Real-time slip-based estimation of maximum tire-road friction coefficient

This paper presents a real-time maximum tire-road friction coefficient estimation method and field test results. The estimator is based on the relationship between the wheel slip ratio and the friction coefficient. An effective tire radius observer and a tire normal force observer have been designed for the computation of the slip ratio from wheel speed and vehicle speed measurements. The effective tire radius observer has been used so that the proposed method works for all driving situations. A tractive force estimator, a brake gain estimator, and a normal force observer have been used for the estimation of the friction coefficient. The proposed estimation method for the maximum tire-road friction coefficient has been implemented using a fifth wheel and typical vehicle sensors such as engine speed, carrier speed, throttle position, and brake pressure sensors.     

The design and characterization of a testing platform for quantitative evaluation of tread performance on multiple biological substrates

In this study, an experimental platform is developed to quantitatively measure the performance of robotic wheel treads in a dynamic environment. The platform imposes a dynamic driving condition for a single robot wheel, where the wheel is rotated on a translating substrate, thereby inducing slip. The normal force of the wheel can be adjusted mechanically, while the rotational velocity of the wheel and the translational velocity of the substrate can be controlled using an open-loop control system. Wheel slip and translational speed can be varied autonomously while wheel traction force is measured using a load cell. The testing platform is characterized by testing one micropatterned polydimethylsiloxane (PDMS) tread on three substrates (dry synthetic tissue, hydrated synthetic tissue, and excised porcine small bowel tissue), at three normal forces (0.10, 0.20, and 0.30?N), 13 slip ratios (-0.30 to 0.30 in increments of 0.05), and three translational speeds (2, 3, and 6?mm/s). Additionally, two wheels (micropatterned and smooth PDMS) are tested on beef liver at the same three normal forces and translational speeds for a tread comparison. An analysis of variance revealed that the platform can detect statistically significant differences between means when observing normal forces, translational speeds, slip ratios, treads, and substrates. The variance due to within (platform error, P = 1) and between trials (human error, P = 0.152) is minimal when compared to the normal force (P = 0.036), translational speed ( P = 0.059), slip ratio (P = 0), tread (P = 0.004), and substrate variances ( P = 0). In conclusion, this precision testing platform can be used to determine wheel tread performance differences on the three substrates and for each of the studied parameters. Future use of the platform could lead to an optimized micropattern-based mobility system, under given operating conditions, for implementation on a robotic capsule endoscope.     

Thermoelectric Properties of Bismuth Micro/Nanowire Array Elements Pressured into a Quartz Template Mold

A quartz template having a length of several millimeters and with holes having diameters on the order of micro/nanometers was fabricated. Bismuth was injected into the template holes by high-pressure injection. A bismuth micro/nanowire array sample was prepared, and the temperature dependence of the Seebeck coefficient and the resistance were measured in the temperature range of 50 K to 300 K. Although the temperature dependence of the Seebeck coefficient is similar to that of polycrystalline bulk bismuth, the temperature coefficient of the resistance is much less than that of the bulk sample. The magnetic-field dependence of the Seebeck coefficient was also measured. The Umkehr effect was observed, demonstrating that the mixed micro/nanowires are a bundle of single-crystal wires. The magnitude of the absolute value of the Seebeck coefficient was found to be large in high magnetic field and at low temperature.     

