Step Motor Systems: The Benefits of Adding Encoders

Use Encoders to Enhance Step Motor System Performance

Because of their low cost, high resolution, precise positioning, minimal control electronics and low cost, step motors are popular in automation. Traditional step motors can be driven in an open loop system without the need to have sensors to send information back to a controller. However, open loop step motors pose challenges.

17HS24-2104D-E1000

Complex projects such as quadcopters require enhanced position control. The stepper motors are designed to provide excellent precision and predictable performance. This is possible when both the gearbox ratio and step angle are known.

Stepper motors are now the preferred choice for many electronic devices.

Some engineers go one step further than the stepper motor's excellent visibility into velocity and position.

They have also added encoders in their motor systems to the stepper's open loop control.

The Motor Encoder: Closed Loop Control is essential

An Stepper Motor w/ Encoder can be attached to an electric motor. It can be attached to an electric motor shaft to provide closed-loop feedback signals.

This functionality may seem redundant at first. Is precision control not what the stepper does by itself? It seems that both yes and no. Recent research has demonstrated that even though it may seem unnecessary, the encoder can make a huge difference in the performance of a stepper motor.

Galil, a motion controller manufacturer, conducted side-by-side tests between closed and open loop stepper motors. The team found that an encoder can make a significant difference in performance metrics.

The closed loop system offers:

Significantly improved velocity smoothness

Reduction in overall consumption

Three-phase brushless motors with comparable torque outputs can produce higher torque at lower speeds than comparable three phase brushless servomotors.

Galil's researchers found that stepper motors could achieve "dramatic" performance improvements by integrating a positional-feedback device with a two phase brushless amplifier. Their website contains their testing methods and results.

These are exciting developments in the world of motion control. Engineers of all levels can make stepper motors more powerful and economically viable by using readily available encoder technology.

Which ENCODERS IS BEST?

Optic encoders are a well-established technology. They offer reliable and accurate performance with a wide range resolutions. However, they can be subject to degradation and loss due to oil, dust, and other contaminants. They work best in clean environments. Capacitive encoders use newer technology and offer similar benefits. They provide the same speed and position information as optical encoders. They are also immune to environmental contaminants.

Tips on How to choose a CNC Spindle motor

It is important to choose the right spindle or milling head. A "toy" brush spindle with a plastic housing might be sufficient for use in plywood and soft plastics. It is not suitable for professional use, i.e. to make money. It is not suitable for professional use (CNC Spindle Motor). It can be completed in just a few hours with hard work, and it can take up to six months with economical work.

Professional spindles use ceramic bearings on brushless inductive spindles with tight engine compartments and absolutely with metal housings. There are many options for spindle revolutions, power and output.

The nominal spindle speed of the identification plate is 12.000, 15.000 and 18.000 respectively. However, this does not necessarily mean that the spindle spins with these revolutions. The inverter can control the revolutions, but it is important to keep in mind that spindle power is the torque multiplied with rotational speed. This means that while the spindle speeds can be reduced by half, the power also falls. Here is where we need to compromise.

There is no one spindle that works for all applications. The spindle speed limitation is caused by the higher spindle power and larger bearing diameters. A larger bearing diameter means that the ball's centrifugal force is greater, which causes more heat to be released. One way to decrease this effect is to use lighter ceramic balls. 40.000 rpm spindles can be made only in low power settings.

Materials such as aluminum and wood, composite materials and laminates require high speed. High speed is not recommended when machining steel, particularly stainless steel, thermoplastics, or drilling with HSS drill bit bits.

The primary criteria for power is the maximum milling cutter diameter and materials to be cut with them. The spindle can be used to machine aluminum, plastic, wood, or laminate up to 5mm. It has cutters that are up to 8mm in diameter, 12mm in diameter, 3.3kW spindle, 16mm in diameter, and 5.6kW spindle. We should choose a lower-rpm spindle for steel. This means cutters between 10mm and 3.3kW spindle, cutters between 12mm and 5.6kW spindle as well as cutters between 16mm to 7kW spindle and cutters between 20mm to 10kW spindle.(Spindle Motor Inverter)

You should always choose a stronger spindle if you plan to drill steel. For example, a 6mm drill with a 5.6kW spindle at 2000rpm can drill steel at 2000rpm. Because spindles have gears, it is impossible to compare their power with conventional milling machines. Another thing. These spindles can last up to 10 years.

Torque vs Speed Characteristics of Steping Motor

The Speed-Torque graph indicates the characteristic relationship between the speed and torque when the stepping motor is driven. The torque vs speed characteristics are the key to selecting the right motor and drive method for a specific application. These characteristics are dependent upon (change with) the motor, excitation mode and type of driver or drive method. On the graph, the horizontal axis is the speed at the motor’s output shaft while the vertical axis is the torque.

1.Maximum Holding Torque
The holding torque is the maximum holding power (torque) the stepping motor has when power (rated current) is being supplied but the motor is not rotating (with consideration given to the permissible strength of the gear when applicable).

