Motor system

Abstract

In a motor system (1), a switch unit (22) selectively switches a target motor among a plurality of motors (23), the target motor to which electric power output by a motor driver (21) is supplied, and from which current is detected by a current sensor (35). The switch unit (22) cyclically switches the target motor among the plurality of motors (23). When the current of the target motor is detected by the current sensor (35), the motor driver (21) is controlled to output power based on the PWM duty ratio obtained on the basis of the current, in the cycle after the cycle in which the current is detected, at the timing when the motor (23) of which current is detected becomes the target motor again.

Description

Technical Field

[0001] The present invention relates to a motor system that drives a plurality of motors by a motor driver.

Background Art

[0002] Conventionally, a motor system that divides the power output by a motor driver among a plurality of motors in a time-division manner is known. Patent Document 1 discloses this type of motor system.

[0003] In the motor driving device disclosed in Patent Document 1, a plurality of motors are connected to only one motor driver via a switching circuit section. The motor driver controls the on / off of six transistors in order to apply appropriate voltages to the U, V, and W phase drive coils provided in each motor. Each transistor is driven by a driving method using a pulse signal based on a pulse width modulation method. By operating the appropriate switching circuit section, a plurality of motors can be driven simultaneously.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the above Patent Document 1, it was not possible to individually control the rotational speeds and rotational directions, etc. of a plurality of motors driven simultaneously. In order to achieve such control, different sine-wave-shaped currents must be passed through the drive coils for each motor. However, near the timing when the switching circuit section makes a switch, there is a risk that an unintended output may be applied to the motor.

[0006] The present invention has been made in view of the above circumstances, and an object thereof is to improve the control quality of each motor in a motor system that supplies power while switching the power output by a motor driver to a plurality of motors and drives them simultaneously. Means and effects for solving the problems

[0007] The problems to be solved by the present invention are as described above. Next, means for solving these problems and their effects will be described.

[0008] According to an aspect of the present invention, a motor system having the following configuration is provided. That is, this motor system includes a plurality of motors, a motor driver, a current detection unit, and a switch unit. The motor driver outputs power for generating a driving force to the plurality of motors. The current detection unit detects the current of the motor. The switch unit selectively switches a target motor, which is a supply target of the power output by the motor driver and a detection target of the current by the current detection unit, among the plurality of motors. A PWM duty ratio for driving the target motor is calculated based on the current detected by the current detection unit. The motor driver is controlled to output power based on the PWM duty ratio. The switch unit cyclically switches the target motor among the plurality of motors. When the current of the target motor is detected by the current detection unit, the motor driver outputs power based on the PWM duty ratio obtained based on the current, in a cycle after the cycle in which the current is detected, at a timing when the motor in which the current is detected becomes the target motor again.

[0009] Thereby, one motor driver can substantially drive a plurality of motors simultaneously, and the output for each motor can be controlled individually. While cyclically switching the output of one motor driver among a plurality of motors, control for each motor can be correctly applied to the motor. Since the motor driver and the current detection unit can be shared by a plurality of motors, simplification of the configuration can be realized.

[0010] In the above motor system, it is preferable to adopt the following configuration. That is, when the current of the target motor is detected by the current detection unit, the motor driver controls to output, in the cycle immediately following the cycle in which the current is detected, the power based on the PWM duty ratio obtained based on the current, at the timing when the motor in which the current is detected becomes the target motor again.

[0011] Thereby, it is possible to avoid controlling the target motor based on the detection values corresponding to different motors.

[0012] In the above motor system, it is preferable to adopt the following configuration. That is, when the current of the target motor is detected by the current detection unit, based on the current, the attenuation due to the power cut-off period occurring until the motor becomes the target motor again in the cycle immediately following the cycle in which the current is detected is predicted, and the current after attenuation is calculated. The motor driver controls to output, in the cycle immediately following the cycle in which the current is detected, the power based on the PWM duty ratio obtained based on the current after attenuation, at the timing when the motor in which the current is detected becomes the target motor again.

[0013] Thereby, considering the influence of the actual current value decaying due to the power cut-off to the target motor, the motor can be controlled. As a result, the control quality can be improved.

[0014] In the above motor system, it is preferable to adopt the following configuration. That is, when the current of the target motor is detected by the current detection unit, the motor driver uniformly controls to output, in the cycle immediately following the cycle in which the current is detected, the power based on the PWM duty ratio obtained based on the current, at the timing when the motor in which the current is detected becomes the target motor again.

[0015] Thereby, a simple process can be realized.

