GB2180194A - Hammer unit for printers - Google Patents

Abstract

This invention provides a hammer unit for use in character printers in which the front end of a plunger (2) of a solenoid (1), operating under control of the print command, is positioned directly opposite to and close to the typeface (7) of the character head. The plunger is provided with a plunger tip (3) which can be attached to and detached from it in a direction perpendicular to the axis of the plunger and which covers part the cylindrical side surface of the plunger and the entire circular end face of the plunger front end. At least the cap part (5) of the plunger tip (3) covering the front end of the plunger being made of synthetic resin material. When the plunger tip (3) has to be replaced owing to wearing out of its cap part, the plunger tip can be replaced easily and quickly by slipping it on and off the plunger in a direction perpendicular to the axis of the plunger. Furthermore, since the print stroke is determined in such a unit by the stroke of the plunger and thickness of the cap part of the plunger tip, adjustment of the print stroke is easy. <IMAGE>

Description

SPECIFICATION Hammer unit for printers This invention reiatesto the print hammer units used in character printers.

The conventional fully formed character printers such as MICR or OCR character printers use a hammer unit ofthe type shown in Figure 6 ofthe ac- companying drawings.

Such a hammer unit consists of a hammer partA which is capable of reciprocating linear motion when driven at its rear part in accordance with the print command, a supporting part Cwith a hole Din it for the plungerto move in, a spring G which is placed within the hole D and which provides the retracting forceforthe plungerto return to its normal position, and a plunger E whose tip F hits against the character to be printed when driven at its rear part B. Normally, the plunger part E is made of metallic material so as effectively to transmitthe impactforcefrom the hammertothe characterto be printed.Further, atthe front end of the plunger is provided a tip F made of a somewhat resilient material such as nylon resin, so thatthe inkfrom the ink ribbon is transferred fully and evenly on to the paper.

Thus, in a conventional hammer unit, the tip F would wear out over long duration of use and hence would need replacement. Atthetime of such replacement, the conventional unit has many drawbacks as explained below.

Firstly, since the tip Fand the plunger E are constructed as an integral structure, the plunger and the tip will both have to be replaced together, thus making it uneconomical.

Secondly, the plunger E is inserted into the hole D in the supporting part C, which is fixed between the hammerA and the characterto be printed. This causes the plunger replacement operation to be unusually complicated because the supporting pa rt C and the hammerAwill first have to be detached from the chassis of the unit (not shown).

Furthermore, since the plunger E is inserted in the hole D along with the spring G,the plungerveryoften jumps out at the time of its removal owing to the force of the spring G, thus causing additional delays in replacing the plunger. Finally, in a conventional hammer unitofthe above type, the stroke ofthe plunger has to be adjusted by adjusting the relative positions ofthe supporting partCandthe plunger E and the relative of the supporting part C a nd the ha mmer A. As a consequence, this adjustment is very cumbersome.

In view ofthe above mentioned drawbacks of the conventional hammer units, the present invention aimsto provide a hammer unit in which the operation of replacing a worn out plungertip can be carried outeasilyand quickly, the part to be replaced is also limited onlyto the worn out part, and the adjustment of the print stroke is also made easy.

In order to achieve the above objectives, in accordance with the present invention, there is provided a hammer unit for character printer units in which the front end of a plunger part of a solenoid, operable under a print command, is arranged to be positioned, in use, directly opposite to and close to the type face of a character head, with a plunger tip provided around the plunger detachable and attachable to the plunger in a direction perpendicularto the axis ofthe plunger, the plungertip consisting of a body part that encircles a cylindrical side of the plunger and a cap partthat covers a front circularface of the plunger and for hitting against the type face, with at leastthe cap partofthe plungertip being madeofsynthetic resin.

In the accompanying drawings: Figure 1 is the side view of a unit constructed in accordance with the invention; Figure2 is an overall perspective view of the plungertip part used in the unit of Figure 1; Figure 3 is a side view of the plunger tip of Figure 2; Figure 4 is a front view of the plunger tip; Figure5isa rearviewoftheplungertip; and, Figure 6shows an example of a unit according to the prior art.

Figures 1 through 5 show a hammer unit as one example ofthe application ofthis invention. In Figure 1, a solenoid 1 is placed close to and directly opposite the type face and its plunger2 moves forward and backward in accordance with the print command.

The position of this solenoid 1 is so selected asto ensure that during printing when the plunger moves forward, a cap part5 of a plungertip 3,fixed tothe plunger as will be described later, hits against a type face7with an appropriateforce. In addition, the position of the solenoid is also such that the front end of the plunger2 does not come in contactwiththetype face 7 when the plunger 2 moves forward with the plungertip 3 not in place. Therefore, the type face 7 will not be damaged by the front end of the plunger 2 when the solenoid 1 is activated inadvertantlywith the plungertip 3 notfixed to the plunger 2.

