MOVING MAGNET TYPE LINEAR MOTOR FOR AUTOMATIC DOOR

Abstract: In a moving magnet type linear motor for automatic door of the invention, a stator (10) fixed inside a guide rail (1) having a substantially ∩ -shaped cross section and a moving unit (20) having a substantially U -shaped cross section are combined so that a height of the linear motor can be the same as that of the guide rail and the moving unit is supported slidably relative to the guide rail and fixing members of the stator has at least the both longitudinal ends or the stroke ends formed of non-magnetic conductive materials in order that the moving magnet type linear motor for automatic door produces only a low sound and is durable.

Description: BACKGROUND OF THE INVENTION The present invention relates to a moving magnet type linear motor comprising a guide rail having an opening in its lower face to have a substantially inverted U-shaped cross-section, a stator having a plurality of flat coils arranged in a longitudinal direction in the space of the guide rail and fixing members which are supported in the upper portion of the guide rail and are surrounding and fixing the flat coils, and a moving unit which has permanent magnets being arranged on mutually facing sides of a yoke with a substantially U-shaped cross section and forming a magnetic circuit, the stator being arranged in a gap between the permanent magnets, said moving unit further comprising a support assembly which supports the moving unit in such a manner as to be slidable along the guide rail and the stator connected thereto. Linear motors of that kind are for example known from FR-A-2 068 155. They are, as well as linear motors disclosed in US-A-3 806 782, mainly adapted for being used with vehicles which comprise the moving unit for being accelerated along the guide rail or rails in order to move over large distances. However, these linear motors are not readily suitable for moving automatic doors which are moved over comperatively short distances only and where this movement has to be controlled very accurately in order to guarantee safety and to minimize the shocks occuring when the moving unit stops at either end of its stroke. It is also known to use a rotating motor as a power source in order to open and close an automatic door. In such applications a decelerator controls an output of the rotating motor and an interlocking mechanism such as a belt or a chain transmits the controlled output to the door. In these cases, a problem of external appearance arises in that the cross-section of the rail cannot be made small because of the sizes of the rotating motor, the decelerator and the interlocking mechanism. Also a noise problem arises in that the decelerator and the chain produce a loud noise. There are automatic doors opened and closed by linear motors. However, a small linear motor for driving an automatic door safely and in a sufficiently controlled manner has not yet been developed. SUMMARY OF THE INVENTION In view of the foregoing, it is an object of the present invention to provide a moving magnet type linear motor for an automatic door which allows to control the movement of the door so that safety is guaranteed and shocks are avoided when the door reaches the end of its stroke either in the fully opened or the fully closed position. The object of the present invention is accomplished by providing that the linear motor is for an automatic door, and that at least the fixing members which are arranged at the stroke ends of the guide rail are made of non-magnetic conductive material so that the permanent magnets of the moving unit generate eddy-currents in said fixing members when moving in their vicinity, thereby generating a braking effect. As a consequence of the construction of the linear motor according to the invention its height can be minimized and also its width can be made small. Since the moving unit is supported slidably on the guide rail the noise accompanying the movement is reduced which results in a quiet operation. BRIEF DESCRIPTION OF THE DRAWINGS The objects and features of the invention may be understood with reference to the following detailed description of an illustrative embodiment of the invention, taken together with the accompanying drawings in which: Fig. 1 is a cross sectional view of a linear motor. Fig. 2 is a partial perspective view of a stator. Fig. 3 is a perspective view of a moving unit. Fig. 4 is an explanatory view showing size and position relationships of flat coils and position relationships of hall elements. Fig. 5 is a schematic block diagram of an electronic control circuit. Fig. 6 is an explanatory view showing typically actuation of the linear motor. DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention is described in accordance with the accompanying drawings. As illustrated in a cross sectional view of Fig. 1, a moving magnet type linear motor for an automatic door is composed by arranging a stator 10, a moving unit 20 and a support assembly 30 of the moving unit 20 inside a guide rail 1 having a cross section of a substantially inverted U shape. The guide rail 1 is a shape material of aluminium or the like and has a cross section of the substantially inverted U shape, that is, the guide rail 1 is so shaped as to open the lower side thereof. The guide rail 1 is formed integral with support projections 2 inside an upper portion thereof and with roller - supporting portions 3 on a lower end thereof. Tracks 4 are formed in the roller - supporting portions 3. As illustrated in Fig. 2, the stator 10 is constituted by lining flat coils of the number corresponding to a length of the guide rail 1 to have a size as described below (see Fig. 4). As illustrated in Fig. 1, each flat coil 11 is sealed, surrounded, and held by fixing members 12 and 13 made of the shape