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Stepper motor sizing and NEMA standards

I’m going to focus on sizing steppers, (like you haven’t figured that out yet) but remember that torque is torque and you’ll be able to apply the information we’re going to cover to any rotary motor technology.

So how do you go about sizing a motor? Well, you could pop out a set of calipers, a tape measure or a scale depending on how accurately you want to “size” it.

(That was a feeble attempt at some motor humor)

But seriously, the physical size of the motor is important. Steppers have been defined by a NEMA (National Electrical Manufacturers Association) standard, NEMA ICS16: Industrial Controls and Systems. This document defines the standards for Motion/Position Control Motors, Controls and Feedback Devices and is available as a free download at https://www.nema.org.

NEMA size 14 (36 mm)

Starting with the smallest size offered by SEM, we have a NEMA 14. The “14” means that the mounting face of the motor is approximately 1.4” square. If you looked at the mechanical specs (https://www.oyostepper.com/category-4-b0-Nema-14-Stepper-Motor.html) you’d see that it’s actually 1.39” square.

This dimension may vary between manufacturers as the NEMA standard only declares that square flange motors fit inside a maximum circular dimension.

In addition to the mounting face, motors that meet the NEMA standard should have the same mounting holes diameters, the same spacing between those mounting holes, the same shaft centering boss size, the same shaft diameter and length.

So in theory, if you purchased a NEMA motor from one manufacturer it would physically fit into the same location as any other manufacturer. However, there may be some mechanical differences, especially with the diameter and length of the shaft. And there is a high probability there are differences between the manufacturer’s motor winding specs.

 The next size up is the NEMA 17 (42 mm)

How quick a learner are you? What is the approximate size of a NEMA 17  mounting face? I hope you said 1.7”. If you didn’t, you’d better reread the above paragraph.

The actual size is 1.67”. The NEMA 17 introduces different motor lengths. The mounting face of the motor stays the same, but the length of the motor now varies. This is done because the manufacturer has added magnet stacks to the rotor shaft. Additional magnets increase the motor’s output torque. A single stack motor would have less torque than a double stack and a double stack would have less torque than a triple stack.

The additional magnet stacks also increase the motor’s rotor inertia. Rotor inertia, we’ll see in later postings, is an important parameter that is used when sizing a motor.

 The next size up is the NEMA 23 (56 mm)

Again the Nema 23 size is the approximate mounting face size in inches. And again this series of steppers has three stack lengths. The MDrive Plus versions have four stack lengths. There is a point, however, where adding to the stack length gets prohibitive. This is because the manufacturing process to make longer and longer motors become difficult. To get more torque, it’s more easily accomplished and more economically done by increasing the diameter of the motor and adding stack lengths to that motor series.

 Then we have the NEMA 34 (85 mm)

And again the 34 is the approximate mounting face size in inches. And this series has three stack lengths for both the motor only and the MDrive versions.

And beyond

While stepper motors are readily available in NEMA size 42, beyond NEMA 34 using steppers become cost-prohibitive, especially when there are other, more, practical motor and drive technologies available to get the job done.

MicroMo and the FAULHABER Group are the leading innovators in the field of miniature DC motion control. Each year our design engineers are challenged by the customer to achieve the next level of miniaturization, power to volume, and precision. Here are one of our most recent innovative additions to our standard product line and recent information about the FAULHABER Group.

ARSAPE 8mm Stepper Motor and Gearbox Combination
This ARSAPE 2-phase permanent magnet stepper motor online and gearhead is the world's smallest combination of its kind and features:
• Just 8mm outer diameter and weighing as little as 6.2 grams!
• 8mm precision stepper motor planetary gearboxes available in exact ratios up to 4096:1capable of up to 17 oz-in of torque.
• Precise open-loop operation.
• Drive electronics available.
• Zero backlash and precision spur gearheads available with the rest of the ARSAPE stepper motor line.
• Available in a wide variety of semi-standard and custom configurations including custom shafts, high precision lead screws, cabling and connectors, vacuum compatible, and extreme low temperature executions.

MicroMo specializes in customizing our miniature DC drive systems to your application by adding gearboxes, encoders, leads, pinions, cams, lead screws, cables, connectors, etc. to your custom configuration.

How Does a Stepping Motor Rotate?

Like servo motors, stepper motors from china are available in both rotary and linear designs. When an application requires force (rather than torque) output and can operate in open loop control, a linear stepper motor is often the preferred solution. Although linear stepper motors are available in both variable reluctance and hybrid designs, the more common version is hybrid linear stepper motors.

In a hybrid linear stepper motor, the base, or platen, is a passive steel or stainless steel plate with slots milled into it. The forcer contains motor windings, permanent magnets, and laminations with slotted teeth that serve to concentrate the flux that’s created when current is applied to the coils. The teeth of the forcer and the platen are staggered by ¼ tooth pitch in relation to one another to ensure that constant attraction is maintained and that the next set of teeth will come into alignment as current is switched in the coils. This means that for each full step of the motor, the forcer moves along the platen by ¼ tooth pitch.

 

In a hybrid linear stepper motor, the platen is passive and the forcer contains laminations with slotted teeth, windings, and permanent magnets.
Image credit: Parker Compumotor

Whereas variable reluctance linear stepper motors can only operate in full step mode, hybrid versions can operate in either full step or microstepping modes. Microstepping, which divides the step angle into smaller increments, enables higher resolution motion and better control of speed and force. Because each phase of the motor is driven with (theoretically) ideal sine waves, 90 degrees apart, microstepping also allows the current to increase in one winding as it decreases in the other, providing smoother operation at low speeds than can be achieved with full- or half-step operation.

