JPH03257338A - Pressure detection circuit - Google Patents

Abstract

PURPOSE:To enhance the reliability in the detection of pressure by connecting a pressure sensor between the inverting input terminal of an operational operator and a reference voltage source, and connecting another reference voltage source to the non-inverting input terminal of the operational amplifier, and connecting a negative feedback resistor between the inverting input terminal and output terminal of the amplifier. CONSTITUTION:The non-inverting input terminal 1a of an operational amplifier 1 is connected to earth 6 through a resistor 5 having a resistance value R1, and a negative feedback resistor 2 having a resistance value Rf is connected between the output terminal 1c and inverting input terminal 1b of the amplifier 1. One end of a pressure sensor 3 changing in its resistance value Rs correspond ing to applied pressure P is connected to the inverting input terminal 1b. As the pressure P becomes higher, the change rate of detected voltage V0 becomes large. Therefore, higher pressure is detected as it is and, as a result, possibility applying damage to foreign matter by high pressure is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pressure detection circuit suitable for use in an automatic opening/closing device such as a power window device of an automobile.

[Summary of the invention]

The present invention provides a pressure detection circuit that detects pressure by detecting a change in the resistance value of a pressure-sensitive sensor whose resistance value changes depending on the applied pressure. Connected between the input terminal and the reference voltage source, another reference voltage source is connected to the non-inverting input terminal of the operational amplifier, and negative feedback is connected between the inverting input terminal and the output terminal of the operational amplifier. By connecting a resistor, the reliability of pressure detection is improved.

[Conventional technology]

In an automatic opening/closing device that uses a motor to move a moving object (for example, a power window device for a car), in order to stop the motor drive when a foreign object is caught in a moving object such as a window glass, Detects entrapment of foreign objects.

In order to detect such trapped foreign matter, the pressure applied to the foreign matter is detected by a pressure sensor using pressure-sensitive conductive rubber or pressure-sensitive conductive paint.

The electrical characteristics of pressure-sensitive sensors using pressure-sensitive conductive rubber or pressure-sensitive conductive paint used for pressure detection are as follows:
When the resistance value corresponding to the applied pressure P is R5,
Generally, as the pressure P increases, the resistance value R decreases, and normally, if N is a positive constant, Rs ccP −' −−−−−−−−−−−−−−
−(1). When the characteristic of the above equation (1) is represented in a diagram, the change in the resistance value R3 with respect to the pressure P becomes a curve as shown in FIG. In addition, in Figure 2,
The horizontal axis is the pressure P, and the vertical axis is the resistance value R8.

In this case, as can be seen from the pressure-resistance value characteristics in FIG. 2, as the pressure P increases, the rate of change in the resistance value R3 decreases. That is, as the pressure P increases,
The detection sensitivity of pinch detection is reduced. For this reason,
In the conventional pressure detection circuit using the above-mentioned pressure sensor,
When detecting pressure by outputting a detection voltage that corresponds to a change in resistance value R3, the detection voltage is almost the same as that corresponding to a relatively low pressure, even though a foreign object is trapped under a high pressure P. Since only the detected voltage is output,
The reliability of pressure detection was poor.

[Problem to be solved by the invention]

The above-mentioned conventional technology lacks consideration for the reliability of pressure detection as described above, and therefore, when applied to an automatic opening/closing device, there is a problem in that the reliability of detecting foreign object entrapment is low. Further, there is a risk that high pressure may be applied unexpectedly to the foreign object, causing damage to the foreign object.

SUMMARY OF THE INVENTION An object of the present invention is to provide a pressure detection circuit that can solve the above-mentioned problems and improve the reliability of detecting foreign object entrapment.

[Means to solve the problem]

In order to achieve the above object, the pressure detection circuit of the present invention includes:
a pressure-sensitive sensor whose resistance value changes in accordance with applied pressure; an operational amplifier for outputting a detected voltage corresponding to the pressure applied to the pressure-sensitive sensor from its output terminal; and an inverting input terminal of the operational amplifier. and the output terminal, a first reference voltage source having a predetermined reference potential, and a second reference voltage source having a predetermined reference voltage with respect to the reference potential. each, the pressure sensitive sensor is connected between the inverting input terminal and one of the first and second reference voltage sources, and
The other reference voltage source is connected to the non-inverting input terminal of the operational amplifier.

〔Example〕

EMBODIMENT OF THE INVENTION Hereinafter, one embodiment of the pressure detection circuit of the present invention will be described in detail using the drawings.

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the pressure detection circuit of the present invention. In FIG. 1, a non-inverting input terminal 1a of an operational amplifier 1 is connected to a ground 6 through a resistor 5 having a resistance value R1.
connected to. Further, a negative feedback resistor 2 having a resistance value R2 is connected between the output terminal 1c and the inverting input terminal 1b of the operational amplifier 1. One end of a pressure sensor 3 whose resistance value R5 changes depending on the applied pressure P is connected to the inverting input terminal 1b. The other end of this pressure sensitive sensor 3 is connected to another reference voltage source 4 which generates a - constant reference voltage E0 between it and ground 6 (that is, a reference voltage source having a constant reference potential). Note that 7 is an output terminal of the pressure detection circuit, and is connected to the output terminal 1c of the operational amplifier 1.

In FIG. 1, since the negative feedback resistor 2 is connected between the inverting input terminal 1b and the output terminal 1c of the operational amplifier 1, an imaginary short circuit occurs between the non-inverting input terminal 1a and the inverting input terminal 1b. be done.

