Page 116 - Handbook of Biomechatronics

112 Naser Mehrabi and John McPhee

Fig. 7 The simplified driver-vehicle model: (A) the two-dimensional (2D) musculoskel-
etal driver model and (B) the simplified vehicle model with a column-assist electric
power steering (EPS) system.

results. The effect of changing the grip position on the moments of muscle
forces on the shoulder and elbow was briefly discussed in Mehrabi et al.
(2014).
Fig. 6B shows the variation of elbow and shoulder angles when the 3D
driver model performs a sinusoidal steering wheel angle with an amplitude of
45degrees. In this research, we have used the Euler XYX convention to rep-
resent the shoulder’s plane of elevation angle (PEA), elevation angle (EA),
and axial rotation, respectively, where X is along the humerus and Y is nor-
mal to X and toward the humerus lateral direction. The change of shoulder’s
PEA and EA is significantly larger than the elbow flexion and extension
angle. The standard deviation of the elbow angle from its mean value during
this simulation is about 5degrees while it is 22 and 18degrees for the shoul-
der’s PEA and EA. As expected, the standard deviation of the shoulder’s axial
rotation is small, around 3degrees. The humerus rotation about the vertical
axis (i.e., parallel to torso) is less than 5degrees when steering wheel angle
varies 14degrees, depicting a mostly planar motion of the arm for small
steering angles. Therefore, the shoulder in the simplified model was reduced
from a spherical joint to a revolute joint, and the elbow joint has been
assumed to be fixed. Based on these assumptions, a simplified 2D driver
model as shown in Fig. 7A was developed, in which the arm segments move
only in the sagittal plane of the driver’s body, pivoting at the shoulder.
As shown by Jonsson and Jonsson (1975), the shoulder muscles are the
prime movers in steering tasks and can be classified into two groups: the
muscles providing clockwise torque and muscles providing counterclock-
wise torque on the steering wheel (Sharif Razavian et al., 2015).