JPS5922966B2 - Temperature control device and recording pen using it - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to a heating element that is directly energized and generates heat using Joule heat, and the operating temperature of the heating element is always maintained at a predetermined level by controlling the current supplied to the heating element. The present invention relates to a temperature control device that sets the temperature at a temperature of

A metal resistor commonly used as this type of heating element,
Alternatively, the resistance value of a semiconductor changes with temperature changes. It is known that metal resistors generally have positive temperature characteristics, and some semiconductors have negative temperature characteristics. On the other hand, even if the current to the heating element is kept constant or the electric power is constant due to differences in heat dissipation characteristics depending on the usage conditions, usage mode, surrounding conditions, etc. of the heating element, that is, the thermal equilibrium conditions, the heating element This means that the operating temperature cannot be set to the desired temperature as designed.

Various types of temperature control devices have been proposed to prevent such temperature fluctuations.

For example, a temperature detection element such as a thermistor may be thermally coupled to the heating element to control the amount of current to the heating element, or a bridge circuit including the heating element may be configured to resist the resistance of the heating element. There is a temperature control device that uses a method such as controlling the power source of a heating element by outputting an unbalanced voltage caused by a change in temperature. However, when providing a temperature detection element thermally coupled to a heating element, the sensitivity depends on the degree of coupling, so there are considerable problems with the method of coupling, and when the heating element is high temperature. In this case, the problem of heat resistance of the detection element arises. Furthermore, if the heating element is a heating element used in a recording pen in a thermal recorder, adding such a detection element to the heating element and therefore to the recording pen will increase the mechanical load on the recording pen. This results in a disadvantage that the responsiveness of the recording pen to the recording paper decreases. Further, in the bridge circuit configuration, each resistance element constituting the bridge circuit must be selected to have a resistance value that is approximately equal to the resistance value of the heating element, which has the disadvantage that power loss is large. The present invention provides a temperature control device free from such drawbacks and a recording pen using the same. First, before explaining the present invention in detail,
In order to facilitate understanding of invention C, the basic idea, also called the principle, of the invention will be explained. Now, the first
As shown in the figure, consider a circuit in which a power source E is connected in series with a heating element 1 having a positive temperature coefficient and a negative resistance -R.
In this circuit, if RT is the resistance of the heating element 1 2 at a certain temperature, the power supply voltage E is a constant voltage, and IO is the circuit current, then the following holds true.

Then, the thermal resistance representing the heat dissipation state of the heating element 1 is β(℃/W
), and if the power consumed by the heating element 1 is P(VV), it becomes \BVlbυノ, and the equilibrium temperature T of the heating element 1 is T=β・P...
...(3).

Now, let us consider the conditions under which the temperature T of the heating element 1 does not change and remains constant even if β changes due to a change in the heat dissipation state of the heating element 1. Here, since T, P, IO and RT are functions of β, and 10 and RT are T(7) functions, (1),
Equations (2) and (3) can be expanded as follows.

First, from equation (3), in Figure 1, negative resistance -R
If the one-way current when there is no current is IO', then 1V1.If the change in the temperature DT degree T of the heating element 1 with respect to the change in the thermal resistance β at this time is (-y), it becomes Aρ from the AD equation.

In other words, what this formula (self) means is that in Figure 1, the circuit current 10 when there is a negative resistance -R is changed to the circuit current 10'6 when there is no negative resistance -R. Sexual resistance-R
If we reduce the power supply voltage E and set it to the same circuit current 1, then at this set current 1, the same heating element and the same β condition when there is -R and when there is no -R. Which shows the ratio of the temperature change to β with respect to RT+R, which circuit has a negative resistance -R? It is shown that the temperature change with respect to β becomes smaller based on the RT-R ratio.

Next, in equation (self), considering the limit state when R is brought close to RT under the restriction that the equal circuit currents of both are finite values, in this case E in Fig. 1 becomes ( DRT cannot be obtained if E approaches O while observing the conditions of formula (a).
The other β, 1 and RT are finite values. DTdT
Since dT, it is understood that 1/(1)' approaches O, and dβ
dβ Yo.

That is, it can be seen that the change in temperature T with respect to the thermal resistance β of the heating element 1 when there is negative resistance -R is closer to 0 than when there is no negative resistance -R. The above is true when the temperature coefficient α is a positive finite value when the resistance value RT of the heating element 1 is expressed as RT=RO(1+αT).

If this temperature coefficient α is exactly 0, then the equation Y of A5)
is O and DTdT' -/(-) is 1, and even if there is an effect of the negative resistance -R dβ dβ, the temperature change of the heating element 1 with respect to β cannot be made small.

