RU2032996C1 - Device for control over temperature of flat billet during induction heating - Google Patents

Abstract

FIELD: electrical engineering. SUBSTANCE: device for control over temperature of flat billet placed between lower and upper mobile inductors during induction heating includes master unit, temperature sensor, pickups of power, speed, armature current, controllers of power, speed, current connected in series, controlled thyristor converter which output is coupled to armature circuit of motor of translation of upper inductor. Shaft of upper inductor is rigidly coupled to shaft of speed pickup and is connected to inductor with the aid of ball-and-screw pair of reduction gear. Inductor is electrically linked to input of power pickup which output is connected to first input of power controller. Second input of current controller is coupled to output of pickup of armature current placed in armature circuit of motor of translation of upper inductor. Output of speed pickup is linked to second input of speed controller. Depending on irregularity of heating device is provided with proportionally integral controllers which inputs are connected to output of model characterizing temperature field of object of heating. EFFECT: enhanced efficiency and reliability of control. 1 dwg

Description

 The invention relates to means of automation of technological processes, and in particular to means of programmed temperature control during induction heating. The device can be widely used in temperature control systems of technological processes in the metallurgical, machine-building, machine-tool and other industries.

A known temperature control system with a program controller [1] The main disadvantage of the system is that at the temperature of the Curie point (700-800 ^o C) the thermophysical properties of the control object change sharply and the gain of the generator decreases, decreasing the gain of the entire system. This leads to an increase in the error in reproducing the real temperature of the object from the one set by the program and the impossibility of its complete compensation by the system, The output voltage of the amplifier of the software controller is limited in magnitude.

где K_ОБ=

коэффициент передачи объекта,
T₁=

постоянная времени первого "полуапериодического" звена,
T₂=

постоянная времени второго "полуапериодического" звена. Представленное соотношение взято из статьи А.В. Нетушила "Объект индукционного или радиационного нагрева как звено системы автоматического регулирования", Известия АН СССР, ОТН, "Энергетика и автоматика", 1962, N 2. Ввиду специфики передаточной функции, представленной двумя "полуапериодическими" звеньями, параболическая статическая характеристика нелинейного элемента описывает переходный процесс по температурному полю приближенно. Другим недостатком является ограниченное быстродействие и склонность к автоколебаниям системы управления из-за наличия в ней нелинейных элементов. Перечисленные недостатки устройства не обеспечивают равномерного нагрева заготовки при индукционном нагреве.A device for automatically controlling the temperature of an induction heating installation [2] This device is taken by the authors as a prototype, because it is closest to the proposed technical essence and the achieved effect. The device contains at least two sensors for measuring temperature over the thickness of the workpiece, each of which is connected to one of the inputs of the unit for setting the final temperatures of the workpiece and through a series-connected control unit and relay element with the input of the power on-off power controller. To increase the productivity of the installation by accelerating the heating of the workpiece, the control unit is made in the form of nonlinear elements with parabolic static characteristics in an amount equal to the number of temperature measuring sensors and an adder connected to their outputs, with the inputs of nonlinear elements serving as the control unit input and the adder output as its output. A significant drawback of this device is the limited accuracy of reproducing the real temperature field of the workpiece, a non-linear element, which is described in the general case by two "semi-periodic" links
W _OB (P)

where K _OB =

transmission coefficient of the object
T ₁ =

the time constant of the first "semi-periodic" link,
T ₂ =

the time constant of the second "semi-aperiodic" link. The presented ratio is taken from the article by A.V. Netushila, “An object of induction or radiation heating as a part of an automatic control system,” Izvestia AN SSSR, OTN, “Energy and Automation”, 1962, N 2. In view of the specificity of the transfer function represented by two “semi-periodic” links, a parabolic static characteristic of a nonlinear element describes a transition the process in the temperature field is approximately. Another disadvantage is the limited speed and a tendency to self-oscillations of the control system due to the presence of non-linear elements in it. The listed disadvantages of the device do not provide uniform heating of the workpiece during induction heating.

