1. Field of the Invention
This invention relates to circuitry for use with a guidance system for an automatically guided vehicle (AGV) and more specifically to circuitry for detecting the presence of a valid guidepath signal from various types of sensors, such as photocell arrays, infrared light, sound, and the like which operates over a large dynamic range without the need to make gain or threshold adjustments.
2. Description of the Prior Art
Automatically guided vehicles are generally known in the art. Examples of such vehicles are disclosed in the following U.S. Pat. Nos.: 4,328,545; 4,345,662; 3,379,497; 4,623,032; 4,602,334; 4,627,511; 3,039,554; 3,610,363; 3,933,099; 4,003,445; 4,151,526; 4,602,334 and 4,500,970. Such automatically guided vehicles are used in a wide variety of applications, including the transfer of raw materials and subcomponent parts in manufacturing and assembly facilities, the cleaning of floors in warehouses and parking lots and the delivery of mail in business offices. AGVs are also used in a wide variety of applications in the agricultural industry such as, plowing, harvesting, mowing, and the like.
In each application the AGV is guided by on-board sensors which follow a guidepath. Various types of systems are used for automatically guiding the vehicle along a guidepath.
In U.S. Pat. No. 4,003,445, the guidepath consists of a fluorescent material, applied to a floor, carpet or the like which emits visible light in a predetermined frequency range. The fluorescent material, however, is normally invisible under ambient lighting conditions. In this type of guidance system, an ultraviolet light located on the vehicle, irradiates the guidepath. This radiation stimulates the fluorescent materials in the guidepath causing it to emit visible radiation which is sensed by sensors onboard the AGV.
Optical guidance systems for use along a predetermined guidepath are susceptible to spurious operation due to background radiation. Thus, the guidance system must be able to detect a "no-line" situation. Also such systems are affected by the non-uniform intensity of the fluorescent guidepath. The solution to this problem has heretofore been attempted. For example, U.S. Pat. No. 4,003,445 discloses an automatic gain control (AGC) circuit for distinguishing between varying intensities of the reflected light from the fluorescent guidepath and background radiation. In this system, AGC feedback circuitry is disclosed for continuously adjusting the gain of the sensor circuit to compensate for the variations in the guidepath intensity. The AGC circuitry is also coupled to other circuitry for detecting a no-line situation. However, such circuitry is relatively complicated and requires a continuous gain adjustment of the sensor circuit to compensate for the varying intensity of the guidepath.