Rotational-linear motion converter

A rotational-linear motion converter includes a cylindrical magnet rotor, a linear rail, a teeth row, and a magnet row. The magnet rotor includes a magnet row magnetized in a radial direction of the magnet rotor. The rail includes a plurality of projecting portions and recessed portions. The teeth row includes teeth and allows a magnetic flux flowing from the magnet row of the magnet rotor to pass between the magnet rotor and the rail. The magnet row includes magnets and is magnetized in an extending direction of the rail in order to align the magnetic flux flowing from the magnet row of the magnet rotor toward the projecting portions and the recessed portions of the rail. In the magnet row magnetized in the extending direction of the rail, the same polarity faces of adjacent magnets oppose each other in the extending direction of the rail.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Application No. 2013-076905, filed Apr. 2, 2013, the entirety of which is incorporated herein by reference.

BACKGROUND

1. Technical Field

The present invention relates to a rotational-linear motion converter utilizing magnetism.

2. Description of Related Art

Hitherto, as a typical rotational-linear motion converter, a device to which a so-called ball screw mechanism is applied is used. In this type of rotational-linear motion converter, since friction is generated between a ball and thread grooves, it is likely that noise or vibration will occur, thereby making it difficult to enhance the longevity of such a converter. Additionally, in this type of rotational-linear motion converter, regular maintenance, such as greasing, is required for reducing the occurrence of noise or vibration caused by aging or for minimizing the wear of a ball. In this manner, the possibility of scattering of grease or the maintenance has to be considered, and thus, installation places of this type of rotational-linear motion converter are restricted, thereby decreasing the design flexibility.

These days, attention is being focused on technologies concerning, for example, non-contact rotational-linear motion converters utilizing magnetism, which may overcome the above-described drawbacks unique to a rotational-linear motion converter using a ball screw mechanism.

Japanese Unexamined Patent Application Publication No. 2008-215429 discloses a magnetic power transmission device which includes a non-contact magnetic rack and pinion mechanism and which converts rotational motion to linear motion. This magnetic rack and pinion mechanism includes a shaft-like member and a pair of support plates. The shaft-like member has permanent magnets which are spirally formed on the outer peripheral surface of the shaft-like member with predetermined pitches. The pair of support plates has permanent magnets on the internal surfaces thereof with the same pitches as those of the permanent magnets of the shaft-like member so that these permanent magnets may oppose the permanent magnets of the shaft-like member. In this magnetic rack and pinion mechanism, due to a magnetic attractive force generated between the permanent magnets of the shaft-like member and the permanent magnets of the support plates which oppose each other, rotational motion of the shaft-like member is converted into linear motion of the support plates. The strength of the magnetic attractive force differs depending on the number of opposing permanent magnets, and the magnetic attractive force becomes stronger as the number of opposing permanent magnets is greater. As the magnetic attractive force becomes stronger, the permissible thrust of the magnetic rack and pinion mechanism also becomes greater.

Japanese Unexamined Patent Application Publication No. 2007-215264 (page 11, FIG. 10) discloses an actuator which includes a non-contact magnetic velocity-reduction drive and which converts rotational motion to linear motion. The non-contact magnetic velocity-reduction drive includes a base, a drive head, and a permanent magnet. The base is constituted by a magnetic body having projecting portions and recessed portions which are alternately disposed at predetermined intervals on the top surface of the base. In the drive head, a magnetic circuit is formed between an internal space of the drive head and a base opposing surface which opposes the top surface of the base. The permanent magnet is rotatably fitted in the internal space of the drive head. In this magnetic velocity-reduction drive, a closed magnetic field which passes through the drive head and the base is formed due to the presence of the permanent magnet. The closed magnetic field is formed along the path of the magnetic circuit of the drive head and the top surface of the base due to the presence of a magnetic flux passing through an area where the magnetic circuit of the drive head opposes the projecting portions of the base. In this magnetic velocity-reduction drive, by a rotating magnetic field (closed magnetic field) generated by rotating the permanent magnet, the thrust in the horizontal direction (restoration force of a magnetic field) is obtained, and then, rotational motion of the permanent magnet is converted into linear motion of the base (in this actuator, since the base is fixed, the drive head, which is movable, actually performs linear motion).

The strength of the thrust of the rotating magnetic field differs depending on the magnetic field intensity (magnetic flux density or the number of magnetic lines of force per unit area). The thrust of the rotating magnetic field becomes stronger as the magnetic field intensity becomes greater. If the thrust of the rotating magnetic field is strong, the permissible thrust that can be transmitted between the drive shaft of the rotating magnet and the base is increased. Accordingly, in order to generate a large permissible thrust, it is necessary to increase the number of magnetic lines of force per unit area which forms a rotating magnetic field.

In the magnetic power transmission device disclosed in Japanese Unexamined Patent Application Publication No. 2008-215429, since permanent magnets are disposed both on the shaft-like member and the support plates, if a long moving distance (stroke) of the support plates which perform linear motion is required, it is necessary to increase the number of permanent magnets or to increase the pitch between the permanent magnets disposed on the shaft-like member. If many permanent magnets are disposed, the shaft-like member is likely to sag, thereby decreasing the positioning precision. Under the current situation, a low-cost, high-precision magnetic power transmission device is demanded. Thus, if a long stroke is required, it is difficult to use the magnetic power transmission device disclosed in this publication.

If the pitch between the permanent magnets is increased, the number of permanent magnets disposed on the shaft-like member which oppose the permanent magnets of the support plates is decreased. Accordingly, the permissible thrust of the magnetic rack and pinion mechanism is decreased. Thus, if a large permissible thrust is desired, it is also difficult to use the magnetic power transmission device disclosed in this publication.

In the magnetic velocity-reduction drive disclosed in Japanese Unexamined Patent Application Publication No. 2007-215264, the magnetic field intensity of the closed magnetic field is determined by the number of magnetic lines of force passing through the area where the magnetic circuit of the drive head opposes the projecting portions of the base. Among these magnetic lines of force, there are some magnetic lines of force which pass through an area where the magnetic circuit of the drive head does not oppose the projecting portions of the base. However, such magnetic lines of force produce very little influence on the magnetic field intensity of the closed magnetic field.

Accordingly, in the magnetic velocity-reduction drive disclosed in this publication, in order to increase the permissible thrust, it is necessary to increase the area by which the magnetic circuit of the drive head and the projecting portions of the base oppose each other. Thus, the size of the magnetic velocity-reduction drive is inevitably increased. Under the current situation, a small magnetic velocity-reduction drive mechanism is demanded. Thus, it is difficult to use the magnetic velocity-reduction drive disclosed in this publication.

If the area by which the magnetic circuit of the drive head and the projecting portions of the base oppose each other is increased while maintaining a small size of the magnetic velocity-reduction drive, the pitch of the projecting portions of the base has to be increased. Then, the number of projecting portions of the base that can be disposed within the same length of the base is decreased, which makes it difficult to increase the acceleration reduction velocity ratio of the magnetic velocity-reduction drive mechanism. Accordingly, if a large acceleration reduction velocity ratio is desired, it is also difficult to use the magnetic velocity-reduction drive disclosed in this publication.

SUMMARY

In view of the above-described background, the present invention has been made to solve the above-described problems. Accordingly, it is an object of the present invention to provide a low-cost, high-precision, small rotational-linear motion converter that implements a large permissible thrust and a wide-range acceleration reduction velocity ratio.

In order to achieve the above-described object, according to an aspect of the present invention, there is provided a rotational-linear motion converter including a cylindrical magnet rotor, a linear rail, a teeth row, and a magnet row.

The cylindrical magnet rotor includes a magnet row magnetized in a radial direction of the magnet rotor. The linear rail includes a plurality of projecting portions and recessed portions. The teeth row includes teeth and allows a magnetic flux flowing from the magnet row of the magnet rotor to pass between the magnet rotor and the rail. The magnet row includes magnets and is magnetized in an extending direction of the rail in order to align the magnetic flux flowing from the magnet row of the magnet rotor toward the projecting portions and the recessed portions of the rail. In the magnet row magnetized in the extending direction of the rail, the same polarity faces of adjacent magnets oppose each other in the extending direction of the rail.

In the above-described rotational-linear motion converter, in the magnet row magnetized in the extending direction of the rail, the same polarity faces of adjacent magnets oppose each other in the extending direction of the rail. Accordingly, the magnetic flux transferred between the drive head and the rail flows in the state in which most of the magnetic lines of force are aligned, thereby substantially eliminating a leakage flux.

According to an aspect of the present invention, it is possible to provide a low-cost, high-precision, small rotational-linear motion converter while implementing a large permissible thrust and a wide-range acceleration reduction velocity ratio.

DETAILED DESCRIPTION

The configurations and the operations of rotational-linear motion converters according to first through eighth embodiments of the present invention will be described below with reference to the accompanying drawings. In a description of the elements shown in the drawings, the same elements are designated by like reference numerals, and an explanation of the same element will be given only once. Additionally, the dimension ratios of the elements shown in the drawings may be exaggerated for the purpose of representation and may be different from the actual dimension ratios.

FIG. 1is a schematic view illustrating a rotational-linear motion converter60according to a first embodiment.FIG. 2illustrates a closed magnetic field formed in the rotational-linear motion converter60shown inFIG. 1.FIG. 3illustrates motion conversion of the rotational-linear motion converter60shown inFIG. 1. The configuration and the operation of the rotational-linear motion converter60according to the first embodiment will be described below.

FIG. 1shows a cross section of the rotational-linear motion converter60which is cut in a direction perpendicular to the direction of the rotational axis of a magnet rotor10. The directions of white arrows indicated within the magnet rotor10shown inFIG. 1are magnetization directions of permanent magnets14aand14b, which will be discussed later. The heads of the arrows indicate the N pole, while the tails of the arrows indicate the S pole.

The rotational-linear motion converter60includes a drive head30and a rail40. The drive head30includes a magnet rotor10and a teeth row20. The magnet rotor10is concentrically disposed within the drive head30so that a gap15may be formed between the magnet rotor10and a cylindrical internal space of the drive head30. The teeth row20extends like octopus' tentacles (legs) from the internal space of the drive head30toward the rail40so that a gap25may be formed between the teeth row20and the rail40. The drive head30and the rail40are disposed such that the teeth row20of the drive head30opposes the rail40, and the drive head30and the rail40are relatively movable in a direction in which the rail40extends. In the first embodiment, the drive head30is fixed so that it will not be movable, and the magnet rotor10is rotatably supported within the drive head30.

The magnet rotor10includes a magnet row12constituted by two semicircular permanent magnets14aand14bwhich are magnetized in the radial direction. The permanent magnet14ais magnetized as the S pole at the inner periphery thereof and as the N pole at the outer periphery thereof. The permanent magnet14bis magnetized as the N pole at the inner periphery thereof and as the S pole at the outer periphery thereof. Accordingly, the magnet rotor10has two poles, which are the N pole on the upper side and the S pole on the lower side, as viewed from the position of the magnet rotor10shown inFIG. 1.

