Drilling torque control using spindle motor current and its effect on tool wear

Drilling torque was estimated using the spindle motor current and controlled through feedrate manipulation for the reduction of drill wear. A PID controller was used to control the cutting torque measured indirectly from the spindle motor current. The effect of cutting torque control on drill flank wear was also investigated. Experimental results showed that the drilling torque was well-regulated at a given reference level and the risk of drill failure and drill flank wear were reduced remarkably through cutting torque control. Moreover, the suggested cutting torque control system does not disturb the cutting process and is practical in an industrial environment.Nomenclature I _rms Root mean square value of spindle motor current (ampere) - I _u,v,w U, V, and W phase current of the spindle motor (ampere) - I _rms,c Spindle motor current due to cutting (ampere) - I _rms,t Tare current of the spindle motor (ampere) - T _c Cutting torque (Nm) - T _s Sampling rate (Hz) - N _r Number of revolution - N _d Number of data per revolution - K _I Spindle motor current gain (ampere N^–1m^–1) - _d Time constant of the spindle system (sec)     

MTPA control of mechanical sensorless IPMSM based on adaptive nonlinear control

In this paper, an adaptive nonlinear control scheme has been proposed for implementing maximum torque per ampere (MTPA) control strategy corresponding to interior permanent magnet synchronous motor (IPMSM) drive. This control scheme is developed in the rotor d–q axis reference frame using adaptive input–output state feedback linearization (AIOFL) method. The drive system control stability is supported by Lyapunov theory. The motor inductances are online estimated by an estimation law obtained by AIOFL. The estimation errors of these parameters are proved to be asymptotically converged to zero. Based on minimizing the motor current amplitude, the MTPA control strategy is performed by using the nonlinear optimization technique while considering the online reference torque. The motor reference torque is generated by a conventional rotor speed PI controller. By performing MTPA control strategy, the generated online motor d–q reference currents were used in AIOFL controller to obtain the SV-PWM reference voltages and the online estimation of the motor d–q inductances. In addition, the stator resistance is online estimated using a conventional PI controller. Moreover, the rotor position is detected using the online estimation of the stator flux and online estimation of the motor q-axis inductance. Simulation and experimental results obtained prove the effectiveness and the capability of the proposed control method.     

Modeling and identification of an electrostatic motor

The present study describes modeling and parameter identification for a high-power electrostatic motor. The motor is a synchronous motor with six phases that is modeled by a six-terminal capacitance network. A method to measure the capacitance coefficient matrix of a network using an LCR tester is proposed and demonstrated. The thrust force of the motor is shown analytically using the proposed model, which shows good agreement with empirical measurements of the motor behavior. Based on the proposed model, the effect of electrode skew is analyzed for force ripple reduction. Using the analysis, a skew motor is fabricated and tested, with the results demonstrating that a skewing electrode with a skew factor π can considerably reduce thrust force ripple.     

Robust control design for a wheel loader using and feedback linearization based methods

The heavy equipment industry is building more and more equipment with electro-hydraulic control systems. The existing industry practices for the design of control systems in construction machines primarily rely on classical designs coupled with ad-hoc synthesis procedures. Such practices produce desirable results, but lack a systematic procedure to account for invariably present plant uncertainties in the design process as well as coupled dynamics of the multi-input multi-output (MIMO) configuration. In this paper, two H_∞ based robust control designs are presented for an automatic bucket leveling mechanism of a wheel loader. In one case, the controller is designed for the base plant model. In another case, the controller is designed for the plant with a feedback linearization control law applied yielding improved stability robustness. A MIMO nonlinear model for an electro-hydraulically actuated wheel loader linkage is considered. The robustness of the controller designs are validated by using analysis and by simulation using a complete nonlinear model of the wheel loader linkage and hydraulic system.     

Study of plowing and friction at the surfaces of plastic deformed metals

Experimental and analytical investigations of plowing and friction were conducted at the surfaces of well-polished lead, aluminum, copper, nickel, molybdenum, and tungsten to study the mechanism of the load/penetration dependency. The experimental tests were performed with a Nano-Indenter XP of MTS and a Scanning Probe Microscope (SPM), Nanoscope IIIa of Digital Instruments. In addition to make indentation and measure the hardness and Young’s modulus, the indenter was used to make scratches at the surface of metals under different normal load while the penetration depth and frictional force encountered during the scratching were recorded. The SPM, operated mostly in the contact mode, was used to examine the scratch profile. Under the test conditions, plastic deformation dominated at the surfaces of the metals. An analytical model was established to express plastically deformed contacts, based on plowing of a conical-shaped indenter with a hemispherical tip at a plastic deformed surface. Penetration depth and scratched volume were calculated, which is in good agreement with experimental observation. The frictional coefficient μ was also calculated with the model, which accounted for plowing as well as the adhesion force between the indenter and surface. Beside fair agreement of experimental data and calculated values on μ under the loads applied, the model indicated a dramatic rise in friction coefficient under very low loads, which was not observed in the tests. The discrepancy was discussed, and it was believed that the dramatic increase in μ is for the calculated μ and may be due to the assumed dominant contribution of adhesion force in actual contact load with decreasing external load, and it appears only the adhesion energy Δγ is significant. The actual adhesion energy Δγ between our diamond indenter and metal surface in our test condition might be smaller than the value used in calculation.     

