JP2008131799A - Stepping-motor drive circuit and control method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To adopt current reduction control in microstep driving. <P>SOLUTION: A stepping-motor driving method is such that a detected current (io) is controlled to make a detected voltage (Vs), based on the detected current (io) of a stepping motor (M), equal to a reference voltage (Vo); in the drive state, the stepping motor is rotationally driven, while using the current (io) as a drive current; in the hold state, the rotor is held at a fixed position in a stopped state, while the current (io) is used as a holding current that is lower than the drive current; (1) when the stepping motor (M) is in a transient state of being shifted from the hold state to the drive state, the current is controlled so that the reference voltage (Vo) is gradually increased, from a holding voltage to a drive voltage; or (2) when the stepping motor (M) is in a transient state of being shifted from the drive state to the hold state, the current is controlled so that the reference voltage (Vo) is gradually reduced, from the drive voltage to the hold voltage, and alternatively, (3) in both the transient states, control corresponding to each transient state is carried out. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a stepping motor drive circuit that realizes smoother drive in microstep drive, particularly high resolution microstep drive, and a control method therefor.

  With the technical progress of micro step drive of stepping motors and the miniaturization of stepping motors, the field of application of stepping motors has expanded, and now it is also used in the nanotechnology field that requires ultra-precision accuracy and the bio field that handles cells. It has become like this.

Along with that, more demand for high-resolution micro-step drive, more specifically,
(a) Switching of drive current during smoother drive, particularly at start / stop and during repositioning described later (that is, drive current supplied when the stepping motor is driven to rotate is used as drive current, and the stop state at a fixed position is High-precision and smooth start-up or re-positioning that does not generate even slight vibrations when the drive current to be held is the hold current (switching between the drive and hold currents)
(b) There has been a demand for a drive system (especially thermal expansion / contraction of a ball screw directly connected to the stepping motor) that influences the heat from the stepping motor, and in other words, a drive that does not affect the entire apparatus. (a) and (b) are conflicting requests as will be described later.

  First, as an example of the micro-step driving shown in (a), there is an invention disclosed in Japanese Patent Laid-Open No. 7-227099. As a further evolution, this is a high-resolution drive (moving angle of one pulse is 0.0036 °) in which one rotation of the rotor is divided into 100,000 divisions or more and step-driven, and this is actually used. Currently, 200,000 divisions are required for optical fiber processing equipment. In the field of biotechnology, there is a claim that a shock at step movement (overshoot or undershoot at the movement destination) is large in the movement of one pulse in 100,000 divisions, and 400,000 divisions are required. There is an increasing number of very sensitive uses such as reducing the shock of repositioning at the stop position to the minimum for actual work such as measurement and machining.

  On the other hand, although it is a problem shown in (b), when a stepping motor is driven, it naturally generates heat, but the heat generated by this stepping motor causes subtle thermal expansion of the ball screw directly connected to the stepping motor, and the accuracy of the control system It has a big influence on. At present, it has been pointed out that not only such adverse effects due to heat conduction but also a slight updraft caused by heat generated by the power supply and motor driver affects the measurement. Such adverse effects of heat generated by motors and the like are hated not only in the biotechnology field but also in the ultra-precision field of nanotechnology, and as a countermeasure there are currently methods for reducing the adverse effects of heat when using motors as follows. It has been adopted.

  In other words, the method generally adopted as the method is that the stop position is held (the hold state at the fixed position of the rotor by the hold current) compared to the rotation of the stepping motor (the motor drive state by the drive current). When the required torque is small and the rotor is in the stop position hold (hold state), the power required for holding (= rotor stop position hold) is reduced to reduce unnecessary power, This is a method of reducing the heat generation of the stepping motor (and driver circuit).

  However, if the hold current and the drive current are properly used, a spike-like damped oscillation at the time of switching between the drive current and the hold current as shown in (100) and (101) of FIG. ) Occurred in the stepping motor, and this was a factor that hindered ultra-precise and smooth start / stop or repositioning of the stepping motor.

  Here, the spike-like damped vibration will be described. As is well known, the amount of drive current flowing through the stepping motor and the torque generated between the rotor and the stator are in a direct proportional relationship. For example, a hold current that is lower than the drive current is passed through the stepping motor to hold the rotor with a weak torque, the heat generation of the stepping motor is reduced, and then the measurement or machining at that point is stopped. When moving to work, drive current is passed through the stepping motor, and at one point where it is stopped, the drive system (for example, the X table moving in the X direction is placed on the Y table moving in the Y direction, in the XY direction) The repositioning is performed again to fix the XY table (moving to (1)) (this point is the same even when starting from the hold state to the drive state).

