Improving the Angular Velocity Measured with a Low-Cost Magnetic Rotary Encoder Attached to a Brushed DC Motor by Compensating Magnet and Hall-Effect Sensor Misalignments

This paper proposes a method to improve the angular velocity measured by a low-cost magnetic rotary encoder attached to a brushed direct current (DC) motor. The low-cost magnetic rotary encoder used in brushed DC motors use to have a small magnetic ring attached to the rotational axis and one or more fixed Hall-effect sensors next to the magnet. Then, the Hall-effect sensors provide digital pulses with a duration and frequency proportional to the angular rotational velocity of the shaft of the encoder. The drawback of this mass produced rotary encoder is that any structural misalignment between the rotating magnetic field and the Hall-effect sensors produces asymmetric pulses that reduces the precision of the estimation of the angular velocity. The hypothesis of this paper is that the information provided by this low-cost magnetic rotary encoder can be processed and improved in order to obtain an accurate and precise estimation of the angular rotational velocity. The methodology proposed has been validated in four compact motorizations obtaining a reduction in the ripple of the estimation of the angular rotational velocity of: 4.93%, 59.43%, 76.49%, and 86.75%. This improvement has the advantage that it does not add time delays and does not increases the overall cost of the rotary encoder. These results showed the real dimension of this structural misalignment problem and the great improvement in precision that can be achieved.

Influence of structure parameters of optical current sensor with iron core on temperature distribution

The accuracy of optical current sensors in power systems will be affected by the interference of the external environment. Among them, temperature has a significant influence on the accuracy of optical current sensors, which is one of the main factors that restrict the practicality of optical current sensors. In this paper, the temperature field distribution of the optical current sensor with iron core is calculated by simulation. The influence of its structural parameters on the temperature field distribution is studied. It is compared with the temperature field distribution of the optical current sensor of the commonly used magnetic ring structure. It is found that under the same current, the temperature of the magneto-optical material with the core optical current sensor is much lower than the optical current mutual inductance of the common magnetic ring structure. The geometric structure parameters of the optical current sensor with iron core have a great influence on its temperature field distribution. The temperature field distribution can be improved by optimizing the structure parameters, thereby improving the measurement accuracy. This article can provide a basis for the design optimization of optical current sensors.

Magnetically Counting Hand Movements: Validation of a Calibration-Free Algorithm and Application to Testing the Threshold Hypothesis of Real-World Hand Use after Stroke

There are few wearable sensors suitable for daily monitoring of wrist and finger movements for hand-related healthcare applications. Here, we describe the development and validation of a novel algorithm for magnetically counting hand movements. We implemented the algorithm on a wristband that senses magnetic field changes produced by movement of a magnetic ring worn on the finger (the “Manumeter”). The “HAND” (Hand Activity estimated by Nonlinear Detection) algorithm assigns a “HAND count” by thresholding the real-time change in magnetic field created by wrist and/or finger movement. We optimized thresholds to achieve a HAND count accuracy of ~85% without requiring subject-specific calibration. Then, we validated the algorithm in a dexterity-impaired population by showing that HAND counts strongly correlate with clinical assessments of upper extremity (UE) function after stroke. Finally, we used HAND counts to test a recent hypothesis in stroke rehabilitation that real-world UE hand use increases only for stroke survivors who achieve a threshold level of UE functional capability. For 29 stroke survivors, HAND counts measured at home did not increase until the participants’ Box and Blocks Test scores exceeded ~50% normal. These results show that a threshold-based magnetometry approach can non-obtrusively quantify hand movements without calibration and also verify a key concept of real-world hand use after stroke.

Method of Far-field Electromagnetic Radiation Prediction and Suppression Based on Equivalence of Capacitance Parameters in Power Converter System

Electromagnetic radiation is one of the key issues in research area of EMC. This paper analyzes that common-mode (CM) current is the main noise source, and transmits through parasitic capacitances between input cables and ground, thus CM current path model (CCP) is established. Moreover, CCP is formed as equivalent prediction model of radiation (EMR) by appropriate simplification. The parasitic capacitances of EMR are extracted, and EMR is iterative designed. Furthermore, the radiation emission of two models is in good agreement. At last, ferrite magnetic ring is selected to change scattering parameter matrix, thus electromagnetic radiation can be suppressed; the recommended installation of magnetic ring is given. Keywords: Radiation; Parasitic Parameter;

Magnetic Ring Multi-Defect Stereo Detection System Based on Multi-Camera Vision Technology

Magnetic rings are the most widely used magnetic material product in industry. The existing manual defect detection method for magnetic rings has high cost, low efficiency and low precision. To address this issue, a magnetic ring multi-defect stereo detection system based on multi-camera vision technology is developed to complete the automatic inspection of magnetic rings. The system can detect surface defects and measure ring height simultaneously. Two image processing algorithms are proposed, namely, the image edge removal algorithm (IERA) and magnetic ring location algorithm (MRLA), separately. On the basis of these two algorithms, connected domain filtering methods for crack, fiber and large-area defects are established to complete defect inspection. This system achieves a recognition rate of 100% for defects such as crack, adhesion, hanger adhesion and pitting. Furthermore, the recognition rate for fiber and foreign matter defects attains 92.5% and 91.5%, respectively. The detection speed exceeds 120 magnetic rings per minutes, and the precision is within 0.05 mm. Both precision and speed meet the requirements of real-time quality inspection in actual production.