JP2021072691A - Electric actuator and motor driving control method - Google Patents

Abstract

To stably keep an output mechanism at a target position and control it even when a DC motor is used in an electric actuator.SOLUTION: A holding control unit 17B supplies a holding brake current for holding a rotational angle θpt of an output axis 14 from a driving circuit 12 to each of windings U, V, and W of a DC motor 11 when a deviation between the rotational angle θpt of the output axis 14 and a target angle θsp is resolved.SELECTED DRAWING: Figure 1

Description

The present invention relates to an electric actuator, and more particularly to a motor drive control technique for driving a DC motor to displace and hold an output mechanism at a target position.

The electric actuator is a device that mechanically displaces the output mechanism according to the rotation of the motor serving as the driving device, and is used in various fields. For example, Patent Document 1 discloses an electric actuator that operates a valve shaft of a rotary type control valve such as a ball valve. This electric actuator transmits the rotation of the motor to the output mechanism, that is, the output shaft via a gear or other power transmission mechanism, and rotates the valve body of the control valve connected to the output shaft. At this time, the electric actuator detects the mechanical displacement in the rotation direction of the output shaft, that is, the rotation angle by a sensor such as a potentiometer composed of a variable resistor, and determines the operation amount of the output shaft based on the detection result. ing.

Further, Patent Document 2 discloses an electric actuator that operates a valve body of a flow rate control valve that controls the flow rate of cold / hot water flowing through a pipe. In this electric actuator, the flow rate is controlled by detecting the actual valve opening degree of the valve body and rotating and controlling the valve body based on the obtained valve opening degree.

Japanese Unexamined Patent Publication No. 2011-74935 Japanese Unexamined Patent Publication No. 2015-194166

In the electric actuator, two controls are executed as drive control using a motor. One of these two controls is a displacement control for displacementing the output mechanism to a target position. For example, in the case of a flow rate control valve, it is necessary to control the valve body to be displaced from the current opening degree to the target opening degree. The other is holding control for holding the output mechanism at the target position. For example, in the case of a flow control valve, a load torque from the fluid is generated on the valve body, so that control for holding the valve body at the target position is required.

In such displacement control and holding control, feedback control such as PID control (Proportional-Integral-Differential Controller) that controls the drive output based on the deviation between the target value and the measured value is used, and the software configuration is simplified. From such a viewpoint, displacement control and holding control may be realized by the same control rule.
Specifically, the deviation between the actually detected displacement position of the output mechanism and the target position is obtained, and if the deviation is larger than a certain allowable range, the motor is driven to rotate the output mechanism to the target position, and the deviation is allowed. If it is within the range, the drive of the motor is stopped.

However, according to the drive control in the conventional electric actuator, there is a problem that the holding control may become unstable due to the drive control accuracy that can control the displacement of the output mechanism.

Generally, a servo motor or a stepping motor rotates by an angle corresponding to a applied pulse signal. Therefore, when these motors are used in electric actuators, drive control can be performed with extremely high accuracy, and holding control does not become unstable, but the configuration is complicated and therefore expensive.
On the other hand, brushless DC motors are cheaper than servo motors and stepping motors, have high efficiency, and are easy to drive and control, so they are widely used in many devices including electric actuators.

A brushless DC motor is a switching element such as a transistor that rotates a rotor using a permanent magnet by switching and controlling the DC current applied to each coil. Therefore, in order to drive control with high accuracy, it is necessary to accurately detect the rotation angle of the rotor with a magnetic sensor such as a hall sensor and feed it back to the direct current switching control. For example, in a three-phase brushless DC motor, three Hall sensors are arranged at intervals of 120 °, and the rotation angle of the rotor is detected at intervals of control angles of every 60 ° to switch and control the DC current.

In this way, brushless DC motors tend to have low control angle intervals, that is, drive control accuracy, for example, 60 °, and even if the number of phases and slots of the rotor pole stator is increased, the servo motor or It does not reach the drive control accuracy of stepping motors and the like. Therefore, due to the cumulative element of the I (integral) component in the feedback control, a phenomenon occurs in which the output mechanism vibrates in small steps, and as a result, the holding control becomes unstable. Further, such a phenomenon is the same not only in a brushless DC motor but also in a brushed DC motor, and occurs commonly in a so-called DC motor that switches and controls the DC current applied to a plurality of windings. ..

The present invention is for solving such a problem, and an object of the present invention is to provide a motor drive control technique capable of stably holding and controlling an output mechanism at a target position even when a DC motor is used as an electric actuator. There is.

In order to achieve such an object, the electric actuator according to the present invention includes a DC motor having a plurality of windings, a drive circuit that selectively supplies a current to the plurality of windings, and the DC motor. It is provided with an output mechanism that mechanically displaces according to the rotation of the output mechanism, a sensor that detects the mechanical displacement of the output mechanism, and a control circuit that controls the current supplied from the drive circuit to the plurality of windings. The control circuit is supplied from the drive circuit to the plurality of windings so that the deviation between the mechanical displacement of the output mechanism detected by the sensor and the target value of the mechanical displacement is eliminated. The first control unit that controls the drive current that rotates the DC motor, and the mechanical displacement of the output mechanism that is supplied from the drive circuit to the plurality of windings when the deviation is eliminated. It is provided with a second control unit that controls the holding brake current for holding the.

In one configuration example of the electric actuator according to the present invention, when the second control unit eliminates the deviation based on the correspondence between the mechanical displacement of the output mechanism and the load torque generated in the output mechanism. The load torque corresponding to the mechanical displacement in the above is specified, and the magnitude of the holding brake current supplied from the drive circuit is calculated based on the load torque.

An example of the configuration of the electric actuator according to the present invention further includes a storage circuit that stores a correspondence relationship between the mechanical displacement of the output mechanism and the load torque generated in the output mechanism, and the second control unit is the second control unit. The load torque is specified by referring to the correspondence relationship stored in the storage circuit.

An example of the configuration of the electric actuator according to the present invention further includes a storage circuit that stores the correspondence between the mechanical displacement of the output mechanism and the load torque generated in the output mechanism, and a communication circuit that communicates via a network. The second control unit identifies the load torque with reference to the correspondence stored in the storage circuit via the communication circuit.

In one configuration example of the electric actuator according to the present invention, the second control unit is supplied from the drive circuit by giving a predetermined margin to the magnitude of the drive current at the time when the deviation is eliminated. The magnitude of the holding brake current is calculated.

