US3199650A - Hammer with dampening means for high speed printer - Google Patents

Description

0, 1965 E. A. BROWN ETAL 3,199,550

HAMMER WITH DAMPENING MEANS FOR HIGH SPEED PRINTER Filed Aug. 2. 1961 2 Sheets-Sheet 1 q- LO A I!) g k\\ 13:

2 EDGAR A. BROWN A GUNTER H. SCHACHL :(JOGSLQ FIGJ ATTORNEY 1965 E. A. BROWN ETAL 3,199,650

HAMMER WITH DAMPENING MEANS FOR HIGH SPEED PRINTER Filed Aug. 2, 1961 2 Sheets-Sheet 2 C5 5 fi i) E? United States Patent HAMMER WITH DAMPENING MEANS FOR HZGH SPEED PRINTER Edgar A. Brown, Gilroy, and Gunter H. Schacht, San

Jose, Calif., assignors to International Business Machines Corporation, New York, N .Y., a corporation of New York Filed Aug. 2, 1961, Ser. No. 128,871 @laims. (61. 197-18) This invention relates generally to high speed printing devices and in particular to those printers in which printing is accomplished on the fly without stopping the movement of the type relative to the paper.

While serial printers are attractive as output devices for low speed applications because of their relatively inexpensive manufacture, the relatively low speed of operation of these devices has prevented their widespread adoption in many potential uses. The on the fly printer, proposed as one approach to the low cost serial printer problem, has a limitation in speed due to the requirement that the firing pin must arrive at the type with a high degree of accuracy and the components must recover after a character has been printed. The achievable time accuracy with which the firing pin arrives at the type and the recovery time of the rest of the components after impact limit the speed of the on the fly printer. To illustrate the problem with respect to the time accuracy, assuming a character velocity of 300 inches per second, the maximum tolerable variation in time for the print hammer after a print command is il6 microseconds. This accuracy is essential if proper registration of the printed image is to be achieved. Print quality may be affected by the tendency of the firing pin to strike the paper more than once due to the oscillations induced, and, at high speeds, these oscillations, if allowed to continue undamped, will affect the next print operations since either the impact or the proper timing of the hammer may not be realized.

Previous devices have allowed a long delay between print operations to allow the firing pin oscillations to deteriorate to the point where they might be ignored. Such devices usually require 20 milliseconds or more delay between print operations. In a device of this invention, the firing pin comes to rest within 4 to 6 milliseconds after hammer impact which allows a considerable increase in the print speed.

It is therefore an object of our invention to provide an improved high speed serial printing device.

Another object of our invention is to provide a high speed printer in which the print hammer is essentially critically damped.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention as illustrated in the accompanying drawings.

In the drawings:

FIG. 1 is a diagrammatic illustration of a serial printing device of the invention.

FIGS. 2a through 2 are schematic representations of the print mechanism at the various points in the print cycle.

The printer shown in FIG. 1 consists generally of a hammer 1 which impels a firing pin 2 against tape 3 to transfer the image of a selected one of the characters of type font 4 located on the periphery of type wheel 5. The firing pin 2 is operated at high speed in response to a signal indicating that the appropriate character is in a position to be printed. In between the print operations an incremental feed mechanism 6 steps the tape into position for the next character to be printed.

The type wheel 5 aflixed to shaft 7 has a type font 4 1 pin 2. A support bracket 23 contains a threaded aparture,

3,199,659 Patented Aug. 10, 1 965 arranged about the periphery of wheel 5. Shaft 7 is driven from any suitable power source (not shown). Shaft 8 is driven at an integral multiple of the speed of shaft 7 by appropriate gears or belts (not shown). Ball bearing 9 affixed to shaft 8 slightly off-center comprises cam 10.

Inking roller 11 mounted on shaft 12 bears against type wheel 5 in a manner to continually replenish the supply of ink on the characters of type font 4. The roller may be of any suitable type for conveying ink to the type wheel. In the preferred embodiment this roller has an internal reservoir and a porous wall for conveying the ink from the reservoir to the type wheel. Power for rotation of inking roller 11 is supplied through the frictional engagement of the roller with the type wheel.

