Patent Publication Number: US-2022221881-A1

Title: Control device

Description:
RELATED APPLICATIONS 
     The content of Japanese Patent Application No. 2021-004383, on the basis of which priority benefits are claimed in an accompanying application data sheet, is in its entirety incorporated herein by reference. 
     BACKGROUND 
     Technical Field 
     Certain embodiments of the present invention relate to a control device. 
     Description of Related Art 
     A spool type flow control valve that controls a flow rate of gas supplied to and discharged from a control target such as an air stage is known. The spool type flow control valve supplies the gas from a supply port to a control port and the control target by operating a spool, and discharges the gas from the control port and the control target to an exhaust port. 
     In the related art, a spool type flow control valve has been proposed in which a spool is supported by a sleeve via a static pressure air bearing in a non-contact manner (refer to the related art). According to the spool type flow control valve, sliding friction is not generated between the sleeve and the spool. Accordingly, the spool can be positioned with high accuracy. Therefore, the flow rate of the gas supplied to the control target can be controlled with high accuracy. 
     SUMMARY 
     According to an embodiment of the present invention, there is provided a control device that controls a controlled variable of a control target to a target value by controlling a flow rate of gas supplied to and discharged from the control target by a spool type flow control valve. The control device includes a controller that generates a spool position command of the spool type flow control valve, based on the target value, and a non-linear compensator that applies a correction for linearly compensating for non-linear flow rate characteristics of the spool type flow control valve to the generated spool position command, and outputs the command to the spool type flow control valve. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view schematically illustrating a spool type flow control valve according to an embodiment. 
         FIGS. 2A and 2B  are views for describing an operation of the spool type flow control valve in  FIG. 1 . 
         FIGS. 3A to 3C  are views for describing flow rate characteristics of the spool type flow control valve. 
         FIGS. 4A and 4B  are sectional views illustrating a valve body and a control port of a spool type flow control valve according to a reference example and a periphery thereof. 
         FIG. 5  is a block diagram illustrating a basic configuration of a control system of a control target. 
         FIG. 6  is a view for describing a function of a non-linear compensator in  FIG. 5 . 
         FIG. 7  is a view for describing a function of a non-linear compensator according to a modification example. 
     
    
    
