JP2645604B2 - Drive circuit for brushless motor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a drive circuit for a brushless motor.

[Summary of the Invention] The present invention provides a detector for detecting the position of a rotor, a signal processing circuit for processing an output signal of the detector, a switching circuit for obtaining the output and flowing a current to an armature coil. In the drive circuit of the brushless motor equipped with, a part of the signal processing circuit has a dead zone characteristic,
When the output signal of the above detector is within a range of the dead zone for a certain period of time or more, the power supply to the drive circuit is cut off to prevent abnormal oscillation of the drive circuit, and in some cases, the motor or the drive An object of the present invention is to provide a highly reliable brushless motor that prevents circuit burnout and destruction.

In particular, when the position detector is a single two-phase brushless motor, the size of the dead zone is defined by the angular width from the position of the detector to the stop position due to the non-excitation torque of the rotor. By setting the detector at an angle smaller than twice on both sides of the arrangement position of the detector, the object can be achieved.

[Prior Art] First, there are conventional problems of a non-starting point, that is, a dead point of a brushless motor, and a problem of oscillation of a drive circuit when switching magnetic poles, which will be described.

The principle of a brushless motor having a single rotor position detector is as shown in FIGS. 11 (a) to 11 (e). In addition, FIG. 11 (a) shows a drive circuit of a two-phase unipolar motor. The output signal of the position detector 3 using, for example, a Hall element, a magnetoresistive element, or the like is input to the differential amplifier Q1,
The output of Q1 is input to a switching element S1 such as a bipolar transistor or FET connected in series with a power supply and a motor coil L1 via a power supply and a motor coil L1 through a comparator and an amplifier 7, and the power is inverted by an inverting amplifier G1. And the switching element S2 connected in series with the motor coil L12.

The cross-sectional views of FIGS. 11 (b) to (d) show the cross-sectional outline and operation principle of the brushless motor. First, when the permanent magnet rotor 1 is positioned as shown in FIG.
The position detector 3 detects the N-pole, applies a current to the coil L2 wound on the stator core 5, excites the fixed core to the S-pole, and indicates an arrow a.
The rotor 1 is rotated in the CCW direction as shown in FIG.

Next, when the permanent magnet rotor 1 rotates to the position shown in FIG. 11 (c), the output of the differential amplifier Q1 in FIG. Thus, no current flows through the coil L1 and the coil L2, and no rotational torque is generated in the rotor 1, but the rotor 1 continues to rotate in the CCW direction due to inertia.

When the permanent magnet rotor 1 further rotates and comes to the position shown in FIG. 11D, the position detector 3 detects the S pole and detects the stator core 5
A current is caused to flow through the coil L1 wound around the coil to excite the stator iron core to the S pole, and the rotor 1 is still rotated in the CCW direction.

As described above, the permanent magnet rotor 1 rotates continuously, and the rotating torque generated at this time depends on the horizontal axis representing the rotation angle,
If the vertical axis is represented by the rotational torque, the characteristic becomes as shown in FIG. 11 (e), and a dead center 6 where the generated torque becomes zero occurs. This corresponds to the case where the rotor is at the position shown in FIG. If the rotor is located at this dead center, the motor cannot start, and if the load on the rotor is large, if the rotor is stopped at this dead center for any reason, There was a problem that rotation stopped. Further, there is a problem that the drive circuit oscillates at the switching point of the magnetic pole before and after the rotor passes through this position.

To solve such a problem, a brushless motor system which has been conventionally implemented is shown in FIGS. 12 (a) to 12 (c).
This will be described. FIG. 12 (a) is a cross-sectional view of an external rotation type (outer rotor type) brushless motor provided with one position detector 3, and is a ring-shaped permanent magnet rotor magnetized to four poles in a radial (radial) direction. It comprises a stator iron core 5 having 1, 4 salient poles, and a coil 4 wound around the stator iron core 5 and connected in series. It is important that the salient pole shape of the stator iron core 5 is not concentric with the rotation axis, and that the air gap length (air gap) with the permanent magnet rotor 1 varies depending on the location. I will explain later. Reference numeral 2 denotes a rotor yoke made of a magnetic material.

The drive circuit is the same as the one described earlier depending on the coil connection method.
The switching element S1 (hereinafter referred to as NP) in FIG. 11A may be the same as that shown in FIG. 11A, or may be a two-phase bipolar type as shown in FIG. 12B.
NPN switching transistor S3, NPN switching transistor S2 between the electrodes)
The PNP switching transistor S4 is connected in series between the power supply and the power supply.The base of S3 is connected to the collector of S2 through a resistor, the base of S4 is connected to the collector of S1 through a resistor, and all four coils are connected in series. It is connected and connected between the collector of S1 and the collector of S2.

