High-accuracy interference-fit assembly utilizing a hybrid actuator

Ensuring an optimal stability degree for building structures represents the basic engineers concern when working on developing projects for new structures or rehabilitation of old ones. The most important dynamic actions with destructive effects threatening a building structure are the seismic actions which place important stress under dynamic regime inside building structural elements but also vibration actions resulting from road or rail traffic acting on the bridge structure types. Special isolation methods have been developed, over time, in order to counteract the destructive effects of the mentioned dynamic actions by using mechanical devices directly mounted on the structural frames of a building, with the declared role of protecting the structure during the occurrence of these unexpected events. A structure having in composition such protective systems is considered an isolated structure against dynamic actions and devices used are classified as insulation systems or energy dissipative systems because they are able to consume an amount from the disturbing action input energy transforming it into another form energy, namely heat. A mechanical device model with energy dissipation properties is described in this paper that can be used for mounting at buildings and bridges in order to achieve energy consumption when a dynamic mode action acts on the isolated structure. This dissipative device assembly is achieved as a hydraulic cylinder with piston operating on the basis of a fluid with special viscosity properties. The piston, being solidary with the rod, has a number of orifices made necessary for the working fluid circulation so that when a request occurs it can perform a relative translational motion relative to the cylinder. The mounting solutions for the hydraulic dissipation system at the insulated structure are made by means of metal flanges positioned on the structural elements that allow a relative displacement during earthquakes and which must be limited by means of the energy dissipation action. An assembly model for the hydraulic dissipative device is built for which fluid flow analysis is performed inside the cylinder and through the piston orifices for different velocity values during rod translational motion. It is also analyzed the dissipation device operation for different orifice diameter values which ensure the working fluid circulation, as well as the different types of hydraulic fluid used. The results are presented for each case analyzed in part, where the role of dissipative device of the analyzed system is being emphasized.

The series manipulator of the demolition robot has different working postures and large self-weight so that the bearing mass of the joint hydraulic cylinder is a variable value, and the change of mass affects the dynamic characteristics of the valve-controlled hydraulic cylinder system. In this paper, an equivalent mass estimation method of the big-arm joint hydraulic cylinder is given, and the natural frequency range of the big-arm hydraulic cylinder-load system is calculated. In order to suppress the influence of the change of the natural frequency and external disturbance of the hydraulic cylinder on the system, the linear active disturbance rejection control is adopted in the closed-loop position control. The simulation results show that the change of load mass of the joint hydraulic cannot be ignored when designing the joint position controller of multi-joint hydraulic manipulator. And the simulation tests prove that the linear active disturbance rejection control strategy keeps good dynamic characteristic and steady-state accuracy for the change of natural frequency and external disturbance of hydraulic cylinder and has good tracking performance for periodic sinusoidal signal. Linear active disturbance rejection control is robust in the variable mass control of the manipulator and meets the requirements of the joint position control of the heavy-duty hydraulic manipulator.

The performance of high-speed and high-precision machine tool spindle is quite sensitive to the variation of system parameters. How to accurately predict the influences of key parameters on spindle characteristics is important for designers to achieve required machining accuracy. In the assembly of spindle system, the interference fit, which is always used to connect bearing and shaft, affects the performances of spindle system directly. Therefore, the quantitative investigation on the effects of interference fit on spindle characteristics are of great practical significance. In this paper, the effect mechanism of interference fit on spindle bearing system is explored and used to modify the analytical spindle bearing model. Firstly, the internal geometric relationships among the assembly bearing parts and shaft is analyzed under the influence of assembly deformation and centrifugal expansion. Then, the static and dynamic characteristics of spindle bearing system, including the bearing stiffness, maximum loosing speed, spindle stiffness as well as modal characteristics, are predicted under different interference fit values based on the modified spindle bearing model. The results show that the interference fit will stiffen the bearing and spindle system and result in obvious increments on bearing stiffness, spindle stiffness as well as the natural frequencies. A specially designed spindle test rig is built to verify the simulation results, and the variation of spindle stiffness and natural frequencies are measured under different interference fit values. The maximum error of the system natural frequencies between the analytical results and the experimental data is 7.36%, which confirmed the accuracy of the proposed analytical model.

