| 摘要 |
PURPOSE: To ensure visibility of a sign device by a method wherein when a temperature reduction signal is received, an ultrasonic vibrator is driven and by effecting ultrasonic vibration of a light transmission plate, snow adhering to the front face is dropped. CONSTITUTION: When the ambient temperature lowers below a given temperature, a temperature lowering detection signal 14a is outputted to a control means 30 by a temperature sensor 14. The control means 30 outputs a heater drive signal 31d to a heater 42. The heater 42 is then energized and generates heat, a light transmission plate 13 is heated, and snow adhering to the front of a nemeral display means 18 is melted and dropped. The control means 30 outputs an ultrasonic vibrator drive signal 31c to an ultrasonic vibrator 40 according to a speed regulation command 15a from a monitoring command means 15. Further, the light transmission plate 13 is caused to effect ultrasonic vibration by the ultrasonic vibrator 40 to drop snow adhering to the front of a numerical display means 18. |
