JPS63233343A - Pressure sensor for detecting liquid level - Google Patents

Abstract

PURPOSE:To reduce cost and to enhance accuracy, by constituting the title sensor so that electrode plate is pressed by a press shaft moving with the expansion of a diaphragm through a projection. CONSTITUTION:When a diaphragm receives the pressure from a pressure introducing pipe 19, the diaphragm 20 expands and a press shaft 22 moves to press one electrode plate 23 from above through a projection 27. The resistance value of pressure-sensitive conductive rubber 26 changes corresponding to the pressing force of said shaft 22 and a microcomputer 9 obtains the output accompanying the change in the resistance value. Herein, since one electrode plate 23 is pressed through the projection 27 and the area of the end surface of the press shaft 22 is made larger than that of the leading end of the projection 27, even when the position of the press shaft 22 is slightly shifted from the positions of electrode plates 23, 24 at an assembling time, so far as the press shaft 22 is brought into contact with the projection 27, the press position of the press shaft 22 to the electrode plate 23 becomes the place provide with the projection 27. By this method, cost is reduced and accuracy can be enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Industrial Application Field The present invention relates to a pressure sensor for detecting liquid level used in washing machines and the like.

(b) Conventional technology A general washing machine will be explained based on the 13th rM.

(1) is the machine frame, (2) is the operation section provided at the upper rear of the machine frame (1), (3) is the outer tank installed inside the machine frame (1), (
4) is placed inside the outer tank (3), and there are dehydration holes (5) around it.
(6) is a large-diameter mountain-shaped rotor blade disposed at the bottom of the inner tank (4), (7) is a drive motor, and the inner tank (4) and the rotor blade (6) The rotary blade (6) is rotated and floated during washing, and both the inner tank (4) and the rotary blade (6) are rotated at high speed during dehydration. (
9) is the drain port installed at the bottom of the outer tank (3), (10) is the drain solenoid valve, (11) is the drain hose, and (12) is the water supply channel (
13) Water supply solenoid valve installed inside. And (14)
is an air trap provided at the bottom corner of the outer tank (3), and is connected to the pressure switch (15) in the operating section (2) via a pressure hose (16).

The pressure switch (15) is, for example,
This is disclosed in Japanese Patent No. 868, and receives the air pressure in the air trap (14), and the contact switches when a specified pressure is received.

However, such a pressure switch (15) can only determine the specified pressure in 3.4 steps at most, and therefore can only detect the water level in steps.
This requires the operator to set the desired water level in advance, so for example, an electronically controlled fully automatic washing machine that automatically detects the amount of laundry and automatically sets the water level accordingly. cannot be applied to

Therefore, a device using a semiconductor pressure sensor instead of this pressure switch (15) was disclosed in Japanese Patent Application Laid-open No. 60-242888.
It is shown in the publication No. This semiconductor pressure sensor uses the fact that a silicon thin film changes its resistance value due to pressure, and attempts to detect the water level inside the sensor by converting the resistance value into voltage.

However, devices that use silicon in this way have different characteristics depending on the surrounding temperature, and in order to be used as a product, temperature compensation is required, and the cost becomes expensive when the circuit for this is taken into account.

(c) Problems to be Solved by the Invention An object of the present invention is to provide a liquid level detection sensor using pressure-sensitive conductive rubber, which is low in cost and highly accurate.

(d) Means for solving the problems The pressure sensor for liquid level detection of the present invention includes a sensor case having a pressure introduction part, and a primary side and a secondary side inside the sensor case.
a diaphragm disposed so as to be partitioned into a next side and a diaphragm that expands and contracts in response to pressure from the pressure introducing section; a plate attached to the secondary side of the diaphragm; and a press provided on the plate. a shaft, and a pair of electrode plates sandwiching the pressure-sensitive conductive rubber; a projection is provided on the upper surface of one of the electrode plates; the pair of electrode plates is arranged such that the projection faces the end surface of the pressing shaft; The sensor is disposed inside the sensor case.

(E) Action: The pressing shaft that moves with the expansion of the diaphragm presses the xi plate (pressure-sensitive conductive rubber) through the protrusion, so the pressing point of the pressure-sensitive conductive rubber is always constant; Even if the pressure axis shifts slightly to the left or right, this suppression point will not go out of order.

