Patent ID: 12203468

In the figures,1—piston rod,2—strain gauge component,3—first strain gauge,4—second strain gauge,5—third strain gauge,6—first bridge arm,7—second bridge arm,8—signal collection unit,9—flywheel,10—photoelectric sensor,11—data processing unit.

DETAILED DESCRIPTION

Specific embodiments of the present disclosure will be described below in detail with reference to the accompanying drawings. According to these detailed descriptions, those skilled in the art can clearly understand the present disclosure and can implement the present disclosure. Without departing from the principle of the present disclosure, features in different embodiments may be combined to obtain new implementations, or some features in some embodiments may be replaced to obtain other preferred implementations.

A strain gauge is a component for strain measurement, which is composed of a sensitive grid or the like. The working principle of a resistance strain gauge is based on a strain effect. That is, when mechanical deformation occurs on a conductor or semiconductor material under the action of external forces, a resistance value thereof changes accordingly. This phenomenon is referred to as the “strain effect”.

A quadrilateral measurement bridge circuit composed of a resistor, a capacitor, an inductor and so on is referred to as an electric bridge, wherein four sides of the electric bridge are bridge arms. As a measurement circuit, a DC power supply is connected to two ends of a diagonal of the quadrilateral to extract voltage across the other diagonal. Based on a balance equation of the electric bridge, parameters (such as resistance, resistance, capacitance, and inductance) of a component to be measured can be obtained according to values of known components in the bridge arms.

With reference toFIG.1toFIG.11, the present disclosure provides a device for monitoring oil pressure in an oil cylinder of a diaphragm compressor, which includes a piston rod1and a strain gauge circuit. The strain gauge circuit includes a strain gauge component2and a bridge circuit connected, and the strain gauge component2is arranged on the surface of the piston rod1.

The strain gauge component2is pasted onto the surface of the piston rod1by an adhesive. An element attached with the strain gauge component2is always in a certain temperature field. If a linear expansion coefficient of the sensitive grid of the strain gauge is not equal to that of construction material, the resistance of the sensitive grid may change when the temperature changes because extensions (or compressions) of the sensitive grid and the element are not equal and thus additional tension (or compression) is exerted on the sensitive grid, which leads to inaccurate measurement. This phenomenon is referred to as a temperature effect.

The strain gauge component2is a sensor whose resistance changes with stress. Almost all the strain gauge components2have lower sensitivity. By using a bridge circuit, the sensitivity of the strain gauge component2can be increased manyfold, and input and output keep a linear relation. The detection of the change of the strain gauge component using the bridge circuit also has the advantages of lower passing electric current and lower self-heating of the strain gauge. Therefore, the bridge circuit is frequently used in the application of the strain gauge sensor. The bridge circuit includes a one-quarter bridge connection mode, a half-bridge connection mode, and a full-bridge connection mode. A lead wire of the strain gauge is a 25 mm silver-coated copper wire (0.12 mm to 0.16 mm in diameter). The piston rods of different compressors have different diameters, and thus different models of strain gauges may be selected. That is, the strain gauges may be selected according to actual needs.

Further, the strain gauge component2includes a first strain gauge3, and the first strain gauge3is connected to the bridge circuit.

The surface of piston rod1is provided with only one strain gauge, i.e., the first strain gauge3. The first strain gauge3is also referred to as a working strain gauge and may be configured to measure the strain of the piston rod1. The first strain gauge3is attached to piston rod1. When the length of the piston rod1changes, the first strain gauge3will be compressed or stretched accordingly. Therefore, the resistance of the first strain gauge3will change, and the change of the resistance will cause the output voltage of the bridge circuit to change. Oil pressure is obtained after processing a voltage signal collected.

Further, the strain gauge component2includes a second strain gauge4and a third strain gauge5, wherein the second strain gauge4is arranged along an axial direction of the piston rod1, and the third strain gauge5and the second strain gauge4are perpendicular to each other. The second strain gauge4is connected to a first bridge arm6, and the third strain gauge5is connected to a second bridge arm7.

