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Application of SUNFAR Inverters in Direct Wire Drawing Machines

Abstract: Electrical control system of direct wire drawing machine production determines product quality and production efficiency. The following is the electrical control system made of SUNFAR E280 dedicated inverters for wire drawing machines, LG (LS) PLC and the WEINVIEW human-computer interface, which is used to illustrate the application and performances of direct-wire drawing machines.
Keywords: Direct Wire Drawing Machines SUNFAR E380

    Electrical control system of direct wire drawing machine production determines product quality and production efficiency. The following is the electrical control system made of SUNFAR E280 dedicated inverters for wire drawing machines, LG (LS) PLC and the WEINVIEW human-computer interface, which is used to illustrate the application and performances of direct-wire drawing machines.

1. Preface

Wire drawing machines are important facilities of metal wire production in the metallurgical industry, whose main function is to draw various wire stocks into fine wires. According to the operation mode, they are divided into the direct type, the looping type, the tank type and so on. The direct wire drawing machine represents most advanced production technology and equipment and is also the most difficult one to control.

It can be said that electrical control system of direct wire drawing machine production determines product quality and production efficiency. Take a manufacturer of wire drawing machines in Shenzhen as an example. They used to use electrical control system developed by an engineering company in Hebei. In high speed operation, tension of the system is not stable and wires are easy to be broken, which directly affects the quality of customers’ equipment. Thus the manufacturer needs a more complete electrical control system to substitute present electrical system to improve its market competiveness. The following is the electrical control system made of SUNFAR E280 dedicated inverters for wire drawing machines, LG (LS) PLC and the WEINVIEW human-computer interface, which is used to illustrate the application and performances of direct wire drawing machines.

2. Requirements of Production Process

This set of equipment is made of a loop, an unwinding roller and 7 drawing rollers. Based on the specification of wire stocks, each roller is installed with wortles arranged in descending order and the last is the required wire diameter. After the unwinding roller, wire stock goes through the firs wortle and to the first roller, then from the first roller to the second wortle. It is drawn cascaded down and finally reaches the winding roller. There is a cylinder arm among each roller, which is used for displacement sensors to feed tension back to inverters. Afterwards, inverters treat the feedback signals as PID closed-loop control to keep constant tension among rollers. The process requires that if joint wire die needs replacing, input die specifications on the human-computer interface and the whole system can work normally after the replacement. Process diagram is shown in the following picture:

 

3. System Control Principle

Speed ratios of motor and roller in each level in direct wire drawing machines are different. The higher the level is, the high the speed ratio will be and wire diameter changes in a descended order, but flow volume per second at any time point in the die wire stock won’t change. Therefore, the change of wire stock results in the change of speed ratio. In actual production, if wire specifications are different, winding wire die needs changing and then speed ratio is changed; in logic control, wire stock goes through 1# roller and gradually to the roller in the last level, where 1# roller works, wingding motor and 1# motor creeps in threading and when wire stock reaches 2# roller, winding motor, 1# motor and 2# creep in linkage. And so forth when the wire stock reaches winding roller, all previous motors is required to be able to creep in linkage. At the same time, each roller may work in single point. Consequently, each roller is controlled by switches, including linkage switches, manual switches and foot inching switches; winding rollers are sliding conic rollers and winding diameter seldom changes. Based on the principle:

There are system start and stop and other logic switches, alarm information (if any inverter fails unexpectedly, the entire system will stop and give out alarms to the operator), display of current production line speed (it is calculated by PLCA based on the speed and diameter of the wingding roller) and settings of each wire drawing die and system operation frequency on the human-computer interface.

PLC handles all logic relation and calculation. Based on the frequency of the last winding motor, each wire diameter is acquired on the interface. Then synthesize mechanical transmission ratio to work out the frequency of each roller motor. Considering the convenient communication of SUNFAR inverters, there is no need controlling operation frequency of motors in each level by D/A module. Real-time frequency can be sent by 485 communication ports of PLC and inverters. Operation and stop signals of inverters are controlled by external ports through switching values output by PLC.

Speed ratio of rollers in each level is changed by the variation of wire dies and consequently tension in acceleration and deceleration is affected. However, there is certain congruent relationship between acceleration and deceleration time of SUNFAR inverters. Therefore, there is no need for inverters, like other brands, to accelerate to start or decelerate to stop with certain slope by current operation frequency. Inching movement and creeping take the advantage of operation signals rather than inching function of inverters for control to prevent broken wires due to the changing of wire dies in system creeping.

    After given frequency and operation signals by PLC, the inverter takes the 0-10V signal fed back by the sensor for internal PID adjustment. E280 series of inverters is controlled by PID with feed-forward compensation. These help to realize high stable tension control. Diagram of system control is shown in the following figure:

 

 

4. Debugging

Debugging may begin after various preparations done. In debugging, the order of drawing wires is descending by level, which means next drawing can only start when the previous level is done. Manual operation comes first and then in linkage. Low speed is comes before high speed.

The position of each cylinder arm and sensor is different due to mechanical error. The maximum and minimum position of sensors should be adjusted in initial debugging to better deal with the maximum and minimum values of inverter feedback channels, which can be acquired on monitor menu ‘D-9’and reasonable value ranges from 0 to 100. Target value of PID adjustment is set according to the position of sensors and PID adjusts itself on the target value. A pulley is installed before the unwinding roller. It will skid automatically in operation and the speed is adjusted freely by the wire speed coefficient on the interface. The entire system operation is running on the base of winding and unwinding motors. Therefore, PID adjustment is not necessary in winding and unwinding inverters, which can work in a general model.

