Advances in optical and laser sensor technologies are increasing assembly equipment precision and reliability by delivering critical position feedback on small parts, while improving setup ease and worker safety. High-gain through-beam sensors provide excellent accuracy even in dirty environments, and a new one-piece through-beam, or "fork" sensor design, speeds setup and simplifies wiring. New Class 1 laser sensors eliminate the potential for accidental eye damage from the laser beam and the need for beam termination. Since effective process control starts with accurate part position feedback, sensor reliability and performance are vital, as assemblies and the machines that build them continue to get smaller.

Through-beam sensors provide high accuracy in detecting small parts, thanks to a tight, well-defined beam, which allows sensing of parts or features as small as 0.03 mm at a range of 10-80 cm. Comprised of an emitter and receiver, through-beam sensors require only beam interruption to determine part presence, making them immune to color, reflectivity, and surface condition. Long sensing range to 50 m (with laser light source) makes sensor mounting less critical by allowing greater "stand off" from small targets and reduces the number of sensors required to cover a big area. (Chart compares excess gain of through-beam, retroreflective and diffuse sensors.)

In addition, through-beam sensors have a high level of excess gain, which is the amount of light energy striking the receiver above the threshold required to activate the receiver for normal sensing. This provides an increased tolerance to dirt, moisture, and debris that can accumulate on the sensor face, allowing high-precision laser sensing in environments normally too hostile for laser sensors.

A one-piece version of the through-beam sensor, the self-contained "fork" sensor, simplifies mounting by eliminating alignment setup of emitter and receiver. These space-saving sensors speed and simplify wiring, and allow mounting sans special brackets or beam alignment procedures. Many have anodized aluminum housings, which resist damage from corrosive media, and an IP65 rating to work in wet environments. They are capable of detecting small parts to 0.3 mm with repeatability of 0.02 mm, and are available in a number sensing gap "slot" sizes from 5 to 120 mm to best match process requirements. Wide-gap models accommodate bulky items like carpet and heavy textiles without risk of sensor contact.

Laser sensors no longer need Class 2 emission -- which increases sensor cost and worker safety precautions -- for effective operation. New Class 1 sensors use lower-power laser diodes to achieve comparable accuracy at a lower cost. Laser position sensors with a Class 1 rating per EN 60825-1 guarantee safety in all applications and eliminate the need, worry, and cost involved with beam termination, as the beam disperses outside of the stated range. (Chart provides list price historical comparison between Class 1 and Class 2 Lasers.)

Class 1 lasers provide a variety of advantages, including:

• Small beam detects targets down to 0.5 mm


• Concentrated beam offers extended sensing range when compared with traditional emission types


• Highly visible beam even in well lit areas


• Not harmful to the human eye


• Requires no "laser warning" signs


• Sensor prices are in line with traditional light sources.

Class 1 lasers are available in all popular sensing modes, including diffuse, retroreflective and through-beam, to cover an assortment of presence-sensing duties. Quick response time of just 0.3 msec. and switching frequency of 1.5 kHz make these sensors ideal for high-speed assembly applications.