Study on the principle of three-stage feeding syst

2022-08-03
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Research on the principle of three-stage feeding system of gravity weighing filling machine

in recent years, in China's food industry, the materials processed mainly include granular materials, powdery materials and liquid materials according to their physical shape, and the corresponding filling equipment mainly includes weighing type and volumetric type. The feeding methods of the filling machine mainly include gravity feeding (suitable for materials with good fluidity) and mandatory feeding (such as belt feeding, screw feeding and electric vibration feeding). For the gravity weighing filling machine, it can automatically divide the loose material into several equal, stable and separated individuals according to the preset weight. Because of its accurate measurement, wide weighing range, strong applicability to materials, and easy to realize the automation of filling production line, it has become the preferred quantitative filling equipment for handling small granular materials with good fluidity in the food industry

since China introduced the quantitative flour filling machine from the United States in the 1980s, after more than 20 years of digestion and absorption, up to now, we have been able to produce filling devices for processing a variety of materials, with high filling speed and high filling precision. Although we have made gratifying achievements, there is still a gap in weighing accuracy and speed compared with similar foreign machines. The main reason is closely related to less investment in filling theory by domestic filling enterprises. There are many factors that affect the weighing accuracy and speed of the filling equipment. This paper does not discuss the mechanism of filling accuracy and speed from the perspective of the feeding mode of the gravity weighing filling machine, rather than from the response speed and accuracy of the controller, the quality of components, the adjustment of system parameters, the structural rationality of the weighing bucket, the working environment and the physical characteristics of materials

quantitative filling is one of the main links in many industrial production processes. With the continuous improvement of the level of industrial modernization, the quantitative filling industry has also bid farewell to the traditional old model and developed rapidly in the direction of high precision, high speed, high reliability and high labor productivity

1 working principle and existing problems of common gravity filling machines

the whole operation cycle of the filling machine includes the following steps: tare weight verification → fast feeding → slow feeding → weighing verification → unloading. After starting the filling machine, the control system will first automatically verify the tare weight of the weighing bucket. If the tare weight is not zero, the weight will be compensated to the set filling weight to ensure that the net weight of the weighed material will not be affected by the tare weight of the weighing bucket and will always remain at the user set value

after the tare weight is verified by the control system, the fast feeding signal is output to the feeding device, so that the fast feeding cylinder in the feeding device controls the feeding door to open quickly, and the materials flow into the weighing bucket with a large flow. At this time, the control system continuously monitors the weight change of the weighing bucket by receiving the sensor signal. When the weight of the material entering the weighing bucket is close to the set weight of the fast feeding, the system controls that the content of MoO3 and mo9o26 in the material changes little, the fast feeding cylinder closes quickly, and the fast feeding signal turns into the slow feeding signal. At this time, the material flows into the weighing bucket with a small flow to ensure that the system controls the material flowing into the weighing bucket with a high accuracy. Through the system mathematical model calculation, the control system can accurately predict an advance, stop the whole feeding process, and make the final weight of the material in the weighing bucket set by the user. After the feeding, the system enters the weighing verification state. The purpose of weighing verification is to further confirm whether the weight of the material entering the weighing bucket is within the allowable range of the user's set weight error after the fast and slow feeding stops. If it is within the error range, the system will unload. Otherwise, the system will alarm and wait for the operator to handle it. After the operator finishes handling it, the system will continue to operate

after the unloading of the system, the unloading door in the weighing bucket will be closed immediately, so that the system will complete a cycle of operation. At this time, if the operator sets the continuous working state, the system will start the operation of the next cycle. The filled bags that have been filled with materials fall on the bag feeding device for the next step of folding, seaming, transfer and other processes

it can be seen from the working principle of the above common filling machine that the gravity filling equipment adopts two-stage feeding in the feeding section, and the large flow rate is used for fast feeding. When the feeding amount reaches 80%~90% of the set weight, the small flow rate is used for slow feeding until the target value is reached. The mathematical model is:

where: q is the actual feeding amount; Qi is the charging flow of section I; Ti (i=1, 2) is the feeding time of the I section; δ J (j=1, 2, 3) refers to weighing error, control error and other errors

it can be seen from equation (1): under the premise of the time and filling amount set by the system, in order to ensure the filling speed, the feeding amount Q1 in the T1 time of the fast feeding section. Try to be as large as possible and at the same time try to be as small as possible; In order to ensure the filling accuracy, the smaller Q2 and the larger T2 are required in the T2 time of the slow feeding section. However, in the process of material conversion from fast feeding to slow feeding, due to the large change of material quantity, the symmetrical measuring bucket of material will produce impact and vibration, which will have a great impact on the sampling of the symmetrical weighing instrument. This is the main problem that cannot be avoided by the two-stage feeding method. The larger the fast feeding flow is, the more obvious the impact vibration is. During the whole feeding process, the weighing instrument continuously samples and compares the sampling results with the set weight. When the maximum amplitude of the weighing bucket exceeds the set amplitude of the system, the weighing instrument will stop the slow feeding as a set weight signal, resulting in unqualified filling volume. Therefore, too large fast feeding volume will not improve the weighing speed, It may also affect the weighing accuracy or extend the whole weighing time. In order to avoid this deficiency, the common practice at present is to increase the filling amount of slow feeding, that is, to extend the slow feeding time and to ensure the filling accuracy at the expense of the filling speed. Therefore, the two-stage feeding can not only improve the filling speed, but also affect the accuracy. How to eliminate the shortage of two-stage feeding is the focus of this paper

2 principle of three-stage variable speed feeding system

to eliminate the shortage of two-stage feeding and reduce the impact of symmetrical measuring bucket of fast feeding materials, the feeding mode of the system must be solved. For example, the industrialization of the system is very difficult

2.1 hopper feeding (first stage feeding)

its basic idea is to add a set of flow adjustable feeding bucket to the original feeder, and change the two-stage feeding, which is an important reference index for quality control and utilization design, into three-stage feeding. Its structure is shown in Figure 1. The role of this feeding bucket is to reduce the height of the material in the user's silo to the weighing bucket, so as to reduce the impact of the symmetrical bucket from no material to large flow material, Ensure measurement accuracy. In addition, the opening of the flow regulating plate is changed to ensure the feeding time of fast feeding. See Fig. 2 for the filling amount Q1

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