Two-Stage Linear Drive With Eccentric Thread Engagement
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Solution Overview
Problem
Existing linear drives, particularly in robotics, face challenges in efficiently adjusting gear ratios to balance movement speed and actuating force, often requiring large, complex, and expensive manually shiftable transmissions, which are not suitable for compact designs like humanoid or animal-like robots.
Innovation Solution
A motor-driven linear drive with two reduction stages, utilizing a drive spindle with an external thread and a drive element with an internal thread, eccentrically offset, allowing for load-dependent switching of reduction ratios through two drive sources, preferably electric motors, and incorporating a cycloidal gear mechanism for efficient conversion of rotary motion to linear motion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a manually shiftable transmission is used to adjust gear ratio, then the actuating force and movement speed can be adjusted, but the device becomes large, heavy, complex, and expensive
Solution Approach 1:
The transmission system is segmented into two distinct reduction stages: a first reduction stage with a first gear ratio and a second reduction stage with a second gear ratio. Each stage can be independently engaged or disengaged, allowing the system to switch between different effective gear ratios without requiring a complex manually shiftable transmission. This segmentation enables adaptability while maintaining simplicity.
Solution Approach 2:
The patent employs a nested configuration where the second reduction stage is integrated within or alongside the first reduction stage. The drive element with internal thread interacts with the drive spindle with external thread in a compact arrangement, allowing multiple reduction functions to be nested within a single integrated structure, thereby reducing overall device complexity and size.
2Force
If the gear ratio is increased to increase actuating force, then the movement speed decreases, but the device size and complexity increase
Solution Approach 1:
The system provides dynamic adaptability by allowing the gear ratio to be changed based on operational requirements. The two reduction stages can be selectively engaged, enabling the system to switch between high gear ratio (for high actuating force) and low gear ratio (for high movement speed) modes. This dynamic configuration eliminates the need for a complex multi-speed transmission while maintaining the ability to optimize force and speed according to task demands.
3Power
If a constant reduction gear is used in electric motor-driven linear drive, then the motor size must be large to provide sufficient power for all conditions, but this increases device size and weight
Solution Approach 1:
The patent changes the reduction ratio parameter dynamically by providing two distinct reduction stages that can be selectively engaged. This allows the motor to operate at optimal power levels for different task conditions: using a higher reduction ratio when high force is needed and a lower reduction ratio when high speed is needed. Consequently, a smaller motor can be used compared to a constant reduction system designed for maximum force, reducing overall device weight while maintaining sufficient power capability.
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
Enables flexible adjustment of gear ratios to match varying operational demands, reducing size and complexity while maintaining high load capacity and efficiency, suitable for compact robotic applications.
Implementation Method 1
a) a drive spindle with an external thread; b) a housing, arranged concentrically around the drive spindle; c) a hollow shaft which is rotatably mounted concentrically around the drive spindle in the housing and can be driven by a first drive source
Implementation Method 2
The radial sliding of inner teeth into the outer teeth is similar to a nut sliding radially into the spindle. This allows for high gear ratios to be achieved
Data Source
Figure 1a~1b
Figure 2a~2b
Figure 3a~3b
AI summary
The invention relates to a linear drive having two reduction stages, the linear drive comprising: - a drive spindle (4) having an external screw thread; - a housing (1), which is concentric around the drive spindle; - a hollow shaft (2), which is rotatably mounted in the housing such that the hollow shaft is concentric around the drive spindle, and which can be driven by means of a first drive source (8, 9); - a drive element (7), which is rotatably mounted in the hollow shaft such that the drive element has an eccentric offset to the drive spindle, and which can be driven by means of a second drive source (10, 11), the drive element having an internal screw thread; and - plain bearing elements (6) for axially guiding the drive spindle; wherein: the screw threads of the drive spindle and of the drive element have the same gear module; the screw-thread inside diameter of the drive element is greater than the screw-thread outside diameter of the drive spindle; the eccentric offset is set such that the internal screw thread of the drive element engages in the external screw thread of the drive spindle only on one side; and the second drive source has overload protection with power limitation or with switch-off.