Abstract:
A thermal head is provided with first and second sets of parallel bar-shaped electrodes which are arranged in slightly spaced parallel planes and cross over one another. Individual crossing resistors are selectively energized to produce a heat generating dot which may be reproduced on a heat sensitive media.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to thermal heads employed in recording apparatuses using heat-sensitive recording media, and more particularly to a thermal head of simple construction which can provide recording dots of a small size. 
     FIG. 1 is a diagramatic plan view showing one example of a conventional, ordinary thermal head. 
     In FIG. 1, reference characters 1a, 1b, 1c and so on designate a group of heat generating elements, and reference characters 2a, 2b, 2c and so on designate a group of lead electrodes connected to the respective heat generating elements in a manner such that they are on one side of the group of heat generating elements and are in parallel with one another. 
     In the thermal head thus constructed, current is applied to the lead electrodes 2a and 2b to allow the heat generating element 1a to record data, and current is applied to lead electrodes 2b and 2c to cause the heat generating element 1b to record data, etc. 
     FIG. 2 is a diagramatic plan view of another example of a conventional thermal head. 
     In FIG. 2, reference characters 3a, 3b, 3c and so forth designate a group of heat generating elements, and reference characters 4a, 4b, 4c and so forth designate a group of lead electrodes connected to the respective heat generating elements in a manner such that they are alternately arranged on either side of the group of heat generating elements 3a, 3b, 3c, and are in parallel with one another. 
     In the thermal head thus constructed, in order to cause the heat generating element 3a to record data, current is applied to the lead electrodes 4a and 4b; and similarly, in order to cause the heat generating element 3b to record data, current is applied to lead electrodes 4b and 4c. 
     The above-described conventional thermal heads suffer from drawbacks in that it is rather difficult to arrange the heat generating elements in matrix form because the construction thereof becomes intricate, and accordingly it is also difficult to decrease the size of the recording dots. 
     SUMMARY OF THE INVENTION 
     An object of this invention is to provide a thermal head in which the above-described difficulties accompanying the conventional thermal head have been eliminated, whereby the construction is made simple and the size of recording dots can be made small. 
     The foregoing object and other objects of the invention have been achieved by the provision of a thermal head which, according to the invention, comprises: first bar-shaped heat generating resistors arranged in a first plane in a manner such that they are substantially parallel to one another; and second bar-shaped heat generating resistors arranged in a second plane in parallel with the first plane in a manner such that they are substantially parallel to one another, the first bar-shaped.heat generating resistors crossing the second bar-shaped heat generating resistors to provide heat generating dots at the crossing points. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 and 2 are diagramatic plan views showing heat generating elements of conventional thermal heads; 
     FIG. 3 is an explanatory diagram showing the positional relationship of heat generating elements and the electrical connection of the same in a thermal head according to a first embodiment of the invention; 
     FIG. 4 is a diagramatic sectional view of the thermal head of FIG. 3; 
     FIG. 5 is an explanatory diagram showing the arrangement and the electrical connection of heat generating elements in a thermal head according to a second embodiment of the invention; and 
     FIG. 6 is an explanatory diagram showing an oblique line recorded with the thermal head of FIG. 5. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIGS. 3 and 4, reference numeral 5 designates an insulating substrate; 6a through 6d, lower bar-shaped heat generating resistors arranged on the insulating substrate 5 in a manner such that they are substantially parallel to one another; and 7, a wear-resisting layer formed so as to cover the insulating substrate 5 and the lower bar-shaped heat generating resistors 6a through 6d. 
     Further in FIGS. 3 and 4, reference characters 8a, 8b, 8c and so on designate upper bar-shaped heat generating resistors arranged substantially parallel to one another within the wear-resisting layer 7, i.e., in a plane substantially parallel to the plane of the lower bar-shaped heat generating resistors 6a through 6d. The resistors 8a, 8b . . . are disposed such that they cross over the heat generating resistors 6a through 6d, creating points of intersection in the plan view of FIG. 3. 
     Further in FIGS. 3 and 4, reference characters 9a, 9b, 9c . . . , 10a, 10b, . . . , 11a, 11b, . . . and 12a, 12b, . . . designate the noted crossing points of the upper bar-shaped heat generating resistors 6a through 6d and lower bar-shaped heat generating resistors 8a, 8b and so on, respectively, namely, heat generating dots. 
