JPH05142068A - Pressure detecting circuit - Google Patents

Abstract

PURPOSE:To improve the detecting reliability when foreign matter is caught in spite of the variation or irregularity of the resistance value of a pressure- sensitive sensor, by obtaining a voltage approximately directly proportional to PN to the pressure-sensitive sensor. CONSTITUTION:A pressure-sensitive sensor 2 which changes its resistance value Rs corresponding to the applied pressure P is connected between an inverting input terminal and are output terminal of a first amplifier 1. An earth resistance 3 is connected between the inverting input terminal of the amplifier 1 and the ground. An output terminal of the amplifier 1 is connected to an inverting input terminal of a second amplifier 4. A reference voltage source 5 generating a reference voltage Eref is connected at a non-inverting input terminal of the second amplifier 4. An output terminal of the second amplifier 4 is connected to a non-inverting input terminal of the first amplifier 1 via a resistance 6. The non-inverting input terminal of the first amplifier 1 is connected to an earthed capacitor 7 and a non-inverting input terminal of a third amplifier 8. An output signal is obtained from an output terminal of the third amplifier 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure detecting device suitable for use in an automatic opening / closing device such as a power window device of an automobile.

[0002]

2. Description of the Related Art An automatic opening / closing device for moving a moving body by driving a motor. For example, in a power window device of an automobile, a motor is driven when a foreign object is caught when the moving body such as a window glass is closed. In order to stop, the foreign matter is detected to be pinched. In order to detect such entrapment of foreign matter, the pressure applied to the foreign matter is detected by a pressure-sensitive sensor using pressure-sensitive conductive rubber or pressure-sensitive conductive paint.

The electric characteristics of a pressure-sensitive sensor using pressure-sensitive conductive rubber or pressure-sensitive conductive paint used for pressure detection are as follows, where Rs is the resistance value corresponding to the pressing force P.
Generally, the resistance value Rs decreases as the pressure P increases, and normally, when K and N are positive constants, Rs∝KP ^−N is represented. In a conventional pressure detection circuit using this type of pressure sensitive sensor, a voltage corresponding to the resistance value Rs of the pressure sensitive sensor is output as a pressure detection signal.

[0004]

The resistance value of this pressure-sensitive sensor not only varies due to manufacturing errors, but also
It changes depending on the ambient temperature, and also changes over time, so that the values of K and P fluctuate or change. A pressure detection circuit that eliminates this variation is disclosed in Japanese Patent Application No. 3-2283.
Proposed in No. 91.

Further, the pressure-sensitive sensor has a non-linear current-resistance value characteristic as shown in FIG. 1, for example, and pressure detection for detecting a foreign object trapped in a power window is performed by a rate of change of the resistance value Rs of the pressure-sensitive sensor. In this case, the larger the pressing force P, the smaller the differential value dRs / dP. That is, there is a problem that the higher the pinching pressure, the lower the pinching detection sensitivity.

An object of the present invention is to provide a pressure detection circuit which solves these problems, guarantees pressure detection without variation, and further increases the detection sensitivity as the pinching pressure increases.

[0007]

In order to achieve this object, the pressure detecting circuit of the present invention comprises a pressure-sensitive sensor whose resistance value changes according to the applied pressure, and this pressure-sensitive sensor has an inverting input terminal and an output. A first amplifier connected to the inverting input terminal and a grounding resistance connected to the inverting input terminal; an output terminal of the first amplifier is connected to the inverting input terminal; and a reference voltage source connected to the non-inverting input terminal. A second amplifier which is connected and whose non-inverting input of the first amplifier may be connected to an output; and a third amplifier which amplifies the voltage applied to the non-inverting input of the first amplifier. Then, the detection signal corresponding to the pressure applied to the pressure-sensitive sensor is obtained from the output end of the third amplifier.

[0008]

According to this structure, the output voltage of the third amplifier is constant regardless of the magnitude of the resistance value of the pressure-sensitive sensor when the pressure is not applied. The pressure sensitive sensor has a large rate of change in resistance value when a minute pressure is applied. However, since the output voltage of the first amplifier is controlled to be equal to the reference voltage by the second amplifier, the applied voltage at the non-inverting input terminal is changed to be small.

On the other hand, the pressure-sensitive sensor has a small rate of change in resistance value when an excessive pressure is applied. Therefore, in the first amplifier, the voltage applied to the non-inverting input terminal is greatly changed. This applied voltage is the same as the applied voltage as shown in FIG.
^{Since N and N} have a characteristic that they are substantially directly proportional to each other and their change width is narrow, they are amplified by the third amplifier. Therefore, the third amplifier
The output voltage is substantially inversely proportional to the resistance change of the pressure sensitive sensor. Further, since the output voltage of the third amplifier changes from the reference value, the value or the differential value can be used as the pressure detection signal.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the pressure detecting circuit of the present invention will be described in detail below with reference to the drawings. FIG. 3 is a circuit diagram showing an embodiment of the pressure detection circuit of the present invention.

In FIG. 3, the first amplifier 1 has a pressure-sensitive sensor 2 whose resistance value Rs changes according to the applied pressure P, which is connected between an inverting input terminal and an output terminal. It is grounded via the grounding resistor 3. The output terminal of the first amplifier 1 is connected to the inverting input terminal of the second amplifier 4. The second amplifier 4 has a non-inverting input terminal connected to a reference voltage source 5 for generating a constant reference voltage Eref, and an output terminal connected via a resistor 6 to the non-inverting input terminal of the first amplifier 1. ing.

On the other hand, the grounded capacitor 7 and the non-inverting input terminal of the third amplifier 8 are connected to the non-inverting input terminal of the first amplifier 1. This third amplifier 8 is
For amplifying the applied voltage x applied to the non-inverting input terminal of the amplifier 1, the resistors 9 and 10 for determining the amplification factor are provided between the output terminal and the inverting input terminal, and between the inverting input terminal and the ground. The output voltage Eo is obtained from the output terminal 11.