InFIG. 1, the two semicircular permanent magnets14aand14bare shown by way of example. Alternatively, one ring-like permanent magnet may be used in which the outer portion of one half is magnetized as the N pole and the outer portion of the other half is magnetized as the S pole.

As shown inFIG. 1, the magnet rotor10has two poles. However, the number of poles of the magnet rotor10may be M (M is an even number) other than two, which will be discussed later in third through eighth embodiment.

The magnet rotor10is formed by punching a magnetic body, such as an electromagnetic steel sheet, silicon steel, carbon steel, electromagnetic stainless steel, a dust core, or an amorphous magnetic core, by using a die.

The teeth row20allows a magnetic flux flowing from the magnet row12of the magnet rotor10to pass through the teeth row20toward the rail40. The teeth row20also allows a magnetic flux passing through the rail40to pass through the teeth row20toward the magnet row12of the magnet rotor10. The teeth row20is constituted by teeth24aand24b. The number of teeth24aand24bassigned to each pole of the magnet rotor10is nine. The shapes and the lengths of the teeth24aand24bare different from each other so that a magnetic flux within each of the teeth24aand24bis directed toward only one of the magnet row12of the magnet rotor10and the rail14.

The distal ends of the teeth24aand24bare interconnected to each other in the circumferential direction of the magnet rotor10so as to form one cylindrical internal space. The interconnecting portions at the distal ends are formed to be thin in the radial direction of the magnet rotor10so that a leakage of a magnetic flux between adjacent teeth24aand24bcan be prevented. The forward ends of the teeth24aand24bare formed so that a teeth pitch will be T in the extending direction of the rail40.

The teeth pitch T of the teeth row20is set by considering the number Mt of teeth assigned to each pole of the magnet rotor10and a magnet pitch P of a magnet row52, which will be discussed later, so that, when the magnet rotor10is rotated, the rail40can be moved, or when the rail40is moved, the magnet rotor10can be rotated. More specifically, the teeth pitch T which satisfies the relationship expressed by equation (1) is formed:
T=(2·P)+k·(P/Mt) (k=±1)  (1)
where P denotes the magnet pitch of the magnet row52, and Mt denotes the number of teeth assigned to each pole of the magnet rotor10.

InFIG. 1, the number Mt of teeth assigned to each pole of the magnet rotor10is nine, as discussed above. Accordingly, when k is −1, the teeth pitch T to be formed in the teeth row20is calculated as (P·17/9) from equation (1), and when k is +1, the teeth pitch T to be formed in the teeth row20is calculated as (P·19/9) from equation (1). In the rotational-linear motion converter60shown in FIG.1, the teeth pitch T at the forward ends of the teeth row20is formed to be (P·17/9).

InFIG. 1, the teeth row20has a symmetrical arrangement on the right and left sides with respect to the magnet rotor10by way of example. However, the teeth row20is not restricted to this arrangement, and may have an asymmetrical arrangement on the right and left sides.

InFIG. 1, the teeth row20is formed all along the periphery of the magnet rotor10byway of example. However, the teeth row20may be formed only on part of the periphery of the magnet rotor10as long as the number of teeth24aand24bis equally assigned to magnetic poles having different polarities of the magnet rotor10, which will be discussed later in a third embodiment.

As in the magnet rotor10, the teeth row20is formed by punching a magnetic body, such as an electromagnetic steel sheet, silicon steel, carbon steel, electromagnetic stainless steel, a dust core, or an amorphous magnetic core, by using a die.

In the rail40, recessed portions having a pitch P are formed in the extending direction of the rail40. The recessed portions contain therein permanent magnets54aand54bmagnetized in the extending direction of the rail40. Accordingly, the magnet pitch of the permanent magnets54aand the permanent magnets54bis also P. Since the permanent magnets54aand54bare contained in the recessed portions, the permanent magnets54aand54band magnetic bodies44aand44bare alternately disposed in the extending direction of the rail40.

The rail40includes the above-described magnet row52, which is magnetized in the extending direction of the rail40. The magnet row52aligns the magnetic flux which will pass through the rail40. Due to the function of the magnet row52, a magnetic flux passes through the rail40in the state in which most of the magnetic lines of force are aligned, thereby reducing a leakage flux. In the magnet row52, the same polarity (N pole) faces of adjacent permanent magnets54aoppose each other with a magnetic body44atherebetween in the extending direction of the magnet row52. Moreover, the same polarity (S pole) faces of adjacent permanent magnets54boppose each other with a magnetic body44btherebetween in the extending direction of the magnet row52. Concerning the magnetization directions of the magnet row52, the heads of the arrows indicate the N pole, while the tails of the arrows indicate the S pole. Accordingly, a magnetic body44ais disposed between two permanent magnets54awith their N pole faces opposing each other, while a magnetic body44bis disposed between two permanent magnets54bwith their S pole faces opposing each other.

In the rail40, the magnetic bodies44a, each being sandwiched between the N-pole faces of the permanent magnets54a, and the magnetic bodies44b, each being sandwiched between the S-pole faces of the permanent magnets54b, are alternately disposed in the extending direction of the rail40. Accordingly, in the rail40, magnetic poles, that is, the S pole and the N pole which are alternately disposed in the rail40, are formed.

As in the magnet rotor10and the teeth row20, the rail40is formed by punching a magnetic body, such as an electromagnetic steel sheet, silicon steel, carbon steel, electromagnetic stainless steel, a dust core, or an amorphous magnetic core, by using a die.

(Formation of Closed Magnetic Field)

A description will first be given, with reference toFIG. 2, of a closed magnetic field H formed in the rotational-linear motion converter60shown inFIG. 1. The arrows shown inFIG. 2indicate magnetic lines of force, and the heads of the arrows indicate the directions of magnetic lines of force.

As shown inFIG. 2, within the magnet rotor10, a magnetic flux φ flowing from the permanent magnet14bto the permanent magnet14ais distributed such that it divides the cylinder of the magnet rotor10into two portions. The magnetic flux φ flowing from the permanent magnet14aflows to the rail40through the teeth24aand24bwhich are assigned to the permanent magnet14a. Then, the magnetic flux φ entering the rail40flows to the magnetic bodies44aand44bwhich oppose the teeth24aand24bassigned to the permanent magnet14bin the state in which the magnetic lines of force are aligned. The magnetic flux φ passing through the rail40flows into the permanent magnet14bof the magnet rotor10via the teeth24aand24bassigned to the permanent magnet14b. In this manner, a closed magnetic field looping within the magnet rotor10, the teeth row20, and the rail40is formed.

As viewed from the position of the rotational-linear motion converter60shown inFIG. 2, the teeth24aand24bon the upper half of the teeth row20are assigned to the permanent magnet14a, while the teeth24aand24bon the lower half of the teeth row20are assigned to the permanent magnet14b. Accordingly, the closed magnetic field H is divided to a closed magnetic field group flowing clockwise and a closed magnetic field group flowing counterclockwise on the right and left sides, respectively. However, depending on the rotation position of the magnet rotor10, teeth24aand24bassigned to the permanent magnets14aand14bare changed. Thus, teeth24aand24bforming the closed magnetic field group flowing clockwise and teeth24aand24bforming the closed magnetic field group flowing counterclockwise are not uniquely determined.

The number of magnetic lines of force forming the magnetic flux φ passing through the teeth24aand24band the flowing direction thereof are changed in accordance with the rotation position of the magnet rotor10. Then, when the number of magnetic lines of force and the flowing direction thereof are changed, the closed magnetic field H looping within the magnet rotor10, the teeth row20, and the rail40is also changed. When the closed magnetic field H is changed, a restoration force of a magnetic field acts on the closed magnetic field H so as to maintain the balance of the closed magnetic field H. This restoration force of a magnetic field serves as a thrust to the rail40in the horizontal direction, thereby implementing relative displacement motion between the rail40and the drive head30. Accordingly, rotational motion of the magnet rotor10can be converted into linear motion of the rail40or the drive head30. The relationship between the rotation position of the magnet rotor10and the flow of the magnetic flux φ will be described in detail in an eighth embodiment, which will be discussed later.

The magnetic flux φ within the rail40will be discussed below more specifically.

In the rail40, receiving areas A in which the magnetic flux φ is received from the permanent magnet14avia the teeth24aand24bassigned to the permanent magnet14aare formed. In the rail40, a transfer area B from which the magnetic flux φ will be transferred to the permanent magnet14bvia the teeth24aand24bassigned to the permanent magnet14bis also formed. Within the rail40, the magnetic flux φ flows from the receiving areas A to the transfer area B. InFIG. 2, both side portions of the rail40serve as the receiving areas A for receiving the magnetic flux φ, while the central portion of the rail40serves as the transfer area B for transferring the magnetic flux φ. Thus, the magnetic flux φ within the rail40flows from the side portions to the central portion of the rail40.

Each of the magnetic bodies44aof the rail40is sandwiched between two permanent magnets54awith their N pole faces opposing each other in the extending direction of the rail40. Each of the magnetic bodies44bof the rail40is sandwiched between two permanent magnets54bwith their S pole faces opposing each other in the extending direction of the rail40. Accordingly, in the receiving areas A of the rail40, the magnetic flux φ flowing from the permanent magnet14acan be forcefully directed to the magnetic bodies44a. In the transfer area B of the rail40, the magnetic flux φ which will flow to the permanent magnet14bcan be forcefully transferred from the magnetic bodies44bto the permanent magnet14b. Due to a magnetic force of the permanent magnets54aand54b, the magnetic flux φ within the rail40can be forcefully directed to the magnetic bodies44aand44b. Thus, when the magnetic flux φ is transferred between the drive head30and the rail40, a leakage flux is substantially eliminated.

In this manner, the magnet row52aligns the magnetic flux φ transferring between the drive head30and the rail40toward the magnetic bodies44aand44b. In this case, the magnet row52is capable of aligning most of the magnetic lines of force forming the magnetic flux φ toward the magnetic bodies44aand44b, thereby substantially eliminating a leakage flux. As a result, the magnetic flux φ can be effectively converted into a thrust.

As discussed above, in the rotational-linear motion converter60of the first embodiment, due to the function of the magnet row52of the rail40, a closed magnetic flux is effectively directed toward the magnetic bodies44aand44b, thereby effectively reducing a leakage flux between the drive head30and the rail40. Additionally, a magnetic coupling force between the drive head30and the rail40can be enhanced, thereby making it possible to increase the permissible thrust. Since a closed magnetic flux can be used effectively, the size of the drive head30can be reduced. Thus, a large permissible thrust can be implemented while maintaining a small size of the drive head30. Transferring of a magnetic flux between the drive head30and the rail40is performed via the teeth row20produced by die-punching. Accordingly, high positioning precision can be achieved when performing relative displacement motion between the drive head30and the rail40without depending on the magnetization precision of the permanent magnets14aand14b.

