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Impedance based kinesthetic haptic devices have been a focus of study for many years. Factors such as delay and the dynamics of the device itself affect the stable rendering range of traditional active kinesthetic devices. A parallel hybrid actuation approach, which combines active energy supplying actuators and passive energy absorbing actuators into a single actuator, has recently been experimentally shown to increase the range of stable virtual stiffness a haptic device can achieve when compared to the active component of the actuator alone. This work presents both a stability and rendering range analysis that aims to identify the mechanisms and limitations by which parallel hybrid actuation increases the stable rendering range of virtual stiffness. Increases in actuator stability are analytically and experimentally shown to be linked to the stiffness of the passive actuator. 

Cooperative robots or “cobots” promise to allow humans and robots to work together more closely while maintaining safety. However, to date the capabilities of cobots are greatly diminished compared to industrial robots in terms of the force and power they are able to safely produce. This is in part due to the actuation choices of cobots. Low impedance robotic actuators aim to solve this problem by attempting to provide an actuator with a combination of low output impedance and a large bandwidth of force control. In short the ideal actuator has a large dynamic range. Existing actuators success and performance has been limited. We propose a high force and high power balanced hybrid active-passive actuator which aims to increase the actuation capability of low impedance actuators and to safely enable high performance larger force and workspace robots. Our balanced hybrid actuator does so, by combining and controlling a series elastic actuator, a small DC motor, and a particle brake in parallel. The actuator provides low and high frequency power producing active torques, along with power absorbing passive torques. Control challenges and advantages of hybrid actuators are discussed and overcome through the use of trajectory optimization, and the safety of the new actuator is evaluated.