Apparatus for double-side polishing work

A double-side polishing apparatus for a workpiece, comprising rotating surface plates having an upper plate and a lower plate, a sun gear provided at a central portion of the rotating surface plates, an internal gear provided around the rotating surface plates and the sun gear, and a carrier plate provided between the upper plate and the lower plate provided with at least one opening for holding the workpiece,

• wherein one of the upper plate and the lower plate has at least one through hole penetrating from an upper surface to a lower surface of said one of the upper plate and the lower plate,
• the double-side polishing apparatus for the workpiece further comprises at least one workpiece thickness measuring instrument that can measure a thickness of the workpiece through the at least one through hole during double-side polishing of the workpiece,
• an inner circumferential surface defined by the through hole in said one of the upper plate and the lower plate is provided with a metal cylindrical member,
• the double-side polishing apparatus for the workpiece further comprises either of:
• a lower window provided in a lower part of the cylindrical member provided in the upper plate, an upper window provided in an upper part of the cylindrical member provided to cover an upper side of the through hole provided in the upper plate, and an upper member having an inner surface configured to be fixed to an outer surface of a projecting portion projecting from the upper surface of the upper plate, the cylindrical member having a first protruded portion and a part of the upper member is directly disposed on the first protruded portion;
• or
• an upper window provided in an upper part of the cylindrical member provided in the lower plate, a lower window provided to cover a lower side of the through hole provided in the lower plate, and a lower member having an inner surface configured to be fixed to an outer surface of a projecting portion projecting from the lower surface of the lower plate, the cylindrical member having a second protruded portion and a part of the lower member is directly disposed on the second protruded portion, and
• an other part of the upper member is placed on an upper surface of the cylindrical member, and the upper window is provided on the upper member;
• or
• an other part of the lower member is placed on a lower surface of the cylindrical member, and the lower window is provided on the lower member.