A clinical pilot study on posture stabilization via light contact with cane-type companion robot
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In this paper, toward robotic gait assistance, we investigate the feasibility of a cane-type assistive mobile robot accompanying the user autonomously through a clinical pilot experiment. As widely known, gait ability is important for all people to keep their quality of life. However, for people having weakened lower limbs such as elderly people, their postural sway during walking could be insuppressible and cause falling. To support the gait motion of elderly people, our group has been developing a series of hand-holding cane robots named Intelligent Cane. Such assistive robots are expected to remove barriers to the independent lives of elderly people. Recently, we have focused on the potential of a companion robot that follows the user ahead and can be touched or grasped for bracing whenever the user needs it. In order to demonstrate proof of our concept through an experiment with a motion capture system, we propose a user companion strategy that enables our cane robot to keep a constant relative distance between the robot and the user walking on a treadmill. We evaluate the accuracy of the user companion in an experiment where a user walks on a treadmill. Then, we conduct a clinical experiment with three healthy subjects walking on with the treadmill with our cane robot as a pilot study. Through the clinical experiment, we evaluate a postural stabilization effect of physical interaction with the robot and discuss the feasibility of our robotic gait assistance methodology.
KeywordsAssistive robotics Cane-type robot Human–robot interaction Companion robot
quality of life
light touch contact
laser range finder
inertial measurement unit
robot operating system
graphical user interface
fast Fourier transform
Increasing elderly population and a shortage of human resources cause that the demand for care exceeds the supply . The unbalanced relationship could lead to insufficient social security for elderly and excessive care burdens to caregivers . As a solution to such a labor shortage, assistive robots are expected to support medical treatment and enhance physical ability more effectively . Furthermore, the robotic devices which can be used without medical observation would help people with a wounded lower limb live independently.
Our goal in this study is to provide sufficient assistive robot interaction for gait stabilization and promote a daily locomotion habit. Demotivated and insufficient gait activities have a possibility to be one of the dominant factors in disuse syndromes . In addition, walking ability is closely related to our quality of life (QOL) . Unbalanced gait puts elderly people at risk for falling and may cause a critical injury such as a bone fracture. Using a walking assistive robot, we address to enrich daily lives of elderly people through supporting gait locomotion.
As one of the approaches to stabilize gait movement, a number of research groups have previously addressed to develop wearable walking assistive robots, called exoskeletons, to rotate or constrain some joints of the user’s whole body or lower limb (see [6, 7] for reviews). Such exoskeletons are designed for elderly people who have difficulty in walking voluntarily without any assistance such as paraplegic patients. Exoskeletons are attached to the lower limbs of the user directly, and physically provide assistive torques to each user’s joint in order to support knee flexion/extension and ankle plantarflexion/dorsiflexion. Notable examples of commercial exoskeleton devices include Lokomat by Hokoma , EksoGT by Ekso Bionics , Indego by Parker Hannifin Corp. , HAL by Cyberdyne  and WPAL by ASKA Corporation . Research platforms for robotic gait assistance exoskeletons include ABLE  and EXPOS , whose objective is to improve mobility of elderly people. These assistive wearable robots are beneficial in increasing gait stability by assisting leg swing and preventing the joints of the lower limb from buckling due to insufficient muscle strength. Recently, the potential for such functionality has been evaluated in clinical tests with patients. However, the structure of the wearable device could restrict free lower limb movements of the users, and attachment mechanism should be carefully designed to be in contact with each patient individually in order to prevent skin issues such as skin wounds and pressure sores . In addition, at the attachment and detachment of such a wearable robot, the therapists normally need to spend some time and labor, which would be time-consuming for the users and medical staff .
In order to support gait locomotion of elderly people with comfortable and straightforward usability, non-wearable assistive robots needing no attachment/detachment have been explored. Typically, these robots are composed of a mobile base with a grip handle to provide walking support for elderly people by adjusting supportive forces, walking speeds and directions. These non-wearable robots do not constrain the leg movement of the user, and the walking ability of the elderly people can be evaluated in situations closer to the natural gait motions (unlike wearable systems with active forced assistance) using vital information. In , a device called intelligently controllable walker (i-Walker) has been introduced, which can analyze users’ risk of falling with the force and position sensing information. In , a passive intelligent walker called RT-Walker has been proposed, which is composed of only passive elements such as servo-brakes to control the velocity of the walker according to the operation force applied by the user. In , a concept and implementations of the personal aid for mobility and monitoring (PAMM) system has been introduced, which provides guidance support for walking under adaptive shared control so that the user can intuitively control the robot. The primary focus of these studies is to support the user’s walking in their living environment based on these robots’ stiffness and mechanical stability.
