EP0330778B1

EP0330778B1 - Slot machine

Info

Publication number: EP0330778B1
Application number: EP88307280A
Authority: EP
Inventors: Kazuo Okada
Original assignee: Universal KK
Current assignee: Universal KK
Priority date: 1988-03-04
Filing date: 1988-08-05
Publication date: 1991-10-16
Anticipated expiration: 2008-08-05
Also published as: ZA885692B; ATE68619T1; AU2039788A; EP0330778A1; JPH01227781A; JPH0630643B2; DE3865667D1; AU611927B2

Abstract

A slot machine having a plurality of symbol rows each having a plurality of symbols disposed at equal pitch pays out a predetermined number of coins when the symbol rows under movement stop and a symbol combination on a prize-winning line becomes coincident with a hit game symbol combination. The slot machine includes a lost game determining unit (20, 42, 43), a symbol determining unit (43, 44, 45) and a symbol row stop position control unit (28, 29, 30). The lost game determining unit (20, 42, 43) determines if a present game is to be set as a lost game or a hit game. The symbol determining unit (43, 44, 45) responds to a present lost game and determines symbols of the respective symbol rows so as to obtain a highest probability of occurrence of a symbol combination nearest to a hit game symbol combination. The symbol row stop position control unit (28, 29, 30) controls the respective symbol rows such that the symbols determined by the symbol determining unit (43, 44, 45) stop on the prize-winning line.

Description

The present invention relates to a slot machine and more particularly, to a slot machine in which losing symbol combinations occur with different probabilities depending on their similarity to a winning combination.
A typical slot machine has a plurality of columns of symbols, each column including a plurality of different symbols disposed at an equal pitch. There are two types of machine: a mechanical reel type having symbols disposed on the peripheral outer surface of several, usually three, reels, and video type in which symbol columns are displayed on a CRT. To play games, coins or tokens are inserted and a start lever is actuated to cause the respective symbol columns to rotate. Rotating symbol columns are either caused to stop automatically or alternatively, they are stopped sequentially upon actuation of stop buttons. A prize win is determined from the combination of symbols stopped on a prize-winning line within display windows. If the symbol combination on the prize-winning line is a hit game combination, a predetermined number of coins are paid out.
Some slot machines use symbol columns each having "blank" symbols and hit game symbols such as "BAR" disposed alternatively on the symbol column. In this type of slot machine, a hit game is assigned to a symbol combination "BAR"-"BAR"-"BAR" on a winning line, and a defeat or lost game is assigned to a symbol combination with at least one "blank" on the winning line.
Since the slot machine of this type has a high probability of obtaining a "blank" symbol, two or three reels often stop with their "blank" symbols stopped on the winning line. For example, assuming that the total number of symbols on each reel is 22 and half the symbols, i.e., 11 symbols are "blank" symbols, the probability of obtaining a combination of "blank" symbols on all the reels is as high as (1/2)³ = (1/8).
Such a high probability of obtaining a combination of two or three "blank" symbols at the winning line will reduce a player's expectation of winning and he will tend to lose interest after a short time. This problem also occurs with the more usual slot machines which use only hit game symbols.
EP-A-0122138 describes a slot machine in which means are provided for setting the probability of different types of win occurring in such a way that while the desired gain ratio is maintained the occurrence of one type of win does not affect the probability of occurrence of another type of win. This is achieved by allotting number ranges to each type of win, the size of the range being set according to the type of win, and choosing between the types by generating a random number and choosing the type of win corresponding to the range in which the number falls.
According to an aspect of the present invention, there is provided a slot machine having a plurality of symbol sets each having hit game symbols and lost game symbols, wherein, when all the symbol sets previously moving stop, a lost game is set if at least one loss game symbol is included within a plurality of symbols on a prize-winning line, and a hit game is set if all symbols on the prize-winning line are hit game symbols, comprising:

first means for determining if a lost game is set or not; characterised by
second means responsive to a lost game set by said lost game determining means for determining symbols of said respective symbol sets so as to increase the probability, as compared with the probability in the absence of such means, of occurrence of a combination of less lost game symbols stopped on said prize-winning line; and
third means for controlling to stop said symbol sets so as to stop said symbols determined by said symbol determining means on said prize-winning line.