(Principle of Acceleration and Reduction of Velocity)

A description will now be given of how the rail40is moved when the magnet rotor10is rotated in the state in which a closed magnetic flux is formed in the magnet rotor10, the teeth row20, and the rail40, as shown inFIG. 2.

It is now assumed that:the number of poles of the magnet rotor10is M (M is an even number);the diameter of the magnet rotor10is D;the circle ratio (pi) is π;the magnet pitch of the magnet row52is P;the coefficient k is 1 or −1;the rotational velocity of the magnet rotor10is F;the peripheral velocity of the magnet rotor10is Vr; andthe motion velocity of the rail40is Vm.

In this case, the peripheral velocity Vr of the magnet rotor10can be expressed by Vr=F·π·D, and the motion velocity Vm of the rail40can be expressed by Vm=k·F·M·P (k=±1).

Accordingly, the relationship between the peripheral velocity Vr of the magnet rotor10and the motion velocity Vm of the rail40can be expressed by equation (2).
Vm/Vr=(k·M·P)/(π·D) (k=±1)  (2)

That is, when the magnet rotor10rotates through one revolution, the rail40moves by M·P. Since the magnet rotor10is supported within the internal space of the drive head30, the peripheral velocity Vr of the magnet rotor10also indicates the motion velocity of the drive head30.

Equation (2) shows that there is a difference between the peripheral velocity Vr of the magnet rotor10and the motion velocity Vm of the rail40and that the velocity can be accelerated and reduced between the drive head30and the rail40. If the sign of the peripheral velocity Vr of the magnet rotor10and the sign of the motion velocity Vm of the rail40are opposite, the rail40is moved in an opposite direction, as viewed from the magnet rotor10.

In the case of the rotational-linear motion converter60of the first embodiment, the number M of poles of the magnet rotor10is two, and the coefficient k is −1. Accordingly, by substituting M=2 and k=−1 into equation (2), the following equation is obtained.
Vm/Vr=−2·P/(π·D)

Thus, if the drive head30is fixed so that it will not be movable, when the magnet rotor10is rotated through one revolution, the rail40moves by −2·P. The thin black arrow and the thick black arrow inFIG. 3indicate the rotating direction of the magnet rotor10and the moving direction of the rail40, respectively.

The configuration and the operation of the rotational-linear motion converter60of the first embodiment have been discussed above. As described above, when the magnet rotor10is rotated or when the rail40is moved, the closed magnetic field H formed between the drive head30and the rail40is disturbed, and in order to maintain the balance of the closed magnetic field H, the drive head30and the rail40perform relative displacement motion. Through the operation for maintaining the balance of the closed magnetic field H, the relationship between the velocity of the drive head30and that of the rail40can be obtained, as expressed by equation (2).

As described above, in the rotational-linear motion converter60of the first embodiment, the rail40includes the magnet row52which is magnetized in the extending direction of the rail40. Since the magnet row52aligns the magnetic flux φ which will pass through the rail40, a leakage flux can be reduced to a minimal level, and a large permissible thrust and a wide-range acceleration reduction velocity ratio can be implemented.

A rotational-linear motion converter160according to a second embodiment will be described below with reference toFIGS. 4, 5, and 6.FIG. 4is a schematic diagram of the rotational-linear motion converter160.FIG. 5illustrates a closed magnetic field formed in the rotational-linear motion converter160shown inFIG. 4.FIG. 6illustrates motion conversion of the rotational-linear motion converter160shown inFIG. 4.

As shown inFIG. 4, the rotational-linear motion converter160of the second embodiment is different from the rotational-linear motion converter60of the first embodiment in that a magnet row152is not contained in a rail140, but is contained in a teeth row120.

The rotational-linear motion converter160includes a drive head130and a rail140. The drive head130includes a magnet rotor110and a teeth row120. The magnet rotor110is concentrically disposed within the drive head130so that a gap115may be formed between the magnet rotor110and a cylindrical internal space of the drive head130. The teeth row120extends like octopus' tentacles (legs) from the internal space of the drive head130toward the rail140so that a gap125may be formed between the teeth row120and the rail140. The drive head130and the rail140are disposed such that the teeth row120of the drive head130opposes the rail140, and the drive head130and the rail140are relatively movable in a direction in which the rail140extends. In the second embodiment, the drive head130is fixed so that it will not be movable, and the magnet rotor110is rotatably supported within the drive head130.

The magnet rotor110includes a magnet row112constituted by two semicircular permanent magnets114aand114bwhich are magnetized in the radial direction. The permanent magnet114ais magnetized as the N pole at the inner periphery thereof and as the S pole at the outer periphery thereof. The permanent magnet114bis magnetized as the S pole at the inner periphery thereof and as the N pole at the outer periphery thereof. Accordingly, the magnet rotor110has two poles, which are the S pole on the upper side and the N pole on the lower side, as viewed from the position of the magnet rotor110shown inFIG. 4. The configurations of the other parts of the magnet rotor110are the same as those of the first embodiment.

The teeth row120is constituted by teeth124aand124b. The number of teeth124aand124bassigned to each pole of the magnet rotor110is 24. The shapes and the lengths of the teeth124aand124bare different from each other so that a magnetic flux within each of the teeth124aand124bis directed toward only one of the magnet row112of the magnet rotor110and the rail140.

The distal ends of the teeth124aand124bare interconnected to each other in the circumferential direction of the magnet rotor110so as to form one cylindrical internal space. The interconnecting portions at the distal ends are formed to be thin in the radial direction of the magnet rotor110so that a leakage of a magnetic flux between adjacent teeth124aand124bcan be prevented.

The forward ends of the teeth124aand124bare formed so that a teeth pitch will be P in the extending direction of the rail140. Each of permanent magnets154aand154bmagnetized in the extending direction of the rail140is contained between the teeth124aand124b. Accordingly, the magnet pitch of the permanent magnets154aand the permanent magnets154bis also P. Since each of the permanent magnets154aand154bis contained between the teeth124aand124b, at the forward ends of the teeth row120, the permanent magnets154aand154band magnetic bodies126aand126bare alternately disposed in the extending direction of the rail40.

The teeth row120includes the above-described magnet row152, which is magnetized in the extending direction of the rail140. The magnet row152aligns the magnetic flux which will pass through the teeth row120. Due to the function of the magnet row152, a magnetic flux passes through the teeth row120in the state in which most of the magnetic lines of force are aligned, thereby reducing a leakage flux. In the magnet row152, the same polarity (N pole) faces of adjacent permanent magnets154aoppose each other with a magnetic body126atherebetween in the extending direction of the rail140. Moreover, the same polarity (S pole) faces of adjacent permanent magnets154boppose each other with a magnetic body126btherebetween in the extending direction of the rail40. Concerning the magnetization directions of the permanent magnets154aand154bof the magnet row152, the heads of the arrows indicate the N pole, while the tails of the arrows indicate the S pole. Accordingly, a magnetic body126ais disposed between two permanent magnets154awith their N pole faces opposing each other, while a magnetic body126bis disposed between two permanent magnets154bwith their S pole faces opposing each other.

At the forward ends of the teeth row120, the magnetic bodies126a, each being sandwiched between the N-pole faces of the permanent magnets154a, and the magnetic bodies126b, each being sandwiched between the S-pole faces of the permanent magnets154b, are alternately disposed in the extending direction of the rail140. Accordingly, at the forward ends of the teeth row120, magnetic poles, that is, the S pole and the N pole which are alternately disposed in the teeth row120, are formed.

InFIG. 4, the teeth row120has a symmetrical arrangement on the right and left sides with respect to the magnet rotor110by way of example. However, the teeth row120is not restricted to this arrangement, and may have an asymmetrical arrangement on the right and left sides.

InFIG. 4, the teeth row120is formed all along the magnet rotor110by way of example. However, the teeth row120may be formed only on part of the periphery of the magnet rotor110as long as the number of teeth124aand124bis equally assigned to magnetic poles having different polarities of the magnet rotor110, which will be discussed later in a fourth embodiment.

As in the magnet rotor110, the teeth row120is formed by punching a magnetic body, such as an electromagnetic steel sheet, silicon steel, carbon steel, electromagnetic stainless steel, a dust core, or an amorphous magnetic core, by using a die.

The rail140allows a magnetic flux flowing from the magnet row112of the magnet rotor110to pass through the teeth row120toward the rail140via the magnetic bodies126aof the teeth row120. The rail140also allows a magnetic flux to pass through the rail140toward the magnet row112of the magnet rotor110via the magnetic bodies126aand126b. In the rail140, magnetic teeth142having a pitch T are formed in the extending direction thereof. The magnetic teeth142receive almost all the magnetic lines of force forming a magnetic flux passing through the magnetic bodies126aof the teeth row120.

The teeth pitch T of the magnetic teeth142provided in the rail140is set by considering the number Mp of teeth assigned to each pole of the magnet rotor110and the magnet pitch P of the magnet row152so that, when the magnet rotor110is rotated, the rail140can be moved, or when the rail140is moved, the magnet rotor110can be rotated. More specifically, the magnetic teeth142having the teeth pitch T which satisfies the relationship expressed by equation (3) is formed:
T=(2·P)+k·(2·P/Mp) (k=±1)  (3)
where P denotes the magnet pitch of the magnet row152, and Mp denotes the number of teeth assigned to each pole of the magnet rotor110.

InFIG. 4, the number Mp of teeth assigned to each pole of the magnet rotor110is 24, as discussed above. Accordingly, when k is −1, the teeth pitch T of the magnetic teeth142to be formed in the rail140is calculated as (P·23/12) from equation (3), and when k is +1, the teeth pitch T of the magnetic teeth142to be formed in the rail140is calculated as (P·25/12) from equation (3). In the rotational-linear motion converter160shown inFIG. 4, the magnetic teeth142having a teeth pitch T of (P·23/12) is formed in the rail140.

Recessed portions are formed between the magnetic teeth142. In this case, when the drive head130or the rail140is moved, a vortex flows within the recessed portions, thereby producing air resistance. Accordingly, in order to reduce air resistance, it is desirable to fill the recessed portions with a non-magnetic material, such as an adhesive or a resin filler.

As in the magnet rotor110and the teeth row120, the rail140is formed by punching a magnetic body, such as an electromagnetic steel sheet, silicon steel, carbon steel, electromagnetic stainless steel, a dust core, or an amorphous magnetic core, by using a die.

(Formation of Closed Magnetic Field)

A description will first be given, with reference toFIG. 5, of a closed magnetic field H formed in the rotational-linear motion converter160shown inFIG. 4. The arrows shown inFIG. 5indicate magnetic lines of force, and the heads of the arrows indicate the directions of magnetic lines of force.

