ROMI: Design and Experimental Evaluation of a Linear Delta Robotic System for High-Precision Applications

Robotic systems achieving submillimetre precision find great use in multiple research fields including surgical clinical interventions, semiconductor manufacturing, and the development of optical links in telecommunications, among others.  

Nowadays, the need for high-precision systems to achieve higher motion resolutions comes at a cost of higher complexity structures. In this scope, extensive research is dedicated to finding the most suitable geometry and fabrication method to overcome the engineering challenges that arise when unraveling the full potential of these high-motion precision robots. 

One of the main difficulties consists of finding the most optimal dimension design, where one needs to take into consideration multiple factors including motion precision, speed, and design specifications for suitable performance in terms of workspace. Multiple examples of different robotic systems for motion precision can be found in the literature [1], [2], [3]. 

In this new chapter, we explore the contribution of the Iceblink Supercontinuum Laser in the design and evaluation of robotic systems in high-precision applications, by the hand of Professor Rodrigo Avilés Espinosa’s group at Sussex University.  

 

ROMI: A Unique and Versatile Parallel Robotic System for High-Precision Applications 

The Robotics and Mechatronics Systems Research group at Sussex University developed the ROMI system, which consists of a linear delta robot based on a parallel manipulator design, showing precision accuracies of <5 µm. Geometry and dimension configurations were chosen according to three main parameters: workspace, motion resolution, and payload. Experimental evaluations in microsurgery, semiconductor wafer testing, and photonic device alignment showed promising conclusions. 

The structure of the ROMI system includes three linear actuators, three pairs of parallel legs [Figure 1 a], and twelve spherical joints for higher stability, low motion inertia, and high motion precision [Figure 1 b and 1 c]. Moreover, the robot design methodology consisted of 5 stages: mechatronic design, dynamic robot performance and motion resolution, evaluation of workspace, evaluation of the robot’s load capacity, and robot reconstruction. Further detailed information on the methodology is described in their paper ROMI: Design and Experimental Evaluation of a Linear Delta Robotic System for High-Precicion Applications.

Figure 1. Simplified Geometrical structure and Mechatronic design of ROMI. 1a) Shows simplified isometric structure where O is the centre of mass, a,b and c represent the linear sliders, B points represent the linear sliders motion directions, and P points indicate the joint connections of the structure. 1b) Shows the mechatronic design of the robot, with the different connectors, stepper motor and linear guides of the robot. 1c) shows the robot hardware with the 3D printed joints, stepper motor, beam connector and the end-effector housing a digital microscope.
Figure 1. Simplified Geometrical structure and Mechatronic design of ROMI. 1a) Shows simplified isometric structure where O is the center of mass, a,b, and c represent the linear sliders, B points represent the linear sliders motion directions, and P points indicate the joint connections of the structure. 1b) Shows the mechatronic design of the robot, with the different connectors, stepper motor, and linear guides of the robot. 1c) shows the robot hardware with the 3D printed joints, stepper motor, beam connector, and the end-effector housing a digital microscope.

 

Furthermore, three different scenarios for the mimicking of different applications were presented to evaluate the performance of the system at the micrometer precision resolution: microsurgical resection test [Figure 2a], high-precision test for probing silicon wafers [Figure 2b] and Photonic components alignment test [Figure 2c].  

Figure 2. Proof-of-concept experiments for high-precision performance assessment. A) shows the histology-fixed mammalian stratified epithelium sample obtained with a digital microscope. The red line represent the motion trajectory of the ROMI on the sample. B) shows the magnified image of the silicon wafer obtained with the digital microscope. The red points represent the tested points with the robotic system. C) shows the optical setup used to launch a laser beam towards an aspherical lens. FYLA´s Iceblink supercontinuum laser and a green filter are used as illumination source while the ROMI system tests the alignment of the photonic components.
Figure 2. Proof-of-concept experiments for high-precision performance assessment. A) shows the histology-fixed mammalian stratified epithelium sample obtained with a digital microscope. The red line represents the motion trajectory of the ROMI on the sample. B) shows the magnified image of the silicon wafer obtained with the digital microscope. The red points represent the tested points with the robotic system. C) shows the optical setup used to launch a laser beam towards an aspherical lens. FYLA’s Iceblink supercontinuum laser and a green filter are used as illumination sources while the ROMI system tests the alignment of the photonic components.

 

Their extensive work opens a new window in the development of systems for high-precision applications, addressing some of the state-of-the-art challenges and proposing the future implementation of closed-loop operation with visual serving devices for error reduction 

 

Role of the Iceblink Supercontinuum Laser in Proof-of-Concepts for High-Precision Robotics Testing.

Previous application note about Experimental Realization of Tunable Ferroelectric / Superconductor 1D Photonic Cyrstials in the Whole Visible Spectrum demonstrated the usage of broadband sources in multiple applications for the testing of Photonic components.

This app note shows once again the versatility of having the broadest spectrum within a small beam spot of 2 mm in diameter. And the possibility of combining the Iceblink supercontinuum laser with tunable or excitation filters for specific wavelength emission. In particular, the purpose of this last experiment was to couple the light of a laser source with an optical fiber achieving µm precision. From the broadband emission of the Iceblink supercontinuum laser, a whole optical setup to ensure the alignment of the small beam spot with the core of an optical fiber was implemented. It included excitation filters for the selection of the wavelengths of interest, aspherical lenses and mirrors, as well as a custom-made end-effector to hold the multimode fiber on the optical setup [Figure 2c]. Several characteristics of the Iceblink that explain why it is an ideal tool to ensure high coupling efficiencies of the light with the core of the fiber can be described: 

  • Broad emission allows for illumination in the VIS and NIR, with the possibility of selecting a specific emission bandwidth for illumination.  
  • Small beam spot collimated output to ensure beam diameters of 1-3 mm. This is indeed essential for ensuring the coupling or focusing efficiency of a free space beam onto an optical fiber. 
  • High average power, with more than 3 W of total power in the whole spectrum, and > 150 mW in the VIS range, to ensure suitable power transmission through the optical fiber. 
  • Great power stability of <0.5% of std. dev, that can affect the high precision measurements, in particular, the repeatability of the photonic components’ alignment test.