JP2557977B2 - Brushless motor drive circuit - Google Patents

Description

The present invention relates to a drive circuit for a sensorless brushless motor.

(Prior Art) A conventional general brushless motor has a magnetic pole detecting means such as a Hall element, and energizes each drive coil according to a detection signal of the magnetic pole detecting means to rotate a rotor. ing. FIG. 8 shows an example of the drive circuit. An origin detection unit 24 and an encoder 25 are integrally attached to a rotary shaft 22 that is integral with a rotor 23 of a motor 21, and an origin signal from the origin signal detection unit 24 is output. Incremental signals P ₁ and P _{2 with} a phase difference of 90 ° from P ₀ and the encoder 25 and detection signals PA, PB and PC from magnetic pole detection means such as a Hall element accompanying the rotation of the rotor 23.
Is input to the control circuit 26. The control circuit 26 controls the drive circuit 27 based on the above signals to drive the u, v, and w drive coils of the motor 21.

However, the brushless motor shown in FIG. 8 has the following various problems caused by using the magnetic pole detecting means. That is, since it is necessary to dispose the magnetic pole detection means inside the rotor, it is difficult to reduce the size. Since the number of terminals of the magnetic pole detection means is large, it becomes difficult to route the circuit pattern on the circuit board. When a Hall element is used as the magnetic pole detection means, there are variations in the chip position within the package, and the motor characteristics also vary. The output of the magnetic pole detection means is obtained by detecting the leakage magnetic field of the drive magnet.However, when the current of the drive coil increases, the magnetic field from the stator, which is not the original signal, jumps into the magnetic pole detection means, and the phase of the output of the magnetic pole detection means. Misalignment, and the rectification timing shifts.

Therefore, in order to solve the above problems, as shown in FIG. 9, a brushless motor drive circuit without a magnetic pole detecting means was developed, and the drive circuit was integrated into an IC as a sensorless brushless motor drive circuit. ing. The example described in JP-A-60-180494 is an example thereof, and the counter electromotive force of each drive coil is detected, and the magnetic pole position of the rotor is detected from this counter electromotive force.

(Problems to be Solved by the Invention) According to the invention described in the above publication, various problems caused by having the magnetic pole detection means can be solved.
However, since it is necessary to detect the counter electromotive force, even if the power is on, the counter electromotive force cannot be obtained once the power is stopped, and the initial operation must be performed again to detect the magnetic pole. Also, when the power is turned on, it is necessary to move the rotor greatly when performing the position detection operation of the rotor, that is, the initial setting operation. Therefore, for example, when the motor and the load are directly connected, the rotor position is It could not be used if the motor does not move during the detection operation.

The present invention has been made in order to solve the problems of the prior art, and in a brushless motor having no magnetic pole detecting means such as a Hall element, for example, the resolution of the encoder is about 2 to 5 pulses. It is an object of the present invention to provide a drive circuit that can perform an initial setting operation with almost no movement of a rotor.

Another object of the present invention is to provide a drive circuit for a brushless motor that does not require an origin signal detector.

(Means for Solving the Problem) The present invention relates to an energizing unit that energizes a drive coil to generate a rotating magnetic field, a rotor that has a permanent magnet and is rotationally driven by the rotating magnetic field, and a rotor. An encoder that outputs a rotation signal corresponding to the rotation position, a position detection unit that detects the rotation position of the rotor based on the rotation signal output from the encoder, and a rotation position of the rotor that receives the output of the position detection unit and a position command signal as input. Position control means for controlling, and an over-rotation detection means which receives the output of the position detection means and detects whether the position control system changes from negative feedback to positive feedback to rotate the rotor by a predetermined amount or more; First logical operation means for sequentially controlling the energizing means to control the exciting current to the drive coil, and an output from the over-rotation detecting means as an input to detect a position where the rotor starts to rotate by a predetermined amount or more. Along with
It is characterized by comprising a second logical operation means for calculating the initial position of the rotor from the detected position.

