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The magical working principle of CMM: How to measure objects with micron-level accuracy?
With the advancement of science and technology, three-dimensional coordinate measuring machines (CMM) have become an important tool for manufacturing and engineering measurement. This device can measure the geometry of an object with micron-level accuracy, acquiring data by sensing discrete points on the object's surface. This article will explore the operating principle, main components and application of CMM in modern industry.
Basic principles and composition
The working principle of CMM is based on the precise movement of its probe in three-dimensional space (XYZ axis). The probe can be manually operated or controlled by a computer, which makes the measurement results more reliable. Typically, the main structure of a CMM is a "bridge" design, allowing the probe to move freely on three orthogonal axes.
Whenever the probe touches a point on the object surface, the machine samples the position sensor of each axis to obtain the three-dimensional coordinates of the point.
After acquiring data from multiple points, CMM will generate a "point cloud", which can describe the surface characteristics of the object. Whether it is manual operation, automatic computer control, or through pre-written programs, CMM can complete these measurements efficiently.
Technical features and precision
CMM usually consists of three main parts: body, probe system and data collection system. Modern CMMs are mostly made of materials such as aluminum alloy, ceramics or black granite to improve the rigidity of their structure and reduce errors during the measurement process. The accuracy of a CMM is defined as an uncertainty factor, usually at the micron level.
A CMM equipped with a contact probe can make repeated measurements with an accuracy of one micron or less.
Research shows that with the development of technology, the application scenarios of CMM have gradually expanded to more diverse fields, such as medical equipment, aerospace and automobile manufacturing.
Various probe technologies
CMM uses a variety of probes for measurement, the most common being mechanical trigger probes and laser probes. Early mechanical probes were usually made of a hard sphere welded to a long rod, a design that allowed them to measure flat and round surfaces. With the advancement of technology, electronic trigger probes have gradually replaced them, which can automatically record three-dimensional coordinates when the probe comes into contact with an object.
The emergence of optical probes and laser probes not only improves the accuracy of measurement, but also speeds up measurement because they can measure without touching the object.
The new scanning probe system is able to slide across the surface of an object while taking points at specified intervals, a method considered more accurate than traditional contact probe measurements.
The rise of portable measuring machines
Most traditional CMMs are fixed, while portable CMMs use articulated arms or armless scanning systems so that they can move randomly and be used in various environments. Portable CMMs, which typically weigh less than 20 pounds, are lightweight and easy to operate, making them ideal for non-repetitive applications such as reverse engineering and rapid prototyping.
Standardization and future development
There are special ISO 10360 series standards for CMM performance verification. These standards define the characteristics and measurement errors of the probe system and ensure the reliability of the measurement. In the future, with the development of automated measurement technology, CMM will likely be combined with other measurement technologies to become a multi-sensor measurement device.
Overall, CMM is not only a basic technology in the manufacturing field, but also a leader in the development of modern engineering measurement. It has shown irreplaceable value in different industries. How will CMM meet new challenges and opportunities in the future and continue to promote innovation in measurement technology?
