反射传感器技术

Functional Principle and Technology of Reflex Light Barriers

The reflex light barriers are part of the photoelectronic sensors and are suited for contactless object detection via LED red light, regardless of color, shape and surface finish. The function of the reflex light barriers is based on a detection method that combines the energy and triangulation principle in one sensor.

The triangulation principle:
The triangulation principle is a geometrical method for determining the distance of an object. With reflex light barriers, the distance between the sensor and the reference background is used as a reference signal.

The energetic principle:
With the energy principle, the intensity of the received signal is evaluated. Reflex light barriers use the light intensity of the diffusely reflected red LED light on a reference background as a reference signal.

Mode of Operation of Reflex Light Barriers

Reflex light barriers use deviations from the reference signal, i.e. changes in distance or light intensity, to detect objects. The sensor transmits or emits light to a static or moving background, such as a conveyor belt. If the light beam is obstructed by an object, a switching process is triggered in the sensor. The only requirement is that any background is within the range of the sensor, which means that the use of a reflector is no longer necessary.

In addition to distance, reflex light barriers also detect the light intensity of the diffuse reflection. This enables detection regardless of object properties such as color or surface finish.

What Is the Difference Between Blind Spot and Minimum Distance?

The blind spot refers to the object to be detected. If an object is in the blind spot, reliable detection is not possible. The minimum distance, on the other hand, defines the lower limit of the range or the permissible distance of the reference background. It indicates the distance at which the background can be placed to the sensor. If the reference background is too close to the sensor, the light will no longer hit the receiving element. This means that correct teach-in of the sensor to the reference background is not possible.

Do Reflex Light Barriers Have a Blind Spot?

Reflex light barriers do not have a blind spot, as they also take into account the change in light intensity to the taught-in reference background in addition to the distance. This means that even an object located directly in front of the optic can be detected, as the light intensity received by the sensor is weakened. However, it should be noted that an object that is at the same distance from the reference background and with identical remission cannot be detected by a reflex light barrier.

Example reflex light barrier P1PM:
Minimum distance of the reference background: 100…1,000 mm on stainless steel (100 mm is the minimum distance between background and sensor, but no minimum distance between object and sensor)
Blind spot: No blind spot due to the two-stage detection principle

Which Teach-In Modes Do Reflex Light Barriers Have?

Both operating modes can be set via IO-Link so that the sensors reliably detect objects against a static or moving background. This allows both modes to be tested in order to optimally adapt the sensor to the application. Setting two separate teach-in modes offers the advantage that extremely flexible and simple teach-in of reflex light barriers is possible. There is also the option of selecting a pre-set variant.

Teach-In to a Static Reference Background

Object detection against a static reference background such as a stainless steel machine part
Teach-in to the background takes place at the touch of a button
Visual confirmation via status LEDs when teach-in is successful

Teach-in to a Moving Reference Background

Object detection in front of moving reference background such as moving conveyors
Teach-in on moving background by pressing the button for application-specific teach-in sequence
Compensation of vibrations, contamination and unevenness through automatic adjustment of the sensor during teach-in

Possible Uses of Reflex Light Barriers for Object Detection

Presence check

Contrast recognition

Fill-level monitoring

Ejection control

The Following Must Be Observed when Installing Reflex Light Barriers

Background Colors

For reliable detection, there must be a clear contrast between the object and the taught-in reference background.

Tip: If there is a small difference in contrast, select a large distance between the object and the background!

Highly Glossy, Reflective and Uneven Backgrounds

In the case of highly reflective, glossy or uneven surfaces, it should be ensured that no direct reflections fall on the receiving optics, as they can impair object detection.

Tip: Place the sensor at a slightly tilted angle!

Steps, Edges and Recesses

To ensure reliable detection, the light spot must be aligned directly with the reference background.

Tip: Align the sensor to a specified background!

Moving Background

For moving reference backgrounds such as conveyor belts, 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!

How Do Reflex Light Barriers Fit in the Portfolio?

Energetic Reflex Sensors
Energetic reflex sensors are used for object detection without a background. They check objects for presence, check stack heights or carry out counting tasks.

Reflex Sensors with Background Suppression
Reflex sensors with background suppression detect and measure objects in front of a specified background irrespective of object properties such as shape, color or gloss.

Universal Retro-Reflex Sensors
Universal retro-reflex sensors are also suitable for detecting shiny, chrome-plated or mirrored surfaces thanks to the integrated polarization filter.

Retro-reflex sensors for transparent objects tile

Retro-Reflex Sensors for Transparent Objects
In addition to glossy, chrome-plated or mirrored surfaces, retro-reflex sensors for transparent objects also detect and count glass, PET or films using red light.

Through-Beam Sensors
Thanks to their long range, through-beam sensors ensure reliable detection even in heavily soiled environments. Variants with laser light can detect even the smallest objects.

Reflex Light Barriers
Reflex light barriers are ideal for contactless object detection without reflectors via red LED light, regardless of object color, shape and surface.

Typical Applications of Sensors with Barrier and Reflex Mode

Reflex light barriers can be used in a variety of ways. Thanks to their reliable barrier and reflex mode, they are ideal for detecting objects regardless of color, shape and surface:

	Range	Response time	Object detection before background	Detection of semi-transparent objects	Detection of glossy and dark objects
Reflex Light Barriers
Energetic reflex sensors
Reflex sensors with background suppression
Universal retro-reflex sensors
Retro-reflex sensors for transparent objects
Through-Beam Sensors