(Operation) If the pattern of the exciting current controlled by the first logical operation means has a predetermined correspondence with the position of the rotor, the rotor rotates. However, since the initial position of the rotor before power-on is indefinite, there is no correspondence between the exciting current pattern at power-on and the rotor position, and the rotor cannot rotate. The first logical operation means sequentially controls the energizing means and the exciting current so that the rotor starts to rotate. When the rotor rotates by a predetermined amount or more, the position control system changes from negative feedback to positive feedback, which the over-rotation means detects. The second logical operation means is
The detection output from the over-rotation detecting means detects the position where the rotor starts to rotate by a predetermined amount or more, and calculates the initial position of the rotor from this detected position.

(Example) Hereinafter, an example of a drive circuit for a brushless motor according to the present invention will be described, but before that, an outline of the present invention will be described.

Since the initial position θo of the rotor before the power is turned on is indefinite, the energization pattern of the exciting current to the drive coil and the rotor position θf deviate from a predetermined correspondence. When the coil is energized in this state, the position command is 0 in the initial state, and the position control loop for stopping is applied, so that the rotor cannot rotate. Strictly speaking, the rotor repeats rotation in the forward direction and the reverse direction alternately by a small angle, but in the present invention, this state is defined as “stop”.

When the energizing pattern of the exciting current to the drive coil is changed by changing the command signal θc that determines the exciting current pattern, the transfer function from the current command of the position control loop to the torque output changes, and when a certain point is reached, the position control loop Is positive feedback,
That is, the motor goes into an oscillating state and the position control does not work, and the motor runs away. In the present invention, this state is defined as “rotation” in the sense that the state has rotated by a certain amount or more.

In the present invention, θc is changed to detect θc at a point where the position control loop changes from negative feedback to positive feedback, and when that point is θd, θd = 90 °, and from the relationship of θd = θc−θf. , The initial position θo of the rotor position is obtained.

When the initial position θo of the rotor is determined, the command signal θc that determines the exciting current pattern can be set to θc = θf, and the command signal θc can be sequentially changed to freely rotate the motor.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In FIG. 1, the rotor indicated by reference numeral 1 is depicted as being composed of a permanent magnet having a pair of magnetic poles of NS for simplification of description. The stator has a three-pole structure of 2u, 2v, 2w, and drive coils 3u, 3v, 3w are wound around each stator. Each drive coil 3u, 3 v, the 3w are excitation currents Iu, Iv, Iw is energized through amplifier A _1, A _2, A ₃ of the energizing means, thereby the stator 2u, 2
A rotating magnetic field is generated in v and 2w.

An encoder E is connected to the rotor 1, and the encoder E outputs a two-phase pulse-shaped rotation signal whose phase is deviated, for example, by 90 ° according to the rotation of the rotor 1. Here, in order to simplify the explanation, the resolution of the encoder E is set to 360PP.
R, that is, one pulse is output for a rotation angle of 1 °. The rotation signal output from the encoder E is input to the up / down counter C ₁ and also to the position detecting means C _{2 including} an up / down counter,
Further, it is input to the speed detector Sd. The position detecting means C ₂ is
The rotation position of the rotor is detected by the rotation signal. The output e of the position detection means C ₂ is input to the position control means 5 as a position feedback signal, and the deviation from the position command signal d is obtained. The position command signal d is a position command Pref when the first switching means SW ₁ selects a contact, and when the switching means SW ₁ selects a contact, the position designation Prefo (= 0). Output e of position detecting means C ₂
Is also input to the over-rotation detecting means F. The over-rotation detecting means F detects from the output e whether or not the rotor has rotated by a predetermined amount or more, and the detected output f is input to the _second logical operation means B ₂ which is a central processing unit (CPU). .

