JPH0113320B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a step motor drive system, and more particularly to a step motor drive system that has been improved to equalize torque characteristics both at startup and during continuous rotation.

Conventionally, in order to make the step motor rotate smoothly, a step motor drive method has been used in which three sets of coils of the step motor are sequentially excited by alternately repeating the excitation of only one set of coils and the simultaneous excitation of two sets of coils. Widely adopted. For example,
This driving method is explained in detail in the publication No. 7016.

Also, the current when exciting one set of coils and 2
It is also known to make the generated torque even more smooth by making the sum of currents when a set of coils are simultaneously excited substantially equal.

FIGS. 1 to 4 are diagrams for explaining such a conventional drive system. FIG. 1 shows an example of the configuration of a circuit for exciting one set of coils, and the second
The figure shows the input signal applied to the drive circuit shown in Figure 1 and the coil current (excitation current), and Figure 3 shows the change from one-phase excitation to two-phase excitation when four sets of coils are used. FIG. 4 shows an excitation current similar to that in FIG. 3 when starting after switching from two-phase excitation to one-phase excitation.

In Figure 1, E _H and E _L are DC voltage sources with high and low output voltages (24 V and 5 V), Q _H and Q _L are switching transistors, and t _H and t _L are transistors Q _H and Q _L base input terminal, _D1 is a reverse current prevention transistor, _D2 is a flyback diode,
_D3 is a diode for preventing oscillation, and C is a coil to be excited. Two transistors Q _H and Q _L are connected in series to the coil C, a high voltage source E _H is connected to the series circuit, and a low voltage source is connected to the series circuit of the coil C and one transistor Q _L. A source E _L is connected via a backflow prevention diode D ₁ . Therefore, the base input terminal t _L of the transistor Q _L
When a positive signal is applied to only the low voltage source E _L , current is supplied to the coil C and the transistor Q _L
When a positive signal and a negative signal are simultaneously applied to both E H and transistor Q _H , the high voltage source E _H
Current is supplied to coil C from.

That is, as shown in FIG.
A positive signal L is applied to the base input terminal _tL of _QL ,
A negative signal H is applied to the base input terminal _tH of the transistor _QH .
is applied, and as a result, the high voltage source _EH applies a voltage to the coil C during the energization start period _T1 , and the current I gradually increases at a relatively large rate of increase. Further, at T and T, voltage is applied to the coil C only from the low voltage source E _L , so the current I gradually decreases and reaches a nearly steady value determined by the internal resistance speed of the coil, back electromotive force, etc. In addition, each of the above excitation periods T
, T, and T are the first periods in which two-phase excitation is performed together with other sets of coils preceding the excitation order,
This corresponds to a second period in which one-phase excitation is performed and a third period in which two-phase excitation is performed together with other sets of coils whose excitation order is delayed.

In the case of a four-phase step motor that excites four sets of coils, the excitation currents φ ₁ , φ ₂ , φ ₃ , φ _{4 of each set are exactly 1, as shown in Figures 3 and 4} . A state is reached in which the period is shifted by the time divided into four equal parts, and the periods during which the one-phase excitation and two-phase excitation are performed alternately appear every period divided into eight equal parts. For example, if the unit is the period during which 1-phase excitation and 2-phase excitation are performed, and the excitation start period of current φ ₁ flowing through a suitable set of coils is the base point, one cycle is the period T ₁ to T as shown in the figure. ₃ , the first phase excitation current φ ₁ flows during the period T ₁ to T ₃ , and similarly, the second phase excitation current φ ₂ flows during the period T ₃ to T ₅ , and the third phase excitation current φ ₄ flows during the period T 3 to T 5. will flow during the period T ₇ to T ₁ .

Now, it is considered that the torque generated by each of these excitation currents φ ₁ to _{φ 4} is roughly proportional to the sum of the excitation currents of each period T ₁ to _{T 3} . Then, in the case shown in FIG. 3, one phase excitation period T ₂ , T ₄ ,
At T ₆ and T ₈ , a large excitation current flows through one set of coils, and during two-phase excitation periods T ₁ , T ₃ , T ₅ , and T ₇ , a relatively small excitation current flows through two sets of coils, so both are approximately equal to each other. Similarly, it can be said that the variation in generated torque is small.

