Drive mechanism for stepping motor in printer

A stepping motor drive for printers including a multi-phase stepping motor that turns as each phase is excited in turn by drive pulses, a movable member that is driven by the turning of said stepping motor, and a stopper that restricts the movement of said movable member when said stopper comes into contact with said movable member, said stepping motor drive comprising:

• a stepping motor drive circuit that outputs drive pulses;
• drive pulse control means, said drive pulse control means causing said stepping motor to become out of step by causing said stepping motor drive circuit to continue to output drive pulses after said movable member has come into contact with said stopper, and thereafter causing said drive pulse control means to stop said output of said drive pulses at a preset fixed phase;
• and
• fixed phase switching means responsive to input entered by an operator for switching said preset fixed phase to any of said stepping motor phases.

A method of positioning a rotor relative to a stator in a multiple-phase stepping motor that is a drive source for driving a carriage, in a printer, to which is attached a print head in a direction either approaching toward or receding from the platen comprising the steps of:

• (a) driving said stepping motor by applying thereto a predetermined first number of drive pulses, causing said stepping motor to be out of step after a movable member attached to said stepping motor has come up against a stopper provided in the printer frame, and provisionally determining any one of stepping-motor excitation phases which said stepping motor takes when it stops;
• (b) placing said movable member in a position that is removed from said stopper by any discretionary distance, and then driving said stepping motor, moving said movable member in a direction approaching said stopper and causing it to come up against said stopper, and stopping said stepping motor in the phase provisionally established in step (a) in a condition wherein it is out of step;
• (c) driving said stepping motor that has been stopped in step (b) by applying thereto a predetermined second number of drive pulses so that said movable member moves in a direction away from said stopper;
• (d) while said stepping motor is turning through a predetermined number of steps as cited in step (c) above, measuring the gap between said print head and platen of said printer;
• (e) repeating processes cited in steps (b) through (d) a plurality of times, obtaining a plurality of measured values, comparing said measured values with a standard value for said gap between said print head and said platen, and determining whether or not they contain an error equivalent to one step of said stepping motor;
• (f) when no said error is found, setting said phase provisionally established in step (a) without modification, thus establishing the positional relationship between said stopper and said phase, whereas, when said error is found, discarding said phase provisionally established in step (a) provisionally determining another phase, repeating steps in (b) and following, and obtaining a stable rotor stop position which said stepping motor takes when it stops.