Drive circuit for a stepper motor and method of driving the same, and electronic device using the same

Abstract

The drive circuit (200) drives the stepper motor (102) synchronously with the input clock (CLK) in a two-phase excitation mode. The constant current chopper circuit (250) uses the coil current (Ic) to drive the stepper motor (102). OUT1 The detected value is close to the current set value (I). REF The pulse modulation signal (S) is generated in a manner that... PWM The detection window generation circuit (260) generates a detection window, which uses the coil current (I) as the input. OUT1 ) less than the predetermined threshold (I) ZC The timing of the pulse modulation signal (S) is taken as the starting point. When the detection window is open, the logic circuit (270) places the full-bridge circuit (202) in a high-impedance state, and when the detection window is closed, it adjusts the pulse modulation signal (S) according to the pulse modulation signal (S). PWM The back electromotive force (EMF) detection circuit (230) controls the full-bridge circuit (202) when the detection window is open. The back EMF detection circuit (230) measures the back EMF (V) of the coil (L1). BEMF1 The current value setting circuit (210) is based on the back electromotive force (V) for detection. BEMF1 To set the current setting value (I) REF Feedback control is implemented.

Description

Technical Field

[0001] This disclosure relates to a stepper motor driving technology. Background Technology

[0002] Stepper motors are widely used in electronic devices, industrial machinery, and robots. As synchronous motors, they rotate in sync with the input clock generated by the main controller, offering excellent controllability in starting, stopping, and positioning. Furthermore, stepper motors enable open-loop position control and possess characteristics suitable for digital signal processing.

[0003] Figure 1 This is a block diagram of a motor system including an existing stepper motor and its drive circuit. The main controller 2 supplies an input clock CLK to the drive circuit 4. The stepper motor 6 includes a first coil L1 and a second coil L2. The position of the rotor of the stepper motor 6 is determined by the current I flowing through the first coil L1 and the second coil L2, respectively. OUT1 I OUT2 The combination determines this.

[0004] The drive circuit 4 includes full-bridge circuits 8_1 and 8_2 connected to the first coil L1 and the second coil L2. The drive circuit 4 synchronously changes the states of the two full-bridge circuits 8_1 and 8_2 with the input clock CLK, thereby changing the current I. OUT1 I OUT2 The combination (excitation position) changes.

[0005] Figure 2 This diagram illustrates the excitation position. The excitation position can be understood as the coil current (drive current) I flowing through the two coils L1 and L2 of the stepper motor 6. OUT1 I OUT2 The combination. In Figure 2 The image shows eight excitation positions, 1 to 8.

[0006] There are several excitation methods for stepper motors.

[0007] Under single-phase excitation, current flows alternately through coils L1 and L2, causing excitation positions 2, 4, 6, and 8 to shift. Under two-phase excitation, current flows through both coils L1 and L2, causing excitation positions 1, 3, 5, and 7 to shift. Under 1-2 phase excitation, a combination of single-phase and two-phase excitation causes excitation positions 1 through 8 to shift. In micro-stepping drive, the excitation position is further precisely controlled.

[0008] Figure 3 This is a waveform diagram of the drive circuit under 1-2 phase excitation. In this example, each pulse of the clock CLK causes... Figure 2The excitation positions 1 through 8 are sequentially shifted clockwise. OUT1A and OUT1B represent the states of full-bridge circuit 8-1, and OUT2A and OUT2B represent the states of full-bridge circuit 8-2. Specifically, "H" indicates a high-voltage output state, "L" indicates a low-voltage output state, and "HZ" indicates a high-impedance state.

[0009] Under normal conditions, the rotor of a stepper motor rotates synchronously in sequence at step angles proportional to the input clock count. However, when abrupt load changes or speed variations occur, synchronization is lost. This is called step loss. Once step loss occurs, special handling is required to drive the stepper motor normally afterward, so preventing step loss is desirable.

[0010] When a motor is driven with a constant high torque, the risk of step loss is reduced, but efficiency is decreased. When a motor is driven with low torque, efficiency improves, but the risk of step loss increases. Patent document 5 proposes a technique that prevents step loss and optimizes the output torque (i.e., current) through feedback, thereby reducing power consumption and improving efficiency (referred to as the high-efficiency mode in this specification). In this high-efficiency mode, the back electromotive force generated in the motor coil is detected, the load angle is estimated based on the back electromotive force, and the current command value, i.e., the torque, is feedback controlled so that the estimated load angle approaches a predetermined target value.

[0011] [Existing Technical Documents]

[0012] [Patent Literature]

[0013] Patent Document 1: Japanese Patent Application Publication No. 9-103096

[0014] Patent Document 2: Japanese Patent Application Publication No. 2004-120957

[0015] Patent Document 3: Japanese Patent Application Publication No. 2000-184789

[0016] Patent Document 4: Japanese Patent Application Publication No. 2004-180354

[0017] Patent Document 5: Japanese Patent No. 6258004 Summary of the Invention

[0018] [The problem the invention aims to solve]

[0019] To detect back electromotive force (EMF), the output of the bridge circuit connected to the coil needs to be set to high impedance. In single-phase excitation or 1-2-phase excitation, at excitation positions 4 and 8, the full-bridge circuit 8-1 on the L1 side becomes high impedance, enabling the detection of the back EMF of coil L1. At excitation positions 2 and 6, the full-bridge circuit 8-2 on the L2 side becomes high impedance, enabling the detection of the back EMF of coil L2. That is, the high-efficiency mode is limited to 1-2-phase excitation or single-phase excitation, and cannot be applied to 2-phase excitation of coils where current always flows through both phases.

