Eccentric Spring Gravity Compensation for Low-Inertia Rotary 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 accuracy due to radial forces and increased inertia.
Innovation Solution
A gravity compensation device with an elastic return element mounted eccentrically on a compensating element, providing a quasi-sinusoidal compensating torque without applying radial force, using a kinematic connection with a drive ratio less than one to minimize inertia and maintain accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional gravity compensation mechanism with a long return spring is used, then the restoring torque can compensate for the imbalance, but the device becomes bulky and cannot be integrated within the limited space of machine tools
Solution Approach 1:
The return spring is nested within the compensating element by mounting its first end eccentrically on the compensating element. This allows the spring to be contained within the limited space of the machine tool while still providing the necessary restoring torque to compensate for the rotating element's imbalance.
Solution Approach 2:
The spring is mounted eccentrically rather than concentrically, utilizing the radial dimension within the compensating element. This eccentric mounting allows the spring to generate the required torque while fitting within the compact space, transforming the space utilization from a linear arrangement to a radial one.
2Reliability
If a force is applied directly to the rotating element containing an imbalance, then the restoring torque compensates for the imbalance, but radial force is applied to the axis of rotation which impairs positioning accuracy and causes premature wear
Solution Approach 1:
A compensating element is introduced as an intermediary between the return spring and the rotating element. The spring applies force to the compensating element, which then transmits the compensating torque to the rotating element through kinematic connection. This intermediary prevents direct radial force application to the rotating element's axis, preserving positioning accuracy while maintaining compensation effectiveness.
3Reliability
If the return spring is made longer to reduce variations in spring tension and orientation, then the restoring torque more closely approximates the sinusoidal function, but the device becomes even more bulky and cannot be integrated
Solution Approach 1:
The return spring is nested within the compensating element, allowing it to be contained within the limited space of the machine tool. This nesting enables the spring to provide accurate sinusoidal torque compensation without requiring excessive length, as the eccentric mounting optimizes the spring's mechanical advantage throughout the rotation range.
Solution Approach 2:
The eccentric mounting position of the spring on the compensating element is optimized to maintain small variations in spring tension and orientation throughout the rotation. By carefully selecting the eccentricity distance and spring characteristics, the system achieves accurate sinusoidal torque compensation within a compact space, eliminating the need for a long spring.
4Reliability
If counterweights are added to balance the rotating element, then the imbalance is compensated, but the inertia increases which negatively impacts speed and accuracy
Solution Approach 1:
The traditional mechanical counterweight system is replaced with an elastic compensation system using a return spring and compensating element. Instead of adding mass to balance the rotating element, the spring provides a restoring torque that compensates for the imbalance dynamically. This substitution eliminates the need for additional counterweights, maintaining low inertia while achieving effective imbalance compensation.
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 effectively compensates for imbalance over a functional angular range, maintaining accuracy and reducing inertia while being compact and reliable, with minimal residual torque.
Implementation Method 1
un elastic return element whose first elastic end is mounted eccentrically on the compensating element
Data Source
Figure 1
Figure 2~3
Figure 4~6
AI summary
The invention relates to a gravity compensation device for a machine tool or measuring machine, designed to compensate for the imbalance of a rotating element (1) pivoted on a support (4). The device comprises a compensation arm (2) pivotally mounted on the support (4) and kinematically connected to the rotating element (1). Originally, the device includes an elastic return element (3) whose first end is mounted directly on the compensation arm (2), in an eccentric manner, to exert a force on the compensation arm whose magnitude and lever arm vary according to the angular position of the rotating element. The characteristics of the device are chosen so that the resulting torque on the rotating element compensates, over a functional angular range, the torque due to the imbalance.