Machine Tool and Workpiece Machining Method

A method of machining a workpiece with a machine tool, comprising:

• retaining the workpiece on a spindle;
• rotating the spindle at a target rotational speed;
• and
• relatively moving a tool and the workpiece at a target moving speed to a target moving position in a cutting feed direction, wherein:
• a rotational speed of the spindle is varied in a waveform having a predetermined amplitude and continuously varying in a periodic or non-periodic manner with respect to the target rotational speed, and
• the tool is continuously moved in a direction orthogonal to both an axis of the spindle and a direction of cut of the tool in synchronization with the variation of the rotational speed of the spindle at least in a predetermined time zone including a point where the rotational speed of the spindle reaches a maximal value and a predetermined time zone including a point where the rotational speed of the spindle reaches a minimal value.

A machine tool comprising:

• a spindle retaining a tool;
• a spindle motor rotating the spindle;
• a feed device having a feed motor and relatively moving a workpiece and the tool in a cutting feed direction;
• and
• a controller having a spindle motor control unit controlling the spindle motor and a feed motor control unit controlling the feed motor, wherein:
• the spindle motor control unit is configured to receive a command for a target rotational speed of the spindle and control the spindle motor to continuously vary a rotational speed of the spindle in a periodic or non-periodic manner with a predetermined amplitude with respect to the target rotational speed;
• and
• the feed motor control unit is configured to receive commands for a relative target moving position and a target moving speed for the tool and the workpiece, control the feed motor to relatively move the tool and the workpiece at the received target moving speed to the target moving position, and control the feed motor in synchronization with the control of the spindle motor by the spindle motor control unit to continuously vary a relative moving speed between the tool and the workpiece such that a ratio of the rotational speed of the spindle to the relative moving speed is not constant, at least in a predetermined time zone including a point where the rotational speed of the spindle motor reaches a maximal value and a predetermined time zone including a point where the rotational speed of the spindle motor reaches a minimal value.

A machine tool comprising:

• a spindle retaining a workpiece;
• a spindle motor rotating the spindle;
• a feed device having a feed motor and relatively moving a tool and the workpiece in a cutting feed direction;
• a shift mechanism moving the tool in a shift direction orthogonal to both an axis of the spindle and a direction of cut of the tool;
• and
• a controller having a spindle motor control unit controlling the spindle motor, a feed motor control unit controlling the feed motor, and a shift control unit controlling the shift mechanism, wherein:
• the spindle motor control unit is configured to receive a command for a target rotational speed of the spindle and control the spindle motor to continuously vary a rotational speed of the spindle in a periodic or non-periodic manner with a predetermined amplitude with respect to the target rotational speed;
• the feed motor control unit is configured to receive commands for a relative target moving position and a target moving speed for the tool and the workpiece and control the feed motor to relatively move the tool and the workpiece at the received target moving speed to the target moving position;
• and
• the shift control unit being configured to control the shift mechanism in synchronization with the control of the spindle motor by the spindle motor control unit to continuously move the tool in the shift direction at least in a predetermined time zone including a point where the rotational speed of the spindle motor reaches a maximal value and a predetermined time zone including a point where the rotational speed of the spindle motor reaches a minimal value.