     DETAILED DESCRIPTION 
     As a result of studying flow rate characteristics of a spool type flow control valve, the present inventor has recognized the following problems. 
     In the spool type flow control valve, due to a relationship of a gap between a valve body of a spool and an opening portion of a control port, non-linearity occurs in the flow rate characteristics, when the spool is located in a vicinity of a neutral position and when the spool is not in the vicinity of the neutral position. Due to the non-linearity, controllability of a control target connected to the control port deteriorates. 
     It is desirable to provide a technique in which a spool type flow control valve can improve controllability of a control target which a gas is supplied to and discharged from. 
     Any desired combinations of the above-described components or those in which the components and expressions according to the embodiments of the present invention are substituted with each other in methods, devices, and systems are also effective as an aspect according to the present invention. 
     According to embodiments of the present invention, it is possible to improve controllability of a control target which a gas is supplied to and discharged from by a spool type flow control valve. 
     The same reference numerals will be assigned to components and members which are the same as or equal to each other in each drawing, and repeated description will appropriately be omitted. In addition, dimensions of the members in each drawing are appropriately enlarged or reduced to facilitate understanding. In addition, in each drawing, some of the members that are not important for describing the embodiments are omitted in the illustration. 
       FIG. 1  is a view schematically illustrating a spool type flow control valve (servo valves)  100 . The spool type flow control valve  100  is a flow control valve that controls a flow rate of gas supplied to a control target. The control target of the spool type flow control valve  100  is not particularly limited. However, for example, the control target is an air actuator. In this case, the spool type flow control valve  100  controls the flow rate of the gas supplied to the air actuator, that is, air. 
     The spool type flow control valve  100  includes a cylindrical sleeve  104 , a spool  106  accommodated in the sleeve  104 , an actuator  108  provided on one end side of the sleeve  104  and driving the spool  106  to move inside the sleeve  104 , a position detection unit  110  provided on the other end side of the sleeve  104  and detecting a position of the spool  106 , and a cover  114  connected to the other end side of the sleeve  104  and accommodating the position detection unit  110 . 
     Hereinafter, a direction parallel to a center axis of the sleeve  104  will be referred to as an axial direction. In addition, a side where the actuator  108  is provided with respect to the sleeve  104  will be referred to as a left side, and a side where the position detection unit  110  is provided with respect to the sleeve  104  will be referred to as a right side. 
     The spool  106  includes a first support portion  118 , a second support portion  122 , a valve body  120 , a first connection shaft  124 , a second connection shaft  126 , and a drive shaft  128 . All of the first support portion  118 , the valve body  120 , and the second support portion  122  have a columnar shape, and are aligned in this order from the left side in an axial direction. The first connection shaft  124  extends in the axial direction, and connects the first support portion  118  and the valve body  120  to each other. The second connection shaft  126  extends in the axial direction, and connects the valve body  120  and the second support portion  122  to each other. The drive shaft  128  protrudes from the first support portion  118  toward the left side in the axial direction. 
     The actuator (linear drive unit)  108  moves the drive shaft  128  and the spool  106  in the axial direction. The actuator  108  is not particularly limited, but is a voice coil motor in the illustrated example. 
     The first support portion  118  and the second support portion  122  of the spool  106  are supported in a state of floating from the sleeve  104  by a static pressure gas bearing, that is, without being in contact with the sleeve  104 . 
     In the present embodiment, an air pad  168  serving as the static pressure gas bearing is provided on an outer peripheral surface of the first support portion  118 . The air pad  168  ejects compressed gas supplied from an air supply system (not illustrated) into a first gap  148  serving as a gap between the first support portion  118  and the sleeve  104 . In this manner, a high-pressure gas layer is formed in the first gap  148 , and the air pad  168  and the first support portion  118  float from the sleeve  104 . Instead of the outer peripheral surface of the first support portion  118 , the air pad  168  may be provided in a portion on an inner peripheral surface  104   a  of the sleeve  104  facing the first support portion  118 . 