In this case, the form of the torque generated by applying a current to the coil L, that is, the form of the excitation torque is similar to that of FIG. 11 (e), and is similar to that of FIG. 12 (c). There are four dead points during one rotation. However, the torque generated between the permanent magnet rotor 1 and the stator core 5 when no current flows through the coil, that is, the non-excitation torque (also referred to as reluctance torque or cogging torque) is used for the stator core 5. For example, as shown in FIG. 12 (a), by changing the gap length with the permanent magnet rotor 1 depending on the location as shown in FIG. 12 (a), as shown in FIG. Can be in any shape.
Therefore, the combined torque of the excitation torque (A) and the non-excitation torque (B) becomes as (A + B), and the dead center can be eliminated.

It should be noted that the drive circuit shown in FIGS. 11 (a) and 12 (b) has a built-in integrated circuit 8 including a comparator Q1 and an amplifier 7, an inverter G1 and switching elements S1 and S2. Integrated circuits are commercially available for general use, and their use is economically effective. Some of the integrated circuits have integrated functions such as protection circuit operation when the motor is locked and sensor signal output when the motor is locked.

[Problems to be Solved by the Invention] However, in the conventional method shown in FIGS. 12 (a) to 12 (c), the gap length between the salient poles of the stator core 5 and the permanent magnet rotor 1 is changed. In addition, efficiency is inevitably sacrificed as compared with a motor having a constant gap length. Also, since the formation of the salient pole portion of the stator core 5 changes the non-excitation torque (B) in FIG. 12 (c) in various ways, it takes a lot of design time and a lot of time to determine its shape. There was a problem that evaluation time had to be required. Further, since the stator core 5 shown in FIG. 12A has an asymmetric shape with respect to the rotation angle, the rotation direction of the rotor is limited to one direction. When the motor is rotated in the opposite direction, the form of the excitation torque (A) does not change, but the form of the non-excitation torque (B) N becomes linearly symmetric with respect to the reference angle, so that the form of the combined torque (A + B) changes. Would. Therefore, there is a problem in any case, such as when the stator is to be rotated in the opposite direction, the stator iron core 5 needs to be turned upside down.

Also, in the case of the circuit of FIG. 12 (b), there remains a problem that the drive circuit oscillates at the switching point of the magnetic poles as in the circuit of FIG. 11 (a). )
Oscillation occurs near the point where the excitation torque (A) at zero is zero.

In particular, when a commercially available integrated circuit 8 is used, the more the function is multi-functional and complicated, such as the operation of the protection circuit when the motor is locked or the output of a sensor signal when the motor is locked, the more the oscillation becomes. Had inconsistent problems, such as rendering the inoperable. Further, in the case of the two-phase bipolar type driving circuit shown in FIG. 12 (b), a short-circuit phenomenon called cross-current conduction occurs during this oscillation and an excessive current flows, and in some cases, the driving circuit is burned or broken. Had the serious problem of

[Means for Solving the Problems] The present invention is that the efficiency of the above-mentioned brushless motor is low, that much time and effort is required for determining the shape of the salient pole portion of the stator core, and that the reverse rotation of the motor is not easy. In addition to eliminating the drawbacks such as the above, the drive circuit for eliminating the oscillation of the drive circuit at the magnetic pole switching point of the rotor and obtaining a highly reliable brushless motor that is easy to design, efficient and does not cause abnormal oscillation etc. It is intended to provide.

For this reason, according to the present invention, a part of the signal processing circuit of the rotor position detector is provided with a dead band characteristic, and when the output signal of the position detector is within a range of the dead band for a predetermined time or more, the drive circuit is provided. The power supply to the power supply is cut off.

In particular, when the position detector is a single two-phase brushless motor, the size of the dead zone is defined by the angular width from the position of the detector to the stop position due to the non-excitation torque of the rotor. The angle is set to be smaller than twice at both sides of the position where the detector is provided.

 Hereinafter, the principle of the present invention will be described.

[Operation] The operation of the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional view of a brushless motor of the present invention cut into a circle, and its structure is the same as that of FIG. However, in the motor to which the circuit of the present invention is applied, the tip shape of the salient pole portion of the stator iron core 5 is concentric with the rotation axis as shown in the figure, and the gap length with the permanent magnet rotor 1 is small. Is constant regardless of Therefore the rotor core is mechanical angle
It becomes symmetrical at 90 degrees. In this case, the shape of the non-excitation torque is also symmetrical at a mechanical angle of 90 degrees, and the permanent magnet rotor 1 stops at the switching point of the magnetic pole located at the center of the gap between the salient poles of the adjacent stator core. When this positional relationship is enlarged and shown in a developed view, it is the same as the position of d in FIG. 2 (b).