Kube) Example Embodiments of the present invention will be described based on the drawings.

However, the same reference numerals will be used for the same parts as in the conventional example, and the explanation will be omitted.

The first flash and the second figure are for water level detection of washing machine.
Pressure sensor (
17), and the structure of this pressure sensor (17) will be explained below.

(18) is a case of the pressure sensor (17),
It is formed by locking together an upper case (18a) and a lower case (18b) having a pressure introduction pipe (19). (20) connects the inside of the case (18) to the primary side (
It is a diaphragm attached to the upper case (18a) so as to divide it into a secondary side (pressure introduction side) and a secondary side (lower case side), and expands and contracts according to the pressure that can be introduced from the pressure introduction pipe (19). do. (21) is the aforementioned diamond flannel (
It is a circular plate attached to the back surface (secondary side) of the diaphragm (20), and is used to average and centralize the pressure received by the diaphragm (20).In the center of the plate, there is a cylindrical pressure shaft (
22) is formed protrudingly. Therefore, the pressing shaft (22) moves up and down in FIG. 1 according to the pressure that the diaphragm (20) receives.

Now, (23) and (24) are electrode plates, both of which have a rectangular shape, one being about half the length of the other, and the base end (23a) of this one electrode plate (23). It is adhered to the end (24a) of the other electrode plate (24) with an insulating adhesive (25), and there is a pressure-sensitive conductive rubber (26) to be described later in between.
is holding. Furthermore, the upper surface of the free end (23b) of the one electrode plate (23) has a cross-sectional area that is equal to the pressing shaft (23b).
A cylindrical projection (27) smaller than the cross-sectional area of 22) is provided.

Then, the other electrode plate (24) is attached to the lower case (1).
8b), and at this time, the end surface of the protrusion (27) is adjusted so that it is in a position close to and facing the end surface of the pressing shaft (22). Note that (28) and (29) can be connected to the pair of electrode plates (23) and (24), respectively, and
This is a terminal for detecting the voltage between 23 and 24.

Here, the pressure-sensitive conductive rubber (26) is a sheet-like material with a thickness of 0.5 to II made by kneading and molding gelaphite particles into silicone rubber. The resistance value in the thickness direction changes continuously. The pressure-sensitive conductive rubber uses silicon like the semiconductor pressure sensor described in the conventional example, but as shown in Figure 4, the output hardly changes with temperature changes and the error is less than 5%. Therefore, there is no need for compensation.

FIG. 5 shows a pressure-sensitive conductive rubber (26) (for example, Yokohama Industrial Rubber Co., Ltd. C3-57 type, etc.) attached to a pair of electrode plates (26) as shown in FIG.
3) Electrode plate when placed between (24) and pressurized from above (
It shows the change in resistance value between 23) and 24. That is,
The resistance value gradually decreases from an insulating state (10MΩ or more) to a conductive state (50Ω or less) depending on the applied pressure.
It is called resistance value change type pressure-sensitive conductive rubber.

Incidentally, Figure 7 shows the change in pressure applied to the diaphragm of a conventional pressure switch (15) when the water level in the tank is changed.
It can be seen that a pressure of 400 g is applied (of course, this pressure varies somewhat depending on the pressure receiving area of the diaphragm).

An example of a circuit (28) for detecting the voltage between a pair of electrode plates (23) and (24) sandwiching the pressure-sensitive conductive rubber (26) is shown in the eighth ryA. 10
As shown in Figure A, a circuit output Vax proportional to the pressure applied to the pressure-sensitive conductive rubber 26) is obtained.

FIG. 9 is a block diagram of the control mechanism of a washing machine centered on a microcomputer (29) (hereinafter referred to as "Maifun").
It consists of CPU, ROM, RAM, system bus, etc. (30) is a comparison circuit, and the microcomputer (
Compare the value obtained by converting the reference value previously stored in the ROM by the D/A conversion circuit (31) with the output Vout of the pressure sensor voltage detection circuit (28) shown in FIG. Then, the comparison output is sent to the microcontroller>-(29). The reference value is the V out (pressure of the first unit *) that can be traced when water is supplied to the specified water level in the tank, and the change in the water level is zero after the rotary blade is driven for a predetermined period of time after water is supplied to the specified water level. V out (second reference voltage) output when the water level is slightly lower than the specified water level (-20m!l)
) is the V (UT (third reference voltage)) that is output when water is supplied up to V (UT), and these are individually memorized.

