At present, some advanced centrifuges abroad have become a high-tech comprehensive technology product. There is still a big gap in this area in China. It is necessary to increase the technical content of domestically produced centrifuges and strive to develop products with independent intellectual property rights. There is a lot of work to be done in this area. As a kind of mechatronics equipment, centrifuge has been widely used in hospital inspection, biological laboratory, bio-pharmaceutical, sewage treatment, traditional Chinese medicine pharmaceutical and beverage production. It has penetrated into scientific research, production and other fields.
Selection of drive motor
Commonly used motors are DC motors and AC motors. The characteristics of the DC motor and the AC motor are as follows.
1) Characteristics of DC motors. The structure is complicated, the cost is high, and it needs frequent maintenance (replacement of the brush). Because there is a spark at the brush, it is generally not used in places where explosion protection is required. However, the DC motor speed control circuit is simple, the cost is low, and the speed regulation performance is superior. At present, the performance of the brushless DC motor has matured. In the low power DC motor, a brushless DC motor has been widely used instead of the ordinary DC motor.
2) Characteristics of AC variable frequency motor. The utility model has the advantages of simple structure, low cost, reliable work and low noise. To obtain excellent control performance, variable frequency speed regulation must be adopted, the speed control controller is complicated, and the cost is high. Since the centrifuge can be equipped with rotors of various speeds, the design of the variable frequency motor for driving the centrifuge should be considered for the low speed and large capacity rotor, so that the motor works in the constant torque working area, and the small capacity high speed rotor can be designed in the variable frequency motor. Constant power working area, which can reduce the design power of the variable frequency motor and save costs.
Because the DC speed control circuit is simple and the control performance is superior, the DC speed control cost in the low power system is relatively low. Therefore, the DC speed regulation is still widely used in the small power simple type centrifuge. In order to improve the reliability of the centrifuge drive, the motor spindle should be used to directly drive the centrifuge rotor. At the same time, the special requirements of the centrifuge installation and the damping system of the whole machine are considered. The motor of the centrifuge generally requires special design in the form of the spindle and the shape of the casing. To meet the special requirements of centrifuge drives. If a belt drive or other variable speed drive mechanism is used, a general standard series of motors can be used, but the reliability of the drive is relatively reduced.
First, the speed control system
DC speed regulation
(1) There are two main types of main circuit DC speed regulation: 1 thyristor rectifier circuit voltage regulation. 2 DC pulse width modulation voltage regulation.
(2) In order to obtain good speed regulation performance, the control system generally adopts a double closed loop control system with speed feedback and current feedback. The double closed loop control system has an analog control mode and a digital control mode.
(3) Selection of sensors in DC speed control system In the DC double closed-loop speed control system, speed sensor and current sensor must be used. The quality of the sensor directly affects the speed regulation accuracy.
2. AC frequency control
The frequency converter is developing in the direction of large capacity and high performance. Its price performance can be compared with DC drag, and the trend of gradually replacing the DC drive system with variable frequency speed regulation has been formed.
At present, the quality of the inverter is stable, the parameters are convenient and flexible, the functions are increasing, the performance is getting better and the price is decreasing. There are various new inverters with slip compensation, vector control and direct closed-loop control. If the quality of the inverter product is directly used as the speed control power supply of the centrifuge, the performance reliability of the centrifuge machine can be greatly improved.
Since the centrifuge is a large inertia load, whether it is DC speed regulation or AC speed regulation, it should consider taking braking measures during shutdown to speed up the downtime of the centrifuge and improve the working efficiency of the centrifuge.
Second, refrigeration electrical control
1. Refrigeration electrical control method
(1) Switching control Switching control has two modes, one is contact control mode and the other is non-contact control mode.
(2) Frequency conversion control Due to the development of frequency conversion speed regulation technology, inverter refrigeration compressors have appeared. The continuity of the variable frequency control can greatly improve the temperature control accuracy, but the cost will increase if a frequency converter is added.
2. Temperature sensor selection
The temperature control range of the refrigerated centrifuge is generally -10 to +40 °C. The working range of the temperature sensor must meet the above temperature range. Since the centrifuge chamber is relatively humid, it is best to use the packaged, easy to install and replace, and have a moisture-proof structure. sensor. A variety of temperature sensors, such as thermal resistance type, integrated circuit type (semiconductor type), thermocouple type and thermistor type, are available.
Third, the development direction of centrifuge control technology
At present, centrifuges have gradually developed towards intelligent, automated and integrated support. The application of the computer on the centrifuge allows for the storage of dozens of centrifuge parameter setting programs. The fully sealed touch button cooperates with the liquid crystal display to realize menu setting and measurement display, and can display setting parameters and actual running time parameters at the same time, and can conveniently use the Chinese menu to realize man-machine dialogue and convenient use. Automatically record data such as quality control and production operating conditions, automatically generate reports, and obtain data from each batch of processed samples at any time from the computer to monitor the entire processing of the samples. It is also possible to form a complete centrifugal network with other centrifuges through a central control computer, so that the entire production process is under computer control.
The intelligence of the centrifuge is also reflected in the ability to automatically identify the various rotors. Automatically identify whether the rotor is in place, the speed setting is reasonable, and alert the operator. It can effectively avoid accidents caused by inadvertent operation. It can realize the automatic calculation of the centrifugal force according to the rotor model and the rotational speed or directly input the centrifugal force to obtain the corresponding rotational speed. The automatic setting means that the operating speed and acceleration and deceleration time of the centrifuge are automatically set according to the rotor type of the automatically recognized centrifuge. Password protection for the set program. The centrifugation process is controlled by an integrator to ensure that the sample is subjected to the same centrifugal force in different batches.
The direct drive technology of variable frequency speed regulation and brushless DC motor has been gradually used in the drive system. In the aspect of temperature control, the high-efficiency cooling system with fluorine-free refrigeration and the special heating system have been alternately operated to maximize the temperature accuracy and prevent sample freezing and frost deposition. Some advanced centrifuge products abroad have successfully applied semiconductor refrigeration (or heating), which has brought the centrifuge temperature control technology into a new technical application field.
More mini centrifuges, high speed centrifuge information registration:
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