[0020] This disclosure was made in view of the above-mentioned problems, and one of the exemplary objectives of one of its solutions is to provide a drive circuit capable of efficiently driving a stepper motor in a two-phase excitation mode.

[0021] [Technical solutions used to address technical problems]

[0022] One aspect of this disclosure relates to a drive circuit that drives a stepper motor in a two-phase excitation manner, synchronized with an input clock. The drive circuit includes: a constant current chopper circuit that generates a pulse-modulated signal, which is pulse-modulated such that a detected value of the stepper motor's coil current approaches a current setpoint; a detection window generation circuit that generates a detection window that begins at a timing point when the stepper motor's coil current becomes less than a predetermined threshold; a logic circuit that, in the open state of the detection window, sets a full-bridge circuit connected to the stepper motor's coil in a high-impedance state, and in the closed state of the detection window, controls the full-bridge circuit according to the pulse-modulated signal; a back electromotive force (EMF) detection circuit that detects the back EMF of the coil in the open state of the detection window; and a current setting circuit that provides feedback control of the current setpoint based on the back EMF.

[0023] Furthermore, the results of arbitrarily combining the above-mentioned constituent elements, as well as the results of mutually substituting the constituent elements or expressions among methods, apparatuses, systems, etc., are also valid as solutions of the present invention.

[0024] Invention Effects

[0025] According to one aspect of this disclosure, a stepper motor can be driven efficiently using a two-phase excitation method. Attached Figure Description

[0026] Figure 1 It is a block diagram of a motor system with an existing stepper motor and its drive circuit.

[0027] Figure 2 This is a diagram illustrating the excitation position.

[0028] Figure 3 This is a waveform diagram of the drive circuit under 1-2 phase excitation.

[0029] Figure 4 It is a block diagram of a motor system including the drive circuit of the implementation method.

[0030] Figure 5 Based on Figure 4 A simplified timing diagram of the two-phase excitation drive of the drive circuit.

[0031] Figure 6 Based on Figure 4 The waveform diagram illustrates the detection of the back electromotive force of the drive circuit.

[0032] Figure 7 This is a circuit diagram illustrating an example of the configuration of a drive circuit.

[0033] Figure 8 This is a circuit diagram of a modified zero-current detection circuit.

[0034] Figure 9 Based on Figure 8 The diagram illustrates the detection of zero-crossing current in a zero-current detection circuit.

[0035] Figure 10 (a)~ Figure 10 (c) is a perspective view showing an example of an electronic device with a drive circuit. Detailed Implementation

[0036] (Summary of the implementation method)

[0037] The following is a summary of several exemplary embodiments of this disclosure. This summary serves as a prelude to the detailed description that follows, and is intended to provide a basic understanding of the embodiments. It simplifies and explains several concepts in one or more embodiments and does not limit the breadth of the invention or disclosure. Furthermore, this summary is not a comprehensive overview of all conceivable embodiments and does not limit the essential components of the embodiments. For convenience, "an embodiment" is sometimes used to refer to one or more embodiments (examples or variations) disclosed in this specification.

[0038] One implementation of the drive circuit drives a stepper motor in a two-phase excitation mode, synchronized with an input clock. The drive circuit includes: a constant current chopper circuit that generates a pulse-modulated signal, which is pulse-modulated such that the detected value of the stepper motor's coil current approaches a current setpoint; a detection window generation circuit that generates a detection window starting at a time when the stepper motor's coil current becomes less than a predetermined threshold; a logic circuit that, in the open state of the detection window, sets the full-bridge circuit connected to the stepper motor's coil to a high-impedance state, and in the closed state of the detection window, controls the full-bridge circuit according to the pulse-modulated signal; a back electromotive force (EMF) detection circuit that detects the back EMF of the coil in the open state of the detection window; and a current setting circuit that provides feedback control of the current setpoint based on the back EMF.

[0039] In two-phase excitation mode, the coil current crosses zero near the boundary between two excitation positions. Therefore, by detecting the zero-crossing of the coil current and setting a back electromotive force detection window at the boundary between excitation positions, the impact on the usual constant current chopper control can be minimized, the back electromotive force can be accurately detected, and it can be reflected in the feedback control of the current command value in high-efficiency mode.

[0040] Alternatively, in one embodiment, the drive circuit further includes a speed detection circuit that detects a period inversely proportional to the speed of the stepper motor. Alternatively, the detection window may have a length obtained by multiplying the length of the period by a predetermined coefficient. This allows the ratio of the length of the detection window to the rotation period to be stabilized.

