Brushless DC motor

Abstract: A brushless DC motor (19) comprises a rotor possessing a plurality of magnetic poles, a stator winding with plural phases (181,182,183) disposed at a specific gap to the rotor, a sensor (11) for generating a sensor signal of plural phases showing a state of rotation of the rotor depending on the rotation of the rotor, a direction detector (13) for detecting a rotating direction of the rotor from the sensor signal of plural phases and issuing a direction signal (d), an initial phase detector (15) for issuing a first phase signal (f1) depending on the direction signal and producing an initial count value corresponding to a position of the rotor, a counter (14) for setting an initial value corresponding to the initial count value, increasing or decreasing the count value depending on at least one sensor signal and the direction signal and issuing a second phase signal (f2), a waveform generator (16) for generating a position signal of plural phases depending on the first phase signal or the second phase signal, and a power supply circuit (17) for supplying an electric power to the stator winding depending on the position signal of plural phases.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brushless DC motor, and more particularly to a brushless DC motor which does not require a position sensor for detecting the rotating position of a permanent magnet rotor. 2. Description of the Prior Art The brushless DC motor is longer in life and lower in electric noise level as compared with a DC motor with brushes because it has no mechanical contact. It is accordingly used widely in industrial equipment and video and audio equipment where high reliability is required lately. Conventionally, the brushless DC motor of this type used a position sensor (for example, Hall element), which corresponds to the brush, for changing over the conductive phases of the stator windings. The position sensor itself is not inexpensive, and it requires complication in the adjustment of mounting position of the sensor and increase in the number of wirings, which results in a much higher cost of the brushless DC motor as compared with the DC motor with brushes. Besides, the motor structure is often limited because the position sensor must be assembled in the motor. Recently, in the downsizing trend of appliances, the motor is becoming smaller and thinner, and the position for mounting the position sensor such as the Hall element is not available sufficiently. Accordingly, several brushless DC motors without position sensor have been so far proposed. As the brushless DC motor without position sensor, for example, the one making use of the output signal of the frequency generator attached to the motor is known. That is, the output pulses of the frequency generator for generating pulses depending on the rotation of the rotor are counted by a counter, and drive currents of a preset current pattern are sequentially passed to three-phase stator windings depending on the count value, thereby rotating the permanent magnet rotor (for example, Japanese Patent Publication No. 63-262088). In such constitution, however, since the initial position of the rotor is not known when turning on the power, a special reset signal generating circuit is provided in the brushless DC motor as shown in the above prior art, and the counter is reset by the reset signal when the power is turned on, while a specific reset current is supplied to the stator windings so that the rotor and the stator windings may be preliminarily set in a specific positional relation. However, when the specific reset current is supplied to the stator windings in order to determine the initial position, the rotor begins to rotate, and the position of the rotor oscillates about the specified position, not standing still at the specified position in a short time. As a result, the starting time is long because the operation cannot be transferred in a short time from the reset mode for supplying the specific reset current to the stator windings when turning on the power to stop the rotor at the specified position, to the normal position detecting mode for counting the output pulses of the frequency generator depending on the rotation of the rotor. It cannot be therefore used in applications requiring a short starting time such as machines repeating rotating and stopping frequently. In the brushless DC motor in the above prior art, since the rotor is rotated forcedly to a specified position in the reset mode, the rotor may largely rotate reversely depending on the initial position of the rotor. Hence, it can be used only in machines allowing a wide reverse rotation, and the scope of application is considerably limited. Furthermore, in the brushless DC motor in the above prior art, if the relative positions of the rotor and stator windings are set in the specified relation in the reset mode, if the rotor is loaded, the relative positions of the rotor and stator windings may vary largely depending on the magnitude of the load. Hence, the rotor may not be fixed at the specified position in the reset mode. Therefore, in the brushless DC motor shown in the above prior art, when the reset mode is transferred to the normal position detecting mode for counting the output pulses of the frequency generator depending on the rotation of the rotor, the current phase supplied to the stator windings is largely deviated from the normal phase, and high efficiency drive cannot be realized. Therefore, the brushless DC motor shown in the prior art is usable only in the application in which the motor is unloaded when the power is turned on. Additionally, EP-A-0313046 discloses a motor control apparatus for a brushless motor which counts output signals from an encoder upon rotation of the rotor and performs switching of a motor coil according to the count value, in particular when the count value reaches a predetermined value. In this document, when it is desired to start up the motor, one of the two phase coils is energized in a fixed direction. The magnetic pole of the energized stator phase and the magnetic pole of the rotor interact and an up stroke down counter is reset to zero by reset signal. The start up position is thereby determined. US-4641066 also discloses a control apparatus for a brushless motor. The apparatus detects a suitable starting point for the rotor and drives the motor to that selected point to effect control of the starting operation of the motor. The present invention provides a brushless DC motor comprising: a rotor possessing a plurality of magnetic poles; plural phase stator windings disposed at a specific gap from the rotor; sensor means for generating plural phase sensor signals