connected to the respective portions of the integrated hammerbank and counterbalance for reciprocal movement thereof. This is accomplished by eccentrically driven connector rods that move 180° in opposite relationship with the eccentrics being formed as part of the motor shaft, and 180° apart from each other. In the preferred embodiment of the invention the system is dynamically balanced so that the flywheel, eccentrics, and connector rods are all dynamically balanced during their movement. This serves to minimize vibrations and unwanted forces throughout the cyclical movement of the printer. Another aspect of the invention provides a printer comprising: a hammerbank having a plurality of hammers; means for driving said hammerbank and releasing said hammers for printing on a print media; and, a counterbalance mechanically linked to said hammerbank in adjacent parallel relationship with said hammerbank. The preferred embodiment of the invention has an integral hammerbank with an overlying and surrounding counterbalance. The relationship of the hammerbank and the counterbalance with its overlying relationship allows the structure to be compatibly and integrally balanced between the two respective members namely the hammerbank and the counterbalance. This overlying relationship causes a dynamically coordinated and balanced relationship to be established between them when connected to the connector rods. The embodiment of the invention further establishes close proximity of the hammerbank and counterbalance to the connector rods as an integral unit, for smoother operation. As can be appreciated the more distal an object is driven, the greater the forces are required and thereby greater dampening and other efforts must be undertaken to prevent unwanted forces to be applied to the dynamic system. Embodiments of the invention alleviate such problems. The embodiment also provides for the integrated hammerbank and counterbalance to be connected with connector rods or drive rods which are in close proximity to each other. The rods drive a dynamically moving system comprised of the hammerbank and counterbalance. This is done in as close a proximity as practical with respect to the drive shaft emanating from the motor. This particular relationship enhances the dynamics so that less vibration and various forces are encountered. The result is to create a dynamically balanced system driven by the motor and connecting rods as an entire integrally formed and balanced system. Another aspect of the invention provides a drive wherein the motor is an "inside out" motor wherein the stator is on the inside. With the flywheel being on the outside, the inertia is enhanced to maintain the angular velocity of the motor and flywheel once it is up to speed and of course the mechanical elements connected thereto. In a preferred embodiment the integral motor is enhanced by a ferrite permanent magnet to enhance efficiency, and the flywheel is a sintered metal providing a high density without the necessity to machine the flywheel. Preferably, the permanent magnet is a sintered barium ferrite material with substantial qualities to enable the motor to function over a highly efficient range. For these reasons, the invention is a substantial step over the prior art and enhances line printer functions as well as smoothness of operation, speed of operation, and provides longevity and finer printing for a line printer than had previously been capable in the art. An integrated motor and flywheel are provided in an embodiment of the invention. The flywheel is on the outside of a circular magnetic ring which overlies a stator for causing the flywheel to move on an integrated basis with the motor shaft connected thereto through the stator. The motor shaft is interconnected to a drive shaft. The drive shaft is provided with two eccentrics thereon. The two eccentrics on the drive shaft are oriented so that they are 180° out of phase from each other. These eccentrics are connected to bearings within two connector rods. The two connector rods are each respectively connected to the hammerbank and the counterbalance for reciprocal movement thereof 180° apart. This effectively allows for the drive shaft to turn the connector rods 180° apart from each other and drive the respective hammerbank and counterbalance. The embodiment of the invention is further enhanced by balancing the counterbalance and the hammerbank on a pair of bearing surfaces and flexures. The bearing surfaces and flexures allow for reciprocal movement on flexible spring connectors while at the same time providing for a smooth bearing operation during lateral movement as the hammerbank and its accompanying counterbalance reciprocate. The entire system is controlled by a host and a central processing unit through detecting movements and causing the system to respond thereto so that the integral unit moves in a smooth and low vibration printing movement. An embodiment of the invention will now be described in detail by way of example only with reference to the accompanying drawings in which: Figure 1 shows a perspective view of the integrally driven and balanced line printer of this invention with its shuttle frame to be mounted on a mechanical base. Figure 2 shows a perspective view of the integrally driven and balanced line printer looking at the opposite side from that shown in Figure 1, and wherein a fragmented portion of the hammerbank cover and ribbon cover have been removed to expose the