JPH01214295A - Stepping motor driving device - Google Patents

Abstract

PURPOSE:To reduce the output torque pulsation of a stepping motor and to decrease a vibration and a noise by so controlling an exciting current that the amplitude of the torque vector of the combined electromagnetic force as to become substantially constant. CONSTITUTION:An exciting phase current is controlled by one-chip CPU 1. Phase drivers 2-5 respectively ON/OFF-control the switching transistors Tr(A), Tr(B), Tr(A'), Tr(B') of the exciting phases A, B, A', B' of a stepping motor, detect the voltage drops of resistors RA, RB, R'A, R'B so as to supply a predetermined current. A CPU 1 so outputs a command value for controlling the current flowing in the exciting phase to the drivers 2-5 that the amplitudes of the torque vectors represented by the combined electromagnetic forces generated in a plurality of exciting phases become substantially constant.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a drive device for smoothly rotating a stepping motor.

[Prior Art] Conventionally, drive devices using a one-phase excitation method, a two-phase excitation method, or a one-two phase excitation method have been widely used to drive a stepping motor.

Further, as the power supply system, a constant voltage system, a dual power supply system, or a chopper type power supply system is used, and each of the above excitation systems and each power supply system are combined.

In each of these drive systems, the stepping motor is generally configured to rotate by one step angle by switching the excitation phase current using a drive trigger pulse, for example.

According to this configuration, the rotation speed of the stepping motor can be controlled by the frequency of the drive trigger pulse, and the rotation angle of the stepping motor can be controlled by the number of pulses of the drive trigger pulse. It can be used as an input/output drive means for equipment.

Among the excitation methods mentioned above, the one-phase excitation method and the two-phase excitation method are only capable of individual step drive (so-called full step drive), which is determined by the structure, such as the number of poles of the stepping motor and the tooth cutting pitch of the stator. be. Therefore, as methods for performing more detailed rotation control, half-step driving using a 1-2 phase excitation method and micro-step driving in which a sinusoidal current is applied to the excitation phase are also used. Furthermore, as an intermediate method between the microstep drive and the half-step drive using the 1-2 phase excitation method, there is also known a method in which the magnitude of the excitation phase current is varied to perform 1/6 step drive.

[Problems to be Solved by the Invention] However, in the so-called mini-step drive described above, the magnitude of the electromagnetic force acting on the rotor changes greatly depending on which phase is excited, resulting in pulsations in the output torque. There is a drawback.

This means that the rotor does not rotate smoothly, which causes vibrations and noise to occur and output torque to become unstable.

For example, to explain the case of the 1-2 phase excitation method, since the magnitude of the phase current is constant in this excitation method,
Since 1.4 times as much torque is generated in the two-phase excitation state as compared to the one-phase excitation state, a 40% torque fluctuation occurs. In addition, in the case of the 1/6 step drive method, there are states in which the rated current flows in both phases and states in which the rated current flows in only one phase, so the maximum value of torque fluctuation is 40%, and the 1-2 phase excitation described above The method is no different.

Therefore, in view of the above-mentioned points, an object of the present invention is to provide a drive device that enables smooth rotational driving of a stepping motor.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a driving device in which the magnitude and direction of the current flowing through each excitation phase of a stepping motor is variable, in which the electromagnetic force generated in a plurality of excitation phases is reduced. means for controlling the current flowing through the excitation phase so that the magnitude of the torque vector expressed as the resultant force of the excitation phase is substantially constant.

Further, in a preferred embodiment of the present invention, there is provided means for setting the magnitude of the excitation phase current in three ways: zero, small, and large, and
When the magnitude of the large current among the excitation phase currents is set to 1, the magnitude of the small current is set to about 0.4.

In other preferred embodiments, the magnitude of the excitation phase current is zero,
It has means for setting in four ways: small, medium, and large, and when the magnitude of the large current among the excitation phase currents is 1, the magnitude of the medium current is about 0.75, and the magnitude of the small current 0
．． Set it to about 4.

[Function] According to the present invention, by providing a means for controlling the current flowing through the excitation phase so that the magnitude of the torque vector expressed as the resultant force of the electromagnetic force generated in the plurality of excitation phases becomes substantially constant, It is possible to reduce vibration and noise by reducing the output torque pulsation of the stepping motor.

