Check-actuated control mechanisms – Including means to test validity of check – By testing material composition
Reexamination Certificate
1999-12-21
2001-05-01
Olszewski, Robert P. (Department: 3652)
Check-actuated control mechanisms
Including means to test validity of check
By testing material composition
Reexamination Certificate
active
06223878
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method and an apparatus for validating coins.
BACKGROUND OF THE INVENTION
It is known to validate coins by monitoring the outputs of a plurality of sensors each responsive to different characteristics of the coin, and determining that a coin is valid only if all the sensors produce outputs indicative of a particular coin denomination. Often, this is achieved by deriving from the sensors particular values indicative of specific parts of the sensor signal. For example, an electromagnetic sensor may form part of an oscillator, and the frequency of the oscillations may vary as a coin passes a sensor. In some arrangements, the peak value of the frequency variation is used as a parameter indicative of certain coin characteristics, and this value is compared with respective ranges each associated with a different coin denomination.
The peak frequency value is often obtained by taking successive samples of the output of the oscillator, and counting the number of cycles within each sample. The coin validator may have a microprocessor-based control circuit, and the microprocessor may be used for this counting operation in addition to other functions, such as checking that the measurements of the coin correspond to those of a valid coin.
FIG. 2
shows one prior art counting technique. The oscillator output is represented by successive cycles
1
,
2
,
3
. . . n of a waveform. At the leading edge of the first cycle, a timer is started. This measures a predetermined interval T, which may for example be 1mS. A second timer is also started at the same instant. Also, a counter starts to count the cycles of the waveform.
When the first timer has timed the predetermined period T, the microprocessor monitors the input waveform until the beginning of the next leading edge. At that point, the second timer is stopped, and the counter is also stopped. Assuming that the second timer has reached a value of t and the counter has reached the value n, the input frequency is given by n/t.
The use of the first counter ensures that the sample time is always approximately equal to T irrespective of the input frequency, and therefore cannot occupy an unduly long period, which would cause problems to other aspects of the validator operation.
In the alternative prior art arrangements shown in
FIG. 3
, a first timer is started at an arbitrary time and measures a predetermined period T. A second timer is started at the same time, and measures the period e
1
to the leading edge of the next pulse. A counter is also started, for counting the cycles of the oscillator. When the first timer reaches the predetermined time T, a further timer measures the period e
2
from the end of that period to the beginning of the next leading edge. The counter is then stopped.
In this arrangement, the frequency of the oscillator is given by n/(T−e
1
+e
2
).
In both these arrangements, the timers operate at clock rates much higher than that of the frequency being measured, and both arrangements allow for precise measurement of frequency. However, each requires a plurality of timers, and each requires the processor to monitor the input waveform for the precise time at which the final leading edge is present.
The predetermined time period T is chosen to provide a compromise between a relatively accurate measurement, requiring a long sample time, and speed of operation, which may be crucial if the microprocessor has to perform other tasks at the same time.
SUMMARY OF THE INVENTION
Various aspects of the invention are set out in the accompanying claims.
According to a further aspect of the invention, the frequency of an oscillator coupled to an inductive sensor in a coin validator is measured by counting the number of oscillator cycles within a sample time period, which number may vary timing the sample period, which may also vary, and calculating the frequency from the cycle count and the timed duration, wherein the sample period is controlled in response to the counting of the oscillator cycles.
This avoids the need for a separate timer for ensuring that the sample period is of a substantially uniform duration. Although, in accordance with this further aspect of the invention, the sample period may vary, it is found in many applications that a coin passing an inductive sensor does not cause the frequency to change by more than a relatively small amount, so that the variation in sample time is not substantial. This sample time may for example vary by around 10%, depending upon the construction of the coin validator and the nature of the coins it is arranged to validate.
In a preferred aspect of the invention, the sample period is terminated in response to the count of the oscillator cycles reaching a predetermined number N, but the sample period does not necessarily terminate exactly at that point; it may terminate at a subsequent oscillator cycle. Meanwhile, the oscillator cycles continue to be counted so that the subsequent measurement of frequency is accurate. This preferred aspect of the invention could be implemented by arranging for a flag to be set when the counter of the oscillator cycles reaches N. At a subsequent point. the microprocessor checks the state of the flag, and if it is set the microprocessor then arranges for the timer and the counter to halt when the next oscillator cycle occurs. This means that the microprocessor can perform other tasks in the period between the oscillator count reaching N and the time at which the sample period ends. This has two possible advantages. First, it means that time-critical operations performed by the microprocessor do not have to be interrupted, or only have to be interrupted for a very brief period, in order to carry out the frequency measurement. Second, the microprocessor could be arranged to lengthen the sample period, if time is available, so as to increase the accuracy of the frequency measurement.
Other aspects of the invention may be used in conjunction with the aspects mentioned above, or may be used independently, for example with prior art counting techniques such as those described earlier.
In accordance with such a further aspect of the invention, a coin validator is operable to sample the output of a sensor for an alterable sampling period. By allowing the period to be altered, it is possible to make the sampling period suitable for different circumstances.
In one preferred arrangement, the coin validator comprises at least two sensors which are passed in succession by a coin. The output of at least the second sensor is sampled for a relatively long sample period, giving a high resolution, to obtain measurements used in the validation of the coin. During the time that the second sensor output is being sampled (which could last for several sample periods), there are one or more intervals in which the first sensor output is sampled in order to determine whether a second coin is adjacent the first sensor. This situation, wherein a first coin is followed in close proximity by a second coin, results in unreliable validation and therefore it useful to sense this circumstance so that both coins can be rejected. According to a preferred arrangement of the present invention, the first sensor is sampled for only a brief sampling period, thereby providing a low resolution. However, as the purpose of this sampling is simply to detect the presence of a coin, rather than to determine accurately the measurements of the coin, this is adequate. The short sampling period enables the operation to be performed quickly.
In a further aspect of the invention, a coin validator can be set up to validate any of a plurality of different coin sets. For example, a coin validator may be programmed to handle, selectively, either a British coin set or a German coin set. This could be achieved by storing the appropriate acceptance criteria in the validator, or by switching between two different sets of acceptance criteria. In accordance with the further aspect of the invention, the sampling period used for the sampling of the output of a
Cattani Thomas J.
Dillon Stephen John
Fish & Richardson P.C.
Jaketic Bryan
Mars Incorporated
Olszewski Robert P.
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