In this article, the trajectory tracking control is developed by implementing a non-singular terminal sliding mode control for the redundantly actuated parallel mechanism system. The proposed control scheme could guarantee that the tracking errors converge to zero asymptotically. The problem of singularity with regard to conventional terminal sliding mode control scheme can be eliminated with the presented novel non-singular terminal sliding mode surface as well. The corresponding stability of the proposed control scheme has also been proved theoretically in terms of Lyapunov method. In addition, simulations and experiments are conducted for trajectory tracking to validate the effectiveness of the proposed scheme. The illustrative results demonstrate that the proposed scheme is available to solve the uncertainties and external disturbances with self-tuning in real time. Furthermore, the prominent characteristics of the presented control scheme are quick convergence, high accuracy, and high robustness, which can achieve excellent tracking performance as compared with computed torque control scheme and conventional sliding mode control scheme.

The structural synthesis of a group of parallel mechanisms can be established by an exhaustive enumeration of all feasible kinematic chains based on the screw theory. However, reliable kinematic limbs can provide mobility constraints for some unqualified supporting legs to guarantee the degrees-of-freedom feasibility of the parallel robots. A systematic design approach is presented for a family of planar single-loop parallel mechanisms with the consideration of infeasible kinematic chains. Different from the other design approaches for single-loop linkages, the fixed and moving platforms are predefined in this research to distinguish different kinematic limbs. The special parallelogram linkage mechanism is incorporated due to its equivalent translation capacity. Three categories of singularity configurations are investigated based on the detailed kinematic models. The reachable workspace is obtained through the spatial search methodology. Several novel kinematic error model associated performance indices are proposed in this work and examined on a translational parallel manipulator. Experiments are carried out and compared to testify the effectiveness of the kinematic analysis and proposed position-based controller.

A hybrid robot structure is capable of merging the advantages of both serial and parallel mechanisms, which guarantees its potential in medical robotic fields, especially in dental surgery applications. This paper presents a novel hybrid robot with three translational and three rotational movements. A systematic mechanical design methodology on the basis of the screw theory is proposed to comprehensively search for feasible five-degrees-of-freedom parallel structures. The usage of only planar kinematic joints is beneficial to large translation/rotation reachable workspaces. A parallel robot is chosen to construct a six-degrees-of-freedom hybrid structure. Both the position and velocity relations between the actuators and the mobile platform are established for the parallel unit. Sloping linkages in the curved shape instead of the straight shape are employed to improve the range of motion of the corresponding rotary joints. Both the translation/rotation workspaces are investigated and the manipulability measure is explored. The novel mean manipulator velocity ratio index is developed and examined on this parallel robot. A multi-objective optimization based on an evolutionary algorithm is conducted.

The planar parallel robots are widely employed in industrial applications due to simple geometry, few linkage interferences, and a large, reachable workspace. The symmetric geometry can bring significant convenience to parallel robots. The complexity of the mathematic models can be simplified since only one calculation method can be proposed to deal with various kinematic limbs in a parallel manipulator. The symmetric geometry can ease the assembly and maintenance procedures due to the modular design of linkages/joints. A novel 2-translation and 1-rotation (2T1R) parallel robot with symmetric geometry is proposed in this research. There is one closed loop in each kinematic limb, and 18 revolute joints are applied in its planar structure. Both the inverse and direct kinematic models are explored. The first-order relationship between robot inputs and outputs are constructed. Various singularity configurations are obtained based on the Jacobian matrix. The reachable workspace is resolved by the discrete spatial searching methodology, followed by the impacts originating from various linkages. The dexterity analysis of the parallel robot is conducted.

This research proposes an innovative dental robot with a 7-DOFs parallel-serial hybrid structure to precisely and efficiently execute dental caries removal surgery. The versatile system is distinguished by its unique 7 DOFs, comprising three rotational and three translational movements, with an additional degree for resin injection. This novel hybrid design combines the advantages of serial and parallel mechanical structures enabling highly flexible operations and large rotational capacity within a compact size. According to its multifunctional integrated design, this dental robot can efficiently perform a series of complex surgical tasks, including caries removal, resin injection and light curing. This robot’s two critical design metrics: the local kinematic isotropic index and the local transmission index are determined. In its application to caries removal, the system augmented with commercial haptic feedback devices for leader-follower control, demonstrates its potential in enhancing surgical efficiency and reducing cross-infection risks through its noncontact treatment method. In the experiment, the outcomes of the overall workload are assessed via the NASA task load index (NASA-TLX) and the evaluation of usability is also conducted using system usability scale (SUS). Finally, the robot’s precision is tested to determine its reliability in executing tasks.

The mobile platform of the parallel robot designed for picking and placing operations is usually equipped with one or two extra degree(s) of freedom to enable flexible grasping orientations. However, additional motors indicate extra loads for the moving platform, and the total payload performance shrinks. This paper proposes a spatial picking-and-placing manipulator, in which one actuator that is supposed to be installed on the mobile platform is placed far away from the mobile platform. The platform has a large workspace along one direction. The comprehensive analytical inverse and forward kinematic solutions of this robot are derived. The reachable workspace of the parallel manipulator module is then explored. The novel performance level index is designed to normalize the performance index and demonstrate the performance rank for any pose. A mathematical proof is provided for this novel index. The manipulability index is taken as an example to examine the level indicator. A multi-objective optimization is implemented to pursue optimal performance; then, the initial design and optimized results are compared in detail. A sample trajectory is provided to verify the correctness of the kinematic mathematical model of the parallel mechanism.