Vincent Hayward

Haptic interfaces and devices

Haptic interfaces enable person‐machine communication through touch, and most commonly, in response to user movements. We comment on a distinct property of haptic interfaces, that of providing for simultaneous information exchange between a user and a machine. We also comment on the fact that, like other kinds of displays, they can take advantage of both the strengths and the limitations of human perception. The paper then proceeds with a description of the components and the modus operandi of haptic interfaces, followed by a list of current and prospective applications and a discussion of a cross‐section of current device designs.

Single state elastoplastic friction models

For control applications involving small displacements and velocities, friction modeling and compensation can be very important. In particular, the modeling of presliding displacement (motion prior to fully developed slip) can play a pivotal role. In this paper, it is shown that existing single-state friction models exhibit a nonphysical drift phenomenon which results from modeling presliding as a combination of elastic and plastic displacement. A new class of single state models is defined in which presliding is elastoplastic: under loading, frictional displacement is first purely elastic and then transitions to plastic. The new model class is demonstrated to substantially reduce drift while preserving the favorable properties of existing models (e.g., dissipativity) and to provide a comparable match to experimental data.

Force can overcome object geometry in the perception of shape through active touch

Haptic (touch) perception normally entails an active exploration of object surfaces over time. This is called active touch. When exploring the shape of an object, we experience both geometrical and force cues. For example, when sliding a finger across a surface with a rigid bump on it, the finger moves over the bump while being opposed by a force whose direction and magnitude are related to the slope of the bump. The steeper the bump, the stronger the resistance. Geometrical and force cues are correlated, but it has been commonly assumed that shape perception relies on object geometry alone. Here we show that regardless of surface geometry, subjects identified and located shape features on the basis of force cues or their correlates. Using paradoxical stimuli, for example combining the force cues of a bump with the geometry of a hole, we found that subjects perceived a bump. Conversely, when combining the force cues of a hole with the geometry of a bump, subjects typically perceived a hole.

Discrete-time adaptive windowing for velocity estimation

We present methods for velocity estimation from discrete and quantized position samples using adaptive windowing. Previous methods necessitate trade-offs between noise reduction, control delay, estimate accuracy, reliability, computational load, transient preservation, and difficulties with tuning. In contrast, a first-order adaptive windowing method is shown to be optimal in the sense that it minimizes the velocity error variance while maximizes the accuracy of the estimates, requiring no tradeoff. Variants of this method are also discussed. The effectiveness of the proposed technique is verified in simulation and by experiments on the control of a haptic device.

A role for haptics in mobile interaction: initial design using a handheld tactile display prototype

Mobile interaction can potentially be enhanced with well-designed haptic control and display. However, advances have been limited by a vicious cycle whereby inadequate haptic technology obstructs inception of vitalizing applications. We present the first stages of a systematic design effort to break that cycle, beginning with specific usage scenarios and a new handheld display platform based on lateral skin stretch. Results of a perceptual device characterization inform mappings between device capabilities and specific roles in mobile interaction, and the next step of hardware re-engineering.

Multiple-goal kinematic optimization of a parallel spherical mechanism with actuator redundancy

A kinematic is presented that is fully parallel and actuator redundant. Actuator redundancy refers to the use of more actuators than are strictly necessary to control the mechanism without increasing the mobility. The uses of this form of redundancy include the ability to partially control the internal forces, increase the workspace, remove singularities, and augment the dexterity. Optimization takes place based on several objective functions. The kinematic dexterity, the forces present at the actuators, and the uniformity of the dexterity over the workspace are all investigated as potential objectives. Global measures are derived from each of these quantities for optimization purposes. Instead, optimization of several factors is done simultaneously by specifying a primary objective and minimum performance standards for the secondary measures. >

The pantograph: a large workspace haptic device for multimodal human computer interaction

A multi-modal user interface taking advantage of kinesthesia force display, soundj and graphics, to improve human-computer interaction is described. This design primarily addresses the needs of visually impaired persons working in an office situation, but is presently applied to numerous other instances of human-machine interaction; such as operator workstations in control rooms or cockpits. The main technological item introduced here is the haptic interface itself (nicknamed the “Pantograph”) which measures position and velocity of a manipulated knob and displays forces in two dimensions over a wide frequency range. Programmed mechanical models are used to kinesthetically describe the features of the interface. These models are analogous to iconic representations in conventional graphic interfaces. Users, acting and perceiving through the haptic channel, simultaneously perceive simulated objects through the visual and auditory channels. Further developments are briefly reported.

Performance Measures for Haptic Interfaces

A haptic interface is distinct from other display devices because it is bi-directional; it is capable of both reading and writing input to and from a human user. Due to both the direct human interaction and bi-directionality there has been much ambiguity in describing and evaluating these devices, making evaluation and comparison difficult. The goal of this paper is to set out requirements and guidelines for the performance measures of haptic devices and to hopefully lead towards resolving the current equivocal situation. In particular, performance measures are introduced which have so far not been pertinent in traditional robotics; these include, peak force, peak acceleration and frequency dependent measurements. Performance measures often quoted in traditional robotics are also discussed, however, the focus and relevance of these measures are different in haptic devices. Each of the suggested performance measures in this paper is discussed with respect to its importance, its measurabilty and the condition under which it should be measured.

Variable structure control of shape memory alloy actuators

A shape memory alloy (SMA) actuator consisting of a number of thin NiTi fibers woven in a counter rotating helical pattern around supporting disks is first described. This structure accomplishes a highly efficient transformation between force and displacement overcoming the main mechanical drawback of shape memory alloys, that being limited strain. Time domain open loop experiments were then conducted to determine the intrinsic properties of the actuator. From these experiments and from the knowledge of the underlying physics of SMAs, a multiterm model, including linear and nonlinear elements, was proposed. After further investigation and simulation, it was found that most of these complexities did not need to be considered in order to explain the reported results, and that the model could be reduced to that of a single integrator. A variable structure controller was then applied to a pair of antagonist actuators. The feedback switches between the two actuators according to the sign of the displacement error. A further improvement was added to compensate for known gross nonlinearities by modulating the current magnitude in a discrete manner as a function of the state space position. It was therefore possible to realize smooth and robust control with very little cost in complexity.

A New Compuatitional Model of Friction Applied to Haptic Rendering

A time-free, drift-free, multi-dimensional model of friction is introduced. A discrete implementation is developed which exhibits four solution regimes: sticking, creeping, oscillating, and sliding. Its computational solution is efficient to compute online and is robust to noise. It is applied to haptic rendering.