The positional error in spatial data is defined as a vector by comparing the coordinates between the true position and the measured position. The standard tests to assess the positional accuracy use only the magnitude of the vector and omit the azimuth. This article suggests that the use of both values allows a much more complete analysis of the positional error. A set of tests is proposed that are relevant for this purpose and demonstrate that some important features are not identified by the common procedures. The test samples come from two datasets. The first is obtained from the comparison of 100 homologous points in two conventional maps, and the second one comes from the geometric calibration of a photogrammetric scanner. The results are analyzed and discussed, showing that important issues such as error anisotropy are detected only by means of the circular statistics tests and density maps of distribution. Therefore, tests that assess the goodness of fit for uniform distribution in azimuths, such as Rayleigh and Rao tests, give low probabilities (P = 0 and P > 0.01). Moreover, density maps working with both magnitude and angle can locate the outlier candidate and offer more information about the spatial distribution of error.

Over the few years civilian and military applications are maneuvering with multi-sensor Unmanned Aerial Vehicles (UAV). The aim of this paper is to improve autonomous UAV positioning by using Inertial measurement unit (IMU) and Global Navigation Satellite System (GNSS) is considered. The positional accuracy of UAV is limited to GNSS signal blockage. The advancements in micro electro mechanical systems (MEMS) helps to design low-cost IMU with meter-level accuracy in positioning. The estimation of attitude, position and velocity measurements are determined from a nine degree of freedom Arduino embedded IMU sensor. The Low-cost IMU sensor has been tested under static condition and then a dynamic movement of sensor is observed under moving base-line conditions on February 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> 2020 at Koneru Lakshmaiah Education Foundation (KLEF). In this paper, covariance filters are implemented to eliminate the gyro bias and accelerometer bias for improving attitude determination of IMU navigation system. The positioning from IMU sensor is derived using standard strap-down inertial navigation system (SINS) formulation. The position error from SINS indicates that IMU sensor is able to perform well with maximum position error of 5 meters and 2.5 meters for static and dynamic environments respectively. The outcome of this work would be useful for integration of navigation sensors using kalman filter based advanced techniques for UAV applications.

Higher revision rates have been reported in patients who have undergone unicompartmental knee arthroplasty compared with patients who have undergone total knee arthroplasty, with poor component positioning identified as a factor in implant failure. A robotic-assisted surgical procedure has been proposed as a method of improving the accuracy of component implantation in arthroplasty. The aim of this prospective, randomized, single-blinded, controlled trial was to evaluate the accuracy of component positioning in unicompartmental knee arthroplasty comparing robotic-assisted and conventional implantation techniques. One hundred and thirty-nine patients were randomly assigned to treatment with either a robotic-assisted surgical procedure using the MAKO Robotic Interactive Orthopaedic Arm (RIO) system or a conventional surgical procedure using the Oxford Phase-3 unicompartmental knee replacement with traditional instrumentation. A postoperative computed tomographic scan was performed at three months to assess the accuracy of the axial, coronal, and sagittal component positioning. Data were available for 120 patients, sixty-two who had undergone robotic-assisted unicompartmental knee arthroplasty and fifty-eight who had undergone conventional unicompartmental knee arthroplasty. Intraobserver agreement was good for all measured component parameters. The accuracy of component positioning was improved with the use of the robotic-assisted surgical procedure, with lower root mean square errors and significantly lower median errors in all component parameters (p < 0.01). The proportion of patients with component implantation within 2° of the target position was significantly greater in the group who underwent robotic-assisted unicompartmental knee arthroplasty compared with the group who underwent conventional unicompartmental knee arthroscopy with regard to the femoral component sagittal position (57% compared with 26%, p = 0.0008), femoral component coronal position (70% compared with 28%, p = 0.0001), femoral component axial position (53% compared with 31%, p = 0.0163), tibial component sagittal position (80% compared with 22%, p = 0.0001), and tibial component axial position (48% compared with 19%, p = 0.0009). Robotic-assisted surgical procedures with the use of the MAKO RIO lead to improved accuracy of implant positioning compared with conventional unicompartmental knee arthroplasty surgical techniques. Therapeutic Level I. See Instructions for Authors for a complete description of levels of evidence.

