RU2074479C1 - Device for detecting neutral position of dc machine brushes - Google Patents

Abstract

FIELD: instrumentation engineering. SUBSTANCE: motor is allowed to run at no load in opposite directions, its electromechanical time constant is measured in either direction, results are compared, and brush neutral is recognized by their difference not exceeding 5% of maximum permissible norm. EFFECT: facilitated procedure. 2 dwg

Description

 The invention relates to a measurement technique and allows you to control the installation of brushes of the DC motor on the neutral.

 The most important factor affecting the operation of a DC motor is the precise installation of brushes on the neutral. Brushes are placed in the brush holders, which are mounted on the end parts of the engine compositions. For example, such fixing of the brush holders to the skeleton is carried out in traction motors of electric rolling stock having a small number of poles (not more than four). With a larger number of poles, the brush holders are placed on a rotary traverse made in the form of a ring gear and allowing them to be moved using an easily accessible adjustable unit consisting of a removable handwheel and a gear wheel. Increased demands are placed on the accuracy of its installation. It is known that the displacement of the brushes from the neutral significantly worsens the operating conditions of the traction motors, which is manifested in a violation of normal switching, a discrepancy in speed characteristics and increased wear of the brushes and the collector.

 The correct installation of the brushes is evaluated in various ways, which provide for the monitoring and measurement of parameters such as EMF, current, engine armature speed.

 There is a method of installing brushes of a DC motor, in which the motor is mounted on a stand with a load connected to it and rotating it in an arbitrary direction [1] The voltage and current of the nominal mode are applied to the motor, which are maintained constant at different crosshead displacements. At each offset measure the frequency of rotation of the armature. The control of the installation of brushes on the neutral is determined by comparing the received frequency with its nominal value according to the motor certificate. Correct installation of brushes on the neutral corresponds to the equality of the rotation speed of the armature to its nominal value. The advantages of this method are the ability to properly install the brushes on the neutral and the assessment of the switching properties of the engine. The disadvantages of the method are the need to stabilize the supplied voltage to the motor during voltage fluctuations in the network and a sufficiently long duration of the experiment due to the need to measure the controlled parameter only in the steady-state stationary process of the engine, which will follow after the start mode. If these conditions are not met, the error in the measurement of the controlled parameter can be 7 8%. In addition, this method requires special additional equipment on the stand and significant expenditures of electric energy to carry out the load mode, which complicate and cost its carrying out.

где U_g напряжение питания двигателя;
I_g ток двигателя;
Sr_д сумма активных сопротивлений обмоток двигателя;
C конструктивная постоянная двигателя;
Φ магнитный поток двигателя.Closest to the technical nature of the invention is a method in which the engine is mounted on a stand and idle with rotation in one or the other direction (reversing) [2] The voltage is applied to the engine and the armature speed is measured in both directions at different displacements traverses. The control of the installation of the motor brushes in neutral is determined by comparing the rotation speed of the armature in both directions at the same voltage and the same motor excitation current. The correct installation of the brushes on the neutral corresponds to the equality of the values of the rotational speed in one direction or another. This method does not require special additional equipment at the stand and a large consumption of electric energy for its implementation, which simplifies and reduces the cost. However, this method has significant disadvantages. First of all, it is the need to stabilize the voltage supplied to the motor during fluctuations in the network. In addition, the measurement of speed must be performed only in the steady-state stationary process of the engine, i.e. only after completion of the start mode, when the motor current reaches its certain steady-state value, and this will require time for measuring the controlled parameter. The frequency of rotation depends on the voltage and current of the motor, which are active and varying in certain cases from external conditions, the parameters of the motor circuit during its operation

where U _{g the} voltage of the motor;
I _g motor current;
Sr _{d is the} sum of the active resistances of the motor windings;
C motor design constant;
Φ magnetic flux of the motor.

