Features
In machine vision, features are referred to as the "objects of interest in the image," and vision inspections are designed around the types of features found in the image.
Types of features in the Locate Part step include:
Linear areas of transition between light and dark pixels. Edges can be things like the ends of parts, pins on a circuit board or threads on a screw. Edges are one of the faster types of features to detect during an inspection, but when used as a Fixture, they should only move in one direction (horizontal or vertical) and be highly contrasted.
Edge Fixture Example
In this example, the air freshener applicators don't appear in the same location in each image; they appear in the same vertical plane but move horizontally. Two Edge Location Tools are used as Fixtures; the one on the left locates the outer edge of the lower housing of the applicator and orients the regions of the other inspection tools on the left side, while the one on the right orients the tools on the right.
Circles are essentially edges, areas defined by a transition between light and dark pixels that defines their geometric shape. Also one of the faster types of features to recognize, as long as they are highly contrasted, however circles do not provide any angular orientation data when used as a Fixture.
Circle Fixture Example
In this example, two Fixtures are being used. The first fixture, a Blob Location Tool, locates the outside of the pipe, while the second fixture, a Circle Location Tool, locates the basic circular shape of the pipe within the found blob. Due to the demands of the application, the length of the screws is determined by measuring their distances from a point relative to a found shape, which must be uniform.
A pattern can be anything from a simple group of repeating shapes to complex configurations like logos or labels. The most reliable type of feature to use as a Fixture, patterns allow for the greatest range of positional rotation, movement and scale variations, but generally require the most amount of time to inspect.
Pattern Fixture Example
In this example, the 2D code appears in varying locations and orientations in each image. A PatMax Patterns Location Tool is used to create a Fixture and orient the search of the Read ID Codes Identification Tool. The PatMax Patterns Location Tool is used because it can locate complicated patterns while accommodating a wide variety of locations, orientations and scales.
A group of dark or light-colored connected pixels, such as a splotch of white paint on a black background or a black screw on a white conveyor belt. Blobs fall between edges and patterns in terms of their detection speed, and blobs allow for a wider variance of the blob feature’s shape and size compared to a pattern, but have limited angular orientation value when used as a Fixture.
Blob Fixture Example
In this example, two Fixtures are used because the features being inspected (the screws) are inside an object (the pipe) whose orientation and vertical and horizontal location can vary from image to image. The flanges of the pipe create an irregular shape, so a Blob Location Tool is used to create a fixture that locates the pipe within the field of view.