CN105091765A - Method of distinguishing the front side from the back side of a cage holder - Google Patents

Abstract

The invention discloses a method of distinguishing the front side from the back side of a cage holder. The method includes the steps: (1) the step of selecting characteristic values for distinguishing by a system: taking the internal and external diameters of circular rings on the two end faces of a holder as the characteristic values for distinguishing or taking the areas of the circular rings on the two end faces of the holder as the characteristic values for distinguishing; (2) the step of eliminating the influence of external factors: controlling brightness through a closed loop control mode, continuously shooting by a camera while the brightness is adjusted to be consistent with a benchmark value, and maintaining the certain brightness before the camera snapshots; and (3) the step of correcting a distinguishing reference: correcting the benchmark values for distinguishing the front side from the back side to ensure that subsequent distinguishing is accurate within the scope allowing the benchmark values to accurately distinguish the front side from the back side of the holder.

Description

A kind of method of discrimination of ball cage retainer pros and cons

Technical field

The invention belongs to a kind of retainer and manufacture field, be specifically related to a kind of method of discrimination of ball cage retainer pros and cons.

Background technology

The widespread use on wheeled vehicle of ball cage.Usually, ball cage by foreign steamer, interiorly to take turns, some steel balls and retainer form, and inside takes turns and be positioned at foreign steamer, retainer is arranged on interiorly takes turns between foreign steamer, and retainer offers steel ball hole.Retainer partly wraps up all or part of rolling body, and moves thereupon, in order to separation roller, guides rolling body and holds it in bearing.The inner cylinder face of foreign steamer and interior convex spheroid machining of taking turns have the steel ball rolling channel straight trough of equal number.Steel ball is placed in foreign steamer, interior raceway straight trough of taking turns, and it is also in the steel ball of retainer simultaneously.For the retainer had at automotive trannsmission system etc. on the equipment of higher rotation speed, the requirement for dimensional accuracy is very high.If retainer in process of production dimensional accuracy is not up to standard, be arranged on the excessive wear that vehicles will cause retainer, affect ball cage serviceable life, or the problem such as traffic safety.Retainer mentioned by the present invention refers to that the surfaces externally and internally formed after turning is sphere, has the rectangle like straight hole of 6 definite shapes in a circumferential direction, and two ends are the hardware of plane.As shown in Figure 1, in prior art, be generally by manually inspecting by random samples same batch products to the detection of retainer, each size of hand dipping retainer.On the one hand, may there is undetected situation in sampling observation, can not reach the verification and measurement ratio of 100%, therefore, namely cannot ensure the qualification rate of each product, in addition, along with the rising gradually of cost of labor, this mode is more and more uneconomical.

Current domestic existing retainer detects patent automatically to be had:

A kind of retainer automatic detection device (patent No.: 201310522733.7): disclose a kind of retainer automatic detection device comprising frame, driving, detent mechanism, testing agency, material loading track, cutting agency, measuring sonde.Described frame is provided with material loading track, for, axis and radial displacement is done relative to retainer, a probe fixed retainer is provided with so that the detent mechanism of detection at the free end of measuring sonde, testing agency, blanking track, a measuring sonde, this measuring sonde can be done axially and radial displacement relative to retainer under external force when the measuring position set, the free end of measuring sonde is provided with a probe, also comprise and drive described detent mechanism, the propulsion system of testing agency and measuring sonde action, described detent mechanism comprises for the outside fix mechanism of the measuring position fixed retainer lateral surface in setting and the center positioning mechanism that to be positioned by measuring sonde in the measuring position of setting on retainer central axis, described testing agency is optical grating ruler measurement element.

A kind of detector of wind power bearing retainer (patent No.: 201120131863.4): disclose a kind of a kind of detector of wind power bearing retainer be made up of star worktable, flat bolster, measurement swing arm, sounding rod, trough of belt backing plate.At the center of star worktable, revolving shaft is housed; The rotating central hole measured in swing arm becomes pendulum structure with the revolving shaft on star worktable by bearing assemble; Sounding rod inserts to be measured in swing arm and fixes; Meter is by showing spiral-lock on sounding rod; Star worktable is equipped with three flat bolsters and two trough of belt backing plates, and positioning pillars is fixed on trough of belt backing plate and also can moves in groove.