In the first amplifier 1, the resistance value of the pressure sensitive sensor 2 is Rs, the resistance value of the ground resistance 3 is Ri, the output voltage of the output end is eo, and the applied voltage applied to the non-inverting input end is x.
Then, due to the action of the second amplifier 4, the output voltage e
The applied voltage x is adjusted so that o becomes equal to the reference voltage Eref. eo = Eref ………………………… (1)

If Ri << Rs, the output voltage eo
Is expressed by the following equation. eo = (Rs / Ri) · x ………………………… (2)

From these equations 1 and 2, the applied voltage x becomes the following equation 3, ∴x = (Ri / Rs) · Eref ……………… (3), and the pressure sensitive sensor 2 Is inversely proportional to the resistance value Rs.

This Rs is generally Rs = k · P ^−N (k:
There is a relation of (constant), and by substituting this into Equation 3, x = (Ri / k) · Eref · P ^N. Therefore, in the P-x characteristic, when N> 1, as shown in FIG. 2, the rate of change of x increases as the pressure P applied to the pressure-sensitive sensor 2 increases.

The resistor 6 and the capacitor 7 shown in FIG. 3 prevent the closed loop circuit formed by the first amplifier 1 and the second amplifier 4 from oscillating, and the variation of x is sufficient for the variation of Rs. It has a time constant that can be followed.

Next, the operation of one embodiment of the pressure detection circuit shown in FIG. 3 will be described. When the pressure P is applied to the pressure sensor 2, the resistance value Rs of the pressure sensor 2 decreases. In the first amplifier 1, after the delay time based on the time constant determined by the capacitance value of the capacitor 7 and the resistance value of the resistor 6, the voltage eo at the output end becomes equal to the reference voltage Eref and the non-inverting input end is applied. The voltage x increases in almost direct proportion to P ^N. This applied voltage x is input to the third amplifier 8 to obtain a desired output voltage Eo. The output voltage Eo is supplied to a differentiating circuit that detects the rate of change of the voltage or a comparator to which the second reference voltage source is input to obtain a pressure detection signal.

When this pressure detecting circuit is applied to an automatic switchgear such as an automobile power window, the output voltage E
When the change rate of o exceeds a predetermined value, or when the output voltage Eo
When the voltage rises above the second reference voltage value, a predetermined control circuit temporarily stops the driving of the motor, then reverses the motor to open the window, thereby detecting the entrapment of the foreign matter, and further detecting the foreign matter. Can be taken out.

As described above, in the pressure detecting circuit of the present embodiment, even if the resistance value Rs of the pressure sensitive sensor 2 varies, or even if the resistance value Rs changes with the ambient temperature or over time, it is possible to detect In the steady state where no pressure is applied to the pressure sensor 2, the voltage eo at the output end of the first amplifier 1 is equal to the reference voltage Eref. On the other hand, when pressure is applied to the pressure-sensitive sensor 2 due to a foreign substance being caught, the applied voltage x rises in direct proportion to P ^N. The value or differential value of the applied voltage can be detected after amplification. Therefore, even if the resistance value Rs of the pressure-sensitive sensor 2 varies due to manufacturing, temperature change, or temporal change, an applied voltage x that is substantially directly proportional to P ^N is obtained, and this applied voltage x is obtained. After being amplified, it is used as a pressure detection signal, and as a result, highly reliable foreign matter entrapment detection is performed.

Although the pressure detecting circuit of this embodiment is an unbalanced type, it may be a balanced type by combining two circuits shown in FIG. In this case, the grounding resistor 3, the reference voltage source 5, the capacitor 7 and the resistor 10 have an unbalanced type grounding terminal whose inverting input terminal is the inverting input terminal of the first amplifier and non-inverting input terminal of the second amplifier. End, the non-inverting input of the first amplifier and the inverting input of the third amplifier. Further, balanced output voltages that are strong against external noise are obtained from the output terminals of the two sets of the third amplifiers.

[0022]

As described above, the pressure detecting circuit of the present invention is not affected by variations in the resistance value of the pressure sensitive sensor due to manufacturing variations, temperature changes, or changes over time, and the applied pressure is further reduced. It is possible to obtain a stable pressure detection signal that is substantially directly proportional to P. Therefore, it is possible to improve the reliability of entrapment of foreign matter.

[Brief description of drawings]

FIG. 1 is a typical characteristic diagram of pressure P-resistance value Rs of a pressure-sensitive sensor.

FIG. 2 is a typical characteristic diagram of pressing force P-applied voltage x when a pressure detection circuit and a pressure-sensitive sensor of the present invention are used.

FIG. 3 is a circuit diagram showing a configuration of an embodiment of a pressure detection circuit of the present invention.

[Explanation of symbols]

 1 1st amplifier 2 Pressure sensitive sensor 3 Ground resistance 4 2nd amplifier 5 Reference voltage source 8 3rd amplifier

Claims (1)

[Claims] 1. A pressure-sensitive sensor whose resistance value changes according to a pressing force, a pressure-sensitive sensor connected between an inverting input terminal and an output terminal, and a ground resistance connected to the inverting input terminal. One amplifier, the output of the first amplifier may be connected to the inverting input, the reference voltage source may be connected to the non-inverting input, and the non-inverting input of the first amplifier may be connected to the output. A second amplifier and a third amplifier for amplifying a voltage applied to a non-inverting input terminal of the first amplifier are provided, and a pressure applied to the pressure sensor from an output terminal of the third amplifier. A pressure detection circuit characterized in that a detection signal according to the above is obtained.