 

Microstepping makes the current waveform more sinusoidal and provides smoother motion at low speeds.
Image credit: Servo-drive LLC.

For guiding the load on hybrid linear stepper motors, either mechanical roller bearings or air bearings are typically used. (Because the platen in a hybrid linear stepper motor is passive, it can serve as the air bearing surface.) The magnetic flux between the forcer and platen creates a strong magnetic attraction, so these support bearings actually serve two purposes – to guide and support the load and to maintain the correct air gap between the forcer and the platen.

Like other linear motor designs, hybrid linear stepper motors can incorporate multiple forcers onto one platen, with each forcer moving independently. In addition to smooth low-speed operation (obtained with microstepping control), they are also able to achieve very high speeds and accelerations with high resolution and low to moderate force generation.

With simple mechanical construction and easy setup (no servo tuning required), hybrid linear stepper motors are ideal for applications that can operate in open-loop mode and that require either high speed with low force production or very smooth motion at low speed.

how to wire my stepper motor without the pinouts?

Source:https://blog.oyostepper.com/2018/08/15/operation-and-applications-on-linear-stepper/

Astepper motor linear actuator converts the rotary motion of a servo or best linear stepper motor into linear motion. There are a range of actuator types, including lead screw actuators, ball screw actuators, planetary roller screw actuators, belt drives, and so on. Designs can be rodless, rod style, or even integrate the motor into the actuator.

So how do you choose?

Like most things in engineering, the choice of actuator comes down to the application. Before you consider the various technologies, be clear about your requirements, from the load, speed, and accuracy, to the lifetime and duty cycle required. Will the actuator be operating in a washdown, vacuum or other harsh environment?

How much space do you have? And, of course, what is your budget?

Armed with this information, you can make an informed choice and find the technology that will provide optimal performance for the investment. “As a design engineer you have four or five technologies looking back at you,” says Scott Frederick, applications engineer at Kerk Motion Products Inc. (Hollis, New Hampshire). “When you go all the way through a specific application, by the time you get to the end of it, you might only have one or two options left.”

Threaded nut, or linear motor lead screw, designs provide good performance for cost. (Courtesy of Kerk Motion Products Inc.)Screw Technology.So what are some of those options? Linear actuators can be broadly divided into screw type and belt type. In the first category, a turning screw generates the motion. Screw-type actuators can be further divided into lead screws, ball screws, and planetary roller screw types.

In the most basic design, commonly referred to as a lead screw actuator, a threaded nut moves with respect to the screw, generating motion in whichever element is not fixed. The term ‘lead screw’ is actually a misnomer, because all of the screw designs are based on lead screws, but for purposes of this article and to minimize confusion, we will use it. Lead screw technology is simple, economical, and widely used. The actuators tend to be quiet and suffer less from back driving than other alternatives.

Because the surfaces of the nut are sliding against the threads of the screw, however, friction, and thus wear, become issues. This reduces lifetime, efficiency, speed, and also performance, because wear on the solid nut may affect accuracy/repeatability. Frictional resistance may even necessitate higher input torques.

Design of Controlling System for Linear Stepper Motor Based on DSP2407

As there are various types of AC and DC rotary type motors, there are also different types of linear motors, which include AC, DC, and Stepper:

Brushless
DC brushless motors provide non-contact operation for maintenance-free operation. Available in both ironless (cog-free) and iron core version, they are capable of high speed and high acceleration motion profiles. They can be driven using standard 3 phase brushless servo amplifiers. Brushless linear motors can achieve an acceleration of up to 12 g’s, and speeds in excess of 200+ inches per second [5+ m/s].

Brush
DC brush linear motors are ideal for long stroke, open or closed loop servo, linear motion applications. They can be used at speeds up to 100 in/sec [2.5 m/sec] and as low as 1 in/sec [25 mm/sec]. They are capable of very precise position, velocity, and acceleration control when coupled with a linear encoder.

Voice Coil
DC voice coil actuators are ideal for short stroke (typically less than 2 inches) closed loop servo applications. Their compact size allows them to fit into small spaces. They have very low electrical and mechanical time constants. The low moving mass allows for high accelerations of light payloads. They are available in both moving coil and moving magnet versions.

Linear Stepper
Linear stepper motors for sale are used in both open loop and closed loop positioning applications. Since the positioning is built into the forcer and platen, no additional feedback devices are required which reduces the overall cost of a system. For open loop operation, no servo tuning is necessary. Multiple forcers can operate on a single platen. With linear steppers, acceleration of 1 g and speeds up to 100 in/sec [2.5 m/s] are typical. They are available in both single-axis and dual-axis versions.

Linear Induction
The flat AC linear induction motor (LIM) is typically run directly off of 3 phase line voltage, with an adjustable frequency, or vector drive if speed control is required. Accelerations of up to 1 g with speeds in excess of 1800 inches per second [45 m/s] are possible with LIMs. They are ideal for high speed, long travel applications moving heavy payloads.

Polynoid
The tubular AC linear induction motor (polynoid) is typically run directly off of single or 3 phase line voltage. Accelerations greater than 1 g are possible with polynoids. They are ideal for short stroke, low duty cycle applications. They can be used to replace air cylinders when compressed air is not available.