CN103132233B - Automatic visual aligning and scutching method for scutcher - Google Patents

Abstract

The invention discloses an automatic visual aligning and scutching method for a scutcher. The method includes collecting fabric from an umbrella stand and transmitting images to an industrial personal computer for identification, recognizing and aiming images of missed stitch seam, receiving deviation value delta s of the image identify subsystem, regulating the speed of a stepper motor through a PID(proportion integration differentiation) controller in real time, so as to achieve the control of the rotating speed of the umbrella stand and ensure the aligning of the missed stitch seam and a splitting cutter. By the automatic visual aligning and scutching method, the defects of low aligning sensitivity, high false rate, untimely mechanical control and the like of a traditional photoelectric sensor are overcome. Since the location of the missed stitch seam is identified and marked through image processing technique, the deviation value delta s of the scutcher and the splitting cutter is calculated, the stepper motor is adjusted through the PID controller according to the deviation value delta s so as to control the rotational direction and speed of the umbrella stand, and thus, the splitting cutter is guaranteed to split the fabric along the missed stitch seam. The automatic visual aligning and scutching method effectively solves the problems of low human checking efficiency and labor intensity and improves the automatic aligning precision of the scutcher.

Description

A kind of automatic vision for scutcher is to line open-width method

Technical field

The invention belongs to scutcher technical field, relate in particular to a kind of automatic vision for scutcher to line open-width method.

Background technology

China is as a traditional weaving big country, and textile industry is the traditional pillar industry of China, plays very important effect in the national economic development.Because the performance such as fabric adaptive capacity and production efficiency of circle latitude machine is better than flat machine, circle latitude machine occupies significant proportion in modern textile application.But the cylindraceous fabric that most of circle latitude machines are produced needs could print and dye after open-width sizing, and therefore, all the dropped stitch of a preset wide about 1mm stitches in knitting process, when open-width, cut open cloth cutter and along this dropped stitch seam, fabric is cut open.At present, the most of manual adjustment mode that adopts of the Tracking Recognition of domestic scutcher dropped stitch seam, operative employee takes and carves the position of noting dropped stitch seam, when dropped stitch seam departs from while cuing open cloth cutter position, by the artificial guiding mechanism of controlling in time, ensures dropped stitch seam and cuts open cloth cutter and align.This manual adjustment mode efficiency is low, and labour intensity is large.In view of importance and the domestic scutcher automaticity lower present situation of textile industry to national economy, research autoscutch has vast potential for future development and huge economic worth.

At present, lot of domestic and international producer is all devoted to research and develop the scutcher with certain automaticity.As the multi-functional rope form fabric scutcher of Italian CORINO company development, can be simultaneously semi-finished product COTTON FABRIC or fabric be completed to the processing of dehydration, untwisting, open-width and four operations of batching, functional integration is high.Domestic scutcher research is started late, and the automaticity of product is lower.But in recent years, China obtains greater advance about the automatic control research of scutcher, the fabric dropped stitch seam tracker of exploitation adopts photoelectric sensor to detect the light-intensity difference with other positions of fabric through dropped stitch seam more, to locate dropped stitch seam.What width friend waits has been developed the infrared ray photoelectric tracker that is applicable to various fabrics, adopts Single-chip Controlling stepper motor, and open-width speed and precision are all greatly improved.Huang Lihua etc. have realized the photodetector array tracker that judges dropped stitch seam position according to the output of sensor.Yang Deliang etc. have designed the arithmetic adopting in software computing replacement traditional circuit to process the signal of PSD (Position Sensitive Detector, Position-Sensitive Detector), have improved the precision and stability of system.

TUBULAR FABRIC scutcher is indispensable equipment in current dyeing, and to be a class cut by TUBULAR FABRIC the machine then launching for it, for after the operation such as dyeing of cloth lay a good foundation, its importance is self-evident.

The fabric dropped stitch seam tracker of domestic-developed adopts photoelectric sensor (as infrared transmitting tube, optoelectronic switch etc.) to detect the light-intensity difference that sees through dropped stitch seam more, but the sensitivity meeting of these centering methods its detection after long-time use declines, the probability of maloperation rises, and adjusts in real time control also inconvenient simultaneously.

