RU2020725C1 - Method for nc positioning of multiphase stepping motor incorporating electric step splitting provision - Google Patents

Abstract

FIELD: robots and NC machine tools. SUBSTANCE: method involves changing of phases in all currents flowing through stepping motor windings simultaneously and at definite moments and increase of current phase by definite angle during start of acceleration. At steady state mode this phase shift is removed and current phase is shifted through other angle dictated by maximum speed. During plugging, current phase angle is reduced depending on maximum acceleration. EFFECT: improved dynamics of electric drive. 2 cl, 2 dwg

Description

 The invention relates to electrical engineering and can be used in programmed electric drives for precise motion reproduction systems in robots and numerically controlled machines with synchronous, in particular stepper motors with high requirements for speed, positioning accuracy and quality of working out a given motion path.

 Known methods for positional control of a stepper motor with a voltage inverter, pulse distributor and electric step crushing unit, forming a two-channel sequence of signals of the same frequency with adjustable phase shift between them, fed to the input of the pulse distributor, providing positioning with frequencies lower than the pickup frequency of the stepper motor [1 ]. There are also known methods of positional control of a stepper motor, similar to the previous one, but with a software acceleration-braking unit, providing positioning with frequencies higher than the pick-up frequency [1].

 The closest in technical essence to the proposed method of positional program control is a method based on the use of a current inverter and an electric step crushing unit with a digital-to-analog converter, which ensures the formation of currents of the same amplitude and variable frequency in the phase windings of the step motor, proportional to the specified programmed speed [2] .

 The disadvantages of the known technical solutions are the lack of a system for controlling the dynamic moment of the engine and, as a consequence, the occurrence of significant errors in reproducing a given trajectory of movement; the need to reduce the average engine torque at the stages of acceleration-braking in order to ensure sufficient stability and reliability of the drive and, as a result, to underutilization of the engine in time, as well as to reduce the speed of the drive; the presence of static positioning errors under the action of the active load moment.

 The aim of the invention is to improve the static and dynamic properties of positional stepwise electric drives, increasing the speed and reliability of the drive.

This is achieved by the fact that with the known method of positional program control of a multiphase stepper motor with electric crushing of a step, in which currents of variable frequency and the same amplitude are formed in the windings of the stepper motor, with an increase in the frequency of currents at the stage of acceleration of the motor in accordance with the optimal acceleration tachogram of acceleration, stabilization of the frequency of currents at the stage of movement with a steady speed, a decrease in the frequency of currents at the stage of braking in accordance with the optimal speed action tachogram braking and locking phases of the currents at the end of deceleration, an additional well-defined discrete times change phase simultaneously of all the currents in the motor windings, wherein at the beginning of acceleration increase phase currents angle _{arcsin [(J Σ ε max +} M c) / M _max ], when switching to the steady state driving mode, the above phase shift of currents is removed and the phase of the currents is increased by an angle arcsin [(βω _max + M _c ) / M _max ], when switching to braking mode, the above phase shift of currents is removed and additionally reduce the Toko phase in the angle arcsin [(J _Σ ε _max - M _c ) / M _max ], at the end of braking during transition to the fixation mode of the specified end position, the above phase shift is removed.

The goal of improving positioning accuracy and reducing static error under the conditions of the active load moment is achieved by an additional increase in the phase of all motor currents by an angle arcsin (M _c ) when switching to the fixation mode for a given end position, where
J _Σ is the total moment of inertia of the drive with a rotating motor or the total mass of the moving part of the linear drive (m _Σ );
ε _max - maximum angular acceleration for the received tachogram of acceleration of a rotating motor or maximum acceleration for a linear motor (a _max );
M _s - moment of static load or static load (F _s ) for rotating and linear motors, respectively;
M _max - maximum static synchronizing moment and maximum static synchronizing force (F _max ), for rotating and linear motors, respectively;
β is the coefficient of equivalent viscous friction, taking into account the presence of a load torque in the drive, losses due to eddy currents and magnetization reversal;
ω _max is the maximum steady-state positioning speed for rotating and linear motors (V _max ), respectively.

+ β

+ M_c= M_maxsin(γ-θ), где θ_m,θ - механическое и электрическое положение ротора (θ=θ_mp);
p - число пар полюсов машины;
γ - программное значение фазы токов двигателя.In FIG. 1 shows a drive positioning cycle with programmable acceleration, movement at a given steady-state speed, programmable braking and fixing of the end position, as well as the equation of motion of the drive when feeding the stepper motor windings from a controlled current inverter and deep electrical division of the machine’s structural pitch
J _Σ

+ β

+ M _c = M _max sin (γ-θ), where θ _m , θ is the mechanical and electrical position of the rotor (θ = θ _m p);
p is the number of pole pairs of the machine;
γ is the programmed phase value of the motor currents.

