| 摘要 |
A wheel alignment measuring system for measuring front wheel toe including a laser beam light projector mounted on a front wheel of a motor vehicle which projects a beam of light onto a pivotally mounted front mirror on the projector which oscillates back and forth through a ten degree angle about a reference line. The beam of light reflected from the oscillating mirror swings ten degrees on either side of a central reference beam line, and during its swing the beam strikes a fixed roof mirror mounted on the opposite front wheel of the vehicle. The thus reflected beam sweeps back and forth across the light projector and is successively intercepted by each of a pair of closely spaced photocells on the light projector, the cells being equally spaced on opposite sides of the reference beam line. The cells develop signals when they intercept the light beam which signals control and up/down counter through a flip-flop. The time interval required for the moving light beam to fall on a first cell, sweep in one outward direction and return in the opposite direction to the second cell is compared with the time interval required for the beam to continue its sweep from the second cell in said opposite direction and return in said one outward direction to the first cell. Such comparison is stored by the counter as a binary difference signal. A digital/analog converter converts the binary difference between these time intervals into a voltage which represents the total toe angle between the front wheels. The toe angle of the projector-mounting front wheel is obtained in a similar manner by sweeping a rearwardly directed light beam across a fixed roof mirror on the rear wheel that is directly behind said front wheel. In the preferred embodiment, the direction or "sense" of the oscillating light beam is obtained by employing two photocells on opposite sides of a reference line so that the paired cells intercept the beam in one order on an outward sweep and in the opposite order on a return sweep. In a modified embodiment, a single cell replaces the paired cells, and a switch, which is operated by a cam on the motor shaft that swings the mirror, provides signals to a circuit which determines the direction of beam swing.
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