Technology
Soft Robotics Using Variable Stiffness Actuators
Quick fact
Some variable stiffness actuators can change their rigidity by a factor of over 100 times in milliseconds, using materials that respond to electric fields or temperature.
Why this is interesting
Imagine a robot that can be as soft as a marshmallow to safely hold an egg, then instantly stiffen to drill a hole. How can one machine be both floppy and rigid on demand?
Read the full explanation
Understanding Soft Robotics Using Variable Stiffness Actuators
Traditional robots are made of rigid metal joints, which are strong but dangerous around humans. Soft robots are made of flexible materials like silicone or rubber, making them safe and adaptable. However, pure softness means limited force. Variable stiffness actuators solve this dilemma: they are soft when needed, but can increase their stiffness to apply force or hold shape. Think of a floppy balloon that can become a firm tire when filled with air. The actuator's stiffness is controlled by an external stimulus: air pressure, electric current, or a magnetic field, changing the material's internal state.
A deeper explanation
The underlying mechanism involves materials that change their internal structure or state in response to stimuli. For example, in pneumatic-based actuators, increasing air pressure in a flexible chamber stretches internal fibers, increasing resistance to bending and thus stiffness. Shape-memory alloys (SMAs) change their crystal structure when heated, becoming rigid. Magnetorheological (MR) fluids contain iron particles that align under a magnetic field, transforming from a liquid to a thick, stiff paste. By integrating such materials into a robot, a control system can adjust stiffness in real time, enabling the robot to perform tasks like gently gripping a strawberry, then switching to a rigid mode to apply a precise force. This capability is crucial for wearable robotics, deep-sea manipulation, and medical devices where safe yet effective interaction is required.