ETH (Switzerland) also developed a mobile platform  for
rough terrain  [4].  It  has  two three-degrees  of  freedom
legs and also has  two one-degree  of  freedom legs  that
have a passive wheel at their  end.  Its number of  active
degree of  freedom is eight.  Tohoku University (Japan)
constructed a leg-wheel separation type robot [5].  It has
two big  active wheels at the both  sides of  the body,  and
four legs with  three joints at the both ends  of  the  body.
Fourteen actuators are used for the robot.
In this paper, classification  of  the  environment for
mobile  robot  is  considered from  the  viewpoint  of
locomotion  mechanism  at  first. In section  3,  a new
locomotion mechanism is proposed, and a prototype robot
that employs  the  mechanism  is  introduced. Section  4 describes moving algorithm  for  the prototype robot.
Implementation of the algorithm is explained in section 5.
2. Locomotion mechanism and environment
Now we  consider classification of  the environment
from the contact between locomotion mechanism and the
ground. When terrain  is flat, the locomotion mechanism
can always keeps contact with  the ground.  We call this
kind  of  terrain continuous contact  locomotion
environment.  In  this environment, conventional wheels
and crawlers  are  available. Although  wheels  and
crawlers have different locomotive capability,  both
mechanisms always keep contact with  the ground during
locomotion.  The trace of movement in this environment
is  continuous lines. One  of  the causes  wheeled  or
tracked vehicle cannot move is existence of obstacles like
steps. We call the terrain that includes such obstacles
discontinuous contact locomotion environment.  In order
to move  in  this kind  of  environment,  robots  that have
actively suspended wheels or  shape-changeable crawlers
have been developed.  In this environment, a mechanism
that switches the contact point  between  the  locomotion
mechanism  and  the ground is essential. The  trace of  the
movement is  line  segments. More serious environment
is discrete contact  locomotion  environment.  In  this
environment, continuous contact  between  locomotion
mechanism and the ground is not allowed.  Locomotion
mechanism has  to  support  and propel  the  robot  only by
using discrete point contacts with  the ground.  Robots in
this environment must be equipped with legs.  The trace
is sequence of points.
Our research target  is  locomotion  in  mountainous
area,  and  it  is  considered as discontinuous contact
locomotion environment.  To move over obstacles such
as steps, legged  locomotion  is  effective.  However,
legged mechanism has demerits also.  The mechanical
configuration  is  complicated, and  it  requires large
number of degrees of  freedom. Generally, three degrees
of  freedom are necessary for each leg.  In  the case of  a
quadruped, total number  of  actuator is  twelve.
Moreover, moving  speed or  energy  efficiency  is  lower
than  wheeled or  tracked  locomotion when  it moves  on
relatively flat terrain. 轮足复合式移动机器人英文文献和中文翻译(2):http://www.751com.cn/fanyi/lunwen_9943.html