Spherical lens surface processing method and spherical lens surface processing apparatus with cup-shaped grinding stone

A spherical lens surface processing apparatus, comprising:

• a cup-shaped grinding stone;
• a grinding stone rotation mechanism for rotating the cup-shaped grinding stone about a central axis thereof;
• a lens holder for holding a lens to be processed;
• a lens movement mechanism for moving the lens held in the lens holder so that a lens surface of the lens moves in directions towards and away from the cup-shaped grinding stone;
• a sphere center oscillation mechanism for causing the cup-shaped grinding stone to oscillate centered on a sphere center as an oscillation center along the lens surface of the lens held in the lens holder;
• and
• a controller for controlling the grinding stone rotation mechanism, the lens movement mechanism, and the sphere center oscillation mechanism,
• wherein the controller has the functions of:
• forming a contact state in which the cup-shaped grinding stone while rotating is brought into contact with the lens surface at a predetermined pressure;
• while maintaining the contact state, forming a sphere center oscillation state in which the cup-shaped grinding stone oscillates along the lens surface centered on the sphere center, and grinding the lens surface to a spherical surface having a predetermined surface precision and center thickness;
• in the sphere center oscillation state, setting a distance to be equal to a radius of the spherical surface, the distance being from an oscillation center of the sphere center oscillation to a contact point where the cup-shaped grinding stone makes contact with the lens surface;
• and
• setting an oscillation width of the sphere center oscillation so that the contact point where the cup-shaped grinding stone makes contact with the lens surface moves past a lens center on the lens surface, from one outer peripheral edge to the other outer peripheral edge of the lens surface;
• the spherical lens surface processing apparatus according further comprising:
• a forced rotation mechanism for forcibly rotating the lens holder about a central axis thereof;
• and
• a one-way clutch configured so as to cease forced rotation of the lens caused by the forced rotation mechanism,
• wherein the controller further has the function of:
• forcibly causing the lens to rotate at a lesser speed than the cup-shaped grinding stone, and
• wherein the one-way clutch is set so as to cease the forced rotation of the lens when a torque exerted on the lens by a frictional force between the lens surface and the cup-shaped grinding stone creates a passively rotatable state in which the lens can rotate passively following the cup-shaped grinding stone at a speed greater than the forced rotation speed, the cup-shaped grinding stone being in the sphere center oscillating state.