An example of the configuration of the electric actuator according to the present invention further includes a storage circuit for storing the correspondence between the mechanical displacement of the output mechanism and the size of the margin, and the second control unit is provided in the storage circuit. The size of the margin is specified by referring to the stored correspondence.

An example of the configuration of the electric actuator according to the present invention further includes a storage circuit that stores the correspondence between the mechanical displacement of the output mechanism and the size of the margin, and a communication circuit that communicates via a network. The control unit is designed to specify the size of the margin by referring to the correspondence stored in the storage circuit via the communication circuit.

Further, the motor drive control method according to the present invention includes a DC motor having a plurality of windings, a drive circuit that selectively supplies a current to the plurality of windings, and a machine according to the rotation of the DC motor. A motor drive used in an electric actuator including an output mechanism that displaces the output mechanism, a sensor that detects the mechanical displacement of the output mechanism, and a control circuit that controls a current supplied from the drive circuit to the plurality of windings. In a control method, the control circuit has a plurality of windings from the drive circuit so that the deviation between the mechanical displacement of the output mechanism detected by the sensor and the target value of the mechanical displacement is eliminated. A first control step that controls a drive current that is supplied to the DC motor to rotate the DC motor, and the control circuit from the drive circuit to the plurality of windings when the deviation is eliminated. It includes a second control step that controls a holding brake current that is supplied to hold the mechanical displacement of the output mechanism.

According to the present invention, when the deviation is eliminated, the displacement of the output function by the second control unit is stopped, and the holding control for holding the output mechanism by the second control unit at a constant mechanical displacement is performed. Is started. Therefore, in the holding control, the displacement control using the feedback control is stopped, and only the holding brake current is supplied to each winding of the DC motor. Therefore, even when a DC motor is used as the power source, the phenomenon that the output shaft and the output mechanism vibrate in small steps can be avoided, and the output shaft and the output mechanism are mechanically displaced when the deviation is eliminated, that is, the target. It is possible to stably hold and control the position.

FIG. 1 is a block diagram showing a configuration of an electric actuator according to the first embodiment. FIG. 2 is an explanatory diagram showing a configuration of a DC motor and a drive circuit. FIG. 3 is a timing chart showing the relationship between the detection signal of the Hall sensor and the energized phase. FIG. 4 is a graph showing load torque characteristic data. FIG. 5 is a flowchart showing the motor drive control process according to the first embodiment. FIG. 6 is a block diagram showing a configuration of the electric actuator according to the second embodiment. FIG. 7 is a flowchart showing the motor drive control process according to the second embodiment. FIG. 8 is a block diagram showing a configuration of the electric actuator 10 according to the third embodiment. FIG. 9 is a block diagram showing a configuration of the electric actuator 10 according to the fourth embodiment. FIG. 10 is an explanatory diagram showing a load torque calculation process (with a return spring). FIG. 11 is an explanatory diagram showing a load torque calculation process (without a return spring).

Next, an embodiment of the present invention will be described with reference to the drawings.
[First Embodiment]
First, the electric actuator 10 according to the first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a block diagram showing a configuration of an electric actuator according to the first embodiment.

The electric actuator 10 is a device for electrically controlling a valve body such as a flow rate control valve for controlling the flow rate of cold / hot water flowing through a pipe and an air volume adjusting damper for adjusting the air volume in equipment such as an air conditioning system. .. In the present invention, as shown in FIG. 1, a case where the electric actuator 10 is attached to the valve body 20 of the flow rate control valve will be described as an example, but the present invention is not limited to this, and electric control such as an air volume adjusting damper is possible. It can be applied in the same manner when it is attached to another device having a valve body 20.

[Valve body]
The valve body 20 is rotatably attached in the middle of the flow path formed inside the valve body, and a valve shaft 21 having one end led out from the valve body to the outside is attached to one end of the valve body 20. It is combined. One end of the valve shaft 21 is connected to the output shaft 14 via a joint 22, and the valve body 20 is rotated by the rotation operation of the output shaft 14 by the electric actuator 10, and the cross-sectional area of the flow path, that is, the valve opening. The degree changes to control the flow rate of the fluid.

In the present invention, the output shaft 14 mechanically displaced by the electric actuator 10 and the valve body 20 connected to the output shaft 14 are an example of the "output mechanism" described in the claims. Further, the rotation angle θpt of the valve body 20 connected to the output shaft 14 and the output shaft 14 is an example of the “mechanical displacement” of the output mechanism described in the claims, and the output shaft 14 and further. The target angle θsp of the valve body 20 connected to the output shaft 14 corresponds to the “target value” of the mechanical displacement of the output mechanism described in the claims.

The output mechanism described in the claims is not limited to the output shaft 14 and the valve body 20 connected to the output shaft 14 shown below, and is referred to as a DC motor (hereinafter, "DC motor"). The present invention can be applied in the same manner as described later as long as the mechanism is mechanically displaced in response to the rotation of the above. Further, the mechanical displacement of the output mechanism described in the claims is not limited to the rotation of the output shaft 14 and the valve body 20 connected to the output shaft 14 shown below, and the output mechanism is not limited to the rotation of the valve body 20. The present invention can be applied to other mechanical displacements such as rotation, movement, expansion and contraction, and twisting as described below.

[Electric actuator]
Next, with reference to FIG. 1, the configuration of the electric actuator 10 according to the present embodiment will be described in detail.
The electric actuator 10 is provided with a DC motor 11, a drive circuit 12, a power transmission unit 13, an output shaft 14, an angle sensor 15, a storage circuit 16, and a control circuit 17 as main configurations.

[DC motor]
The DC motor 11 is a motor having a plurality of windings and rotating based on a motor current I selectively supplied to these windings. In the present embodiment, a case where a three-phase brushless DC motor is used as the DC motor 11 will be described as an example, but the present invention is not limited to this. For example, a so-called DC motor that switches and controls the motor currents I applied to a plurality of windings, such as a brushed DC motor, may be used as the DC motor 11.

FIG. 2 is an explanatory diagram showing a configuration of a DC motor and a drive circuit. As shown in FIG. 2, the DC motor 11 composed of a three-phase brushless DC motor mainly includes a rotor 11R, three windings U, V, W, and three Hall sensors HU, HV, HW. I have. In FIG. 2, components such as a stator and a bearing are omitted.