In other words, it can be seen from equation 05) that the larger the positive value of the temperature coefficient α, the greater the effect. To summarize the above conclusions, in Figure 1, negative resistance -
When setting the resistance value R of R to a value close to the resistance RT of the heating element 1 having a positive temperature coefficient α, the heat dissipation state β of the heating element 1
Regardless of the above, it can be said that the temperature of the heating element 1 can be set to a substantially constant desired temperature T.

The present invention has been made based on such a basic idea, and the configuration of the present invention will be explained next.

In the present invention, for example, as shown in the block diagram of FIG. an operating temperature setting electrical signal supplying means 3 for obtaining an operating temperature setting electrical signal for setting the operating temperature to a desired operating temperature under predetermined heat dissipation conditions; The above heating element 1
A current supply means 4 supplies current to the heating element 1, and detects a change in a signal based on the current flowing through the heating element 1 as the heat radiation condition changes from a predetermined heat radiation condition depending on the temperature coefficient of the heating element 1, and generates a heat radiation condition dependent electrical signal. thermal condition dependent electric signal detection means 5 that outputs
Then, the signal obtained from the detection means 5 is regulated to a predetermined magnitude and applied to the current supply means 4 so as to return the signal in the direction of positive feedback with respect to the direction of current flowing to the heating element 1, as seen from the heating element side. and positive feedback means for making the value of the negative resistance component formed in the circuit have an operating point close to the resistance value of the heating element.

This positive feedback means consists of a current supply means 4, a regulating circuit 6, and a combining circuit 7. The example shown in FIG. 2 is a case where the heating element 1 has a positive temperature coefficient. Although not shown, the recording pen incorporating the heating element 1 is configured to scan a temperature-sensitive recording paper according to a recording signal, and local heating by the recording pen 2 causes a scanning pattern of the pen 2 to be formed on the recording paper. For example, a visible image of a corresponding pattern is formed and recorded. As described above, the operating temperature setting electrical signal supplying means 3 is constituted by, for example, a DC power supply E that obtains a signal voltage E for setting the heating element 1 to a desired operating temperature under predetermined heat dissipation conditions.

The current supply means 4 is composed of an amplifier having an amplification degree A, for example.

The detection means 5 may be constituted by a resistor RD having a resistance value sufficiently lower than the resistance value of the heating element 1, for example.

In the illustrated example, the means 3, i.e. the combining circuit 7 is connected across the power supply E.
A series circuit including an amplifier 4, a resistor 5, and a heating element 1 is connected. The positive feedback means [4, 6, 7] are, for example, output voltage positive feedback amplifiers 6a having amplification factors of k1 and K2, respectively, between both ends of the resistor 5 and the combining circuit 7.
and an amplifier 6b for negative feedback of the voltage supplied to the heating element 1.

In this configuration, if the output voltage of the amplifier 4 is EO and the current flowing through the load is 10, then (E+k1・EO−
K2・RT-10) A=EO...(A).

The equivalent circuit of this relationship is none other than the circuit shown in FIG. That is, if the values of k1 and K2 are set so as to satisfy the condition K2>k1, then with the circuit configuration shown in FIG. 2, the reference voltage (E/(K2-
k1)), negative resistance ({-k1/(K2-k1)}・R
A relationship in which the power sources with D) are connected is obtained. Therefore, as is clear from the correspondence with FIG. 1, even if the heat radiation conditions of the heating element 1 change, the heating element
In order to prevent the operating temperature from fluctuating, it is necessary to bring rn7・RD close to the resistance value RT of the heating element (for example, by changing K2 while keeping k1 constant,
The operating temperature of the heating element 1 can be set constant by changing E to bring IO closer to the current that should be used, that is, the current that provides the desired operating temperature under predetermined heat dissipation conditions. become.

Note that, as in the case described above, the amplification factor A is not limited to the case where A→1, and there is no problem in taking a finite value. Furthermore, in equation 1, if we set k1=K2=k, then

In this case, the block diagram is shown in FIG. 4, and in this case, RD functions as a current detection resistor. In equation (25), the amplification factor A and k are assumed to be finite values. Here, the equivalent circuit of Mr. (26) becomes the circuit shown in FIG.

In other words, if the amplification factors A and k are chosen to satisfy the condition (Ak-1)>0, then the output resistance will have a negative resistance of -RO(Ak-1) at a constant voltage of (AE). Power source is heating element R
It is equivalent to the one connected to T. Therefore, as is clear by making this circuit correspond to Fig. 1,
Since A can be chosen to be any value, for example, if A=1, then k? '． ':[MO囗MI::;:The operating temperature of the body 1 can be set constant.

FIG. 6 shows a specific circuit example of the device of the present invention, and when the heating element 1 has a positive temperature coefficient, parts corresponding to those in FIG. do. Now, the temperature control device of the present invention having the circuit configuration shown in FIG. 6 is attached to two heating elements A and B having a positive temperature coefficient, and the ambient conditions of the heating element 1 are set to ice water at 0°C and 27°C. When the heating element resistance values were measured in air under various ambient conditions and plotted on a graph, solid lines 14A and 14B in FIG. 7 were obtained.

