The value of a stepper motor for the precise movement of a machine is highly valuable. When a project necessitates precision of movement, high torque at low speeds, and the ability to hold positions without fluctuating, the stepper motor should be utilized. The stepper motor normally operates by turning one full step with every pulse of electrical current, but what if a project requires finer, miniscule steps? At Leading Edge Industrial (LEI), we utilize a technique called microstepping, which can rotate the motor less than one full step. Described below is the function of microstepping and how it can benefit you in future projects!
What is Microstepping?
In a normal stepper motor (a DC motor that moves in discrete, equal steps), the electromagnets located within the stator send pulses to the rotor, and in turn rotate the shaft by one full step. Microstepping is an extremely beneficial function in which the electromagnets do not send a full pulse of current to the rotor, meaning the shaft within a stepper motor will not turn one full step. By carefully controlling the current that is emitted to the rotor, a machine will have the ability to move by fractional amounts, such as 1/2 or 1/8 of a full turn—resulting in higher resolution and improved vibration features.
How does Microstepping Work?
Microstepping works by manipulating the amount of current that a rotor will receive. To better understand the operation of microstepping, picture the hands on a clock. Twelve o’clock and three o’clock are situated ninety degrees apart from one another. Now imagine the clock hand is situated at twelve o’clock. Let’s say this hand (at twelve o’clock) just received a sine wave. Twelve o’clock now has maximum force, while three o’clock is at zero, or has no force. The force (the hand on the clock) slowly moves to three o’clock. As the hand moves, twelve o’clock will lose force until it is at zero, and three o’clock will eventually gain full force. This pattern is then repeated, which completes the process of microstepping.
How Do You Calculate Microstepping from Sample Equations?
Normal intervals for microstepping usually include 1/2, 1/4, 1/8, 1/16, and 1/64 microsteps per one full rotation. In order to make a motor take finer steps, the driver must output a fraction of current, which then sends the correct amount of pulses to the rotor. To calculate the number of steps required per revolution (one full step), based on the microstepping mode the driver is in, follow the steps and equation below.
- Establish the degrees of resolution per step found within the motor. For this example, I will use 1.8º degrees of resolution per step.
- Next, take 360º (the degrees of a complete circle) and divide it by the degrees of the motor, which is 1.8º in our example.
- 360º / 1.8º = 200 steps. It takes 200 steps to move one full revolution in full-step mode.
- Finally, take the total steps of the motor and divide it by the microstepping size that is given by the driver. For this example, our driver is in 1/4 (quarter-step mode).
- 200 steps / (1/4) = 800 steps.
- The new number of steps is the amount of steps required by the controller to complete a full revolution, which is 800 in this example.
360º (degrees of full circle) / 1.8º (degrees of motor) = 200 steps
200 steps (Step/Rev of the motor) / 1/4 (microstepping size set by the driver) = 800 steps (Step/Rev set by the driver)
By calculating the number of steps set by the driver, we are able to precisely program the amount of desired steps per revolution.
What are the Benefits of Microstepping?
Microstepping is a great way to produce fine, controlled, and even steps. But what are the other inherent benefits? By making the motor turn at less than one full step per rotation, the resolution increases (without producing a change in the top speed), which creates less vibration in the machinery. Microstepping also allows the motor to utilize full torque while maintaining a smooth operation—free from unnecessary vibration.
What are the Disadvantages Found in Microstepping?
Though microstepping can be an excellent way of producing smaller steps and increasing resolution, this process is not without disadvantages. There is a false belief that by increasing the number of steps within a rotation, the accuracy of the motor will increase. Though an enticing idea, this notion is inaccurate. The small changes in torque make it difficult to overcome the load with each additional microstep. This means that in some cases, the motor will not be able to handle the load and must be programmed to move additional steps before it actually operates.
How Does Leading Edge Industrial Use Microstepping in Our Electronics?
In order to execute projects that require precision and controlled speed, Leading Edge Industrial utilizes stepper motors and microstepping. The drivers we use at LEI have an adjustable low-speed smoothness trimpot (a trimpot is a meter that adjusts and alters the calibration in circuits). By utilizing a trimpot, we are able to control motor nonlinearity at low frequencies and ensure that resonance remains at a reliable level so that it does not interfere with the torque.
By using microstepping, LEI is able to create fine, even movements that function at a higher resolution and are less susceptible to problems with vibration. Utilizing this technology in conjunction with our mechanical design allows Leading Edge Industrial CNC machinery to have a measured X-, Y-, and Z-axis repeatability of 0.0005″ over 6 inches – which is about 1/8th the width of the average human hair!