Touch Force Research Articles

Force-touch measurement methodology based on user experience

The touch interface is an input method widely used in smart devices. Recently, new touch interface which supports force value has been introduced. The force-touch interface adds a factor called depth to the plane coordinates as compared to the existing touch interface. Despite the advantages of force-touch, which can provide touch position and force intensity information with one input, there are still many devices that cannot support force values. To provide them with a force-touch interface, we developed a force-touch cover for existing smart devices that do not support the existing force value. It is a way to provide the force value to the smart device by recognizing the force value through the sensor installed in smartphone case. However, it is difficult to apply the force value obtained through such a device directly to the force-touch interface, because it is necessary to distinguish between force touch and general touch. Therefore, in order to use the force-touch interface using the force-touch cover proposed in this article, the force value measured at the time of general touch is analyzed by user experiment to set the general touch area. Also, an area outside the general touch area is set as the force-touch area. In the force-touch and general touch area, the area is applied considering the error of the force value actually measured in the developed force-touch cover. Therefore, in this article, we analyze the force value input through the proposed force-touch cover and find a reference value that can distinguish force touch from general touch by user experiment and propose a method to apply it.

A multi-layered touch-pressure sensing ionogel material suitable for sensing integrated actuations of soft robots

Soft robots have been a focus of studies for their advances of softness and body compliance. They are needed to be developed using materials that integrate sensors and actuators to fulfill their application potentials. This work followed our previous study on a capacitor-like ionogel-based soft actuator. Capacitance responses to loads of this ionogel-based parallel capacitor were observed, indicating its pressure sensing possibilities. Furthermore, a linear relationship between capacitance and pressure was found despite of gel thickness. In order to locate the pressure, a novel touch-pressure sensing material was built. It was a multi-layered material with a layer of VHB tape (3M, United States) sandwiched by this pressure sensing capacitor on the bottom and a single layer of gel on the top for touch locating. Studies on a simple array (2×2) of distributed sensing systems based on this material showed good touch and pressure sensing performances. This design would allow a large scale distributed sensing system with low interferences between physical stimulations. It will then benefit quick control algorithms based on a single physical stimulation, such as touch avoidance or force control. Further research will be carried out to integrate this material with ionogel soft actuators.

External Force Sensing Based on Cable Tension Changes in Minimally Invasive Surgical Micromanipulators

Force sensing plays an irreplaceable role in minimally invasive surgery. Effective force sensing leads to more successful operations by preventing secondary damage to the body. Force feedback is a crucial part of any minimally invasive surgical robotic system. Very compact construction and the challenging disinfection method are challenging in regard to building force sensors into the end of micromanipulator. This paper focuses on clamping force sensing and 2-D touch force sensing for a three-degrees-of-freedom cable-driven micromanipulator. The clamping and touch forces can be detected based on the changes in cable tension. A complete dynamic model of the micromanipulator wrist and driving cable is established. A comprehensive resistance neural network model of the system was obtained through comprehensive resistance tests and data fitting. An external force estimation strategy is proposed based on the changes in driving system resistance. The performance and accuracy of the 2-D force and clamping force estimations were verified experimentally; the results show that the force estimation precision is acceptable. The force-sensing technique discussed here may assist in the future to realize micromanipulator force feedback in minimally invasive surgical robots.

User-Oriented Piezoelectric Force Sensing and Artificial Neural Networks in Interactive Displays

Force touch based interactivity has been widely integrated into displays equipped in most of smart electronic systems such as smartphones and tablets. This paper reports on application of artificial neural networks to analyze data generated from piezoelectric based touch panels for providing customized force sensing operation. Based on the experimental results, high force sensing accuracy (93.3%) is achieved when three force levels are used. Two-dimensional sensing, also achieved with the proposed technique, with high detection accuracy (95.2%). The technique presented here not only achieves high accuracy, but also allows users to define the range of force levels through behavioral means thus enhancing interactivity experience.

Multifunctional Woven Structure Operating as Triboelectric Energy Harvester, Capacitive Tactile Sensor Array, and Piezoresistive Strain Sensor Array.

