High-resolution Position Sensor Research Articles

Multi-Agent Position Estimation in Modular Motor Drives Using Low-Resolution Sensors

Because a modular motor drive is composed of multiple identical pole drive units and controllers, it can be considered as a multi-agent system. This makes modular motor drives particularly interesting during faults, when the remaining healthy agents assure the continuity of operation. Nevertheless, for some crucial information such as the rotor position, these drives still rely on a single sensor which introduces a single point of failure. In this work, this single high-resolution position sensor is replaced by multiple binary, low-resolution position sensors. A vector tracking observer algorithm, implemented in the different controllers, processes this low-resolution sensor data into a position estimate. Subsequently, these position estimates of the different agents are exchanged with other agents using a distributed averaging algorithm. For this latter approach, it is shown in this work that it improves the position estimation under healthy conditions as well as during agent malfunctions. The concept is demonstrated on a modular axial-flux permanent magnet synchronous machine with fifteen pole drive units, each equipped with a low-resolution position sensor, that are assigned to five agents.

Sensorless Control of Separately Excited Synchronous Electrostatic Machines

This article presents the analysis and demonstration of sensorless position estimation methodologies for separately excited synchronous electrostatic machines (SEMs). The torque density of the SEM comes at the cost of a high pole count (p >50) along with other enhancements. The high pole count makes the use of high-resolution position sensors necessary, driving up the cost of the system. The sensorless estimation of rotor position is seen as a solution for alleviating the need for high-resolution and high-cost position sensors. Key features of electrostatic machines that make them suitable for sensorless operation are identified. Back MMF (current) based rotor position sensing for medium to high speeds is investigated. High-frequency injection-based position estimation is investigated for zero and low-speed operating regions. The proposed methods are experimentally demonstrated using a current-source inverter-based drive platform.

Fault Tolerant and Nano Displacement Drive Control Method of Photoelectric Motor for Battery Electric Vehicle

The low-resolution photoelectric position sensor is used, that is, Hall position sensor replaces the traditional photoelectric encoder and other high-resolution position sensors to monitor the rotor position. However, because the three-phase Hall position sensor can only output six position signals, a hardware circuit design of low-resolution position sensor monitoring rotor position signal is proposed. Meanwhile, nanotechnology has been introduced in the study of micro drive of battery electric vehicle (BEV). BEV driver has some disadvantages such as hysteresis, creep and nonlinearity, which seriously affects its application in nano environment. A nano displacement sensor is designed for the characteristics of BEV driver. The nonlinear problem of micro driver is solved through the closed-loop control of position feedback. In the test, through the verification of rotor position and current waveform, it can be proved that the method based on photoelectric position sensor and rotor position signal monitoring can ensure the low deviation of rotor position calculation and correct output signal of three-phase photoelectric position sensor. The decoupling performance of vector control is verified by 3/2 transformation. In the displacement detection of micro driver, the designed nano displacement sensor has higher resolution and its performance is better than that of the previous three generations of displacement sensors.

Ultra-high resolution position sensors with self-assembled nanowire arrays

High-resolution position sensor with integrating self-assembled, half-dimensional zinc oxide nanowires as nanopixels.

Parabola‐trapezoid and staircase current supply methods for PMBLM with full inverter utility and reduced torque ripple

The permanent magnet brushless motors (PMBLM) are utilised extensively in many high-performance applications where smoothness of output torque is necessary. When driven with conventional square-wave current, the PMBLM is hard to make full use of inverter capacity because of short current supply time. Besides, it is hard to produce smooth output torque because the phase inductances slow down the desired step response of the phase current seriously. Although the sinusoidal-wave current changes continuously, there exists a fixed-frequency torque ripple for trapezoid back-electromotive force motor. To solve the problems, two novel current supply methods, called as staircase waveform and parabola-trapezoid waveform, are proposed in this study. With the same phase current magnitude as square waveform, the staircase waveform can output two times torque with low-resolution position sensors. The parabola-trapezoid supply method can further improve the smoothness of doubled output torque by unique parabolic rising and falling edge waveform design, while a high-resolution position sensor is needed. Simulation and experimental tests of four different current supply methods are given to corroborate the effectiveness of the proposed method in inverter utility and torque ripple reduction.

Optical position sensor based on a digital wavelength-encoding grating ruler

A wavelength-encoding optical position sensor was designed in this study. The critical component of the sensor is its innovative digital encoding grating ruler (DEGR), which is a substrate on which several blazed grating units with different line densities are arranged parallel to one another following a certain order. Two types of multi-DEGR were designed. We obtained over 100,000 codes that significantly assisted in designing long-range and high-resolution position sensors by optimizing the coding algorithm. The wavelength signals generated by the multi-DEGR were demodulated using concave grating and several photosensitive elements. A 100-mm multi-DEGR with 1000 codes was successfully fabricated using the combined methods of direct laser writing and holographic technology. We described the principle of the sensor in detail and established the entire sensor system. A bench test was conducted to test the signal response of the sensor. Bench test results exhibited 100% accuracy of the signal response of the optical sensor and an excellent temperature performance within −55°C and 75°C.

