Patent ID: 9370848
Filing Date: 2016-06-21
CPC Classification: B23P,B25J,G05B,Y10T

Claim Text:
1. A screw fastening device comprising: a bit that is engageable with a screw, wherein the screw is acquirable from a screw supplying device and the acquired screw is screwable onto a workpiece, the screw having an axial direction, the workpiece having a workpiece surface; a bit driving section configured to hold the bit and drive the held bit such that the bit engages with the screw and the screw is rotated to advance or return in the axial direction, the screw supplying device having a placement surface; a first driving section configured to drive the bit driving section so as to produce a screw acquisition state provided when the screw is acquired from the screw supplying device, the bit being engaged with the screw and pressing the screw onto the placement surface of the screw supplying device for acquisition of the screw in the screw acquisition state; a first bit position measuring section configured to measure, as a first bit position, a position of the bit which is relative to the placement surface of the screw supplying device in the screw acquisition state; a second bit driving section configured to drive the bit driving section so as to produce a screw fastening completion state provided when the fastening of the screw into a hole of the workpiece has been completed by the bit driven by the bit driving section, the bit being still engaged with the screw in the screw fastening completion state; a second bit position measuring section configured to measure, as a second bit position, a position of the bit which is relative to the workpiece surface of the workpiece in the screw fastening completion state; and a screw loosening judging section configured to judge whether or not loosening of the screw has occurred in the screw fastening completion state, based on a comparison between a difference between the first bit position and the second bit position and an allowable range set in advance for the difference.