Touch Signals Research Articles

The Finger-Based Interactive Projection using a Monocular Camera

Ordinary projection screen is not sensitive to interaction, it cannot meet the demands of teaching, virtual reality, and other applications. Due to the fact that people always use hands to complete a variety of human–computer interaction, the finger-based interactive projection technology is worth being researched. In this paper, an ordinary monocular camera is used to acquire video frame on projection screen, and the touch signal of finger in frame is used as the input of interactive projection system. Because the differences between spatial frequency of common digital camera and the projection screen is small, the frame obtained from camera will contain moire fringe, which needs to be filtered in image frequency domain. Then the difference between current frame edge and previous frame edge is calculated to obtain moving object edge clues. According to these clues, the most possible contour curve is searched in current frame edge, and the curve is fitted by polynomial approximation method. Its curvature integration is used to match with the curvature integration of finger template curve. After that the fingers in the curve are recognized. Because color information is not needed, this method can be used to recognize gloved fingers. Finally, finger shadow is used to judge whether the finger touches projection screen to complete interactive process. The experiments of writing and collaboratively rotating picture on projector screen show that this method can effectively complete interactive operation with the projection screen and can realize the multi-user operation.

Highly Reliable a-Si:H TFT Gate Driver With Precharging Structure for In-Cell Touch AMLCD Applications

This paper presents a novel bidirectional gate driver circuit based on hydrogenated amorphous silicon thin-film transistors (TFTs), especially for use in active-matrix liquid-crystal displays with in-cell touch technology. The proposed circuit exploits the time-division driving method to implement the in-cell touch panels with a high report rate and prevent the distortion of touch signals. The proposed structure employs a highly reliable precharging circuit to ameliorate the degradation of the driving TFT during the long-term touch-sensing stages. The output TFTs in the precharging structure are activated only once at the end of the touch-sensing stage in a frame, effectively extending the lifetime of the circuit. The experimental and simulated results illustrate that the proposed gate driver circuit generates uniform output waveforms regardless of whether the circuit operates in forward and backward transmission or stops in any row. To verify the high reliability of the proposed gate driver circuit, long-term stress tests at 85 °C are conducted. After the proposed circuit is operated for 720 h, the falling time of the output waveforms after the touch-sensing stage slightly varies by only $0.51~\mu \text{s}$ , confirming that the output TFT in the proposed precharging structure with a low duty ratio of 0.15% can achieve the high reliability of the proposed circuit. Therefore, the proposed gate driver circuit is highly feasible for use in high-report-rate in-cell touch panels.

High Sensitive Readout Circuit for Capacitance Touch Panel With Large Size

A readout circuit for large sized capacitive touch screens is presented in this letter. Being different from the conventional readout circuit, the phase conversion module is inserted between the differential sensing structure and the integrating amplifier, to take advantage of both the positive and negative edge of the touch sensing signal for the following integrator. Thus, the sensing output value can be increased as the touch signals are integrated by twice for every clock cycle. Both simulation and measurement results verify that, thanks to the insertion of the proposed phase conversion module, the amplitude of touch sensing circuit’s output is increased from 1.4 to 2.8 V. In addition, compared with the frequency increasing method, the proposed scheme features an increase of 40% in the sensing output voltage.

Frequency Hopping and Parallel Driving With Random Delay Especially Suitable for the Charger Noise Problem in Mutual-Capacitive Touch Applications

Charger noise can cause inaccurate touch points and fake touch points to appear; this can cause a device to behave incorrectly. The intensity of charger noise could be much larger than the intensities of the original touch signals. Furthermore, the frequency of charger noise varies for each different charger. Therefore, industry experts have identified charger noise as the most difficult problem in capacitive touch applications. The demand for a solution to this problem has become crucial for the mobile market. In this paper, we prove that a particular combination of frequency hopping and repeated integration is an effective method to handle this problem. In addition, we propose an efficient discrete Fourier transform-based algorithm to select an effective sensing frequency. We propose parallel driving with random delay to enhance the signal-to-noise ratio (SNR). We show an efficient hardware–software co-design that facilitates the application of our methods in touch ICs. The experimental results show that our methods can increase SNR by over 45 dB and can find an effective sensing frequency fast and dynamically.