 The aim of the invention is to increase the uniformity of heating due to the exact reproduction of the real temperature field of the workpiece while maintaining high productivity of induction heating.

где R линейный размер (радиус) нагреваемой заготовки, а температуропроводность, μ_N π˙N собственное число, а коэффициенты усиления соответствующих N апериодических звеньев объекта управления определяются соотношением
K_N=

· cosμ_N

где х расстояние от центра заготовки до точки контроля по радиальному сечению. Установлено, что при заданной неравномерности ε _зад +20 30^oC температурное поле объекта должно быть представлено двумя апериодическими звеньями (N=2), а при ε _зад +15^oC тремя апериодическими звеньями (N 3).To achieve this goal, a device for controlling the temperature of induction heating of a workpiece located between the lower fixed and upper movable inductors, comprising a master and a temperature sensor of the workpiece, power, speed, and armature current sensors, serially connected power controller, speed controller, current controller, controlled thyristor converter, the output of which is connected to the anchor circuit of the motor moving the upper inductor, the shaft of which is rigidly connected to the shaft of the speed sensor, and e by means of a ball screw pair of the gearbox is connected to an inductor electrically connected to the input of the power sensor, the output of which is connected to the first input of the power regulator, the input of the current regulator is connected to the output of the armature current sensor included in the armature circuit of the upper inductor displacement motor, the output of the speed sensor is connected to the second input of the speed controller, it is additionally equipped with N temperature controllers with a proportional-integral dependence of the output voltage on the input, each of which has toyannuyu integration time equal to the time constant corresponding N-delay element that represents the temperature field of the object, which number is determined by a predetermined uneven heating + ε _backside gain of each regulator is the quotient of the product of the gain of the power sensor and the time constant τ _N corresponding N-aperiodic link to the product of the doubled small time constant of the temperature circuit, the gain of the temperature sensor and the coefficient Corresponding gain K _N N-delay element, first inputs of N temperature controllers connected to the output of the temperature sensor, the second inputs to the output of the temperature setpoint, controller output are combined and connected to the second input of the power controller, wherein the units of time constants determined by the relation
τ _N =

where R is the linear size (radius) of the heated workpiece, and the thermal diffusivity, μ _N π˙N is an eigenvalue, and the gains of the corresponding N aperiodic parts of the control object are determined by the relation
K _N =

Cosμ _N

where x is the distance from the center of the workpiece to the control point along the radial section. It was found that for a given non-uniformity of ε _ass +20 30 ^o C, the temperature field of the object should be represented by two aperiodic links (N = 2), and for ε _ass +15 ^o C three aperiodic links (N 3).

 Comparative analysis with the prototype shows that the claimed device is characterized by the presence of new units: a mathematical representation of the real temperature field of the workpiece in the form of N connected aperiodic units in parallel, N temperature regulators with different transfer functions, their connections with the rest of the device. Thus, the proposed device meets the criteria of the invention of "novelty." Comparison of the proposed solution with other technical solutions shows that PI controllers are widely known, however, their introduction in this connection with the other elements of the device, as well as the control of an object presented in the form of parallel connected N aperiodic links, increases the uniformity of heating due to the exact reproduction of real temperature field of the workpiece while maintaining high productivity of induction heating. This allows us to conclude that the technical solution meets the criterion of "significant differences".

