Understanding And Applying Machine Vision Part 11 pot

Page 315 4— Straightforward The installation of the machine vision system should not require extensive line rearrangements or line modifications associated with delivering the product to the vision station. Ideally, an idle station should exist in a line that holds the parts well organized and in a repeatable position. Indexed motion may be preferable and touching and overlapping parts should be avoided. Room should be available to install the system. 5— Corrective Action It should be possible to do something about the condition being detected. Detection should not be an end unto itself. 6— Technical Feasibility The first installation of machine vision systems should employ "off-the-shelf" technology that has been applied in similar applications. 7— User-Friendly Potential The machine vision technology deployed should not be intimidating to the operator or to plant engineering who must maintain the equipment. Ideally, the technology will be virtually transparent, and a computer language should not have to be learned. 8— Dedicated Line Ideally, the first installation, although of a system with potential for reconfigurability, should not be required to be reconfigurable. Essentially, a fixed automation scenario would be preferred. 9— Long Line Life Installations of the machine vision system should be associated with a new model or one that has been introduced recently. This should guarantee the payback from the system. Ideally, the system should be incorporated with new tooling. 10— Operation Champion The plant selected for the installation should have someone, preferably in manufacturing engineering, who wants to see it work and will ensure it does. 11— Management Commitment Management must agree to the value of the application and be committed to doing something about it. 13.2— Specification Development Having established the objectives along the lines of those depicted in Chapter 4 for the project, the next step is to develop a set of detailed specifications for the application. Specifications are technical data that describe all the necessary functional characteristics that the system must have to perform the required job. They should not state how the vendor is to do the job. Specifications must state the required productivity and capability of the system as well as all significant operational requirements. They should also explain the requirements of the related fixtures, material handling, and so on. Similarly, requirements for machine control and line interfaces should be detailed as well as plant requirements and limitations. The importance of specifications cannot be overstressed for the time and effort put into proper specifications will be more than repaid in terms of reduced start-up time and a reduction in maintenance and quality problems. By analyzing the present methods, observing the present operation, and getting input from all those involved, a detailed description of the operation and a Page 316 review of all anticipated variables can be developed. For example, it may appear that an operator is simply performing a sorting function, separating containers by their size or shape. On closer scrutiny, one will also observe that once in a while the operator throws a container into a scrap bin. While probably not classified as an inspector, by virtue of innate intelligence, the operator knows enough to separate incomplete or misshapened containers. By virtue of increased sensitivity to exceptions, an operator can become more sensitive to specific conditions. For example, because training has emphasized the importance of separating all green containers, the person has a heightened awareness when such objects pass. Similarly, a machine vision system might have to somehow include a weighting factor (e.g., a complementary color detector) that will increase sensitivity to a specific factor - color in this example. The converse is also true. An operator may be trained to be tolerant of color shade variations: For example, all yellows, regardless if pale gold or virtually orange, might be acceptable since it is the basic color itself that provides the distinction. In this case, therefore, the machine vision system must be equally tolerant of these normal variations while also maintaining sensitivity to the fundamental defects the system is supposed to capture. Developing the specifications includes a quantification of existing procedures in terms of productivity and quality: number of shifts, scrap, warranty repairs, machine downtime, and so on. When examining the operations, the following should be considered: How are goods routed for the vision inspection task presently? Does the operation require automating loading/unloading? Is the operation inventoried? Are products stored in bins? Magazines? And so on? What are the actual inspection functions that must be performed by the system? Is it gauged by "eyeball" or with instruments (micrometer)? Is cosmetic inspection done by detail or is it performed by a cursory look for more gross appearance differences? Does the inspection first require identification? If so, is it by shape? By reading characters? And so on? Is the inspection itself one of verifying shape conformance? Again, with or without instruments? Is the operation one of just verifying that an assembly is complete before another operation is performed or that objects are oriented properly? If, in fact, it is a