EP0023153A1

EP0023153A1 - Print hammer mechanism

Info

Publication number: EP0023153A1
Application number: EP80302468A
Authority: EP
Inventors: Sean Kevin O'brien; Thomas Alan Davenport
Original assignee: NCR Canada Ltd
Current assignee: NCR Canada Ltd
Priority date: 1979-07-23
Filing date: 1980-07-21
Publication date: 1981-01-28
Also published as: JPS5617279A; CA1139988A

Abstract

A print hammer mechanism (20) is provided which includes a pivotably mounted relatively rigid actuating member (30) having a hammer member (46) in the form of a flexible cantilever mounted thereto, the hammer member (46) and the actuating member (30) moving together upon actuation of the actuating member (30) in a printing direction. The hammer member (46) is deflected away from the actuating member (30) upon the stopping of the actuating member (30) after moving a predetermined distance in a printing direction. The flexing of the hammer member (46) results in the tip (48) of the hammer member (46) striking the record medium (54) and aligning itself with the impact surface (50) of a type element (52) to provide a uniform sharp print.

Description

Technical Field

The present invention relates to a print hammer mechanism. The invention has particular application to a print hammer mechanism used, for example, in high-speed printers, in which a type element carrier, such as a durm or ribbon, is moved to present a succession of type elements to a hammer which is selectively actuated at the proper instant to produce an imprint of a character on a record medium positioned, usually together with a printing ribbon, between the hammer and the type element. Such mechanisms must provide a positive printing impact of the hammer at high operating speeds which normally occur in on-the-fly printing operations.

Background Art

To provide high energy impact of a hammer on the record medium, print hammer mechanisms were proposed in the prior art in which the hammer is propelled into engagement with a selected type element after an actuating member for the hammer has been stopped. Such an arrangement is disclosed, for example, in the U. S. Patent No. 3 643 594. This patent discloses a print hammer mechanism including two rigid rocker arms independently pivoted on a common axle, a first of which has mounted thereon a striker positioned adjacent a type wheel and is held against the second by a return spring. The second rocker arm is arranged to be actuated by an electromagnet to move the first rocker arm with its striker towards the type wheel. During this movement the second rocker arm is stopped but the first rocker arm continues to move bringing the striker into engagement with the type wheel.
A problem arising with print hammer mechanisms of the above kind is the difficulty of obtaining a sharp uniform print therewith due to the precision required for ensuring that the face of the striker be in complete alignment upon impact with the face of the type element carried on the wheel.

Disclosure of the Invention

It is an object of the invention to provide a print hammer mechanism in which the above mentioned problem is overcome in

a simple manner.

Thus, according to the invention, there is provided a print hammer mechanism including a lever means pivotally mounted for movement between a rest position and an actuated position; actuating means positioned adjacent one end of said lever means and arranged, when operated, to rotate said lever means to, and to stop said lever means upon reaching, said actuated position; and a hammer member arranged to move together with said lever means upon operation of said actuating means until rotational movement of said lever means is stopped, said hammer member being arranged to continue its movement to bring a hammer tip mounted thereon into engagement with a type element, characterized in that said hammer member is in the form of a flexible cantilever secured at one end to said lever means, said hammer tip being mounted on the free end of said hammer member, whereby upon the stopping of the rotational movement of said lever means the hammer member flexes away from said lever means to a position in which said hammer tip engages said type element.
The print hammer mechanism according to the invention is of a simple, low cost, construction allowing the face of the hammer tip to align itself automatically with the face of the print element upon impact. A further advantage of the print hammer mechanism according to the invention is that the hammer member can be arranged to be of low mass thereby permitting high speed of operation.

Brief Description of the Drawings

One embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:-

Fig. 1 is a perspective view of the print hammer mechanism according to the present invention;
Fig. 2 is a schematic drawing of the print hammer mechanism of the present invention showing a lever means in a rest position with a portion of the lever means cut away showing the mounting of a hammer member to an actuating arm of the lever means;
Fig. 3 is a schematic drawing of the print hammer mechanism of the present invention showing the lever means in an actuated position.

