Stepping-motor control device and control method

A control device is a control device (1) configured to be switched between open control and servo control and control a stepping motor (3), and includes a control unit (11) configured to reduce a switching frequency to the servo control, to be switched to open control after being switched to servo control to stop a mover at a target position and determine a current supplied to the stepping motor (3) in the open control based on a current command value when the mover is stopped at the target position in the servo control when a deviation between a position of the mover and the target position is a predetermined threshold or more when control of stopping the mover of the stepping motor (3) at the target position through the open control is performed.

TECHNICAL FIELD

The present invention relates to a control device and a control method of a stepping motor.

Priority is claimed on Japanese Patent Application No. 2013-119912, filed Jun. 6, 2013, the content of which is incorporated herein by reference.

BACKGROUND ART

As a control method of a stepping motor, open control of performing switching of excitation by a pulse signal and servo control of feeding a position of a rotor of a stepping motor back and performing excitation according to the position are switched (for example, Patent Literature 1).

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

When the switching of the servo control occurs frequently, precision of positioning of the stepping motor by the open control and responsiveness thereof may be deteriorated.

The present invention provides a control device and a control method of a stepping motor that are capable of reducing a switching frequency to servo control.

Solution to Problem

According to a first aspect of the present invention, a control device of a stepping motor includes a control unit configured to be switched to open control after being switched to servo control to stop a mover at a target position and determine a current supplied to the stepping motor in the open control based on a current command value when the mover is stopped at the target position in the servo control when a deviation between a position of the mover and the target position is a predetermined threshold or more when control of stopping the mover of the stepping motor at the target position through the open control is performed.

According to a second aspect of the present invention, in the control device of the stepping motor according to the first aspect, the control unit determines the current supplied to the stepping motor when the control of stopping the mover at the target position through the open control is performed based on the current command value when the mover is stopped at the target position through the servo control.

According to a third aspect of the present invention, in the control device of the stepping motor according to the first aspect or the second aspect, when a maximum value of the current command value upon stoppage of the mover at the target position through the servo control is larger than the current supplied to the stepping motor in the open control, the control unit updates the current supplied to the stepping motor to the maximum value in the open control.

According to a fourth aspect of the present invention, a control method is performed by a control device configured to drive a stepping motor, and the control method includes a control step of switching the control device to open control after switching to servo control to stop a mover at a target position and determining a current supplied to the stepping motor in the open control based on a current command value when the mover is stopped at the target position in the servo control when a deviation between a position of the mover and the target position is a predetermined threshold or more when control of stopping the mover of the stepping motor at the target position through the open control is performed.

Advantageous Effects of Invention

According to the above-mentioned control device and control method of the stepping motor, based on a current command value used when a mover is returned to a target position through servo control when a position at which the mover is stopped deviates from the target position, a current supplied to the stepping motor in the open control is determined. Accordingly, a torque that endures disturbance in which the position of the stopped mover deviates can be generated in the open control, and the switching frequency to the servo control can be reduced.

DESCRIPTION OF EMBODIMENT

Hereinafter, a control device and a control method of a stepping motor according to an embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 1is a block diagram showing a configuration example of a motor control system100including a control device1according to the embodiment. The motor control system100includes the control device1, a power supply unit2, a stepping motor3, an encoder4, a shaft coupling5, a drive shaft6, a base7and a drive table8.

As shown inFIG. 1, the control device1drives the stepping motor3by outputting power supplied from the power supply unit2to the stepping motor3according to a position command input from the outside. The stepping motor3outputs rotational movement by rotating a rotor (a mover) according to the input power. The encoder4configured to detect a position of the rotor and output a signal showing the detected position of the rotor is attached to the stepping motor3.

The shaft coupling5is connected to the rotor of the stepping motor3. The shaft coupling5transmits the rotational movement output by the stepping motor3to a drive shaft (a ball screw)6. The drive shaft6rotates according to the rotational movement output by the stepping motor3, and slides the drive table8provided on the base7.

When the driving of the stepping motor3is started, the control device1performs energization based on the position of the rotor detected by the encoder4. At this time, the control device1drives the stepping motor3such that the drive table8is moved to a target position shown by a position command input from the outside. The control device1performs switching of open control of supplying a pulse signal (power) and driving the stepping motor3, and servo control of supplying power and driving the stepping motor3based on a difference between the position of the rotor of the stepping motor3and the target position.

