Twin Ball Screw Injection Device Force Equalization
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Solution Overview
Problem
Conventional twin-ball-screw injection devices face issues with unequal forces on ball screws due to differing spring constants of load cells and dummy load cells, leading to potential overloading of servomotors and ball screws, and increased costs.
Innovation Solution
Incorporating a force detector on one ball screw and a deformable dummy member on the other, with a control unit that adjusts the servomotors based on the output of the force detector and the properties of the dummy member to equalize forces applied to both force transmission units, considering their respective spring constants.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a load cell is used on one ball screw and a dummy load cell on the other to reduce costs, then manufacturing cost is reduced, but force equality between the two ball screws deteriorates due to differing spring constants
Solution Approach 1:
The patent applies parameter changes by introducing a correction coefficient that accounts for the difference in spring constants between the load cell and dummy load cell. The control unit calculates and applies this coefficient to the output signal from the load cell, thereby compensating for the inherent physical parameter difference and achieving force equality between the two ball screws despite using different components
Solution Approach 2:
The system implements feedback control by continuously monitoring the output signal from the load cell, processing it through the correction coefficient, and using the corrected signal to control both servomotors. This closed-loop feedback mechanism ensures that force equality is maintained dynamically, compensating for the asymmetry introduced by using a real load cell on one side and a dummy load cell on the other
2Strength
If a twin-ball-screw injection device is used to reduce loads on individual servomotors and ball screws, then component loads are reduced, but device complexity and cost increase
Solution Approach 1:
The patent uses the copying principle by implementing a dummy load cell that replicates the structural form of a real load cell but without the sensing functionality. This allows the system to maintain the symmetric twin-ball-screw configuration for load distribution while avoiding the need for two expensive, complex real load cells. The dummy load cell serves as a structural copy that simplifies the overall device complexity
Solution Approach 2:
The system applies segmentation by separating the sensing function from the structural function. The real load cell handles only the sensing function on one side, while the dummy load cell provides the structural support on the other side without sensing capabilities. This functional segmentation allows the use of a single inexpensive load cell while maintaining the load-distributing benefits of the twin-ball-screw configuration
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
This configuration allows for accurate control of injection pressure and speed, reduces the risk of overloading, and simplifies the dummy member's design, thereby lowering costs while maintaining precise control.
Implementation Method 1
the body of a load cell...is slightly elastically deformed by an injection pressure
Implementation Method 2
a dummy member disposed on the second force transmission unit and having such a property as to be deformable depending on a force applied to the second force transmission unit
Data Source
AI summary
An injection device is provided with a stationary-side frame supporting a barrel, a movable-side frame rotatably supporting a screw, a pair of ball screws, and injection drive mechanisms includes servomotors configured to rotate the ball screws. A force detector such as a load cell and the like is disposed between the first ball screw and the movable-side frame. A dummy member is disposed between the second ball screw and the movable-side frame. A control unit controls the first injection drive mechanism based on the output of the force detector and controls the second injection drive mechanism based on the output of the force detector and an arithmetic operation performed in consideration of the respective spring constants of the force detector and the dummy member.