Research On Capacitive Multi-parameter Detection Method For Metal Particles

As a kind of metal particles,the chips in the metal cutting process are an important carrier of machine tool operating conditions and product quality information.In the centralized chip removal system of the machining and manufacturing industry,the application of metal particles detection technology to achieve the detection of chip characteristics can greatly improve production efficiency and safety,reduce the incidence of equipment failures,and benefit the optimal control of the production process.In this paper,the capacitive multi-parameter detection technology of metal particles is studied,and a new type of capacitive sensor structure is designed to achieve the measurement of metal chip flow rate and size in motion in the pipeline.Firstly,for the uneven distribution of the sensitive field of traditional capacitive sensors and the special properties of metals different from non-metals in the electrostatic field,this paper first proposes a triangular electrodes differential capacitive sensor,which extends the measurement object of capacitive sensors to metals substance.Based on the multi-electrode theory,a mathematical model for measuring metal substances in a capacitive sensor is established:the metal substance in the electrostatic field can be regarded as an extra electrode,which increases the output capacitance value of the sensor.The increment of the capacitance value mainly depends on the shape of the metal substance and spatial location.On this basis,the COMSOL Multiphysics finite element simulation tool is used to establish a three-dimensional simulation model of the sensor,and the structural parameters of the sensor were optimized in conjunction with the quasi-dynamic simulation method.A dimensionless model was established to expand the applicability of the structure.Starting from the axial direction and cross section,the distribution characteristics of the sensitive field of the sensor are deeply analyzed.Taking the sensitive field uniformity error parameter as the evaluation index,the influence trends of several important structural parameters on the sensitive field of the sensor are further discussed,and a set of guiding sensor optimization design schemes are summarized.Finally,this sensor is applied to the measurement of metal chip flow velocity.The differential structure of the sensor can effectively improve the extraction accuracy of the peak frequency fm in the spatial filtering method.In terms of size measurement,theoretical analysis shows that the effective signal width τ is proportional to the particle size.A multi-parameter measurement system for metal particles was built based on the triangular electrodes differential capacitive sensor and the Pcap01,and the flow velocity and size parameters of metal chips were measured on the gravity conveying experimental platform.The experimental content includes the measurement of the moving velocity of multiple small iron balls of different diameters and the length of a single small iron rod under different working conditions.The choice of different measurement objects in the experiment is mainly due to the large difference in shape of different types of chips.Spherical metal particles are more representative in velocity measurement,and rod-shaped metal particles can better represent the chip size in size measurement.Theoretical analysis and experimental results show that the measurement system has good accuracy and repeatability.The experimental structure shows that in the velocity range of 2.44～5.34 m/s,the RSD of the measured velocity of three small iron balls of different sizes are less than 7%during continuous measurement.In the measurement of the size of the small iron rod,the reference length is in the range of 20～50mm,and the maximum error of the measurement result is about 27%.The standard deviation of the repeatability of this size measurement method is less than 8%,which is within the acceptable range.This structure can effectively improve the sensitive field distribution characteristics of the capacitive sensor and significantly reduce the influence of the spatial distribution of particles on the measurement results.