[Example] Hereinafter, the present invention will be described in detail based on examples.

FIG. 1 is a block circuit diagram showing one embodiment of the present invention. In this figure, 1 is a one-chip CPU that controls the excitation phase current. 2 to 5 are switching transistors Tr(^), Tr(B), and Tr(A) for excitation phases A, B, A, and B of the stepping motor, respectively.

It is a phase drive circuit that turns on/off the Tr (B), and the resistor R
It has a feedback circuit that detects voltage drops across A, RB, R^, and R5 and allows a predetermined current to flow.

Before explaining the operation of this embodiment, the relationship between the phase current and the behavior of the rotor will first be explained using the conceptual diagram of the stepping motor shown in FIG.

As shown in FIG. 2, a motor with four poles has a step angle of 90 degrees and is represented by a model that makes one rotation in four steps. When only the A phase is excited in the initial state, the magnetic poles of the rotor 6 are stationary toward the A phase. The position of the magnetic pole 7 in this state is considered to be the origin, and the rotation angle θ is taken in the counterclockwise direction.

When the A-phase current is cut off from the initial state (A-phase is excited) and the B-phase is turned on and excited at the same time, the magnetic pole 7 of the rotor 6
is pulled by phase B and rotates, making the direction of phase B a new stable point. In other words, the rotor 6 rotates by 90'' phase with one switching (hereinafter, the rotation angle will be expressed by the rotation of this phase angle). If done, it will continue to rotate by 90 degrees.This method is a one-phase excitation force type.

Next, considering the case where the A phase and the B phase are excited at the same time, the stable point exists between the A phase and the B phase, that is, at θ=45°. From this state, if you cut off only the excitation of the A phase while continuing the excitation of the B phase, and turn on the excitation of the τ phase at the same time, the stable point will move to the middle (θ-135°) between the B phase and the τ phase. Therefore, the rotor 6 rotates 90 degrees. A method that repeats this is the two-phase excitation force method.

Furthermore, if only the A phase is cut off from the state in which the A and B phases are simultaneously excited, the rotor will be in the initial state (θ = 45'
) to θ=90° by 45”. Then, B
When the A phase is turned on while the phase is energized, the rotor changes to θ-13
Rotate by 45° up to 5°. By repeating this, rotation with a step angle of 45°, which is half of the step angle of 90° in the one-phase excitation force type or the two-phase excitation force type, can be obtained. That is, 1-2
A half-step drive called a phase excitation magnetic force type is obtained.

A timing chart of these exciting currents is shown in FIG.

Next, FIG. 4 shows a torque vector diagram representing the wJ magnetic state in the case of the l-phase excitation method. The horizontal axis of this figure represents the magnitude of the A-phase excitation current, the vertical axis represents the magnitude of the B-phase excitation current, and the negative direction of each axis represents the magnitude of the τ-phase and τ-phase excitation currents. represents the Then, an electromagnetic force proportional to the magnitude of these excitation currents is obtained, so if a point on the torque vector diagram is P, the distance from the origin to point P is l! IOP represents the magnitude of the resultant force of the electromagnetic forces generated in each excitation phase, and therefore the magnitude of the rotor's axial torque.Furthermore, the angle θ between the polar axis and the line segment I represents the phase angle of the rotor position.

In the torque vector diagram shown in FIG. 4, the stable points of the one-phase excitation force type are at the positions indicated by O20, ■, and ■, and the magnitude of the torque vector at each stable point is constant.

FIG. 5 is a torque vector diagram of the two-phase excitation force type, and there are four stable points. However, the magnitude of the torque vector at the stable point is twice that of the one-phase excitation force type, that is, 40
% increase.

However, in the case of the 1-2 phase excitation force type that can be driven in half steps, as shown in Figure 6, there are eight stable points within one phase cycle, and the torque vector at each stable point is large. The value will alternate between 1 and JT times. Therefore, the output torque pulsates for each step, causing rotational irregularities, and the difference in stiffness characteristics at each stable point also causes angular errors when the motor stands still.

In this way, the behavior of the output torque of the stepping motor and the rotation angle of the rotor can be explained using the torque vector diagram, so the operation of the embodiment of the present invention will be explained below using the torque vector diagram.

