Harmonic Drive Bearing Layout for Compact Industrial Robot Drives
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Solution Overview
Problem
Existing electric drives for industrial robots are not compact or lightweight, as they occupy excessive space and weight due to inefficient bearing arrangements.
Innovation Solution
The electric drive features a motor housing with a drive shaft rotatably mounted by at least two roller bearings, a stator, and a rotor connected to the drive shaft, integrated with a stress wave gearing system including a rigid outer ring and a flexible output sleeve. The first roller bearing is positioned within the flexible output sleeve, utilizing the free annular gap space to reduce dimensions, and the motor and gear housings are connected via a flange plate for a compact design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the drive shaft is supported by roller bearings arranged in the transmission housing, then the drive shaft is properly supported, but the overall size and weight of the electric drive increase
Solution Approach 1:
The first roller bearing is nested within the flexible output sleeve, utilizing the annular gap between the drive shaft and the output sleeve. This nesting arrangement allows the bearing to be housed within existing components rather than requiring additional external space, thereby reducing the overall size and weight of the electric drive while maintaining proper drive shaft support.
Solution Approach 2:
The bearing arrangement transitions from a conventional external mounting to a radial arrangement within the annular gap of the flexible output sleeve. By utilizing the radial dimension of the existing structure, the design eliminates the need for additional axial or external space, achieving compact integration that reduces overall dimensions and weight.
2Ease of manufacture
If separate motor and gear housings are used, then assembly and maintenance are easier, but the overall size and weight of the electric drive increase
Solution Approach 1:
The motor housing and gear housing are merged into a single integrated housing structure. This consolidation eliminates the need for separate housings and their associated mounting flanges, directly reducing the overall weight and volume of the electric drive while simplifying the manufacturing process by reducing the number of parts that need to be produced and assembled.
Solution Approach 2:
The integrated housing serves multiple functions simultaneously: it houses both the motor and gear components, provides structural support, and eliminates the need for separate mounting structures. This multi-functionality approach consolidates what would traditionally require separate components, thereby reducing weight without compromising ease of manufacture or assembly.
3Manufacturing precision
If additional bearings are added to ensure accurate rotor-stator alignment, then alignment precision improves, but device complexity and weight increase
Solution Approach 1:
The first roller bearing serves dual functions: it supports the drive shaft rotation and simultaneously ensures accurate rotor-stator alignment. By making the bearing multi-functional, the design achieves precise alignment without adding extra bearings, thereby avoiding increased device complexity and weight while maintaining manufacturing precision.
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 configuration results in a compact and lightweight electric drive with reduced size and weight, enabling more efficient use of space and easier assembly, while maintaining accurate rotor-stator alignment without additional bearings.
Implementation Method 1
a stress wave gearing comprising a gear housing, a rigid outer ring (circular spline) with internal gearing, a flexible output sleeve (flexspline) with external gearing, and a shaft generator that can be rotated in the gear housing and rolls on the flexible output sleeve, the external gearing of the flexible output sleeve meshing with the internal gearing of the rigid outer ring as a function of a rotational movement of the wave generator
Implementation Method 2
a drive shaft rotatably mounted by means of at least two roller bearings
Data Source
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AI summary
The invention relates to an electrical drive (13) and an industrial robot (1) that comprises at least one such electrical drive (13), having: an electric motor (14) that comprises a motor housing (15), a drive shaft (18) rotatably mounted by means of at least two roller bearings (21, 22), a stator (16) secured in said motor housing (15), and a rotor (17) that is connected to said drive shaft (18) and can rotate in said motor housing (15); as well as a harmonic drive gear (19) that comprises a gear housing (20), a circular spline (23) with an inner toothing (24), a flex spline (25) that has an outer toothing (26), and a wave generator (27) that can be rotated in the gear housing (20) and that rolls on the flex spline (25), said outer toothing (26) of the flex spline (25) engaging with the inner toothing (24) of the circular spline (23) such that they become meshed as a function of a rotational movement of the wave generator (27). The rotor (17) is secured on the drive shaft (18), and a first of said at least two roller bearings (21, 22) is arranged inside the flex spline (25) and is designed to mount said drive shaft (18) such that it can rotate inside the gear housing (20).