## 1 Introduction  
Calibration is a technique that is used to maximise robot positioning accuracy. Owing to the cost and mechanical structure of industrial robots, it is becoming impossible to change the hardware structure of the robot to obtain improved positional accuracy. Precise accuracy was not very necessary in the beginning era of robotics, but because of the increase in robot population and the demands of industry for efficiency and repeatability of the robot, it is currently becoming a sought-after area of research.  
There are numerous types of errors that can deviate a robot from its original intended position. Some are geometrical and some are nongeometrical, for example, backlash, wear and tear, etc. ISO 9283 also measures the robot performance by using various parameters that include accuracy, repeatability, pose, variation, drift, path, trajectory, etc. [1]. The project also tries to apply the calibration mechanism by using this standard, which guides use of a high-accuracy, large-volume 3D or 6 DOF measurement system to test a robot's performance statically and dynamically.  
There are ranges of errors that can affect the positional accuracy of the robot. These can be:  
* Dynamic/systematic--via servo system, friction, inertia, etc.;
* Static--effected by the environment, e.g., load, temperature, and noise;
* Kinematics--related to the geometrical error of robot mechanics.  
Calibration generally has three levels that depend on the application and its requirements [2]:  
Level 1 includes the joint level that needs to determine the relationship between actual joint displacement and its signal generated by its transducer, which is known as mastering. This is similar to image restoration or factory reset on a machine.  
Level 2 includes kinematics modelling. To perform this type of calibration, the actual rather than assumed kinematics/geometry of the entire robot must be well known.  
Level 3 includes the nonkinematics or nongeometrical error handling, which affects the position of the robot; these can be friction, noise, temperature, etc.  
In the early days of robotics, the maximum error of a robot was corrected using the mastering/remastering technique, and it is often recommended by robot manufacturers as well to remaster the robot after performing certain activities, for example, change of motor or gearbox. It is a known fact that 97% of positional accuracy can be achieved by removing the position-zero error of robots, and the solution is remastering [3].  
However, it is becoming impossible to remaster the robot after performing every single task, and remastering should not be used to achieve positional accuracy without a reason, for example, severe collision, relocation or disassembly of the robot. Remastering deletes all the tool and base calibrations. Because of the change of era and demand for accurate position during runtime, especially in the aerospace sector, it is now becoming necessary to achieve the correct position during the execution of the program on the robot controller. Calibration needs to correct the position of the robot, which can be affected by different kinds of errors, ranging from wear and tear to kinematics.