Hollow Rotor Linear Actuator with Integrated Ball Screw
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Solution Overview
Problem
Existing servo-motor driven linear actuators for fluid dispensing pumps face issues with increased size, instability, and decreased precision due to high rotational inertias, axial load handling, and misalignment, which affect accuracy and reliability, especially when dealing with a wide range of viscosities and dispensing volumes.
Innovation Solution
An electronically controlled linear pump actuator with a compact, integrated design featuring a servo motor with a cylindrical hollow rotor and a fixed ball screw nut, where the rotor is supported by wider bearings and a shorter length, eliminating twisting effects and allowing precise control through an optical encoder, and incorporating a housing that acts as a heat sink for efficient heat dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a conventional servo motor with ball screw system is used, then linear movement is achieved, but the length and volume of the actuator increase due to separate coupling elements and long ball screw shaft
Solution Approach 1:
The rotor is designed with an integrated ball screw shaft and nut structure, eliminating separate coupling elements. The ball screw shaft is formed as an integral part of the rotor, and the nut is directly mounted on the rotor, merging multiple components into a compact unified structure that reduces overall actuator volume while maintaining linear actuation capability
Solution Approach 2:
The ball screw nut is positioned within the hollow interior of the rotor, and the ball screw shaft extends through the rotor structure. This nested arrangement allows the ball screw mechanism to be contained within the rotor volume, significantly reducing the external dimensions of the actuator while preserving the linear movement function
2Ease of operation
If a long thin ball screw shaft with conforming hollow rotor is used, then coupling between rotor and shaft is achieved, but stability and mass-balancing become difficult
Solution Approach 1:
The rotor is divided into distinct functional sections: a front portion with larger diameter hollow opening for nut travel, and a rear portion with stepped hollow interior for shaft reception. This segmentation allows each section to be optimized for its specific function while maintaining overall structural stability and facilitating mass-balancing
Solution Approach 2:
Instead of having the ball screw shaft rotate within a stationary nut, the design inverts the arrangement by making the nut stationary relative to the rotor and having the shaft extend through the rotor structure. This inversion provides better structural support and stability while maintaining the required coupling functionality
3Productivity
If the ball screw shaft is attached to the rotor, then direct drive is achieved, but rotor inertia increases limiting acceleration and deceleration
Solution Approach 1:
The ball screw shaft is designed to move dynamically within the rotor structure rather than being rigidly attached. The shaft can slide axially within the hollow interior of the rotor, allowing the system to adjust its effective mass distribution during operation, which reduces the effective rotor inertia and improves acceleration and deceleration performance while maintaining direct drive efficiency
4Ease of operation
If conventional bearings are used in the rotor, then rotational movement is supported, but axial force capacity is limited reducing bearing life and accuracy
Solution Approach 1:
The rotor is constructed with composite structural features combining different bearing types and material properties. The front portion uses bearings optimized for axial load capacity while the rear portion uses bearings optimized for rotational support. This composite bearing arrangement allows the rotor to simultaneously handle both radial and axial forces, significantly improving bearing life and positioning accuracy
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 solution provides a compact, stable, and precise linear actuator capable of maintaining high accuracy across varying loads and viscosities, reducing the need for separate components and wiring, and enabling factory calibration for consistent performance.
Implementation Method 1
The rotation movement is generally converted into a linear movement by means of a ball screw system comprising a shaft and a nut
Implementation Method 2
precise control through an optical encoder
Implementation Method 3
incorporating a housing that acts as a heat sink for efficient heat dissipation
Data Source
Figure 1~2
Figure 3~5
Figure 6
AI summary
Electronically controlled linear pump drive actuator for operating a dispensing pump comprising: - a servo motor unit that has: - a stator with a central hollow cavity; - a rotor extending coaxially in the hollow cavity of the stator with a front portion that has a central bore open at the front end; and a rear shaft with a stepped diameter forming a rear extension of the front portion; - respective front and rear support members attached to the front and rear faces of the stator; - a support bearing in the rear support member designed to take and resist substantial axial loads; - a front bearing; and - a position sensor; - a ball screw drive mechanism with a ball screw nut and a ball screw shaft, the ball screw nut is arranged in and attached to the rotor; - a hollow cylinder attached to a front end of the front support member that extends in forward direction; - an actuator member guided for axial movement in the hollow cylinder and has a central rear part fixed to a front end section of the ball screw shaft, and a hollow front part; - a pump plunger adaptor fixed in the hollow front part of the actuator member for releasable attachment of a plunger element of the dispensing pump.