Technical Field

The present invention relates to a printing apparatus and more particularly, but not exclusively, to a dot matrix printing apparatus having heat transfer means associated with the print head for transferring heat therefrom.

Background Art

A dot matrix printer having a print head of circular configuration and of multiple element type operates its print head at high speed and with a large electrical loading. There is therefore a requirement for transferring heat by conduction and convection away from the print head during its operation. This may be accomplished by providing a heat sink within the print head itself and by employing additional heat transfer means, such as a plurality of fins, external to and surrounding a portion of the print head. A prior art print head of this type has been proposed in U.S. Patent No. 4,389,128 which describes an arrangement in which the fins are disposed between a magnetic member of the print head and a fastening belt securing the print head to a carriage of the printer.

One of the drawbacks of the above-mentioned prior art arrangement is that the servicing time for a print head, as well as the initial installation time and time for replacing a print head, is substantially increased by the extra work involved in assembling the - fins around the print head. The extra work increases installation time and the period during which the printer is inoperative during a maintenance operation.

Disclosure of the Invention

It is an object of this invention to provide an arrangement in which a heat sink can be more easily

assembled around a print head and, when required, more easily removed thereby reducing maintenance time and cost.

Accordingly the present invention provides a printing apparatus including a carriage for carrying a print head and heat transfer means operably associated with said print head for transferring heat therefrom, characterized in that said carriage includes pivot means coupled with said heat transfer means for allowing swinging thereof from a first position covering said print head to a second position uncovering said print head to permit removal thereof from said carriage _r and securing means coupled to said carriage and to said heat transfer means for retaining said heat transfer means in said first position.

Brief Description of the Drawings

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

Fig. 1 is a side elevational view of a print head assembly in accordance with an embodiment of the present invention;

Fig. 2 is an elevational view taken on the line 2-2 of Fig. 1; and

Fig. 3 is a perspective view of a printer incorporating the print head assembly of Fig. 1.

Best Mode for Carrying Out the Invention

Figs. 1 and 2 illustrate a side elevational view and a front elevational view, respectively, of the print head assembly in accordance with one embodiment of the invention. A pair of guide rails or shafts 20 and 22 carry a carriage 24 in transverse manner across a printer 26 of the type, as shown in Fig. 3. The printer 26 includes a journal station 28, a receipt station 30, and a slip station 32. The

journal station 28 is positioned on the right hand side of the printer 26 and the receipt station 30 and the slip station 32 occupy the left hand side of the printer 26.

The carriage 24 is of unitary construction and includes a pair of spaced bearings 34 and 36 at the rear part of the carriage 24. The carriage 24 has a single bearing 38 of U-shaped construction at the front, part. The details of the carriage 24 are more fully described in a co-pending PCT application, entitled "Printing Apparatus" and claiming priority from U.S. application 176,957 and assigned to the same assignee as the present application.

A print head 40 of the dot matrix type in a circular configuration (Fig. 2) is mounted on the carriage 24. The print head 40 includes a plurality of print wires (not shown) which are moved in back and forth manner by a plurality of actuating coils (also not shown) in printing operation. The print head 40 operates in a compact environment and generates an amount of heat that must be transferred or transmitted away from the print head 40 for efficient operation.

The means for transferring or dissipating heat from the print head 40 is effected with a heat sink, generally indicated by reference numeral 42. The die cast aluminum heat sink 42 generally covers and surrounds the actuating or rear portion 44 of the print head 40. The heat sink 42 includes a top plate portion 46, a right hand plate portion 48, and a left hand plate portion 50. The heat sink 42 is of unitary construction and includes ribs 52 on the exterior of plate portion 48 and ribs 54 on the exterior of plate portion 50.. The heat sink 42 also includes ribs 56 formed in an arcuate arrangement which bridges the side plate portion 48 and the top plate portion 46. Ribs 58 are formed in an arcuate arrangement and bridge the side plate portion 50 and the top plate

portion 46. The top plate portion 46 extends to the right of Fig. 1 and covers the nose portion 60 of the print head 40.

The heat sink 42 includes a pair of doglegs 62 and 64 at the right hand side thereof. A pivot pin 66 is secured to the doglegs 62, 64 to provide for swinging movement of the heat sink 42. The carriage 24 has a bearing 68 as an integral part at the right hand, side thereof and of a length occupying the space between, the doglegs 62 and 64. The bearing 68 and the pivot pin 66 ^" provide means for swinging the heat sink 42 from a position covering the print head 40 to a position wherein the print head is uncovered for the purpose of servicing the print head or for removal thereof.

A latch or clamp 70 is provided at the left hand side of the heat sink 42 to maintain the heat sink in position during printing operation. The carriage 24 has a pair of spaced bearings 72 as an integral part at the left hand side thereof, and the latch or clamp 70 is formed in wire bail manner and has ends 74 journaled in the bearings 72. The latch or clamp 70 is formed with a curved portion 76 to fit over a ledge 78 of the heat sink 42. The wire bail construction of the latch 70 provides for maintaining the heat sink 42 in a secure position by reason that as the heat sink 42 is started to be raised by an operator or other person from the operational mode position, the latch exerts an increased force on the ledge 78 to retain the parts in position.

An additional feature of the print head assembly is the provision of a knife mechanism 80 for use in receipt printing operation. The knife mechanism 80 includes a solenoid 82 coupled with a crank arm 84 that is journaled at pivot 86. A bifurcated arm 88, as an integral part of the crank arm 84, supports a knife blade 90 which is movable to

a cutting position for severing the receipt paper. A detailed description of the knife mechanism is found in Shipos et al. U.S. Pat. No. 4,525,088..

If the knife mechanism is not required in the printing operation, a modification of the print head assembly includes the carriage 24, the print head 40, and the heat sink 42. Fig. 3 illustrates the print head 40 and the swingable heat sink 42 but does not show the knife mechanism.

It is thus seen that herein shown and described is a print head assembly that includes a swingable heat dissipating element.