How to Choose and integrate a medical device with stepper motor

Recently almost every medical device I design requires a stepper motor. After working with these motors so frequently, I’d like to share what I’ve learned about medical device stepper motors, the different types of stepper motor configurations, and how to drive stepper motors properly.

How to Choose and integrate a medical device with stepper motor

Stepper Motor Drive Configurations
Stepper motors typically come in two motor winding configurations. Before selecting which configuration is appropriate for your application, you should understand the basic difference between the two. This choice will be important when selecting how to drive the motor.

Pro Tip: You can use a unipolar motor as a bipolar motor if you ignore the center tap. This can come in handy if a particular design of motor is only available in a unipolar configuration.

How to Choose and integrate a medical device with stepper motor

Stepper Motor Drive Signals

Typically three types of drive signals are used to control the motion of a stepper motor. Each drive type increases in complexity, but adds additional features and options.

How to Choose and integrate a medical device with stepper motor

A wave drive only energizes one phase at a time. Wave drives are simple to implement with basic hardware, but are rarely used. Because only one coil is energized at a time, torque is significantly reduced.

Stepper Motor Drive Circuits
The most common methods for driving a stepper motor include a simple constant voltage or L/R (L refers to electrical inductance and R stands for electrical resistance) driver, a chopper drive, or a sine wave/micro-stepper driver.

Stepper Motor Integrated Drivers
Once a stepper motor hybrid has been selected to suit its mechanical requirements, the next thing is to get that motor turning. It is easier than ever to make a motor operational by selecting an off the shelf stepper motor driver IC or development board. Many of these boards provide features such as current feedback, built in acceleration profiles, and even onboard path planning for more complicated motion control.

Something About Holding Brakes for NEMA23 Stepping Motors

Choice For A Pancake Stepper Motor With Absolute Encoder

Brush DC Motor VS Brushless DC Motor

The motor and motor control markets are thriving in a number of areas, particularly medical and robotic applications. Also, there is a rich demand for small, efficient, high- and low-torque, and high- and low-power motors in the automotive sector.

Brush DC Motors
Around since the late 1800s, dc brush motors are one of the simplest types of motors. Sans the dc supply or battery required for operation, a typical brush dc motor consists of an armature (a.k.a., rotor), a commutator, brushes, an axle, and a field magnet (Fig. 1) (see “Brushed DC Motor Fundamentals”).

Brush DC Motor VS Brushless DC Motor

Brushless DC Motors
In terms of differences, the name is a dead giveaway. BLDC motors lack brushes. But their design differences are bit more sophisticated (see “Brushless DC (BLDC) Motor Fundamentals”). A BLDC motor mounts its permanent magnets, usually four or more, around the perimeter of the rotor in a cross pattern (Fig. 3).

Brush DC Motor VS Brushless DC Motor

To Brush
When it comes to a loosely defined range of basic applications, one could use either a brush or brushless motor. And like any comparable and competing technologies, brush and brushless motors have their pros and cons。

Or Not To Brush
BLDC motors have a number of advantages over their brush brothers. For one, they’re more accurate in positioning apps, relying on Hall effect position sensors for commutation. They also require less and sometimes no maintenance due to the lack of brushes.

The Choice Lies In Our Apps
The bottom lines for making a choice between components of any type are the type of application and the cost cutoff for the end product. For instance, a toy robot targeting the six- to eight-year-old market may require four to nine motors. They can all be brush or brushless dc components or a mixture of both.

The automotive industry also puts higher-power BLDC motors to work in electric and hybrid vehicles. These motors are essentially ac synchronous motors with permanent magnet rotors. Other unique uses include electric bicycles where motors fit in the wheels or hubcaps, industrial positioning and actuation, assembly robots, and linear actuators for valve control.

How to Use Hall Effect To Drive Brushless DC Motor

What makes brushless vibration motors long life? The clue’s in the title!

The precious metal brushes are typically the most common source of failure that limits the lifetime of normal DC motors. They are integral to the operation of our eccentric rotating mass vibration motors in the ‘Vibration Motor’ section of our Product Catalogue.

How to Use Hall Effect To Drive Brushless DC Motor

Whilst our recent Application Bulletin demonstrated our miniature vibrating motors are achieving an MTTF in the region of 1,500 – 2,000 hours some applications demand even longer performance.

