JPS6326855B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an object detection element whose heat capacity changes upon contact with an object, and which detects the presence or absence of an object by detecting the change.

Generally when you need to detect the presence or absence of an object,
For example, when maintaining a constant amount of ice in the ice storage compartment of an ice maker, etc., the presence of ice in the bell is detected using a photoelectric element or mechanical means. Otherwise, mechanical means such as thermostats or reed switches are used, and the mechanical strength of the parts that come into direct contact with ice at low temperatures must be specially improved. Care must be taken, and the contacts may freeze due to moisture or frost.

The present invention has been made in view of the above points, and provides a novel object detection device that is completely different from conventional detection elements. The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a sectional view showing an embodiment of the present invention,
1 is a heat sink, 2 is a semiconductor element, 3 is a lead wire, 4
is the sealing part.

The heat sink 1 is a pipe made of a metal with good thermal conductivity, such as aluminum, and is closed at one end. A semiconductor element 2 is thermally coupled and fixed to the heat sink 1 inside the heat sink 1, and the lead wire 3 of the semiconductor element 2 is led out from the open part at the other end of the heat sink 1, and further heat radiation is carried out. Open part of container 1 and lead wire 3
is hermetically sealed by the sealing portion 4.
Nitrogen or the like may be filled in to prevent moisture from remaining inside during hermetic sealing. Further, the semiconductor element 2 uses a PNP type or NPN type transistor, and heat generated in the PN junction is transmitted to the heat sink 1 when a collector current is passed. The object detection element formed in this way is installed at an arbitrary position in the ice storage compartment of an ice maker, for example, and when the ice reaches a certain level, the ice 5 becomes a part of the radiator 1 as shown by the broken line in FIG. Contact.

Next, the principle of detecting the presence or absence of an object will be explained. FIG. 2 is a thermal equivalent circuit of the object detection element shown in FIG. 1, where 6 is a heat source indicating the juncture of the semiconductor element 2, R ₁ is the thermal resistance of the juncture and the entire semiconductor element 2, and C ₁ is the heat capacity of the entire semiconductor element 2, _R2 is the thermal resistance between the semiconductor element 2 and the radiator 1, Cn is the heat capacity component of the radiator 1, the air in contact with the radiator 1, and the material that supports the object detection element, Rn indicates the thermal resistance component of the radiator 1, the air in contact with the radiator 1, and the material that supports the object detection element, and the equivalent circuit of the object detection element is the heat source 6 and the thermal resistance R ₁ , R ₂ , Rn. connected in series, heat capacity
C ₁ and Cn are connected in parallel, resulting in a thermal resistance
A thermal time constant is formed depending on R ₁ , R ₂ , Rn and heat capacity C ₁ , Cn. When the ice 5 comes into contact with the radiator 1 of the object detection element as shown by the broken line in FIG. 1, the contact area absorbs heat to melt the ice 5, and the temperature of that area is fixed at 0°C. Ru. If this is shown as an equivalent circuit, it becomes a circuit in which the thermal zener 7 is inserted in the middle of the time constant circuit formed by the thermal resistances R ₁ , R ₂ , Rn and the thermal capacities C ₁ , Cn.
It is thermally shot, and the heat is no longer transmitted beyond that point. Therefore, the thermal time constant of the object detection element as a whole is different when the ice 5 is in contact with the heat sink 1 and when it is not, and the temperature increase rate of the juncture of the semiconductor element 2 and the time until it reaches the saturation state are different. and different temperatures.

FIG. 3 shows the relationship between temperature and time for the juncture of the semiconductor element 2. The curve shown by a shows the case where the ice 5 is not in contact with the radiator 1, and the curve shown by b shows the case where the ice 5 is in contact with the radiator 1.
During T ₀ after the current starts flowing through the semiconductor element 2, the junction temperatures a and b rise in the same way depending on the time constant determined by the thermal resistance R ₁ and heat capacity C ₁ of the entire semiconductor element 2. But after that,
When the ice 5 is not in contact with the heat sink 1, all the thermal resistances R ₁ , R ₂ , Rn and the time constant determined by the heat capacities C ₁ , Cn rise as shown in a. . On the other hand, when the ice 5 is in contact with the radiator 1, the overall time constant becomes significantly smaller due to the thermal zener 7, so the time for the juncture temperature to reach the saturated state is shortened, and the temperature also increases. Since it becomes lower, it becomes a curve indicated by b. Therefore, measure the temperature of the junction at T ₀ and T ₁ ,
If the difference is above a certain level, it can be determined that the curve shown by a, that is, there is no ice 5, and if it is below a certain level, it can be determined that the curve shown by b, that is, ice 5 is present. Since direct measurement is impossible, the electrical signal output from the semiconductor element 2 is used.

