Abstract:
A slot machine has inner and outer coaxial overlying reels. Each reel is formed with symbols on its transparent outer circumferential frame. The inner and outer reels are rotated independently by motors. The outer reel has a transparent outer circumferential frame to allow a player to see symbols on the inner reels. A combined symbol of superposed inner and outer reel symbols is produced.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a reel-type slot machine, and more particularly to a slot machine which presents combined symbols visible on overlying concentric reels. 
     2. Description of the Related Art 
     Slot machines are grouped into two types, namely, a mechanical reel type in which reels are rotated, and a video type in which an electronic display is used to simulate the rotation of reels. In a slot machine of the video type, the rotation and stopping of mechanical reels are simulated by using graphical data and displayed on a display such as a CRT. Many players prefer the mechanical reel type because they suspect that the results of play have been intentionally controlled with the video type. 
     In a slot machine of the mechanical reel type, three reels for example are rotated at the same time, mechanically upon actuation of a start lever, or electrically with the help of motors, upon actuation of the start lever. The three reels are thereafter stopped sequentially by operating a stop button provided for each reel or by a stop signal randomly generated by a random timer. A win or hit is determined by a combination of symbols on the three stopped reels along a winning line viewed from the observation windows. If the symbol combination is a winning symbol combination, dividend coins are paid out or a special favor such as a bonus game is given to the player. 
     A drawback of conventional mechanical reel type slot machines is that the game is simple and monotonous because the conventional machines have all adopted the same method whereby a winning symbol combination is determined by a sequence of starting and stopping a single set of reels appearing in the observation windows. Moreover, the number of symbols on the outer circumference of each reel is limited by the outer diameter of the reel, it being impossible to increase the number of symbols above a certain limit. Therefore, the number of symbol combinations is limited, which reduces the interest in playing the game. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a slot machine capable of providing complicated and thrilling games. 
     It is another object of the present invention to provide a slot machine capable of displaying a larger number of symbols without using reels of a large size. 
     The above and other objects of the present invention can be achieved by providing, in a slot machine, an outer reel having at least one transparent part on the outer circumferential frame of the outer reel, and an inner reel mounted within coaxially with the outer reel and being capable of rotating independently from the outer reel. Symbols formed on the outer circumference of the outer reel can be viewed through transparent parts. As a result, symbols on the inner and outer reels are combined, it being possible to view the combined symbols through an observation window. The combined symbol is a new symbol, different from two original symbols, composed of an inner reel symbol visible through a transparent area on the outer reel, plus an outer symbol on the outer reel. 
     According to the present invention, a greatly increased number of symbols can be formed without using a reel having a large diameter. By independently rotating the inner and outer reels, the combined display of the two reels provides a novel game sense and eliminates the monotony of a conventional slot machine. By stopping the reels at different times, interest in the game is increased. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects and advantages of the present invention will become apparent from the detailed description of the preferred embodiments when read in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a front view of a slot machine according to an embodiment of the present invention; 
     FIG. 2 is an exploded perspective view showing the structure of the reels; 
     FIG. 3 is a cross section showing the main parts of a reel assembly; 
     FIG. 4 is a functional block diagram showing an arrangement of electronic components of the slot machine of the invention; 
     FIG. 5 is a flow chart explaining the game sequence; 
     FIG. 6 shows an example of displayed symbols; and 
     FIG. 7 shows another example of displayed symbols. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1 showing the slot machine of the invention, three observation windows 2, 3 and 4 are formed at the central area of the housing 17 of the slot machine, and first to third reels 5, 6 and 7 are rotatably mounted behind the observation windows 2, 3 and 4. Symbols (including blank regions) are spaced about the outer periphery of the first to third reels 5 to 7 at a preferred pitch. When all the reels 5 to 7 stop, three symbols per reel, or a total of nine symbols, can be viewed via the observation windows 2 to 4. Winning lines 8 are used for identifying combinations of symbols for each game when the reels 5 to 7 stop. The number of winning lines to be made effective is determined by the number of coins inserted into a coin inlet 9 prior to starting each game. 
     When a start lever 10 is operated after inserting a coin or coins, the first to third reels 5 to 7 start rotating at the same time, and after a predetermined time lapse, a stop operation is permitted. The stop operation is effected independently for each reel by using stop buttons 11, 12 and 13. If a combination of three symbols on an effective winning line 8 appearing when the reels 5 to 7 stop is a winning symbol combination, as many coins as have been predetermined for the winning symbol combination are paid out onto a saucer 14. 
     Each of the first to third reels 5 to 7 has an outer reel and an inner reel. FIG. 2 shows the structure of the first reel 5. An outer reel 5a has a transparent plastic outer circumferential frame 15 on which a plurality of symbols are formed including &#34;1BAR&#34;, &#34;3BAR&#34;, &#34;star&#34;, &#34;7 &#34;, &#34;cherry&#34;, and the like. An inner reel 5b has an opaque outer circumferential frame 16 like a conventional reel on which a plurality of symbols are formed. 
