The unbalancing vibration monitoring and control of rotating machinery is an important engineering problem. In order to correct the unbalance of rotor system online, an active dynamic balancing head is designed based on the ratchet-pawl mechanism and pneumatic technology. The inner mass distribution state of balancing head can be changed to correct the unbalance when the rotor system is working in unbalancing condition. The mechanical principle and pneumatic control system of the balancing head are introduced in the paper. Based on a double-face online dynamic balancing experiment system, the balancing effect of the balancing head has been proved by many experiments. In order to improve the dynamic balancing accuracy of the balancing head in the practical application, the possible influencing factors of dynamic balancing accuracy are analyzed in the paper.
This paper presents a novel study on the analysis of the “fully compliant” spatial four-bar mechanism. To the best of our knowledge, any research on “fully compliant” spatial four-bar mechanism is not available in the literature. In the previous study performed by the authors, a “partially compliant” version of the spatial four-bar mechanism was introduced. There was a rigid spherical joint in that case, thus there was no torsional loading at flexural hinges. For the fully compliant case, there is no spherical joint in the structure of the mechanism, thereby there is also torsion available at multiple axis flexural hinges. Design of this fully compliant mechanism is different from the partially compliant case. In this study, deflections of the multiple axis flexural hinges are determined separately as bending and twist. Essential angles for manufacturing a mechanism are determined. A prototype is built and results of the mathematical model are verified with experiments. Finally, a fatigue test is performed. After one and a half million cycles it is observed that there is no indication of any failure. Since there are many applications of rigid spatial four bar mechanisms, it is strongly believed that a fully compliant version of such a mechanism may also find applications.
The crown worm drive is a new type of worm drive, it is consisting of an internal gear and a crown worm generating by the internal gear surface, and it is characterized with small size yet high-loading capacity. To satisfy the high precision requirement of crown worm tooth surface, a grinding method based on virtual center distance manufacturing principle is proposed and a grinding machine is reformed. A mathematical model was derived to calculate the theoretical probe center surface, and a measuring method is proposed to check the accuracy of crown worm tooth surface. A crown worm sample is manufactured and measured, the results show that the accuracy is 0.079mm on the upside tooth surface and 0.082mm on the underside tooth surface. The study is expected to provide the experimental foundation for the future application of the crown worm drive.
The friction of rolling guideways in the prerolling region displays hysteretic behavior known as nonlinear spring behavior (NSB). NSB deteriorates motion accuracy and causes vibration in the feed direction. Therefore, the influences of NSB on the dynamic characteristics of rolling guideways should be clarified. This paper describes the influence of NSB on the dynamic characteristics of a rolling guideway. A simple friction model is constructed based on the Masing rule. Because the proposed friction model is described with only three parameters, the factor that inherently affects the dynamic characteristics can be clearly identified. To clarify the influence of NSB, the impulse response, frequency response, and steady state motion are analyzed by numerical analysis. According to the results, the dynamic characteristics in the feed direction depend only on the change rate of friction in the prerolling region, which is introduced to the friction model as the shape factor, n. The stiffness and damping are high when the change rate of friction is high in the prerolling region. The frequency response function is force- dependent, and its tendency is varied by n. The frequency response function includes harmonic and super harmonic resonances. When the carriage is excited with a frequency lower than that of the super harmonic resonance, a displacement spike (quadrant glitch) is observed. Additionally, the nonlinearity cannot be ignored when the carriage is excited with a frequency lower than the harmonic resonance. Finally, an experiment with a roller guideway is conducted to prove the validity of the analysis. The resonance frequency and compliance at the harmonic resonance measured by the experiment accurately conform to the analytical results.
The generation principle and meshing characteristics of conjugate-curve circular arc gears, which is proposed based on the theory of conjugate curves, are studied in this paper. The generation principle and mathematical model of this gear drive are introduced according to the given spatial screw curve. Tubular meshing surfaces contacting in the orientation of designated contact angle are provided to build up circular arc tooth profiles, which inherit all properties of conjugate curves. Geometrical three-dimensional models are established based on a numerical example and the results of motion simulation show that the generated gear drive meets general meshing and motion conditions. The comparisons between this designed gear drive and conventional circular arc gearing for the generation method and meshing characteristics are carried out. And the transmission efficiency of gear pair manufactured by hobbing cutter tools is also test. Through the analysis, it shows not only the general corresponding relationship between two gears, but also the conjugate meshing essence of circular arc gears. Theoretical and experimental results demonstrate the feasibility and correctness of proposed conjugate curves theory and the application to new types of gear drive with high performance will be carried out.
We studied the effectiveness of diamond nanoparticles (DNPs) dispersed in water as a lubricant additive between stainless steel plates and sintered tungsten carbide (WC) balls. DNP dispersions with concentrations of 0.01, 0.1 and 1 wt.% were prepared and used as lubricants under a load of 1.88 N, for 240,000 friction cycles. High-friction coefficients of more than 0.3 were observed in an initial period. Then friction coefficients declined and stabilised at values of approximately 0.1. The steady-state friction coefficients were independent of the DNP concentration and lower than that for distilled water. In the initial period, wear of both the plates and ball was obvious. In the steady-state period, additional wear on the plates was a little; however, ball wear scars were clearly observed. The size of the ball wear scars decreased with decreasing the DNP concentration. It is likely that DNPs were embedded mainly in the stainless steel plates, and the embedded DNPs protected the plates and wore the balls in the steady-state period. Compared with the lubrication under distilled water, the friction coefficient and wear of the plate under the lubrication by the 0.01 wt.% DNP dispersion were lower, and the wear of the ball by this lubrication condition was not higher.
