FORMING AND FABRICATING AUTOMATION
6.2: Sensoring
Pairing Sensor Types with the Problems They Address W hen developing a die-sensor connection scheme, metal formers can rely on certain sensors for specific applications. Diffuse reflective photosensors, inductive proximity sensors and electromechanical material-buckle sensors are purpose-built devices to detect part ejection, feed progression and material buckle.
Diffuse reflective photosensors provide the coverage necessary to detect air- ejected parts.
Inductive-proximity sensors are ideal for detecting misfeeds, or for any application requiring a high level of precision.
contact—the presence of a metallic object. Often, two of these sensors are needed to verify proper strip position. One sensor verifies that the strip has fed far enough (short-feed sensor) and another ensures that the strip has not fed too far (overfeed). If material buckle were to occur, a short-feed sensor almost certainly would detect it—even- tually. However, detecting a material buckle as early as possible gives the press maximum time to stop. This is best accomplished by in- stalling a sensor on a magnetic base between the feeder and the die to detect if the material buckles up or down more than a prescribed amount. The preferred sensor for this detection is an electromechanical material-buckle sensor.
Detecting air-ejected parts is a challenge. These parts tend to be smaller than parts that are pushed or fall out of the die. They follow somewhat unpredictable trajectories on the way out of the die, with the parts presented to the sensor at random angles as they tumble by. The diffuse reflective photosensor is optimal to detect air-ejected parts. A few special electromechanical sensors are purpose-built to detect one specific problem, including end of material, feed progression and material buckle. Of all commonly monitored die malfunctions, feed progression requires the highest level of precision. Inductive-proximity sensors perform best, as they can detect—without any physical
Electronic and electromechanical sensors for die protection are capable of detecting almost any die malfunction. With that said, certain sensors are best used in specific applications. Knowing which sensors match which problems they address helps stampers achieve optimal die protection. Metal formers should consider two primary (and opposite) attributes when selecting sen- sors for die protection—precision and coverage. In some instances, sensors will need to detect an object in a precise place at a specific time; for example, to detect whether a strip feeds properly. At other times, they need to detect an object for which its exact position is unpredict- able, such as an air-ejected part.
The electromechanical material-buckle sensor is still effective—70 yr. after it was introduced.
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