showing a state of rotation of the rotor depending on the rotation of the rotor; direction detecting means for detecting the direction of rotation of the rotor from the plural phase sensor signals and producing a direction signal; initial position detecting means for issuing a first phase value, and for detecting an initial count value corresponding to the position of the rotor; counter means, in which a count value is set initially according to the initial count value, for increasing or decreasing the count value depending on the direction signal and at least one of the plural phase sensor signals to produce a second phase value; waveform generating means (16) for generating plural phase position signals depending on the first phase value or second phase value; and power supply means for supplying electric power to the plural phase stator windings depending on the plural phase position signals, characterized in that the initial position detecting means comprises; phase value increasing or decreasing means for increasing or decreasing the first phase value depending on the direction signal; phase value storing means for storing a plurality of values of the first phase value depending on a change of the direction signal; and initial count value calculating means for calculating the initial count value from at least two values of the first phase value stored in the phase value storing means; the initial position detecting means being arranged to detect the initial count value corresponding to the position of the rotor by oscillating a rotary magnetic field generated in the plural phase stator winding in normal and reverse directions. The invention thus advantageously presents a brushless DC motor capable of detecting a positional relation between the rotor and the stator winding in a short time when the power is turned on, and promptly changing over from the phase matching mode when the power is turned on to the normal position detecting mode for counting the output pulses produced depending on the rotation of the rotor. The invention also advantageously detects the position of the rotor precisely regardless of the magnitude of the load if the motor is already loaded when the power is turned on, and further detects the position of the rotor within a remarkably small amount of rotation of the rotor. Therefore a brushless DC motor is provided capable of driving at a high efficiency although no position sensor is needed, and applicable in a wide scope. Having the above constitution, the brushless DC motor of the invention counts by the counter means the output signals of the sensor means generated depending on the rotation of the rotor. Since the position signal is produced on the basis of this count value, a position sensor required in the conventional brushless DC motor is not needed. Therefore, unlike the conventional brushless DC motor, the position sensor is not needed, and the complication in adjustment of mounting position of the sensor and the number of wirings can be reduced, so that the cost can be saved significantly. Besides, since the position sensor is not needed in the motor, the motor is not limited structurally, and can be further reduced in size and thickness. Furthermore, the initial phase detecting means produces the first phase signal depending on the rotating direction of the rotor, while the waveform generating means produces the position signal depending on the first phase signal, thereby detecting the position of the rotor. Hence, the position of the rotor can be detected by a small extent of rotation, not depending on the initial position of the rotor. Even if the rotor is loaded, yet, the position of the rotor can be detected accurately. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram showing the constitution of an embodiment of a brushless DC motor of the invention, Fig. 2 is a circuit composition diagram showing an embodiment of a direction detector circuit of the invention, Fig. 3 is a signal waveform diagram of the parts of the direction detector circuit in Fig. 2, Fig. 4 is a signal waveform diagram of the parts in normal rotation of a brushless DC motor of the invention, Fig. 5 is a vector diagram showing the relation of magnetic pole vector Φ of permanent magnet rotor and magnetomotive force vector I generated by a stator winding in normal rotation of a brushless DC motor of the invention, Fig. 6 is a block diagram showing the constitution of direction detector circuit, counter unit, initial phase detector, and waveform generator for composing a brushless DC motor of the invention, Fig. 7 is a flow diagram in an embodiment for operation of the selector of the invention, Fig. 8 is a flow diagram in an embodiment for processing of position detecting mode in usual rotation, Fig. 9 is a flow diagram in an embodiment for phase matching operation, Fig. 10 is a vector diagram of magnetic pole vector Φ and magnetomotive force vector I for explaining the amount of rotation in phase matching operation, Fig. 11 is a vector diagram of magnetic pole vector Φ and magnetomotive force vector I for explaining the phase matching operation, Fig. 12 is a vector diagram of magnetic pole vector Φ and magnetomotive force vector I for explaining the phase matching operation, and Fig. 13 is a diagram showing the configuration of a permanent magnet rotor and a stator winding. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, some of the embodiments of the brushless DC motor of the invention are described in detail below. Fig. 1 is a block diagram showing the constitution of a brushless DC motor in an embodiment of the invention. A permanent magnet rotor 19 and three-phase stator windings 181, 182, 183 in Fig. 1 are disposed as shown in Fig. 13. In Fig. 13 (a), the permanent magnet rotor 19 which rotates together with a rotary shaft 1302 is disposed oppositely to a stator 1301. In the permanent magnet rotor 19, as shown in Fig. 13 (b), plural poles (eight poles herein) are disposed in a disc form at equal intervals along the circumferential direction. In the stator 1301, as shown in Fig. 13 (c), a plurality of flat windings (six herein) 181a, 182a, 183a, 181b, 182b, 183b are disposed at equal intervals in a disc form about the rotary shaft 1302 on a flat plane. The flat windings remote from each other by 180 degrees are mutually connected to compose three-phase stator windings 181, 182, 183. A frequency generator (sensor means) 11 in Fig. 1 generates two-phase frequency signals m1, m2 different in phase from each other, in proportion to the rotation of the permanent magnet rotor 19. The two-phase frequency signals m1, m2 are fed in a waveform shaping circuit 12 to be converted into square wave signals s1, s2, and