The rotor 11R has a permanent magnet 11M polarized in a direction orthogonal to the motor shaft, and is rotatably bearing. The windings U, V, and W are wound around the magnetic poles of the corresponding phases of the magnetic poles of the stator so as to face the magnetic poles of the permanent magnet 11M in the process of rotating the rotor 11R around the axis. These windings U, V, and W are star-connected as a whole, and one end of each is connected to the corresponding terminals Tww, Twv, and Tww, and the other end is commonly connected. The Hall sensors HU, HV, and HW are Hall elements that detect the orientation of the permanent magnet 11M, and are evenly distributed at 120 ° intervals around the motor shaft. The detection signals SU, SV, and SW output from the Hall sensors HU, HV, and HW are input to the control circuit 17 via the terminals Tu, Thv, and Thw.

[Drive circuit]
The drive circuit 12 includes a plurality of switching elements, and selectively supplies a DC motor current I to each winding of the DC motor 11 based on the motor control signal SC output from the control circuit 17. It has a function and a function of outputting a monitor signal SD indicating the values of the motor current I and the drive voltages VU, VV, and VW of the windings U, V, and W to the control circuit 17. The motor current I during displacement control may be referred to as a drive current, and the motor current I during hold control may be referred to as a hold brake current.

As shown in FIG. 2, the drive circuit 12 includes three pairs of switching elements Quu, Qul; Qv, Qvl; Qwoo, Qwl that selectively supply and control the motor current I to the windings U, V, and W. ing. In the following, a case where the switching element is composed of a MOSFET will be described as an example, but other switching elements such as a bipolar transistor may be used.

The three pairs of switching elements Quu, Qul; Qvu, Qvl; Qwoo, Qwl are connected in series with each other. The control circuit 17 appropriately turns on / off these switching elements Quu, Qul; Qv, Qvl; Qu, Qwl based on the motor control signal SC, so that the output voltage output from each pair is set to the power supply potential. Switching control is performed to either Vc, the ground potential GND, or the intermediate potential Vc / 2 between the power supply potential Vc and the ground potential GND. Thereby, among the three windings U, V, and W of the DC motor 11, the energized phase, that is, the winding, and the direction of the motor current I, that is, the direction of the magnetic field generated by the winding can be switched.

FIG. 3 is a timing chart showing the relationship between the detection signal of the Hall sensor and the energized phase. For example, as shown in FIG. 3, when the rotation angle θ of the DC motor 11 is in the range of 0 ° to 60 °, the north pole of the permanent magnet 11M is close to the Hall sensors HU and HV and far from the Hall sensor HW. , The detection signals SU and SV indicate the "H" level, and the detection signal SW indicates the "L" level. According to this, Qwoo and Qvl are selected as the upper energized phase and the lower energized phase, the switching elements Qwoo and Qvl are controlled to be in the on state, and the other switching elements are controlled to be in the off state.

Therefore, for the W phase, since the switching element Qw is on and the switching element Qwl is off, the power supply potential Vc is output as the drive voltage VW. Further, regarding the V phase, since the switching element Qvu is in the off state and the switching element Qvl is in the on state, the drive voltage VV becomes the ground potential GND. Further, in the U phase, since both the switching elements Quu and Qul are in the off state, the drive voltage VU becomes the intermediate potential Vc / 2. As a result, the motor current I flows from the terminal Tww to the terminal Twv via the winding W and the winding V in the DC motor 11. Therefore, the S pole of the permanent magnet 11M is pushed from the winding V in the winding W direction, and as a result, the rotor 11R rotates clockwise.

Further, the current value (magnitude) of the motor current I supplied to the windings U, V, W of the DC motor 11 may be adjusted according to the load torque Tq. Regarding the adjustment of the motor current I, a general PWM (Pulse Width Modulation) control is used to perform high-speed switching of the switching element controlled to be in the ON state as the upper energizing phase and the lower energizing phase shown in FIG. There is a way. If the high-speed switching cycle is sufficiently shorter than the switching cycle of the energized phase, the current value of the motor current I can be adjusted according to the duty ratio of the high-speed switching.

[Power transmission unit]
The power transmission unit 13 includes a power transmission mechanism such as a gearbox in which a plurality of gears having different numbers of teeth are meshed with each other, and reduces the rotation speed of the shaft 11S connected to the rotor 11R of the DC motor 11 to reduce the rotation speed of the output shaft 14. Has a function of rotating.

[Output axis]
The output shaft 14 is a shaft for rotating the valve body 20 from the electric actuator 10, one end of which is connected to the power transmission unit 13 and the other end of which is connected to the valve body 20 via the joint 22 and the valve shaft 21. ing.

[Angle sensor]
The angle sensor 15 is an angle sensor that is attached to the power transmission unit 13 or the output shaft 14 to detect the mechanical displacement of the output shaft 14 along the rotation direction, that is, the rotation angle θpt, and output it to the control circuit 17. is there. The angle sensor 15 may be a relativity sensor such as an incremental encoder, but is an absolute that detects the absolute rotation angle θpt of the output shaft 14 from an arbitrary reference position, such as a potentiometer composed of a variable resistor. It is desirable that it is a sensor.

[Memory circuit]
The storage circuit 16 is composed of a storage device such as a semiconductor memory as a whole, and has a function of storing various processing data and a program 16P used for motor drive control in the control circuit 17.
The program 16P is a program that realizes various processing units that perform motor drive control in cooperation with the CPU by being executed by the CPU of the control circuit 17. The program 16P is stored in advance in the storage circuit 16 from an external device or a recording medium via a communication line.

The load torque characteristic data 16A is the main processing data stored in the storage circuit 16. FIG. 4 is a graph showing load torque characteristic data. As shown in FIG. 4, the load torque characteristic data 16A is data showing the correspondence relationship between the opening degree of the valve body 20 and the load torque Tq generated in the valve body 20, and the horizontal axis is the opening degree [%] of the valve body 20. ], And the vertical axis shows the load torque [Nm] generated in the valve body 20.

In general, the opening degree [%] of the valve body 20 and the rotation angle [°] of the output shaft 14 have a predetermined relationship such as a proportional relationship and can be easily converted, so that the load torque Tq is specified. The rotation angle θpt may be converted into an opening degree at a time point. Further, the horizontal axis of the graph of FIG. 4 may be converted into the rotation angle θpt in advance.
The load torque characteristic data 16A may be stored in a table format or as a function expression. The load torque characteristic data 16A is data indicating the load torque generated in the valve body 20 at each opening degree of the valve body 20, that is, each rotation angle θpt of the output shaft 14, and can be measured in advance. The actual measurement of the load torque will be described later.

[Control circuit]
The control circuit 17 has a CPU and peripheral circuits thereof, and has a function of realizing various processing units that perform motor drive control by reading and executing the program 16P of the storage circuit 16.
The displacement control unit 17A and the holding control unit 17B are the main processing units realized by the control circuit 17.

