JP2001205839A - Thermal head drive controller and controlling method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal head drive controller for ensuring recording with uniform density at all times regardless of variation in the number of heating elements by making the voltage being applied to a thermal head constant regardless of the number of heating elements. SOLUTION: The thermal head drive controller comprises a control section 19 for connecting a dummy load 17 being driven upon start of conduction control to regulate the quantity of current flowing through a thermal head 11, and a dummy load drive circuit 18 in parallel with the thermal head 11 and a thermal head drive circuit 12, detecting the number of heating elements to be conducted based on record information and controlling conduction of the dummy load 17 such that a constant voltage is applied to the thermal head 11 at all times depending on the number of heating elements.

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head drive control device and a thermal head drive control method, and more particularly to a thermal head drive control device and a thermal head drive control device in which a thermal head and a thermal head drive circuit are connected to a power supply via wiring. The present invention relates to a head drive control method.

2. Description of the Related Art Conventionally, in a thermal printer which performs a desired thermal transfer recording on recording paper by a thermal head having a plurality of heating elements formed thereon, a selective energization control is performed for each heating element of the thermal head. Therefore, a thermal head drive control device for driving the thermal head has been used. As shown in FIG. 3, the thermal head drive control device 1 has a thermal head 2 in which a plurality of heating elements (not shown) are formed in parallel.
The thermal head 2 is connected in series with a thermal head drive circuit 3 that drives the thermal head 2 by selectively energizing each heating element of the thermal head 2. The thermal head drive circuit 3 includes a control unit 4 for controlling the thermal head drive circuit 3.
Is connected. The thermal head 2 and the thermal head drive circuit 3 are connected to wirings 5 and 5, respectively.
6 is connected to a bipolar terminal of a power source 7. When the energization control of the thermal head 2 is performed by using the thermal head drive control device 1, only the heating elements that the thermal head drive circuit 3 generates heat are connected to the power supply 7 by a command from the control unit 4. By letting
Selective energization control for each heating element is performed.

However, in the conventional thermal head controller 1, the voltage applied to the thermal head 2 fluctuates depending on the number of heating elements that generate heat. That is, as shown in FIG. 3, the voltage applied to the thermal head 2 and the thermal head drive circuit 3 (hereinafter, simply referred to as the voltage applied to the thermal head 2) is Vh [V], the power supply voltage is Vs [V], and the power supply 7 The voltage drop due to the wiring resistance between the head and the thermal head 2 is V11
[V], assuming that the voltage drop due to the wiring resistance between the thermal head drive circuit 3 and the power supply 7 is V12 [V], the following relationship is established between them: Vs = Vh + V11 + V12. The current flowing through the closed circuit of FIG. 3 is I [A], the resistance of the thermal head 2 is Rhon [Ω],
The wiring resistance between the power supply 7 and the thermal head 2 is set to R11.
[Ω], assuming that the wiring resistance between the thermal head drive circuit 3 and the power supply 7 is R12 [Ω], Vs = I × (Rhon + R11 + R12) Formula (2) is established. Here, the resistance Rhon of the thermal head 2 is
Is a combined resistance of the heating elements connected in parallel with each other in an energized state, so that the resistance Rhon is inversely proportional to the number of heating elements that generate heat as shown in FIG. Further, the wiring resistances R11 and R12 vary depending on the heating element that generates heat.
hon is so small that it can be ignored. Therefore,
The resistance Rhon of the thermal head 2 varies with the number of heating elements that generate heat, and accordingly, the voltage Vh applied to the thermal head 2 also varies. Since the voltage Vh applied to the thermal head 2 affects the print density, print density unevenness occurs due to the difference in the number of heating elements that generate heat depending on each recording portion of the recording paper. As a means for solving such a problem, there is a method of applying a voltage corresponding to a change in the resistance Rhon of the thermal head 2 to the power supply voltage Vs. In such a method, as shown in FIG. Since a fixed delay time occurs between the output of the command to perform the operation and the voltage reaching the predetermined voltage value, the responsiveness is lacking. Further, for example, in a state where the current variable device for changing the current flowing through the thermal head is connected in parallel with the thermal head, the total current flowing through the thermal head is detected first, It is also conceivable to keep the voltage of the thermal head constant by controlling the energization of the current variable device according to the total current. However, even in such a case, a delay time for detecting the total current and a delay time from the detection of the total current to the driving of the current variable device occur. For this reason, energization of the thermal head with a predetermined amount of current and energization control of the current variable device with a control amount corresponding to the energization of the predetermined amount of current cannot be performed simultaneously. Therefore, even in such a case, the voltage of the thermal head cannot be made exactly constant. Further, conventionally, the current I flowing in the closed circuit has changed due to the change in the resistance Rhon of the thermal head 2, but the power supply voltage Vs changes with the change in the current I, and the power supply voltage Vs Recovery required a certain recovery time as shown in FIG. For this reason, there has been a problem that it is not possible to perform uniform recording with the thermal head 2 without affecting the power supply voltage Vs. SUMMARY OF THE INVENTION The present invention has been made in view of such a problem, and by always keeping a voltage applied to a thermal head constant irrespective of the number of heating elements that generate heat, the thermal head can be controlled regardless of the variation in the number of heating elements that generate heat. Accordingly, it is an object of the present invention to provide a thermal head drive control device that can always perform uniform density recording.

