The "Hidden Champion" in Robotic Joint Modules: Application and Technical Value of Friction Shims
I. Core Functions of Friction Shims in Robotic Joint Modules
In essence, the primary function of a friction shim is to efficiently convert the axial preload of bolted joints into substantial radial frictional torque through a high-friction-coefficient interface. This friction-based connection transmits torque, withstands applied loads, and simultaneously eliminates microscopic clearances and relative motion between mating components.
The core value of friction shims can be summarized in three key aspects:
Achieving backlash-free power transmission
Providing high-rigidity joint connections
Protecting critical precision components
DAOLER Diamond Friction Shims – DAOLER
II. Specific Application Locations of Friction Shims in Joint Modules
Friction shims are typically deployed at the following most critical interface points within robotic joint modules:
1. Connection Between the Harmonic Drive Output and the Arm Link
Location: Between the flexspline of the harmonic drive and the robot arm link (or output flange).
Functional Requirements: This interface is subject to the highest torque output and most complex loading conditions within the joint module. The connection must be absolutely reliable, with zero rotational clearance (backlash); otherwise, end-effector vibration and loss of positional accuracy will directly result.
Limitations of Conventional Solutions: Spline connections exhibit micron-level lateral clearances and consume significant spatial volume. Interference fits are difficult to assemble and risk damaging the flexspline.
Friction Shim Solution:
An annular friction shim is inserted between the flexspline end face and the arm-link mounting flange.
Precisely controlled preload is applied via circumferentially distributed bolts, generating sufficient frictional torque to counteract the robot's maximum output torque.
Result: Completely backlash-free torque transmission, an exceptionally compact structural layout, and ease of disassembly for maintenance.
2. Connection Between the Motor Shaft and the Reducer Input
Location: Between the servo motor shaft and the input bore of the reducer (typically the wave generator).
Functional Requirements: Efficient, backlash-free transmission of motor torque into the reducer is essential. Any backlash at this stage is amplified by the reduction ratio, severely compromising control precision.
Limitations of Conventional Solutions: Keyed connections introduce inherent backlash; shrink-disc locking assemblies are comparatively complex in structure and higher in cost.
Friction Shim Solution:
The friction shim is placed either between the motor shaft flange and the reducer input flange, or a sleeve-type friction insert is fitted into the connection bore.
Upon bolt preloading, frictional torque directly transmits the motor output.
Result: A simple, compact connection that entirely eliminates backlash at the front end of the drivetrain and enhances overall system rigidity.
3. Connection Between the Brake and the Motor Housing
Location: Between the brake flange and the motor housing.
Functional Requirements: The brake housing must be securely fixed, with no displacement under frequent start-stop cycles and vibration.
Friction Shim Solution:
The use of a friction shim prevents joint loosening induced by vibration, ensuring absolute positional stability of the brake assembly.
4. Bearing Preload and Retention
Location: On the clamping end faces (either outer or inner ring) of bearing housings requiring high-rigidity support.
Functional Requirements: Elimination of bearing clearance, precise preload application, and improved spindle rigidity.
Friction Shim Solution:
Friction shims ensure that preload does not degrade under prolonged vibration, maintaining a consistent bearing preload condition over time.
DAOLER Diamond Friction Shims – DAOLER
III. Summary of Core Advantages Offered by Friction Shims
In the specific context of robotic joint modules, the application advantages of friction shims are particularly pronounced:
Ultimate Compactness: Eliminates the need for splines, keyways, and other radial-space-consuming features, allowing for smaller flange designs. This directly reduces the joint module diameter and enables higher power density.
Zero Backlash and High Rigidity: Provides a purely planar contact interface, eliminating microscopic clearances arising from fit tolerances and wear. This markedly improves joint torsional stiffness and positional accuracy.
Damping, Anti-Loosening, and Fretting Wear Resistance: The shim material absorbs vibrational energy, preventing spontaneous bolted-joint loosening. Additionally, acting as a sacrificial layer, it accommodates micro-scale relative motion (fretting) at the interface, protecting costly core components such as the harmonic drive flexspline and motor shaft, thereby significantly extending their service life.
Simplified Design and Assembly: The standardized and straightforward "bolt + shim" connection method reduces machining precision requirements for mating parts, streamlines assembly procedures, and enhances production efficiency and maintainability.
IV. Technological Evolution – The Case of DAOLER® Diamond Friction Shims
Taking DAOLER® diamond friction shims as an exemplar, the technological superiority of this solution elevates the above advantages to new heights:
Superior Coefficient of Friction (μ > 0.20): Enables higher torque transmission at equivalent preload, or alternatively, permits the use of smaller bolts and thinner flanges while transmitting the same torque.
Exceptional Compressive Strength and Wear Resistance: Withstands surface pressures exceeding 300 MPa, ensuring that connection performance does not degrade even under extreme robotic loading. Its extended service life matches the design life of the joint module itself.
Outstanding Thermal Stability: Performance remains unaffected by temperature fluctuations within the joint, providing all-weather reliability assurance for robots operating at high speeds and under heavy loads.
Conclusion
Within highly integrated robotic joint modules, friction shims have transcended their status as simple functional components to become a pivotal technology that defines the performance boundaries of the module. By harnessing fundamental tribological principles, they resolve the engineering challenge of achieving highly reliable power transmission within compact spatial envelopes. They are the "unsung heroes" driving the evolution of robots toward smaller footprints, greater precision, and enhanced power. The selection of high-performance friction shims—exemplified by DAOLER® diamond friction shims—has become an indispensable choice in the design of premium robotic joint modules.
