A Miniature Endoscopic Flexible Mechanical Arm Type Processing Tool Movement Posture And Material Removal Rate

There is currently no efficient way to quantitatively (precisely) remove materialfrom work pieces in hard-to-reach cavities, such as turbine blades in a jet engine. There isa need to be able to smooth the cracks from the turbine blades with a controlled amount ofmaterial removal. Endoscopy is useful for navigating and inspecting features in internalcavities with a flexible body and a semi-rigid bending section. By turning control knobson the endoscope, the bending section can access a workpiece on its lateral direction. Inthis research, it is hypothesized that an endoscope can be used to remotely grind apredetermined amount of material and smooth the cracks on a work piece. The researchobjectives are to set up a precise flexible machining operation and to measure theaccuracy of the estimated amount of material that can be removed. Experiment resultsshows that a reasonable accuracy was achieved using a modified flexible medicalendoscope.The main results are follows:1. A computer vision based nonintrusive optic measuring system was built tomeasure the bending section pose (position and orientation) of the modified endoscopictool. A new chroma-key filtering algorithm was proposed to compensate the glaring spotintroduced measuring error. A2D calibration object with checkerboard pattern was usedto nullify the camera distortion. Test results showed that the position measuringaccuracy was1mm and the sampling rate was25to30fps while tracking15targetssimultaneously. This system was used as a reference channel for subsequent studies.2. Two models were built to estimate the pose and force on the modified endoscopictool. The pose model was based on geometric analysis of the endoscope bending section.When the internal force was compensated in calculation, the average pose estimationerror was less than2mm of distance and±4°of bending angle in preferred work space.The force model was based on equilibrium analysis of the bending section and theaverage force prediction error was0.5N in the range of1to6N. The experimental andestimated results prove that the pose and force of the flexible bending section can be predicted and monitored when subjected to varying loads from work piece.3. In grinding processes, vibration (chatter) will seriously degrade the geometricaccuracy and surface finish of the workpiece. The proposed endoscopic machining toolis naturally vulnerable to vibration due to its high degrees of freedom and low structuralrigidity. A dynamic model was built to study the self-excited vibration characteristics ofthe endoscopic machining tool. By analyzing the stability lobe diagram (SLD),optimized machining parameters were found to reduce the chatter. An on-line vibrationdetecting method is proposed to identify vibration in its early stage.4. Finally, a material removal model was formulated to estimate the amount ofmaterial removal in this endoscopic grinding process. By calculating the energy wastedby vibration and the effective energy spent on grinding, the material removal wasestimated using the specific energy theory. Several machining experiments wereconducted to validate the repeatability of the model and evaluate its accuracy. Theaverage material removal estimation error is22%related to measured values.Experiment results reveals that the current material removal estimation accuracy(in the scale of0.5mg) is not high enough to meet the industry requirement, which isbelieved to be0.004mg for smoothing sub-millimeter size cracks. Recommendations ofimproving pose estimation and material removal estimation accuracies such asdesigning a more predictable endoscopic tool structure, using a sphere grinding toolhead and adopting a pneumatic driving mechanism or tip mounted motor are proposed.