Electromagnetic actuator using permanent magnets

An actuator mechanism having a different magnet polarity arrangement than the conventional mechanisms is provided. The actuator mechanism 100 has a magnet unit 210 that includes magnets 30 and an electromagnetic coil unit 110 that includes an electromagnetic coil. the relative positions of the magnet unit 210 and the magnetic coil unit 110 can change. The magnet unit 210 includes a yoke member 20 and two or more magnets 30. The two magnets 30 are pulled toward the yoke member 20 in the state where identical poles face each other across the yoke member 20.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the priority based on Japanese Patent Application No. 2005-214838 filed on Jul. 25, 2005, the disclosure of which is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electromagnetic actuator that uses permanent magnets.

2. Description of the Related Art

Electromagnetic actuators that use permanent magnets have been widely employed (see JP2002-90705A, and JP2004-264819A, for example).

With an electromagnetic actuator that uses permanent magnets, electromagnetic force is generated using the N and S poles of the magnets, but the problem arises that, when constructing the electromagnetic actuator, various limitations exist in connection with the placement of the magnetic poles of the magnets (i.e., due to the existence of the N and S poles). However, in the conventional art, it has been acknowledged that there is no room for design modification to alleviate the structural limitations in connection with the placement of the magnetic poles.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an electromagnetic actuator that has a different placement of the magnetic poles than the technology of the prior art.

In an aspect of the present invention, a first actuator that uses electromagnetic drive power is provided. The first actuator comprises an electromagnetic actuator mechanism that has a magnet unit including magnets and an electromagnetic coil unit including an electromagnetic coil, wherein relative positions of the magnet unit and the electromagnetic coil unit are variable. The magnet unit includes: a yoke member including a plate portion; and first and second magnets that are magnetically pulled onto either side of the plate portion with the identical poles of each of the magnets facing each other across the plate portion. Main surfaces of the plate portion of the yoke member are set to have a size which encompasses respective surfaces of the first and second magnets that face the plate portion, thereby causing the first and second magnets being magnetically pulled onto the plate portion.

In this first actuator, because first and second magnets that are pulled onto either side of the plate portion of the yoke member such that identical poles face each other across the plate portion of the yoke member, a construction in which identical magnetic poles face various directions outward from the yoke member can be obtained. As a result, an actuator that efficiently uses the magnet flux generated by these magnets can be constructed. Moreover, because the first and second magnets are pulled onto the same plate portion, identical magnetic pole can face the two opposite directions facing outward from the center of the plate portion. In addition, the pulling force between the magnets and the yoke member can be made larger than the repulsion force between the first and second magnets because the main surfaces of the plate portion of the yoke member are set to have a size which encompasses respective surfaces of the first and second magnets that face the plate portion.

The first and second magnets may have substantially same magnet thicknesses, and a thickness of the plate portion may set to at least 40% of the magnet thickness.

With this construction, the pulling force between the magnets and the yoke member can be made sufficiently large.

The electromagnetic coil unit may includes an electromagnetic coil that revolves around the magnet unit, and the relative positions of the magnet unit and the electromagnetic coil unit may change along a central axis of the electromagnetic coil.

Alternatively, the electromagnetic coil unit may include a first electromagnetic coil that faces the first magnet and a second electromagnetic coil that faces the second magnet, and the relative positions of the magnet unit and the electromagnetic coil unit may change along a line perpendicular to a line that travels through the first electromagnetic coil, magnet unit and second electromagnetic coil.

According to another aspect of the present invention, there is provided a second actuator that uses electromagnetic drive power, comprising: an electromagnetic actuator mechanism that has a magnet unit including magnets and an electromagnetic coil unit including an electromagnetic coil, wherein relative positions of the magnet unit and the electromagnetic coil unit are variable. The magnet unit includes: a yoke member including a plate portion; first and second magnets that are magnetically pulled onto either side of the plate portion with the identical poles of each of the magnets facing each other across the plate portion. The yoke member is constructed so that the plate portion has a protrusion portion protruding from the first and second magnets when viewed along a direction of thickness of the plate portion, thereby causing the first and second magnets being magnetically pulled onto the plate portion.

In this second actuator, because first and second magnets that are pulled onto either side of the plate portion of the yoke member such that identical poles face each other across the plate portion of the yoke member, a construction in which identical magnetic poles face various directions outward from the yoke member can be obtained. As a result, an actuator that efficiently uses the magnet flux generated by these magnets can be constructed. Moreover, because the first and second magnets are pulled onto the same plate portion, identical magnetic pole can face the two opposite directions facing outward from the center of the plate portion. In addition, the pulling force between the magnets and the yoke member can be made larger than the repulsion force between the first and second magnets because the yoke member is constructed so that the plate portion has a protrusion portion protruding from the first and second magnets when viewed along a direction of thickness of the plate portion.

According to still another aspect of the present invention, there is provided a third actuator that uses electromagnetic drive power, comprising: an electromagnetic actuator mechanism that has a magnet unit including magnets and an electromagnetic coil unit including an electromagnetic coil, wherein relative positions of the magnet unit and the electromagnetic coil unit are variable. The magnet unit includes: a yoke member; and first and second magnets that are magnetically pulled onto either side of the yoke member with the identical poles of each of the magnets facing each other across the yoke member. The electromagnetic coil unit includes an electromagnetic coil that revolves around the magnet unit, and the relative positions of the magnet unit and the electromagnetic coil unit change along a central axis of the electromagnetic coil.

In this third actuator, because first and second magnets that are pulled onto either side of the yoke member such that identical poles face each other across the yoke member, a construction in which identical magnetic poles face various directions outward from the yoke member can be obtained. As a result, an actuator that efficiently uses the magnet flux generated by these magnets can be constructed.

PREFERRED FEATURES OF THE INVENTION

The actuator may further include a control device that controls the electromagnetic actuator mechanism, wherein the control device includes a reference current value determination unit that determines a reference current value in accordance with a deviation of a controlled variable related to the position of the electromagnetic actuator mechanism as well as a drive unit that drives the electromagnetic coil based on the reference current value, and the reference current value determination unit determines the reference current value to be a positive value, zero or a negative value where the deviation is a negative value, zero or a positive value, respectively.

