Design and implementation of a two-axis micro-manipulator to enhance the gripper positional accuracy of a single flexible link

Accurate and versatile robots are required to perform advanced assembly and manufacturing tasks. To improve the end effector positional accuracy of lightweight robot arms, a two-axis micro-manipulator is mounted between the robot wrist and its manipulator. The rationale is to reduce the wrist sensitivity to the structural deflections of the robotic manipulator.; In an attempt to separate the problem of the end-of-arm deflections from the overall control problem of multi-link systems, the micro-manipulator is tested on a single flexible link. A laser head with a dual axis photodetector is used to provide direct measurements of the transverse deflections at the free-end of the beam and to detect mechanical inaccuracies caused by manufacturing imperfections and assembly misalignment.; The advantages of the integrated system of the micro-manipulator with a single compliant beam are demonstrated and compared to the one without the micro-manipulator for two different control schemes, "rigid body controller (RBC)" and "rigid and flexible motion controller (RFMC)".; Both theoretical and experimental results have proven the capability of the micro-manipulator in significantly improving the gripper positional accuracy. Furthermore, it was demonstrated that the micro-manipulator tends to complement rather than overlap the efforts exerted by the host beam controller.; The experimental results have revealed the significant adverse effects of the backlash in gearing on the overall performance of the macro- and micro-manipulators. To address this problem, the dynamic model of the macro- and micro-manipulators is modified to include the dynamics of joint actuators along with the effects of backlash in the indirect drive mechanism of the compliant beam.; A general method is developed to handle the dynamic characteristics of backlash in gearing. It entails the derivation of a variable structure model with one auxiliary degree-of-freedom. The latter serves to increase the number of degrees of freedom of the system during the phase of gear separation. A set of rules is generated to define the moments at which the matching gears separate or re-engage. The principle of impulse and momentum is then implemented to compute the discontinuities in the instantaneous angular velocities of the gears immediately after their impact.; A "backlash controller" is introduced to replace the original controller of the beam whenever the backlash is being taken up in one direction or the other.; The experimental and numerical results provide a qualitative validation of the backlash model. They investigate the relationships with which the backlash in gearing would interact with both the servo-loop controller and the structural flexibility of the system. In addition, the digital simulations have proven that the "backlash controller" provides a more viable alternative than the micro-manipulator approach in dealing with the dynamic characteristics of backlash in gearing.