A liquid lens-based optical sensor for tactile sensing

Abstract

Tactile sensing plays a crucial role in robot manipulation, robot interaction, and health monitoring. Because of high sensitivity, simple structure, and superior interference immunity, optical tactile sensors based on optical imaging or optical conduction have been one of the most active research. Herein, a novel liquid lens-based optical sensor (LLOS) is presented. Different with existed optical tactile sensors, the main body of the proposed sensor belongs to a variable-focus optical lens with a liquid-membrane structure, and its focal length is changed with the contact force, thereby changing the propagation direction of light and affecting the perceived light intensity of the photosensitive element. By conducting some testing experiments, the LLOS demonstrates fast response (about 0.021s), stable dynamic response characteristics, and good linearity (R-squared is about 0.99), repeated measurement accuracy(<0.006V), and measurement accuracy (< 0.2N). Hence, the LLOS provides a new and promising method to measure tactile and has potential application in robotics nondestructive grasping and interactive input devices.

A Tactile Sensing Concept for 3D Displacement and 3D Force Measurement using Light Angle and Intensity Sensing

“…A typical working principle of a non-camera-based optical tactile sensor utilizes the detection of a change in light intensity by a photodetector [7] when a contact force occurs, which allows tactile information to be extracted from these changes in measured intensity. Tactile optical-based sensors take a variety of shapes and use different materials such as elastomers, optical fibers [22], photodiodes [7], and liquid lenses [23].…”

“…3) that can estimate 3D point displacements and 3D point forces by interpreting the measured angle and intensity of light (i.e., the light vector) arriving at an optical sensor; thus, we named it the LiVec sensor. Compared with other existing optical-based tactile sensors [9], [23], [27], [28], the LiVec sensor has a simple structure consisting of a soft deformable skin, LEDs, and a light angle and intensity sensor. All the sensing elements are combined onto a singular printed circuit board (PCB), giving it the potential for substantial volume reduction compared to other existing tactile sensors [7] [10], [21], [25], [29]- [31] [32] and significantly reducing the complexity of the manufacturing process.…”

Research on a flexible optical tactile sensor based on a liquid lens structure

“…Based on the different development principles, the existing tactile sensors are mainly divided into capacitive 7 , piezoresistive 8 , piezoelectric 9 , triboelectric 10 , and optical 11,12 . Among them, the optical tactile sensor has the advantages of no electromagnetic interference, simple structure, low power consumption, wide dynamic range, and high resolution 13,14 .…”

Liquid Lens‐Based Optical Tactile Sensor with a Touch‐Sensing Separable Structure

“…Therefore, according to this, different with existed optical conduction‐based tactile sensors, the output of our tactile sensor increase with the increase of external contact force. However, in our previous work, we only preliminarily explored the feasibility of the sensing method based on the liquid lens, so the proposed sensor has many drawbacks in sensing structure, [ 38 ] which are embodied in large dimension, small measurement range, and low resolution (as shown in Table 1 ). Moreover, the proposed sensor contains a big and rigid liquid vessel and many optics components, which makes the sensor becomes a bulky integration.…”

“…To reduce the interference caused by optical loss, in our previous work, we presented an optical tactile sensor based on the principle of the liquid lens. [38] The liquid lens as a kind of variable-focus lens has many advantages, such as simple structure, fast response, and low optical loss, [39−41] and thus has been applied to the optical imaging field. [42,43] Moreover, the liquid lens has the characteristic that its focal length can decrease with the increase of liquid volume in the lens, which makes the incident light converge toward a center point.…”