Composite Thrust Rod Stiffness in Linear Actuators
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Solution Overview
Problem
Linear actuators in robotic welding applications face challenges with deflection and positioning accuracy due to high electromagnetic reaction forces during aluminum welding, which can lead to electrode displacement and reduced weld quality, and existing solutions either increase cost and weight or are difficult to manufacture with high elastic modulus materials.
Innovation Solution
A composite thrust rod structure is used, where the outer diameter is made of carbon steel for machinability and the inner diameter is reinforced with a high elastic modulus material like tungsten or molybdenum, along with a bearing assembly to enhance stiffness and resistance to deflection, while maintaining reduced weight and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a high elastic modulus material (e.g., tungsten, molybdenum) is used for the thrust rod to increase stiffness and reduce deflection, then positioning accuracy is improved, but manufacturing difficulty increases significantly
Solution Approach 1:
The thrust rod is constructed as a composite structure with a high elastic modulus insert (tungsten or molybdenum) positioned within a carbon steel outer diameter. This composite configuration provides the stiffness and positioning accuracy of high elastic modulus materials while maintaining the machinability and manufacturing ease of carbon steel. The insert is secured within the outer diameter through interference fit, welding, or other securing mechanisms.
Solution Approach 2:
Instead of making the entire thrust rod from high elastic modulus material, the patent applies the high elastic modulus insert only in specific regions where stiffness is most needed. The insert can be positioned centrally or off-center depending on the specific loading conditions and deflection patterns, providing localized reinforcement where it matters most while keeping other regions manufacturable with conventional materials.
2Manufacturing precision
If the thrust rod diameter is increased to reduce deflection and improve stiffness, then positioning accuracy is improved, but the weight and size of the actuator system increases
Solution Approach 1:
The composite thrust rod structure achieves higher stiffness-to-weight ratio by combining carbon steel (providing structural framework) with high elastic modulus insert materials (providing stiffness). This allows the thrust rod to maintain or improve positioning accuracy without increasing overall diameter or weight, as the high elastic modulus insert provides exceptional stiffness per unit weight compared to solid carbon steel of equivalent size.
Solution Approach 2:
The patent changes the material parameter (elastic modulus) rather than the geometric parameter (diameter) to achieve stiffness improvement. By selecting materials with higher elastic modulus for the insert, the thrust rod achieves greater stiffness without increasing its physical dimensions, thereby avoiding weight and size penalties associated with larger diameter rods.
3Manufacturing precision
If a high elastic modulus material is used for the thrust rod to reduce deflection, then weld quality is improved, but cost increases due to material and manufacturing complexity
Solution Approach 1:
The composite thrust rod uses a cost-effective carbon steel outer diameter combined with a relatively small high elastic modulus insert (tungsten or molybdenum). This approach achieves the weld quality and positioning accuracy benefits of expensive high elastic modulus materials while keeping overall material costs manageable. The carbon steel provides structural integrity and is inexpensive, while the smaller amount of high elastic modulus insert provides the critical stiffness enhancement needed for quality welds.
Solution Approach 2:
The high elastic modulus insert is applied locally in regions where stiffness is most critical for maintaining weld quality, rather than using expensive material throughout the entire thrust rod. This localized application of premium material achieves the necessary weld precision while minimizing material costs and manufacturing complexity compared to constructing the entire rod from high elastic modulus material.
Data Source
AI summary
An apparatus comprises an actuator having a motor, a housing and a thrust rod, where the actuator is configured to convert rotational motion of the motor into axial motion of the thrust rod. A movable holder is coupled to the thrust rod, and configured for axial motion of a tool coupling therewith. A bearing assembly is coupled to the actuator, extending along an axis thereof. The bearing assembly is configured to engage with the bearing to provide positional stability for the movable holder and tool coupling, when positioned along the actuator axis by motion of the thrust rod.