Mechanical design and analysis of a novel variable stiffness actuator with symmetrical pivot adjustment

Abstract

The safety of human-robot interaction is an essential requirement for designing collaborative robotics. Thus, this paper aims to design a novel variable stiffness actuator (VSA) that can provide safer physical human-robot interaction for collaborative robotics. VSA follows the idea of modular design, mainly including a variable stiffness module and a drive module. The variable stiffness module transmits the motion from the drive module in a roundabout manner, making the modularization of VSA possible. As the key component of the variable stiffness module, a stiffness adjustment mechanism with a symmetrical structure is applied to change the positions of a pair of pivots in two levers linearly and simultaneously, which can eliminate the additional bending moment caused by the asymmetric structure. The design of the double-deck grooves in the lever allows the pivot to move freely in the groove, avoiding the geometric constraint between the parts. Consequently, the VSA stiffness can change from zero to infinity as the pivot moves from one end of the groove to the other. To facilitate building a manipulator in the future, an expandable electrical system with a distributed structure is also proposed. Stiffness calibration and control experiments are performed to evaluate the physical performance of the designed VSA. Experiment results show that the VSA stiffness is close to the theoretical design stiffness. Furthermore, the VSA with a proportional-derivative feedback plus feedforward controller exhibits a fast response for stiffness regulation and a good performance for position tracking.

Design and Analysis of a Novel Compliant Actuator With Variable Stiffness by Spring Pretension Adjustment

“…As shown in Figs. 12-14, a pair of elastic modules (parts [15][16][17][18][19][20] are supported and installed in the input and output frames respectively through a pair of small bearings (part 23), which can be can be driven by the stiffness adjustment motor (part 11) and rotated relative to the input frame or the output frame. To avoid motion interference, a ring (part 24) is installed between the two elastic modules.…”

“…By changing pretension of a nonlinear spring, Mechanically Adjustable Compliance and Controllable Equilibrium Position Actuator (MACCEPA) Has been studied by many scholars [18,19]. By designing a rope driven winding mechanism, Li Z. et al proposed a reconfigurable variable preload flexible robot joint named as JVSR [20].…”

Design and Analysis of a Novel Variable Stiffness Joint Based on Leaf Springs

“…In the case of a VSA, stiffness adjustment can also be achieved by introducing a variable lever mechanism between the elastic element and the load connection point. Specifically, the compression of the spring can be dynamically adjusted by changing the point of action of the elastic element on the lever, the load connection point [18], or the lever fulcrum [19], thereby adjusting the output stiffness of the driver. Based on this principle, researchers have proposed various VSMs, such as the variable stiffness actuator vsaUT-II [20], the pseudo-linear variable ratio lever variable stiffness actuator (PLVL-VSA) [21], a rotational joint actuator based on the mechanism of a flexible rack and gear (vsaFGR) [22], the variable stiffness actuator based on a rocker-linked epicyclic geartrain (REGT-VSA) [23], and the variable stiffness actuator based on a second-order lever mechanism [24], among others.…”

Design of a torsional compliant mechanism with given discrete torque-deflection points for nonlinear stiffness elastic actuator

“…To address the limitation of SEA, variable stiffness actuator (VSA) was proposed and developed rapidly [20][21][22][23][24][25][26][27][28][29][30][31][32][33]. However, most VSAs are equipped with two actuators (usually motors) to actively adjust the stiffness and equilibrium position independently, which leads to bulky and complex structures and causes additional power consumption.…”