 The drawing shows a diagram explaining the operation of the temperature control device during induction heating, the designations on which correspond to: I temperature controller, 2 first temperature controller, 3 second temperature controller, 4-Nth temperature controller, 5 power controller, 6 speed controller, 7 current regulator, 8 controlled thyristor converter, 9 and 10 anchor circuit and the mechanical part of electric motor 11, 12 gearbox, 13 inductor, 14,15,16 first, second, Nth aperiodic unit of the temperature field of the object, 17 sensor of anchor t OKA, 18 speed sensor, 19 power sensor, 20 temperature sensor. The heated product is located between the lower fixed and upper 13 movable inductors. The output of the temperature setter 1 is connected to the second inputs of the first temperature controller 2, the second temperature controller 3, and the Nth temperature controller 4. The outputs of the temperature controllers 2-4 are combined and connected to the second input of the power controller 5. The power controller 5, the speed controller 6, the current controller 7 and the controlled thyristor converter 8 are connected in series, the output of which is connected to the armature circuit 9 of the motor 11 for moving the upper inductor 13. The shaft the motor 11 is rigidly connected to the shaft of the speed sensor 18, and also through a ball screw pair of the gearbox 12 is connected to the inductor 13. The inductor 13 is electrically connected to the input of the power sensor 19, the output of which is connected to the the input of the power regulator 5. The second input of the current regulator 7 is connected to the output of the anchor current sensor 17 included in the anchor circuit 9 of the motor 11. The output of the speed sensor 18 is connected to the second input of the speed regulator 16. The first inputs of the temperature controllers 2-4 are combined and connected to the output of the temperature sensor 20. The temperature sensor 20 is electrically connected at the input to the heated product, which is represented by the first 14, second 15 and Nth aperiodic link 16.

The optimal mode of heating the product to a given temperature T _{back is} provided by the temperature control device during induction heating in one interval, during which the full power P _{floor of the} power source is supplied to the upper and lower inductors, the minimum allowable gap between the workpiece and the upper inductor is automatically set. Each temperature controller compensates for a given time constant of the corresponding N-aperiodic link τ _N. When the real heating non-uniformity ε reaches a value close to the value of the given non-uniformity ε _rear heating, the temperature control device stops the process of controlling the temperature field of the object. The power source is turned off. This point is characterized in that the surface temperature of the preform and arbitrary interior points of the radial section reaches the value T _ass + ε and internal temperature points through the thickness T _back - ε Thus, regulation of the temperature field of the object represented in the form of parallel-connected N aperiodic links, N temperature regulators allows to increase the uniformity of heating due to the exact reproduction of the real temperature field of the workpiece and maintain high performance induction heating a.

A device that implements the described induction heating mode operates as follows. The current circuit, consisting of 7-9, 17, is tuned to a technical optium and compensates for the electromagnetic time constant of the anchor circuit T _i . The transient in the circuit is determined by the small time constant of the current circuit T ^t _m . The current regulator 7 has a proportional-integral dependence of the output voltage on the input. The _high -speed circuit, consisting of 6, 10, 18, is tuned to the technical optium and compensates for the electromechanical time constant T _{m of the} mechanical inertial part 10 of the electric motor 11. The transient in the circuit is determined by the doubled small time constant of the high-speed circuit 2T ^with _m . The proportional-type speed controller 6 stabilizes the speed of the electric motor 11 at a predetermined level and sets the voltage level of the input signal to the current controller 7. The power circuit, comprising 5, 12, 13, 19, is configured for technical optium. The transient in the circuit is determined by the doubled small time constant of the power circuit 2T ^p _m. A proportional type power regulator 5 stabilizes the power in the circuit of the upper inductor 13 at a predetermined level and sets the voltage level of the input signal to the speed regulator 6. The temperature circuit, consisting of 2-4, 14, 15, 16, 20, is set to technical optium and compensates for time constants N aperiodic links τ ₁ τ _N. The transient in the circuit is determined by the doubled small time constant of the temperature circuit 2T ^t _m . The temperature regulators 2-4 proportional-integral type stabilize the temperature in the temperature circuit and set the input voltage level to the power regulator 5.

