Brushless DC linear motor

Abstract: A brushless DC linear motor includes a coil unit (2) in which electric flow terminals of each of three flat coils are connected with a star connection or with a delta connection; and the three flat coils have the same shape whose empty core section and winding section have their dimension of breadth determined on 1/2 of a magnetic pole-pitch of a magnet body and are arranged in a shifted position of the magnetic pole-pitch by n/3 ( n is a natural number excluding multiples of 3 ) on the coil unit. The motor also includes a sensor unit (3a-3c) in which three magnetic detection sensors corresponding to the respective flat coils are arranged at intervals of 1/3 + 2m ( m = 0, 1, 2, 3,.. ) of the magnetic pole-pitch and any of these magnetic detection sensors and its corresponding flat coils are arranged at the determined distance in accordance with the magnetic pole-pitch. In accordance with the signal from each of the sensors detecting the polarity of the magnet body, an electric flow switching means transfers the electric flow polarity to three terminals of a star connection or a delta connection.

Description: BACKGROUND OF THE INVENTION The present invention relates to a brushless DC linear motor according to the precharacterizing clause of claim 1. In a brushless DC linear motor the current can be transmitted to the coils without the use of brushes. Therefore, such motor has the advantages that no abrasion of brush parts occurrs and no maintenance works, such as exchanging worn brushes, have to be done. Also negative effects upon electronic equipments as electric noises which are generated when a brush switches the current are avoided. Thus, several proposals for such motors have been made, as, for example, in Jpn. examined publication No. Toku-Ko-Sho 59-1061, and 61-24907 and the like. US-A-4 151 447 discloses a brushless DC linear motor of the above mentioned kind, having a coil unit with two flat coils the dimension in the direction of movement of each of which is related to the magnetic pole-pitch of the magnet unit by a given rule. The same is true for the pitch by which the coils are arranged as well as for the distance each of the sensors has from its associated coil. However, it is not possible to enhance the thrust of this known motor by readily adding one or more coil units especially if each of the coil units is supposed to comprise three flat coils. SUMMARY OF THE INVENTION In view of the foregoing, it is the main object of the present invention to provide a brushless DC linear motor which uses two or more coil units each comprising a set of three flat coils and thus showing a little change of its thrust, for which one sensor unit suffices and no additional one is necessary irrespective how many coil units are attached to increase the thrust, and which requires only three electric wires, to transmit the currents to the coils and thus does not complicate the wiring. The foregoing object of the present invention is accomplished by providing a brushless DC linear motor by the features listed in claim 1. According to the concrete means, the dimension of breadth of the empty core section and the winding section of the flat coils and the positional relationship among the three flat coils and, further, the positional relationship among the three sensors are precisely determined in reference to the magnetic pole-pitch of the magnet body. Moreover, the corresponding positional relationship among the three sensors constituting the sensor unit and the three flat coils constituting the coil unit is determined and then the electric flow polarity to the three terminals of the delta connection or the star connection which connect the electric flow terminals of each flat coil is transferred by the electric flow switching means in accordance with the position detecting signal of the sensor constituting the sensor unit. The current force according to Fleming's left-hand rule is always generated in the same direction in the winding sections of at least two-flat coils corresponding to the magnetic pole-faces of the magnet body in reference to the polarity of the magnetic pole-faces of the magnet body. In consequence, the relative movement can be generated between the magnet body and the coil unit. 