PH12016000310A1

PH12016000310A1 - Motor control apparatus

Info

Publication number: PH12016000310A1
Application number: PH12016000310A
Authority: PH
Inventors: Ide Yuji; Kitahara Michio; Hiraide Toshio
Original assignee: Sanyo Electric Co
Priority date: 2015-09-09
Filing date: 2016-09-06
Publication date: 2018-03-12
Also published as: TW201711824A; TWI725053B; CN106533270B; PH12016000310B1; JP6745661B2; CN106533270A; JP2017055636A

Abstract

A motor control apparatus is provided which can synchronously control three or more motors and also can synchronize the motors accurately even when a torque command is saturated. When a torque command for any of the motors is saturated, the motor control apparatus limits the rates of change of speed of the other motors to the acceleration of the motor having the smallest acceleration.

Description

accordance with the torque-limited first torque command to drive the first motor 410. -

The motor control apparatus 1000 takes the time derivative of the second 5 position to obtain a speed (second speed) V2 of the second motor 430, and takes the time - derivative of the second position twice to obtain an acceleration (second acceleration) A2 5 ofthe second motor 430. The differentiator that obtains the second speed V2 may be placed, for example, between the second rotational position sensor 440 and a speed " controller 230 in Fig. 1. The differentiator that obtains the second acceleration A2 may ~ be realized by, for example, two differentiators located downstream of the second = rotational position sensor 440 in Fig. 1. oy

A position compensator 210 computes a compensation value (a compensation command) based on a difference between the first position and the second position.

The compensation value is configured (calculated) in such a manner as to compensate the difference between a position command for the second motor 430 (the first position) and the second position. In other words, the position compensator 210 calculates the compensation command that compensates the position of the second motor 430 based on the difference between the position of the first motor 410 and the position of the second motor 430. The difference between the first position and the second position may be calculated by a subtractor placed, for example, between the second rotational position sensor 440 and the position compensator 210 in Fig. 1.

The motor control apparatus 1000 adds the compensation value output from the position compensator 210 and the first speed command value to calculate a second speed command for the second motor 430. The addition of the compensation value (compensation command) and the first speed command may be performed by an adder (totalizing device) placed, for example, between the position compensator 210 and the second speed change rate limiter 220 in Fig. 1. In other words, the adder adds up the first speed command and the compensation command to calculate the second speed command for the second motor 430. ©

The second speed change rate limiter 220 limits the second speed command to = limit the rate of change of speed of the second motor 430. In other words, the second . speed change rate limiter 220 holds down the rate of change of the second speed on command when a torque command (first torque command) for the other motor (here, the first motor 410) is saturated. Consequently, the second speed change rate limiter 220 i. synchronizes the second motor 430 to the first motor 410. The details are described - below. @

The speed controller 230 calculates the second torque command for the second - motor 430 based on a difference between the speed command in which the rate of change has been held down by the second speed change rate limiter 220 and the second speed

V2. The second torque command is configured (calculated) in such a manner as to compensate the difference between the second speed command and the second speed V2.

The difference between the second speed command and the second speed V2 may be calculated by a subtractor placed, for example, between the second speed change rate limiter 220 and the speed controller 230 in Fig. 1.

A torque limiter 240 limits the second torque command to prevent the second torque command from the torque limiter 240 from exceeding a maximum torque limit when the second torque command from the speed controller 230 is increased to or above the maximum torque limit. In other words, the torque limiter 240 limits the torque for the second torque command.

A second torque command saturation detector 250 determines that the second torque command is saturated when the second torque command is increased to or above the maximum torque limit. The second torque command saturation detector 250 notifies the other motor's speed change rate limiter (here, the first speed change rate limiter 120) of the saturation of the second torque command. A torque controller 260 controls the torque of the second motor 430 in accordance with the torque-limited second © torque command to drive the second motor 430. hy

When the second torque command from the speed controller 230 is less than the maximum torque limit, the torque limiter 240 may output the second torque command - from the speed controller 230 as itis. The torque controller 260 controls the torque of wn the second motor 430 in accordance with the second torque command to drive the second - motor 430. ~

When having detected the saturation of the second torque command, the first @ speed change rate limiter 120 sets the rate of change of the first speed command to the © second acceleration A2. Consequently, the first speed change rate limiter 120 holds down (limits) the rate of change of the first speed command to avoid an event that the rate of change of the first speed command is increased to or above the second acceleration A2. When the second torque command is not saturated, the first speed change rate limiter 120 outputs the first speed command output from the position controller 110 as it is without performing the process of holding down (limiting) the rate of change of the first speed command. In other words, the first speed change rate limiter 120 limits the first speed command (for example, limits the rate of change of the first speed command) to limit the rate of change of speed of the first motor 410.