  In this case, in the hold state before re-fixing or starting, the friction load of the drive system itself and the torque generated by the stepping motor (in this case, a low hold current flows through the stator to fix the rotor in the stopped state). Although it is balanced, if a repositioning is performed by passing a drive current through the stepping motor to the stator for actual work such as measurement or machining from this hold state, torque fluctuation generated between the rotor and stator will occur and the rotor will be slightly Rotate (position shift). Conversely, if the drive current for positioning is lowered to the hold current in order to suppress heat generation after the work such as measurement or machining is completed, the generated torque also decreases in proportion to this, so the direction of the friction load A slight rotation (position misalignment) is caused and the balance is balanced. At this time, a spike-like damping vibration is generated in the stepping motor.

  Here, in the case of the high-precision repositioning required in the high-precision processing, high-precision measurement, or high-precision operation in the nanotechnology field and the cell-related biotechnology field as described above, repositioning is currently performed with drive current. After that, when there is no need for positioning, an external drive / hold signal is input to reduce the operating current flowing to the stepping motor to the hold current, or the elapsed time from the last input command pulse is longer than the predetermined time When the time elapses, the operating current is automatically lowered to the hold current by the timer signal.

  Then, when performing the repositioning operation at that point by resuming the work that is appropriately adopted as necessary, the lowered operating current is switched to a value (drive current) necessary for the repositioning operation.

  With this current change (increase), the torque between the rotor and the stator increases, and the balance position changes. That is, the angle changes to the balanced position with a restoring force increased by the increased torque. This change in angle appears on the shaft as a damped vibration and is transmitted to the mechanical system as the aforementioned spike-like displacement (damped vibration) .In particular, in high-resolution microstep drive, the precision repositioning required in precision machining and precision measurement is required. This causes various problems.

  In other words, in ultra-high resolution micro-step drive that is required for precision machining and precision measurement, at the time of start-up, repositioning, or stop caused by a change in torque accompanying the change in operating current for operating the stepping motor The smooth vibration of ultra-high resolution micro-step drive is hindered by the slight damped oscillation in the transient state when switching the current, and the method of reducing the operating current to prevent heat generation of the stepping motor and control circuit can be adopted could not.

  The same thing occurs when switching between drive / hold currents at the start and stop times. When switching the operating current at the time of start-up, the operating current instantaneously switches from the hold current to the drive current as in the case of the above-mentioned repositioning. At this time, the torque increases instantaneously due to the sudden increase in current, resulting in this. The instantaneous torque increase is transmitted to the mechanical system as a spike-like displacement as described above. On the other hand, at the time of stop, the operating current suddenly decreases when the drive current is momentarily switched from the drive current to the hold current, and as a result, the torque decreases instantaneously, and the instantaneous torque decrease due to this decreases as a spike-like displacement. This is transmitted to the mechanical system and causes the above-mentioned troubles. Therefore, as described above, current reduction control for suppressing heat generation cannot be employed in high-resolution microstep driving.

In order to realize smooth step drive in ultra-high resolution micro-step drive, the stepping motor is micro-stepped with the drive current during the entire motor-off period from the motor-on time including the hold state at the stop time. Although it may be driven, it cannot be adopted because of the above-mentioned “heat generation suppression”. From this point of view, the problems (a) and (b) are contradictory problems and are considered to be very difficult to solve.
JP 7-227099 A

  However, if the above-mentioned problems are overcome, that is, when switching from the hold current to the drive current, and conversely, when switching from the drive current to the hold current, the spike-like angular displacement of the motor shaft is prevented. Current switching that suppresses heat generation of the motor is effectively utilized in an ultra-precise repositioning device using high-resolution microstep drive.

  From this point of view, the present invention has been made. By devising switching between hold current / drive current, current reduction control can be adopted in high-resolution microstep driving.

