Understanding linear stepper motors

In summary, the two actuators in the video are linear ballscrews that use a parallel linear stage to constrain rotation. Changing the number of steps per rotation is possible with a microstepping motor controller.
  • #1
dislect
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Hi guys,

1.
In this video:


Could someone explain me how the linear stepper motor responsible for drawing/injecting the syringe works?
I mean, the threaded rod going through the motor is suppose to turn around its axis in order to advance linearly and in this mechanism there's a rail to the right/left to make sure it dosen't.
So how does it still move linearly ?

2.
With external stepper motors could someone please explain if the external linear nut rotates and moves along with the threaded rod or does the threaded rod simply rotates without moving linearly like a non-captive motor and the nut rotates and moves along it?

Example:
http://www.haydonkerk.com/LinearAct...size_8_external_stepper_motor_linear_actuator

3.
Is there a way to reduce step angle from the typical 1.8 deg per step to 1.4 deg without using gears?
Like when using linear stepping motors, is there a way to control that via the threaded rod?

Thanks a lot!
 
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  • #2
Sorry, no youtube here.

Where the feed screw is the shaft of the motor, the motor is fixed. The nut is constrained to prevent rotation while still being free to travel axially along the guides as the stepper motor screw shaft rotates.

A stepper motor with 1.8° steps has very fine control. The flexibility of the mounting structure and the pitch of the screw will set the sensitivity in microlitre per step. A gearbox would increase the resolution but would require an improved structure. There are other ways to improve resolution such as to reduce the diameter of the syringe or change the pitch of the thread. Most ways of changing the step rate will require an improved structure.

For fine metering of a fluid it is an advantage to rotate the piston in the syringe as it is advanced. That prevents steps due to a sticky seal, but requires a very different drive topology.
 
  • #3
See, I don't get the nut part being constrained to the shaft to prevent rotation of this it move linearly WITH the shaft ? Is a bearing being used?

I'm talking about exclusively changing the 1.8 step as a resolution of 1.4 is needed.
 
  • #4
Is it a ball screw?
http://en.wikipedia.org/wiki/Ball_screw

1.8° per step is 200 steps per turn. That is decided by the way the stepper motor is built.
1.4° per step needs 257.142857 steps per turn which is impossible because there must be an even number of magnetic poles in the motor.
So you must change the diameter of the syringe or the pitch of the screw.
 
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  • #5
Hi dislect,

The two actuators in the video are definitely linear ballscrews, it's an interesting application actually where Nippon applies two of their "Linear Stepper Motors"; one motor is stationary and the shaft moves up and down, the other motor moves up on down on the "stationary" (e.g. vertically contrained) shaft. Both utilize what looks like a parallel linear stage to constrain rotation of the motor.

http://www.nipponpulse.com/articles/view/tin-can-and-linear-stepper-stirrer-and-syringe-applications

Regarding your question about changing the number of steps per rotation, the best way to achieve this is with a motor controller capable of "micro-stepping" which allows many intermediate steps per each full step. See here for an explanation: http://www.nmbtc.com/step-motors/engineering/full-half-and-microstepping/

I've seen microstepper drives that support up to 64,000 microsteps per revolution on a 200 step/rev motor, they allow for much finer resolution positioning although this sometimes comes at the cost of motor torque/speed and positioning repeatability.
 
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1. What is a linear stepper motor?

A linear stepper motor is a type of motor that converts electrical pulses into precise linear movements. It uses a series of electromagnetic coils to move a rod or shaft in a linear motion, rather than a rotational motion like traditional motors.

2. How does a linear stepper motor work?

A linear stepper motor works by using a series of electromagnetic coils and a permanent magnet to create a magnetic field. By sending electrical pulses to each coil in a specific sequence, the magnet is pulled towards the coils, causing the motor to move in a linear direction.

3. What are the advantages of using a linear stepper motor?

Linear stepper motors offer several advantages, including precise positioning, high torque at low speeds, and the ability to move in small increments. They also have a simple design, low maintenance requirements, and are less prone to wear and tear compared to other types of motors.

4. What are the applications of linear stepper motors?

Linear stepper motors are commonly used in various industries, including robotics, automation, and manufacturing. They are also used in medical equipment, 3D printing, and CNC machines for their precise and controlled movements.

5. How do I choose the right linear stepper motor for my application?

When choosing a linear stepper motor, consider factors such as required speed, torque, and accuracy. You should also consider the size and weight of the motor, as well as the type of control and power supply needed. It is important to consult with a knowledgeable supplier or engineer to ensure you choose the right motor for your specific application.

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