A kind of ball bearing retainer pick-up unit (patent No.: 201420044863.4): disclose a kind of dial gauge fixed leg and be fixedly mounted on base plate, dial gauge is arranged on dial gauge fixed leg, positioning seat is fixedly mounted on base plate, positioning seat top is shaped with location short column, retainer to be measured placed by location short column, be placed with fixing pressure head above retainer to be measured, in the pocket hole of retainer to be measured, be placed with standard ball; Middle, positioning seat upper end is shaped with boss, and boss contacts with the standard ball in retainer to be measured; Afterburning lever holder is fixedly mounted on base plate, afterburning lever holder is installed and is shaped with afterburning lever; One end of spring is arranged on afterburning lever by adjusting nut, and the other end contacts with afterburning lever holder; The horizontal direction of afterburning lever holder and vertical direction manufacture respectively and has bar-shaped trough.

As can be seen from these patents existing at present, the method that relevant retainer detects or device have following features:

(1) by mechanical proving installation and auxiliary body, the measurement of dimensional accuracy, circularity, cylindricity and many ribs circle is carried out to the retainer detected, and contrast with standard value, solve the measurement problem of retainer.

(2) achieve the on-line Full detection of retainer and the automatic sorting of certified products and substandard products, reduce hand labor cost, physical construction is simple, easy to operate.

But the method detected at these retainers or device have following shortcoming:

(1) generally be the measuring method of Purely mechanical, in large batch of testing process, because the wearing and tearing of mechanical component or the undesirable element of external environment can cause accuracy of detection to decline, the consistance of accuracy of detection can not be ensured.

(2) mechanical detection means and instrument, needs certain detection time when detection, and is easily subject to the impact of the factors such as mechanical vibration friction, can not realize aborning measuring fast and accurately.

Design a kind of method of discrimination of ball cage retainer pros and cons for this reason, this device is all carry out with the form serialization of streamline to the detection of retainer, retainer that is in enormous quantities, different size can be applicable to detect, directly over it, image taking is carried out to needing the retainer detected by quick high-pixel camera head in detection, then the image of main control computer to shooting processes, judge the pros and cons of retainer, detect rapidly accurately, avoid the harmful effects such as general detection efficiency is low, machine error is large.Full-automatic pick-up unit decreases manual labor, improves the detection efficiency of retainer, can well be applicable in production.

Summary of the invention

The object of this invention is to provide a kind of method of discrimination of ball cage retainer pros and cons, realize the full-automatic online of retainer and differentiate, thus improve the differentiation accuracy rate of retainer, low to solve existing detection efficiency, the problem such as undetected.

In order to achieve the above object, of the present invention adopted technical scheme is a kind of method of discrimination of ball cage retainer pros and cons, comprises the steps:

It comprises the eigenwert step that Systematic selection differentiates; That eliminates external factor affects step; Revise judgment standard step:

The eigenwert that described Systematic selection differentiates is carried out judging or being judged as eigenwert by the size of each for retainer end face annulus as eigenwert at the inner and outer diameter size of each for retainer both ends of the surface annulus;

As eigenwert, the inner and outer diameter size of each annulus of described retainer both ends of the surface carries out judging that system to be maintained the positive and negative interior diameter of two transverse plane annulus of frame and the size of overall diameter by the method for circle matching, determine the pros and cons of retainer according to the difference size inside and outside each end face;

Described both ends of the surface front end face called after A face, reverse side called after B face, and the size of A face transverse plane annulus interior diameter is d _a, the size of overall diameter is D _a, the size of B face transverse plane annulus interior diameter is d _b, the size of overall diameter is D _b; The difference DELTA H of A face inner and outer diameter _a=| D _a-d _a|, the difference DELTA H of B face inner and outer diameter _b=| D _b-d _b|;

The size of each annulus of described retainer end face carries out judging that system passes through to process the image collected the size of positive and negative two the transverse plane annulus of the frame that is maintained as eigenwert, is determined the pros and cons of retainer by the size of these two annulus areas;

The impact of described elimination external factor is that in the process that brightness adjustment is consistent with reference value, camera is ceaselessly clapped, and photographs before grabbing and is stabilized in certain brightness by adopting the mode of closed-loop control to control brightness;

Described correction judgment standard is by retainer front end face called after A face, reverse side called after B face, and the size obtaining A face according to the eigenwert recorded is S _a, the size in B face is S _b; The area S in A face just can be drawn after n retainer is measured _awith the area S in B face _bdispersion, described dispersion is Δ _s; This n retainer draws the area S in A face after measuring _awith the area S in B face _bmeet normal distribution, the area S in A face _athe peak value of normal distribution curve is S _a', the area S in B face _bthe peak value of normal distribution curve is S _b';