Next, similar measurements were made when two similar heating elements A and B were subjected to constant electric heating, and when these were expressed in a graph, the broken lines 15A and 15B in Figure 7 were obtained under the surrounding conditions. It's changing a lot. In addition, heating element A as a sample,
The temperature coefficient of B is approximately +0.05%/°C, which is a measure of the resistance value of the heating element. was calculated from the supply voltage and current. As is clear from this result, according to the present invention, it is effectively possible to prevent the heating element from changing due to the influence of the surrounding conditions, that is, the heat dissipation conditions.

Note that the specific circuit example of the temperature control device according to the present invention is not limited to the above-mentioned example, and various configurations may be adopted.

For example, as shown in FIG. 8, a pulse converter 8 may be provided to operate the heating element 1 with a pulsed current. Incidentally, FIG. 8 shows a case where integrating circuits 6a and 6b are used as the signal regulation circuit 6. As described above, the temperature control device according to the present invention can reliably maintain a predetermined operating temperature even if there are variations in heat dissipation conditions due to the surrounding conditions of the heating element, and moreover, the temperature control device according to the present invention can reliably maintain a predetermined operating temperature. Since no temperature detection element is provided, there is no problem of thermal coupling as mentioned at the beginning.

Another advantage is that there is no problem of power loss when configuring a bridge circuit. Further, according to the recording pen according to the present invention using the temperature control device according to the present invention,
Since no temperature detection element is attached to the recording pen itself, the scanning response speed can be increased without causing an increase in mechanical load.

Moreover, by adding a temperature control device, recording can be performed at a constant temperature even when the surrounding conditions change, and even recording can be performed. In addition, at the start of operation, unlike conventional recording pens that do not have a temperature control device, there is no longer a long startup time until the recording pen heats up to a recordable temperature, and the temperature control device operates. This has the advantage that the rise time is shortened and clear recording can be started immediately.

[Brief explanation of the drawing]

FIG. 1 shows an equivalent circuit for explaining the basic idea of the present invention.
FIGS. 2 and 4 are block diagrams of examples of the present invention, FIGS. 3 and 5 are equivalent circuit diagrams thereof, FIG. 6 is a circuit diagram showing a specific circuit example of the present invention, and FIG. 7 is a block diagram of an example of the present invention. 8 is a measurement diagram showing the change in resistance value due to changes in the surrounding conditions between the example of the present invention and the conventional example.
The figure is a block diagram of another example of the present invention. 1 is a heating element, 2 is a recording pen, 3 is an operating temperature setting electric signal supply means, 4 is a current supply means to the heating element, 5 is a heat dissipation condition dependent electric signal detection means, 6 is a signal regulation circuit, and 7 is a synthesis circuit. It is.

Claims (1)

[Scope of Claims] 1. A temperature control device that controls the current flowing directly through the heating element itself to control the heating element to a desired operating temperature, which controls the heating element to operate at a desired temperature under predetermined heat dissipation conditions. an operating temperature setting electrical signal supplying means for obtaining an operating temperature setting electrical signal to set the temperature; and a current supplying means whose output current is controlled by the operating temperature setting electrical signal from the means and supplies the output current to the heating element. and a heat dissipation condition dependent device that detects fluctuations in a signal based on the energizing current of the heat generating body depending on the temperature coefficient of the heat dissipation condition from the predetermined heat dissipation condition and outputs a heat dissipation condition dependent electrical signal. electric signal detecting means; and regulating the signal obtained from the detecting means to a predetermined magnitude and applying it to the current supply means so as to return the signal in the direction of positive feedback with respect to the direction of current flowing through the heating element, thereby generating the heat. 1. A temperature control device comprising: positive feedback means for making the value of a negative resistance component formed in the circuit viewed from the body side close to the resistance value of the heating element. 2. A heating element is incorporated in a recording pen that is movable relative to thermal recording paper, and an operation of obtaining an operating temperature setting electrical signal for setting the heating element to a desired operating temperature under predetermined heat dissipation conditions. temperature setting electric signal supply means; current supply means whose output current is controlled by the operating temperature setting electric signal from the means and supplies the output current to the heating element; heat dissipation condition dependent electric signal detection means for detecting a change in a signal based on the current flowing through the heating element as the heat dissipation condition changes from the predetermined heat dissipation condition and outputting a heat dissipation condition dependent electric signal; A negative signal formed in the circuit as seen from the heating element side is applied to the current supply means so as to regulate the signal to a predetermined magnitude and return the signal in the direction of positive feedback with respect to the direction of current flowing through the heating element. A recording pen connected to a temperature control device including positive feedback means for having an operating point where the value of the resistance component approaches the resistance value of the heating element.