3-DOF Translational Parallel Manipulator Stiffness and Accuracy

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Solution Overview

Problem

Current 3-DOF translational parallel manipulators face limitations in stiffness, accuracy, load/weight ratio, and operational speed due to their topological structures, which include complex joint combinations, anisotropic constraints, and high numbers of 1-DOF joints, leading to low performance in industrial applications.

Innovation Solution

A 3-DOF translational parallel manipulator design featuring three serial kinematic subchains with a minimal number of 1-DOF joints, including a prismatic and revolute joint configuration, where the prismatic joints are driven by lead screws or linear motors, and the actuators are placed on the fixed platform to enhance stiffness and accuracy, with a movable platform having a star arrangement of revolute joints to achieve orthogonal translational motions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If traditional parallel manipulator structures are used with multiple 1-DOF joints, then the manipulator can achieve translational motions, but the stiffness and accuracy deteriorate due to cumulative effects of joints

Engineering Contradiction:

Improveoutput accuracyVSAvoidnumber of joints

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent combines multiple 1-DOF joints into planar joints (2-DOF) and spherical joints (3-DOF) to reduce the total number of joints in the manipulator structure, thereby eliminating cumulative joint errors and improving output accuracy

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent uses universal joints that can accommodate multiple degrees of freedom, allowing a single joint to perform functions that would traditionally require multiple separate joints, thus reducing the overall joint count and improving precision

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Adaptability or versatility

If prismatic joints are placed on the movable platform to increase workspace range, then the workspace is enlarged, but the load/weight ratio deteriorates due to large-sized movable platform

Engineering Contradiction:

Improveworkspace rangeVSAvoidmovable platform weight

Core Design Contradiction:

Adaptability or versatilityVSWeight of moving object

Solution Approach 1:

The patent inverts the traditional configuration by placing actuators on the fixed platform rather than the movable platform. This allows the movable platform to be minimized in size while still achieving the required workspace range through the mechanical advantage of the inverted architecture

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent extends the workspace in the vertical dimension by using inclined subchains that can achieve large horizontal and vertical ranges without requiring a large movable platform, thus maintaining a compact moving mass while enlarging the effective workspace

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Device complexity

If orthogonal constraints are used in Cartesian parallel manipulators, then the structure is simplified, but the stiffness deteriorates due to anisotropic constraints

Engineering Contradiction:

Improvestructural simplicityVSAvoidoutput stiffness

Core Design Contradiction:

Device complexityVSStrength

Solution Approach 1:

The patent uses asymmetric, inclined subchain configurations rather than orthogonal arrangements. This asymmetric design provides isotropic stiffness characteristics in all directions while maintaining structural simplicity through the regular repetition of the inclined subchain pattern

Inventive Principle:

Principle #4Asymmetry

4Adaptability or versatility

If three revolute joints are included in each subchain, then the manipulator can achieve rotational capability, but the stiffness and accuracy of the output movable platform deteriorate

Engineering Contradiction:

Improverotational capabilityVSAvoidplatform accuracy

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

The patent merges three revolute joints into a single spherical joint (3-DOF) at the end of each subchain. This reduction in joint count eliminates cumulative errors while maintaining the rotational capability needed for the manipulator's function

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent places spherical joints with high-precision bearings at critical locations (the end of subchains and on the movable platform) to provide rotational capability where needed while maintaining high stiffness and accuracy at these localized positions

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS10583552B2Translational parallel manipulators and methods of operating the same

Publication Date: 2020.03.10 NORTHWESTERN UNIV

AI summary

In one aspect, a translational parallel manipulator is provided and includes a fixed platform including three guide members. The three guide members include first ends and second ends, and the first ends of the three guide members are all coupled to each other and the second ends of the three guide members are all spaced-apart from each other. The manipulator also includes a movable platform spaced-apart from the fixed platform and three serial subchains coupled between the three guide members and the movable platform. In one aspect, a translational parallel manipulator is provided and includes a fixed platform, a movable platform spaced-apart from the fixed platform, and a plurality of subchains coupled between the fixed platform and the movable platform. At least one of the plurality of subchains includes no more than four one degree-of-freedom joints.