Deflection Error Research Articles

Analytical modelling and numerical simulation of 0–3 PZT/PVDF composite actuated micropump

ABSTRACT In this paper the flow characteristic of laminar flow through planar diffuser was studied for different flow regime and its geometry, including angle, length and width were optimized. The diffuser shows flow recirculation and its efficiency is negative for diffuser angle larger than 30°. The analytical modelling of the micropump is solved by sectioning it as two separate units, an actuator unit and a flow unit. The actuator unit is a circular plate made of lead zirconate titanate (PZT) filler in polyvinyldene fluoride (PVDF) matrix composite material. The deflection of the actuator unit for bilaminar plate is analytically solved using theory of bending plates. The deflection profile of the actuator for the applied voltage is used to determine the stroke volume. The stroke volume from the actuator unit is used to solve the flow rate of the micropump analytically in the flow unit using mass balance equation. The flow rate of the micropump is numerically simulated in 3D for varying geometric and electrical parameters. The results obtained were compared and the numerical procedure was found to have less percentage error in the actuator deflection and flow rate up to a chamber depth of 250 µm.

Prediction of machining accuracy based on geometric error estimation of tool rotation profile in five-axis multi-layer flank milling process

In five-axis multi-layer flank milling process, the geometric error of tool rotation profile caused by radial dimension error and setup error has great influence on the machining accuracy. In this work, a new comprehensive error prediction model considering the inter-layer interference caused by tool rotation profile error is established, which incorporates a pre-existing prediction model dealing with a variety of errors such as geometric errors of machine tool, workpiece locating errors, and spindle thermal deflection errors. First, a series of tool contact points on the tool swept surface in each single layer without overlapping with others are calculated. Second, the position of the tool contact points on the overlapped layers is updated based on the detection and calculation of inter-layer interferences. Third, all evaluated tool contact points on the final machined surface are available for completing the accuracy prediction of the machined surface. A machining experiment has been carried out to validate this prediction model and the results show the model is effective.

Investigations into the influence of tool helix angle during end milling of open straight and curved thin-wall parts

In this paper, the influence of cutting tool helix angle on performance parameters viz., milling force, part deflection, surface finish, chip morphology and micro-hardness considering open straight and curvilinear thin-walled parts is analysed. It was found that end mills with helix angle of 45° and 55° helped in achieving good surface finish and form accuracy while machining thin-wall parts. During machining, parts having concave geometry due to its inherent rigidity, generated higher milling force. But the wall deflection and form error was relatively lower in comparison with the straight wall thereby resulting in better surface finish. Also, formation of built-up-edge (BUE) at the cutting edge of end mills having 35° helix was noted which aided in surface defects. Back surface of the chips machined using 35° tools showed prominent lamella like structures but tools having higher helix angles were found to produce relatively lamella free surface.

Investigations into the influence of tool helix angle during end milling of open straight and curved thin-wall parts

In this paper, the influence of cutting tool helix angle on performance parameters viz., milling force, part deflection, surface finish, chip morphology and micro-hardness considering open straight and curvilinear thin-walled parts is analysed. It was found that end mills with helix angle of 45° and 55° helped in achieving good surface finish and form accuracy while machining thin-wall parts. During machining, parts having concave geometry due to its inherent rigidity, generated higher milling force. But the wall deflection and form error was relatively lower in comparison with the straight wall thereby resulting in better surface finish. Also, formation of built-up-edge (BUE) at the cutting edge of end mills having 35° helix was noted which aided in surface defects. Back surface of the chips machined using 35° tools showed prominent lamella like structures but tools having higher helix angles were found to produce relatively lamella free surface.

Robot Manipulator Calibration Using a Model Based Identification Technique and a Neural Network With the Teaching Learning-Based Optimization

This paper proposes a new calibration method for enhancing robot positional accuracy of the industrial manipulators. By combining the joint deflection model with the conventional kinematic model of a manipulator, the geometric errors and joint deflection errors can be considered together to increase its positional accuracy. Then, a neural network is designed to additionally compensate the unmodeled errors, specially, non-geometric errors. The teaching-learning-based optimization method is employed to optimize weights and bias of the neural network. In order to demonstrate the effectiveness of the proposed method, real experimental studies are carried out on HH 800 manipulator. The enhanced position accuracy of the manipulator after the calibration confirms the feasibility and more positional accuracy over the other calibration methods.

