Active pressure reduction wheelchair cushion based on multi-channel driving and two-parameter regulation and control

Abstract

The invention discloses an active decompression wheelchair cushion based on multi-channel driving and two-parameter regulation, which comprises a cushion system, a sensing system, a driving system and a control system, all the systems are integrated and packaged through a bus or serial communication, and compact structure and function layering are realized. According to the intelligent pressure reduction cushion system integrating the large-area flexible deformation / pressure monitoring sensor and the multi-channel pneumatic driver module, dynamic adjustment of cushion pressure distribution is achieved according to data monitored by the air bag pressure sensor and the cushion surface pressure sensor in real time; therefore, the occurrence rate of hip pressure sores of disabled or semi-disabled elderly wheelchair users or sedentary people is reduced, development of a wheelchair pressure-reducing pad pressure sore prevention technology is promoted, and the pressure-reducing pad has important significance in improving the life quality of the elderly and the disabled and relieving medical burdens.

Description

Technical Field

[0001] This invention belongs to the field of medical and health care device design technology, specifically relating to an active decompression wheelchair cushion based on multi-channel drive and dual-parameter control. Background Technology

[0002] Pressure ulcers are common, chronic, and difficult-to-heal wounds, a challenging healthcare problem worldwide, and the third most expensive disease after cancer and cardiovascular disease. The main cause of pressure ulcers is the sustained accumulation of high pressure in a specific area, combined with the effects of pressure, shear force, and friction, leading to skin or tissue damage. Essentially, it results from prolonged sitting or lying down, causing continuous pressure on local capillaries, affecting blood circulation, and leading to ischemia and hypoxia in the affected skin, resulting in tissue degeneration or necrosis. These injuries are accompanied by severe pain, loss of function, and complex complications, posing a high risk to bedridden or wheelchair-bound patients.

[0003] When a person is in a wheelchair, the greatest force is exerted on the hips and thighs, accounting for approximately 75% of the total weight. The ischial tuberosity area is the main area supporting the weight; bones can withstand greater forces without deformation, but muscles and fat are prone to deformation under smaller forces. Because the muscles in the hip area of ​​wheelchair users have less tension and cannot resist tissue deformation, this area is prone to tissue damage.

[0004] Pressure ulcers primarily occur in individuals who are disabled or partially disabled, confined to wheelchairs, and unable to change position independently. It is estimated that approximately 3 million people are diagnosed with pressure ulcers annually, with over 500,000 requiring hospitalization, and this proportion is rapidly increasing. Due to the increased life expectancy in my country, the number of elderly patients and disabled / partially disabled individuals is constantly rising. These individuals spend extended periods in wheelchairs, unable to alleviate the pressure and shear forces on their tissues through independent repositioning. This continuous pressure and shear force allows pressure ulcers to form in a very short time (approximately 30 minutes). Once pressure ulcers develop, they not only significantly reduce quality of life but are also extremely expensive to treat. Clinically, emphasis is placed not only on treating pressure ulcers after they appear but also on prevention, with weight distribution being a crucial principle in prevention.

[0005] Most wheelchair pressure-relief cushions on the market today are passive pressure-relief methods, using various materials to reduce localized pressure on the cushion surface. These include one-piece cushions made of single soft materials like foam or gel, and composite cushions based on air cushions. However, these methods cannot fundamentally prevent pressure sores and do not meet the needs of most wheelchair users (due to varying weights and postures). Each patient's pressure distribution is also different; therefore, using a single passive pressure-relief cushion product for all users is inappropriate.

[0006] Preliminary research has been conducted both domestically and internationally on active wheelchair pressure-relief cushions. For example, the literature [CARRIGAN W, NUTHI P, PANDE C, et al. Design and operation verification of an automated pressure mapping and modulating seat cushion for pressure ulcer prevention [J]. MedEng Phys, 2019, 69: 17-27] proposes a sensor-based airbag seat cushion system. Through real-time pressure mapping, redistribution, and unloading functions, it reduces the risk of pressure ulcers in people who sit for long periods. This system achieves uniform pressure distribution through a pressure redistribution algorithm. However, due to the relatively simple gas channel design, it cannot achieve individual airbag inflation and deflation, and only the airbag pressure parameter exists, without the parameter of pressure distribution on the seat cushion surface. Summary of the Invention

[0007] In view of the above, the present invention provides an active pressure-reducing wheelchair cushion based on multi-channel drive and dual-parameter control. Based on the closed-loop feedback mechanism of airbag pressure and cushion surface pressure, it dynamically adjusts the local pressure distribution to reduce the incidence of pressure ulcers. By coupling pressure sensing with distribution control strategy, it can significantly improve the sensitivity and personalization of pressure reduction control, and is especially suitable for people who are susceptible to pressure ulcers and sit in wheelchairs for a long time.

