1、Introduction

Batching production is an important part of rubber production, including raw materials, fuel crushing, batching, mixing, batching and screening, etc., of which batching is the key to the whole batching production process. In the past, the dosage mostly uses intelligent meter controller to carry out simple weighing and PID adjustment, which has simple function, low control accuracy, weak management function and low reliability. For this reason, the program is given.

The automatic batching system uses powerful plc to replace the previous complex control algorithm which is completed by secondary meter or upper computer, and the secondary meter is only used for data collection; the weighing and batching machine replaces the simple PID regulator in the control algorithm, and adopts the FUZZY-PID algorithm which is based on artificial intelligence, so as to make the control more stable; and the batching machine replaces the 485 of the communication rate which is low with Profibus_DP. communication rate is low.

2、Overall design

Batching system software and hardware configuration

The batching machine is divided into two levels: process monitoring level and basic automation level.

Basic automation level:

① 6 sets of disk feeder adopts frequency conversion control, and the frequency converter adopts Schneider ATV71, which has the dual control function of on-site on-site manual control and upper computer automatic control to control the feeding quantity of the disk feeder.

② 6 sets of disc batching belt scale adopts constant speed belt scale, with on-site manual and upper automatic dual function. The belt scale adopts Beijing Hengxin Tianzheng series electronic belt scale.

③ 7 sets of direct-dragging belt scale adopts speed-regulated belt scale, and the frequency converter adopts Schneider ATV71, and the electronic belt scale has the dual functions of on-site manual and upper automatic. The control principle is shown in Figure 3.

Two spiral star feeders are driven by frequency converter, and the frequency converter adopts Schneider ATV71 products, with constant speed of metering spiral, and the control principle is shown in Figure 2. Measuring scale adopts Beijing Hengxin Tianzheng series of electronic belt scale products.

⑤Siemens S7-300 series PLC (CPU315-2DP) is used for data acquisition, smooth control and automatic control of batching system. PLC programming software is adopted: STEP7V5.3.

(6) Weighing and batching controller is adopted to realize the backup instrument control function of the batching system.

(7) PLC automatic control and meter control are optional.

Batching process monitoring level

The weighing and batching system is equipped with an upper computer as the operation station. The upper computer adopts Taiwan Advantech's industrial control machine IPC, with main frequency not less than P42.4G, 80G hard disk and 512MB memory, which can be used as an engineer's station during the development of quantitative batching system. The monitoring level has the functions of database management and maintenance, dosage optimization calculation and setting, real-time display of weighing and dosage system data, over-limit alarm, trend recording and archiving and printing. The dosage system is equipped with an EPSON printer. The monitoring software is WINCC6.

Mixed communication configuration

Speed control adopts two-level communication network

In order to ensure the accuracy of data collection and fast transmission, Profibus-DP is used for communication between weighing controller and PLC.

②Industrial Ethernet is adopted between PLC and industrial controller.

3、Variable Frequency Batching Function

3.1 Process requirements of speed-controlled batching

The main task of mixing and batching is to calculate, allocate and control the amount of raw material ore trough discharging according to the demand of material by batching machine, so as to ensure the material balance and chemical composition in accordance with the requirements. The process requirements for controlling the batching system are.

(1) Realize the sequence start-stop, single machine start-stop and simultaneous start-stop of each batching scale and aggregate belt conveyor; (2) Realize the sequence start-stop, single machine start-stop and simultaneous start-stop of each batching scale and aggregate belt conveyor.

(2) Realize the weight proportioning control of each dosage scale; (3) Realize the weight proportioning control of each dosage scale; (4) Realize the weight proportioning control of each dosage scale.

(3) Proportioning calculation function

Calculate the flow rate setting value of each scale according to the total amount and the proportion of each scale; (3) Calculate the flow rate setting value of each scale according to the total amount and the proportion of each scale.

(4)Flow rate calculation function

According to the detected weight signal and belt speed signal, the mixing automatic feeding system calculates the average flow rate of the material in a period of time, and takes this average flow rate as the feedback quantity for PID adjustment; (5) Alarm function.

(5)Alarm function

Sound and light alarm for frequently occurring faults such as material blockage, belt slippage, motor overcurrent overload, etc. When material blockage occurs, it is required to automatically start the vibrator motor on the ore chute, and automatically stop vibration after resumption of material feeding.

(6) Backup function

When the PLC dosage system fails, it can quickly switch to the back instrument controller for control;.

(7)Report printing function

Manual intervention and timed printing of various reports such as Times, Shift Reports, Monthly Reports, etc.; (7) Report Printing Function

(8)Power failure protection function

When power is supplied again after a power failure, the dosage is initialized and reset to ensure that each piece of equipment is in a state of shutdown, in order to prevent personal accidents and equipment accidents from occurring.