Simulation-based compensation of deflection errors in helical flute grinding

Static deflections of cylindrical blanks in tool grinding processes lead to core diameter deviations that vary with the axial workpiece position. This paper presents an approach to compensate these errors automatically in process planning. Hybrid modelling is used to predict the current local load, the stiffness based on the moment of inertia and the resulting elastic deflection at each time step. Subsequently, the process is optimized by adapting the process parameters and the tool path in the NC-code. In an experimental study, the core diameter deviation after flute grinding has been reduced in a range from 68% up to 87% using the developed approach.

A MECHANICS-BASED MODEL FOR SIMULATING THE NEEDLE DEFLECTION IN TRANSVERSE ISOTROPIC TISSUE FOR A PERCUTANEOUS PUNCTURE

During the percutaneous puncture for robot-assisted brachytherapy, a medical needle is usually inserted into fiber-structured soft tissue which has transverse isotropic elasticity, such as muscle and skin, to deliver radioactive seeds that kill cancer cells. To place the radioactive seeds more accurately, it is necessary to assess the effect of the transverse isotropic elasticity on the needle deflection. A mechanics-based model for simulating the needle deflection in transverse isotropic tissue is developed in this paper. The anisotropic needle–tissue interaction forces are estimated and used as inputs to drive the model for simulating needle deflections for different insertion orientation angles. Automatic insertion experiments were performed on a single-layered porcine muscle at five different insertion orientation angles. The results show that the maximum difference in the tip deflection for the different insertion orientation angles is 2.99[Formula: see text]mm when the insertion depth is 50[Formula: see text]mm. The maximum simulated error of the needle axis deflection is 0.62[Formula: see text]mm for all insertion orientation angles. The developed model can successfully simulate the needle deflections inside transverse isotropic tissue for different insertion orientation angles. This work is useful for predicting and compensating for the deflection error for automatic needle insertion.

Influence of micro-grooves on the lubrication performance of a misaligned bearing

Surface texturing for improving the lubrication performance of journal bearings has been widely investigated in the last two decades. In practical applications, the misalignment of a journal bearing occurs due to the asymmetric bearing load, elastic deflection, manufacturing tolerances, and installation errors. However, there has been little discussion on the influence of grooves on the lubrication performance of misaligned bearings. In the present work, numerical predictions of lubrication performances are presented to test the influence of the grooves. Based on the JFO boundary condition, a mass conservation algorithm is implemented to automatically determine the position of oil film rupture and reformation. The load-carrying capacity, friction force, friction coefficient, and bearing moment are computed numerically. The influence of angular position of the groove is first conducted in a misaligned bearing. Subsequently, the groove depth and width are investigated with different values of [Formula: see text] and [Formula: see text] ratios, respectively.

Geometric correction for TanSat atmospheric carbon dioxide grating spectrometer

Carbon Observing Satellite (TanSat) is the first of Chinese experimental satellite for monitoring the CO2 column densities in the atmospheric, while identifying sources and sinks on regions scales. Three grating spectrometers are equipped on TanSat to measure the reflected sunlight in the 0.76μm O2A-band, 1.61μm weak CO2 band and 2.06μm strong CO2 band respectively. Three bands have high spectral resolution and signal to noise ratio (SNR), while their spectral and radiometric calibration have been reported in many articles. This paper describes the geometric calibration of the essential payload (ACGS) on the TanSat. In the assembly process, the flatness only in the spatial dimension is strictly controlled owing to the physical obstruction. The geometric deflection error in one band should be tested and corrected by adjusting the starting rows of different spectral samplings. Meanwhile, the alignment error among the three bands also need processing in the same way to ensure that the slits of the three bands were matched the corresponding geographic target. Finally, the geometric correction results of the thermal-vacuum testing suggested that the alignment accuracy is well enough to match the requirements.