Thus, lost game symbol combinations which are nearer to hit game symbol combinations will appear at a higher probability so as to maintain a player's interest in the game.
The invention will be further described by way of non-limitative example with reference to the accompanying drawings, in which:

Fig. 1 is a perspective view of an embodiment of a slot machine according to the present invention;
Fig. 2 is a block diagram showing the circuit arrangement of the slot machine shown in Fig. 1;
Fig. 3 shows one example of symbol sheets on the reels in a developed form;
Fig. 4 is a flow chart showing a process of a hit game and a process of a lost game with three "blanks";
Fig. 5 is a flow chart showing a process of a lost game with two "blanks"; and
Fig.6 is a flow chart showing a process of a lost game with one "blank".

Referring to Fig. 1 showing a perspective view of a slot machine according to the present invention, three reels 4, 5 and 6 driven by respective stepper motors are mounted within the main frame 2 of the slot machine. Each reel 4 to 6 has a cylindrical reel member about which a symbol sheet 7 to 9 as shown in Fig. 3 in a developed form is wound.
The symbol sheets 6 to 9 have the same symbol arrangement. Namely, "BAR" symbols 10 and "blank" symbols 11 represented by white areas are alternately disposed on each symbol sheet. Reference numerals 7a to 9a represent areas which are used to bond both ends of respective symbol sheets wound about the reel members. By rolling the symbol sheets 7 to 9 about each peripheral outer surface of the reel member, the reels 4 to 6 are obtained with the eleven "BAR" symbols 10 and the eleven "blank" symbols 11 disposed alternately on the reel members.
The slot machine is provided with a front panel 3 capable of being opened and closed. Three display windows 12 are formed in the front panel 3 in correspondence with the three reels 4 to 6 the partial areas of which can be observed through the display windows 12. A prize-winning line 13 is formed at the center of the display windows 12. A hit game or a lost game is determined based on a combination of symbols stopped at the prize-winning line 13. A plurality of winning lines may be used each of which is made effective in accordance with the number of inserted coins. Further, narrower display windows may be used to allow the observation of only one symbol per one reel. In this case, the prize-winning line can be omitted since such narrow display windows serve per se as the prize-winning line.
As coins are inserted from a coin inlet 15, the start lever 16 is unlocked. Upon activation of the start lever 16, the reels 4 to 6 start rotation at the same time. The reels 4 to 6 are automatically stopped at random timings. If a combination of symbols stopped at the winning line 13 coincides with a hit game symbol combination, a hit game is set and a predetermined number of coins are paid out. In this embodiment, a combination "BAR"-"BAR"-"BAR" is a hit game symbol combination so that when this combination is obtained, coins are ejected out onto a saucer 17. If three "BAR" symbols with the same numeric value stop on the winning line, the number of dividend coins is multiplied by that number. If the combination of symbols on the prize-winning line 13 includes at least one "blank" symbol 11, then a lost game flag is set.
Fig. 2 shows a control circuit of the slot machine. A central processing unit (CPU) 20 controls the rotation and stops of the reels 4 to 6. CPU 20 is connected via an input/output interface 21 to a start signal generator 23, drivers 24 to 26 and counters 28 to 30. The start signal generator 23 supplies a game start process signal to CPU 20 when the start lever 16 is activated. The drivers 24 to 26 supply drive pulses to the stepper motors 31 to 33 which drive the reels 4 to 6, respectively.
The counters 28 to 30 count the drive pulses supplied from the drivers 24 to 26 to the respective stepper motors 31 and 33. The count values are fed back to CPU 20. A reset signal outputted from each photosensor 35 to 37 is applied to a reset terminal "R" of each counter 28 to 30. Upon reception of the reset signal, the count value of each counter 28 to 30 is reset to a preset value, e.g. "0". Each photosensor 35 to 37 generates a reset signal when it photoelectrically detects that each light shielding tongue 4a to 6a projected at the reference position of each reel 4 to 6 passes through the photosensor. Then, the counter 28 to 30 is reset to "0" every one rotation of the reel 4 to 6.
CPU 20 executes a game process sequence program written in a program memory 41 in response to master clock pulses from a clock pulse generator 40. A random number sampling circuit 42 supplies random numbers to CPU 20 at necessary stages during executing a game process sequence program. For instance, random numbers for determining if a present game is to be set as a hit game or not, or for determining what type of symbols are to be displayed in case of a lost game, are supplied to CPU 20.
When determining if there is a hit game or not, a prize-winning probability table 43 is referred to. The table 43 stored in a ROM stores the random numbers to be generated from the random number sampling circuit 42 by grouping them into a big hit area, a middle hit area, a small hit area, and a lost game area. For instance, of random numbers having a range from "0" to "9999", the big hit area is assigned the range from "0" to "49", the middle hit area the range from "50" to "249", the small hit area the range from "250" to "1499", and the lost game area the range from "1500" to "9999". The occurrence and type of a hit game or a lost game are determined based on what area the random number obtained from the random number sampling circuit 42 belongs to.