Summary of the invention

The object of the embodiment of the present invention is to provide a kind of automatic vision for scutcher to line open-width method, being intended to solve the long-time sensitivity meeting that uses rear its detection of current scutcher declines, the probability of maloperation rises, and adjusts in real time the also inconvenient problem of controlling simultaneously.

The embodiment of the present invention is achieved in that a kind of automatic vision for scutcher is to line open-width method, and the method comprises:

CCD camera is responsible for fast, is accurately gathered the fabric of process from umbrella stand, and image transfer is identified to industrial computer;

Identification and demarcation dropped stitch seam image;

Umbrella stand control and emulation based on PID, umbrella stand RACS receives the departure Δ s of image recognition subsystem, adjusts in real time the speed of stepper motor by PID controller, thereby realizes the control to umbrella stand rotating speed, ensures dropped stitch seam and cuts open cloth cutter and align.

Further, the fabric of process from umbrella stand is responsible for fast, is accurately gathered to CCD camera, and to industrial computer, identification comprises following methods image transfer:

A part for scutcher, for fixing or support centralising device, is cutd open cloth cutter and is fixed on scutcher, and it aligns with dropped stitch seam initial position; CCD camera is placed in and cuts open cloth cutter and fabric top, requires CCD camera vertical with fabric place plane, and ensures to cut open cloth cutter and fabric in CCD viewing field of camera central authorities, makes the CCD phase function moment capture dropped stitch to stitch and cut open the position of cloth cutter; In the course of work, CCD camera is transferred to industrial computer by the textile image capturing and identifies to demarcate dropped stitch seam, and calculates dropped stitch seam and the position deviation amount Δ s that cuts open cloth cutter.When Δ s has exceeded the deviation range allowing, centralising device can send the signal corresponding with departure automatically, umbrella stand RACS receives deviation signal, adjusts umbrella stand rotary speed by PID controller control motor, makes dropped stitch seam get back to gradually desired center position.

Further, dropped stitch seam image recognition and scaling method comprise:

Image pre-processing method in image recognition subsystem adopts histogram equalization to eliminate the impact of shooting environmental on original image;

If n is the summation of pixel in image, n _jthat gray level is r _knumber of pixels, L is gray level sum possible in image, s _kbe called histogram equalization, can be based on formula obtaining gray level in input picture is r _keach pixel to be mapped to gray level in output image be s _krespective pixel;

Image in image recognition subsystem is cut apart and is taked binarization method processing;

If i, j is ranks number, and f (i, j) is that (i, j) locates gray value, and T is threshold value, and after can obtaining cutting apart based on formula below, (i, j) locates gray value g (i, j),

$g(i,j)=\left\{\begin{array}{cc}255& f(i,j)\&GreaterEqual;T\\ 0& f(i,j)<T\end{array}\right.---\left(1\right)$

Because carrying out processing to piece image, different threshold setting methods can produce different binary conversion treatment results, the threshold value T=5 of use; Dropped stitch after Threshold segmentation is sewn on and in image, shows as a black line, and background is white; So, be easy to according to its characteristics of image mark dropped stitch seam position, and calculate itself and the departure Δ s that cuts open cloth cutter.

Further, increment type PID controller is selected in the umbrella stand control based on PID and emulation;

Further, increment type PID principle and algorithm design;

Using T as the constant sampling period, k, as sampling sequence number, obtains discrete PID controller expression formula:

$u_k=k_p\mathrm{\&Delta;}{s}_k+k_i\underset{j=0}{\overset{k}{\mathrm{\&Sigma;}}}\mathrm{\&Delta;s}\left(j\right)+k_d(\mathrm{\&Delta;}{s}_k-\mathrm{\&Delta;}{s}_{k-1})+u_0---\left(2\right)$

Wherein, u _kbe the output valve of the k time sampling instant, Δ s _k, Δ s _k-1be k, the input deviation value of k-1 sampling instant, k _pfor proportionality coefficient, k _ifor integral coefficient, k _dfor differential coefficient, u ₀for output initial value;

Can obtain according to the fundamentals of successive deduction:

$u_{k-1}=k_p\mathrm{\&Delta;}{s}_{k-1}+k_i\underset{j=0}{\overset{k}{\mathrm{\&Sigma;}}}\mathrm{\&Delta;s}\left(j\right)+k_d(\mathrm{\&Delta;}{s}_{k-1}-\mathrm{\&Delta;}{s}_{k-2})+u_0---\left(3\right)$