A character image is transferred from type wheel 5 to a printing medium which may be a paper tape 3, as shown in FIG. 2, by means of a firing pin 2. When suitably impelled toward type wheel 5, firing pin 2 depresses paper tape 3 against the character located thereunder at the time of contact to transfer the ink from the character to the tape 3. A pair of flat springs 13 and 14 are afiixed to firing pin 2 and to block 15 by appropriate mounting means. A stop 16 is also afiixed to mounting block 15 to limit the travel of firing pin 2 away from type font 4. Hammer 1. provides means for impelling firing pin 2 toward type font 4. Shaft 17 provides means for pivotally mounting hammer 1. Collars 18 and 19 retain'hammer 1 for pivotal movement on shaft 17. Compression spring 2%, wound about guide 21 and slidably mounted Within guide 22, biases hammer 1 in the direction of firing through which guide 22 is passed. Support bracket 23 is afiixed to the base plate by means of screws 24. Threaded guide 22 may be adjusted within support bracket 23 to vary the force applied to hammer 1 by spring 21. Hammer 1 is retained in the ready position by means of electromagnet 25 having a core 26 and a Winding 27. Screws 23 hold electromagnet 25 to the base plate. When energized, winding 27 created sufiicient magnetic flux at pole face 29 and 3% to retain hammer l in engagement therewith against the force of compression spring 24).

When Winding 27 is momentarily deenergized, ham

mer 1 is free to move under the force of spring and rotates about shaft 17, allowing face 31 to strike firing pin 2 and impel it toward type font 4. Firing .pin 2 contains sufiicient kinetic energy to deflect the tape 3 downward against the moving type font and transfer the ink on the particular character in position at that time to the lower surface of tape 3. Stop 32 affixed to the base plate by means of screw 33 limits the travel of hammer 1. Thus, after a print operation, firing pin 2 returns to a position abutting hammer 1 which is at rest against stop to deenergization, a current pulse of opposite polarity could be applied to the winding 27. Power may then be restored to the winding without affecting subsequent op eration of the hammer l and firing pin 2. After the impression of the character has been transferred to the printing medium and power has been restored to winding 27, hammer 1 will still remain against stop 32 since the strength at pole faces 29 and Si) is not suflicient to attract hammer 1 against the action of spring 20. Electromagnet 27 is used as a latch and therefore does not require sufiicient magnetic field strength to attract hammer 1 out only sufiicient field strength to retain hammer 1 in engagement with pole faces 29 and 39 against the force of spring 26. The magnet can be made substantially smaller than would be required if it operated to restore hammer 1. The use of an electromagnet in this manner reduces the power dissipation by a large factor.

Mechanical restoration of hammer 1 to the ready position is accomplished by means of restore arm 34 which is pivotally mounted on shaft 35 and retained thereon by means of collars 36 and 37. Restore arm 34 is one lever of a bell crank having a second lever 38. A compression spring 39 wound about guide 40 which is retained within guide 41 biases lever 34 against the ball bearing 9. Mounting bracket 42 has a threaded aperture therein for guide 41 is afiixed to be base plate by means of screws 43.

Restore arm 34 is retained in the idle position by means of electromagnet 44 having a winding 45 and which is mounted against the base plate by means of screws 46. Energization of Winding 45 provides sufiicient magnetic flux at pole faces 47 and 48 to retain restore arm 34 against the pole faces in the idle position. With restore arm 34 in the idle position, it rides out of contact with cam 10. When the high point of cam 1 is adjacent the restore arm 34, electromagnet winding 45 may be deenergized, thereby allowing the restore arm 34 to be moved upward by the action of spring 39 against lever 38 of the bell crank. Release of restore arm 34 from electromagnet 44 is accomplished by means of timing circuitry associated with type wheel 5. By releasing the restore arm 34 only when the high point of cam is adjacent the restore arm, a much smoother, predictable motion is achieved.