Best Mode of Carrying Out the Invention

Referring to Fig. 1 there is shown a perspective view of the print hammer mechanism generally indicated by the numeral 20 and comprising a U-shaped support member 22 preferably composed of a metal such as soft iron and having a depending arm portion 24 on which is positioned a coil 26 illustrated in phantom lines. Mounted adjacent the lower edge of a second arm portion 28 of the support member 22 is a lever means indicated generally by the numeral 30 and which comprises an armature arm 32 preferably composed of a metal such as soft iron and rotatably supported on a pin 34 or other suitable pivot means. Secured to the rear portion of the armature arm 32 adjacent the pin 34 by means of a pair of screw members 36 (one only shown) is an elongated actuating arm 38 of an inverted T cross-section having an upright portion 40 to which is attached one end of a return spring 42. The actuating arm 38 is preferably fabricated from a plastic material manufactured by the DuPont Corporation of Delaware and sold under the trademark "Delrin". The return spring 42 normally urges the lever means 30 to a rest position where the armature arm 32 is rotated counter-clockwise about the pin 34 (Fig. 2) until engaging a stop 44 (Figs. 2 and 3) located adjacent the lower edge of the armature arm 32.
As shown more clearly in the cutaway portion of Fig. 2, a hammer member 46 in the form of a flexible cantilever and preferably constructed of spring steel has one end secured to one end of the lower portion of the actuating arm 38 by means of the screws 36 described previously for mounting the actuating arm 38 to the armature arm 32. Secured to the free end of the hammer member 46 is a hammer tip 48. The hammer tip 48 may be soldered or cemented to the hammer member 46 in any conventional manner.
Cooperating with the hammer tip 48 is a type element 50 secured to a type support member 52 mounted at a precise angle to allow the hammer tip 48 to impact the type element 50 in a direction which is perpendicular to the face of the type element 50. In the present embodiment, the type support member 52 is a part of a rotating drum member which sweeps past the hammer tip 48 in a manner that is well-known in the art and which constitutes an on-the-fly printing operation. Upon energization of the coil 26, the armature arm 32 is attracted to the arm portion 24 of the support member 22, thereby moving in a clockwise direction as viewed in Fig. 2 against the action of the spring 42. The clockwise movement of the armature arm 32 results in the actuating arm 38, together with the hammer member 46 carried by the arm 38 moving towards the type element 50 until the armature arm 32 impacts on the lower end of the arm portion 24. The impacting of the armature arm 32 on the arm portion 24 results in the sudden stopping of the actuating arm 38 at which time the free end of the hammer member 46 flexes away from such actuating arm 38 (Fig. 3) resulting in the hammer tip 48 impacting against a record medium 54 (such as a paper web) moving the record medium against the type element 50 resulting in the printing of a character on the record medium. At the conclusion of the printing stroke, the coil 26 is de-energized, allowing the return spring 42 to rotate the lever means 30 counter-clockwise to the rest position against the stop 44 (Fig. 2). Because of the flexible construction of the hammer member 46, the hammer tip 48 upon impacting the type element 50 will be rotated to a degree, thereby aligning itself, to . provide a uniform contact area between the record medium 54 and the type element 50 resulting in a uniform printing of the character on the record medium. This arrangement eliminates the need for adjusting the mounting of the hammer member 46 with respect to the face of the type element 50 to provide a uniform printing.
An important advantage of the present construction resides in the impact time of the hammer tip 48 on the record medium 54. During the initial acceleration movement of the lever means 30, the hammer member 46 and the actuating arm 38 moving together function as an effective rigid assembly. But upon impact of the armature arm 32 against the arm portion 24 of the support member 22, both the actuating arm 38 and the hammer member 46 become separate decoupled masses. Because it acts as being decoupled from the actuating arm 38, the hammer tip 48 functions as a light disconnected mass thereby providing a small impact time on the record medium 54 and allows for the use of a small mass for the hammer tip 48. By mounting the hammer member 46 adjacent the point of rotation of the lever means 30, the maximum flexing of the hammer member 46 will be attained providing a high impact force between the hammer tip 48 and the type element 50. This condition is contrasted to the situation in which the hammer member 46 and the actuator arm 32 were rigidly coupled at the time of contact with the record medium 54. This latter condition would present more mass on impact, and therefore, a longer duration of contact or dwell time between the hammer tip 48 and the type element 50. By reducing the dwell time, the printing speed of the print hammer mechanism 20 may be increased without the attending danger of smearing the image of the printed character.
While the spring 42 has been disclosed as the means to return the lever means 30 to its rest position, it has been found that under certain circumstances a permanent magnet (not shown) located adjacent the upright portion 40 of the actuating arm 38 provides an effective dampening means to return the lever means 30 to the rest position upon the de-energization of the coil 26. In this case the coil 26 when energized, is capable of overcoming the strength of the permanent magnet enabling a hammer operation to occur in the manner described previously. When used with a permanent magnet, the actuating arm 38 is preferably constructed of a'metal such as soft iron.

