BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to vibrating devices and more particularly to vibrating devices for plows. 
     2. Description of Related Art 
     U.S. Pat. No. 1,190,501 discloses a gyratory structure in which a crank shaft imparts a rotary motion to sieve boxes. 
     U.S. Pat. No. 4,142,451 discloses a vibrator with pistons which move toward and away from the axis. Movement of the pistons is controlled by approach ramp surfaces. 
     U.S. Pat. No. 4,241,615 discloses a vibrating device in which weights at the end of a rotating arm are effectively moved in and out with respect to the axis by the rotation of unbalanced masses. 
     U.S. Pat. No. 4,617,832 discloses a vibratory apparatus having a movable weight which is moved by fluid pressure against a spring. 
     U.S. Pat. No. 5,054,331 discloses a gyroscopic propulsion apparatus in which sliding rods which bear weights are used to vary the radius of rotation of the weights. The positions of the weights with respect to the radius are controlled by a cable and pulley. 
     U.S. Pat. No. 5,146,798 discloses a transmission apparatus using wedge hinge assemblies which cause a weight to move toward and away from the axis of rotation. 
     The prior art disclosures do not meet the needs which are met by the present invention, the need for a simple, inexpensive, reliable vibratory device. 
     SUMMARY OF THE INVENTION 
     The vibrator of this invention is based on the fact that vibration results from the rotation of weights of equal mass located at the ends of rotating arms if the effective radius of the arms is different. 
     In this vibrator, a rotating radius variation subassembly is rotated. In this subassembly the effective radius of each weight located at the end of a rotating arm is varied mechanically during the rotation of each weight through a full circle. Each weight is attached to arms located on each of two collars. The upper collar is given an eccentric motion with respect to the lower collar due to the rotation of the upper collar about a bent axle. Variation in the effective radius of the weights is caused by the effect of the eccentric motion of the upper collar. 
     The location of the upper collar on the axle may be varied using a ring and setscrew attached to the axle. The eccentricity of movement of the upper collar is increased, along with the variation in effective radius of the weights, and the resulting vibration, when the ring is used to secure the upper collar relatively far from the lower collar. 
     A motor or other source of rotary motion is used to rotate the radius variation subassembly. 
     An objective of this invention is a vibrator having unbalanced weights wherein the amount of unbalance may be varied. 
     Another objective is a vibrator in which the weights are rendered unbalanced by differences in the effective radius of their rotation. 
     Another objective is a vibrator in which the effective radius of the weights varies continuously during the rotation of the vibrator. 
     A final objective is a vibrator which is simple, inexpensive, reliable, and long lasting. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic representation of the vibrator in side view. 
     FIGS. 2, 3, 4, and 5 are diagrams showing the effective radius of the weights during the rotation of the radius variation subassembly through a complete circle. 
     FIG. 6 is a diagram showing the directions of the forces generated by the rotation of the radius variation subassembly through a complete circle. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a diagram of the side view of the vibrator 10. A base 40 supports the vibrator 8. A C-shaped support member 26 is rigidly attached to the base 40. Holes 24 and 25 are located in support member 26. A nonrotating axle 36 is inserted into holes 24 and 25 in the support member 26 and the axle is welded to the support member at holes 24 and 25. The axle 36 has a bend 38, which is exaggerated for clarity in FIG. 1. The intensity of vibration imparted by the vibrator is in part due to the size of the bend 38, which may be from 0.01° to 45°. A preferred range is 1° to 45°. 
     A freely rotating lower collar 17 is axially located on the axle 36 between the bend 38 and the weld 24. Lower arms 16 and 29 are radially attached at a first end to lower collar 17 along a single diameter to collar 17. Lower arms 16 and 29 are equal in length. Hinge 30 is attached at a second end to arm 29, and hinge 46 is attached at a second end to arm 16. Connecting link 31 is attached at a first end to hinge 30, and connecting link 15 is attached at a first end to hinge 46. Connecting link 31 is equal in length to connecting link 15. 
     A freely rotating upper collar 37 is axially located on the axle 36 on the other side of the bend 38. Upper arms 11 and 35 are radially attached at a first end to upper collar 37 along a single diameter to collar 37. Upper arms 11 and 35 are equal in length and are equal in length to lower arms 16 and 29. Hinge 34 is attached at a second end of arm 35, and hinge 12 is attached at a second end of arm 11. Connecting link 33 is attached at a first end to hinge 34, and connecting link 13 is attached at a first end to hinge 12. Connecting link 33 is equal in length to connecting link 13 and both are equal in length to connecting links 31 and 15. 
     Connecting links 31 and 33 are connected at a second end to weight hinge 47 and connecting links 13 and 15 are connected at a second end to weight hinge 48. 
     Weight 32 is attached to weight hinge 47 and weight 14 is connected to weight hinge 48. The mass of weight 32 is equal to the mass of weight 14. 
     The subassembly 11 consisting of lower and upper collars, arms, connecting links, hinges, and weights is termed the radius variation subassembly 9. 
     Rotation of lower collar 17 causes rotation of the entire radius variation subassembly 9. 
     The location of upper collar 37 along the length of axle 36 may be fixed by ring 42 axially located on axle 36 and is secured by setscrew 44. By varying the location of ring 42, the location of upper collar 37 on axle 36 is varied. 
     Rotating spacer 18 is axially located on axle 36 and is firmly attached to the underside of collar 17. Rotating gear 19 is axially located on axle 36 and is firmly attached to the underside of spacer 18. Gear 19 meshes with gear 20. Gear 20 is attached at one end to second axle 21. Second axle 21 is supported by journal bearings 22 and 27. Bearings 22 and 27 are attached to the arms of C-shaped support member 26. Pulley 28 is attached to second axle 21. Pulley 28 is driven by electric motor 50 via pulley 45 on the motor and v-belt 49. 