Tool orientation optimization considering cutter deflection error caused by cutting force for multi-axis sculptured surface milling

Multi-axis milling (especially five-axis) is in the ascendant for high precision manufacturing of a product with a sculptured surface such as ship propeller, owing to its multi-axis linkage and resulting outstanding superiorities. Needs of a faster-improving manufacturing level of sculptured surface milling are derived by higher performance requirement of complicated equipment, which makes the planning of tool orientations more significant and challenging. This paper builds a tool orientation optimization model with inclusion of the influence of deflection error caused by cutting force to achieve better machining precision controlling in five-axis sculptured surface milling. The basic idea of the optimization method is described firstly, followed by the prediction of cutter deflection error. Then determining processes of the related subset to restrain the tool orientations are developed. Lastly, comparative experiments are designed and performed through milling a propeller rotor possessing numerous blades in a five-axis machining center. By comparison with several other tool orientation methods, the average values and volatility of deflection error are both suppressed better utilizing the optimization modeling. The experiment results reflect that it is insufficient to consider single geometric constraint or kinematic constraint, and greater attention should be paid to the role of cutter deflection caused by cutting force in planning the tool orientations.

A simple insertion technique to reduce the bending of thinbevel-point needles

Objective: Needle insertion is a common component of most diagnostic and therapeutic interventions. Needles with asymmetrically sharpened points such as the bevel point are ubiquitous. Their insertion path is typically curved due to the rudder effect at the point. However, the common planned path is straight, leading to targeting errors. We present a simple technique that may substantially reduce these errors. The method was inspired by practical experience, conceived mathematically, and refined experimentally.Methods: Targeting errors are reduced by flipping the bevel on the opposite side (rotating the needle 180° about its axis), at a certain depth during insertion. The ratio of the flip depth to the full depth of insertion is defined as the flip depth ratio (FDR). Based on a model, FDR is constant 0.3.Results: Experimentally, the ratio depends on the needle diameter, 0.35 for 20Ga and 0.45 for 18Ga needles. Thinner needles should be flipped a little shallower, but never less than 0.3.Conclusion: Practically, a physician may expect to reduce ∼80% of needle deflection errors by simply flipping the needle. The technique may be used by hand or with guidance devices.

Modification of Tool Orientation and Position to Compensate Tool and Part Deflections in Five-Axis Ball End Milling Operations

Tool-workpiece deflection is one of the major error sources in machining thin walled structures like blades. The traditional approach in industry to eliminate this error is based on modifying tool positions after measuring the error on the machined part. This paper presents an integrated model of cutting force distribution on the tool–blade contact, automatic update of blade static stiffness matrix without resorting to time-consuming finite element solutions as the material is removed, the prediction and compensation of static deflection marks left on the blade surface. The main focus of the paper is to compensate the deflection errors by respecting the maximum form errors, collision of tool/machine/workpiece, cutting speed limit at the tool tip, and ball end—blade surface contact constraints. The compensation has been carried out by two modules. The first module adjusts the tool orientation along the path to reduce the error by constructing an optimization problem. This module is computationally inexpensive and results in about 70% error reduction based on the conducted experiments. The modified tool path resulted from the first module is fed to the second module for further reduction of the form errors if needed at the violated cutter locations; hence it takes less computational time than the stand alone approach proposed in the literature. The proposed algorithms have been experimentally validated on five-axis finish ball end milling of blades with about 80% reduction in cutting force induced form errors.

A new calibration method for enhancing robot position accuracy by combining a robot model–based identification approach and an artificial neural network–based error compensation technique

Robot position accuracy plays a very important role in advanced industrial applications. This article proposes a new method for enhancing robot position accuracy. In order to increase robot accuracy, the proposed method models and identifies determinable error sources, for instance, geometric errors and joint deflection errors. Because non-geometric error sources such as link compliance, gear backlash, and others are difficult to model correctly and completely, an artificial neural network is used for compensating for the robot position errors, which are caused by these non-geometric error sources. The proposed method is used for experimental calibration of an industrial Hyundai HH800 robot designed for carrying heavy loads. The robot position accuracy after calibration demonstrates the effectiveness and correctness of the method.

