Thermal Recording Print Head

This invention relates to a thermal recording print head which is used in various heat-sensitive recording systems as a printer, a facsimile or the like.

A conventional thermal recording print head is constructed as shown in FIG. 1. A process of driving such a print head is shown in FIG. 2. In FIG. 2, the horizontal axis represents time. In the operation of the FIG. 2 process, one printing line is divided into four blocks shown on the vertical axis. "Transferring and printing" appearing in FIG. 2 as "T" and "P" means that a time series signal from an external signal source is stored in a shift register or the like during the transfer, and upon completion of the storage, printing is carried out simultaneously. The external signal is transferred to the second block after the printing in the first block is completed. Printing is therefore carried out successively in such a fashion. For instance, in the case where a large part of a line is blank, printing can be carried out with one line as one block, and in this case, one line printing time is much shorter. However, since sheet feeding time is always included for a line to determine total printing time, as can be appreciated from FIG. 3, the sheet feeding time cannot be reduced by itself. Therefore, the sheet feeding time is an obstruction tending to reduce a high speed printing operation.

The reason why printing is carried out twice is that the electric source lines are separated into a group of odd-number lines and a group of even-number lines. For instance, in order to cause the shaded part of the heat generating resistor unit in FIG. 8 to generate heat, the signal line 2 and the electric source lines 1 and 1' are selected. If, in this case, the line 2' is selected, the part indicated by the arrow also generates heat. That is, printing is achieved as required by selecting every other power source line with respect to a particular signal line.

Accordingly, an object of this invention is to provide a thermal recording print head in which the above-described drawbacks accompanying a conventional thermal recording print head are eliminated.

Another object of the invention is to provide a thermal recording print head in which heat generating elements are arranged in two lines, to reduce the sheet feeding time to a time that is shorter than that in a conventional thermal recording print head.

The foregoing objects of the invention have been achieved by the provision of a thermal recording print head using a heat generating resistor unit made up of elements arranged adjacent to one another. In accordance with the invention, the heat generating resistor units are arranged in a plurality of lines in the auxiliary scanning direction.

FIG. 1 is a perspective view showing one example of a conventional thermal recording print head;

FIG. 2 is a diagram showing one example of a process of driving the print head in FIG. 1;

FIG. 3 is a diagram showing another example of the driving process of FIG. 1;

FIG. 4 is a plan view of a thermal recording print head forming one embodiment of this invention;

FIG. 5 is a diagram showing one example of a process of driving the print head in FIG. 4;

FIG. 6 is a plan view of a thermal recording print head forming a second embodiment of the invention;

FIG. 7 is a diagram showing one example of a process of driving the print head in FIG. 6; and

FIG. 8 is a diagram showing electric source lines and signal lines in a thermal recording print head.

The invention will be described with reference to its preferred embodiments.

FIG. 4 is a plan view of a print head forming one embodiment of this invention. In FIG. 4, reference characters 2-1 and 2-2 designate heat generating resistor units arranged in two lines. Each of the units is made of a plurality of heat generating elements disposed adjacent to one another. The heat generating resistor units extend in parallel with the auxiliary scanning direction of the print head. Current is applied through individual signal lines 3-1, 3-2, et seq. and common signal lines 5-1, 5-2, et seq. to the heat generating resistor unit 2-1 to heat this unit. Similarly, current is applied through individual signal lines 4-1, 4-2, et seq. and the common signal lines 5-1, 5-2, et seq. to the heat generating resistor unit 2-2 to heat this unit.

In this case, the relation between the sheet feeding time and the printing time is indicated in FIG. 5. As shown, the printing operation is carried out with one line forming one block. In this embodiment, two lines can be printed every sheet feeding operation. Accordingly, the sheet feeding time is only one-half (1/2) of that with the conventional print head in which one heat generating resistor unit is employed; that is, printing can be achieved at higher speed.

In this embodiment, the common signal lines 5-1, 5-2, 5-3, et seq. extend alternately in the opposite directions on both sides of the heat generating resistor unit, with the connection to an external circuit therefore taken into account. However, it is apparent that the common signal lines can extend solely in one direction if the external circuit is suitably arranged. Furthermore, if the electric source has a sufficiently large capacity, the first and second lines may be printed simultaneously depending on the design of the external circuit. In this case, the printing time is further reduced.

FIG. 6 is a plan view of a printing head showing the second embodiment of the invention. In FIG. 6, reference characters 10-1, 10-2, et seq. designate heat generating resistor units made up of heat generating elements.

The "odd" numbered heat generating resistors 10-1, 10-3, 10-5, et seq. are arranged in one line, while the "even" numbered heating generating resistor units 10-2, 10-4, 10-6, et seq. are arranged also in one line, separate from the first line. Current is applied through individual signal lines 7-1, 7-2, 7-3, et seq. and a common signal line 9 to selective heat generating resistor units 10-1, 10-3, 10-5, et seq. in the first group to heat those units. Similarly, current is applied through individual signal lines 8-1, 8-2, 8-3, et seq. and the common signal line 9 to selective heat generating resistor units 10-2, 10-4, 10-6, et seq. in the second group to heat those units. In the second embodiment, the relation between the sheet feeding time and the printing time is indicated in FIG. 7.

In this embodiment, the rate of the sheet feeding time with respect to one line printing time is longer than the printing time, and therefore the superiority of the embodiment to the conventional system is further increased. Also, in this embodiment, the first and second lines can be printed simultaneously as described before.

In the above-described embodiments, the distance between two lines of heat generating resistor units should coincide with the auxiliary scanning density. However, it may be set to twice the auxiliary scanning density if the external circuit is suitably designed. In this case, printing is carried out in the order of the first line and the third line, the second line and the fourth line, and so forth.

In the above-described embodiments, the heat generating resistor units are arranged in two lines; however, the invention is not limited thereto or thereby. Theoretically, the heat generating resistor units can be arranged in more than two lines. In this case, problems with the heat generating resistor units being partially short-circuited or individual signal lines short-circuited because the heat generating resistors units are arranged adjacent to one another, can be eliminated.

Other modifications of this invention may be practiced without departing from the scope thereof.