CN103611767A - Method for controlling position of sliding block of electro-hydraulic double-cylinder bending machine - Google Patents

Abstract

The invention discloses a method for controlling the position of a sliding block of an electro-hydraulic double-cylinder bending machine. The method includes the steps of process improvement and pressure maintaining. When the sliding block does not reach an effective position point of an integral action, the magnitude of the action is adjusted through a proportional gain; when the sliding block moves to the effective position point of the integral action, the magnitude of the action is adjusted through an integral gain; when the sliding block continues to move to a switching position point of the integral action, the controlled quantity threshold value u(Y2) at the moment is recorded; when the sliding block continues to move downwards to a dead point, the integral action of a controller is reduced from the u(Y2) to 0. According to the method, in the whole operation process that the sliding block makes contact with a workpiece, is formed through compression moulding, is steered and leaves from the workpiece, the action of the controller continuously changes in a self-adaptive mode, a system is free from impact and sudden changes due to stressing, the motion trail of the sliding block is smooth, and moving parts are little in loss. Compared with a conventional method, the method has the advantages that the parameter action scope is enlarged, not only can steady accuracy of the system be guaranteed, but also responsiveness of the system is quickened, the sliding block can reach a target location more quickly, and machining efficiency is greatly improved.

Description

A kind of electric liquid twin-tub slider of bender position control method

Affiliated technical field

The invention belongs to bender technical field of automatic control, relate to electric liquid bender control technology, be specially a kind of electric liquid twin-tub slider of bender position control method.

Background technology

Electricity liquid twin-tub bender is widely used in sheet material manufacture field, and the quality of sheet material processing depends on stability and the accuracy that slide position is controlled.

Electricity liquid twin-tub bender is controlled hydraulic cylinder by two proportional servo valves, hydraulic cylinder is equipped with displacement transducer for Real-Time Monitoring and feedback physical location, the signal that displacement transducer collects after filtering, controller is sent in the processing such as signal conversion, controller includes the special-purpose software of controlling, according to movement command signal and the feedback signal set, after analytical calculation, try to achieve the control signal of system, give respectively two proportional servo valves, according to the power of the signal of telecommunication, carry out the opening flow of control ratio servo valve, thereby control the position of two hydraulic cylinders, band movable slider moves up and down.

According to the requirement of technique, Forging Process comprises following step:

Under fast: controller forward is opened proportional servo valve, opens prefill valve, and cylinder upper cavity oil is oil-filled, cavity of resorption is discharged fluid and is flowed to epicoele through differential circuit, and hydraulic cylinder relies on deadweight fast-descending, makes slide block run to fast speed change point from top dead-centre.

Work is entered: controller, after receiving speed change point signal, cuts out prefill valve, opens proportional pressure valve, and differential circuit remains unchanged, and the forward opening of proportional servo valve reduces, and makes slide block slow running to bottom dead centre.

Pressurize: after receiving bottom dead centre signal, controller passing ratio pressure valve is to system persistent pressure, and differential circuit remains unchanged, and the position of slide block continues to be controlled by proportional servo valve, the output of system closing proportional servo valve, system reaches poised state and maintains a period of time.

Off-load: controller control ratio servo valve reverse opening, in oil circuit, set up buffer brake simultaneously.

Backhaul: proportional servo valve opening continues to increase, and under the effect of buffer brake, slide block fast moving is returned to top dead-centre, and after receiving top dead-centre signal, valve Close All, completes a bending work period.

Due to the hysteresis quality of hydraulic circuit, in system, there is tracking error always.Based on this specific character, current Forging Process is controlled and is extensively adopted PI control method, according to the tracking error between given position and physical location, form control deviation, the ratio of deviation (P), integration (I) are formed to controlled quentity controlled variable by linear combination, controlled device is controlled, and the control law of discretization is:

$u\left(k\right)=K_{P}e\left(k\right)+K_I\underset{j=0}{\overset{k}{\mathrm{\Σ}}}e\left(j\right)$ (formula 1)

Wherein:

K is sampling sequence number, k=0,1,2

K _pfor proportional gain;

K _ifor storage gain;

E (k) is the deviate of the k time sampling instant input;

E (j) is the deviate of the j time sampling instant input;

U (k) is the controlled quentity controlled variable of the k time sampling instant controller output.

