Imagine the Perfect Photoelectric Sensor

Photoelectric sensors have been around for a long time and have made huge advancements in technology since the 1970’s.  We have gone from incandescent bulbs to modulated LED’s in red light, infrared and laser outputs.  Today we have multiple sensing modes like through-beam, diffuse, background suppression, retroreflective, luminescence, distance measuring and the list goes on and on.  The outputs of the sensors have made leaps from relays to PNP, NPN, PNP/NPN, analog, push/pull, triac, to having timers and counters and now they can communicate on networks.

The ability of the sensor to communicate on a network such as IO-Link is now enabling sensors to be smarter and provide more and more information.  The information provided can tell us the health of the sensor, for example, whether it needs re-alignment to provide us better diagnostics information to make troubleshooting faster thus reducing downtimes.  In addition, we can now distribute I/O over longer distances and configure just the right amount of IO in the required space on the machine reducing installation time.

IO-Link networks enable quick error free replacement of sensors that have failed or have been damaged.  If a sensor fails, the network has the ability to download the operating parameters to the sensor without the need of a programming device.

With all of these advancements in sensor technology why do we still have different sensors for each sensing mode?  Why can’t we have one sensor with one part number that would be completely configurable?

BOS21M_Infographic_112917

Just think of the possibilities of a single part number that could be configured for any of the basic sensing modes of through-beam, retroreflective, background suppression and diffuse. To be able to go from 30 or more part numbers to one part would save OEM’s end users a tremendous amount of money in spares. To be able to change the sensing mode on the fly and download the required parameters for a changing process or format change.  Even the ability to teach the sensing switch points on the fly, change the hysteresis, have variable counter and time delays.  Just imagine the ability to get more advanced diagnostics like stress level (I would like that myself), lifetime, operating hours, LED power and so much more.

Obviously we could not have one sensor part number with all of the different light sources but to have a sensor with a light source that could be completely configurable would be phenomenal.  Just think of the applications.  Just think outside the box.  Just imagine the possibilities.  Let us know what your thoughts are.

To learn more about photoelectric sensors, visit www.balluff.com.

Back to the Basics – Photoelectric Light Source

Welcome to the first in a series of getting back to the basic blogs about photoelectric sensors.

LightTypeAll photoelectric sensors require a light source to operate. The light source is integral to the sensor and is referred to as the emitter. Some light sources can be seen and may be of different colors or wavelengths for instance red, blue, green, white light or laser or one you cannot see, infrared. Many years ago photoelectric sensors used incandescent lights which were easily damaged by vibration and shock. The sensors that used incandescence were susceptible to ambient light which limited the sensing range and how they were installed.

Today light sources use light emitting diodes (LED’s). LED’s cannot generate the light that the incandescent bulbs could. However since the LED is solid state, it will last for years, is not easily damaged, is sealed, smaller than the incandescent light and can survive a wide temperature range. LED’s are available in three basic versions visible, laser and infrared with each having their advantages.

Visible LED’s which are typically red, aid in the alignment and set up of the sensor since it will provide a visible beam or spot on the target. Visible red LED’s can be bright and should be aimed so that the light will not shine in an operator’s eyes. The other color visible LED’s are used for specific applications such as contrast, luminescence, and color sensors as well as sensor function indication.

Laser LED’s will provide a consistent light color or wavelength, small beam diameter and longer range however these are generally more costly. Lasers are often used for small part detection and precision measuring. Although the light beam is small and concentrated, it can be easily interrupted by airborne particles. If there is dust or mist in the environment the light will be scattered making the application less successful than desired. When a laser is being used for measuring make sure the light beam is larger than any holes or crevasses in the part to ensure the measurement is as accurate as possible. Also it is important to ensure that the laser is installed so that it is not aimed into an operator or passerby’s eyes.

Lastly, the infrared LED will produce an invisible, to the human eye, light while being more efficient and generating the most light with the least amount of heat. Infrared light sources are perfect for harsh and contaminated environments where there is oil or dust. However, with the good comes the bad. Since the light source is infrared and not visible setup and alignment can be challenging.

LED’s have proved to be robust and reliable in photoelectric sensors. In the next installment we will review LED modulation.

You can learn more about photoelectric sensors on our website at www.balluff.us

Precision Optical Measurement and Detection

In applications that require precise measurement and detection of one or more objects, what type of sensor should one use? If objects that are very small and far apart need to be detected, what type of sensor provides high resolution over its entire sensing range?

The answer: a laser micrometer.

A laser micrometer can identify, compare, or sort objects based on minimal size or height differences. Similar to a standard micrometer caliper, a laser micrometer provides precise measurements.

But how is this done exactly? Let’s find out!

A laser micrometer consists of two opposed sides, a transmitter side and a receiver side. These two sides sit opposite of each other to detect any object that enters in-between them.

On the transmitter side, a laser light source is positioned so that its emitted light enters a lens. The lens then collimates the light from the laser by refraction into a collimated beam of light (see Figure 1). By definition, a collimated light beam is a light beam where each light path in the beam is travelling parallel to one another. This collimated light beam has minimal divergence, even over large distances.

LightBand_BLA
Figure 1

On the other side, the receiver side, a CCD (charge-coupled device) is positioned to collect the light emitted from the transmitter side. CCDs are made up tiny light-sensitive cells. These cells convert the amount of light intensity received into a corresponding electric charge, which can then be measured (see Figure 2).

CCD_BLA
Figure 2

The combination of these two components, a collimated light beam and a CCD, make up the foundation of a standard laser micrometer. The collimated light beam, which consists of a homogeneous light band, is directed at the CCD, which consists of hundreds of tiny light-sensitive cells. With this configuration, even a slight change in an object (e.g., its diameter, height, position, etc.) causes a change in the object’s corresponding shadow that is projected onto the CCD. This slight change can then be measured.

A few examples of the measurement capabilities for a laser micrometer are listed below, along with a video.

Position_BLA
Position Monitoring
Diameter_BLA
Diameter Detection
Gap_BLA
Gap/Height Measurement
Edge_BLA
Edge Guide — even with semi-transparent materials

The following video showcases the capabilities of the Balluff Light Array sensor: http://www.youtube.com/watch?v=btumxuIgj_4.