RU2313173C2 - Method for controlling direct-current drive - Google Patents

Abstract

FIELD: electrical engineering; controlling stepping-rotor motors for high-precision positioning of optical devices such as microscope stage and the like.

SUBSTANCE: proposed method for controlling DC drive includes electric motor connection to power supply by means of switching unit controlled by pulse-width modulated signal generated by feedback computing device using results of comparing actuating device sensor data and target data, power-supply pulse-to-pulse interval being longer than braking time till complete stop of motor.

EFFECT: enhanced precision of control attained by simple means.

2 cl

Description

The claimed invention relates to electrical engineering, in particular to devices for regulating electric motors with stepwise rotation of the rotor, and can be applied, in particular, for high-precision positioning of optical devices: a microscope stage, etc.

A known method of pulsed control of an electric drive (Nagorsky VD Control of DC motors using high-frequency pulses, "Izv. AN SSSR. Branch of Technical Sciences", 1960, V.2). The method of controlling the rotational speed or torque of DC motors is based on periodically connecting and disconnecting its winding from the supply voltage. For example, when the switch closes the motor power circuit, it accelerates, when opened, it is braked by the static load moment. The average value of the rotational speed is determined by the relative turn-on time of the supply voltage and the load, i.e., by changing the duration of the supply voltage pulse, it is possible to adjust the rotational speed over a wide range. The disadvantage of this method: the instability of the regulatory characteristics and, as a consequence, the low accuracy of motion control.

The closest in combination of features is a method of controlling a direct current electric drive (RF Patent No. 2258297, IPC 7 Н02Р 5/06, 2003), in which an increase in the accuracy of stabilization of speed and the current position of the shaft is achieved by introducing feedback with a computing device forming the control law power converter taking into account the data of the speed sensor. The disadvantage of this method is that the control system effectively manages the averaged dynamic characteristics of the electric drive and is not effective enough in the transition region: during acceleration and braking. It is these modes that prevail in high-precision positioning systems, and not the stability of the high-speed driving mode.

The claimed invention is intended to improve positioning accuracy in an electric drive with pulsed power supply of a DC motor. The main task to which the claimed invention is directed is to propose a method for optimizing the feedback of the electric drive for transient modes: during acceleration and braking, completely eliminating the uniform movement mode. This is possible only in step mode with a complete stop between periods of movement. The technical result that can be obtained in this case is the achievement of high positioning accuracy by simple means.

The technical result is achieved by the fact that in the known method of controlling a DC electric drive, consisting in the fact that the motor is connected to a power source by a switch controlled by a pulse-width modulated signal generated by a feedback computing device by comparing the sensor data of the actuator with the target data, according to the invention, the interval between the power pulses exceeds the braking time until the engine stops completely.

To obtain a technical result - an increase in the speed of movement in step-by-step mode, according to the invention, when the power source is turned off, the switch closes the motor winding to load resistance. This allows you to reduce the time spent on braking.

Imagine a moving platform in the form of some mass M, which includes the inertial mass of the motor rotor, the mass of the object table and the inertial mass of the gearbox. If at some point in time the motor winding is connected to a power source and a force F begins to act on the mass M, exceeding the static friction force F _T

F≥F _T ,

then the platform will move in time t to a distance S

Here a is the acceleration

The work W performed by the engine power source in time t, W = FS = UIt, where

U is the voltage of the motor;

I is the motor current;

t is the time of connecting the motor to the voltage source.

We can represent S as

where R is the effective resistance of the motor winding.

From the last expression it follows that the path traveled by the platform in acceleration mode is a function of the voltage on the motor winding, the effective resistance of the motor winding, the equivalent mass and time during which the winding is connected to the power source

Thus, S is a function of time, i.e. function of the duration of the motor power pulse. All other parameters can be represented as constants. It does not follow from the expression for S that the minimum step ΔS of the platform displacement is fundamentally determined. This step will be determined by many parameters - the ratio between mass, rest friction force and sliding friction, system stiffness, shock effects due to backlash, etc. The evaluation of this parameter is difficult. It is quite simple to determine ΔS experimentally.

Obviously, it is also possible to set the distance traveled not only by the duration of the voltage, but also by changing the magnitude of this voltage. However, this case is hypothetical, because the path traveled will always depend on the time and introducing a new variable does not make sense.

The next stage of movement, included in one step, is the stage of braking to a complete stop. To do this, at the end of the time interval for the acceleration of the engine, the supply voltage is turned off, and the rotor winding is loaded with resistance, dissipating energy in the braking mode - for a powerful engine, for a low-power one, a short circuit mode is permissible. The engine enters forced braking mode until it stops. By changing the time interval of acceleration, you can change the step size.

The proposed operation mode of the DC motor made it possible to solve the main problem — to rotate the motor rotor by a discrete, arbitrarily small value that can be controlled. At the same time, it remains possible to obtain the maximum torque of the motor, since the full supply voltage is connected to the winding.

If there is a mover with such capabilities, the problem of moving toward a target with high resolution and the problem of eliminating the backlash of the mechanical system are completely solvable. To do this, you must have a high-precision platform position sensor and an electronic feedback tracking system. The difference signal between the target value and the position sensor signal is used to generate a motor control signal. The software manages the feedback tracking system.

The electronic measuring system of the industrial measuring instrument “TsI 0-150 mm / 0.01 mm” from INSTRIMPEX was used as a position sensor. The standard design has been modified to measure the X and Y coordinates of the MOTIC microscope stage.

Claims (2)

1. The method of controlling a DC electric drive, consisting in the fact that the engine is connected to a power source by a switch controlled by a pulse-width modulated signal generated by a feedback computing device by comparing the sensor data of the actuator with the target data, characterized in that the interval between power pulses exceeds the braking time until the engine stops completely. 2. The method according to claim 1, characterized in that when the power source is turned off, the switch closes the motor winding to load resistance.