The tip 3 is constructed as a single part using some synthetic resin. This plunger tip 3 consists of a body part4which has the shape of a part hollow cylinder whose internal diameter is almostthe same asthe external diameter of the plunger of the solenoid 1, and the cap part 5, which is provided at one end ofthe body part 4. The cap part5 covers the front end ofthe plunger2 and an outerface5a ofthecap parthits against a typeface 7 during printing. Two grooves6 and 6 are provided atthe two ends of the body part4 so that the two sides of the body part 4 can be spread apart.Further, the length of the body part 4 is such thatthe body part can be fixed around the part of the plunger2extending beyondthesolenoid 1 whenthe plunger2 is in the retracted position. Also, the rear end of the body part is provided with an inward projecting part 4a which engages with a groove 2a provided circumferentially on the periphery of the plunger2.

The synthetic resin material used for the plunger tip3isselectedasforconventional hammertipsso that when the plunger tip hits against the type face, it comes into full contact with the entire surface ofthe type face evenly so that the ink from the ink ribbon, not shown in the figure, gets transferred onto the paper completely and evenly. In order to achieve this objective, the synthetic resin used for the plungertip 3 should have the appropriate resilience and soft ness.

A paper guide 8 is fixed to the chassis ofthe printer.

The use of the unit will now be described. The plungertap3 is held withthefingers atthe body part4 and is positioned above the plunger 2so that the cap part5 covers thefront end ofthe plunger 2 and the inward projection 4a is in a position to engage with the groove 2a. The two open ends of the body part are pressed against the plunger 2 from the above, the lower end ofthe body part4 opens out dueto this pressure and the plungertip 3 gets fixed around the plungerandthenthe lowertipofthe bodypart4 closes itself around the plunger by its own elastic force. Of course, it is also possibleto fix the plunger tip aroundthe plunger 2 as long as it is positioned parallel to the axis ofthe plunger.

In this condition, if the solenoid is activated owing to the print command, the plunger2 and the plunger tip 3 move forward and the face 5a of the cap part5 of the plungertip3 hits againstthe type face which in turn produces an impression of the type on the paper via the ink ribbon. This process is repeated for printing each new character.

However, since the inward projection 4a ofthe plungertip 3 is engaged with the groove 2a ofthe plunger,theplungertipwill notslipalongtheaxial direction around the plunger and also there will be no fluctuations in the print stroke. In addition, when the plunger tip 3 impacts against the type face 7, the mass of the plunger too will be effective thereby ensuring that the type face is imparted with sufficient impact energy. When the plungertip 3 isto be replaced owing to wearing out of the face 5a of the cap part 5 orto some other reason, the plungertip 3 can be detached from the plunger 2 with a sequence of operations reverse to that described above for fixing the plungertip around the plunger.In otherwords, the body part 4 is held with thefingers andthe hammer part is pulled away perpendicular to the axis of the plunger, whereupon the plungertip 3 gets detached easily from the plunger 2. Therefore, itwill be possible to replace only the plunger tip 3 of synthetic resin and hence the cost of the part being replaced will be much lowerthan in a conventional unit.

In the example of application of this invention des cribed above, the body part and cap part of the plun gertip were constructed integrally using some synthetic resin. However, the present invention is not limited to such a structure but can be extended to various other design modifications. For example, the body partcan be made ofathin metallic material with appropriate springiness while only the cap part is made of some synthetic resin.

In the present invention as described using the above example,the plunger part of the solenoid activated bythe print command is provided with a hammer cap which can be easily attached to and detached from the plunger along a direction parallel to the diameter of the plunger,with at leastthecap part of the plungertip covering the front end of the plunger being made of some synthetic resin so that the face of the cap part hits against the type face. Because of the above feature, when the face ofthe cap part gets worn out owing to repeated impact with the typeface,itwill be possible to replace only the pl u n- gertipwhich results in an economical hammer unit.

Furthermore, the operation of such plunger tip replacement is also made easy because it is sufficient to slip on and siip offthe plunger tip around the plunger in the radial direction. In addition, the force of the retractive spring retaining the plungerwill not cause any hindrance to the operation of replacing the plunger tip unlike in conventional units, thereby making the replacement operation simple and quick.

Further, the print stroke is determined by the stroke of the plunger of the solenoid and the thickness ofthe cap part of the plungertip whereby the adjustment of the print stroke will become easier as compared with a conventional unit.

Claims (4)

1. A hammer unitfor character printer units in which the front end of a plunger part of a solenoid, operable under a print command, is arranged to be positioned, in use, directly opposite to and close to the type face of a character head, with a plungertip provided around the plunger detachable and attachable to the plunger in a direction perpendicular to the axis of the plunger, theplungertip consisting of a body partthat encircles a cylindrical side of the plunger and a cap part that covers a front circularface of the plungerandfor hitting againstthetypeface,with at least the cap part ofthe plunger tip being made of synthetic resin.

2. Ahammerunitaccording to claim 1,wherein the body part and the cap part of the plungertip are constructed integrally using from a synthetic resin.

3. A hammer unit according to claim 1,wherein the body part ofthe plungertip is made of metallic material with a springiness while the cap part is made of synthetic resin.

4. Ahammerunitfor printers, substantially as described with reference to Figures 1 to 5 of the accompanying drawings.