When having detected the saturation of the first torque command, the second speed change rate limiter 220 sets the rate of change of the second speed command to the first acceleration Al. Consequently, the second speed change rate limiter 220 holds down (limits) the rate of change of the second speed command to avoid an event that the rate of change of the second speed command is increased to or above the first acceleration Al. When the first torque command is not saturated, the second speed change rate limiter 220 outputs the second speed command as it is without performing the process of holding down (limiting) the rate of change of the second speed command.

In other words, the second speed change rate limiter 220 limits the second speed = command (for example, limits the rate of change of the second speed command) to limit ~ the rate of change of speed of the second motor 430. pi.

When a torque command for any of the motors is saturated, the above or operations of the first speed change rate limiter 120 and the second speed change rate ~ limiter 220 limit the rate of change of a speed command for the other motor to the ’ acceleration of the motor, the torque command for which is saturated. Therefore, even . if there are variations in friction with each motor shaft and/or the torque constant of each =

LI motor when a torque command is saturated, the accelerations of the motors can be = synchronized to each other. The time derivative of the rotational position of the motor is taken twice to obtain the acceleration of the motor. Therefore, in the embodiment, a positional difference between the motors can be suppressed in the dimension of acceleration.

The first speed change rate limiter 120 may limit the rate of change of speed of the first motor 410 to the smallest of the accelerations of the motors when the torque command for the second motor 430 is saturated. Furthermore, the second speed change rate limiter 220 may limit the rate of change of speed of the second motor 430 to the smallest of the accelerations of the motors when the torque command for the first motor 410 is saturated.

As described above, the motor control apparatus 1000 includes the motor control unit that controls each of a plurality of motors in such a manner as to synchronize the motors to each other. The motor control unit includes the torque command saturation detector that detects that a torque command for the motor is saturated due to reaching a given limit. Furthermore, when a torque command for any of the motors is saturated, the motor control unit may limit the rates of change of speed of the other motors to the smallest of the accelerations of the plurality of motors.

<Embodiment 2> | ©

Fig. 2 is a control block diagram illustrating the configuration of the motor = control apparatus 1000 according to a second embodiment (Embodiment 2) of the x present invention. The motor control apparatus 1000 according to Embodiment 2 - controls the drive of the first motor 410, the second motor 430 and a third motor 450, - which drive the machine 500, synchronizing the first motor 410, the second motor 430 - and the third motor 450 to each other. A third rotational position sensor 460 detects a = rotational position (third position) of the third motor 450. The motor control apparatus @ 1000 according to Embodiment 2 includes a similar configuration to that of Embodiment ol 1 except different points involved in the control of the three motors. The different points of Embodiment 2 from Embodiment 1 are mainly described below.

When a torque command (here, the second torque command or a third torque command) for another motor (that is, the second motor 430 or the third motor 450) is saturated, the first speed change rate limiter 120 holds down the rate of change of the first speed command. Consequently, the first speed change rate limiter 120 synchronizes the first motor 410 to the other motor. When the first torque command is increased to or above the maximum torque limit, the first torque command saturation detector 150 notifies the other motors' speed change rate limiters (the second speed change rate limiter 220 and a third speed change rate limiter 320 described below) of the saturation of the first torque command. Any other part of the configuration of the control system that controls the first motor 410 is similar to that of Embodiment 1.

The second speed change rate limiter 220 holds down the rate of change of the second speed command when a torque command (here, the first torque command or the third torque command) for another motor (that is, the first motor 410 or the third motor 450) is saturated. Consequently, the second speed change rate limiter 220 synchronizes the second motor 430 to the other motor. When the second torque command is increased to or above the maximum torque limit, the second torque command saturation rE detector 250 notifies the other motors’ speed change rate limiters (the first speed change 5 rate limiter 120 and the third speed change rate limiter 320 described below) of the v saturation of the second torque command. Any other part of the configuration of the = control system that controls the second motor 430 is similar to that of Embodiment 1. N

A position compensator 310 computes a compensation value based on a difference between the first position and the third position. The compensation value is - configured (calculated) in such a manner as to compensate the difference between a © position command for the third motor 450 (the first position) and the third position. z

The difference between the first and third positions may be calculated by a subtractor placed, for example, between the third rotational position sensor 460 and the position compensator 310 in Fig. 1.

The motor control apparatus 1000 adds the compensation value output from the position compensator 310 and the first speed command value to calculate a third speed command for the third motor 450. The addition of the compensation value (compensation command) and the first speed command may be performed by an adder (totalizing device) placed, for example, between the position compensator 310 and the third speed change rate limiter 320 in Fig. 1. In other words, the adder adds up the first speed command and the compensation command to calculate the third speed command for the third motor 450.

The third speed change rate limiter 320 limits the third speed command to limit the rate of change of speed of the third motor 450. In other words, the third speed change rate limiter 320 holds down the rate of change of the third speed command when a torque command (here, the first torque command or the second torque command) for another motor (that is, the first motor 410 or the second motor 430) is saturated.

