Abstract:
A high torque resistant and strong screwless plastic gear box has a reduced thickness at its output shaft. The gear box and a reduction drive assembly therein may be used particularly, but not exclusively, in a slot machine with a spinning drum or hopper which holds coins or tokens to be released therefrom. The gear box includes a main body and a cover which is ultrasonically welded thereto. Locating posts, holding tubes, inner welding pads, outer surrounding tubes, and locating ribs are provided to weld the cover to the main body. Acoustical chambers are formed between outer walls and inner arcuate walls of the main body. The inner arcuate walls surround all of the shafts and gears inside the main body. This double-walled construction reduces noise and provides surprising mechanical strength. All of the gears are mounted on only three shafts secured between the main body and the cover. Four of the gears are stacked on a single central shaft and rotate in two pairs independently of each other.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]    This application is related to a U.S. Design Patent Application (Our Docket No. 223620US51) filed concurrently herewith. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention relates to machine elements and mechanisms generally, but more particularly to small but strong plastic gear boxes with reduction drive assemblies inside.  
           [0004]    2. Description of the Related Art  
           [0005]    U.S. Pat. No. 5,598,746 to Chen describes a transmission assembly having a plastic box and cover employing locating posts. U.S. Pat. No. 5,737,968 to Hardey et al. discloses a gear motor assembly with a three-part molded housing having plural cylindrical connector bosses which may be ultrasonically welded together. U.S. Pat. No. 4,825,727 to Komuro relates to a speed reducer having a gear mounting plate formed with ribs for noise reduction. These three prior art devices appear to be most relevant to the gear box of the present invention, in the applicant&#39;s view.  
           [0006]    U.S. Pat. No. 2,908,180 to Swenson reveals a gear reduction unit for a fractional horsepower motor comprising a stationary stub shaft and a rotatable work shaft with a train of intermeshing reduction gears floating free on both shafts to drive a final fixed output gear on a power shaft in the last stage. Power is received from a motor pinion driving a floating gear on a power shaft in the first or input state. U.S. Pat. No. 5,038,629 to Takimoto discloses a drive transmission mechanism having plural stages of gear reduction. Plural gears are supported by the same shaft and are rotatable relative to each other. For an example, see column 4 at lines 22-27. European Patent No. 617,213 to Masumi refers to a motorized actuator having a train of reduction gears. Plural supporting shafts each have more than one gear thereon and are able to rotate relative to one another. See column 5, line 56, through column 6, line 39. These three earlier patents appear to be the most relevant references in relation to the reduction drive assembly of the present invention, in the applicant&#39;s view.  
           [0007]    An exemplary prior art device is illustrated in a cross-sectional view in FIG. 1. A gear box  10  has a main body  11  made of die cast zinc metal and is attached to a direct current (D.C.) motor  12  which drives a small input gear  14  held on an input shaft  16 . The small input gear  14  drives a first cluster gear  18  which rotates with a first pinion gear  20  that, in turn, drives a second cluster gear  22  which rotates with a second pinion gear  24 . The first cluster gear  18  and the first pinion gear  20  are mounted on a first shaft  26  while the second cluster gear  22  and the second pinion gear  24  are mounted on a second shaft  28 . The first shaft  26  and the second shaft  28  are topped by spacers  30  and  32 , respectively, that separate the shafts  26  and  28  from a cover  34  which is connected by screws (not shown) to the main body  11  and which is also made of the same die cast zinc metal as the main body  11 . The second pinion gear  24  drives a third cluster gear  36  which rotates with a third pinion gear  38  that, in turn, drives a large output gear  40  mounted on an output shaft  42 . A first collar  44  secures one end of the output shaft  42  to the main body  11  while a second collar  46  secures an opposite end of the output shaft  42  to the cover  34 . A small, flat sheet of steel is rolled to form a C-shaped pin  48  that is inserted at the opposite end of the output shaft  42  in order to spin a drum or hopper  6  holding coins or tokens in a slot machine  1 . The gear box  10  is fastened to the slot machine  1  through a wall  4  by a plurality of bolts  8 .  
