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PAS CMM Overview

1. Summary

PAS-CMM automates the preparation of inspection programs for computerized measuring machine. The engineering specifications and QA requirements that are provided by the part’s 3D CAD model and the associated drawings are automatically interpreted and translated to the appropriate inspection commands. (The program is stored in DMIS format and than transferred to the native machine environment) PAS-CMM can be used efficiently by non expert users and help to realize significant time savings (50%-90%) when compared to conventional CMM programming in the machine environment

2. Inspection Concept

The inspection of machined parts is an integral part of the manufacturing process. The design data that is used to manufacture the part is also the basis for the inspection process.

The engineering requirement as specified in the drawing relate to specific geometric features of the part.

Tolerances are specified for the position and diameter of holes, distances between planar faces, position and shape of slots etc.

Each such feature will be inspected by a certain number of points that is determined the type of the feature and the type of the required tolerance.

When a hole is measured with 3 points it’s center and diameter can be calculated and compared to the design value (as defined in the CAD model). However if the tolerance specifies also a cylindricity check we’ll need 6 or more points in order to verify the accuracy of the cylindrical surface and the direction of it’s axis.

In the same manner we can verify the location and orientation of a plane by 3 points but it will require 4 points or more if a flatness check is specified.

The inspection of a feature is performed as follows:

  • Inspection points are calculated for a geometric feature (nominal points)
  • The inspection machine measures the points on the physical part (actual points)
  • A geometric feature of the same type is constructed using the actual points (represent the actual feature)
  • The geometric properties (center, diameter…) of the actual and the nominal features are compared and the deviation is reported.
  • Optionally the report may include also the deviation of individual inspected points from their nominal position. The content and form of the report is defined by the engineering drawing. Locations and orientations of features may be specified in different coordinate systems (such local coordinate systems will be calculate from the actual measured features) , other geometric properties may be reported in relation to some reference features (Datum).

3. Design Data

The design data includes the shape of the part (3D model), manufacturing requirements (surface quality and general accuracy) and QA specifications (the later two are defined in the drawing)

The QA specifications are mostly derived from the functional requirements of the part within a product (assembly). Tolerances that specify flatness of planes, true position of holes, size of slots etc. are required so that the part will fit into an assembly and meet its specified function.

4. Inspection Environment

A CMM (Coordinate Measurement Machine) includes an inspection application (Camio-Studio, MCOSMOS, PC_DMIS, Metrolog..) that controls the machine and provides an interactive environment for the creation of inspection programs.

These applications may vary in their functional capabilities and performance but thy all share the same operational concept – manual programming of an inspection program in a specialized programming language.

The creation of inspection programs with such application is a time consuming process and requires a high level of expertise, - the user creates measurements commands for every inspected feature and has to interpret the QA requirements as specified in the drawing (CAD domain) to the relevant commands and parameters of the inspection application (Inspection domain).

5. PAS-CMM Solution

PAS-CMM provides an efficient and highly automated link between the CAD domain (3D model and drawing) and the Inspection domain (DMIS code).

Automatic feature extraction and analysis of optimal inspection directions are employed in the creation of probe locations, and with the highly intuitive tools for dimension specifications and properties assignments an inspection program can be completed in a fraction of the time it would take in the conventional CMM environment.

PAS-CMM CAD like tools provide a smooth integration of the CAD and the Inspection environments and enables the creation of inspection processes by non expert users either in the engineering environment or in the QA environment.

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