Abstract
This paper deals with the idea that one of the inner thermal insulation layers of a garment may be replaced by expanding the air chambers in the form of an expanding thermal insert, which is inflated with air causing the chamber thickness and thermal insulation properties to change. The chambers are controllable so that the thermal insulation properties can be changed, and by connecting with an appropriate control, the architecture of an article of clothing can be designed such that it can independently monitor changes in its environment and change its thermal insulation properties in accordance with changes in its external and internal environment. In this way, it acquires the characteristics of intelligent clothing.
The paper presents idea concepts, development, structural architecture and general characteristics of two generations of intelligent clothing with adaptive thermal insulation properties. The expanding thermal inserts are situated between the outer shell and the lining and are the key element of this type of new clothing. In the first generation of intelligent clothing the expanding inserts were designed in combination with three horizontal chambers that can be sealed in three horizontal layers, whereby it is possible to make six adaptable discontinuous levels of thermal insulation. In the second generation, ribbed expandable chambers were used. Their thickness is continuously changeable according to the pressure change in the chambers, whereby the value of thermal insulation of the chambers can be continuously adapted. The functioning of this clothing is based on the integration of sensors for internal and external temperature and air pressure in the chambers, on a microcontroller with regulation software and actuators to control the expanding insert. When wearing this kind of clothing, the microcontroller system monitors changes in ambient temperature and clothing microclimate depending on the wearer’s physical activity, compares them with the achieved thermal protection and makes autonomous decisions on the required increase or decrease in thermal protection. Since this clothing follows changes in its internal and external environment, estimates the real and necessary state, makes decisions and independently performs the adaptation of thermal insulation to a level that it ensures constant thermal comfort, it can be claimed that such a garment has the basic attributes of intelligent clothing.
The paper describes the functioning of two types of thermal insulation chambers, the sensor system used, micropneumatic components, the microcomputer system, the flow chart of the algorithm of intelligent behavior, the complete built-in architecture of all technical subsystems, features of the first and second generation and the observed good and bad points of the conceptual approach to the development of intelligent clothing with adaptive thermal insulation properties.
Keywords
The miniaturization of semiconductor electronic components and the emergence of nanotechnology elements have resulted in small sizes that have enabled the integration of these components into textile materials. The generally accepted definition of smart textiles has evolved mostly thanks to the reduction of electronic components as well as to original approaches to engineering in textile materials. Smart textiles are defined as textile constructions, such as fibers or filaments and yarns, from which more complex constructions, such as woven, knitted or non-woven fabrics, whose mutual feature is the reaction or interaction with the surroundings or the users, are manufactured. Initially, the built-in electronic structures were rigid and inflexible; however, today’s developments are targeted at designing flexible and adaptable components, such as textile materials, which significantly facilitates their integration into these materials without impairing their original properties. Stoppa and Chiolerio
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divided smart textiles into three subgroups:
passive smart textiles (based on sensors able to sense the environment/user); active smart textiles (reactive sensing to stimuli from the environment, integrating an actuator function and a sensing device); very smart textiles (able to sense, react and adapt their behavior to the given circumstances).
Although sensor miniaturization has progressed well, and it is evident that there is a wide range of sensors for different purposes so that, along with the fact that they require very little energy for their operation, their small dimensions enable their integration into textile materials. Another more complex story is related to the development of actuators. Generally, actuators are much larger than sensors and must carry out work whereby it is necessary to create relatively high forces, and thus they often contain complex mechanical elements. Consequently, actuators have significantly larger dimensions, stiffness or inflexibility; they are bulky and consume much more energy for their operation than sensors. This is the reason why it is very difficult to integrate them into textile materials. The development of actuators for smart textiles will certainly be one of the great challenges of the nanotechnology industry. Furthermore, the adaptive behavior of very smart textiles implies the installation of extremely miniaturized microcomputers or microcontrollers, presenting an even greater challenge for the nanotechnology industry. In order for such a system to function in very smart textiles, it will be necessary to develop miniature power sources built into textiles as well as wiring to transfer enough electrical power to activate the actuators. The future development of very smart textiles will therefore depend on the success of miniaturization and nanotechnology. Thus, it is certain it will take some more time.
These difficulties of installing electronic components into garments do not exist practically because today’s sensors, actuators, microcomputers and microcontrollers, power supplies, wiring, communication elements and other technical subsystems, such as micropneumatic subsystems, can be successfully integrated into complex garments, as will be described in this paper.
Installing electronic components into garments is now a widely known fact. For example, in 2005 Tao 2 did not see any obstacles for the integration of complex systems into clothing. This paper should also prove that expanding inserts, sensors, microcomputers (microcontrollers), actuators (microcompressors, valves and other micropneumatic components), displays, control keys, the battery supply and all wiring can be integrated into the functioning intelligent article of clothing or that their integration is invisible from the outside.
According to Fraile et al., 3 there are two basic categories of sensors that can be integrated into wearable solutions. These are sensors for vital signs of the human body and sensors for detecting movements and locations.
The above-mentioned sensors are able to determine states of health, the user’s location and activities, as well as his physiological parameters, relatively accurately. It is also possible to determine the state of the garment microclimate in the nearby environment quite accurately. 4
Although the sensor technology features an enormous progress, especially in the area of miniaturization, scientists are just at the beginning of the use of actuators in clothing. Development hitches are expected in force amplification caused by actuators and mechanical protection of such small mechanisms built into clothing because they will operate in relatively unclean conditions (even small dust trains can block the operation of tiny mechanisms), in conditions of increased humidity and temperature, and they will be subjected to dirt and relatively strong impacts when wearing clothing. Their resistance to washing and dry cleaning will constitute serious problems.
