Why Robot Calibration is Non-Negotiable
An uncalibrated or poorly calibrated IRB 6700 can introduce a host of problems that impact production efficiency, product quality, and overall safety. Precise calibration ensures that the robot's internal position references match its actual physical position, forming the foundation for all programmed movements and tasks.
Inaccurate Positioning
The robot may not reach programmed points precisely, leading to defects in tasks like welding, sealing, or material handling.
Path Deviations
The actual path taken might differ from the programmed path, risking collisions with fixtures, workpieces, or safety barriers.
Increased Wear & Tear
Inaccurate movements can put undue stress on motors, gears, and the robot structure, potentially shortening component life.
Safety Risks
Unexpected movements due to poor calibration pose a significant risk to personnel and equipment in the robot's operational area.
Key Insight
Understanding and correctly performing calibration procedures are vital for maintaining the IRB 6700's reliability and efficiency. Calibration is not just a maintenance task—it's a foundation for operational success.
Understanding Calibration Types: Standard vs. Absolute Accuracy
ABB offers two primary levels of calibration for the IRB 6700, each serving different purposes and precision requirements.
Standard Calibration
(Calibration Pendulum Method)
What it is
This is the fundamental calibration ensuring the robot knows its "home" position (all axes at 0 degrees). It aligns the internal resolver values (which measure motor rotation) with the physical position of each robot axis.
How it's done
Typically performed using the Calibration Pendulum toolkit. This method is highly accurate for establishing the robot's zero position.
Key Benefit
Ensures high repeatability. The robot can consistently return to the same taught points. Calibration data is stored on the Serial Measurement Board (SMB).
Absolute Accuracy Calibration
(Optional - CalibWare Method)
What it is
Builds upon standard calibration. It compensates for minor mechanical tolerances within the robot's structure and the deflection caused by the robot carrying a load. Its goal is high positioning accuracy in the Cartesian coordinate system (X, Y, Z world or tool coordinates).
How it's done
Requires the CalibWare software and measurement equipment. It generates detailed compensation parameters.
Key Benefit
Provides high absolute accuracy (also known as "true position" accuracy). This is crucial for applications requiring precise TCP (Tool Center Point) positioning relative to external fixtures or for reliable offline programming.
Key Differences
| Feature | Standard Calibration | Absolute Accuracy |
|---|---|---|
| Primary Focus | Joint space accuracy | Cartesian space accuracy |
| Best For | Taught-point applications | Offline programming, fixture-based tasks |
| Equipment Needed | Calibration Pendulum | CalibWare software + measurement equipment |
| Identification | Standard for all robots | Special sticker near identification plate |
Important Note
If a robot with Absolute Accuracy undergoes significant structural changes or repairs, a new Absolute Accuracy calibration is required to restore full performance. For many motor/gearbox replacements, a standard calibration might suffice, but Absolute Accuracy will be compromised until recalibrated.
When is Calibration Necessary?
The IRB 6700 system requires calibration intervention in several key scenarios. Recognizing these situations is crucial for maintaining robot accuracy and performance.
After Replacing Calibration-Affecting Components
Replacing motors or transmission parts changes the relationship between the motor resolver and the axis position.
Required: Standard Calibration (e.g., with Calibration Pendulum)
For Absolute Accuracy robots: Absolute accuracy will be degraded until a new Absolute Accuracy Calibration (with CalibWare) is performed
Loss of Revolution Counter Memory
This is a common scenario requiring immediate attention. The revolution counters track the number of full turns each motor has made. This memory is lost if:
- The SMB battery is discharged or disconnected
- A resolver communication error occurs
- An axis is moved manually while the controller power is off
- During the very first installation after connecting the robot to the controller
Required: Revolution Counter Update (see details in next section)
After a Robot Rebuild or Crash
Significant structural changes or repairs necessitate complete recalibration.
Required: Full Standard Calibration
For Absolute Accuracy robots: A new Absolute Accuracy Calibration
Proactive Approach
While calibration is mandatory in the scenarios above, regularly verifying the robot's zero position as part of routine maintenance is recommended as a proactive approach to detecting potential calibration issues before they impact production.
Critical Procedure: Updating Revolution Counters
Updating revolution counters is not the same as a full standard calibration, but it's a vital step to ensure the robot knows which turn each axis is on. An incorrect update is a common source of major positioning errors.
Why it's critical
The robot needs to know the absolute position of each axis, including how many times it has rotated. The calibration marks only show the position within one revolution. If the memory is lost (e.g., dead battery), the robot might think axis 4 is at 0 degrees when it's actually at 360 or 720 degrees.
The Revolution Counter Update Process
Step-by-Step Procedure
-
1
Manually Jog to Calibration Marks
Carefully jog each axis individually until its physical calibration marks align within the tolerance zone. Ensure you are moving the axis in the correct direction towards the mark as specified by the software or manual procedures.