This paper presents a power-generating sensor array in a flexible and stretchable form. The proposed device is composed of resistive strain sensors, capacitive tactile sensors, and a triboelectric energy harvester in a single platform. The device is implemented in a woven textile structure by using proposed functional threads. A single functional thread is composed of a flexible hollow tube coated with silver nanowires on the outer surface and a conductive silver thread inside the tube. The total size of the device is 60 × 60 mm2 having a 5 × 5 array of sensor cell. The touch force in the vertical direction can be sensed by measuring the capacitance between the warp and weft functional threads. In addition, because silver nanowire layers provide piezoresistivity, the strain applied in the lateral direction can be detected by measuring the resistance of each thread. Last, with regard to the energy harvester, the maximum power and power density were measured as 201 μW and 0.48 W/m2, respectively, when the device was pushed in the vertical direction.

Press touch code: A finger press based screen size independent authentication scheme for smart devices.

Due to recent advancements and appealing applications, the purchase rate of smart devices is increasing at a higher rate. Parallely, the security related threats and attacks are also increasing at a greater ratio on these devices. As a result, a considerable number of attacks have been noted in the recent past. To resist these attacks, many password-based authentication schemes are proposed. However, most of these schemes are not screen size independent; whereas, smart devices come in different sizes. Specifically, they are not suitable for miniature smart devices due to the small screen size and/or lack of full sized keyboards. In this paper, we propose a new screen size independent password-based authentication scheme, which also offers an affordable defense against shoulder surfing, brute force, and smudge attacks. In the proposed scheme, the Press Touch (PT)—a.k.a., Force Touch in Apple’s MacBook, Apple Watch, ZTE’s Axon 7 phone; 3D Touch in iPhone 6 and 7; and so on—is transformed into a new type of code, named Press Touch Code (PTC). We design and implement three variants of it, namely mono-PTC, multi-PTC, and multi-PTC with Grid, on the Android Operating System. An in-lab experiment and a comprehensive survey have been conducted on 105 participants to demonstrate the effectiveness of the proposed scheme.

Decoupling research on a flexible tactile sensor array with novel structure

This paper presents a flexible tactile sensor, which uses a novel structure and effective decoupling method to detect multi-point three-dimensional touch force. Firstly, the structure characteristics of the sensor are introduced. According to the theories of force-sensitive conductive rubber, the relationship between the resistance and the force exerted on the sensor is analyzed. Furthermore the mathematical model of the sensor based on finite element method is conducted. The simulation result is consistent well with the theory result. Then a decoupling method based on the RBF neural network is proposed in order to obtain the force from the resistance. The research indicates that the flexible tactile sensor with the novel structure and the decoupling method can accurately detect the three-dimensional force.

Ultrathin Multifunctional Graphene-PVDF Layers for Multidimensional Touch Interactivity for Flexible Displays.

This paper presents a flexible graphene/polyvinylidene difluoride (PVDF)/graphene sandwich for three-dimensional touch interactivity. Here, x-y plane touch is sensed using graphene capacitive elements, while force sensing in the z-direction is by a piezoelectric PVDF/graphene sandwich. By employing different frequency bands for the capacitive- and force-induced electrical signals, the two stimuli are detected simultaneously, achieving three-dimensional touch sensing. Static force sensing and elimination of propagated stress are achieved by augmenting the transient piezo output with the capacitive touch, thus overcoming the intrinsic inability of the piezoelectric material in detecting nontransient force signals and avoiding force touch mis-registration by propagated stress.

P‐209: Augmenting Capacitive Touch with Piezoelectric Force Sensing

In this work, force touch sensing is achieved in conventional capacitive touch panels, by employing piezoelectric materials. To achieve high sensitivity and stability in force detection, deep analysis of employing piezoelectric material in interactive displays is provided, together with possible solutions for piezoelectric principle related force sensing issues.

A Three-Dimensional Resonant Triggering Probe for Micro-CMM

To achieve true 3D nano-measurement with sub-nanometer resolution and very low touch force through a micro/nano coordinate measuring machine, a new 3D resonant trigger probe based on a quartz tuning fork is proposed. In this trigger probe, a quartz tuning fork with a microsphere tip vibrates at its resonant frequency, and is used as the sensing element. The resonance parameters of this quartz tuning fork (e.g., vibrating amplitude and resonant frequency) are extremely sensitive to external 3D microforces. The distinguished feature of this probe is its ability to interact with the sample surface in the actual three directions. The microsphere tip of the probe interacts with the sample surface in tapping mode in the Z direction, whereas it interacts in friction mode in the X and Y directions. The dynamic contact mechanism of the probe is based on interfacial force theory, and mechanical models of the interactions between the microsphere tip and sample surface in the X, Y, and Z directions are constructed and simulated. The experiment shows that the probe has sub-nanometer resolution in 3D directions and triggers repeatability of approximately 40 nm in each direction. Theoretical analysis and experimental results verify that this 3D resonant trigger probe can be used for true 3D profile measurement.

