Immersion, interaction, and imagination are three features of virtual reality (VR). Existing VR systems possess fairly realistic visual and auditory feedbacks, and however, are poor with haptic feedback, by means of which human can perceive the physical world via abundant haptic properties. Haptic display is an interface aiming to enable bilateral signal communications between human and computer, and thus to greatly enhance the immersion and interaction of VR systems. This paper surveys the paradigm shift of haptic display occurred in the past 30 years, which is classified into three stages, including desktop haptics, surface haptics, and wearable haptics. The driving forces, key technologies and typical applications in each stage are critically reviewed. Toward the future high-fidelity VR interaction, research challenges are highlighted concerning handheld haptic device, multimodal haptic device, and high fidelity haptic rendering. In the end, the importance of understanding human haptic perception for designing effective haptic devices is addressed. IntroductionIn 1965, Ivan Sutherland proposed the concept "the ultimate display", which represents the birth of virtual reality (VR) [1] . In his seminal work, he introduced three features of VR: immersion, interaction, and imagination. In past 50 years, thanks to the research in computer graphics and sound synthesis, existing VR systems possess fairly realistic visual and auditory feedback. However, haptic feedback is far from user's perceptual expectations. The experiences of haptic sensation in most VR systems are rather poor compared to the abundant haptic properties that human can perceive in the physical world.Haptic feedback is indispensable for enhancing immersion, interaction, and imagination of VR systems.Interaction can be enhanced by haptic feedback as users can directly manipulate virtual objects, and obtain ·Review· Dangxiao WANG et al: Haptic display for virtual reality: progress and challenges immediate haptic feedback. Immersion of the VR system can be enhanced in terms of providing more realistic sensation to mimic the physical interaction process. Imagination of users can be inspired when haptics can provide more cues for user to mentally construct an imagined virtual world beyond spatial and/ or temporal limitations.The haptic sensation obtained through virtual interaction is severely poor compared to the sensation obtained through physical interaction. In our physical life, the haptic channel is pervasively used, such as perception of stiffness, roughness and temperature of the objects in external world, or manipulation of these objects and motion or force control tasks such as grasping, touching or walking etc. In contrary, in virtual world, haptic experiences are fairly poor in both quantity and quality. Most commercial VR games and movies only provide visual and auditory feedbacks, and a few of them provide simple haptic feedback such as vibrations. With the booming of VR in many areas such as medical simulation and product design, there is a...

A divide-and-merge approach is introduced for automatic generation of high-level, discrete contact state space, represented as contact state graphs, between two contacting polyhedral solids from their geometric models. Based on the fact that a contact state graph is the union of the subgraphs called a goal-contact relaxation (GCR) graph, the approach consists of algorithms (1) to generate a complete GCR graph automatically given the most constrained contact state in the GCR graph and (2) to merge GCR graphs automatically. The algorithms are implemented for cases in which the most constrained contact state in a GCR graph consists of up to three principal contacts. The ability to capture and represent contact state information effectively and efficiently is essential for robotic operations involving compliant motions, for simulation of contact motions, and for haptic interactions.

This paper introduces a novel and general real-time adaptive motion planning (RAMP) approach suitable for planning trajectories of high-DOF or redundant robots, such as mobile manipulators, in dynamic environments with moving obstacles of unknown trajectories. The RAMP approach enables simultaneous path and trajectory planning and simultaneous planning and execution of motion in real time. It facilitates real-time optimization of trajectories under various optimization criteria, such as minimizing energy and time and maximizing manipulability. It also accommodates partially specified task goals of robots easily. The approach exploits redundancy in redundant robots (such as locomotion versus manipulation in a mobile manipulator) through loose coupling of robot configuration variables to best achieve obstacle avoidance and optimization objectives. The RAMP approach has been implemented and tested in simulation over a diverse set of task environments, including environments with multiple mobile manipulators. The results (and also the accompanying video) show that the RAMP planner, with its high efficiency and flexibility, not only handles a single mobile manipulator well in dynamic environments with various obstacles of unknown motions in addition to static obstacles, but can also readily and effectively plan motions for each mobile manipulator in an environment shared by multiple mobile manipulators and other moving obstacles.