A new 3-DOF Z-tilts micropositioning system using electromagnetic actuators and air bearings

A new 3-DOF Z-tilts (z, pitch, and roll motion) micropositioning system has been developed. It uses electromagnetic actuators and air bearings. An electromagnetic actuator produces an attraction force between the air bearing and the base plate. An air bearing has the role of suspension and guidance, with a clearance of several tens of micrometers in the z-direction. Therefore, this system has design features of guiding 3-DOF XYθ motion without limiting the plane motion and playing the role of a z-directional position actuator. With the control of current, the equilibrium position between magnetic attraction force and air bearing thrust force can be controlled with inherently infinite resolutions. The theoretical background of an electromagnetic actuator is explained. Then, an air bearing is analyzed in the point of z-directional positioning mechanism. The air bearing can be modeled as a second-order system with parameter variation—stiffness and damping vary with respect to the z-directional displacement. Therefore, a simple robust control algorithm is applied to improve the control performance. With the aid of robust control, this system provides 25 nm positioning resolution over the total range of 40 μm along the z-direction and, accordingly, 0.29 μrad resolution over the total range of 460 μrad in pitch and roll motion.     

Control of electromechanical systems in sliding conditions

An algorithm of controlling the angular velocity of a two-weight system with an elastic motion transmission mechanism is synthesized. The system’s dynamics is investigated theoretically; the domain of the existence of stable conditions is estimated; and it is shown that the system’s image point slides along the phase trajectory of the reference model, which serves to assign the dynamic characteristics of the designed system. The results of the mathematical simulation of control processes are presented.     

Robust control using recursive design method for flexible joint robot manipulators

A flexible joint robot manipulator can be regarded as a cascade of two subsystems: link dynamics and the motor dynamics. Using this structural characteristic, we propose a robust nonlinear recursive control method for flexible manipulators. The recursive design is done in two steps. First, a fictitious robust control for the link dynamics is designed as if it has a direct control input. As the fictitious control, a nonlinear H _∞-control using energy dissipation is designed in the sense of L ₂-gain attenuation from the disturbance caused by uncertainties to performance. In the process, Hamilton-Jacobi (HJ) inequality is solved by a more tractable nonlinear matrix inequality (NLMI) method. In the second step, the other fictitious and the actual robust control are designed recursively by using the Lyapunov’s second method. The proposed robust control is applied to a two-link robot manipulator with flexible joints in computer simulations. The simulation results show that the proposed robust control has robustness to the model uncertainty caused by changes in the link inertia and the joint stiffness.     

In-situ neural network process controller for copper chemical mechanical polishing

Process control is one of the key methods to improve manufacturing quality. This research proposes a neural network based run-to-run process control scheme that is adaptive to the time-varying environment. Two multilayer feedforward neural networks are implemented to conduct the process control and system identification duties. The controller neural network equips the control system with more capability in handling complicated nonlinear processes. With the system information provided by this neural network, batch polishing time (T) an additional control variable, can be implemented along with the commonly used down force (p) and relative speed between the plashing pad and the plashed wafer (v). Computer simulations and experiments on copper chemical mechanical polishing processes illustrate that in drafting suppression and environmental changing adaptation that the proposed neural network based run-to-run controller (NNRTRC) performs better than the double exponentially weighted moving average (d-EWMA) approach. It is also suggested that the proposed approach can be further implemented as both an end-point detector and a pad-conditioning sensor.     

Stress analysis of metallic rocket motor cases reinforced with a viscoelastic fibre overwind

Analytical stress solutions are presented for a metallic rocket motor case reinforced with a prestrained fibre overwind, with viscoelastic properties, under both constant and varying temperature histories. The treatment is in terms of the ‘reduced time’ proposed by Schwarzl and Staverman, with the Williams et al. form of the ‘shift function’.The analysis is reduced to the solution of a Volterra integral equation. For a constant temperature history and using the ‘standard linear solid’ representation of the material properties of the overwind, this equation can be solved in closed-form. For varying temperature histories the equation is solved using a finite-difference technique proposed by Lee and Rogers and improved by Margetson. The effects of fibre relaxation on the internal pressure required for the initiation of yield in the motor case are evaluated and discussed for a number of temperature histories and end conditions.     