     Similarly, an air pad  170  serving as the static pressure gas bearing is provided on an outer peripheral surface of the second support portion  122 . The air pad  170  ejects the compressed gas supplied from the air supply system (not illustrated) into the second gap  150  serving as a gap between the second support portion  122  and the sleeve  104 . In this manner, the high-pressure gas layer is formed in the second gap  150 , and the air pad  170  and the second support portion  122  float from the sleeve  104 . Instead of the outer peripheral surface of the second support portion  122 , the air pad  170  may be provided in a portion on the inner peripheral surface  104   a  of the sleeve  104  facing the second support portion  122 . 
       FIG. 1  illustrates the first gap  148  and the second gap  150  which are exaggerated. In actual, a size of the first gap  148  and the second gap  150  is preferably approximately several microns in order to form the static pressure gas bearing. 
     The position detection unit  110  is not particularly limited. However, in this example, the spool  106  is configured to be detectable in a non-contact manner. For example, a laser sensor is used for the position detection unit  110 . 
     The cover  114  has a bottomed cup shape in which a cylindrical portion  114   a  and a bottom portion  114   b  are integrally formed. The cover  114  is connected to a right end of the sleeve  104  so that the bottom portion  114   b  is located on the right, that is, the opening portion in the right end of the sleeve  104  and the opening portion face each other. 
     The cover  114  may be formed integrally with the sleeve  104 . In other words, instead of a configuration in which the spool type flow control valve  100  does not include the cover  114 , the sleeve  104  may be formed in a bottomed cylindrical shape in which only a left end is open. 
     The actuator  108  includes a yoke  112 , a magnet  162 , a coil bobbin  164 , and a coil  166 . The yoke  112  is made of a magnetic body such as iron. The yoke  112  has a bottomed cup shape in which a cylindrical portion  112   a  and a bottom portion  112   b  are integrally formed. The yoke  112  is connected to the left end of the sleeve  104  so that the bottom portion  112   b  is located on the left, that is, the opening portion in the left end of the sleeve  104  and the opening portion face each other. 
     The yoke  112  further has a columnar protrusion  112   c  that protrudes rightward from the bottom portion  112   b  in the axial direction. The magnet  162  is bonded and fixed to an inner peripheral surface of the cylindrical portion  112   a  to surround the protrusion  112   c . The magnets  162  may be continuous in the circumferential direction, or may be discontinuous in the circumferential direction, that is, may intermittently be provided. 
     The coil bobbin  164  is provided inside the magnet  162 . The coil bobbin  164  surrounds the protrusion  112   c , and one end side is connected to the drive shaft  128 . The coil  166  is wound around an outer periphery of the coil bobbin  164 . The actuator  108  generates a force that moves the coil bobbin  164  around which the coil  166  is wound, and the spool  106  to any place in the axial direction, in response to a current supplied to the coil  166  and a current direction. A positional relationship between the magnet  162  and the coil  166  may be reversed. That is, the magnet  162  may be provided inside the coil  166 , specifically, on the outer peripheral surface of the protrusion  112   c.    
     A portion between the sleeve  104  and the yoke  112  of the actuator  108  and a portion between the sleeve  104  and the cover  114  are respectively sealed by sealing members  146  such as an O-ring and a metal seal. Therefore, the sleeve  104 , the yoke  112 , and the cover  114  are internally sealed except for a plurality of ports (to be described later). 
     The sleeve  104  has a supply port  130 , a control port  132 , and an exhaust port  134 . The supply port  130 , the control port  132 , and the exhaust port  134  are respectively communication holes that communicate with the inside and the outside of the sleeve  104 , and extend in a direction perpendicular to the axial direction. 