Smart clothing development began in 1980. Smart clothing is defined as innovative clothing providing interactive reactions by using signals from the sensory organs, data processing and encouraging responses. Smart clothing development is also divided into four periods. 5
The period of the first stage of smart clothing development lasted from 1980 to 1997. The concept of smart clothing was based on the idea of a clothing computer. Clothing was selected as the most general interface between human beings and computers, since people are very attached to clothing.
The second stage of smart clothing development, in the period from 1998 to 2001, can be characterized by uniting the fashion and textile sectors in developing products such a garment.
Numerous collaborative projects resulted between the manufacturers of electronic devices and the fashion industry. Thus, the cooperation between Phillips Electronics and Levy Strauss in 1999 resulted in the launch of the first commercial clothing with built-in electronic devices.
The third stage of smart clothing development lasted from 2002 to 2005. While the previous development of smart clothing was focused mainly on technical feasibility, marketing development began to attract increasing attention.
The fourth stage of smart clothing development began in 2006. Smart clothing, in which a digital media player can be installed, achieved market maturity. It was observed that several high-fashion brands entered the domain of smart clothing development. The function of smart clothing is not limited as regards the wearer’s handling of such clothing. At first, information flow about environmental topics was recorded by the user, but later it became inverse or expressed in both directions. It is the technique of installing electronic circuits and devices that enabled the reception, analysis and transformation of information from the environment in order to be helpful to the user or the wearer of smart clothing. It is also mentioned that smart clothing began to attract great interest in producing renewable energy and wearable energy sources, starting with solar energy or the kinetic energy of movement of the garment wearer.
Later, besides the term smart clothing, the other term, intelligent clothing, was tentatively introduced.6,7
To define the term intelligent clothing properly, it is necessary to take the common and mostly used definition of intelligence.
Many biological definitions define intelligence as the adaptation to the environment, which is best described by one of the most important psychologists, Piaget.
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Some of his definitions of intelligence are as follows (citations):
“… the state of equilibrium achieved when a person is able to adequately handle the data with which he has come into contact. But this is not a static state, but a dynamic one, because it is about the continuous adaptation to environmental stimuli.” “Intelligence is a form of adaptation… Its function is to structure the whole world just as the organism structures its direct environment.”
Naidenova
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describes the technical application of Piaget’s theory (citations): …Piaget believed the intelligence to be a mechanism (both on biological and on cognitive level) by the use of which an organism adapts to the environment, i.e. creates such the schemata of his activity or behavior that allow him to be in an equilibrium with his environment. This equilibrium is a dynamic one, it is achieved by means of two global processes appearing in the different forms depending on the sphere of intellectual activity: assimilation and accommodation.
Commercially available sensors were used, and an original microcontroller system with the necessary periphery and a special type of actuator were developed. Originally developed and patented expandable thermal insulation chambers, which could change their thickness depending on the pressure of the inhaled air, were the actuators. Depending on the quantity of the inflated air, the chamber thickness changed, causing a change in the thermal insulation properties of the garment. The chamber was inserted between the outer shell and the lining of the garment and was the thermal insulation insert whose properties could be continuously adjusted and, as such, it was an excellent adjustable thermal insulation actuator. In addition to the sensor–computer–actuator architecture, micropneumatic systems to control the chambers as actuators, the power supply system, wiring and display with control keys were developed. From 2000 to 2014, two generations of intelligent clothing with adaptive thermal insulation properties (ICAT) were developed and are described in the following sections of the paper.
At this point it is believed that a prototype of intelligent clothing that will adjust its properties in accordance with environmental changes may be developed; in this case, it will automatically adjust its thermal insulation properties in accordance with use in the environment.
Cold protection has always been carried out by wearing garments with higher or lower thermal protection, as well as wearing multiple layers of clothing. The thermal protection of clothing can be divided into several groups as follows.
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Passive thermal protection against low temperatures based on different solutions in the construction of clothing. Nicholas D Gracey
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developed the idea of different zones with various thermal insulation properties that add the effect of enhanced exchange of moist air in certain parts of the clothing or body. Passive thermal protection against low temperatures by selecting complex designs of protective layers. The use of miniature air chambers proved to be interesting also for the function of thermal insulation properties for special purposes.
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The idea of Robert C Kauffeld
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is to use air bubbles located inside a diving suit. Air bubbles increase resistance to heat flow and thus reduce the diver's heat loss in cold waters. Markus Weder
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filed a patent entitled the “Planar thermal-insulating device”, in particular for the human body. Changes in the context of reducing the insulating properties are achieved by the suction of the air from the air chamber. Semi-active thermal protection against low temperatures in complex laminate structures. Semi-active thermal protection can be regarded as the combination of passive thermal protection based on reducing the conduction of body heat toward the environment and the dual effect of reflection of the infrared radiation of the human body into the inside of the garment, as well as the absorption of external thermal radiation and its retransmission into the inside of the garment.
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Complex multi-functional laminated materials for garment thermal protection were invented by George S Carr.
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The complex laminate, besides well-known thermal insulation properties, has the absorption ability of solar-thermal radiation and the reflection of body infrared radiation. Carr achieves this using laminates that have a conventional layer for thermal protection with two new reflection layers and one dark absorption layer.
The physical principles of heat accumulation and emission in changing the physical state of solid, liquid or gas were used by Robert R Scaring, Jay A Buckman and Lawrence R Grzyll in 1989 in the patent Micro-Climate Control Vest.