As the restore arm is moved from the idle to the restore position, a shoulder 49 engages a corresponding portion 50 of hammer 1 and moves hammer 1 from a position abutting stop 32 to a position adjacent pole faces 29 and 313. Since winding 27 is now energized, hammer 1 is retained in engagement with electromagnet 25. Restoration of hammer 1 compresses spring 20, and hammer 1 is once again prepared for a print operation.

Lever 38 of the bell crank has a foot 51 and pawl 52 arrangement at the extremity thereof. A spring 53 biases pawl 52 against foot 51 in a manner to retain the printing medium 3 against the foot during motion away from the print position. It can be seen that pawl 52 is mounted slightly off-center and therefore exerts a clamping action against tape 3 as it moves away from the print position. The foot and pawl oscillates in a direction away from the print position and toward the print position. During this latter portion of the cycle, pawl 52 glides freely along tape 3. The tape is thus released and the pawl 52 assumes a normal position without a corresponding movement on the part of the tape. This portion of the operation is enhanced by means of a second pawl 54 and spring 55 cooperating with guide pin 56 to prevent reverse movement of the tape 3. Also it is apparent that the desired releasing and damping action is ensured at high speed by its own inertia. Pawl 54 is pivotally mounted to the base plate and does not move with foot 51 and pawl 52. Movement of the tape away from the print position is not prevented by pawl 54 since this provides an unclamping action between the pawl 54 and guide pin 56. However, return motion is prevented since pawl 54 exerts a clamping action against guide pin 56 to prevent motion of tape 3 in the direction of the print position.

The rapid stepping motion of the foot 51 and pawl 52 for feeding the tape 3 through the print position is ideal for moving the paper between print operations since it achieves this result during the time hammer 1 is being restored. However, this rapid incremental movement of the tape 3 is incompatible with the high inertia of the tape feed roll 57 and requires means for smoothing out this incremental motion so that the tape will not be broken.

While it is possible to drive the feed roll 57 in synchronism with the feed foot 51 and pawl 52, this represents an unsatisfactory solution due to the high inertia of the done.

ieaeso roll 57 and the changing diameter which alters the feed requirements. Similarly, a continuously operating capstan drive is unacceptable since there are occasions when it is esired to hold up the feed of tape, for example, during a period of time when no printing is being done. The continuous feed would result in a blocking or clogging of the print position during the time when no printing is being Thus, some satisfactory means is necessary to smooth out the incremental feed from the foot and pawl to a relatively smooth feed from the storage roll.

To smooth the incremental tape motion to a smooth feed a capstan 58 is mounted on a continuously rotating shaft 59. The tape medium 3 passing from storage roll 57 to the print position is deflected about capstan 58 by means of guide pins 6%, 61, and 62. A spring 63, aflixed to the base plate by means of screws, deflects the tape medium between guide pins 69 and 61. The deflection of spring 63 depends upon the tension in the tape 3 which is in turn a function of the feed requirements from storage roll 57. When the storage roll has not supplied sufficient tape to the print position, the tension increases and the deflection of spring 63 is likewise increased. Spring 63 may be positioned between pin 2 and capstan 58 to deflect the tape in that region to provide the same function. The increased tension in the print medium results in an increase of the normal force of the tape medium against the capstan. Since the capstan 58 is continuously rotating, the increased normal force in conjunction with the angular wrap and the coefiicient of friction results in a feed operation from the storage roll 57 by means of the capstan 58. Thus, the relatively jerky movement caused by the incremental feed of the foot 51 and pawl 52 is converted into a smooth feed operation and breakage of the tape medium is avoided. If no print cycle takes place, the decreased tension on the tape medium permits an air bearing to exist between tape and capstan. This assures undamaged tape if the printer idles any length of time.

