JP2006067715A - Motor controller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a motor controller that is capable of accurate position control using a DC motor and performs stable control operation. <P>SOLUTION: Counter-electromotive voltage arising from the inductance component of a DC motor 5 is measured by switching the switching elements 36 to 39 in a voltage generation circuit 13 and a switch provided in a signal processing circuit 15, and information on the angular position of the armature is thereby obtained. Thus, torque variations are corrected based on a torque correction table 18. This enhances positioning accuracy and reduces the time required for positioning. In addition, a speed is thereby determined, and the accuracy of speed control is enhanced by carrying out speed control relative to the determined speed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a motor control device, and more particularly to a device that uses a small DC motor and performs precise position control.

  A DC motor incorporating a brush and a commutator is simple and inexpensive, and has features such as small size, high efficiency, high output, and no need for a special drive device, and is therefore used in many devices. On the other hand, when a DC motor is required to have high-precision positioning and stable rotation at an extremely low rotational speed, the DC motor has the following obstacles and cannot exhibit sufficient performance.

  The first is that the motor alone can basically control only the torque. In the case of a stepping motor, the angular position can be directly controlled by a single motor by the ratio of drive currents to a plurality of phases. Since the angular position can be directly controlled, the speed can be easily controlled. On the other hand, the DC motor can only control the torque by the drive current in the motor alone. Although it is possible to control the speed by the counter electromotive voltage to some extent, this cannot be used when the rotational speed is low, and the angular position cannot be directly controlled by the motor alone. For this reason, when controlling displacement and speed using a DC motor, a device that detects and feeds back speed and displacement is required separately from the motor.

  The second is the presence of torque unevenness. There are two main causes of torque unevenness. One of them is the presence of cogging torque. The cogging torque is generated by imbalance of the magnetic circuit of the motor, and is generated to try to position the rotor of the motor at a certain angular position, and is generated even when no drive voltage is applied to the motor. The other is unevenness of the torque generated by the motor. A small DC motor has few poles and usually has three poles. For this reason, the generated torque unevenness during one rotation is large, and the cogging torque is large because the number of poles is small.

  The third is that the rotor has a large moment of inertia. Since a small DC motor uses a permanent magnet for the field, the space for the field is small, and a rotor with a larger diameter can be used. While this contributes to the realization of characteristics such as high efficiency and high output, increasing the diameter of the rotor causes an increase in the moment of inertia. Depending on the device, the equivalent mass of this moment of inertia often reaches several times the mass of the original controlled object. This causes a decrease in positioning speed. When performing position control of such a controlled object having a large moment of inertia, it is necessary to use speed feedback. However, since the values of torque unevenness and moment of inertia are known in advance, if there is no disturbance due to friction or the like, even the DC motor having such characteristics controls the position and speed to some extent by controlling the torque. be able to.

  Patent Document 1 is known as a technique for reducing the influence of disturbance due to friction or the like with respect to the above-described problem. Hereinafter, the configuration disclosed in Patent Document 1 will be described with reference to the drawings. FIG. 11 is a block diagram showing a main circuit configuration of an optical disk apparatus using the motor control device disclosed in Patent Document 1, and FIG. 12 is an upper plan view showing the mechanical relationship of the apparatus. In these figures, 101 is an optical disk device, 102 is an optical disk, 103 is an optical head for recording / reproducing the optical disk 102, 107 is a thread motor for driving the optical head 103 in the radial direction of the optical disk 102 (direction of arrow A in FIG. 12), 108 is a rotating shaft of the sled motor 107, 181 is a lead screw fixed to the rotating shaft 108 and becomes a worm gear by the rotation of the rotating shaft 108, 109 is a control means for controlling the rotation of the sled motor 107 via the driver 171, and 121 is an optical disk A tracking error signal generation circuit 122 for tracking the track 102 with the optical head 103, a tracking servo circuit 122 for generating a tracking (TS) signal based on the tracking error (TE) signal from the tracking error signal generation circuit 121, 12 Is a sled servo circuit that generates a sled servo (SS) signal to the sled motor 107 based on the TS signal of the output signal of the tracking servo circuit 122, 124 is a comparator that compares the voltage of the SS signal from the sled servo circuit 123, and 191 A pulse generation circuit that generates a pulse at the timing of a signal from the comparator 124, 132 is an objective lens that is provided in the optical head 103 and converges a light beam, and 141 is a radial direction (hereinafter referred to as a radial direction) of the optical disk 102 and an objective lens. An actuator for driving the objective lens 132 in each of the optical axis directions 132, a tracking driver 142 for outputting a driving voltage for driving the actuator 141 in the tracking direction by a TS signal from the tracking servo circuit 122, and a radial direction for the optical disk 102 A guide shaft for guiding the optical head 103, 115 is a lead screw 181, a rack gear that transmits the decelerated driving force to the rotational speed of the sled motor 107 via a worm wheel 241 and the pinion gear 242. The control means 109 is a microcomputer (CPU) that controls the entire optical disk device 101 such as the optical head 103, the sled motor 107, the tracking servo circuit 122, the sled servo circuit 123, and the like. Accordingly, a deviation amount detecting means for detecting a deviation amount between a desired track of the optical disk 102 and the optical axis of the objective lens 132 is configured.

  The operation of the above components will be described. The light beam emitted from the optical head 103 is reflected by the optical disk 102 and returned to the optical head 103, and the signal voltage photoelectrically converted by a photodetector (not shown) provided in the optical head 103 is input to the tracking error signal generation circuit 121 and input to the TE signal. Is generated. The TE signal is input to the tracking servo circuit 122, and a TS signal is generated. The level (that is, voltage value) of the TS signal corresponds to the magnitude and direction of the deviation of the objective lens 132 in the radial direction from the reference position. The TS signal is input to the tracking actuator 141 via the driver 142 and also input to the sled servo circuit 123.

  The actuator 141 drives the objective lens 132 in the radial direction based on the TS signal, and by driving the actuator 141 in the radial direction, the objective lens 132 moves toward the center of the track, that is, tracking servo is applied (hereinafter referred to as the actuator). 141 is described as a tracking actuator driven only in the radial direction). Only by driving the tracking actuator 141, there is a limit in causing the objective lens 132 to follow the track. To cover this, the sled motor 107 is driven to move the optical head body 131 in the direction in which the objective lens 132 has moved. Control is performed so that the objective lens 132 is returned to the reference position by moving in the same direction (thread control is performed).

  The sled servo circuit 123 generates an SS signal. The SS signal level, that is, the voltage value, corresponds to the magnitude and direction of deviation of the objective lens 132 in the radial direction from the reference position. The SS signal is input to a comparator (comparator) 124 and binarized by the comparator 124. This binarized signal voltage is output from the comparator 124 and input to the control means 109.

  FIG. 13 is a timing chart of the SS signal voltage value of the optical disc apparatus 101, the signal voltage from the comparator 124, and the signal voltage from the pulse generation same path 191, and FIG. 14 shows the control operation procedure of the control means 109 in thread control. It is a flowchart.

  As shown in FIG. 13, the signal voltage level from the comparator 124 is high (H) when the SS signal voltage level is equal to or higher than the threshold level (reference voltage value), and the sled servo signal level (voltage value). Becomes low level (L) when the threshold level (reference voltage value) is full. In this optical disc apparatus 101, when it is determined that the level of the signal from the comparator 124 has changed from the low level (L) to the high level (H), the amount of deviation of the objective lens 132 from the reference position reaches a certain limit value. The control means 109 generates and outputs a pulse signal (pulse signal voltage) of a predetermined pattern by the pulse generation circuit 191. The pattern of the pulse signal voltage generated by the pulse generation circuit 191 is set in advance so that the objective lens 132 returns to the reference position when the sled motor 107 is driven based on the pulse signal voltage. The pulse signal voltage from the pulse generation circuit 191 is applied to the thread motor 107 via the driver 171. The sled motor 107 is driven based on the pulse signal voltage. By driving the sled motor 107, the optical head main body 131 moves in the same direction as the moving direction of the objective lens 132, and the objective lens 132 is moved to the reference position. Return.

  As shown in FIG. 13, the pulse signal voltage output from the pulse generation circuit 191 includes a first pulse voltage (positive pulse voltage) 151 and a second pulse voltage (negative pulse voltage) 152 having different polarities. It consists of and. The absolute value of the first pulse voltage 151 is sufficiently larger than the absolute value of the voltage (starting voltage) at which the sled motor 107 operates in a state where the sled motor 107 is incorporated in the optical disc apparatus 102. In this case, the absolute value of the first pulse voltage 151 is set to about 120 to 170% of the absolute value of the voltage at which the thread motor 107 operates. The absolute value of the second pulse voltage 152 is less than the absolute value of the first pulse voltage 151. In this case, the absolute value of the second pulse voltage 152 is set to about 50 to 90% of the absolute value of the first pulse voltage 151. When the pulse signal voltage described above is applied to the sled motor 107 via the driver 171, the sled motor 107 is actuated by the first pulse voltage 151 to accelerate the rotation, and the sled motor 7 is braked by the second pulse voltage 152. Then, the sled motor 107 stops so that the objective lens 132 is positioned at the reference position.

  Next, a control operation procedure of the control unit 109 in thread control will be described. As shown in FIG. 14, it is determined in step 201 whether or not the level of the signal voltage from the comparator 124 has changed from a low level (L) to a high level (H). If the determination in step 201 is “NO”, the pulse generation circuit 191 does not output the pulse signal voltage (step 202), returns to the determination in step 201, and executes step 201 and subsequent steps again. If the determination in step 201 is “YES”, as described above, a pulse signal voltage is generated by the pulse generation circuit 191 in step 203 and the pulse signal voltage is output. After step 203, the process returns to step 201 and step 201 and subsequent steps are executed again. With such a configuration, the sled motor 107 is driven to rotate stably and accurately even when the load of the mechanism varies.

  The optical disk apparatus 101 has a performance of moving the optical head 103 to be controlled to the target track position of the optical disk 102 at a high speed and positioning the optical axis of the objective lens 132 with respect to the target rack with high accuracy with respect to the optical disk 102. It has been demanded. Patent documents 2 and 3 are known as such techniques.

  That is, Patent Document 2 detects a DC motor drive current as a voltage value with a predetermined resistance, and processes the detected voltage with a plurality of low-pass filters and comparators, thereby outputting a fixed number of pulses per rotation of the DC motor. The technique to obtain is disclosed. Information on the position and speed is obtained from the pulse output, and the DC motor is controlled based on the information, that is, the change in the DC motor driving current is detected, and the rotational speed of the DC motor is controlled. Stable rotation can be obtained.

