Vision Sensor SIMATIC VS 110 Tipps und Tricks · Vision Sensor SIMATIC VS 110 Tips and Tricks A5E00188390-01 1-1 1 Introduction This document is intended for the user of the Vision

SIMATICVision Sensor VS 110Tips and Tricks Edition 10/2002

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©Siemens AG 2002Technical data subject to change.

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Vision Sensor SIMATIC VS 110 Tips and TricksA5E00188390-01 iii

Contents

1 Introduction 1-1

2 Optimum Settings for the SIMATIC VS 110 2-1

2.1 Optimizing the Image Window ..........................................................................2-12.2 Aligning the Sensor Field of View .....................................................................2-22.3 Avoiding Reflections..........................................................................................2-32.4 Aligning the Conveyor .......................................................................................2-52.5 Selecting Triggers and Using Them Effectively ................................................2-72.5.1 Automatic Trigger..............................................................................................2-72.5.2 External Trigger.................................................................................................2-82.6 Obtaining a Useful Quality Limit........................................................................2-92.7 Setting the Y-Limit Quality Limit ........................................................................2-92.8 Compensating Height Variations ....................................................................2-112.9 Using the "Info" Menu Command....................................................................2-112.10 Counting Objects.............................................................................................2-12

3 Mastering Borderline Applications for the SIMATIC VS 110 3-1

3.1 Parts Larger than Permitted by the Specification..............................................3-13.2 Deliberate Use of an Inclined Conveyor ...........................................................3-33.3 Parts Smaller than Permitted by the Specification............................................3-43.4 The Individual Test Objects of a Model are too Similar ....................................3-53.5 The Individual Test Objects of a Model are too Different..................................3-83.6 Round Objects with Asymmetrical Characteristics ...........................................3-93.7 Testing Endless Material...................................................................................3-93.8 The Maximum Number of 15 Models in Total Is not Enough..........................3-113.9 Precise Setting of a "Dimension Check" .........................................................3-11

Contents

Vision Sensor SIMATIC VS 110 Tips and Tricksiv A5E00188390-01

Vision Sensor SIMATIC VS 110 Tips and TricksA5E00188390-01 1-1

1 Introduction

This document is intended for the user of the Vision Sensor SIMATIC VS 110. Itcontains notes on installation and tips for typical applications. Some solutions forunusual applications are also included. The aim of the document is to bring you astep nearer to simple and successful solutions.

We start by outlining some of the main points to be considered when setting up theSIMATIC VS 110. You will see several sample images of the sensor field of viewthat illustrate points you should note.

The next chapter describes applications that violate the specifications

for operating the Vision Sensor VS 110 but that can nevertheless be used for areliable and successful evaluation.

Introduction

Vision Sensor SIMATIC VS 110 Tips and Tricks1-2 A5E00188390-01


2 Optimum Settings for the SIMATIC VS 110

2.1 Optimizing the Image Window

The following picture shows the sensor field of view of a correctly aligned sensorhead:

The following important conditions are met:

• The object being tested is located correctly in the middle of the viewing windowand does not touch the edge at any point. Only the lower edge of the object isin contact with a black surface caused by the upper edge of the conveyor.

• There are no reflections from the conveyor or the object.

• The conveyor is aligned parallel to the lower edge of the image

• The object is sharp.

• The dimensions of the object are within the SIMATIC VS 110 specifications.

• The sensor head has been correctly adjusted using the "Settings" menucommand.

If your application meets these conditions, correct and reliable evaluation with theVision Sensor SIMATIC VS 110 is guaranteed.

The next sections contain further pictures of the sensor field of view that may leadto problems in evaluation. Approaches that will avoid the problems are alsodescribed.

Optimum Settings for the SIMATIC VS 110


2.2 Aligning the Sensor Field of View

In the picture shown below, the sensor head is not correctly aligned: The objectbeing tested in the sensor field of view (in this example a screw) is touching theupper edge of the illuminated and therefore visible evaluation area. If youattempted to train with this part, the error message "Error Object too far at top"would appear.

