Addressing Positioning Drift and Loosening in Robotic Joints: A Detailed Look at the Diamond Friction Shim Anti-Loosening Solution

After several years of service, industrial robot operators often encounter a troubling issue: the robot's repeat positioning accuracy begins to degrade, joints exhibit micro-vibrations during emergency stops or directional changes, and abnormal noises may sometimes be heard. These problems all point to a common root cause—positioning drift resulting from loosened bolts inside the joints.

Is there a method that can fundamentally resolve joint positioning drift and loosening issues? The answer is yes: replace conventional anti-loosening solutions with diamond friction washers that offer a high coefficient of friction.

The Essence of Positioning Drift: Loss of Preload

The positioning accuracy of robot joints depends on the geometric precision of the drive train. When the bolt preload inside a joint decreases, a chain reaction occurs:

Preload reduction → Bolt loosening → Increased transmission backlash → Enlarged hysteresis → End-effector positioning deviation

In this process, vibration is the primary driving factor. Every start/stop, acceleration/deceleration, and directional change of the robot generates impact vibrations within the joints. Over time, the frictional self-locking torque of the bolts is progressively overcome, causing minute rotational back-off.

Measured data indicate that a 6-axis robot with a 5 kg payload can experience over 100,000 vibration cycles per joint annually. Under such operating conditions, conventional spring washers may exhibit significant preload degradation within 1 to 2 years.

DAOLER Diamond Friction Washers

Anti-Loosening Mechanism of Diamond Friction Washers

DAOLER® diamond friction washers operate on the principle of physical friction-based anti-loosening, which is fundamentally distinct from chemical thread-locking adhesives and structural lock washers.

The washer substrate (stainless steel or spring steel) is uniformly embedded with high-density diamond particles on its surface. When the bolt is tightened, these diamond particles intimately engage with the bolt head and flange surface, generating exceptionally high interfacial frictional resistance. This frictional resistance elevates the bolt's self-locking critical torque by a factor of 2 to 3, making back-off significantly more difficult under vibratory conditions.

The key differentiator lies in durability. Thread-locking adhesives soften and fail at elevated temperatures; nylon materials age and become brittle; however, diamond is the hardest natural material known—its frictional properties remain stable regardless of temperature or time. DAOLER® washers maintain a stable coefficient of friction of 0.3–0.5 across a temperature range of –60 °C to +300 °C, and can be repeatedly installed and removed over 500 times without performance degradation.

Practical Case Study

A 6-axis industrial robot used in an automotive parts production line experienced positioning drift in its 3rd axis after three years of operation (deviation increased from ±0.05 mm to ±0.15 mm), accompanied by noticeable abnormal joint noise. Inspection revealed that the flange bolt preload had dropped by approximately 40%.

After replacing with DAOLER® diamond friction washers:

• Preload was recalibrated, and positioning accuracy was restored to ±0.03 mm;

• Re-measurement after six months of operation showed a positioning deviation of only ±0.04 mm, with no indication of degradation;

• Abnormal joint noise was eliminated, and motion smoothness was significantly improved.

Applicable Scenarios

DAOLER® diamond friction washers are suitable for bolt anti-loosening in various industrial robot joints, including:

• Flange connections at each joint of 6-axis robots

• Output flanges of RV reducers

• Input/output flanges of harmonic reducers

• Mounting bolts of linear module slides