Consider the operation of the temperature control device in the process of induction heating. The temperature controller 1 sets the input voltage signal to the temperature controllers 2-4, corresponding to a given temperature T _ass . The voltage appears at the outputs 5-8, and the motor 11, rotating, brings the upper inductor 13 closer to the heated workpiece to a predetermined power value in the power circuit. If the set temperature 1 and the actual 20 are equal, the output voltage of the regulators 2-4 is equal to zero, which leads to a zero output voltage of 5-8, while the electric motor 11 stops and sets the inductor 13 to the position corresponding to the required heating power to the set temperature. Next, the working process of heating the product. If in the process of heating the product there is a deviation of its temperature from the set, an output voltage of 2-8 appears, and the electric motor 11, turning on, compensates for the temperature error by the corresponding installation of the inductor relative to the product, bringing the inductor closer or removed. In the process of heating the product, each controller 2, 3, 4 compensates for the corresponding time constants τ ₁ τ _{N of} aperiodic links 14-16 describing the actual temperature field of the product reproduced by the device with an accuracy of + ε _back .

где Т^т _m Т_утп + Т_дт малая постоянная времени токового контура;
T_утп постоянная времени управляемого тиристорного преобразователя;
Т_дт постоянная времени датчика тока.Let us synthesize a temperature control device for implementing the described induction heating mode. The open transfer function of the current loop tuned to the optium modulo will
W $\genfrac{}{}{0ex}{}{\text{then}}{\text{tj}}$ (P)

where T ^t _m T _utp + T _dt small time constant of the current circuit;
T _utp time constant of the controlled thyristor converter;
T _dt is the time constant of the current sensor.

·

·

Тогда передаточная функция регулятора тока 7 будет
W_рт(P)

·

· β_рег
Отсюда следует, что регулятор тока 7 имеет пропорционально-интегральную зависимость выходного напряжения от входного, а коэффициент усиления пропорциональной части будет
β_рег=

Замкнутая передаточная функция токового контура, настроенного на оптиум по модулю
W $\genfrac{}{}{0ex}{}{\text{то}}{\text{зт}}$ (P)

≃

Разомкнутая передаточная функция скоростного контура, настроенного на оптиум по модулю

₌

где Т^с _m 2Т^т _m + Т_дс малая постоянная времени скоростного контура;
Т_дс постоянная времени датчика скорости.Open transfer function of the current loop (valid):
W _td (P)

·

·

Then the transfer function of the current regulator 7 will be
W _rt (P)

·

Β _reg
It follows that the current regulator 7 has a proportional-integral dependence of the output voltage on the input, and the gain of the proportional part will be
β _reg =

Closed transfer function of a current loop tuned to optium modulo
W $\genfrac{}{}{0ex}{}{\text{then}}{\text{ht}}$ (P)

≃

Open-loop transfer function of a speed loop tuned to optium modulo

₌

where T ^s _m 2T ^t _m + T _{ds is a} small time constant of the velocity loop;
T _{ds the} time constant of the speed sensor.

·

·

·

Тогда передаточная функция регулятора скорости 6 будет
W_pc(P)

β_рег
Следовательно, регулятор скорости 6 является пропорциональным регулятором. Замкнутая передаточная функция скоростного контура, настроенная на оптиум по модулю

₌

₌

_≃

Разомкнутая передаточная функция контура мощности, настроенного на оптиум по модулю

₌

где Т^p _m 2Т^с _m + Т_дм малая постоянная времени контура мощности;
Т_дм постоянная времени датчика мощности. Разомкнутая передаточная функция контура мощности
W_дm(P)

· W $\genfrac{}{}{0ex}{}{\text{то}}{\text{зс}}$ (P)

K_и=

K_и
Тогда передаточная функция регулятора мощности 5 будет
W_рm(P)

= β_рег
Таким образом, регулятор мощности 5 пропорциональный регулятор. Замкнутая передаточная функция контура мощности, настроенного на оптиум по модулю, имеет вид

₌

₌

_≃
≃

Разомкнутая передаточная функция контура температуры, настроенного на оптиум по модулю

₌

где Т^t _m 2Т^р _m + Т_дt малая постоянная времени контура температуры;
Т_дt постоянная времени датчика температуры. Разомкнутая передаточная функция контура температуры имеет вид
W_tд(P) W $\genfrac{}{}{0ex}{}{\text{то}}{\text{зр}}$ (P)

Тогда передаточная функция регулятора температуры 2-4 примет вид
W_pt(P)

