虚拟现实（virtual reality，VR）环境下的自然行走交互是增强VR沉浸感、提高VR任务完成度、优化运动感知觉保真度的关键技术。全向跑步机是实现大范围VR行走交互的有效设备，研究跑步机的运动控制策略、行走运动与VR场景运动之间的匹配以及VR视觉运动错觉的增强，具有重要的理论意义和应用价值。本文针对跑步机的加速度抑制、VR环境的步态束缚程度判断、视觉速度感知与运动速度感知的单值化匹配、VR环境的自我运动错觉强度提升四个方面展开研究。为降低跑步机的加减速对行走过程造成的侵入感，提出了一种基于虚拟力矩平衡模型的跑步机加速度抑制方法。该方法基于运动觉感知的力反馈理论，建立虚拟力矩平衡模型作为跑步机加速度约束，结合速度观测器和变参考位置方法，设计了跑步机的运动控制策略，实现跑步机加速度的有效抑制。利用去趋势波动分析法揭示了跑步机加速度对步态时空参数长程相关性的作用机制，验证了抑制跑步机加速度能够减小步态束缚、降低跑步机对用户行走过程的侵入感。针对长程相关性判断VR跑步机行走交互系统中步态束缚程度存在的固有缺陷，提出了一种基于复杂度的步态束缚程度判断方法。该方法引入了多尺度熵表征步态的复杂度，通过对比定速与自适应式跑步机行走、偏好与非偏好速度行走下不同步态参数的多尺度熵，构建出内外侧足底压力中心的复杂度与步态束缚程度的对应关系，即内外侧足底压力中心的复杂度越大则步态束缚程度越小。为解决VR跑步机行走交互的视觉速度感知与运动速度感知之间的匹配问题，提出了一种感知相等比的单值化方法。通过引入内外侧足底压力中心的复杂度，建立了感知相等比的最大值、最小值与步态束缚程度之间的联系，并以步态束缚程度更小为原则得到了感知相等比的单值化策略。该策略以感知相等比的最小值作为VR场景的视觉增益值，在实现视动觉感知匹配的同时降低了步态束缚程度。为提升VR跑步机行走交互的自我运动错觉（vection）强度，产生身临其境的行走交互体验，同时考虑视动觉耦联机制对用户步态束缚程度的影响，提出了一种垂向视点振荡的幅频值寻优方法。通过对比不同振荡幅频下vection打分值与内外侧足底压力中心的复杂度，揭示了垂向视点振荡的幅频值对vection强度和步态束缚程度的影响规律。将该影响规律与用户主观口述的评价方法结合，获得垂向视点振荡幅频值的寻优策略，实现了vection强度和步态束缚程度的协同优化。
Enabling natural walking in virtual reality (VR) environment is a key technology to enhance VR immersion, improve user task performance and optimize the fidelity of VR motion perception. Omnidirectional locomotion platform is an effective device to realize large scale VR walking interaction. The research on the motion control strategy of the platform, the congruence between the walking motion and the objects motion in the VR scene and the enhancement of VR visual motion illusions have important rationale and application value. This dissertation focus on the acceleration suppression of the locomotion platform, the judgement of gait constraint in VR environment, the uniformized matching between the visual speed perception and the locomotion speed perception, and the enhancement of self-motion illusion in VR environment.To reduce the sense of intrusion from the acceleration and deceleration of the locomotion platform (treadmill) during walking, a treadmill acceleration suppression method based on a virtual moment balance model is proposed for the adaptive treadmill. Based on the force feedback theory of proprioception, a virtual moment balance model is established to restrict the treadmill acceleration. Combined with the speed observer and the variable reference position method, the motion control strategy of the treadmill is designed to achieve effective suppression of the treadmill acceleration. By using the detrended fluctuation analysis, the mechanism of treadmill acceleration on the long-term correlation of spatiotemporal parameters is revealed. The results prove that suppressing treadmill acceleration can reduce gait constraint and the intrusiveness of locomotion platform to user’s walking process.Aimed at the inherent defect of long-range correlation for judging the degree of gait constraint in the VR treadmill walking interaction system, an evaluation method of gait constraint based on complexity is proposed. The proposed method introduces the multiscale entropy to quantify gait complexity. By comparing the multiscale entropy of different gait parameters between fixed-speed treadmill and adaptive treadmill walking conditions, preferred and non-preferred speed walking conditions, the correspondence between the complexity of mediolateral center of pressure and gait constraint is constructed, that is greater complexity of mediolateral center of pressure indicating smaller gait constraint.To deal with the reduced intensity of self-motion illusions (vection) in VR scene caused by treadmill walking interaction, and to consider the influence of visuomotor entrainment on user’s gait constraint, an amplitude-frequency optimization method of the vertical viewpoint oscillation is proposed. By comparing the rated value of vection and the complexity of mediolateral center of pressure under different oscillation frequencies and amplitudes, the effect of vertical viewpoint oscillation frequency and amplitude on vection strength and gait constraint is unraveled. Combined with user’s subjective assessment, the optimization strategy of oscillation frequency and amplitude is obtained. The synergistic optimization of vection strength and gait constraint is then realized. To deal with the perception matching problem of walking speed and visual speed during VR walking interaction, a uniformization method of perceptual equivalence ratio is proposed. The relationship between the maximum and minimum values of perceptual equivalence ratio and the degree of gait constraint was established by introducing the complexity of mediolateral center of pressure. The uniformization strategy of perceptual equivalence ratio is then derived based on the principle of achieving smaller gait constraint. The strategy adopts the minimum value of perceptual equivalence ratio as the visual gain of VR scene, which can achieve visual kinesthetic perception matching while the gait constraint is reduced.