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 of the attached drawings is a perspective view of a coil unit and a sensor unit. Fig. 2 is a cross sectional view. Fig. 3 is an outlined perspective view of a brushless DC linear motor. Fig. 4 is a wiring diagram for showing an example of a controlling circuit. Fig. 5 - 7 are explanatory figures for showing a concrete example of a dimension relationship and a condition of wiring. Fig. 8 - 10 are explanatory figures for showing schematically the relationship between the current direction flowing into each of the flat coils which switch the electric flow polarity and the magnet body; Fig. 11 - Fig. 13 are diagrams for showing the patterns of the thrust which occurs; Fig. 14 is a front view of a coil unit and a sensor unit for showing other embodiments. DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to Fig. 1, there is shown a perspective view of the coil unit 2 constituting the brushless DC linear motor 1 of this invention and the sensor unit 3 attached as one body to this coil unit 2. The coil unit 2 incorporates three flat coils of the same shape 2a, 2b and 2c. And the sensor unit 3 incorporates the magnetic detection sensors 3a, 3b and 3c made of three Hall elements and the like and corresponds the flat coils 2a - 2c to the respective magnetic detection sensor 3a - 3c severally. Their corresponding positional relationship will be described in details afterwards. The electric supply wire to send the current to each flat coil 2a - 2c and the signal wire of each sensor 3a - 3c are connected by the use of the flexible printed substrate 4. The coil unit 2 and the sensor unit 3, as shown in the sectional view of Fig. 2, are hung and installed movably in the traveling portion 11′ of the rail 11 consisting of the outer rails 12, 12 and the inner rails 13, 13 and thus constitute the brushless DC linear motor 1 of the coil traveling type. The magnet body 16 is constituted with the yokes 14, 14 standing between the outer rails 12, 12 and the inner rails 13, 13 and with the several permanent isometric magnets 15, 15 arranged in the longitudinal direction and moreover, their polarities are inverted between the adjacent and opposite magnets to each other. In consequence, an uniform magnetic field is formed between the magnets 15, 15 facing each other. In this case the magnetic circuit may be formed with the magnet 15 arranged on only one side and with the yoke 14 on the other side. One edge of the electric supply wire using the flexible printed substrate 4 is connected with the rail end 17 installed on the edge section of the rail 11 ( Fig. 3 ). The wire harness 19 is connected with this rail end 17 through the connector 18. The control circuit 20 is connected with one edge of this wire harness 19. The control circuit 20 constitutes the electric flow switching means which inputs the detecting signals of the magnetic detection sensors 3a - 3c to detect the relative position between the coil unit 2 and the magnet body 16 in accordance with the polarity of the magnets 15, 15 and transfers the electric flow polarity of the flat coils 2a - 2c. One of examples of the control circuit 20 is shown in Fig. 4. The control circuit 20 has the positional detection circuit 21 to input the magnetic detecting signal of the magnetic detection sensors 3a - 3c and detect the relative position between the coil unit 2 (the flat coils 2a - 2c) and the magnet body 16 and the electric flow switching circuit 22. Further between both circuits 21 and 22 there are installed the driving circuit 24 for driving logically switching elements of the electric flow switching circuit 22 and a moving direction control circuit 24 connected with the moving direction transfer switch 25. The dimension and the corresponding positional relationship of the flat coils 2a - 2c constituting the coil unit 2, the corresponding positional relationship of the magnetic detection sensors 3a - 3c constituting the sensor unit 3 and the determination of the corresponding distance between the coils 2a - 2c and the following in reference to the dimension of the isometric magnets 15. The arranged pitch L of the flat coils 2a, 2b and 2c is L = 2nℓ/3. where n : natural number excluding multiples of 3 2ℓ : the magnetic pole-pitch of the magnet body 16. And the arranged pitch M of the magnetic detection sensors 3a, 3b and 3c is ; M = 2ℓ/3 + 2ℓ x 2m where m : 0, 1, 2, 3... 