US Patent 7927019 Slewing bearing structure

A slewing bearing includes: an outer ring section having first and second circumferential grooves formed on an inner circumferential surface in parallel; an inner ring section formed on an inner side of the outer ring section and having first and second circumferential grooves formed on an outer circumferential surface in parallel in correspondence to the first and second circumferential grooves of the outer ring section; a first row of rolling elements provided in the first circumferential groove of the outer ring section and the first circumferential groove of the inner ring section; and a second row of rolling element provided in the second circumferential groove of the outer ring section and the second circumferential groove of the inner ring section. The inner ring section rotates via the first and second rolling element rows around a rotation axis in a relatively opposite direction to the outer ring section.