hammers of the hammerbank. Figure 3 shows an exploded view of the components of the integrally driven and balanced line printer shown in the same direction as that of Figure 1. Figure 4 shows a side elevation view of the connecting rods for respectively driving the hammerbank and counterbalance. Figure 5 shows a side elevation view of the respective hammerbank and counterbalance connecting rods driven 90° from the position shown in Figure 4. Figure 6 shows a view of the drive shaft with the eccentrics and bearings thereof as sectioned along line 6-6 of Figure 4. Figure 7 shows a side sectional view of the linear bearings, shafts and connectors related to the hammerbank as seen in the direction of line 7-7 of Figure 4. Figure 8 comprises a top plan view looking downwardly at the printer of this invention. Figure 9 shows an exploded view of the integrated motor and flywheel of this invention. Figure 10 shows a cross-sectional view of the magnet portion of this invention along lines 10-10 of Figure 9. Looking more particularly at Figures 1 and 2, it can be seen that a base 10 or shuttle frame has been shown. The base 10 or shuttle frame is attached to a mechanical base by means of various attachments. The mechanical base can form a large portion of a cabinet such as a stand alone printer cabinet or a printer mechanical base that can be portable or placed on a surface such as a table. The shuttle frame or base 10 which attaches to the mechanical base, which is not shown in this case is formed from a die cast alloy. It can be in the form of an aluminum zinc alloy or any other suitable material which will form a firmly fixed and rigid base upon which the printer movement will not be torqued, moved, or unduly provided with forces which will disorient it. Underlying the shuttle frame or base 10, are a series of cross members in a pattern to provide reinforcement. The entire base 10 can be concave with struts and structures crisscrossing and rigidifying the entire shuttle frame or base 10. The shuttle frame or base 10 is mounted to a mechanical base by means of mounting or support member shafts 12 and 14. The mounting or support member shafts are held such that they can be rotated on the mechanical base. This allows the entire printer structure formed on the base or shuttle frame 10 to be rotated such that the hammers can be adjusted with respect to a platen or other surface against which they impinge. The two mounting or support member shafts 12 and 14 comprise two portions of a three part mounting. The third portion of the mounting is a bracket 16 which extends from the shuttle frame or base 10. The bracket 16 is integrally formed with the shuttle frame or base 10 and forms a strong component thereto for maintaining it in rigid relationship with a mounting screw 18 having an alien head 20. The mounting screw 18 threads downwardly against the mechanical base which is not shown to which the entire printer is mounted. In effect, the base 10 is mounted by the three mountings including the support member shafts 12 and 14 as well as the bracket 16. Thus, adjustment around the rotational axis of mounting or support member shafts 12 and 14 allow for the base to be moved inwardly and outwardly as to the hammerbank's position this adjustment can be made by raising and lowering and adjusting the mounting screw 18. Figure 1 shows a hammerbank 22 of the embodiment of this invention from the back thereof. Figure 2 shows the hammerbank 22 with the hammers exposed. In particular, hammers 24 are formed and supported in this case in a series of three on frets 26 which are screwed to the hammerbank 22. Such frets 26 can have hammers 24 in multiple numbers significantly higher than the three on fret 26 shown here. Each hammer 24 as is known in the art comprises a hammer supported and formed on the fret 26 which extends upwardly and provides a pin like member 64. The pin like member 64 impacts against a ribbon which is driven across the face of the hammers 24 to be printed against an underlying print media such as paper. The ribbon which is imparted and impressed by the hammers 24 passes between a ribbon mask 30 and a hammerbank cover 32. The hammerbank cover 32 and the ribbon mask 30 are held together and joined at the bottom thereof namely at bottom interface 34. In order to secure the combination ribbon mask 30 and the hammerbank cover 32, four magnets, one of which is shown as magnet 38 pull the respective hammerbank cover 32 and ribbon mask 30 against the magnet 38 for securement. This allows for easy removal of the ribbon mask 30 and hammerbank cover 32 for cleaning and access to the hammers 24. The hammerbank 22 is formed with a permanent magnet therein for holding the hammers 24 until released by coils which are not seen that are activated in part by drivers on an integrated hammerbank circuit board 42. The circuit board 42 has a plurality of electronic components thereon which electrically drive the hammers 24. The circuit board 42 is connected to a flex cable or connection 44 that is in turn connected to a terminator board 46. The terminator board 46 interconnects to a central and data processing unit or other means for driving the printer which in turn is connected to a host as is known in the art. A power connection through a connector is provided through terminals seen in a terminal block 50, while a logic connection is provided through a logic connector 52. The circuit board 42 of the hammerbank 22 can be formed in any particular