Introduction
In the field of surface topography analysis, roughness measurement is a critical part of evaluating the surface quality of a workpiece. Choosing the right measuring instrument is crucial to ensure data accuracy and suitability. At present, stylus and laser are two mainstream roughness measurement technologies, and there are significant differences in their working principles, performance characteristics and application scenarios. This article will systematically compare the two technologies from the aspects of technical principles, key parameters, applicable standards and selection considerations, aiming to provide a selection reference for professionals in related fields.
How it works:
The stylus roughness gauge performs a contact scan of the workpiece surface with a diamond stylus. The vertical displacement of the stylus is converted into an electrical signal by the sensor, which reconstructs the surface profile. Its measurement is directly dependent on physical contact and generally follows the definition of the contact profile method in standards such as ISO 4287 and ASME B46.1.
The laser roughness measuring instrument adopts the principle of non-contact optics. A beam of laser is focused on the surface being measured, inverting surface height information by detecting spot position, intensity, or phase changes in reflected or scattered light. Common techniques include laser triangulation, confocal microscopy, etc., and their methodologies often refer to the section of the ISO 25178 series on non-contact 3D surface measurement.
Comparison of key parameters
The following table summarizes the key features of both technologies from multiple dimensions.
| Measurement principle | Physical contact scanning |
| Optical non-contact detection | |
| Lateral resolution | Depends on stylus tip radius (typically 2 μm, 5 μm, etc.) |
| Depending on the laser spot diameter (sub-micron possible) | |
| Vertical resolution | Usually down to the nanometer |
| It can reach the nanometer or sub-nanometer level | |
| Measure speed | Relatively slow, limited by mechanical scanning |
| Faster and can perform area scanning | |
| Effect on samples | May scratch soft or sensitive surfaces |
| There is basically no physical impact | |
| Applicable surfaces | Most solid materials are not suitable for soft, sticky or damaging surfaces with needle tips |
| Most materials, but may require special treatments for highly reflective, transparent, or light-absorbing surfaces | |
| Typical standard | ISO 4287, ASME B46.1 |
| ISO 25178 |
Selection considerations
When choosing a measurement method, the following factors should be evaluated comprehensively:
Characteristics of the tested sample:The material's hardness, brittleness, reflectivity, transparency, and whether the surface allows contact are the primary considerations. For scratch-prone or flexible samples, non-contact is more suitable.
Measurement parameter requirements:If traditional 2D profile parameters (e.g., Ra, Rz) need to be strictly followed, the stylus method is widely accepted. If 3D area parameters (e.g. Sa, Sz) or fast area scanning are required, the laser type is more advantageous.
Measurement environment:Stylus is relatively sensitive to ambient vibrations, while some laser instruments may require ambient light or cleanliness.
Data traceability and standards compliance:In specific industries, such as precision manufacturing, quality control may explicitly require the use of methods and data that meet specific contact measurement standards.
Technology development trends
Both technologies are constantly evolving. The stylus instrument continues to improve in terms of reducing force measurement and improving scanning efficiency. Laser and other optical technologies have made significant progress in improving the adaptability to complex material surfaces, measurement speed, and data processing algorithms. Hybrid measurement systems are also starting to emerge to combine the advantages of different technologies.
Conclusion
Both stylus and laser roughness measuring instruments have their own clear areas of application and limitations. The stylus type has the advantages of high standard compliance and direct measurement in the measurement of two-dimensional contour parameters. The laser type excels in non-contact, fast 3D measurement and fragile surface inspection. The fundamental reason for the selection is to match the characteristics of the measurement technology to the characteristics of the workpiece to be measured, the specific parameter requirements and the technical standards to be followed. It is recommended that users conduct sufficient sample testing and method verification before selection.
References
1. Working principle part: refer to the definition of measurement methods in the international standards ISO 4287 and ISO 25178.
2. Comparison of key parameters: synthesize multiple instrument technology white papers and discussions on measurement technology comparison in academic journals.
3. Selection considerations: The recommendations on the selection of measurement methods in the application guidelines issued by various standards bodies are cited.