CONTROL SYSTEM OF THE WIREDRAWING MACHINE

WITH ANNEALING MODULE

Vadim CAZAC, Ilie NUCA, Petru TODOS, Iurie NUCA*

Technical University of Moldova * Technical University of Cluj-Napoca

vadimcazac@gmail.com, nuca_ilie@yahoo.com, todos@adm.utm.md, nuca.iurie@yahoo.com

Summary – This paper is focused on developing unified microprocessor control system of a wiredrawing machine which integrates the modules of the following subsystems: wiredrawing, winding and annealing of the metal wire. The main aim of this work consists in elaborating a system of better control for the wiredrawing and for the annealing module, all this for elevating the productivity and the quality of the technological process of making electrical wires. The reference object of this paper work is referred to a machine of the B-24 type [7], which contains the asynchronous motor with belts of the wiredrawing line transmission, the controlled drive system of the drum winding and the wire annealing module with manual prescription of the necessary temperature (fig.1). Thus has appeared the necessity of upgrading the automation system of this wiredrawing machine according to the requirements of the economical agent [8]. According to the technological process the developed control system must control the necessary wiredrawing force, speed and tension force prescribed to the wire, slow start depending on the tension force, maintaining of a constant tension force for excluding the breaking of the wire at high speeds of winding, regulation of the energy flux of the annealing module depending on the linear speed of the wire. The system ensures a gain of productivity and quality of the technologic process of electric wire’s production. For the winding mechanism a vector control system with three contours of current and speed regulation, and one exterior contour of the wire’s tension force. Through computer simulation the control system’s performance indices were proven.

Keywords: drawing, annealing, control system, electric drive, vector control.

1. INTRODUCTION

The main course in developing of wire and cable production is implementation of new technologies, which allow intensifying the technological process and elevating the economical efficiency, as well as obtaining products with wanted physical and mechanical proprieties.

Wiredrawing is the main method of wire production and consists of pulling the metal wires through dies [1-3] . The wires obtained after the drawing have exact geometrical measurements with wanted physical and mechanical proprieties (elasticity, plasticity). Compared to other methods wiredrawing excludes any losses of the processed material.Modern wiredrawing machines are completely automated and integrate in a unique system the equipments of the wiredrawing process as well as of the annealing process [4-6]. Older wiredrawing machines have less automation which leads to the decrease of the productivity, or breaking of the wire.

2. STRUCTURE OF THE CONTROL SYSTEM

According to the imposed task a control system of the drawing machine was developed, which consists of 3 subsystems: of the wiredrawing asynchronous motor drive, of the winding motor drive and of the wire annealing module (fig.2). The general control of the system is entrusted to a programmable microcontroller 1, whose control parameters can be changed through the operator’s panel 2. For feedback are used current transducers 3, 4, 5; speed 6, wire’s tension force 7.The mechanical connection between drawing and winding mechanisms is made through the drawn wire.

Fig.1. General view of the wiredrawer B-24

2.1. The drive system of the wiredrawing machine

The wiredrawing process takes place at a speed of 50 m/s (averaging 20-25 m/s). The drawing force is developed by the traction drums and the friction force between the drum and the processed wire by it. It depends, mostly, on the friction factor in the dies of the machine. The wiredrawer’s drive system must develop the necessary speed to overcome the drawing force to the prescribed speed. The system consists of: an asynchronous motor 8, a frequency converter with scalar control 9. The motor does not require a drive with high dynamical parameters, thus it functions with its natural characteristic, without feedback loops.

2.2. The drive system of the winding machine

The winding machine’s drive system maintains the prescribed speed and tension force to avoid breaking the wire. It contains an asynchronous motor 10 and a vector control frequency converter 11.

2.3. The control system of the annealing module

Annealing is a way of thermal processing, which consists of heating, maintain and sudden chilling a plastic and soft, free of inner stress, metal is obtained. The temperature for annealing can be higher or lower than of the critical, at which the metal suffers inner changes. The operating principle of this module is based on the induction of a electromotor tension into the drawn wire, which cause appearance of eddy currents

thus producing the necessary heat for the annealing through the Joule effect [9]. Temperature’s adjusting according to the wire’s speed is made through the one-phased converter of high frequencies 12.The analysis of the processes which take place when wiredrawing and the problems that occur, like wire tear, has imposed the integration in a single control system the 3 processes: regulating the wiredrawer, regulating the annealing module and regulating the winding mechanism (fig.3)

Fig. 3. The structural scheme of the control system

3. VECTOR CONTROL SYSTEM OF THE WINDING MECHANISM

In the following scheme (fig.4) is represented the simplified structure of the winding mechanism’s vector drive, in which the pillar elements of this drive are presented. The regulating of the wire’s tension force at