Although the first reference voltage and the second reference voltage are the same value, the pressure-sensitive conductive rubber in this example has a creep phenomenon (ffl deformation occurs over time under constant stress). Therefore, under a constant pressure and the first water level, the amount of strain in the pressure-sensitive conductive rubber increases with the passage of time, and the output changes as shown in Figure 11 occur. . Therefore, the second and third reference voltages are set to values that take into account the increase in output due to this creep. Further, since the first reference voltage is continuously pressurized by water supply from zero water level and reaches the set water level before creep occurs, there is no need to take creep into consideration.

(32) is an input operation key circuit composed of a group of various operation keys. The microcomputer (29) controls various load drive circuits, namely supply and drainage solenoid valve drive circuits (33) and (34), based on information from the comparison circuit (30) and the input operation key circuit (32). and controls the operation of the drive motor left and right rotation circuits (35), (36), etc. (37) is an output buffer that relays the signal from the microcomputer (29) to the load drive circuit. (38) is a reset signal generation circuit, and (39) is an oscillation circuit that inputs a clock reference signal to the microcomputer (29).

The operation based on such a configuration will be explained according to the flowchart of FIG. 12.

After the laundry is put into the washing tub (4), water supply to the outer tub (3) is started, and as the water level rises, the diaphragm (20) receives pressure from the pressure introduction pipe (19). Then, the diaphragm (20) expands, the pressing shaft (22) moves, and presses the one electrode plate (23) from above via the protrusion (27). The resistance value of the pressure-sensitive conductive rubber (26) changes in accordance with this pressing force, and the microcomputer (29) obtains the output vCXJT in accordance with this resistance value change.

Here, for example, if there is no protrusion 27), if the positions of the pressing shaft (22) and the electrode plates (23, 24) shift during assembly, the pressing shaft (27)
) will be shifted from its pressing position with respect to the one IE electrode plate 23). That is, the distance from the pressure-sensitive conductive rubber (26) to the pressed position! will change, and!
changes, the resistance value of the pressure-sensitive conductive rubber (26) changes to 35! changes in proportion to. Therefore, this! If there is even a slight change in the pressure-sensitive conductive rubber (26), the characteristics of the pressure-sensitive conductive rubber (26) will be greatly affected (that is, the characteristics will change as shown in FIGS. 10B and 10C).

However, in this embodiment, the one electrode plate (23) is pressed through the protrusion (27), and the pressing shaft (27) is pressed against the one electrode plate (23).
Since the area of the end surface of 22) is made larger than the area of the tip of the protrusion (27), even if the positions of the pressing shaft (22> and the electrode plates (23) and (24) are slightly shifted during assembly, the pressing shaft (22) is in contact with the protrusion (27), the pressing shaft (22)
) with respect to one electrode plate (23) is the location where this protrusion (27) is provided, and the distance 81 is always constant.

Now, the output VGJT is compared with each reference voltage value stored in the microcomputer (29) through a comparison circuit (30). First, when the output V (XJT is compared with the first reference voltage, 5-1) matches, it is determined that the water level in the tank has reached the specified water level, and the water supply is stopped (S-2).
Next, the microcomputer (29) rotates the rotary blade (6) (S-3) to agitate the laundry in the tub, thereby expelling air present between the fibers of the laundry. This stirring operation is continued for a predetermined period of time (S-4), and after the elapse of a predetermined period of time, the rotary blade (6) is stopped (S-5). At this point, the water level in the tank should have fallen by the volume of the air expelled from the laundry, so wait until the water surface calms down and obtain an output vCM commensurate with the water level at this time. Next, compare it with the third reference voltage (S-6>), and if the output of 7 inches at this time is higher than the third reference voltage, the water level drop is less than 20 mm, so there is no problem in washing. It is determined that there is no rotation, and then the drive of rotation g (6) is started 5-7).
When the washing process is carried out, if the voltage is less than the third reference voltage, the water level will drop by more than 20 m, which will affect the washing action, so water will be supplied into the tank again in order to return it to the specified water level. -8), L, since a creep phenomenon has occurred in the pressure-sensitive conductive rubber (26) with the passage of time, the specified water level is now detected by comparing it with the second reference voltage (S -9) Then, when the output Vout reaches the second reference voltage, the water supply is stopped (S-10), and the rotary blade (6) is driven again.

