Quality Magazine

Quality 101: Portability at Arm's Length

January 28, 2006
Portable arm coordinate measurement machines efficiently measure large or bulky parts on the shop floor.

Portable coordinate measuring machines (CMMs) are a viable solution to making the power of coordinate metrology flexible. Traditionally, when engineers think of portable CMMs, the first image that comes to mind is an articulated arm CMM. Articulated arm CMMs offer portability and are available in many different configurations.

The tube inspection station, which includes a six-axis articulating arm CMM, is designed to inspect tube products such as hydraulic tubing, exhaust pipes, lines and hoses. Source: Hexagon Metrology


Portable coordinate measuring machines (CMMs) are a viable solution to making the power of coordinate metrology flexible. Traditionally, when engineers think of portable CMMs, the first image that comes to mind is an articulated arm CMM. Articulated arm CMMs offer portability and are available in many different configurations.

Traditional, manually operated articulated arm CMMs are used in many manufacturing operations because they can be moved quickly and easily around the shop floor to perform fast, accurate measurements. Articulated arm CMMs use an anchored, jointed arm with an attached probe tip at the moveable end. The length of each arm section is combined with the encoder angle at each joint to compute the probe's position.

Portable arm CMMs come in a range of arm lengths and in configurations of six and seven axes. Their primary advantage is to measure parts too bulky or inconvenient to bring to a fixed measurement station. Newer portable arm CMMs are lightweight, more accurate and more ergonomic than their predecessors. Some models now have Wi-Fi capability and are designed to handle a wide range of probes, including touch and noncontact laser scanning probes.

Large workpieces such as complete auto bodies, auto body sheet metal panels and subassemblies, airframe components, and molds and dies are particularly good candidates for portable articulated arm CMMs. Because large parts require more time to move and set up, the use of portable CMMs to inspect them in place on the shop floor helps reduce inspection cycle time.

Some parts, such as welding fixtures, must be inspected at the place they are constructed, making them prime candidates for portable, articulated arm CMMs.

In most cases, a portable shop floor measuring machine with a moveable stand and locking casters does not require recalibration after it has been moved. Such a CMM only requires an electrical hookup for power. Source: Hexagon Metrology
Parts with unique features often can be inspected more quickly with portable arm CMMs. Because of its flexibility, the portable, articulated arm CMM makes it easier to inspect parts with features in difficult-to-reach areas-a feature located inside a large bore, for example.

Tubular workpieces can be efficiently inspected with portable arm CMMs because of the difficulty of programming this type of part on a traditional fixed CMM. These devices come equipped with an infrared noncontact probe that allows the operator to determine tube diameter and bend angle orientation and move the device along the assembly. Some CMM manufacturers have special tube stations specifically designed for this application.

Sometimes there is a need to inspect both small and large parts at the same facility. Inspecting small parts with the same portable arm used for large parts is difficult and awkward, and it is not as accurate as a smaller arm. There are, however, portable arm CMMs that are field-reconfigurable into short arm length or long arm length systems, essentially providing two arms in one. These systems provide accuracy and ergonomics in the smaller configuration, and the "reach" for large parts in the larger configuration.

Portability is necessary because of the size and shape of certain parts, but programmability also is necessary, because a long inspection cycle or awkward location results in operator fatigue, which can affect measurement results. For such an application, a computer numerical control, powered portable arm may be the correct solution. Various mounting configurations, such as motorized cart, tripod or linear rail, allow these automatic measurement systems to be located adjacent to the workpiece, or even inside of it for hands-off inspection.

This CMM incorporates an articulating arm CMM with a combination hard probe/laser scanning probe assembly that accommodates laser cameras. The handle of the combination probe can be removed to access difficult-to-reach part features. Source: Hexagon Metrology
Another alternative to portability for higher volume, smaller parts with greater accuracy requirements is the moveable CMM. Some bridge-type CMMs have wheels so that they can be moved around the factory wherever needed. When this type of CMM comes equipped with hard bearings, no air supply is required-just a power connection-so it can be placed almost anywhere, even if that location changes daily.

Ultimately, the choice of a portable CMM depends on the size and number of workpieces to be inspected and the accuracy necessary to determine if features are within tolerances. Fortunately, today's quality professionals have a wide variety of device technologies to choose from, each with strengths in particular applications, making the matching of application and device easier than ever.

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