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Application of linear screw stepper motor in biochemical analyzer


1. Application background
    Biochemical analyzer is one of the necessary instruments for clinical diagnosis, life science, biochemical research and other research institutions in medical institutions. It is mainly used to determine various routine biochemical indicators in human body fluids. With the continuous progress of modern science and technology, the development of medical devices is becoming more and more high-tech. Biochemical analyzers have also moved from manual operation to full automation.
   The automatic biochemical analyzer has the functions of accurate sampling and automatic loading, with high precision, good repeatability, complete functions, multiple test items and other characteristics, and its fast, simple, micro and other characteristics are particularly outstanding. In the pharmaceutical filling, different from the traditional stepper motor driving mode, linear stepper motor is more and more widely used in the automatic biochemical instrument.
In the automatic biochemical instrument, the sampling function is realized through the sampling system, the accuracy of the sampling system determines the accuracy of the whole instrument to a large extent. The sampling system is generally composed of "cantilever mechanism + drive mechanism", and the transmission mechanism is connected with the cantilever mechanism, so as to realize the automatic sampling function. The traditional driving mechanism is generally composed of "rotary stepper motor + transmission mechanism".
   The traditional transmission mechanism generally includes synchronous belt, rack and pinion, ball screw. Synchronization belt, rack and pinion accuracy is not high, noise is relatively large, the most critical is that the life can not be guaranteed; Ball screw has high precision and long life, but its volume is large, the cost is high, and the adjustment level of the mechanism is high.

The linear lead screw step realizes the conversion from rotary motion to linear motion inside the motor, so that the cantilever mechanism is directly connected with the motor, making the mechanism as delicate as possible. At the same time, no intermediate transmission link enables it to achieve higher accuracy, higher efficiency and higher life.

2. Main structure and process of sampling system of biochemical analyzer

The sample adding system of the automatic biochemical analyzer is mainly composed of the following three parts, as follows:

Part I, sample turntable
The biochemical analyzer can be placed in a small sample cup or test tube.

Part II. Reagent Room (Warehouse)
Different automatic biochemical analyzer reagent rooms can accommodate different numbers of kits, generally can accommodate more than 20 kinds of reagents. Some reagent rooms are equipped with cold storage devices, and reagent rooms with barcode recognition devices can be arbitrarily placed in the position of the kit.

The third part, sampling device
Some automatic biochemical analyzer sample and reagent use the same sampling needle, controlled by the internal diverter valve sample and reagent; Some automatic biochemical analyzer has two sets of sampling devices, respectively sampling and reagent. There is a liquid level sensor at the front end of the sampling needle to prevent suction or liquid hanging on the outer wall of the sampling needle, and a pre-temperature device in the sampling arm.

3.vertical three linear lead screw step system

  LEESN hybrid linear screw stepper motor adopts high efficiency transmission thread design and unique bearing technology, and the motor is superior to similar products on the market in transmission efficiency, reliability, bearing capacity and life, which is more obvious than the commonly used metal nut structure design, and the life is at least 10 times higher. Suitable for limited space, high motor performance and reliability requirements, precise positioning, fast movement and long life occasions.

   LEESN currently listed products are: 20mm series, 28mm series, 35mm series, 42mm series, 57mm series, 86mm series two-phase hybrid linear stepping motor. The product covers 28 different step sizes, from 0.00006 inch (0.001524mm) to 0.005 inch (0.127mm) micro steps, providing uniform fine resolution. Each frame number has three structure options: through shaft type, external drive type, fixed shaft type.


● High precision, positioning accuracy up to 0.1μm
Linear screw stepper motor because the transmission mechanism simply reduces the problem of interpolation lag, positioning accuracy, repeat accuracy, absolute accuracy, will be higher than the "rotary servo motor & ball screw", and easy to achieve. Linear screw stepper motor positioning accuracy up to 0.1μm, "rotary servo motor ball screw" up to 2~5μm.

● High speed, up to 300m/min
From the comparison of speed and acceleration, linear screw stepper motor has considerable advantages, linear screw stepper motor speed can reach 300m/min, acceleration 10g; The ball screw speed is 120m/min and the acceleration is 1.5g. Moreover, the speed of the linear screw stepper motor will be further improved after successfully solving the heating problem, while the "rotary servo motor & ball screw" is limited in speed and it is difficult to increase more.

● High life, easy maintenance
Linear screw stepper motor due to the moving parts and fixed parts between the installation gap, no contact, will not wear due to the high-speed reciprocating movement of the actuator, long use of the motion positioning accuracy does not change, suitable for high-precision occasions. Ball screw can not ensure accuracy in high-speed reciprocating movement, because of high-speed friction, will cause the screw nut wear, affect the accuracy of the movement requirements, the need for high precision occasions can not be met.

4. Field debugging results
The basic parameters of a type of biochemical analyzer are as follows:

· Constant speed 400 T/H(single/double reagent), maximum 640 T/H(optional ISE)
· 77 colorimetric items and 3 electrolyte items can be tested simultaneously (optional ISE)
·90 daily usable sample bits and 80 refrigerated reagent bits, automatic barcode scanning
· Holographic concave flat image field grating after splitting, cluster light path, the whole reaction process monitoring
· The reaction cup adopts the "solid direct heat" temperature control technology, and automatically cleans with 8 stages of warm water
· Automatic equal, incremental, decrement and pre-diluted sample retest and enzyme linear expansion function

Field tests prove that the sampling speed and accuracy are more than 30% higher than the traditional step.

5. Conclusion
The application of vertical linear screw stepper motor in the sampling system of biochemical analyzer makes its structure simple and effective, improves the overall quality and grade of domestic biochemical analyzer, and is in a favorable position in the competition with similar products at home and abroad.

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