Gear manufacturing apparatus and gear manufacturing method

A gear manufacturing apparatus for machining a gear workpiece over an entire circumference thereof in a state in which the gear workpiece and a tool for grinding or cutting are in contact with each other and are rotated, comprising:

• a first spindle configured to hold the gear workpiece;
• a first holding table holding the first spindle such that the first spindle is rotatable about a first axis that is an axis of the first spindle;
• a second spindle configured to hold the tool including one or more screw-like or ring-like teeth formed on an outer circumferential surface of the tool;
• a second holding table holding the second spindle such that the second spindle is rotatable about a second axis that is an axis of the second spindle;
• a drive device configured to rotate the second spindle about the second axis and to move at least one of the first holding table and the second holding table;
• and
• a control device configured to control the drive device to adjust a relative position of the tool to the gear workpiece;
• wherein the control device includes a storage storing target-shape data relating to a target shape of teeth of the gear workpiece and tool-shape data relating to a shape of the tool,
• wherein a direction orthogonal to an imaginary plane that includes the second axis and that is parallel to the first axis is defined as an X-axis direction,
• wherein, in each of the target-shape data and the tool-shape data, a cross section of each of the one or more teeth of the tool cut along a plane orthogonal to the X-axis direction at a position at which at least one of the teeth of the gear workpiece is included is defined as an X-axis-orthogonal cross section,
• wherein a direction orthogonal to a tooth trace direction in the X-axis-orthogonal cross section is defined as a thickness direction,
• wherein a direction orthogonal to a straight line parallel to the first axis in the X-axis-orthogonal cross section is referred to as a Z-axis direction,
• wherein each of the one or more teeth of the tool is shaped in the X-axis-orthogonal cross section such that a length of each of the one or more teeth in the thickness direction decreases from a central portion thereof in the tooth trace direction toward opposite ends thereof in the tooth trace direction,
• wherein, in the X-axis-orthogonal cross section, an intersection between an imaginary straight line and an outer edge line of the tool is defined as a normal machining point, the imaginary straight line passing a center point of the central portion in the thickness direction and parallel to the Z-axis direction,
• wherein a computational position at which the tool performs machining of the gear workpiece is defined as a machining reference position,
• wherein each of the teeth of the gear workpiece has opposite end portions in the tooth trace direction, each of the opposite end portions being defined as an end region, and
• wherein, when at least one of the end regions is machined, the control device executes a specific machining control for adjusting the relative position based on information about the relative position computed by setting, as the machining reference position, a position of the tool on the outer edge line in the X-axis-orthogonal cross section different from the normal machining point such that a distance between a center of the tool and a center of the gear workpiece in the X-axis-orthogonal cross section when the at least one of the end regions is machined is larger as compared with a case in which the at least one of the end regions is machined by setting the normal machining point as the machining reference position.