Coin mechanism with a piezoelectric film sensor

A coin mechanism includes a piezoelectric film sensor in contact with a coin debounce device. When a coin is inserted into the coin mechanism, the coin strikes the coin debounce device as it travels along a coin path. Micro-movement of the coin debounce device is sensed with the piezoelectric film sensor. The coin mechanism changes from a quiescent mode of operation to an active mode of operation in response to sensing the presence of the coin in the coin path. Coin recognition can then be performed. Overall power consumption of the coin mechanism can be reduced.

BACKGROUND 
The present invention relates in general to a coin mechanism with a 
piezoelectric film sensor. 
Low average power consumption is desirable in various coin-operated devices 
such as pay telephones, vending machines and parking meters. Such devices 
typically include a coin mechanism for determining whether an inserted 
coin or token is genuine and for determining the denomination of the 
inserted coin or token. While the coin mechanism must be ready for use at 
all times, the coin mechanism can consume a significant amount of power 
when not in use. Moreover, where a battery or other low power source 
serves as the primary source of power, the continual power drain reduces 
the lifetime of the power source, thereby increasing the frequency at 
which the power source must be replaced. 
A number of techniques have been devised to reduce the electrical power 
consumption of coin-operated devices. For example, U.S. Pat. No. 
4,733,766, assigned to the assignee of the present invention, discloses a 
technique for leaving electrical power-consuming aspects of a coin 
checking apparatus unpowered when the apparatus is not being used. A 
piezoelectric ceramic element is arranged such that insertion of a coin 
into the apparatus stresses the piezoelectric ceramic element and produces 
a corresponding voltage. As explained in the foregoing patent, vibrations 
that occur upon impact of the coin with a snubber placed in the coin path 
stress the ceramic material sufficiently to generate the output voltage. 
The piezoelectric ceramic element can, therefore, be used to sense the 
arrival of the coin, and the generated voltage can be used to switch on 
the power of the apparatus. 
While the use of piezoelectric ceramic sensors in coin mechanisms has been 
reasonably successful, several difficulties can arise. First, vibrations 
caused by events other than insertion of a coin into the coin mechanism 
can cause the piezoelectric ceramic sensor to generate a voltage and 
switch on the power. Switching on the power of the coin mechanism under 
such circumstances is, of course, undesirable. Second, the mechanical 
mounting of the piezoelectric ceramic sensor in the coin mechanism 
sometimes requires the use of an adhesive such as glue. Such mounting 
techniques can affect the mechanical-to-electrical energy conversion of 
the ceramic sensor, making the determination of whether power should be 
turned on more difficult. Third, some of the piezoelectric ceramic 
materials are sensitive to high temperatures. The properties of the 
ceramic can be degraded during soldering or other high temperature 
processes if proper care is not taken to protect the ceramic from damage. 
Additionally, the output signal generated by the piezoelectric ceramic 
sensor often requires the use of a front end amplifier circuit to provide 
a sufficiently high signal level. Such circuitry increases the overall 
cost of the coin mechanism and can increase the power consumption of the 
unit. 
Accordingly, it is desirable to improve the techniques for sensing the 
insertion of a coin in a coin mechanism and to reduce the overall power 
consumption of such mechanisms. 
SUMMARY 
In general, in one aspect, a method of using a coin mechanism includes 
inserting a coin into the coin mechanism, causing the coin to strike a 
coin debounce device as it travels along a coin path, and causing a 
piezoelectric film sensor in contact with the coin debounce device to be 
deflected when the coin debounce device moves in response to being struck 
by the coin. An output signal from the piezoelectric film sensor is 
provided to indicate presence of the coin in the coin path. The coin 
mechanism is caused to change from a quiescent mode of operation to an 
active mode of operation in response to the output signal from the 
piezoelectric film sensor. 
