Q: I am using stepper motors in a vibration sensitive application. However, most of the stepper motors we've tried are vibrating too much and are also too noisy. What types of stepper motors does Oriental Motor offer for low vibration applications? What are other methods to reduce vibration without sacrificing positioning accuracy?
A: Since a stepper motor provides rotation by combining small increments, or steps, of a certain angle, there are cases when the vibration caused by steps becomes a problem for certain applications. While it may not be possible to completely eliminate vibration from a stepper motor system, there are many ways to approach this issue both mechanically or electrically. In this article, we will discuss the most common and effective methods to achieve this.
First, we will go over the most recommended mechanical methods to reduce vibration on stepper motors.
Use a higher resolution motor with 100 tooth rotor compared to the common 50 tooth rotor. The increased number of teeth provides smaller full step sizes which help reduce the amplitude of vibration. The 100 tooth rotor also increases stop position accuracy. In addition to the popular 2-phase 1.8 deg per step resolution, our stepper motors also offer higher resolution alternatives such as 0.9 deg, 0.72 deg, and 0.36 deg. If you want even finer resolutions, we can offer geared motors or microstepping drivers.
Install a mechanical clean damper on the rear shaft of the motor. Our mechanical clean dampers are basically hermetically sealed plastic cases with an inertia body packed with silicon gel. The extra inertia and silicon gel help absorb the vibration and provides a stable damping effect.
Use geared stepper motors. The gearhead would help suppress the transmission of noise from the motor to load as well as provide more stable operation with consistent torque output.
Perform a thorough sizing of the motor for the specific application. The application should only require from 30~70% of the motor's capabilities. If you size a motor that's too small for the application, it may stall because of insufficient torque. If you size a motor that's too big for the application, the excessive torque may increase the amount of vibration. Also, do not exceed the motor's axial (thrust) or radial (overhung) load specifications as it will reduce the life of the bearings.
There may be many components that also generate noise or amplify the noise in the machine. Make sure nothing is loose and use rubber grommets if necessary.
If you have exhausted the mechanical methods, there are several ways you can also reduce vibration electrically. Current control of drive circuitry is also important in reducing vibration of the stepper motor since inconsistent torque increases vibration. If your driver cannot regulate current accurately or provide a uniform current waveform, then the motor will vibrate no matter how well the motor is made. If less current is supplied to the motor than necessary, the motor may stall. If too much current is supplied to the motor, the motor may generate too much excessive torque which eventually turns into vibration.
Oriental Motor has recently released the compact CVD constant current chopper bipolar microstepping drivers which are designed specifically to operate stepper motors in low vibration applications. Besides the utilization of new efficient FET's which save space and eliminate the requirement for heat sink, these drivers can regulate current very well and provide a very uniform current waveform. Compared to the traditional method of setting motor current with an analog potentiometer, the CVD series drivers provide a much more accurate current setting method since it incorporates a new standard of digitized current control. When used with our PKP series stepper motors, the combination can provide high torque at ultra low vibration levels. With better current control, motor stop accuracy is also improved. While we specify the stop position accuracy at +/-0.05 degrees, the motor should perform much better (see below).
The CVD stepper motor driver provides smooth motion by microstepping a stepper motor over the entire speed range with no torque loss, and therefore features low vibration regardless of speed. In addition to this feature, Oriental Motor's unique Smooth Drive function reduces vibration in the low speed range of 0 to 50 RPM. The Smooth Drive function makes low vibration, microstepping performance possible even with lower resolution pulse output from the pulse generator. Also built into the driver is Oriental Motor's current phase correction function which reduces vibration in the 50 to 200 RPM speed range. Furthermore, our vibration suppression control reduces vibration at 500 RPM and above. The vibration characteristics do not change even when resolution is changed. This is the result of Oriental Motor’s unique microstepping and vibration suppression control.
For more information regarding the combination between PKP series stepper motors and CVD series drivers, please read our white paper:
http://www.orientalmotor.com/technology ... r-cvk.html
Now we will show some vibration performance data. By utilizing a speed sensor called the DC tachogenerator which transforms speed into voltage, the relationship between speed and speed fluctuation (Vp-p) can be indicated as vibration.
Note: The CVK series is a combination package series which includes one PKP series stepper motor and one CVD series driver.
Below shows the comparison between the CVK 1.8° stepper motor and a conventional stepper product.
Below shows the CVK 0.72° stepper motor and a conventional stepper product.
Below shows the comparison of vibration characteristics between the CVK 1.8° and 0.72° stepper motors. As indicated in the graph, the 0.72° stepper motor has lower vibration compared to the 1.8° stepper motor.
Below shows the comparison of vibration characteristics between the CVK 1.8° package and the same motor with a commercially available driver IC for stepper motors. Compared to the commercially available driver, the CVK 1.8° package has lower vibration.
For information about the products we discussed in this article, please refer to the following links:
CVD SERIES DRIVERS:
http://www.orientalmotor.com/products/s ... ivers.html
PKP SERIES HIGH TORQUE STEPPER MOTORS:
http://www.orientalmotor.com/products/s ... -only.html
CVK SERIES COMBINATION PACKAGE SERIES (PKP+CVD):
http://www.orientalmotor.com/products/s ... stems.html
As always, if you need assistance with any topics discussed in this article, please contact our knowledgeable technical support engineering group, or utilize the many helpful online tools we offer on our website.
MOTOR SIZING CALCULATOR FOR SPECIFIC APPLICATIONS
http://www.orientalmotor.com/support/motor-sizing.html (registration is required)
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