This video demonstrates collaborative mobile manipulation between humans and a team of
mobile cobots, or mocobots for short.
The Omnid mocobots are capable of autonomous multirobot mobile manipulation, but here we
focus on collaboration with humans.
The Omnids allow one or more human operators to easily manipulate large, awkward payloads,
while providing passive elasticity for the safety of delicate payloads as well as the
humans.
The Omnids are a research platform for developing control algorithms for warehouse, construction,
or factory manipulation and assembly tasks that can benefit from the adaptability and
the situational awareness of a human partner.
Each Omnid consists of an omnidirectional mecanum-wheel mobile base; a three degree-of-freedom
Delta parallel manipulator driven by series-elastic actuators; and an instrumented passive three-degree-of-freedom
gimbal wrist.
Each robot is capable of high-fidelity control of three linear forces at its wrist, independent
of the motion of its mobile base.
The passive elasticity and freely-rotating wrist mean that the Omnids are specifically
designed for collaborative manipulation: a single Omnid cannot control all the degrees
of freedom of a rigid body.
Each series-elastic actuator is implemented using two antagonistic linear springs.
When the actuators are locked, the mechanical compliance is evident in the oscillation of
the end-effector.
This passive mechanical compliance contributes to the safety of the payload and the human.
The manipulator can also be actively impedance-controlled, in this case demonstrating a reduced effective
stiffness at the end-effector.
The mobile manipulator has three planar degrees of freedom at the chassis, three controlled
linear motions or forces at the end-effector, and three passive rotational freedoms at the
gimbal wrist.
When the manipulator is force-controlled to cancel gravity and zero the contact force,
the user can easily reposition an Omnid by light forces at the end-effector.
The mobile base simply moves to keep the end-effector centered.
When the manipulators are programmed to cancel the gravitational force of a payload, the
15-kilogram pipe assembly feels to the human like it's floating in space.
Each manipulator also implements a virtual spring near its workspace boundary, to prevent
the payload from hitting manipulator workspace limits.
Even if control of the mobile bases is imprecise, as with legged or outdoor robots, the high-fidelity
force control of the manipulators ensures that this imprecision is not apparent at the
payload.
Using the payload float mode with mobile base recentering control, the human operator easily
disassembles and assembles the pipes into a fixture with only a 2 millimeter tolerance.
The Omnids also permit multi-human multi-robot collaborative manipulation of articulated
payloads.
In this example, the payload has seven total degrees of freedom, including one joint.
The three Omnids are capable of autonomously manipulating this payload, or other payloads
with up to nine degrees of freedom, but if the wrists are moved into a line, as shown
here, there is a singularity: the Omnids cannot generate a torque about the line.
Currently the Omnids rely on mechanical communication through the payload.
Future work will include coordinated control facilitated by wireless communication, such
as autonomous force-controlled assembly and real-time estimation of payload kinematic
and inertial properties.