In this paper, we consider a single machine scheduling problems integrating with deterioration effect and rate-modifying activities (RMAs). The scheduling problem assumes that the machine may have multiple RMAs and each job has the processing time with deterioration effect increased depending upon the gap between recent RMA and starting time of the job. In practical industrial applications, the determination of the number and position of RMAs is a critical issue, because the RMAs recover deteriorated processing time of jobs bringing back to normal processing time. In this paper, we simultaneously determine the schedule of time-dependent deteriorating jobs and the number and positions of RMAs to minimize the makespan. To solve the problem, a mathematical model is derived to obtain the optimal solution and hybrid meta-heuristic algorithms are proposed for the problem. The performance of the algorithms is compared using randomly generated examples.
In this study, we consider the positioning of a pneumatic stage in order to compensate effects of different length of pipes, which connect servo valves and cylinders. Since, in industrial scenes, it is difficult to use pipes of the same length due to the structure of industries, the length of each pipe is often different. In this case, the characteristic of the pneumatic system, which consists of the pipes, servo valves, and chambers, changes in accordance with the pipe length. It leads to two issues: The first one is that the performance of proportional-derivative-double derivative (PDD2) control, which is effective for the control of pneumatic actuators, is degraded. To overcome this issue, the parameter of a pre-compensator for the PDD2 control is tuned. The suitable value of this tuned parameter increases with the length of the pipes. The second one is that the effects of flow disturbance increase due to the different pipe length. When the length of the pipes is not same, it is probable that the magnitude of flow disturbance transmitted to each pipe is different. For this reason, multiple flow disturbance observers (FDOBs) are implemented in a control system. Experimental results show that the repeatability of the positioning is improved by using the FDOBs
For variable oscillation mechanisms, if output stroke is decreased, output-link force will increase for a same input due to the mechanical advantage. Thus, in order to eliminate input actuator stall phenomena for cases where sudden increase occurs at output load, variable oscillation mechanisms can be employed. In this study, a novel design procedure for seven link two degree-of-freedom variable oscillation mechanisms is proposed. The mechanisms run as a six-link mechanism for a fixed position of a control-link. With this method, a variable oscillation mechanism is designed. It is shown that the design procedure is consistent by performing a kinematic analysis. Also, an approach to switch to second oscillation mode is introduced via underactuation. Finally, it is verified that the theoretical approach proposed is consistent for underactuated switching with Nastran simulation.
In a head-positioning system of hard disk drives, various mechanical resonances may degrade performance or stability of the control system. In these mechanical resonances, a torsional mode of a head-stack assembly (HSA), in which a resonant frequency is between 3 kHz and 4 kHz, has a large negative impact for the performance of hard disk drives because it can be easily excited by operational vibrations of other hard disk drives in a data-storage server. To overcome this issue, we have developed a vibration control method with a thin-film-coil actuator (called ”film actuator”) for the head-positioning control system of hard disk drives. The film actuator is attached to a coil of a Voice Coil Motor (VCM). This proposed control system is a triple-stage-actuator system: the first stage is a VCM actuator for moving the HSA, the second stage is a PZT actuator for moving a suspension in the HSA, and the third stage is the film actuator to control the torsional mode of the HSA. The proposed triple-stage actuator system can compensate for the vibrations of the torsional mode by using the film-actuator. Comparison of sensitivity functions showed that the triple-stage-actuator system can improve a sensitivity function at the torsional mode's frequency without decreasing a servo bandwidth of the control system.
Nano/micro scale surface structure on precision machined parts dominates the various product functions such as friction, wear resistance, corrosion, fatigue, and wetting. This paper presents a multi-dimensional surface texture assessment using laser speckle pattern analysis. From the observation result of laser speckle in precision machined surface, the probability density distribution of light intensity on laser speckle changes with the surface roughness. In addition, the autocorrelation function of speckle intensity distribution changes with the periodicity of micro surface structure. By analyzing the relation between surface texture and laser speckle pattern, characteristic parameters of laser speckle reflecting surface texture properties are identified; i.e. the mean light intensity, the deviation of the probability density distribution of light intensity, the autocorrelation length of intensity distribution, and the degree of dissimilarity between adjacent speckle patterns. The proposed parameters can evaluate the roughness, the period, and the degree of dissimilarity in periodic micro surface structure. Furthermore, the surface texture distribution and the anisotropy of micro surface structure can be assessed by detecting the variation of the proposed parameters. In consequence, the proposed method can quantitatively assess the nano/micro scale surface texture.
The geometric dimensioning and tolerancing is one of the most important characteristics of machined parts. A systematic method is proposed in the paper to simulate the shape generation processes in turning operations, to estimate the geometric dimensioning and tolerancing of the turned faces, based on the machining parameters. The simulation model includes both the models of the shape generation motions considering kinematic motion deviations and the cutting tool geometries. The shape generation motions with deviations are mathematically described by combining 4 by 4 transformation matrices. A set of points on the turned faces are generated through the simulations, and an assessment surface is obtained as the datum reference to estimate the 3-dimensional (3D) tolerances, based on the points generated by the turning process simulations. The proposed method provides us with a systematic method to estimate the geometric dimensioning and tolerancing in the turning processes including the kinematic motion deviations.