The above operation is an application of the pressure sensor of this embodiment to the water supply operation.
It can also be widely applied to other functions such as drainage control and detergent solution injection control, promoting the automation of washing machines.

Here, in this embodiment, by arranging the protrusion (27) so as to closely face the pressing shaft (22) during assembly, the initial value of the pressure applied to the pressure-sensitive conductive rubber (26) is is only the weight of the one electrode plate (23).

Therefore, by unifying the weight of this one electrode plate (23), it is possible to eliminate the work of unifying and adjusting the initial sensitivities of a plurality of pressure sensors.

The positional relationship between the projection (27) and the pressing shaft (22) is aimed at the above-mentioned purpose, so even if they are in contact, the pressing shaft (22) As long as no initial pressure is applied to 27), the abstract will not be exempt from tax.

(G) Effects of the Invention The pressure sensor for liquid level detection of the present invention has a pressing shaft that moves as the diaphragm expands, and the electrode plate (
Since the pressure-sensitive conductive rubber is pressed, the pressing point of the pressure-sensitive conductive rubber is always constant, and even if the pressing axis shifts slightly to the left or right, this pressing point will not go out of order.Furthermore, the structure is simple. In addition, complicated adjustment work such as temperature guarantee and sensitivity adjustment is reduced.

Therefore, a low cost and highly accurate pressure sensor can be provided.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view of the pressure sensor for liquid level detection of the present invention;
Figure 2 (a) is a cross-sectional view taken along line p-p', and figure (b) is a cross-sectional view taken along line Q-
Q' sectional view, Fig. 3 is an explanatory diagram of the pressing mechanism of the electrode plate by the pressing shaft, Fig. 4 is a temperature characteristic diagram of pressure-sensitive conductivity;
The figure is a resistance value characteristic diagram associated with the same pressure change, Figure 6 is a measurement principle diagram for obtaining the characteristics shown in Figure 5, Figure 7 is a characteristic diagram of a conventional pressure switch, and Figure 8 is a pressure-sensitive conductivity diagram. A detection circuit diagram for extracting the change in resistance value of the rubber as an output change. Figure 9 is a block circuit diagram of the control mechanism. Figures 10 and 11 are the circuit diagrams of the control mechanism.
Figure 12 is a flowchart showing the water supply operation of a washing machine that uses a pressure sensor, and Figure 13 is a conventional one. 1 is a cross-sectional view of the internal mechanism of a washing machine that employs the pressure switch of FIG. 18)...Sensor case, (19)...Pressure introduction pipe (pressure introduction part), (20)...Diaphragm,
(21)...Plate, <22)...Press shaft, (2
3)...one electrode plate, (24)...other electrode plate, (26)...pressure-sensitive conductive rubber, (27)...protrusion.

Claims (2)

[Claims] (1) A sensor case that detects pressure changes due to fluctuations in liquid level as output changes due to changes in resistance of pressure-sensitive conductive rubber, and a sensor case with a pressure introduction part and an inside of the sensor case. a diaphragm arranged to divide the air into a primary side and a secondary side and expands and contracts in response to pressure from the pressure introducing section; a plate attached to the secondary side of the diaphragm; a pair of electrode plates sandwiching the pressure-sensitive conductive rubber; a protrusion is provided on the top surface of one of the electrode plates; A liquid level pressure sensor, characterized in that it is disposed within the sensor case so as to face an end face. (2) The liquid level detection device according to claim 1, wherein the pressing shaft has a cylindrical shape, and the area of the end face thereof is larger than the area of the tip of the projection. pressure sensor.