T-TIME: A Password Scheme Based on Touch Signal Generation Time Difference

T-TIME: A Password Scheme Based on Touch Signal Generation Time Difference

Unlocking the molecular mechanisms behind our sense of touch

Molecular biologists don’t typically conduct their research knee deep in muck, checking underground traps for an elusive mole. But Diana Bautista needed those moles to help her understand the mysterious underpinnings of humans’ sense of touch. “The mechanisms that drive mechanical hypersensitivity and mechanical sensing have been really, a big black box in the field,” says Bautista, an associate professor of cell and developmental biology at University of California, Berkeley. The genes of the star-nosed mole and its remarkable, nerve-fiber–packed nose could point to molecular mechanisms underlying the enigmatic sense of touch. Image courtesy of ScienceSource/Gary Meszaros. Bautista’s quarry, the star-nosed mole, offers a rare opportunity to study a sense of touch few other creatures possess. The mole’s centimeter-sized touch organ (the star of tentacles on its face) is bedecked with 100,000 nerve fibers, called mechanonociceptors. That is five times the number of fibers on a human hand (1). Mechanonociceptors are the first step in the journey of sending a touch signal to the brain. And the genes of this peculiar mole and its nerve fiber-packed nose could point to molecular mechanisms underlying the enigmatic sense of touch. Scientists are on the hunt for the ion channels or any signaling molecules involved in touch sensation. Thus far, these discoveries provide only a small window into the complex machinery of mechanosensation. Still, any step closer to mastering the circuitry that controls mechanical pain is a welcome development for patients and physicians overly reliant on potentially addictive opioids. And mechanosensation research goes far beyond touch and pain. Scientists are discovering that mechanosensory channels play a crucial role in the very function of internal organs. A basic understanding of the sense of touch has been elusive and for good reason. Unlike other senses, touch receptors are not limited to one location in the …

Sensory integration of a light touch reference in human standing balance.

In upright stance, light touch of a space-stationary touch reference reduces spontaneous sway. Moving the reference evokes sway responses which exhibit non-linear behavior that has been attributed to sensory reweighting. Reweighting refers to a change in the relative contribution of sensory cues signaling body sway in space and light touch cues signaling finger position with respect to the body. Here we test the hypothesis that the sensory fusion process involves a transformation of light touch signals into the same reference frame as other sensory inputs encoding body sway in space, or vice versa. Eight subjects lightly gripped a robotic manipulandum which moved in a circular arc around the ankle joint. A pseudo-randomized motion sequence with broad spectral characteristics was applied at three amplitudes. The stimulus was presented at two different heights and therefore different radial distances, which were matched in terms of angular motion. However, the higher stimulus evoked a significantly larger sway response, indicating that the response was not matched to stimulus angular motion. Instead, the body sway response was strongly related to the horizontal translation of the manipulandum. The results suggest that light touch is integrated as the horizontal distance between body COM and the finger. The data were well explained by a model with one feedback loop minimizing changes in horizontal COM-finger distance. The model further includes a second feedback loop estimating the horizontal finger motion and correcting the first loop when the touch reference is moving. The second loop includes the predicted transformation of sensory signals into the same reference frame and a non-linear threshold element that reproduces the non-linear sway responses, thus providing a mechanism that can explain reweighting.

A cellular mechanism for age-induced itch.

Age-induced loss of touch signaling causes mechanical itch

A theory of how active behavior stabilises neural activity: Neural gain modulation by closed-loop environmental feedback.

During active behaviours like running, swimming, whisking or sniffing, motor actions shape sensory input and sensory percepts guide future motor commands. Ongoing cycles of sensory and motor processing constitute a closed-loop feedback system which is central to motor control and, it has been argued, for perceptual processes. This closed-loop feedback is mediated by brainwide neural circuits but how the presence of feedback signals impacts on the dynamics and function of neurons is not well understood. Here we present a simple theory suggesting that closed-loop feedback between the brain/body/environment can modulate neural gain and, consequently, change endogenous neural fluctuations and responses to sensory input. We support this theory with modeling and data analysis in two vertebrate systems. First, in a model of rodent whisking we show that negative feedback mediated by whisking vibrissa can suppress coherent neural fluctuations and neural responses to sensory input in the barrel cortex. We argue this suppression provides an appealing account of a brain state transition (a marked change in global brain activity) coincident with the onset of whisking in rodents. Moreover, this mechanism suggests a novel signal detection mechanism that selectively accentuates active, rather than passive, whisker touch signals. This mechanism is consistent with a predictive coding strategy that is sensitive to the consequences of motor actions rather than the difference between the predicted and actual sensory input. We further support the theory by re-analysing previously published two-photon data recorded in zebrafish larvae performing closed-loop optomotor behaviour in a virtual swim simulator. We show, as predicted by this theory, that the degree to which each cell contributes in linking sensory and motor signals well explains how much its neural fluctuations are suppressed by closed-loop optomotor behaviour. More generally we argue that our results demonstrate the dependence of neural fluctuations, across the brain, on closed-loop brain/body/environment interactions strongly supporting the idea that brain function cannot be fully understood through open-loop approaches alone.