[0008] An active pressure-reducing wheelchair seat cushion based on multi-channel drive and dual-parameter control, comprising: The seat cushion system uses an airbag-filled cushion structure and is installed in the seat of the wheelchair. The sensing system is used to collect information on the pressure distribution on the surface of the seat cushion structure and the air pressure inside each airbag. The drive system is equipped with an independent airbag drive module for each airbag, which inflates and deflates the airbag through a multi-channel air passage. The control system analyzes the information collected by the sensor system and uses closed-loop control to drive the airbags in the corresponding areas to inflate and deflate, dynamically adjusting the local pressure distribution.

[0009] Furthermore, the airbag sandwich-type seat cushion structure is composed of outer fabric, sponge, array-type airbags, and bottom fabric layered sequentially from top to bottom.

[0010] Furthermore, the sensing system includes N One sensing unit, NThe number of airbags is specified. Each sensing unit includes a pressure sensor, a pressure sensor array, and a data acquisition card. The pressure sensor is installed in the air path of the corresponding airbag. The pressure sensor array consists of 16 pressure sensors arranged in a 4×4 array, which is located between the outer fabric and the sponge and in the area corresponding to the airbag.

[0011] Furthermore, the drive system is arranged in the space below the wheelchair seat, and includes... N Each airbag drive module includes an airbag inflator, an airbag deflater, a solenoid valve, and a three-way valve. The three ports of the three-way valve are connected to the solenoid valve, the corresponding airbag, and the corresponding air pressure sensor via air tubes, respectively. The solenoid valve is connected to the airbag inflator and airbag deflater via air tubes. The solenoid valve is controlled by the controller. The power supply provides power to the airbag inflator and airbag deflater.

[0012] Furthermore, both the inflation pump and the deflation pump are connected to the power supply via relays, and the on / off state of the relays is controlled by a controller; the controller controls the opening and closing of the solenoid valve via a PWM electronic switch.

[0013] Furthermore, the data acquisition card is used to acquire the pressure signals generated by each pressure sensor in the pressure sensor array, and upload the acquired signals to the control system via serial communication; the pressure sensor is a piezoresistive pressure sensor, and the pressure signal it generates is acquired and uploaded to the control system through the analog pin of the controller in the drive system.

[0014] Furthermore, the drive system is encapsulated with customized acrylic sheets around its perimeter and on its upper and lower layers, and the upper and lower acrylic sheets are fixed together by 3D-printed support columns.

[0015] Furthermore, the control system employs a host computer and achieves data synchronization and command transmission with the controller via the Firmata protocol.

[0016] Furthermore, the control system arranges the pressure signal values ​​collected by each pressure sensor into a pressure value matrix according to the planar position distribution of the pressure sensors, and visualizes the matrix as a heat map. If a 2×2 local area is detected in the pressure value matrix, and all four pressure values ​​in the area exceed the set threshold, it is determined that the local area is prone to stress concentration and pressure sores. In this case, the airbag in the area is activated to relieve pressure. That is, a command is sent to the controller, which controls the solenoid valve and relay in the corresponding airbag drive module to inflate the airbag in the area and release the pressure. At the same time, the air pressure sensor detects the air pressure of the airbag in the area. When the air pressure reaches the optimized value, the airbag stops inflating.

[0017] Furthermore, the optimized value is equal to 8000Pa + αW, where α is a proportionality coefficient and W is the weight of the wheelchair user.

[0018] This invention develops an intelligent wheelchair pressure-reducing pad with active dynamic pressure regulation. By integrating a large-area flexible deformation / pressure monitoring sensor and a multi-channel pneumatic actuator module, the intelligent pressure-reducing pad system dynamically adjusts the pressure distribution of the seat cushion based on real-time monitoring data from airbag pressure sensors and seat surface pressure sensors. This reduces the incidence of pressure sores on the buttocks of disabled or semi-disabled elderly wheelchair users or those who sit for long periods, and promotes the development of wheelchair pressure-reducing pad pressure sore prevention technology. It is of great significance for improving the quality of life of the elderly and disabled and reducing the medical burden. The inventiveness and beneficial technical effects of this invention are mainly reflected in the following aspects: 1. Modular Multi-Channel Active Air Pressure Regulation System Structure. This invention comprises three main modules: a pressure and air pressure sensing module, a seat cushion airbag module, and a multi-channel inflation / deflation drive module. Each module is integrated and packaged via bus or serial communication, achieving a compact structure and hierarchical functionality. Theoretically, more airbag control and pressure sensing resolution can be achieved by adding serial ports. The seat cushion module employs an array-type airbag structure, with each airbag independently equipped with an air pressure sensor and capable of independent air pressure control. A typical system structure is an 8×8 sensor array, totaling 64 pressure sensing points. Pressure data from each 4×4 area controls the corresponding airbag, resulting in more precise and sensitive control.

[0019] 2. Based on the coupled feedback regulation of airbag internal pressure and seat cushion surface pressure. Existing active decompression systems mostly rely on single air pressure or surface pressure parameters for control, resulting in limited control accuracy. This invention employs dual closed-loop control by simultaneously acquiring and fusing two key parameters: airbag internal pressure (used to accurately calculate the current state of the medium within the airbag) and seat cushion surface pressure distribution (monitoring the user's pressure concentration state through load transfer). This dual-parameter control strategy allows the control system to respond more quickly and accurately to environmental changes, user positional shifts, and subtle changes in airbag airtightness, thereby effectively maintaining pressure balance.

