Half angle mechanism for a heliostat

Claim 1

An improved heliostat device for an electro-optical system comprising: a mirror gimbaled in two axes with the mirror supported from an azimuth gimbal pivotally mounted from an elevation gimbal for line-of-sight direction and stabilization, with a half angle drive system connected to the mirror for controlling azimuth rotation of the mirror relative to the stable body from which the mirror is mounted and which half angle drive system includes torque motor means coupled to the mirror for controlling rotation of the mirror; the improvement wherein the half angle drive system comprises an N-2N-speed synchro transmitter-receiver pair in which the output signal from the 2N synchro control receiver has an amplitude proportional to sin (Nθ SB -2Nθ M ), with an N-speed synchro control transmitter comprising a transmitter stator and transmitter rotor, with the transmitter stator coupled to the elevation gimbal, and the transmitter rotor coupled to the stable body, and a 2N-speed synchro control receiver comprising a receiver stator and receiver rotor, with the receiver stator coupled to the elevation gimbal and the receiver rotor coupled to the mirror drive shaft, with the torque motor means coupled to the mirror drive shaft, which half angle drive system includes control electronics coupled between the 2N-speed synchro control receiver and the torque motor means, with the synchro control receiver output signal applied as a torque motor current command signal fed to the torque motor means, and wherein the control electronics includes means for comparing the torque motor current command signal to the actual torque motor current such that a null signal difference is provided when mirror angular displacement is one-half the stable body angular displacement.