Offset-Axis Drive Train With Through-Bore Encoder Alignment
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Solution Overview
Problem
Conventional drive trains for robot arms are too expensive, heavy, and complex, making them unsuitable for low-cost, smaller-scale applications, and they often suffer from entanglement issues with wires and inaccuracies due to worn bearings.
Innovation Solution
A drive train design with offset input and output axes, using an annular gear for power transmission, a modular encoder assembly, and a flexible mounting system to maintain alignment and absorb eccentric movements, allowing for a compact, low-cost, and low-backlash solution that simplifies manufacturing and maintenance while enabling wire passage through the axis of rotation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional drive trains are used, then power transmission is reliable, but cost and weight are too high for low-cost applications
Solution Approach 1:
The drive train is divided into separate functional modules: motor assembly, gearbox assembly with planetary gears, and encoder assembly. This modular segmentation allows each component to be optimized independently and assembled from standard off-the-shelf parts, significantly reducing manufacturing cost while maintaining reliability through proven design elements in each segment
Solution Approach 2:
The invention uses conventional, readily available motor and gearbox components rather than custom-engineered expensive parts. By accepting that these components may have limited service life and can be easily replaced, the system achieves low cost while maintaining operational reliability through redundancy and ease of replacement
2Ease of operation
If wires pass through the drive train along the axis of rotation, then wire entanglement is prevented, but the motor assembly cannot be positioned centrally
Solution Approach 1:
The motor assembly is extracted from the central axis position and relocated to an offset position on the gearbox housing. This extraction allows the central axis to be dedicated solely for wire passage, eliminating wire entanglement issues while the offset motor position is accommodated through the flexible mounting system with elastomeric material
Solution Approach 2:
An elastomeric mounting material acts as an intermediary between the motor assembly and the gearbox housing. This flexible intermediary absorbs the misalignment caused by offset motor positioning while maintaining secure mechanical connection, enabling both central wire passage and motor functionality without direct rigid alignment requirements
3Manufacturing precision
If the motor assembly is built around the central opening, then central alignment is achieved, but cost and complexity increase
Solution Approach 1:
The motor assembly is deliberately positioned asymmetrically (offset) relative to the central axis rather than requiring symmetric central alignment. This asymmetric positioning simplifies manufacturing by allowing standard components to be mounted on the gearbox housing without precise central alignment, reducing both cost and complexity while the flexible mounting compensates for the offset
4Reliability
If main bearing wears over time, then lateral movement of encoder components occurs, but encoder accuracy is maintained through separate encoder bearing
Solution Approach 1:
The encoder bearing function is extracted from the main bearing and implemented as a separate, dedicated bearing specifically for encoder alignment. This separate encoder bearing is positioned independently to maintain encoder component alignment even when the main bearing wears, ensuring long-term encoder accuracy without being affected by main bearing service life limitations
Solution Approach 2:
The separate encoder bearing acts as an intermediary support element between the encoder components and the gearbox housing. It provides dedicated radial support for the encoder shaft, isolating the encoder alignment function from the load-bearing main bearing, so that main bearing wear does not transmit lateral movements to the encoder components
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 design achieves a significant cost reduction, maintains precision, and allows for easy maintenance and replacement of components, ensuring accurate and reliable operation even with wear, while preventing wire entanglement and maintaining high accuracy in robot arm movements.
Implementation Method 1
an encoder bearing between the first and second portions of the encoder to rotatably support and maintain the alignment of the first and second portions
Implementation Method 2
the mounting for the second portion of the encoder with respect to the fixed portion of the gearbox is flexible in a direction transverse to the output axis
Data Source
AI summary
A drive train is provided comprising: a motor assembly, a gear box assembly (40) and an encoder assembly. The motor assembly comprises an electric motor (21) and a rotatable shaft (26) defining an input axis (27), the shaft (26) comprising a first set of gear teeth (28). The gear box assembly (40) comprises an annular gear (48, 50) comprising a second set of gear teeth (48, 50) which intermesh with the first set of gear teeth (28), and a housing (42, 44, 45) which comprises a fixed portion (42) to which the motor assembly is mounted and a rotatable portion (45) fixed to the annular gear (48, 50) and providing the output from the drive train about an output axis (72) offset from the input axis (27). The encoder assembly is arranged and configured to measure the rotation at the output axis (72). A central opening is defined through the gearbox assembly (40) in alignment with the output axis (72) and passing through the housing (42, 44, 45) and the annular gear (48, 50). The motor assembly is mounted so as to not obstruct the central opening. The encoder assembly comprises an annular first portion (71) mounted to the rotatable portion (45) of the gearbox assembly (40) about the central opening, and a second portion fixed with respect to the fixed portion (42) of a gearbox assembly housing (42, 44, 45) to measure the rotation of the annular first portion (71).