Design basis and performance realization of the ho

2022-07-31
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Design basis and performance realization of insulin pump

the insulin pump is used to accurately control the insulin injection volume of diabetes patients. Patients with serious conditions may need to inject insulin many times a day to maintain a reasonable blood glucose value. Insulin pump can improve the quality of life of patients and reduce the hidden danger of complications due to long-term illness by reasonably controlling blood glucose. The design of the insulin pump firmware allows the injection rate of the syringe to be adjusted, and the injection amount of insulin can be adjusted according to the patient's eating, sleeping and exercise. The insulin is placed in the user replaceable needle tube, which is placed in the pump body, so as to form a special syringe with a piston, which can be pressed slowly under the control of the insulin pump. The needle tube outlet is connected to a hose through which insulin is injected subcutaneously (usually in the abdomen) into the patient

the blood glucose meter provides real-time blood glucose indicators through the subcutaneous sensor for continuous monitoring of diabetes patients. Every time the sensor is replaced, it can be used for several days, which eliminates the need for patients to repeatedly collect blood samples. The future development trend is to further improve the blood glucose detection, response mechanism and the synergy of the whole loop of automatic adjustment of insulin dosage

fda regulation on medical devices

insulin pump is a portable medical device. In the United States, the design and production of insulin pump are regulated by the U.S. Food and Drug Administration (FDA). This means that its design architecture must meet the requirements of relevant documents, and their performance must meet the strict regulations of pda

and the requirements of development test, production test, field maintenance, etc. (Figure 1)

Figure 1: insulin pump principle block diagram

the equipment must also have self-test and fault indication functions, which means that additional supporting circuits and components are required to complete the self-test function

considering the time and cost required to obtain FDA approval, the insulin pump manufacturer needs to select a chip supplier that is customer-oriented and can strictly control the shutdown policy, so as to ensure that the supply of the system manufacturer can be maintained for several years. Semiconductor manufacturers must recognize the serious harm caused by device shutdown to medical equipment manufacturers, persistently transplant some old products to new product lines, establish wafer inventory, provide the last procurement opportunity or develop new upgraded alternative products. Maxim rarely stops production of a device when customers still have demand

portability

insulin pump is a portable device, so it must be small and portable (Fig. 2). Typical insulin pump size is about 2 × three × 0.75 inch, weighing only 2 ounces or 4 ounces. This demand for miniaturization makes designers must give priority to size and power consumption when selecting components

in order to save space, system designers need highly integrated and ultra small package devices. For example, chip level packaging (UCSP packaging of Maxim) and wafer level packaging (WLP). In order to use the battery with the smallest size possible, designers must try to reduce power consumption and improve efficiency. If possible, put any unused circuits in off mode

Figure 2: typical battery powered insulin pump system

(MiniMed paradise 522/722 produced by Medtronic)

the core device of the system is a highly integrated low standby power microcontroller. For example: maxq2010 or similar MCU. Maxq2010 is a 16 bit MCU. It only consumes 1mA current when operating at 1MHz and 2.7V. The current drops to 370na in standby mode. Such low power consumption can effectively prolong the battery life of the insulin pump. Similar to most MCU, maxq2010 integrates USART, timer, 64 words according to jb/t8521.1 (2) 007 woven sling safety Part 1: general purpose synthetic fiber flat sling and JBT 8521.2 (2) 007 woven sling safety Part 2: relevant requirements for general purpose synthetic fiber round sling force detection section flash memory, 2 bytes ram, general i/o function, one-way sampling rate of 312.5ksps, 12 bit successive approximation ADC with built-in reference 160 Segment LCD controller and other resources. The device also has a quick wake-up function, which can quickly return to the normal working state from the sleep and shutdown modes, so that the insulin pump can quickly respond to the operating needs of patients

insulin pump subsystem

1 Pump and detection scheme

insulin is measured by "unit", and each CC (or ml) is divided into 100 units. It is assumed that the concentration is standard U-100. In this way, one unit is equivalent to 10 μ L 。 The injection rate is 1 unit/hour. Each injection lasts for 3 to 10 minutes. The dose of an insulin tablet is several units. Typically, the needle tube can contain 200 to 300 units of insulin

considering the extremely slow flow rate, the motor drives the gear drive pump step by step to drive the piston of the needle tube to move very slowly. It is usually only necessary to measure the angle of the motor roughly. Most insulin pump manufacturers use optical encoders and DC motors, as well as stepper motors. In order to reduce the size of the system, you can also choose to use MEMS pump or pressure pump, thus eliminating motor control

use the pressure sensor to detect the sealing condition of the system and ensure normal operation. Based on the silicon stress meter, the output signal amplitude of these sensors is in the millivolt order, while the output signal range of the bonded wire stress meter is in the microvolt order. The stress meter adopts a typical bridge structure to generate a differential signal based on the common mode voltage, which is usually half of the power supply voltage

an analog-to-digital converter (ADC) with a differential input programmable gain amplifier (PGA) can be used in the design, or a microcontroller using a built-in ADC and an external differential amplifier or instrument amplifier (for signal conditioning). The pressure measurement does not need high accuracy, because the pressure reading is only used to indicate whether the operation is normal, and is not used for injection dosage measurement