[0020] 3. Multi-channel independent inflation / deflation control unit design. The system of this invention introduces an expandable multi-channel air path control module, each channel is equipped with two miniature air pumps (supporting forward and reverse airflow) and a precision electronic valve, and the control speed can reach millisecond-level response; the combination of air pumps and solenoid valves can realize various action modes such as precise inflation, slow deflation, and rapid depressurization in each airbag.

[0021] 4. Communication and Control Mechanism Based on Firmata Protocol. To solve the communication problem between the embedded system and the host computer, this invention adopts the standard open-source Firmata protocol to achieve high-speed data synchronization and command transmission between the control motherboard and the host computer. This protocol supports multi-threaded task assignment, remote parameter tuning, and other functions, and requires no additional code to be written in the control motherboard, greatly improving the system's scalability and flexibility, allowing users to monitor and control the cushion status in real time through a graphical interface.

[0022] 5. Pressure Concentration Detection and Dynamic Pressure Relief Algorithm Design. Addressing the core mechanism of pressure ulcer formation—localized pressure concentration leading to capillary necrosis—this invention specifically designs a pressure concentration identification and control algorithm. This algorithm uses the sensing values ​​of an 8×8 pressure sensor to detect whether there are excessively high pressure values ​​in local areas (such as a 2×2 area) as the core indicator, constructing a real-time judgment model. Once abnormally high pressure is detected in a local area (such as exceeding ±15% of the average cushion pressure), the system immediately mobilizes adjacent airbags for coordinated pressure relief. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the overall appearance design model of the pressure-relieving seat cushion and wheelchair integration of the present invention.

[0024] Figure 2 This is a schematic diagram showing the connection of each electrical module in this invention.

[0025] Figure 3 This is a schematic diagram of the circuit connection of a single sensing unit in this invention.

[0026] Figure 4 This is a schematic diagram of the drive system in this invention.

[0027] Figure 5 This is a schematic diagram of the circuit connection of a single airbag driving module in this invention.

[0028] Figure 6 This is a schematic diagram of the structure of a single airbag driving module in this invention.

[0029] Figure 7 This is a schematic diagram of the airflow direction of the airbag driving module in this invention. In the figure, (a) corresponds to the airbag inflation state and (b) corresponds to the airbag deflation state.

[0030] Figure 8 This is a schematic diagram of the physical assembly of the drive system in this invention.

[0031] Figure 9 This is a schematic diagram of the seat cushion system in this invention.

[0032] Figure 10 This is a schematic diagram of the hardware system integration and packaging of the pressure-relieving seat cushion of the present invention.

[0033] Figure 11 This is a schematic diagram of the data matrix of the pressure sensor in this invention.

[0034] Figure 12 This is a pressure thermogram of the pressure sensor in this invention.

[0035] Figure 13 This is an example diagram showing pressure concentration in a small area of ​​a pressure heat map.

[0036] Figure 14 To generate a pressure heat map when pressure is concentrated.

[0037] Figure 15 This is a pressure thermogram taken after decompression. Detailed Implementation

[0038] To describe the present invention in more detail, the technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0039] The main requirement of this invention is to sense the pressure distribution on the surface of the seat cushion and the air pressure in the airbags, and to use this data to dynamically adjust the pressure at the contact points between the user and the seat cushion. Based on these requirements, this invention mainly includes the design of a pressure and air pressure sensing system, the design of a multi-channel inflation / deflation drive system, and the design of a dynamic pressure control method.

[0040] First, in the design of the sensing system, it is necessary to select sensors and determine their distribution structure, and then calibrate the sensors. After calibration, the data needs to be preprocessed for subsequent control, and the processed data should be visualized. For the design of the multi-channel inflation / deflation drive system, the morphology of the drive system needs to be designed and modeled. After a reasonable layout, the components are selected to meet project requirements. Finally, the module is physically built, and continuous optimization and integration are carried out during the construction process. Regarding the dynamic pressure control method, based on the pressure ulcer formation conditions in existing literature, the drive system is controlled in conjunction with sensor signals, and decompression effect experiments are conducted to continuously optimize the control method.

[0041] The seat cushion hardware system of this invention comprises three main parts: a sensing system, a seat cushion system, and a drive system. Figure 1 The layout design of the hardware system and its integration with the wheelchair are demonstrated. The seat cushion is installed in the seat of the wheelchair, while the sensing system and drive system are installed and arranged using the space under the seat.

[0042] To clarify the hardware used in the pressure-reducing seat cushion of this invention, we have listed the hardware of the entire seat cushion hardware system as shown in Table 1. The hardware is classified and sorted according to its functional modules. Serial numbers 1 to 3 are the hardware required for the seat cushion system, 3 to 12 are the hardware required for the drive system, 11 to 15 are the hardware required for the sensing system, and 16 to 18 are used for system integration and packaging.

