The Machine Accepts Money
When a customer approaches a machine and becomes interested in making a purchase, he must first insert money to pay for his item. If the machine accepts paper money, the money is pulled in using rollers. Once inside, the machine uses a digital scanner to identify the bill's denomination before storing the bill away in a cash box. For coins, the machine identifies the value of the coin using certain values specific to each coin. A quarter, for example, is identified by its diameter of .955 inches, its thickness of 1.75 millimeters and its 119 ridges around its edge. A dime is recognized by its diameter of .705 inches and its thickness of 1.35 millimeters. Other coins are similarly recognized, making counterfeiting possible but exceptionally difficult.
The Customer Makes a Choice
Once sufficient money is inserted, the customer informs the machine of which product he would like to purchase. In older vending machines, pulling or turning a knob activates a strictly mechanical dispensing mechanism. In more modern machines, the customer enters a series of letters and numbers corresponding to his selection before a basic processor electronically activates a motor to dispense the merchandise. Finally, the machine compares the selection's programmed price to the amount of money inserted; if the inserted funds total less than the price of the item, the machine either simply refuses to dispense or sends an electronic message to a display asking the customer to insert additional funds.
The Macine Dispenses the Product
Once the selection is made and has been paid for, the machine must dispense the product. While some vintage machines used a strictly mechanical dispensing coil, most modern machines electronically activate a motor which spins a spiraled merchandise dispenser. The metal coil is shaped in a spiral with products inserted between each ridge. As a motor spins the coil, the rotation pushes products forward in much the same way as a screw pulls debris out of a hole. The metal coils are sized very slightly longer than the shelf supporting the product, so when the purchased item reaches the end of the shelf it simply falls (due to gravity) into a receiving bin at the bottom of the machine. After the product falls, the customer simply retrieves the item from the bin. On many machines, a simple door protects the item from bouncing out of the machine after reaching the bin; this door also folds into the machine on hinges to prevent customers reaching additional items on the bottom shelf.