Patent Document 3 discloses a technique for obtaining information for correcting torque unevenness based on a torque command value for a DC motor and a drive current value actually flowing to the DC motor, and correcting the actual drive current command value. Is disclosed.
JP 2000-020974 A JP-A-4-172984 JP 7-337069 A

  The technique disclosed in Patent Document 1 described above has a certain effect in suppressing excessive rotation due to a large moment of inertia of the rotor and improving accuracy. However, the DC motor control device has the following problems.

  First, since the motor itself has no reference for speed and displacement and is basically open control, the moving distance and moving speed depend on disturbance. In the application of the DC motor to the moving means of the optical head used in the optical disk apparatus, there is no problem at first glance because the position information can be obtained from the optical disk when the optical head performs the focusing operation on the optical disk. The high-precision positioning of the optical head and the stable rotation at a low speed are not only necessary when position information can be obtained from the optical disk. For example, when the power of the drive is turned on and the optical head starts a focusing operation, information specific to the optical disk such as information signal recording or reproduction speed and recording density is in the innermost circumference of the optical disk. Since it is necessary to read the information first, the focus pull-in operation must be performed on the innermost circumference of the optical disc. This is because the optical head is located on the innermost circumference of the optical disc, and the surface deflection of the disc is the smallest on the innermost circumference, so that the focus pull-in operation is reliable, and the objective lens of the optical head is more than the normal recording or reproducing operation. However, even during the focus pull-in operation that may approach the optical disc, the optical head is the most effective in the optical disc due to the advantage that the possibility that the objective lens contacts the optical disc can be reduced. Information described in the inner periphery is first reproduced. Therefore, when the optical disk device is turned on, the optical head must be moved to the innermost peripheral position of the optical disk before the optical head starts the focusing operation.

  By the way, since the optical head may move due to vibration during transportation, the position of the optical head before activation, that is, before the power is turned on, is unknown. In many cases, a switch or the like for detecting that the optical head is located on the innermost circumference cannot be provided for cost reasons. In order to reliably move the optical head to the innermost circumference of the optical disk from a state having such an unstable element, the motor is driven for a time sufficient to move it more than a full stroke, and the optical head is moved to the innermost position. It is practically necessary to perform an operation of pressing against a circumferential mechanical stopper.

  Furthermore, the load such as friction when the optical head is moved varies greatly depending on the state and environment of the optical disk apparatus. Further, when the optical head is pressed to the innermost circumference, the rack and the lead screw are disengaged, and the lead screw is idled, and the rack is damaged. Therefore, idling must be avoided. For example, in the case of open control, the generated torque must be a value with sufficient margin for the load such as changing friction, while the lead screw must be a value that does not disengage, and the range of usable torque Becomes a very narrow range in practice, and there are many cases where the value cannot be set by strictly estimating the range of values where the load such as friction and the engagement of the lead screw cannot be disengaged.

  In addition, since the time required for this movement directly affects the startup time of the optical disk apparatus, it needs to be as short as possible. On the other hand, when the optical head collides with the stopper at a high speed, a collision sound is generated and the quality of the optical disk apparatus as a product. Falls. In addition, as described above, since the inertia moment of the rotor of the DC motor is large, even if the optical head is stationary due to a collision, the rotor continues to rotate and the lead screw is idled.

  As described above, the range of the speed that satisfies the requirement of the time required for the movement of the optical head and does not cause the lead screw to idle due to the collision is very narrow. For this reason, a rotary encoder that generates a fixed number of pulses per rotation by the rotation of the DC motor may be provided, but the cost increases. Also, as in Patent Document 1, when there is no reference for speed or displacement, it is very difficult to make the actual speed fall within this narrow speed range.

  The second problem is that there is an influence of torque unevenness. As described above, Patent Document 1 has a configuration in which the influence of the friction load can be made relatively small by using a relatively large driving pulse voltage with respect to the frictional force. It has not been. For this reason, the amount of movement per pulse greatly fluctuates due to torque unevenness, which hinders high-precision positioning of the optical head.

  Further, as described above, Patent Document 2 discloses a configuration in which a change in motor driving current is detected and thereby a rotational speed of the motor is detected. However, the method disclosed in Patent Document 2 cannot be used when pulse driving is performed at such a very low rotational speed. This is because the drive current changes due to unevenness of the counter electromotive voltage, but the counter electromotive voltage is small when the rotational speed is low and does not reach a practically detectable level. Another factor that causes the drive current to change is the variation in resistance at the brush switching timing. This resistance fluctuation occurs even when the rotational speed is low, but it occurs only at a very narrow angle in the entire rotational angle. For this reason, when pulse driving is performed, there is a high possibility that this change will be missed, and stable detection cannot be performed. Even if it can be detected, the fluctuation of the resistance is generated in a pulse shape only at the position of the brush switching timing. For example, in the case of a small three-pole DC motor, only 6 pulses are generated per rotation. Is rough and cannot be used to correct torque irregularities.

  Further, as described above, Patent Document 3 discloses a configuration in which information for correcting torque unevenness is obtained from the torque command value for the motor and the actual drive current value, and the actual drive current command value is corrected. However, for the same reason as described above in Patent Document 2, when the rotational speed is very low, the back electromotive voltage is also small and the drive current fluctuation is not at a level that can be practically detected. Uneven correction is also impossible.

  That is, the DC motor is small and operates at a low voltage, and its efficiency is relatively good. However, although the output torque is almost proportional to the drive current, the switching of excitation is a mechanical contact and the number of poles is also minimal, so the output torque unevenness during one rotation is large, and the output torque is proportional to the drive current. It can be said that the average torque of 360 ° per rotation is large, and when a small rotation angle such as 3.6 ° is taken out, the torque varies greatly depending on the angular position. Further, since the field of the DC motor 5 is composed of a permanent magnet, the field space can be small, but the diameter of the rotor is relatively large. For this reason, relatively high efficiency is obtained, but on the other hand, the rotor, which is a solid body of iron and copper, has a high density and a large diameter, and therefore has a problem of a large moment of inertia, which cannot be solved by the conventional configuration.

  Accordingly, the present invention has been made in view of the above problems, and an object thereof is to provide a motor control device that uses a DC motor, can perform precise position control, and has a stable control operation.

  In order to solve the above problem, the motor control device of the present invention includes a DC motor, a drive mechanism that drives an object having a mass to which the drive of the DC motor is transmitted against a load, and the DC motor. A motor control device comprising voltage generating means for applying a voltage to the terminal, terminal voltage measuring means for the DC motor, control means for controlling the voltage generating means and the terminal voltage measuring means, wherein the control means generates the voltage Means for applying a measurement pulse voltage to the DC motor, and changing the drive of the motor according to a measured value measured by the terminal voltage measuring means for a back electromotive voltage with respect to the measurement pulse voltage due to an electric self-inductance component of the motor. It is a thing.

  In the motor control device of the present invention, no voltage for driving the motor is applied when the measurement pulse is applied.

  In the motor control apparatus of the present invention, the motor is driven by a pulse voltage.

  In the motor control apparatus of the present invention, the measurement pulse voltage is output at a timing different from the pulse voltage for driving the motor.

  In the motor control apparatus of the present invention, the voltage generating means is constituted by a switching element, and generates the measurement pulse voltage and the pulse voltage for driving the motor.

  In the motor control apparatus of the present invention, the voltage generating means opens one or both of the motor terminals from the power source when measuring the counter electromotive voltage.

  In the motor control device of the present invention, the pulse width and pulse voltage of the measurement pulse are set so that the counter electromotive voltage generated thereby falls within the measurement range of the terminal voltage measuring means.

  In the motor control apparatus of the present invention, the measurement pulse is applied a plurality of times, and the drive of the motor is changed by a plurality of measured values measured by the voltage measuring means for each applied pulse.

  Moreover, the motor control apparatus of this invention changes the drive of the said motor with the average value of these measured values.

  In the motor control device of the present invention, the application pulses are applied a plurality of times, and the applied pulses include those having different polarities.

  In the motor control device of the present invention, the drive of the motor is changed by the difference in absolute value of the measurement values by the measurement pulses having different polarities.

  In the motor control device of the present invention, the drive of the motor is changed so that torque unevenness of the motor is reduced according to the measured value.

  In the motor control device of the present invention, the drive has a mathematically linear relationship with respect to the measured value, so that torque unevenness of the motor is reduced.

  In addition, the motor control device of the present invention has a table that stores the drive value with respect to the measured value, and the torque unevenness of the motor is reduced by performing the drive according to this table.

  The motor control device of the present invention detects the position and speed of the object from the measured values, and uses this to change the drive of the motor so that the position and speed of the object become predetermined values. It is.

  Further, the motor control device of the present invention obtains a certain number of pulses per one rotation of the motor by binarizing the measured value with a predetermined threshold value, so that the position and speed of the object become predetermined values. The drive of the motor is changed.

  According to the motor control apparatus of the present invention, a DC motor, a drive mechanism that drives an object having a mass to which the drive of the DC motor is transmitted against a load, and a voltage generation unit that applies a voltage to the DC motor. And a motor control device comprising a control means for controlling the terminal voltage measuring means of the DC motor, the voltage generating means, and the terminal voltage measuring means, wherein the control means measures the DC motor with the voltage generating means. By applying a pulse voltage and changing the drive of the motor according to the measured value measured by the terminal voltage measuring means with respect to the measured pulse voltage due to the electric self-inductance component of the motor, the DC motor Because the DC motor can be controlled by detecting the angular position, it is possible to obtain a motor controller with stable operation and high accuracy. It is intended.

  Further, according to the motor control device of the present invention, since the voltage for driving the motor is not applied when the measurement pulse is applied, the back electromotive voltage can be detected stably and accurately, so that the operation is stable. A highly accurate motor control device can be obtained.

  Further, according to the motor control device of the present invention, since the motor is driven with a pulse voltage, a pulse for measuring the back electromotive voltage can be generated during a period when the drive pulse is not generated. A voltage can be detected more stably and accurately, and a motor control device with stable operation and high accuracy can be obtained.

  Further, according to the motor control device of the present invention, the measurement pulse voltage is output at a timing different from the pulse voltage for driving the motor, so that the back electromotive voltage can be detected more stably and accurately. Thus, it is possible to obtain a motor control device that is stable and highly accurate.

  Further, according to the motor control device of the present invention, the voltage generating means is constituted by a switching element, and generates the pulse voltage for driving the measurement pulse voltage and the motor. Since the voltage generating means and the voltage generating means for driving can be shared, an inexpensive motor control device can be obtained.

