JP2011067063A - Driver circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To drive a stepping motor with a proper current. <P>SOLUTION: The stepping motor 200 includes two coils 22, 24. A driver circuit 100 supplies currents of different phases to the two coils 22, 24 to drive the stepping motor 200. Then, one coil 22 (24) is set in a high impedance state to detect an induced voltage generated in the coil. A zero crosspoint of an induced voltage waveform is estimated from an inclination of the detected induced voltage. A motor drive current to be supplied to the two coils 22, 24 is controlled according to the position of the estimated zero crosspoint. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a driver circuit for a stepping motor that includes two coils and rotates a rotor driven by the coils by changing the phases of currents supplied to the two coils.

  Although there are various types of motors, there is a stepping motor as a representative motor that can accurately determine the position, and it is widely used in various devices. For example, camera focusing, camera shake correction, paper feed of OA equipment, and the like can be given.

  The driving of this stepping is usually performed by changing the rotational position of the rotor with the current phase to the two stator coils. Therefore, if the rotor rotates according to the current phase to the coil, the rotor rotates a predetermined amount regardless of the amount of current to the coil. Therefore, in general, the amount of current to the coil is sufficiently large so that the rotor can rotate reliably.

JP 2006-288056 A JP-A-8-37798

  Here, there is a demand for reducing the power consumption of the electrical equipment as much as possible. In particular, the demand is large in battery-powered portable devices and OA devices that require a large current. On the other hand, when the stepping motor is driven, setting the amount of current to a size that can reliably rotate the rotor means that an extra current is passed through the coil and an extra power is consumed. In addition, driving the motor with a large electric power causes uneven rotation of the rotor, causing vibration, noise, and heat generation.

The present invention is a driver circuit for a stepping motor that includes two coils and rotates a rotor driven by the coils by differentiating phases of currents supplied to the two coils.
The slope of the induced voltage generated at the phase where the drive currents of the two coils are 0 is detected, the zero cross point of the induced voltage waveform is estimated from the detected slope, and the two coils according to the estimated phase of the zero cross point Controlling the magnitude of the motor drive current supplied to the motor.

  In addition, it is preferable that the slope of the induced voltage is detected at a monotonically increasing portion after a kickback waveform of the induced voltage caused by setting the coil in a high impedance state.

  Thus, according to the present invention, the phase of the rotor can be estimated from the induced voltage, and the motor drive current can be controlled in accordance with the phase. Therefore, the motor drive current can be made appropriate. Further, the slope of the induced voltage generated at the phase where the drive current of the coil becomes 0 is detected, the zero cross point of the induced voltage waveform is estimated from the detected slope, and the two coils are applied according to the estimated position of the zero cross point. Appropriate motor drive current control can be performed by controlling the magnitude of the motor drive current to be supplied.

It is a figure which shows the whole structure of the system containing a driver circuit and a motor. It is a figure which shows the structure of an output circuit. It is a figure which shows the structure of a drive current adjustment circuit. It is a figure which shows the output and control state of an output circuit. It is a figure which shows the relationship between the state of a drive current, and a drive voltage waveform. It is a figure which shows the state of an induced voltage waveform. It is a figure which shows the estimation of a zero cross point.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

"overall structure"
FIG. 1 is a diagram illustrating an overall configuration, and the system includes a driver 100 and a motor 200. The input signal is input to the driver 100, and the driver 100 supplies a driving current corresponding to the input signal to the motor 200. Thereby, the rotation of the motor 200 is controlled according to the input signal.

  Here, the driver 100 has an output control circuit 12, and an input signal is supplied to the output control circuit 12. The output control circuit 12 determines a drive waveform (phase) having a predetermined frequency according to the input signal, determines the amplitude of the drive current by PWM control, and creates a drive control signal. Then, the generated drive control signal is supplied to the output circuit 14.

  The output circuit 14 is composed of a plurality of transistors, and controls the current from the power source by switching them to generate a motor driving current and supplies it to the motor 200.

