Torque Fluctuation Research Articles

Dynamics modeling and simulation analysis of wet clutch considering spline pair

PurposeDuring the operation of a wet clutch, there are fluctuations in speed and torque, which have an impact on the stability of the clutch and the strength of the friction plate and the spline pair of the dual steel plate. The purpose of this study is to investigate the vibration characteristics of the wet clutch and the dynamic load characteristics of the spline pairs.Design/methodology/approachThe spline pair model is established by the piecewise linear function method, and on this basis, dynamic equations considering the spline pair of dual steel plates and friction plates are established. Considering that the wet clutch has multiple spline pairs, an equivalent model of the number of teeth and the equivalent model of the tooth width were proposed, and the Runge-Kutta numerical method was used for the wet clutch for these two models.FindingsThe research results show that the equal tooth number model has greater meshing stiffness and smaller fluctuation than the constant tooth width model, which shows that increasing the meshing stiffness of the system is beneficial to reduce system fluctuation and improve system stability.Research limitations/implicationsThe friction plate has the system that multiple splines are independent of each other, which is relatively complicated. Therefore, an equivalent calculation is performed on multiple pairs of steel plates (friction plates) to simplify the calculation of the spline pairs.Social implicationsThis paper provides a theoretical basis for further dynamic characteristics analysis of wet clutch and reducing fluctuation of speed and torque.Originality/valueDynamic equation considering the spline pair of the dual steel plates and the friction plates is established to study the vibration characteristics of the wet clutch and the dynamic load characteristics of the spline pair, etc.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-03-2023-0078/

Improved Rotor Flux-Based SMO and RBF-PID Control Strategy for PMSM

This paper proposes a control strategy that combines an improved flux-based sliding mode observer with a Radial Basis Function Proportional-Integral-Derivative (RBF-PID) controller for the control of Permanent Magnet Synchronous Motors (PMSM). The strategy aims to address the issues of electrical angle estimation errors and torque fluctuations in traditional sliding mode observer control. The improved sliding mode observer utilizes the flux model of the PMSM to enhance the accuracy of electrical angle estimation, thereby reducing the estimation errors and improving the control of the current loop and speed. The RBF-PID controller ensures system stability while achieving faster response and reduced torque fluctuations. Simulation and experimental results demonstrate that compared to traditional PI control and sliding mode observer control methods, the proposed strategy improves the performance of electrical angle estimation by 7.05% and reduces overshoot in the q-axis current by 28.6%, exhibiting better control performance and smaller errors.

Efficient Fault Detection of Rotor Minor Inter-Turn Short Circuit in Induction Machines Using Wavelet Transform and Empirical Mode Decomposition.

This paper introduces a novel approach for detecting inter-turn short-circuit faults in rotor windings using wavelet transformation and empirical mode decomposition. A MATLAB/Simulink model is developed based on electrical parameters to simulate the inter-turn short circuit by adding a resistor parallel to phase "a" of the rotor. The resulting high current in the new phase indicates the presence of the short circuit. By measuring the rotor and stator three-phase currents, the fault can be detected as the currents exhibit asymmetric behavior. Fluctuations in the electromagnetic torque also occur during the fault. The wavelet transform is applied to the rotor current, revealing an effective analysis of sideband frequency components. Specifically, changes in amplitude and frequency, particularly in d7 and a7, indicate the presence of harmonics generated by the inter-turn short circuit. The simulation results demonstrate the effectiveness of wavelet transformation in analyzing these frequency components. Additionally, this study explores the use of empirical mode decomposition to detect faults in their early stages, observing substantial changes in the instantaneous amplitudes of the first three intrinsic mode functions during fault onset. The proposed technique is straightforward and reliable, making it suitable for application in wind turbines with simple electrical inputs.