     Mounting plates 15a and 16a are integrally formed with the outer circumferential frames 15 and 16, the plates being coupled to the shafts of stepping motors. 
     FIG. 3 shows a reel assembly of the first to third reels 5 to 7. Reel retaining brackets 19 are fixed to a base plate 18. Fixed to the brackets 19 by means of, for example, hexagonal bolts, are two stepping motors 20a and 20b, 21a and 21b, 22a and 22b for each reel and rotation support plates 23 and 24 formed with central openings 23a and 24a for each reel. 
     The shafts of the stepping motors 20a, 21a and 22a are fixed to the outer reels 5a, 6a and 7a of the first to third reels, and the shafts of the stepping motors 20b, 21b and 22b are fixed to the inner reels 5b, 6b and 7b of the first to third reels. Each of the outer reels 5a to 7a rotates while sliding on the inner surface of the rotation support plate 23, and each of the inner reels 5b to 7b rotates while sliding on the inner surface of the rotation plate 24. 
     The arrangement of electronic components of the slot machine of the illustrated embodiment is shown in FIG. 4. In FIG. 4, a microprocessor unit (MPU) 30 controls each game in accordance with a sequence program stored in a program ROM 31. A coin sensor 32 detects the number of coins entered into the coin inlet 9 and supplies the number to MPU 30 to determine the number of effective winning lines 8. When a start signal generator 33 detects an operation of the start lever 10, it supplies a start signal to MPU 30 which in turn rotates the first to third reels 5 to 7. 
     The first to third reels 5 to 7 start rotating when MPU 30 supplies clock pulses to drivers 35a, 35b, 36a, 36b, 37a and 37b. As each of the drivers 35a to 37b receives clock pulses from CPU 30, it supplies drive pulses corresponding to the frequency of clock pulses to each of the stepping motors 20a to 22b. Each stepping motors 20a to 22b rotates by a predetermined angle each time a drive pulse is supplied. Therefore, by counting the number of drive pulses, the angle of rotation of each stepping motor can be known. Drive pulses outputted from each driver 25a to 37b are counted by a corresponding one of the counters 38a to 40b. The stepping motors 20a to 22a are used for rotating the outer reels 5a to 7a, and the stepping motors 20b to 22b are used for rotating the inner reels 5b to 7b. The rotation direction of the stepping motors 20b to 22b is opposite to the rotation direction of the stepping motors 20a to 22a. 
     Reset pulses are applied to reset terminals of the counters 38a to 40b each time the stepping motors 20a to 22b pass by the rotation origin, and the counters are cleared to &#34;0&#34;. As a result, the counts of the counters 38a to 40b correspond to the rotary angles during one rotation of the stepping motors. Since the order of disposing symbols on the outer circumferential frame of each reel 5a to 7b is known, symbols on the wining line 8 can be identified based on the counts of the counters 38a to 40b. 
     A stop signal generator 42 supplies an outer reel stop signal to MPU 30 when one of the stop buttons 11 to 13 is depressed. Upon reception of the outer reel stop signal, MPU 30 stops the rotation of the corresponding one of the outer reels 5a to 7a. For example, when the stop button 11 is depressed while the first reel 5 rotates, a supply of clock pulses to the driver 35a and a supply of drive pulses to the stepping motor 20a are intercepted, thereby to stop the rotation of the outer reel 5a. 
     A random timer 43 starts operating after the rotation of the outer reels 5a to 7a is stopped in response to the outer reel stop signals. The random timer 43 generates three inner reel stop signals at random timings and supplies them to MPU 30 which in turn stops the rotation of the inner reels 5b to 7b as in the stopping of the outer reels. 
     After the rotation of the first to third reels 5 to 7 has been stopped, a winning judgment unit 44 judges whether a symbol combination of an effective winning line is a win or not. The types of the symbols on the effective winning line can be identified from the counts of the counters 38a to 40b as described previously. If the winning judgment indicates a win, a coin pay-out unit 45 operates in response to an instruction from MPU 30 and pays out dividend coins corresponding in number to the win rank. 
     The operation of the above embodiment will be described with reference to the flow chart of FIG. 5. If one coin is inserted from the coin inlet 9, the center winning line 8 No. 1 is made effective and lamps on opposite ends of this line are turned on. If two coins are inserted, two winning lines 8, namely No. 1 and No. 2 are made effective and lamps on opposite ends of these lines are turned on. If three coins are inserted, all three winning lines 8 are made effective. 
     When the start lever 10 is operated after inserting three coins, for example, MPU 30 supplies clock pulses to all the drivers 35a to 37b which supply drive pulses to the stepping motors 20a to 22b. These stepping motors 20a to 22b start at the same time to rotate all the first to third reels 5 to 7. Of the first to third reels 5 to 7, the outer reels 5a to 7a rotate in the counterclockwise direction as viewed in FIG. 2, and the inner reels 5b to 7b rotate in the clockwise direction. The symbols on the outer reels 5a to 7a which move downward can be observed, and those on the inner reels 5b to 7b which move upward can be observed through the transparent outer reels 5a to 7a. Two series of symbol trains moving in opposite directions can be observed via the observation windows 2 to 4, providing a fresh impression to a game player. Even if two series of symbol trains are moved in the same direction, a similar fresh impression can be given to a player by changing the rotation speed of each of the two series of symbol trains so that they do not move in unison. 