  Further, according to the motor control device of the present invention, the voltage generating means opens one or both of the motor terminals from the power source when measuring the counter electromotive voltage. It is possible to obtain a motor control device that can detect stably and accurately, has a stable operation, and is highly accurate.

  Further, according to the motor control device of the present invention, the pulse width and / or pulse voltage of the measurement pulse is set so that the counter electromotive voltage caused thereby falls within the measurement range of the terminal voltage measurement means. An electromotive voltage can be detected with certainty, and a highly accurate motor control device with stable operation can be obtained.

  According to the motor control device of the present invention, the measurement pulse is applied a plurality of times, and the driving of the motor is changed by a plurality of measured values measured by the voltage measuring means for each applied pulse. Thus, a counter electromotive voltage can be detected more stably and accurately, and a motor control device with stable operation and high accuracy can be obtained.

  In addition, according to the motor control device of the present invention, since the drive of the motor is changed by the average value of the plurality of measured values, the influence of the back electromotive voltage error is reduced, the operation is stable and high. An accurate motor control device can be obtained.

  In addition, according to the motor control device of the present invention, since the applied pulses are applied a plurality of times and have different polarities, only the influence of the back electromotive force due to the external magnetic field can be taken out, and the operation is stable. Thus, a highly accurate motor control device can be obtained.

  In addition, according to the motor control device of the present invention, the drive of the motor is changed by the difference in absolute value of the measurement values due to the measurement pulses having different polarities. Thus, the motor can be driven by this, and a motor control device with stable operation and high accuracy can be obtained.

  Further, according to the motor control device of the present invention, since the drive of the motor is changed so that the torque unevenness of the motor is reduced by the measured value, the torque unevenness of the DC motor can be corrected, It is possible to obtain a motor control apparatus with high accuracy and no operation delay.

  Further, according to the motor control device of the present invention, since the drive has a mathematical linear relationship with respect to the measured value, the torque unevenness of the motor is reduced. The table storing the correction values can be omitted, and a motor control device having a simple structure can be obtained.

  In addition, according to the motor control device of the present invention, there is a table that stores the drive value with respect to the measured value, and by performing the drive according to the table, torque unevenness of the motor is reduced. A highly accurate motor control device can be obtained.

  In addition, according to the motor control device of the present invention, the position and speed of the object are detected from the measured values, and the motor drive is changed using the detected position and speed so that the position and speed of the object become predetermined values. Thus, it is possible to obtain a motor control device that can control the moving speed of the object well, can shorten the moving time of the object, and can eliminate the adverse effects caused by the collision with the stopper.

  Further, according to the motor control device of the present invention, the measurement value is binarized with a predetermined threshold value to obtain a certain number of pulses per one rotation of the motor, whereby the position and speed of the object are predetermined values. Since the drive of the motor is changed so as to be, the speed can be detected with a simple configuration, and a motor control device with a simple structure can be obtained.

  Hereinafter, an embodiment of a motor control device of the present invention will be described with reference to the drawings. 1 and 2 are schematic configuration diagrams showing an example in which the motor control device of the present invention is applied to an optical disk drive. In the figure, 1 is an optical disk drive, 2 is an optical disk to be recorded and / or reproduced by an optical head 23 provided in the optical disk drive 1, and 4 is a radial direction of the optical disk 2 (hereinafter referred to as an optical head 23 via a nut piece 3 and a slider 31). A lead screw that moves in the radial direction), 6 is a guide shaft on which the slider 31 slides, 5 is a DC motor that rotates the lead screw 4 around the bearing 7 via the pinion 10 and the spur gear 11, and 9 is a turn. A spindle motor for rotating the optical disk 2 placed on the table 25 around the rotation shaft 24, and 8 is a traverse base for placing the spindle motor 9, the DC motor 5, the bearing 7, and the like. The nut piece 3, the lead screw 4, the DC motor 5, the pinion 10 and the spur gear 11 are collectively referred to as an optical head moving mechanism 12. Reference numeral 28 denotes an objective lens that converges a light beam emitted from a light source 26 such as a semiconductor laser and focuses the light beam on an information layer (indicated by reference numerals) of the optical disk 2. Reference numeral 29 denotes an objective lens that is orthogonal to the main surface of the optical disk 2. Actuator (moving in the radial direction of the optical disk 2) and tracking driving means 30 for driving the actuator 29 in the radial direction, and 27 is a light beam emitted from the light source 26 reflected by the information layer. A photodiode 73 that receives the return light and converts it into an electrical signal is an inner peripheral stopper that regulates the inner peripheral side of the optical disk 2 of the optical head 23.

  Next, a circuit configuration for operating each component of the optical disk drive 1 described above is as follows. 17 is a tracking servo circuit that applies a drive signal for driving the objective lens 28 in the radial direction to the tracking actuator 30 via the tracking driver circuit 21; 22 is a sled servo circuit, 13 is a voltage generating circuit having first to fourth switching means 36 to 39 that receives an input of a power source, and 14 is a first switching means 36 and a second switching means 36 of the voltage generating circuit 13. A terminal voltage measuring circuit for measuring the voltage between the switching means 37 and between the third switching means 38 and the fourth switching means 39, 15 is a signal circuit for processing the output voltage of the terminal voltage measuring circuit 14, and a control circuit 19 described later. It is a signal processing circuit which gives a signal to. The control circuit 19 includes a switching control circuit 16, a switching circuit 34, a constant speed feed control circuit 33, an A / D converter 35, a torque correction table 18, and a thread control circuit 20.

  The mechanical operation and electrical signal operation of the above configuration will be described by taking a DVD-RAM disk as an example of the optical disk 2. When the optical disk 2 is placed on the turntable 25, the spindle motor 9 rotates the optical disk 2 around the rotation shaft 24 at a predetermined rotational speed. When the spindle motor 9 starts to rotate, the optical head 23 moves by the optical head moving mechanism 12 toward the innermost periphery of the optical disc 2. When the optical head 23 moves to the innermost circumference of the optical disc 2, a light source driving circuit (not shown) causes the light source 26 to emit light with a predetermined intensity, irradiates the information layer of the optical disc 2 through the objective lens 28, Reflected light from the information layer is received by the photodetector 27, a tracking drive signal is given to the tracking actuator 30 so as to follow a track (not shown) provided on the optical disc 2, tracking control, and the objective lens 28 is controlled in the vertical direction by the actuator 29. Perform focus control. After performing the tracking control and the focus control in this way, for example, information relating to the medium of the optical disc 2 such as recording / reproducing speed, recording density, information layer type, and unrecorded area is read from the lead-in area. An information signal is recorded or recorded in an information area (also referred to as a data area) to reproduce the information signal.

  The objective lens 28 is provided with a suspension spring (not shown) so that the radial reference position and the vertical neutral position coincide in the optical head 23. For example, in the case where the objective lens 28 is moved in the radial direction, when no voltage is applied to the tracking drive unit 30, the objective lens 28 is positioned at the reference position by the elastic force of the suspension spring. When a predetermined voltage is applied to the tracking drive unit 30 via the tracking driver circuit 21, the tracking drive unit 30 is driven and the objective lens 28 moves in the radial direction according to the sign and absolute value of the voltage value. To do. That is, according to the sign and absolute value of the voltage value output from the tracking driver circuit 21, the objective lens 28 is deviated from the reference position by a predetermined amount in the radial direction (inner or outer periphery of the optical disc 2).

  Further, the nut piece 3 attached to the optical head 23 meshes with the thread groove of the lead screw 4 with one end biased by a spring, and constitutes a part of the optical head moving mechanism 12. The lead screw 4 is integrally connected to the spur gear 11 and is rotatably supported by a bearing 7 fixed to the traverse base 8. The screw pitch of the lead screw 4 is 4 mm, for example. The spur gear 11 meshes with a pinion 10 directly connected to the output shaft (not shown) of the DC motor 5, whereby the rotational speed of the motor is reduced and transmitted to the lead screw 4. Accordingly, the optical head 23 linearly reciprocates along the radial direction of the optical disc 2 along the guide shaft 6 according to the rotation of the DC motor 5. When the optical head 23 is positioned at the innermost inner peripheral position of the optical disc 2, an inner peripheral stopper 73 that restricts further movement of the optical head 23 is provided. That is, when the optical head 23 comes into contact with the inner peripheral stopper 73 at the innermost position of the optical disc 2, the position at which the optical head 23 should perform the focus pull-in operation when the optical disc drive 1 is started is determined. The reduction ratio by the pinion 10 and the spur gear 11 is 2, for example. When the screw pitch of the lead screw 4 is 4 mm and the reduction ratio of the pinion 10 and the spur gear 11 is 2, the optical head 23 moves in a radial direction of 2 mm per one rotation of the DC motor 5. Since the maximum rotational speed of the DC motor 5 is generally 9000 rpm, the optical head 23 can be moved at a maximum speed of 300 mm / s and a high-speed seek operation is possible. In order to obtain the required positioning accuracy of ± 20 μm, the rotor of the DC motor 5 needs to be stopped with an accuracy within ± 3.6 °.

  The DC motor 5 is a small three-pole motor using, for example, a permanent magnet as a field magnet. The brush and the commutator built in the DC motor 5 make it known only by a DC power source without using any other special driving device. Can be rotated.

  The voltage generating means 13 is composed of four switching means of a first switching means 36 to a fourth switching means 39 and is connected to a 5V power supply (not shown), and the entire optical disc drive 1 operates with this 5V power supply. A switching signal is input to the voltage generating unit 13 from the control unit 19 to each of the four switching units. The first switching means 36 to the fourth switching means 39 are constituted by semiconductor elements or the like, and are turned on and off by a switching signal from the control means 19. Further, the first switching means 36 to the fourth switching means 39 are turned on, and the voltage generating means 13 and the DC motor 5 are directly connected with a low impedance, so that the DC motor 5 has a power supply voltage of 5V. A voltage close to is applied. However, as described above, the first switching means 36 to the fourth switching means 39 are constituted by semiconductor elements and have a slight ON resistance even in the ON state, so strictly speaking, the output voltage is completely the power supply voltage. In the following description, it is assumed that the voltage is 5V.