Then $S_A={S_A}^{\′}\±{\mathrm{\Δ}}_{S_A},S_B={S_B}^{\′}\±{\mathrm{\Δ}}_{S_B}$

The reference value that can determine pros and cons is P,

(1)S _A＜S _B

Namely ${S_A}^{\&prime;}+{\mathrm{\&Delta;}}_{S_A}<{S_B}^{\&prime;}-{\mathrm{\&Delta;}}_{S_B}$

Determining reference value $P\&Element;({S_A}^{\&prime;}+\frac{{\mathrm{\&Delta;}}_{S_A}}{2},{S_B}^{\&prime;}-\frac{{\mathrm{\&Delta;}}_{S_B}}{2}),$

Now can accurately judge the pros and cons of retainer;

(2)S _A＞S _B

Namely ${S_A}^{\&prime;}+{\mathrm{\&Delta;}}_{S_A}>{S_B}^{\&prime;}-{\mathrm{\&Delta;}}_{S_B}$

① $({S_A}^{\&prime;}+{\mathrm{\&Delta;}}_{S_A})-({S_B}^{\&prime;}-{\mathrm{\&Delta;}}_{S_B})\&Element;(0,\frac{{\mathrm{\&Delta;}}_S}{2}),$ Δ _sget with in less one

If ${\mathrm{\&Delta;}}_{S_A}<{\mathrm{\&Delta;}}_{S_B},$ Determining reference value $P={S_A}^{\&prime;}+\frac{{\mathrm{\&Delta;}}_{S_A}}{2}$

If ${\mathrm{\&Delta;}}_{S_A}>{\mathrm{\&Delta;}}_{S_B},$ Determining reference value $P={S_B}^{\&prime;}-\frac{{\mathrm{\&Delta;}}_{S_B}}{2}$

Now just can judge the pros and cons of retainer;

② $({S_A}^{\&prime;}+{\mathrm{\&Delta;}}_{S_A})-({S_B}^{\&prime;}-{\mathrm{\&Delta;}}_{S_B})>\frac{{\mathrm{\&Delta;}}_S}{2},$ Δ _sget with in less one

Determining reference value P cannot determine

Now cannot judge the pros and cons of retainer.

This n described retainer dispersion is by obtaining as shown in the formula calculating:

${\mathrm{\&Delta;}}_S=\sqrt{\frac{{\mathrm{\&Sigma;}}_{i=1}^n{(x_i-\stackrel{\&OverBar;}{x})}^2}{n(n-1)}},\stackrel{\&OverBar;}{x}=\frac{\underset{i=1}{\overset{n}{\mathrm{\&Sigma;}}}{x}_i}{n}$

Wherein, Δ _srepresent the dispersion of retainer eigenwert, x _irepresent the eigenwert of i-th retainer, n represents the number of retainer.

The described mode by employing closed-loop control controls brightness and comprises the following steps:

(1) before mechanical arm grabbing workpiece, camera reads the brightness of lower images, i.e. intensity profile, the image now read is original image.

(2) original image and the benchmark image that presets are contrasted, if original image is brighter than benchmark image just reduce light-source brightness, otherwise strengthen light-source brightness.

(3) in light-source brightness adjustment process, camera ceaselessly captures image, until identical with benchmark image brightness.

Due to the employing of technique scheme, compared with prior art, the present invention has the following advantages:

1. the present invention adopts camera to differentiate retainer pros and cons, when detecting, with camera, retainer is taken pictures, the pros and cons of retainer is differentiated by the size of the diameter difference or two annulus that read retainer both ends of the surface annulus, testing agency is simple, improves automaticity and production efficiency.

2. in further technical scheme, eliminate the impact of the external environment except the factor of camera own, make camera imaging more stable, ensure that the accuracy that retainer pros and cons differentiates.

3. in retainer deterministic process, the method of self-correction is adopted constantly to revise retainer pros and cons reference value, make the accuracy rate of each retainer when pros and cons judges higher, avoid because mechanism's long benchmark caused working time is inaccurate and judge by accident.

Accompanying drawing explanation

Fig. 1 is the structural representation of retainer in the present invention.

