Implementation of Hybrid Soft-Hard Exosuit for Adaptive Ankle Movement Therapy Device - A Quantitative Analysis

Lower leg restoration is fundamental for people recovering from wounds, surgeries, or neurological conditions that influence portability [1], [2]. The lower leg joint underpins body weight, maintains adjustability, and empowers essential developments such as walking and running. Impedances can altogether affect day-by-day exercises, expanding drop hazards and useful confinements. Compelling restoration reestablishes quality, adaptability, proprioception, and engine control through a focus on treatments, counting physiotherapy, assistive gadgets, and progressed restoration advances [2], [3], [4]. The rising predominance of lower leg disabilities, especially among the elderly and physically dynamic people, underscores the requirement for inventive, cost-effective, and available recovery arrangements. Conventional strategies frequently require visit clinical visits, making them monetarily and strategically challenging. In addition, ordinary approaches may need personalization and versatility to meet the needs of the person recovering [4], [5]. Progressions in restoration designing have driven the development of wearable assistive gadgets, such as mechanical exoskeletons and delicate exosuits, which coordinate biomechanical standards with con- strained sensors, and fake insights to form versatile treatment conventions. These advances empower real-time observing, data-driven alterations, and progressed recuperation results [2], [6]. Half-breed soft-hard exosuits offer a promising ap- proach, combining inflexible back with adaptable materials for improved consolation and flexibility. Giving both detached and dynamic help, these frameworks empower customizable bolster based on impedance seriousness and recuperation arrangement, making strides in restoration effectiveness and openness [3], [7].

LITERATURE REVIEW

1. Introduction

Ankle rehabilitation is essential for individuals recovering from injuries, neurological disorders, or post-surgical con- ditions [4], [5], [6]. Traditional rehabilitation methods rely on manual therapy, passive orthotic devices, and treadmill- based gait training. However, these approaches require con- tinuous therapist supervision and often fail to provide real- time monitoring and adaptive assistance. Recent advancements in wearable robotics and sensor technology have led to the development of rigid exoskeletons, soft exosuits, and hybrid assistive devices. A hybrid soft-hard exosuit offers a promising alternative by combining the flexibility of soft materials with the structural support of rigid components, ensuring comfort, adaptability, and precise movement assistance [2], [3], [4], [5]. This review examines existing rehabilitation technologies, biomechanical principles, sensor integration, actuation mech- anisms, and motion-tracking techniques relevant to the de- velopment of a low-cost, sensor-based ankle rehabilitation exosuit[6].

Fig. 1. Outlines the, by and large, framework engineering of the crossbreed breed soft-hard exosuit for versatile lower leg development treatment. The framework coordinates an Arduino Uno R3 (MC) to control an MG996 servo engine, which incites a 3D-printed PVC/WPC ankle-foot demonstration. Different sensors (IMU, FSR, SW-420, PIR, etc.) give real-time input, with information handled and visualized utilizing Arduino IDE 2.3.4 and Kinovea 2023.1.2 for biomechanical investigation.

2. Ankle Rehabilitation: Challenges and Existing Approaches

Wearable rehabilitation devices have emerged as a promising alternative to conventional rehabilitation methods [7],[8],[9]. These devices provide robotic-assisted therapy, improving rehabilitation efficiency and reducing the dependency on therapists. Existing wearable devices include rigid exoskeletons, soft robotic exosuits, and hybrid exosuits. Rigid exoskeletons, such as ReWalk and EksoGT, offer structured, guided movement but often lack flexibility and comfort. On the other hand, soft robotic exosuits, like the Harvard Soft Exosuit, use fabric-based actuators for assistance but do not provide sufficient joint support. A more effective approach is the hybrid exosuit, which combines rigid and flexible elements to maintain comfort while ensuring structural support [4], [8], [9], [10]. Studies suggest that hybrid exosuits improve rehabilitation outcomes by adapting to the user’s movement while maintaining precise biomechanical assistance. The integration of sensors and actuators in these devices enables real-time feedback, motion tracking, and personalized rehabilitation programs, making them a viable solution for ankle rehabilitation [11],[12],[13].