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The vest consisted of a layer of phase change material (PCM) directly on the body and an outer insulating layer made of conventional fabrics. Applications of phase change textiles include apparel, blankets, the medical field, insulation, protective clothing and many others.18,19
Active thermal regulations, which include different ways of heating the inside of the garment. As active thermal protection, one can consider the process of heating a garment using an outside source, or by supplying additional energy required for heating. Most often there are versions with heaters and the use of additional sources of electricity, inflating heated air from an external device into an item of clothing, the flow of heated fluid through tubes embedded in clothing or using other techniques of additional heating where the energy source is not only the human body or the immediate environment.
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Edward K Metcalf 20 was one of the first to integrate electric heaters into garments. He patented the invention under the title “Heated Garment.” Electric heaters are connected to the hood, protective vest, sleeves, pants, socks and gloves, and connected to a supply voltage of 6 V. The amount of electricity and developed heat can be regulated by the rheostat. 20
Heating power is a problem. Rantanen et al. 21 studied the power consumption of a smart garment and found the battery capacity was 30–40 min of heating. This means heating should be allowed only in an emergency or in situations where it is possible to change or recharge the battery. 22
Additional technical devices related to the clothing are often very large, heavy and awkward, requiring more powerful additional energy sources, which significantly complicates and limits the autonomy of the wearing of clothing and the wearer’s mobility.
Conceptual starting points of the development of the first generation of intelligent clothing with adaptive thermal insulation properties
The primary goal of the author’s conceptual solution of the first generation of ICAT is that the passive nature of thermal clothing protection is converted into an active nature so that the clothing itself determines the thermal state of the body (body temperature, heat flow, relative humidity and air temperature inside the clothing and/or another thermodynamic parameter) and the environment, adjusting itself to the characteristics and values of clothing thermal insulation (Figure 1). The thermal comfort of conventional clothing is achieved using layered clothing so that during warm weather two or three clothing layers are put on (Figure 1(a)). However, if the weather is fresher, one thicker clothing layer is put on the other already used layers (Figure 1(b)), and during very cold weather the greatest number of clothing layers by far is put on (Figure 1(c)).
Conventional clothing used for layered clothing and replacement using ICAT.
The conceptual starting point of the development of intelligent clothing is the development of an adaptive insulation layer with changeable thickness in the form of thermal insulation chambers filled with air. If the weather conditions are warmer, the thermal insulation chambers are deflated (Figure 1(d)). If the weather is slightly fresher, they are partially inflated (Figure 1(e)), and in very cold weather conditions, they are maximally inflated (Figure 1(f)) and they take maximum thermal insulation properties.
Since the thickness of the thermal insulation chambers is changeable by changing the air pressure within them, the thermal insulation properties of the intelligent article of clothing is changed. In this way layered clothing, as well as the use of several clothing layers (or several articles of clothing), can be avoided. Thus, one intelligent article of clothing regulating its thermal insulation properties can be used in a wide range of cold weather in the environment of the wearer.
ICAT of the first generation has measuring sensors and devices, an electronic control device (computer) and actuators that automatically adjust thermal properties in a relatively wide range. There is also a possibility to manually adjust insulation properties by activating the hand pump or manually activating the electric compressors.
The thermal insulation chambers
Thermal properties of the ICAT of the first generation are adjusted by activating various combinations of insulating chambers and/or by adjusting the thickness of the insulating chambers of the thermal insulation insert that is placed between the upper fabric and the lining.
Therefore, the thermal insulation insert has three horizontal air chambers that can be inflated with compressed air: the shoulder, breast and waist sealing chamber. The chambers inflated with air reduce heat flow from the body outwards under cold conditions, and additionally the sealing effect makes the movement of hot air from inside the garment into the environment impossible (the so-called Chimney Effect) and thus prevent heat loss by convection.
Figure 2 shows the basic elements of the intelligent clothing with active thermal protection of the first generation with three expandable chambers, built-in sensors and the micropneumatic system for inflating and deflating air from the chambers.
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Thermal protection is achieved through a higher or lower pressure of compressed air inflated through tubes into the air chambers of the thermal insulation insert. Higher pressure of the inflated air increases the chamber volume and the thickness of the insulating insert on which the degree of thermal protection directly depends. Depending on the relationship of the measured parameters inside and outside the garment, a decision on the activated combination of the thermal insulation chambers is made, and thus on the required level of thermal insulation properties of the garment. Different values of thermal insulation properties can be achieved by different combinations of activated and non-activated thermal insulation chambers. In the event that the sensors measure a temperature drop in of the wearer’s skin temperature or a temperature drop in the microclimate between the wearer’s body and the intelligent article of clothing, a decision is made to increase thermal protection. The amount or degree of thermal protection will depend on the values of the thermodynamic parameters measured in the external environment. Depending on the relationships between external and internal thermodynamic parameters, partial thermal insulation is possible in such a way that the thermal protection of particular combinations of thermal insulation chambers is used.
Basic elements of the insulation insert of the intelligent clothing with adaptive thermal insulation properties of the first generation with built-in sensors.
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The expanding thermal insert is located between the outer shell of the garment and its lining as an independent and complete insert. During care and maintenance it can be easily removed. Because of its independence and integrity, the expanding thermal insert can be integrated into any kind of garment (vest, jacket, trousers or overalls) or other products (e.g. sleeping bag, tent, etc.). Although this design does not contain chambers for sleeves, retrofitting is possible. So far it has not been done because it could reduce the mobility of the arms. In this way, other authors showed articles of clothing in their patents in which they planned two or more zones with different values of thermal insulation.
In the second case it is possible that during increased physical effort, when the skin temperature of the wearer of such clothing increases, the air can be partially or completely released from the thermal insulation chambers whereby thermal protection is reduced or air-permeability or heat transfer from the human body increase.