[0016] In the above motor system, the following configuration is preferably adopted. That is, the motor driver is controlled according to a predetermined output control cycle. In one cycle, the time from when power supply to one of the target motors starts until it stops includes a first output control cycle and a second output control cycle. In the first output control cycle, in the same cycle as the cycle in which the current of the target motor is detected by the current detection unit, the motor driver outputs power based on the PWM duty ratio obtained based on the current. In the second output control cycle, in the cycle immediately following the cycle in which the current of the target motor is detected by the current detection unit, the motor driver outputs power based on the PWM duty ratio obtained based on the current.

[0017] Thereby, delaying the output timing of the power based on the control so that it becomes the cycle immediately following is performed only in a part of the period during which the motor is the target motor. Therefore, the controllability can be improved.

[0018] In the above motor system, the following configuration is preferably adopted. That is, the motor driver is controlled according to a predetermined output control cycle. The switch unit switches the target motor at a predetermined switching cycle in each cycle. The output control cycle and the switching cycle are synchronized.

[0019] Thereby, it is possible to realize a change in the control content linked to the switching of the switch unit.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0021] Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of the motor system 1 of this embodiment.

[0022] The motor system 1 is a system for controlling a plurality of motors 23. As shown in FIG. 1, the motor system 1 includes a control unit 10, a motor driver 21, a switch unit 22, a plurality of motors 23, and a plurality of encoders 24.

[0023] The control unit 10 controls a plurality of motors 23 via the motor driver 21 and the switch unit 22. The configuration of the control unit 10 will be described later.

[0024] The motor driver 21 supplies power to a plurality of motors 23 to operate the motors 23. The motor driver 21 is, for example, a servo amplifier or an inverter. The motor driver 21 is electrically connected to the control unit 10 and can transmit and receive signals.

[0025] The motor driver 21 is controlled by a driver control signal output by the control unit 10. The motor driver 21 includes an inverter 31. The inverter 31 generates a drive waveform according to the output of the control unit 10. The motor driver 21 outputs a voltage based on the obtained drive waveform to the switch unit 22. The detailed configuration of the current sensor 35 will be described later.

[0026] The motor driver 21 is provided with a current sensor (current detection unit) 35, a current control unit 36, and a delay control unit 37.

[0027] The current sensor 35 detects the magnitude of the current supplied from the motor driver 21 to the motor 23.

[0028] The current control unit 36 controls the inverter 31 to generate a drive waveform for the motor 23 in accordance with a signal input from an output control unit 11 (described later) provided in the control unit 10. Details of the current control unit 36 will be described later.

[0029] The delay control unit 37 appropriately delays the operations of the position control unit 13 or the speed control unit 14 provided in the control unit 10. Details of this delay control will be described later.

[0030] The switch unit 22 selectively supplies the power output from the motor driver 21 to a plurality of motors 23. The switch unit 22 is communicatively connected to the control unit 10 via the motor driver 21 and can transmit and receive signals. In the present embodiment, the motor driver 21 and the switch unit 22 are provided to correspond one-to-one. However, the motor driver 21 and the switch unit 22 may correspond one-to-many or many-to-one instead of one-to-one.

[0031] The motor driver 21 is connected to the input side of the switch unit 22. A plurality of motors 23 are respectively connected to the output side of the switch unit 22. The number of motors 23 is arbitrary as long as it is plural, but in the present embodiment, it is three. Hereinafter, in order to identify each of the three motors 23, they may be referred to as a first motor 23a, a second motor 23b, and a third motor 23c.

[0032] The switch unit 22 is configured as a circuit including a plurality of switches. The switch unit 22 is mounted on a substrate, for example. By switching the switches included in the switch unit 22, the motor 23 that is the power supply destination is switched. Hereinafter, the motor 23 that is the power supply destination may be referred to as a target motor.

[0033] At a certain moment, the target motor, which is the power supply destination, is only one of the plurality of motors 23 connected to the switch unit 22, that is, any one of the first motor 23a, the second motor 23b, and the third motor 23c. The switch unit 22 repeatedly switches the target motor among the three motors 23 at high speed in a cyclic manner. As a result, the three motors 23 can be driven substantially simultaneously.

[0034] The switching operation of the switch unit 22 is performed so as to repeat this cycle with a combination of the period when the first motor 23a is the target motor, the period when the second motor 23b is the target motor, and the period when the third motor 23c is the target motor as one cycle. As a result, the target motor cyclically switches among the first motor 23a, the second motor 23b, and the third motor 23c.

[0035] Each motor 23 includes a stator and a rotor. Preferably, either the stator or the rotor includes a permanent magnet, and the other includes a coil. When power is supplied from the motor driver 21 to the coil, the coil becomes an electromagnet. As a result, a repulsive force or an attractive force acts between the stator and the rotor, and as a result, the rotor moves relative to the stator. The motor 23 of the present embodiment is a linear motor in which the rotor linearly moves (slides) with respect to the stator. As the motor 23, a rotary motor in which the rotor (rotor, rotor) rotates with respect to the stator (stator) can also be used.

