Dimensional inspection to ensure that products and parts are finished to the specifications is an important process in manufacturing. In the past, inspections by human visuals were the mainstream, but it took time and effort, and inspection mistakes occurred. Today, automation using dimensional inspection equipment is progressing, and dimensional inspection without mistakes can be realized efficiently.

In this column, we will introduce the mechanism and merits of dimensional inspection with dimensional inspection equipment.

1. What is Dimensional Inspection?

First, let’s review the purpose and method of dimensional inspection.

(1) Purpose of Dimensional Inspection

① Check that it is made according to specifications

The manufacturer is obliged to ensure that the quality of the products and parts manufactured is produced as designed. To this end, we conduct dimensional inspections to ensure that products and parts are finished according to drawings and specifications. In addition, if it is judged to be a defective product as a result of dimensional inspection, the quality is guaranteed by excluding the defective product from the good product.

 Maintain and improve product quality

Manufacturers must strive to maintain the quality of the products and parts they manufacture in-house. Quality can be maintained by continuously performing and checking dimensions. In addition, it is important to continuously improve quality by analyzing defective products found through dimensional inspections, identifying the cause of occurrence, and turning the cycle of making improvements at the manufacturing site.

(2) How To Perform dimensional inspection

The method of dimensional inspection can be roughly divided into the following three patterns:

① Measuring tool

This is a method of manually inspecting dimensions using measuring tools such as calipers, micrometer, and dial gauge. The disadvantage is that the measurement is inefficient due to manual measurement, and the measurement results vary depending on the skill of the measurer.

② Measuring equipment

This is a method of dimensional inspection using measuring instruments operated by human hands. By using measuring instruments such as projectors and image dimension measuring instruments, dimensional inspections can be performed with higher accuracy than dimensional inspections with measuring tools. However, since it is necessary for a person to set and operate the measurement material, it is not highly efficient, and it is not suitable as a method for measuring things manufactured at large volumes and high speeds.

③ Dimension inspection device

This is a method of unattended dimensional inspection by introducing a dimensional inspection device that operates automatically. By combining conveyance equipment and image processing systems, we will build a mechanism for automatic dimensional inspection. Compared to other methods, the cost of implementation is high, but dimensional inspection can be performed quickly and accurately.

2. Mechanism of Dimensional Inspection Equipment

In dimensional inspection equipment, it is common to perform dimensional inspection by image processing. We will briefly introduce the mechanism of how dimensional inspection by image processing is performed.

① Edge detection

In dimensional inspection by image processing, edge detection is performed first. An edge is a boundary area in an image where the shade of color changes significantly.

In this way, edge detection is to clarify the shape of the object to be measured by detecting the place where the shade of color changes greatly. However, the actual measurement may not have a clear shape or the image may be blurred and the border may not be detected well, so it is necessary to preprocess the image to emphasize the border.

② Various measurements based on the edge

Various dimensional measurements are made using the edges detected by edge detection.

Measurement of various dimensions based on edges, such as measuring the distance from edge to edge, measuring angles, and calculating and measuring intersection coordinates between edges, is instantaneously performed to determine whether they are within dimensional tolerances.

In this way, dimensional inspection by dimensional inspection equipment realizes automation and speedup of dimensional measurement by instantaneously performing various measurements ⇒ edge detection.

3. Applications of dimensional inspection equipment

Introducing what kind of use the dimensional inspection device is used for.

(1) Confirmation of workmanship

It measures whether the manufactured product or part is made up of the dimensions according to the drawings and specifications. There are two types of inspection: intermediate inspection that performs dimensional inspection in the middle of manufacturing, and finished product inspection that performs dimensional inspection after manufacturing. As a result of dimensional inspection, defective products judged to be out of specification are excluded from the production line, and only good products that pass dimensional inspection are transferred to the next process and shipping process.

(2) Positioning

Dimensional inspection equipment is also used for positioning in the manufacturing process. The position of workpieces such as parts, films, labels, etc. can be identified by dimensional inspection, and the assembly work can be accurately performed by transmitting the position information to a robot or the like.