According to this actuator, because the reference current value is determined to be a positive value, zero or a negative value where the deviation of the controlled variable is a negative value, zero or a positive value, respectively, and the electromagnetic coil is driven based on this reference current value, good control characteristics can be obtained even where the controlled variable has a non-linear relationship to the manipulated variable (i.e., the coil current).

It is acceptable if the reference current value determination unit determines the reference current value to be a positive value, zero or a negative value that is preset in response to whether the deviation is a negative value, zero or a positive value, and the drive unit drives the electromagnetic coil using the reference current value.

According to this construction, because the electromagnetic coil is driven using any of the three current values, simple control may be realized.

The control device may further include a counter that counts the number of continuous occurrences of a deviation having the same positive or negative sign when a deviation having the same sign is continuously generated in prescribed cycles; a first correction coefficient generator that generates a first correction coefficient that decreases as the number of continuous occurrences of a deviation having the same sign increases; and an accumulator that multiplies the reference current by the first correction coefficient and accumulates the results, wherein the drive unit drives the electromagnetic coil based on a current value corresponding to the accumulated result obtained by the accumulator.

According to this construction, the current value can be gradually increased after the sign of the deviation changes, and therefore excessive positional change can be prevented when the deviation is near zero.

The control device may further include a second correction coefficient generator that generates a second correction coefficient that increases as the number of continuous occurrences of a deviation having the same sign increases; and a multiplier that multiplies the accumulated result of the accumulator by the second correction coefficient, wherein the drive unit drives the electromagnetic coil based on a current value corresponding to the result obtained by the multiplier.

According to this construction, the rate of increase of the current value after the sign of the deviation changes can be further reduced, and therefore excessive positional change when the deviation is near zero can be prevented with increased efficiency.

The present invention can be implemented in various forms, and can be realized as an actuator, a control device for an actuator or a actuator control method, for example.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Embodiments of the present invention will be described below in the following sequence.A. Various embodiments of electromagnetic actuator mechanismsB. Various embodiments of control devicesC. Application examples of actuatorD. Variations

A. Various Embodiments of Electromagnetic Actuator Mechanisms

FIG. 1Ais a plan view of a magnet unit210used by an electromagnetic actuator mechanism according to an embodiment of the present invention, andFIG. 1Bis a front view thereof. This magnet unit210comprises a yoke member20having a flat plate configuration and two flat plate-shaped permanent magnets30having an identical configuration. The two permanent magnets30are pulled toward the yoke member20in the state where identical poles are made to face each other. In this example, the S poles of the two permanent magnets30are in contact with the main surfaces of the yoke member20. Incidentally, the ‘main surfaces’ of a flat plate-shaped member refers to the widest surfaces of the six surfaces of such member. In the discussion below, the ‘main surfaces’ may be referred to simply as ‘surfaces’, and the other surfaces may be referred to as the ‘side surfaces’. Furthermore, where the configuration of the yoke member is not that of a simple flat plate, but includes flat plate sections and a non-flat plate section (such as a protrusion), the surfaces comprising the flat plate sections are termed the ‘main surfaces’.

In this Specification, the magnet unit is also termed a ‘magnet structure’, and the electromagnetic coil unit (described below) of the electromagnetic actuator mechanism is also termed an ‘electromagnetic coil structure’ or ‘coil structure’.

As shown inFIG. 1A, the area of each main surface of the plate-shaped yoke member20is set to a size larger than that of each magnet30. In other words, the main surfaces of the yoke member20are set to a size that completely encompasses the adjacent surfaces of the magnets30.

FIGS. 2A and 2Bare explanatory drawings showing the magnet units of an embodiment and a comparison example. In the magnet unit of the comparison example shown inFIG. 2A, the main surfaces of the yoke member20and the magnets30have the same size. In this case, because the lines of electromagnetic force emitted from the two magnets30are oriented in mutually opposing directions as indicated by the arrows, a strong repulsion force operates between the two magnets30. As a result, it is difficult to hold the two magnets30in place with the yoke member20.

On the other hand, in the magnet unit of the embodiment shown inFIG. 2B, because the main surfaces of the yoke member20are larger than the main surfaces of the magnets30, the lines of electromagnetic force from the two magnets30are guided by the yoke member20to form an electromagnetic closed circuit (N pole→yoke member→S pole). Consequently, repulsion force does not operate between the two magnets30, and each magnet30is maintained in a state in which it is pulled toward the yoke member20. Therefore, in the magnet unit of this embodiment, a construction will be stably maintained in which common poles of the two magnets30(in this example, the N poles) are oriented in opposing directions (the vertical directions in the drawing) while the magnets30are disposed across the yoke member20.

In order to respectively pull the two magnets30to the yoke member20in a stable fashion, it is preferred that the main surfaces of the yoke member20be larger than the main surfaces of the magnets30over their entire circumference, as shown inFIG. 1A(i.e., it is preferred that the yoke member20protrude beyond the outer edges of the magnets30). However, it is acceptable if the main surfaces of the magnets30extend as far as the edges of the main surfaces of the yoke member20over a part of the total circumference thereof. It is furthermore preferred that the thickness t20of the yoke member20(seeFIG. 1B) be set to at least 40% of the thickness t30of each magnet30. The reason for this is that if the yoke member20is too thin, there is increased leakage of electromagnetic force and a strong repulsion force may occur between the two magnets30. From the standpoint of minimizing the actuator size, it is preferable that the thickness t20of the yoke member20is not more than the thickness t30of the magnet30. It is preferred that the yoke member20comprise a number of stacked thin plates, but it may comprise a single plate. Furthermore, while the yoke member20may comprise any highly magnetic material, it is preferred that it be made of SPCC steel.