Claims

1. A print hammer mechanism (20) including a lever means (32, 38) pivotally mounted for movement between a rest position and an actuated position; actuating means (22) positioned adjacent one end of said lever means (32, 38) and arranged, when operated, to rotate said lever means (32, 38) to, and to stop said lever means (32, 38) upon reaching, said actuated position; and a hammer member (46) arranged to move together with said lever means (32, 38) upon operation of said actuating means (22) until rotational movement of said lever means (32, 38) is stopped, said hammer member (46) being arranged to continue its movement to bring a hammer tip (48) mounted thereon into engagement with a type element (50), characterized in that said hammer member (46) is in the form of a flexible cantilever secured at one end to said lever means (32, 38), said hammer tip (48) being mounted on the free end of said hammer member (46), whereby upon the stopping of the rotational movement of said lever means (32, 38) the hammer member (46) flexes away from said lever means (32, 38) to a position in which said hammer tip (48) engages said type element (50).

2. A mechanism according to claim 1, characterized in that said hammer member (46) is secured to said lever means (32, 38) adjacent the pivot (34) of said lever means (32, 38).

3. A mechanism according to either claim 1 or 2, characterized in that said lever means (32, 38) comprises a pivotally mounted armature arm (32) and an actuating arm (38) secured to said armature arm (32) adjacent the pivot point of said armature arm (32), said hammer member (46) being mounted on said lever means (32, 38) adjacent the point of attachment of said actuating arm (38) to said armature arm (32).

4. A mechanism according to claim 3, characterized in that said actuating arm (38) and said hammer member (46) are parallel to and in contact with each other in the rest position of said lever means (32, 38).

5. A mechanism according to claim 3, characterized in that said actuating arm (38) and said hammer member (46) are secured to said armature arm (32) by common fastening means (36).

6. A mechanism according to claim 3, characterized by resilient means (42) attached to said actuating arm (38) for urging said lever means (32, 38) to its rest position.

7. A mechanism according to claim 3, characterized in that said actuating arm (38) is a flat elongated plate having an upright rib (40) extending along a surface thereof such that said actuating arm (38) has an inverted T cross-section.

8. A mechanism according to claim 3, characterized in that said armature arm (32) is of soft iron, said actuating arm (38) of plastics material, and said hammer member (46) of spring steel.

9. A mechanism according to claim 3, characterized in that said actuating means (22) includes a U-shaped magnetic core having a coil (26) wound on one leg (24) thereof, which leg is positioned adjacent and coplanar with one end of said armature arm (32) such that, upon energization of said coil (26), said lever means (32, 38) is rotated until said one end of said armature arm (32) engages said one leg (24) of said actuating means (22).