entered in a direction detecting circuit (direction detecting means) 13. The direction detecting circuit 13 issues a direction signal d depending on the normal or reverse rotating direction of the permanent magnet rotor 19. A counter unit 14 receives the square wave signal s1 and the direction signal d issued by the direction detecting circuit 13, and counts up or counts down the number of pulses of the square wave signal s1 generated depending on the rotation of the permanent magnet rotor 19 according to the rotating direction of the permanent magnet rotor 19. The counter unit 14 issues the value corresponding to the count value c as a second phase value f2 (second phase signal). An initial phase detecting unit 15 receives the direction signal d of the direction detecting circuit 13, rotates the rotary magnetic field generated in the stator winding at the time of phase matching in the normal or reverse direction depending on the direction signal d, determines the initial position of the permanent magnet rotor 19 by calculation, and issues the initial count value c o to the counter unit 14. The initial phase detecting circuit 15 not only issues the initial count value c o to the counter unit 14, but also issues a first phase value f1 (first phase signal) to a selector unit 161 at the time of phase matching. The selector unit 161 selects either the first phase value f1 or second phase value f2 depending on the phase matching command st supplied in a terminal 163, and issues the selected phase value f to a position signal generator unit 162. A waveform generator unit (waveform generating means) 16 is composed of the selector unit 161 and position signal generator unit 162. The position signal generator unit 162 issues three-phase position signals p1, p2, p3 depending on the selected phase value f issued by the selector unit 161. A power supply unit 17 receives the three-phase position signals p1, p2, p3. The three-phase position signals p1, p2, p3 are amplified by driving amplifiers 171, 172, 173, respectively, and currents i1, i2, i3 proportional to the magnitude of the position signals p1, p2, p3 are supplied to stator windings 181, 182, 183. Thus, the brushless DC motor is composed of the permanent magnet rotor (rotor) 19, stator windings 181, 182, 183, frequency generator (sensor means) 11, direction detecting circuit (direction detecting means) 13, initial phase detector unit (initial phase detecting means) 16, counter unit (counter means) 14, waveform generator unit (waveform generating means) 16, and power supply unit (power supply means) 17. In thus composed brushless DC motor, the operation of the invention is described in detail below. First is explained the case in which the permanent magnet rotor 19 is rotating continuously (position detection mode). Fig. 2 is a circuit composition diagram in an embodiment of the direction detecting circuit 13, of which signal waveform diagram of parts is shown in Fig. 3. In Fig. 2, a D-type flip-flop circuit 21 receives two-phase square wave signals s1, s2 issued by the waveform shaping circuit 12. The square wave signal s1 is fed to a data input terminal D of the flip-flop circuit 21, while the square wave signal s2 is fed to a clock input terminal CK. Fig. 3 (a) shows square wave signals s1, s2 when the permanent magnet rotor 19 is rotating in normal direction, and Fig. 3 (b) shows square wave signals s1, s2 when the permanent magnet rotor 19 is rotating in reverse direction. The D-type flip-flop circuit 21 holds the state of the data input terminal D at every leading edge of the input signal to the clock input terminal CK, and delivers that state from the output terminal Q. Therefore, while the permanent magnet rotor 19 is rotating in normal direction as in Fig. 3 (a), the output Q of the D-type flip-flop circuit 21 is always in high potential state (hereinafter called the H state). On the other hand, while the permanent magnet rotor 19 is rotating in reverse direction, the square wave signal s1 is behind the square wave signal s2 by 90 degrees as shown in Fig. 3 (b), and the output Q is always in low potential state (hereinafter called the L state). As clear from the above, the rotating direction of the permanent magnet rotor 19 may be detected by the direction detecting circuit 13 in Fig. 2. That is, the direction signal d of the output of the direction detecting circuit 13 is in the H state while the permanent magnet rotor 19 is rotating in normal direction, and in the L state while rotating in reverse direction. The square wave signal s1 delivered by the waveform shaping circuit 12 and the direction signal d of the direction detecting circuit 13 are fed to the counter unit 14, and therefore the counter unit 14 counts up or counts down the pulses of the square waveform signal s1 depending on the direction signal d. That is, the number of pulses of the square wave signal s1 generated depending on the rotation of the permanent magnet rotor 19 is counted up or counted down depending on the rotating direction of the permanent magnet rotor 19, and therefore the rotation amount of the permanent magnet rotor 19 may be obtained from the count value of the counter unit 14. However, the count value of the counter unit 14 is unstable in the initial state right after turning on the power, and it is necessary to set a proper initial count value c o . The method of setting the initial count value c o is explained in detail in Fig. 9 in relation to the description of the operation of the phase matching mode. Fig. 4 is a signal waveform diagram of parts in normal rotation of the brushless DC motor of the invention. In Fig. 4, e1, e2, e3 are generated voltage waveforms induced in stator windings 181, 182, 183, respectively. On the other hand, p1, p2, p3 are three-phase position signals produced from the waveform generating unit 16, which are generated to be nearly in phase with the generated voltage waveforms e1, e2, e3 depending on the rotating position of the permanent magnet rotor 19. The position signals p1, p2, p3 are sinusoidal signal waveforms, and the power supply unit 17 amplifies the power of the position signals p1, p2, p3 in three phases, and sinusoidal three-phase drive currents i1, i2, i3 are supplied to the individual phases of the stator windings 181, 182, 183. As a result, by the three-phase drive currents i1, i2, i3, rotary magnetic fields are generated in the stator windings 181, 182, 183, and by the mutual action of the rotary magnetic field and the magnetic poles of the permanent magnet rotor 19, the permanent magnet rotor 19 receives the rotary force and rotates. Fig. 5 is a vector diagram showing the phase relation of the magnetomotive force vector of the rotary magnetic fields