[0036] The motor 23 can be configured as, for example, a three-phase motor or a two-phase motor. The inverter 31 included in the motor driver 21 includes a number of semiconductor switch elements corresponding to the number of phases of the motor. When a voltage command value is input from the current control unit 36 to the inverter 31, the inverter 31 repeatedly switches the opening and closing of the switch elements at high speed according to a known PWM control so as to realize a duty ratio corresponding to the voltage command value. As a result, the motor driver 21 can generate a drive waveform for distributing and driving power to the three motors 23 in a time-division manner.

[0037] The encoder 24 detects the operating state of the motor 23, specifically, the relative displacement of the mover with respect to the stator.

[0038] When the motor 23 is a linear motor, the encoder 24 can be, for example, a magnetic sensor provided on the moving path of the mover. The magnetic sensor can detect the position of the mover with respect to the stator. When the motor 23 is a rotary motor, the encoder 24 can be, for example, a known Hall element. The Hall element can detect the rotation angle of the mover.

[0039] The encoder 24 is electrically connected to the switch unit 22 and can output a detection signal to the switch unit 22. The detection result of the encoder 24 is transmitted to the control unit 10 via the motor driver 21.

[0040] The control unit 10 includes an output control unit 11.

[0041] The control unit 10 is configured as a known computer including, for example, a CPU, a ROM, a RAM, an auxiliary storage device, etc. The auxiliary storage device is configured as, for example, an HDD, an SSD, etc. Various programs and the like are stored in the auxiliary storage device. By executing these programs, the control unit 10 can perform various controls regarding the motor system 1. In this way, by the cooperation of hardware and software, the control unit 10 can function as the output control unit 11.

[0042] The control unit 10 may execute processes other than the above-described control. Part or all of the output control unit 11 may be realized by hardware (for example, the motor driver 21) physically different from the control unit 10.

[0043] The output control unit 11 generates a driver control signal and transmits it to the motor driver 21. In the present embodiment, the driver control signal is a current command signal output by the speed control unit 14 described later. The motor driver 21 controls the duty ratio of PWM control based on the current command and outputs it as PWM from the inverter 31.

[0044] The output control unit 11 includes a position control unit 13, a speed control unit 14, and a switching control unit 15.

[0045] The position control unit 13 has a function of controlling the position of the mover for each motor 23. The position control unit 13 compares, for example, the current position of the mover detected by the encoder 24 with the target position of the mover, and outputs a speed command corresponding to the position deviation to the speed control unit 14.

[0046] The speed control unit 14 has a function of controlling the speed of the mover for each motor 23. The speed control unit 14 compares, for example, the current speed based on the change in the position of the mover detected by the encoder 24 with the speed command input from the position control unit 13, and generates a current command corresponding to the speed deviation. The current command is a signal indicating a current value. In the present embodiment, this current command corresponds to the output of the output control unit 11. Although details will be described later, this current command is input to the current control unit 36 provided in the motor driver 21.

[0047] The switching control unit 15 performs control to output the current commands generated by the speed control unit 14 for each of the three motors 23 to the motor driver 21 while cyclically switching them. This switching is performed corresponding to the switch unit 22 cyclically switching the target motor among the three motors 23.

[0048] Here, the operation of the current control unit 36 provided in the motor driver 21 will be described in relation to the output control unit 11. This current control unit 36 determines the voltage command value for PWM control for each motor 23.

[0049] Hereinafter, the first motor 23a will be described in detail. The current control unit 36 compares the current value obtained from the current sensor 35 with respect to the first motor 23a and the current command input from the motor system 1 (in other words, the speed control unit 14 provided in the output control unit 11), and calculates, by computation, the voltage to be applied to the coils of each phase of the first motor 23a according to the deviation of the current value. This calculation is performed, for example, based on known vector control. Thus, in the present embodiment, the current value acquired by the current sensor 35 is used for feedback control.

[0050] The current control unit 36 similarly obtains the voltage to be applied to the coils of each phase included in the second motor 23b and the third motor 23c.

[0051] Based on the voltage obtained by computation, the current control unit 36 generates and outputs a PWM voltage command value. When the plurality of motors 23 are, for example, three-phase motors, the voltage command value is generated corresponding to each of the three phases.

[0052] In the control unit 10, the operation of the output control unit 11 is performed at a fixed cycle, and as a result, the current command changes. Hereinafter, the cycle, which is the minimum time unit for controlling the current command, may be referred to as the output control cycle. The output control cycle coincides with the control cycle in which the voltage command value is controlled in the current control unit 36 of the motor driver 21.