3.2 Working principle of mixing

When the mixing and batching starts to work, the industrial control machine firstly carries out all kinds of initialization according to the production task, including the name of each component of the raw material, bin number, output, standard ratio, and optimally calculates the standard flow rate of each bin, etc. Then the industrial control machine passes the calculated standard flow rate to the plc and the instrument controller. the plc controls the startup of each feeder and the belt scale according to a certain sequence, and each feeder feeds the material according to a certain flow rate. The instrument controller calculates the actual flow rate according to the speed signal and weight signal of the belt conveyor collected on site, and passes this signal to the plc and industrial controller, the plc calculates the current actual ratio according to the cumulative value of each component, and corrects the feeding amount of each feeder by comparing it with the standard ratio, and controls the frequency converter of the belt motor and the feeding flow rate, so as to make the dosage system work in the optimal proportioning state.

3.3 Speed control strategy

At present, the conventional automatic batching control strategy

Batching instrument accepts the weighing signal and speed measuring signal from the scale, displays the instantaneous flow rate and cumulative amount after calculation, and sends the instantaneous flow rate in the form of 4～20mA analog current to the PID regulator as the regulating measuring input signal, which outputs 4～20mA analog regulating signal after comparing and calculating the signal with the set value in the machine, and then controls the speed of the feeding motor, thus further controlling the feeding flow rate of the material. The flow rate of several kinds of coal materials can be further controlled by controlling the speed of the feeding motor, so that the instantaneous flow rate of several kinds of coal materials and the cumulative amount of the stages can be kept within the range required by the users. To change the flow rate and proportioning can be set directly on the regulator, the operation is simple and convenient.

The process site to which the above solution applies must first satisfy the prerequisite that the amount of material given must be proportional to the rotational speed of the feed control motor. In order for the dosage to have good regulation qualities, i.e. high stability, accuracy and rapidity, the weighing and dosage system must also have two conditions:

1) Stability of its own structural properties, which includes its capacity coefficient, resistance and transfer distance and other elements.

2) The regulator has reasonable PID parameters. Only the intensity of these three roles for appropriate cooperation, can make the regulator fast, smooth and accurate operation, so as to obtain a satisfactory control effect.

In both, condition 1) is the premise of condition 2), because the PID parameters depend on the dynamic characteristics of the dosage, and the main factors affecting the dynamic characteristics of the measured dosage is the nature of the structure of the system itself.

Because in the past the commonly used speed weighing and dosing program design is the use of general PID control algorithms, its parameters are generally according to the transition process time of the step response to the rectification of the higher sensitivity, for fixed parameters of the mixing and dosage system has a better quality of the regulation, theoretically speaking, can be done without error regulation, in the range of error is indeed its superiority. However, in practice, the electronic belt scale dynamic automatic dosage control accuracy will be affected by a number of factors. Such as: physical properties of materials, mechanical vibration, feeding equipment installation accuracy, silo structure shape and other factors; and the site environment is more complex, harsh, and other external interference is frequent. Due to the presence of the above factors, the dosage error is often larger, its dynamic characteristics are not ideal, the amount of overshooting is generally larger, resulting in the weighing of the dosage can not achieve the desired control effect. At this time, the measurement performance of the belt scale and batching accuracy will be affected. Here we use the fuzzy-PID composite control technology, the fuzzy control technology combined with the traditional PID control strategy applied in the regulation of quantitative dosage, can effectively solve the above problems.

FUZZY-PID control model

The mixing system is characterized by an upper computer for monitoring, a set of plc to control multiple feeders, in order to achieve a certain ratio, the work between the feeders and interconnected, and the amount of feed to be modified with the current actual ratio, so its control structure is more complex.

The mixing and feeding system belongs to a multi-closed-loop associated control structure. As far as the feeding bin No. i is concerned, there are two closed loops and one feed-forward, and the inner loop is a FUZZY-PID controller, which controls the speed regulating feeder according to the given flow rate Fgi, so that its feeding flow rate Fi is controlled near the ideal given value Fgi, which is realized by plc. The outer loop corrects the given value of the inner loop according to the difference ΔP between the current accumulated value and the desired output as well as the current flow rate of the feeder in the feed-forward link, which is realized by the host computer.

The controller adopts FUZZY-PID composite control, fuzzy control is used when the deviation is large, and PID control is used when the deviation is reduced to a smaller range. This can solve the dosage system error is large, its dynamic characteristics are not ideal, the overshooting amount of control problems.

FUZZY-PID composite controller design

Speed dosage using FUZZY-PID composite control, when the deviation is large fuzzy control, when the deviation is reduced to a smaller range of PID control. The two controls are used in parallel and switched by Bang-Bang switch.

1) Bang-Bang changeover switch

The Bang-Bang switch is actually a software switch in the controller, which determines which control algorithm is used.

2) PID controller

The PID controller uses a general incremental digital algorithm, and its parameters are calibrated according to the norm.

(3) Fuzzy control principle and fuzzy controller realization

Fuzzy control through fuzzy logic and approximate reasoning methods, the human experience formalized, modeled, into a computer acceptable control model, so that the computer instead of people to carry out effective real-time control, in order to achieve fuzzy control, the computer as a fuzzy controller, must solve the following three problems:

Fuzzy quantization of input quantities output quantities;

Establishment of fuzzy control rules, or fuzzy control rule table;

Fuzzy judgment of output information.

The set value of the speed regulation, which is the exact quantity.

Fixed frequency dosage system deviation and deviation change rate, are exact quantities.

After fuzzy quantization, the deviation and deviation change rate become fuzzy quantities.