full Paper - Nguyen Dang Binh

Figure 22: An example of arm trajectory recorded to derive quantitative
requirements for the actuation system
analyse intrinsically 3D solution, such as the transmission
system described in Subsection 7.1. Moreover, it has been
possible an iterative process of design, by changing the dimensional
parameters of a part in consequence of the results
of the analyses performed on the whole system.
Secondly, a software tool has been developed in order to
evaluate the lowest resonant mode associated to the multi
DOFs, coupled transmission system. Such tool implements
the dynamic model of such type of tendon driven robot.
Finally, a dynamical simulation software application has
been developed to evaluate quantitatively the performance
required to the actuators (see Section 8.1.
8.1. Dynamical simulation tool
The derivation of quantitative requirements for the actuators
has been based on the following specifications:
A the kinematics and dynamics of the device, in terms of
joint variables;
B the transmission structure, in terms of the relationship it
introduces between joint variables and motor variables;
C a description of the arm free movements workspace, in
terms of joint positions, velocities, accelerations during
the expected usage of the device. Since the haptic device
has no repetitive usage, a quite large set of typical operation
has been chosen and arm trajectory acquisition has
been done using infrared markers attached on user arm
(see Figure 22 for an example trajectory).
D a specification of the peak forces the haptic device is requested
to apply on the human arm.
c­ The Eurographics Association 2005.
Massimo Bergamasco / Haptic Interfaces
19
Figure 23: Anthropomorphic haptic device for the upper limb in
reference posture
Given the complexity of the anthropomorphic haptic device,
the first two items have been determined with confidence
only thanks to the adoption of a 3D CAD environment
capable of computing masses and inertia of the complex assemblies
of mechanical parts, which forms the links of the
device.
Items A,B,C and D have been used as inputs to the dynamical
simulation software tool (see the precedent Section)
which solves the inverse dynamic problem along all the arm
trajectories and computes the associated motor trajectories,
under the hypothesis of rigid transmissions. From the motor
trajectories, a set of indexes, such as peak continuous
and rms values of motor torque, velocity, acceleration and
mechanical power output are computed. These values have
been used to select the motors (see Table 3).
9. Design solutions
The device closely follows the human arm from the shoulder
to the palm; it features 7 rotational joints in order to fully
preserve the freedom of movement of the user arm (see Figure
23 for an global view).
The choices, already experienced in the Arm Exoskeleton,
of a totally anthropomorphic kinematics and of the usage
of electrical actuation, cable transmission and joint torque
control approach, have been renewed.
The kinematic congruence of the device to the user arm
kinematics is guaranteed by means of a regulation system
for the arm and forearm links. The lengths of the arm link
and the forearm link are continuously adjustable within a
range of 005m and 003m. The adjustments induce no rotation
on the actuators and they can be performed with the
device powered and controlled by a special software.