Parametric Damping of Microgrid Frequency Fluctuations at Synchronous Machines with Using Lyapunov Theory for Exciter Regulation

In synchronous machines, electromechanical swinging can be damped by parametric control of the excitation current. This is possible only in case the excitation time constant is much smaller than the mechanical constant of the machine. The method described in this paper is effective for damping oscillations caused by oscillations in the grid frequency, grid voltage, and mechanical torque fluctuations. The method is based on the Lyapunov stability theory and demonstrated on a real synchronous machine. This machine operates as a noninterruptible backup power system. The original power fluctuations were up to 50% of the nominal power of the machine. With the described control, a sevenfold increase in the damping of fluctuations caused by grid frequency variations has been achieved.

Influence of the shutdown process of the driveline on the generator bearing life in the diesel generator set

Diesel generator sets are commonly used as power sources in transportation due to their versatility and cost-effectiveness. During the shutdown process, the diesel engine’s cylinder compression pressure would cause forced vibration in the driveline system through the crank linkage mechanism, resulting in unsteady loads that pose a threat to the bearing life. To address this issue, a coupling forward design method is proposed that takes into account the impact of unsteady loads on bearing life. An experiment was conducted on a 16V280 diesel generator set shutdown process, and a driveline dynamic model was established. The cumulative damage value that connects unsteady loads and bearing life was introduced to quantify the effect of unsteady loads on the bearing life during the shutdown process. The unsteady loads included torque fluctuation and collision forces. The results showed that reducing the driveline key gap and increasing the coupling stiffness can decrease the combined load on bearings and improve bearing life. A large stiffness coupling was designed to achieve shutdown smoothness and a 43.19% reduction in bearing life damage, confirming the design method’s feasibility concerning bearing life.

Aerodynamic analysis of a novel pitch control strategy and parameter combination for vertical axis wind turbines

The performance of a vertical axis wind turbine (VAWT) deteriorates at low tip speed ratios (TSR) and it is mainly characterized by flow separation and dynamic stall. Several mitigating techniques have been developed recently based on flow separation and dynamic stall research activities. One of such techniques is the use of blade pitch angle control, which shows very promising optimal performance in VAWTs. However, its adaptation for periodic variation of the angle of attack remains an important issue that needs to be addressed urgently. Therefore, this paper proposes a novel pitch control strategy based on the VAWT-shape pitch motion to achieve blade dynamic pitch with the rotational parameters (TSR and azimuth angle). The pitch scale factor (μ) is introduced to proportionally vary the angle of attack. High accuracy computational fluid dynamics (CFD) methods are used to simulate dynamic changes in pitch angle, flow field and vortex shedding vorticity, with the turbulence modelled using the SST k-ω model. The results show that a 146% increase in power coefficient can be achieved using a μ of 0.3 at TSR of 1.25. Additionally, the use of dual pitch scale factors (dpsf) in the windward and leeward regions causes intense transient torque fluctuations at 0° (360°) and 180° azimuths due to a breaking distance in pitch angular velocity at these azimuths. Adding a weight function into the fitting process of the dpsf pitch curve effectively minimize these fluctuations.

A Study of the Dynamic Characteristics of an Electrical Rotating Machine Applying No-Insulation HTS Field Coils

This paper presents a dynamic characteristic analysis of an electrical rotating machine that applies no-insulation (NI) high-temperature superconductor (HTS) field coils. The HTS electrical rotating machine applying HTS field coils has high power density compared to conventional electrical rotating machines that utilize normal conductor field coils, meaning that it has great potential for next-generation mobility applications such as electric ships and aircraft. Recently, several studies have reported the possibility of solving the quench protection problem of the HTS field coil, which is one of the most pressing issues in HTS electrical rotating machines, and the key technology is the no-insulation (NI) winding technique. The NI winding technique enhances the electrical and thermal stability of the HTS field coil because the over-current can be automatically bypassed through the turn-to-turn contacts. Although there have been many studies of the electrical and thermal stability of NI HTS field coils, there are still issues related to NI HTS field coil applications to electrical rotating machines. In particular, there are few studies of the behavior of electrical rotating machines with a NI HTS field coil under dynamic conditions, such as active shortcircuit and speed drop conditions. In this study, we designed an electrical rotating machine that utilizes NI HTS field coils and analyzed the dynamic characteristics of the designed machine. The results demonstrate there is a possibility of larger torque fluctuations and armature current fluctuations in the NI HTS machine than in the insulated HTS machine.