Consequently, the third speed change rate limiter 320 synchronizes the third motor 450 to the other motor. | ©

A speed controller 330 calculates the third torque command for the third motor = 450 based on a difference between the speed command in which the rate of change has . been held down by the third speed change rate limiter 320 and a third speed V3. The - third torque command is configured (calculated) in such a manner as to compensate the ~ difference between the third speed command and the third speed V3. The difference - between the third speed command and the third speed V3 may be calculated by a - subtractor placed, for example, between the third speed change rate limiter 320 and the @ speed controller 330 in Fig. 1. o

A torque limiter 340 limits the third torque command to prevent the third torque command from the torque limiter 340 from exceeding a maximum torque limit when the third torque command from the speed controller 330 is increased to or above the maximum torque limit. In other words, the torque limiter 340 limits the torque for the third torque command.

When the third torque command is increased to or above the maximum torque limit, a third torque command saturation detector 350 determines that the third torque command is saturated. The third torque command saturation detector 350 notifies the other motors’ speed change rate limiters (the first speed change rate limiter 120 and the second speed change rate limiter 220) of the saturation of the third torque command. A torque controller 360 controls the torque of the third motor 450 in accordance with the torque-limited third torque command to drive the third motor 450.

When the third torque command from the speed controller 330 is less than the maximum torque limit, the torque limiter 340 may output the third torque command from the speed controller 330 as itis. The torque controller 360 may control the torque of the third motor 450 in accordance with the third torque command to drive the third motor 450.

The other members (such as differentiators) of a control system of the third - motor 450 function similarly to their corresponding members of the control system of the - second motor 430, respectively. ©

When a torque command for any of the other motors is saturated, the speed wr change rate limiter (the first speed change rate limiter 120, the second speed change rate = limiter 220, and the third speed change rate limiter 320) of each control system limits the ~~” rate of change of a speed command of its own control system to the smallest of the = accelerations of the other motors. When torque commands for the other motors are not = saturated, the process of limiting the rate of change of a speed command is not = performed.

For example, the first speed change rate limiter 120 limits the rate of change of the first speed command to the smaller of the second acceleration A2 and a third acceleration A3 when the second or third torque command is saturated. Consequently, the rate of change of the first speed command is controlled in such a manner as not to exceed the smallest motor acceleration.

When a torque command for a certain control system is saturated, the above operation of each speed change rate limiter limits the rate of change of a speed command of the control system to the smallest of the accelerations of the other control systems.

Therefore, when a torque command for any of the motors is saturated, the accelerations of the motors are controlled in such a manner as to be synchronized to each other.

Consequently, when a torque command for any of the motors is saturated, even if there are variations in friction with the motor shafts and/or torque constants of the motors, the accelerations of the motors can be synchronized to each other. As a result, a positional difference between the motors can be suppressed. <Embodiment 3>

Fig. 3 is a control block diagram illustrating the configuration of the motor control apparatus 1000 according to a third embodiment (Embodiment 3) of the present © invention. The motor control apparatus 1000 according to Embodiment 3 includes an : average position calculator 170 in addition to the configuration described in Embodiment ~ 1 whereas not including the position compensator 210. Any other part of the o configuration is generally similar to that of Embodiment 1. Hence, different points of o

Embodiment 3 from Embodiment 1 are mainly described below.

The average position calculator 170 calculates an average (average position) of ~ the first position and the second position. The position controller 110 calculates the @ first speed command based on a difference between the average position and the position y command. The difference between the average position and the position command may be calculated by, for example, a subtractor located between the position controller 110 and the average position calculator 170 in Fig. 3. The first speed command is configured (calculated) in such a manner as to compensate the difference between the position command and the average position. In other words, the first speed command is controlled in such a manner as to bring the average position close to the position command. Any other part of the configuration of the control system of the first motor 410 is similar to that of Embodiment 1.

The second speed change rate limiter 220, unlike Embodiment 1, uses the first speed command as the speed command for the second motor 430 (that is, the second speed command). In other words, the position controller 110 according to Embodiment 3 calculates the first speed command for the first motor 410 and the second speed command for the second motor 430 based on the difference between the position command for the first motor 410 and the average position. The second speed change rate limiter 220 limits the second speed command to limit the rate of change of speed of the second motor 430. The rotational position of the second motor 430 is controlled by compensating the difference between the average position and the position command.

Any other part of the configuration of the control system of the second motor 430 is & similar to that of Embodiment 1. =

Also in Embodiment 3, when a torque command for any of the motors is " saturated, the rates of change of speed commands for the other motors are limited to the - acceleration of the motor, the torque command for which is saturated, as in Embodiment fos 1. Consequently, the accelerations of the motors can be synchronized to each other. : <Embodiment 4>

Fig. 4 is a control block diagram illustrating the configuration of the motor > control apparatus 1000 according to a fourth embodiment (Embodiment 4) of the present o invention. The motor control apparatus 1000 according to Embodiment 4 includes a position controller (second position controller) 270 instead of the position compensator 210 described in Embodiment 1. Any other part of the configuration is generally similar to that of Embodiment 1. Hence, different points of Embodiment 4 from

Embodiment 1 are mainly described below.