generated by the stator windings 181, 182, 183, together with the magnetic pole vector of the permanent magnet rotor 19. In Fig. 5, Φ denotes the magnetic pole vector showing the magnetic poles of the permanent magnet rotor 19, and I is the magnetomotive force vector of the rotary magnetic fields generated by the stator windings 181, 182, 183. Fig. 5 (a) is a vector diagram showing the phase rotation of the magnetic pole vector Φ and the magnetomotive force vector I when the permanent magnet rotor 19 is rotating in normal direction. Fig. 5 (b) is a vector diagram showing the phase relation of the magnetic pole vector Φ and the magnetomotive force vector I when the permanent magnet rotor 19 is rotating in reverse direction. The magnetic pole vector Φ obtains a rotary force by mutual action with the magnetomotive force vector I, and rotates in the direction indicated in Fig. 5. Here, in order that the permanent magnet rotor 19 rotates continuously, it is required to rotate the magnetomotive force vector I in the direction shown in the drawing depending on the rotation amount of the magnetic pole vector Φ . That is, the phase of the magnetomotive force vector I is always advanced in the rotating direction by 90 degrees from the phase of the magnetic pole vector Φ , and the rotation amount of the magnetic pole vector Φ is detected, and the magnetomotive force vector I must be rotated depending on that rotation amount. (The angle on the vector diagram expressing the magnetic pole vector Φ and the magnetomotive force vector I is called the angle expressed by electric angle.) Fig. 6 is a constituent diagram showing an embodiment of direction detecting circuit 13, counter unit 14, initial phase detecting unit 15, and waveform generating unit 16 for composing the brushless DC motor of the invention. In this embodiment, the counter unit 14, initial phase detecting unit 15, and waveform generating unit 16 are composed of arithmetic unit (calculating means) 61, memory 62, and D/A converters (digital-analog converting means) 63, 64, 65. The arithmetic unit 61 operates according to the specified built-in program mentioned below which is stored in the ROM (read only memory) region of the memory 62, takes in the square wave signal s1, direction signal d, direction command md fed in the terminal 141, and phase matching command st fed in the terminal 163, and calculates as specified by making use of the RAM (random access memory) region, thereby obtaining the selected phase value f. Consequently, depending on the selected phase value f, the arithmetic unit 61 refers to the function table of the sinusoidal wave of one period preliminarily stored in the ROM region of the memory 62, and determines three-phase digital position signals dp1, dp2, dp3 depending on the selected phase value f, and produces them to D/A converters 63, 64, 65, respectively. The D/A converters 63, 64, 65 convert the three-phase digital position signals dp1, dp2, dp3 to analog values respectively, and produces three-phase position signals pl, p2, p3. The built-in program stored in the ROM region of the memory 62 is described below. First is shown a flow diagram of a built-in program for operating the selecting unit (selecting means) 161 of the waveform generating unit 16 in Fig. 7. At step 71, the phase matching command st fed in the terminal 163 is entered. Then the processing at step 72 is done. At step 72, according to the data of the phase matching command st entered at step 71, the selection action in the next step is operated. When the phase matching command st indicates the phase matching mode, the action of the phase matching mode (step 73) is effected. When the phase matching command st indicates the phase detecting mode, the action (step 74) of the position detecting mode is carried out. At step 73, the action of the phase matching mode is operated. That is, the action of the initial phase detecting unit 15 and the action of the position signal generating unit 162 of the waveform generating unit 16 are effected, and the position of the permanent magnet rotor 19 is detected, while the initial count value c o corresponding to the position of the permanent magnet rotor 19 is calculated. Afterwards, the operation returns to the action of the step 71. At step 74, the action of the position detecting mode is carried out. That is, the action of the counter unit 14 and the action of the position signal generating unit 162 of the waveform generating unit 16 are carried out, and the processing in usual rotation is done. Afterwards, the operation returns to the processing of step 71. By carrying out these actions, either the action of the phase matching mode or the action of the phase detecting mode is selected depending on the phase matching command st entered in the terminal 163. That is, depending on the content of the phase matching signal st, either the output signal (second phase value) of the counter unit 14 or the output signal (first phase value) of the initial phase detecting unit 16 is selected as the input of the position signal generating unit 162, and therefore the action of the selector unit (selecting means) 161 is realized by processing as described above. The position detecting mode to be processed at the time of usual rotation is explained below by referring to the basic flow diagram shown in Fig. 8. At step 811, the initial count value c o calculated in the phase matching mode is set as the initial value of the count value c. That is, the count value c is set as the value of the initial count value c o . Later, the processing at step 821 is done. At step 811, the initial value setting part (initial value setting means) 81 is composed. The step 821 waits for arrival of the pulse of square wave signal s1. That is, if the pulse has not reached yet as the square wave signal s1 is entered, the processing of step 821 is done repeatedly until the pulse arrives. When the pulse of the square wave signal s1 arrives, the processing of step 822 is done. At step 822, the direction signal d of the direction detecting circuit 13 is entered. Then the processing of step 823 is done. At step 823, when the direction signal d is H, that is, when the permanent magnet rotor 19 is rotating in normal direction, the processing of step 824 is done. When the position signal d is L, that is, when the permanent magnet 19 is rotating in reverse direction, the processing of step 825 is done. At step 824, the counting of the count value c is increased by one. That is, the value adding one to the count value c is a new count value c. Then the processing of step 831 is done. At step 825, the counting of the count value c is decreased by one. That is, the value 1 is subtracted from the count value