Violation of these conditions leads to an increase in the measurement error of the controlled parameter, which may be 9 10%
The basis of the invention is the task of creating a simplified and more reliable way to control the installation of brushes of a DC motor on neutral, in which increasing the accuracy of the measurement is ensured by measuring a passive parameter that is independent of external conditions.

 The problem is solved in that in a method for determining the installation of brushes of a DC motor on neutral, which consists in rotating the engine idling in opposite directions, in measuring the controlled parameter and in judging the accuracy of installing brushes in neutral by the difference of the controlled parameter when the motor rotates in opposite directions, the electromechanical time constant of the engine, measured in start mode, is selected as a controlled parameter. The magnitude of the difference between the measured parameters is judged on the accuracy of the installation of brushes on the neutral.

 Thanks to the measurement of the electromechanical constant of the motor, accuracy of control of the installation of brushes on the neutral is achieved. This is due to the fact that the electromechanical time constant of the engine is a passive parameter and is practically independent of external conditions.

где I момент инерции двигателя;
r_а активное сопротивление якоря двигателя;
C конструктивная постоянная двигателя;
Φ магнитный поток возбуждения двигателя.The electromechanical time constant T _em depends on the design and passive parameters of the motor circuit

where I is the moment of inertia of the engine;
r _{a the} active resistance of the motor armature;
C motor design constant;
Φ magnetic flux of the motor excitation.

During the action of the transient on the motor, the magnetic flux of excitation F can be considered constant, since its change in time occurs much more slowly than the change in the current and voltage of the motor, which caused the transient. Thus, the controlled parameter - the electromechanical time constant of the motor - is a parameter independent of voltage and current, and therefore the determination of the installation of brushes on the neutral is more reliable and accurate. The error is 2 - 3%
In FIG. 1 shows a diagram of a device for implementing a method for determining the installation of brushes of a DC motor in neutral, figure 2 shows the graphs of the operation of the elements of the device.

 The device for implementing the method contains two current sensors of the motor 1, each of which is connected via a change unit 2 [3] to a comparison element 3 having an indication board on which the result of comparison (difference) of the electromechanical time constants of the engine is recorded when it rotates in opposite directions. In turn, each measurement unit 2 contains an integrating 4 and differentiating circuit 5, a voltage extreme indicator 6, an electronic switch 7, a trigger 8, a pulse generator 9, a logic circuit And 10, and a counting circuit 11.

 The method is as follows.

On a non-rotating engine, a traverse with brushes is installed in a certain position. In the outgoing state, at t <t _1, the pulse generator 9 generates a periodic sequence of pulses U ₉ with a repetition period t _u . The trigger 8 is in the zero state U ₈ (t <t ₁ ) 0 and the logic circuit And 10 is closed U ₁₀ (t <t ₁ ) 0. At time t _{1 the} engine is idling and from the sensor 1 included in the anchor circuit of the motor, an input signal U ₁ proportional to the current of the motor in the starting mode is supplied to the measuring unit 2. The output signal of the differentiating circuit U ₅ (t _1M ) puts the trigger 8 into a single state U ₈ (t ₁ ), the logic circuit And 10 opens and starts to transmit pulses from the generator 9 to the counting circuit 11 U ₁₀ (t ₁ ).

In the time interval t ₁ t _{2 the} instantaneous value of the output signal U _{4 of the} integrating circuit 4 increases and is fed to the input of the voltage extreme indicator 6. Its output signal U ₆ remains equal to zero until the signal U ₄ has not yet reached the extreme value. Moreover, the counting circuit 11 continues to count pulses U ₁₀ (t ₁ - t ₂ ). At time t _{2, the} instantaneous value of the output signal U _{4 of the} integrating circuit 4 takes an extreme value and the signal U ₆ (t ₂ ) appears at the output of indicator 6, as a result of which the electronic key 7 is triggered. The signal from its output U ₇ (t ₂ ) is supplied to the second input of trigger 8 and puts it in the zero state. The logic circuit And 10 is closed and the circuit 11 stops counting pulses U ₁₀ (t> t ₂ ). On the display panel of the comparison element 3, the number of pulses m is calculated, calculated during the time that the output signal U _{4 of the} integrating circuit 4 reaches the extreme value t _e t ₁ t ₂ m • t _u .

