Power assistive device for stair ascent and descent

A device for assisting a user in motion in a system comprising at least an upper rail and a support rail parallel to the upper rail, the device comprising:

• a mobile platform;
• a first engagement mechanism attached to the mobile platform and having at least one contact means for contacting a top surface of the upper rail, wherein the first engagement mechanism is above the upper rail when the at least one contact means of the first engagement mechanism contacts the top surface of the upper rail;
• a second engagement mechanism attached to the mobile platform having a contact means having a surface complementary to a driving surface of the support rail, wherein the driving surface of the support rail is a top surface of the support rail, and further wherein the second engagement mechanism is above the support rail when the contact means of the second engagement mechanism contacts the driving surface of the support rail;
• a human interface for grasping by the user;
• and
• a motor for causing relative motion of the contact means with respect to the driving surface, wherein the human interface comprises an upper bar for holding by the user when descending a flight of stairs and a lower bar for holding by the user when ascending the flight of stairs.