2-D discontinuous chip cutting model by using strain energy density theory and elastic-plastic finite element method

The formation of discontinuous chip is investigated in this paper. The cutting simulation was conducted on 60–40 brass (60% Cu, 40% Zn) under an extremely low cutting speed. The region of the maximum strain energy density (SED) distribution value relative to the minimum value, i.e. (dw/dv)_min^max, was used as the criterion to predict the initial breakage location under the presumption that the curvature direction of the maximum SED was the direction of crack growth. The shape and cutting force of discontinuous chip crack, the stress and strain distribution of the workpiece and chip, and the variation of various nodal force on the chip–tool interface were derived.     

Output tracking control of mobile manipulators based on dynamical sliding-mode control

A dynamical sliding-mode controller is devised to track the output of mobile manipulators. During the investigation, firstly a reduced dynamic model considering the dynamics of the driving motor is developed for mobile manipulators. Then, the system is decomposed into four lower-dimensional subsystems by means of diffeomorphism and nonlinear input transformation. Moreover, a design method of the dynamical sliding-mode controller that is applied to the output tracking of mobile manipulators is proposed. The simulation results indicate that the dynamical sliding-mode controller can not only track the given trajectory correctly but also reduce the chattering of sliding-mode control system considerably. __________ Translated from Journal of South China University of Technology (Natural Science Edition), 2006, 34(6): 29–33 [译自: 华南理工大学学报 (自然科学版)]     

Modeling and control strategy of flexible joint servo system in humanoid manipulator driven by tendon-sheath

The control effect of rotational speed in joints directly affects the motion accuracy of a humanoid manipulator driven by tendon-sheath. The dynamic parameters of the joint have time-varying characteristics due to the posture change of the manipulator. The joint driven by tendon-sheath has a specific torsional stiffness, so flexibility should be considered in the humanoid manipulator’s servo system. The time-varying of the parameters in the servo system and the joint flexibility can cause fluctuation of the output speed. To improve the motion accuracy of the humanoid manipulator, a fuzzy-tuned PI control strategy is used to suppress the instability of the output speed. First, the change law of the inertia on the motor side of the flexible joint is calculated by the dynamics equation of the humanoid manipulator. Next, a mathematical model of the joint is established, and the transfer function from the load speed to the electromagnetic torque is obtained. Furthermore, according to the pole-placement strategy, the fuzzy-tuned PI controller parameters are selected appropriately for the manipulator in different postures. Finally, the effectiveness of the proposed method is verified by numerical simulations and control experiments of the manipulator. The results show that the fuzzy-tuned PI control strategy can significantly reduce the tracking errors and improve the control performance of the manipulator.

     

Stability, bifurcation and chaos of closed flexible cylindrical shells

Complex vibrations of closed cylindrical shells of infinite length and circular cross-section subjected to transversal local load in the frame of the classical non-linear theories are studied. A transition from partial differential equations (PDEs) to ordinary differential equations (ODEs) is carried out using a higher-order Bubnov–Galerkin approach and Fourier representation. On the other hand, the Cauchy problem is solved using the fourth-order Runge–Kutta method.In the first part of this work, static problems of the theory of closed cylindrical shells are studied. Reliability of the obtained results is verified by comparing them with the results taken from literature. The second part is devoted to the analysis of stability, bifurcation and chaos of closed cylindrical shells. In particular, an influence of sign-changeable external pressure and the control parameters such as magnitude of pressure measured by ₀, relative linear shell dimension λ=L/R, frequency ω_p and amplitude q₀ of external transversal load, on the shell's non-linear dynamics is studied.     

Adaptive robust motion trajectory tracking control of pneumatic cylinders with LuGre model-based friction compensation

