1. AC frequency conversion speed regulation will gradually replace DC speed regulation
   The speed regulation system is the core part of the centrifuge. It consists of three major elements: control, power drive and motor. It mainly controls the speed of the motor. In the development process of centrifuges, DC speed regulation is indispensable. Its main features are good braking, wide speed range, simple structure, low cost, mature theory and practice, etc., so it was before the 1980s. The centrifuge has been widely used in a wide range of applications. Therefore, it has been widely used in centrifuges before the 1980s. It is still in application and continuous improvement, such as improving the wear resistance of DC motor copper heads and carbon brushes to extend The life of the motor and the replacement cycle of the carbon brush.
   The thyristor phase-controlled DC speed regulation is a classic DC speed regulation scheme. It has a simple structure and mature technology, and basically meets the requirements of centrifugal speed regulation. Therefore, it is widely used in centrifuges at home and abroad. The main disadvantages are that the rectification waveform is poor, the current ripple is large, and the current interruption is easy when the load is light. To maintain the continuity of the DC motor current, a heavy and smooth inductor is added, which increases the volume and weight of the instrument. After the 1980s, with the development of fully controlled power devices, such as power transistors and FETs, switching power conversion technology has gradually been applied in centrifuge DC speed control systems, such as the German eppendorf 5410 and 5402 centrifuges. The technology mainly uses high-frequency DC chopping, adjusts the pulse width ratio, changes the auxiliary voltage, and supplies power to the DC motor. Because the switching frequency is very high, generally less than 50KHZ can only obtain smooth DC current by the motor's own inductance filtering, which overcomes the shortcomings of the thyristor phase-controlled DC speed regulation, so the speed is smoother and the speed regulation range is wider.
   Switching speed regulation is a simple speed regulation scheme of Zui. Even a dozen discrete components or an integrated block can form a system. Therefore, some low-cost centrifuges in China still adopt this scheme. The main disadvantage is that manual operation is required. Speed ​​regulation, can not control the current of the motor, the speed accuracy and technical added value are relatively low. In view of the limitations of open-loop speed regulation, most centrifuges at home and abroad generally adopt a double closed-loop speed regulation scheme with both current feedback and speed feedback. The main advantages are automatic speed regulation, fast speed increase, small speed overshoot, and accuracy. High and current limiting function to avoid motor overcurrent damage.
   Although the DC speed regulation has a long history and mature technology, the DC motor mechanical commutator commutation is its fatal weakness, which limits the speed of the motor, the commutator causes interference, and needs to replace the carbon brush, which makes the early overspeed or high speed centrifuge. Indirect speed-up solutions such as gear shifting or other methods have to be used, increasing cost and volume, reducing life and reliability. At the end of the 1970s, foreign ultracentrifuges took the lead in adopting variable frequency speed control technology, mainly by changing the power supply frequency of the induction motor to adjust the speed. Since the induction motor does not need mechanical commutator, it not only eliminates the trouble of replacing the carbon brush, but also increases the motor speed. Even the ultracentrifuge of hundreds of thousands of revolutions can be directly driven, which greatly simplifies the structure of the centrifuge. The key technology of frequency conversion speed regulation: First, the development and application of fully controlled power devices, simplifying the technical key of speed regulation: First, the development and application of fully controlled power devices, simplifying the main circuit of the inverter; second, SPWM technology Improve the performance index of the inverter; Third, the development of control technology, such as vector control technology, so that the control performance of the induction motor meets or exceeds the level of the DC motor; Fourth, the large-scale integrated circuit and microprocessor for variable frequency speed regulation The frequency conversion circuit is greatly simplified, such as Siemens three-phase programmable pulse width modulation integrated circuit SIH4520, In company's SX196MC and TI's TMS 320C240 motor control single-chip microcomputer, etc. At present, the frequency conversion speed regulation can be comparable with the DC speed regulation. After the 1990s, almost all foreign major centrifuge manufacturers used variable frequency speed control technology, regardless of overspeed, high speed, or low speed centrifuges, such as Germany Heraeus, Hettich, etc., China also listed frequency conversion speed centrifuge as a research Plan, some manufacturers have introduced variable frequency speed control centrifuges, such as Shanghai Anting Scientific Instrument Factory, Institute of Biophysics, Chinese Academy of Sciences. According to the different AC motors, the frequency conversion speed regulation is also different. At present, there are three main types of motors used in the frequency conversion speed control centrifuge: asynchronous induction motor, brushless DC motor and variable reluctance motor. In 1988, SORVALL applied brushless DC motor for the first time to introduce RC-285 sub-super speed centrifuge. Beckman applied variable reluctance motor to produce Avanti series centrifuge with speed up to 30,000 rpm. Its braking acceleration and deceleration rate is faster than similar centrifuges. Doubled, but currently the application of Zui popular and Zui mature or asynchronous induction motor.
