Opticalstuff's Blog

Some info about optical comparators

opticalstuff — Wed, 30 Dec 2009 17:28:41 +0000

Optical comparators are optical inspection tools. They allow for non-contact inspection of factory-made parts in result being repellent to external variables, such as extra press, vibration or wear off of contact points, which in final result could in malformed inspection results. Optical comparators are also known as profile projectors or shadow graphs. The major function of these devices is to amplify inspected material onto projection screen. Optical comparators are normally used in thread inspection.
Optical comparator was invented in early 20th century. It was invented by James Hartness. First optical comparator, known then as shadow graph, projected a shadow of an object onto a projection screen a few ft away. Then the target was compared with a chart showing allowance levels for that part. The optical comparator was invented to standardize screw thread sizes. Shortly it became one integrated machine that could be set on top of a work bench (hence the name benchtop comparator).
The optical comparators became widely applied during World War II as they were accommodated by US military. They became popular inspection instruments in artillery production. Virtually every mass-produced part was inspected with optical comparator then. Soon afterwards military, aerospace and automotive industry started using optical comparators in their quality departments. Rapid increase of optical comparators use allowed for faster development of new applied sciences. Their accuracy was improving due to better lenses implementations.
In the following years the maturation of optical comparators was focussed on adding additional features and further improvements to accuracy. Additional efforts were made to fully automate optical comparators. By the end of 20th century features such as automated edge detecting, digital readouts, programmable motorized stage control became standard equipment of optical comparator.
In the future, optical comparators will probably be substituted by video measuring systems. These systems have a few advantages over optical comparators. Image processing capabilities, various zoom lenses, color and profile images, capturing image of audited part are among others.

Setting bore gage

opticalstuff — Tue, 29 Dec 2009 16:56:55 +0000

A dial bore gage must be “set” to a reference master that has a known dimension. The master may be a cylindrical master ring or two flat surfaces that are accurately spaced to a given dimension.Mastering a dial bore gage to a master ring gage is the desired method because the ring gage duplicates the geometry of the workpiece being gaged. It is accepted as the fastest and most cost-effective for high production gaging. It is also the most accurate, especially for bore sizes under 1 inch, or any bore sizes that require master quality finer than “X” accuracies. Master rings have the further advantage of being more directly traceable to the National Bureau of Standards than any variable or multiple component device.Mastering to flat parallel surfaces is a practice generally associated with dial bore gaging of larger margins – or short-run job-shop applications that do not justify the cost of a special master ring gage. Mastering to flat parallel surfaces requires considerable operator skills in making an accurate gaging contact axis in two right-angle planes at one time.

Any dial bore gage “set” between parallel flat surfaces (as with gage blocks or bore gage setting master) must have gaging contacts free from wear. Any “flats” on the gaging contacts will cause an error in “setting” that is about equal to twice the height of the chordal segment that is produced by the radius of the bore and the width of the flat on the gaging point. The use of maximum wear-resistant material considerably reduces the possibility of worn contact errors. Norbide, tungsten carbide or diamond-tipped gage points are examples of the materials that should be applied.

Manufacturing challenge

opticalstuff — Fri, 18 Dec 2009 20:39:50 +0000

The demand and application of micron and sub-micron manufacturing requirements is growing, which offers unique challenges and immense opportunities to a wide group of tool shops and production parts manufacturers in the United States. The term micromachining broadly refers to part details and holes smaller than the human hair that are measured only in microns-or one thousandth of a millimeter.

This stress on micromachining has seized the imagination of nearly every industrial segment.

Technical and application engineers say that such industries as biomedical, medical appliance, personal electronics, fluid transfer, optical comparators, optics and fiber optics, RF electronics, communications, military, aerospace products, and the automotive world are centered on micromanufacturing. They all see the future in new and exciting consumer and industrial products coming daily.

These smaller, lighter parts with higher levels of functionality have set new requirements on original equipment manufacturers to reevaluate the design and concepts of different machining systems and technologies. You may have already got a number of approaching uses in micromachined parts in your computer, heart monitor or pacemaker, automobile, cell phone, and many more applications.

The capacity to produce parts with such high accuracy and surface quality on a variety of newer materials, including metal alloys and ceramic, is in very high demand. Unique new machines can make holes as tiny as 0.00078 inches in diameter, 100 times smaller than many recent machining operations.

The application of micromanufacturing represents a “business reality” to machine makers and providers. Learning to use these high-tech designs, concepts and machine tools will permit U.S. manufacturers to offer a larger understanding and service capability to combat foreign manufacturing competition.

Optical inspection instruments

opticalstuff — Fri, 18 Dec 2009 19:11:17 +0000

Optical inspection instruments can be put into four basic categories. Optical comparators, video systems, microscopes and laser systems.

Optical comparators utilize traditional optics to magnify and project the image of an object onto a glass screen. This type of optical inspection instrument is by far the most widely utilized and is also the to the lowest degree expensive method of optical non-contact inspection in use now. The optical comparator also offers the biggest versatility in regard to parts that can be inspected. Light weight parts as well as parts weighing 100s of pounds can be inspected on many available instruments. The evolution of the optical edge finder eliminated the subjectivity of the operator from the measurement and also allowed the system to become fully automated. Optical comparators are available in a wide variety of styles and configurations from domestic as well as foreign manufacturers. Normal options are – projection screen sizes from 10â€ to 80â€, horizontal or vertical light path configurations, profile and surface illumination systems, various stage travel options, magnifications from 5x to 200x and digital readout selections from a basic two axis display to fully computerized automatic CNC systems. Accuracy and repeatability of instruments presently available on the market today can vary depending upon the feature being inspected but can be expected to be within +/- .00010â€ under certain conditions.

Video systems utilizing a magnification lens and camera are relatively new to the mainstream inspection instrument market. Although these systems are typically more costly than optical comparators and offer less versatility with regard to the size and weight of parts that can be audited. These deficits are often more than offset by the advantages that this type of system can offer. Vision systems, which are generally small and compact, are better suited for relatively lightweight and or flat parts. Camera and computer progressions have allowed the offering of magnifications in the 1x-1300x range and some systems in reality offer full three axis measurements under CNC control. Video edge signal detection is also available that eliminates operator subjectivity from the measurement process. The image digitization process utilized by video systems also allows for computer handling and storage of the image being displayed. With the add-on of a printer and driver a video inspection system can actually print out a pictorial view of the part being inspected for documentation purposes. Due to the specialized staging, computer manipulation of lighting, image processing and the extremely high magnifications available, the accuracy and repeatability of some vision systems can be expected to be within +/- .00005 under certain conditions.

Inspection microscopes utilize traditional optics to magnify a wanted detail. Many inspection microscopes today are linked with a video system to offer the inspector the versatility of manual optical inspection as well as automated video inspection. Microscopes are generally best suited to inspect lightweight and or flat parts.

The latest development in optical inspection instruments are Laser inspection instruments which offer the biggest accuracy of any type of optical inspection instrument. Accuracy and repeatability within +/-.0000010 under certain conditions can be expected. This type of instrument reflects a laser beam from a detail being inspected and checks distances using time delay calculations. This extremely specialized method of measurement requires fixturing to locate the laser device as well as substantial setup time to align the instrument. Laser inspection instruments are best accommodated for specialized yield inspection or calibration applications.