Modifed Pre-stretching Assembly Method for Cable-Driven Systems

Soft cable-driven systems have been employed in many assembled mechanisms, such as industrial robots, parallel kinematic mechanism machines, medical devices, and humaniform hands. A pre-stretching process is necessary to guarantee the quality of cable-driven systems during the assembly process. However, the stress relaxation of cables becomes a critical concern during long-term operation. This study investigates the effects of non-uniform deformation and long-term stress relaxation of the driven cables owing to moving parts in the system. A simple closed-loop cable-driven system is built and an alternating load is applied to it to replicate the operation of transmission cables. Under different experimental conditions, the cable tension is recorded and the boundary data are selected to be curve-fitted. Based on the fitted results, a formula is presented to estimate the stress relaxation of cables to evaluate the assembly performance. Further experimental results show that the stress relaxation is mainly caused by cable creep and the assembly procedure. To remove the influence of the assembly procedure, a modified pre-stretching assembly method based on the stress relaxation theory is proposed and verification experiments are performed. Finally, the assembly performance is optimized using a cable-driven surgical robot as an example. This paper proposes a dual stretching method instead of the pre-stretching method to assemble the cable-driven system to improve its performance and prolong its service life.

Aluminum(Ⅲ) triflate-catalyzed selective oxidation of glycerol to formic acid with hydrogen peroxide

Glycerol is a by-product of biodiesel production and is an important readily available platform chemical.Valorization of glycerol into value-added chemicals has gained immense attention.Herein,we carried out the conversion of glycerol to formic acid and glycolic acid using H2O2 as an oxidant and metal(Ⅲ)triflate-based catalytic systems.Aluminum(Ⅲ)triflate was found to be the most efficient catalyst for the selective oxidation of glycerol to formic acid.A correlation between the catalytic activity of the metal cations and their hydrolysis constants(Kh)and water exchange rate constants was observed.At 70 ℃,a formic acid yield of up to 72% could be attained within 12 h.The catalyst could be recycled at least five times with a high conversion rate,and hence can also be used for the selective oxidation of other biomass platform molecules.Reaction kinetics and 1H NMR studies showed that the oxidation of glycerol(to formic acid)involved glycerol hydrolysis pathways with glyceric acid and glycolic acid as the main intermediate products.Both the [Al(OH)x]^n+ Lewis acid species and CF3SO3H Brosted acid,which were generated by the in-situ hydrolysis of Al(OTf)3,were responsible for glycerol conversion.The easy availability,high efficiency,and good recyclability of Al(OTf)3 render it suitable for the selective oxidation of glycerol to high value-added products.