Measurement is an important part of manufacturing, and high precision is crucial. Assembly lines operate in a sequence, and the deviation of even a millimeter can compound errors. For this reason, measuring machines are used over conventional instruments like calipers and gauges.
Enter the technology of computer-based measurement. Measuring machines like VMMs and CMMs optimize manufacturing by simplifying 3D measurements. They are versatile instruments that can measure angles, curvatures, and distances. However, they differ in their capabilities. By the end of this article, we will give you a wholesome understanding of the ins and outs of measuring machines.
What is a VMM?
Vision Measuring machines (VMMs) are optical measuring instruments. They are compact and ideal for measuring small objects. VMMs analyze an object without touching it, thereby providing contactless measurements.
The main component of a VMM is its vision sensor, which includes a camera and an optical lens. In addition, there are the laser and touch probes. The laser probe is used for measuring transparent and semi-transparent objects. The touch probe enables the measurement of 3D distances. VMMs capture an object’s image with a camera and use computer software to generate a 3D model. The operator uses this to measure distances.
VMMs report linear attributes like points, lines, and angles. They measure geometrical attributes like straightness or flatness. They are also called video-measuring systems or image-measuring systems.
What is a CMM?
Coordinate measuring machines use mechanical probes and computer software to analyze objects. They can measure angularity, circularity, and distance. They are larger than VMMs. The working area is a granite stage suitable for heavy objects. Over this extends a bridge to which the contact probes are attached.
CMMs analyze objects by touching various points through probes. These coordinates are then converted into a CAD model. Using computer software, this model is measured to reveal the distances on the object.
The Main Differences Between VMM and CMM
Both VMM and CMM quantify an object’s geometric features. However, they have some key differences. Let us evaluate some key aspects that contrast vision and coordinate-based measuring machines.
Measuring Methods
VMM
VMMs use optical metrology to measure an object’s dimensions. The main sensing component is a vision sensor, composed of a camera and an optical zoom lens. Additionally, a VMM has a laser probe and a touch probe. The camera takes a picture of the object, which is then analyzed using computer software.
CMM
CMMs, on the other hand, use tactile probes as their main sensing component. These probes touch the object at the points that need to be measured. Using the coordinates of the points that the probe touched, a 3D model is created. This 3D model is used to measure distances on the object. CMMs have a larger stage than VMMs, therefore they can assess larger and heavier parts.
Precision and Accuracy
VMM
Since VMMs utilize optical lenses and computer software tools. They offer a high level of precision in measuring small objects. They can measure distances with up to an accuracy of 0.25 microns. They offer features like automatic edge detection, tracking, autofocus, and light adjustment tools.
CMM
CMMs also offer high precision compared to conventional metrology. They can measure distances with an accuracy of 2 to 5 microns. They can be operated with the cartesian, cylindrical, and spherical coordinate systems.
Suitability of Part Types
VMM
They are used in industries where precise measurements are essential. The main sectors are electronics, manufacturing, mechanical and plastic. The stage area of a VMM is under one foot. Therefore, it is only suitable for small parts. Commonly used parts include screws, gears, molds, rubber, soft components, PCBs, springs, etc.
CMM
Because CMMs have a large stage area, they are suitable for measuring big industrial parts. They are widely used in the aerospace and automotive industries to calculate the parameters of machine parts. CMMs are excellent at measuring parts like automobile prototypes, CNC fixtures like spindles and rams, and heavy machine components.
Cost and Maintenance
VMM
VMMs are generally affordable. They are easier to maintain because of their smaller working parts. They require a small initial investment. However, their price is influenced by factors such as the VMM’s movement mode, sensor type, software functionality, and hardware configuration.
CMM
They require a higher initial investment than VMMs. They are also bulkier and have complex moving parts. For this reason, maintaining them can prove challenging. CMMs require a trained operator to work them. Factors such as professional training, work hours, and shift timings may influence the cost of operating a CMM. Other cost factors may include licensing fees, calibration costs, and replacement of probe tips.
Choosing the Right Machine
Want to know which one is right for you? Start by asking yourself these questions:
- Think in terms of space. Is your workshop large or small? CMMs are big and might be unsuitable for small workshops. VMMs, on the other hand, are compact machines. If you are working in a small area, they are the ideal choice.
- How many parts do you need to process in a day? Many workshops process large quantities of parts daily. In this case, a VMM may be ideal for you. However, if you work with fewer parts, CMMs will suit you well. CMMs are also better at analyzing objects of varying sizes.
- The type of workpiece you want to measure also determines your needed machine. If you measure 3D objects, an image-measuring system cannot perform the necessary operations. This is because a VMM’s strength lies in its high resolution, which allows it to generate accurate 2D images.
- Do you want extreme precision down to a micron level? In that case, VMMs might suit you better. While both machines are excellent, VMMs provide precision of up to 0.25 microns.
- Are the parts that you measure fragile or moldable? In that case, opt for the VMM. They are non-contact machines. They can measure moldable objects, whereas CMMs cannot.
Conclusion
Whether you go for VMMs or CMMs, both are high-performing metrological instruments. They are guaranteed to accelerate your manufacturing process. Choosing the right machine will optimize your measuring and design pipelines. While both of them have similar functions, they have widely different applications. For a faster work rate, higher precision, and small objects, go for VMM. For versatility, 3D mapping, and heavy parts, go for CMM. If you remember the key points we shared in this article, buying a measuring machine will be smooth and easy.
About MXP
MXP is a leader in vision measuring instruments. We provide efficient, reliable, quality inspection solutions using advanced optical tech and precise measurement systems. Contact us now.
Each MXP visual measuring instrument has a high-resolution camera and professional software, ensuring a perfect balance of accuracy and speed.
