Design of an optimal damper to minimize the vibration of machine tool structures subject to random excitation
The vibration of machine tools during machining adversely affects machining accuracy and tool life, and therefore must be minimized. The cutting forces for stable turning are generally known to be random, and hence excite all the resonance modes. Of all these modes, those that generate relative motions between a cutting tool and a workpiece are of concern.This paper presents a new approach for designing an optimal damper to minimize the relative vibration between the cutting tool and workpiece during stable machining. An approximate normal mode method is employed to calculate the response of a machine tool system with nonproportional damping subject to random excitation. The major advantage of this method is that it reduces the amount of computation greatly for higher-order systems when responses have to be calculated repeatedly in the process of optimization. An optimal design procedure is presented based on a representative lumped parameter model that can be constructed by using existing experimental or analytical techniques. The two-step optimization procedure based on the modified pattern search and univariate search effectively leads the numerical solution to the global minimun irrespectively of initial values even under the existence of many local minima.
Optimization of Functional Properties of Machine Tool Structures—a Finite Element Analysis
The accuracy and stability of machine tools depend on the effective cross stiffness between tool and workpiece. The desired cross stiffness is a function of the nature of the cutting process and the installed power on the machine tool. In a number of machine tool structures studied using finite element method, it has been observed that the use of structural members having the maximum stiffness to weight ratio need not necessarily exhibit high stiffness at toolpoint. Greater care should be taken to arrive at proper shape and orientation of the members so that local deformations, torque and deflection arms are optimised. The examples of centre lathe, slant bed lathe, planomiller, etc. have been discussed.
The bradykinin B1 receptor and the central regulation of blood pressure in spontaneously hypertensive rats
We evaluated if the brain bradykinin (BK) B1 receptor is involved in the regulation of blood pressure (BP) in conscious rats. Basal mean BP and HR were 115±2 and 165±3 mmHg and 345±10 and 410±14 beats min−1 in Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR), respectively. Intracerebroventricular (i.c.v.) injection of 1 nmol B1 receptor agonist Lys‐desArg9‐BK significantly increased the BP of WKY and SHR by 7±1 and 19±2 mmHg, respectively. One nmol Sar[D‐Phe8]‐desArg9‐BK, a kininase‐resistant B1 agonist, increased the BP of WKY and SHR by 19±2 and 17±2 mmHg, respectively and reduced HR in both strains. I.c.v. injection of 0.01 nmol B1 antagonists, LysLeu8‐desArg9‐BK or AcLys[D‐βNal7,Ile8]‐desArg9‐BK (R715), significantly decreased mean BP in SHR (by 9±2 mmHg the former and 14±3 mmHg the latter compound), but not in WKY. In SHR, the BP response to R715 was associated to tachycardia. I.c.v. Captopril, a kininase inhibitor, increased the BP of SHR, this response being partially prevented by i.c.v. R715 and reversed into a vasodepressor effect by R715 in combination with the B2 antagonist Icatibant. I.c.v. antisense oligodeoxynucleotides (ODNs) targeted to the B1 receptor mRNA decreased BP in SHR, but not in WKY. HR was not altered in either strain. Distribution of fluorescein‐conjugated ODNs was detected in brain areas surrounding cerebral ventricles. Our results indicate that the brain B1 receptor participates in the regulation of BP. Activation of the B1 receptor by kinin metabolites could participate in the pathogenesis of hypertension in SHR.