As shown inFIG. 5, within the magnet rotor110, a magnetic flux φ flowing from the permanent magnet114ato the permanent magnet114bis distributed such that it divides the cylinder of the magnet rotor110into two portions. The magnetic flux φ flowing from the permanent magnet114bis directed toward the magnetic teeth142of the rail140via the teeth124aand124bof the teeth row120assigned to the permanent magnet114b. The magnetic flux φ entering the rail140flows to the magnetic teeth142which oppose the teeth124aand124bassigned to the permanent magnet114ain the state in which the magnetic flux φ is aligned. Then, the magnetic flux φ passing through the rail140flows to the permanent magnet114aof the magnet rotor110through the teeth124aand124bassigned to the permanent magnet114a. In this manner, a closed magnetic field H looping within the magnet rotor110, the teeth row120, and the rail140is formed.

As viewed from the position of the rotational-linear motion converter160shown inFIG. 5, the teeth124aand124bon the upper half of the teeth row120are assigned to the permanent magnet114a, while the teeth124aand124bon the lower half of the teeth row120are assigned to the permanent magnet114b. Accordingly, the closed magnetic field H is divided to a closed magnetic field group flowing counterclockwise and a closed magnetic field group flowing clockwise on the right and left sides, respectively. However, depending on the rotation position of the magnet rotor110, teeth124aand124bassigned to the permanent magnets114aand114bare changed. Thus, teeth124aand124bforming the closed magnetic field group flowing clockwise and teeth124aand124bforming the closed magnetic field group flowing counterclockwise are not uniquely determined.

The number of magnetic lines of force forming the magnetic flux φ passing through the teeth124aand124band the flowing direction thereof are changed in accordance with the rotation position of the magnet rotor110. Then, when the number of magnetic lines of force and the flowing direction thereof are changed, the closed magnetic field H looping within the magnet rotor110, the teeth row120, and the rail140is also changed. When the closed magnetic field H is changed, a restoration force of a magnetic field acts on the closed magnetic field H so as to maintain the balance of the closed magnetic field H. This restoration force of a magnetic field serves as a thrust to the rail140in the horizontal direction, thereby implementing relative displacement motion between the rail140and the drive head130. Accordingly, rotational motion of the magnet rotor110can be converted into linear motion of the rail140or the drive head130. The relationship between the rotation position of the magnet rotor110and the flow of the magnetic flux φ will be described in detail in the eighth embodiment, which will be discussed later.

The flow of the magnetic flux φ between the teeth row120and the rail140will be discussed below more specifically.

There are two paths via which the magnetic flux φ directing from the permanent magnet114bof the magnet rotor10to the rail140passes through the magnetic bodies126aat the forward ends of the teeth row120.

In one path, the magnetic flux φ first enters the permanent magnets154afrom the teeth row120and is then directed by the permanent magnets154afrom the magnetic bodies126ato the magnetic teeth142of the rail140. This path will be referred to as a “first path”. In the other path, the magnetic flux φ directly enters the magnetic bodies126afrom the teeth row120and then flows to the magnetic teeth142of the rail140. This path will be referred to as a “second path”. A magnetic flux φ1reaches the magnetic teeth142of the rail140via the first path. A magnetic flux φ2reaches the magnetic teeth142of the rail140via the second path.

Each of the magnetic bodies126aof the teeth row120is sandwiched between two permanent magnets154awith their N pole faces opposing each other in the extending direction of the rail140. Each of the magnetic bodies126bof the rail140is sandwiched between two permanent magnets154bwith their S pole faces opposing each other in the extending direction of the rail140. Accordingly, the magnetic flux φ1can be directed from the permanent magnet114bto the magnetic bodies126a. The magnetic flux φ2, which would be possible to be a leakage flux which enters the magnetic body126bfrom the permanent magnet114band reaches the magnetic teeth142of the rail140, can be forcefully directed to the magnetic body126adue to a magnetic force of the permanent magnet154b.

In this manner, the magnet row152aligns the magnetic flux φ1and the magnetic flux φ2which will pass through the teeth row120toward the magnetic bodies126a. In this case, the magnet row152causes the magnetic flux φ1and the magnetic flux φ2to pass through the teeth row120such that most of the magnetic lines of force are aligned toward the magnetic bodies126a, thereby substantially eliminating a leakage flux. As a result, the magnetic flux φ1and the magnetic flux φ2can be effectively converted into a thrust.

In the rail140, a receiving area A are formed in which the magnetic flux φ1and the magnetic flux φ2are received from the permanent magnet114bvia the teeth124aand124bassigned to the permanent magnet114b. In the rail140, transfer areas B from which the magnetic flux φ1and the magnetic flux φ2will be transferred to the permanent magnet114avia the teeth124aand124bassigned to the permanent magnet114aare also formed. Within the rail140, the magnetic flux φ1and the magnetic flux φ2are converged to a magnetic flux φ3, which then flows from the receiving area A to the transfer areas B. InFIG. 5, the central portion of the rail140serves as the receiving area A for receiving the magnetic flux φ1and the magnetic flux φ2, while both side portions of the rail140serve as the transfer areas B for transferring the magnetic flux φ1and the magnetic flux φ2. Thus, the magnetic flux φ3within the rail140is distributed such that it is divided into two portions on the right and left sides from the central portion to the side portions of the rail140. There are two paths via which the magnetic flux φ3, which will be directed to the permanent magnet114aof the magnet rotor110from the rail140, passes through the magnetic bodies126aand126bat the forward ends of the teeth row120.

In one path, the magnetic flux φ first enters the permanent magnets154afrom the magnetic teeth142and is directed by the permanent magnets154afrom the magnetic bodies126ato the permanent magnet114a. This path will be referred to as a “third path”. In the other path, the magnetic flux φ directly enters the magnetic bodies126bfrom the magnetic teeth142and reaches the permanent magnet114a. This path will be referred to as a “fourth path”. The magnetic flux φ1reaches the permanent magnet114aof the magnet rotor110via the third path. The magnetic flux φ2reaches the permanent magnet114aof the magnet rotor110via the fourth path. In the adjacent teeth124aand124bpositioned at both sides of the boundary between the permanent magnets114aand114bof the magnet row112, a loop magnetic flux φL which does not pass through the rail140is formed by a magnetic force of the permanent magnets154aand154b.

In this manner, the magnet row152aligns the magnetic flux φ transferring between the drive head130and the rail140toward the magnetic bodies126aand126b. In this case, the magnet row152is capable of aligning most of the magnetic lines of force forming the magnetic flux φ toward the magnetic bodies126aand126b, thereby substantially eliminating a leakage flux. As a result, the magnetic flux φ can be effectively converted into a thrust.

As discussed above, in the rotational-linear motion converter160of the second embodiment, due to the function of the magnet row152, a closed magnetic flux is effectively directed toward the magnetic bodies126aand126b, thereby effectively reducing a leakage flux between the drive head130and the rail140. Additionally, a magnetic coupling force between the drive head130and the rail140can be enhanced, thereby making it possible to increase the permissible thrust. Since a closed magnetic flux can be used effectively, the size of the drive head130can be reduced. Thus, a large permissible thrust can be implemented while maintaining a small size of the drive head130. Transferring of a magnetic flux φ between the drive head130and the rail140is performed via the teeth row120produced by die-punching. Accordingly, high positioning precision can be achieved when performing relative displacement motion between the drive head130and the rail140without depending on the magnetization precision of the permanent magnets114aand114b.

(Principle of Acceleration and Reduction of Velocity)

A description will now be given of how the rail140is moved when the magnet rotor110is rotated in the state in which a closed magnetic flux is formed in the magnet rotor110, the teeth row120, and the rail140, as shown inFIG. 5.

It is now assumed that:the number of poles of the magnet rotor110is M (M is an even number);the diameter of the magnet rotor110is D;the circle ratio (pi) is π;the teeth pitch of the magnet teeth142of the rail140is T;the coefficient k is 1 or −1;the rotational velocity of the magnet rotor110is F;the peripheral velocity of the magnet rotor110is Vr; andthe motion velocity of the rail140is Vt.

In this case, the peripheral velocity Vr of the magnet rotor110can be expressed by Vr=F·π·D, and the motion velocity Vt of the rail140can be expressed by Vt=−k·F·M·T/2 (k=±1).

Accordingly, the relationship between the peripheral velocity Vr of the magnet rotor110and the motion velocity Vt of the rail140can be expressed by equation (4).
Vt/Vr=(−k·M·T/2)/(π·D) (k=±1)  (4)

That is, when the magnet rotor110rotates through one revolution, the rail140is moved by M·T/2. Since the magnet rotor110is supported within the internal space of the drive head130, the peripheral velocity Vr of the magnet rotor110also indicates the motion velocity of the drive head130.

Equation (4) shows that there is a difference between the peripheral velocity Vr of the magnet rotor110and the motion velocity Vt of the rail140and that the velocity can be accelerated and reduced between the drive head130and the rail140. If the sign of the peripheral velocity Vr of the magnet rotor110and the sign of the motion velocity Vt of the rail140are opposite, the rail140is moved in an opposite direction, as viewed from the magnet rotor110.

In the case of the rotational-linear motion converter160of the second embodiment, the number M of poles of the magnet rotor110is two, and the coefficient k is −1. Accordingly, by substituting M=2 and k=−1 into equation (4), the following equation is obtained.
Vt/Vr=T/(π·D)

Thus, if the drive head130is fixed so that it will not be movable, when the magnet rotor110is rotated through one revolution, the rail140is moved by T. The thin black arrow and the thick black arrow inFIG. 6indicate the rotating direction of the magnet rotor110and the moving direction of the rail140, respectively.

The configuration and the operation of the rotational-linear motion converter160of the second embodiment have been discussed above. As described above, when the magnet rotor110is rotated or when the rail140is moved, the closed magnetic field H formed between the drive head130and the rail140is disturbed, and in order to maintain the balance of the closed magnetic field H, the drive head30and the rail40perform relative displacement motion. Through the operation for maintaining the balance of the closed magnetic field H, the relationship between the velocity of the drive head130and that of the rail140can be obtained, as expressed by equation (4).

As described above, the rotational-linear motion converter160of the second embodiment includes the magnet row152having the permanent magnets154aand154bwhich are magnetized in the extending direction of the rail140and which are formed between the forward ends of the teeth row120. Since the magnet row152aligns the magnetic flux φ which will pass through the teeth row120, a leakage flux can be reduced to a minimal level, and a large permissible thrust and a wide-range acceleration reduction velocity ratio can be implemented.

A rotational-linear motion converter260according to a third embodiment will be described below with reference to a schematic diagram ofFIG. 7. The thin black arrow and the thick black arrow inFIG. 7indicate the rotating direction of a magnet rotor210and the moving direction of a rail240, respectively.

As shown inFIG. 7, the rotational-linear motion converter260is different from the rotational-linear motion converter60of the first embodiment in that a teeth row220is not formed all along the periphery of the magnet rotor210, but is formed only on part of the periphery of the magnet rotor210.

The rotational-linear motion converter260may be considered as a compact size of the rotational-linear motion converter60of the first embodiment.