Note

The object being tested must maintain at least the following minimum distancefrom the top, left, and right edges of the field of view (in other words the visiblebright area) to allow reliable evaluation:

• 4 mm with the camera head for large objects (MLFB 6GF2 002-8AA)

• 2 mm for the camera head for small objects (MLFB 6GF2 002-8BA)

The object being tested must only touch the lower edge of the image in the sensorfield of view or a surface that is visible at the bottom of the image.



2.3 Avoiding Reflections

In the following picture, you can see reflections of the illumination unit on thesurface of the conveyor (light areas on the dark surface resulting from an obliqueview of the conveyor "from above").

These reflections may have a negative influence on the evaluation since theSIMATIC VS 110 cannot distinguish clearly between the visible illuminated areaand fixed components in your system.

Not only reflections from fixed components (for example the conveyor system)cause problems but also temporary reflections on the test objects themselves.These can result in different silhouettes and therefore lead to different test results.A temporary reflection is shown in the picture below.



One way of avoiding reflections is to mask the unused illuminated area responsiblefor the reflections.

• Select the sensor field of view so that there are as few reflections as possible(bright patches) on the test object and the conveyor. There are threaded holeson the front of the illumination unit that can be used to fit opaque masks to theillumination unit.

• As a rule of thumb for masking; you should attempt to leave only the minimumdistance between the upper edge of the test object and the lower edge of themask so that a maximum cover is achieved. You should also make sure thatyou use the highest object when determining the necessary minimum distancebetween the object and mask!

• You can achieve the same effect by arranging the illumination behind theobject so low that the upper edge of the illuminated area effectively takes overthe function of a mask.

The following picture shows an ideal image of a test object (on the left) when usinga mask. On the right-hand side, you can see the negative effects of a temporaryreflection: Compared with the ideal image of the test object, the test object appearsto be too flat in the middle.



Reflections can also be reduced significantly if the test object is in the upper part ofthe possible sensor field of view. You can achieve this by arranging the mid axis(optical axis) of the sensor head somewhat below the upper edge of the conveyor.With this solution, however, you must make sure that the object being testedremains completely visible in the image. This arrangement is only suitable forrelatively flat objects.

If you mask the illumination, you must make sure that the mask completely blocksthe infrared light being used. A translucent mask as shown in the following picturemay have very detrimental effects on reliable evaluation.

Note

For more information on the topic of arranging the illumination and using masks,refer to the Vision Sensor SIMATIC VS 110 manual, page 4-5.

2.4 Aligning the Conveyor

When training the background (in other words the fixed components of yoursystem), the device records the area in which the objects being tested areexpected for future evaluation. When training the background, a distinction is madebetween fixed and moving objects. On completion of the background training, theSIMATIC VS 110 calculates the largest "free" rectangle in the sensor field of view(in other words the rectangle in which no fixed objects were located during thebackground training). The sides of this rectangular evaluation area are alignedparallel to the edges of the image window.

The size of the evaluation area obtained during training can be checked in the runmode using the INFO menu command. Based on the length and height inmillimeters, it is possible to gauge whether the background training achieved auseful result.



It is therefore important that the upper edge of the conveyor is aligned parallel tothe lower edge of the image window to achieve reliable results with the SIMATICVS 110. If this condition is not met as shown in the picture below (on the left), thedevice will evaluate in an invalid or at least unnecessarily reduced area as shownin the picture below on the right.

Area cannot be evaluatedand will be ignored!

Evaluation area

Conveyor

Tool Holder Transport or Grab Unit

Conveyors of all shapes and sizes without a horizontal top edge, such as toolholders or grab units may lead to a reduction of the area available for evaluation.

The area that is cut off in the picture below is, for example, not evaluated.

Evaluation area

All the areas that are not within the trained evaluation window are treated by thedevice as "don't care" regions during evaluation and they are ignored. If, due tounfavorable mounting of the camera or "indented" arrangements on a tool holder,this area is too large, the quality and reliability of the evaluation will suffer.



