RU2058573C1 - Apparatus for controlling metal cutting machine tool - Google Patents

Abstract

FIELD: automatic control systems for metal cutting machine tools. SUBSTANCE: apparatus includes the setter 1 and the pickup 7 of a power parameter, the adder 2, the adaptive regulator 3 of a power parameter, the feed electric drive 4, being kinematically connected through the reduction gear 5 and the working member 6 of the machine tool with a cutting process. The unit 9 for simulation of the cutting process has two circuits. One of these circuits, having the inverting amplifier 15, the switch 16, the integrator 17, the adder 18, the threshold member 19 and the divider 20, is being tuned with the aid of a pickup, detecting revolution number of the drive unit 8 and the spindle 10. The second circuit has the multiplier 21, the unit 22 for simulation of the power parameter pickup, the adder 23, the divider 24 and the integrator 25. The regulator 3 includes the integrator 11, the divider 12, the adder 13 and the divider 14. EFFECT: development of the adaptive simulation unit of cutting process, while taking into account dynamics of transition modes and non-stable conditions of cutting process, organization of controlling the feed drive unit of the machine tool on a base of parameters, being identified. 1 cl, 3 dwg

Description

 The invention relates to automatic control systems for metal cutting machines and can be used, for example, in lathes to optimize cutting conditions.

 A device for stabilizing power parameters for lathes is known, which contains an adder of the setpoint and a power parameter sensor, a regulator, a multiplier, a feed drive connected to the working body of the machine and through a cutting process with a power parameter sensor.

 The disadvantage of this device is the decrease in the degree of stability of the system with increasing regulation errors. This drawback is due to the fact that with an increase in the load simultaneously with an increase in the transmission coefficient characterizing the cutting process, the transmission coefficient of the correction link implemented on the basis of the multiplier and having a quadratic characteristic increases.

 A device for controlling a metalworking process is known, comprising a task unit, an adder, a feed drive, the output of which through a speed sensor is connected to a cutting process model unit, a feedback circuit including a main drive drive power sensor, an adder, an inverter adder, and a threshold element. The model block contains a constant coefficient and a variable coefficient of the model, the outputs of which are connected through an adder and an aperiodic link to an adjustable variable coefficient input. The signal from the output of the model block is summed with the signal from the power sensor at the inputs of the adder-inverter and their difference is used as a feedback correction signal.

 In this device, the control system is implemented according to the principle of proactive correction. Moreover, the variable transmission coefficient of the model of the object of regulation (cutting process) is implemented in the form of a power law as a function of the feed rate.

 Such a representation of the cutting process does not reflect the dependence of its transfer coefficient on the cutting depth, hardness of the workpiece material, degree of tool wear and other factors. It is known that if proactive correction is used, the mismatch of the transfer coefficients of the model and the object leads to a decrease in the static accuracy of the control system.

 In addition, the coverage of an object with large time constants with a differential plug reduces the performance of the stabilization system of power parameters, since the properties of the system become close to open by main feedback.

 Closest to the technical nature of the present invention is a device for controlling a metal cutting machine, comprising sequentially connected power parameter setter, adder, multiplication unit, correction unit, feed drive loaded on the machine tool, feed speed sensor and feed parameter sensor, outputs which are connected to the corresponding inputs of the divider, the output of which is connected to the control input of the multiplier, the second input of the adder is connected to the output of the force sensor wow parameter.

 The disadvantage of this device is the low static and dynamic performance of the stabilization system of the power parameter. This drawback is due to the fact that the nonlinear correction of the system as a function of the power parameter and the feed rate of the tool is not effective, since the resultant parameter characterizing the cutting process itself is the amount of feed per spindle revolution.

 In addition, the cutting process, characterized by continuous changes in the feed rate as a function of the current value of the power parameter, is a dynamic process. To identify the dynamic process, the operation of taking the pure derivative is necessary, which is physically unrealizable, especially only with the help of the division unit.

 The aim of the invention is to improve the accuracy of the device.

