Category Archives: Motors

What are Axial Flux Motors?

AC induction motors are no doubt the most popular and widely used electric motors today. For DC applications, there are permanent magnet motors. However, newer applications are demanding different types of motors with higher efficiency and better speed-torque characteristics. One such application is the electric vehicle sector, where axial flux motors are gaining traction.

Axial flux motors are not new. For the past few decades, manufacturers have been using these motors for stationary applications like agricultural machinery and elevators. With modifications and innovations over the past decades, axial flux motors are now capable of running airport pods, electric motorcycles, delivery trucks, aircraft, and electric cars.

Induction motors and permanent magnet motors are most often known as radial flux motors, as the flux they generate radiates out perpendicularly, relative to their axle. With extensive development, engineers are aiming to optimize the weight and cost of radial flux motors, but the going has been asymptotic. Therefore, moving to a completely different type of machine like an axial flux makes better sense.

With the axial flux design, a permanent magnet motor can provide higher torque for a given volume than a similar motor of radial flux design can. This is because the axial flux design works with a much larger active magnetic surface area to generate torque rather than the motor’s outside diameter.

Therefore, the axial flux motor can be much more compact, with an axial length far shorter than that of their radial counterparts. Because of their shorter axial length, axial flux motors are more suitable for applications that use a motor inside the wheel. Although these motors are slim and lightweight, they can provide the machine where they are mounted with higher power and torque density than a comparable radial motor can, without resorting to high-speed rotation.

The shorter, single-dimensional flux path also provides the axial flux motors with high efficiency, typically over 96%. This is a tall order for the best 2D radial flux motors available on the market.

Compared to radial flux motors, axial flux motors can be five to eight times shorter, and two to times lighter. Both these factors improve the options for designers of EV platforms.

Axial flux motors are available in two principal technologies—dual-rotor, single stator, and single rotor, dual stator.

In a permanent magnet motor using radial flux technology, the magnetic flux loop starts from a permanent magnet on the rotor. It then passes through the first tooth of the stator, continues to flow radially along the stator, and passes through a second tooth, arriving at the second magnet in the rotor.

In an axial flux motor, using the dual rotor technology, the flux loop begins at the first magnet. It then passes axially through the stator tooth arriving immediately at the second magnet. Therefore, the flux has to travel a much shorter distance compared to that in the radial flux motor. This allows the axial flux motor to be much smaller for the same power, increasing its power density and efficiency. In contrast, the flux has to follow a 2-dimensional path inside a radial flux motor.

What are Motor Starters?

Starting up small motors is usually through a manual starter that can make or break the power supply line to the motor. The method is also known as DOL or direct online start. If the motor gets too hot due to an overload, a thermal protection circuit in the starter opens and disconnects the motor. DOL starters are the most common method of starting and stopping single-phase motors up to 5 HP, 230 VAC, and three-phase motors up to 15 HP, 600 VAC.

Magnetic starters can have controls such as float switches, pressure switches, timers, relays, limit switches, and push buttons, as they have a separate mechanism for closing and opening a set of contacts for the motor circuit. They also include a thermal overload protection device. The mechanism consists of a coil, which, when energized, closes contacts to complete the electrical circuit of the motor. Likewise, de-energizing the coil opens the contacts, switching off the motor.

However, one of the problems with DOL or magnetic starters is both allow the motor to start with a high current. Under normal conditions, motors must start with a current that is nearly 6 to 7 times the rated running current of the motor. This is necessary for the motor to overcome the initial torque due to friction. However, for some motors, the starting current can go up to 9-10 times the rated current.

Reversing any two phases of a three-phase induction motor results in the motor reversing its direction of rotation. Adding an extra set of contacts to a basic starter can turn it into a reversing starter. Appropriate electrical and mechanical interlocking mechanisms must also be present for safeguarding the motor operations.

A soft starter applies a low voltage to the motor, ensuring a low starting current and torque. The torque gradually increases as the soft starter begins to apply higher voltage.  Semiconductor switches such as thyristors, inside the starter, accomplish the gradual increase in the voltage that the starter applies to the motor.

A slow start is essential to prevent stress on the internal components of the motor, and to the machinery, the motor is driving, especially belts and gear drives. The soft starter also features soft stopping. This is essentially helpful for stopping conveyor belts and pumps, where a sudden stop may cause water hammering in the pipe system.

