For the leg-lifting function, only the thigh part and the shank
part are involved. The schematic design of the leg-lifting task
is shown in Fig. 6. Hence, two linear actuators, installed under
the shank part, are used to perform the task. One is used to
raise the thigh part and the other is for raising the shank part.
The same mechanism is used for the sitting function. The actuators
are connected to the fixed chassis by one pin, and the
extension axis of the linear actuator is connected to the shank
part. LA4 denotes the linear actuator connected to E, and LA5
denotes the linear actuator connected to F. D denotes the joint
that connected the upper body part and the bottom part. G is the
connection between the thigh part and the shank part. E and F
denote the connecting locations of the linear actuator and the
bed chassis, respectively. G and H denote the connecting locations
between the extended axis of linear actuator and the shank
part. The variable L1 denotes the distance betweenGand H. The
bed achieves the leg-lifting task, including lifting thigh, knee,
and shank. These motions are achieved by operating two linear
actuators cooperatively. One of them is to let the axis of LA5 be
fixed first.When the axis of LA4 is extended, LA5 rotates about
F with a fixed radius, and the trajectory of G rotating about D
is a circle. The variable R2 denotes the radius of the circle, θ3r
denotes the angle measured from the thigh part to the X-axis,
θ4r denotes the angle measured from the shank part to the axis
parallel to theX-axis, LH denotes the vertical distance between
D and E, Lf 4 denotes the horizontal distance between G and E,
Lf 5 denotes the horizontal distance between H and F, and Lp4
and Lp5 are the extended distances of LA4 and LA5 , respectively.
The relation between Lp4 and θ3r can be represented as
follows