[0041] Alternatively, in one implementation, the drive circuit also includes a register that holds the set value of the coefficient. By rewriting the set value of the register, the length of the detection window can be controlled.

[0042] Alternatively, in one implementation, the detection window generation circuit terminates the detection window when the detection of the back electromotive force based on the back electromotive force detection circuit is completed. In this case, the length of the detection window can be minimized, thereby further suppressing the impact on the constant current chopper control.

[0043] Alternatively, in one embodiment, the driving circuit further includes a zero-current detection circuit that compares a current detection signal corresponding to the voltage drop across the detection resistor in the full-bridge circuit with a threshold value. When the current detection signal becomes less than the threshold value, the zero-current detection signal is made valid. Alternatively, the detection window generation circuit may use the assertion of the zero-current detection signal as the starting point of the detection window.

[0044] Alternatively, in one embodiment, the constant current chopper circuit includes: a comparator that compares a detected value of the coil current with a threshold based on a current setpoint; an oscillator that oscillates at a predetermined frequency; and a trigger that outputs a pulse-modulated signal that transitions to an off level based on the output of the comparator and to an on level based on the output of the oscillator.

[0045] Alternatively, in one embodiment, the driving circuit is integrated onto a single semiconductor substrate. "Integration" encompasses both cases where all circuit components are formed on the semiconductor substrate and cases where the main circuit components are integrated. Some resistors or capacitors may also be located outside the semiconductor substrate to adjust circuit constants. By integrating the circuit onto a single chip, the circuit area can be reduced, and the characteristics of the circuit elements can be maintained uniformly.

[0046] (Implementation Method)

[0047] Hereinafter, preferred embodiments will be described with reference to the accompanying drawings. The same or equivalent constituent elements, components, and processes shown in the various drawings are labeled with the same reference numerals, and repeated descriptions are omitted where appropriate. Furthermore, the embodiments are not intended to limit the invention, but are merely illustrative; not all features or combinations thereof described in the embodiments are substantive aspects of the invention.

[0048] In this specification, the term "the state of connection between component A and component B" includes not only the case where component A and component B are physically directly connected, but also the case where component A and component B are indirectly connected via other components that do not substantially affect their electrical connection state or impair the function or effect of their connection.

[0049] Similarly, the phrase "the state in which component C is positioned between component A and component B" includes not only the case where component A and component C, or component B and component C are directly connected, but also the case where they are indirectly connected via other components that do not substantially affect their electrical connection state or impair the function or effect achieved through their combination.

[0050] In this specification, for ease of understanding, the vertical and horizontal axes of the referenced waveforms or time graphs have been appropriately enlarged or reduced. In addition, for ease of understanding, the waveforms shown have been simplified, exaggerated, or emphasized.

[0051] Figure 4This is a block diagram of a motor system 100 with a drive circuit 200 according to an implementation method. The drive circuit 200, together with the stepper motor 102 and the main controller 2, constitute the motor system 100. The stepper motor 102 can be any one of PM (Permanent Magnet), VR (Variable Reluctance), and HB (Hybrid) types.

[0052] The input clock CLK is input from the main controller 2 to the input pin IN of the drive circuit 200. In addition, the direction indication signal DIR, which indicates clockwise (CW) and counterclockwise (CCW), is input to the direction indication pin DIR of the drive circuit 200.

[0053] Whenever the input clock CLK is input, the drive circuit 200 causes the rotor of the stepper motor 102 to rotate by a predetermined angle in the direction corresponding to the direction indication signal DIR.

[0054] The drive circuit 200 includes full-bridge circuits 202_1 and 202_2, current value setting circuit 210, back EMF detection circuit 230, speed detection circuit 232, constant current chopper circuits 250_1 and 250_2, detection window generation circuit 260, and logic circuit 270, all of which are integrated on a semiconductor substrate.

[0055] In this embodiment, the stepper motor 102 is a two-phase motor, including a first coil L1 and a second coil L2. The drive circuit 200 is configured to drive the stepper motor 102 by two-phase excitation.

[0056] The full-bridge circuit 202_1 of channel CH1 is connected to the first coil L1. The full-bridge circuit 202_2 of channel CH2 is connected to the second coil L2.

[0057] Full-bridge circuits 202_1 and 202_2 are H-bridge circuits containing four transistors M1 to M4. In full-bridge circuit 202_1, transistors M1 to M4 are switched based on the control signal CNT1 from logic circuit 270, thereby controlling the voltage V of the first coil L1 (also called the first coil voltage). OUT1 The switch was turned on / off.

[0058] The full-bridge circuit 202_2 is constructed in the same way as the full-bridge circuit 202_1. Its transistors M1 to M4 are switched based on the control signal CNT2 from the logic circuit 270. As a result, the voltage of the second coil L2 (also called the second coil voltage) V OUT2 The switch was turned on / off.

[0059] The current setting circuit 210 generates the current setting value I. REF Immediately after the stepper motor 102 starts, the current set value I...REF It is fixed to a certain predetermined value (called the full torque setpoint) I FULL Preset value I FULL It can also be set to the current setting value I REF The maximum value of the acceptable range, in which stepper motor 102 is driven with full torque. This state is referred to as high torque mode.