According to another aspect, a coin mechanism includes a coin path with a 
coin track and an energy transfer device having an upper surface arranged 
to be struck by a coin traveling along the coin path. A piezoelectric film 
sensor is in contact with the energy transfer device. When a coin strikes 
the energy transfer device, movement of the energy transfer device 
deflects the piezoelectric film sensor, thereby causing a change in an 
output signal from the sensor. The coin mechanism includes a circuit to 
process the output signal from the piezoelectric film sensor. The coin 
mechanism changes from a quiescent mode of operation to an active mode of 
operation in response to the output signal from the piezoelectric film 
sensor indicating the presence of a coin in the coin path. 
Preferably, the energy transfer device which the coin strikes is a coin 
debounce device which reduces bouncing of the coin. 
Various implementations can include one or more of the following features. 
The coin mechanism can include a coin identification sensor, positioned 
downstream of the coin debounce device, past which a coin travels as the 
coin moves along the coin track. The coin mechanism also can include a 
controller and power supply for providing power to the controller. Prior 
to receipt of a wake-up signal, the controller can operate in a quiescent 
or low-power mode. The controller receives a wake-up signal when the 
output signal from the piezoelectric film sensor indicates the presence of 
a coin in the coin path. In response to the wake-up signal, the controller 
changes from the low-power mode to a powered-up mode to allow coin 
validation functions to be performed. In some implementations, power from 
the supply is completely or substantially shut off from the controller 
until receipt of the wake-up signal. In that case, the power supply also 
receives the wake-up signal and provides power to the controller in 
response to receiving the wake-up signal. 
An upper surface of the coin track can be substantially in line with the 
upper surface of the coin debounce device to allow the coin to travel past 
the coin identification sensor with little or no bounce. The piezoelectric 
film sensor can be mounted adjacent the coin debounce device such that a 
coin travelling along the coin path does not directly strike the 
piezoelectric film sensor. 
The piezoelectric film sensor and the coin debounce device can be secured 
to the coin mechanism lid. For example, the piezoelectric film sensor and 
the coin debounce device can include substantially aligned holes for 
receiving a fastening rod, such as a bolt, screw or pin, to secure the 
piezoelectric film sensor and the coin debounce device to the lid. Also, a 
section of the piezoelectric film sensor can be supported by a ledge 
secured to the track side of the lid. 
The lid of the coin mechanism can include a first slot through which a 
portion of the piezoelectric film sensor passes to a second side of the 
lid. Electrical connections from the piezoelectric film sensor to the 
circuit that processes the output signal can be connected to a section of 
the piezoelectric film sensor located on the second side of the lid. The 
section of the piezoelectric film sensor to which the electrical 
connections are connected can include a hole which fits over a projection 
on the second side of the lid to help retain the piezoelectric film sensor 
in place. 
The piezoelectric film sensor can include multiple bends. For example, the 
piezoelectric film sensor can have a first section disposed between the 
coin debounce device and the lid and a second section adjacent a lower 
surface of the coin debounce device. The first section of the 
piezoelectric film sensor can include tabs to position the piezoelectric 
film sensor. Lugs can be molded to the first side of the lid for 
positioning the tabs of the piezoelectric film sensor. The second section 
of the piezoelectric film sensor can be supported by the ledge secured to 
the lid. The lid can have a second slot to help increase the amount of 
bending of the piezoelectric film sensor caused by micro-movement of the 
coin debounce device. For example, the second slot can be located adjacent 
the first section of the piezoelectric film sensor. 
Various implementations can include one or more of the following 
advantages. Using a piezoelectric film sensor rather than a piezoelectric 
ceramic sensor can provide a coin arrival sensor which is less sensitive 
to vibrations caused by events other than insertion of a coin. Therefore, 
the piezoelectric film sensor makes it more likely that the coin mechanism 
will be powered up only when the presence of a coin is detected. The 
overall consumption of power can, therefore, be reduced. Providing 
multiple bends in the film sensor and multiple slots in the lid can help 
improve the sensitivity of the piezoelectric film sensor. 
