Figure 5: Common Process for Mid-Level Control via Kinematic Reference Trajectories.

(i) Motion capture data is collected from able-bodied subject walking. (ii) The average and standard deviation is computed of each joint trajectory, such as the trajectory of the knee angle, θ_knee, with respect to the percent gait cycle. (iii) A function, y_d(ϕ_{θ,t}), is fit to the average data, parameterized by some state- or time-based phase variable ϕ{θ,t}. (iv) A torque, τ, is computed based on this desired trajectory and the actual trajectory, y_a(θ), of the prosthesis. (v) This torque is commanded of the prosthesis actuators. (vi) The resultant joint trajectory of the prosthesis, y_a(θ), is close to the desired trajectory, y_d(ϕ_{θ,t}). Steps (i) - (iii) are part of data-driven approaches to generate reference trajectories, described in Subsection 7.1, and steps (iv) - (vi) are part of tracking controller methods, described in Subsection 7.2.