Knee Unilateral Retractor (Post-Surgical Rehab Brace)

A knee brace design for controlled staged rehabilitation after knee surgery. The system helps patients regain full range of motion (ROM) safely using an angle-limited actuator and phase-based constraints.

1. Project Goals

• Support safe controlled flexion/extension after surgery.
• Enforce progressive ROM limits per recovery stage.
• Provide repeatable motion control with safety stops and user/clinician override.
• Log usage and provide simple status feedback.

2. Rehab Stages and Target ROM

1. Stage 0 - Immobilization/Protection
   • Goal: protect repair, limit flexion to 0-30°
2. Stage 1 - Early Motion
   • Goal: gradual flexion to 0-60°
3. Stage 2 - Mid-phase Recovery
   • Goal: 0-90° with increasing tolerance
4. Stage 3 - Full ROM
   • Goal: 0-120°+ (or as patient-specific target)

Note: Clinician must define angles and progression cadence for each patient.

3. High-Level System Architecture

• Inputs

  • User buttons / app commands
  • Physical limit switches / I/O safety

• Control Logic

  • Current stage values: stage, angle_min, angle_max, max_rate
  • PID / bang-bang output for actuator
  • Emergency stop handling

• Outputs

  • Actuator (motor, stepper, linear actuator, servo)
  • Brake/lock mechanism
  • UI (web app)

4. Hardware Components

• Chassis: adjustable knee frame + straps
• Actuator: 12V stepper with current sense and brake
• Microcontroller: Arduino nano
• Power: 12V battery/AC adapter with overcurrent and thermal protection
• Safety chains: mechanical hard stops, emergency release, quick disconnect

5. Software Flow

1. Start and self-check (sensor range, actuator readback, safety switches)
2. Load stage from config or clinician input
3. Enforce stage bounds: target_min, target_max
4. Read current angle at 50-100 Hz
5. Compute control output and cap by max_speed
6. Check safety (overextension, current/torque limit, timeout, emergency)
7. Log and display status
8. On stage change: gradually adjust limits rather than abrupt unlock

6. Safety / Certification Notes

• Include mechanical fail-safe that cannot overflex if electronics fail.
• Add redundant sensing for angle limit (active and passive stops).
• Implement watch-dog and galvanic isolation for patient safety.
• Validate with a licensed physical therapist and surgical team.