[Displacement control unit]
The displacement control unit 17A is a drive circuit based on the motor control signal SC so that the deviation between the rotation angle θpt of the output shaft 14 detected by the angle sensor 15 and the target angle θsp with respect to the rotation angle θpt is eliminated. It is configured to control 12. As a result, the drive current supplied from the drive circuit 12 to the windings U, V, W of the DC motor 11 to rotate the DC motor 11 is controlled, and the output shaft 14 is rotated to the target angle θsp by the DC motor 11. To. The displacement control unit 17A corresponds to the "first control unit" described in the claims.

At this time, the displacement control unit 17A uses feedback control such as PID control that controls the drive current based on the deviation between the target value and the measured value, completes the displacement control when the deviation is eliminated, and uses the feedback control. The rotation of the output shaft 14 due to the displacement control that has been performed is stopped. The deviation elimination judgment may be made on the condition that the rotation angle θpt and the target angle θsp are equal, that is, the deviation becomes zero, and the deviation is included in the preset allowable range. May be a condition.

[Holding control unit]
The holding control unit 17B mechanically displaces the output shaft 14, that is, rotates when the deviation between the rotation angle θpt of the output shaft 14 detected by the angle sensor 15 and the target angle θsp with respect to the rotation angle θpt is eliminated. The drive circuit 12 is controlled based on the motor control signal SC so that the moving angle θpt is kept constant. As a result, the holding brake current supplied from the drive circuit 12 to the windings U, V, W of the DC motor 11 for keeping the rotation angle θpt of the output shaft 14 constant when the rotation of the output shaft 14 is stopped is increased. Controlled, the output shaft 14 is held by the DC motor 11 at the rotation angle θpt at the time of eliminating the deviation. Such a holding control unit 17B corresponds to the "second control unit" described in the claims.

At this time, the holding control unit 17B identifies the load torque Tq corresponding to the rotation angle θpt at the time when the deviation is eliminated based on the load torque characteristic data 16A of the storage circuit 16, and drives based on the load torque Tq. The magnitude of the holding brake current supplied from the circuit 12, that is, the current value Ik is calculated.

Generally, when the reduction ratio of the power transmission unit 13 is G, the gear efficiency of the power transmission unit 13 is η, and the torque constant of the DC motor 11 is KT, the output is opposed to the load torque Tq generated in the valve body 20. The current value Ik of the holding brake current required to hold the rotation angle θpt of the shaft 14 is obtained by the following equation (1). The current value Ik of the holding brake current is adjusted by the PWM control as described above.

[Operation of the first embodiment]
Next, the operation of the electric actuator 10 according to the present embodiment will be described with reference to FIG. FIG. 5 is a flowchart showing the motor drive control process according to the first embodiment.

As shown in FIG. 5, when the output shaft 14 is rotated to the designated target angle θsp in the electric actuator 10, the displacement control unit 17A of the control circuit 17 first starts displacement control using feedback control. (Step S100). As a result, the drive current for rotating the output shaft 14 is increased so that the deviation between the rotation angle θpt of the output shaft 14 and the target angle θsp with respect to the rotation angle θpt detected by the angle sensor 15 is eliminated. , Is supplied from the drive circuit 12 to the windings U, V, W of the DC motor 11.

After that, the displacement control unit 17A confirms whether the deviation between the rotation angle θpt of the output shaft 14 and the target angle θsp with respect to the rotation angle θpt has been eliminated (step S101), and performs displacement control until the deviation is eliminated. Continue (step S101: NO).
When the deviation between the rotation angle θpt and the target angle θsp is eliminated and the rotation to the target angle θsp is completed (step S101: YES), the displacement control unit 17A stops the displacement control using the feedback control (step S101: YES). Step S102).

On the other hand, when the deviation is eliminated by the displacement control of the displacement control unit 17A, the holding control unit 17B has a load torque corresponding to the rotation angle θpt at the time when the deviation is eliminated from the load torque characteristic data 16A of the storage circuit 16. Tq is specified (step S103).
Next, the holding control unit 17B sets the windings U, V, W of the DC motor 11 to hold the output shaft 14 at the rotation angle θpt based on the above-mentioned equation (1) from the specified load torque Tq. The current value Ik of the motor current I to be supplied is calculated (step S104).

After that, the holding control unit 17B uses the motor control signal SC to supply the motor current I corresponding to the calculated current value Ik as the holding brake current to the windings U, V, and W of the DC motor 11. (Step S105) to end a series of motor drive control processes. As a result, the supply of the holding brake current is started from the drive circuit 12 to the windings U, V, W of the DC motor 11, and the output shaft 14 and the valve body 20 rotate at a rotation angle θpt against the load torque Tq. Will be held in.

[Effect of the first embodiment]
As described above, in the present embodiment, the holding control unit 17B holds the rotation angle θpt of the output shaft 14 when the deviation between the rotation angle θpt of the output shaft 14 and the target angle θsp is eliminated. The holding brake current is supplied from the drive circuit 12 to the windings U, V, and W of the DC motor 11.

As a result, when the deviation is eliminated, the rotation of the output shaft 14 by the displacement control unit 17A is stopped, and the holding control for holding the output shaft 14 by the holding control unit 17B at the rotation angle θpt is started. To. Therefore, in the holding control, the displacement control using the feedback control is stopped, and only the holding brake current is supplied to the windings U, V, and W of the DC motor 11. Therefore, even when the DC motor 11 is used as the power source, the phenomenon that the output shaft 14 and the valve body 20 vibrate in small steps can be avoided, and the output shaft 14 and the valve body 20 can be rotated when the deviation is eliminated. It is possible to stably hold and control the moving angle θpt, that is, the target angle θsp.

Further, in the present embodiment, the storage circuit 16 stores the load torque characteristic data 16A indicating the correspondence between the rotation angle θpt of the output shaft 14 and the load torque Tq generated on the output shaft 14, and the holding control unit 17B However, the load torque Tq corresponding to the rotation angle θpt at the time when the deviation is eliminated is specified based on the load torque characteristic data 16A, and the load torque Tq is supplied from the drive circuit 12 to the DC motor 11 based on the specified load torque Tq. The current value Ik of the brake current may be calculated. This makes it possible to accurately and easily calculate the current value Ik of the holding brake current.
Further, in the present embodiment, since the brake current is calculated based on the load torque characteristics of the actual valve body, the brake current is an optimum value and can contribute to energy saving.

[Second Embodiment]
Next, the electric actuator 10 according to the second embodiment of the present invention will be described with reference to FIG. FIG. 6 is a block diagram showing a configuration of the electric actuator according to the second embodiment.