Large-Area Cross-Aligned Silver Nanowire Electrodes for Flexible, Transparent, and Force-Sensitive Mechanochromic Touch Screens

Silver nanowire (AgNW) networks are considered to be promising structures for use as flexible transparent electrodes for various optoelectronic devices. One important application of AgNW transparent electrodes is the flexible touch screens. However, the performances of flexible touch screens are still limited by the large surface roughness and low electrical to optical conductivity ratio of random network AgNW electrodes. In addition, although the perception of writing force on the touch screen enables a variety of different functions, the current technology still relies on the complicated capacitive force touch sensors. This paper demonstrates a simple and high-throughput bar-coating assembly technique for the fabrication of large-area (>20 × 20 cm2), highly cross-aligned AgNW networks for transparent electrodes with the sheet resistance of 21.0 Ω sq-1 at 95.0% of optical transmittance, which compares favorably with that of random AgNW networks (sheet resistance of 21.0 Ω sq-1 at 90.4% of optical transmittance). As a proof of concept demonstration, we fabricate flexible, transparent, and force-sensitive touch screens using cross-aligned AgNW electrodes integrated with mechanochromic spiropyran-polydimethylsiloxane composite film. Our force-sensitive touch screens enable the precise monitoring of dynamic writings, tracing and drawing of underneath pictures, and perception of handwriting patterns with locally different writing forces. The suggested technique provides a robust and powerful platform for the controllable assembly of nanowires beyond the scale of conventional fabrication techniques, which can find diverse applications in multifunctional flexible electronic and optoelectronic devices.

Glycolipid Storage and Phenotypes in a New Rat Model of Fabry Disease

Fabry disease is an X‐linked lysosomal storage disease caused by mutations in the GLA gene, which encodes for the acid hydrolase, α‐galactosidase A (α‐Gal A). When α‐Gal A activity is deficient, glycolipids with terminal α‐galactosyl residues accumulate and lead to cellular dysfunction and ultimately organ pathophysiology. Patients with Fabry disease experience severe pain starting in childhood, develop corneal and lenticular opacities, and eventually suffer from end stage renal disease. In order to study the development of these phenotypes on a molecular level, we generated an α‐Gal A deficient (Gla KO) rat using CRISPR/Cas9 technology. Gla KO rats have undetectable serum α‐Gal A activity, but have similar levels of serum α‐mannosidase activity as wild type (WT) rats. As measured by mass spectrometry in serum and tissues (kidney and heart), Gla KO rats have dramatic increases in molecules containing terminal α‐galactosyl residues, including globotriaosylceramide (>100‐fold), globotriaosylsphingosine (>30‐fold), and blood group B glycolipids (>10‐fold), which are established biomarkers for patients with Fabry disease. Non‐α‐galactosyl glycolipids, such as ganglioside GM3, exist in similar concentrations in both Gla KO and WT rat serum and tissues. Electron microscopy of Gla KO kidneys and dorsal root ganglia reveal the presence of electron dense lamellar structures, which are classically seen in patients with Fabry disease. On a macroscopic level, male Gla KO rats weigh ~10% less on average and have enlarged tongues (P < 0.001) compared to WT controls. Behavioral studies show that Gla KO rats have increased sensitivity to touch and sharp punctate force (P < 0.001), which are suggestive of a pain phenotype. Slit lamp biomicroscopy shows that male and female Gla KO rats develop corneal and lenticular opacities to a greater degree than WT controls (P < 0.01) by 13 weeks of age. Urinalysis shows that aging Gla KO rats develop increased urine calcium excretion (P < 0.001), increased urine flow (P < 0.001), and decreased urine osmolarity (P = 0.09), all of which suggest the development of distal tubule pathology. As the Gla KO rat recapitulates phenotypes seen in patients with Fabry disease, this rat model can be used to test new therapies and study the mechanistic basis of disease pathogenesis.Support or Funding InformationNIH funding: F30DK113641, K08EY024645, P30EY001931, R21NS095627, R24HL114474, T32GM080202