[0053] As described above, the voltage output by the motor driver 21 is selectively supplied to the first motor 23a, the second motor 23b, and the third motor 23c via the switch unit 22 that repeats a cyclic switching operation. Correspondingly, the current command generated by the output control unit 11 is a time-division synthesis of signals instructing current values for each of the first motor 23a, the second motor 23b, and the third motor 23c.

[0054] The inverter included in the motor driver 21 includes a number of semiconductor switch elements corresponding to the number of phases of the motor 23. When a voltage command value is input from the current control unit 36 to the inverter 31, the inverter 31 repeatedly switches the switch elements at high speed according to known PWM control so as to achieve a duty ratio corresponding to the voltage command value. Thereby, the motor driver 21 can generate a drive waveform for driving the three motors 23 by time-divisionally distributing power to them.

[0055] The output control cycle coincides with the carrier cycle of the PWM control performed by the motor driver 21. Thereby, the motor driver 21 can obtain a voltage waveform for satisfactorily realizing the current command output from the control unit 10 by PWM control and supply it to the switch unit 22.

[0056] In one cycle of switching the target motor among the three motors 23, the period during which power is supplied to one motor 23 is equal to the output control cycle or an n-fold thereof (where n is an integer of 2 or more). Thereby, it is possible to realize switching of the drive waveform in conjunction with the switching of the target motor.

[0057] By the above control, each of the three motors 23 can be driven in different directions and speeds.

[0058] In this embodiment, a plurality of motors 23 correspond to one motor driver 21, and the switch unit 22 performs switching so that power is distributed to the plurality of motors 23 in a time-division manner. Thereby, one motor driver 21 can substantially drive a plurality of motors 23 simultaneously. Therefore, the number of motor drivers 21 can be reduced as compared with a configuration in which a motor driver 21 is provided individually for each of the motors 23a, 23b, and 23c. Similarly, the current sensor 35 is also provided in common for the plurality of motors 23 to which power is distributed. Therefore, the number of current sensors 35 can be reduced. As a result, the installation cost of the motor system 1 can be reduced.

[0059] Next, the delay control unit 37 included in the motor driver 21 will be described in detail.

[0060] In the present embodiment, the output control unit 11 included in the control unit 10 controls the motor driver 21 according to a predetermined output control cycle. The control of the motor driver 21 substantially means PWM control of the voltage waveform output by the motor driver 21.

[0061] In order to perform feedback control of the current value via the duty ratio, a series of processes from the first process to the fourth process shown below are necessary. (1) In the first process, the current sensor 35 detects the magnitude (current value) of the current flowing through the target motor. (2) In the second process, when the position control unit 13 and the speed control unit 14 of the output control unit 11 operate, the speed control unit 14 generates a current command, and this current command is output from the control unit 10 to the motor driver 21 as a driver control signal. (3) In the third process, the current control unit 36 of the motor driver 21 calculates a voltage value based on the current command and the detection value of the current sensor 35, and outputs a corresponding voltage command value to the inverter 31. (4) In the fourth process, the inverter 31 performs PWM control on the switching element according to the duty ratio corresponding to the voltage command value.

[0062] Hereinafter, this series of processes may be referred to as control processing. Although the control processing is performed at high speed by the control unit 10 and the motor driver 21, a corresponding amount of time is required. For example, when the output control cycle is shortened to improve the accuracy of motor control, the required time for the control processing may become longer than the output control cycle.

[0063] FIG. 2 shows a case where the time for supplying power to each of the three motors 23 in one cycle corresponds to one cycle of the output control cycle. In other words, by the switching operation of the switch unit 22, the target motor switches to another motor 23 every output control cycle among the three motors 23.

[0064] Hereinafter, the period in which the switch unit 22 performs the switching operation may be referred to as the switching period. The switching period can be determined to be equal for the three motors 23, or can be determined to be different for each motor 23. When the switching period is constant, the product of the switching period and the number of motors 23 corresponds to the period of one cycle.

[0065] In the present embodiment, the switching period is synchronized with the output control period of the output control unit 11. Therefore, it is possible to prevent the motor 23 from operating unintentionally in the vicinity of the timing when the target motor is switched, with a simple configuration.

[0066] In the graph of FIG. 2, the horizontal axis represents time. The intervals between the dashed lines arranged horizontally correspond to the output control period. As described above, the output control period coincides with the carrier period of the PWM control. The rectangles of M1, M2, and M3 drawn at the top of the graph indicate the periods during which the first motor 23a, the second motor 23b, and the third motor 23c are the target motors, respectively. In this example, since the number of motors 23 is three, the period of one cycle corresponds to three cycles of the output control period.