           [0008]    Although the exemplary prior art device illustrated in FIG. 1 is made of metal, it requires screws (not shown) to fix the cover  34  to the main body  11 . Thus, because the holes required for the screws weaken the solid structure of both the main body  11  and the cover  34 , the gear box  10  is not as strong as it could be if there were no screw holes therethrough.  
           [0009]    Also, because of the positioning of the various cluster gears and pinion gears on five separate shafts, the amount of force which can be transmitted from the small input gear  14  to the large output shaft  42  is limited. Thus, it remains a problem in the prior art to produce a high torque resistant and strong screwless gear box holding a reduction gear assembly inside.  
         SUMMARY OF THE INVENTION  
         [0010]    A primary object of the present invention is to provide a high torque resistant and strong screwless plastic gear box to overcome the problems existing with prior art metal gear boxes.  
           [0011]    A secondary object of the present invention is to reduce substantially the thickness of the gear box at the output shaft.  
           [0012]    The present invention relates generally to a plastic gear box and a reduction drive assembly for mounting in the gear box to achieve the above-stated goals. The gear box and the reduction drive assembly may be used particularly, but not exclusively, in a slot machine with a spinning drum or hopper which holds coins or tokens to be released therefrom upon receiving an electrical signal after a predetermined number of coins have been deposited into the slot machine.  
           [0013]    The gear box includes a plastic main body and a plastic cover which is ultrasonically welded to the main body. Welding pads and surrounding tubes are provided at intervals around a periphery of the main body and the cover. Also, locating ribs are provided inside the cover of the gear box. Plural locating posts on the cover are ultrasonically welded into corresponding hollow holding tubes in the main body to increase the strength of the gear box so that it can withstand high torque levels without fracturing.  
           [0014]    This arrangement results in an empty gear box, without the drive assembly inside, being capable of withstanding torques up to 300 inch-pounds and weights up to at least 225 pounds without breakage and without the use of any screws to retain the cover on the main body.  
           [0015]    This main body also has acoustical chambers between outer straight walls and inner arcuate walls. The inner arcuate walls surround all of the various shafts and gears inside the main body. This double-walled construction reduces noise and provides surprising mechanical strength greater than that of any other known prior art plastic gear boxes. This characteristic of the present invention was an unexpected result for a plastic gear box resulting in strength comparable to a metal gear box.  
           [0016]    The drive assembly mounted between the cover and the main body includes gears mounted on only three shafts instead of the five shafts of the prior art device shown in FIG. 1. Power from a D.C. motor is supplied to the gear mounted on a first input shaft. This gear, in turn, drives gears stacked on a single central shaft. The last of the central gears then drives an output gear on the output shaft.  
           [0017]    To summarize the invention, it relates to a high torque resistant and strong screwless plastic gear box, particularly characterized by ultrasonically welded pads, locating ribs and support posts. The invention also relates to the drive assembly described above by which four of the central gears are stacked to rotate in pairs independently on a single central shaft.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    A more complete appreciation of the invention and its advantageous features will be readily understood by reference to the following detailed discussion when considered with the accompanying drawings that are briefly described below.  
         [0019]    [0019]FIG. 1 is a cross-sectional side elevation view of a known prior art device.  
         [0020]    [0020]FIG. 2A is a cross-sectional side elevation view of the gear box of the present invention with the internal drive assembly under a cover.  
         [0021]    [0021]FIG. 2B is a partial top plan view taken along line  2 B- 2 B of FIG. 2A.  
         [0022]    [0022]FIG. 3A is a bottom plan view of the main body of the gear box.  
         [0023]    [0023]FIG. 3B is a top plan view of the main body of the gear box with the internal drive assembly removed therefrom.  
         [0024]    [0024]FIG. 3C is a cross-sectional side elevation view taken along line  3 C- 3 C of FIG. 3B.  
         [0025]    [0025]FIG. 4A is an underside view of the cover of the gear box.  
         [0026]    [0026]FIG. 4B is a cross-sectional side elevation view taken along line  4 B- 4 B of FIG. 4A.  