Embodiment

Below in conjunction with accompanying drawing 1 and embodiment, the invention will be further described, but protection scope of the present invention is not limited to this.

Shown in accompanying drawing 1, retainer 1 mentioned in the present invention, refer to that the inside and outside surface formed after turning is sphere, two ends are the metal construction of plane.

Ball cage retainer, will using one of them end face as the reference field adding man-hour when carrying out punching processing, but owing to not needing reference field in process before, process the retainer when entering punching operation not necessarily to enter by a same reference field direction, institute thinks that guarantee retainer is all that same direction enters punching operation, will judge each retainer, turn out before the retainer in reverse side is entered punching operation.

Judge time using two of retainer end faces as basis for estimation, first by the mode of streamline, retainer is allowed to enter discriminating gear one by one, the post-positioning device entered is located retainer, after having located, the figure of the first whole retainer of high-pixel camera takes, due to when there being illumination, retainer end face can reflective one-tenth annulus, by judging that the size of the ring of annulus is to judge the pros and cons of retainer.

A method of discrimination for ball cage retainer pros and cons, comprises the following steps:

(1) eigenwert differentiated is selected

1. the inner and outer diameter size of each for retainer both ends of the surface annulus is judged as eigenwert:

The method of circle matching is adopted to be maintained the positive and negative interior diameter of two transverse plane annulus of frame and the size of overall diameter.

Here retainer front end face called after A face, reverse side called after B face, and the size supposing A face transverse plane annulus interior diameter is d _a, the size of overall diameter is D _a, the size of B face transverse plane annulus interior diameter is d _b, the size of overall diameter is D _b.

The difference DELTA H of A face inner and outer diameter _a=| D _a-d _a|, the difference DELTA H of B face inner and outer diameter _b=| D _b-d _b|.

The pros and cons of retainer then just can be determined according to the difference of these two end faces.

2. the area of each for retainer end face annulus is judged as eigenwert:

By processing the size of positive and negative two the transverse plane annulus of the frame that is maintained to the image collected.

Here retainer front end face called after A face, reverse side called after B face, and the size that hypothesis obtains A face area is S _a, the size of B face area is S _b.

The pros and cons of retainer then directly can be determined by the size of the area of these two annulus.

One of them eigenwert (diameter or area) above can be selected as the basis for estimation of pros and cons differentiating retainer, or in order to the accuracy that improves differentiation is using both as basis for estimation.

(2) impact of external factor is eliminated

Due to the change of external environment brightness, temperature and the impact of other external factor in the process that pros and cons differentiates, the picture quality of camera shooting also can change.In order to the impact of maximum elimination external environment, ensure camera working stability, adopt the mode of closed-loop control to correct brightness:

(1) before mechanical arm grabbing workpiece, camera reads the brightness of lower images, i.e. intensity profile, the image now read is original image.

(2) original image and the benchmark image that presets are contrasted, if original image is brighter than benchmark image just reduce light-source brightness, otherwise strengthen light-source brightness.

(3) in light-source brightness adjustment process, camera ceaselessly captures image, until identical with benchmark image brightness.

In the process judging pros and cons, be generally separated in time do a gamma correction, but be consistent as far as possible in order to the value making video camera read, each retainer can do before judging and once correcting.

(3) judgment standard is revised

After retainer enters discriminating device at every turn, camera claps a figure to retainer, by contrasting with reference value after image procossing, thus differentiates pros and cons.For the size of each annulus of eigenvalue retainer end face, make reference value be P, retainer front end face area is S _areverse side area is S _b, triangular pass is S _a<P<S _b.The face area S obtained after image procossing is less than P and is A face.Therefore the setting of reference value is the key differentiating success or not, but due to the randomness in workpiece process, sample space as study workpiece can not contain whole batch, and therefore this method provides the modification method of judgment standard, could keep the accuracy of follow-up judgement like this.

Modification method:

Here retainer front end face called after A face, reverse side called after B face, the size obtaining A face according to the eigenwert recorded is S _a, the size in B face is S _b.

The area S in A face can be drawn after supposing to measure n retainer _awith the area S in B face _bdispersion Δ _s.