[0067] In the vertical axis of the graph of FIG. 2, the processing contents for driving each of the three motors 23 are displayed as labels. In the labels on the vertical axis, SW is an abbreviation for software, and HW is an abbreviation for hardware. The numbers in parentheses attached to each label correspond to each of the above-described first process to fourth process included in the control process.

[0068] In the graph of FIG. 2, the control process is represented by four rectangles connected by arrows. The arrows connecting the four rectangles indicate that information flows from the upstream process to the downstream process. The hatching attached to the rectangle corresponds to the hatching of the rectangles of M1, M2, and M3 at the top of the graph, and indicates for which of the three motors 23 the control process is.

[0069] The control process is started for each output control cycle. The graph in FIG. 2 shows a case where, in the first process, after the current sensor 35 acquires the current value of a certain motor 23, the time required until, in the fourth process, the motor driver 21 drives the switching element at an appropriate duty ratio for the motor 23 exceeds one cycle of the output control cycle. In the example of FIG. 2, the fourth process is delayed by two cycles of the output control cycle with respect to the first process.

[0070] Focusing on the control process for the first motor 23a shown at the far left in the graph of FIG. 2, an explanation will be given. Based on the current value of the first motor 23a detected in the first process, even if the switching element of the motor driver 21 is turned on / off for the first motor 23a in the fourth process, the switch unit 22 has been switched twice from the start of the first process until immediately before the fourth process. Therefore, at the timing when the fourth process is performed, the third motor 23c different from the first motor 23a has become the target motor.

[0071] In this way, the current for driving the first motor 23a is consequently supplied from the motor driver 21 to the third motor 23c, causing an unintended operation. The same applies to the control regarding the second motor 23b and the third motor 23c.

[0072] In consideration of the above, the motor driver 21 of the present embodiment includes a delay control unit 37. This delay control unit 37 controls, in the process of the control process, for example, to intentionally delay the start of the second process by exactly one cycle of the output control cycle. The delay can be realized, for example, by performing an appropriate standby process before the second process.

[0073] The third process and the fourth process are premised on the completion of the previous process. Therefore, due to the delay of the second process, the start and end of the third process and the fourth process are also inevitably delayed.

[0074] As a result of this delay control, as shown in FIG. 3, the fourth process with respect to the first process will be delayed by three cycles of the output control cycle. Therefore, after the current value of the first motor 23a is acquired in the first process, until the motor driver 21 starts PWM control for the first motor 23a in the fourth process, the switch unit 22 switches three times, and the first motor 23a has become the target motor again.

[0075] In this way, the delay control unit 37 delays the control process so that the timing at which the motor driver 21 performs PWM control for the first motor 23a in the fourth process is included in the period when the first motor 23a is the target motor in the cycle immediately after the cycle to which the first process belongs. Thereby, the PWM control performed by the motor driver 21 for the first motor 23a can be correctly applied to the first motor 23a.

[0076] The time for delaying the control process is not limited to one cycle of the output control cycle. The delay time is appropriately determined according to the original required time of the control process, the length of the switching cycle, the number of motors 23 to which the power of the motor driver 21 is distributed, and the like.

[0077] FIG. 4 shows a case where the time for supplying power to each of the three motors 23 in one cycle corresponds to four cycles of the output control cycle. The switching cycle is four cycles of the output control cycle. Since the number of motors 23 is 3, the cycle of one cycle corresponds to 12 cycles of the output control cycle.

[0078] In the graph of FIG. 4, in order to avoid complication of the drawing, the control processes related to the second motor 23b and the third motor 23c are omitted. The same applies to FIGS. 5 and 6.

[0079] In FIG. 4, for example, during the period when the first motor 23a is the target motor, the control process for driving the first motor 23a is started four times, once per output control cycle. In the example of FIG. 4, for the control process started every output control cycle, delay control for 10 cycles of the output control cycle is uniformly performed. As a result, in the fourth process, the timing at which the motor driver 21 performs PWM control for the first motor 23a can be included in the period when the first motor 23a is the target motor in the cycle immediately after the cycle to which the first process belongs.

[0080] FIG. 5 shows a modified example of the delay control in FIG. 4. Also in the example of FIG. 5, during the period when the first motor 23a is the target motor, the control process for driving the first motor 23a is started four times. The delay control unit 37 performs delay control only for two of the four control processes that are started at a later timing.

[0081] Unlike FIG. 3, in the example of FIG. 5, the switching cycle is long compared to the original required time of the control process. Therefore, in the example of FIG. 5, for the two control processes that are started at an earlier timing among the four control processes, even without performing delay control, the PWM control in the fourth process after the current acquisition in the first process can be performed before the switch unit 22 performs the switching operation. Therefore, the delay control unit 37 does not perform delay control for these two control processes.