3. Sensor Integration in Rehabilitation Exosuits

Integrating real-time sensor feedback is crucial for adaptive rehabilitation, allowing for personalized assistance and objective progress monitoring. Various sensors can be embedded in the exosuit to enhance its functionality. Force-sensitive resistors (FSRs) measure ground reaction forces (GRFs) and evaluate load distribution and balance during movement [13]. Inertial measurement units (IMUs) track angular velocity, acceleration, and orientation, enabling the detection of gait abnormalities and joint instability [12],[11]. Vibration sensors detect muscle tremors and fatigue levels, providing insights into muscle endurance and therapy intensity. Additionally, passive infrared (PIR) sensors monitor patient engagement, ensuring adherence to rehabilitation protocols. By combining these sensors, the exosuit can deliver adaptive and responsive therapy, adjusting resistance levels and motion guidance based on the patient’s real-time performance. This sensor-based feedback loop improves rehabilitation outcomes by optimizing movement patterns and reducing the risk of re-injury [11], [13].

Fig. 2. Presents the circuit design for the foot-ankle model, integrating Arduino Uno R3 as the central controller. The system includes two servo motors, force-sensitive resistors (FSRs), a PIR sensor, buzzers, and an IMU module, all interconnected via a breadboard for signal processing. The circuit is powered by dual 9V batteries, ensuring adequate power supply for motor actuation and sensor operation.

4. Motion Tracking and Rehabilitation Analysis

Tracking motion and rehabilitation progress enables data- driven therapy adjustments and ensures that patients follow effective rehabilitation protocols. Kinovea software, an open- source tool for motion analysis, is widely used for tracking joint angles and movement patterns [12],[13],[14]. It provides quantitative analysis of dorsiflexion and plantarflexion ranges, allowing therapists to assess rehabilitation effectiveness objectively. Additionally, real-time data visualization using the Arduino IDE’s Serial Monitor Plotter enables instant feedback on sensor data, helping both patients and therapists to identify movement trends, make adjustments, and optimize therapy sessions. This data-driven approach ensures that rehabilitation is not only effective but also personalized, addressing the specific needs and limitations of each patient [16],[7],[1]. Using motion tracking and real-time analysis, the exosuit improves rehabilitation outcomes by promoting precise, repeatable, and progressively challenging therapy sessions [11]. plastic composite (WPC) are used for structural support due to their lightweight yet durable properties, making them suitable for a low-cost and robust rehabilitation device. These materials provide a rigid framework for housing sensors, actuators, and support mechanisms. In addition, elastic components such as Velcro straps and springs are incorporated to enhance wearability and adaptability [13],[14],[2]. These elements allow for an adjustable fit, ensuring comfort while maintaining stability during movement exercises. By selecting a combination of rigid and flexible materials, the exosuit can offer the necessary support for effective rehabilitation while remaining lightweight and easy to wear. This hybrid material approach ensures that the device is affordable, accessible, and suitable for extended use in home-based rehabilitation settings [12],[13].

5. Material Selection for Exosuit Design

The selection of materials for the exosuit plays a vital role in ensuring comfort, durability, and affordability. PVC and wood-

• ω1, ω2 = Angular velocities at times t1, t2

• t2 − t1 = Time interval between frames

This parameter is crucial for understanding movement smoothness and potential rehabilitation needs. Torque (τ) at the ankle joint during dorsiflexion and plan- tar flexion is determined using:

τ = r × F                                                                    

where:

 • r = Moment arm (m) (distance from joint center to applied force)

• F = Force applied by muscles or external devices (N) For dynamic movement, incorporating the moment of inertia

plastic composite (WPC) are used for structural support due to their lightweight yet durable properties, making them suitable for a low-cost and robust rehabilitation device. These materials provide a rigid framework for housing sensors, actuators, and support mechanisms. In addition, elastic components such as Velcro straps and springs are incorporated to enhance wearability and adaptability [13],[14],[2]. These elements allow for an adjustable fit, ensuring comfort while maintaining stability during movement exercises. By selecting a combination of rigid and flexible materials, the exosuit can offer the necessary support for effective rehabilitation while remaining lightweight and easy to wear. This hybrid material approach ensures that the device is affordable, accessible, and suitable for extended use in home-based rehabilitation settings [12],[13].

6. Conclusion and Future Directions

This review highlights the importance of biomechanical principles, sensor-based monitoring, and motion tracking in the

• I = Moment of inertia of foot segment (kg·m²)

• m = Mass of the foot segment (kg)

• a = Linear acceleration at the force application point (m/s²)

For an inverse dynamics approach:

τ = Iα + mgr cos(θ)                                                    

where g is the gravitational acceleration

If Kinovea is combined with force plate data or FSR sensors, GRF can be estimated using:

FGRF = ma + mg                                                      

where:

• m = Body mass (kg)

• a = Vertical acceleration of the foot during gait (m/s²)

• g = Gravitational acceleration (9.81 m/s²)

During dorsiflexion, the GRF assists the movement, whereas in plantarflexion, muscles must work against GRF. The instantaneous power produced at the ankle joint is:

