Coordinate-measuring Machine
Introduction
A Coordinate-measuring Machine (CMM) is a device used in manufacturing and assembly processes to measure the physical geometrical characteristics of an object. This machine can be manually controlled by an operator or it can be computer-controlled. Measurements are defined by a probe attached to the third moving axis of this machine. Probes can be mechanical, optical, laser, or white light, among others.
History
The development of CMMs dates back to the early 1960s. The first CMMs were developed by Ferranti in Scotland. These early models were manually operated and had only two axes. By the late 1960s, the Italian company DEA introduced the first three-axis CMM. The advent of computer technology in the 1970s allowed for the automation of CMMs, significantly increasing their accuracy and efficiency.
Types of Probes
CMMs utilize various types of probes to capture measurements. The most common types include:
Touch Trigger Probes
Touch trigger probes are the most widely used in CMMs. They operate by physically touching the part to be measured. When the probe contacts the part, it sends a signal to the computer to record the coordinates.
Scanning Probes
Scanning probes continuously contact the part and send a stream of data points to the computer. These probes are useful for capturing complex surfaces and contours.
Optical Probes
Optical probes use light to measure the part. They are non-contact probes that can be used to measure delicate or soft materials without causing damage.
Laser Probes
Laser probes use a laser beam to measure the part. They are also non-contact and are particularly useful for measuring large parts or parts with complex geometries.
Components of a CMM
A typical CMM consists of the following components:
Frame
The frame provides the structural support for the CMM. It is usually made of granite or steel to ensure stability and minimize thermal expansion.
Bridge
The bridge is the moving part of the CMM that holds the probe. It moves along the X, Y, and Z axes to position the probe at the desired measurement points.
Probe
The probe is the measuring device attached to the bridge. It can be a touch trigger, scanning, optical, or laser probe.
Controller
The controller is the computer system that processes the data from the probe and controls the movement of the bridge.
Software
CMM software is used to program the measurement routine, process the data, and generate reports. The software can also be used to create a CAD model of the part being measured.
Measurement Techniques
CMMs use various measurement techniques to capture the dimensions of a part. These techniques include:
Point-to-Point Measurement
In point-to-point measurement, the probe touches specific points on the part to capture their coordinates. This technique is useful for measuring simple geometries.
Scanning Measurement
In scanning measurement, the probe continuously moves along the surface of the part, capturing a stream of data points. This technique is useful for measuring complex surfaces and contours.
Non-Contact Measurement
Non-contact measurement techniques, such as optical and laser probing, are used to measure delicate or soft materials without causing damage.
Applications
CMMs are used in various industries for quality control and inspection. Some common applications include:
Aerospace
In the aerospace industry, CMMs are used to measure the dimensions of aircraft components to ensure they meet strict tolerances.
Automotive
In the automotive industry, CMMs are used to measure the dimensions of car parts, such as engine components and body panels.
Medical Devices
In the medical device industry, CMMs are used to measure the dimensions of implants and surgical instruments to ensure they meet stringent quality standards.
Electronics
In the electronics industry, CMMs are used to measure the dimensions of circuit boards and other electronic components.
Advantages of CMMs
CMMs offer several advantages over traditional measurement techniques:
Accuracy
CMMs provide highly accurate measurements, often within microns. This level of accuracy is essential for ensuring the quality of manufactured parts.
Efficiency
CMMs can quickly measure complex geometries, reducing the time required for inspection.
Flexibility
CMMs can be programmed to measure a wide variety of parts, making them versatile tools for quality control.
Automation
CMMs can be automated to perform measurements without human intervention, reducing the potential for human error.
Challenges and Limitations
Despite their advantages, CMMs also have some challenges and limitations:
Cost
CMMs can be expensive to purchase and maintain, making them a significant investment for manufacturers.
Complexity
CMMs require skilled operators to program and operate, which can be a barrier for some companies.
Environmental Sensitivity
CMMs can be sensitive to environmental conditions, such as temperature and vibration, which can affect their accuracy.
Future Trends
The future of CMM technology is likely to be influenced by several trends:
Integration with Industry 4.0
CMMs are expected to become more integrated with Industry 4.0 technologies, such as the Internet of Things (IoT) and Artificial Intelligence (AI). This integration will enable real-time data collection and analysis, improving the efficiency and accuracy of quality control processes.
Advances in Probing Technology
Advances in probing technology, such as the development of new types of probes and improved sensors, will enhance the capabilities of CMMs.
Increased Automation
The trend towards increased automation in manufacturing is likely to drive the development of more advanced and autonomous CMMs.