Control of the thermal insulation chambers and attainment of various levels of thermal protection
Methods of active control of the necessary thermal protection can be carried out fully automatically using electronic circuits or the computer that controls the compressor for supplying compressed air into the expandable thermal insulation chambers, power supply units, miniature solenoid valves and the measuring system. Thus, the ICAT of the first generation can be used in industrial occupational protective clothing and sportswear, as well as in conventional articles of clothing that can, depending on the need, gradually increase or decrease the thermal insulation properties of clothing.
Variants of the level of thermal protection that is achieved through different combinations by activating air thermal insulation chambers
The procedures described make an active thermal protection possible, dependent upon the measured thermodynamic parameters within the article of clothing, on the environment near to the body of the wearer and on the parameters of the environment. In the case that the temperature sensor detects a drop in the temperature of the skin of the wearer, or some other change in thermodynamic parameters in the microclimatic conditions between the wearer’s body and the intelligent article of clothing, a decision can be made to increase the level of thermal protection. Depending upon the ratio of the thermodynamic parameters, partial thermal insulation can also be achieved, so that the thermal protection of a particular combination of thermal insulation (gasket) chambers is activated.
In the case of increased bodily effort, when the skin temperature of the wearer rises, the air from the thermal insulation (gasket) chambers can be, partially or entirely, released, thus reducing the thermal protection and increasing air circulation and conducting the heat from the body. 9
The algorithm of intelligent behavior
The level of protection to be selected depends on the measured values of the built-in internal and external temperature sensors and on the data about the activated chambers. The algorithm for controlling the article of clothing makes a decision on the necessary increase or reduction of the level of thermal protection. Figure 3 shows the operation flow diagram of the intelligent article of clothing with active thermal protection.
Operation flow diagram of the intelligent article of clothing with active thermal protection.
It was found that ICAT should contain the so-called sensors of input variables in order to get information on the condition of its environment and the microclimate space between the intelligent article of clothing and human body, as well as information on the pressures in the thermal insulation chambers of the thermal insulation insert. These are the sensor of the environmental temperature of the ICAT (so-called external or ambient environmental temperature), the temperature sensor inside the ICAT (so-called internal or microclimate temperature) and the pressure sensors of the thermal insulation chambers, which provide information as to whether a chamber is activated or not.
Creating hardware for the first generation of intelligent clothing with adaptive thermal insulation properties
In accordance with the representation in Figure 4, the system of measuring input variables is composed of the temperature measurement subsystem, pressure measurement subsystem and the subsystem for the stabilization of drive voltage.
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Sensors and measuring system for input variables of the intelligent article of clothing.
Conditioned and amplified measuring voltages of the input variables of the environmental temperature and microclimate of the intelligent article of clothing, as well as the air pressure in the air thermal insulation chambers, are guided by a measuring bus to the microcontroller ports. A subsystem for the stabilization of the drive voltage, which is necessary for the operation of the measuring system for input variables, contributes to the stabilization and accuracy of the system operation and is also used to supply the microcontroller system.
The integration of technical subsystems into the first functioning prototype of ICAT was carried out in such a way that all printed circuit boards of the microcontroller system, measuring amplifier, displays, sensors, microcompressor, electric solenoid valves and wiring were integrated into the outer surface of the thermal insulation chambers (Figure 4).
All three thermal insulation chambers (shoulder, breast and waist sealing), along with all technical subsystems, constitute a unique insert that can be fully functional and independent in its functioning. The described technical solution can be installed between the outer shell and the lining whereby the intelligent article of clothing can take intelligent attributes, and in that case its outward appearance is not in contrast with the appearance of conventional clothing.
The integration of all technical subsystems allowed for the first ICAT to measure independently the environment and microclimate temperature in itself, to properly interpret the measuring data and to make decisions on the necessary response in terms of the level of thermal protection and in line with the flowchart from the algorithm of intelligent behavior. It independently carries out the decisions made by activating the microprocessor and other actuator elements, controlling their operation by means of the integrated pressure sensors. Independent and efficient operation of the ICAT is made possible through the described integration of all the technical subsystems.
Figure 5 shows the actual design of the thermal insulation insert with all technical subsystems and the connected sensors of the garment environment and microclimate temperature DS18B20 made by Dallas Maxim Semiconductors. The circuit board of the microcontroller houses the main chip PIC 16F628 made by Microchip containing the basic control program for the ICAT as well as the auxiliary microcontroller PIC 16F877 made by Microchip for the rational control of the electric power systems and the integrated circuit for serial communication with the external personal computer. The integrated display for communication between the wearer of the article of clothing and the microcontroller system can also be seen. It is usually integrated into the visible and available section of the left-hand sleeve of the intelligent article of clothing.
Integration of all technical subsystems into the first functioning prototype of intelligent clothing with adaptive thermal insulation properties.
A three-channel measuring amplifier for amplifying pressure measuring signals in the thermal insulation chambers is also visible. The bus wiring with three pressure sensors, RS235-5784 made by RS Computer, runs to the bottom part of the circuit board from the shoulder, breast and waist sealing chamber, and in the upper part of the board a multi-strand bus for amplified measuring pressure signals is situated. They are introduced into the microcontroller system.