[0060] When the stepper motor 102 begins to rotate stably, in other words, when the risk of losing steps decreases, it switches to high-efficiency mode. In high-efficiency mode, the current setting circuit 210 uses the back electromotive force V of coils L1 and L2 as the current setting factor. BEMF1 V BEMF2 The current setpoint I is adjusted through feedback control. REF This reduces power consumption.

[0061] The constant current chopper circuit 250_1 generates a pulse modulation signal S. PWM1 The pulse modulation signal S PWM1 During the energization of the first coil L1, pulse modulation is applied, causing the coil current I flowing through the first coil L1 to... OUT1 The detection value I NF1 Approaching the current setpoint I REF The target quantity. The constant current chopper circuit 250_2 generates a pulse modulation signal S. PWM2 The pulse modulation signal S PWM2 When the second coil L2 is energized, pulse modulation is applied, causing the coil current I flowing through the second coil L2 to... OUT2 The detection value I NF2 Proximity current setpoint I REF .

[0062] Coil current I OUT1 I OUT2 The detection method is not limited, but for example, full-bridge circuits 202_1 and 202_2 respectively include current sensing resistors R. NF And can detect current through resistor R NF The voltage drop is used as the coil current I OUT The detected value. Additionally, the current sensing resistor R... NF The position is not limited; it can be set on the power supply side or connected in series with the coil L# of the driven object between the two outputs OUT#A and OUT#B of the full-bridge circuit 202_# (hereinafter, "#" represents channel number 1, 2).

[0063] Logic circuit 270 operates based on pulse modulation signal S PWM1 This is used to switch one of the outputs of the two branches of the full-bridge circuit 202_1 connected to the first coil L1. Furthermore, the logic circuit 270 switches according to the pulse modulation signal S.PWM2 This is used to switch one of the outputs of the two branches of the full-bridge circuit 202_2 connected to the second coil L2.

[0064] Whenever the input clock CLK is input, logic circuit 270 changes the excitation position and adjusts the voltage V applied to each coil L1, L2. OUT1 V OUT2 Switching is performed. The excitation position can be considered as a combination of the magnitude and direction of the coil current of coil 1 L1 and the coil current of coil 2 L2. The excitation position can be changed based on the positive edge of the input clock CLK alone, the negative edge alone, or both.

[0065] The detection window generation circuit 260 generates a detection window, which uses the coil current I of the stepper motor 102 as the detection window. OUT1 The timing is taken as the starting point when the magnitude becomes less than a predetermined threshold. For example, the detection window generation circuit 260 generates a detection window signal BEMF_WIND1, which becomes a first level (e.g., high level) indicating the open state during the detection period of the back electromotive force on the first coil L1 side, and a second level (e.g., low level) indicating the closed state during the non-detection period. Similarly, the detection window generation circuit 260 generates a detection window, which is based on the coil current I. OUT2 The timing is set when the value of the detection window becomes less than a predetermined threshold. Detection window signals BEMF_WIND1 and BEMF_WIND2 are supplied to logic circuit 270.

[0066] When the detection window signal BEMF_WIND# is open, logic circuit 270 sets the output of the corresponding full-bridge circuit 202_# to a high-impedance state. Furthermore, when the detection window signal BEMF_WIND# is closed, logic circuit 270 adjusts the output according to the pulse modulation signal S. PWM# To control the full-bridge circuit 202_#.

[0067] The back electromotive force detection circuit 230, with the detection window signal BEMF_WIND# open, measures the back electromotive force V based on the terminal voltage of coil L#. BEMF# Perform testing. To determine the current setpoint I in high-efficiency mode. REF Feedback control, back electromotive force V BEMF1 V BEMF2 It is supplied to the current value setting circuit 210.

[0068] The speed detection circuit 232 acquires the speed (angular velocity ω) of the stepper motor 102 and generates a detection signal (speed detection signal) representing the speed ω. For example, the speed detection circuit 232 may measure the period T (=2π / ω), which is proportional to the reciprocal of the speed ω, and output the period T as a detection signal (period detection signal). In the absence of step loss, the frequency (period) of the input pulse IN is proportional to the speed (period) of the stepper motor 102. Therefore, the speed detection circuit 232 may also measure the period based on the input pulse IN, or based on an internal signal generated therefrom, and use it as the period detection signal.

[0069] In this embodiment, the period detection signal T is supplied to the detection window generation circuit 260. The detection window generation circuit 260 sets the length of the open state (detection period) of the detection window signal BEMF_WIND based on the period detection signal T. Specifically, the detection period has a length obtained by multiplying the length of the period T by a predetermined coefficient (k < 1).

[0070] For example, the coefficient k can be set to 1 / 32, 1 / 16, 1 / 8, 1 / 4 (=1 / 2) n In this case, the length of the detection period can be obtained by shifting the digital value representing the period T.

