Bill position correction method using the characteristic of step loss of step motor

A bill position correction method used in a bill acceptor comprising a housing defining a bill slot for the insertion of a bill and a bill-receiving unit accommodated in said housing and defining a bill passage in communication with said bill slot, said bill-receiving unit comprising a bill box for collecting bills, a bill transmission mechanism, said bill transmission mechanism comprising at least one drive unit, at least one bill-transfer roller set rotatable by said at least one drive unit to transfer a bill and a bill-pressing roller set controllable to press each inserted bill, an alignment correction unit formed of at least one step motor, at least one transmission device and two correction devices and adapted for correcting the moving direction of each inserted bill into accurate alignment with a center line of said bill passage, and a sensor unit, said sensor unit comprising a control circuit and a set of sensor components, the bill position correction method comprising the steps of:

• (a) starting up said bill acceptor;
• (b) enabling said sensor components of said sensor unit to sense the insertion of a bill through said bill slot into said bill passage;
• (c) enabling said at least one bill-pressing roller set of said bill transmission mechanism to press said bill and said at least one bill-transfer roller set to transfer said bill to a predetermined location in said bill passage;
• (d) moving the bill-pressing roller set of the bill transmission mechanism to release the inserted bill and enabling said at least one step motor of said alignment correction unit to move said two correction devices toward each other in correcting said bill into accurate alignment with the center line of said bill passage subject to a predetermined number of steps;
• (e) determining the resistance force received by said two correction devices from said bill to be larger or smaller than the thrust force produced during rotation of said at least one step motor to drive said at least one transmission device in moving said correction devices, and then returning to step (d) if said resistance force is larger than said thrust force, or proceeding to step (f) if said resistance force is smaller than said thrust force;
• (f) utilizing the step loss status of said at least one step motor to be unable to keep pushing said bill, and then enabling said at least one transmission device of said alignment correction unit to move said correction devices away from said bill when the rotation of said at least one step motor reaches said predetermined number of steps;
• (g) enabling said at least one bill-pressing roller set of said bill transmission mechanism to press said bill again, and then enabling said at least one bill-transfer roller set to transfer said bill;
• and
• (h) ending.