FIGS. 2a2f represent a step-by-step description of the coaction between hammer it, firing pin 2, and restore arm In FIG. 2a hammer 1 is in the ready position, firing pin 2 is at the rest position, and restore arm 34 is in the idle position. All electromagnets are energized to retain the elements at this point. The print operation is initiated by deenergizing the winding on electromagnet 25, allowing hammer i to move into the position shown by FIG. 2b. The hammer 1 is now in the strike position and the firing pin 2 has not yet moved from the rest position. In FIG. 2c the hammer 1 has continued its motion to impel firing pin 2 against print wheel 5 by the energy contained in the hammer. In FIG. 2d the firing in has returned to the rest position after the print operation and has been damped by means to be described later. The restore arm 34 has been released from electromagnet 44 by deenergization of the winding associated therewith, and restore arm 34 is following earn it). This results in hammer 1 being moved back into engagement with electromagnet 25, now energized to retain hammer 1 against the pole faces thereof.

In FIG. 2e hammer 1 has been completely restored into engagement with electromagnet Z5, and is retained there. The restore arm 34 is in the complete restore position. This is the low point of cam 10. As cam It) continues to rotate, it approaches a position shown in FIG. 2] in which the restore arm 34 is again placed into engagement with electromagnet 44, now energized to retain the restore arm in the idle position. Thus, the condition shown in FIG. 2a again exists with the hammer 1 in the ready position, firing pin 2 in the rest position, and restore arm 34 in the idle position.

A substantial increase in speed is possible by proper damping of the firing pin. Without an additional damping arrangement it is necessary to wait for the oscillations to damp themselves out before initiating another print operation. If this is not done, there is always the possibility that the hammer may strike the firing pin as the 5 firing pin is oscillating in a direction toward the hammer. This would result in a slower movement of the firing pin from the ready to the strike position and would produce type which is improperly spaced and not as dark as would normally occur. The exploded view of firing pin 2, as shown in FIG. 1, illustrates the additional means which provides essentially critical damping. A chamber 64 within firing pin 2 is sealed and contains a piston 65. Piston 65 has an aperture 66 extending from end 67 to end 68, permitting air to travel through the piston from one end of the chamber to the other. A spring 69 biases the piston to one end of the sealed chamber. It can be seen that the damping means has absolutely no effect on the travel of the firing pin as it is initially struck by hammer 1, since the piston is spring urged toward the end of the firing pin adjacent the hammer. However, when the pin strikes the type wheel, the piston 65 moves downward against the action of the spring and reduces the rebound velocity of firing pin 2 from the type wheel.

In addition to compressing spring 69, the motion of piston H 65 is effective to increase the air pressure in the side of the chamber toward which it is moving. The aperture 66 through piston 65'allows the compressed air in one end of the cylinder to pass to the other lower pressure end. The energy expended in this transfer of air is dissipated as heat. The size of this aperture is a function of the masses involved, velocities and the spring 69, and will therefore vary from case to case and with the damping desired. Movement of the piston within the sealed chamber downwardly compresses the spring 69 and causes air to be displaced from the end of the chamber including the spring to the end of the chamber above the moved piston. As the firing pin returns to its previous position, the spring acts upon the piston to compress the air in the upper chamber. of the cylinder and the spring between the piston and the lower end of the cylinder balance each other out and serve to essentially critically damp the motion of the firing pin, quickly arresting its oscillations. The aperture within the cylinder is of a size sufiicient to assure high velocity airflow for energy dissipation and is relatedto the mass of the cylinder and the firing pin, together with the physical constants of spring, and the velocities of the various components to provide the desired damping. It is entirely possible that the aperture could be placed as a groove along the outside of the piston or merely by making the piston of sufficiently smaller diameter than the inside diameter of the chamber.

In the embodiment shown and described, cam 10 rotates at four times the speed of rotation of the type wheel. Thus, it is possible to print two characters for each revolution of the Wheel. For example, a character would be printed in the first quadrant, the hammer restored and tape stepped during the passage of the second quadrant, another character printed in the third quadrant, and the hammer restored in the fourth quadrant. Since this may be a fairly high speed, conventional cam followers which increase the moment of inertia of the oscillating arm or have poor wear characten's-tics have been found to be unsatisfactory. The use of an eccentrically mounted ball bearing 9 in place of the conventional cam has been found to substantially increase the life of cam follower 34 without any sacrifice in performance of the device. In operation the outer rim of cam 10 does not rotate but remains practically stationary when the follower is bearing against it. Thus, there is no wear on the follower portion of restore arm 34 or the outer surface of the cam even at the high speeds involved.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in the form and details may be made therein without departing from the spirit and scope of the invention.