         [0027]    [0027]FIG. 4C is a top plan view of the cover with the main body of the gear box thereunder.  
         [0028]    [0028]FIG. 5 is a partially cutaway cross-sectional view of the gear box with the internal drive assembly removed therefrom. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0029]    Referring now to the drawings, like reference numerals designate identical or corresponding parts throughout the several views.  
         [0030]    A cross-sectional view of the invention is shown in FIG. 2A. A gear box  110  has a main body  111  made of ABS plastic and is attached to a direct current (D.C.) motor  112  which turns a small input shaft  116  that carries and rotates a small input gear  114 . Teeth  115  on the small input gear  114  mesh with and drive teeth  117  on a first central gear  118  which carries and rotates with a first pinion gear  120 . This gear  120  has teeth  121  that, in turn, drive a second gear  122  which carries and rotates with a second pinion gear  124 .  
         [0031]    The small input gear  114  is made of hard plastic while the small input shaft  116  is made of steel. The first central gear  118  is made of plastic while the first pinion gear  120  is made of steel. Both the second gear  122  and the second pinion gear  124  are formed integrally of steel. Note that the first steel pinion gear  120  and the second steel pinion gear  124  have diameters of the same size.  
         [0032]    The first central gear  118  and the first pinion gear  120  are mounted on a single central shaft  126  while the second gear  122  and its pinion gear  124  are mounted on a second shaft  128 . The single central shaft  126  is held at one end  126 A in a first raised boss  111 A of the main body  111  and is held at its opposite end  126 B in a first raised boss  134 A of a cover  134 . Similarly, the second shaft  128  is held at one end  128 A in a second raised boss  111 B of the main body  111  and is held at its opposite end  128 B in a second raised boss  134 B of the cover  134 .  
         [0033]    Teeth  125  on the second pinion gear  124  mesh with teeth  135  on a third gear  136  which carries and rotates with a third pinion gear  138  that has teeth  139  which, in turn, drive a large output gear  140  mounted on an output shaft  142 .  
         [0034]    A first collar  144  of the main body  111  has a bore  144 B which surrounds a midsection of the output shaft  142  while a second collar  146  secures a nonworking end  142 B of the output shaft  142  to the cover  134 . A gap  143  is provided between the nonworking end  142 B of the output shaft  142  and a bottom  145  of the second collar  146 . A lubricant such as grease may be squirted into the gap  143  through a channel  147  bored through the cover  134 .  
         [0035]    Both the first collar  144  and the second collar  146  are formed integrally with the main body  111  and the cover  134 , respectively. This integral formation reduces the number of parts needed for manufacturing the gear box  110  by eliminating the separate collars  44  and  46  in the prior art gear box  10  illustrated in FIG. 1.  
         [0036]    Returning to FIG. 2A, the third gear  136 , the third pinion gear  138 , the output gear  140 , and the output shaft  142  are all made of steel. Thus, the gear assembly starts with the small plastic input gear  114  and eventually transitions to the large steel output gear  140  by the unique internal arrangement of the various reduction gears constituting the drive assembly.  
         [0037]    At a working end  142 A of the output shaft  142 , there is a solid steel pin  148  which spins a drum or hopper  106  holding coins or tokens in a slot machine  100 . Although the solid steel pin  148  is preferred, any other suitable type of coupling may be used, such as a threaded shaft, a D-shaft, a shaft with double flat ends, etc.  
         [0038]    So, there are three shafts, namely the central shaft  126 , the second shaft  128  and the output shaft  142 . The output shaft  142  has a longer length and a thicker diameter than the central shaft  126  and the second shaft  128  so that the output shaft  142  is able to carry the output gear  140  which is much larger than the first gear  118 , the second gear  122 , and the third gear  136 . Although the central shaft  126  and the second shaft  128  have the same length and the same diameter and each of the shafts  126  and  128  carry gears  136  and  122 , respectively, which have the same diameter, the pinion gears  138  and  124  have different diameters. However, the pinion gear  120  carried with the first central gear  118  has the same diameter as the pinion gear  124  formed integrally with the second gear  122 . Thus, although the first central gear  118  and the third gear  136  are mounted on the same central shaft  126 , these gears  118  and  136  are driven independently of each other by the input gear  114  and the second pinion gear  124 , respectively.  
