An exoskeleton is a wearable structure that works in parallel with the human body. Passive versions store and return energy with springs; active exoskeletons add powered actuators at the joints, controlled by a computer that reads the wearer's intent and delivers assistive torque — reducing fatigue, augmenting strength, or restoring motion after injury.
Working principle
The control loop runs three stages. Sense: encoders, IMUs and force sensors track joint angles and loads, while EMG can detect muscle activation to infer intent. Decide: a controller estimates the desired motion and computes the assistive torque, often using gait phase or impedance control. Act: electric or hydraulic actuators apply torque at the hips, knees or elbows, synchronised with the wearer's movement.
| Property | Passive | Active |
|---|---|---|
| Power source | Springs / structure | Motors / hydraulics |
| Assistance | Fixed, energy return | Adaptive, controllable |
| Weight | Lighter | Heavier (battery, motors) |
| Best use | Repetitive support | Strength aug., rehab |
Key constraintThe central design tension is power-to-weight and battery life: more actuation means more assistance but also more mass to carry — pushing research toward efficient actuators and quasi-passive designs.
Applications
- Industrial lifting support to prevent back injury
- Gait rehabilitation for stroke and spinal-cord patients
- Mobility restoration for paraplegic users; military load carriage
References & further reading
- Dollar & Herr, “Lower Extremity Exoskeletons and Active Orthoses,” IEEE Trans. Robotics, 2008.
- Sawicki et al., “The exoskeleton expansion: improving walking and running economy,” J. NeuroEng. Rehab., 2020.
- Young & Ferris, “State of the Art and Future Directions for Lower Limb Robotic Exoskeletons,” IEEE TNSRE, 2017.