Stable haptic rendering in virtual environment

• Main Author: Hou, Xiyuan
• Other Authors: Wang Lipo
• Format: Theses and Dissertations
• Language: English
• Published: 2014
• Subjects: DRNTU::Engineering::Electrical and electronic engineering::Computer hardware, software and systems
• Online Access: https://hdl.handle.net/10356/61783
• Institution: Nanyang Technological University

Haptics refers to the science of perception and manipulation of objects in virtual environments. Its applications spread rapidly from a human-computer interface to manufacturing, scientific discovery, medical training, etc. In a complex dynamic virtual environment, it is important to have smooth and realistic haptic feedback. In this project, we focus on research and development of stable haptic rendering methods and algorithms to provide continuous force and torque feedback in dynamic virtual environments. In haptic rendering, many algorithms and methods were proposed such as the god-object method, spring-damper method, virtual proxy method, Voxmap Point Shell (VPS) method, constraint-based method, Quasi-Static Approximation (QSA) method, etc. Currently, for six degrees-of-freedom (6-DOF) haptic rendering, the direct haptic rendering methods only support geometric rendering without physically based dynamic simulation. Virtual coupling based methods separate the haptic device from the virtual tool. It enables high stable force feedback and supports dynamic simulation of the virtual objects with physical properties. Although these algorithms have greatly improved performance of haptic rendering, there are still unsolved and challenging problems as follows. 1) Buzzing. If a virtual tool has physically based properties (for example, mass), the buzzing would appear as continuous high frequency vibrations. 2) Inaccurate manipulation. When the virtual tool has a large mass value, the displacement would become larger because of the gravity. This large displacement would introduce an inaccurate movement during the haptic manipulation that can cause accuracy problems. 3) Discontinuous force update. When there are complex models and/or deformable models, the physical simulation may produce a low update rate of force which causes discontinuous force output on the haptic device. The aim of the research is to propose general haptic rendering algorithms to improve stability of haptic rendering systems. To improve stability of haptic rendering, we propose new stable haptic rendering algorithms based on virtual coupling. The algorithms can be used for various static or dynamic applications to provide stable haptic force and torque feedback. First, we propose a stable dynamic algorithm based on virtual coupling for 6-DOF haptic rendering. It can overcome the “buzzing” problem when a virtual tool with small mass values is used. The novelty is that a nonlinear force/torque algorithm is proposed to calculate the haptic interaction when the collision happens between the virtual tool and virtual objects. The force/torque magnitude is automatically saturated to the maximum force/torque value of the haptic device. The algorithm is tested on the standard benchmarks and outperforms available algorithms such as spring-damper algorithm and QSA algorithm. Experimental results show that this algorithm is capable to provide stable 6-DOF haptic rendering for dynamic rigid virtual objects with physical properties. Second, we propose an adaptive haptic rendering algorithm based on virtual coupling to overcome the inaccurate manipulation problem caused by the large mass values of the virtual tool. The algorithm can automatically adjust virtual coupling parameters according to the mass values of the simulated virtual tools. In addition, the force/torque magnitude is saturated to the maximum force/torque values of the haptic device when large interaction force is generated. The algorithm is tested on the standard haptic rendering benchmarks. Compared to other algorithms, the adaptive algorithm supports more accurate haptic manipulation. Third, we propose a new prediction algorithm for smooth haptic rendering to overcome the low update rate of the force during physical simulation of complex and/or deformable models. We propose to use a prediction method combined with an interpolation method to calculate smooth haptic interaction force. An auto-regressive model is used to predict the force value from the previous haptic force calculation. We introduce a spline function to interpolate smooth force values for the haptic force output. The proposed method can provide smooth and continuous haptic force feedback in a high update rate during the virtual manipulation of complex and/or deformable objects. It outperforms other force estimation/prediction methods. A haptic enabled molecular docking system HMolDock is developed to find the correct docking positions between ligand and receptor. Here, a stable haptic rendering algorithm is implemented at the application level of the system to enable stable haptic manipulation of large molecules. HMolDock can help the drug designer to find the correct docking positions between molecular systems. For medical applications, we develop a haptic-based serious game "T Puzzle" and an EEG-enabled haptic-based serious game “Basket”. In the game "T Puzzle", virtual blocks are assigned with small mass values, and the stable dynamic algorithm is implemented to provide stable haptic manipulation in virtual environments. This game can be used for intellectual development and post stroke rehabilitation exercises. The EEG-enabled haptic based post stroke rehabilitation serious game “Basket” is developed to help patients to perform rehabilitation activities. In the game, the haptic device is used to manipulate various virtual objects and move them into the basket. The adaptive haptic rendering algorithm is implemented to guarantee an accurate haptic manipulation of the virtual objects with different mass values. The EEG based emotion recognition algorithm is implemented to recognize emotions of the patient and automatically adjust the difficulty level of the game. The proposed haptic rendering algorithms are also integrated in CHAI 3D library.