WO2021018288A1 - High-precision control method for electronic pipette - Google Patents

Abstract

Disclosed is a high-precision control method for an electronic pipette. The method comprises the following steps of: S1, calculating corresponding number of rotation turns N of a motor according to the volume of liquid required to be pipetted; S2, setting number of turns N3 of the motor running at a predetermined low velocity V2 and a braking overshoot amount N4 corresponding the predetermined low velocity; S3, monitoring number of rotation turns N1 of the motor in an initial stage and a real-time rotational velocity V1 of the motor in real time, and performing real-time calculation of number of rotation turns N2 required when the motor decelerates to the predetermined low velocity V2; and S4, determining, according to the monitored number of rotation turns N1 of the motor in the initial stage and the monitored real-time rotational velocity V1, a relationship between N1+N2+N3+N4 and the total number of turns N in real time. According to the high-precision control method for the electronic pipette of the present invention, by braking in a low velocity state, the overshoot amount can be effectively controlled, so that the influence of the overshoot amount on the external world is minimized, and the accuracy, stability, and consistency of a machine are effectively improved.

Description

A high-precision control method of electronic pipette Technical field

The invention relates to the field of pipettes, in particular to a high-precision control method of an electronic pipette.

Background technique

Pipettes are mainly used to perform operations such as pipetting and distribution of liquids, and are the most commonly used instruments in laboratories. The accuracy of pipettes has an important effect on experimental results. In the use of traditional manual pipettes, the operator’s operating experience and proficiency have a great impact on the accuracy and stability of the pipette; while the electronic pipette is controlled by a program and has higher accuracy than manual pipettes. , Good stability and many other advantages. At the same time, the pipetting speed can be precisely controlled by the software, which can provide a variety of pipetting speed options, so it is generally favored by users. For electronic pipettes, the precision control of pipetting is mainly achieved by controlling the stop and positioning of the motor. At present, there are two common implementation methods:

Realization method 1: Use electronic brake. The realization method is to fix a grooved code disc to the rotating shaft of the motor. When the motor rotates to drive the piston to remove the set capacity, the program controls the electromagnet to extend the brake rod into the groove to stop the motor. This method has the following disadvantages: 1. The electromagnet realizes the expansion and contraction of the brake lever through the principle of electromagnetic conversion to achieve the purpose of controlling the stop of the motor, but the electromagnet is large in size and needs to occupy a large installation space; in addition, electromagnetic brake The power consumption of the battery-powered pipette is relatively large, and the use time of the battery-powered pipette is relatively large, which is difficult for the experimenters to accept; 2. Because the code disc with grooves often serves as a brake notch and an encoder for the motor At the same time, it must be fixed with the motor, which increases the difficulty of the product's structural design; 3. The action principle of the electronic brake is similar to the mechanical brake. The more times it is used, the greater the impact on the life, stability and reliability of the machine. Therefore, in actual use, such electric pipettes are difficult to manufacture in batches and promoted and used in the market.

Implementation method 2: The motor of the electronic pipette is a stepper motor. The speed and stop position of the stepper motor depend only on the frequency and number of pulses of the pulse signal, and are not affected by load changes. When the stepper driver receives a Pulse signal, it drives the stepper motor to rotate a fixed angle in the set direction, but the stepper motor is easy to lose step, resulting in inaccurate accuracy; in addition, the speed of the stepper motor is very low, resulting in low pipetting efficiency. Pipetting takes a lot of time; therefore, electronic pipettes with stepper motors can only be used in low-demand situations.

To this end, the applicant has developed "A precision control method for electronic pipettes", the application number is 2019100135603. The patent has not yet been published. The application obtains the speed and overshoot of the electronic pipette motor during braking. Calculate the number of rotations of the corresponding motor according to the volume of liquid that needs to be transferred to determine the stop position; monitor the number of rotations of the motor and the motor speed after starting the liquid transfer, and advance the overshoot corresponding to the current speed by braking Braking, stop at the target position after the motor inertia continues to run overshoot. Although this method takes into account the overshoot of the motor, it is difficult to determine the overshoot of the motor by high-speed direct braking due to temperature, mechanical wear and other factors. Moreover, the whole machine shakes too much at the moment of braking, which affects operation. The user’s comfort and grip feel, so the accuracy of the pipette still needs to be improved.

Summary of the invention

For this reason, the technical problem to be solved by the present invention is to overcome the above-mentioned shortcomings of existing pipettes, and further provide an electronic pipette with high pipetting accuracy, low operating jitter, better operating experience and comfort. Precision control method.

