An ink composition includes: a pigment; water; a polymerizable monomer that is capable of being polymerized by an active energy ray; and an initiator that is capable of initiating polymerization of the polymerizable monomer by the active energy ray, wherein a number of particles contained in the ink composition having a particle diameter of 0. In certain embodiments a surfactant system is disclosed which includes extended anionic surfactants, linker surfactants, and a multiply charged cation component. In the walking aid provided by the present invention, a buffering structure is disposed between a support frame structure and an omni-directional wheel of the walking aid. The compact exoskeleton arm support device compensating for gravity effectively uses the actuators, thereby increasing operating efficiency and reducing production costs. An alignment system that includes alignment electronics that is responsive to a charge-coupled device facilitate adjusting the scanning optics to allow precise alignment of individual ones of the light-emitting sources and to detect burnt out individual ones of the light-emitting sources.