For example, a Hall element is used as the position detector 3 of the rotor 1, and this set position is set to be lower than the position b in FIG. 2B, that is, the position of the central arm d of the gap between the salient poles of the adjacent stator cores. The rotation direction is set to the front (leading phase) by the angle θ1. Even if this is a lag phase, the effect of the present invention does not change in principle.

On the other hand, the permanent magnet rotor 1 of the motor is generally magnetized in a sine wave shape, and the horizontal axis represents the rotation angle, and the vertical axis represents the output voltage Vs with respect to the magnetic flux density at the detection position, as shown in FIG. This is a characteristic curve diagram.

Next, a description will be given of a two-phase unipolar drive circuit with reference to the circuit diagram of FIG. 3, focusing on differences from the conventional drive circuit of FIG. 11 (a). In the circuit shown in FIG. 3, the output of the phase detector 3 is input to a differential amplifier Q2, and the output of Q2 is input to signal processing circuits Q3, Q4, which are composed of window comparators, to S3.

The Q3, Q4 has a dead band characteristics, the upper limit reference voltage Vu, the input-output characteristic by the lower limit reference voltage V _l is processed as Figure 4. That is, the operation of Q3 and Q4 as shown in FIG.
The output relationship is obtained. Therefore the input voltage Vs is rising and falling by the reference voltage Vu and V _l of the upper and lower as shown in FIG. 3 (c) are determined, the width of the drive signal function of the output Vo is defined. The Vu, sets the V _l small appropriate value θ2 than twice the previous angle .theta.1. When this relationship is converted into the output voltage of the position detector, the results are as shown at positions a, b, c, and d in FIG. 2 (c). However, it is desirable that θ2 be arranged as equally as possible on both sides with the set position b of the position detector 3 as the center.

Next, the output Vo of S3 in the circuit of FIG. 3 passes through an integrating circuit composed of a resistor R1 and a capacitor C1, and then passes through the comparator Q5.
Are connected by the + input terminal. A reference voltage Vr divided by a resistor is input to a negative input terminal of Q5. The output of Q5 is input to the base of NPN switching transistor S4 and
The collector of 4 is connected to the base of the control NPN transistor S5 that is connected in series with the + side of the power supply. A resistor R2 is connected between the collector of S4 and the power supply + Vcc.

The operation when the motor of FIG. 1 is driven by the circuit as described above is as shown in FIGS. 5 (a) to 5 (c). The horizontal axis is the rotation angle, and the vertical axis is the voltage of each part. The measurement points are common to the symbols in the circuit of FIG. FIG. 5 (a) shows when the motor is rotating, FIG. 5 (b) shows when the rotor is constrained outside the range of the angle θ2 for some reason, and FIG. 5 (c) shows when the rotor is for some reason Shows waveforms of the respective parts when the position is restricted within the range of the angle θ2. FIG. 5 (a) and (b)
In this case, the operation is the same as that of the conventional driving method, but FIG.
When the rotor is constrained within the range of the angle θ2 as described above, the charging voltage of the capacitor C1 increases and the reference voltage
When it exceeds Vr, S4 turns on, S5 turns off and the power supply voltage + Vcc
Cut off supply.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of an outer rotor type brushless motor in which an iron core 5 having four salient poles and four coils is used as a stator. The tip shape of the salient pole portion of the stator core 5 is concentric with the rotation axis, and the gap length with the permanent magnet rotor 1 may be constant regardless of the location.

One position detector 3 for detecting the position of the ring-shaped permanent magnet rotor 1 magnetized to four poles in the radial direction is a stop position due to the non-excitation torque of the rotor, that is, between the stator core salient poles. The center portion of the air gap is disposed at an angle θ1 in the rotation direction (advance phase) with respect to d in FIG. 2 (b).

FIG. 3 shows a two-phase unipolar driving circuit. The output signal of the position detector 3 is applied to Q3, Q4 and S3 having a dead zone as shown in the input / output characteristics of FIG.
Dead zone portion θ2 of FIG. 2 (c) is, V _l, it can be set arbitrarily by Vu, as much as possible evenly on both sides around the setting position b of the position detector 3, smaller than twice the previous angle θ1 Set to an appropriate value θ2. The output Vo of the transistor S3 passes through an integrating circuit composed of the resistor R1 and the capacitor C1, and is then connected to the + input terminal of the comparator Q5. Q5−
A reference voltage Vr divided by a resistor is input to the input terminal. The output of Q5 is input to the base of an NPN switching transistor S4, and the collector of S4 is connected to the base of a control NPN transistor S5 in series with the + side of the power supply. S4
The resistor R2 is connected to the collector of the power supply and the power supply + Vcc.