Mitigation of the Pressure Pulsations in an Axial Turbine at Speed-No-Load With Independent Guide Vanes Opening

Abstract Hydraulic turbines are operated more frequently at no-load conditions, also known as speed-no-load (SNL), to provide a spinning reserve that can rapidly connect to the electrical grid. As intermittent energy sources gain popularity, turbines will be required to provide spinning reserves more frequently. Previous studies show vortical flow structures in the vaneless space and the draft tube and rotating stall between the runner blades of certain axial turbines operating at SNL conditions. These flow phenomena are associated with pressure pulsations and torque fluctuations which put high stress on the turbine. The origin of the instabilities is not fully understood and not extensively studied. Moreover, mitigation techniques for SNL must be designed and explored to ensure the safe operation of the turbines at off-design conditions. This study presents a mitigation technique with independent control of each guide vane. The idea is to open some of the guide vanes to the best efficiency point (BEP) angle while keeping the remaining ones closed, aiming to reduce the swirl and thus avoid the instability to develop. The restriction is to have zero net torque on the shaft. Results show that the flow structures in the vaneless space can be broken down, which decreases pressure and velocity fluctuations. Furthermore, the rotating stall between the runner blades is reduced. The time-averaged flow upstream of the runner is changed while the flow below the runner remains mainly unchanged.

Design Optimization of Electrical Structure Parameters of Induction Asynchronous Mechanical–Electric–Hydraulic Power Coupler

In response to the problems of considerable size, loose structure, and low energy conversion efficiency of multi-energy power coupling devices, this paper makes improvements based on the mechanical–electric–hydraulic power coupler proposed by our research group. We propose a new asynchronous mechanical–electric–hydraulic power coupler (IA-MEHPC). This mechanism integrates a traditional three-phase asynchronous motor with a swashplate axial piston pump/motor to realize the mutual conversion of electrical, mechanical, and hydraulic energy. Compactness, efficiency, and adaptability are the distinguishing features of the complex. This paper builds a three-dimensional model of the IA-MEHPC and a two-dimensional theoretical model of the electrical structure (motor part). Moreover, the electrical structure parameters of the IA-MEHPC are optimized using an approximate response surface-based optimization method. The maximum motor peak torque and minimum torque fluctuation are identified as optimization objectives, and we obtain the optimal combination of parameters. The simulation results show that, compared to the pre-optimized structure, the peak motor torque of the optimized IA-MEHPC is increased by 5.78%, and the torque pulsation coefficient is reduced by 15.83%, in line with engineering practice expectations. This paper innovatively proposes and optimizes IA-MEHPC, which is significant for developing hybrid mechanical devices and subsequent research.

A Sage-Husa Prediction Algorithm-Based Approach for Correcting the Hall Sensor Position in DC Brushless Motors.