Note

Particularly when using grab units, you should make sure that only the relevantevaluation areas of the object exist in the field of view and not parts of the grabunit. If this proves to be impossible due to the mechanical properties of the system,the grab unit should be moved when training the background to avoid creatingadditional "don't care" areas for the evaluation. When training the good parts, youmust, however, then make sure that all the components of the grab unit visible inthe picture and in contact with the actual test object are also evaluated andtherefore directly influence the quality of the result!

"Fine Tuning" of the Qualtiy Limit

The evaluation of the test object; in other words the comparison of the test objectwith the trained good part is based on the match between the expected/referencesurface of the object and the surface of the object actually detected. A percentageis used to determine the quality ("Q-Limit").

Due to this relationship, the qualtiy limit can be set by "Fine Tuning" (in other wordsin extremely small steps of absolute surface deviation) if the object visible in thepicture has a small surface (within the permitted specifications).

This does, however, only relate to the setting of the qualtiy limit. This has no effectwhatsoever on the basic evaluation accuracy of the device related to the resolutionof the sensor chip and the algorithmic picture preprocessing. For this reason, youshould always attempt to display the characteristics of interest of the object beingtested as large as possible and the irrelevant characteristics should be visible aslittle as possible in the picture.

2.5 Selecting Triggers and Using Them Effectively

2.5.1 Automatic Trigger

If you use the automatic trigger (the device permanently records pictures anddecides automatically whether and when a new part is present for evaluation), theparts in the field of view of the sensor must only move horizontally from left to rightor right to left. The conveyor speed must be constant so that the objects can bemanipulated after the test at the right position (for example at an ejector).

If the speed changes during operation, the objects will be selected andmanipulated either too early or too late by the SIMATIC VS 110. Your system is nolonger functioning correctly.

While the objects are moving through the sensor field of view one of the twosilhouettes is visible depending on the position of the object in the image field. Withtest objects that extend a long way in the z direction this effect can lead to incorrecttest results in the automatic trigger mode since the visible surface changesdepending on the perspective. In this case, an external trigger should be used.



Note

To achieve a reliable and error-tolerant evaluation, the Vision Sensor SIMATICVS 110 also returns a NOK signal if the image obtained cannot be evaluated (forexample due to an image or illumination disturbance). It is therefore absolutelynecessary in the autotrigger mode to use the evaluation signal of the VS 110directly. Linking the quality signal of the SIMATIC VS 110 and an initiator signal atthe ejector position using a shift register in the additional controller should beavoided!

2.5.2 External Trigger

The use of a precise external trigger (for example a precise light barrier) alwaysimproves the maximum achievable precision of the evaluation. The test object isalways recorded at the same position and therefore always has the same distortionresulting from the perspective.

It is also advisable to use the external trigger particularly with test objects whosedimensions or transport speed approaches the limits of the permitted specificationsfor the SIMATIC VS 110 you are using.

In the setup mode, the SIMATIC VS 110 returns a live image of the sensor field ofview via the serial port. To set the optimum trigger position and arrangement of thesensor head during setup, the SIMATIC VS 110 shows the corresponding image inthe stop mode for 4 seconds after each trigger signal (in later versions for 60seconds). On completion of this time, the device returns to the live image mode.

If the time in which the triggered image is displayed is not adequate, it is possibleto display the triggered image permanently until the next trigger signal is received.To do this, follow the steps outlined below:

1. Select the "Train" menu command from the main menu and then select amodel. Confirm with OK.

2. "Train background" is displayed on the device.IMPORTANT: Do not confirm this display with OK but remain in this menu item(before training the background). Otherwise, you would delete the previouslytrained model stored at this memory location!

3. As of the next incoming trigger signal, only the triggered pictures are sent overthe serial interface. You can now set the optimum trigger position and sensorhead position.

