JP2020156226A - Driving circuit of stepping motor, driving method of the same, and electronic apparatus using them - Google Patents

Abstract

To improve followability for a load change.SOLUTION: A counter electromotive power detection circuit 230 detects a counter electromotive power VBEMF generated in a coil of a stepping motor 102. A rotational number detection circuit 232 generates a rotational number detection signal indicating a rotational number of the stepping motor 102. A current value setting circuit 210 includes a feedback controller 220 that generates a curent setting value IREF so that the feedback signal based on a counter electromotive power and an error of a target value get close to zero. A parameter of the feedback controller 220 is changed on the basis of the rotational number detection signal. A constant current chopper circuit 250 generates a pulse modulation signal SPWM that is modulated to a pulse so that a detection value of a coil current flowing in a coil gets close to the target value based on the current setting value. A logical circuit 270 controls a bridge circuit 202 connected to the coil in accordance with the pulse modulation signal SPWM.SELECTED DRAWING: Figure 4

Description

The present invention relates to a driving technique for a stepping motor.

Stepping motors are widely used in electronic devices, industrial machines, and robots. The stepping motor is a synchronous motor that rotates in synchronization with the input clock generated by the host controller, and has excellent controllability for starting, stopping, and positioning. Further, the stepping motor has a characteristic that it can control the position in an open loop and is suitable for digital signal processing.

FIG. 1 is a block diagram of a conventional stepping motor and a motor system including a drive circuit thereof. The host controller 2 supplies the input clock CLK to the drive circuit 4. The drive circuit 4 changes the excitation position in synchronization with the input clock CLK.

FIG. 2 is a diagram for explaining the excitation position. The exciting position is grasped as a combination of coil currents (driving currents) I _OUT1 and I _OUT2 flowing through the two coils L1 and L2 of the stepping motor 6. In FIG. 2, eight excitation positions 1 to 8 are shown. In one-phase excitation, a current flows alternately through the first coil L1 and the second coil L2, and transitions between the excitation positions 2, 4, 6, and 8. In two-phase excitation, a current flows through both the first coil L1 and the second coil L2, and transitions between the excitation positions 1, 3, 5, and 7. The 1-2 phase excitation is a combination of the 1 phase excitation and the 2 phase excitation, and transitions between the excitation positions 1 to 8. In the microstep drive, the excitation position is further finely controlled.

FIG. 3 is a diagram illustrating a drive sequence of the stepping motor. At start-up, the frequency f _IN of the input clock CLK rises over time and the stepping motor accelerates. Then, when the frequency f _IN reaches a certain target value, the frequency is kept constant and the stepping motor rotates at a constant speed. After that, when the stepping motor is stopped, the frequency of the input clock CLK is lowered to decelerate the stepping motor. The control of FIG. 3 is also referred to as trapezoidal wave drive.

Under normal conditions, the rotor of the stepping motor rotates synchronously with step angles proportional to the number of input clocks. However, synchronization is lost when sudden load fluctuations or speed changes occur. This is called step-out. Once the step-out is performed, a special process is required to drive the stepping motor normally after that, so it is desired to prevent the step-out.

Therefore, during acceleration and deceleration, where there is a high possibility of step-out, the target value I _REF of the drive current is fixed so that a sufficiently large output torque can be obtained so that step-out does not occur with respect to speed changes. Set to the value I _FULL (high torque mode).

In a situation where the rotation speed is stable and the possibility of step-out is low, the target value I _REF of the drive current is reduced to improve the efficiency (high efficiency mode). Patent Document 5 proposes a technique for reducing power consumption and improving efficiency by optimizing the output torque (that is, the amount of current) by feedback while preventing step-out. Specifically, the load angle φ is estimated based on the back electromotive force V _BEMF, and the target values I _REF of the drive currents (coil currents) I _OUT1 and I _OUT2 are feedback-controlled so that the load angle φ approaches the target value φ _REF. Will be done. The counter electromotive force V _BEMF is represented by the equation (1).
_{V BEMF = K E × ω ×} cosφ ... (1)
ω is the stepping motor angular velocity (hereinafter, referred to as rotational speed or frequency) and, K _E is a counter electromotive force constant.

