Sensor Sense: Retroreflective-Area Sensors

May 3, 2010
Retroreflective-area sensors use a rectangular beam of light to detect an object anywhere within the sensing area.

The usual way of detecting objects of varying shapes, heights, or positions has been through the use of an array of single-beam photoelectric sensors or a thru-beam light grid: a photoelectric array in two separate housings. This method can’t precisely sense an object’s true leading edge, especially when the leading edge is indistinct. For example, various types of pallets, parts ejected from a die, stacks of newspapers, bent rods, and cartons of varying height, width, or shape, can all provide indefinite leading edges making part detection erratic.

Retroreflective-area sensors are now replacing these older methods. This type of sensor uses multiple transmitter beams and multiple receiver elements in a single sensor housing to produce a continuous height-detection field. The sensor housing mounts opposite a corner-cube reflector. Without a target object present, light from the transmitters in the sensor housing travels to the reflector where it bounces back to the receivers housed with the transmitters. The simple press of a pushbutton initiates a teach mode in the sensor that lets it learn what conditions signify that no target is present. Conditions change when a target object enters the sensing area between the sensor and the reflector, triggering the sensor output.

Unlike an array of single-beam sensors that have conical light patterns with a small diameter, retroreflective-area sensors have a rectangular pattern of light with a continuous height. This makes it possible to detect the same size object consistently throughout the entire sensing area. Moreover, the sensor can detect an object’s true leading edge even if the object has no defined shape or position.

Retroreflective-area sensors only have a single sensor housing along with a reflector. Thus their material and installation costs are well under that of thru-beam light grids or a comparable array of single-beam sensors. Operationally, they are mechanically and electrically the same as a single beam device.

Pepperl+Fuchs (www.am.pepperl-fuchs.com) supplied information for this column.

Edited by Robert Repas

About the Author

Robert Repas

Robert serves as Associate Editor - 6 years of service. B.S. Electrical Engineering, Cleveland State University.

Work experience: 18 years teaching electronics, industrial controls, and instrumentation systems at the Nord Advanced Technologies Center, Lorain County Community College. 5 years designing control systems for industrial and agricultural equipment. Primary editor for electrical and motion control.

Sponsored Recommendations

The entire spectrum of drive technology

June 5, 2024
Read exciting stories about all aspects of maxon drive technology in our magazine.

MONITORING RELAYS — TYPES AND APPLICATIONS

May 15, 2024
Production equipment is expensive and needs to be protected against input abnormalities such as voltage, current, frequency, and phase to stay online and in operation for the ...

Solenoid Valve Mechanics: Understanding Force Balance Equations

May 13, 2024
When evaluating a solenoid valve for a particular application, it is important to ensure that the valve can both remain in state and transition between its de-energized and fully...

Solenoid Valve Basics: What They Are, What They Do, and How They Work

May 13, 2024
A solenoid valve is an electromechanical device used to control the flow of a liquid or gas. It is comprised of two features: a solenoid and a valve. The solenoid is an electric...

Voice your opinion!

To join the conversation, and become an exclusive member of Machine Design, create an account today!