The sensor, the valve and the microcompressor are connected to the air duct, which is made of highly flexible plastic tubing designated PUN-4x0,75-BL, made by FESTO, and a T plug-in connection designated QSMT-4. The air duct is attached over the two-piece conical connection element to the thermal insulation chamber so that the air pressure inside the chamber could be transferred to the pressure sensor. The voltage data in the measuring bridge of the pressure sensor is transferred to the plug-in connector and afterwards via the signal bus of the measuring converters to the measuring amplifier of the pressure signal. In the prototype designed there are three pairs of electric solenoid valves intended for the shoulder, breast and waist sealing thermal insulation chamber: the FESTO solenoid valve is used to fill the compressed air and the Matrix solenoid valve to release the air from the chambers. The DR-4X2PN microcompressor made by Clark is situated above the thermal insulation chambers and is attached to the air duct of the micropneumatic system. All the elements of the technical systems integrated into the ICAT are relatively thin, that is, they are thinner than the thermal insulation chambers and can be integrated imperceptibly into the article of clothing.
The software forms the basis of the control of the article of clothing with adaptive thermal insulation properties. Its main part consists of the algorithm of intelligent behavior, which allows evaluating the outside temperature and the microclimatic temperature inside the garment and making decisions on the optimal required level of thermal protection of the garment. Necessary protection is provided automatically, irrespective of the will of the wearer of the article of clothing or activating the manual compressor. After the system has been started, the software-defined self-diagnosis of the state of the technical system of the article of clothing is performed. The proper operation of the temperature and pressure sensors in the chambers, microcompressor, valves and batteries is tested. Upon completion of the self-diagnosis the state is shown on the display and the external and internal temperature is measured. By the automatic control arrangement, the external and internal temperature is measured in order to collect the parameters for the determination of the algorithm of intelligent behavior. In the case that the measurement shows that the internal temperature is higher than the upper limit temperature, a decision is made that the garment wearer is too warm, and it is necessary to deflate the thermal insulation chambers. In the event that the internal temperature is not higher than the temperature of the lower limit of the microclimate, the system concludes that the garment wearer is cold, and it is necessary to switch on garment protection. In order for the system to make a decision on the intensity of reaction of the level of thermal protection, it is necessary to calculate the difference between the desired temperature of the microclimate and the measured external temperature. The degree of activation of the thermal insulation chambers and the achieved level of thermal protection will depend on the amount of the mentioned difference.
Reactions to the adaptation of thermal protection when the outdoor temperature is changed
Figure 6 shows an example of the flowchart of intelligent adaptation of the ICAT when the difference between the desired microclimate temperature and the environment temperature was higher than 5℃ and lower than 10℃ during wearing. The reaction of the first generation of the ICAT was visible when it was necessary to activate the second level of thermal protection or the waist sealing chamber. Measurements proved that after a decline in the environment temperature to 12℃ (when the wearer of the intelligent article of clothing went out of the warm and heated room into the cold open one) there was a gentle decline in the microclimate temperature too. After the microclimate temperature falls below comfort limits (below 18℃), the microcompressor is activated and air is inflated into the waist thermal chamber (U3).
Flowchart of the adaptation to changes in outdoor temperature of the first generation of the intelligent clothing with adaptive thermal insulation properties during wearing.
After reaching the second level of thermal protection, the system retains the existing state because the microclimate temperature has returned to the comfort limits (20℃ ± 2℃). If then there is a certain physical activity (e.g. the wearer of the intelligent article of clothing starts running), there is also an increase in the microclimate temperature of the garment, so that this level of thermal protection is switched off by deflating the waist sealing chamber (I3). In the case under consideration a drop in the microclimate was registered again, so that the thermal insulation chamber was reactivated (U3). This experiment further confirmed the correct operation of the microcontroller software and the algorithm of intelligent behavior in the case when the difference between the desired microclimate (20℃) and the environment temperature (12℃) was higher than 5℃ and lower than 10℃ (in the case under consideration the difference was 8℃). The system reacted properly again, activating the second level of thermal protection, and upon reaching thermal comfort it retained the existing state of thermal protection (level 2, Table 1). After exceeding the comfort limit, it decreased the level of thermal protection by one level (level 1, Table 1).When it was necessary to increase the microclimate temperature, it reactivated protection level 2, maintaining the microclimate temperature within the given comfort limits. If manual control is selected, it is necessary to perform evaluation of thermal comfort. In a similar way, the intelligent article of clothing reacts when it is necessary to activate higher levels of thermal protection (1–6), so that the chambers are activated as shown in Table 1.
Starting points of the conceptual idea of the development of adaptive thermal insulation chambers of the first generation
The basic difficulty in applying Weder’s patent for intelligent clothing is the use of fillers in thermal insulation chambers. This is the reason why it is not simple to manufacture these chambers industrially. During their subsequent operation, the filler is compressed permanently. Thus, the thickness dependence of the thermal insulation chamber becomes inconstant as a result of the repeatability of the control cycle. It is therefore necessary to perform periodical additional calibrations of the system, which makes the practical application of the solution difficult. Likewise, Weder decided to regulate active thermal protection by controlling heat conduction through the chambers, while the research team of the Faculty of Textile Technology of the University of Zagreb decided on the regulation by heat convection and conduction. Therefore, a number of other technical solutions are based on diametrically different considerations.
Recent studies point to the fact that maximum thermal insulation could be achieved if the thermal insulation chamber contained the fillers, which would prevent free convection, and this fact should be taken into account in further research and development of adaptive thermal insulation chambers. 25
The main disadvantages of the first generation were excessive energy consumption from the batteries. In fact, when changing the combination of the inflated chambers shown in Table 1, it is necessary to completely deflate several inflated chambers and several empty chambers are to be filled with air. For example, when increasing the level of thermal protection from level 4 (medium level of thermal protection) to level 5 (increased level of thermal protection) according to Table 1, it is necessary to deflate the inflated sealing shoulder and waist sealing chamber and inflate the breast sealing chamber. Thus, the energy consumed to inflate the chamber when changing the combination got lost irretrievably. With frequent changes of outside temperature or during physical activities of the wearer, it was necessary to change the thermal protection level frequently. As a consequence, the microcompressor (consuming the most power) worked often and consumed too many battery resources. Another significant drawback is the possibility of achieving only six levels of thermal protection. A better solution would be to use thermal insulation chambers that can continuously change their thickness. Furthermore, when wearing clothing for test purposes in cold conditions and according to the wearer's subjective assessment, it was found that one of major objections was sweating and subjective feeling of cold in the places where the chambers were deflated.
