Ball screw: Maintaining Z axis position when step motor is OFF

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Ball screw: Maintaining Z axis position when step motor is OFF

We have a load of 15 kg, which is a weight force of 147.15 N, PLUS the bed. Let's take into account about two kilograms of bed and cables that need to be carried too, so 166.77 N. That is in the margin of error of 150 N, which simplifies calculations a lot, so let's just assume that.

Fgtotal=166N

Let's assume we use 2 lead screws, one left, one right, and both go exactly vertical. Then we get, that the load is half, so

Fgper lead=83N

Now, let's look at the specs of the lead screw: Pitch is 4 mm, Diameter is 12 mm. For the calculator we need Pitch Diameter (=Diameter) and the Thread Density (=Threads/cm), so I pull up the pitch conversion table and look under 4 mm Pitch. Also, we check the table and grab an intermediate "steel on steel" friction coefficient of 0.2 for dry, or 0.15 for oiled.

The results I get with those numbers are τdry=0.0478 Nm and τoiled0.0222 Nm respectively. That's the torque that needs to be applied to our motors to move it down. Wait, that number is negative?! Yes, it is, and that is actually not a bad sign:

Let's assume a higher high pitched thread. Like, REALLY high: 1 rotation per inch. One thread. It is pretty much "straight". The calculator drops us a result of τdry,super-steep=0.273 Nm for 0.2 friction coefficient that the motor would need to keep working against to not have it moving.

So, when do we stay, when to we move? Well, if τcalculated>τdetent, it moves down on its own. if τcalculated<τdetent it stays put for friction. The τdetent=0.027 Nm for a single length NEMA 23. Our negative Torque just means we need to apply some extra torque to overcome friction before we get the bed going.

That means, with the 15kg load (+2kg bed), it is to be expected that the bed stays up. If you would use a more slick combination of materials, you might start to slide.

Always remember, there is the caveat of overcoming the detention strength with a short impact, or applying force directly to the rods when bumping into them. If the machisnism starts to spin, the friction from the nut on the bar and from the motor is all that can provide a breaking to the machine.

Cloudray Stepper Motor Series has set the standard for quality, reliability, and durability in stepping motors. The precision of our Torque Power motors is matched only by the dependability of their performance. All Torque Power motors are bi-directional and totally enclosed with permanently lubricated ball bearings for long-lasting, smooth operation.

High Torque, High Precision and Long life is Cloudray's core advantage

 

Low vibration,Low heating, No loss of step
Fast Response,Better Acceleration Performance
Thanks to a robust design they can be selected for the harshest environments. Precise, open-loop, speed and position control can be achieved with the application of full step, half step, or microstepping electronics.

Higher Resolution,Avoidance of Resonance Regions
Stepping angle is adjustable( rang in 18°±5%), 0.9 °stepper motor's stepping angle is smaller, fineness is higher and positioning is more accurate.Avoiding vibration,runs more smoothly and gets lower noise.

Sturdy structure, extremely long life
High quality materials including bearings and shaft made in Japan
Robust assembly, high speed range, and exceptional performance in even the harshest environments make Cloudray Stepper Motors the perfect solution for demanding positioning applications.

Short length and light weight allow them to be used in highly integrated systems

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Stepper motor application
Cloudray stepper motor and Stepping Motor Driver are widely used in engraving machine, cutting plotter, textile machine, 3D printer, medical devices,stage lighting equipment, robot, CNC machine, music fountain and other industrial automatic equipment.

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