     The supply port  130  is connected to a compressed gas supply source (not illustrated) via a tube or a manifold (all are not illustrated). The control port  132  is connected to a control target (not illustrated) via a tube or a manifold (all are not illustrated). When viewed in a radial direction, the control port  132  is formed in a rectangular shape having four sides parallel to the axial direction and the circumferential direction. The exhaust port  134  is open to the atmosphere via a tube or a manifold (all are not illustrated). In  FIG. 1 , the spool  106  is located at a neutral position, and the control port  132  is closed by the valve body  120 . The neutral position refers to a position of the spool  106  where positions in the axial direction of a central portion of the valve body  120  in the axial direction and a central portion of the control port  132  in the axial direction coincide with each other. 
     The above-described configuration is a basic configuration of the spool type flow control valve  100 . Subsequently, an operation thereof will be described.  FIGS. 2A and 2B  are views for describing the operation of the spool type flow control valve  100  in  FIG. 1 . 
       FIG. 2A  illustrates a state where the spool  106  in a state illustrated in  FIG. 1  is driven by the actuator  108  and moves rightward in the axial direction. In this state, the control port  132  closed by the valve body  120  is opened. The supply port  130  and the control port  132  communicate with each other. The compressed gas from the compressed gas supply source is supplied to the control target through the supply port  130 , the inside of the sleeve  104 , and the control port  132 . In this case, a position of the spool  106  is controlled, based on a detection result obtained by the position detection unit  110 , and the opening area of the control port  132  is controlled by the valve body  120 , thereby controlling a flow rate of the compressed gas supplied to the control target. 
       FIG. 2B  illustrates a state where the spool  106  in a state illustrated in  FIG. 1  is driven by the actuator  108  and moves leftward in the axial direction. In this state, the control port  132  closed by the valve body  120  is opened. The control port  132  and the exhaust port  134  communicate with each other. The compressed gas from the control target is exhausted to the atmosphere through the control port  132 , the inside of the sleeve  104 , and the exhaust port  134 . In this case, the position of the spool  106  is controlled, based on a detection result obtained by the position detection unit  110 , and the opening area of the control port  132  is controlled by the valve body  120 , thereby controlling the flow rate of the compressed gas exhausted from the control target. 
       FIGS. 3A to 3C  are views for describing flow rate characteristics of the spool type flow control valve. In  FIGS. 3A to 3C , a positive flow rate indicates a flow rate supplied from the supply port to the control port and the control target, and a negative flow rate indicates a flow rate exhausted from the control port and the control target to the exhaust port. 
       FIG. 3A  illustrates ideal flow rate characteristics.  FIG. 3B  illustrates flow rate characteristics having non-linearity. The non-linearity of the flow rate characteristics leads to a decrease in the controllability of the flow rate.  FIG. 3C  illustrates flow rate characteristics having a dead zone in the vicinity of a neutral position. When a lap amount increases, the flow rate characteristics appear. The lap amount is the length at which the valve body  120  protrudes in the axial direction from the control port  132  when the sleeve  104  is located at the neutral position, in other words, the length at which the valve body  120  and the sleeve  104  are superimposed with (overlap) each other outside the control port  132  in the axial direction. When there is a dead zone, the control target cannot realize high responsiveness. Accordingly, this configuration is not preferable. 
       FIGS. 4A and 4B  are sectional views illustrating a valve body  220  and a control port  232  of a spool type flow control valve  200  according to a reference example and a periphery thereof.  FIG. 4B  is an enlarged view of a portion surrounded by a broken line in  FIG. 4A . 
     Theoretically, in order to realize the ideal flow rate characteristics illustrated in  FIG. 3A , at least the followings are required. 
     (i) Corner portions  232   d  and  232   e  where right and left axial end surfaces  220   a  and  220   b  of the valve body  220  and the outer peripheral surface  220   c  are connected to each other are formed at a so-called pin angle. That is, the corner portion  220   d  is formed at a right angle in a cross section passing through the center axis of the valve body  220 .
 