Equal channel angular pressing with converging billets—Experiment

Effects of sonic speed on location accuracy of acoustic emission source in rocks

ObjectivesThis study compares the biofilm inhibition effects of denture cleaning tablets, carvacrol, and their combined use against Candida albicans on denture bases produced with different techniques. Additionally, the surface roughness and contact angles of these denture bases were evaluated.Materials and methodsTest samples were prepared from four different denture base materials (cold-polymerized, heat-polymerized, CAD/CAM milling, and 3D-printed). The surface roughness and contact angles of the test samples were measured using a profilometer and goniometer, respectively. For the evaluation of biofilm inhibition, samples were divided into 5 subgroups: Corega and carvacrol, separately and combined treatments, positive (inoculated with C. albicans) and negative control (non-inoculated with C. albicans, only medium). Biofilm mass was determined using the crystal violet method. An additional prepared test sample for each subgroup was examined under scanning electron microscopy (SEM).ResultsThe surface roughness values of the 3D-printed test samples were found to be statistically higher than the other groups (P < .001). The water contact angle of all test materials was not statistically different from each other (P > .001). Corega and carvacrol, separately and combined, significantly decreased the amount of biofilm on all surfaces (P < .0001). Treatment of corega alone and in combination with carvacrol to the 3D-printed material caused less C. albicans inhibition than the other groups (P < .001; P < .05).ConclusionsThe surface roughness values of all test groups were within the clinically acceptable threshold. Although Corega and carvacrol inhibited C. albicans biofilms, their combined use did not show a synergistic effect.Clinical relevanceCarvacrol may be used as one of the disinfectant agents for denture cleaning due to its biofilm inhibition property.

The use of interference-fitted assemblies is very common in engineering practice, for example, in bolted connections and fitting of sleeves into cylindrical shafts. For practical-purposes, it is important to prevent stress concentrations which are generated at contact surfaces of the components assembled with interference fits. In this paper, a method for determining the interferences to uniform stress distribution at the contact boundary of the components is proposed. The finite-element method is used to solve stress and displacements in two component systems in contact with each other in which slip does not occur. The difference between maximum and minimum stresses at the contact boundary is minimized under a constraint of contact pressures, as nodal interferences are taken as design variables. The proposed method is applied to two basic examples of a rectangular plate fitted with a circular plate and a column fitted with a sleeve, to show its effectiveness.

Interference fit is widely uesd in micro gas turbine to transfer large torque and offer significant cost advantages. In this paper, a interference fit model was developed to research the contection characteristics of quill shaft for micro gas turbine. The radial stress, tangential stress, radial displacement and the Von Mises stress of the quill shaft are derived by using elastic theory to analyze the influence of the contact surface pressure and angular velocity on the strength of the quill shaft. Numerical calculated results show that The radial stress of the quill shaft is identically greater than zero and positively correlated with the contact press and angular velocity. The direction of the tangential stress of the quill shaft is determined by the value of the contact pressure. The radial displacement of the quill shaft is a monotony decrease function of the contact pressure and a monotony increase function of the angular velocity. Generally, the maximum stress of the quill shaft happens in the inner surface of the quill shaft regardless of the angular velocity.

It is important that manufacturers of robots provide sufficient information about the positional accuracy of robots(1). A mathematical model and test rig, are presently being developed for this purpose. Based on vector analysis, this mathematical model, when used in conjunction with the test rig will provide sufficiently precise information about the robot’s “static” and dynamic position accuracy. This includes orientation error, idling servoing behaviour, repeatability errors, overshoot and undershoot, and settling time. The proposed method can be used to determine the relation between positioning speed and dyanmic behavior and accuracy so that the robot can then be made to work at the highest positioning speed compatible with a required dynamic behaviour and positioning accuracy. The important novel feature of the work is that measurements are based on the use of an arrangement of non contacting transducers(2) so that the robot is able to move about freely while measurements are being taken.In some previous work by other researchers(3)(4), a contacting type of positional transducer has been used. This makes it very difficult to obtain reliable test results, particularly when the robot is moving at high speed. Impact between the robot end-effector and the transducers could result in large dynamic errors of transducer output. Such errors have now been eleminated.

