Innovations: Modular Arm Makes Custom Lengths
The quality tech is jammed in, measuring under the dash. The portable coordinate measuring machine (CMM) articulating arm is stretched to the limit, and the probe head is rotating toward the part to be measured. It won't reach.
But, if the arm were longer or cut to the exact length needed, or could be upgraded to a different size when an inspection called for it, and the arm was still lightweight and accurate, then that operator might not feel so jammed in. The Sigma arm from Axila Inc. (Farmington Hills, MI) is now available in eight standard lengths that range from 6 feet to 17 feet, and lengths are customizable. The extended length gives it the longest reach of any arm currently on the market, without the aid of sensors, linear rails or other extension systems.
After purchase, the two carbon graphite tube components, which make up the physical bulk of the arm, can be changed to a length more suitable for the application. Changes to the arm are made in Axila's facility and after the new arm is swapped out, recalibration is required.
"The Sigma is no longer a fixed-length arm," says Jean-Charles Granger, vice president of Axila. "We can upgrade its length. For example, you can purchase a 6-foot model, but you are no longer stuck for life with this length. If you have new projects where this arm happens to be too short, you just need to ask for a length change, and you can get a 10-foot or longer model."
In the past, the maximum length for an arm had been about 12 feet while still achieving "high accuracy," Granger says. Granger says that the arm combines three factors that gave the company confidence that the Sigma could be released in longer lengths and still hit required accuracy levels.
The first factor is weight. The 6-foot model weighs 10 pounds and the 8.3-foot model weighs 11.1 pounds. The longest arms weigh 12.2 pounds for the 15-foot arm and 13.4 pounds for the 17-foot model.
Granger says the second factor is the high-resolution electronics including encoders and miniaturized electronics. The final factor is the robust mechanical design, which is due in part to the arm's material makeup.
"You can't have a high accuracy in large volumes if you don't have these factors," Granger says. "Heavy weight creates stress in the arm, and is hard for the operator to use. Low resolution loses accuracy immediately, and a weak mechanical design becomes a visible problem for large volumes."
The Sigma arms have volumetric length accuracy that ranges from ±0.024 millimeter for the 6-foot Sigma arm to 0.11 millimeter for the 17-foot arm. The accuracy levels were determined by measuring a certified length bar at different locations through the measuring volume of the arm.
The Sigma has an Ethernet connection and has its own IP address that allows the user to plug the portable CMM into a computer or directly onto a computer network.
Driving the portable CMM is Delcam PowerInspect from Delcam (Windsor, Canada). The software allows the user to make comparisons to all mainstream CAD formats, rapid alignment for complex freeform shapes, inspection of user-defined sections, the ability to inspect along the edge of a part and full geometric inspection capabilities.
Measurements can be taken with contact probes, or with Axila's laser scanner, the G-Scan. The scanner plugs into the Sigma at the same time as contact probes, and because it has a rotary axis allowing the probe head to completely swivel, there is no need for a dedicated 7-axis scanning arm. "The Sigma is a scanning arm too," Granger says.
For more information on the Sigma, contact:
24407 Halsted Rd.
Farmington Hills, MI 48335
(877) 992-9452, Fax: (248) 426-0940
• The 6-axis portable arm comes standard in eight lengths up to 17 feet. Custom lengths are available.
• The portable CMM weighs less than 10 pounds and features an Ethernet connection with its own IP address.
• The arm can be fitted with a laser scanner with rotary axis.