c to obtain a new count value c. Then the processing of step 831 is done. Here, the count value increase and decrease unit (count value increasing and decreasing means) is composed of step 821, step 822, step 823, step 824 and step 825, and the pulse of the square wave signal s1 is counted up or counted down depending on the direction signal d. At step 831, the direction command md of the terminal 141 is entered, and when the direction command md is a normal rotation command, the processing of step 832 is done. When the direction command md is a reverse rotation command, the processing of step 833 is done. At step 832, a specific value (a value corresponding to 45 to 135 degrees, preferably 90 degrees, as converted to the rotational angle of the magnetomotive force vector I) is added to the count value c, and the sum is issued as the second phase value f2. Then the processing of step 841 is done. At step 833, a specific value (a value corresponding to 45 to 135 degrees, preferably 90 degrees, as converted to the rotational angle of the magnetomotive force vector) is subtracted from the count value c to obtain the second phase value f2. Then the processing of step 841 is done. Here, the phase adjusting unit (phase adjusting means) 83 is composed of the step 831, step 832, and step 833. The operation of the first counter part (counter means) 14 in Fig. 1 is executed by the initial value setting part (initial value setting means) 81, count value increase or decrease unit (count value increasing or decreasing means) 82, and phase adjusting unit (phase adjusting means) 83. At step 841, to obtain the position signals p1, p2, p3, three addresses a1, a2, a3 for referring to the function table of sinusoidal wave for one period disposed in the ROM region in the memory 62 are calculated. That is, the phases of the position signals p1, p2, p3, are shifted by 120 degrees each (see Fig. 4), and therefore the three addresses a1, a2, a3 are calculated in the following equations. a1 = f2 a2 = f2 + (120) a3 = f2 - (120) In the above equations, (120) is the specified address value corresponding to 120 degrees as converted to the rotational angle of the magnetomotive force vector. Then the processing of step 842 is done. At step 842, on the basis of the three address values a1, a2, a3 obtained at step 841, the function table of the sinusoidal wave stored in the ROM region of the memory 62 is referred to, and three-phase digital position signals dp1, dp2, dp3 are obtained. Afterwards, processing of step 843 is done. At step 843, the three-phase digital position signals dp1, dp2, dp3 obtained at step 842 are delivered to the D/A converters 63, 64, 65 shown in Fig. 6. In the D/A converters 63, 64, 65, the digital position signals dp1, dp2, dp3 are converted to analog values, and position signals p1, p2, p3 shown in Fig. 4 are delivered. Consequently, the operation returns to the processing of step 821. The position signal output unit (position signal output means) 84 is composed of the step 841, step 842, and step 843. The position signal generating unit 162 in Fig. 1 is composed of the position signal output unit (position signal output means) 84, memory (memory means) 62, and D/A converters (digital-analog converting means) 63, 64, 65. Furthermore, the waveform generating unit 16 is composed of the selector (selecting means) 161 and position signal transmitter 162 in Fig. 7. As a result of the above processing, corresponding to the rotation of the permanent magnet rotor 19, the position signals p1, p2, p3 are issued to the power supply unit 17. In the power supply unit 17, sinusoidal drive currents i1, i2, i3 are supplied to the stator windings 181, 182, 183. That is, square wave signals s1, s2 are produced depending on the rotation of the permanent magnet rotor 19. In the direction detecting circuit 13, from these square wave signals s1, s2, the direction signal d corresponding to the rotation of the permanent magnet rotor 19 is produced. In the count value increasing and decreasing unit 82, the count value c is increased or decreased depending on the square wave signal s1 and direction signal d. While the permanent magnet rotor 19 is rotating normally, the count value c is increased, and while the permanent magnet rotor 19 is rotating reversely, the count value c decreases. That is, the count value c is a value corresponding to the rotation amount of the permanent magnet rotor 19. In the waveform generating unit 16, as position signals p1, p2, p3, the position signals corresponding to the count value c are delivered. Accordingly, the position signal causes to rotate the phase by the amount corresponding to the rotation amount of the permanent magnet rotor 19. In this way, the magnetomotive force vector I of the rotary magnetic field and the magnetic pole vector Φ of the permanent magnet rotor 19 always maintain the specific phase difference as shown in Fig. 5. By the mutual actions of the magnetomotive force vector I and the magnetic pole vector Φ , the permanent magnet rotor 19 receives a torque and continues to rotate. The initial count value c o of the initial value setting unit 81 is such a value of the count value c of the counter 14 that the magnetic pole vector Φ and the magnetomotive force vector I may coincide with each other when the specified address value is zero in the phase adjusting unit 83. This initial count value c o is calculated in the phase matching mode. On the other hand, in the phase adjusting unit 15, depending on the direction command md, the specified value is added to or subtracted from the count value c to calculate the second phase value f2. By such calculation, the phase difference of the magnetomotive force vector I of the rotary magnetic field and the magnetic pole vector Φ of the permanent magnet rotor 19 may be set as the phase difference of +90 degrees or -90 degrees depending on the direction command md. Therefore, the permanent magnet rotor 19 may be rotated normally or reversely depending on the direction command md. That is, by varying the direction command md, the rotating direction of the permanent magnet rotor 19 may be easily changed. In this way, the magnetomotive force vector I of the rotary magnetic field and the magnetic pole vector Φ of the permanent magnet rotor 19 always maintain the phase difference of 90 degrees as shown in Fig. 5. By the mutual actions of the magnetomotive force vector I and the magnetic pole vector Φ , the permanent magnet rotor 19 receives a torque and continues to rotate. However, in the initial state when the power is turned on, for example, the count value c of the counter unit 14 is unstable, and it is necessary to set the initial count value c o of the count value c. Below