Vibrating Thermal Printing

This invention pertains to dot matrix type printing and, more particularly, to dot matrix type printers employing thermal print heads.

At present there are available thermal print heads which are used in dot matrix printing. These print heads comprise effectively miniature resistors which when fed a pulse of current generate enough heat to melt a portion of the ribbon opposite the element. The melted portion is transferred by contact to a record medium such as paper immediately opposite the ribbon. This type of head has several limitations. The main limitation is that the printing rate is slower than some other types of printers because of the thermal inertia. In order to enhance the print rate, people have generally applied very large current pulses to the resistors. However, the use of large current pulses introduces thermal and electrical shocks into the head structure, shortening its life.

It is a general object of the invention to provide an improved thermal printing.

Briefly, the invention contemplates selectively transferring, from a ribbon regions of pigmented thermoplastic material from a base onto a record medium by moving the ribbon past the record medium, selectively heating the desired regions to melt the thermoplastic material in these selected regions and locally vibrating the ribbon to shake off the melted thermoplastic material from such regions of the base.

It is another object of the invention to provide an improved print head.

Briefly, this further aspect of the invention contemplates a thermal/print device having a substrate of non-conductive material with an electrically resistive element fixed to the substrate. There are provided means for inducing the substrate to vibrate along with means for selectively passing electric current through the electrically resistive element.

According to another aspect of the invention, there is provided a print head having a plurality of print elements with each print element being a resistive ribbon printed on a nonconductive substrate. The substrate per se or an element coupled thereto is of piezoelectric material. There is applied to the piezoelectric material a continuously varying electric field to cause small amplitude vibrations in the substrate. Thus, when current is applied to the resistive material, heat is generated. The combination of the application of heat and the vibration should enhance the transfer of thermoplastic ink from the ribbon to the record medium.

Other objects, features and advantages of the invention, will be apparent from the following detailed description when read in conjunction with the accompanying drawing wherein:

FIG. 1 is a top view of a print head opposite a thermoplastic ribbon which presses against a record medium according to one embodiment of the invention;

FIG. 2 is a perspective view partially in schematic of the print head of FIG. 1; and

FIG. 3 is a top view of a print head and vibrating wedge element opposite a thermoplastic ribbon which is opposite a record medium in accordance with another embodiment of the invention.

In FIG. 1, there is shown a printer 2 whose face presses against a ribbon 4 of thermoplastic ink. The ribbon is of the solid ink transfer type having a base film opposite the print head 2, a peeling layer disposed on the base film and a non-wax type ink layer resisting on the peeling layer. The ribbon 4 also presses against a record medium 6 such as rough paper resting against a platen 7. In general, there is movement of the print head with respect to the ribbon 4 and the record medium 2, but there is no relative movement between the ribbon 4 and the record medium 2. The ribbon may be in a cassette having a supply reel, not shown, a supply pulley 8, a take-up pulley 10 and a take-up reel, not shown. It may be desirable to improve the rate of printing to pre-heat the ribbon. This can be accomplished by making the feed pulley 8 a heated pulley, i.e., by incorporating a heating element therein and supplying the heating element with current from a source 12. Then, as the pre-heated ribbon moves opposite the print head 2, the print head 2 will be energized to perform dot matrix type printing.

In FIG. 2 is shown a perspective view of a print head 2. In the embodiment of FIG. 2, the print head is shown including a substrate 14 having printed therein a plurality of resistive elements 16a, 16b and 16c. (It should be noted that the number of resistive elements is merely representative. It should also be noted that for the sake of clarity, the resistive elements are shown greatly out of scale. In fact, the elements are small enough so that they will merely print the equivalent of dots.) In any event, the elements 16 each have one end connected via a lead 18 to a heater current source 20 and another end grounded. The heater current source 20 can be a current source which is connected via switching means to each of the leads 18. The switching means can selectively connect any one of the leads to the current source. In this way, selective dots can be printed.

Furthermore, the substrate 14 is bonded to piezoelectric element 22. The piezoelectric element 22 has a substrate 22a of piezoelectric material such as barium titanate. Fixed to opposed faces of the substrate 22a are electrodes 22b and 22c. The electrodes are connected to a high-frequency voltage source 24. The source 24 operating through the electrodes 22b and 22c causes the lengthwise vibration in the piezoelectric substrate 22a. This vibration is carried over into the substrate 14 of the print element portion. Thus, the entire print head 22 is continuously vibrating with low amplitude and high frequency in the direction of the ribbon. Accordingly, when selective resistive elements 16 are heated, the combination of the heat and the vibration will facilitate the depositing of "dots" of ink from the ribbon onto the record medium 6.

In FIG. 3, there is shown a print head 32 whose face presses against the ribbon 34 of the thermoplastic ink opposite record medium 36 resting against the platen 37. The ribbon is the same as the ribbon 4 of FIG. 1.

The ribbon 34 may also be in a cassette having a supply reel, not shown, and a supply pulley 38, a take-up pulley 40 and a take-up reel, not shown. It may be desirable to improve the rate of printing to pre-heat the ribbon. This can be accomplished by making the feed pulley 38 a heated pulley, i.e., by incorporating a heating element therein and supplying the heating element with current from a source 42. Then, as the pre-heated ribbon moves opposite the print head 32, the print head 2 will be energized to perform dot matrix type printing.

The ribbon 34 after moving past the head 32 moves over vibrating wedge 44, a piezoelectric element energized to vibrate by source 48. Since vibration to shake off the molten ink is performed by wedge 44, the print head 32 can be a conventional thermal print head selectively energized by source 46 as in FIG. 1. In order to compensate for any heat loss in the ribbon on its travel to and over wedge 44, the wedge can be heated by energizing a resistive element thereon. In any event the peeling angle should be 45.degree. and 75.degree..

There has thus been shown an improved thermal printing which because of the vibration of the ribbon requires lower amplitude heating pulses into the respective resistance elements. Again, the use of pre-heating will further lower the amplitude of the current pulses and consequently raise the printer throughout and increase the life of the print head.

While only a limited number of embodiments have been shown and described in detail, there will now be obvious to those skilled in the art many modifications and variations satisfying many and all of the objects of the invention while not departing from the spirit thereof.

In particular, it is possible to make the entire substrate piezoelectric material to provide a unitary structure for the print head. It is also possible to use a different configuration of the piezoelectric such as piezoelectric bender.