The second logical operation means B ₂ detects the position at which the rotor 1 rotates by a predetermined amount or more based on the output f from the over-rotation detecting means F, and at the time of rotation 1 from this detected position.
The initial position θo of is calculated. The second logical operation means B ₂ is
The initial value of the counter C ₁ is set by the calculated initial position θo, and the reset signal g is input to the position detecting means C ₂ . The second logical operation means B ₂ exchanges data with the _first logical operation means B ₁ . The first logical operation means B ₁ is for controlling the exciting currents to the drive coils 3u, 3v, 3w by sequentially controlling the amplifiers A ₁ , A ₂ , A ₃ as energizing means, and the exciting current pattern Outputs a command signal θc ₂ for determining. This command signal θc ₂ is the second switching means.
When SW ₂ selects the contact, it is input to the memories R ₁ , R ₂ and R ₃ as the designated signal θc. When the second switching means SW ₂ selects the contact, the counting signal θc ₁ from the counter C ₁ is input to the memories R ₁ , R ₂ and R ₃ as the command signal θc. The memories R ₁ , R ₂ and R ₃ store, as data, the excitation current waveforms that are applied to the drive coils 3u, 3v and 3w, respectively. However, α: constant, θc: memory address, a, b, c: memory output. The outputs a, b, c of each memory are converted into analog signals by the digital / analog converters D ₂ , D ₃ , D ₄ .

Position detection means obtained by the position control means 5
The deviation signal between C ₂ , output e and position command signal d is digital
After being converted into an analog signal by the analog converter D ₁ , it is amplified by the position deviation amplifier Com ₁ . This position deviation amplifier Com ₁
Is further output by the speed deviation detecting means 6 to the speed detector.
The deviation from the velocity signal from Sd is determined. This deviation signal is amplified by the speed deviation amplifier Com ₂ , and the torque command Tr
It is input as ef to the three multipliers M ₁ , M ₂ and M ₃ . Each multiplier
M _1, M _2, M ₃ in the torque command Tref and the digital-to-analog converter D _2, D _3, D ₄ in converted into an analog signal a the output a of the memory, b, the product of the c prompted , The amplifier A respectively
Input to ₁ , A ₂ and A ₃ .

The switching control of the _first switching means SW ₁ is performed by the second logical operation means B.
₂ and the switching control of the second switching means SW ₁ is performed by the first
Is performed by the logical operation means B ₂ .

Next, the operation of the above embodiment will be described with reference to FIGS. 2 to 7.

In the present invention, an initial setting operation is first performed when the power is turned on, and then a normal operation is performed. However, for convenience of description, the normal operation will be described first.

The data stored in each of the memories R ₁ , R ₂ , and R ₃ as the waveform of the current flowing through each of the drive coils 3u, 3v, and 3w is expressed by the equation (1) above.
It is as follows. Further, the torque constants Ktu, Ktv, Ktw of each phase with respect to the rotor position θf can be considered as the following equations.

However, ψu, ψv, ψw: the number of magnetic flux linkages of each coil Here, according to the equation (1), the current flowing in each group is However, β is a constant.

Therefore, the torque Tg generated by the motor is the product of the torque constant and the phase current, and Tg (θf, θc) = Tref · β · Kt {sin θc · sin θf + sin (θc-120) · sin (θf-120) + sin (θc + 120) ) ・ Sin (θf + 120)} ... (4) Assuming that θc = θf, Tg is given by the following equation.

Tg = (3/2) · Tref · β · Kt ··· (5) Therefore, the motor generates maximum torque when θc = θf.

Next, the operation of the counter C ₁ will be described. The input / output relationship of the counter C ₁ is as shown in FIG. 2, and the number of pulses output from the encoder E is 360 when the rotor 1 makes one rotation.
Then, the counter C ₁ is cleared and its output θc ₁ becomes 0.
Becomes Also, the rotation direction of the rotor is detected from the phase difference between the output pulses of the two phases of the encoder E, and upcounting or downcounting is switched depending on the rotation direction. Output .theta.c ₁ of the counter C ₁ by operation of the counter C ₁
And the rotor position θf always have a one-to-one correspondence. Therefore, if the second switching means SW ₂ is switched to the contact side, the memories R ₁ , R ₂ and R ₃ output a current pattern signal according to the rotor position θf, and according to this pattern. Since an exciting current is applied to each of the drive coils 3u, 3v, 3w, the rotor 1 is rotationally driven.

In the normal operation, the first switching means SW ₁ is on the contact side, the position command Pref is input, and it is rotationally driven to the position according to this command.