4. When you are finished, remember to close the menu with "ESC" otherwise youwill trigger a new training sequence.



2.6 Obtaining a Useful Quality Limit

After training the background and the good parts in view A and B, the SIMATICVS 110 expects a number ("Samples") of good parts in both views to calculate theuseful quality limit for this particular application.

Please make sure that during the calculation of the quality limit only good parts arefed through since the evaluation would otherwise classify the bad parts as OK.

The number of samples can be modified using the system settings. The followingnotes will make your selection easier:

• Using a low number of samples (approximately 10) means that you cancomplete the training run quickly. This low number of samples should only beused when the parts are fed through extremely precisely and only have veryslight variations in their surface appearance.

• With an increased number of samples (at least 50), you can achieve a morereliable evaluation. This is particularly useful for objects that can varyconsiderably from part to part. The "Screw Test" example illustrates this point.

- When screws with a hexagon head are fed through, the head of the screwcan occur at any position relative to the longitudinal axis in the image.Depending on its position, it has a higher or flatter contour in the image.

- Depending on the position of a screw relative to its longitudinal axis, thethread will appear differently in the image.

2.7 Setting the Y-Limit Quality Limit

The use of this parameter ("Y-Limit enable") is important when two objects of thesame shape can differ in height as illustrated by the two bolts of different lengths inthe picture below.

The evaluation of a test object compared with the trained reference test object ismade exclusively based on the fundamental surface match if the "Y-Limit disable"parameter is set and does not take into account the difference height of an objectcompared to the trained reference part. This ensures that differences in height ofthe test objects, for example due to unevenness in the conveyor belt does not havea negative influence on the evaluation.



If, however, it is necessary to evaluate the height of the object as a qualitycharacteristic (evaluation of the height of a part with an identical silhouette), the"Y-Limit enable" parameter should be set. In this case, the permitted heightvariation of the object is checked first and only then the permitted surface variation.The basic check of the surface variation cannot be deselected.

To be able to evaluate the different lengths of the two bolts in the picture above,the two bolts should be trained in view A/longer bolt and view B/shorter bolt with"Y-Limit enable" set. On the one hand, this allows the two bolts to be distinguishedfrom each other (quality signal OK_A for long bolts, OK_B for short bolts) and onthe other hand, bad parts (damaged bolts, foreign parts) can be sorted out basedon the NOK quality signal.

If you had set the parameter "Y-Limit disable" for the two bolts discussed aboveduring training, you may receive the "Identical Objects" error message. The reasonfor this is the fact that the two bolts differ only in their length but not in their basicshape. When training the objects in view A and B, the device would detect them asbeing identical. This means they cannot be distinguished and therefore not trained.

Note

• In applications in which higher and flatter but otherwise practically identicalobjects need to be distinguished, you should always select the "Y-Limit enable"parameter and train the objects in the A and B views. The parts are thendistinguished as OK_A and OK_B and test objects differing from these twotrained objects are classified as NOK.

• In applications in which the required object must be distinguished in the imagefrom similar objects with an identical shape but different height, select "Y-Limitdisable" and train the object only in the A view. All test objects that do notmatch this part will then be classified as NOK.



2.8 Compensating Height Variations

Depending on the conveyor you are using you may experience differences inheight due to unevenness of the conveyor. These are differences that are notcaused by any variation in the height of the object but are caused in some way bythe conveyor. One possible cause could be, for example, a seam in a belt.

Variations in height of this type are recognized in the image recorded by the sensorhead as an enlargement or reduction in size of the test object; it is not possible toidentify the exact cause (conveyor or bad part). There are, however ways ofimproving the evaluation:

• Increasing the precision of the conveyor (this generally involves more work butachieves the best results)

• Using a large number of "Samples" to eliminate the "Accidental" variations fromthe evaluation.

• Training the largest sample (highest permitted test object).Explanation: If the test object is raised by the conveyor (enlarged in the imagefield), the SIMATIC VS 110 evaluates the additional visible surface as aninvalid enlargement of the test object. If, however, the test object is lying in adepression in the conveyor belt where it is transported, the SIMATIC VS 110detects this and does not evaluate it (within the permitted tolerances) as anerror. For this reason, the highest possible test object should be trained.