The compressed air in the upper end What is claimed is:

1. In an on the fly printer having a rotating type font and a firing pin for coaction therewith to create an impression thereof on a print medium, hammer means for operating said firing pin, spring actuator means for moving said hammer from a ready position to a strike position to operate said firing pin, first magnetic latch means, means for energizing said latch means to retain said hammer in the ready position against the force of said spring actuator, pivot means supporting said hammer for movement by said actuator means to operate said firing pin upon deenergization of said latch means, restore means for said hammer comprising a cam, means for continuously driving said cam at an integral multiple of the speed of said print wheel, a cam follower operable between an idle and a restore position, second magnetic latch means, means for energizing said second latch means to hold said follower in the idle position, means for deenergizing said second latch means to release said follower at selected points during rotation of said type font to follow said cam, and means affixed to said follower for engaging said hammer during movement from the idle to the restore position to move said hammer into said ready position against said first latch means.

2. In an on the fly printer having a rotating type font and a firing pin for coaction therewith to create an impression thereof on a print medium, hammer means for operating said firing pin, spring actuator means for moving said hammer from a ready position to a strike position to operate said firing pin, first magnetic latch means, means for energizing said latch means to retain said hammer in the ready position against the force of said spring actuator, pivot means supporting said hammer for movement by said actuator means to operate said firing pin upon deenergization of said latch means, restore means for said hammer comprising a cam, means for continuously driving said cam, a cam follower operable between an idle and a restore position, second magnetic latch means, means for energizing said second latch means to hold said follower in the idle position, means responsive to the posit-ion of said cam for deenergizing said second latch means to release said follower at selected points during rotation of said cam, and means afiixed to said follower for engaging said hammer during movement from the idle to the restore position to move said hammer into said ready position against said first latch means.

3. In an on the fiy printer having a rotating type font and a firing pin for coaction therewith to create an impression thereof on a print medium, hammer means for operating said firing pin, spring actuator means for moving said hammer from a ready position to a strike position to operate said firing pin, first magnetic latch means, means for energizing said latch means to retain said hammer in the ready position against the force of said spring actuator, pivot means supporting said hammer for movement by said actuator means to operate said firing pin upon deenergization of said latch means, restore means for said hammer comprising a cam, means for continuously driving said cam at a higher speed than the speed of said print wheel, a cam follower operable between an idle and a restore position, second magnetic latch means, means for energizing said second latch means to hold said follower in the idle position, means responsive to the position of said cam for deenergizing said second latch means to release said follower at selected points during rotation of said cam, and means affixed to said follower for engaging said hammer during movement from the idle to the restore position to move said hammer into said ready position against said first latch means.

4. In an on the fly printer having a rotating type font and a firing pin for coaction therewith to create an impression thereof, on a print medium hammer means for operating said firing pin, spring actuator means for moving said hammer from a ready position to a strike position to operate said firing pin, first magnetic latch means, means for energizing said latch means to retain said hammer in the ready position against the force of said spring actuator, pivot means supporting said hammer for movement by said actuator means to operate said firing pin upon deenergization of said latch means, cam restore means for said hammer comprising an eccentrically mounted ball bearing, means for continuously driving said cam at an integral multiple of the speed of said print wheel, a cam foll wer operable between an idle and restore position, second magnetic latch means, means for energizing said second latch means to hold said follower in the idle position, means for deenergizing said second latch means to release said follower at selected points during rotation of said type font to follow said cam, and means afiixed to said follower for engaging said hammer during movement from the idle to the restore position to move said hammer into said ready position against said first latch means.

