Kinematic Calibration Of Delta Parallel Robot

The application and development of industrial robotics reflected the transforming direction of modern industry. There are a lot of benefits could be obtained by industrial automation, it means higher efficiency. Automation equipment can work in worse environment that human beings can never do, and the managers don’t ever need to worry about their emotional issues, which can rarely be controlled for human beings. The invention of robotics indicated the trend of transformation from specific equipment to universe and intelligent equipment. Delta robot is one of parallel mechanism. Its function includes conveying, sorting, packing, etc. It has been widely applied in industries such as:electronics, food, pharmacy, medical treatment, etc. However, according to the practical application and the market’s feedback information, robotics can hardly be utilized in areas when high precision is demanded. This is quite simple because of the low positioning accuracy of robotics. The fact is that the relative positioning accuracy of robotics can reach as high as0.05mm, but, there could be about several millimeters or even several centimeters deviation between their actual positions and ideal ones. There are many factors could bring this absolute positioning deviation:the manufacturing and assembling discrepancies, for instances. Because of this, robotics can hardly be competent for works like machine vision or off-line programing needed. Aimed at solving this problem, we tried to propose a new calibration method by studying on a3-DOF Delta parallel robot.Firstly, we obtained possible error terms by analyzing the kinematic module and every single critical component of Delta industrial robot.Secondly, we acquired that there must be some absolute positioning deviation of Delta robot’s end-effector by adding the error terms into its kinematic module. And then linearizing the kinematic equation to divide the error terms, therefore, we can use the absolute positioning deviation data to calculate Delta robot’s kinematic parameter errors. The absolute positioning deviation can be easily measured by a laser tracker once the transformation equation between the frame of a Delta robot and a laser tracker. In order to complete the calibration procedure, we need to modify the kinematic parameters in the controller. Besides, we compensated the manufacturing and assembling discrepancies during the calibration procedure, which makes the actual module can be conform to the ideal one as precise as possible.In the end, we have done an experiment utilizing the calibration method we proposed in this paper. As a matter of fact, the result turns out to be positive. The absolute positioning accuracy of the Delta robot for studying is significantly improved indeed.