Vibrotactile sensitivity in active touch: effect of pressing force

An experiment was conducted to study the effects of force produced by active touch on vibrotactile perceptual thresholds. The task consisted in pressing the fingertip against a flat rigid surface that provided either sinusoidal or broadband vibration. Three force levels were considered, ranging from light touch to hard press. Finger contact areas were measured during the experiment, showing positive correlation with the respective applied forces. Significant effects on thresholds were found for vibration type and force level. Moreover, possibly due to the concurrent effect of large (unconstrained) finger contact areas, active pressing forces, and long duration stimuli, the measured perceptual thresholds are considerably lower than what previously reported in the literature

Perception of Compliance in Laparoscopic Surgery

Laparoscopic surgery provides major benefits to patients in terms of decreased pain and post-operative hospital stays, but also increases their risks of intra-operative injuries because of the reduction in feedback in the tactile and visual channels compared to open surgery. Although the limitations of laparoscopy have been studied, the specific role of force feedback in laparoscopic surgery performance is not well understood. The purpose of this thesis is to determine the effect of force feedback on the ability to accurately discriminate tissue compliance by comparing subjective tissue softness assessment, force output, and subjective force assessment, in conventional and laparoscopic setups. The experimental trials involved eleven participants providing evaluations for a range of compliant samples, and analyzed their force output as well as their subjective evaluation of force output. The results of this investigation show that the accuracy of compliance discrimination is worse when using indirect probing compared to direct probing, and that the force used in direct probing is lower than the indirect scenario. Further, the subjective assessment of force output in direct probing is not significantly different compared to indirect probing. Further research involving more replication, expert of laparoscopy, and a focus on grip force are recommended to better understand our awareness of the subjective force output

Modeling of frictional forces during bare-finger interactions with solid surfaces

Touching an object with our fingers yields frictional forces that allow us to perceive and explore its texture, shape, and other features, facilitating grasping and manipulation. While the relevance of dynamic frictional forces to sensory and motor function in the hand is well established, the way that they reflect the shape, features, and composition of touched objects is poorly understood. Haptic displays -electronic interfaces for stimulating the sense of touch- often aim to elicit the perceptual experience of touching real surfaces by delivering forces to the fingers that mimic those felt when touching real surfaces. However, the design and applications of such displays have been limited by the lack of knowledge about what forces are felt during real touch interactions. This represents a major gap in current knowledge about tactile function and haptic engineering. This dissertation addresses some aspects that would assist in their understanding. The goal of this research was to measure, characterize, and model frictional forces produced by a bare finger sliding over surfaces of multiple shapes. The major contributions of this work are (1) the design and development of a sensing system for capturing fingertip motion and forces during tactile exploration of real surfaces; (2) measurement and characterization of contact forces and the deformation of finger tissues during sliding over relief surfaces; (3) the development of a low order model of frictional force production based on surface specifications; (4) the analysis and modeling of contact geometry, interfacial mechanics, and their effects in frictional force production during tactile exploration of relief surfaces. This research aims to guide the design of algorithms for the haptic rendering of surface textures and shape. Such algorithms can be used to enhance human-machine interfaces, such as touch-screen displays, by (1) enabling users to feel surface characteristics also presented visually; (2) facilitating interaction with these devices; and (3) reducing the need for visual input to interact with them.Ph.D., Electrical Engineering -- Drexel University, 201

