Optical Comparators: What They Are and How to Use Them

Since its invention in 1925, the optical comparator (profile projector) has been used to inspect parts for deformities and other flaws. The device’s design has changed little, except for some digital and software enhancements. The continuing popularity of this device shows how useful it is for checking parts optically.

In this article, we’ll talk about what comparators are, how they work, and how traditional models compare to digital ones. Let’s get started!

What is an Optical Comparator?

Optical comparators are measurement tools that are used in the manufacturing industry. They inspect, measure, and compare the dimensions of manufactured parts. Optical comparators use light and mirrors to project a magnified image of a part so that it can be compared to its limits.

Optical comparators are used to check the dimensions and surface of an object. It is done by measuring the thing without having to touch it. It is helpful because it minimizes the object’s handling and allows for close inspection.

Optical comparators are available in two primary forms: horizontal and vertical. Here’s how they work:

  • ¬†Horizontal comparators:

The optical comparator’s light travels across the object you measure in a horizontal model, allowing you to see it from the side. This model is suitable for objects in a fixed position – for example, screws that don’t move or castings that are held in a vise.

  • Vertical comparators:

The optical comparator’s light travels vertically in a vertical model. It is suitable for flat components, like gaskets, that can lie on the work stage. It also works well on flexible or soft elements that need to lie on a flat surface to provide an accurate measurement.

Optical comparators, also known as sight-testing devices, are utilized in quality control and inspection to determine how close a product is to its intended specification. They’re most common in industrial sectors like science, automotive, medical manufacturing, aerospace, and military production.

How Does an Optical Comparator Work?

Optical comparators have been used for a long time. It is because the technology employs optics, which have changed in quality but not function. Similar to overhead projectors, optical profile projectors function similarly. Optical comparators use the same concept. Attaching a part to a stage and shining a light source on it produces a shadow image of the part. The shadow is magnified with lenses and reflected onto the back of a screen using mirrors. This screen is positioned at a known distance for measurement.

In the optical comparison, the size of the projected image is determined by the optics and screen size. Comparator screens range from 12 to 36 inches, though some models feature larger displays. Comparator screens range from 12 to 36 inches, but some models have even bigger screens. However, a larger screen size is only possible if there is more space for the image to be projected without distortion.

There are three different ways optical comparators can measure:

  1. Silhouette measurement: The easiest way to measure an image is to project it onto a screen. You can then use the silhouette to get accurate measurements. It is because you know the magnification of the image.
  2. Point comparison: The second way to measure things is to compare the image’s silhouette to points on a screen. The user centers the part on the screen and then hits various points. Doing this measures how much the stage had to move to match the part with the point.
  3. Software analysis: The last measuring process is done with a computer. The computer uses software to measure the image created by the optical comparator.

There are three ways to compare two objects. The first way is used by traditional optical comparators and is the most common industry. The second way is used by digital optical comparators, which handle the entire process electronically.

Flaws of Traditional Optical Comparators

Profile projectors are easy to use and don’t require a lot of training. You must just put the part in place and look at the screen.

Although traditional optical comparators are easy to use and operate, they also have disadvantages. Some of these primary flaws include the following:

  • ¬†Limited complexity required: Production parts are becoming more complex, and observing them from more than one angle is necessary. However, traditional comparators don’t accommodate this well.
  • Less accurate: How accurate is an optical comparator? Although traditional optical comparators can accurately measure things, today’s modern parts need even more accuracy. It reduces the margin for error associated with manual measurement techniques.
  • Labor intensive: Traditional optical comparators can only measure one part at a time. It makes it difficult to inspect large quantities of parts at once. It is often needed in the manufacturing industry, where you might need to check many functions simultaneously. However, a vision system allows you to place multiple parts on the stage for inspection simultaneously.
  • 2D limitations: Traditional optical comparators can only project 2D images onto a screen. It can sometimes make it difficult to analyze multiple dimensions simultaneously.

Although these limitations present no issues for non-repetitive tasks used to analyze 2D parts, anything outside this defined operating bubble can be an obstacle for traditional optical comparators. For large-scale, complex analysis, a different model is necessary. It might include using another tool or technique altogether.

Digital Optical Comparators vs. Traditional Optical Comparators

Digital optical comparators are better than traditional visual profile projectors because they can handle more complex parts and are necessary for large-scale manufacturing. Manual comparator technology is still helpful for small-quantity applications. Still, it cannot compare to the capabilities of digital optical comparators.

The following are some of the benefits of using digital optical comparators:

  • ¬†Automation capabilities: These models use software and cameras to measure parts quickly. The software automates and completes the process more quickly than a human can.
  • 3D capabilities: Digital optical comparators can use multiple lighting techniques and 3D inspection methods to analyze parts in all three dimensions. It means they can automatically analyze numerous parts without human intervention.
  • Accuracy: Digital optical comparators are highly accurate in their measurements. It is essential for many modern industries and technologies.

These advantages make it more likely that optical comparator measurements will be accurate and reduce the labor needed.

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Frequently Asked Questions About Optical Comparators

What Are Optical Comparators Used For?

Optical comparators are machines that check objects’ size, shape, and surface. It is done by comparing the object to one known to be accurate. It is done by looking at the object from a distance, so it does not have to be touched.

Which Is an Advantage of the Optical Comparator?

The optical comparator is an excellent choice for high accuracy because it has few moving parts. It is also less heavy than other comparators due to fewer parts. Additionally, the parallax error will be avoided with this comparator. And lastly, the high magnification makes it perfect for accurate measurements.

How Do You Measure Angles on an Optical Comparator?

To measure the angle, use the staggered or hairline line on one edge and move the protractor until it matches up with the other. Then read the angle scale.

What Does a Comparator To Measure?

A comparator is a device that compares an unknown length to a standard. This type of measurement is called comparison measurement. Comparators are usually used for linear measurements.

Is an Optical Comparator a CMM?

Optical comparators, like CMMs, have been used to measure the size of two-dimensional objects for a long time. It is achieved through the projection of the object onto a glass screen. This method is used because it is simple and can be used to measure small objects.