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As the number of elderly people increases and their leg muscles deteriorate, wheelchairs have become an important means of their transportation. In previous research, we proposed a design that combines a double planetary gears’ wheels with the crawler mechanism to enable wheelchairs to climb upstairs and downstairs. However, while climbing downstairs the situation is different from climbing upstairs. The double planetary gears’ wheels cannot be provided with sufficient friction. Thus, the carrier of the planetary gears cannot revolute as if climbing upstairs and the moving on the stairs will be not stable. To solve the problem, we have designed single planetary gears’ wheels to drive the wheelchair. Both theoretical calculations and proportional models have proved that it will generate fewer accelerations than the previous way, which will ensure a safer and smoother process of climbing downstairs.

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.