Design of a flexibly-constrained revolute pair with non-linear stiffness in multiple directions

Abstract

In order to synthesize a human-friendly flexible mechanism with a simple structure, a revolute pair with flexible kinematic constraint in multiple directions is proposed. It is called the multi-directionally flexibly constrained revolute pair (MFCRP). The structure of the MFCRP is composed of a link with two same spherical surfaces and a link with two same cam surfaces, and each set of the cam surface and the spherical surface is in contact at a point. The connection between the two links is kept by two linear springs arranged between the two links. The MFCRP can generate 1-axial relative rotation between the two links and relative motions in the other directions are flexibly constrained. In order for the MFCRP to have both flexibility for safety and rigidity for the force transmission, the specified non-linear stiffness can be implemented in the two relative translational directions between the two links. This flexible translational constraint is generated by the spring forces and the reaction forces between the two links. In this paper, two methods to design the cam surfaces to implement the specified non-linear stiffness are proposed. The validity of the proposed design methodology is confirmed by comparing measured stiffness characteristics between two links of some prototypes with the theoretical characteristics. As an application, a flexible closed-loop linkage with the MFCRP is fabricated and its flexibility and kinematic performance are investigated through some experiments.

Keywords

• linkage
• kinematic pair
• higher pair
• non-linear stiffness
• passive compliance
• cam profile design
• underactuated mechanism