In the technique described in Patent Document 5, a feedback loop is formed so that the detected value cosφ based on the load angle approaches the target value cos ( _φREF ), and the coil currents I _OUT1 and I _OUT2 in the high efficiency mode are optimal. Be transformed.

Japanese Unexamined Patent Publication No. 9-103096 Japanese Unexamined Patent Publication No. 2004-120957 Japanese Unexamined Patent Publication No. 2000-184789 Japanese Unexamined Patent Publication No. 2004-180354 Japanese Patent No. 6258004

Conventionally, when a load fluctuation occurs while the high efficiency mode is selected, the load fluctuation cannot be followed and the rotation of the stepping motor becomes unstable.

The present invention has been made in such a situation, and one of the exemplary objects of the embodiment is to provide a drive circuit having improved followability to load fluctuations.

One aspect of the present invention relates to a drive circuit of a stepping motor. The drive circuit includes a countercurrent force detection circuit that detects the countercurrent force generated in the coil of the stepping motor, a rotation speed detection circuit that generates a rotation speed detection signal indicating the rotation speed of the stepping motor, and a feedback signal based on the countercurrent force. A current value setting circuit that generates a current setting value so that the error of the target value approaches zero, and the parameters of the feedback controller change based on the rotation speed detection signal, and the coil current flowing through the coil. A constant current chopper circuit that generates a pulse-modulated signal that is pulse-modulated so that the detected value approaches the target amount based on the current set value, and a logic circuit that controls the bridge circuit connected to the coil according to the pulse-modulated signal. , Equipped with.

According to this aspect, the response characteristic of the feedback loop can be optimized according to the rotation speed, and the followability to the load fluctuation and the input fluctuation can be improved.

The feedback controller is a PI controller having proportional gain and integrated gain as parameters, and the proportional gain may change based on the rotation speed detection signal, and the integrated gain may be constant. By making only the proportional gain variable, it is possible to prevent the system from becoming unstable when the parameters are changed.

The proportional gain may increase monotonically with respect to the number of revolutions.

The feedback controller may compare the rotation speed detection signal with at least one predetermined threshold value and select a parameter value according to the comparison result.

The rotation speed detection signal may be the period of the input clock input to the drive circuit or the internal signal based on the input clock.

The current value setting circuit may include a load angle estimation unit that estimates the load angle based on the counter electromotive force. The feedback signal may depend on the load angle.

The feedback signal may be counter electromotive force. The PI controller may adjust the current set value so that the counter electromotive force approaches the target value.

The constant current chopper circuit has a comparator that compares the detected value of the coil current with a threshold value based on the current set value, an oscillator that oscillates at a predetermined frequency, and an oscillator that transitions to an off level according to the output of the comparator. It may include a flip-flop that outputs a pulse-modulated signal that transitions to the on-level according to the output.

The drive circuit may be integrally integrated on one semiconductor substrate. "Integrated integration" includes cases where all the components of a circuit are formed on a semiconductor substrate or cases where the main components of a circuit are integrated integrally, and some of them are used for adjusting circuit constants. A resistor, a capacitor, or the like may be provided outside the semiconductor substrate. By integrating the circuit on one chip, the circuit area can be reduced and the characteristics of the circuit element can be kept uniform.

It should be noted that any combination of the above components or the components and expressions of the present invention that are mutually replaced between methods, devices, systems, and the like are also effective as aspects of the present invention.

According to a certain aspect of the present invention, it is possible to improve the followability to load fluctuations and input fluctuations.

It is a block diagram of a motor system including a conventional stepping motor and its drive circuit. It is a figure explaining the excitation position. It is a figure explaining the drive sequence of a stepping motor. It is a block diagram of the motor system including the drive circuit which concerns on embodiment. It is a circuit diagram which shows the structural example of a drive circuit. 6 (a) and 6 (b) are diagrams showing the relationship between the rotation speed ω and the proportional gain K _P. It is an operation waveform diagram of the drive circuit of FIG. It is a circuit diagram which shows the structural example of the rotation speed detection circuit and the parameter generation part. It is a figure which shows another configuration example of the current value setting circuit. 10 (a) to 10 (c) are perspective views showing an example of an electronic device including a drive circuit.