In the first embodiment, the current value (magnitude) of the holding brake current is based on the load torque Tq corresponding to the rotation angle θpt at the time when the deviation between the rotation angle θpt of the output shaft 14 and the target angle θsp is eliminated. The case of calculating Ik has been described as an example. In the present embodiment, a case where the current value Ik of the holding brake current is calculated based on the current value Id of the drive current at the time of eliminating the deviation will be described.

That is, in the present embodiment, the holding control unit 17B gives a predetermined margin to the current value Id of the drive current at the time when the deviation between the rotation angle θpt of the output shaft 14 and the target angle θsp is eliminated. , The current value Ik of the holding brake current supplied from the drive circuit 12 is calculated.

Specifically, the storage circuit 16 has a function of storing the margin characteristic data 16B indicating the correspondence between the rotation angle θpt of the output shaft 14 and the size of the margin, instead of the load torque characteristic data 16A. .. The margin characteristic data 16B may be stored in a table format or as a function expression.
The holding control unit 17B has a function of specifying the size of the margin corresponding to the rotation angle θpt at the time when the deviation is eliminated, based on the margin characteristic data 16B of the storage circuit 16.

For the margin according to the present embodiment, a current value indicating an increment of the current value Id of the drive current may be used, but an increment rate of the drive current with respect to the current value Id may be used. Further, the size of the margin may be adjusted by the application of the electric actuator 10. Therefore, depending on the application, zero may be used as the margin. That is, the current value Id of the drive current at the time when the deviation between the rotation angle θpt of the output shaft 14 and the target angle θsp is eliminated may be used as it is as the current value Ik of the holding brake current.
Other configurations of the electric actuator 10 according to the present embodiment are the same as those in FIG. 1, and the description thereof will be omitted here.

[Operation of the second embodiment]
Next, the operation of the electric actuator 10 according to the present embodiment will be described with reference to FIG. 7. FIG. 7 is a flowchart showing the motor drive control process according to the second embodiment.

As shown in FIG. 7, when the output shaft 14 is rotated to the designated target angle θsp in the electric actuator 10, the displacement control unit 17A of the control circuit 17 first starts displacement control using feedback control. (Step S200). As a result, the drive current for rotating the output shaft 14 is increased so that the deviation between the rotation angle θpt of the output shaft 14 and the target angle θsp with respect to the rotation angle θpt detected by the angle sensor 15 is eliminated. , Is supplied from the drive circuit 12 to the windings U, V, W of the DC motor 11.

After that, the displacement control unit 17A confirms whether the deviation between the rotation angle θpt of the output shaft 14 and the target angle θsp with respect to the rotation angle θpt has been eliminated (step S201), and performs displacement control until the deviation is eliminated. Continue (step S201: NO).
When the deviation between the rotation angle θpt and the target angle θsp is eliminated and the rotation to the target angle θsp is completed (step S201: YES), the displacement control unit 17A stops the displacement control using the feedback control (step S201: YES). Step S202).

On the other hand, when the deviation is eliminated by the displacement control of the displacement control unit 17A, the holding control unit 17B acquires the current value Id of the drive current at the time of the deviation elimination from the monitor signal SD of the drive circuit 12 (step S203). From the margin characteristic data 16B of the storage circuit 16, the margin corresponding to the rotation angle θpt at the time when the deviation is eliminated is specified (step S204).
Next, the holding control unit 17B adds the specified margin to the current value Id of the drive current at the time of eliminating the deviation to hold the output shaft 14 at the rotation angle θpt, so that the windings U, V of the DC motor 11 are held. , The current value Ik of the motor current I to be supplied to W is calculated (step S205).

After that, the holding control unit 17B uses the motor control signal SC to supply the motor current I corresponding to the calculated current value Ik as the holding brake current to the windings U, V, and W of the DC motor 11. (Step S206) to end a series of motor drive control processes. As a result, the supply of the holding brake current is started from the drive circuit 12 to the windings U, V, W of the DC motor 11, and the output shaft 14 and the valve body 20 rotate at a rotation angle θpt against the load torque Tq. Will be held in.

[Effect of the second embodiment]
As described above, in the present embodiment, the holding control unit 17B gives a predetermined margin to the current value Id of the drive current at the time when the deviation between the rotation angle θpt of the output shaft 14 and the target angle θsp is eliminated. As a result, the current value Ik of the holding brake current supplied from the drive circuit 12 is calculated.

This makes it possible to calculate the current value Ik of the holding brake current without using the load torque Tq at the time when the deviation between the rotation angle θpt and the target angle θsp is eliminated. Therefore, the configuration and processing load required for the actual measurement and calculation of the load torque Tq can be omitted, the configuration of the electric actuator 10 can be simplified, and the cost can be reduced.

Further, in the present embodiment, the storage circuit 16 stores the margin characteristic data 16B indicating the correspondence between the rotation angle θpt of the output shaft 14 and the size of the margin, and the holding control unit 17B stores the storage circuit 16 Based on the margin characteristic data 16B of the above, the size of the margin corresponding to the mechanical displacement at the time when the deviation is eliminated may be specified.
This makes it possible to specify the margin with an extremely simple configuration and processing load.

[Third Embodiment]
Next, the electric actuator 10 according to the third embodiment of the present invention will be described with reference to FIG. FIG. 8 is a block diagram showing a configuration of the electric actuator 10 according to the third embodiment.
In the present embodiment, a case where the load torque characteristic data 16A according to the first embodiment is stored outside the electric actuator 10 will be described as an example.

That is, as shown in FIG. 8, in the present embodiment, the electric actuator 10 includes a communication circuit 18 that performs data communication with the host device 30 via the communication network (network) NW.
The holding control unit 17B refers to the load torque characteristic data 32A stored in the storage circuit 32 of the host device 30 via the communication circuit 18, and refers to the rotation angle θpt of the output shaft 14 detected by the angle sensor 15 and the target. It is configured to specify the load torque Tq corresponding to the rotation angle θpt at the time when the deviation from the angle θsp is eliminated.
Other configurations of the electric actuator 10 according to the present embodiment are the same as those in FIG. 1, and the description thereof will be omitted here.

[Upper device]
As shown in FIG. 8, the host device 30 is composed of an information processing device such as a server device as a whole, and includes a communication circuit 31, a storage circuit 32, and a processing circuit 33 as main circuit configurations.
The communication circuit 31 has a function of performing data communication with the host device 30 via the communication network NW.
The storage circuit 32 is composed of a storage device such as a semiconductor memory as a whole, and has a function of storing load torque characteristic data 32A used for motor drive control in the electric actuator 10. The load torque characteristic data 32A is equivalent to the load torque characteristic data 16A according to the first embodiment, and the description thereof will be omitted here.