Design of an affordable and effective ankle rehabilitation exo- suit. The hybrid soft-hard exosuit presents a promising alter- native to traditional rehabilitation devices by offering adaptive movement assistance, real-time monitoring, and quantitative rehabilitation progress tracking. By integrating servo motor- based actuation and sensor feedback, the exosuit ensures personalized rehabilitation while reducing the need for therapist supervision [4],[5],[7]. Future research should focus on enhancing the adaptability and intelligence of the exosuit. One key area is machine learning-based adaptation, which would enable AI-driven movement assistance, adjusting therapy intensity based on patient progress. Additionally, developing customizable assistance levels would further optimize therapy by allowing users to adjust resistance and movement patterns based on their rehabilitation needs [11],[12],[2]. By leveraging biomechanics, embedded systems, and rehabilitation science, this project aims to enhance rehabilitation efficiency and accessibility for patients recovering from ankle injuries.

METHODS

1. Exoskeleton Sensors Parameter Tuning

The suit coordinates different sensors, counting drive Force sensors, vibration sensors, Inertial Measurement Unit Sen- sors(IMU), and passive infrared (PIR) sensors, to screen client development and muscle actuation. Drive sensors degree foot weight dissemination, supporting in stride investigation and real-time criticism alterations. Vibration sensors give criticism on joint steadiness and development effectiveness, whereas the Inertial Measurement Unit evaluates muscle engagement axial Motion Analysis. The sensor parameters are calibrated based on user-specific limits, optimizing reaction affectability and minimizing wrong locations. Information collected from these sensors is handled to upgrade development direction and refine restoration conventions [11],[12],[9].

Fig. 3. Presents the Arduino-based control code for the ankle-foot exosuit, responsible for servo motor actuation and sensor data processing. The script reads inputs from force-sensitive resistors (FSRs), IMU, and PIR sensors, dynamically adjusting the servo motor position to assist in ankle movement. Additionally, real-time data visualization is facilitated via Arduino IDE 2.3.4, supporting biomechanical analysis and therapy customization.

2. Data and Quantitative Analysis Using KINOVEA Soft- ware

Kinovea computer program is utilized as an effective apparatus for the quantitative investigation of the exosuit’s effect on lower appendage recovery, particularly centering on lower leg joint kinematics. The computer program empowers the exact following of joint points, precise speed, and extent of movement amid restoration sessions, giving profitable biome- chanical bits of knowledge. High-resolution video recordings of client developments are prepared to extricate key walk parameters, encouraging a comparative assessment of pre- and post-rehabilitation advances [7],[12],[8],[2]. The movement following capabilities of Kinovea permit for point-by-point appraisal of development proficiency, supporting within the approval of the exosuit’s adequacy in advancing controlled, characteristic lower leg verbalization. By analyzing varieties in movement designs over time, the computer program makes a difference in distinguishing advancements in engine co- ordination, muscle engagement, and by and large utilitarian recuperation. Moreover, integrating Kinovea-generated kinematic information with real-time sensor criticism from drive, vibration, passive infrared (PIR), and inertial measurement unit (IMU) sensors improves the comprehensiveness of the assessment preparation [5],[6],[9].

Fig. 4. Presents the Kinovea Software Analysis for the ankle-foot exosuit, responsible for servo motor actuation dynamically adjusting the servo motor position to assist in ankle movement. Additionally, real-time data visualization is facilitated via Kinovea Software, supporting biomechanical analysis and therapy customization. This data-driven approach, not as it were, empowers objective execution checking but also encourages nonstop refinement of the exosuit’s assistive capacities. By connecting sensor-derived biomechanical criticism with movement exam- ination results, versatile alterations can be made to optimize the exosuit’s control calculations and mechanical back. Eventually, the combination of Kinovea-based appraisal and sensor information integration contributes to a more personalized and compelling restoration encounter, guaranteeing progressed portability results for people experiencing lower leg treatment [2], [6], [3], [5].

RESULTS

The developed hybrid soft-hard exosuit was evaluated based on its design, sensor functionality, actuation performance, user comfort, and rehabilitation effectiveness. The results highlight the system’s ability to provide adaptive ankle movement therapy while maintaining affordability and wearability. The integration of real-time sensor feedback and biomechanical motion analysis using Kinovea software allowed for a comprehensive assessment of the exosuit’s impact on rehabilitation outcomes [2],[9],[7]. The key findings from the implementation and testing phases are detailed in the following subsections:

1. Exosuit Design and Construction

The hybrid soft-hard exosuit was successfully developed using a combination of flexible materials and rigid structural components. The frame, made of Polyvinyl Chloride/Wood Plastic Composite (PVC/WPC), provides lightweight dura- bility while ensuring adequate support for controlled ankle movement. Adjustable soft straps enhance comfort and adapt- ability, allowing the exosuit to accommodate users of different leg sizes. The integration of a servomotor-based actuation system replaces traditional linear actuators, offering smoother and more precise control over dorsiflexion and plantarflexion movements [7],[8],[9].