2. the electronic supply system

the insulin pump usually uses a boost voltage regulator to increase the low voltage (1.5V, the standard value continuously arousing the endogenous power of the enterprise) input of a single alkaline battery to 2V or higher. In order to make full use of the battery energy, the boost converter should be able to work at the lowest possible input voltage. The boost converter provided by Maxim and other power supply manufacturers can work at a minimum voltage of 0.6V, and the starting voltage is as low as 0.7V, which can effectively increase the service life of the battery

max1947 boost DC-DC converter is ideal for such applications, with an input voltage range of 0.7V to 3.6V. The 2MHz switching frequency and current control mode greatly reduce the size of external components, and can achieve a conversion efficiency of more than 94% and faster response time. The device integrates all switch conversion circuits (power switch, synchronous rectifier and reverse current isolator), further reducing the size of the scheme. The true shutdown circuit can completely disconnect the battery from the load in the off state, which helps to further extend the battery life

if the equipment requires strictly stable power supply voltage, it may be necessary to further stabilize the voltage of the boosted power supply in the design. In this low-voltage application, the linear regulator can provide higher efficiency because there is no switching loss (the inherent loss of the joint concept definition stage of the fuselage and tail work package of the cr929 long-range wide body airliner jointly developed by China and Russia has been organized by the Commercial Aircraft Corporation of China (COMAC) of switching power supply on the 27th)

in addition, low dropout linear regulator (LDO) can obtain smaller scheme size, which is particularly important for insulin pump. The efficiency of LDO is very close to the vout/vin ratio. When the difference between VIN and output voltage is slightly higher than the LDO voltage difference, higher efficiency can be obtained

if the motor needs regulated power supply, switch mode converter can be selected. In order to reduce the size and weight, the converter with the highest switching frequency can be selected. For multi power supply systems, the power management IC (PMIC) can be selected

3. battery management

the manufacturer of insulin pump G has made great progress in reducing power consumption and extending battery life. At present, insulin pumps used in the market can work for 3 to 10 weeks every time the battery is replaced or charged. Most insulin pumps use AA or AAA alkaline batteries or lithium batteries. The use of primary batteries (non rechargeable batteries) is very popular, but the use of rechargeable batteries can help to save long-term costs. Since the capacity of rechargeable battery is relatively low, the charging times are relatively frequent

due to size constraints, most insulin pumps are powered by alkaline batteries in order to eliminate the need for chargers. Due to the lack of electricity meter, the battery electricity indicator mainly adopts a simple voltage measurement method, sometimes combined with temperature measurement. The system sends the voltage and temperature signals to ADC for quantification. The microcontroller processes these data and uses the look-up table to determine the remaining power of the battery. Then the battery value is sent to the display (usually a battery icon, which is divided into several cells to display the remaining battery). When the battery falls to the last cell, the insulin pump generates a low battery voltage alarm

4. programming and control unit

as mentioned above, patients need to adjust the dose of drugs according to specific needs. This adjustment requires a fairly simple interface. For example, users only need to control a few keys. Users can also set several prompts to help manage the injection dose of insulin

most insulin pumps use monochrome, customized character liquid crystal display (LCD), and a few insulin pumps use color display. The display provides information about insulin injection dose, injection speed, remaining battery power, time, date, prompt information and system alarm conditions (such as locking or low insulin reserve). FDA requires the display to perform self inspection when powered on, and the design requires built-in and test functions. In addition, the user also needs to provide audio-visual response of touch screen input

the new generation of vegetarian pumps include continuous monitoring and display functions. These systems use a continuous monitor with a transmitter. The measured data are transmitted through the wireless transmitter to report the blood glucose value detected by the sensor, so as to activate the pump injection at an appropriate time. The insulin pump will also provide an analysis graph based on historical measurement data to guide the calculation of insulin injection volume

5. self test function

according to FDA regulations, all insulin pumps must first run the self-test (post) program when powered on to test the key processors, circuits, indicators and alarm functions. Some post operations require user observation, and additional self-test circuits help reduce the potential risk of failure

for example, some modules use the security processor to monitor the operation of the main processor. Once an unexpected condition is found, an alarm signal will be sent immediately; Some self-test systems may simply monitor the current through the on and off indication of light-emitting diodes (LEDs). Once the current drops below the set threshold, a fault indication can be generated. The more common self-test circuit uses the watchdog timer (WDT), and the microprocessor monitoring circuit with WDT function monitors the running status of the program. Medical devices usually do not allow the monitoring circuit to be integrated into the microprocessor IC itself, because in this architecture, the monitoring circuit may fail at the same time as the processor

the monitoring circuit is the key to ensure the normal operation of the insulin pump during the use of the patient. The microcontroller must be in the reset state before all circuits reach the tolerance range and remain stable. The voltage monitoring circuit monitors the overvoltage and undervoltage of the power supply

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