     Switches are connected to the lower bar-shaped heat generating resistors 6a through 6d so that the latter may be energized successively in agreement with the conveyance of a recording sheet, and switches are connected to the upper bar-shaped heat generating resistors 8a, 8b, 8c and so on so that current may be applied to the latter according to an input video signal. 
     The data recording operation of the thermal head thus constructed will now be described. 
     In the case of recording data using the heat generating dots 9a, 9b, . . . of the first line, current is applied to the lower bar-shaped heat generating resistor 6a, and the upper bar-shaped heat generating resistors 8a, 8b, . . . are selectively energized according to the input video signal. 
     The crossing points (or the heat generating dots) of the upper and lower bar-shaped heat generating resistors 8a, 8b, . . . and 6a through 6d, where the upper bar-shaped heat generating resistors are selectively energized are heated to a higher temperature which permits thermal recording, because the heat generated by two (e.g. 6a, 8a; 6a, 8b, etc.) bar-shaped heat generating resistors is added. However, those portions of the thermal head where no such crossing point exists, or where two quantities of heat are not so added together, are not heated to such a high temperature, and thus do not affect the recording. 
     In recording data with the heat generating dots 10a, 10b, . . . of the second line, current is applied to the lower bar-shaped heat generating resistor 6b, while the upper bar-shaped heat generating resistors 8a, 8b . . . are selectively energized according to the input video signal. 
     In recording data using the heat generating dots 11a, 11b, . . . of the third line or with the heat generating dots 12a, 12b, . . . of the fourth line, the procedure is similar to that employed in recording data with the dots of the first or second lines. 
     The size of the dots thus recorded depends on the width of the upper and lower bar-shaped heat generating resistors. Accordingly, recorded dots of small size can be obtained by merely reducing the width of the resistors. 
     In experiments performed by the inventors, the insulating substrate 5 was made of alumina, and the upper and lower bar-shaped heat generating resistors 8a, 8b, . . . and 6a through 6d were made of ruthenium oxide. In addition, the wear-resisting layer was made of a hard (lead) glass, and gold electrodes were employed. 
     With the thermal head as described above, a recording operation was carried out in the above-described manner. As a result, an image of small dot size and high resolution was recorded. 
     FIG. 5 is a diagram showing the positional relationship between the heat generating resistors and the electrical connection of the same according to a second embodiment of the invention. In FIG. 5, reference numeral 5 designates an insulating substrate; 13a and 13b, the lower bar-shaped heat generating resistors, which are arranged substantially parallel to each other on the insulating substrate 5; and 14a, 14b, and so on, the upper bar-shaped heat generating resistors, which are arranged so as to be substantially parallel to one another and oblique to the lower bar-shaped heat generating resistors 13a and 13b. The heat generating dots 15a, 15b, . . . and 16a, 16b, . . . are shifted by 1/2 pitch with respect to one another from one line to the next. 
     With the thermal head as described above, an oblique line can easily be recorded as follows: Current is applied to the lower bar-shaped heat generating resistor 13a and the upper bar-shaped heat generating resistor 14a, to allow the heat generating dot 15a to generate heat; and current is then applied to the lower bar-shaped heat generating resistor 13b and the upper bar-shaped heat generating resistor 14b, to allow the heat generating dot 16b to generate heat, etc. 
     In the second embodiment described above, the upper bar-shaped heat generating resistors 14a, 14b, . . . and the lower bar-shaped heat generating resistors 13a and 13b are arranged in a manner such that the former and the latter cross each other and are oblique to each other, and the heat generating dots are successively shifted 1/2 pitch in the main scanning direction. Accordingly, an oblique line of excellent quality, and relatively smooth, as shown in FIG. 6, can be recorded. 
     As is apparent from the above description, the thermal head of the invention is designed such that the first bar-shaped heat generating resistors are arranged in a first plane in a manner so as to be substantially parallel to one another, while the second bar-shaped heat generating resistors are arranged in a second plane, which is parallel to the first plane, in a parallel manner, the first bar-shaped heat generating resistors crossing the second bar-shaped heat generating resistors to form heat generating dots at the crossing points. Therefore, the thermal head of the invention is advantageous in that it is simple in construction, and can record dots of small size.