Introduction
Replacing a gearbox on an ABB IRB 6700 (specifically Axes 1, 2, 3, or 6) is a significant repair task that demands precision, adherence to safety protocols, and the correct tooling. While the robot is built for durability, gearboxes can require replacement due to wear, damage from collisions, or lubricant issues.
Crucial Disclaimer
This article provides a general overview applicable to Axes 1, 2, 3, and 6. However, procedures vary significantly between these axes. Always consult the specific, up-to-date ABB IRB 6700 Product Manual section for the exact axis you are working on before commencing any work. This task should only be performed by trained and qualified personnel.
Gearbox Replacement Process Overview
I. Pre-Repair Essentials
Before touching the robot, thorough preparation is paramount to ensure safety and success.
1 Safety First - Lockout/Tagout (LOTO)
- Absolute Priority: Ensure all energy sources are completely isolated and de-energized. This includes electrical power (main switch OFF and locked), hydraulic pressure, and pneumatic pressure.
- Verification: Physically verify that power is off. Never assume.
Safety Tip: Always locate and operate the correct main power switch for your controller configuration before starting work.
2 Gather Tools & Parts
Required Components
- Correct Gearbox: Verify you have the exact replacement gearbox specified for the axis and robot model/serial number.
- Consumables: New O-rings, seals, correct lubricant type and quantity, locking liquid (Loctite 243/2701/574).
Specialized Tools
- Lifting accessories (rated for component weights)
- Guide pins (M10, M12, M16 - essential for alignment)
- Calibrated torque wrenches (critical for correct tightening)
- Leak-down tester
ESD Protection:
The SMB (Serial Measurement Board) and potentially other electronics are sensitive. Use ESD wrist straps connected to the designated point.
3 Robot Positioning
- Manoeuvre the robot into the specific starting position detailed in the manual for the axis being repaired.
- Gravity & Stored Energy: Be acutely aware that robot arms can move unexpectedly when brakes are released or components are removed due to gravity or stored energy in balancing devices.
Critical Safety: Secure axes as instructed (e.g., using lock screws like M16x120 for Axis 2/3). Failure to secure moving parts can result in unexpected movement and serious injury.
4 Documentation
Have the latest revision of the IRB 6700 Product Manual, Spare Parts List, and potentially Circuit Diagrams readily available. Check ABB Library for updates.
II. The Gearbox Replacement Process
Remember: These are common steps. The sequence and details differ per axis. Always follow the axis-specific procedure in the manual.
1 Drain Gearbox Oil (if applicable)
For relevant axes (e.g., Axis 1, 2, 3, 6), drain the oil before removing the motor or gearbox. Heat the oil slightly by running the robot (if safe) for easier draining. Dispose of used oil correctly.
Tip: Handle lubricants with care, use correct types, and dispose of waste oil responsibly.
2 Disconnect Motor & Cables
Carefully disconnect motor power and signal cables. Remove cable gland covers, noting orientation. Protect connectors from damage and contamination.
3 Remove Motor (Axis-Specific)
Procedures vary between axes. Some axes require motor removal for gearbox access. Use guide pins, lifting accessories, and potentially removal tools as specified in the manual.
Important: Support the motor's weight; do not let it hang by cables.
4 Access & Unbolt Gearbox
Remove covers or other components blocking access. Use guide pins. Progressively loosen and remove attachment screws, potentially leaving one or two loosely fitted for safety until lifting gear is attached.
5 Lift & Remove Old Gearbox
Attach the specified lifting accessory securely. Take the weight, remove final screws, and carefully lift/move the old gearbox using appropriate equipment (crane, forklift adapter).
Warning: Note the significant weight (e.g., Axis 1 gearbox is 92kg, Axis 3 is 56kg). Use proper lifting techniques and equipment rated for the load.
6 Clean & Prepare Surfaces
Thoroughly clean all mating surfaces on the robot structure and the new gearbox. Remove old sealant/gasket material, paint residues, and any contaminants. Inspect surfaces for damage.
7 Install New Gearbox
- Apply new O-rings/seals (lubricate lightly with specified grease). Ensure correct seating.
- If specified, apply sealant (e.g., Loctite 574) to mounting surfaces.
- Using the lifting accessory and guide pins, carefully position the new gearbox. Ensure correct orientation.
- Mate the gearbox, ensuring alignment (use alignment tool for Axis 1 if needed).
- Insert and progressively tighten attachment screws in a criss-cross pattern to the specified torque using a calibrated torque wrench.