2.Pull-in Curve
The pull-in curve defines a area refered to as the start stop region. This is the maximum frequency at which the motor can start/stop instantaneously, with a load applied, without loss of synchronism.

3.Pullout Torque Curve
Pullout torque is the maximum torque that can be output at a given speed. When selecting a motor, be sure the required torque falls within this curve.

4.Maximum Starting Frequency
This is the maximum pulse speed at which the hybrid stepping motor can start or stop instantaneously (without an acceleration or deceleration time) when the frictional load and inertial load of the stepping motor are 0. Driving the motor at greater than this pulse speed requires gradual acceleration or deceleration. This frequency drops when thereis an inertial load on the motor.

5. Maximum Slew Rate
The maximum operating frequency of the motor with no load applied.

Source:https://www.oyostepper.com/article-1110-Torque-vs-Speed-Characteristics-of-Stepper-Motor.html

A Simple guide to identify the stepper motor you have

You’ve got your stepper motor from Ebay, the manual is in Chinese and you don’t have a clue if the motor is unipolar or bipolar.

Summarizing quickly.
If 8 wires, it will probably be unipolar 8 wires stepper motor, 4 per coil.
If 6 wires, probably unipolar, 3 for one coil and another 3 for the other. This means each coil has its own ground.
If 5 wires, probably also unipolar. 2 for one coil, 2 for the other and a common ground for both coils.
If 4 wires, probably a bipolar 4 wires stepper motor, 2 cables per coil.
I’ve also found this video which can help you differentiate the motor type you’ve got:

Wiring the stepper motors.
This will be a guide to connect the most common stepper motors for 3D printers. They usually mount NEMA17 with 4 wires.

Quick version.
If the motor comes with coloured wires, the typical colours are Red/Blue/Green/Black
Issues: It is not guaranteed to be like this! Who knows where the motors come from, how are they wired, etc. I’ve known many people who were not able to make them work and at the end, they realized the problem was in the wiring.

Longer version
The most common drivers which the 3D printers and home machines use are bipolar. The most known drivers for bipolar motors are pololus a4988 and DRV8825.
The motor will have 4 wires. 2 per coil, therefore what we have to figure out is which ones are the coils.

Figure out the coils
If we are going to wire a stepper motor, we have to figure out which wires belong to which coil.
We can name them coil A and coil B, or coil 1 and coil 2.
Luckily, the drivers designers decided to use both systems (/ironic)
If you read the driver’s label, the DRV8825 specifies A2 A1 B1 B2 and the A4988 specifies 1B 1A 2A 2B.
Just read it several times, and make sure you understand it is exactly the same.

Size and NEMA standard of Stepper Motor You Should Consider

Deciding when to use a non-captive linear actuator

Non-captive types of lead screw driven linear motor actuators are different from the more common external versions in that they allow the lead screw to completely pass through the motor. This fundamental difference offers advantages for those that have limited space available or are looking to shrink the overall size of their design package.

With an external actuator, the object being moved is mounted to the nut, and the screw rotates providing the motion along the length of the screw.
By contrast, in a non-captive actuator, the payload or object being moved is attached to the motor, and has screw ends that are typically fixed. In most cases, this setup can allow for a shorter overall screw to be used. It is also ideal for adding the external linear guide bearings that are almost always required for non-captive applications. They provide stiffness and eliminate deflection that causes premature wear on the nut, screw, and internal motor bearings.

A less common situation is where the device or payload is attached to the end of the screw. This is only used for very light loads and requires external linear guidance for stiffness. It is an arrangement that also requires clearance for the screw to extend out the opposite side of the motor.

One feature common to all non-captives is that the nut driving the screw is internal to the motor. Traditionally, this nut has been a standard nut with no mechanism to account for the play between the external threads of the screw and the internal threads of the nut. If, in this scenario, an anti-backlash capability was needed, manufacturers might be able to provide a custom solution, but with significantly higher cost and extended lead times.

To avoid this problem, PBC Linear offers the choice of a standard nut or anti-backlash nut within their non-captive linear actuators. We have the only anti-backlash nut and lead screw assembly available off-the-shelf in a non-captive configuration. This unique combination offers the best positional performance available in a non-captive hybrid actuator by utilizing our patented Constant Force Technology (CFT), which provides greater than two-times the superior backlash compensation as tested against competitors.

This advantage means that the self-lubricating nut will provide lubricant-free, consistent performance and preload over its lifetime. In addition, screws are available either uncoated or with a proprietary PTFE coating. These screws come with standard lead accuracy of 0.003 inches per foot, which is three-times better than typical screws on the market.

Non-captive linear actuators from PBC Linear go beyond the simple definition of motor and lead screw. They excel because they have been designed from the inside out, providing superior performance in linear motion applications.

With an external actuator, the object being moved is mounted to the nut, and the screw rotates providing the motion along the length of the screw.

By contrast, in a non-captive actuator, the payload or object being moved is attached to the motor, and has screw ends that are typically fixed. In most cases, this setup can allow for a shorter overall screw to be used. It is also ideal for adding the external linear guide bearings that are almost always required for non-captive applications. They provide stiffness and eliminate deflection that causes premature wear on the nut, screw, and internal motor bearings.