  The terminal voltage measuring means 14 is composed of an operational amplifier or the like, measures a potential difference (that is, voltage) generated between DC motor terminals, and outputs it as a voltage from a reference potential of 0V. For example, 2.5V when the voltage generated between DC motor terminals is 0, 5V when the positive terminal of the motor is + 5V with respect to the negative terminal, and 0V when the positive terminal is -5V with respect to the negative terminal. Is output. In the present embodiment, as described above, the drive voltage of the DC motor 5 is 5V, and the terminal voltage measuring means 14 is also operated by a 5V power source. Therefore, the maximum voltage generated between the measurable motor terminals is 5V. It is.

  As will be described later, the signal processing means 15 is composed of a sample hold circuit, an adder, and the like. The signal processing means 15 samples and holds the output of the terminal voltage measurement means 14 at a specific timing, and performs output such as addition and subtraction on the output.

  The control circuit 19 is usually composed of a microcomputer (CPU) or the like, and includes an actuator 29, a laser diode 26, etc. housed in the optical head 23, a DC motor 5, a spindle motor 9, a tracking servo circuit 17, and a thread servo circuit. Control of the entire optical disc drive 1 such as 22 is performed. The control circuit 19 includes a switching control circuit 16, a torque correction table 18, a thread control circuit 20, a constant speed feed control circuit 33, a switching circuit 34, and an A / D converter 35. The control circuit 33 includes The above elements are as follows.

  The switching control circuit 16 is constituted by a timer or the like, and outputs a timing signal to each of the four switching means of the first switching means 36 to the fourth switching means 39 of the voltage generating circuit 13, whereby the first switching means 36. The fourth switching means 39 is turned ON or OFF for a short time, and a power supply voltage of 5 V is applied to the DC motor 5 in a short pulse, or the terminals of the DC motor 5 are opened from the power supply voltage. Note that the output of the switching means 34 described later is input to the switching control means 16.

  The torque correction table 18 incorporates a table that records the relationship between the output of the signal processing means 15 and the torque unevenness, and converts the output signal from the signal processing means 15 into an output signal that is A / D converted by the A / D converter 35. The corresponding torque unevenness correction value is output to the thread control means 20.

  The thread control circuit 20 performs so-called “thread control state” control. When a thread servo (SS) signal and an output of a torque correction table are input, and the value of the SS signal exceeds a preset threshold value, a specific pattern is obtained. The switching control circuit 16 is controlled via the switching circuit 34 so that the pulse is applied to the DC motor 5. Note that when the value of the SS signal becomes equal to or less than the threshold value, the application of the pulse to the DC motor 5 is stopped.

  The constant speed feed control circuit 33 performs control of a so-called “constant speed feed control state”, the output of the A / D converter 35 and the speed command value are input, and the optical head 23 is output from the output of the A / D converter 35. And the switching control means 16 is controlled based on the difference between the actual moving speed and the speed command value, so that the speed of the optical head 23 becomes the speed of the input speed command value regardless of the value of the SS signal. To control.

  The switching means 34 receives the outputs of the constant speed feed control means 33 and the thread control means 20 and the mode switching signal, switches the outputs of the constant speed feed control means 33 and the thread control means 20 according to the mode switching signal, and switches to the switching control means 16. input.

  The A / D converter 35 receives the output of the signal processing circuit 15 and performs A / D conversion on this with a resolution of 6 bits, for example.

  Next, the operation of the optical disc drive 1 having the above configuration will be described. The optical disk drive 1 has several operation states such as a reproduction operation and a constant speed feeding operation. For example, in the reproduction operation, the optical head 23 is moved to a target track or a target address (hereinafter, both are collectively referred to as a target track), and focus control, tracking control, thread control, rotation speed control (rotational speed control), etc. are performed on the target track. The information signal (data) recorded on the information layer of the optical disc 1 is read while performing the above. In the constant speed feed operation, the speed of the optical head 23 is controlled to be the speed of the input speed command value regardless of the value of the SS signal.

  First, the control in the reproduction operation will be described in detail regarding tracking control and thread control.

  A signal after photoelectric conversion by the photodiode 27 of the optical head 23 is input to the tracking servo circuit 17. The tracking servo circuit 17 generates a TE signal as a voltage from a signal obtained by current-voltage conversion based on the signal from the photodiode 27. The tracking error signal is a signal indicating the magnitude and direction of deviation of the objective lens 28 from the track center in the radial direction of the optical disc 2 (hereinafter, both are collectively referred to as deviation from the center of the track).

  The TE signal is subjected to predetermined signal processing such as phase inversion and amplification, and a TS signal is generated as a voltage. This TS signal is a signal of a driving voltage that drives the tracking actuator 29 so that the objective lens 28 moves to the center of the track (the level of the TE signal becomes 0 level). The level of the TS signal, that is, the voltage value, corresponds to the magnitude of the deviation of the objective lens 28 in the radial direction from the reference position and its direction (hereinafter, both are collectively referred to as a deviation amount with respect to the reference position). .

  The TS signal is input to the tracking actuator 28 via the tracking driver circuit 21 and also to the sled servo circuit 22. The tracking actuator 29 is driven based on the TS signal, and by driving the tracking actuator 29, the objective lens 28 moves toward the center of the track, that is, tracking servo (TS) is applied. Only by driving the tracking actuator 29, there is a limit in causing the objective lens 28 to follow the track. The DC motor 5 is driven to cover this, and the optical head 23 is moved in the same direction as the objective lens 28 is moved. Then, the objective lens 28 is controlled to return to the reference position (so-called thread control is performed).

  For example, in the case of a reproduction-only device such as a CD-ROM device, the range in which the tracking actuator 29 can cause the objective lens 28 to follow the track is generally about ± 200 μm. When the target track is outside this range, sled control is performed to move the optical head 23 and control is performed so that the target track falls within this range. The positioning accuracy of the optical head 23 at this time must naturally be ± 200 μm or less.

  On the other hand, in the case of the DVD-RAM disk of the present embodiment, which has a higher density than a CD-ROM and also performs recording, the range following the track is narrower, for example, ± 20 μm or less, and the positioning accuracy of the optical head 23 is naturally. Must be ± 20 μm or less.

  The thread servo circuit 22 performs predetermined signal processing such as high-frequency component removal and amplification on the tracking servo signal input from the tracking servo circuit 17, and thereby a thread servo (SS) signal (ie, A voltage corresponding to the driving voltage of the tracking actuator is generated. The level of the SS signal, that is, the voltage value corresponds to the amount of deviation from the reference position in the radial direction. By the way, the SS signal is input to the thread control means 20, and when the absolute value of this voltage exceeds a certain reference, the thread control means 20 outputs a switching signal to the voltage generation means 13 by the switching control means 16, thereby the DC motor 5 And the optical head is moved in the direction in which the absolute value of the SS signal decreases. This will be described with reference to FIG.

  FIG. 3 is a flowchart showing the control operation of the thread control means 20 in thread control. When performing thread control, the switching means 34 selects the output of the thread control means and outputs it to the switching control means 16. First, when the job starts (step 40), it is determined in step 41 whether or not the absolute value of the SS signal exceeds the reference value. As described above, this voltage value corresponds to the shift amount with respect to the reference position in the radial direction. The reference value is set such that the amount of deviation of the objective lens 28 has a slight margin with respect to the range in which the tracking actuator 29 can cause the objective lens 28 to follow the track.

  If it is determined in step 41 that the absolute value of the SS signal does not exceed the reference value, the determination in step 41 is repeated. If it is determined in step 41 that the absolute value of the SS signal exceeds the reference value, the reference pulse width is set to 300 μs in step 50. The reference pulse width is a reference for the pulse width of the pulse voltage for driving the DC motor 5.

  Next, in step 45, the switching signal is output to the voltage generating means 13, an extremely short pulse voltage is applied to the DC motor 5, the back electromotive voltage at that time is measured by the terminal voltage measuring circuit 14, and this is processed by the signal processing circuit. By processing at 15, the rotor position of the DC motor 5 is measured.

  Next, in step 46, the torque correction value is determined by referring to the output of the signal processing circuit 15 in the torque correction table 18, and the torque unevenness is corrected by correcting the pulse width of the pulse voltage output in step 43 and thereafter. Perform the correction operation. Details of these operations will be described later.

  Next, in step 42, the polarity of the SS signal is determined. If it is determined that the polarity of the SS signal is positive, a positive pulse is applied to the DC motor 5 in step 43. The pulse width at this time is a value obtained by multiplying the value of the reference pulse width by the value of the pulse width correction value obtained from the torque correction table 18, and actual application is performed according to the following procedure. In a state where no pulse is applied, the switching means of FIG. 1 is in a state where the first switching means 36 and the third switching means 38 are off, and the second switching means 37 and the fourth switching means 39 are on. In this state, both terminals of the DC motor 5 are directly connected to GND, and both terminals are short-circuited at the same time as no voltage is applied. When a pulse voltage is applied, the second switching means 37 is turned off and the first switching means 36 is turned on for the time during which the pulse voltage is applied from this state, whereby the + terminal of the DC motor 5 is connected to the 5V power supply. Directly connected to the + side, and the-terminal is directly connected to the-side (GND) of the 5 V power supply. A short-time pulse voltage is applied to the DC motor 5, and after the pulse is applied, the original state (first switching) The means 36 and the third switching means 38 are turned off, and the second switching means 37 and the fourth switching means 39 are turned on. A positive pulse is applied to the DC motor 5 by the above procedure. Next, after waiting for a certain time in step 47, it is determined in step 48 whether or not the absolute value of the SS signal still exceeds the reference value.

  If it is determined that the polarity of the SS signal is negative, a negative pulse is applied to the DC motor 5 in step 44. The pulse width at this time is a value obtained by multiplying the value of the reference pulse width by the value of the pulse width correction value obtained from the torque correction table 18 as in the case where the polarity of the sled servo signal is positive. The procedure is the same as that when the polarity of the sled servo signal is positive. However, when a pulse voltage is applied, the fourth switching means 39, not the second switching means 37, is turned off and the third switching means 38, not the first switching means 36, is turned on for the time during which the pulse voltage is applied. Is different. Next, after waiting for a certain time in step 47, it is determined in step 48 whether the absolute value of the sled servo signal still exceeds the reference value.

  If it is determined in step 48 that the absolute value of the sled servo signal still exceeds the reference value, the reference pulse width is increased by 30 μs in step 49, and step 42 and subsequent steps are repeated. Since the reference pulse width is set to 300 μs in step 50, the reference pulse width is increased to 330 μs here. After step 50, it is determined in step 48 that the absolute value of the sled servo signal still exceeds the reference value. Each time it is increased by 30 μs. If it is determined in step 48 that the absolute value of the sled servo signal is equal to or less than the reference value, the determination in step 41 is repeated.

