Abstract:
A wheel assembly having a braking mechanism that is actuated by centrifugal force. The braking mechanism includes a rotating hub insert having a first pocket, a thread guard having a second pocket fixed relative to the frame of the wheel assembly, and an internal ball between the rotating hub insert and the thread guard. The internal ball can be flung by centrifugal force from the first rotating pocket to the second fixed pocket to cause a braking force from contact of the ball in the second pocket with the rotating hub insert. The amount of centrifugal force required to fling the ball into the second pocket can be calculated for rotation of the wheel greater than a certain predetermined speed.

Description:
BACKGROUND  
       [0001]     The present disclosure relates to a braking mechanism in a wheel assembly that is actuated by centrifugal force. More particularly, the disclosure relates to a braking mechanism having an internal ball that is flung by centrifugal force from one rotating pocket to another pocket in association with the braking force.  
         [0002]     Casters are small wheels that are attached to objects to make them easier to move. Often, controlling the speed of the object using the casters is desirable. For example, shopping carts, furniture moving carts, trolleys, baby walkers, or wheelchairs may have braking mechanisms to slow the object or avoid runaway carts. Damage or injury may occur if carts move too quickly or out of control. For example, an unattended shopping cart can roll due to wind or an incline into objects or people.  
         [0003]     Certain brake mechanisms require the user to manually operate a brake. However, such manual brakes are often inconvenient, and the user cannot always be relied upon to set the brake when use of the cart is finished. Other mechanical brakes can operate automatically without user intervention. A braking mechanism that is actuated by centrifugal force created when the wheel is rolling faster than a certain predetermined speed is particularly advantageous to stop runaway carts or to help maintain carts below a predetermined speed. The automatic operation avoids the necessity to be engaged or activated by the user of the cart.  
         [0004]     The terms “brake” and “braking” as used in this disclosure include both slowing and stopping. It includes reducing the speed of a cart as well as a stopping action. Certain other prior art brakes are meant to completely stop the rotation of a wheel, but in the present disclosure, “braking” is specifically intended to include slowing the rotation of the wheel.  
         [0005]     Braking mechanisms that automatically operate are known in the art. Friction brakes, such as U.S. Pat. No. 5,002,163, are used for self-decelerating wheels. Additional types of devices including hooks, springs, brake shoes, brake pawls, ratchets, etc. have not always held up well in the field. Other patents disclose activation by centrifugal force or using an internal ball to assist with braking.  
         [0006]     U.S. Pat. No. 3,623,575 discloses a wheel with a locking device including two movable locking members. A series of notches (8) are formed in the inner circular edge of a ring 9 of a wheel rim. Two balls (12) are each in opposing inclined tubular guideways. Each locking member engages when the floor is inclined so gravity causes the ball to roll into a notch. This stops and holds a cart from rolling downhill.  
         [0007]     U.S. Pat. No. 5,607,030 discloses a centrifugal shopping cart brake that engages when a predetermined speed is reached. The braking mechanism is enclosed within the wheel and operates with rotating weights and ratchet assemblies. Sliding weights 4 are moved by centrifugal force against an object having spring resistance. In another example, at a predetermined speed, a tang 55 on an arm 54 engages ratchet teeth that transfers energy to a ring and friction band to slow the wheel. Alternately, in FIG. 15, a weight 61 on a lever arm rotates due to centrifugal force and pushes on an object having spring resistance.  
         [0008]     U.S. Pat. No. 6,070,701 discloses a wheel having a roller 50 that operates in a semi-spherical half 30 of a wheel to act as a brake and reduce speed. The ball in between a stop piece 40 and the wall of the semi-spherical half of a wheel, and a slide way 42 has a variable width. When the wheel is rolled to a predetermined speed, the ball moves to the narrower width of the slide way, and the friction force of the ball on the stop piece/wall half acts as a braking force.  
         [0009]     U.S. Pat. No. 6,076,839 discloses, as best seen in FIG. 3, a safety brake device using a ball. FIG. 3 with the ball is cited prior art to that patent, and FIG. 6 is the brake device of the &#39;839 patent using a cylindrical pillar. FIG. 3 shows ball 18 inside an arched trough 17 of the ring groove 15. On each end of the trough are protruding arcs 23 of the fixed piece (block) 19 that form a tapered cavity narrower than the ball. When moving slowly, the ball remains in the lower wider portion of the arched trench. When the ball moves with centrifugal force, the friction of the ball against an arch 23 causes some braking action. FIG. 6 shows a cylindrical pillar 43 in a space with an obliquely arched edge 47, wherein friction of the pillar against walls of the internal space having a narrowing arch.  
