Bearing, strain wave gear device, and industrial robot

A bearing comprising:

• an inner ring having an inner raceway surface formed in an outer peripheral surface thereof;
• an outer ring having an outer raceway surface formed in an inner peripheral surface thereof;
• a plurality of rolling elements placed between the inner raceway surface and the outer raceway surface;
• an insertion groove formed in an axially-facing side surface of the inner ring for inserting the plurality of rolling elements between the inner raceway surface and the outer raceway surface;
• a blocking plug configured to block the insertion groove, the blocking plug having a part of the inner raceway surface formed thereon;
• and
• a bolt for securing the blocking plug in the insertion groove,
• wherein the blocking plug includes:
• a plug body having a bolt insertion hole formed therethrough in an axial direction, the bolt insertion hole being configured to receive the bolt;
• and
• a mating surface formed on the plug body and configured to overlap a bottom surface of the insertion groove, and
• wherein each of the inner raceway surface and the outer raceway surface has a V-shaped groove,
• wherein the plurality of rolling elements includes cylindrical rollers and is arranged so that inclination angles thereof alternate in a circumferential direction,
• wherein the inner raceway surface has an apex where a groove depth is the largest,
• wherein a relief groove is formed at the apex of the inner raceway surface,
• wherein in the mating surface, when a length provided by excluding the relief groove from a length between the bolt insertion hole and the inner raceway surface is shown as a shortest length La, and a length between the bolt insertion hole and a peripheral surface radially opposite to the inner raceway surface is shown as a shortest length Lb, the shortest lengths La and Lb satisfy a following formula:
• La/Lb>0.65,
• wherein, when a head of the bolt is projected onto the mating surface in the axial direction, the head of the bolt is within the mating surface, and
• wherein a radially outermost portion of the head of the bolt is not located radially outside a point of the mating surface corresponding to the shortest length La as viewed in the axial direction.