In some cases, the output signal from the piezoelectric film sensor can be 
processed without front end amplification circuitry to reduce the overall 
cost and power consumption of the coin mechanism even further. In 
addition, the piezoelectric film sensor can be placed out of the direct 
path of a coin traveling through the coin mechanism. That can reduce the 
wear of the sensor and extend its lifetime. 
Techniques for mounting the piezoelectric film sensor are relatively easy, 
and can avoid some of the difficulties encountered in the use of ceramic 
sensors. Furthermore, by designing the piezoelectric film sensor so that 
it extends on both sides of the lid of the coin mechanism, the electrical 
connections to the piezoelectric film sensor can be made away from the 
coin track. Proper positioning and operation of the piezoelectric film 
sensor can be enhanced. 
Other features and advantages will be readily apparent from the following 
detailed description, the drawings and the claims.

DETAILED DESCRIPTION 
As used herein, the terms "coin" and "coins" include genuine coins, as well 
as tokens, slugs, and similar objects. 
As shown in FIG. 1, a coin mechanism receives an inserted coin 10 through a 
coin entry 12. The coin falls onto a coin debounce device 14 which absorbs 
or dissipates most of the coin's kinetic energy so that the coin rolls 
substantially smoothly along a track 16 past electrically-powered coin 
identification sensors 18, 20. Such energy debounce devices are known in 
the art and sometimes are referred to as snubbers. In some 
implementations, the energy debounce device, or snubber 14, can comprise, 
for example, a piece of ceramic or a piece of sintered metal. In the 
illustrated arrangement, the snubber 14 causes a change in direction of 
the coin path and reduces bouncing of the coin as it travels along the 
coin track. A piezoelectric film sensor 22 is positioned adjacent the 
snubber 14 and is physically deflected by the snubber when it is struck by 
a coin 10. Thus, the piezoelectric film sensor 22 senses the arrival of 
the coin 10 and generates an output signal which causes a change in the 
amount of power provided to the coin mechanism and/or a microcontroller 
(not shown in FIG. 1) associated with the coin mechanism. In particular, 
prior to sensing a coin in the coin mechanism, the system is in a 
quiescent or low-power state, whereas when arrival of a coin is detected 
by the piezoelectric film sensor 22, the system is caused to power up. 
As the coin 10 rolls past the sensors 18, 20, electrical signals are 
generated by the sensors and are provided to the microcontroller. The 
electrical signals generated by the coin identification sensors 18, 20 
contain information corresponding to the measured characteristics of the 
coin, such as the coin's diameter, thickness, metal content and 
electromagnetic properties. The microcontroller can use the electrical 
signals to discriminate whether the coin 10 is acceptable, and if so, the 
denomination of the coin. 
The coin 10 rolls down the track 16 and falls toward a gate 24 which is 
automatically retracted if the coin is found to be valid, so as to direct 
the coin along an accepted coin path or chute. If the coin 10 is not found 
to be valid, then the gate 24 is left in position so that the coin hits 
the gate and rolls off it to a reject path or chute. 
As shown in FIG. 2, the coin mechanism includes a lid 26 connected to a 
flight deck 28 by a hinge 30. Although the lid 26 is shown in an open 
position, it is closed during normal operation. The protruding and sloping 
coin track 16 can be molded or otherwise secured to the inside of the lid 
26 as can be two locating lugs 32 and a ledge 34. The snubber 14, which 
can be made, for example, of a metal or ceramic material, is positioned 
near the upper end of the track 16. Recesses at either end of the snubber 
14 fit around the lugs 32. The snubber 14 is positioned slightly above the 
ledge 34 and can be mounted to the lid 26 by a fastening rod 36 such as a 
screw, bolt or pin, which passes through a hole 38 (see FIGS. 4 and 5) in 
the snubber. The lid 26 has a corresponding pre-drilled bore 37 (see FIGS. 
