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

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.

This chapter focuses on the biological and behavioral basics of the haptic modality. On one side, several concepts for describing interaction are presented in Sect. 2.2, and on the other side, the physiological and psychophysical bases of haptic perception are discussed in Sect. 2.1. The goal of this chapter is to provide a common basis to describe interactions and to convey a basic understanding of perception, and the description via psychophysical parameters. Both aspects are relevant to the formal description of the purpose of a haptic system and the derivation of requirements, which are further explained in Chap. 5. Several conclusions arising from the description of perception and interaction are given in Sect. 2.4.

This chapter deals with the general design processes for the development of task-specific haptic systems. Based on known mechatronic development processes such as the V-model, a specialized variant for haptic systems is presented that incorporates a strong focus on the intended interaction and the resulting impacts on the development process. Based on this model, a recommended order of technical decisions in the design process is derived. General design goals of haptic systems are introduced in this chapter as well. These include stability, haptic quality, and usability that have to be incorporated in several stages of the design process. A brief introduction to different forms of technical descriptions for electromechanical systems, control structures, and kinematics is also included in this chapter to provide a common basis for the second part of the book.

In this chapter, the process of requirement definition is described, starting with the definition of the intended application together with the customer. In particular, the derivation of technical parameters from the customers’ expectation and useful tools for this step are discussed. Further, the analysis of the intended interaction and the effects on the requirement identification are discussed. To alleviate the identification of requirements, main requirement groups are derived from the intended type of interaction and presented in five technical solution clusters. A review of the relevant standards and guidelines on safety serves as another source of requirements of a haptic system.

Haptic systems exhibit several basic structures defined by the mechanical inputs and outputs, commonly known as impedance or admittance system structures. This chapter describes these structures in open-loop and closed-loop variants and presents commercial realizations as well as common applications of these structures. Based on the different properties of the structures and the intended application, hints for the selection of a suitable structure are given.

This chapter reviews some aspects of the control of haptic systems, including advanced forms of technical descriptions, system stability criteria and measures, as well as the design of different control laws. A focus is set on the control of bilateral teleoperation systems including the derivation of control designs that guarantee stability as well as haptic transparency and the handling of time delay in the control loop. The chapter also includes an example for the consideration of thermal properties and non-ideal mechanics in the control of a linear stage made from an EC motor and a ball screw as well as a perception-orientated approach to haptic transparency intended to lower the technical requirements on the control and component design.

The kinematic design of haptic interfaces is a crucial step especially when designing interfaces with mainly kinaesthetic feedback (see Sect.12.2). This is often the case in the context of robotic applications. In these devices, a mechanical mechanism is used to link the user and the feedback generating actuators. Furthermore, the user’s input commands are often given by moving a mechanical mechanism, e.g., a joystick.Accordingly, the kinematic design is a crucial aspect for a device with ergonomic design and good haptic transmission. This chapter gives an introduction to the classes of mechanisms and how they are designed.

Actuators are the most important elements of every haptic device, as their selection, respectively, their design influences the quality of the haptic impression significantly. This chapter deals with frequently used actuators structured based on their physical working principle. It focuses on the electrodynamic, electromagnetic, electrostatic, and piezoelectric actuation principle. Each actuator type is discussed as to its most important physical basics, with examples of their dimensioning, and one or more applications given. Other rarely used actuation principles are mentioned in several examples. The previous chapters were focused on the basics of control-engineering and kinematic design. They covered topics of structuring and fundamental character. This and the following chapters deal with the design of technical components as parts of haptic devices. Experience teaches us that actuators for haptic applications can rarely be found “off-the-shelf”. Their requirements always include some outstanding features in rotational frequency, power density, working point, or geometry. These specialties make it necessary and helpful for their applicants to be aware of the capabilities and possibilities of modifications of existing actuators. Hence, this chapter addresses both groups of readers: users who want to choose a certain actuator and the mechanical engineer who intends to design a specific actuator for a certain device from scratch.

Multiple sensors are applied in haptic devices designs. Even if they are not closed-loop controlled in a narrow sense of force or torque generation, they are used to detect movement ranges and limits or the detection of the presence of a user and its type of interaction with an object or human–machine interface (HMI). Almost any type of technical sensor had been applied in the context of haptic devices. Especially, the emerging market of gesture-based user interaction and integration of haptics due to ergonomic reasons extends the range of sensors potentially relevant for haptic devices. This chapter gives an introduction in technologies and design principles for force/torque sensors and addresses common types of positioning, velocity, and acceleration sensors. Further, sensors for touch and imaging sensors are addressed briefly in this section.

This chapter deals with different interface technologies that can be used to connect task-specific haptic systems to an IT system. Based on an analysis of the relevant bandwidth for haptic interaction depending on the intended application and an introduction to several concepts to reduce the bandwidth for these applications (local haptic models, event-based haptics, movement extrapolation, etc.), several standard interfaces are evaluated for use in haptic systems.

This chapter addresses the main steps in the development of software for virtual reality applications. After a definition of virtual reality, the general design and architecture of VR systems are presented. Several algorithms widely used in haptic applications such as the definition of virtual walls, penalty- and constraint-based methods, collision detection, and the Voxmap-PointShell Algorithm for 6 DoF interaction are presented. The chapter further includes a brief overview about existing software packages that can be used to develop virtual reality applications with haptic interaction. The concepts of event-based haptics and pseudo-haptics are introduced as perception-based approaches that have to be considered in the software design.

In this chapter, a number of measurement methods and tests are presented that can be used either for verification or validation or—sometimes—both. We therefore refrain from an ordering based on these steps, but will present the methods based on the focus of the evaluation method. In that sense, one can identify three main foci of evaluation methods: system-centered methods that will test system properties (and are mostly used for verification, Sect. 13.1), task-centered methods that will test the task performance of a user working with the haptic system (such tests are mainly used for validation, but they can also verify system properties depending on the test design, Sect. 13.2), and user-centered methods that will measure the impact of the haptic system on the user. The latter are almost exclusively used for system validation and further described in Sect. 13.3.

In this section, several examples of task-specific haptic systems are given. They give an insight into the process of defining haptic interactions for a given purpose and illustrate the development and evaluation process outlined in this book so far. Examples were chosen by the editors to cover different basic system structures. Section 14.1—Tactile You-Are-Here-Maps illustrates the usage of a tactile display in an assistive manner, enabling a more autonomous movement of people with visual impairments. Section 14.2—User Interface for Automotive Applications presents the development of a haptic interface for a new kind of user interaction in a car. It incorporates touch input and is able to simulate different key characteristics for intuitive haptic feedback. Section 14.3—HapCath describes a comanipulation system to provide additional haptic feedback in cardiovascular interventions. The feedback is intended to reduce exposure for both patient and physician and to permit new kinds of diagnosis during an intervention.