On Improvement of the Accuracy and Speed in the Process of Measuring Characteristics of Thermoelectric Materials

Results are presented on creation of novel methods for reduction of errors in measured properties of thermoelectric materials obtained by using object-oriented computer simulation for study of real physical models of the absolute method. The effects of radiation, heat losses along the electrodes, design elements of the measurement setup, non-dot-matrix of probes and sensors, and imperfection of thermal and electric contacts have been determined. Methods of eliminating errors due to these effects have been developed. Automated measuring equipment for complex study of thermoelectric material properties has been created, offering accuracy in thermoelectric figure of merit determination several times higher than conventional analogs. Values of errors obtained during measurements of Bi-Te-based materials within the temperature range from 30°C to 500°C include ～0.5% for electrical conductivity, ～0.7% for thermoelectromotive force, ～3% for thermal conductivity, and ～4.7% for figure of merit (Z). The dynamic processes of achieving steady-state measurement conditions and possible errors due to deviations from these conditions are investigated. Functions of current through the sample, reference heater, and radiation shield heater are determined, whereby measurement speed is increased, which is of particular importance for investigation of large-size samples, such as parts of thermoelectric material ingots.     

Longitudinal wheel slip control using dynamic neural networks

The control of automotive braking systems performance and a wheel slip is a challenging problem due to nonlinear dynamics of a braking process and a tire–road interaction. When the wheel slip is not between the optimal limits during braking, the desired tire–road friction force cannot be achieved, which influences braking distance, the loss in steerability and maneuverability of the vehicle. In this paper, the new approach, based on dynamic neural networks, has been employed for improving of the longitudinal wheel slip control. This approach is based on dynamic adaptation of the brake actuation pressure, during a braking cycle, according to the identified maximum adhesion coefficient between the wheel and road. The brake actuated pressure was adjusted on the level which provides the optimal longitudinal wheel slip versus the brake actuated pressure selected by a driver, the current vehicle speed, load conditions, the brake interface temperature and the current value of the wheel slip. The dynamic neural network has been used for modeling of a nonlinear functional relationship between the brake actuation pressure and the longitudinal wheel slip during a braking cycle. It provided preconditions for control of the brake actuation pressure based on the wheel slip change.     

Effect of mechanical process parameters on friction behavior and material removal during sapphire chemical mechanical polishing

The effect of mechanical process parameters such as down force and rotation speed on friction behavior and material removal rate (MRR) was investigated during chemical mechanical polishing (CMP) of sapphire substrate. It was found that the increase in both rotation speed and down force can enhance the MRR and friction force almost linearly depends on the down force and rotation speed. The coefficient of friction (COF) decreases with increasing rotation speed under a fixed down force but keeps constant regardless of variation in down force under a fixed rotation speed. Moreover, the relationship between friction force and MRR was obtained. MRR was proportional to friction force with increasing down force whereas converse proportional to that with increasing the rotation speed. In addition, MRR data are fitted to the Preston equation in the sapphire CMP.     

迭代学习控制在飞机全电刹车系统中的应用

飞机全电刹车系统具有传统的液压刹车系统不可比拟的优势,是未来飞机刹车系统的发展方向。针对现有液压刹车系统控制律的不足和全电刹车系统的特点,建立了以飞机纵向速度、滑移率为状态变量,滑移率为输出变量的刹车系统非线性状态方程。根据滑移率与结合系数的关系,在线辨识不同路面条件下的最大结合系数和最佳滑移率,提出了在常规PI控制器的基础上,施加一D型迭代学习前馈控制器的控制策略,以提高系统的快速跟随性,并将最佳滑移率作为迭代学习控制的期望输出。经过对干跑道状态下的仿真验证,表明加入迭代学习控制律后,可以满足飞机全电刹车系统的技术性能,在刹停时间、刹停距离及刹车效率等方面得到了改善,具有良好的收敛速度、稳定性和跟踪性。     

Micro-calorimetric sensor for vapor phase explosive detection with optimized heat profile

A heater design, used in a micro-calorimetric sensor, has been optimized for temperature uniformity in order to increase the sensitivity and reliability of detection of trace amounts of explosives. In this abstract the design, fabrication and characterization is described. The performance of the novel heater design is characterized by measuring the temperature coefficient of resistivity (TCR) values and by mapping the temperature distribution using Raman spectroscopy. The new heater design is seen to have increased the temperature uniformity by a factor of 2.3.     