Multispeed induction motors have multiple windings that require special starters. For instance, two-speed motors with separate windings need starters with two built-in standard starters within a single enclosure with mechanical and electrical interlocks.

Consequent-pole two-speed motors need a three-pole starter unit or a five-pole starter unit. The design of the motor winding determines whether the three- or five-pole unit makes a slow-speed or fast connection.

Delta-type multi-speed motors require different power circuits for the currents circulating within the unconnected and inactive windings. Two-speed motors with separate open-delta windings require a pair of four-pole starter. For each speed, a different four-pole starter is necessary. Therefore, very complex starters are necessary for motors with open-delta windings capable of running at three or four speeds.

Stepper Servo Motors

Although many designers prefer to relegate stepper motors to the realm of low-cost low-performance technology, a new technique is bringing the step motors a fresh lease of life. This new drive technique is the stepper servo, and it uses the generic stepper motor, yet extracts significantly more performance out of it. The technique requires adding an encoder and operating the motor effectively as a commuted two-phase brushless DC motor.

While the inclusion of an encoder makes the stepper servo idea non-suitable for low-cost applications, designers are increasingly considering the technique an alternate approach to applications requiring a brushless DC motor.

This is because the cost of a stepper servo motor is considerably less than a comparable brushless DC motor, while the former actually outperforms brushless DC motors in areas of torque output and acceleration. Therefore, designers are considering the stepper servo motor as a candidate for high-speed applications such as coil winding, point-to-point moves, textile equipment, high-speed electronic cams, and more.

Stepper motors are easy to use, making them popular. They maintain their position without external aids such as encoders. Neither do they require a servo control loop when designers use them for positioning, as other DC motors do. Their brushless operation, high torque output, and low cost are their biggest advantages. However, their limited speed range, noisy operation, and vibrations are their main disadvantages.

Being a multi-phase device, stepper motors require the excitation of multiple coils and driving control waveforms for their operation. The usual configuration for stepper motors will have 1.8 mechanical degrees for a full step of 90 electrical degrees—making it 200 full steps for every mechanical rotation. Other stepper motors may have 7.2- or 0.9-degree configurations in place of the customary 1.8.

A stepper servo motor has an encoder attached to the shaft. For a typical 1.8-degree stepper motor, the resolution of the encoder must be of the order of 2000 counts per mechanical rotation. The encoder verifies the final position of the rotor through a traditional step motor control scheme.

The stepper servo motor operates more like a brushless DC motor, with the actual encoder position commuting the phase angle, instead of the commanded position. The phase angle and amplitude of the driving waveform need to vary continuously depending on the output from a position PID loop. This allows the motor to servo to the commanded position.

The presence of the encoder frees the stepper servo from losing steps—the encoder determines the location. The motor operation is now more efficient, causing much lower heat generation. Traditional stepper motors require driving at large currents adequate for handling worst-case motions.

Traditional stepper motors always have problems achieving positional accuracy. With the encoder driving the stepper servo motor to its location, these vagaries of position do not arise. The encoder frees the stepper servo motor from the restrictions of the 1.8 degrees per step of the regular stepper motor. Simply increase the resolution of the encoder to get better positional accuracy.

The addition of the encoder also produces a smooth acceleration to the desired position without the customary bouncing and noise.

Intelligent Phase Control for BLDC Motors

Many applications use BLDC or Brushless DC motors for powering several types of high-speed equipment. These include industrial machines, data center cooling fans for servers and home vacuum cleaners. One of the challenges designers face is to ensure the motors operate effectively and reliably. Now, Toshiba is making it easy for designers to do this with its intelligent phase control motor controller.

While other manufacturers also offer intelligent phase control devices, they usually meet a specific design need. Toshiba’s TC78B016FTG has a driver rated for 40 VDC and 3 A maximum. The fully integrated motor control driver requires a power supply ranging from 6 to 36 VDC, and provides a sine wave output drive. ON resistance of the driver is only 0.24 ohms, representing the total of low and high sides. This typically reduces the self-heating of the device during operation and allows driving 1 to 1.5 A loads without a heat sink.

