The terms  “precision” and “accuracy” are often tossed around interchangeably in everyday language, despite representing distinct concepts. In the world of robotics, understanding this difference is crucial for developing well-functioning robotic applications. Not every task demands pinpoint accuracy, for example, but most require precision. This blog dives into the nuances of precision and accuracy, unpacking their importance and how they influence the diverse landscape of robotic applications.

 

Precision: The Art of Consistent Repetition

Imagine a robotic arm meticulously assembling a complex circuit board. Precision, in this context, refers to the robot’s remarkable ability to repeat the same movement consistently. Each delicate component placement, each intricate soldering maneuver – these actions are executed with minimal variation, ensuring a uniform and reliable outcome.

Repeatability emphasizes a robot’s ability to return to a previously taught position consistently, but typically refers to taking the same approach path each time. Imagine a robot meticulously placing delicate components on a circuit board. Here, high repeatability translates to consistently placing components with minimal deviation, leading to a reliable and efficient assembly process

 

Accuracy: Hitting the Bullseye Every Time

Accuracy, on the other hand, signifies a robot’s ability to perform a movement and achieve the exact intended result, without online teaching. It’s about going beyond consistent repetition and ensuring the movement translates to the desired outcome.

 

Here’s how accuracy manifests in robotics.

 

Absolute Accuracy reflects a robot’s ability to position its end-effector (the tool attached to its arm) at a specific, calculated location with respect to the robot’s base frame. This is important for tasks where the locations to be visited are calculated and cannot be taught online, such as in material removal applications.

 

Relative Accuracy is similar to absolute accuracy but refers to the robot’s ability to accurately perform small movements with respect to the end-effectors current location. For instance, relative accuracy is important when picking parts on a grid wherein, parts are separated evenly, and the positions can be calculated, from the positions of a few corner points that are taught. Relative accuracy is also crucial, for example, when you are testing a sensor and want to rotate it exactly 90 degrees about a given axis.

 

Both absolute and relative accuracy are essential in robotics, but their importance depends on the specific application and task requirements. It is also important to note that relative accuracy is better than absolute accuracy.

 

The Significance of the Distinction: When Does Each Matter?

Understanding the difference between precision and accuracy holds immense value when determining if a robotic system is well-suited for a particular application. Here’s a breakdown of when each concept takes center stage.

 

High precision is necessary for applications that require high repeatability. Repetitive tasks like pick-and-place operations or assembly line processes often prioritize precision over pinpoint accuracy. As long as the robot consistently picks an object from a similar location and places it in a designated area, the exact coordinates might not be critical. Consistency is key in these scenarios, ensuring a smooth and efficient workflow.

However, what is crucial to understand is that the robot’s repeatability quoted by the manufacturer is not the repeatability that you will consistently achieve in your actual robotic application. Factors like warmup of the robot, the end-effector, the speed of execution, and the rigidity of the structure on which the robot is fixed will lead to an order of magnitude deterioration of the actual repeatability. For example, if a robot’s repeatability as quoted by the manufacturer is 10 micrometers (which is measured with a special test where only 30 repetitions are executed), you may end up having 0.5 mm of deviation from the end-effector location taught y to the actual visited location after several days of repetitions.

In other words, never assume that a robot’s precision is too good for your application solely based on the robot’s specifications.

 

Accuracy is necessary for tasks that cannot rely on teaching every single point. Applications that require accuracy include testing, inspection, material removal, or instances where you may be swapping robots. 

 

 

Confused by the accuracy vs. precision debate?  We can help!  Contact us to discuss the perfect solution for your application

 

Calibrating for Enhanced Performance

Robot calibration plays a crucial role in achieving optimal performance. It’s akin to fine-tuning a musical instrument – adjustments are made to ensure the system performs at its best. In the context of robotics, calibration involves the following steps.

 

Refining the Internal Model: A robot relies on an internal mathematical model to translate programmed movements into real-world actions. Calibration helps identify and address discrepancies between this model and the physical robot. Factors like manufacturing tolerances and slight variations in component assembly can influence accuracy.  Factors normally unaccounted for in the nominal mathematical model of the robot, such as the flexibility of its joints, are now included in the new refined model.

 

Measurements: Next, the actual robot’s end-effector position is measured accurately with a metrology tool such as a laser tracker for various joint positions.

 

Identification: Finally, optimization algorithms are used to identify the set of parameters of the new mathematical model that minimize the deviation between the actual end-effector position and the position according to the new mathematical model. This set of parameters is called the robot’s signature.

 

Final implementation: Finally, the new mathematical model with the specific robot’s signature is implemented in the robot, replacing the old simplistic mathematical model.

 

Mecademic Calibration

Mecademic now offers an out-of-the-box calibration service for the Meca500 industrial robot arm. Thanks to the compact size of our robot, we use a Coordinate Measuring Machine (CMM) for the calibration process, which is an order of magnitude more accurate than a laser tracker. Our service provides up to x10 more accuracy on the Meca500, Improving performance, mitigating risk and reducing deployment times.

 

Unlock the full potential of your Meca500 – contact us today to find out whether you would benefit from calibration.