         [0039]    A bore  150  through the main body  111  allows a user to locate the one end  128 A of the second shaft  128  from outside the gear box  110 . Likewise, a concave dimple  152  in the main body  111  serves to allow the user to locate the one end  126 A of the central shaft  126  from outside the gear box  110 . However, unlike the bore  150 , the dimple  152  does not penetrate completely through an exterior surface of the main body  111 , but may be easily drilled through in order to reach the central shaft  126 , if necessary.  
         [0040]    By engaging both the central shaft  126  through the drilled dimple  152  and the second shaft  128  through the bore  150 , the user may extract the gear box  110  from the D.C. motor  112 , if the gear box  110  cannot be removed because it is stuck in place by the D.C. motor  112 .  
         [0041]    In FIG. 2B, there is seen a partial top plan view of the main body  111  from which the first collar  144  protrudes to retain the output shaft  142  with its working end  142 A through which the solid steel pin  148  extends.  
         [0042]    Clearly, the solid steel pin  148  of the present invention is stronger and more torque resistant than the C-shaped pin  48  of the prior art device seen in FIG. 1. Thus, the pin  148  of the present invention is able to work harder than the weak pin  48  of the prior art device.  
         [0043]    In FIG. 3A, there is illustrated a bottom plan view of the main body  111  of the gear box  110 . The pin  148  extends through the output shaft  142  which is surrounded at its midsection (not shown) by the first collar  144 .  
         [0044]    There are four vertically grooved holes  158  of which only two are shown on a left side of the main body  111 . On a right side of the main body  111 , there are seen two of four heads  160  on threaded bolts  162 , not shown in FIG. 3A but seen instead in FIG. 2A, where two of the four heads  160  are also illustrated. As shown in both FIGS. 2A and 3A, a washer  164  separates each head  160  from a top  166  of a raised protuberance  168  formed integrally with the main body  111 .  
         [0045]    As seen in FIG. 3A, the four holes  158 , of which only two are shown, are positioned on the main body  111  symmetrically and equidistantly from the output shaft  142  so that, when the bolts  162  (not shown) under the heads  160  are threaded into the holes  158 , the output shaft  142  has superior stability and maximum strength whenever the pin  148  is exerting torque to perform work.  
         [0046]    Of course, instead of the bolts  162  seen in FIG. 2A, a plurality of other types of suitable fasteners, such as long screws, may be placed in the holes  158  to stabilize the output shaft  142  and also may be used to mount the gear box  110  securely to a wall  104  of the slot machine  100 .  
         [0047]    Preferably, as seen in FIG. 3A, the vertically grooved holes  158  are provided with correspondingly grooved steel or brass inserts  170  which are internally threaded for receiving the bolts  162  seen in FIG. 2A.  
         [0048]    [0048]FIG. 3B shows a top plan view of the main body  111  of the gear box  110  with the internal drive assembly and the cover  134  (not shown) removed therefrom.  
         [0049]    The four holes  158  are positioned symmetrically and equidistantly from a center of the bore  144 B through the first collar  144 . An end view of each of a plurality of hollow holding tubes  156  is seen adjacent to each of the four holes  158 .  
         [0050]    A plurality of inner welding pads  172  is formed integrally and is arranged along an outer periphery of the main body  111 . Each pad  172  is separated by a space from a surrounding short outer tube  174 . Each pad  172  is preferably circular and each tube  174  is preferably cylindrical in shape. However, other shapes may be used, if desired. These pads  172  are heated ultrasonically so that each pad  172  partially melts with its corresponding short tube  174  in order that the main body  111  is welded to the cover  134 , seen in FIG. 2A, to keep the gear box  110  securely sealed shut.  