  The motor 200 is a stepping motor and has two coils 22 and 24 and a rotor 26. The two coils 22 and 24 are disposed so that their positions are deviated from each other by 90 ° in electrical angle. Therefore, the direction of the magnetic field with respect to the rotor 26 is also deviated by 90 ° in terms of electrical angle with respect to the central angle of the rotor. The rotor 26 includes a permanent magnet, for example, and a stable position is determined according to the magnetic field from the two coils 22 and 24. That is, by supplying alternating currents having a phase difference of 90 ° to two coils arranged at positions shifted by 90 ° with respect to the rotation angle of the rotor, the rotor 26 can be moved and rotated by the current phase. Further, by stopping the change of the current phase at the timing of the specific current phase, the rotor can be stopped at a position corresponding to the current phase at that time, and thereby the rotation of the motor 200 is controlled.

  The voltages of the outputs OUT1 to OUT4 of the four current paths to the two coils 22 and 24 are supplied to the drive current adjusting circuit 30. The drive current adjustment circuit 30 determines the current amplitude to the motor 200 based on the voltages of the outputs OUT1 to OUT4. Then, an adjustment signal for the current amplitude is supplied to the output control circuit 12. Therefore, the output control circuit 12 generates a drive control signal from the input signal and the adjustment signal.

"Configuration of output circuit"
FIG. 2 shows a configuration of a part of the output circuit 14 and one coil 22 (24) of the motor 200.

  As described above, an arm composed of two transistors Q1 and Q2 connected in series and an arm composed of two transistors Q3 and Q4 connected in series are provided between the power source and the ground. The coil 22 (24) is connected between the intermediate points of the transistors Q3 and Q4. Then, by turning on the transistors Q1 and Q4 and turning off the transistors Q2 and Q3, a one-way current flows through the coil 22 (24), turning off the transistors Q1 and Q4 and turning on the transistors Q2 and Q3. A current in the opposite direction is supplied to 22 (24) to drive the coils 22 and 24.

  By providing two such circuits, the current supplied to the two coils 22 and 24 can be individually controlled.

"Configuration of drive current adjustment circuit"
A configuration example of the drive current adjustment circuit 30 is shown in FIG. The voltages OUT1 to OUT4 are input to the ADC 34 through the four switches 32, respectively. The ADC 34 converts the voltage selected and input by the switch 32 into a digital signal and sequentially outputs it. The output of the ADC 34 is supplied to the control logic 36. The control logic 36 determines a current amplitude to the motor 200 based on the supplied voltage waveforms of OUT1 to OUT4, and supplies an adjustment signal for the current amplitude to the output control circuit 12.

  The output control circuit 12 creates a drive control signal in PWM control according to the adjustment signal. Here, the PWM control method includes a direct PWM control method and a constant current chopping method.

  In the case of the direct PWM control method, the PWM control is performed on the assumption that the duty ratio of the rectangular wave is proportional to the current output. At this time, if an induced voltage is generated in the motor, the actual current output value becomes small. In the direct PWM control method, the current output value can be adjusted by controlling the target duty ratio of the rectangular wave and the coefficient for adjusting the amplitude of the rectangular wave.

  In the case of the constant current chopping method, the current that drives the motor is detected by detecting the current flowing through the resistor Rt, and control is performed to change the pulse width of the rectangular wave so that the current becomes a target value. In the constant current chopping method, the current output value can be adjusted by changing the target value.

  In the present embodiment, a driver circuit adopting a direct PWM control method will be described.

  Here, in the present embodiment, the output voltages OUT1 to OUT4 to the four coil ends are AD-converted by the ADC 34 as they are.

  For this purpose, a timing circuit 38 is provided. The timing circuit 38 controls the switching of the switch 32 and the switching of the transistors Q2 and Q4 in the output circuit 14 based on the driving phase of each coil. . That is, in the coil 22 (24), one terminal OUT is connected to the ground, and the other terminal OUT is opened. As a result, an induced voltage appears at the open-side terminal OUT. This is input to the ADC 34, and the ADC 34 outputs a digital value indicating the amplitude.

