SU1650256A1 - Method of automatic balancing of a centrifuge - Google Patents

Abstract

The invention relates to laboratory technology, can be used in biology, medicine, biochemistry, and other areas in the separation of substances in centrifugal fields and is aimed at increasing the service life of the centrifuge by reducing dynamic loads. In the centrifuge, when it is accelerated at a frequency of rotation less than the first critical, automatic balancing is performed, when the balancing weight by angular and radial movements takes positions at which the minimum level of vibrations is carried out. This position of the balancing weight is remembered. At frequencies of rotation &

Description

The invention relates to laboratory technology and may find application in biology, medicine, biochemistry, and other areas in the separation of substances and in centrifugal fields.

The purpose of the invention is to increase the service life of the centrifuge by reducing the dynamic loads.

Fig. 1 shows schematically a centrifuge for carrying out the proposed method; 2 is a kinematic diagram of a centrifuge.

In the centrifugal chamber 1 (FIG. 1) a rotor 2 is mounted on the shaft 3 of the drive motor 4. The actuator 5 of the automatic balancing device, mounted under the fairing 6, consists of a servo motor 7, which

connected with the lead screw 8, providing radial movement of the balancing weight 9. Limiter 10 limits the movement of the load 9 in the direction of the shaft 3. The servomotor 7 is fixed on the sleeve 11, the lower end of which has a jagged periphery and is in engagement with the worm 12. The latter is fixed to the shaft of the servomotor 13, which provides the angular movement of the load 9. The drive motor 4 is mounted on the elastic elements 14.

In Fig.2, A is the center of the oscillation of a drive motor system — a shaft-rotor; hi is the distance from the plane of the center of mass of the balancing weight to the center of swing; ha is the distance from the oaspoo plane. ate about ate about

The center of mass of the rotor to the center of the swing.

The essence of the proposed method consists in the following.

In the designs of laboratory centrifuges, a vertical kinematic scheme for the arrangement of a motor-shaft-rotor system, the rotor 2 being an interchangeable component and mounted on the shaft 3 from above (Fig. 1) is installed. The only place to install the automatic balancing device actuator 5 is the free space between the bottom of the rotor 2 and the bottom of the centrifuge chamber 1 (Fig. 1). In this plane, in which the centers of mass of the rotor and the balancing weight are located, are located at different heights (figure 2).

At the centrifugal rotation frequency, less than the first critical one, automatic balancing is carried out, the essence of which is that the balancing weight takes the position by angular and radial displacements when the condition

Kj.p. + Fii.e-O, (1)

where Kip A mi of p is the vector of centrifugal force created by the unbalanced mass of the rotor;

Ami is the unbalanced mass of the rotor;

o) - current rotation frequency;

FT is the radius vector of the center of mass of the unbalanced mass of the rotor;

Rts.b. t2 ag ga is the vector of centrifugal force created by the balancing weight;

t2 is the mass of the balancing weight;

d is the radius vector of the center of mass of the balancing weight.

However, the moments created by the forces Rc.r. and Rts.b relative to the center of rolling A (FIG. 2) are not equal to each other due to the inequality hi and ha. Therefore, from the side of the rotating rotor 2, a torque is applied to the shaft 3, which rotates around the axis of rotation. Its value is determined from the expression

 Ami ri (h2 -hi). (2)

With small values of "o, corresponding to rotational frequencies lower than the first critical one,". the value of Mh is small and the vibrations created by this moment are small.

As a quadratic dependence of Mh on w, its value increases with increasing w and causes significant vibrations at the values ofpoh. And when o) oh comes the self-centering of the rotor and the need to fulfill the condition (1) almost disappears.

Therefore, if at frequencies of rotation a) the balancing weight is returned to the position of the minimum balancing effect, then the moment Mh will actually become zero due to the fact that the forces Rc.r. and Рц.б decrease almost to zero, since n and gg become equal to zero: n due to the self-centering effect, G2 - as a result of the return of the balancing weight to the position of the minimum balancing effect.

During the braking process

when approaching o) to Zde from above to ensure a balanced state of the rotor, it is necessary to return the balancing weight to the position corresponding to maximum balance.

To this end, it is necessary to remember the position of the balancing weight, corresponding to the best balance. Position memory can be implemented by various devices

for example, by memorizing the revolutions of servo motors made by balancing or by memorizing the time interval required for moving the balancing weight from

position of maximum balance to the position of the minimum balancing effect.

The centrifuge works as follows.

Let the rotor 2 be unbalanced and start its acceleration to a given rotation frequency. When reaching the rotor 2 in the process of acceleration of the frequency with Mo on the signal of the vibration sensor (not shown) starts to work

one of the servomotors 7 and 13 or both servomotors, moving the balancing weight 9 until the specified minimum is reached; vibration level at which further acceleration of the centrifuge rotor is allowed.

Upon further acceleration of the centrifuge, for example, when w (2–3), the balance weight is moved by the servomotor 7 in the radial direction to the centrifuge rotor center to the limiter 10 installed in close proximity to the axis of rotation of the rotor. This position corresponds to the minimum balancing effect. The time interval during which the balancing weight moves to the limiter 10 is memorized. The centrifuge continues to accelerate to the set speed and

further operates at this rotational speed.

In the process of braking with ew (2–3) ftfc, the balancing weight is moved by the servomotor 7 in the radial direction from the axis of rotation of the rotor during the memorized time interval. Due to this, the balancing weight is in the position corresponding to the maximum balancing effect when approaching the rotational speed from above.

Thus, the possibility of significant vibrations at rotational frequencies is prevented from occurring when the rotational speed approaches the value (OO from above. The proposed method allows to significantly reduce the dynamic effects on the centrifuge bearing assemblies and thereby increase its service life.

Claims (1)

Invention Formula A method of automatically balancing the centrifuge, consisting in moving five 0 balancing weight depending on the rotation frequency and vibration level, which is different in that, in order to increase service life by reducing dynamic loads, the radial position of the balancing weight is additionally controlled by its position with a minimum level of vibrations, a) (2 - 3) ak where a is the current value of the rotational speed; UB - the first critical rotational speed, with an increase in the rotational frequency to the nominal one, the balancing weight is moved to a position that is at a distance from the axis of rotation for a minimum distance, and when the rotational frequency decreases from the nominal flou) (2-3) uJb, the balancing load is returned to the stored position . J g m ///////////////////////// Phie.1 fut. / / 7 l 7 7 7 7 7 7 / / FT 2