A Soft Touch: Wearable Tactile Display of Softness Made of Electroactive Elastomers

Abstract

Fingertip‐mounted tactile displays of softness are needed for various virtual‐ or augmented‐reality applications such as surgical simulation, tele‐operation, computer‐aided design, 3D model exploration, and tele‐presence. Displaying a virtual softness on a fingertip requires the generation of quasi‐static large displacements at moderate forces (as opposed to high‐frequency small vibrations at high forces), via a deformable surface, to control both the contact area and the indentation depth of the skin. State‐of‐the‐art actuation technologies are unable to combine simple structure, low weight, and low size, as well as energy efficiency and silent operation. Here, the progress on the development of a non‐vibratory display of softness made of electroactive polymers is reported. It consists of a hydrostatically coupled dielectric elastomer actuator, shaped as a bubble interfaced to the fingertip, having a weight of 6 g. Prototypes can generate displacements up to 3.5 mm and forces up to 1 N. By combining this technology with a compact hand tracking sensor, a simple and cost‐effective virtual‐reality system is demonstrated. A psychophysical study engaging 15 volunteers in poke and pinch tactile tasks shows that users can properly distinguish between different stimuli rendered by the display, with an accuracy correlated to the perceptual difficulty of the tactile comparative task.

Soft Sensors and Actuators for Wearable Human–Machine Interfaces

“…These advancements have led to the achievement of high mechanical output force of up to 2 N and large displacements of up to 9.3 mm (Figure ). − ,, The high force and large displacement capabilities of soft actuators have made them valuable for practical applications, including haptic displays and soft grippers. , …”

“…57 These advancements have led to the achievement of high mechanical output force of up to 2 N and large displacements of up to 9.3 mm (Figure 14). [56][57][58]357,358 The high force and large displacement capabilities of soft actuators have made them valuable for practical applications, including haptic displays and soft grippers. 359,360 DEAs offer several advantages, including a large strain of 503%, 361 fast operation with a frequency of 280 Hz, 362 and lightweight characteristics.…”

“…363 To enhance the output force of DEAs, an incompressible and insulating fluid, such as silicone grease, has been mechanically coupled with DEAs (Figure 14a). 358 In this configuration, an active membrane is coupled to a passive membrane through the insulating fluid. When a voltage is applied, the electrostatic stress greatly expands the dielectric elastomer layer, leading to a significant increase in curvature of the active membrane on the opposite side of the fingertip.…”

“…When a voltage is applied, the electrostatic stress greatly expands the dielectric elastomer layer, leading to a significant increase in curvature of the active membrane on the opposite side of the fingertip. 358 This hydrostatically coupled DEA (HC-DEA) allows for the generation of quasi-static (nonvibratory) force, resulting in a large strain. By increasing the number of elastomeric layers coated with compliant electrodes up to four layers, the HC-DEA is capable of achieving displacements up to 3.5 mm and forces of up to 1 N.…”

A Soft Electro-Hydraulic Pneumatic Actuator with Self-Sensing Capability toward Multi-Modal Haptic Feedback

“…The actuator was composed of a thin plastic pouch containing a low-boiling-point liquid. The maximum output force of the actuator could reach almost 1.5 N. Carpi et al [19] reported a nonvibratory display of softness made of electroactive polymers. It consisted of a hydrostatically coupled dielectric elastomer actuator, shaped as a bubble interfaced to the fingertip, having a weight of 6 g. Prototypes could generate displacements up to 3.5 mm and forces up to 1 N. Leroy et al [20] proposed multimode hydraulically amplified electrostatic actuators for wearable haptics.…”