manner provided with local logic, drivers, and various other electronic conditioning means for amply allowing the hammers 24 to fire when necessary in a well timed and readily functioning manner. As previously stated, the hammerbank 22 moves reciprocally across the print media in order to release the hammers and effect printing by the ribbon against the underlying print media. Looking again more particularly at Figure 7, it can be seen that the hammerbank 22 incorporates the frets 26 and hammers 24. Each hammer 24 has a narrow neck portion 60 that terminates in an enlarged portion 62 with a tip 64 at the end thereof. The hammerbank 22 is further provided with a printed circuit board 42 which terminates at the flex cable or connection 44 to provide the logic to the components on the printed circuit board 42. These components as previously mentioned allow the hammers 24 to be fired with respect to their being fired through the release of the permanent magnetism drawing them inwardly toward the hammerbank 22. The hammerbank 22 is secured for driving purposes to two lugs. These two respective lugs are referred to as the driving lug 72 and the trailing lug 74. The respective driving lug 72 and trailing lug 74 are each respectively connected to a concave portion 76 of the hammerbank 22 by means of a high strength glue. The driving lug 72 and trailing lug 74 of course can be attached in any other suitable manner. Attached to the driving lug 72 is a block driver 80. The block driver 80 is formed and secured to the driving lug 72 by means of the driving lug 72 having a flat portion 84 which is formed as a portion of the driving lug. The driving lug 72 can be seen more effectively in Figures 4 and 5 with the block driver 80 secured thereon. Securement of the block driver 80 to the lug flat 84 can be in any suitable manner such as by a bolt attachment or other suitable means. The respective driving lug 72 and trailing lug 74 each have a shaft 90 and 92 passing therethrough. These shafts 90 and 92 each allow the hammerbank 22 to move reciprocally backwardly and forwardly on the shafts. Each shaft 90 and 92 supports the driving lug 72 and trailing lug 74 respectively with a linear bearing 94 which can be seen such as the linear bearing shown in Figure 7. The linear bearing 94 is supported within the driving lug 72 in a manner whereby it allows reciprocal movement of the shaft 90. In like manner, the shaft 92 and trailing lug 74 reciprocate with respect to each other on a similar linear bearing 94. The shafts 90 and 92 are secured to the shuttle frame or base 10 by means of four respective clamps 104, 106, 108 and 110. Each clamp as can be seen in greater detail in Figure 3 incorporates a rounded concave interior surface 114 to receive the outer circumference of a portion of the respective shafts 90 and 92. They serve to clamp the shafts 90 and 92 against flats which again can be seen in Figure 4 namely flats 116. These flats 116 allow the shafts 90 and 92 to be held tightly against the shuttle frame or base 10 and to be secured by the respective screws and a washer such as screws 118 securing each respective clamp 104, 106, 108 and 110 and its attendant shaft. The hammerbank 22 and the counterbalance 130 as will now be described are driven reciprocally. This will now be described in greater detail. Looking more particularly at the counterbalance 130 to the hammerbank 22, it can be seen that a general rectangular configuration in the form of counterbalance 130 has been shown overlying and surrounding in part the hammerbank 22. This counterbalance 130 moves reciprocally and in opposite direction to the hammerbank 22. The counterbalance 130 is aligned for parallel movement with the hammerbank 22 in close proximate relationship. The counterbalance 130 is a die cast aluminum alloy which forms a frame with an upper member 132 and a lower member 134 which overlies the hammerbank 22. The ends of the counterbalance 130 are provided with upright portions 136 and 138 which roughly define a rectangular opening 140 in which the hammerbank 22 moves backwardly and forwardly. The counterbalance 130 is supported on the shuttle frame or base 10 by means of flexures, flexural support or spring leaves 144 and 146. Each support flexure or spring leaf 144 and 146 is secured respectively to the shuttle frame or base 10 by means of clamps 150 and 152. The clamps 150 and 152 have screws with allen heads threaded into openings within the upper portion of the counterbalance 130. Clamps 154 and 156 which can be seen in the reverse view from Figures 1 and 3 in Figure 2 support and counterbalance 130 at the lower position where it is attached to the frame 10. The support or spring leaves 144 and 146 allow for reciprocal movement backwardly and forwardly of the counterbalance 130. In this manner they provide for not only strong vertical support, but movement in the direction of the length of the counterbalance 130. The flex supported movement of the counterbalance 130 can be seen in Figures 4 and 5 wherein the counterbalance 130 support leaves are shown flexed in Figure 4 in their driving motion. Returning now to the hammerbank 22 and the way it is driven in reciprocal movement with the counterbalance 130, it can be seen that a first shaft, connector, or drive rod, namely shaft 170 is shown on a connecting rod or crank arm 172. The crank arm or connecting rod 172 has a ball bearing 174 pressed fit with lock tight into an opening 176 provided by a