Full-State Tracking Control for Flexible Joint Robots With Singular Perturbation Techniques

This paper proposes a practical method to realize multivariable full-state tracking control for industrial robots with elastic joints. Unlike existing methods, the proposed method does not require high-order derivatives of the link states such as acceleration and jerk. Therefore, the proposed method does not suffer from chatter related to inaccurate estimation of high-order derivatives. The method is derived by adopting a singular perturbation technique. A decoupled error dynamics is achieved by two decoupling control loops: a fast loop that controls the deflection error and a slow loop for tracking control on the link side. Our stability analysis based on a linear system shows that the proposed control system is stable as long as the fast system is at least twice as fast as the slow system. A practical method to select the gain is also presented such that the closed-loop poles are placed at the desired locations. In simulation, we compare the proposed method with feedback linearization. The results indicate that in an ideal scenario the proposed method can obtain a similar performance as feedback linearization. However, the proposed method obtains a superior performance in a realistic scenario. A real-world experiment with a six degree-of-freedom commercial industrial robot is carried out to further validate our approach.

A comparison between simulation and experiment of virtual machining in CNC turning machine considering kinematic motion deviations, tool wear and workpiece deflection errors

A comparison between simulation and experiment of virtual machining in CNC turning machine considering kinematic motion deviations, tool wear and workpiece deflection errors

Analyzing wire deflection errors of WEDM process on small arced corners

Wire electrical discharge machining (WEDM) is an advanced machining process capable of precise machining of parts with complicated shapes. Machining inaccuracy at small arced corners is a major problem of WEDM process. It is aimed to develop a novel mathematical methodology validated by experimental data for analyzing the wire deflection and evaluating total machining errors of arced corners during the WEDM process. The maximum spark gap, spark angle around the wire, spark forces applied to the wire and the resulting deflection are mathematically described based on the nature of the electrical discharge process and plasma channel properties to clarify the causes of wire deflection error in the small arced corners. The influence of the driving WEDM parameters, including discharge frequency and wire tension, are theoretically and experimentally studied in regard to the wire deflection and total machining errors for various experimental sets. Finally, the estimated wire deflection and total machining errors are compared and evaluated. The results indicate that wire deflection error is one of the major causes of machining errors in the arced corners; this error is almost 57% of the total machining error. In addition, the effect of wire vibration and excitation of discharges on the total machining errors are mentioned. According to the results, it is concluded that the proposed theoretical formulations can be used for prediction and compensation of wire deflection errors in the arced corner machining.

Method of deflection corrected tonometry with phantom vessel experiments

BackgroundThe Continuous Non-Invasive measurement of arterial Blood Pressure [CNIBP] is possible via the method of arterial tonometry and the arterial volume clamp methods. Arterial tonometry successfully measures continuous arterial pressure but requires large vessel deformation and a highly miniaturized pressure sensor to obtain a direct calibration of pressure. A properly designed tonometer is capable of achieving pressure accuracy of less than 5% error at the radial artery. The volume clamp method achieves comparable errors but is generally restricted to the very peripheral arteries. Since the brachial or radial arteries are preferable sites to record blood pressure, tonometry is generally preferred. However, due to its strict operating requirements, tonometry requires a highly skilled operator. The greatest source of measurement error results from slight deviation from the artery wall applanation position. In this study, a method for correcting tonometry deflection error is introduced and evaluated using preliminary experiments. Methods-modelingIn prior analysis it has been shown that arterial wall flattening causes contact stress to become uniform and equal to the arterial pressure. In this article, we derive the contact stress for deflections other than the ideal applanation position and to allow variable vessel deflection. This analysis permits the contact stress to be corrected for tonometer positions that are not exact so that pressure accuracy is maintained in spite of less than ideal positioning. This will alleviate the necessity for highly skilled users and allow rapid determination of the pulse pressure. Methods-experimentalExperiments were performed to evaluate applied model corrections for tonometer accuracy versus vessel deflection. Two experiments were performed to evaluate tonometer accuracy when deflection is varied. The first experiment used no deflection correction and the second experiment applied model derived deflection correction. A force sensor was used to deflect a phantom latex vessel of known internal pressure. The corrected contact pressure was then compared with known pressures to evaluate the pressure accuracy. Results-modelinga geometric model was derived for vessel contact area versus deflection. This resulted in a formula that provides contact area continuously for any amount of deflection. Once the contact area is known the average tonometer contact pressure was obtained that corresponds with the vessel internal pressure. Results – experimentalA latex tubing phantom vessel was pressurized to a known amount and was deflected in increments over its full diameter while measuring contact force at each position. The model-derived formula was then used to calculate pressure at each position. The calculated pressure was then compared with known internal pressure to evaluate pressure accuracy for all the phantom pressure and deflection points. ConclusionsA modeling method for tonometer deflection correction was derived and evaluated using a phantom vessel. Average error was significantly reduced over the non-corrected data. The variability of error was also reduced for all data points collected. The experiments reveal that blood pressure measurement error can be reduced to levels obtained in near ideal tonometry conditions without the need for precise position control. The relaxed user precision is anticipated to simplify the use and design requirements for arterial tonometry in practice.