FIGS. 3A-3Fare explanatory drawings showing in detail an example of the construction of the magnet unit of an embodiment.FIGS. 3A and 3Bare a plan view and a front view of a magnet30. Two notches34are formed in one of the main surfaces of the magnet30close to opposing corners of the rectangular shape.FIGS. 3C and 3Dare a plan view and a front view of the yoke member20. Protrusions21,22that come into contact with the outer edge surfaces of a magnet30, locking protrusions24that engage with the notches34in the magnet30, and two screw holes26are formed in the main surface of the top side of the yoke member20. The bottom side of the yoke member20has the same construction.FIGS. 3E and 3Fare a plan view and a front view of the magnet unit where the two magnets30are assembled onto the yoke member20. During assembly, first, one of the two notches34of each magnet30is fitted under one of the locking protrusions24formed on the yoke member20, a clamp member27is fitted into the other notch34, and the clamp member27is secured to the screw hole26using a screw28. As a result, the magnet30is secured to the yoke member20by the locking protrusion24and the clamp member27. However, as explained with reference toFIGS. 1A-1Band2A-2B, because the magnets30are pulled onto the yoke member20by electromagnetic pulling force, the magnets30can also be secured to the yoke member20via simpler securing means. For example, they may both be secured by adhesive. In addition, another member may be inserted between each magnet30and the yoke member20, but from the standpoint of increasing the pulling force between the magnets and the yoke member, it is preferred that no other member be inserted between each magnet and the yoke member.

FIG. 4Ais a side view of the construction of an actuator mechanism of a first embodiment. This actuator mechanism100has an electromagnetic coil unit110and a magnet unit210. The coil of the electromagnetic coil unit110revolves around the magnet unit210. Furthermore, the electromagnetic coil unit110is secured to a support member not shown, and a position sensor120that detects the position of the magnet unit210is disposed on this support member. An electromagnetic sensor such as Hall element can be used as this position sensor. Alternatively, an optical encoder or other type of position sensor may be used.

With this construction, because the coil of the electromagnetic coil unit110revolves around the magnet unit210, when electric current is impressed to the electromagnetic coil unit110, the electrical current in the top portion of the coil, shown inFIG. 4A, flows in a direction opposite to that of the current flowing in the bottom portion. At the same time, electromagnetic fields are generated upward and downward from the magnet unit210. Therefore, when current is impressed to the coil, drive power oriented in the same direction (i.e., leftward or rightward) can be generated in both the top and bottom portions of the coil. For example, when the magnet unit210is to be moved rightward from the leftmost position (FIG. 4A), current flowing in a prescribed direction is impressed to the electromagnetic coil unit110. When the magnet unit210is to be moved in the leftward direction, a current is impressed in the opposite direction from this prescribed direction.

As described above, using the actuator mechanism100shown inFIGS. 4A-4C, because drive force in the same direction is generated in both the top portion and the bottom portion of the electromagnetic coil that revolves around the magnet unit210, the wasteful operation of force in directions other than the direction of driving can be prevented. As a result, the actuator mechanism100offers the advantage of causing virtually no vibration or noise due to the wasteful generation of electromagnetic force running in directions other than the direction of driving.

FIGS. 5A-5Dshow various yoke constructions for a magnet unit. The magnet unit201ofFIG. 5Ahas a construction in which second yoke members40are added above and below the magnet unit210shown inFIG. 1B. The electromagnetic coil unit is disposed in the spaces between the magnets30and the second yoke members40. According to this construction, the leakage of electromagnetic force from the coil can be prevented. The magnet unit202ofFIG. 5Bhas a construction in which a third yoke member42is added to one of the lateral sides of the magnet unit201shown inFIG. 5A. The magnet unit203ofFIG. 5Chas a construction in which third yoke members42are respectively added to both lateral sides of the magnet unit201shown inFIG. 5A. In the constructions ofFIGS. 5B and 5C, because a closed magnetic circuit will be formed, efficiency will be improved. The magnet unit204ofFIG. 5Dhas a construction in which magnets32are respectively added to the inside of the top and bottom second yoke members40of the magnet unit203shown inFIG. 5C. According to this construction, the magnetic flux of the electromagnetic coil is used more effectively, resulting in the generation of a larger amount of torque.

FIGS. 6A-6Fshow other constructions of a magnet unit.FIGS. 6A,6B are a front view and a side view of an assembly comprising only a yoke member20eand magnets30e.FIG. 6Cis a perspective view of the yoke20eand a magnet30e. The magnet unit210ehas a long yoke member20ehaving a roughly cross-shaped cross-sectional configuration and four long magnets30ethat are wedged into the four triangular spaces formed by the cross-shaped yoke member20e. As shown inFIG. 6B, the cross-section of each magnet30eis a quarter-circle (i.e., a fan shape with a central angle of 90°), and each magnet30eis magnetized such that the area at the central angle comprises one pole (the S pole), and the outer arc area comprises the other pole (the N pole). As shown inFIG. 6B, it is preferred that, of the surfaces of the yoke member20eand the magnets30ethat are in contact with each other (referred to as contact surfaces), the contact surfaces of the yoke member20ebe larger than the contact surfaces of the magnets30e.FIGS. 6D and 6Ecomprise a side view and a front view of a cap50. Both ends of the assembled yoke member20eand four magnets30eare covered respectively using caps50, as shown inFIG. 6F. A roughly cross-shaped groove50ais formed on the inside of each cap50, and this groove50ahouses an end of the cross-shaped yoke member20e. The caps50are secured to the yoke member20eby screws52. This magnet unit210ehas a construction wherein the cross-sectional configuration is roughly circular and the entire circumference is magnetized to one pole (here, the N pole). Therefore, by placing a cylindrical electromagnetic coil around the magnet unit210e, drive power will be generated from nearly all portions of the electromagnetic coil.

FIGS. 7A-7Dshow other constructions of a magnet unit. The magnet unit210fshown inFIGS. 7A and 7Bhave a long and hollow yoke member20fhaving a roughly square cross-sectional configuration, and four long magnets30fdisposed on the outer surfaces of the yoke member20f. Each magnet30fhas a plate-shaped configuration and is magnetized such that the inner surface comprises the S pole and the outer surface comprises the N pole. Protrusions that operate to partition the spaces in which the magnets30fare housed are disposed at the four corners of the yoke member20f. This magnet unit210fhas a roughly rectangular cross-sectional configuration, and the entire outer circumference thereof is magnetized to one pole (in this example, the N pole). Therefore, by placing a roughly rectangular pillar-shaped electromagnetic coil around the magnet unit210e, drive power will be generated from nearly all portions of the electromagnetic coil.

