Available on-demand - *F.SM03.01.01
Soft Electrically-Driven Actuators for Wearable Haptics
Herbert Shea1
Ecole Polytechnique Federale de Lausanne, Switzerland1
Show Abstract
For virtual reality (VR) to be truly immersive, the sense of touch must be stimulated: a tennis ball should feel light and rubbery, a wall must be impenetrable, a lightswitch must click when pressed. Why don’t we have haptic suits with thousands of individual actuators (taxels) when every smartphone display has millions of individually addressed pixels? Generating localized forces on the human body in a comfortable and safe way is a major challenge for soft actuation: both fast motion and high forces are needed, yet the device must conform to the human body, and consume low power.
I will present some approaches developed in my lab for flexible actuators combining high strain and high force, operating at high speed, and that do not rely on external compressed air or vacuum supplies. Due to its high energy density, we have focused on electrostatic actuation, using high electric fields to deform elastomers or textile structures.
For kinesthetic feedback, which can be described as controlling the motion of joint, we have focused on textile-based brakes, only 1 mm thick, that can block the motion of two sliding strips in a few milliseconds[1]. By coating conductive textile strips with high permittivity dielectrics, we developed a clutch that blocks up to 20 N pulling force per square centimeter of active region, for a power consumption of under 2 mW. We integrated these clutches into thin gloves. Users wearing them are much more accurate when manipulating virtual objects and feel deeper immersion. We will report a new fabrication method allowing for even higher forces for use in full-body kinesthetic haptics, blocking shoulder and elbow motion to allow feeling virtual objects as being heavy, and virtual tables as blocking hand motion.
Cutaneous feedback requires dense arrays of actuators to locally stimulate to skin to provide the illusion of touching an object. We use our fingers to identify objects by sliding our fingertips over them, and we know if a glass is about to slip out of our hand by sensing shear forces. Simulate this in VR requires being able to generate normal and shear forces with high spatial resolution. We have developed arrays of sub-mm thick flexible actuators that generate over 60% strain and operate at over 300 Hz. A 6 mm diameter actuator generates 300 mN normal force and 500 µm displacement. This is achieved using fluidically coupled electrostatic zipping and a combination of flexible polymers with high breakdown field and silicone elastomers that allow for high displacement[2]. We have made 5x5 arrays, mounted them directly on the arm and on consumer products, and report on user feedback for notification, control and navigation.
By use of thin dielectrics, high permittivity films, and low stiffness electrodes, we have reduced the drive voltage of Dielectric Elastomer Actuators (DEAs) to 400 V, a level at which we can use SMD components for compact control electronics[3]. We report “feel-through” untethered cutaneous haptics, with DEA actuators only 18 µm thick, so thin the user does not feel them mounted on his or her fingertip when they are off. However, when the 3 mm diameter devices are turned on, the user feels localized pulsation that allows receiving rich haptic information.
I will close by going over the challenge of integrating these technologies in a glove or suit, and the promise of this field.
[1] R. Hinchet and H. Shea, “High Force Density Textile Electrostatic Clutch,” Advanced Materials Technologies, vol. 5, p. 1900895, 2019, doi: 10.1002/admt.201900895.
[2] E. Leroy, R. Hinchet, and H. Shea, “Multimode Hydraulically Amplified Electrostatic Actuators for Wearable Haptics,” Advanced Materials, 2020. in press.
[3] X. Ji et al., “An autonomous untethered fast soft robotic insect driven by low-voltage dielectric elastomer actuators,” Science Robotics, vol. 4, no. 37, 2019, doi: 10.1126/scirobotics.aaz6451.