material such as aluminium, respectively. A circuit board 14 is provided horizontally on an upper end of the flat coil 11. The stator 10 is overall formed into a T-letter shape. Electronic control circuits 15 are arranged on a circuit board 14 at each flat coil 11 and are connected with the circuit board 14 in a predetermined manner. A set of hall elements 16a and 16b are placed in each flat coil 11 as illustrated in Fig. 4. The stator 10 constructed as above is provided in a space of the guide rail 1 and upper ends of the fixing members 12 and 13 are supported by the support projections 2, 2, so that the lined flat coils 11 are positioned in a center of the space of the guide rail 1. As illustrated in Fig. 3, in the moving unit 20, a yoke whose cross section is formed into a substantially U-letter serves as a moving unit body 21 and a plurality of permanent magnets 22, 22 with an isometric length (2 ℓ ) are arranged in a longitudinal direction to constitute a magnetic circuit, and moreover their polarities are inverted between adjacent and opposite magnets to each other. In consequence, an uniform magnetic field is formed between the permanent magnets 22, 22 facing each other. Rollers 31 are attached to both outsides of the moving unit body 21 to form a support assembly 30 of the moving unit 20. The moving unit 20 constructed as above is inserted in the guide rail 1 so that the rollers 31 are supported by the tracks 4, 4 of the roller-supporting portions 3, 3 formed at lower ends of the guide rail 1. Thereby, the flat coils 11 of the stator 10 are positioned at a gap between the permanent magnets 22, 22. A door 40 is fixed on a lower face of the moving unit body 21. The number of the permanent magnet 22 arranged in the moving unit 20 is determined according to a required thrust. In case that the fixing members 12 and 13 are formed of non-magnetic conductive materials such as aluminium, eddy currents are generated in the fixing members 12 and 13, due to the movement of the moving unit 20 so that a braking operation generates in the moving unit 20. As a result thereof, the moving unit 20 can be decelerated, allowing the maintenance of safety as an automatic door. Further, the fixing members 12 and 13 of both stroke end portions in a longitudinal direction of the guide rail 1 are formed of non-magnetic conductive material, so that a shock can be reduced when the moving unit 20 stops at both ends of the guide rail 1. The above-mentioned braking operation can be regulated by means of changing the conductivity of the non-magnetic conductive material, i.e. areas in which the braking operation generates and positions in which the braking operation starts generating. In case that the door is opened manually, an initial velocity is 0. Therefore, the braking operation does not generate, so that the door starts moving smoothly. Fig. 4 illustrates size and position relationships of the flat coils 11 and position relationships of the hall elements 16a and 16b in case of magnetic pole pitches 2 ℓ of the permanent magnets arranged in the moving unit 20. Each flat coil 11 has an overall length of 3 ℓ, including a coil winding portion 11a and 11b with a length of ℓ on a right and left thereof, respectively and a space with a length of ℓ at a center thereof. The flat coils 11 are arranged with an interval of ℓ /3 from each other. The hall elements 16a and 16b are arranged at centers of the coil winding portions 11a and 11b with an interval of 2 ℓ relative to each other. Fig. 5 illustrate a schematic block view of the electronic control circuit 15. A driving IC 16 is connected with each flat coil 11 to send current to the flat coil 11 in accordance with signals of a direction switching circuit 17 which switches the direction of the current sent to the flat coil 11. The direction switching circuit 17 is connected with hall ICs 18a and 18b which amplify and output detection signals of the hall elements 16a and 16b of magnetic detection elements. The hall ICs 18a and 18b detect magnetism of the permanent magnet 22 of the moving unit 20 and output signal to the direction switching circuit 17. Then, in accordance with the signal outputted to the direction switching circuit 17, the direction switching circuit 17 outputs signal to the driving IC 16 and the driving IC sends current to the coil 11 in accordance with polarities of the permanent magnet 22 so that the moving unit 20 moves in a predetermined direction. A driving direction of the driving IC is switched by outputting direction control signal to the direction switching circuit 17. The signals of the hall IC 18a and 18b can be utilized as position signals. A power circuit (not shown) supplies power to the driving IC 16. Referring to Fig. 6, there is shown an actuation of the moving magnet type linear motor for an automatic door having the aforementioned structure. Fig. 6 (1) to Fig. 6 (5) typically show states in which the direction switching circuit 17 control switching of a direction of the current supplied to each flat coil 11 of the stator 10 in accordance with the position signal of the hall elements 16a and 16b detecting the magnetism of the permanent magnet 22, 22 arranged in the moving unit 20, so that the moving unit 20 receives the thrust according to Flemming's left-hand rule to move in the right. In Fig. 6 (1), in case that magnetic fields shown in the first, the third and the fifth magnetic circuit from the left, of the magnetic circuits constituted by the permanent magnets 22, 22 of the moving unit 20, acts, the direction switching circuit 17 switches the direction of the current supplied to the flat coil 11, based on the position signal which the hall element 16a or 16b outputs. The current is supplied to the flat coil 11 in a direction in which the current flowing to the coil winding portion 11a or 11b of