  We construct a Virtual Kinematic Chain (VKC) that readily consolidates the
kinematics of the mobile base, the arm, and the object to be manipulated in
mobile manipulations. Accordingly, a mobile manipulation task is represented by
altering the state of the constructed VKC, which can be converted to a motion
planning problem, formulated, and solved by trajectory optimization. This new
VKC perspective of mobile manipulation allows a service robot to (i) produce
well-coordinated motions, suitable for complex household environments, and (ii)
perform intricate multi-step tasks while interacting with multiple objects
without an explicit definition of intermediate goals. In simulated experiments,
we validate these advantages by comparing the VKC-based approach with baselines
that solely optimize individual components. The results manifest that VKC-based
joint modeling and planning promote task success rates and produce more
efficient trajectories.
