JPH02211094A - Method of determining driving current of stepping motor - Google Patents

Abstract

PURPOSE:To obtain an optimum waveform of currents IA, IB by maintaining the sum I0 of the currents IA, IB of two adjacent phases of a stepping motor constant, and obtaining a function (f) of theta=f(IB) and a reverse function IB=h(theta) for a rotating angle theta. CONSTITUTION:Two adjacent phase currents IA, IB of a stepping motor 6 are so complementarily increased or decreased from '0' to I0 that the sum I0 of the currents IA, IB always becomes constant. In this case, a basic stepping angle is divided into a plurality of microsteps of equal intervals, the current IB is varied in proportion to the number of the microsteps, the rotating angle theta at that time is obtained by a tachometer 7, amplified, D/A-converted by a D/A converter 9, and input to a computer 1. The computer 1 obtains a function of theta=f(IB) and its reverse function IB=h(theta), and the IA, IB are determined from IA= I0-IB. The currents IA, IB are D/A-converted by D/A converters 2, 3, ampli fied by amplifiers 4, 5 to step the motor 6. Thus, the optimum waveforms of the current IA, IB are obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for determining a driving current for a stepping motor.

[Prior Art] FIG. 2 is a schematic cross-sectional view for explaining the operation of a stepping motor.
(20) is the rotor, (21) is the stator, and (22) is the stator.
is a coil. Coils A-1 and A-2 form one phase, and coils B-1 and B-2 form an adjacent phase.

When current flows only through coils A-1 and A-2, rotor tooth R-1 is attracted to the magnetic pole of coil A-1, R-3 is attracted to the magnetic pole of coil A-2, and the magnetic flux is It will stop at the position shown by the dotted line. That is, this stop position is the position where the magnetic reluctance is the minimum.

Next, the current in coils A-1 and A-2 is cut off, and coil B-
When current is applied only to 1 and B-2, R-2 stops at the position where it opposes the magnetic pole of coil B-1, and R-4 opposes the magnetic pole of coil B-2.

The stopping position of the rotor when current is passed only through the phases of coils A-1 and A-2, and the stopping position of the rotor when current is passing only through the coils B-1 and B-2 of the adjacent phase. The angle between is called the basic step angle.

Stepping motor driving methods include a driving method that performs driving in basic step angle units and a driving method called microstep driving.

Basic step angle unit drive switches the current flowing in the winding of one phase and flows it to the winding of the adjacent phase.
The rotor of a stepping motor is rotated by a basic step angle, and microstep drive gradually transfers the current flowing in the winding of one phase to the winding of the adjacent phase while moving within the basic step angle. The control is performed so that the entire current is transferred to the winding of the adjacent phase when the basic step angle movement is completed. That is, at the starting point of movement by one basic step angle unit, the current IA flowing in the winding of one phase is equal to the total current Io, and the current IB flowing in the winding of the adjacent phase is 0. , In this state, IA + IB = Io..., while maintaining the condition (1), increase ■, and at the end point of the movement of the basic step angle unit, IA = O.

The current is controlled so that IB=Io.

Microstep drive can improve the static position accuracy and therefore suppress vibrations, so
Although it is more commonly used than basic step angle unit drive, in order to sufficiently suppress vibrations even in microstep drive, it is necessary to maintain the angular acceleration of the rotor as constant as possible. In other words, the rotation angle of the rotor is θ1 rotational inertia (consider including the connected load; the same applies hereinafter)
1. If the friction coefficient is F and the torque acting on the rotor is T, then T=I(d2θ/dt2)+F(dθ/dt)・
(2), but it must be controlled so that no torque other than that determined by equation (2) is applied. To do this, the current IB must be controlled while maintaining the conditions of equation (1). It is necessary to change it as an appropriate time function, but there is no conventional method for determining this appropriate time function.For example, if the basic step angle is θ, then the angle within the basic step angle θ is θ. When expressing, while maintaining the relationship of equation (1), IB=Ioθ/θ, - (3) As shown by 1. is changing linearly.

[Problems to be Solved by the Invention] The conventional stepping motor drive current determination method described above determines the drive current as described above, but when a current with such a waveform is applied, harmful torque is generated. This may cause vibration.

FIG. 4 is a diagram showing the measured values of the static point θ of the rotor (20) when varying the IQ according to the conditions of equations (1) and (3). When = θ8, I, = IX according to equation (3), but for ■, θb is the stationary point, so the rotor (20) at θ8
There was a problem in that a torque was generated to try to pull back the angle θb to θb, causing vibration.

The present invention has been made to solve the above-mentioned problems in the conventional method, and an object of the present invention is to provide a method for determining a driving current for a stepping motor that can determine an optimum current waveform by a simple method.