 This is achieved by the fact that in the device for controlling the metal-cutting machine, comprising a power parameter setter with a first adder at the output, a feed drive, a gearbox, a machine tool and a power parameter sensor, the output of which is connected to another input of the first adder, a drive speed sensor feed, connected between the output of the feed drive and the information input of the first divider, and the spindle speed sensor, additionally between the output of the first adder and the input of the electric drive, the first integrator, the second adder and the third divider are connected in series, and a circuit is introduced from the key, the second integrator, the multiplier, the model of the power parameter sensor and the fourth adder, the output of the second integrator through the third adder and the threshold element connected in series the key input, the output of the fourth adder through a fourth divider and a third integrator connected in series to other inputs of the multiplier and of the divider, the output of the first adder through the second divider is connected to the second input of the second adder, the output of the spindle speed sensor is connected to the control inputs of the first and second dividers, the output of the speed sensor of the feed drive is connected directly to the first input of the key, and the output through the inverter to the second the first divider is connected to another input of the third adder, the output of the second integrator is connected to the second input of the fourth divider, and the second input of the fourth adder is connected to the output of the sensor force parameter.

 In FIG. 1 shows a functional diagram of a device for controlling a metal cutting machine: in FIGS. 2 and 3, structural diagrams defining a part of an object and a self-tuning circuit.

 The proposed device (see Fig. 1) contains a serially connected power parameter setter 1, an adder 2, an adaptive power parameter regulator 3, a feed electric drive 4 kinematically connected through a reducer 5 to the working body of the machine 6 with a cutting process, a power parameter sensor 7, an output which is connected to the second input of the adder 2, a serially connected sensor 8 of the feed drive rotation frequency and a cutting process model 9, a spindle rotation sensor 10.

 The controller 3 consists of an integrator 11 and a divider 12, the outputs of which through an adder 13 are connected to the information input of the divider 14. The information input of the divider 12 together with the input of the integrator 11 is connected to the output of the adder 2, and the control to the output of the sensor 10 of the spindle speed.

 The model of the cutting process 9 contains an adjustable loop of dynamic cutting processes and a loop for self-tuning the gear ratio of the process. The dynamic process circuit is based on an inverter 15, a series-connected key 16, an integrator 17, an adder 18 and a threshold element 19 connected by an output to the control input of the key 16, as well as a divider 20, the output of which is connected to the second input of the adder 18. Information input of the divider 20 together with the first input of the key 16 is connected to the output of the sensor 8 of the rotational speed of the feed drive, the second input of the key 16 is connected to the output of the sensor 8 through the inverter 15.

 The process gain self-tuning loop contains a series-connected multiplier 21, a model of the power parameter sensor 22, an adder 23, a divider 24, an integrator 25, the output of which is connected to the control inputs of the multiplier 21 and the divider 14. The control input of the divider 24 together with the information input of the multiplier 21 is connected to the output of the integrator 17. The second input of the adder 24 is connected to the output of the sensor 7.

 The device (see figure 1) works as follows.

 The mismatch signal between the task from block 1 and the feedback from the sensor 7 is generated by the adder 2 and through the power parameter 3 regulator is fed to the control input of the feed drive 4. When changing processing modes, for example, cutting depth, stabilization of the power parameter (cutting power, cutting force, and t .d.) is carried out by changing the feed rate.

Transients caused by a change in cutting conditions lead to a change in chip thickness. This change can be written as follows
gh / dt vf (h 'h), where v is the tool feed rate;
h'2πv / w steady state chip thickness;
w the spindle speed of the machine,
1 for (h 'h)> 0
f (h 'h) 0 for (h' h) 0
-1 when (h 'h) <0 The function f (h' h), taking into account the moving (average) value, is replaced by the function sign (h 'h) and implemented using the adder 18, the threshold element 19 and the sign switch, which includes the key 16 and the inverter 15. In this case, a value proportional to the steady-state value of the chip thickness h ′ is formed at the output of the divider 20, and its current thickness h at the output of the integrator 17 of block 9.

