RU2790860C1 - Method of controlling electric drive to stop the mechanism with one limit switch - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: effect is achieved due to the fact that only one limit switch is used, which determines the beginning of the stop, which allows, with the proposed law of changing the speed of movement of the mechanism, to quickly change the final stop point by changing the distance value specified in the control device S _t between the limit switch that determines the start of the stop and the final stop point. The law of speed change formed by the control device provides braking of the electric drive from the current initial speed V _n to zero in the shortest time. If you want to change the distance S _t , which is a specified segment of the mechanism’s path when it stops, you have to to set a new value greater than that determined by the formula:

.

To do this, the algorithm checks the given value and if it is less than that calculated by the above formula, then its value is taken, determined by the above formula, otherwise it is taken equal to the given value.

EFFECT: simplified design, reduced time for installation and commissioning.

1 cl, 3 dwg

Description

The invention relates to the field of automation of mechanisms by means of an electric drive and can be used to effectively control the stop of mechanisms when using one limit switch in the deceleration section before stopping.

A known method of controlling the stop of the mechanism with an electric drive and the use of two limit switches, one of which gives a signal for a preliminary deceleration to a reduced speed, and the second for the final stop [1].

The disadvantage of this technical solution is the lack of conditions for minimizing the stopping time, due to the fact that it is not supposed to change the braking law depending on the value of the initial stop speed V _H and, in addition, it is not supposed to use the maximum allowable deceleration rate. As a result, the maximum possible performance of the driven mechanism is not achieved.

The closest in technical essence to the proposed invention is a method for controlling an electric drive to stop a mechanism with two limit switches [2], according to which the length of the mechanism's path to a stop is determined and the law of speed change during the stop process is introduced on the path between the limit switches of preliminary deceleration and final stop , set by the control device according to the proposed law, in which the signal for braking the mechanism is not given immediately after the limit switch of the preliminary deceleration is activated, but after a certain time, depending on various physical factors of this process.

The technical objective of the present invention is the exclusion of the final stop limit switch from the system in order to simplify the design, reduce the number of components and minimize installation and commissioning time. The solution of this problem involves the use of new functional and calculated dependencies implemented by the control device, in which the distance from the limit switch, which determines the start of the stop, to the point of complete stop of the mechanism is set.

A method is proposed for controlling an electric drive to stop a mechanism using a limit switch that determines the start of a stop at a predetermined section of the path, using a control device that sets the law of speed change that provides deceleration of the electric drive on a given section of the path from the initial speed according to the expression:

in which:

- текущее время, отсчитываемое с момента срабатывания концевого выключателя определяющего начало процесса остановки;

- current time, counted from the moment of operation of the limit switch, which determines the beginning of the stop process;

- скорость механизма в начале процесса остановки, определяемая текущими условиями работы механизма, известная по результатам текущих измерений скорости механизма;

- the speed of the mechanism at the beginning of the process of stopping, determined by the current operating conditions of the mechanism, known from the results of current measurements of the speed of the mechanism;

- максимально допустимый темп замедления, известный из конструктивных особенностей механизма и его электропривода,

- the maximum allowable deceleration rate, known from the design features of the mechanism and its electric drive,

- время, в течение которого механизм продолжает работу после момента срабатывания концевого выключателя начала остановки до начала торможения, отличающийся тем, что расстояние между концевым выключателем, определяющим начало остановки, и точкой остановки механизма, определяют согласно выражению:

- the time during which the mechanism continues to work after the moment of operation of the limit switch to stop before the start of braking, characterized in that the distance between the limit switch that determines the start of the stop and the stop point of the mechanism is determined according to the expression:

in which:

- расстояние между концевым выключателем, определяющим начало остановки и точкой окончательного останова, представляющее собой задаваемый отрезок пути механизма при остановке;

- the distance between the limit switch, which determines the beginning of the stop, and the final stop point, which is a specified segment of the mechanism's path when it stops;

- максимально возможная скорость механизма в начале процесса остановки, задаваемая из условий работы механизма.

- the maximum possible speed of the mechanism at the beginning of the process of stopping, set from the operating conditions of the mechanism.

определяют как:In this case, in the law of speed change, formed by the control device, the value of the parameter

defined as:

Figure 1 shows a functional diagram of the stop device.

Figure 2 shows the law of setting the speed when stopping for the minimum time.

Figure 3 shows the algorithm of the control device.

The known system is characterized by the fact that it sets the law of change in the speed of movement of the mechanism, in which two limit switches are used: preliminary deceleration and final stop, located at a certain distance from each other, and the braking process is performed according to a predetermined law in such a way that by the time reaching the mechanism of the second limit switch, its speed would be close to zero.

The difference in the implementation of the proposed control method is the absence of a second limit switch in the deceleration section, which allows, with the proposed law of changing the speed of movement of the mechanism, to quickly change the final stop point by changing the value S _T specified in the control device.

