In the fabrication process of aspheric glass lens and molds, shape characterization is a fundamen... more In the fabrication process of aspheric glass lens and molds, shape characterization is a fundamental task to control geometrical errors. Nevertheless, the more significant geometrical functional aspect related to the optical properties is the curvature, which is rarely investigated in the manufacturing process of lenses. Algorithms for the assessment of shape and curvature errors on aspheric surface profile are presented. The method has been investigated on profiles measured before and at different steps of the membrane polishing process. The results show how surface roughness, shape, and curvature change during the polishing process as a function of the machining time.
Precision surfaces of optical grade have been in great demand for various applications such as hi... more Precision surfaces of optical grade have been in great demand for various applications such as high-power laser systems, astronomical reflecting telescopes glass mirrors, folding mirrors of avionics displays, reflectors, guides for transmission of hot and cold neutron beams for neutron exploration setups, electronic substrate, display covers and substrates for biomedical imaging and sensing, etc. Generation of such surfaces has been a challenge; particularly the polishing operation of optical fabrication process is quite critical which determines the final surface quality. To achieve the required optical surface parameters, a good control and systematic understanding of polishing process and its parameters are required. However, the conventional or full aperture optical polishing process still depends on operator's skills to achieve the target surface quality. To exploit the process to the extent, it is must to have a scientific understanding of material removal behavior of the polishing process, which will lead to the process becoming deterministic. This article has attempted to address this issue. Authors have summarized different material removal theories and discussed various mathematical models as proposed by researchers so far. Attempt has been made to come up with knowledge gaps which are required to be bridged in future.
Precision surface quality is required for the optical components used in military and aerospace a... more Precision surface quality is required for the optical components used in military and aerospace applications. Optical polishing process is one of the critical steps in fabrication of optical components. Final surface quality of the optical surfaces defines the life and performance of the system. Final surface figure and finish of the optical surface depends upon material removal characteristics of the polishing process. Rate of material removal is not uniform across the workpiece surface; it varies according to number of parameters such as pressure distribution, variation in relative motion at different points, abrasive slurry distribution at the workpiece-polisher interface, etc. Being a loose abrasive based process, the fundamental mechanism of material removal during polishing is still not well understood. One of the cumulative parameter which affects material removal during polishing is friction coefficient. Friction coefficient is a complex parameter and plays an important role in material removal during optical polishing process. This paper reviews the work carried out to understand the role of friction in material removal during optical polishing process.
It has been a challenge to finish optical glass surface due to their hard and brittle nature. Mor... more It has been a challenge to finish optical glass surface due to their hard and brittle nature. Moreover tight tolerances of surface figure and finish make polishing a more critical operation. This work reports the results of an experimental study performed for full aperture polishing of BK7 optical glass. Flat samples of BK7 glass are polished using optical pitch polisher and cerium oxide slurry. Taguchi’s L9 orthogonal array is used for design of experiments. Abrasive concentration, pressure and overarm speed are taken as variable process parameters. Polishing is performed for duration of 120 minutes for each combination of parameters. Material removal is measured using the precision weighing balance. Surface roughness was measured using Form Talysurf PGI 120 profiler. Abrasive slurry concentration is observed to be one of the most significant parameters in optical polishing process. It affects material removal rate as well as surface roughness. Pressure applied at workpiece-polisher interface affects material removal rate but variation of pressure is not found to affect surface roughness significantly. Relative motion at workpiece-polisher interface is also observed to be significant in defining final polishing outputs.
This paper deals with the design and analysis of a manipulator to control the position and orient... more This paper deals with the design and analysis of a manipulator to control the position and orientation of an endoscope during minimally invasive abdominal surgery. The endoscope manipulator assists the surgeon to manipulate endoscope orientation for viewing the area of interest inside the abdomen. The designed manipulator has three degrees of freedom (DOF): one translational (for taking the endoscope in and out of the abdomen) and two rotational (for desired orientation of endoscope) and is operated by the surgeon using a foot-pedal to eliminate the need of an endoscope assistant. Foot pedal control allows the surgeon to use both hands for the surgery. The elimination of the need for manual stabilisation of endoscope leads to removal of tremor, which occurs due to handling of endoscope manually. Thus endoscope can be placed closer to the target organ with fewer collisions with inner parts of the body and other surgical tools being used. The designed endoscope manipulator presented in the study is small in size, light weight, simple, easy to setup and use, when compared to conventional laparoscopic surgical systems. It has been tested for its motions at the laboratory, which were found satisfactory.
The aim of advanced optical fabrication is to produce highly accurate optical surface with better... more The aim of advanced optical fabrication is to produce highly accurate optical surface with better reproducibility. It demands a good control and systematic understanding of the process and its parameters. Optical polishing process defines the final surface figure and finish of the component. Controlled amount of finishing forces and material removal rate are necessary for polishing of brittle materials. However, the conventional or full aperture polishing process still depends on the operator’s skills to achieve the desired surface figure and finish. The process may be well optimized at individual manufacturing setups but there appears to be a little prediction about polishing outputs. Thus, it is essential to study the fundamental mechanisms of material removal during polishing in order to achieve the accurate prediction of process outputs. This paper reviews the work carried out in the area of full aperture optical polishing.