Two strain gauges are used, one is the working strain gauge, i.e., the second strain gauge4, and the other one is a compensation strain gauge, i.e., the third strain gauge5. The working strain gauge is pasted along the axial direction, and the compensation strain gauge is pasted perpendicular to the axial direction. The working strain gauge and the compensation strain gauge are distinguished by the direction of pasting. A compensation strain gauge is pasted to the same member. However, in a direction no force is exerted (a direction perpendicular to the axial direction), the strain of the strain gauge1is ε1, and the strain of the compensation strain gauge is ε2, wherein the ε1includes a deformation caused by axial tension and compression and deformation caused by temperature, and the ε2only includes the deformation caused by temperature. Therefore, by subtracting, the deformation caused by temperature is cancelled out. In this way, the temperature effect is eliminated. There are three modes for pasting the strain gauge: one-quarter bridge connection mode, a half-bridge connection mode, and a full-bridge connection mode, all of which are reasonable. In both the one-quarter bridge connection mode and the half-bridge connection mode, only two strain gauges are connected; and in the full-bridge connection mode, four strain gauges are connected. Here, the bridge circuit is constructed by using the half-bridge connection mode, such that the output of the strain gauge is increased and the temperature effect on the lead wire is eliminated. One working strain gauge is pasted along the axial direction in a lateral side of the piston rod, and one compensation strain gauge is pasted close to the working strain gauge and perpendicular to the working strain gauge. In the half-bridge connection mode as shown inFIG.8, one working strain gauge and one temperature compensation strain gauge are respectively connected to two adjacent bridge arms, namely the first bridge arm6and the second bridge arm7, and the other two bridge arms are connected to a fixed resistor, respectively.

Further, the strain gauge component2includes a fourth strain gauge, a fifth strain gauge, a sixth strain gauge, and a seventh strain gauge. The fourth strain gauge is arranged along the axial direction of piston rod1, the fifth strain gauge and the fourth strain gauge are perpendicular to each other, the fourth strain gauge is connected to a full-bridge circuit, and the fifth strain gauge is also connected to the full-bridge circuit. The sixth strain gauge is arranged along the axial direction of piston rod1, the seventh strain gauge and the sixth strain gauge are perpendicular to each other, the sixth strain gauge is connected to the full-bridge circuit, and the seventh strain gauge is also connected to the full-bridge circuit.

Here the bridge circuit is constructed by using the full-bridge connection mode. However, as far as the present disclosure is concerned, most preferably the bridge circuit is constructed by using the half-bridge connection mode.

Further, the device for monitoring oil pressure in the oil cylinder of the diaphragm compressor also includes a photoelectric sensor unit and a signal collection unit8. The photoelectric sensor unit includes a flywheel9, wherein the flywheel9and a photoelectric sensor10are arranged correspondingly. The signal collection unit8is connected to the strain gauge component2, the signal collection unit8is connected to the photoelectric sensor unit, and the signal collection unit8is also connected to a data processing unit11.

There are many methods for detecting piston dead center signals. Hall type sensors and photoelectric sensors are commonly used in compressor technologies. A transmitting end of a sensor is generally arranged on flywheel9, and the photoelectric sensor10generally is a reflective photoelectric sensor. An installation location of a probe of the photoelectric sensor10needs to be accurately positioned. That is, the flywheel9is rotated such that the piston is located at an inner dead center and an outer dead center respectively, and then the probe is aligned with a transmitting point (magnetic steel, iron block or reflective stripe).

The flywheel9rotates around a central vertical axis until a barring gear reaches the position of a top dead center of the piston, which is used as a benchmark of phase reference. At this moment, a marker is made at any location of the flywheel9, and a light spot sensor is mounted on a chassis, ensuring that the light spot sensor is aligned with the marker. Under normal circumstances, after the photoelectric sensor10collects a stable signal, and when the marker shifts to the photoelectric sensor10, an impact signal appears and serves as a cycle start location. There is one cycle between every two continuous impact signals.

The photoelectric sensor unit obtains a periodic signal to determine a complete cycle. The photoelectric sensor10is mounted at the flywheel9, and an initial value of a crank angle θ of the compressor is determined as 0 by an outer dead center signal obtained. An analog signal outputted by the photoelectric sensor10is converted by the signal collection unit8into a final required digital signal, which is stored for subsequent analysis and processing.

Strain collection cards NI9237 and NI9205 and a collection suitcase cDAQ-9185 from National Instruments (NI) Corporation are used here for signal collection, and data collection is performed by writing a LabVIEW program.

