3D printing enables muscle-like movements for robots

Engineers at Northwestern University have developed a new type of actuator that enables robots to perform muscle-like movements. The research group led by Professor Samuel Truby used 3D printing to produce flexible components that can move through expansion and contraction.

The team constructed two prototypes. A worm-like robot and an artificial bicep. The worm robot successfully navigated through tight spaces, while the biceps was able to lift a 500-gram weight 5,000 times. The cost per robot is around 3 dollars, excluding the small motor to change its shape.

The researchers used cylindrical ‘Handed Shearing Auxetics’ (HSAs) made of rubber, which expand and widen when twisted. Earlier HSA versions made of rigid plastic were less flexible. Taekyoung Kim, postdoctoral researcher and first author of the study, solved this problem by using thermoplastic polyurethane and a low-cost desktop 3D printer.

A key innovation was the integration of soft, stretchable rubber bellows as a deformable rotating shaft. This allowed the actuator to be controlled by a single servo motor, which simplified the design and increased softness. The resulting 26-centimetre-long robot reaches a speed of over 32 centimetres per minute.

Professor Truby emphasises the importance of this development for safety in human-robot interaction: ‘If a soft robot hits a human, it would not hurt nearly as much as a rigid, hard robot. Our actuator could be used in robots that are more practical for human-centred environments.’

The ability of soft actuators to stiffen during operation, similar to human muscles, is an important advance. This bio-inspired property improves the ability to move and extends the range of applications of soft robots compared to conventional systems.

The research results, published in the journal ‘Advanced Intelligent Systems’, show the potential of 3D-printed soft actuators for the development of safe and flexible robots. Future applications could range from industrial automation to medical assistance systems.