Fig.2 The functional scheme of the control system of the wiredrawer and of the annealing module ului cu modul de recoacere

winding takes places in a direct way, using a transducer for determining the tension force in the wire.The scheme has 3 contours with subordinate regulating of the internal of current, speed and the outer contour of the wire’s tension force. Changing the regulating modes is performed automatically after the influence of the tension regulator over the limit block. In case the wire is not a whole component of the regulator it drives the regulator into saturation. The limit value is prescribed by the signal Upv, prescribes the necessary speed to an empty winding.The force of stretching will start to rise and the tension regulator will exit saturation and allow the contour of stretch force regulator to work, considering that the

angular velocity of the drum is prescribed to be higher that the linear speed of the drum.At wire breakage a reverse process will start, the signal from the tension force regulator’s exit will start to rise until saturation. The winding’s speed will also start to rise. To stop a full winding it is necessary to decrease the limit value of the tension regulator until it reaches nil. The multiplication and division device provides the granting of the speed contour at function with weakened magnetic flux or with changing the inertia summary moment at the motor shaft. The law of modification for the wire’s tension force is ensured by the correcting block of tension force’s prescription.

Fig. 4 Simplified structural scheme of vector regulation system for speed and tension force [2]

The correction block of the prescribed tension BCTP represents a proportional controller with a factor:

( 1 )

Where - reserve coefficient, decreasing the influence of the winding’s radius on the tension force, being

chosen =1, - radius of the winding’s drum;

- radius of the winding.BCRB is calculus block of the winding’s radius.

3.1 Calculus of the magnetic flux’s canal

The structural scheme of the magnetic flux’s canal at a vector control includes two loops of automatic regulation: the internal loop of the magnetization

reactive current Isx=Im and the outer loop of the magnetization flux (fig.5).

Fig.5 Structural scheme of the magnetic flux’s canal

The turning system of coordinates x-y is oriented after

the rotor flux , which ensures the simplest structure of the SRA. This scheme does not take into consideration the ABC /α-β, α-β/x-y and reverse x-y/ α-β and α-β/ABC,

In the outer loop a magnetization current’s limit block is introduced (BLCM).

3.2 Calculus of the magnetization current’s loop

Having determined the parameters of the motor, belonging to the winging mechanism, we make the calculus for the system regulation loops. The frequency converter can be approximated with a first order element

(2)Where:

(3)TCF=0,005s-inner constant of the CF without a prescription integrator element. If a Hall type current transducer is chosen, then it can be described through a noninertial element

(4)Tuning of RCM is made, relative simply, based on the criteria of the module of the transfer function of the closed loop of current

(5)

Where: - the small constant (uncompensated by the controller) of the current’s loop The RCM’s regulation object

(6)

Where: ;

(7)

The current loop’s

transfer function

(8)

As a result, if the following equals

(9) The RCM’s controller be a PI type. The time constant of this controller compensates the big constant of the loop – the rotor constant TIZ.C= TS=0,248 SThe RCM’s integration constant is:

(10)

The coefficient of RCM’s proportional piece:

(11)

The transfer function of the closed current loop

(12)

w

here: - the inverse transfer function of the

TCM, introduced in the prescription current’s circuit

.3.3 Calculus of the exterior loop of flux The transfer function for the flux transducer

(13)Transfer function of this loop controller:

where: (14-15)For tuning of the RF flux controller we use the same criteria of the module with it’s desired function

¿16)The necessary transfer function for the RF is analogically determined, gaining a PI controller

(17)

where: The isodrome constant of the flux regulator, in this case:

The RF’s integration constant:

(18)

The proportional amplification constant:¿19)

3.4

Calculus of the motor’s speed vector control

canal

The calculus of vector control canal of the, winding drum’s drive, motor’s speed has, the inner loop of the active stator current, connected in cascade, Is y =Ir with the RCA regulator and an outer speed loop (RV) and a speed transducer (fig.6). This canal includes three DMD multiplication-division devices of the parameters’ at the RV’s exit, and another one at the current loop’s exit

Fig.6 The simplified structural scheme of the speed’s vector control channel

The division devise at the RV’s device is determined by the fact that this controller generates a prescription signal for the motor’s electromagnetic couple, which is

proportional with the flux and the active stator current ISA ≈Ir.As consequence, the prescription signal for the active

stator current: (20)The division device at the RV’s exit is meant for the couple’s protection according to drum’s inertial variable momentum.

3.5 Calculus of the active stator current’s loop

The active stator current transducer must be chosen with the same exit signal UTCA.N=3,5 V at a nominal current of 3.5 A. The current, being twice as much, at the RCA’s entrance a voltage divider with a 0,5 coefficient is introduced

¿21)The converter’s transfer function is the same as in the reactive stator current’s case

¿22)

Where:

- the uncompensable constant of the current’s loop.Thanks to the current’s open loop, we get an current PI controller with transfer function:

¿23)

Whre: (24)

The RCA’s amplification coefficient

¿25)The transfer function of the current’s closed loop:

(26)3.6 The calculus of the speed’s loopWe pick a speed transducer with a transfer coefficient:(27)The inertial summary momentum of the drum and motor:

¿28)

