Gravity Compensation Mechanism for Low-Inertia Rotating Axes
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Solution Overview
Problem
Existing gravity compensation mechanisms for rotating elements in machine tools and measuring machines are bulky, complex, unreliable, and increase inertia, leading to motor wear, increased electricity consumption, and reduced precision due to unbalance, especially when the support is mobile and undergoes significant angular accelerations.
Innovation Solution
A gravity compensation device with a compensation mobile and an elastic return element, where one end is eccentrically mounted on the mobile and the other on the support, providing a torque that compensates for unbalance over a functional angular range without applying radial forces, maintaining simplicity, reliability, and low inertia.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a spring is used to compensate for the weight of a rotating element, then the unbalance torque is compensated, but the spring length becomes considerable making integration in limited space impossible
Solution Approach 1:
The spring is nested within the housing structure, with its winding axis aligned along the rotation axis of the rotating element. This allows the spring to be contained within the limited radial space of the machine tool, eliminating the need for external long springs while maintaining the gravity compensation function
Solution Approach 2:
The spring is oriented along the axial dimension (parallel to the rotation axis) rather than extending radially outward. This dimensional reorientation allows the spring to achieve its required length within the axial space of the housing, solving the space integration problem
2Reliability
If a spring is attached directly to the rotating element to compensate for unbalance, then the compensation torque is provided, but radial forces are applied to the rotation axis causing positioning errors and premature wear
Solution Approach 1:
The spring force is extracted from direct attachment to the rotating element and transferred through a cam mechanism. The cam converts the spring's radial force into a tangential torque on the rotating element, eliminating radial forces on the rotation axis while maintaining the gravity compensation function
Solution Approach 2:
The cam acts as an intermediary between the spring and the rotating element. It transforms the spring's linear elastic force into a rotational torque that compensates for unbalance without applying radial loads to the rotation axis, thereby preserving positioning accuracy
3Reliability
If a long spring is used for gravity compensation, then the unbalance is compensated, but the device becomes bulky and complex making it unsuitable for mobile supports with limited space
Solution Approach 1:
The spring's winding axis is merged with the rotation axis of the rotating element, and the cam's rotation axis is also merged with the same axis. This coaxial arrangement integrates multiple functions (spring storage, force transmission, and torque generation) into a compact unified structure, reducing overall device complexity
4Reliability
If the spring attachment point is moved far from the rotation axis to reduce force variations, then the restoring torque approaches sinusoidal function, but the device requires more space
Solution Approach 1:
Instead of increasing the radial distance of the spring attachment point, the spring is reoriented to wind along the axial dimension. This allows the spring to achieve its required length and force characteristics without increasing the radial footprint of the device
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The device achieves accurate, quasi-sinusoidal compensation torque without increasing inertia, reducing motor wear and improving precision by simulating a sinusoidal torque through lever arm and tension variations, suitable for angular ranges up to +/-180°.
Implementation Method 1
an elastic return element (3), a first elastic end of which is eccentrically mounted on the compensation mobile (2) to exert a force on the compensation mobile (2)
Implementation Method 2
the torque exerted by the weight of the mobile varies according to a sinusoidal function of the angle formed between the vertical and the straight line passing through the axis of rotation of the mobile and its center of gravity
Data Source
AI summary
The invention concerns a gravity compensation designed to compensate for the unbalance of a rotating element (1) pivoted on a support (4). The device comprises a compensating mobile (2) pivotally mounted on the support (4) and kinematically connected to the rotating element (1). The device also comprises an elastic return element (3), a first end of which is mounted directly on the compensation mobile (2), eccentrically, to exert on the compensation mobile a force whose intensity and lever arm vary as a function of the angular position of the rotating element. In an original way, a second end of the elastic return element (3) is mounted on the support (4) or on a second compensating mobile (2) pivotally mounted on the support (4) and kinematically connected to the rotating element (1), the characteristics of the device being chosen so that the resulting torque on the rotating element compensates, over a functional angular range, for the torque due to the unbalance.