4, 6 and 7) for receiving the fastening rod 36. Although not visible in 
FIG. 2, the piezoelectric film sensor 22 is positioned adjacent the 
snubber 14, as described in greater detail below with respect to FIGS. 4 
through 7. 
When properly positioned, the upper surface of the snubber 14 is 
substantially in line with the upper surface of the coin track 16. During 
normal operation the lid 26 is closed, and the snubber 14 and coin track 
16 lie against the front face 40 of the deck 28 as indicated by the broken 
line 42. The sensors 18, 20 are located downstream of the snubber 14 on 
the front side of the lid 26. The positions of the sensors 18, 20 are 
indicated in broken lines on the inside (or track-side) of the lid in FIG. 
2. 
To avoid excessive wear of the piezoelectric film sensor 22, it is 
preferably not positioned directly in the path of the coins. Rather, as 
previously mentioned, the sensor 22 is designed to be mounted adjacent the 
snubber 14 out of the path of a coin or similar object traveling through 
the coin mechanism. The piezoelectric sensor 22 is mounted in direct 
contact with the snubber 14 such that when the snubber 14 is struck by a 
coin 10 or similar object, micro-movement of the snubber physically 
deflects the sensor 22 to cause a change in the output signal generated by 
the sensor. 
As shown in FIG. 3, in one implementation, the piezoelectric film sensor 22 
includes a first section 44 which is positioned on the track-side of the 
lid 26 between the lid and the snubber 14. The first section 44 includes 
tabs 46 which are located at its side ends and which fit below the 
locating lugs 32 (see FIG. 5) to position the sensor 22 in place. The 
first section 44 also has a hole 48 which is substantially aligned with 
the hole 38 in the snubber. Thus, a single fastening rod 36 can be used to 
secure the snubber 14 and the piezoelectric film sensor 22 to the lid 26. 
A second section 50 of the sensor 22 is provided at the lower end of the 
first section 44 and forms a substantially right angle with the first 
section when secured to the lid by the snubber 14 and fastening rod 36. 
When positioned in place, the second section 50 of the piezoelectric film 
sensor 22 is supported by the ledge 34 (see FIG. 5). The snubber 14 then 
rests on the upper surface of the second section 50 which is supported 
directly by the ledge 34. 
The sensor 22 also includes a curved third section 52 which is provided at 
the upper end of the first section 44. The third section 52 projects from 
the first section 44 in the opposite direction from the second section 50 
and extends through a first slot 68 (see FIGS. 4 and 6) in the lid 26. A 
fourth section 54 projects from the third section 52 in a direction away 
from the first section 44 and in a plane substantially parallel to the 
first section 44. The fourth section 54 also has a hole 56 which fits over 
a projection 62 (see FIG. 7) formed on the sensor-side of the lid 26. The 
projection 62 also helps retain the sensor 22 in place. Two crimped lugs 
57, 59 are attached to the fourth section 54 and provide the electrical 
connection to two wires or electrodes 58, 60 which lead to a printed 
circuit board with circuitry for processing the output from the sensor 22. 
When properly positioned, the first and second sections 44, 50 of the 
sensor 22 are located on the track-side of the lid 26 (see FIG. 5), 
whereas the fourth section 54 is located on the opposite or sensor-side of 
the lid (see FIG. 7). As previously noted, the third section 52 extends 
through the slot 68. The lid 26 also includes a second slot 64 (see FIGS. 
4, 6 and 7) below the first slot 68. The second slot 64, which is adjacent 
the sensor 22, can increase the deflection of the sensor 22 that results 
from micro-movement of the snubber 14 when it is struck by a coin 10. 
Similarly, providing multiple bends in the sensor 22 can increase its 
sensitivity. The sensitivity of the sensor 22 can, therefore, be improved. 
As shown in FIG. 3, in one implementation the piezoelectric film sensor 22 
includes several layers, including a thin polyvinylidene fluoride (PVDF) 
base film 80. In one implementation, the PVDF film 80 has a thickness of 
about 110 microns and is annealed at about 85.degree. C. On one side of 
the PVDF film 80 a positive silver ink layer 82 is provided. A negative 
silver ink layer 84 is provided on the opposite side of the PVDF film 80. 