Accurate knowledge of the rotor position is essential for the control of brushless DC motors (BLDCM). Any deviation in this identification can cause fluctuations in motor current and torque, increase noise, and lead to reduced motor efficiency. This paper focused on a BLDCM equipped with a three-phase binary Hall sensor. Based on the principle of minimum deviation, this paper estimated the relative installation offset between the Hall sensors. It also provided a clear method for ideal phase commutation position recognition and eliminated the Hall sensor installation position deviation. The proposed pre-calibration method identified and eliminated the offset of the permanent magnet poles, the delay time caused by the Hall signal conditioning circuit, and the offset of the sensor signal identification due to armature response under different loads. Based on the pre-calibration results, a correction strategy for correcting the rotor position information of BLDCMs was proposed. This paper presented a self-adaptive position information prediction algorithm based on the Sage-Husa method. This filters out rotor position information deviations that are not eliminated in pre-calibration. Experimental results on a hydrogen circulation pump motor showed that, after the pre-calibration method was adopted, the Mean Square Error (MSE) of motor speed fluctuations decreased by 92.0%, motor vibration was significantly reduced, average phase current decreased by 62.8%, and the efficiency of the hydrogen circulation pump system was significantly improved. Compared to the traditional KF prediction algorithm, the Sage-Husa adaptive position information prediction algorithm reduced the speed fluctuation during the uniform speed operation stage and speed adjustment stage, the speed curve overshoot, and the commutation time deviation throughout the process by 44.8%, 56.0%, 54.9%, and 14.7%, respectively. This indicates a higher disturbance rejection ability and a more accurate and stable prediction of the commutation moment.

Sensorless Scheme for Permanent-Magnet Synchronous Motors Susceptible to Time-Varying Load Torques

This paper is devoted to designing a sensorless high-speed tracking control for surface-mount permanent-magnet synchronous motors, considering a time-varying load torque. This proposal consists of an extended-state observer interconnected with a PI-compensated controller, considering only the measurement of electrical variables for feedback. First, to design the extended-state observer, a rotary coordinate model of the motor is extended in one state to estimate the load torque and the rotor’s position and speed. Later, the estimations are fedback to a PI-compensated controller to attenuate the time-varying load torques. Our proposed methodology aims to overcome a restriction regarding the solution of the Riccati equation respecting the Lipschitz condition for observer stability analysis. Therefore, a PI-compensated controller described as a closed-loop provides a sensorless scheme. Lyapunov stability analysis is applied to determine sufficient conditions to ensure that the states of the closed-loop system are ultimately bounded, which is one of our main contributions. The proposed observer-based controller scheme deals with unmeasured load torque fluctuations. Furthermore, we carry out high-precision emulations to provide testing scenarios of the permanent-magnet synchronous motor with some challenging load torque magnitudes and behaviors. Finally, we conduct experiments on the Technosoft® development platform to corroborate the feasibility of the proposed control scheme in a real-world scenario.

Operational instability of a high-rotational-speed electric pump in a hybrid rocket motor

Electric pumps capable of operating at high rotational speeds have enormous potential for application in hybrid rocket motors because of their light weight and ability to made rapid adjustments in rotational speed. Previous studies have assessed the performance of electric pumps; however, the physical mechanisms underlying the operational instabilities of high-rotational-speed pumps remain obscure. Simulations were accordingly conducted in this study to explore the physical mechanism of experimentally observed operational instabilities. The average head deviation between the simulated and experimental results was within 2%. The results of the instability analysis at low mass flow rates indicated that the reflux at the impeller outlet intensified, resulting in increased velocity, turbulent Reynolds number, and vorticity. The flow structure at a mass flow rate of 4.2 kg/s caused significant rotor torque fluctuation (2.1 times that at 5.88 kg/s), which coupled with the electric motor rotation and gradually increased the instability of the electric pump until shutdown. The minimum mass flow rate at which the electric pump operated stably was between 4.2 and 4.47 kg/s. The results of the instability analysis also indicated that severe cavitation occurred at 7.4 kg/s that reduced the head and significantly disrupted the flow stability. Furthermore, this cavitation led to an increased torque fluctuation amplitude and more dispersed frequency distribution (compared with that at 4.2 kg/s), which affected the stability of the electric motor and ultimately led to shutdown. These findings provide theoretical guidance for the development of thrust adjustment schemes for electric-pump rocket motors, benefiting the aerospace community.