When the processing circuit 33 confirms the reference request from the electric actuator 10 by data communication with the electric actuator 10 via the communication circuit 31 and the communication network NW, the processing circuit 33 performs reference processing regarding the load torque characteristic data 32A of the storage circuit 32. It has a function of providing the electric actuator 10 via the communication circuit 31 and the communication network NW.

[Operation of the third embodiment]
Next, the operation of the electric actuator 10 according to the present embodiment will be described with reference to FIG. 5 described above.

As shown in FIG. 5, when the output shaft 14 is rotated to the designated target angle θsp in the electric actuator 10, the displacement control unit 17A of the control circuit 17 first starts displacement control using feedback control. (Step S100). As a result, the drive current for rotating the output shaft 14 is DC from the drive circuit 12 so that the deviation between the rotation angle θpt of the output shaft 14 and the target angle θsp detected by the angle sensor 15 is eliminated. It is supplied to the windings U, V, W of the motor 11.

After that, the displacement control unit 17A confirms whether the deviation between the rotation angle θpt of the output shaft 14 and the target angle θsp with respect to the rotation angle θpt has been eliminated (step S101), and performs displacement control until the deviation is eliminated. Continue (step S101: NO).
When the deviation between the rotation angle θpt and the target angle θsp is eliminated and the rotation to the target angle θsp is completed (step S101: YES), the displacement control unit 17A stops the displacement control using the feedback control (step S101: YES). Step S102).

On the other hand, when the deviation is eliminated by the displacement control of the displacement control unit 17A, the holding control unit 17B refers to the load torque characteristic data 32A stored in the storage circuit 32 of the host device 30 and the deviation is eliminated. The load torque Tq corresponding to the rotation angle θpt at the time point is specified (step S103).

When referring to the load torque characteristic data 32A, the holding control unit 17B transmits a reference request regarding the load torque characteristic data 32A from the communication circuit 18 via the communication network NW. When the processing circuit 33 of the host device 30 confirms the reference request from the electric actuator 10 by data communication with the electric actuator 10 via the communication circuit 31 and the communication network NW, the load torque characteristic stored in the storage circuit 32. Reference processing for the data 32A is provided to the electric actuator 10 via the communication circuit 31 and the communication network NW.

Next, the holding control unit 17B sets the windings U, V, W of the DC motor 11 to hold the output shaft 14 at the rotation angle θpt based on the above-mentioned equation (1) from the specified load torque Tq. The current value Ik of the motor current I to be supplied is calculated (step S104).

After that, the holding control unit 17B uses the motor control signal SC to supply the motor current I corresponding to the calculated current value Ik as the holding brake current to the windings U, V, and W of the DC motor 11. (Step S105) to end a series of motor drive control processes. As a result, the supply of the holding brake current is started from the drive circuit 12 to the windings U, V, W of the DC motor 11, and the output shaft 14 and the valve body 20 rotate at a rotation angle θpt against the load torque Tq. Will be held in.

[Effect of the third embodiment]
As described above, in this embodiment, the holding control unit 17B is detected by the angle sensor 15 with reference to the load torque characteristic data 32A stored in the storage circuit 32 of the host device 30 via the communication circuit 18. The load torque Tq corresponding to the rotation angle θpt at the time when the deviation between the rotation angle θpt of the output shaft 14 and the target angle θsp is eliminated is specified.

As a result, it is not necessary to store the load torque characteristic data 16A in the storage circuit 16 of the electric actuator 10, so that the storage capacity of the storage circuit 16 can be significantly reduced, and the circuit scale and circuit cost of the electric actuator 10 can be reduced. Is possible.
Further, the plurality of electric actuators 10 may refer to the same load torque characteristic data 32A of the host device 30. As a result, the hardware scale and hardware cost of the entire system including the plurality of electric actuators 10 can be reduced, and the maintenance cost required for updating the load torque characteristic data 32A can be significantly reduced.
Further, in the present embodiment, since the brake current is calculated based on the load torque characteristics of the actual valve body, the brake current is an optimum value and can contribute to energy saving.

[Fourth Embodiment]
Next, the electric actuator 10 according to the fourth embodiment of the present invention will be described with reference to FIG. FIG. 9 is a block diagram showing a configuration of the electric actuator 10 according to the fourth embodiment.
In the present embodiment, a case where the margin characteristic data 16B according to the second embodiment is stored outside the electric actuator 10 will be described as an example.

That is, as shown in FIG. 9, in the present embodiment, the electric actuator 10 includes a communication circuit 18 that performs data communication with the host device 30 via the communication network NW.
The holding control unit 17B refers to the margin characteristic data 32B stored in the storage circuit 32 of the host device 30 via the communication circuit 18, and refers to the rotation angle θpt and the target angle of the output shaft 14 detected by the angle sensor 15. It is configured to specify the size of the margin corresponding to the rotation angle θpt when the deviation from θsp is eliminated.
Other configurations of the electric actuator 10 according to the present embodiment are the same as those in FIG. 6, and the description thereof will be omitted here.

[Upper device]
As shown in FIG. 9, the host device 30 is composed of an information processing device such as a server device as a whole, and includes a communication circuit 31, a storage circuit 32, and a processing circuit 33 as main circuit configurations.
The communication circuit 31 has a function of performing data communication with the host device 30 via the communication network NW.
The storage circuit 32 is composed of a storage device such as a semiconductor memory as a whole, and has a function of storing margin characteristic data 32B used for motor drive control in the electric actuator 10. The margin characteristic data 32B is equivalent to the margin characteristic data 16B according to the second embodiment, and the description thereof will be omitted here.

When the processing circuit 33 confirms the reference request from the electric actuator 10 by data communication with the electric actuator 10 via the communication circuit 31 and the communication network NW, the processing circuit 33 communicates the reference processing regarding the margin characteristic data 32B of the storage circuit 32. It has a function of providing the electric actuator 10 via the circuit 31 and the communication network NW.

[Operation of the fourth embodiment]
Next, the operation of the electric actuator 10 according to the present embodiment will be described with reference to FIG. 6 described above.

As shown in FIG. 6, when the output shaft 14 is rotated to the designated target angle θsp in the electric actuator 10, the displacement control unit 17A of the control circuit 17 first starts displacement control using feedback control. (Step S200). As a result, the drive current for rotating the output shaft 14 is increased so that the deviation between the rotation angle θpt of the output shaft 14 and the target angle θsp with respect to the rotation angle θpt detected by the angle sensor 15 is eliminated. , Is supplied from the drive circuit 12 to the windings U, V, W of the DC motor 11.

