| 摘要 |
The focus angle 8 of a search light (12) mounted on a helicopter (10) or oth er platform (10) is narrowed or widened by rotating a bidirectional focus contr ol cam (42) in a clockwise or counterclockwise direction as selected by a manually operated three- position control switch (SW1) which determines the rotational direction of a DC motor (28) driving the bidirectional focus control cam (42). The DC motor (28) has first and second terminals (92, 93) which are selectively connected to either a DC pow er source (72) or ground (73) by a double-pole, single throw dual relay (60) which reverses the polarity and thus the direction of rotation of the DC motor (28). The dual relay (60) is connected by the same single wire interface (32) to the manually operated control switch (SW1), which manually operated control switch (SW1) is within a control box (62) located in the helicopter (10). By operating the manually operated control switch (SW1) to connect coils (76,78) in the dual relay (60) to either a power source (72 ) or to ground (73), the coils (76,78) are selectively energized or deenergized causing the dual relay (60) to operate switches (SWR, SW3) that reverse polarity of current flowing through the DC motor (28). This selectively changes the direction of rotation of the bidirectional cam (42) which advances and retracts a focusing reflector (47) within the search light (12) to widen and narrow its focus angle 8, thereby widening and narrowing the area (16) illuminated by the search light beam (14).
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