2ℓ: the magnetic pole-pitch of the magnet body 16. The corresponding distance Nx between the flat coils 2a - 2c and the magnetic detection sensors 3a - 3c corresponding respectively differentiates depending on the connection between the electric flow terminals of the flat coils 2a - 2c and can be described as follows. (1) In case of the star connection (type 1) Nx = ( 2 p x + 1 ) ℓ (2) In case of the star connection (type 2) Nx = 2 ( p x + 1/3 ) ℓ or N x = 2 ( p x + 2/3 ) ℓ (3) In case of the delta connection Nx = 2 ( p x + 1/3 ) ℓ or N x = 2 ( p x + 2/3 ) ℓ where 2ℓ = the magnetic pole-pitch of the magnet body 16 p = 0, 1, 2, 3, 4... x = a, b, c Provided that N a indicates the distance from the center of the flat coil 2a to the magnetic direction sensor 3a. The same applies to the case of N b and N c . N b and N c indicates the distances from the centers of the flat coils 2b, 2c to the magnetic detection sensors 3b and 3c respectively. Some examples of the dimension relationship prescribed as aforementioned and their actions will be explained in the following. Fig. 5 is an example in case of the star connection (type 1) of the (1). L = 10ℓ/3, the distance between the flat coils 2a and 2b and between 2b and 2c, is obtained by substituting n = 5 for L = 2nℓ/3. And N a = 11ℓ , the corresponding-distance from the center of the flat coil 2a to the magnetic detection sensor 3a, is obtained by substituting P a = 5 for N a = (2p a + 1)ℓ, and in the same way, N b = 7ℓ by substituting p b = 3 for it and N c = 3ℓ by substituting p c = 1 for it. The start ends of winding of the flat coils 2a - 2c are referred to as A₁, B₁ and C₁ respectively and the finish ends of winding, as A₂, B₂ and C₂ respectively. And the finish end of winding A₂ of the flat coil 2a, the start end of winding B₁ of the flat coil 2b and the finish end of winding C₂ of the flat coil 2c are connected together. Then, the star connection is applied to it. Fig. 6 shows an example in case of the star connection (type 2). L = 10ℓ/3, the distances between the flat coils 2a and 2b and between 2b and 2c, is obtained by substituting n = 5 for L = 2nℓ/3. N a = 32ℓ/3, the distance from the center the flat coil 2a to the magnetic detection Sensor 3a, is obtained by substituting p = 5 for N a = 2(p a + 1/3)ℓ and in the same way, N b = 20ℓ/3, by substituting p b = 3 for it and N c = 8ℓ/3, by substituting p c = 1 for it. The start ends of winding of the flat coils 2a, 2c are referred to as A₁, B₁ and C₁ respectively and the finish end of winding A₂, B₂ and C₂ respectively. And the finish end of winding A₂ of the flat coil 2a, the start end of winding B₁ of the flat coil 2a, the start end of winding B₁ of the flat coil 2b and the finish end of winding C₂ of the flat coil 2c are connected together. Then, the star connection is applied to it. Fig. 7 shows an example in case of the delta connection. The distances between the flat coils 2a and 2b and between 2b and 2c, and the corresponding distances from the center of the flat coils 2a - 2c to the respective magnetic detection sensors 3a - 3c are of the same kind as in case of the star connection (type 2) (Fig. 6). The start end of winding of the flat coils 2a - 2c are referred to as A₁, B₁ and C₁ respectively and the finish end of winding, as A₂, B₂ and C₂ respectively. And A₁ is connected with B₁, and in the same way, A₂, with C₁ and B₂ with C₂. Their terminals are referred to as A′, C′ and B′ respectively and the delta connection is applied to them. The action of the brushless DC linear motor 1, which arranges the flat coils 2a - 2c and the magnetic detection sensors 3a - 3c in the coil unit 2 and the sensor unit 3 respectively, prescribing each of their dimension relationship, and which is hung and installed in the rail 11, as mentioned above, will be explained on reference to Fig. 8 - Fig. 10. In case of the star connection (type 1) as shown in the Fig. 5, the electric flow switching circuit 22 of the control circuit 20 is controlled to impress + V (v) on the terminal A when the magnetic detection sensor 3a corresponds to the N pole of the magnet body 16 and 0 (v), when it corresponds to