[0071] The above describes the configuration of the drive circuit 200. Next, its operation will be explained. Figure 5 Based on Figure 4 A simplified timing diagram of the two-phase excitation drive of the drive circuit 200. The logic circuit 270, synchronized with the input clock CLK, changes the excitation position in the order of 1, 3, 5, 7 (or their reverse order).

[0072] Figure 6 Based on Figure 4 The waveform diagram illustrates the detection of the back electromotive force in the drive circuit 200. Here, we focus on... Figure 5 The shift of the excitation position from position 1 to position 3 affects the back electromotive force V of the first coil L1. BEMF1 The testing process will be explained.

[0073] At time t0, the circuit transitions to excitation position 1. During excitation position 1, constant current chopper control is performed. Specifically, the constant current chopper circuit 250_1 ensures that the coil current I... OUT1 Proximity current command value I REF The method generates the PWM signal S. PWM1 The output OUT1A of the first branch (M1, M3) of the full-bridge circuit 202_1 is based on the PWM signal S. PWM1To switch on, the output OUT1B of the second branch (M2, M4) is fixed to "low".

[0074] At time t1, when the coil is switched to excitation position 3, OUT1A becomes "low" and OUT2A becomes "high", and the coil current I... OUT1 It started to decrease.

[0075] At time t2, when the coil current I OUT1 When the signal crosses a threshold near zero, the detection window generation circuit 260 sets the detection window signal BEMF_WIND1 to "high", and then sets it to "low" at time t3 after (k×T). In this example, k = 1 / 8.

[0076] During the period when the detection window signal BEMF_WIND1 is "high," i.e., the detection window is open, logic circuit 270 sets OUT1A and OUT1B to high impedance. In this state, back EMF detection circuit 230 measures the voltage V across the first coil L1. OUT1A V OUT1B The potential difference is used as the back electromotive force V. BEMF1 To obtain.

[0077] Alternatively, with the detection window open, the output OUT1B of the full-bridge circuit 202_1 can be set to high impedance, and the other output OUT1A can be set to "low". During this period, the back EMF detection circuit 230 can also measure the terminal voltage V on the OUT1B side of the first coil L1. OUT1B As the back electromotive force V BEMF1 To obtain.

[0078] Current setting circuit 210 is based on back electromotive force V BEMF1 To the current command value I REF Update the circuit. The constant current chopper circuit 250_1 is used to ensure the coil current I... OUT1 Approaching the new current command value I REF The method of generating PWM signal S PWM1 The output OUT1B of the second branch (M2, M4) of the full-bridge circuit 202_1 is based on the PWM signal S. PWM1 To switch on, the output OUT1A of the first branch (M1, M3) is fixed to "low".

[0079] The above describes the operation of the drive circuit 200.

[0080] In a two-phase excitation mode, near the boundary between a certain excitation position (1) and a certain excitation position (3), the coil current I OUT1 It crosses zero. Therefore, by adjusting the coil current I... OUT1The zero crossing is detected, and a back electromotive force V is set at the boundary between the excitation position (1) and the excitation position (3). BEMF1 The detection window minimizes the impact on typical constant current chopper control and accurately detects the back electromotive force V. BEMF1 This can be reflected in the feedback control of the current command value in high-efficiency mode.

[0081] It could also be, such as Figure 6 As shown, in addition to the detection window at the boundary between excitation positions 1 and 3, or alternatively, a detection window is set at the boundary between excitation positions 5 and 7. By increasing the number of detection windows to two, the current command value I in high-efficiency mode can be increased. REF The control cycle is shortened, and responsiveness is improved.

[0082] Here, the detection of the back electromotive force of the first coil L1 has been explained, but the back electromotive force can be detected in the same way for the second coil L2.

[0083] Figure 7 This is a circuit diagram showing an example of the configuration of the drive circuit 200. Figure 7 Only the portion associated with the first coil L1 is shown in the diagram.

[0084] Next, the current setting circuit 210 will be described. The current setting circuit 210 includes a feedback controller 220, a feedforward controller 240, and a multiplexer 212. The feedforward controller 240 outputs a fixed current setting value Ix (=I) used in the high torque mode immediately after startup. FULL The current setting value Ix is set to a large value to prevent loss of synchronization.

[0085] The feedback controller 220 becomes active in high-efficiency mode and outputs a value based on the back electromotive force V. BEMF The current setpoint Iy is used for feedback control.

[0086] Multiplexer 212 selects one of two signals, Ix and Iy, as the current setpoint I based on the mode selection signal MODE. ref To output.

[0087] The feedback controller 220 includes a load angle estimation unit 222, a subtractor 224, and a PI (proportional, integral) controller 226.

[0088] Feedback controller 220 so that the estimated load angle Approaching the predetermined target angle In this manner, the current setpoint Iy is generated. Specifically, the subtractor 224 generates the current setpoint Iy relative to the load angle. Corresponding detection value and its target value cos The error ERR is calculated. The PI controller 226 performs PI control calculations to make the error ERR zero and generates the current setpoint Iy. The processing of the feedback controller 220 can also be implemented using analog circuitry that uses an error amplifier.