Hereinafter, the present invention will be described with reference to the drawings based on preferred embodiments. The same or equivalent components, members, and processes shown in the drawings shall be designated by the same reference numerals, and redundant description will be omitted as appropriate. Further, the embodiment is not limited to the invention but is an example, and all the features and combinations thereof described in the embodiment are not necessarily essential to the invention.

In the present specification, the "state in which the member A is connected to the member B" means that the member A and the member B are physically directly connected, and that the member A and the member B are electrically connected to each other. It also includes the case of being indirectly connected via other members, which does not substantially affect the connection state, or does not impair the functions and effects performed by the combination thereof.

Similarly, "a state in which the member C is provided between the member A and the member B" means that the member A and the member C, or the member B and the member C are directly connected, and their electricity. It also includes the case of being indirectly connected via other members, which does not substantially affect the connection state, or does not impair the functions and effects performed by the combination thereof.

The vertical and horizontal axes of the waveform charts and time charts referred to in the present specification are appropriately enlarged or reduced for ease of understanding, and each waveform shown is also simplified for ease of understanding. Or exaggerated or emphasized.

(Embodiment)
FIG. 4 is a block diagram of the motor system 100 including the drive circuit 200 according to the embodiment. The drive circuit 200 constitutes the motor system 100 together with the stepping motor 102 and the host controller 2. The stepping motor 102 may be any of PM (Permanent Magnet) type, VR type (Variable Reluctance) type, and HB (Hybrid) type.

The input clock CLK is input from the host controller 2 to the input pin IN of the drive circuit 200. Further, a direction indicator signal DIR for instructing clockwise (CW) and counterclockwise (CCW) is input to the direction indicator pin DIR of the drive circuit 200.

Each time the input clock CLK is input, the drive circuit 200 rotates the rotor of the stepping motor 102 by a predetermined angle in the direction corresponding to the direction indicating signal DIR.

The drive circuit 200 includes a bridge circuit 202_1, 202_2, a current value setting circuit 210, a counter electromotive force detection circuit 230, a rotation speed detection circuit 232, a constant current chopper circuit 250_1, 250_2, a logic circuit 270, and a mode selector 290. It is integrated on a semiconductor substrate.

In the present embodiment, the stepping motor 102 is a two-phase motor and includes a first coil L1 and a second coil L2. The drive system of the drive circuit 200 is not particularly limited, and may be either 1-phase excitation, 2-phase excitation, 1-2-phase excitation, or microstep drive (W1-2 phase drive, 2W1-2 phase drive, etc.). Good.

The bridge circuit 202_1 of the first channel CH1 is connected to the first coil L1. The bridge circuit 202_2 of the second channel CH2 is connected to the second coil L2.

The bridge circuits 202_1 and 202_2 are H-bridge circuits including four transistors M1 to M4, respectively. The transistors M1 to M4 of the bridge circuit 202_1 are switched based on the control signal CNT1 from the logic circuit 270, whereby the voltage of the first coil L1 (also referred to as the first coil voltage) V _OUT1 is switched.

The bridge circuit 202_2 is configured in the same manner as the bridge circuit 202_1, and the transistors M1 to M4 are switched based on the control signal CNT2 from the logic circuit 270, whereby the voltage of the second coil L2 (also the voltage of the second coil). V _{OUT 2} is switched.

The current value setting circuit 210 generates the current set value I _REF . Immediately after starting the stepping motor 102, the current set value I _REF is fixed to a certain predetermined value (referred to as a full torque set value) I _FULL . The predetermined value I _FULL may be the maximum value in the range that the current set value I _REF can take, in which case the stepping motor 102 is driven with full torque. This state is called a high torque mode.

When the stepping motor 102 starts to rotate stably, in other words, when the risk of step-out is reduced, the mode shifts to the high efficiency mode. In the high efficiency mode, the current value setting circuit 210 adjusts the current set value I _REF by feedback control, thereby reducing power consumption.

