Robots are reliant on a complex system of power sources, wires, composite microstructures and circuitry to make them function. One important component which enables them to travel is the actuator, the part of the machine responsible for moving and controlling a mechanism or system, like a valve opening.
An actuator needs a control signal – something low energy, like an electric voltage or current, or hydraulic or pneumatic pressure, even human touch – and an energy source. When the control signal is received, the actuator responds by converting the signal’s energy into a mechanical motion, i.e. the valve actually opening.
Applications of Electrostatic Actuators
Electrostatic actuators are preferred for surface-micromachined structures as they are easily implemented and scaling laws for electrostatic forces are favorable, meaning a large field can be obtained from a modest voltage because the small distances involved. They require low direct current power, and are fast switching compared to other actuation mechanisms such as MEMS. Their fabrication process is also compatible with standard microelectronics techniques. However, they can require large voltages and therefore necessitate high-voltage electronics for control, which becomes a barrier for integration with standard electronics.
This kind of actuator typically consists of a set of movable conducting electrodes – conductive plates or combs – separated by an insulating dielectric (an electrical insulator that can be polarized by an applied electric field). Actuation relies on the force between the two conducting electrodes when a voltage is applied between them. Depending on how the electrodes are arranged various actuators are possible, but whichever configuration they are in, so long as there is mutual capacitance, there is nearly always an attractive force when the voltage is applied.
Conventional robots can be rigid, powerful and robust, but what happens if they need to squeeze into a tight space, or cope with complex terrains or changing environments? They find it difficult to adapt, so researchers have been developing soft robots.
Robots are often constructed from smart composite microstructures; thin-film or sheets of various materials that are painstakingly patterned, layered and bonded together individually to yield a functional, multi-layer composite. Each layer of the composite can be tailored depending on the required function; structure, actuation, flexibility, or as a sensor.
Thin-Film Electrostatic Actuators in Robot Construction
However, these more flexible robots have been hampered by the fact that actuation methods and materials are large, heavy, slow and difficult to fabricate. Thin-film electrostatic actuators could help solve the problem. Such actuators and adhesives operate at high voltages and have potential as light-weight, low-cost force sources in millimeter and centimeter scale robots.
A team from the Thayer School of Engineering at Dartmouth College in the USA have used thin-film electrostatic actuators to create a robotic bug that can climb an ascending incline of up to 30°, recover its shape after crushing, and can adapt to walk on rough and smooth surfaces. It is also highly maneuverable and can steer precisely into a designated space. Such soft robots could find uses in surveillance, search and rescue and detection operations where traditional robots are fairly impractical.
Other uses might include a robotic swarm that can be flat packed and deployed when needed – it has potential uses in microgravity and space operations to monitor the outside of a satellite, or even the International Space Station. Another novel application could see them integrated into petri dishes where they would as a mechanical stimulation for cells in cell assays, or they could be applied as a thin film coating to airplane wings to modulate air flow and reduce turbulence over the wing, or on the windows of buildings to control film transparency and reflect or transmit light.
References and Further Reading