D’Arsonval Movement-Based Precise Milligram Force Control for Individual Touch Sense Assessment

Humans cannot feel the contact (or touching) force when it is too weak and falls in a specific range. For instance, if it is between several dozens and hundreds of milligram force, then humans may not be able to distinguish whether the object has come in contact with their skin or not. The minimum contact force that the human can feel is called the light touch threshold (LTT). This paper presents a novel apparatus to measure the LTT, which is referred to as an active von Frey (AVF) in this paper. To the best of the authors’ knowledge, an LTT measurement device with a precise weak force range is proposed for the first time in this paper. It is possible for the AVF to provide the touching force range from 1 to 400 [mgf]. In order to provide a precise touching force for individual subjects, D’Arsonval movement is chosen as an actuator to rotate the touching AVF pin. Both an electric current applied to the D’Arsonval movement and a rotational angle of the AVF pin are utilized to calculate the touching force by the electromechanical statics. As outcomes of this paper, we found out that the LTTs are very different from individual to individual and they are approximately proportional to the vibration perception thresholds with the results of 13 participants. It is expected that the AVF for LTT measurement can be utilized to design or control the personalized haptic device and, furthermore, to research the human nervous system diseases.

Design of force measurement module for force touch screens

Design of force measurement module for force touch screens

Wearable Force Touch Sensor Array Using a Flexible and Transparent Electrode

Transparent electrodes have been widely used for various electronics and optoelectronics, including flexible ones. Many nanomaterial‐based electrodes, in particular 1D and 2D nanomaterials, have been proposed as next‐generation transparent and flexible electrodes. However, their transparency, conductivity, large‐area uniformity, and sometimes cost are not yet sufficient to replace indium tin oxide (ITO). Furthermore, the conventional ITO is quite rigid and susceptible to mechanical fractures under deformations (e.g., bending, folding). In this study, the authors report new advances in the design, fabrication, and integration of wearable and transparent force touch (touch and pressure) sensors by exploiting the previous efforts in stretchable electronics as well as novel ideas in the transparent and flexible electrode. The optical and mechanical experiment, along with simulation results, exhibit the excellent transparency, conductivity, uniformity, and flexibility of the proposed epoxy‐copper‐ITO (ECI) multilayer electrode. By using this multi‐layered ECI electrode, the authors present a wearable and transparent force touch sensor array, which is multiplexed by Si nanomembrane p‐i‐n junction‐type (PIN) diodes and integrated on the skin‐mounted quantum dot light‐emitting diodes. This novel integrated system is successfully applied as a wearable human–machine interface (HMI) to control a drone wirelessly. These advances in novel material structures and system‐level integration strategies create new opportunities in wearable smart displays.

Encoding of Tactile Stimuli by Mechanoreceptors and Interneurons of the Medicinal Leech.

For many animals processing of tactile information is a crucial task in behavioral contexts like exploration, foraging, and stimulus avoidance. The leech, having infrequent access to food, developed an energy efficient reaction to tactile stimuli, avoiding unnecessary muscle movements: The local bend behavior moves only a small part of the body wall away from an object touching the skin, while the rest of the animal remains stationary. Amazingly, the precision of this localized behavioral response is similar to the spatial discrimination threshold of the human fingertip, although the leech skin is innervated by an order of magnitude fewer mechanoreceptors and each midbody ganglion contains only 400 individually identified neurons in total. Prior studies suggested that this behavior is controlled by a three-layered feed-forward network, consisting of four mechanoreceptors (P cells), approximately 20 interneurons and 10 individually characterized motor neurons, all of which encode tactile stimulus location by overlapping, symmetrical tuning curves. Additionally, encoding of mechanical force was attributed to three types of mechanoreceptors reacting to distinct intensity ranges: T cells for touch, P cells for pressure, and N cells for strong, noxious skin stimulation. In this study, we provide evidences that tactile stimulus encoding in the leech is more complex than previously thought. Combined electrophysiological, anatomical, and voltage sensitive dye approaches indicate that P and T cells both play a major role in tactile information processing resulting in local bending. Our results indicate that tactile encoding neither relies on distinct force intensity ranges of different cell types, nor location encoding is restricted to spike count tuning. Instead, we propose that P and T cells form a mixed type population, which simultaneously employs temporal response features and spike counts for multiplexed encoding of touch location and force intensity. This hypothesis is supported by our finding that previously identified local bend interneurons receive input from both P and T cells. Some of these interneurons seem to integrate mechanoreceptor inputs, while others appear to use temporal response cues, presumably acting as coincidence detectors. Further voltage sensitive dye studies can test these hypotheses how a tiny nervous system performs highly precise stimulus processing.