The counter electromotive force detection circuit 230 detects the counter electromotive force V _BEMF1 (V _BEMF2 ) generated in the coil L1 (L2) of the stepping motor 102. The method for detecting the counter electromotive force is not particularly limited, and a known technique may be used. Generally, the counter electromotive force can be obtained by setting a certain detection window (detection section), setting both ends of the coil to high impedance, and sampling the voltage of the coil at that time. For example, in 1-phase excitation or 1-2-phase excitation, the back electromotive force V _BEMF1 (V _BEMF2 ) is excited at one end (bridge circuit output) of the coil to be monitored to have high impedance (2, 4 in FIG. 2). It can be measured every 6,8), that is, every predetermined excitation position.

The rotation speed detection circuit 232 acquires the rotation speed (ω) of the stepping motor 102 and generates a detection signal indicating the rotation speed ω. For example, the rotation speed detection circuit 232 may measure the period T (= 2π / ω) proportional to the reciprocal of the rotation speed ω and output the period T as a detection signal. In a situation where step-out has not occurred, the frequency (cycle) of the input clock CLK is proportional to the rotation speed (cycle) of the stepping motor 102. Therefore, the rotation speed detection circuit 232 may measure the period of the input clock CLK or an internal signal generated based on the input clock CLK and use it as a detection signal.

The constant current chopper circuit 250_1 is pulse-modulated so that the detected value I _NF1 of the coil current _IL1 flowing through the first coil L1 approaches the target amount based on the current set value I _REF while the first coil L1 is energized. Modulation signal S _PWM1 is generated. The constant current chopper circuit 250_2 is a pulse modulation signal S _{PWM2 in which} the detection value I _NF2 of the coil current I _L2 flowing in the second coil L2 is pulse-modulated so as to approach the current set value I _REF while the second coil L2 is energized. To generate.

Each bridge circuit 202_1,202_2 includes a current detection resistor _{R NF,} the voltage drop across the current detection resistor _{R NF} becomes the detected value of the coil current _{I L.} The position of the current detection resistor R _NF is not limited and may be provided on the power supply side or may be provided in series with the coil between the two outputs of the bridge circuit.

The logic circuit 270 controls the bridge circuit 202_1 connected to the first coil L1 in response to the pulse modulation signal S _PWM1 . Further, the logic circuit 270 controls the bridge circuit 202_2 connected to the second coil L2 in response to the pulse modulation signal S _PWM2 .

The logic circuit 270 changes the excitation position each time the input clock CLK is input, and switches the coil (or coil pair) that supplies the current. The exciting position is grasped as a combination of the magnitude and direction of the coil current of the first coil L1 and the coil current of each of the second coil L2. The excitation position may transition only according to the positive edge of the input clock CLK, may transition only according to the negative edge, or may transition according to both of them.

As described above, the current value setting circuit 210 has (i) a high torque mode in which the current set value I _REF that defines the amplitude of the coil current is fixed to a large value corresponding to the full torque, and (ii) the current set value I _REF. Is configured to be switchable from the high efficiency mode that adjusts by feedback control.

The current value setting circuit 210 includes a feedback controller 220. The feedback controller 220 generates the current set value I _REF so that the error between the feedback signal D _FB based on the counter electromotive force V _{BEMF 1} and its target value REF approaches zero. The parameters of the feedback controller 220 change based on the rotation speed detection signal T.

The operation mode of the current value setting circuit 210 is selected according to the mode selection signal MODE generated by the mode selector 290. In the mode selection signal MODE, high is assigned to the high efficiency mode and low is assigned to the high torque mode.

For example, the mode selector 290 may monitor the rotation speed detection signal T and select the high efficiency mode when the rotation speed of the stepping motor 102 is higher than a predetermined threshold value.

More preferably, the mode selector 290 asserts (high) the mode selection signal MODE when the rotation speed detection signal T generated by the rotation speed detection circuit 232 is stable over a plurality of consecutive cycles, and is unstable. The mode selection signal MODE is negated (for example, low).

FIG. 5 is a circuit diagram showing a configuration example of the drive circuit 200. FIG. 5 shows only the portion related to the first coil L1.

The logic circuit 270 changes the excitation position in synchronization with the input clock CLK. In the logic circuit 270, some intermediate signals are generated. Among them, the timing signals PHASE_A and PHASE_B can be used as signals indicating the period or timing when the output OUT1A becomes high impedance and the period or timing when the output OUT1B becomes high impedance.