2.9 Using the "Info" Menu Command

With many simple applications, it is possible to commission the Vision SensorSIMATIC VS 110 without attaching it to a PC for visualization as long as youadhere to the installation instructions. The operator is, however, left with a certainsubjective uncertainty as to whether the training run really took place successfully.

To be able to check that the training was successful, the operator can use the"Info" menu command in the RUN menu. Here, the current dimensions of theusable evaluation window as length x width and the test objects in height for view Aand B and width for view A and B. This display is always in millimeters so that theoperator can interpret them directly. The evaluation area ("Background") should notchange from model to model if the conveyor itself has not changed. The actualdimensions of the test object can be obtained directly by measuring the object andcan then be compared with the information provided by the device (± 1 mmtolerance).



2.10 Counting Objects

The SIMATIC VS 110 itself is not capable of counting a specific number of objectsand then outputting an appropriate digital signal. To be able to implementapplications in which a specific number of parts, tablets etc. must be counted priorto packing, a separate controller, such as a SIMATIC S7-200 can be used.

The use of an external controller is also always useful when more complexhandling is required for bad parts such as using a Pick-and-Place unit.


3 Mastering Borderline Applications for theSIMATIC VS 110

As a basic rule: The closer your application comes to the limits specified forsuccessful use of the SIMATIC VS 110 (for example in terms of part dimensions,distance between parts), the more important precise (reproducible) feed of the testobjects and reduction of the feed rate become.

The use of an external trigger also improves the evaluation when the application isclose to the specified limits. By using a precise sensor, the part being checked isthen always recorded at the same point in the image window and effects such asdistortion caused by perspective are reduced significantly.

3.1 Parts Larger than Permitted by the Specification

If you test a part that has dimensions exceeding the specified limits, the message"Error object too large" appears when you attempt to train the part. To be able totest such parts with the SIMATIC VS 110, you can use the following tricks:

If you need to check the entire object, you can make the image of the objectsmaller by increasing the distance between the sensor head and object. The object"appears" smaller. The image is, however, not as sharp and the achievableevaluation quality is reduced. You must also make sure that the object is fullyvisible without touching the edge in the active area of the illumination. This solutionis only possible when you do not need a detailed check and the part you aretesting is only slightly larger than the permitted specification.

If you do not need to check the complete object but only a part of it, you can try thefollowing approach: Select an arrangement of the sensor head/illumination and testobject so that only the part of the object relevant for the test is visible in the imagefield. Make sure that the area of interest does not touch the right/left/top edge inthe sensor field of view. The part of the test object that is of no interest must onlyextend beyond the bottom of the sensor field of view.

Mastering Borderline Applications for the SIMATIC VS 110


Special situation: "Extra long" objects

If you have objects that are too long according to the specification (the objectwould extend beyond the sensor field of view to the left and/or right duringhorizontal transport, for example long bolts or shafts), two tests are neverthelesspossible:

• Type distinction/position detection based on characteristics at one end of theobject.

• Under some circumstances, type distinction/position detection due to thedifferent lengths of the objects

To be able to use the functionality of the vision sensor for this application, refer tothe following graphic:

Evaluation area of the camerathis is turned through 90°clockwise

Left edge

Right edge

Conveyor Conveyor

The sensor is mounted turned through 90° so that the object to be tested extendsbeyond the bottom of the image.

Note

Make sure that you always check the end of the test object that has at least oneimportant characteristic that allows the type to be distinguished.

A gap must be created in the conveyor system so that the end of the object to beevaluated is freely visible in front of the illumination unit. To allow the SIMATICVS 110 to function reliably, the largest possible free area is helpful, however forproblem-free transportation of the objects (wherever possible without interruptionand limit stop), a mechanical compromise is necessary here. The minimum lengthof the gap should, however, be at least 25 mm (for sensor head type6GF1 002-8AA) or approximately 20 mm (for sensor head type 6GF1 002-8BA).Based on experience, the test objects must then be at least 2.5 to 3 times longerthan this gap.