In some implementations, the positive and negative conductive layers 82, 
84 cover substantially the entire surface of the PVDF film 80. However, 
the conductive materials also can be deposited in a pattern to help reduce 
the overall capacitance of the sensor 22 and improve its sensitivity. 
Exemplary patterns for the silver ink layers 82, 84 are illustrated in 
FIGS. 3C, 3D and 3E. FIGS. 3C and 3D show a positive silver ink pattern 
82. Similarly, FIG. 3E shows a negative silver ink pattern 84 as seen from 
the side of the sensor 22 with the positive ink pattern. As can be seen 
from those figures, the conductive ink patterns 82, 84 are provided over 
the second section 50 and the third section 52 of the sensor 22 and extend 
over curved portions of the sensor. Preferably, the stretch direction of 
the PVDF film 80 is as indicated by the arrow 92 in FIG. 3D. 
As further shown in FIG. 3B, a protective coating 86 is provided over the 
surface of the sensor with the positive ink layer 82. An adhesive layer 88 
and a substrate layer 90 are provided over the surface of the negative ink 
layer 84. In one implementation, the adhesive layer 88 has a thickness of 
about 0.001 inches, and the substrate layer 90, which can include MYLAR, 
has a thickness of about 0.002 inches. 
Initially, the sensor 22 can be substantially flat and is bent as shown in 
FIG. 3A when it is positioned in place. To position the piezoelectric film 
sensor 22 and secure it to the lid 26, the following sequence of steps can 
be performed. The sensor 22 is held on the track-side of the lid 26 and 
the fourth section 54 is guided through the slot 68 so that the fourth 
section appears on the sensor-side of the lid 26. The fourth section 54 
then is bent upward so that it is positioned as shown in FIG. 7. The first 
and second sections 44, 50 are bent so that the sensor 22 appears as shown 
in FIG. 5. The snubber 14 then is positioned adjacent to the sensor 22 on 
the track-side of the lid 26, and the fastening rod 36 is inserted through 
the pre-drilled bore 37 to secure the piezoelectric film sensor 22 and the 
snubber 14 in place. 
As shown in FIG. 8, the output of the piezoelectric film sensor 22 is 
provided to an input of a high impedance switch circuit 70. The switch 
circuit 70 can be any one of several types, including a transistor 
circuit, such as a field effect transistor or bipolar junction transistor 
circuit, or an integrated circuit, such as a comparator or CMOS logic 
gate. The output of the high impedance switch circuit 70 is provided to a 
latch circuit 72. When a coin impacts the snubber 14 such that the sensor 
22 generates a corresponding output signal, the voltage appearing at the 
output of the switch circuit 70 is sufficient to switch the latch 72 from 
a reset condition to a set condition. The latch 72 remains in the set 
condition after the transient output signal from the piezoelectric film 
sensor 22 has terminated. When set, the latch 72 provides a wake-up signal 
which is used to switch the power of the system from a low-power or 
quiescent mode to an active or powered-up mode. In the implementation 
shown in FIG. 8, a regulated voltage is continuously provided by a voltage 
regulator 74 to the microcontroller 76 associated with the coin mechanism. 
The wake-up signal from the latch 72 is provided to an input of the 
microcontroller 76 which causes the microcontroller to power up. As a 
result of the wake-up signal, power also is provided to other elements of 
the coin mechanism, such as the coin identification sensors 18, 20, so 
that coin validation functions can be performed. Once the microcontroller 
76 completes the coin validation and related processes, it resets the 
latch 72 and enters the low-power mode again. In some cases, the 
microcontroller 76 is programmed to wait a predetermined period of time 
prior to entering the low-power mode. If additional coins are inserted 
into the coin mechanism within the predetermined period, the 
microcontroller is already powered up. 
