Flexible three-axial force sensor for soft and highly sensitive artificial touch

Abstract

A soft tactile sensor able to detect both normal and tangential forces is fabricated with a simple method using conductive textile. Owing to the multi-layered architecture, the capacitive-based tactile sensor is highly sensitive (less than 10 mg and 8 μm, for minimal detectable weight and displacement, respectively) within a wide normal force range (potentially up to 27 N (400 kPa)) and natural touch-like tangential force ranges (from about 0.5 N to 1.8 N). Being flexible, soft, and low cost, this sensor represents an original approach in the emulation of natural touch.

Keywords: artificial touch; conductive textile; soft tactile sensor; three-axis force; wearable electronics.

Figure 1

Schematic representation and description of the sensor architecture (a) with corresponding cross‐sectional view (b). c,d) Illustration of the flexible sensor. Inset in (d) shows an optical microscopy picture of the conductive textile electrode.

Figure 2

Typical sensor responses to normal and tangential force load–unload cycles. a,b) Sketches and optical microscopy pictures of the sensor's cross section depicting the experimental protocols performed: a) applying forces in the normal direction F_z; b) applying a static normal force and tangential displacement inducing a tangential force stimulation F_x (scale bars: 200 μm). c,d) Responses of the sensor, positioned on a flat surface, to F_z = 1 N normal force (c) and to the tangential force F_x produced with a static normal force F_z = 1 N and tangential movement (d) (S5, Supporting Information). The same experiments were repeated with the sensor on a 2 cm radius curved surface (e) and (f). Sensor responses related to the perpendicular axis, and due to non‐pure axis applied forces are represented in dashed lines.

Figure 3

Sensor performances: a,b) Normalized capacitance variation of the sensor versus normal force/pressure in the 0–1 N (0–20 kPa) and the 0–12 N (0–190 kPa) range, respectively. The sensitivity S_z (in kPa⁻¹) is indicated in brackets for different pressure ranges for comparison with the literature. c) Capacitance variation signals for a weight of 80, 15, and 10 mg, corresponding to average values of ΔC of 0.15, 0.05, and 0.025 pF, respectively, after contact. d) Normalized capacitance variation versus the tangential force F_x, in the case of either 0.5 N or 1 N applied static normal force F_z. The sensitivity S_x in the linear region was 0.3 N⁻¹.