Haptic perception in virtual reality in sighted and blind individuals

The incorporation of the sense of touch into virtual reality is an exciting development. However, research into this topic is in its infancy. This experimental programme investigated both the perception of virtual object attributes by touch and the parameters that influence touch perception in virtual reality with a force feedback device called the PHANTOM (TM) (www.sensable.com). The thesis had three main foci. Firstly, it aimed to provide an experimental account of the perception of the attributes of roughness, size and angular extent by touch via the PHANTOM (TM) device. Secondly, it aimed to contribute to the resolution of a number of other issues important in developing an understanding of the parameters that exert an influence on touch in virtual reality. Finally, it aimed to compare touch in virtual reality between sighted and blind individuals. This thesis comprises six experiments. Experiment one examined the perception of the roughness of virtual textures with the PHANTOM (TM) device. The effect of the following factors was addressed: the groove width of the textured stimuli; the endpoint used (stylus or thimble) with the PHANTOM (TM); the specific device used (PHANTOM (TM) vs. IE3000) and the visual status (sighted or blind) of the participants. Experiment two extended the findings of experiment one by addressing the impact of an exploration related factor on perceived roughness, that of the contact force an individual applies to a virtual texture. The interaction between this variable and the factors of groove width, endpoint, and visual status was also addressed. Experiment three examined the perception of the size and angular extent of virtual 3-D objects via the PHANTOM (TM). With respect to the perception of virtual object size, the effect of the following factors was addressed: the size of the object (2.7,3.6,4.5 cm); the type of virtual object (cube vs. sphere); the mode in which the virtual objects were presented; the endpoint used with the PHANTOM (TM) and the visual status of the participants. With respect to the perception of virtual object angular extent, the effect of the following factors was addressed: the angular extent of the object (18,41 and 64°); the endpoint used with the PHANTOM (TM) and the visual status of the participants. Experiment four examined the perception of the size and angular extent of real counterparts to the virtual 3-D objects used in experiment three. Experiment four manipulated the conditions under which participants examined the real objects. Participants were asked to give judgements of object size and angular extent via the deactivated PHANTOM (TM), a stylus probe, a bare index finger and without any constraints on their exploration. In addition to the above exploration type factor, experiment four examined the impact of the same factors on perceived size and angular extent in the real world as had been examined in virtual reality. Experiments five and six examined the consistency of the perception of linear extent across the 3-D axes in virtual space. Both experiments manipulated the following factors: Line extent (2.7,3.6 and 4.5cm); line dimension (x, y and z axis); movement type (active vs. passive movement) and visual status. Experiment six additionally manipulated the direction of movement within the 3-D axes. Perceived roughness was assessed by the method of magnitude estimation. The perceived size and angular extent of the various virtual stimuli and their real counterparts was assessed by the method of magnitude reproduction. This technique was also used to assess perceived extent across the 3-D axes. Touch perception via the PHANTOM (TM) was found to be broadly similar for sighted and blind participants. Touch perception in virtual reality was also found to be broadly similar between two different 3-D force feedback devices (the PHANTOM (TM) and the IE3000). However, the endpoint used with the PHANTOM (TM) device was found to exert significant, but inconsistent effects on the perception of virtual object attributes. Touch perception with the PHANTOM (TM) across the 3-D axes was found to be anisotropic in a similar way to the real world, with the illusion that radial extents were perceived as longer than equivalent tangential extents. The perception of 3-D object size and angular extent was found to be comparable between virtual reality and the real world, particularly under conditions where the participants' exploration of the real objects was constrained to a single point of contact. An intriguing touch illusion, whereby virtual objects explored from the inside were perceived to be larger than the same objects perceived from the outside was found to occur widely in virtual reality, in addition to the real world. This thesis contributes to knowledge of touch perception in virtual reality. The findings have interesting implications for theories of touch perception, both virtual and real

Understanding Vibration Transmitted to the Human Finger

Prolonged exposure of the hand to tool-induced vibrations is associated with the occurrence of debilitating conditions such as vibration white finger. The primary aim of this work is to gain a better understanding of the effects of different aspects of exposure to finger transmitted vibration (FTV) related to operators using hand-held vibrating tools. To achieve this, firstly, a new method for measuring finger transmitted vibration was developed and assessed, including a tool vibration test rig and measurement protocol. The effect on FTV measurement of using a small accelerometer attached to the back of the finger was investigated using 2D finite element modelling. Comparisons were also made using a laser vibrometer. Analysis showed that the new test rig is capable of measuring FTV at frequencies ranging from 10 to 400 Hz, under different grip force levels, and that adding a small accelerometer mass (0.3 grams) did not significantly affect measurements. A human participant study then carried out using the new rig. Various characteristic measurements were collected in tandem, including anthropometry, skin characterisation and behaviour under loading to investigate the effect of different factors on FTV. The results showed that FTV varied among individuals and the key finding was that exposure to vibration has a significant effect on finger temperature even for a short period of testing. Anti-vibration (AV) glove materials were investigated using dynamic mechanical analysis (DMA) and tested using human participants. The results showed that the mechanical properties of AV materials change under real world industrial conditions such as excitation frequencies and temperature. Finally, a new artificial test-bed was developed to replicate the transmitted vibration of the index finger. Studies were conducted on a range of 5 test-beds, to allow comparison with the human measurements, including indentation, vibration transmissibility and FE modelling. FE modelling showed that the distribution of dynamic strain was found to be highest in the vasculature region of the finger, indicating that this could be one of the contributing factors of VWF. One of the finger test-bed was selected as best replicating the mechanical properties of the real finger. The artificial test-bed provided better consistency than human participants, for testing parameters, such as grip force, and can be used in future for testing AV gloves with no need for human subjects.ii Further investigations are suggested to be made to enhance the limitations of this project, including material analysis, testing protocol and finite element modelling. Keywords:, hand-arm vibration syndromes, vibration white finger, FTV, transmissibility, resonance frequency, grip force, AV glove, finger mechanical properties, artificial finger, finite element modellin

A Novel Screen-Printed Textile Interface for High-Density Electromyography Recording