Crucial: Using incorrect torque values can lead to premature failure or leaks.
8 Reassemble
Refit the motor (if removed), ensuring correct pinion engagement and using new, lubricated O-rings. Tighten motor screws to specified torque. Reconnect cables, refit covers, cable brackets, DressPack components, etc.
9 Refill Gearbox Oil (if applicable)
Refill with the correct type and quantity of oil. Check the oil level plug/indicator as per the manual.
Axis-Specific Considerations
Axis 1 Gearbox (Base)
Challenge: This is the foundational axis. Misalignment during installation can propagate errors throughout the entire robot's workspace.
Key Step: The use of an aligning tool ensures the gearbox is perfectly centered relative to the robot base frame before final tightening.
Axis 2 & 3 Gearboxes (Lower & Upper Arm Pivot)
Challenge: Direct interaction with the high-tension balancing device springs. This is the most safety-critical aspect.
Key Step: The unloading/restoring procedure for the balancing device must be followed precisely using the correct ABB tool.
Axis 6 Gearbox (Wrist Flange)
Challenge: Located within the compact wrist assembly. Working space can be tighter, and cable routing is more intricate.
Key Step: Careful management of the axis 5/6 motor cables and potentially DressPack cabling during removal and installation.
III. Post-Replacement Verification
Leak-Down Test
After reassembly, perform a leak-down test to verify seal integrity. Pressurize the gearbox moderately (typically 0.2-0.25 bar) and monitor for pressure loss. Use leak detection spray if necessary.
Recalibration
Revolution Counters
Updating revolution counters is essential after replacing motors or gearboxes. Use the FlexPendant procedure. Failure to do so will result in incorrect robot positioning.
Standard Calibration (Pendulum)
Depending on the extent of the repair, a full standard calibration might be advisable to ensure optimal accuracy.
Absolute Accuracy (If Applicable)
If the robot has the Absolute Accuracy option, a new AbsAcc calibration might be required for optimal performance, although standard calibration often suffices after component replacement.
Final Checks & Test Run
- Double-check all fasteners, connections, and covers.
- Perform the "First Test Run" procedure with extreme caution, starting at low speed in manual mode, ensuring no personnel are inside the cell.
- Verify smooth movement and correct positioning.
Calibration: More Than Just Updating Counters
Simply updating the revolution counters tells the controller the robot's current zero position after reassembly. However, replacing a major component like a gearbox can subtly alter the precise relationship between the motor's rotation and the arm segment's actual angle.
Why Standard (Pendulum) Calibration is Recommended
- Purpose: This method refines the resolver offset values, ensuring high accuracy relative to the robot's own base frame.
- Why? Manufacturing tolerances in the new gearbox, slight shifts during assembly, or minute differences in mounting can affect the precise zero angle. Standard calibration compensates for these, restoring optimal relative accuracy.
- It's often considered best practice after such a major component change.
IV. Critical Considerations & Pro Tips
Axis Variation is Key
Re-emphasize that Axes 1, 2, 3, and 6 have distinct procedures due to their location, function, and associated components (like the balancing device for Axis 2/3). Never assume similarity.
The "Why" Behind Key Tools & Procedures
Guide Pins (Essential)
The manual frequently specifies using guide pins (M10, M12, M16 depending on the interface) when removing/installing heavy components.
Why Use Them?
- Alignment: They ensure precise alignment between components.
- Damage Prevention: They prevent scraping or gouging of precision-machined mating surfaces.
- Safety & Control: They provide controlled guidance, reducing risk during handling.
Removal Tools
These threaded tools (often resembling long bolts) are used to press a component out of its fitted position.
Why Use Them?
Components can be tightly fitted due to precision tolerances or corrosion. Using these tools applies even pressure, preventing component skewing or damage that hammering or prying would cause.
Gearbox Lubrication: Best Practices for Longevity
Correct Type is Non-Negotiable
The manual stresses using the specific oil type listed in the Technical reference manual - Lubrication in gearboxes. Different gearboxes on the same robot might even use different oils.
Using the wrong type can lead to:
- Incorrect viscosity at operating temperature (poor lubrication, overheating).
- Seal incompatibility (leaks).
- Additive conflicts (reduced lubricant life, potential corrosion).
- Foaming or aeration issues.
Fill Level Importance
-
Underfilling
Leads to inadequate lubrication, increased friction, overheating, and rapid wear.
-
Overfilling
Can cause churning (excessive heat generation, power loss), pressure buildup leading to seal failure and leaks, and potential foaming.
