Abstract: An improved local positioning system (10) utilizing two fixed sonic transmitters (16A,16B) and an omni directional audio receptor (20) mounted on an automated lawn mower (12). Distance between each audio transmitter and the mower is measured by transmitting an RF trigger pulse (88) from the mower to each of the sonic transmitters. Upon being triggered, the first transmitter (16A) sends out an audio pulse which is received by an audio sensor, condenser microphone (22) and the time it takes is measured by a counter (62). Likewise the second transmitter (16B) is later triggered and the time it takes that pulse to be received is measured by the counter (62). The counts are converted to distances and the x-y coordinate which is the location of the mower is calculated by simple trigonometry. The location data which is relative to the sonic transmitters (16A,16B) is available to the microprocessor computer board (72) which utilizes the information to output control signals to a steering and control interface (74).

Abstract: An improved automated, self propelled lawn mower (14) utilizing a rotating directional loop antenna (36) that determines its position within the cutting area by measuring the angle between transmitters(20A, B, & C) placed in a known configuration beyond the cutting area, and by calculating the solution of simultaneous circle equations (96 & 98) defined by that configuration. Orientation is determined by comparing present and previous positions. Stored path information is compared with the calculated position to determine steering signals which direct the mower to move directly toward the next point in the desired path. When the mower reaches that point the next coordinates are retrieved from memory and the process is repeated similarly for all successive points in the path. The simplicity of programming the path makes this automated lawn mower very versatile and flexible.