The first two graphs show a tachogram of a positional electric drive corresponding to the proposed control method — the dependence of the change in the mechanical speed of the motor ω (t) and the electric position of the rotor θ (t) on time. Dots mark the points in time when discrete changes in the phase of the motor currents are made. The third graph shows the law of change in the phase increment of the motor currents as a function of time γ _d (t).

Discrete phase shift currents during acceleration γ _dob leads to a discrete shift of the electromagnetic field in the air gap of the machine and the creation of the required value of the dynamic moment in accordance with the specified maximum drive acceleration ε _max . Discrete phase shift of currents during the transition from acceleration to steady movement _PDE γ provides the creation of an electromagnetic moment sufficient to compensate for the moment of viscous friction at a speed equal to the positioning speed ω _max , as well as the moment of static load M _s . Discrete phase shift of currents upon transition to the braking mode γ _d.t. provides the creation of a braking electromagnetic moment in accordance with a given deceleration (- ε _max ). A discrete phase shift of the currents during the transition to the fixing mode provides the creation of an electromagnetic moment sufficient to compensate for the active load moment M _s at the end point of the motion path.

The fourth graph illustrates the law of changing the programmed value of the phase of the motor currents γ _Σ (t) = θ (t) + γ _d (t), determined by the sum of two components: the programmed value of the electric position of the motor rotor and the discrete increment of the phase of the motor currents.

A distinctive feature of this invention is the formation of additional phase shifts of the currents in accordance with the magnitude of the acceleration and load on the corresponding interval of the positioning path, which minimizes the dynamic errors of the drive and improves the quality of movement; a significant increase in permissible acceleration-deceleration rates up to acceleration values corresponding to the engine torque (0.7-0.8) M _max , compared with acceleration values corresponding to the engine moment (0.3-0.4) M _max for traditional systems management; practically optimal in terms of speed, the start-stop nature of movement, regardless of the size and required speed of movement; minimizing static errors and improving positioning accuracy under the conditions of the active load moment.

The invention is as follows (see Fig. 2). At the inputs of adder 1, two digital signals are added: the signal of the current rotor program electric position γ (t) = θ (t) produced by the device for planning the motion path, and the signal of the discrete phase shift of the currents γ _d (t) generated by the generator of discrete field shifts, working in conjunction with a trajectory planner. The output digital signal of the adder γ _Σ (t) = γ (t) + + γ _d (t), which determines the instantaneous phase value of the total stator current vector, is fed to the address inputs of a read-only memory (ROM) 2 that stores the m-phase sequence of digital codes currents of individual phases of the m-phase stepper motor. A digital-to-analog converter (DAC) 3 provides the conversion of phase current setting codes into analog phase current input signals supplied to the inputs of a current inverter (UT) 4, and the latter generates predetermined current levels in the motor windings 5.

Claims (2)

1. METHOD FOR PROGRAM POSITIONAL CONTROL OF MULTI-PHASE STEP-BY-STEP ELECTRIC MOTOR WITH ELECTRIC CRUSHING OF STEP, in which currents of variable frequency and the same amplitude are formed in the phases of the step-by-step motor winding, with the current frequency being increased at the stage of acceleration of the motor by the electrode in accordance with the stage of acceleration of the electric motor by acceleration in accordance with the motion with a steady speed, a decrease in the frequency of currents at the stage of braking and fixing the currents of the phases of the winding at the end of braking, excellent in that, in order to improve the dynamic properties of the electric motor, the quality of motion and increase the reliability in working out a given trajectory under the action of external disturbances, in addition, at strictly defined discrete time instants, the phase of all currents in the windings of the stepper motor is simultaneously changed, while at the beginning of acceleration they increase phase of the currents at an angle arcsin (I _Σ ε _max + M _c ) / M _max , when switching to a steady-state speed mode, the above phase shift of the currents is removed and the phase of the currents in the winding is increased x step motor at an angle arcsin (β ω _max + M _c ) / M _max , when switching to braking mode, remove the above phase shift of the currents and reduce the phase of the currents in the windings of the step motor by an angle arcsin (I _Σ ε _max - M _c ) / M _max , at the end of braking when switching to the fixed position fixing mode, the above-mentioned phase shift is removed. 2. The method according to claim 1, characterized in that, in order to increase static accuracy under the conditions of the active load moment, in addition to the transition to the fixation mode of a given end position, the current phase is increased by an angle arcsin M _c ,
where I _Σ is the total moment of inertia for a rotating stepper motor or the total mass of the supplied part for a linear stepper motor;
ε _max - the maximum angular acceleration of the acceleration tachogram for a rotating stepper motor or the maximum acceleration for the acceleration tachogram for a linear stepper motor;
M _c - the moment of static load or the force of static load, respectively, for rotating and linear stepper motors;
M _max - maximum static synchronizing moment or maximum static synchronizing force, respectively, for rotating and linear stepper motors;
β is the coefficient of equivalent viscous friction, taking into account the presence of a load torque in the drive, losses due to eddy currents and magnetization reversal;
ω _max - maximum steady-state positioning speed for a rotating or linear stepper motors, respectively.

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