=

Cледовательно, регуляторы температуры 2-4 являются ПИ-регуляторами, настроенными на постоянные времени соответствующих N-апериодических звеньев с коэффициентами усиления пропорциональной части

Интервал нагрева цилиндрической стальной заготовки с диаметром 850 мм и высотой 145 мм до 1000^oC характеризуется следующими параметрами. Температурное поле объекта представлено тремя параллельно-соединенными апериодическими звеньями. Заданная неравномерность нагрева при этом составляет +15^oC. В качестве источника питания верхнего и нижнего индукторов используется индукционная установка УПИ2-500/1Н c преобразователем частоты ППЧВ-500-1,0-6000 с управлением по цепи возбуждения. Расстояние от центра заготовки до точки контроля по радиальному сечению составляет 212,5 мм. В начальный момент интервала нагрева в контуры индукторов подается полная мощность P_пол=

Три регулятора температуры на протяжении всего интервала нагрева компенсируют заданные постоянные времени первого, второго, третьего апериодических звеньев объекта, которым соответствуют значения 52,3 мин; 13,1 мин; 5,8 мин. В конце интервала нагрева температуры поверхности заготовки и произвольных внутренних точек по радиальному сечению равны 1015^oC, а температуры внутренних точек по толщине 975^oC. Равномерность нагрева за счет точности воспроизведения реального температурного поля заготовки по сравнению с передовой технологией ускоренного индукционного нагрева повышается при этом на 30% при достаточно высокой производительности индукционного нагрева. В качества привода перемещения верхнего индуктора использовано устройство воспроизведения УВЗ-21, изготавливаемое Новосибирским электромеха- ническим заводом с приводом типа IЭМ8-012, имеющим усилие на штоке при заторможенном роторе 8КН. Приводной электродвигатель имеет мощность Р1,3 кВт, номинальный ток I_ном 23 А, напряжение питания U_п 45,5 В. В качестве регуляторов 2-4 используется серийный регулятор Ф5173, выпускаемый отечественной промышленностью. Этот блок входит в комплекс средств Государственной системы промышленных приборов, например на суперблоках СУПС (Комплекс технических средств для локальных информационно-управляющих систем (КТС ЛИУС)). Средства управления с переменной структурой. Том 4, вып. 2, М. ЦНИИТЭИприборостроения, 1980). Годовой экономический эффект от внедрения устройства управления температуры при индукционном нагреве будет окончательно определен при внедрении устройства за счет уменьшения угара металла, а также уменьшения бракованных заготовок по качеству нагрева.The open transfer function of the speed loop has the form
W _sd (P) W $\genfrac{}{}{0ex}{}{\text{then}}{\text{ht}}$ (P)

·

·

·

Then the transfer function of the speed controller 6 will be
W _pc (P)

β _reg
Therefore, the speed controller 6 is a proportional controller. Closed speed loop transfer function tuned to optium modulo

₌

₌

_≃

Open transfer function of a power circuit tuned to optium modulo

₌

where T ^p _m 2T ^with _m + T _{dm is a} small time constant of the power circuit;
T _dm time constant of the power sensor. Open loop power transfer function
W _dm (P)

W $\genfrac{}{}{0ex}{}{\text{then}}{\text{ss}}$ (P)

K _and =

K _and
Then the transfer function of the power regulator 5 will be
W _pm (P)

= β _reg
Thus, the power controller 5 is a proportional controller. The closed transfer function of the power circuit tuned to the optium modulo has the form

₌

₌

_≃
≃

Open transfer function of a temperature loop tuned to optium modulo

₌

where T ^t _m 2T ^p _m + T _{dt is a} small time constant of the temperature circuit;
T _dt is the time constant of the temperature sensor. The open transfer function of the temperature circuit has the form
W _td (P) W $\genfrac{}{}{0ex}{}{\text{then}}{\text{sp}}$ (P)

Then the transfer function of the temperature controller 2-4 takes the form
W _pt (P)