[0043] Table 1 In terms of electrical connections, the system is divided into four main modules: a pressure sensor serial port signal acquisition module, a pneumatic pressure sensor analog signal acquisition module, a solenoid valve control module, and an air pump-relay control module. Each module is responsible for implementing different functions, and the stable operation of the entire system is achieved through reasonable electrical connections. Figure 2 It shows the connection relationships and signal transmission paths between the various modules.

[0044] Since the system requires multiple pressure sensor sensing points, connecting each sensing point to the analog signal line of the control board would result in insufficient analog signal pins. Therefore, this implementation uses serial communication, transmitting data through the Tx (transmitter) and Rx (receiver) lines of the serial port. Serial communication can read data from 16 sensing points at once, solving the problem of insufficient analog signal pins and effectively processing data from multiple sensors.

[0045] To achieve a larger sensing coverage area, this implementation uses four sensors with 16 pressure sensing points each, requiring four independent serial ports for data transmission. However, the host computer's built-in serial ports are insufficient, so a serial port expansion board is used to expand one USB serial port into four Tx and Rx serial ports, thus meeting the system's need for multiple serial ports. A piezoresistive barometric pressure sensor is used to monitor the air pressure inside the airbag. It measures the air pressure value by detecting changes in the sensor's internal resistance caused by pressure changes. This type of sensor features high accuracy and good long-term stability, with a measurement range of 40 kPa.

[0046] In terms of programming language selection, considering simplicity, scalability, and compatibility with the Arduino control board, this implementation uses Python to complete all the code, including reading sensor signals, controlling the drive system, and visualizing sensor data. Python has rich library support and concise syntax, making it particularly suitable for rapid development and debugging.

[0047] Unlike most methods that use the Serial library in Python to control the Arduino board, this implementation uses the Firmata protocol to read and control signals from the Arduino pins. The PyFirmata library is a Python library based on the Firmata protocol, allowing direct control of Arduino pins via Python code. The advantage of using the PyFirmata library is that all code can be centralized in a single Python file, eliminating the need to separately burn Arduino code onto the board, greatly simplifying the development process. This method not only improves code readability and maintainability but also enhances the overall flexibility and controllability of the system.

[0048] Hardware system: 1. Design of pressure and air pressure sensing systems The circuit connection of the sensing unit is as follows Figure 3 As shown, the pressure sensor is directly connected to the control board, reading the sensing signal through analog pins. The serial port expansion board is connected to the host computer, transmitting the data from the pressure sensor acquisition card to the host computer for processing. The entire sensing system consists of four identical sensing units, each containing a pressure sensor, an acquisition card, and a pressure sensor. This sensing system design solves the problem of insufficient hardware interfaces, improves the efficiency and accuracy of data acquisition, and provides reliable data support for real-time monitoring and dynamic control, enabling the system to comprehensively perceive the pressure distribution of the seat cushion and the pressure changes of the airbags.

[0049] 2. Design of a multi-channel inflation / deflation drive system According to project requirements, each airbag needs an independent inflation and deflation pump to control inflation and deflation. To simplify the airflow control method and ensure the independence of each airbag, this implementation uses eight air pumps to control the inflation and deflation of four airbags. Due to the large weight of a person and the need for a fast airflow rate, small air pumps cannot meet the requirements. Therefore, 12V air pumps and a 12V-10A power supply were selected. The air pump has a flow rate of 10L / min and a pressure of up to 10... 5 Pa can inflate a 10×10×7cm airbag in a short time, in just 4.2 seconds.

[0050] In addition, since the small current in the microcontroller cannot directly control the large current required by the 12V air pump, a relay is needed to achieve small current control of large current. This implementation uses a 12V eight-channel relay with a 5V trigger signal. To ensure that inflation and deflation do not interfere with each other, solenoid valves are added to the ends of the inflation and deflation tubes, effectively preventing air leakage. Since a pressure sensor is needed to measure the airbag pressure, a gas passage is added via a three-way connector to connect to the sensor, with the other two ends connected to the solenoid valves and the airbag.

[0051] The main control board of the drive system is an Arduino Mega2560, located in the center of the drive system. The power supply and relays are located on both sides of the main control board, and the air pumps are arranged on both sides of the system. The overall structure of the multi-channel inflation / deflation drive system is as follows: Figure 4 As shown.

[0052] The circuit connections and gas flow design of the drive system are crucial to ensuring the system's effective operation. For ease of explanation, the circuit connections of a single airbag drive module are described below, such as... Figure 5 As shown: First, one positive and negative terminal of the power supply is connected to the relay, and the positive terminal of the other circuit is connected to the positive terminal of the air pump. To achieve control of a large current from a small current, the negative terminal of the air pump is not directly connected to the negative terminal of the power supply, but instead connected to the common terminal C of the relay, and the normally open terminal A of the relay for that circuit is connected to the negative terminal of the power supply. The trigger terminal of the relay is connected to the 5V of the control board, and the corresponding control terminal Y1 is connected to the I / O port of the control board to control the opening and closing of the relay.