The effect of each correction link of PI controller is as follows:

Proportional component: the deviation signal e of proportional reflection control system (t), once deviation produces, controller produces control action immediately, to reduce deviation.The power of proportional action depends on proportional gain, and proportional gain is larger, and proportional action is stronger, otherwise more weak.

Integral element: be mainly used in eliminating static difference, improve system without margin.The power of integral action depends on storage gain, and storage gain is larger, and integral action is stronger, otherwise more weak.

In whole Forging Process, system, by regulating the proportional gain of PI controller and the size of storage gain, regulates the controlled quentity controlled variable of output, by changing the openings of sizes of proportional servo valve, realizes the Position Control to slide block.

For the work in bending technique, enter process, because it is the committed step of contact workpiece bending and molding, therefore, the position control accuracy of this step has been determined to the precision of whole Forging Process.The conventional PI controller adopting at present, its proportional action can be so that slide block be followed given trace operation; But when system is during in positioning stage, owing to having tracking error between slide block physical location and given position, therefore the accumulative action of integration causes system output to continue to increase, when slide block arrival impact point needs holding position motionless, the output of controller is not 0, and system cannot enter stable state.For this situation, existing two kinds of processing modes: mode one, the output of closing controller immediately, now system is stressed will there is sudden change, cause slide block to rock, processing work is of low quality; Mode two, reduce gradually the output of controller, because being reduced to 0, the output of controller needs a period of time, during this period of time slide block will continue operation, until controller is output as 0, but now the stop position of slide block has surpassed target location, cause processing work to occur overshoot phenomenon, bending angle changes, and cannot meet processing request.

Summary of the invention

Technical problem to be solved by this invention is: slide block location difficulty in controlling for existing bender, the problem that processing work precision is low, the invention provides a kind of electric liquid twin-tub slider of bender position control method, can high accuracy control slide position, can effectively improve the problems referred to above that prior art exists, realize the accurate positioning control to slide block under dynamic operation condition.The inventive method adopt to improve PI and controls+Front feedback control based on model, wherein, improve PI controller in the control structure of conventional PI controller, integral action is carried out to self adaptation adjustment, effectively solve the adjusting problem repeatedly that conventional PI controller exists at system positioning stage, avoid the overshoot phenomenon of processing work; Front feedback control based on model, the relationship model of model slide position, system pressure and proportional servo valve, then utilize the feedback signal of system, obtain corresponding compensation rate, continuous Correction and Control amount, accelerate system responsiveness, thereby improve position control accuracy, improve workpiece crudy.

The basic principle of the present invention's electricity liquid twin-tub slider of bender position control method: the control software of PI controller has trajectory planning module and position control module.Trajectory planning module, for giving the movement locus order of the left cylinder of fixed slider and right cylinder.Position control module, for regulating the opening of proportional servo valve, realizes the accurate control to slide position.

The control method of PI location of controls control module adopts improves PI control (further prioritization scheme, has also increased the Front feedback control based on model).Improve PI controller and comprise proportional action and integral action.Proportional action, carries out proportion control to the position deviation of system, integral action, controls the accumulation of position deviation, it realizes principle: take predefined storage gain as basis, according to the target location of slide block, when the trajectory planning module of the control software of integral action active position point Y1(PI controller is assigned the order of slide block arrival dead point, the residing true location point Y1 of slide block), integral action switching position point Y2(sets a slide position threshold value S in advance according to different application occasion, when the physical location of slide block and the distance of bottom dead centre equal this threshold values, now the residing true location point of slide block is exactly integral action switching position point Y2), and the current physical location of feedback, integral action is carried out to self adaptation adjustment.Specific to work, enter and pressure maintaining period: slide block moves from speed change point to bottom dead centre, when slide block does not arrive integral action active position point Y1, effectively, effect size is regulated by proportional gain, that is: u (k)=K in proportional action output _pe (k) (formula 2), when slide block movement arrives integral action active position point Y1, effectively, effect size is regulated by storage gain in integral action output, and now, due to the existence of tracking error, the cumulative system control amount that makes of integral action continues to increase, that is:

(formula 3), when slide block continues motion arrival integral action switching position point Y2, system control amount starts adaptive change, its variation tendency is the reducing and reduce to bottom dead centre distance with slide block, specific implementation is: when slide block arrives integral action switching position point Y2, record controlled quentity controlled variable threshold value u (Y2) now, when slide block continues to move to bottom dead centre, the integral action of controller is no longer cumulative, on the contrary, about integral action switching position point Y2, controlled quentity controlled variable threshold value u (Y2), the function of location following error e (k), be that slide position moves to bottom dead centre from Y2, integral action is reduced to 0 from u (Y2), that is: u (k)=K _pe (k)+u (Y2) * e (k)/S(formula 4).When slide block finally arrives bottom dead centre, because tracking error is now zero, therefore proportional action is zero, meanwhile integral action is also adjusted into zero, therefore system control amount synchronous self-adapting is changed to 0, system reaches poised state, starts pressurize; Until arrive the dwell time, top dead-centre is got back in slide block counter motion.