In order to achieve the above objectives, the present invention adopts the following technical solutions:

A high-precision control method of an electronic pipette includes the following steps:

S1: Calculate the corresponding motor rotation number N according to the volume of liquid to be removed;

S2: Set the number of turns N3 of the motor running at the predetermined low speed V2, and the braking overshoot N4 corresponding to the predetermined low speed;

S3: After starting the pipette, monitor the number of rotations N1 of the motor in the initial stage and the real-time speed V1 of the motor in real time, and calculate in real time the rotation circle required when the motor is decelerated from the real-time speed V1 to the predetermined low speed V2 according to the set deceleration method Number N2;

S4: According to the monitored number of rotations N1 and real-time speed V1 of the motor in the initial stage, real-time judge whether N1+N2+N3+N4 is greater than the total number of rotations N, once it is detected that N1+N2+N3+N4>=N , The position corresponding to the real-time speed is the predetermined deceleration position.

Preferably, the set deceleration mode in step S3 includes a fixed step deceleration and a fixed number of turns deceleration, the fixed step deceleration means that the step of deceleration is the same when the motor rotates half a revolution or one revolution is the same, and the fixed number of turns decelerates The motor decelerates to the set low speed within the preset number of rotations.

Preferably, the method further includes step S5: monitoring the rotation speed of the motor during braking and the amount of overshoot generated by the motor, saving and updating the corresponding relationship, and using the value of V2 and N4 in step S2 of the next pipetting process.

Preferably, the predetermined low speed rotation of the motor in the step S2 is greater than or equal to zero.

Preferably, the motor braking method in step S2 is to cut off the power of the motor and make the motor windings form a closed loop. The current generated in the closed loop causes the motor to instantaneously generate a braking torque to quickly brake the motor.

Preferably, the motor is a DC coreless rotor motor or a DC coreless motor.

Preferably, the motor is a brushed DC coreless motor or a brushless DC coreless motor.

Preferably, the braking mode in step S2 is short-circuit braking or dynamic braking.

The high-precision control method of the electronic pipette of the present invention has at least the following beneficial effects:

The high-precision control method of the electronic pipette of the present invention reduces the rotation speed of the motor from a higher speed to a set lower speed during the pipetting process, and then decelerates to a lower speed and runs at its corresponding The overshoot is braked in advance, and the overshoot is run through inertia to reach the target position, which improves the accuracy of liquid transfer. Therefore, no matter which liquid transfer speed the user selects, after the deceleration operation, the brake is at a low speed. The overshoot at this time It is more controllable and minimizes the impact on the outside world through overshoot, which effectively improves the accuracy, stability and consistency of the machine; and through deceleration, the machine runs smoothly and smoothly, with good user experience and long life.

Description of the drawings

In order to make the content of the present invention easier to be understood clearly, the present invention will be further described in detail below in conjunction with the accompanying drawings, in which:

Fig. 1 is a principle block diagram of the high-precision control method of the electronic pipette of the present invention.

Detailed ways

The electronic pipette used in the present invention is composed of a motor, a microprocessor, a transmission part, a piston, etc., and is controlled by a program to rotate the motor. Through the conversion of the transmission part, the rotary motion of the motor is converted into the linear movement of the piston, and the principle of air replacement is adopted. Or the principle of an external piston to realize pipetting; for the set pipetting capacity, there is the following relationship with the number of turns of the motor:

Capacity=Cross-sectional area*Screw stroke Type 1

Screw stroke = screw pitch * screw rotation number 2 type

Number of screw rotation turns = Number of motor turns * Mechanism speed ratio Type 3

Obtained by formula 1, 2, and 3:

Capacity = cross-sectional area * screw pitch * mechanism speed ratio * motor turns;

Among them, the number of motor turns = the amount of overshoot + the number of turns when the motor is braked.

The high-precision control method of the electronic pipette of the present invention adopts a direct current motor to drive the suction liquid, which can ensure higher pipetting accuracy and has less jitter during operation.

Referring to Fig. 1, the high-precision control method of an electronic pipette of the present invention includes the following steps:

S1: Calculate the corresponding motor rotation number N according to the volume of liquid to be removed;

S2: Set the number of turns N3 of the motor running at the predetermined low speed V2, and the braking overshoot N4 corresponding to the predetermined low speed;

S3: After starting the pipette, monitor the number of rotations N1 of the motor in the initial stage and the real-time speed V1 of the motor in real time, and calculate in real time the rotation circle required when the motor is decelerated from the real-time speed V1 to the predetermined low speed V2 according to the set deceleration method Number N2;

S4: According to the monitored number of rotations N1 and real-time speed V1 of the motor in the initial stage, real-time judge whether N1+N2+N3+N4 is greater than the total number of rotations N, once it is detected that N1+N2+N3+N4>=N , The position corresponding to the real-time speed is the predetermined deceleration position.

