Christian Hatzfeld

Engineering Haptic Devices

This chapter introduces the philosophical and social aspects of the human haptic sense as a basis for systems addressing this human sensory channel. Several definitions of haptics as a perception and interaction modality are reviewed to serve as a common basis in the course of the book. Typical application areas such as telepresence, training, and interaction with virtual environments and communications are presented, and typical haptic systems from these are reviewed. The use of haptics in technical systems is the topic of this book. But what is haptics in the first place? A common and general definition is given as Definition Haptics Haptics describes the sense of touch and movement and the (mechanical) interactions involving these. but this will probably not suffice for the purpose of this book. This chapter gives a detailed insight into the definition of haptics (Sect. 1.2) and introduces four general classes of applications for haptic systems (Sect. 1.3) as the motivation for the design of haptic systems and—ultimately—for this book. Before that, we give a short summary of the philosophical and social aspects of this human sense (Sect. 1.1). These topics are not addressed any further in this book, but should be kept in mind by every engineer working on haptics. C. Hatzfeld (B) Institute of Electromechanical Design, Technische Universität Darmstadt, Merckstr. 25, 64283 Darmstadt, Germany e-mail: c.hatzfeld@hapticdevices.eu T.A. Kern Continental Automotive GmbH, VDO-Straße 1, 64832 Babenhausen, Germany e-mail: t.kern@hapticdevices.eu

Platypus: Indoor Localization and Identification through Sensing of Electric Potential Changes in Human Bodies

Platypus is the first system to localize and identify people by remotely and passively sensing changes in their body electric potential which occur naturally during walking. While it uses three or more electric potential sensors with a maximum range of 2 m, as a tag-free system it does not require the user to carry any special hardware. We describe the physical principles behind body electric potential changes, and a predictive mathematical model of how this affects a passive electric field sensor. By inverting this model and combining data from sensors, we infer a method for localizing people and experimentally demonstrate a median localization error of 0.16 m. We also use the model to remotely infer the change in body electric potential with a mean error of 8.8 % compared to direct contact-based measurements. We show how the reconstructed body electric potential differs from person to person and thereby how to perform identification. Based on short walking sequences of 5 s, we identify four users with an accuracy of 94 %, and 30 users with an accuracy of 75 %. We demonstrate that identification features are valid over multiple days, though change with footwear.

Just noticeable differences of low-intensity vibrotactile forces at the fingertip

The presented study measures JNDs of vibrotactile force amplitudes at nine frequencies in the bandwidth of 5 ... 1000 Hz with 29 subjects taking part in the study. Reference stimuli are placed near the absolute perception threshold of these frequencies, therefore very high discrimination thresholds of 20 dB on average (with a runaway value of 40 dB @ 1000 Hz) are measured. This is in accordance to observations of Webers Law for reference stimuli near the perception threshold. Statistical analysis suggests influence of fingertip size on the results, but no influence of fine motor activity (i.e. playing musical instruments, handicraft, computer games) could be asserted with the given dataset. Results can be used to facilitate task-specific design of sensors and actuators in near-threshold contact situations.

Pseudo-Haptic Feedback in Teleoperation

In this paper, we develop possible realizations of pseudo-haptic feedback in teleoperation systems based on existing works for pseudo-haptic feedback in virtual reality and the intended applications. We derive four potential factors affecting the performance of haptic feedback (calculation operator, maximum displacement, offset force, and scaling factor), which are analyzed in three compliance identification experiments. First, we analyze the principle usability of pseudo-haptic feedback by comparing information transfer measures for teleoperation and direct interaction. Pseudo-haptic interaction yields well above-chance performance, while direct interaction performs almost perfectly. In order to optimize pseudo-haptic feedback, in the second study we perform a full-factorial experimental design with 36 subjects performing 6,480 trials with 36 different treatments. Information transfer ranges from 0.68 bit to 1.72 bit in a task with a theoretical maximum of 2.6 bit, with a predominant effect of the calculation operator and a minor effect of the maximum displacement. In a third study, short- and long-term learning effects are analyzed. Learning effects regarding the performance of pseudo-haptic feedback cannot be observed for single-day experiments. Tests over 10 days show a maximum increase in information transfer of 0.8 bit. The results show the feasibility of pseudo-haptic feedback for teleoperation and can be used as design basis for task-specific systems.

Mechanical impedance as coupling parameter of force and deflection perception: experimental evaluation

This paper investigates the mechanical impedance of a human subject as a potential coupling parameter between force and deflection perception. Measurements of the force perception threshold of 27 subjects at the fingertip and the mechanical impedance of 29 subject at the same location in the frequency range of 5 ... 1000 Hz were conducted. From the results, a model for the impedance was fitted and thresholds for the perception of deflections were calculated. These were compared to already published thresholds from other research groups. The results show a good fit of both data sets, therefore confirming the mechanical impedance as coupling parameter between these two dimensions of perception.

