Abstract: Biochemical analyzer is one of the necessary instruments for medical institutions to conduct clinical diagnosis, life sciences, biochemical research, and other research institutions. It is mainly used to measure various conventional biochemical indicators in human fluids. With the continuous progress of modern technology, the development of medical devices is also becoming increasingly high-tech. The biochemical analyzer has also entered the fully automated stage from manual operation. The fully automatic biochemical analyzer has the functions of precise sampling and automatic loading, with high accuracy, good repeatability, complete functions, and multiple testing items. Its characteristics of speed, simplicity, and trace amount are particularly prominent. In terms of drug dispensing, unlike traditional stepper motor drive methods, linear stepper motors are increasingly being used in fully automatic biochemical instruments.

1、 Application background

Biochemical analyzer is one of the necessary instruments for clinical diagnosis and research in life sciences, biochemistry, and other fields in medical institutions. It is mainly used to measure various conventional biochemical indicators in human fluids. With the continuous progress of modern technology, the development of medical devices is also becoming increasingly high-tech. The biochemical analyzer has also entered the fully automated stage from manual operation.

The fully automatic biochemical analyzer has the functions of precise sampling and automatic loading, with high accuracy, good repeatability, complete functions, and multiple testing items. Its characteristics of speed, simplicity, and trace amount are particularly prominent. In terms of drug dispensing, unlike traditional stepper motor drive methods, linear stepper motors are increasingly being used in fully automatic biochemical instruments.

In a fully automatic biochemical analyzer, the sampling function is achieved through its sampling system, and the accuracy of the sampling system largely determines the accuracy of the entire instrument. The sampling system generally consists of a cantilever mechanism and a driving mechanism, with the driving mechanism connected to the cantilever mechanism to achieve automatic sampling function. The traditional driving mechanism generally consists of a rotating stepper motor and a transmission mechanism.

Traditional transmission mechanisms generally include synchronous belts, gear racks, and ball screws. The accuracy of synchronous belts and gear racks is not high, and the noise is relatively loud. The most critical issue is that their lifespan cannot be guaranteed; Ball screw has high precision and long service life, but its large volume and high cost require high level of mechanism calibration.

Figure 1 Comparison of mechanical transmission structures between linear screw motors and traditional steppers

The linear screw stepper realizes the conversion from rotary motion to linear motion inside the motor, making the cantilever mechanism directly connected to the motor, making the mechanism as delicate as possible. At the same time, without the need for intermediate transmission links, it can achieve higher accuracy, higher efficiency, and longer lifespan.

Figure 2 Biochemical analyzer loading arm with linear screw motor

2、 The main structure and process of the biochemical analyzer sampling system

The sampling system of the fully automatic biochemical analyzer mainly consists of the following three parts, as shown below:

Part 1: Sample turntable

Small sample cups or test tubes can be placed.

Part 2: Reagent Room (Warehouse)

The number of reagent kits that can be accommodated in different fully automatic biochemical analyzer reagent rooms varies, generally accommodating more than 20 types of reagents. Some reagent rooms have refrigeration devices, and reagents with barcode recognition devices can be placed in any position of the reagent kit.

Part 3: Sampling Device

Some fully automatic biochemical analyzers share the same sampling needle for sample and reagent collection, which is controlled by an internal shunt valve for sample and reagent collection; Some fully automatic biochemical analyzers have two sets of sampling devices, one for taking samples and the other for taking reagents. The front end of the sampling needle has a liquid level sensor to prevent air suction or liquid hanging on the outer wall of the sampling needle, and there is a preheating device in the sampling arm.

Figure 3 Sample adding system of fully automatic biochemical analyzer

3、 Devison Linear Screw Stepping System

Devison's hybrid linear screw stepper motor adopts a high-efficiency transmission thread design and unique bearing technology. The motor is superior to similar products on the market in terms of transmission efficiency, reliability, load-bearing capacity, and service life. It has obvious advantages over commonly used metal nut structural designs, and its lifespan is at least 10 times longer. Suitable for situations with limited space, high requirements for motor performance and reliability, precise positioning, fast movement, and long lifespan.

The products currently launched by Devison include: 20mm series, 28mm series, 35mm series, 42mm series, 57mm series, and 86mm series two-phase hybrid linear stepper motors. The product covers 28 different step sizes, ranging from 0.00006 inches (0.001524mm) to 0.005 inches (0.127mm) microsteps, providing uniform and fine resolution. There are three structures to choose from for each seat number: through shaft type, external drive type, and fixed shaft type.

High precision, positioning accuracy can reach 0.1 μ M

The linear screw stepper motor reduces the problem of interpolation lag due to its simple transmission mechanism. Its positioning accuracy, repetitive accuracy, and absolute accuracy are generally higher than those of the rotary servo motor and ball screw, and it is easy to achieve. The positioning accuracy of the linear screw stepper motor can reach 0.1 μ m. Rotate the servo motor ball screw to a maximum of 2-5 μ M.

High speed, up to 300m/min

In terms of speed and acceleration, the linear screw stepper motor has significant advantages, with a speed of up to 300m/min and an acceleration of 10g; The ball screw has a speed of 120m/min and an acceleration of 1.5g. Moreover, the speed of the linear screw stepper motor will further increase after successfully solving the heating problem, while the "rotating servo motor&ball screw" is limited in speed and difficult to increase further.

● Long lifespan and simple maintenance

The linear screw stepper motor has an installation gap between the moving and fixed parts, no contact, and will not wear due to the high-speed reciprocating motion of the moving parts. Long term use does not change the positioning accuracy of the motion, making it suitable for high-precision situations. Ball screws cannot guarantee accuracy in high-speed reciprocating motion, as high-speed friction can cause wear on the screws and nuts, affecting the accuracy requirements of the motion, which cannot be met in high-precision situations.

4、 On site debugging results

The basic parameters of a certain model of biochemical analyzer are as follows:

·Constant speed 400 T/H (single/double reagent), maximum 640 T/H (optional ISE)

·Can simultaneously detect 77 colorimetric items and 3 electrolyte items (optional ISE)

·90 daily available sample positions and 80 refrigerated reagent positions, with automatic barcode scanning

·Holographic concave flat image field grating rear splitting, beam focusing optical path, monitoring of the entire reaction process

·The reaction cup adopts "solid direct heating" temperature control technology and automatically cleans with 8-stage warm water

·Automatic equal, incremental, subtractive, and pre dilution sample retesting and enzyme linear expansion function

The configuration plan of Devison Company is as follows:

Axis class

Handelberg Plan

Sample arm X-axis

ASD422R+11E3408

Y-axis of sampling arm

ASD422R+11E3408

The basic parameters of the linear screw motor are as follows:

model

Holding torque (mN. m)

Phase current (A)

Phase resistance (Ohms)

Motor length (mm)

Adapt driver

11E3408

fifty-nine

zero point seven five

six point five

thirty-four

ASD422R

On site testing has proven that the sampling speed and accuracy are more than 30% higher than traditional stepping.

5、 Conclusion

The application of the DiWeiXun linear screw stepper motor in the sampling system of biochemical analyzers has made its structure simple and effective, improving the overall quality and grade of domestic biochemical analyzers, and placing it in a favorable position in competition with similar products at home and abroad.