. Работа элементов второго блока измерения происходит аналогично работе первого, описанного выше. Если щетки неточно установлены на нейтрали, то кривая сигнала

будет спадать иначе и экстремум напряжения сигнала

индикатор 6 зафиксирует, например, при t₃>t₂ (фиг.2), в результате чего счетная схема 11 второго блока измерения будет больше работать по времени

и на табло индикации элемента сравнения 3 высвечивается сигнал разности U₃=Δ числа импульсов m, полученных при вращении в ту и другую стороны

. По величине разности Δ судят о точности установки щеток на нейтрали.Next, the engine is reversed and it is again started idling at time t ₁ . From the second sensor 1, also included in the engine armature circuit, an input signal is supplied to the second measurement unit 2

. The operation of the elements of the second measurement unit occurs similarly to the operation of the first described above. If the brushes are not accurately set to neutral, then the signal curve

will fall off differently and the extreme voltage of the signal

indicator 6 will fix, for example, at t ₃ > t ₂ (figure 2), as a result of which the counting circuit 11 of the second measurement unit will work more in time

and on the display panel of the comparison element 3, the signal of the difference U ₃ = Δ of the number of pulses m received during rotation in either direction is displayed

. The difference Δ is judged on the accuracy of the installation of brushes on the neutral.

датчиков тока двигателя при вращении его в ту и другую стороны будут достаточно близко совпадать, так как электромеханическая постоянная времени зависит только от конструктивных и пассивных параметров цепи двигателя и не зависит от величины напряжения и тока двигателя:

где I момент инерции двигателя;
r_a активное сопротивление якоря двигателя;
c конструктивная постоянная двигателя;
Φ магнитный поток возбуждения двигателя.With a fairly accurate installation of the brushes are not neutral signals U ₁ and

sensors of current of the motor when it rotates in both directions will be close enough to coincide, since the electromechanical time constant depends only on the design and passive parameters of the motor circuit and does not depend on the magnitude of the voltage and current of the motor:

where I is the moment of inertia of the engine;
r _a active resistance of the motor armature;
c motor design constant;
Φ magnetic flux of the motor excitation.

When the engine is idling in one direction or another, the parameters I, r _a , C are unchanged and only the value of F can affect the value of T _em, which will slightly differ from each other when reversing if the brushes are not installed accurately. The difference is obtained as a result of the appearance of the longitudinal component of the magnetizing force of the armature resulting from the displacement of the brush from the neutral, which enhances or weakens the magnetic flux of excitation depending on the direction of the displacement of the brushes relative to the neutral. With the exact installation of the brushes on the neutral, the longitudinal component of the magnetizing force of the armature disappears. Consequently, the magnetic fluxes of the excitation of the reversible motor will be equal, and the electromechanical time constants are the same. The error in the change of T _em with this method will be very small and will be no more than 2 3%
To assess the quality of the measurement system in the transition process, which is the starting mode of the engine, a quality indicator such as measurement accuracy, characterized by dynamic and static errors, is used. The maximum permissible norm of such accuracy is 5%

Claims (1)

 A method for determining the installation of brushes of a DC motor on neutral, which consists in rotating the engine idling in opposite directions, in measuring the controlled parameter and in judging the accuracy of installing brushes in neutral by the difference of the controlled parameter when rotating the motor in opposite directions, characterized in that as the controlled parameter, choose the electromechanical time constant of the engine, the parameters are measured in the start mode, and the accuracy of installation Nets on the neutral are judged by the difference in the values of the electromechanical time constants of the reversible engine, not exceeding 5% of the maximum permissible norm.

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