circular loop or opening 180 forming a portion of the crank arm or connecting rod 172. The connecting rod 172 terminates at a rod spring flexure 190 which can be seen screwed to the end of the connecting rod or crank arm 172 into the top of the block driver 80. In Figure 4, it can be seen that the movement is such wherein it is in a relatively aligned position with the axis of the connecting rod 172, while in Figure 5 it is shown flexed during its drive movement. The crank arm or connecting rod 172 serves to reciprocate the hammerbank 22 in response to the movement of the motor drive shaft. Looking at the counterbalance 130 it can be seen that a second crank arm or connecting rod 200 is shown having an elongated connection portion 202 with a looped opening 204. The looped opening 204 contains a ball bearing 206. The connecting rod 200 terminates in a rod flexure spring member 212 which is secured by screws to the counterbalance 130 at a clamp 220 held again by screws. In order to drive the hammerbank 22 with its associated counterbalance 130, the crank arms or connecting rods respectively 172 and 200 are driven in a relationship wherein they are 180° offset from each other as to their reciprocal movement. This is accomplished by a crank or shaft 230 having two integral offset eccentric circular portions. Eccentric 232 is associated with the connector rod 200 and eccentric 234 is associated with crank arm or connector rod 172. These two respective eccentrics 232 and 234 move within the respective ball bearings 206 and 174. In order to support the crank or shaft 230, a front support plate 240 is utilized having a bearing 242 inserted within an opening 244 for rotational movement. The crank or shaft 230 rotates around an axis established by the center of the crank or shaft 230 thereby causing the eccentric circular portions 232 and 234 to drive respectively crank arms or connecting rod 172 and 200 in a reciprocating manner 180° offset from each other. The foregoing movement can be seen in Figures 4 and 5 wherein the crank arms or connecting rods 172 and 200 are displaced from each at the farthest point of drive to the right, in Figure 4. In Figure 5 movement is such wherein the crank or shaft 230 has moved 900 so that the eccentric circular portions 232 and 234 are respectively directly overlying each other. As can be seen in Figure 5, the rod spring flexures 190 and 212 have been bent to provide for this eccentric movement of the crank arms or connecting rods 172 and 200 and their respective loop portions 180 and 204 in displaced relationship from each other. It is now seen that the hammerbank 22 moves reciprocally backwardly and forwardly along the shafts 90 and 92 as supported by the driving lug 72 and the trailing lug 74 within their respective linear bearings. As reciprocal movement is encountered, it can be seen that the hammerbank 22 can rotate around the axis of the shafts 90 and 92 to some extent. In order to prevent this rotation, an anti-rotation plate 300 is utilized. The anti-rotation plate 300 is secured to the hammerbank 22 by two screws on the inset portion 302. The anti-rotation plate 300 provides a surface which can be held tightly in secured relationship against a button disk, or seating surface 304. The button disk, or seating surface 304 is a disk like member having a rounded or convex portion or surface 306 and a flat portion or surface 308. The rounded portion or surface 306 is seated within an anti-rotation boss member 310. The boss member 310 has a convex rounded cup like seat to receive the rounded portion or disk surface 306 therein. This allows for the disk like member 304 to adjust its flat surface in relationship to the antirotation plate 300 so that the two flats are against each other. This provides for various disorientation of positioning while at the same time allowing the plate to move reciprocally across the flat portion or surface 308. The engaged relationship maintains the third portion of the planar orientation of the hammerbank 22. The hammerbank 22 is biased against the antirotational plate 300 by a coil spring 320. The spring 320 is secured to a pin 322 on the shuttle frame or base 10 and through an opening 324 within the anti-rotational plate 300. In order to rotate the crank or shaft 230, a dc stepper motor is utilized that is emplaced within a round or circular housing 350. The round or circular housing 350 receives the stepper motor in part with a portion exposed. The stepper motor is driven by three wire leads 352 connected to a circuit board 354 with terminals for the motor. The circuit board 354 has a series of terminals or connectors in order to distribute power to a stator 356. The stator 356 has a number of stator coils 358 that are connected to the circuit board terminals 354. In this manner stepped pulses can be provided for causing the motor to rotate in a stepped relationship. The motor is an inside out type of motor with a ferrite magnetic ring 360 having north south polarities oriented in the manner shown in Figure 10. The polarization of the ferrite material is through quadrants giving a north south orientation so that the stepper motor can be driven with the magnetic ring 360 pulsed to move depending on the output of the stator coils 358 connected to the wire leads 352. This allows for the pulsing of the motor on a continuum when started with a great degree of accuracy and precision. The motor includes a flywheel 364. The flywheel 364 is connected to the