Patent ID: 8210556

Claim:
An electronically controlled midwheel drive wheelchair comprising: a chair; a frame for supporting the chair, the frame housing a battery between left and right frame side portions, with each frame side portion having a front arm frame mount fixed to the frame, a rear arm frame mount fixed to the frame, and a spring frame mount; left and right drive wheels located along the respective frame side portions for supporting the frame and the chair, each drive wheel connected to a separate motor drive unit for propelling the wheelchair along a selected path; and left and right linkage/suspension assemblies located along the respective frame side portions, each linkage/suspension assembly including: a front arm defining a front arm pivot point and a front arm linkage mount, the front arm provided with a front caster defining a front caster rotational axis, the front arm pivot point connected to the front arm frame mount so as to pivotally attach the front arm to the respective frame side portion; a rear arm defining a rear arm pivot point and a rear arm linkage mount, the rear arm provided with a rear caster for helping support the frame, the rear arm pivot point connected to the rear arm frame mount so as to pivotally attach the rear arm to the respective frame side portion; a linkage coupling the front and rear arms together at the front and rear arm linkage mounts, the linkage operative such that rotation of one of the front or rear arms about its pivot point in one direction relative to the frame translates via the linkage to rotation of the other one of the front and rear arms about its pivot point in an opposite rotational direction relative to the frame; and a single spring having one end connected to the spring frame mount and an opposite end connected to one of the front and rear pivot arms at a spring mounting point located between the respective caster and the respective frame pivot point, the single spring being operative to generate a biasing force on the one arm, wherein there is no spring connected between the frame and the other arm, and wherein the linkage is operative to transfer the biasing force from the one arm to the other arm such that the single spring is operative to affect movement of both the front and rear arms as the respective casters encounter surface irregularities during travel.