Recording electrical muscle activity using a dense matrix of detection points (high-density electromyography, EMG) is of interest in a range of different applications, from human-machine interfacing to rehabilitation and clinical assessment. The wider application of high-density EMG is, however, limited as the clinical interfaces are not convenient for practical use (e.g., require conductive gel/cream). In the present study, we describe a novel dry electrode (TEX) in which the matrix of sensing pads is screen printed on textile and then coated with a soft polymer to ensure good skin-electrode contact. To benchmark the novel solution, an identical electrode was produced using state-of-the-art technology (polyethylene terephthalate with hydrogel, PET) and a process that ensured a high-quality sample. The two electrodes were then compared in terms of signal quality as well as functional application. The tests showed that the signals collected using PET and TEX were characterised by similar spectra, magnitude, spatial distribution and signal-to-noise ratio. The electrodes were used by seven healthy subjects and an amputee participant to recognise seven hand gestures, leading to similar performance during offline analysis and online control. The comprehensive assessment, therefore, demonstrated that the proposed textile interface is an attractive solution for practical applications

Understanding Vibration Transmitted to the Human Finger

Prolonged exposure of the hand to tool-induced vibrations is associated with the occurrence of debilitating conditions such as vibration white finger. The primary aim of this work is to gain a better understanding of the effects of different aspects of exposure to finger transmitted vibration (FTV) related to operators using hand-held vibrating tools. To achieve this, firstly, a new method for measuring finger transmitted vibration was developed and assessed, including a tool vibration test rig and measurement protocol. The effect on FTV measurement of using a small accelerometer attached to the back of the finger was investigated using 2D finite element modelling. Comparisons were also made using a laser vibrometer. Analysis showed that the new test rig is capable of measuring FTV at frequencies ranging from 10 to 400 Hz, under different grip force levels, and that adding a small accelerometer mass (0.3 grams) did not significantly affect measurements. A human participant study then carried out using the new rig. Various characteristic measurements were collected in tandem, including anthropometry, skin characterisation and behaviour under loading to investigate the effect of different factors on FTV. The results showed that FTV varied among individuals and the key finding was that exposure to vibration has a significant effect on finger temperature even for a short period of testing. Anti-vibration (AV) glove materials were investigated using dynamic mechanical analysis (DMA) and tested using human participants. The results showed that the mechanical properties of AV materials change under real world industrial conditions such as excitation frequencies and temperature. Finally, a new artificial test-bed was developed to replicate the transmitted vibration of the index finger. Studies were conducted on a range of 5 test-beds, to allow comparison with the human measurements, including indentation, vibration transmissibility and FE modelling. FE modelling showed that the distribution of dynamic strain was found to be highest in the vasculature region of the finger, indicating that this could be one of the contributing factors of VWF. One of the finger test-bed was selected as best replicating the mechanical properties of the real finger. The artificial test-bed provided better consistency than human participants, for testing parameters, such as grip force, and can be used in future for testing AV gloves with no need for human subjects.ii Further investigations are suggested to be made to enhance the limitations of this project, including material analysis, testing protocol and finite element modelling. Keywords:, hand-arm vibration syndromes, vibration white finger, FTV, transmissibility, resonance frequency, grip force, AV glove, finger mechanical properties, artificial finger, finite element modellin

Human haptic perception in virtual environments: An investigation of the interrelationship between physical stiffness and perceived roughness.

Research in the area of haptics and how we perceive the sensations that come from haptic interaction started almost a century ago, yet there is little fundamental knowledge as to how and whether a change in the physical values of one characteristic can alter the perception of another. The increasing availability of haptic interaction through the development of force-feedback devices opens new possibilities in interaction, allowing for accurate real time change of physical attributes on virtual objects in order to test the haptic perception changes to the human user. An experiment was carried out to ascertain whether a change in the stiffness value would have a noticeable effect on the perceived roughness of a virtual object. Participants were presented with a textured surface and were asked to estimate how rough it felt compared to a standard. What the participants did not know was that the simulated texture on both surfaces remained constant and the only physical attribute changing in every trial was the comparison object’s surface stiffness. The results showed that there is a strong relationship between physical stiffness and perceived roughness that can be accurately described by a power function, and the roughness magnitude estimations of roughness showed an increase with increasing stiffness values. The conclusion is that there are relationships between these parameters, where changes in the physical stiffness of a virtual object can change how rough it is perceived to be in a very clear and predictable way. Extending this study can lead to an investigation on how other physical attributes affects one or more perceived haptic dimensions and subsequently insights can be used for constructing something like a haptic pallet for a haptic display designer, where altering one physical attribute can in turn change a whole array of perceived haptic dimensions in a clear and predictable way