In the same way, electronic and pneumatic components, wiring and batteries could not be removed for cleaning purposes (laundering, dry cleaning, etc.). Thanks to the first generation it turned out in spite of the mentioned shortcomings that it is possible to create an article of clothing that will automatically adjust its thermal insulation properties in accordance with environmental changes. The technique of making thermal insulation chambers and their integration into the garment, construction architecture, which includes all necessary sensors, a microcontroller with control keys and display, necessary software, micropneumatic actuators, wiring and a battery system with rational methods of using battery resources, were adopted.
The integrated components increased the total weight of the garment, which can also be regarded as unfavorable.
All identified good and bad properties of the first generation served as a starting basis for the development and patent protection of the second ICAT generation.
Second generation of intelligent clothing with adaptive thermal insulation properties
The research team of the Laboratory for Processing Parameters in the Department of Clothing Technology at the Faculty of Textile Technology, Zagreb University, made the first functioning prototype. They carried out investigations of the ICAT of the first generation stretching over several years. It turned out that the prototype worked properly, the algorithm of intelligent behavior was improved and proved to be very good at achieving optimal thermal protection automatically, and provided good thermal comfort when wearing. However, the technical solution of the prototype of the ICAT of the first generation showed several deficiencies.
This is the reason why the prototype of the second generation of the ICAT with several new and improved technical solutions was made. Segmented thermal insulation chambers were made of high-elastic polyurethane foil designated as Walopur 4201AU, made by Bayer Epurex Films GmbH, Germany. It is characterized by a material density of 1.15 g/cm3, a softening point from 140℃ to 150℃, material thickness of 0.196 mm and a very high elongation at breaking force, amounting to 550%. Moreover, the material is highly ultraviolet (UV) light resistant, hydrolytically stable, has good properties in joining thermal and ultrasonic methods, and a good microbiological stability, which is important for the incorporation into the clothes. The measuring samples of the thermal insulation chambers were joined by the ultrasonic welding machine for foils made from artificial polymers.
The thermal insulation chambers of the second generation of intelligent clothing with adaptive thermal insulation properties
Segmented thermal insulation chambers are connected with net-like or elastic materials or semi-permeable membranes which let the sweat-saturated air pass through, eliminating the sweat from the body, which allows unimpeded air leakage of saturated steam from the inside of the garment to the outside.
In order to determine the relative area of the net-like connecting structure, vapor permeability measurements were performed on a hot plate instrument made by Company Measurement Technology Northwest, USA. The device performed fully automated testing according to standards ISO (ISO 11092, 1993) and ASTM (ASTM F1868). On a hot plate were examined samples of a net-like material and samples of polyurethane foil with different widths of net-like material (1, 3 and 5 cm). 26 Samples were tested at a temperature of 35℃. The relative humidity was 45% and air velocity was 1 m s–1.
All samples were of dimensions 300 mm × 300 mm. The sample A net material width is 1 cm, the sample B 3 cm and sample C is 5 cm. The thermal and water vapor resistance of the net-like material are also examined (sample D).
For designing the thermoinsulating chamber we used net-like material with a width of 5 cm and relative surface of 17%, which has a satisfactory value of thermal resistance and vapor resistance (the heat resistance is 0.0886 m2℃ W–1 and water vapor resistance 22.828 m2 Pa W–1), and is not too wide for the integrity of the thermal insulation chamber.
Recalculated to the area of the largest thermal insulation chamber of 0.75 m2, the net-like structure should be larger than 0.13 m2, which can be achieved and exceeded when the chambers are connected.
Shapes of segmented thermal insulation chambers are ergonomically designed so that at extreme ergonomic movements of the body no bending of the segmented thermal insulation chambers occurs, but the insert bends at the joints between the segmented chambers. This preserves the original shape of the segmented chambers, keeping their thermal conductivity and garment aesthetics unchanged.
The printed circuit board of the microcontroller system, three-channel measuring amplifier, electric solenoid valves for inflating and deflating compressed air into the thermal insulation chambers and the microcompressor for inflating the thermal insulation chambers with compressed air were miniaturized.
Significantly smaller and lighter electronic and pneumatic components are situated in the waist part of the thermal insulation insert on the special waist carrier, which can be detached from the thermal insulation insert (in contrast to the first prototype in which all components were situated over the whole section of the thermal insulation insert), which makes it easier for the manufacture, mounting and service and reduces possible damages of the segmented thermal insulation chambers in the course of wearing and using.
The two-piece metal conical connection element for the attachment of the air duct is omitted because the air duct is directly attached to the thermal insulation chambers by high-frequency welding.
The problem of self-diagnosis (calibration) for this new type of clothing with adaptive thermal insulation properties was also solved. Upon starting the system, the software performs the specific self-diagnosis for the technical system in an article of clothing. According to the mentioned procedure, the accuracy of all temperature and pressure sensors in the segmented chambers of the thermal insulation insert, the microcompressor and all valves for inflating and deflating and the state of the batteries is tested. After the beginning of the self-diagnosis, the system first deflates the compressed air from the segmented chambers. Subsequently, air is inflated into the segmented chambers to a pressure of 50 mbar, followed by deflating until the chambers are completely emptied.