The set deceleration mode in step S3 includes fixed-step deceleration and fixed-turn deceleration. The fixed-step deceleration means that the step of deceleration is the same when the motor rotates half a circle or one circle. /Min); the fixed number of rotations deceleration means that the motor decelerates to the set low speed within the preset number of rotations. Specifically in this embodiment, it can be decelerated from the real-time speed V1 to the set low speed when the motor is in the N2 rotation stage V2.

The following will give an example to further explain the high-precision control method of the electronic pipette of the present invention:

According to the volume of liquid that needs to be pipetted, when the pipette is running, the system first initializes by default. For example, the default setting of N3 is 5 turns, the corresponding low speed of stage N3 is set to 1000rpm, and N4 is the overshoot of the motor at 1000rpm. , Assuming that the corresponding overshoot of N4 is 1 turn; since the deceleration step of the motor is preset, the number of turns of N2 is proportional to the real-time speed V1 of the motor, for example: when the real-time speed of the motor is 5000 rpm, it must decelerate To the predetermined low speed 1000rpm, if the deceleration is 100rpm every half revolution, it will decelerate from 5000rpm at the real-time speed V1 at the initial stage of the motor to 1000rpm at the set low speed V2, which requires 20 revolutions; according to this relationship, the deceleration distance corresponding to any speed can be known ; At this time the pipette system is running, the system adjusts the speed in real time and monitors the real-time speed V1 and the number of turns N1 of the motor; therefore, the pipette system is always judging whether N1+N2+N3+N4 is greater than the total The number of turns N (where N1 is monitored by the pipette system, N2 can be calculated by the system based on the current real-time speed V1 and the preset deceleration step, N3 is the default 5 turns of the pipette system, and the overshoot is N4 It can be obtained directly according to the preset speed V2); after the pipette starts to run, the motor is gradually accelerated from the initial speed 0, and the real-time speed V1 of the motor from 0 to the deceleration position is the initial rotation of the motor described in this application During the initial stage, the maximum rotation speed of the motor can be set by the system according to the liquid transfer capacity, or the maximum rotation speed can be set by the user. In this initial rotation stage, the rotation speed and the number of rotations of the motor It is always monitored. The pipette control system also adjusts the speed while monitoring to ensure optimal rotation. Once N1+N2+N3+N4 is greater than the total number of rotations N, the real-time speed of the motor from that position V1 Enter the deceleration phase directly, and decelerate according to 100rpm per half circle. After the deceleration phase, the speed should theoretically reach the preset low speed V2 1000rpm, because the number of rotations at the preset deceleration V2 has been set (assuming 5 revolutions) , And the overshoot amount N4 corresponding to the set low speed corresponds to the rotation speed of V2, so through the above control process, it can be guaranteed that N1+N2+N3+N4=N, that is, the final liquid transfer accuracy control purpose of the present invention is achieved . Of course, when the motor is reduced from a high speed to a predetermined low speed, it may not be able to accurately reduce to the predetermined low speed of 1000 rpm. Even if there is a deviation, such as 1100 rpm or 900 rpm, because the speed of the motor at this time is very low, the overshoot of the motor changes very little. Within the allowable error range, of course, the motor will also adjust the speed during the predetermined low-speed phase to ensure that the actual speed of the motor is as close to the set speed as possible to ensure accuracy. In addition, even if the result of speed adjustment in the low-speed stage is deviated, the pipette system will monitor the current speed in real time, and each low speed corresponds to an overshoot; once the pipette system detects N1+N2+N3+N4= N, brake in time.

Refer to the following table, which is the relationship between the motor under different speed and temperature conditions and the overshoot (converted to the number of pulses of the motor encoder) through experiments:

Rotating speed	Overshoot (20℃)	Overshoot (40℃)	Overshoot (60℃)
1000rpm	3	4	5
2000rpm	9	12	13
3000rpm	19	twenty one	twenty four
4000rpm	27	32	36
5000rpm	39	42	50
6000rpm	48	53	62
7000rpm	60	65	74
8000rpm	71	76	89

It can be seen from the above table that the effect of temperature on overshoot is that the higher the speed, the greater the impact; the lower the speed, the smaller the change in overshoot. Therefore, the precision control method of the pipette of the present invention can effectively ensure the precision of pipetting by controlling the motor to firstly change from high speed to low speed, and then include the overshoot corresponding to the low speed into the monitoring measurement range.