[0082] On the other hand, for the two control processes that are started at a later timing, delay control for 8 cycles of the output control cycle is performed. As a result, in the fourth process, the timing at which the motor driver 21 performs PWM control for the first motor 23a can be included in the period when the first motor 23a is the target motor in the cycle immediately after the cycle to which the first process belongs.

[0083] In the example of FIG. 5, for the two control processes that start at a later timing out of the four times, it is also possible to predict the current value after attenuation during the period when the current to the motor 23 is cut off until the next cycle. FIG. 6 is a schematic diagram for explaining this example. When the delay control of FIG. 6 is performed, the output control unit 11 of FIG. 1 includes a current attenuation prediction unit (not shown).

[0084] In the example of FIG. 6, the two control processes that start at a later timing out of the four times are delayed by eight cycles of the output control cycle, similar to FIG. 5. However, the delayed third process (generation of voltage command) is performed based on the predicted current value after attenuation instead of the current value detected by the current sensor 35.

[0085] FIG. 7 shows an example of the current waveform of one of the coils of the first motor 23a along with the period of one cycle. Each cycle period includes a period when the first motor 23a is the target motor and a period when the second motor 23b or the third motor 23c is the target motor. Power is supplied to the first motor 23a only during the period when the first motor 23a is the target motor, and the power supply is cut off during other periods. During the period without power supply, the current decays towards zero. Therefore, the current waveform of the first motor 23a has a shape like a combination of a sine wave and a sawtooth wave as shown in the graph of FIG. 7. In the waveform of FIG. 7, the portion corresponding to the period when power is supplied to the first motor 23a is shown by a solid line, and the portion corresponding to the period when the power supply is cut off is shown by a broken line.

[0086] Similarly, the current sensor 35 can detect the current value of the first motor 23a only during the period when the first motor 23a is the target motor, and cannot detect the current value during other periods.

[0087] When performing delay control, the delay control unit 37 stores the latest current value acquired immediately before the target motor is switched from the first motor 23a to another motor. The symbol P in Fig. 6 indicates the process of acquiring current among the control processes performed at the latest timing for the first motor 23a in a certain cycle. The current value obtained by the process indicated by this symbol P is stored in an appropriate storage device of the motor driver 21. This current value can be substantially regarded as the current value immediately before the power supply to the first motor 23a is cut off. An example of the stored current value is i shown in the graph of Fig. 7. mem is indicated.

[0088] In the next cycle, for the first motor 23a, a process of predicting the current value after attenuation described above is performed based on the previously stored current value i. mem In Fig. 6, this prediction process is indicated by the dashed rectangular areas indicated by symbols Q1 and Q2. An example of the predicted current value is i shown in the graph of Fig. 7. est is indicated.

[0089] The current value i after attenuation est is expressed by the following formula, where the stored current value is i mem , the elapsed time after power cut-off is t, and the time constant is T.

Equation

[0090] The time constant T is determined based on the resistance and inductance of the motor 23 and is stored in the motor driver 21 in advance. When predicting the current value after attenuation at the time of process Q1 in Fig. 6, the elapsed time t after power cut-off is constant throughout all cycles. The same applies when predicting the current value after attenuation at the time of process Q2. Therefore, it is preferable to calculate in advance the value of the exponential function part of the above formula for each of the timings of process Q1 and process Q2 and store it as a constant. Generally, the calculation load of the exponential function is high, but the estimated current value i after attenuation mem can be obtained by simply multiplying the stored current value i est by the constant.

[0091] In the example of FIG. 6, each motor 23 can be controlled based on a current value closer to an actual value than in the example of FIG. 5. The process of predicting the attenuated current value from the current value of the immediately preceding cycle can also be applied to the delay control shown in FIG. 3 or FIG. 4.

[0092] As described above, the motor system 1 of the present embodiment includes a plurality of motors 23, a motor driver 21, a current sensor 35, a switch unit 22, and an output control unit 11. The motor driver 21 outputs electric power for generating a driving force to the plurality of motors 23. The current sensor 35 detects the current of the motor 23. The switch unit 22 selectively switches the target motor, which is the supply target of the electric power output by the motor driver 21 and the detection target of the current by the current sensor 35, among the plurality of motors 23. The PWM duty ratio for driving the target motor is calculated based on the current detected by the current sensor 35, and the motor driver 21 is controlled to output electric power based on this PWM duty ratio. The switch unit 22 cyclically switches the target motor among the plurality of motors 23. When the current of the target motor is detected by the current sensor 35, the motor driver 21 outputs electric power based on the PWM duty ratio obtained based on the current in a cycle after the cycle in which the current is detected, at the timing when the motor 23 in which the current is detected becomes the target motor again.