The driving method of the stepping motor (M) according to claim 1 is as follows: “A current (io) for operating the stepping motor (M) is detected, and a detection voltage (Vs) based on the current (io) is detected by the stepping motor (M). The current (io) is controlled to be equal to a reference voltage (Vo) that defines the operating state of
In the drive state, the stepping motor (M) is rotationally driven with the current (io) as the drive current, or in the hold state, the current (io) is held as a hold current lower than the drive current and the rotor is held at a fixed position. A stepping motor (M) driving method,
(1) When the stepping motor (M) is in a transient state in which it shifts from the hold state to the drive state, the reference voltage (Vo) is controlled so as to gradually increase from the hold voltage to the drive voltage, or
(2) When the stepping motor (M) is in a transient state in which the drive state shifts from the drive state to the hold state, the reference voltage (Vo) is controlled so as to gradually decrease from the drive voltage to the hold voltage, or
(3) In both transient states, control according to the transient state is performed '', and it is possible to suppress the damping vibration at the time of start-up, re-positioning or stop, and extremely smoothly in the transient state. It is made to be able to pass through.

The stepping motor drive circuit according to claim 2 comprises:
`` Constant current output circuit section (10) for driving the stepping motor (M) to rotate at the current (io) for operating the stepping motor (M) or holding it at a fixed position in a stopped state,
The current (io) flowing through the constant current output circuit unit (10) is detected, and the detection voltage (Vs) based on the current (io) is a reference voltage (Vo) that defines the operating state of the stepping motor (M). In a stepping motor drive circuit configured with a control circuit unit (1) having a constant current control unit (9) for controlling the current (io) to be equal to
The control circuit (1)
In the transition state from the drive state to the hold state, the reference voltage (Vo) is gradually decreased from the drive reference voltage (VoH) to the hold reference voltage (VoL), or in the transition state from the hold state to the drive state. A reference voltage operation unit (7) having a function of gradually increasing the reference voltage (Vo) from the hold reference voltage (VoL) to the drive reference voltage (VoH) or both of them is provided.

  Claim 3 is a more detailed description of the stepping motor drive circuit (A) according to claim 2, wherein “the reference voltage operating section (7) sets a time constant for changing the reference voltage (Vo) in a transient state. The calculated value calculated based on the transfer function G (S) having is multiplied by the reference voltage constant (Vk) in the motor drive, and this is output as a reference voltage (Vo) to the constant current controller (9). '' In the transient state at start-up, re-positioning, or stop, the reference voltage (Vo) gradually changes according to the transfer function, and the drive current based on this reference voltage (Vo) ( i2-i3) gradually changes, and this makes it possible to suppress the damped oscillation in the transient state. The reference voltage constant (Vk) is a constant that sets the reference voltage (Vo) so that the rated current or less flows through the stepping motor (M).

  A fourth aspect is for carrying out the invention according to any one of the first to third aspects, wherein “the rate of change of the current (io) is within a range that the stepping motor (M) can follow”. Features.

  A fifth aspect of the present invention relates to the “followable range” according to the fourth aspect of the invention, wherein “τ as a time coefficient of the transfer function is in a range of 2.5 to 10 ms”.

  The feature of the present invention is that the reference voltage (Vo) is gradually increased / decreased in the transient state at the time of switching from the drive to the hold or vice versa, or at the time of repositioning in which the current changes from the hold to the drive. The stepping motor (M) has a time constant and a calculated value calculated based on the transfer functions G1 (S) and G2 (S) corresponding to the hold or drive state so that the rated current or lower current flows through the stepping motor (M). By multiplying the reference voltage constant (Vk) set to the reference voltage (Vo) to obtain the reference voltage (Vo) and gradually changing the reference voltage (Vo) having this time constant, the rotor angular position with respect to the generated torque change This makes it possible to smoothly switch the operating current (io) for operating the stepping motor (M) between the drive and hold while suppressing the spike-like displacement.

  In other words, when the change in the rotor angular position can follow the change in the torque generated by the current change in the motor coil (i.e., the stator coil), the torque is changed from the drive torque to the hold torque while the rotor angular position remains balanced. It is considered that the current [that is, the operating current (io)] for operating the stepping motor (M) can be smoothly switched while suppressing the spike-like displacement. Is an attempt to achieve this.

