Zhuofu Liu

Studying thermal characteristics of seating materials by recording temperature from 3 positions at the seat-subject interface

AIM OF THE STUDY To determine whether 3 fixed positions of seat-subject interface temperature measurement offer more information than a single point of measurement. MATERIALS AND METHODS Temperature data was simultaneously acquired (sampling frequency 1 Hz/sensor) from each of three sensor positions (right & left mid-thigh and coccyx), from the subject-seat interface. The data was acquired whilst subjects (6 males, 5 females: 21-40 yrs: BMI 19.3-26.4) sat for 20 min on each of three types of seat material (foam, gel mould and solid wood). Data collection was performed at the same time of day for each subject: ambient temperature between 21.1 and 21.2 °C, ambient relative humidity 50.9%. RESULTS Analysis of data from the sensors, post mathematical smoothing, for each subject (n = 11; ANOVA, followed by post-hoc t-tests) revealed each of the measurement positions to have a significantly different recorded temperature (p < 0.01). However, profile of temperature change at the same measurement position using the same seating material during the 20 min sitting period, was highly correlated (r > 0.99) between subjects, a consistent finding across all 11 subjects regardless of seat material selected. CONCLUSION Use of 3 positions of measurement (3 sensors) appears necessary when performing detailed studies of temperature change at the seat-subject interface. The high level of comparability of results between subjects supports potential of this method to resolve quantitative components of qualitative measurements, e.g., thermal comfort.

Assessment of humidity and temperature sensors and their application to seating

Humidity and temperature are considered to be important factors in designing comfortable seat surfaces. A small number of studies have attempted to address this; however the methods used were limited regarding the placement of their sensors. This study aimed to design a sensor array system to investigate changes in humidity and temperature for eventual use in the study of factors affecting sitting comfort and incontinence detection. The system was subjected to three types of experiments: sensor response verification, thermal radiation testing and in situ trials. The variance in output within each type of sensor was small (±3.5% and ±0.3°C) and there was no apparent change to the variance in output of the sensors, when used in air or on a foam cushion loaded with a 50 kg sandbag (p > 0.1). In the human sitting experiments, although the profile from sensors under the thighs and ischial tuberosities were similar, the magnitude of change could be affected by position and body mass of the subject. This was especially noticeable with the sensors under the coccyx. These results support the use of multiple sites for sensor placement over the use of a single site when studying these parameters at the interface between subject and seating material at the seat base.

A methodology using in-chair movements as an objective measure of discomfort for the purpose of statistically distinguishing between similar seat surfaces

This study presents a method for objectively measuring in-chair movement (ICM) that shows correlation with subjective ratings of comfort and discomfort. Employing a cross-over controlled, single blind design, healthy young subjects (n = 21) sat for 18 min on each of the following surfaces: contoured foam, straight foam and wood. Force sensitive resistors attached to the sitting interface measured the relative movements of the subjects during sitting. The purpose of this study was to determine whether ICM could statistically distinguish between each seat material, including two with subtle design differences. In addition, this study investigated methodological considerations, in particular appropriate threshold selection and sitting duration, when analysing objective movement data. ICM appears to be able to statistically distinguish between similar foam surfaces, as long as appropriate ICM thresholds and sufficient sitting durations are present. A relationship between greater ICM and increased discomfort, and lesser ICM and increased comfort was also found.

Research of Modeling and Sliding Mode Advanced Control for Four Rotor Aircraft

In the process of the design of the four rotor, control system design is a crucial link. The real thing shows a certain or strong nonlinearity. By using the classical method, the control object is simplified to the linear and small perturbation model, and then we control the small perturbation model. However, the non-linear model is controlled directly in many advanced control theories. Advanced control theory can get rid of the traditional classical control modeling of imperfection. Variable structure sliding mode adaptive control system, is a kind of advanced controller, can use the switch sliding surface makes the system achieve good stability. This article first to the four rotor model, and then designed based on sliding mode control method, and has carried on the simulation research, proved the effectiveness of the method.

Investigating thermal performance of different chairs at the user-seat interface by a temperature sensor array system while participants perform office work

Recently, there has been an escalating trend towards sedentary lifestyle in the modern society (i.e. reading books, watching movies or driving cars). It has been estimated that the proportion of time spent sitting accounts for more than one third of a persons total life-time [1]...

