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PLC system planning and debugging of pre punching cold bending forming line

Abstract: This paper mainly describes the specific application of SIMATIC s programmable controller in pre punching cold bending forming production line, verifies and analyzes the control accuracy of shelf components and the satisfaction of product production process through shelf cold bending equipment, and expounds the software and hardware settings of cold bending equipment, the composition and functions of main programs PID control principle and system debugging characteristics

key words: programmable controller; Pre punching cold bending forming production line; Full digital servo system

1. Introduction

1.1 with the continuous growth of the market demand for cold-formed sections, especially the demand for perforated cold-formed sections, the design and manufacturing technology of pre punching cold-formed production line also need to be continuously developed and matured, such as the high-precision evolution of pre punching hole position distribution, the diversification of product varieties and the requirements of small batch quantification The improvement of material utilization and the ease of operation of the equipment have put forward higher requirements for the compounding and electrical control technology of the equipment. This paper intends to discuss the specific application of SIMATIC SPLC in the pre punching cold bending production line, the software and hardware settings, the composition and functions of the main programs, the PID control principle and system debugging

2. PLC system configuration

2.1 according to the requirements of pre punching cold bending product processing technology, single machine function configuration and motion analysis, equipment operation and maintenance, the electrical control part of the unit adopts Siemens SPLC, and the communication between PLC and monitoring system and each slave station adopts PROFIBUS-DP fieldbus mode; The main power of the cold bending forming unit is realized by the 6ra28 series DC speed controller and DC motor of Simens company. In order to reduce the troubleshooting time, the electrical control system of the whole line has startup prompt, fault alarm and automatic shutdown, and displays the details and prompts of some faults through the Chinese character display terminal

2.2 PLC hardware configuration: 1) SIMATIC s cpu315c-2dp is selected as the central processing unit, which has large program storage capacity and PROFIBUS-DP master/slave interface, and can be configured into a distributed automation structure, which is easy to expand the system in the future. 2) Servo motor positioning module Siemens 6ES7 354, 3), SIMATIC s op27, 4), five relay output units Siemens 6ES7 322, 5), one SIMATIC s 6ES7 fm350 high-speed counting module, 6), one SIMATIC s ps3075a power module, 7), two interface modules im153, 8), ten digital input and output modules Siemens 6ES7 321, 9) one human-machine interface TP170A, Convenient man-machine interface services have been integrated into s operating system to obtain data from S. s transmits these data at the refresh rate specified by the user, and s operating system automatically processes the transmission of data. 10) A set of PROFIBUS station, etc

2.3 program design: the SPLC program of Simens company mainly adopts the structured design method. The main function blocks such as PID control, fault handling, TP170A communication interface, etc. are realized by sub function blocks FC, which are called in the main program ob1 when necessary. The program structure is shown in Figure 1. The following describes the software design of SPLC mainly through the AC servo control system that communicates and controls through PROFIBUS DP bus. Its programs mainly include ob100, ob1 Fb40 and fb41

Figure 1 program structure

2.4 ob100 is a warm start organization block, which is called when the system starts. Its main function is to initialize the opened background data block and set the input/output bus address for the servo controller; The following program segment:

program segment 1:

call "pos_init"//initialization of the user DB

db_ NO :=1//DB number

CH_ NO :=1//Channel number

LADDR :=256//Module address

RET_ VAL:="DBEX". ERR_ CODE_ INIT//Error code

L "DBEX". ERR_ CODE_ INIT//Error code evaluation

L B#16#0


R "DBEX". INIT_ ERR//Reset error for INIT function


S "DBEX". INIT_ Err//flag error for init function

nwe: NOP 0

program segment 2:

opn "dbex"

l B 16//clear dbex

t dbd0//begin with d0

t dbd4//

t dbd8//

t DBD 12

t DBW 16

program segment 3:

l B 1664

t "dbex" OVERRIDE//Set override to 100%


S "DBEX". SERVO_ EN//Set servo enable

S "DBEX". DRV_ EN//Set drive enable

S "DBEX". AD_ EN//set read enable (EX3)


2.5 ob1 is the main program block. According to the realized job functions, it compiles the display block, parameter setting block, work operation block, automatic circulation block, power group adjustment block, etc. This program block is called by ob1 to realize the coordination between the whole and the program. Water property, high solid content and single component are the traditional advantages of Bayer adhesive raw material products, including function fc32, function block fb40, function fc37 and background data block db40. Among them, the function of fc32 is to regularly read and update the data from the background data block on the bus; Function block fb40 is the main program block for controlling the servo controller, which will complete the initialization and position control of the servo controller, mainly including function fc40 and function fc41; Fc40 mainly completes the initialization of the axis; Fc41 is the core part of the whole servo control system, which can realize control such as speed command, position command, torque command, zero point reset command and reading the feedback value of servo controller from the bus; Fc37 is a reset module, which can clear the error information of the bus and generate a reset command to reset the servo controller; Db40 is the background data block of function block fb40

