Laser displacement sensors offer reliable, fast and high-precision non-contact measurement of distance, displacement and position of objects. They have been used for measurement in industrial environments for quality control, monitoring and process automation. There are two types of laser displacement sensors; triangulation laser sensors, which offer a high precision measurement and measure at shorter distances and long-range laser sensors which use the time-of-flight measuring principle. The main advantages of integrating distance laser sensors in the industrial measurement system are their versatility to measure on almost all types of objects, including measurement on matt, metallic, shiny and reflecting surfaces. Laser sensors can also be easily integrated into existing industrial communication systems for automation and monitoring applications. Therefore, it has been used for measurement in challenging environments such as in high-temperature environments or in applications where space is limited or restricted. Examples of applications include:
- Diameter monitoring on rolled rings
- Distance measurement in robot positioning tasks
- Fill-level measurement of bulk solids
- Structural Health monitoring applications, ie: measuring deformation on lightweight structures, monitoring the deflection of concrete ceilings etc.
There are currently two technologies used in laser displacement sensors; Red and Blue laser sensors. Although red lasers have been successfully used in almost all measurement applications, there are certain conditions where blue laser sensors offer a better solution. Selecting between red or blue laser technology depends on whether the laser can generate a focussed beam reflected by the optics for accurate measurement.
Blue and Red laser Technology
Red laser sensors use a red laser diode that operates at 700nm in the visible spectrum to generate a laser beam. They are the favoured technology due to their high sensitivity and high intensity which make them ideal to measure objects that are dark, lowly reflected or fast-moving. It generally performs well under most applications, except in a niche situation when accuracy cannot be compromised. In some applications, the red laser may diffuse on the target surfaces and create measurement errors due to the lack of focus.
The blue laser sensor uses a blue laser diode to emit a light beam in the wavelength range of 400nm to 500nm. The light beam produced by a blue laser is temporally coherent and can be well-adjusted accurately at the line of sight, allowing it to have numerous applications in industry and science. Characteristics of different blue lasers are predominantly determined by the gain media used and their corresponding properties. Due to its shorter wavelength, the blue laser does not penetrate as far on the target surface, compared to the red laser. Therefore, it generates a more stable, more focused beam to ensure accurate measurement on diffusing and challenging surfaces such as woods, plastics or red-hot glowing metals. This has opened the possibility of measurement applications where red laser sensors are not suitable.
Blue laser sensors were originally designed for the steel industry to measure red-hot glowing metals. They have also been used for brake disc deformation testing in the automotive industry and for measuring vibration on exhaust manifolds. Red lasers are not readily suitable for this measurement as a red-hot glowing target object emits high-intensity light at a wavelength similar to that of a red laser. This will mask the measurement and generate a false signal to the detectors, resulting in inaccuracy and measurement error.
When blue laser sensors are used for the above-mentioned applications, the measurement errors are eliminated as blue lasers operate at the opposite end of the visible light spectrum. Therefore, it will generate stable and accurate results, unaffected by the object’s temperature. In addition, blue laser sensors have also been successfully used for the measurement of transparent or translucent materials due to their shorter wavelength characteristics.
The availability of red and blue laser sensors has provided a wide range of options for engineers to choose from in designing their measurement systems. Furthermore, these sensors can also be used for measuring 2-D and 3-D profiles of objects. Selecting suitable sensors can be confusing due to the vast range of products available and the requirement of your projects. For instance, you must know the characteristics of target surfaces where the sensors measure, whether the surface reflection changes during operation, will the object move when measurement takes place and what level of accuracy is needed.
At Bestech Australia, our experts can assist you to streamline the selection process and choose the ideal sensor for your measurement applications. We are an authorized partner of Micro-Epsilon in Oceania and provide measurement support for the application of non-contact laser displacement sensors for industrial tests and measurement tasks. We can also offer special-version non contact displacement sensors for specialized applications and custom designs that are adapted to the customer’s specifications.