motor by means of emplacing it in any suitable manner over the magnetic ring 360. The flywheel 364 has a flywheel shaft 366 with an opening 368. The opening 368 receives the crank or shaft 230 passing therethrough and is seated within an opening 370 of the shuttle frame or base 10. The opening 370 has a retainer 372 and a bearing (not seen) which supports the flywheel shaft 366 in order to turn the crank or shaft 230. The flywheel 364 has a plurality of teeth, notches, or lands and grooves respectively 380, and 382 around the surface thereof. The lands 380 and grooves 382 are equally spaced around the outer circumference thereof except where an enlarged space or groove 386 can be seen in Figure 1. The enlarged space or groove 386 allows for a detection of non-continuity of the lands and grooves 380 and 382. This permits telemetry of the orientation and speed of the flywheel 364 and the shaft with the attendantly oriented hammerbank 22 and counterbalance 130. The lands and grooves 380 and 382 allow for detection of movement and orientation by a magnetic detector that is shown in dotted outline form in Figure 8. Namely, a detector 390 having a permanent magnet 392 connected to leads 394 detects the rotational movement of the flywheel 364. Every time a land passes, the magnetic orientation between a permanent magnet 392 and a coil 391 causes a signal to be generated on leads 394. These signals or pulses are then directed toward the logic of the system in order to determine where the flywheel 364, and attendant portions of the crank or shaft 230 attached hammerbank to 22 are oriented. Although, a magnetic sensor 390 has been shown with a coil 391 and permanent magnet 392, it should be appreciated that other types of sensors can be utilized. Such sensors can incorporate Hall effect sensors or optical pickups with regard to movement of the flywheel 364. Also, it should be appreciated that the orientation of the flywheel 364 at the outside is particularly advantageous in this respect, in that it allows for the stator 356 to be emplaced therein with the magnetic ring surrounding it between it and the flywheel. The initial startup of the printer with the shaft 230 turned by the motor causes it to rotate to approximately 300 rpm after which the pickup pulse becomes more stable by the sensor 390. The pickup pulse orients the flywheel and drive with regard to the enlarged space, gap or groove 386. Detection by the logic of the circuit determines where the orientation of the printer is as to the crank or shaft 230 and of course attendant relationships of the hammers 24 on the hammerbank 22. The flywheel 364 and the remaining portion of the motor are dynamically balanced. This is done by compensating for the lesser material in the gap or groove 386 being offset by removing material from the flywheel at a point opposite from where the gap 386 is. The motor as shown in Figures 9 and 10 operates on an open loop basis until the proper timing is sensed. It then operates on a completely closed loop basis so that it moves in correspondence to the printing duty requirements in order to move the hammerbank 22 to release the respective hammers 24 at the appropriate point so that impact upon the part of the print tips 64 is at the right location with regard to the underlying print media. The integral motor shaft and flywheel create a situation wherein dynamic forces are reduced significantly. Of particular consequence is the fact that the center of gravity of the hammerbank 22 and the counterbalance 130 is placed at the position of the axis of the crank or shaft 230 such wherein the center of gravity is at approximately point 400. This causes dynamic forces to diminished from the standpoint of the counterbalance and hammerbank. orientation of the unit. Another point to note is that the assembly is dynamically balanced so that the weight of the flywheel 364 is placed to optimize inertia while at the same time allowing smooth overlying operation of the hammerbank 22 and the counterbalance 130. The particular relationship of the integral hammerbank 22 with the overlying counterbalance and the movement of the center of gravity at point 400 as closely as possible to the shaft 230 axis improves the overall performance. Furthermore, with the flywheel 364 integral to the inside out motor, a substantial amount of inertia is maintained to enhance the angular velocity and smoothness. The flywheel 364 is made of a sintered material of high density without the requirement of machining. The magnetic material of the magnetic ring 360 is of barium ferrite, to provide high density and strong magnetic properties to the magnetic ring. It should be specifically noted that the connecting rods 172 and 200 are in as close proximity as practical with regard to the spacing and adjacent relationship to the combined hammerbank 22 and counterbalance 130. This close proximate spacing and orientation of the center of gravity 400 allows for a smooth operation and avoids the placement of the connector rods 172 and 200 outside of the balanced reciprocal orientation in which they are connected to the respective hammerbank 22 and counterbalance 130. From the foregoing, it can be seen that the invention hereof is a substantial step in the art to provide significant improvement over those printers known in the art and particularly with regard to the line printer art. Accordingly, the invention should be accorded the scope of the following claims as set forth hereinafter.