2. Versatility, automation and computer control
   With the development of centrifuge manufacturing and application technology, centrifuges not only make progress in speed control technology, but also make great progress in multi-function and automation, such as variable speed braking, program shifting, direct input centrifugal force, operating procedures. The storage and recall, the automatic diagnosis of the instrument status, the requirement to display the parameters and status information of the centrifuge as much as possible, and the more perfect safety protection functions, etc., some functions are not only the icing on the cake, but also directly affect the centrifugal effect, such as variable rate Braking and program shifting can improve zone centrifugation and shorten centrifuge time. The early centrifuge control system consisted of discrete components, the circuit was complex, the cost was high, and many functions were difficult to achieve. After adopting the microcomputer technology, the function of the hardware can be replaced by software or the functions that are difficult to implement by the hardware, such as the centrifuge program control and the motor control, which not only greatly simplify the structure of the hardware, but also become multifunctional and automated. The core of the general centrifuge computer control system is a single-chip microcomputer. The hardware system includes: operation interface, motor control interface, temperature control interface, security protection monitoring interface, system monitoring and so on. The operation interface manages the keyboard and display. For the convenience of user operation and monitoring of operating parameters, the operation interface should follow the principle of simple and concise, logical and clear parameters. The Biofugestratos centrifuge from Heraeus, Germany, uses the "EasyCon-trol" interface to fully display and separately process operating parameters, using an internationally recognized graphic language and as few single function keys as possible; the German Hettich centrifuge uses only three keys. It can handle the operating parameters; Germany Hermle new centrifuge inherits the operating characteristics of the traditional centrifuge, and still uses the knob to adjust the parameters. The input of the motor control interface is the current and speed signal of the motor, the output is the control signal of the motor speed, the speed sensor generally has : Coaxial generator speed measurement, magnetoresistive speed measurement, Hall device speed measurement, photoelectric projection and refractive speed measurement, high integration, low cost, reliability and simple application by thousand photoelectric and Hall speed measurement, so many applications have been applied recently. Centrifuge The principle and structure of the rotor cavity temperature control system is almost the same as that of the ordinary refrigerator, but the advanced and higher precision variable frequency press thermostat technology has not been widely used: there is also the application of semiconductor (vehier) device refrigeration, but it is not common; some centrifuges For example, 16 and 30F of HettiCh, Germany, to reduce the heat transfer of the motor and the heat resistance of the rotor The influence of the product adopts air-cooling and cooling technology. The air duct design of the air-cooled centrifuge is the key. Generally, the wind is sucked from the top and discharged from the bottom. The flowing gas takes away the heat of the rotor and the motor. The scientific air duct can be Cooling can also reduce noise; some centrifuges control and display the sample temperature in the rotor, while others control and display the temperature of the rotor cavity. The former requires a lot of experiments, and the technical content is high. The user's welcome. The security protection monitoring interface mainly includes: overspeed, over temperature, rotor imbalance, rotor recognition and door lock monitoring, etc. System monitoring should supervise the state of the system itself, timely protect and give fault information, and facilitate maintenance. The single-chip microcomputer Zui is good for selecting a high-level, dedicated and bus-in-chip microcontroller. The high degree of integration can reduce the cost and improve the reliability. The specialization can simplify the design and improve the integration. The internal bus is isolated from the outside through the I/O port. Electromagnetic noise on the bus, the core of the eppendorf5415C control system consists of only one microcontroller (38ADP70) with ADC and a peripheral Into blocks (ULN2802A composition, the circuit is very simple.
