Design and Experimental Characterization of Hydraulically-actuated Revolute Joint based on Multimaterial Additive Manufacturing

Design of fluidic actuators remain challenging in specific contexts such as the medical field, when solutions have for instance to be compatible with the stringent requirements of magnetic resonance imaging. In this paper, an innovative design of hydraulically-actuated revolute joint is introduced. The design originality is linked to the use of multimaterial additive manufacturing for its production. Hydraulic actuation and polymer manufacturing are selected to have compatibility with the medical context. A design taking advantage of the process capabilities is proposed. The proposed component associates a large stroke compliant revolute joint and miniature pistons. An helical rack-and-pinion mechanism is integrated to the compliant joint to control the joint rotation. A specific gear geometry is elaborated to minimize the joint size. It is experimentally characterized in terms of range of motion, stiffness and available torque, to discuss the suitability of the component as a fluidic actuator. The component offers an interesting compactness, range of motion and the process is shown to be adequate for the design of functional systems.

Dynamic Parameter Identification of a Pointing Mechanism Considering the Joint Clearance

The clearance of the revolute joint influences the accuracy of dynamic parameter identification. In order to address this problem, a method for dynamic parameter identification of an X–Y pointing mechanism while considering the clearance of the revolute joint is proposed in this paper. Firstly, the nonlinear dynamic model of the pointing mechanism was established based on a modified contact model, which took the effect of the asperity of contact surface on joint clearance into consideration. Secondly, with the aim of achieving the anti-interference incentive trajectory, the trajectory was optimized according to the condition number of the observation matrix and the driving functions of activate joints that could be obtained. Thirdly, dynamic simulation was conducted through Adams software, and clearance was involved in the simulation model. Finally, the dynamic parameter identification of the pointing mechanism was conducted based on an artificial bee colony (ABC) algorithm. The identification result that considered joint clearance was compared with that which did not consider joint clearance. The results showed that the accuracy of the dynamic parameter identification was improved when the clearance was taken into consideration. This study provides a theoretical basis for the improvement of dynamic parameter identification accuracy.

Design of Revolute Joint With Bi-Stability Using Permanent Magnets

Bi-stable mechanisms are systems with two distinct stable equilibrium positions within their range of operation. They are capable of steadily staying in positions without external power input and require less energy to move to the next stable state because of their snap-through behavior. Diverse applications including switches, deployable structures, and reconfigurable robots can benefit from bi-stability characteristics. However, the complexity of implementation and the limitation of structure configuration have made it difficult to apply conventional bi-stable mechanisms to the structures that require rotational bi-stability. Thus, in this paper, we proposed an implementation method using cylindrical magnets for the rotational bi-stable mechanism. The proposed bi-stable mechanism consists of a revolute joint with two links; one is the rotational link and the other is the fixed link. It has rotational bi-stability through the magnetic force relationship between the array of magnets on each link. To identify the characteristics of the proposed bi-stable mechanism, a cylindrical permanent magnet is considered as an electromagnet model that consists of one ring with a virtual electric current. Consequently, the magnetic field of the cylindrical permanent magnet can be calculated using Biot-Savart law. Similarly, the magnetic force between two cylindrical permanent magnets of the electromagnet model is calculated using Lorentz force law. The criteria of the magnet array for symmetric bi-stability are proposed and the potential energy diagram of the rotation link is considered as the performance criterion to identify the stable state.

A Study on Dynamic Characteristics of Satellite Antenna System considering 3D Revolute Clearance Joint

Clearances in the joints of real mechanisms are unavoidable due to assemblage, manufacturing errors, and wear. The dual-axis driving and positioning mechanism is one kind of space actuating mechanism for satellite antenna to implement precise guidance and positioning. However, in dynamics analysis and control of the satellite antenna system, it is usually assumed that the revolute joint in the satellite antenna system is perfect without clearances or imperfect with planar radial clearance. However, the axial clearance in an imperfect revolute joint is always ignored. In this work, the revolute joint is considered as a 3D spatial clearance joint with both the radial and axial clearances. A methodology for modeling the 3D revolute joint with clearances and its application in satellite antenna system is presented. The dynamics modeling and analysis of the satellite antenna system are investigated considering the 3D revolute clearance joint. Firstly, the mathematical model of the 3D revolute clearance joint is established, and the definitions of the radial and axial clearance are presented. Then, the potential contact modes, contact conditions, and contact detection of the 3D revolute clearance joint are analyzed. Further, the normal and tangential contact force models are established to describe the contact phenomenon and determine the contact forces in the 3D revolute clearance joint. Finally, a satellite antenna system considering the 3D revolute clearance joint with spatial motion is presented as the application example. Different case studies are presented to discuss the effects of the 3D revolute clearance joint. The results indicate that the 3D revolute clearance joint will lead to more severe effects on the dynamic characteristics of the satellite antenna system. Therefore, the effects of axial clearance on the satellite antenna system cannot be ignored in dynamics analysis and design of the satellite antenna system.

Kinematic analysis and optimal design of a novel 3-PRR spherical parallel manipulator

This paper introduces a novel three degree-of-freedom spherical parallel manipulator with 3-PRR topology, where P and R denote a curved prismatic joint and a revolute joint, respectively. The first revolute joint of each PRR leg is actuated via a double Rzeppa-type driveshaft, and hence underlined. The manipulator has at most eight working modes and eight assembly modes. However, only one working mode and one assembly mode of the manipulator are acceptable during its motion which can be easily identified. Singularity and kinematic dexterity analyses reveal that the proposed 3-PRR spherical parallel manipulator has no forward kinematic singularity for a wide range of rotation of the moving platform around its central axis. An optimal design of the manipulator is also presented having a workspace with good kinematic dexterity.