In order to achieve the above object, a thermal head drive control device according to the present invention is characterized in that it can be driven by energization control and can adjust the amount of current flowing through the thermal head. Dummy load,
A dummy load drive circuit for driving the dummy load is connected in parallel to the thermal head and the thermal head drive circuit, and the number of heating elements to be energized is detected based on recording information. And a control unit for controlling the energization of the dummy load so that the voltage applied to the thermal head is always constant. By adopting such a configuration, the energization control to the dummy load can be performed simultaneously with the energization control to the thermal head based on the recording information, so that the voltage applied to the thermal head is always a constant value. Accordingly, it is possible to always perform uniform density recording by the thermal head regardless of the number of heating elements that generate heat, and realize such uniform density recording even under high-speed driving. it can. Also, a feature of the thermal head drive control device according to the present invention is that the dummy load is formed by forming a plurality of resistance elements that can be selectively energized in parallel, and the control section of the dummy load includes the thermal load. It is configured to control the energization of the dummy load so that the combined resistance of the combined resistance of each heating element in the energized state of the head and the combined resistance of each resistance element in the energized state of the dummy load is always constant. It is in the point. And, by adopting such a configuration, the voltage applied to the thermal head can be always kept at a constant value with a simple configuration.
Irrespective of the number of heating elements for generating heat, recording with a uniform density can always be performed by the thermal head, and recording with such a uniform density can be realized even under high-speed driving. A feature of the thermal head drive control method according to the present invention is that a dummy load whose current amount flowing through the thermal head can be adjusted by energization control is connected in parallel to the thermal head, and heat is generated by turning on the thermal head based on recording information. The number of elements is counted, and in accordance with the number of heating elements, a control amount of the dummy load is calculated so that the voltage applied to the thermal head is always constant. The point is to do.
By adopting such a method, the energization control to the dummy load can be performed simultaneously with the energization control to the thermal head based on the recording information, so that the voltage applied to the thermal head is always set to a constant value. Accordingly, it is possible to always perform uniform density recording by the thermal head regardless of the number of heating elements that generate heat, and realize such uniform density recording even under high-speed driving. it can.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a thermal head drive control device according to the present invention will be described below with reference to FIG.
FIG. 1 shows an embodiment of a thermal head drive control device 10 according to the present invention. The thermal head drive control device 10 has a thermal head 11 in which a plurality of heating elements (not shown) are formed in parallel. I have. A thermal head drive circuit 12 that drives the thermal head 11 by selectively turning on each heating element of the thermal head 11 by, for example, ON / OFF of a switching transistor is connected to the thermal head 11 in series. ing. The heating elements that are turned on by the thermal head drive circuit 12 are connected in parallel with each other. Therefore, assuming that the resistance of each heating element in the energized state is Rh [Ω], the resistance Rhon [Ω] of the thermal head 11 can be expressed as 1 / Rhon = Σ (1 / Rh) by using a general formula of a combined resistance in parallel. ). And the thermal head 1
1 and the thermal head drive circuit 12 are connected to bipolar terminals of a power supply 15 via wirings 13 and 14, respectively. Further, the thermal head drive control device 10 according to the present embodiment has a dummy load 17 that can be driven by energization control and that can adjust the amount of current flowing through the thermal head 11. This dummy load may be, for example, a plurality of resistance elements 20 formed in parallel, or a transistor. In this embodiment, the dummy load has a configuration in which a plurality of resistance elements 20 are formed in parallel. In this case, the current flowing through the thermal head 11 can be adjusted by selectively turning on the resistance elements 20. The dummy load 17 is connected in series with a dummy load driving circuit 18 that drives the dummy load 17 by selectively turning on each of the resistance elements 20 by, for example, ON / OFF of a switching transistor. The resistance elements 20 that are turned on by the dummy load drive circuit 18 are connected to each other in parallel. For this reason,