[0089] The constant current chopper circuit 250-1 includes a D / A converter 252, a PWM comparator 254, an oscillator 256, and a trigger 258. The D / A converter 252 converts the current setpoint I... REF Convert to analog voltage V REF The PWM comparator 254 will feed back signal I. NF1 With reference voltage V REF Comparison, when I NF1 >V REF When the signal S is disconnected, OFF Set to active (high). Oscillator 256 generates a periodic on signal S with a specified chopping frequency. ON The trigger 258 outputs the PWM signal S. PWM1 The PWM signal S PWM1 According to the connection signal S ON To transition to the on level (e.g., "high"), based on the off signal S OFF To transition to an off level (e.g., "low").

[0090] As described above, the back EMF detection circuit 230 detects the back EMF V generated in the coils L1 (L2) of the stepper motor 102. BEMF1 (V BEMF2 ) to conduct testing.

[0091] The speed detection circuit 232 acquires the speed (angular velocity ω) of the stepper motor 102 and generates a detection signal representing the speed ω. For example, the speed detection circuit 232 may measure the period T (=2π / ω), which is proportional to the reciprocal of the speed ω, and output the period T as a detection signal. In the absence of step loss, the frequency (period) of the input pulse IN is proportional to the speed (period) of the stepper motor 102. Therefore, the speed detection circuit 232 may also measure the period based on the input pulse IN, or based on an internal signal generated therefrom, and use it as a detection signal.

[0092] Load angle estimation part 222 is based on back electromotive force V BEMF The load angle is estimated using the rotational speed ω. Load angle This is equivalent to the difference between the current vector (i.e., position command) determined by the driving current flowing through the first coil L1 and the position of the rotor (movable element). Back electromotive force V BEMF1 It is given by the following equation (1).

[0093]

[0094] K E Let V be the back electromotive force constant, and ω be the rotational speed. Therefore, it is possible to determine the back electromotive force V by measuring V. BEMF And the rotational speed ω to generate the load angle It has relevant detection values. For example, it can also be... As the detection value, in this case, the detection value is represented by equation (2).

[0095]

[0096] Zero-current detection circuit 290 in coil current I OUT1 The absolute value becomes less than the predetermined threshold I. ZERO At that time, the zero current detection signal S ZC Set to active (e.g., "high"). While not limited to this, it is also possible for the zero-current detection circuit 290 to include a comparator 292 that compares the current with the detection resistor R set in the full-bridge circuit 202_1. NF The voltage drop and corresponding current detection signal I NF1 and threshold voltage V ZERO Comparison. The detection window generation circuit 260 will generate the zero-current detection signal S. ZC The effective starting point of the detection window is placed at the beginning.

[0097] The driver circuit 200 includes an interface circuit 280 and a register 282. The interface circuit 280 receives input from an external processor (e.g., ...). Figure 4 The main controller 2) receives the setting data for coefficient k. Register 282 holds the setting data received by interface circuit 280. The type of interface is not limited, but for example, it can use I... 2 C (Inter-IC: Inter-integrated circuit) interface or SPI (Serial Peripheral Interface), etc.

[0098] The embodiments have been described above. Those skilled in the art should understand that these embodiments are merely illustrative, and various modifications may exist in the combination of their constituent elements or processing steps, and such modifications are also within the scope of this invention. Hereinafter, such modifications will be described.

[0099] (Variation Example 1)

[0100] exist Figure 7 In the driving circuit 200, the zero current detection circuit 290 is based on the current sensing resistor R. F The voltage drop affects the coil current I OUT1The zero-crossing is detected, but not limited to this. For example, the zero-current detection circuit 290 can also detect the coil current I based on the terminal voltage of coil L1. OUT1 Zero crossings are detected.

[0101] Figure 8 This is a circuit diagram of a modified zero-current detection circuit 290A. The zero-current detection circuit 290 includes a comparator 294, which converts the terminal voltage V of coil L1... OUT1A The threshold voltage V near zero ZC Compare them.

[0102] Figure 9 Based on Figure 8 The diagram illustrates the zero-crossing detection of the 290A zero-current detection circuit. During the period before time t0, the OUT1A side is chopping-controlled by a PWM signal. During the high-range of the PWM signal, the terminal voltage V... OUT1A It can be represented by equation (3).

[0103] V OUT1A =V DD -R ON1 ×I OUT1 …(3)

[0104] R ON1 This is the on-resistance of transistor M1. Furthermore, in the low range of the PWM signal, the terminal voltage V... OUT1A It can be represented by equation (4).

[0105] V OUT1A =-(R) NF +R ON3 )×I OUT1 …(4)

[0106] R ON3 It is the on-resistance of transistor M3.

[0107] At time t1, when OUT1A becomes "low" and OUT1B becomes "high", the coil current I OUT1 It begins to decrease. At this time, the voltage V at terminal OUT1A... OUT1A It is expressed by equation (4). Therefore, the terminal voltage V OUT1A Will be related to the coil current I OUT1 The decrease is accompanied by an increase. When the coil current I... OUT1 The threshold I is reduced to near zero ZC Until then, the terminal voltage V OUT1A With current I ZC The corresponding threshold V ZC Cross, zero current detection signal S ZC It is placed in a valid position.