TC78B016FTG uses a simple speed control mechanism using pulse width modulation. It has several built-in protections, and these include protection from over-current, thermal runaway, and motor lock. Toshiba offers the TC78B016FTG in a 5 x 5 mm VQFN32 package.

Other controllers from Toshiba include the TC78B941FNG and TC78B042FTG. These intelligent phase controllers allow users to tailor the power requirement of an application by selecting a proper MOSFET and its gate driver for the design. Toshiba offers these devices in SSOP30 and VQFN32 packages respectively. Both measure 5 x 5 mm.

Another controller from Toshiba is the TC78B027FTG, which incorporates a gate driver, for which the user can select the proper MOSFETs according to the application. This controller also has a one-Hall drive system for the user to drive a less expensive one-sensor BLDC motor. Toshiba offers the device in a VQFN24 device measuring 4 x 4 mm.

Conventional drive technology adjusts the phase or lead angle of the voltage and current it feeds to the motor for achieving high-level efficiency. However, high-speed rotation prevents the magnetic drive from reaching maximum power, as phase lag delays the voltage applied to the coil from rising until the current has increased to a maximum.

Intelligent phase controllers avoid the above situation by advancing the rotor by a certain angle from the calculated position. This is the new lead angle that depends on the BLDC motor’s characteristics, its rotational speed, and load conditions.

Designers try to achieve optimal efficiency over rotational speeds ranging from almost zero rpm at motor startup to several thousand rpm at high speeds. As this requires several characterizations for adjusting the phase, they achieve optimal efficiency only for a limited range of speeds. Intelligent phase controllers allow BLDC motors to rotate at high speeds with uniform accuracy and efficiency.

Compared to earlier technologies, the approach taken by Toshiba is different. Rather than adjust the phase difference between the voltage and current to the motor at different points in its operating range, Toshiba automatically and continually adjusts the phases of voltage and current the controller feeds to the motor. Intelligent phase controllers from Toshiba thereby achieve the highest possible efficiency for the entire operating range of the motor.

Industrial Motors for Machine Automation

Industrial engineers use different types of motion control devices for improving the production rates and efficiencies on the floor of automated factories. Three major types of motion control devices are in demand for machine automation—stepper motors, servomotors and variable frequency drives (VFDs).

In general, stepper motors along with their drives, and controllers are widely used as they offer simple implementation, beneficial price/performance ratios, and high torque at low speeds. This motor is essentially a brushless DC version, moving in equal fixed steps during rotation, and only a single step at a time. Not requiring tuning or adjustments, stepper motors provide very high torque at speeds below 1000 RPM. They are cost-effective, as their prices are substantially lower than the cost of comparable servo systems. Since the torque they produce decreases as they speed up, it makes their operation difficult. Therefore, the work done by stepper motors becomes impractical at speeds in excess of 1000-1500 RPM.

Servomotors come with a motor, drive, a controller, and a device for positional feedback. For variable load applications, engineers prefer them to stepper motors, as they deliver high torque when rotating at speeds above 2000 RPM. Servos require adjustments and tuning, making them more complex to control compared to stepper motors. Including maintenance costs, their positional feedback arrangement can push their prices well beyond those of stepper motors.

Costing less than stepper motors or servomotors, VFD systems include an AC motor and a drive, but are unable to provide positioning. However, they can be good for applications requiring speed control on variable loads. For applications where the motor need not run continuously at full load, a VFD system can save considerable amount of energy. Another feature of VFDs is their soft-start capability, allowing a limit to high inrush currents.

In a stepper motor system, the controller regulates the position of the step, the torque generated by the motor, and the speed of the motor as it moves from one step to another. The driver operates on the control signals the controller generates by modifying and amplifying these signals to regulate the direction and magnitude of the current flowing into the motor’s windings. This way, it drive rotates the shaft of the motor to its desired position, and holds it in position with the required torque for the required time.

Controllers for stepper motors can be either open or closed loop types. Open-loop controllers are simpler, not requiring any feedback from the motor, but are less efficient. Open-loop controllers operate on the assumption the motor is always at the programmed step position and is producing the desired torque.

On the other hand, closed-loop controllers always operate with feedback based on the effective load on the motor. Therefore, the performance of the closed-loop stepper motor controller is similar that of a servo motor, and makes the operation more efficient.