Let the magnitude of the excitation current flowing in the A phase be iA, and the magnitude of the excitation current in the B phase be iB. Furthermore, when a unit current flows through an excitation phase, the torque generated in that phase is a unit torque vector, and if the unit torque vectors of the A phase and B phase are respectively eA and ea, the torque vectors are T = 1AeA+ i, e.

It is expressed as Here, referring to FIG. 4 again, it can be seen that -□ 1Tl=OP tanθ-ia/iA= (1). Therefore, in order for the magnitude of the torque vector to be constant, iA2+i,2. − i, 2 (=constant) ・・
- (2) is necessary and sufficient. Here i,>
Let it be O.

The magnitude of the phase current in the initial state is IA=IAO*18” ta.

Then, the initial angle θ of the rotor. is θo -tan-' (iaa/1ao)
−(3). Furthermore, if the phase step angle is S and N is a natural number, θ = N-500.
...(4), so equation (4) and equation (1)
get from.

Solving equations (1) and (5) for IA+18 yields, and considering the sign, we obtain. Kat here. /ia.

, and the phase step angle S is the step angle θ8 when the step angle θ8° obtained by the one-phase excitation force formula or the two-phase excitation force formula is expressed as π/2, and is expressed as 0. For example, θ3 1-2 Stepping motor whose angle is 1.8°
If phase drive is performed, θ is −0.9°, so S=(π/2)·(0,9/1.8) −π/4. If such a phase angle is used, motors with different step angles θso can be handled using the same equation.

Here, the case of 3×π/4 will be explained below.

In Figure 7, line segments P and P represent the electromagnetic force generated when the rated excitation current flows through the A phase.Similarly, considering the rated excitation current for the B phase, the motor is used within the rated specification range. If so, stable points can only exist within the area of quadrilaterals P, P, P3P4. θ to have the largest torque vector within this region. =S/2 may be used.

Therefore, k = iao/iao = tan (S/2)
-(7), and the stable point is 8 at the position shown in Figure 7.
It exists in some places. The magnitude of the torque vector at this time is l
T l = FR7ηW = l iA Ol・F
■F Represented by Wawa sword * IAO is good as rated current, so output torque Gt Dtan S 2) - times,
tst) When 5=yc/4, it becomes 1.08 times, 1
Torque increases by 8% compared to the phase excitation magnetic force type.

FIG. 8 is a circuit diagram showing the phase drive circuits 2 to 5 in FIG. 1 in detail.
Parallel data shown in the table of FIG. 9 is output according to o and L. Each bit of data 1°S is the first . Second
The bit i is connected to the chip select terminal of the pulse generator 12 via the inverter 11.

Here, when calculating iao when it is 1Ao-is (rated current) from equation (7), 1ao= 13-tan (S/2) = 0.414・i
It becomes s. This magnitude is equal to the magnitude of the A-phase excitation current at the first stable point (see FIG. 7), which is rotated by one step from the initial state (■). Therefore, the first comparator 9
and the reference input voltage of the second comparator lO is 1:0.
．． It should be set to 414. In other words, it is sufficient to set R21 to -470Ω and R3 to -330Ω. Further, R11 is a limiting resistor, which may be determined depending on the circuit power supply voltage VCC and the rated input voltage of the comparator.

Furthermore, the input terminal C is a terminal for feeding back a current value, and inputs the voltage drop of Rτ to the phase current detection resistors RA, Re, and R shown in FIG. 1 to a comparator 9.10.

Now, in the drive circuit shown in FIG.
~5 input signals, and each phase drive circuit has 9th input signal.
It is driven as shown in the table in the figure.

FIG. 10 shows a timing chart of the output signals obtained from the output ports P0 to P7 and the phase excitation current.

In the itt diagram, in order to further realize mini-angle step drive, S=π/8. θ. It is a torque vector diagram in the case of ~π/16. In this case, compared to the one-phase excitation method, an increase in torque can be expected by only J1+tan2 (6 to π) = 1.02 (times), that is, 2%. Moreover, as can be seen from FIG. 11, control cannot be achieved unless the phase current is changed in four ways.