Key stages of the entire system debugging are the start-up, the deceleration stop and settings of PID adjustment. Start-up and stop are key points in initial debugging.

From above process diagram, it can be seen that tension feedback device is installed at the back of the roller. When wire stock reaches each roller, inching movement comes first, and then in linkage after adjustment. If wire in the earlier stage is loose, which may result from PID limit, increase PID limit properly (for specific parameters, see F7.8). Every roller motor is running in PID model. If last linkage motor is running in this model as well, it may cause loose wires in earlier stage. We should be aware that cylinder arm may be in the maximum position due to lack of wire stocks in roller. Feedback signal will affect the speed of current running motors. Then, PID limit is restricted. PID limit varies because of different linkage ratio in each level. In this situation, PID limit is descending gradually. Therefore, linkage and inching movement should be done in an order to the winding motors.

Motor starts running in linkage model with a low speed. Then stop the motor. If wire stock is too loose, reduce the DC brake starting frequency of next linked motor (for specific parameters, see F4.4). If wire stock is too tight, check internal D-9 value of the inverter. It is the feedback value from displacement sensor. If D-9 value is large than the given value by PID, it is necessary to increase the DC brake starting frequency of relevant motor. Increase or decrease with the minimum amount. Don’t modify too much each time. Modify it over and over to a reasonable value. It is better of D-9 value between 10 and the given value by PID when the motor stops. Brake starting frequency is set in an increasing order based on the sequence of wire drawing machine process.

System starts running with a low speed after adjustment in stop. According to production process, vibration of wire stocks in the later stage is affect by that in the former stage. If PID parameters are not set reasonably, this phenomenon will be aggravated. Finally, wires can be easily broken if PID adjustment is not satisfying. In the setting of PID parameters, P value is descending from 1# motor to winding motor. Conversely, I value is increasing. Don’t change the value of D frequently. This setting model is to ensure tension stability of the entire system by eliminating vibration through the former stages.

Operation frequency of electrical system with E380 dedicated inverters for wire drawing machines is sent to all inverters as unified one. Linkage ratio of each inverter is worked out by PLC referring to winding motors, mechanical transmission and parameters of drawing wires sent to PLC from the interface. Linkage ratio is sent to EEPROM region of inverters. Linkage ratio parameters can only be changed when drawing die is to be substituted. In operation, E380 inverters adjust acceleration and deceleration time on linkage ratio and ensure constant tension without broken wires in the process.  Acceleration and deceleration time of each inverter can be the same. Acceleration time is controlled between 15S to 50S. Deceleration time is controlled within 10S. The problem of broken wires due to too short acceleration and deceleration time of ordinary wire drawing machine system is solved.

Self-correcting function of inverters on linkage ratio can be activated in initial debugging. Operation frequency read on inverter keyboard and get optimal linkage ratio fastest without human-based computation to save debugging time. Setting parameters of inverters are set on site on mechanical features, because parameters may not stay the same due to mechanical errors.

Parameter settings of each inverter are as follows:

Function Code

Unwinding Inverter

1# Inverter

2# Inverter

3# Inverter

4# Inverter

5# Inverter

6# Inverter

Winding Inverter

F0.0

 0000

 0001

 0001

0001

 0001

 0001

 0001

 0000

F0.1

   2

   2

   2

  2

   2

  2

   2

   2

F0.4

 0001

 0001

 0001

 0001

 0001

 0001

 0001

 0001

 F0.10

  40

  40

  40

  40

  40

  40

  40

  40

 F0.11

  10

  10

  10

  10

10

  10

  10

  10

F4.5

   0

   2

  2.1

  2.2

 2.3

  2.4

  2.5

  2.7

F4.6

   1

   1

   1

  1

   1

  1

   1

   1

F4.7

  30

  50

  50

  50

  50

  50

  50

  50

F7.0

  ___

   1

   1

  1

   1

  1

   1

  ___

F7.1

  ___

 0001

 0001

0001

  0001

 0001

  0001

  ___

F7.2

  ___

  0.8

  0.8

  0.7

  0.7

  0.55

  0.5

  ___

F7.3

  ___

  10

  10

  20

  20

  25

  25

  ___

F7.4

  ___

  20

  20

  25

  35

  40

  50

  ___

F7.8

  ___

  40

  35

  30

  27

  15

  10

  ___

F8.2

  ___

  20

  10

  10

  10

  10

  20

  ___

 F8.11

  ___

  25

  25

  25

  25

  25

  25

  ___

F9.0

 0015

 0015

 0015

 0015

 0015

 0015

 0015

 0015

F9.1

  7

  0

  1

  2

  3

  4

  5

  6

F9.3

 0000

 0000

 0000

 0000

 0000

 0000

 0000

 0000

 

5. Debugging Results

    Electrical system of direct wire drawing machines with SUNFAR E280 dedicated inverters for wire drawing machines has gone through tests and optimized its parameters. System stability after change dies is also tested. Finally, wire speed is improved by a third to the original electrical system in normal equipment production and tension keeps stable in key stages (acceleration, PID adjustment and deceleration) of high speed operation. If the equipment needs to be improved, it must be substitute ordinary motors to inverter motors. Speed can be also increased. The completion of electrical system enhances market competitiveness of customers’ products.