JP2014057391A - Motor control device, and method of controlling the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten a time required from brake operation to motor stop by appropriately operating a brake to a motor.SOLUTION: A motor control device comprises: an inverter bridge circuit (13) configured by an upper arm and a lower arm respectively having switching elements of three phases, converting a DC supplied from a power supply side into an AC by on-off operations of the switching elements, and outputting the AC to a motor (4); and a motor control circuit (14) controlling the on-off operations of the switching elements of each phase to drive the motor (4). The motor control circuit (14) turns on all of the switching elements of each phase of any one of the upper arm and the lower arm, and thereby, short-circuits between terminals of each phase of the motor (4) to generate a brake current, and restricts the brake current flowing in the motor (4) to a predetermined current restriction value by the control of the on-off operations of the switching elements.

Description

  The present invention relates to a motor control device that activates a dynamic brake for each motor that is mechanically connected and driven in parallel, and a control method for the motor control device.

  2. Description of the Related Art Conventionally, a motor control device that operates a dynamic brake for a three-phase motor is known in which an external brake circuit is added to the motor output (see, for example, Patent Document 1). In the brake circuit described in Patent Document 1, the relay is turned on when the brake is operated, and the terminals of the motor are short-circuited through a plurality of resistors in the brake circuit. In this motor control device, resistance is added to the impedance of the motor itself, so that a brake current does not flow excessively in the motor. However, when the induced voltage is lowered with a decrease in the rotational speed of the motor, the brake current flowing through the motor is also reduced and the brake torque is weakened. Therefore, the time required from the brake operation to the motor stop becomes longer.

  There has also been proposed a motor control device that short-circuits motor terminals by turning on and off an inverter bridge circuit (see, for example, Patent Document 2). In the motor control device described in Patent Document 2, the switching element of each phase of the upper arm or the lower arm is simultaneously turned on in the inverter bridge circuit of the three-phase half bridge, thereby short-circuiting the motor terminals and performing the dynamic brake. It is operating. In this case, since the ease of flow of the brake current is determined mainly only by the impedance of the motor itself, compared with the motor control device of Patent Document 1 to which the resistance of the external brake circuit is added, the brake operation is stopped from the motor stop. The time required is getting shorter.

JP-A-01-209973 Japanese Patent No. 4817116

  By the way, it is known that the brake torque of a motor changes according to the brake current which flows into a motor. However, the brake torque does not depend only on the brake current, and actually the brake torque may decrease even if the brake current increases. For this reason, in the motor control device described in Patent Document 2, even in a high speed region where the brake current is large, the brake cannot be operated strongly with respect to the motor, and the time required to stop the motor cannot be shortened.

  The present invention has been made in view of such circumstances, and a motor control device and a control method for the motor control device which can shorten the time required from the brake operation to the motor stop by appropriately operating the brake on the motor. The purpose is to provide.

  The motor control device of the present invention is composed of an upper arm and a lower arm each having a three-phase switching element, converts the direct current supplied from the power supply side to alternating current by the on / off operation of the switching element, and outputs it to the motor An inverter bridge circuit, and a motor control circuit that drives the motor by controlling the on / off operation of each phase switching element, and the motor control circuit includes each of the upper arm and the lower arm. All the phase switching elements are turned on, the terminals of each phase of the motor are short-circuited to generate a brake current, and the brake current flowing to the motor is controlled to a predetermined current limit value by controlling the on / off operation of the switching element. Restrict.

  The control method of the motor control device of the present invention is composed of an upper arm and a lower arm each having a three-phase switching element, and converts the direct current supplied from the power source side to alternating current by the on / off operation of the switching element, A control method for a motor control device comprising: an inverter bridge circuit that outputs to a motor; and a motor control circuit that controls the on / off operation of each phase switching element to drive the motor, the motor control circuit comprising: By turning on all the switching elements of each phase of either the upper arm or the lower arm, short-circuiting the terminals of each phase of the motor to generate a brake current, and controlling the on / off operation of the switching element The brake current flowing through the motor is limited to a predetermined current limit value.

  According to these configurations, since the brake current is limited to a predetermined current limit value, the current does not flow excessively in the motor. In this case, by setting the current limit value in the range where the brake torque operates strongly, the brake torque does not become weak due to the increase of the brake current in the high speed range, and the time required from the brake operation to the motor stop can be shortened. .

  In the motor control device of the present invention, the motor control circuit drives a plurality of motors, and limits a brake current flowing through the plurality of motors to a predetermined current limit value. According to this configuration, since the brake current flowing through the plurality of motors is limited to the predetermined current limit value, the brake torque can be appropriately operated for the plurality of motors.

  Further, in the motor control device of the present invention, the plurality of motors are mechanically coupled so as to be driven in parallel, and the motor control circuit transmits a brake current flowing through the plurality of motors by the plurality of motors. Limit to a common current limit value. According to this configuration, it is possible to generate the brake torque substantially uniformly in the plurality of motors. Therefore, it is possible to reduce the positional deviation of the mechanically connected motors and suppress mechanical stress between the motors.