Investigation on feedback control of linear motors in ultraprecision-machine feed-drive systems

Linear motors offer many advantages over ac or dc servo motors. More and more ultraprecision machines use linear motors in their feed-drive systems. The distance measured by the linear encoder is used to calculate the linear motor’s velocity. A linear-motor controller needs a high-resolution position sensor for smooth velocity control. However, the high-resolution position sensor may sense the vibration of the mechanical structure and therefore cause instability. This article presents a simulation model to analyze the impact of linear encoder feedback on a linear motor’s motion control and stability. Experiments are designed to validate the simulation model. Both simulation and experiment demonstrate that proper selection of linear encoder’s resolution can satisfy a smooth velocity control and stability requirements.

A Modular and High-Precision Motion Control System With an Integrated Motor

This paper describes the design and control of an integrated direct-drive joint suitable for applications that require a high-precision motion control system. The joint integrates a direct-drive synchronous motor with axial air gap, a torque sensor, and a high-resolution position sensor. The key design aspects of the integrated joint, like the motor's armature, cooling system, motor housing, bearing arrangement, sensors, and power electronics are detailed. We also present a number of advanced implementations in motor torque control, optimal joint torque sensory feedback, and motion control using positive joint torque feedback. Experimental results illustrate an outstanding performance regarding thermal response, torque ripple, reference trajectory tracking, torque disturbance rejection, and joint stiffness.

Development of a digital control system for high-performance pneumatic servo valve

Abstract Pneumatic servo systems are used in many fields, such as pneumatic robot systems or vibration isolation systems. To improve the controllability of the pneumatic servo system, a higher performance servo valve is needed. In the present paper, a pneumatic spool type servo valve having an air bearing and a high-resolution position sensor was developed. We attempted to achieve high-frequency, high-accuracy flow rate control by digitization of the controller. We present herein a control algorithm for digital control of this valve. The characteristics of this valve were measured and the natural frequency of the valve was clarified to be up to 300 Hz. The spool position accuracy and the dynamic characteristics of the developed servo valve are greatly improved compared to existing valves.

Monolithic folded pendulum accelerometers for seismic monitoring and active isolation systems

A new class of very low noise low-frequency force-balance accelerometers is presented. The device has been designed for advanced mirror isolation systems of interferometric gravitational wave detectors. The accelerometer consists of a small monolithic folded pendulum with 2 s of natural period and an in-vacuum mechanical quality factor of 3000. The folded pendulum geometry, combined with the monolithic design, allows a unique 0.01% cross-axis residual coupling. Equipped with a high-resolution capacitance position sensor, it is capable of a noise-equivalent inertial displacement of 1-nm root mean square integrated over all the frequencies above 0.01 Hz. The main features of this new accelerometer are here reviewed. New possible applications of monolithic folded pendula in geophysical instrumentation are discussed.

Servo and tracking algorithm for a probe storage system

Very fast, precise and robust servo algorithm and tracking algorithm for a probe storage system are proposed, which use only probes without any additional high-resolution position sensors. Servo algorithm uses the values read by servo probes as the coordinate of every data bit with one-to-one correspondence so that it provides high accuracy, short seek-time, and robustness. Also the concept of virtual subsection of data field is introduced to reduce the number of the servo probes. Tracking algorithm can detect two-axis position errors used for off-track control and synchronization independently and continuously. By vibrating the scanner and by multiplying two decomposition signals, position errors are modulated and demodulated from probe reading signal. Servo+track code is designed to reduce total number of additional probes for servo and tracking and to have stable noise characteristics.

DITC-direct instantaneous torque control of switched reluctance drives

This paper presents an online instantaneous torque control technique for switched reluctance machines called direct instantaneous torque control. The method comprises two novel aspects. First, torque is estimated as a function of terminal quantities, i.e., flux linkage and phase current. Hence, torque estimation is independent of the rotor position. Secondly, high-bandwidth drive performance is obtained by implementing a digital torque hysteresis controller. Thus, the method works without torque profile functions and auxiliary phase commutating strategies. Therefore, the control algorithm offers a wide drive operating range without the use of a high-resolution shaft position sensor or sensitive position estimation techniques. Experimental and simulation results are presented in this paper.

High-performance current-sensorless drive for PMSM and synRM with only low-resolution position sensor

This paper proposes the current-sensorless drive system with only low-resolution position sensor in order to simplify the synchronous motor drive system. The high-performance current vector control can be achieved in the proposed drive system, where the current sensors are eliminated but the simulated currents based on motor model are used for current control. The low-resolution position sensor, which has a resolution of only 60 electrical degrees, is used instead of a conventional high-resolution position sensor, and the position information with higher resolution is estimated. The steady-state performance and dynamic performance are examined by several drive tests with respect to the interior permanent-magnet synchronous motor and the synchronous reluctance motor. The effectiveness of the proposed drive system is clarified from several experimental results.