Upon completion of the self-diagnosis, the state is shown on the display and the environment and microclimate temperature are measured. The percentage of filling of the segmented thermal insulation chambers is shown in increments of 10%. The memory recorder of the behavior of ICAT records the state every minute (both the temperature and level of the inflated state of the segmented chambers) during 13,107 min or for 9 days of the operation of the prototype. Upon starting it displays the mode of operation so that manual or automatic mode of operation can be selected.
In the case that the temperature of the clothing microclimate is too high, and the deflated segmented chambers, in which the article of clothing has minimum thermal protection, are not sufficient to achieve a favorable microclimate, this improvement provides additional forced air circulation inside the garment. For these purposes, compressed air used to fill segmented thermal insulation chambers is re-directed to the cooling nozzles. The cooling nozzles are positioned at the front, side and back center of the garment, in principle along the connecting channel structures created by linking the segmented chambers using net-like fabrics or semi-permeable membranes. In these areas increased sweat-saturated air circulation occurs; the air forced into the connecting channels will only additionally stimulate the evaporation and elimination of sweat, which will result in additional cooling of the body and comfortable microclimatic conditions within the garment.
For the operation of the electronic and electromechanical assemblies of the system for inflating an intelligent article of clothing with adaptive thermal insulation properties, a battery based on NiMH technology was ultimately selected. The battery consists of two cells with a nominal voltage of 7.2 V. At that time, the NiMH technology had many more features than the previously used NiCd batteries.
Preliminary tests of prototypes have shown a relatively high autonomy of operation with a relatively low energy capacity of installed batteries. The first ICAT generation lasted for 24 hours due to the frequent operation of the microprocessor, which had to charge and discharge the chambers depending on the required combination of the activated chambers. The work autonomy of the second and third ICAT generation lasted up to 72 hours since it is necessary to deflate the chambers partially or to inflate them additionally in order to achieve the desired level of thermal protection. Thus, the microprocessors operate in much shorter intervals and consume much less electrical energy.
The elimination of the identified deficiencies resulted in the development of completely new technical solutions and operation of the second generation of an intelligent article of clothing using changes in the thickness of the segmented thermal insulation chambers in the thermal insulation insert.
Figure 7 shows the thermal insulation insert of the second generation of the intelligent article of clothing with adaptive thermal insulation properties with the representation of the shaped segmented thermal insulation chambers, connecting channel structures with net-like fabrics or semi-permeable membranes (for sweat elimination) and the main construction elements positioned on the waist carrier.
The thermal insulation insert of the second generation of the intelligent article of clothing with adaptive thermal insulation properties.
The construction of the insert is based on the application of numerous segmented thermal insulation chambers, designed according to anthropometric measurements of the wearer population (men, women and children of various ages and various body statures) even during extreme movements. It offers a new manner of segmented thermal protection for parts of human body, so that more sensitive body parts are layered with chambers of various thicknesses, which can, at the same level of pressure, be of different thickness. In this way, the level of thermal protection is varied in a pre-determined and controlled manner, according to the individual needs of the wearer.
Tests of heat transfer resistance on ICAT were conducted on the measuring system for assessing static and dynamic thermal properties of textile composites and clothing. The necessary power of the activated and deactivated thermal insulation chambers in the thermal insert was measured. When the thermal insulation chamber is deactivated, the air pressure in the thermal insulation insert was 0 mbar, and the measured thickness of the chamber between the inner and outer layer was 28 mm.
The equilibrium power of the heater of all the surfaces of the torso was determined when the thermal manikin was in idle state and when the walking speed of the manikin was 10, 20, 30, 40, 50 and 60 double strides/min and simultaneous movements of the hands were simulated. The stride length, measured from toe to toe, was 63 cm, and the length of the arm movements, measured between the wrists at the base of the thumbs, was 53 cm. According to ISO 15831: Physiological effects – Measurement of thermal insulation by means of a thermal manikin, the temperature of the heated surfaces of the manikin was 34.0℃, the ambient temperature was 19℃, the air flow velocity in the chamber was 0.4 ms–1 and the air relative humidity was 50%.
In the idle state of the manikin with the deactivated thermal insulation chamber, power of 79.0 W is necessary to keep the torso temperature of the thermal manikin constant, and with the activated thermal insulation chamber the necessary power is reduced to 57.5 W. At the same time, the heat transfer resistance rises from 0.0886 to 0.1475 m2KW–1, which increases the effective insulation value by 66.5%. In determining the heat transfer resistance of the ICAT in motion or walking simulation, there was an even greater increase in the effective thermal insulation from 0.0775 to 0.1420 m2KW–1, which increases the effective insulation value by 83%. This high amount of increasing value of effective thermal insulation can be attributed to increased sealing due to the activated thermal insulation chambers that are tightly attached to the body, thus further reducing heat transfer through the body by conduction into the environment. At the same time, the remaining air pockets are reduced more and more so that a very small amount of hot air from the inside of the garment when in motion is transmitted to the environment with the activated thermal insulation chambers. Based on the conducted measurements and the results presented it can be concluded that the thermal insulation chambers filled with air can be an extremely suitable insulation material for creating ICAT. 27
Creating the hardware of the second generation of intelligent clothing with adaptive thermal insulation properties
Figure 8(a) shows a photo of the outer shell (with the communication display on the sleeve) of the second generation of ICAT, and Figure 8(b) shows the thermal insulation insert with thermal insulation chambers and the waist section with electronic and pneumatic components.
