Architecture, Design Methodology, and Component-Based Tools for a Real-Time Inspection System

We describe a real-time, component-based system for an inspection application. We chose the inspection application and the accompanying task (or scenario) so that we might fully exercise and test our theories about real-time complex systems, system architectures, design methodologies, and software tools. We will describe the application, give a history and description of our system architecture and design methodology, describe the real-time software tools we used, and conclude with a discussion of real-time and object-oriented challenges solved. 1 The Inspection Application Our inspection workstation consists of a coordinate measuring machine (CMM), an analog 3D contact probe, a charge-coupled device (CCD) camera with frame grabber, and control computers. The CMM is Cartesian (i.e., axis motion and axis position sensing are along the three orthogonal axes). The contact probe and camera are mounted on the CMM arm. The software controller sends velocity commands to each of the three axis motors every 5 ms and it reads each of three axis positions every 2 ms. The axis velocity commands are converted to voltages by a digital-to-analog converter. The voltages drive the motors. Figure 1 shows the CMM arm, the part to be measured, the camera mounted on the arm, and the analog contact probe. The application is more fully described in [Messina 99]. The application performs the following scenario. The operator specifies the features that need to be verified by measurement. An inspection plan is generated automatically from the computer-aided design (CAD) solid model of the part. The plan is translated into dimensional measurement interface standard (DMIS) code. A DMIS interpreter [Kramer 99] converts the DMIS code into canonical control commands for the CMM and vision subsystems. The CMM is commanded to move to a predefined “bird’s eye view” position. The part to be measured is placed on the CMM table in an arbitrary position and orientation. The human operator signals that the part is on the table. The system determines the position and orientation (i.e., pose) of the part using the camera and computer vision algorithms. The inspection plan is performed. Real-time, dependable control of CMM arm motion is imperative in order to achieve efficient Figure 1: The inspection workstation.