  In the motor control device of the present invention, the motor control circuit sets the current limit value common to the plurality of motors to a second current limit value lower than the first current limit value at which the brake torque becomes maximum. Set. According to this configuration, since the brake current is limited to a current limit value lower than the current value at which the brake torque becomes maximum, the difference in brake current due to the impedance variation of the motor itself is absorbed, and the brake torque between the motors is absorbed. The difference can be reduced.

  Further, in the motor control device of the present invention, the plurality of motors are mechanically coupled so as to be driven in parallel, and the motor control circuit transmits a brake current flowing through the plurality of motors by the plurality of motors. Limit to individual current limit values. According to this configuration, the current deviation value is individually set so as to absorb the difference in motor characteristics, so that the positional deviation of the mechanically connected motors can be further reduced, and mechanical stress between the motors can be reduced. Can be suppressed.

  In the motor control device of the present invention, the motor control circuit sets the individual current limit values of the plurality of motors to a second current limit value lower than the first current limit value at which the brake torque becomes maximum. Then, the individual current limit value is corrected for each motor. According to this configuration, since the brake current is limited to a current limit value lower than the current value at which the brake torque becomes maximum, it is possible to absorb the difference in brake current due to the impedance variation of the motor itself.

  In the motor control device of the present invention, the motor control circuit corrects the individual current limit values based on position deviations of the plurality of motors. According to this configuration, since the individual current limit value for each motor is corrected according to the position deviation, it is possible to suppress an increase in the position deviation due to a dynamic change in the load.

  In the motor control device of the present invention, the motor control circuit corrects the individual current limit values based on measured values of brake currents flowing through the plurality of motors. According to this configuration, the current limit value is corrected in consideration of not only the difference in motor characteristics but also the impedance of the motor cable and the resistance of the switching element, so that the brake can be operated more appropriately for the motor. it can.

  The motor control device according to the present invention further includes a current sensor that detects a brake current flowing through the motor, and the motor control circuit includes the upper arm and the motor when the brake current flowing through the motor exceeds a current limit value. By temporarily turning off all the switching elements of the lower arm, the brake current flowing through the motor is limited to a predetermined current limit value. According to this configuration, the brake current flowing through the motor can be limited to the current limit value by simple switching control.

  According to the present invention, by limiting the brake current flowing through the motor, the brake can be appropriately operated with respect to the motor, and the time required from the brake operation to the motor stop can be shortened.

It is a schematic diagram of the moving mechanism of the mounting head which concerns on this Embodiment. It is a block diagram of the motor control device according to the present embodiment. It is a figure which shows an example of an armature resistance, an armature inductance, and an induced voltage constant. It is a figure which shows the change of the impedance with respect to rotation speed. It is a figure which shows the change of the brake current with respect to rotation speed, and brake torque. It is a figure which shows the brake evaluation of a general short brake system. It is a figure which shows the brake evaluation of the 1st brake system which concerns on this Embodiment. It is a figure which shows the brake evaluation of the 2nd brake system which concerns on this Embodiment. It is a flowchart which shows an example of the process operation | movement of the electric current limitation which concerns on this Embodiment.

  Hereinafter, the present embodiment will be described in detail with reference to the accompanying drawings. In the following description, a configuration in which the motor control device of the present invention is applied to a mounting head moving mechanism of a component mounting device such as a chip mounter will be described as an example. However, the present invention is not limited to this. The motor control device of the present invention can be applied to any device as long as the motor is used. FIG. 1 is a schematic diagram of a mounting head moving mechanism according to the present embodiment. For convenience of explanation, only a minimum configuration is shown here.

  As shown in FIG. 1, the mounting head moving mechanism 1 is configured to move the mounting head 3 to mount an electronic component on the substrate W on the base 2. The mounting head moving mechanism 1 is supported by pillars (not shown) erected at the four corners of the base 2 and moves the mounting head 3 in the X axis direction and the Y axis direction at a predetermined height from the upper surface of the base 2. Move. Further, the mounting head moving mechanism 1 has both a pair of Y-axis stages 5 parallel to the Y-axis direction, a pair of motors 4A and 4B that move on the pair of Y-axis stages 5, and a pair of motors 4A and 4B. And an X-axis stage 6 supported by. The mounting head 3 is supported on the X-axis stage 6 so as to be movable in the X-axis direction.

