 |  |  |
| HOW A COINT TESTER WORKS | ||
| QUESTIONS OR COMMENTS | ||
 | AUTHOR: | David Hu |
| E-MAIL: | dhu@mit.edu | |
| COURSE: | 2 | |
| CLASS/YEAR: | 2 | |
MAIN FUNCTIONAL REQUIREMENT:Test different denominations of coins and reject counterfeit ones whileaccepting correct coins to be sorted and counted
DESIGN PARAMETER: CoinTester
GEOMETRY/STRUCTURE:
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| Figure 1: Coin Testing Apparatus Schematic |
Center: coin to be identified; |
| Figure 2: Electric Identification Probe |
EXPLANATION OF HOW IT WORKS/ IS USED:
1. User deposits coin into coin slot on outside of machine. Coin slot is dimensioned tothe width and height for the thickest and largest diameter coin to be accepted.
2. Coin rolls down a chute and past identification probe that determines the denominationby the coins material properties. The probe consists of two solenoids withtheir axis perpendicular to the longitudinal wall of the chute. Current is runthrough one solenoid which then generates a B field perpendicular to the coin axis of revoluion. The magnetic field passes through thecoin, is attenuated by the coin's material properties and geometry before being receivedby the solenoid at the opposite end. The B field passing along the axis ofthe second coil generates a specific pattern of electric current, which can be matchedwith the correct coin.
3. a) Coin also activates switch that b) pulls slide member toward wall of chute (intopage) by means of electromagnet, thereby preventing another coin from entering.
4. The probe sends information to timing mechanism for turning on of electromagneticdevice that opens flap armature.
5. Coin falls down chute and onto first sorting weigher. The number of denominations to beaccepted determines the number of sorting weighers (e.g. quarter,dime,nickel =3 weighers).Each sorting weigher is pivoted and contains a slot dimensioned to diameter of specificcoin. The sorting weighers are arranged by size of coin to be accepted, with the largestcoin size weigher on top. The left arm of the sorter weigher holds a counterweight thatwill be lifted only if the coin is the correct weight.
6. Sorting weigher pivots under the weight of coin and coin rolls toward chute.
7. Electromagnet turns on and the coins specific flap armature opens momentarilyallowing coin to fall through chute.
8. Coin rolls down chute to be sorted.
DOMINANT PHYSICS:
tI=time to i event
Opening of Flap armature: ttotal = tcoin + tarmature
tcoin = timefor specific coin to roll from probe chute onto sorting weigher + time for sorting weigherto pivot and coin to roll off sorting weigher
tarmature =time for armature to rise enough for coin to continue down chute
LIMITING PHYSICS:
The performance/use of the machine is limited by the position of the machine. If themachine is not seated on a level plane, then the coin will take longer to roll down thechute and the timing mechanism will open the flap armature before the coin can passthrough.
PLOTS/GRAPHS/TABLES:
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| Figure 3: Detection of Counterfeit Coins |
WHERE TO FIND COINT TESTERS:
This design for the coin tester limits it to places where either electricity can byobtained or a battery connected. Coin testers have few moving parts and simple circuitry,making them inexpensive to manufacture. They are in most vending machines and slotmachines where counterfeit coins need to be detected.
REFERENCES/MORE INFORMATION:
Prumm, Georg J. "Electronic Coin Tester with Controlled Mechanical TestingDevice." US patent 4,234,072. Nov 19, 1980.
Parker, Donald and Rollins, Robert. "Coil configuration for electronic cointester and method of making."US Patent 4,905,814. March 6, 1990
