Compressed Sensing Imaging with Compensation of Motion Errors for MIMO Radar

Using a multiple-input-multiple-output (MIMO) radar for environment sensing is gaining more attention in unmanned ground vehicles (UGV). During the movement of the UGV, the position of MIMO array compared to the ideal imaging position will inevitably change. Although compressed sensing (CS) imaging can provide high resolution imaging results and reduce the complexity of the system, the inaccurate MIMO array elements position will lead to defocusing of imaging. In this paper, a method is proposed to realize MIMO array motion error compensation and sparse imaging simultaneously. It utilizes a block coordinate descent (BCD) method, which iteratively estimates the motion errors of the transmitting and receiving elements, as well as synchronously achieving the autofocus imaging. The method accurately estimates and compensates for the motion errors of the transmitters and receivers, rather than approximating them as phase errors in the data. The validity of the proposed method is verified by simulation and measured experiments in a smoky environment.

Rigid–flexible coupling dynamics analysis with joint clearance for a 5-DOF hybrid polishing robot

SUMMARY Considering the polishing requirements for high-precision aspherical optical mirrors, a hybrid polishing robot composed of a serial–parallel manipulator and a dual rotor grinding system is proposed. Firstly, based on the kinematics of serial components, the equivalent load model for the parallel manipulator is established. Then, the elastodynamic model of kinematic branched-chains of the parallel manipulator is established by using the spatial beam element, and the rigid–flexible coupling dynamic model of the polishing robot is obtained with Kineto-elasto dynamics theory. Further, considering the dynamic properties of the joint clearance, the rigid–flexible coupling dynamic model with the joint clearance for the polishing robot is established. Finally, the equivalent load distribution of the parallel manipulator is analyzed, and the effect of the branched-chain elasticity and joint clearance on the motion error of the polishing robot is studied. This article provides a theoretical basis for improving the motion accuracy and dynamic performance of the hybrid polishing robot.

Simulation, Modeling and Experimental Research on the Thermal Effect of the Motion Error of Hydrostatic Guideways

Hydrostatic guideways are widely applied in ultra-precision machine tools, and motion errors undermine the machining accuracy. Among all the influence factors, the thermal effect distributes most to motion errors. Based on the kinematic theory and the finite element method, a 3-degrees-of-freedom quasi-static kinematics model for motion errors containing the thermal effect was established. In this model, the initial state of the closed rail as a “black box” is regarded, and a self-consistent setting method for the initial state of the guide rails is proposed. Experiments were carried out to verify the thermal motion errors simulated by the finite element method and our kinematics model. The deviation of the measured thermal vertical straightness error from the theoretical value is less than 1 μm, which ensured the effectiveness of the model we developed.

Human gait modelling and tracking based on motion functionalisation

This paper proposes a mathematical function movement model based on the gait movement of the human body and, in particular, on the trajectory of the limbs during human movement. The article systematically measures and experimentally deals with the trajectory of the limbs of 40 students in the walking movement. The linear high-order polynomial fitting method eliminates the motion error. Simultaneously, the linear relationship least square method is used to obtain the expression of the limb motion function. Finally, the mathematical model of the limb motion trajectory is obtained. It is verified through experiments that the model proposed in the thesis can calculate the law of limb movement and movement parameters of any person under normal walking movement. This research has high research value for human movement rehabilitation and the design of wearable equipment.

Algorithm and design improvements for indirect time of flight range imaging cameras

<p>This thesis describes the development of a compact and modularised indirect time of flight range imaging camera. These cameras commonly use the Amplitude Modulated Continuous Wave (AMCW) technique. For this technique, an entire scene is illuminated with light modulated at a high frequency. An image sensor is also modulated and the phase shift introduced between the two modulation signals, due to the transit time of the light reflecting off objects in the scene and returning to the camera, is used to measure the distance. The system constructed for this thesis is controlled by a Cyclone III FPGA and is capable of producing full field of view range images in real time with no additional computational resources. A PMD19K-2 sensor is used as the modulatable image sensor, and is capable of modulation frequencies up to 40 MHz. One significant issue identified with this range imaging technology is that the precision of the range measurements are often dependent on the properties of the object being measured. The dynamic range of the camera is therefore very important when imaging high contrast scenes. Variable Frame Rate Imaging is a novel technique that is developed as part of this thesis and is shown to have promise for addressing this issue. Traditional theory for indirect time of flight cameras is expanded to describe this technique and is experimentally verified. A comparison is made between this technique and traditional High Dynamic Range Imaging. Furthermore, this technique is extended to provide a constant precision measurement of a scene, regardless of the properties of the objects in the scene. It is shown that the replacement of the standard phase detection algorithm with a different algorithm can both reduce the linearity error in the phase measurements caused by harmonics in the correlation waveform and ameliorate axial motion error caused by relative motion of the camera and the object being measured. The new algorithm requires a trivial increase in computational power over the standard algorithm and can be implemented without any significant changes to the standard hardware used in indirect time of flight cameras. Finally, the complete system is evaluated in a number of real world scenarios. Applications in both 3D modelling and mobile robotics are demonstrated and tests are performed for a variety of scenarios including dynamic scenes using a Pioneer 2 robot.</p>

Algorithm and design improvements for indirect time of flight range imaging cameras