The big hit corresponds to a hit game symbol combination of three "CRAZY BAR" symbols which results in a pay-out of, e.g., 100 coins per one coin inserted. The middle hit corresponds to a hit game symbol combination of three "same numeric value BAR" symbols which results in a pay-out of, e.g., 6 coins multiplied by the number. The small hit corresponds to a hit game symbol combination of three symbols including "BAR" and "numeric value BAR" symbols which results in a pay-out of, e.g., 6 coins.
A blank number probability table 44 stored in a ROM is referred to by CPU 20 while it executes a lost game process. In particular, if the random number falls within the range from "1500" to "9999", a lost game process is performed. In this case, the number of "blank" symbols on the winning line 13 is determined by referring to the table 44. A random number is again sampled by the random number sampling circuit 42 and used in referring to the blank number probability table 44.
Similar to the prize-winning probability table 43, the blank number probability table 44 stores the random numbers to be generated from the random number sampling circuit 42 by grouping them into a "three blank" area, a "two blank" area and a "one blank" area. For instance, of random numbers having a range from "0" to "9999", the "three blank" area is assigned the range from "0" to "499", the two blank" area the range from "500" to "3999", and the one blank" area the range from "4000" to "9999".
Accordingly, the probability of obtaining a lost game with "three blanks" is "1/20" the total number of lost games, and has the lowest probability among three types of lost games. The probability of a lost game with "one blank" is "1/6" which is highest. In determining the number of blanks, only the least significant digit of a random number (decimal) generated by the random number sampling circuit 42 may be used while using a blank number probability table which groups the numbers 0 to 9 into the "three blank", "two blank" and "one blank" areas, to thus allow a smaller capacity of a table memory.
A reel selection table 45 is used for determining on which reel a single "BAR" symbol or a single "blank" symbol is to be displayed after a lost game combination with "two blank" symbols or "one blank" symbol was determined using the blank number probability table 44. The reel selection table 45 stored in ROM stores the random numbers to be generated by the random number sampling circuit 42 by grouping them into approximately three areas respectively assigned to the reels 4 to 6. With the same manner as in the case of the blank number probability table, the capacity of the reel selection table 45 may be made smaller.
The operation of the slot machine constructed as above will be described. Upon activation of the start lever 16 after inserting coins, a start signal is supplied from the start signal generator 23 to CPU 20 which then starts executing the game process sequence program read out from the program memory 41.
CPU 20 supplies master pulses with gradually increasing periods via the input/output interface 21 to the drivers 24 to 26 for driving the stepping motors. The drivers 24 to 26 supply drive pulses to the stepping motors 31 to 33 in response to the master pulses. The stepping motors 31 to 33 are thus activated to start rotating the reels 4 to 6. After a predetermined time, the frequency of the master clock pulses becomes constant so that the reels 4 to 6 continue to rotate at a constant speed.
The numbers of clock pulses supplied to the respective stepping motors 31 to 33 are counted by the counters 28 to 30, while the counts of the counters 28 to 30 are reset on every rotation of the wheels 4 to 6. Since the relation between the positions of the light shielding tongues 4a to 6a of the reels 4 to 6 and the positions of symbols on the reels are previously known, and the counts of the counter 28 to 30 are reset on every rotation of the reels, the rotary positions of the reels 4 to 6 can be determined based on the counts of the counters 28 to 30. On the contrary, by stopping the supply of drive pulses when the counts of the counters 28 to 30 reach predetermined values, it is possible to stop the reels 4 to 6 at proper positions.
While the reels 4 to 6 are rotating, a first random number R1 is sampled by the random number sampling circuit 42. When the reels rotate at a low speed, the reel stop control process shown in Fig.4 starts. First, the sampled random number R1 is used in referring to the prize-winning probability table 43 so that the sampled random number is determined if it corresponds to a hit game or a lost game. If the random number R1 corresponds to any one of the big hit area from "0" to "49", middle hit area from "50" to "249" and small hit area from "250" to "1499", CPU 20 sets a big hit flag, middle hit flag, or small hit flag in accordance with the corresponding area, into a predetermined register.
Upon setting a hit flag, CPU 20 executes a hit game process and controls the stopping of the reels 4 to 6 so as to obtain a hit corresponding to the set flag. The stop control of the reels are conducted as well known based on the counts of the counters 28 to 30.
If the sampled random number is within the range from "1500" to "9999", CPU 20 sets a lost game flag into a predetermined register to thereafter execute a lost game process.