In this study, we have proposed a notion of providing gait assistance considering human original stabilization ability as well as mechanical support. The related papers mentioned above present the assistive devices providing physical support to prevent the users’ falling kinematically or dynamically. Although such a usual assistive strategy is useful to obtain a numerical balance margin, e.g., the zero moment point, our proposed notion focuses on human medical functionality to reduce the redundant interaction and help the user, who feels a fear to walk slightly, recovers more natural gait motion via light physical contact. Such a force propagation which is useful for posture stabilization has been discussed in the medical field. Light touch contact (LTC), which stands for lightly touching an object through a fingertip of a user, is known to have the potential to lead a hopeful physiological phenomenon that is strongly related to keeping balance . An LTC with a static object is reported to be able to decrease postural sway while standing [20, 21, 22]. In addition, an LTC is useful to control postural sway caused by predictive and reactive disturbance . The benefit of an LTC is also demonstrated in subjects with postural control dysfunctions, such as individuals with vestibular loss and peripheral sensory neuropathy [24, 25]. Effects of the LTC while walking on a flat floor and a treadmill are also reported [26, 27]. However, in these studies, equipped handrails are used as touched objects, and the subjects were instructed to stand or walk along with them. Recently, a mobile device that replaces such a touchable handrail is expected to investigate the touching effect in a living environment. In , the authors have developed a virtual LTC (VLTC) based wearable haptic device composed of an acceleration sensor and a vibration stimulator. By stimulating the user’s fingertip according to its motion, the device provides an illusion that the user can lightly touch a virtual partition. Although the VLTC device has high usability, it could not support a user’s weight physically in case of falling. In order to provide both the touching effect-based assistance and the mechanical assistance, we have addressed to develop a robot following the user ahead and providing a point which can be touched whenever the user requires.
In this paper, we propose a touchable robotic device accompanying the user automatically and supporting the user’s weight in case of emergency, and investigate the feasibility of the robot in terms of the touching effect based postural stabilization through a clinical pilot experiment. Previously, our research group has been developing a series of cane-type robots named Intelligent Cane as a mobile hand-holding device [29, 30]. With the focus on safe walking, we have introduced design strategies for an admittance control model for fall prevention of the user and robotic gait rehabilitation . As another practical usage of our cane robot, recently, we have been exploring a robotic user companion system which enables the user to touch or grasp the cane robot whenever the user feels some necessity of some assistance during walking. We have designed a new prototype of the cane robot which is capable of providing the LTC effect based gait assistance mentioned above. In this paper, as a pilot study, we address to conduct a clinical experiment where subjects walk on a treadmill system including a motion capture in order to evaluate the touching effect from a view of the subjects’ kinematics. For this experiment, we propose a motion planning strategy that enables the robot to move on the treadmill and follow the user. Then, through the pilot experiment, we evaluate the postural sway reduction based on the subjects’ kinematic data and demonstrate a proof of our concept of human stabilization functionality based gait assistance using our cane-type companion robot.
Gait assistive robot “Intelligent Cane ver.6”
This section presents an overview of a prototype of the cane-type robots named Intelligent Cane ver.6 proposed in this paper.
Capable of supporting the user’s weight while the user leaning on it.
Movable at the speed of up to 1.3 m/s which could be considered as a maximum walking speed of the elderly .
Intuitive user interface (UI) is important for instructors who are not familiar with robotics such as medical doctors and physical therapists. We design the graphical and auditory UIs to improve the usability of the cane robot.
In addition to the GUI, we develop an auditory user interface for the cane robot in order to take simplified communication with a user. At the beginning and the end of a gait trial, the robot speak specific sentences, e.g., “Let’s walk with me!” in Japanese. In our previous research , we have reported that such an auditory communication has the potential to provide an affinity for the robot. This functionality is useful for the instructors as well to know the robot state without having a look at the above GUI and to concentrate on supporting the user physically during gait trials.
User companion on treadmill
This section presents the proposed self-localization and motion planning algorithm of our cane robot for user companion during treadmill walking.
Note that, in this paper, we use the board where the AR markers are pasted and put in front of the treadmill. For better usability, we are planning to project the markers onto a screen where the user can see a virtual walking scene. Besides, we are looking into replacing the markers with another thing to make the landmark more natural.
Manual update according to the operation force applied by the user, and
Autonomous update to keep the selected relative position between the user and the cane robot.
Interaction force based manual update
Relative position based autonomous update
User companion test
This section presents an evaluation of the proposed user companion algorithm, especially the 2nd rule: autonomous update to keep a constant relative distance between the user and the cane robot.