Formula (2) deducts formula (3) and obtains increment type PID control algolithm:

Δu _k＝k _p[Δs _k-Δs _k-1]+k _iΔs _k+k _d[Δs _k-2Δs _k-1+Δs _k-2]

＝(k _p+k _i+k _d)Δs _k-(k _p+2k _d)Δs _k-1+k _dΔs _k-2(4)

While adopting increment type PID control algolithm, once determine k _p, k _i, k _d, as long as three departures before and after using can be obtained controlling increment Δ u, the increment of its corresponding this executing agency position.Because stepper motor has summation, the controlled quentity controlled variable of its physical location can realize the accumulation of automatic controlling increment.

Further, system simulation method is: in image recognition subsystem, required by the initial position of dropped stitch seam with cut open cloth cutter and align, open-width departure Δ s=0 now; The departure Δ s of this system allows left-right deviation 10mm centered by initial dropped stitch seam, and, when dropped stitch seam left avertence is in the time that initial dropped stitch seam position exceedes 10mm, Δ s is negative value; When dropped stitch seam right avertence is in the time that initial dropped stitch seam position exceedes 10mm, Δ s be on the occasion of; Determine pid parameter value, first tentatively determine initial parameter value k with experience trial and error procedure _p=5.5, k _i=0.8, k _d=0.25, determine tri-parameters of PID, make system obtain good steady-state error and dynamic property.

Automatic vision for scutcher provided by the invention, to line open-width method, is realized jointly by image acquisition subsystem, image recognition subsystem and umbrella stand RACS.In image acquisition subsystem, CCD camera is responsible for fast, is accurately gathered the fabric of process from umbrella stand, and image transfer is identified to industrial computer; In image recognition subsystem, eliminate the impact of environment on original image by image preliminary treatment, use the position of image processing techniques identification, mark dropped stitch seam, and calculate itself and the departure of cuing open cloth cutter; Umbrella stand RACS receives the departure of image recognition subsystem, and according to the Changing Pattern between the stepper motor rotating speed of dropped stitch seam departure, umbrella stand rotary speed and the rotation of control umbrella stand, by PID controller control step motor to adjust umbrella stand rotary speed, thereby ensure dropped stitch seam and cut open cloth cutter and align.

The method is combined vision-based detection for scutcher automatic vision with automatic control technology is to line open-width; The image collecting in image acquisition subsystem is realized by CCD fabric dropped stitch seam centralising device; It is to adopt histogram equalization to eliminate the impact of shooting environmental on original image that image in image recognition subsystem carries out pretreated method; It is to take binary conversion treatment that image in image recognition subsystem carries out image dividing processing; Dropped stitch after binary conversion treatment is sewn on and in image, shows as a black line, and background is all white.So, be easy to according to its characteristics of image mark dropped stitch seam position, and calculate itself and the departure Δ s that cuts open cloth cutter; PID controller is increment type PID controller.

Brief description of the drawings

The automatic vision for scutcher that Fig. 1 embodiment of the present invention provides is to line open-width method flow diagram;

Dropped stitch seam image recognition and scaling method flow chart that Fig. 2 embodiment of the present invention provides;

The umbrella stand control based on PID and emulation mode flow chart that Fig. 3 embodiment of the present invention provides.

Detailed description of the invention

In order to make object of the present invention, technical scheme and advantage clearer, below in conjunction with drawings and Examples, the present invention is further elaborated.Should be appreciated that specific embodiment described herein, only in order to explain the present invention, is not intended to limit the present invention.

Fig. 1 shows a kind of automatic vision for scutcher that the invention process case provides to line open-width method, and the method comprises:

In step S101, the image collecting in image acquisition subsystem is realized by CCD fabric dropped stitch seam centralising device;

A part for scutcher, for fixing or support centralising device, is cutd open cloth cutter and is fixed on scutcher, and it aligns with dropped stitch seam initial position; CCD camera is placed in and cuts open cloth cutter and fabric top, requires CCD camera vertical with fabric place plane, and ensures to cut open cloth cutter and fabric in CCD viewing field of camera central authorities, makes the CCD phase function moment capture dropped stitch to stitch and cut open the position of cloth cutter.In the course of work, CCD camera is transferred to industrial computer by the textile image capturing and identifies to demarcate dropped stitch seam, and calculates dropped stitch seam and the position deviation amount Δ s that cuts open cloth cutter.When Δ s has exceeded the deviation range allowing, centralising device can send the signal corresponding with departure automatically, umbrella stand RACS receives deviation signal, adjusts umbrella stand rotary speed by PID controller control motor, makes dropped stitch seam get back to gradually desired center position.