To start the lost game process, CPU 20 again causes the random number sampling circuit 42 to sample a random number R2 which is used in referring to the blank number probability table 44. If the sampled random number R2 is within the range from "0" to "499", a lost game process with "three blank" symbols is executed.
In the lost game process with "three blank" symbols, the stepping motors 31 to 33 are controlled to stop all the reels 4 to 6 with the "blank" symbols 11 aligned on the winning line 13, based on the counts fed back from the counters 28 to 30. The lost game process with "three blank" symbols is limited to the random number R2 within the range from "0" to "499", so that the probability of such lost game is low at "1/20" the total occurrences of lost games.
If the random number R2 is within the range from "500" to "3999", a lost game process with "two blank" symbols is executed. As shown in the flow chart of Fig.5, in the lost game process with "two blank" symbols, a random number R3 is again sampled by the random number sampling circuit 42 which is used in determining to which reel among the three reels 4 to 6 a "BAR" symbol 10 is to be assigned. The random number R3 is used in referring to the reel selection table 45 so that one of the reels is selected at a probability of "1/3". The selected reel is controlled such that the "BAR" symbol 10 stops on the prize-winning line 13. The other two reels are controlled such that the "blank" symbols 11 stop on the prize-winning line 13. The probability of occurrence of a lost game with "two blank" symbols is "17/60" of the total occurrences of lost games.
If the random number R2 is within the range from "4000" to "9999", a lost game with "one blank" symbol is executed. Similar to the case of the lost game with "two blank" symbols, a random number R3 is sampled and used in determining to which reel among the three reels 4 to 6 a "blank" symbol 11 is to be assigned. The selected reel is controlled such that the "blank" symbol 11 stops on the prize-winning line 13. The other two reels are controlled such that the "BAR" symbols 10 stop on the prize-winning line 13. The probability of occurrence of a lost game with "one blank" is "2/3" of the total occurrences of lost games, which is the highest probability among three types of lost games.
With the above lost game processes, the probability of obtaining a symbol combination with the least number of lost game symbols becomes high. The probabilities of the lost game processes with "two blank" and "three blank" symbols may be set to the same value so long as the object of the invention is being achieved, i.e., so long as the occurrence probability of a game lost symbol combination with a greatest deviation from the hit game symbol combination is being suppressed to a minimum. As above, the player is given an impression that the game was lost at the last moment, to thus cause the player to expect to win the next game. In the lost game process with "one blank" symbol, the reel to which the "blank" symbol is to be assigned is arranged to be changed randomly among the three reels during games so that it does not give unnatural impression to the player.
In the above embodiment, the blank number probability table 44 may be omitted on condition that the number of "blank" symbols in the lost game process is arranged to be determined from the prize-winning probability table 43 which is modified to further group the lost game range from "1500" to "9999" into similar areas to those in the blank number probability table which is accessed using the first sampled random number R1. Also, the reel selection table 45 may be omitted on condition that various lost game symbol combinations are assigned to the lost game range to identify a reel to which a "BAR" symbol or a "blank" symbol is assigned.
In the reel of the above embodiment, both the hit game and lost game symbols are used. However, the present invention is also applicable to those slot machines using only hit game symbols wherein a hit game is set for the case that all symbols on a prize-winning line are identical or for the case that symbols of a predetermined number or more are on the prize-winning line. In particular, in the usual three reel type slot machine using "cherry", "water melon", "lemon" and "bell" symbols, if three same symbols, e.g., "water melon" symbols are aligned on the prize-winning line, a predetermined number of coins are paid out. A symbol combination of "water melon", "water melon" and "lemon" at a lost game will give the player an expectation that the next game will become a hit game than a symbol combination of "water melon", "bell", and "lemon". Therefore, the probability of obtaining a combination with a single symbol different from a hit game symbol combination ("water melon", "water melon", and "lemon") is set higher than that with two symbols different from the hit game symbol combination ("water melon", "bell", and "lemon"). The present invention is also applicable to such arrangement.
The present invention is applicable to video type slot machines which give graphics display of symbols on a CRT, and to those using four reels or more. Similar functions to the above embodiment can be obtained when applying the present invention to slot machines provided with reel stop buttons in which reel positions are controlled by the amount corresponding to one to two symbol frames in accordance with the stop button operation timings.