Where: =10 kg ; =0,15m; =0,05mThe transfer function of the speed regulation object: (29)

Where If we start from this transfer function, thanks to the speed’s closed loop:

¿30)Then we get a pure proportional regulator for speed:

(31)The speed’s loop’s transfer function closes with a proportional regulator is:

¿32)But a pure proportional speed regulator does not provide a stationary error reporting to the motor’s load couple. The cable’s winding mechanism does not require a null stationary error, which is why we choose a PI speed regulator.For simplifying the grant of the system, the whole drive of the wiredrawer and of the winding mechanism is equated to a transfer function of second degree.Following this equation we get the following structural scheme (fig.7.):

Fig.7. The simplified structural scheme of the drive

systemThe transfer function of the speed loop:

(33)

Where:

(34)

(35)

4. THE MODEL OF THE WIREDRAWING MACHINE’S CONTROL SYSTEM

The Simulink model of the wiredrawing machine’s integrated control system (fig.8) contains drives of : the module of wiredrawing, the mechanical parts’ movement equations, and wire annealing and winding. The mathematical models of the wiredrawer’s drive contain transfer functions of the drive motor and of the frequency converter. The scalar drive of this motor is made of the following reason: the wiredrawer does not require a drive with high dynamical parameters, the

motor having functioned on its natural characteristic, without feedback loops.The cascade vector control system if the winding drum’s motor speed is made of an outer loop of the active stator current Is y =Ir with the RCA regulator, the outer speed loop (RV) and the correction loop of the TT transducer’s tension force. The mathematic model of the wiredrawing and winding machine’s parts’ contains the following relations [10]

(36)

w

here:

FT – tension force;VLM1-wire’s linear speed; VLM2-winding mechanism’s drum’s linear speed; Scond.-conductor’s section; Lk-lathe’s work length; RT-drum’s radius; ECu-elasticity coefficient of the metal’s wire.

When modeling of the annealing module, because of the load’s active character, the frequency correction of the phase shift was excluded, and the load’s impedance has a constant value. The converter is esteemed with a first degree element, and the force section has the following relation as basis:

(37)

Fig.8 The Simulink model of the control system

5. SIMULATION RESULTS

Based on the developed model the transitional processes at start, acceleration and deceleration of the vector control winding machine’s drive, the study of the wire’s tension force in dynamical modes, the dependence of the transmitted power to the inductor of the annealing module compared to the wire’s linear speed, adjusting the regulators’ processes etc.From fig.9 and fig.10 a following fact is observed: the control system of the annealing module ensures the proportional regulation of the element’s energy depending on the wire’s linear speed, after it has been wiredrawn. An overregulation of the tension force can be observed when simulating the winding systems, without considering the reaction of the tension force, (fig.11) which may lead to tearing of the wire. As a result, in the control system, a tension s force transducer was introduced for eliminating of this overvoltage and for ensuring the prescribed value (fig.10.).

6. CONCLUSIONS

In order to improve the regulation indices and to gain in productivity of the wiredrawing machine a single control system was developed through integration of the

winding and wiredrawing machines’ drive control, as well as of the annealing module, subsystems. Based on the transfer functions the mathematical model for the system: of automatic regulation for the wire’s tension

Fig. 9. The variation of the wire’s linear speed

force and of regulation of energy flux for the annealing module depending on the wire’s linear speed has been eveloped. The computer simulation of the developed control system proves: the adequate behaving of the wiredrawing machine for different variations of the prescription signals and for different perturbations; the optimization of the dynamic and static processes vs. the quickness and exclusion of oscillations and overregulation of the controlled dimensions.

References

1. S.Kalpakjian, S.Schmid, Manufacturing engineering & technology. Prentice-Hall, 2006.  

2. R.N. Wright. Wire technology: process engineering and metallurgy. Elsevier, 2010.

3. Фетисов Г.П. и др. Материаловедение и технология металлов. M.: Высшая школа. 2001.

4. Drawing technology. www.sampsistemi . com/.../13146.html

5. Solutions for your wiredrawing machine. www.automation.siemens.com/.../wire-drawing-machines.aspx

6. Wiredrawing Machines and Accessories http://morgan-koch.com/

7. B24 stainless steel wiredrawing machine. http :// factory . dhgate . com / cable - manufacturing - equipment / b 24- stainless - steel - wire - drawing - machine - p 44716833. html

8. Utilaj pentru producerea cablulu. /www.tehelectro-sv.com/index.php

9. N.Golovanov, I Şora. Electrotermie şi Electrotehnologii. Vol.1. Ed. Tehnică, Bucureşti, 1997. ISBN 973-31-1144-9.

10.V.Cazac. Sistem de trefilare microprocesoral cu motoare asincrone. Teză de licenţă, Chişinău, 2010.

Fig. 12 The variation of the tension force when starting the drive with a feedback loop

Fig. 11 The tension froce when regulating without a reaction loop

Fig. 10 The variation of the induction element’s emited energy

Fig. 12 The tension froce when regulating with a reaction loop

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