Laser sensors are used in various fields of application for industrial automation. The variety in application areas entails a demand for different types of laser sensors. There are applications for detections, measurements or positioning. What different laser sensors have in common are the advantages that the use of laser light provides. A first advantage is the high light intensity, which enables very accurate measurement, positioning or detection (down to nanometers). Another advantage is the measurement speed; this is very high due to the use of light as a medium.
Different types of sensors that work on the basis of laser light are:
- Laser distance sensors
- Displacement sensors
- Laser projectors
- Laser light curtains
- Laser photoelectric sensors
- Positioning lasers
- Laser edge detection sensors
Below we will discuss the different laser sensors with an explanation of their workings and usability in different applications.
Laser distance sensors
Laser distance sensors measure distances and allow it to take measurements at great distances. These distance sensors work on the basis of the Time-Of-Flight (ToF) principle, which means that the sensor emits a laser beam and receives the reflection from it. The time that elapses between sending and receiving the laser light ensures that the laser distance sensor can internally determine the distance. The distance over which the measurements can be taken differs per series.
For example, there is the LAM 300 series, from Sensor Partners, with a measuring range of up to 3000 meters! Applications for these types of sensors are: Level measurements in silos, flow optimization in warehouses and the mooring of ships in container terminals. The sensor accurately calculates what the distance to a certain object is and ensure that for example a silo is not filled further than a predefined maximum. Several laser distance sensors are available in ATEX version, so that they can be used in environments with a risk of explosion due to the presence of gas and/or dust in the air.
These sensors are not so much aimed at measuring distances, but at detecting objects and/or people within a certain range. An example of this type of laser sensors is the L-LAS-LT-130-SL with a measuring range between 50 and 210 mm. The sensor emits a laser light beam and receives a reflection from a passing object, allowing it to judge the received reflection as a detection.
With regard to applications, one can think of counting bottles that are supplied on a conveyor belt so that the supply speed can be adjusted. This prevents build-up on the accumulation belt.
Displacement lasers are much more versatile in applicability. These sensors can serve in thickness measurements of, for example, steel plates, profile measurements of shape-specific products and the positioning of materials over a conveyor belt.
These are lasers that can provide a laser projection onto a desired surface. The projection is used to determine margins and dimensions or just a positioning within an application. The explanation about the operation and usability of the laser projector is an entire article in itself.
The laser projector is useful in several industries such as automotive, textile or electronics. The ZLP1 laser projector from Z-Laser has been used, for example, in the production of the body of the Audi R8. The projection lasers can be used for positioning purposes, such as to guarantee correct attachment of components.
Laser light curtains
These lasers consist of a transmitter and a receiver. There is a barrier of parallel laser beams emitted between these. Objects that pass through these are not only detected, but also measured.
For example, the L-LAS-TB-CL series consists of laser light grids that are used for determining diameters, positioning or web edge control. Think of detecting deviations in the diameter of PVC pipes on a conveyor belt.
Laser photoelectric sensors
These laser sensors are very suited in their own areas of application where processes are carried out at high speeds, such as counting or detecting products. The photoelectric laser sensors, also known as trigger sensors, are unique because they are capable of performing detections at high speeds. These laser sensors have a switching frequency of up to 300 kHz. Because of this, these laser trigger sensors are used in applications such as counting the chain rings on bicyle chains in high volumes at high speeds on a conveyor belt.
In such applications, the trigger sensors can be configured not only as a counting sensor, but also as a trigger that ensures that another sensor does not have to constantly detect and only has to work when something has actually been detected. The photoelectric laser sensor “activates” the other sensor in this. The operation is comparable to most laser sensors: a laser light is emitted and the sensor detects a detection based on a reflection from an object. Furthermore, the photoelectric laser sensors come in different designs: fork-, cube- and cylinder-shaped.
Another common application that can be considered with these sensors is that in which a printed line on embossed paper must be continuously inspected for deviations.
These laser are used in several application as a visual tool for the positioning of and on products. Think of the positioning of a wood saw over a tree trunk to cut it in a straight line. In addition, these lasers also serve for positioning, for example, screws to be attached. For example, the ZM18 series from Z-Laser consists of positioning lasers in the colors green, red and infrared that can project the laser light in different shapes: dot-, line-, and cross-shaped..
The operation of these laser sensors is different from most. Namely, the positioning lasers transmit a projection and do not receive or process any further reflection.
Laser edge detection sensors
The RED-series of Sensor Instruments consists of edge detection sensors that are used for inline detections and counting one side of a product or object. The sensors are mounted in the production line and perform the counting from the side. This laser also works with an emitted laser light and a processing of the received reflection from the material.
These sensors are often used in application areas where (thin) sheets and plates of different materials (paper, cardboard, iron, etc.) must be detected on the basis of thickness in order to limit accumulations and production errors. For example, the RED-110 recognizes a transition difference between materials of no more than 0.1 mm! The sensor is also equipped with software that is optimized in such a way that it is insensitive to differences in contrast and gloss of the object to be detected.