In this article we will discuss what laser light grids are, how it works, the line laser of the laser light grid and what the laser curtain can be used for.
What is a laser light grid?
The emitter part of the laser light grid sends out parallel laser beams that from a laser light barrier. These laser beams then shine on a line sensor on the receiver side. An object will partially or completely obstruct the laser light barrier which because of that will not reach the receiver. The amount of obstucted beams is used to measure.
Think of a plastic foil that moves through the field between the transmitter and receiver. In this application specifically, the transmitter and receiver must be positioned so that the foil is within a range of 50 mm. The laser curtain can then detect the position and presence of even transparent films.
The operation of a laser light grid
An object in the laser curtain makes it possible that a part of the laser curtain is not received by the receiver part. The parallel laser beams allow the object to cast a shadow on the receiver. The transmitter and receiver can be used as separate modules or in a complete form in a U-shape mounting.
Part of the laser light is interrupted by the presence of the foil from the previous example. The interrupted part does not reach the recipient. This part perceives the sensor as the foil.
The line laser of a laser light grid
The line sensor consists of hundreds of small light-sensitive cells, so-called pixels. The laser light that falls on pixels ensures that these pixels emit an intensity signal. Pixels that do not receive laser light do not emit a signal. In case a pixel is half exposed, it also emits a half intensity signal. The intensity signals of each pixel are converted by the sensor processor into a video signal. This video signal is used to set a threshold value. Where the video signal crosses the threshold represents the edge of an object in the laser curtain.
With one edge it is possible to use it as a position. Two edges make it possible to measure a diameter. With three or four edges it is possible to also measure the distance between two objects. The measurement accuracy starts from 2 μm, depending on the measurement range of the set. The L-LAS-TB laser light curtain sensors are available with a measurement range in height between 8mm and 98mm.
It is possible to transfer these signals through RS-232, Ethernet, usb or via an analog output to the controller. It is also possible via digital outputs to let the sensor control whether an object falls within or outside the set tolerances.
Applications for laser light grids
Determining diameter and position
Measure diameters, positions or distances from or between objects very accurately. Diameters or widths of objects can be measured within the range of the sensor, but can also be measured by means of two sensors.
Measuring casting molds in the automotive industry
Consider, for example, the diameters of molds in the automotive industry. These molds are used to produce the turbo. The laser curtain helps control the diameter of the turbo by passing it between the transmitter and receiver. The interrupted laser light allows the sensor to determine the diameter very precisely. This guarantees the quality of the parts because they meet the desired diameter.
Width-inspection of roll materials
The same can be done for objects whose width needs to be checked. Think of adhesive tape. The adhesive tape is fed continuously between the transmitter and receiver. The smallest deviations can be detected, so that only well-cut pieces can be rolled up into a roll of adhesive tape.