The magnet unit210gshown inFIGS. 7C and 7Dhas a long yoke member20ghaving a roughly triangular cross-sectional configuration and three long magnets30gdisposed on the outer surfaces of the yoke member20g. Each magnet30ghas a plate-shaped configuration and is magnetized such that the inner surface forms the S pole and the outer surface forms the N pole. Protrusions that operate to partition the spaces in which the magnets30gare housed are disposed at the three corners of the yoke member20g. This magnet unit210ghas a roughly triangular cross-sectional configuration, and the entire outer circumference thereof is magnetized to one pole (in this example, the N pole). Therefore, placing a triangular pillar-shaped electromagnetic coil around the magnet unit210g, drive power will be generated from nearly all portions of the electromagnetic coil.

As can be seen from the various examples provided above, the magnet unit may have various types of cross-sectional configurations including geometric shapes such as a polygon or circle. Furthermore, it is preferred that the configuration of the electromagnetic coil match or resemble the cross-sectional configuration of the magnet unit. If such a matching magnet unit and an electromagnetic coil are used, an efficient linear actuator may be obtained. Furthermore, because this type of linear actuator does not generate unnecessary force that operates in directions perpendicular to the direction of driving, an actuator having minimal vibration and noise may be formed.

FIGS. 8A and 8Bare explanatory drawings showing the construction of an actuator mechanism of a second embodiment. The magnet unit210aof this actuator mechanism100has two pairs of magnets30adisposed on both the top and bottom surfaces of the yoke member20a. While two protrusions21aare disposed in the center of the yoke member20ain order to partition off the spaces in which the two magnets30aare housed, these protrusions21amay be omitted. As shown inFIG. 8B, the magnet unit210ahas a roughly rectangular cross-sectional configuration, and the coil of the electromagnetic coil unit110arevolves around the magnet unit210a. The position sensor is not shown for convenience of illustration. This actuator mechanism100acan also generate drive power using the method employed by the mechanism shown inFIGS. 4A-4C. In addition, a construction may be adopted in which the yoke member is extended in the longitudinal direction and a larger number of magnets are used.

FIGS. 9A and 9Bare explanatory drawings showing the construction of an actuator mechanism of a third embodiment. The magnet unit210bof this actuator mechanism100bcomprises three concentric hollow tube-shaped magnets30bthat are separated from each other by yoke members20bdisposed in the spaces therebetween. As shown inFIG. 9B, the magnet unit210bhas a roughly hollow cylindrical cross-sectional configuration, and the coil of the electromagnetic coil unit110brevolves around the magnet unit210b. The position sensor is omitted from the drawing for convenience of illustration. This actuator mechanism100bcan also generate drive power using the method employed by the mechanism shown inFIGS. 8A-8B. In addition, a construction may be adopted in which the yoke member is extended in the longitudinal direction and a larger number of magnets are used.

FIGS. 10A-10Care explanatory drawings showing the construction of an actuator mechanism of a fourth embodiment. The magnet unit210cof this actuator mechanism100ccomprises four magnets30cdisposed on the top and bottom surfaces of the yoke member20csuch that each surface has two magnets. The two magnets30cdisposed on the top surface of the yoke member20care magnetized in opposite directions, as are the two magnets30cdisposed on the bottom surface of the yoke member20c. However, the magnets30cthat face each other across the yoke member20care disposed so that identical poles are oriented toward the yoke member20c. The coils of electromagnetic coil unit110care respectively disposed above and below the magnet unit210c. A position sensor120is disposed on the upper coil. The magnet unit210ccan be driven to move within the range shown inFIGS. 10A-10Cthrough the impression of current to the electromagnetic coil unit110b. During such movement, opposite currents flow in the upper coil and the lower coil.

FIGS. 11A-11Care explanatory drawings showing the construction of an actuator mechanism of a fifth embodiment. The magnet unit210dof this actuator mechanism100dalso comprises four magnets30cdisposed on the top and bottom surfaces of the yoke member20csuch that each surface has two magnets. However, unlike the mechanism shown inFIGS. 10A-10C, the poles of each magnet30dare oriented along the directions of movement (the directions indicated by the arrows). In this embodiment as well, the identical poles of the magnets30ddisposed on either side of the yoke member20dface each other across the yoke member20d, and as in the embodiment shown in FIGS.10A-10C, each magnet30dis pulled to the yoke member20dvia magnetic force. This embodiment is also similar in that the magnet unit210dcan be moved within the range shown inFIGS. 11A-11Cthrough the application of currents to the electromagnetic coil unit110d.

FIGS. 12A and 12Bare a front view and a side view of the construction of an actuator mechanism of a sixth embodiment. This actuator mechanism100ecomprises the magnet unit201shown inFIG. 5Ato which an electromagnetic coil unit110is added. The magnet unit and the electromagnetic coil unit are then housed in a case44. The coil of the electromagnetic coil unit110is held in place by a coil holding member (coil bobbin)112. As indicated by the arrows inFIG. 12A, in this example, the electromagnetic coil unit110moves laterally. As shown byFIG. 12B, a movable unit60is connected to the electromagnetic coil unit110, and the movable unit60moves in tandem with the movement of the electromagnetic coil unit110.

FIGS. 13A and 13Bare a front view and a side view of the construction of an actuator mechanism of a seventh embodiment. This actuator mechanism100fcomprises the magnet unit203shown inFIG. 5Cto which an electromagnetic coil unit110is added. The coil of the electromagnetic coil unit110is held in place by a coil holding member (coil bobbin)112. Because the outer circumference of the magnet unit203ofFIG. 5Cis covered by yoke members40,42, in the example ofFIG. 13, these yoke members40,42also operate as a case.

