JPS62196161A - Driving circuit for thermal recording head - Google Patents

Abstract

PURPOSE:To prevent nonuniformity in recorded density from being generated at an end of a resistor element group, by driving a group of resistor elements in each block on a time sharing basis, and constantly preheating the resistor elements located at ends of the resistor element group of each block independently of the time-sharing driving. CONSTITUTION:In a switching circuit group D1 supplied with a strobe signal ST1, a switching circuit Ti corresponding to recording data set in a register RG1 is turned ON, and an electric current is passed to a resistor element Ri, whereby heat is generated. At this time, resistor elements R11, R1n having resistors R0 connected in parallel with switching circuits T11, T1n, respectively, are supplied with an electric current through the resistors R0 even when the circuits T11, T1n are tuned OFF. Accordingly, the resistor elements R11, R1n located at ends of a resistor element group 1B, the temperatures of which become lower than those of other resistor elements under a uniform input power condition, are preheated even when the switching circuits T11, T1n are in the OFF state, so that recorded density can be prevented from being lowered at the ends of the resistor element group B1 (namely, at the boundary between adjacent resistor element groups).

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a drive circuit for a thermal recording head that drives a plurality of resistor element groups in a time division manner.

[Conventional technology]

Conventionally, in a thermal recording head, a plurality of resistor elements are divided into a plurality of blocks, and the resistor element groups in each block are driven in a time division manner, as described in Japanese Patent Application Laid-Open No. 55-87581. A drive circuit designed to reduce power consumption is used.

[Problem that the invention seeks to solve]

However, in conventional circuits, although power consumption can be reduced by time-divisionally driving the resistor elements, no consideration is given to the fact that time-divisionally driving causes recording density unevenness at the ends of the resistor elements. Because this was not done, there was a problem that uneven recording density occurred.

In other words, non-thermal images such as those produced by facsimiles are usually recorded in black and white binary format, and even if the continuously arranged resistor elements are divided into a plurality of resistor element groups and these are time-divisionally driven, recording is not possible. @Concentration unevenness was hardly a problem.

However, in recent years, mainly for color recording, there has been an increasing need for a halftone recording method that achieves high gradation recording by varying the amount of heat input to the resistor element. When divisional driving is performed, a problem arises in that the recording density at the ends of the resistor element group decreases. This decrease in density causes thin colored stripes on the recorded image, resulting in image deterioration and multi-P? Such stripes are particularly disliked in J-key records. It was confirmed that this decrease in recording density occurs because when the resistor element group is time-divisionally driven, heat radiation at the end of the resistor element group is large, and the temperature at the end of the resistor element group decreases. .

[Purpose of the invention]

The present invention has been made in view of the above-mentioned conventional problems, and an object thereof is to provide a drive circuit for a thermal recording head that can prevent uneven recording density from occurring at the ends of a group of resistive elements. There is a particular thing.

[Means for solving problems]

To achieve the above object, the present invention provides a drive circuit for a thermal recording head that divides a plurality of resistor elements into a plurality of blocks and drives the resistor elements of each block in a time-division manner. A drive circuit for a thermal recording head is provided with an energizing circuit that constantly preheats at least the resistor element located at the end of the resistor element group of each block among the body element groups.

[Effect]

The resistor element groups in each block are driven in a time-division manner, and the resistor elements located at the ends of the resistor element groups in each block are constantly preheated without being driven in a time-division manner.

[Embodiments of the invention]

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 shows the configuration of a preferred embodiment of the present invention. In FIG. 1, a plurality of resistor elements R11 to R3n
)'31. F12°Bn are switch circuit groups Di, D2. Connected to Dn,
Each switch-circuit group 01. D2゜Dn are each AND
Gate A11-A1n.

It is connected to registers RG1, RO2, and RGn via A21...A2n and A31...A3n. And each resistor element B1. B2. Bn resistor wires R11 to R3n are respectively connected to switch circuit groups D1 and D2.
．． Time-division driving is performed by signals from Dn. Note that since the resistor element groups Bl and B2°Bn each have the same configuration, only the configuration of the resistor element group B1 will be described below.

Each of the resistor elements R11 to R1n of the resistor element group B1 is a switch circuit Til...Tl consisting of a transistor.
It is connected to Tl, and the switch circuit Tll...Ti
It is designed to be driven by turning on and off n.

And each switch circuit Tll-T1. The control signal system of the switch circuit D1 is constituted by signals from AND gates All to Aln which take the logical product of the recording data set in the register RGt and the external signal STI. Among the resistor elements R1,1 to R1n, switch circuits TLI, T1 . A resistor RO is connected in parallel to n.

In the above configuration, in order to set recording data in register RGI, data is set in data number 43, and the data is shifted by clock signal CK. When the latch signal is input when the data has been shifted to a predetermined position, the recording data is set in the latch register, and the signal corresponding to the recording data is output from the AND gates All to
It is output to A 1 n. Thereafter, when the strobe signals STI to STn are sequentially time-divided and inputted in a predetermined order, the resistor element group B1 is time-divisionally driven accordingly. In the switching circuit group D1 to which the strobe signal STI is input, the switch circuit Ti corresponding to the recording data set in the register RGI is turned on, and current flows through the resistor element Ri, generating heat. At this time, switch circuit T:
Current flows through the resistor elements R11°R1n to which the resistor RO is connected in parallel to LL and Tin through the resistor RO even when the switch circuits T 11 and T1 n are off. Therefore, with the same input power, the resistor elements R11°R1n located at the ends of the resistor element group B1, which have a lower temperature, are preheated even when the switch circuits Tll and Tin are off, and the resistor elements It is possible to prevent a decrease in recording density between group B1.

It is desirable to set the amount of preheating to a value that minimizes recording density unevenness by adjusting the resistance value of the resistor RO.

In this way, in this embodiment, since the resistor elements R11 and R1,n located at the ends of the resistor element group B1 are always preheated, even if the resistor element group B1 is time-divisionally driven, the concentration remains constant. Recording with less unevenness becomes possible.

Note that when connecting the resistor RO in parallel to the switch circuits Tl and Tin, it can be formed on the same substrate at the same time as the process of forming the resistor elements R11 to R1n, or it can also be done by attaching the resistor outside the substrate. It is.

Furthermore, in the above embodiment, the resistor elements R1i and Run located at the ends of the resistor element group B1 are provided with the resistor RO as a current-carrying circuit, but depending on the density of the resistor elements and the recording conditions, further It is also possible to provide an RO as a current-carrying circuit for a plurality of resistor elements located at the ends.

〔Effect of the invention〕

As explained above, according to the present invention, an energizing circuit is provided that constantly preheats at least the resistor element located at the end of the resistor element group of each block among the resistor element groups of each block. By driving the resistor element group in a time-division manner, a drop in recording density at the end of the resistor element group is compensated for, and an excellent effect can be obtained in that recording density unevenness can be eliminated.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention.

Claims (1)

[Claims] 1. In a drive circuit for a thermal recording head that divides a plurality of resistor elements into a plurality of blocks and drives the resistor element groups in each block in a time-division manner, at least the resistance of each block among the resistor element groups in each block is 1. A drive circuit for a thermal recording head, characterized in that a current supply circuit is provided for constantly preheating a resistor element located at an end of a group of body elements.