JPS59147256A - Piezoelectric sensor - Google Patents

Abstract

PURPOSE:To enable stable detection with high accuracy by simplifying an output mode and reducing load, by subjecting drive voltage applied to one terminal to voltage conversion by the amplitude variation of a piezoelectric vibrator while outputting the converted voltage from the other terminal as the change of oscillation frequency. CONSTITUTION:The metal electrode 11 and an opposed electrode 12 molded on the magnetic element 10a of a piezoelectric vibrator 10 in a closely adhered state are connected between a transistor 20 and an earth 30. The high voltage to be applied between both electrodes is subjected to voltage conversion by the amplitude variation of the piezoelectric vibrator 10 to be obtained as the change of oscillation frequency from a resistor 40 and the frequency change is taken out from an output terminal 60 through a capacitor 50 from the collector of the transistor 20. The vibrator 10 of this piezoelectric sensor is arranged so as to be attached toner hopper of an electronic copier. When toner remains, the piezoelectric vibrator 10 is not vibrated by the toner wt. but, when the toner is consumed, the piezoelectric vibrator 10 is enabled in vibration by load release and an oscillation signal is outputted from the output terminal 60.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to improvements in piezoelectric sensors using piezoelectric vibrators.

BACKGROUND ART Conventionally, a piezoelectric sensor used for detecting the remaining amount of toner in an electronic copying machine, for example, is a three-terminal piezoelectric vibrator 10 as shown in FIG.
The main electrode 11 and a metal diaphragm 12 serving as a counter electrode are connected between the output terminal of the amplifier 20 and the ground 30, and a divided electrode 13 is insulated and separated from the main electrode 11. is connected to the input terminal of the amplifier 20 to form an automatic oscillation circuit (see Japanese Patent Laid-Open No. 55-38874). However, in a piezoelectric sensor using this three-terminal piezoelectric vibrator, the vibration mode is complicated and the load on the lead wires etc. is large, so stable detection characteristics cannot be obtained. This also has the drawback that it cannot be checked.

DISCLOSURE OF THE INVENTION An object of the present invention is to provide a piezoelectric sensor that can obtain stable detection characteristics by eliminating such drawbacks.

That is, in the piezoelectric sensor according to the present invention, the drive voltage applied to one end is converted into voltage by the amplitude fluctuation of the piezoelectric vibrator, and is output from the other end as an oscillation frequency change. By incorporating a terminal type piezoelectric vibrator, the output voltage is obtained by a resistor connected in series with the piezoelectric vibrator without having a feedback electrode section.

The structure of the invention will now be described based on the embodiment shown in FIG. 2.

This piezoelectric sensor is constructed by incorporating a piezoelectric vibrator lO that vibrates due to the load action from the object to be detected. As the piezoelectric vibrator 10, a unimorph type can be used, and a metal electrode 1 is formed on one side of the ceramic body 10a.
It is constructed of a two-terminal type in which the counter electrode 12 is a metal diaphragm which is closely molded with the porcelain body 10a and is integrally attached to the porcelain body 10a. Each of the electrodes 11 and 12 is connected between the transistor 20 and the ground 30, and a resistor 40 connected in series converts the high voltage applied between the two electrodes by the amplitude fluctuation of the piezoelectric vibrator 10. can be obtained as an oscillation frequency change. Further, the circuit is configured such that the oscillation output is taken out from the collector of the transistor 20 through the capacitor 50 and from the output terminal 60.

Although the oscillation circuit of the piezoelectric element 10 uses the transistor 20 to amplify the output voltage, an operational amplifier may be used instead to control the sensitivity.

Effect of the Invention The piezoelectric sensor configured as described above can be incorporated into an electronic copying machine as a sensor for detecting the amount of remaining toner. In that case, the vibrator 10 of the piezoelectric sensor is installed or arranged inside or on the side of the 1-ner hopper, and when toner remains, the piezoelectric vibrator 10 is not vibrated by heavy pressure, and when the toner is depleted, the load is It is possible to configure the piezoelectric vibrator 10 to be turned off by releasing the vibration function. The vibration mode can be a simple oscillation output because the high voltage applied to the metal electrode 11 of the piezoelectric vibrator IO is directly extracted from the counter electrode 12 as a change in oscillation frequency without being fed back.

Further, this piezoelectric sensor can also be used as a pressure sensor for liquid or gas, and in this case, the piezoelectric vibrator 10 may be mounted in the flow path of the liquid or gas so that the amplitude can be varied by the action of a load.

As described above, according to the piezoelectric sensor according to the present invention, by incorporating a two-terminal type piezoelectric vibrator, the output mode can be simplified, and the load on lead wires etc. can be reduced, resulting in stable and accurate performance. This makes it possible to perform high-level detection, and to easily maintain and manage the device itself.

[Brief explanation of drawings]

FIG. 1 shows an oscillation circuit of a piezoelectric sensor according to a conventional example, and p
Figure lS2 shows an oscillation circuit of a piezoelectric sensor according to the present invention. 10: 2-terminal piezoelectric vibrator, 11, 12: electrode. Patent applicant Tokyo Denki Kagaku Kogyo Co., Ltd. Figure 1

Claims (1)

[Claims] A piezoelectric sensor characterized in that it incorporates a two-terminal piezoelectric vibrator that detects amplitude fluctuations due to a load of a detection target by a voltage change applied between both electrodes and outputs the same as an oscillation frequency change.