FIGS. 14A and 14Bare a front view and a side view of the construction of an actuator mechanism of an eighth embodiment. This actuator mechanism100gcomprises the magnet unit204shown inFIG. 5Dto which an electromagnetic coil unit110is added. The coil of the electromagnetic coil unit110is held in place by a coil holding member (coil bobbin)112. In this example as well, the yoke members40,42operate as a case.

FIGS. 15A-15Eare explanatory drawings showing the construction of an actuator mechanism of a ninth embodiment.FIGS. 15D and 15Eare a front view and a side view of a magnet unit210. An electromagnetic coil unit110is disposed around the magnet unit210. The position of the electromagnetic coil unit110is detected by a central position sensor120and an encoder130.FIGS. 15A and 15Cshow the movement of the electromagnetic coil unit110from the central position to the right side or the left side. Where the direction of movement is to change from the rightward to the leftward direction or vice versa, the direction of current is reversed.

As can be seen from the above descriptions, various different constructions may be adopted for the actuator mechanism. It can also be seen that the various different actuator mechanisms described above share the common feature that a plurality of magnets are pulled to a yoke member that is sandwiched by identical magnet poles that face each other across such yoke member. In addition, in these actuator mechanisms, because unnecessary force is not generated in the directions perpendicular to the direction of driving, an actuator having minimal vibration or noise can be obtained.

B. Various Embodiments of Control Devices

B-1. First Embodiment of Control Device

FIG. 16shows a change in current during position control in connection with a first embodiment of an actuator mechanism control device. In the first embodiment, where the actuator mechanism100(FIGS. 4A-4C) is to be moved in the leftward direction, a constant positive current value Ip is impressed to the electromagnetic coil unit110. Where the actuator mechanism100is to be moved in the rightward direction, on the other hand, a constant negative current In is impressed to the electromagnetic coil unit110. In this way, according to the control device of the first embodiment, the controlled variable (the position of the actuator mechanism) and the manipulated variable (the current value impressed to the electromagnetic coil unit110) are set to have a nonlinear relationship. Therefore, as described below, position control is executed using a principle different from PID control. The reason that the position and the current value are set to have a nonlinear relationship is that if they were set to have a linear relationship, when the position deviation is small, such deviation could not be brought sufficiently close to zero.

FIG. 17is a block diagram of the actuator mechanism control device of the first embodiment. This control device400executes position control by adjusting the current value A7impressed to the electromagnetic coil unit110based on a user-specified position command value A0and a position signal A3from the position sensor120. When the various parameter values are set by the user, the various parameter values are registered via the CPU410. The user operations to input the parameter values are omitted from the drawing.

FIG. 18is a timing chart showing the operation of the control device400. The various components of the control device400execute processing in synchronization with a first clock signal generated by a PLL circuit490and a second clock signal A2generated by a control signal generator480. For example, as shown inFIG. 18, each time a pulse of a second clock signal A2is generated, the deviation A4between the command value A0and the position signal A3is calculated and the current value is determined based on this deviation A4. In the example shown inFIG. 18, the second clock signal A2pulses are generated at a ratio of 1/128thof the first clock A1pulses.

As shown inFIG. 17, the position signal from the position sensor120is converted to a digital signal by the A-D converter420and input to the position comparator (subtracter)440. The user-input position command value A0is stored in a position command storage unit430by the CPU410and supplied to the position comparator440from the position command storage unit430. The position comparator440calculates the deviation A4between the position signal A3and the position command value A0, and supplies the result A4(=A3−A0) to the current value determination unit450. In the example ofFIG. 18, the deviation A4is initially a negative value and becomes zero when the target position is reached, but thereafter fluctuates somewhat in the vicinity of zero. This is because a slight external force (such as gravity or the like) is at work. The actuator can be used as an actuator that moves at a constant speed by having the CPU410supply a command value in accordance with a sine wave having a fixed frequency in place of a fixed command value.

FIG. 19is a block diagram showing the internal construction of a current value determination unit450shown inFIG. 17. The current value determination unit450has a three-value determination unit452and three reference current value registers454-456. The three-value determination unit452determines whether the deviation A4is a negative value, zero or a positive value. If the deviation A4is a negative value, a prescribed positive reference current value CVref (=+127) is output from the first reference current value register454. If the deviation A4is zero, a zero current value CVref (=0) is output from the second reference current value register455, while if the deviation A4is a positive value, a prescribed negative reference current value CVref (=−128) is output from the third reference current value register456. As can be seen from this description, a ‘positive current value’ refers to the direction of the current used to generate drive power to bring the position deviation closer to zero from a negative value. A ‘negative current value’ refers to the direction of the current used to generate drive power to bring the position deviation closer to zero from a positive value. The absolute values of the positive reference current value and the negative current value may be set to the same value, or may be set to be different values.

The three-value determination unit452also outputs three deviation sign signals UP, EQU, and DOWN to indicate whether the deviation A4is a negative value, zero or a positive value. As shown inFIG. 18, the first deviation sign signal UP becomes H level when the deviation A4is a negative value and becomes L level when the deviation A4is zero or a positive value. The second deviation sign signal EQU becomes H level only when the deviation A4is zero, and becomes L level when the deviation A4is a negative value or a positive value. The third deviation sign signal DOWN becomes H level when the deviation A4is a positive value and becomes L level when the deviation A4is zero or a negative value. The signals A5generated by the current value determination unit450(the reference current value CVref and the deviation sign signal UP, EQU and DOWN) are supplied to a rive signal generator460shown inFIG. 17.

FIG. 20is a block diagram showing the internal construction of the drive signal generator460. The drive signal generator460has a positive/negative determination unit461, an absolute value obtaining unit462, a counter463, a pole selection unit464and a comparator465. The positive/negative determination unit461determines the sign for the reference current value CVref (positive, zero or negative) and the absolute value obtaining unit462obtains the absolute value of the reference current value CVref and supplies it to the comparator465. The counter463counts the number of pulses of the first clock Al and supplies this number to the comparator465. The count value obtained by the counter463is reset to zero in response to a pulse of the second clock A2. Therefore, the counter463repeatedly generates count values from 0 to 127.