Battery and Flywheel hybridization of a reversible Pumped-Storage Hydro Power Plant for wear and tear reduction

Energy security and environmental challenges are some of the drivers for increasing the electricity generation from non-programmable Renewable Energy Sources (RES), adding pressure to the grid, especially if located in weakly connected (or isolated) islands, like Sardinia. Variable-speed Pumped Storage Hydro Power (PSHP) can offer a high degree of flexibility in providing ancillary services (namely primary and secondary regulations), but due to the hydro-mechanical nature of the equipment, sudden variations in the power output cause wear and tear. Other energy storage devices cannot compete with PSHP in terms of energy and power availability. The aim of this research is to assess the benefits derived from the hybridization of a PSHP with Battery Energy Storage System (BESS) and Flywheel Energy Storage System (FESS), to be installed in the Sardinia island (Italy). A dynamic model of the hybrid plant was made in MATLAB–Simulink® environment. A detailed model of the variable-speed pump-turbine was obtained from experimental data, and a simplified model of a fixed-speed turbine was produced. A detailed FESS model was provided by CIEMAT (Madrid, Spain) and a simplified BESS model was included. A dedicated control strategy to manage the power flows and accounting for State Of Charge (SOC) control, was implemented. A total of 100 combinations of BESS and FESS powers were taken into account, and the control strategy was calibrated for each one of them. The plant was simulated open-loop over a 3600s time period, feeding historical frequency and Automatic Generation Control (AGC) data. The simulations covered three PSHP operation modes: variable/fixed-speed turbine and variable-speed pump, and with/without hybridization. The performances of the hybridization were evaluated with wear and tear indicators for the PSHP (distance travelled by and number of movements of the wicket gate for turbine, fluctuations of the shaft torque for the pump) and capacity loss (life consumption) for the BESS. The results show that all the combinations of BESS and FESS powers result in the reduction of both the travelled distance and number of movements of the guide vanes. The best hybrid combination for the PSHP does not affect the BESS life consumption, which still is always in an acceptable range. A comparison between the non-hybrid variable-speed turbine and the hybrid fixed-speed counterpart shows that the electric powers do not differ substantially, but the hybridization smooths the movement of the guide vanes. The pump torque fluctuations sharply decrease with the hybridization, but more research is needed to validate that the change in the fluctuation index corresponds to a physical phenomenon. Overall, the hybridization improves the plant performances in terms of wear and tear reduction, and the presence of an additional FESS benefits both the BESS and the PSHP. The results also highlight the necessity for more research in variable-speed pumps providing ancillary services, and their impact.

Rotation tracking control strategy of underwater flexible telescopic manipulator based on neural network compensation for water environment disturbance

The underwater flexible telescopic manipulator (UFTM) can be installed on a submersible to achieve underwater operation, which is conducive to the exploration and development of deep-sea resources. However, the motion of the UFTM is affected by underwater disturbance torque, which may lead to a decrease in operational accuracy. In addition, the flexible components in the UFTM, including flexible deformation and torsional deformation, will exacerbate fluctuations in the rotation angle underwater environment disturbance torque. In this paper, a control method using neural networks to identify underwater disturbance torques is proposed to improve the rotational tracking accuracy of the UFTM. Firstly, based on the assumed modal method (AMM) and Lagrange equation, the UFTM dynamic model considering two-dimensional deformation and underwater disturbance torque is derived. Then, based on the UFTM dynamic model and Lyapunov theorem, the adaptive law and control law of neural networks are designed. Finally, simulation and control experiments prove the effectiveness of the neural network compensation for underwater disturbance torque control strategy. Compared with the classical PID strategy and the sliding mode control, the control strategy of neural network compensation for underwater disturbance can effectively improve the tracking control accuracy of the UFTM.

