Anti-stringing device for a coin acceptor

A coin acceptor comprises a main plate and a side plate which together define a coin path for allowing the passage of coins therebetween. A slot is positioned between the main plate and the side plate for catching any strings that may be attached to coins. Barbs are provided inside the slot for retaining the strings. The width of the slot is smaller than the thickness of the smallest coin and is so arranged that, when a string attached to a coin is tightened, the string is moved into the slot. An acceptance and a rejection channel are positioned downstream from the coin path. The acceptance channel has an additional slot for catching strings. First and second coin sensors are positioned adjacent the acceptance channel. If the first sensor detects the presence of a coin after the second sensor has already detected the same coin, then it is likely that a string is being used to manipulate the coin acceptor and the generation of a credit signal is disabled.

BACKGROUND OF THE INVENTION 
The present invention relates to a device for inhibiting the use of a coin 
on a string to defraud a coin acceptor. 
Users who wish to defraud a coin acceptor have been known to attach a thin 
string to a coin and to insert the coin into the coin acceptor. The 
presence of a genuine coin with the timing of a genuine coin causes the 
coin sensor checking the coin to judge the coin to be genuine and to move 
the coin to an acceptance area. An acceptance switch causes genuine coins 
to move to an acceptance channel for delivery to a coin box and causes all 
other articles to move to a rejection channel for return to the user. A 
coin sensor arranged downstream from the acceptance switch generates a 
credit signal when a coin passes through the acceptance channel toward the 
coin box. However, when a coin is attached to a string, the coin is not 
supplied to the coin box but rather the user tries to draw the coin back 
to the coin slot or a point above the acceptance switch so that the coin 
can be manipulated into the rejection channel and improperly retrieved. 
Another technique for defrauding a coin acceptor is to attach a genuine 
coin to one end of a string and to attach a counterfeit coin or disk to 
the other end. The genuine coin is inserted first and, after it has been 
accepted for credit, the counterfeit coin is inserted. The counterfeit 
coin is rejected back to the user through the rejection channel. The user 
tries to manipulate the string attached to the counterfeit coin to 
improperly retrieve the genuine coin. 
Prior designs have addressed this stringing problem. German Application 
Nos. DE 39 29 729 and DE 41 17 096 and EPO Application No. EP 0 358 946 
show a lever or similar mechanism which is moved by a string attached to a 
coin. The string prevents the lever from returning to its original 
position. The position of the lever is optically sensed for the purpose of 
transmitting a signal to a control and evaluation circuit which detects 
stringing based on the position of the lever. 
German Application No. DE 27 33 636 shows a string catching mechanism in a 
coin acceptor which retains the string and, consequently, the coin to 
prevent the latter from giving a signal to the credit memory. In practice, 
it has been found that the elements used to catch and retain the thin and 
light string must be mechanically sensitive and they may be easily damaged 
when a force is exerted on the string. Damage to the string catching 
mechanism may render it inoperable and may even block the coin travel path 
thus necessitating a service call. The above-described devices for 
preventing a string manipulation are also relatively sensitive. 
German Application No. G 92 00 559.3 shows a heater for a coin acceptor 
which cuts a string thermoelectrically. The heater is switched on and off 
in response to a pressure switch in the area of the heating element. This 
requires additional expense and, in any event, may be circumvented by a 
clever manipulation. 
SUMMARY OF THE INVENTION 
Among the objects of the present invention are to provide improved coin 
acceptors which are reliable, durable and compact; to provide improved 
coin acceptors which safely and reliably inhibit efforts to cheat them; to 
provide improved coin acceptors which inhibit stringing; and to provide 
improved coin acceptors which are inexpensive to manufacture. 
Generally, one form of the invention is a coin acceptor for inhibiting a 
user from using a string attached to a coin to defraud the coin acceptor. 
The coin acceptor includes a main plate and a coin path attached to the 
main plate. The coin path and the main plate define a slot therebetween. 
The coin acceptor also includes a side plate corresponding to the main 
plate. The slot is narrower than a thinnest coin to be protected against 
use of the string. The slot opens towards an end of the coin path. The 
slot is positioned to receive the string after the coin to which the 
string is attached has passed downstream of the coin path. 
Another form of the invention is a coin acceptor for inhibiting a user from 
using a string attached to a coin to defraud the coin acceptor. The coin 
acceptor includes a coin acceptance channel for retaining genuine coins 
within the coin acceptor and a coin rejection channel for ejecting 
nongenuine coins from the coin acceptor. A wall is positioned between the 
coin acceptance channel and the coin rejection channel. The wall includes 
a slot for cetching the string to prevent the coin attached to the string 
from being retrieved from the coin acceptor through the coin rejection 
channel. 