         [0051]    In FIG. 3B, thin rib walls  176  radiate from some of the short tubes  174  to an inner periphery which is made up of a plurality of arcuate wall sections  178  formed integrally inside the main body  111 . Thus, the outer periphery of the main body  111 , the short tubes  174 , the thin rib walls  176 , and the arcuate wall sections  178  together form differently shaped acoustical chambers  180  which may be full of insulating air or packed with grease for noise reduction. Note that each chamber  180  is formed integrally in the main body  111 .  
         [0052]    The arcuate wall sections  178  together form an enclosed space within which lubricant for the drive assembly is readily retained. Because the lubricant cannot fly out of the enclosed space surrounding all of the shafts and the gears of the drive assembly while the gears are turning on the shafts, the gears have a longer work life and need to be lubricated less frequently. Within the arcuate wall sections  178 , besides the first collar  144 , there is the first raised boss  111 A and the second raised boss  111 B. A blind hole  111 C in the first raised boss  111 A receives the one end  126 A of the central shaft  126  seen in FIG. 2A while a flanged hole  111 D in the second raised boss  111 B receives the one end  128 A of the second shaft  128 , also seen in FIG. 2A.  
         [0053]    In FIG. 3B, thick ribs  182  radiate from the first collar  144 , the first raised boss  111 A, and the second raised boss  111 B to the arcuate wall sections  178  which form an internal space for retaining the drive assembly so that no individual gear may fly away in the unlikely event that a shaft breaks and a gear slips off.  
         [0054]    [0054]FIG. 3C shows a cross-sectional side elevation view of the main body  111  taken along line  3 C- 3 C in FIG. 3B. The curvature of three arcuate wall sections  178  is clearly illustrated throughout most of FIG. 3C. Along the left side of the main body  111 , there are seen the first collar  144 , the first raised boss  111 A, and the second raised boss  111 B. Two of the four raised protuberances  168  are also shown. Behind one of the thin rib walls  176 , there is seen in phantom lines part of one of the acoustical chambers  180 .  
         [0055]    [0055]FIG. 4A shows the cover  134  with its underside that faces the internal drive assembly. Around the periphery of the underside, there are arranged a plurality of locating posts  154 , a plurality of welding rings  184 , and a plurality of locating ribs  186 .  
         [0056]    Referring back to FIG. 3B, each welding ring  184  seen in FIG. 4A is fitted snugly into the space between its corresponding inner welding pad  172  and its corresponding outer short tube  174  so that, when ultrasonic radiation is applied to each combination of the ring  184 , the pad  172  and the tube  174 , the combination melts together in order to weld the cover  134  onto the main body  111  to close the gear box  110  securely.  
         [0057]    Referring again to FIG. 3B, each locating rib  186  seen in FIG. 4A is positioned so as to snap into a corresponding acoustical chamber  180  along the outer periphery of the main body  111  to help in providing secure closure of the cover  134  over the main body  111 .  
         [0058]    In FIG. 4A, away from the outer periphery of the cover  134 , there are arranged the second collar  146 , the first raised boss  134 A, and the second raised boss  134 B. A flanged hole  134 C in the first raised boss  134 A receives the opposite end  126 B of the central shaft  126  seen in FIG. 2A while a blind hole  134 D in the second raised boss  134 B receives the opposite end  128 B of the second shaft  128 , also seen in FIG. 2A.  
         [0059]    In FIG. 4A, thick ribs  194  radiate from each of the second collar  146  and the bosses  134 A,  134 B to reinforce the cover  134 . The channel  147  is seen at the bottom  145  of the second collar  146 .  
         [0060]    A circular opening  188  is provided in the cover  134  so that the input gear  114 , seen in FIG. 2A, may be inserted therethrough for meshing with the first central gear  118 , also seen in FIG. 2A.  
         [0061]    Referring again to FIG. 4A, there is a pair of holes  190  spaced equidistantly from a center of the circular opening  188 . Each hole  190  has an internal flange  192  for retaining a head of a screw (not shown) which secures the D.C. motor  112 , seen in FIG. 2A, to a top side of the cover  134 .  