Making a stepper motor rotate through each of its steps requires energizing the several windings within the motor in a specific sequence. Typically, stepper motors rotate 1.8 degrees per step, necessitating 200 steps to make a complete revolution.

Difference between AC, DC, and EC Motors

People have been using different types of motors for ages. Primarily, motors can be broadly classified into AC and DC types, depending on the power source they require to operate. However, the basics of operation remain the same for all types of motors. Current running through a wire generates magnetic fields around it, and if there is another magnetic field present such as from an external magnet, the two interact to generate a mechanical force on the wire capable of moving the wire. This is the basic principle on which all motors operate.

AC and DC Motors

AC induction motors have a number of coils controlled and powered by the AC input voltage. This input voltage also creates the stator field, which then induces the rotor field. Another type of AC motor, a synchronous motor, can operate with precision supply frequency.

An AC motor operates at a specific point on its performance curve, which coincides with the peak efficiency of the motor. If forced to operate beyond this point, the motor runs with a significant reduction in efficiency. As the magnetic field in an AC motor is created by inducing a current in the rotor, AC motors consume extra energy from the input. This makes the AC motors less efficient than DC motors are.

DC motors generate their secondary magnetic field using permanent magnets rather than windings. They rely on commutation rings and carbon brushes to switch the direction of the current and the polarity of the magnetic field in the rotating armature. The interaction between the magnetic field from the fixed permanent magnets and the magnetic field from the internal rotor induces rotation in the rotor.

Although DC motors run at high efficiency, they suffer from specific losses. The initial resistance in the rotor, brush friction, eddy current losses cause the motor to lose efficiency.

EC Motors

To achieve higher energy efficiency and control the energy output, engineers have designed the EC or electronically commuted motors. They combine the best of both AC and DC motors by removing the brush and slip ring system of commutation, and replacing them with solid-state devices. This electronic control allows them to operate with a higher efficiency.

EC motors are also called brushless DC motors, and they are controlled by external electronics, which may be an electronic circuit board or a variable frequency drive. Permanent magnets are on the rotor, while the fixed windings are on the stator.

The circuit board keeps the motor running by switching the phases in the fixed windings as necessary. This supplies the armature with the right amount of current at the right time, resulting in the motor achieving higher accuracy and efficiency.

EC motors offer several benefits. Absence of brushes eliminates sparking and increases the life of the motor. As electronics controls the power to the motor, there is less wastage with better performance and controllability. This allows even small EC motors to equal the performance of larger AC or DC motors. Heat generation in EC motors is also lower than that generated in AC or DC motors.

Stepper Motors with Higher Efficiency

Stepper Motors are essentially open loop systems working efficiently when required to produce torque. However, when the motor faces low torque situations, its efficiency falls drastically. By simply closing the current loop, it is possible to make the entire system operate more efficiently.

Users find them to be economical as stepper motors offer the advantages of excellent positioning with their simplicity. This feature makes them highly popular for use In general automation tasks such as positioning, indexing, inserting, feeding, and more. Now, with closed loop operations, users are finding stepper motors equally adequate for applications involving force and torque control.

Optimizing the operational performance requires users to understand certain characteristics of stepper motors. Traditionally, users operate stepper motors in open loop control. That means the drive electronics has no feedback regarding the torque the motor has to handle at any time. Therefore, the drivers continuously supply full load current even when the motor has no load to drive. The excess load current heats up the motor, reducing the efficiency of the system.

Such operation of stepper motors in open loop systems tends to classify them as inefficient devices because of the loss of power involved. However, this is not true, as stepper motors are highly efficient when called upon to deliver torque, only losing their operational efficiency when not driving a load. The problem is readily solved by providing a feedback to control the amount of current the motor actually requires for handling the present load.

Manufacturers have noticed the benefits of closed loop operation and offer integrated motors that produce higher torque, greater throughput, faster acceleration rates, reduced noise, and higher operational efficiency. These motors have a built-in closed loop system to reduce the input current to the motor automatically as the load reduces.

Such closed loop systems commonly employ a feedback device, usually an incremental encoder, for monitoring the error between the present shaft position as against its commanded position. The drive electronics runs algorithms to control motor current dynamically based on the error information from the feedback device.

