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 © Springer-Verlag London 2014 C. Hatzfeld and T.A. Kern (eds.), Engineering Haptic Devices, Springer Series on Touch and Haptic Systems, DOI 10.1007/978-1-4471-6518-7_1 3 4 C. Hatzfeld and T.A. Kern 1.1 Philosophical and Social Aspects An engineer tends to describe haptics primarily in terms of forces, elongations, frequencies, mechanical tensions, and shear forces. This of course makes sense and is important for the technical design process. However, haptics starts before that. Haptic perception ranges from minor interactions in everyday life, e.g., drinking from a glass or writing this text, to a means of social communication, e.g., shaking hands or giving someone a pat on the shoulder, and very personal and private interpersonal experiences. This section deals with the spectrum and influence haptics has on humans beyond the technological descriptions. It is also a hint for the development engineer, to be responsible and conscious when considering the capabilities to fool the haptic sense. 1.1.1 Haptics as a Physical Being’s Boundary Haptics is derived from the Greek term “haptios” and describes “something which can be touched.” In fact, the consciousness about and understanding of the haptic sense has changed many times in the history of humanity. Aristoteles puts the sense of touch in the last place when naming the five senses: 1. Sight 2. Hearing 3. Smell 4. Taste 5. Touch Nevertheless, he attests this sense a high importance concerning its indispensability as early as 350 BC [2]: Some classes of animals have all the senses, some only certain of them, others only one, the most indispensable, touch. The social estimation of the sense of touch experienced all imaginable phases. Frequently, it was afflicted with the blemish of squalor, as lust is transmitted by it [91]: Sight differs from touch by its virginity, such as hearing differs from smell and taste: and in the same way their lust-sensation differs. It was also called the sense of excess [33]. In a general subdivision between lower and higher senses, touch was almost constantly ranged within the lower class. In Western civilization, the church once stigmatized this sense as forbidden due to the pleasure which can be gained by it. However, in the eighteenth century, the public opinion changed and Kant [49] is cited with the following statement: This sense is the only one with an immediate exterior perception; due to this it is the most important and the most teaching one, but also the roughest. Without this sensing organ we would be able to grasp our physical shape, whose perception the other two first class senses (sight and hearing) have to be referred to, to generate some knowledge from experience. 1 Motivation and Application of Haptic Systems 5 Kant thus emphasizes the central function of the sense of touch. It is capable of teaching the spatial perception of our environment. Only touch enables us to feel and classify impressions collected with the help of other senses, put them into context, and understand spatial concepts. Although stereoscopic vision and hearing develop early, the first-time interpretation of what we see and hear requires connection between both impressions perceived independently and information about distances between objects. This can only be provided by a sense, which can bridge the space between a being and an object. Such a sense is the sense of touch. The skin, being a part of this sense, covers a human’s complete surface and defines his or her physical boundary, the physical being. 1.1.2 Formation of the Sense of Touch As mentioned in the previous section, the sense of touch has numerous functions. The knowledge of these functions enables the engineer to formulate demands on the technical system. It is helpful to consider the whole range of purposes the haptic sense serves. However, at this point, we do not yet choose an approach by measuring its characteristics, but observe the properties of objects discriminated by it. The sense of touch is not only specialized in the perception of the physical boundaries of the body, as said before, but also in the analysis of the immediate surroundings, including the objects present and their properties. Humans and their predecessors had to be able to discriminate, e.g., the structure of fruits and leaves by touch, in order to identify their ripeness or whether they were edible or not, e.g., a furry berry among smooth ones. The haptic sense enables us to identify a potentially harming structure, e.g., a spiny seed, and to be careful when touching it, in order to obtain its content despite its dangerous needles. For this reason, the sense of touch has been optimized for the perception and discrimination of surface properties, e.g., roughness. Surface properties may range from smooth ceramic-like or lacquered surfaces with structural widths in the range of some micrometers, to somewhat structured surfaces such as coated tables and rough surfaces as in coarsely woven cord textiles with mesh apertures in the range of several millimeters. Humans have developed a typical way to interact with these surfaces enabling them to draw conclusions based on the underlying perception mechanism. A human moves his or her finger along a surface (see Fig. 1.1), allowing shear forces Fig. 1.1 Illustration for the interaction of movements, normal forces on the finger pad, and frictional coupling m