the S pole. And in the same way, it is controlled to impress 0 (v) on the terminal B when the magnetic detection sensor 3b corresponds to the N pole and + V (v), when it corresponds to the S pole, and it is also controlled to impress + V (v) on the terminal C when the magnetic sensor 3c corresponds to the N pole and 0 (v), when it corresponds to the S pole, as shown in Fig. 8. The condition of the electric flow to the terminals A₁, B₂ and C₁ at this point depending on the magnetic detection timing of the respective magnetic detection sensors 3a - 3c is a timing shown in this figure if it is indicated as the position of the magnetic detection sensor 3c. For example, in case of the position (1) of the magnetic detection sensor 3a, all of the magnetic detection sensors 3a, 3b and 3c which are shifted by 2ℓ/3 correspond to the S pole and 0 (v) is impressed on the terminals A₁ and C₁ and + V (v), on the terminal B₂. And the current flows from B₂ to B₁, from A₂ to A₁ and from C₂ to C₁ through the star connection in the flat coils 2a - 2c. As aforementioned, the condition of the electric flow to the three terminals A₁, B₂ and C₁ of the star connection changes, depending on the magnetic detection signal which the magnetic detection sensors 3a - 3c output in accordance with the polarity of the magnet body 16 and the direction of the current flowing into the flat coils 2a - 2c switches successively depending on the timing. And at this point the flat coils 2a - 2c are situated in such a position as prescribed by the dimension relationship, receive the action of the thrust according to Flemming's left-hand rule, depending on the direction of the current flowing in each of the winding sections and the corresponding polarity of the magnet body 16 and successively from the left to the right, as shown schematically in Fig. 8 (a) - (h). In case of the star connection (type 2) shown in the Fig. 6, the condition of the electric flow to send the current to the terminals A₁, B₂ and C₁ are referred to as + V (v), 0 (v) and - V (v) respectively, as shown in Fig. 9, and its switching timing is a timing shown in Fig. 9 if it is indicated as the position of the magnetic detection sensor 3a. For example, at the position (2) of the magnetic detection sensor 3a, - V (v) is impressed on the terminal A₁ and + V (v) on B₂ and 0 (v) on C₁. Then, the electric potential of the connecting point of the terminals A₂, B₁ and C₂ to which the star connection is applied always indicated 0 (v) and the current does not flow to the terminal C₁ (0 (v)) but flows from the terminal B₂ to B₁ and from A₂ to A₁. In this case, in the same way as aforementioned, the flat coils 2a - 2c receive the thrust according to Flemming's left-hand rule, depending on the direction of the current flowing into each of the winding sections of the flat coils 2a - 2c and the corresponding polarity of the magnet body 16 and move successively from the left to the right, as shown schematically in Fig. 9 (a) - (h). In case of the delta connection shown in the Fig. 7, the electric flow switching circuit 22 of the control circuit 20 is controlled to impress + V (v) on the terminal A′ when the magnetic detection sensor 3a corresponds to the N pole of the magnet body 16 and 0 (v), when it corresponds to the S pole. And in the same way, it is controlled to impress 0 (v) on the terminal B′ when the magnetic detection sensor 3b corresponds to the N pole and V (v), when it corresponds to the S pole, and it is also controlled impress + V (v) on the terminal C′ when the magnetic detection sensor 3c corresponds to the N pole and 0 (v), when it corresponds to the S pole, as shown in Fig. 10. The condition of the electric flow to the terminals A′, B′ and C′ at this point depending on the magnetic detection timing of the respective magnetic detection sensors 3a - 3c is a timing shown in this figure if it is indicated as the position of the magnetic detection sensor 3a. For example, in case of the position (3) of the magnetic detection sensor 3a, all of the magnetic detection sensors 3a, 3b and 3c which are shifted by 2ℓ/3, correspond to the S pole and 0 (v) is impressed on the terminals A′ and + V (v), on the terminals B′ and C′. The current does not flow between the terminal B′ and the terminal C′ whose