Device for fastening screw onto workpiece and method of judging loosening of screw

Patent metadata

Field	Value
Publication number	US-9370848-B2
Application number	US-201213609687-A
Country	US
Kind code	B2
Filing date	Sep 11, 2012
Priority date	Sep 12, 2011
Publication date	Jun 21, 2016
Grant date	Jun 21, 2016

Abstract

In judging loosening of a crew, a measuring section measures a position of a bit as a relative position in relation to a placement surface of a screw supplying device when the screw is acquired from the screw supplying device. The measuring section also measures the position of the bit as a relative position in relation to a workpiece surface when fastening of the screw onto a workpiece has been completed. A judging section judges that screw loosening has not occurred when, based on the first and second bit positions, a difference between the first and second bit positions falls within an allowable range. The judging section judges that screw loosening has occurred when the difference does not fall within the allowable range.

First claim

What is claimed is:

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.

2. The screw fastening device of claim 1 , further comprising a storage section that temporarily stores therein information indicative of the first bit position until the second bit position is measured by the second bit position measuring section.

3. The screw fastening device of claim 2 , wherein the bit driving section is provide with a suction pipe arranged relatively movable to the bit in the axial direction, the suction pipe having an end surface touchable to the placement surface in the screw acquisition state, and touchable to the workpiece surface in the screw fastening completion state,
wherein the first bit position measuring section and the second bit position measuring section are configured to measure the first bit position and the second bit position, respectively, as positional amounts of the bit which are relatively changed to the suction pipe in the axial direction.

4. The screw fastening device of claim 3 ,
wherein the suction pipe suctions the screw when the screw is acquired from the screw supplying device; and
the suction pipe is arranged to accommodate therethrough the bit such that the suction pipe is movable relatively to the bit, and is provided with the end surface having an opening through which the screw is suctioned,
wherein the end surface is touched to both the placement surface in the screw acquisition state and the workpiece surface in the screw fastening completion state.

5. The screw fastening device of claim 3 , further comprising notifying means for providing a notification of an occurrence of the loosening of the screw when the screw loosening judging section judges that the loosening of the screw has occurred.

6. The screw fastening device of claim 2 , wherein the bit driving section is provided with a suction pipe arranged relatively movable to the bit in the axial direction, the suction pipe accommodating therein the bit,
wherein the first bit position measuring section and the second bit position measuring section are provided with sensing means for sensing a relative position between the suction pipe and the bit in the axial direction when the screw acquisition state and the screw fastening completion state are realized.

7. The screw fastening device of claim 6 , further comprising a holder that holds the bit such that the bit is movable in the axial direction,
wherein the sensing means comprises
a flange fixedly secured to an outer surface of the suction pipe,
a sensor that outputs an electric signal corresponding to both the first bit position and the second bit position, the sensor being fixedly secured to an outer surface of the holder, and
a probe having two ends, a first one of the two ends being fixedly secured to the flange and a second one of the two ends providing the sensor with positional changes of the suction pipe in the axial direction.

8. The screw fastening device of claim 7 , wherein the suction pipe suctions the screw when the screw is acquired from the screw supplying device, the suction pipe being configured to be used for both suctioning the screw and measuring the first bit position and the second bit position.

9. The screw fastening device of claim 6 , wherein the suction pipe suctions pipe the screw when the screw is acquired from the screw supplying device, the suction pipe being configured to be used for both suctioning the screw and measuring the first bit position and the second bit position.

10. The screw fastening device of claim 1 , further comprising notifying means for providing a notification of an occurrence of the loosening of the screw when the screw loosening judging section judges that the loosening of the screw has occurred.

11. The screw fastening device of claim 1 , wherein the screw loosening judging section is configured to (i) calculate the difference, (ii) compare the calculated difference with the allowable range to determine whether or not the calculated difference is outside the allowable range, and (iii) determine that the loosening of the screw has occurred when the comparison shows that the calculated difference is outside the allowable range.

12. The screw fastening device of claim 11 , further comprising notifying means for providing a notification of an occurrence of the loosening of the screw when the screw loosening judging section judges that the loosening of the screw has occurred.

Assignees

• Harada Toyoo
• Denso Wave Inc

Inventors

• Harada Toyoo

Classifications

• G05B2219/45091

  Screwing robot, tighten or loose bolt · CPC title

• B25J9/1679

  characterised by the tasks executed · CPC title

• Y10T29/49764

  with testing or indicating · CPC title

• B23P19/06 Primary

  Screw or nut setting or loosening machines · CPC title

• B23P19/066

  by electrical means · CPC title