         [0062]    [0062]FIG. 4B shows a cross-sectional side elevation view of the cover  134  taken along line  4 B- 4 B of FIG. 4A. At the top of FIG. 4B, there are seen side views of locating posts  154 , side views of the welding rings  184 , and end views of the locating ribs  186 . These locating posts  154 , welding rings  184  and locating ribs  186  are formed integrally on an inner side of the cover  134 . The second collar  146  and the bosses  134 A,  134 B are also clearly illustrated.  
         [0063]    [0063]FIG. 4B also shows the gap  143  which receives lubricant through the channel  147  in the bottom  145  of the second collar  146 . Furthermore, there are clearly illustrated the flanged hole  134 C in the first raised boss  134 A and the blind hole  134 D in the second raised boss  134 B of the cover  134 .  
         [0064]    A mounting pad  196  is formed integrally with the top side of the cover  134 . The mounting pad  196  holds the D.C. motor  112 , seen in FIG. 2A, by the screws (not shown) which pass through the holes  190  seen in FIG. 4A.  
         [0065]    [0065]FIG. 4C shows a top plan view of the cover  134  with the main body  111  (not shown) underneath. The mounting  196  surrounds the circular opening  188 . The holes  190  bored through a first pair of thick arms  196 A of the mounting  196  receive screws (not shown) which secure the D.C. motor  112 , seen in FIG. 2A, to the top side of the cover  134 . A second pair of thin arms  196 B helps balance the motor  112  on the cover  134  so that there is no wobble of the motor  112  during operation.  
         [0066]    Also in FIG. 4C, there are illustrated portions of the four protuberances  168  and the channel  147  through which lubricant may be squirted.  
         [0067]    A second dimple  152 A is provided to allow access, upon drilling therethrough, to the first central gear  118 , seen in FIG. 2A.  
         [0068]    Also, in FIG. 4C, there is a bore  198  through which the opposite end  126 B of the central shaft  126 , shown in FIG. 2A, may be viewed and accessed, if necessary.  
         [0069]    [0069]FIG. 5 is a partially cutaway cross-sectional view of the gear box  110  with the internal drive assembly removed therefrom. The mounting pad  196 , seen in a side elevational view, is formed integrally on the top side of the cover  134 .  
         [0070]    In the partially cutaway view in the upper right corner of FIG. 5, there is seen a side elevational view of one of the welding rings  184  and one of the locating posts  154  projecting into a corresponding hollow holding tube  156 .  
         [0071]    The cover  134  has a plurality of these locating posts  154 , of which only one is shown for the sake of simplicity, around a periphery of the cover  134 . Each locating post  154  extends into its corresponding hollow holding tube  156  which is formed integrally on the main body  111  and which corresponds in position to its post  154  so that the cover  134  is located securely on the main body  111 . Each post  154  is ultrasonically welded into its corresponding hollow holding tube  156  in order to increase the strength of the gear box  110  to resist high levels of torque and also to improve alignment of the cover  134  on the main body  111 .  
         [0072]    Adjacent to the tube  156 , one of the acoustical chambers  180  is illustrated in phantom lines behind one of the thin rib walls  176 .  
         [0073]    The channel  147  bored through the cover  134  into the bottom  145  of the second collar  146  allows the user to squirt lubricant into the gap  143  behind the output shaft  142  (not shown) which is surrounded at its midsection by the first collar  144 . Thus, the output shaft  142 , seen in FIG. 2A, is securely aligned as it is held at its midsection by the bore  144 B of the first collar  144  and at its nonworking end  142 B, seen in FIG. 2A, in the gap  143  at the bottom  145  of the second collar  146 .  
         [0074]    Similarly, as also shown in FIG. 5, the blind hole  111 C in the first raised boss  111 A of the main body  111  receives the one end  126 A of the central shaft  126 , seen in FIG. 2A, while the flanged hole  134 C in the first raised boss  134 A of the cover  134  receives the opposite end  126 B, also shown in FIG. 2A, so that the central shaft  126  is secured at both ends  126 A,  126 B and is aligned between the first raised boss  111 A of the main body  111  and the first raised boss  134 A of the cover  134  when the cover  134  is ultrasonically welded to the main body  111  to form the gear box  110 .  
