Ungrounded Reaction Wheel Neurorehabilitation
Mitti replaces rigid orthotic bracing with ungrounded angular momentum (T = I · α), 100 Hz Dual-IMU intention gating, and Assist-as-Needed kinesthetic stimulation for pediatric patients with hypotonia.
Core Biomechanical Rationale & Physics
Why ungrounded reaction wheels represent a paradigm shift over conventional exoskeletons and passive corsets.
Ungrounded Torque Generation
Traditional assistive devices are grounded: they push against the floor or brace adjacent limbs with rigid mechanical exoskeletons. This severely restricts natural joint degrees of freedom and induces muscle disuse atrophy.
Mitti generates ungrounded torque purely through the angular acceleration of spinning flywheel rotors mounted on the torso. The child experiences pure corrective rotational moments without any rigid grounding structures or joint constraints.
- ✓ Complete anatomical freedom of movement
- ✓ Lightweight wearable form factor (< 250 g per capsule)
- ✓ Instantaneous dynamic response without structural backlash
Active Kinesthetic Cueing & Assist-as-Needed
Aligned with the clinical principles of Dynamic Movement Intervention (DMI), Mitti does not carry the patient's body weight. Instead, it provides brief tactile cues to stimulate the child's own proprioceptive reflex arc.
When a deviation is sensed, a brief torque impulse cues the central nervous system, prompting the child to actively recruit stabilizing trunk muscles and fostering authentic neuroplastic motor learning.
Pulsed Sawtooth Dithering
Continuous pressure leads to sensory habituation (neural adaptation). Mitti utilizes an asymmetric pulsed sawtooth profile with asynchronous phase resets to maintain neural alertness without sensory fatigue.
100 Hz Dual-IMU APA Intention Gating
How Mitti distinguishes voluntary pediatric movement from involuntary falls, eliminating unwanted resistance while providing immediate fall arrest.
Dual-IMU Differential Kinematics
Mitti continuously samples synchronized 6-DoF IMUs located at the thoracic spine and the pelvic girdle, coordinating kinematics via deterministic low-latency telemetry (<10ms).
- Differential Inclination: Computes Δθ = θspine - θpelvis to isolate true spinal flexion from hip bending.
- Differential Angular Velocity: Computes Δω = ωspine - ωpelvis to detect sudden postural collapse.
- Zero Inter-Module Drift: Bi-directional time-synchronization eliminates phase jitter across the torso.
Anticipatory Postural Adjustments (APAs)
Assist-as-Needed control requires that assistive torque never fights the child's intentional exploration. Voluntary reaching is always preceded by feedforward pelvic weight shifts.
- Voluntary Motion (1.6× Deadband): Pelvic acceleration precursor (0.15 ≤ |alat| ≤ 2.5 m/s²) latches a 250ms voluntary window, widening the deadband by 1.6× for complete movement freedom.
- Involuntary Stumble (0.6× Deadband): Sudden spine jerk (|jspine| ≥ 15 m/s³) or angular acceleration (|Δω̇| ≥ 250°/s²) without pelvic shift instantly contracts the deadband by 0.6× for immediate fall arrest.
Trapezoidal Neuromuscular Pulse Shaping
Accommodates peripheral demyelinating conduction delays (~200 ms latency) without triggering oscillatory stretch reflex recoil or joint capsule shock.
- 50 ms Jerk-Limited Ramp: Constrains dT/dt ≤ 30 Nm/s to protect pediatric cartilage and soft tissue.
- 150–300 ms Sustained Plateau: Bridges the 200 ms reflex delay so proprioceptive feedback stays coherent during active motor recruitment.
- 100 ms Controlled Ramp-Down: Eliminates antagonist reflex rebound and contralateral postural overshoot.
3 System Pillars: Mechatronics & Control Architecture
A modular, distributed architecture engineered for pediatric clinical safety, low latency, and zero rigid mechanical constraint.
Bilateral Kinetic Capsules
Ultra-compact, whisper-quiet (<35 dBA) slotless direct-drive reaction wheel capsules nestled into a breathable pelvic band. Delivers sub-maximal ungrounded rotational impulses (T = I · α, ≤1.5 Nm) to awaken deep postural reflexes without rigid immobilization or floor struts.
Synchronized Dual-IMU Array
Bilateral kinematic tracking between the thoracic spine and pelvis at 100 Hz. Differentiates intentional child movements (APAs) from involuntary postural collapse, widening assistance deadbands by 1.6× during active play and contracting them instantly upon detecting an unexpected stumble.
Clinician Control & Telemetry Suite
Dedicated clinician and parent interface providing real-time spine inclination feedback, torque delivery metrics, instantaneous therapy mode switching across the 6 clinical profiles, and automated Level G4 neuroplastic progress reporting.
Ultra-Compact Hip Actuator Capsule (< 250 g)
Biocompatible medical-grade enclosure nestled seamlessly in an ergonomic breathable pelvic band with quick-release magnetic clasp. Engineered for zero cogging torque, acoustic silence (<35 dBA), and unrestricted pediatric mobility.
6 Clinical Operational Modes
The embedded control firmware supports 6 dedicated operational modes, coordinated between the thoracic Hub and bilateral Actuators. To maintain clean architectural boundaries, comprehensive therapeutic rationales and clinical protocols reside in the Clinical Overview hub.
Rigorous Clinical Safety Architecture
Controlled Exponential Washout
Upon packet loss or heartbeat timeout, motor torque decelerates along a calibrated exponential curve, preventing sharp angular momentum backlash into pediatric spinal segments.
Active Low-Side Dynamic Braking
If the link remains unrecovered, the inverter engages low-side FET dynamic braking to safely dissipate kinetic energy from the reaction wheel rotor before power disconnection.
Independent Hardware Power Cut
The independent hardware watchdog isolates the power bus via high-side MOSFET switches and redundant overcurrent protection if communication fails to recover.
Continuous Spectral Fatigue Attenuation
Enforces a hard limit of max 40 impulses per 2-minute rolling window, continuously monitoring patient tremor frequency to prevent muscle exhaustion.
Software-in-the-Loop (SITL) MuJoCo Physics
Uncompromised first-principles physics validation linking native C++ firmware loops with high-fidelity robotic simulations.
Virtual Proving Ground Before Clinical Trials
Mitti's native firmware code is compiled directly as an x86/ARM host binary that communicates via real-time UDP packets with a MuJoCo multi-body physics simulation.
- •Humanoid Standing Balance: Evaluates active trunk stabilization under external perturbations and simulated hypotonia.
- •Balance Bike Dynamic Damping: Validates roll-axis stabilization on moving pediatric balance bikes.
- •Automated Parameter Sweeps: Validates motor saturation, inertia sizing, and thermal profiles across 30+ simulated scenarios.
1-DoF Inverted Pendulum validation: SITL simulated kinematics vs. physical bench telemetry.
Interactive 60 Hz Browser Physics Sandbox
Inject lateral perturbations, test Trapezoidal DMI assistive torque cues, and observe 3-stage graduated failsafe washout across clinical pathology profiles in real time.
Interactive Real2Sim & Trapezoidal DMI Physics Sandbox
Simulate pediatric trunk posture under lateral perturbations. Compare delayed CNS reflex loops (CMT1B 200ms vs Hypotonia 50ms), active reaction-wheel momentum exchange, and 3-stage graduated failsafe washout in real time.