Redundant Parallel Positioning Table for Compact High-Load Precision
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Solution Overview
Problem
Current positioning devices for synchrotron diffractometer applications face challenges with load capacity, workspace size, and precision, particularly in accommodating heavy loads and performing complex motions within tight spaces, due to limitations in hexapod structures and other kinematic mechanisms.
Innovation Solution
A redundant parallel positioning table device with a 6-4-213 topology, featuring four symmetric kinematic chains with redundant legs and active 2 dof pillars, allowing for modular design and compact, high-stiffness, high-precision motion capabilities, including translations and rotations, by using planar and spherical guiding units and bidirectional linear actuators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If hexapod structures are used for positioning, then precision and dynamics are improved, but device volume and height become too big for available diffractometer space
Solution Approach 1:
The positioning device is segmented into four independent kinematic chains (legs) connecting the stationary base to the movable table, each leg capable of independent actuation. This segmentation allows compact arrangement of actuators and reduces overall device volume compared to traditional hexapod structures while maintaining positioning precision through parallel kinematics.
Solution Approach 2:
The kinematic chains are designed with nested components where actuators, guides, and supporting elements are arranged concentrically and in overlapping configurations. The planar and spherical guiding units are integrated within the leg structures, and redundant legs are positioned to minimize external dimensions, effectively reducing the device footprint while preserving functional capabilities.
2Force
If hexapod structures are used for positioning, then payload capacity is improved, but device height becomes too big for available diffractometer space
Solution Approach 1:
The device uses four legs instead of six, with asymmetric arrangement optimized for the specific diffractometer workspace constraints. The legs are positioned at different orientations and lengths to achieve both high payload capacity and reduced height, departing from the symmetric hexapod configuration to better fit the available space while maintaining structural strength.
Solution Approach 2:
The kinematic chains incorporate both planar (2 dof) and spherical (3 dof) guiding units, transitioning from purely linear actuation to multi-dimensional motion control. This allows the device to achieve high payload capacity through distributed force application while reducing height by utilizing angular and rotational degrees of freedom in addition to linear displacement.
3Measurement precision
If redundant parallel kinematic chains are used, then precision and avoidance of singularities are improved, but device complexity increases
Solution Approach 1:
Each of the four kinematic chains is designed with universal components that can perform multiple functions: the planar guiding units provide both linear guidance and angular adjustment, while the spherical guiding units handle rotational degrees of freedom. This multi-functionality reduces the need for separate specialized components, thereby reducing overall structural complexity while maintaining high positioning precision and singularity avoidance through redundancy.
4Volume of stationary object
If compact design is implemented, then device footprint is reduced, but load capacity may be compromised
Solution Approach 1:
The device merges the functions of multiple traditional positioning mechanisms into a single integrated parallel kinematic structure. The four kinematic chains work together in parallel, with their actuators and guiding units combined in a compact arrangement, to achieve both reduced footprint and high load capacity through collective force application and distributed structural support.
Data Source
AI summary
A positioning table device with six or fewer degrees of freedom and redundancy. Four modular legs extend from a base to a table. Each leg has three joints. In one embodiment, the bottom joint is planar and active, the middle joint is prismatic and passive, and the top joint is spherical and passive. In another embodiment, fewer than six degrees of freedom is achieved by reducing the number of degrees of freedom of selected joints. In another embodiment, the middle joint is active, and the bottom and top joints are passive.