Development and Evaluation of a Novel Overground Robotic Walker for Pelvic Motion Support Kyung-Ryoul Mun, Zhao Guo, and Haoyong Yu Dept. Biomedical Engineering National University of Singapore Singapore
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body weight support (BWS) system to support lower limb movements. However, use of treadmills in gait rehabilitation is still widely controversial as there is an ambiguity on the assumption that walking on a treadmill could represent an actual gait on the over-ground in terms of sensorimotor feedback and proprioceptive input. It has been shown that walking on treadmill is indication of greater cadence, smaller stride length and stride time as well as reduced joint angles, moments, powers and pelvic rotation excursion compared with over-ground walking [8, 9]. These systems provide only single anatomical plane of movement (sagittal) with predetermined path causing constraints to the patients in a fixed platform. The constrained and pre-determined gait may lead to less satisfactory functional outcomes and the lack of cycle-to-cycle variation, reducing sensory responses, and may ultimately impair motor learning [10].
Abstract Restriction of pelvic lateral and rotation motions caused by robotic devices can hinder successful gait rehabilitation. To tackle this issue, this paper presents a novel pelvic motion supported over-ground robotic walker developed for gait training. This device consists of an omni-directional mobile platform, a pelvic and trunk motion support brace unit, and an intuitive human-machine interface with force/torque sensor. With this proposed device, over-ground walking with 6 degrees of freedom (DoFs) pelvic motion facilitation was achieved in an intuitive and natural way. Preliminary gait experiments were carried out on three conditions of free walking, walking with and without pelvic lateral and rotational motions in order to evaluate the feasibility of the walker. The results showed that gait with pelvic motion facilitation strongly resembled free over-ground walking without alteration of the normal gait dynamics, while gait with pelvic restriction led to gait performances with reduction in the range of motion of lower limb. The findings of this research revealed that the pelvic motion facilitation with developed walker can provide better functional outcomes for gait rehabilitation.
Furthermore, overhead harness BWS systems emplaced often restrict pelvic rotation and lateral movements that can lead to less satisfactory functional outcomes after intervention. The pelvis contributes to optimization of energy consumption and to aesthetic walking pattern during the gait. The fixation of the pelvic lateral and rotational motion greatly affects gait dynamics by shortening step width and reducing the coronal trunk rotation, and lengthening the step length and sagittal trunk rotation [11]. Therefore, the fixation of pelvis should be avoided to obtain more realistic and aesthetic locomotion upon post-rehabilitation.
Keywords robotic walker; gait rehabilitation; pelvic motion support; body weight support (BWS); admittance controller; active split off-set castor (ASOC)
I. INTRODUCTION Walking is one of the most important human activities in daily life. To improve the walking ability of elderly people and stroke patients, robotic assisted devices have attracted much attention as an alternative of the conventional gait rehabilitation since they have facilitated or replaced the physical training effort of the therapists [1, 2].
From the perspective on an effective robotic gait rehabilitation, the facilitation of pelvic lateral and rotational movements have been accentuated with over-ground walking platform to provide better functional outcome after gait training. Many attempts were put into action to increase efficacy of robotic gait rehabilitation by actualizing overground walking platform with pelvic motion support ability. These include KineAssist (Kinea Design LLC) [12], WalkTrainer (Swortec SA) [13], NaTUre-gait (Univ. Nanyang Tech) [14], and a BWS system with a pelvic
Current robotic gait rehabilitation devices, such as Locomat [3, 4], LOPES [5], ALEX [6], and LokoHelp [7] were built on treadmill based platform with active or passive exoskeleton robots in combination with overhead harness
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intervention will be limited. On the other hand, degree of freedoms (DoFs) for pelvic motions is limited in the robotic devices such as RGR trainer [16] and a robotic device designed by Watanabe [15]. RGR trainer was mainly designed to support pelvic obliquity, while the device reported in [15] was developed only for the pelvic lateral movement. The limited DoFs may not be applicable enough to broad spectrums of the neurologically challenged patients. In these regards, a compromise between intricate mechanical design with a large number of DoFs and simplicity with limited DoFs is strongly recommended for maximizing the training effects of gait rehabilitation. As a novel approach, an omni-directional walking platform with active split off-set castor (ASOC) and control system for a personal aid for mobility and health monitoring 6$1$#$5$+./$#!83'$ 43'.1=2/1$5(.421$2$ 1"' 7, 18]. It was reported that the omni-directional mobility can support at least three DoFs without additional actuators for the pelvic motion support. Therefore, we believe the omni-directional platform can be utilized for effective design of the robotic device as it does not require additional actuators for pelvic lateral and rotational movements.