The exact position of the test object must be signaled to the SIMATIC VS 110 byan external trigger (light barrier, etc.). If you also want the length of the object to beincluded in the evaluation, the other end of the object (the end that is not tested bythe SIMATIC VS 110) must be used as the trigger point. The trigger signal mustbe a rising edge. The layout of the conveyor therefore only shows the "upper"(actually the front or back) edge of the test object, the major condition of thespecification for the SIMATIC VS 110 (test object touching the edge only at thebottom) is therefore adhered to.

By training the test object (in the graphic above this is a shaft with a turned,tapered end) in view A (shaft in correct position) and view B (shaft the wrong wayround), both the position of the test object can be detected and an incorrect type(different shape of the shaft end, different diameter, possibly also a differentlength) can be detected. If the trigger operates extremely precisely and you select"Y-Limit enable" and set a comparatively low tolerance, the correct length of thetest object can also be evaluated relatively accurately!

3.2 Deliberate Use of an Inclined Conveyor

The solution above for long objects has several mechanical disadvantages. Themost obvious disadvantage is the need to open the conveyor belt so that it is notvisible in the sensor field of view. This solution is suitable only for long andmechanically robust objects, it cannot be used for objects that are "slightly toolong". Here, a different approach is necessary.

By skewing the sensor head through approximately 15° to 30° compared with theconveyor system, the test object appears inclined in the image. When training thebackground, however, it is always the largest possible rectangle parallel to themain axes of the sensor head that is selected. For the evaluation, this means thatonly the upper triangle of the test object is evaluated as shown in the picture below.



Note the following restrictions with this arrangement:

• This application is only genuinely useful for position checks or type distinction.Testing for faults or anomalies is not possible since only a smaller section ofthe test object is visible.

• This application must be externally triggered. The requirements in terms ofreproducibility of the trigger position are high (laser light barrier, etc.).

• In particular for comparatively flat objects, the trigger position should beselected so that the test object is located close to the side margin (while stillmaintaining the minimum distance to the margin).

• The angle of inclination should be selected so that the distinguishingcharacteristic on which the position detection/type distinction is based isadequately captured in the image and so that at the same time no part of theobject is visible any longer at the other edge of the image field; in otherwords, the edge contact due to the excess length is below the visible area.

• On the illumination unit, you should fit a mask at an angle, so that in the actualimage field of the sensor, a horizontal lower edge is produced and so thatreproducible training of the background is forced over the entire width of thesensor field of view.

3.3 Parts Smaller than Permitted by the Specification

If you test a part with dimensions less than those permitted by the specification, themessage "Error object too small" appears on the display. To be able to test suchparts with the SIMATIC VS 110, you can use the approach described below:

• A precise external trigger should be used to ensure that the object is alwaystested at the same position and that distortion resulting from the differentperspectives at different positions in the image (and consequently differentperspectives in the view of the test object) does not affect the evaluation.

• In particular with round, highly reflective objects (with a smooth, polishedsurface), masks should be fitted to mask unnecessary parts of the illuminatedarea. This causes an apparent sharpening of the object edges and maximizesthe visible surface of the test object. See also Section 2.3.

• By reducing the distance between the sensor head and object, the objectappears larger in the image. Although it appears larger, the image is, however,not as sharp and the achievable evaluation quality is reduced. This solution isonly possible when you do not need a detailed check and the part you aretesting is only slightly smaller than the permitted specification.



3.4 The Individual Test Objects of a Model are too Similar

It is possible that you want to test objects and distinguish them reliably from eachother although they only have slight differences in their silhouettes when you usethe normal arrangement of the Vision Sensor SIMATIC VS 110 according to theinstallation instructions. These test objects appear very similar and, in the worstcase, even identical.

