This invention relates to rotary solenoids having constant air gaps and more particularly to a rotary solenoid incorporating a rotary armature plate and captured balls in ball races defining the extent and degree of rotation of the armature.
Many rotary solenoids have been made according to the teachings of the expired U.S. Pat. No. 2,486,880, of Leland in which a fixed assembly includes a housing and an electromagnet, and a movable assembly includes an armature and an output shaft. The armature is movable toward the magnet upon energization of the magnet while the output shaft is connected with the armature for rotation when the armature is attracted by the magnet. A plate is secured to the shaft connected with the armature and arranged in opposed relation to a surface portion of the housing. The plate and the aforesaid surface portion are separated by rotatable elements, preferably balls. The plate or the housing surface, or both of them, are provided with arcuate, inclined recesses presenting cam surfaces arranged with relation to the balls such that the action of the cam surfaces on the balls will cause the plate and armature to rotate when the armature is attracted toward the magnet. Specifically, the plate is normally biased so that a ball is located within the shallow end of its recess, or recesses, as the case may be. Upon attraction of the armature toward the magnet, the balls are forced to roll along their corresponding recesses toward the deeper ends thereof. After each energization of the coil, the shaft and plate are returned to their initial positions with the balls at the shallow ends of the recesses.
One possible disadvantage of the structure defined above is the fact that rotary motion is accompanied by a certain amount of axial motion of the output shaft. An arrangement in a rotary solenoid for eliminating such axial motion is shown in Yost, U.S. Pat. No. 3,743,987 issued July 3, 1973 and assigned to the same assignee as this invention. However, both Yost and Leland employ a solenoid structure which has an axially closing air gap or, in other words, an air gap which varies in spacing with the rotation of the shaft. Another advantage of the non-inclined raceway structure as compared to the use of inclined raceways is that the solenoid of the present invention is balanced and is therefore shockproof.
Attempts to increase the stroke or provide for linear operation and at the same time eliminate axial motion of the shaft include the U.S. Pat. No. 3,435,394 of Egger, issued Mar. 24, 1969; Myers, U.S. Pat. No. 3,750,065 issued July 31, 1973 and Sommers, U.S. Pat. No. 3,753,180 issued Aug. 14, 1973, each assigned to the same assignee as this invention. In each of these patents an armature is attached to the shaft and rotates between an axially opposed pair of pole members, and either external or internal stop means are provided to define and limit the desired extent of rotation. Further, the armature shafts have been journeyed at each opposite end of the magnetic structure requiring two axially spaced sleeve bearings to support the armature.
The present invention incorporates certain of the best features of the Leland rotary solenoid in which ball bearing races define the extent of rotation, and yet utilizes a rotor and stator assembly which have a constant-dimension or clearance air gap, permitting proportional operation. For this purpose, an armature is mounted on a shaft for rotation on a single bearing sleeve at one axial end of the magnetic structure, and carries an armature plate at the other end exteriorly of the magnetic case. The plate and exterior surface of the case are provided with one or more arcuately cooperating ball raceways. However, rather than providing axially inclined ball raceways as taught by Leland, the ball recesses are preferably true to a plane perpendicular to the axis of the shaft; that is, they are not inclined. The armature carries one or more arcuately spaced poles and rotates within a stator structure having a corresponding number of poles, defining radially disposed air gaps between the armature and stator poles. The air gaps remain constant in radial dimension as the armature moves between defined extreme positions from one in which the cooperating poles are just beginning to overlap to one in which the cooperating poles are substantially overlapped.
The angular extent of rotation of the output shaft is preferably defined by the available movement of the armature plate on the ball races and the shaft movement is approximately twice the arcuate extent of the cooperating races in either the case or the armature plate. The limits of rotation are defined when the balls come to their respective ends of the raceways. Maintenance of rolling contact of the armature plate on the balls is assured by a snap ring on the shaft and further by reason of the fact that there is a net axial attracting force tending to draw the armature into the case, during actuation, and thereby urging the armature plate against the balls in their respective raceways.
Accordingly, it is an object of this invention to provide a constant air gap rotary solenoid in which the rotary motion is carried and defined by arcuate raceways and balls therebetween in low-friction rolling contact.
Another object of the invention is the provision of a rotary solenoid having a non-axial moving shaft using many of the same components as conventional rotary solenoids, yet having a constant air gap and providing for a proportional operation.
These and other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.