         [0010]     U.S. Pat. No. 6,332,513 discloses a safety wheel having a ball 4 in an elongated trench 34 inside half of a wheel. The ball rolls to the lower end of the trench due to gravity when the wheel moves at slower speeds. The trench changes position when the wheel rolls. A side cover 5 has a stopping part 53 that does not rotate. At higher speeds, the ball does not roll to the lower end and stays in one end of the trench due to centrifugal force, and when this happens, the ball will be stopped by the stopping part and the wheel stops rolling.  
         [0011]     U.S. Pat. No. 6,374,954 discloses a speed control caster. A ball is in a chamber between the inner walls of two wheels on each side of an axle. The inner walls 22 are tapered forming a narrowing chamber for the ball as seen in FIG. 5B. A braking effect occurs due to friction between the axle piece and the walls due the rubbing of the ball when the ball is swept upward by the curves 23.  
         [0012]     One aspect of many of these wheels is that the brakes completely stop rotation, rather than a slowing braking action. Also, others do not automatically disengage in one rotation of the wheel after decelerating below a predetermined speed or the device must be stopped or reversed to disengage the brake.  
         [0013]     These do not include a rotating insert with a pocket that flings a ball into a fixed pocket located in the wheel&#39;s thread guard that accepts the ball due to centrifugal force at a predetermined speed of the wheel, wherein the ball in the fixed pocket acts as a brake due to friction with an outer ring of the insert.  
       SUMMARY  
       [0014]     The present invention is for centrifugal brakes for wheels using an internal ball that may be forced from a pocket by centrifugal force. A preferred wheel assembly has a centrifugal brake including a ball, a rotating hub insert and a thread guard. A rotating hub insert has a pocket for a ball used in conjunction with a fixed pocket in the thread guard that accepts the ball due to centrifugal force at a predetermined speed. The term “pocket” in this disclosure is meant to broadly cover any receptacle, cavity or opening.  
         [0015]     Instead of hooks, springs, brake shoes, brake pawls, or ratchets, the present disclosure includes a brake with only one new moving part, a ball (i.e. ⅜ inch steel), to the wheel for the intended braking use. The simplicity of the design allows for increased durability and performance, while being less costly to make and quieter to operate than other designs.  
         [0016]     The centrifugal brake in this disclosure automatically slows the wheel at a predetermined speed to avoid runaway carts and associated damages or injury. Also, the centrifugal brake automatically disengages in one rotation of the wheel after decelerating below a predetermined speed. The braking mechanism is internal so environmental conditions or debris cannot easily spoil, ruin, hamper, encumber or obstruct the wheel.  
         [0017]     A pocket for the ball on the circumference of the rotating insert is used in conjunction with a fixed pocket located in the thread guard.  
         [0018]     As an example only, an intended use for the centrifugal brake for a wheel is for a shopping cart, but this is not meant to limit the invention because it is apparent that the centrifugal brake could be used for a baby walker, wheelchair or other objects. The centrifugal brake for a wheel can be designed to be used on a shopping cart to control the speed of a runaway cart. The wheel assembly has a braking mechanism activated by centrifugal force created when the wheel is rolling faster than a certain predetermined speed, such as 3.5 miles per hour. The brake engages at the predetermined speed and creates a braking motion to slow the wheel. The predetermined speed can be regulated for each use based on components used in making the wheel assembly. The brake is intended to automatically disengage when the speed of the cart is slowed below the predetermined speed and the cart has rolled for at least a full revolution of the wheel.  
         [0019]     The braking force applied is weak enough to not impede the shopper or user who insists on walking faster than the predetermined speed, but it is strong enough to slow down an unattended shopping cart that is coasting in a parking lot to avoid or minimize damage of the cart hitting parked cars or other objects. Similarly, the centrifugal brake for a wheel can control the speed of furniture moving carts on a ramp or baby walkers and wheelchairs on an incline.  
         [0020]     As shown in the storyboard of  FIGS. 13-20 , the brake works when the speed of the wheel exceeds a predetermined speed, creating enough centrifugal force to fling the ball out of a pocket of the rotating insert into a fixed pocket located in the thread guard. One or both thread guards may have two anti-rotational ribs or stops on either side of the caster fork legs to keep the thread guard fixed relative to the legs. The ball is then trapped and pinched between the thread guard and the insert&#39;s outer ring of preferably soft polyurethane. The wheel will continue to roll, but the drag, friction or resistance of the trapped ball will slow the wheel as it is pushed over the soft polyurethane ring until the ball reaches the pocket of the rotating hub insert. If the wheel is still rolling too quickly, the ball will not drop back into the insert pocket, thereby starting another rotation of the braking action. When the wheel is traveling slower than the predetermined speed, the ball will drop back into the normal travel ball position in the insert pocket.  