electric potential indicate the same because of the delta connection but flows from A₂ to A₁ and from B₂ to B₁ . In this case, in the same way as, aforementioned, the flat coils 2a - 2c receive the thrust according to Flemming's left-hand rule, depending on the direction of the current flowing into each of the winding sections of the flat coils 2a - 2c and the corresponding polarity of the magnet body 16 and move successively from the left to the right, as shown schematically in Fig. 10 (a) - (h). The thrusts Fa, Fb and Fc, which act on the respective flat coils 2a - 2c in case of the star connections (type 1), (type 2) and the delta connection, are shown in Fig. 11 - Fig. 13 respectively when the magnetic field is kept uniform. where V : voltage R : resistor of a coil B : magnetic flux density N : winding number of a coil ℓ : operating length of magnetic flux. In case of the star connection (type 1); F a = F b = F c = ( 4V/3R ) · BNℓ is applied, as shown in Fig. 11. The thrust pattern generates a 2ℓ/3 phase shift according to the dimension relationships, such as those of the flat coils 2a - 2c and the magnet body 16, and the maximum thrust to act an the coil unit 2 is; F = ( 20 V/9R ) · BNℓ. And the decline of the thrust which occurs at every 2ℓ/3 is; F′ = ( 2V/R ) · BNℓ. Thus, the change of the thrust can be restricted to 10 % of the maximum thrust. In case of the star connection ( type 2 ); Fa = Fb = Fc = ( V/R ) · BNℓ, and Fa′ = Fb′ =Fc′ = ( 2V/3R )·BNℓ are applied, as shown in Fig, 12. And the maximum thrust is; F = ( 2V/3R ) · BNℓ and the decline of the thrust which occurs at every 2ℓ/3 is; F′ = ( 5V/3R ) · BNℓ. Thus, the change of the thrust can be restricted to 17 % of the maximum thrust. In case of the delta connection; Fa = Fb = Fc = ( 2V/R ) · BNℓ, and Fa′ = Fb′ = Fc′ = ( 4V/3R ) · BNℓ are applied, as shown in Fig. 13. The maximum thrust F is; F = ( 4V/R ) · BNℓ and the decline of the thrust which occurs at every 2ℓ/3 is; F′ = ( 10V/3R ) · BNℓ. Thus, the change of the thrust can be restricted to 17 % of the maximum thrust. The brushless DC linear motor 1 which has such constitution and actions as aforementioned can not only aim at the better durability and the reduction of the electric noise because of being brushless but also perform the excellent controllability because the traveling part becomes coreless on account of the little change of the thrust and the traveling coil. Furthermore, several coil units 2 can be attached in order to increase the thrust. In this case, the star connection or the delta connection is applied in order to get every winding of the flat coils 2a - 2c which constitute each of the coil units 2 and 2′ reversed in every adjoining coil units, depending on the dimension relationship between the magnet body 16 and each of the flat coils 2a - 2c. As shown in Fig. 14, the finish end of winding A₂ of the flat coil 2a, the start end of winding B₁ of the flat coil 2b and the finish end if winding C of the flat coil 2c are connected with the wire in the coil unit 2 and the start end of winding A₁′ of the flat coil 2a, the end of winding B₂′ of the flat coil 2b and the start end of winding C₁′ of the flat coil 2c are connected with the wire in the coil unit 2′. As for the three terminals A₁, B₂ and C₁ of the coil unit 2 and the three terminals A₂′, B₁′ and C₂′ of the coil unit 2′, A₁ and A₂′, B₂ and B₁′ and C₁ and C₂′ are connected together to be the common terminals A, B and C respectively. Thus, even in case that several coil units 2 are attached, the number of wires to switch the electric flow polarity of the flat coils 2a - 2c is three, remaining as it in in case of one coil unit. and does not need to increase. And a pair of the magnetic detection sensors 3a - 3c to control the switching timing of the electric flow polarity will suffice regardless of the number of the coil units 2. And the arranged positions of the magnetic detection sensors 3a - 3c are not restricted by the positions shown in each of the embodiments and any position will suffice as far as it effectuates the switching timing of the electric flow polarity. Further, in case that the moving direction is reversed, the electric flow polarity will be switched to send the reverse current to the embodiment into each of the flat coils.