However, as shown in Figure 4, the step
If the motor is stopped in a two-phase excitation state and then started from that state, equal currents must flow through the two sets of coils at the time of stop shown in period T ₁ , so both must be connected to a low voltage source. connected, and at start-up T ₂ one current φ ₄ is disconnected and the other current φ ₁
will remain, but since this current _φ1 was not supplied from a high voltage source in the immediately preceding period, it is significantly smaller than the current during one-phase excitation or two-phase excitation during continuous rotation. .

In other words, when starting while switching from 1-phase excitation to 2-phase excitation as shown in Fig. 3, and when starting while switching from 2-phase excitation to 1-phase excitation as shown in Fig. 4, the starting torque is large. have different drawbacks.

Therefore, it is an object of the present invention to provide a step motor drive method that eliminates these drawbacks and does not cause variations in torque characteristics at startup. For a step motor having multiple sets of coils that are attracted to a certain position, each coil is sequentially excited while alternately repeating one-phase excitation that excites one set of the above-mentioned coils and two-phase excitation that simultaneously excites two sets of the above-mentioned coils. In this step motor driving method, the coil drive circuit applies a first voltage to the coil during an excitation period and a second voltage higher than the first voltage. During the excitation period of the coil, the first voltage is applied, and during the excitation period, the first voltage is applied during a one-phase excitation period in which only one set of the coils is excited, and the excitation order is During the two-phase excitation period together with other preceding coils, each coil is applied with the second voltage higher than the first voltage for a predetermined period in the first half of the excitation period. This is achieved by controlling the drive circuit of the following, and one embodiment thereof will be described in detail below with reference to the drawings.

5 to 8 are diagrams showing an embodiment of the present invention, and FIG. 5 shows the respective excitation current on/off control signals L, H' corresponding to those in FIG. 2 and the excitation current I' of the coil. FIG. 6 and FIG. 7 show the excitation current of each phase near the time of startup corresponding to FIGS. 3 and 4, and FIG. An example of the configuration of a circuit for this purpose is shown.

In this embodiment, as shown in FIG.
The excitation current I′ in the phase excitation period T is the period immediately before
It is generated independently without depending on the current supply from the high voltage source at _T1 , which is a big difference from the conventional method.

That is, current is supplied from the high voltage source during approximately the first half of this one-phase excitation period T. Furthermore, if this current is supplied during the one-phase excitation period T, then during the next two-phase excitation period T,
Since a current larger than the substantially steady current supplied simply from the low voltage source flows for a while, the current of the other sets of coils excited simultaneously with this two-phase excitation,
That is, in order to slightly reduce the excitation current during period T, the current supply period from the high voltage source is reduced. Therefore, the torque characteristics during continuous rotation are substantially uniform.

On the other hand, regarding the torque characteristics at startup, see 1 above.
Uniformity is achieved by supplying current from a high voltage source during the phase excitation period T, and this point will be explained next with reference to FIGS. 6 and 7.

As shown in Figure 6, the 1-phase excitation period T ₈ to 2
When switching to the phase excitation period T ₁ and starting for a long time, the current φ ₄ ' flowing through the coils of the set that is previously excited during two-phase excitation is supplied from the low voltage source,
The current φ' flowing through the delayed set of coils is supplied from the high voltage for a predetermined time and then from the low voltage source. Although the above current φ ₄ ' is slightly smaller than the current during continuous rotation (for example, the current φ ₁ ' in period T ₃ ), this decrease amount is less than the current during period T ₁
This is negligible compared to the sum of the currents φ ₄ ′ and φ ₁ ′. Therefore, the generated torque during this period T ₁ can be made comparable to that during other periods T ₂ , T ₃ , . . . .

Moreover, as shown in FIG. 7, the two-phase excitation period T ₁
When starting while switching from 1-phase excitation period T ₂ to 1-phase excitation period T 2 , the current φ ₁ ′ during 2-phase excitation changes to the other period T ₃ ,
The current of T ₄ ,... is the same, and therefore the generated torque is also the same.

As described above, in this embodiment, by passing the excitation current shown in FIG. 5 through the coil, it is possible to obtain approximately the same generated torque at the time of starting shown in FIG. 6 and at the time of starting shown in FIG. 7. The torque characteristics during continuous rotation will not be affected.

