Since the inception of the field of robotics, robotic designers have attempted to mimic biological systems. However, the realization of this goal has been impaired by the complexity of biological systems. More specifically, biological organisms have developed many adaptations over evolutionary timeframes. For example, the driving force of some types of biological movement, the muscle, is a highly developed mechanical system that is configured to generate high forces, contract at high velocities, and use relatively low amounts of energy.
In vertebrate motion, the muscles are coupled to skeletal elements via tendons. Movement is produced by the contraction of the muscle tissue, which thereby pulls one skeletal element toward another skeletal element; a second muscle tissue is required to reverse the movement. One type of known biomimetic robots employs anatomical-style joints with cable actuated linkages that replicate muscle; however, these joints are difficult to control and require highly complex mathematical simulation. Therefore, directly driven linkages are used to simplify control of the robot and the mathematical simulations.
Yet, one of the greatest challenges to robotic designers is to develop a mechanism that accurately and mathematically replicates vertebrate muscle by providing high levels of force within the space and mass limitations of a typical vertebrate joint. In some embodiments, designers tether the robot to a power source. This is undesirable for at least the reason that it limits the robot's mobility. Alternatively, a limited power supply may be placed on-board the robot and may include batteries; however, batteries add large amounts of weight to the robot and require still more energy to power the robot.
To overcome the weight issue, robotic designers have attempted to under actuate movements, e.g., provide fewer motors than there are degrees of freedom (“DOF”) in a replicated joint system. The missing DOFs are then actuated through passive mechanisms, such as through the inclusion of springs. One such example is a biomimetic hand, which attempts to replicate the human hand's over 20 DOFs all contained within a relatively small volume. Known solutions for the biomimetic hand have included integrating micro motors with large gearing ratios into fingers of robotic hands. But these solutions have not provided satisfactory levels of force within the permitted space. Still further, this method again sacrifices control and oversimplifies the joint system.
Capstans are known to utilize friction in order to amplify work output. According to the conventional theory, capstans were believed to operate in accordance with:
T2=T1eμβ where T2 is the force derived from operating the capstan system, T1 is the force that is input into the capstan system, μ is the coefficient of friction of the cord, and β is the angle of contact (measured in radians) formed by the cord at the capstan. However, this conventional equation supposes that a constant friction input into the capstan system at a given angle of contact will amplify at a constant rate. Capstans generally operate by creating friction between the cord 66 and the drive rod 78. After a load is coupled to the load bearing end 68 of the cord 66, the opposing, actuating end 70 is pulled by winding the cord 66 around the tensioning rod 72 and friction develops between the cord 66 and the drive rod 78 (i.e., the capstan). This friction transfers a portion of the force needed to move the load from the tensioning rod 72 to the drive rod 78. An understanding of capstan operation may be beneficial in various applications, such as in robotics.
Thus, there remains a need for a mechanical system that is capable of producing the forces and speeds of biological organisms while minimizing the mechanical system's weight, volume, and power consumption.