In step S102, identification and demarcation dropped stitch seam image;

In step S103, umbrella stand control and emulation based on PID.

Umbrella stand RACS receives the departure Δ s of image recognition subsystem, adjusts in real time the speed of stepper motor by PID controller, thereby realizes the control to umbrella stand rotating speed, ensures dropped stitch seam and cuts open cloth cutter and align.

Fig. 2 shows dropped stitch seam image recognition and the demarcation that the invention process case provides, and the method comprises:

In step S1021, the image pre-processing method in image recognition subsystem adopts histogram equalization to eliminate the impact of shooting environmental on original image;

If n is the summation of pixel in image, n _jthat gray level is r _knumber of pixels, L is gray level sum possible in image, s _kbe called histogram equalization, can be based on formula obtaining gray level in input picture is r _keach pixel to be mapped to gray level in output image be s _krespective pixel.Histogram equalization is that one makes the equally distributed mapping algorithm of the approximate obedience of output image histogram, to strengthen picture contrast, has positive effect to eliminating picture noise.

In step S1022, the image in image recognition subsystem is cut apart and is taked binarization method processing;

If i, j is ranks number, and f (i, j) is that (i, j) locates gray value, and T is threshold value, and after can obtaining cutting apart based on formula below, (i, j) locates gray value g (i, j).

$g(i,j)=\left\{\begin{array}{cc}255& f(i,j)\&GreaterEqual;T\\ 0& f(i,j)<T\end{array}\right.---\left(1\right)$

Because carrying out processing to piece image, different threshold setting methods can produce different binary conversion treatment results, under example resolution ratio of the present invention, and the threshold value T=5 that the present invention uses.Dropped stitch after Threshold segmentation is sewn on and in image, shows as a black line, and background is white.So, be easy to according to its characteristics of image mark dropped stitch seam position, and calculate itself and the departure Δ s that cuts open cloth cutter.

Fig. 3 shows umbrella stand control and the emulation based on PID that the invention process case provides, and the method comprises:

In step S1031, select PID controller;

Digital PID Controller is divided into two kinds of position type PID and increment type PIDs in actual applications.Position type PID will add up to control deviation value, not only calculates loaded down with trivial detailsly, and in the time that output valve significantly changes, can cause the significantly variation of executing agency position.And increment type PID is only exported the increment of controlled quentity controlled variable, so misoperation time impact is very little, be used for the motion control of stepper motor.

In step S1032, increment type PID principle and algorithm design;

Using T as the constant sampling period, k, as sampling sequence number, obtains discrete PID controller expression formula:

$u_k=k_p\mathrm{\&Delta;}{s}_k+k_i\underset{j=0}{\overset{k}{\mathrm{\&Sigma;}}}\mathrm{\&Delta;s}\left(j\right)+k_d(\mathrm{\&Delta;}{s}_k-\mathrm{\&Delta;}{s}_{k-1})+u_0---\left(2\right)$

Wherein, u _kbe the output valve of the k time sampling instant, Δ s _k, Δ s _k-1be k, the input deviation value of k-1 sampling instant, k _pfor proportionality coefficient, k _ifor integral coefficient, k _dfor differential coefficient, u ₀for output initial value.

Can obtain according to the fundamentals of successive deduction:

$u_{k-1}=k_p\mathrm{\&Delta;}{s}_{k-1}+k_i\underset{j=0}{\overset{k}{\mathrm{\&Sigma;}}}\mathrm{\&Delta;s}\left(j\right)+k_d(\mathrm{\&Delta;}{s}_{k-1}-\mathrm{\&Delta;}{s}_{k-2})+u_0---\left(3\right)$

Formula (2) deducts formula (3) and obtains increment type PID control algolithm:

Δu _k＝k _p[Δs _k-Δs _k-1]+k _iΔs _k+k _d[Δs _k-2Δs _k-1+Δs _k-2]

＝(k _p+k _i+k _d)Δs _k-(k _p+2k _d)Δs _k-1+k _dΔs _k-2(4)

While adopting increment type PID control algolithm, once determine k _p, k _i, k _d, as long as three departures before and after using can be obtained controlling increment Δ u, the increment of its corresponding this executing agency position.Because stepper motor has summation, the controlled quentity controlled variable of its physical location can realize the accumulation of automatic controlling increment.