         [0021]     The soft polyurethane material is abrasion resistant and capable of deflecting with the ball, creating drag, and then springing back into its original shape. Polyurethane can be the same tough plastic material used for the tread of the shopping cart wheel.  
         [0022]     This particular embodiment discloses use of a ball, such as the ⅜ inch steel ball as detailed, in conjunction with an insert ring adapted to work with the ball for braking action, but the ball could also include a variety of friction and anti-friction ball bearings, including different dimensions, sizes, materials, and weights. More or less friction, drag or resistance (braking force) can be generated by varying the interference fit of the ball with the polyurethane ring and the thread guard. Changing the diameter of the ring where the ball travels can change the speed required to centrifugally fling the ball, actuating the braking action. The weight and size of the ball can also affect the traveling speed when braking action occurs. The braking action slows motion by contact friction, but does not necessarily completely stop the rotation of the wheel.  
         [0023]     An optional feature of adding serrations to the ring surface of the insert can produce a pulsing effect to help identify when the brake is engaged. The optional serrated insert could be made of compressible, abrasion resistant polyurethane.  
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0024]     The features of this disclosure and the manner of obtaining them will become more apparent, and the disclosure itself will be best understood by reference to the following description of embodiments of the brake for a wheel taken in conjunction with the accompanying drawing in which  FIGS. 13-20  show a storyboard of the function and operation of the centrifugal brake, and others show particular embodiments of the centrifugal brake assemblies, wherein:  
         [0025]      FIG. 1  shows a side view of an embodiment of a wheel assembly;  
         [0026]      FIG. 2  shows a cross sectional view of a wheel assembly through a vertical center axis;  
         [0027]      FIG. 3  shows a side view of a wheel, insert and dual sealed bearing;  
         [0028]      FIG. 4  shows an inner side view of a thread guard;  
         [0029]      FIG. 5  shows a cross sectional view of a thread guard through a vertical center axis;  
         [0030]      FIG. 6  shows an outer side view of a thread guard;  
         [0031]      FIG. 7  shows a side view of an insert;  
         [0032]      FIG. 8  shows a cross sectional view of an insert through a vertical center axis;  
         [0033]      FIG. 9  shows a side view of another embodiment of a wheel assembly having a damping material and serrations in the ring surface of the insert;  
         [0034]      FIG. 10  shows a cross sectional view of a wheel assembly having a damping material and serrations in the ring surface of the insert through a vertical center axis;  
         [0035]      FIG. 11  shows a side view of a wheel with an insert having serrations in the ring surface;  
         [0036]      FIG. 12  shows a thread guard having a dampening material;  
         [0037]      FIG. 13  shows a wheel at rest or at travel slower than the predetermined speed with the ball resting in the pocket of the insert;  
         [0038]      FIG. 14  shows the ball remaining in the pocket at rest or at travel slower than the predetermined speed;  
         [0039]      FIG. 15  shows the ball approaching the fixed pocket;  
         [0040]      FIG. 16  shows the ball being centrifugally flung out of the pocket of the insert into the fixed pocket of the thread guard;  
         [0041]      FIG. 17  shows the ball being trapped and pinched between the thread guard and a ring surface of the insert;  
         [0042]      FIG. 18  shows the ball being pushed over the ring surface of the insert;  
         [0043]      FIG. 19  shows the ball reaching the pocket of the insert;  
         [0044]      FIG. 20  shows the ball dropping back into the normal travel ball position in the pocket of the insert. 
     
    
     DETAILED DESCRIPTION  
       [0045]     While the present invention will be fully described hereinafter with reference to the accompanying drawings, in which particular embodiments are shown, it is to be understood at the outset that persons skilled in the art may modify the embodiments disclosed herein while still achieving the desired result. Accordingly, the description that follows is to be understood as a broad informative disclosure directed to persons skilled in the appropriate art and not as limitations of the present disclosure.  
         [0046]      FIGS. 1 and 2  show a wheel assembly  10  as part of a caster  12  as often set between a pair of legs  14  and  16  connected by a base  17  of an inverted U-shaped frame  18  of which legs  14  and  16  are a part thereof. Preferably, the legs  14  and  16  extend away from the base  17  parallel to each other. The legs  14  and  16  preferably taper in width as they extend away from the base  17 . The ends  19  and  21  of legs  14  and  16  may be semi-circular, forming substantially U-shaped end portions  23  and  25 . Each end portion  23  and  25  has a hole  27  and  28  respectively concentric with the semi-circular ends  19  and  21 . The base  17  of the frame  18  can be attached by a stem  29  extending therefrom to a shopping cart, furniture moving cart, trolley, baby walker, wheelchair or other objects with a potential for wheels. The stem  29  can also be threaded. The base  17  may be a plate for various types of attachment to objects.  
