Research on Human-Friendly Robot Design
In recent years, there has been increased interest in the emerging field of human-centered robotics, involving close physical interaction between robots and humans. The applications include important areas such as medical robots, manufacturing, and entertainment. A major challenge in the development of human-centered robotics is safety: How can robots be sufficiently strong, precise and dexterous to do useful work while also being inherently safe for physical interaction?
Robots have traditionally relied on electromagnetic actuators, which offer excellent controllability but poor power/weight ratios compared to muscle. Even more limiting is their inability to exert large sustained forces without high transmission ratios between the motor and load. The high transmission ratios result in arms with high mechanical impedance, which are inherently less safe than their lowimpedance biological counterparts whenever unexpected contacts occur.
During the past several years our group has investigated new actuation techniques to overcome the safety and performance limitations of existing technologies. We have developed the distributed macro–mini (DM2) actuation approach to address the problem of a large reflected inertia by partitioning torque generation into low- and high-frequency domains, which are controlled by distributed pairs of actuators. Taking advance of DM2 approach, two prototypes of hybrid actuation were developed with a combination of pneumatic and electromagnetic actuation.
Hybrid Actuation
Pneumatic McKibben actuators provide high power and force density and inherently low mechanical impedance. However, the underlying nonlinear compressible gas dynamics involved make precise control difficult. By combining them with small electromagnetic actuators we were able to achieve a 10-fold reduction in effective inertia while maintaining high-frequency torque capability. The combination of two different actuation technologies comes at the expense of complexity in comparison to traditional robot design.
Compact Pressure Regulator
To make this complexity manageable, we use miniaturized integrated pressure controllers and multi-material structures. A controller using small proportional valves and pressure sensors is much lighter and more compact than a traditional pressure controller. By linking the pressure controllers with a single pressure line, we are further able to reduce the weight and part count.
Bone-Inspried Robotic Link
The next step is to integrate these components, along with additional sensors, into a single light-weight structure using the Shape Deposition Manufacturing (SDM) rapid prototyping process. SDM allows multiple materials, as well as sensors, actuators and other discrete parts, to be integrated in a single heterogeneous structure. The technology has been demonstrated for various bio-inspired robots in Cutkosky’s lab. The ability of SDM to provide local variations in materials properties also permits structures with high specific strength and stiffness in selected areas while providing high impact energy absorption in other areas.
Sensor-Embedded Compliant Skin
Built-in tactile sensing capabilities will improve the overall control and safety of the system in conjunction with new control strategies that take advantage of the hybrid actuation approach.