[0108] (Variation Example 2)

[0109] In one implementation, the length of the detection window varies with the rotational speed of the stepper motor 102, but is not limited to this. For example, the detection window generation circuit 260 may also adjust the length based on the back electromotive force V of the back electromotive force detection circuit 230. BEMF When the detection is complete, the detection window ends. In this case, the length of the detection window can be minimized, and the impact on the constant current chopper control can be further suppressed.

[0110] (Variation Example 3)

[0111] The full-bridge circuit 202 can be a chip different from the driver circuit 200, or it can be a discrete component.

[0112] (Variation Example 4)

[0113] The method for generating the current setpoint Iy in high-efficiency mode is not limited to the method described in the implementation. For example, the back electromotive force V could also be predetermined. BEMF1 Target value V BEMF(REF) and with back electromotive force V BEMF1 Approaching the target value V BEMF(REF) This forms a feedback loop.

[0114] (Variation Example 5)

[0115] In this implementation, a PI controller is used to form the feedback controller 220, but it is not limited to this and a PID controller or the like can also be used.

[0116] Finally, the application of the drive circuit 200 will be explained. The drive circuit 200 is used in various electronic devices. Figure 10 (a)~ Figure 10 (c) is a perspective view showing an example of an electronic device equipped with a drive circuit 200.

[0117] Figure 10 The electronic device in (a) is an optical disc device 500. The optical disc device 500 includes an optical disc 502 and a pickup 504. The pickup 504 is used to write data onto and read data from the optical disc 502. The pickup 504 is movable (tracking) along the radial direction of the optical disc on the recording surface of the optical disc 502. Furthermore, the distance between the pickup 504 and the optical disc is also variable (focusing). The pickup 504 is positioned by a stepper motor (not shown). A drive circuit 200 controls the stepper motor. With this configuration, the pickup 504 can be positioned with high efficiency and high precision while preventing step loss.

[0118] Figure 10(b) refers to an electronic device 600 with video recording capabilities, such as a digital still camera, digital camcorder, or mobile phone terminal. Device 600 includes an image sensor 602 and an autofocus lens 604. A stepper motor 102 positions the autofocus lens 604. A drive circuit 200 drives the stepper motor 102. With this configuration, the autofocus lens 604 can be positioned efficiently and accurately while preventing step loss. In addition to the autofocus lens, the drive circuit 200 can also be used to drive a lens for image stabilization. Alternatively, the drive circuit 200 can be used for aperture control.

[0119] Figure 10 The electronic device in (c) is a printer 700. The printer 700 includes a head 702 and a guide rail 704. The head 702 is supported and can be positioned along the guide rail 704. A stepper motor 102 controls the position of the head 702. A drive circuit 200 controls the stepper motor 102. With this configuration, the head 702 can be positioned efficiently and with high precision while preventing step loss. In addition to driving the head, the drive circuit 200 can also be used to drive the motor for the paper feeding mechanism.

[0120] Not only like Figure 10 (a)~ Figure 10 The civilian equipment shown in (c) can also preferably be used in industrial machines or robots.

[0121] The embodiments described herein merely illustrate the principles and applications of the present invention. Many modifications or configuration changes can be made to the embodiments without departing from the spirit of the present invention as defined in the claims.

[0122] [Industrial Availability]

[0123] This invention relates to a stepper motor drive technology.

[0124] [Explanation of reference numerals in the attached figures]

