Laser-based measurement system

Abstract

A laser beam three dimensional position measurement system includes a laser transmitter mounted at a stationary reference position at a work site and a receiver mounted on a mobile machine at the site. The transmitter produces a laser reference plane by sweeping a laser beam about the transmitter. The receiver includes a retroreflector which intercepts and reflects laser energy back to the transmitter when the laser beam sweeps past the retroreflector. The system also includes at the transmitter a circuit composed of a photodetector, timer, clock and counter. The photodetector senses laser energy reflected back to the transmitter from the retroreflector. The timer modulates the laser beam produced by the transmitter in response to detection of the beam. The counter is connected to the clock and timer, and is enabled by the timer to start counting electrical pulses received from the clock when the beam is modulated. The counter is disabled to stop counting electrical pulses when the modulation is detected. The number of pulses counted by the counter is indicative of the range of the receiver from the transmitter. The orientation of the beam relative to a fixed reference axis at the time reflected laser energy is detected defines the direction of the receiver relative to the transmitter.