When it comes to inspecting and measuring the very smallest parts, there are limits that are being pushed back by developments in sensor technology.

Parts for critical applications in the automotive, aerospace, medical, and electronics industries are getting smaller, and have more complicated features that can prove elusive to the best sensing efforts of traditional measuring technologies.

The familiar and widely-used touch-trigger probe has proven itself in countless applications on CMMs. Generally, the smallest probe tip available for tactile probing is 0.3-mm diam with a stylus length in the 2-3-mm range. Size can be a limiting factor when it comes to measuring the smallest parts and their features.

However, touch-trigger probes in combination with optical image processing sensors, analog scanning probes, and lasers have created a whole class of versatile multisensor machines that can be configured to tap the respective strengths of each technology for shop-floor or quality-control laboratory measurement and inspection.

What is considered small, of course, is relative. For a long time, medical devices and other Swissturned precision parts offered the most serious challenge to production measurement and inspection. Rowan Precision (Birmingham, England, UK), for example, adopted two noncontact measuring systems as effective ways of providing gaging of "first-off" parts, and automating measuring systems and programming routines for part traceability.

Rowan Precision's products tend to be small, precision-turned components with a number of complex internal and external features. They range in size from 0.5 to 85-mm diam, and are machined from aluminum alloys, stainless, and plastics, such as PTFE, for the medical and defense industries.

A typical application involves connectors that must be manufactured to a defense specification that is backed up by component traceability. These connectors have a number of key broached features that ensure that the finished component will only be located in the correct socket.

Accurate gaging of these broached features for Rowan Precision relative to the datum proved to be an extremely difficult and lengthy operation. Using a shadowgraph required sectioning the product before a measurement could be made. Besides destroying the product, the procedure was time-consuming for the operator.

To confirm that products were produced to the tight tolerances demanded by its customers, Rowan Precision chose Vision Engineering Inc.'s (New Milford, CT) Kestrel two-axis gaging system for the shop floor, and its Hawk three-axis automatic measuring system for the QC laboratory.

The Kestrel gaging system is located alongside the CNC machine, allowing first-off components to be taken directly from the machine for immediate inspection and measurement. In the QC lab, the Hawk motorized three-axis system with automatic Video Edge Detection (VED) runs alongside QC5000 PC-based software that allows measurement routines to be programmed and stored for future use.

When frequent or multiple checks are needed on a particular component, the quality engineer recalls a previously configured program, locates the component on the Hawk's stage, and starts an inspect cycle, which runs automatically. Once the routine is completed, a data report can be stored and printed, forming part of the data trail that is vital for quality systems and component traceability.

Parts are smaller, and more complex. The trend toward more sophisticated combinations of multisensor machines to meet specialized measuring requirements is not new. What is new are the choices in sensors that are available to characterize the form and fit of smaller and smaller, even microsized, precision parts.

According to William oilman, vice president, Optical Gaging Products Inc., (OGP, Rochester, NY), today's multisensor measurement machines go beyond vision, laser, and touch-trigger probes. As much as the combination of these sensors on a single platform improves productivity, each has its limitation, especially when applied to the latest manufacturing processes. These requirements have led to the development of "a new breed of microsensor technologies" that extend the capabilities of multisensor systems.

"The power of today's CAD software allows companies to design parts that have complex surface shapes that can be difficult to define geometrically. These surfaces may have intricate features with important distance or spatial requirements for proper fit or finish," Gilman explains.