Seat lift with non-linear spring assist

A wheelchair including a wheelchair lift assembly configured to assist an individual sitting into and/or rising from a wheelchair, comprising:

• a frame providing a seat surface configured for supporting a seated individual;
• a first and second wheel attached to the frame at left and right transversely opposed sides of the seat surface supporting the frame and positioned for rotation by the seated individual;
• a lift assembly positioned between the seat surface and the frame to urge the seat surface upward with respect to the frame from a lowered position when supporting the seated individual during use to an elevated position with respect to the frame assisting the individual during ingress or egress to or from the wheelchair, the lift assembly comprising a first portion mounted to the frame, a second portion mounted to the seating surface;
• a mechanical linkage extending from the first portion to the second portion, and an actuator assembly extending from the first portion to the mechanical linkage;
• the actuator assembly producing a nonlinear lift force comprising a first period having a first rate of amplitude increase when the second portion of the lift assembly is nearer the lowered position and a second period having a second rate of amplitude change that is less than the first rate of amplitude increase when the second portion of the lift assembly is nearer the elevated position, wherein the actuator assembly comprises a seat lift actuator providing a lifting force and an antagonistic actuator providing an opposing attenuation force.