Realized prototype of the second generation of clothing with adaptive thermal insulation properties: (a) outer shell with integrated display on the sleeve; (b) thermal insert with thermal insulation chambers and a technical subsystem.
Starting points of the conceptual idea of the development of adaptive thermal insulation chambers of the second generation
The first and second generation of ICAT differs substantially on 16 basic points. The basic differences showed formed a good basis for the patent protection of the second generation of intelligent article of clothing with adaptive thermal properties.
It should be noted that it is not possible to establish a set of different varieties of thermal protection for the second generation because it does not have different variants (only six combinations) any more than the first generation. The second generation can continuously change the thickness of the thermal insulation chamber (unlimited number of combinations) according to the pressure of the inflated air in the chamber, as described in the second paper.
The operating principle of controlling active thermal protection: necessary chamber thickness is continually adjusted for an infinite number of protection levels. Thermal insulation chambers are only slightly inflated or deflated during the creation of the thermodynamic equilibrium. This is why the consumption of compressed air is several times lower.
Some electronic components of sensors and microcontroller systems have great similarities in the first and second generation. However, there is a great difference in the actuator system because the first generation has only one microcompressor for inflating (deflating is performed freely), while the second generation has two microcompressors (for inflating and forced deflating).
Generations are distinguished also in the segmented structure of the chambers and the addition of net-like connecting structures. The sensor–microcontroller–actuator system is located in the waist region, which is easily detachable, unlike the first generation where it was impossible.
However, the most important difference between the first and second generation is the way in which the thermal insulation chambers function. In the first generation there are three chambers that are activated in only six possible combinations allowing only six levels of thermal protection. In the second generation the chambers function on the basis of a change in their thickness depending on the pressure of inflated air, so that theoretically they can achieve an infinite number of different levels of protection.
Conclusion
The paper describes the new conceptual starting points of the authors, the creation of the first prototypes and the development of the first and second generation of intelligent clothing, which itself changes thermal insulation properties in accordance with the observations of environmental changes. Thermal insulation chambers are described in a documented manner where the chambers filled with air can successfully replace one of the insulating layers in an article of clothing used to protect against cold. Air sealing chambers can be activated according to the principle of different combinations of activated or deactivated chambers, resulting in a change in insulation properties (first generation) or in a change in their thickness depending on the pressure of inflated air, which causes a change in chamber thickness and, hence, the thermal protection level (second generation). Since a change in the combination of activated chambers or a pressure change in the chambers may change thermal insulation properties, it is possible to carry out the automatic regulation of thermal insulation properties of the article of clothing. The paper explains that the mentioned regulation can be carried out by sensors that track changes in the garment environment, by using a microcomputer system that properly interprets these changes, makes necessary decisions on the basis of the algorithm of intelligent behavior and performs them with the use of actuators. According to this idea concept, the actuator represents a thermal insulation insert with expanding chambers, a microprocessor, pneumatic electric valves and connecting elements of micropneumatic. The setting system of thermal insulation properties is based on the sensor–actuator–microcomputer architecture.
This approach to the idea concept has produced results that an article of clothing may be created that will be able to adapt its thermal insulation properties independently. Thus, an article of clothing is created that shows signs of simple intelligence: it independently performs a meaningful adaptation in accordance with the observed changes in the environment, which is an essential prerequisite and general definition of intelligent behavior. Therefore, it may be assumed that articles of clothing with attributes of intelligent clothing may be created in two described ways.
The first and second generation of ICAT has shown very good adaptability in different environmental temperature ranges and physical activities of the wearer. Wearing this type of intelligent clothing reduces the need for layered clothing by the use of several types of conventional articles of clothing. Constant thermal comfort is also ensured when wearing this kind of clothing.
Apart from very acceptable behavior of garments during adaptations, during the development of the first functioning prototypes several shortcomings were observed. It was very quickly noticed that it is very comfortable to wear garments with inflated chambers because they allow a great ease of movement and wear comfort with an adequate level of thermal protection. However, a high consumption of capacities of integrated batteries was observed, which reduced the autonomy of work to a relatively short time. Besides the sweating problem and other minor shortcomings, the research team abandoned the concept of achieving the level of thermal protection by using the combination of activated chambers. Thus, the production of new types of ribbed chambers was started where chamber thickness was achieved with relatively small amounts of inflating and deflating air, resulting in a several times greater autonomy of work.
The second generation of ICAT has significantly improved technical and performance characteristics, but it also has several weaknesses that challenge the development of the third generation. Likewise, it is still necessary to measure and research the described concept in order to determine the acceptability of the use of this new kind of clothing. It represents a challenge for the research team that has made first steps, as well as for the wider scientific community that will assess the need for research and use of the concept described.
The weight of electronic and pneumatic components increases the overall weight of the garment, but the benefit is high. As a consequence of further miniaturization, the mass will be reduced even further and its impact on the overall weight of the garment will be smaller. During the development of the second generation the sweat elimination was partially solved, free convection was partially reduced by built-in barriers in chambers that facilitate air circulation, and the possibility of fillers being used in order to increase total thermal insulation for very cold conditions should be investigated.
Footnotes
Declaration of conflicting interests
The authors declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.
Funding
The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: We would like to express our sincerest appreciation and thanks to the Ministry of Science, Education and Sports of the Republic of Croatia for the financial support in two research projects dealing with the development of intelligent clothing, as well as to the Croatian Institute of Technology for financing the technological applicative project of developing garments with adaptive thermal insulation properties and thermal mannequin to be used in investigating thermal properties of intelligent clothing with adaptive microclimatic conditions.