Active in‐cell touch circuit using floating common electrode as sensing pad for the large size in‐plane‐switching liquid crystal displays

AbstractIn this paper, we propose an in‐cell active touch circuit using the concept of floating common electrode for large size in‐plane‐switching liquid crystal displays. Compared with the conventional passive in‐cell touch circuit, the proposed method can greatly reduce the readout channel numbers by sharing the sensing bus for one column. Because the touch signal is amplified in the pixel, the touch panel can be easily scaled up in size. Simulation results show that the difference between touch and no‐touch signals can be as large as 10 μA even with threshold voltage shift of ±1 V. The possible issues of the proposed method are experimentally verified.

Graphene-Based Three-Dimensional Capacitive Touch Sensor for Wearable Electronics.

The development of input device technology in a conformal and stretchable format is important for the advancement of various wearable electronics. Herein, we report a capacitive touch sensor with good sensing capabilities in both contact and noncontact modes, enabled by the use of graphene and a thin device geometry. This device can be integrated with highly deformable areas of the human body, such as the forearms and palms. This touch sensor detects multiple touch signals in acute recordings and recognizes the distance and shape of the approaching objects before direct contact is made. This technology offers a convenient and immersive human-machine interface and additional potential utility as a multifunctional sensor for emerging wearable electronics and robotics.

Haptic information for reliable displays

Humans have several senses, all of which are usually used to navigate through life. Technical systems are much simpler, often engaging only one sense. Literature suggests that this might be the reason for some of the problems encountered with human–system interaction. In modern railways, operators almost exclusively interact with technical systems. Information is provided on displays; operators act on what they see. In some safety-critical situations, it is crucial that the displayed information is indeed showing the state of the outside situation and that the operator can rely on it. Failures of the system must be exposed. In two methods, the authors have researched how acoustic (i.e. transmitted via hearing) and haptic (i.e. transmitted via touch) signals can be used in combination with visual information to help people to identify errors of displayed items. After an overview of today’s research into the use of haptic displays and the basic ideas of transmission of multisensory information, the concept for using a multisensory approach in railway operator workstations has been explained. Then the two methods are described. The first one is a computer game style application in which erroneous symbols need to be identified. In the second method, a simple workstation layout is given in which participants need to identify signals which show an erroneous red aspect. In both cases, the participants are aided in their task by receiving information about the symbols and signals via haptic, acoustic or combined haptic and acoustic feedback. Regarding the error detection rates, a significant difference between the three versions of feedback modes was not determined in any method. However, in the second method (workstation), participants were faster when provided with haptic feedback. Also, the participants rated haptic and haptic–acoustic feedback subjectively better than acoustic feedback alone. The methods have shown that the idea of using a variation of feedback modes to reveal mistakes on a display does work. The results are a first step to develop systems which make it possible for the operator to detect inaccuracies in the information displayed without complex electronic systems but with a modern, multisensory approach.

Multisensory components of rapid motor responses to fingertip loading.

Tactile and muscle afferents provide critical sensory information for grasp control, yet the contribution of each sensory system during online control has not been clearly identified. More precisely, it is unknown how these two sensory systems participate in online control of digit forces following perturbations to held objects. To address this issue, we investigated motor responses in the context of fingertip loading, which parallels the impact of perturbations to held objects on finger motion and fingerpad deformation, and characterized surface recordings of intrinsic (first dorsal interosseous, FDI) and extrinsic (flexor digitorum superficialis, FDS) hand muscles based on statistical modeling. We designed a series of experiments probing the effects of peripheral stimulation with or without anesthesia of the finger, and of task instructions. Loading of the fingertip generated a motor response in FDI at ~60 ms following the perturbation onset, which was only driven by muscle stretch, as the ring-block anesthesia reduced the gain of the response occurring later than 90 ms, leaving responses occurring before this time unaffected. In contrast, the motor response in FDS was independent of the lateral motion of the finger. This response started at ~90 ms on average and was immediately adjusted to task demands. Altogether these results highlight how a rapid integration of partially distinct sensorimotor circuits supports rapid motor responses to fingertip loading.NEW & NOTEWORTHY To grasp and manipulate objects, the brain uses touch signals related to skin deformation as well as sensory information about motion of the fingers encoded in muscle spindles. Here we investigated how these two sensory systems contribute to feedback responses to perturbation applied to the fingertip. We found distinct response components, suggesting that each sensory system engages separate sensorimotor circuits with distinct functions and latencies.