Friction compensation is particularly important for motion trajectory tracking control of pneumatic cylinders at low speed movement. However, most of the existing model-based friction compensation schemes use simple classical models, which are not enough to address applications with high-accuracy position requirements. Furthermore, the friction force in the cylinder is time-varying, and there exist rather severe unmodelled dynamics and unknown disturbances in the pneumatic system. To deal with these problems effectively, an adaptive robust controller with LuGre model-based dynamic friction compensation is constructed. The proposed controller employs on-line recursive least squares estimation（RLSE） to reduce the extent of parametric uncertainties, and utilizes the sliding mode control method to attenuate the effects of parameter estimation errors, unmodelled dynamics and disturbances. In addition, in order to realize LuGre model-based friction compensation, the modified dual-observer structure for estimating immeasurable friction internal state is developed. Therefore, a prescribed motion tracking transient performance and final tracking accuracy can be guaranteed. Since the system model uncertainties are unmatched, the recursive backstepping design technology is applied. In order to solve the conflicts between the sliding mode control design and the adaptive control design, the projection mapping is used to condition the RLSE algorithm so that the parameter estimates are kept within a known bounded convex set. Finally, the proposed controller is tested for tracking sinusoidal trajectories and smooth square trajectory under different loads and sudden disturbance. The testing results demonstrate that the achievable performance of the proposed controller is excellent and is much better than most other studies in literature. Especially when a 0.5 Hz sinusoidal trajectory is tracked, the maximum tracking error is 0.96 mm and the average tracking error is 0.45 mm. This paper constructs an adaptive robust controller     

High accuracy motion control of linear motor drive wire-EDM machines

This paper aims to develop and investigate a permanent magnet linear-motor-driven table system for a wire-EDM machine. A dynamic model and system identification of `the linear motor system have been derived and analyzed. The linear motor drive system has nonlinear and time-varying behaviors because of the effect of irregular friction of the sliding surface and cogging force. Therefore, a conventional digital controller may not suffice to provide a high contouring accuracy as well as adequate disturbance rejection and parameter variation robustness. An indirect adaptive controller (IAC), combined with a neural network-based feedforward controller (NNBFC) is proposed to improve the contouring performance of the linear motor system. Experimental results not only indicate that the proposed control scheme can achieve a high contouring accuracy of ± 0.3 μm, they also demonstrate that the developed linear motor drive wire-EDM machine can meet the requirement for micro machining. The maximum contour error of circular trajectory at a feed-rate of 0.1 mm/min was significantly reduced from 8 μm to 0.5 μm in comparison with proportional-integral-derivative (PID) controller.     

永磁型电主轴多频率振动的主动控制

为了有效抑制由砂轮质量不平衡及外部干扰引起的永磁型电主轴转子系统砂轮端的多频率成分振动,在无轴承永磁电机径向磁悬浮力产生原理的基础上,提出了一种基于最小方差快捷分块(FBLMS)的自适应滤波的永磁型双绕组电主轴柔性转子系统砂轮端多频率成分振动的主动控制方案。首先研究了双绕组永磁型电主轴结构及工作原理和径向控制力的模型,借助有限元法建立了永磁型电主轴柔性转子系统的动力学模型,分析了控制电流的不同成分对永磁体涡流损耗及电机定子铁损的影响,设计了永磁型电主轴柔性转子系统砂轮端多频率成分振动的主动控制系统,结果表明,提出的永磁型电主轴柔性转子系统砂轮端多频率成分振动控制方案具有明显的控制效果。     

Analysis of force patterns and tool life in milling operations

The paper describes the practical effects of the operating parameters in the milling operation. Experiments have been conducted to measure cutting force and tool life under dry conditions. Based on the experimental results, three mathematical models have been developed: Force, TLife and Force/TLife. Further analyses have been conducted on the cutting force patterns: seasonal pattern and nonlinear trend. A process optimisation that is based on the minimum production cost has been applied to relate Force model, TLife model and machinability criteria, such as power consumption, cutting parameters and surface roughness.Nomenclature C _w cost of workpiece ($) - C _s set-up cost ($) - C _m machining cost ($) - C _o overhead cost ($) - C _r tool replacement cost ($) - C _t tool cost ($) - D diameter of the cutter (inch) - d depth of cut per pass (inch) - d ₀ required depth (inch) - e _t random error attth sample - F cutting force (N) - f feedrate (ipm) - L length of workpiece (inch) - N spindle speed (r.p.m.) - n number of teeth - P power of the motor (h.p.) - R surface roughness (µm) - R _e real part of a complex function - T tool life (min) - t sample number - t _m machining time (s) - t ₀ overhead time (s) - t _r tool replacement time (s) - t _s set-up time (s) - U _i unit cost of itemi ($/unit)v - v cutting speed (i.p.m.)     

Electro-dynamic planar motor

The control behaviour of an electro-dynamic motor, also known as a moving coil motor, is superior to other motor types. This is also true for the linear version of this motor type. The classic solution to produce an x–y movement with a long-stroke is to apply a stack of at least two linear motors. A rising moving mass, combined with a limited mechanical stiffness, limits the bandwidth. An alternative is the planar motor, which generates x- and y-movements. This paper describes an electro-dynamic planar motor with moving coils, which levitates and propels itself over long x- and y-strokes under full control over six degrees of freedom (6-DOF).