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Robots are not omnipotent, the more projects you do, the more you feel the limitations of the robot, not as powerful as we think, robots are generally used in occasions where the accuracy is not high, such as handling, welding, painting, etc., and for cutting, assembly, etc. is not enough, the root cause of this problem is that the accuracy of the robot repeat path is too low, far less than the manipulator or linear module.

Before we engaged in a cutting project, the cutting tool was fixed at the end of the robot, and the robot was used to complete the cutting, but when the actual execution was performed, it was found that the trajectory of the robot cutting was crooked, not a very straight line at all, and the expected effect was too different.

In the robot programming instructions, there are straight walking instructions, such as the straight line instruction of the Japanese FANUC robot is L, such as L P[1] 200mm/sec FINE, but the straight line command can not let the robot out of the ideal straight line, from point A to point B of the straight line, programming only gives the coordinates of point A and point B, the middle point is the control system using the interpolation algorithm to find out, interpolation, it involves a subdivision problem, the smaller the subdivision, the closer the straight line goes, therefore, The robot is not actually walking an absolute straight line, but a line fitted with many points, and it is normal for this line to have a deviation, and the deviation is still very large, this deviation is the accuracy of the robot's repeated path.

Let's take a look at the difference and connection between repeating positioning accuracy and repeating path accuracy.

Definition of repeatability (RP): The degree of consistency of the actual pose after repeating the response from the same direction n times for the same command pose.

The repeatability is the distance size shown in below.

It was pitted, the robot could not walk in a straight line, in addition to positioning accuracy, it turned out that there was a repeating path accuracy

Definition of repeat path accuracy (RT): the degree of consistency between real and real trajectories when the same command trajectory is repeated n times.

The repeating path accuracy is the distance size shown below.

It was pitted, the robot could not walk in a straight line, in addition to positioning accuracy, it turned out that there was a repeating path accuracy

When selecting a robot, you have to look at the robot repeat positioning accuracy, such as the Japanese FANUC R-2000iC/165F repeat positioning accuracy is ± 0.05, in fact, in addition to the repeat positioning accuracy, there is also a repeat path accuracy, some applications have requirements for the robot repeat path accuracy, but the FANUC official website does not provide repeat path accuracy, at present I only know that ABB is to provide repeat path accuracy information, such as ABB IRB4600 The repeatability accuracy is 0.05mm, but the repeatability path accuracy is 0.46mm, the difference between the two is an order of magnitude, as shown in the figure below:

What are the problems with poor repeatability of the path? As long as it involves the application requirements related to the trajectory path, be careful, especially the application with high precision requirements, avoid the direct use of robots, and give priority to linear modules.

The concept of repeated positioning accuracy is very common, such as various automated production line tenders, there must be robot repeat positioning accuracy requirements, but many people only know the skin, do not know the specific meaning, even many robot manufacturers of technicians, the explanation of repeated positioning accuracy is also vague, and repeat path accuracy, know fewer people, as a technician, must know the reason for it, so that it can be done handily.