In Embodiment 4, the position command for the first motor 410 is also used as the position command for the second motor 430. In other words, the motors are controlled based on a position command common to the motors (a common position command). Specifically, the position controller 110 calculates the first speed command for the first motor 410 based on a difference between the common position command common to the motors and the position of the first motor. The position controller 270 calculates the second speed command based on a difference between the common position command and the second position. The second speed command is configured (calculated) in such a manner as to compensate the difference between the common position command and the second position. The difference between the common position command and the second position may be calculated by a subtractor placed, for example, upstream of the position controller 270 (between the second rotational position sensor 440 and the position controller 270) in Fig. 4. The second speed change rate - limiter 220 receives the second speed command calculated by the position controller 270 ol asitis. Any other part of the configuration is similar to that of Embodiment 1. .

Also in Embodiment 4, when a torque command for any of the motors is - saturated, the rates of change of speed commands for the other motors are limited to the pos acceleration of the motor, the torque command for which is saturated, as in Embodiment - 1. Consequently, the accelerations of the motors can be synchronized to each other. <Embodiment 5> =

Fig. 5 is a control block diagram illustrating the configuration of the motor ” control apparatus 1000 according to a fifth embodiment (Embodiment 5) of the present invention. The motor control apparatus 1000 according to Embodiment 5 does not include the position controller 110 and the position compensator 210 in the configuration described in Embodiment 1. Moreover, the motor control apparatus 1000 receives a speed command for the first motor 410 instead of the position command for the first motor 410 from, for example, an external device. Any other part of the configuration is generally similar to that of Embodiment 1. Hence, different points of Embodiment 5 from Embodiment 1 are mainly described below.

The first speed change rate limiter 120 uses the speed command received by the motor control apparatus 1000 (the first speed command for the first motor) instead of the first speed command in Embodiment 1. The second speed change rate limiter 220 uses the first speed V1 as the second speed command for the second motor instead of the second speed command in Embodiment 1. Consequently, the speeds of the motors are controlled in such a manner as to be synchronized to each other. Any other part of the configuration is similar to that of Embodiment 1.

Also in Embodiment 5, when a torque command for any of the motors is saturated, the rates of change of speed commands for the other motors are limited to the acceleration of the motor, the torque command for which is saturated, as in Embodiment o 1. Consequently, the accelerations of the motors can be synchronized to each other. @ <Embodiment 6> »

Fig. 6 is a control block diagram illustrating the configuration of the motor = control apparatus 1000 according to a sixth embodiment (Embodiment 6) of the present i invention. The motor control apparatus 1000 according to Embodiment 6 does not - include the position controller 110 and the position compensator 210 in the configuration h described in Fig. 1 as in Embodiment 5. However, the second speed change rate limiter 5 220 of Embodiment 6, unlike Embodiment 5, uses the speed command for the first motor ” 410 as the second speed command instead of the first speed V1. In other words, the motors are controlled based on a speed command common to the motors. Any other part of the configuration is similar to that of Embodiment 5. Embodiment 6 can also exert similar effects to those of Embodiment 5. <Embodiment 7>

In Embodiments 1 to 6 above, when a torque command for any of the motors is saturated, each speed change rate limiter of the other motors may limit the rate of change of speed of a corresponding motor to the smallest of the accelerations of the motors. In order to exert the effects of this technique more effectively, the speed change rate limiters may limit the rates of change of speed of the motors to the smallest of the accelerations of all motors, the torque commands for which are saturated. In other words, when torque commands for any of the motors are saturated, the motor control unit may limit the rates of change of speed of the other motors to the smallest of the accelerations of the motors, the torque commands for which are saturated.

For example, assume that the second and third torque commands are saturated in the configuration described in Embodiment 2. At this point in time, the first speed change rate limiter 120 limits the rate of change of the first speed command to the smaller of the second acceleration A2 and the third acceleration A3. Consequently, the + rate of change of the first speed command is controlled in such a manner as not to exceed 2 the smallest of the accelerations of the motors, the torque commands for which are pe saturated. If the number of motors, the torque commands for which are saturated, is - only one, the rates of change of speed of the other motors are simply required to be nN controlled in such a manner as not to exceed the acceleration of the relevant motor. A . case where the number of motors is two is also alike. ~ <Regarding Modifications of the Present Invention> Zl

The present invention is not limited to the above-mentioned embodiments and “ includes various modifications. For example, the above-mentioned embodiments are described in detail for the purpose of facilitating the description of the present invention.

The above-mentioned embodiments are not necessarily limited to those including all the members (configurations) described. Moreover, part of the members of a certain embodiment can be replaced with members of another embodiment. Moreover, a member of a certain embodiment can also be added to another embodiment. Moreover, other members can be added to, deleted from, and replaced with part of the members of each embodiment.

