Wheelchair Able to Assist the Elderly to Move on Stairs and Stand up

With the increasing in the number of elderly people and the deterioration of their leg muscles, wheelchairs have become an important mean of transportation. In the market, most wheelchairs that can climb stairs use a crawler-type or double planetary gears' wheel. But the crawler has the disadvantages of being bulky and has big friction on the ground and double planetary gears' wheel will cause big shake while climbing stairs. Rocker-bogie is also a mechanism can step over high obstacles but cannot climb stairs. To climb stairs smoothly and safely, we designed a wheelchair that based on the three mechanisms with advantages of all of them. With linkage mechanisms, the wheelchair can also adjust the location of the center of gravity (COG) of the user for safer climbing. Additionally, the linkage mechanism can also assist the user to stand up, which is more helpful for the user of the wheelchair. It is composed of four-linkage and parallelogram mechanisms. To assist the user to stand up with the normal posture of a healthy elderly, three parameters were taken into account in the design of chair part: trajectory of COG, the change of the upper body angle and the trajectory of the hip joint of the user while standing up. From the simulation results, the torque of the knee and ankle joint of the user being assisted to stand up decreased much. From theoretical calculations and experiments of the scaled models, different new mechanisms were compared and the one that was able to climb stairs most smoothly and stably was chosen. The effectiveness of the new mechanism was confirmed.