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Biologically Inspired Robotics
the arch structure resolves the problem faced when using the joint structure
type of machine). Fu, Wang, and Wang (2008) developed a hand rehabilitation machine with an arch structure, and they were able to successfully control four joints in a single finger. The above-mentioned examples show that
machines can possibly substitute for physical therapists because they can
suitably control finger movement. A disadvantage of both the joint and arch
structure type of machines is the difficulty involved in attaching them to the
fingers; that is, the rotational centers of the joints of these structures should
match that of the corresponding finger joint. Moreover, each finger has a different length; hence, the structure of the machine must be suitably modified
for each user and different finger lenths. One of the solutions to this problem
is the arm structure type of machine, which was proposed by Fu, Zhang, and
Wang (2004); Kawasaki et al. (2007) developed an arm structure consisting of
a closed four-link mechanism: four links (i.e., two metal links and two human
finger links) and four joints (one actuated joint, two free joints, and one human
finger joint). The finger joint is not directly controlled by the actuated joint.
The geometry of the links indirectly controls the finger. In the closed four-link
mechanism, the distance between Base 1 and Base 2 (Figure 15.2c) is adjustable
because of the free joints. Thus, this structure can be adjusted to suit any user
without any design modification, which enhances its practical usability.
However, the closed four-link mechanism has three structural problems:
(1) The finger joint has two possible configurations for an angle of the actuated joint. Thus, it becomes necessary to avoid some angles of the actuated
joint; that is, this mechanism limits the range of joint motion. (2) The machine
is heavy because the motor is placed inside the mechanism. Thus, this structure is not suitable for long-term use. (3) The mechanism overloads the finger
joint when the finger joint bends more than 90 degrees. This is because the
free joints cannot generate rotational torque; instead, they apply shear forces
to the finger joint. This, too, limits the range of the joint angle.
In this study, we developed a new hand rehabilitation machine that is based
on arm structure. We aimed to reduce the weight of the machine and increase
the range of joint motion by using a wire-driven mechanism. Furthermore,
we propose a hand rehabilitation system in which fingers affected by paralysis can be moved using the proposed hand rehabilitation machine, and the
finger joints can be controlled using a data glove worn on the healthy hand.
15.2 Proposed Design
15.2.1 Four-Link Mechanism with the Wire-Driven Mechanism
The arm structure type of hand rehabilitation machine uses a closed four-link
mechanism, and this machine can be attached to fingers of any length. To
Biologically Inspired Robotics
the arch structure resolves the problem faced when using the joint structure
type of machine). Fu, Wang, and Wang (2008) developed a hand rehabilitation machine with an arch structure, and they were able to successfully control four joints in a single finger. The above-mentioned examples show that
machines can possibly substitute for physical therapists because they can
suitably control finger movement. A disadvantage of both the joint and arch
structure type of machines is the difficulty involved in attaching them to the
fingers; that is, the rotational centers of the joints of these structures should
match that of the corresponding finger joint. Moreover, each finger has a different length; hence, the structure of the machine must be suitably modified
for each user and different finger lenths. One of the solutions to this problem
is the arm structure type of machine, which was proposed by Fu, Zhang, and
Wang (2004); Kawasaki et al. (2007) developed an arm structure consisting of
a closed four-link mechanism: four links (i.e., two metal links and two human
finger links) and four joints (one actuated joint, two free joints, and one human
finger joint). The finger joint is not directly controlled by the actuated joint.
The geometry of the links indirectly controls the finger. In the closed four-link
mechanism, the distance between Base 1 and Base 2 (Figure 15.2c) is adjustable
because of the free joints. Thus, this structure can be adjusted to suit any user
without any design modification, which enhances its practical usability.
However, the closed four-link mechanism has three structural problems:
(1) The finger joint has two possible configurations for an angle of the actuated joint. Thus, it becomes necessary to avoid some angles of the actuated
joint; that is, this mechanism limits the range of joint motion. (2) The machine
is heavy because the motor is placed inside the mechanism. Thus, this structure is not suitable for long-term use. (3) The mechanism overloads the finger
joint when the finger joint bends more than 90 degrees. This is because the
free joints cannot generate rotational torque; instead, they apply shear forces
to the finger joint. This, too, limits the range of the joint angle.
In this study, we developed a new hand rehabilitation machine that is based
on arm structure. We aimed to reduce the weight of the machine and increase
the range of joint motion by using a wire-driven mechanism. Furthermore,
we propose a hand rehabilitation system in which fingers affected by paralysis can be moved using the proposed hand rehabilitation machine, and the
finger joints can be controlled using a data glove worn on the healthy hand.
15.2 Proposed Design
15.2.1 Four-Link Mechanism with the Wire-Driven Mechanism
The arm structure type of hand rehabilitation machine uses a closed four-link
mechanism, and this machine can be attached to fingers of any length. To