E-2155 Troubleshooting: Joint Over-Torque / High Friction Due to Incorrect Lubrication

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Tools Required

• Grease gun (compatible with cartridge)
• Torque wrench
• Hex key set / Socket set
• Lint-free cloths
• Personal Protective Equipment (PPE) as required

Article

Overview

The error code E-2155 (Joint Over-Torque / High Friction) is triggered when a robot's controller detects that a joint motor is drawing excessive current to produce movement, indicating abnormal resistance. This issue is frequently linked to the condition of the joint's internal lubrication. This article provides a systematic approach to diagnose and resolve this error by inspecting and replacing the grease using the NexBot Robotics 731-004 Joint Grease Cartridge (NXB-GEN-731-004).

This procedure applies to all joints (J1, J2, J3, J4, J5, J6) on compatible NexBot Robotics platforms, including the R-20, R-50, C-10, and S-5 series.

Symptom

• Primary Symptom: The robot controller displays alarm E-2155, often referencing a specific joint axis. The robot may halt operation.
• Secondary Symptoms:
• Audible grinding, whining, or chattering sounds from the affected joint during operation.
• Sluggish or jerky movement of the corresponding robot arm axis.
• The joint housing feels unusually warm to the touch after operation (use appropriate thermal detection tools; do not touch potentially hot surfaces).

Cause

The most common cause of high joint friction is compromised lubrication. This can result from one or more of the following conditions:

1. Grease Degradation: The grease has exceeded its operational lifespan, leading to a breakdown in viscosity and lubricating properties.
2. Contamination: Foreign materials such as metal particles, dust, or cutting fluid have mixed with the grease, creating an abrasive paste that increases friction and wear.
3. Insufficient Lubricant: The joint does not have an adequate amount of grease due to leaks or incomplete servicing during previous maintenance cycles.
4. Incorrect Lubricant: A non-specified grease was used previously, which is incompatible with the robot's internal components or the existing NXB-GEN-731-004 grease, causing it to separate or solidify.

Resolution Steps

Safety First: Before beginning any work, perform a full lockout/tagout (LOTO) procedure on the robot controller and any related power sources according to your facility's safety protocols.

1. Identify the Faulty Joint: Note the specific joint axis indicated by the E-2155 error message on the teach pendant or controller interface.

1. Position the Robot: If possible, manually move the robot arm to a position that provides safe and easy access to the affected joint's grease fittings and inspection ports. This may require releasing the brakes (follow the robot's specific manual for this procedure).

1. Prepare the Grease Cartridge: Load a new NexBot Robotics 731-004 Joint Grease Cartridge into a compatible manual or pneumatic grease gun. Purge a small amount of grease from the gun nozzle to ensure no air is in the line.

1. Access Grease Fittings: Locate the grease inlet (zerk fitting) and outlet/purge port on the affected joint housing. You may need to remove a small access panel. Clean the area around both fittings with a lint-free cloth to prevent contaminating the joint.

1. Purge Old Grease:

• Remove the plug from the grease outlet port.
• Attach the grease gun to the inlet zerk fitting.
• Slowly pump the new NXB-GEN-731-004 grease into the joint.
• Continue pumping until you see new, clean grease emerging from the outlet port. The purged grease may appear dark, watery, or contain visible metallic particles.
• Note: The volume of grease required varies by joint. Refer to the robot's specific maintenance manual for approximate quantities.

1. Clean and Close:

• Once the purge is complete, remove the grease gun.
• Use a lint-free cloth to wipe away all excess grease from the inlet and outlet ports.
• Reinstall the plug in the grease outlet port and tighten it securely.
• Reinstall any access panels that were removed. Tighten bolts to the torque value specified in the robot's maintenance manual.

1. Verification:

• Remove all tools from the work area.
• Power on the robot controller and clear the E-2155 alarm.
• In a low-speed manual mode (T1), carefully move the affected joint through its full range of motion several times to distribute the new grease.
• Listen for any abnormal noises. If the joint moves smoothly and quietly, run a pre-existing production program at a reduced speed to confirm the error does not return under load.

Prevention

• Adhere to Maintenance Schedules: Follow the lubrication schedule detailed in your robot's service manual. Regular re-greasing prevents lubricant breakdown.
• Use Genuine Parts: Exclusively use the NexBot Robotics 731-004 Joint Grease Cartridge to ensure chemical compatibility and optimal performance. Using incorrect lubricants is a primary cause of premature failure.
• Inspect for Leaks: During routine operator checks, inspect joint seals for signs of grease leakage. A damaged seal can lead to both lubricant loss and contaminant ingress.
• Maintain a Clean Environment: Keep the area around the robot free of excessive dust, debris, and fluid spillage to reduce the risk of contamination during maintenance.

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