FIG. 7 shows an example in which the present invention is applied to a two-phase bipolar drive circuit. The configuration and operation after the differential amplifier Q2 are the same as those in FIG.

FIG. 8 is a schematic sectional view of another embodiment to which the present invention is applied, which is a cross-sectional view of a two-pole, two-coil iron-core brushless motor, and its driving circuit is common to FIG.

FIGS. 9 and 10 are plan views showing a permanent magnet rotor and a stator of a flat type ironless brushless motor having four poles and two coils, and the drive circuit is the same as that of FIG.

It is of course possible to apply only the drive circuit of FIG. 3 or FIG. 7 of the present invention to the conventional brushless motor of FIG. 12 (a), but in that case, the rotor is stopped by the non-excitation torque of the rotor. A similar operation can be obtained by noting that the position changes and d in FIG. 2 becomes the position d in FIG.

Also, a three-phase brushless motor with three position detectors,
The same operation can be performed for a drive circuit of a four-phase brushless motor having two position detectors by adding a circuit after the differential amplifier Q2.

[Effects of the Invention] As described above, the present invention provides a detector for detecting the position of a rotor, a signal processing circuit for processing an output signal of the detector, and switching for flowing a current to an armature coil based on a signal obtained therefrom. And a drive circuit for a brushless motor having a circuit, wherein a part of the signal processing circuit has a dead zone characteristic, and when the output signal of the detector is within a range of the dead zone for a predetermined time or more, the drive is performed. The power supply to the circuit was cut off.

In addition, by avoiding the problem of the dead point of the brushless motor by the operation of the protection circuit, the salient pole portion shape of the stator iron core can be designed with a symmetrical and constant gap length. Becomes unnecessary and becomes easy. Further, since the shape of the salient pole portions of the stator iron core is symmetric, even when the rotation direction of the motor is reversed, it is not necessary to turn the stator iron core upside down, and this can be easily performed by selecting a drive circuit. Further, since the gap length between the stator core salient pole portion and the permanent magnet rotor is constant, it is possible to achieve many effects such as efficient motor design.

[Brief description of the drawings]

1 to 5 are explanatory views of an embodiment of the present invention. FIG. 1 is a cross-sectional view of a brushless motor according to the present invention, and FIG. 2 (a) is a development view of a relationship between a rotor and a stator of the motor. , FIG. 2 (b) is an enlarged view of the main part of FIG.
2 (c) is a waveform diagram showing the output voltage of the position detector, FIG. 3 is a drive circuit diagram, and FIGS. 4 (a), (b) and (c) are diagrams of a signal processing circuit constituting a dead zone. (A) is a circuit diagram,
(B) is a state diagram of the operation, (c) is an input / output characteristic diagram, FIG. 5 is a waveform diagram of each part in each state, and (a) is a waveform diagram showing a state of each part of the drive circuit during rotation. (B) is a waveform diagram showing the state of each part of the drive circuit when the rotor is restrained outside the range of dead zone θ2, and (c) is driving when the rotor is restrained within the range of dead zone θ2. FIG. 3 is a waveform diagram showing a state of each part of the circuit. 6 (a), 6 (b) and 6 (c) are diagrams for explaining the arrangement of a position detector when only the drive circuit of the present invention is applied to a conventional brushless motor, and FIG. FIG. 8 is a cross-sectional view of a motor according to another embodiment of the present invention, FIG. 9 is a plan view of a rotor of another embodiment of the present invention,
FIG. 10 is a plan view of a stator applied to the rotor of FIG. 11 (a) to 11 (e) are drawings for explaining a conventional problem, in which (a) is a drive circuit diagram, (b) to (d) are plan views for explaining an operation state of a rotor, and (e). ) Is a characteristic diagram showing a generated torque and a dead point, FIGS. 12 (a), (b) and (c) are explanatory views of an improved conventional motor, (a) is a sectional view, and (b) is a drive FIG. 4C is a circuit diagram of the circuit, and FIG. 4C is a characteristic diagram illustrating generation of a synthetic torque. DESCRIPTION OF SYMBOLS 1 ... Permanent magnet rotor 2 ... Rotor yoke 3 ... Position detector 4, 4 '... Armature coil 5 ... Stator iron core 6 ... Dead zone part 7 ... Comparator, amplifier 8 ... Integration circuit

Claims (1)

(57) [Claims] 1. A detector for detecting a position of a rotor, a signal processing circuit for processing an output signal of the detector, and a switching for obtaining an output signal of the signal processing circuit and flowing a current to an armature coil. And a drive circuit for a brushless motor including a circuit, wherein a part of the signal processing circuit is provided with a dead zone characteristic, and the driving is performed when an output signal of the detector is within a range of the dead zone for a predetermined time or more. A drive circuit for a brushless motor, wherein supply of power to the circuit is cut off.