Each of the above members (the controllers, the limiters, the compensators, the detectors, the adders, the subtractors, and the differentiators) may be configured using hardware, such as a circuit device, that achieves its function, or can also be realized by an arithmetic unit such as a CPU (Central Processing Unit) executing software implanting its function.

The position controllers and the position compensators, which are described in

Embodiments 1 to 7 above, can be configured by, for example, proportional controllers.

Moreover, the speed controllers and the position compensators can be configured by, for example, proportional integral controllers. As long as a difference can be appropriately compensated, other appropriate controllers may be used as these controllers and/or © compensators. hy

Also in Embodiments 3 to 6, a similar technique to that of Embodiment 2 - enables synchronous control of three or more motors, and synchronization of the accelerations of the motors when any of torque commands is saturated. Specifically, in for example, (a) each torque command saturation detector notifies the speed change rate on limiters of the other control systems of the saturation of the torque command, and (b) - each speed change rate limiter limits the rate of change of the speed command to the = smallest motor acceleration when the torque command for another motor is saturated. -

In Embodiments 1 to 7 above, the maximum torque limit of the torque limiter may be determined based on the maximum torque limit based on the limit of a mechanical system instead of the maximum output current of the motor control apparatus 1000. For example, the maximum torque limit of the torque limiter may be set to be equal to or less than the maximum torque limit based on the limit of the mechanical system. Alternatively, for example, the maximum torque limit can also be provided to the motor control apparatus 1000 from the outside via an appropriate interface. Any other appropriate means can also calculate the maximum torque limit. Also in these cases, the accelerations of the motors can be synchronized as in Embodiments 1 to 7.

The speed controller 130 may calculate the first torque command for the first motor 410 based on a difference between a speed command obtained by the first speed change rate limiter 120 holding down the first speed command, and the first speed V1.

The speed controller 230 may calculate the second torque command for the second motor 430 based on a difference between a speed command obtained by the second speed change rate limiter 220 holding down the second speed command, and the second speed

V2.

The torque limiter 140 may limit the first torque command to prevent the first torque command from exceeding the maximum torque limit when the first torque - command is increased to or above the maximum torque command. The torque limiter 240 may limit the second torque command to prevent the second torque command from = exceeding the maximum torque limit when the second torque command is increased to or = above the maximum torque command. =

Embodiments of the present invention may be the following first to seventh 0 motor control apparatuses. i

The first motor control apparatus includes a motor control unit configured to © control a plurality of motors in such a manner as to synchronize the motors to each other, ~ in which the motor control unit has a torque command saturation detector configured to detect that a torque command for the motor is saturated due to reaching a given limit, and when a torque command for any of the motors is saturated, the motor control unit limits the rates of change of speed of the other motors to the smallest of the accelerations of the motors to synchronize the accelerations of the motors.

The second motor control apparatus is the first motor control apparatus in which the motor control unit controls a first motor and a second motor as the plurality of motors, the motor control unit has a position controller configured to calculate a first speed command for the first motor based on a difference between a position command for the first motor and the position of the first motor, a position compensator configured to calculate a compensation command to compensate the position of the second motor based on a difference between the positon of the first motor and the position of the second motor, a first speed change rate limiter configured to limit the rate of change of speed of the first motor by limiting the first speed command, a totalizing device configured to calculate a second speed command for the second motor by adding up the first speed command and the compensation command, and a second speed change rate limiter configured to limit the rate of change of speed of the second motor by limiting the second speed command, the first speed change rate limiter limits the rate of change of : es speed of the first motor to the smallest of the accelerations of the motors when a torque command for the second motor is saturated, and the second speed change rate limiter = he limits the rate of change of speed of the second motor to the smallest of the accelerations ~~ of the motors when a torque command for the first motor is saturated. N

The third motor control apparatus is the first motor control apparatus in which . the motor control unit controls a first motor and a second motor as the plurality of motors, the motor control unit has an average position calculator configured to calculate an 2 average position obtained by averaging the position of the first motor and the position of = the second motor, a position controller configured to calculate a first speed command for the first motor and a second speed command for the second motor based on a difference between a position command for the first motor and the average position, a first speed change rate limiter configured to limit the rate of change of speed of the first motor by limiting the first speed command, and a second speed change rate limiter configured to limit the rate of change of speed of the second motor by limiting the second speed command, the first speed change rate limiter limits the rate of change of speed of the first motor to the smallest of the accelerations of the motors when a torque command for the second motor is saturated, and the second speed change rate limiter limits the rate of change of speed of the second motor to the smallest of the accelerations of the motors when a torque command for the first motor is saturated.

