These 3D-Printed "Pneumatic Logic Gates" Make for Robust, Electronics-Free Soft Robotics

Researchers from the University of Freiburg have come up with a way to replace electronics in robots with simple 3D-printed pneumatic logic gates — capable of performing Boolean feats and robust enough to withstand being driven over by a car.

“Our design makes it possible for anyone with 3D printing experience to produce such logic modules and use them to control a soft robot without the need for high-end printing equipment," claims project co-lead Stefan Conrad, PhD, of the team's work. "This marks a significant step towards completely electronics-free pneumatic control circuits that can replace increasingly complex electrical components in soft robots in the future."

The modules, which can be put together to form surprisingly complicated soft-body robots entirely free from electronics, can be printed on off-the-shelf 3D printers using standard low-cost filaments. Each module has two pressurized chambers separated by a channel which can be compressed to stop the air flow — creating a simple valve which, by virtual of its binary nature, can be used to make the Boolean logic gates AND, OR, and NOT, all without electronics.

"The potential applications of these modules are enormous," co-lead Falk Tauber, PhD, claims. "We have developed a flexible 3D-printed robotic walker that is controlled by an integrated circuit using air pressure. The flexibility of the logic modules is demonstrated by the fact that this walker can even withstand the load of a car driving over it. As an example of more complex control systems, we have also developed an electronics-free drinks dispenser."

Said drinks dispenser features a pneumatic ring oscillator, built from eight of the modules, and a one-bit memory. "These eight PLGs [Pneumatic Logic Gates] formed a ring oscillator that periodically switched eight independent output signals," the researchers write. "By connecting one signal to each segment of the pump, the circuit caused a full closing cycle from the bottom to the top before it started opening again. To stop the oscillation, the output signal of the last buffer is fed through an OR gate before returning to the NOT module."

"Pressing the button sent a LOW signal to the SET input of the latch," the team continues, "which changed its output signal to LOW. This then activated the peristaltic pump by allowing the oscillating signal to pass the OR gate. The water level in the beaker rose, causing an increase in the load on the platform. The weight sensor below the platform consisted of a compliant lever and a pressurized tube that kinked when the lever bent under the increasing force.

"As soon as the load obstructed the airflow in the tube, the pressure at the sensor output dropped because of a small hole acting as a pull-down resistor, and the latch received a LOW signal on its RESET input. This switched its output back to HIGH, and the ring oscillator was deactivated, because the LOW signal could not pass the OR gate any more."

The team's work has been published under open-access terms in the journal Science Robotics.