Experimental investigation of a Wells turbine under dynamic stall conditions for wave energy conversion

Marine energy still plays a marginal role in the current global energy scenario, despite the incessant effort by research for more than thirty years in the exploitation of the so-called blue energy. Among the wide range of marine technologies, wave energy harvesting can play a significant role in view of its potential and Oscillating Water Column (OWC) systems, coupled with Wells turbines, can be considered among the most mature wave energy technology. Due to the oscillating nature of the flow rate in this kind of applications, Wells turbines are affected by dynamic stall, which has significant effects in terms of performance, fatigue, noise and structural integrity of the turbine.Actually, during dynamic stall, the Wells turbine experiences evident high frequency torque fluctuations which overlay on the typical hysteresis loop, mainly during flow deceleration. The amplitudes of these fluctuations are damped as the flow rate decreases toward reattachment. Often these fluctuations are not evident because hysteresis loops are usually provided with phase-averaged data, which can significantly smoothen or even conceal them. Indeed, it is difficult to find in the literature high frequency torque measurements able to show these fluctuations. With the aim to better investigate how the stall triggers this phenomenon, a monoplane Wells turbine has been manufactured in 3D printing and tested in the open wind tunnel of the Polytechnic University of Bari, Italy. The interest of the experimental campaign has been mainly focused on the effects of main parameters of the oscillating inlet flow rate (mean flow rate, amplitude and period of the oscillations, modifying the controlling parameters of the inverter driving the squirrel cage blower) on the performance of the machine. The machine has been firstly investigated under steady state inlet flow conditions, then under dynamic stall conditions. As a result, unsteady torque fluctuations occur during the flow deceleration till the flow reattachment. After the stall, the investigated Wells turbine experiences a drastic reduction of the torque coefficient of about 90%. Moreover, the torque coefficient shows a number of peaks during deceleration phases ranging from 2 to 4. Specifically, the case with the maximum period of the flow rate under investigation (i.e., T = 20 s) shows a greater number of peaks (4) than those related to the other cases (3). Moreover, it has been found that this unsteady behavior is due neither to the mass flow rate crossing the turbine, nor to the stagnation pressure drop, nor to the rotational speed control, which is correctly performed keeping the rotational speed within 1% of the target value. Hence, detecting these oscillations can be relevant in the turbine design phase to enhance the structural strength of the turbine.

Unified Vector Torque Control for Reluctance Motor With Different Coil Pitch

This paper unifies the vector torque control of reluctance motor with different coil pitch in the classic vector model frameworks, including the typical switched reluctance motor (SRM), mutually coupled switched reluctance motor (MCSRM), synchronous reluctance motor (SynRM) and so on. Based on the proposed vector model, the instantaneous electromagnetic torque of the reluctance motor is decoupled into two components. The first partial torque is called as the Synchronous-Speed Reluctance Force (SSRF), generated by the interaction of the <i>d</i>-axis and <i>q</i>-axis currents. The second partial torque is the Double-Speed Reluctance Force (DSRF), generated by the interaction between the <i>dq</i>-plane current and the 0-axis current. The torque formula can reflect the torque generation and fluctuation reasons, and the proportion of the two torque components is related to the ratio of the varying components of the motor&#x0027;s self-inductance and mutual inductance. Different types of reluctance motors can be summarized in the unified vector model. The conclusion is that the SynRM only contains the SSRF torque while the typical SRM and MCSRM contain both the SSRF torque and DSRF torque. The proposed unified vector torque control method is verified by simulations and experiments of 12-slot 8-pole reluctance motors with different coil pitch.

Speed Regulation Method Using Genetic Algorithm for Dual Three-phase Permanent Magnet Synchronous Motors

Dual three-phase Permanent Magnet Synchronous Motor (DTP-PMSM) is a nonlinear, strongly coupled, high-order multivariable system. In today's application scenarios, it is difficult for traditional PI controllers to meet the requirements of fast response, high accuracy and good robustness. In order to improve the performance of DTP-PMSM speed regulation system, a control strategy of PI controller based on genetic algorithm is proposed. Firstly, the basic mathematical model of DTP-PMSM is established, and the PI parameters of DTP-PMSM speed regulation system are optimized by genetic algorithm, and the modeling and simulation experiments of DTP-PMSM control system are carried out by MATLAB/SIMULINK. The simulation results show that, compared with the traditional PI control, the proposed algorithm significantly improves the performance of the control system, and the speed output overshoot of the GA-PI speed control system is smaller. The anti-interference ability is stronger, and the torque and double three-phase current output fluctuations are smaller.

