Thomas Industrial Library

Modern Measurement Technology

The high degree of mechanical precision built into products for the survival and comfort of humans has reached a point where it is possible to:

• Travel into space and view the universe; send messages and images around the world in the matter of seconds; and bounce radar waves off neighboring planets.

• Fly at speeds and match the earth’s rotation; harness pent-up energy that took nature millions of years to store and release it in a flash.

All of these things, and many more, are the result of human’s ingenuity in the harmonious functioning of mechanical parts through Dimensional Quality Control. It is the key to precision measurement, the very access around which the modern age revolves.

In the last half of the 20th century, the need to produce high-quality, reliable products, at a reasonable cost has resulted in the development of better-quality machine tools and with them better-quality measuring tools to match their accuracy. It is as easy to measure within .000020 millionths accuracy now as it was to measure within .001 in. in the 1940’s. This is the result of the constant improvement in measuring tools since then. A few of the notable improvements have been:

• The application of digital readouts to micrometers, dial and vernier caliper, height gages, indicators and many other tools, Fig. 6-9.

· This speeds up the measurement process and eliminates the common error of misreading a measuring tool.

• Linear scales, encoders, and digital readouts on machine tool slides, Fig. 6-10, makes the setting of a cutting tool or workpiece to exact positions a simple, yet very exact operation.

· The Moiré Fringe Pattern, incorporated in many linear scales, is an electrical-optical system that counts moiré fringes to produce a resolution accuracy of .0001 in. (0.002 mm).

· This addition to machine tools eliminated many operator errors and resulted in better quality parts with less scrap.

• Coordinate Measuring Machines (CMM)

an advanced, multipurpose quality control system used to quickly and accurately measure (inspect) parts produced during a production process, Fig. 6-11.

· It consists of an indicating probe supported on three perpendicular axes that can show a digital readout of any dimension of a part to within .000020 in. accuracy.

· Newer model CMM machines use noncontact triangulation, in combination with a fiber-optic system, to measure part dimensions and forms.

• In-Process Gaging - A system that can use snap-on gages, indicators, probes, lasers, and optical devices to measure a part while it is being manufactured, Fig. 6-12.

· Contact measuring tools such as snap-on gages and indicators must contact the section of the part to be measured.

· Noncontact measuring tools such as lasers and optical devices do not contact the part and measure during the manufacturing process.

· On CNC machine tools, these measuring tools can make adjustments to the cutting tool position when a part nears its tolerance.

• Laser Measuring Devices - Laser-equipped measuring tools are used in gaging and inspecting parts while they are being manufactured and they can adjust the machine tool automatically to .000020 to .000080 in. accuracy, Fig. 6-13.

· They are capable of doing what quality control standards require; perform 100% inspection with 100% accuracy at full production speeds.

· Laser scanning probes used on CMMs can scan contoured surfaces 50 times faster than conventional probes.

• Vision Systems - Combine Artificial Intelligence technology with computers, software, television cameras, and optical sensors to allow machines to do jobs normally performed by humans.

· Triangulation-type optical scanners used on CMMs can accurately measure the distance between the probe and the surface of the part, and an optical sensor completes the three-point dimensioning, Fig. 6-14.

· This is similar to the Global Positioning

System (GPS) that is available in some automobiles to indicate the position of a car anywhere on earth. It uses three satellites to transmit information to a receiver in the car that can translate the information into locational data.