         [0047]     The legs  14  and  16  straddle the wheel assembly  10  and a bolt  31  may extend through a pair of axially aligned holes  27  and  28  in the legs  14  and  16  and a hollow interior  33  of an axle  34  to render the wheel assembly  10  relatively rotatably supported on the frame  18 . Preferably, the base  17  includes a swivel to permit free turning of the caster  12  relative to the cart or similar other objects. As such, the wheel  36  may rotate in one direction. The particular preferred frame is not meant to limit the invention, and “frame” may include a structure designed to hold the wheel  36 .  
         [0048]     Wheel  36  may have a hub  37  with a central opening  38 . A bearing assembly  40  is preferably mounted in the opening  38 , and the bearing assembly  40  is preferably dual sealed, as shown in  FIG. 3 .  FIG. 10  shows a common 6002ZZ precision ball bearing. Regarding bearing assemblies, roller bearings carry heavier loads while ball bearings roll more easily but carry lesser loads. The wheel  36  can be rotatably supported on a cylindrical axle  34  by means of the bearing assembly  40 . As such, the axle  34  can be part of the bearing assembly  40 . The radial periphery  42  of the hub  37  preferably defines a tread mounting surface. The outer periphery  42  of the hub  37  may have synthetic resin material tread  44  secured thereto. A moldable synthetic resin tread material, particularly polyurethane, may be used as the tread  44 .  
         [0049]     The thread guards  46  and  48  each have a circular hole  50  and  52  respectively. Thread guards  46  and  48  are on opposite side of the wheel  36 . As shown, the small thread guard  46  may be made from a compressible or flexible nylon or similar wear-resistant material. The thread guard  48  forming a housing  54  is preferably made from a rigid nylon or similar wear-resistant material. Holes  27  and  28  of the legs  14  and  16  are coaxially aligned with the holes  50  and  52  of the thread guards  46  and  48 . The thread guards  46  and  48  are fixed against rotation relative to the frame  18 . A bolt  31  may be inserted through a hollow interior  33  of the axle  34  and the sets of coaxially aligned holes  27  and  28  of the legs  14  and  16  are coaxially aligned with the holes  50  and  52  of the thread guards  46  and  48 , respectively, so that the axle  34  is mounted upon the legs  14  and  16  of the frame  18 . A nut  56  can be screwed on the threaded end of the bolt  31  in order to prevent removal of the bolt  31  from the frame  18 .  
         [0050]     The thread guard  48  forming the housing  54  has an outer side  58  as shown in  FIG. 6  and an inner side  60  as shown in  FIG. 4 . The outer side  58  preferably forms a circle extending to the outer periphery  42  of the hub  37  to minimize contamination of the wheel  36 . The outer side  58  may have stops  62  and  64  on each side of end  19  of leg  14 . The inner side  60  may have a recessed area  66  with a fixed pocket  68 , which preferably remains at the top of thread guard  48 . Other features of the thread guard  48  could be a semi-circular groove  70  on the inner side  60  as shown in  FIG. 4  and a dampening material  72  as shown in  FIGS. 10 and 12 . As an option, a soft material can be adhered or molded to the inside of the thread guard  48  to absorb the clack of the ball  74  as the wheel  36  rotates. Preferably, this soft material is an elastomer that dampens sound and eliminates the clack and rattle of the moving ball  74 . The groove  70  may extend around a portion of the thread guard  48  to form a wall as the portion of the perimeter of the recessed area  66  that does not include the fixed pocket  68 . As shown in  FIG. 12 , the thread guard  48  can form a housing  54  without a groove and smaller than outer periphery  42  of the hub  37 .  
         [0051]     The fixed pocket  68  has rounded ends  76  and  78  forming corners  80  and  82  respectively. The area of the fixed pocket  68  between rounded ends  76  and  78  is sufficient to hold ball  74 , but the pocket  68  is preferably shallower in the radial depth from hole  52  than the diameter of the ball  74 . Thus, the ball  74  extends slightly from the pocket  68  when the ball  74  is in the pocket  68 . The fixed pocket  68  is preferably about 80-90 degrees (shown at 87 degrees in the drawings) of the perimeter of the recessed area  66 . The fixed pocket  68  is preferably at the top of the recessed area  66  so gravity will allow the ball  74  to drop from the fixed pocket  68  under the appropriate circumstances. Also, in operation, the ball  74  can be forced up against gravity (flung) by centrifugal force into the fixed pocket  68 .  
