Sensorless Homing System for Stepper Motor System

A method of determining a home position for a mechanism moved by a stepper motor, the method comprising:

• rotating a stepper motor;
• while rotating the stepper motor, sensing a value of a current passing through a motor winding of the stepper motor;
• determining whether a portion of the sensed value of the current varies from an expected value of the current;
• in response to determining that the portion of the sensed value of the current varies from the expected value of the current, calculating a characteristic of the portion of the sensed value of the current;
• determining whether the calculated characteristic meets a predefined criterion, the predefined criterion representative of a collision of a mechanism moved by the stepper motor with an end stop of the mechanism;
• and
• in response to determining that the calculated characteristic meets the predetermined criterion, storing data relating to a current position of the stepper motor in a memory of a control system coupled to the motor.

A method of determining a home position for a mechanism moved by a stepper motor, the method comprising:

• rotating a stepper motor at a first speed in a first direction;
• while rotating the stepper motor, sensing a first value of a current passing through a motor winding of the stepper motor;
• determining whether a first portion of the sensed first value of the current varies from a first expected value of the current;
• in response to determining that the first portion of the sensed first value of the current varies from the first expected value of the current, calculating a first characteristic of the first portion of the sensed first value of the current;
• determining whether the calculated first characteristic meets a first predefined criterion, the first predefined criterion representative of a collision of a mechanism moved by the stepper motor with an end stop of the mechanism;
• in response to determining that the calculated first characteristic meets the first predetermined criterion, rotating the stepper motor in a second direction opposite from the first direction for a predetermined period;
• after rotating the stepper motor in the second direction for the predetermined period:
• rotating the motor in the first direction at a second speed, the second speed being slower than the first speed;
• while rotating the stepper motor at the second speed, sensing a second value of the current passing through the motor winding of the stepper motor;
• determining whether a second portion of the sensed second value of the current varies from a second expected value of the current;
• in response to determining that the second portion of the sensed second value of the current varies from the second expected value of the current, calculating a second characteristic of the second portion of the sensed second value of the current;
• determining whether the calculated second characteristic meets a second predefined criterion, the second predefined criterion representative of a second collision of the mechanism with the end stop of the mechanism;
• and
• in response to determining that the calculated second characteristic meets the second predetermined criterion, storing data relating to a current position of the stepper motor in the memory of the control system coupled to the motor.