2.6 fc30 is a sub block of fc40, which completes the command transmission from PLC to servo controller, checks whether the command is correctly executed and handles errors; Fc31 is a sub block of fc41, which diagnoses the completion of fc41 and transmits it to the bus; Fc33 and fc34 are accessories of function block fb40. The former checks the status of the current servo controller in order to send the next command; The latter deals with the synchronization of multiple servo controllers (there is a multi station servo control mode in the actual cold bending products), etc

2.7 STEP7 provides two commonly used PID algorithms: continuous PID (fb41) and discrete PID (fb42). Fb41 is selected for this system. It is the output control obtained according to the sampling period of the system. It determines the sensitivity of the PID loop, that is, the speed of adjustment. In the initial PID parameter setting, PID parameters cannot be determined by theoretical calculation alone, The actual PID parameter setting must be adjusted by the realization degree of the real-time curve and distribution law of the controlled parameters, that is, its accuracy and operation stability, in order to achieve the best control effect

3. System PID parameter analysis and tuning

3.1 PID parameters: in view of the discontinuous characteristics of the specific production process of the shelf cold-formed section steel cold-formed production line, it is conducive to using the field experience tuning method to obtain effective PID parameters and achieve a better control effect. At the initial stage, the PID proportional parameters are set according to the empirical data, and the PID parameters are adjusted in the order of proportion first, integration second, and differentiation last. After observing the field control process While measuring and comparing the process value and motion control accuracy, slowly change the PID parameter value and try again and again until the motion control accuracy and stability meet the requirements. After the PID optimal setting parameters are determined, it does not mean that it is always the best. It will still be fundamentally changed by external disturbances and requires that the optimal parameters be adjusted again as needed. In the actual process, the relationship between output and error can be found as follows:

in the above formula, u (n) is the control output of the nth sampling period; E (n) is the position error of the nth sampling period; N is the normal sampling period; Is the differential sampling period; KP is the proportional gain; Ki is the integral proportional gain; KD is the differential proportional gain. The PID control system adjusts the output to ensure that the deviation value E is zero, and the solution of the system is to clean the buffer valve system to reach an expected stable state

3.2 parameter setting of control system: PID parameter setting and system motion analysis in the main control PLC program to see whether the given parameters meet the requirements of the control system. This process needs parameter setting. The main task of parameter tuning is to determine KP, Ki, KD, sampling period n and differential sampling period; The proportional gain KP provides an output that is proportional to the position error. The increase of the proportional coefficient Kp makes the servo drive system sensitive and responsive, while too much will cause oscillation and lengthen the adjustment time; The integral proportional gain ki provides the output that increases with time, so the static position error is guaranteed to be 0, and the integral coefficient ki increases, which can eliminate the steady-state error of the system, but the stability decreases; The differential proportional gain kd provides an output proportional to the position change rate, plays the role of advance control, reduces the overshoot of the system, and ensures the good dynamic characteristics of the system. The differential control KD can improve the dynamic characteristics, reduce the overshoot and shorten the adjustment time. The sampling period should be much smaller than the disturbance period of the object, much smaller than the time constant of the object, and should consider the response speed of the actuator and the regulation quality required by the object. In fact, try to select a small value as much as possible; The specific setting process needs to formulate the on-site adaptive parameters and the actual adjustment settings on site according to the PID parameters. Because the PID parameters in the system master PLC program cannot be adjusted in real time, they need to be set separately according to different products or load conditions, and through the touch screen in the process of production tools, we are confident to provide consumers with both safety and convenience For plastic materials that can make people's life more convenient, do not input the setting value to achieve effective control, otherwise it is easy to form overshoot or oscillation in the position control process

4 debugging points and precautions

4.1 the dynamic performance of the AC position servo system is an important stage in the debugging process of the cold bending equipment, which directly determines the working performance of the cold bending equipment and the hole position accuracy distribution law and control accuracy of the product. For example, the control requirements of the servo system in the shelf cold bending unit are very high, and there should be no oscillation and overshoot, otherwise it will cause large hole position error on the side elevation of the shelf components, uneven hole position distribution, seriously affect the assembly accuracy and use performance of the shelf, reduce the yield and increase the production and operation cost. The servo fixed length feeding in the shelf cold bending unit is an intermittent feeding mode. The feeding length and the processing time of the supporting equipment depend on the motion beat of the AC position servo system, the control positioning accuracy and the dynamic performance of the AC position servo system. Its dynamic performance can generally be described by the time response curve of the system under the action of the unit step input signal. As shown in Figure 2, the positioning point can be reached gradually through a variety of adjustment and change forms. We hope to obtain the monotonic change mode marked as 1 in the figure, and we don't want to have the oscillation waveform marked as 2 or 3. The adjustment mode marked as 4 will form the phenomenon of not in place fault, large servo system follow-up error, extended adjustment time, etc., which will affect the speed matching and control accuracy of the whole machine. The commonly used dynamic performance indicators shown in the figure are rise time TR, adjustment time Ts and overshoot σ%。 The rise time tr reflects the dynamic sensitivity of the system and the rapidity of the system transition process; Adjustment time Ts, also known as transition time, is the main index to measure the rapidity of the system; Overshoot σ% It is an indicator reflecting whether the system transition process is smooth

4.2 during system debugging, the dynamic performance of the system can be

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