[0125] L1, first coil

[0126] L2, second coil

[0127] 2. Main Controller

[0128] 100 motor system

[0129] 102 stepper motor

[0130] 200 drive circuit

[0131] 202 Full-bridge circuit

[0132] RNF sense resistor

[0133] 210 Current value setting circuit

[0134] 212 Multiplexer

[0135] 214 Adders

[0136] 220 Feedback Controller

[0137] 222 Load Angle Estimation Section

[0138] 224 Subtractors

[0139] 226 PI controller

[0140] 230 Back EMF Detection Circuit

[0141] 232 Speed ​​Detection Circuit

[0142] 240 Feedforward Controller

[0143] 250 Constant Current Chopper Circuit

[0144] 252 D / A Converter

[0145] 254 PWM comparator

[0146] 256 Oscillators

[0147] 258 triggers

[0148] 260 Detection Window Generation Circuit

[0149] 270 Logic Circuits

[0150] 290 Zero Current Detection Circuit

[0151] 292 comparators

[0152] 280 interface circuit

Claims

1. A drive circuit that drives a stepper motor in a two-phase excitation manner in sync with an input clock; The driving circuit is characterized by including: A constant current chopper circuit generates a pulse modulation signal, which is then pulse-modulated to make the detected value of the stepper motor's coil current close to the current set value. A detection window generation circuit generates a detection window that starts at a timing point when the coil current of the stepper motor becomes less than a predetermined threshold. The logic circuit (i) when the detection window is open, places the full-bridge circuit connected to the coil of the stepper motor in a high-impedance state, and (ii) when the detection window is closed, assigns one output of the full-bridge circuit to a high output state and the other output to a low output state, switches the output of the one assigned to the high output state according to the pulse modulation signal, and keeps the output of the other assigned to the low output state at a low level. The back electromotive force detection circuit, when the detection window is open, detects the back electromotive force of the coil. The current setting circuit uses the back electromotive force to provide feedback control for the current setting value. (i) Before the current zero-crossing detection, the above logic circuit responds to the rising edge of the above input clock by switching the allocation of the high output state and the low output state of the above full-bridge circuit, and in order to reduce the coil current, the output of the above full-bridge circuit that has been newly allocated to the above high output state is fixed at a high level, and the switching operation is stopped. (ii) When the coil current passes through the threshold, the detection window generation circuit sets the detection window to the open state. (iii) When the detection window is closed, the logic circuit restores the allocation of the high output state and the low output state to the same state as when the detection window was last closed, and restarts the switching of the output of the full bridge circuit that was allocated to the high output state.

2. The driving circuit as described in claim 1, characterized in that, It also includes a speed detection circuit that detects the period that is inversely proportional to the speed of the stepper motor. The detection window described above has a length obtained by multiplying the length of the aforementioned period by a predetermined coefficient.

3. The driving circuit as described in claim 2, characterized in that, Also includes: The interface circuit receives the setting data for the aforementioned coefficients from an external processor, and The register holds the aforementioned setting data received by the interface circuit.

4. The driving circuit as described in claim 1, characterized in that, When the detection of the back electromotive force based on the aforementioned back electromotive force detection circuit is completed, the detection window ends.

5. The driving circuit according to any one of claims 1 to 4, characterized in that, It also includes a zero current detection circuit, which compares a current detection signal corresponding to the voltage drop of the detection resistor set in the full-bridge circuit with a threshold, and makes the zero current detection signal valid when the current detection signal becomes less than the threshold. The detection window generation circuit described above uses the zero-current detection signal as the starting point of the detection window.

6. The driving circuit according to any one of claims 1 to 4, characterized in that, It also includes a zero-current detection circuit, which compares the terminal voltage of the coil with a threshold voltage, and makes the zero-current detection signal valid when the terminal voltage of the coil crosses the threshold voltage. The detection window generation circuit described above uses the zero-current detection signal as the starting point of the detection window.

7. The driving circuit according to any one of claims 1 to 4, characterized in that, The above constant current chopper circuit includes: A comparator compares the detected value of the coil current with a threshold value based on the current setting. An oscillator that oscillates at a predetermined frequency, and The trigger outputs the aforementioned pulse modulation signal, which is switched to an off level according to the output of the comparator and switched to an on level according to the output of the oscillator.

8. The driving circuit as described in claim 5, characterized in that, The above constant current chopper circuit includes: A comparator compares the detected value of the coil current with a threshold value based on the current setting. An oscillator that oscillates at a predetermined frequency, and The trigger outputs the aforementioned pulse modulation signal, which is switched to an off level according to the output of the comparator and switched to an on level according to the output of the oscillator.

9. The driving circuit as described in claim 6, characterized in that, The above constant current chopper circuit includes: A comparator compares the detected value of the coil current with a threshold value based on the current setting. An oscillator that oscillates at a predetermined frequency, and The trigger outputs the aforementioned pulse modulation signal, which is switched to an off level according to the output of the comparator and switched to an on level according to the output of the oscillator.

10. The driving circuit according to any one of claims 1 to 4, characterized in that, The driving circuit is integrated into a single semiconductor substrate.

11. An electronic device, characterized in that, include: Stepper motor, and The drive circuit described in any one of claims 1 to 10 drives the aforementioned stepper motor.

12. A driving method, which is based on a two-phase excitation mode and drives a stepper motor synchronously with an input clock, characterized in that, include: The step of generating a pulse-modulated signal that makes the detected value of the coil current of the aforementioned stepper motor close to the target amount based on the current set value. The step involves generating a detection window that is opened when the coil current of the aforementioned stepper motor becomes less than a predetermined threshold. With the detection window closed, the steps include assigning one output of the full-bridge circuit connected to the coil of the stepper motor to a high output state and assigning the other output to a low output state. In the closed state of the aforementioned detection window, the steps of switching the output of the one assigned to the high output state and fixing the output of the other assigned to the low output state to a low level according to the aforementioned pulse modulation signal are as follows: The step of placing the full-bridge circuit in a high-impedance state under the aforementioned open state of the detection window. The step of detecting the back electromotive force of the coil in the above-mentioned open state of the detection window. The steps for feedback control of the current setpoint based on the aforementioned back electromotive force are as follows. Before the current zero-crossing detection, in response to the rising edge of the input clock, the allocation of the high and low output states of the full-bridge circuit is reversed. Furthermore, to reduce the coil current, the output of the full-bridge circuit newly assigned to the high output state is fixed at a high level, thus stopping the switching operation. The step of setting the detection window to the open state when the coil current crosses the threshold, and When the detection window is closed, the allocation of the high output state and the low output state is restored to the same state as when the detection window was last closed, and the switching of the output of the full bridge circuit that was allocated to the high output state is restarted.

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