Claims

1. A slot machine having a plurality of symbol sets (4, 5, 6) each having hit game symbols and lost game symbols, wherein, when all the symbol sets (4, 5, 6) previously moving stop, a lost game is set if at least one lost game symbol is included within a plurality of symbols on a prize-winning line (13), and a hit game is set if all symbols on the prize-winning line (13) are hit game symbols, comprising:

first means (43) for determining if a lost game is set or not; characterised by

second means (20, 44) responsive to a lost game set by said lost game determining means (43) for determining symbols of said respective symbol sets so as to increase the probability, as compared with the probability in the absence of such means, of occurrence of a combination of less lost game symbols stopped on said prize-winning line (13); and

third means (20) for controlling to stop said symbol sets so as to stop said symbols determined by said symbol determining means on said prize-winning line.

2. A slot machine according to claim 1, wherein said symbol determining means (20, 44) comprises means (44) for determining the number of lost game symbols to be stopped on said prize-winning line; and means (45) for determining the assignment of lost game symbols to said symbol sets if the number of symbols determined by said symbol number determining means is smaller than the total number of said symbol sets.

3. A slot machine according to claim 2, wherein said lost game symbol number determining means (44) and said symbol assignment determining means (45) perform said determination in accordance with a sampled random number (42).

4. A slot machine according to claim 2 or 3, wherein said lost game symbol number determining means (44) includes a lost game probability table (43) which includes a table of natural numbers "0" to "N" divided into a plurality of groups, each group being indicative of the number of lost game symbols to appear on the prize-winning line (13).

5. A slot machine according to claim 2, 3 or 4, wherein said symbol assignment determining means (45) includes a symbol set selection table which includes a table of natural numbers of "0" to "N" divided into a plurality of groups, each group being indicative of a said symbol set.

6. A slot machine according to claim 5, wherein said symbol assignment determining means (45) determines one symbol set (4, 5, 6) for a hit game symbol and assigns the remaining two symbol sets (4, 5, 6) with said lost game symbols by referring to said symbol set selection table (45) if the determined number of lost game symbols are two, and if the number of lost game symbols is determined to be one, determines the symbol set to be assigned with said lost game symbol by referring to said symbol set selection table (45).

7. A slot machine according to any preceding claim, wherein the number of said symbol sets is three.

8. A slot machine according to any preceding claim, wherein said lost game symbols include blank symbols (11).

9. A slot machine according to any preceding claim, wherein said hit game symbols include "BAR" symbols.

10. A slot machine according to claim 9, wherein said hit game symbols include "BAR" symbols having a numeric value, and wherein if three "BAR" symbols with a same numeric value are aligned on said prize-winning line (13), the winning dividend is multiplied by said numeric value.

11. A slot machine according to any preceding claim, wherein each said symbol set (4, 5, 6) is constructed of a rotatable reel having a plurality symbols (10, 11) on the circumferential outer surface thereof.

12. A slot machine according to claim 11, wherein said reel is rotatable by a pulse motor.

13. A slot machine according to any one of the preceding claims wherein in use, in the event of a win coins corresponding in number to the rank of the hit game symbol combination are paid out and in which the second means is operative in response to a lost game set by said lost game determining means (43) to determine symbols of said respective symbol sets so as to obtain the highest probability of occurrence of a combination of less lost game symbols nearest to said hit game symbol combination.

14. A slot machine according to claim 13, wherein said symbol determining means determines symbols, if the number of said symbol sets are three, such that the probability of occurrence of a lost game symbol combination with one different symbol from said hit game symbol combination is set higher than that of a lost game symbol combination with three different symbols from said hit game symbol combination.