  The mounting head moving mechanism 1 moves the mounting head 3 in the X-axis direction along the X-axis stage 6 by a motor (not shown). The mounting head moving mechanism 1 moves the mounting head 3 along the Y-axis stage 5 in the Y-axis direction together with the X-axis stage 6 by a pair of motors 4A and 4B. With such a configuration, the mounting head 3 can be moved horizontally above the substrate W and transport the electronic component to a desired position on the substrate W. The motor control device according to the present embodiment is applied to the mounting head moving mechanism 1. In the configuration in which the pair of motors 4A and 4B are mechanically connected via the X-axis stage 6, the time required for stopping the motor is shortened and the positional deviation between the motors 4A and 4B is minimized.

  Next, the motor control device for the mounting head moving mechanism according to the present embodiment will be described. FIG. 2 is a block diagram of the motor control device according to the present embodiment. FIG. 2 shows an example, and the present invention is not limited to this configuration, and any configuration including an inverter bridge circuit may be used. Here, although the motor drive device of the motor 4A will be described, the motor drive device of the motor 4B has the same configuration.

  As shown in FIG. 2, the motor control device includes a rectifier 12 that converts alternating current from a three-phase alternating current or single-phase alternating current main power supply 11 into direct current, and direct current from the rectifier 12 is converted into alternating current and output to the motor 4A. And an inverter bridge circuit 13 that performs PWM control of the inverter bridge circuit 13. A smoothing capacitor 15 that smoothes the output (DC voltage) of the rectifier 12 is connected to the rectifier 12 in parallel. Further, an inrush current suppression circuit 16 including a resistor and a bypass switch for suppressing an inrush current at the time of power supply startup is provided between one end of the rectifier 12 and one end of the smoothing capacitor 15. The rectifier 12, the smoothing capacitor 15, and the inrush current suppression circuit 16 constitute a main power supply circuit unit 17.

  The inverter bridge circuit 13 includes a half-bridge circuit 18 for three phases connected in parallel to the rectifier 12. The U-phase half-bridge circuit 18u includes an upper arm (high side) switching element T1 and a lower arm (low side) switching element T4 connected in series, and each of the switching elements T1 and T4 has a freewheeling diode D1, It is configured by connecting D4 in parallel. Similarly, the V-phase half-bridge circuit 18v connects the switching element T2 of the upper arm and the switching element T5 of the lower arm in series, and the free-wheeling diodes D2 and D5 are connected in parallel to the switching elements T2 and T5, respectively. Connected and configured.

  The W-phase half-bridge circuit 18w includes an upper arm switching element T3 and a lower arm switching element T6 connected in series, and freewheeling diodes D3 and D6 connected in parallel to the switching elements T3 and T6, respectively. Composed. The connection points of the U-phase switching elements T1 and T4, the connection points of the V-phase switching elements T2 and T5, and the connection points of the W-phase switching elements T3 and T6 are the three-phase excitation coils in the motor 4A. They are connected to each other through resistors. The PWM signal is input from the motor control circuit 14 to the three-phase half-bridge circuits 18u-18w.

  An input line from the motor control circuit 14 is connected to the gates of the switching elements T1 to T6. The switching elements T <b> 1 to T <b> 6 are switched between an on state and an off state when a PWM signal is applied from the motor control circuit 14. The switching elements T1-T6 are turned on and off to convert direct current into alternating current and supply necessary power to the motor 4A. Between the connection point of the U-phase switching elements T1, T4 and the connection point of the W-phase switching elements T3, T6 and each terminal of the motor 4A, a current sensor 19u that feeds back each phase current to the motor control circuit 14, 19w is provided. Here, a configuration for performing current detection of two phases of Iu and Iw is illustrated, but current detection of three phases of Iu, Iv, and Iw may be performed.

  The motor 4A is provided with an encoder 21 that detects the position and speed of the motor 4A. The position and speed detected by the encoder 21 are output to the motor control circuit 14, and the motor 4A is servo-controlled by the motor control circuit 14.

  Further, the motor control device includes a three-phase AC or single-phase AC control power supply 22 separately from the main power supply 11, a rectifier 23 that converts alternating current from the control power supply 22 into direct current, and an output voltage from the rectifier 23. A switching power supply circuit 24 is provided. A smoothing capacitor 25 that smoothes the output (DC voltage) of the rectifier 23 is connected to the rectifier 23 in parallel. In addition, an inrush current suppression circuit 26 including a resistor and a bypass switch for suppressing an inrush current at the time of power supply startup is provided between one end of the rectifier 23 and one end of the smoothing capacitor 25. The rectifier 23, the smoothing capacitor 25, and the inrush current suppression circuit 26 constitute a control power supply circuit unit 27.

  A logic capacitor 28 is connected in parallel to the switching power supply circuit 24, and a voltage (for example, + 5.0V or + 3.3V) required by the motor control circuit 14 is generated via the logic capacitor 28. The motor control circuit 14 controls the inverter bridge circuit 13 by such an input from the switching power supply circuit 24. In this motor control device, a so-called short brake system is adopted as a brake system. Specifically, the motor 4A is stopped by a brake current generated by a short circuit between the terminals of the motor 4A by simultaneously turning on any one of the three switching elements of the upper arm and the lower arm.