The rotational-linear motion converter260includes a drive head230and a rail240. The drive head230includes a magnet rotor210and a teeth row220. The magnet rotor210is concentrically disposed within the drive head230so that a gap215may be formed between the magnet rotor210and a cylindrical internal space of the drive head230. The teeth row220extends like octopus' tentacles (legs) from the internal space of the drive head230toward the rail240so that a gap225may be formed between the teeth row220and the rail240. The drive head230and the rail240are disposed such that the teeth row220of the drive head230opposes the rail240, and the drive head230and the rail240are relatively movable in the extending direction of the rail240. The magnet rotor210is rotatably supported within the drive head230.

The magnet rotor210includes a magnet row212constituted by four sector-shaped permanent magnets214athrough214dwhich are magnetized in the radial direction. The permanent magnets214aand214care disposed such that they oppose each other, and are magnetized as the N pole at the inner peripheries thereof and as the S pole at the outer peripheries thereof. The permanent magnets214band214dare disposed such that they oppose each other, and are magnetized as the S pole at the inner peripheries thereof and as the N pole at the outer peripheries thereof. Accordingly, the magnet rotor210has four poles, more specifically, the S pole on the upper and lower sides and the N pole on the right and left sides, as viewed from the position of the magnet rotor210shown inFIG. 7. The S pole and the N pole are alternately disposed in the peripheral direction of the magnet rotor210. The configurations of the other parts of the magnet rotor210are the same as those of the first embodiment.

In the teeth row220, teeth224aand224bare formed only on part of the periphery of the magnet rotor210such that the number of teeth224aand224bassigned to the N pole of the magnet rotor210and that assigned to the S pole of the magnet rotor210are the same. In the third embodiment, the teeth224aand224b, six being assigned to each pole, are disposed on part of the periphery of the magnet rotor210positioned closer to the rail240so as to decrease the lengths of the teeth224aand224b. As the teeth224aand224bare shorter, magnetic resistance within the teeth224aand224balso becomes smaller. The configurations of the other parts of the teeth row220are the same as those of the first embodiment.

The rail240includes a magnet row252having a magnet pitch P and magnetized in the extending direction of the rail240. The magnet row252aligns the magnetic flux which will pass through the rail240. Due to the function of the magnet row252, the magnetic flux passes through the rail240in the state in which most of the magnetic lines of force are aligned, thereby reducing a leakage flux. In the magnet row252, the same polarity (N pole) faces of adjacent permanent magnets254aoppose each other with a magnetic body244atherebetween in the extending direction of the magnet row252. Moreover, the same polarity (S pole) faces of adjacent permanent magnets254boppose each other with a magnetic body244btherebetween in the extending direction of the magnet row252. The configurations of the other parts of the rail240are the same as those of the first embodiment.

A closed magnetic field H formed in the rotational-linear motion converter260is not shown. As in the rotational-linear motion converter60of the first embodiment, a closed magnetic field H looping in the magnet rotor210, the teeth row220, and the rail240is formed. In the third embodiment, since the teeth row220is formed on part of the periphery of the magnet rotor210positioned closer to the rail240, the magnetic flux within the magnet rotor210also passes through part of the periphery thereof positioned closer to the rail240.

The number of magnetic lines of force forming the closed magnetic field H in the rotational-linear motion converter260is smaller than that of the rotational-linear motion converter60of the first embodiment. However, the teeth224aand224bforming the teeth row220are shorter, thereby making it possible to reduce the size of the rotational-linear motion converter260. Thus, a large permissible thrust can be provided with the small rotational-linear motion converter260.

The principle of the acceleration and reduction of the velocity of the rotational-linear motion converter260is the same as that of the rotational-linear motion converter60of the first embodiment.

As in the rotational-linear motion converter60of the first embodiment, in the rotational-linear motion converter260, the magnet row252magnetized in the extending direction of the rail240aligns the magnetic flux which will pass through the rail240. Thus, a leakage flux can be reduced to a minimal level, and a large permissible thrust and a wide-range acceleration reduction velocity ratio can be implemented.

Additionally, in the rotational-linear motion converter260, a closed magnetic field is formed by using the teeth row220only having short teeth224aand224b. Accordingly, a large permissible thrust can be provided with the small rotational-linear motion converter260.

A rotational-linear motion converter360according to a fourth embodiment will be described below with reference to a schematic diagram ofFIG. 8. The thin black arrow and the thick black arrow inFIG. 8indicate the rotating direction of a magnet rotor310and the moving direction of a rail340, respectively.

As shown inFIG. 8, the rotational-linear motion converter360is different from the rotational-linear motion converter160of the second embodiment in that a teeth row320is not formed all along the periphery of the magnet rotor310, but is formed only on part of the periphery of the magnet rotor310.

The rotational-linear motion converter360may be considered as a compact size of the rotational-linear motion converter160of the second embodiment.

The rotational-linear motion converter360is realized by incorporating a technical concept of the rotational-linear motion converter260of the third embodiment and by applying such a technical concept to the rotational-linear motion converter160of the second embodiment.

The rotational-linear motion converter360includes a drive head330and a rail340. The drive head330includes a magnet rotor310and a teeth row320. The magnet rotor310is concentrically disposed within the drive head330so that a gap315may be formed between the magnet rotor310and a cylindrical internal space of the drive head330. The teeth row320extends like octopus' tentacles (legs) from the internal space of the drive head330toward the rail340so that a gap325may be formed between the teeth row320and the rail340. The drive head330and the rail340are disposed such that the teeth row320of the drive head330opposes the rail340, and the drive head330and the rail340are relatively movable in the extending direction of the rail340. The magnet rotor310is rotatably supported within the drive head330.

The magnet rotor310includes a magnet row312constituted by four sector-shaped permanent magnets314athrough314dwhich are magnetized in the radial direction. The permanent magnets314aand314care disposed such that they oppose each other, and are magnetized as the N pole at the inner peripheries thereof and as the S pole at the outer peripheries thereof. The permanent magnets314band314dare disposed such that they oppose each other, and are magnetized as the S pole at the inner peripheries thereof and as the N pole at the outer peripheries thereof. Accordingly, the magnet rotor310has four poles, more specifically, the S pole on the upper and lower sides and the N pole on the right and left sides, as viewed from the position of the magnet rotor310shown inFIG. 8. The S pole and the N pole are alternately disposed in the peripheral direction of the magnet rotor310. The configurations of the other parts of the magnet rotor310are the same as those of the second embodiment.

In the teeth row320, teeth324aand324bare formed only on part of the periphery of the magnet rotor310such that the number of teeth324aand324bassigned to the N pole of the magnet rotor310and that assigned to the S pole of the magnet rotor310are the same. In the fourth embodiment, the teeth324aand324b, thirteen being assigned to each pole, are disposed on part of the periphery of the magnet rotor310positioned closer to the rail340so as to decrease the lengths of the teeth324aand324b. As the teeth324aand324bare shorter, magnetic resistance within the teeth324aand324balso becomes smaller.

The teeth row320includes a magnet row352having a magnet pitch P and magnetized in the extending direction of the rail340. The magnet row352aligns the magnetic flux which will pass through the teeth row320. Due to the function of the magnet row352, the magnetic flux passes through the teeth row320in the state in which most of the magnetic lines of force are aligned, thereby reducing a leakage flux. In the magnet row352, the same polarity (N pole) faces of adjacent permanent magnets354aoppose each other with a magnetic body326atherebetween in the extending direction of the rail340. Moreover, the same polarity (S pole) faces of adjacent permanent magnets354boppose each other with a magnetic body326btherebetween in the extending direction of the rail340. The configurations of the other parts of the teeth row320are the same as those of the second embodiment.

The rail340allows a magnetic flux flowing from the magnet row312of the magnet rotor310to pass through the teeth row320toward the rail340via the magnetic bodies326aof the teeth row320. The rail340also allows a magnetic flux to pass through the rail340toward the magnet row312of the magnet rotor310via the magnetic bodies326aand326b. In the rail340, magnetic teeth342having a pitch T are formed in the extending direction thereof. The magnetic teeth342receive almost all the magnetic lines of force forming a magnetic flux passing through the magnetic bodies326aof the teeth row320. The configurations of the other parts of the rail340are the same as those of the second embodiment.

A closed magnetic field H formed in the rotational-linear motion converter360is not shown. As in the rotational-linear motion converter160of the second embodiment, a closed magnetic field H looping in the magnet rotor310, the teeth row320, and the rail340is formed. In the fourth embodiment, since the teeth row320is formed on part of the periphery of the magnet rotor310positioned closer to the rail340, the magnetic flux within the magnet rotor310also passes through part of the periphery thereof positioned closer to the rail340.

The number of magnetic lines of force forming the closed magnetic field H in the rotational-linear motion converter360is smaller than that of the rotational-linear motion converter160of the second embodiment. However, the teeth324aand324bforming the teeth row320are shorter, thereby making it possible to reduce the size of the rotational-linear motion converter360. Thus, a large permissible thrust can be provided with the small rotational-linear motion converter360.

The principle of the acceleration and reduction of the velocity of the rotational-linear motion converter360is the same as that of the rotational-linear motion converter160of the second embodiment.

As in the rotational-linear motion converter160of the second embodiment, in the rotational-linear motion converter360, the magnet row352magnetized in the extending direction of the rail340aligns the magnetic flux which will pass through the teeth row320. Thus, a leakage flux can be reduced to a minimal level, and a large permissible thrust and a wide-range acceleration reduction velocity ratio can be implemented.

Additionally, in the rotational-linear motion converter360, a closed magnetic field is formed by using the teeth row320only having short teeth324aand324b. Accordingly, a large permissible thrust can be provided with the small rotational-linear motion converter360.

A rotational-linear motion converter460according to a fifth embodiment will be described below with reference to a schematic diagram ofFIG. 9. The thin black arrows and the thick black arrows inFIG. 9indicate the rotating directions of a magnet rotor410and the moving directions of rails440aand440b, respectively.

As shown inFIG. 9, the rotational-linear motion converter460may be considered as two rotational-linear motion converters260of the third embodiment having the same configuration which use the same magnet rotor210and which integrates the two drive heads230into a single drive head. Accordingly, in the rotational-linear motion converter460, the teeth row420has a symmetrical arrangement on the upper and lower sides with respect to the magnet rotor410.