is explained in detail the operation of the phase matching mode for setting the initial count value c o of the counter unit 14 by the brushless DC motor of the invention. The initial phase detecting unit 15 in Fig. 1 rotates the rotary magnetic field generated in the stator windings 181, 182, 183 depending on the direction signal d of the direction detecting circuit 13 by force in normal or reverse direction when the count value c when the power source is turned on is improper, and detects the magnetic pole of the permanent magnet rotor 19. The phase matching mode executed when the power source is turned on or when the count value in the counter unit 14 is improper is explained by reference to the basic flow diagram shown in Fig. 9. At step 91, zero is set as the initial value of the variable k for counting the number of changes of rotating direction of the permanent magnet rotor 19. That is, the value of the variable k is zero. Afterwards, the processing at step 921 is done. At step 921, the direction signal d of the direction detecting circuit 13 is entered. Then, the processing of step 922 is done. At step 922, when the direction signal d is H, that is, when the permanent magnet rotor 19 is rotating in normal direction, the process of step 923 is done. When the direction signal d is L, that is, when the permanent magnet rotor 19 is rotating reversely, the processing of step 924 is done. At step 923, the content of the first phase value f1 is decreased by one. That is, the value subtracting one from the first phase value f1 is set as a new first phase value f1. Then the processing of step 931 is done. At step 924, the content of the first phase value f1 is increased by one. That is, the value adding one to the first phase value f1 is set as a new first phase value f1. Then the processing of step 931 is done. Here, the phase value increasing or decreasing part (phase value increasing or decreasing means) 92 is composed of step 921, step 922, step 923 and step 924. At step 931, to obtain the position signals p1, p2, p3, three address values a1, a2, a3 for referring to the function table of the sinusoidal wave for the portion of one period disposed in the ROM region in the memory 62 are calculated on the basis of the first phase value f1. That is, since the phases of the position signals p1, p2, p3 are individually deviated by 120 degrees (see Fig. 4), it follows that a1 = f1 a2 = f1 + (120) a3 = f1 - (120) and the three address values a1, a2, a3 are calculated. In the above equations, (120) is a specified address value corresponding to 120 degrees as converted to the rotational angle of the magnetomotive force vector. Then the processing of step 932 is done. At step 932, on the basis of the three address values a1, a2, a3 obtained at step 931, referring to the function table of sinusoidal wave stored in the ROM region of the memory 62, three-phase digital position signals dp1, dp2, dp3 are obtained. Then the process of step 933 is done. At step 933, the three-phase digital position signals dp1, dp2, dp3 obtained at step 932 are sent to D/A converters 63, 64, 65 shown in Fig. 6. In the D/A converters 63, 64, 65, the digital position signals dp1, dp2, dp3 are converted to analog values, and position signals p1, p2, p3 as shown in Fig. 4 are issued. Then the processing of step 941 is done. Here, the position signal output unit (position signal output means) 93 is composed of the step 931, step 932 and step 933. At step 941, the direction signal d of the direction detecting circuit 13 is entered. Then the processing of step 942 is done. At step 942, if the direction signal d entered in the step 941 is changed from the state one timing before, the processing of step 943 is done. When the direction signal d is not changed from the state one timing before, the operation returns to the processing of step 921. At step 943, first one is added to the variable k. That is, the value adding one to the variable k is set as a new variable k. Next, the value of the first phase value f1 is sequentially stored in the store region M[k] corresponding to the value of the variable k. That is, the value of the store region M[k] is set as the value of the first phase value f1. Then the processing of step 951 is done. Here, the phase value storing part (phase value storing means) 94 is composed of the step 941, step 942, and step 943. At step 951, the magnitude of the value of the variable k is compared with a specific value k max (here k max is an integer of 2 or more, or 2 preferably), and when the magnitude of the value of the variable k is greater, the processing of step 952 is done. When the magnitude of the value of the variable k is not greater, the operation returns to the processing of step 921. At step 952, the initial count value c o is calculated on the basis of the values stored in the store region M[n] (n = 1, 2, ---, k max ). That is, by calculating the arithmetic mean of the value stored in the store region M[n], the initial count value c o is determined. Preferably, the arithmetic mean is calculated from an even number of stored values excluding the initial stored value M[1], and the initial count value c o is determined. More preferably, the initial count value c o is determined by calculating the arithmetic mean by using the stored values M[2] and M[3]. That is, the initial count value c o is determined as c o = (M[2] + M[3]) / 2 Then the operation returns to the processing of step 71 in Fig. 7. Here, the initial phase calculating part (initial phase calculating means) 95 is composed of the step 951 and step 952. By processing in this way, the position of the permanent magnet rotor 19 can be detected, and moreover the rotation amount of the permanent magnet rotor 19 at the time of detection may be extremely decreased. This point is further described below. In the above constitution, the phase value increasing or decreasing part 92 decreases the first phase value f1 when the rotating direction of the permanent magnet rotor 19 is normal direction, and increases the first phase value f1 in reverse rotation. In the waveform generating unit 16, the position signal is issued depending on the first phase value f1, and therefore the magnetomotive force vector I rotates reversely when the magnetic pole vector Φ rotates normally, and rotates normally when the magnetic pole vector Φ rotates reversely. That is, the magnetomotive force vector rotates in reverse direction to the rotating direction of the permanent magnet rotor 19. Suppose the magnetomotive force vector I is issued in a specific phase without rotating reversely to the rotating direction of the permanent magnet rotor 19, as shown in Fig. 10 (a), the magnetic pole vector Φ rotates by mutual