In step S1033, system emulation.

In image recognition subsystem, required by the initial position of dropped stitch seam with cut open cloth cutter and align, open-width departure Δ s=0 now.Umbrella stand RACS of the presently claimed invention is a Nonlinear Closed Loop Control, and the departure Δ s of this system allows left-right deviation 10mm centered by initial dropped stitch seam, and, when dropped stitch seam left avertence is in the time that initial dropped stitch seam position exceedes 10mm, Δ s is negative value; When dropped stitch seam right avertence is in the time that initial dropped stitch seam position exceedes 10mm, Δ s be on the occasion of.Determine pid parameter value, the present invention first tentatively determines initial parameter value k with experience trial and error procedure _p=5.5, k _i=0.8, k _d=0.25.This system upper strata programming language adopts C++ to realize, and debugs pid control algorithm under Visua1C++ environment, determines tri-parameters of PID, makes system obtain good steady-state error and dynamic property.

The automatic vision for scutcher that the embodiment of the present invention provides is to line open-width method, and in image acquisition subsystem, CCD camera is responsible for fast, is accurately gathered the fabric of process from umbrella stand, and image transfer is identified to industrial computer; In image recognition subsystem, eliminate the impact of environment on original image by image preliminary treatment, use the position of image processing techniques identification, mark dropped stitch seam, and calculate itself and the departure of cuing open cloth cutter; Umbrella stand RACS receives the departure of image recognition subsystem, and according to the Changing Pattern between the stepper motor rotating speed of dropped stitch seam departure, umbrella stand rotary speed and the rotation of control umbrella stand, by PID controller control step motor to adjust umbrella stand rotary speed, thereby ensure dropped stitch seam and cut open cloth cutter and align.

The automatic vision that dropped stitch seam is demarcated in the identification based on CCD and PID controls motor that the embodiment of the present invention provides is to line open-width method, this method can overcome that the sensitivity of conventional photoelectric sensor centering method easily reduces, False Rate is high and the mechanical control shortcoming such as not in time, adopt image processing techniques identification and mark dropped stitch seam position, and calculate it and cut open the departure Δ s of cloth cutter, PID controller is adjusted direction and the speed of step motor control umbrella stand rotation according to departure Δ s, to ensure that cuing open cloth cutter cuts fabric open along dropped stitch seam, has realized the automation processing of scutcher.

The present invention effectively solves the difficult problem that manual detection efficiency is low, labour intensity is large, improves scutcher automatic centering precision.

The foregoing is only preferred embodiment of the present invention, not in order to limit the present invention, all any amendments of doing within the spirit and principles in the present invention, be equal to and replace and improvement etc., within all should being included in protection scope of the present invention.

Claims (1)

1. For the automatic vision of scutcher to a line open-width method, it is characterized in that, the method comprises:

   Regulate CCD viewing field of camera center line and cut open cloth cutter and align, gather textile image with it, image processing software automatically calculates dropped stitch seam and cuts open the position deviation amount Δ s of cloth cutter;

   According to the characteristics of image identification after Threshold segmentation and demarcation dropped stitch seam position;

   Adopt increment type PID controller to umbrella stand control and emulation, adjust in real time the speed of stepper motor by increment type PID controller, thereby realize the control to umbrella stand rotating speed, ensure dropped stitch seam and cut open cloth cutter and align;

   The fabric of CCD collected by camera process from umbrella stand, and image transfer is identified to industrial computer, the method comprises:

   A part for scutcher, for fixing or support centralising device, is cutd open cloth cutter and is fixed on scutcher, and it aligns with dropped stitch seam initial position; CCD camera is placed in and cuts open cloth cutter and fabric top, requires CCD camera vertical with fabric place plane, and ensures to cut open cloth cutter and fabric in CCD viewing field of camera central authorities, makes the CCD phase function moment capture dropped stitch to stitch and cut open the position of cloth cutter; In the course of work, CCD camera is transferred to industrial computer by the textile image capturing and identifies to demarcate dropped stitch seam, and calculate dropped stitch and stitch and the position deviation amount Δ s that cuts open cloth cutter, when position deviation amount Δ s has exceeded the deviation range allowing, centralising device can send the corresponding deviation signal with position deviation amount Δ s automatically, umbrella stand RACS receives deviation signal, adjusts umbrella stand rotating speed by PID controller control step motor, makes dropped stitch seam get back to gradually desired center position;