Therefore, we propose a mini-angle step drive system based on the torque vector diagram shown in FIG. 12, which allows for slight torque fluctuations. From this figure, S=π/8°θ. -〇, and the current value at each stable point is 0.765 for medium current and 0.414 for small current, assuming that the magnitude of A-phase current in the initial state @ is 1.

FIG. 13 shows a phase drive circuit. Its operation is substantially the same as the example shown in FIG. The first comparator 14 and the third comparator 16 output bits 1 to 1 of the parallel data output from the decoder 13. Each is selected by bit S. dog here,
Ratio of medium and small current values 1: 0.765: 0.41
In order to satisfy 4, for example, R22-220Ω, R3□
-330Ω and R42-390Ω.

Figure 14 shows the human input signal 1 of the decoder 13 (see Figure 13).
This is a table showing output data for 0.11, and based on this table, a timing chart of the output ports P0 to P of the CPU and the phase excitation current is shown in FIG.

The phase drive circuit of this embodiment (FIG. 13) completely includes the functions of the circuit of FIG. 8, and converts the output signal of FIG.
If the output is output from , half-step driving of S=π/4 becomes possible. Here, the one-chip CPU may have a bit pattern table shown in FIG. 16, and sequentially output bit patterns from 0 to F in response to a trigger signal of the device. It goes without saying that the value returns to 0 after F.

1.3.5. ..., F and every other output, S;π/ as shown in Fig. 10 is obtained.
4 drive signals are obtained.

Up to now, the explanation has been based on unipolar drive, but A
Exactly the same effect can be obtained with bipolar drive in which currents flow in opposite directions to the phase and the X phase. In other words, in this case as well, by setting the magnitude of the small current to 0.4 when the magnitude of the large current flowing through the excitation phase is 1, the output torque can be made larger than in microstep drive that applies a sine wave current. It becomes possible to do so.

[Effects of the Invention] As explained above, according to the present invention, the current flowing through the excitation phases is controlled so that the magnitude of the torque vector expressed as the resultant force of electromagnetic forces generated in a plurality of excitation phases is approximately constant. By providing means for reducing the output torque of the stepping motor, it is possible to reduce the output torque pulsation of the stepping motor.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a drive circuit diagram according to an embodiment of the present invention, FIGS. 2 to 6 are torque vector diagrams explaining conventional drive systems, and FIGS. 12 is a torque vector diagram explaining the operation of one embodiment of the present invention, FIGS. 8 and 13 are phase drive circuit diagrams according to this embodiment, and FIGS. 9 and 14 are human power signal codes, respectively. FIG. 10 and FIG. 15 are timing diagrams showing the relationship between drive signals and phase excitation current, respectively. FIG. 16 is a diagram showing an output bit pattern table for operating a drive device according to an embodiment of the present invention. It is. 1... One-chip CPυ, 2-5... Phase drive circuit, 8.13... Decoder, 9.10, 11, 14.15.18-... Comparator, 12.18... Pulse generator . M ” o Ku no l< + (Co
t(l of 1<1 Fig. 4 Fig. 5 Fig. 6 Fig. 7N Fig. 8 CLOCK P7 Fig. 10 Fig. 11 Fig. 12 Fig. cc Fig. 13 CLOCK PI Fig. 15 Q D O I O 5P4P3 P2 PI PO l 1 1 1 to. +110100 + l + 1010 01 II 101 Figure 6

Claims (4)

[Claims] (1) In a drive device that varies the magnitude and direction of the current flowing through each excitation phase of a stepping motor, the magnitude of the torque vector, which is expressed as the resultant force of the electromagnetic force generated in multiple excitation phases, is approximately constant. A stepping motor drive device comprising means for controlling a current flowing through the excitation phase. (2) The stepping motor drive device according to claim 1, further comprising means for setting the magnitude of the excitation phase current in three ways: zero, small, and large. (3) The stepping motor drive device according to claim 2, wherein when the magnitude of the large current among the excitation phase currents is set to 1, the magnitude of the small current is set to about 0.4. (4) The stepping motor drive device according to claim 1, further comprising means for setting the magnitude of the excitation phase current in four ways: zero, small, medium, and large. (5) Among the excitation phase currents, when the magnitude of the large current is set to 1, the magnitude of the medium current is set to about 0.75, and the magnitude of the small current is set to about 0.4. The stepping motor drive device according to claim 4.