Next, what kind of drive circuit should be constructed in order to obtain the excitation current shown in FIG. 5 will be specifically explained with reference to FIG. 8. The drive circuit shown in FIG. 8 is different from the conventional circuit shown in FIG.
2 monostable multivibrators
It is constructed by adding MM ₁ , MM ₂ and an OR gate. These additional circuits convert negative signals into logic “1”
operates as That is, the negative signal H shown in FIG. 2 is applied to the first monostable multivibrator _MM1 , and its fall generates a negative pulse having a pulse width of a predetermined time, and Monostable multivibrator MM ₂
The transistor on the low voltage source side of the drive circuit (not shown) for the other set of coils is excited in advance.
Base input signal applied to Q _L ′ (not shown)
t _L ′ is applied in a branched manner. That is, 1
A falling signal at the start of the phase excitation period Tn is applied to the second monostable multivibrator _MM2 , and a negative pulse having a pulse width of a predetermined time is generated. The negative pulses generated from these two monostable multivibrators MM ₁ and MM ₂ are applied to the base input terminal t _H ' of the transistor Q _H via an OR gate (operating with negative logic). This applied signal is shown in FIG. 5H). Note that the signal applied to the base input terminal _tL of the transistor _QL is exactly the same as the conventional one shown in FIG.

In this way, among the one-phase excitation period T ₁₁ and two-phase excitation periods T ₁ and T ₁₁₁ of each coil in which the transistor Q _L is turned on, the first two-phase excitation period (other than the previously excited When the transistor Q _H is turned on during approximately the first half of the one _- phase excitation period _{T 11} (which is carried out with the coils of ^the set of Current flows through the coil. Then, in the first two-phase excitation period T ₁ , the current increases from zero, so this period T ₁
On the other hand, the average current during the one-phase excitation period T ₁₁ is large because the current is increased starting from the state where the current is _already being supplied from the low voltage source. Therefore, the coil current of one set during one-phase excitation can be made approximately equal to the sum of the two sets of coil currents during two-phase excitation.

In addition, the coil current of one-phase excitation always has the same value regardless of whether the step motor stopped during the previous period or whether it rotated continuously, and the torque at the time of starting does not drop significantly.

As described above, according to the present invention, there is little variation in the torque characteristics during startup and during continuous rotation, and it is possible to drive a step motor that can be started and rotated smoothly.

In the above embodiment, the case of a four-phase step motor has been described, but the present invention is not limited thereto, and can be similarly applied to a three-phase, five-phase or more step motor. Furthermore, it goes without saying that the drive circuit is not limited to that shown in FIG.

[Brief explanation of drawings]

Figures 1 to 4 are diagrams for explaining the conventional drive system, Figures 5 to 8 are diagrams for explaining an embodiment of the present invention, and Figure 5 is a diagram for explaining the excitation of each coil. A diagram showing the control signal and excitation current to explain the operation. Figure 6 is a diagram showing the excitation current when switching from 1-phase excitation to 2-phase excitation. Figure 7 is a diagram showing the excitation current when switching from 2-phase excitation to 1-phase excitation. FIG. 8 is a diagram showing an excitation current when starting to switch to excitation, and FIG. 8 is a diagram showing an example of the configuration of a coil drive circuit. E _H ...High voltage source, E _L ...Low voltage source, Q _H , Q _L ...
…Switching transistors, D ₁ , D ₂ , D ₃ …
...Diode, C...Coil, MM ₁ , MM ₂ ...
Monostable multivibrator, OR...
Orgate.

Claims (1)

[Scope of Claims] 1. For a step motor having multiple sets of coils that attract the rotor to different rotational positions, 1-phase excitation that excites one set of the coils and 2 that simultaneously excites two sets of the coils. This is a step motor drive method in which each coil is sequentially excited while alternately repeating phase excitation, and the coil drive circuit applies a first voltage as the voltage to the coil during the excitation period, and , is configured to be able to apply a second voltage higher than the first voltage for a predetermined period, and during the excitation period of the coils, the first voltage is applied, and only one set of the coils is applied during the excitation period. During the one-phase excitation period in which the coil is excited and the two-phase excitation period together with other sets of coils that precede the excitation order, the voltage is higher than the first voltage for a predetermined period in the first half of the excitation period. A drive method for a step motor, characterized in that a drive circuit for each coil is controlled so as to apply the high second voltage.