the flat coil 11 to which the hall element 16a or 16b outputs the position signal flows from current down direction to current up direction. The hall element 16a or 16b outputting the position signal is shown by a mark ▴. In this case, the moving unit 20 receives the thrust F generating for the right according to the Flemming's left-hand rule. In Fig. 6 (2), in case that the hall elements 16a and 16b of the second flat coil 11 from the left just approach switching points of the permanent magnets 22, 22, a strength of the magnetic field is 0, so that the hall elements 16a and 16b do not output the position signals. As a result thereof, the current is not supplied to the flat coil 11. In Fig. 6 (3) to Fig. 6 (5), as mentioned above, the thrust F can be adapted to act in the right on the moving unit 20 by switching the direction of the current flowing to the flat coil 11 corresponding to the permanent magnet 22 of the moving unit 20. Also, the moving unit 20 can be moved in the left by supplying the reverse current of the aforementioned direction to the flat coil 11, based on the position signal which the hall elements 16a and 16b as shown by the mark ▴ output. The moving unit 20 can be stopped smoothly in the stroke ends, cooperating with the braking operation of the eddy current generating in the fixing members 13 and 14 formed of the aforementioned non-magnetic conductive material by supplying the reverse current to the flat coils 11 of the stroke ends. The aforesaid embodiment is described in respect of the moving magnet type linear motor for automatic door. However, it is to be understood that the linear motor of the present invention can be employed for a power source in case that an article or the like is carried between predetermined positions. In accordance with the above structure of the moving magnet type linear motor for automatic door, a stator fixed inside the guide rail having the substantially ∩ -shaped cross section and the moving unit having the substantially U -shaped cross section are combined, so that a height of the linear motor can be the same as that of the guide rail. Further, the moving unit is supported slidably relative to the guide rail, therefore a noise can be reduced, which results in a quiet operation. In addition, the fixing members of the stator has at least the both longitudinal ends or the stroke ends formed of the non-magnetic conductive materials, therefore a magnetic field of the permanent magnet of the moving unit generates an eddy current in the fixing members to produce a braking operation, thereby lessening a shock when the moving unit stops at the stroke ends and heightening durability of the linear motor.

Claims: A moving magnet type linear motor comprising a guide rail (1) having an opening in its lower face to have a substantially inverted U-shaped cross-section, a stator (10) having a plurality of flat coils (11) arranged in a longitudinal direction in the space of the guide rail (1) and fixing members (12, 13) which are supported in the upper portion of the guide rail (1) and are surrounding and fixing the flat coils (11), and a moving unit (20) which has permanent magnets (22, 22) being arranged on mutually facing sides of a yoke (21) with a substantially U-shaped cross section and forming a magnetic circut, the stator (10) being arranged in a gap between the permanent magnets (22, 22), said moving unit (20) further comprising a support assembly (30) which supports the moving unit (20) in such a manner as to be slidable along the guide rail (1) and the stator (10) connected thereto, characterized in that the linear motor is for an automatic door (40), and in that at least the fixing members (12, 13) which are arranged at the stroke ends of the guide rail (1) are made of non-magnetic conductive material so that the permanent magnets (22, 22) of the moving unit (20) generate eddy-currents in said fixing members (12, 13) when moving in their vicinity, thereby generating a braking effect. A linear motor as claimed in claim 1, wherein the guide rail (1) is a shape material of aluminium and is formed integral with support projections (2, 2) inside an upper portion thereof for supporting the stator (10) and with roller-supporting portions (3,3) on a lower end thereof, the roller-supporting portions (3, 3) having tracks (4, 4) formed therein. A linear motor as claimed in claim 1 or 2, wherein the stator (10) is overall formed into a T-letter shape and has the flat coils (11) sealed and surrounded by the fixing members (12, 13) formed of the shape material of aluminium. A linear motor as claimed in any of claims 1 to 3, wherein each flat coil (11) has an overall length of 3 l, including a coil winding portion (11a, 11b) with a length of l on a right and a left side and a space with a length of l at the center thereof, and wherein the flat coils (11) are arranged with an interval of l/3 from each other. A linear motor as claimed in claim 4, wherein the moving unit (20) includes a yoke (21) having a substantially U-shaped cross-section and serving as a moving unit body, and a plurality of permanent magnets (22) with an isometric length 2 l arranged longitudinally on a mutually facing inner face of the yoke (21), the polarities of said permanent magnets (22) being inverted between adjacent magnets (22) and magnets (22) being opposite to each other. A linear motor as claimed in claim 5, wherein the support assembly (30) includes rollers (31) travelling on tracks (4) of the guide rail (1) on both outer sides of said yoke (21). A linear motor as claimed in claim 5 or 6, wherein the door (40) is fixed on the lower face of said yoke (21).

Inventors: NAGASAWA, YOSHIAKI, SAKAGAMI, SHIGERU
Applicants: TOYOTA SHATAI KABUSHIKI KAISHA
Application year: 1990
Main classification: H02K41
IPC codes: H02K41, E03C1, E05D15, E05F15