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Linear Actuators - Stepper Motors

Welcome to our FAQs on linear actuators and stepper motors.
  • What is a stepper motor? +

    A linear actuator is a device that develops a force and a motion through a straight line. A stepper motor-based linear actuator uses a stepping motor as the source of rotary power. Inside the rotor, there’s a threaded precision nut instead of a shaft. The shaft is replaced by a lead-screw. As the rotor turns (as in a conventional stepper motor), linear motion is achieved directly through the nut and threaded screw. It makes sense to accomplish the rotary to linear conversion directly inside the motor, as this approach greatly simplifies the design of rotary to linear applications. This allows high resolution and accuracy ideal for use in applications where precision motion is required.

    Stepper motors have been used in a wide array of applications for many years. With trends towards miniaturization, computer control and cost reduction, “hybrid” style stepper motor actuators are being used in an ever increasing range of applications. In particular the use of linear actuators has rapidly expanded in recent years. These precise, reliable motors can be found in many applications including blood analyzers and other medical instrumentation, automated stage lighting, imaging equipment, HVAC equipment, valve control, printing equipment, X-Y tables, integrated chip manufacturing, inspection and test equipment. This attractive technical solution eliminates the use of numerous components and the associated costs related to assembly, purchasing, inventory, etc. The applications for these motors are only limited by the designer’s imagination.

    Video: Stepper Motor Linear Actuator Technology
    Technical Document: Stepper Motor Theory

  • Why use a stepper motor instead of a conventional rotary motor? +

    Unlike other rotary motors, steppers are unique in that they move a given amount of rotary motion for every electrical input pulse. This makes steppers a perfect solution for use in positioning applications. Depending on the type of stepper motor, our motors can achieve resolutions from 18 rotational degrees per step to 0.9 rotational degrees per step. This unique “stepping” feature coupled with the characteristics of the lead-screw provides a variety of very fine positioning resolutions.

  • Are your motors UL, CSA, or CE approved? +

    No, due the low voltage at which they operate UL, CSA, or CE are not required. However, many systems that have these approvals utilize our motors and ultimately get approved as a complete system.
  • Can I run the linear actuator into a hard stop? +

    This is not recommended on the finer pitch resolutions due to the high forces generated which may cause lock-up. It is possible however under reduced power input.

    Video: Can I Run the Linear Actuator Into a Hard Stop?
  • Can the linear actuator be back-driven when the power is removed? +

    This depends on the thread lead of the lead screw. Fine pitches will not back-drive, while course pitches will.

  • What is the difference between a 4 wire and 6 wire stepper motor? +

    The 4-wire motor is a "bipolar" which means two coils. In its operation two coils are on at any given time and current is reversed in the coils to achieve rotation. The 6-wire motor is a "unipolar" device with four coils with the commons are tied together in each phase and brought out.
  • Explain the difference between the Captive , Non-captive, and external linear actuators? +

    The captive actuator has a built in anti-rotation mechanism through the use of a splined output shaft that allows it to extend and retract as a unit with no requirements for additional anti-rotation. The captive actuator is designed for shorter strokes.

    The Non-captive actuator has a leadscrew going through the motor and has no reasonable stroke limits but must be attached to an assembly that will not rotate. This will then allow the leadscrew to extend and retract without rotating.

    The External linear actuator uses a leadscrew and nut combination that extends out from the motor. Linear motion is created by the nut traversing back and forth as the leadscrew turns. 

    Video: Comparing External Linear, Non-Captive and Captive Linear Actuators
    Video: What is a Captive Linear Actuator?
    Video: What is a Non-Captive Linear Actuator?
    Video: What is an External Linear Actuator?

