Tactile Modules Research Articles

Design & characterization of a bio-inspired 3-DOF Tactile/Force sensor and implementation on a 3-DOF decoupled parallel mechanism for human-robot interaction purposes

This paper presents the design and implementation of a Tactile/Force sensor which has been used on a 3-DOF decoupled parallel mechanism for Human-Robot Interaction purposes.The sensor, called HexaTactile, is a soft tactile sensor array based on six MEMS barometers, where each of them is covered by a silicone layer in the form of an incomplete pyramid. HexaTactile consists of six soft and highly sensitive tactile modules which are placed on six sides of a cube to allow simultaneous measurement of the force in the positive and negative directions along the x, y and z axes. Some of the advantages of this sensor can be regarded as its high precision, excellent linearity (coefficient of determination r2=0.99), low cost and low noise. The accuracy of the sensor is 0.01 N, within a range of 4 N and therefore HexaTactile can be suitably attached to a robot end-effector for human-robot interaction applications. Then, using the proposed force sensor some control scenarios, including fixed admittance control and active admittance control are applied for human-robot interaction purposes. From the experimental tests, it has been revealed that the active admittance control solved the drawbacks of fixed admittance control, for the considered case studies.

Development of an Electrostatic Beat Module for Various Tactile Sensations in Touch Screen Devices

One of the most dominant factors in developing tactile modules is the ability to generate abundant vibrotactile sensation. This paper presents a new vibrotactile module which can stimulate two mechanoreceptors at the same time without any mechanical vibration motors. To realize that, we first design an electro-tactile beat module (an ETB module) consisting of a lower part, a connection part and an upper part. The two electrodes were designed in an interdigitated pattern and were applied to the upper part. By applying two voltage inputs with slightly different frequencies to two electrodes in the proposed ETB module, respectively, we can create beat-patterned vibration. Furthermore, we can create normal vibration with the proposed ETB module by applying same frequency to the two electrodes. Experiments were conducted to validate the haptic performance of the proposed prototype. The results show that the proposed ETB module can create not only beat-patterned vibration but also normal vibration. The results also show that it can generate strong enough vibration to stimulate mechanoreceptors in wide frequency ranges.

Alignment turning system for precision lens cells

This research increases the ability and value of a traditional vertical lathe and applies to manufacture a precise lens cell for the optical industry. The optical performance is limited by the residual centration error and position accuracy of conventional assembly methods. Recently, the development of a poker-chip assembly system with high-precision lens barrels has overcome these limitations and provided a solution for ultra-high-performance optical systems. To develop a high-precision lens cell by using poker-chip assembly, an alignment turning system (ATS), is developed based on a vertical lathe and equipped with tactile and optical measurement modules. Inside the ATS, the building-in the vibration/temperature monitoring sensors, which help to self-monitoring and network communication with the intelligent manufacturing techniques, to understand and master the reliability and efficiency of ATS. This system can manufacture precise lens cells, applied for optical metrology, high numerical aperture objective lenses, and lithography projection lenses. This paper describes the design and development of the ATS and its capabilities. The ATS is composed of measurement, alignment, and turning modules. After the ATS completes the measurement, alignment, and turning processes, the centration error of a lens cell, which is 200 mm in diameter, can be controlled to within 10 arcsec. Here, a lens cell with three subcells was assembled through the poker-chip method; each subcell was measured and then it underwent alignment and turning processes. The lens assembly test was performed five times by three technicians, and the average transmission centration error of the assembly lens was 12.45 arcsec. The results demonstrate that the ATS can achieve considerable assembly efficiency for high-precision optical systems.

An Extreme Learning Machine-Based Neuromorphic Tactile Sensing System for Texture Recognition.

Despite significant advances in computational algorithms and development of tactile sensors, artificial tactile sensing is strikingly less efficient and capable than the human tactile perception. Inspired by efficiency of biological systems, we aim to develop a neuromorphic system for tactile pattern recognition. We particularly target texture recognition as it is one of the most necessary and challenging tasks for artificial sensory systems. Our system consists of a piezoresistive fabric material as the sensor to emulate skin, an interface that produces spike patterns to mimic neural signals from mechanoreceptors, and an extreme learning machine (ELM) chip to analyze spiking activity. Benefiting from intrinsic advantages of biologically inspired event-driven systems and massively parallel and energy-efficient processing capabilities of the ELM chip, the proposed architecture offers a fast and energy-efficient alternative for processing tactile information. Moreover, it provides the opportunity for the development of low-cost tactile modules for large-area applications by integration of sensors and processing circuits. We demonstrate the recognition capability of our system in a texture discrimination task, where it achieves a classification accuracy of 92% for categorization of ten graded textures. Our results confirm that there exists a tradeoff between response time and classification accuracy (and information transfer rate). A faster decision can be achieved at early time steps or by using a shorter time window. This, however, results in deterioration of the classification accuracy and information transfer rate. We further observe that there exists a tradeoff between the classification accuracy and the input spike rate (and thus energy consumption). Our work substantiates the importance of development of efficient sparse codes for encoding sensory data to improve the energy efficiency. These results have a significance for a wide range of wearable, robotic, prosthetic, and industrial applications.