Assuming that the resistance of each resistance element 20 in the energized state is Rd, the resistance Rdon of the dummy load can be obtained from the relationship of 1 / Rdon = Σ (1 / Rd), similarly to the resistance Rhon of the thermal head 11. The dummy load 17 and the dummy load driving circuit 18 are connected in parallel to the thermal head 11 and the thermal head driving circuit 12 connected in series to the thermal head 11. The thermal head drive circuit 12 and the dummy load drive circuit 18 are connected to a control unit 19 that controls these drive circuits 12 and 18. The control unit 19 outputs to the thermal head drive circuit 12 a command to selectively generate heat in the heating element of the thermal head 11 based on the recording information. In response to a command from the unit 19, the heating element is selectively energized. Further, the control unit 19 includes:
For example, the number of heating elements to be energized is detected based on recording information input from a host device such as a host computer. In accordance with the detected number of heating elements, a control amount of the dummy load 17 is calculated so that the voltage applied to the thermal head 11 is always constant. Further, the energization control of the dummy load 17 is performed according to the control amount.
The control unit 19 may have, for example, a CPU or a circuit such as an ASIC. As an example of controlling the energization of the dummy load 17 to keep the voltage applied to the thermal head 11 constant, the control unit 19 determines that the combined resistance of the resistance Rhon of the thermal head 11 and the resistance Rdon of the dummy load 17 is The dummy load driving circuit 18 is instructed to drive the dummy load 17 so as to be always constant.
In this case, the resistance Rdon of the dummy load 17 that satisfies the condition that the combined resistance with the resistance Rhon of the thermal head 11 becomes a constant value may be used as the control amount of the dummy load 17. Here, if the combined resistance of Rhon and Rdon is expressed as Rhon + Rdon for convenience, the power supply voltage Vs can be expressed as follows: Vs = I × (Rhon + Rdon + R11 + R12) (3) Here, Rl1 and Rl2 are
Since the resistance is caused by the wires 13 and 14 as in the related art, the resistance varies depending on the heat generating element that generates heat. Therefore, if the combined resistance Rhon + Rdon of the resistance Rhon of the thermal head 11 and the resistance Rdon of the dummy load 17 is always constant, the power supply voltage Vs is constant, and accordingly, the value of Vh is also constant from Equation (1). become. Therefore, the voltage Vh applied to the thermal head 11 is always controlled to be constant irrespective of the number of heating elements that generate heat. In addition, since the energization control for driving the heat generation of the thermal head 11 and the energization control of the dummy load 17 can be performed simultaneously, for example, high-speed recording or a pause period so as not to exceed the upper limit of the head temperature. Even when performing so-called high-speed driving such as provided recording,
The voltage applied to the head can always be kept constant. In addition,
Each resistance element 20 of the dummy load 17 may be variously changed as needed. For example, when the number of the resistance elements 20 of the dummy load 17 is x and the total number of the heating elements of the thermal head 11 is n, the resistance Rdx of each resistance element 20 is R
It may be as dx = nRh / 2 ^x. In this case, for example, x
If = 8 and can control the resistance Rdon dummy load 17 with NRH / 2 ⁸ units. The resistance Rd of all the resistance elements 20 is not limited to this, and Rd = nRh /
It may be x. In this case, for example, if x = 8, then n
Rdon can be controlled in Rh / 8 units. Next, an embodiment of a thermal head drive control method according to the present invention to which the thermal head drive control device 10 is applied will be described with reference to FIG. In this embodiment, the energization control of the dummy load 17 is performed so that the combined resistance of the resistance Rhon of the thermal head 11 and the resistance Rdon of the dummy load 17 becomes a constant value C [Ω]. First, as shown in step 1 of FIG. 2, the control unit 19 detects the number of heating elements to be driven for heating, that is, to be energized, based on recording information input from a higher-level device. Then, proceeding to step 2, the control unit 19 calculates a control amount of the dummy load 17 corresponding to the detected number of heating elements. As an example of the calculation of the control amount, first, in step 3, the combined resistance of the heating elements in the energized state, that is, the resistance Rhon of the thermal head 11,
Is calculated. This resistance Rhon is 1 / Rhon = Σ
It can be calculated from the relationship (1 / Rh). next,
In step 4, the resistance R of the thermal head 11
By subtracting hon from the constant value C, the resistance Rdon of the dummy load 17 as the control amount is calculated. Then, after the control amount is calculated, step 5
Then, the energization control of the dummy load 17 is performed according to the control amount. That is, a command for selectively energizing the resistance element 20 is output to the dummy load driving circuit 18 so that the combined resistance of the energized resistance element 20 becomes equal to the control amount Rdon calculated in step 4. . In addition, when the energization control of the dummy load 17 is performed, the energization control of the thermal head 11 and the energization control of the dummy load 17 are performed at the same time by energizing the heat generating element for causing the thermal head 11 to generate heat. .