It may nevertheless be possible to distinguish them using the approaches outlinedbelow:

• When training the objects in view A and B (in other words, either two differentobjects in the same position or one object in two positions) you should only useobjects with the original dimensions (i.e. test objects with zero dimensionaltolerance) when training the original views (train view A, train view B). Whentraining the qualtiy limit, on the other hand, all possible deviations up to thepermitted smallest and largest dimensions should be used. The advantage ofthis is that when you train view A and B, the largest possible differencesbetween the objects result.

• With very small test objects, the automatically calculated qualtiy limit may needto be corrected manually. Due to the algorithm, the automatically calculatedvalue for the Q-limit is very seldom at values higher than 98.1%. However, toallow minimal deviations in smaller objects to be detected, this correction maybe useful.



• If two test objects are very similar, it is usually helpful to include and evaluateonly the relevant characteristics in the image. This is illustrated by the followingfour images:

The two original views of the bolt reveal only minimal differences (smallchamfer at one end of the bolt). With a well-positioned mask on the illuminationunit, only the upper part of the bolt is seen, the relative difference betweenchamfer left and chamfer right (relative to the remaining visible surface of thebolt) is now greater. With this arrangement, the minimum required height of thetest object in the image as explained in the manual of the SIMATIC VS 110must be kept to. This effect could, of course, be greatly increased if the bolt isfed through standing with only the end of the bolt being visualized.



• This effect is much greater in the following images:

By masking the unimportant parts, only the upper clamp is taken into accountin this example, the base with the large thread is excluded from the surfacecomparison. The upper clamp can now be evaluated with greater precision andsensitivity.

• With a skillfully modified arrangement of the sensor head and illumination unit,it may well be possible to achieve a clear distinction between parts that differfrom each other as objects in space, but that would have no significantdifferences when viewed with an arrangement according to the SIMATIC VS110 specification and could therefore not be tested. This trick involves, inparticular, deep objects or objects with a significant difference in contour alongthe depth axis. By inclining the sensor head to the transport axis (depending onthe application and mechanical setup, approximately 30° to 60°), it is alsopossible to include the depth axis of the test object in the evaluation.Depending on the application, it may then be necessary to incline theillumination unit as well.

The basic arrangement is shown in the following diagram:

The parts would be identical in thebacklight with the normal installationof the sensor .The inclined angle of the sensormakes recognition possible.

Conveyor

Illumination

Sensor head



This method does, however, only allow a rough evaluation due to theconsiderable perspective distortion; a precise comparison with the guaranteedevaluation accuracy according to the specification is therefore not possible.

3.5 The Individual Test Objects of a Model are too Different

If the variation of the objects of a single model is too high, internal NOKclassifications may result during training of the qualtiy limit; in other words, these"mavericks" are ignored during the automatic calculation of the qualtiy limitbecause the device assumes bad parts among the good batch. This is a processthat takes place within the device and is not to be confused with the NOK signalthat is always triggered during training! In this case, it is advisable to train the testobject both in view A and view B (with the objects in the same position!) to be ableto cover the possible or necessary variation in the evaluation. Outputs OK_A andOK_B must then have the same significance.

The two pictures below provide an example. The difference in shape (with orwithout hole) of the individual objects of this type it too great to achieve acceptanceduring training of the qualtiy limit simply by feeding through an adequately highnumber of samples. Here, the approach outlined above is necessary.



3.6 Round Objects with Asymmetrical Characteristics

When feeding through round objects (bolts, screws, shafts etc.) with a through holein them or flattened on one side, you may encounter problems during evaluation.

If the position of these objects can change around the longitudinal axis so that thisasymmetrical characteristic is more or less visible as a contour in the silhouettedue to the rotational position, two different applications must be distinguished:

• The task of the SIMATIC VS 110 should be the detection of the correctrotational position. In this case, only view A should be learnt, if a seconddistinguishing position needs to be detected, view B must, of course, also betrained. When training the qualtiy limit, the parts must also be fed through inthis distinguishing position so that the device can evaluate precisely later.