Humanoid Multimodal Tactile-Sensing Modules

In this paper, we present a new generation of active tactile modules (i.e., HEX-O-SKIN), which are developed in order to approach multimodal whole-body-touch sensation for humanoid robots. To better perform like humans, humanoid robots need the variety of different sensory modalities in order to interact with their environment. This calls for certain robustness and fault tolerance as well as an intelligent solution to connect the different sensory modalities to the robot. Each HEX-O-SKIN is a small hexagonal printed circuit board equipped with multiple discrete sensors for temperature, acceleration, and proximity. With these sensors, we emulate the human sense of temperature, vibration, and light touch. Off-the-shelf sensors were utilized to speed up our development cycle; however, in general, we can easily extend our design with new discrete sensors, thereby making it flexible for further exploration. A local controller on each HEX-O-SKIN preprocesses the sensor signals and actively routes data through a network of modules toward the closest PC connection. Local processing decreases the necessary network and high-level processing bandwidth, while a local analog-to-digital conversion and digital-data transfers are less sensitive to electromagnetic interference. With an active data-routing scheme, it is also possible to reroute the data around broken connections-yielding robustness throughout the global structure while minimizing wirings. To support our approach, multiple HEX-O-SKIN are embedded into a rapid-prototyped elastomer skin material and redundantly connected to neighboring modules by just four ports. The wiring complexity is shifted to each HEX-O-SKIN such that a power and data connection between two modules is reduced to four noncrossing wires. Thus, only a very simple robot-specific base frame is needed to support and wire the HEX-O-SKIN to a robot. The potential of our multimodal sensor modules is demonstrated experimentally on a robot platform.

Development of a miniature tunable stiffness display using MR fluids for haptic application

For realistic haptic interaction, both tactile and kinesthetic information should be simultaneously conveyed to users. Haptic display units generally require miniaturization of tactile and kinesthetic modules, particularly, in small consumer electronic products (such as hand-held devices). While minimizing tactile modules is relatively easy, it is quite challenging to minimize the size of kinesthetic actuators for hand-held device applications. In an effort to address this issue, this study investigates a miniature tunable stiffness display. Actuated by MR fluids, the stiffness display is intended to provide kinesthetic information to users in small electric devices. In this study, a prototype stiffness display was designed and constructed, which consists of three parts: (1) an elastic returning part (which generates an elastic force), (2) a stiffness tuning part (which creates a resistive force), and (3) a PDMS membrane reservoir part (which serves as a repository for the MR fluids). In designing the prototype, the three operating modes of MR fluids (i.e., flow mode, direct shear mode, and squeeze mode) are used in order to maximize the resistive force generated by the fluids in a given size of the device. The stiffness display was then fabricated by using the MEMS technology as well as precision machining. For performance evaluation of the prototype, a micro stage, which is equipped with a precision load cell, was used. Using the micro stage, the stiffness changes of the display were measured by varying indented depth discretely (0.5, 1, and 1.5 mm). The results show that the stiffness change rate is nearly 30%, which is sufficient to create a stiffness sensation, for all indented depths considered in this study. The results further show that the proposed display can offer a range of stiffness change that can be conveyed to human operators.

Tiny Feel: A New Miniature Tactile Module Using Elastic and Electromagnetic Force for Mobile Devices

