Mechanics and stiffness limitations of a variable stiffness actuator for use in prosthetic limbs

Biomimetic Design of Low Stiffness Actuator Systems for Prosthetic Limbs

“…Alternatively passive mechanical elements can be used to introduce significant stiffness into the drive train. We are interested in the second method for this research [8].…”

“…There are many designs using artificial muscles called McKibben, rubbertuators or Soft Arms, which are pneumatically driven [5]. Other methods used are hydraulic cylinders, fluidfilled bladders, pneumatic bladders, shape memory alloys [8] and ultrasonic motors [22]. Despite the above reasoning supporting the use of compliant robots, the lack of compliant actuators with acceptable performance and a lack of adequate controller architectures and computer techniques needed to take advantage of such actuators, means that progress is slow [28].…”

“…In this case the stiffness elements change length and, if they are nonlinear the net stiffness of the joint will change. Other configurations of springs and two actuators can be found that also allow this feature [8].…”

Variable-stiffness joints with embedded force sensor for high-performance wearable gait exoskeletons

“…Many studies suggest that one reason why biological systems can successfully interact with the environment is that they have the ability to modulate joint impedance [15], understanding mechanical impedance as the additional force created at the output by load motion. The implementation of an impedance control approach requires the actuator to be a high-precision force source [58].…”

“…Dynamic control of joint stiffness is crucial for humans to adapt to changes in environmental conditions [38]. Muscles in biological systems modulate the stiffness and position of the joint achieving high adaptability, force transmission and significant reduction of energy expenditure [15].…”