Next, the initial setting operation will be described. The flow of the initial setting operation is shown in FIG. 6 and the timing chart is shown in FIG. When the power is turned on, the initial value of the counter C ₁ and the position of the rotor 1 do not have a predetermined correspondence, that is, θc = θf, so the initial operation is performed to detect the position of the rotor, enter the .theta.o corresponding to the position of the counter C _1, the initial value of the counter C ₁ is set to the above values .theta.o. Hereinafter, the initial setting operation will be specifically described.

In the normal operation, both the first and second switching means SW ₁ and SW ₂ are on the contact side, but they are switched to the side when the power is turned on.
Therefore, the position command becomes the position command Prefo at the time of initial operation, and the value becomes 0. When the power is turned on, the position detecting means C ₂ is reset and its output becomes 0.

Rotor position θf and command signal θ of current flowing to coil
The difference from c, that is, θc−θf is set to θd. FIG. 3 shows the relationship between this θd and the generated torque Tg, which can be expressed as Tg = (3/2) · Tref · β · Kt · cos θd (5).

The simple block diagram of the embodiment shown in FIG. 1 is shown in FIG. In FIG. 5, H is the transfer function of the position deviation amplifier Com ₁ , I is the transfer function of the speed deviation amplifier Com ₂ , N is the gain of the position detecting means C ₂ , M is the transfer function of the speed detector Sd, J is the motor and It is the inertia of the load. As is clear from FIGS. 3 and 5, when θd is between 90 ° and 270 °, the feedback of velocity and position becomes positive, that is, positive feedback, the control system oscillates and becomes unstable, and the motor becomes unstable. I will run out of control. The over-rotation detecting means F is turned on by the runaway of the motor.

In this embodiment, the value of θc is swept while the motor is stopped by the position control loop to change the value of θd. Then, when θd falls within the range of 90 ° to 270 ° with the point indicated by “a” in FIG. 3 as a boundary, a runaway begins, so the point at which this runaway begins is detected by the over-rotation detecting means F, and at that time The value of θc of θc ′ is taken.
The second logical operation means B ₂ applies the above value θc ′ to θo = θc′−91 (6), finds the rotor position θf at that time, and counts the value by the counter C ₁ Initial setting value θo.

The value obtained by the equation (6) is output as the command signal θc ₂ via the _first logical operation means B ₁ , and the rotor is again stopped by the position control. After confirming the stop, the second logical operation means B ₂
Thus, the counter C ₁ is set to the initial value θo. After that, the first and second switching means SW ₁ , SW ₂ are switched to the contact side, and the normal operation is started.

Note that Fth shown in FIG. 4 is a threshold value of the over-rotation detecting means F. The threshold value Fth is slightly larger than the maximum value of noise when the position control is operating normally, and is set to, for example, about 2 pulses, and at most about 5 pulses.

Next, how the above operation is performed in a specific case will be described with reference to FIG.

In case 1), it is assumed that θf = −60 ° (300 °). Initially, since θc ₂ = 0, θd = 0 = − (− 6
0) = 60. In FIG. 7, the point is "a", the sign of Tg is +, and the rotor stops. θc ₂ increases by 1 and θc ₂ = 30
When it becomes +1 the rotor starts to rotate. Therefore, the initial position θo of the rotor is θo = 31−91 = −60 (°). However, since θo = 60 <0, θo = 360−60 = 300 (°). Therefore, θo = θf. Here, −90 in equation (6) is set to − (90 + 1) = − 91, which is the point where the runaway surely starts.

In case 2), θf = -120 ° (240 °). Initially, since θc ₂ = 0, θd = 0 = − (− 12
0) = 120. In FIG. 7, the point is “b”, the sign of Tg is −, and the rotor rotates. When θc ₂ becomes 180, θd = 1
80-(-120) = 300. In FIG. 7, it is a point “C”. θc ₂ increases by 1 and θc ₂ = (150 + 180 + 1) = 331
When it reaches (°), the rotor starts to rotate. Therefore, the rotor position θo = 331−91 = 240 (°) and θo = θf.