[0093] Thereby, one motor driver 21 can substantially drive a plurality of motors 23 simultaneously and can individually control the output for each motor 23. While cyclically switching the output of one motor driver 21 among a plurality of motors 23, the control for each motor 23 can be correctly applied to the motor 23. Since the motor driver 21 and the current sensor 35 can be shared by a plurality of motors 23, simplification of the configuration can be achieved.

[0094] Also, in the motor system 1 of the present embodiment, when the current of the target motor is detected by the current sensor 35, the motor driver 21 outputs, in the cycle immediately following the cycle in which the current is detected, the power based on the PWM duty ratio obtained based on the current, at the timing when the motor 23 in which the current is detected becomes the target motor again.

[0095] Thereby, it is possible to avoid controlling the target motor based on the detection values corresponding to different motors.

[0096] Also, in the example of FIG. 6, when the current of the target motor is detected by the current sensor 35, the output control unit 11 predicts the attenuation due to the power interruption period that occurs until the motor 23 becomes the target motor again in the cycle immediately following the cycle in which the current is detected, based on the current, and calculates the current after attenuation. The motor driver 21 is controlled to output, in the cycle immediately following the cycle in which the current is detected, the power based on the PWM duty ratio obtained from the current after attenuation, at the timing when the motor 23 in which the current is detected becomes the target motor again.

[0097] Thereby, the motor 23 can be controlled in consideration of the influence of the actual current value decaying due to the power interruption to the target motor. As a result, the control quality can be improved.

[0098] In the examples of FIGS. 3 and 4, when the current of the target motor is detected by the current sensor 35, the motor driver 21 is uniformly controlled to output, in the cycle immediately following the cycle in which the current is detected, the power based on the PWM duty ratio obtained based on the current, at the timing when the motor 23 in which the current is detected becomes the target motor again.

[0099] Thereby, simple processing can be realized.

[0100] In the example of FIG. 5 or FIG. 6, the motor driver 21 is controlled according to a predetermined output control cycle. The time from when power supply to one target motor starts until it stops in one cycle is equivalent to four cycles of the output control cycle. These four cycles are divided into two cycles that come earlier in time (the first output control cycle) and two cycles that come later in time (the second output control cycle). In each of the first two cycles, the motor driver 21 outputs power based on the PWM duty ratio obtained based on the current in the same cycle in which the current of the target motor is detected by the current sensor 35. In each of the last two cycles, the motor driver 21 outputs power based on the PWM duty ratio obtained based on the current in the cycle immediately following the cycle in which the current of the target motor is detected by the current sensor 35.

[0101] This delays the output timing of the power based on the control to be the cycle immediately following, and this is done only in part of the period during which the motor 23 is the target motor. Therefore, the controllability can be improved.

[0102] In the motor system 1 of this embodiment, the switch unit 22 switches the target motor every predetermined switching cycle in each cycle. The output control cycle and the switching cycle are synchronized.

[0103] This enables the realization of a change in the control content linked to the switching of the switch unit 22.

[0104] Although the preferred embodiments of the present invention have been described above, the above configuration can be changed, for example, as follows. The changes may be made individually or a plurality of changes may be arbitrarily combined.

[0105] When the current of the target motor is detected by the current sensor 35, the delay control unit 37 may control the motor driver 21 so that the power based on the PWM duty ratio obtained based on the current is output by the motor driver 21 two cycles after the cycle in which the current is detected, or in a subsequent cycle.

[0106] The delay is not limited to targeting the second process among the control processes, and for example, the third process or the fourth process may also be targeted. The delay control unit 37 may be provided in the output control unit 11.

[0107] The switching period can be appropriately set to be the length of several cycles of the output control period.

[0108] The motor driver 21 and the switch unit 22 may be physically realized by separate devices or may be realized by one device.

[0109] From the embodiments and their modifications described above, at least the following technical ideas can be grasped.

[0110] [Item 1] A plurality of motors, A motor driver that outputs power for generating a driving force for the plurality of motors, A current detection unit that detects the current of the motor, A switch unit that selectively switches the target motor, which is the supply target of the power output by the motor driver and the detection target of the current by the current detection unit, among the plurality of motors, Comprising, The PWM duty ratio for driving the target motor is calculated based on the current detected by the current detection unit, The motor driver is controlled to output power based on the PWM duty ratio, The switch unit cyclically switches the target motor among the plurality of motors, When the current of the target motor is detected by the current detection unit, the motor driver controls to output, in a cycle after the cycle in which the current is detected, the power based on the PWM duty ratio obtained based on the current, at the timing when the motor in which the current is detected becomes the target motor again. A motor system characterized by this.