The counter electromotive force detection circuit 230 measures the counter electromotive force V _BEMF1 in response to the timing signals PHASE_A and PHASE_B.

The rotation speed detection circuit 232 includes a counter 234. The counter 234 measures the period T of at least one of the timing signals PHASE_A and PHASE_B. The period T of the timing signals PHASE_A and PHASE_B is a rotation speed detection signal that is inversely proportional to the rotation speed of the stepping motor 102.

The mode selector 290 monitors the rotation speed detection signal, sets the mode selection signal MODE high when the frequency of the input clock CLK is constant and larger than the threshold value, and lowers the mode selection signal MODE otherwise. And. The mode selection signal MODE is supplied to the current value setting circuit 210. The current value setting circuit 210 is in the high torque mode when the mode selection signal MODE is low, and is in the high efficiency mode when the mode selection signal MODE is high.

The current value setting circuit 210 includes a feedback controller 220, a feedforward controller 240, and a multiplexer 212. The feed forward controller 240 outputs a fixed current set value Ix (= I _FULL ) used in the high torque mode immediately after the start of starting.

The feedback controller 220 is activated in the high efficiency mode and outputs a current set value Iy that is feedback controlled based on the back electromotive force V _BEMF .

The multiplexer 212 selects one of the two signals Ix and Iy according to the mode selection signal MODE and outputs the current set value I _REF .

The feedback controller 220 includes a load angle estimation unit 222, a subtractor 224, and a PI (proportional / integral) controller 226.

The load angle estimation unit 222 estimates the load angle φ based on the back electromotive force V _BEMF1 . The load angle φ corresponds to the difference between the position of the rotor (movable element) and the current vector (that is, the position command) determined by the drive current flowing through the first coil L1. As described above, the counter electromotive force V _BEMF1 is given by the following equation.
_{V BEMF1 = K E · ω ·} cosφ
_KE is the counter electromotive force constant, and ω is the rotation speed. Therefore, by measuring the counter electromotive force V _BEMF , it is possible to generate a detected value having a correlation with the load angle φ. For example, cosφ may be used as the detection value, and in this case, the detection value is represented by the equation (2).
^{_{cosφ = V BEMF1 · ω -1 /}} K E
_{= V BEMF1 · (T / 2π} ) · K E -1 ... (2)

The feedback controller 220 generates the current set value Iy so that the estimated load angle φ approaches a predetermined target angle φ _REF . Specifically, the subtractor 224 generates an error ERR of the detected value cos φ based on the load angle φ and its target value cos (φ _REF ). The PI controller 226 performs a PI control operation so that the error ERR becomes zero, and generates a current set value Iy.

PI controller 226 as a control parameter, including proportional gain _{K P} and the integral gain _{K I.} The proportional gain K _P changes based on the rotation speed detection signal T, and the integrated gain K _I is constant. The parameter generation unit 228 sets the proportional gain K _P corresponding to the rotation speed detection signal T in the PI controller 226.

The constant current chopper circuit 250_1 includes a D / A converter 252, a PWM comparator 254, an oscillator 256, and a flip-flop 258. The D / A converter 252 converts the current set value I _REF into an analog voltage V _REF . The PWM comparator 254 compares the feedback signal I _NF1 with the reference voltage V _REF, and asserts (high) the off signal S _OFF when I _NF1 > V _REF . Oscillator 256 generates a periodic ON signal S _ON to define the chopping frequency. The flip-flop 258 outputs a PWM signal S _PWM1 that transitions to an on level (for example, high) in response to an on signal S _ON and transitions to an off level (for example, low) in response to an off signal S _OFF .

6 (a) and 6 (b) are diagrams showing the relationship between the rotation speed ω and the proportional gain K _P. The proportional gain K _P preferably increases monotonically with respect to the rotation speed ω. The proportional gain K _P is monotonically decreasing with respect to the period T.

As shown in FIG. 6A, the proportional gain K _P may be selected from a plurality of discrete values. Alternatively, as shown in FIG. 6B, it may change continuously as a function of the rotation speed ω.