     As the stop buttons 11 to 13 are depressed at desired timings, the outer reels 5a to 7a are stopped in response to the outer reel stop signals from the stop signal generator 32. Let is be supposed that symbols on the outer reels 5a to 7a stop on winning lines. 
     Such symbol combinations on winning lines can be determined as in the case of a conventional slot machine, and the game is over. However, in the embodiment slot machine, even at this time the stepping motors 20b to 22b continue to be driven. Therefore, the inner reels 5b to 7b are still rotating, and moving symbols can be observed through transparent outer circumferential frames of the outer reels 5a to 7a. 
     After all the outer reels 5a to 7a have stopped, the random timer 43 starts operating, and three inner reel stop signals are sequentially supplied to MPU 30. As a result, the three inner reels 5b to 7b are sequentially stopped. At this time, as shown in FIG. 6, the symbols on the outer reels 5a to 7a superposed upon the symbols of the inner reels 5b to 7b are viewed through the observation windows 2 to 4. Of the symbols on only the outer reels 5a to 7a, a winning symbol combination of &#34;Cherry&#34; &#34;-&#34; &#34;-&#34; is obtained on the winning line 8b. However, from the symbols of both the outer and the inner reels 5a to 7a and 5b to 7b, winning symbol combinations are formed on three winning lines 8a, 8b and 8c. On the winning line 8a in particular, although the symbol combination of only the outer reels 5a  to 7a is &#34;1 BAR&#34; &#34;3BAR&#34; &#34;1 BAR&#34;, which is a miss, the symbol combination of both the outer and the inner reels 5a to 7a and 5b to 7b is &#34;3BAR&#34; &#34;3BAR&#34; &#34;3BAR&#34; which is a high rank hit. 
     The inner reels 5b to 7b are stopped by use of the random timer 43. They may be stopped by generating inner reel stop signals in response to the depression of the stop buttons 11 to 13 after the outer reels 5a to 7a have stopped. The stop buttons 11 to 13 rnay be omitted and the outer reels 5a to 7a stopped in response to stop signals from the random timer 43, thereby to provide a self-stopping slot machine. 
     Thereafter, MPU 30 identifies the types of symbols on the winning lines 8 by referring to the counts of the counters 38a to 40b. In accordance with the symbol combination data, the winning judgment unit 44 judges whether there is a win. The coin pay-out unit 35 pays out dividend coins corresponding in number to the wins on the winning lines 8a, 8b and 8c, to thereafter terminate one game. 
     Since the reels 5 to 7 are of composite structure, having the outer and inner reels 5a to 7a and 5b to 7b, the number of symbols that can be displayed by the slot machine can be increased. Namely, a symbol on the inner reel appears in the observation window via the blank symbol on the outer reel, and another symbol is formed by a combination of two symbols on the inner and outer reels. For example, if three combined symbols of the &#34;star&#34; and &#34;7&#34;, shown in the upper area of the outer circumferential frame of the second reel 6 in FIG. 6, are on a winning line, a jack pot is allotted to thereby give a unique interest in game which a conventional slot machine cannot provide. 
     Symbols may be formed only on certain ones of the outer reels a to 7a and inner reels 5b to 7b, and background colors in place of symbols can be displayed on the other reels. In this case, various winning ranks are determined by combinations of background colors on winning lines, by combinations of symbols on winning lines, and by combinations of symbols and background colors on winning lines. 
     FIG. 7 shows examples of symbols used by a slot machine for playing poker. Similar to the first embodiment, first to fifth reels include outer reels and inner reels. Symbols of &#34;heart&#34;, &#34;club&#34;, &#34;diamond&#34; and &#34;spade&#34; suits are formed on the outer circumferential frames of the outer reels, and alphanumeric symbols including &#34;A&#34; to &#34;10&#34; and &#34;J&#34; to &#34;K&#34; are formed for the inner reels. Various combinations of symbols of the reels are produced from the symbols on the outer reels. 
     In a conventional slot machine of the driven reel type for playing a poker game, the number of trump cards per reel is limited by the outer diameter of the reel, the reel being unable to use the whole set of cards. In this embodiment, the whole set of trump cards can be prepared, allowing a player to have a simulation of a real poker game. 
     In the above embodiment, one of the first to third reels may be of a two-stage structure having an outer reel and an inner reel, and the remaining two reels may be conventional reels. The inner reels may be first stopped, and then the outer reels stopped. The winning judgment and dividend coin pay-out may be effected when the outer reels stop, or they may be effected later when the inner reels thereafter stop. 
     Although the present invention has been described with reference to the preferred embodiments shown in the drawings, the invention should not be limited by the embodiments but, on the contrary, various modifications, changes, combinations and the like of the present invention can be effected without departing from the spirit and scope of the appended claims.