Based on the background of atomic force microscope (AFM) driven by piezoelectric actuators (PEAs), this paper proposes a sliding mode control coupled with an inverse Bouc–Wen (BW) hysteresis compensator to improve the positioning performance of PEAs. The intrinsic hysteresis and creep characteristics degrade the performance of the PEA and cause accuracy loss. Although creep effect can be eliminated by the closed-loop control approach, hysteresis effects need to be compensated and alleviated by hysteresis compensators. For the purpose of dealing with the estimation errors, unmodeled vibration, and disturbances, a sliding mode control with perturbation estimation (SMCPE) method is adopted to enhance the performance and robustness of the system. In order to validate the feasibility and performance of the proposed method, experimental studies are carried out, and the results show that the proposed controller performs better than a proportional-integral-derivative (PID) controller at 1 and 2 Hz, reducing error to 1.2% and 1.4%, respectively.

This article aims to present a minimum-jerk trajectory planning approach to address the smooth trajectory generation problem of 3-prismatic-universal-universal translational parallel kinematic manipulator. First, comprehensive kinematics and dynamics characteristics of this 3-prismatic-universal-universal parallel kinematic manipulator are analyzed by virtue of the accepted link Jacobian matrices and proverbial virtual work principle. To satisfy indispensable continuity and smoothness requirements, the discretized piecewise quintic polynomials are employed to interpolate the sequence of joints’ angular position knots which are transformed from these predefined via-points in Cartesian space. Furthermore, the trajectory planning problem is directly converted into a constrained nonlinear multi-variables optimization problem of which objective function is to minimize the maximum of the joints’ angular jerk throughout the whole trajectory. Finally, two typical application simulations using the reliable sequential quadratic programming algorithm demonstrate that this proposed minimum-jerk trajectory planning approach is of explicit feasibility and appreciable effectiveness.

Abstract. Flexure-based mechanisms have been widely used for scanning tunneling microscopy, nanoimprint lithography, fast servo tool system and micro/nano manipulation. In this paper, a novel planar micromanipulation stage with large rotational displacement is proposed. The designed monolithic manipulator has three degrees of freedom (DOF), i.e. two translations along the X and Y axes and one rotation around Z axis. In order to get a large workspace, the lever mechanism is adopted to magnify the stroke of the piezoelectric actuators and also the leaf beam flexure is utilized due to its large rotational scope. Different from conventional pre-tightening mechanism, a modified pre-tightening mechanism, which is less harmful to the stacked actuators, is proposed in this paper. Taking the circular flexure hinges and leaf beam flexures hinges as revolute joints, the forward kinematics and inverse kinematics models of this stage are derived. The workspace of the micromanipulator is finally obtained, which is based on the derived kinematic models.

Controlling the contact force on workpieces is a challenging task for industrial deburring operations. To solve this issue, a novel constant force mechanism (CFM) based on the combination of positive and negative stiffness mechanism is proposed by using folding beam and bi-stable beam mechanisms. Without using any additional sensors and control algorithms, the proposed CFM can produce a travel range in constant force manner. In this paper, the design concepts, analytical model, finite element analysis (FEA) simulation and experimental studies are presented and discussed. Firstly, a novel spatial CFM is proposed and the pseudo rigid body (PRB) method is used to establish the mathematical model of the whole mechanism. Then, the FEA simulation is performed to validate the correctness of theoretical analysis. In addition, to eliminate the force variation, particle swarm optimization (PSO) method is utilized to find optimal architectural parameters solutions of the CFM. Finally, the experimental tests are performed to verify the performance of the designed CFM. The configuration design and parameter optimization proposed in this paper can be further applied to the design of other types of CFM mechanisms for polishing operations as well.

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