SELECTING THE PROPER LINEAR ACTUATOR OR STEPPER MOTOR
In order to select the proper motors or linear actuators, several factors must be considered. Is linear or rotary motion required? Following is a list of some of the basic requirements to consider when choosing a motor. This will help determine if a linear actuator or rotary motor should be used.
Linear Actuators
How much force is required from the linear actuator?
What is the duty cycle of the linear move?
What is desired step increment from the linear actuator?
What is the step rate or speed of travel?
Bipolar or unipolar coils in the stepper motor prime mover?
Stepper motor coil voltage?
Must the lead screw hold position with power off or must it be “backdrivable” with power off?
Are there size restrictions (max footprint of the linear actuator)?
What is anticipated life requirement?
Temperature of operating environment?
Captive, external, or non-captive linear actuators?
Rotary Motor
How much torque is required from the stepper motor?
What is the stepper motor duty cycle?
What is desired step angle?
What is the step rate or RPM?
Bipolar or unipolar coils?
Stepper motor coil Voltage?
Detent or holding torque requirements?
Are there size restrictions?
What is anticipated life requirement of the stepper motors?
Temperature of operating environment?
Sleeve or ball bearings in the stepper motors?
Radial and axial load?
AC Synchronous Motors
Stepping motors can also be run on AC (Alternating Current). However, one phase must be energized through a properly selected capacitor. In this case the motor is limited to only one synchronous speed. For instance, if 60 hertz is being supplied, there are 120 reversals or alterations of the power source. The phase being energized by a capacitor is also producing the same number of alterations at an offset time sequence. The motor is really being energized at the equivalent of 240 steps per second. For a 15° rotary motor, 24 steps are required to make one revolution (24 SPR). This becomes a 600 RPM synchronous motor.
In the case of linear actuators the linear speed produced is dependent on the resolution per step of the motor. For example if 60 hertz is supplied to a .001”/step motor the resulting speed is .240” per second (240 steps per second times .001”/step). Many of HSI’s stepping motors are available as 300 or 600 RPM AC synchronous motors.