Without proper calibration, most industrial robots don’t have the accuracy required for precision tasks. Robot calibration transforms the high repeatability of robots into reliable accuracy. But what are the best tools for calibration?
There are a few types of calibration, each suited to different levels of precision. Some solutions are accessible within your programming software, while others might require extra sensing hardware or the services of a robot calibration provider.
Whether you only need basic Tool-Center Point calibration or full robot calibration, this article gives you the essential introduction to finding the right robot calibration for you.
Why Robot Calibration Matters: Accuracy vs Repeatability
The distinction between accuracy and repeatability is fundamental in robotics and shows why calibration is necessary.
Here’s what the two terms mean:
- Repeatability — The robot returns to the same position every time its control program sends the same command. For example, if you instruct a welding tool to the point (1,1,1) and it instead moves to (1,2,1), the robot will always move to (1,2,1). Industrial manipulators tend to have high repeatability.
- Accuracy — The robot moves to the exact position specified in the command. In our example, sending the welding tool to (1,1,1) will cause it to move to exactly (1,1,1). Industrial manipulators usually require calibration to achieve high accuracy.
If you are paying attention to our welding example above, you will notice that it isn’t complicated to turn a high-repeatability robot into a high-accuracy one. You just need to add (0,1,0) whenever the robot moves to position (1,1,1). This is a simplified example of calibration.
What causes lower accuracy in robots?
You might think… Why don’t we just build accurate robots in the first place? In practice, this wouldn’t actually be desirable.
Research into kinematic calibration shows that most positioning errors stem from slight geometrical differences between the robot’s theoretical model and the real physical structure. These are influenced by many factors, including manufacturing tolerances, component wear, and part replacement.
Practically, this means that robots will always require calibration to achieve consistent, high precision. Even if a robot is highly accurate out of the box, its dimensions will drift over time and it will need to be recalibrated.
TCP Calibration vs Full Robot Calibration: Which Do You Need?
Most users don’t need the most accurate robotic system possible. There are different ways to calibrate a robot, with different costs and complexities depending on your needs.
Here are the three basic calibration options in most cases:
Option 1: No Calibration
It’s worth mentioning that some tasks might not require you to calibrate your robot. For rough tasks like heavy-duty palletizing, material handling, or pick and place, the robot’s factory precision might be sufficient.
As long as you remember that calibration might be necessary in the future, as the robot mechanism ages, you may be able to avoid calibrating for now.
Option 2: Tool Center Point (TCP) Calibration
For most applications, a simple TCP calibration is more than enough. This involves using an off-the-shelf calibration tool to correct for the TCP at different points in the robot workspace.
This type of calibration is suitable for tasks that require a medium level of accuracy, like pick and place, surface finishing, and welding.
Option 3: Full Robot Calibration
Finally, full kinematic calibration is a four-step process for modeling, identifying, and compensating for subtle variations in the robot model.
Full robot calibration is necessary for tasks that require high positional accuracy, such as laser cutting, precision drilling, and coordinate measuring.
Find out about our full calibration service on our calibration page.
Best Robot Calibration Tools Available: A Comparison
What’s the best option for robot calibration? This table shows some of the most common options, along with their advantages and drawbacks.
| Tool Category | Accuracy | Compatibility | Key Features |
|---|---|---|---|
| Automated TCP Calibration Tools (e.g. TwinTool) | Good Accuracy | 1400+ robots from 90+ manufacturers | Uses off-the-shelf linear gauge sensors (Mitutoyo, KEYENCE, Sylvac); Wizard-guided 3-step process; No programming required. |
| Laser Trackers | High Accuracy | Universal | Tracks end effector position; Used for TCP and full calibration; Higher cost; Best for stringent tolerances. |
| Full Robot Calibration Service | Up to 0.200 mm accuracy | 1200+ robot models | Complete kinematic calibration (30 parameters); Completes in under 20 minutes; Automated collision avoidance. |
How Frequently Should a Robot Be Calibrated?
Robot calibration is not usually a onetime task. It should form part of your ongoing maintenance to keep your robot application running at top performance.
Various factors contribute to the degradation that reduces robot accuracy over time, including:
- Component wear — Like all mechanical components, robots will wear over time, causing changes to the robot model. Calibration will be necessary when purchasing a second-hand robot, and accuracy should be reassessed regularly.
- Part replacement or repair — Any mechanical change to the robot will usually require calibration, such as after replacing a part or repairing a damaged one.
- Environmental changes — Factors like temperature and humidity can affect the robot’s mechanical structure (studies show that temperature changes contribute to 0.1% of total robot positioning error).
- New tools or end effectors — A new tool will usually require some TCP calibration, especially if the tool is to be used for a high-precision task.
- New programming tools — Moving to a new programming system may also require calibration. However, if you have an existing kinematic model for your calibrated robot, you may be able to copy these values across and use them in the new software using dedicated calibration tools.
The best way to account for such factors is simply to include accuracy testing in your ongoing robot maintenance. This data will help you decide if and when you need to calibrate.
How to Find a Robot Calibration Solution With the Best Results
What’s the best calibration solution? The one that matches your current needs for accuracy.
A common mistake people make is to invest in a full robot calibration when a simple TCP calibration would be sufficient. Remember that you only need enough accuracy for your specific task and no more. A tool like RoboDK TwinTool is an ideal middle ground.
Start by measuring your current robot’s accuracy and check out our calibration service if you think you need full robot calibration.
Which of your robot applications do you think needs calibration? Join the discussion on LinkedIn, Twitter, Facebook, Instagram, or in the RoboDK Forum.. Also, check out our extensive video collection and subscribe to the RoboDK YouTube Channel