The object of research is a mathematical model describing the movement of a robot with five degrees of freedom for a warehouse. The work was aimed at analyzing the kinematic structure of the manipulator, on the basis of which the base and local coordinate systems were selected, as well as further formalized recording of the kinematic equations in matrix form. It is noted that one of the most problematic places is that the algorithms for controlling the robot most often contain local rules for the interaction of robots between themselves and the external environment, and emergent behavior is manifested as a result of the application of these rules, which does not have a formal description. Therefore, it is important to modernize the models describing the motion of a robot with five degrees of freedom for a warehouse. Using the matrix method, the sequence of constructing coordinate systems is described and its mathematical description is given, which will make it possible to eliminate this drawback in the future. The computer implementation of the developed algorithms was carried out using methods for processing matrix data structures. The principle of constructing a kinematic model of a robot is presented, with the help of which the main coordinate transformation matrices are obtained for robot with five degrees of freedom, and the possibility of taking into account the size of the gaps in the joints is shown. The resulting model is obtained, which is proposed for use in building control algorithms for a robot with an automatic gap selection, as well as in robot calibration. This is due to the fact that the proposed model has a number of features, in particular, the basic coordinate system and the coordinate system of each link of robot with five degrees of freedom are taken into account. This makes it possible to obtain the values of the indicators for the projection of the robot position vector in the initial state, in the rotation of the fourth link at a well-defined angle and in the case of a vertically straightened manipulator. Compared to similar known studies, this provides advantages such as minimizing errors in position, speed and motion accuracy. The object of research is a mathematical model describing the movement of a robot with five degrees of freedom for a warehouse. The work was aimed at analyzing the kinematic structure of the manipulator, on the basis of which the base and local coordinate systems were selected, as well as further formalized recording of the kinematic equations in matrix form. It is noted that one of the most problematic places is that the algorithms for controlling the robot most often contain local rules for the interaction of robots between themselves and the external environment, and emergent behavior is manifested as a result of the application of these rules, which does not have a formal description. Therefore, it is important to modernize the models describing the motion of a robot with five degrees of freedom for a warehouse. Using the matrix method, the sequence of constructing coordinate systems is described and its mathematical description is given, which will make it possible to eliminate this drawback in the future. The computer implementation of the developed algorithms was carried out using methods for processing matrix data structures. The principle of constructing a kinematic model of a robot is presented, with the help of which the main coordinate transformation matrices are obtained for robot with five degrees of freedom, and the possibility of taking into account the size of the gaps in the joints is shown. The resulting model is obtained, which is proposed for use in building control algorithms for a robot with an automatic gap selection, as well as in robot calibration. This is due to the fact that the proposed model has a number of features, in particular, the basic coordinate system and the coordinate system of each link of robot with five degrees of freedom are taken into account. This makes it possible to obtain the values of the indicators for the projection of the robot position vector in the initial state, in the rotation of the fourth link at a well-defined angle and in the case of a vertically straightened manipulator. Compared to similar known studies, this provides advantages such as minimizing errors in position, speed and motion accuracy.

In interference fit assembly, the magnitude and deviation of the assemble force are large so that it is hard to reach high accuracy of position for components of multiple parts stacked up. A force/stiffness compensation method is proposed to control the positioning accuracy in the interference fit assembly for multi-peg-hole components. Based on the force and displacement information measured in the assembly process, the position errors are acquired, and the stiffness of the assembly system under the exerted assemble force is calculated. According to the stiffness, the deviation from the target position is calculated and compensated. An experimental equipment based on this method was developed. As an example, assembly of rings, 6.2 mm in diameter and 0.25 mm in thickness, was carried out to demonstrate the feasibility of the proposed method. The assembly results show that high positioning accuracy of the assembled rings can be achieved with a large variation of assembly force. The presented method provides a simple, feasible, and efficient solution for interference fit assembly for multi-peg-hole components.

An Optimization Method of Assembly Process for Bolt Flange Connection Structure with Manufacturing Characteristics