Adhere strictly to the oil level check procedures (using level plugs) after filling.
O-Ring Lubrication
When lubricating O-rings (e.g., on motor covers) with grease (like 3HAB3537-1), apply only a thin, even film.
Excessive grease can attract dirt or hinder proper seating. The goal is smooth installation without pinching or tearing.
Beyond Static Lockout: Hazards During the Process
While LOTO addresses electrical/pneumatic/hydraulic energy, significant mechanical risks exist during the disassembly and assembly:
-
Component Shifts During Fastener Removal
Even with guide pins, removing the final retaining bolts from a heavy component like a gearbox can cause a slight shift or rotation due to uneven weight distribution or residual tension.
Solution: Maintain control and ensure lifting equipment takes the load before removing the last fastener.
-
Unexpected Movement During Lifting
When lifting a component, ensure the lift is perfectly vertical. Any sideways pull can cause unexpected swinging or binding on guide pins.
Solution: Clear the surrounding area completely. Use tag lines if necessary to control the load.
-
Pinch Points
Be constantly aware of pinch points between the component being moved and the robot structure, lifting gear, or temporary supports.
Solution: Keep hands and feet clear during lowering/raising operations.
V. Common Mistakes & Pitfalls to Avoid
Based on the procedures and potential complexities, here are some common mistakes technicians might encounter during an IRB 6700 gearbox replacement:
Inadequate LOTO
Failing to isolate all energy sources (electrical, pneumatic, hydraulic) or neglecting to verify the zero-energy state before starting work. This is a critical safety failure.
Ignoring Axis-Specific Procedures
Treating all axis gearbox replacements identically. Failing to account for the balancing device on Axes 2/3 or specific access/alignment needs for other axes is dangerous and can lead to errors.
Incorrect / Uncalibrated Torque
Applying incorrect torque values to fasteners. Over-tightening can strip threads or damage castings; under-tightening leads to leaks, vibration, and potential component loosening.
Skipping the Leak-Down Test
Assuming the seals are fine after assembly without performing the mandatory leak-down test. This can lead to lubricant loss, contamination ingress, and premature gearbox failure soon after the repair.
Forgetting Revolution Counter Updates
Neglecting to update the revolution counters via the FlexPendant after replacing a motor or gearbox. The robot will not know its true position, leading to significant positioning errors and potential collisions upon program execution.
Improper Handling of Balancing Device
Attempting to unload or restore the balancing device without the correct, specified ABB tools or bypassing safety steps. This is extremely hazardous due to stored spring energy.
VI. Recognizing Potential Gearbox Issues
While this guide focuses on replacement, recognizing early warning signs can sometimes allow for planned intervention rather than emergency repair:
| Warning Sign | Potential Indication | Detection Method |
|---|---|---|
| Increased Noise/Unusual Sounds | Bearing wear, gear tooth damage, or lubrication breakdown | Auditory observation during operation |
| Excessive Vibration | Bearing issues or developing backlash | Physical observation, vibration analysis |
| Positioning Inaccuracy/Drift | Excessive backlash or wear within the gearbox | Program execution monitoring, calibration checking |
| Temperature Increase | Lubrication problems or increased internal friction due to wear | Thermal imaging, temperature sensors |
| Leaks | Seal issues, pressure problems, bearing wear causing shaft movement | Visual inspection around gearbox seals and mating surfaces |
| Increased Motor Current | Increased resistance from a failing gearbox | Controller monitoring, current measurement |
Note: These signs require investigation. Sometimes issues might stem from the motor, cabling, or programming rather than the gearbox itself. However, recognizing these symptoms prompts closer inspection and potential scheduling of maintenance before a critical failure occurs.
VII. Safety Recap
LOTO
Non-negotiable. Verify zero energy state before beginning work.
Stored Energy
Be aware of springs (balancing device) and potential gravitational forces.
Heavy Loads
Use appropriate lifting gear and practices. Never allow personnel under suspended loads.
Lubricants
Use correct PPE (gloves, glasses) and handle/dispose of responsibly.
ESD
Protect sensitive electronics with proper ESD safety measures.
Post-Repair Test Run
Conduct with extreme caution from a safe location, ensuring no personnel are in the work cell.
Conclusion
Replacing an axis gearbox on the IRB 6700 is a complex but manageable task for qualified technicians equipped with the right tools, parts, and documentation. Prioritizing safety, meticulous preparation, adherence to axis-specific procedures, and thorough post-repair verification are essential for a successful and reliable repair.
Always refer to the official, current ABB documentation for the specific axis before starting work.