complete assembly operation that is performed, does the operator locate parts and guide them into place? Is this operation a combination of several of the preceding tasks: location guidance, cosmetic examination, and gauging, for example? Is the present task 100% inspection or sample inspection? Page 317 Does the operator perform tasks other than vision (e.g., assembly and machine loading)? Is there contrast in what must be observed, that is, can you visually see the condition without picking up the part to manipulate it in the light? How small is the smallest detail you want to see? How big is the object (field of view)? As in photography one can see both large and small objects with television cameras, but the detail that can be detected reliably is proportional to the field of view. Where necessary, machine vision systems can employ more than one camera so detail versus field of view need not be a factor that would preclude considering machine vision. Are there normal variations in the appearance of the object that are ignored? A vision system will somehow have to normalize those conditions. Are there variations in the appearance of the background? Is the part repeatably and consistently located? If not, image capture will dictate a requirement for an even larger field of view, reducing the detectable detail. It will also require location analysis to reconcile the image captured with respect to position. Are parts overlapping? Touching? Jumbled? Can they be presented registered and not touching? Are parts moving or indexed where they can be held in place in front of the scanner? If in motion, at what conveyor speed? How well regulated is the speed? Other considerations are as follows: Does the operator perform three-dimensional analyses? Is the decision based on color interpretation? How much time is there to make a decision? What of the performance of any system substituted for a person? What percentage of the reject objects will one tolerate to pass as good? What false reject rate (number of good units that are rejected) will be allowed? No system is perfect! How much start-up time will be allowed? If the system is not dedicated forever to a specific task, how much time will be permitted to get the system ready between product changeovers? How much floor space is available? Overhead space that may be needed to mount cameras and/or lighting arrangements? Will much equipment rearrangement be required? Are power, air, and so on available? How much downtime can be tolerated for other routine maintenance? In what kind of environment will the equipment operate? In the presence of dirt and dust? Grease and lubricants? Water? Shock and vibration? Temperature and humidity? Electrical noise? To support the specification of a system can the following be made available to the prospective vendors for bidding: job descriptions, present specifications, drawings, samples, photographs and/or videotapes of the facility and inspection area? What kind of personnel will be available to operate and service the system following installation? Page 318 If a system is in place today to perform the function, answer the following: (a) What technology is used? (b) What are the system's capabilities and limitations? (c) What actual performance is being experienced? (d) What problems are being experienced that hamper productivity and effectiveness? (e) What is the utilization factor? (f) If starting today, what would be done differently? (g) What problems were experienced and how were they overcome? (h) What impact did the project have on the user organization? Was it measurable? If not, why not? (i) Is the impact more or less than target levels? Why? (j) Does upper management perceive improvements attributable to the project? (k) What is currently perceived as the system's greatest contribution or benefit? Is it the intended one? If not, why not? (l) Was the budget maintained? The time schedule? If not, why not? The following can be used as a guide in the "system" analysis: 1. Straightforwardness of installation a. Parent equipment modifications required b. Rearrangements c. Floor space restrictions d. Material handling 2. In-house skills required and available a. Ability to do material handling b. Ability to do installation c. Personnel available to operate d. Personnel available to service e. Environment 3. Availability of a. Job descriptions b. Specifications as now performed c. Samples d. Photographs of floor space e. Management support f. Labor/union support What should you use to obtain the comprehensive insight reviewed in the preceding? This can come from the following: Page 319 (a) Written description of the operation that might be available. These should be reviewed to determine if observed activities agree with the written descriptions. (b) Review any drawings: equipment layout drawings (are there critical dimensions?), those that affect functional capabilities, and part drawings. What are the tolerances? (c) Job descriptions - do they agree with observations? (d) Part specifications. (e) Samples - do they experience corrosion or discoloration or other change with time? (f) Photos of the prospective installation site as well as parts. The following checklist can serve as a guideline in systematically examining the requirement as observations are made: 1. Scene complexity (a) Number of stable states (b) Number of parts in view at one time (1) Touching (2) Evenly spaced (3) Registered (4) Overlapping (5) In a bin (c) Number of features and description (d) Contrasts (e) Field of view vs. detail for gaging, part tolerances (f) Part positioning (g) Variations in acceptable appearances (1) Color, saturation (2) Specularity, texture (markings, lubricants, corrosion, dirt, perishability) (h) Sizes (i) Temperature (j) Other (k) Positional variations (1) Registration (x, y, z, theta) (2) Object distance (1) Part sensitivity to heat 2. Cycle time (a) < 100 min (b) 100–300 min (c) > 300 min (d) Hand loaded (e) Indexing (triggering possibilities) still time (f) Continuous (triggering possibilities) Page 320 3. Line speed (a) Regulated speed (b) Synchronous operations 4. Perspectives (camera, subject) (a) Multiple perspectives (b) Variable perspectives (c) Vision access 5. Background contrast good (a) Backlighting possible (b) Gray scale, front light (c) Structured lighting possible (d) Color interpretation required (e) Three-dimensional and/or depth contrast (f) IR and/or temperature contrast (g) X-ray contrast 6. Image precision (a) Subject observation area (b) Subject size (c) Minimum feature, flaw size (d) Height variations (depth of field) (e) Other 7. For character-reading applications (a) Reading or verification (b) Inked, painted; molded, cast; stamped; raised; laser-etched; dot matrix; acid-etched; engraved; recessed; other (c) Describe single-font style and type and multiple-font style and types for each font style: (1) Stroke width (2) Aspect ratio (3) Character height (4) Character width (5) Character depth (6) Center-to-center spacing (7) Space between characters (8) Characters per string and per line (9) Numbers of strings and lines (d) Read rate (characters per second) (e) Character positioning, repeatability (1) Vertically (2) Horizontally (3) Skew (f) If "no read," what to do? (g) Percentage of misreads allowed per character string Page 321 8. System performance (a) Percentage of subjects flawed (b) False rejects allowable (c) Escape rate allowable (how many bad ones can be allowed to pass?) (d) Warm-up time allowable (e) Setup time permissible per batch (changeover time) (f) Skill level of person performing changeover (g) Training time allowed (1) For new subjects (2) Modified subjects (3) Frequency of new and modified designs (h) System reliability (i) Response if triggered with no part in view 9. Physical and interface requirements (a) Floor space (b) Camera location relative to the subject, feet per inches (c) Light source (d) Processor distance (e) Mechanical (1) Parent equipment modifications (2) Rearrangements (3) Air available for cooling (filtered)? (4) Vacuum available (5) Floor vibrations 10. Electrical (a) Power available, power preferred (b) Line conditioned and/or regulated (c) EMI/RFI in environment (d) Computers and program controllers 11. Interfaces (a) Interconnected equipment (b) Communications protocols required (c) Trigger signals, time delays (d) Reject signal delays (e) Data log; specify details required (CRT display, hardcopy/printer, indicator lights) 12. Operator interface (a) Preferred CRT/keyboard, menu, and icons (b) Report generation, describe (c) On-line programming skills available (d) Setup and calibration 13. System reliability and availability Page 322 (a) Number of hours used per week (up time) (b) Number of hours available for maintenance per week (c) Maximum hours to wait for repair (d) Redundancy, back-up required 14. Environment hostile (a) Washdown (b) Corrosive (c) Dirt (d) Oil mist (e) Shock and vibration (f) Ambient temperature (g) "Storage" temperature (during shutdown) (h) Humidity (i) Electrical noise: EMI, RFI (j) Ambient light 15. Miscellaneous (a) Layout drawings available? (b) Material handling to be whose responsibility? (c) Special enclosures to be specified (d) Personnel available (1) To operate (2) To service (e) Material handling (f) Training: operator, service (g) Service spares (h) Future modifications and enhancements desired 13.2.1— Specification Review from Machine Vision Perspective Having distilled the preceding and written a specification, give some thought to the application from the machine vision perspective and review and revise the specification accordingly. The following can serve as a guideline. 13.2.1.1— Lighting Is special lighting needed to provide even illumination? Will reflections be a problem? Are strobes required? Can lighting exaggerate contrast of attribute to be observed? Gauging. Exaggerate edges, structured edges, backlighting, directional light and/or shadow. Flaws. Dark- and light-field illumination, UV fluorescence. Recognition. Back illumination, structured light, directional light. Identification. Light trapped, light scattered. Verification. Structure, specular, directional. Guidance/location analysis. Backlighting, structured light. 13.2.1.2— Optics Adequate field of view is needed to compensate for positional variations. Distortion and magnification influences accuracy. Polariz- Page 323 sers reduce unwanted specular reflections. These are considerations regardless of application. 