         [0075]    Likewise, as also seen in FIG. 5, the flanged hole  111 D in the second raised boss  111 B of the main body  111  receives the one end  128 A of the second shaft  128 , seen in FIG. 2A, while the blind hole  134 D in the second raised boss  134 B of the cover  134  receives the opposite end  128 B so that the second shaft  128  is received at both ends  128 A,  128 B and is aligned securely between the second raised boss  111 B of the main body  111  and the second raised boss  134 B of the cover  134  when the cover  134  is ultrasonically welded to the main body  111  to form the gear box  110 .  
         [0076]    Referring again to FIG. 5, the main body  111  and the cover  134  are secured to each other by ultrasonic welding to form the gear box  110  without screws. Although screws (not shown) are used to secure the D.C. motor  112 , seen in FIG. 2A, to the top side of the cover  134 , and the threaded bolts  162 , also seen in FIG. 2A, are used to secure the gear box  110  through the wall  104  to the slot machine  100 , these screws (not shown) and bolts  162  do not secure the cover  134  onto the main body  111  so as to form the gear box  110 .  
         [0077]    The assembly of the invention is as follows, with initial reference to FIG. 2A. When the main body  111  is empty with the cover  134  off, the drive assembly is put into place in the following manner.  
         [0078]    First, the output shaft  142  with the output gear  140  attached thereto is dropped into the bore  144 B of the first collar  144 . To prevent slippage of the output gear  140  along the output shaft  142 , the first collar  144  retains the output gear  140  on the output shaft  142  at one side. The pin  148  is then slipped through the working end  142 A of the output shaft  142  to prevent the output shaft  142  from falling out of the other side of the first collar  144 .  
         [0079]    Next, the one end  126 A of the central shaft  126  is inserted into the first raised boss  111 A of the main body  111 . Then, the third gear  136  with the third pinion gear  138  is slipped onto the central shaft  126  until the third pinion gear  138  abuts against the first raised boss  111 A.  
         [0080]    Subsequently, the one end  128 A of the second shaft  128  is inserted into the second raised boss  111 B of the main body  111 . Then, the second gear  122  with the second pinion gear  124  is slipped onto the second shaft  128  until the second pinion gear  124  abuts against the second raised boss  111 B.  
         [0081]    The first central gear  118  with the first pinion gear  120  is then slipped over the central shaft  126  until the first pinion gear  120  abuts against the third gear  136  already on the central shaft  126 .  
         [0082]    Now referring to the cover  134 , the small input gear  114  is slipped over and secured onto the input shaft  116  of the D.C. motor  112  which is next secured to the mounting  196  of the cover  134  by tightening screws (not shown) through the holes  190  seen in FIGS. 4A and 4C. As a result, the input gear  114  of FIG. 2A is extended through the circular opening  188  seen in FIGS. 4A and 4C.  
         [0083]    As illustrated in FIG. 5, the cover  134  with the motor  112  (not shown) secured to the mounting  196  is then fitted onto the main body  111  by placing each locating post  154  into its corresponding hollow holding tube  156 .  
         [0084]    Simultaneously, as shown in FIG. 4A, each welding ring  184  on the cover  134  will fit into the space between its corresponding welding pad  172  and short tube  174  shown in FIG.  3 B. Likewise, each locating rib  186  in FIG. 4A will snap into its corresponding acoustical chamber  180  in FIG. 3B.  
         [0085]    With reference to FIG. 2A, when the cover  134  is secured by ultrasonic welding onto the main body  111 , the output gear  140  will be retained on the output shaft  142  between the first collar  144  of the main body  111  and the second collar  146  of the cover  134 . Thus, the first collar  144  retains the output gear  140  on one side while the second collar  146  retains the output gear  140  on an opposite side.  