For tactile feedback in mobile devices, the size and the power consumption of tactile modules are the dominant factors. Thus, vibration motors have been widely used in mobile devices to provide tactile sensation. However, the vibration motor cannot sufficiently generate a great amount of tactile sensation because the magnitude and the frequency of the vibration motor are coupled. For the generation of a wide variety of tactile sensations, this paper presents a new tactile actuator that incorporates a solenoid, a permanent magnet and an elastic spring. The feedback force in this actuator is generated by elastic and electromagnetic force. This paper also proposes a tiny tactile module with the proposed actuators. To construct a tiny tactile module, the contactor gap of the module is minimized without decreasing the contactor stroke, the output force, and the working frequency. The elastic springs of the actuators are separated into several layers to minimize the contactor gap without decreasing the performance of the tactile module. Experiments were conducted to investigate each contactor output force as well as the frequency response of the proposed tactile module. Each contactor of the tactile module can generate enough output force to stimulate human mechanoreceptors. As the contactors are actuated in a wide range of frequency, the proposed tactile module can generate various tactile sensations. Moreover, the size of the proposed tactile module is small enough to be embedded it into a mobile device, and its power consumption is low. Therefore, the proposed tactile actuator and module have good potential in many interactive mobile devices.

Frequency‐dependent tactile responses in rat brain measured by functional MRI

We measured frequency-dependent functional MRI (fMRI) activations (at 11.7 T) in the somatosensory cortex with whisker and forepaw stimuli in the same alpha-chloralose anesthetized rats. Whisker and forepaw stimuli were attained by computer-controlled pulses of air puffs and electrical currents, respectively. Air puffs deflected (+/-2 mm) the chosen whisker(s) in the right snout in the rostral to caudal direction, and electrical currents (2 mA amplitude, 0.3 ms duration) stimulated the left forepaw with subcutaneous copper electrodes placed between the second and fourth digits. In the same subject, unimodal stimulation of whisker and forepaw gave rise to significant blood oxygen level-dependent (BOLD) signal increases in corresponding contralateral somatosensory areas of whisker barrel field (S1BF) and forelimb (S1FL), respectively, with no significant spatial overlap between these regions. The BOLD responses in S1(BF) and S1(FL) regions were found to be differentially variable with frequency of each stimulus type. In the S1BF, a linear increase in the BOLD response was observed with whisker stimulation frequency of up to approximately 12 Hz, beyond which the response seemed to saturate (and/or slightly attenuate) up to the maximum frequency studied (i.e. 30 Hz). In the S1FL, the magnitude of the BOLD response was largest at forepaw stimulation frequency between 1.5 and 3 Hz, beyond which the response diminished with little or no activity at frequencies higher than 20 Hz. The volume of tissue activated by each stimulus type followed a similar pattern to that of the stimulation frequency dependence. These results of bimodal whisker and forepaw stimuli in the same subject may provide a framework to study interactions of different tactile modules, with both fMRI and neurophysiology (i.e. inside and outside the magnet).

A Flexible Polymer Tactile Sensor: Fabrication and Modular Expandability for Large Area Deployment

In this paper, we propose and demonstrate a modular expandable capacitive tactile sensor using polydimethylsiloxsane (PDMS) elastomer. A sensor module consists of 16times16 tactile cells with 1 mm spatial resolution, similar to that of human skin, and interconnection lines for expandability. The sensor has been fabricated by using five PDMS layers bonded together. In order to customize the sensitivity of a sensor, we cast PDMS by spin coating and cured it on a highly planarized stage for uniform thickness. The cell size is 600times600 mum <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and initial capacitance of each cell is about 180 fF. Tactile response of a cell has been measured using a commercial force gauge having 1 mN resolution and a motorized z-axis precision stage with 100 nm resolution. The fabricated cell shows a sensitivity of 3%/mN within the full scale range of 40 mN (250 kPa). Four tactile modules have been successfully attached by using anisotropic conductive paste to demonstrate expandability of the proposed sensors. Various tactile images have been successfully captured by single sensor module as well as the expanded 32times32 array sensors

A conceptual structure for a robot station programming system

Task level programming systems previously proposed by several authors are briefly discussed and another approach is also offered. The possibilities of integration of components such as vision and tactile modules, cad systems, robot simulators, specialized planners, etc., are analysed. This should help us to understand their interrelations and limitations when their integration in a system is attempted. The notion of robot station, rather than a mere manipulator, will be kept in view. The conceptual structure presented has two phases: • - off-line: automatic plan generation (implicit programming) and plan testing (in simulated execution) • - on-line: execution supervision with sensorial feedback and local planning capability. The usual limitations of an off-line approach are analyzed and a more active role of simulation of the whole station is suggested, specially in what concerns a comprehensive sensorial simulation, allowing moving to this phase most verifications, previously mandatory on the on-line phase. This should allow a more realistic plan generation and, eventually, interactive planning (with better debugging tools). In the on-line stage, emphasis is placed on the relationship between execution supervision and sensorial feedback. One suggestion of automatic plan repair, valid for any of the phases is also presented.