Fig. 1. (A) The conceptualized design of the novel robotic walker for pelvic motion support. (B) The system consists of omni-directional mobile platform with ASOC, pelvic and trunk motion support brace unit, humanmachine interface with F/T sensor. (C) The prototype of the robotic walker.
holding mechanism [15]. These devices are mobile gait training robotic systems with actuated trunk and pelvic support mechanisms. These devices enable realistic walking patterns with proper sensory input from actual ground and increase active participation of patients. However, the pelvic lateral and rotational movements were passively implemented in Kineassist. The WalkTrainer and NaTUregait have accomplished pelvic motion support with complex mechanical structures and pre-fixed paths from normal pelvic excursion. As a result, controls of pelvis are highly complicated and the effectiveness of rehabilitation during
In this research, we present a novel pelvic motion supported over-ground walking device which allow the gait rehabilitation at-home or outpatient rehabilitation center, and investigate the gait performances of the pelvic lateral and rotational facilitations with the developed device. Investigation on kinematic gait parameters of the developed device was performed by comparing walking with and without pelvic motion facilitation in healthy young subjects. II.
NOVEL ROBOTIC OVER-GROUND WALKER FOR PELVIC MOTION SUPPORT
The overall concept and actual prototype of the novel pelvic motion supported over-ground gait rehabilitation device is shown in Fig. 1. The implementation of pelvic support function of the walker system consists of i) an omnidirectional mobile platform with ASOC; ii) a pelvic and trunk motion support brace unit; iii) an intuitive humanmachine interface with force/torque (FT) sensor for robot control [19]. With this system, subjects can move in any direction without being constrained in one plane of movements so that the therapist can facilitate the gait rehabilitation more effectively and practically with less laboring efforts. A. Omni-directional Mobile Platform The omni-directional mobile platform was designed for fundamental gait principles. Center of mass (CoM) of the body is simultaneously shifted in forward-backward, side-toside (lateral), and rotational directions during gait.
Fig. 2. The pelvic and trunk motion support brace with BWS actuator
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Of all the pelvic motions, the role of lateral and rotational motions are critical to have natural walking pattern because these are related to the six major gait determinants to minimize the energy consumption during walking by smoothing out the vertical displacement of center of mass (CoM) [20].
2015 IEEE International Conference on Rehabilitation Robotics (ICORR)
rotation in frontal plane of torso. As a result, trunk lateral bending was achieved and at the same time the fiberglass allowed trunk flexion and extension in sagittal plane to achieve the anterior-posterior trunk bending. The pelvic brace unit is connected with a BWS actuator by a six DOF FT sensor assembly mechanism. This BWS actuator (Tol-O-Matic, Inc.) provides all-in-one control with controller, drive, and motor integrated in one compact component, and the active body weight of the subject is collected via the vertical axis of the FT sensor during dynamic walking (Fig. 2). The forward-backward, lateral, and vertical forces with 3-aixs torques between human body and robot were measured by the sensor for interaction control. C. Intuitive user interface control
Fig. 3. Human-machine interface with mass-damper admittance controller
Therefore, there are strong demands to implement pelvic lateral and rotational movements to the walker. As shown in Fig. 1B), the omni-directional mobile platform has been integrated into the walker to support pelvic anterior-posterior (Vcx), medio-lateral (Vcy) movements as well as rotation in vertical axis (). This platform was developed using two sets of ASOC units consisting of two coaxial conventional wheels. The ASOC was driven independently according to velocity commands at the central point. The velocity of central point can be defined by the velocity of each wheel [17]. With the use of the omni-directional platform, it was possible to simplify the mechanical structure to support 3 DoFs pelvic motions, and it could also provide a number of advantages including high energy efficiency, and robust mobility on uneven terrain. Hence, a user can consistently move in any direction and any configuration by using this omni-directional platform. B.
Pelvic and trunk motion support brace with BWS actuator The pelvic and trunk motion support brace are shown in Fig. 2. In this study, the pelvic support harness not only served as the physical interface between machine and user, but also passively supported the pelvic tilt and obliquity. The pelvic pads were wrapped around the waist of subject, especially at pelvis with an adjustable design as per the 24!)$"3=2 - 3.,8 '$pelvic pads were mounted to pelvic brace with spherical flange bearing, allowing pelvic anteriorposterior tilt. The back side of pelvic brace was connected to swivel joint covered by fiberglass. The property of fiberglass was stiff, but it also had compliance characteristics, that allowed up-down movement of anterior-superior iliac spine (ASIS) and restricted the exaggerated vertical movement of ASIS for the stroke patients [21]. Thus, pelvic obliquity was accomplished passively. The trunk support brace was connected to swivel joint with the fiberglass providing
The robotic walker is a typical co-robot system that has direct physical human robot interaction. User interface is critical for the safe and efficient operation. The interface should provide a natural sensation to the user and be easy to learn to use. The feel of force or haptics is important for physical interaction control. We propose a FT sensor based control interface with a virtual dynamic model which defines exactly the dynamic behavior of the system to present an intuitive haptic feel to the user, making the user feel as if he or she is pulling a load. As can be seen in the Fig 3A, the FT sensor was fixed between the pelvic support harness and the BWS system of the walker. Based on the interaction force detected, speeds in the forward, lateral and rotational directions are generated with an admittance/ mass-damper model. This method can achieve the most intuitive human machine physical interaction. The user can just focus on walking without thinking of direction and speed control, with much reduced mental workload. The admittance control uses an admittance model that emulates a dynamic system and &(5$2 3'$ 42$1 :%$$+(-&
