Three-dimensional Tactile Sensor Research Articles

An improved BP neural network‐based calibration method for the capacitive flexible three‐axis tactile sensor array

Flexible tactile sensing based on capacitive sensing has become a research hotspot in recent years because of its low energy consumption, high performance and wide application prospects. However, the axis error caused by the coupling deformation of the dielectric will seriously affect the accuracy of the sensor. In this paper, a capacitive flexible three-axis tactile sensor array is modelled and simulated, and a neural network-based calibrator for the three-axis sensor array is proposed, which can be used to calibrate the simulated measurement data. The simulation results show that even though the correlation coefficient of linear regression for each axis is very close to 1, the effect of dielectric nonlinear coupling distortion cannot be eliminated. The calibration method based on the neural network can effectively suppress the nonlinear coupling distortion of the dielectric, and reduce the measurement coupling rate of the sensor model from 26% to 1%. At the same time, in order to ensure the measurement accuracy and robustness of different units in the sensor array, the input layer of the calibrator is expanded, and the data set containing capacitance information and two-dimensional location information is used for training. The experimental results show that the proposed calibration method combining two-dimensional position information training accurately calibrates the capacitive flexible three-dimensional tactile sensor array.

Softness-Adaptive Pinch-Grasp Strategy Using Fingertip Tactile Information of Robot Hand

We develop a tactile information-based pinch-grasp strategy enabling a robot hand to adaptively grasp easily deformable soft objects. When a robot hand has to perform grasping tasks, the grasp planner develops the grasping strategy based on visual information. However, the intrinsic properties of the target object, such as softness, cannot be detected appropriately using only visual feedback. To overcome this fundamental limitation, we aim to develop a softness-adaptive pinch-grasp strategy using fingertip tactile information. To achieve this, we first categorize soft objects based on the characteristic of resistance to deformation. Moreover, we design a three-dimensional tactile sensor that provides tactile information by measuring and localizing the distributed forces induced on its fingertip. In devising the adaptive grasp strategy, we focus on developing an algorithm that enables a robot hand to grasp soft objects by minimizing object deformation by controlling the pinch force based on the tactile feedback. The experimental results demonstrate that object deformation can be reduced by up to approximately 83.5% by the proposed strategy.

Triboelectric Self-Powered Three-Dimensional Tactile Sensor

Three-dimensional tactile sensing in smart devices is witnessing an increasing demand. In this study, a three-dimensional tactile sensor is proposed according to the principle of triboelectricity by using polydimethylsiloxane (PDMS) and polyethylene oxide (PEO) films. Use of PDMS-ZnO composite films increases the output voltage of the electrodes. The sensor is designed with a cross beam-shaped pressure head to enable sensing normal forces in five directions. The working mechanism of the sensor is analyzed using the finite element method. The calculation results indicate a linear relationship between the output voltage and the force. The simulation results also demonstrate that the output voltage is linearly correlated with the applied force in the range of 1–30 N. Test results show that the sensor can sense the magnitude, frequency, and direction of the force as well as measure the duration of the force. The hardness of the object has a significant effect on the output voltage. Finally, the sensor is tested on a manipulator grasping an object to demonstrate its ability to sense the contact and sliding of the object.

Development of a three-dimensional tactile sensor for minimally invasive instruments

This paper proposes a three-dimensional tactile sensor that can be attached to the tip of an endoscope or catheter to detect the tip contact conditions. Because conventional minimally invasive instruments (MIIs) without a sensor cannot detect the posture and applied force at the tip, operators cannot obtain accurate information during minimally invasive surgery (MIS). The sensor consists of an elastic cylinder and three strain g auges. The gauges, located on the surface of the cylinder at intervals of 120 � , are used to detect deformation of the cylinder caused by contact with the inner walls of the patient's organs. The output voltage signals of the gauges are approximated by a sinusoidal function with a phase difference of 120 � . The three-dimensional contact angle and applied force at the tip of the sensor can be estimated accurately from the three sinusoidal functions and measured output voltage signal from the gauges. The operating principle of the sensor is examined through several experimental conditions. To improve the effectiveness of minimally invasive surgery (MIS), it is necessary to develop better endoscope and catheter techniques. Conventional minimally invasive instruments (MIIs) improve the quality of life (QOL) of patients, because they can begin rehabilitation only a few days after MIS. However, the manipulation of MIIs is difficult because opera tors cannot obtain accurate information about the tip contact conditions of MIIs with the walls of the patient's organs. In conventional MIS, the operator manipulates the MII based on both the tactile sensations transmitted to their hand via the MII and the two-dimensional X-ray image information. However, tactile sensations are a mixture of the contact and friction forces with the walls of organs, and it is difficult to discriminate these forces precisely. Therefore, operators need to be highly trained; a lack of this skill on their part may lead to critical accidents. The abovementioned issues have necessitated the development of mechanisms for detecting the posture of the MII tip. Some active devices (1-4) have been developed to help manipulate catheters (3) and endoscopes (4). In these devices, shape memory alloys (SMAs) are used as actuators. In addition, inchworm locomotion (5) has been developed. An inchworm-like robot with a bellows mechanism

A New Multifunctional Three-Dimensional Tactile Sensor Using Three Coils

A new three-dimensional tactile sensor has been developed imitating the human finger based on multifunctional sensing technology. This sensor consists of three coils and two mediums. A step-by-step method is used to realize the multifunctional sensing and in each step, a different quantity is sensed. The processing method in spherical coordinates is introduced to resolve the force vector. On the basis of the unique structure of the sensor and ingenious measurement methods, the authors realized the aim of testing more than one quantity, that is, the magnitude and two direction angles of the force vector, with a single sensor. Here, we discuss the design guideline for and the structure of the sensor, with in-depth studies of the step-by-step measurement method and the experimental results.

An integrated MEMS three-dimensional tactile sensor with large force range

An integrated three-dimensional tactile sensor with robust MEMS structure and soft contact surface suitable for robotic applications was developed. The sensor has a maximum force range of 50 N in the vertical direction and ±10 N in the x and y horizontal directions. The tactile sensor includes 4×8 sensing cells each exhibiting an independent, linear response to the three components of forces applied on the cells. By finite element analysis, optimal cell structures and piezoresistor positions were determined. Post bulk-micromachining was performed on foundry-fabricated CMOS chips to produce the sensor cells. With neural network training, the tactile sensor produced reliable three-dimensional force measurements and repeatable response on tactile images. Design analysis, fabrication procedures, and experimental results are presented in this paper.