Q20-2: A Polarized Retroreflective Sensor For Reliable Object Detection

Banner Engineering, known for automation and safety components, has recently added to its line of retroreflective sensors with the Q20-2 polarized retroreflective photoelectric sensor.

 

Banner Engineering has added the Q20-2 polarized retroreflective photoelectric sensor to its sensing offerings. Image used courtesy of Banner Engineering

 

Retroreflective Sensors

Detection sensors are special sensors that will detect objects with light. Typically they will have a min, max, and optimal distance they need to be mounted from an object to be able to detect it accurately.

The retroreflective style sensor requires a reflector to direct the beam back to the sensor, unlike a through-beam sensor where there is a sending and receiving device, the retroreflective sensor only requires a sending device. This reduces set-up time by not having to align the sending and receiving devices. With a retroreflective sensor, the object's color, texture, or reflectivity is not a concern, making this sensor style a robust option for object detection.

 

Object Detection Logic

When detecting objects with sensors, the logic is very simple. A beam of light is cast perpendicular to the object’s direction of travel. When the object breaks the beam, the sensor will output a 24 VDC signal to the control system. The control system can now solve other program logic, knowing that a part or object is present. This logic works no matter which light object detection sensor you are using.

 

The Q20-2 can detect objects regardless of color, texture, or reflectivity. Image used courtesy of Banner Engineering

Q20-2 Polarized Retroreflective Sensor

Banner Engineering's Q20-2 polarized retroreflective sensor uses top-of-the-line optical to mechanical alignment and a visible red LED emitter to aid with aligning the sensor to the reflector. The Q20-2 retroreflector sensor has an extended sensing range of 5 m and can detect objects of any color, texture, or reflectivity thanks in part to the polarized optics.

The back of the unit has two bright LEDs for status and a single-turn gain potentiometer for tuning the sensing range. The Q20-2 has two modes, light operate and dark operate, which refers to when the 24 VDC signal will be transmitted to the control system. The Q20-2 comes in eight variations consisting of different electrical connections, cable lengths, and NPN or PNP models. Standard mounting holes are provided on both sides of the device to allow easy mounting to purchased or custom brackets.

 

The Q20-2 calculates an object's location and speed and communicates that to the control system. Image used courtesy of Banner Engineering

 

Q20-2 Applications

There are many applications for object detection sensors, as these sensors are a great way to inform a PLC where parts are located. A common use for a retroreflective sensor is on a conveyor system. The PLC needs to know when pallets or objects that travel on conveyors enter stations or work cells. Proximity sensors are commonly used for part detection, but when you need to detect objects such as cardboard boxes or wood/plastic pallets, a retroreflective sensor works best.

A common place to find retroreflective sensors is at the end of conveyor spurs. A spur is a short section of a conveyor that enters a work cell from a main conveyor line. Pallets are directed onto these spurs when the work cell calls for materials or parts. Once the pallet is directed to the spur, a motor will turn on, driving the rollers which drive the pallet to the end of the spur. The control system needs to know when to stop the motors, so a retroreflective sensor is placed near the end of the spur, and when the pallet breaks the beam, the control system will turn off the motor.