Investigation of the usability of pseudo-haptic feedback in teleoperation

Pseudo haptic sensation is an illusion based on visual stimuli. In virtual environments the principle of pseudo haptic feedback is used to simulate material properties such as stiffness, mass and friction. Transfering the principle of pseudo haptic feedback to real haptic teleoperation systems can provide a haptic sensation for properties of material, manipulated without active haptic feedback. Hence, the implementation of pseudo haptic feedback to teleoperation systems reduces the requirements for kinematic structures and actuators of the used haptic user interface .In this work, we discuss the usability of pseudo haptic feedback for its application in teleoperation systems. The mechanisms of pseudo-haptic feedback are theoretically explained for an exemplary teleoperation task. Options to vary the intensity of the users pseudo haptic sensation are derived. The effect of pseudo haptic feedback for teleoperation is based on changing the input-output ratio by actual measured interaction forces at the end-effector. A one degree of freedom teleoperation system is used for first experiments with pseudo haptic feedback in teleoperation. The used teleoperation system couples users input force to a defined displacement of an end-effector. Our results prove the validity of pseudo-haptic feedback in teleoperation by a compliance discrimination experiment.

Simulation und Auswahl von psychometrischen Verfahren zur Ermittlung von Kennwerten menschlicher Wahrnehmung

Zusammenfassung Zur Bestimmung von Wahrnehmungskennwerten des Menschen werden psychometrische Verfahren verwendet. Diese werden wiederum in einer Vielzahl von Anwendungen zur Optimierung und Anpassung von Systemen zur Mensch-Technik-Interaktion benötigt. Zur Auswahl eines geeigneten Verfahrens werden in diesem Beitrag unterschiedliche psychometrische Verfahren, ein Rahmenwerk für die Simulation solcher Messverfahren und mögliche objektive Bewertungskriterien vorgestellt. Die Leistungsfähigkeit der Simulation wird an Beispielen zum Methodenvergleich und dem Einfluss einzelner Konfigurationsparameter gezeigt.

Systematic Consideration of Haptic Perception in the Design of Task-Specific Haptic Systems

This work proposes a new additional step in the development of task-specific haptic teleoperation systems. This step termed interaction analysis leads to a better insight for relevant requirements for the design of the system. This is based on an analysis of human force perception with respect to external influencing factors and the coupling of the perception of forces and kinematic quantities by the mechanical impedance of the user. Furthermore, the concept of haptic transparency is extended to form a evaluation criterion with consideration of haptic perception capabilities.

Vibrotactile Force Perception – Absolute and Differential Thresholds and External Influences

Three experiments were carried out to determine absolute and differential thresholds for vibrotactile forces and external influences in the frequency range of 5 to 1,000 Hz at the tip of the index finger. Differential thresholds were obtained for reference stimuli of 0.5, 0.25 N, and near the individual threshold. Frequency, temperature, age, fingertip size, and contact force were investigated as parameters in a full-factorial design. Experiments were conducted with at least 27 subjects and a 1up-2down staircase procedure with 3IFC paradigm. We find absolute thresholds ranging from 1.7 to 19 mN with the lowest threshold at 320 Hz. Weber fractions from 18 to 41 dB are found near the absolute threshold. For larger references, they range from 4.9 to 23 dB. ANOVA finds frequency as significant medium effect for both absolute and differential thresholds. Results imply impact of age on the absolute threshold, but no effect of motor skill, temperature, fingertip size, and contact force. Differential thresholds are affected by frequency only, which is attributed to saturation effects of the Pacinian channel. Fingertip size and motor skill are not able to explain effects on thresholds and the interpersonal variance. Results of this work are intended as requirement source for the design of task-specific haptic interfaces.

Motivation and Application of Haptic Systems

This chapter introduces the philosophical and social aspects of the human haptic sense as a basis for systems addressing this human sensory channel. Several definitions of haptics as a perception and interaction modality are reviewed to serve as a common basis in the course of the book. Typical application areas such as telepresence, training, and interaction with virtual environments and communications are presented, and typical haptic systems from these are reviewed. The use of haptics in technical systems is the topic of this book. But what is haptics in the first place? A common and general definition is given as Open image in new window but this will probably not suffice for the purpose of this book. This chapter gives a detailed insight into the definition of haptics (Sect. 1.2) and introduces four general classes of applications for haptic systems (Sect. 1.3) as the motivation for the design of haptic systems and—ultimately—for this book. Before that, we give a short summary of the philosophical and social aspects of this human sense (Sect. 1.1). These topics are not addressed any further in this book, but should be kept in mind by every engineer working on haptics.