[0053] The positive and negative terminals of the solenoid valve are connected to the V and G pins of one end of the PWM electronic switch, and the S pin of the other end is connected to the I / O port of the control board to control the opening and closing of the solenoid valve; the relay module is connected to the digital output pin of the Arduino Mega2560, and the relay is triggered by a low-level signal to control the switching of the air pump.

[0054] The system uses a 12V power supply, which powers both the air pump and the relay module. Through reasonable power distribution and wiring, it ensures that each component can work stably.

[0055] To ensure that each airbag can inflate and deflate independently, while preventing gas backflow and leakage, the system employs a combination of solenoid valves and three-way valves in its gas flow design. For example... Figure 6 As shown, each airbag is equipped with an inflation pump and a deflation pump. The inflation pump is connected to the airbag via an air tube, and a solenoid valve is installed at the end of the air tube to control the airflow. To monitor and regulate the internal pressure of the airbag in real time, a pressure sensor is installed in the air tube of each airbag. The pressure sensor is connected to the airbag and the solenoid valve via a T-junction to monitor and regulate the gas path. A leak-proof design incorporates solenoid valves at the ends of the inflation and deflation tubes to effectively prevent gas leakage. The opening and closing status of the solenoid valves is controlled by an Arduino Mega2560 via a relay module.

[0056] When the airbag inflates, the inflation pump operates, the solenoid valve releases and blocks the deflation pump's passage, allowing airflow to enter the airbag through the three-way tube. The pressure sensor monitors the air pressure value in real time. Figure 7 As shown in (a) above. When the airbag deflates, the deflator pump operates, the solenoid valve engages and blocks the pump's passage, drawing the gas out of the airbag and releasing it into the atmosphere, as shown in (a). Figure 7 As shown in (b) of the diagram.

[0057] Based on the aforementioned hardware design, circuit connections, and airflow design, the physical construction of the airbag drive module requires precise connection of each component to ensure the system's functionality and stability. First, prepare the necessary hardware, including an Arduino Mega2560 control board, a 12V power supply, a relay module, air pumps, a pressure sensor, a T-junction, a solenoid valve, and corresponding connecting tubing and wires. To address the insufficient 12V power interface and increase user operability, an eight-way splitter is added to the system, extending one power supply to eight channels to power eight air pumps. Each air pump can be individually controlled via a switch on the splitter; the power supply output current can reach 10A, thus powering eight air pumps simultaneously.

[0058] like Figure 8 As shown, the Arduino Mega2560 control board is placed in the center of the system for easy connection to other components; the 12V power supply is connected to the relay and splitter to ensure a stable power supply; the air pump and solenoid valve are arranged around the perimeter of the system to increase space utilization. The air pump is connected to the airbag via an air tube, at the end of which a solenoid valve is installed. The solenoid valve is connected to a PWM electronic switch, and its opening and closing are controlled by the control board's I / O ports; the air pressure sensor is connected to the airbag and the solenoid valve via a T-junction to ensure real-time monitoring of the airbag's internal pressure and feedback to the control board.

[0059] During the physical connection process, ensure that the positive and negative terminals of the 12V power supply are connected to the power input terminals of the relay module and the air pump respectively to avoid short circuits or insufficient power. Connect the common terminal C of each group of relay modules to the negative terminal of the corresponding air pump, the normally open terminal A to the negative terminal of the power supply, and the trigger terminal to the 5V pin of the control board. Connect the control terminal Y of each group to the I / O port of the control board to achieve relay switching control. Connect the positive and negative terminals of the solenoid valve to the PWM electronic switch, and connect the other end (S pin) to the I / O port of the control board to control the opening and closing of the solenoid valve. Ensure that the air hose connections are tight and leak-free. Connect the air pressure sensor to the T-junction, and connect the sensor's data output terminal to the analog input terminal of the control board for easy data acquisition and processing.

[0060] After completing the above steps, confirm that the airbag can inflate and deflate independently, and that the pressure sensor accurately monitors pressure changes, indicating that the system is operating normally.

[0061] 3. Seat Cushion System Design The seat cushion features a layered structure, consisting of an outer fabric, pressure sensor, sponge, airbag, and bottom fabric from top to bottom. This structure ensures that all components work together effectively to achieve the best pressure relief effect.

[0062] like Figure 9As shown, the top and bottom layers are both external fabrics, ensuring comfort and durability while protecting internal components. Below the external fabrics are pressure sensors that monitor the pressure distribution between the user and the seat cushion in real time, providing crucial data for the dynamic adjustment of the airbags. Below the pressure sensors is a sponge layer, which provides excellent cushioning, evenly distributing body weight pressure, increasing seat comfort, and protecting the pressure sensors from direct impact. Below the sponge layer is the airbag layer, which can adjust inflation and deflation based on sensor data to achieve active decompression. The airbag layout is based on previous research on air cushion pressure distribution, ensuring sufficient support and decompression in key areas.

