Design concept
Movements during sleep were aimed to be detected via a network of pressure sensors along the back part of the sleeping bag. While nominal movements could be expected during normal sleeping conditions, frequent changes of pressure sensor data would indicate awakening. Eventually, a vibration system would be activated according to the signals received from the sensor to provide an oscillatory motion. The vibration waveform, amplitude, frequency, and duration could be manipulated to produce positive health benefits (Bressel et al. 2011). Stationary weights were intended to be mounted on the front part of the bag to impart a feeling of deep pressure touch as a semblance of a human presence to act as a calming tool (Grandin 1992). The conceptualized intelligent sleeping bag is shown in Fig. 1, and has three interactive sections: eight weight-carrying compartments, actuating motors distributed along the weight compartments and connected to networks of sensors, and a facility to withhold related hardware devices.
The design idea involved forming a network of pressure sensors along the back (down side) of the bag consisting two sewn layers of conductive fabrics separated by an insulating layer (Song et al. 2016). In a normal sleeping situation, the conductive layers are connected, forming a full circuit. However, in the event of frequent body movement, one or more sensor would become disconnected, thus sending a signal to the microcontroller, which can be placed on the closed side (opposite the zipper) in a specially protected compartment. Corresponding to the intensity of the change in sensor connectivity, the microcontroller unit would activate the connected vibrating motors that are situated between the front (upper) fabric layers of the sleeping bag. Sensor to actuator drive initiation time, duration, delay, and intensity information can be regulated (“Fading,” 2015) by the coded data uploaded in the microcontroller, with the flexibility to override any new command following changed circumstances. The small, weighted bags inside the front part provide continuous deep pressure stimuli and can be adjusted by removing any number of weighted bags according to wearer’s comfort level.
Prototype construction and operation
Material assembling
All the materials, devices, and software system used in this construction process are listed in Table 1 with their respective pictures and specifications.
Table 1 List of materials and devices used
The prototype was sewn using polyamide-based shell fabrics, ensuring lightweight and durable features. Neoprene was used as a filling and as an insulating material having adequate loft and expansion properties to ensure the wearer’s comfort. Silver-coated conductive yarns were used to replace metal wiring and to produce the layers of pressure sensors. Two pieces of such conductive fabric were plain knitted and were placed on both of the insulating layers. At the pressure sensing area, three holes of 2 cm in diameter were made on the insulating neoprene piece, thus allowing the conductive fabrics to contact each other under pressure, as illustrated in Fig. 2.
Following the outline in Fig. 1, connections between the sensors and the microcontroller unit were made using conductive yarns. The controller unit was placed along the sidewall heights of the bag, ensuring minimum contact with the wearer’s body in various sleeping positions. Similarly, another set of connections linked the controller unit to the vibrating motors situated between the front parts of the fabric layers. The front part of the bag had eight evenly spaced compartments to distribute the weighted parts evenly across the body. Zipper bags filled with polypropylene granules were used as weighted components for reasons of economy and fatigue resistance. The zipper bags allow for the adjustment of the amount of granules to control the mounted load. They also provide flexibility, as they can be removed partially or completely according to the individual user’s needs.
An open-source platform-based Arduino hardware and software system was used in this project, which includes an easy-to-use microcontroller system to read sensor inputs and thereby activate any connected actuator devices. An Arduino Uno microcontroller board was used to provide 14 digital input/output pins to be powered by dry-cell batteries. Arduino Integrated Development Environment (IDE) software, which contains a text editor for writing code for further extensions, was used.
Sensor–actuator operation
Each sensor unit operated as an on–off switch. Conductive layers of a sensor unit were initially separated by the insulating material but, under the wearer’s body pressure, they were exposed to each other and formed a closed circuit. Whenever this contact was detached due to movements of the sleeping wearer, the circuit was broken (Fig. 3), and this information was sent to the microcontroller unit. By analyzing a number of movements for a given period via the set software system, the controller enabled the vibrating motors to run for two minutes at a frequency of 28 Hz (Bressel et al. 2011), providing a relaxing sensation for the wearer.
Built-in software sketches were edited to develop suitable programs for different units of this assistive sleeping bag. A “Digital Read Serial” (2015) sketch for the pressure sensor unit, a “Keyboard Message” (2015) sketch for activating the vibrating motor, and a “Fading” (2015) sketch for the desired pattern of vibration were employed. Three pushButton inputs were adapted for the built-in Digital Read Serial code for the three pressure sensors units. These were integrated with Keyboard Message codes, termed as buttonState, along with a SimpleTimer sketch to determine the frequency of bodily movements, and a digitalWrite sketch to introduce the duration of vibration.
Prototype validation
Human subjects and ratings
The prototype system was tested on two female and one male student volunteers who had no history related to ASD, who were between 19–25 years of age, and who weighed in the range of 48–73 kg. They subjectively rated the efficacy of deep pressure touch and vibration to exert a relaxing and soothing sensation (Grandin 1984; Krauss 1987) according to a five-grade scale (Excellent > Very Good > Good > Fair > Poor).
Testing and analysis procedure
To evaluate the effect of the time of day of the sleeping bag on its efficiency level, each responder was subjected to experience the actuation in different sessions: early morning, afternoon, and late in the evening, reflecting the sleeping patterns of children with ASD (Kotagal and Broomall 2012), and on 3 separate days to provide the opportunity for a fair assessment. The front part of the bag was filled with weights corresponding to 8% of the responder’s body weight based on the recommendations of occupational therapists (“What is the Right Sized,” n.d.). Each responder was subjected to ten vibration intervals during a session, leading to 90 observations for three responders in total. The duration of each observation was approximately 5 min (movement sensing and vibrating), providing sufficient time to evaluate the sensation. A break of 2–3 min was allowed between consecutive observations to maintain the usual bodily states of the responders.