Actuator

Abstract: An actuator has a pair of magnetic pole pieces separated by a subsidiary air gap. A magnetic source connects the pole pieces in a magnetic circuit including at least one reluctance portion. A member formed from a permanent magnet is located between or adjacent the pole pieces. This member can be coupled to a drive shaft and is movable within a main air gap of the actuator so as to be biased towards its position in the main air gap in which magnetic energy stored in the actuator is at a minimum.

Description: The present invention relates to an actuator. A common form of actuator used to control the position of a moving member, for example a rotor, is a rotary solenoid, the position of which depends upon the coil current. The basic arrangement of such a rotary solenoid involves a rotor formed from a permanent magnet disposed between a pair of opposing magnetic pole pieces. The rotor is rotated by using magnetic flux from a magnetic source produced according to the operating current. To control the position of the rotor to a desired position, a spring is required to provide a counterforce proportional to the rotor position. The stop position of the rotor is determined by the balance between the torque induced by the coil current and the counterforce of the spring. Such prior proposed apparatus involves the necessary provision of a mechanical element, namely a spring which inevitably involves problems in terms of reliability, for example vibration and wear of operating parts. The present invention has arisen from our work seeking to provide an actuator which avoids the need for mechanical elements such as a spring providing a return or biasing force. U.S. patents 4,510,403 and 5,234,192 disclose actuators of similar construction which avoid the need of a mechanical element such as a spring providing a return or biasing force. U.S. patent specification 5,234,192 discloses an actuator comprising a permanent magnetic rotor disposed in a main air gap between a pair of opposed claw poles offset from one another by 180° in the circumferential direction. The claw poles provide pole gaps at opposite sides to promote engagement of the rotor with the pole gaps. The claw poles are connected in a magnetic circuit with a ring casing radially spaced from the claw poles to provide a toroidal space in which a current-receiving winding is disposed. To ensure strong engagement of the rotor with the pole gaps, each claw pole has a reluctance portion associated with it to increase the ratio of the magnetic resistances in the magnetic return path and in transverse direction of the claw poles aiding the provision of a return moment on the rotor to the position of engagement with the pole gaps. The claw poles with the rotor therebetween are mounted within a toroidal winding. Current supplied to the winding deflects the rotor from the position engaged with the pole gaps. In accordance with the present invention, there is provided an actuator, comprising; a pair of magnetic pole pieces separated by two subsidiary air gaps and a main air gap located between the subsidiary air gaps, a permanent magnet member adapted to be coupled to a drive shaft, said permanent magnet member being disposed in said main air gap to be movable therein in response to a magnetic field developed between said pole pieces, a magnetic circuit including a magnetic source connected to said pole pieces to develop a magnetic field between said pole pieces, said magnetic circuit including a further air gap between said magnetic source and one of said pole pieces. As will become clear from the description of a preferred embodiment given below, an actuator may be readily constructed in accordance with the present invention without any need for mechanical elements such as springs. The invention is hereinafter more particularly described by way of example only with reference to the accompanying drawing, in which:- Fig. 1 is a schematic view of a first embodiment of actuator constructed in accordance with the present invention; Fig. 1 shows the'arrangement of one embodiment of the actuator according to the present invention. In Fig. 1, an actuator body 1 has a U-shaped magnetic path 2, and a pair of magnetic pole pieces 3-1 and 3-2 which are disposed at both ends, respectively, of the magnetic path 2. It should be noted that an air gap 4-1 is provided between the pole piece 3-1 and the magnetic path 2, and another air gap 4-2 between the pole piece 3-2 and the magnetic path 2. The air gaps 4-1 and 4-2 function as magnetic reluctance portions. A main air gap 5 is provided between the pole pieces 3-1 and 3-2. Sub-air gaps 8-1 and 8-2 are provided at both sides, respectively, of the main air gap 5 . A rotor 6 which is formed from a permanent magnet is disposed in the main air gap 5 . The rotor 6 is adapted to rotate through a shaft 7. Reference numeral 9 denotes an electromagnetic coil (magnetic source). The operation of this embodiment will be explained below. When the electromagnetic coil 9 is not energized, no magnetic flux passes through the magnetic path 2. Accordingly, magnetic flux from the north pole of the rotor 6 flows to the south pole of the rotor 6 through the pole pieces 3-1 and 3-2 as shown by the solid lines in the figure. In this case, all the magnetic flux flows via the main air gap 5 . Therefore, there is no magnetic flux in either of the sub-air gaps 8-1 and 8-2, which lie at both sides (upper and lower sides as viewed in Fig. 1) of the rotor 6. That is, this state is the most stable in terms of magnetism, and the rotor 6 is at rest in this position (position shown in the figure). Next, when the electromagnetic coil 9 is energized, magnetic flux from the magnetic source 9 passes through a path comprising the magnetic path 2, the magnetic reluctance 4-1, the sub-air gap 8-1 or 8-2, the pole piece 3-2, the magnetic reluctance 4-2 and the magnetic path 2. Accordingly, magnetomotive force thus produced is stored as magnetic energy in the air gaps 4-1 and 4-2 and the sub-air gaps 8-1 and 8-2, which function as magnetic reluctances in the magnetic path. Therefore, the rotor 6 rotates and comes to rest at a position where the stored magnetic energy becomes the smallest. At this time, energy produced by the rotation of the rotor 6, which is formed from a permanent magnet, is also stored in the air gaps 4-1, 4-2, 8-1 and 8-2. Thus, according to this embodiment, the magnetic energy stored in the air gaps functions as a spring which has been used in the conventional rotary solenoid to store mechanical energy in order to determine a stop position. It should be noted that the amount of stored energy can be determined by the air gap width t and the cross-sectional area 1 of the magnetic path. As can be seen, in the embodiment described above there is no need for a mechanical element such as a spring.

Claims: An actuator comprising: a pair of magnetic pole pieces (3-1, 3-2) separated by two subsidiary air gaps (8-1, 8-2) and a main air gap (5) located between the subsidiary air gaps (8-1, 8-2), a permanent magnet member (6) adapted to be coupled to a drive shaft (7), said permanent magnet member (6) being disposed in said main air gap (5) to be movable therein in response to a magnetic field developed between said pole pieces (3-1, 3-2), a magnetic circuit (2) including a magnetic source (9) connected to said pole pieces (3-1, 3-2) to develop a magnetic field between said pole pieces (3-1, 3-2), said magnetic circuit (2) including a further air gap (4-1) between said magnetic source (9) and one (3-1) of said pole pieces. An actuator as claimed in Claim 1 in which said magnetic circuit includes another air gap (4-2) between said magnetic source (9) and the other (3-2) of said pole pieces. An actuator as claimed in Claim 1 or 2 in which said magnetic source comprises a winding energisable by a current to develop a magnetic field between said pole pieces (3-1, 3-2) that is dependent on the energising current. An actuator as claimed in Claim 1, 2 or 3 in which said permanent magnet member (6) is a rotor mounted for rotation in said main air gap (5) to a position dependent on the magnetic field developed between said pole pieces (3-1, 3-2).

Inventors: MURAJI TETSUO, MURAJI, TETSUO
Applicants: MIKUNI KOGYO KK, MIKUNI CORPORATION
Application year: 1996
Main classification: H02K26
IPC codes: H02K41, H02K33, H02K26, H01F7