The accuracy control method of this embodiment also includes step S5: monitoring the rotational speed of the motor during braking and the amount of overshoot that it generates, saving and updating this corresponding relationship, and using it for the value of V2 and N4 in step S2 of the next pipetting process This method is equivalent to the real-time tracking error value, which can effectively overcome the overshoot change caused by the motor heating and the overshoot change caused by other factors; the change of the overshoot is also slowly affected by the environment, and there is basically no sudden change. It can further improve the stability and accuracy of the system.

The motor of the pipette in this embodiment can have multiple motor starting speeds, such as the speed of each gear between 1000 and 9000 rpm, no matter which pipetting speed the user selects, after decelerating operation through the above example, all Therefore, when braking at a predetermined low speed, the amount of overshoot is more controllable, and the impact on the outside world through the amount of overshoot is minimized, which effectively improves the accuracy, stability, and consistency of the machine; through deceleration, the machine runs smoothly, Stable, good user experience and long life of the organization.

In order to further improve the accuracy of the pipette using this method, the motor selected in the accuracy control method of the present invention is an iron-core rotor motor, and preferably a DC coreless motor, which can realize accurate real-time positioning. The measurement error of the stepping motor rotating at a certain step angle according to the pulse is avoided, and the accuracy of liquid transfer can be further improved.

For the high-precision control method of the electronic pipette of the present invention, the braking mode of the motor is preferably short-circuit braking or energy-consumption braking. The specific short-circuit form is not limited. For the pipette, as long as the power supply is cut off and used The motor windings form a closed loop, so that the motor instantly generates a great braking torque.

The above specific embodiments only explain the technical solution of the present invention in detail. The high-precision control method of the electronic pipette of the present invention is mainly carried out by controlling the rotation of the motor, and can be applied in the field of precise position control of the motor, such as Automated pipetting workstations, pipetting aids, bottle-top dispensers and other laboratory pipetting precision pipetting fields are not limited to electronic pipettes, nor are they limited to the above-mentioned embodiments. Those skilled in the art should It is understood that all improvements and substitutions based on the above-mentioned principle and spirit on the basis of the present invention should fall within the protection scope of the present invention.

Claims (8)

1. A high-precision control method of an electronic pipette is characterized in that it comprises the following steps:

   S1: Calculate the corresponding motor rotation number N according to the volume of liquid to be removed;

   S2: Set the number of turns N3 of the motor running at the predetermined low speed V2, and the braking overshoot N4 corresponding to the predetermined low speed;

   S3: After starting the pipette, monitor the number of rotations N1 of the motor in the initial stage and the real-time speed V1 of the motor in real time, and calculate in real time the rotation circle required when the motor is decelerated from the real-time speed V1 to the predetermined low speed V2 according to the set deceleration method Number N2;

   S4: According to the monitored number of rotations N1 and real-time speed V1 of the motor in the initial stage, real-time judge whether N1+N2+N3+N4 is greater than the total number of rotations N, once it is detected that N1+N2+N3+N4>=N , The position corresponding to the real-time speed is the predetermined deceleration position.
2. The high-precision control method of an electronic pipette according to claim 1, wherein the set deceleration mode in step S3 includes a fixed step deceleration and a fixed number of turns deceleration, and the fixed step deceleration is a motor The step of deceleration is the same for one half-turn or one-turn, and the fixed-turn deceleration means that the motor decelerates to a set low speed within a preset number of turns.
3. The high-precision control method of an electronic pipette according to claim 1, characterized in that it further comprises step S5: monitoring the rotational speed of the motor during braking and the amount of overshoot generated by it, and saving and updating the corresponding relationship for downloading The V2 value and N4 value in step S2 of this pipetting process.
4. The high-precision control method of an electronic pipette according to claim 1, wherein the predetermined low-speed rotation of the motor in the step S2 is greater than or equal to zero.
5. The high-precision control method of an electronic pipette according to any one of claims 1-4, wherein the motor braking method in step S2 is to cut off the motor power supply and make the motor windings form a closed loop, and The current generated in the loop causes the motor to instantaneously generate braking torque to quickly brake the motor.
6. The high-precision control method of an electronic pipette according to claims 1-4, wherein the motor is a DC ironless rotor motor or a DC coreless motor.
7. The high-precision control method of an electronic pipette according to any one of claims 1 to 4, wherein the motor is a brush DC coreless motor or a brushless DC coreless motor.
8. The high-precision control method for an electronic pipette according to any one of claims 1 to 4, wherein the braking mode in step S2 is short-circuit braking or dynamic braking.

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