Automatic actuator calibration using back EMF
AssigneeJohnson Controls Technology Company
InventorsClaudio Viscardi, Achim Reinders
Life of this patent
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Abstract
A self-calibrating linear actuator is configured to control a spring return valve with variable stroke. The actuator includes a motor, a spindle coupled to an output of the motor, a motor controller coupled to the motor, a microcontroller coupled to the motor controller, and a back electromotive force (BEMF) circuit, coupled to the motor, configured to provide to the microcontroller a BEMF value for each motor step. The microcontroller is configured to determine a difference of a number of motor steps during operation of the actuator and to store the difference as a calibrated touch point for the actuator.
Claims20
A self-calibrating linear actuator configured to control a spring return valve with variable stroke, wherein the actuator comprises:
- a motor;
- a spindle coupled to an output of the motor;
- a motor controller coupled to the motor;
- a microcontroller coupled to the motor controller;
- a back electromotive force (BEMF) circuit, coupled to the motor, configured to provide to the microcontroller a BEMF value for each motor step,
- wherein the microcontroller is configured to cause the actuator to:
- drive the spindle downward for a first predetermined number of motor steps at power on;
- drive the spindle upward until upper stall point is reached, wherein the spindle is determined to have reached the upper stall point when the BEMF value is measured to be zero;
- drive the spindle downward from the upper stall point until stroke end stall point is reached, wherein the spindle is determined to have reached the stroke end stall point when the BEMF value is measured to be zero;
- drive the spindle upward from the stroke end stall point to the upper stall point, wherein the microcontroller is configured to count a first number of motor steps from the stroke end stall point to the upper stall point, and store the first number of motor steps;
- drive the spindle downward from the upper stall point for a second predetermined number of motor steps, wherein the microcontroller is configured to measure a BEMF value for each of the second predetermined number of motor steps, and calculate and store a mean average of the BEMF values for the second predetermined number of motor steps;
- drive the spindle downward beyond the second predetermined number of motor steps, wherein the microcontroller is configured to measure BEMF value for each motor step and count a second number of motor steps until touch point is reached, wherein the spindle is determined to have reached the touch point when the BEMF value is measured to be lower than the stored average BEMF value by a predetermined threshold;
- and
- wherein the microcontroller is configured to subtract the second predetermined number of motor steps and the second number of motor steps from the first number of motor steps, and store the difference of number of motor steps,
- wherein the difference of number of motor steps is calibrated touch point for the actuator.
A method for self-calibrating a linear actuator configured to control a spring return valve with variable stroke and comprising a motor, a spindle, a motor controller, a microcontroller, a back electromotive force (BEMF) circuit, the method comprising:
- driving the spindle downward for a first predetermined number of motor steps at power on;
- driving the spindle upward until upper stall point is reached, wherein the spindle is determined by the microcontroller to have reached the upper stall point when the BEMF value is measured by the microcontroller to be zero;
- driving the spindle downward from the upper stall point until stroke end stall point is reached, wherein the spindle is determined by the microcontroller to have reached the stroke end stall point when the BEMF value is measured by the microcontroller to be zero;
- driving the spindle upward from the stroke end stall point to the upper stall point while counting by the microcontroller a first number of motor steps, and storing by the microcontroller the first number of motor steps;
- driving the spindle downward from the upper stall point for a second predetermined number of motor steps, measuring by the microcontroller a BEMF value for each of the second predetermined number of motor steps, and storing by the microcontroller a mean average of the BEMF values for the second predetermined number of motor steps;
- driving the spindle downward beyond the second predetermined number of motor steps and measuring by the microcontroller BEMF value for each motor step while counting by the microcontroller a second number of motor steps until touch point is reached, wherein the spindle is determined by the microcontroller to have reached the touch point when the BEMF value is measured by the microcontroller to be lower than the stored average BEMF value by a predetermined threshold;
- subtracting by the microcontroller the second predetermined number of motor steps and the second number of motor steps from the first number of motor steps;
- and
- storing by the microcontroller the difference of number of motor steps as calibrated touch point of the actuator.
Dependencies are inferred from the claim text.