Synchronous Motors FAQs

Can I drive a unipolar stepper motor with a bipolar driver?

A six-lead stepper motor, which is a unipolar stepper motor, can be used when a bipolar drive is being used to run the motor. Since bipolar motors only need four wires to run, there are options in connecting a six-lead wire to a bipolar drive. Typically, we refer to the six wires as A, /A, A Common, B, /B, B Common. Half-coil connection would be to use A, A Common, and B, B Common (or /A, A Common, and /B, B Common). To use full-coil, also known as series connection, you would use A, /A and B, /B. For full-coil the two common wires are ignored. The full-coil connection (or series) is ideal for lower speeds requiring more torque. The half-coil connection will give an overall amount of torque across a wider range of speeds.

How can 4 wire, 6 wire and 8 wire motors be connected?

A 4-lead motor can only be connected to a bipolar driver. The 6-lead and 8-lead motors can be connected to either a unipolar or bipolar driver. See the wiring diagrams under "Are the wiring diagrams available for your motors?" to view the possible connections.

How can an encoder be used to determine position and speed?

There are many different types of encoders. The basic function of an incremental encoder is to output signals that help the control electronics determine the speed and direction of travel of the motor. The control electronics then use calculations to determine the relative position of the motor. The basic function of an absolute encoder is to output signals that help the control electronics determine the exact position of the motor. The control electronics then use calculations to determine the relative speed and direction of travel of the motor.

How do step accuracy and microstepping relate to each other?

Step accuracy is inherent in a motor's mechanical design and is controlled by the torque stiffness. Microstepping increases the number of steps required to move between each motor pole, but does not increase the step accuracy. Microstepping a motor without good step accuracy will not provide the smoothest motion.

Should I worry about heat dissipation?

If your motor will operate in a confined space, or if you plan to run your motor beyond its rated capabilities, you should be concerned about heat dissipation in your application. If your motor is in a confined space, you should consider how the heat given off from the motor might affect nearby components and raise the ambient temperature. If you plan to run the motor above its rated specs, you should consider ways to cool the motor proportionally to keep it operating near its specified maximum temperature.

What are the advantages of using stepper motors?

There are several advantages of using stepper motors. Speed can easily be determined and controlled by remembering speed equals steps per revolution divided by pulse rate. Stepper motors can also make fine incremental moves and do not require a feedback encoder (open loop). Stepper motors also have fast acceleration capability and have non-cumulative positioning error. Along with excellent low speed/high torque characteristics without gear reduction, stepper motors can also be used to hold loads in a stationary position without creating overheating. All stepper motors have the ability to operate on a wide speed range.

What does “Maximizing Torque at Desired Speed” mean?

Every stepper motor can be wound with more or fewer coils in order to change the characteristics of performance. Thus, if you need a certain amount of torque at high or low speeds, we would build the right kind of motor with the right number of coils in order to maximize the motor's ability to perform at its best in those ranges.

What is cogging?

Cogging is a resistive torque or force caused by the interaction of a magnetic field with a ferrous (magnetic, iron-containing) material, even when there is no current present. Cogging causes jerky, uneven motion in servo systems.

Because our Linear Shaft Motor contains no ferrous material, it does not experience cogging effects.

What is continuous current? What is peak current?

Continuous current is the current that can be supplied from the driver indefinitely. The peak current refers to the maximum amount of current the driver outputs.

Non-microstepping drivers
Peak Current = Rated Current

When using a driver that only does full stepping, the rated current is the same as the peak current. (Rated current = Peak Current).

Microstepping Drivers
Peak Current = 1.4 x Rated Current

When using a driver that is capable of taking microsteps (at a rate of a half-step, fourth-step or any other fraction of a step), the definition of peak current becomes 1.4 times the rated current. Microstepping drivers are made differently in order to maximize their ability to drive the stepper motor. Therefore, step motors can handle up to their rated current multiplied by 1.4. (Peak Current = 1.4 x Rated Current). This will not damage the motor because the power output is more or less the same.

What is microstepping?

Microstepping increases the number of steps required to move between each motor pole by controlling the phase-current ratio. Microstepping allows a motor to run more smoothly and with less noise, though it does not improve step accuracy. When microstepping, you should always stop on either a multiple of the microstep or the full step position every time. This will allow the motor to stop at a magnetic pole, which is the rotor's natural position, giving you the best possible accuracy.

What is motor motion duty cycle for a motor?

Motion duty cycle is defined as (time moving/total time). It is possible for motor power duty to be 100 percent while the motor is not moving, or the motor's motion duty to be nearly 100 percent with very low motor power duty.

What is motor power duty cycle for a motor?

Duty cycle for a linear motor is different than for other types of systems. While it is defined as (time on) / (time on + time off) per cycle, in servo systems the motor can be on even when not in motion. Thus, for a servo motor, the duty cycle is based upon the time the motor is actually working (when current is applied) and NOT the percentage of time the motor is moving. It is possible for motor power duty to be 100 percent while the motor is not moving, or for the motor's motion duty to be nearly 100 percent with very low motor power duty.

What is RMS Current?

RMS stands for "Root Mean Square." It is the effective average current. It is most commonly used when referring to AC current.

What is system resonance?

To determine system resonance, take the square root of (torque stiffness divided by total inertia). Although resonance frequency cannot be completed eliminated, it can be changed by altering the rotor or system inertia or by altering the torque stiffness.

 

What is the difference between Holding Torque and Pull Out Torque?

Holding torque is the maximum torque generated to prevent the motor from moving. Pull out torque is the maximum dynamic torque that can be generated at a given speed to start the motor moving. Pull out torque varies at different speeds with different drivers and power input.

What is the minimum number of steps to get the best accuracy?

Due to resonance, it can be very difficult for a stepping motor to make only a single step. As such, the best results are seen when the motor moves at least one electrical cycle. For Nippon Pulse's stepping motors, this will be four full steps.

When using half-stepping or microstepping drives, multiply the level of microstepping by 4. Example: 1/16 microstepping would mean 16*4=64 steps.

In addition, when microstepping you should always stop on either a multiple of the microstep or on the full step position every time. This will allow the motor to stop at a magnetic pole, which is the rotor's natural position, giving you the best possible accuracy.

Will the step motor heat up if it stalls?

No. A stepper motor does not draw any increased current when in a stalled position.

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