超声电机温升、结构参数和输出特性的相互关系

通过超声电机温度特性实验,分析超声电机产生热量的途径;研究预压力和摩擦层厚度对超声电机温升、运行转速和堵转力矩的影响规律;提出估计温升、转速和堵转力矩关系的经验公式。研究有助于控制温升,改善电机运行特性。     

激光织构化形貌对密封配副摩擦学性能的影响

为了研究表面织构化对端面密封材料摩擦性能的影响,采用Nd:YAG固体脉冲激光对GCr15钢盘表面进行了织构化处理,形成了微孔型和凹槽型两种表面形貌。在摩擦试验机上模拟端面密封形式对聚四氟乙烯环/GCr15盘进行摩擦学性能测试,并对试样表面的磨损形貌进行了分析。结果表明,在油润滑条件下,织构化试样的摩擦因数和磨损量均低于光滑试样的,且微孔型织构的耐磨性优于凹槽形的,因为凹槽型织构排列使油膜厚度不均匀,摩擦因数波动大;在干摩擦条件下,适当的织构形貌对转移膜的保持有利,同时可以捕获磨屑,减少磨粒磨损的作用。与光滑配副相比,表面织构降低了配副双方的磨损率。     

Load sensing bearing based road-tyre friction estimation considering combined tyre slip

This work discusses a road-tyre friction estimator considering combined tyre slip. The friction estimator design is motivated by its importance in vehicle dynamics control as accurate friction estimation can improve performance and safety. The estimator uses tyre force measurements from Load Sensing Bearing (LSB) technology and does not rely on parameterized tyre model. The tyre force measurements benefit the estimator mainly because of the uncertainties and nonlinearities of the tyre force characteristics. The proposed estimator uses tyre slip and tyre force representations where the longitudinal and lateral tyre slips and forces are combined into a single tyre slip and tyre force values. This representation makes the method effective during pure longitudinal dynamics, pure lateral dynamics and for combined slip. In addition, individual tyre-road friction estimation is possible with the proposed estimator and a computationally inexpensive algorithm, suitable for real-time implementation, is used to estimate the friction. The estimator is studied in simulation during pure braking, pure cornering and for combined slip. Further, the estimator is simulated in closed loop with a yaw rate controller to study whether the estimator improves vehicle safety. Finally the estimator is validated using test data from several maneuvers performed on a test vehicle instrumented with LSB technology.     

Integrated thin film heater-thermocouple systems

A novel system of integrated thin-film heater with an embedded thermocouple was developed. Thin-film metallic heaters are widely used today in various fields of electronics and microelectronics applications. The main goal of the heater is usually to maintain the temperature in the heated zone. A deterministic method to manufacture an in situ heater––thermocouple system, with a pre-determined heater resistance, to give a required heat power, was developed. In order to examine this novel method, thin-film heaters were made using layers of Al and NiCr alloys. The temperature of the thin-film heater was measured while heating by an embedded thin-film thermocouple, positioned in the vicinity of the heater. This thin-film thermocouple system consisted of Ni–Ag alloy. A precise control of the growing heater film, while deposition, became possible using a simultaneous measurement of the heater sample resistance.     

