US Patent 7140818 Tool, tool holder, and machine tool

A tool attachable to a spindle of a machine tool in the same way as an ordinary tool, capable of being driven without connecting with an external power supply etc., giving a higher rotational speed than that of the spindle of the machine tool without supplying electric power from the outside, and able to be changed automatically, provided with a machining tool for machining a workpiece, a motor for driving the machining tool, a generator for generating electric power to drive the motor by the rotation of the spindle, and a rotational speed detecting device for detecting the rotational speed of the motor based on a received light signal.