  That is, the reference voltage (Vo) that gradually increases and decreases with the time constant and the detected value (Vs) of the operating current (io) are input to the constant current control unit (9), and the constant current control unit (9) The reference voltage (Vo) and the detection voltage (Vs) are compared, and the power supply voltage is switched by the step-down chopper (9a) so that the detection voltage (Vs) matches the reference voltage (Vo) that increases or decreases. Is converted into operating current (io). As a result, the torque gradually increases and decreases without abruptly changing in the initial transition stage at the start and stop, and further in the initial transition stage at the time of repositioning, and no shock is applied to the drive system. Therefore, the “operation current reduction method” that shows an important effect on heat countermeasures can be adopted for high-resolution microstep drive.

The present invention will be described below with reference to the illustrated embodiments. In the circuit of the present embodiment, it is roughly classified as follows.
(A) The operating current (io) that always flows through the stepping motor (M) at the time of steady drive (drive) or hold, and also in the transient state from the drive state to the hold state or vice versa, Drive to the stepping motor (M) controlled so as to follow the reference voltage (Vo) in the “state” and “transient state”, so that the stepping motor (M) performs a predetermined high resolution microstep drive according to the sequence. Hold / transient, constant current output circuit section (10) for supplying the operating current (io) in each state, and
(B) A control circuit unit (1) that performs current control of the operating current (io) of the constant current output circuit unit (10) in each state of drive / hold / transition. FIG. 1 shows a circuit diagram thereof. The stepping motor (M) to be controlled will be described using a five-phase stepping motor as a representative example, but is not limited to this.

The constant current output circuit (10)
(a) a known rectifier circuit (11) for converting commercial alternating current into direct current,
(b) A fuse (F1) inserted on the (+) side of the rectified DC circuit to protect the constant current output circuit (10) from overload,
(c) Chopper (9a) for chopping (on / off) the rectified direct current according to control by a constant current control unit (9) described later and supplying a current value according to the control value of the constant current control unit (9) In this embodiment, a power MOS • FET is used as the chopper (9a).
(d) For supplying the supply current (i1) connected between the ground (GND) connected to the zero volt line (Z) of the constant current output circuit (10) and the positive line (+) input side. First capacitor (C1),
(f) A flywheel diode (D1) connected between the zero volt line (Z) of the constant current output circuit section (10) and the output side of the chopper (9a),
(g) A reactor (L1) provided in series on the output side of the chopper (9a), for smoothing the chopped current in cooperation with the capacitor (C2),
(h) Terminals (t1) to (t5) connected to the stepping motor (M) are provided, connected to the output side of the reactor (L) and the zero volt line (Z), and a switching element (Tr) described later is connected. The output stage (S) as its main component,
(i) small value sense resistors (R1) (R2) connected in series to the output stage (S),
“In this embodiment, the sense resistor is composed of a first sense resistor (R1) and a second sense resistor (R2), and the first sense resistor (R1) is the (−) side of the first capacitor (C1). And the second sense resistor (R2) are connected in series, and the second sense resistor (R ₂ ) is connected to the (−) side of the output stage (S) and the second capacitor (C2) [or the first sense resistor. (R1)]. In this case, sensing is performed by both the first sense resistor (R1) and the second sense resistor (R2), and the current to be detected is the total current for operating the stepping motor (M), that is, the operating current (i1 + i2-i3). In other words, the sense resistor (R1) is a supply current that circulates from the first capacitor (C1) to the chopper (9a), the reactor (L1), the second capacitor (C2), and the sense resistor (R1) in the clockwise direction in the figure. (i1) is detected, and the sense resistor (R2) detects the excitation current (i2) flowing in the zero volt line (Z) direction from the (+) side through the output stage (S) and the stepping motor (M). A drive current (i2-i3), which is the sum of an electromotive current (i3) generated in the stepping motor (M) and flowing in the opposite direction during operation, is detected. ]
(j) Driving voltage application unit (DV) for supplying a constant current to the stepping motor (M) (The higher the rotational speed of the stepping motor (M), the less the driving current (i2-i3) flows). Since the circuit is a constant current circuit, the motor drive voltage application unit (DV) increases the motor drive voltage as the rotational speed increases, so that the constant current flows to the stepping motor (M).)
(k) A second capacitor (between the output side of the reactor (L1) and the connection part of the sense resistors (R1) and (R2) for supplying the exciting current (i2) to the output stage (S) ( C2).