A less common situation is where the device or payload is attached to the end of the screw. This is only used for very light loads and requires external linear guidance for stiffness. It is an arrangement that also requires clearance for the screw to extend out the opposite side of the motor.

One feature common to all non-captives is that the nut driving the screw is internal to the motor. Traditionally, this nut has been a standard nut with no mechanism to account for the play between the external threads of the screw and the internal threads of the nut. If, in this scenario, an anti-backlash capability was needed, manufacturers might be able to provide a custom solution, but with significantly higher cost and extended lead times.

To avoid this problem, PBC Linear offers the choice of a standard nut or anti-backlash nut within their non-captive linear actuators. We have the only anti-backlash nut and lead screw assembly available off-the-shelf in a non-captive configuration. This unique combination offers the best positional performance available in a non-captive hybrid actuator by utilizing our patented Constant Force Technology (CFT), which provides greater than two-times the superior backlash compensation as tested against competitors.

This advantage means that the self-lubricating nut will provide lubricant-free, consistent performance and preload over its lifetime. In addition, screws are available either uncoated or with a proprietary PTFE coating. These screws come with standard lead accuracy of 0.003 inches per foot, which is three-times better than typical screws on the market.

Non-captive linear motor actuators from PBC Linear go beyond the simple definition of motor and lead screw. They excel because they have been designed from the inside out, providing superior performance in linear motion applications.

Source:https://blog.oyostepper.com/2019/12/31/deciding-when-to-use-a-non-captive-linear-actuator/

Stepper Actuator - Full-Step VS Half-Step

Stepper Actuator - Full-Step
In full step operation, stepper actuator motors step through the normal step angle e.g. 200 step/revolution motors take 1.8 steps stepper motor while in half step operation, 0.9 steps are taken. There are two kinds of full-step modes. Single-phase full-step excitation, where stepper actuator motors are operated with only one phase energized at-a-time. This mode should only be used where torque and speed performance are not important, e.g. where the motor is operated at a fixed speed and load conditions are well defined. Problems with resonance can prohibit operation at some speeds. This type of mode requires the least amount of power from the drive power supply of any of the excitation modes. Dual phase full-step excitation is where the stepper actuator motors are operated with two phases energized at-a-time. This mode provides good torque and speed performance with a minimum of resonance problems. Dual excitation, provides about 30 to 40 percent more torque than single excitation, but does require twice the power from the drive power supply.

Stepper Actuator - Half-Step
Stepper actuator motors have half-step excitation, alternate single and dual-phase operation resulting in steps one half the normal step size. This half-step mode provides twice the resolution. While the motor torque output varies on alternate steps, this is more than offset by the need to step through only half the angle. This mode has become a commonly used mode by Anaheim Automation because it offers almost complete freedom from resonance problems, and is cost-effective. Stepper actuator motors can be operated over a wide range of speeds and used to drive almost any load commonly encountered.


Stepper Actuator - Micro-Step
In Actuator Motors microstep mode, a stepper actuator motor's natural step angle can be divided into much smaller angles. For example, a standard 1.8 degree motor has 200 steps-per-revolution. If the motor is microstepped with a 'divide-by-10', then each microstep would move the motor 0.18 degrees and there would be 2,000 steps-per-revolution. Typically, micro-step modes range from divide-by-2 to divide-by-256 (51,200 steps per revolution for a 1.8 degree motor). The micro-steps are produced by proportioning the current in the two windings according to sine and cosine functions. This mode is only used where smoother motion or more resolution is required. Generally, the greater the divisor, the more costly the microstep driver will be. Also, some microstep drivers have a fixed divisor (least costly) while other have a selectable divisor (most costly).

HOW TO CHOOSE THE RIGHT BUILT-IN TECHNOLOGY
How are Stepper Actuators Controlled?

What are Brushless DC Motors Used For?

Brushless DC motors typically have an efficiency of 85-90%, while brushed motors are usually only 75-80% efficient. Brushes eventually wear out, sometimes causing dangerous sparking, limiting the lifespan of a brushed motor. Brushless DC motors are quiet, lighter and have much longer lifespans. Because computers control the electrical current, brushless DC motors can achieve much more precise motion control.


Because of all these advantages, brushless DC motors are often used in modern devices where low noise and low heat are required, especially in devices that run continuously. This may include washing machines, air conditioners and other consumer electronics. They may even be the main power source for service robots, which will require very careful control of force for safety reasons.

Brushless DC motors provide several distinct advantages over other types of electric motors, which is why they’ve made their way into so many household items and may be a major factor in the growth of service robots inside and outside of the industrial sector.

If you think your application could benefit from this technology, browse a list of brushless DC motor here:

https://www.oyostepper.com/article-1105-What-are-Brushless-DC-Motors-Used-For.html

https://forum.nutsvolts.com/viewtopic.php?f=45&t=18023
http://blogs.rediff.com/myloveou/2019/12/21/some-useful-tips-of-controlling-a-bldc-motor/