  Here, as described above, the output circuit for one coil 22 (24) has a configuration as shown in FIG. The driving of one coil 22 (24) repeats the state in which the transistor Q1 is PWM-controlled while the transistor Q4 is on and the state in which the transistor Q2 is on and the transistor Q3 is PWM-controlled.

  FIG. 4 shows a voltage waveform between OUT1 and OUT2 in which a drive voltage is applied to the coil 22, and a voltage waveform between OUT3 and OUT4 in which a drive voltage is applied to the coil 24. Thus, the drive waveforms to the two coils 22 and 24 are 90 degrees out of phase, and the drive waveform of the coil 22 is advanced by 90 degrees compared to the drive waveform of the coil 24.

  In the example of the voltage waveform between OUT3 and OUT4, when the transistor Q4 in FIG. 2 is turned on and the transistor Q1 is PWM controlled, the transistor Q2 is turned on and the transistor Q3 is PWM controlled. In other words, when the step of 180 degrees of the drive waveform and the state where the transistor Q2 is turned on and the transistor Q3 is PWM controlled, the transistor Q4 is turned on and the transistor Q1 is PWM controlled, that is, the drive waveform is 0. In this step, the induced voltage is detected.

  That is, the transistors Q1 and Q3 remain off during this period, and the transistor Q2 (or Q4) that should be turned on in the next phase is turned on. Note that the transistor Q4 (or Q2) is kept off.

  In the example of FIG. 4, in the vicinity of the electrical angle of 0 degrees, OUT1-OUT2 with respect to the coil 22 is in a state in which the transistor Q4 is turned on and the transistor Q1 is PWM-controlled. Turns on and connects OUT1 to the ground GND, turns off the transistors Q1, Q3, and Q4 and opens OUT2 in an open state. Thereby, an induced voltage in the coil 22 is obtained at OUT2, and the induced voltage is input to the ADC 34 by turning on the switch 32-2. In the step of electrical angle 270 degrees, the transistor Q4 is turned on, OUT2 is connected to the ground GND, the transistors Q1, Q2, and Q3 are turned off, and the OUT1 is opened. Thus, an induced voltage in the coil 22 is obtained at OUT1, and the induced voltage is input to the ADC 34 by turning on the switch 32-1. Since the phase of the coil 24 is delayed by 90 degrees, OUT3 is opened at an electrical angle of 0 degrees, OUT4 is connected to the ground, the switch 32-3 is turned on, and an induced voltage of OUT3 is supplied to the ADC 34, and an electrical angle of 180 At this time, OUT4 is open, OUT3 is connected to the ground, the switch 32-4 is turned on, and the induced voltage of OUT4 is supplied to the ADC 34.

  The timing circuit 38 controls the switching of the transistors Q1 to Q4 and the control of the switch 32 in the output circuit 14 for the coils 22 and 24 for measuring the induced voltage, based on the switching phase signal from the output control circuit 12. .

  The induced voltage of the coil 22 (24) is obtained as a difference between voltages at both ends. However, in the present embodiment, since one end of the coil 22 (24) is connected to the ground when measuring the induced voltage, the potential difference between both ends of the coil 22 (24) at the other end in the open state. The value of is obtained directly. Therefore, it is not necessary to detect the potential difference between both ends of the coil with the operational amplifier, and the circuit is simplified. Further, OUT on the open side is a terminal on the side where the induced voltage rises, and the input to the ADC 34 is basically a positive voltage, and can be converted into a digital signal as it is in the ADC 34.

  In this way, the induced voltage in the phase where the drive current waveform becomes 0 can be sequentially detected by the ADC 34. Therefore, in the two coils 22 and 24, detection can be performed four times in one cycle of the electrical angle of the motor. The induction voltage detection period is 1/8 cycle in the 1-2 phase excitation mode employed in the present embodiment, and 1/16 cycle in the W1-2 phase excitation mode.