This means that the voltage output by the operational amplifier 1 to the output terminal 1c causes the same voltage at the inverting input terminal 1b as that at the non-inverting input terminal 1a. On the other hand, the non-inverting input terminal 1a is grounded to earth 6 via a resistor 5. However, since the human power impedance of the operational amplifier 1 is extremely large, the voltage generated at the non-inverting input terminal 1a is substantially 0 [V]. Therefore, a voltage of O(V) is generated at the inverting input terminal 1b (that is, the inverting input terminal 1b is virtually grounded).

Further, the other end of the pressure sensor 3 is connected to the negative electrode side of a reference voltage source 4, as shown in FIG. The positive electrode side of the reference voltage source 4 is connected to the ground 6. As a result of this,
- A current flows through the pressure sensor 3 from one end on the inverting input terminal lb side to the other end on the reference voltage source 4 side. As described above, since the input impedance of the operational amplifier 1 is extremely large, the current flowing through the pressure-sensitive sensor 3 is substantially supplied from the output terminal 1c of the operational amplifier 1 via the negative feedback resistor 2. In other words, the voltage output to the output terminal 1c becomes a positive voltage.

Note that the resistance value R1 of the resistor 5 is for preventing offset, and the resistance value Rs at the reference operating point of the pressure sensitive sensor 3 is
' and the resistance value R of the negative feedback resistor 2 are connected in parallel.

In FIG. 1, the detection voltage V output from the output terminal 7. is expressed by the following equation (2).

Vo −(Rt / Rs) ・E, -----
--(2) Here, from the above equation (1), the resistance value R3 can be expressed by the following equation (3).

R, −K −P−”−−−−−−−−−−−−−−−
~---------, -(3) However, K is a proportionality constant. Then, by substituting equation (3) into equation (2), Vo = -(R, /KP-N) ・Eo--(R, -
E, /K) ・pH...(4). However, E
o is a negative voltage.

Therefore, according to the above equation (4), the detected voltage v0 is P
Proportional to N.

Next, the characteristics of the detection voltage V0 of the circuit shown in FIG. 1 will be explained using FIGS. 3 and 4. In addition, in FIGS. 3 and 4, the horizontal axis is the pressure P, and the vertical axis is the detected voltage ■. It is.

FIG. 3 shows the case where N is 1 in equation (4). As shown in FIG. 3, the detection voltage ■.

is substantially linearly proportional to the pressure P, and the rate of change of the detected voltage v0 is constant regardless of the magnitude of the pressure P. Therefore, the reliability of detecting the pressure P is improved, which in turn improves the reliability of detecting the presence of a foreign object.

FIG. 4 shows the case where N is greater than 1 in equation (4). As shown in FIG. 4, the larger the pressure P, the higher the detection voltage ■. The rate of change in will increase. therefore,
Higher pressures are detected as higher pressures. This eliminates the risk of damaging the foreign object due to high pressure, improving the reliability of detecting foreign object entrapment.

In addition, in the above-described embodiment, the voltage E of the reference voltage source 4. Although it is assumed to be a negative value, it may be a positive value, and in this case, the vertical axes of FIGS. 3 and 4 will show negative values. In addition, when the voltage E0 is set to zero (that is, when the other end of the pressure-sensitive sensor 3 is substantially grounded), another terminal corresponding to the reference voltage source 4 is connected between the resistor 5 and the ground 6. A reference voltage source may be provided to supply a bias voltage to the non-inverting input terminal 1a. However, when the bias voltage is supplied in this way, the same voltage as this bias voltage is included in the detection voltage V0 in the above equation (4).

〔Effect of the invention〕

Since the pressure detection circuit of the present invention is configured as described above, it improves the reliability of pressure detection when detecting pressure by outputting a detection voltage according to a change in the resistance value of the pressure sensor. As a result, the reliability of detecting a foreign object being trapped can be improved. Furthermore, it is possible to eliminate the risk of damaging foreign objects due to high pressure.

0

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing the configuration of an embodiment of the pressure detection circuit of the present invention, and Fig. 2 is a diagram showing general electrical characteristics of a pressure-sensitive sensor using pressure-sensitive conductive rubber or pressure-sensitive conductive paint. , FIG. 3, and FIG. 4 are diagrams showing the characteristics of the detected voltage of the circuit shown in FIG. 1, respectively. In addition, in the symbols used in the drawings, 1-------
-------1-Operation amplifier 1 a-----
- Non-inverting input terminal 1 b - - - - - - Inverting input terminal 1 c - - - - - - Output terminal 2 - = - = - - - - - −−− Negative feedback resistor 3 −−−
−−−−−−−−−One pressure-sensitive sensor 4 −−−−−−−−
---One reference voltage source 6- ----=ground.

Claims (1)

[Scope of Claims] A pressure-sensitive sensor whose resistance value changes according to applied pressure; an operational amplifier for outputting a detected voltage from its output terminal according to the pressure applied to the pressure-sensitive sensor; a negative feedback resistor connected between the inverting input terminal of the amplifier and the output terminal; a first reference voltage source having a predetermined reference potential; and a second reference voltage source having a predetermined reference voltage with respect to the reference potential. a reference voltage source, wherein the pressure sensitive sensor is connected between the inverting input terminal and one of the first and second reference voltage sources, and the other reference voltage source is connected between the inverting input terminal and the first and second reference voltage sources. is connected to a non-inverting input terminal of the operational amplifier.