13.2.1.3— Sensors and Cameras The significance of delectability versus resolution should be recognized, that is, the ability to observe a single object versus the ability to separate objects. The relationship of pixel arrangement to minimum detail observable should be understood. Gauging may require use of line scanners to obtain required accuracy. It may be necessary to use a multiple-camera arrangement to make differential measurements, and stereo techniques may be needed to compensate for magnification changes due to part motion in the field of view. Flaw detection is required for field-of-view analysis. The smallest reliably detectable flaw will typically be on the order of 0.3% of the field of view, not the object size. For reliable verification or recognition the minimum size of the attribute upon which the decision should be based is 1% of the field of view assuming relatively high contrast associated with that attribute. 13.2.1.4— Preprocessing and Processing Preprocessing and enhancement needs can be eliminated or reduced by the following conditions: registration, contrast (real or artificial), and windowing unwanted areas. [...]... and identifying and evaluating the most appropriate vendors to be solicited 13.3.4— Technical Society Meetings and Papers Meetings and proceedings can provide insight into experiences with machine vision as well as provide information concerning new developments: Automated Imaging Association, 900 Victors Way, Ann Arbor/Ste 132, MI 48108 SME/MVA, the Society of Manufacturing Engineers and Machine Vision. .. alternatives: 1 Rely on the machine vision equipment supplier for overall direction of the project 2 If line automation and/ or material-handling equipment is involved that must be integrated with the machine vision system, a system integrator may be the one to take on overall project direction The system integrator should be one with experience integrating machine vision with line equipment and, ideally, experienced... installation, and acceptance testing They can also provide training on machine vision that is appropriate for all involved in the project In general, it is not a good idea to have the machine vision vendor serve as the project director if there is any material handling or other specialized equipment needed The small machine vision companies generally do not have the personnel trained in product handling... Review in detail the specific functions the machine vision system is to perform Describe part( s) in detail indicating variables in parts, process, suppliers, and so on Make sure tolerances are realistic from a production point of view and are in fact currently being met Review all defects anticipated and outline their properties 2 Describe how the machine vision system will be integrated into the line,... advice and assistance, vendor representatives can furnish written materials and brochures Recommendations generally have to be taken with a grain of salt since they may lack objectivity 13.3.3— Consultants Consultants who do not design and build machine vision systems or act as sales agents for machine vision vendors or system integrators can objectively examine plants to identify technically feasible and. .. design or image processing techniques, and so on Rather it should specify the application The specification should include the following 1— Scope This section should include an overview of the existing process and the overall system requirements as well as what the vision system will be required to do Material handling and interface requirements to existing machines and control systems as well as future... product line breadth 3 Understanding of application 4 Capital and human resources to support and service installation Page 334 5 Physical facilities 6 Business philosophy with respect to a Warranty b Training c Installation support d Service e Spares f Documentation 7 Project schedules and possible conflicts with other projects 8 Financial stability and staying power 9 Review experience and obtain references... service, etc 13.5— Project-Planning Advice In conjunction with hands-on machine vision clinics offered by the Society of Manufacturing Engineers, panel sessions were conducted One panel consisted of Page 337 known users and the other of vendor-applications people They were asked to share their experiences in dealing with machine vision and to offer recommendations to prospective users that might guarantee... before shipment, one for preliminary off-line trials at the site, and one for final on-line acceptance The acceptance test might include number of parts, total hours of operation, accuracy or repeatability, acceptable standard deviation for measurements or other statistical details about the test, and so on 13.3— Getting Information on Machine Vision 13.3.1— Company Personnel Staff Line personnel with experience... automation will sometimes run articles on machine vision These include Manufacturing Engineering, Industrial Engineering, Managing Automation, to name a few 13.4— Project Management 13.4.1— Determine Project Responsibility The best manner to handle a project should be found For example, if the division or company does not have experienced staff in machine vision or related automated equipment, it . integrating machine vision with line equipment and, ideally, experienced with the machine vision vendor whose equipment is best suited for the application. 3. Consider using a consultant in machine vision. the machine vision equipment supplier for overall direction of the project. 2. If line automation and/ or material-handling equipment is involved that must be integrated with the machine vision. not design and build machine vision systems or act as sales agents for machine vision vendors or system integrators can objectively examine plants to identify technically feasible and cost-effective