Next, a description will be given of an embodiment showing specific numerical values in the above-described thermal head drive control method. In this embodiment, the resistance of each heating element of the thermal head 11 is Rh. Further, the total number n of the heating elements is eight. In this case, the relationship between the number of heating elements in the energized state and the combined resistance of these heating elements in the energized state, that is, the resistance Rhon of the thermal head 11, is expressed by the general formula of parallel combined resistance as follows. I have. Number of heating elements in energized state Resistance of thermal head Rhon 1 Rh 2 Rh / 2 3 Rh / 34 Rh / 45 Rh / 56 Rh / 67 Rh / 78 Rh / 8 In this embodiment, dummy The total number x of the resistive elements 20 of the load 17 is eight, and the resistance value of each resistive element 20Rdx is n / 2 ^× Rh. Here, since n = 8,
The resistance of each resistance element 20Rd1 to 8 is as follows. Further, in this embodiment, the driving control of the dummy load 17 is performed such that the combined resistance Rhon + Rdon of the resistance Rhon of the thermal head 11 and the resistance Rdon of the dummy load 17 always becomes a constant value Rh / 33. Under such conditions, first, the control unit 19 outputs a command to the thermal head drive circuit 12 to cause one heating element to generate heat based on the recording information.
At this time, the resistance Rhon of the thermal head 11 is the resistance Rh of one heating element. When a command is issued to the thermal head drive circuit 12, the control unit 19 sets the combined resistance Rhon + Rdon of the resistance Rhon of the thermal head 11 and the resistance Rdon of the dummy load 17 to Rh / 33 for the dummy load drive circuit 18. A power supply command to the resistance element 20 is output to satisfy the following condition. In this case, assuming that the combined resistance of the resistance element 20 is X, from the general formula of the combined resistance in parallel, 1 / Rh + 1 / X = 33 / Rh Formula (4) is established. From equation (4), X = Rh / 32. Therefore, when one heating element of the thermal head 11 is to be heated, the resistance element 2 is
Only 0Rd8 is turned on. Next, based on the new recording information, the control unit 19 outputs a command to the thermal head drive circuit 12 to cause the two heating elements to generate heat. The resistance Rh of the thermal head 11 at this time
on is the combined resistance Rh / 2 of the two heating elements connected in parallel with each other. When a command is issued to the thermal head drive circuit 12, the control unit 19 sends the resistance Rhon of the thermal head 11 to the dummy load drive circuit 18.
Resistance Rho of the resistance Rdon of the dummy load 17
It outputs an energization command to the resistance element 20 so that n + Rdon becomes Rh / 33. In this case, assuming that the combined resistance of the resistance element 20 is Y, from the general formula of the combined combined resistance, 2 / Rh + 1 / Y = 33 / Rh Expression (5) is established. From equation (5), Y = Rh / 31. In this case, if Rd3 to Rd7 are energized, these Rd
The combined resistance of the 3 to 7 resistance elements 20 is given by the general formula of the combined resistance in parallel: 1 / Rh + 2 / Rh + 4 / Rh + 8 / Rh + 16 / Rh = 31 / Rh The reciprocal of Expression (6), that is, Rh / 31 Becomes Therefore, when the two heating elements generate heat, the resistance elements 20Rd3 to 20Rd7 are turned on by the dummy load driving circuit 17. Furthermore, in the case of generating heat for three heating elements, the resistance elements 20 of Rd4 to Rd7 may be similarly turned on. Accordingly, the resistance Rhon of the thermal head 11 is independent of the number of heating elements that generate heat in the thermal head 11.
Resistance Rho of the resistance Rdon of the dummy load 17
n + Rdon can always be controlled to a constant value Rh / 33. For this reason, according to equation (3), the power supply voltage Vs can be kept constant regardless of the number of heating elements, and accordingly, according to equation (1), the voltage Vh applied to the thermal head 11 is always kept constant. Can be a value. Therefore, according to the present embodiment, since the energization control of the dummy load 17 can be performed based on the recording information, the energization control of the thermal head 11 and the energization control of the dummy load are simultaneously performed without any delay time. be able to. Thus, the voltage Vh applied to the thermal head 11 can be always kept constant without affecting the power supply voltage Vs irrespective of the number of heat-generating elements of the thermal head 11, and therefore, regardless of the number of heat-generating elements. The thermal head 11 can always perform good recording with uniform density. Further, good recording with uniform density can be realized even under high-speed driving.
Note that the present invention is not limited to the above-described embodiment, and can be variously modified as needed.

