condition of a mating task  (T,)  is  the  set of states such that  it is impossible
predicates are  indd  to  repnscnt these  two  relationships.
Debition 2: Sum  Ti and  Ti  an  two  mating tasks in an assembly
plan P,  the predicates  MP(  4  ,  Tj  )  and  NL( Ti ,  Ti  )  ~n  defined as  follow.%
MP(  4,  Ti)=
TRUE.  orherwise
NL(  ’  Ti  )=  {FALSE,  Ti is  performed aftu  Tj in  P
DefidiW 3  A  symbolic  np.esentstiOn of plecedence knowledge of
an assembly is a well-fonned  famula Consisting of  pedicetes MP and  NL
such that
R=TRUE  ifandonlyif  Pisfeasibk.
where P  is an  assembly plan.
TheFefarc,  the inteq”  of R  is always TRUE  far feasible assembly
plans and FALSE  far infeasible assembly plans. Thc  above rq”tati0n
scheme  can also repteent  pncedence  knowledge  of  wmbly  [lo].
When  representing disassunbly pra%dence  knowledge, Ti’s iue used to
represent  the disassembly of  mating  tasks.
The pmcess  of essemblying a component  or  subassembly  is to  move it
from acertain location  toaspecitiedposition and  orientation such that itis
fitted into the mt  of  the components of the  assembly.  From  the  disassem-
bly point of  view, such a process  is to  move a component from  its assan-
bled position and  orientation  to  infinity. Each  instence  of  this disassembly
process  cOrreSpOndS to  a trajectory  in space.  According to  previousdiscus-
sions, certain  precedence  constraints  have to  be satisfied  in order  for the tra-
jectories not to be blocked  Some trajectories have the  same  precedence
constraints. while others  do  not We can  pp  a  set  of trajectories  with the
same precedence consmints  togethex and call that set of  trajectories an
operawn.  Since  the number of assembly scquamxs is finite,  the expression
for precedence  knowledge  is a finite formula of pedicates  MP  and  NL.
Each operation conesponds  to a different precedence constraint,  thus the
number of operations  is also finite.
Then are  two cases in which a component can  block an operation  of a
mating task, one  is that the component  is mated to  at least one  of the  cun-
ponents connected by the  task,  theother is that the  component is mated to
neither one of the  components  of  the task.  For the  convenience of discus-
sion. we define a psuh mating task  between every pair of mantact
components, and  refer the mating  task  for contact  components  as  red mat-
ing task  and  treat them the same. However, the knowledge acquisition will
only be  performed for real mating tasks  because precedence  knowledge for
pseudo mating  tasks  does  not  have much practical use. Suppose  Ti.  is one of
the  mi  operations  of  real  mating  task  4:  that  is.  [TJ, when
j=1.2,  .mi.  [St). A=1.2.  ,m’ij, is  the  set  of  mating  tasks
(including real and  pseudo) such  that  the establiihing of  any one  of  them 自动装配规划系统英文文献和中文翻译(6):http://www.youerw.com/fanyi/lunwen_6791.html