=

Consequently, temperature controllers 2-4 are PI controllers tuned to the time constants of the corresponding N-aperiodic links with gain factors of the proportional part

The heating interval of a cylindrical steel billet with a diameter of 850 mm and a height of 145 mm to 1000 ^o C is characterized by the following parameters. The temperature field of the object is represented by three parallel-connected aperiodic links. The specified unevenness of heating in this case is +15 ^o C. As the power source of the upper and lower inductors, the UPI2-500 / 1N induction unit with a frequency converter ППЧВ-500-1,0-6-6000 with control along the excitation circuit is used. The distance from the center of the workpiece to the control point along the radial section is 212.5 mm. At the initial moment of the heating interval, the total power P _floor =

Three temperature controllers throughout the heating interval compensate for the set time constants of the first, second, third aperiodic parts of the object, which correspond to values of 52.3 min; 13.1 min; 5.8 minutes At the end of the heating interval, the temperatures of the surface of the workpiece and arbitrary internal points along the radial section are 1015 ^o C, and the temperature of the internal points along the thickness of 975 ^o C. The uniformity of heating due to the accuracy of reproducing the real temperature field of the workpiece in comparison with the advanced technology of accelerated induction heating increases 30% with a sufficiently high productivity of induction heating. As a drive for moving the upper inductor, a UVZ-21 playback device was used, manufactured by the Novosibirsk Electromechanical Plant with an IEM8-012 type drive having a rod force with a locked rotor 8KN. The drive electric motor has a power of P1.3 kW, rated current I _nom 23 A, supply voltage U _p 45.5 V. As regulators 2-4, the serial regulator F5173 manufactured by the domestic industry is used. This unit is included in the complex of tools of the State Industrial Instrumentation System, for example, on the super-blocks of EMSS (Complex of hardware for local information and control systems (KTS LIUS)). Variable structure controls. Volume 4, no. 2, M. TsNIITEIPriborostroeniya, 1980). The annual economic effect of the introduction of a temperature control device during induction heating will be finally determined during the implementation of the device by reducing the waste of metal, as well as reducing defective billets for heating quality.

Claims (1)

DEVICE FOR CONTROLLING A TEMPERATURE OF A FLAT BID FOR INDUCTION HEATING, located between the lower fixed and upper movable inductors, comprising a master and a temperature sensor for the workpiece, a power sensor, speed of the armature current, serially connected power controller, speed controller, current controller, controlled thyristor converter, the output of which connected to the anchor chain of the motor for moving the upper inductor, the shaft of which is rigidly connected to the shaft of the speed sensor, and also by means of a ball the reducer pair is connected to an inductor electrically connected to the input of the power sensor, the output of which is connected to the first input of the power regulator, the second input of the current regulator is connected to the output of the armature current sensor included in the armature circuit of the upper inductor displacement motor, the output of the speed sensor is connected to the second input a speed controller, characterized in that the device is additionally equipped with N-temperature controllers with a proportional-integral dependence of the output voltage on the input, each of which has an integration time constant equal to the time constant of the corresponding N-aperiodic link, which represents the temperature field of the object, the number of which is determined by the given heating unevenness ± ε _ass , the gain of each controller is equal to the quotient of the product of the gain of the power sensor and the time constant τ _{N of the} corresponding N-aperiodic link to the product of the doubled time constant of the temperature circuit, the gain of the temperature sensor and oeffitsienta gain k _N N-corresponding delay element, first inputs of N-temperature regulators are connected to the output of the temperature sensor, the second inputs to the output of the temperature setpoint, controller output are combined and connected to the second input of the power controller, wherein when ε _ass = ± (20-30 ) ^° C the number of aperiodic links is N 2, and for ε _ass = ± 15 ^° C the number of aperiodic links corresponds to N 3, time constants τ _N and gain K _{N of} aperiodic links are determined by the relations

where R is the linear size (radius) of the heated workpiece;
a thermal diffusivity;
μ _N = πN is an eigenvalue;
X is the distance from the center of the workpiece to the control point along the radial section.

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