To effectively enhance the spatial sensation for an immersive user experience (UX) in virtual reality (VR), the locomotion interface (LI) is one of the most critical factors. To offer a room-scale LI suitable for use in typical office or home environments, it is imperative that the LI device enables a natural walking experience while occupying minimal space. To realize LI for all directions, an omnidirectional treadmill (ODT) can successfully achieve 2-dimensional holonomic motion (X and Y axes) and provide the most natural walking experience, such as walking on real ground. However, a problem arises due to the excessive system thickness caused by the torus structure of a large treadmill (X-axis) carrying several small treadmills (Y-axis), along with the installation of a complex power transmission mechanism inside the ODT. To reduce the thickness of its double-layer and complex structure, we propose an ODT with a novel transmission mechanism. The proposed ODT utilizes helical timing pulleys (HTPs) to generate Y-axis motion and helical gears (HGs) to synchronized-actuate the HTPs. As a result, the proposed ODT achieves a super-thin configuration and fast actuation performance. A pilot test of the proposed ODT was conducted to assess its maximum performance. The results indicate achievable speeds of 3.175 m/s and 4 m/s, along with an acceleration of 5 m/s2for both the X and Y axes, respectively.

For immersive interaction in a virtual reality (VR) environment, an omnidirectional treadmill (ODT) can support performance of various locomotive motions (curved walk, side walk, moving with shooting stance) in any direction. When a user performs lateral locomotive motions on an ODT, a control scheme to achieve immersive and safe interaction with the ODT should satisfy robustness in terms of position error of a user to keep a reference position of the ODT by accurately estimating intentional walking speed (IWS) of the user, and it should guarantee postural stability of the user during the control actions. Existing locomotion interface (LI) control focuses on the reference position tracking performance regarding the position of the user's center of mass (COM) in order to respond to forward locomotion that can move at high speed. However, in sideways walking, the movement of the lower extremities is different from that of forward walking, and when the conventional LI control was directly applied to sideways walking, it was observed that excessive acceleration commands caused postural instability. For appropriate interface of sideways walking, we propose an estimation scheme based on an accurate walking model including the movement of the ankle joint. The proposed observer estimates the acting torque generated by the force of both lower extremities through the position information of COM and ankle joint to more accurately predict the user's intentional walking speed (IWS). In the sideways walking experiment conducted using a 1-dimensional user-driven treadmill (UDT), the proposed method allowed more natural interface of the lateral-side locomotion with better postural stability compared to the conventional estimation method that uses only the COM position information.

The control problem in self-adjustable treadmills is to keep the position of the user at a reference position. The position error is the key obstacle in facilitating the abrupt stopping on self-adjustable treadmills. Another difficulty in this application is the oscillatory response of the closed-loop system. The conventional control methods utilize a high-gain observer to estimate the user velocity and exploit this information beside feedback signals to decrease the position error. Utilizing the high-gain observer, however, applies anomalous force (AF) to the user, leading to an unnatural feeling, and does not guarantee an oscillation-free response for the output. This paper aims to alleviate these problems by proposing a supervisory control scheme. First, a RISE controller is utilized for walking/running stage to compensate for slowly varying uncertainties in the system model without applying a large AF. Then, a positive-output controller is exploited for the stopping stage to guarantee the convergence of the position error without oscillation. Using the estimated intentional velocity and acceleration, a supervisory system is designed to switch between the controllers. Experimental results show the superiority of the proposed approach over the existing methods.

To achieve immersive and natural navigation in a virtual environment through human locomotion, it is necessary to generate a 2-dimensional infinite ground for omnidirectional walking. However, the existing omnidirectional treadmills are heavy, complex and exhibit low acceleration due to power transmission inefficiency. In this paper, we present a novel fast-omnidirectional treadmill (F-ODT) with a new power transmission mechanism called the Geared Omni-pulley. This mechanism ensures higher power transmission efficiency for driving the belts of the multiple transversal treadmills for independent Y-axis motion. Due to the improved power transmission performance combined with a simpler and relatively light-weight structure, the proposed 2D treadmill can generate a maximum speed of 3m/sec with an acceleration of 3m/sec2. Based on the improved performance, the F-ODT system can be used as a locomotion interface platform in various virtual reality environments such as training of soldiers, gaming/educational experiences and gait rehabilitation.

Among most existing gait rehabilitation robots, it is difficult to find adequate devices for gait rehabilitation of chronic stroke patients who can already stand and move but still need to rehabilitate the affected lower limb through simple, compact, and easy-to use devices. This paper presents a novel haptic based gait rehabilitation system (HGRS) which has the potential to provide over-ground gait training regimens for post-stroke ambulatory subjects. It consists of a portable cane for kinesthetic sensing and a wearable vibrotactor array for tactile biofeedback. Contact of user with the handle provides light grip force, it serves the purpose of balance assurance and increased muscle activity through light touch concept and vibrotactors contribute in enhancing the gait modification through afferent signal of vibration. Walking trials conducted with stroke patients indicate increased muscle activation and balance, and improved temporal symmetry with use of HGRS. HGRS is capable of assisting physical therapists in training individuals with stroke suffering from gait abnormalities. In addition, it is easy to use and low-cost which makes it reachable to a vast domain of subjects suffering from gait abnormalities.

This research aims to develop a novel gait assistive device with enhanced gait stability and training efficiency for stroke patients. The proposed assistive device for mobility aid is composed of a motored wheel and a cane for providing only a light grip force, which prevent a patient using excessive support force of an upper limb like a conventional cane and motivate the patient to use more actively a paralyzed limb due to the reduced weight support. In addition, the proposed device can provide the user with intuitive and safe interaction during walking by integrating an F/T sensor and a tilt sensor at the cane, and a switch sensor at the hand grip. Also, admittance control has been implemented for a patient, it intuitively changes cane speed by measuring interaction forces at the hand grip. A hemi-paretic stroke patient participated in the walking experiments as a pilot study to verify effectiveness of the proposed system. The results showed that the patient could improve walking speed and muscle activation during experiments with a constant speed mode of the haptic cane. Moreover, in the admittance control mode of the haptic cane, the patient could keep higher preferred walking speed and higher gait stability regardless of magnitude of resistance forces. The proposed gait assistive device with cheap, compact and easy-to-use characteristics can provide efficient gait training modes to chronic stroke patients.