After that, the displacement control unit 17A confirms whether the deviation between the rotation angle θpt of the output shaft 14 and the target angle θsp with respect to the rotation angle θpt has been eliminated (step S201), and performs displacement control until the deviation is eliminated. Continue (step S201: NO).
When the deviation between the rotation angle θpt and the target angle θsp is eliminated and the rotation to the target angle θsp is completed (step S201: YES), the displacement control unit 17A stops the displacement control using the feedback control (step S201: YES). Step S202).

On the other hand, when the deviation is eliminated by the displacement control of the displacement control unit 17A, the holding control unit 17B acquires the current value Id of the drive current at the time of the deviation elimination from the monitor signal SD of the drive circuit 12 (step S203). With reference to the margin characteristic data 32B stored in the storage circuit 32 of the host device 30, the margin corresponding to the rotation angle θpt at the time when the deviation is eliminated is specified (step S204).

When referring to the margin characteristic data 32B, the holding control unit 17B transmits a reference request regarding the margin characteristic data 32B from the communication circuit 18 via the communication network NW. When the processing circuit 33 of the host device 30 confirms the reference request from the electric actuator 10 by data communication with the electric actuator 10 via the communication circuit 31 and the communication network NW, the margin characteristic data stored in the storage circuit 32. Reference processing relating to 32B is provided to the electric actuator 10 via the communication circuit 31 and the communication network NW.

Next, the holding control unit 17B adds the specified margin to the current value Id of the drive current at the time of eliminating the deviation to hold the output shaft 14 at the rotation angle θpt, so that the windings U, V of the DC motor 11 are held. , The current value Ik of the motor current I to be supplied to W is calculated (step S205).

After that, the holding control unit 17B uses the motor control signal SC to supply the motor current I corresponding to the calculated current value Ik as the holding brake current to the windings U, V, and W of the DC motor 11. (Step S206) to end a series of motor drive control processes. As a result, the supply of the holding brake current is started from the drive circuit 12 to the windings U, V, W of the DC motor 11, and the output shaft 14 and the valve body 20 rotate at a rotation angle θpt against the load torque Tq. Will be held in.

[Effect of Fourth Embodiment]
As described above, in the present embodiment, the holding control unit 17B refers to the margin characteristic data 32B stored in the storage circuit 32 of the host device 30 via the communication circuit 18, and the output detected by the angle sensor 15. The margin corresponding to the rotation angle θpt at the time when the deviation between the rotation angle θpt of the shaft 14 and the target angle θsp is eliminated is specified.

As a result, it is not necessary to store the margin characteristic data 16B in the storage circuit 16 of the electric actuator 10, so that the storage capacity of the storage circuit 16 can be significantly reduced, and the circuit scale and circuit cost of the electric actuator 10 can be reduced. It will be possible.
Further, the plurality of electric actuators 10 may refer to the same margin characteristic data 32B of the host device 30. As a result, the hardware scale and hardware cost of the entire system including the plurality of electric actuators 10 can be reduced, and the maintenance cost required for updating the margin characteristic data 32B can be significantly reduced.

[Fifth Embodiment]
Next, the electric actuator 10 according to the fifth embodiment of the present invention will be described.
In the first embodiment described above, it is necessary to prepare in advance the correspondence relationship between the opening degree of the valve body 20 and the load torque Tq generated in the valve body 20 as the load torque characteristic data 16A. At this time, since the load torque Tq changes depending on the application of the electric actuator 10, it is desirable to calculate it in advance by actual measurement using the predictive maintenance function of the electric actuator 10. The calculation of the load torque Tq may be executed by the holding control unit 17B of the control circuit 17, or may be executed by providing a new processing unit, for example, a load torque calculation unit, in the control circuit 17. In the present invention, the opening degree of the valve body 20 may be referred to as the rotation angle of the valve body 20 or the output shaft 14, and vice versa.

[If there is a return spring]
First, with reference to FIG. 10, a method of calculating the load torque Tq when the electric actuator 10 has the return spring RS will be described. FIG. 10 is an explanatory diagram showing a load torque calculation process (with a return spring).
As one of the electric actuators 10 for electrically opening and closing the operation ends of valves and dampers, the output shaft 14 is returned to a predetermined rotation angle when the power supply is cut off by the return force of the return spring RS attached to the output shaft 14. There is a so-called spring return type electric actuator.

At the time when the rotating output shaft 14 passes through an arbitrary opening, the torques generated by the DC motor 11, the power transmission unit 13, the return spring RS, and the valve body 20 are in a balanced state with each other. The sum of these torques is zero. As shown in FIG. 10, for example, at the opening degree θax, the motor torque of the DC motor 11 is Tm, the spring torque of the return spring RS is Ts, the power transmission torque of the power transmission unit 13 is Td, and the valve body 20 When the valve body torque is Tv, the balance of these torques at the opening degree θax is expressed by the following equation (2).

When the output shaft 14 is rotating, the power transmission torque Td is generated, but when the output shaft 14 is held at an arbitrary constant opening degree θax, the power transmission torque Td becomes zero.
On the other hand, for the motor torque Tm, where the torque constant of the DC motor 11 is KT and the motor current flowing through the DC motor 11 at the opening θax is I, the motor torque Tm of the DC motor 11 at the opening θax is as follows. Obtained in (3).

On the other hand, when the spring constant of the return spring RS is k, the spring torque Ts at the opening degree θax is expressed by the following equation (4).

Therefore, based on these equations (2), (3) and (4), the load torque Tq applied to the power transmission unit 13 and the valve body 20 is the motor torque Tm as shown in the following equation (5). Is equal to. Therefore, if the motor current I is detected, the load torque Tq can be obtained.

[If there is no return spring]
Next, with reference to FIG. 11, a method of calculating the load torque Tq when the electric actuator 10 does not have the return spring RS will be described. FIG. 11 is an explanatory diagram showing a load torque calculation process (without a return spring).

When the output shaft 14 is rotating, or when the output shaft 14 is held at an arbitrary constant opening degree θax, the torques generated by the DC motor 11, the power transmission unit 13, and the valve body 20 are mutually exclusive. It is in a balanced state, and the sum of these torques is zero. As shown in FIG. 11, for example, when the motor torque of the DC motor 11 at an arbitrary opening degree θax is Tm, the power transmission torque in the power transmission unit 13 is Td, and the valve body torque of the valve body 20 is Tv. The balance of these torques at an arbitrary opening degree θax is expressed by the following equation (6).

