Control stepper motor with sine wave in MATLAB

I want to control a stepper motor to perform the motion of a sine wave using a DAQ National Instruments board.

I want to syncronize data acquisition in MATLAB (I am acquiring by using the NI DAQ) with control of the stepper.

I used the example code provided in the documentation to control the stepper. This works but I could not figure out how to accelerate and deccelerate the stepper to create the sine function.

How can I control this stepper in a way I can achieve a sine-wave like motion?

step1 = [1 0 1 0]; %Each step rotates motor 18 degrees
step2 = [1 0 0 1];
step3 = [0 1 0 1];
step4 = [0 1 1 0]; 
%Use write to output the sequence to turn the motor 72 degrees counterclockwise.
write(dq,step1);
write(dq,step2);
write(dq,step3);
write(dq,step4);

Answer 1

[Sanchari]

Hello Sara,

I understand that you want to control a stepper motor to perform a sine wave motion using a DAQ National Instruments board; And synchronize the data acquisition in MATLAB with control of the stepper.

To achieve a sine-wave-like motion with a stepper motor, you need to vary the speed of the motor such that it accelerates and decelerates according to the derivative of a sine wave. This means that the motor should move fastest when the sine wave's slope is steepest (around zero crossings) and slowest when the sine wave's slope approaches zero (at the peaks and troughs).

Here's a high-level approach to achieve this:

1. Calculate the Sine Wave Position Profile: Create an array representing the desired position of the motor at each point in time. This array should be based on the sine function.
2. Calculate the Velocity Profile: Compute the derivative of the sine wave to get the velocity profile. This will tell you how fast the motor should be moving at each point.
3. Generate Step Sequences: Convert the velocity profile into a sequence of steps for the motor. Higher velocities will require more frequent stepping, while lower velocities will require less frequent stepping.
4. Implement Acceleration and Deceleration: Adjust the timing between steps to speed up or slow down the motor according to the velocity profile.

Here's a MATLAB code snippet that demonstrates this concept. Note that this is a simplified example, and you will need to adjust the parameters and timing based on your specific motor and DAQ capabilities:

% Define the parameters for the sine wave motion
amplitude = 10;                 % Amplitude of the sine wave in steps
frequency = 0.5;                % Frequency of the sine wave in Hz
duration = 10;                  % Duration of the motion in seconds
sampleRate = 100;               % Sampling rate in Hz
t = 0:1/sampleRate:duration;    % Time vector

% Calculate the desired position profile based on the sine wave
positionProfile = amplitude * sin(2 * pi * frequency * t);

% Calculate the velocity profile as the derivative of position
velocityProfile = [0, diff(positionProfile) * sampleRate];

% Convert the velocity profile to step intervals (time between steps)
maxStepRate = 100; % Maximum step rate in steps per second
minStepInterval = 1 / maxStepRate;
stepIntervals = minStepInterval ./ abs(velocityProfile);
stepIntervals(velocityProfile == 0) = Inf; % No step needed when velocity is 0

% Initialize the DAQ session
dq = daq("ni");
% Add digital output channels, configure them according to your setup

% Control the stepper motor to follow the sine wave motion
for i = 1:length(stepIntervals)
    % Write the step sequence to the DAQ board
    write(dq, step1);
    write(dq, step2);
    write(dq, step3);
    write(dq, step4);    
    % Wait for the next step interval
    pause(stepIntervals(i));
end

The position and velocity profiles for the sine wave motion are calculated in the attached code snippet. We then convert the velocity profile into step intervals, which determine how long the program should wait between each step sequence. The pause function is used to create the necessary delays between steps.

However, the actual implementation will depend on the stepper motor's specifications, the resolution of the DAQ board, and the real-time performance of the system. Additionally, you may need to consider the physical limits of the motor, such as maximum speed and torque, to avoid missing steps or damaging the motor.

Hope this information is helpful to you!