Patent ID: 7793874

Claim:
A grinder comprising: a transmission shaft; a hollow base, said hollow base having a grinding chamber in which said transmission shaft suspends, and a plurality of open spaces in a bottom side thereof in communication with said grinding chamber; a grinding unit, said grinding unit comprising a grinding wheel and a grinding base, said grinding wheel being connected to said transmission shaft for rotation with said transmission shaft in said grinding chamber and kept spaced from said grinding base by a gap; a receptacle mounted on a top side of said hollow base, said receptacle comprising a bottom chamber, which holds said grinding base of said grinding unit in place; a housing, which houses said hollow base and a lower part of said receptacle; an automatic open/close control device for closing/opening said open spaces of said hollow base, said automatic open/close control device comprising a follower member connected to a bottom side of said hollow base opposite to said receptacle, said follower member comprising an axle holder fastened to one end of said transmission shaft and a plurality of radial blocks and guide slots radially and alternatively disposed at a bottom side thereof, a bottom cover, said bottom cover comprising a plurality of outlets cut through top and bottom sides thereof corresponding to the guide slots of said follower member, a position-limitation structure provided between said follower member and said bottom cover to secure said bottom cover to said follower member and to limit relative rotary motion between said follower member and said bottom cover within a predetermined angle, and a torsion spring connected between said follower member and said bottom cover; wherein when rotating said housing relative to said receptacle, said bottom cover, said follower member, said transmission shaft and said grinding wheel are rotated with said housing; when the friction force produced between said grinding wheel and said grinding base is greater than the torsional force of said torsion spring, said follower member is rotated relative to said bottom cover from a first position where said radial blocks of said follower member block said outlets of said bottom cover to a second position where said radial blocks of said follower member are moved away from said outlets of said bottom cover and said guide slots of said follower member are moved into alignment with said outlets respectively for discharge of ground powder out of the grinder through said guide slots and said outlets, and at the same time said torsion spring is twisted to preserve energy.