Work vehicles such as material handling vehicles, for example, lift trucks, platform trucks, AGV's (automatic guided vehicles), and the like are provided for transporting loads between spaced apart locations in factories, warehouses, and the like. Often there are several work vehicles operating within close proximity to one another which makes it necessary to provide a detection system to identify when another vehicle is in its path of travel. This is particularly the case when the vehicle is of the driverless type.
U.S. Pat. No. 4,345,662 dated Aug. 24, 1982 to Michael Deplante depicts an automatic guided vehicle with a radar detector consisting of one or more ultrasonic emitters and one or more ultrasonic receivers for detecting obstacles in the path of the vehicle. These radar detectors are rigidly secured to the vehicle and disperse ultrasonic signals fore and aft of the vehicle. One problem with such a system is that vehicles of this type operate in environments that are often noisy and disruptive to ultrasonic sensors of this type. As a result, false signals received would adversely affect the operation of the vehicle and cause frequent shutdowns of the AGV and adversely affect the overall operation of the workplace.
In order to improve over the reliability of a ultrasonic obstacle detection system, it was envisioned that a light signal response system would overcome the heretofore mentioned problem and provide a reliable and preferable solution to the problem since a light signal response system consisting of a transmitter and receiver would not be influenced by noise or other factory generated signals. This solution appeared to be successful. However, it was found that certain objects did not adequately reflect the light signal back to the receiver due to a weakness in the intensity of the light signal. The option of replacing a single transmitter and receiver with several fixedly mounted transmitters and receivers of a substantially higher intensity and narrow beam width was considered, but found impractical due to space and cost limitations.
It is necessary, therefore, to provide a transceiver arrangement capable of sensing the presence of an object in front of the work vehicle in all potential operating environments and in a simple and low cost manner.