  By the way, the DC motor 5 rotates when the output voltage 5V of the voltage generating means 13 is applied in the form of pulses, and the optical head 23 moves. When the SS signal is positive, the objective lens 28 is shifted to the outer peripheral side of the optical disc 2, and when it is negative, the objective lens 28 is shifted to the inner peripheral side. On the other hand, the DC motor 5 moves the optical head 23 toward the outer peripheral side of the optical disc 2 when a positive voltage is applied, and moves the optical head 23 toward the inner peripheral side of the optical disc 2 when a negative voltage is applied. To move. Thereby, the shift amount of the objective lens 28 with respect to the track of the optical disk 2 is reduced.

  When trying to move such a small distance, it is easy to be affected by load fluctuations due to various frictions, but since the pulse voltage is the highest possible voltage of 5V, the influence of load fluctuations is relatively reduced. Has been. In addition, since the pulse width is gradually increased, there is little phenomenon that even if a pulse is applied, it does not move at all or moves too much. However, as described above, in this type of small DC motor, the number of poles is small (three poles in this embodiment), and therefore, the unevenness of the torque generated during one rotation is large. Also, since the number of poles is small, the cogging torque is large and the total torque unevenness is large. When the moving distance is large, the torque unevenness is averaged and is not noticeable. However, when such a small distance is moved, it greatly affects. Even when the pulse width is gradually increased as in this embodiment, if the initial pulse width is set in accordance with the case where the torque is maximized due to the torque unevenness during one rotation, the movement starts when the torque is minimum. It may take too long. For this reason, in the present embodiment, in the flowchart showing the thread control operation of FIG. 3, the rotor position of the DC motor 5 is measured at 45 and the torque unevenness is corrected at 46. These operations will be described.

  The small DC motor has a structure in which the armature rotates by the action of a magnetic field generated by passing an electric current through an armature having a coil wound around an iron core and a field magnetic field generated by a permanent magnet. If the current is simply passed through the armature, it will rotate to the dead point and stop, so the direction of the current flowing through the armature can be switched one after another by the brush and commutator, and the rotation can be continued. Yes. The principle of the rotation operation of the DC motor will be described with reference to FIG. 4, 51, 52 and 53 are magnetic poles, 54 and 55 are field magnets, 56 is a commutator having the same number of divided conductors as the number of magnetic poles 51, 52 and 53, 57 is a brush, 58 is a DC power source, 59a, 59b is the direction of the magnetic flux due to the current, 60 is the direction of the magnetic flux due to the field magnets 54 and 55, 61 is the armature, which is composed of the magnetic poles 51, 52 and 53, the commutator 56 and the iron core (reference numeral omitted).

  A coil is wound around the magnetic poles 51, 52, and 53 in the direction shown in the figure, and connected to the commutator 56 as shown in the figure to constitute an armature 61. The commutator 56 rotates integrally with the magnetic poles 51, 52 and 53, and a pair of fixed brushes 57 come into contact with each other via the commutator 56 and energize the windings of the magnetic poles 51, 52 and 53, and at the same time, the magnetic poles 51, 52. The direction of the current to the windings 53 and 53 is switched in synchronization with the rotation of the armature 61. Thereby, it can be rotated only by the DC power source 58 without using any other special drive circuit. Hereinafter, the manner in which the DC motor rotates will be described in more detail with reference to FIG.

  In FIG. 4, the rotation direction of the armature 61 is a clockwise direction as indicated by an arrow. The commutator 56 is formed of a conductor divided into three at intervals of 120 °, and the pair of brushes 57 facing each other at 180 ° and the commutator 56 rotate while being in contact with each other. The direction of the current to the line is switched every 60 °. 4A and 4B show a state immediately after such switching of the current direction is performed.

  In FIG. 4A, a power source 58 is directly connected to the magnetic pole 53, and as a result of current flowing as shown, the magnetic pole 53 is excited to the N pole. The magnetic poles 51 and 52 are connected in series, and a current flows as shown in the figure and is excited to the S pole. As a result, the direction of the magnetic flux by the magnetic poles 51, 52, and 53 is 59a as a whole, which is 120 ° different from the direction 60 of the magnetic flux by the field magnets 54 and 55. For this reason, a rotational torque is generated by generating a force that matches these, and the armature 61 is rotated by the rotational torque.

  When the current flowing through the magnetic poles 51, 52, and 53 is rotated by 60 ° in this state, the state shown in FIG. 4B is obtained, and the conductors of the commutator 56 that are in contact with the pair of brushes 57 are switched. The state of the current flowing through the battery changes. In other words, the current rotates for 60 ° until the divided conductor of the commutator 56 in contact with the brush 57 changes. In the state of FIG. 4 (a), the angle formed by the magnetic field direction 60 by the magnetic fields 54 and 55 and the magnetic field direction 59a by the magnetic poles 51, 52 and 53 is 120 °. It will rotate at the same electric current until °.

  When the state of the current to the magnetic poles 51, 52 and 53 is changed by changing from the state of FIGS. 4A to 4B in this way, the magnetic pole 51 is in a state where the power source 58 is directly connected, as shown in the figure. As a result of the current flowing through, the S pole is excited. The magnetic poles 52 and 53 are connected in series, and a current flows and is excited to the N pole as shown. As a result, the direction of the magnetic flux by the magnetic poles 51, 52, and 53 becomes 59b as a whole, and the direction of the magnetic flux 60 by the field magnets 54 and 55 is also different by 120 ° as in FIG. When such a force is generated, rotational torque is generated. The armature 61 is further rotated by this rotational torque, and the current flowing through the magnetic poles 51, 52, and 53 is further rotated by 60 ° in this state. ). However, since it is rotated 120 ° with respect to FIG. 4A, the magnetic pole 53 is positioned at the position of the magnetic pole 51 in FIG. 4A, and the other magnetic poles 52 and 53 are the same. As a result, the divided conductors of the commutator 56 in contact with the brush 57 are switched, and the state of the current flowing through the magnetic poles 51, 52 and 53 changes. In other words, the rotation is performed in the same current state for 60 ° until the current state is changed by the brush 57 and the commutator 56. In the state of FIG. 4B, the angle formed by the magnetic flux direction 60 by the field magnets 54 and 55 and the magnetic flux direction 59b by the magnetic poles 51, 52 and 53 is 120 °. From 60 ° to 60 °, the rotation was performed with the same current.

  As described above, the relationship between the magnetic field formed by the magnetic fields 54 and 55 and the magnetic poles 51 to 53 is as shown in FIG. There is no change in being (b). For convenience of explanation, different magnetic poles 51 to 53 are attached to the respective magnetic poles. However, since the magnetic poles 51 to 53 are originally made identically electrically, magnetically, and mechanically, they are basically distinguished from each other. There is no. Accordingly, the armature 61 rotates by repeating the above-described procedure in the same manner.

  Thus, the angle formed by the magnetic field direction 60 and the magnetic field directions 59a and 59b by the magnetic poles 51, 52 and 53 is always in the range of 120 ° to 60 °, and the armature 61 continues to rotate. However, the rotational torque varies within this range. That is, the rotational torque is maximum when the angle between the two magnetic fluxes is approximately 90 °, and is zero between 0 ° and 180 °. Therefore, the rotational torque varies depending on the change in the torque depending on the angle between the two magnetic fluxes. As a result, torque unevenness occurs.

  Next, the cause of this torque unevenness will be described in detail with reference to FIG. FIG. 5 shows the rotation angle of the armature 61 on the horizontal axis with one of the current switching positions of the commutator 56 and the brush 57 taken as 0 °, and the vertical axis shows the output torque (FIG. A) and cogging (FIG. B). , Torque unevenness (Fig. C), cross angle (Fig. D), counter electromotive voltage (Fig. E), counter electromotive voltage difference with respect to pulse of opposite polarity (Fig. F) and reverse effect on output voltage of signal processing circuit It is the graph which took each electromotive voltage difference (the same figure g) on the vertical axis | shaft. The rotation angle on the horizontal axis is positive in the clockwise direction in FIG.

  As described above, the output torque varies depending on the angle formed by the two magnetic fields (hereinafter referred to as the angle formed), as indicated by 67 in FIG. 5a. The range of the change of the angle is smaller as the number of poles is larger, so that the torque fluctuation is smaller in a large motor having a larger number of poles. However, since most of the small DC motors have three poles, which is the minimum number of poles, the output torque unevenness increases.

  At the same time, the DC motor has another cause of torque unevenness called cogging torque. In the DC motor, the field is a permanent magnet and the rotor is a magnetic body, so the rotor is attracted to the field permanent magnet. Torque is generated without energizing the motor. This torque is generated so that the rotation angle of the magnetic rotor is positioned in a stable state in the magnetic flux generated by the field that is a permanent magnet. That is, the torque is 0 at the angle position where the stable state is obtained, and the torque is generated in the direction to be positioned at the angular position where the stable state is obtained at the angular position away from the stable state, and from the angle position where the stable state is obtained. The torque increases as the distance increases.

  Although the angular position at which the stable state is obtained varies depending on the configuration of the DC motor, in the case of a general small DC motor, the magnetic poles 51, 52, 53 of the armature 61 are schematically shown in FIGS. 4 (a) and 4 (b). Is the state closest to the center of either one of the two-pole field magnets 54 and 55. For example, in FIG. 4A, the magnetic pole 51 is closest to the center of the field 54 (S pole), which is one of the stable states. When the armature 61 is rotated in the clockwise direction, the magnetic pole 52 becomes closest to the center of the field 55 (N pole) as shown in FIG. It is in a stable state. Since the armature 61 has three magnetic poles and two magnetic fields, there is an angle that is stable in one place every 60 ° and a total of six places during one rotation.

  When the armature 61 is rotated clockwise (by an external force or the like) from the state shown in FIG. 4A in a state where the DC motor 5 is not energized, the field 54 is separated from this stable state. Therefore, a torque in the direction opposite to the rotation is generated, and this increases as the rotation angle increases. However, this torque has a peak at a rotation angle of about 15 °, and thereafter becomes smaller due to the influence of the stable state shown in FIG. Then, it becomes 0 at about 30 °, and thereafter, the torque drawn into the stable state of FIG. 4 (b) becomes superior, so that torque is generated in the direction to rotate clockwise. This torque increases until the rotation angle reaches about 45 °, and thereafter decreases as the stable state of FIG. 4B approaches, and becomes 0 in the state of FIG. 4B of 60 °. Since such torque fluctuations are repeated every 60 °, as a result, the relationship between the rotation angle of the armature 61 and the magnetically generated torque when the DC motor 5 is not energized is as shown by 70 in FIG. become.