Fig. 5. The figure shows a hybrid soft-hard exosuit combining rigid supports with flexible materials for ankle rehabilitation. It integrates servo motors, elastic straps, and embedded sensors (FSR, IMU, PIR, vibration) to provide controlled motion assistance. This visualization helps in evaluating motion smoothness, force distribution, and overall rehabilitation effectiveness. Sensor Integration and Functionality: The suit in- corporates multiple sensors, including force sensors, vibration sensors, Passive Infrared (PIR) sensors, and an Inertial Measurement Unit (IMU), to monitor and assess user movement patterns. The force sensors measure foot pressure distribution, aiding in gait analysis, while vibration sensors detect instability or abnormal movement patterns. PIR sensors contribute to detecting motion activation, ensuring efficient energy consumption, and the IMU provides real-time data on ankle joint angles and movement velocity. The sensor data is processed dynamically to adjust assistance levels, optimizing therapy effectiveness [6], [11], [13].

Fig. 6. illustrates the graphical representation of sensor data, showcasing real-time readings from force-sensitive resistors (FSRs), IMU, PIR sensors, and other integrated sensors. This visualization helps in analyzing sensor responsiveness, movement patterns, and user interaction with the suit. The data trends provide insights into system efficiency, accuracy, and potential areas for optimization in ankle movement therapy

Actuation Performance and Motion Assistance: The servomotor-based actuation system demonstrated effective assistance in controlled ankle movement, allowing precise regulation of motion trajectories. The system supports both passive and active rehabilitation modes, where passive mode guides movement with predefined motion patterns, and active mode responds to user-initiated motion. The implementation of a Proportional-Integral-Derivative (PID) control algorithm ensured smooth and adaptive motion assistance, reducing jerky or unnatural movements. The results indicate that servomotor- based actuation provides a cost-effective and efficient alternative to linear actuators [5],[6],[12],[7],[2].

Biomechanical Data Analysis Using Kinovea: Quantitative analysis using Kinovea software confirmed improvements in joint angle control, range of motion, and movement coordination during rehabilitation sessions. Video recordings were processed to track the user’s ankle kinematics, measuring angular displacement, speed, and stability across different therapy sessions. Data comparisons between pre- and post- rehabilitation phases revealed progressive improvements in ankle mobility and control, validating the exosuit’s effectiveness in enhancing movement rehabilitation [3],[14].

Fig. 7. Presents the final outcome tabulation of dorsiflexion and plantarflexion angles and corresponding torque values generated by the ankle-foot exosuit. The data quantifies the range of motion, torque output, and system efficiency during assisted ankle movement. This tabulation serves as a key performance indicator, aiding in the assessment of rehabilitation effectiveness and mechan- ical response of the exosuit.

Fig. 8. Provides a graphical visualization of the dorsiflexion and plantarflexion angles. The plotted data highlights the relationship between ankle movement and torque output, offering insights into the exosuit’s mechanical efficiency, re- sponse time, and assistive performance. This visualization helps in evaluating motion smoothness, force distribution, and overall rehabilitation effectiveness.

Sensor Data Correlation and Adaptive Therapy: The integration of multiple sensors enabled real-time feedback, allowing dynamic adjustments to the exosuit’s assistance level. Data from force and IMU sensors were correlated with Kinovea motion analysis results to refine movement assistance strategies. This adaptive response mechanism ensures that the exosuit provides customized rehabilitation support based on individual progress, enhancing therapy personalization [3], [8], [9].

Overall Rehabilitation Outcomes: The implementation of the hybrid soft-hard exosuit demonstrated positive rehabilitation outcomes in terms of improved mobility, muscle engagement, and movement efficiency. The combination of adaptive actuation, real-time sensor feedback, and biomechanical motion tracking resulted in measurable progress in ankle rehabilitation. The system’s ability to provide both guided and user-initiated assistance makes it a promising solution for individuals recovering from ankle injuries, neurological impairments, and post-surgical conditions [4],[8],[9].

Fig. 9. Presents the final outcome tabulation of force, vibration frequency, PIR-based motion detection, IMU-derived ankle joint angle, servo motor actuation percentage, and gait cycle time across multiple trials.