Research status and application of the hottest pie

With the popularization of automation and semi automation in various industries of the national economy, the automatic feeding device, as an indispensable part of the production line, puts forward higher requirements for its structure, noise, working principle, conveying accuracy and control difficulty, and the traditional vibrating feeding device can no longer meet the requirements. Therefore, in recent ten years, new vibration feeding devices using piezoelectric ceramics as the driving source have developed rapidly []

piezoelectric vibration feeding device is a new type of vibration feeding device that applies piezoelectric technology to vibration conveying. It uses the inverse piezoelectric effect of piezoelectric sheet to produce vibration, and uses it as a driving source to drive the chute to realize material conveying

1 research status at home and abroad

for this new type of vibrating feeding device, its structure and working principle are different from the traditional electromagnetic or mechanical driven vibrating feeding device, so it has many characteristics that the traditional vibrating feeding device does not have []:

(1) simple structure, more convenient installation and maintenance

(2) using piezoelectric film as the driving source, there is no need for motor, electromagnetic exciter and other driving devices, and there is no need for shaft, rod, belt and other mechanical transmission parts, with simple structure and easy processing

(3) changing any of the amplitude, pulse width and frequency of the driving signal can adjust the delivery rate, with many control parameters and good controllability

(4) no rotational inertia, almost no acceleration and deceleration process, rapid start and stop, fast response performance

(5) it does not produce interference electromagnetic fields and is not affected by electromagnetic interference signals

(6) low noise when working in low-frequency section or ultrasonic section

(7) work in resonance or sub resonance state, so the energy consumption is less

(8) the driving force is insufficient, so this kind of device is mostly used for micro or precision conveying of materials

piezoelectric vibration feeding device is a major breakthrough in the field of vibration feeding. Scientific and technological personnel at home and abroad have carried out research to varying degrees and achieved certain results [8], which can be divided into straight type and spiral type according to the way of material advance

1.1 research status abroad

in industrialized countries or regions, Japan and the United States are the most representative. Especially in Japan, the research on the theory, design and calculation of piezoelectric vibration feeding device is relatively in-depth and complete, and many new and special-shaped mechanism vibration feeding devices have also been introduced [9]

for the direct feed piezoelectric driven vibration feeding device, Japan has now reported three devices []. Figure 1 shows the first structure of the piezoelectric vibration feeding device reported in Japan. The piezoelectric sheet adopts double piezoelectric crystal sheets. When alternating current is added to the piezoelectric sheet, the double piezoelectric crystal sheet produces periodic bending movement, which drives the chute to move obliquely, so as to realize the transportation of materials

Figure 2 shows the second structure of the new machine that has been reported in Japan after one hour of use, and the piezoelectric chip also uses a double piezoelectric crystal chip

Figure 3 shows the third structure that has been reported in Japan. Instead of using double piezoelectric crystal chips, the alternating current applied to a pair of piezoelectric chips is in the opposite phase

Figure 4 shows a piezoelectric driven helical piezoelectric vibrating hopper reported in the United States. When an AC voltage with opposite phases is applied to a pair of piezoelectric sheets, the piezoelectric crystal generates a telescopic movement in the length direction, driving the steel sheets and spring sheets to conduct reciprocating bending and torsional vibration []

great progress has been made in the research of piezoelectric vibration feeding devices abroad. In addition to the common characteristics of the above piezoelectric vibration feeding devices, they also have their own unique features:

(1) the piezoelectric sheet applies its telescopic vibration mode in the length direction

(2) the use of specially made double piezoelectric crystal chips, or the application of opposite phase voltage on a pair of piezoelectric chips, not only increases the production cost, but also greatly improves the requirements for power supply

(3) the direct feed piezoelectric vibrating feeding device adopts the method of separating the vibrating element from the chute support element, which simplifies the stress system of the vibrating element

(4) most of them need to increase the vibration body to expand the vibration amplitude and complicate the structure of the device

(5) although the supporting element of the chute (tray) and the vibrating element are separated from each other, the vibrating element still bears the weight of the chute (tray) and the material, which makes the stress of the vibrating element complex and affects the working stability of the device

(6) the vibration elements of the second straight feed structure and the helical piezoelectric vibration feeding device adopt a fixed installation method, which brings great constraints to the movement of the chute, and overcoming this constraint will consume more energy

1.2 domestic research status

the overall level of research on piezoelectric vibration feeding devices in China still lags behind developed countries and regions, and there are few molding products. Most of the piezoelectric vibration feeding devices on automatic production lines or equipment of domestic manufacturers come from countries and regions with relatively developed manufacturing industries such as Japan and the United States []. The more successful structural forms in China include ultrasonic powder conveying device, piezoelectric vibrating hopper, floating piezoelectric vibrating feeding device and floating piezoelectric vibrating screw feeding device, which will be introduced one by one below

1.2.1 ultrasonic powder feeding device []

the structure of ultrasonic powder feeding device is shown in Figure 5. This research fills the gap in the domestic research on ultrasonic powder conveying, and it has the following characteristics:

(1) it works in the ultrasonic frequency band, so there is no noise

(2) the piezoelectric sheet used needs special customization because it works in the ultrasonic frequency band

(3) only carborundum powder with good flow performance can be transported, and large particle materials and small parts with irregular shape cannot be transported

(4) the piezoelectric sheet is clamped between two pressing plates, and the heat dissipation condition is extremely poor, which seriously affects the service life of the piezoelectric sheet and the working stability of the device

1.2.2 piezoelectric vibrating hopper [22]

piezoelectric vibrating hopper is based on the existing Japanese piezoelectric vibrating feeding device, which combines the support element of the vibrating body with the vibrating element, so that the element not only supports the chute, but also completes the vibration task. As shown in Figure 6:

compared with similar foreign products, the piezoelectric vibrating hopper has the following characteristics:

(1) the support element of the chute and the vibrating element are combined into the same element, but the vibrating element is used to support the chute and cooperate with the piezoelectric sheet to generate vibration. Therefore, the weight of the material and the chute acts on the vibrating element for a long time, which has a great impact on the vibration stability of the vibrating element and the piezoelectric sheet

(2) there is no need to add a vibrator to increase the vibration amplitude, simplifying the structure of the device

(3) the piezoelectric sheet applies the inverse piezoelectric effect in the thickness direction, and there is no need to apply a special power supply

(4) the lower end of the vibrating element is fixed on the base, which will restrict the vibration of the chute, limit the movement of the chute, and consume more energy

1.2.3 floating piezoelectric vibration feeding device [23]

floating piezoelectric vibration feeding device is shown in Figure 7, and its main component is the floating base. It uses the vibration mode in the thickness direction of the piezoelectric sheet to drive the material trough to move and realize the material transportation

the floating piezoelectric vibrating feeding device also has its unique features:

(1) the chute adopts a floating structure, which not only separates the vibrating element from the chute support element, but also avoids the long-term effect of the weight of the chute and materials on the vibrating element, which affects its working stability

(2) low working frequency and low noise

(3) the piezoelectric chip used in the device does not need special customization. Xie Ying said in her speech that the vibration mode in the thickness direction of the piezoelectric chip is applied, so there is no need for a special driving power supply to generate phase difference

(4) adjusting any one of voltage, frequency and pulse width can control the transmission efficiency, so there are many control parameters and good controllability

(5) the size of the elastic plate has a great influence on the working frequency of the device

(6) the resonance of the device marks that after three years of hard work by the technology center, production center and participating units, the phase II ethylene glycol project, which has attracted much attention, has officially shifted from the project construction stage to the trial production stage. The frequency band is very narrow, and the adjustment and stability of the resonance frequency are not easy to control; There is some vibration, so the noise of the device is greatly reduced

(7) the elastic plate is small, so the driving force is insufficient, and the conveying speed is relatively slow

2. Application

in various fields of industry and agriculture and laboratory 2 Rotating the screw on the zigzag rod, the transportation, weighing, sub loading, adding and other operations of various solid particle materials are extremely frequent [18]. Especially in the field of chemical industry, the use of floating piezoelectric vibration feeding device to treat granular materials that are not suitable for contact with human body can reduce or

avoid environmental pollution due to loss; Similarly, in the field of medicine and food, the use of floating piezoelectric vibration feeding device to treat drugs and food particles can avoid unhealthy factors caused by human direct contact

1.2.4 floating piezoelectric vibrating screw feeding device [24]

as an ideal automatic feeding device for solid particle materials, floating piezoelectric vibrating feeding device can be applied in the following aspects []:

(1) micro precision conveying with accurate weighing, testing and control system can realize automatic micro precision conveying of solid particle materials and improve work efficiency and operation accuracy. For example, the micro precision transportation of a small amount of chemical components in pharmaceutical production

(2) it is used for variable conveying to cooperate with sensors and automatic control system, which can realize variable conveying of materials according to the actual situation. For example, it is used for variable rate fertilization and variable rate seeding

(3) it is used in automatic production line. On the automatic production line, it realizes the automatic continuous, timed and quantitative addition of solid particle materials, reduces the error caused by human factors, and also reduces the harm of harmful substances to human body. For example, in the automatic production line of chemical products, a small amount of harmful ingredients are added automatically

(4) for other solid particle material processing equipment combined with screening, grinding, filling, packaging and other processing equipment, the floating piezoelectric vibrating screw feeding device has the same working principle as the floating piezoelectric vibrating feeding device, and its structure is shown in Figure 8

conclusion

in conclusion, as a new member in the field of vibration feeding, piezoelectric vibration feeding device has attracted the attention of scientific and technological personnel at home and abroad, and the research in this area is also increasingly perfect. Because of its simple structure, low noise, low power consumption, good working stability and controllability, it can be predicted that the piezoelectric vibration feeding device has broad application prospects in industry, agriculture, chemical industry, medicine and other fields. (end)