5. In an on the fly printer having a rotating type font and a firing pin for coaction therewith to create an impression thereof on a print medium, hammer means for operating said firing pin, damping means for said firing pin comprising: a chamber within said firing pin, a. piston movable within said chamber, said piston having a length less than the length of said chamber, an aperture through said piston connecting the ends thereof, spring means urging said piston into abutting relationship with the end of said chamber adjacent the point of impact of said hammer whereby said pin moves undamped in a first direction after impact but subsequent movements are damped by the piston and spring within said chamber, spring actuator means for moving said hammer from a ready position to a strike position to operate said firing pin, first magnetic latch means, means for energizing said latch means to retain said hammer in the ready position against the force of said spring actuator, pivot means supporting said hammer for movement by said actuator means to operate said firing pin upon deenergization of said latch means, cam restore means for said hammer comprising an eccentrically mounted ball bearing, means for continuously driving said cam at an integral multiple of the speed of said print wheel, a cam follower operable between an idle and a restore position, second magnetic latch means, means for energizing said second latch means to hold said follower in the idle position, means for deenergizing said second latch means to release said follower at selected points during rotation of said type font to follow said cam, and means affiXed to said follower for engaging said hammer during movement from the idle to the restore position to move said hammer into said ready position.

References Cited by the Examiner UNITED STATES PATENTS 1,542,129 6/25 Hayes 226-160 2,323,388 7/43 Fitch et al. 19749 2,328,636 9/43 Fitch et a1. 19749 2,504,759 4/50 Thompson 197133 2,531,875 11/50 Dodge et a1. 197-133 2,592,013 4/52 Curley 14529.2 2,625,100 1/53 Williams et a1. 101-93 2,854,100 9/58 Bowser et a1 188103 3,041,964 7/62 Simpson et a1 101-93 FOREIGN PATENTS 815,046 7/37 France.

1,163,525 9/58 France.

RGBERT E. PULFREY, Primary Examiner.

F ROBERT A. LEIGHEY, EUGENE R. CAPOZIO,

Examiners.

Claims (1)

1. IN AN ON THE FLY PRINTER HAVING A ROTATING TYPE FONT AND A FIRING PIN FOR COACTION THEREWITH TO CREATE AN IMPRESSION THEREOF ON A PRINT MEDIUM, HAMMER MEANS FOR OPERATING SAID FIRING PIN, SPRING ACTUATOR MEANS FOR MOVING SAID HAMMER FROM A READY POSITION TO A STRIKE POSITION TO OPERATE SAID FIRING PIN, FIRST MAGNETIC LATCH MEANS, MEANS FOR ENERGIZING SAID LATCH MEANS TO RETAIN SAID HAMMER IN THE READY POSITION AGAINST THE FORCE OF SAID SPRING ACTUATOR, PIVOT MEANS SUPPORTING SAID HAMMER FOR MOVMENT BY SAID ACTUATOR MEANS TO OPERATE SAID FIRING PIN UPON DEENERGIZATION OF SAID LATCH MEANS, RESTORE MEANS FOR SAID HAMMER COMPRISING A CAM, MEANS FOR CONTINUOUSLY DRIVING SAID CAM AT AN INTEGRAL MULTIPLE OF THE SPEED OF SAID PRINT WHEEL, A CAM FOLLOWER OPERABLE BETWEEN AN IDLE AND A RESTORE POSITION, SECOND MAGNETIC LATCH MEANS, MEANS FOR ENERGIZING SAID SECOND LATCH MEANS TO HOLD SAID FOLLOWER IN THE IDLE POSITION, MEANS FOR DEENERGIZING SAID SECOND LATCH MEANS TO RELEASE SAID FOLLOWER AT SELECTED POINTS DURING ROTATION OF SAID TYPE FONT TO FOLLOW SAID CAM, AND MEANS AFFIXED TO SAID FOLLOWER FOR ENGAGING SAID HAMMER DURING MOVEMENT FROM THE IDLE TO THE RESTORE POSITION TO MOVE SAID HAMMER INTO SAID READY POSITION AGAINST SAID FIRST LATCH MEANS.

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