FIG. 7 is an operation waveform diagram of the drive circuit 200 of FIG. FIG. 7 shows operations (i) to (iii) corresponding to the waveforms of the three input clocks CLK having different frequencies.

The input clock CLK is input at time t ₀ , and its frequency increases with time. During this time, the high torque mode is selected and the current command value I _REF is fixed to the high torque set value I _FULL .

Then, when the frequency f _IN of the input clock CLK, in other words, the rotation speed of the stepping motor 102 becomes stable at time t ₁ , the mode shifts to the high efficiency mode.

In the operations (i) to (iii), the frequency f _{IN of} the input clock CLK, that is, the rotation speed of the stepping motor is different, and the parameter (proportional gain K _{P) of the} feedback controller 220 is based on the frequency f _IN of the input clock CLK. ) Is selected. Specifically, K _P1 , K _P2 , and K _{P 3} are selected for each of the frequencies f ₁ , f ₂ , and f ₃ .

In the high efficiency mode, the current set value I _REF converges to different values I ₁ , I ₂ , and I ₃ according to the frequency f _IN of the input clock CLK, that is, according to the rotation speed.

Between time _t 2 ~t _3, the load is increased. As the load increases, feedback is applied so that the current command value I _REF increases in order to maintain the rotation speed of the rotor. As the rotation speed of the motor increases, the current command value I _REF is adjusted with a larger proportional gain K _P , so that the current command value I _REF rapidly increases to a value corresponding to a high load. When the load is returned to the original time t _3, the current command value I _REF is rapidly reduced to a value corresponding to the original load. As a result, the actual number of revolutions hardly decreases.

For comparison, the operation (referred to as the comparison technique) when the proportional gain K _P is constant (K _P1 ) regardless of the frequency f _IN is shown by a alternate long and short dash line. Regarding the waveform (i) when the frequency f _IN = f ₁ , the embodiment (solid line) and the comparison technique (dashed line) are the same.

When f _IN = f ₂ , the proportional gain K _{P of the} comparative technique is lower than that of the embodiment. That is, when the load increases, the rate at which the current command value I _REF increases slows down. As a result, torque is insufficient, and the actual rotation speed drops significantly as shown by the alternate long and short dash line. When f _IN = f ₃ , the drop in the actual rotation speed in the comparative technique (dashed line) becomes even more remarkable.

Suppose that in the comparative technique, the proportional gain K _P is fixed to a large value K _{P 3} regardless of the frequency f _IN . In this case, at low speed rotation, the proportional gain K _P becomes excessive and the current command value I _REF becomes oscillating. That is, when a load fluctuation occurs, the stability of the actual rotation of the motor is impaired.

According to the drive circuit 200 according to the embodiment, by optimizing the proportional gain K _P according to the rotation speed, it is possible to improve the followability to the load fluctuation while maintaining the stability of the system.

FIG. 8 is a circuit diagram showing a configuration example of the rotation speed detection circuit 232 and the parameter generation unit 228. The rotation speed detection circuit 232 includes an edge detector 236, a counter 234, and a coefficient circuit 238. The edge detector 236 detects an edge (for example, a positive edge) of the input clock CLK. The counter 234 receives the output of the system clock CLK _SYS and the edge detector 236, and counts the number of the system clock CLK _SYS included in the interval between the positive edges detected by the edge detector 236. The output of the counter 234 indicates the period T _CLK of the input clock CLK. The coefficient circuit 238 multiplies the period T _CLK by a coefficient and converts it into a rotation speed detection signal indicating the rotation speed T of the motor.

The parameter generation unit 228 compares the rotation speed detection signal T with a plurality of (three in this example) threshold values T _TH1 , T _TH2 , and T _TH3, and sets the value of the proportional gain K _P according to the comparison result. select. For example, the parameter generation unit 228 may include a plurality of comparators COMP1 to COMP3 and a multiplexer MUX. The multiplexer MUX selects one of a plurality of proportional gains K _P values K _{P1 to} K _P4 according to the outputs of the plurality of comparators COMP1 to COMP3.

FIG. 9 is a diagram showing another configuration example of the current value setting circuit 210. The feedback controller 220 is activated in the high efficiency mode and generates a current correction value ΔI whose value is adjusted so that the load angle φ approaches the target value φ _REF . The current correction value ΔI is zero in the high torque mode.