Other objects and features will be in part apparent and in part pointed out 
hereinafter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIGS. 1 and 2 show a coin acceptor 10 having a coin receiving channel 12 
for inserting coins into coin acceptor 10. Coin acceptor 10 includes a 
main plate 18 and a side plate 25 which together define a coin path for 
allowing the passage of coins between plates 18 and 25. A ramped coin path 
19 is supported from side plate 25 and engages the corresponding wall of 
main plate 18. Ramped coin path 19 is positioned downstream from coin 
receiving channel 12. A rejection channel 14 and an acceptance channel 16 
which leads to a coin box or safe are positioned downstream from ramped 
coin path 19. A counterfeit coin path 20 is supported from main plate 18 
for guiding coins when side plate 25 is moved away from main plate 18. 
Several coin sensors (not shown) are positioned along ramped coin path 19 
for checking the genuineness of a dropping coin. A control and evaluating 
circuit (not shown) receives the output signals of the coin sensors and 
determines whether or not the passing coin is genuine. The coin then moves 
to an acceptance switch 22. Acceptance switch 22 is closed when a genuine 
coin has been detected so that the coin passes over rejection channel 14 
and into acceptance channel 16. For all other inserted coins and articles, 
acceptance switch 22 is opened so that the dropping coin or article moves 
into rejection channel 14 for return to the user. 
Optical presence sensors 24 and 26 are positioned adjacent acceptance 
channel 16 and rejection channel 14, respectively. After the coin sensors 
determine that an inserted coin is genuine and after presence sensor 24 
detects the coin, a credit signal is generated for providing the 
corresponding goods or service. Additional presence sensors 28 and 30 are 
located upstream from acceptance switch 22 and presence sensor 24, 
respectively. 
As shown in FIG. 2, a slot 32 is positioned between main plate 18 and 
counterfeit coin path 20. Slot 32 includes a recess 34 in main plate 18 
and a recess 36 in counterfeit coin path 20. Slot 32 is preferably narrow 
enough to retain the smallest coin to be protected against stringing. As 
shown at reference number 38, slot 32 is wider towards the open end of the 
slot near the end of counterfeit coin path 20. Barbs 40 are provided 
inside slot 32. Slot 32 is preferably formed from cooperating recesses 
provided within counterfeit coin path 20 and main plate 18, with barbs 40 
positioned along the coin path. 
FIG. 1 shows how a coin 42 hangs on a thin string 44. The different 
directions of pull F.sub.a are demonstrated in FIG. 1 by the angle alpha. 
When the coin 42 is judged to be genuine, it runs against locked 
acceptance switch 22 and moves to a position 42' with the run of the 
string being indicated by a dashed line 44'. Presence sensor 24 generates 
a credit signal so that the goods can be made available or the service can 
be rendered at this time. The user who intends to manipulate coin acceptor 
10, however, pulls on string 44 to retrieve coin 42. The tension from this 
pulling causes the coin and string to move from the position along dashed 
line 44' into the position of coin 42 and string 44 (shown by the solid 
line). Coin 42 is thereby pulled against the underside of counterfeit coin 
path 20 because slot 32 is smaller than the thickness of the coin 42. 
Accordingly, slot 32 is so arranged that, when force is applied to string 
44 with the coin having travelled beyond counterfeit coin path 20, string 
44 is moved into slot 32 in the direction of an arrow 46. This occurs 
without difficulty given the dimensions and position of slot 32 described 
above. Barbs 40 prevent the string from being moved out of slot 32. Slot 
32 preferably includes at least one such barb for retaining string 44 in 
the event the user tries to remove string 44 from slot 32 at the side. 
This prevents the improper retrieval of the coin back through coin 
receiving channel 12 by means of such manipulation. It is therefore 
permissible to generate a credit signal for a coin attached to a string so 
long as the coin cannot be improperly retrieved from coin acceptor 10. 
Accordingly, the coin path through coin acceptor 10 from ramped coin path 
19 to a position behind acceptance switch 22 requires the string connected 
to the coin to follow a more or less sharp curve which causes the string 
to move to the side when pulled tight. This moving force is used for 
inserting the string into slot 32. Slot 32 must be wide enough to permit 
the string to enter without problems; however, slot 32 must not be so wide 
that a coin can be pulled through. 