The fourth motor control apparatus is the first motor control apparatus in which the motor control unit controls a first motor and a second motor as the plurality of motors, the motor control unit has a first position controller configured to calculate a first speed command for the first motor based on a difference between a common position command common to the first and second motors and the position of the first motor, a second position controller configured to calculate a second speed command for the second motor based on a difference between the common position command and the position of the Hw second motor, a first speed change rate limiter configured to limit the rate of change of 3 speed of the first motor by limiting the first speed command, and a second speed change pi rate limiter configured to limit the rate of change of speed of the second motor by - limiting the second speed command, the first speed change rate limiter limits the rate of change of speed of the first motor to the smallest of the accelerations of the motors when . a torque command for the second motor is saturated, and the second speed change rate ~ limiter limits the rate of change of speed of the second motor to the smallest of the = accelerations of the motors when a torque command for the first motor is saturated. il

The fifth motor control apparatus is the first motor control apparatus in which the motor control unit controls a first motor and a second motor as the plurality of motors, the motor control unit has a first speed change rate limiter configured to limit the rate of change of speed of the first motor by limiting a first speed command for the first motor, and a second speed change rate limiter configured to limit the rate of change of speed of the second motor by limiting a second speed command for the second motor, the first speed change rate limiter limits the rate of change of speed of the first motor to the smallest of the accelerations of the motors when a torque command for the second motor is saturated, and the second speed change rate limiter limits the rate of change of speed of the second motor to the smallest of the accelerations of the motors when a torque command for the first motor is saturated.

The sixth motor control apparatus is the fifth motor control apparatus in which the first speed command and the second speed command are configured as a common speed command for the first and second motors.

The seventh motor control apparatus is the first motor control apparatus in which when torque commands for any of the motors are saturated, the motor control unit limits the rates of change of speed of the other motors to the smallest of the accelerations of the motors, the torque commands for which are saturated, to synchronize the @ accelerations of the motors. =

The foregoing detailed description has been presented for the purposes of . illustration and description. Many modifications and variations are possible in light of ~ the above teaching. It is not intended to be exhaustive or to limit the subject matter foi

REN described herein to the precise form disclosed. Although the subject matter has been - described in language specific to structural features and/or methodological acts, it is to . be understood that the subject matter defined in the appended claims is not necessarily © limited to the specific features or acts described above. Rather, the specific features o and acts described above are disclosed as example forms of implementing the claims appended hereto.

MOTOR CONTROL APPARATUS ©

BACKGROUND . 1. Technical Field -

The present invention relates to a motor control apparatus. N 2. Description of the Related Art .

In a large chip mounter and a large machine tool, one movable part is driven by - two motors to increase the position accuracy while suppressing yaw occurring on the = movable part. In a large injection molding machine, one movable part is driven by two = motors to achieve a reduction in the size of the machine.

In a technology described in JP-A-61-237615, ball screws are respectively provided on both sides of an injection screw. The injection screw is driven by two motors. The two motors are synchronously controlled. A motor control apparatus that drives the motors causes a torque limiter to limit a torque command based on the limit of the maximum current that can be output by the motor control apparatus. However, if there is a difference between the torque constants of the two motors, the torque command of a shaft having a smaller torque constant reaches the limit first to result in saturation.

When the torque command is saturated, a larger torque cannot be output. Hence, in proportion to the torque of this shaft, the torque of a shaft having a larger torque constant isincreased. As a result, a coupling portion of the ball screws of the two motors becomes not square to the ball screws. Hence, there is the possibility of damaging the ball screws due to the application of an excessive force to the ball screws.

JP-A-2015-120302 below discloses a technology that increases synchronism between motors when torque is limited. In the technology of the document, in order to protect a driven member, a correction is made in such a manner as to excellently maintain the synchronism between the motors when a torque limit is reduced below a value determined by the limit of the maximum current that can be output by a motor @ control apparatus. Specifically, a correction value that is obtained by a proportional = integral operation for a difference in position or a difference in speed (a synchronization » error) between two shafts is used to correct the torque limit. Consequently, the torque - limit of each shaft is corrected in such a manner as to reduce the synchronization error. pos

Jr

As a result, the synchronism between the two shafts can be excellently maintained. .

Consideration is given to the application of the technique described in i.

JP-A-2015-120302 above to a configuration including three or more shafts. In the = document, only the torque limit of the slave shaft is corrected. In other words, = consideration is not given to making corrections for both the master shaft and the slave shaft. In that case, for example, when the torque limit is at the maximum output value of the motor control apparatus, if there is friction with the slave shaft, the torque limit of the slave shaft cannot be further increased. Accordingly, a positional difference between both shafts is caused. Moreover, in the technology of the document, the torque limit is corrected based on a difference in position or a difference in speed. Hence, it is difficult to instantaneously detect the influence of a difference in torque between both shafts. Hence, it becomes difficult to adjust proportional integral operation parameters.

As aresult, it may become difficult to sufficiently reduce the synchronization error.

SUMMARY

The present invention has been made considering the above problems. One objective of the present invention is to provide the following motor control apparatus: the motor control apparatus can synchronously control three or more motors; furthermore, the motor control apparatus can synchronize the motors accurately even when a torque command is saturated.

When a torque command for any of the motors is saturated, a motor control apparatus according to one aspect of the present invention limits the rates of change of © speed of the other motors to the acceleration of the motor having the smallest = acceleration. .