P‐236: A Coupling of Crossing Lines between MIPI and Touch Signals

A coupling of crossing lines due to two layers structures of flexible printed circuit board (FPCB) is studied in the present paper. Simulation results show that the signal integrity of the layout including crossing lines is rarely degraded comparing that without such layout. And we also identify that it is well operated through the proto‐product with such layout. The rule fitting to the signal characteristics of the product is the good solution for reducing cost.

Self-powered flexible touch sensors based on PZT thin films using laser lift-off

Touch screens have become an inherent part of the user interface in many electronics applications such as smartphones. The two types of developed touch sensors, the resistive and capacitive sensing devices, may face several difficulties when applied to flexible device applications such as touch signals arising from bending motions. In this study, we assess the feasibility of flexible touch sensors based on piezoelectric PbZr0.52Ti0.48O3 (PZT) thin films. Piezoelectric ceramic based flexible touch sensors possess unique advantages including scalable fabrication, fast response time, durability, and being self-powered. A demonstration device has been fabricated with a sandwich structure consisting of Pt electrode/functional PZT/Pt electrode/flexible substrate structure using laser lift-off (LLO) method. In order to anneal the functional PZT layer at high temperature (600°C), the device was first fabricated on the sapphire substrate and transferred via melting sacrificial PZT layer with an excimer laser. We demonstrate the detection of x- and y-axis touch location via piezoelectric materials and confirm that the flexible piezoelectric touch sensors can distinguish between touch-induced and bending-induced signals via signal location, signal shape, and duration time. A notable feature of this fabrication technique involves its possibility to be fabricated in high resolution. This device may potentially achieve high resolution with suitable fabrication techniques, thus, providing the possibility for the next generation touch sensors.

Discrimination of Dynamic Tactile Contact by Temporally Precise Event Sensing in Spiking Neuromorphic Networks.

This paper presents a neuromorphic tactile encoding methodology that utilizes a temporally precise event-based representation of sensory signals. We introduce a novel concept where touch signals are characterized as patterns of millisecond precise binary events to denote pressure changes. This approach is amenable to a sparse signal representation and enables the extraction of relevant features from thousands of sensing elements with sub-millisecond temporal precision. We also proposed measures adopted from computational neuroscience to study the information content within the spiking representations of artificial tactile signals. Implemented on a state-of-the-art 4096 element tactile sensor array with 5.2 kHz sampling frequency, we demonstrate the classification of transient impact events while utilizing 20 times less communication bandwidth compared to frame based representations. Spiking sensor responses to a large library of contact conditions were also synthesized using finite element simulations, illustrating an 8-fold improvement in information content and a 4-fold reduction in classification latency when millisecond-precise temporal structures are available. Our research represents a significant advance, demonstrating that a neuromorphic spatiotemporal representation of touch is well suited to rapid identification of critical contact events, making it suitable for dynamic tactile sensing in robotic and prosthetic applications.

Optimal delineation of single C-tactile and C-nociceptive afferents in humans by latency slowing.