3. Pay attention to safety, environmental protection and international standards
   Improper use of centrifuges, such as overspeed, overload, unbalance, etc., may damage the instrument, or even the head, threatening personal safety, so manufacturers pay special attention to safety design, international and national standards are also set, such as Germany Centrifuge accident protection specifications (UVV, VBG 7Z), industry standards for centrifuges and centrifuge tubes (DIN 58970, PARTI, 2, 3and4). The mechanical safety design mainly includes the following contents: 1 door lock protection system, using mechanical and electronic double-layer door locks. After the door lock is closed, the centrifuge can be started. After the motor stops moving, the g2 centrifuge chamber and cover can be opened. The use of sturdy armor steel to prevent unbalanced detection of the rotor head and the rotor is essential. The imbalance of the rotor will cause the motor shaft to oscillate, affecting the life of the centrifuge. In severe cases, the motor shaft will be broken or even blown. head. Generally, the unbalance of the motor shaft is detected, and the commonly used methods are: mechanical position switch, magnetoresistance (MSR), ultrasonic ranging, acceleration sensing, and the like. The mechanical position switch is simple and practical. Zui Guang, Heraeus Biofuge Stratos centrifuge uses an acceleration sensor with data processing software to develop an intelligent unbalance identification system that can monitor the entire weight of each rotor for the specific process of centrifugation. In the past, the mechanical position imbalance recognition system needs to hate the swing distance of the shaft, and only has the disadvantage of being used in the acceleration phase, so that even at any speed, even at high speed, it can detect even the test tube crack and sample. The imbalance caused by overflow; 4 improve the anti-unbalance ability of the centrifuge itself, not only can improve the robustness of the centrifuge, but also avoid the strict balance and even the visual balance when the rotor is operated, so it is convenient. User action. Generally, a small centrifuge places the entire motor on a seismic elastic bracket, such as a rubber mat. The high-speed centrifuge also often uses a sturdy shaft to resist earthquakes. The eppendorf 5415C hangs the entire motor on a rubber bracket. The Heraeus Biofuge Statos centrifuge uses the shock-driven drive system of the “Spindie Driver†for the first time. The entire shaft is placed in an anti-vibration buffer container, which overcomes the easy-to-fold and fragile shaft. Disadvantages, thus more robust, more unbalanced, faster braking (about 305); 5 rotor recognition system can automatically identify the rotor, limit the high speed of the rotor, effectively preventing the user's misoperation. The basic principle of rotor recognition is to set a unique code for each rotor, or to inlay a certain number of small magnets at the bottom of each rotor, using Hall sensing, or using photoelectric refraction ring sensing, more complicated Ultrasound and wireless RF rotors recognize, the rotor can be identified without running, and even the cover can be detected.
   Environmental protection is mainly manifested in two aspects. First, the refrigeration system uses fluorine-free refrigerant or semiconductor (Peltier) refrigeration. However, centrifuges using semiconductor refrigeration are still rare. Second, noise reduction, generally speaking, is 60 cents. Public air-vehicle driving sound is 70 to 80 decibels. Medical research shows that noise above 70 decibels can interfere with conversations, causing upsets, affecting work, and even causing accidents. According to China's product quality inspection agency measurement certification technical assessment specification (fiG102 one 90), the noise of the test laboratory shall not exceed 70dBo. Generally, the noise reduction measures of the centrifuge are: the outer casing and the rotating head cavity plus the sound absorbing coating; the strong and stable seismic base ton machine is separated from the mechanical frame by the elastic shock absorber. ; Application of commutatorless motor, etc. Generally, after the shock absorption treatment, the noise of the centrifuge can be limited to 60 decibels.