Performance Assessment of a Humidity Measurement System and Its Use to Evaluate Moisture Characteristics of Wheelchair Cushions at the User–Seat Interface

Little is known about the changes in moisture that occur at the body–seat interface during sitting. However, as increased moisture can add to the risk of skin damage, we have developed an array of MEMS (Micro-Electro-Mechanical System) humidity sensors to measure at this interface. Sensors were first evaluated against traceable standards, followed by use in a cross-over field test (n = 11; 20 min duration) using different wheelchair cushions (foam and gel). Relative humidity (RH) was measured at the left mid-thigh, right mid-thigh and coccyx. Sensors were shown to be unaffected by loading and showed highly reliable responses to measured changes in humidity, varying little from the traceable standard (<5%). Field-test data, smoothed through a moving average filter, revealed significant differences between the three chosen locations and between the gel and foam cushions. Maximum RH was attained in less than five minutes regardless of cushion material (foam or gel). Importantly, RH does not appear to distribute uniformly over the body–seat interface; suggesting multiple sensor positions would appear essential for effectively monitoring moisture in this interface. Material properties of the cushions appear to have a significant effect on RH characteristics (profile) at the body–seat interface, but not necessarily the time to peak moisture.

Design of Vehicle-Mounted Medical Temperature Control System

Temperature control has been widely applied in many fields, such as medical product transportation, living tissue storage and blood transfusion. Therefore, it is very important to design a vehicle-mounted medical temperature control system. The priority of the developed system must meet stability and accuracy requirement. Based on the fuzzy PID control, a system design solution was proposed in this paper. The control system includes thermal resistor used as a front end to measure temperature, AD7705 chip used as the Analogy Digital Converter (ADC), and TEC component used as the heating or the cooling unit. According to the water tank experiment, a combined control method is offered to meet the temperature control and overcome the controllers non-linearity and hysteresis. When temperature error between the set value and actual temperature value is large, the look-up table control method is used to reduce the heating or cooling time of temperature. When the error is within 1°C, the incremental PID control method is applied to decrease the overshoot. The purpose of the control system is within the range of 37±0.1°C. Meanwhile, the fuzzy PID control and BP-NN PID control algorithms have been studied and analyzed by Mat-lab simulation, which offers further improvement for system update.

Analysis and Research on EEG Signals Based on HHT Algorithm

In this paper, EEG (electroencephalogram) signals are processed by HHT (Hilbert-Huang Transform). First, a new de-noising method is employed to smooth the EEG signals based on EMD (Empirical Mode Decomposition) and Monte Carol method. Then, the filtered EEG signals are analyzed by Hilbert-Huang Transform to obtain the corresponding Hilbert spectrum. Finally, useful information is extracted on the basis of Hilbert spectrum. Through simulation experiments, the results demonstrate that the Hilbert-Huang Transform can be used for EEG processing, and further illustrate that the Hilbert-Huang Transform exhibits some unique advantages in dealing with EEG.

Design and Analysis of Static Pressure Distribution and Measurement on Contact Interface

The developed human body-seat surface pressure measurement system is rational and feasible, and can measure the human body and the pressure distribution dynamically and in real time. The human body seat surface pressure distribution measurement system mainly includes FSR pressure sensor array and STC15F2K60S2 microcontroller. First, the standard weight scale is used to calibrate the FSR sensor and draw the output voltage curve under different pressure inputs. STC15F2K60S2 microcontroller has eight 10-bits AD converters. System adopts RS232 serial interface with the PC for serial communication. The MATLB is employed to conduct data processing and analysis, while the band pass filter is applied for noise suppression. After filtering data in the pre-processing stage, Fourier transform is used to analyze the valid data, then use SP Tool tools for simulation.

Temperature and Humidity Sensor Location Optimization Based on BP Neural Network

A system for sensor location optimization based on BP neural network is described in this research, which consists of the digital temperature and humidity sensors, microcontrollers, data transmission unit and the PC. The system is tested by experiments and the results show that temperature standard deviation is ± 0.3°C and relative humidity standard deviation is ± 0.5%RH, which meets the accuracy requirements of the design. In the process of sensors distribution optimization, by building and solving the contact degree function, characteristic analysis method is used to pick up the best information collection point. The BP neural network model is built, and the temperature and humidity data and other factors (such as height, weight, etc.) are used as network input. The experimental conclusion is that the two evaluation methods have high consistency (the average accuracy rate > 81.1%, the trained sample n = 6, the test sample n = 4), which is sufficient to prove that objective office chairs comfort evaluation method has good evaluation effect using temperature and humidity acquisition system and BP neural network.