(ii) Opening portion peripheral edges  232   a  and  232   b  on the inner peripheral surface side of the control port  232  are formed at a so-called pin angle. That is, the opening portion peripheral edge  232   a  is formed at a right angle in a cross section passing through the center axis of the sleeve  204 .
 
(iii) The valve body  220  and the control port  232  are formed so that the right and left axial end surfaces  220   a  and  220   b  of the valve body  220  and right and left peripheral surfaces  232   c  and  232   d  of the control port  232  are flush with each other when the spool  206  is located at the neutral position as illustrated in  FIG. 4A .
 
     However, in reality, due to limitation of a processing technique, not only the corner portions  232   d  and  232   e  of the valve body  220  but also the opening portion peripheral edges  232   a  and  232   b  of the control port  132  cannot be formed exactly at the pin angle, and microscopically, both are formed at a round angle. Therefore, for example, in a case where the valve body  220  and the control port  232  are configured so that the right and left axial end surfaces  220   a  and  220   b  of the valve body  220  and the right and left peripheral surfaces  232   c  and  232   d  of the control port  232  are flush with each other when the spool  206  is located at the neutral position, a gap G 1  between the outer peripheral surface  220   c  of the valve body  220  and the opening portion peripheral edges  232   a  and  232   b  of the control port  132  when the spool  206  is located at the neutral position is wider than a gap G 0  between the outer peripheral surface  220   c  of the valve body  220  and the inner peripheral surface  204   a  of the sleeve  204 . As a result, the flow rate characteristics of the spool type flow control valve according to the reference example become the flow rate characteristics having non-linearity as illustrated in  FIG. 3B . 
     For example, the valve body  220  and the sleeve  204  are overlapped with each other to bring the gap G 1  closer to the gap G 0  to such an extent that the dead zone is not generated. In this manner, the flow rate characteristics can be close to the ideal flow rate characteristics illustrated in  FIG. 3A  to some extent. 
     However, it is actually impossible to realize the ideal flow rate characteristics illustrated in  FIG. 3A . Although there is a difference in some degrees, the flow rate characteristics of the spool type flow control valve have non-linearity. 
     Therefore, the present inventors have recognized that the non-linearity of the flow rate characteristics of the spool type flow control valve  100  are linearly compensated by performing control. Hereinafter, a configuration will be described in detail. 
       FIG. 5  is a block diagram illustrating a basic configuration of a control system  300  of a control target which the gas is supplied to and discharged from by the spool type flow control valve  100 . The control system  300  includes a controller  310 , a non-linear compensator  320 , the spool type flow control valve  100 , and a control target  330 . Here, the control target  330  is an air actuator. In addition, a spool position command (manipulated variable) u for the spool type flow control valve  100  is input, and a stroke position (that is, the controlled variable) x of the air actuator is output. The stroke position x of the air actuator is detected by a position detector (not illustrated). 
     The controller  310  is a feedback controller in this example, and includes a subtractor  312  and a controller  314 . The controller  310  generates the spool position command u for the spool type flow control valve  100  so that a detection value x fb  of the stroke position x is closer to a target position (target value) x ref . For example, the target position x ref  is assigned to the controller  310  by another higher-ranking controller. 
     Specifically, the subtractor  312  generates an error (difference) x e  between the detection value x fb  of the stroke position x of the air actuator and the target position x ref . The controller  314  performs a PI (proportional/integral) control calculation so that the error x e  becomes zero, and generates the spool position command u for the spool type flow control valve  100 . The controller  314  may perform a P (proportional) control calculation, a PID (proportional/integral/differential) control calculation, or other control calculations instead of the PI control calculation. Processing of the controller  314  can also be realized by an analog circuit using an error amplifier. 
       FIG. 6  is a view for describing a function of the non-linear compensator  320 . The non-linear compensator  320  applies a correction for linearly compensating the non-linear flow rate characteristics (solid line graph) of the spool type flow control valve  100  to the spool position command u. Then, the non-linear compensator  320  outputs a spool position command to which the correction is applied (hereinafter, referred to as a correction spool position command u′) to the spool type flow control valve  100 . 
     The “linear compensation” is to linearize the flow rate characteristics, specifically, to linearize a relationship between the spool position command u and a flow rate Q of the spool type flow control valve  100  corresponding to correction spool position command u′ corresponding to the spool position command u. 
     In the present embodiment, the correction for linearly compensating the flow rate characteristics is to multiply an inverse function (broken line graph) of the flow rate characteristics. A relationship between the spool position command u and the flow rate Q corresponding to the correction spool position command u′ obtained by multiplying the spool position command u by the inverse function is a straight line (linearity) of Q=u (y=x). 
     The inverse function of the flow rate characteristics may be derived in advance and stored in a storage device (not illustrated) of the controller  310 . For example, the inverse function may be derived, based on measured flow rates for a large number of spool positions over an entire stroke range of the spool  106 . 
     In the spool type flow control valve  100 , the spool  106  moves in response to the spool position command u′, and the gas is supplied to and discharged from the control target  330 . In this manner, the stroke position x of the air actuator is changed to be closer to the target position x ref . 
     According to the present embodiment described above, the non-linear flow rate characteristics of the spool type flow control valve  100  are linearly compensated. That is, the spool type flow control valve  100  can behave as the spool type flow control valve having the linear flow rate characteristics. Therefore, it is possible to improve the controllability of the control target over the entire area of the spool position command. 
     In addition, according to the present embodiment, the non-linear flow rate characteristics of the spool type flow control valve  100  is linearly compensated by performing control. Therefore, the flow rate characteristics do not need to be closer to the ideal flow rate characteristics by processing the spool type flow control valve  100 , and manufacturing cost of the spool type flow control valve  100  can be reduced. 
     Hitherto, the present invention has been described with reference to the embodiments. The embodiments are merely examples. Those skilled in the art will understand that various modification examples can be made for combinations of the respective components or the respective processes, and that the modification examples also fall within the scope of the present invention. 
     Modification Example 1 
     As the correction for linearly compensating the flow rate characteristics, in the embodiment, the same correction (correction equation) is applied to the spool position command u in the entire stroke range of the spool  106 . However, different corrections may be applied to the spool position command u in the middle range including the neutral position in the stroke range and the spool position command u in two adjacent ranges adjacent to the middle range. 
       FIG. 7  is a view for describing a function of the non-linear compensator  320  according to a modification example. 
     The non-linear compensator  320  approximates the flow rate characteristics in a middle range Rc of the spool type flow control valve  100  by a linear equation. An approximate equation in the middle range Rc is expressed below. 
         Q=a×u (− u   b   ≤u≤u   b )  (1)
 
