1. Technical Field
The present invention is directed to a light transmitting device. More particularly, the present invention is directed to a light transmitting lens for use with a photoelectric sensor.
2. Background Information
A photoelectric sensor enables non-contact detection of objects and/or persons. Thus, photoelectric sensors have found particular utility in the detection of objects conveyed along a conveyor belt in various automated processes, as well as the detection of persons approaching an automatic door.
Turning to FIG. 9, a sectional view of a conventional photoelectric sensor transmitter is illustrated. Convex lens A transmits light emitted from photoelectric element 51, which is preferably located at the focal point of the lens. Photoelectric element 51 is attached to wiring substrate 22, along with various other electronic components 23 which comprise the circuitry for the photoelectric sensor's operation. Motion indicating lamp 24 is connected to wiring substrate 22 via wire C. The convex lens is disposed on the front side of casing B and the bottom of wiring substate 22 is protected by rear panel 31. The photoelectric sensor transmitter is mountable on a wall via brackets (not shown).
In recent years, as photoelectric sensors came into use in various applications, the detection length, defined herein as the distance at which a photoelectric sensor is able to sense an object, has increased. A typical detection length for a direct-reflection type photoelectric sensor is about 3 meters, about 8 meters for a mirror-polarizing-reflection type, and about 20 meters for a transmission type photoelectric sensor.
The prior art has achieved an increase in detection length by increasing the amplification rate of the amplifier in the photoelectric sensor's circuitry, thereby increasing the sensitivity of the photoelectric sensor. However, as the sensitivity increases, so does the potential for degradation of the sensor's accuracy due to external noise interference, e.g., electromagnetic radiating energy.
The prior art has also achieved an increase in detection length by increasing the amount of light which is transmitted by employing a larger convex lens. However, with an increased lens size, the overall dimensions of the photoelectric sensor transmitter is also increased. This can be problematic where space requirements are severe.
The prior art has further achieved an increase in detection length by increasing the amount of light which is output from the photoelectric element. This method increases the signal-to-noise ratio of the device and is therefore typically the preferred approach.
The prior art has attempted to increase the amount of light output from the photoelectric element by, e.g., employing a larger light emitting element, and increasing the current to, and therefore the output from, the light emitting element. These approaches, however, have their drawbacks, including higher cost, size requirements and reduced life cycles.