где Е(w, t) 2π/w постоянная времени процесса резания, равная времени одного оборота шпинделя, характеризует время выхода интегратора 17 на установившееся значение при скачкообразном изменении частоты вращения шпинделя или скорости подачи. Данная постоянная в процессе обработки может меняться в десятки раз. Для ее компенсации регулятор 3 содержит цепь, образованную интегратором 11, делителем 12 и сумматором 13, соответствующую пропорционально-интегральному звену.Correction of the system is carried out using the proportional-integral controller 3 with variable parameters. The choice of a controller of this type is based on the approximation of a nonlinear integrator, which includes a signed switch and integrator 17, by a non-stationary aperiodic link
W ′ (p, t)

where E (w, t) 2π / w is the time constant of the cutting process, equal to the time of one turn of the spindle, characterizes the time of the integrator 17 reaching a steady-state value with an abrupt change in the spindle speed or feed speed. This constant during processing can change dozens of times. To compensate for it, controller 3 contains a circuit formed by an integrator 11, a divider 12, and an adder 13 corresponding to a proportional-integral link.

 Another significant factor determining the non-stationary nature of the cutting process is the dependence of its transmission coefficient on the processing conditions (hardness of the workpiece material, cutting depth, condition of the cutting tool, etc.).

где K

,T

коэффициент передачи и постоянная времени датчика силового параметра;
К(μ, t) обобщенный коэффициент передачи, является функцией изменения параметров резания во времени (I(t) глубины резания; Н_w(t) твердости материала заготовки; С_F(t) геометрии резания, степени затупления инструмента и неучтенных условий обработки);
U_F(p) выходной сигнал датчика 7.To identify the transmission coefficient of the process, a self-tuning loop is used (see Fig. 2), implemented in the form of a nonlinear tracking system. In this case, part of the cutting process, characterizing its transmission coefficient, can be described as the following transfer function:
W ″ (p, t)

where k

, T

gear ratio and time constant of the power parameter sensor;
To (μ, t) the generalized transmission coefficient is a function of the cutting parameters changing over time (I (t) of the cutting depth; Н _w (t) of the hardness of the workpiece material; With _F (t) of the cutting geometry, the degree of blunting of the tool and unaccounted processing conditions) ;
U _F (p) sensor output 7.

рассогласование между выходным сигналом объекта U_F и модели U

;
g h сигнал с выхода блока 17;
b, λ- коэффициенты.The law of changing a custom parameter
K _msn bε / λg where ε = U _F U

the mismatch between the output signal of the object U _F and the model U

;
gh signal from the output of block 17;
b, λ are the coefficients.

2 T

настроен на модульный (технический) оптимум, что соответствует коэффициенту демпфирования ξ

для звена 2-го порядка.The transition from a substantially nonlinear structure (see Fig. 2) to a system with variable or quasistationary coefficients (see Fig. 3) is carried out by replacing the multiplication and division blocks 21 and 24 with equivalent coefficients, respectively. The latter structure is identical to an ordinary follower circuit, in which the introduction of a divider 24 eliminates the influence of the parameter h on the dynamics of the self-tuning circuit. Contour when choosing b / λ = 1 / K

2 T

tuned to a modular (technical) optimum, which corresponds to a damping coefficient ξ

for the link of the 2nd order.

Self-tuning circuit is astatic. The output value K _msn K (μ t) is generated at the output of the integrator 25. During cutting, the resulting error between the output of the power parameter sensor 7 and its model 22 causes a change in the output signal of the integrator 25. This process continues until the transmission coefficient of the multiplier 21, tunable by the integrator 25, will not be equal to the generalized transmission coefficient of the regulatory object. Simultaneously with the adjustment of the transmission coefficient of the model using the divider 14, an inversely proportional change in the transmission coefficient of the regulator 3 is made. In this case, the overall transmission coefficient of the stabilization loop of the power parameter remains unchanged.