The pole selection unit464generates two sets of drive signals (PH, PL) and (NH, NL) based on signals from the positive/negative determination unit461and the comparator465. These two sets of drive signals (PH, PL) and (NH, NL) are signals supplied to the gates of the four transistors of an H bridge circuit in a drive circuit unit470shown inFIG. 17. The first set of drive signals (PH, PL) are maintained at H level when the reference current value CVref is a positive value but only until the count value of the counter463reaches a pulse count equal to the absolute value of the reference current value CVref, while these drive signals (PH, PL) are otherwise set to L level. On the other hand, the second set of drive signals (NH, NL) are maintained at H level when the reference current value CVref is a negative value but only until the count value of the counter463reaches a pulse count equal to the absolute value of the reference current value CVref, while these drive signals (NH, NL) are otherwise set to L level. When the reference current value CVref is zero, the two sets of drive signals (PH, PL) and (NH, NL) are maintained at L level. The drive signals A6that include the two sets of drive signals (PH, PL) and (NH, NL) obtained in this fashion are supplied to the drive circuit unit470.

As can be seen fromFIG. 18, in the control device of the first embodiment, the first set of drive signals (PH, PL) have a waveform identical to that of the first deviation sign signal UP generated by the current value determination unit450. Similarly, the second set of drive signals (NH, NL) have a waveform identical to that of the third deviation sign signal DOWN. Therefore, in the first embodiment, the drive signal generator460can be omitted.

FIG. 21shows the internal construction of the drive circuit unit470. The drive circuit unit470has a level shifter circuit472and an H-bridge circuit474. The level shifter circuit472has the function of increasing the voltage level of the two sets of drive signals (PH, PL) and (NH, NL) to a voltage level appropriate for the gate voltage of the transistors of the H-bridge circuit474. The two sets of drive signals (PH, PL) and (NH, NL) for which the voltage level is adjusted in this way are impressed to the gates of the four transistors of the H-bridge circuit unit474, in response to which current A7flows to the electromagnetic coil unit110. This coil current A7has one of the following values: the positive reference current value Ip, zero or the negative reference current value In as shown inFIG. 16. The positive reference current value Ip and the negative reference current value In correspond to the reference current values CVref determined by the current value determination unit450(FIG. 19). InFIG. 18, the letters “HiZ” indicating a high impedance state are shown for periods during which the coil current A7is zero.

As described above, in the first embodiment, the reference current value CVref is set to a prescribed positive value, zero or a prescribed negative value in response to whether the deviation A4between the target value (command value) and the measured value regarding the position is a negative value, zero or a positive negative value, and coil current A7corresponding to this reference current value CVref is impressed to the electromagnetic coil unit110. Therefore, despite the fact that the controlled variable (position) and the manipulated variable (current) have a nonlinear relationship as shown inFIG. 16, the actuator will be positioned at a desired position.

In addition, because the current value for the electromagnetic coil unit110is determined by a digital circuit, it is much easier to employ an integrated circuit than it would be if an analog circuit were used. Using an integrated circuit is for the control device offers the advantages that not only can the component cost be reduced, but variations in the operation that are attributable to changes in components and temperature fluctuations can be reduced.

B-2. Second Embodiment of Control Device

FIG. 22is a block diagram showing the internal construction of a current value determination unit450aof a second embodiment.FIG. 23is a timing chart showing the operation of the control device of the second embodiment. The construction of the second embodiment differs from that of the first embodiment solely in regard to the construction of the current determination unit, and is otherwise identical thereto.

This current value determination unit450ahas a deviation limit value storage unit600, a three-value determination unit602, a current value table604, a counter606, a coefficient generator608, a multiplier610and an integrator (accumulator)612. The three-value determination unit602, like the three-value determination unit452shown inFIG. 19, outputs three deviation sign signals UP, EQU and DOWN, and supplies the deviation A4to the current value table604. The three-value determination unit602also has the function of clipping the deviation A4to the upper or lower limit value where the input deviation A4exceeds either the upper limit or lower limit stored in advance in the deviation limit value storage unit600. This is carried out in order to harmonize the range of the deviation A4with the input range for the current value table604. The current value table604is a table that outputs the reference current value A4-3in accordance with the deviation A4output from the three-value determination unit602.

FIG. 24is a graph showing the contents of the current value table604. The horizontal axis represents the deviation A4, while the vertical axis represents the reference current value A4-3. The reference current value A4-3corresponds to the reference current value CVref used by the current value determination unit450of the first embodiment (FIG. 19). However, in the second embodiment, the reference current value A4-3is not a fixed value, and changes along a curved slope in accordance with the deviation A4. However, in the zero proximity range ZPR in which the deviation A4is close to zero, the reference current value A4-3is maintained at zero. This zero proximity range ZPR is set to a range corresponding to the margin of error for positioning accuracy. The reference current value A4-3output from the current value table604is supplied to the multiplier610.

The counter606counts the number of the clock signal A2pulses while the deviation A4is maintained at the same sign (positive or negative) in accordance with the three deviation sign signals UP, EQU and DOWN, and outputs a count value A4-1. This count value A4-1represents the number of continuous occurrences of a deviation A4having the same sign, and is reset to zero if the deviation A4becomes zero or if the sign of the deviation A4changes (seeFIG. 23). This count value A4-1is also termed the ‘number of continuous same-sign occurrences’. The count value A4-1is supplied to the coefficient generator608.

The coefficient generator608outputs a coefficient A4-2that decreases in size as the number of continuous same-sign occurrences A4-1increases. Specifically, as shown inFIG. 23, the coefficient A4-2starts at 1 and takes a value that is obtained by sequentially multiplying the preceding value by ½, (i.e., 1, 0.5, 0.25, 0.125 . . . ). When the number of same-sign occurrences A4-1becomes zero, the coefficient A4-2is initialized to 1. However, the method for reducing the coefficient A4-2may be set in some other way. This coefficient A4-2is multiplied by the reference current value A4-3in the multiplier610, and the results of this multiplication are totaled by the integrator612. An upper limit value (+127) and lower limit value (−128) are preset in the integrator612, and the accumulation result CVm is clipped to fall within these limits. The output CVm from the integrator612is used as a current value supplied to the electromagnetic coil. This current value CVm and the three deviation sign signals UP, EQU and DOWN are output from the current value determination unit450aand supplied to the drive signal generator460(FIG. 17).

