Page 27 - Mechatronics for Safety, Security and Dependability in a New Era

Ch03-I044963.fm Page 11 Tuesday, August 1, 2006 12:24 PM
Page 11
Tuesday, August 1,2006
12:24 PM
Ch03-I044963.fm
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steering shaft loaded by a spring[l]M/mm]. The distance during both grips shows the handle width w,
and it is examined about 170, 240, and 430 mm in this experiment. A subject (24 years old, shoulder
width 520 mm) gripped the handle of a measurement device tightly. The wrist was fixed to simulate
elderly people's function. During each trial, the subject's wrists were kept in a specific posture. The
arm posture shaped by shoulders and elbow joints was varied by handling the measurement device, the
grips of which were fixed. A subject turns a handle with following the sine wave signal indicated in the
oscilloscope may be followed. The rotation angle and torque around a steering axis and the rotation
angle and torque in a grip were measured. The rotation angle of steering axis 6 s, torque of steering
axis Ts, the rotation angle of grip (? , and torque of grip T were shown in Figure 2.
R R

RESULTS
When the operator normally turned the conventional oval handle, no restrictions conditions were
operated using torsion of an elbow. Therefore, when it was operated without using torsion of an
elbow, the amount of compensation was decided by the rotation angle of grip. A subject steered
without using torsion of an elbow, and measured rotation angle of grip # ..
R
The measurement results were shown in Figure 3. In case of conventional oval handle operation, the
rotation angle of right wrist increased according to the increase in steering angle &s. It was very
important to reduce the rotation of wrist joint for the elderly people, whose limit angle of bending
motion of wrists was smaller than that of young people. The same examination has been done to
perform the link type handle. As Figure 3 shows, the staring shaft can be turned with only little
bending of a wrist. When K is 0.83, rotation angle of grip varied in the region from-20 degrees to
0 degrees. When K is 0.47 and 0.33, it turned out that the rotation angle of a grip decreased
extremely. The torque of wrist was measured in case of the conventional oval handle and the link
type handle. Experiment results were shown in Figure 4. On conventional oval handle, change of
the torque of wrist was few only in the region of steering angles from -20 degrees to 20 degrees, and
the torque violently increased out of this region. On link type handle ( K= 0.47 , 0.33 ), the value of
torque reduced very much. However, the much wider handle, for example K = 0.83, resulted little
increase of torque to drive handle.

60 R [deg] 60 K=0.83
Right wrist angle θ R [deg] 0 K =0.83 Right wrist angle θ 0 0.33
30
30
0.47

-30
0.47
0.33 -30
-60 -60
-60
-60 -30 0 0 30 60 -60 -30 0 0 30 60
-30
30
-30
30
Steering angle θ S [deg]
Steering angle θ S [deg] Steering angle θ S [deg]
Steering angle θ S[deg]
(a) Conventional oval handle (b) Link type handle
(b) Link type handle
(a) Conventional oval handle
Figure 3: Relationship between steering angle and right wrist angle