Kinematic Analysis and Dimensional Synthesis of Exechon Parallel Kinematic Machine for Large Volume Machining

A parallel kinematic machine (PKM) topology can only give its best performance when its geometrical parameters are optimized. In this paper, dimensional synthesis of a newly developed PKM is presented for the first time. An optimization method is developed with the objective to maximize both workspace volume and global dexterity of the PKM. Results show that the method can effectively identify design parameter changes under different weighted objectives. The PKM with optimized dimensions has a large workspace to footprint ratio and a large well-conditioned workspace, hence justifies its suitability for large volume machining.

Long-term graft survival in patients with flexible open-loop anterior chamber intraocular lenses

Purpose. To evaluate the long-term graft survival in patients with flexible open-loop anterior chamber intraocular lenses (AC IOL). Methods. We retrospectively reviewed the records of patients with aphakic/pseudophakic bullous keratopathy who underwent penetrating keratoplasty and flexible open-loop AC IOL implantation in our institution from 1983 to 1988. Results. 79 eyes from 77 patients were included in the study. Mean follow-up was 50 months (range 1 to 123 months). At last follow-up 61 eyes (77.2%) had clear grafts. Among them, the visual acuity was = 20/40 in 14 eyes (23.0%), 20/50-20/100 in 22 eyes (36.1%), 20/200-20/400 in 9 eyes (14.8%) and = CF in 16 (26.2%). Increment of glaucoma medications and/or glaucoma surgery was the most frequent complication (37 eyes, 46,8%). Cystoid macular edema was newly diagnosed in 10 eyes (12.7%). Conclusions. Flexible, open-loop anterior chamber lens are a viable option in the treatment of patients with aphakic or pseudophakic bullous keratopathy undergoing penetrating keratoplasty.

Long-term graft survival in patients with flexible open-loop anterior- chamber intraocular lenses

Purpose. To evaluate the long-term graft survival and complications of flexible, open-loop anterior-chamber intraocular lenses in patients with penetrating keratoplasty for pseudophakic or aphakic bullous keratopathy. Methods. We reviewed charts of all consecutive patients who underwent penetrating keratoplasty for pseudophakic or aphakic bullous keratopathy combined with implantation of a flexible, open-loop, anterior-chamber intraocular lens at our institution between 1983 and 1988. One-hundred one eyes of 99 patients were evaluated. Graft-survival rates were calculated by using the Kaplan-Meier actuarial method. Results. Mean follow-up was 49.8 months (range. 1-144). The probability of graft survival at 1, 2, 4, 6, and 8 years was 93, 87, 78, 65, and 65%, respectively. A total of 25 (24.8%) grafts failed. Progressive corneal edema without signs of rejection was the most common finding in patients with failed grafts (10 eyes, 40%). The most frequent complication observed was newly diagnosed or worsening of preexisting glaucoma (46 eyes, 45.5%). Conclusions. Our long-term results support flexible, open-loop anterior-chamber intraocular lenses as a reasonable option, at the time of penetrating keratoplasty, in patients with pseudophakic and aphakic bullous keratopathy.

The development of a surface defect machining method for hard turning processes

Hard turning (HT) is a material removal process employing a combination of a single point cutting tool and high speeds to machine hard ferrous alloys which exhibit hardness values over 45 HRC. In this paper, a surface defect machining (SDM) method for HT is proposed which harnesses the combined advantages of porosity machining and pulsed laser pre-treatment processing. From previous experimental work, this was shown to provide better controllability of the process and improved quality of the machined surface. While the experiments showed promising results, a comprehensive understanding of this new technique could only be achieved through a rigorous, in depth theoretical analysis. Therefore, an assessment of the SDM technique was carried out using both finite element method (FEM) and molecular dynamics (MD) simulations.
FEM modelling was used to compare the conventional HT of AISI 4340 steel (52 HRC) using an Al2O3 insert with the proposed SDM method. The simulations showed very good agreement with the previously published experimental results. Compared to conventional HT, SDM provided favourable machining outcomes, such as reduced shear plane angle, reduced average cutting forces, improved surface roughness, lower residual stresses on the machined surface, reduced tool–chip interface contact length and increased chip flow velocity. Furthermore, a scientific explanation of the improved surface finish was revealed using a state-of-the-art MD simulation model which suggested that during SDM, a combination of both the cutting action and rough polishing action help improve the machined surface finish.

An efficient and flexible synthesis of model lignin oligomers

The use of model compounds in the development of selective lignin depolymerisation processes has been limited by the lack of complexity of these models compared with lignin itself. In this paper we report a convergent and efficient synthetic method for the flexible, multi-gram preparation of model lignin hexamers and octamers containing three of the most common connectivity motifs found within native lignin, namely ß-O-4', 5-5' and ß-5', which will be used to further the mechanistic understanding of lignin depolymerisation processes.

A theoretical assessment of surface defect machining and hot machining of nanocrystalline silicon carbide

In this paper, a newly proposed machining method named “surface defect machining” (SDM) [Wear, 302, 2013 (1124-1135)] was explored for machining of nanocrystalline beta silicon carbide (3C-SiC) at 300K using MD simulation. The results were compared with isothermal high temperature machining at 1200K under the same machining parameters, emulating ductile mode micro laser assisted machining (µ-LAM) and with conventional cutting at 300 K. In the MD simulation, surface defects were generated on the top of the (010) surface of the 3C-SiC work piece prior to cutting, and the workpiece was then cut along the <100> direction using a single point diamond tool at a cutting speed of 10 m/sec. Cutting forces, sub-surface deformation layer depth, temperature in the shear zone, shear plane angle and friction coefficient were used to characterize the response of the workpiece. Simulation results showed that SDM provides a unique advantage of decreased shear plane angle which eases the shearing action. This in turn causes an increased value of average coefficient of friction in contrast to the isothermal cutting (carried at 1200 K) and normal cutting (carried at 300K). The increase of friction coefficient however was found to aid the cutting action of the tool due to an intermittent dropping in the cutting forces, lowering stresses on the cutting tool and reducing operational temperature. Analysis shows that the introduction of surface defects prior to conventional machining can be a viable choice for machining a wide range of ceramics, hard steels and composites compared to hot machining.