Laser Displacement Sensors

One of the major reasons that these sensors can measure targets with diverse materials and characteristics is that they can perform highly precise, non-contact measurements. The optimal laser displacement sensor can be selected to match the application or target material (such as transparent or glossy targets).

If the target is made of metal or some other hard material that does not scratch easily, it can be measured with a caliper, micrometer, or other such instrument that touches the target directly or with an LVDT or other such contact displacement sensor in an inline situation. However, errors may occur due to the measurement pressure when the target is soft. For delicate targets whose quality is affected by contact, such as wafers, thin films, and sensitive hairline metal surfaces, non-contact laser displacement sensors can be used to measure without worrying about errors and target damage. Since they allow for stable, non-contact measurement even of transparent or glossy surfaces, laser displacement sensors enable a wide range of possible applications.

Accurate device positioning is necessary for the automation of processes such as coating, welding, and component mounting. The compact, lightweight head of KEYENCE’s multi-colour confocal method laser displacement sensor can be easily installed on devices and accurately determines the distance to the target, allowing for highly precise position control without sacrificing device operation.

Separating the spectroscope unit and leaving the lens as the only key part in the head has given the CL-3000 confocal displacement sensor a compact and lightweight head that can be installed easily in machines. Measurement is performed with light along the same axis, so the heights of narrow gaps in targets can also be measured with no blind spots. Furthermore, the head generates no errors due to heat or electrical/magnetic noise, ensuring stable measurement. For device control, laser displacement sensors can measure target height at high speeds, feeding back this information to control devices. This allows for heights of stepped targets or targets that are slightly tilted during conveyance to be measured in real-time. The result is that quality can be maintained in automatic processes.

When the surface reflectance differs between the glass surface and the pattern surface, tracking errors traditionally occur at the pattern surface when the thickness is measured with laser displacement sensors positioned on each side of the glass. The CL-3000 confocal displacement sensor uses a multi-colour confocal method that measures the position where the projected light is in focus, allowing for stable and highly precise measurement unaffected by differences in the intensity of the light reflected from the target. This minimises the effect of tracking errors, improving the inspection cycle time.

Ensuring advanced, high-accuracy, automatic coating requires not only a sophisticated dispenser robot but also a high-performance displacement sensor that moves together with the nozzle, working as the eye of the dispenser. Installing the CL-3000 Series confocal displacement sensor so that it follows the dispenser nozzle enables nozzle height control through real-time measurement and feedback of the target height. The compact and lightweight head can be installed easily next to the dispenser nozzle and reduces residual vibration when the operation stops. The multi-colour confocal technology uses a coaxial system to provide a wider measurement range and ensures stable height measurement and feedback control without being affected by the transparent, mirror, or glossy surfaces of materials or by shapes such as concaves, differences in height, and inclined or rounded surfaces.

CL-3000 Series confocal displacement sensors can stably measure not only transparent glass but also a wide variety of target materials and shapes with high precision. Of course, the non-contact measurement eliminates the concern of damaging the glass. With the CL-3000 Series, up to six heads can be connected simultaneously to a single controller. For example, the glass's flatness can be checked stably by measuring the four sides and the centre of the glass with a system consisting of one controller and five heads or by measuring six ends with four to six heads. Furthermore, as discussed above, all sensors are compact and lightweight, making them suitable for mounting in narrow spaces or robotic arms. The electronics are kept away from the measurement location in the optical unit, thus providing a stable result that’s unaffected by both heat and electromagnetic noise.

Generally, diffuse reflections occur due to the laser light penetrating the inside of the PCB or its solder mask, which is a lacquer-type material that usually comes in several different colours. The semi-transparent nature of the solder mask paired with different colours could potentially cause diffuse reflections when it is measured with a laser displacement sensor. This may lead to unstable measured values. KEYENCE CL-3000 Series confocal displacement sensors can emit laser light at multiple wavelengths to calculate and measure just the wavelength band of the light that brought the surface of the target into focus. Stable measured values can be obtained with high precision even for PCBs and other such targets easily penetrated by light—glass, silicon wafers, micro lenses, etc. The advantage of this technology is that it can even enable you to measure the surface displacement of a soap bubble without physically affecting the surface.

The purpose of a distance displacement sensor is to measure the amount of movement or displacement of an object concerning the reference point. Thanks to their design, these sensors usually measure displacements in the micron and even nanometre range, with some models being capable of measuring finer than the nanometre range. The purpose of these sensors, at least in the manufacturing sense, is to provide precise measurement of position—a feature that has many applications.
Measuring position can tell us about the object’s movement. For instance, it can be used to monitor machinery operating within a certain range and for quality control. The latter is perhaps the most interesting, as it’s associated with metrology, allowing us to check the product’s exact measurement specifications by measuring displacement.

Several factors play a crucial role in determining the adequate sensor for your application, ensuring the device and its measurement method suit your specific need. Range, resolution, and accuracy are, by far, the most important factors when selecting your displacement measurements.
However, as seen above, not all measurement methods suit all materials, and some sensors are better at scanning certain materials over others. You should also consider sampling speed, especially if you’re measuring dynamic displacement—in which case you’d want a sensor with an adequate sampling speed.

Though they’re both non-contact laser displacement sensors, confocal and laser triangulation sensors operate on fundamentally different principles, which makes them suitable for different applications. Laser triangulation relies on emitting the light onto a surface and measuring the light the surface reflects onto the receiving element. Any changes in the angle of reflected light are proportional to the displacement in the target surface.
Confocal sensors, on the other hand, transmits a variety of wavelengths of lights and looks at which wavelength is in focus on the target surface. As the focused wavelength changes, we can determine the change in the position of the target. However, thanks to their design, which includes a series of optical lenses housed inside a cylindrical tube, confocal sensors tend to be more stable compared to laser triangulation sensors. However they also tend to be slower, giving the edge for high-speed applications to laser triangulation sensors.