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United States Patent m
[ii] Patent Number: 4,555,645  Date of Patent: Nov. 26, 1985
 MOVEABLE COIL LINEAR MOTOR
 Inventor: Robert W. Atkinson, Dover, Ohio
 Assignee: Snyder Laboratories, Inc., Dover, Ohio
 Appl. No.: 581,514
 Filed: Feb. 21, 1984
Related U.S. Application Data
 Continuation of Ser. No. 445,792, Dec. 1, 1982, abandoned.
 Int. a.4 -. H02K 33/00
 U.S. CI 310/27; 310/13
 Field of Search 310/13, 27
 References Cited
U.S. PATENT DOCUMENTS
3,417,268 12/1968 Lace 310/27 X
3,439,198 4/1969 Lee 310/27 X
3,666,977 5/1972 Helms 310/27 X
4,220,878 9/1980 Asano 310/27 X
Primary Examiner—Donovan F. Duggan
Attorney, Agent, or Firm—Paul David Schoenle
A linear motor comprising a moveable coil, a stationary core in which the coil moves, and a drive member including a shaft and a bearing, the shaft moveable in the bearing and passing through the core. In the preferred embodiment, the drive member includes a pair of circular plates connected by three shafts that slide in bearings passing through the motor core, with the coil attached to the periphery of one of the plates. Springs having varying coil spacing are seated between the plates and the motor core to damp the motor's motion, with the strongest damping at the ends of its reciprocating stroke.
6 Claims, 4 Drawing Figures
U.S. Patent Nov. 26,1985 Sheet 1 of2 4,555,645
MOVEABLE COIL LINEAR MOTOR
BACKGROUND OF THE INVENTION
This is a continuation of application Ser. No. 445,792, 5 filed Dec. 1, 1982, now abandoned.
1. Field of the Invention
The invention in general relates to the field of electrical motors, and more particularly to a motor having a coil that moves linearly in a reciprocating motion. 10
2. Description of the Prior Art
Linearly reciprocating motors (that is, motors in which the moving element moves back and forth along a line) having moving coils have been known since the earliest days of electrical motors. See for example, U.S. 15 Pat. No. 524,044 issued Aug. 7, 1894 to Frank W. Merritt and Arthur R. Roe, which describes an electrical pump. However, as the art of electrical motors developed the linear motor disappeared from uses requiring substantial forces, such as in liquid pumps. At the pres- 20 ent time, the use of moving coil linear motors is generally limited to functions requiring rapid response and small forces. Typical modern applications are in loudspeakers, or the movement of magentic heads or pens in information processing systems. See for example, U.S. 25 Pat. No. 3,917,987 issued to Yuji Inoue. Moving coil type linear motors used for functions requiring significant forces generally have been extremely large motors. For example, the moving coil motor disclosed in U.S. Pat. No. 3,863,082 issued to Donald H. Gillott et al. 30 requires a motor occupying a volume of more than 1,600 cubic inches to provide a maximum force of about 46 pounds.
U.S. Pat. No. 2,669,937 issued to Shelley Presentey, on Nov. 8, 1950 describes a loudspeaker type linear 35 motor, ostensibly to be used for pumps and ostensibly rugged in design. However, no performance characteristics are given, so it is not known whether this motor solved the problem of relatively large size associated with powerful moving coil linear motors. Further, the 40 disclosure of the Presentey patent explicitly calls for elimination of all mechanical members such as shafts, journals, bearings and the like, which as will be seen below is directly contrary to the present invention.
SUMMARY OF THE INVENTION 45
It is an object of this invention to provide a moving coil linear motor that produces relatively large forces and yet is relatively small; for example a motor that can produce up to 300 pounds per square inch of force and 50 takes up a volume of about 85 cubic inches.
It is another object of the invention to provide a motor of the above size that is rugged enough to be used for pumping water continuously for long periods.
It is a further object of the invention to provide a 55 linear motor that also operates very quietly, in addition to the above features, so that it can be used for example in the quietest hospital environments.
It is yet a further object of the invention to provide a linear motor that includes one or more of the preceed- 60 ing objects and is very efficient.
The invention provides a linear motor having a moveable coil, a stationary core, and a drive member which includes a shaft and a bearing, the shaft being moveable in the bearing and passing through the core, 65 the coil being connected to the drive member. Preferably the shaft passes through the coil and the drive member includes a circular plate connecting the coil and the
shaft. In the preferred embodiment there are three shafts and three bearings, and the drive member includes a first plate to which the coil and one of each of the shafts are connected, and a second plate to which the other ends of the shafts are connected, with the shafts and bearings being spaced apart along a circle about the axis of the coil. Preferrably the motor includes a variable damping means, for example a coil spring with varying coil spacing. In the preferred embodiment the motor includes a pair of such coil springs, one spring of each pair extending between the first plate and the motor core, the other spring of each pair extending between the second plate and the motor core. Preferrably the drive member is made of a material that is lightweight and conducts heat well, such as aluminum.
. The motor of the invention has a number of synergistic features. For example, the design of the drive member not only provides significant additional stability to the motor, but also provides significant cooling function to the motor, since the aluminum shafts which pass through the motor interior carries away the heat of the motor, and the plates act as excellent radiators and also contribute a fanning effect. This significantly increases the ability of the motor to handle large amounts of power and to do correspondingly large amounts of work without over heating. The increased cooling means that there will be less expansion and distortion in the motor, and thus permits closer tolerances, which in turn permits the moving coil and the stationary core to be closer together than in previous linear motor, thus increasing their interaction, and further increasing the efficiency and power of the motor.
Numerous other features, objects, and advantages of the invention will now become apparent from the following detailed description when read in conjunction with the accompanying drawings, in which:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a top view of the preferred moving coil linear motor according to the invention;
FIG. 2 is a bottom view of the motor of FIG. 1;
FIG. 3 is a cross-sectional view of the motor of FIG. 1, taken along lines 3—3; and
FIG. 4 is a (cut-away) sectional view of an alternative embodiment of the motor according to the invention also showing an example of a pump which the motor has been used to operate.
DESCRIPTION OF THE PREFERRED
Referring to FIGS. 1-3, the preferred embodiment of the linear motor is shown. A top view of the motor is shown in FIG. 1, a bottom view in FIG. 2 and a crosssectional view in FIG. 3. Motor 10 comprises a core 11, a moveable coil 20, and a drive member 30. Core 11 includes a magnetically permeable top plate 12, a magnetically permeable bottom plate 14, an inner magnetically permeable core 15 and a permanent magnet 17. Coil 20 moves in a cylindrical slot 18 between magnet 17 and inner core 15. Drive member 30 comprises coil support 32, a pair of connecting members 33 and 34 in the form of circular plates, shafts 36 and screws 37. Coil 20 is attached to cylindrical coil support 32 which in turn is attached to a ring-shaped flange 35 extending from the bottom of upper connecting plate 33. Upper plate 33 is secured to lower plate 34 by the three shafts