In case 3), θf = −200 ° (160 °). Initially, since θc ₂ = 0, θd = 0 = − (− 20
0) = 200. In FIG. 7, the point is “d”, the sign of Tg is −, and the rotor rotates. When θc ₂ becomes 180, θd = 1
80-(-200) = 380. In FIG. 7, the point is “e”. When θc ₂ increases by 1 and becomes θc ₂ = 180 + 71 = 251 (°), the rotor starts rotating. Therefore, the rotor position θo =
251-91 = 160 (°) and θo = θf.

In case 4), it is assumed that θf = −345 ° (15 °). Initially, since θc ₂ = 0, θd = 0 = − (− 34
5) = 345. In FIG. 7, it is the point “F”, the sign of Tg is +, and the rotor stops. θc ₂ increases by 1 and θc ₂ = 10
When it reaches 5 + 1, the rotor begins to rotate. Therefore, the rotor position θo = 106−91 = 15 (°) and θo = θf.

As another embodiment, the over-rotation detecting means F in the embodiment shown in FIG. 1 uses the output of a speed detector Sd for detecting the speed by counting the number of speed signal pulses within a unit time as the position detecting means C ₂ The position detection means C ₂ may have the same function as the speed detector Sd. Further, the speed detector Sd may be one that detects an analog signal and outputs a signal that turns on when the speed exceeds a specified speed.

(Effect of the Invention) According to the present invention, the energizing means is sequentially controlled by the logical operation means to control the exciting current, and when the rotor starts to rotate and rotates for a predetermined amount or more, this position is detected to detect the rotor. Since the initial position is calculated, when calculating the initial position of the rotor, the rotor may be rotated by a few pulses at the output level of the encoder, which is equivalent to almost no movement. Therefore, for example, it is possible to apply the present invention to a drive target such as a robot or a machine tool that must not move in the initial motion.

Also, unlike the conventional sensorless brushless motor, it is not necessary to detect the back electromotive force of the drive coil, so there is no need to perform the initial position detection operation again even if the rotor stops while the power is on. Therefore, the rotational position can be detected stably and reliably.

Further, it is not necessary to provide any special element for detecting the origin signal.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a brushless motor drive circuit according to the present invention, FIG. 2 is a timing chart showing the operation of the counter in the above embodiment, and FIG. 3 is an exciting current pattern and a rotor position. 4 is a timing chart showing the operation of the above embodiment, FIG. 5 is a block diagram showing the operation of the above embodiment in a simplified manner, and FIG. 6 is an initial setting in the above embodiment. FIG. 7 is a flow chart showing the operation, FIG. 7 is a diagram for explaining the operation of the above embodiment in a more specific case, and FIG. 8 is a block diagram showing an example of a conventional brushless motor drive circuit.
FIG. 1 is a block diagram showing another example of a drive circuit for a conventional brushless motor. 1 …… Rotor, 2u, 2v, 2w …… Stator, 3u, 3v, 3w …… Drive coil, Iu, Iv, Iw …… Exciting current, A ₁ , A ₂ , A ₃ …… As energizing means amplifier, 5 ...... position control means, E ...... encoder, F ...... over rotation detecting means, C ₂ ...... position detection means, B ₁ ...... first logical operation means, B ₂ ...... second logic operation Means, d ... Position command signal, e ... Output of position detecting means.

Claims (1)

(57) [Claims] 1. A rotor having an energizing means for supplying an exciting current to a driving coil to generate a rotating magnetic field in a stator, a rotor having a permanent magnet and driven to rotate by the rotating magnetic field, and a rotor for rotating the rotor. An encoder that outputs a rotation signal, a position detection unit that detects the rotation position of the rotor based on the rotation signal output from the encoder, and a rotation position of the rotor that receives the output of the position detection unit and a position command signal. And a position control means for controlling the above, and an over-rotation detection means for detecting whether the position control system changes from negative feedback to positive feedback to rotate the rotor by a predetermined amount or more by using the output of the position detection means as an input. A first logical operation means for sequentially controlling the energizing means to control an exciting current to the drive coil; and an output from the over-rotation detecting means as an input, the rotor is rotated a predetermined number of times or more. Detects the to start position, the brushless motor driving circuit comprising and a second logical operation means for calculating the initial position of the rotor from the detected position.