JPS63173660A - Driving circuit for thermal head - Google Patents

Abstract

PURPOSE:To uniformize the heat generating temperature of all heat generating elements, by dividing M heat generating elements arranged in an array into N groups, grouping the same order ones of the elements in the groups into the same block to form N blocks, and sequentially driving the elements with each block as a unit. CONSTITUTION:Heat generating elements m1-m512 constituted of 512 dots arranged in an array in a thermal head 1 are made to correspond respectively to AND gates A1-A512, a shift register SR and a latch circuit LA by one bit. When first to fourth strobe signals ST1-ST4 are sequentially outputted from a driving-controlling circuit 2, the 512 heat generating elements m1-m512 are selectively energized according to recording data D, in the order a first block consisting of the elements m1; m5...m509; a second block consisting of the elements m2, m6...m510,...; a fourth block consisting of the elements m4, m8...m512. Thus, the heat generating temperature is uniformized for all of the heat generating elements, and favorable image quality can be obtained through removal of ununiformity of density.

Description

DETAILED DESCRIPTION OF THE INVENTION A) Industrial Application Field The present invention relates to a drive circuit for a thermal head in which a plurality of heating elements are arranged in a row.

(b) Conventional technology FIG. 3 shows a typical example of this type of thermal head.

For example, a heating element (ml) consisting of 512 dots ~ ("s
12) are arranged in a line at equal intervals. 512 AND gates (A1) to (As 12 ) are associated with each of these heating elements (ml) to (m512).

The shift register (SR) and the latch circuit M (LA) each consisting of 512 bits are divided into an ant game (A1
) to (As 12 ).

The 512-bit recording data D is serially input to the shift register (SR) in response to the clock signal CLK, and then transferred to the latch circuit (LA) in response to the latch signal.

First, second, third and fourth strobe signals ST. Therefore, when the first to fourth strobe signals ST1 to ST4 are sequentially output, 128 successive heat generating elements (m
l) ~ (mslz) latch circuit (LA) (D content 4
In response to C15, an energizing pulse is applied.

That is, the first to fourth strobe signals ST1 to ST4Δlock and the fourth block of elements (m3as) to Cm512) are divided into four blocks of 128 dots each and driven.

By performing divided driving in this manner, the supply source to the thermal head can be made smaller, and abnormal heat accumulation in the thermal head can be prevented.

(c) Problems to be Solved by the Invention By the way, when all black information is recorded in the direction in which the heat generating elements are arranged by the driving method as described above, the recording density at the boundary between the blocks is different from that at the other parts. It will be much lower than that of . This is because the heating elements located inside each block reach a high temperature because they are affected by heat generation from both sides in addition to their own heat generation, but the heating element at the end of each block (for example, This is thought to be because the heating cord (71tn) (ga 129), etc.) is only affected by heat generation from one neighbor, so the temperature is lower than that of the heating element located inside each block. .

In order to eliminate this drawback, according to Japanese Patent Application Laid-Open No. 60-132771, the length of the energizing pulse applied to the heating element at the boundary between each block is longer than that applied to other heating elements. However, this prevents the recording density from decreasing at the boundary between blocks as described above.

However, in such driving, a plurality of types of energizing pulses must be selectively used when recording a portion, which makes the driving circuit complicated.

2) Means for Solving the Problems The thermal head drive circuit according to the present invention has M heating elements of fnl, 012, . . . , ml arranged in a row (fnl, 1nH+1, n12)141
, In(1(-1+1)), (fn2.

”)l+2 m ””e −(M-11+2.))
I-e (ms + m2)11...' ttnm)
The present invention is characterized by comprising a thermal head which is divided into N blocks and wired together, and a drive control circuit which sequentially drives the thermal head for each of the blocks.

(E) Effect According to the present invention, since the M heating elements arranged in a row are driven in blocks so as to be in a discrete state, all the heating elements are influenced by other heating elements. Embodiment FIG. 1 is a block diagram showing an embodiment of the present invention. The heating elements (ml) to (m512) consisting of 512 dots provided on the thermal head (1) are arranged at equal intervals, and each of these heating elements (ml) to (ms12) has 512 ANDs. Gate (A1) ~ (A512)
are associated. Further, a shift register (SR) and a latch circuit (LA) each consisting of 512 bits are arranged in correspondence with each bit of AND gates (A1) to (A512).

First, second, third and fourth strobe signals ST1. ST2. Sr3 and Sr
1 controls 128 AND gates (A1) to (As1z) for every four dollars. Therefore, the first to fourth
When strobe signals STI to ST4 are sequentially output, 128 AND gates corresponding to each strobe signal are sequentially driven, and 512 dot heating elements (ml) to ("5
12) is the element (ml) w (ms) s''
? ) e...(m509) first block, element (ni2) e (m6) # ("10J,...+
(-51o) second block, element (rns) t
(my) + (m11...., 3rd block of (msll), element (m4) * ("a) * (m12)s
...Each 4th block of the 4th block of e(-s12)
It is divided into four blocks of 28 dots each and driven.

Note that the 512-bit recording data D is clock signal CL.
After being serially input to the shift register (SR) according to the signal K, the signal is transferred to the latch circuit (LA) by the latch signal.

FIG. 2 is a timing diagram showing the operation of one embodiment of the present invention.

First, recording data D consisting of 512 bits is written into the shift register (SR) based on the clock signal CLK. Thereafter, the data is transferred to the latch circuit (LA) by the latch signal.

The drive control circuit (2) then sequentially sends first, second, third and fourth strobe signals STI, ST2 . ST! i and S
Output r1. As a result, the 512 dot heating elements (ml) to ("512) are divided into first, second, third and fourth blocks of 128 dots every fourth and driven.

Note that the number of divisions of the heating element is not limited to the above embodiments, and can be determined arbitrarily.

(G) Effects of the Invention According to the present invention, a plurality of heating elements arranged in a line are divided into a plurality of blocks in a discrete state and driven.
The heat generation temperature of all the heating elements becomes uniform, and the occurrence of density unevenness can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a timing diagram explaining its operation, and FIG. 3 is a block diagram showing the configuration of a conventional thermal head. (11... Thermal spatula I', (ml) ~ (m512
)...heating element, (2)...drive control circuit.

Claims (1)

[Claims] (1) m_1, m_2, ..., m_M heating elements arranged in a row (m_1, m_N_+_1, m_2_N_+
_1, ..., m_(_M_-_N_+_1_))(m_2
, m_N_+_2, ..., m_(_M_-_N_+_2_
)), . Thermal head drive circuit.