CN2591601Y - Photoelectric vibrating string type force-measuring sensor - Google Patents

Abstract

The utility model relates to a novel photoelectric vibrating string type force-measuring sensor, which comprises a tension metal string which is fixed on a deformable body. One end of the metal string is connected with ground, the other end is connected with a pulse current source, and both sides of the metal string are provided with magnetic fields. The utility model is characterized in that both the sides of the metal string are respectively provided with a laser and a photoelectric position-sensitive device, the tension of the metal string is changed through the deformable body by the applied force, and the metal string in the magnetic fields generates free vibration through pulse current. A laser irradiates the metal string, the photosensitive surface of the photoelectric position-sensitive device generates the vibrating shadow of the metal string, and the output photoelectric current is converted to the frequency of photoelectric voltage through a signal processing circuit which comprises an I/V converting circuit and a frequency meter. The frequency of the photoelectric voltage is measured, and the loading force information that the tension relative to the frequency of a vibrating string is obtained. The utility model has the advantages that the sensor can avoid the noise which is provided by an electromagnetic induction method, wherein, the electromagnetic induction method is easily disturbed by the strong electromagnetism on site, and the utility model obtains the stable vibrating string frequency signals, enlarges the measuring range, and enhances the load detection capability.

Description

A photoelectric vibrating wire load cell device

Technical field:

The utility model relates to a device for measuring force by using a semiconductor laser and a photoelectric potential sensitive device in a vibrating wire sensor.

Background technique:

"Construction Technology" magazine, No. 12, 1997, page 31, pointed out that the vibrating wire force sensor is a commonly used sensor for force measurement using the corresponding relationship between the natural frequency of the vibrating wire and the force of the vibrating wire. Its structure is generally to install a tensioned metal wire as a resonant element, usually called a vibrating wire, on a bow-shaped deformable body. Under electromagnetic excitation, the vibrating wire vibrates according to its natural frequency; by changing the tension T of the vibrating wire, different vibration frequencies f can be obtained, that is, there is a functional relationship between the tension force and the resonance frequency. Therefore, the force of the sensor can be obtained by measuring the vibration frequency of the vibrating wire through electromagnetic induction, so as to finally achieve the purpose of force measurement.

In order to obtain high accuracy of the vibrating wire load cell, the vibration frequency of the vibrating wire must be accurately measured. Because there is a functional relationship between the tension force of the vibrating wire and the vibration frequency of the vibrating wire, the measurement of the frequency of the vibrating wire is very important to improve the accuracy of the sensor. The existing frequency measurement method mainly adopts the electromagnetic method, and the frequency of the vibrating wire is obtained by measuring the induced current by cutting the magnetic force line in the magnetic field by the vibrating wire. Due to the presence of inductive loads such as coils, this method is easily disturbed by external electromagnetic fields and has poor stability. So far, there has been no report on a device for measuring force using the principle of a photopotential sensitive device (PSD).

Technical content:

The utility model provides a device for measuring the force of a photoelectric vibrating wire with a semiconductor laser and a photoelectric potential sensitive device, which has high precision and is not disturbed by external environmental factors.

This device for measuring force by photoelectric vibrating wire includes a deformable body (1) that can withstand force; both ends of the metal string (4) are tightened and fixed in the middle of the deformable body (1); one end of the metal string is grounded, and the other end is connected to a pulse On the current source (5); the magnetic field (3) fixed on both sides of the metal string; it is characterized in that a laser (2) as a light source is arranged on one side of the metal string and relatively fixed on the laser optical path on the other side of the metal string A photoelectric potentiometer (6) for receiving metal string shadows; the photoelectric current output by the photoelectric potentiometer (6) is converted to the frequency of photovoltage by a signal processing circuit (7) comprising an I/V conversion circuit and a frequency meter; Both the photoelectric potentiometer and the semiconductor laser are packaged in the load sensor box.

During the measurement, the two ends of the metal string are tightened and fixed in the middle of the deformable body, and the force applied on the deformable body changes the tension of the metal string through the deformable body; in the metal string in the magnetic field, the pulse current is used to make the string oscillate freely; The laser is irradiated on the metal string, and the distance between the laser and the photoelectric potentiometer and the metal string is adjusted, so that an obviously amplified vibration shadow of the metal string is generated on the photosensitive surface of the photoelectric potentiometer, and the photocurrent output by the photoelectric potentiometer is converted into Photovoltage, by measuring the frequency of the photovoltage, the tension or loading force information related to the frequency of the vibrating wire can be obtained.

The utility model adopts the method of photoelectric vibrating wire to measure the load, which is based on the principle of the photoelectric position sensitive device: the photoelectric position sensitive device is a side-effect silicon photoelectric device, which has a complete photosensitive surface through the planar diffusion manufacturing process. There are two anode contact points on both ends of the face. When the incident light spot is irradiated at the position of the photosensitive surface S, the photogenerated carriers generated by the incident photons are separated by the electric field, and a photocurrent is formed in the external circuit, and the photocurrent flowing through one of the anodes can be expressed by the following formula:

I ₁ =I ₀ (1-S/L) (1) Another I ₂ =I ₀ S/L (2)

In the formula, I ₀ is the photogenerated current; L is the distance between the two anodes; S is the distance between the incident spot and the anode;

Equations (1) and (2) show that the photocurrent has a linear relationship with the spot position S; the change of the spot position, that is, the position of the shadow cast by the metal string will immediately cause the change of the photocurrent.

Compared with the prior art, the utility model has the following advantages and positive effects:

Since the utility model uses optoelectronic devices such as photoelectric potentiometers and semiconductor lasers that have not been used in vibrating wire sensors in the past, they do not belong to inductive loads, and are all packaged in the load sensor box, without introducing interference from other light sources , so it can avoid the electromagnetic induction method being susceptible to the noise caused by the strong electromagnetic interference at the measurement site, so the photoelectric laser measurement can obtain a more stable vibration frequency signal than the existing method.