     In operation, motor 50 causes gear 20 to rotate, which causes gear 19, spacer 18, and lower collar 17 to rotate. Rotation of lower collar 17 causes the entire radius variation subassembly to rotate. Since axle 36 is bent at 38, the center of rotation of upper collar 37 is displaced from the center of rotation of lower collar 17. The displacement of upper collar 37 from lower collar 17 varies with the location of the radius variation subassembly in a complete circle. The displacement of upper collar 37 from lower collar 17 affects the distance between hinge 34 located on upper arm 35 and hinge 30, located on lower arm 29. Similarly, this displacement affects the distance between hinge 12 located on upper arm 11 and hinge 46 located on lower arm 16. The distance of weights 32 and 14 from axle 36 at lower collar 17 is termed the effective radius of rotation of each weight. In FIG. 1, the effective radius of rotation of weight 32 is greater than the effective radius of rotation of weight 14. Rotation of the radius variation subassembly causes the vibration of the vibrator. 
     The degree of displacement of upper collar 37 with respect to lower collar 17 may be varied by the location of upper collar 37 on axle 36. The variation will be greater the farther away upper collar 37 is from lower collar 17. The greater the distance of upper collar 37 is from lower collar 17, the greater is the variation in effective radius of rotation of the weights, and the greater the vibration of the vibrator. Ring 42, secured by setscrew 44, is used to fix upper collar 37 at a desired location on axle 36. 
     FIGS. 2, 3, 4, and 5 diagrammatically depict the displacement of upper collar 37 from lower collar 17 and the effective radius of rotation of weights 14 and 32 during one complete rotation of radius variation subassembly 9. For the purposes of FIGS. 2-5, it will be assumed that the length of lower arms 16 and 29 equals 20 inches and that the length of connector links 31 and 15 equals 10 inches. These numbers are used only as an example. The invention may have arms and connector links of other lengths, and may have other ratios between the lengths of the arms and connector links. The orientation of the arms through a complete rotation is indicated by the circle 52 with marks indicating 0, 90, 180, and 270 degrees. 
     FIG. 2 shows the radius variation subassembly 9 with weight 14 at 0 degrees and weight 32 at 180 degrees. Because of the displacement of collar 37 relative to collar 17 the effective radius of rotation of weight 14 is at its minimum and is the length of arm 16 plus approximately one half of the length of connector link 15, or 20 inches plus 5 inches or 25 inches. Similarly, because of the displacement of collar 37 relative to collar 17 the effective radius of rotation of weight 32 is the length of arm 29 plus approximately the length of connector link 31, or 20 inches plus 10 inches or 30 inches. 
     FIG. 3 shows subassembly 9 with weight 14 at 90 degrees and weight 32 at 270 degrees. In this position, the effective radius of rotation of both weights 14 and 32 are the same, and the effect of the displacement of collar 37 from collar 17 is the same for each weight and is intermediate between the effect when a weight is at 0 or at 180 degrees. The effective radius of rotation of weights 14 and 32 is 20 inches plus approximately 71/2 inches or 271/2 inches. 
     FIG. 4 shows subassembly 9 with weight 32 at 0 degrees and weight 14 at 180 degrees. The effective radius of rotation of weight 32 is 25 inches and the effective radius of rotation of weight 14 is 30 inches. 
     FIG. 5 shows subassembly 9 with weight 32 at 90 degrees and weight 14 at 270 degrees. The effective radius of rotation of both weight 32 and weight 14 is 271/2 inches. 
     When the weights are at 0 and 180 degrees as in FIGS. 2 and 4 the difference in effective radii of weights 14 and 32 are at a maximum and the contribution to vibration is at a maximum. When the weights are at 90 and 270 degrees as in FIG. 3 and FIG. 5 the effective radii of the weights are equal and there is no contribution to vibration. 
     It should be noted that the displacement of collar 37 from collar 17 does not vary during the course of a rotation. The vibratory impulse occurs at the same points in each rotation of the subassembly. Because of this invariant relationship between vibratory impulse and rotation, the direction of the vibration is determined and controlled. 
     FIG. 6 is a diagram which shows the direction of the forces generated by the clockwise rotation of a radius variation subassembly. A and B represent weights at the arms of a subassembly. Clockwise rotation of weights A and B through 1/4 turn, i.e. rotation of A from E to F and B from L to H, produces forces in the direction of arrows C and D for the duration of the 1/4 turn. These forces give momentum in the direction represented by arrow G. 
     A further 1/4 turn rotation, i.e. rotation of A from F to L and B from H to I, produces forces in the direction of arrows J and K. 
     These forces and momentum are repeated by further rotation of the subassembly. 
     The over all movement is first forward in direction as indicated by momentum G, followed by the generation of opposing forces which bring the whole device to a halt. 
     It will be apparent to those skilled in the art that the examples and embodiments described herein are by way of illustration and not of limitation, and that other examples may be used without departing from the spirit and scope of the present invention, as set forth in the appended claims.
This invention provides a simple and inexpensive vibrator. Upper and lower linked arms are used to hold equal weights attached at the ends of the arms. The arms are attached to collars which spin. A bent axle is used to cause displacement of the upper collar with a resultant shortening of the effective radius of rotation of one of the weights at a determined position in the circle of rotation. This shortening of the effective radius of rotation imparts a vibratory motion to the vibrator.