Separation of Comprehensive Geometrical Errors of a 3-DOF Parallel Manipulator Based on Jacobian Matrix and Its Sensitivity Analysis with Monte-Carlo Method


 To meet the increasing requirements for precision hybrid machine tools, this paper presents a geometric error propagation model based accuracy synthesis method for parallel manipulators (PMs) with one translational and two rotational (1T2R) motion abilities. A unified geometric error propagation model of a family of 1T2R PMs is established with the first-order kinematic perturbation method. A set of geometric error propagation intensity indexes is formulated to describe the geometric error propagation characteristics in a quantitative manner. The equivalent effects of specified terminal accuracy are derived to directly determine the allowable values of all geometric source errors. Based on these, a computation algorithm is summarized for designating tolerance allocation scheme to meet the specified terminal accuracy of a 1T2R PM. To demonstrate the accuracy synthesis method, a novel 1T2R PM with a 2UPR-1RPS (‘R’: revolute joint, ‘U’: universal joint, ‘S’: spherical joint, ‘P’: prismatic actuated joint) topology is taken as an example to allocate geometric tolerances under the specified terminal accuracy. Following the tolerance allocation scheme, a laboratory prototype of the exemplary PM is fabricated and further experimentally measured. The measured kinematic results indicate that the prototype possesses an acceptable position error smaller than 0.15mm, verifying the feasibility of the proposed accuracy synthesis method. Hence, the proposed method can be applied as a forward tolerance design tool to reduce the design iterations and development risks of low-mobility parallel robots.

Geometric error propagation model based accuracy synthesis and its application to a 1T2R parallel manipulator

A Novel Hybrid Machine Tool Integrating a Symmetrical Redundantly Actuated Parallel Mechanism: Design, Kinematics, Prototype and Experiment

Abstract Due to the merits of high rigidity and good dynamics, hybrid machine tools have been gradually applied to efficient machining of thin-walled workpiece with complex geometries. However, the discontinuity of tangential component of toolpath in hybrid machine tools may cause velocity fluctuations, leading to poor surface quality of workpiece. In this paper, a novel 5-axis hybrid machine tool is taken as an example to demonstrate a smooth toolpath interpolation method. First, an adaptive acceleration and deceleration control algorithm is presented to realize the smooth transition between two constrained velocity points. Second, a spline curve-based interpolation algorithm is proposed to realize the smoothness of the trajectory. Meanwhile, a parameter synchronization method is proposed to ensure the synchronization of the interpolated tool-axis vector and the interpolated tool tip. Thirdly, an inverse kinematic analysis is conducted based on an inverse position solution model and a velocity mapping model. Finally, a set of machining tests on S-shape workpiece in line with the ISO standard is carried out to verify the effectiveness of the proposed smooth toolpath interpolation method.

Smooth toolpath interpolation for a 5-axis hybrid machine tool

Error modeling and accuracy evaluation of parallel manipulators with mixed DoFs based on motion/force transmissibility and constrainability

A minimal-error-model based two-step kinematic calibration methodology for redundantly actuated parallel manipulators: An application to a 3-DOF spindle head

The invention relates to a five-freedom-degree hybrid moxibustion robot. The five-freedom-degree hybrid moxibustion robot comprises a sliding seat, a frame, a static platform, a movable platform, a two-freedom-degree rotating head, a moxibustion clamp, a first motion chain, a second motion chain, a third motion chain and a fourth motion chain; the frame is fixed on the sliding seat; the static platform is fixed on the top of the frame; the movable platform is arranged in front of the static platform; the movable platform is connected to the static platform through the first motion chain, the second motion chain, the third motion chain and the fourth motion chain; the two-freedom-degree rotating head is connected on the movable platform in series; and the moxibustion clamp is arranged on asecond rotating head of the two-freedom-degree rotating head and is used for fixing a moxibustion box. The moxibustion box moves along an appointed movement track by the first movement chain, the second movement chain, the third movement chain and movement control of two rotational freedom degrees of the two-freedom-degree rotating head, the automation degree is high, positioning is accurate, movement is flexible, and the moxibustion robot can adapt to curved surfaces of human bodies for moxibustion.

Chi Changcheng

Papers

A minimal-error-model based two-step kinematic calibration methodology for redundantly actuated parallel manipulators: An application to a 3-DOF spindle head

Five-freedom-degree hybrid moxibustion robot