• The task of the SIMATIC VS 110 should be simply to recognize the correcttype of part fed through. In this case, depending on the rotational position, thevariable contours will cause problems in precise evaluation. Here, a largenumber of samples should be used for automatic training of the qualtiy limitand the parts fed through in all possible positions during training. Therestrictions (as described in the previous section) must, of course, not beignored.

3.7 Testing Endless Material

Basically endless material (railing, material for punching etc.) cannot be testedaccording to the specification of the SIMATIC VS 110 since such material wouldlead to invalid contact with the right and left edges of the image. Under certainconditions, however, it may nevertheless be possible to check the correct punchingof materials.The following conditions must be met:

• It must be possible to arrange a rectangular frame around the detail to bechecked that touches the test object only at the bottom edge.

• The object being checked must be positive, in other words, you must checkwhat is produced by the punch and not the remnants of punching (i.e. not thehole left by punching).

• The object to be checked must not be too "fine"; in other words, the individualdetails must be significantly larger than the minimum qualtiy limit.

• The application (as usual with punch material) must be triggered externally.



The two pictures below illustrate such an object. It is possible to arrange arectangle around the contact stud that touches the test object only at the loweredge. You could, for example, create this frame with a suitable mask on theillumination unit. If, however, as in this example, you only want to check theparallelism of the contact studs, you can significantly raise the precision of theevaluation. In this case, you select an image section so that only the ends of thetwo contact studs are visible (left image). Changes compared with the trainedreference image (right image) then count for a significantly higher percentage inthe evaluation.

Note

If you are testing an object similar to the one in the picture above, make sure thatyou choose an external trigger. Since the two contact studs have an identicalshape, if it was triggered automatically, the SIMATIC VS 110 would assume twoindividual, identical parts and evaluate each stud separately. All the separate,unconnected parts in the sensor field of view are interpreted as belonging togetheronly when you use external triggering!



3.8 The Maximum Number of 15 Models in Total Is notEnough

If you need to save more models and if each type only needs to be checked in oneposition (only in view A), view B can be interpreted as a second storage level onthe device. In this case, part 1 is trained as view A under model 1, part 2 as view Balso under model 1 etc. In this way, instead of 15 models, it is possible to store upto 30 different models in non-volatile memory on the device.

Two restrictions do, however, apply here:

• To train two different types in view A and view B, they must be similar parts.Parts with considerable differences cannot be stored under the same model.

• To evaluate the quality signals OK_A and OK_B, an additional control isnecessary. This control must know which type is currently being tested and beable to interpret the other quality signal OK_x as NOK, so that parts of type 2are not classified as OK when testing parts of type 1.

3.9 Precise Setting of a "Dimension Check"

SIMATIC VS 110 cannot measure, its mode of operation is to compare.Nevertheless, to set the comparison to a precise tolerance in terms of dimensions,the following method is helpful:

• A good part within the permitted tolerance is trained as view A.

• To inform the device of the fluctuations in tolerance that can be acceptedduring evaluation, the largest and smallest samples of this type are fed throughalternately when training the qualtiy limit automatically.

• SIMATIC VS 110 adapts itself to the variation of the good parts during trainingof the qualtiy limit, in this case to the largest and smallest permitted parts. Allparts within this tolerance are evaluated as 100% matches during laterevaluation.

• By keeping the tolerance of the Q-limit qualtiy limit tight (for example 98%), if aslight violation of the tolerance occurs during the evaluation, a NOK reactionfrom the SIMATIC VS 110 can be forced.

Note

This method aiming at high evaluation precision can only be used to any practicalpurpose when the test objects are fed through very precisely and an externaltrigger is used. This remains a comparative method based on the comparison ofthe contour surface of the test object before the backlight with the trained referencesurface. There is no actual measurement of the test object even with thisapproach.



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Vision Sensor SIMATIC VS 110 Tipps und Tricks · Vision Sensor SIMATIC VS 110 Tips and Tricks A5E00188390-01 1-1 1 Introduction This document is intended for the user of the Vision