Design of an FPGA-Based Fuzzy Feedback Controller for Closed-Loop FES in Knee Joint Model

Micromachines, 2021 · DOI: 10.3390/mi12080968 · Published: August 16, 2021

Simple Explanation

This paper proposes a digital fuzzy feedback controller (FFC) embedded in a field-programmable gate array (FPGA) board for functional electrical stimulation (FES) in knee joint rehabilitation. The FFC monitors knee extension movement by regulating stimulus pulse width duration to meet a target angle (30, 40, or 70 degrees). The high processing speed of the digital FFC enables the stimulus pulse width duration to be updated every stimulation cycle, which is useful for real-world closed-loop FES applications.

Study Duration

Not specified

Participants

Not specified

Evidence Level

Not specified

Key Findings

1
The digital FFC utilizes only 4% of the total FPGA (Cyclone IV E) logic elements (LEs).
2
The digital FFC required 238 µs to regulate stimulus pulse width data, including 3 µs for the FLC computation.
3
The implemented digital FFC has demonstrated good control performance in accurately controlling the stimulus pulse width duration to reach the desired reference angle with very small overshoot (1.4◦) and steady-state error (0.4◦).

Research Summary

The paper presents the design and implementation of an FPGA-based fuzzy feedback controller (FFC) for closed-loop functional electrical stimulation (FES) in a knee joint model, aiming to reduce early muscle fatigue. The digital FFC, consisting of an ADC Data Acquisition and FLC sub-modules, monitors knee extension movement and regulates stimulus pulse width duration to meet target angles. Experimental results show that the implemented digital FFC offers high processing speed, low resource utilization, and good control performance with small overshoot and steady-state error, making it suitable for real-world closed-loop FES applications.

Practical Implications

Reduced Muscle Fatigue

Closed-loop FES with the proposed FFC can potentially reduce early muscle fatigue in SCI patients by providing accurate stimulation.

Improved Rehabilitation

Accurate control of knee extension movement can enhance rehabilitation exercises and improve motor function.

Wearable FES Device

The FPGA-based implementation facilitates the development of wearable, real-time closed-loop FES devices.

Study Limitations

1
The system was tested using a knee extension model and potentiometer, not on human subjects.
2
The study focused on knee extension only; other movements were not considered.
3
The design's performance was evaluated based on simulation and hardware measurements; clinical trials are needed.

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