action with the magnetomotive force vector I, and finally both vectors coincide. As a result, the position of the magnetic pole vector Φ is detected. However, depending on its initial position, the permanent magnet rotor 19 rotates a maximum of 180 degrees (Fig. 10 (a)). In the embodiment of the invention, the magnetomotive force I is rotated in the reverse direction of the rotating direction of the permanent magnet rotor 19. Accordingly, the magnetomotive force vector I and the magnetic pole vector I are matched in phase by a small rotation of the magnetic pole vector Φ . This mode is shown in Fig. 10 (b). That is, by rotating the magnetomotive force vector I in the reverse direction of the rotating direction of the magnetic pole vector Φ , the magnetic pole vector Φ and the magnetomotive force vector I are matched while the rotation amount of the magnetic pole vector Φ is small, and therefore the position of the magnetic pole vector Φ may be detected in an extremely small state of rotation amount of the magnetic pole vector Φ . By the above processing, if there is a load torque in the permanent magnet rotor 19, the position of the permanent magnet rotor 19 may be detected at high precision. This point is further described below. Suppose the magnetomotive force vector I is generated in a specific phase. When the load torque of the permanent magnet rotor 19 is not zero, the magnetomotive force vector I and the magnetic pole vector Φ are not matched, and a phase angle ϑ depending on the magnitude of the load torque is maintained. The phase deviation direction is as follows: when the permanent magnet rotor 19 rotates in normal direction, as shown in Fig. 11 (a), the magnetic pole vector Φ is deviated by the angle ϑ in the reverse direction from the magnetomotive force vector I, and when the permanent magnet rotor 19 rotates in the reverse direction, as shown in Fig. 11 (b), the magnetic pole vector Φ is deviated by the angle ϑ in the normal direction from the magnetomotive force vector I. Therefore, when the permanent magnet rotor 19 is loaded, only bypassing the specified phase current to the stator winding, the position of the permanent magnet rotor 19 cannot be detected accurately. In the embodiment of the invention, by rotating and driving the magnetomotive force vector I in the normal or reverse direction depending on the rotating direction of the permanent magnet rotor 19, the initial count value c o corresponding to the position of the permanent magnet rotor 19 is calculated. Accordingly, the position of the permanent magnet rotor 19 may be detected at high precision. This point is further described below. In this constitution, the magnetomotive force vector I is rotated in the reverse direction to the rotating direction of the permanent magnet rotor 19. Besides, every time the rotating direction of the permanent magnet rotor 19 is changed, the first phase value f1 is saved in the phase value storing unit 94. Fig. 11 (a) shows the mode of the magnetomotive force vector I and magnetic pole vector Φ at the time of the j-th inversion of the rotating direction. In Fig. 11 (a), the magnetic pole vector Φ is rotating counterclockwise, but receives the torque in the clockwise rotation by the mutual actions with the magnetomotive force vector I, and the moment of changing the rotating direction to the clockwise rotation is shown. At the j + 1-th (next to the j-th) inversion of the rotating direction, the mode of the magnetomotive force vector I and magnetic pole vector Φ is shown in Fig. 11 (b). In Fig. 11 (b), the magnetic pole vector Φ is rotating clockwise, but receives the torque in the counterclockwise rotation by the mutual action with the magnetomotive force vector I, and the moment of changing the rotating direction to the counterclockwise rotation is shown. Supposing here the value of the first phase value f1 corresponding to the position of the magnetic pole vector Φ to be ϑ o , the value of the first phase value f1 corresponding to the phase angle of the magnetomotive force vector I and the magnetic pole vector Φ in Fig. 11 (a) to be ϑ j , and the value of the first phase value f1 corresponding to the phase angle of the magnetomotive force vector I and the magnetic pole vector Φ in Fig. 11 (b) to be ϑ j+1 , the stored value M[j] is as follows: where j is a positive odd number. Calculating the phase value calculating unit 95, it yields c o = (M[2] + M[3]) / 2 = ((ϑ o +ϑ₂) + (ϑ o -ϑ₃)) / 2 = ϑ o + (ϑ₂-ϑ₃) / 2 By repeating the inverting actions of the permanent magnet rotor 19, the magnitude of the phase angle ϑ j and the magnitude of the phase angle ϑ j+1 are nearly equal. Hence, it follows that ϑ₂ = ϑ₃ and hence c o = ϑ o Thus, the initial count value c o of the counter unit 14 is obtained. Besides, since the initial count value c o is calculated from the stored values M[k] (k = 1, 2, ---, k max ) of the first phase value f1 at the time of rotation of the permanent magnet rotor 19 in normal or reverse direction, if the load torque increases, only the magnitude of ϑ j or ϑ j+1 in equation (8) or (9) increases, and the effect of the load torque may be eliminated by the calculation of equation (9). In the embodiment, moreover, the initial count value c o is calculated by using the stored values M[2] and M[3] of the phase value storing unit 94, in particular. Since the value of the stored value M[1] depends greatly on the initial phase difference of the magnetic pole vector Φ and the magnetomotive force vector I, if the stored value M[1] is included in the calculation of the initial count value c o , a large error is caused in the position detection of the magnetic pole vector Φ in the event of a large initial phase difference. Besides, when using the value after the stored value M[4], the specified value k max must be set in a large value. In this case, many inverting actions of the permanent magnet rotor 19 are required, and the phase matching time is substantially extended. In this embodiment, by using the stored values M[2] and M[3], elevation of position detecting precision and shortening of the phase matching time are both realized. It is also possible to enhance the position detection precision by using multiple stored values. By such operation of the phase matching mode, the initial count value of the counter unit 14 may be detected even by a small rotation amount of the permanent magnet rotor 19. Or even when the permanent magnet rotor 19 is loaded, the position of the permanent magnet rotor 19 may be detected at high precision. Besides, while the rotation of the permanent magnet rotor 19 is stopped, by holding the count value in the counter unit 14, it is not necessary to match the phase again when resuming operation, so