Stepper Motors: Linear Motors

JE can offer stepper motors with integrated spindle-nut (leadscrew) feature.

The rotor magnet is not fixed to the rotor shaft but mounted on a nut.
The round shaft is replaced by a spindle.

With an anti-rotation guidance, inside or outside the motor, the spindle is forced to move forward or backward.

Example: Linear stepper motor type UAL (diameter 20mm, travel distance 15mm):

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Spindle shaft:

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The anti-rotation guidance is

  • either incorporated into the motor stator, as an internal guidance (picture left, with customized connection to a flap application)
  • or located outside the motor, to be designed into customer’s appliance (picture right)
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Lead and Travel

Travel distance at one rotor revolution is called “lead”, being 0.5mm to 1.0mm.

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Travel speed is effected by this spindle lead, step angle and step frequency.

Example, motor UCL with a lead of 1 mm and a step angle of 15°:
Travel per step is 15°/360° x 1 mm = 0.042 mm and speed gets 8.33mm/s at 200Hz.

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Efficiency

Due to the sliding friction of the leadscrew, the efficiency of conversion from rotary motion into linear motion is rather low, < 50%.

It is effected by lead dimensions and by lubrication.

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Force and Static load

Linear motors are specified by

  • Force, generated by motor operation (active force). See Performance Curve example below.
  • Static force load being able to resist at standstill (passive force), without bending the shaft or damage other motor components.

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Lateral force on shaft

Customer appliances should be designed to avoid any lateral force on the shaft or limit to few N.

Furthermore, the shaft must be aligned precisely to the motor axis. The permissible angular deviation is about 0.5° only.

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End stop hit

Without electrical limit switches located in the application, the shaft will hit mechanical end stops.
It is either a motor internal end stop (in pulling direction) or an external one in customer application.

This can cause a locking (clamping) of the shaft. The shaft might not be able to leave this end position again.
It can occur particularly if the shaft rests a longer time in this end position and substantial temperature change occurs.

If the stepper motor is operated by current controlled chopper driver circuitry, there is opportunity to vary the current: High value in starting instance to unlock the position, then reduce the level.