Arm Prosthesis Control Using Inertial Sensing for Coordinated Joints
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Solution Overview
Problem
Conventional myoelectric arm prostheses lack coordinated control of multiple joints, requiring sequential movement due to limited control signals from muscle contractions, making it difficult for above-elbow amputees to perform simultaneous movements of shoulder and elbow joints, restricting the ability to follow complex paths or trajectories.
Innovation Solution
Incorporating inertial measurement sensors (IMS) to measure the motion of the residual limb relative to an inertial reference frame, allowing for coordinated control of powered joints, such as the elbow joint, based on upper arm spatial orientation and angular velocity, enabling simultaneous movement with the shoulder joint, and combining with EMG control for enhanced functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If sequential control method is used with limited EMG signals, then device complexity is reduced, but productivity and movement speed are worsened due to inability to perform simultaneous joint movements
Solution Approach 1:
The patent introduces an intermediary computational model that maps limited EMG signals to multiple joint control commands. This intermediary layer processes the relationship between residual limb muscle activity and prosthetic joint configurations, enabling coordinated multi-joint movements without requiring separate control signals for each joint. The computational model acts as a mediator that translates scarce biological signals into comprehensive control commands.
Solution Approach 2:
The patent makes the single EMG control signal serve multiple functions by using it to control multiple joints simultaneously. Instead of dedicating specific EMG channels to specific joints, the system uses the universal EMG input to coordinate control of shoulder, elbow, and wrist joints through a unified computational model, thereby maximizing the utility of limited control signals.
2Adaptability or versatility
If sequential joint configuration is used, then control signal requirements are reduced, but adaptability and flexibility are worsened due to inability to follow complex paths
Solution Approach 1:
The computational model serves as an intermediary that expands the information content of limited control signals. It processes EMG measurements in conjunction with prosthetic state information to generate coordinated commands for multiple joints, effectively multiplying the control capability from the limited EMG input without requiring additional control signals.
Solution Approach 2:
The patent transitions from one-dimensional sequential control to multi-dimensional coordinated control by introducing a computational layer that processes control signals in multiple dimensions simultaneously. The system controls multiple joints (shoulder, elbow, wrist) with multiple degrees of freedom using the same EMG input, effectively adding dimensional complexity to the control output without increasing signal quantity.
3Ease of operation
If EMG signals from biceps and triceps are used for elbow control, then ease of operation is improved, but reliability is worsened due to interference from shoulder joint movement
Solution Approach 1:
The patent implements feedback by continuously monitoring the state of multiple joints and using this information in the computational model to disambiguate EMG signals. The system uses feedback from joint position sensors and the known mechanical relationships to determine whether EMG activity should produce elbow movement or shoulder movement, thereby resolving the interference problem while maintaining intuitive control.
Solution Approach 2:
The computational model acts as an intermediary that filters and interprets EMG signals in the context of overall arm configuration. It processes the raw EMG measurements through a model that understands the biomechanical relationships between shoulder and elbow joints, thereby separating the intended control signal from the interference caused by two-joint muscle activity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables above-elbow amputees to perform coordinated, simultaneous movements of shoulder and elbow joints, improving movement speed and flexibility in achieving desired arm configurations, allowing the hand to follow complex paths, thereby enhancing the functionality and efficiency of arm prostheses.
Implementation Method 1
at least one inertial measurement sensor (IMS), where the inertial measurement sensor is used to measure the motion of the prosthetic limb, and by association the residual limb, relative to the inertial reference frame
Implementation Method 2
the at least one joint of the myoelectric arm prosthesis is typically controlled with input from a pair of electromyogram (EMG) measurements, each of which measures the electrical activity resulting from a muscle contraction
Data Source
AI summary
A control method for an arm prosthesis having at least one powered joint and at least one inertial measurement sensor (IMS) includes determining a motion and an orientation of the arm prosthesis relative to the inertial reference frame based at least on an output of the IMS and generating control signals for the at least one powered joint based on the motion and the orientation of the prosthetic arm.