From the previous discussion of trouble analysis regarding the automation of screw fastening, we learned the following countermeasures are required on the screw fastening automation equipment side:
(1) fastening failures
(2) screw parts feeding errors
(3) screw positioning errors, etc.
This section describes fastening failures.

(1)Evaluation of screw fastening quality

・Evaluation methods for screw fastening are summarized for reference in considering countermeasures for fastening failures in automating screw fastening (Fig. 1).

・Quality of screw parts, mostly evaluated in the context of elaborate fabrication, indirectly affects the quality of fastening section.

(2)Trouble countermeasure for screw fastening failures

・Fig. 2 shows causes for screw fastening failures in the order of the rate of occurrence (%). This graph suggests that factors for failures (indicated by arrows) need some countermeasures on the screw fastening automation equipment side, excluding machining of pilot hole, or quality of screw appearance.

・The top factor on the equipment side, bit sliding, is a serious defect which is caused by combined simple factors such as when the screw position relative to the screw hole is shifted, or the shape of cross recess of the screw head and the bit shape are inappropriate.

・Therefore, empirical pursuit for the optimal shape in the first place, and durability such as countermeasure for friction reduction are essential for bits.

・Also the handling section of screw needs to have a clamp mechanism ensuring reliable holding property.