<p>This thesis describes the development of a compact and modularised indirect time of flight range imaging camera. These cameras commonly use the Amplitude Modulated Continuous Wave (AMCW) technique. For this technique, an entire scene is illuminated with light modulated at a high frequency. An image sensor is also modulated and the phase shift introduced between the two modulation signals, due to the transit time of the light reflecting off objects in the scene and returning to the camera, is used to measure the distance. The system constructed for this thesis is controlled by a Cyclone III FPGA and is capable of producing full field of view range images in real time with no additional computational resources. A PMD19K-2 sensor is used as the modulatable image sensor, and is capable of modulation frequencies up to 40 MHz. One significant issue identified with this range imaging technology is that the precision of the range measurements are often dependent on the properties of the object being measured. The dynamic range of the camera is therefore very important when imaging high contrast scenes. Variable Frame Rate Imaging is a novel technique that is developed as part of this thesis and is shown to have promise for addressing this issue. Traditional theory for indirect time of flight cameras is expanded to describe this technique and is experimentally verified. A comparison is made between this technique and traditional High Dynamic Range Imaging. Furthermore, this technique is extended to provide a constant precision measurement of a scene, regardless of the properties of the objects in the scene. It is shown that the replacement of the standard phase detection algorithm with a different algorithm can both reduce the linearity error in the phase measurements caused by harmonics in the correlation waveform and ameliorate axial motion error caused by relative motion of the camera and the object being measured. The new algorithm requires a trivial increase in computational power over the standard algorithm and can be implemented without any significant changes to the standard hardware used in indirect time of flight cameras. Finally, the complete system is evaluated in a number of real world scenarios. Applications in both 3D modelling and mobile robotics are demonstrated and tests are performed for a variety of scenarios including dynamic scenes using a Pioneer 2 robot.</p>

Dual Band GNSS Antenna Phase Center Characterization for Automotive Applications

High-accuracy Global Navigation Satellite System (GNSS) positioning is a prospective technology that will be used in future automotive navigation systems. This system will be a composite of the United States' Global Positioning System (GPS), the Russian Federation's Global Orbiting Navigation Satellite System (GLONASS), China Beidou Navigation Satellite System (BDS) and the European Union’s Galileo. The major improvement in accuracy and precision is based on (1) multiband signal transmitting, (2) carrier phase correction, (3) Real Time Kinematic (RTK). Due to the size and high-cost of today’s survey-grade antenna solutions, this kind of technology is difficult to use widely in the automotive sector. In this paper, a low-cost small size dual-band ceramic GNSS patch antenna is presented from design to real sample. A further study of this patch antenna illustrates the absolute phase center variation measured in an indoor range to achieve a received signal phase error correction. In addition, this low-cost antenna solution is investigated when integrated into a standard multi-band automotive antenna product. This product is evaluated both on its own in an indoor range and on a typical vehicle roof at an outdoor range. By using this evaluation file to estimate the receiver position could achieve phase motion error-free result.

Research on the Optimal Allocation of Tolerances of CNC Machine Tools Based on Small Deformation of Grinding Wheel

In order to solve the problem of precision optimization design of CNC machine tools, this paper proposes an optimized allocation method of machine tool tolerance parameters that takes into account the slight deformation of the machine tool. First, establish a tolerance-based geometric error prediction model, and establish a spatial motion error model based on the theory of multi-body systems(MBS); Homogeneously, perform finite element analysis(FEA) on the CNC internal cylindrical compound grinding machine to obtain the slight deformation of the machine tool, and apply the result to the optimal tolerance allocation In the constraint conditions, the final optimal allocation plan is obtained; Finally, the genetic algorithm is used to simulate and analyze the plan, and the optimal tolerance allocation result is obtained. The result shows that most of the tolerance parameters have been relaxed, which means that the machine tool’s manufacturing cost. Through experiments, it is verified that the optimized machine tool machining accuracy pass rates are 98.5%, 98.25%, and 97.85%, respectively. Therefore, the optimal allocation method of tolerances that considers small deformations proposed in this paper is effective.

A Novel Generation Method of High Quality Video Image for High Resolution Airborne ViSAR

Video synthetic aperture radar (ViSAR) can provide long-time surveillance of a region of interest (ROI), which is one of the hotspot directions in the SAR field. In order to better display ViSAR, a high resolution and high frame rate are needed. Azimuth integration angle and sub-aperture overlapping ratio, which determine the image resolution and frame rate, respectively, are analyzed in depth in this paper. For SAR imaging algorithm, polar format algorithm (PFA) is applied, which not only has high efficiency but is also easier to integrate with autofocus algorithms. Due to sensitivity to motion error, it is very difficult to obtain satisfactory focus quality, especially for SAR systems with a high carrier frequency. The three-step motion compensation (MOCO) proposed in this paper, which combines GPS-based MOCO, map-drift (MD) and phase gradient autofocus (PGA), can effectively compensate for motion error, especially for short wavelengths. In ViSAR, problems such as jitter, non-uniform grey scale and low image signal noise ratio (SNR) between different aspects images also need to be considered, so a ViSAR generation method is proposed to solve the above problems. Finally, the results of ViSAR in THz and Ku band demonstrate the effectiveness and practicability of the proposed method.