[0063] The seat cushion system works in conjunction with pressure sensors, a control system, and airbag layers to adjust the inflation and deflation of the airbags in real time, thereby achieving dynamic control of pressure distribution.

[0064] 4. Hardware System Integration After the three major hardware modules are designed, they need to be integrated and packaged to ensure the compact layout, stability, and portability of the hardware system. This implementation method uses custom acrylic sheets around the drive system and on its upper and lower layers, and employs 3D-printed support pillars to complete the system integration and packaging.

[0065] First, the dimensions of the acrylic sheet are designed based on the dimensions of the drive system and the seat cushion, such as... Figure 10 As shown, the base plate has 16 countersunk holes around its perimeter for assembly with the support columns. The countersunk design prevents the nuts from protruding and maintains the flatness of the device surface. Due to some errors in the processing of the acrylic sheet, the hole diameter is designed to be slightly larger, and a 5mm wide groove around the perimeter is used to mate with the surrounding acrylic sheet.

[0066] The length and width of the four side panels are designed according to the groove size of the upper and lower base plates. The left and right side panels have grooves in the middle to allow the air tubes and pressure sensors to pass through and connect to the seat cushion system. The front and rear side panels have grooves to leave space for the power cord and the USB interface for communication with the host computer. The height of the support column is designed to support the weight of the system and the user while ensuring sufficient space.

[0067] Through the above design and manufacturing methods, the hardware system was integrated and packaged, achieving a tight connection between the various components and ensuring the overall stability and portability of the system.

[0068] Control methods: For the signals transmitted by the four pressure sensors, the total number of data points is 64. This invention processes these 64 data points into an 8×8 matrix using matrix operations. The top left 4×4 matrix corresponds to the 4×4 data of sensor 1, the bottom left 4×4 matrix corresponds to the 4×4 data of sensor 2, the top right 4×4 matrix corresponds to the 4×4 data of sensor 3, and the bottom right 4×4 matrix corresponds to the 4×4 data of sensor 4. Figure 11 As shown.

[0069] To more intuitively visualize the distribution of seat pressure values, this invention uses the matplotlib library to visualize the data, plotting an 8×8 matrix as a heatmap. The intensity of the force is represented by shades of blue. The processing results are shown below. Figure 12 As shown.

[0070] On the Arduino Mega2560 control board, due to the limitations of its serial communication interface—only three sets of Rx and Tx pins are available (with Rx0 and Tx0 dedicated to programming)—serial port expansion is necessary when connecting multiple serial communication sensors. However, once the serial port expansion is complete, the traditional single-control-board programming architecture faces challenges when attempting to read data from four serial sensors in a single loop.

[0071] To address this issue, the initial proposed solution was to utilize a host computer program to assist in data reading and system control. Specifically, the host computer would send commands to the control board via a Serial library, and the control board would execute the corresponding operations upon receiving the commands. This architecture required both the control board and the host computer program to run simultaneously to achieve sensor data reading and system control. However, this approach presented numerous inconveniences in practical applications, such as operational complexity and unstable sensor signal readings, ultimately leading to its abandonment.

[0072] To overcome the above problems, this invention uses the Firmata library. Firmata is a protocol for communicating with microcontrollers, allowing Arduino to be controlled from a computer or other devices in a standardized way. Only the FirmataStandard program needs to be burned into the Arduino sample program; no Arduino code needs to be written. Communication between the host computer and Arduino can be completed by creating a "board" class using the pyFirmata library. Using the board.get_pin statement, users can set the Arduino pins to different modes, including analog input, analog output, digital input, and digital output.

[0073] Pins A0, A1, A2, and A3 of the four barometric pressure sensors are set as analog inputs, pins 2-7, 12, and 13 of the eight control relays are set as digital outputs, and pins 8-11 of the four control solenoid valves are set as servo outputs. Using the pyFirmata library, only simple Python code needs to be written on the host computer to read sensor data and control output devices; the pin.read() function can directly read the barometric pressure sensor values, while the pin.write() function can control the relays and solenoid valves.

[0074] According to existing research, pressure ulcers are caused by stress concentration in a small area, where the pressure exceeds capillary pressure (32 mmHg), making this area prone to pressure ulcer formation. Based on this research, this invention designs an algorithm to detect whether there exists a small area (set as a 2x2 area) with a high pressure value within a 4x4 matrix of four pressure sensors; for example... Figure 13 As shown, if this situation occurs within a small area, it is considered as pressure concentration. Therefore, the control system will control the corresponding airbag pump to inflate and release the pressure.

[0075] In addition, based on the experimental results, we will set a threshold for the airbag pressure to control the amount of air pumped in.