The rotational-linear motion converter460includes a drive head430and rails440aand440b. The drive head430includes a magnet rotor410and a teeth row420. The magnet rotor410is concentrically disposed within the drive head430so that a gap415may be formed between the magnet rotor410and a cylindrical internal space of the drive head430. The teeth row420is constituted by two teeth rows420aand420bobtained by dividing the teeth row420on the upper and lower sides with respect to the magnet rotor410. The teeth row420aextends like octopus' tentacles (legs) from the internal space of the drive head430toward the rail440aso that a gap425amay be formed between the teeth row420aand the rail440a. The teeth row420bextends like octopus' tentacles (legs) from the internal space of the drive head430toward the rail440bso that a gap425bmay be formed between the teeth row420band the rail440b. The rails440band440aare disposed above and below the drive head430such that they are in parallel with each other. The drive head430and the rail440aare disposed such that the teeth row420aof the drive head430opposes the rail440a, and the drive head430and the rail440aare relatively movable in the extending direction of the rail440a. The drive head430and the rail440bare disposed such that the teeth row420bof the drive head430opposes the rail440b, and the drive head430and the rail440bare relatively movable in the extending direction of the rail440b. In the fifth embodiment, the drive head430is fixed so that it will not be movable, and the magnet rotor410is rotatably supported within the drive head430.

The configurations of the magnet rotor410, the teeth rows420aand420b, and the rails440aand440bare the same as those of the magnet rotor210, the teeth row220, and the rail240, respectively, of the third embodiment.

A closed magnetic field H formed in the rotational-linear motion converter460is not shown. In practice, the closed magnetic field H is divided into a closed magnetic field H1looping within the magnet rotor410, the teeth row420a, and the rail440aand a closed magnetic field H2looping within the magnet rotor410, the teeth row420b, and the rail440b. The divided closed magnetic fields H1and H2are independent of each other, and the mixing of the magnetic flux does not occur. Accordingly, each of the closed magnetic fields H1and H2may be considered to be substantially the same as the closed magnetic field formed in the rotational-linear motion converter260of the third embodiment. Thus, the principles of the operation of the rotational-linear motion converter460and the acceleration and reduction of the velocity of the rotational-linear motion converter460are the same as those of the rotational-linear motion converter260of the third embodiment.

In the rotational-linear motion converter460, the relationship between the relative displacement motion of the rail440ato the drive head430and that of the rail440bto the drive head430may be considered to be substantially the same as that obtained when two rotational-linear motion converters260of the third embodiment having the same configuration independently perform rotational-linear motion conversion. Accordingly, when the drive head430is fixed so that it will not be movable, the relative displacement motion of the rail440ato the drive head430and that of the rail440bto the drive head430have the same velocity and the opposite directions.

As in the rotational-linear motion converter60of the first embodiment, in the rotational-linear motion converter460, magnet rows magnetized in the extending direction of the rails440aand440balign the magnetic flux which will pass through the rails440aand440b, respectively. Thus, a leakage flux can be reduced to a minimal level, and a large permissible thrust and a wide-range acceleration reduction velocity ratio can be implemented.

Additionally, in the rotational-linear motion converter460, the drive head430has a symmetrical arrangement on the upper and lower sides, and also, the magnet pitch P of the magnet row of the rail440band that of the rail440aabove and below the drive head430are the same. Accordingly, it is possible to shift the two rails440aand440bwith respect to the drive head430at the same time and at the same velocity in opposite directions. Thus, the rotational-linear motion converter460of the fifth embodiment is applicable to, for example, an opening/closing mechanism that is moved to the right and left sides by a certain distance in opposite directions.

A rotational-linear motion converter560according to a sixth embodiment will be described below with reference to a schematic diagram ofFIG. 10. The thin black arrow and the thick black arrows inFIG. 10indicate the rotating direction of a magnet rotor510and the moving directions of rails540aand540b, respectively.

As shown inFIG. 10, the rotational-linear motion converter560may be considered as two rotational-linear motion converters360of the fourth embodiment having the same configuration which use the same magnet rotor310and which integrates the two drive heads330into a single drive head. Accordingly, in the rotational-linear motion converter560, a teeth row520has a symmetrical arrangement on the upper and lower sides with respect to the magnet rotor510.

The rotational-linear motion converter560is realized by incorporating a technical concept of the rotational-linear motion converter460of the fifth embodiment and by applying such a technical concept to the rotational-linear motion converter360of the fourth embodiment.

The rotational-linear motion converter560includes a drive head530and rails540aand540b. The drive head530includes a magnet rotor510and a teeth row520. The magnet rotor510is concentrically disposed within the drive head530so that a gap515may be formed between the magnet rotor510and a cylindrical internal space of the drive head530. The teeth row520is constituted by two teeth rows520aand520bobtained by dividing the teeth row520horizontally, that is, on the upper and lower sides, with respect to the magnet rotor510. The teeth row520aextends like octopus' tentacles (legs) from the internal space of the drive head530toward the rail540aso that a gap525amay be formed between the teeth row520aand the rail540a. The teeth row520bextends like octopus' tentacles (legs) from the internal space of the drive head530toward the rail540bso that a gap525bmay be formed between the teeth row520band the rail540b. The rails540band540aare disposed above and below the drive head530such that they are in parallel with each other. The drive head530and the rail540aare disposed such that the teeth row520aof the drive head530opposes the rail540a, and the drive head530and the rail540aare relatively movable in the extending direction of the rail540a. The drive head530and the rail540bare disposed such that the teeth row520bof the drive head530opposes the rail540b, and the drive head530and the rail540bare relatively movable in the extending direction of the rail540b. In the sixth embodiment, the drive head530is fixed so that it will not be movable, and the magnet rotor510is rotatably supported within the drive head530.

The configurations of the magnet rotor510, the teeth rows520aand520b, and the rails540aand540bare the same as those of the magnet rotor310, the teeth row320, and the rail340, respectively, of the fourth embodiment.

A closed magnetic field H formed in the rotational-linear motion converter560is not shown. In practice, the closed magnetic field H is divided into a closed magnetic field H1looping within the magnet rotor510, the teeth row520a, and the rail540aand a closed magnetic field H2looping within the magnet rotor510, the teeth row520b, and the rail540b. The divided closed magnetic fields H1and H2are independent of each other, and the mixing of the magnetic flux does not occur. Accordingly, each of the closed magnetic fields H1and H2may be considered to be substantially the same as the closed magnetic field formed in the rotational-linear motion converter360of the fourth embodiment. Thus, the principles of the operation of the rotational-linear motion converter560and the acceleration and reduction of the velocity of the rotational-linear motion converter560are the same as those of the rotational-linear motion converter360of the fourth embodiment.

In the rotational-linear motion converter560, the relationship between the relative displacement motion of the rail540ato the drive head530and that of the rail540bto the drive head530may be considered to be substantially the same as that obtained when two rotational-linear motion converters360of the fourth embodiment having the same configuration independently perform rotational-linear motion conversion. Accordingly, when the drive head530is fixed so that it will not be movable, the relative displacement motion of the rail540ato the drive head530and that of the rail540bto the drive head530have the same velocity and the opposite directions.

As in the rotational-linear motion converter160of the second embodiment, in the rotational-linear motion converter560, magnet rows magnetized in the extending direction of the rails540aand540balign the magnetic flux which will pass through the teeth rows520aand520b, respectively. Thus, a leakage flux can be reduced to a minimal level, and a large permissible thrust and a wide-range acceleration reduction velocity ratio can be implemented.

Additionally, in the rotational-linear motion converter560, the drive head530has a symmetrical arrangement on the upper and lower sides, and also, the magnet pitch T of the rail540band that of the rail540aabove and below the drive head530are the same. Accordingly, it is possible to shift the two rails540aand540bwith respect to the drive head530at the same time and at the same velocity in opposite directions. Thus, the rotational-linear motion converter560of the sixth embodiment is applicable to, for example, an opening/closing mechanism that is moved to the right and left sides by a certain distance in opposite directions.

A rotational-linear motion converter660according to a seventh embodiment will be described below with reference to a schematic diagram ofFIG. 11. The thin black arrows and the thick black arrows inFIG. 11indicate the rotating directions of a magnet rotor610and the moving directions of rails640aand640b, respectively.

As shown inFIG. 11, the rotational-linear motion converter660may be considered as two rotational-linear motion converters260of the third embodiment having different configurations which use the same magnet rotor210and which integrates the two drive heads230into a single drive head.

The rotational-linear motion converter660is different from the rotational-linear motion converter460of the fifth embodiment in that a teeth row620has an asymmetrical arrangement on the upper and lower sides with respect to the magnet rotor610.

The rotational-linear motion converter660includes a drive head630and rails640aand640b. The drive head630includes a magnet rotor610and a teeth row620. The magnet rotor610is concentrically disposed within the drive head630so that a gap615may be formed between the magnet rotor610and a cylindrical internal space of the drive head630. The teeth row620is constituted by two teeth rows620aand620b. The teeth row620aextends like octopus' tentacles (legs) from the internal space of the drive head630toward the rail640aso that a gap625amay be formed between the teeth row620aand the rail640a. The teeth row620bextends like octopus' tentacles (legs) from the internal space of the drive head630toward the rail640bso that a gap625bmay be formed between the teeth row620band the rail640b. The rails640band640aare disposed above and below the drive head630such that they are in parallel with each other. The drive head630and the rail640aare disposed such that the teeth row620aof the drive head630opposes the rail640a, and the drive head630and the rail640aare relatively movable in the extending direction of the rail640a. The drive head630and the rail640bare disposed such that the teeth row620bof the drive head630opposes the rail640b, and the drive head630and the rail640bare relatively movable in the extending direction of the rail640b. The magnet rotor610is rotatably supported within the drive head630.

The configurations of the magnet rotor610and the rails640aand640bare the same as those of the magnet rotor210and the rail240, respectively, of the third embodiment.

The teeth row620aincludes teeth624aand624bhaving different shapes and lengths. The number Mta of teeth624aand624bforming the teeth row620aassigned to each pole of the lower half of the magnet rotor610is five. The teeth row620bincludes teeth624aand624bhaving different shapes and lengths. The number Mtb of teeth624aand624bforming the teeth row620bassigned to each pole of the upper half of the magnet rotor610is six.

The teeth pitch Ta of the teeth row620aand the teeth pitch Tb of the teeth row620bare determined so that they will satisfy the above-described equation (1) and also satisfy the following equation (5):
Tb<2·P<Ta(Tb<Ta)  (5)
where P denotes the magnet pitch of magnet rows652aand652b.

InFIG. 11, the number Mta of teeth624aand624bforming the teeth row620aassigned to each pole of the lower half of the magnet rotor610is five and the number Mtb of teeth624aand624bforming the teeth row620bassigned to each pole of the upper half of the magnet rotor610is six, as discussed above. Accordingly, concerning the teeth row620a, kis set to be +1 in equation (1), and the teeth pitch Ta is calculated as (P·11/5). Concerning the teeth row620b, kis set to be −1 in equation (1), and the teeth pitch Tb is calculated as (P·11/6). The configurations of the other parts of the teeth rows620aand620bare the same as those of the third embodiment.