  On the other hand, since there is a friction torque 62 as shown in FIG. 5b, the torque to be actually reversed or forward is 63 as shown in FIG. 5b, and the DC motor 5 is not energized in the negative range. Since the torque in the reverse direction is actually generated in this state, when the DC motor 5 is deenergized at this position, the reverse rotation is made to a stable position. Such torque is generally called cogging torque.

  Torque unevenness when the DC motor is energized is generated by combining the cogging torque 63 shown in FIG. 5b and the output torque unevenness 67 shown in FIG. 5a. As a result, the torque unevenness varies as 64 shown in FIG. 5c. Since the torque unevenness during energization is affected by the cogging torque and occurs depending on the rotation angle of the armature 61 at a cycle of 60 °, it can be corrected if the angular position of the armature 61 can be detected.

  By the way, since the wound iron core rotates in the magnetic field 60 formed by the field magnets 54 and 55, the DC motor 5 operates as a generator during rotation and generates a counter electromotive voltage proportional to the rotational speed. To do. The counter electromotive voltage also varies in the same manner as the output torque unevenness even if the rotation speed is constant. Therefore, the torque unevenness can be corrected by detecting the angular position of the armature 61 of the DC motor 5 by this variation. Thus, when the rotational speed is low, the back electromotive voltage is also small, so this method cannot be used. On the other hand, since the DC motor 5 has a structure wound around an iron core, the electric resistance includes a self-inductance component. Therefore, when the current is changed, a voltage in the opposite direction is generated as one counter electromotive voltage.

For example, when a pulse voltage is applied to the terminal of the DC motor 5 (that is, the brush 57), the DC motor terminal voltage changes as shown in FIG. FIG. 6 is a graph showing the relationship between the counter electromotive voltage due to the self-inductance component and time, where 71 is a potential difference generated at the terminal of the DC motor due to the current due to the input pulse, and 72 is the electromotive voltage generated due to the self-inductance component. The electromotive voltage 72 is generated so as to pass a current in the same direction as the 71 input pulse, but when measured at the DC motor terminal, it is observed as a voltage having a polarity opposite to that of the input pulse 71. This is due to the difference between the potential difference due to the current in the same direction and the electromotive voltage that causes it. The counter electromotive voltage 72 is proportional to the rate of change of the magnetic flux, and in this case, increases in proportion to the rate of decrease of the magnetic flux. Since the winding of the DC motor 5 exists in the magnetic field formed by the field magnets 54 and 55 as described above, the speed at which the magnetic flux decreases is affected by the external magnetic field 60 formed by the field magnets 54 and 55. The state of the magnetic flux with respect to the winding changes according to the angular position of the armature 61 as described above. In the state of FIG. 4A, the direction 59a of the magnetic flux generated by the DC power source 58 and the crossing angle of the magnetic flux due to the field are At 120 °, this angle varies from 60 ° to 120 ° depending on the angular position of the armature of the motor.
Further, this change is 120 ° immediately after the current switching by the brush 57 and the commutator 56 and decreases in proportion to the rotation angle of the armature and becomes 60 ° immediately before the next current switching performed when rotating by 60 °, and again immediately after the current switching. It becomes 120 ° and the same is repeated thereafter. Reference numeral 68 in FIG. 5d is a graph showing the relationship between the generated magnetic flux, the crossing angle of the magnetic flux due to the field, and the rotation angle of the armature. Thus, the crossing angle changes in a sawtooth shape with the current switching point between the brush 57 and the commutator 56 as a vertex according to the rotation angle, and the current switching point between the brush 57 and the commutator 56 is linear. It becomes a unique function that decreases.

  The decrease rate of the magnetic flux when the DC power source 58 in FIG. 4A is turned off is the fastest when the external magnetic field is in the reverse direction with respect to the magnetic field generated by the DC power source 58, that is, when the crossing angle is 180 °. That is, it is the slowest when the crossing angle is 0 °. Therefore, the back electromotive voltage is the lowest when the crossing angle is 0 °, and the back electromotive force is the highest when the crossing angle is 180 °. The back electromotive force is roughly proportional to the cosine of this crossing angle. As described above, the relationship between the crossing angle and the armature rotation angle is a unique function that linearly decreases from 120 ° to 60 ° between the current switching points of the brush 57 and the commutator 56. The relationship between the counter electromotive voltage and the rotation angle is also a unique function that decreases substantially linearly between the current switching points of the brush 57 and the commutator 56 and repeats at a cycle of 60 °. This is shown at 65 in FIG. Reference numeral 65 in FIG. 5e indicates the relationship between the angular position of the armature and the counter electromotive voltage generated at the angle, and the peak value of the counter electromotive voltage generated when the pulse voltage is applied at the angular position and turned off.

  As shown at 64 in FIG. 5c, the torque unevenness is also repeated at a period of 60 ° between the current switching points of the brush 57 and the commutator 56, so that the torque unevenness with respect to this counter electromotive voltage can be uniquely determined. It is possible to correct the torque unevenness by measuring. However, the value of the back electromotive voltage varies due to various factors. In order to solve this problem, the back electromotive force for pulses having opposite polarities is measured and the difference is taken. The pulse width for this measurement is as short as about 100 μs, and the generated back electromotive voltage is also generated in such a short time. Therefore, the time required for the measurement can be very short. For this reason, the measurement can be performed a plurality of times for one drive pulse of the DC motor 5, and the rotation of the motor between the measurements can be almost ignored, so that such a measurement is possible.

  In the case of pulses having opposite polarities, the influence of the magnetic field due to the field is opposite to each other, but the influence due to other factors is exactly the same, so that the influence other than the magnetic field can be eliminated by taking the difference. In particular, since the output is 0 when the crossing angle is 90 °, various standards can be set here. As a result, the relationship 66 shown in FIG. 66 in FIG. 5f is generated by inputting pulses having opposite polarities at the angular position in relation to the angular position of the armature and the back electromotive voltage difference with respect to the pulses having opposite polarities generated at the angle. The difference of back electromotive force is plotted. The crossing angle of 90 ° at which the output is 0 is a position rotated by 30 ° from the current switching position between the commutator 56 and the brush 57, and 66 in FIG. 5f is the current switching position between the commutator 56 and the brush 57 at 0 °. Therefore, the value becomes 0 at 30 °. Moreover, since the current switching position by the commutator 56 and the brush 57 is every 60 °, it becomes 0 at 30 °, 90 °, 150 °. Moreover, it changes from the minimum value to the maximum value at 0 °, 60 °, 120 °,.

  Hereinafter, the operation of actually measuring the back electromotive force in step 45 in FIG. 3 and correcting the torque unevenness will be described. The counter electromotive voltage is measured by applying a short-time pulse voltage to the DC motor 5 and releasing the motor terminal from the power supply after the application. The voltage application and the opening of the terminal are performed by turning on and off the switching elements 36 to 39 of the voltage generating means 13 in FIG. 1, and no special hardware is required. Further, the terminal voltage is detected by the terminal voltage measuring means 14 as described above. Since the output of the terminal voltage measuring means is the waveform of the motor terminal voltage itself, it includes unnecessary parts such as the applied pulse voltage. Only the necessary counter electromotive voltage portion is extracted from this signal, and the signal processing means 15 performs the above-described operation for obtaining the difference between the counter electromotive voltages due to the pulses of opposite polarity.

  FIG. 7 is a schematic configuration diagram of the signal processing means 15. In FIG. 7, 76 is a buffer, 77 and 78 are sample and hold circuits, 79 and 80 are sample and hold switches, 81 and 82 are capacitors, and 83 is an adder. The output of the terminal voltage measuring means 14 is input to two sample and hold circuits 77 and 78 via two buffers 76 and sampled and held. A total of four buffers 76 and two sample and hold circuits 77 and 78 are the same. Since there are two sample and hold circuits 77 and 78, two voltages can be sampled and held from a voltage that changes over time. This output is input to the adder 83 through the two buffers 76 and added.

  FIG. 8 is a graph showing the relationship between the operation procedure of the switching means and the sample hold switch at the time of measuring the back electromotive voltage, and the output voltage waveform of the terminal voltage measuring means 14. FIG. 8 shows an example of the state of the switching elements 36 to 39 in the period 91 to 95 from the start to the end, the state of the sample hold switches 79 and 80 provided in the two sample hold circuits 77 and 78, respectively, and the operation time. Shown in 1).

  When the rotor position is measured by measuring the back electromotive voltage in step 45 in FIG. 3, the voltage generating means 13 in FIG. 1 is in a state where both terminals of the DC motor 5 are shorted to GND before the measurement is started. ing. As shown in Table 1, the operations of the switching means 36 to 39 at this time are on with the switching means 37 and the switching means 39, and the switching means 36 and the switching means 38 are off. Since the voltage between the terminals of the DC motor 5 is naturally zero at this time, the terminal voltage measuring means 14 outputs +2.5 V as its reference voltage. At this time, the sample hold switches 79 and 80 are both off as shown in (Table 1).

  When the measurement starts, as shown at 91 in (Table 1), the switching means 36 and the switching means 39 are turned on, the switching means 37 and the switching means 38 are turned off, and as shown at 91 in FIG. Thus, the voltage generating means 13 applies +5 V to the + terminal side of the DC motor 5 in a pulsed manner. The time in this state, that is, the pulse application time is 100 μs. This application time is determined so that the counter electromotive voltage generated thereby falls within ± 5 V, which is the 14 measurement range of the terminal voltage measuring means. Since + 5V is applied to the + terminal side of the DC motor 5, the output voltage of the terminal voltage measuring means 14 is + 5V as indicated by 91 in FIG. At this time, the sample hold switches 79 and 80 are both off as shown in (Table 1).

  Next, as indicated by 92 in (Table 1), the switching means 36 to 39 are all turned off, and as indicated by 92 in FIG. 8, the voltage generating means 13 in FIG. 1 thereby connects both terminals of the DC motor 5. Release from the power supply. As a result, a counter electromotive voltage is generated at both terminals of the DC motor 5, and a waveform as shown at 92 in FIG. At this time, as shown in Table 1, the sample hold switch 79 is turned on and 80 is turned off. As a result, the sample hold capacitor 81 is charged. A resistor 84 is connected to the sample-and-hold capacitor 81, thereby operating as an integrating circuit, and the sample-and-hold capacitor 81 is charged with a voltage having an average value of 92 waveforms in FIG. The time in this state, that is, the time required for measurement is 50 μs.