Effect of normal forces on fretting corrosion of tin-coated electrical contacts

Electrical connectors have been extensively used as the electrical connecting component in various electronic systems. The performance of the electrical connector directly affects the performance of an entire system. Fretting corrosion is generally recognized as an essential failure mechanism for an electrical contact. Major factors affecting the fretting corrosion include current magnitude, normal contact force, displacement amplitude, relative humidity, frequency, and temperature. In order to investigate the effect of normal forces on fretting corrosion behavior, normal forces were fixed at 1 N, 1.25 N, 1.5 N, 2 N, 2.5 N for various displacement amplitudes. Riders and flats made of 0.3 mm-thick brass sheet were coated with tin. The change of the electrical resistance was measured by applying constant current and displacement amplitudes to the upper sphere contact specimen, fixing the flat specimen. The normal force (F) shows a linear relationship with the threshold displacement amplitude (δ_th). When the displacement amplitude increases with increasing normal force, the plating layer was severely worn due to contact pressure. Dimples were found on the surfaces of the central part of the specimens showing infinite lifetime, suggesting that a soft metal-to-metal contact formed just before separation of the mated specimens at the end of the test. Specimens with an infinite lifetime tested under partial slip condition showed a relatively low oxygen concentration on the center of the wear surface. It is very important to design an electrical connector contact to maintain partial slip by using the information on the normal force and displacement amplitude in order to achieve infinite lifetime.     

WS_x薄膜的脉冲激光沉积可控制备

采用脉冲激光沉积法(PLD)在单晶硅基底上制备了WSx固体润滑薄膜。利用X射线能谱仪(EDS)、扫描电子显微镜(SEM)、X射线衍射仪(XRD)对薄膜的成分、形貌和微观结构进行了分析,采用球盘式磨损试验机在大气(相对湿度为50%～55%)环境下评价薄膜的摩擦学特性。结果表明:薄膜中S和W的原子数分数比(简称S/W比)在1.05～3.75之间可控,摩擦系数为0.1～0.2;S/W比高于2.0时薄膜成膜质量和摩擦系数显著恶化。正交试验法得出影响薄膜S/W比的因素主次顺序分别是气压、温度、靶基距和激光通量;最优工艺参数是温度150℃、靶基距45mm、激光通量5J/cm2、气压1Pa,可获得结构致密、成分接近化学计量比的WSx薄膜。     

Development of a Measurement System for the Figure of Merit in the High-Temperature Region

New equipment has been developed for evaluating the figure of merit, ZT, on the basis of the Harman method in the temperature range between room temperature and 650 K. In this temperature range, the sample holder in the vacuum chamber has a different construction as compared with the sample holder constructed for the temperature range below room temperature. Several issues that need to be considered, such as compensation for the thermal radiation effect, suppression of heat leakage from the lead wires, and the setup method for the lead wires on the sample, are examined in the considered temperature region. Evaluations of ZT are successfully made for typical thermoelectric materials, (Bi,Sb)₂Te₃ and CeFe₃CoSb₁₂. We then demonstrate that the influence of thermal radiation between the high- and low-temperature edges of the sample induced by the Peltier effect on the estimated value of ZT is negligible at around 600 K. Furthermore, the change in the thermoelectric properties due to repetition of the thermal cycle is studied, and a typical hysteresis behavior is observed in the considered thermoelectric materials. It is revealed that heating the sample to a high temperature causes a change in its thermoelectric properties, which one must take into account for practical applications of thermoelectric materials.     

Investigation of the thermal properties of thin solid materials at different temperature levels using a set of microresistors

The measurement of thermal properties of solid materials at different temperatures above ambient is investigated using a set of microresistors. Samples consisted of suspended films with sets of long, parallel resistive wires deposited on their surfaces. One resistive wire was heated by an alternating current. Surface temperature changes in DC and AC regimes were then detected by measuring the change in electrical resistance of the other wires deposited on the surface. The length of wires was chosen so that they may be assumed isothermal and such that heat diffusion acts perpendicularly to their axes. By measuring the dependence of the surface alternating temperature oscillation on the modulation frequency f and on the separation between the heating wire and the probing wires, the thermal diffusivity of the sample was determined. Through adjustment of the alternating current amplitude in the source wire, the temperature at which the thermal diffusivity of the sample was evaluated was finely controlled. For the validation of the method, pure silicon samples were first studied. An experimental bench was set up and resistive source and probes were experimentally characterized. Results obtained from ambient temperature to 500 K for pure silicon are in accordance with reference data found in the scientific literature.     