   Dropped stitch seam image recognition and scaling method comprise:

   Image pre-processing method in image recognition subsystem adopts histogram equalization to eliminate the impact of shooting environmental on original image;

   If n is the summation of pixel in image, n _jthat gray level is r _knumber of pixels, L is gray level sum possible in image, s _kbe called histogram equalization, can be based on formula obtaining gray level in input picture is r _keach pixel to be mapped to gray level in output image be s _krespective pixel;

   Image in image recognition subsystem is cut apart and is taked binarization method processing;

   If i, j is ranks number, and f (i, j) is that (i, j) locates gray value, and T is threshold value, and after can obtaining cutting apart based on formula below, (i, j) locates gray value g (i, j),

   $g(i,j)=\left\{\begin{array}{cc}255& f(i,j)\&GreaterEqual;T\\ 0& f(i,j)<T\end{array}\right.---\left(1\right)$

   Because carrying out processing to piece image, different threshold setting methods can produce different binary conversion treatment results, the threshold value T=5 of use; Dropped stitch after Threshold segmentation is sewn on and in image, shows as a black line, and background is white; So, be easy to according to its characteristics of image mark dropped stitch seam position, and calculate itself and the position deviation amount Δ s that cuts open cloth cutter;

   Increment type PID controller is selected in umbrella stand control based on PID and emulation;

   Increment type PID principle and algorithm design;

   Using T as the constant sampling period, k, as sampling sequence number, obtains discrete PID controller expression formula:

   $u_k=k_p{\mathrm{\&Delta;s}}_k+k_1\underset{j=0}{\overset{k}{\mathrm{\&Sigma;}}}\mathrm{\&Delta;s}\left(j\right)+k_d({\mathrm{\&Delta;s}}_k-{\mathrm{\&Delta;s}}_{k-1})+u_0---\left(2\right)$

   Wherein, u _kbe the output valve of the k time sampling instant, Δ s _k, Δ s _k-1be k, the input position departure of k-1 sampling instant, k _pfor proportionality coefficient, k _ifor integral coefficient, k _dfor differential coefficient, u ₀for output initial value;

   Can obtain according to the fundamentals of successive deduction:

   $u_{k-1}=k_p{\mathrm{\&Delta;s}}_{k-1}+k_1\underset{j=0}{\overset{k-1}{\mathrm{\&Sigma;}}}\mathrm{\&Delta;s}\left(j\right)+k_d({\mathrm{\&Delta;s}}_{k-1}-{\mathrm{\&Delta;s}}_{k-2})+u_0---\left(3\right)$

   Formula (2) deducts formula (3) and obtains increment type PID control algolithm:

   Δu _k＝k _p[Δs _k-Δs _k-1]+k _iΔs _k+kd[Δs _k-2Δs _k-1+Δs _k-2]

   ＝(k _p+k _i+k _d)Δs _k-(k _p+2k _d)Δs _k-1+k _dΔs _k-2(4)

   While adopting increment type PID control algolithm, once determine k _p, k _i, k _d, as long as three position deviation amounts before and after using can be obtained controlling increment Δ u, the increment of its corresponding this executing agency position; Because stepper motor has summation, the controlled quentity controlled variable of its physical location can realize the accumulation of automatic controlling increment;

   System simulation method is:

   In image recognition subsystem, required by the initial position of dropped stitch seam with cut open cloth cutter and align, position deviation amount Δ s=0 now; The position deviation amount Δ s that this system allows allows left-right deviation 10mm centered by initial dropped stitch seam, and, when dropped stitch seam left avertence is in the time that initial dropped stitch seam position exceedes 10mm, position deviation amount Δ s is negative value; When dropped stitch seam right avertence is in the time that initial dropped stitch seam position exceedes 10mm, position deviation amount Δ s be on the occasion of; Determine pid parameter value, first tentatively determine initial parameter value k with experience trial and error procedure _p=5.5, k _i=0.8, k _d=0.25, determine tri-parameters of PID, make system obtain good steady-state error and dynamic property.