This n retainer dispersion is by obtaining as shown in the formula calculating:

${\mathrm{\&Delta;}}_S=\sqrt{\frac{{\mathrm{\&Sigma;}}_{i=1}^n{(x_i-\stackrel{\&OverBar;}{x})}^2}{n(n-1)}},\stackrel{\&OverBar;}{x}=\frac{\underset{i=1}{\overset{n}{\mathrm{\&Sigma;}}}{x}_i}{n}$

Wherein, Δ _srepresent the dispersion of retainer eigenwert, x _irepresent the eigenwert of i-th retainer, n represents the number of retainer.

This n retainer draws the area S in A face after measuring _awith the area S in B face _bmeet normal distribution, suppose the area S in A face _athe peak value of normal distribution curve is S _a', the area S in B face _bthe peak value of normal distribution curve is S _b'.

Then $S_A={S_A}^{\&prime;}\&PlusMinus;{\mathrm{\&Delta;}}_{S_A},S_B={S_B}^{\&prime;}\&PlusMinus;{\mathrm{\&Delta;}}_{S_B}$

The reference value supposing to determine pros and cons is P,

(1)S _A＜S _B

Namely ${S_A}^{\&prime;}+{\mathrm{\&Delta;}}_{S_A}<{S_B}^{\&prime;}-{\mathrm{\&Delta;}}_{S_B}$

Determining reference value $P\&Element;({S_A}^{\&prime;}+\frac{{\mathrm{\&Delta;}}_{S_A}}{2},{S_B}^{\&prime;}-\frac{{\mathrm{\&Delta;}}_{S_B}}{2}),$

Now can accurately judge the pros and cons of retainer;

(2)S _A＞S _B

Namely ${S_A}^{\&prime;}+{\mathrm{\&Delta;}}_{S_A}>{S_B}^{\&prime;}-{\mathrm{\&Delta;}}_{S_B}$

① $({S_A}^{\&prime;}+{\mathrm{\&Delta;}}_{S_A})-({S_B}^{\&prime;}-{\mathrm{\&Delta;}}_{S_B})\&Element;(0,\frac{{\mathrm{\&Delta;}}_S}{2}),$ Δ _sget with in less one

If ${\mathrm{\&Delta;}}_{S_A}<{\mathrm{\&Delta;}}_{S_B},$ Determining reference value $P={S_A}^{\&prime;}+\frac{{\mathrm{\&Delta;}}_{S_A}}{2}$

If ${\mathrm{\&Delta;}}_{S_A}>{\mathrm{\&Delta;}}_{S_B},$ Determining reference value $P={S_B}^{\&prime;}-\frac{{\mathrm{\&Delta;}}_{S_B}}{2}$

Now just can judge the pros and cons of retainer;

② $({S_A}^{\&prime;}+{\mathrm{\&Delta;}}_{S_A})-({S_B}^{\&prime;}-{\mathrm{\&Delta;}}_{S_B})>\frac{{\mathrm{\&Delta;}}_S}{2},$ Δ _sget with in less one

Determining reference value P cannot determine

Now cannot judge the pros and cons of retainer.

So by the reference value P that each correction is current in the process of camera judgement, make it to be stabilized in one and can accurately judge in the scope of retainer pros and cons, so just can ensure that follow-up accuracy of judgement is without erroneous judgement.

Above-described embodiment is preferred embodiment of the present invention; it is not the restriction to technical solution of the present invention; as long as without the technical scheme that creative work can realize on the basis of above-described embodiment, all should be considered as falling within the scope of the rights protection of patent of the present invention.

Claims (3)

1. a method of discrimination for ball cage retainer pros and cons, is characterized in that: it comprises the eigenwert step that Systematic selection differentiates; That eliminates external factor affects step; Revise judgment standard step;

The eigenwert that described Systematic selection differentiates is carried out judging or being judged as eigenwert by the size of each for retainer end face annulus as eigenwert at the inner and outer diameter size of each for retainer both ends of the surface annulus;

As eigenwert, the inner and outer diameter size of each annulus of described retainer both ends of the surface carries out judging that system to be maintained the positive and negative interior diameter of two transverse plane annulus of frame and the size of overall diameter by the method for circle matching, determine the pros and cons of retainer according to the difference size inside and outside each end face;

Described both ends of the surface front end face called after A face, reverse side called after B face, and the size of A face transverse plane annulus interior diameter is d _a, the size of overall diameter is D _a, the size of B face transverse plane annulus interior diameter is d _b, the size of overall diameter is D _b; The difference DELTA H of A face inner and outer diameter _a=| D _a-d _a|, the difference DELTA H of B face inner and outer diameter _b=| D _b-d _b|;