Claims: A printer comprising: a hammerbank (22) having a plurality of hammers (24); means (350) for driving said hammerbank and releasing said hammers for printing on a print medium; and, a counterbalance (130) mechanically linked to said hammerbank; wherein the counterbalance (130) is adjacent and parallel to said hammerbank; and the means for driving said hammerbank comprises a shaft (230) dynamically balanced having regard to the hammerbank and counterbalance, first and second crank arms (172,200), the first crank arm being connected to the counterbalance, and means (232,234) for rotating said first and second crank arms 180° apart in substantially parallel relationship to each other; the printer being characterised in that said counterbalance (130) has at least a portion (134) underlying said hammerbank (22). A printer according to claim 1, further comprising: said counterbalance (130) having a portion overlying and underlying said hammerbank and two end portions (136) to form a structure roughly framing said hammerbank (22). A printer according to any preceding claim, further comprising: at least one support shaft (90) for supporting said hammerbank; and, means (172) for linearly moving said hammerbank as supported on said support shaft. A printer according to any preceding claim further comprising: two support shafts (90,92) for supporting said hammerbank; linear bearing means (94) for connecting said hammerbank to said support shafts. A printer according to any preceding claim, further comprising: a motor (350) for turning said crank arms (172,200); a shaft (230) extending from said motor; and, eccentric means (232,234) formed on said shaft and respectively connected to said first (17) and second (200) crank arms for rotating said crank arms. A printer according to claim 5, wherein; said crank arms (172,200) are in parallel relationship to each other and in adjacent proximity to said hammerbank (22) and said counterbalance (130). A printer according to any preceding claim further comprising: flexural members (190,212) connected between said first crank arm (172) to said hammerbank and said second crank arm (200) to said counterbalance. A printer according to any preceding claim, further comprising: a flywheel (264) on the outside of said motor and a stator (356) interiorially thereof with a rotor (360) disposed between said flywheel portion and said stator for rotating said shaft for movement of said crank arms. A printer according to any preceding claim further comprising: a pair of shafts with lugs (72,74) overlying said shafts connected to said hammerbank; and, a first surface (76) on said hammerbank for movement against a second surface (74) to provide a third point of contact to support said hammerbank. A printer according to any preceding claim further comprising: spring flexures (144,146) connected to said counterbalance for allowing said counterbalance to reciprocally move with respect to said hammerbank. A printer according to any preceding claim further comprising: circular portions (176) of said crank arms (172,200) having bearings therein for receiving said eccentrics. A printer according to claim 11 wherein: said eccentrics (232,234) are formed in opposing relationship on said shaft (230). A printer according to claim 8 further comprising: a plurality of lands (380) and grooves (382) on said flywheel (364); and, means (390) for detecting the lands and grooves as said flywheel moves. A printer according to claim 13 wherein: said detection means (390) is a magnetic detection means for differentiating differences in relative magnetic relationship between said lands (380) and grooves (382). A printer according to claim 13 or 14 wherein: said detection means (390) provides pulses corresponding to movement of said lands and grooves. A printer according to claim 13, 14 or 15 wherein: said lands (380) and grooves (382) are substantially equally spaced apart except for one larger grooves (386) for orienting the position of said flywheel of said motor with respect to that one groove. A printer according to claim 10, wherein the crank arms (172;200) have circular portions (180) which receive the eccentrics (232;234). A printer according to any preceding claim in which at least a portion of the counterbalance (130) is in overlying relationship to said hammerbank (22).

Inventors: BARRUS GORDON BRENT, BARRUS, GORDON BRENT
Applicants: PRINTRONIX INC, PRINTRONIX, INC.
Application year: 1996
Main classification: B41J25
IPC codes: B41J25, B41J2, B41J9, B41J19