The so-called Front feedback control based on model, it realizes principle: first based on theory analysis and test data of experiment, set up the relationship model of slide position, system pressure and proportional servo valve opening, then utilize the feedback signal of system, the opening compensation rate of the proportional servo valve that Real-time Obtaining and slide position, system pressure are corresponding, it revises rule is the nonlinear curve about system pressure and slide block tracking error:

$u_{\mathrm{comp}}\left(k\right)=K_{\mathrm{comp}}e\left(k\right)/\sqrt{\mathrm{Press}}$ (formula 5)

Wherein:

U _comp(k) be the opening compensation rate of the k time sampling instant proportional servo valve;

K _compit is the adjusting parameter of default;

Press is current system pressure.

Front feedback control module based on model is by the controlled quentity controlled variable of continuous Correction and Control device output, and responding system state regulates in advance before system puts in place in advance, improves the response of system.

Left cylinder or right cylinder for twin-tub bender, after the movement locus order of the given left and right cylinder of trajectory planning module, by employing, improve PI to control+Front feedback control algorithm based on model, the oil cylinder of both sides can reach to the accurate tracking of given movement locus.Because the movement locus order of two cylinders is consistent, so slide block arranged on left and right sides is also consistent with respect to the tracking error of movement locus, and this has just fundamentally solved the problem of slide block arranged on left and right sides position synchronism.Therefore, adopt algorithm of the present invention, system has also realized the synchronism control of two cylinder positions when guaranteeing positioning precision.

The present invention adopts and improves the Front feedback control algorithm based on model that PI controls and further optimizes, even in two hydraulic cylinder characteristics slightly the processing of difference or unbalance loading in the situation that, also can guarantee that slide block is in the stability of running, and the slide block accuracy of locating while arriving bottom dead centre, eliminate the overshoot phenomenon that adds man-hour.Slide block touching workpiece, compressing, commutation is left in the whole course of work of workpiece, the effect self adaptation of controller changes continuously, system is stressed without impacting, without sudden change, slide block movement smooth trajectory, moving component loss is low.Control method of the present invention, has expanded parameter role territory than conventional method, not only can guarantee systematic steady state precision, and has accelerated the response of system, makes slide block arrive more quickly target location, has greatly improved working (machining) efficiency.High precision position control method provided by the invention, real-time, control effectively, be applicable to industry spot application.

Accompanying drawing explanation

Fig. 1 is the inventive method control flow chart.

Fig. 2 is existing methodical control design sketch.

Fig. 3 is the control design sketch of the inventive method.

The specific embodiment

Application of the present invention is electric liquid twin-tub bender, and this electricity liquid twin-tub bender comprises with lower component: two proportional servo valves are controlled hydraulic cylinder, and band movable slider pumps; Stroke detection parts, the physical location of detection and feedback slider of bender.Electricity liquid twin-tub bender carrys out the opening flow of control ratio servo valve by the power of the given signal of telecommunication of response controller, realize the positioning control to slide block.

Work enter with pressure maintaining period in, the inventive method:

The processing of trajectory planning module to movement locus order.The parameter that controller is set according to machining, comprising: slide block target location, system maximal rate and Acceleration and deceleration time, the running orbit of planning slide block, and by the data information memory of having planned in controller main control chip.

Stroke detection component retrieval slide block arranged on left and right sides is with respect to the physical location of workbench reference point.

Position control module is calculated the track of planning and the deviation between the slide block physical location of feedback.

Improve PI location of controls control module, according to slide block position, calculate respectively the required aperture of proportional servo valve.