In an alternative implementation illustrated in FIG. 9, the wake-up signal 
from the latch 72 also controls the output of the voltage regulator 74. 
Thus, the voltage regulator 74 is turned on to provide the regulated 
output voltage only when the latch 72 is set, in other words, after the 
piezoelectric film sensor 22 senses the presence of a coin in the coin 
mechanism. After completing the coin validation and related processes, the 
microcontroller 76 clears the latch 72. The system then returns to its 
low-power or quiescent mode, and the regulated voltage is shut off from 
the system. Thus, during the low-power mode, power is supplied only to the 
high impedance switch circuit 70 and the latch circuit 72. 
Although the configurations of either FIGS. 8 or 9 may be suitable for 
particular applications, the configuration of FIG. 9 can provide a 
quiescent current many times lower than the configuration of FIG. 8. In 
some implementations, a quiescent current as low as about one micro-ampere 
can be obtained for the configuration of FIG. 9. 
FIG. 10 illustrates an exemplary circuit for implementing the configuration 
of FIG. 9. The high impedance switch circuit 70 includes a transistor T1 
which serves as the switching element whose state is controlled by the 
output of the piezoelectric film sensor 22. The switch circuit also 
includes several resistors R1, R2, R3 and capacitors C1, C2 which serve as 
a filter to reduce noise. The output of the transistor T1 serves as an 
input to a NAND gate NG1 in the latch circuit 72. The NAND gate NG1 is 
powered by an input voltage and has an output which is clamped by a pair 
of diodes D1 and a resistor R4 to a regulated voltage. Two additional NAND 
gates NG2, NG3 form a flip-flop which can be set as a result of the 
transistor T1 changing state or reset by a signal from the microcontroller 
76. A resistor R5 and capacitor C3 provide a turn-on delay for the reset 
signal from the microcontroller 76. In one embodiment, the switch circuit 
70 and the latch circuit 72 can be provided, along with other electronics, 
on a circuit board secured to the deck of the coin mechanism opposite the 
lid 26. 
Still referring to FIG. 10, the output of the latch 72 is provided to an 
ON/OFF pin of the voltage regulator 74. The voltage regulator 74 also 
receives an input voltage at the pin V.sub.in from a power supply (not 
shown). When the latch 72 is set, the regulated voltage is provided from 
an output pin (V.sub.out) of the voltage regulator 74 to the 
microcontroller 76 which controls the coin validation circuitry. The 
capacitors C7, C8 serve as a filter for the regulated voltage. When the 
latch 72 is reset by the microcontroller 76, the regulated voltage is 
turned off. A resistor R7 serves as a pull-up to an ERROR pin which 
provides a signal to the microcontroller 76 to indicate whether the 
voltage regulator 74 is functioning properly. 
Input signals provided through the diodes D3, D4 can be used during testing 
of the system to override the signal from the sensor 22 and place the 
system in a powered-up mode regardless of the output signal from the 
piezoelectric film sensor. 
As described above, a coin inserted into the coin mechanism falls onto the 
coin debounce device 14 which absorbs or dissipates most of the coin's 
kinetic energy so that the coin rolls substantially smoothly along a track 
16 past the coin identification sensors 18, 20. In other implementations, 
the coin debounce device 14 can be replaced by a block of material which 
does not substantially reduce bouncing of the coin. Even in such 
situations, when the coin strikes the block of material, micro-movement of 
the block of material is sensed by the piezoelectric film sensor 22 as 
discussed above. The block of material, thus, serves as an energy transfer 
device by transferring at least some of the coin's kinetic energy to be 
sensed by the piezoelectric film sensor 22. 
The coin mechanism can be used in various coin-operated devices such as pay 
telephones and vending machines. Power can be supplied to the voltage 
regulator 74, the high impedance switch 70, the latch 72 and the sensor 
22, for example, from the payphone chassis or the vending machine. The 
coin mechanism can be used in other coin-operated device as well, 
including parking meters. 
Other implementations are within the scope of the claims.