In the fabrication process of aspheric glass lens and molds, shape characterization is a fundamen... more In the fabrication process of aspheric glass lens and molds, shape characterization is a fundamental task to control geometrical errors. Nevertheless, the more significant geometrical functional aspect related to the optical properties is the curvature, which is rarely investigated in the manufacturing process of lenses. Algorithms for the assessment of shape and curvature errors on aspheric surface profile are presented. The method has been investigated on profiles measured before and at different steps of the membrane polishing process. The results show how surface roughness, shape, and curvature change during the polishing process as a function of the machining time.
Precision surfaces of optical grade have been in great demand for various applications such as hi... more Precision surfaces of optical grade have been in great demand for various applications such as high-power laser systems, astronomical reflecting telescopes glass mirrors, folding mirrors of avionics displays, reflectors, guides for transmission of hot and cold neutron beams for neutron exploration setups, electronic substrate, display covers and substrates for biomedical imaging and sensing, etc. Generation of such surfaces has been a challenge; particularly the polishing operation of optical fabrication process is quite critical which determines the final surface quality. To achieve the required optical surface parameters, a good control and systematic understanding of polishing process and its parameters are required. However, the conventional or full aperture optical polishing process still depends on operator's skills to achieve the target surface quality. To exploit the process to the extent, it is must to have a scientific understanding of material removal behavior of the polishing process, which will lead to the process becoming deterministic. This article has attempted to address this issue. Authors have summarized different material removal theories and discussed various mathematical models as proposed by researchers so far. Attempt has been made to come up with knowledge gaps which are required to be bridged in future.
Precision surface quality is required for the optical components used in military and aerospace a... more Precision surface quality is required for the optical components used in military and aerospace applications. Optical polishing process is one of the critical steps in fabrication of optical components. Final surface quality of the optical surfaces defines the life and performance of the system. Final surface figure and finish of the optical surface depends upon material removal characteristics of the polishing process. Rate of material removal is not uniform across the workpiece surface; it varies according to number of parameters such as pressure distribution, variation in relative motion at different points, abrasive slurry distribution at the workpiece-polisher interface, etc. Being a loose abrasive based process, the fundamental mechanism of material removal during polishing is still not well understood. One of the cumulative parameter which affects material removal during polishing is friction coefficient. Friction coefficient is a complex parameter and plays an important role in material removal during optical polishing process. This paper reviews the work carried out to understand the role of friction in material removal during optical polishing process.
It has been a challenge to finish optical glass surface due to their hard and brittle nature. Mor... more It has been a challenge to finish optical glass surface due to their hard and brittle nature. Moreover tight tolerances of surface figure and finish make polishing a more critical operation. This work reports the results of an experimental study performed for full aperture polishing of BK7 optical glass. Flat samples of BK7 glass are polished using optical pitch polisher and cerium oxide slurry. Taguchi’s L9 orthogonal array is used for design of experiments. Abrasive concentration, pressure and overarm speed are taken as variable process parameters. Polishing is performed for duration of 120 minutes for each combination of parameters. Material removal is measured using the precision weighing balance. Surface roughness was measured using Form Talysurf PGI 120 profiler. Abrasive slurry concentration is observed to be one of the most significant parameters in optical polishing process. It affects material removal rate as well as surface roughness. Pressure applied at workpiece-polisher interface affects material removal rate but variation of pressure is not found to affect surface roughness significantly. Relative motion at workpiece-polisher interface is also observed to be significant in defining final polishing outputs.
This paper deals with the design and analysis of a manipulator to control the position and orient... more This paper deals with the design and analysis of a manipulator to control the position and orientation of an endoscope during minimally invasive abdominal surgery. The endoscope manipulator assists the surgeon to manipulate endoscope orientation for viewing the area of interest inside the abdomen. The designed manipulator has three degrees of freedom (DOF): one translational (for taking the endoscope in and out of the abdomen) and two rotational (for desired orientation of endoscope) and is operated by the surgeon using a foot-pedal to eliminate the need of an endoscope assistant. Foot pedal control allows the surgeon to use both hands for the surgery. The elimination of the need for manual stabilisation of endoscope leads to removal of tremor, which occurs due to handling of endoscope manually. Thus endoscope can be placed closer to the target organ with fewer collisions with inner parts of the body and other surgical tools being used. The designed endoscope manipulator presented in the study is small in size, light weight, simple, easy to setup and use, when compared to conventional laparoscopic surgical systems. It has been tested for its motions at the laboratory, which were found satisfactory.
The aim of advanced optical fabrication is to produce highly accurate optical surface with better... more The aim of advanced optical fabrication is to produce highly accurate optical surface with better reproducibility. It demands a good control and systematic understanding of the process and its parameters. Optical polishing process defines the final surface figure and finish of the component. Controlled amount of finishing forces and material removal rate are necessary for polishing of brittle materials. However, the conventional or full aperture polishing process still depends on the operator’s skills to achieve the desired surface figure and finish. The process may be well optimized at individual manufacturing setups but there appears to be a little prediction about polishing outputs. Thus, it is essential to study the fundamental mechanisms of material removal during polishing in order to achieve the accurate prediction of process outputs. This paper reviews the work carried out in the area of full aperture optical polishing.
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