自动装配规划系统英文文献和中文翻译(6)
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
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