How Do Optical Reflex Sensors for Object Detection Work?
Which Technologies Are Used in Reflex Sensors?
Reflex Sensors with Background Suppression
Check reflex sensor with background suppression whether the object is below the set switching distance. Objects that are further away from the sensor are hidden as the background. The switching point for reflex sensors with background suppression is almost independent of the remission properties of the object. The wenglor portfolio includes reflex sensors with background suppression that work according to the triangulation or time-of-flight principle:Triangulation (Electronic)
In electronic triangulation as a method of background suppression, the light emitted by the object is mapped to a receiving element in the sensor, e.g. to a PSD. The position of the light spot on the receiving element is evaluated electronically.
Triangulation (Mechanical)
If the receiving element is mechanically moved with an external adjustment screw so that the light spot hits the receiving element in the sensor (e.g. double diode) at the desired switching distance, this is referred to as mechanical triangulation. The switching distance can only be set via the control element (multi-turn, single-turn).
Time-of-Flight Principle (ToF)
The time-of-flight principle uses the constant light velocity property to check whether the object is below the set switching distance. For this purpose, the sensor sends continuous light pulses that are reflected by the object. The phase shift of the transmitted and received signal is then determined. A weighted average is calculated for a larger light spot.
Energetic Reflex Sensors
Energetic reflex sensors use the light intensity reflected by an object as a signal. The switching threshold is set accordingly to a desired signal value. In addition to the distance, the switching point also depends on the remission properties of the object. This is because the material, color, gloss or structure determine the factors of the received light intensity.Which Principle Is Best Suited for What?
Background Suppression with Triangulation Principle
| Precise detection of objects even at a short distance from the background |
| Detection of small objects |
| Object detection up to 1,200 mm |
| High switching frequency and short response times |
| Different light sources, designs, operating concepts |
Background Suppression According to the Time-of-Flight Principle (ToF)
| Presence check of objects at high detection range |
| Material-independent detection, including black and shiny objects |
| Object detection up to 2,500 mm |
| High ambient light resistance |
| Insensitive to interferences such as dust and contamination |
Object Detection Using the Energetic Principle
| Presence check for standard applications |
| Detection range depending on the remission properties of the object |
| Object detection up to 700 mm |
| Sorting tasks, such as distinguishing between light and dark objects |
| Special light spot dimensions, e.g. reflex sensors with line |
In addition to switching reflex sensors for object detection, wenglor offers a wide portfolio of optical laser sensors for distance measurement.
Broad Range of Applications for Each Functional Principle
Precise Background Suppression with Triangulation
Presence Detection of Packaging on Conveyor Belts with Reflex Sensors with Background Suppression
Packaging made from different materials must be reliably detected from the front edge on conveyor lines before and after filling. Reflex sensors with background suppression are installed at several points above the conveyor belt. Thanks to the laser sensors with high switching frequency and small spot, the edges of the objects are detected quickly and precisely. The background suppression ensures reliable switching behavior despite different backgrounds.
Packaging made from different materials must be reliably detected from the front edge on conveyor lines before and after filling. Reflex sensors with background suppression are installed at several points above the conveyor belt. Thanks to the laser sensors with high switching frequency and small spot, the edges of the objects are detected quickly and precisely. The background suppression ensures reliable switching behavior despite different backgrounds.
Interference-Proof Background Suppression at Long Distances with Time of Flight
Presence Check of Wooden Panels via Reflex Sensors with Background Suppression
In the wood industry, wooden panels of different colors, shapes and surfaces are transported from one processing step to the next by chain conveyors. Several reflex sensors with background suppression mounted above the conveyor line ensure the presence of the panels. Thanks to their large detection range and the enlarged light spot, the sensors detect a wide variety of wooden panels, even panels with dark spots, grains or damage are reliably detected.
In the wood industry, wooden panels of different colors, shapes and surfaces are transported from one processing step to the next by chain conveyors. Several reflex sensors with background suppression mounted above the conveyor line ensure the presence of the panels. Thanks to their large detection range and the enlarged light spot, the sensors detect a wide variety of wooden panels, even panels with dark spots, grains or damage are reliably detected.
Presence Check of Objects with the Energetic Principle
Presence Check, Stack Height Checks or Counting Tasks with Energetic Reflex Sensors
In order for hot water in coffee machines to be pressed evenly through the coffee capsules and thus ensure a uniform taste, wafer-thin white nonwoven fabric must be inserted into the capsules. Once the coffee powder has been poured into the capsules and the nonwoven fabric has been placed on it, energy reflex sensors check the presence of the nonwoven fabric. Mounted above the conveyor belt, they reliably detect the difference between the darker coffee powder and the white nonwoven fabric – even at high belt speeds.
In order for hot water in coffee machines to be pressed evenly through the coffee capsules and thus ensure a uniform taste, wafer-thin white nonwoven fabric must be inserted into the capsules. Once the coffee powder has been poured into the capsules and the nonwoven fabric has been placed on it, energy reflex sensors check the presence of the nonwoven fabric. Mounted above the conveyor belt, they reliably detect the difference between the darker coffee powder and the white nonwoven fabric – even at high belt speeds.
Industries Where Reflex Sensors Are Preferred
Wood Industry
In the wood industry, reflex sensors with background suppression based on the runtime principle, e.g. the P1PH9 sensors, are preferred.
Automotive Industry
Reflex sensors with background suppression based on the principle of angle measurement (triangulation), such as the P1PH sensors, are used in the automotive industry.
Packaging Industry
The reflex sensors with background suppression based on the triangulation principle, such as the P1KH series, solve applications in the packaging industry.
Electronics Industry
P1KT sensors, i.e. energetic reflex sensors, are used in the electronics industry.
Logistics
Reflex sensors with background suppression based on the triangulation principle, such as the P1KH series, are used in logistics.
Food Industry
Energetic reflex sensors, such as the OTII series in hygienic design, are used in the food industry.
Notes on the Correct Installation of Reflex Sensors
Highly Glossy, Reflective and Uneven Objects
Care should be taken to ensure that no direct reflections fall on the receiving optics in the case of highly reflective, shiny or uneven surfaces, as these can impair object detection.
Tip: Avoid direct reflections due to positioning.
Steps, Edges and Recesses
To ensure reliable detection, the light spot must be aligned directly with the object. For variants with a large light spot, make sure that the object is large enough.
Tip: Align the light spot completely to the object.
Object Movement
For moving objects, the movement should be perpendicular to the transmitter/receiver axis of the sensor to avoid direct reflections on the receiver.
Tip: Install the sensor orthogonally.
Background
If possible, align reflex sensors with background suppression to a defined, static background. Ensure that the object is at a sufficient distance from the background in accordance with the switching hysteresis of the sensor.
Tip: Align the sensor to a defined background, such as a static machine part.
