# Influence of Drift on Robot Repeatability and Its Compensation
## 1 Introduction
In addition to detection and compensation of the 6 DOF position of the robot, it offers an option of quick identification and calibration of the whole workspace (camera subsystem or another periphery, for example) that is based on a pose detection [17]. Highly accurate robotic assembly is sensitive to temperature change. However, in [18], it was presented that by choosing a suitable position inside the robot workspace, a higher probability of assembling the parts correctly can be achieved. Error compensation, based on cokriging is proposed in [19]. The methodology presented in this article is used for an absolute accuracy error compensation and verified in robot drilling applications. The average positional error was reduced from 0.717 mm to 0.115 mm. Robot machining in the aerospace industry is a challenging task and considering the fact that the requirements for a robot precision are higher than the ordinary robot precision, a real-time pose control and guidance presented in [20] offers a solution. Few studies have presented another way of dealing with the thermal expansion repeatability error. The solution proposed by the [21] is to find an area inside the robot's working envelope in which the influence of thermal expansion on the repeatability is less significant. By defining the movement inside such an area or avoiding the surrounding area that is less suitable for precise movements, a higher level of repeatability could be reached. The differences between the most common robot kinematics, the 6 DOF, SCARA, and gantry structures and their thermal behavior is discussed in [22]. The article includes suggestions for compensation for thermal expansion errors. A simulation of thermal influence on robot structure is described in [23]. A thermally stable material used for the robot body would increase the resistance against the influence of gearbox heat on TCP precision. The theoretical study [24] presents this idea. The article follows up on our previous research [25], which described the principle of improving the repeatability by changing the robot-to-target approach direction. During experimental measurements performed for this research, we have found that the effect of drift was significant, and a time-consuming preheating of the robot was necessary to neutralize the influence of the changing temperature. Therefore, the question arose whether it was possible to compensate for the drift effect by knowing the actual temperature of the robot structure. We, therefore, present a hypothesis: knowing the current temperature of the robot structure, it is possible to compensate for the drift effect and thus eliminate the need to heat the robot to operating temperature before starting. It is generally accepted that an industrial robot is a universal device; however, when a robot is equipped with a single-purpose tool and performs a simple repetitive task for years, the robot can be considered as a part of a single-purpose process and thus a machine that is not universal in its application. Based on this assumption, the article is focused on increasing task-specific repeatability.