Soft Driving Coils for Conformal Electromagnetic Actuators

New developments in magnetically driven soft actuators typically focus on the magnetic materials’ orientation, microstructure and reconfigurability. Meanwhile the driving apparatus is usually a rigid circuit at some distance from the magnet. These setups enable researchers to control the magnetic field strength and direction in free space, controlling untethered magnetic materials. However, in soft robotic skins, soft active surfaces, and in wearable applications such as haptics for augmented reality, the driving circuit and magnetically actuated material are usually integrated into the same surface. In these systems, there are fewer requirements for magnetic actuation at a distance, and more requirements for the system to be be conformal, thin, and lightweight. This presentation describes a textile-based method for designing thin electromagnetic driving coils with surface actuation in mind. It covers methods for modeling the magnetic forces specifically from thin wire coils, describes coil fabrication methods, and evaluates the produced coils’ blocking forces, thermal performance, and bandwidth.<br/>For haptic systems that generate pressure sensations, devices are usually designed to produce vertical forces by inflation or by solenoid-type actuation. While the thin driving coils discussed in this work can produce vertical forces, their lateral force production is stronger over longer distances because lateral operation keeps the magnetic material close to the coils where the field and its gradient are strongest. These lateral motions produce lesser-explored haptic brushing sensations in the 5-mN “pleasant touch” range.<br/>Toward actuators that produce such lateral forces, a new rotary actuator is demonstrated on a 250-micron thick driving surface consisting of embroidered magnet wire in a nonwoven porous textile. Its thermal characteristics are measured in the 0- to 1 Ampere driving current range. A flexible and breathable 3D woven spacer fabric provides both thermal and mechanical isolation for the actuator coils and a moving magnet. Methods will be discussed for using stationary magnetic materials to provide restoring torque and latching forces for position holding. In addition, textile and thin sheet cutting methods can translate rotary magnetic motion into vertical motion of curved thin-film or thin-fabric beams by twisting the attachment points. This alternative to direct vertical magnetic motion is able to lift thin beams &gt;5 centimeters above the surface for light-touch haptic actuators, soft robotic skins that can change their surface texture, and other applications requiring soft active surfaces. High-speed automated assembly methods will also be discussed for placing magnetic materials on top of coils using textile machinery.