         [0052]     In the wheel assembly  10 , a rotating insert  84  can be attached to the hub  37  or can be part of the hub  37 . The rotating insert  84  is preferably located inside the recessed area  66  of the thread guard  48 . The rotating insert  84  has a pocket  86 . The insert pocket  86  is of sufficient size to hold the ball  74 , and the insert pocket  86  may be the same depth as the diameter of the ball  74  or preferably slightly deeper. The insert pocket  86  has two edges  88  and  90 . Leading edge  88  is preferably somewhat rounded with a slope into the pocket  86 . The trailing edge  90  may form a lip so the pocket  86  forms a cup with a partial circumference similar to the ball  74 . The trailing edge  90  forming a lip is preferred for a wheel  36  designed to rotate in one direction, such as for swivel casters. Edges  88  and  90  can both be rounded with a slope into the pocket  86  for wheel designed to rotate in both directions.  
         [0053]     The outer radial surface of the insert  84  can be called the brake ring surface  92 , which is adapted to work with the ball  74  for braking action. The brake ring surface  92  extends from edge  88  to edge  90  around the portion of the insert  84  not including the pocket  86 . The ball  74  can be trapped and pinched between the thread guard  48  and a brake ring surface  92  of preferably soft polyurethane, which is capable of deflecting with the ball  74 , creating drag, friction, or resistance, and then springing back into its original shape. More or less drag, friction, or resistance (braking force) can be generated by varying the interference fit of the ball  74  with the brake ring surface  92  and the thread guard  48 . The brake ring surface  92  can include constant surface of the insert  84 , an inserted semi-circular band, or similar circular objects with an aperture in the center. An optional feature of adding serrations  94  to the brake ring surface  92  can produce a pulsing effect to help identify when the brake is engaged. The brake ring surface  92  with optional serrations  94  could also be made of compressible, abrasion resistant polyurethane.  
         [0054]     Ball  74  can be flung by centrifugal force from insert pocket  86  to fixed pocket  68  in association with the braking force. The ball  74  remains internal to the wheel assembly  10  between thread guard  48  and insert  84 . For the shopping cart embodiment, a ⅜ inch steel ball is disclosed, but the ball  74  could also include a variety of friction and anti-friction balls, including different dimensions, sizes, materials, and weights. The ball  74  optionally may be lightly lubricated with grease or silicone to diminish built up frictional heat.  
         [0055]      FIGS. 13-20  shows how the braking action works when the speed of the wheel  36  exceeds a predetermined speed, creating enough centrifugal force to fling the ball  74  out of a pocket  86  of the rotating insert  84  into a fixed pocket  68  located in the thread guard  48 .  FIG. 13  shows the wheel  36  at rest or at travel slower than the predetermined speed. The ball  74  rests in the pocket  86  of the insert  84 .  FIG. 14  shows the ball  74  remaining in the pocket  86  at rest or at travel slower than the predetermined speed. In  FIG. 15 , the ball  74  approaches the fixed pocket  68 . In  FIG. 16 , the ball  74  is centrifugally flung out of the pocket  86  of the insert  84  into the fixed pocket  68  of the thread guard  48 , such as when the wheel  36  is moving faster than the predetermined speed. In  FIG. 17 , the ball  74  is then trapped and pinched between the thread guard  48  and a brake ring surface  92  of the insert  84 . The ball  74  is shown in the rounded end  78 . As shown in  FIG. 18 , the wheel  36  will continue to roll, but the drag, friction, or resistance of the trapped ball  74  will slow the wheel  36  as the ball  74  is pushed over the brake ring surface  92 —at least until the ball  74  reaches the pocket  86  of the insert  84  as shown in  FIG. 19 . If the wheel  36  is still rolling faster than the predetermined speed, the ball  74  will not drop back into the pocket  86  of the insert  84 , thereby starting another rotation of the braking action. When the wheel  36  is traveling slower than the predetermined speed, the ball  74  will drop back into the normal travel ball position in the pocket  86  of the insert  84  as shown in  FIG. 20 .  
         [0056]     Although preferred embodiments of the disclosure are illustrated and described in connection with particular features, it can be adapted for use with a wide variety of wheels. Other embodiments and equivalent assemblies, brakes, balls, and wheels are envisioned within the scope of the claims. Various features of the disclosure have been particularly shown and described in connection with illustrated embodiments. However, it must be understood that the particular embodiments merely illustrate and that the invention is to be given its fullest interpretation within the terms of the claims.