Prosthetic Joint Control Using Force Rejection and Force Following
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Solution Overview
Problem
Existing prosthetic or orthotic devices (PODs) struggle to seamlessly transition between active and passive modes, leading to instability or inefficiency during various activities, such as walking and standing, due to proactive joint behaviors that may startle users or inhibit gait dynamics.
Innovation Solution
A hybrid control scheme that dynamically switches between passive and active modes based on gait parameters, using a multi-layer control system architecture with a learning, inference, and reactive layer to manage actuator behaviors, including force rejection and force following, and actively modified joint behaviors like toe-off assist and braking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If proactive joint behaviors are used to assist gait, then gait support is improved, but user stability deteriorates due to startling effects
Solution Approach 1:
The control system dynamically adjusts between passive and active modes based on real-time gait phase detection. During swing phase, the system transitions to active mode to provide proactive joint behavior assistance, while during stance phase it switches to passive mode to ensure stability. This dynamic switching resolves the contradiction by making the level of assistance adaptive rather than fixed.
Solution Approach 2:
The system changes the control parameter from passive to active based on gait phase detection. By monitoring gait parameters and switching control modes accordingly, the system provides high assistance during swing phase when needed, while maintaining stability during stance phase, thus resolving the contradiction between gait support and user stability.
2Reliability
If passive mode is used to ensure stability, then user stability is improved, but gait assistance deteriorates due to lack of proactive support
Solution Approach 1:
The system dynamically switches between passive and active control modes based on the detected gait phase. During swing phase when gait assistance is most needed, the system activates proactive joint behaviors. During stance phase when stability is paramount, it maintains passive mode. This dynamic adaptation resolves the contradiction by providing the right level of assistance at the right time.
Solution Approach 2:
The system performs preliminary detection of gait phase to anticipate when assistance is needed. By detecting the transition to swing phase in advance, the system can proactively switch to active mode before the user needs assistance, ensuring smooth transition and effective gait support without compromising stability.
3Productivity
If active mode is used continuously to provide gait support, then gait assistance is improved, but energy consumption increases
Solution Approach 1:
The system uses periodic gait cycle detection to activate active mode only during the swing phase when assistance is needed, rather than continuously. By synchronizing active assistance with the periodic nature of the gait cycle, the system provides effective gait support during critical phases while conserving energy during stance phase when passive support suffices.
Solution Approach 2:
The system applies active assistance partially, only during the swing phase when it is most needed, rather than continuously throughout the entire gait cycle. This partial action approach provides sufficient gait assistance during critical moments while significantly reducing overall energy consumption compared to continuous active mode operation.
4Productivity
If continuous active control is used to manage joint behavior, then gait control is improved, but device complexity increases
Solution Approach 1:
The control system is segmented into distinct passive and active modes, each with simplified control logic. Rather than implementing a single complex continuous control algorithm, the system divides control into two manageable segments that can be switched based on gait phase detection. This segmentation reduces overall system complexity while maintaining effective gait control.
Solution Approach 2:
The gait phase detection mechanism serves as an intermediary that automatically determines when to switch between passive and active modes. This intermediary component simplifies the control architecture by providing clear, objective criteria for mode transitions, eliminating the need for complex continuous control algorithms and reducing overall system complexity.
Data Source
AI summary
A prosthetic or orthotic device (POD) can include first and second limb members coupled at a joint, an actuator, and a controller. The actuator can be configured to actuate the first limb member relative to the second limb member. The controller can cause the actuator to exhibit a force rejection behavior during a portion of stance phase and cause the actuator to exhibit a force following behavior during a portion of swing phase. The controller can, based on a determination that a gait parameter satisfies a gait parameter threshold, cause the actuator to at least one of: apply a first torque at the joint to cause the POD to flex during a portion of stance phase, decelerate flexion of the POD during at least a first portion of the swing phase, or decelerate extension of the POD during at least a second portion of the swing phase.