Multi-sensor inspection system: the best choice for measuring complex workpieces

The OGP SmartScope multi-sensor measurement system is used for 3D dimensional measurement. The system uses two or more different sensor technologies to acquire data points from the surface of the part, allowing more measurements to be made than with a single sensor on a single machine. The choice of sensor depends on the size and shape of the part, color and reflectivity, surface finish and texture, material and hardness that need to be measured.

The part below has a set of holes and slots, surfaces at different depths and some complex details. Assume that the blue edges of the

CAD model in Figure 1b need to be measured to determine the distance between them. It can be assumed that any of these edges is the intersection of two perpendicular planes. In this case, the touch probe can collect data points on each of the above perpendicular surfaces. The software then maps the data points to the planes and then re-intersects the planes. These intersections represent those edges. Through holes and corner radii increase the difficulty of using a probe. We can directly measure those edges using video. The edge display is parallel to the worktable and therefore perpendicular to the optical axis of the video sensor. Collecting data Figure 1a shows a video measurement of an arc on a physical part. Some video tools can automatically track an edge, collecting points even as it changes direction. This example also shows that even though each edge is in a different plane, it can still be measured using video.

Figure 1 Some video tools can automatically find edges and collect data points

On the same part, Figure 2b shows that the two blue planes must be parallel to each other. In addition, the degree to which each surface deviates from the plane (its flatness) must be known. This is best measured using a laser . The focus of each plane can be scanned, resulting in a data grid. Each set of data corresponds to a plane. The deviation from each plane can be measured. In addition, the relationship between the two planes can be compared to determine their parallelism. However, not all parts can be inspected with lasers, only parts with important features that can be inspected with lasers can be used.

Figure 2 The most suitable sensor for this component is a laser because its focus can be scanned in every plane.

Note the perpendicular surface between the two planes. Measuring larger planes requires an appropriate working distance to avoid collision with higher surfaces (see the laser spot and its path in Figure 2a).

Measuring planes close to vertical surfaces can be challenging for some laser triangulation methods because the surface can block incident or reflected light. Some through-the-lens lasers can measure to the bottom of a vertical plane. When this part is in this position, it also has several holes that are perpendicular to the upper surface. If we need to measure the perpendicularity of the cylindrical axis of one of the holes to the drilled surface of the hole, a probe is the best tool. Then, a star probe can be used to collect data points along the cylinder wall. These points correspond to a plane and a cylinder, and their angular relationship can be measured separately.

Smart Choices

If the part is in one position, all of the above measurements can be performed on a multi-sensor measurement system. However, not all measurements can be completed with a single sensor. Only by fully understanding the optimal application range of each sensor can the best sensor be selected for different measurement types.