A current sensorless drive system of a synchronous motor with a low‐resolution position sensor

AbstractHigh‐performance drive of synchronous motors such as a permanent magnet synchronous motor and a synchronous reluctance motor can be achieved by current vector control. In such drive systems, the armature current is controlled as a sinusoidal waveform based on rotor position information from a high‐resolution position sensor, and the current vector (d‐ and q‐axis currents) is suitably controlled by current feedback control.This paper proposes a current sensorless drive system with a low‐resolution position sensor in order to simplify the SM drive system. High‐performance current control is achieved in the proposed drive system, where the current sensors are eliminated and the simulated currents are used for current control. The low‐resolution position sensor is used instead of a conventional high‐resolution position sensor, and the higher position information is estimated. The steady‐state and transient characteristics are examined in several experiments with respect to the synchronous reluctance motor and the interior permanent magnet synchronous motor. It is confirmed that sinusoidal current drive, high‐performance current vector control, and speed control can be achieved by the proposed drive system. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(4): 34–43, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10072

A new type of high-resolution position sensor for ultra-relativistic beams

The radiation emitted by the interaction of an ultra-relativistic particle with a metallic grating (Smith–Purcell radiation) could be used as a very sensitive position sensor for a future Linear Collider or X-ray Free Electron Laser, with position resolution of 1 μm , or better. This article analyzes the physical principles underlying the operation of such a device and concludes with some of the practical issues in its implementation.

Current Sensorless Drive System of Synchronous Motor with Low-resolution Position Sensor

The high-performance drives of synchronous motors such as a permanent magnet synchronous motor and a synchronous reluctance motor can be achieved by the current vector control. In such drive system, the armature current is controlled as a sinusoidal waveform based on the rotor position information from a high-resolution position sensor and the current vector (d and q-axis currents) is suitably controlled by the current feedback control.This paper proposes the current sensorless drive system with a low-resolution position sensor in order to simplify the SM drive system. The high-performance current control is achieved in the proposed drive system, where the current sensors are eliminated and the simulated currents are used for current control. The low-resolution position sensor is used instead of a conventional high-resolution position sensor, and the higher position information is estimated. The steady-state and transient characteristics are examined by the several experiments with respect to the synchronous reluctance motor and the interior permanent magnet synchronous motor. It is confirmed that the sinusoidal current drive, the high-performance current vector control and the speed control can be achieved by the proposed drive system.

Real-time precision concentration measurement for flowing liquid solutions

The precise, real-time measurement of liquid concentration is important in fundamental research, chemical analysis, mixing processes, and manufacturing, e.g., in the food and semiconductor industries. This work presents a laser-based, noninvasive technique to measure concentration changes of flowing liquids in real time. The essential components in the system include a 5 mW laser diode coupled to a single-mode optical fiber, a triangular optical cell, and a high-resolution beam position sensor. The instrument provides a large range of concentration measurement, typically 0%–100% for binary liquid mixtures, while providing a resolution on the order of 0.05% concentration or better. The experimental configuration is small, reliable, and inexpensive. Results are presented for NaCl and MgCl2 aqueous solutions with concentrations ranging from 0% to 25%, with very good agreement found between measured and true concentrations.

Three-dimensional high-resolution particle tracking for optical tweezers by forward scattered light.

A quadrant photodiode placed in the back-focal plane of the microscope of a laser trap provides a high-resolution position sensor. We show that in addition to the lateral displacement of a trapped sphere, its axial position can be measured by the ratio of the intensity of scattered laser light to the total amount of the light reaching the detector. The addition of the axial information offers true three-dimensional position detection in solution, creating, together with a position control, a photonic force microscope with nanometer spatial and microsecond temporal resolution. The measured position signals are explained as interference of the unscattered trapping laser beam with the laser light scattered by the trapped bead. Our model explains experimental data for trapped particles in the Rayleigh regime (radius a <0.2lambda) for displacements up to the focal dimensions. The cross-talk between the signals in the three directions is explained and it is shown that this cross-talk can be neglected for lateral displacements smaller than 75 nm and axial displacements below 150 nm. The advantages of three-dimensional single-particle tracking over conventional video-tracking are shown through the example of the diffusion of the GPI-anchored membrane protein Thy1.1 on a neurite.

High-resolution position sensor based on two sensing elements

A high-resolution optical position sensor based on two sensing elements is described. The important system nonlinearities and error sources are identified, and correction methods are presented. An autozeroing scheme is employed to obtain an accurate center point and to reduce the effects of temperature variations and component tolerances on the overall system. The predicted results are verified experimentally using commercial parts. >

A low cost high resolution optical position sensor

A fast high-resolution analog position sensor that provides real-time analog output corresponding to the position of the centroid of a diffuse optical source focused on its surface, is described. Theoretical performance equations are presented. Linear and two-dimensional position sensors have been fabricated and tested to verify the basic theory. Analytic results for system static transfer function and transient response are presented and verified experimentally for a 3- mu m p-well CMOS process. The main component sensitivities are identified and verified using computer-aided modeling techniques. >