на порядок по крайней мере меньше постоянных привода подачи, влияние переходных процессов в контуре самонастройки на процесс перестройки параметров в основном контуре существенно не сказывается.The nature of the change in the parameters is generally unpredictable. The depth of cut may vary due to changes in the tolerances of the workpiece from product to product as a result of the eccentricity of the installation of the workpiece (i.e. the appearance of reverse pulsations of the depth of cut). Blunting the tool and changing the hardness of the workpiece is also quite slow. Given that the time constant of the sensor T

an order of magnitude less than the constant feed drives, the effect of transients in the self-tuning loop on the process of tuning parameters in the main loop is not significantly affected.

где К_v коэффициент передачи датчика скорости;
Т_v эквивалентная постоянная времени контура.The structure of controller 3 is selected from the condition of tuning the system to a modular optimum in accordance with the principles of constructing systems with subordinate control parameters. In this case, the feed drive is considered adjusted, and its transfer function is described as follows:
W _v (p)

where K _v the transmission coefficient of the speed sensor;
T _v equivalent circuit time constant.

При настройке контура стабилизации силового параметра на модульный оптимум передаточная функция регулятора 3 будет
W

(p, t)

+

где T

=T_v+T

сумма малых постоянных времени для контура.Taking into account transient conditions, the transfer function of the cutting process for the main circuit can be represented as
W _F (p, t)

When tuning the stabilization loop of the power parameter to the modular optimum, the transfer function of controller 3 will be
W

(p, t)

+

where T

= T _v + T

the sum of the small time constants for the circuit.

(p,t)

+

Блок 14, реализующий коэффициент

, совместно воздействует на пропорциональную (блока 12) и интегральную (блока 11) составляющие регулятора 3. Причем пропорциональная составляющая блока 12 с учетом коэффициента передачи К_w датчика частоты вращения шпинделя должна быть
K_п=

где U_w(t) K_w w(t) напряжение на выходе датчика скорости 10.The difference between the coefficients of the model K _msn (t) and the object K (μ, t) can be neglected, then the transfer function of the controller will be
W

(p, t)

+

Block 14 that implements the coefficient

, together acts on the proportional (block 12) and integral (block 11) components of the regulator 3. Moreover, the proportional component of block 12, taking into account the transmission coefficient K _w of the spindle speed sensor, should be
K _p =

where U _w (t) K _w w (t) is the voltage at the output of the speed sensor 10.

 Thus, the proposed principles for constructing a stabilization system for the power parameter make it possible to compensate for the influence of non-stationary processing conditions, eliminate the conditions for the occurrence of self-oscillations, and ensure technically optimal processes in the entire range of cutting parameters.

 Using the device allows to increase processing productivity, and in some cases, for example, when face processing, and the quality of the product by reducing roughness.

 It is advisable to implement the proposed structure using microprocessor technology. Algorithmic support in this case is not difficult and is reduced mainly to replacing continuous integrators with discrete ones.

Claims (1)

 DEVICE FOR MANAGING A METAL-CUTTING MACHINE, comprising a power parameter setter with a first adder at the output, serially connected feed actuator, gearbox, machine tool and a power parameter sensor, the output of which is connected to another input of the first adder, a feed drive rotation speed sensor connected between the drive output feed and the information input of the first divider, and the spindle speed sensor, characterized in that between the output of the first adder and the input of the electric drive VK the first integrator, the second adder and the third divider are connected in series and the circuit is introduced from the key, the second integrator, the multiplier, the model of the power parameter sensor and the fourth adder, and the output of the second integrator through the third adder and the threshold element connected in series is connected to the key control input , the output of the fourth adder through the fourth divider and the third integrator connected in series is connected to other inputs of the multiplier and the third divider, you One of the first adder through the second divider is connected to the second input of the second adder, the output of the spindle speed sensor is connected to the control inputs of the first and second dividers, the output of the speed sensor of the feed drive is connected directly to the first input of the key, and the output of the first divider is connected to the second through the inverter to another input of the third adder, the output of the second integrator is connected to the second input of the fourth divider, and the second input of the fourth adder is connected to the output of the sensor power parameter .

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