  In addition, although switching element T1-T6 of this Embodiment was comprised with the power transistor, it is not limited to this structure. The switching element may be a current-voltage control element that can control the current voltage. For example, the switching element may be an IGBT (Insulated Gate Bipolar Transistor), a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), or a bipolar transistor. The free-wheeling diodes D1 to D6 may be elements that constitute a path for the regenerative current, and a parasitic diode built in the power transistor can also be used.

  By the way, as a short brake system described above, a combination with a resistance short brake system has been studied. In this brake system, the brake current is controlled to be constant using a short brake in the high speed range, and when the brake current cannot be kept constant, switching to a resistance short circuit is performed. As a result, the deceleration time can be freely adjusted according to the application of the apparatus. However, in this brake system, when the pair of motors 4A and 4B are mechanically connected via the X-axis stage 6 as in the mounting head moving mechanism 1, between the motors 4A and 4B (between two axes). Mechanical damage due to an increase in the positional deviation is assumed (see FIG. 1).

  In order to suppress the expansion of the position deviation, a method of operating the brakes on the motors 4A and 4B based on the ratio of the load to the pair of motors 4A and 4B can be considered. A load acts on the pair of motors 4A and 4B in an unbalanced manner according to the movement position of the mounting head 3 on the X-axis stage 6 in the X-axis direction. In this brake system, the brakes are actuated on the motors 4A and 4B in accordance with the load imbalance. However, the position deviation cannot be sufficiently suppressed only by the brake operation corresponding to the load imbalance. This is because not only the load imbalance but also the motor characteristics, the rotational speed and the like affect the brake torque.

  Hereinafter, with reference to FIG. 3 to FIG. 5, the relationship between the motor characteristics and the rotational speed and the brake torque will be described. FIG. 3 is a diagram illustrating an example of armature resistance, armature inductance, and induced voltage constant. FIG. 4 is a diagram showing a change in impedance with respect to the rotational speed. FIG. 5 is a diagram showing changes in the brake current and the brake torque with respect to the rotational speed. 3 to 5, the motors A and B of the same type will be exemplified to explain the relationship between the motor characteristics and the rotational speed and the brake torque.

FIG. 3 shows variations in motor characteristics of the motors A and B. Here, the armature resistance R of the motor A, armature inductance L, and the induced voltage constant K _e 100 respectively, to determine the percentage of variation of the motor B. As a result, the motor B is armature resistance R is 104.2, the armature inductance L is 95.5, the induced voltage constant _{K e} is a variation that 98.1 was measured. Further, according to the specifications, it is assumed that the armature resistance R has a variation of ± 10%, the armature inductance L is ± 30%, and the induced voltage constant _Ke is ± 10%. Thus, even in the same type motor, variation occurs armature resistance R, armature inductance L, the motor characteristics such as induced voltage constant K _e.

Here, assuming that the impedance Z of the motors A and B is a complex number, assuming that the armature resistance is R, the armature inductance is L, and the angular frequency is ω, the following expression (1) is obtained. Note that “·” attached to the symbol Z indicates that the impedance is in complex notation.
(1)
Z ^· = R + jωL
At this time, the phase θ is expressed by the following equation (2), and the current is delayed with respect to the voltage.
(2)
θ = ATAN (ωL / R)

The magnitude of the impedance Z of the motors A and B is expressed by the following equation (3), where R is the armature resistance, L is the armature inductance, ω is the angular frequency, and f is the commutation frequency.
(3)
Z = √ (R ² + (ωL) ² ) = √ (R ² + (2πfL) ² )
Further, the commutation frequency f is expressed by the following equation (4), where N is the number of rotations and P is the number of magnet magnetic poles.
(4)
f = N / 60 × P / 2

When the equation (4) is substituted into the equation (3), the magnitude of the impedance Z is expressed by the following equation (5).
(5)
Z = √ (R ² + (πNPL / 60) ² )
As described above, even in the same type of motor, the impedance Z varies among the motors A and B depending on the values of the armature resistance R and the armature inductance L. It can be seen that the degree of variation in the impedance Z of B changes.

The motor A, the induced voltage constant K _e of B is known to be a value proportional to the torque constant K _t. For this reason, the variation of the induced voltage constant K _e can be considered as the variation of the torque constant K _t . In this case, the motor torque T _m is expressed by the following equation (6), where K _t is the torque constant and I _m is the phase current flowing through the motors A and B.
(6)
T _m = K _t × I _m
For this reason, it is considered that the motor torque Tm also varies depending on the variation of the induced voltage constant Ke.

Here, a case where a short brake is operated for each of the motors A and B is considered. The brake current I _dbk flowing through the motors A and B is expressed by the following equation (7), where the induced voltage is V _emf and the impedance is Z.
(7)
I _dbk = V _emf / Z
The brake current I _dbk is obtained as described above, but the brake current I _dbk does not necessarily become the brake torque.