In essence, the primary function of a friction shim is to efficiently convert the axial preload of bolted joints into substantial radial frictional torque through a high-friction-coefficient interface. This friction-based connection transmits torque, withstands applied loads, and simultaneously eliminates microscopic clearances and relative motion between mating components.
The core value of friction shims can be summarized in three key aspects:
Achieving backlash-free power transmission
Providing high-rigidity joint connections
Protecting critical precision components
DAOLER Diamond Friction Shims – DAOLER
II. Specific Application Locations of Friction Shims in Joint Modules
Friction shims are typically deployed at the following most critical interface points within robotic joint modules:
1. Connection Between the Harmonic Drive Output and the Arm Link
Location: Between the flexspline of the harmonic drive and the robot arm link (or output flange).
Functional Requirements: This interface is subject to the highest torque output and most complex loading conditions within the joint module. The connection must be absolutely reliable, with zero rotational clearance (backlash); otherwise, end-effector vibration and loss of positional accuracy will directly result.
Limitations of Conventional Solutions: Spline connections exhibit micron-level lateral clearances and consume significant spatial volume. Interference fits are difficult to assemble and risk damaging the flexspline.
Friction Shim Solution:
An annular friction shim is inserted between the flexspline end face and the arm-link mounting flange.
Precisely controlled preload is applied via circumferentially distributed bolts, generating sufficient frictional torque to counteract the robot's maximum output torque.
Result: Completely backlash-free torque transmission, an exceptionally compact structural layout, and ease of disassembly for maintenance.
2. Connection Between the Motor Shaft and the Reducer Input
Location: Between the servo motor shaft and the input bore of the reducer (typically the wave generator).
Functional Requirements: Efficient, backlash-free transmission of motor torque into the reducer is essential. Any backlash at this stage is amplified by the reduction ratio, severely compromising control precision.
Limitations of Conventional Solutions: Keyed connections introduce inherent backlash; shrink-disc locking assemblies are comparatively complex in structure and higher in cost.
Friction Shim Solution:
The friction shim is placed either between the motor shaft flange and the reducer input flange, or a sleeve-type friction insert is fitted into the connection bore.
Upon bolt preloading, frictional torque directly transmits the motor output.
Result: A simple, compact connection that entirely eliminates backlash at the front end of the drivetrain and enhances overall system rigidity.
3. Connection Between the Brake and the Motor Housing
Location: Between the brake flange and the motor housing.
Functional Requirements: The brake housing must be securely fixed, with no displacement under frequent start-stop cycles and vibration.
Friction Shim Solution:
The use of a friction shim prevents joint loosening induced by vibration, ensuring absolute positional stability of the brake assembly.
4. Bearing Preload and Retention
Location: On the clamping end faces (either outer or inner ring) of bearing housings requiring high-rigidity support.
Functional Requirements: Elimination of bearing clearance, precise preload application, and improved spindle rigidity.
Friction Shim Solution:
Friction shims ensure that preload does not degrade under prolonged vibration, maintaining a consistent bearing preload condition over time.
DAOLER Diamond Friction Shims – DAOLER
III. Summary of Core Advantages Offered by Friction Shims
In the specific context of robotic joint modules, the application advantages of friction shims are particularly pronounced:
Ultimate Compactness: Eliminates the need for splines, keyways, and other radial-space-consuming features, allowing for smaller flange designs. This directly reduces the joint module diameter and enables higher power density.
Zero Backlash and High Rigidity: Provides a purely planar contact interface, eliminating microscopic clearances arising from fit tolerances and wear. This markedly improves joint torsional stiffness and positional accuracy.
Damping, Anti-Loosening, and Fretting Wear Resistance: The shim material absorbs vibrational energy, preventing spontaneous bolted-joint loosening. Additionally, acting as a sacrificial layer, it accommodates micro-scale relative motion (fretting) at the interface, protecting costly core components such as the harmonic drive flexspline and motor shaft, thereby significantly extending their service life.
Simplified Design and Assembly: The standardized and straightforward "bolt + shim" connection method reduces machining precision requirements for mating parts, streamlines assembly procedures, and enhances production efficiency and maintainability.
IV. Technological Evolution – The Case of DAOLER® Diamond Friction Shims
Taking DAOLER® diamond friction shims as an exemplar, the technological superiority of this solution elevates the above advantages to new heights:
Superior Coefficient of Friction (μ > 0.20): Enables higher torque transmission at equivalent preload, or alternatively, permits the use of smaller bolts and thinner flanges while transmitting the same torque.
Exceptional Compressive Strength and Wear Resistance: Withstands surface pressures exceeding 300 MPa, ensuring that connection performance does not degrade even under extreme robotic loading. Its extended service life matches the design life of the joint module itself.
Outstanding Thermal Stability: Performance remains unaffected by temperature fluctuations within the joint, providing all-weather reliability assurance for robots operating at high speeds and under heavy loads.
Conclusion
Within highly integrated robotic joint modules, friction shims have transcended their status as simple functional components to become a pivotal technology that defines the performance boundaries of the module. By harnessing fundamental tribological principles, they resolve the engineering challenge of achieving highly reliable power transmission within compact spatial envelopes. They are the "unsung heroes" driving the evolution of robots toward smaller footprints, greater precision, and enhanced power. The selection of high-performance friction shims—exemplified by DAOLER® diamond friction shims—has become an indispensable choice in the design of premium robotic joint modules.