According to the motor control apparatus, even if there is a difference in the - torque constant of each motor and mechanical friction, when the torque command is os saturated, the accelerations of the motors can be accurately synchronized. Moreover, - also if three or more motors are synchronously controlled, the motor control apparatus . canbe used. For example, the motor control apparatus includes a motor control unit © configured to control a plurality of motors in such a manner as to synchronize the motors = to each other. The motor control unit includes a torque command saturation detector configured to detect that a torque command for the motor is saturated due to reaching a given limit, and upon a torque command for any of the motors being saturated, the motor control unit limits the rates of change of speed of the other motors to the smallest of the accelerations of the plurality of motors.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a control block diagram illustrating the configuration of a motor control apparatus according to Embodiment 1;

Fig. 2 is a control block diagram illustrating the configuration of a motor control apparatus according to Embodiment 2;

Fig. 3 is a control block diagram illustrating the configuration of a motor control apparatus according to Embodiment 3;

Fig. 4 is a control block diagram illustrating the configuration of a motor control apparatus according to Embodiment 4;

Fig. 5 is a control block diagram illustrating the configuration of a motor control apparatus according to Embodiment 5; and

Fig. 6 is a control block diagram illustrating the configuration of a motor control “ apparatus according to Embodiment 6. © »

DESCRIPTION OF THE EMBODIMENTS ~

In the following detailed description, for purpose of explanation, numerous fo specific details are set forth in order to provide a thorough understanding of the disclosed - embodiments. It will be apparent, however, that one or more embodiments may be - practiced without these specific details. In other instances, well-known structures and = devices are schematically shown in order to simplify the drawing. - <Embodiment 1>

Fig. 1 is a control block diagram illustrating the configuration of a motor control apparatus 1000 according to a first embodiment (Embodiment 1) of the present invention.

The motor control apparatus 1000 according to Embodiment 1 controls the drive of a first motor 410 and a second motor 430, which drive a machine 500, synchronizing the first motor 410 and the second motor 430 to each other. In Fig. 1, from the point of ease of seeing, a control system that controls the first motor 410 and a control system that controls the second motor 430 are enclosed in dotted frames, respectively. These control systems configure a motor control unit. The operation of each member (such as a controller) included in the motor control apparatus 1000 is described below.

A first rotational position sensor 420 detects a rotational position (first position) of the first motor 410. A second rotational position sensor 440 detects a rotational position (second position) of the second motor 430. Examples of theses sensors include encoders. However, these sensors are not limited to the encoders.

The motor control apparatus 1000 takes the time derivative of the first position to obtain a speed (first speed) V1 of the first motor 410, and takes the time derivative of the first position twice to obtain an acceleration (first acceleration) A1 of the first motor

410. These differential operations can be performed by, for example, appropriate © differentiators. The differentiator that obtains the first speed V1 may be placed, for 5 example, between the first rotational position sensor 420 and a speed controller 130 in -

Fig. 1. The differentiator that obtains the first acceleration Al may be realized by, for o example, two differentiators located downstream of the first rotational position sensor - 420 in Fig. 1. Other differential operations described below may also be performed by - appropriate differentiators likewise. -

The motor control apparatus 1000 receives a position command for the first © motor 410 from, for example, an external device. A position controller (first position ye controller) 110 calculates a first speed command for the first motor 410 based on a difference between the position command and the position (first position) of the first motor 410. The first speed command is configured (calculated) in such a manner as to compensate the difference between the position command and the first position. The difference between the position command and the first position is acquired using a subtractor. The subtractor may be placed, for example, between the first rotational position sensor 420 and the position controller 110 in Fig. 1. Other subtraction processes and addition processes described below may also be performed by appropriate subtractors and adders likewise.

A first speed change rate limiter 120 limits the first speed command to limit the rate of change of speed of the first motor 410. In other words, the first speed change rate limiter 120 holds down the rate of change of the first speed command when a torque command (second torque command) for the other motor (here, the second motor 430) is saturated. Consequently, the first speed change rate limiter 120 synchronizes the first motor 410 to the second motor 430. The details are described below.

The speed controller 130 calculates a first torque command for the first motor 410 based on a difference between the first speed command in which the rate of change has been held down by the first speed change rate limiter 120 and the first speed V1. ©

The first torque command is configured (calculated) in such a manner as to compensate @ the difference between the first speed command and the first speed V1. The difference between the first speed command and the first speed V1 may be calculated by a ~ subtractor placed, for example, between the first speed change rate limiter 120 and the ot speed controller 130 in Fig. 1. - — A torque limiter 140 limits the first torque command to prevent the first torque w command from the torque limiter 140 from exceeding a maximum torque limit when the s first torque command from the speed controller 130 is increased to or above the i maximum torque limit. In other words, the torque limiter 140 limits the torque for the first torque command. The maximum torque limit can be predetermined based on, for example, the maximum output current of the motor control apparatus 1000. The other motor’'s torque limit described below is also alike.

