Types of Optical Comparators

Different Types of Optical Comparators

The easiest optical design used in optical comparators is named the simple optics design. This optical comparator incorporates a light source, a magnification lens, the main reflecting mirror and a screen. Optical Comparator machines with this design display images that are both upside down and reversed.

Another Optical Comparator is named the corrected optics design. This Optical Comparator system uses two internal mirrors to flip the image so that it’s displayed right side up, but it is reversed on the horizontal axis.

On systems with simple optics and corrected-optics designs, the working distance decreases as the magnification increases. More sophisticated Optical Comparator machines incorporate a relay lens system that provides a constant working distance at all magnifications.

Another type of Optical Comparator design is the fully corrected system, which displays images that are both erect and unreversed. The convenience of seeing parts on the screen in the same orientation as they are seen on the worktable makes the machine easier to use, particularly by inspectors new to optical comparators.

Another useful addition to the Optical Comparator design that is found in many modern comparators is telecentric optics. A small opening, similar to a camera’s shutter opening and named telecentric stop, is placed in the optical path to block light rays that aren’t parallel to the optical path. This Optical Comparator design increases the depth of field, which in turn ensures magnification consistency across a range of focal settings. The size of the image does not change even when it is slightly out of focus. This reduces measurement variability from one inspector to another. Optical Comparator Telecentric systems provide a flat field and a more accurate representation of 3-D parts in relation to their 2-D drawings.

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What is an Optical Comparator?

What is an Optical Comparator?

An optical comparator is a device that applies the principles of optics for the inspection of manufactured parts. In a comparator, the magnified silhouette of a part is projected on a screen, and the dimensions and geometry of the part are measured against the prescribed limits.

Optical comparators provide a cost effective solution for non-contact measurement. Optical Comparators are found in shop and lab environments that are often related to product manufacturing activity. An optical comparator is used for a wide range of dimensional inspection applications. Optical Comparator horizontal models work well with parts that need to be fixed, held in a vise, or on centers. Optical Comparator vertical models provide accuracy and are ideal for parts that are placed on the glass insert of the work stage. Optical Comparator vertical systems work well when the parts to be measured are flexible or soft.

What is an Optical Comparator used for?

Optical comparators are inspection machines that project magnified images of parts onto a glass screen using illumination sources, lenses and mirrors for the primary purpose of making 2-D measurements. Optical Comparators have been used for more than 50 years and remain a versatile and cost-effective technology for the monitoring and the processes and quality of a broad range of manufactured parts. An Optical Comparator Originates from static overhead projectors that displayed magnified images of screw threads onto a wall for manual measurement, optical comparators have evolved into full-featured machines that use modern mechanical, electrical and optical technology to minimize inspection time and maximize cost savings.

Optical comparators are easy measurement instruments to use. In less than a couple of hours, users with only a little amount of gaging experience can make accurate measurements using an optical comparator. Because an optical comparator displays the part’s 2-D image on-screen, the image can be easily associated with the part’s 2-D CAD drawing. This simplifies the process of developing measurement procedures for parts from drawings and minimizes the subjectivity of more complex measuring methods.

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Optical Comparators

Optical Comparators Optical comparators are instruments that project a magnified image or profile of a part onto a screen for comparison to a standard overlay profiles or scales. These are non-contact devices that function by producing images that are magnified of the parts or the components and displays them on a glass screen that uses illumination sources, lenses and mirrors for the purpose of making 2-D measurements. Also, comparators are used to measure, gage, test, inspect or examine parts for compliance with specifications.

Optical Comparators Configurations

Optical comparators are available in two configurations, inverted and erect, defined by the type of image that they project. Inverted image optical comparators are the general standard and less advanced type. They have a relatively simple optical system, which produces an image that is inverted vertically (upside-down) and horizontally (left-to-right). Adjustment and inspection require a trained or experienced user (about two hours of practice time and manipulation). Erect models have a more advanced optical system that renders the image in its natural or “correct” orientation. The image appears in the same orientation as the part being measured or evaluated.

Also, comparators are similar to micrometers, except that they are not limited to simple dimensional readings. Optical comparators can be used to detect burrs, indentations, scratches and incomplete processing, in addition to length and width measurements. In addition, an Optical Comparator’s screen can be simultaneously viewed by more than one person and provide a medium for discussion, whereas micrometers provide no external viewpoints. The screens of optical comparators typically range between 10″-12″ diameters for small units to 36″-40″ for the larger units. Even larger screen sizes are available in specialized units. In addition, Comparators handheld devices are also available, which have smaller screens as would be expected.

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