Claims: A brushless DC linear motor (1) comprising: a magnet unit (16) in which several isometric magnets (14) are arranged with a regular magnetic pole-pitch (21) to alternate their magnetizing directions and to have their magnetic pole-faces in a row the direction of which is perpendicular to their magnetizing direction, a coil unit (2) arranged for a relative movement along the magnetic pole-faces of said magnets (14) and comprising a number of flat coils (2a, 2b, 2c) all having the same shape, and each coil (2a, 2b, 2c) comprising a leading winding section, an empty core section and a trailing winding section, the dimension of the coils (2a, 2b, 2c) in the direction of the relative movement as well as the pitch of their arrangement being determined in accordance with said magnetic pole-pitch (21), a sensor unit for detecting the relative position of said coil unit (2) with respect to said magnet unit (16), said sensor unit (3) being fixed with respect to said coil unit (2) and comprising several magnetic detection sensors (3a, 3b, 3c) the number of which corresponds to the number of flat coils (2a, 2b, 2c) in said coil unit (2), each sensor (3a, 3b, 3c) being associated with one of said coils (2a, 2b, 2c) and having a distance therefrom which is determined in accordance with said magnetic pole-pitch (21), a current switching means (20) providing currents of different phases for each of said coils (2a, 2b, 2c) and alternating the polarity of said currents in dependence on the signals from said magnetic detection sensors (3a, 3b, 3c), characterized in that said motor (1) includes two or more coil units (2, 2′) each of which comprises three flat coils (2a, 2b, 2c), in that the three sections of each of said coils (2a, 2b, 2c) have the same dimension in the direction of said relative movement, which dimension is 1/2 of said magnetic pole-pitch (21), in that said coils (2a, 2b, 2c) are arranged with a pitch (L) which is equal to n/3 of said magnetic pole-pitch (21) [where n is any natural number except multiples of 3], in that said coil units (2, 2′) are attached to each other and have several common terminals (A, B, C) which are connected with corresponding outputs of said current switching means (20) which provides said currents of different phases to said common terminals (A, B, C) in dependence on the signals from said one sensor unit (3) which is common to all of said coil units (2, 2′) and in that said sensor unit (3) comprises three sensors (3a, 3b, 3c) which are arranged with a pitch (M) which is equal to 1/3 + 2m of said magnetic pole-pitch (21) [m = 0,1, 2, 3, ....]. A brushless DC linear motor (1) according to claim 1, wherein said sensor unit (3) is attached as one body to said coil units (2, 2′). A brushless DC linear motor (1) according to claim 1, wherein said magnetic detection sensors (3a, 3b, 3c) incorporated in said sensor unit (3) are made of Hall elements. A brushless DC linear motor (1) according to claim 1, wherein the electric supply wires by which the current is transferred to said flat coils (2a, 2b, 2c) and the signal wires connecting said sensor unit (3) with said current switching means (20) are made of a flexible printed substrate (4). A brushless DC linear motor (1) according to claim 1, wherein said magnet unit (16) comprises yokes (14) standing between outer rails (12) and inner rails (13). A brushless DC linear motor (1) according to claim 1, wherein said coil unit (2) and said sensor unit (3) form a travelling unit which is arranged to be movable on a rail unit consisting of outer rails (12) and inner rails (13), thus constituting a linear motor of the travelling coil type. A brushless DC linear motor (1) according to claim 1, wherein said current switching means (20) is constituted by a control circuit which comprises a positional detection circuit (21) for detecting the relative position between the coil unit (2) and the magnet unit (16), a current switching circuit (22), a driving circuit (23) which is connected between the detection circuit (21) and the switching circuit (22) for driving logically switching elements of the switching circuit (22), and a moving direction control circuit (24) connected with a moving direction transfer switch (25).

Inventors: ANDOU TOSHIHIRO, NAGASAWA YOSHIAKI, ONOYAMA TOSHIAKI, SAKAGAMI SHIGERU, ANDOU, TOSHIHIRO, NAGASAWA, YOSHIAKI, ONOYAMA, TOSHIAKI, SAKAGAMI, SHIGERU
Applicants: TOYOTA AUTO BODY CO LTD, TOYOTA SHATAI KABUSHIKI KAISHA
Application year: 1990
Main classification: H02K41
IPC codes: H02K41