based position sensors are interfaced to the Sensoray 626 I/
O (Sensoray Company Inc., USA) interface card.
The graphical user interface runs on a computer with
Windows operating system (Microsoft Corporation, USA)
and is connected with the real time target by a local area
network using TCP/IP protocol.
Two graphical displays are used: (1) the therapist robot
interface (TRI)—a standard LCD monitor display, and (2)
the patient robot interface (PRI)—a double-projector system
with polarized images to generate graphical 3D
scenarios for the patient. The TRI contains a dialog-based
graphical user interface, which allows the therapist to enter
the patient’s data, choose the therapy mode, display the
actual patient performance and save the therapy log file.
These data are not shown to the patient, who, instead, looks
onto the screen of the PRI, where the tasks are displayed by
animated 3D scenarios (Fig. 6).
2.6 Dynamic model and basic control issues
A dynamic model of the robot and the human arm has been
developed to simulate and evaluate different control
schemes. An inverse dynamic and a direct dynamic model
have been derived using Lagrange methodology. The direct
dynamic model is given by
q€ ¼ M1ðqÞðs Cðq; q_Þq_ GðqÞÞ ð1Þ
where M is the inertia matrix, Cðq; q_Þq_ is the vector of
Coriolis and centrifugal torques, GðqÞ is the vector of
gravity torques and q is the vector of joint positions. The
elements of the robot have been modelled in 3D and the
matrices of inertia and the centres of gravity have been
calculated using the CAD numerical finite element calculation
(AutoCAD, Autodesk, USA). The upper arm and the
lower segments of the human arm have been modelled as
conical frustums with homogeneous mass, equal to that of
water [8].
The inverse dynamic model can be expressed by
s ¼ MðqÞq€þ Cðq; q_Þq_ þ GðqÞ ð2Þ
where s is the vector of joint torques. In general, the
following torque contributions appear [31]