  • What is the difference between the standard linear actuator and the high resolution actuator? +

    The high-resolution actuators have a smaller step angle. The High Resolution Can-Stack actuator is 3.75 degrees per step and the high-resolution Hybrid is 0.9 degrees per step. The standard Can-Stack actuator is 7.5 degrees per step and the standard Hybrid actuator is 1.8 degrees per step.
  • Do your motors have IP ratings? +

    Our standard motors are not IP rated although they may be customized to meet certain IP number ratings.

  • When used for positioning, does a stepper motor require a position feedback device? +

    The stepper motor is designed to achieve positioning open loop and normally does not need feedback. An optional encoder may be necessary when exact positioning must be known.
  • Does the lead screw rotate on a non-captive linear actuator? +

    No. Once one end of the lead screw is secured to a non-rotating assembly that needs to be moved, it will actuate back and forth without rotating. Non-captive linear actuators a designed for longer stroke applications.
  • How do I specify a special Connector/Terminal option for a Haydon Kerk Stepper actuator? +

    Haydon Kerk Motion Solutions can offer a wide array of value added features such as connector assemblies, encoders, sensors, high temperature windings, interior and exterior coatings to name just a few. If you would like Haydon Kerk Motion Solutions to provide your motorized application with a connector assembly we would need to have the following information on a pdf format drawing. Also add any special features or requirements to this drawing.

    1. The manufacturer’s housing part number.
    2. The manufacturer’s terminal part number is strip or reel form as we only do automated crimping.
    3. A pin out box to show which color wire goes to which pin in the housing.
    4. The length of the lead wires with tolerance from the motor egress point to the back side of the connector housing.
    5. Also include manufacturer’s part numbers for labels, sheathing, etc. If we do have this exact part number we will contact you to see if an alternative material will work in your application.
  • How much backlash can I expect from a linear actuator? Is there any way to compensate for it? +

    Typical backlash can be between .001" to .005" depending on the leadscrew pitch.
    Backlash can be compensated by using our optional Integrated or  External Anti-Backlash nuts.

  • If I use micro-stepping, will the accuracy of my system improve? What about the torque/force output? +

    No, if may even get worse as the rotor is now resting between poles. To improve the accuracy an encoder is required.
    The torque/force will be reduced by approximately be 20% to 30%.

  • I'm running the motor/actuator intermittently. Can I temporarily over drive the it for more torque/force output without damaging it? +

    Yes. You can apply twice the rated voltage using a L/R drive and twice the rated current using a Chopper drive. However, you should limit it to a max 25% duty cycle with a 75% off time.

  • My stepper motor/actuator appears to get extremely hot when in the static or holding position. Is this normal? +

    With rated current as holding current, the motor/actuator will have a 75c degree rise. This is indeed very hot, but normal. The motor/actuator has a class B insulation system (130c degree) rating. To minimize the heat rise try reducing the holding current 0.25 times the rated current.

    Video: My Stepper Motor Gets Extremely Hot When in the Static/Holding Position. Is That Normal?

  • What is the performance difference between unipolar and bipolar wired motors? +

    The bipolar will have about 30% more torque and force than that of the unipolar unit per given input power. Bipolar is typically the motor of choice.
  • The stepper motor seems to exhibit a lot of vibration in my application. What are some of the things I can do to correct it? +

    This could be resonance. In a Can-Stack motor the resonance range is 75 to 90 steps per second range and in the Hybrid motor within 140 to 200. Try starting your acceleration ramp at above these levels. Micro-stepping will also help through these ranges.
  • What is static torque and pull-out torque? +

    Static torque or pull-in torque is the amount of torque that a motor can overcome when starting from rest. Pull-out torque is the amount of torque it takes to stall the motor after it is running at speed.
  • When should I use a Chopper drive over a L/R drive? +

    The Chopper drive will result in about 30% higher output force and can achieve faster speeds. The L/R drive would be better used in low voltage battery applications.
  • Will I need to re-lubricate the leadscrew or shaft on the linear actuator? +

    The linear actuators are lubricated by the factory for the life of the product and do not need re-lubrication under normal operating circumstances.