The operation of the drive signal generator460is the same as the operation described in the first embodiment. However, as can be seen from a comparison ofFIGS. 18 and 23, among the signals A5input to the drive signal generator460, while the current value CVref of the first embodiment was one of three reference current values (+127, 0, −128), the current value CVm of the second embodiment varies among a greater number of values. As a result, the two sets of drive signals (PH, PL) and (NH, NL) generated by the drive signal generator460are different from those shown inFIG. 18. In other words, the first set of drive signals (PH, PL) is maintained at H level when the current value CVm is positive but only until the count value counted by the counter463(FIG. 20) reaches the value equal to the absolute value of the current value CVm, and is set to L level otherwise. At the same time, the second set of drive signals (NH, NL) is maintained at H level when the current value CVm is negative but only until the count value counted by the counter463reaches the value equal to the absolute value of the current value CVm, and is set to L level otherwise. As a result, the two sets of drive signals (PH, PL) and (NH, NL) are signals that become H level signals only during a period whose length corresponds to the current value CVm. In addition, the current A7supplied to the electromagnetic coil becomes the fixed current value Ip or In only during the periods corresponding to the waveforms of the two sets of drive signals (PH, PL) and (NH, NL). Therefore, it can be seen that the effective value of the current A7flowing in the electromagnetic coil (i.e., the effective amount of electric power) corresponds to the current value CVm.

As described above, in the second embodiment, where a deviation A4having the same sign occurs continuously, a gradually declining coefficient A4-2is generated, this coefficient A4-2is multiplied by the reference current value A4-3determined in response to the deviation A4, the results of the multiplication are accumulated, and the electromagnetic coil is driven by a current equivalent to the value Cvm resulting from this accumulation. As a result, when the sign for the deviation A4changes at a position near zero, an excessive change in position will be prevented by gradually increasing the absolute value of the current value CVm. Specifically, with reference toFIG. 23, when the sign of the deviation A4changes from zero to a plus sign, the current value CVm changes gradually from zero to −40 and to −65. On the other hand, in the first embodiment shown inFIG. 18, the current value CVref for these timings is −128 and −128, showing the absolute value of the current value to be larger than in the second embodiment. Therefore, in the second embodiment, the possibility that excessive positional change will occur in the range in which the deviation A4is close to zero is smaller than in the first embodiment, and therefore the advantage of better positioning control accuracy is obtained.

B-3. Third Embodiment of Control Device

FIG. 25is a block diagram showing the construction of a control device of a third embodiment.FIG. 26is a timing chart pertaining to the operation of the control device of the third embodiment. This control device400adiffers from the control device of the first embodiment (FIG. 17) in that it has the current value determination unit450aof the second embodiment (FIG. 22) in place of the current value determination unit450(FIG. 17), and includes a polarity reduction unit620between the current value determination unit450aand the drive signal generator460. In other words, the control device of the third embodiment comprises the control device of the second embodiment to which a polarity reduction unit620is added.

FIG. 27is a block diagram showing the internal construction of the polarity reduction unit620. The polarity reduction unit620has an up/down continuous determination unit622, a counter624and a reduction coefficient table626. The up/down continuous determination unit622, like the counter606of the current value determination unit450a(FIG. 22), counts the number of continuous occurrences Mt of the same sign (positive or negative) in response to the three deviation sign signals UP, EQU and DOWN. Therefore, the value obtained for this number of continuous occurrences Mt is the same value as that of the number of continuous same-sign occurrences A4-3generated by the counter606of the current determination unit450a. The reduction coefficient table626outputs a reduction coefficient or mitigated coefficient A5Sin in response to this number of continuous occurrences Mt. This reduction coefficient A5Sin is derived, for example, using the equation
A5 Sin=sin(Mt/k)
where k is a constant that is set to k=6 in the example shown inFIG. 26.

For the reduction coefficient A5Sin, any coefficient that increases as the number of continuous same-sign occurrences Mt increases may be used. However, it is preferred that the value of the reduction coefficient A5Sin falls between 0 and 1.

The multiplier628multiplies the reduction coefficient A5Sin by the current value CVm and supplies the product A5S to the drive signal generator460as the final current value. As can be seen fromFIG. 26, this current value A5S gradually increases in value while the sign of the deviation A4remains the same. The electromagnetic coil is driven by a current corresponding to this current value A5S.

As described above, in the third embodiment, the coil current value is determined such that the coil current increases gradually while the sign of the deviation A4remains the same. Therefore, in addition to achieving the effects of the second embodiment, the third embodiment also achieves the effect of enabling control to be performed such that the coil current value increases steadily after the sign of the deviation A4changes from positive to negative or from negative to positive. In other words, the danger of an excessive change in position occurring when there is a change in the sign of the deviation A4will be reduced.

C. Application Examples of Actuator

FIGS. 28A and 28Bare explanatory drawings showing a blade member drive mechanism comprising a first application example of an actuator according to an embodiment of the present invention. This blade member drive mechanism510includes a revolving blade member514that can turn around a central shaft512and an actuator mechanism100that moves this blade member514. This actuator mechanism100comprises the mechanism shown inFIGS. 10A-10Cmodified to have a curved configuration. The magnet unit210of the actuator mechanism100is secured to one end of the blade member514, and the electromagnetic coil unit110is secured to a support member not shown. The electromagnetic coil unit110and the magnet unit210are positioned on the circumference of a circle that is formed with the central shaft512as its center. When the actuator mechanism100is operated, the blade mechanism514turns around the central shaft512. Because the actuator mechanism100can be position-controlled, the blade mechanism514can be positioned at a desired position. In this application, the term ‘position’ indicates the rotational angle of the blade mechanism514. By using several blade mechanisms514, an aperture mechanism for an optical device can be formed.

