Project CauseIM

Robot the Next Generation

Toward Most Agile and Cost Effective Life-sized Robot

Robotic Legs by
Coaxial Spherical Parallel Mechanism

Power X 4

Each legs have four actuators on its pelvis
The legs use all the outputs of the four actuators in a vertical direction

Life X 64

Vertical, radial and lateral load on end effector is equally distributed on actuators
When the load is reduced to 1/4, the gear life is increased by 64 times

Light Design

Due to the distribution effect of the load, the size of motor and gear could be reduced.

Integrated Actuator

Because all the actuators are located at pelvis, the leg has lower inertia
Thermal management is easy as parts with a lot of heat are located at the pelvis

Simpler Solution

This unique mechanism have analytic solution as simple as serial link kinematics

Load Distribution

While the leg exerts force along the vertical direction,
the load from end effector is distributed equally to all four actuators.
This unique characteristics make robot 4 times stronger than its capacity.

Gear Capacity

Due to the distribution effect of the load,
the force applied to the gear is reduced to 1/4.
This has the effect of increasing the life of the reducer by 64 times.
In addition, reducing the size of the reducer allows the legs to be designed lighter.

Gear Limited GRF(Cont. Limit)

The Ground Reaction Force is the force that the end effector pushes against the ground.
It is usually limited by capacity of gears and motors.

The left figure shows maximum GRF based on continuous gear output.
The values are calculated based on the product manual.

Body weight to GRF Ratio

The GRF should be evaluated relative to body weight(BW).

The designed leg have under 12 kg of mass.
Then the mechanical part of biped would have 24 kg of mass.
Including the electronics and chassis, it would weigh around 35 kg.

In this case, the continuous GRF limit exceeds BW in most areas.
Moreover, the continuous GRF limit is 2 times higher than BW in some region.

Utilization as a Bipedal Robot

This manipulator is mainly designed to be utilized as a robotic leg.
As introduced on video clips, it has 4 degrees of freedom.
If the two legs with the advantages listed above are placed side by side,
it will become an agile biped robot.