[0111] [Item 2] The motor system according to Item 1, When the current of the target motor is detected by the current detection unit, the motor driver controls to output, in the cycle immediately after the cycle in which the current is detected, the power based on the PWM duty ratio obtained based on the current, at the timing when the motor in which the current is detected becomes the target motor again. A motor system characterized by this.

[0112] [Item 3] The motor system according to Item 2, When the current of the target motor is detected by the current detection unit, based on the current, the attenuation due to the power cut-off period occurring until the motor becomes the target motor again in the cycle immediately after the cycle in which the current is detected is predicted, and the current after attenuation is calculated. The motor driver controls to output, in the cycle immediately after the cycle in which the current is detected, the power based on the PWM duty ratio obtained by the current after attenuation, at the timing when the motor in which the current is detected becomes the target motor again. A motor system characterized by this.

[0113] [Item 4] The motor system according to Item 2 or 3, When the current of the target motor is detected by the current detection unit, uniformly, the motor driver controls to output, in the cycle immediately after the cycle in which the current is detected, the power based on the PWM duty ratio obtained based on the current, at the timing when the motor in which the current is detected becomes the target motor again. A motor system characterized by this.

[0114] [Item 5] The motor system according to Item 2 or 3, wherein the motor driver is controlled according to a predetermined output control cycle, in one cycle, the time from when power supply to one of the target motors starts until it stops is in the same cycle as the cycle in which the current of the target motor is detected by the current detection unit, a first output control cycle in which the motor driver outputs power based on the PWM duty ratio obtained based on the current; in the cycle immediately after the cycle in which the current of the target motor is detected by the current detection unit, a second output control cycle in which the motor driver outputs power based on the PWM duty ratio obtained based on the current; A motor system, characterized by including these.

[0115] [Item 6] The motor system according to any one of Items 1 to 5, wherein the motor driver is controlled according to a predetermined output control cycle, the switch unit switches the target motor every predetermined switching cycle in each cycle, A motor system, characterized in that the output control cycle and the switching cycle are synchronized.

Explanation of Signs

[0116] 1 Motor system 21 Motor driver 22 Switch unit 23 Motor 35 Current sensor (current detection unit)

Claims

1. A plurality of motors, A motor driver that outputs electric power for generating a driving force for the plurality of motors, A current detection unit that detects the current of the motor, A switch unit that selectively switches a target motor, which is a supply target of the electric power output by the motor driver and a detection target of the current by the current detection unit, among the plurality of motors, Comprising, The PWM duty ratio for driving the target motor is calculated based on the current detected by the current detection unit, The motor driver is controlled to output electric power based on the PWM duty ratio, The switch unit cyclically switches the target motor among the plurality of motors, The motor driver, when the current of the target motor is detected by the current detection unit, outputs electric power based on the PWM duty ratio obtained based on the current, at a timing when the motor in which the current is detected becomes the target motor again in a cycle after the cycle in which the current is detected. A motor system characterized by being controlled as such.

2. The motor system according to Claim 1, The motor driver, when the current of the target motor is detected by the current detection unit, outputs electric power based on the PWM duty ratio obtained based on the current, at a timing when the motor in which the current is detected becomes the target motor again in the cycle immediately after the cycle in which the current is detected. A motor system characterized by being controlled as such.

3. The motor system according to Claim 2, When the current of the target motor is detected by the current detection unit, based on the current, the attenuation due to the power interruption period occurring until the motor becomes the target motor again in the cycle immediately after the cycle in which the current is detected is predicted, and the current after attenuation is calculated, The motor driver is controlled to output electric power based on the PWM duty ratio obtained by the current after attenuation, at a timing when the motor in which the current is detected becomes the target motor again in the cycle immediately after the cycle in which the current is detected. A motor system characterized by being controlled as such.

4. The motor system according to Claim 2, When the current of the target motor is detected by the current detection unit, the motor driver uniformly outputs, in the cycle immediately after the cycle in which the current is detected, the power based on the PWM duty ratio obtained based on the current, at the timing when the motor in which the current is detected becomes the target motor again. A motor system characterized by being controlled as such.

5. The motor system according to claim 2, wherein the motor driver is controlled according to a predetermined output control cycle, the time from when power supply to one of the target motors starts until it stops in one cycle is a first output control cycle in which the motor driver outputs the power based on the PWM duty ratio obtained based on the current in the same cycle as the cycle in which the current of the target motor is detected by the current detection unit, and a second output control cycle in which the motor driver outputs the power based on the PWM duty ratio obtained based on the current in the cycle immediately after the cycle in which the current of the target motor is detected by the current detection unit, A motor system characterized by including these.

6. The motor system according to claim 1, wherein the motor driver is controlled according to a predetermined output control cycle, the switch unit switches the target motor every predetermined switching cycle in each cycle, A motor system characterized in that the output control cycle and the switching cycle are synchronized.

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