Figure 4 shows an NPN transistor in semiconductor element 2.
This is a circuit diagram when using a transistor.
A load resistor R ₀ is connected to the collector of the Tr between it and the power supply voltage Vcc, and dividing resistors R _B1 and R _B2 are connected between the base and the collector and between the base and the emitter, respectively. When the power supply voltage Vcc is applied now, the collector current Ic determined by the dividing resistors R _B1 and R _B2 flows through the load resistor R ₀ , and a voltage of Vcc - IcR ₀ is generated at the collector voltage, that is, the output voltage out. . It is well known that the collector current Ic has temperature dependence, and therefore the collector current Ic
When the temperature rises due to the heat generated by the juncture, the collector current Ic increases, and the collector voltage, that is, the output voltage out, decreases. FIG. 5 shows the relationship between output voltage out and time. Until time T ₀ , the temperature of the junction rises in the same way regardless of whether the ice 5 is in contact with the heat sink 1 or not, so the output voltage out also becomes small. Thereafter, if the ice 5 is not in contact with the radiator 1, the juncture temperature increases as shown in FIG. 3a, so the output voltage out decreases as shown in FIG. 5c.
On the other hand, if the ice 5 is in contact with the radiator 1, the third
Since the junction temperature becomes constant for a short period of time as shown in FIG. 5B, the output voltage out becomes a constant voltage for a short period of time as shown in FIG. 5D. Therefore, the output voltages at times T ₀ and T ₁ are measured, and if the difference between them is above a certain level, it can be determined that there is no ice 5, and if the difference is below a certain level, it can be determined that there is ice 5.

If the measurement of the output voltage and the determination of the presence or absence of ice are performed using a microcomputer, a more reliable determination can be made.

In this embodiment, the object detection element was explained using the detection of ice as an example, but it is possible to detect anything other than ice as long as the object that comes into contact with the radiator has a large heat capacity and gives a thermal Zener effect. Become.

As described above, according to the present invention, a semiconductor element is thermally bonded and fixed to a heat sink with good thermal conductivity, and the thermal time constant of the detection element as a whole decreases when an object comes into contact with it. The object detection element has no moving parts, which simplifies the structure and increases mechanical strength.Furthermore, since it relies on electrical signals for detection, there is no possibility of malfunction. This allows reliable detection. In particular, in the present invention, a pipe-shaped heatsink with one end closed and an opening at the other end is used, a semiconductor element is fixed inside, and the opening is sealed with the lead wire of the semiconductor element led out. As a result, it is possible to realize a small-sized and highly durable detection element, which is suitable for detecting ice in ice making machines and the like that come into direct contact with ice.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of the present invention, FIG. 2 is a thermal equivalent circuit of the embodiment shown in FIG. 1, FIG. 3 is a junction temperature characteristic diagram, and FIG. 4 is a diagram shown in FIG. The circuit diagram used in the embodiment shown in FIG. 5 is an output voltage characteristic diagram. DESCRIPTION OF SYMBOLS 1... Heat sink, 2... Semiconductor element, 3... Lead wire, 4... Sealing part, 5... Ice, 6... Heat source, 7
...It's a hot zener.

Claims (1)

[Claims] 1 A semiconductor element having a PN junction, and a pipe-shaped device having one end closed and an opening at the other end,
The semiconductor element is fixed inside so as to be thermally coupled, the opening is sealed with the lead wire of the semiconductor element led out from the opening, and a current is passed through the lead wire to the semiconductor element. and a radiator for dissipating heat generated in the PN junction, and whether or not a temperature rise in the PN junction when a current is passed through the semiconductor element is caused by whether an object is in contact with the radiator. 1. An object detection element that detects the presence or absence of an object based on a difference in .