As described above, according to the thermal head drive control apparatus and the thermal head drive control method according to the present invention, recording with a uniform density is always performed by the thermal head regardless of the number of heat generating elements to generate heat. And recording with such a uniform density can be realized even under high-speed driving.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a thermal head drive control device according to the present invention.

FIG. 2 is a flowchart illustrating an embodiment of a thermal head drive control method according to the present invention.

FIG. 3 is a block diagram showing an embodiment of a conventional thermal head drive control device.

FIG. 4 is a graph showing a relationship between the number of heating elements to generate heat and the resistance of a thermal head.

FIG. 5 is a diagram showing a problem of a conventional thermal head drive control device.

FIG. 6 is a diagram showing a problem of a conventional thermal head drive control device different from FIG. 4;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Thermal head drive control device 11 Thermal head 12 Thermal head drive circuit 13, 14 Wiring 15 Power supply 17 Dummy load 18 Dummy load drive circuit 19 Control unit 20 Resistance element

Claims (3)

[Claims] 1. A thermal head in which a plurality of heating elements are formed in parallel, and a thermal head driving circuit for driving the thermal head to generate heat by selectively turning on each heating element in the thermal head. connection,
A thermal head drive control device, wherein a control unit for controlling the thermal head drive circuit is connected to the thermal head drive circuit, and the thermal head and the thermal head drive circuit are respectively connected to bipolar terminals of a power supply via wires. A dummy load capable of being driven in accordance with energization control and capable of adjusting the amount of current flowing through the thermal head, and a dummy load driving circuit for driving the dummy load, the thermal head and the thermal head Connected in parallel to the drive circuit, the number of heating elements to be energized is detected based on the recorded information, and the voltage applied to the thermal head is always constant in accordance with the number of heating elements. A thermal head drive control comprising a control unit for controlling the energization of the dummy load. apparatus. 2. The dummy load includes a plurality of resistance elements selectively energizable, which are formed in parallel, and a control unit of the dummy load combines a plurality of heating elements in an energized state of the thermal head. 2. The dummy load energization control is performed so that a combined resistance of a resistance and a combined resistance of each resistance element in the dummy load energized state is always constant. The thermal head drive control device according to the above. 3. A thermal head drive control method for driving a thermal head by generating heat by selectively turning on each of the heat generating elements of a thermal head in which a plurality of heat generating elements are formed in parallel. A dummy load, which can be driven together with the thermal head and is capable of adjusting the amount of current flowing through the thermal head, is connected in parallel to the thermal head, and the number of heating elements to be energized is detected based on the recorded information. A thermal head, wherein a control amount of a dummy load is calculated such that a voltage applied to the thermal head is always constant according to the number of the generated heating elements, and energization control of the dummy load is performed according to the control amount. Drive control method.