C-mechanoreceptors in humans comprise a population of unmyelinated afferents exhibiting a wide range of mechanical sensitivities. C-mechanoreceptors are putatively divided into those signaling gentle touch (C-tactile afferents, CTs) and nociception (C-mechanosensitive nociceptors, CMs), giving rise to positive and negative affect, respectively. We sought to distinguish, compare, and contrast the properties of a population of human C-mechanoreceptors to see how fundamental the divisions between these putative subpopulations are. We used microneurography to record from individual afferents in humans and applied electrical and mechanical stimulation to their receptive fields. We show that C-mechanoreceptors can be distinguished unequivocally into two putative populations, comprising CTs and CMs, by electrically evoked spike latency changes (slowing). After both natural mechanical stimulation and repetitive electrical stimulation there was markedly less latency slowing in CTs compared with CMs. Electrical receptive field stimulation, which bypasses the receptor end organ, was most effective in classifying C-mechanoreceptors, as responses to mechanical receptive field stimulation overlapped somewhat, which may lead to misclassification. Furthermore, we report a subclass of low-threshold CM responding to gentle mechanical stimulation and a potential subclass of CT afferent displaying burst firing. We show that substantial differences exist in the mechanisms governing axonal conduction between CTs and CMs. We provide clear electrophysiological "signatures" (extent of latency slowing) that can be used in unequivocally identifying populations of C-mechanoreceptors in single-unit and multiunit microneurography studies and in translational animal research into affective touch. Additionally, these differential mechanisms may be pharmacologically targetable for separate modulation of positive and negative affective touch information.NEW & NOTEWORTHY Human skin encodes a plethora of touch interactions, and affective tactile information is primarily signaled by slowly conducting C-mechanoreceptive afferents. We show that electrical stimulation of low-threshold C-tactile afferents produces markedly different patterns of activity compared with high-threshold C-mechanoreceptive nociceptors, although the populations overlap in their responses to mechanical stimulation. This fundamental distinction demonstrates a divergence in affective touch signaling from the first stage of sensory processing, having implications for the processing of interpersonal touch.

Modeling and analysis of touch on flexible ultra-thin touch sensor panels for AMOLED displays employing finite element methods

The work employs the finite element method (FEM) to model the touch on the flexible ultra-thin touch sensor panel for analyzing touch characteristics and signals. Touch sensor panel readout circuits typically depend on touch signals to determine whether the touch sensor panel is touched or not. However, the ultra-thin touch sensor panel encountered a problem which cannot correctly recognize touch points on this type of touch sensor panel (TSP) on active-matrix organic light emitting diodes (AMOLED) displays since its electrical characteristics are different from the one of the conventional TSP. The modeling techniques for the flexible ultra-thin touch sensor panel on an AMOLED display is used to analyze touch signals from the influence of the thickness of top over layer of the flexible ultra-thin TSP and to observe the variations of mutual capacitance from touch on the flexible ultra-thin TSP. When the flexible ultra-thin touch sensor panel with the thickness of the top over layer less than the threshold thickness of the top over layer is on multi-touch, the phenomenon of the ghost points are generated. The simulation to find the threshold thickness of the top over layer based on the FEM model is conducted, and the simulation results show the top layer thickness should be larger than 107 µm to eliminate the ghost points. Furthermore, a new solution that is an optimization of the electrode pattern of transmitters and receivers in the ultra-thin touch sensor panel to further minimize the threshold thickness of the top over layer of TSP without changing the physical structure of TSP is proposed. The results conducted by using this proposed solution show that TSP top over layer threshold thickness can be reduced to 65 µm without appearance of the ghost points.

Frequency Selection Concurrent Sensing Technique for High-Performance Touch Screens

In this paper, we present a frequency selection concurrent sensing (FSCS) technique for multi-touch detection of the projected mutual capacitance touch screens. The proposed technique improves the signal-to-noise ratio (SNR) and the frame scan rate of large touch screens. With the proposed technique, the controller concurrently applies sine waves with different frequencies to all drive lines. It converts the output signals of each sense line to the frequency domain using a Fast Fourier Transform, and measures the touch signal strength at the frequency corresponding to each touch position. We show that the proposed method can substantially improve the SNR by properly selecting the frequencies for the excitation signals to avoid the ambient noise. We also demonstrate that the FSCS technique can significantly increase the frame scan rate by concurrently driving all lines. Experimental results show that the proposed technique provides a frame scan rate of 128.2 Hz and an SNR of 70.5 dB with a large touch screen of 23 in.

Reduction of Common Mode Noise and Global Multivalued Offset in Touch Screen Systems by Correlated Double Sampling

Touch-based interactivity has become an important function in displays. This paper reports on the signal processing of touch signals in which touch interactivity is processed as an image, and correlated double sampling (CDS) algorithm is applied for both common-mode noise reduction and global multivalued offset cancellation. Based on experimental results, we achieved a boost in SNR of 7.6 dB. The processed signal reduces detection errors and power consumption of the system.