As an electrical device, the centrifuge must also meet the appropriate electrical safety and electromagnetic compatibility (EMC) standards, such as the International Electrotechnical Commission (IEC) "IEC Medical Electrical Equipment Safety General". The European Union's "EN61010-and and 61010-2-020", the electromagnetic compatibility standards have the EU "EN55082-1" and so on. In accordance with international standards, China has also formulated electrical safety and electromagnetic compatibility standards suitable for China's national conditions, "General safety requirements for medical electrical equipment" and "Measurement methods and allowable values ​​for radio interference characteristics of power tools, household appliances and similar appliances (GM343- 84)" and so on. The safety rules mainly specify four indicators: insulation resistance, leakage current, grounding wire resistance and grounding resistance. Users are required to check these four indicators after overhaul or periodically. In January 1996, the European Union officially promulgated and implemented the electromagnetic compatibility index, which stipulated that all equipments with the CE mark should be issued with the CE mark and the EU participating countries should allow transit. Do not stay in trouble. Electromagnetic standards require electrical equipment not to generate electromagnetic interference from the outside world, and also have the ability to resist electromagnetic interference. Since the centrifuge has both an electric drive system that generates strong electromagnetic interference and a weak system that is sensitive to electromagnetic interference, both the manufacturer and the user should pay attention to the electromagnetic compatibility of the centrifuge. In short, the centrifuge's mechanical and electrical Heraeus' highconic people are increasingly demanding quality and safety, and standards-certified products can gain more user trust.
4. Turnaround improvements and types   Â
Commonly used rotors in the laboratory are: angle head, flat head, vertical head, and special and recent development of rotating heads, such as continuous flow head, panning head, zone head, enzyme head, capillary head, oil test head, Roller heads and biosafety heads have increased the number of rotors, improving the centrifugation method and broadening the application field. In addition to the increase in types, the material and structure of the rotor have also made great progress. The material of the rotor is mainly aluminum alloy and titanium alloy. Aluminum alloy is light in weight, high in strength and low in cost, but has poor corrosion resistance and high temperature resistance. In addition to the advantages of aluminum alloy, titanium alloy can also resist corrosion and high temperature resistance, directly perform high pressure and high temperature sterilization, and work at high temperature. In order to reduce the load on the motor and increase the capacity of the sample, many manufacturers have improved the material and structure of the rotor, and introduced ultra-light turning heads: Beckman and Hitachi have introduced carbon fiber rotors, which weigh only one-third of the weight of aluminum alloy heads; Sorval series Ultra-light aluminum head weight is reduced by half; IEC developed anti-corrosion and temperature-resistant polypropylene head, which can be bleached and disinfected, or directly high-pressure high-temperature disinfection; Heraeus highconic (45-degree high-speed angle head) head with hollow body Structure, in a small centrifuge, load 6 X 50ml sample, high-speed operation; eppendorf uses a thin aluminum alloy plate, with a mold pressed into a hollow angle head; Hettich uses a thin steel plate around the slot to hang the blue method to make a flat head. In other respects, Heraeus improved the material and structure of the biological head, solved the shortcomings of the high-speed sealing of the biological head, the number of high-pressure high-temperature disinfection is not limited, and passed the CAMR test of the British Applied Microbiology Research Center.
   When the rotor is running at high speed, centrifugal stress will be generated inside. When the centrifugal stress exceeds a certain limit, it will cause premature failure of the rotor or even the head. Therefore, the user must pay attention to the correct use and proper storage of the rotor. After the rotor is used, it should be cleaned in time. Do not bump or scratch. If it is accidentally lost, X-ray examination of the rotor should be carried out to confirm that the inside is non-invasive before use. In use, the use of the super-life rotor should be terminated in time. Usually, the manufacturer indicates the number of revolutions and the number of centrifugation. No matter which indicator comes first, the life of the rotor has arrived. The extension of the life of the dry rotor should strictly follow the manufacturer's instructions. Generally, in the following cases, the high speed of the rotor should be reduced: the life of the first rotor has arrived, but the rotor is well preserved, and the speed is extended according to the manufacturer's instructions. 2 partial local damage or slight corrosion; 3 use stainless steel centrifuge tube and cannula sample when the average density exceeds 1.2g / ml.
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