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排序方式: 共有305条查询结果,搜索用时 34 毫秒
1.
为了提高四轮转向(4WS)汽车的操纵稳定性和主动安全性,建立汽车二自由度四轮转向模型和系统状态方程,应用LQR最优控制理论建立了以横摆角速度和质心侧偏角为优化目标的四轮转向线性控制二次型最优控制模型,并基于路径跟踪策略建立预瞄驾驶员方向控制模型。基于"人-车-路"闭环控制系统,在Matlab/Simulink、CarSim联合仿真环境下对普通前轮转向、前后轮转角比例控制、LQR控制的控制效果进行验证。结果表明:LQR控制器能够很好地改善汽车质心侧偏角和横摆角速度的动态响应特性,高速控制效果最佳,基于LQR控制的4WS汽车具有更好的道路循迹能力、高速稳定性和主动安全性。  相似文献   
2.
We report on an unusual failure pattern resulting from thermally driven fracture of laser amplifier single crystals. The pattern led to some confusion with regard to the point of initiation due to the coalescence of hackle lines to a region within the fracture surface, rather than the more common divergence of hackle away from the origin. The pattern leads to new fracture terms: Hackle node - the coalescence of hackle marks to a point of prior compression. The feature is produced as a thermally-generated, centrally-located compressive region transforms to tension thereby drawing crack propagation and hackle to the compressive region, forming an internal terminus. Hackle terminus – a hackle node formed by final crack propagation within the component. As part of the analysis, the fracture toughness and slow crack growth constants of neodymium doped, yttrium ortho-vanadate (Nd:YVO4) were measured. Nd:YVO4 exhibits slow crack growth and is very brittle with a fracture toughness of only 0.48 MPa√m.  相似文献   
3.
基于牛顿力学和欧拉刚体动力学原理,建立了考虑侧滑、横摆、侧倾三个自由度的汽车转向三自由度动力学模型,并推导出了四轮模型和两轮简化模型的状态空间运动方程。在此基础之上,分别对前轮转向、四轮转向在低速、高速两种不同行驶工况下转向角阶跃输入的侧向速度、质心侧偏角、横摆角速度和侧倾角速度响应进行了仿真分析,仿真结果表明:四轮转向比两轮转向具有更好的低速转向机动性和高速稳定性;两轮模型和四轮模型具有相近的稳定时间和稳态响应,但两轮模型的超调量要明显大于四轮模型。  相似文献   
4.
This paper presents a new design of mobile micro manipulation system for robotic micro assembly where a compliant piezoelectric actuator based micro gripper is designed for handling the miniature parts and compensation of misalignment during peg-in-hole assembly is done because piezoelectric actuator has capability of producing the displacement in micron range and generates high force instantaneously. This adjusts the misalignment of peg during robotic micro assembly. The throughput/speed of mobile micro manipulation system is found for picking and placing the peg from one hole to next hole position. An analysis of piezoelectric actuator based micro gripper has been carried out where voltage is controlled through a proportional-derivative (PD) controller. By developing a prototype, it is demonstrated that compliant piezoelectric actuator based micro gripper is capable of handling the peg-in-hole assembly task in a mobile micro manipulation system.  相似文献   
5.
郭旭东  杨世春 《计算机仿真》2020,37(4):123-127,133
针对自动驾驶车辆高速主动转向工况下传统的控制算法的控制效果容易出现较多的超调量和较长调节时间的问题,提出了基于车辆动力学模型的轨迹预测跟踪主动转向控制算法,并基于轮胎侧偏刚度非线性的特性设计了权系数线性最优二次型(LQR)后轮转角控制算法,通过联合仿真对控制算法效果进行了验证。仿真结果表明:自动驾驶四轮转向车辆在低、高速工况下进行自主换道行驶时,算法控制效果满足汽车操纵稳定性要求,且权系数LQR后轮转向算法比定侧偏刚度的LQR线性控制算法有更优越的操控性能。  相似文献   
6.

Purpose

To describe a ranked symptoms scale (RSS) discriminating subjective responses in contact lens (CL) wear in various situations.

Method

Forty experienced clinical trial participants were interviewed for their perceptions of ocular comfort scales, resulting in a numerical RSS. For further evaluation, 20 CL wearers enrolled into a prospective, randomised, crossover trial. Two silicone-hydrogel CLs and a lens care solution (LCS) [Combinations A & B] were selected based on prior performance identifying best/worst combinations for end-of-day comfort. The RSS and a numerical rating scale (NRS) were administered at two time-points (insertion/removal) on alternating days for 6 days.