Speed Synchronization Control of Dual-SRM Drive With ISMC-Based Cross-Coupling Control Strategy

To improve the speed synchronization performance of dual switched reluctance motor (SRM) drive with traditional sliding mode control (TSMC), the improved sliding mode control (ISMC) based cross-coupling control strategy is proposed. Firstly, the overall control structure of the dual-SRM drive is represented. Secondly, the state variable is introduced to reduce the torque fluctuation and adjustment time of the dynamic process of each SRM drive in the system based on the traditional sliding surface and sliding mode reaching law. The adaptive law is introduced into the sliding mode controller to avoid the load torque observation. Thirdly, the ISMC-based cross-coupling control method for the speed synchronization of the dual-SRM drive is designed. The novel sliding surface is proposed considering the speed synchronization deviation. The novel sliding mode reaching law is represented by introducing the state variables. Then the ISMC-based cross-coupling control method is realized for speed synchronization. The stability is proved by Lyapunov function. Simulations and experiments are implemented to verify the effectiveness of the proposed method.

Flow structure and performance analysis of Darrieus vertical axis turbines with swept blades: A critical case study on V-shaped blades

Blade geometric modification is one favorite way of enhancing the performance of vertical axis turbines. In this regard, V-shaped blades are a novel design featuring some leading-edge sweep angle. Currently, the relevant literature only focuses on finding the optimum parameters of the V-shaped blades and lacks a deep understanding of how they alter flow structure and whether they offer any performance improvement compared to other conventional types. To this aim, using three-dimensional numerical simulations, the flow structure and performance of two different V-shaped blade turbines, twisted and untwisted, are compared with straight and helical-blade turbines at tip speed ratios (TSRs) ranging from 0.69 to 1.5. Turbine torque average and fluctuation amplitude are chosen as the performance metrics. It is shown that the sweeping configuration of the V-shaped and helical types causes an inevitable spanwise flow, resulting in a performance loss, which makes neither type of V-shaped blade turbine advantageous at low TSRs.

Influence of nonlinearity of servo system electrical characteristics on motion smoothness of precision CNC machine tools

The ball screw feed system of CNC machine tools is a typical mechatronic motion mechanism. During the operation of the machine tool, not only the dynamic characteristics of the mechanical structure will affect its performance, but also the electrical characteristics of the servo system will affect the movement of the worktable, which will lead to displacement fluctuation and bring adverse effects on the precision of the machine tool and even the quality of the processed parts. Therefore, the electrical system and the mechanical system are strongly coupled to each other due to their high integration. In this paper, the fluctuation of current, torque, and displacement during the motion of the worktable is studied. Firstly, the mechatronic model of the ball screw feed system, which not only consists of all components of the feed system but also takes different nonideal characteristics of each component into consideration, is established to realize the physical simulation of the whole system. Then, with the consideration of the impacts of inverter dead zone, motor cogging torque, rotor mixed-eccentricity, winding asymmetry, and collecting error of feedback current, the frequency components of fluctuations caused by the nonlinear electrical characteristics of inverter and servo motor in the servo drive system are obtained. Finally, the influences of load, feedrate, servo parameters, and dynamic characteristics of mechanical structure on fluctuation are analyzed in the time domain and frequency domain. The phenomenon of displacement fluctuation of the worktable caused by the electrical characteristics of the servo system indicates that it is necessary and meaningful to build the integrated model to study the ball screw feed system from the view of the whole system.