Modeling and experimental validation for surface error caused by axial cutting force in end-milling process

The high-speed milling is now the primary machining method of the thin-walled structures. Study on the surface error caused by part deflection has been comparatively mature, yet the deformation mode of the workpiece remains incomplete. This paper studies the milling error caused by the axial cutting force. On the basis of deflection function of the rectangular cantilever plate, a method is proposed to predict the deflection and surface error of the thin-walled part. There is an interplay of cutting force and surface error after machining. As the work suggests, workpiece will be warping under the axial cutting force. And the deformation increased with the increase of cutting depth and the decrease of the spindle speed.

The Development of a New Piezoresistive Pressure Sensor for Low Pressures

This paper presents the design methodology and fabrication process of a novel piezoresistive pressure sensor with a combined cross-beam membrane and peninsula (CBMP) diaphragm structure for micropressure measurements. The sensor is then analyzed through various experiments. The sensor is primarily designed based on the optimized sensitivity, and a finite-element method is used to predict the stresses that are induced in the piezoresistors and the deflection of the membrane under different pressures. Compared to other traditional diaphragm types, a significant increase in sensitivity can be achieved by the proposed sensor, and the membrane deflection and nonlinearity error considerably decrease. The sensor fabrication process is performed on an n-type single-crystal silicon wafer, and photolithography is used with five masks to fabricate the sensing elements. Additionally, piezoresistors are formed by boron implantation. The experimental results indicate that the fabricated sensor with the CBMP membrane yields a high sensitivity of 25.7 mV/kPa and a low nonlinearity of −0.28% full-scale span for a pressure range of 0–5 kPa at room temperature.

Modeling of cutting force, tool deflection, and surface error in micro-milling operation

Micro-milling has shown great potential in producing complex miniaturized components over wide range of materials. It can also fabricate micro-products in small batches efficiently and economically. In spite of these advantages, several challenges hinder its ability to produce components with better dimensional accuracy. Among several factors, tool deflection is one of the major sources of surface error on machined parts and features. Therefore, it is necessary to develop accurate and reliable process models to analyze and improve performance of the process. This study presents a methodology to determine cutting forces and surface error in the presence of tool deflections for micro-milling operation. Tool deflections have considerable influence on instantaneous uncut chip thickness. As tool deflection alters tooth trajectories and instantaneous uncut chip thickness, the rigid cutting force model needs to be modified suitably to consider the effect of deflections. This aspect has been incorporated in the model by modifying tool center location and tooth trajectories iteratively. The convergence of an iterative algorithm determining stable chip thickness is obtained by comparing RMS deviation of average chip thickness between two successive tooth passes. The axial variation of surface error due to tool deflections is estimated using surface generation mechanism. The proposed model is implemented in the form of a computational program to predict cutting force and surface error. The results of computational model are substantiated further by conducting machining experiments. It is shown that the proposed model predicts cutting forces fairly well in the presence of tool deflections. A comparison between predicted variation of surface error and 3D images of machined surface captured using optical microscope showed good qualitative agreement in the error profiles.