As shown inFIG. 1, the control device1includes a control unit11, a position detection unit12and a motor drive unit13. A position command and position information are input into the control unit11. The position information is information showing an electrical angle of the rotor calculated by the position detection unit12based on a signal input from the encoder4. The control unit11selects which of the open control or the servo control is used to drive the stepping motor3. When the open control is used, the control unit11generates a control signal for outputting a pulse signal, which drives the rotor from the position of the rotor shown by the position information input from the position detection unit12to the target position, to the motor drive unit13. When the servo control is used, the control unit11generates a control signal including a current command value calculated by PI control or PID control based on the difference between the position of the rotor shown by the position information and the target position. The control unit11outputs the generated control signal to the motor drive unit13. The motor drive unit13converts the power supplied from the power supply unit2to supply the power to the stepping motor3, and rotates the rotor of the stepping motor3based on the control signal output from the control unit11.

FIG. 2is a flowchart showing control processing performed by the control device1according to the embodiment.

When a position command is input to the control device1of the stepping motor3, the control unit11drives the stepping motor3using the servo control (step S101).

The control unit11is switched to the open control to stop the rotor at the target position when the position of the rotor of the stepping motor3reaches the target position (step S102).

The control unit11sets a pulse signal supplied to the stepping motor3to a current value β while the rotor is disposed at the target position (step S103).

Here, in an initial state, the current value β is set to the current value that applies a predetermined torque to maintain stoppage of the rotor.

The control unit11determines whether deviation of a predetermined threshold or more occurs at the target position and the position of the rotor while the rotor is stopped at the target position (step S104). When the deviation of the threshold or more does not occur (step S104: NO), the control unit11continues the control for stopping the rotor by the open control (step S105).

Meanwhile, when deviation of the threshold or more occurs (step S104: YES), the control unit11causes the processing to advance to step S107.

The threshold is applied at, for example, an electrical angle. When an angle of a difference between an electrical angle corresponding to the target position and an electrical angle showing position information input from the position detection unit12is a threshold (n degrees) or more, the control unit11determines that the deviation of the threshold or more occurs. The threshold is determined in advance based on resolution of the encoder4, resolution in driving of the stepping motor3, or the like. For example, a value smaller than the deviation when loss of synchronism in the stepping motor3occurs may be set to the threshold. Accordingly, the stepping motor3can correct the deviation before the loss of synchronism even when the deviation occurs.

The control unit11determines whether a new position command is input (step S106), and when the new position command is input (step S106: YES), causes the processing to return to step S101to repeatedly perform the processing.

Meanwhile, when the new position command is not input (step S106: NO), the control unit11causes the processing to return to step S104to continue the control of stopping the rotor.

When the deviation of the threshold or more occurs (step S104: YES), the control unit11is switched to the servo control (step S107) and performs the control of rotating the rotor to the target position (step S108).

The control unit11determines whether the current command value calculated when the rotor is rotated to the target position is larger than the current value β (step S109), and when the current command value is larger than the current value β (step S109: YES), updates the current value β to a value shown by the current command value (step S110). Meanwhile, when the current command value is the current value β or less (step S109: NO), the control unit11causes the processing to advance to step S111.

Here, determination of whether the rotor returns to the target position in step S111is performed by, for example, determination of whether the difference between the position of the rotor and the target position is the above-mentioned threshold or less. In addition, step S111may be performed, for example, when a predetermined time elapses from the switching to the servo control, when the current command value calculated by the control unit11is less than the predetermined value, or the like.

In addition, the error processing is processing performed when the position of the rotor does not return to the target position after deviation from the target position, for example, when the rotor cannot return to the target position due to an influence of the disturbance or the like, and processing of outputting a notice to a user or an operator of the control device1of occurrence of abnormalities.

As the control device1according to the embodiment performs the above-mentioned control processing (FIG. 2), when the stepping motor3is stopped in the open control, as a control is switched to the servo control to returns the rotor to the target position and stops when the drive table8or the like receives the disturbance and the position of the rotor deviates from the target position, even though the loss of synchronism in the open control occurs and origin return processing or the like is not performed, the control of the stepping motor3can continue.