Further, data processing unit11is an intelligent terminal.

The intelligent terminal here refers to equipment that can perform calculation and analysis on data, such as computers. In addition to storing data, the computers also run data collection programs to control the sampling and display of signals, for example, setting parameters such as sampling frequency and sample storage length. The computers display the collected dead center signals of the photoelectric sensor10and the voltage signals outputted by the strain gauge circuit. The display may be monitored in real-time.

Further, signal collection unit8includes a collection card and a signal conditioning module. A data sampling frequency and a corresponding collection channel are set.

The signal collection unit8implements a series of functions such as signal filtering, amplification, conditioning and A/D conversion.

The present disclosure also provides a method for monitoring oil pressure in an oil cylinder of a diaphragm compressor. The method includes the following steps.

In Step 1, the signal collection unit synchronously collects a first voltage signal outputted by a photoelectric sensor and a second voltage signal outputted by a strain gauge circuit, converts the collected first voltage signal into a first digital signal for storage, and converts the collected second voltage signal into a second digital signal for storage.

In Step 2, the starting and ending time of one complete cycle is determined according to the first digital signal.

In Step 3, the second digital signal is processed according to the starting and ending time of the complete cycle to obtain an oil pressure value.

The first voltage signal is the output of the photoelectric sensor10, i.e., the dead center signals.

Further, processing the second digital signal in Step 3 includes:(1) the calculating strain of a piston rod:

ɛ⁡(θ)=4⁢e⁡(θ)(1+v)⁢E⁢Ks,wherein θ represents a crank angle, ε(θ) represents the strain, e(θ) represents the second digital signal, ν represents a Poisson's ratio, E represents an elastic modulus, and Ksrepresents a sensitivity coefficient of a strain gauge;(2) calculating the load of the piston rod: Fp(θ)=ARε(θ),wherein ARrepresents a cross-sectional area of the piston rod, and F(θ) represents the load of the piston rod; and(3) calculating an oil pressure: Fo(θ)=Fp(θ)−F1(θ), po(θ)=Fo(θ)/AP,wherein Fo(θ) represents an oil side pressure, F1(θ) represents a reciprocating inertial force, the reciprocating inertial force F1(θ)=mprω2(cos θ+λ cos 2θ), wherein mprepresents a reciprocating inertial mass, r represents a crank radius, ω represents a rotation speed of the compressor, λ represents a crank radius-connecting rod length ratio θ represents the crank angle, and po(θ) represents an oil pressure, and APrepresents a cross-sectional area of a piston.

During calculation, the computers may be used to perform calculation according to the above formulas, and an implementation method may be software programming or may be Excel.

The calculation is carried out using the formulas based on the data collected. The computers are used here, and the LabVIEW program is written to carry out the calculation.

Further, in Step 1, the first voltage signal is subjected to filtering, amplification, conditioning and A/D conversion, then is converted into a first digital signal, and the first digital signal is transmitted to an intelligent terminal for processing. The second voltage signal is subjected to filtering, amplification, conditioning and A/D conversion, then is converted into a second digital signal, and the second digital signal is transmitted to the intelligent terminal for processing.

In the device for monitoring oil pressure in the oil cylinder of the diaphragm compressor provided by the present disclosure, the strain gauge component2is arranged on the surface of piston rod1, and the strain gauge component2is connected to the bridge circuit. In this way, the sensibility of the strain gauge component2is improved, and input and output keep a linear relation. The strain gauge component2is noninvasively arranged on the piston rod1of the diaphragm compressor to measure the load of the piston rod1, such that the oil pressure can be measured indirectly, and thus the oil pressure of the diaphragm compressor can be measured nondestructively. Nondestructive and noninvasive monitoring of the diaphragm compressor is safe and reliable and can achieve accurate monitoring of the oil pressure, especially in high-pressure working conditions.

“First and second . . . ” in the present disclosure are merely for the purpose of distinguishing the corresponding strain gauges, which have the same structures.

Although the present disclosure is described above with reference to specific embodiments, those skilled in the art should understand that within the principle and scope disclosed in the present disclosure, numerous modifications may be made to the configuration and details disclosed in the present disclosure. The protection scope of the present disclosure is determined by the appended claims, and the claims are intended to cover all modifications included in the literal meaning or scope of equivalent technical features in the claims.