As a supplier of industrial robots, I understand the critical importance of accurate calibration for these machines. Calibration is not just a technical process; it’s the key to ensuring that industrial robots perform their tasks with the highest level of precision, efficiency, and safety. In this blog, I’ll share some in – depth insights on how to calibrate an industrial robot. Industrial Robot
Understanding the Basics of Industrial Robot Calibration
Before diving into the calibration process, it’s essential to understand what calibration means in the context of industrial robots. Calibration is the process of aligning the actual performance of the robot with its theoretical model. It addresses discrepancies that can arise due to various factors, such as manufacturing tolerances, mechanical wear and tear, and environmental influences.
There are two main types of calibration: geometric calibration and kinematic calibration. Geometric calibration focuses on the physical dimensions and positions of the robot’s components, such as the lengths of the robot’s links and the offsets between joints. On the other hand, kinematic calibration takes into account the relationship between the joint angles and the position and orientation of the robot’s end – effector. By combining these two types of calibration, we can achieve a highly accurate representation of the robot’s real – world behavior.
Pre – calibration Preparations
- Inspection and Maintenance
- Before starting the calibration process, it’s crucial to conduct a thorough inspection of the industrial robot. Check for any visible signs of damage, such as worn belts, loose bolts, or bent components. Perform routine maintenance tasks, such as lubricating joints and cleaning the robot’s workspace. A well – maintained robot is more likely to yield accurate calibration results.
- For example, if a joint bearing is worn, it can cause significant errors in the robot’s movement. Replacing the bearing before calibration ensures that the calibration is based on the robot in its optimal mechanical condition.
- Establishing a Reference Frame
- Define a stable and accurate reference frame for the robot. This reference frame serves as the basis for all subsequent measurements and calculations during the calibration process. In most cases, the factory – calibrated base frame of the robot is used as the reference. However, it’s important to verify the accuracy of this frame and, if necessary, correct any deviations.
- Use precision measurement tools, such as laser trackers or coordinate measuring machines (CMMs), to establish the reference frame. These tools can provide highly accurate measurements of the robot’s position and orientation relative to the reference frame.
Geometric Calibration Process
- Measurement of Link Parameters
- One of the first steps in geometric calibration is to measure the physical dimensions of the robot’s links. This includes the lengths of the links, the distances between joints, and the angles between the axes of adjacent joints. These measurements can be obtained using a variety of techniques, such as direct measurement with mechanical gauges or indirect measurement using sensors.
- For example, a laser – based measuring system can be used to measure the length of a robot link with high precision. By taking multiple measurements from different angles, we can reduce measurement errors and obtain a more accurate representation of the link’s actual length.
- Offset Calibration
- In addition to link lengths, it’s important to calibrate the offsets between joints. These offsets can occur due to manufacturing tolerances or misalignment during installation. Offset calibration involves determining the actual position and orientation of each joint relative to its nominal position.
- This can be done by using calibration fixtures or by performing a series of carefully planned movements with the robot. By comparing the actual position of the end – effector with the expected position, we can calculate the offsets and adjust the robot’s control parameters accordingly.
Kinematic Calibration Process
- Joint Angle Measurement
- Kinematic calibration starts with accurately measuring the joint angles of the robot. High – precision encoders are typically used to measure the rotation angles of the joints. However, these encoders can also have small errors, which need to be calibrated.
- To measure the joint angles more accurately, we can use external measurement devices, such as optical sensors or inertial measurement units (IMUs). These devices can provide independent measurements of the joint angles, which can be used to correct the encoder readings.
- End – effector Pose Measurement
- The position and orientation of the robot’s end – effector, also known as the pose, are crucial for kinematic calibration. The end – effector pose can be measured using a variety of methods, such as a laser tracker or a vision system.
- In a laser – tracker – based system, the laser tracker emits a laser beam that is reflected off a target attached to the end – effector. By measuring the time of flight and the angle of the laser beam, the position and orientation of the end – effector can be calculated accurately.
- Model Identification and Parameter Estimation
- Once the joint angles and end – effector poses are measured, the next step is to identify the kinematic model of the robot and estimate its parameters. This involves using mathematical algorithms to fit the measured data to the theoretical kinematic model.
- Optimization algorithms, such as the least – squares method, are commonly used to estimate the kinematic parameters. These algorithms minimize the difference between the measured end – effector poses and the poses predicted by the kinematic model.
Post – calibration Validation
After completing the calibration process, it’s essential to validate the results. This can be done by performing a series of test movements with the robot and comparing the actual performance with the expected performance.
- Accuracy Testing
- Use precision measurement tools to measure the accuracy of the robot’s movements. For example, measure the position and orientation of the end – effector at multiple points in the robot’s workspace. Compare these measurements with the nominal values to determine the accuracy of the calibration.
- If the measured accuracy does not meet the required specifications, it may be necessary to repeat the calibration process or to make further adjustments to the robot’s control parameters.
- Repeatability Testing
- Repeatability is another important aspect of robot performance. It refers to the ability of the robot to return to the same position and orientation repeatedly. Conduct repeatability tests by having the robot perform the same movement multiple times and measuring the variations in the end – effector’s position and orientation.
- A high – repeatability robot is more reliable and can be used for tasks that require consistent performance, such as assembly or welding.
Importance of Regular Calibration
Industrial robots are subject to continuous mechanical stress, wear, and environmental factors. These factors can cause the robot’s performance to degrade over time. Regular calibration is therefore essential to maintain the accuracy, precision, and reliability of the robot.
- Improved Product Quality
- Accurately calibrated robots can perform tasks with greater precision, resulting in improved product quality. For example, in a manufacturing process where parts need to be assembled with high precision, a well – calibrated robot can ensure that the parts are correctly aligned and joined, reducing the number of defective products.
- Increased Productivity
- Calibrated robots can operate more efficiently, reducing cycle times and increasing productivity. By eliminating errors and optimizing the robot’s movement, it can complete tasks faster, leading to higher throughput in the manufacturing process.
Contact for Industrial Robot Purchasing and Calibration Services
If you are in the market for an industrial robot or need calibration services for your existing robots, I’m here to assist you. Our company offers a wide range of industrial robots with advanced calibration capabilities. Our team of experts can provide you with detailed information on the calibration process and help you choose the right robot for your specific application.
Collaborative Robot Contact us today to start a discussion about your industrial robot needs. We’ll be happy to provide you with quotes, product specifications, and any other information you may require. Let us help you achieve the highest level of performance and efficiency with our industrial robots.
References
- Craig, J. J. (2005). Introduction to Robotics: Mechanics and Control. Pearson Education.
- Siciliano, B., Sciavicco, L., Villani, L., & Oriolo, G. (2010). Robotics: Modelling, Planning and Control. Springer.
- Leitão, P., & Restivo, F. (Eds.). (2016). Handbook of Research on Industrial Communication and Factory Automation. IGI Global.
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