         [0086]    Because the D.C. motor  112  is secured onto the cover  134  instead of onto the main body  111 , the entire drive assembly inside the gear box  110  can be fully tested prior to sealing by ultrasonic welding of the cover  134  onto the main body  111 . In contrast thereto, in the prior art device shown in FIG. 1, the motor  12  is secured to the main body  11  so that the internal drive assembly cannot be tested until the cover  34  is sealed thereon to form the closed gear box  10 .  
         [0087]    As best seen in FIG. 5, an assembler can ultrasonically weld the cover  134  to the main body  111  by causing each locating post  154  to melt in its corresponding hollow holding tube  156 . As the assembler runs an ultrasonic welding rod (not shown) around the outer periphery of the top side of the cover  134  seen in FIG. 4A, each welding ring  184  will likewise melt and fuse in the space between its corresponding pad  172  and its short tube  174  seen in FIG. 3B. Similarly, each locating rib  186  in FIG. 4A will be fused by the heat of the ultrasonic welding rod (not shown) along an inner edge of its corresponding acoustical chamber  180  in FIG. 3B.  
         [0088]    The assembled gear box  110  shown in FIG. 2A is now ready to be secured to the drum or hopper  106  of the slot machine  100 . After the pin  148  is engaged into the drum or hopper  106 , the gear box  110  is secured to the slot machine  100  by screwing the threaded bolts  162  through an inner side of the wall  104  of the slot machine  100  into the raised protuberances  168  of the main body  111 .  
         [0089]    The gear box  110  is now ready for operation. Initially, an operator programs the slot machine  100  to dispense a predetermined number of coins or tokens from the drum or hopper  106  after another predetermined number of coins or tokens are inserted into the slot machine  100 .  
         [0090]    For example, after a player inserts  12  quarters into the slot machine  100 , an electrical signal is sent to energize the D.C. motor  112 . With reference to FIG. 2A, the motor  112  on the mounting  196  of the cover  134  turns the input shaft  116  so as to rotate the small plastic input gear  114 . The teeth  115  on the input gear  114  mesh with the teeth  117  on the first central gear  118  so as to turn the gear  118  and the first pinion gear  120 . The teeth  121  on the gear  120  mesh with the teeth on the larger second gear  122  and consequently turn the gear  122  and the second pinion gear  124 . The teeth  125  on the gear  124  mesh with the teeth  135  on the third gear  136  so that the third gear  136  and the third pinion gear  138  are rotated together.  
         [0091]    Note that the third gear  136  and the third pinion gear  138  rotate independently of the first central gear  118  and the first pinion gear  120 , even though all four gears  118 ,  120 ,  136  and  138  are mounted on the same central shaft  126 . The teeth  139  on the gear  138  mesh with the teeth on the large output gear  140  so as to turn the gear  140  and the output shaft  142  secured through the center of the gear  140 .  
         [0092]    At the working end  142 A of the output shaft  142 , the pin  148  turns the drum or hopper  106  filled with coins or tokens for a predetermined short period of time until about only ten coins or tokens fall out into a receiving tray (not shown) for the player to collect.  
         [0093]    Occasionally, with the prior art device illustrated in FIG. 1, the drum or hopper  6  of the slot machine  1  would become stuck in an open position so that all of the coins or tokens therein would be dumped out and overflow the receiving tray for the player.  
         [0094]    Such jackpots, although joyous for the players, are not profitable for the operators of the casinos and other licensed gambling institutions.  
         [0095]    As the reader can realize, these jackpots were caused when the prior art gear box  10  failed and allowed the drum or hopper  6  of the slot machine  1  to remain open so that all of the coins or tokens were emptied out as winnings for the players.  
         [0096]    With the present invention which is more reliable in operation than the prior art device of FIG. 1, such jackpots will be eliminated and only the predetermined number of coins or tokens will be dispensed after a higher predetermined number of coins or tokens are inserted into the slot machine  100  by each player.  
         [0097]    Although the present invention has been described by way of a preferred embodiment, other modifications will be realized by those persons skilled in this particular technology after reading this disclosure. However, these modifications may be considered within the scope of the appended claims if such modifications do not depart from the spirit of this invention.