-
2
Use the FlexPendant
- Navigate to
ABB Menu > Calibration - Select the correct mechanical unit
- Tap
Update Revolution Counters... - Acknowledge the warning about potential position changes
- Select the axis/axes you have correctly positioned at their marks
- Tap
Updateand confirm the final warning
- Navigate to
CRITICAL WARNING: Axes 4 & 6 Calibration Position
- For certain manipulators (including potentially variants of the IRB 6700 family), axes 4 and 6 have non-integer gear ratios.
- This means aligning the visual marks alone might not be sufficient. The axis could be visually aligned but actually be one full rotation (or more) off.
- ALWAYS verify the correct revolution count. Check the specific calibration values noted on a label on the robot (often on the lower arm, base, or frame).
- If calibration seems off after an update, try rotating the suspect axis (4 or 6) one full turn in either direction and perform the update again, then re-check against the marks and label values.
CAUTION: Incorrectly updating revolution counters will cause incorrect positioning and can lead to severe damage or injury. Double-check your work meticulously.
Verifying Calibration: The Essential Final Check
Before running any production programs after calibration or revolution counter updates, always verify the calibration position.
Using MoveAbsJ
Create a simple RAPID program with the following instruction:
MoveAbsJ[[0,0,0,0,0,0],[9E9,9E9,9E9,9E9,9E9,9E9]]\NoEOffs, v1000, z50, Tool0;Run this in manual mode at low speed. Observe if all axes smoothly move to their 0-degree position and check if the calibration marks align correctly.
Using the Jogging Window
In manual mode, select axis-by-axis jogging on the FlexPendant:
- Select each axis individually
- Jog to its 0-degree value displayed on the pendant
- Visually confirm that the calibration marks align
If the marks do not align correctly after commanding the robot to its zero position, the revolution counters may be incorrect, or a full standard calibration might be required.
Signs of Successful Calibration
- All axes move smoothly to their 0-degree positions
- Calibration marks align correctly
- No unexpected resistance or sounds during movement
- The robot can repeatedly return to the same position with high precision
Calibration Workflow Visualization
The following diagram illustrates the decision process for determining when and what type of calibration is needed for your IRB 6700 robot.
flowchart TD
A[Robot Status Check] --> B{Calibration
Issue?}
B -->|No| C[Normal Operation]
B -->|Yes| D{What type
of issue?}
D -->|Component Replacement| E[Standard Calibration
Required]
D -->|Revolution Counter Loss| F[Revolution Counter
Update Required]
D -->|Robot Rebuild/Crash| G[Full Recalibration
Required]
E --> H{Has Absolute
Accuracy?}
G --> H
H -->|No| I[Perform Standard
Calibration]
H -->|Yes| J[Perform Standard
Calibration]
F --> K[Manually Align
to Calibration Marks]
K --> L[Update Revolution
Counters via FlexPendant]
J --> M[Absolute Accuracy
Calibration Required]
I --> N[Verify Calibration
with MoveAbsJ]
L --> N
M --> N
N --> O{Verification
Successful?}
O -->|Yes| P[Return to
Production]
O -->|No| Q[Troubleshoot
and Repeat]
Q --> B
Calibration Confidence = Robot Performance
Accurate calibration is paramount for the safe, precise, and efficient operation of your ABB IRB 6700 robot. By diligently following correct procedures and verifying results, you ensure your IRB 6700 operates at its peak potential, maximizing both precision and valuable uptime. Always refer to the official ABB documentation for the specific calibration method you are using.
Advanced Calibration Considerations
Environmental Factors
Temperature fluctuations can subtly affect calibration, particularly Absolute Accuracy. For high-precision applications, perform calibration in a stable temperature environment close to typical operating conditions. Significant thermal changes may require recalibration.
Foundation Levelness
Foundation levelness impacts calibration quality. An uneven foundation affects repeatability relative to factory calibration. For Absolute Accuracy, foundation levelness is critical, as it fundamentally alters the robot's posture relative to the world coordinate system.
Payload Definition Accuracy
Accurate payload definition (weight, center of gravity) significantly impacts positioning during operation. Absolute Accuracy compensates for arm deflection under load, but relies on accurate payload data. Incorrect payload definitions lead to TCP positioning errors, especially at longer reaches.
SafeMove Integration
Safety systems like SafeMove rely on accurate calibration data. Poor calibration can cause false safety triggers or, more dangerously, fail to trigger when needed. After any calibration activity, always re-validate configured SafeMove zones and functions.
Training Recommendation
Performing calibration, especially standard (fine) calibration with tools like the Calibration Pendulum or Absolute Accuracy calibration with CalibWare, requires specific knowledge and skill. ABB offers specialized training courses covering robot maintenance and calibration procedures. Investing in proper training ensures procedures are performed correctly, efficiently, and safely.
In Conclusion
Calibration is not just a maintenance task—it's the foundation for your IRB 6700's performance, safety, and longevity. By understanding the different calibration types, recognizing when calibration is needed, and following proper procedures, you ensure your robot operates at its full potential.
Remember that calibration data is valuable—back it up regularly and treat calibration tools as the precision instruments they are. Always verify your calibration results before returning to production to avoid costly errors or safety issues.
A well-calibrated robot is a reliable, precise, and productive asset to your operation.