The feed forward controller 240 outputs a predetermined high efficiency set value I _LOW in the high efficiency mode. The relationship of I _FULL > I _LOW may be established. The current value setting circuit 210 includes an adder 214 instead of the multiplexer 212 of FIG. 5, and the adder 214 adds the current correction value ΔI to the high efficiency set value I _LOW generated by the feed forward controller 240. As a result, the current set value I _REF = I _LOW + ΔI is adjusted so that the load angle φ approaches the target value φ _REF .

Finally, the use of the drive circuit 200 will be described. The drive circuit 200 is used in various electronic devices. 10 (a) to 10 (c) are perspective views showing an example of an electronic device including a drive circuit 200.

The electronic device of FIG. 10A is an optical disk device 500. The optical disk device 500 includes an optical disk 502 and a pickup 504. The pickup 504 is provided for writing and reading data to the optical disc 502. The pickup 504 is movable on the recording surface of the optical disc 502 in the radial direction of the optical disc (tracking). Further, the distance between the pickup 504 and the optical disk is also variable (focusing). The pickup 504 is positioned by a stepping motor (not shown). The drive circuit 200 controls the stepping motor. According to this configuration, the pickup 504 can be positioned with high accuracy while preventing step-out.

The electronic device of FIG. 10B is a device 600 with an image pickup function, such as a digital still camera, a digital video camera, or a mobile phone terminal. The device 600 includes an image sensor 602 and an autofocus lens 604. The stepping motor 102 positions the autofocus lens 604. According to this configuration in which the drive circuit 200 drives the stepping motor 102, the autofocus lens 604 can be positioned with high accuracy while preventing step-out. In addition to the autofocus lens, the drive circuit 200 may be used to drive the camera shake correction lens. Alternatively, the drive circuit 200 may be used for aperture control.

The electronic device of FIG. 10C is a printer 700. The printer 700 includes a head 702 and a guide rail 704. The head 702 is positionally supported along the guide rail 704. The stepping motor 102 controls the position of the head 702. The drive circuit 200 controls the stepping motor 102. According to this configuration, the head 702 can be positioned with high accuracy while preventing step-out. In addition to driving the head, the drive circuit 200 may be used to drive the motor for the paper feed mechanism.

The present invention has been described above based on the embodiments. It is understood by those skilled in the art that this embodiment is an example, and that various modifications are possible for each of these components and combinations of each processing process, and that such modifications are also within the scope of the present invention. is there. Hereinafter, such a modification will be described.

(Modification example 1)
The logic circuit 270 adjusts the power supply voltage _VDD supplied to the bridge circuit 202 instead of or in combination with adjusting the current set value I _REF so that the load angle φ approaches the target angle φ _REF. You may. By changing the power supply voltage _VDD , the power supplied to the coils L1 and L2 of the stepping motor 102 can be changed.

(Modification 2)
In the embodiment, the case where the bridge circuit 202 is composed of the full bridge circuit (H bridge) has been described, but the present invention is not limited to this, and the bridge circuit 202 may be composed of a half bridge circuit. Further, the bridge circuit 202 may be a chip different from the drive circuit 200, or may be a discrete component.

(Modification 3)
The method for generating the current set value I _REF (Iy) in the high efficiency mode is not limited to that described in the embodiment. For example previously determined target values _{V BEMF} of the back electromotive force _{V BEMF1 (REF),} as the counter electromotive force _{V BEMF1} approaches the target value _{V BEMF (REF),} may constitute a feedback loop.

(Modification example 4)
In the embodiment, the currents I _OUT1 and I _OUT2 flowing through the two coils are turned on and off according to the exciting position, but the amount of the current is constant regardless of the exciting position. In this case, the torque will fluctuate in the case of 1-2 phase excitation. Instead of this control, the currents I _OUT1 and I _OUT2 may be modified so that the torque is constant regardless of the excitation position. For example, in 1-2 phase excitation, the amount of the currents I _OUT1 and I _{OUT2 at} the excitation positions 2, 4, 6 and 8 may be √2 times the amount of the currents at the excitation positions 1, 3, 5 and 7.