The actual brake torque acting on the motors A and B is generated by the brake current I _{dbk · real} expressed by the following equation (8) in consideration of the phase delay.
(8)
I _{dbk · real} = I _dbk × cos θ
For this reason, as is clear from the equations (2) and (4), the phase θ changes according to the rotational speed N of the motors A and B. Therefore, the relationship between the brake current and the brake torque changes depending on the rotational speed. I understand.

  The graphs of FIGS. 4 and 5 are obtained from the above calculation formula. FIG. 4 shows the variation in the impedance Z of the motors A and B. As shown in FIG. 4, the impedances of the motors A and B change non-linearly up to about 300 rpm where the rotational speed is low, and thereafter change linearly as the rotational speed increases. Further, as described above, due to variations in the armature resistance R and the armature inductance L of the motors A and B, the impedance Z of the motors A and B is displaced. In this case, the difference between the impedances Z of the motors A and B increases as the rotational speed increases.

FIG. 5 shows variations in brake current I _dbk and brake torque (I _{dbk · real} ) of motors A and B. As shown in FIG. 5, the brake currents I _dbk of the motors A and B rapidly increase up to about 600 rpm, and thereafter gradually increase as the rotational speed increases and _approach a constant current value. Further, since there is a deviation in the impedance Z of the motors A and B, there is also a deviation in the brake current I _dbk . In addition, the actual brake current I _{dbk · real} that generates the brake torque in the motors A and B has a peak around about 400 rpm, and thereafter decreases as the rotational speed increases. As described above, since the brake current I _dbk of the motors A and B has a deviation, the actual brake current I _{dbk · real} also has a deviation.

At this time, the maximum value of the brake torque is when the phase θ = 45 °, and it can be seen from the above equation (2) that R = ωL. Therefore, the rotational speed N _{dbk · max at} which the brake torque is maximized is expressed by the following equation (9), where ωL = πNPL / 60 = R in the above equation (5).
(9)
N _{dbk · max} = 60 × R / (πPL)
The rotational speeds N _{dbk · max} of the motors A and B are 390 rpm and 425 rpm, respectively, and there is a deviation in the rotational speed at which the brake torque is maximum.

From the above results, when the short brake is operated, the brake current I _dbk corresponding to the induced voltage of the motors A and B flows, but the brake torque is not determined only by the brake current I _dbk and the rotation speed N It was found that the relationship between the brake current and the brake torque changes according to the condition. In particular, the brake torque does not increase at high _speeds where the brake current I _dbk is large, and the brake torque is maximum at N _{dbk · max} .

  As described above, the present applicant has found that the brake torque acts strongly on the motors A and B by suppressing the brake current flowing through the motors A and B to a predetermined current limit value based on FIG. Further, the present applicant has discovered that the positional deviation is adversely affected by variations in the impedances and motor characteristics of the motors A and B. That is, the gist of the present invention is to shorten the time required from the brake operation to the motor stop by supplying an appropriate brake current to the motors A and B. Furthermore, in consideration of variations in motor A and B impedance and motor characteristics, the position deviation is minimized by operating the brake.

  Hereinafter, the brake system of the motor control device according to the present embodiment will be described in detail with reference to FIGS. FIG. 6 is a diagram showing a brake evaluation of a general short brake system. FIG. 7 is a diagram showing a brake evaluation of the first brake system according to the present embodiment. FIG. 8 is a diagram showing a brake evaluation of the second brake method according to the present embodiment. 6 to 8, the solid line W1 is the brake current of the motor A, the broken line W2 is the brake current of the motor B, the solid line W3 is the speed of the motor A, the broken line W4 is the speed of the motor B, and the solid line W5 is the motor A, B Each position deviation is shown. Here, the motors A and B of the same type will be described as an example.

  FIG. 6 shows a brake evaluation of a general short brake system, and measures the state of deceleration until the brake is operated and stopped at the maximum rotation of the motor. Immediately after the brake operation, the brake current is a large value (37.84 A for motor A and 36.20 A for motor B). This instantaneous increase in the brake current stabilizes in a time of about a sine wave number cycle, but this is not preferable because the brake current flows excessively to the motor and the deceleration of the motor becomes disturbed. The brake current peaks after stabilization are 21.24 A for motor A and 20.84 A for motor B, and a substantially constant current flows.

  At this time, the deceleration indicating the inclination of the speed of the motors A and B is gradually changing, and the time required for deceleration becomes as long as about 152 ms even though the current values of the motors A and B are as large as about 21 A. ing. This is because, as shown in FIG. 5, the brake torque increases until the brake current reaches a predetermined value, but when the brake current exceeds the predetermined value, the brake torque starts to decrease. That is, the brake torque is weak in the high speed range. Thus, even if the brake current is large, the brake does not operate strongly for the motors A and B. Further, the motors A and B are decelerated at different decelerations, and the positional deviations of the motors A and B are large.