  The output stage (S) shown in (h) is a known one having the switching element (Tr) as its main component as described above, and in this embodiment, a power MOS-FET is used. It is a simple configuration. The output stage transistors which are the switching elements (Tr) of the output stage (S) are divided into 5 sets, and two sets are connected in series, and these 5 sets are connected in parallel to form the output stage (S). Yes. The output stage transistor is connected to a wire connecting portion of the stepping motor (M) connected in a ring shape. The switching means (S) is controlled to be turned on / off according to the sequence, thereby causing the stepping motor (M) to step in the sequence.

  The current (i1) is the driving voltage (DV voltage) of the stepping motor (M). In the stepping motor (M), the driving current (i2-i3) gradually becomes difficult to flow as the rotational speed increases. In this circuit, which is a current circuit, the voltage (DV voltage) gradually increases as the rotational speed increases. ”Supply current for raising and lowering and charging the second capacitor (C2) The current (i2) is the exciting current of the stepping motor (M) generated by the discharge of the second capacitor (C2). As shown by the broken line in the figure, the second capacitor (C2), the output stage (S), It circulates as the second sense resistor (R2). The current (i3) is an electromotive current generated by the rotational motion of the rotor of the stepping motor (M), and is a surplus current in the direction opposite to the excitation current (i2). The electromotive current (i3) is circulated through a diode (not shown) of the output stage (S) to the second capacitor (C2), the second sense resistor (R2), and the output stage (S). As a result, the drive current (i2−i3) obtained by subtracting the electromotive current (i3) from the excitation current (i2) flows through the sense resistor (R2). The current detection circuit unit (8) outputs the sum (V1 + V2) of the detection voltages detected by the sense resistors (R1) and (R2) to the constant current control unit (9).

  The constant current control circuit (1) consists of the command pulse period measurement unit (3), excitation sequence counter unit (4), excitation pattern output unit (5), selector (6), reference voltage operation unit (7), constant current It consists of a control circuit unit (9), a detection circuit unit (8), etc., and has an external device (not shown) with command pulse (CW / CCW) output, current switching external input (6a), selection switching (6b) Connected).

  The command pulse period measurement unit (3) operates the excitation sequence counter unit (4) while receiving the command pulse (CW / CCW) from the external device and measures this period (T) [see FIG. 3]. If the cycle (T) is shorter than or equal to the set drive holding time (t), a drive current maintaining signal is output to the selector (6), and the drive holding time with the cycle (T) set. If it is longer than (t), it is judged that the command pulse input has been completed, and a release command (indicated as drive hold timer output in FIG. 1) for maintaining the drive current of the drive / hold signal to hold current (H → L) is selected. Output to (6). The step (movement angle in FIG. 3) is maintained or stopped at the rising edge of the final command pulse (CW / CCW).

  Conversely, when the command pulse (CW / CCW) is input, the step starts at the rising edge, but the drive hold timer output is L → H at the falling edge of the command pulse (CW / CCW) (Fig. 3). Is output to the selector (6). Note that the command pulse (CW / CCW) is output from an external device, and advances the stepping motor clockwise or counterclockwise by the number corresponding to the number of pulses.

  The excitation sequence counter unit (4) receives the command pulse (CW / CCW) input through the command pulse period measurement unit (3) and assigns the address (command signal) for specifying the excitation pattern to the next drive pattern. Output to the output unit (5). Furthermore, when the resolution is 2000 decomposition (division), the sequence is 4 × 10 = 40 periods (advance), and when 2500 resolution (division) is 5 × 10 = 50 periods (advance), 5000 decomposition In the case of (division), 10 × 10 = 100 cycles (advance), and in the case of 10,000 decomposition (division), 20 × 10 = 200 cycles (advance), which corresponds to the excitation pattern designation address corresponding to the resolution. The excitation pattern is output as a gate signal from the excitation pattern output section (5) to the output stage (S), and the excitation of the stepping motor (M) is switched by turning on / off the power element (Tr) of the output stage (S). Step forward. An example of a driving method (10,000 divisions) related to micro-step driving of the five-phase stepping motor (M) is as described in detail in the above-mentioned Japanese Patent Application Laid-Open No. 7-227099.

  The detection circuit unit (8) is for detecting the sum [V1 + V2 = Rs] of the sense voltages of the first sense resistor (R1) and the second sense resistor (R2). That is, the reference voltage (Vo) is compared with the detection voltage (Vs) from the current detection circuit unit (8) based on the operating current (io), and the detection voltage (Vs) matches the reference voltage (Vo). The chopper (9a) is controlled as follows. Therefore, at the change (transient) stage of the reference voltage (Vo), the operating current (io = i1 + i2-i3) also changes accordingly. This point will be described in detail later.