[0076] Stress Reduction Effect Experiment: Due to limitations in experimental conditions, no wheelchair was available to accommodate the drive system for installing the pressure-reducing seat cushion. Therefore, this experiment involved placing the entire pressure-reducing seat cushion system on a platform. After securing the system, the power supply and host computer were connected to begin the experiment. The experimenter sat fully on the cushion, with all support provided by the pressure-reducing seat cushion. The experimenter weighed 75 kg.

[0077] Since the body weight affects the airbag pressure during use, and the effect is unknown, preliminary experiments are needed before searching for the optimal solution to estimate the impact of body weight on the airbag pressure value, so as to better analyze the results caused by changes in airbag pressure.

[0078] The specific procedure was as follows: With the airbag deflated, the subject sat on the cushion. Because some air was present in the airbag, sitting down increased the airbag pressure, and the pressure sensor data was recorded at approximately 4000 Pa. The excess air was then released, and the initial pressure sensor reading was recorded. The airbag was then gradually inflated, and the pressure value was continuously recorded. The results showed that the airbag pressure varied within the range of 0–30000 Pa during the process from the subject sitting down to full inflation. This provides reference data for subsequent experiments and ensures that the airbag pressure can be accurately adjusted for optimal comfort in actual use.

[0079] Next, an experiment was conducted to find the optimal airbag pressure. Preliminary results showed that when the subject sat on the cushion with the airbag uninflated, the airbag pressure fluctuated greatly and was highly unstable as it was gradually inflated; therefore, this method was not used in this experiment. Since the only controllable variable in the experiment was the initial airbag pressure, five different initial pressure values ​​were set: 2000 Pa, 4000 Pa, 6000 Pa, 8000 Pa, and 10000 Pa. These initial pressure values ​​corresponded to the initial pressure values ​​used in the airbag modulus measurement experiment, to observe the airbag pressure and its changes after a person sat on it. The airbag pressure corresponding to the best pressure dispersion effect was recorded as the optimal airbag pressure. Because the airbag pressure tends to fluctuate within a small range, a nearby integer value was used as the optimal value. P m .

[0080] First, the airbag is inflated to the preset initial air pressure value. Unlike the airbag modulus measurement experiment, this experiment cannot use a stop clamp to ensure that the gas will not leak. Therefore, when the initial airbag air pressure value is obtained, the air pressure value will fluctuate. The specific fluctuation is shown in Table 2. Then, the experimenter sits on the cushion and the reading of the pressure sensor and the air pressure value inside the airbag are recorded after stabilization.

[0081] Table 2 Repeat the above steps, adjusting the initial air pressure value of the airbag sequentially through the program. The air pressure values ​​after the subjects sat on the cushion in five experiments are shown in Table 3. In each experiment, by recording and analyzing the pressure sensor readings, it was determined which initial air pressure value could better distribute pressure, reduce pressure concentration areas, and thus improve the comfort of the cushion.

[0082] Table 3 Analyzing the above experimental results, as the initial air pressure of the airbags increases, the air pressure after the experimenter sits on the cushion also gradually increases. Due to the influence of airbag inflation on sitting posture, the air pressure of the four airbags is not exactly the same. For the analysis of the 8×8 pressure heatmap, subjectively, the pressure distribution can be judged by the intensity of the color; objectively, an evaluation index for pressure distribution should be introduced. D , D Defined as the variance of 64 data points from the pressure sensor, the calculation method is as follows: in: μ This is the average of 64 data points.

[0083] The above five sets of data can be calculated. D Judging by the size DThe smaller the value, the more uniform the pressure distribution. Calculations show that pressure sensors with initial pressures ranging from 2000 to 10000 Pa are suitable. D The values ​​are 1.0037, 0.5703, 0.5767, 0.4796, and 0.7060, respectively.

[0084] Experimental results show that an initial air pressure of 8000 Pa provides the best pressure dispersion effect, and the final air pressure after a person sits on the seat is around 18000 Pa. Therefore, 18000 Pa was chosen as the optimal pressure level. P m When the initial air pressure increases further, for example to 10,000 Pa, the effect of dispersing the airbag pressure decreases. One possible explanation is that excessive airbag pressure causes the airbag to inflate too much, resulting in a smaller contact area between the airbag and the seat cushion, which in turn increases the possibility of pressure concentration.

[0085] Finally, a decompression effect verification experiment was conducted to verify the effectiveness of using the optimal initial air pressure value. P m When a person sits on the cushion, observe whether the pressure is distributed more evenly on the cushion and whether the pressure concentration phenomenon is effectively alleviated.

[0086] Use the optimal initial air pressure value P m The test was conducted at 18000Pa, and the air pressure threshold was set in the program. P m Furthermore, a pressure concentration condition is added: when the sensing values ​​of four adjacent sensing points (i.e., a 2×2 area) in the 4×4 matrix corresponding to the four pressure sensors are all greater than 1400, and the airbag pressure has not reached the specified value, the pressure concentration condition is further adjusted. P m At that time, the airbag corresponding to the sensor continues to inflate; when it reaches P m Stop inflating and observe the pressure changes during this dynamic process.

