1 Introduction

Poultry feed, animal feed, fish feed and most of the feed is some flow is not good, fragile powder granular feed, in order to ensure the control system precision and speed, finished product dosing quantitative bulk scale feeding device, most of the use of direct-fall feeding, double screw feeding or double vibration feeding and so on. After the quantitative start, the size of the feeder work at the same time, when the weight of the material reaches the big feeding set value stop big feeding, and continue to keep small feeding, when the weight of the material reaches the final set value, close the small feeding.

2 Structure and technical parameters

2.1 Structure composition

At present, domestic and foreign production of automatic bulk scales, according to the form of measuring bucket is mainly divided into bucket and bucketless type; according to the form of weight is mainly divided into net and gross weight type, but most of the modular design ideas. The designed prototype adopts bucketless gross weight weighing, which mainly consists of storage silo, screw feeder, transition, cut-off device, weighing unit, pneumatic part, and electrical control unit.

2.2 Screw feeder

Feeding part of the form of more, usually straight down, spiral feeding, scraper type, vibration and spiral feeding and so on. According to the different materials can be selected in different ways, this part of the selection of the appropriate directly affects the speed and accuracy of the quantitative bulk scale. Due to the special nature of the feed industry process, in order to overcome the use of hopper-type easy to block the material, scraper easy to make the material broken, vibration feeding dust pollution is serious and other issues, for this reason, in the equipment we choose the spiral feeding method.

2.3 Weighing unit

Weighing part mainly consists of hopper scale, weighing module, weighing controller, etc. It can complete the accurate measurement of materials and send the control signals required by the control system: over and under quantity signals, preset advance signal, advance signal, target value signal, 4~20mA analog signal and standard RS232/485 signal.

2.4 Clip bag receiving hopper

The bag clamping part is round, which can ensure the sealing after clamping the bag, and there is an exhaust port, so that the dust and air inside the bag can be discharged in time, and this part mainly relies on the pneumatic actuator to complete its actions.

3 working principle

3.1 The main structure of the control unit

The control unit is mainly composed of measuring instruments, programmable controllers and frequency converters.

3.2 Working principle

The equipment will be placed in the automatic working state, open the automatic button, start the spiral feeder for the first level of feeding, when the preset amount of advance is reached, the weighing unit sends out a signal, the frequency converter switches to the second level of feeding, when the amount of advance is reached, the weighing unit sends out a signal, the frequency converter switches to the third level of feeding, when the target value is reached, the cut-off hopper is closed, the bag is loosened, the bag is put on the bag, and the system is switched automatically to the frequency state to carry out the next cycle. next cycle.

3.3 Functions to be accomplished

(1) It is used to control the starting and stopping of the feeding screw machine, the three-stage feeding control, the opening of the gate, the cut-off hopper and the baffle plate, the enabling of metering and the transportation of the finished products, etc. in this equipment;

(2) Used to control the chain control of this equipment and the peripheral system;

(3) It is used to detect the working status of the state weighing module;

(4) It can transmit the working condition and data of the equipment to the upper computer and carry out data processing.

3.4 Design of frequency conversion control part

The control part of the frequency converter is the core of the device, the choice of model, the optimization of parameter setting, directly related to the reliability, stability, dosing speed and dosing accuracy of the device. The size of the feeding quantity is mainly determined by the rotational speed of the screw feeder, that is, the final control object of the system is the screw feeder. The rotational speed of the spiral feeder is controlled by the frequency converter, and the size of its capacity is directly related to the selection of the specifications of the frequency converter.

4 test effect

The device adopts the frequency converter multi-level control, the system runs smoothly, feeds the material evenly, the speed change is smooth, there is no mechanical impact, and the impact on the dynamic weighing data is very small. Mainly in the following aspects:

(1) The dosing system has high accuracy, which is better than ±0.5% in single machine operation;

(2) The system protection function is perfect, the parameters can be set and modified through the man-machine interface, and the result of fault self-diagnosis is directly displayed on the man-machine interface, which shortens the overhaul time and greatly improves the working efficiency;

(3) Soft start is adopted to avoid mechanical impact on the motor and prolong the service life of the motor;

(4) Over-current, over-voltage and under-voltage protection can be easily realized through the parameters set by the inverter itself;

(5) The equipment runs stably and reliably, and the energy-saving effect is obvious;

(6) The environmental pollution (dust, noise and impact on the power grid, etc.) is low, and the physical and mental health of workers is protected.

5 concluding remarks

Multi-stage speed control by frequency converter has been widely used in many industries, but it is still rare in quantitative bulk scale in China, which may be due to people's deep-rooted control methods. With the rapid development of frequency converter technology, frequency conversion technology should have a broader development space in the batching industry.