When the first torque command from the speed controller 130 is less than the maximum torque limit, the torque limiter 140 may output the first torque command from the speed controller 130 as itis. A torque controller 160 may control the torque of the first motor 410 in accordance with the first torque command to drive the first motor 410.

A first torque command saturation detector 150 determines that the first torque command is saturated when the first torque command is increased to or above the maximum torque limit. The first torque command saturation detector 150 notifies the other motor's speed change rate limiter (here, a second speed change rate limiter 220 described below) of the saturation of the first torque command. The reason why the first torque command is saturated is that the torque limiter 140 imposes a limit to prevent the first torque command from becoming a higher value than the maximum torque limit.

The saturation of a torque command for the other motor is also alike.

The torque controller 160 controls the torque of the first motor 410 in

Claims

1. A motor control apparatus comprising = _amotor control unit configured to control a plurality of motors in such a manner . as to synchronize the motors to each other, wherein - the motor control unit includes a torque command saturation detector configured Jon to detect that a torque command for the motor is saturated due to reaching a given limit, i and upon a torque command for any of the motors being saturated, the motor control > unit limits the rates of change of speed of the other motors to the smallest of the > accelerations of the plurality of motors.

2. The motor control apparatus according to claim 1, wherein the motor control unit controls a first motor and a second motor as the plurality of motors, the motor control unit includes a position controller configured to calculate a first speed command for the first motor based on a difference between a position command for the first motor and a position of the first motor, a position compensator configured to calculate a compensation command to compensate a position of the second motor, based on a difference between the position of the first motor and the position of the second motor, a first speed change rate limiter configured to limit the rate of change of speed of the first motor by limiting the first speed command, a totalizing device configured to calculate a second speed command for the second motor by adding up the first speed command and the compensation command, and a second speed change rate limiter confi gured to limit the rate of w change of speed of the second motor by limiting the second speed command, 5 upon a torque command for the second motor being saturated, the first speed ~ change rate limiter limits the rate of change of speed of the first motor to the smallest of o the accelerations of the motors, and upon a torque command for the first motor being saturated, the second speed change rate limiter limits the rate of change of speed of the second motor to the smallest - of the accelerations of the motors. ©

3. The motor control apparatus according to claim 1, wherein the motor control unit controls a first motor and a second motor as the plurality of motors, the motor control unit includes an average position calculator configured to calculate an average position of a position of the first motor and a position of the second motor, a position controller configured to calculate a first speed command for the first motor and a second speed command for the second motor based on a difference between a position command for the first motor and the average position, a first speed change rate limiter configured to limit the rate of change of speed of the first motor by limiting the first speed command, and a second speed change rate limiter configured to limit the rate of change of speed of the second motor by limiting the second speed command, upon a torque command for the second motor being saturated, the first speed change rate limiter limits the rate of change of speed of the first motor to the smallest of the accelerations of the motors, and upon a torque command for the first motor being saturated, the second speed change rate limiter limits the rate of change of speed of the second motor to the smallest & of the accelerations of the motors. =

;

4. The motor control apparatus according to claim 1, wherein - the motor control unit controls a first motor and a second motor as the plurality pot of motors, : the motor control unit includes a first position controller configured to calculate a first speed command o for the first motor based on a difference between a common position command common 7 to the first and second motors and a position of the first motor, a second position controller configured to calculate a second speed : command for the second motor based on a difference between the common position command and a position of the second motor, a first speed change rate limiter configured to limit the rate of change of speed of the first motor by limiting the first speed command, and a second speed change rate limiter configured to limit the rate of change of speed of the second motor by limiting the second speed command, upon a torque command for the second motor being saturated, the first speed change rate limiter limits the rate of change of speed of the first motor to the smallest of the accelerations of the motors, and upon a torque command for the first motor being saturated, the second speed change rate limiter limits the rate of change of speed of the second motor to the smallest of the accelerations of the motors.

5. The motor control apparatus according to claim 1, wherein the motor control unit controls a first motor and a second motor as the plurality :

‘ of motors, © the motor control unit includes © a first speed change rate limiter configured to limit the rate of change of vo speed of the first motor by limiting a first speed command for the first motor, and o a second speed change rate limiter configured to limit the rate of - Pe change of speed of the second motor by limiting a second speed command for the second on motor, ” upon a torque command for the second motor being saturated, the first speed © change rate limiter limits the rate of change of speed of the first motor to the smallest of 0 the accelerations of the motors, and upon a torque command for the first motor being saturated, the second speed change rate limiter limits the rate of change of speed of the second motor to the smallest of the accelerations of the motors.

6. The motor control apparatus according to claim 5, wherein the first speed command and the second speed command are a common speed command for the first and second motors.

7. The motor control apparatus according to claim 1, wherein upon torque commands for any of the motors being saturated, the motor control unit limits the rates of change of speed of the other motors to the smallest of the accelerations of the motors, the torque commands for which are saturated.