[0087] To make the experimental results more obvious, the experimenter shifted their body center of gravity towards sensor number 3. At this point, the pressure sensor readings were as follows: Figure 14 As shown, the pressure distribution presented in this result is similar to previous findings on air cushion pressure distribution; when the rear airbag is inflated, the pressure sensor readings are as follows. Figure 15 As shown. Experimental results show that when the airbag reaches... P m At that time, the pressure value distribution was more even, proving the effectiveness of the pressure-reducing seat cushion.

[0088] The above description of the embodiments is provided to enable those skilled in the art to understand and apply the present invention. Those skilled in the art can readily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without creative effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made to the present invention by those skilled in the art based on the disclosure thereof should be within the scope of protection of the present invention.

Claims

1. An active pressure-reducing wheelchair seat cushion based on multi-channel drive and dual-parameter control, characterized in that, include: The seat cushion system uses an airbag-filled cushion structure and is installed in the seat of the wheelchair. The sensing system is used to collect information on the pressure distribution on the surface of the seat cushion structure and the air pressure inside each airbag. The drive system is equipped with an independent airbag drive module for each airbag, which inflates and deflates the airbag through a multi-channel air passage. The control system analyzes the information collected by the sensor system and uses closed-loop control to drive the airbags in the corresponding areas to inflate and deflate, dynamically adjusting the local pressure distribution.

2. The active pressure-reducing wheelchair seat cushion based on multi-channel drive and dual-parameter control according to claim 1, characterized in that: The airbag sandwich-type seat cushion structure is composed of outer fabric, sponge, array-type airbags, and bottom fabric layered sequentially from top to bottom.

3. The active pressure-reducing wheelchair seat cushion based on multi-channel drive and dual-parameter control according to claim 2, characterized in that: The sensing system includes N One sensing unit, N The number of airbags is specified. Each sensing unit includes a pressure sensor, a pressure sensor array, and a data acquisition card. The pressure sensor is installed in the air path of the corresponding airbag. The pressure sensor array consists of 16 pressure sensors arranged in a 4×4 array, which is located between the outer fabric and the sponge and in the area corresponding to the airbag.

4. The active pressure-reducing wheelchair seat cushion based on multi-channel drive and dual-parameter control according to claim 3, characterized in that: The drive system is located in the space below the wheelchair seat and includes N Each airbag drive module includes an airbag inflator, an airbag deflater, a solenoid valve, and a three-way valve. The three ports of the three-way valve are connected to the solenoid valve, the corresponding airbag, and the corresponding air pressure sensor via air tubes, respectively. The solenoid valve is connected to the airbag inflator and airbag deflater via air tubes. The solenoid valve is controlled by the controller. The power supply provides power to the airbag inflator and airbag deflater.

5. The active pressure-reducing wheelchair seat cushion based on multi-channel drive and dual-parameter control according to claim 4, characterized in that: Both the inflation pump and the deflation pump are connected to the power supply via relays, and the on / off state of the relays is controlled by a controller; the controller controls the opening and closing of the solenoid valve via a PWM electronic switch.

6. The active pressure-reducing wheelchair seat cushion based on multi-channel drive and dual-parameter control according to claim 4, characterized in that: The data acquisition card is used to acquire the pressure signals generated by each pressure sensor in the pressure sensor array, and upload the acquired signals to the control system via serial communication; the pressure sensor is a piezoresistive pressure sensor, and the pressure signal it generates is acquired and uploaded to the control system through the analog pin of the controller in the drive system.

7. The active pressure-reducing wheelchair seat cushion based on multi-channel drive and dual-parameter control according to claim 4, characterized in that: The drive system is encapsulated with custom acrylic sheets around its perimeter and on its upper and lower layers, and the upper and lower acrylic sheets are fixed together by 3D-printed support columns.

8. The active pressure-reducing wheelchair seat cushion based on multi-channel drive and dual-parameter control according to claim 6, characterized in that: The control system uses a host computer and achieves data synchronization and command transmission with the controller through the Firmata protocol.

9. The active pressure-reducing wheelchair seat cushion based on multi-channel drive and dual-parameter control according to claim 5, characterized in that: The control system organizes the pressure signal values ​​collected by each pressure sensor into a pressure value matrix based on the planar distribution of the pressure sensors, and visualizes this matrix as a heat map. If a 2×2 local area is detected in the pressure value matrix, and all four pressure values ​​in this area exceed a set threshold, it is determined that the local area is prone to stress concentration and pressure sores. In this case, the airbag in the area is activated to relieve pressure. A command is sent to the controller, which controls the solenoid valve and relay in the corresponding airbag drive module to inflate the airbag in the area and release the pressure. At the same time, the air pressure sensor detects the air pressure of the airbag in the area. When the air pressure reaches the optimized value, the airbag stops inflating.

10. The active pressure-reducing wheelchair seat cushion based on multi-channel drive and dual-parameter control according to claim 9, characterized in that: The optimized value is equal to 8000Pa + αW, where α is the proportionality coefficient and W is the weight of the wheelchair user.

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