Functional diagram of the device that implements the proposed method of stopping is shown in Fig.1. There is a control device 1 in the circuit, consisting of a digital device for generating the braking speed reference 2 and a digital device for setting constant parameters 3, the outputs of which are connected to the inputs of the digital device for generating the braking speed reference 2. The output signal of the digital device for generating the braking speed reference 2 (V(t), connected to the control stroke of the frequency converter 4, which feeds the motor 5. The outputs of the digital speed sensor 6 and the limit switch D ₁ stop start 7 is connected to the inputs of the digital device for generating the braking speed reference 2.

The law of changing the speed reference in time V (t) during braking, provided by the control device 1, is shown in Fig.2. According to the proposed algorithm shown in Fig.3, the law of changing the speed reference shown in Fig.2 is formed. This algorithm ensures that the drive is braked from the current initial speed V _H to zero in the minimum time. This takes into account the limitation on the rate of deceleration a ₃ .

The distance S _T from the limit switch that determines the start of the stop to the final stop point must be numerically equal to the braking distance, defined as the time integral of the current speed V(t)n, numerically equal to the area between the speed graph and the time axis. In this case, the following restrictions are taken into account in the law of changing the speed reference: the speed V(t) should not increase during braking, and the deceleration rate should not exceed the maximum value a ₃ .

Taking into account the noted limitations, to obtain the minimum braking time, the speed change law should consist of two sections (figure 2). In the first section, the speed reference is constant, and in the second, the speed reference decreases with the maximum allowable deceleration rate a ₃ . The path traveled in the second section is numerically equal to the area between the graph of the speed reference V(t) and the time axis, and is calculated by the expression

accordingly, the path traveled in the first section is equal to

and the time of passage of the first section

Any deviation of the law of changing the speed reference in the direction of its decrease will lead to an increase in the stop time, since the braking distance, numerically equal to the area between the speed graph and the time axis, must remain the same. On the other hand, any increase in the speed reference is impossible due to restrictions imposed on it and the deceleration rate. Thus, the stop according to the proposed speed setting law occurs in the minimum possible time under the existing restrictions.

The stop control device according to the proposed method works as follows. First, according to the algorithm of the control device 1 (figure 3) is determined by the current braking time t, counted from the moment of operation of the limit switch D ₁ that determines the start of the stop. If the limit switch D ₁ , which determines the start of the stop, has not yet been triggered (D ₁ =0), then the initial deceleration rate is equal to the current speed V _H =V(t) and the braking time does not start, i.e. t=0. If the limit switch D ₁ , which determines the start of the stop, is triggered (D ₁ ≠ 0), then according to the expression

the time of movement of the mechanism with the speed V _H is calculated, after which, according to the expression

the given speed V(t) is calculated. If speed reference V(t)<0, then speed reference V(t)=0 and current deceleration time are reset

Далее устройство управления 1, вычисляющее закон изменения задания скорости, переходит на следующий цикл работы.Otherwise, the current time is incremented by the sampling interval

Next, the control device 1, which calculates the law of changing the speed reference, goes to the next cycle of work.

большее, чем определяемое по формулеIf you want to change the distance between the limit switch, which determines the beginning of the stop and the final stop, which is a set segment of the mechanism's path when it stops, then you need to set a new value

greater than determined by the formula

и, если оно меньше, чем вычисленное по вышеприведенной формуле, то берется его значение, определяемое по вышеприведенной формуле, а иначе, принимается равным заданному значению.To do this, the algorithm (figure 3) checks the specified value

and, if it is less than that calculated by the above formula, then its value is taken, determined by the above formula, otherwise, it is taken equal to the given value.

We emphasize that it is possible to quickly change the stop point of the mechanism without changing the location of the limit switch that determines the start of deceleration, in the absence of a final stop limit switch.

BIBLIOGRAPHY

1. Margolin Sh.M. Precise stop of electric drives, Moscow, Energoatomizdat, 1984, p. 104).

2. Patent for invention No. 2741337, BI-3-25, 01.2021.

Claims (13)

A method for controlling an electric drive to stop a mechanism using a limit switch that determines the start of a stop at a predetermined section of the path, using a control device that sets the law of speed change that ensures the deceleration of the electric drive on a given section of the path from the initial speed according to the expression:

, in which:

- current time, counted from the moment of operation of the limit switch, which determines the beginning of the stop process;

- the speed of the mechanism at the beginning of the process of stopping, determined by the current operating conditions of the mechanism, known from the results of current measurements of the speed of the mechanism;

- the maximum allowable deceleration rate, known from the design features of the mechanism and its electric drive;

- the time during which the mechanism continues to work after the moment of operation of the limit switch of the beginning of the stop before the start of braking, characterized in that the distance between the limit switch, which determines the start of the stop, and the stopping point of the mechanism is determined according to the expression:

, in which:

- the distance between the limit switch, which determines the beginning of the stop, and the final stop point, which is a specified segment of the mechanism's path when it stops;

- the maximum possible speed of the mechanism at the beginning of the stopping process, set from the operating conditions of the mechanism, while in the law of speed change formed by the control device, the value of the parameter t ₁ is calculated as

.

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