The above process tends to reduce the overall current consumption, thereby saving power over conventional open loop stepper motor systems and improving the efficiency of the system greatly. The improvement is readily demonstrated by comparing the power consumption between two stepper motors, one operating in open loop and the other in a closed loop system.

A comparison of power consumption between the two motor systems driving identical loads shows the closed loop system will consume only a third of the power taken in by the traditional open loop stepper motor system for doing the same work. This proves the closing of the current loop results in the stepper motor operating with less power, improved efficiency, and lower costs. This also results in lower downtime, as there is a drastic reduction in motor heating.

Closed loop systems offer additional benefits apart from higher energy efficiency. A stepper motor operating in a closed loop offers faster acceleration and greater throughput because of the higher peak torque it generates—nearly 1.5 times its rated holding torque. The motor also runs more quietly.

What are Stepper Motors Good For?

Stepper motors rotate in discrete steps. These are DC motors with multiple coils arranged in groups or phases. Energizing each phase sequentially enables the shaft of the motor to rotate in single steps. It is possible to achieve very fine positioning and speed control with a computer controlling the stepping. This allows use of stepper motors for several industrial applications involving precision motion control. As stepper motors come in various sizes, styles, and electrical characteristics, it is important to know the parameters that allow selecting the right motor for the job.

Stepper motors are good for three things—positioning, speed control, and generating low-speed torque. As they move in repeatable and precise steps, stepper motors are appropriate for applications requiring meticulous positioning such as in 3-D printers, XY plotters, CNC machines, and camera platforms. With their precise incremental movement, stepper motors allow excellent control of their rotational speed suitable for robotics and process automation. Where regular DC motors generate very little torque at low speeds, stepper motors are the opposite, generating their maximum torque at low speeds. This makes then the right choice for applications requiring high precision at low speeds.

It is also necessary to know the limitations of stepper motors—low efficiency, limited high-speed torque, and no feedback. Stepper motors are notoriously low efficiency devices, as their current consumption is independent of the load they are driving. Moreover, when it is stationary and not doing work, a stepper motor draws the maximum current. The low efficiency of these motors manifests itself in the high amount of heat they generate. Contrary to that of other motors, stepper motors exhibit lower torque at high speeds than they do at low speeds. Even for steppers optimized for better high-speed operation, achieving that requires them to be paired with appropriated drivers. Servomotors achieve their positions aided by integral feedback. However, steppers have no such provision, achieving high precision when running open loop. Limit switches or home detectors are necessary for safety and for achieving a reference position.

Selecting a stepper motor for a specific task requires considering three major characteristics—motor size, step count, and gearing. The general concept is larger motors will deliver higher power. Manufacturers specify motor power in torque ratings, and NEMA numbers to specify their frame sizes. To decide whether the motor has the strength to meet your requirement, look at its torque ratings. While NEMA 57 is a monster size, 3-D printers and CNC mills usually use a NEMA 17 size motor. The NEMA numbers also specify standardized faceplate dimensions for mounting the motor.

The step count defines the positioning resolution. A motor can have a specific number of steps per revolution, which usually ranges from 4-400. For instance, step counts commonly available are 24, 48, and 200. Resolution of a stepper motor is specified in degrees per step. For instance, a motor rotating 1.8 degrees per step is actually rotating at 200 steps per revolution. A higher resolution motor usually sacrifices speed and torque. Therefore, motors with high step counts have lower RPMs and lower torques than do similar sized but low-step-count motors running at similar speeds.

Different Types of E-Bike Motors

The major difference between electric bikes is the various types of drive systems they use. These include shaft drives, mid-drives, geared and gearless hubs. In addition, there are differences between the motors, chiefly brushed and brushless. Therefore, if you are looking for an e-bike for a specific use, this article will help you to understand and focus on finding the right one.

The shaft drive

This system works more like the arrangement in an automobile, with the motor positioned more towards the center of the bike and driving the rear wheel with a shaft. These are not popular nowadays, because of the customized frames required to support the motor and shaft. The entire arrangement is awkward and difficult to service.

A mid-drive motor

Mid-drive motor systems are used in e-bikes meant for climbing. You will find this design close to the bottom bracket, at the point near the pedals. The system drives the chain forward rather than the wheel, benefitting from mechanical drivetrain systems such as use of gears for going fast or for climbing. Therefore, when approaching a hill, the rider can shift to a lower gear, making it easier to pedal and climb.

