An Adjustable Constant-Force Mechanism for Adaptive End-Effector Operations

Abstract

Force regulation is a challenging problem for robot end-effectors when interacting with an unknown environment. It often requires sophisticated sensors with computerized control. This paper presents an adjustable constant-force mechanism (ACFM) to passively regulate the contact force of a robot end-effector. The proposed ACFM combines the negative stiffness of a bistable mechanism and positive stiffness of a linear spring to generate a constant-force output. Through prestressing the linear spring, the constant-force magnitude can be adjusted to adapt to different working environments. The ACFM is a monolithic compliant mechanism that has no frictional wear and is capable of miniaturization. We propose a design formulation to find optimal mechanism configurations that produce the most constant-force. A resulting force to displacement curve and maximal stress curve can be easily manipulated to fit a different application requirement. Illustrated experiments show that an end-effector equipped with the ACFM can adapt to a surface of variable height, without additional motion programming. Since sensors and control effort are minimized, we expect this mechanism can provide a reliable alternative for robot end-effectors to interact friendly with an environment.

Novel Quasi-Passive Knee Orthosis with Hybrid Joint Mechanism

“…We have a desired load reduction and a coupler-calf gap size, both dependent on calf angle, causing our desired elastic element to have a nonlinear force-displacement relationship. This can be achieved by a cam system, which would modify the gap size in such a way to allow a linear spring to be used, or by compliant mechanisms, for example a bistable beam combined with a linear spring (Chen and Lan 2012). A leaf spring design possessing arc geometry was chosen.…”

“…Its geometry is represented by two arcs whose angles of rotation are parametrized with respect to their arc lengths by 2rd order polynomials (Chen and Lan 2012). Its cross sectional geometry is rectangular.…”

On the infinitely-stable rotational mechanism using the off-axis rotation of a bistable translational mechanism

“…Different from the above reported works in Lassooij et al (2012), Chen and Lan (2012), Hansen et al (2007), Dunning et al (2012), Kim and Ebenstein (2012), Holst et al (2011) and Zhang and Chen (2013) which employ the primary translation to achieve finite multi-stable statuses, this paper studies on the multistable off-axis rotation behaviour of the bistable translational mechanism in order to obtain an infinitely-stable rotational mechanism. This off-axis rotation behavior with multistable points has also potential applications in human joint rehabilitative devices, dynamic and static balancing of machines, and human mobility-assisting devices (Hou and Lan, 2013) when combining with a positive stiffness spring.…”

“…Multistable compliant mechanisms have a variety of successful applications such as switches, valves, relays, grasper, adaptive end effectors, sensors, energy harvesting devices and vibration isolators (Oh, 2008;Howell et al, 2013;Lassooij et al, 2012;Chen and Lan, 2012;Hansen et al, 2007;Liu et al, 2013;Shaw et al, 2013). Unlike the traditional ways of using locking mechanisms and detents, a compliant mechanism based multistable mechanism obtains multistability through the storage and release of potential energy stored in their flexible members during post-buckling.…”

“…Unlike the traditional ways of using locking mechanisms and detents, a compliant mechanism based multistable mechanism obtains multistability through the storage and release of potential energy stored in their flexible members during post-buckling. This paper focuses on bistable translational mechanisms using fixed-clamped beams (Lassooij et al, 2012;Chen and Lan, 2012;Hansen et al, 2007;Dunning et al, 2012;Kim and Ebenstein, 2012;Holst et al, 2011;Zhang and Chen, 2013), rather than using the fixed-pinned (Qiu et al, 2004) and the pinned-pinned beams (Sonmez and Tutum, 2008) that are hard to manufacture monolithically. There are mainly two methods to design the fixed-clamped bistable translational mechanism (Dunning et al, 2012).…”