Jiangping Mei

Dynamic Formulation and Performance Comparison of the 3-DOF Modules of Two Reconfigurable PKM—the Tricept and the TriVariant

Utilizing the virtual work principle, this paper presents a method for the inverse dynamic formulation of the 3-degree-of-freedom (DOF) modules of the well-known Tricept robot and a newly invented hybrid robot named TriVariant. The TriVariant is a modified version of the Tricept, achieved by integrating one of the three active limbs into the passive one. Both local and global conditioning indices are proposed for the dynamic performance evaluation and comparison of these two robots. These indices are designed on the basis of the maximum actuated joint force required for producing a unit acceleration of the mobile platform. For a given set of geometrical and inertial parameters, it has been shown that the TriVariant has a similar overall dynamic performance compared with that of the Tricept.

A Method for Estimating Servomotor Parameters of a Parallel Robot for Rapid Pick-and-Place Operations

By taking a 2-DOF high-speed translational parallel manipulator as an object of study, this paper presents an approach that enables the servomotor parameters of parallel robots for pick-and-place operations to be estimated in an effective manner using the singular value decomposition. These parameters include the moment of inertia, speed, torque, and power of the motor required for producing the specified velocity and acceleration of the end effector. An example is given to determine these parameters of a device for the rechargeable battery quality inspection.

Tolerance design of a 2-DOF overconstrained translational parallel robot

This paper deals with the tolerance design of a two-degree-of-freedom translational parallel robot module for high-speed pick-and-place operations. The module is an overconstrained parallel mechanism using two sets of parallelograms in each limb. A probabilistic model of the uncompensatable pose error is formulated, together with a compatibility condition to ensure the mobility of the robot. Based upon this model, optimization of the tolerances of the geometric source errors and joint clearances is conducted, subject to a set of appropriate constraints. Simulation and experimental results are given to demonstrate the effectiveness of this approach.

Dimensional synthesis of the delta robot using transmission angle constraintsdimensional synthesis of the delta robot using transmission angle constraints

This paper deals with dynamic dimensional synthesis of the Delta robot using the pressure/transmission angle constraints. Two types of pressure/transmission angles are defined, with which the direct and indirect singularities can be identified in a straightforward manner. Two novel global dynamic metrics are proposed for minimisation, which are associated respectively with the inertial and centrifuge/Coriolis components of the driving torque. Various geometrical and performance constraints are taken into account in terms of workspace/machine volume ratio, pressure/transmission angles, etc. The effects of pressure/transmission angle constraints on the feasible domain of design variables are investigated in depth via an example, and a set of optimised dimensional parameters is obtained for achieving a good kinematic and dynamic performance throughout the entire task workspace.

Finite Element Analysis and Comparison of Two Hybrid Robots-the Tricept and the TriVariant

This paper deals with the finite element analysis (FEA) of two 5-DOF reconfigurable hybrid robots, the Tricept and the TriVariant, by means of ANSYS parametric design language (APDL). The research interests are focused on: (1) precise FEA formulation of different types of joints by setting of contact elements, and (2) the development of an effective modeling strategy for the rapid stiffness and natural frequencies estimation associated with different configurations. The computational results show that two robots are of similar static and dynamic performances provided that they have identical geometrical dimensions, elastical and inertial parameters

Kinematic Calibration of the 3-DOF Module of a 5-DOF Reconfigurable Hybrid Robot using a Double-Ball-Bar System

This paper deals with the kinematic calibration of a 3-DOF parallel mechanism using a double-ball-bar (DBB) system. The mechanism forms the main body of a 5-DOF reconfigurable hybrid robot named TriVariant that is a modified version of the Tricept, achieved by integrating one of its three active limbs into the passive one. The first order error mapping function is formulated to link the measured data and the geometric source errors affecting the compensatable pose accuracy. Issues to enhance the accuracy and efficiency of the calibration are investigated. The results are employed to a prototype machine calibration

Controller parameter tuning of delta robot based on servo identification

High-speed pick-and-place parallel robot is a system where the inertia imposed on the motor shafts is real-time changing with the system configurations. High quality of computer control with proper controller parameters is conducive to overcoming this problem and has a significant effect on reducing the robot’s tracking error. By taking Delta robot as an example, a method for parameter tuning of the fixed gain motion controller is presented. Having identifying the parameters of the servo system in the frequency domain by the sinusoidal excitation, the PD+feedforward control strategy is proposed to adapt to the varying inertia loads, allowing the controller parameters to be tuned by minimizing the mean square tracking error along a typical trajectory. A set of optimum parameters is obtained through computer simulations and the effectiveness of the proposed approach is validated by experiments on a real prototype machine. Let the traveling plate undergoes a specific trajectory and the results show that the tracking error can be reduced by at least 50% in comparison with the conventional auto-tuning and Z-N methods. The proposed approach is a whole workspace optimization and can be applied to the parameter tuning of fixed gain motion controllers.

Kinematic calibration of Delta robot using distance measurements

This paper deals with kinematic calibration of the Delta robot using distance measurements. The work is mainly placed upon: (1) the error modeling with a goal to classify the source errors affecting both the compensatable and uncompensatable pose accuracy; (2) the full/partial source error identification using a set of distance measurements acquired by a laser tracker; and (3) design of a linearized compensator for real-time error compensation. Experimental results on a prototype show that positioning accuracy of the robot can significantly be improved by the proposed approach.

Layout analysis and path planning of a robot palletizing production line

This paper deals with facility layout analysis and path planning of a robot palletizing production line using a 4-DOF partial closed-loop palletizing robot and two carton conveyors. The layout of the production line is arranged by the reachable workspace of the robot with a goal to achieve the minimum footprint. A straight-line and arc based motion planning approach is proposed under the constraints of joint velocity and acceleration to achieve higher productivity and easier implementation. An example is given to demonstrate the effective of this method.

Tolerance Design and Kinematic Calibration of a Four-Degrees-of-Freedom Pick-and-Place Parallel Robot

This paper presents a comprehensive methodology for ensuring the geometric pose accuracy of a 4-DOF high-speed pick-and-place parallel robot having an articulated travelling plate. The process is implemented by four steps: (1) formulation of the error model containing all possible geometric source errors; (2) tolerance design of the source errors affecting the uncompensatable pose accuracy via sensitivity analysis; (3) identification of the source errors affecting the compensatable pose accuracy via a simplified model and distance measurements; and (4) development of a linearized error compensator for real-time implementation. Experimental results show that a tilt angular accuracy of 0.1/100, and a volumetric/rotational accuracy of 0.5 mm/±0.8 deg of the end-effector can be achieved over the cylindrical task workspace