When the load changes and the tension of the vibrating wire changes the natural frequency of the vibrating wire, since the frequency response of the photoelectric potentiometer and the semiconductor laser are very high, the sensor can reflect the frequency in time by using this photoelectric method for measurement. change, while expanding the measurement range.

By changing the position of the semiconductor laser and the photoelectric potentiometer to the metal string, the size of the shadow projected on the photosensitive surface of the photoelectric potentiometer can be nearly ten times the diameter of the string, thus amplifying the vibration amplitude by nearly ten times and improving the load detection. ability.

Description of drawings:

Figure 1 is a schematic diagram of a device for measuring load using a photoelectric vibrating wire using a semiconductor laser and a photoelectric potentiometer.

Figure 2 is a schematic diagram of the PSD signal processing circuit.

Figure 3 shows the laser drive circuit for automatic power control.

Detailed ways:

Example 1:

The specific implementation device of this embodiment adopts Jinghu strings with a diameter of 0.2mm and a string length of 30mm as the vibrating strings (4). On a pulse current source (5), the pulse current source adopts the method of capacitive discharge to provide a sharp pulse current with a duty cycle of 1% through the metal vibrating wire; two permanent magnets are fixed on both sides of the metal string to form magnetic field (3); the semiconductor laser (2) and the photoelectric potential sensitive device (6) are arranged on both sides of the metal vibrating wire (4), and the metal vibrating wire (4) and the photoelectric potential sensitive device (6) are arranged on the laser beam On the road, the photoelectric position sensitive device (6) with a time response of less than 1 μs is adopted here; the output of the photoelectric position sensitive device (6) is converted into The frequency of the photovoltage; the photoelectric potentiometer and the semiconductor laser are all packaged in the load sensor box.

The signal processing circuit (7) is shown in FIG. 2 . Here the I/V conversion circuit uses a 4558 dual operational amplifier F1, the two signal outputs of PSD are connected to the two positive inputs of F1 respectively, R1, C1 are connected in parallel, R2, C2 are connected in parallel as negative feedback, and one end is connected to the output of F1 terminal and the negative input of F1. The two outputs of F1 are connected to a frequency meter to measure the frequency of the resulting photovoltage. Convert the photocurrent output by the photopotential sensor into photovoltage, and measure the frequency of the photovoltage,

The semiconductor laser used in this embodiment is equipped with an automatic power control semiconductor laser driving circuit, as shown in FIG. 3 . In this drive circuit, one end of LD and PD is connected to positive 5 volts; C5 is used to stabilize the power supply voltage, one end is connected to positive 5 volts, and the other end is grounded. R4 and D1 provide a stable working voltage for K1, one end of R4 is connected to positive 5 volts, and the other end is connected to the emitter of the amplifier K1. One end of D1 is grounded and the other end is connected to the emitter of K1. R3 is used to provide the DC bias of K1, one end is grounded, and the other end is connected to the base of K1. The base of K1 is connected to one end of PD, and the collector is connected to the base of K2. K2 is used to provide the driving current of LD. R5 is a current limiting protection resistor, one end is connected to LD, and the other end is connected to the base of K1. C4 and C3 are used to filter out the influence of high-frequency interference on LD. One end of C4 is grounded and the other end is connected to the base of K2. One end of C3 is connected to positive 5 volts, and the other end is connected to the collector of K2. The emitter of K2 is grounded. Use the PD that comes with the semiconductor laser to feed back the light intensity of the LD, and control the drive current of the LD through K1 to stabilize the light intensity.

During the test, the laser is irradiated vertically on the vibrating wire, and a shadow is produced on the photosensitive surface of the photopotential sensor. When the pulse current is passed into the vibrating wire in the magnetic field of the permanent magnet, the vibrating wire will vibrate at different frequencies according to the magnitude of the tension. Since the pulse current with a very low duty cycle is used, the frequency is very low, several Hz, so The generated induction force can only make the vibrating wire vibrate freely, but will not produce forced vibration, so the measured frequency is the natural frequency of the vibrating wire. At the same time, the vibration will make its shadow move up and down in the photosensitive surface, and the photocurrent of the photoelectric potentiometer will produce the same frequency change as the frequency of the vibrating string. The photocurrent is amplified and transformed into a corresponding voltage signal. By measuring the voltage From the frequency of the signal, the magnitude of the load related to the frequency of the vibrating wire can be obtained.

The measurement method of the utility model will not be disturbed by the external magnetism that the magnetic induction sensor is susceptible to, and can obtain a stable vibrating wire frequency signal. The vibrating wire frequency signal and the measured force are in a linear relationship, so stable signal of force. The measurement accuracy of the sensor can be greatly improved, the measurement range is expanded, and the load detection capability is improved.

Claims (1)

1. A device for measuring force by a photoelectric vibrating string, comprising a deformable body (1) capable of bearing force; a metal string (4) fixed at the middle of the deformable body (1) at both ends; one end of the metal string is grounded, and the other end is connected to the A pulse current source (5); a magnetic field (3) fixed on both sides of the metal string; it is characterized in that a laser (2) as a light source is arranged on one side of the metal string and is relatively fixed on the laser optical path and the other side of the metal string The photoelectric potentiometer (6) that is used to receive the shadow of the metal string on the side; the photoelectric current that the photoelectric potentiometer (6) outputs is converted into photovoltage by the signal processing circuit (7) that includes I/V conversion circuit and frequency meter Frequency; photoelectric position sensitive devices and semiconductor lasers are packaged in the load cell box.

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