A cooperative rotary servo indenting system for machining anti-counterfeiting micro-images on titanium alloys

To achieve flexible fabrication of anti-counterfeiting micro-images on titanium alloy produces, this study proposes a cooperative rotary servo indenting (CRSI) system by integrating a uniaxial fast servo motion (FSM) platform into multi-axis rotary servo indenting system. In CRSI, the rotary servo indenting system is used to fabricate inverted pyramid micro-pits with different orientation angles, to represent the pixels with different grayscale values and security codes. Meanwhile, the FSM platform cooperatively moves according to the feed distance of Z guideway to compensate the material spring back errors, in which way the visual grayness deviation of each pixel can be corrected. To determine the optimum compensating distance of FSM, a simplified spring back error model is proposed by considering subsurface strain-stress distribution of workpiece material. The tool path planning algorithm of the CRSI system is proposed to fabricate desired micro-images with deliberately designed security codes. A piezoelectrically actuated quadruple parallelogram flexure mechanism is also designed for the FSM platform to fulfil the requirement of stroke and working bandwidth. The proposed CRSI approach is experimentally validated by machining the famous “Mona Lisa Smile” image on Ti6Al4V alloy with the security code π, and the three-dimensional morphology of the pixel micro-pits are measured to validate the spring back error compensation strategy and the anti-counterfeiting strategy. The results demonstrate that the proposed CRSI can efficient fabrication of complex micro-images with hidden security codes on titanium alloys with high form accuracy and sharpness.