  The selector (6) is (a) a signal input forcibly switching to drive current / hold current from an external device (shown as current switching external input (6a) in the figure, from drive current to hold current or from hold current to drive current. And (b) drive hold timer output from the command pulse period measurement unit (3) (as described above, the period (T) from the drive hold time (t)) Drive / hold signal output by the selector (6) for switching the drive current maintaining signal when the signal is short or equal, or the release command when the period (T) is longer than the set drive retention time (t). The signal is input to the reference voltage operation unit (7). The selection switching (6b) is to select the (a) and (b) that are the outputs of the selector (6) from the outside.

  As shown in FIG. 2, the reference voltage operation unit (7) includes a transfer function calculation unit (71), an input side switch (72), an output side switch (73), and a multiplier (74). A drive coefficient (α = 1) or a hold coefficient (α <1) in a reference voltage constant (Vk) (= a constant set so that a rated current or lower current flows in the stepping motor (M)) as a control reference. ) Is D / A converted and output as a reference voltage (Vo). The transfer function calculation unit (71) has a transfer function 1 [G1 (s) = 1 / (τ1S + 1)] when shifting from the hold state to the drive state, and a transfer function 2 when shifting from the opposite drive state to the hold state. [G2 (s) = 1 / (τ2S + 1)] is stored in memory, and a transfer function is selected according to the state. Selection of a drive coefficient and a hold coefficient is switched internally by the drive / hold signal described above. Here, τ is a time constant and is 2.5 to 10 ms in this embodiment. S is a Laplace operator.

  The input side switch (72) is configured to select a drive coefficient (α = 1) and a hold coefficient (α <1) by inputting a drive / hold signal. Similarly, the output side switch (73) selects the result of the transfer function 1 or the transfer function 2 by the input of the drive / hold signal and outputs it to the multiplier (74).

  The multiplier (74) multiplies the output value of the output side switch (73) by the reference voltage constant (Vk), and constant current as a reference voltage (Vo) that gradually increases to a certain value or gradually decreases to a certain value. It is output to the control circuit unit (9). The reference voltage (Vo) is output as an analog signal by D / A conversion.

  Next, the operation of the circuit of the present invention will be described.

(a) When starting or repositioning starts In the state before starting, the rotor is stopped at a certain hold position by the hold current. When the command pulse (CW / CCW) is input to the command pulse cycle measurement unit (3), the signal to the selector (6) of the command pulse cycle measurement unit (3) switches from the hold signal to the drive signal (or current switching external When a switching signal from the hold signal to the drive signal is input from the input (6a)), the drive signal is input from the selector (6) to the reference voltage operation unit (7).

  Conventionally, since this switching is directly input to the constant current control unit (9) without passing through the reference voltage operation unit (7), a sudden torque fluctuation as shown in FIG. 3 (conventional moving angle) occurs. However, a spike-like damped vibration was generated in the initial transient state during start-up or repositioning, and this was transmitted to the mechanical system, hindering precision machining and precision measurement.

  On the other hand, in the present invention, when the drive / hold signal is input to the reference voltage operation unit (7), first, the input side switch (72) has a drive coefficient (α = 1) and the exit side switch (7) has a transfer function. As a result, the multiplier (74) multiplies the reference voltage constant by the transfer function 1, and the multiplier (74) outputs the reference voltage (Vo). Gradually increases to the drive reference voltage according to the transfer function 1. The gradually increasing reference voltage (Vo) is D / A converted and output as an analog value to the constant current control unit (9).

  On the other hand, the excitation sequence counter unit (4) counts command pulses (CW / CCW) and commands the excitation pattern output unit (5) to output the excitation pattern based on the address. Upon receiving this command, the excitation pattern output unit (5) sequentially outputs excitation patterns to the output stage (S) based on the address. In the output stage (S), the output stage switching element (Tr) is turned on / off according to this excitation pattern, and the stepping motor (M) is driven in accordance with the sequence.