  Next, as shown in 93 of (Table 1), the switching means 37 and the switching means 39 are turned on, the switching means 36 and the switching means 38 are turned off, and as shown in 93 of FIG. 8, the voltage of FIG. The generating means 13 thereby short-circuits both terminals of the DC motor 5 to GND. Although the back electromotive voltage continues to be generated at the terminals of the DC motor 5, the voltage decreases with time and does not contribute to effective measurement. Therefore, the back electromotive force generated at both terminals of the DC motor 5 by this operation. Terminate the voltage. Since the voltage between the terminals of the DC motor 5 is naturally zero at this time, the terminal voltage measuring means 14 outputs +2.5 V which is the reference voltage. At this time, the sample hold switches 79 and 85 are both off as indicated by 93 in (Table 1). Therefore, the value of the counter electromotive voltage measured at 92 is held in the sample hold circuit 77. The time in this state is 100 μs.

  Next, as indicated by 94 in (Table 1), the switching means 37 and the switching means 38 are turned on, and the switching means 36 and the switching means 39 are turned off. As indicated by 94 in FIG. Thus, the generating means 13 applies +5 V in a pulsed manner to the negative terminal side of the DC motor 5. The time in this state, that is, the pulse application time is 100 μs. Since + 5V is applied to the negative terminal side of the DC motor 5, the output voltage of the terminal voltage measuring means 14 is 0V as shown at 94 in FIG. At this time, the sample hold switches 79 and 80 are both off as shown in (Table 1). For this reason, the value of the back electromotive voltage measured at 92 continues to be held in the sample hold circuit 2.

  Next, as indicated by 95 in (Table 1), the switching means 36 to 39 are all turned off. As indicated by 95 in FIG. 8, the voltage generating means 13 in FIG. Release from the power supply. As a result, a counter electromotive voltage is generated at both terminals of the DC motor 5, and a waveform as shown at 95 in FIG. 8 is output from the terminal voltage measuring means 14. At this time, as shown in Table 1, the sample and hold switch 80 is turned on, and the sample and hold switch 79 is turned off. As a result, the sample hold capacitor 82 is charged. A resistor 85 is connected to the sample-and-hold capacitor 82, thereby operating as an integrating circuit, and the sample-and-hold capacitor 82 is charged with a voltage having an average value of the waveform 95 in FIG. On the other hand, since the sample hold switch 79 remains off, the value of the counter electromotive voltage measured at 92 in FIG. The time in this state, that is, the time required for measurement is 50 μs.

  Finally, when the measurement is completed, each switch returns to the state before the measurement is started. That is, the switching means 36 to 39 in FIG. 1 are in a state where both terminals of the motor are shorted to GND. As for the operation of the switching means 36 to 39 at this time, the switching means 37 and the switching means 39 as shown in Table 1 are on, and the switching means 36 and the switching means 38 are off. Since the voltage between the terminals of the DC motor 5 is naturally zero at this time, the terminal voltage measuring means 14 outputs +2.5 V which is the reference voltage. At this time, the sample hold switches 79 and 80 are both off as shown in (Table 1). Therefore, the sample and hold circuit 77 holds the back electromotive voltage value measured at 92 in FIG. 8, and the sample and hold circuit 78 holds the back electromotive voltage value measured at 95 in FIG. .

  The outputs of the sample hold circuits 77 and 78 are input to the adder 83 through the two buffers 76, and the added value is output. The sample hold circuits 77 and 78 hold back electromotive voltage values for pulses having different polarities. Since these back electromotive voltages have different polarities, the difference between the absolute values is obtained by adding them. As a result, the adder 83 outputs the difference between the absolute values of the back electromotive voltages for the pulses having different polarities. As described above, in the case of pulses having opposite polarities, the influence of the magnetic field due to the field is opposite to each other, but the influence due to other factors is exactly the same, so that the influence other than the magnetic field can be eliminated by taking the difference. In particular, since the output is 0 when the crossing angle is 90 °, various standards can be set here. Since the reference voltage of the adder is set to 2.5V, 2.5V is actually a level of 0.

  Further, the constant of the adder is such that the output is 4.5 V due to the difference in counter electromotive voltage at the crossing angle of 120 °, and the output is 0.5 V due to the difference between the counter electromotive voltage at the crossing angle of 60 °. Is set. As a result, in relation to the rotation angle of the armature 61, as shown by 69 in FIG. 5g, an output of a sawtooth waveform that changes between 0.5V and 4.5V around 2.5V is obtained. . As described above, the crossing angle is 90 ° at a position rotated by 30 ° from the current switching position between the commutator 56 and the brush 57, and the graph of FIG. 5G shows the current switching position between the commutator 56 and the brush 57. Since it is 0 °, the value becomes 2.5V at 30 °. Moreover, since the current switching position by the commutator 56 and the brush 57 is every 60 °, it becomes 2.5 V at 30 °, 90 °, 150 °,. Moreover, it changes from 0.5V to 4.5V at 0 °, 60 °, 120 °.

  With the above procedure, an output including information on the angular position of the armature 61 of the DC motor 5 can be obtained from the adder 83, that is, the signal processing means 15.

  Next, the operation for actually correcting the torque unevenness from this data in step 46 of FIG. 3 will be described. The output of the signal processing means 15 is input to the control means 19. In the control means 19, this output is A / D converted by the A / D converter 35 and converted into 6 bits, that is, data of 64 steps from 0 to 63. As described above, the output of the signal processing means 15 varies between 4.5V and 0.5V. This is A / D converted so that it becomes 63 at 4.5V and 0 at 0.5V.

  As shown by 69 in FIG. 5g, the output of the signal processing means 15 is between the current switching positions by the commutator 56 and the brush 57 generated at a rotation angle of 60 ° in relation to the rotation angle of the armature 61. Thus, it changes monotonously from 4.5V to 0.5V. Further, as shown at 64 in FIG. 5c, the torque unevenness repeats the same change at a rotation angle of 60 °. Therefore, the torque unevenness value and the torque unevenness correction value can be uniquely determined with respect to the output of the signal processing means 15. Therefore, it is possible to uniquely determine the value after A / D conversion. Thus, from the data after A / D conversion, it is possible to know the angular position information of the armature 61 of the DC motor 5 necessary for correcting the torque unevenness, and it is possible to know the torque unevenness from this angular position. It can be corrected. Specifically, the torque correction value is determined by referring to the torque correction table 18 with respect to the output of the A / D converter 35, thereby correcting the pulse width of the pulses output after steps 43 and 44 in FIG. .

  (Table 2) is an example of a torque correction table. In the table, a value of 0 to 63 is written as the angular position of the armature, and a pulse width correction value corresponding to this is written. This correction value is defined as a value that can correct the torque unevenness generated from the sum of the cogging torque and the output torque unevenness indicated by 64 in FIG. 5c. The data of the A / D converter is referred to in this table, and the correction value of the pulse width corresponding to this is obtained. Torque unevenness is corrected by correcting the pulse width by multiplying this value by the reference pulse. For example, when the data after A / D conversion is 21, the pulse width correction value is 0.88 from (Table 2). The correction value is 1 or less when the torque is larger than the average value due to torque unevenness. This is multiplied by the reference pulse width. If the pulse to be output is the first pulse and the reference pulse width is 300 μs, it is multiplied by 0.88 to be 300 μs × 0.88 = 264 μs, resulting in a shorter pulse width than before correction, and torque due to torque unevenness A part larger than the average value is corrected. The torque unevenness is corrected by the above procedure.

  In this driving method, a plurality of driving pulses are applied while gradually increasing. When the load is small, it moves while the pulse width is narrow, and when the load is large, it starts moving after the pulse width is widened, but the movement amount per pulse after moving is relatively constant, several μm Degree. For this reason, after starting to move, the shift amount of the objective lens 28 is decreased by several μm for each pulse, and as a result, the shift amount range of the objective lens 28 is within ± 20 μm. That is, the relative position of the target track can be located within a range of ± 20 μm in which the tracking actuator 29 can cause the objective lens 28 to follow the track. If there is torque unevenness, it may move too much from the first pulse, or it may take too much time to start moving, but since the torque unevenness is corrected by the method described above, such a phenomenon does not occur and is stable. Movement is possible.

  Next, the operation in the “constant speed feeding state” will be described. As described above, when the drive power is turned on and the optical head 23 starts the focus operation, the focus pull-in operation must be performed on the innermost circumference of the disk. Therefore, by satisfying the requirement of the time required to move the optical head 23 against the inner peripheral stopper 73 by driving the motor for a sufficient time, the range of the speed at which the lead screw does not idle due to the collision is very narrow, It is necessary to control the moving speed within this range. As described above, the “constant speed feeding state” is controlled so that the speed of the optical head 23 becomes the speed of the inputted speed command value regardless of the value of the sled servo signal (SS). In this state, by processing the output of the A / D converter 35, the actual speed of the optical head 23 is detected, and compared with the speed command value. The error between the actual speed of the head 23 and the speed command value is reduced. When performing constant speed feed control, the switching means 34 selects the output of the constant speed feed control means and outputs it to the switching control means 16.

  FIG. 9 is a block diagram illustrating an exemplary configuration of the constant speed feed control means 33. In FIG. 9, 86 is a zero cross detecting means, 87 is a period measuring means, 88 is a comparator, 89 is an offset generating means, and 90 is a pulse generating means. Data of the A / D converter 35 is input to the zero cross detection means 86, and the zero cross of the difference in the back electromotive voltage is detected. This result is input to the period measuring means 87, and the actual speed of the optical head 23 is detected by measuring the period of zero crossing. FIG. 10 is a graph showing an example of the relationship between the output of the D / A converter and the period. In the graph in the figure, the horizontal axis represents time, and the vertical axis represents the output of the D / A converter 35. When the DC motor 5 rotates at a substantially constant speed, the relationship between the output of the D / A converter 35 and time is a sawtooth waveform as shown in the figure. As described above, when the data changes suddenly from 0 to 63, the armature 61 of the DC motor 5 is the current switching angle position by the commutator 56 and the brush 57. Further, as described above, when the crossing angle is 90 °, the difference between the counter electromotive voltages with respect to the pulses having opposite polarities is 0. In this state, the output of the D / A converter 35 is 31.