(Modification 5)
In the embodiment, the feedback controller 220 is composed of a PI controller, but the present invention is not limited to this, and a PID controller or the like may be adopted.

Although the present invention has been described using specific terms and phrases based on the embodiments, the embodiments merely indicate the principles and applications of the present invention, and the embodiments are defined in the claims. Many modifications and arrangements can be changed without departing from the ideas of the present invention.

L1 1st coil L2 2nd coil 2 Host controller 100 Motor system 102 Stepping motor 200 Drive circuit 202 Bridge circuit R _NF detection resistance 210 Current value setting circuit 212 Comparator 214 Adder 220 Feedback controller 222 Load angle estimation unit 224 Subtractor 226 PI Controller 228 Parameter generator 230 Counter electromotive force detection circuit 232 Rotation speed detection circuit 234 Counter 236 Edge detector 238 Coefficient circuit 240 Feed forward controller 250 Constant current chopper circuit 252 D / A converter 254 PWM comparator 256 Oscillator 258 Flip flop 270 Logic Circuit 290 mode selector

Claims (11)

It is a drive circuit of a stepping motor
A counter electromotive force detection circuit that detects the counter electromotive force generated in the coil of the stepping motor, and
A rotation speed detection circuit that generates a rotation speed detection signal indicating the rotation speed of the stepping motor, and
A current value that includes a feedback controller that generates a current setting value so that an error between the feedback signal based on the counter electromotive force and its target value approaches zero, and the parameters of the feedback controller change based on the rotation speed detection signal. Setting circuit and
A constant current chopper circuit that generates a pulse-modulated signal that is pulse-modulated so that the detected value of the coil current flowing through the coil approaches the target amount based on the current set value.
A logic circuit that controls a bridge circuit connected to the coil in response to the pulse modulation signal,
A drive circuit characterized by being provided with. The feedback controller includes a PI controller having a proportional gain and an integrated gain as the parameters, and the proportional gain changes based on the rotation speed detection signal, and the integrated gain is constant. The drive circuit according to 1. The drive circuit according to claim 2, wherein the proportional gain increases monotonically with respect to the rotation speed. The feedback controller according to any one of claims 1 to 3, wherein the feedback controller compares the rotation speed detection signal with at least one predetermined threshold value, and selects a value of the parameter according to the comparison result. The drive circuit described. The drive circuit according to any one of claims 1 to 4, wherein the rotation speed detection signal is a period of an input clock input to the drive circuit or an internal signal based on the input clock. The current value setting circuit is
Includes a load angle estimation unit that estimates the load angle based on the counter electromotive force.
The drive circuit according to any one of claims 1 to 5, wherein the feedback signal corresponds to the load angle. The feedback signal is the counter electromotive force, and the feedback controller adjusts the current set value so that the counter electromotive force approaches the target value, according to any one of claims 1 to 5. Drive circuit. The constant current chopper circuit
A comparator that compares the detected value of the coil current with the threshold value based on the current set value.
An oscillator that oscillates at a predetermined frequency and
A flip-flop that outputs the pulse-modulated signal that transitions to the off-level according to the output of the comparator and transitions to the on-level according to the output of the oscillator.
The drive circuit according to any one of claims 1 to 7, wherein the drive circuit comprises. The drive circuit according to any one of claims 1 to 8, wherein the drive circuit is integrally integrated on one semiconductor substrate. With a stepping motor
The drive circuit according to any one of claims 1 to 9 for driving the stepping motor.
An electronic device characterized by being equipped with. It is a method of driving a stepping motor.
The step of detecting the counter electromotive force generated in the coil of the stepping motor, and
A step of generating a rotation speed detection signal indicating the rotation speed of the stepping motor, and
A step of generating a current set value by the feedback controller so that the error between the feedback signal based on the counter electromotive force and its target value approaches zero.
A step of changing the parameters of the feedback controller based on the rotation speed detection signal, and
A step of generating a pulse-modulated signal in which the detected value of the coil current flowing through the coil is pulse-modulated so as to approach a target amount based on the current set value.
A step of controlling a bridge circuit connected to the coil according to the pulse modulation signal,
A driving method characterized by being provided with.

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