Forging Process specific to electric liquid twin-tub bender plate: slide block moves from speed change point to bottom dead centre, when slide block does not arrive integral action active position point Y1, effectively, effect size is regulated by proportional gain, that is: u (k)=K in proportional action output _pe (k); When slide block movement arrives integral action active position point Y1, effectively, effect size is regulated by storage gain, that is: in integral action output

when slide block continues motion arrival integral action switching position point Y2, record controlled quentity controlled variable threshold value u (Y2) now, when slide block continues to move to bottom dead centre, the integral action of controller is no longer cumulative, on the contrary, be that slide position moves to bottom dead centre from Y2 about the function of integral action switching position point Y2, controlled quentity controlled variable threshold value u (Y2), location following error e (k), integral action is reduced to 0 from u (Y2), that is: u (k)=K _pe (k)+u (Y2) * e (k)/S is when slide block finally arrives bottom dead centre, because tracking error is now zero, therefore proportional action is zero, meanwhile integral action is also adjusted into zero, therefore system control amount synchronous self-adapting is changed to 0, system reaches poised state, starts pressurize; Until arrive the dwell time, top dead-centre is got back in slide block counter motion.

Front feedback control module, according to the relationship model of slide position, system pressure and the proportional servo valve opening set up, provides the correction of proportional servo valve opening, and the size of correction is calculated according to formula (5).Revising rule is that is: system pressure is larger about the nonlinear curve of system pressure and slide block tracking error, and Front feedback control amount is less; Slide block tracking error is larger, and Front feedback control amount is larger.According to above correction rule, Front feedback control module is exported and is revised controlled quentity controlled variable.

Improve the actuating quantity of PI controller and the addition of the actuating quantity of Front feedback control module, form the controlled quentity controlled variable that finally needs output.Proportional servo valve corresponding to slide block arranged on left and right sides give respectively revised controlled quentity controlled variable, according to the power of the signal of telecommunication, carry out the opening flow of control ratio servo valve, thereby control the position of slide block.

By above step, system realizes to be controlled the high accuracy of slide position.The method applied in the present invention, the process that can arrive bottom dead centre to slide block is effectively predicted, and carry out deceleration in advance and control, having solved system control amount controlled quentity controlled variable when slide block arrives bottom dead centre is not 0 overshooting problem producing, and meets the requirement of bender high accuracy processing.

As shown in Figure 2, because system has self adaptation, do not regulate, slide block has produced overshoot phenomenon after arriving target location.Fig. 3 is the control design sketch after algorithm improves, express system control amount with the change procedure of slide position, comprise that dynamic tracking phase, cumulative stage of controlled quentity controlled variable, self adaptation adjusting stage and system reach the stage of stable state, the self adaptation regulatory function of algorithm makes slide block have accurate positioning precision.

Claims (2)

1. an electric liquid twin-tub slider of bender position control method, comprises that work enters and pressurize step, it is characterized in that:

Described work progress is rapid, and when slide block does not arrive integral action active position point (Y1), effectively, effect size is regulated by proportional gain in proportional action output:

u(k)=K _Pe(k)

Wherein: k is sampling sequence number, k=0,1,2 ..., K _pfor proportional gain, e (k) is the deviate of the k time sampling instant input, and u (k) is the controlled quentity controlled variable of the k time sampling instant controller output;

When slide block movement arrives integral action active position point (Y1), effectively, effect size is regulated by storage gain in integral action output:

$u\left(k\right)=K_{P}e\left(k\right)+K_I\underset{j=0}{\overset{k}{\mathrm{\Σ}}}e\left(j\right)$

Wherein: K _ifor storage gain, e (j) is the deviate of the j time sampling instant input;

When slide block continues motion arrival integral action switching position point (Y2), record controlled quentity controlled variable threshold value u (Y2) now;

When slide block continues to move to bottom dead centre, the integral action of controller is reduced to 0 from u (Y2):

u(k)=K _Pe(k)+u(Y2)*e(k)/S

Wherein: slide position threshold value S;

When slide block finally arrives bottom dead centre, start pressurize.

2. a kind of electric liquid twin-tub slider of bender position control method according to claim 1, is characterized in that: the U obtaining according to the following formula _comp(k) controlled quentity controlled variable of controller output is revised:

$u_{\mathrm{comp}}\left(k\right)=K_{\mathrm{comp}}e\left(k\right)/\sqrt{\mathrm{Press}}$

Wherein: U _comp(k) be the opening compensation rate of the k time sampling instant proportional servo valve, K _compbe the adjusting parameter of default, Press is current system pressure.

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