  The interval between the current switching angle positions by the commutator 56 and the brush 57 of the DC motor 5 is 60 ° as described above. At this time, since the crossing angle is 60 ° or 120 °, the angle difference from the angular position of the armature 61 at the crossing angle of 90 ° where the output of the D / A converter 35 is 31 is 30 °. For this reason, as shown in FIG. 10, when the timing at which the output crosses 31 is obtained and the time interval between them is measured, this is the time required for the armature 61 of the DC motor 5 to rotate 30 °. Therefore, the actual moving speed of the optical head 23 can be obtained from this time interval. For example, if this time interval is 20 ms, it will rotate 30 ° in 20 ms, so the time required for one rotation is 20 × 360/30 = 240 ms, and the optical head 23 moves 2 mm in one rotation. Is 2/240 × 1000 = 8.33 mm / s. In this way, the actual speed of the optical head 23 is output from the period measuring means 87. This value is input to the comparator 88. A speed command value is also input to the comparator 88, and the actual speed is compared with this. The speed command value is such that the drive start-up time is sufficiently short, and when the optical head 23 collides with the innermost peripheral stopper 73, a collision noise is generated, or the teeth of the nut piece 3 come out of the groove of the lead screw 4 and lead screw The speed is selected so that 4 does not slip. In the case of this embodiment, it was set to 15 mm / s. The comparator 88 outputs a voltage value proportional to the difference between the two values under an appropriate proportionality factor. This voltage is a negative value when the actual speed is larger than the speed command value, and a positive value when the actual speed is small.

  A positive offset is added to this output by the offset generation means 89. As the offset value, a voltage at which the DC motor 5 can overcome the friction load and rotate in a normal state is selected. As a result, the speed command value becomes equal to the actual speed, and when the output of the comparator 88 becomes 0, the motor torque and the frictional force are almost balanced, and a state in which neither acceleration nor deceleration is realized can be realized. Accuracy is improved. In this embodiment, the offset value is set to 1.5V. Even in this operating state, the DC motor 5 is pulse-driven. This is because by driving with pulses, it is possible to drive with a higher voltage than with DC driving, so that the influence of friction can be relatively reduced. For this reason, a value to which a positive offset is added by the offset generating means 89 is input to the pulse generating means 90 and converted into data for generating a pulse of this voltage value. The pulses used for driving the motor have a pulse width of 2 ms and a period of 12 ms. The voltage value of the pulse having a width of 2 ms becomes a value to which a positive offset is added by the offset generation means 89. Since the voltage generating means 13 is composed of switching means 36 to 39 capable of only an on-off operation, PWM driving is performed when a voltage other than 0 or 5 V is generated.

  With the configuration and operation as described above, the actual speed of the optical head 23 can be detected, the speed command value is compared with the actual speed, and if the actual speed is higher than the speed command value, the drive voltage is set. If it is low and the drive voltage is reduced, the optical head 23 can be moved at a speed close to the speed command value regardless of the magnitude of the friction load.

As described above, according to the present embodiment, the following effects can be obtained.
That is,
First, since the position of the armature of the DC motor can be detected from the back electromotive force and the torque unevenness can be corrected, the optical head may go too far in the thread control state, or on the contrary until it starts to move. Therefore, stable movement is possible without taking too much time. The position of the armature of the DC motor can be detected even when the rotation speed is zero, and the influence of the field can be detected by taking the difference of the counter electromotive voltages with respect to the pulses having opposite polarities, so that stable detection is possible. can do. For this reason, there are few DC level offsets, level fluctuations due to variations, etc., a device for correcting these and procedures such as learning are unnecessary, and the structure can be simplified.

  Secondly, the position of the armature of the DC motor can be detected from the back electromotive voltage, and thus the moving speed of the optical head can be detected. Therefore, the moving speed of the optical head must be accurately controlled during constant speed feed control. Can do. As a result, the actual moving speed of the optical head can be kept within the very narrow speed range where the lead screw does not slip due to a collision, and the time required for starting the drive can be shortened. However, it is possible to prevent the generation of noise due to a collision and to prevent abnormal wear of the nut piece due to idling.

  In the present embodiment, the voltage for driving the DC motor is not applied during the measurement of the counter electromotive voltage, but a voltage in a range that does not affect the measurement may be applied.

  Further, although the torque unevenness is corrected by changing the pulse width, it may be performed by changing the pulse voltage or both the voltage and the width.

  In addition, the DC motor is driven by pulse drive, but it is normal analog drive. Only during measurement, the drive voltage is measured for a short time without affecting the measurement, and the torque unevenness is corrected by changing the drive voltage. It may be.

  Further, although the pulse for measurement is separated from the pulse for driving, at least one of the pulses having different polarities inputted for measurement may be shared with the driving pulse.

  In addition, although a switching element is used to generate a pulse for measurement, an analog drive circuit may be used to drive the pulse, and the drive for measurement needs to be a square wave pulse. There may be a sine wave or a triangular wave.

  In addition, both motor terminals are opened from the power supply during measurement, but only one of them is opened, and the voltage applied to the other terminal is switched to 0V or 5V, for example. The electromotive voltage may be within the measurement range of the terminal voltage measurement means.

  The pulse application time was determined so that the counter electromotive voltage generated by this was within ± 5 V, which is the measurement range of the terminal voltage measurement circuit. However, the pulse application time was arbitrarily set to constitute the terminal voltage measurement means. Depending on the resistance value, the pulse output from the measurement range may be in a measurable range.

  In addition, as a measurement pulse, a set of pulses having different polarities is input and used as the data on the angular position of the armature. Also good.

  Further, although two sample hold circuits are provided in the signal processing circuit, the output of the terminal voltage measuring means may be directly A / D converted to perform processing such as taking a difference digitally.

  Further, although the torque correction table describing the relationship between the armature angle position and the torque correction value is provided, the correction value may be obtained from the armature angle position by a certain procedure without providing the table.

  Further, although the speed is detected by measuring the zero-crossing period, the pulse period may be measured by pulsing with an appropriate threshold.

  Further, the speed may be detected by processing the detected angular position of the rotor by a practical differential operation.

  Further, although the speed correction is performed by changing the pulse voltage, it may be performed with a pulse width and / or a pulse period.

  In order to obtain a constant speed, the speed was detected and compared with the speed command value. For example, the speed fluctuation was roughly corrected by simply making the zero-cross cycle proportional to the pulse voltage. May be.

  Further, only the speed information is used in the constant speed control state, but the displacement may be obtained from the obtained angular position of the rotor and this information may be used together.

  Since the motor control device of the present invention can perform high-precision drive control, it can be applied to, for example, magic hand drive that requires precise rotation control.

Schematic configuration diagram showing an example configuration of an embodiment of the present invention Main part enlarged view of the same embodiment Flow chart showing thread control control operation (A) is an operation explanatory diagram of the DC motor, (b) is an operation explanatory diagram of the DC motor. Relationship diagram between armature rotation angle, torque unevenness and back electromotive force Relationship between back electromotive force due to self-inductance component and time Schematic configuration diagram of signal processing means Output voltage waveform diagram of switching circuit Block diagram of constant speed feed control means Output waveform diagram of D / A converter Block diagram of an optical disc apparatus as an example of the prior art Plan view for explaining the mechanism of the optical disc apparatus Waveform diagram of optical disk device in the same example Flow chart showing thread control operation in the example

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical disk drive 2 Optical disk 3 Nut piece 4 Lead screw 5 DC motor 6 Guide shaft 7 Bearing 8 Traverse base 9 Spindle motor 10 Pinion 11 Spur gear 12 Optical head moving mechanism 13 Voltage generation circuit 14 Terminal voltage measurement circuit 15 Signal processing circuit 16 Switching Control circuit 17 Tracking servo circuit 18 Torque correction table 19 Control circuit 20 Thread control circuit 21 Tracking driver circuit 22 Thread servo circuit 23 Optical head 24 Rotating shaft 25 Turntable 26 Light source 27 Photodiode 28 Objective lens 29 Actuator 30 Tracking drive means 31 Slider 33 constant speed feed control circuit 34 switching circuit 35 A / D converter 36 first switching means 37 second switching Means 38 the third switching means 39 within the fourth switching means 73 circumferential stopper

Claims (16)

A DC motor;
A driving mechanism for driving an object having a certain mass to transmit the driving of the DC motor against a load;
Voltage generating means for applying a voltage to the DC motor;
A terminal voltage measuring means of the DC motor;
Control means for controlling the voltage generation means and the terminal voltage measurement means,
The control means applies a measurement pulse voltage to the DC motor by the voltage generation means, and measures a back electromotive voltage with respect to the measurement pulse voltage due to an electric self-inductance component of the DC motor by the terminal voltage measurement means. A motor control device characterized by changing the drive of the motor according to a value. 2. The motor control apparatus according to claim 1, wherein a voltage for driving the motor is not applied when the measurement pulse is applied. The motor control device according to claim 1, wherein the motor is driven by a pulse voltage. The motor control device according to claim 2, wherein the measurement pulse voltage is output at a timing different from the pulse voltage for driving the motor. 4. The motor control apparatus according to claim 3, wherein the voltage generating means is constituted by a switching element and generates the measurement pulse voltage and the pulse voltage for driving the motor. 6. The motor control device according to claim 5, wherein the voltage generating means opens one or both of the terminals of the motor from a power source when measuring the counter electromotive voltage. 2. The motor control device according to claim 1, wherein the pulse width and pulse voltage of the measurement pulse are set so that the counter electromotive voltage generated thereby falls within the measurement range of the terminal voltage measurement means. 2. The motor control apparatus according to claim 1, wherein the measurement pulse is applied a plurality of times, and the driving of the motor is changed by a plurality of measured values measured by the voltage measuring means for each applied pulse. The motor control device according to claim 8, wherein the driving of the motor is changed according to an average value of the plurality of measurement values. 9. The motor control device according to claim 8, wherein each of the applied pulses is applied a plurality of times and has different polarities. 9. The motor control device according to claim 8, wherein the driving of the motor is changed based on a difference in absolute value of the measurement values due to the measurement pulses having different polarities. The motor control device according to claim 1, wherein the drive of the motor is changed so that torque unevenness of the motor is reduced according to the measured value. 13. The motor control device according to claim 12, wherein torque unevenness of the motor is reduced by having a mathematically linear relationship with respect to the measured value. 13. The motor control device according to claim 12, further comprising a table storing the drive values with respect to the measurement values, and performing the drive according to the table to reduce torque unevenness of the motor. 2. The motor control device according to claim 1, wherein the position and speed of the object are detected from the measured values, and the driving of the motor is changed using the detected position and speed so that the position and speed of the object become predetermined values. . The measurement value is binarized with a predetermined threshold value to obtain a certain number of pulses per rotation of the motor, thereby changing the driving of the motor so that the position and speed of the object become predetermined values. The motor control device according to claim 15, characterized in that:

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