ForcePhone: Software Lets Smartphones Sense Touch Force

To enhance the input capability on the severely limited space of a phone's screen, touch force has been a vital way to expand user-phone interactions. For example, users can get an options menu by hard-pressing a button or can surf the previous webpage by squeezing the phone. Researchers have shown the usefulness and importance of this expressive input interface (especially for the one-hand operation), but this advanced function has not yet been realized and deployed in most state-of-the-art smartphones. Unlike many other proposals, which require the addition of specialized hardware, the authors propose a software-based solution called ForcePhone. Their solution exploits a well-known physical property, called structure-borne sound propagation, to enable commodity phones to recognize the force applied to their touchscreen and body.

Visual-Haptic Aid Teleoperation Based on 3-D Environment Modeling and Updating

This paper presents a novel method for a visual-haptic aid teleoperation system (VHATS). The human operator sends commands to the remote manipulator using a haptic device while observing the virtual environment at the local site. The virtual environment also generates aiding force, which helps the human operator feeling the real touching force and drive the remote manipulator to avoid obstacles. In our system, high-resolution point cloud data of the remote environment are collected by a Kinect sensor. Then three-dimensional (3-D) graphic models are reconstructed at the master site. The environment information is transmitted to the local site to create and update the virtual models after the time delay. The feedback force is divided into two parts, guiding force and virtual contact force. The guiding force is derived from the Artificial Potential Field Method (APFM) for obstacles avoiding. The virtual contact force is based on the parameters of geometric and dynamic models. An adaptive Window-based Sliding Least-Squares Method (AW-SLSM) is adopted to update the parameters of the dynamic models on-line. At last, the experimental platform is established, while a moving, obstacle avoiding, target picking task is carried out and verified in the presence of a round-trip communication delay of 2 s.

P-180: Force Sensing Technique for Capacitive Touch Panel

A force sensing technique is presented for capacitive touch panels. By measuring force induced stress, force touch can be detected even when the panel deflection is very small. In addition to that, image based down-sampling methods are proposed to reduce power consumption and boost readout speed of touch panel.

Representation of Mechanosensory Forces in Somatosensory Cortex during Object Localization

Our understanding of active touch is still in its infancy. The rodent vibrissal system offers us the perfect model to study touch from mechanosensation to perception. Rodents have whiskers in their mystacial pad that correlate on a 1:1 ratio to a specific column of cells within the somatosensory cortex (S1), known as barrels. The lemniscal pathway is the primary afferent responsible for relaying touch information from each whisker to the cortex, specifically to layer (L) 4 before proceeding to L3 and L5b. We currently know that L4 is highly correlated to touch onset and phase characteristics in whisking. However, knowing just one aspect of touch does not allow us to fully decode ‘when’ the object was touched and most importantly ‘where’ it is in space. This present study seeks to examine how L3 and L5b represent mechanosensory forces to aid in object localization. Mice are trained to locate objects by active whisking while in-vivo juxtacellular loose-seal patch records single neuron spike patterns, and high-speed video (1000Hz) captures whisker movement. Optogenetics is used to differentiate between inhibitory and excitatory neurons. Whisker kinematics and touch forces are quantified with micron and sub-microNewton resolution. Initial analysis reveals firing rates of 3.5 and 70 spikes/second for L3 and L5b, respectively. Excitatory neurons in L3 code for touch onset and offset whereas L5b codes for both mechanosensory forces and whisker motion. These studies will provide insight into how mechanosensory information is transformed in the cortex to aid in object localization.