When the output shaft 14 is rotating, the power transmission torque Td is generated, but when the output shaft 14 is held at an arbitrary constant opening degree θax, the power transmission torque Td becomes zero.
On the other hand, for the motor torque Tm, assuming that the torque constant of the DC motor 11 is KT and the motor current flowing through the DC motor 11 at the opening θax is I, the motor torque Tm of the DC motor 11 at the opening θax is the above equation. Obtained in (3).

Therefore, based on these equations (3) and (6), the load torque Tq applied to the power transmission unit 13 and the valve body 20 becomes equal to the motor torque Tm as shown in the following equation (7). Therefore, if the motor current I is detected, the load torque Tq can be obtained.

[Effect of the fifth embodiment]
According to the present embodiment, the load applied to the power transmission unit 13 and the valve body 20 is based on the opening degree of the output shaft 14 and the valve body 20 that can be easily detected by the existing configuration of the electric actuator 10, and the motor current I. The torque Tq can be easily calculated. Therefore, it is possible to easily calculate the current value Ik of the holding brake current used for holding control without adding a new configuration.
Further, in the present embodiment, since the brake current is calculated based on the load torque measured in real time, it is possible to deal with aging changes such as clogging of foreign matter and wear of the valve body. Furthermore, since the brake current is calculated based on the load torque of the valve body measured in real time, the brake current is the optimum value and can contribute to energy saving.

[Extension of Embodiment]
Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above embodiments. Various changes that can be understood by those skilled in the art can be made to the structure and details of the present invention within the scope of the present invention. In addition, each embodiment can be implemented in any combination within a consistent range.

10 ... electric actuator, 11 ... DC motor, 11M ... permanent magnet, 11R ... rotor, 11S ... shaft, 12 ... drive circuit, 13 ... power transmission unit, 14 ... output shaft, 15 ... angle sensor, 16 ... storage circuit, 16A ... Load torque characteristic data, 16B ... Margin characteristic data, 16P ... Program, 17 ... Control circuit, 17A ... Displacement control unit, 17B ... Holding control unit, 18 ... Communication circuit, 20 ... Valve body, 21 ... Valve shaft, 22 ... Joint, 30 ... Upper device, 31 ... Communication circuit, 32 ... Storage circuit, 32A ... Load torque characteristic data, 32B ... Margin characteristic data, 33 ... Processing circuit, U, V, W ... Winding, HU, HV, HW ... Hall sensor, Tw, Twv, Tww, Thu, Thv, Thw ... Terminal, Quu, Qul, Qvu, Qvl, Qw, Qwl ... Switching element, RS ... Return spring, θsp ... Target angle, θpt ... Rotation angle, SC ... Drive control signal, SD ... monitor signal, I ... motor current, Id, Ik ... current value, VU, VV, VW ... drive voltage, Vc ... power supply potential, GND ... ground potential, SU, SV, SW ... detection signal, Tq ... load torque, Tm ... motor torque, Td ... power transmission torque, Ts ... spring torque, Tv ... valve body torque, θax ... opening, k ... spring constant, KT ... torque constant, NW ... communication network.

Claims (8)

A DC motor with multiple windings and
A drive circuit that selectively supplies current to the plurality of windings, and
An output mechanism that mechanically displaces according to the rotation of the DC motor,
A sensor that detects the mechanical displacement of the output mechanism and
A control circuit for controlling the current supplied from the drive circuit to the plurality of windings is provided.
The control circuit
The DC motor is supplied from the drive circuit to the plurality of windings to rotate the DC motor so that the deviation between the mechanical displacement of the output mechanism detected by the sensor and the target value of the mechanical displacement is eliminated. The first control unit that controls the drive current to be driven, and
When the deviation is eliminated, a second control unit that is supplied from the drive circuit to the plurality of windings and controls a holding brake current for holding the mechanical displacement of the output mechanism is provided. Electric actuator. In the electric actuator according to claim 1,
The second control unit
Based on the correspondence between the mechanical displacement of the output mechanism and the load torque generated in the output mechanism, the load torque corresponding to the mechanical displacement at the time when the deviation is eliminated is specified, and the load torque corresponds to the load torque. An electric actuator characterized in that the magnitude of the holding brake current supplied from the drive circuit is calculated. In the electric actuator according to claim 2,
A storage circuit for storing the correspondence between the mechanical displacement of the output mechanism and the load torque generated in the output mechanism is further provided.
The second control unit
An electric actuator characterized in that the load torque is specified with reference to the correspondence relationship stored in the storage circuit. In the electric actuator according to claim 2,
A storage circuit that stores the correspondence between the mechanical displacement of the output mechanism and the load torque generated in the output mechanism and a communication circuit that communicates via a network are further provided.
The second control unit
An electric actuator characterized in that the load torque is specified with reference to the correspondence relationship stored in the storage circuit via the communication circuit. In the electric actuator according to claim 1,
The second control unit
An electric actuator characterized in that the magnitude of the holding brake current supplied from the drive circuit is calculated by giving a predetermined margin to the magnitude of the drive current at the time when the deviation is eliminated. In the electric actuator according to claim 5,
A storage circuit for storing the correspondence between the mechanical displacement of the output mechanism and the size of the margin is further provided.
The second control unit
An electric actuator characterized in that the size of the margin is specified with reference to the correspondence relationship stored in the storage circuit. In the electric actuator according to claim 5,
A storage circuit that stores the correspondence between the mechanical displacement of the output mechanism and the size of the margin and a communication circuit that communicates via a network are further provided.
The second control unit
An electric actuator characterized in that the size of the margin is specified with reference to the correspondence relationship stored in the storage circuit via the communication circuit. A DC motor with multiple windings and
A drive circuit that selectively supplies current to the plurality of windings, and
An output mechanism that mechanically displaces according to the rotation of the DC motor,
A sensor that detects the mechanical displacement of the output mechanism and
A motor drive control method used in an electric actuator including a control circuit for controlling currents supplied from the drive circuit to the plurality of windings.
The control circuit is supplied from the drive circuit to the plurality of windings so that the deviation between the mechanical displacement of the output mechanism detected by the sensor and the target value of the mechanical displacement is eliminated. The first control step for controlling the drive current for rotating the DC motor, and
A second control circuit that controls the holding brake current supplied from the drive circuit to the plurality of windings to hold the mechanical displacement of the output mechanism when the deviation is eliminated. A motor drive control method comprising a control step.

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