FIGS. 29A and 29Bare explanatory drawings showing a lever drive mechanism comprising a second application example of an actuator according to an embodiment of the present invention. This lever drive mechanism520includes a revolving lever524that can turn around a central shaft522and an actuator100that moves this lever524. Mutually engaging gears526,528are secured at the locations at which the magnet unit210of the actuator mechanism100and the lever524face each other. One gear526comprises a spur gear and the other gear528comprises a semicircular gear. The electromagnetic coil unit110is secured to a support member not shown. The linear movement of the actuator mechanism100is converted into rotational motion by the gears526,528. When the actuator mechanism100is operated, the lever524turns around the central shaft522. As a result, the lever524can be positioned at a desired position.

FIG. 30is an explanatory drawing showing a protrusion member drive mechanism comprising a third application example of an actuator according to an embodiment of the present invention. This protrusion member drive mechanism530includes a revolving protrusion member534that can turn around a central shaft532and two actuator mechanisms100that move this protrusion member534. A link securing member538is secured to one end of the magnet unit210of each actuator mechanism100. The electromagnetic coil units110are secured to support members not shown. The two link securing members538are respectively connected to the protrusion member534by two linear links536disposed on the same plane (the two links536comprising X1 and X2 axes). When the two actuator mechanisms100are operated, the protrusion member534turns around the central shaft532. As a result, the protrusion534adisposed at the distal end of the protrusion member534can be positioned at a desired angle.

FIG. 31is an explanatory drawing showing a three-dimensional drive mechanism comprising a fourth application example of an actuator according to an embodiment of the present invention. This three-dimensional drive mechanism540includes three actuator mechanisms100that move a driven member542in a three-dimensional fashion. A link securing member548is secured to one end of the magnet unit210of each actuator mechanism100, and the electromagnetic coil units110are secured to support members not shown. The three link securing members548are respectively connected to the driven member542by linear links546. The magnet units210and link securing members548belonging to the three actuator mechanisms100move along three mutually perpendicular axes (X, Y and Z axes). As a result, when the three actuator mechanisms100are operated, the driven member542can be positioned in a three-dimensional fashion.

FIGS. 32A and 32Bare explanatory drawings showing an annular actuator comprising a fifth application example of an actuator according to an embodiment of the present invention. This annular actuator550includes a hollow cylindrical case552and a rotor556that is housed in the case552and rotates around a rotational shaft556. The rotational shaft554of the rotor556is supported by a bearing556belonging to the case552. A magnet unit210is disposed on the rotor556and an electromagnetic coil unit110is disposed around the magnet unit210.FIG. 32Bshows the arrangement of the coil and magnets. Using this annular actuator550, the rotor556can rotate within a range of 45 degrees.

FIGS. 33A and 33Bare explanatory drawings showing an electromagnetic suspension comprising a sixth application example of an actuator according to an embodiment of the present invention. This electromagnetic suspension560includes a suspension main unit562to which a magnet unit210is secured, an electromagnetic coil unit110secured to a support member564at a position at which it faces the magnet unit210, and a lower limiter566. A position sensor120is disposed on the electromagnetic coil110. Using this actuator560, the force and position of the suspension can be adjusted by adjusting the current impressed to the electromagnetic coil unit110, thereby absorbing the upward and downward vibration stress.

FIG. 34is an explanatory drawing showing a print head drive device comprising a seventh application example of an actuator according to an embodiment of the present invention. This print head drive device570moves a carriage572of a print head using the same mechanism as that of the actuator mechanism100hshown inFIGS. 15A-15E. The carriage572is linked to the electromagnetic coil unit110and is guided along a guide rail574. This actuator mechanism100comprises a kind of linear motor and can move the carriage572at a constant speed when current is impressed thereto.

FIGS. 35A-35Dare explanatory drawings showing an angle servo-controller comprising an eighth application example of an actuator according to an embodiment of the present invention.FIG. 35Ais a plan view andFIG. 35Bis a side view. The magnet unit210of the actuator mechanism used in this device comprises a disk-shaped yoke member20and two magnets30that are respectively disposed on the top and bottom surfaces of the yoke member. Each magnet30is magnetized parallel to the main surfaces. In the state shown inFIG. 35A, the right sides of the magnets30are the S poles while the left sides are the N poles. Two coils of an electromagnetic coil unit110are disposed around the magnet unit210. These coils are wound perpendicular to the main surfaces of the magnet unit210such that they sandwich the top and bottom surfaces of the substantially disk-shaped magnet unit210. The center of the magnet unit210is secured to a rotational shaft582, which is supported by a bearing584. Second yoke members40are disposed on the top and bottom surfaces of the case44. In this angle servo-controller580, the magnet unit210can be rotated clockwise or counterclockwise as shown inFIGS. 35A,35C and35D by impressing current to the electromagnetic coil unit110. A position sensor120to detect the angle of rotation is disposed outside the magnetic unit210.

The present invention is not limited to the examples and embodiments described above, and can be implemented in various other forms within the essential scope thereof For example, the following variations are possible.

In the control devices of the various embodiments, the controlled variable pertained to position, but control can be exerted regarding various other controlled variables than position. For example, the controlled variables can be light amount (i.e., in the case of an actuator that adjusts the aperture of an illumination optical system, for example), or flow volume or flow speed (i.e., in the case of an actuator for a flow control valve). Because the controlled variable changes depending on the position of the actuator in these cases as well, it can be thought to be related to the position of the actuator. In general, it is preferred that a sensor be included in order to directly or indirectly measure the controlled variable.

In the control devices of the embodiments, the reference current value was set to one of three values, i.e., a positive value, zero or a negative value, in accordance with whether the controlled variable (position) representing the deviation was a negative value, zero or a positive value, but it is also acceptable if instead the reference current value is set to a prescribed positive value or a prescribed negative value depending on the sign of the deviation. In this case, when the deviation is zero, the reference current value is set to whichever of the positive value or the negative value is selected in advance.

The constructions of the various actuator mechanisms and control devices used in connection with the embodiments described above are examples. Various other constructions may also be used.