Orientational precision of a delta manipulator under drone

Introduction
This research focuses on compensation of orientational movements of a delta manipulator attached under a drone. The broader objective of this work is a drone which manufactures small components. The tool is attached to the end effector of the manipulator. The technology utilized in such systems so far is additive manufacturing, hence, these systems are termed as mobile additive manufacturing devices.

A delta manipulator is constructed and attached under a drone which compensates for small orientational movements of the drone during hover so as to keep the tool tip stable during manufacturing.

Methods
The method used is to separate the control of the tool i.e. print head from the drone. This is achieved by mounting a delta manipulator under the drone. The print head is attached on the end effector of the delta manipulator. Therefore, the drone hovers and the end effector is responsible for the translational movement of the print head. However, during hover, there is some translational and orientational movement. Since the delta manipulator is a 3 degree of freedom robot, it can not directly compensate for orientation. Hence, the orientation is converted to translation and then the proportional controller compensates for it. MPU 6050 is used to measure the roll and pitch angles and the corresponding displacements of the tool tip are calculated and given as input to the controller.

Results
The data measured by the sensor MPU 6050 is almost insensitive to the effect of vibrations. The controller seems to actively compensate for small orientations. The compensated trajectory obtained with Kp = 0.96 closely matches the reference trajectory (without orientation).

Conclusion
The RMS error decreased from 1.707 for Kp = 0.1 to 0.25 for Kp = 0.96. These results show that Kp = 0.96 performs much better than Kp = 0.1. However, these results are generated by the software. Further, VICON motion capture system can be used to validate the results with hardware.