  FIG. 7 shows the brake evaluation of the first brake system, in which the current limit value of the brake current flowing through the motors A and B is limited to 12.0A. Here, the current limit value is set so that the brake torque acts strongly on the motors A and B. Also in the first brake system, as in a general short brake, the brake is operated at the maximum rotation of the motor and the state of deceleration until it stops is measured. In this system, the brake currents of the motors A and B do not become large immediately after the brake operation, and the brake current is suppressed to 12.0 A which is the current limit value. Details of the current limiting processing operation will be described later.

  In addition, the deceleration indicating the speed gradient of each motor A, B approaches a straight line, and the gradient of the deceleration increases. For this reason, although the brake current is limited, the brake is stopped more quickly than a general short brake system. Specifically, although the current values of the motors A and B are as small as about 12.0 A, the time required for deceleration is greatly reduced to about 88 ms. This is because by suppressing the brake current to a current value at which the brake torque works strongly, a strong brake torque can be applied without the phase of the brake current being delayed too much in the high speed range. Further, the speed difference between the motors A and B is small, and the positional deviation between the motors A and B is also small.

  FIG. 8 shows the brake evaluation of the second brake system, in which the current limit value of the motor A is limited to 11.5A and the current limit value of the motor B is limited to 12.0A. Here, individual current limit values are set so as to absorb differences in characteristics of the motor itself such as the impedances and induced voltage constants of the motors A and B, and differences in loads of the motors A and B. In the second brake method, as in a general short brake method, the brake is operated at the maximum rotation of the motor, and the state of deceleration is measured until it stops. Even in this method, the brake currents of the motors A and B do not become large immediately after the brake operation, and the brake currents are suppressed to the respective current limit values.

  Compared with the first brake system shown in FIG. 7, the time required for deceleration is not significantly different, but the decelerations of the motors A and B are substantially the same and are decelerated and stopped at the same speed. For this reason, the maximum position deviation of the motors A and B is small. Here, when the maximum values of the positional deviations of the motors A and B in the general short brake system and the first and second brake systems according to the present embodiment are compared, the general short brake system has 26300 pulses, The first brake system has 7170 pulses and the second brake system has 1440 pulses. Thus, since the position deviation can be reduced in the second brake method, when the motors A and B are mechanically coupled so as to be driven in parallel, mechanical stress and shaft torsion can be minimized. it can.

  Next, the setting of the current limit values of the first and second brake methods will be described with reference to FIG. When the motors A and B are mechanically connected, even if only the load imbalance with respect to the motors A and B is considered, the brake cannot be operated properly, and it is difficult to suppress the position deviation. For example, when the brake current increases in a high speed range, the brake torque becomes weak, which may have an adverse effect. Therefore, in the brake system according to the present embodiment, the current limit value is set in consideration of the difference in motor impedance, the difference in characteristics of the motor itself, and the load imbalance.

  First, setting of a common current limit value for the motors A and B will be described. As shown in FIG. 5, the first current limit value with the largest brake torque in the calculation and the second current limit value 10% to 20% lower than the first current limit value are calculated. The first and second current limit values can be obtained from the above formula (5), formula (7), formula (8), and the like. In the first brake system, the current value flowing through the motors A and B is limited to a common second current limit value, for example, 12.0 A. This is because if the current value flowing through the motors A and B is limited to the first current limit value, it becomes complicated when setting different values as the current limit values of the second brake method described later.

  That is, since the first current limit value is set near the maximum value of the brake torque, it is difficult to determine whether the brake torque is reduced if the current limit value is increased or the brake torque is decreased if the current limit value is decreased. . Therefore, in this embodiment, for both the first and second brake systems, the current limit value is limited to a second current limit value that is 10% to 20% lower than the first current limit value. The relationship between the change and increase / decrease in brake torque is clarified. This facilitates correction of the current limit value when changing from the first brake system to the second brake system. In this way, by making the common current limit values coincide with each other, a substantially uniform brake torque is generated in the motors A and B, and by making the current limit value lower than the maximum current limit value, Absorbs the difference in impedance.

  Next, the setting of individual current limit values for the motors A and B will be described. The setting of the individual current limit value is used in the second brake method. In the setting of the individual current limit values, the brake currents of the motors A and B are limited to the second current limit value, and then the current limit values of the motors A and B are corrected based on the second current limit value. (Increase or decrease). Here, the brake currents (brake torque) of the motors A and B are measured, and the current limit values of the motors A and B are corrected with fixed values. For example, when the brake torque of the motor B is weaker than that of the motor A, the current limit value of the motor A is corrected to 11.5A and the current limit value of the motor B is corrected to 12.0A.