A closed magnetic field H formed in the rotational-linear motion converter660is not shown. In practice, the closed magnetic field H is divided into a closed magnetic field H1looping within the magnet rotor610, the teeth row620a, and the rail640aand a closed magnetic field H2looping within the magnet rotor610, the teeth row620b, and the rail640b. The divided closed magnetic fields H1and H2are independent of each other, and the mixing of the magnetic flux does not occur. Accordingly, each of the closed magnetic fields H1and H2may be considered to be substantially the same as the closed magnetic field formed in the rotational-linear motion converter260of the third embodiment. Thus, the principle of the operation of the rotational-linear motion converter660is the same as that of the rotational-linear motion converter60of the first embodiment.

In the case of the rotational-linear motion converter660of the seventh embodiment, the relationship between the peripheral velocity Vr of the magnet rotor610and the motion velocity Vm1of the rail640acan be calculated as follows. The number M of poles of the magnet rotor610is four, and the coefficient k is +1. Accordingly, by substituting M=4 and k=+1 into equation (2), the following equation is obtained.
Vm1/Vr=+4·P/(π·D)
The relationship between the peripheral velocity Vr of the magnet rotor610and the motion velocity Vm2of the rail640bcan be calculated as follows. The number M of poles of the magnet rotor610is four, and the coefficient k is −1. Accordingly, by substituting M=4 and k=−1 into equation (2), the following equation is obtained.
Vm2/Vr=−4·P/(π·D)

Thus, if the drive head630is fixed so that it will not be movable, when the magnet rotor610is rotated through one revolution, the rail640amoves by +4·P and the rail640bmoves by −4·P. As viewed from the magnet rotor610, the rails640aand640bmove by the same distance in the same direction. Accordingly, the relative displacement motion of the rail640ato the drive head630and that of the rail640bto the drive head630have the same velocity and the same direction.

If the rails640aand640bare fixed such that they will not be movable, when the magnet rotor610is rotated, the drive head630can relatively move between the rails640aand640bin one direction. In this case, a magnetic attractive force is canceled between the upper and lower faces of the drive head630. Accordingly, a load imposed on the rails640aand640bduring the relative displacement motion of the drive head630is reduced, thereby decreasing the occurrence of friction. As a result, higher positioning precision between the rails640aand640band the drive head630can be implemented.

As in the rotational-linear motion converter60of the first embodiment, in the rotational-linear motion converter660, magnet rows magnetized in the extending direction of the rails640aand640balign the magnetic flux which will pass through the rails640aand640b, respectively. Thus, a leakage flux can be reduced to a minimal level, and a large permissible thrust and a wide-range acceleration reduction velocity ratio can be implemented.

Additionally, in the rotational-linear motion converter660, the teeth pitches Ta and Tb of the teeth rows620aand620bare set so that they can satisfy both of the above-described equations (1) and (5), and the magnet pitch P of the two rails640band640aabove and below the drive head630is the same. Accordingly, it is possible to shift the two rails640aand640brelatively to the drive head630at the same time and at the same velocity in the same direction. Thus, a magnetic attractive force is canceled between the upper and lower faces of the drive head630. Accordingly, a load imposed on the rails640aand640bduring the relative displacement motion to the drive head630is reduced, thereby decreasing the occurrence of friction. As a result, higher positioning precision between the rails640aand640band the drive head630can be implemented.

A rotational-linear motion converter760according to an eighth embodiment will be described below with reference to a schematic diagram ofFIG. 12. The thin black arrow and the thick black arrows inFIG. 12indicate the rotating direction of a magnet rotor710and the moving directions of rails740aand740b, respectively.

As shown inFIG. 12, the rotational-linear motion converter760may be considered as two rotational-linear motion converters360of the fourth embodiment having different configurations which use the same magnet rotor310and which integrates the two drive heads330into a single drive head.

The rotational-linear motion converter760is different from the rotational-linear motion converter560of the sixth embodiment in that a teeth row720has an asymmetrical arrangement on the upper and lower sides with respect to the magnet rotor710.

The rotational-linear motion converter760is realized by incorporating a technical concept of the rotational-linear motion converter660of the seventh embodiment and by applying such a technical concept to the rotational-linear motion converter360of the fourth embodiment.

The rotational-linear motion converter760includes a drive head730and rails740aand740b. The drive head730includes a magnet rotor710and a teeth row720. The magnet rotor710is concentrically disposed within the drive head730so that a gap715may be formed between the magnet rotor710and a cylindrical internal space of the drive head730. The teeth row720is constituted by two teeth rows720aand720b. The teeth row720aextends like octopus' tentacles (legs) from the internal space of the drive head730toward the rail740aso that a gap725amay be formed between the teeth row720aand the rail740a. The teeth row720bextends like octopus' tentacles (legs) from the internal space of the drive head730toward the rail740bso that a gap725bmay be formed between the teeth row720band the rail740b.

The rails740band740aare disposed above and below the drive head730such that they are in parallel with each other. The drive head730and the rail740aare disposed such that the teeth row720aof the drive head730opposes the rail740a, and the drive head730and the rail740aare relatively movable in the extending direction of the rail740a. The drive head730and the rail740bare disposed such that the teeth row720bof the drive head730opposes the rail740b, and the drive head730and the rail740bare relatively movable in the extending direction of the rail740b. The magnet rotor710is rotatably supported within the drive head730.

The configuration of the magnet rotor710is the same as that of the magnet rotor310of the fourth embodiment.

The teeth row720aincludes teeth724aand724bhaving different shapes and lengths. The number Mpa of teeth724aand724bforming the teeth row720aassigned to each pole of the lower half of the magnet rotor710is 13. The teeth row720bincludes teeth724aand724bhaving different shapes and lengths. The number Mpb of teeth724aand724bforming the teeth row720bassigned to each pole of the upper half of the magnet rotor710is 15.

The teeth row720aincludes a magnet row752ahaving a magnet pitch Pa and magnetized in the extending direction of the rail740a. The teeth row720bincludes a magnet row752bhaving a magnet pitch Pb and magnetized in the extending direction of the rail740b. The magnet rows752aand752balign the magnetic flux which will pass through the teeth rows720aand720b, respectively. Due to the functions of the magnet rows752aand752b, the magnetic flux passes through the teeth rows720aand720bin the state in which most of the magnetic lines of force are aligned, thereby reducing a leakage flux. In the magnet rows752aand752b, the same polarity (N pole) faces of adjacent permanent magnets754aoppose each other with a magnetic body726atherebetween in the extending direction of each of the rails740aand740b. Moreover, the same polarity (S pole) faces of adjacent permanent magnets754boppose each other with a magnetic body726btherebetween in the extending direction of each of the rails740aand740b. The configurations of the other parts of the teeth rows720aand720bare the same as those of the second embodiment.

The rail740aallows a magnetic flux flowing from the magnet row712of the magnet rotor710to pass through the teeth row720atoward the rail740avia the magnetic bodies726aof the teeth row720a. The rail740aalso allows a magnetic flux to pass through the rail740atoward the magnet row712of the magnet rotor710via the magnetic bodies726aand726b. In the rail740a, magnetic teeth742ahaving a pitch T are formed in the extending direction thereof. The magnetic teeth742areceive almost all the magnetic lines of force forming a magnetic flux passing through the magnetic bodies726aof the teeth row720a.

The rail740ballows a magnetic flux flowing from the magnet row712of the magnet rotor710to pass through the teeth row720btoward the rail740bvia the magnetic bodies726aof the teeth row720b. The rail740balso allows a magnetic flux to pass through the rail740btoward the magnet row712of the magnet rotor710via the magnetic bodies726aand726b. In the rail740b, magnetic teeth742bhaving a pitch T are formed in the extending direction thereof. The magnetic teeth742breceive almost all the magnetic lines of force forming a magnetic flux passing through the magnetic bodies726aof the teeth row720b.

The teeth pitch T of the magnetic teeth742aand742bprovided in the rails740aand740b, respectively, are determined so that it will satisfy the above-described equation (3) and also satisfy the following equation (6):
2·Pb<T<2·Pa(6)
where Pb and Pa denote the magnet pitches of magnet rows752band752a, respectively.

InFIG. 12, the number Mpa of teeth724aand724bforming the teeth row720aassigned to each pole of the lower half of the magnet rotor710is 13 and the number Mpb of teeth724aand724bforming the teeth row720bassigned to each pole of the upper half of the magnet rotor710is 15, as discussed above. Accordingly, concerning the teeth row720a, kis set to be −1 in equation (3), and the relationship between the teeth pitch T of the magnetic teeth742aand the magnet pitch Pa of the magnet row752ais calculated as T=Pa·24/13. Concerning the teeth row720b, kis set to be +1 in equation (3), and the relationship between the teeth pitch T of the magnetic teeth742band the magnet pitch Pb of the magnet row752bis calculated as T=Pb·32/15. The configurations of the other parts of the rails740aand740bare the same as those of the second embodiment.

A closed magnetic field H formed in the rotational-linear motion converter760is not shown. In practice, the closed magnetic field H is divided into a closed magnetic field H1looping within the magnet rotor710, the teeth row720a, and the rail740aand a closed magnetic field H2looping within the magnet rotor710, the teeth row720b, and the rail740b. The divided closed magnetic fields H1and H2are independent of each other, and the mixing of the magnetic flux does not occur. Accordingly, each of the closed magnetic fields H1and H2may be considered to be substantially the same as the closed magnetic field formed in the rotational-linear motion converter360of the fourth embodiment. Thus, the principle of the operation of the rotational-linear motion converter760is the same as that of the rotational-linear motion converter160of the second embodiment.

In the case of the rotational-linear motion converter760of the eighth embodiment, the relationship between the peripheral velocity Vr of the magnet rotor710and the motion velocity Vt1of the rail740acan be calculated as follows. The number M of poles of the magnet rotor710is four, and the coefficient k is −1. Accordingly, by substituting M=4 and k=−1 into equation (4), the following equation is obtained.
Vt1/Vr=+2·T/(π·D)
The relationship between the peripheral velocity Vr of the magnet rotor710and the motion velocity Vt2of the rail740bcan be calculated as follows. The number M of poles of the magnet rotor710is four, and the coefficient k is +1. Accordingly, by substituting M=4 and k=+1 into equation (4), the following equation is obtained.
Vt2/Vr=−2·T/(π·D)

Thus, if the drive head730is fixed so that it will not be movable, when the magnet rotor710is rotated through one revolution, the rail740amoves by +2·T and the rail740bmoves by −2·T. As viewed from the magnet rotor710, the rails740aand740bmove by the same distance in the same direction. Accordingly, the relative displacement motion of the rail740ato the drive head730and that of the rail740bto the drive head730have the same velocity and the same direction.

If the rails740aand740bare fixed such that they will not be movable, when the magnet rotor710is rotated, the drive head730can relatively move between the rails740aand740bin one direction. In this case, a magnetic attractive force is canceled between the upper and lower faces of the drive head730. Accordingly, a load imposed on the rails740aand740bduring the relative displacement motion of the drive head730is reduced, thereby decreasing the occurrence of friction. As a result, higher positioning precision between the rails740aand740band the drive head730can be implemented.

