1 Introduction
A structure is a combination of resistant bodies made to bear loads. In
general no internal mobility or relative motions among its members are
allowed. However, there exists a family of unconventional structures,
found in many places from common household items such as umbrellas
and foldable chairs to solar panels of spacecrafts and retractable roofs, that
are capable of large shape changes. These structures are commonly known
as deployable structures. The purpose of adopting deployable structures is
to have convenience in transportation or storage, but some, e.g. the retractable roofs, are concerned primarily with provision of instant coverage or
shelter to create a desirable environment. In accordance with the deployment process, they fall into two categories. The first category is the deformable structure characterised by the fact that the overall strain energy of the
structure varies during geometrical transformation. Typical examples
include the inflatable structures such as balloons and cardiovascular stents,
a type of medical device placed via minimum invasive surgery for treatment of blockage in blood vessels. The other category is essentially mechanism. The deployment is executed by activation of one or a number of
carefully designed internal mechanisms. Retractable roofs for sports facilities and a toy called the Hoberman sphere belong to the second category.
This book focuses on the second category. The term Motion Structures
is adopted to represent this branch of the deployable structure family
owing to the existence of internal mechanisms.
A mechanism in machine theory, which is referred to as a conventional
mechanism hereafter, is commonly identified as a set of moving or working
parts used essentially as a means of transmitting motions or controlling
movement of one part relative to another. It is often assembled from gears,
cams and linkages, though it may also contain other specialised components, e.g. springs, ratchets, brakes, and clutches, etc. There are close
similarities as well as distinct differences between a motion structure and a
conventional mechanism. First, the primary function of a motion structure
is to have shape alteration essential to practical requirements, rather than
transmitting or controlling motions. Second, as a structure, a motion structure is usually composed of far more parts than a conventional mechanism.
A structure is a combination of resistant bodies made to bear loads. In
general no internal mobility or relative motions among its members are
allowed. However, there exists a family of unconventional structures,
found in many places from common household items such as umbrellas
and foldable chairs to solar panels of spacecrafts and retractable roofs, that
are capable of large shape changes. These structures are commonly known
as deployable structures. The purpose of adopting deployable structures is
to have convenience in transportation or storage, but some, e.g. the retractable roofs, are concerned primarily with provision of instant coverage or
shelter to create a desirable environment. In accordance with the deployment process, they fall into two categories. The first category is the deformable structure characterised by the fact that the overall strain energy of the
structure varies during geometrical transformation. Typical examples
include the inflatable structures such as balloons and cardiovascular stents,
a type of medical device placed via minimum invasive surgery for treatment of blockage in blood vessels. The other category is essentially mechanism. The deployment is executed by activation of one or a number of
carefully designed internal mechanisms. Retractable roofs for sports facilities and a toy called the Hoberman sphere belong to the second category.
This book focuses on the second category. The term Motion Structures
is adopted to represent this branch of the deployable structure family
owing to the existence of internal mechanisms.
A mechanism in machine theory, which is referred to as a conventional
mechanism hereafter, is commonly identified as a set of moving or working
parts used essentially as a means of transmitting motions or controlling
movement of one part relative to another. It is often assembled from gears,
cams and linkages, though it may also contain other specialised components, e.g. springs, ratchets, brakes, and clutches, etc. There are close
similarities as well as distinct differences between a motion structure and a
conventional mechanism. First, the primary function of a motion structure
is to have shape alteration essential to practical requirements, rather than
transmitting or controlling motions. Second, as a structure, a motion structure is usually composed of far more parts than a conventional mechanism.