that starting is possible in a short time. Moreover, by allowing the frequency generator to issue signals even when the rotation of the permanent magnet rotor 19 is stopped, if the permanent magnet rotor 19 is rotated by an external factor during stopping, the count value in the counter unit 14 is updated depending on the rotation, so that it is not necessary to match the phase except when turning on the power source. Thus, since the brushless DC motor of the invention produces three-phase position signals on the basis of two-phase frequency signals mutually different in phase as produced by the frequency generator, it is not necessary to use position sensor such as Hall sensor. Meanwhile, in the memory means 62 relating to the embodiment, by storing the function table of sinusoidal wave of one period only in the memory, the address value is changed by the portion of only the different phase and the function table is referred to, and therefore the three-phase position signals are delivered to three D/A converters 63, 64, 65 as shown in Fig. 6. However, needless to say, it is possible to convert into analog values sequentially by using only one D/A converter, hold the obtained analog values in three sample hold circuits, and produce as three-phase position signals. Moreover, instead of storing the function table of sinusoidal wave of only one period in the memory, needless to say, it is possible to store the sinusoidal waves of three phases in individual function tables, and produce the digital signals corresponding to three-phase position signals directly in three D/A converters 63, 64, 65. In the position matching mode, meanwhile, the rotating speed of the magnetomotive force vector I is nearly constant, but, the rotating speed may be variable. Still more, in the embodiment, a motor of three phases is used, but the number of phases is not limited to three, as a matter of fact. Various other modifications are possible without departing from the true spirit of the invention.

Claims: A brushless DC motor comprising: a rotor (19) possessing a plurality of magnetic poles; plural phase stator windings (1301,181,182,183) disposed at a specific gap from the rotor; sensor means (11) for generating plural phase sensor signals showing a state of rotation of the rotor depending on the rotation of the rotor; direction detecting means (13,21) for detecting the direction of rotation of the rotor from the plural phase sensor signals and producing a direction signal; initial position detecting means (15) for issuing a first phase value, and for detecting an initial count value corresponding to the position of the rotor; counter means (14), in which a count value is set initially according to the initial count value, for increasing or decreasing the count value depending on the direction signal and at least one of the plural phase sensor signals to produce a second phase value; waveform generating means (16) for generating plural phase position signals depending on the first phase value or second phase value; and power supply means (17) for supplying electric power to the plural phase stator windings depending on the plural phase position signals, characterized in that the initial position detecting means (15) comprises; phase value increasing or decreasing means (92) for increasing or decreasing the first phase value depending on the direction signal; phase value storing means (94) for storing a plurality of values of the first phase value depending on a change of the direction signal; and initial count value calculating means (95) for calculating the initial count value from at least two values of the first phase value stored in the phase value storing means; the initial position detecting means (15) being arranged to detect the initial count value corresponding to the position of the rotor by oscillating a rotary magnetic field generated in the plural phase stator winding in normal and reverse directions. A brushless DC motor according to claim 1, wherein the waveform generating means (16) comprises: selecting means (161) for selecting either the first phase value or the second phase value to obtain a selected phase value; and position signal generating means (162) for generating the plural phase position signals depending on the selected phase value. A brushless DC motor according to claim 2, wherein the position signal generating means (162) comprises: memory means (62) having preliminarily stored therein sinusoidal signals; position signal output means (84,93) for obtaining plural phase sinusoidal signals stored in the memory means depending on the selected phase value; and means (63,64,65) for producing the plural phase position signals from the plural phase sinusoidal signals obtained by the position signal output means. A brushless DC motor according to claim 3, wherein the memory means (62) has preliminarily stored therein sinusoidal signals of one period or 1/2 period or 1/4 period. A brushless DC motor according to claim 1, wherein the counter means (14) comprises: initial value setting means (81) for setting the initial value depending on the initial count value; count value increasing or decreasing means (82) for increasing or decreasing the count value depending on the direction signal and at least one of the plural phase sensor signals; and phase adjusting means (83) for adding or subtracting a specific value to or from the count value of the count value increasing or decreasing means depending on a rotating direction command. A brushless DC motor according to claim 5, wherein the phase adjusting means (83) rotates a phase of a rotary magnetic field generated by the plural phase stator windings by adding or subtracting the count value of the count value increasing or decreasing means depending on the rotation direction command by 90 degrees in electric angle from a phase of a magnetic pole of the rotor. A brushless DC motor according to claim 1, wherein the sensor means (11) generates a sensor signal showing a state of the rotor when the rotor is stopped still. A brushless DC motor according to claim 1, wherein the initial position detecting means (15) operates only when the power source is turned on. A brushless DC motor according to claim 1, wherein the operations of the counter means (14), initial position detecting means (15) and waveform generating means (16) are performed by an arithmetic unit comprising: memory means (62) for storing a specified processing program; and arithmetic means (61) for executing a processing according to the specific processing program.

Inventors: INAJI TOSHIO, UEDA EIJI, INAJI, TOSHIO, UEDA, EIJI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1993
Main classification: H02P6
IPC codes: H02P6