FIG. 1 also shows the position of a coin 42" in rejection channel 14 for 
completeness. 
FIG. 3 shows how string 44 may be connected to a coin 42" which coin is 
intentionally chosen to be unacceptable. Accordingly, coin 42" is moved 
through the non-actuated acceptance switch 22 into rejection channel 14. 
The user now manipulates the string to try to move genuine coin 42 
positioned at 42' into rejection channel 14 to thereby retrieve coin 42. 
As shown, however, slot 32 prevents coin 42 from being moved into 
rejection channel 14. 
The presence sensor 30 also provides a safeguard against stringing. If 
sensor 30 detects the presence of a coin after presence sensor 24 has 
already detected the same coin, then it is likely that a string is being 
used to manipulate coin acceptor 10 and the generation of a credit signal 
is disabled. 
FIGS. 4 through 6b show a coin acceptor 10a having a coin receiving channel 
12a for inserting coins into coin acceptor 10a. Coin acceptor 10a includes 
a main plate 18a and a side plate 25a which together define a coin path 
for allowing the passage of coins between plates 18a and 25a. A ramped 
coin path 19a is supported from side plate 25a and engages the 
corresponding wall of main plate 18a. Ramped coin path 19a is positioned 
downstream from coin receiving channel 12a. A rejection channel 14a and an 
acceptance channel 16a which leads to a coin box or safe are positioned 
downstream from ramped coin path 19a. A counterfeit coin path 20a is 
supported from main plate 18a for guiding coins when side plate 25a is 
moved away from main plate 18a. As with FIGS. 1 and 2, a slot such as slot 
32 is provided between main plate 18a and counterfeit coin path 20a for 
preventing a coin 42a from being retrieved from coin acceptor 10a via a 
string 44a. 
Several coin sensors (not shown) are positioned along ramped coin path 19a 
for checking the genuineness of a dropping coin. A control and evaluating 
circuit (not shown) receives the output signals of the coin sensors and 
determines whether or not the passing coin is genuine. The coin then moves 
to an acceptance switch 22a. Acceptance switch 22a is opened when a 
genuine coin has been detected so that the coin passes into acceptance 
channel 16a. For all other inserted coins and articles, acceptance switch 
22a is locked closed so that the dropping coin or article passes over 
acceptance channel 16a and into rejection channel 14a for return to the 
user. 
Optical presence sensors 24a and 26a are positioned adjacent rejection 
channel 14a and acceptance channel 16a, respectively. After the coin 
sensors determine that an inserted coin is genuine and after presence 
sensor 26a detects the coin, a credit signal is generated for providing 
the corresponding goods or service. 
FIGS. 4 through 6b also show a recess 21 provided in main plate 18a which 
recess engages side plate 25a in the lower area. On the side facing 
acceptance channel 16a, a recess 23 comprises a ramp 27 which is not as 
wide as recess 23. In this way, a slot 29 is defined between the exterior 
face of ramp 27 and main plate 18a which, with the acceptance switch 22a 
being open, prevents coin 42a in the above-described manner from being 
moved upstream past ramp 27 by causing the coin 42a to run against an edge 
31. Accordingly, acceptance switch 22a will not be damaged in a locked 
position if the manipulator tries to draw coin 42a towards switch 22a when 
it is locked. 
As shown in FIG. 7, slot 29 inhibits manipulation of coin acceptor 10a 
using string 44a having a genuine coin 42a attached to one end and having 
a counterfeit coin 42a" attached to the other end. In particular, slot 29 
prevents a user from pulling on the end of string 44a attached to 
counterfeit coin 42a" via rejection channel 14a to thereby improperly 
retrieve genuine coin 42a. 
As shown in FIGS. 4 through 7, slot 29 is preferably located within 
acceptance channel 16a behind acceptance switch 22a. This location is 
especially advantageous where, as in FIG. 4, acceptance channel 16a is 
arranged behind acceptance switch 22a in the coin dropping direction and 
where acceptance switch 22a is usually open. This is because acceptance 
switch 22a (which may be locked closed in response to a counterfeit coin 
on the second end of string 44a) will not be damaged if string 44a is 
pulled. 
In view of the above, it will be seen that the several objects of the 
invention are achieved and other advantageous results attained. 
As various changes could be made in the above constructions without 
departing from the scope of the invention, it is intended that all matter 
contained in the above description or shown in the accompanying drawings 
shall be interpreted as illustrative and not in a limiting sense.