     Here, the approximate equation is defined as follows.
         a: coefficient   u b , −u b : spool position at a boundary between the middle range Rc and the two adjacent ranges Ra       

     In addition, the non-linear compensator  320  approximates the flow rate characteristics in the two adjacent ranges Ra of the spool type flow control valve  100  by a linear equation. An approximate equation in the two adjacent ranges Ra is expressed below. 
         Q=b×u+c ( u&gt;u   b )  (2)
 
         Q=b×u−c ( u&lt;−u   b )  (3)
         Here, the approximate equation is defined as follows. b, c: coefficient       

     When the flow rate characteristics of the spool type flow control valve  100  are approximated by the equations (1) to (3), the non-linear compensator  320  applies the correction expressed by the following equation to the spool position command u in the middle range Rc. 
         u′=n×u ( n  is an arbitrary positive real number)(− u   b   ≤u≤u   b )  (4)
 
     In addition, the non-linear compensator  320  applies the correction expressed by the following equation to the spool position command u in the two adjacent ranges Ra. 
         u ′=( n×a×u−c )/ b ( u&gt;u   b )  (5)
 
         u ′=( n×a×u+c )/ b ( u&lt;−u   b )  (6)
 
     A relationship between the spool position command u and the flow rate corresponding to the correction spool position command u′ obtained by applying the correction of the equations (4) to (6) to the spool position command u is a straight line of Q=na×u (straight line of one-dot chain line). 
     The illustrated example indicates a case of n=1. In the example of n=1, it can be considered that the correction is not applied to the spool position command u in the middle range. 
     In this modification example, the corrections applied to the spool position command u are switched when the position of the spool  106  is switched from the middle range Rc to the adjacent range Ra and when the position of the spool  106  is switched from the adjacent range Ra to the middle range Rc. Behavior can be unstable when the applied corrections are suddenly switched. Therefore, when the position of the spool  106  is switched between the middle range Rc and the adjacent range Ra, the correction to be applied is gradually changed with the lapse of time. That is, the correction is changed gently or in a stepwise manner. 
     Specifically, for example, when the position moves from the middle range Rc to the adjacent range Ra, a value obtained by multiplying (u−c) and (u+c) in the equations (5) and (6) is gradually changed from n to na/b with the lapse of time. In addition, for example, when the position moves from the adjacent range Ra to the middle range Rc, a value obtained by multiplying u in the equation (4) is gradually changed from na/b to n with the lapse of time. 
     According to this modification example, an advantageous effect the same as that of the embodiment can be achieved. 
     In addition, according to this modification example, when the position is switched between the middle range Rc and the adjacent range Ra, the correction applied to the spool position command u is gradually changed with the lapse of time. Therefore, unstable behavior caused by the suddenly switched correction can be suppressed. In addition, when the position frequently moves between the middle range Rc and the adjacent range Ra, it is possible to prevent the corrections to be applied from being switched in a vibrational manner. 
     Modification Example 2 
     In the embodiment, a case has been described where the controller  310  generates the spool position command u by performing feedback-control. However, the controller  310  may generate the spool position command u by performing feedforward-control in addition to the feedback-control or instead of the feedback-control. 
     Any desired combination of the above-described embodiments and modification examples is also useful as an embodiment of the present invention. Anew embodiment generated by the combination has advantageous effects of the respectively combined embodiment and modification examples. 
     It should be understood that the invention is not limited to the above-described embodiment, but may be modified into various forms on the basis of the spirit of the invention. Additionally, the modifications are included in the scope of the invention.