  Next, FIG. 5 shows three examples of the drive voltage waveform and the induced voltage waveform in one coil 22. The phase of the induced voltage waveform tends to advance when the drive current is large. When the drive current is optimal, the phase of the drive voltage waveform and the induced voltage waveform are substantially the same. On the other hand, if the drive current is small, the rotor cannot be driven and a step-out state occurs, so that the induced voltage waveform remains zero.

  When the drive current is adjusted so that the induced voltage waveform has a phase that maximizes the drive efficiency, there is a high risk of stepping out when the motor load fluctuates. Therefore, although it depends on the actual use situation of the motor and the like, it is desirable not to control the phase so that the driving efficiency is maximized, but to control the phase so that it has a little margin.

“Judgment by induced voltage waveform”
FIG. 6 shows an example of an induced voltage waveform in the induced voltage detection period. <State 1> is monotonically increasing after kickback. In this state, it is considered that the zero cross is located around the beginning of the detection period. Therefore, it can be considered that the driving current has a slight margin as compared with the above-described optimal (minimum) driving current. Therefore, it is determined that this is appropriate or more detailed determination is required. That is, when the load fluctuation is relatively large depending on the use state of the motor, the risk of step-out is great, and the amount of drive current is small. Therefore, it can be determined that it is necessary to increase this.

  In <State 2>, the driving voltage after kickback is a mountain. In this case, the phase of the induced voltage is advanced compared to the drive voltage waveform. Therefore, it is considered that it corresponds to the excessive drive current in FIG. 5, and it is determined that the amount of current should be reduced.

  In <State 3>, there is no induced voltage after kickback. Therefore, it can be determined that there is no rotation of the rotor and the step-out state.

  The control logic 36 of the drive current adjustment circuit 30 controls the output control circuit 12 based on such a determination result. In the case of state 3, the control logic 36 outputs a signal indicating that a step-out has been detected. The above signal is received by a controller (not shown) that controls the driver circuit 20.

  Thus, in the present embodiment, the motor drive state is determined and the motor drive current is controlled according to the induced voltage waveform in the induced voltage detection period. Therefore, the motor drive state can be accurately grasped and appropriate motor drive control can be performed.

  The control logic 36 makes a determination based on the digital data of the induced voltage. For example, it is preferable to perform the above-described waveform determination from a comparison of detected values at three points. Here, the magnitude of the kickback differs depending on the magnitude of the coil current and the like. Therefore, in order to eliminate the influence of kickback as much as possible and detect the induced voltage waveform, it is preferable to perform actual detection in the latter half of the detection period. For example, it is preferable to divide the detection period into eight periods and perform detection at timings of 6/8, 7/8, and 8/8. Note that it is possible to detect a step-out by being 8/8 and 0V.

"Estimation of zero cross"
As described above, in the present embodiment, the target phase is set so that the induced voltage waveform basically increases monotonically and the zero-cross point exists before the timing of 4/8 of the detection period. Therefore, when the induced voltage waveform monotonically increases, the slope is obtained from the detected values of 6/8 and 8/8, the zero cross is estimated, and this is compared with the target phase, and the estimated zero cross point is the target. It is preferable to control the increase / decrease of the drive current depending on where the zero cross point is located. Such waveform detection is performed by the control logic 36 of the drive current adjusting circuit 30, and the output control circuit 12 is controlled in accordance with the output of the control logic 36.

  FIG. 7 shows the estimated state of the zero cross point. For example, two points are detected for the induced voltage waveform in a monotonically increasing state after kickback. When the time between two points is ΔT and the difference in induced voltage between the two points is ΔV, the slope of the induced voltage waveform is represented by ΔV / ΔT. For example, if the induced voltage at the time of 6/8 and 8/8 when the above-described detection period is equally divided is detected, ΔT is a quarter of the detection period, and ΔV × 4 = V0, if the induced voltage at the timing of 8/8 is V0, the time of 0/8 is estimated as the zero cross point.

