Stepper motor control
View Patent ↗A new method and circuit arrangement for operating a stepper motor in a voltage-based operating mode with a control loop over the whole operating range of speeds of a stepper motor. The method/circuit arrangement includes calculating a load angle of the stepper motor. The load angle is then used to calculate a voltage-based control signal suitable for operating a known motor driver circuit, such as a chopper, to drive the stepper motor coils. This enables improved control over the stepper motor which can improve control stability.
1. A circuit arrangement for operating a stepper motor, the circuit arrangement comprising:
a micro-step sequencer configured to:
store micro-step values associated with discrete values of a quantised waveform, and
output: a first micro-step value associated with a first phase angle position of the quantised waveform, and a second micro-step value associated with a second phase angle position of the quantised waveform;
a register configured to store a fractional value, wherein the fractional value represents a fraction between the first micro-step value and the second micro-step value; and
an interpolator configured to:
receive the first micro-step value, the second micro-step value, and the fractional value,
interpolate, between the first micro-step value and the second micro-step value, based on the fractional value, and
determine a fractional micro-step value from the interpolation; and
wherein the circuit arrangement is configured to operate the stepper motor based on the fractional micro-step value.
2. The circuit arrangement of claim 1 , wherein:
the circuit arrangement further comprises an adder configured to add the first micro-step value and the fractional micro-step value; and
the stepper motor is operated based on an output of the adder.
3. The circuit arrangement of claim 2 , wherein the adder is configured to add the first micro-step value and the fractional micro-step value once per period of a time rate.
4. The circuit arrangement of claim 2 , wherein:
the circuit arrangement further comprises a timing unit for operating the stepper motor at a target velocity;
the timing unit determines a first time rate having first time rate periods and a second time rate having second time rate periods;
the second time rate is a multiple of the first time rate;
the micro-step sequencer is configured to output one of the micro-step values upon each of the first time rate periods of the first time rate; and
the interpolator is configured to determine the fractional micro-step value upon each of the second time rate periods of the second time rate.
5. The circuit arrangement of claim 4 , wherein the adder is configured to add the first micro-step value and the fractional micro-step value once per each of the second time rate periods of the second time rate.
6. The circuit arrangement of claim 4 , wherein:
the fractional value is the fraction represented by a mathematical expression 1/b, where b is an integer number; and
the second time rate is the multiple of b times the first time rate.
7. The circuit arrangement of claim 1 , wherein:
the circuit arrangement further comprises a timing unit for operating the stepper motor to a target position;
the timing unit determines a time rate having periods;
the micro-step sequencer is configured to output one of the micro-step values upon each of the periods of the time rate; and
the interpolator is configured to determine the fractional micro-step value, based on a corresponding fractional value, upon each of the periods of the time rate.
8. The circuit arrangement of claim 1 , further comprising a switch which disconnects an output of the interpolator If a velocity of a rotor of the stepper motor is greater than a velocity threshold.
9. The circuit arrangement of claim 1 , wherein the fractional micro-step value represents a phase angle position between the first phase angle position and the second phase angle position.
10. The circuit arrangement of claim 1 , wherein:
the micro-step sequencer comprises a look-up table;
the first micro-step value is in a first row of the look-up table, and the second micro-step value is in a second row of the look-up table; and
the second row immediately follows the first row.
11. The circuit arrangement of claim 1 , wherein the micro-step sequencer is configured to receive a signal which increments a position of the quantised waveform.
12. The circuit arrangement of claim 1 , wherein the stepper motor is operated based on a target current value determined based on the fractional micro-step value.
13. The circuit arrangement of claim 12 , wherein the target current value is a vector representing a first target current of a first motor coil of the stepper motor and a second target current of a second motor coil of the stepper motor.
14. The circuit arrangement of claim 1 , wherein the quantised waveform is sinusoidal.
15. The circuit arrangement of claim 1 , wherein the interpolator is a linear interpolator configured to linearly interpolate between the first micro-step value and the second micro-step value to generate the fractional micro-step value.
16. The circuit arrangement of claim 1 , wherein the interpolator is a filter configured to filter the first micro-step value and the second micro-step value to generate the fractional micro-step value.
17. The circuit arrangement of claim 1 , wherein the interpolator is a weighted time slot assignment applied to the first micro-step value and the second micro-step value to generate the fractional micro-step value.
18. A method for determining a target current of a motor coil of a stepper motor, the method comprising:
providing a quantised waveform representing micro-stepped current;
generating a first micro-step value associated with a first phase angle position of the quantised waveform;
generating a second micro-step value associated with a second phase angle position of the quantised waveform;
providing a fractional value representing a fraction between the first micro-step value and the second micro-step value;
interpolating, between the first micro-step value and the second micro-step value, based on the fractional value, to generate a fractional micro-step value; and
generating a target current value based on the fractional micro-step value, wherein the target current value is suitable for operating the stepper motor.
19. A method for determining a target current of a motor coil of a stepper motor, the method comprising:
providing, by a micro-step sequencer, a quantised waveform representing micro-stepped current;
generating, by the micro-step sequencer, a first micro-step value associated with a first phase angle position of the quantised waveform;
generating, by the micro-step sequencer, a second micro-step value associated with a second phase angle position of the quantised waveform;
providing, by a register, a fractional value representing a fraction between the first micro-step value and the second micro-step value;
interpolating, by an interpolator, between the first micro-step value and the second micro-step value, wherein interpolating is based on generating a fractional micro-step value base on the fractional value; and
generating a target current value based on the fractional micro-step value, wherein the target current value is suitable for operating the stepper motor.
20. The method of claim 19 , further comprising:
outputting the first micro-step value or the second micro-step value upon each period of a time rate having periods; and
determining the fractional micro-step value, based on a corresponding fractional value upon each of the periods of the time rate.