As a treadmill system platform, this study uses GRAIL (Motekforce, see ) at the National Center for Geriatrics and Gerontology, Japan. The system consists of (1) a 3D motion capture system, (2) a motorized fully instrumented treadmill, (3) a force plate, and (4) a cylindrical screen. Mainly using (1) the motion capture system, we capture the user’s kinematic motion at a frequency of 100 Hz.
In order to synchronize the motion data measured by GRAIL and the cane robot data, the robot sends trigger signals every 10 s and vertical force data through an analog signal connected to the GRAIL. These signals are recorded by the GRAIL system at a frequency of 100 Hz. In addition, considering the size of the used treadmill, we set the desired position limitation of the cane robot in (4).
In this section, we present an experiment where subjects walk on a treadmill with the cane robot and we evaluate the posture stabilization effect by touching the robot. We introduce an experimental condition and conduct a clinical experiment using the treadmill used in the user companion test mentioned above. Then, we analyze the experimental result and discuss the potential of our strategy for the postural sway reduction using our cane robot.
Descriptive characteristics of the subjects in the experiment (values are given in mean ± SD)
27.6 ± 6
M 1/F 2
As the evaluation indices, in this paper, we focus on the oscillations of the sacrum position and tenth thoracic vertebrae (T10) position during gait trials in each condition (see Fig. 6). Note that, considering bipedal gait characteristics, it is obvious that the oscillation in y-axis and x-axis would be affected by each gait cycle motion (two step cycles) and each step cycle motion, respectively. We apply the fast Fourier transform (FFT) analysis to the oscillated motions and compare the two conditions in terms of the amplitude and harmonic ratio at around the gait cycle frequency in y-axis and around the twofold frequency of the gait cycle in x-axis. The harmonic ratio is known as quantification of oscillation symmetry and often used to evaluate gait stability using acceleration data measured by an IMU as a simplified way in the physiological field . In this paper, we apply this index to the measured position data measured by the motion capture system and discuss the user’s stability.
Results and discussion
Figure 11 illustrates the mean and the standard division of gait cycle duration calculated from the motion data of the subjects’ heel during walking. Although the gait cycle duration of one subject was reduced significantly, we found no significance in the ones of the other subjects. The gait cycle duration is proportional to the step length since the walking speed is constant 0.8 m/s in this experiment. The result suggests that the appearance of our cane robot may cause some change of gait posture or disturb some users to swing the leg physically or psychologically. For further investigation of postural sway reduction by light touch in future work, we will address to eliminate the effect on the swing leg, e.g., by adding a spring mechanism to absorb unexpected shock and limit the amount of interactive force. In the following evaluation, we focus on the postural sway of the subjects at frequencies of each subjects’ gait cycle.
Note that this experiment was conducted with three healthy subjects having no disability, and it would be insufficient to conclude the assistive effectiveness of our research concept with statistical evaluation. We demonstrate proof of our concept on our cane-type companion robot for gait stabilization through the experimental result.
In this paper, we proposed a user companion algorithm for our cane robot moving on the treadmill with the user in order to investigate the postural sway reduction by slightly touching the robot. To solve the problems peculiar to the gait trial on the treadmill, the AR markers are placed in front of the robot and used as a landmark for the self-location. Then, we introduced a manual and autonomous motion planning methodologies according to the applied force from the user and the relative position between the robot and the user, respectively. Through a simple walking test with one user, we evaluated the accuracy of the user companion achieved by the proposed autonomous motion planning. In addition, we conducted an experiment to investigate the touching effect with three healthy subjects walking on the treadmill with our cane robot as a pilot study, and evaluated the amplitude and the harmonic ratio of the sway. Through the experiments, we demonstrated proof of concept of our walking assistance strategy using the cane-type companion robot.
As mentioned, we could not conclude the effectiveness of our robotic stabilization approach with statistical evaluation. In future work, we will conduct experiments with more number of healthy and elderly people, and compare various conditions such as faster/slower walking speed to confirm the effectiveness of the proposed walking assistance. In addition, we will address redesigning the cane robot hardware not to disturb the user’s leg swing as well as motion control algorithm to enable the robot to accompany the user walking around on a flat floor.
This research was funded in part by the Research Funding for Longevity Sciences (28-34) form the National Center for Geriatrics and Gerontology (NCGG).
SI, TA, and YH developed the cane robot and designed the control algorithm. KA, KK, and IK designed and conducted the experiment. SI and KA analyzed and interpreted the data, and drafted the manuscript. All authors read and approved the final manuscript.
Ethics approval and consent to participate
The study protocol was approved by the National Center for Geriatrics and Gerontology and was carried out in accordance with their recommendations. All subjects were given a written informed consent in accordance with the Declaration of Helsinki.
Consent for publication
The authors declare that they have no competing interests.
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