Patent ID: 8967925
Filing Date: 2015-03-03
Classification: B23F,Y10T

Abstract:
1. A machine tool for performing gear cutting on a workpiece with a hob, comprising: a first holding member for holding the hob; a second holding member for holding the workpiece; first drive means having a first drive motor for rotating the hob held by the first holding member about its axis; second drive means having a second drive motor for rotating the workpiece held by the second holding member about its axis; first detecting means transmitting a first detection signal when detecting that a rotational position of the first drive motor is at its zero position; second detecting means transmitting a second detection signal when detecting that a rotational position of the second drive motor is at its zero position; and control means for controlling the operation of the first and second drive motors, either rotational speeds of the first drive motor and the hob or rotational speeds of the second drive motor and the workpiece being set at rotational speeds different from each other, wherein, the first drive means is configured to be able to be switched between a connected state where the first drive motor and the hob are connected to each other and a released state where the connection therebetween is released, and the control means is configured to, when stopping the drive motors and switching the first drive means into the released state, recognize, on the basis of a first speed ratio of the rotational speed of the first drive motor to the rotational speed of the hob and a second speed ratio of the rotational speed of the second drive motor to the rotational speed of the workpiece and on the basis of detection signals transmitted from the first and second detections means, detection signals transmitted when the rotational positions of the drive motors and the rotational positions of the hob and the workpiece correspond to their respective zero positions, and stop the drive motors so that the rotational positions of the drive motors, the hob and the workpiece correspond to their respective zero positions, and then switch the first drive means into the released state.