52 formed in the central part and is secured the rotating shaft 53 is rotated counterclockwise fig6 by means of a drive unit comprising an electric motor and a gear apparatus not illustrated the main disc 51 is equipped in a peripheral direction with four fairly large openings 54 at equal intervals the circumference part of the under surface of the main disc 51 is equipped in a peripheral direction with four triangular type fairly large hollows 55 at equal intervals therefore four long and slender cutoff notches formed on the long side part of the triangle of a hollow 55 are formed on the circumference of the main disc 51 the top part of the hollow 55 formed against a cutoff notch is connected to a through hole 53 a long and slender arm 56 is formed between adjacent hollows in addition the long and slender arm 56 is notched therefore when the main disc 51 rotates contact between a guide pin not shown and the long and slender arm 56 is prevented some small holes 57 are formed on the circumference part of the upper surface of the main disc 51 a small hole 57 embeds a forceful magnet 58 made from a.