Robust Estimation of Contact Force and Location for Magnetic-Field-Based Soft Tactile Sensor Considering Magnetic Source Inconsistency.

Flexible magnetic-field-based tactile sensors (FMFTS) have numerous advantages including low cost, ease of manufacture, simple wiring, high sensitivity, and so on. Flexible magnetic-field-based tactile sensors need to be calibrated before use to build accurate mapping between contact force and magnetic field intensity measured by magnetic sensors; however, when considering remanence inconsistency of magnetic source, each FMFTS needs to be calibrated independently to enhance accuracy, and the complex preparation prevents FMFTS from being used conveniently. A robust estimation method of contact force and location that can tolerate remanence inconsistency of magnetic source in FMFTS is proposed. Firstly, the position and orientation of magnetic source were tracked using the Levenberg-Marquart algorithm, and the tracking results were insensitive to the remanence of magnetic source with appropriate cost function. Secondly, the mapping between magnitude and location of contact force and position and orientation of magnetic source was built with calibration of one sensor; the mapping only depends on the structural response of flexible substrate, and thus can be extended to estimate external force and location for other sensors with the same structure. The proposed method was evaluated in both simulations and experiments, and the results confirm that the estimation of magnitude and location of external force for FMFTS with the same structure and different remanence could reach acceptable accuracy, depending on single calibration. The proposed method can be used to simplify the calibration procedure and remove the barrier for large-scale application of FMFTS and replacement of damaged FMFTS.

An Improved Model Predictive Current Controller of Switched Reluctance Machines Using Time-Multiplexed Current Sensor.

This paper presents a fixed-switching-frequency model predictive current controller using multiplexed current sensor for switched reluctance machine (SRM) drives. The converter was modified to distinguish currents from simultaneously excited phases during the sampling period. The only current sensor installed in the converter was time division multiplexing for phase current sampling. During the commutation stage, the control steps of adjacent phases were shifted so that sampling time was staggered. The maximum and minimum duty ratio of pulse width modulation (PWM) was limited to keep enough sampling time for analog-to-digital (A/D) conversion. Current sensor multiplexing was realized without complex adjustment of either driver circuit nor control algorithms, while it helps to reduce the cost and errors introduced in current sampling due to inconsistency between sensors. The proposed controller is validated by both simulation and experimental results with a 1.5 kW three-phase 12/8 SRM. Satisfied current sampling is received with little difference compared with independent phase current sensors for each phase. The proposed controller tracks the reference current profile as accurately as the model predictive current controller with independent phase current sensors, while having minor tracking errors compared with a hysteresis current controller.

Core muscle functional strength training for reducing the risk of low back pain in military recruits: An open-label randomized controlled trial.

BACKGROUND: Core muscle functional strength training (CMFST) has been reported to reduce injuries to the lower extremity. However, no study has confirmed whether CMFST can reduce the risk of low back pain (LBP). OBJECTIVE: This study identified the effects of CMFST on the incidence of LBP in military recruits. DESIGN, SETTING, PARTICIPANTS AND INTERVENTION: We performed a prospective, open-label, randomized, controlled study in a population of young healthy male naval recruits from a Chinese basic combat training program. Participants were randomly assigned to either the core group or the control group. In additional to normal basic combat training, recruits in the core group underwent a CMFST program for 12 weeks, while recruits in the control group received no extra training. MAIN OUTCOME MEASURES: At the beginning of the study and at the 12th week, the number of participants with LBP was counted, and lumbar muscle endurance was measured. In addition, when participants complained of LBP, they were assessed using the visual analog scale (VAS) and Roland Morris Disability Questionnaire (RMDQ). RESULTS: A total of 588 participants were included in the final analysis (295 in the core group and 293 in the control group). The incidence of LBP in the control group was about twice that of the core group over the 12-week study (20.8% vs 10.8%, odds ratio: 2.161-2.159, P < 0.001). The core group had better lumbar muscle endurance at 12 weeks than the control group ([200.80 ± 92.98] s vs [147.00 ± 84.51] s, P < 0.01). There was no significant difference in VAS score between groups, but the core group had a significantly lower RMDQ score at week 12 than the control group (3.33 ± 0.58 vs 5.47 ± 4.41, P < 0.05). CONCLUSION: This study demonstrated that the CMFST effectively reduced the incidence of LBP, improved lumbar muscle endurance, and relieved the dysfunction of LBP during basic military training.

Dynamic Modeling and Anti-Disturbing Control of an Electromagnetic MEMS Torsional Micromirror Considering External Vibrations in Vehicular LiDAR.

Micromirrors based on micro-electro-mechanical systems (MEMS) technology are widely employed in different areas, such as optical switching and medical scan imaging. As the key component of MEMS LiDAR, electromagnetic MEMS torsional micromirrors have the advantages of small size, a simple structure, and low energy consumption. However, MEMS micromirrors face severe disturbances due to vehicular vibrations in realistic use situations. The paper deals with the precise motion control of MEMS micromirrors, considering external vibration. A dynamic model of MEMS micromirrors, considering the coupling between vibration and torsion, is proposed. The coefficients in the dynamic model were identified using the experimental method. A feedforward sliding mode control method (FSMC) is proposed in this paper. By establishing the dynamic coupling model of electromagnetic MEMS torsional micromirrors, the proposed FSMC is evaluated considering external vibrations, and compared with conventional proportion-integral-derivative (PID) controls in terms of robustness and accuracy. The simulation experiment results indicate that the FSMC controller has certain advantages over a PID controller. This paper revealed the coupling dynamic of MEMS micromirrors, which could be used for a dynamic analysis and a control algorithm design for MEMS micromirrors.