  The corrected current limit value only needs to be lower than the first current limit value, and the current limit value of motor A may be corrected to 11.75A and the current limit value of motor B may be corrected to 12.25A. In setting individual current limit values, only the current limit value of either motor A or motor B may be corrected, or both current limit values may be corrected.

  As described above, the current values flowing through the motors A and B are limited to individual current limit values, thereby absorbing differences in motor characteristics such as induced voltage constants. However, this setting method can absorb differences in motor impedance and motor characteristics, but does not consider dynamic changes in load. Further, it is necessary to actually measure the motors A and B, and the correction value determination is complicated. In this case, a method of correcting the current limit value based on the position information of the load is conceivable, but appropriate correction cannot be performed in a high speed range.

  Therefore, as the setting of the individual current limit value, it is also possible to correct the current limit value according to the position deviation which is the difference between the current positions of the motors A and B. As a result, the current limit values of the motors A and B can be dynamically changed according to the dynamic change of the load. In setting the current limit value according to the position deviation, the brake current of the motors A and B is limited to the second current limit value, and the position deviation amount of the motors A and B exceeds a predetermined threshold value. The current limit value is corrected (increased or decreased) by multiplying the current limit value by a correction coefficient corresponding to the position deviation amount. In setting the current limit value according to the position deviation, only the current limit value of either the motor A or the motor B may be corrected, or both current limit values may be corrected.

  By the way, the above correction becomes invalid in the low speed range where the rotational speeds of the motors A and B are 400 rpm or less. Therefore, when the brake current is limited in a low speed region of 400 rpm or less to suppress the position deviation, it is possible to set the third current limit value as shown in FIG. The third current limit value is set so that the current limit value decreases as the rotational speed (speed) decreases. Then, the current limit value is corrected (increased or decreased) based on the second current limit value according to the position deviation in the high speed range of 400 rpm or more, and the third current limit value is set according to the position deviation in the low speed range of 400 rpm or less. The current limit value is corrected (increased / decreased) as a reference. Accordingly, the brake current can be limited to an appropriate current limit value according to the position deviation even in the low speed range.

  In setting the current limit value according to the position deviation, it is necessary to actually take into account the impedance of the motor cable and the resistance of the switching element.

  As described above, the current limit value is set by limiting the brake current flowing through the motors A and B to the second current limit value lower than the first current limit value at which the motor torque is maximum. , B absorbs the difference in impedance. Moreover, the difference in the motor characteristics of the motors A and B is absorbed by individually correcting the current limit values for the motors A and B. Further, the position deviation amount is minimized by correcting the current limit values for the motors A and B individually according to the position deviation amount.

  The mounting head moving mechanism 1 according to the present embodiment employs the first brake method, thereby shortening the time required to stop the motor as compared with a general short brake method, and between the motors 4A and 4B. The position deviation is reduced (see FIG. 1). Furthermore, the mounting head moving mechanism 1 adopts the second brake method, thereby shortening the time required for the motor to stop and reducing the positional deviation between the motors 4A and 4B as compared with the first brake method, Prevents mechanical stress and shaft torsion. The current limit value setting process and the correction process may be performed by the motor control circuit 14 or may be performed by a higher-level device.

  Here, with reference to FIG.2 and FIG.9, the process operation | movement of the electric current limitation in a motor control apparatus is demonstrated. FIG. 9 is a flowchart showing an example of the current limiting processing operation according to the present embodiment. Here, the current limit of the motor 4A will be described, but the same applies to the current limit of the motor 4B.

  As shown in FIGS. 2 and 9, when the dynamic brake is operated, the three switching elements of the upper arm or the lower arm of the inverter bridge circuit 13 are turned on (step S01). As a result, the terminals of the motor 4A are short-circuited to generate a brake current. The brake current flowing through the motor 4A is detected by the current sensors 19u and 19w and output to the motor control circuit 14. The motor control circuit 14 determines whether or not the brake current exceeds the current limit value (step S02). If the brake current does not exceed the current limit value (NO in step S02), the process proceeds from step S02 to step S06.

  On the other hand, when the brake current exceeds the current limit value (YES in step S02), all six switching elements of the inverter bridge circuit 13 are turned off and the brake is temporarily stopped (step S03). When a certain time has elapsed (step S04), the three switching elements of the upper arm or the lower arm of the inverter bridge circuit 13 are turned on again to operate the brake (step S05). The fixed time is about several hundred μs and may be the shortest cycle of the control cycle. Next, the motor control circuit 14 determines whether or not the brake current is sufficiently smaller than the current limit value (step S06). For example, the determination value sufficiently lower than the current limit value is compared with the brake current.

  If it is determined that the brake current is sufficiently lower than the current limit value (YES in step S06), the dynamic brake is terminated. On the other hand, if it is determined that the brake current is not sufficiently lower than the current limit value (NO in step S06), the processes from step S02 to S05 are repeated until the brake current becomes sufficiently low. Thus, in the motor control device according to the present embodiment, the peak of the brake current becomes the current limit value by repeatedly turning on the three switching elements of the upper arm or the lower arm and temporarily turning off all the switching elements. It is controlled not to exceed.

