Method and apparatus for precise positioning of an object with linear stepper motors

A method of positioning an object with high precision using a linear stepper motor operating in a microstepping mode without using a position feedback device, the stepper motor having a platen and a forcer that moves linearly along the platen, wherein the object is attached to the forcer, the method comprising:

• receiving a command to move the forcer to a desired position;
• determining whether a movement forward or backward along the platen is required based on a current position of the forcer;
• determining a first number of microsteps required to move the forcer from the current position to the desired position using a compensation table storing a plurality of values representing actual positions of the object in relation to a number of microsteps from a home position of the forcer;
• and
• moving the forcer said first number of microsteps in the forward or backward direction to the desired position.

A method of precisely homing a stepper motor operating in a microstepping mode, the motor including a platen and a forcer having two coils for moving the forcer linearly along the platen in microsteps, the method comprising;

• attaching a homing sensor to the platen;
• determining a number of microsteps between a homing sensor activation position and a closest full current-in-coil position for a first one of said coils;
• determining the direction of motion from the homing sensor activation position to said closest full current-in-coil position;
• and
• storing the number of microsteps and the direction in a memory.

A linear stepper motor, comprising:

• a platen;
• a forcer capable of moving linearly along the platen;
• a controller for controlling movement of the forcer in microsteps;
• a compensation table stored in a memory, the table including values representing actual positions of an object attached to the forcer along the platen in relation to a number of microsteps from a starting position of the forcer,
• wherein responsive to a signal to move the object to a desired position, the controller determines from the compensation table a first number of microsteps required to move the forcer to the desired position, and wherein the controller controls the forcer to move said first number of microsteps to the desired position without the use of a position feedback device.

An X-Y-stage, comprising:

• a first linear stepper motor configured to control movement of an object in the X-direction;
• and
• a second linear stepper motor configured to control movement of said object in the Y-direction;
• wherein each linear stepper motor has a forcer capable of moving along a platen in microsteps, and a compensation table stored in a memory, each compensation table including values representing actual positions of the object in relation to a number of microsteps from a starting position of the respective forcer, wherein each forcer operates without a feedback device to move to a precise position using the compensation table.