So to improve life the solution seems simple, find a replacement for the brushes! This is actually quite complicated, the job of the brushes was to reverse the direction of the current through the internal metal windings (this ensures a constant direction of rotation of the shaft).

This is achieved by sensing the position of the internal windings and electrically changing the direction of the current at exactly the right time. To do this, we use the Hall Effect to calculate the position of the motor and change the drive signal accordingly. For more information on this, see Application Bulletin 018: Driving Brushless Vibration Motors.

Instead, with this blog post, we wanted to share an interesting infographic found on Those interested in seeing exactly how the drive signal changes with the output from the Hall Effect sensors can study the image below.

Thankfully if you find the graphics confusing, you don’t really need to fully understand it. Our 910-101 has an integrated driver chip that handles the communication automatically, and we have a suggested circuit for the 912-101 that you can easily implement.

Of course, if you have any questions about brushless dc motors or how to drive them, please get in touch with us!

What is a stepper motor?

A stepper motor for sale is a type of brushless synchronous DC motor that, unlike many other standard types of electric motors, doesn’t just rotate continuously for an arbitrary number of spins until the DC voltage passing to it is shut off.

Instead, stepper motors are a type of digital input-output device for precision starting and stopping. They’re constructed so that the current passing through it hits a series of coils arranged in phases, which can be powered on and off in quick sequence. This allows the motor to turn through a fraction of a rotation at a time – and these individual predetermined phases as what we refer to as ‘steps’.

What is a stepper motor?

A stepper motor is designed to break up a single full rotation into a number of much smaller (and essentially equal) part-rotations. For practical purposes, these can be used to instruct the stepper motor to move through set degrees or angles of rotation. The end result is that a stepper motor can be used to transfer minutely accurate movements to mechanical parts that require a high degree of precision.

Stepper motors are typically digitally controlled, and function as key components in an open-loop motion-control positioning system. They’re most commonly used in holding or positioning applications where their ability to assert much more clearly defined rotational positions, speeds and torques make them ideally suited to tasks demanding extremely rigorous movement control.

Hybrid step motors are an incredibly versatile, reliable, cost-effective and accurate way of controlling precise motor movements, allowing users to increase the dexterity and efficiency of programmed movements across a huge variety of applications and industries. As such, they form an important and widely used subset within the much broader category of automation and control gear.

With so many stepper motor brands, sizes, torque ratings, design styles and intended applications on sale in the UK and worldwide, it’s vital to figure out precisely which configuration is best suited to what sorts of user environments when planning a purchase.

How Stepper Motors Inductance Affect Performance of Stepper Motor

The inductance of the motor affects how fast the stepper motor driver can drive the motor before the torque drops off. If we temporarily ignore the back emf due to rotation (see later) and the rated motor voltage is much less than the driver supply voltage, then the maximum revs/second before torque drops off is:

How Stepper Motors Inductance Affect Performance of Stepper Motor
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revs_per_second = (2 * supply_voltage)/(steps_per_rev * pi * inductance * current)

If the motor is driving a GT2 belt via a pulley, this gives the maximum speed in mm/sec as:

speed = (4 * pulley_teeth * supply_voltage)/(steps_per_rev * pi * inductance * current)

Example: a 1.8deg/step (i.e. 200 steps/rev) motor with 4mH inductance run at 1.5A using a 12V supply, and driving a GT2 belt with 20 tooth pulley would start losing torque at about 250mm/sec. This is the belt speed, which on a CoreXY or delta printer is not the same as the head speed.

In practice the torque will drop off sooner than this because of the back emf caused by motion, and because the above doesn’t allow for the winding resistance. Low inductance motors also have low back emf due to rotation.

What this means is that if we want to achieve high speeds, we need low inductance motors and high supply voltage. The maximum recommended supply voltage for the Duet 2(Wifi or Ethernet) is 25V.

Resistance and rated voltage
These are simply the resistance per phase, and the voltage drop across each phase when the hybrid stepper motor is stationary and the phase is passing its rated current (which is the produce of the resistance and the rated current). These are unimportant, except that the rated voltage should be well below the power supply voltage to the stepper drivers.