Cable-Drum Transmission Assembly for Backlash-Free Robot Joints
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Solution Overview
Problem
Existing bevel gear stages and belt drives in robotics are heavy, require large installation space, exhibit backlash, and have low stiffness, making them unsuitable for dynamic movements and cost-effective applications.
Innovation Solution
A gear arrangement using rotatable drums and cables with a circular cross-section, allowing for angular offset without twisting, and featuring grooves, tensioning devices, and optional deflection elements to achieve high rigidity, low weight, and compact design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bevel gear stages are used to change the orientation of rotary axes, then the transmission function is achieved, but the weight increases and backlash occurs
Solution Approach 1:
The patent replaces the traditional bevel gear mechanical transmission system with a cable-driven drum system. The drive body and driven body are connected via cables wrapped around drums, eliminating gear teeth and mechanical meshing. This substitution achieves backlash-free operation while significantly reducing weight, as cables and drums are much lighter than gear stages with equivalent torque capacity.
Solution Approach 2:
The patent employs flexible cables with circular cross-section to transmit force between the drive body and driven body. These cables wrap around drums to change the orientation of rotary axes without requiring rigid gear connections. The flexibility of the cables allows for compact arrangement and eliminates the need for heavy, rigid gear structures.
2Area of stationary object
If belt drives with trapezoidal cross-section are used, then the orientation of axis of rotation can be changed, but the installation space increases due to required twisting section
Solution Approach 1:
The patent uses cables with circular cross-section instead of belts with trapezoidal cross-section. The circular geometry allows the cable to bend and wrap around drums in any orientation without requiring a free twisting section. This eliminates the need for additional installation space that would be required for belt twisting, while still enabling flexible changes in axis orientation.
3Strength
If belt drives are used to change axis orientation, then transmission is achieved, but the stiffness decreases compared to alternative drive concepts
Solution Approach 1:
The patent employs tensioned cables wrapped around drums to transmit torque. The cables are pre-tensioned to maintain high stiffness during operation, while their ability to wrap around drums of different sizes and orientations provides the necessary adaptability. This combination of tensioned flexible elements with drum-based torque transmission achieves both high stiffness and orientation flexibility simultaneously.
4Area of stationary object
If ropes with circular cross-section are used instead of belts, then the installation space is reduced and stiffness is increased, but the device complexity increases due to winding mechanism
Solution Approach 1:
The drums in the patent serve multiple functions: they act as torque transmission elements, guide the cables, provide the winding mechanism, and enable orientation changes. This multi-functionality eliminates the need for separate components for each function, reducing overall device complexity despite using cables instead of belts. The drum-cable system achieves compact installation space while maintaining simple structure through functional integration.
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 gear arrangement provides backlash-free, lightweight, and space-efficient transmission with high stiffness, enabling dynamic robotic movements while reducing installation space and manufacturing costs.
Implementation Method 1
a cable (32, 38) which can be wound onto the at least one drive-side drum (20, 22) and the at least one driven-side drum (28, 30)... By rotating the at least one drive-side drum (20, 22) around the drive axis (18), the rotational speed and torque can be transmitted via the at least one cable (32, 38) to the at least one driven-side drum (28, 30)
Data Source
Figure 1a~1b
Figure 2~3
Figure 4~5
AI summary
Gear arrangement (14, 14a) with the following features: • a drive body (16, 16a) with at least one drive-side drum (20, 22) rotatably arranged about a drive axis (18, 18a), • a driven body (24, 24a) with at least one output-side drum (28, 30) rotatably arranged about an output axis (26, 26a), • at least one rope (32, 38) that can be wound onto the at least one drive-side drum (20, 22) and onto the at least one output-side drum (28, 30), and has a drive-side rope end (34, 40) and an output-side rope end (36, 42), wherein the drive-side rope end (34, 40) is connected to the at least one drive-side drum (20, 22) and the output-side rope end (36, 42) on which at least one output-side drum (28, 30) is arranged, as well as robot (12) with a gear arrangement (14, 14a).