Table 4.
Controller sequence for different activities
| FSM sequence | Functional activities |
|---|---|
| 1 | Standing; stand-to-sit; backward walking |
| 1–2–3 | Level-ground and up-slope walking |
| 1–2–4–3 | Slow walking (level-ground and up-slope) |
| 1–3 | Down-slope and down-stair walking |
| 1–5 | Sit-to-stand |
| 1–2–6–1–5 | Up-stairs walking |
Within each FSM state, knee torque is governed by a unique control law based upon a combination of sensor inputs: knee angle (
) and velocity (
), thigh angle (
), shank axial force (
), and walking speed estimation (
). Each torque control law (
) has between one and three tunable parameters (
). For
,
is a system parameter that indicates the maximum achievable motor braking impedance (i.e., when the motor leads are connected at 100% duty cycle). For
and
,
is a tunable parameter that indicates the crossover walking speed, which is the walking speed where the motor provides neither assistance nor resistance and swing-flexion motion is governed by passive dynamics alone. For
,
is the equilibrium position of the virtual spring, which is a function of the thigh kinematics, as described in Lee and Goldfarb (2021). For
,
is time as relevant for the filter term.