A comparator is a device that uses optic principles to take measurements of many different tangible items. Many people may be more familiar with something like an overhead projector. In these projectors, something is affixed to a stage, a light source shines on it, and the resulting shadow is projected onto a screen. Comparators work in much the same way except the distance between the stage and screen is fixed and allows for calibration. This calibration allows for more exact measurements and comparison of new parts to master part dimensions or standard measurements. In fact, many machine shops and other fabrication companies use comparators for quality control to check the 2-D geometry and dimensions of parts against set limits. There are 3 basic types of optical comparators based on how they measure.
Graduated optical comparator
A graduated optical comparator takes a magnified silhouette of a part and projects it onto a screen. The screen on these comparators has graduation marks similar to a ruler. By using these marks, an operator can measure the dimensions and geometry of parts against limits to quickly determine if the part meets specifications. These types of comparators can use custom tool room charts or standard gages on the screen to help an operator determine the quality of the products.
Center Point or Reticle Optical Comparator
A center point optical comparator takes the silhouette of a part and magnifies the projection on a screen. The operator then lines up various points on the part to the reticle at the center of the screen. By lining up point after point with the reticle, the machine can determine a variety of measurements based on how the stage the part lies on moves as the operator aligns the reticle with each point on the silhouette. The measurements from this machine are reported via a digital readout.
Software analysis and video integration
The most advanced comparators on the market can use software to automatically analyze the image and report measurements. This type of comparator is not yet widely used and is fairly new. This type of comparator is most often used by larger volume shops where speed and efficiency is most valued. Other comparators have also been retrofitted with video cameras to help to see details not able to be seen by shadows.
Types of measurements
Depending on the specific machine, optical comparator can be used to determine the following measures and geometry calculations:
Advantages of Comparators
Optical comparators can provide a lot of information about a part very quickly. Comparators can quickly determine angles, whereas without a comparator, an inspector may need to use a sine plate and a height gage to measure an angle requiring a detailed procedure and much more time.
Low Learning Curve
Unlike lengthier processes such as using calipers or other gages along with charts, comparator operators can begin taking precise and accurate measurements with as little as 2 hours of training.
If you have parts that are delicate or may be deformed or changed when direct force is applied, such as rubber, having a non-contact gage may really help. Unlike calipers, micrometers, or plug gages, comparators do not need to apply pressure to a part to measure it. This eliminates the human error of hand gages and the feel factor when trying to measure delicate parts with manual tools.
Many comparators have various powers of magnification available from 10X magnification up to a 100X lens. This type of magnification allows for easily measurements of small parts. For example, a small, delicate part may have a radius as small as 0.005 inches. It would be very difficult to measure such a radius using a radius chart and a contact gage. However, using a comparator with a 100X lens would allow this task to be accomplished with relative ease.
Optical comparators save time and therefore money. The ergonomic design and ease of use reduces inspection time, training cost, and operator fatigue all while increasing productivity and reducing time spent measuring each part. Optical comparators are flexible and general purpose meaning that they are easily adaptable to changes in part design and are equally useful for repetitive inspection.
If you would like to know more about optical comparators and the right type based on your specific needs, please feel free to browse through our current inventory and do not hesitate to contact us. We are just a phone call or an email away.