  The stepping motor (M) is excited by the drive current (i2-i3) flowing through the output stage (S), but this drive current (i2-i3) is sensed by the sense resistor (R2), and the sense resistor The detection voltage (Vs) of the operating current (io = i1 + i2-i3) detected by (R1) and (R2) is input from the current detection circuit unit (8) to the constant current control unit (9).

  In the current detection circuit unit (8), the gradually increasing reference voltage (Vo) input from the reference voltage operation unit (7) is compared with the detection voltage (Vs) from the current detection circuit unit (8) to detect the detection voltage (Vs). The chopper 9a is chopped and controlled so as to coincide with the gradually increasing reference voltage (Vo), and the drive current (i2-i3) flowing through the stepping motor (M) is controlled so as to gradually increase to the drive current. As a result, the rotor gradually rotates in a transient state up to a position balanced with the torque generated by the drive current without causing a spike-like displacement, and finally balances with the torque in the drive state. In the case of repositioning, actual work such as measurement or measurement is performed in this state. On the other hand, in the case of rotational driving, the drive current is supplied as it is to perform step rotational driving.

(b) When stopped The rotor is step-driven with drive current in the drive state. When the last command pulse (CW / CCW) is input, the next command pulse (CW / CCW) is not input after a predetermined period (T), so (T <t) as described above. Then, a command pulse input end signal (or forced switching by the current switching external input (6a)) is input to the selector (6), and a hold signal is output from the selector (6) to the reference voltage operation unit (7).

  Conventionally, as described above, since there is no reference voltage operation unit (7) and it is directly input to the constant current control unit (9), this switching is performed instantaneously, and as shown in FIG. Torque fluctuations occurred, and spike-like damped vibrations were generated, which were transmitted to the mechanical system and hindered smooth stopping.

  On the other hand, in the present invention, when the hold signal is input from the selector (6) to the reference voltage operation unit (7), the input side switch (72) transmits the hold coefficient (α <1) and the outlet side switch (7) transmits. The function calculation unit (71) is connected to the transfer function 2 side. As a result, the multiplier (74) multiplies the reference voltage constant by the transfer function 2, and outputs the reference voltage (Vo) as the output of the multiplier (74). ) Gradually decreases to the hold reference voltage according to the transfer function 2. The gradual decrease reference voltage (Vo) is similarly D / A converted and output to the constant current control unit (9) as an analog value.

  In the current detection circuit section (8), the gradually decreasing reference voltage (Vo) input from the reference voltage operation section (7) is compared with the detection voltage (Vs) from the current detection circuit section (8) to detect the detection voltage (Vs). The chopper 9a is chopped and controlled so as to coincide with the gradually decreasing reference voltage (Vo), and the drive current (i2-i3) flowing through the stepping motor (M) is controlled to gradually decrease. As a result, a spike-like displacement does not occur as in the case of starting or repositioning, and a smooth stop is possible.

  In the above embodiment, the case where the control at the time of starting or repositioning and at the time of stopping is realized by one microstep drive, but in some cases it can be adopted only at the time of starting or repositioning. On the contrary, it can be adopted only when the vehicle is stopped.

  4 to 10 are comparison graphs of the present invention and the conventional example, and are graphs showing changes in time versus movement angle with the vertical axis indicating the movement angle and the horizontal axis indicating time. 4 to 8 show the case where the rotor is started from the stopped state, and FIGS. 9 and 10 show the case where the driven state is shifted to the rotor stopped state.

  FIG. 4 (conventional example) shows a case where the stepping motor that has been stopped by the drive current is started with the drive current as it is, and since there is no change in the current, there is no spike-like damped vibration at the start. However, as shown in the description of the conventional example, there is a problem that the heat generated by the stepping motor is large because the drive current continues to flow through the stepping motor even when stopped.

  FIG. 5 is also a conventional example, in which the stepping motor (M) is driven with a drive coefficient α = 1 (ie, τ = 0), and the hold current is switched to the drive current instantaneously when the hold current is switched to the drive current. Sometimes large damped oscillations appear first.

  On the other hand, FIG. 6 shows an example of the present invention. It takes τ = 2.5 ms to switch the drive current (i2-i3) from the hold current to the drive current to change the generated torque from 30% to 100%. Therefore, the damped vibration that appears in the transient state is an allowable limit.

  FIGS. 7 and 8 also show examples of the present invention. It takes τ = 6 ms and 10 ms to make the torque from 30% to 100%, and no large damped vibration appears in the transient state.