The geared hub motor

There are two types of hub motors – geared and gearless. The geared hub motor provides mechanical advantage with smaller and lightweight motors. However, they also produce more friction and hence more noise and wear out faster. A built-in flywheel mechanism unlatches the shaft from the axle while the rider is coasting, preventing addition of any resistance.

The gearless hub motor

The simplicity of the gearless hub motor delivers smooth and quiet performance, much eulogized by shops selling e-bikes. These motors rely greatly on electromagnets and most do not even include a freewheel mechanism. That may be due to the extremely low magnetic resistance to be overcome when the electromagnets are powered off. Usually, such motors are also called direct drive systems, enabling regeneration of electricity from repelling magnets within the motor.

Gearless hub motors are generally larger than other types, because they need to accommodate magnets, ultimately making them weigh more. However, improvements in technology are helping to produce small and lightweight direct drive hub motors nowadays.

Hub motors usually operate even when the rider is not pedaling. Whether geared or gearless, the system can fit in the rear or the front wheel. However, with increased unsprung weight, hub motors can experience reduced traction, limited efficiency and strain the spokes and rims of the wheel.

The drive system you select will affect the overall weight and weight-distribution of your electric bike. The cost will depend on whether you need a customized frame, regeneration and special sensors for shifting gears. Motorized e-bikes provide improved efficiency, help in riding fast, in climbing and in navigating bumps. For lightweight around-the-town transportation, geared hub motors are fine. If you like quieter rides with more power and regenerative braking, go for direct drive hub motors. However, if you ride your bike more in the mountains and do lots of hill climbing, you definitely need mid drive motors.

Increasing the Accuracy of Peristaltic Pumps

There are vast applications of peristaltic pumps because of their simple construction and ease of use. The construction of peristaltic pumps does not allow the liquid being pumped to be exposed to the pump’s mechanism. That helps hospitals using these pumps to circulate blood during bypass surgery as a critical part. Used in heart-lung machines, the design of these pumps prevents significant hemolysis – the rupture of destruction of red blood cells. The chief advantage of the design is the compressible polymer tube through which the dispensing liquid passes.

For fluids that must be isolated from the environment, this simple arrangement works very well. For example, it allows pumping slurries with a high solid content and other aggressive chemicals. However, rollers inside the peristaltic pump produce pulsations as they move an on and off a pressure shoe that compresses the tube. These pulsations prevent accurate dispensing.

Drug development and delivery depends largely on accurate dispensing. For example, accurate dispensing and aspirations are extremely important for addressing safety concerns related to tremendously expensive high-potency compounds such as biotech designer molecules used by leading-edge pharmaceuticals. The proteins and synthetic molecular chains composing these compounds are very fragile and highly susceptible to tear. That calls for short setup times and the dispensing tube meeting or exceeding the safety and contamination concerns. The peristaltic pump finds wide applications because it is able to address the above requirements.

One simple method of reducing the pulsations from the peristaltic pump is to increase the number of rollers. However, that is not a very practical idea. A pump with three rollers can greatly reduce its fluid-dispensing variance provided it has one roller in the same starting position when starting each dispense – the pump repeats its starting position every 180 degrees.

An integrated motor solution with signal inputs and outputs for roller positioning makes this a possibility. The design allows the pump to dispense volumes made from multiple revolutions plus some fraction of a revolution. With roller positioning, it is possible to take into consideration the fraction of the revolution and ignore the complete revolutions. External valves help with the dispensing of fluid from the peristaltic pump to control the starting position of the next roller without dispensing.

In practice, the motor allows the pump to dispense and then operates the valve, allowing the rollers to be positioned to the same starting point for the subsequent dispense cycle. The process ensures a precise and repeatable quantity of dispensing. Usually, drip retention is also used to bring back the fluid into the tube. This is to prevent a drip of the fluid when closing the dispense valve. Usually, that causes a small amount of fluid to be wasted. This can be prevented by repositioning the next roller in a positive or a negative direction to minimize the fluid waste.

Another method is to use multiple tube peristaltic system. The rollers in this system are intentionally offset and the output of the tubes combined. This effectively increases the total number of rollers, minimizing pulsations. Here, one of the legs becomes the waste tube and the dispense valve is positioned after the combined outlet.