The size of each annulus of described retainer end face carries out judging that system passes through to process the image collected the size of positive and negative two the transverse plane annulus of the frame that is maintained as eigenwert, is determined the pros and cons of retainer by the size of these two annulus areas;

The impact of described elimination external factor is by adopting the mode of closed-loop control to control brightness;

Described correction judgment standard is by retainer front end face called after A face, reverse side called after B face, and the size obtaining A face according to the eigenwert recorded is S _a, the size in B face is S _b; The area S in A face just can be drawn after n retainer is measured _awith the area S in B face _bdispersion, described dispersion is Δ _s; This n retainer draws the area S in A face after measuring _awith the area S in B face _bmeet normal distribution, the area S in A face _athe peak value of normal distribution curve is S _a', the area S in B face _bthe peak value of normal distribution curve is S _b';

Then $S_A={S_A}^{\&prime;}\&PlusMinus;{\mathrm{\&Delta;}}_{S_A},S_B={S_B}^{\&prime;}\&PlusMinus;{\mathrm{\&Delta;}}_{S_B}$

The reference value that can determine pros and cons is P,

(1)S _A＜S _B

Namely ${S_A}^{\&prime;}+{\mathrm{\&Delta;}}_{S_A}<{S_B}^{\&prime;}-{\mathrm{\&Delta;}}_{S_B}$

Determining reference value $P\&Element;({S_A}^{\&prime;}+\frac{{\mathrm{\&Delta;}}_{S_A}}{2},{S_B}^{\&prime;}-\frac{{\mathrm{\&Delta;}}_{S_B}}{2}),$

Now can accurately judge the pros and cons of retainer;

(2)S _A＞S _B

Namely ${S_A}^{\&prime;}+{\mathrm{\&Delta;}}_{S_A}>{S_B}^{\&prime;}-{\mathrm{\&Delta;}}_{S_B}$

① $({S_A}^{\&prime;}+{\mathrm{\&Delta;}}_{S_A})-({S_B}^{\&prime;}-{\mathrm{\&Delta;}}_{S_B})\&Element;(0,\frac{{\mathrm{\&Delta;}}_S}{2}),$ Δ _sget with in less one

If ${\mathrm{\&Delta;}}_{S_A}<{\mathrm{\&Delta;}}_{S_B},$ Determining reference value $P={S_A}^{\&prime;}+\frac{{\mathrm{\&Delta;}}_{S_A}}{2}$

If ${\mathrm{\&Delta;}}_{S_A}>{\mathrm{\&Delta;}}_{S_B},$ Determining reference value $P={S_B}^{\&prime;}-\frac{{\mathrm{\&Delta;}}_{S_B}}{2}$

Now just can judge the pros and cons of retainer;

② $({S_A}^{\&prime;}+{\mathrm{\&Delta;}}_{S_A})-({S_B}^{\&prime;}-{\mathrm{\&Delta;}}_{S_B})>\frac{{\mathrm{\&Delta;}}_S}{2},$ Δ _sget with in less one

Determining reference value P cannot determine

Now cannot judge the pros and cons of retainer.

2. the method for discrimination of a kind of ball cage retainer pros and cons according to claim 1, is characterized in that: this n described retainer dispersion is by obtaining as shown in the formula calculating:

${\mathrm{\&Delta;}}_S=\sqrt{\frac{{\mathrm{\&Sigma;}}_{i=1}^n{(x_i-\stackrel{\&OverBar;}{x})}^2}{n(n-1)}},\stackrel{\&OverBar;}{x}=\frac{\underset{i=1}{\overset{n}{\mathrm{\&Sigma;}}}{x}_i}{n}$

Wherein, Δ _srepresent the dispersion of retainer eigenwert, x _irepresent the eigenwert of i-th retainer, n represents the number of retainer.

3. the method for discrimination of a kind of ball cage retainer pros and cons according to claim 1, is characterized in that: the described mode by employing closed-loop control controls brightness and comprises the following steps:

(1) before mechanical arm grabbing workpiece, camera reads the brightness of lower images, i.e. intensity profile, the image now read is original image.

(2) original image and the benchmark image that presets are contrasted, if original image is brighter than benchmark image just reduce light-source brightness, otherwise strengthen light-source brightness.

(3) in light-source brightness adjustment process, camera ceaselessly captures image, until identical with benchmark image brightness.