Results

Both NRS and RSS showed acceptable internal consistency for comfort, vision and handling (Cronbach alpha = 0.71 for both scales) and similar repeatability for comfort and handling (coefficients-of-repeatability within 0.1 and 0.2 units, respectively, for each scale). The NRS and RSS discriminated differences between combinations for comfort (p  0.031) and vision (p  0.026) at both time-points. Additionally, the RSS showed lens/edge awareness influenced discomfort the most, ranking higher at insertion (p = 0.038) and higher for Combination-B at both time-points (p  0.002). Symptoms of dryness and tired eyes increased for both combinations at removal (p < 0.02). The RSS also showed haziness and blurred distance vision influenced vision dissatisfaction with Combination-B at lens removal (p  0.038) while eye strain/headache increased for both combinations by time of removal (p  0.013).

Conclusions

The RSS is able to discriminate subjective responses between combinations and time-of-day. The RSS’s ability to rank symptoms may be a useful tool in understanding perceptions of discomfort or dissatisfaction with CL wear.  相似文献   
7.
《Ergonomics》2012,55(9):1167-1178
The effect of job rotation on the physical workload was investigated for male employees working at a refuse collecting department. Before the introduction of job rotation, an employee worked as a street sweeper, as a refuse collector or as a driver. After the introduction of job rotation, every employee was allowed to alternate between two of the three possible jobs during the day, i.e. refuse collecting/street sweeping, refuse collecting/driving or street sweeping/driving. Two non-rotation groups (i.e. refuse collectors and street sweepers) and two rotation groups (i.e. refuse collectors/street sweepers and street sweepers/drivers) were mutually compared. The physical workload was determined by measuring the perceived load, energetic load and postural load during a full working day. Job rotation resulted in a significant decrease of the perceived load and energetic load and a slight decrease of the postural load. The results indicate that the total amount of work performed by means of job rotation resulted in an overall reduced physical workload of the employees of the refuse collecting department.  相似文献   
8.
《Fusion Engineering and Design》2014,89(9-10):2294-2298
ITER standards Tesini (2009) require hardware mock-ups to validate the Remote Handling (RH) compatibility of RH class 1- and critical class 2-components. Full-scale mock-ups of large ITER components are expensive, have a long lead time and lose their relevance in case of design changes. Interactive Virtual Reality simulations with real time rigid body dynamics and contact interaction allow for RH Compatibility Assessment during the design iterations.This paper explores the use of interactive virtual mock-ups to analyze the RH compatibility of heavy component handling and maintenance. It infers generic maintenance operations from the analysis and proposes improvements to the simulator capabilities.  相似文献   
9.
The Automated Materials Handling System (AMHS) in the semiconductor industry plays a vital role in reducing wafer cycle times and enhancing fabrication facility (fab) productivity. Due to the complexity of the manufacturing process and the stochasticity introduced by the inherent variability of processing times, the vehicle allocation for the AMHS is a challenging task, especially in 300?mm?wafer fabs where the AMHS comprises both the interbay and intrabay systems to perform the timely deliveries. This paper studied the vehicle allocation problem in a typical 300?mm?wafer fab. We formulated it as a simulation optimisation problem and proposed a conceptual framework to handle the problem. A discrete event simulation model was developed to characterise the AMHS, and the technique of simulation optimisation was applied to obtain the optimal vehicle allocation for both the interbay and intrabay systems. To demonstrate the feasibility and advantages of the simulation optimisation approach, a photobay example was used to compare the solution derived from the analytical model and simulation optimisation model. Finally, an empirical problem based on real data was conducted to show the viability of the proposed framework in practice.  相似文献   
10.

The safety and productivity of workers engaged in materials handling has been a topic of interest to industrial engineers and ergonomists for some time. One of the fundamental questions that has generated considerable research is that of how to define and measure material handling capacity. The potential role of human muscle power and the resultant capacity to exert power on an external load as a measure of materials handling capacity is explored. Aside from applied literature in the exercise and sports science disciplines supporting this notion, a more theoretical basis is provided by the muscle physiology and morphology literature. The further empirical investigation of power as a means of defining materials handling capacity is supported.  相似文献   
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