Vibration Characteristics Analysis of Human- Robot Coupled System for Walking Posture of Elderly-Assistant Robot

The ever-increasing need for nursing care due to the aging population necessitates the need for safe and efficient elder-assistant robots that can reduce the care burden on the societies.However, most of the existing studies focus only on the robot-user sitting posture.In this paper, the vibration characteristics of the human-robot coupled system for the walking posture of the elderly-assistant robot is analyzed.The work is particularly important as it assesses the possible resonance, which if present, will adversely affect the comfort of the elderly.Initially, the dynamic model of the human-robot coupled system is derived.Then, the modal analysis of the robot is carried out to assess the possible resonance of the system during walking.Thirdly, MATLAB software is used for the vibration simulation analysis of the human-robot coupled model under different scenarios, namely, sudden impact and uneven road situations.Moreover, real-time experiments are conducted on the lab-scale robot to verify the effectiveness of the derived model under the same road conditions.Finally, the sensitivity analysis of the vibration responses to the damping ratio, mass ratios, and the natural frequencies is conducted to assess the effects of the parameters on the vibration responses.The simulation and the real-time analysis show that the model can be effectively used to assess the road-robothuman vibration transmissibility, particularly human hand comfort.Thus, the results demonstrate that the designed robot can be safely used by the elderly as it does not resonate during walking.INDEX TERMS Vibration, elderly-assistant robot, tactile-slip drive, vibration comfort, human-robot coupled model.The four-wheel walker had two 152-192cm adjustable arms support and was equipped with incremental encoders and cameras for effective navigation.Goher [19] presented the design and development of a reconfigurable wheelchair with the mechanism to transform the user from sit to stand and vice versa.However, the application of the prototype was limited to children within seven years.Furthermore, Song et al.[20] introduced the design and analysis of a wheelchair-exoskeleton hybrid robot.With the three incorporated functions namely, wheelchair, support and exoskeleton configurations, the system provided motion assistant and rehabilitation.The main shortcoming of the prototype was that the exoskeleton configuration was not suited for the elderly.Young et al. [21] developed another robot walking helper that provided motion guidance for the elderly by considering the physical and psychological comfort of the user.Furthermore, a concept prototype of an intelligent walking aid robot was designed by the Shanghai Jiao Tong University [22].The intelligent robot was equipped with operating handles at both ends of the frame above the car body.The handles guided the operations of the robot, namely, forward movement, left movement, right movement, braking, and acceleration.A laser proximity sensor was used to detect and avoid obstacles, while the pulse detector was used to detect the physical condition of users.In [23], a multi-modal walking assistant robot was developed that provided human-walker interaction using the wearable inertial measurement units (IMU) and onboard IMU.Huang et al. [24] presented an omnidirectional walking-aid using wearable sensors that estimate the posture of the elderly.The robot could detect possible fall orientation of the elderly and appropriately react to prevent the fall by analyzing the distance between the elderly center of pressure and the mid-point of the elderly feet.Other studies that discussed the human-robot interaction for assisting the sick and the elderly include MOBOT [25], intelligent walker ANG [26], and Hobbit [27], and ENRICHME [28].Since 2009, our lab has developed many types of the elderly-assistant and walking-assistant service robots.Within this decade, a detection and recognition method using tactile and slip sensors was proposed for the control of the robot.In [29], tactile and slip sensor was used to identify and classify the elderly's walking intensions.The preliminary research using the K-nearest neighbor technique showed that up to 98% of the user's intention could be identified.The control technology of the robot driven by the tactile-slip sensation was presented in [30], [31].Furthermore, our lab carried out researches on a new generation elderly-assistant robot that was fully functional, structurally stable, safer and reliable as compared to the existing elderly-assistant service mechanism.In [32]-[34], the structure of the robot, motion analysis, posture conversion and a natural man-machine interactive control method based on the tactile-slip sensation were presented.However, the studies mentioned above only present the development of the systems without assessing the induced