  As described above, according to the motor control device according to the present embodiment, the brake current is limited to the predetermined current limit value, so that no current flows through the motor. In this case, by setting the current limit value in the range where the brake torque operates strongly, the brake torque does not become weak due to the increase of the brake current in the high speed range, and the time required from the brake operation to the motor stop can be shortened. . When motors are mechanically connected and driven in parallel, individual current limit values can be set to absorb differences in motor impedance, motor characteristics, and loads on each motor. In addition, the mechanical stress between the motors can be suppressed by minimizing the positional deviation.

  In addition, this invention is not limited to the said embodiment, It can change and implement variously. In the above-described embodiment, the size, shape, and the like illustrated in the accompanying drawings are not limited to this, and can be appropriately changed within a range in which the effects of the present invention are exhibited. In addition, various modifications can be made without departing from the scope of the object of the present invention.

  For example, in the present embodiment, the individual current limit value is set to the second current limit value for each motor, and the current limit value is individually corrected for each motor on the basis of the second current limit value. However, the present invention is not limited to this configuration. The setting method is not particularly limited as long as the individual current limit value is set for each motor.

  In the present embodiment, the individual current limit value is corrected by each motor based on the actually measured value and the position deviation. However, the present invention is not limited to this configuration. The individual current limit value for each motor may be corrected in any way as long as the motor characteristics can be absorbed.

  As described above, the present invention has an effect that the time required from the brake operation to the motor stop can be shortened by appropriately operating the brake to the motor, and in particular, the two shafts mechanically connected. Is useful for motor control devices that are driven in parallel.

1 Mounting head moving mechanism 3 Mounting head (load)
4A, 4B Motor 5 Y-axis stage 6 X-axis stage (load)
11 Main power supply
13 Inverter bridge circuit 14 Motor control circuit 18u-18w Half bridge circuit 19u, 19w Current sensor 21 Encoder T1-T6 Switching element D1-D6 Free-wheeling diode

Claims (10)

An inverter bridge circuit configured by an upper arm and a lower arm each having a three-phase switching element, converting a direct current supplied from the power source side by an on / off operation of the switching element into an alternating current, and outputting the alternating current to the motor;
A motor control circuit for controlling the on / off operation of the switching element of each phase and driving the motor;
The motor control circuit turns on all of the switching elements of each phase of either the upper arm or the lower arm, short-circuits the terminals of the phases of the motor to generate a brake current, and the switching element. A motor control device that limits a brake current flowing through the motor to a predetermined current limit value by controlling the on / off operation of the motor.   The motor control device according to claim 1, wherein the motor control circuit drives a plurality of motors and limits a brake current flowing through the plurality of motors to a predetermined current limit value. The plurality of motors are mechanically coupled to drive in parallel,
The motor control device according to claim 2, wherein the motor control circuit limits a brake current flowing through the plurality of motors to a current limit value common to the plurality of motors.   The motor control circuit sets a current limit value common to the plurality of motors to a second current limit value that is lower than the first current limit value at which the brake torque is maximized. The motor control device described in 1. The plurality of motors are mechanically coupled to drive in parallel,
The motor control device according to claim 2, wherein the motor control circuit limits a brake current flowing through the plurality of motors to an individual current limit value by the plurality of motors.   The motor control circuit sets the individual current limit values for the plurality of motors to a second current limit value lower than the first current limit value at which the brake torque is maximum, and then sets the individual current limit value for each motor. The motor control device according to claim 5, wherein the current limit value is corrected.   The motor control apparatus according to claim 6, wherein the motor control circuit corrects the individual current limit values based on position deviations of the plurality of motors.   The motor control device according to claim 6, wherein the motor control circuit corrects the individual current limit value based on an actual measurement value of a brake current flowing through the plurality of motors. A current sensor for detecting a brake current flowing through the motor;
When the brake current flowing through the motor exceeds a current limit value, the motor control circuit temporarily turns off all the switching elements of the upper arm and the lower arm, thereby reducing the brake current flowing through the motor. The motor control device according to any one of claims 1 to 8, wherein the motor control device is limited to a predetermined current limit value. An inverter bridge circuit configured by an upper arm and a lower arm each having a three-phase switching element, converting a direct current supplied from the power source side by an on / off operation of the switching element into an alternating current, and outputting the alternating current to the motor;
A control method of a motor control device comprising a motor control circuit for controlling the on / off operation of each phase switching element to drive the motor,
The motor control circuit turns on all of the switching elements of each phase of either the upper arm or the lower arm, short-circuits the terminals of the phases of the motor to generate a brake current, and the switching element. A control method for a motor control device, wherein a brake current flowing through the motor is limited to a predetermined current limit value by controlling on / off operation of the motor.

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