As in the rotational-linear motion converter160of the second embodiment, in the rotational-linear motion converter760, the magnet rows752aand752bmagnetized in the extending direction of the rails740aand740b, respectively, align the magnetic flux which will pass through the teeth rows720aand720b, respectively. Thus, a leakage flux can be reduced to a minimal level, and a large permissible thrust and a wide-range acceleration reduction velocity ratio can be implemented.

Additionally, in the rotational-linear motion converter760, the teeth pitches of the teeth rows720aand720bare set so that they can satisfy both of the above-described equations (3) and (6), and the magnet pitch T of the magnetic teeth742band742aprovided in the two rails740band740a, respectively, above and below the drive head730is the same. Accordingly, it is possible to shift the two rails740aand740brelatively to the drive head730at the same time and at the same velocity in the same direction. Thus, a magnetic attractive force is canceled between the upper and lower faces of the drive head730. Accordingly, a load imposed on the rails740aand740bduring the relative displacement motion to the drive head730is reduced, thereby decreasing the occurrence of friction. As a result, higher positioning precision between the rails740aand740band the drive head730can be implemented.

A description will now be given, with reference toFIGS. 13 through 17, of a change in the closed magnetic field H in accordance with the rotation position of the magnet rotor710. As shown inFIGS. 13 through 17, as the magnet rotor710is rotated counterclockwise starting from the position shown inFIG. 13from 0° to 180° by 45°, the arrangement of the closed magnetic field H and the flowing direction of the magnetic flux are different in accordance with the rotation position of the magnet rotor710. InFIGS. 13 through 17, a mark Y is shown only for the purpose of indicating a current rotation position of the magnet rotor710, and a reference line I-I is also shown only for the purpose of indicating relative displacement of the rails740aand740b.

FIG. 13illustrates a closed magnetic field formed when the magnet rotor710is positioned at 0°. As viewed from the position of the magnet rotor710shown inFIG. 13, the top and bottom sides of the magnet rotor710are magnetized as the S pole, while the right and left sides of the magnet rotor710are magnetized as the N pole. Accordingly, in the closed magnetic field H1looping within the magnet rotor710, the teeth row720a, and the rail740aand in the closed magnetic field H2looping within the magnet rotor710, the teeth row720b, and the rail740b, the magnetic flux flows in the following manner.

The magnetic flux of the closed magnetic field H1flows from the N pole of the magnet rotor710to the receiving areas of the rail740avia the teeth724aand724bpositioned at both sides of the teeth row720ainFIG. 13. The magnetic flux of the closed magnetic field H1also flows back from the transfer area B of the rail740ato the S pole of the magnet rotor710via the teeth724aand724bpositioned at the central portion of the teeth row720ainFIG. 13.

The magnetic flux of the closed magnetic field H2flows from the N pole of the magnet rotor710to the receiving areas of the rail740bvia the teeth724aand724bpositioned at both sides of the teeth row720binFIG. 13. The magnetic flux of the closed magnetic field H2also flows back from the transfer area B of the rail740bto the S pole of the magnet rotor710via the teeth724aand724bpositioned at the central portion of the teeth row720binFIG. 13.

FIG. 14illustrates a closed magnetic field formed when the magnet rotor710is positioned at 45°. As viewed from the position of the magnet rotor710shown inFIG. 14, the top left and bottom right sides of the magnet rotor710are magnetized as the S pole, while the bottom left and top right sides of the magnet rotor710are magnetized as the N pole. Accordingly, in the closed magnetic field H1looping within the magnet rotor710, the teeth row720a, and the rail740aand in the closed magnetic field H2looping within the magnet rotor710, the teeth row720b, and the rail740b, the magnetic flux flows in the following manner.

The magnetic flux of the closed magnetic field H1flows from the N pole of the magnet rotor710to the receiving area of the rail740avia the teeth724aand724bpositioned at the left half side of the teeth row720ainFIG. 14. The magnetic flux of the closed magnetic field H1also flows back from the transfer area B of the rail740ato the S pole of the magnet rotor710via the teeth724aand724bpositioned at the right half side of the teeth row720ainFIG. 14.

The magnetic flux of the closed magnetic field H2flows from the N pole of the magnet rotor710to the receiving area of the rail740bvia the teeth724aand724bpositioned at the right half side of the teeth row720binFIG. 14. The magnetic flux of the closed magnetic field H2also flows back from the transfer area B of the rail740bto the S pole of the magnet rotor710via the teeth724aand724bpositioned at the left half side of the teeth row720binFIG. 14.

When the drive head730is fixed so that it will not be movable, from equation (4), it is seen that the rails740aand740bmove to the right side ofFIG. 14by T/4 with respect to the reference line I-I.

FIG. 15illustrates a closed magnetic field formed when the magnet rotor710is positioned at 90°. As viewed from the position of the magnet rotor710shown inFIG. 15, the right and left sides of the magnet rotor710are magnetized as the S pole, while the top and bottom sides of the magnet rotor710are magnetized as the N pole. Accordingly, in the closed magnetic field H1looping within the magnet rotor710, the teeth row720a, and the rail740aand in the closed magnetic field H2looping within the magnet rotor710, the teeth row720b, and the rail740b, the magnetic flux flows in the following manner.

The magnetic flux of the closed magnetic field H1flows from the N pole of the magnet rotor710to the receiving area of the rail740avia the teeth724aand724bpositioned at the central portion of the teeth row720ainFIG. 15. The magnetic flux of the closed magnetic field H1also flows back from the transfer areas B of the rail740ato the S pole of the magnet rotor710via the teeth724aand724bpositioned at both sides of the teeth row720ainFIG. 15.

The magnetic flux of the closed magnetic field H2flows from the N pole of the magnet rotor710to the receiving area of the rail740bvia the teeth724aand724bpositioned at the central portion of the teeth row720binFIG. 15. The magnetic flux of the closed magnetic field H2also flows back from the transfer areas B of the rail740bto the S pole of the magnet rotor710via the teeth724aand724bpositioned at both sides of the teeth row720binFIG. 15.

When the drive head730is fixed so that it will not be movable, from equation (4), it is seen that the rails740aand740bmove to the right side ofFIG. 15by T/2 with respect to the reference line I-I.

FIG. 16illustrates a closed magnetic field formed when the magnet rotor710is positioned at 135°. As viewed from the position of the magnet rotor710shown inFIG. 16, the bottom left and top right sides of the magnet rotor710are magnetized as the S pole, while the top left and bottom right sides of the magnet rotor710are magnetized as the N pole. Accordingly, in the closed magnetic field H1looping within the magnet rotor710, the teeth row720a, and the rail740aand in the closed magnetic field H2looping within the magnet rotor710, the teeth row720b, and the rail740b, the magnetic flux flows in the following manner.

The magnetic flux of the closed magnetic field H1flows from the N pole of the magnet rotor710to the receiving area of the rail740avia the teeth724aand724bpositioned at the right half side of the teeth row720ainFIG. 16. The magnetic flux of the closed magnetic field H1also flows back from the transfer area B of the rail740ato the S pole of the magnet rotor710via the teeth724aand724bpositioned at the left half side of the teeth row720ainFIG. 16.

The magnetic flux of the closed magnetic field H2flows from the N pole of the magnet rotor710to the receiving area of the rail740bvia the teeth724aand724bpositioned at the left half side of the teeth row720binFIG. 16. The magnetic flux of the closed magnetic field H2also flows back from the transfer area B of the rail740bto the S pole of the magnet rotor710via the teeth724aand724bpositioned at the right half side of the teeth row720binFIG. 16.

When the drive head730is fixed so that it will not be movable, from equation (4), it is seen that the rails740aand740bmove to the right side ofFIG. 16by 3·T/4 with respect to the reference line I-I.

FIG. 17illustrates a closed magnetic field formed when the magnet rotor710is positioned at 180°. As viewed from the position of the magnet rotor710shown inFIG. 17, the top and bottom sides of the magnet rotor710are magnetized as the S pole, while the right and left sides of the magnet rotor710are magnetized as the N pole. Accordingly, in the closed magnetic field H1looping within the magnet rotor710, the teeth row720a, and the rail740aand in the closed magnetic field H2looping within the magnet rotor710, the teeth row720b, and the rail740b, the magnetic flux flows in the following manner.

The magnetic flux of the closed magnetic field H1flows from the N pole of the magnet rotor710to the receiving areas of the rail740avia the teeth724aand724bpositioned at both sides of the teeth row720ainFIG. 17. The magnetic flux of the closed magnetic field H1also flows back from the transfer area B of the rail740ato the S pole of the magnet rotor710via the teeth724aand724bpositioned at the central portion of the teeth row720ainFIG. 17.

The magnetic flux of the closed magnetic field H2flows from the N pole of the magnet rotor710to the receiving areas of the rail740bvia the teeth724aand724bpositioned at both sides of the teeth row720binFIG. 17. The magnetic flux of the closed magnetic field H2also flows back from the transfer area B of the rail740bto the S pole of the magnet rotor710via the teeth724aand724bpositioned at the central portion of the teeth row720binFIG. 17.

When the drive head730is fixed so that it will not be movable, from equation (4), it is seen that the rails740aand740bmove to the right side ofFIG. 17by T with respect to the reference line I-I.

[Examples of Applications of Rotational-Linear Motion Converter to Motion Power Transmission Device]

An example of applications of rotational-linear motion converters having the above-described configurations will be discussed below briefly.

FIG. 18illustrates an example of applications of a rotational-linear motion converter860having a configuration of, for example, the eighth embodiment.

As shown inFIG. 18, the rotational-linear motion converter860includes a power input/output unit870which contains a magnet rotor810to be connected to a power generator, such as a motor, or an electrical generator Ge.

The magnet rotor810, a teeth row820, and the power input/output unit870are coupled to each other by a coupling component880so as to form a drive head830. Two slide blocks890are fixed to the coupling component880, and more specifically, one slide block is fixed to one side of the coupling component880and the other slide block is fixed to the other side of the coupling component880, and the heads of slide rails are embedded in the respective slide blocks890.

Rails840aand840bof the rotational-linear motion converter860are slidably connected to the heads of the respective slide rails. In this example, the rails840aand840bare coupled to each other by a coupling component881so that the rails840aand840bcan be moved only in one direction. If it is not necessary to move the rails840aand840bin the same direction, the provision of the coupling component881may be eliminated.

In the rotational-linear motion converter860, when the power input/output unit870receives power from an external power generator, such as a motor, rotational motion of the magnet rotor810to be rotated by the motor can be converted into linear motion of the drive head830or the rails840aand840b. When the power input/output unit870outputs power to, for example, an external electrical generator Ge, linear motion of the drive head830or the rails840aand840bcan be converted into rotational motion of the magnet rotor810.

As discussed above, by the use of the coupling component880, the slide blocks890, the slide rails, and so on, the rotational-linear motion converter860is fixed to a motor or an electrical generator Ge, and is used.