Here, the control device1updates the current value β to the current command value when the current command value calculated while the rotor returns to the target position and stops from the switching to the servo control is larger than the current value β when the rotor is stopped in the open control. Accordingly, the current value (the current command value) corresponding to the torque required when the rotor returns to the target position and stops can be reflected in the open control even when the influence of the disturbance is received, and the rotor can be continuously stopped at the target position in the case in which the same disturbance occurs again when the rotor stops in the open control. That is, the torque that can endure the disturbance that causes deviation of the position of the stopped rotor can be generated in the open control, and a frequency of switching from the open control to the servo control can be reduced.

In addition, as the control processing is performed by determining the current value β as a small value, for example, determining the minimum current value to stop the rotor as an initial value, the open control of stopping the rotor using a stopping torque required according to a use status of the motor control system100can be performed. Accordingly, even when a value appropriate for the current value β is not determined in advance, the current value β appropriate for the use status of the motor control system100can be set, and thus unnecessary power consumption can be suppressed.

FIGS. 3 and 4are views showing an application example of the motor control system100according to the embodiment. In the application example shown inFIG. 3, inspection of a conveyance article92or the like is performed based on an image obtained by photographing the conveyance article92placed on the drive table8using a fixed camera91. The conveyance article92is, for example, a CD, a DVD, electronic parts, or the like. In the application example shown inFIG. 3, inspection of the CD, DVD, electronic parts, or the like is performed based on an image of a carved seal or a print of a surface obtained by the camera91. For this reason, if the drive table8is moved due to the disturbance or the like when the conveyance article92(the drive table8) is stopped (upon photographing), determination of inferiority is performed. As the above-mentioned control processing is performed, deviation of the conveyance article92from the target position due to the influence of the disturbance can be suppressed, and probability of the determination of inferiority caused by the drive system can be reduced.

In the application example shown inFIG. 4, the base7is fixed such that the drive table8is moved in a vertical direction, a nozzle93attached to the drive table8is moved vertically, and ink or the like injected from the nozzle93is attached to a target94placed immediately under the nozzle93. In the above-mentioned device, the nozzle93may be moved when the control of stopping the nozzle93(the drive table8) is performed due to the weight of the nozzle93. As the above-mentioned control processing is performed, movement of the nozzle93due to the influence of the weight when the nozzle93is stopped can be suppressed, and the ink or the like can be attached to a predetermined position of the target94.

The above-mentioned control device1may have a computer system provided therein. In this case, a process of the above-mentioned control processing is recorded on a computer-readable recording medium in the form of a program and the program is executed by the computer to perform the processing. Here, the computer-readable recording medium may be a magnetic disk, a magneto-optical disc, a CD-ROM, a DVD-ROM, a semiconductor memory, or the like. In addition, the computer program may be distributed to computers by a communication line, and the computers that have received the program may execute the program.

The embodiment is exemplarily provided and is not intended to limit the scope of the present invention. Novel embodiments may be realized in various other types, and various omissions, substitutions and modifications may be made without departing from the scope of the present invention. These embodiments and modifications thereof are included in the following claims and the scope of the present invention and included in the equivalent scope of the present invention disclosed in the claims. For example, instead of the processing (step S101) driven by the servo control after the position command is input, the rotor may be rotated to the target position through the open control. In addition, the switching timing between step S101and step S102may be set to switching to the open control when a distance with respect to the target position is a predetermined distance or less.

In addition, in the embodiment, while the control device1has a configuration of driving the rotary type stepping motor3, a linear type stepping motor (a linear motor) may be driven to move the mover.

In addition, in the above-mentioned control processing, the stepping motor3may be driven at a pulse signal according to the current value β in cases other than the control of stopping the motor in the open control as well.

In addition, in the above-mentioned control processing, the current command value in step S109and step S110may be a maximum value of the current command value from movement of the rotor to the target position in the servo control to stoppage at the target position. Accordingly, the rotor can be stopped upon the open control using the torque corresponding to the maximum torque required when the rotor returns to the target position, and the influence of the disturbance can be suppressed.

INDUSTRIAL APPLICABILITY

The present invention can be applied to a device or a system that requires the control of stopping the rotor or the mover through the open control with respect to the stepping motor.

REFERENCE SIGNS LIST