  9 and 10 show the case where the drive state is set to the hold state, and FIG. 9 is a conventional example in which the drive current is instantaneously set to the hold current, and a large damped oscillation occurs. On the other hand, FIG. 10 shows an example of the present invention, in which a time of τ = 2.5 ms is required to change the torque from 100% to 30%, and no large damped vibration appears.

  As described above, the present invention eliminates the problems caused by the spike displacement at the time of exciting current switching, and can positively utilize current switching even in high resolution micro-step driving to suppress useless motor heat generation. . As a result, current switching control is possible in ultra-high resolution micro-step driving, which can greatly contribute to the field of nanotechnology and biotechnology.

Circuit diagram of stepping motor to which the present invention is applied Circuit configuration diagram of reference voltage operation unit of the present invention Timing chart showing relationship between command pulse, drive holding timer output and rotor moving angle in the present invention and the conventional example Change graph of time vs. movement angle showing the stepped state from the stop position in the conventional example Change graph of other time vs. movement angle showing stepping state from stop position in conventional example In the present invention (when excitation current is 30% to 100% and τ = 2.5 ms), the graph of change of time vs. movement angle indicating the stepping state from the stop position In the present invention (when the exciting current is 30% to 100% and τ = 6 ms), the graph of change of the time vs. the moving angle indicating the stepping state from the stop position In the present invention (when excitation current is 30% to 100% and τ = 10 ms), a graph of change of time vs. movement angle indicating a stepped state from the stop position Change graph of time vs. moving angle from the drive state to the rotor stop in the conventional example Change graph of time vs. moving angle from drive state to rotor stop (when τ = 2.5 ms when excitation current is 100% to 30%) in the present invention

Explanation of symbols

(M)… Stepping motor
(Tr) ... Switching means
(io) ... Current to operate the stepping motor = Operating current
(i1) ... Supply current
(i2) ... Excitation current
(i2-i3) ... Drive current
(i3) ... electromotive current
(Vo) ... Reference voltage
(VoH) ... Drive reference voltage
(VoL): Hold reference voltage
(Vs)… Detection voltage
(Vk) ... Reference voltage constant
G (S): Transfer function
(1) Control circuit section
(7)… Reference voltage operation section
(9)… Constant current controller
(10)… Constant current output circuit

Claims (5)

Detecting a current for operating the stepping motor, and controlling the current so that a detection voltage based on the current is equal to a reference voltage defining an operation state of the stepping motor;
In the drive state, the stepping motor is driven to rotate with the current as the drive current, or in the hold state, the current is set as a hold current lower than the drive current and the rotor is held at a fixed position in a stopped state.
(1) When the stepping motor is in a transient state in which it shifts from the hold state to the drive state, the reference voltage is controlled to gradually increase from the hold voltage to the drive voltage, or
(2) When the stepping motor is in a transient state in which it shifts from the drive state to the hold state, the reference voltage is controlled so as to gradually decrease from the drive voltage to the hold voltage, or
(3) A stepping motor driving method characterized in that control is performed in accordance with the transient state in both transient states. A constant current output circuit unit for rotating the stepping motor with a current for operating the stepping motor or holding the stepping motor in a stopped state at a fixed position;
A control circuit having a constant current control unit that detects the current flowing through the constant current output circuit unit and controls the current so that a detection voltage based on the current is equal to a reference voltage that defines an operating state of the stepping motor. In the stepping motor drive circuit configured with
The control circuit section
In the transition state from the drive state to the hold state, the reference voltage is gradually decreased from the drive reference voltage to the hold reference voltage, or in the transition state from the hold state to the drive state, the reference voltage is changed from the hold reference voltage to the drive reference voltage. A stepping motor drive circuit comprising a reference voltage operation unit that gradually increases the voltage or has both functions.   The reference voltage operation unit multiplies the calculated value calculated based on the transfer function for changing the reference voltage in the transient state by the reference voltage constant in the motor drive, and outputs this to the constant current control unit as the reference voltage. The stepping motor drive circuit according to claim 2.   4. The stepping motor drive circuit according to claim 2, wherein the rate of change of the current increases and decreases within a range in which the stepping motor can follow.   5. The stepping motor drive circuit according to claim 4, wherein the followable range is a range in which τ, which is a time coefficient of the transfer function, is 2.5 to 10 ms.

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