[Means for Solving the Problems] The method for determining the driving current of a stepping motor according to the present invention is to obtain the inverse function of the function f from the relationship between IB and θ, that is, θ=f(IB), and calculate I+5=h (θ).

[Operation] In this invention, the inverse function is calculated and IB=h(θ)
Therefore, it becomes possible to match the current position of the rotor with the rest position of the rotor.

[Examples] Examples of the present invention will be described below with reference to the drawings. 1st
The figure is a block diagram showing an embodiment of the present invention, in which (1) is a host computer and (2) is a host computer.

(3) is a digital-to-analog converter (hereinafter abbreviated as DAC), (4) and (5) are amplifiers, (6) is a stepping motor, and (7) is an angle meter directly connected to the stepping motor (6). , (8) is an amplifier, and (9) is an analog-to-digital converter (hereinafter abbreviated as ADC). When the angle meter (7) outputs the value of θ as a digital value, (8).

(9) becomes unnecessary.

If IB is changed under the conditions of equations (1) and (3) in a state where the rotational speed dθ/dt of the rotor is actually 0, the rotor will be at the angular position of T = 0 in equation 2). Stop. This is called a resting point. The value of θ at the stationary point and I
When the relationship with B is measured, the state shown in FIG. 3(a) is obtained.

Next, consider the case where the rotor rotates at a constant speed.

In this case, since T in equation (2) becomes a function of θ and IB, the relationship between θ and IB becomes complicated and changes depending on the value of dθ/dt. However, this relationship can be measured by the apparatus shown in FIG.

Instead of formula (3), IB=Iot/τ...(4) (τ is the time corresponding to θ) If IB is varied linearly with respect to time and θ is measured, then , θ over time approximately coincides with the curve shown in FIG. 3(a). That is, in general, the relationship between θ and IB can be approximated by the characteristics shown in FIG. 3(a).

The relationship shown in Figure 31 (a) θ=f(Ia,)...Represented by (5).

Further, from the relationship shown in FIG. 3(a), the inverse function of the function f can be determined as follows: 1, = h (θ) (6).

IB in FIG. 3(b) represents the relationship of equation (6), and is expressed using the number of microsteps instead of θ. Note that a microstep is a division between basic steps into an arbitrary number of steps N, and the relationship between θ and the number n of microsteps is n=Nθ/θ. In the same figure, ■^ is the value obtained from equation (1). In this diagram, ■Itoko and I゛. It is shown normalized with respect to the value of .

That is, the current waveform determined by the relationship between IB and microstep shown in FIG. 3(b) becomes the optimum drive current waveform.

Once the value of IB for the microstep is determined as described above, it is stored in a storage device such as a ROM, read out at a speed proportional to the rotational speed of the rotor, and D
It can be applied to the stepping motor (6) via AC (2), (3), amplifiers (4), (5). In this case, IA is determined by equation (1), so DAC(2
), (4) are omitted, and after obtaining the analog quantity of IQ,
It may be calculated by the calculation of equation (1).

The value of the number of microsteps N when storing IB indicates the sampling density of data, and N=20 or so can sufficiently achieve the purpose.

A stepping motor (
7) can be measured with the apparatus shown in FIG. 1, and a linear angle change as shown in FIG. 3(c) can be obtained.

Conventionally, the current was changed linearly or sinusoidally with respect to time, but in either case, linearity as shown in FIG. 3(c) could not be obtained.

[Effects of the Invention] As explained above, the present invention has the advantage that the optimum waveform of the current to be passed through the coil of the stepping motor can be determined in a simple manner.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a schematic sectional view for explaining the operation of a stepping motor, FIG. 3 is a characteristic diagram for explaining the invention in detail, and FIG. 4 is a diagram showing the relationship between the static point of the rotor and the current. (1)...Host computer, (2), (3)・DAC1
(4), (5)...Amplifier, (6)・Stepping・
Motor, (7)...angle meter, (20)...rotor,
(21)... Stator, (22)... Coil. In addition, the same reference numerals in each figure refer to the same or corresponding parts in the second ai.
3 4th vIJ

Claims (1)

[Claims] When the stepping motor moves within a basic step angle, while keeping the sum of the current values of the windings of two mutually adjacent phases related to the movement within the basic step angle at a constant value I_0, The current I_B of the phase is increased from 0 to I_0, and the current I_A of the other phase is increased from I_0 to 0.
In the stepper motor drive current determination method that determines the change in the current waveform when the current waveform decreases to a step of determining a function f of θ=f(I_B) by measuring the rotation angle θ of the stepping motor corresponding to each I_B; a step of determining an inverse function h of the function f from the function f; I_B=
h(θ), I_A=I_0-I_B to I_B, I_A
A stepper motor drive current determination method comprising: a step of determining .