3D Measurement Arm Technology

3D Measurement Arm Technology

Introduction

3D measurement arms, commonly known as articulating arms, are portable coordinate measuring machines (CMMs). Portable arms determine and record the location of a probe in 3D space and report the results through software. The name derives from the actual look of the hardware, resembling a human arm with a shoulder, elbow, forearm and a wrist. To ascertain the position of a probe, the arms contain proprietary glass discs in each joint, called encoders, that calculate the probe’s position as the arm moves freely throughout its workspace.

Radial reach of an arm when fully extended typically ranges from 2 to 6 feet. In the CMM industry, arms are classified by the overall working volume, from 1.2 meter feet all the way to 4.0 meters. The shorter the arm is more accurate, because it reduces mechanical error linked to the length of the sections. Arms may also be classified by the number of rotation axes. Arms typically come with 6 axes of rotation. If an arm is equipped with a handle at the end of the unit to control a rotating wrist, it is considered a 7-axis arm.

One of the main benefits of using an arm is its portability. Compared to a traditional CMM, arms are considerably smaller and lighter and thus, can be taken to a part for inspection instead of the part traveling to the CMM, minimizing machine downtime and quality control bottlenecks. Furthermore, manufacturers designed arms to adapt to most temperature conditions. They can work in a wide range of environments. No temperature-controlled inspection room is needed. The accuracy of arm CMMs exceeds a majority of the hand tools often used to do an inspector’s job.

Articulating Arm Applications

• Typical applications for an articulated arm include
• Dimensional Analysis: Collect information on parts to compare data to drawings and blueprint
• CAD-Based Inspection: Compare your part to a 3D CAD model in real time for instant feedback
• On-Machine Inspection: Utilize the portability of an arm and inspect a part before, during and after
  its production, all while mounted on a machine tool
• First Article Inspection: Review pre-production samples and compare against nominal data
• Alignment: Align tools and fixtures to the correct orientation
• Reverse Engineering: Capture unique details on a part with the arm or laser line scanner to create
• CAD models for fabrication or digital documentation

Articulating Arms vs Other Measurement Methods

For hundreds of years, engineers used hand measurement tools such as micrometers and Vernier calipers to capture dimensions on parts. However, due to their mechanical simplicity, hand tools could only provide basic measurements such as widths, lengths, and thicknesses. If we need to measure complex dimensions such as form (flatness, circularity, etc.) or hole-to-hole, manual measurements will be more time-consuming. Although they provided the best accuracy and precision at the time, hand tools often required skilled operators as manual measurements were always susceptible to human error.

Coordinate measuring machines were then introduced in the 1960s. Main users were machinists and engineers. They  need to capture various geometries and measurements with higher accuracy than with hand tools. Fixed CMMs typically consist of a measurement bed, a measurement probe (fixed to a bridge), a computer and measuring software to program the measurement probe. The probe can only move in three axes and only travel within the extent of the CMMs
measurement bed. With the advancement of technology, manufacturers crated articulating arm to provide the same functionality as a fixed CMM, but with portability and flexibility as well. Though articulating arms
may not have as fine an accuracy as fixed CMMs. They are lightweight (10 kilos or less), simple to operate, and far less expensive than a fixed CMM, all while providing the necessary accuracy for a wide variety of measurement applications.

Summary

Articulating arms combine the efficiency, reliability and accuracy of a traditional CMM with the portability and simplicity of hand tools. With the addition of a laser line scanner, parts that were once considered
sophisticated or complex can now be easily inspected with an arm. Reduced scrap, faster inspections, less defects and an improvement in product quality. These are just some of the many benefits a company will experience when they implement measurements with articulating arm for inspection and manufacturing needs. These benefits ultimately result in a significant return on investment for a company.