Pattern evolution in shallow trench isolation chemical mechanical planarization via real-time shear and down forces spectral analyses

This study explores the transition of force spectral fingerprints of shallow trench isolation chemical mechanical planarization during early evolution of wafer topography and layer transition from silicon dioxide to silicon nitride. Polishing was done on a polisher and tribometer capable of measuring shear force and down force in real-time. Fast Fourier Transformation is performed to convert the force data from time domain to frequency domain and to illustrate the spectral amplitude distribution of the force. Such frequency spectra provide in-depth insights into the interactions among abrasive particles, pad and wafer. Shallow trench isolation patterned wafers are over-polished using cerium oxide slurry. Results show that shear force increases during polishing when the silicon dioxide layer is removed thus exposing the silicon nitride layer. Unique and consistent spectral fingerprints are generated showing significant changes in several fundamental peaks during the early evolution of wafer topography and subsequent layer transition to silicon nitride polishing. Variance of force is also plotted to show the progression of pattern evolution. Results show that a combination of unique spectral fingerprinting, coefficient of friction as well as analyses of force and its variance (based on shear and down force) can be used as to monitor in real-time the polishing progress during shallow trench isolation chemical mechanical planarization.     

Solutions for fretting corrosion

Application of electronics in systems that are exposed to high vibratory and shock stresses requires the use of fretting protected electrical connections. Fretting corrosion is caused by a relative motion of mated contact surfaces and results in contact failures. This paper presents a design concept that eliminates the relative motion at the contact point by introducing an additional elastic element. When the male half of a connector assembly moves relative to the female half, the contact regions on the male and female contacts will move some distance together before they start slipping. The onset of slip is predictable and measurable. This paper discusses the formula that determines the limit from where slip starts to occur. Also discussed are the effects of connector and application parameters such as coefficient of friction, normal force, spring rate, size of displacement, and lubrication. Evidence is presented that confirms the validity of the approach. The AMP Micro-MaTch contact system is used as example. Two statements about fretting were verified extra to confirming the validity of the approach. The first is that a small motion is worse than a large motion. The second that unplated phosphor-bronze behaves better than tinplated phosphorbronze. Unplated phosphor-bronze was also tested with anti-fretting lubricant and showed very good performance     

Doppler-Based Ground Speed Sensor Fusion and Slip Control for a Wheeled Rover

High-speed unmanned ground vehicles evolving on natural terrains can exhibit a significant slip and skid. An estimation of both friction and traction forces can allow to achieve a better control. In order to implement a control architecture based on the vehicle dynamic model and the wheel–soil interaction model, the knowledge of the wheels slip rate is required. The wheel angular velocities can be precisely measured. But the true measurement of the ground speed of the vehicle is much more challenging. A low-cost Doppler radar is used, in conjunction with an accelerometer, to obtain the ground speed. Thus, the knowledge of the slip rate allows us to setup an in situ procedure for the estimation of soil parameters that is based on the measurement of the motors torques. A wheel slippage controller has also been implemented, which is a first step toward high-level dynamic control.      

Study on I-V characteristics of lead free NTC thick film thermistor for self heating application

The resistivity of several materials varies predictably with temperature; this makes them suitable for the use as temperature sensors. If these material gets heated due to the electric current passing through it and if it preserves a uniform temperature distribution during heating, then its total resistance would accurately reflect its temperature, allowing it to simultaneously act as both a temperature sensor and a self heater. This paper describes the results of indigenously formulated lead free thick film NTC thermistor paste composition with sheet resistance of 1 kΩ/□ used for heater application. The current-voltage, temperature-current characteristics, dissipation constant, response and recovery time of the heater are reported. The maximum current handling capacity of the prepared thick film thermistor was observed at 300 mA and the temperature achieved to 340 °C. Therefore, the heater was tested at a constant current of 300 mA for 24 h, which did not show any extreme change in behaviour and the temperature of the thermistor/heater remained constant to 340 ± 5 °C.