Bidirectional torsional negative stiffness mechanism for energy balancing systems

Abstract

A new concept of an integrated bidirectional torsional negative stiffness mechanism is introduced which allows for passive energy balancing of mechanical systems by reducing actuation requirements and improving energy efficiency. This novel design is a modular device, is bidirectional and is easily integrated and customised for different applications. The energy balance concept is achieved by employing a negative stiffness system to couple with a positive stiffness system of the mechanical system to create a zero stiffness system which can be driven with lower energy requirements. The bidirectional torsional negative stiffness mechanism proposed here uses a series of pre-compressed springs around a bidirectional torque shaft to convert decreasing force in the springs into increasing torque output through geometric reconfiguration to generate the negative stiffness characteristic. The kinematics of the negative stiffness mechanism were derived and a physical model was assembled from LEGO ® components for validation. An analytical model was developed for prediction and the numerical results showed that a satisfactory performance can be generated to match the torque requirements. An experimental demonstrator was then built and tested to verify the predictions from the analysis. To show the impact of the energy balancing concept on actuator efficiency, a representative case study is made of a tendon-driven morphing active camber mechanism. The performance of the optimised bidirectional negative stiffness device is investigated to shows an improvement by the kinematics tailoring.

Passive energy balancing design for a linear actuated morphing wingtip structure

“…A bidirectional torsional negative stiffness (BTNS) mechanism by using a series of pre-compressed springs has been investigated for energy balancing systems. This integrated BTNS mechanism was verified to tailor the kinematics of the required torque driving the active camber and the results showed a similar torque-rotation profile can be generated [13]. The proposed device provides actuation to change the state of the system, such as deforming a structure or lifting a mass; hence the energy provided by the actuator was transformed into an increased potential energy in the system.…”

Static Balancing of Four-Bar Compliant Mechanisms With Torsion Springs by Exerting Negative Stiffness Using Linear Spring At the Instant Center of Rotation

“…Commonly, this behavior is achieved by adding a negative stiffness system to a positive stiffness system in such a way that the global stiffness is zero or close to zero across the range of motion. Several works center on this idea to obtain zero-stiffness behavior, such as Zhang et al [8], Woods and Friswell [9], and Hoetmer et al [10]. Stiffness compensation is a necessary but not sufficient condition to achieve static balancing since zero stiffness is also a condition to obtain constant force mechanisms [11].…”

Design and Analysis of a Novel Compliant Tensile Testing Module Based on Buckled Fixed-Guided Beam

“…While there exist many kinds of flexures [10][11][12], this work focuses mainly on negative stiffness mechanism. In some literatures negative mechanism works as a displacement amplifier, which is used to increase the motion range of the piezoelectric actuator.…”

“…The negative mechanism acts as an additional energy stream to maintain the total energy constant in the system. Zhang et al [12] developed a bidirectional torsional negative stiffness mechanism for energy balancing systems. In their design the negative stiffness mechanism is coupled to the target positive stiffness system to produce an energy balancing system.…”