EP-4734886-A1 - POWERED PROSTHESIS WITH IMPROVED SIT-STAND TRANSITIONS

Abstract

A powered knee-ankle prosthesis includes an impedance controller to improve transitions between standing and sitting positions and to permit use at various chair heights. A thigh-based phase variable is used to parameterize optimized data-driven impedance parameter trajectories for sitting, standing, and walking, with only two classification modes. Stand-to-sit and sit-to-stand equilibrium angles are decoupled via a knee velocity-dependent scaling term, which significantly reduces model-fitting error. The prosthesis produces biomimetic joint mechanics, resulting in improved loading symmetry and reduced time to complete sit-to-stand tasks compared to passive prostheses. The controller can be integrated with an impedance-based walking controller to facilitate sit-to-walk transitions from different chair heights. The controller's biomimetic assistance can reduce user overreliance on their natural limb, thereby helping improve mobility for people with above-knee amputations.

Inventors

• GREGG, ROBERT D.
• WELKER, Cara G.
• Best, Thomas K.

Assignees

• The Regents of the University of Michigan

Dates

Publication Date

20260506

Application Date

20240627

Claims (1)

1. CLAIMS 1. A powered prosthesis comprising a joint and an impedance controller configured to continuously vary impedance at the joint during a user transition between a standing position and a seated position. 2. The powered prosthesis of claim 1, wherein the impedance at the joint is a continuous function of one or more impedance parameters, each impedance parameter being a continuous function of a sit-stand phase defined between the standing position and the seated position. 3. The powered prosthesis of claim 2, wherein each impedance parameter function is optimized based at least in part on able-bodied data independent from the user. 4. The powered prosthesis of claim 2, wherein the controller estimates the sit-stand phase in real- time. 5. The powered prosthesis of claim 4, wherein the controller estimates the sit-stand phase based at least in part on a phase variable that monotonically increases or decreases during the user transition. 6. The powered prosthesis of claim 5, wherein the phase variable is a thigh angle of the user. 7. The powered prosthesis of claim 3, wherein at least one of the one or more impedance parameters is also a function of a decoupling variable which is zero when the user transition is from the standing position to the seated position and non-zero when the user transition is from the seated position to the standing position. 8. The powered prosthesis of claim 7, wherein an equilibrium angle of the joint is one of the impedance parameters and the decoupling variable is an angular velocity of the joint. 9. The powered prosthesis of claim 8, wherein the joint is a knee joint. 10. The powered prosthesis of claim 1, wherein the impedance controller is configured to continuously vary impedance at the joint both during a user transition from the standing position to the seated position and during a user transition from the seated position to the standing position. 11. A powered knee-ankle prosthesis according to claim 1, wherein the joint is a knee joint and the prosthesis further comprises an ankle joint, the controller being configured to continuously vary impedance at both joints during the user transition. 12. The knee-ankle prosthesis of claim 11, further comprising a hybrid walking controller configured to control impedance at both joints during a stance phase of walking and to control kinematics of both joints during a gate phase of walking, wherein both controllers control impedance as a function of a thigh angle of the user. 13. The knee-ankle prosthesis of claim 12, wherein the prosthesis is configured to transition between a sit-stand mode and a walk mode based at least in part on a thigh angle and a thigh angular velocity of the user.

Description

POWERED PROSTHESIS WITH IMPROVED SIT-STAND TRANSITIONS GOVERNMENT LICENSE RIGHTS This invention was made with government support under HD094772 awarded by the National Institutes of Health. The government has certain rights in the invention. TECHNICAL FIELD This disclosure is related to powered prostheses and control strategies intended to make artificial joint movement more natural. BACKGROUND Conventional passive and semi-active lower leg prostheses cannot supply net positive energy like biological joints. This causes users to compensate with their natural limb, which can lead to kinematic and kinetic asymmetries during walking and during transitions between sitting and standing. Such compensations can cause secondary complications such as osteoarthritis and lower back pain. Powered prostheses have the ability to supply net positive energy and can help reduce secondary complications by producing more normative mechanics. However, effective prosthetic control strategies, particularly for non-rhythmic tasks, remain elusive. The majority of research and development on controllers for powered knee-ankle prostheses has focused on control strategies for rhythmic locomotion—i.e., steady-state walking on level ground. But the reality is that almost half of a person’s movement bouts last less than 12 steps each, and a healthy adult transitions between sitting and standing more than 60 times each day on average. For powered prostheses to ever become clinically viable, control strategies accounting for transitional activities will be necessary. Generally, joint control strategies in powered prostheses include kinematic control strategies and impedance control strategies. Kinematic strategies seek to control joint angles in a manner that replicates healthy human motion. Impedance control, on the other hand, seeks to control resistance to movement about joints by treating each joint as a spring and damper system and varying the spring constant and damping coefficient via application of torque at the joint in a manner that simulates human musculoskeletal resistance to motion. Impedance control dictates joint torque as a function of the joint’s angular position θ and velocity ^^^ , parameterized by a stiffness K, damping coefficient B, and equilibrium angle ^^^^: ^^ ൌ ^^൫ ^^^^ െ ^^൯ െ ^^ ^^^. (1) The small number of divide those motions into discrete segments and assign constant values to K, B, and ^^^^ for each segment, using separate controllers for stand-to-sit and sit-to-stand movements and tuning the multiple sets of constants for each individual user. Attempts at kinematic controllers have either failed to provide enough torque to mimic human knee strength or have provided sufficient torque at the expense of asymmetry at critical portions of the motion. In all cases, the time and effort required for tuning the prosthetic to the individual for multiple discrete segments of the sit-stand movements is excessive, requiring up to five hours with certain multi-activity controllers. In addition to the practical challenges of long tuning times, the risk of task misclassification increases with the number of distinct controllers employed for different activity modes. Such misclassifications can cause unwanted prosthesis behavior ranging from mildly uncomfortable to highly dangerous and likely to result in a fall, depending on the type and timing of the misclassification. Some studies have presented strategies in which transitions from one task to another among sitting, standing, and walking were properly identified but included a percentage of false positives. Other studies have used measured electromyography (EMG) from the intact biceps femoris as an input to a controller that allows for transitions between different tasks with a single controller. However, EMG as a source for a real-time input signal is limited by its tendency to drift over time, which leads to the need for frequent recalibration. SUMMARY An embodiment of a powered prosthesis include a joint and an impedance controller configured to continuously vary impedance at the joint during a user transition between a standing position and a seated position. Another embodiment of the powered prosthesis includes all of the features of the previously listed embodiment, and the impedance at the joint is a continuous function of one or more impedance parameters, each impedance parameter being a continuous function of a sit-stand phase defined between the standing position and the seated position. Another embodiment of the powered prosthesis includes all of the features of any of the previously listed embodiments, and each impedance parameter function is optimized based at least in part on able-bodied data independent from the user. Another embodiment of the powered prosthesis includes all of the features of any of the previously listed embodiments, and the controller estimates the sit-stand phase in real-time. Another embodiment of the powered prosthesis inclu