Monolithic Electric Motor Shaft Nut Locking
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Solution Overview
Problem
Existing electric motors intended for actuators, such as robotic arms, face challenges in compactness, precision, and reliability due to alternating loads on the shaft, which require precise rotation without axial play.
Innovation Solution
A monolithic shaft with a threaded portion that engages a nut to exert tensile stress, combined with sealed and greased front bearings, eliminates the need for a lip seal and enhances alignment and rotation accuracy by stiffening the shaft over a greater distance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a two-part shaft assembly with screw connection is used, then the shaft can be assembled with bearings, but axial play and precision are compromised
Solution Approach 1:
The shaft is divided into two parts: a monolithic front shaft portion containing the drive thread and magnets, and a rear shaft portion with bearings. These parts are connected via a screw connection with the nut engaged on the threaded portion extending behind the stator, creating a segmented but precisely aligned assembly that eliminates axial play while maintaining rotation precision.
2Ease of manufacture
If the threaded portion of the shaft is short, then the nut can be easily positioned, but the shaft stiffness and alignment precision are reduced
Solution Approach 1:
The threaded portion extends not only axially along the shaft but also radially behind the stator, creating a three-dimensional engagement path. This extended threaded portion allows the nut to be engaged at an optimal position that provides both ease of manufacture and sufficient shaft stiffness for precise alignment, as the thread engagement length correlates with shaft portion stiffness.
3Reliability
If a lip seal is used behind the front bearings, then sealing is provided, but friction and device complexity increase
Solution Approach 1:
The lip seal component is extracted and removed from the system. Instead of using a lip seal behind the front bearings, the invention relies on the sealed and greased bearings themselves to provide the necessary sealing function, thereby reducing device complexity and friction while maintaining sealing reliability.
4Device complexity
If the shaft portion under traction is short, then the nut engagement is simple, but the shaft stiffness and rotation accuracy are compromised
Solution Approach 1:
The threaded portion is pre-formed on the monolithic front shaft portion extending behind the stator, and the nut is pre-positioned to engage this threaded portion at an optimal location. This preliminary configuration ensures that when the nut is tightened, it applies tensile stress to the shaft over a relatively long length, stiffening the shaft over a greater distance and improving rotation accuracy without increasing engagement complexity.
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 design improves motor performance and precision by preventing nut loosening and reducing friction, while maintaining compactness and reliability.
Implementation Method 1
by screwing the nut, to exert a tensile stress on the shaft on a portion of the latter of relatively long length, extending from the aforementioned shoulder to the rear of the stator
Implementation Method 2
permanent magnets rotating with the shaft and interacting mechanically with a stator
Implementation Method 3
The front bearing(s) preferably being sealed and greased
Data Source
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AI summary
The present invention relates to an electric motor (1) comprising: - a rotor having a shaft (2) having a shoulder (16), - at least one front bearing (4) for guiding the shaft, - at least one rear bearing (5) for guiding the shaft, - permanent magnets (25) rotating with the shaft and mechanically interacting with a stator, characterized in that the shaft (2) is monolithic and the front bearing(s) (4) are axially locked against the shoulder (16) by a nut (30) screwed onto the shaft (2).