Stair Gait Classification from Kinematic Sensors

Gait measurement is of interest for both orthopedists and biomechanical engineers. It is useful for analysis of gait disorders and in design of orthotic and prosthetic devices. In recent years portable sensors have been studied as a complement to vision based (Morris & Paradiso, 2002). They have been used to measure both the kinematics of gait such as accelerations and angles as well as kinetics such as torques and forces. The main contribution of using portable sensors is the possibility of long time measurement of daily life situations. But the technique has also been included in active control of foot for rehabilitation. The research has mainly been focusing on the area of drop foot control see e.g. (Pappas et al., 2001: Veltink et al., 2003). The objective is to provoke foot lifting just in time for swing phase. The time to control is estimated often from gyros and force sensitive resistors. An alternative approach is to actively control foot ankle orthosis (Blaya & Herr, 2004). Recently also an active controlled foot ankle in a foot prosthesis has been studied (Svensson & Holmberg, 2006) for adapting to hill variations. But the existing systems are still limited in their capability of adapting to stair climbing. Just as orthoses, many prosthetic feet have fixed ankle position and attempting to move the body’s center of mass forward may cause a sense of instability. With pressure sensors, characteristics of stair climbing and descending can be detected as the “foot down” often differs to horizontal walking. In a typical case of a sound person with two biological feet going up a stair, peak plantar pressures increase in the rear foot sensors. While at down stair there is a significant increased rate of pressure change in the frontal part. But both speed of gait and size of staircases can influence the accuracy of classification. Gyros or accelerometers have typically been attached to the waist, hip or shank. The sensors detect compensations made for different walking situations. But internal noise and temperature sensitivity of kinematical sensors tend to drift the angle estimation. In this chapter an algorithm is presented to suit estimation of one foot angle in the sagital plane, independent on gait conditions. Only one gyro is used during swing and two accelerometers are needed for calibration during stance. Also, the sensor placement at the front of the foot avoids the need for heel strike for stance transition. Stair walking can therefore be studied. From the estimated swing trajectory three different gait conditions: up stair, horizontal and down stair are classified.