  As described above, the zero cross point can be estimated by detecting the induced voltage at two points of the set time interval ΔT. Then, it is preferable to set a margin for the motor drive current based on a load fluctuation of the motor, set a target for the zero cross point, and perform control so that the zero cross point approaches the target phase.

  If the estimated zero cross point is delayed from the target phase, the current amount is increased. If the estimated zero cross point is advanced, the current amount is decreased. When the difference from the target phase is large, the unit amount of increase or decrease may be changed, and when the difference from the target phase is within a predetermined range, it may not be increased or decreased.

  Furthermore, the unit amount may be changed by changing the frequency instead of changing the single change amount. That is, if one unit amount is changed twice for one detection, the gain is doubled.

  In particular, when the amount of current is insufficient, there is a risk of step-out, so it is necessary to recover the amount of current at an early stage. Therefore, it is preferable to increase the gain. For example, the unit amount (1 step) is set to 1/256 with respect to the control range for the drive current, and the normal electrical angle is controlled once per cycle (change of one unit amount), which is close to step-out. On the other hand, the control is performed four times (4 unit amount is changed). In the present embodiment, since detection is performed four times in one cycle of the motor (electrical angle 360 degrees), the control can be performed for each detection and the control can be performed four times. In the case of a change only once, it is also preferable to perform the increase / decrease control only when the same determination result is obtained four times from the four determination results.

  Furthermore, it is necessary to change the control depending on the characteristics of the motor, the magnitude of the drive voltage, and the like. Therefore, it is preferable that the control gain (unit amount) can be changed.

  In addition, depending on the characteristics of the motor, there is a case where the kickback width becomes large and the waveform of the induced voltage cannot be detected. When such an induced voltage waveform cannot be detected, it is also preferable to drive with the maximum current without performing adjustment control of the drive current.

  Furthermore, when applied to a system in which the load fluctuation applied to the motor is small, the terminal for detecting the induced voltage can be only OUT1. As a result, the number of switches 32 can be reduced, and the driver 100 can be made smaller.

"About the effect"
According to this embodiment, the motor can be operated with high efficiency. Therefore, it is possible to reduce the power consumption and perform effective motor driving. In addition, since the driving is smooth, the generation of vibration and noise can be suppressed. In addition, the high efficiency operation can suppress the generation of heat and the effect of simplifying the cooling mechanism and the like can be obtained.

  Further, when detecting the induced voltage, the waveform can be detected by inputting the voltage as it is to the ADC 34 without obtaining the difference. For this reason, the operational amplifier can be omitted to simplify the circuit.

  This high-efficiency control is the most effective control during normal operation in which the rotation operation is continued, and it is preferable to perform driving at the maximum current or other control during startup. This control should be performed only when the rotational speed is equal to or higher than a predetermined value.

  In the above description, when detecting the induced voltage, one end of the coil 22 (24) is connected to the ground and the other end is set to high impedance. However, all the transistors Q1 to Q4 may be turned off so that both ends of the coil 22 (24) are in a high impedance state, and the difference between the voltages at both ends of the coil 22 (24) may be detected by an operational amplifier or the like.

  12 output control circuit, 14 output circuit, 22, 24 coil, 26 rotor, 30 drive current adjustment circuit, 32 switch, 36 control logic, 38 timing circuit, 100 driver, 200 motor.

Claims (2)

A driver circuit for a stepping motor that includes two coils and rotates a rotor driven by the coils with different phases of currents supplied to the two coils.
Detecting the slope of the induced voltage generated in the phase where the drive currents of the two coils are 0;
A driver circuit characterized by estimating a zero cross point of an induced voltage waveform from a detected slope and controlling a magnitude of a motor drive current supplied to two coils in accordance with the phase of the estimated zero cross point. The driver circuit according to claim 1,
The driver circuit is characterized in that the slope of the induced voltage is detected at a monotonically increasing portion after a kickback waveform of the induced voltage caused by setting the coil in a high impedance state.

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